96_s~OIlIIaISS£lI1C€ Geology and eochronology of the Precam man of the UH GEOLOGIAL SURVEY PROFESSIONAL, PAPER“ 19055:; /' «)M [ I us. bEPOSITORY ‘ - JUL 10 1978 IERKELEY LIBRARY UNIVERSITY OF CALIFORNIA Reconnaissance Geology and GeOchrOnology of the Precambrian of the Granite Mountains, Wyoming . By ZELL E. PETERMAN and R. A. HILDRETH GEOLOGICAL SURVEY PROFESSIONAL PAPER 1055 Radiometric dating establishes ages of 2,860 my. for an extensive metamorphic complex and 2,550 my. for a major granite batholith in the Granite Mountains UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1978 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Peterman, Zell E. Reconnaissance geology and geochronology of the Precambrian of the Granite Mountains, Wyoming (Geological Survey Professional Paper 1055) Bibliography: p. 20 Supt. of Docs. no.: I 19.16:1055 1. Geology, Stratigraphic-Precambrian. 2. Geology—Wyoming—Granite Mountains. 3. Radioactive dating. 1. Hildreth, R. A., joint author. II. Title. III. Series. QE653.P46 551.7'1’09787 77—608349 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 Stock Number 024-001—03090—0 CONTENTS Page Page Abstract .............................................................................................. l Geochronology—Continued Introduction ........................................................................................ l Metamorphic complex ................................................................. 9 Regional Precambrian geology ........................................................... 3 Granite ........................................................................................ 12 Metamorphic complex ..... 3 Diabase dikes and nephrite veins . l4 Granite ................. 6 Mineral ages ............................ . lS Diabase ..... 9 Conclusions ........... . 18 Geochronology ................................................................................... 9 References cited .................................................................................. 20 ILLUSTRATIONS Page FIGURE l. lndex map of exposed Precambrian in the Wyoming area ............................................................................................................... l 2. Map of the geology of the Precambrian of the Granite Mountains 2 3. Diagram of modal quartz, plagioclase, and alkali feldspar ........... 5 4. Rb-Sr isochron plot for the metamorphic complex .............. [0 5. Rb-Sr isochron plot for the granite rocks ........................................................................................................................................ l3 6. Chart of Rb-Sr and K-Ar mineral ages ............................................................................................................................................ l5 7. Chart of Rb-Sr and 207Pb/206Pb ages of microcline .............. l6 8. K-Ar and Rb-Sr ages of biotite from Precambrian W rocks ............................................................................................................ l8 TABLES Page TABLE 1. Descriptions and modal analyses of metamorphic rocks .................................................................................................................. 4 2. Descriptions and modal analyses of granitic rocks ........................................................................................................................... 7 3. Analytical data for metamorphic rocks .............. l | 4. Analytical data for granitic rocks l2 5. Analytical data for 3‘JAr/‘OAr ages .. l5 6. Conventional K-Ar ages ................................................................................................................................................................... l6 % 8 RECONNAISSANCE GEOLOGY AND GEOCHRONOLOGY OF THE PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING By ZELL E. PETERMAN and R. A. HILDRETH ABSTRACT The Precambrian of the western part of the Granite Mountains, Wyoming, contains a metamorphic complex of gneisses, schists, and amphibolites that were derived through amphibolite-grade metamorphism from a sedimentary-volcanic sequence perhaps similar to that exposed in the southeastern Wind River Mountains. Whole-rock Rb-Sr dating places the time of metamorphism at 2,860180 million years. A high initial “Sr/“Sr ratio of 0.7048 suggests that either the protoliths or the source terrane of the sedimentary component is several hundred million years older than the time of metamorphism. Following an interval of 3001100 million years for which the geologic record is lacking or still undeciphered, the metamorphic complex was intruded by a batholith and satellite bodies of medium- to coarse-grained, generally massive biotite granite and related pegmatite and aplite. The main body of granite is dated at 2,550160 million years by the Rb-Sr method. Limited data suggest that diabase dikes were emplaced and nephrite veins were formed only shortly after intrusion of the granite. Emplacement of the granite at about 2,550 million years ago appears to be related to a major period of regional granitic plutonism in the Precambrian of southern and western Wyoming. Granites, in the strict sense, that are dated between 2,450 and 2,600 million years occur in the Teton Range, the Sierra Madre, the Medicine Bow Mountains and the Laramie Range. This episode of granitic plutonism occured some 50 to 100 million years later than the major tonalitic to granitic plutonism in the Superior province of northern Minnesota and adjacent Ontario—the nearest exposed Precambrian W terrane that is analogous to the Wyoming province. Initial 87Sr/ “Sr ratios of some of the Wyoming granites are higher than expected if the rocks had been derived from juvenile magmas and it is likely that older crustal rocks were involved to some degree in the generation of these granites. Slightly to highly disturbed Rb-Sr and K-Ar mineral ages are obtained on rocks of the metamorphic complex and on the granite. These ages range from about 2,400 to 1,420 million years and are part of a regional pattern of lowered mineral ages of Precambrian W rocks of southern Wyoming. A major discontinuity in these mineral ages occurs along a line extending from the northern Laramie Range, through the northern part of the Granite Mountains, to the southeastern Wind River Mountains. North of this line, Rb-Sr and K-Ar biotite ages are 2,300 million years or greater, whereas to the south, the biotite ages decrease drastically over a short distance, to a common range of l,600-l,400 million years. We suggest that these lowered ages represent regional cooling below the 300° C isotherm as a consequence of uplift and erosion of the large crustal block occurring south of the age discontinuity. In this interpretation, the westerly-trending age discontinuity would be a zone of major crustal dislocation that resulted from vertical tectonics in late Precambrian X or early Precambrian Y time. INTRODUCTION Precambrian igneous and metamorphic rocks are exposed in the Granite Mountains of central Wyoming—a block of Precambrian basement that was uplifted during the Laramide orogeny when vertical tectonics and thrust faulting resulted in the exposure of several major terranes of crystalline rock in Wyoming (fig. 1). The Granite Mountains uplift trends west-northwest and lies between the Wind River uplift on the west and the Laramie uplift on the east. The Phanerozoic and particularly the Cenozoic history of the Granite Mountains is complex, but a comprehensive account of this facet of the geology is given by Love (1970). Because of the economic importance of the Phanerozoic sedimentary rocks along the flanks and in basins adjacent to the Granite Mountains, geologic studies have emphasized these younger rocks. A few gold and sulfide occurences in Precambrian rocks were prospected and some were mined to a limited extent, but these did not prove sufficiently substantial to sustain operations. Nephrite (jade) occurs in Precambrian vein deposits and in Eocene conglomerates and Holocene alluvium derived therefrom; these deposits are important in a local gemstone trade. Love (1970) reviewed the investigations of Precambrian rocks that had been made prior to 1965. Sherer (1969), in his study of nephrite deposits of central Wyoming, completed a 45- \1 110‘ 108' 106' 194“ ' I I l l a \‘J la BEARTOOTH MTS BIGHOFIN MTS TETON 44° /RA°NGE . s OWL CREEK MTS WYOMING ‘ Q “Q ‘12,, § a o . HARTVILLE 43 ‘6‘ UPLIFT ‘94, GRANITE MTS \7, I )K ' / ° 0 FIG. 2 v 42. SEMINOE MTS SHIRLEY 0 ' \ MTS I MEDICINE BOW 0 LARAMIE “"5 RANGE SIERRA l 41. . . MADRE O 50l 100 150 ZOOKILOMETERS L_l__l_l_.l FIGURE l.——Areas of exposed Precambrian in the Wyoming area (King and Beikman, 1974). l 2 PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING R.94 W 108° R.93 W. R.92 W. R.9| W. - R30 W. €100— CO at GM-103 FREMONT NATRONA .1GM-35 - -’I 56 ML38;;‘-7§' I Warn :. :1"... )01784 GM-77‘78 4: I 5 ‘ .. 7 . . I' ‘ dd» 42°_ ”er GM-1, w2—cP - 4‘ “ 30’ “ ' J: U S 4 ~ . Hum 287 2T9. Tsr City 4 N. I // q / I / / \ 4 0 2 4 6 8 10 12 KILOMETERS I | 1 I l | I q E X P L A N A T l O N TERTIARY « \ V \\v\\ Moonstone Formation (Pliocene) c lnequigranular biotite- quartz-feldspar auger: gneiss s \\ .5 g 2 c a , , Tsr split Rock Formation (Miocene) '5 2‘ , Dark-gray, fine-grained, thinly banded biotite gneiss inter- : 3 ' ted to be met ra wacke 4 . . . . g 3 N— \ 9'9 as v Whlte River Formation (0“90‘39'“) >_ c? figment/1‘ Fine- to medium-grained amphibolite. Contains numerous E 3 ' dikes and sills of granite and pegmatite *‘ Wagon Bed Formatlon (Eocene) % L; - Finegrained, banded epidote-rich gneiss A 5 .. Alkalic igneous TOCKS. 44 Why. old (Eocene) (Pekarek § - Dominantly medium grained, well-banded, biotite-quartz- and others, 1974) feldspar gneiss of tonalitic to granitic composition. In- «— terlayared with subordinate amounts of mica schist, v y/VW MESOZO'C AND PALEOZO'C amphibolite, epidote gneiss, serpentinite, and augen gneiss L := . Sediments rocks undivided * ////////% 'y g PR ECAMBRIAN W -——-— Contact —— dashed where approxnmately located __ F — h ' l 4 Mafic dikes of Itic composition 65 ault dashed w ere approximate y located —A— Strike and dip of foliation and banding Medium- to coarse-grained biotite granite with numerous + Strike and dip °f horizontal f°'iati°" dikes of splits and pegmatita 01686, Sample locality and number FIGURE 2.—Reconnaissance geology of the Precambrian of the western part of the Granite Mountains. Base and Phanerozoic geology from Love (1970, pl. 1). Sample numbers abbreviated for clarity. detailed [map of a small area of Precambrian gneisses in the petrologic study of the granite in the Granite Mountains. western part of the Granite Mountains. Houston (1974) The present study emphasizes the regional geology and prepared reconnaissance maps of the Precambrian from geochronology of the Precambrian rocks of the western part several types of remote-sensing data. Stuckless and others of the Granite Mountains. We completed reconnaissance (1977) have completed a preliminary geochemical and mapping in the summers of 1968 and 1969 and collected ,fipt‘r r5: 7‘ war“ .. _ V” 7 C0 FREMONT REGIONAL PRECAMBRIAN GEOLOGY 3 R88 W. R.B9 W. NArfiow' _c0 k H \\ 3N? \ \¢ $733 I ..‘.o\‘:“\\\\\\ g3: samples for the geochronological study at that time. Preliminary results of our geochronology study were previously summarized (Peterman and others, 1971). Other isotopic studies have emphasized the U-Th-Pb systematics in the granite and the metamorphic rocks. Rosholt and Bartel (1969) demonstrated that a large fraction of the uranium in the granite had been removed in relatively recent geologic time, the last 100 my. (million years), and suggested that the granite may have been a source for much or all of the uranium that forms the important economic deposits in adjacent Tertiary sandstones. Further work on the granite (Rosholt and others, 1973) and on gneisses of the metamorphic complex (NKomo and Rosholt, 1972) rein- forced these earlier conclusions. This hypothesis conflicts with that of Love (1970) who, on the basis of geologic and geochemical data, concluded that the uranium in the Tertiary sandstones was probably derived by leaching of lacustrine tuff beds of the Pliocene Moonstone Formation. We are especially grateful to Robert G. Coleman who introduced the senior author to the geology of the Granite Mountains, encouraged the study, and provided several samples for isotopic analyses. John Stacey assisted in the field work in the summer of 1968. The late William T. Henderson completed most of the chemical work attendant with the Rb 'and Sr analyses. G. T. Cebula and Jack Groen prepared all of the whole-rock and mineral samples. M. A. Lanphere and GB. Dalrymple determined the 39 Ar/ 40Ar ages and R. F. Marvin and H. H. Mehnert provided the conventional K-Ar ages. T. W. Stern analyzed zircon from the granite at Tincup Mountain. John Stuckless provided core samples from US. Geological Survey drill hole GM-l. J. David Love, Robert Houston, and John Stuckless provided many valuable comments on the manuscript. To all of these people, we express our sincere appreciation. REGIONAL PRECAMBRIAN GEOLOGY The Precambrian geology of the western part of the Granite Mountains (Tps. 29-31 N., Rs. 88-94 W.) is shown in figure 2. Three major terranes or lithologies are readily differentiated: (1) An assemblage of amphibolite-grade metamorphic rocks crops out in the northwestern and northern part of the area. (2) Granitic rocks, whence the name Granite Mountains, are part of a large batholith extending eastward beyond the map area. (3) Diabase dikes with dominant northeasterly trends intrude both the granitic and metamorphic rocks. The geologic maps prepared by Houston (1974) from various remote-sensing data and the reconnaissance mapping completed for this study are in excellent agreement. METAMORPHIC COMPLEX The metamorphic complex contains the oldest Precam- brian rocks of the area and consists of a variety of schists and gneisses that attained amphibolite grade but locally have been retrograded. Foliation and compositional banding in this terrane trend northeasterly to easterly, and dips are generally in a southerly direction towards the granite. The metamorphic complex is divided into five major units based upon the dominant lithology in each (fig. 2): quart- zofeldspathic gneiss; epidote-rich gneiss; amphibolite; biotite gneiss (interpreted to be metagraywacke); and augen gneiss. More detailed mapping would undoubtedly result in the recognition of a greater number of units. The relative ages of most of the metamorphic rocks are unknown. Some amphibolite and granitic gneiss are clearly intrusive but have been involved in the major period of folding and metamorphism. The major emphasis on the metamorphic rocks in the present study was on those cropping out in Tps. 30 and 31 N., Rs. 92 and 93 W. Other areas were examined in less detail and to the extent necessary to identify the major lithologic types present. Little effort was devoted to the metamorphic rocks cropping out in T. 31 N., R. 88 W., and the mapping of Carey (1959) was used for the northern part of this township. A photogeologic map of the central part of the township was prepared by Houston (1974), and his ground check identified an occurrence of Precambrian iron-formation, a unit not encountered elsewhere in the area. It is noteworthy that Love (1970) reported the presence of fragments of banded iron-formation in the Eocene Wagon Bed Formation (T. 32 N., R. 86 W.) and suggested that Precambrian and Paleozoic rocks to the south and southwest should be examined as potential sources for these PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING TABLE l.—De.rcriptions and modal analyses of metamorphic rocks [Asterisk by sample number indicates modal analysis by point counting (500-600 points). Other modes are visual estimates. Sample localities illustrated in figure 2] Sample Locality Description "GM-35-68 42°35'21” N. 107° 5537” W. ‘GM-38-68 42°35’04” N. 107° 54’55” W. ‘GM-76—68 42°35’04” N. 107° 5455" W. ‘GM-77-68 42°33’58” N. 107°52’18” W. *GM-78-68 42° 3358" N. 107°52’18” W. *GM-98-68 42°32’38” N. 107°12’40” W. GM-103A-69 42° 3808" N. 107° 30’58” W. l'GM-104-69 42°38’46” N. 107° 3058” W. W2-CR-4(114) 42°36’40” N. 107°46’10” W. FCA-R-l 42° 50’19” N. 107°52’54” W. Light-gray, fine— to medium-grained, xenoblastic, inequigranular granodioritic gneiss. Leucocratic bands from 2 to 10 mm wide alternate with more biotite-rich bands from 1 to 10 mm wide. Plagioclase (Ann, 46 percent) is moderately sericitized. Microcline (11 percent) is fresh and occurs mainly as grains interstitial to plagioclase and quartz (34 percent), although a few larger porphyroblasts of microcline as much as 10 mm occur in the leucocratic bands. Epidote (1.1 percent) occurs as discrete subhedral grains in association with biotite (7.0 percent). Zircon, apatite, hornblende, altered allanite, and opaques are minor constituents. Medium-gray, fine- to medium-grained, xenoblastic, inequigranular tonalitic gneiss. Alternating light and dark bands range from a few millimeters to several centimeters in thickness. Plagioclase (Ann, 52 percent) is only slightly altered to sericite—-—notab1y less so than in GM-35-68. Quartz (37 percent) locally forms composite ameboid lenses in the plane of foliation. A few grain boundaries show suturing. Biotite (8.1 percent) is completely unaltered and associated with epidote (1.0 percent) and trace amounts of allanite. Apatite, zircon, hornblende, and opaques are common accessory minerals. Medium-gray, medium-grained, xenoblastic, inequigranular tonalitic gneiss. Banding is less distinctly developed than in sample GM-38-68 from the same locality. Composite grains of quartz (36 percent) and plagioclase (Ann, 51 percent) occur as eyes and discontinuous layers in the more biotite (10 percent) rich portions of the rock. Microcline (0.2 percent) occurs only as patch antiperthite in plagioclase. Plagioclase is somewhat saussuritized and biotite is locally partially chloritized and associated with epidote (1.2 percent). A few discrete grains of muscovite (1.7 percent) occur. Sphene, zircon, apatite, and opaques are accessory minerals. Dark—gray, fine- to medium—grained, xenoblastic, inequigranular granodioritic gneiss with thin discontinuous leucocratic layers (as much as 5 mm) alternating with thicker (l to several cm) mafic layers. Quartz (36 percent) occurs as both equant grains and as composite lenses elongated in the foliation plane defined by biotite (15 percent). Plagioclase (Anzs, 29 percent) is only slightly sericitized. Microcline (12 percent) occurs both as discrete grains and as patches in plagioclase. Blue-green hornblende (5.6 percent) is concentrated in the mafic layers. Epidote (1.8 percent), euhedral sphene (0.5 percent), and opaques (0.2 percent) are abundant trace minerals. Apatite, zircon, and allanite are present. Light-gray, fine-grained, xenoblastic, inequigranular granitic gneiss with thin (l-2-mm) and continuous leucocratic layers imparting aidistinct fine-scale banding. Plagioclase (Ann, 30 percent) is only slightly altered to sericite. Microcline (30 percent) is a major constituent and locally is poikiloblastic with inclusions of quartz and plagioclase. Quartz (32 percent) locally occurs as composite lenses elongated in the extremely well developed foliation defined by the biotite (8.1 percent). Epidote, zircon, apatite, opaques, and chlorite are present in trace amounts. Medium-gray, medium-grained, xenoblastic, inequigranular tonalitic gneiss. The rock has a well-developed foliation but is not banded. Plagioclase (Ann, 39 percent) is only slightly sericitized and biotite (6.7 percent) is locally chloritized. Only trace amounts of microcline occur (0.2 percent). Quartz (39 percent) occurs in places as very elongate lenses as much as 10 mm in length and 3 mm in width. Epidote (0.4 percent) occurs as discrete grains in association with biotite. Apatite, zircon, allanite, and opaques are common trace minerals. Dark-gray, fine-grained amphibolite intercalated with quartzofeldspathic gneiss. Amphibolite has welbdeveloped nematoblastic texture. Hornblende and plagioclase in a ratio of about 2:1 dominate the mineralogy. Quartz is an important varietal mineral. Most of the plagioclase is extremely fresh but local areas within the section show intense saussuritization. Opaques, apatite, epidote, and white mica are minor phases. Light-gray, fine-grained, xenoblastic, equigranular granodioritic gneiss. The rock is foliated but only faintly banded with sparse leucocratic layers as much as 5 mm in width alternating with massive bands from 2 to several cm in width. The foliation of the rock is defined by alinement of the hornblende (8.9 percent). Biotite is not present, a feature that distinguishes this rock from the other quartzofeldspathic gneisses described herein. Plagioclase (38 percent), virtually unaltered, is more calcic (A1737) than in the other gneisses, but the rock contains significant amounts of microcline (9.4 percent). Accessory minerals include sphene (0.7 percent), epidote (0.3 percent), and apatite (0.2 percent). Quartz is 43 percent. Dark-gray, fine- to medium-grained amphibolite. Hornblende and plagioclase (Anw) in approximately equalamounts constitute most of the rock. Quartz, biotite, sphene, apatite, opaques, epidote, and white mica are present in small amounts. Plagioclase is, for the most part, fresh, but locally it is saussuritized. This sample is mineralogically and texturally similar to GM-IO3A-69 but is slightly coarser in grain size. Medium-gray, medium- to coarse-grained, well-foliated granodioritic gneiss. Rock is not compositionally banded, but well-developed foliation is imparted by alined hornblende and biotite. Approximate mode: plagioclase, 40 percent; quartz, 30; hornblende, 15; biotite, 10; microcline, 5. Allanite, sphene, epidote, apatite, and zircon are accessory minerals. Altered allanite grains are commonly rimmed by epidote. White mica, epidote, chlorite, and carbonate are minor alteration minerals. L {Li 4 ' '1 "' £""T"', ‘7“ f'f' i-T—v—T—Y‘Wgwu v “"7 L REGIONAL PRECAMBRIAN GEOLOGY 5 fragments. No outcrops of iron-formation had been iden- tified in the region at that time. The unit designated as quartzofeldspathic gneiss in figure 2 contains a variety of biotite-quartz-feldspar gneisses that are interlayered with subordinate amounts of mica schist, amphibolite, augen gneiss, epidote gneiss, and serpentinite. Most of the samples (table 1) used for radiometric dating of the metamorphic complex are from this unit. The gneisses are characteristically well foliated and form a layered sequence of alternating and compositionally distinct units. The thickness of the layers ranges from a few centimeters to several meters. Migmatitic varieties contain thin discontinuous layers of leucocratic phases as much as a centimeter thick with sparse porphyroblasts of microcline. Locally, very tight small-scale folding is present in the gneisses, and layers of amphibolite have been distended to form boudins and rotated blocks. The gneisses are intruded by numerous dikes and stringers of granitic material, some of which have been deformed and metamorphosed. Other dikes are undeformed and are apparently related to the younger granite (fig. 2) that intrudes the metamorphic complex. Some of the biotite augen gneiss that is in- terlayered in places with the finer grained quartzofeldspathic gneisses is similar to that shown as a separate unit (fig. 2). The compositional range of the gneisses is shown on figure 3. Using the nomenclature for igneous rocks (Streckeisen, 1973) without any genetic implications, the gneisses range in composition from tonalitic to granitic. The granitic gneisses are subordinate in volume to the tonalitic and granodioritic gneisses. In T. 31 N., Rs. 92-93 W., Sherer(l969) identified three major lithologies of gneisses—the dominant biotite gneiss, granite gneiss of uncertain relationship to the biotite gneiss, and quartzofeldspathic gneiss derived from granitic dikes and sills that are intrusive into both the biotite gneiss and granite gneiss. Gneisses in the granite field of figure 3 are mainly the granite gneiss and quartzofeldspathic gneiss of Sherer (.1969). Intense alteration adjacent to the zones of nephrite veins has produced a variety of epidote-rich gneisses similar to but generally coarser grained than the fine-grained epidote-rich gneiss of figure 2. Sherer (1969, 1972) concluded that the nephrite veins formed as a consequence of hydrous metasomatic alteration of amphibolite with iron, aluminum, and calcium being mobilized during this alteration to produce epidotization of the country rocks. Much of the gneiss exposed in a series of low-lying hills centered in the area outlined by Tps. 30 and 31 N. and Rs. 91 and 92 W. is pervasively altered. In the field, a major lithologic unit was called “green” gneiss because of its faint greenish-gray color. Thin sections show that the gneiss contains 30 to 50 percent quartz, but the feldspar, presumably plagioclase, has been completely altered to fine-grained, felted aggregates of white mica. Sherer (1969) described similar alteration and has identified the secondary mica as paragonite. In one sample, biotite has been totally QUARTZ QUARTZ 5/ ' [I . : \\ s I K / GWODIORITE I GRANITE \ 2° 20 PLAEIOCLASE ALKALIxELDSPAR FIGURE 3.—Samples of quartzofeldspathic gneiss (dots) plotted on a portion of ternary diagram of modal quartz, plagioclase, and alkali feldspar with the IUGS classification for plutonic rocks (Streckeisen, 1973). Data are from Sherer (1969) and this report (table I). altered to chlorite that is dusted with fine-grained opaque inclusions, but in others the biotite is fresh, although it is extremely pale brown, suggestive of a low-iron content. Coarse muscovite occurs in one sample that transects the plagioclase relics and altered biotite. Epidote and zircon are trace constituents. Unaltered gneisses also occur in this area. Amphibolite and serpentinite layers are common but volumetrically small compared to the altered and unaltered quartzofeldspathic gneisses. A variety of medium- to coarse-grained epidote-bearing gneisses occur throughout the metamorphic complex, but in T.3l N., Rs. 92 and 93 W., fine—grained epidote gneiss is mapped as a distinct unit (fig. 2). These rocks are extremely fine grained (0.1-0.5 mm), gray to pastel shades of green, yellow and pink gneisses that in outcrop resemble metarhyolite or fine—grained quartzite. They exhibit blocky fracturing and are extremely tough and brittle. The epidote gneisses are variable in composition but are characterized by quartz, epidote, and fresh to altered plagioclase. Some samples of the epidote gneiss contain significant amounts of actinolite both as poikiloblastic grains that include the other minerals and as fibrous aggregates. Compositional layering ranges from a few millimeters to several centimeters and results from variable epidote and actinolite concentrations. Granoblastic quartz-plagioclase layers alternate with strongly nematoblastic epidote- and actinolite-rich layers. One sample examined contains approximately equal amounts of epidote and quartz but no plagioclase. Sphene and apatite are ubiquitous accessory minerals. Aggregates of granular sphene are strung out in the direction of the foliation and are characteristically associated with epidote The origin of the epidote gneiss is problematic. Sherer (1969) related epidote—rich gneisses to alteration associated with the nephrite veins. The fine-grained epidote gneiss described here may have been derived from intermediate to silicic volcanic rocks, a speculation supported by its association with layered amphibolite, which is probably derived from a mafic volcanic rock. 6 PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING Dark-gray, fine- to medium-grained amphibolite (fig. 2) occurs as thin, discontinuous layers throughout the metamorphic complex and is the dominant lithology in a northeasterly trending belt in T. 31 N., R. 93 W. and in the northwestern part of T. 30 N., R. 92 W. In both areas, but particularly in the latter, quartzofeldspathic gneiss is abun- dantly interlayered with the amphibolite. In these areas the amphibolite is commonly banded with alternating mafic and very thin more leucocratic layers, and weathers to produce slabby or flaggy outcrops. Detailed petrographic studies of the amphibolite were not completed, but a few thin sections show it to consist dominantly of plagioclase and hornblende, with minor amounts of quartz. Epidote, sphene, and apatite are common accessory minerals and trace amounts of biotite are present in some samples. Some of the amphibolite within the quartzofeldspathic gneisses is dominated by hornblende with only small amounts of plagioclase. In T. 31 N., R. 93 W., the amphibolite is pervaded by numerous dikes and sills of granite and pegmatite. ‘ Dark-gray, fine-grained biotite gneiss (fig. 2) is poorly exposed in low-lying outcrops in thecenter ofT. 31 N., R. 93 W. The rock is strongly foliated with 20 to 30 percent biotite and approximately equal amounts of quartz and sodic plagioclase, much of which is untwinned. Apatite, epidote, zircon, and opaques are accessory minerals. The biotite occurs as subparallel grains as much as 1 mm in length in a granoblastic mosaic composed of 0.1-0.2-mm grains of quartz and feldspar. Compositional banding in outcrop is presumed to represent relic sedimentary layering and the rock is interpreted to be, on the basis of this and the composition, a metagraywacke. In comparison with the quartzofeldspathic gneisses (fig. 2), this biotite gneiss unit is characterized by its finer grain size, greater abundance of biotite, and absence of K-feldspar. The metagraywacke is intruded by numerous small dikes and stringers of granitic rock and pegmatite. A similar rock type is intercalated in places with the quartzofeldspathic gneiss and with the amphibolite. Medium- to coarse—grained biotite augen gneiss (fig. 2) occurs in many places throughout the metamorphic complex and is distinguished as a sizable unit in T. 31 N., Rs. 92, 93 W. The gneiss is strongly inequigranular with distinct augens as much as several centimeters in length. The augens are commonly composites of ~ quartz, plagioclase, and poikiloblastic microcline. These are contained within a finer ‘ grained groundmass of mainly quartz, plagioclase, microcline, and biotite. Biotite is in lenticular aggregates and imparts a distinct but wavy foliation to the rock. Muscovite, epidote, sphene, apatite, zircon, opaques, and altered allanite are common accessory minerals. In places, the augen gneiss has been highly sheared and the augen have been stretched into long, recrystallized leucocratic streaks. Within the main outcrop area, the augen gneiss is extensively intruded by granitic and pegmatitic dikes that are undeform- ed. GRANITE The western part of a large granitic batholith crops out in the map area (fig. 2), where these rocks form a major part of the Precambrian. For purposes of discussion here, three masses of granite separated by metamorphic rocks are referred to as the granite at Long Creek Mountain (eastern part of T. 31 N., R. 94 W. and the northwestern part of T. 31 N., R. 93 W.), the granite at Tincup Mountain (a belt extending northeasterly across T. 31 N., R. 93 W.), and the granite of Lankin Dome (Tps. 29-30 N., Rs. 88—92 W.). The batholith extends eastward several kilometers beyond the limit of the map area. Excellent exposures of the granite occur in rounded to craggy knobs and hills that rise a few hundred meters above the plain of flat-lying Tertiary sedimentary rocks. The granite is clearly younger than the enclosing metamorphic rocks and both units- are cut by diabase dikes. Samples that were used in the dating, a few of which are from outside the map area, are described in table 2. The granite at Long Creek Mountain is a massive to foliated light—gray to reddish-gray biotite granite with inclusions and schlieren of biotite gneiss and amphibolite. Small dikes and stringers of pegmatite, aplite, and quartz are common throughout the body. At the north end of the mass, the granite becomes gneissic with faint banding, and an inclusion or screen of migmatite approximately 30 m thick was observed. The foliation in the gneissic phase strikes N. 50° E., parallel to the regional structure of the metamorphic rocks, but dips approximately 35° to the northwest. The granite at Long Creek Mountain was not sampled for Rb-Sr dating because of pervasive weathering, but U-Pb dating of zircons suggests that the granite may be slightly older than the granites of Lankin Dome and Tincup Mountain (K. R. Ludwig and J. S. Stuckless, oral commun., 1976). The granite at Tincup Mountain is a fine- to medium-grained, medium-gray, foliated muscovite-biotite granite that is cut by numerous dikes of pegmatite, aplite, and quartz. Some of the aplite dikes are unusually gar— netiferous, and very coarse grained muscovite-bearing pegmatite is present locally. The granite of Lankin Dome is the main body of granite and is typically massive and medium to coarse grained. Dikes of pegmatite ranging from several centimeters to a meter or more in width are common. Phenocrysts of microcline as much as several centimeters in length are dispersed throughout the granite at spacings of a meter or more. Isolated pegmatitic clots as much as several tens of centimeters long are also common. The major rock type exposed contains approximately equal amounts of quartz, plagioclase, and perthitic microcline, which form 90-95 percent of the rock. Plagioclase composition ranges from albite to oligoclase, and the appropriate rock names are biotite granite and biotite alkali-feldspar granite, according to the IUGS classification (Streckeisen, 1973). The average composition of the biotite granite (Stuckless and others, LJ __L__\'_1._t._.4-_L LIA—f—J—Ll 4 A I I -7 r‘ I REGIONAL PRECAMBRIAN GEOLOGY 7 TABLE 2.—Descriptions and modal analyses of granitic rocks [Asterisk by sample number indicates modal analysis by point counting (500 to 600 points). Other modes are visual estimates. Sample localities illustrated in figure 2] Sample Locality Description GM-55-68 42°32’03” N. 107° 5306” W. GM-56-68 42°32'07" N. 107°52'51" w. GM-81-68 42°33'04” N. 107°43'47” w. W2-CR-l(99) 42°41'50” N. 107°19’46” W. W2-CR-l(153) 42°41'50” N. 107°19’46” w. I"W2-CR-l4(101) 42°32’35” N. 107°39’15” W. *W2-CR-l4(157) 42°32’35" N. 107°39’15” W. *W2-CR-26(99) 42°33’46” N. 107°22’09” W. *W2-CR-26(l65) 42°33’46” N. 107°22’09” W. *ZW-263 41°31’02” N. 107° 4804” W. I’Dl686 42° 39’00" N. 107° 5430” W. Medium-grained, faintly foliated biotite granite collected from within 1.2 m of the contact with an lS-m-wide diabase dike. Contains approximately 40 percent plagioclase; 30 quartz; 20 microcline; 10 biotite; and trace amounts of epidote, white mica, chlorite, zircon, apatite, and opaques. Plagioclase is severely altered to white mica, and cryptoperthitic microcline is clouded with minute inclusions. Biotite is mainly fresh and appears to have been recrystallized, as cleavage lies at right angles to grain elongation in places. Epidote, commonly subhedral, generally occurs in association with the biotite. Alteration of the granite is apparently related to heating attendant with emplacement of the diabase. Hand specimen and thin section of this sample was inadvertently lost. Rock is described in field notes as a strongly foliated and locally sheared porphyritic granite intruded by stringers and dikes of pegmatite and biotite granite. Sample was collected for its fresh biotite. Light-greenish-gray, medium-grained epidotized granite. Contains approximately equal amounts of plagioclase (chessboard albite) and quartz (30—40 percent each), epidote (20 percent), and about 10 percent chlorite. Zircon and apatite are trace minerals. Epidote occurs both as composite aggregates and as discrete euhedral grains interspersed in quartz and feldspar. Anhedral to euhedral sphene is commonly in association with composite chlorite aggregates. Albite is locally poikilitic with numerous inclusions of quartz as well as epidote. Pinkish-gray, coarse-grained granite. Quartz, plagioclase and microcline, in roughly equal amounts, constitute about 90 percent of the rock. Chlorite, formed from biotite, is the next most abundant mineral. Epidote, sphene, apatite, zircon, opaques, and leucoxene occur in trace amounts. Plagioclase (albite or sodic oligoclase) shows faint zoning and is moderately to strongly saussuritized. Sphene, both as granular grains in chlorite and as discrete euhedral wedges, is strongly altered to leucoxene. Euhedral epidote grains occur in association with the mafic minerals. Microcline is fresh and commonly poikilitic with inclusions of quartz, plagioclase, and epidote. Composite grains of quartz are common with moderately sutured grain boundaries. Texturally and mineralogically similar to sample W2—CR-l(99) except not nearly as altered. Biotite, for the most part, is fresh with only a few grains showing alteration to chlorite. Plagioclase is somewhat altered to white mica but generally fresher than in W2-CR-l(99). Light—gray, medium- to coarse-grained, inequigranular biotite granite. Quartz (29 percent) is strained and commonly occurs as composite grains with some suturing of grain boundaries. Microcline (33 percent) is fresh, strongly perthitic, and poikilitically includes quartz, plagioclase, and biotite. Plagioclase (Anms, 3] percent) is moderately altered to white mica, faintly zoned, and locally shows bent twin lamellae. Biotite ( l .4 percent) is partially altered to chlorite (1.1 percent) and granular sphene. Epidote (1.6 percent) occurs mainly as subhedral grains in association with the mafic minerals, and muscovite is present as discrete grains (1.6 percent). Sphene, zircon, apatite, and opaques are present in trace quantities. Texturally and mineralogically similar to W2-CR-l4(101). Modal analysis: quartz, 34 percent, microcline, 36; plagioclase, 26; biotite, 1.4; chlorite, 1.4; muscovite, 1.1; epidote, 0.4; and trace amounts of sphene, zircon, opaques, and white ,mica. - Medium-grained, light-gray biotite granite. Quartz (26 percent) occurs as strained, composite grains with some sutured boundaries. Plagioclase (An12_15, 29 percent) is moderately saussuritized with some bent and broken twin lamellae and healed mortar structure around larger grains. Perthitic microcline (37 percent) is fresh and commonly poikilitic with inclusions of quartz, plagioclase, and biotite. Biotite (5.1 percent) is partially altered to chlorite (0.3 percent) and traces of granular sphene. Epidote (1.5 percent) and opaques (0.2 percent) are commonly associated with the biotite aggregates. Sphene, zircon, apatite, white mica, and monazite (I) are present in trace amounts. Generally similar to W2-CR-26(99). Modal analysis: plagioclase (zoned from An 3 to An”, 34 percent); microcline, 31; quartz, 30; biotite, 2.6; epidote, 1.6; muscovite, 0.2; chlorite, 0.2; and trace amounts ofmonazite(?), zircon, apatite, opaques, carbonate, sphene, and white mica. Very light gray, coarse-grained, leucocratic porphyritic granite. Approximately 10 percent of the rock is composed of poikilitic microcline phenocrysts attaining lengths of 25 mm but more commonly about 10 mm. Groundmass is medium to coarse grained. Plagioclase (Ans, 32 percent) is altered to white mica and epidote and in places shows bent twin lamellae. Microcline (38 percent) is fresh and is poikilitic in both the groundmass and phenocryst phases with inclusions of quartz, plagioclase, and epidote. Quartz (28 percent) is strained and commonly forms composite grains. Biotite (0.3 percent), chlorite (0.2 percent), and epidote (0.3 percent) are commonly associated. Granular sphene in chlorite, zircon, and opaques are trace minerals. Muscovite (0.3 percent) occurs as discrete grains but commonly restricted to the plagioclase. Light-gray, medium-grained, faintly foliated biotite granite. Quartz (27 percent) is strained with some sutured boundaries in composite grains. Plagioclase (albite or sodic oligoclase, 34 percent) is moderately altered to white mica and in places shows bent twin lamellae. Microcline (30 percent) is commonly poikilitic. Biotite (4.4 percent) is slightly chloritized (0.3 percent). Muscovite (2.9 percent) is a significant varietal mineral. Epidote, zircon, allanite, garnet, and opaques are trace constituents. 8 PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING TABLE 2,—Descriptions and modal analyses of granitic rocks—Continued Sample Locality Description *DDH-l 42°31’00” N. 107°38’30” W. Light-gray, medium-grained biotite granite with some iron staining. Plagioclase(a1bite or sodic oligoclase, 37 percent) is moderately saussuritized with bent twin lamellae locally. Quartz (37 percent) is in strained composite grains showing some incipient mortar structure in places. Microcline (22 percent) is fresh and commonly poikilitic. Subhedral grains of epidote (0.5 percent) are associated with slightly chloritized biotite (3.4 percent). Muscovite (0.4 percent) occurs both as discrete grains and in the alteration products of plagioclase. Apatite, zircon, and opaques are trace constituents. Light-gray, medium-grained biotite granite. Approximately 95 percent of the rock comprises nearly equal amounts of quartz, plagioclase, and microcline. Biotite, somewhat chloritized. is the major varietal mineral. Plagioclase is somewhat saussuritized. Epidote also occurs as discrete subhedral grains associated with biotite. A few grains of monazite are present. Protoclasis is indicated by bent and broken twin lamellae in plagioclase and incipient mortar Light-gray, medium-grained biotite granite collected from the abutment of the Kortes Dam (Rosholt and Bartel, 1969). Hand specimens of these particular samples are not available but others from the area show marked similarity to Drill core of coarse-grained biotite granite from the Little Man mine. Described in Rosholt and Bartel (1969). DDH-2 42°32’55” N. 107°49’14” W. structure. D114944 42° 10’27” N. D114945 106°52’47” W. samples from the granite of Lankin Dome. 256179 42°18’28” N. 106°50’46” W. GM-l 42°32’35” N. 107°39’15” W. listed below: Medium— to coarse-grained, leucocratic granite from USGS drill hole GM-l (Stuckless and others, 1977). Descriptions of samples and modes are given by Stuckless and others (1976). Abundances of the major minerals, in percent, are Sample Quartz Plagioclase Mirrocline Biotite GM-l (739) ................................................... 29 43 23 [.8 (771) .. 37 30 31 .6 (891) .. 30 20 45 2.0 (1021).. 39 37 21 2.l (l 156) ................................................... 39 59 0 2.3 1977) is 31 percent quartz, 30 percent plagioclase, 34 percent microcline, and 5 percent biotite and chlorite, with alteration and accessory minerals constituting less than 2 percent. Texturally, the biotite granite is allotriomorphic ine- quigranular. Perthitic microcline is poikilitic with inclusions of plagioclase, quartz and biotite. Plagioclase is altered to white mica and granular epidote. Epidote also occurs as subhedral grains in association with clusters of biotite and opaque minerals. Biotite shows all degrees of alteration to chlorite and granular sphene, which is partially altered to leucoxene. Quartz occurs as composite grains with marked undulatory extinction, and some sections show sutured grain boundaries within the quartz composites. Protoclastic textures are further evidenced by bent and broken twin lamellae in plagioclase. Zircon, apatite, allanite, monazite, and opaques are common accessory minerals. Stuckless and others (1977) identified a second major phase of the granite that was encountered in a drill hole but is not exposed or at least was not recognized in outcrop. These authors described the rock as a leucocratic phase with an average modal composition of 38 percent quartz, 29 plagioclase, 30 microcline, 1.2 biotite, 1.2 muscovite and minor amounts of epidote, garnet, opaques, and other accessory minerals. The leucocratic phase is significantly lower in Th, Fe, Sr, and Rb than the biotite granite (Stuckless and others, 1977). The granite is locally foliated at the western end of the batholith, where it is in contact with the metamorphic rocks and forms a mixed zone of granite and gneiss. The metamorphic rocks have been extensively intruded by numerous dikes and sills of pegmatite, aplite, and fine- to medium-grained granite. The metamorphic rocks adjacent to the granite at Long Creek Mountain and the granite at Tincup Mountain are pervaded in similar fashion by abundant granitic material. In addition to the minor cataclasis and alteration that has occurred in the biotite granite, intense alteration has taken place along linear zones within the batholith. Here the granite has been strongly epidotized and converted to an extremely tough and brittle rock. The zones of epidotized granite stand above the unaltered granite as resistant ridges and are characterized by a blocky fracture pattern. Stuckless and others (1977) described this alteration and referred to the zones as being silicified and epidotized. Epidotization seems to be the dominant alteration in samples examined during the present study. Biotite and microcline, which are ubiquitous in the biotite granite, are sparse or lacking in the alteration zones. Plagioclase is altered and epidote has been ._.L La X 1' . “41 GEOCHRONOLOGY ' 9 introduced in significant quantities. The allochemical nature of the alteration is exemplified by the mineralogy and by the Rb and Sr contents. The biotite granite contains ap- proximately 200 ppm Rb and 100 ppm Sr, whereasa sample of epidotized granite (GM-81-68, table 4) derived from the biotite granite has 2 ppm Rb and 700 ppm Sr. An epidote separate from this sample contains approximately 1,000 ppm Sr. Significant amounts of material were added to and removed from the biotite granite to accomplish this altera- tion. It is likely that hydrothermal fluids of undefined nature and source rose along fractures within the granite to produce the extensive exchange of material and alteration that occurred. It is not known whether or not significant movement occurred along these fractures. As mentioned earlier, similar alteration has modified rocks of the metamorphic complex in places, especially in areas of nephrite mineralization. DIABASE Dikes of fine- to medium-grained diabase (fig. 2) intrude the granite and the metamorphic complex with a dominant east-northeast trend. The dikes range in width from less than a meter to several tens of meters; The dikes are chilled against the granite and metamorphic rocks and the wider dikes have baked the enclosing rocks, producing a contact zone that is commonly more resistant to weathering than either the diabase or the unaltered granite and gneiss. Sherer (1969) described variable degrees of alteration in the dikes, which he attributed to late-stage deuteric processes. The sample collected for dating in the present study is remarkably fresh, with olivine and pyroxene as mafic minerals and completely unaltered labradorite as the feldspar. The texture is subophitic with approximately equal amounts of plagioclase and pyroxene. Sparse grains of olivine are rimmed and veined with an opaque mineral. GEOCHRONOLOGY Most of the radiometric dating was done by the Rb-Sr method on whole-rock and mineral samples. Outcrops were sampled only where least weathered rock could be obtained; hence, the sampling is not representative of the actual lithologic abundances because of variable weathering susceptibilities of the rock types. A few core samples were obtained from holes that were sponsored by the Space and Missile Systems Organization (SAMSO) (Saucier, 1970) and by the US. Geological Survey (Stuckless and others, 1976). The greatest part of the Rb-Sr analytical work was completed from late 1968 through 1970, following procedures described by Peterman, Doe, and Bartel (1967). During this period, 26 analyses of the Eimer and Amend strontium were made, and an average 87Sr/“Sr of 0707971000010 (1 standard deviation) was obtained. Duplicate analyses of rock samples completed about this same time indicate an uncertainty in the 37Sr/ 86Sr ratio of 10.00026 (1 s.d.). This uncertainty is substantially greater than that of the standard and the increased variance is thought to be related to additional errors attendant in obtaining 0.2—0.5-gram aliquots of sample from material that contains minerals with drastically different 87Sr/“Sr values, that is, slight sample inhomogeneity problems. Duplicate 87Rb/ 86Sr values, also obtained on rock samples, indicate a coefficient of variation of :1 .3 percent of the ratio. These uncertainties are used in regressing the data by the method of McIntyre and others (1966). Uncertainties in the ages and initial 87Sr/“Sr values obtained from the regressions are given at the 95-percent confidence level. The isotopic and decay constants used in calculating the ages are those recommended by the IUGS Subcommission on Geochronology (Steiger and J'ager, 1977). Ages herein quoted from published reports are recalculated using these constants where necessary. METAMORPHIC COMPLEX Rb and Sr data (table 3) when plotted on an isochron diagram (fig. 4) show scatter beyond experimental uncer- tainty, especially for samples with 87Rb/“Sr values of less than 0.8. However, the data can be separated into two' groups on both statistical and geological grounds, and a reasonably precise isochron is obtained by eliminating samples FCA-R-l, CR-4(ll4), GM-103, and GM—98 from the regression. (Sample numbers are shortened for con- venience here and in subsequent discussions.) The slope of the isochron based upon the remaining samples corresponds to an age of 2,860180 my, and the initial 87Sr/“Sr is 0.7048:0.0012. The data for this regression still show slight variance in excess of experimental uncertainty (MSWD=3.54), and a Model 111 fit is used. (See McIntyre and others (1966) for explanations of the terminology and the statistical calculations.) NKomo and Rosholt (1972) determined whole-rock U-Th-Pb analyses on some of the same samples used in our study and obtained a 207Pb/ 2“Pb age of 2,9101120 m.y. Of the four samples that are excluded from the regression, GM-103 and CR-l4(ll4) are amphibolites that are in- terlayered with the quartzofeldspathic gneisses. Samples FCA-R-l and GM-98 are gneisses collected outside of the map area (fig. 2), in T. 33 N., R. 88 W., and T. 30 N., R. 95 W., respectively. These are well-foliated but massive gneisses that have only faint or no compositional banding in outcrop. In contrast, all of the data that define the main isochron (solid line, fig. 4) were obtained from layered gneisses. A reference isochron (dashed line, fig. 4) is drawn parallel to the main isochron through the four samples that are excluded from the regression. This reference isochron intersects the ordinate at 0.7017, a value significantly lower than the initial 87Sr/36Sr of 0.7048 for the main isochron. Coexistence of rocks with different primary 87Sr/“Sr ratios that have maintained an isotopic identity through periods of amphibolite-grade metamorphism has been 10 PRECAMBRIAN OF THE GRANITE MOUNTAINS. WYOMING 1'000 l l I 1 r T I 0.960 0.920 0.880 0. 840 0.800 0.760 0.720 87Rb/86Sr FIGIiRE 4.~Rb—Sr isochron plot for samples from the metamorphic complex. Rock types and modes are given in table 1. Solid circles, amphibolites (GM-103, CR-4(1 14)) and massive gneisses(FCA-R-l ); open circles with dots, layered gneisses. Solid isochron corresponds to an age of 2.860180 m.y. with an initial “Sr/“Sr value of 07048100012. Dashed line is a reference isochron drawn parallel to the solid isochron but with an initial 87Sr/“Sr value of 0.7017. observed elsewhere. Subparallel isochrons for associated paragneisses and orthogneisses that were metamorphosed 1,710 my. ago were determined by Hedge, Peterman, and Braddock (1967) on rocks of a metamorphic complex of north-central Colorado. The metasedimentary rocks have an initial 87Sr/“Sr of 0.7079 whereas the orthogneisses, including amphibolite, have a lower initial of 0.7021. Hofmann and K'ohler (1973) observed similar differences between orthogneisses and diatexites—gneisses in in- termediate and advanced stages of anatexis—of the Schwarzwald of southwest Germany. Thus, it is possible that the massive gneisses of the Granite Mountains have a different origin than gneisses of the layered sequence and that primary differences in the isotopic composition of the common Sr were at least partially preserved during the metamorphism. Inherent uncertainties in interpreting Rb-Sr isochron ages defined on whole-rock samples of metamorphic rocks may be considerably greater than in interpreting similar data for plutonic igneous rocks. The collinearity of data on the main isochron of figure 4 implies that the samples shared a uniform or nearly uniform composition of common Sr at 2,860 my. ago. The major problem is interpreting the geologic significance of this age. We will not attempt to GEOCHRONOLOGY 11 TABLE 3.—Analy!ical data for metamorphic rocks Sample No.‘ Rb (ppm) Sr(ppm) "Rb/“Sr "Sr/“Sr GM-35-68R 44.3 398 0.322 0.7179 GM-38—68R 37.6 338 .323 .7191 GM-76-68R 28.0 318 .255 .7149 GM-77-68R 91.0 171 1.550 .7680 GM-78—68R 212 96.0 6.55 .9773 GM-78-68Mi 401 102 11.90 1.1348 GM-78-68P1 78.9 155 1.497 .8449 GM-78-68Bi 1,299 17.9 403 10.088 GM—98-68R 67.2 264 .739 .7328 GM-98-68P1 8.45 375 .065 .7093 GM-98-68Bi 662 14.4 246 9.379 GM-103A-69R 19.0 114 .479 .7198 GM-104-69R 61.3 71.1 2.50 .8091 W2-CR-4(114)R 11.3 . 118 .278 .7142 FCA-R-l-69R 44.6 686 .188 .7090 lSuffix letters on sample number indicates type of sample analyzed: R, whole rock; Pl, plagioclase; Mi. microcline. Bi. biotite. review all of the literature pertinent to this problem but only mention a few studies that have particular bearing on our interpretation; Impure sedimentary rocks such as shales and graywackes, and volcanic rocks that are subjected to prograding metamorphism will undergo a series of physical and mineralogical changes until the highest pressure-temperature conditions are attained, at which time a stable mineral paragenesis may be approximated (Winkler, 1974). A fluid phase may be particularly important in facilitating the mineralogic reactions and in modifying the compositions of the rocks through dewatering (Norris and Henley, 1976). Thus, ample opportunity exists for open system conditions to obtain, beginning with diagenesis, through the final stages of metamorphism. Indeed, a number of studies have shown that whole-rock Rb-Sr systems of sedimentary and volcanic rocks are highly susceptible to partial or complete resetting during postdepositional metamorphism (Pidgeon and Compston, 1965; Compston and others, 1966; Peterman, 1966; Turek and Stephenson, 1966; Lanphere, 1968; Turek and Peterman, 1968; Gorokhov and others, 1970; Clauer and Bonhomme, 1970; Hofmann and Grauert, 1973; Lyon and others, 1973; Gebauer and Griinenfelder, 1974). Some of these studies show that only relatively low grades of metamorphism are required to disturb the Rb-Sr systems. The results obtained - by Pidgeon and Compston (1965) are particularly important in interpreting and understanding whole-rock Rb-Sr ages of metamorphic rocks. They analyzed a series of metasedimen- tary rocks that circumscribe a granitic intrusion and increase in grade from the chlorite zone to migmatitic rocks of amphibolite facies. The whole-rock ages decrease toward and become concordant with the age of the granite in the cordierite-orthoclase and migmatitic zones. Hofmann and Grauert (1973) found similar systematics in a progressively metamorphosed contact zone within Belt Supergroup sedimentary rocks that are intruded by an early Tertiary phase of the Idaho batholith. Their results demonstrated a systematic lowering of ages obtained on small whole-rock samples (1-2-cm-thick slabs), with some complexities, and the ages were totally reset in the sillimanite-muscovite zone. The complex mineralogical changes and the disturbances in the Rb-Sr systems that. occur during prograding metamorphism strongly suggest that whole-rock Rb-Sr isochrons obtained on intermediate to high-grade rocks can be assumed to approximate the time of metamorphism; that is, the time that these rocks attained their stable or near-stable mineral assemblages. Once the rocks have gone through a cycle of metamorphism that produced a relatively simple mineral suite, such as quartz+ plagioclase+biotitetK-feldsparigarnet in a metagraywacke, the Rb-Sr whole-rock systems may remain closed or respond in a manner similar to those of granitic rocks during subsequent metamorphic events. Even in complexly banded gneisses, individual bands may retain their isotopic integrity through rather severe later metamorphism (Jager, 1970; Krogh and Davis, 1973; Grauert and others, 1974; Hanny and others, 1975; Steiger and others, 1976), although exceptions have been documented and the scale of com- positional banding is a particularly critical factor (Grauert and Hall, 1974; H‘anny and others, 1975). If severe shearing and recrystallization occurs during the later metamorphism, the Rb-Sr systems may be partially or totally reset (zartman and Stern, 1967; Hanson and others, 1969; Hunziker, 1970; Turek and Peterman, 1971; Abbott, 1972; Sims and Peter- man, 1976). Although the effects of cataclasis are recognized locally in the metamorphic complex of the Granite Mountains such as in the augen gneiss (fig. 2), the samples collected for radiometric dating have not been sheared subsequent to their metamorphism (table 1). All of the samples were collected from bands that are uniform in composition over a half meter or more and none were taken in proximity to major lithologic boundaries. In view of these factors and the previous results obtained on studies of metamorphic rocks, we interpret the whole-rock Rb-Sr age of 2,860i80 m.y. as representing the time of major regional metamorphism. All of the Precambrian rocks of the area have been subjected to a late Precambrian X or early Precambrian Y cryptic thermal event that has disturbed the Rb-Sr mineral systems. This later thermal event does not seem to have affected the whole-rock Rb-Sr systems of the gneisses to any great extent, although some of the excess scatter on the isochron plot (fig. 4) may have resulted from this heating. The initial 87Sr/“Sr value of 07048100012 determined for the main isochron (fig. 4) suggests that the protoliths of the gneisses may have had a significant crustal history prior to the major metamorphism. The crustal residence time of the Sr can be estimated if we assume that the six gneisses defining the isochron, admittedly a small and biased sampling, are approximately representative of the gneiss 12 PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING terrane as a whole and that the Rb/ Sr ratios have not been drastically modified by the metamorphism. The mean 87Rb/“Sr ratio of the tonalitic and granitic gneisses is 0.94. An Rb-Sr system with this ratio and an 87Sr/8‘5Sr value of 0.7048 at 2,860 my. ago would have separated from the mantle or mantle-like (in terms of Rb/Sr) source between 3,200‘and 3,300 my. ago. Geologic models can be invoked to agree with this isotopic speculation. A volcanic pile or a sedimentary sequence, or combination thereof, could have formed with mantle-like 87Sr/“Sr ratios a few hundred million years before the major metamorphic event. The presently observed initial ratio of 0.7048 would be the consequence of isochron rotation during the metamorphism. Alternatively, a sedimentary pile could have been deposited just shortly before the metamorphism, and the initial ratio of 0.7048 would have resulted through the derivation of these rocks from a crustal terrane that was several hundred million years older. The assumptions in this simplistic interpretation contain many uncertainties; nevertheless, a premetamorphic crustal residence time of several hundred million years is suggested for the Sr contained in the protoliths. GRANITE Twenty samples of granitic rocks were analyzed for Rb-Sr dating (fig. 5, table 4). Several of these samples are from granite bodies that lie outside of the map area (fig. 2). Samples 114944 and 114945 from the Seminoe Mountains, and 256179 from the Pedro Mountains were described briefly by Rosholt and Bartel (1969). These localities are 40-50 km southeast of the southeastern corner of the area covered by figure 2. Samples W2-CR-1(99) and W2-CR-l(153) are from a SAMSO drill hole in the southern part of T. 32 N., R. 88 W. All of the Rb-Sr data are plotted in figure 5 with the open circles representing core samples and the solid circles representing surface samples. Two core samples (DDH-l and DDH-2) were collected with a 'Winkie drill and are considered to be surface samples because of the shallow depth from which they were obtained. A number of the data points depart from colinearity by considerably more than analytical error (fig. 5). Regression of all the points (20) results in a Model IV isochron with an age of 2,500i70 my. and initial 87Sr/“Sr ratio of 07074100045. By deleting all data points that deviate substantially from the isochron (samples GM-1(1156), GM-1(1021), ZW-263, GM-81, DDH—l, DDH-2, GM-55, and 256179), regression of the remaining data (12 points) results in a Model I fit with an age of 2,540130 my. and an initial Sr ratio of 0.705 1:0.0013. The statistical screening has some geologic meaning as suggested by the fact that it resulted in elimination of data for many of the surface samples. The granite weathers more readily than do the gneisses of the metamorphic complex, and surface samples of the granite commonly show some effect of weathering, such as iron staining. The scatter of data for some of the surface samples (fig. 5) indicates that weathering indeed has had a deleterious effect on the Rb-Sr systems. The whole-rock Rb-Sr systems are particularly susceptible to disturbance because the constituent minerals yield ages that are discor- dant with respect to the whole-rock ages. Thus, open-system behavior in the mineral Rb-Sr systems as a consequence of weathering can result in a shift of the whole-rock data point away from the isochron. However, additional complexities are indicated because some of the fresh-appearing core samples also deviate from the isochron by more than experimental error. GM-1(1156) is a plagioclase—rich phase of the leucogranite and contains no microcline (table 2). Thus, the sample may have acted as a receptor or sink for radiogenic 87Sr that was mobilized during the cryptic thermal event that disturbed the mineral systems, and the position of the data point above the isochron (fig. 5) is consistent with this speculation. GM-1(1021) does not have an unusual modal composition, and the reason for its departure from the isochron is not known. TABLE 4,—Analytical data for granitic rocks [Rb and Sr concentrations for GM-81-68R/ Ep and G M-55-68R were determined by XRF analyses; all others were determined by isotope dilution] Sample No.| Rb (ppm) Sr (ppm) “Rb/“Sr “Sr/“*Sr GM-55-68R 126 272 1.35 0.7481 GM—56-6SBi 404 19.2 69.4 2.155 GM-81—68R 2 724 .008 .7073 GM-81-68E 2 1,090 .005 .7070 W2-CR—1(99))R 136 254 1.545 .7607 W2-CR-1(153)R 115 289 1.149 .7481 W2-CR-14(101)R 241 87.5 7.98 .9989 W2—CR-14(157)R 223 95.6 6.92 .9632 W2-CR-14(157)Mi 445 111 11.96 1.0760 W2-CR-26(99)R 169 117 4.25 .8603 W2-CR-26(165)R 176 124 4.19 .8606 W2-CR-26(165)Mi 357 137 7.72 .9483 ZW-263R 133 85.2 4.53 .8606 ZW-263Mi 421 97.0 13.02 1.0841 D1686R 166 83.8 5.84 .9169 D1686Mi 465 155 8.96 1.0100 D1686P1 49.5 126 1.145 .7612 D168631 736 22.6 136.2 5.277 D1686Mu 486 15.1 132.7 5.098 DDH-lR 146 40.6 10.76 1.0752 DDH-ZR 111 196 1.643 .7717 D114944R 197 80.1 7.31 .9750 D114944Mi 547 54.6 31.3 1.4977 D114945R 192 85.1 6.70 .9491 D114945Mi 356 37.3 29.7 1.4321 256179R 113 154 2.14 .7899 256179Mi 447 215 6.14 .8965 GM-1(739)R 191 17.0 37.0 2.0844 GM-1(771)R 221 30.5 22.7 1.5371 GM-1(771)Mi 425 47.4 28.5 1.7006 GM-1(891)R 143 27.6 15.86 1.2811 GM-l(102|)R 99.2 35.5 8.33 .9964 GM—I(1156)R 33.3 40.4 2.41 .8051 'Suffix letters on sample number indicate type of sample analyzed: R. whole rock; Pl. plagioclase: Mi. microcline: Bi. biotite: Mu. muscovite; Ep. epidote. A 1 GEOCHRONOLOGY i3 2.200 I I I I I I I I I I I I I I I I I I I I I ‘ GM-1(739) - ‘ 2.000 " _ 1.800 " .. 1.600 " 1.100 — GM-1(771) . L _ _ ._ 8U, E1.400 ‘ °OGM—1(1021)- - .i” 0114944 co _ ‘ GM-1(891) . _ .. 1.200 ' 0.900 _ _ _ /_._____ _ _ / I 1.000 ' / 0.800 — - / | / I _ - i GM—81\ " 0.70 1 I I _ ”00 | o 2 4 6 8 10 l I L l I L I I I I I I I I I I I I I I I J 0 4 8 12 16 20 24 28 32 36 40 44 87Rb/868r FIGURE 5.—Rb-Sr isochron plot for samples of granite rocks. Open circles represent core samples; solid circles represent surface or near-surface samples. Regression of selected data points as outlined in the text gives an age of 2,550160 m.y. with an initial ”Sr/“Sr of 07053100056. One further selection of data points can be made solely on the basis of geologic grounds. If some surface samples are isotopically disturbed by weathering, the data for all surface samples can appropriately be excluded from the regression. Similarly, data for samples that were not taken from the main body of granite (fig. 2), granite of Lankin Dome, can be deleted. The resultant regression, based only on data from cores (7 samples) gives an age of 2,550160 m.y. with an initial 87Sr/“Sr ratio of 07053100056. It should be emphasized that none of these screening procedures changes the whole-rock isochron age significantly. In the last regression, which is a Model I fit, the 95-percent confidence levels on both the age and intercept are increased significantly because of the smaller number of samples. Rosholt, Zartman, and NKomo (1973) reported a whole-rock 207Pb/206Pb isochron age of 2,750180 m.y. for the granite. They interpreted this as a maximum age because of loss of uranium from the rocks in the Cenozoic. Data obtained on additional samples of the granite have lowered the whole—rock 207Pb/206Pb age slightly, and it is in better agreement with the Rb-Sr age (Stuckless and others, 1975). T. W. Stern (written commun., 1976) determined U-Th-Pb ages of zircon from the granite at Tincup Moun— tain (D1686): U=l,250 ppm 208Pb/Z"“Pb=8l.47 Th=l,363 ppm 207F'b/ 20“Pb=0.2364 Pb=565 ppm 206Pb/204Pb2184.9 Ages based on a common Pb correction using a 2,500-m.y. composition are: ' 206Pb/238U=l,635 m.y. 207Pb/235U=2,075 m.y. 2°7Pb/206Pb=2,540 m.y. 208Pb/232Th=1,395 m.y. Although the ages are discordant, they are in agreement with the Rb-Sr age of the granite if it is assumed that the data lie on a chord that intersects concordia at a reasonable lower value; that is, 50-100 m.y. K. R. Ludwig and J. S. Stuckless (written commun., 1976) have determined an age of 2,5951-40 my. on zircons from the granite of Lankin Dome and on similar granites that crop out east of the map area (fig. 2). Data for the zircon at Tincup Mountain plot on the same l4 PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING chord as their data. They report a slightly older age of 2,640,120 m.y. for zircon from the granite at Long Creek Mountain. On the basis of the Rb-Sr whole-rock data and the , additional radiometric evidence from U—Th-Pb whole rock and zircon studies, we conclude that the granite at Tincup Mountain and the granite of Lankin Dome are coeval and were emplaced 2,550 my. ago. We also suggest that the granites represented by samples from drill hole W2-CR-1 and the granites of the Pedro and Seminoe Mountains represented by samples 256179, 114944 and 114945 (table 4) were emplaced at approximately this time. The emplacement of these granites appears to be part of a major period of granitic plutonism, in the strict sense, in the Precambrian of western and southern Wyoming. (See summary of ages by Reed and Zartman, 1973.) Ages of major granitic bodies of this region are as follows: million years Granite Mountains: Granites of Lankin Dome and Tincup Mountain Whole rock Rb-Sr (this report) .................................. 2,550260 Zircon U-Pb (Ludwig and Stuckless, written commun., 1976) .......................................... 2,595140 Wind River Mountains, Bears Ear pluton: Zircon U-Pb (Naylor and others, 1970) ................ 2,570115 Teton Range, Mount Owen Quartz Monzonite: Whole rock Rb-Sr (Reed and Zartman, 1973) ........... 2,440175 Sierra Madre, Baggot Rocks Granite: Whole rock Rb-Sr (Divis, 1976) ............................... 2,5001100 Medicine Bow Mountains, Baggot Rocks Granite: Whole rock Rb-Sr (Hills and others, 1968) ................ 2,430i50 Laramie Range, granite: ‘ Whole rock Rb-Sr (Hills and Armstrong, 1974) ........ 2,490140 Whole rock Rb—Sr (Johnson and Hills, 1976) ............. 2,510125 This period of granitic plutonism in southern and western Wyoming occurred slightly but distinctly later than tonalitic to granitic plutonism in the Superior Province of northern Minnesota and adjacent Ontario, where a number of intrusions are well dated at between 2,650 and 2,700 my. (Goldich, 1972). The dominantly granodioritic Louis Lake batholith of the Wind River Mountains, dated at 2,650115 m.y. by Naylor and others (1970), is the approximate temporal equivalent of the Precambrian W intrusions of northern Minnesota. The 2,450- to 2,600-m.y.-old granitic intrusions of Wyom- ing also differ from the silicic intrusions of northern Minnesota in that their initial 87Sr/ 86Sr ratios are consistent- ly higher. When normalized to a common value of 0.7080 for 87Sr/ 86Sr of the Eimer and Amend standard, the initial ratios for the Wyoming granites are: (1) 0.7053 for granite of the Granite Mountains (this report), (2) 0.7022 for granite of the northern Laramie Range (Johnson and Hills, 1976), (3) 0.7044 for granite of the southern Laramie Range (Hills and Armstrong, .1974), (4) 0.7046 for the Baggot Rocks Granite , of the Medicine Bow Mountains (Hills and others, 1968), (5) 0.7010 for the Baggot Rocks Granite of the Sierra Madre (Divis, 1976), and (6) 0.732 for the Mount Owen Quartz Monzonite of the Teton Range (Reed and Zartman, 1973). These contrast with initial ratios consistently between 0.7000 and 0.7010 for the Minnesota granitic rocks (Hanson and others, 1971; Prince and Hanson, 1972; Peterman and others, 1972; Jahn and Murthy, 1975). To explain the unusually high initial 87Sr/ 86Sr ratio for the Mount Owen Quartz Monzonite, Reed and Zartman (1973) suggested that older crustal rocks were somehow involved in the genesis of the quartz monzonite, even thOugh the country rocks did not have sufficiently high 87Sr/ 86Sr values at 2,500 my. ago to account for the extremely high initial of the quartz monzonite. Whatever the exact mechanism may have been, it seems likely that older crustal rocks may have been involved to varying degrees in the genesis of the Wyoming granitic rocks. Alteration of the granite as manifested by linear zones of epidotization has not been directly dated in the present study. However, some reasonable inferences are in order. Similar alteration in the metamorphic complex is associated with nephrite mineralization, which, as shown in the following section, is dated at 2,510 my In addition, Rb and Sr analyses were completed on a whole-rock sample of strongly epidotized granite and epidote separated therefrom (table 4, GM-8l-68). Nearly all of the Rb has been removed and Sr has been enriched by almost an order of magnitude during the alteration. The 87Sr/ 86Sr ratios of 0.7070 and 0.7073 for the epidote and the whole—rock sample respective- ly are virtually identical and are indistinguishable from the initial 87Sr/ 86Sr ratio of the whole-rock isochron (fig. 5). If it is assumed that the Sr was derived locally, it had to have been separated from Rb only shortly after the granite crystallized. For example, if we take the average Rb / Sr value of the biotite granite as 1.9 and the isochron intercept at face value, the Sr in the epidotized granite would had to have been separated from a system with this mean Rb/ Sr value within a few tens of millions of years after the granite crystallized. More precise calculations are unwarranted because of the large uncertainty in the initial 87Sr/ 86Sr ratio of the granite. Based upon these calculations and the relationship of epidotization in other rocks with the nephrite mineraliza- tion, we conclude that this alteration occurred between 2,500 and 2,600 my. ago. DIABASE DIKES AND NEPHRITE VEINS Conventional K-Ar ages of approximately 1,600 my were previously reported (Peterman and others, 1971) for diabase and nephrite veins in the Granite Mountains. These ages are now known to be erroneous because of the difficulty in determining the potassium contents at the very low concentrations present—approximately 0.03 percent K20 in labradorite from the diabase and 0.01 percent in the nephrite. G. B. Dalrymple and M. A. Lanphere (written commun., 1976) determined 39Ar/ 40Ar ages of approximate- ly 2,600 my. on these same mineral separates (table 5). The diabase from which the separate of labradorite was obtained GEOCHRONOLOGY ’ 15 is described in an earlier section. The sample of nephrite was obtained from R. G. Coleman and was sawed from a piece of massive nephrite that occurred in a vein approximately 10 cm wide. A 2-cm cube was crushed and a sized fraction of -40 and +80 was prepared. The material was repeatedly washed with distilled water to remove the fines. We conclude from these data that both the diabase and the nephrite veins were emplaced only shortly after the granite was intruded. Older mafic dikes that are metamorphosed occur in the metamorphic complex, but it is not known whether all of the younger diabase dikes are of the same age. MINERAL AGES Rb and Sr analyses completed on various mineral phases from samples of the granite and of the metamorphic rocks are given in tables 3 and 4. Microcline was the major mineral analyzed, but all of the essential minerals were analyzed from three samples (GM-78, GM-98, and D1686). Mineral ages, calculated from the whole-rock-mineral isochrons are illustrated in figure 6. Internally consistent mineral ages were obtained on only two samples. GM-98, a tonalitic gneiss, is essentially composed of plagioclase, quartz, and biotite. Data for plagioclase, biotite, and the whole rock define a 2,440-m.y. isochron with an initial 37Sr/ 86Sr ratio of 0.7067. D1686, the granite at Tincup Mountain, yields a plagioclase, total rock, biotite, muscovite isochron of 2,300 my. with an intercept of 0.7203. Microcline from this sample deviates from the mineral isochron beyond experimental error with a microcline-total-rock age of 2,080 my. Minerals from GM-78, a granitic gneiss, are highly discordant as shown in figure 6. Microcline-whole-rock ages of the remaining samples range from approximately 1,500 to 2,100 my. Conventional K-Ar ages (table 6) were obtained on biotites—1,570 m.y. (GM-56), 1,780 my (D1686), and 2,310 my. (GM-98)—and on hornblende—2,680 m.y.(FCA—R-1). All of these data show clearly that the Rb-Sr and K-Ar mineral systems have been disturbed at some time subse- quent to the emplacement of the granite at 2,550 my. ago. Rosholt and others (1973) observed a remarkable colinearity of Pb isotope data obtained on microcline separates from the Metamorphic complex ‘k GM—98 GM—78 FCA-R-1 Granite * D1686 ZW—263 GM—56 CR—14 (157) CR-26 (165) GM—l (771) D114944 D114945 256179 Diabase GM—106 . Nephrite D1784 ‘ 1400 " 1600 - 1800 *- 2000 *8 2200 - 2600 - 2800 ' 3000 - FIGURE 6. —Rb—Sr and K- Ar mineral ages. Rb-Sr mineral ages are calculated from the mineral-whole~rock line. Open symbols are Rb-Sr ages; stars, whole-rock isochrons; circles, plagioclase; squares, microcline; diamonds, biotite; square with cross, muscovite. Solid symbols are conventional K~Ar and 39Ar/ “Ar ages: circle, labradorite; triangles, amphibole; diamond, biotite. granitic rocks. They concluded that this secondary isochron resulted from uptake of radiogenic Pb by microcline from other phases in the granite as the consequence of a thermal event at 1,6201120 m.y. ago—the age defined by the microcline isochron. Had the Pb in the mineral systems totally equilibrated at this time, the appropriate whole-rock-microcline isochrons would have given this same age. Complete isotopic homogenization was not attained, however, and ages calculated from the whole-rock-microcline points are variable, but greater than 1,640 my. On the basis of regional variations in these ages, Rosholt and others (1973) suggested that the intensity of the thermal event increased from the western part of the Granite Mountains eastward to the Seminoe Mountains. The mineral ages obtained in the present study support the interpretation of Rosholt and others (1973). Minerals from TABLE 5. —Ana1ytical data for 3‘A’Ar/M’Ar ages [The 37Ar/ ”Ar value 15 corrected for J7Ar decay using a half- life of 35.1 days. The percentages of “Arrad ”Area and J"Area are calculated using assumptions in Dalrymple and Lanphere (1971). The uncertainties on the ages are estimates of analytical precision at the l. orlevel of confidence. Analytical techniques, methods of calculation, and the monitor mineral are described in Dalrymple and Lanphere (I971). lrradiations were made with a dose of approximately 4x10” nvt. Sample localities are: D1784, lat 42°33’40” N., long 107°53’28” W GM—lO6—69, lat 42°34’10” N.,long 107°48’34” W.] Percent Sample “Ar/”Ar J7Ar/ ”Ar “Ar/ ”Ar .1' ”Ar-rad N‘Arm J9A1 ca Age (my) D1784 235.3 322.1 0.1864 0.01122 87.6 47.1 20.4 2,460145 (nephrite). Do ............. 292.5 347.1 .4151 .01234 67.6 22.8 22.0 2,560145 GM-106-69 310.6 223.1 .2451 .01122 82.4 24.8 14.1 2,650i130 (labradorite). 'J is a function of the age of the monitor and of the integrated fast neutron flux (Dalrymple and Lanphere, 1971). 16 PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING TABLE 6.—Conventiona1 K-Ar ages [Analystst R. F. Marvin, H. H. Mehnert. and Violet Merritt. ”“Ar refers to radiogenic “Ar. The age uncertainty is given at the 2-0' level] Sample K20, percent “0Ar "“Ar "‘JAr/‘oK Age (my) ([040 moles/ gm) Percent GM-56-68 8.36 301.2 99 0.1426 1,570150 (biotite). FCA-R-l .895 79.18 96 .350 2,6801160 (hornblende). D1686 5.40 236.1 99 .177 1,780140 (biotite). GM-98-68 8.99 604.7 99 .272 231101.55 (biotite). the westernmost sample (GM-98) give concordant ages of 2,440 my. Progressing eastwards, D1686 minerals are nearly concordant at 2,300 my. Minerals from GM-78 are strongly discordant with the lowest age of 1,600 my. recorded by biotite. Biotite from GM-56 is dated at 1,460 my. by Rb-Sr and 1,570 my. by K-Ar. Microcline from granitic rocks eastward to the Seminoe Mountains gives variably lowered ages that reach a lower limit of 1,500—1,600 m.y. Some of the microcline separates analyzed by Rosholt and others (1973) and by NKomo and Rosholt (1972) were also analyzed in the present study. Two alternate comparisons of the results are given on figure 7. The 207Pb/ 206Pb age for each sample is calculated from the whole-rock and microcline tie line. Two Rb-Sr ages are given for each sample. The open circles (fig. 7) represent a comparison of microcline-whole-rock 207Pb/ 20‘SPb ages with the Rb-Sr ages as calculated from the appropriate whole-rock and microcline pairs. This follows conventional assumptions in the interpretation of Rb—Sr systematics of disturbed mineral systems (Lanphere and others, 1964). In effect, the Rb-Sr mineral isochron is assumed to rotate about the whole-rock point, and if the event is sufficiently strong to cause complete isotopic homogenization among the mineral phases, the resultant isochron will record the time of this disturbance. The solid circles (fig. 7) represent a comparison of microcline-whole-rock 207Pb/ 20‘5Pb ages with the Rb-Sr ages as calculated on the basis of the microcline data points and the whole-rock isochron initial ratio of 0.7053. Brooks (1968) has documented a situation in which exchange of parent and daughter nuclides has occurred only between microcline and secondary alteration products of plagioclase. K—feldspar lost not only radiogenic 87Sr but also significant amounts of Rb and common Sr. Thus, in crystalline rocks that have undergone a mild thermal metamorphism without recrystallization, moderate isotopic disturbances of microcline may not involve exchange of common Sr with that of the host reservoir, that is, the whole-rock system. Regardless of the method used for calculating the microcline ages, the correlation of the Rb-Sr and 207Pb/ 2"’6Pb ages as shown in figure 7 is reasonably good. The correlation is somewhat better if the Rb-Sr microcline ages 2800 I _I I I I I I I l l I I 1 >1 - - E 0-— — —— — 0 01686 g 2600 - _ g _ o ——————— o GM-78 _ < W2-CR-14 (157) o- _ ._ _ _ __ _ 5 2400 - U ————— —-'0 W2-CR-26 (165) . g o———o ZW-263 Q _ - .D G. 5 2200 - _ N x ‘ - 8 o— — 0 114944 c; 2000 - _ "_',‘ o— —- —0 114945 0 - _ I 3| 1800 - _ LU a _ I .1 I ‘ U o 1600 - ' 1:: | e g I 2 - ' - 1400 I l l L I l I l L I J l l 1600 1800 2000 2200 2400 2600 2800 MICROCLINE Rb—Sr AGE, IN M.Y. FIGURE 7.—Comparison of Rb-Sr and 207Pb/20‘5Pb ages of microcline. Open circles, Rb-Sr ages calculated from microcline-whole rock isochrons. Closed circles, Rb-Sr microcline ages calculated from the microcline-whole—rock initial 87Sr/“Sr value. Vertical broken bar represents the l,6201120—m.y. thermal event as defined by the Pb isotope data on microcline (Rosholt and others, 1973). are computed on the basis of the isochron intercept. In both cases, with the exception of sample GM-78, the Pb-Pb ages are greater than the Rb-Sr ages. The general coherence of these ages is striking because resetting of the Rb-Sr microcline systems was accomplished by loss of radiogenic 37Sr whereas the lead-isotope system records the disturbance by addition of radio genic lead to the microcline. On the basis of a study in a contact metamorphic zone, Doe and Hart (1963) concluded that the lead-isotope system in feldspars was more easily affected than the Rb-Sr microcline and K-Ar hornblende systems but less easily than the K-Ar and Rb-Sr biotite systems. The disturbance of mineral-age systems in rocks of the Granite Mountains is part of a regional pattern that is recognized in several areas of the Precambrian of Wyoming (Giletti and Gast, 1961; Hills and Armstrong, 1974; Reed and Zartman, 1973). The lowered mineral ages are generally interpreted as being the consequence of thermal events or episodes of metamorphism. Naylor, Steiger, and Wasser- burg (1970) reported lowered Rb-Sr mineral ages in the southeastern Wind River Mountains and concluded that the rocks had been subjected to one or more events that occurred later than 2,000 my. ago. In this same area, biotites were dated at 2,200 and 1,430 my, whereas hornblende gave an older age of 2,620 m.y.—all by K—Ar (Bayley and others, 1973). Reed and Zartman (1973) concluded that rocks of the Teton Range had been affected by two thermal events—one GEOCHRONOLOGY 17 about 1,800 my. ago and a second between 1,300 and 1,500 my ago. Giletti and Gast (1961) also reported lowered mineral ages in the Teton and Gros Ventre Ranges, and Bassett and Giletti (1963) found similar lowered ages in the northwestern Wind River Mountains. Hills and Armstrong (1974) demonstrated the existence of a regional variation in K-Ar ages in Precambrian W rocks of the Laramie Range and of the Medicine Bow Mountains. They postulated the presence of a thermal or “geochronologic” front at the northernmost end of the Laramie Range, north of which micas yield 2,500 my. K-Ar ages, whereas micas from rocks of similar age farther south were lowered to between 1,400 and 1,600 my. Hills and Armstrong (1974) suggested that the front strikes southwestward from the northern Laramie Range towards the Seminoe Mountains. The existence of such a front seems to be supported by our mineral data from the Granite Mountains, and it can be fairly well defined by considering both Rb-Sr and K-Ar biotite ages from the Laramie Range, the Granite Moun- tains, and the Wind River Mountains (fig. 8). The front appears to trend westerly from the northern Laramie Range, inasmuch as mineral ages in the Seminoe Mountains and in all but the northwestern part of the Granite Mountains have been lowered. It can be projected farther West into the Wind River Mountains, where biotite ages are systematically lowered from north to south at the southeastern end of the range (fig. 8). The biotite that gives the 1,420-my. K-Ar age in the southeastern Wind River Mountains was obtained from a mylonitized granite (Bayley and others, 1973), and possibly the age dates the movement of a major shear zone. West of this locality, on the southern flank of the range, biotite from a basement core is dated at 1,840 my, whereas a whole—rock Rb-Sr determination clearly establishes the age as Precambrian W (Goldich and others, 1966). The consistent lowering of K-Ar and Rb-Sr biotite ages in rocks of Precambrian W age in the region south of the front (fig. 8) is an impressive feature. Geologic evidence that might support the presence of a metamorphic event is lacking except in proximity to the major terrane of Precambrian X and Y rocks in southern Wyoming and Colorado. An alternative interpretation to that of a discrete metamorphic event is that the reset mineral ages reflect crustal uplift and cooling below temperatures at which the radiometric systems in the minerals attain closure or cease to diffuse daughter products (Armstrong, 1966; Wetherill, 1966; Harper, 1967). This interpretation would require differential uplift of large crustal blocks in late Precambrian X or early Precambrian Y time, with the obvious possibility of one or more second-order events or cooling episodes superimposed on the uplifted blocks, which would account for some of the variability in mineral ages as presently observed. At the northern end of the Laramie Range, in the northwestern part of the Granite Mountains and in the southeastern part of the Wind River Mountains, the gradient in Rb-Sr and K-Ar biotite ages is steep—ages are drastically lowered over distances of 10-20 km. These steep age gradients are more likely to have resulted from one or more zones of major vertical dislocation than from a thermal or metamorphic event somehow related to younger Precam- brian orogenesis some 100-150 km to the south. A series of westerly trending faults is present in Phanerozoic rocks (Bayley and Muehlberger, 1968); these roughly coincide with or parallel the front defined by the biotite ages (fig. 8). Some or all of these may well have had precursors in the Precambrian. In the Granite Mountains, this hypothetical fault zone would lie near sample D1686 (fig. 2). Although a fault was not mapped, the existence of one is not precluded by our field study, as rocks with strongly developed vertical foliation occur near this locality. In the southeastern Wind River Mountains, several large Precambrian faults are mapped (Bayley and others, 1973) and, as mentioned previously, the K-Ar age of 1,420 my. is on biotite from a mylonitized granite apparently associated with one of the fault zones. If the lowered mineral ages in Precambrian W rocks south of the front (fig. 8) are indeed the result of cooling as a consequence of regional uplift, estimates of temperatures and depths at which the presently exposed rocks resided prior to this uplift can be made. Biotite loses radiogenic Ar and Sr at temperatures in excess of about 300°C (Hanson and Gast, 1967; Hanson, 1971). Using estimates of average geothermal gradients that might have existed approximately 1,500 my ago (Hargraves, 1976), presently exposed Precambrian W rocks with lowered biotite ages would have been uplifted from depths of 11-13 km between 1,400 and 1,600 my ago. Local survival of amphibole ages such as of the nephrite in the Granite Mountains (table 5), and of hornblende in the Wind River Mountains from the same locality as the 2,210 my. biotite age (Bayley and others, 1973), suggests temperatures of less than 500°C (Steiger and others, 1976) and depths of less than 18—22 km in the northern part of the block. K-Ar hornblende ages of 1,690 to 1,820 my. from Precambrian W rocks of the central Laramie Range (Hills and Armstrong, 1974) suggest that these rocks cooled below about 500°C at this time and subsequently below 300°C between 1,400 and 1,600 my. ago, as indicated by the biotite ages. The depth calculations are not meant to be highly precise; they have large uncertainties because of the known variability of present- day geothermal gradients from one geologic province to another (Roy and others, 1968) and imprecise knowledge of the blocking temperature and diffusion characteristics of biotite. The actual geothermal gradients may in fact have been greater than average because of the high radioelement content of some of the constituent rocks such as in the Granite Mountains (Rosholt and others, 1973), and, more than likely, the depth estimates are maximum values. In spite of these uncertainties, the temperature and depth l8 PRECAMBRIAN OF THE GRANITE MOUNTAINS, WYOMING 110° ., ,, 104° 43° 0 138 l 1(|)6 2400 /2230 320. @ WIND RIVER 2 2300 1780 —~ / ‘\ / r \2440 232%008 ¥_-_/ i% 2200 / 1320 15701460 1920 W%: GRANITE MTS j:& a? SEMINOEMS) Q 42"- l I I I GDLARAMIE g zsoor J \ RANGE 2 C 2 IL’ - 2000— uJ Q g luo’ V m | ~: 1380 O I— 1 — ' ' 7 ,: 500 |,. ..: u' . _: 75537,? % MEDICINE g . , BOW MTS m 1000 l I I I ’I North 50 o 50 100 150 200 South , KM 41° l | 0 50 100 150 KILOMETERS l l l J FIGURE 8. —l(- Ar and Rb- Sr ages, in millions of years of biotite from Precambrian W granitic and metamorphic rocks of southern Wyoming Rb- Sr ages are italicized Patterned areas are underlain by Precambrian X and Y rocks, here undifferentiated. The east- west- trending—line marks the front that separates biotite ages of2, 300 m. y. and older from those of2 230 m. y and younger. The inset shows ages plotted as a function of north or south distance from the dashed line. Data are from this study, Giletti and Gast (I961) Goldich and others ( I966), Hills and others (1968), Naylor, Steiger, and Wasserburg (1970), Bayley, Proctor, and Condie (I973), Hills and Armstrong (I974), and Divis (1976), and M. A. Lanphere (written commun., 1977). Precambrian outlines from Bayley and Muehlberger (I968). (pressure) parameters suggested by the mineral ages corres- pond to conditions of “very 'low grade” to “low grade” metamorphism as defined by Winkler (1974). Thus, the lack of definitive geologic evidence for a thermal event is not surprising, although pervasive chloritization of biotite, saussuritization of plagioclase, and protoclastic textures in ‘ the granite of Lankin Dome (table 2) could be the result of the granite having been held at these metamorphic con- ditions for some 1,000 to 1,200 my after crystallization. If the foregoing interpretation has any basis in fact, the uplift of a large block of Precambrian W rocks in late Precambrian X or early Precambrian Y time has important implications to the regional tectonics of the area. Several kilometers, perhaps 10 km or more, of material would had to have been removed by erosion subsequent to or concomitant with the uplift. In Precambrian Y time, large sedimentary basins to the northwest, west, and southwest of southern Wyoming received voluminous amounts of sediments that formed the Belt Supergroup and correlative rocks (Stewart, 1976). The Uinta Mountain Group would be a particularly attractive repository for material eroded from the uplifted block, and the source of the Uinta Mountain Group is thought to be toward the north (Hansen, 1965; Crittenden and Wallace, 1973). CONCLUSIONS Reconnaissance mapping of the western end of the Granite Mountains in central Wyoming has identified a metamorphic complex composed mainly of a layered sequence of quartzofeldspathic gneisses, amphibolites, and schists. Metagraywacke and amphibolite form sizable units at the westernmost end of the Granite Mountains. Tonalitic to granodioritic gneisses interlayered with lesser amounts of amphibolite, biotite schist, serpentinite, augen gneiss, and epidote gneiss form a sizable portion of the exposed metamorphic complex. The gneisses are well banded and range from layers of relatively uniform composition to migmatitic varieties. Interlayers of amphibolite are locally broken and distended to form boudins and rotated blocks within the gneisses. Rocks of the metamorphic complex are at amphibolite grade and were probably derived from a sequence of interlayered mafic volcanic rocks and graywackes or silicic volcanic rocks. The sequence may be correlative with or compositionally analogous to the greenstone-graywacke terrane exposed in the southeastern Wind River Mountains. Here, Bayley, Proctor, and Condie (1973) have described a thick section of graywacke, greenstone, and iron-formation. CONCLUSIONS I9 A migmatitic complex containing amphibolites and serpen- tinites is suggested to be the remnant of a mafic volcanic basement on which the sedimentary-volcanic sequence was deposited. Compositional banding and foliation within the metamorphic complex commonly dip southeast and south toward the younger granite batholith. Other than com- positional banding, primary structures in the metamorphic complex have been obliterated by metamorphism. The metamorphic complex was intruded by a batholith and two satellite bodies of biotite granite. The granite is medium to coarse grained, generally massive but locally foliated near the margin and in the satellite bodies, and is cut by late-stage dikes of granite, aplite, and pegmatite. Rocks of the metamorphic complex are also pervasively intruded by these late-stage dikes especially in proximity to the main bodies of granite. As a result of well-developed exfoliation, the granite g typically forms rounded hills and knobs. In most areas, weathering has affected the granite to depths of several tens of meters or more and surface samples are characteristically stained with iron oxides. Strongly altered zones, generally linear and steeply dipping, occur within the granite; they contrast sharply with unaltered phases by virtue of a well-developed blocky fracturing and a greater resistance to weathering. The alteration has been allochemical in that substantial amounts of epidote have been introduced, biotite has been partially to completely converted to chlorite and granular sphene, and microcline has been removed. In some of these alteration zones, the granite has been intensely silicified (Stuckless and others, 1977). Similar alteration occurs in the metamorphic complex where these zones are commonly associated with the nephrite mineralization. Numerous diabase dikes with a dominant east-northeast trend intrude both the granite and the metamorphic complex. These dikes range in thickness from several meters to several tens of meters. They are chilled against the enclosing rocks and generally coarser in grain size toward the centers. The dikes show variable degrees of alteration (Sherer, 1969), although some are remarkably fresh; olivine, pyroxene, and labradorite are their essential minerals. It is not known whether more than one age of dikes is present. Within the metamorphic complex, some of the amphibolite bodies are discordant with the compositional banding; these are presumably metamorphosed mafic intrusions. The discordant amphibolites, however, are clearly dis- tinguishable from the younger diabase dikes. Veins of nephrite (jade) occur within the metamorphic complex, mainly at the western end of the area. These are of local economic interest and are mined on a small scale. The nephrite veins were not studied in detail, and the reader is referred to Sherer (1969) for a comprehensive account of these deposits. Geochronologic studies have established a time framework into which the major Precambrian events of the Granite Mountains can be placed. An Rb-Sr isochron obtained on whole-rock samples of gneisses gives an age of 2,860+.80 m.y. This age is interpreted as the time at which the rocks of the metamorphic complex attained amphibolite-grade metamorphism. An initial 87Sr/“Sr of 0.7048t0.0012 is unusually high for juvenile material at 2,900 my. ago and suggests that the Sr in the protoliths of the metamorphic complex had a significant pre-metamorphic crustal history. Estimations based upon this initial Sr ratio, the metamorphic age of 2,860 my, and the average Rb/Sr ratio of the gneisses suggest that the Sr may have separated from the mantle some 300 to 400 my before metamorphism. Geologically this implies that the rocks themselves or the source terrane from which they were derived may be that old. Data obtained on four samples of amphibolite and massive tonalitic gneisses fall below the main isochron defined by the quartzofeldspathic gneisses and indicate an initial Sr ratio of approximately 0.7017. The amphibolites, at least, are likely ‘ to have been of volcanic origin; the lower initial Sr ratio would favor an interpretation that the layered quart- zofeldspathic gneisses are partly or completely sedimentary in origin. Twenty samples of granitic rock from the immediate area of study and from adjacent areas were analyzed for Rb and Sr. In general, data obtained from surface samples and on cores from shallow drill holes show excessive scatter on an isochron plot. Data for seven samples from deep drill holes define an isochron of 2,550t60 m.y. with an initial 87Sr/ 86Sr ratio of 0.7053_+.0.0056. This age is interpreted as dating the time of emplacement of the main body of granite in the Granite Mountains. Samples from other granite bodies in adjacent areas north of the map area and in the Seminoe Mountains provide data that plot on or close to the isochron, suggesting, at least provisionally, that these granites are approximately the same age. The Rb-Sr isochron age is in agreement with U-Pb data obtained on a zircon from the granite of Tincup Mountain and with zircon ages by K. R. Ludwig and J. S. Stuckless (written commun., 1976) on the main body. A sample of nephrite and one of labradorite from a fresh diabase yielded 39Ar/“OAr ages of 2,510i35 and 2,6501130 m.y. respectively. These data suggest that the diabase dikes were emplaced and the nephrite veins were formed only shortly after the granite was intruded. Ratios for 87Sr/ 86Sr determined on epidote and on a whole-rock sample from an epidotized zone in the granite also suggest that this alteration occurred within a few tens of millions of years after the granite was emplaced. Similar alteration in gneisses adjacent to nephrite mineralization, and the age of the nephrite, support this interpretation. Rb-Sr and K-Ar ages of feldspars and micas from both the metamorphic complex and from the granite have been lowered to varying degrees. Within the western part of the Granite Mountains, mineral ages are increasingly lowered 20 from west to east. This pattern in Rb-Sr and K-Ar ages is consistent with that observed earlier by Rosholt and others (1973) from the Pb-isotope systematics in microclines from the granite. When the mineral ages, especially Rb-Sr and K-Ar biotite ages, of the Granite Mountains are considered in a regional context with those from the Laramie Range and from the Wind River Mountains, a regional pattern emerges that can best be explained by major vertical tectonics in late Precambrian X or early Precambrian Y time. A biotite-age discontinuity in Precambrian W rocks extends from the north end of the Laramie Range, through the Granite Mountains, to the southeast end of the Wind River Mountains. North of this discontinuity, biotite ages are 2,300 my. or greater, whereas ages to the south decrease rapidly to between 1,400 and 1,600 my. 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ChronOlogigai narrative of the 1969—71 :yyMaunaUlu eruption of Kilauea VOICanojg Hawaii GEOLOGICAL SURVEY PROFESSIONAL PAPER 1056 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO, HAWAII l .> g < l '3. Lava fountain 300 m high plays from Mauna Ulu vent area on east rift zone of Kilauea Volcano, 1510 December 80, 1969. Lava flows fed by fountain cascade into Aloi Crater, 600 m from vent. Flow into Aloi was more Vigorous before a dam near vent area diverted most of lava southward. Hot lava fountaining upward is yellow; cooler lava falling back to ground is orange and dark gray. Foun- tain is widest of eruption and, as color pattern shows, appears to fan outward from vent. This was the last major fountain of the 1969—71 Mauna Ulu eruption. Scientists of the Hawaiian Volca- no Observatory remain close to vehicles in case wind should shift and send fallout westward into observation area. Chronological narrative of the 1969—71 Mauna Ulu eruption of Kilauea Volcano, Hawaii By DONALD A. SWANSON, WENDELL A. DUFFIELD, DALLAS B. JACKSON, and DONALD W. PETERSON GEOLOGICAL SURVEY PROFESSIONAL PAPER 1056 Description of the longest, most voluminous, and most varied flank eruption in Kilauea’s recorded history UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1979 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress catalog-card No. 78-600154 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 Stock Number 024-001-03136-1 CONTENTS Page Page Abstract _____________________________ 1 First stage of eruption—Continued Introduction __________________________ 1 October 14—19, 1969 ___________________ 25 Acknowledgments _______________________ 4 October 20, 1969 _____________________ 25 Events before the eruption __________________ 4 October 21—December 28, 1969 _____________ 29 Summary of eruption _____________________ 4 December 29-30, 1969 __________________ 31 First stage of eruption _____________________ 10 Second stage of eruption ___________________ 33 May 24—26, 1969 _____________________ 10 December 31, 1969-April 8, 1970 ____________ 33 May 27—June 11, 1969 __________________ 12 April 9—May 14, 1970 ___________________ 35 June 12—24, 1969 _____________________ 13 May 15—July 5, 1970 ___________________ 39 June 25—July 6, 1969 ___________________ 14 Third stage of eruption ____________________ 40 July 7—14, 1969 ______________________ 16 July 6—31, 1970 ______________________ 40 July 15—19, 1969 ______________________ 16 August 1—October 27, 1970 ________________ 42 July 20—August 2, 1969 __________________ 17 October 28—November 18, 1970 ____________ 44 August 3—4, 1969 _____________________ 17 November 19—December 24, 1970 ____________ 45 August 5—6, 1969 _____________________ 18 December 25, 1970—January 27, 1971 __________ 46 August 7—21, 1969 _____________________ 19 January 28—February 20, 1971 ______________ 47 August 22, 1969 _____________________ 20 February 21—June 14, 1971 _______________ 48 August 23—September 5, 1969 ______________ 20 Fourth stage of eruption ____________________ 50 September 6—7, 1969 ___________________ 22 June 15—October 15, 1971 ________________ 50 September 8—October 9, 1969 ______________ 24 Significance of the eruption __________________ 51 October 10—13, 1969 ___________________ 24 References cited ________________________ 54 ILLUSTRATIONS [Plates in pocket] Page FRONTISPIECE. Lava fountains 300 m above Mauna Ulu vent area, December 30, 1969. PLATE 1. Map of upper and middle east rift zone of Kilauea Volcano, showing vent fissures for eruptions between 1961 and 1971. 2. Summary of tilt, daily number of earthquakes, and important volcanic events during 1969—71 Mauna Ulu erup- tion. 3. Map showing sequential development of field of lava flows produced during 1969-71 Mauna Ulu eruption. 4. Maps showing changes in configuration and location of vents at Mauna Ulu, July 1970 to June 1971. FIGURE 1. Index map of Kilauea Volcano _____________________________________________ 3 2. Graph showing tilt at Uwekahuna vault and horizontal strain across Kilauea Caldera, February 1969-October 1971 __________________________________________________________ 5 3. Map showing location of five geodimeter lines across Kilauea Caldera ______________________ 6 4. Map showing area covered by lava flows of 1969—71 Mauna Ulu eruption ____________________ 7 5-9. Graphs showing: 5. Maximum fountain height compared with average eruption rate during first stage of 1969—71 Mauna Ulu erup- tion __________________________________________________________ 8 6. Rate of growth in height of Mauna Ulu, May 1969—June 1970 ___________________________ 9 7. Decline of level of lava lake in Mauna Ulu’s summit crater, May—October 1971 _________________ 9 8. Increase with time in cumulative volume of lava produced by the 1969—71 Mauna Ulu eruption _______ 11 9—39. Photographs showing: 9. Lava flow covering Ainahou Road, May 1969 _____________________________________ 12 10. Lava fountains from eastern and western areas, May 28, 1969 ____________________________ 12 11. Craggy spatter rampart, June 14, 1969 _________________________________________ 13 12. Basin surrounding western vent area, June 14, 1969 _________________________________ 14 13. Two fountains more than 200 m high, June 26, 1969 _________________________________ 14 14. Lava cascading over Holei Pali, June 26, 1969 __________________________________ 15 15. Flows erupted on June 25—26, 1969 covering Chain of Craters Road ________________________ 16 16. Man collecting lava from flow emptying from spatter cone, August 5, 1969 ____________________ 19 17. Fifteen-m-high fountain feeding flow draining back underground, August 15, 1969 _______________ 20 18. Partly filled Alae Crater and lava drapery on west rim, August 24, 1969 _____________________ 21 19. Partly drained lava lake in eastern vent basin, August 24, 1969 __________________________ 21 VI CONTENTS FIGURE 20. Tephra ridge extending south-southwest from vent area, August 30, 1969 ____________________ 22 21. Bark stripped off tree by falling pumice, August 30, 1969 ______________________________ 22 22. Newly formed western and eastern compartments in the western vent, August 24, 1969 ____________ 23 23. Lava flow in graben east of Alae Crater, September 8, 1969 ____________________________ 23 24. Aerial view of Mauna Ulu vent area, September 24, 1969 ______________________________ 24 25. Irregular profile of tephra mound on September 8, 1969 ______________________________ 24 26. Piece of reticulite caught in tree downwind from vent area _____________________________ 25 27. Eastern compartment of vent area, September 28, 1969 _______________________________ 26 28. Dome fountain, October 11, 1969 ____________________________________________ 27 29. Slump scars in welded spatter on flank of Puu Huluhulu, November 1969 ____________________ 27 30. Final minutes of fountaining at vent area, October 20, 1969 ____________________________ 28 31. Crusted pool of lava in eastern compartment, November 9, 1969 _________________________ 30 32. Sequence of drainback and refilling of eastern compartment, November 13, 1969 ________________ 32 33. Drainback at vent area, December 29, 1969 ______________________________________ 34 34. Lava falls into Aloi Crater, December 30, 1969 ____________________________________ 34 35. Tilted slabs of welded spatter blanketed by pumice and spatter erupted mainly on December 30, 1969 _ _ _ 34 36. Puddle of lava nearing display case at Aloi Crater, April 9, 1970 __________________________ 36 37. Lava flow spilling from Aloi Crater and covering Chain of Craters Road, April 9, 1970 _____________ 37 38. Aerial view of Mauna Ulu vent area, May 9, 1970 __________________________________ 38 39. Driblet spires in Aloi Crater formed on May 21, 1970 _________________________________ 39 40. Photograph of Mauna Ulu shield from top of Puu Huluhulu, June 20, 1970 ___________________ 41 41. Tracings from photographs showing profiles of Mauna Ulu as seen from Pauahi Crater, May 22, 1970 to mid- June 1971 _______________________________________________________ 41 42—51. Photographs showing: 42. Man sampling lava through skylight in lava tube, September 1970 ________________________ 43 43. Burning asphalt as lava flow crosses Chain of Craters Road, August 15, 1970 __________________ 44 44. Skylight in lava tube 100 m southeast of Alae Crater, November 5, 1970 _____________________ 45 45. Aerial view of subsidence bowl at Alae Crater and surrounding area, March 28, 1971 ______________ 48 46. Aerial View of trench and summit crater of Mauna Ulu, May 25, 1971 ______________________ 49 47. Characteristics of trench on east flank of Mauna Ulu, June 28, 1971 _______________________ 50 48. Blunt east end of trench and field of lava flows farther east, June 28, 1971 ____________________ 51 49. Man measuring depth to surface of lava lake with rangefinder, July 1971 ____________________ 52 50. Flat-topped ridge dividing Mauna Ulu lava lake into two pools, July 17, 1971 __________________ 52 51. East end of summit crater and dike, September 7, 1971 _______________________________ 53 TABLES Page TABLE 1. Papers dealing with aspects of the 1969—71 Mauna Ulu eruption ______________________________ 9’9”???” Motion pictures dealing wholly or largely with the 1969—71 Mauna Ulu eruption _____________________ Data for eruptions along east rift zone of Kilauea Volcano, 1961—71 Summary of episodes of high or sustained fountaining during the 1969—71 Mauna Ulu eruption ____________ 2 2 2 Cumulative extensional strain for distances in summit strain monitor during two periods of inflation, Kilauea Volcano— 6 9 0 Calculation of volume of 1969—71 Mauna Ulu lava CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO, HAWAII By DONALD A. SWANSON, WENDELL A. DUFFIELD, DALLAS B. JACKSON, and DONALD W. PETERSON ABSTRACT The 1969—71 Mauna Ulu eruption on the upper east rift zone of Kilauea Volcano lasted from May 24, 1969 to October 15, 1971; it was the longest and most voluminous flank eruption at Kilauea during historic time. About 185 X 10" m3 of basaltic lava was erupted; the lava covered an area of approximately 50 km2 and built a parasitic shield 80 m high. The eruption can be divided into four stages, each of which was dominated by a particular pattern of behavior. The first stage, May 24 to December 30, 1969, was characterized by episodes of high or sustained fountaining, each lasting from a few hours to about 3 days and interspersed with longer periods of weak activity. Most fountaining during this stage occurred in one general vent area located 600 m south-southeast of Puu Huluhulu, midway between two large pit craters (since filled), Aloi and Alae Craters. Fountains reached or exceeded 300 m in height during six of the episodes, once towering to a maximum of 540 m. The foun- tains supplied lava to fast-moving voluminous flows that travelled as far as the coastline, 12 km from the vent. The flows ultimately filled Alae Crater and partly filled Aloi Crater. The periods of weak activity between episodes of strong fountaining lasted from a few days to several weeks, during which time lava splashed and circu- lated in the vent, sometimes forming low fountains, sometimes qui- etly upwelling and overflowing the vent. Cyclic rise and fall of the lava column characterized the periods of weak activity. This phe— nomenon, termed gas-piston activity, is apparently caused by the expansion and subsequent vigorous loss of gas from the column as the gas neared the surface. The second stage, December 31, 1969 to July 5, 1970, was marked by weak activity at the vent similar to that which characterized the periods between major fountains of the first stage. Lava from a new fissure that opened across Aloi Crater in April completed filling the crater. During this stage, particularly in late May and June, over- flows of short duration from the main vent area built a shield, even- tually 80 m high; it was at this time that Mauna Ulu (“growing mountain” in Hawaiian) received its name. Much of the activity during this stage was characterized by gas-piston cycles. The third stage, July 6, 1970 to June 14, 1971, was marked by cessation of overflows from the main vent area and the opening of several vents along a new fissure on the east flank of the Mauna Ulu shield. Activity at the new vents was often dominated by gas- piston behavior, and overflows were common. The walls of the fis— sure at the summit of Mauna Ulu after progressively collapsing formed an ovoid crater within which an active lava lake circulated. Underground conduits from this lake probably supplied lava to the vents on the east flank of Mauna Ulu. Tubes carried lava from these vents into the crusted lava lake occupying Alae Crater, and an outlet tube transported lava from the lake and distributed it downslope. Much surface and tube-fed pahoehoe entered the ocean in September 1970 and March-May 1971. Beginning in Octo- ber 1970, small craters formed around the individual vents on the east flank of Mauna Ulu. These craters enlarged by collapse and merged to form a continuous trench along the fissure by the spring of 1971. The trench ultimately intersected the east end of the sum- mit crater. In late May, the vents on the east flank gradually stopped feeding lava to the reservoir in Alae Crater and the reser- voir in turn, stopped supplying lava to the flows and tubes to the south. The fourth stage, June 15 to October 15, 1971, was characterized by the slow decline and eventual cessation of eruptive activity. The surface of the lava lake in the summit crater progressively with- drew to lower levels, and circulation of lava grew increasingly slug- gish. The end of the eruption was marked by the disappearance of visible lava beneath rubble on the floor of the crater. The four stages of the eruption accompanied other important changes at Kilauea Volcano. Each stage was accompanied by har- monic tremor and a characteristic pattern of ground deformation in the summit area of Kilauea, 10 km west of Mauna Ulu. The first three stages (the fourth was not sampled) were typified by lava with chemistry that differed from one stage to the next. These pat- terns demonstrate a systematic relation between the eruptive be- havior of Mauna Ulu and the more fundamental process of magma supply to the entire volcano. Observations of the 1969—71 Mauna Ulu eruption provided a wealth of information regarding the development of parasitic shield volcanoes, the nature of the gas-piston process, the forma- tion of lava tubes and their importance in carrying lava long dis- tances, and a host of other processes not generally available for study during shorter eruptions. Consequently, the eruption must be considered one of the most important of all historic Kilauea eruptions. INTRODUCTION The longest-lived and most voluminous rift erup- tion in the recorded history of Kilauea Volcano began at 0445 May 24, 1969. For 21/2 years thereafter, 0b- servers were treated to a magnificent volcanic display that was unprecedented in its variety. At times, the heat from towering fountains of lava forced observers to cower behind barricades hundreds of meters away. At other times, the activity was so benign that one could peer directly into the vent, a seething cauldron 2 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO of bubbling, red-hot lava. The varied nature of activ- ity afforded members of the Hawaiian Volcano Obser- vatory unparalleled opportunities to observe first- hand the complex growth and evolution of a parasitic shield volcano, Mauna Ulu. The eruption is termed the 1969—71 Mauna Ulu eruption to distinguish it from other Kilauea erup- tions in 1971 (August and September) and from later eruptions of Mauna Ulu in 1972—74 (Peterson and others, 1976). Many papers have already been written dealing with specific aspects of the eruption (table 1), but they provide no broad overview of it. In this paper, we pre- sent a detailed chronological narrative of the entire eruption, summarizing as neccessary the pertinent ob- servations of the previous papers. Several motion pic- tures consisting wholly or largely of scenes from the eruption (table 2) provide additional visual documen- tation. TABLE 1.—Papers dealing with aspects of the 1969-71 Mauna Ulu eruption Topic Reference Swanson, Jackson, Duffield and Peterson (1971); Peter- son, Christiansen, Duffield, Holcomb, and Tilling (1976). Wright, Swanson, and Duffield (1975). Peterson and Swanson (1974); Cruikshank and Wood (1972); Greeley (1971, 1972). Swanson (1973); Schmincke (1971). Swanson, Duffield, Jackson, and Peterson (1972). Swanson and Peterson (1972). Duffield (1972). Duffield, Jackson, and Swan- son (1976); Endo (1971). Swanson (1972). Davis, Jackson, Field, and Sta- cey (1973). Anderson, Jackson, and Frisch- kencht (1971). Moore, Phillips, Grigg, Peter- son and Swanson (1973); Pe- terson (1976). Cristofolini (1969). Swanson and Fabbi (1973). General summary _______ Lava chemistry _________ Lava tubes ___________ Pahoehoe flows _________ Alae Crater, filling Alae Crater, partial draining Crust of Mauna Ulu lava lake May 1970 intrusive event Magma supply rate ______ Volcanomagnetic effect Detection of lava in tubes using geophysical methods _ _ _ _ Lava delta Mechanism of fountaining _ _ Volatile loss during eruption and lava flow Pele’s hair Duffield, Heiken, and Gibson (1974). Muenow (1973). Naughton (1973). Naughton, Lee, Keeling, Fin- laysen and Dority (1973). Naughton, Lewis, Hammond and Nishimoto (1974); Naughton, Greenberg, and Goguel (1976). Holcomb, Peterson, and Tilling (1974). Pele's tears __________ Volcanic flames ________ Gas chemistry _________ Fume sublimates ________ Volcanic landforms ______ TABLE 2.—Motion pictures dealing wholly or largely with the 1969-71 Mauna Ulu eruption. Name Producer Heartbeat of a volcano Subject General eruptive activity and how volcanologists Encyclopedia Britannica Educational Corporation, Chicago. monitor it. Fire Mountain _____ do. Eruption scenes artfully coordinated with music (no narration). Fire under Lee Tepley, Lava movement under the sea Moonlight Productions water; 2650 California St., Mountain View, CA., 94040. W. A, Duffield (U.S. Geological Survey) Menlo Park, CA., 94025. pillow formation. Movement of crust of Mauna Ulu plate ' lava lake. tectonics The eruption took place along part of the upper east rift zone of Kilauea (fig. 1), where much volcanic ac— tivity had occurred during the preceding eight years (table 3; pl. 1). The line of eruptive fissures between Aloi and Alae Craters, where most of the 1969—71 ac- tivity occurred, crosses at a small angle the trace of the December 1965 fissure system; principal vents of Mauna Ulu are less than 100 m south of the December 1962 fissure (pl. 1; Moore and Krivoy, 1964; Fiske and Koyanagi, 1968). Fumarolic activity, which had char- acterized this general area since the early 1960’s, in- creased after the December 1965 eruption and formed thick deposits of sulfurous sublimates along ground TABLE 3.—Data for eruptions along east rift zone of Kilauea Volcano, 1961—1971 [See plate 1 for precise locations) Area Volume covered of lava‘ by lava Date Locality (IO'ma) (km?) Reference 1961 Sept. 22—25 Near Napau Crater 1.39 0.76 Richter, Ault, Eaton, and 22 km eastward and Moore(1964). 1962 Dec. 7—9 Aloi Crater to Kane .12 .08 Moore and Krivoy Nui o Hamo (1964). 1963 Aug. 21—23 In and near Alae .63 .07 Peck, Wright, and Crater Moore(1966). 1963 Oct. 5—6 Between Napau Crater 6.8 3.3 Moore and Koyanagi and Kalalua Cone (1969). 1965 Mar. 5—15 Makaopuhi Crater to 15.2 7.05 Wright, Kinoshita, and Kalalua Cone Peck(1968). 1965 Dec. 24—25 Aloi Crater to Kane .59 .63 F iske and Koyanagi Nui o Hamo (1968). 1968 Aug. 22—26 Hiiaka Crater and .014 .02 Jackson, Swanson, 20 km eastward Koyanagi, and Wright(1975). 1968 Oct. 7~22 Napau Crater and 7.5 3.5 Do. 6 km eastward and westward 1969 Feb. 22v28 Near Aloi Crater and 20 6 Swanson, Jackson, 11 km eastward Koyanagi, and Wright(1976). 1969 May 244 1971 Oct. 15 Mauna Ulu (between 185 50 This paper. Aloi and Alae Craters) and vicinity 'Includes only volume remaining on surface. Does not include volume of lava that drained back into fissures before eruption ended. INTRODUCTION 3 155° 30' 155° 15' 155° 00' | | 1 Mountain View . Kapoho 19° 30' — 0 % Pahoa. g 6 _ '6 V‘ #Honuaula \ ‘\ 1 IzKaliu Kilauea Caldera q. 1 \ F 4? . . oKilauea lki a \ Helhelahulu 0 J} 5/ A 5 T #Kalalua 5’ Puu Huluhulu ,b Halemaumau Hiiaka C) Napau Koae/55mm.“ G7 PMakaopuhi é $<° —F8U't Alor Mauna Ulu fi " System [1’0 // A E C O 19 15 _ EXPLANATION _ O Pit crater Ulaula 3i Cone _‘__. O 5 1O 15 20 KILOMETERS Fault | l l | I Bar and ball on I . l j downthrown side FIGURE 1.—Kilauea Volcano, showing rift zones, fault systems, and localities mentioned in text. Aloi and Alae Craters have been buried by flows from Mauna Ulu. The subaerial part of the east rift zone is loosely divided into three parts: the upper part extends from the summit caldera to Makaopuhi Crater; the middle part, from Makaopuhi to Heiheiahulu; the lower part, northeastward from Hei- heiahulu to the seacoast. cracks and former vents. Other eruptions occurred within 1 km of the Mauna Ulu area in August 1963 (Peck and others, 1966) and February 1969 (Swanson, Jackson, Koyanagi, and Wright, 1976), only three months before the 1969—71 Mauna Ulu eruption be- gan. Throughout the 1960’s, the area centered around Aloi and Alae Craters was the western limit Of volcanic activity on the rift zone, except for a small eruption in and near Hiiaka Crater (pl. 1) in 1968 (Jackson and others, 1975). Much activity took place farther east (downrift), however (see pl. 1; Moore and Koyanagi, 1969, pl. 1; Swanson, Jackson, Koyanagi, and Wright, 1976, pl. 1). The Aloi-Alae area occupies an important structur- al location at the southeast end of the area where the Koae fault system and the east rift zone intersect (fig. 1). This area of intersection is doubtless complex at depth, magma conduits extend southeast from the summit caldera crossing and interact with east-north- east-trending fractures of the Koae system (Swanson, Duffield, and Fiske, 1976; Duffield, 197 5). Such struc- tural complexity may facilitate temporary blockages in magma conduits connecting with the summit reser- voir, leading to temporary storage, increased magma- tic pressure, and eruption uprift from the blockage. In their discussion, Swanson, Jackson, Koyanagi, and Wright (1976) relate this theme to the origin of magma reservoirs and pit craters along the upper east rift zone. ACKNOWLEDGMENTS Scores of individuals, from long-time personnel of the Hawaiian Volcano Observatory to mainland tour- ists on their Hawaiian holiday, contributed the obser- vations that make this narrative rather complete despite the long duration and complicated nature of the eruption. It is impossible to single out all these friends, but we hope they realize how important their observations were and how grateful we are for them. Personnel of Hawaii Volcanoes National Park made particularly valuable contributions in many ways, and without their assistance, our job would have been much more difficult. We take special pleasure in ex- pressing gratitude to three foreign geologists who had long visits at Kilauea during the eruption and contrib- uted ideas, helpful observations, and strong backs: Drs. Renato Cristofolini (Catania, Italy), Kazuaki Na- kamura (Tokyo), and Hans-Ulrich Schmincke (Bo- chum, West Germany). Two astronomers from the University of Hawaii, Dale Cruikshank and David Morrison, lowered their sights but retained keen ob- servational abilities, repeatedly applying them to Mauna Ulu in 1970—71. Finally, we thank H. A. Pow- ers, scientist-in-charge of the observatory until Au- gust 1970, and T. L. Wright, on the staff until mid- August 1969, for advice, field assistance, and ideas. EVENTS BEFORE THE ERUPTION The 1969—71 Mauna Ulu eruption was only one in a series of Kilauea eruptions that began in November 1967 and continued through December 1974. The No- vember 1967—July 1968 eruption (Kinoshita and oth- ers, 1969) was confined to Halemaumau Crater in Kilauea’s summit caldera (fig. 1). Thereafter, activity shifted to the upper and middle parts of the east rift zone, with eruptions in August and October 1968 (Jackson and others, 1975) and February 1969 (Swan- son, Jackson, Koyanagi, and Wright, 1976). Each rift eruption was larger than its predecessor; the February 1969 eruption, with a volume of lava of 20 X 106 m3, was probably the largest historic rift eruption at Ki- lauea prior to the 1969—71 Mauna Ulu eruption. The summit area of Kilauea began swelling even be- fore the end of the February eruption and continued to swell at a nearly constant rate until the Mauna Ulu eruption began (fig. 2). By May 10, summit strain had reached about the same level as just before the Febru- ary eruption (table 4; fig. 3). On this basis, we antici- pated an eruption in the near future, and on May 21 a CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO staff meeting was held to plan our course of study when the eruption began. Along with the greater strains, seismic activity in the upper east rift and summit areas increased episodically several days before the eruption (pl. 23 and C). SUMMARY OF ERUPTION The 1969—71 Mauna Ulu eruption lasted almost 29 months, from May 24, 1969 to October 15, 1971; the end of the eruption is taken arbitrarily as the last date on which lava was seen in the vent. About 185 X 106 m3 of basaltic lava was erupted from a 4-km-long set of fissures centered at a vent area between Alae and Aloi Craters (since buried), where most activity took place and where a large parasitic shield, Mauna Ulu (“grow- ing mountain” in Hawaiian), was built. Lava flows that erupted from this set of fissures eventually cov- ered an area of approximately 50 km2 (fig. 4). In addi- tion, a small volume of lava was erupted in August 1969 from a fissure 7—8 km downrift from Mauna Ulu. During the eruption, magma was supplied to the high- level storage complex with Kilauea at a rate of about 3 X 105 m3/day (about 0.1 kayr); some of this magma was erupted to the surface, and some remained under- ground (Swanson, 1972). The eruption can be divided into four stages (pl. 2; fig. 3) on the basis of the type of activity. The first stage, ending on December 30, 1969, was characterized by 12 short-lived (41/2 hrs—3 days) episodes of high or sustained fountaining separated by periods of weaker activity a few days to several weeks long. Six episodes of the first stage produced lava fountains 300 m or more in height, and one fountain was 540 m high. Fountain height correlated roughly with the rate of FIGURE 2.—Summary of ground tilt and horizontal strain in sum- mit area of Kilauea Volcano before and during the 1969—71 Mauna Ulu eruption. A, Ground tilt. East—west and north- south components of tilt measured with short-base water-tube tiltmeter in Uwekahuna vault (UWE in inset map in B). B, Horizontal strain. Extension and extensional strain for geodi- meter line across Kilauea Caldera between stations HVO 113 and HVO 10 (inset). Vertical bars, periods of strongest or un— usual eruptive activity during the 1969-71 eruption. Erup- tions also took place in late February 1969 (Swanson, Jackson, Koyanagi, and Wright, 1976) and in mid-August and late Sep- tember 1971 (Peterson and others, 1976); all three of these brief eruptions were accompanied by marked changes in ground tilt(A) and horizontal strain (B). CUMULATIVE EXTENSIONAL STRAIN, TILT, IN MICRORADIANS IN UNITS OF 10‘5 SUMMARY OF ERUPTION 20‘0 — 190 — 180 — 170— 160 — 150— 140 *— 130 — (inflation) 120 — West and north down ——> 110 — 100— 90% 80— 70— 60— 50 E-W component N-S component 1° _ k———1969 - 71 Mauna Ulu eruption —————>| “ 0 _ |<——Stage 1—>|<—Stage 2—>I<—Stage 3——>I<—Stage 4-)I _ II II | || ll I] I I I I I ‘I 45 _ J , n B — 140 155 17 30 _ 130 4° ’— F 120 — 110 35 — — 100 30 T _ 90 Halemaumau ‘ _ 80 25 _ 2 KILOMETERS -- 7O 20 — — 60 — 50 15 — — 40 10 ~ I — 30 ' . — 20 5 q Ié———1969 - 71 Mauna Ulu erupt:on———-————>I |<——-—Stage 1—>I<——Stage 2—)k—StageS—fl65tage 4-)] — 1O 0 II II I I II II o 1969 1970 I II 1 FIMIAIMIJIJIAISIOINID JTFIMIAIM'JIJIAISIOINID‘JfFIMI AlMIJlJlA’slo 1971 CUMULATIVE EXTENSION, IN CENTIMETERS 6 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO TABLE 4.——Cumulative extensional strain for distances in summit strain monitor during two periods of inflation, Kilauea Volcano1 Cumulative extensional strain“ Geodimeter Approximate (units 0f 10—5) ““93 length (m) 12 Oct. was 24 Fel» 12 Feb. 1969 20 May 1969 HVO 113-HVO 10 ‘ ‘ 3097 6.56 6.83 HVO 119—HVO 10 “ — 2893 4.94 4.80 HVO 113—HVO 114 ‘ " 5128 4.74 5.23 HVO 119—HVO 114 — ‘ 3070 5.15 5.18 HVO 119—HVO 113 — " 3155 4.75 4.12 'From Swanson, Jackson, Koyanagi, and Wright (1976). fsee figure 3 for location of measured lines. 3Relative to assumed zero strain at start of each period of inflation. Determined by comparing geodimeter measurements at different times and dividing the change in length by the initial length of the line. 155° 15’ l 19° 25' — EXPLANATION O Tilt station HVO 114 o Trilateration O 1 2 3 Kl LOMETERS ;|_;| station FIGURE 3.—Locations of Uwekahuna (UWE) vault containing short-base water-tube tiltmeter and trilateration stations used in determining the level of summit strain. See figure 2 and table 4. eruption (fig. 5A), which ranged from 0.05 to 1.45 X 106 thr for the 12 episodes (table 5). The total vol— ume of lava produced during short-lived episodes gen- erally varied directly with eruption rate (fig. 5B), consistent with model (Shaw and Swanson, 1970) and empirical (Walker, 1973) studies. A large mound of partly welded spatter and pumice was built downwind of the vent area. Lava flows fed by the fountains filled Alae Crater, which subsequently drained and then was quickly refilled (Swanson and others, 1972); lava also partly filled Aloi Crater. Flows advanced far to the south, and one flow entered the ocean 12 km away. Periods of weak activity between episodes of strong fountaining were typified by the presence of an ob- servable lava column within the Mauna Ulu vent. Nu— merous small flows were fed by the lava column when it rose high enough to spill out of the vent. Short-lived spatter cones were formed from time to time. A cyclic rise and fall of the lava column, termed gas—piston ac- tivity, was often observed. During such cycles, the lava column, capped by a solidified but flexible crust, first rose quietly a distance of a few meters to several tens of meters in 15—20 minutes. No spattering accompa- nied this rise. The column either continued its slow rise until the next stage began or stopped rising a short time before the next part of the cycle began. The next part of the cycle was violent. Suddenly, vigorous bubbling within the column generated intense spat- tering, the crust was torn to shreds, and the column withdrew turbulently to its starting level. The time from the onset of bubbling to the completion of with- drawal was generally a minute or two. This type of ac- tivity is ascribed to uplift of the column by expanding gases trapped beneath a relatively impermeable crust; eventually gas pressure overcame the strength of the crust, degassing of the column quickly resulted, and the lava withdrew to fill the void evacuated by the lost gas. The second stage of the eruption, December 31, 1969 to July 5, 1970, was marked by weak activity and no major fountaining episodes. The lava column was visible deep within the main vent for most of the time. Occasionally, however, it rose to the surface and spilled out as thin flows that added to the height of Mauna Ulu (fig. 6). Hundreds of such flows were erupted in five major pulses during a major period of growth at Mauna Ulu between late May and the end of June. Mauna Ulu broadened and nearly doubled its height between January and July to become a promi- nent shieldlike edifice standing 80 m above its base. This was the last period in which the height of Mauna Ulu increased during the eruption. Throughout the first two stages of the eruption, the height of the shield increased episodically but at a nearly linear rate of about 6 m per month, if averaged over periods of several weeks (fig. 6). The rate of volume increase with time could not be calculated owing to inadequate data on the shape of the shield, which grew asymmetrically. After June 1970, lava outpourings were confined to fissures on the flanks of Mauna Ulu and beyond its base; only during Mauna Ulu’s later eruptions in 197 2—1974 did its height again increase (Peterson and others, 1976). A new fissure opened across Aloi Crater on April 9, 1970 and erupted lava that eventually filled the crater. This activity continued until April 29. On May 15—16, a swarm of earthquakes (pl. 2B and C; Endo, 1971) ac- SUMMARY OF ERUPTION 969959 -I 19° 22' 30" 1) coo Puu . Pauahi Huluhulux x Kane Nu: o Hamo Ci . I Alae $19). AID! , V 3 ’I, /e\ ‘1 z. e: / . ‘\i:.£«’ -\<{-LL_‘.// \\ akaopuhn I Summit of / D 0 Mauna Ulu \ E \\ Road covered by lava to \ in February 1969 h g ' x ‘1' ‘ I) “a 0 0/ /% % 19° 20' / . / / I I \\ ‘\ o r ' Naulu P g , , . 0 Forest \ \ v o 3' P a l i e / \ b - l/ EXPLANATION 97 ° \ 0 I\ “ \ a U 6 \~ Chain of C4, Pit crater P a I i re“ 0 1 n V a k 0 4;, 4I19 17 30 \‘L ‘7 e a I “90' a . Pit crater (filled) x Summit of cone . a Q (“Q/‘0’" Kaena Point 0. Fissure of August ' «5'3" Kealakomo 4-11,1969 9/ BAN _ ______ ‘ Kahue 0C Road covered by I lPomt PAchIC l lava flow 155° 12' 30 Apua 155° 10' 155° 07, 30” Point O 1 2 3 4 5 6 7 KILOMETEFIS I I I I I I I I_LLI I I FIGURE 4.—Area covered by basalt flows of the 1969-71 Mauna Ulu eruption. See plate 3 for progressive development of the flows. All flows except those northeast of Napau crater were erupted from a narrow system of fissures trending east-northeast between the Ainahou Road and a point north of Alae Crater. The word “pali” means cliff in Hawaiian. 8 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO companied what we interpret to be the forceful intru- sion of magma beneath the southeast part of Kilauea Caldera (Duffield and others, 1976). This intrusion apparently caused structural readjustments in the up- per east rift zone, reopening or widening magma con- duits to Mauna Ulu and leading to the shield-building of late May and June. 12_llllllllili||.9||—‘ (I) 2 B 9 0 j 10_ 123. 11 _ E Z ‘~$ em 8— — ,_i- u_|.u 32 $9 6— ‘ to <3 >0 <11 01 .4 40 4—010 0 70.5 _ L5 °2 3 6' 8' w E 3 2~ — .1 2 12A. ||||l|l|l|il|l| O llllllllilillll U, A I 600—. — LIJ I— E” 9' E 500— _ ,: I 9 L; 400— 8o 123. fl 2 5- <( _ 7 11 _ ’2 30° ' EXPLANATION ' D E 4. ' 2 200 — Fountaining episode lasting — g 6 less than 9% hours _ O E o E 100 — 3° Fountaining episode lasting 10 0201 .12A 21% hours or more 0 lillllilillllli 0 O 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.01.1 1.2 1.3 1.41.5 AVERAGE RATE OF ERUPTION, IN MILLIONS OF CUBIC METERS PER HOUR FIGURE 5.—Average rate of eruption compared with maximum fountain height (A) and volume of lava erupted (B) for the 12 episodes of high or sustained fountaining in 1969. Episodes, rates of eruption, volume of lava erupted, and maximum fountain height given in table 5. For most episodes of fountaining, the average rate of eruption is probably not much less than the maxi- mum rate, as fountains typically varied in height by no more than a factor of 1.5—2 except during brief periods at the start and end of an episode. Note that both fountain height and volume of lava tend to vary directly with eruption‘rate. The four long—lived episodes (1, 2, 3, and 10) produced more lava at low eruption rates than predicted by the other data. The third stage of the eruption, July 6, 1970 to June 14, 1971, was characterized by repeated activity at several vents along an extension of the fissure system on the east flank of Mauna Ulu. Vent activity was of- ten dominated by gas-piston behavior, with or with- out overflows. Concurrently, the walls of the summit fissure progressively collapsed, forming a large elon- gate crater containing a constantly circulating lava lake. Underground conduits from this lake probably fed the vents along the eastern fissure. Lava flowed nearly continuously from these vents through lava tubes (Peterson and Swanson, 1974) into and out of the molten part of the lava lake in Alae Crater, which served as a holding reservoir that modulated the rate of outflow despite some fluctuation in rate of inflow. Lava left Alae through a tube system and eventually spilled out to form a complex tube-fed pahoehoe flow. This flow, a compound flow in Walker’s (1972) ter- minology, advanced 12 km southward and poured into the ocean on two occasions, September 21—26, 1970 and March 8—May 14, 1971 (Moore and others, 1973; Peterson, 1976). The crust of the Alae lake subsided twice, in early August 1970 and late February 1971, when the clogged outlet tube reopened and some lava drained from the lake to resupply the tube-fed flow (Swanson and Peterson, 1972). Throughout late 1970 and early 1971, a subsidence trench gradually developed along the fissure system on the east flank of Mauna Ulu as craters at several of the vents enlarged by collapse and eventually merged. The trench was separated by a narrow septum from the elongate summit crater. A new fissure opened across the site of Aloi Crater on January 28, 1971 and erupted lava until February 10. The flows built a low mound on the west flank of the Mauna Ulu shield. The fourth stage of the eruption, June 15 to October 15, 1971, was marked by the slow decline and eventual cessation of eruptive activity. No flows were added to the surface, and the only molten lava visible was in the circulating lake in the summit crater. The surface of the lava lake lowered at a nearly constant rate of 0.7m/day (fig. 7), and circulation became increasingly sluggish. The eruption was arbitrarily considered at an end on October 15, when the lava lake could no longer be seen beneath rubble at the bottom of the crater, 145 m below the rim. The crater and trench continued to widen by collapse as the eruption died. Eventually, the summit crater was more than 185 m long and 100 m wide, and the trench was 520 m long, 40—60 m wide, and 50 m deep. The total volume of lava produced during the erup- tion was calculated in three steps, which involved ac- counting for the volumes of new lava flows and of the SUMMARY OF ERUPTION Table 5.—Summary of episodes of high or sustained fountaining during the 1969—71 Mauna Ulu eruption Average Episode Date (1969) Volume rate of Maximum Duration erupted eruption‘ fountain Started Ended (hours) (105mg) (10‘m3/hr) height (m) 1 _________ 0445 May 24 1500 May 25 34% 4.5 0.13 50 2 _________ 1900 May 27 0900 May 29 38 3.5 0.09 50 3 _________ 1330 June 12 1100 June 13 211/2 4.0 0.19 100 4 _________ 2145 June 25 0700 June 26 91/4 4.5 0.49 220 5 _________ 0345 July 15 1220 July 15 8V2 4.0 0.47 375 6 _________ 1715 Aug. 3 0010 Aug. 4 7 3.5 0.50 150 7 _________ 2100 Aug. 5 0545 Aug. 6 8% 4.0 0.46 300 8 _________ 0015 Aug. 22 0440 Aug. 22 41/2 3.5 0.78 400 9 _________ 1930 Sept. 6 0430 Sept. 7 9 12.0 1.33 540 10 _________ 0900 Oct. 10 1100 Oct. 13 74 4.0 0.05 30 11 _________ 0100 Oct. 20 0820 Oct. 20 7% 10.5 1.45 300 12A ________ 0500 Dec. 30 0825 Dec. 30 31/2 1.0 0.29 75 12B ________ 1000 Dec. 30 1830 Dec. 30 8V2 10.0 1.18 390 ‘Average eruption rate was computed by dividing the volume of lava erupted, estimated from the area and thickness of new flows, by the duration of fountaining. ‘ 90 3 lllllllllllll 3 80— E 3 70 - E s g 60 '— m E 50 — m < Lu ,3 E 40 —— EXPLANATION w 2 > ' so — _ 0 __ g TheodolIte measurement < 20 — go I:I_: qe‘°/ 0 1° _ / Actual growth curve Estimated height —‘ E (schematic) Vertical bar indicates error I ° ngI>IéIgI5ISId :~I,,I;;I_-I«>,I2I_> " w a 233330§03£§<233 1969 1970 FIGURE 6.—Increase in height of Mauna Ulu shield with time. Ephemeral spatter cones occasionally rose 10—15 in higher than summit of shield (fig. 41). Heights determined by theodolite measurements from the top of Fun Huluhulu. Estimated eleva- tion of preeruption ground surface directly beneath summit of Mauna Ulu, 951 m (3,120 ft), is calculated from the US. Geologi- cal Survey’s 1224,000 topographic map of the Makaopuhi Crater quadrangle and adjusted for the thickness of the December 1965 flow. shield itself, and the filling of Alae Crater (table 6). The volume of lava filling Aloi Crater is too small to be considered in the calculation in light of the probable errors in the measurements, estimated at about 15 per cent. The results show that the field of new flows is about 71 percent, the shield about 19 percent, and the Alae filling about 10 percent of the total volume of 185 x 106 In3 (table 6). The four stages of the eruption broadly correlate with the degree and rate of tumescence in the Kilauea summit area (fig. 2; pl. 2). During the first stage, ex- pansion took place between fountaining episodes and contraction during each episode. The expansion and contraction nearly cancelled each other, leaving only a small net contraction (fig. 23) at the end of the first 5° I | I | I 60 —— o , — 70—- . __ 80 — o _ 90 — o _ 100 — ., — 110 — o _‘ 120— ‘ DEPTH T0 LAVA, IN METERS 130 — 140 -— 0 End of eruption l 150 1 May June I July lAugust lSsptembsrl October 1971 FIGURE 7.—Depth to surface of lava lake below northwest rim of summit crater of Mauna Ulu from May 12 to October 14, 1971. Depth was determined with rangefinder (see fig. 49) and dip an- gle. stage. During the second stage, the summit expanded at a rapid rate until late May 1970 and at a reduced rate thereafter, during the period of copious overflows at Mauna Ulu. During the third stage, horizontal ex— pansion (fig. 2B) continued at a roughly constant rate except for an inflation-deflation cycle centered around the January—February 1971 outbreak. Sum- mit tilt (fig. 2A; pl. 2A) increased and then decreased during the third stage. During the fourth stage, the southern part of the summit area began to inflate rap- idly (fig. 2A, N—S component), and this inflation con- tinued throughout the summer. Eruptions took place in Kilauea Caldera and along the southwest rift zone in August and September 1971, but neither visibly af- fected the dying Mauna Ulu activity. 10 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO TABLE 6.-—Calculation of volume of 1969—71 Mauna Ulu lava Lava field: Area covered, 44 X 106 m2 Average thickness (estimated), 3 m Volume of Lava field, VL, = (44 X 106 m2)(3 m) = 132 X 106 m3 Mauna Ulu shield: Approximates ellipsoidal cone with height h of 80 m and major and minor half axes a and b of 800 m and 500 m respectively 7‘, Volume of Mauna Ulu shield, VMU: = — (abh) = 34 X 106 m3 Alae Crater 3 Preeruption pit approximates sum of two ellipsoidal cylinders: 2al = 600m, 2bl = 400 m, hI = 64 m and 2a, = 350 m, 2b, = 280 m, h, = 92 m Volume ofAlae, VA, = Vl + V2 = 1r(a,b,h, + a2b2h2) = 119 X 106m3 Total volume of Mauna Ulu lava = VL + VMU+ VA = 185 X 106m3 'Excluding more than 3 X 10"mJ of lava that drained out of the crater on August 4, 969. The first three stages of the eruption represent a pe- riod of continuous magma supply at a nearly constant rate to Kilauea (Swanson, 1972). The first and third stages each produced flows at average rates of about 9 X 106 m3 per month (fig. 8). The rate was less during the second stage, coincident with increased swelling and assumed storage of magma in the Kilauea summit area. The volume of stored magma computed from ground-deformation data, combined with that of the second-stage lava, indicates an average rate of magma addition to Kilauea of about 8.3 x 106 m3 per month during the second stage, close to the rate for stages 1 and 3 when uncertainties in the deformation models are considered (Swanson, 1972). Three of the four stages of the eruption are charac- terized by slightly different chemical compositions of the basaltic lava. Of the five chemical variants defined by Wright, Swanson, and Duffield (1975), variants 1—3 were erupted during only the first stage, variant 4 dur- ing only the second stage, and variant 5 during the third stage. No samples could be collected during the fourth, dying stage. A hybrid involving mixtures of variants 3 and 4 was erupted early in the second stage. These variants cannot be related to each other by any recognized fractionation scheme (Wright and others, 1975). Chemical variations during the three main stages apparently reflect processes of magma genera- tion or supply not usually acting during a single Ki- lauea eruption; most Kilauea eruptions generally produce lava that is rather uniform chemically except for the effect of shallow mixing and fractionation. In part, the chemical variations may simply be related to the longer duration of this eruption than most Kilauea eruptions. However, at least some past Kilauea erup- tions lasting several months, such as the 1967—68 Ha- lemaumau eruption, produced chemically similar lava throughout the duration of activity (Wright, 1971). The eruption was the first flank eruption at Kilauea during historic time to include a long-lived active lava lake. Lava in this lake, which can be considered as the upper part of the magma column supplying Mauna Ulu, actively circulated and degassed throughout most of the eruption. Previously, active lakes at Ki- lauea had been observed only in Halemaumau Crater, in the summit caldera. All other so-called lava lakes observed to form at Kilauea have been “inactive” lakes, as they were simply lava flows that ponded within pit craters and were not formed directly on top of a magma column. This kind of lake formation is true even for the well known 1959 Kilauea Iki and 1965 Makaopuhi “lava lakes,” which were fed from vents on the crater walls that ceased activity when the level of ponded lava reached and “drowned” them (Richter and Moore, 1966, p. 3; Wright and others, 1968, p. 3196—3197). The easily accessible and long- lasting 1969—71 Mauna Ulu eruption afforded good opportunities to study the long-term processes of cir- culation, growth of crust, drainback, and degassing in the active lava lake (Duffield, 1972). FIRST STAGE OF ERUPTION MAY 24—26, 1969 The first episode of fountaining began at about 0445 May 24 from a zone of fissures that crossed the northern part of Aloi Crater and extended as far east as due north of Alae Crater (pl. 3A). Lava flooded the broad area of active fumaroles just west of Aloi, de- stroying a bordering swath of forest and leaving a grove of lava trees. The fissure zone quickly opened westward, crossing the Chain of Craters Road by 0500. Several earthquakes were felt by local residents at about this time. By 0830, a fissure extended across the Ainahou Road (fig. 9) and soon thereafter reached a point 150 m west of the road. Color aerial photographs taken by personnel of San- dia Laboratories at 0940 show that spatter cones and ramparts were forming at two main areas of fountain- ing, one between the western end of the fissure zone and the Chain of Craters Road, the other about half— > way between Aloi and Alae Craters, where fountains jetted as high as 50 m (table 5). The photographs also show that Aloi Crater, earlier filled to a depth of 25 m with a pool of new lava, was now largely empty owing to drainback into a gaping fissure in the floor. Lava was pouring into Alae Crater and had already covered the floor, burying drilling equipment being used in a study of the February 1969 lava lake (Swanson, J ack- son, Koyanagi, and Wright, 1976). Most of the pahoehoe flows from the western area of fountaining advanced southward before ponding at 190 180 170 160 150 140 130 120 110 100 90 80 7O 60 50 CUMULATIVE VOLUME OF ERUPTED LAVA. IN MILLIONS OF CUBIC METERS 40 30 20 1O FIRST STAGE OF ERUPTION llilllll IIIIIIITTIIT |||| E — .9 ,_, _ D. 3 5 _ '6 _ "U C LU — _l C .9 E —+—3 _ 5 ‘5 o-v _§ _ U) Stage 1 ‘ Stage 2 Stage 3 Stage 4—1 > olglafiTflgld :- fil£|£|>~l°l3idldiul$lu c n- g .; >lm|>la|a|a 5 o' zggggsgszzgéé£22§8232:§2§§22§828 1969 1970 1971 11 FIGURE 8.—-Cumulative volume of lava, including tephra, produced during 1969—71 Mauna Ulu eruption, plotted against time. All vol- umes during stage 1 and stage 2 and some during stage 3 and stage 4 computed from estimated area and thickness of lava flows and tephra deposits. Most volumes during stage 3 and stage 4 computed from eruption rate determined from observations of lava flowing in lava tubes between Mauna Ulu vent area and Alae Crater. 12 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO FIGURE 9.—View northward along trace of Ainahou Road (pl. 3), buried by lava flow erupted from fissure that crossed road near most distant figure on May 24, 1969. Lava trees (right edge) that line trace of road indicate maximum height of flow before spreading laterally and downslope. the foot of north-facing Kalanaokuaiki Pali (pl. 3A). The flow from the eastern area was briefly impounded behind a row of spatter cones built during the Febru- ary 1969 eruption just west of Alae Crater (pl. 1; Swanson, Jackson, Koyanagi, and Wright, 1976, fig. 15), but soon the dam was breached, and the flow eventually reached about 1.5 km from the vent. The February cones were completely buried on May 27, but their location was marked by an abrupt increase in slope of the new lava flows (fig. 15). The steep slope, which persisted for many months despite repeated covering with fresh flows, provided a good geographic reference in an otherwise constantly changing waste- land. The activity along the western part of the fissure system stopped by 2200 May 24, but weak fountaining continued at the vent area between Aloi and Alae Craters until about 1500 May 25. Harmonic tremor, a type of seismicity that indicates the underground flow of magma, continued thereafter, so that we suspected that the eruption was not over. The western vents of the fissure system are located within what is generally accepted as the extreme east- ern part of the Koae fault system, the first activity in the system in historic time. This part of the fissure system closely follows the gently curved trend of pre- existing faults and ground cracks, and the main fis- sure may coincide with one of these ruptures, although this cannot be documented because of the cover of new lava. The westernmost vent area is lo- cated along the trace of a preexisting, north-facing scarp. The chemical composition of lava from this vent (Wright and others, 1975, sample DAS691—10) suggests some mixing with differentiated magma, per- haps stored for some time in this part of the Koae fault system, where eruptions are infrequent but in- trusive events common (Swanson, Duffield, and Fiske, 1976, table 1). The vent area between Aloi and Alae Craters devel- oped into by far the most important vent area of the entire eruption, for it was here that Mauna Ulu, a large parasitic shield, was eventually constructed. This area is designated the Mauna Ulu vent area throughout the rest of the paper. MAY 27—JUNE 11, 1969 At 1900 May 27, the second episode of major foun- taining began in the Mauna Ulu vent area from two distinct vents, designated the eastern and western vents, about 150 m apart, along offset segments of the same fissure (pl. 3A; fig. 10). An arcuate spatter ram- part 8—10 m high was built up along the west and north edges of the vents, and a low ridge of spatter formed a few tens of meters downwind to the south- southWest. Lava fountained from both vents, gener- ally higher, as much as 50 In (table 5), from the eastern vent. These two vents remained separate entities for nine weeks, until the eastern one became inactive. FIGURE 10.—Fountains play from eastern and western vents in the Mauna Ulu vent area, May 28, 1969. View northeast from point 400 m east of Aloi Crater. Note spatter ridge forming between the vents. FIRST STAGE OF ERUPTION 13 Pahoehoe spread eastward from the eastern vent into Alae Crater and southward from the western vent across the flows of May 24—25 and February 22 (Swan- son, Jackson, Koyanagi, and Wright, 1976). By 1700 May 28, the longest flow reached 1.5 km south of Alae Crater, and it continued another kilometer before stopping on May 29 (pl. 3A). Fountaining stopped at 0900 May 29, and no fur- ther visible activity took place before June 12. Har- monic tremor continued, however, and dull rumbling and sloshing sounds were heard during several visits to the vent area. As the lull continued, we became less confident that another episode of fountaining would ensue and hypothesized that the sounds and tremor were related to degassing of stagnant lava left in the fissure system after the late May activity. We were wrong. JUNE 12—24, 1969 During reconnaissance for new survey lines at 1315 June 12, we heard roaring noises coming from the Mauna Ulu vent area a kilometer away. They sounded much like strong winds but persisted for several min- utes. One of us investigated, topping a low rise 100 m away in time to see a column of lava 3—4 m high .well- ing from the western vent and feeding a flow less than 5 m long. The column was rapidly growing in height and changing from a calm outwelling to a vigorous fountain. The eruption had indeed resumed, with its third episode of fountaining, surprisingly with no pre- monitory increase in seismicity. Within two hours, the fountain reached 100 m (ta- ble 5) above the western vent and 75 m above the east- ern vent (Swanson and others, 1971, p. 12, photograph). Fallout of spatter was heavy around the vents, quickly adding to the height of the existing cones, and pumice and smaller bits of spatter blew to- ward the south-southwest for hundreds of meters, building a low, broad ridge. Strong fountains contin- ued through the night and were still 50—75 m high at 1045 the next morning. Then, with remarkable swift- ness, the fountaining declined and ended. Within 10 minutes, all surface activity was over except for slight overflow from the western vent, and the overflow stopped only 5 minutes later. The fountains surged as they waned, each successive surge lower than the pre- ceding one. Subsequent periods of high fountains in 1969 ended in a similarly rapid, surging manner (for example, fig. 20). Lava pooled above and near the fis- sure drained back as the fountains stopped. A small volume of fountain-fed lava cascaded into Alae Crater. Most, however, flowed southward, ad- vancing down and eventually filling and overspilling the channel of the May 27—29 flow. The fluid pahoe- hoe flow reached the end of the May flow in the early evening and continued downslope through a sparse forest. By midnight, the flow had begun cascading brilliantly over Poliokeawe Pali, changing from pa- hoehoe to aa in the process. By early morning, the flow was pouring over the even steeper Holei Pali and spreading slowly seaward, eventually coming to rest shortly before noon, about 1 km from Apua Point and nearly 11 km from the Mauna Ulu vent area (pl. 3B). Despite this long flow, the total volume of lava erupted was close to that of the preceding two epi- sodes of strong fountaining (table 5), because most of the lava went into the flow, with only a small amount emptying into Alae Crater or piling up near the vents. An unusually sharp-peaked, craggy spatter ram- part, largely formed by modification of the preexisting rampart, was constructed between the western and eastern vents during the fountaining (fig. 11). This rampart had a shiny, glazed surface created when still molten spatter landed and flowed down the nearly vertical flanks. A broad, discontinuous rampart made of spatter and fragments of crust from natural levees surrounded the entire vent area but was higher on the downwind side. The rounded flanks of the rampart were deeply scored with cracks that formed when the rapidly deposited, still hot tephra began to flow. Some large blocks of the rampart were undermined or bull- FIGURE 11.—-Craggy, furrowed spatter rampart between the west- ern and eastern vents in the Mauna Ulu vent area, viewed from south edge of western vent on June 14, 1969. Peak of rampart about 10 m above its base. Material in foreground consists of partly welded spatter that slumped toward western vent when lava drained into fissure after fountaining stopped on June 13. 14 dozed by the lava flow and carried downslope several hundred meters. The Mauna Ulu vent area was several meters lower than the area just outside the rampart, owing to drain- back into the fissure after fountaining ceased. We call this low area the vent basin (fig. 12). The vent basin remained distinct until the spring of 1970, often filling with lava that drained away as activity waned. The vent basin was generally several times as wide as the fissure, and its floor usually sloped toward the fissure. As Mauna Ulu grew in height, the rampart and basin floor maintained about the same difference in eleva- tion except for short periods during which the basin partly or entirely filled. Many statements in this nar- rative are referenced to some height above the floor of the vent basin, which is taken to be the low point of the basin at the rim of the eruptive fissure. As long as both the eastern and western vents were active, each developed itsown basin (fig. 12). For almost 2 weeks, following cessation of fountain- ing, no lava was visible. Harmonic tremor continued to be detected by nearby seismometers, and low- pitched, thunderous sounds were commonly heard, accompanied at times by a sloshing noise that we later FIGURE 12.-—Basin surrounding western vent, June 14, 1969. Fume issues from the last active vent of the previous day. Ledge to left of fume indicates level of lava pooled above vent before drain- back. Low spatter rampart is just beyond ledge. J umbled area in front of fume is slumped material, chiefly Viscous lava with some smooth plates of crust, that slid downslope as lava withdrew. Height of ledge above rim of vent, about 7 m. Puu Huluhulu in background. CHRONOLOGICAL NARRATIVE OF THE 1969-71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO learned to associate with slowly bubbling lava. Small amounts of fume often rose from both vents. JUNE 25—JULY 6, 1969 The fourth fountaining episode of the eruption be- gan at 2145 June 25 and ended at 0700 June 26. In that short 9% -hour interval, 4.5 X 106 m3 of lava erupted, a rate 21/2 times that for the previous fountaining epi- sode (table 5). In other respects, however, the episode was similar to that of June 12—13. Twin fountains ris- ing from the two vents (fig. 13) reached a maximum height of 220 m, giving rise to a thick pumice fallout that added substantially to the tephra ridge down- wind (pl. 30) and blanketed the parking lot and road at Aloi Crater to a depth of 50 cm. Flows produced by fallback at the base of the fountains poured across the early June pahoehoe and cascaded over Poliokeawe and Holei Palis (fig. 14). A small volume of aa entered FIGURE 13.—Twin fountains in Mauna Ulu vent area more than 200 m high erupting during the early morning of June 26, 1969. Defoliated trees are silhouetted above rapidly growing ridge of tephra downwind from vent area. View from southwest. FIGURE 14.———Holei Pali viewed from several hundred meters sea- ward of its base, showing lava cascade of June 26, 1969. Note how lava, probably with a fluidity transitional between pahoehoe and aa, surges down the steep slope, much as water moving in a flume. Sticky aa flow (foreground) slowly advances from base of pali. This flow entered the ocean several hours later. Visible height of pali, about 220 m. Photograph by D. W. Reeser, Na- tional Park Service. 15 FIRST STAGE OF ERUPTION 16 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO the sea 2 km east of Apua Point at 0835 June 26, an hour and a half after fountaining ended, forming a jag- ged point extending 40 m seaward from the shoreline. Moore, Phillips, Grigg, Peterson, and Swanson (1973, p. 537—539) describe the submarine part of this flow; the flow is estimated to have a volume of about 0.1 X 106 m3 (Peterson, 1976). About 1 X 106 m3 of lava was added to Alae Crater, raising the floor of the crater by 7 m to 30—35 m below the low point on the rim. Most of the Chain of Craters Road near Alae Crater was now covered with new flows (fig. 15). The basic configuration of the Mauna Ulu vent area remained unchanged during this outburst. The spat- ter ramparts grew slightly higher and became less craggy. The fissure widened to nearly 5 m at the east- ern vent, and one could peer into it and into a hole beneath the rampart separating the two vents (Swan- son and others, 1971, cover photograph). The broad ridge of spatter and pumice downwind from the vent area increased several meters in height and en- croached still more on the forest, now almost com— pletely denuded by falling tephra within 1 km of the vent area. jULY 7—14, 1969 Ten days of subterranean sounds, harmonic tremor, and periodic outrush of hot gas from the vents fol- lowed the June 25—26 activity, but no lava was ob- served until July 7, when it reappeared in the eastern vent of the Mauna Ulu vent area. The lava remained unagitated in the fissure except for brief periods when it emitted short-lived bursts of spatter or rose to the lip of the vent and spilled out into the vent basin as flows of only a few square meters extent. We could easily approach and sample the lava column at such times. This was the first episode of what was to be- come one of the dominant modes of eruption at Mauna Ulu; in fact, after December 30, 1969, all activ- ity was basically this type, although with many embel- lishments and degrees of vigor. It was at this time that we first observed a cyclic rise and fall of the lava col- umn, a process that we saw many times subsequently and ascribed to a gas-piston mechanism. One of the best examples of this process occurred on July 29—30; it is described in the section dealing with that period. The frequency of spattering, fissure overflows, and cy- clic rise and fall of the lava column gradually in- creased from July 7—14, as if leading up to another period of high fountaining. JULY 15—19, 1969 The fifth episode of strong fountaining began at 0345 July 15, and by 0430 lava was spraying nearly 375 m into the air. The highest fountains issued from the eastern vent in the Mauna Ulu vent area, although FIGURE 15.—Flows erupted on June 25—26, 1969 cover Chain of Craters Road near southwest rim of Alae Crater. Large crack off- setting center line of road formed during February 1969 eruption (Swanson, Jackson, Koyanagi, and Wright, 1976). Arrow indi- cates abrupt increase in slope of new flows across buried row of February 1969 spatter cones. Mauna Ulu vent area hidden be- hind trees on right. Photograph taken June 29, 1976. fountains from the western vent reached heights of over 200 m. Two parallel ridges of coarse pumice and spatter forming part of a broad complex tephra mound were built by the double fountain, one east and the other west of the channel of the main lava flow moving southward (pl. 3D). This flow eventually reached the coastal flat below Holei Pali at about 1800 July 15 but stopped short of the ocean. The flow bull- dozed large blocks of welded spatter, some the size of a house, from the cone and carried them hundreds of meters downslope. A second flow coursed though a well—developed channel northeast from the east foun- tain, spilling 2 X 106 m3 of lava into Alae Crater. Most of this new lava plunged through the thin crust on the June 25—26 fill and hydraulically lifted the crust about 15 m, to within 15—20 m of the rim of the crater (Swan— son and others, 1972). A third, smaller flow advanced northwest from the east fountain, turned west and then south around the growing pumice and spatter mound, and spread over the parking area just east of Aloi Crater before joining the main stream moving southward. During fountaining, a pool of lava fed directly by molten fallout accumulated in the vent basin, im- pounded by spatter ramparts. This pool, which con- tinuously overflowed the ramparts, was the main FIRST STAGE OF ERUPTION 17 source of the flows. When fountaining stopped at 1220 July 15, lava in the pool quickly drained into the two eruptive fissures, leaving a glaze on the ramparts that was much richer in olivine than the associated flows. The abundant olivine phenocrysts may be “lag gravel” left after liquid drained away, or, more likely, they may indicate that the last lava erupted was enriched in olivine while still underground. The eastern vent produced much more than half the total volume erupted, 4 X 106 m3 (table 5), but this was the last time that it was visibly active until August 2—3, 1970. Ten hours after fountaining ended, welded spatter and large masses of glowing semisolid material were still oozing and rolling from the steep ramparts back down the east vent, which was about 5 m in diameter. Hot sand-sized debris abraded from falling blocks was blasted into the faces of observers by gases rushing from the vent. Harmonic tremor slackened markedly when the July 15 fountaining stopped, then increased only two hours later, seemingly a premonition of future erup- tive activity, but no lava was seen until July 20. JULY 20—AUGUST 2, 1969 The lava column reappeared in the western vent on July 20 and periodically rose and fell for the next sev- eral days. Generally the pumping action changed the level of lava by only a few meters, but occasionally the top of the column would drop 45—50 m, to a point about 50 m below the lip of the fissure, within 5—10 minutes. Then the column would begin slowly rising, regaining its old level in an hour or less. Relatively small quantities of spatter were ejected during this ac- tivity, almost always as the column receded. Lava re— mained within the fissure, which varied in width between 3 and 7 m daily depending on the amount of accretion or collapse of the walls, until the night of July 28, when a thin overflow partly covered the floor of the vent depression. On July 29—30, a notable sequence of events pro- vided fine examples of the gas—piston mechanism for observers, who could look down into the fissure from their perch on a spatter rampart a few meters away. The lava column, capped by a shimmering layer of flexible but solidified crust several centimeters thick, would slowly rise from a depth of 30—50 m to the ground surface in 10—15 minutes, accompanied by lit- tle or no spattering. Lava would then spill outward from the fissure, pooling against the gentle slope (about 1 in 20) of the vent basin. The top of the lava column was convex upward, and the edge of the lava pool was about 1 m lower than the central part di— rectly above the feeding column. Sometimes the pool reached a diameter of 150 m, but generally it was half that size. Suddenly, spattering would start from the east end of the drowned fissure, and the pooled lava would begin to drain rapidly back into the fissure, ac- companied by extremely vigorous spattering and gas discharge. This drainback was most dramatic; the lava column would drop 25—30 m within 30 seconds and would reach 50 m depth in another minute. Then the cycle would repeat itself, after a brief recovery time of 1—3 minutes. A complete 10—20 minute cycle, includ- ing a surface pool and deep drainback, was typical, but sometimes the column never reached the surface be- fore drainback, and at other times the level sank only a few meters during drainback before a new uprising began. Several times on these two days, we were able to trigger drainbacks by throwing rocks through the thin crust on the pool. Vigorous spattering began immedi- ately after the crust was broken and gases could es- cape. During subsequent months, we repeatedly triggered drainbacks using various materials to break through the crust. Generally, the experiments caused drainback only when the system was already prepared to drain back naturally. Slightly premature drainback could sometimes be induced by throwing containers filled with water or gasoline through the crust. These bombs burst forcefully after immersion for several seconds, tearing large holes in the crust and stirring the lava, leading to vigorous degassing, loss of volume of the columns, and drainback. The total volume of lava and gas that evacuated the fissure during a typical drainback, whether natural, artificially triggered, or induced prematurely, varied from 104 to 3 X 104 m3, calculated from the observed dimensions of the fissure and the surface pool. Such a volume typified all subsequent gas-piston activity for which calculations were made, despite very different vent configurations in 1970 and 1971. The fissure became largely roofed over by July 31, the result of accretion of crust and spatter to the up- per part of its walls, leaving a lens-shaped opening 3 m by 7 m. The seal was completed the next day except for two holes, around which low spatter cones were built. Eerie blue and green flames of burning hydro- gen played from the cones, a common occurrence around vents from which hot gas escapes (Naughton, 1973; Cruikshank and others, 1973). Conditions re- mained unchanged until the afternoon of August 3. AUGUST 3—4, 1969 The sixth episode of strong fountaining began at 1715 August 3; it was one of the most noteworthy se- quences of events of the entire eruption. This episode differed from the previous two in that the fountains were lower (150m) (table 5), the eastern vent was inac- 18 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO tive, and several vents periodically erupted west of the main vent complex. These subsidiary vents were not alined along the trend of the main fissure and define no trend of their own. We suspect that they were openings in small lava tubes developed in the July 15 flows and that lava was fed into the tubes from the main vent itself. The basin around the inactive eastern vent filled when lava that had ponded in the western vent spilled over the intervening spatter rampart. Lava then flowed through a low point in the eastern rampart and cascaded into Alae Crater, raising lake level to within 10 m of the low part of the rim. As on July 15, the surface crust on the Alae lake floated upward as lava from the cascades plunged beneath it; now the crust was more than 20 m higher than when it originally formed on June 25—26. About half of the newly erupt— ed lava entered Alae; the rest was distributed as thin flows that extended short distances away from the vent area. The basic configuration of the vent area was little modified, but the large mound of welded spatter and pumice downwind of the fountains grew several meters higher. The fountaining episode ended at about 0010 Au- gust 4, and those observers still on the scene quickly went home to bed. However, they got little rest, as Swanson, Duffield, Jackson and Peterson (1972, p. 114—116) described: A vigorous epsiode of harmonic tremor and earthquakes took place between 0400 and 0430, August 4—just 4 hours after the Mauna Ulu vents quieted and lava stopped flowing into Alae. The sky was lit in a brilliant glow over Alae during that dramatic half hour, prompting observers to suspect resumption of eruptive activ- ity. Actually, however, Alae lava lake was catastrophically draining into one or more cracks that had suddenly opened and intersected the still molten February 1969 lava in the bottom of Alae’s deepest pit. In this half hour, the level of the lake dropped 80 m as about 10 million In“ of lava drained out. The mezzanine [the flat floor of an older crater exposed at the west end of Alae] was uncovered, even though coated by several meters of viscous lava and solidified crust. This episode was accompanied by violent ground cracking between Alae Crater and Kane Nui o Hamo, a cone north of Ma— kaopuhi Crater. A complex deep crack and fault-bounded graben 10 m wide and locally more than 70 m deep extended 800 m east— ward from near the rim of Alae Crater, and a shallow topographic trough continued eastward for another 700 m. The graben and re- lated cracks are probably the surface expressions of the fissure that drained the crater. Prehistoric lava veneer clinging to the walls of the graben shows it to be an old structure reactivated during the draining event. The lava that drained from Alae apparently intruded eastward beneath the graben and trough, for rocks along the fractured zone were too hot to touch as late as 1000 that morning. About 1400 that same day a lava flow began issuing quietly from a new fissure 3 km east-north-east of Napau crater [p]. 1; pl. 3E]. This lava is the same chemically and petrographically as that drained from Alae. * **The volume of lava ***[added]*** to the surface is only 25 percent of the volume of lava drained, so about 7.5 million m3 of lava was added in storage to the rift conduit system. No draining took place from Alae during daylight hours of Au- gust 4, but cool viscous lava continued to ooze from pockets left on the crater walls. Masses of partly molten, partly solidified lava as large as houses slowly slid across the gently sloping mezzanine floor like hot earthflows, draped over the newly exposed rim, and ploughed into the sticky degassed lava left in the deeper pit. Occa- sionally large plates or solidifed lava veneer clinging to the vertical wall of the crater broke loose and crashed to the floor. A black ‘bathtub ring’ marking the highest stand of the lake encircled the crater walls. The eruptive activity east-northeast of Napau Crater continued until August 10 or 11. We originally thought (Swanson and others, 1972, p. 115) that this lava might have been stored in the east rift zone since the August 1968 eruption (Jackson and others, 1975), but further chemical study shows instead that this lava is more similar to that erupted at the Mauna Ulu vent area during the summer of 1969 (Wright and other, 1975, table 6, sample DAS69—67—4). Hence the new flow may well have contained some of the same lava that drained out of Alae Crater. We do not know the reason for the draining of Alae and the severe ground cracking and dilation of the rift zone (one 250-m-long geodimeter line across the gra- ben lengthened 2.7 m). One interpretation is that the weight of new lava added to Alae Crater since Febru- ary 21, 1969 (between 1010 and 10‘1 kg) caused the floor of the crater to collapse into a magma reservoir, whose initial draining hundreds of years previously had caused Alae Crater to form. The south flank of Ki- lauea underwent no detectable seaward displacement during this event (Swanson, Duffield, and Fiske, 1976, fig. 10), as commonly accompanies the forceful injec- tion of magma into the rift zone. AUGUST 5—6, 1969 No eruptive activity was noted at the Mauna Ulu vent area on August 4, but spattering was observed at 1000 August 5. Such activity continued throughout the afternoon, building a horseshoe-shaped spatter cone 8 m high around the west end of the western vent. Occasionally lava spilled out of the fissure and fed small flows in the vent basin, much as before the August 3—4 activity (fig. 16). Fountaining to heights of 15—20 m began slowly at about 1900 that evening. The activity waned at 2000, allowing close approach to the vent, then picked up quickly at 2100, with lava Spurting to 30 In. The height of the fountain continued to increase, eventually at- taining 300 m, so that we arbitrarily set the start of the seventh episode of high fountaining at 2100 August 5. The western vent was again the principal source of lava, although two subsidiary vents a few tens of me- ters west contributed a small volume; these subsidiary FIRST STAGE OF ERUPTION 19 FIGURE 16,—Spattering from horseshoe—shaped cone at west end of western vent, 1500 August 5, 1969. Man is using rock hammer to collect sticky, molten lava from flow slowly advancing from cone. vents were probably two of those active on August 3. The basin around the western vent was filled by 2115, submerging the spatter cone formed earlier in the day, and lava spilled over the intervening ramparts into the basin around the inactive eastern vent, in which lava pooled 20 m deep. Nearly all the erupted lava, fed either directly by the fountains or via the eastern pool, flowed to the northwest rim of Alae Crater and cas- caded more than 100 m into the pit, which had nearly emptied only two days before. This great glowing cas- cade, more than 300 m wide, was one of the most mag— nificent sights of the eruption (Swanson and others, 1972, p. 116—117 and fig. 8). About 3.5 X 10“ m” of lava, almost ninety percent of the total volume erupted during the episode (table 5), had entered Alae by the time the fountaining episode ended at 0545 August 6. A small aa flow, apparently fed as the lava pond in the west vent area periodically sloshed over its banks, ad- vanced 100 m northward form the vent. The lava ponded above the eastern vent did not drain away, in- dicating that the vent had become plugged. AUGUST 7—21, 1969 Lava returned to the western vent early on August '7 and remained visible for the next two weeks. For the first week, activity was cyclic, with alternating slow rises and rapid falls of the lava column similar to that of July 29—30, except that there were fewer overflows. The fissure gradually roofed itself with spatter and congealed crust, leaving only a changeable number of small openings through which the pulsating column could be seen. When the column degassed during withdrawal, spatter would thud against the base of the roof, producing hollow sounds and thickening the roof enough to support the weight of the adventurous ob- servers. Activity picked up at 1130 August 15, and spatter from fountains 15 m high rapidly built a cone at the west end of the fissure. The spatter produced a flow that moved 15 m eastward before plunging into a hole in the roof of the same fissure (fig. 17). The volume rate of eruption was about 180 m3/min, but almost all the erupted lava returned underground. Sometimes 20 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO FIGURE 17.—Fifteen-m-high fountain at west end of fissure feed- ing flow that moves 15 m toward observer before plunging into a hole in the roof of the fissure, August 15, 1969. Lava also issues from small hole in right flank of newly built spatter cone. large pieces of the new cone spalled off and floated to- ward the drainback hole, temporarily plugging it and causing lava to pond within the basin. Short-lived holes commonly pierced the walls of the spatter cone and, before sealing, fed small flows that buried the ad- jacent part of the rampart surrounding the vent basin. Over the next several days, fountain height de- creased and the cone, after growing 15 m high, largely roofed itself, although spattering continued to occur within it. Lava was fed to the surface through a vent in the cone, and the drainback hole progressively en- larged by collapse. From time to time, holes opened for a few hours in the thin roof of the fissure and lava poured from them. The tempo of activity slowly increased during the afternoon of August 21. By 2100 a flow was advancing from the vent area toward Puu Huluhulu, and har- monic tremor intensified. AUGUST 22, 1969 The eighth episode of strong fountaining began at about 0015 August 22. The fountain was 300 m high within an hour and reached its peak height, about 400 m, in another hour. The western vent was again the principal source of lava, but low, weak fountains issued from several new vents along the trace of the May 24 fissure system (pl. 3E). One set of vents ex- tended about 300 m downrift (eastward) from the main vent complex, the other set, 200 m uprift. Low spatter cones formed at several of these new vents. A flow moved southward but stopped only 2 km from the vent area. Most of the erupted lava again entered Alae, adding about 2.7 X 106 m3 to the crater and rais- ing the crusted surface of the lake to within 34 m of the low point on the rim (fig. 18). A thin sheet flood of pahoehoe advanced to the base of Puu Huluhulu, cov- ering much of the aa flow erupted on August 5—6. The inactive eastern vent opened at some stage, though it did not emit fountains, and much of the still-liquid lava ponded above it since August 6 drained away (fig. 19). Winds were strong and fallout heavy during fountaining, resulting in substantial growth of the welded spatter and pumice mound, now nearly 30 m high, and more devastation of the neighboring forest (fig. 20, 21). As during previous fountaining episodes, large masses of welded, still hot spatter from the inte- rior of the cone were remobilized beneath the heavy blanket of newly fallen spatter and sloughed downs- lope as aa-like flows with very rough surfaces. Spatter falling on the cone which formed on August 15 built it more than 25 m high. The episode was the shortest of the series, about 41/2 hours, but it produced lava at the highest rate up to that time (table 5). AUGUST 23—SEPTEMBER 5, 1969 We waited a day to let the newly erupted flows cool; then we returned to the vent area on August 23 and found an important change in the western vent. The roof over the fissure had been largely destroyed dur- ing fountaining, leaving two openings, designated as the eastern and western compartments of the western vent; each compartment was in the bottom of a broad, shallow basin (fig. 22). The eastern compartment, measuring 5 m by 12 m, was centered over the main drainback hole of August 15—21 and was separated by a 4-m-wide bridge from the western compartment, which was 5 m by 8 m. Both compartments narrowed downward, and at the deepest visible level in the east- ern compartment, about 50 m wide, the orifice was only 1—2 m wide. N0 lava was visible, but bubbling noises came from deep within the eastern compart- ment. The rampart along the north edge of the west- ern vent area was barely recognizable, as the vent basin was largely filled. Relicts of a rampart were still prominent along the north and, especially, south sides of the inactive eastern vent. Lava was next seen on August 28 at a depth of 30 m in the eastern compartment, but it had overflowed twice the previous night, leaving thin flows. From then through September 5, the lava column remained visible deep in the eastern compartment, bubbling and emitting large volumes of fume. The western compartment remained inactive until September 4, when degassing noises were heard, and the wall of the FIRST STAGE OF ERUPTION 21 FIGURE 18.—View east from northwest lip of Alae Crater, August ery below light—colored wallrock in right half of photograph. 24, 1969. Floor of crater is 34 m below low point on rim (to right Cones formed in February 1969 and tree-covered parasitic shield of view), about 50 m below rim in center of view. Highest level of of Kane Nui o Hamo visible beyond crater. lava prior to draining event on August 4 indicated by top of drap- FIGURE 19.—Partly drained lava lake in eastern vent basin of eastern vent on August 22: and lava drained 0‘“ 0f the lake. Mauna Ulu, August 24’ 1969. View from northernmost spatter Fume in background rises from western vent area. Tephra ridge rampart shown in figure 22 on northeast side of eastern vent ba- forms Skyline to left 0f fume. Diameter 0f collapse pit, about sm. Prlor to August 22, surface of lake, formed on August 6, was 10 m. at level of prominent ledge. Collapse pit formed above site of 22 CHRONOLOGICAL NARRATIVE OF THE 1969-71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO FIGURE 20,—Devastated area downwind (south—southwest) from Mauna Ulu vent area. Tephra deposit forms hill. Covered with a lush hardwood forest before the eruption, area is now buried be— neath tens of centimeters of pumice. Photograph taken August 30, 1969. compartment was glowing red within 10 m of the sur- face. By September 1, yellow and orange encrustations of sulfur and other sublimates had formed along cracks in the spatter and pumice mound, and a light sulfur ‘bloom’ coated much of the ground surface. Some of the sulfur probably sublimated from fume given off by the west vent, but most was deposited from gases given off by tephra in the slowly cooling mound. Some sulfur deposits formed 4- to 7-sided po- lygonal patterns a few meters in diameter, possibly reflecting cooling cells or columnar joints in welded tephra. Sulfur also coated surfaces of old cones and ramparts in the vent area. SEPTEMBER 6—7, 1969 Fume emission and harmonic tremor declined sharply at 1045 September 6. A few minutes later, a short burst of fume and tremor occurred. We noted this from the Volcano Observatory and surmised a re- sumption of the gas—piston activity, correlating the decline in fuming and tremor amplitude with a rising lava column and their increase with vigorous drain- back. This surmisal was confirmed when we reached the vent area at noon. The rise and fall cycles lasted from 25—50 minutes, depending on the amount of rise (15—30 m). Lava col- umns in both compartments (fig. 22) participated in the cycles and were almost certainly connected at FIGURE 21.—Bark on left side of ohia tree stripped away by falling, partly wind—driven pumice. Bits of pumice embedded in wood. Devastated area 1 km downwind (south-southwest) of Mauna Ulu vent area, August 30, 1969. shallow depth. In fact, during periods of drainback the lava in the eastern compartment emptied into a hole 50 m underneath the bridge separating the two com- partments, and lava came from this hole during filling episodes. The column in the wider eastern compart- ment started its rise several minutes before that in the western. Once started, however, the column in the western compartment rose much faster, so that before long it was several meters higher than the column in the eastern compartment. There was a similar lag be- tween initiation of drainback in the two compart- ments, but once started, the western column drained more rapidly, though with far less turbulence and spattering. A total of 2—3 X 10‘ m3 of lava was involved in the pistonlike action, with drainback lasting 5 min- utes or less. The cyclic activity lasted all afternoon, gradually increasing in vigor so that after dusk a red glow was easily visible from Hilo, 42 km away. At about 1930, the situation abruptly changed. Har- monic tremor increased in intensity, and quickly growing fountains developed, ushering the ninth and most voluminous episode of high fountaining. All eruptive activity was confined to the western vent area. Lava jetted from both compartments and merged to produce a single mighty fountain centered over the bridge between the two compartments. At 2200, the fountain reached 540 m, the greatest height observed for the entire eruption, but by 2300 was FIRST STAGE OF ERUPTION 23 FIGURE 22.—Panorama looking east from cone at west end of fis- sure on August 24, 1969, showing newly formed western and eastern compartments in the western vent (foreground). Kane Nui o Hamo forms skyline beyond fume cloud rising from east- ern compartment. Remnants of jagged spatter rampart, first down to 400 m. This height was maintained until 0130 September 7, when it decreased so abruptly that we thought the episode was nearly over. Fountaining from the western compartment ended at this time, and lava pooled around it drained into the inactive fis- 1 sure. Fountaining from the eastern compartment un— expectedly continued, but at a reduced height of 300 m. The fountain continued at this height, with brief (5 minutes or less) pulsations from about 100 m to 400 m, until 0425, when within 5 minutes it ended. A voluminous sheet flood of lava added 4.8 X 106 m3 to the Alae Crater pool, mostly below the August 22 crust. The high lava mark of August 3—4 was reached at 0230, lava spilled into the graben of August 4 at 0300, and by 0415 a flow was oozing over the southeast rim of the filled crater; only 61/2 months earlier this crater had been 150 m deep (Swanson and others, 1972). Lava flowed eastward along the floor of the gra- ben (fig. 23), advancing about 900 m from Alae. An aa flow inched its way westward from the vent area and began tumbling into Aloi Crater at 2100. Flow into Aloi continued until the morning of Sep- tember 8, more than a day after fountaining ended; the flow covered the floor of the crater with 10 meters of jagged aa. A branch of this flow bypassed the crater, crossing the Chain of Craters Road and extending a few hundred meters farther south. Two other flows headed south (pl. 3F). A rootless aa flow, fed exclusively by fallout and remobilized welded spatter on the flank of the tephra mound (fig. 24), spread about 2 km downslope. A larger pahoehoe flow, fed directly from the base of the fountain with only minor addition of welded spatter, flowed south- formed on June 12—13, flank inactive eastern vent, largely hid- den behind fume. Arrow indicates ledge, modified by activity of August 22, from which figure 17 was photographed. Jumbled area near right edge of View is remobilized spatter that slumped toward vent from tephra cone during drainback on August 22. ward in a fluid river for about 3 km. This river then gradually changed within several hundred meters into aa, which continued to the top of Poliokeawe Pali and branched into two tongues, one ending below the pali, the other continuing over Holei Pali before stopping. FIGURE 23.—View east along graben from near Alae Crater across the lava flow that entered graben from Alae on September 7, 1969. Surface of flow was higher, indicated by terrace, before de- gassing and draining laterally and downward into rubble—cov- ered floor of graben. Photograph taken September 8, 1969. 24 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO FIGURE 24.——Aerial view from the south of Mauna Ulu vent area (fuming), tephra mound (broken area below fume cloud), and pumice blanket (smooth area toward camera from tephra mound). Rootless aa flow (see text) extends toward lower right corner from source on slumped tephra mound. Subdued north wall of Alae Crater visible to right of Mauna Ulu vent area. Note sulfurous sublimates (light color) on tephra mound, particularly bordering prominent crack near surface area of rootless aa flow. Slope of Mauna Loa forms skyline. September 24, 1969. The combined effect of unusually high fountains and strong tradewinds widened and thickened the fallout blanket of tephra and added substantially to the tephra mound, now 35—40 m high (fig. 25). Reticu- lite, an exceedingly porous type of pumice, was formed during the highest fountaining, and lumps several centimeters across were blown at least 15 km down- ward (fig. 26). As in previous fountaining episodes, the latest lava erupted was richer in olivine than that of the early and middle stages. The episodes produced the greatest volume of lava (12 X 106 m3) at the second fastest aver- age rate (1.33 X 106 thr) of the entire eruption (table 5). The eastern compartment had been enlarged dur- ing the episode and now was 50 m long by 10 m wide. The cone at the west end of the west compartment, which first began forming on August 15, had been to- tally blasted away by the fountains. SEPTEMBER 8-OCTOBER 9, 1969 Activity much like that before the September 6—7 fountaining typified this period. The lava column, confined to the two compartments in the western vent area except for brief overflows on September 27 and October 2—3, underwent repeated rise-fall cycles. Again the lava column in the western compartment FIGURE 25.-—Tephra mound and associated lower hills after foun— taining of September 6—7, 1969. View is toward east from near the east rim of Aloi Crater. Mound is 35—40 m above its base and has a very irregular profile. Foreground consists of pahoehoe, slab pahoehoe, and aa erupted on September 6—7. Photograph taken on September 8, 1969. began rising after that in the eastern compartment, but it ended higher. In the eastern compartment, 1— 1.5 X 104 m3 of lava and gas typically rose 20—25 m in 15-20 min and withdrew in 4 min to a level about 50 m below the surface. Spatter ejected during particularly vigorous periods of fountaining between September 26 and 29 began to close the eastern compartment (fig. 27) and built a small cone on the bridge between the two compartments. For some periods of several hours duration, the col- umns in both compartments remained at an approxi- mately constant height, continuously bubbling. Eventually, a crust formed on each of the columns, which then began to rise as the volume of gas trapped beneath the crust increased, initiating another se- quence of rise-fall activity. Gas escape from the west- ern compartment was strong at times, lasting from several hours to several days without significant letup. A dull glow was visible at night as the wallrock was heated red by the hot escaping gas. OCTOBER 10—13, 1969 The tenth episode of sustained fountaining started at about 0900 October 10 and lasted for 74 hours, nearly twice as long as any other fountaining episode of the eruption (table 5). This episode was character- ized by low, often dome-shaped fountains and a low rate of discharge (table 5). Both compartments of the FIRST STAGE OF ERUPTION 25 FIGURE 26.—-Piece of reticulite 15 cm in diameter caught in ohia tree several kilometers downwind from Mauna Ulu vent area. Reticulite was erupted on September 6, 1969, during period of high fountaining. western vent area were active for most of the three- day period. A remarkably symmetrical dome fountain (fig. 28; Swanson and others, 1971, p. 15, photograph), occasionally 20 m high but usually half that, often welled from the eastern compartment for periods of several hours. Most of the lava from this fountain flowed away from the vent, but some formed a narrow river that poured back into the western compartment. Every few seconds, gases burst explosively from the western compartment, carrying spatter possibly de— rived from the lava drainback. The activity at both compartments was more episodic during the after- noon of October 12 and morning of October 13. Spells of continuous activity tens of minutes long were punc- tuated by brief periods when output dwindled to nothing, at which time lava ponded in the vent drained into both compartments. Lava flows entered Alae Crater, eventually filling the shallow subsidence depression created by cooling and degassing of the September 6—7 lava (Swanson and others, 1972). Lava spilling from the crater spread 1.5 km south and southeast through the forest, solidi- fying to rather dense pahoehoe (pl. 30). Several flows again inundated the area between Puu Huluhulu and the vent, and others advanced short distances south- ward. A low horseshoe-shaped cone formed around the west end of the western compartment, but tephra accumulation was small elsewhere. All of the rampart originally surrounding the vent basin was covered be- neath new flows, although that part north of the east- ern vent was still recognizable as new flows draped over and mimicked the old rampart. The jagged, sul- fur-coated remains of the remnant on the south side of the inactive eastern vent still projected 5—8 m above its base. During much of October 11-12, the input into Alae Crater was much greater than the combined rates of filling and observed outflow over the drowned crater rim. At the time we thought that some lava was drain- ing through cracks related to the August 4 graben (Swanson and others, 1972). We now believe that the outflow over the drowned rim equaled inflow, but that most of this flow took place via small lava tubes and hence was not visible. This interpretation was reached as a result of repeated observations of how lava tubes developed later in the eruption (Swanson, 1973; Pe- terson and Swanson, 1974). OCTOBER 14—19, 1969 Lava was visible in both compartments when the vent was reexamined on October 14, and cyclic gas- piston activity characterized both lava columns from then until October 19. Small overflows were infre- quent, but heavy showers of spatter accompanied the many degassing events. Throughout October 19, ex- tremely hot gases carrying Pele’s hair and small bits of spatter roared from the western compartment. OCTOBER 20, 1969 Vigorous fountaining began at 0100 October 20, ushering in the eleventh major episode of the erup- tion. Lava quickly filled the vent depression, spilled outward, and cascaded into Alae and Aloi Craters. By 0230 a fountain was playing 300 m above the western vent area, apparently centered over the west end of the eastern compartment. At 0330, the fountain sud- denly developed a strong horizontal component di- rected toward Puu Huluhulu (pl. 3H), where observers huddled for protection behind a stone wall. After a few minutes, the fountain gradually returned to vertical, but not before sending a heavy shower onto 26 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO FIGURE 27.——View west along eastern compartment of Mauna Ulu vent area, September 28, 1969. Glow (white) below overhang near upper center of photograph comes from spattering column of lava. Note overhang on which men stand, built since September 26 by accretion of spatter and one overflow of fissure. FIRST STAGE OF ERUPTION 27 FIGURE 28.—Dome fountain about 10 m high erupting from east— ern compartment of Mauna Ulu vent area, October 11, 1969. Left part of dome is sliding away, revealing that core is made of lava and that dome is not simply a large bubble. Mottled surface, caused by solidified crust interspersed with still-liquid lava, is typical of dome fountains. Photograph by J. B. Judd. the lower flank of Puu Huluhulu, where the spatter welded into a coherent mass that slid a short distance down the steep slope leaving slump scars (fig. 29). This frightening interlude was probably occasioned by collapse of the bridge between the two compart- ments, temporarily choking the vent and deflecting the fountain jet toward one side. As the obstruction cleared, the fountain righted itself. Large volumes of spatter and pumice were blown into previously un- scathed areas by strong winds generated during, and probably by, the directed fountaining. Fires started by the hot spatter enveloped forest on and west of Puu Huluhulu, and several trees in Pauahi Crater, 2.5 km west of the vent, were set aflame by falling pumice. Vehicles parked in normally safe locations were sand- blasted and their Windshields broken by the thick, wind-driven fallout. Most of the lava went into two flows, both of which changed from pahoehoe to aa, then cascaded over Po- liokeawe and Holei Palis before coming to rest (pl. 3H). One of the flows followed preexisting channels FIGURE 29.—Slump scars in welded spatter on south flank of Puu Huluhulu, November 1969. Spatter fell during vigorous directed fountaining on October 20, accumulated while still hot, and welded together to form a coherent fluid mass, which then slumped down the steep slope. 28 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO southward from the vent. The other was routed through the filled Alae Crater before making its way across forest land, endangering the Chain of Craters Road (p1. 3H) and plunging over the steep cliffs. A smaller but still voluminous flow spread 3 km east- ward from the main vent, and a minor flow entered Aloi Crater. Much material was added to the tephra mound, raising its height to about 50 m above the preeruption base. The height of the fountain remained between about 270 and 300 m from 0230 to 0615, then gradually low- ered to 150 m at 0640 before stabilizing (fig. 30A). FIGURE 30.—Final minutes of fountaining at Mauna Ulu vent area on October 20, 1969. A, 0800, fountains are 150 m high and play from both compartments in western vent area. B, 0817, fountain starting to die. Level of lava is already below rim of vent basin, and surging fountain is confined to western compartment. C, 0819, fountain nearly dead, level of lava in vent basin lower be— cause of drainback. D, 0820, fountaining ended, fume (light col— ored) mixed with dark cloud contains small pieces of solidified crust of draining lava. E, 0821, final surge of fume. F, 0823, dark, fragment-laden cloud issues from entire width of western com- partment. Views from summit of Puu Huluhulu. FIRST STAGE OF ERUPTION 29 Fountaining fell off very abruptly at 0817, and three minutes later no molten lava issued from the vent (fig. 30, B—F). The fountain surged as it rapidly diminished (fig. 30B), each surge lower than the one before. As output decreased, lava pooled in the vent basin began pouring down the fissure, carrying large plates of so- lidified crust with it. Pulsating jets of gas from the west end of the fissure propelled small fragments of this dark crust back out of the vent and high into the air, forming an ominous black cloud (fig. 30, D—F) that lasted several minutes until strong gas discharge stopped. Weak spattering lasting about two hours occurred from two short fissures east of the main vent area while fountaining was at its peak (p1. 3H). One fissure was between 200 and 300 m from the main fountain in an area active on August 22. The other fissure was just northwest of Alae Crater, along the general trend of the May 24, 1969 fissure system (pl. 3A). This was the farthest from the Mauna Ulu vent area that lava had erupted since May 24, except for the isolated fissure east of Napau Crater on August 4—11. Three wide cracks with a total opening of 30—50 cm cut across the reconstructed road 225 m west of Aloi Crater sometime between 0415 and 0615, stopping traffic to the crater. The cracks formed in a zone 5—7 5 m south of the trace of the May 24 fissures. About 10.5 X 106m3 of lava was erupted in little more than 7% hours, a rate of 1.45 X 106 thr — the highest rate of the eruption (table 5). Nonetheless, the basic configuration of the vent area remained un- changed. The bridge between the eastern and western compartments had been destroyed, but parts of its foundation remained, forming a partition 10—15 m be— low ground level. The compartments were each 5—10 m wide but had lost much of their identity. The jagged remains of the spatter rampart on the south edge of the east vent were completely mantled by 2—3 m of new flows, transforming it to a subdued, flat-topped ridge. The spatter cone at the west end of the western compartment likewise had been mantled with new lava and spatter but still retained its shape and promi- nence. The top of the broad mound of welded spatter and pumice downwind from the vent area was now about 57 m above the preeruption surface; this mound formed the highest part of the Mauna Ulu complex. Except for the mound, the new ground surface sloped very gently away from the vent area with only a slight accumulation of flows around it, for most of the lava erupted up to this time had flowed elsewhere rather than piling up to form a distinct basaltic shield. The vent area was about 25 m above the preeruption ground surface. OCTOBER 21—DECEMBER 28, 1969 Lava was visible in the fissure of the western vent area on October 22, but no overflows extended beyond the area until November 12. However, we unexpected- ly discovered viscous, gas-poor pahoehoe oozing down the Kalapana Trail, 2.5 km southeast of Alae Crater, on October 24 (pl. 3H ). Further investigation showed that this lava was issuing from small tubes in the Oc- tober flow, which headed in Alae. By hand-leveling from a point of known elevation, we also found that the lava fill in Alae was several meters higher than the low point on the buried rim; the fill was apparently ponded behind natural levees constructed over the buried rim. The surface of the Alae fill was saucer- shaped, suggesting withdrawal of lava from it. Conse- quently we assume that the lava flowing down the trail came from the Alae fill, which was apparently slowly draining through one or more narrow tubes (Swanson and others, 1972). This flow continued until October 27 or 28, a full week after the last fountaining. In the vent area, the lava column generally hovered near or at the top of the fissure during this period; lit— tle gas-piston action (fig. 31) was observed. A marked circulation pattern was apparent in the small active lake. Lava rose at one end of the fissure and flowed about 75 m to the other end before cascading back un- derground. The circulation rate was usually a few me- ters per minute, but occasionally, when inflow was rapid, a noticeable gradient developed on the surface of the column and flow rates increased to several me- ters per second. Circulation was normally east to west, but rather abrupt reversals were common. Less' fre- quently, circulation stopped, but after a few minutes this stoppage generally led to marked withdrawal back down the vent from which the lava had been ris- mg. Circulation of lava typified activity in the lake throughout the eruption. We were unable to docu- ment the cause of either the circulation itself or its re- versal of direction. The two most favored ideas, convection within a closed system and different rates of supply and drainback at submerged vents (open system), seemed equally likely at most times. The continuous loss of gas from the circulating lava sug- gests that volatiles were being added to the lake, pos— sibly forcing convection. Perhaps both open- and closed-system circulation took place at various times during the eruption. Pele’s hair was an interesting minor product of this type of activity. Several times, a night’s production blanketed tens of square meters with long strands of light brown glass, creating a scene resembling a field of newly cut grain. 30 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO On three occasions in November (November 12—13, 16, and 19), lava from the fissure filled the 9-m-deep vent basin and formed short-lived flows that ad— vanced across the perched lake in Alae Crater (pl. 31 ). These and numerous other active periods, typically several hours in duration, were characterized by dome-shaped upwelling of lava from the vent without much spattering (fig. 320), as if the lava column were simply projecting 5—10 m above ground level. The up- welling, from both the western and eastern compart- ments, was broken every 10—15 minutes by brief episodes of drainback accompanied by vigorous spat- tering (fig. 32A—F). Drainback was localized at the east end of the fissure. The episodic upwelling and drainback seemed to be a variant of the gas-piston ac— tivity. The spatter cone at the west end of the fissure, J FIGURE 31.——View westward from east end of western vent area, November 9, 1969. Crusted pool of lava occupies part of vent ba- sin above eastern compartment. Slight drainback of lava has just begun, indicated by lower level of pool. Spatter in front of man is generated by lava flowing back down vent. Low mound left of man is top of cone being built by spatter; this cone developed which began to form on October 10, gradually became coated with sulfurous deposits following the October 20 fountaining, then on November 12 began acquiring a thick blanket of new spatter and quickly grew to, a height of 10—12 m above the floor of the vent basin. A cone at the far east end of the fissure began forming on November 8 (fig. 31) and eventually reached a height of 12 m above the floor of the basin. This horseshoe- shaped cone was periodically drowned by lava when the basin filled (fig. 320); upon withdrawal, a thin lay- er of lava was left mantling the cone (fig. 32E). This repeated process, combined with spattering, added significantly to the height of the cone and produced a curious-looking flat roof overhanging the vent itself, leading to our informal designation, the pedestal cone (fig. 32H). The pedestal cone was a prominent land- mark from mid-November to December 30. Another into the pedestal cone of figure 32H. Low cone with glowing (white) interior at far end of pool is built against bridge separat— ing eastern and western (upper right) compartments. Jagged remnant of cone at west end of western compartment in extreme upper right corner. FIRST STAGE OF ERUPTION 31 spatter cone began forming on November 10 along the southwest edge of the eastern compartment; this cone, which also underwent repeated drowning episodes though it never became as high or wide as the pedestal cone, lasted only until November 21, when it collapsed into the fissure. Other cones, built on the remains of the partition between the two compartments, lasted only a few hours before being destroyed by collapse or overflows. On the morning of November 30, lava fed by a low dome fountain at the west end of the western com- partment flowed 80 m on the surface along the trace of the fissure before plunging 15—20 m into a seething pool at the base of the pedestal cone, now 12 m above the floor of the vent basin. At 1030, we watched the pool rapidly but quietly rise and blossom into a foun- tain 5—8 m high. This started 21/2 days of surface activ- ity similar to that earlier in the month, including flows into and around the site of Alae Crater. The pool was at times 9—10 m deep, washing over remnants of the old spatter rampart along the south edge of the east- ‘ ern vent but not over the pedestal cone. The surface activity stopped during the night of December 2, and there was no further visible activity, except rare spat- tering deep in the fissure, until December 13. Fuming was heavy during this lull, and sounds of a rising and falling lava column remained audible. Meanwhile, three new fissures had opened along the trend of the May 24 system, between 800 and 1500 m downrift from the Mauna Ulu vent area (pl. 31). This activity occurred sometime between December 3 and 8, most likely during the night of December 7—8, when a small flurry of earthquakes was recorded from the area (pl. 20). Small spatter ramparts were built along the three fissures, each of which was about 100 m long and offset in a right-en-echelon sense from the Mauna Ulu fissure and from each other. Small pahoehoe flows with a total volume of 0.5 X 106 m3 spread short dis— tances from the fissures. Surface activity at the Mauna Ulu vent resumed on December 13 and continued for five days, with lava again entering Aloi Crater and adding to the surface of the complex lava lake filling Alae Crater. Again the fountains were commonly dome shaped, and lava in the vent circulated from west to east during pauses be- tween fountains and drainbacks. The volume rate of circulation ranged from 500—1,000 mein on Decem- ber 14 to LOGO—1,500 mein on December 15—18, as determined from the dimensions of the basin between compartments through which the lava moved. From December 19 to 28, the top of the lava column was deep within the fissure, sometimes out of sight, al- though its presence was confirmed by a reddish glow reflected from glassy spatter clinging to the fissure walls. In summary, activity after the high fountaining epi- sode on October 20 greatly changed the shape of the Mauna Ulu edifice. The vent area itself had increased in elevation by about 15 m. The top of the spatter cone at the west end of the fissure, the highest and most prominent point in the vent area, was about 56 m above the preeruption surface and only 1 m below the top of the tephra mound downwind from the vent area. The last remaining traces of the old spatter ram- part along the south edge of the inactive eastern vent area were almost entirely obliterated beneath younger flows. All these changes contributed to the develop- ment of a shieldlike form centered at the active (west— ern) vent area of Mauna Ulu, though the edifice remained markedly asymmetric owing to the broad tephra mound extending south-southwest from the vent area. DECEMBER 29—30, 1969 Lava returned to a high level in the fissure at mid- day December 29, and periodic overflows began soon thereafter, accompanied by gas-piston action (fig. 33). Weak and pulsating activity continued throughout the night but gave way to continuous, gassy fountains at 0500 December 30, when the twelfth and last epi- sode of vigorous fountaining began. Fountain height was rather steady at 30 m until 0745, when it started to increase, reaching a maximum of '75 m at 0820. Five minutes later, the fountain ended abruptly. Flows spread eastward across the December fissures, south- eastward across Alae Crater, and westward to Aloi Crater, where majestic lava falls plunged 25 m into the crater, forming a new lake (fig. 34). Harmonic tremor continued after the fountain stopped, and soon thereafter, we observed weak spat- tering events and occasional overflows from our van- tage point on Puu Huluhulu. This activity slowly picked up, and at 0950 flows were advancing in all di- rections from the vent area. Strong fountaining re- sumed at 1000, growing from 25 m to 55 m high in 45 minutes. Fountain height increased in spurts to 150 m at 1400, then quickly sprouted to 240 m at 1430, 275 m at 1500, 350 m at 1525, and 390 m at 1540. Pumice probably erupted at this time was collected the next' day from the coast highway 13 km southeast of Mauna Ulu, and spatter fell 600 m upwind on the summit of Puu Huluhulu. The fountain then declined to about 225 m, where it stayed until just before the end of ac- tivity at 1830. When viewed from Aloi Center, the fountain appeared to fan outward on both sides of the fissure and, together with the thick envelope of fall— 32 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION 0F KILAUEA VOLCANO SECOND STAGE OF ERUPTION 33 out, reached a measured breadth of 500 m on several occasions (frontispiece). The largest flow generated by the fountain spread eastward, reaching the northwest base of Kane Nui o Hamo (pl. 31), 3 km distant, by 1415. Another volumi- nous flow coursed into Alae, plunged beneath the crust of the perched lava lake, and drained over the south rim of the crater. Subsequent leveling showed that 24 m of basalt now overlay the buried southeast rim of Alae (Swanson and others, 1972). Most of the area between the vent and Puu Huluhulu was inun- dated by slowly moving sheet floods, which heated the air so much that complex wind circulation patterns were created, including forceful whirlwinds, similar to but often larger than those described at Etna (Whit- ford-Stark and Wilson, 1976); the winds tore large fragments of crust from the flows. A vigorous flow poured into Aloi Crater, which filled at a rate of 0.2 X 106 thr to within 21 m of the rim until 1500, when-a dam near the fountain temporarily stopped most of the flow (frontispiece). The dam broke at 1550, and the crater resumed filling at the same rate as before. Filling finally stopped at 1900, one-half hour after fountaining ceased, ending with the new floor within 13 m of the crater rim; subsequent cooling and degass— ing caused the floor to subside 2—3 m. About 11 X 106 m3 of lava was erupted during the December 30 episode, more than 90 percent after 1000 (table 5). Much new pumice and spatter was added to the tephra mound (fig. 35). The vent area underwent large changes, most notably by enlargement of the fis- sure to a gaping orifice 130 m long and 35 m wide. No remnant of the partition between the two former com- partments remained. Most of the pedestal cone was destroyed, leaving only a low mound above an embay- FIGURE 32.—Drainback and refilling of eastern compartment of Mauna Ulu vent area on November 13, 1969, (A—G), and com- partment after activity had ceased on November 14, 1969 (H). A, Drainback begins, exposing top of pedestal cone (see text) on right, which has been drowned by the pooled lava. B, Vigorous spattering takes place as level of lava drops. C, Same as B, except lava has withdrawn farther in compartment and spattering is finer, almost a spray. D, Spattering has stopped, and crusted lava pours into compartment. E, Lava continues to drain into compartment, but top of rising column of lava is visible at base of cone. F, Rising lava column fills compartment and projects slightly above lip of compartment. G, Dome fountain projects above lava spilling outward from compartment; note that lava covers top of pedestal cone. Time between A and E, 2 minutes; between E and G, 3 minutes. H, Eastern compartment and ped- estal cone on November 14, viewed from southwest from slightly different location (chiefly lower) than A—G; low cone that man stands on is just to left of View in A—G. ment at the east end of the fissure. The cone at the west end of the fissure stood higher by several meters because of spatter accumulation. This was the last time strong, persistent fountaining occurred at Mauna Ulu. Whether this is related to the enlarge- ment of the fissure from a relatively narrow fissure to a much wider vent is an interesting speculation. SECOND STAGE OF ERUPTION DECEMBER 31, 1969—APRIL s, 1970 The top of the lava column fluctuated from a few meters to .60 m or more below the ground surface for most of this period. Only rarely did the column remain within 10 m of the surface for longer than a day or two. The walls of the vent periodically failed, presumably when suppport was withdrawn because of the low level of lava, and by February 7, the vent had widened to 40 m by collapse. Thick fume generally obscured the lava when it was deeper than 20—30 m, but bub- bling sounds always confirmed its presence at depth. A slow but steady circulation pattern, usually from east to west but sometimes reversed, was often evi- dent whenever lava was visible. Periodic rises, drain- backs, and low fountains of short duration took place from time to time within the fissure. The amplitude of rise and fall was much less than during the preceding months, but the volume involved, 1—2 X 710‘ ms, was equivalent because of the much greater surface area of the lava column. The vent overflowed only six days during this pe- riod, January 25 and 30, February 13—15, and March 1. These flows entered Aloi Crater and extended north to Puu Huluhulu and downrift for 2 km (pl. 3J), cover- ing most of the December 5 spatter cones that were not previously inundated. The volume of these flows was about 3 X 106 m3. Many of the smaller flows ad- vanced only 200—300 m from the vent, adding substan- tially to what by now was a distinct but low shield- shaped edifice. By March 1, this broad shield, nearly 60 m high above the pre-eruption base but much less above the apron of new flows that surrounded it, had overrun a considerable part of the pumice and spatter cone built previously. The cone at the west end of the fissure, initially formed on October 10, 1969, continued its growth dur- ing periods of spattering accompanying drainback of overflows. The cone partially collapsed from time to time and assumed a craggy appearance, but it was still 8 m higher than the rim of the vent at the end of March. Another spatter cone formed on February 11 at the east end of the fissure and grew to a height of 6— 8 m by April. 34 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO . 4. w*”\"?‘i‘“f‘rrm _ FIGURE 33.-—Drainback sequence at Mauna A, Lava has just started to drain down vent from its high level, indicated by black coating on sublimate-coated cone. Spattering typically accompanied drainbacks. FIGURE 35.—Tilted slabs of welded spatter blanketed by pumice FIGURE 34.—Lava falls into Aloi Crater, about 0730 December 30, and spatter erupted on October 20 and, mainly, December 30, 1969- Lava advances from .Mauna U1“ vent area, 600 m away, 1969. Note contrast between chaotic terrain in foreground and where 30-m-h1gh fountam 1s V1§1ble‘ Falls are about 25.1“ hlgh undisturbed bedding in tephra in background. The chaotic area and plunge beneath crust floating on a rapidly deepening lava is at head of rootless aa flow generated on September 6—7, 1969 lake. (fig. 24). Photograph taken in March 1970. SECOND STAGE OF ERUPTION 35 Ulu vent area, December 29, 1969. B, Drainback nearly completed, and dark crust on flow plunges over rim into fissure; rapidity of cooling indicated by color gradation around edge of plate of crust slipping off slower-moving liquid part of flow. Level of lava in fissure in B, 10—12 11) lower than high lava mark. Cone in background is relict of pedestal cone (fig. 32H). A thin roof, built outward from the fissure walls by accreted spatter, began to form in late February. Overflows on March 1 added to the roof and sealed the fissure for 25 m eastward from the temporarily inac- tive west cone. The roof continued to grow eastward as spatter and crust from the rising and falling lava col- umn were added to it. By March 18, the fissure was roofed over, except for an opening 8 m in diameter. The roof remained largely intact until the night of April 8-9. APRIL 9—MAY 14, 1970 The nature of the eruption changed on the morning of April 9, when low fountaining began from a new set of fissures cutting Aloi Crater and the adjacent flank of Mauna Ulu (pl. 3J). The outbreak was not discov- ered until 0830, when the floor of the crater was al— most completely covered, but tilt and seismic data (not shown in pl. 2) suggest that ground cracking be- gan between 0400 and 0500 and eruption about 0600. By 0830, small puddles of lava had erupted from a fis- sure across the Chain of Craters Road near the tourist overlook (fig. 36) and from two right-offset fissures 200—250 In farther west. Fountains within Aloi and cascades down the east wall combined to fill the re- maining 15 m of the crater by 1010. A flow spilled over the rim (fig. 37) and spread southward. Twelve hours later, this flow reached its maximum extent at the base of Holei Pali, 7.5 km distant (pl. 3J). Observations between 0900 and 0930 revealed mol— ten, gas-poor lava at depths of a few meters to several tens of meters within a wide crack west of the western- most vent. The lava slowly moved westward in the crack, and at 1145 reached a point about 300 m be- yond the westernmost vent. N0 lava was seen beyond this point. We could not determine if the lava was at the top of a dike intruded from below or was part of a flow channeled by the crack away from the western- most vent. The zone of ground cracking also migrated west— FIGURE 36.—Lava puddle approaches display case at tourist overlook at Aloi Crater, 0900 April 9, 1970. Crater is not yet filled; puddle was erupted from fissure outside crater. Note new crack cutting pavement between the two posts. ward, accompanied by emission of fume. At 0935, the western limit of cracking was about 340 m from the westernmost vent; at 1005, 380 m; at 1228, 945 m; and at 1415, 1,065 m. The average rate of migration during this time was 2.7 m/min and the maximum about 4 m/min. The zone of cracking reached its westernmost point, the Ainahou Road, by 1000 April 10 (pl. 3J). The cracks continued to widen after they first formed. For example, the hairline crack that opened at 0935 grew to a width of 20 cm by 1013, 46 cm by 1136, 61 cm by 1253, and 91 cm by 1017 April 10. This widening was caused by actual dilation, not by col- lapse of the walls of the crack. Collapse did take place subsequently, however, and as a result the crack was 135 cm wide three months later. Some cracks showed small vertical offsets, most commonly downward to the south. Surprisingly, we felt no ground movement while standing in the zone of active cracking. However, por- table seismometers set up within the zone detected hundreds of microearthquakes, typically occuring in short bursts at intervals of 5—10 minutes. Meanwhile, the fissure in and above the east rim of Aloi Crater continued to erupt lava at a rate of about 0.1 X 10‘5 thr until midnight. The vents in the crater then apparently stopped erupting, and lava drained back into them. By 0830 April 10, the lake had lowered 9 m, although the cascade of lava from the eastern- most vents continued. Inflow and drainage nearly bal- anced each other for the next 4 days. Discharge from the fissure east of the crater increased during the afternoon of April 14. By 2200, flows or spatter issued from 10 vents along the fissure, the farthest 250 m east of the rim. Lava in the rising lake began to spill over the crater rim at 0015; the resulting flow had ad- vanced only 1 km southward by noon, when the erup- tion rate decreased and the lake surface lowered to 10 m below the rim. No visible activity occurred on April 16, but on the afternoon of April 17, lava began to trickle into the crater from the easternmost vent. A small perched lake impounded by its own levees began forming on the crust of the crater fill. Periodically the inflow rate increased, and the perched lake overflowed, a process SECOND STAGE OF ERUPTION 37 FIGURE 37.—Lava flow spilling over rim of Aloi Crater, 1030 April 9, 1970. Flow crosses deposits of pumice and spatter erupted on December 30, 1969 and scraped off road by highway crew. that helped build still higher levees above the crater fill. Such activity continued throughout April 18, and the surface level of the perched lake reached an eleva- tion 6 m higher than the low point on the crater rim. The perched lake began to drain, presumably by leak- ing through its floor into buried vents, on April 19. The lake and surrounding levee had subsided several meters by the next day, and visible inflow ceased on April 21. Lava resumed gushing into Aloi on the morning of April 24, and by 1600 the crater was filled and over- flowing along its southwest lip. A spatter cone 10 m high grew rapidly along the fissure near the margin of the lake. Soon the inflow rate lessened, and lake level dropped several meters. Until April 29, inflow was at a low rate, and another perched lake was formed, nes- tled against the east crater wall adjacent to the fissure. Self-constructed levees confined the small pond on the north, west, and south. Inflow stopped for the last time late on April 29, and by the next day the surface of the perched lake had lowered 6 m, where it stabi- lized. Meanwhile, the summit vent of Mauna Ulu re- mained active. Rising lava broke the roof on the fis- sure and spilled out in a small flow between the evening of April 8 and 0830 April 9, when fountaining began in Aloi. Thereafter, strong fuming and sporadic bursts of spatter generated during drainbacks charac- terized the activity. Two brief but spectacular epi- sodes of overflow and dome fountaining 30 m or more high enlivened the afternoon of April 10, but other- wise the lava lake rose, fell, and circulated quietly, generally toward the west. Dome fountaining again occurred on April 26. Thereafter, a thin roof was built over the fissure when lava rose to the surface, hovered there for tens of min- utes while lava cooled and accreted to the fissme walls, and then withdrew slowly without vigorous de- gassing. Gradually the roof thickened as the process repeated itself, and spatter that erupted during drain- backs at some depth plastered itself to the underside of the roof. The roof was thick enough to walk on by April 29, although it was rather disconcerting to feel the thudding of spatter beneath one’s feet during per- 38 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO iods of drainback. The spatter cones at both ends of the fissure grew several meters; the eastern cone was highest, about 7 m above the roof, and had a gaping hole in its side (fig. 38). A hole pierced the roof be- tween the two cones on April 28, and another on April 29. These holes formed by collapse and provided vents for the lava column; spatter and small flows were occa- sionally erupted through them, building cones 2—3 m high (fig. 38). The largest overflows took place on April 30 from the westernmost new hole, but thin flows reached only a short distance toward Aloi. No further overflows took place during the first half of May. The activity during the last three weeks in April is interesting for several reasons. The Mauna Ulu vent continued its normal behavior during the time that the new fissure system in and near Aloi was active. The new fissures are not part of the May 24, 1969 sys- tem that gave rise to Mauna Ulu but instead are locat- ed some 200 m south. The trend of the fissure segment east of Aloi (p1. 3J), about N. 48° E., differs markedly from the typical trend of N. 60—70° E. for this part of the east rift zone. This segment cuts the southwest flank of Mauna Ulu and projects back to the west end of the Mauna Ulu vent area, as if it were a radial fis- sure related directly to the shield edifice. At no time, however, did we observe any coordinated relation be- tween activity at Mauna Ulu and along the fissure, al- though the circulation in the Mauna Ulu lake was dominantly westward, toward Aloi. Two tests of possible interconnection between Mauna Ulu and the new fissure system were made. One involved chemical analysis of the April 8—9 flow from Mauna Ulu and the first products of the April 9 outbreak in Aloi. The results (Wright and others, 1975, samples DAS70—1213—25 and 26) show that the compositions are olivine-controlled and identical to each other within analytical precision but different from preceding Mauna Ulu compositions. Thus it ap- pears that a batch of new magma entered both the FIGURE 38.—-Aerial view looking southwest over Mauna Ulu vent area, May 9, 1970. Fissure is mostly roofed, but four cones (westernmost obscured by fume) indicate its location. Fume issues from large hole in west side of easternmost cone, which is about 7 m high. Note fresh (relatively dark) flow erupted from low, heavily fuming cone on April 30. Remains of tephra mound formed in 1969 are in center background. SECOND STAGE OF ERUPTION 39 Mauna Ulu and Aloi plumbing systems just before the outbreak, implying that the systems were intercon- nected at some unknown depth. The second test used a chemical tracer in an unsuc- cessful attempt to determine if a direct, shallow con- nection existed between the Mauna Ulu vent and the new fissures. About 455 kg of bastnaesite ((Ce, La)C03F) was thrown into the Mauna Ulu lake, and samples of erupting lava were taken at intervals of 20 minutes for the next five hours from the fissure seg- ment east of Aloi and on several successive days from both the new fissure and the Mauna Ulu lake. Neu- tron-activation analysis for lanthanum by L. P. Greenland shows no detectable increase in any of the samples, including those from the Mauna Ulu vent, suggesting that the bastnaesite was either flushed quickly out of the system or diluted to an undetecta- ble concentration. MAY 15—JULY 5, 1970 A swarm of earthquakes on May 15—18 (pl. 23, C; Endo, 1971) occurred along Kilauea’s east rift zone be- tween Mauna Ulu and the summit caldera. Consider- able ground deformation accompanied the earthquakes. Duffield, Jackson, and Swanson (1976) interpreted these events as accompanying shallow in- trusion of magma beneath the south part of Kilauea Caldera, near its intersection with the east rift zone. They speculated that structural adjustments resulting from this intrusion reopened the underground con- duit system connecting the summit of Kilauea and Mauna Ulu, ending a 4 1/2 month period in 1970 during which the eruptive activity at Mauna Ulu had waned relative to that in 1969. Vigorous activity resumed at Mauna Ulu, and weak spattering occurred in Aloi Crater, on May 21, only three days after the earthquake swarm. The Aloi ac- tivity lasted only one day, adding a small volume of lava to the crater and forming two driblet spires (fig. 39). The vigorous Mauna Ulu activity continued for more than a month. Hundreds of small, short-lived overflows spilled through new vents in the largely roofed fissure and through the four pre-existing cones FIGURE 39.—Driblet spires in Aloi Crater formed on May 21, 1970. Whether the spires are hornitos—“rootless vents on the backs of lava flows” (Wentworth and Macdonald, 1953, p. 52)——or cones built over true vents is not known. 40 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO on May 21—23, 26—31, June 5—11, 14-20, and 23—28. Each flow lasted 5—15 minutes, followed by a 10—15- minute period of drainback and renewed rise of the lava column. During two typical 7 -hour periods on June 5 and 15, we counted 19 and 30 flows, respective- ly. The gassy flows formed shelly pahoehoe of both sheet-flood and amoeboid varieties (Swanson, 1973). The volume rate of discharge was small, of the order of 103 mein, and the slope gentle, 1—3 degrees. Conse- quently flowage was rather slow, generally 0.5-1 m/sec, and a plastic crust had time to form on the sur- face of the moving flows. The flows “stopped moving because the feeding lava column withdrew back down the vent, and the hydrostatic head was then insuffi- cient to rupture the chilled skin on the toes at the leading margin of the flow” (Swanson, 1973, p. 619). Thus, most flows halted as soon as drainback began, after having advanced only a few hundred meters. Overflows only rarely lasted long enough to advance much beyond the Mauna Ulu edifice itself. We esti- mate that less than 20 percent of the lava erupted dur- ing this period flowed beyond the margins of the shield. Most of these longer flows travelled as rapidly flowing rivers in distinct, narrow channels for hun- dreds of meters downslope from the vents before spill— ing out and forming pahoehoe lobes. Many of these flows moved southwestward, eventually covering al- most all of the tephra mound built in 1969; other flows entered the Alae area and still others flowed short dis- tances eastward (p1. 3K). In late June, a lava tube formed by roofing of a channel carried lava two-thirds of the way down the northwest flank of the shield. Flows and rootless spat— ter built a low mound at the mouth of the tube, and pahoehoe continued to flow northward toward Puu Huluhulu and westward into the Aloi Crater area until June 29. Lava entered the tube through a hole high in the wall of the roofed fissure. When the lava column rose, the tube was active; when the column fell, the tube became inactive. The spatter cones, the largest at the east end of the fissure (fig. 40,), grew substantially during spattering accompanying drainback events. Occasional periods of more vigorous fountaining broke up fragile cones, but later, weak spattering largely restored their origi- nal shapes. Virtually all lava erupted from Mauna Ulu between May 22 and 30 was added to the south flank and the summit, largely filling the saddle between the two cones (fig. 41A, profile 2). By noon June 7, however, the north as well as the south flank had been covered (profile 3). Between noon on June 7 and the morning of June 8, both flanks and the two cones grew substan- tially higher, and this growth continued through June 20 (profiles 4 and 5). Later in June, flows were added preferentially to the north flank (profile 6). The low point along the fissure, protected between two cones, remained at nearly the same elevation be- tween May 30 and June 20. Theodolite measurements indicate that this low point increased in height only 3.3 m between May 31 and June 27, at which time it was 79.9 m above the base of Mauna Ulu, estimated from the topographic map to be at an elevation of 951 m (3,120 ft), after allowing for a 2-m-thick flow erupt- ed in December 1965 (Fiske and Koyanagi, 1968). The east cone was 94.3 m above this base on June 20 and 27; it was this height, recomputed as about 100 m on the basis of an improbable base elevation (3,100 ft) that was given as the height of the shield by Swanson, Jackson, Duffield and Peterson (1971, p. 12). This period of shield growth was the last for the western half of Mauna Ulu during the eruption, ex- cept for a brief period in January and February 1971. Most subsequent flows issued from vents on the east flank of the shield. After June 1970, the height of the summit gradually decreased by collapse of spatter cones and segments of the rim into the ever-widening crater (fig. 41B). During the 13-month period of growth from May 1969 to June 1970, the height of the shield increased in a linear fashion if averaged over periods of several weeks (fig. 6). Over shorter inter— vals, however, the rate of growth was decidedly epi- sodic (figs. 6 and 41A). THIRD STAGE OF ERUPTION jULY 6—31, 1970 Early on July 6, a swarm of small earthquakes, mostly recorded only by instruments near Mauna Ulu (p1. 2C), accompanied the opening of a 250-m-long fis- sure between 400 and 650 m downrift from the sum- mit of Mauna Ulu (pl. 4A). This event is taken as the beginning of the third stage of the eruption. A row of spatter cones was quickly built by low fountains along the fissure, and flows advanced southward to the site of Alae Crater and downrift to a point north of Kane Nui o Hamo (pl. 3). On July 8, activity became cen- tralized at three vents along the new fissure, where dome fountains 15—20 m high played through July 9. The western two vents erupted much lava in August and are designated from east to west vent 1 and vent 2, respectively (pl. 4A). Lava erupted during this time differs in chemical composition from that produced earlier, as chemical variant 5 (Wright and others, 1975) of the eruption first appeared. Dome fountain- ing and somewhat more gassy fountaining occurred from the three vents on July 13—15, 16—17, and 20—21, and flows again moved south and east-northeast. Many small lava tubes formed at this time by crusting over narrow channels. THIRD STAGE OF ERUPTION 41 FIGURE 40.—Mauna Ulu shield during a lull in activity on June 20, 1970. View from top of Fun Huluhulu. Compare figure 30A, tak- en from nearly the same location. Note shieldlike form of flanks, composed of hundreds of narrow pahoehoe streams. East cone is N 15 In higher than low point at summit just east (left) of west cone. Low mound of flows and rootless spatter at mouth of lava tube mentioned in text is along right edge. EAST CON E\ 1045 1030 1015 1000 985 WEST CONE / 1045 1030 1015 1000 ELEVATION ABOVE SEA LEVEL, IN METERS 6 NO VERTICAL EXAGGERATION I | | l | 50 100 150 200 250 300 l | l l | 350 400 450 500 550 600 HORIZONTAL DISTANCE, IN METERS FIGURE 41.—Profiles of Mauna Ulu as seen from parking lot at west end of Pauahi Crater (pls. 1 and 3K) during and after period of rapid growth in May and June 1970. A, Profiles during period of growth: 1, May 22; 2, May 30; 3, June 7; 4, June 10; 5, June 20; 6, July 2, 1970. B, Profiles after period of growth: 6, same as in A; 7, mid-June 1971. Note lower eleva- tion of summit area in 1971, caused principally by collapse of material into the enlarging summit crater. Profiles 1—6 traced from photographs taken with an exactly positioned camera by H. A. Powers. Profile 7 traced from photograph taken with a different camera no more than 3 m from Pow- er’s site. Scales are approximate. 42 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO The roof over the summit vent of Mauna Ulu foun- dered during the early part of this activity, possibly triggered by ground motion during either opening of the new fissure or during later strong fountaining ac- tivity. An elongate crater 25 m wide by 120 m long with treacherous overhanging walls was developed by the repeated collapse, but the prominent east cone and much of the west cone were not destroyed. The lava column remained 25—40 m below the surface, visi- bly unaffected by fountaining a short distance down- rift. Lava in the pool constantly circulated, generally emerging quietly at the west end of the crater, moving slowly eastward, and plunging downward at the east end accompanied by degassing and low fountaining. Occasionally the circulation pattern reversed, but at no time did the lava column rise high enough to over- flow. The east flank of Mauna Ulu began to emit copious amounts of fume, especially after rains, a few days after the summit roof foundered. The fume issued from a narrow zone extending from the east cone half- way to vent 2, along the trace of the Mauna Ulu fissure (pl. 4A). Over the next 6 months, this zone, last active on August 22, 1969, became important to the develop- ment of Mauna Ulu, and it was here that a large col- lapse trench eventually formed. AUGUST l—OCTOBER 27, 1970 After 12 days without surface activity, a nearly cir- cular hole, designated vent 3, opened during the night of August 2—3 high on the east flank of Mauna Ulu, only 150 m from the east cone along the zone of fume emission (pl. 4B). This hole was at the site of the old eastern vent area, inactive since July 15, 1969. The 3-5 m hole pierced the thin roof of a much wider chamber, within which lava was observed in constant turmoil, vigorously spattering at depths of 30 m or more. As the month progressed, lava rose to the sur- face of vent 3 and spilled out several times, although only two of these overflows, on August 8 and 16, were observed in motion. The flows extended north, south, and east in narrow streams no longer than 800 m. More vigorous periods of spattering accompanying rapid drainback built a low cone around the hole. We were seldom able to approach the hole closely, because of the instability of the thin roof and the overwhelm- ing heat. On the rare occasions when observation was possible, we saw either no circulation pattern in the lava column or at most a very slow west-to-east move- ment, and we detected no obvious coordination be- tween the nature of activity in this vent and that at the summit or vents farther downrift. At least once, violent emission of gas explosively destroyed the cone, littering the ground surface with debris for tens of me- ters around the vent. Vent 1 reopened sometime between August 4 and the morning of August 7, probably on August 6, as suggested by slight detumescence of Kilauea’s summit (pl. 2A). As Swanson and Peterson (1972, p. 4) de- scribed, “Lava quietly welled out of this vent, flowed in a surface river for 50—100 m, and then disappeared into a tube [pl. 4B] which carried the lava for several tens of meters before feeding it beneath the crust into the molten part of the lava lake in Alae Crater.” Con- currently, vent 2 resumed activity, sending small flows part way across the crust of the Alae lake. Vent 2 con- tinued to erupt surface flows until midday on August 8, the same day that vent 3 briefly emitted two narrow flows, one eastward, the other southward. Greeley (1971, fig. 2) shows maps illustrating this activity at five times between August 7 and 11. Meanwhile, lava began draining out of the molten lake within Alae Crater through the lava tube last ac- tive in late October 1969 and now buried 21—22 m be— neath new lava (pl. 4B; Swanson and Peterson, 1972). Lava issued from the mouth of this tube 2.5 km south of Alae and formed a flow that was first discovered at 0830 August 11, when it was within 100 m of the Chain of Craters Road 4.5 km downslope from Alae. We do not know when the draining began but suspect it was late on August 7 or early on August 8, when the crust on the lake began to subside. The crust had nearly completed its 13—m subsidence by 1030 August 11, at which time the rate of outflow had dropped from 3.4 X 104 thr to 1.3 X 10“ thr, a rate that just balanced inflow. For the next 12 days, lava continued to pour at this reduced rate into the Alae lake from vent l and leave the lake through the exit tube. On August 23, vent 1 ceased erupting but vent 2 began feeding lava at about the same rate through another inlet tube (pl. 4C and fig. 42) into the molten lake in the crater. Lava continued to leave the lake through the same exit tube, and the remarkable balance between inflow and outflow was maintained. Observations through sky- lights in the roofs of lava tubes (Peterson and Swan- son, 1974, pl. 52 and 53; Swanson, 1973, fig. 9) confirmed the role that tubes played in carrying lava into and out of Alae, which served as a holding reser- voir along the route of flow from the vents to the sea- coast (Swanson and Peterson, 1972). The development of the complex pahoehoe and aa flow that formed from the Alae outflow was described by Swanson (1973) and Peterson and Swanson (1974). Quoting from Swanson (1973, p. 621), ***Lava that first emptied from [the exit tube] onto the ground surface *** changed to aa after a few hundred meters of surface flowage. Gradually, however, the pahoehoe tube system extended itself, in part by a continuing flow of lava through interconnecting pahoehoe toes and in part by crusting over of small surface chan— nels. The formation of the crust slowed cooling, so that hot, rela- THIRD STAGE OF ERUPTION 43 FIGURE 42.—Skylight in tube between vent 2 and Alae in Septem- ber 1970 provided good opportunity to sample lava with small dipper attached to stainless steel rod. Results were poor, because the relatively high flow rate and tensile strength of the lava made tively fluid pahoehoe encroached on and eventually covered the slightly older aa flows. As each pahoehoe lobe broke onto the sur— face from the end of the new tube and advanced downslope, it changed gradually to aa that was covered shortly afterward by still newer pahoehoe that emerged at the surface from the ever-length- ening tube system. This process—pahoehoe changing to aa only to be covered by slightly younger pahoehoe as the tube system ad- vanced—was repeated over and over again *** By the evening of August 13, the flow was descend- ing Poliokeawe Pali, and early on August 15, it began to pour over Holei Pali. Meanwhile, the east side of the flow covered an BOO-m segment of the Chain of Craters Road above Poliokeawe Pali (fig. 43) and started a major fire in the tinder-dry forest. On Au- gust 17, lava began to pool in a broad flat area at the base of Kealakomo Pali, 2 km south of Holei Pali (pl. 3K). Large tumuli (Swanson, 1973, fig. 10), flat— topped uplifts, and sag structures commonly formed on the surface of the pooled lava, which was fed by a complex system of anastomosing distributary tubes. The pooled flow slowly moved seaward from the base it difficult to submerge the clumsy, relatively light probe. Better penetration was obtained by hurling a heavy steel bucket, teth- ered by a stainless steel cord, with as much force as possible into the lava. of Kealakomo Pali, a month later trickling into tide pools on September 21. The rate of flow into the sea later increased, and the new front eventually became more than 650 m wide (pl. 3K). The flow constructed a small lava delta that extends about 10 m from the old shoreline, has an area of about 1.4 X 104 m2, and a vol- ume of about 0.6 X 10“ m3 (Peterson, 1976). No movement of lava over the cliffs south of Alae was seen between September 27 and 30, although lava continued to enter and leave the crater through the inlet and outlet tubes. Apparently the tube system was blocked somewhere below Alae, although no up- lift of the floor of the crater was noted, an expected consequence if the tube system were closed. On Octo- ber 1, voluminous flows broke out from the system 2 km south of Makaopuhi Crater, inundating more for- est and roadway. A lava-tube system began to form, and the flow gradually advanced over the palis in a series of surges of pahoehoe and aa. The older tube system was not reactivated. Lava continued flowing 44 FIGURE 43.—Asphalt burns as pahoehoe flow crosses Chain of Craters Road above Poliokeawe Pali, August 15, 1970. This flow started a large fire in the ohia and kukui forest, threatening rare native Hawaiian plants and trees before being brought under control. Photograph by J. B. Judd. through the new system until October 26, stopping just short of the coast when inflow to Alae temporarily ended. Throughout this entire period, a slowly circulating, rising and falling, and periodically degassing lava lake occupied the summit crater of Mauna Ulu. The activ- ity was similar to that of the preceding month, with the lava generally 15—20 m and occasionally 30 m be- low the rim. The dominant direction of circulation continued to be west to east, with nearly constant low fountaining at the east end. The crater was periodi- cally widened by rockfalls from its walls. Vent 4 (pl. 4D), initially a tiny spatter cone, opened on September 23 or 24. Within a week, a small collapse crater 2 m across formed at the east base of the cone; the crater was roofed over a few days later. When viewing conditions were favorable, lava could be seen at a depth of 20—30 m within vents 1 to 4 moving east- ward though underground passageways. Each vent overflowed several times, sending lava northward to- ward the edge of the lava field and southwestward, sometimes reaching as far as the Alae subsidence bowl, where the flows constructed a “lava fan” extend- ing to the floor of the bowl (Swanson and Peterson, 1972). The four vents increased activity in early October, each of them going through several episodes of violent degassing with minor spattering, quiet lava flows, and fountaining. Small spatter cones were constructed at all the vents, with three cones clustered at vent 2 (pl. 4D). On October 26, the cone at vent 4 caved in, form- ing a small hole that within a day enlarged by collapse to a pit 18 X 13 m in diameter. Continued collapse eventually made the crater nearly circular (pl. 4D). CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO Also on October 26, all flow in the inlet tube between vent 2 and Alae Crater stopped, and lava was visible only in vent 4 and the summit crater. Accompanying this decline was an increase in tilt and seismic activity in Kilauea Caldera (pl. 2), as if pressure were building behind some constriction in the magma conduit sys- tem connecting the summit reservoir and Mauna Ulu. OCTOBER 28—NOVEMBER 18, 1970 Pressure was relieved on October 28, when many overflows poured from vents 1, 2, and 4. Seismic activ- ity at the summit of Kilauea sharply declined and summit swelling stopped at the same time. The flows advanced north and northeast in open channels that quickly roofed over to form tubes (Cruikshank and Wood, 1972, fig. 9). The cyclic activity at vent 4 was especially interest- ing during this period. A cycle began as the level of lava gradually rose 10—15 m to the brim of the crater, then overflowed for periods of several minutes to sev- eral hours. Finally, a low fountain broke the crust on the overflowing pool and quickly grew in volume and vigor to a height of 10—15 m, accompanied by a sudden drop in the level of lava and cessation of overflow. The fountains stopped as the lava withdrew, crusted over, and began its slow rise once more. The gas-piston ac- tivity first observed at the summit vent was clearly in operation. All the while we recognized no effect of ac- tivity at vent 4 on other vents, where lava continued to issue at a relatively uniform rate or maintained its own slow rise-fall cycles. Vent 1, inactive for several days, collapsed on November 5, forming a crater 15 m in diameter and 15—20 m deep (pl. 4E). When discovered, the new crater contained no lava, although the walls were red hot in places. Lava had returned to the crater by the next morning and took part in many episodes of over- flow and drainback during the next week. Then the lava stagnated and solidified at a high level in the crater, ending activity at vent 1 until February 1971. At 1430 November 13, a loud boom and a rising cloud of fume and dust issued from the east flank of Mauna Ulu. Rushing from the Alae area, Peterson and Swanson found a new collapse crater still forming 75 m east of vent 4. This crater, designated vent 5 (pl. 4F), quickly reached 30 m in diameter (Cruikshank and Wood, 1972, fig. 25). The crater at vent 4 enlarged to 25 m by 40 m, perhaps enhanced by ground motion caused by the opening of vent 5. During the ensuing five days, the two craters participated together in the cycle of slowing rising lava, overflow, and fountaining with drainback. Vent 5, the rim of which was about 10 m lower than that of vent 4, began overflowing sev- eral minutes sooner, but otherwise the two craters acted in unison, implying a connection between them. THIRD STAGE OF ERUPTION Drainback episodes at vents 4 and 5 were often fol- lowed within a few tens of seconds by especially vio- lent degassing from the cone at vent 3, upslope from the two craters. This evidence suggests that the main source of lava in vents 4 and 5 was located beneath vent 3, the site of the eastern vent area so active dur- ing the first two months of the eruption. A loud roar lasting a few seconds to several minutes accompanied the degassing at vent 3, and small bursts of spatter were sometimes thrown to heights of 60 111. During this time, the overflows from vents 4, 5, and occasionally 2 spread 3 km downrift and repeatedly poured into Alae Crater, adding to the lava fan and completely covering the floor of the recently surveyed depression (pl. 3L; Swanson and Peterson, 1972). Overflows stopped on November 18, and lava pools in the vents remained about 10 m below the rim. Meanwhile, lava resumed coursing through the Alae inlet and outlet tubes on November 2 (fig 44). Thin streams of pahoehoe, which fed through the tube sys- tem, reached the base of Holei Pali several days later. The rate of inflow to the crater increased on Novem- ber 14, and a new skylight revealed a bilevel tube with 8-m lava falls carrying lava into Alae (Cruikshank and Wood, 1972, fig. 11). On November 15, surface flows broke out 3.5 km south of Makaopuhi Crater; they soon covered several hundred meters of the highway and advanced toward a grove of rare native Hawaiian vegetation in Naulu Forest (pl. 3L). National Park Service personnel bulldozed up part of the pavement and used it, together with rock scrapings, to construct low dams that successfully diverted the thin, slowly moving pahoehoe flow off the road and over the cliffs, thereby saving the forest. The floor of Alae Crater subsided during the night of November 12—13 as much as 3 m near the exit tube. Swanson and Peterson (1972) interpreted this to indi- cate deepening of the exit tube by the removal of a partial blockage. NOVEMBER 19—DECEMBER 24, 1970 Flows continued over Holei Pali until November 25, then at a decreasing rate until November 29, when visible activity stopped. However, lava was observed in both the inlet and outlet tubes of Alae for the next few days, though flowing at a slower speed than pre- viously. A large new collapse depression formed on the east flank of Mauna Ulu during the night of November 28— 29 (pl. 4G). The collapse enlarged vent 5 and extended 100 In downrift, engulfing two cones built at the west end of vent 2. A pool of lava covered the western third of the floor of the depression to within 15 m of the rim; the rest of the floor was a jumble of fallen rock from 45 FIGURE 44.—Skylight in outlet tube 100 m southeast of Alae Crater, November 5, 1970. Lava pours over falls developed on collapsed part of roof of tube. Note recently fallen rubble below man. the roof and walls. This area enlarged during the next few days to maximum dimensions of 150 m by 35 m, with a depth of 25—30 m. The north rim of the summit crater of Mauna Ulu receded at the same time that the collapse depression formed, and the crater now measured about 130 m X 80 m (pl. 40). The circulating lava lake continued its activity as before. On December 2, a rapidly moving stream of lava is- sued from the west end of the collapse area, filled the trench to the brim, and entered a tube at the east end of the depression (pl. 40). This tube is probably the one that had connected vent 2 and Alae Crater before the collapse area captured it. A wide skylight pierced the roof of the tube 30 m farther east, and lava could be seen plunging over an underground ledge, rounding a broad curve, and disappearing in the direction of Alae. A similarly vigorous flow was observed through 46 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO skylights in the Alae exit tube. By December 3, the flow had slackened and crust had formed on it, but lava continued to enter the tube into Alae. A new flow broke out above Poliokeawe Pali on the afternoon of December 4, covering part of the November 15-29 field. This flow continued until December 8, when it completely roofed over. No flowing lava was visible again south of Alae until January 21, 1971. On December 6, numerous flows that erupted suc- cessively from vent 4 spilled into the November 28—29 collapse depression, cascaded over the rough floor, and entered the inlet tube to Alae. Other flows spread northward, and still others advanced onto the floor of Alae. The western two-thirds of the collapse depres- sion was filled with congealed lava by December 8, when renewed collapse at the site of vent 5 formed a small crater (pl. 4H) containing a pool of bubbling lava. Strong flow into the tube leading to Alae contin- ued, apparently unaffected by the cyclic gas—piston activity that characterized the pools of lava in vents 4 and 5. By December 13, visible inflow to Alae had stopped, although continued outflow suggested that the lake was supplied through deeper tubes. By this time, overflows and cyclic drainbacks in vents 4 and 5 had ended, and by December 20, the pools of lava had dropped to 20 m below the surface in vent 4 and 15 m in vent 5. On December 20, the sulfur-encrusted cone at vent 3 collapsed into a crater that quickly became 20 m by 35 m in diameter (pl. 4H ). A lava pool slowly circulated from west to east 15—20 m below the rims 0f vents 3, 4 and 5, suggesting a connection. The rate of flow increased on December 21, but the level of lava dropped to 25—30 m below the surface. Flow was still vigorous on December 24, but it had stopped when next examined on December 26. The walls of the craters at vent 3, 4, and 5 gave way on December 21, and large blocks tumbled into the flowing lava and disappeared. Enlargement of the craters continued over the next several days, acceler- ating as the underground stream lowered and finally vanished beneath the rubble. The most rapid collapse occurred at the east and west sides of the craters, which consequently elongated toward one another. During this entire period, the lava lake in the sum- mit crater of Mauna Ulu showed little of the varied activity that characterized the vents farther east. From November 19 to December 4, the level fluctu- ated between 13 m and 25 m below the rim, remaining in constant circulation, nearly always west to east. The level rose rapidly to within 6 m of the rim on De- cember 6 at the same time that vent 4 began frequent overflows. The lake than experienced several gas-pis- ton cycles, with a few bursts of spatter reaching a height of 35 m during particularly vigorous drain- backs. Lake level dropped on December 7 and re— mained at depths of 25—35 m for the rest of the period. The crater continued to enlarge by collapse (pl. 4H), and on December 20, huge blocks peeled away from the northeastern and eastern walls, carrying away the 8—m-high remains of the east summit cone. The crater was about 150 m long by 85 m wide on December 24, (pl. 41). DECEMBER 25, 1970—JANUARY 27, 1971 This period began with a general lull. Harmonic tremor dropped to its lowest intensity in months, and no moving lava was observed until January 14. None- theless, great changes occurred on the east flank of Mauna Ulu. On January 1, 1971, a narrow bridge separating the enlarged vents 4 and 5 collapsed unseen, and the two craters merged into a trench (pl. 41). On January 2, a bridge 60—70 m long, 30 m wide, and 10—15 m thick separated the crater at vent 3 from the trench, and one could look beneath the bridge from one opening to the other. At 1030, the bridge slowly sagged, cracked in the middle, broke along its edges, and finally plunged into and covered the lava 40 m below. This collapse, closely observed from a point only 50 m downrift, completed the opening of the trench, which now ex- tended 340 m between vent 3 and the east end of the November 28—29 collapse depression (pl. 4J). The trench was 25—35 m wide, 30—40 m deep, and was floored by a jumble of rubble left from collapse of its roof. Thick fume issued from the trench for the next 2 weeks, combining with fog generated by evaporation of heavy rains to create very poor viewing conditions. We could sometimes distinguish stagnant, often crusted pools of lava through the dense cloud, and oc- casionally we heard “sticky’ sounds similar to those made by a viscous fluid such as grease moving slowly through a constricted opening. Our impression was that lava was slowly working its way along the trench beneath or through the rubble pile, but no lava was seen in the inlet and outlet tubes to Alae Crater. Visible activity resumed on the morning of January 14, and by afternoon the trench was filled by an east- ward-flowing river of lava that spilled over the south- east rim and poured onto the floor of the Alae subsidence bowl. No lava was observed in the inlet tube to Alae. Accompanying this renewed activity, the level of lava in the summit crater 0f Mauna Ulu rose to within 12 m of the rim, but otherwise its circulation and fountaining pattern remained unchanged. The activity in the trench was again cyclic, with quiet in- flow followed by drainback-related fountaining cen- tered at the location of vent 3, at the west end of the THIRD STAGE OF ERUPTION 47 trench. This type of activity persisted through Janu- ary 15 and perhaps longer, but stormy weather pre- vented observations on January 16—20, when the old inactive cone at vent 2 crumbled away. By January 21, the trench had drained, and the 10—20-m-deep floor was covered with rubble except for a pool of circulat- ing and periodically degassing lava at the site of vent 3. Lava fed from this pool must have been moving un- seen beneath the rubble, for a vigorous stream was pouring through the inlet tube to Alae Crater (pl. 4K). Also on January 21, several narrow fingers of pahoe— hoe emerged from tubes south and southeast of Alae, indicating that lava was again flushing through the Alae holding reservoir. On January 23, small flows fed by the tube system spilled into Makaopuhi Crater (pl. 3L), the first time that lava had entered the crater since the eruption in February 1969 (Swanson, Jack- son, Koyanagi, and Wright, 1976). Flows descended Poliokeawe and Holei Palis the next day (pl. 3L) and continued through January 27. JANUARY 28—FEBRUARY 20, 1971 A new fissure opened west of the summit of Mauna Ulu across the site of Aloi Crater during the evening of January 28 (pl. 4L). A line of low fountains extended about 700 m uprift from the lower west flank of Mauna Ulu between the fissures of October 20, 1969 and April 9, 1970. Activity continued until February 10, building a broad satellitic shield 20 m high on the west flank of Mauna Ulu and covering an area of 2—3 km2 south of the fissure (pl. 3M). Much of the early fountaining was concentrated along the western half of the fissure, but from February 1, the activity was centered on the eastern third, where a lava pond was confined behind natural levees. The pond, located over the northeast part of buried Aloi Crater, over- flowed irregularly, and these flows constructed most of the satellitic shield. After each period of overflow- ing, the pond largely emptied by draining back into the fissure, leaving a flat-floored shelf behind the lev- ees. Such a cycle of filling and emptying occurred sev- eral times a day. An irregular depression 2—10 m deep (Cruikshank and Wood, 1972, fig. 5) was left after the pond last drained on February 10. The lava lake in the summit crater of Mauna Ulu was lower than usual on January 29 and circulated from east to west; it then began rising and was only 3 m below the rim on February 7—9, the highest level in months. The level dropped when the new fissure stopped fountaining on February 10, and the next day it returned to its normal depth, 15—30 m, which it maintained for the rest of the period. We saw a section of the southwest wall of the crater about 100 m long by 5—10 m wide fall into the lake on February 18, produc- ing a splash that reached about 50 m above the crater rim. This disturbance only briefly interrupted the west-to-east circulation pattern. The flows south and southeast of Alae Crater de- clined and stopped less than a day after the fissure west of Mauna Ulu opened. This timing suggested that the input to Alae had ended when the new activ- ity began, and also that a magma conduit system con- nected the trench and new fissure. As if a valve had been turned, vent 1 (pl. 4M), inactive since November 10—12, began erupting less than three hours after the vents on the west flank had stopped activity. By the morning of February 11, a vigorous stream of lava was pouring into the subsidence bowl in Alae, which had already begun to overflow. The 9.7 X 105 m3 depression had filled in less than 20 hours, indicating an eruption rate of at least 4.85 X 104 thr (1.16 X 106 ma/day). A rapidly flowing river emerging from a tube at the north edge of Alae (Cruikshank and Wood, 1972, fig. 8) was the only observed source of the flow. This tube was apparently the same one that was active in August 1970, when vent 1 was also active (pl. 4B). Overflows from Alae again entered Makaopuhi Crater and ex- tended 3 km southward. Lava accretion built the southeast rim of Alae 5 In higher, to about 29 m above the preeruption rim (Swanson and Peterson, 1972, fig. 2E). Vent 1 stopped erupting on February 19, and a spatter cone built since February 10 caved in, forming a crater 8—10 m in diameter (pl. 4N). Throughout this activity, strong fume was emitted from a skylight in the old (west) inlet tube to Alae (pl. 4M), suggesting active inflow fed by a vent in the trench, probably vent 3. On February 20, lava was seen through skylights in the outlet tube, but no new tube-fed flows formed downslope from Alae until Feb- ruary 21. A new area of collapse formed about 1 km south of Alae Crater during either the fountaining west of Mauna Ulu or the filling and overflowing of Alae. The collapse area (fig. 45 and pl. 4M), some 200 m by 800 m long in a downslope direction, was characterized by jumbled and tilted blocks of surface crust overlying rough, spiny lava that was apparently still liquid, though quite viscous, during the collapse. A rootless aa flow extended a short distance downslope from the lower end of the area. Crust at the upper end of the area was mostly unbroken but sagged 6—8 m; the jum- bled area had apparently moved downslope as well as sagged. No connection was evident between this area and any vent at Mauna Ulu. We speculate that over- flows from Alae Crater in mid-February formed a pool behind an unstable dam that later failed, allowing downslope flowage of the relatively cool, viscous lava. 48 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO FIGURE 45.—Aerial view looking north over subsidence bow] at Alae Crater on March 28, 1971, showing fume cloud billowing from Mauna Ulu trench and summit crater and smaller cloud from a skylight in the roof of the inlet tube to the crater. Open cracks parallel northeast margin of subsidence bowl, and lobate ridges of thrust-fault origin (Swanson and Peterson, 1972) occur closer to center of bowl. Dark area in lower left is new collapse area referred to in text. FEBRUARY 21—JUNE 14, 1971 The crust of the Alae lava lake began to subside soon after surface inflow ended (fig. 45). As Swanson and Peterson (1972, p. 11) summarized: The lake crust had already subsided a maximum of 8 m by Feb- ruary 23, when the crater was visited on the ground. We presume that the subsidence began somewhat earlier, probably on February 21. By February 26, the crust had lowered 17 m, and most of the surface structures [cracks, thrust faults, and sinuous compres- sional ridges at the toes of thrust faults] related to subsidence had already formed. Deformation was largely complete by March 2, when the subsidence bowl was about 19 m deep. *** Slow settling of the crust continued over the next several months, amounting to an additional 4 m by June 28 *** Swanson and Peterson (1972) further described the results of this subsidence, which included observing an active thrust fault, and interpreted the subsidence to have developed as the pre-February lake crust sank into the molten lake because of the weight of new overlying flows. This subsidence displaced un— derlying molten lava upward and out of the lake through the outlet tube. The elevation of the base of the crust after both draining events [August 1970 and February—March 1971] was controlled in a crudely hydrostatic fashion by the elevation of the outlet tube. Meanwhile, lava continued to pour from the inlet tube through the molten part of the lake and out the outlet tube during and after the crustal subsidence. On February 22, lava once again flowed over Polio-. keawe and Holei Palis, pooled at the base of Holei Pali, and began sending narrow fingers seaward. By February 26, the flow crossed the Chain of Craters Road above Kealakomo Pali (p1. 3M), and another 2- km section of the road was covered by March 20. On March 5, the slowly advancing pahoehoe en- tered the abandoned Hawaiian village Kealakomo (pl. 3M), burying noted archeologic sites. On March 8, the tube-fed pahoehoe reached the ocean and began form- ing a delta, the development of which was described in detail by Moore, Phillips, Grigg, Peterson, and Swan— son (1973) and Peterson (1976). Four days later, its area above sea level was about 2.5 X 104 m2, and by the time lava visibly stopped entering the sea on May 14, the delta was 4.7 X 105 In2 in area, extended more than 400 m seaward from the old coastline, and had a vol— ume of more than 13.5 X 106 m3 (Peterson, 1976). Lava may have continued to flow into the sea through sub- merged tubes until at least May 25, as suggested by glowing cracks and persistent areas of steaming, very hot rock at the surface. Moreover, lava was seen flow- ing in the outlet tube from Alae as late as early June. The period of 82 days (February 22 to May 14) during which the tube-fed pahoehoe was definitely active constitutes the longest period of continuous flow dur- ing the eruption. The trench on the east flank of Mauna Ulu contin- ued to enlarge as its unstable walls, consisting of thin, highly jointed flows, repeatedly gave way. By March 20, the chasm was 350 m long, 35—45 m wide, and from 15 m to 50 m deep. The trench grew rapidly westward, toward the summit crater. On March 23, the distance between the trench and crater was 50 m (pl. 4N), on March 28, 13 m, and on April 6, 3 m (pl. 40). The up- per part of the trench and crater merged on April 13 (pl. 4P), but a septum of wallrock capped by collapse debris to within 15 m of the ground surface separated the deeper parts, preventing the lava lake in the sum- mit crater from draining into the trench. Rubble con— tinued to slough off the septum, which by April 20 had lowered to 30 m below the rim, where it more or less stabilized. By this time, the trench had lengthened to about 430 m and widened to from 40 m to 60 m; it reached its maximum length of 530 m by June 1 (pl. 4P and fig. 46). The floor of the trench through this period was mostly covered by rubble (fig. 47). Bubbling and gur- gling noises were frequently heard and strong heat waves seen from several places along the trench east of vent 3. Consequently, we assume that vent 3 was erupting and that other vents along the trench may also have been active during this period. In places, small pools of lava collected in low areas on the floor, THIRD STAGE OF ERUPTION FIGURE 46.—Aerial view looking west over trench, with summit crater of Mauna Ulu in background, May 25, 1971. Jagged pile of rubble (arrow) separating trench from crater barely visible through fume. Cracks bound incip- ient slump blocks. Trench is about 530 In long from east end to rubbly partition. 49 50 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO FIGURE 47.—View looking west from near east end of trench, June 28, 1971. Note rubble-strewn floor, tilted remnants of pre- trench ground surface (upper right), and V-shaped profile. Fume obscurestrench in distance. Depth from rim on left to top of ridge of rubble, about 5 m. apparently when the level of the underground river rose for brief periods. Lava could be seen in a deep tube leaving the east end of the trench (fig. 48) and at a depth of several tens of meters through a fuming skylight in the inlet tube to Alae (fig. 45). The lava lake in the summit crater continued its typical activity, described for this period of time by Duffield (1972). By early April, the crater was oval shaped, 165 m by 100 m at the widest point (pl. 40). Lake level remained 40—50 m below the rim through April, then began to lower gradually to 57 m by June 14 (fig. 7). Fuming increased as the level dropped, making observations of the lake very difficult. An especially noteworthy collapse was observed at 2018, March 28. This collapse was so large that it reg- istered on all seismometers within a 25-km radius. Prior to the collapse, the lake was fountaining at the east end of the crater. Suddenly, a block at least 40 m long by 15 m wide fell from the northeast wall, tearing a wide hole through the crust. The entire surface of the lake reacted immediately, vigorously degassing and fountaining, and the level dropped about 10 m in a few seconds, despite the addition of the block. The drop in level was probably caused by loss of gas, facili- tated by destruction of the crust that normally kept the gas from escaping. The new lake level, lower than at any previous time, revealed a stream of lava pour- ing into the lake from an elevated area hidden within the south side of the septum between the crater and trench. Both the stream and the lake itself were drain- ing into a sump at the east end of the crater. We could not determine if the stream drained a perched pond within the septum, was produced by a separate vent, or flowed into the crater from the trench. Subsequent observations made when lake level was low before the end of the eruption suggest a perched pond connected to the main body of the lake. The level gradually rose after the dramatic withdrawal. By 2045 the lake had regained half the drop and covered the stream, and by 2100 the level was within 3—4 m of its former position. FOURTH STAGE OF ERUPTION JUNE 15—OCTOBER 15, 1971 The eruption slowly waned and finally ended dur- ing this period. No surface flows were erupted, and all activity was concentrated in the summit lake, which lowered at. a remarkably constant rate of 70 cm/day (fig. 7), dropping from 60 m to 140m below the rim by September 20 (fig. 49). Lava disappeared from sight on October 15, leaving a crater about 145 m deep with arubble-strewn floor. This disappearance is arbitrari- ly taken as the end of the 1969—71 Mauna Ulu erup- tion. The nature of activity in the lake changed when the level began its steady decline. In early June, the lake underwent minor rises and falls of 3—4 m amplitude superimposed on a slow but continuous circulation pattern from west to east, and fountaining a few me- ters high was common, especially around the east pe- riphery of the lake. On about June 15, when lake level began to recede, the rate of circulation became more sluggish, the frequency and intensity of fountaining diminished, and the amplitude of the pistonlike ac- tion decreased to only a meter or so. The lake some- times stagnated for a few minutes, and plates of crust foundered as is common in other stagnant lava lakes (see, for example, Wright and others, 1968, p. 3,197; Shaw and others, 1971, p. 878). A flat-topped ridge 6—10 m wide, dividing the lake into two separate pools, was uncovered on July 17, when lake level stood at 87 m below the rim (fig. 50). The two pools behaved independently, suggesting that each was fed by a separate vent which may be the same as those that supplied the eastern and western compartments of the old western vent area between August 20 and December 31, 1969. On July 19, the ridge stood well above the 95-m-deep pools. On July 20, however, the ridge had sunk to about the same lev- el as the pools, presumably because lateral support had been removed when the pools receded, thereby al- lowing the semisolid material of the ridge to subside and creep outward under the influence of gravity. A lava-filled channel crossed the northern part of the ridge, connecting the two pools. Both pools continued SIGNIFICANCE OF THE ERUPTION 51 FIGURE 48.—Blunt east end of trench, June 28, 1971. Entrance to Alae inlet tube shown by arrow. Kane Nui o Hamo in background. Man (circled) gives scale. Cones of February 1969 eruption are indicated by letters used by Swanson, Jackson, Koyanagi, and Wright (1976). to behave independently, and lava flowed east or west through the connecting channel depending on relative levels. The dropping lake level also revealed a nearly verti- cal east-northeast-trending dike in the south side of the septum separating the crater and trench (fig. 51). This dike may have been injected on May 24, 1969, between the eastern and western vent areas. Its top, about 95 m below the rim, is about 15 m below ground level before the eruption. The dominant direction of circulation in the pools remained eastward. With lowered lake level, we could see that the east wall of the crater was deeply under- cut, as if it were the mouth of a tunnel (fig. 51). Lava tended to flow into this area and possibly into the trench although this was never confirmed. Meanwhile, the level of the two pools continued to drop at about the same rate. This sinking, together with the accumulation of rubble from numerous rock falls, reduced the size of the pools to only a few meters across before they finally sank from sight on October 15. The separating ridge subsided at about the same rate as the pools, before becoming obliterated with ta- lus in September. According to our measurements, the level of the lake dropped below the preeruption ground surface, about 80 m below the rim of the crater, in early July (fig. 7). No evidence of this surface, such as a terrace, narrowing of the crater, or change in character of the wallrock lava flows, was revealed at this or any other stage of development of the crater. Whatever the crater-enlarging process was—stoping, thermal ero- sion, collapse, melting, or a combination of these—it was most efficient in tailoring the shape of the crater to a similar form throughout its depth. SIGNIFICANCE OF THE ERUPTION The 1969—71 Mauna Ulu eruption was the first of a series of eruptions, continuing until 1974, that stand unique in historically recorded accounts of Kilauea. For the first time in at least 150 years, flank activity on Kilauea continued for a period longer than a few weeks. The variety of behavior and persistence of events and processes allowed repeated and systematic 52 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO FIGURE 49.—Technique for measuring depth to surface of Mauna Ulu lava lake. Man sights with rangefinder to distinctive point on lake surface, and vertical angle to point is measured with cli— nometer. Depth is product of sine of angle and rangefinder dis- tance. Repeated measurements to various points were averaged to reduce observational errors. Note the septum separating the east end of the crater from the fuming trench. July 1971. observations, which have led to an improved under- standing of the relations between the internal work- ings of the volcano and the eruptive behavior and processes of lava eruption and transport. The eruption illustrated well the integrated system that constitutes a volcano in Hawaii, as seismicity and ground deformation in Kilauea’s summit region were systematically correlated with the eruptive behavior of Mauna Ulu 8—9 km away. These correlations dem- onstrated that magma continually entered a shallow reservior of complex nature beneath Kilauea’s summit at a rate of about 0.3 X 106 ms/day. Ground deforma- tion and seismic studies showed that the reservoir in- flated when the rate of magma supply exceeded outflow, deflated when outflow exceeded supply, and remained in equilibrium when rates of supply and outflow were balanced. The eruption displayed, for the first time histori- cally, the development and sustained operation of an active lava lake at a locality other than Halemaumau at Kilauea’s summit. The eruption revealed the sig- nificance of the gas-piston cyclic activity in the behav- ior of the lake and subsidiary vents. At times, gas- piston cycles dominated the eruptive behavior, and at other times they were secondary and subtle, but evi- dence of gas-piston action could be perceived in some FIGURE 50.—Flat-topped ridge dividing lava lake into two pools, from north rim of Mauna Ulu crater. Note that east pool (left) is higher than west pool and encroaches on ridge. Depth to surface of east pool is 87 m; ridge is 6—10 m wide. Photo taken on July 17, 1971, the day ridge first appeared. Ledges on crater wall record past levels of lake surface. degree during most of the eruption. This type of cycle may play an important role in the mechanism of erup- tion of basaltic lava, and its dynamics deserve further investigation. The 1969—71 Mauna Ulu eruption also allowed, for the first time in recent history at Kilauea, repeated observations of prolonged lava flows. These observa- tions led to new insights concerning the significance of several types of pahoehoe, the transition of pahoehoe to aa, the processes by which lava tubes develop, and the significance of prolonged flows in the development of certain landforms and in the major growth pro- cesses of basaltic islands. The construction of a parasitic shield volcano was well exemplified by Mauna Ulu. Its growth was for the most part very rapid, particularly within one month in 1970 (though later eruptions in 1972—74 added further height to the edifice), and involved the relatively calm outflow of short-lived flows from the vent with little spatter activity. The apparently parental relation be- tween the main vent of Mauna Ulu and vents on its west and east flanks suggests an analogy to the larger— scale summit-rift systems of the principal Hawaiian shield volcanoes, and this analogy should be further examined. To summarize, the 1969—71 Mauna Ulu eruption SIGNIFICANCE OF THE ERUPTION 53 was, because of its long duration, unparalleled variety tion gathered during this immensely stimulating of activity, and easily accessible nature, one of the event will improve our knowledge of many important most significant eruptions ever at Kilauea. Informa- volcanic processes. FIGURE 51.—East end of summit crater of Mauna Ulu, from north rim of crater, on September 7, 1971. Depth to floor about 123 m. Alcove in septum between crater and trench contains small pool of crusted lava (dark). East edge of eastern pool in crater at bottom of view. Note dike (arrow). 54 CHRONOLOGICAL NARRATIVE OF THE 1969—71 MAUNA ULU ERUPTION OF KILAUEA VOLCANO REFERENCESCHTED Anderson, L.A., Jackson, DE, and Frischknecht, RC, 1971, Ki- lauea Volcano: Detection of shallow magma bodies using the VLF and ELF induction methods: Am. Geophys. Union Trans., v. 52, no. 4, p. 383. , Cristofolini, Renato, 1969, Alcuni aspetti dell’eruzione del Kilauea (Hawaii), nell’estate 1969 [in Italian with English summary]: Boll. Sedute dell’Accad. Gioenia di Science nat. Catania, ser. 4, v. 10, p. 1—32. Cruikshank, DR, and Wood, C.A., 1972, Lunar rilles and Hawai- ian volcanic features: Possible analogues: The Moon, v. 3, p. 412—447. Cruikshank, D.P., Morrison, David, and Lennon, Kenneth, 1973, Volcanic gases: Hydrogen burning at Kilauea Volcano, Ha- waii: Science, v. 182, p. 277-279. Davis, P.M., Jackson, D.B., Field, James, and Stacey, RD, 1973, Kilauea Volcano, Hawaii: A search for the volcanomagneti'c ef- fect: Science, v. 180, p. 73—74. Duffield, W.A., 1972, A naturally occurring model of global plate tectonics: ’Jour. Geophys. Research, v. 77, p. 2543—2555. 1975, Structure and origin of the Koae fault system, Kilauea Volcano, Hawaii: US. Geol. Survey Prof. Paper 856, 12 p. Duffield, W.A., Heiken, Grant, and Gibson, E.K., Jr., 1974, Some physical and chemical characteristics of Pele’s hair: Geol. Soc. America Abst. with Prog., v. 6, no. 3, p. 167-168. Duffield, W.A., Jackson, D.B., and Swanson, D.A., 1976, The shal- low, forceful intrusion of magma and related ground deforma— tion at Kilauea Volcano, May 15—16, 1970: Inter. Assoc. Volcanology and Chemistry of Earth’s Interior, Symp. Andean and Antarctic Volcanology Problems, Proceedings, p. 577—597. Endo, ET, 1971, Focal mechanism for the May 15—18, 1970, shal- low Kilauea earthquake swarm: San Jose State Col., San Jose, Calif., M.S. thesis, 165 p. Fiske, RS, and Koyanagi, R.Y., 1968, The December 1965 erup- tion of Kilauea Volcano, Hawaii: US. Geol. Survey Prof. Pa— per 607, 21 p. Greeley, Ronald, 1971, Observations of actively forming lava tubes and associated structures, Hawaii: Modern Geology, v. 2, p. 207—223. 1972, Additional observations of actively forming lava tubes and associated structures, Hawaii: Modern Geology, v. 3, p. 157—160. Holcomb, R.T., 1976, Preliminary map showing products of erup- tions, 1962-1974, from the upper east rift zone of Kilauea Vol- cano, Hawaii: US. Geol. Survey Misc. Field Inv. Map MF—811, scale 124,000. Holcomb, R.T., Peterson, D.W., and Tilling, R.I., 1974, Recent landforms at Kilauea Volcano, a selected photographic compi- lationL in Greeley, R., ed., Hawaiian Planetology Conference, NASA TMX 62362, Washington, DC, p. 49—86. Jackson, D.B., Swanson, D.A. Koyanagi, R.Y., and Wright, T.L., 1975, The August and October 1968 east rift eruptions of Kilauea Volcano, Hawaii: US. Geol. Survey Prof. Paper 890, 33 p. Kinoshita, W.T., Koyanagi, R.Y., Wright, T.L., and Fiske, RS, 1969, Kilauea Volcano: The 1967—1968 summit eruption: Sci- ence, v. 166, p. 459—468. Moore, J .G., and Koyanagi, R.Y., 1969, The October 1963 eruption of Kilauea Volcano, Hawaii: US. Geol. Survey Prof. Paper 614—C, 13 p. Moore, J.G., and Krivoy, H.L., 1964, The 1962 flank eruption of Kilauea Volcano and structure of the east rift zone: Jour. Geophys. Research, v. 69, p. 2033—2045. Moore, J.G., Phillips, R.L., Grigg, R.W., Peterson, D.W., and Swanson, D.A., 1973, Flow of lava into the sea, 1969—1971, Kilauea Volcano, Hawaii: Geol. Soc. America Bull., v. 84, p. 537—546. Muenow, D.W., 1973, High temperature mass spectrometric gas- release studies of Hawaiian volcanic glass—Pele’s Tears: Geo— chim. Cosmochim. Acta, v. 37, p. 1551—1561. Naughton, J .J ., 1973, Volcanic flame: Source of fuel and relation to volcanic gas-lava equilibrium: Geochim. Cosmochim. Acta, v. 37, p. 1163—1169. Naughton J.J., Greenberg, V.A., and Goguel, R., 1976, Incrusta— tions and fumarolic condensates at Kilauea Volcano, Hawaii: Field, drill-hole and laboratory observations: Jour. Volcanol. Geothermal Research, v. 1, p. 149—165. Naughton, J.J., Lee, J.H., Keeling, Diana, Finlayson, J.B., and Dority, Guy, 1973, Helium flux from the earth’s mantle as esti- mated from Hawaiian fumarolic degassing: Science, v. 180, p. 55—57. Naughton, J.J., Lewis, V.A., Hammond, D., and Nishimoto, D., 1974, The chemistry of sublimates collected directly from lava fountains at Kilauea Volcano, Hawaii: Geochim. Cosmochim. Acta, v. 38, p. 1679—1690. Peck, D.L., Wright, T.L., and Moore, J .G., 1966, Crystallization of tholeiitic basalt in Alae lava lake, Hawaii: Bull. Volcanol., v. 29, p. 629—656. Peterson, D.W., 1976, Processes of volcanic island growth, Kilauea Volcano, Hawaii, 1969—1973: Inter. Assoc. Volcanology and Chemistry of Earth’s Interior, Symp. Andean and Antarctic Volcanology Problems, Proceedings, p. 172—189. Peterson, D.W., Christiansen, R.L., Duffield, W.A., Holcomb, RT, and Tilling, R.I., 1976, Recent activity of Kilauea Volcano, Hawaii: Inter. Assoc. Volcanology and Chemistry of Earth’s Interior, Symp. Andean and Antarctic Volcanology Problems, Proceedings, p. 646—656. Peterson, D.W., and Swanson, D.A., 1974, Observed formation of lava tubes during 1970—1971 at Kilauea Volcano, Hawaii: Studies in Speleology, v. 2, p. 209—222. Richter, D.H., Ault, W.U., Eaton, J.P., and Moore, J .G., 1964, The 1961 eruption of Kilauea Volcano, Hawaii: US. Geol. Survey Prof. Paper 474—D, p. Dl-D34. Richter, DH, and Moore, J.G., 1966, Petrology of the Kilauea Iki lava lake, Hawaii: US. Geol. Survey Prof. Paper 537—B, 26 p. Schmincke, H.-U., 1971, Lavastrome auf Hawaii: Umschau, v. 71, p. 424—425. Shaw, H.R., Kistler, R.W., and Evernden, J.F., 1971, Sierra Ne- vada plutonic cycle: Part II, tidal energy and a hypothesis for orogenic-epeirogenic periodicities: Geol. Soc. America Bull., v. 82, p. 869—896. Shaw, HR, and Swanson, D.A., 1970, Eruption and flow rates of flood basalts, in Gilmour, E.H., and Stradling, Dale, eds., Pro- ceedings of the Second Columbia River Basalt Symposium: Cheney, Eastern Washington State Coll. Press, p. 271—299. Swanson, D.A., 1972, Magma supply rate at Kilauea Volcano, 1952-1971: Science, v. 175, p. 169—170. 1973, Pahoehoe flows from the 1969—1971 Mauna Ulu erup- tion, Kilauea Volcano, Hawaii: Geol. Soc. America Bull., v. 84, p. 615-626. Swanson, D.A., Duffield, W.A., and Fiske, RS, 1976, Displace- ment of the south flank of Kilauea Volcano: The result of forceful intrusion of magma into the rift zones: U.S. Geol. Sur- vey Prof. Paper 963, 39 p. Swanson, D.A., Duffield, W.A., Jackson, DB, and Peterson, D.W., 1972, The complex filling of Alae Crater, Kilauea Volcano, Ha- waii: Bull. Volcanol., V. 36, p. 105-126. REFERENCES CITED 55 Swanson, D.A., and Fabbi, B.P., 1973, Loss of volatiles during fountaining and flowage of basaltic lava at Kilauea Volcano, Hawaii: Jour. Research U.S. Geol. Survey, v. 1, p. 649—658. Swanson, D.A., Jackson, D.B., Duffield, W.A., and Peterson, D.W., 1971, Mauna Ulu eruption, Kilauea Volcano: Geotimes, v. 16, no. 5, p. 12—16. Swanson, D.A., Jackson, D.B., Koyanagi, R.Y., and Wright, T.L., 1976, The February 1969 east rift eruption of Kilauea Volcano, Hawaii: U.S. Geol. Survey Prof. Paper 891, 30 p. Swanson, D.A., and Peterson, D.W., 1972, Partial draining and crustal subsidence of Alae lava lake, Kilauea Volcano, Hawaii, in Geological Survey research 1972: U.S. Geol. Survey Prof. Paper 800—C, p. C1—C14. Walker, G.P.L., 1972, Compound and simple lava flows and flood basalts: Bull. Volcanol., v. 35, p. 579—590. 1973, Lengths of lava flows: Royal Soc. [London] Philos. Trans. A, v. 274, p. 107—118. Wentworth, C.K., and Macdonald, G.A., 1953, Structures and forms of basaltic rocks in Hawaii: U.S. Geol. Survey Bull. 994, 98 p. Whitford-Stark, J .L., and Wilson, L., 1976, Atmospheric motions produced by hot lava: Weather, v. 31, p. 25—27. Wright, T.L., 1971, Chemistry of Kilauea and Mauna Loa in space and time: U.S. Geol. Survey Prof. Paper 735, 40 p. Wright, T.L., Kinoshita, W.T., and Peck, D.L., 1968, March 1965 eruption of Kilauea Volcano and the formation of Makaopuhi lava lake: Jour. Geophys. Research, v. 73, p. 3181-3205. Wright, T.L., Swanson, D.A., and Duffield, W.A., 1975, Chemical compositions of Kilauea east-rift lava, 1968—1971: Jour. Pe- trology, v. 16, p. 110—133. GPO 689-863 UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 1056 PLATE 1 155°05' \ ,0 GEOLOGICAL SURVEY 0 I 12'30', 10’ 7,30,] 1902155!5 15 , _ , , t , * «. r r_ ,, \ ~. , i , , ,/ , , , ' , ’3: I ,_ x \ \ ‘ 3 , ‘ , ‘ ,’ __ ¥ 1 _ I ‘ I, , I y/ I 1 ‘ \ 19°25, * I V ‘ ‘ "A“; ‘5 i ' _ 5’ / _ I" ' ,, - I \ I E ' { , , I ,3 I / x/ : / I ' x / ,1] I , 3 (~ 1 ‘ u__ ‘x‘ \ E , / ' \ \ 2 ‘ g ’ : 3' ‘ \\ x x \ I », x A ._ E _ \m ‘ ‘ - 1 z ,5 I , I I , , / I; <3 \ ,/ r ‘ d \ ,A’3 ,3? i ,I i I I f I K _ ‘ g :1 z E 3 f g g / } , , f , \, I / r ‘\ *7 «if / \\\1 , . 2 / E ‘2 x / , , / , I x, I I ’ I if \ j I S / /, ‘ I E \ I [I . , / / : I / ,,/f ; g , / N _ x/EN/ \. \ fl/ ’1’ x / / \ \ fl - 2440M, ‘1 / \ / -_,~\\ \\ \\ \ \ /h / f I O ‘ arch‘z1965: X l I, L g ,2 s L — l \ ow") i X: 5 \x, \“I I / / , I \ I r . g ‘ / \ t I (f E ' ‘\ E“ E‘ ' (x \ ‘ f i - \ I I \ , UU , \ \ K/ K I 51 a If: at ,u a I e a > i ‘, . t Oct 196? / w/ MmMVW/, I [w “xv, ‘ w ‘ : f M / ,w [I / / ,«ENVLM/ i/ /~../ ‘1 00‘.” ~va /- L') z/y ‘\ (i " ,J \ k * \ ,i- x s k E '5 I ‘ c3 , I \ :- I x; "\ \ I W 5; \ g M 3 3 f , t , ~. E: .\/ I I/ r' E 3 ‘- = a 5 ‘ 1 I z‘ , , W- ..... ; ; , 3 1‘ ( 4-H: Feb 1969 , Ir (.4 “wk _ m _ z; \\ ‘ j 3' 'I—H‘I' - x ~~~~~~~~~~ I, / E ‘ I ’ ‘, I I g, mm M x I = , , I I : f g»: / g i , r’ I 3/ ‘N «3 i ‘ ‘ 1 / / it, “I” 1“ . ,r f s ; xs xx , , z I ,, Aug 1969 ,6 )x’ [I y I /' / ~<"“I é \ f , / ggy J ‘\ {/1 / , , “3:? j w " .. , Y / x' \ Kd'I , , ' QC I E‘ E / f / // g . ._§r\—.—.. x I ,l I ’ . r - x z 4/ I; ;/ \Sept»i§6%?g ./” 3‘, 1 :f ,7, ‘ 2’ ,f ’ _ _ / if. A} I} [A / _ -_ I ,1 g / : , / ,x' . , ,f A , / ’ k" \ y _ I I ’7 3,7 / / ,r / , , / ’ / FYI} / " ,./ \ / \ , fr . , y/V K y&\%?pt,1961 A/ 1959;,» 1 f‘ / rug / \ME 3 “March/1965, /' , 33%;} 1953. , March 1965, ’ March 63 \‘ ‘3 3' Wfims 22'30" g, / f9 /“/// /, 22’30" r’” , ,tz’i‘LDee 1969‘: \ “4* 7‘9, 209:,Dec #1965\/f / 1.1 , ‘ , May1969 E /{m‘( \ ’, ( Mau’na'UID‘ _\ :x‘summ‘lt grater V * M Dec“ . I , /,' tax , , /, IV) (I): 1 and” K V Nb, , Am r, /T’\A/pril1970 , ' ,/" ;;/»~” ‘«»~~w«\“// r"/ . ' /: ; \_;' , ~ ‘ix;; ”' ;" ,/rrr3\ j , so :1 . z ' ,,,nr " E,x» ,,~~ _. ,/ g _, _, /, / , , , , , M , _ K . , , _ ’ /- ' ~ , , I “,: ~ x; ' «A A,* //19 / \r~ , ,.~ ”1 ~; ’ 7' '// Q ' I i i - . ~-' : , r K 1 E g9 7t\ a: Q i} I” K” E ‘1 /,*' 1 ‘ ;“*¥\, EXPLANAJION Fissure of 1969-1971 Mauna Ulu eruption (unless otherwise noted, active for long periods during the eruption) +I-H-I—H-I—I—I—I—H Fissure of February 1969 eruption -9—G—-9— Fissure of October 1968 eruption ‘ Fissure of August 1968 eruption Fissure of December 1965 eruption -I-I-I++I+I+I-H-+ Fissure of March 1965 eruption . ‘13—’5— B ,,,,,,,,,,,,,,,, Fissure of October 1963 eruption —9—-—G—9— I y/ ‘/ Fissure of August 1963 eruption QHHFX- Fissure of December 1962 eruption —B—E—B— Fissure of September 1961 eruption NL No lava erupted from indicated fissure CZ:Z> . ,, ,- ,r H , ,/ y/ ' , ‘ ,. _ __ , , / . ,« / , ‘ I , I / / / ' .1 ' . ' { {i , l, I /” ' Mauna Ulu summit crater, OCtOber 15’ 1971 ' 19°20’ fiLnterior — Geological Survey, Reston, Va. — 1978 — G77283 155005! w: 19°20' " " ,‘ ,, ' , 155°15' 12 30 10 153/? SCALE 1'24'000 Sources of data: Moore and Koyanagi (1969); 1 . : a I / ; i : a ‘3 1, 'V“ LE Q Peck, Wright, and Moore (1966); Fiske and (:2; Koyanagi (1968); Swanson, Jackson, Koyanagi, 95> and Wright (1976); this paper Base from US. Geological Survey Kalalua, 1966; Makaopuhi, 1963; Kalapana; 1966;Volcano, 1963 1 .5 o 1 KILOMETER I—-I I—-I I—I I-—I +——I I———--———-——-—I CONTOUR INTERVAL 20 FEET HAWAIIAN ISLANDS DATUM IS MEAN SEA LEVEL 3‘ APPROXIMATE MEAN QUADRANGLE LOCATION DECLINATION, 1978 TRUE NORTH MAP OF UPPER AND MIDDLE EAST RIFT ZONE OF KILAUEA VOLCANO, SHOWING VENT FISSURES FOR ERUPTIONS BETWEEN 1961 AND 1971 PROFESSIONAL PAPER 1056 l l UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PLATE 3 Quiet effusion of lava, :9 <9 «x «x 1400 Aug 4 — Aug 10-11\ ‘6 .,. d- m an A Os 5; <9 0 a Fountaining ‘9 ,9 ‘9 5) Major fountaining, D.‘ Aug 3 ?/ 1329 0445 May 24 '1500 May 25" 99° Fountalning 1 09,) Fountainlng, °e°_ Fountalning, 08c» 1715 Aug 3 - 0010 Aug 4,- ”’9’ ° 1900 May 27 - 0900 May 29 . 1330 June 12 — 2145 June 25 ‘ 1 0345-1220 July 15 , 210° Aug 5 ‘ 0545 Aug 5" 15°" 7’ Hiiaka Hllaka 1100 June 13 Huaka 0700 June 26 Hllaka Hnaka 0015.0440 Aug 22 ”0“ ’ C} Pu“ - o (:3 P“” 1 K n N ' H 0 6:3 Pu” ‘ Kane Nui o Hamo Napa“ 0 63 Pu” 1 K n N ' H o (3 P”” A'ae drained' GMT (3’0“ Pauahi Huluhulux x Kane Nu: o Hamo «.190 22130:, 68," Pauahi Huluhulux x a e “' ° amo «.191: 22: 30" 6% PauahI Huluhulux l x <‘ 190 22: 30" ’59,. Pauahi Huluhulux ‘ x a e “' ° amo «{190 22130” 1%. Pauahl morning of x Kane “' ° Hamo «1190 22, 30" 3 of 9 0f 0" 9 of 9 of <1 Alae (1%, Alae Q Q (1 9’0 A101 ”§' ’1’ /e\ 2. [C— //e\ . $% $ /8\ . Gas” ”030' 7/??? I. 6415//// \\1akaopuh1 /”‘(/n_f/’/ \\vakaopuh1 \\vakaopuh1 d" l/ 0 _ M51124 Approximate \\ \ \\ , terminus of R d d b | d b l K a | a n a o k u May 2425 flow Road covered by lava g \\ oa covere Y 8V3 E 2 Road covere y ava E Road covered by lava 5 an“, P all in February 1969 (to \\ 1n February 1969 to (to in February 1969 é, in February 1969 it b b a g Q Q 0 o 5‘! Flow front, \\ § \ ~§ \\ ~§ \\ 41$ 5 1700 May 28 -S Flow front, -S -S S ,5 V 1800 June 12 V V V Y \ 9 O 9 D b b “A “a 0 o/ " 0/ 0 0/ o 0/ /% 919° 20' /% 919° 20’ /% 919° 20' /% 919° 20' -119° 20' // / / / / / / - / /l / ,/ 1/ 1/ , 1 / l l l l \ \\ \\ \\ \‘\ f ‘\ \\ ‘\ t Flow ront, o . t 0 a a w e o/ I 1' \\\ Naulu 2400 June12 1 P [g I i \\\ Naulu I i \\\ , P 1% l i \\‘ Naulu Naulu ‘1 o \< 5 Ga Foresr _ o k e Forest Forest \ Forest \ \ fi \ ' \ 0 P 1 0 P a i P a | 1 o a '1 " Q1 1 a V 1 1 1 " ' / B / e / D l/ \ D l/ D l/ D l/ b o <7 l \ 0 l\ O l\ O l \A \ \ \A N \ 14 & \~Cha/” of ore Early morning U 61 \‘ Cha’" of 0,9 U 6 \‘Cha/” of o, 11 & \‘Cbam of 0,5 \‘Cha/” 0 0,5 F a l i [9’s 0 1 H June 13 P a I 1 (9’3‘ 0 1 I, P a l i a 1 n P a l i ’9’: o 1 n P a l 1 (9'3 k ° oofi191730 3k 0 290419 17 30 3k 0 191730 N 0 90.119 17 30 40%1901710” e a‘ a “’0 4 e a‘ 90' e a ‘ 1800 Juiy15’ d e a‘ '90 ‘90 a 1 fl r~ .4, 1‘ ‘90 / ' ‘ '00 / - .(\° / . ‘ “\0 / , ~ ‘2» — Kaena Pomt Q 0‘») _ Kaena Po1nt 0‘2); ~ Kaena Pomt °(¢\//"- Kaena Pount Kaena Ponnt 0.. . . (510/ Keaiakomo 1200 June 13 “59:; Keaiakomo “5‘; Kealakomo “530’ Kealakomo Kealakomo °‘/ N 0/ N 0/ N 0/ N N / CEA / GEA / cEA / GEA CEA Kahue C O ‘ Kahue C O Kahue C 0 Kahue C O Kahue 1 0 ' P ' t P ‘ t P ' ' l IPomt PAchI 1 l om PACIFI 1 l 0835 June 26 l om PACIFI l l l omt PAchI l Pomt PAchlC l 155° 12' 30' Apua 155° 10' 155° 07' 30" 155° 12' 30' Arm 155° 10' 155° 07' 30" 155° 12’ 30 AIM 155° 10‘ 155° 07‘ 30" 155° 12' 30 Apua 155° 10' 155° 07’ 30” 155° 12' 30' Apua 155° 10' 155° 07' 30" Point Point Point Point Point A. May 2429,1969 B. June 1213, 1969 C- June 2526' 1969 D. July 15,1969 E. August 3-6 and 22, 1969 “a; «a; «"23 «a; ~1900 Dec 30 «a; °‘ ‘9 °<3 . . 923 . . . 33 . "' °o Aa flow into Aloi > . 91: a Strong fountamlng s Maior fountalnlng, o / 2100 Sept 6 _ Lava “OWS ""0 0100-0820 Oct 20 0500—1830 Dec 30; morning of Sept 8 graben from Alae, Small Spatter from minor fountelnlng at other times t 7 F tainin , - . 9 0300 Sep .9 . 0“" 9 . ' fires f"°"" 1; directed Weak fountainjng ‘9 Fissures active ’5’ 1% Major fountaining, C; espeCIally dome fountalnlng, felling pumice, % fountain, 0400 0600 O 20 99 7 8 °u ° 1930 s t 6 - ° 0900 Oct 10 — 1100 Oct 13 0345 Oct 20 ° ' °t 9 Smarter fall, °"'V °" Dec 3‘ ) Flow front, 9 _ ep .. 1. 0330 Oct 20 .. .. Huaka 0430 Sept 7 Hilaka Huaka Puu ' 0730 Oct 20 Hilaka 1550 Dec 30 1415 Dec 30 HIIaka PUU , Puu . , Puu ‘ Puu . 0693 Q Pauahl Hululu)l(1u x Kane Nu1o Hamo «I 190 22, 30.. 9&4 Pauahl Huluhulux x Kane Nu1o Hamo «J 19,, 22, 30,, 069% Pauah1 x Kane Nu1 o Hamo ‘_‘ 190 22, 30,, @646.) (:3 Pauahi Huluhulu ._;_ X Kane Nu1 o Hamo 41190 22130;: 05% 6:? Pauahi Huluhulu x Kane Nu1 o Hamo «{190 22, 30,, l ‘ . of a. (3;, 1/ Alae of (3.; of 0;, 0 (23 /e 1‘ A101 ‘w ’ e a (A a- ’ \\ Makaopuhi 0’3“ ” '1 er” ’\\ Makaopuhi 8'3 Makaopuhi 9‘" a?" \ 1 \ " \ v 1 ‘ Lava overflows ' \\ . crater rim, 70415 Sept 7 \\ Road covered by lava :3 Road covered by lava E Road covered by lava 1? E _ ~° \\ in February 1969 (to in February 1969 [£3 Crack: in February 1959 g ‘g Ground cracks of g Lava first overflows g opena . . g g April 9.10 \‘ § crater, 1200 Oct 10 \ 15 0415-0615 - Tube-fed flow of 5 fi -5 -5 Oct 20 Oct 21-28(?) S -S V ‘1' V T D 9 S b a o/ O I 0 0/ D l o I O i o I //Q 411g 20 //Q ‘l 19 20 Flow front nears 4119 20 41-19 20 ‘1 19 20 // // Chain of Craters Road, I/ I/ 0400-0500 Oct 20 l l \ \\ \‘\ ‘\ i \\ Naulu P Q ~ \\ Naulu Naulu Naulu l 1 ‘ l i ‘ ' Forest . 0 K Forest , o \4 Forest , 0 Forest \ \ P o \ \ o \ \ P 1 ° a l a i a l i ' ,‘ a | 9 *5 ,‘ . v 9 a l 1 e / / D / D I/ <7 1 1 O 1 \ ‘ \A 9 \ Ch - Ch - Ch 1 Ch - c . Early U ‘ a,” 0’ 0 U \‘ am °’ 0’6 \‘ am 0" Cr \‘ a,” 0’ 049 2200 April 9 \‘ ham 0’ or afternoon P a I i are/3. o I O P a I i [any 0 I P a I i 6’60 0 l l P a I i [6/3. 0 I r P a l i 6129,: ' ° 1 17 30” 4 —1191730" 9 91 1 0’ o fi191730' ‘1 ° . ~ Sept 7 e a 1 a K 00.90% 9 ad e a 1 a K 0.90, 090 9 7 3 060 0090 19 17 30 C , ' , 0 “hi : e(\<‘°_/ Kaena point 0““ —’ Kaena Point 3. Kaena Point Kaena Point Kaena Point 0 / v0 / 540/ Kealakomo a," / Kealakomo Keaiakomo Kealakomo Kealakomo 9/ EAN \/ BAN EAN BAN AN Kahue C 0C ‘ Kahue C 0C Kahue C 0C Kahue C 0C Kahue OCE Po" t Point I Point Point I Poin C 1 1 '" 13,1ch1 1 1 P,1ch 1 1 1 PAch1 1 1 1 P,1ch 1 1 1 ‘ PAcIFI 1 155° 12‘ 30' Apua 155° 10’ 155° 07’ 30" 155° 12‘ 30 AIM 155° 10’ 155° 07' 30” 155° 12’ 30’ Apua 155° 10’ 155° 07' 30" 155° 12' 30 AIM 155° 10' 155° 07’ 30" 155" 12' 30' Arm 155° 10’ 155° 07’ 30" Point Point Point Point Point F, September 6-7, 1969 G. October 10-13, 1969 H October 20-28, 1969 1. November 12-30, December 1-2 and 13-18, 1969 (Horizontal ruling) J. January 25 - March 1, 1970 (Vertical ruling) December 3(?)-8,1969 (Vertical ruling) April 9-30, 1970 (Solid pink) December 29-30, 1969 (Solid pink) ' a, 15 x 1% EXPLANATION Vent area active 0 ‘ Fl f O t 28- 1% Fissu re erupted and after July 6 5% 0:312:34”: ‘30 Vent for all flows {:3 9 shield-building flows, (see plate 4) f <> C» Maui“ U'” after Feb 10 _ Hiiaka Lava tub- May 21 —June 28 4 H,” '3“; 7 Hliaka V33: :29? 7d” Hliaka “mm" ”at” P” ”at“ a . morning 0 u y r 0 active in Puu , I _ Puu 4 . Napau Puu , Napau 2 (39/ late June 111’ x Kane Nu1 o Hamo ‘I 190 22, 30,, (3%} <3 Pauahl x Kane Nu10 Hamo 4‘ 19,, 22, 30,, (3%} (D Pauahl Huluhulu x Kane Nu1 o Hamo «i 190 22, 30,, 3“: Note: Outlines of flows and locations of lava ¢ ,0" o ‘ r ”f o ”f o ' ' tubes for specified time periods are Pauah' 1% ‘ I ‘ 9’9 79,3, e\ Filled P1t crater approximate, but outline of entire ’3" Makaopuhi iikaOF’l-lhi \ MakaOPuhl x . . _ V 1 . \ 4 field ,5 from a photogeologlc map w Lava enters Makaopm, Jan 23 , w Flow enters Mekaopul, Summit of cone accurately prepared by Holcomb (1976). Flow of Jan 2145(7) » Feb 11-12 V ‘6 Road covered by lava b Road covered by lava b \ Road covered by lava ““““““ é Fissure active in February 1969 g in February 1969 g“ Vent for a” la a \ in February 1969 Road covered by lava flow g in Aloi. g g Jen 28—Feb 10 - 1 \ a May 21-22 a 4: 1 Fissure .E L Lava issues from mouth of lava tube, g é" "Area of Feb ‘ Shown only when active V \ morning of Aug 11 V Y coflme 9 4-H—l—r—H—H—l—l—l—l» Flow from mouth of tube, Terminus of flow, Lava tube 0 t 1 F . ' c eb 11 20(7) Shown only when active 1 Fl f J 23-27 —119° 20 . . °w ° 3" 19° 20’ ~119° 20' \ Volumlnous surface flow, Nov 15 Deposit of spatter and pumice oFl30c1’7v front,1 ‘ more than about 10 cm 8 Aug . \ Flow covers road, afternoon Nov 15 thlck away from vent area. v Shown only for indicated Naulu " Naulu Naulu period oferuption, , _\ 0 Forest \ 0 K e Forest , 0 Forest \ \ \ \ v ° a 1 i 9 ° P a I i 9 ° P a 1 E: 7 Flow over Holei Pali, ' Lava pools at base Lava flows erupted during in- Nov 15-29, Dec 4-8, and of cliff, Feb. 22 dicated time period. Other Jan 23'” symbols used as noted Road crossed by flow, Feb 26 \A Flow front, Nov 7(7) Ch ' ‘ Ch - Ch . \ am a f rate am 0 f 949,9 am of .0955, P a l ‘ ’3 a , ,. P a ' ' '3 o 1 h . P a I ' 4' o 1 u Lava flows erupted prior to 909 19 17 30 19% 19 17 30 ’90:; 19 17 30 d d 0’ 0' or in icate time eriod O 1 2 3 4 5 6 7 KI LOMETERS .‘ p 111 1 11 I | I l I I Lava delta formed, March 8 — May 14 Lava flows erupted later Kaena Point Kaena Point {é}93.../’ Kaena Point than 1ndlcatedt1me period Kealakomo Kealakomo 09%;, Kealakomo 4 “A V 1. CEAN CEAN . 6/ Lava enters CEAN V > ’I 1 Kahue O Kahue O Kahue Kealakomo, O A f1 Flow enters sea, Point IFIC Point IFIC Point March 5 [FIG 8 0w 0 I Sept 21 I PAC I l I PAC I I I Lava enters PAC 1 155 12’ 30 A?“ 155° 10' 155° 07' 30" 155° 12' 30' Apua 155° 10’ 155° 07’ 30" 155° 12' 30 Arm 155° 10’ see. 155° 07’ 30" Paint Point Point March 8 K May 21 —June 28, 1970 (Horizontal ruling) L. October 28 — December 8, 1970 (Solid pink) M. January 28 — February 10,1971 (Horizontal ruling) July 6-21, 1970 (Vertical ruling) January 14—27, 1971 (Horizontal ruling) February 11 — May 14,1971 (Solid pink) August 2 - September 26, 1970 (Solid pink) October 1-26,1970 (Slash ruling) firlnterior — Geological Survey, Reston, Va. — 1978 —— G77283 MAP SHO W IN G SEQUENTIAL DE V ELOPMENT OF FIELD OF LAVA FLO W S PRODUCED DURING 1969-71 MA 1 1 NA ULU ERUP'I'ION UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 1056 PLATE 4 15§1ZBU' Puu 19° 22'30" Huluhulu Fuming area West cone (East cone /\ Summit crater Aloi K Crater) \_/ Alae Crater \ A. July 6-31,1970 155°12'30" Puu 190 22/30" Huluhulu 3 X West cone ’East cone /\ /Aloi \ K Crater) _/ B. August 1-22,1970 155°12'30” Puu 19° 22' 30" Huluhulu 3 X West cone ’East cone C. Augusr 23 — September 22, 1970 156123d' Puu 19° 22’30” Huluhulu \\\ \\\ West cone ’East cone /\ Alae Crater \\ r5; / . \ K grimy) \\ \\\_,/ D. September 23 — October 27, 1970 155°12’30” Puu 190 22: 30:! Huluhulu 4 3, Q West cone ’East cone /\ Aloi K Crater) \\I_// E. October 28 — November 12,1970 155° 12' 30” Puu 190 22:30" Huluhulu 2 5 /\ 4 3. W \\ West cone.."East cone { \ /\ Alae Crater oi \ K Slater) \\ \ V / t 7% E November 13 - 27,1970 155°12'30" Puu 19° 22’30” Huluhulu 2 /\ 4o \ 3 o \ West cone ’East cone ( \ /_\ Alae Crater /A|ci \ Crater) \J ‘2 G. November 28 — December 5, 1970 1591236' Puu 19° 2230!! Huluhulu West cone : . /'\ Aloi k Crater) \\IL,/ H. December 6-20, 1970 155°12'30" Puu 19° 22’30” Huluhulu 2. /\ Trench / \ West cone . I \ /\ Alae Crater \ /A|oi \ Crater \\\_,/ 1. December 21,1970 — January 1,1971 155°12’30” Puu 19° 22'30” Huluhulu West cone J. January 2-20,1971 155°12’30" Puu 19° 22'30H Huluhulu /\ Aloi K Crater) \\,_,/ K January 2127,1971 15V1st' Puu 19° 22’ 30" Huluhulu /\ Alae Crater \ New / L \ Efitfiff \\¥d/ Crater \__/ L. January 28 — February 10,1971 1591230’ Puu 190 22,30" Huluhulu /\ Aloi K Crater) \\\I,/ M February 11-19,1971 1591230’ Puu 19° 22’30" Huluhulu /\ Aloi K Crater) \\\_,/ N. February 20 - March 23,1971 15§123U’ Puu 19° 2230/! Huluhulu 0. March 24 — April 12,1971 15§123U' Puu 19° 22: 30" Huluhulu /\ Aloi Crater \\s__,/ P. April 13 —June1,1971 No changes occurred between June 1971 and end of eruption. Buried sites of Aloi and Alae Craters, and selected topographic contours of Puu Huluhulu, indicated for reference. 200 400 600 800 1000METERS EXPLANATION Crater o Cone X Vent with no marked crater or cone ++Ht++tH+> Lava tube, arrow shows flow direction Fissure of January 28 - February 10, 1971 Note: These symbols indicate only those features that contained lava during the indicated time interval ‘9? Interior — Geological Survey, Reston, Va.— 1978 — G77283 MAPS SHOWING CHANGES IN CONFIGURATION AND LOCATION OF VENTS AT MAUNA ULU, JULY 1970 TO JUNE 1971 mZ<.Q. Z. .._...._._. >....>_...0< “.0 m.n.>... 0 0 0 7 n0 5 : . . PLATE 2 .:0.00300 :0 0cm .000000 0E .E3m E 0.0.03 000:0. o: 0>0n. 1015 20 25 30 OCTOBER l .0:0~ 0:.0 0003:0300 I. Hf 0:0 0000.00 0030_.v. E :0.0030m. PROFESSIONAL PAPER 1056 5 10 15 20 25 SEPTEMBER 5 filnterior — Geological Survey, Reston, Va. — 1978 ~ G77283 .>00\E0 on :0 0000 000000.200 m ill 0000.00 0030.0. E 50035 i 0 00 0000.50. 0.0. 020. :0 000:03m I 0 000 00030”. 10 15 20 25 30 AUGUST ll In B and C, break in curve denotes no data because of instrument malfunction. Harmonic tremor varied from weak to strong throughout eruption and obscured 5 In A, tiltmeter is read frequently during major events, daily otherwise. Location of Uwekahuna vaults shown in figure 2. 3852 calender day are included in the count for the previous many small earthquakes. Seismic data from Hawaiian Volcano Observatory Summaries 54 through 64. Earthquakes that occurred before about 0800 of one 00000000 000000 0.EE3m E 2000 0.50 :00>>000 000.0 00000000.”. 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E 00.0. 023 5 0:2. 30.5 20:00.3 08.0 .0250: 002 .03 :0 00.0 000000 0033.: .502 :0 :0300 Ev. :0000 0000.60 I %..:3000v.0_>_ 000:0 0E0w .00_< 0 80 300 026 0 .0 3 .3053 | :0 :0 :0: 0... I >0 50:5 00:00... .0001 00:. £50.”. .0>0. :0...> 00...: :0:00F 10 15 20 25 30 JANUARY 00:00 :0 000: :0 0.0030 0.03005 mE>>0.: 0>00 5 .m 0:0 0V 0m mwcw> :0 mmtm 00 >20... | mmwww Ctr—F .005 0002050 550 0000.60 .vm 000 E0000 _.0:3 0000.325 0. E .000 020». .m 0:0> 00 00E00: 000000 .m0 000E800 :0 000:0 .N 000000000 :0 :0000 00.< | .00.< 00:. 5.300000 E00: 050.“. | HT :0 0.030.... 00:00:00 00:00:... .._0:v.000 >0 0:00.05 000000 0.EE3m 3.3 0:305. .m 0:0> | l 00:.3mc0 00.300000 0000.60 0000000 m>>o_:00>O .00E0o: m 0c0> .m: 000E062 I :000:00000:0 00000“. 3.302 .00:00:m0 00:.0030 0>.00< 10 15 20 25 30 DECEMBER 5 02000:. .. 000> 00...: F 0c0> 00 000000 10 15 20 25 NOVEMBER ._. «Ew> Hm 0mumLU 5 .0 0:0 .N .0 m0c0> E00: 030.:00>O 0000000 0030 00_:. 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UWEKAHUNA SHORT-BASE WATER-TUBE Ti LTMETER .0_m:00000 0.00.0 0:8 >0 0.26:0 mEE00:30: :0 0000.00 655. .0002 B. SHALLOW KiLAUEA SUMMIT C, UPPER AND MIDDLE EAST RIFT ZONE A. E-W COMPONENT 51015 20 25 30 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 1000 — 600 — 400 — 800 — O 200 ‘ . _ _ 0 0 0 7 6 5 2000 0 1400 — 1200 - wZ<.D. Z. .....:._. >.:..>.._.o< ”.0 90>... 2% 3x A Q“ “vs ' :«m fr w .;’ Early Triassic Terebratulid Brachiopods from the Western Interior of the United States By PETER R. HOOVER GEOLOGICAL SURVEY PROFESSIONAL PAPER 1057 Description and illustration of five species of terebratulid brachiopods, and discussion of their distribution and developmental and evolutionary history UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1979 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Hoover, Peter R. Early Triassic Terebratulid Brachiopods from the Western Interior of the United States (Geological Survey Professional Paper 1057) Bibliography: p. 19 Includes index Supt. of Docs. No.2 1 1921621057 1. Terebratulida, Fossil. 2. Paleontology~Triassic. 3. Paleontology—The West. I. Title. II. Series: United States Geological Survey Professional Paper 1057 QE797.T29H66 564'.8 77—608314 For sale by the Superintendent 0f.Documents, US. Government Printing Office Washington, DC. 20402 Stock Number 024—001—03182—5 CONTENTS Page Page Systematic paleontology‘ Continued Abstract ............................................ 1 Family DielasmatidaeiContinued Introduction ......................................... 1 Subfamily Dielasmatinae ......................... 8 Previous work ..................................... 1 Rhaetz'na Waagen .......................... 8 Present study ..................................... 3 Family Terebratulidae .............................. 9 Acknowledgments ................................. 3 Subfamily Plectoconchiinae ....................... 9 Fossil localities cited in this report .......................... 3 Vex, n. gen. .............................. 9 Stratigraphic setting of the brachiopods ..................... 4 Family Cryptonellidae .............................. 11 Faunal relationships ................. ' ................... 6 Subfamily Cryptacanthiinae ...................... 11 Biostratigraphic implications ............................. 6 Obnzbcm, n. gen. ........................... 11 Systematic paleontology ................................. 7 Family Zeilleriidae ................................. 17 Family Dielasmatidae ............................... 7 Perz'allus, n. gen. .................. 1 ............ 17 Subfamily Zugmayeriinae ........................ 7 References cited ........................... i ............ 19 Portneufz'a, n. gen. ......................... 7 Index ............................................... 21 ILLUSTRATIONS [Plates follow index] PLATE 1. Portneufz'a, Rhaetz‘na, and Vex, 2. Oan'xzkz, Plectoconcha, and Vex. 3. Obnzbcz'a. 4 Perl’allus. Page FIGURE 1. Index map showing locations of collections cited in this report ..................................................... 2 2. Generalized correlation chart of Lower Triassic (Scythian) stratigraphic units in parts of the western interior of the United States. . . . 5 3. Scattergram of dimensions of Obnz'xz'a thaynesmna (Girty) from southeastern Idaho and southeastern California ................ 12 4. Scattergram of dorsal valve length and loop length of Obnzbczkz thaynexz'ana (Girty) from southeastern California ................ 13 5. Scattergram of dorsal valve width and loop width of Obm'xz'a thaynesz'ana (Girty) from southeastern California ................. 13 6. Scattergram of loop length and length of ascending lamellae of Obnz'xm thaynesmna (Girty) from southeastern California ......... l4 7. Scattergram of loop length and distance to crural processes of Obm'xz'a thaynesz'ana (Girty) from southeastern California .......... 14 8. Thirty-five parallel serial sections of a paralectotype specimen of Obm'xz'a thayneszkzna (Girty) from southeastern Idaho ........... 16 TAB LE Page TABLE 1. Measurements of dorsal valve and loop parameters for a simulated ontogenetic series of Obnzbczkz lhaynesz'ana (Girty). from southeastern California .............................................................................. 13 Ill EARLY TRIASSIC TEREBRATULID BRACHIOPODS FROM THE WESTERN INTERIOR OF THE UNITED STATES By PETER R. HOOVER1 ABSTRACT This study of five species of terebratulid brachiopods from Lower Triassic marine rocks of the western interior of the United States is based entirely on existing museum collections. New genera and species described in this paper are: Parlneufz'a epimlcata, n. gen. and n. sp. (Dielasmati. dae); Rhaetz‘na z'ncurw‘roslm, n. sp. (Dielasmatidae); Vex, n. gen. (type species: Terebralula semz‘sz‘mplex White) (Terebratulidae); Obm'xzkz, n. gen. (type species: Terebmtula thaynesz'ana Girty) (Cryptonellidae); and Perz'allus woodsz'densz's, n. gen. and n. sp. (Zeilleriidae). The develop- mental history of the cryptacanthiine Oblu'xl'a lhaynesimm is discussed in detail on the basis of studies of exceptionally well preserved silicified mate~ rial. The terebratulids here described are endemic elements of the poorly known Early Triassic shelly fauna. Although they clarify evolutionary changes across the era] boundary, their closest associations are with Meso- zoic, rather than Paleozoic faunas. Although knowledge of the associated fauna is meager, the brachiopods themselves can be used as the basis of a crude biostratigraphic zonation suitable for correlation. ABTopecbepaT OnucaHo u oécymneno UHTb BHnOB Tepeépary— anHux opaxuonon us MOpCKHX anaerpuacosux ornoxennn sananHux pafioaoa BHyTpeHHen qacrn CoenHHeHHHx mTaTOB. K 3THM TaxconaM ornoc— HTCH Portneufia episulcata, HOBHFI p011 H Bun (Dielasmatidae), Rhaetina incurvirostra, HO— Bufl Bun (Dielasmatidae), Vex, Honan pon (TH- ‘IIOBOI‘JI Bun: Terebratula semisimplex White) (Terebratulidae), Obnixia, Honun pon (THHOB— of?! Ban: Terebratula thaynesiana Gir'ty)(Cr'yp— tonellidae), Periallus woodsidensis, HOBHH pon H Bun (Zeilleriidae). Ha OCHOBaHHH Hay- quuH ucxannTeano xopomo coxpaHHBmeroca OerMHeHHOFO MaTepnana neTaano oocyxnaercn HCTOpHH paaBHTua KpHHTaKaHTHHH Obnixia thagnesiana. OnucaHHme Tepeépawynnnu upen- crannnmr cooofl saneanHue anemeHTu nnoxo n3- BeCTHofi annerpuaconon paKOBuHHofi oayHu. Xorn OHH paabacnnwr 330nmuuoanme HBMeHeHKH Ha rpaHuue 3p, OHM éonee 6nn3xn x meaoaofic— KHM, qu K naneosoficxnm @opmaM. HsyquHe ocaonaHo TOHbKO Ha Konnexuuu, uMemmefica B mysexx. XOTH 3HaHHH o conyrcrsywmnx ¢ayHax Henocraroquu, caMn 6paxnononu M0ryT 5HTL npnMeHeHH nun oéoCHOBaHKa rpyéoro 6HOCTpa- Turpaouqecxoro pacqneHeHua, ronHoro nun Kop- penauun. ‘Director. Paleontological Research Institution. Ithaca. N. Y. INTRODUCTION This study was designed to enhance the meager biostrati— graphic data base for the Triassic of the Western United States. Marine strata are uncommon in the Lower Triassic of the western interior of the United States, and well-pre- served fossils are rare. This situation has led to a basically lithostratigraphic approach in most previous geologic recon- naissance studies. Ammonites were recognized early as potential biostratigraphic indices (White, 1880), and the distributions of other relatively common mollusks, particu- larly the pelecypods, were later brought to bear on the prob- lem. Even the ammonites, biostratigraphically the most use- ful Early Triassic faunal elements, are quite provincial (Dagys, 1974), and correlations across the great distances separating their rare occurrences commonly have been quite subjective (Silberling and Tozer, 1968). During the last 20 years, our knowledge of the stratigraphic range of the cono- donts has been extended across the Permian~Triassic bound- ary, and conodonts now show great potential for Triassic biostratigraphic zonation. The contribution of this report to the knowledge of Early Triassic terebratulid brachiopods not only adds to our understanding of the organisms them- selves, but also increases their usefulness in the Lower Triassic. PREVIOUS WORK Early Triassic terebratulid brachiopods, rare in the west- ern interior of the United States, usually occur monospecifi- cally in bands or zones. Thus, published descriptions rarely cover a diverse terebratulid assemblage. The first descrip- tions (White, 1880), from a section in southeastern Idaho (fig. 1, Ice. 44), included no illustrations, but were repeated later with figures (White, 1883). Of the two forms discussed, only Terebmtula semzlsz'mplex was illustrated. The other, cited as Terebratula augusta Hall and Whitfield, was neither described nor illustrated, and White was dubious about his identification. His specimens of T. augusta (USNM 8191) are preserved at the USNM (US. National Museum of Natural History, of the Smithsonian Institution) in Washington, DC Although they are too fragmentary and poorly preserved to identify with any terebratulids de- 1 2 TEREBRATULID BRACHIOPODS FROM THE WESTERN INTERIOR OF THE UNITED STATES 125° 1200 1150 110° 450‘ I i T (\\/\ I \ \ \ x I—-——--— l \\ \ | \\ \ .. ' ONNEVILLE \\\ V . \ 8_.5 BINGHAM 1‘ B \\\\ . 4.7 \ \\\ I .9 .35 iii-l Gm” \\\\\\\\\ \\\\\ .10 i Lake \\\\\\\ \\\J _ _ _ _ -———— IDAHO ¥~‘ I 2 .11 I WYOMING ( .34 .3 (See inset) N i 25.26 ) '2 __ 27 X .33,41 ——-——I—___/ __ 15 /’ / O CARIBOU /// /. if“ / / 28 I 1‘ //,r / . L L 1 / / / 29 — -— — — —l_- 40°_ ,____— . .12 / l / I 5 \\/\l /// I // l L / BANNOCK I / I I] \ Lf/ // a L // I IL___I—L_ / I g l / l G _ l P 40 ‘ J \ 18—23 .1116 //[ UTAH I 1 \ BEAR LAKE | _\\ l_.I / // I I / ONEIDAJ FRANKLIN \ // l // l | i o 10 zoMILEs 24,38 / I 30 | I \\ Bear / n 39 I 0 25 KILOMETERS Lake / - ~43 I \ 42 .13,31 \ NEVADA IP—_——'IT—“—"—‘T' \ ~36 \ l . \ I l \ \ m’ l \\ I 35“ CALIFORNIA I \ ‘I ARIZONA \ 37'\\< L I I I l \\ I 0 100 200 300 MILES l 1 1 l V I I I 0 100 200 300 KILOMETERS FIGURE I. v Index map showing locations of collections cited in this report. scribed here, they may easily be distinguished from types of T. augusta Hall and Whitfield (USNM 12548a,b) by their weaker beak ridges, larger size, and lack of a prominent median septum. Nearly 50 years elapsed before publication of the next report describing Early Triassic terebratulids. Girty (1927) described a rhynchonellacean, two spiriferina- ceans, and Terebratula thaynesz'ana. Types of T. thayneszlzna also come from southeastern Idaho (fig. 1, loc. 21). Newell and Kummell (1942) included brief de- scriptions and illustrations of a form, referred to Tere— bratula margarz'towz' Bittner, from the Dinwoody Formation at several localities in southeastern Idaho and southwestern Montana. Closely spaced serial sections of forms used by Newell in making this identification suggest they are identi- cal with Perz'allus woodsz'densz's, n. gen., n. sp., and are not dielasmatids as heretofore supposed (Dagys, 1965, p. 137). FOSSIL LOCALITIES CITED IN THIS REPORT 3 PRESENT STUDY Collections of Triassic marine fossils housed at several in- stitutions were examined, and all identifiable North Ameri can Early Triassic brachiopods were brought to the USNM for more intensive examination. Previous paleontological in- vestigators did not examine the comparatively conservative terebratulids in detail, and internal characters now thought to be of primary taxonomic importance were rarely documented. Most Early Triassic terebratulids are small (less than 10 millimeters (mm) in maximum dimension) and are pre- served as calcium carbonate. The only feasible accurate method of studying the internal details of such forms, other than laborious preparation with a needle, is to make three- dimensional reconstructions based on closely spaced serial sections. The making of such sections is extremely time con— suming and, unless considerable care is exercised in the maintenance of parallel sections, the results may be mislead- ing. (See Westbroek', 1969, and Singeisen-Schneider, 1976.) Though this technique permits the use of calcareous speci- mens to document ontogenetic development and population variability of internal structures (for examples, see Baker, 1972), it is not practical on a large scale when other methods can be used. Many of the collections surveyed in this study include silicified specimens, which commonly may be removed from the calcitic matrix by etching with dilute acids. In the pro« cess, structures of extreme delicacy may be revealed, as shown in the specimens of Obm'xz'a thaynesz'ana (Girty) from locality 37 (pl. 3, figs. 1—13). Through the combined use of several preparation tech- niques, topotypic material of previously described North American Early Triassic terebratulids has been studied in detail. Both ontogenetic development and population varia— tion have been documented for Obm'xz'a thaynesz'amz (Girty). The study shows that, rather than two very generalized terebratulids in the North American Lower Triassic, there are at least five endemic species that have taxonomically and functionally distinctive internal skeletal elements. These fossils are not only diagnostic of the strata in which they occur, but they also illustrate, in a single or- ganic group, the nature of evolutionary links across an era boundary of prime importance. ACKNOWLEDGMENTS The studies leading to this report were made during tenure of a National Research Council Postdoctoral Fellow- ship, held at the U.S.G.S. (U.S. Geological Survey) in Wash- ington, D.C. The writer and this report have materially benefitted from discussions with and critical review by]. M. Berdan, G. A. Cooper, J T. Dutro, Jr., R. E. Grant, N. J. Silberling, F. G. Stehli, and B. R. Wardlaw. Illustrations were in part drafted by Elinor Stromberg, of the U.S.G.S. Photographic services were provided by R. H. McKinney, H. E. Mochizuki, and Kenji Sakamoto of the U.S.G.S. and by G. A. Cooper of the Smithsonian Institution, Washing- ton, D.C. Russian translation of the author’s abstract was kindly provided by Dr. M. A. Semikhatov, of the Geological Institute of the Academy of Sciences, Moscow, USSR. FOSSIL LOCALITIES CITED IN THIS REPORT The material studied for this report comes from several different sources. Most specimens were collected by U.S.G.S. geologists during investigations of the phosphate reserves of the western interior of the United States, around the turn of the century. (See fig. 1 and the list of fossil locali- ties below.) Because those phosphate deposits are of late Paleozoic age, many of the fossil collections bear that desig- nation, despite their derivation from rocks now known to be of Triassic age. Locality numbers having the suffix “PC" are from the U.S. Geological Survey's upper Paleozoic catalog, kept in Washington, D.C. Those having the suffix “(Green)" belong to G. H. Girty's old upper Paleozoic catalog at the U.S.G.S. in Washington, D.C. Numbers without prefix or suffix are from the Survey’s Mesozoic catalog, also in Washington, D.C. Those having the prefix “M” come from a similar Mesozoic catalog at U.S.G.S. offices in Menlo Park, Calif. Those having the prefix “USNM" are held by the U.S. Na- tional Museum of Natural History, which also houses the Washington, D.C., collections of the U.S.G.S. All type, figured, and measured specimens from this report have been assigned USNM catalog numbers and are in the USNM Paleobiology Collections in Washington, D.C. Locality information on specimen labels has been supple- mented by information on original register file cards, field labels, maps and notebooks, and more recent geologic and topographic maps. Such additions appear in brackets. Map index Original Description of locality, stratigraphic assignment. collector, and year number locality of collection (see fig. 1) number I 76 PC Idaho, Caribou County, Snowdrift 1:24.000 quad, SE corner of NEVASI‘ZVANEW sec. 27. T. 9 5.. R. 45 E. [Peak at alt. 8.640 8,660 ft.] Woodside Formation. [G. R.] Mansfield and [C. H] Cirty, Aug.3l. 1911. 2 8237 PC Idaho [Caribou County. Lane's Creek 15-min quad]: sec. 1, T. 7 S., R. 44 1-2. [Probably] Thaynes Formation. [G. R.] Mansfield. 1912. 3 826 PC Idaho [Caribou County, Lane‘s Creek 157mm quad.: section un‘ known] T. 6 S., R. 44 E. [Probably] Thaynes Formation. [R. W.] Richards. 1912. ‘ 4 12717PC Idaho [Bingham County, Yandell Springs 15-min quad: NW‘ASWV‘ sec. 31, T. 3 S.. R. 38 E.]. Porineuf Limestone [Member] of Thaynes Formation. [0. R.] Mansfield and [(1. H] Girty, Aug. 27, 1913. 5 1274 PC Idaho [Bingham County, Higham Peak 7‘/z~min quad: SW ‘ASWV‘ sec. 25, T. 3 S.. R. 37 E]. Portneuf Limestone [Member of Thaynes Formation]. [0. R.] Mansfield and [6. H.]Girty. Aug. 28, 1913. 6 1284 PC Idaho [Bingham County, Higham Peak 7V2~min quad]; low spur, east 'scarp [SW‘ASW‘A sec. 2, T, 3 5., R. 37 E.]. Portneuf Lime- stone [Member of Thaynes Formation]. [G. R.] Mansfield and [0. H.]Girty. Sept. 5, 1913. 7 1289 PC Idaho [Bingham County. Yandell Springs 157min quad. NW‘fiSWVA sec. 31, T. 3 S.. R. 38 E.], Portneuf Limestone [Member of Thaynes Formation]. [?] Merritt and [0. H.]Girty, Sept. 1913. 8 1291 PC Idaho. Bingham County, Higham Peak 7‘/2-rnin quad. SEV‘NW‘A sec. 24, T. 3 S., R. 37 E] Portneuf Limestone [Member of Thaynes Formation]. [(3. R.] Mansfield and [G. H.]Girty. Aug. 29. 1913. 9 1304a PC Idaho [Bingham County, Yandell Springs 15-min quad]; 775 ft southwest of top of hill. [SWVANW‘A sec. 1, T. 4 S., R. 37 E. Probably Thaynes Formation. G. R.] Mansfield and [6. H.] Girty, Sept. 6. I913. 4 TEREBRATULID BRACHIOPODS FROM THE WESTERN INTERIOR OF THE UNITED STATES Map index Original Description of locality. stratigraphic assignment, collector, and year Map index Original Description of locality, stratigraphic assignment, collector, and year number locality of collection number locality of collection (see fig, 1) number (see fig. 1) number 10 13157PC Idaho, Bingham County. Yandell Springs 15-min quad]; SEVASE‘A 36 7885 (Green) Nevada [Clark County, probably in the Moapa 15-min quad]; sec. 36. T. 4 5., R. 37 E. [Probably Thaynes Formation.] [G. R.] “Valley of Fire.“ Muddy Mtns., 1/a mi east of White Basin fault. Mansfield and [C. H.]Girty, Aug. 25, 1918. V4 mi south of Old Arrowhead Road. Moenkopi Formation in fault 11 13367PC Idaho [Caribou County, jeff Cabin Creek 7l/rmin quad]; sec. 24, block. C. R. Longwell,_]uly8. 1924. T. 5 5., R. 57 E. ”Ross Fork [Limestone Member" of Tha nes 37 7897 (Green California, San Bernardino Count , Ivan ah and Mescal Ran e l r M y y P l 3 Formation . G. R. Mans ie .July26.1913. 15-min quads., near center, sec, 32. T. 151/: N., R. 14 E. -, 1 mi 12 180177PC Nevada, Elko County, Carlin [15-min] quad; NEV4 sec. 16, T. 51 northwest of Kokoweef Peak. [Probably Moenltopi Formation] N.. R. 52 E. [Railroad District]. Permian of J. F. Smith and D. F. Hewett, Oct. 28. 1926. K. B. Ketner.[ .F.]Smith and [K. B.]Ketner, 1958. 38 5013 Idaho Bear Lake Count , Mont lier 7Vrmin uad.; a rox. 1 pt q PP 13 614a (Green) Utah [Washington County. probably La Verkin No. 4 NW 7l/r sec. 13, T. 15 S.. R. 44 E.]: from slide on east side of gulch east min quad], canyon east of Toquerville on road to Virgin City. of Hot Springs. [Probably Thaynes Formation] F. B. Weeks, [Probably Moenltopi Formation”. E. Whitfield, Oct. 3, 1885. Sept. 27. 1907. 14 961 (Green) Arizona Mohave or Coconino County. Fredonia NE 71/1-min 39 18595 Utah, Washin on Count , robabl in the Zion National Park 8‘ Y P 1' quad], 10 mi south-southwest of Kanab, Utah. [Probably Moen- 50-min quad; Kolob Section S.;] Dry Creek Section. Virgin Lime- kopi Formation]; thin limestones interbedded in reddish-brown stone [Member of Moenkopi Formation]. H. E. Gregory, Sept. arenaceous shales. C. D. Walcott and party. Sept. 6. 1882. 22. 1940. 15 3769(Green) Wyoming [Lincoln County, Cokeville 30-min quad]; center of sec. 40 M~108 Utah [Millard County. Cowboy Pass 15-min quad]; secs, 18 and 32, T. 25 N.. R. 118 W. Fork ofRock Creek, 7% mi north ofNug- 19, [T. 16 S., R. 16 W]. Confusion Range. Measured section. get. Thaynes Formation. A. C. Veatch.]uly 27, 1905. about 870 ft above base of Triassic section [probably Moenkopi 16 7515(Green) Idaho [Bear Lake County, Montpelier Canyon 7‘/:-min quad, Formation]. [C. A.] Repenning and [R. K.]Hose. Oct. 19. 1955. SW1/4NEV0]SE‘/4 sec. 6, T. 13 S., R. 45 E., Waterloo Mountain. 41 M7853 Idaho, Caribou County. Upper Valley 7‘/z-min quad; NEl/chl/e Questionable basal [part of] Woodside Formation, but structurally sec. 13. T. 7 8.. R. 44 15-: on CBS! Side Of drain between Bacon 30d very complex. C. L. Breger,_]une 16, 1909. Timothy Creeks. Upper [part of] Portneuf Limestone Member 17 7576(Green) Idaho [Bear Lake County, Montpelier 71/1-rnin quad]; sec. 1, of Thaynes Formation, about 100 ft above the top of the Lanes T, 13 S., R. 44 11.; [measured section in] Montpelier Canyon [just Tongue [of Ankareh Formation] redbeds. R. Rioux and]. Dyni. east of town of Montpelier]; Thaynes Formation [about 717 ft 1959. above the base and 1,565 ft below the top of the unit there 42 USNM 9342 Utah [Washington County]. 9 mi southwest of St. George, Virgin exposed]. [C. L.]Breger,]une 9, 1909. Limestone Member of Moenkopi Formation. A. A. Graffam, 18 7590 (Green) Idaho [Bear Lake County, Montpelier 71/2-min quad; sec, 2. T. 13 [Date unknown.) 5., R, 44 E.; measured section in] Montpelier Canyon [just east 45 USNM 9343 Utah. Kane County, Moenkopi Formation (P). [Probably collected of town of Montpelier]. Thaynes Formation [about 1,849 ft bylFawcett. [Date unknown.] above the base and 435 ft below the top of the unit there exposed]. 44 USNM 9544 Idaho, [Bingham County;] about 65 mi north of the Utah line. [C. L.]Breger and [C. H.]Girty,]une 11, 1909, 18 mi west of the Wyoming line. and 5 mi west of Gray‘s Lake. 19 7395 (Green) [Same as 7390 (Green)]; about 3 mi east of the town of Montpelier, [Probably Portneuf Limestone Member of Thaynes Fonnation] on the north side of the road. [About 418 ft above the base and A. C. Peale. 1877. 1,864 ft below the top of the unit there exposed]. G. H. Girty. june11,1909. 20 7397 (Green) [Same as 7590 (Green). Same horizon as 7576 (Green).] C. L. Breger and c. H, Girty.june 11. 1909. 21 7406 (Green) [Same as 7390 (Green). About 2072 ft above the base and 210 f1 STRATIGRAPHIC SETTING 0F below the top of the unit there exposed; probably equivalent of Portneuf Limestone Member of Thaynes Formation.] C. L. THE BRACHIOPODS Breger. june 5, 1909. 22 7409 (Green) [Same as 7590 (Green).]C, L. Breger, June 7, 1909. ~ - - 23 7431 (Green) [Probably same as 7390 (Green).]Near base of Thaynes Formation. An inherent disadvantage 1“ a study Of museum collec- [C-LrlBrescranle-H-lGirtyJunelor1909a tions is that the investigator must rely almost entirely upon 24 7435 (Green) Idaho [Bear Lake County, Montpelier 7%»min quad; approx. . f . k f h h. see. is, r, 15 s.. R. 44 13,). Thaynes rumour. [equivalent the Jndgenient o prevxous field wor em or t e geograp 1c, 5"“{18"P"EC““Y‘°7397(G"°“)l~c-FB'CW'SEPL[909- , stratigraphic, and temporal annotations of the collections. 25 7444 (Green) Wyoming [Lincoln County, Montpelier, Idaho-Wyoming 30«min , , , , quad; NE‘ASW‘ASE‘A sec. 30, r. 27 N.. R. 119 w.]. Thaynes In an area of rapid lateral faCies change and rare diagnostic Formation. G. H. Girty,]uly6. 1909. ’ ’ ' ' ' 26 7466 (Green) Wyoming [Lincoln County, Montpelier, Idaho~Wyoming 30-min Early T113551? fOSSIIthrlZOnS, SECh as the. N011}? Amirlfian quad; SEVASW‘ASWV. sec. 30. T. 27 N., R. 119 W.]; west western lntCI’lOI‘, t. C approac t0 stratigrap y 15 It 1C. f beIt R , th dC .Th F- - - - ' “in; g. afarfynfif‘ “22"1931 ”m“ “1°" ”"5 °' FaCies and (or) formation boundaries are commonly dia- 27 7470(Grcen) Wyoming [Lincoln County. Montpelier, Idaho-Wyoming 30-min chronous in such a situation, so that it is not surprising that quad: NE corner of SEl/eNEl/rNEVa sec. 6. T. 26 N., R. 119 . . . - - formation names have roliferated or that the formal a - W.], Thaynes Formation. G. H. Girty, July 2, 1909. 28 7478(Green) Utah [Rich County. Woodruff 7‘/r«min quad]; Woodruff. branch plicability Of these names 15 regionally I'CSU'ICted. hollow of Twelve Mile Creek south of Road Hollow. Thaynes , , Formation.C. L. Breger,Aug,24, 1907. The brachiopods discussed here were collected from the 29 7717 (Green) Utah [Morgan County, Devil‘s Slide 7V2-min quad]; north side of ‘ ' ‘ ' Weber Canyon, 1 mi west of Devil's Slide. [Probably Moenkopi WOOdSIder Dlnwoody,'Th21‘ynes, and Moenkopi Formations Forrnation.]G.H.Girty.Sept.15.1911. and commonly occur in thin, monospec1fic bands or zones, 30 7758 (Green) Utah [Iron County. Kanarraville 7V2-min quad]; V2 mi east of ' ‘ ' Km“ [Probably Moenkopi Formation] IR] Gram July 18, isolated from one another and from most other diagnostic 1907. fossfls. The age of these units and their regional interrela- 51 7787 (Green) Utah [Washington County. La Verkin No. 4 NW 7V:-min quad], - - “mm,“ m. m T. 42 S” R. ,2 w, “0,1,6 mimmwmf tionships are unclear. McKee and others (1959) produced a Virgin Ciry- Lower limestone [Pm] of Moenkoni Formation. generalized correlation chart for TriaSSic stratigraphic units 300 ft above base ofunit. U. 13.] Reeside, Oct. 5, 1919. . . . 32 7813(Green) Idaho [BinghamCounty,]Crane'sFlat 15-min quad.;nearS‘/4 corner ln the Unlted States- Pertlnent Parts Of that Chart appear [?], sec. 2, T. 4 S., R. 41 15.; about 13 mi north and 5% mi west of here as fi h side Formation ori 'nal] de_ Henry, Idaho. Thaynes Formation. [P, V.] Roundy and [C. R.] f d (B gurell2lg‘07e) wolfdp k C, d , ’ gl 1') y Mansfield. Aug. 1916. me outwe , In t C ar lty lStI‘lCt, nort eastern 33 7825 (Green) Idaho [Caribou County, Upper Valley 7V1-min quad]; SEl/aNEl/4 _ m 13' r. 7 s” R' 44 E [Probably Thaynes ”madam”. w. Utah, was later extended to northern Utah, western Wyo Richards, 1912. ming, and southwestern Montana (Kummel, 1954). Beds in 34 7855 (Green) Idaho [Caribou County,] Lane's Creek 15-min quad; near SE corner. - - - - sec, 5. r. 6 s,. R. 43 15.; about 5 mi east and a little north of the Confusron Range 1“ west-central Utah, originally re- F133;: 2 “all: knob at llmc 0; the 7:317de 1:319 UliP" [1:ng ferred to the WOOdSIde (Newcll, 1948), were rcass1gned to o t e aynes ormation. G. R. Mans 1e an P. V. Roun y, . . July10.1915- the Thaynes Formation (Hose and Repenning, 1959). The 55 7879 (Green) Idaho [Bingham County,] Crane's Flat 15-min quad; 5151/4 sec, 9. T. 4 S., R. 40 E. “Ross Fork Limestone [Member" of Thaynes Formation]. G. R. Mansfield. 1923. so-called “Mackentire Tongue” of the Woodside Formation, defined in Duchesne County, Utah, is of demonstrable STRATIGRAPHIC SETTING OF THE BRACHIOPODS .mBSm 95:3 2: we BEBE 5883 2: mo sham E 31.5 uEmF—wtabm Annmaiumv 233:. 5304 we “page coca—oboe uni—82.80! .N 5505 .cocmctou. gift. *0 :SnEw—z wcoumeS fol mmomau .cOZuEBm 3:22: *o iwnEos. =mI tour: “BEES”. coszBm 5.5.50“. 00 . 2282.5“. u 2E5 289550 >uoo§£0 ”0:250". uEmuoo‘S c2355”. “595:5 $3825 scam—Eon. wcofisz sonar—to”. w a 00 030 . €330; u. u 3 h< “5...; 223E: “.85 293E: um E5 '— e 856:... mcoumoE: w. w. W. E3 530: >25 cm... M H. w. c2555“. cease—ton. «U E5 w w e W 39.:on 856;... m. w m... o cosmEbou. 9.2383 ocoumoE: .. mcoszLOw O 8 9 . m0 >m Jam—m w umEmcc: w m ml; W waist c E. «a “:5 m. 95 E3 53o: m m. m 3.5: .950: cocmESu J .3 3:3 .530: 293E: E3505. 53:on w m c2365“. ucm wcofiUcmw . Wm 33:85. n Sancho”. .m :95 m. AWMMmHfi”. n 528:3 *o ocofimEfi U . 5235‘ @395... 8:3 I; Smctom coszEu scum—FE“. «9.39:. we .BEwE «8.6:... .0 .onEwS. mcouonS Sacco; 9.3me3 chtom tap—:00 Em to: 598; more 59me oEEmEmm $659.2 wZ 530w :hwummwctoz mm >>m Eoummgztoz Ewummzztaom 49;ch .Emammmfizom 49:ch camv mm . <_Zm0n=._mz I<._.D >> OI 5 2‘ n: w 3_ . _ ° 5 o , o 2_. o _ . End of cryptacanthiform stage . . 2» . a 1 1— ‘ — O 1 f - l l l | 1 2 3 4 5 1 ' 1 1 l I LOOP LENGTH (mm) 0.5 1.0 1.5 2.0 2.5 3.0 LOOP WIDTH (mm) FIGURE 4. iscattergram of dorsal valve length and loop length of Obnzlxz'a thaynesiana (Girty) from southeastern California FIGURE 5.7Scattergram of dorsal valve width and loop width of (IOC. 37). Obm'xz'a thaynexz'mm (Girty) from southeastern California (10c. 37). 14 TEREBRATULID BRACI-IIOPODS FROM THE WESTERN INTERIOR OF THE UNITED STATES Total Total Total Dorsal valve length width thickness length (mm) (mm) (mm) (mm) Locality21: USNM 121558 12.3 9.7 7.3 10.8 (lectotype) USNM121559a 8.8 7.5 4.7 7.8 USNM121559b 10.6 9.7 5.3 9.2 USNM121559c 12.2 10.3 6.8 10.5() USNM121559d 12.3 11.7 6.3 11.8 USNM 242084 6.0 5.4 3.0 5.2 USNM 242085 8.6 7.8 4.0 7.7 USNM 242086 8.1 7.56 4.56 7.2e USNM 242087 9.0 7.89 5.0 7.9 USNM 242088 8.4 8.7 4.8 7.1 USNM 242089 9.0 8.8 4 9 7.5 USNM 242090 10.0 8.46 5 09 8.9 USNM 242091 10.3e 9.6e 5 -1e 9.1e USNM 242092 10.6,. 9.2 5.36 9.3 USNM 242093 10.2 11.4 6 02 9.0 Locality 37: USNM 242094 1.8 1.7 0.9 1.5 USNM 242095 1.8 1.8 1.0 1.4 USNM 242096 2.2 2.1 1.3 1.9 USNM 242097 2.5 2.2 1.3 2.0 USNM 242098 3.1 3.2 1.6 2.7 USNM 242099 3.9 3.6 3.1 3.2 USNM 242100 4.1 3.6 2.0 3.5 USNM 242101 5.0 5.3 1.7 4.3 USNM 242102 5.7 5.6 3.1 4.9 USNM 242103 5.7 5.6 3.2 4.8 USNM 242104 6.2 5.6 3.5 5.3 USNM 242105 6.5 6.3 3.3 5.7 USNM 242106 6.8 5.9 3.9 6.0 USNM 242107 7.1 7.1 3.7 6.4 USNM 242108 7.1 7.2 3.7 6.2 USNM 242109 7.7 7.8 4.5 6.9 USNM 242110 8.0 7.5 4.9 6.9 USNM 242111 8.3 8.4 4.3 7.4 USNM 242112 8.6 9.3 4.8 7.8 USNM 242113 8.8 8.7 .4.8 7.7 USNM 242114 9.0 9.0 5.5 8.2 USNM 242115 9.0 9.2 4.7 8.2 USNM 242116 9.3 9.2 5.3 8.4 USNM 242117 9.5 8.8 5.0 8.6 USNM 242118 11.0 10.8 6.1 9.8 Types. —Lectotype: USNM 121558; figured specimens: USNM 121558, 242095, 242098, 242100, 242101, 242104, 242105, 242108, 242111, 242115, 242116, 242119—242125, 242128, 242129, 242131—242139; measured specimens: USNM121558, 121559a—d, 242084242134. Occurrence. —0. thaynesiana has been confidently iden» tified from the Thaynes Formation and from its strati- graphic equivalents from southeastern Idaho to southeast- ern California (locs. 10, 12—31, 36740, 42, 43). (See fig. 1 and “Fossil Localities Cited in this Report.") Its morphology changes very little over this broad geographic range, though more southern examples are somewhat more transverse. Comparison. —The genus Obnz'xia is monotypic. 0. thaynesiana may be distinguished from its most similar ap‘ parent relative, Anadyrella z'nfrequens Dagys, by its smaller size, less robust septalial plates, and distinctive loop develop- ment scheme. It may easily be distinguished from other 5 l I LOOP LENGTH (mm) l l 1 2 3 LENGTH OF ASCENDING LAMELLAE (mm) FIGURE 6.—Scattergram of loop length and length of ascending lamellae of Obnixia thaynesiana (Girty) from southeastern Cali- fornia (10c. 37). _. (.71 .. o b l P U1 | . a l l l l 1 2 3 4 5 LOOP LENGTH (mm) DISTANCE T0 CRURAL PROCESSES (mm) FIGURE 7. iScattergram of loop length and distance to crural pro» cesses of Obnz'xz'a thaynesiana (Girty) from southeastern Cali- fornia (10c. 37). North American Early Triassic terebratulid brachiopods by its sulcate anterior commissure. Loop development in Obnixia thaynesiana (Only).— Terebratulid classification is made difficult by extensive homeomorphy. Shell form and outline not only may vary considerably within a single small genetic unit, but also they may appear similar in genetically distantly related forms. Until recently, however, it was less well understood that such presumably conservative structures as the terebratulid loop might also be subject to the vagaries of homeomorphy (Dagys, 1974; Cooper and Grant, 1976). Recent studies of loop development in late Paleozoic and Mesozoic terebratu- lids (Cooper, 1957; Dagys, 1968, 1972, 1974; Baker, 1972) have shown that many different genetic stocks may achieve SYSTEMATIC PALEONTOLOGY 15 similar mature brachial support (loop) structures and that the previous simplistic terebratulid classification on the basis of “short" or “long” loops needs reevaluation. The differ- ence between forms having similar mature loop designs often can only be discerned, for many species, if a relatively complete developmental series is available for study. In calcareous specimens, loop detail can rarely be ob- served directly and commonly is reconstructed on the basis of serial sections or acetate peels. Pearson (1977) has re viewed serial grinding as applied to brachiopodfl. This tech- nique has the advantage in that it reveals the successive laminae, laid down during the growth of an individual, that are preserved in many calcareous specimens. These laminar traces may then be used to reconstruct ontogenetic stages. Cooper (1959) was justifiably critical of serial grinding tech- niques as used at that time. His main criticisms were the dif- ficulty of maintaining parallel sections and the difficulty in making the intervals between successive sections sufficiently small that minute structures of taxonomic significance could be seen. Silicified specimens, such as those used by Cooper (1957) in his study of loop development in Cryptacanthz'a, are much more easily prepared, as one need only remove the surrounding calcareous matrix and shell infilling by etching in a weak acid. However, disadvantages are inherent in the use of Silicified specimens. Silicification is a poorly under— stood phenomenon, but we do know that structures so pre- served need not be replaced in their entirety. In addition, detail of ontogenetic significance within the shell is com- monly lost during silicification. As time was short during this study and as the equipment available was not specifi- cally designed for serial grinding, I have used that technique only where necessary to show the internal structures of un- silicified type specimens of taxonomic importance (for example, Obm'xia thaynesmna (Girty) and Vex semz’sz'mplex (White)). Calcified paralectotype specimens of Obnz'xz'a thaynesz'ana from southeastern Idaho were serially sectioned at intervals of 0.15 mm, and acetate peel impressions were taken at each interval. Selected diagnostic sections normal to the longitudinal axis of one such specimen (USNM 242139) are shown in figure 8. Sections of another paralectotype speci- men (USNM 242135), oriented in the commissural plane, were projected onto plexiglass sheets and stacked to form a three-dimensional replica of the valve interiors. A stereo- pair photograph of this reconstruction appears on plate 2, figure 24. These figures illustrate the characteristic lack of inner hinge plates, the weak dorsal median myophragm, and the long anteriorly spinose glossothyropsiform loop of the mature Obmlxz'a thaynesz'am. Unfortunately, topotypic specimens were not Silicified, and serial sectioning of a rep- resentative sample to document loop development would not have been feasible. Finely preserved specimens from locality 37 (San Bernar- dino County, Calif.) were, however, judged conspecific with the syntypic suite. Etched from the surrounding limy matrix, these Silicified specimens provide a good sampling of representative postembryonic stages in the development of the loop of 0. thaynesz'ana. Loop terminology in the follow- ing discussion is used in the sense of Cooper (1957). The precentronelliform stage of O. thaynesz'ana is repre- sented here by three specimens, all between 1 and 2 mm in length. In the most paedomorphic of these (USNM 242119; pl. 3, fig. 1), the loop consists only of the descending branches. These are oriented normal to the commissural plane, except at the anterodorsal tips, which are deflected slightly dorsomesially. The descending lamellae diverge anteriorly to about one-fourth valve width, terminating at about two-fifths valve length. There is no anteromedian ridge on the valve floor at this or any subsequent develop mental stage. The next precentronelliform specimen (USNM 242120; pl. 3, fig. 2) is more coarsely Silicified, but it shows broad descending lamellae, the tips of which have turned not only mesially but ventrally. In lateral view, their growing anterior margins are inclined anteroventrally at about 45°, the same attitude at which the echmidium of the centronelliform stage lies. The entire loop at this stage is concave in ventral view, although the tips of the descending lamellae do not yet meet to form a complete bowl. In the most advanced of the three precentronelliform individuals (USNM 242121; pl. 3, fig. 3), the tips of the descending lamellae are almost in contact. Spines are developed on the dorsal surfaces of the loop even at this early stage. Within this stage no correlation between valve size and level of loop development was discerned, but the precentronelliform stage commonly is completed by the time the dorsal valve has attained a length of 2 mm. The centronelliform stage is reached very quickly, with little change in the length of the shell, but it is accompanied by a deepening of the ventral valve. A single specimen (USNM 242122; pl. 3, fig. 4) represents this extremely brief developmental stage. No median ventral plate is present; rather the two branches are simply fused. They do not butt squarely but are directed ventromesially, and their ends are broadened anteroventrally to form the echmidium—the tip of which projects ventrally beyond the commissural plane. The cryptacanthiform stage is represented by three speci- mens (USNM 242123, 242124, 242125; pl. 3, figs. 5A7) hav- ing valve lengths of about 2 mm. In this stage a typical cryptacanthid “ring" or “hood," closed both anteriorly and posteriorly, is not developed. Instead, the growing edges, in the median line, quickly shift from the anteroventrally di- rected oblique position of the centronelliform stage to a ventrally directed orientation by means of more rapid growth of the dorsal parts of the ascending lamellae. As this growth progresses, the two branches of the loop are joined only proximally, and the distal (anterior) extremities remain separated. At the close of this stage (USNM 242125; pl. 3, fig. 7), the mesial parts of the ventral margin of the ascend- ing lamellae begin to grow anteriorly, subparallel to the commissural plane, and the proximal junction of the descending lamellae is resorbed. At this point the crypt- acanthiform stage ends, and the glossothyropsiform stage begins. The glossothyropsiform stage, present during most of the postembryonic development of O. thayneszkzm, is initiated 16 TEREBRATULID BRACHIOPODS FROM THE WESTERN INTERIOR OF THE UNITED STATES POSTERIOR 0 15 CECEGEQ; Cm 015 O _| 01 0.25 O 0.15 9 _. o 020 _O _| O 020- 0.15 0 0.15 0 020020 0.20 do 0 .3 U1 0 0.30 < m .0 _. 01 (9% ) O _a 0| v \ ( 2.00 ANTERIOR FIGURE 8. # Thirty-five parallel serial sections of a paralectotype specimen (USNM 242139) of Obnzbczll thaynesz'ana (Girty) from southeastern Idaho (loc. 21). Section planes are oriented normal to the longitudinal axis of the shell. Numbers indicate distance (in millimeters) between successive sections. All sections X 4‘0. SYSTEMATIC PALEONTOLOGY 17 at a valve length of about 2.5 mm. It is represented in the present collection by nine specimens, of which six are figured (USNM 242128, 242129, 242131—242134; pl. 3, figs. 8—13). The anterior growth of the ascending lamellae is not so rapid in this stage as that of the descending lamellae, which continue to broaden and grow anteriorly. The junc- tion of the two sets of lamellae becomes increasingly marked, through anterior growth and posterior resorption, so that in the mature glossothyropsiform loop, dorso- ventrally oriented elements in the posteromesial parts of the ascending branches are totally resorbed, and only those parallel to the commissural plane and to the shell’s longi- tudinal axis remain. During this stage the loop grows dis— tally, but the flat surfaces of the descending and ascending lamellae remain essentially parallel. In the adult loop the planar surfaces of all parts of the loop and the crural pro- cesses are oriented anteroventrally and (or) laterally (distally). Superfamny DALLINACEA Beecher, 1893 Family ZEILLERIIDAE Rollier, 1915 Genus PERIALLUS. :1. gen. Etymology of name. —Gr. perz'allos = before all others. Diagnosis.—Rectimarginate to uniplicate or paraplicate zeilleriids having a distinct pedicle collar, inner hinge plates and (or) septalial plates, and profusely spinose descending lamellae. Description. —Zeilleriids having smooth unequally bicon- vex valves, wide ventral umbo, and semierect beak. Anterior commissure variable; rectimarginate in smaller specimens to uniplicate or paraplicate in larger. Ventral valve having large mesothyridid pedicle foramen and prominent disjunct deltidial plates. Beak broad; beak ridges prominent, sharp, in dbrsal view defining large in- terarea. Dorsal valve markedly transverse, has small beak and low umbo. Ventral interior having distinct pedicle collar and strong dental plates. Hinge teeth strong. Muscle scars elongate tri- angular, commonly extending about one-half valve length. Dorsal interior having broadly divergent sockets and pos- terodistally hooked inner socket ridges. Narrow outer hinge plates arising at about midheight of inner socket ridges, directed approximately in plane of commissure. Crural bases with short crural processes; arising from midwidth of hinge plates. Inner hinge plates present or absent; septalial plates variably disposed—vertical, joining valve floor, or dorsomesially directed, forming small septalium. Median septum of variable strength, extending about one-half valve length, present in all observed growth stages. Septal pillar and (or) median septum involvement in loop development not observed. Mature zeilleriiform loop long, commonly about two-thirds valve length; wide, commonly about one- half valve width; composed entirely of primary elements. Dorsal surface of descending lamellae profusely spinose. Cardinal area not well developed, commonly expressed as low shelf, overhanging umbo. Type species. —Periallus woodsidensis, n. sp. Occurrence. —P. woodsidensis, n. sp., has been recovered from the Woodside Formation in Caribou and Bear Lake Counties, southeastern Idaho, and from the Dinwoody For- mation in nearby Wyoming and Montana. A larger form, less confidently assigned to that species, but definitely refer- able to the genus, comes from the “Ross Fork Limestone Member" of the Thaynes Formation in Caribou County, Idaho. Comparison—Periallus is easily distinguished from the four known Triassic zeilleriid genera by its rectimarginate to uniplicate or paraplicate anterior commissure. In addition, it differs from Zeilleria Rollier, A ulacothyris Douville, and Kolymithyris Dagys, in bearing a distinct pedicle collar. It differs from both Zeilleria and Woroboviella Dagys in its long dorsal median septum. Kolymithyris is easily distin- guished by its thickened cardinalia. Discussion—The Zeilleriidae, placed within the Dalli- nacea following the usage of Dagys (1974), includes those forms in which the loop is not connected to any anteromesial structure in the dorsal valve during ontogeny. Although not even a relatively complete loop development series is avail- able for Periullus, the smallest specimens examined (about 2 mm long) show no evidence of such an anteromesial structure. Dagys (1974) stated that profusely spinose loops are com- mon in Middle Jurassic and younger dallinids but are un- usual in the older true zeilleriids. This trait, however repre- sentative, cannot be construed as an argument against the assignment of Periallus to the Zeilleriidae, That assignment is made on the basis of the basic loop character and diag- nostic features of the dorsal cardinalia. Poi-hung woodsldonsis, 11. ll). Plate 4, figures 1715. Terebratula margaritowi Bittner, in Newell and Kummel, 1942, Geol. Soc. America, Bull., v. 53, p. 954, pl. 2, figs. 5a,b (non T. margaritowi Bittner, 1899, Comité Geol. St. Petersburg Mém., v. 7, p. 27, 28, pl. 4, figs. 9715 =Fletcherithyris Campbell). Etymology of name. — Woodside = Formation name + L. -ensz's = at the place of. Diagnosis. ——Small Periallus. Description. —Small smooth unequally biconvex zeil— leriid, having a wide ventral umbo and semierect beak. Sub- trigonal or oval to subpentagonal in outline; commonly widest slightly anterior to midlength; deepest at about mid- length. Anterior commissure rectimarginate, uniplicate, or paraplicate. Outermost growth increments commonly im- bricate or lamellose. Ventral'valve more convex, having large mesothyridid pedicle foramen and prominent disjunct deltidial plates. 18 TEREBRATULID BRACI-IIOPODS FROM THE WESTERN INTERIOR OF THE UNITED STATES Beak ridges prominent, sharp, defining curved palintrope. Beak wide, large, in dorsal view producing large interarea. Dorsal valve less convex, markedly transverse, has small beak and low umbo. Ventral interior having distinct pedicle collar and strong dental plates. Hinge teeth strong, tabular, hooked dorsally, directed anteromesially. Growth traces of hinge teeth present as low ridges on dorsomesial surfaces of dental plates. Muscle scars elongate triangular, commonly extend- ing about one-half valve length. Dorsal interior having broadly divergent sockets and posterodistally hooked inner socket ridges. Narrow outer hinge plates arising at about midheight of inner socket ridges, directed approximately in plane of commissure. Crural bases have short crural processes directed ventro- mesially at about 45°, arising from midwidth of hinge plates. Disjunct, narrow, elongate triangular inner hinge plates present or absent, variably expressed, produced mesially in plane of commissure; parallel bordered pos- teriorly, margins diverging anteriorly. Septalial plates vari- ably expressed: as short vertical apical plates connecting inner hinge plate and crural base to valve floor or as obliquely inclined plates uniting dorsally with low median septum to form septalium. Median septum commonly prominent, extending about one-half valve length, present in all observed growth stages. Neither septal pillar nor median septum involvement in loop development observed. Mature loop zeilleriiform: long, commonly about two—thirds valve length; wide, commonly about one-half valve width, composed entirely of primary elements; having broadly curved anteriorly convergent but widely separated descend- ing lamellae and broad ascending lamellae. Entire dorsal surface of descending lamellae profusely spinose. Cardinal area not well developed, commonly expressed as low trans- verse bipartite smooth shelf overhanging umbo. Holotype Paratypes USNM 242140 USNM 242141 USNM 242142 USNM Locality] ..................... 242143 Measured in millimeters Length ................ 5 8 Width ................ 5.7 Thickness .............. 2.9 Dorsal valve length ....... 5 0 Dorsal valve width ....... Loop length ............ Loop width ............ Distance to crural processes ............. Length of ascending lamellae ............. Loop depth ............ Anterior separation ...... Types—Holotype: USNM 242140; figured paratypes: USNM 242143—242153; measured paratypes: USNM 242141—242143. OccurrenceiPeriallus woodsz'denszls was recovered only from Caribou and Bear Lake Counties, southeastern Idaho, where it occurs in the Woodside Formation (locs. 1, 11; fig. 1; “Fossil Localities Cited in this Report"). Specimens de- scribed by Newell and Kummel (1942) as T. margarz'towz' Bittner are here referred to Perz'allus on the basis of the broad ventral beak, rectimarginate to paraplicate commis- sure, zeilleriid loop, and characteristic septalial plates and median septum. Those specimens were collected from the Dinwoody Formation in the Salt River Range, Lincoln County, Wyo. Newell and Kummel cited the distribution of this form as including southeastern Idaho but did not specify other localities further. Comparison. —The genus Periallus is monotypic. P. woodsz'densz's is easily distinguished from Obmlxia thayne- siana (Girty) by its rectimarginate to paraplicate anterior commissure and persistent strong dorsal median septum, which commonly extends half the length of the valve. It is very similar to Fletcherz'thyrz's margarz'towz' (Bittner), re- ported from the Induan Stage (Proptychz’tes zone) of eastern Siberia (Primor’ye) and from the Olenekian Stage of Mangyshlak, U.S.S.R. (Dagys, 1965). It differs from F. marga'rz'towz‘ in bearing a zeilleriiform (“long") rather than a dielasmatid (“short") loop. In view of the recent justi- fied combination of long- and short-looped forms within the Dielasmatidae (Dagys, 1972, 1974), it may be that the zeil- leriids and dielasmatids represent stocks more closely related than heretofore thought. Discussion—The terminology conventionally used (see Campbell, 1965) to describe terebratulid cardinalia is use- less to describe P. woodsz'densz's because P. woodsz‘densz's has two distinct forms that might logically be termed “inner hinge plates.” In the above description, those structures mesial to the crural bases and approximately in the hinge plane are referred to as “inner hinge plates.” Those mesial to the crural bases but dorsally joining either a median sep- tum or the dorsal valve floor are termed “septalial plates," following the usage of Dagys (1974). A wide range of varia- tion in dorsal cardinalia is observed in a single population sample of P. woodsz'densz's from locality 1. At the one ex- treme, apical straight septalial plates extend almost ver- tically from the crural bases to the valve floor, flanking the median septum, and distinct inner hinge plates are mesial to the growth traces of the crural bases (pl. 4, fig. 12). In con- trast (pl. 4, figs. 11, 14), in some forms, inner hinge plates cannot be discerned, and curved septalial plates join either at the valve floor or atop the median septum, in the latter case forming a septalium. Peflfllus an. wood-idensIS, n. sp. Plate 4, figures 16 20. Description—One specimen has the following measure- ments (in millimeters): Locality 35: USNM 242154 Total length ............ 19.3 Fold height ............. 1.5 Total width ............. 17.9 Distance to crural processes . 4.0 Total thickness .......... 8.6,Je Loop length ............. 12.4be Dorsal valve length ........ 16.6 Loop width ............. 8-34,: Types—Figured and measured 242154. Discussion—Several specimens of Periallus questionably assigned to P. woodsz‘densz's were recovered from locality 35, specimen: USNM . REFERENCES CITED 19 in the “Ross Fork Limestone Member" of the Thaynes For- mation, Bingham County, Idaho. Although no complete loop is preserved intact in any of the specimens, one speci- men (USNM 242154) contained fragments of the descending and ascending lamellae sufficiently complete to determine the spinose character of the former and the zeilleriid form of the latter. The uniplicate commissure of these forms seems a reasonable outgrowth of the shell form seen in P. wood- sz'densz’s. The dorsal median septum, however, is not well preserved. The variations in cardinal plate arrangements are similar to those in P. woodsz'demz's, and the larger speci- men may represent an adult of that form. The absence of forms intermediate in size and development between the two at any examined locality is the rationale for excluding the above specimens from formal specific status. REFERENCES CITED Baker, P. G., 1972, The development of the loop in theJurassic brachiopod Zez‘llerm leckenbyz‘: Palaeontology, v. 15, pt. 3, p. 4507 472, pls. 82—85. Beecher, C. E., 1895, Revision of the families of loop-bearing Brachio- poda: Connecticut Acad. Arts and Sci. Trans. (1893), v. 9, pt. 2, p. 376~391,395—398,pls.33734. Bittner, Alexander, 1899, Versteinerungen aus den Trias-Ablagerunger des SiidAUssuri-Gebietes in der Ostsibirischen Kfistenprovinz: Comité Géol. St. Petersburg Mem., v. 7 (188841889), no, 4, 35 p., 4 pls. (in Russian with German translation). Boutwell, J. M., 1907, Stratigraphy and structure of the Park City mining district, Utathour. Geology, v. 15, p. 434458. Campbell, K. S. W., 1965, Australian Permian terebratuloids: Australia Bur. Mineral Resources, Geology and Geophysics Bull. 68, 146 p., 17 pls., 44 figs. Condit, D. D., 1917, Relations of the Embar and Chugwater formations in central Wyoming: U.S. Geol. Survey Prof. Paper 98—0, p. 2637270, map. Cooper, G. A., 1957, Loop development of the Pennsylvanian terebratulid Cryptacanthz'a: Smithsonian Misc. Colln., v. 134, no.3, 18 p., 2 pls. — 1959, Genera of Tertiary and Recent rhynchonelloid brachiopods: Smithsonian Misc. Colln., v. 139, no. 5, 90 p., 22 pls. Cooper, G. A., and Grant, R. E., 1976, Permian brachiopods of west Texas, V: Smithsonian Contr. Paleobiology, no. 24, p. 26093159, pls. 6637780, fig. 42. Dagys, A. S., 1963, Verkhnetriasovye brakhiopody yuga SSSR: Moscow, Akad. Nauk SSSR, Sibirsk. Otdeleniye, 238 p., 31 pls., 106 figs. — 1965, Triasovye brakhiopody Sibiri: Moscow, Akad. Nauk SSSR, Sibirsk. Otdeleniye, Inst. Geologii i Geofiziki, 186 p., 26 pls., 67 figs. A1968, Yurskiye i rannemelovyye brakhiopody Severa Sibiri: Akad. Nauk SSSR, Sibirsk. Otdeleniye, Inst. Geologii i Geofiziki, Trudy, no. 41,160 p., 26 plsi, 81 figs. 1972, Postembrional‘noye razvitiye brakhidiya pozdnepaleozoyskikh i mesozoyskikh Terebratulida, 1'71, Morfologichyeskiye i filogyenye- tichyeskiye voprosi palyeontologii: Akad. Nauk SSSR, Sibirsk. Otdele- niye, Inst. Geologii i Geofiziki, Trudy, no. 112, p. 22758, 28 figs. 1974, Triasovyye brakhiopody (morfologiya, sistema, filogeniya, stratigraficheskoye znacheniye i biogeografiya): Akad. Nauk SSSR, Sibirsk. Otdeleniye, Inst. Geologii i Geofiziki, Trudy, no. 214, 387 p., 48 pls., l7l figs. Gemmellaro, G. G., 1899, La fauna dei calcari con Fusulz'na della Valle del Fiume Sosio nella provincia di Palermo: Gior. Sci. Nat. Econ. [Palermo], v. 22, p. 957214, pls. 25—36, 46 figs. Girty, G. H., 1927, New species of Lower Triassic fossils from the Woodside and Thaynes formations, in G. R. Mansfield, Geography, geology, and mineral resources of part of southeastern Idaho, with descriptions of Carboniferous and Triassic fossils by G. H. Girty: U.S. Geol. Survey Prof. Paper 152, p. 434446, pl. 30. Gray, J. E., 1840, Synopsis of the contents of the British Museum: 42d ed., London, 370 p. Hose, R. K., and Repenning, C. A., 1959, Stratigraphy of Pennsylvanian, Permian, and Lower Triassic rocks of Confusion Range, west-central Utah: Am. Assoc. Petroleum Geologists Bull., v. 43, p. 216772196. Kummel, Bernhard, 1954, Triassic stratigraphy of southeastern Idaho and adjacent areas: U.S. Geol. Survey Prof. Paper 254—H, p. 165—194, figs. 18—21. McKee, E. D., and others, 1959, Paleotectonic maps, Triassic System: U.S. Geol. Survey Misc. Geol. Inv. Map 1-300, 33 p., 9 pls., 32 figs. McKelvey, V. E., and others, 1956, Summary description of Phosphoria, Park City, and Shedhorn Formations in the western phosphate fields: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 12, p. 2826—2863. w 1959, The Phosphoria, Park City, and Shedhorn Formations in the western phosphate field: U.S. Geol. Survey Prof. Paper 313—A, 47 p. Mansfield, G. R., 1916, Subdivisions of the Thaynes limestone and Nugget sandstone, Mesozoic, in the Fort Hall Indian Reservation, Idaho: Washington Acad. Sci.Jour., v. 6, no. 2, p. 31—42. — 1920, Geography, geology and mineral resources of the Fort Hall In- dian Reservation, Idaho: U.S. Geol. Survey Bull. 713, 152 p., 13 pls., 4 figs. Moisseiev, A. S., 1938, Otriasovykh i yurskikh brakhiopodakh Pamirya: Soc. Nat. Leningrad, Sec. Géologie et Minéralogie, Travaux, v. 67, no. 2, p. 220—237. Newell, N. D., 1948, Key Permian section, Confusion Range, western Utah: Geol. Soc. America Bull., v. 59, no. 10, p. 1053—1058. Newell, N. D., and Kummel, Bernhard, Jr., 1942, Lower Eo-Triassic stratigraphy, western Wyoming and southeast Idaho: Geol. Soc. America Bull., v. 53, no. 6, p. 937—995, 3 pls., 5 figs. Pearson, D. A. B., 1977,,Rhaetian brachiopods of Europe: Vienna, Natur- historisch. Museums Neue Denkschrift., v. 1, 70 p., 7 pls. Rollier, H. L., 191571919, Synopsis des Spirobranches (Brachiopodes) Jurassiques Celtosouabes. [Pt.] 1, Lingulidés-Spiriférides. [Pt.] 2, Rhynchonellidés. [Pt.] 3, Terebratulidés. [Pt.] 4, Zéilleridés-Réper- toires: Soc. Paléont. Suisse Mem., v. 41 (1915), p. 1769 [pt. I]; v. 42 (1917), p. 717184 [pt. 2]; v.43 (1918), p. 185—275 [pt. 3]; v.44 (1919), p. 279422 [pt. 4]. Schuchert, Charles, 1913, Class 2. Brachiopoda, Duméril, in K. A. von Zittel, Textbook of paleontology. Translated and edited by C. R. Eastman: London, Macmillan & Co., v. 1 (2d ed.), p. 355420, figs. 526—636. Silberling, N. J., and Tozer, E. T., 1968, Biostratigraphic classification of the marine Triassic in North America: Geol. Soc. America Spec. Paper 110, 63 p.,l fig.,1 pl. Singeisen-Schneider, V., 1976, Interpretation von Serienschliffen bei Brachiopoden, am Beispiel von Dogger-Terebratuliden aus dem BaslerJura: Eclogae Geol. Helvetiae, v. 69, no. 1, p. 937110, 10 figs. Stehli, F. G., 1962, Notes on some upper Paleozoic terebratuloid brachio- pods:Jour. Paleontology, v. 36, no. 1, p. 977111. 1965, Paleozoic terebratulida, in R. C. Moore, ed., Treatise on in- vertebrate paleontology, Part H, Brachiopoda, v. 2: New York and Lawrence, Kans., Geol. Soc. America and Univ. Kansas Press, p. H730~H762. Suess, Eduard, 1854, Uber die Brachiopoden der Kossener Schichten: Akad. Wiss., Wien, Math.-naturwiss. K1. Denkschr., v. 7, p. 29—65, pls. 14. Thomson, J. A., 1926, A revision of the subfamilies of the Terebratulidae (Brachiopoda): Ann. and Mag. Nat. History, 9th ser., v. 18, p. 523—530. Waagen, W. H., 18824885, Salt-range fossils. Productus—Limestone Group; Brachiopoda: India Geol. Survey Mem., Palaeont. Indica, ser. 13, v. 1, pt. 4, fasc. 2 (Aug. 1883), p. 391546, pls. 29749. Ward, L. F., 1901, Geology of the Little Colorado Valley: Am. Jour. Sci., 4th ser., v. 12, p. 401—413. Westbroek, Peter, 1969, The interpretation of growth and form in serial sections through brachiopods, exemplified by the Trigonirhynchiid septalium: Palaeontology, v. 12, pt. 2, p. 3217332, pl. 61, 9 figs. White, C. A., 1880, Paleontological Papers No. 9; Fossils of theJura-Trias of southeastern Idaho: U.S. Geol. and Geog. Survey Territories (Hayden), Bull. (1879780), v. 5, no. 1, art. 5, p. 105—117. 20 TEREBRATULID BRACHIOPODS FROM THE WESTERN INTERIOR OF THE UNITED STATES 1883, Contributions to paleontology, no. 5, Triassic. Triassic fossils Williams, Alwyn, and Rowell, A. J., 1965, Morphological terms applied to of southeastern Idaho: U.S. Geol. and Geog. Survey Territories brachiopods, in R. C. Moore, ed., Treatise on invertebrate paleon- (Hayden), Ann. Rept. 12 (1878), pt. 1, p. 105—118, pls. 31—32. (Ad- tology, Part H, Brachiopoda, v. 1: New York and Lawrence, Kans., vance print. 1880.) Geol..Soc. America and Univ. Kansas Press, p. H139—H155. Page Adygella ................................... 8 Adygelloides ............................... 7. 8 aequiplicata. Plectocancha .................. 10; pl. 2 Anadyrella ................................. 8. 11 infrequens .............................. 11, 14 Ankareh Formation . 6 restriction. . .. 8 Aspidathyn's . . . 8 Athyridaceans ................... 6 augusta. Terebratula . .............. 1. 6 Aulacothyn's ............................... 17 Aulacothyroideidae ......................... l 1 Aukwothyroides ............................ 8. 11 B. defined .................................. 7 Bell Canyon Formation. Anadyrella infrequens 1 1 C, defined .................................. 7 Carnian Series . . 9 Coenathyn's ................................ 8 Confusion Range. Utah ..................... 4 Crane's Flat 15-min quadrangle . l . . 10 Crural processes. defined .......... 7 Cruratula ............. 8 Cryptacanthia . .. 11.15 Cryptcanthiinae . 6. 11 Cryptonellidae . . ....................... 11 Descriptive terms .......................... 7 Dielasma .................................. 8. 9 Dielasmina ....................... 9 Dielasmatidae .................. . 2, 7. 18 Dielasmatinae . . . 8 Dienerian .. 6 Dinarella ........... . . . 8 Dinwoody Formation ......................... 4. 6. 7 Periallus woodsidensis .................. 17. 18 Terebratula margaritowi ................. 2. 18 Duchesne County. Utah ..................... 4 E. defined .................. . . . 7 episulcuta. Partneufia ...................... 7, 8; pl. 1 Fletcherithyris ............................... 6. 8. 9 margaritowi ............................ 6. 18 Fort Hall Indian Reservation. Partneufia epi- sulcata ......................... 8 Fort Hall Member .......................... 6 Fossils. localities ........................... 3 Gucina ................................. . l 1 Glossothyropsis . 11 juvenis .......................... 1 1 Girty. G. H.. terebratulid brachiopods ........ 2 gracilimtis, Meekoceras ..................... 10 gregaria. Terebratula ........................ 8 Hegler Limestone Member. Anadyrella infre- q uens .......................... 1 l Hemiptychina . . . .. .......................... INDEX [Italic page numbers indicate major references] Page Heterelasmim'dae ........................... 9 incuruirostra. Rhaetina ................... 7. 8. 9; pl. 1 infrequens, Anadyrella ...................... 11. 14 Induan Stage .............................. 6, l8 juuenis, Glossothyropsis .................... 11 Kalymithyn's ............................... 17 Kosseerschiehten Series ............... 8 Ladinian Series ............................. 11 lepton. Rhutimz ............................ 9 Localities, fossil ............................ 3 Loops. measurements defined ................ 7 Mackentire Tongue, Woodside Formation ..... 4 margaritowi, Fletchen'thyris ............. 6. 18 Terebmtula ..................... 2. 6. 17 Meekocems ammonite zone . ...... 7 gracilizatis ............................. 10 Moenkopi Formation .......................... 4. 6. 7 Morphologic features. defined ............... 7 Mutationellidae ............................ l 1 Norian Series .............. . 9. 11 Notothyn'didae ............................. 9 Obnixia .................................... 11 thaynesiana ............... 3. 7, 11. 12. 18; pls. 2. 3 serial grinding ...................... 15 Olenekian Stage ............................ 16, 18 Park City district ........................... 4 Park City Formation . . 6 Periallus ................................... 6. 17 aff. woodsidensis ....................... 18; pl. 4 woodsidensis .................. . 2. 7. 17; pl. 4 Phosphate deposits ............... 3 Phosphoria Formation . 6 Plectoconcha ..... 6 aequiph'cata .. 10; pl. 2 Plectoconchiinae . ....................... 6. 9 Portneuf Limestone Member ................ 6 index fossil ............................. 7 Portueufia episulcata .................... 8 Vex semisimplex ........... 10 Partneufia .................... 7 episulcata . . 7. 8; pl 1 Primor'ye ................. 6. 18 Praptychites zone . ........ 18 Propygape ................................. 8 pyn‘formis. Rhaetina ........................ 9 Rader Limestone Member. Anadyrella infre- quens .......................... 1 1 References ..................... . . . 19 Rhaetian Series ............................. 8 Rhaetina ................................... 6. 8 Page Rhaetina incurvirostra ................... 7. 8. 9; pl. 1 lepton ............................ 9 pyn‘formis . 9 taurica ....... 9 Rhychonellacean ........... .. 2. 6 Ross Fork Limestone Member ............... 6. 7 Periallus woodsidensis .................. 17 Periallus eff. woodsidensis ............... 19 Salt River Range. Wyo.. Terebratula margari- towi ............................ 18 semisimplex. Terebratula . . . 1. 6. 9. 10 Vex ........ Serial grinding ......... 15 Serial sections. method. . ................. 3 Shedhorn Formation . . .. ................. 6 Smithian ................................... 6 Spathian ................................... 6 Spiriferinacean .................... 2. 6 Subscripts. defined ................ . . 7 Sulcatinella ................................ 6. 8 taurica. Rhaetina ........................... 9 Terebratula augusta ........................ 1. 6 gregaria ................................ 8 margaritowi ............................. 2. 6. 17 semisimplex ........................... 1. 6. 9. 10 thaynesiana .......................... 2. 6. 11. 12 Terebratulid brachiopods. descriptive terms . . 7 Terebratulidae ............................. 9 Thaynes Formation ........ . . . . . 4, 7 base. Meekaceras gracilitatis . . . . 10 defined ................................ 6 middle, Vex semisimplex ................ 10 Obnixiu thaynesiana .................... l4 Pen'allus woodsidensis .................. 17 Pariallus eff. woodsidensis 19 Portneufia episulcata . . . 8 Vex ............... 9 Thaynes Group . , . . ................. 6 Thaynes Limestone . ................. 6 thaynesiana. Obnixia .......... 3. 7. 11. 12, 18; pls. 2. 3 Terebratula .......................... 2. 6. ll. 12 Uinta Mountains, Utah ..................... 6 Vex ............................ 9 semisimplex ...... . 7. 10; pls. 1. 2 serial grinding ...................... 15 White. C. A.. terebratulid brachiopods ........ 1 Wind River Mountains. Wyo ................. 6 Woodside Formation ....... . 4. 6. 7. 17. 18 woodsidensis. Periallus . . . . . 2. 7, 17; pl. 4 Periallus aff .............. 18: pl. 4 Warobouiella . . . ................. 17 Zeilleria .................................... l7 Zeilleriidae ................................. 6. 17 Zugmayeria ........................ . 7 Zugmayeriinae ............................. 6. 7 21 PLATES 1—4 Contact photographs of the plates in this report are available. at cost, from the U.S. Geological Survey Photographic Library. Federal Center, Denver, Colorado 80225. PLATE 1 [The object plane parallax for stereo views is 6°] FIGURES 1~10. Portneufz'a epz'sulcata, n. gen., n. sp. (p. 8). l. Paratype, articulated valves, dorsal view, X 1; showing asymmetric ap- parent immature invididual; USNM 242049; USGS loc. 1271 vPC. 2A8. Holotype, separable dorsal and ventral valves; 2. Articulated valves, dorsal view, X 1, for scale. 3. Dorsal view, X 2, for comparison. 4. Dorsal valve, ventral (interior) view, X 3, showing median septum and character of cardinalia. 5. Ventral valve, dorsal (interior) view, X 3, showing pedicle foramen, deltidial plates, and character of hinge teeth. 6. Articulated valves, anterior view, X 2, showing episulcate commissure. 7. Dorsal valve, lateral view, X 2, showing resected beak area at left. 8. Ventral valve, lateral view, X 2, showing expanded beak area at left. Specimens shown in figs. 2»8: USNM 242051; USGS 10c. 1271~PC. 9, 10. Paratype, fragment containing loop e'lements, dorsal and ventral views, X 3, showing long descending and ascending lamellae and anteromesially directed crural processes; USNM 242053; USGS 10c. 12717PC. 11~24. Rhaetz'na z'ncurvz'mstm, n. sp. (p. 9). “~15, Holotype, articulated valves; dorsal, ventral, anterior, posterior, and lateral views, X 1; USNM 242054; USGS 10c. 1291APC. 16,17. Paratype, fragment of ventral valve; ventral view, X 2, showing elongate pedicle foramen; dorsal (interior) view, X 3, showing elongate tubular pedicle collar, concave surface of disjunct deltidial plates, and lack of dental plates; USNM 242058; USGS loc. l291—PC. 18, 19. Paratype, fragment of slightly crushed ventral valve; dorsal view (inverted), X 3, showing relation of hinge tooth to deltidial plates; anterodorsolateral view, X 2, showing relation of pedicle foramen and hinge tooth; USNM 242059; USGS 10c. 1291—PC. 20. Paratype, fragment of slightly crushed articulated valves, oblique posterior view, X 1, showing relation of ventral beak to hinge; USNM 242060; USGS loc. 12917PC. 21. Paratype, nearly complete articulated valves, ventral beak missing, dorsal view, X 1, showing small acute dorsal umbo; USNM 242055; USGS loc. 12917PC. 22. Paratype, fragment of dorsal valve of apparent immature individual, ventral (interior) View, X 8, showing descending lamella and transverse band; USNM 242056; USGS loc. 12917PC. 23. Paratype, fragment of dorsal valve, ventral (interior) view (stereo), X 2, showing relation of crural processes, inner and outer hinge plates, and median septum; USNM 242057; USGS loc. 1291 —PC. 24. Paratype, fragment of dorsal valve, ventral (interior) view (stereo), X 1.5, showing partial dielasmoid loop with broad descending lamellae and long slender transverse band; USNM 242731; USGS lot. 1291 vPC. 25742. Vex semisz'mplex (White) (p. 10). 25432. Figured specimens, articulated valves, dorsal views, X 1, showing simu- lated growth series and variation in form and radial ornament; USNM 242071, 242072, 242065, 242073, 242074, 242063, 242069, and 242075; figs. 25, 26, 28, and 29 from USGS loc. 12897PC; fig. 27 from USGS loc. M—853; fig. 30 from USGS 10c. 826—PC; fig. 31 from USGS loc. 12847PC; fig. 32 from USGS loc. 78137(Green). 33-36. Paralectotype, articulated valves. (This specimen was serially sectioned parallel to the commissural plane; selected sections appear on pl. 2, figs. 1—5.) 33. Dorsal view, X 1, for scale. 34. Dorsal View, X 2, for comparison. 35. Anterior view, X 2, showing rectimarginate to incipiently unipli- cate commissure. 36. Lateral view, X 2, showing equibiconvex profile and semierect ventral beak. Specimen shown in figs. 3336: USNM 8190b; USNM loc. 9344. 37740. Lectotype, articulated valves, views and magnifications as in figs. 33—36 above, for comparison; USNM 8190a; USNM loc. 9344. 41. Figured specimen, Fragment of articulated valves, anteroventral (interior) view (inverted; stereo), X 3, showing pedicle collar, cardinal process, hinge structures, and nature of dorsal cardinalia; USNM 242081; USGS loc. 1284—PC. 42. Figured specimen, fragment of descending lamellae of dorsal valve, lateral view, X 8, showing elongate crural processes; USNM 242082; USGS loc. 12847PC. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1057 PLATE 1 PORTNEUFIA, RHAETINA, AND VE'X PLATE 2 [The object plane parallax for stereo views is 6°] FIGURES 175. Vex semzlsz‘mplex (White), (p 10) paralectotype, articulated valves, serial peels parallel to commissural plane (peel interval 0.15 mm) X 3, showing ventral valve pedicle collar (p.c.), hinge teeth (h.t.), dorsal valve crural processes (c.p.), descending lamellae (d.l.), and transverse band (t.b.); sections proceed from dorsal to ventral; USNM 8190b; USNM loc. 9344, 677. Plectoconcha aequz’filicala (Gabb) (p. 10), fragment of dorsal valve, ventral (interior) and lateral views, X 3, showing short descending lamellae and wide transverse band of loop, for comparison with figs. 1 5, above; USNM 242083; Leland Stanford Junior University loc. 2532 (Pershing County, Nev., Sonoma Range 1° quad; sec. 21, T. 28 N., R. 39 E.; Tobin Range, north wall of “Keyhole" Canyon, elev. 6,200 ft; Upper Triassic; Collector: S. W. Muller, August 1941). 8727. Obnzbczkz lhayneszana (Girty) (p. 12). 8717. Figured specimens, articulated valves, dorsal views, X 1, simulated partial ontogenetic series, showing size range and variation in shape and form; USNM 242095, 242098, 242100, 242101, 242104, 242105, 242108, 242111, 242115, and 242116; all from USGS 10c. 78977(Green). 18 21. Figured specimens, articulated valves, dorsal, ventral, anterior, and lateral views, X 3, showing low beak, rounded beak angles and sulcate anterior commissure of a mature individual; USNM 242116 (same as fig. 17 above); USGS loc. 7897r(Green). 22, 23. Lectotype, articulated valves, dorsal views, X l, for scale, X 2, showing form and outline; USNM 121558; USGS loc. 74067(Green). 24. Paralectotype, stacked, oriented projections of commissural plane serial peels (peel interval approx. 0.15 mm) of articulated valves, ventral (in- terior) view (stereo), X 5, showing long anteriorly spinose loop; USNM 242135; USGS loc. 7406 (Green). 25. Figured specimen, fragment of articulated valves, ventral (interior) view (stereo), X 8, showing dental plates and pedicle collar in ventral valve, and lack of prominent median septum or inner hinge plates in dorsal valve; USNM 242136; USGS 10c. 78977(Green). 26. Figured specimen, fragment of articulated valves, anterior (interior) view (dorsal valve down; stereo), X 8, showing tight articulation of recurved hinge teeth and sockets, vestigial apical dorsal median septum, and rudi- mentary septalial plates; USNM 242137; USGS loc. 7897 (Green). 27. Figured specimen, fragment of articulated valves, anteroventrolateral view (stereo), X 8, showing anterior spines at junction of descending and as- cending lamellae of loop; USNM 242138; USGS loc. 7897 (Green). GEOLOGICAL SURVEY PROFESSIONAL PAPER 1057 PLATE 2 OBNIXIA, PLECTOCONCHA, AND VEX PLATE 3 [The object plane parallax for stereo views is 6”] FIGURES 1713. Obmbcz'a thaynesiana (Girty) (p. 12), figured specimens, fragments of articulated valves, dorsal views (stereo), X 8, showing development of glossothyropsiform loop through precentronelliform (figs. 173), centronelliform (fig. 4), cryptacanthiform (figs. 577), and glossothyropsiform (figs. 8-13) stages; USNM 2421197242125, 242128, 242129, 2421317242134; USGS loc. 78977(Green). GEOLOGICAL SURVEY PROFESSIONAL PAPER 1057 PLATE 3 OBNIXIA PLATE 4 [Unless otherwise noted, the object plane parallax for stereo views is 6"] FIGURES 1715. Periallus woodsz'densz's, n. gen., n. sp. (p. 17). l. Paratype, fragment of articulated valves, dorsal view, X 1, showing small pedicle foramen, wide beak, and well-defined beak ridges; USNM 242144; USGS 10c. 767PC. 275. Holotype, articulated valves, dorsal views, X l, for scale, X 3, showing form and outline; lateral view, X 3, showing profile and form of commissure; anterior View, X 3, showing rectimarginate commissure; USNM 242140; USGS 10c. 76vPC. 6. Paratype, fragment of ventral valve, anterodorsal View (stereo: object plane parallax 3°), X 3, showing dental plates; USNM 242145; USGS 10c. 767PC. 7—9. Paratypes, fragments of articulated valves, anteroventral views (stereo), X 8, showing variation in relationship of septalial plates and median sep- tum in dorsal valve; USNM 242146, 242147, 242149; USGS loc. 767PC. 10. Paratype, fragment of articulated valves, anterior view (dorsal valve down), X 8, showing distinct pedicle collar, strong dental plates of ventral valve, and strong median septum in dorsal valve; USNM 242148; USGS loc. 76»PC. 11. Paratype, dorsal valve, anteroventral view, X 8, showing individual in which septalial plates do not contact median septum; USNM 242153; USGS loc. 767 PC. 12. Paratype, dorsal valve, ventral View (stereo), X 8, showing differentiation of septalial plates and inner hinge plates; USNM 242150; USGS 10c. 767PC. 13. Paratype, dorsal valve, ventral view (stereo), X 8, showing high crural pro- cesses of mature individual; USNM 242151; USGS 10c. 767PC. l4. Paratype, dorsal valve, ventral view, X 8, showing septalial plates joining median septum to form septalium; USNM 242152; USGS loc. 767PC. 15. Paratype, partial dorsal valve, ventral view, X 8, showing dorsally spinose descending lamella and portion of ascending lamella; USNM 242143; USGS loc. 767PC. 16720. Perz'allus aff. woodsldensis, n. sp. (p. 18). 16719. Figured specimen, articulated valves, dorsal, ventral (interior), anterior and lateral Views, X 1, showing form, outline, and incipient uniplicate commissure; USNM 242154; USGS loc. 78797(Green). 20. Figured specimen, fragments of loop, recovered after etching from within the above specimen, various orientations, X 2.5, suggesting that the loop was zeilleriiform; USNM 242154; USGS loc. 7879 (Green). GEOLOGICAL SURVEY PROFESSIONAL PAPER 1057 PLATE 4 PERIALLU S 9U.S. GOVERNMENT PRKNTING OFFICE; 197946777026/44 fi— [DAYS E 7S 3055, tplication of Landsat Products _ _, Range- and Water-Management Problems in the Sahelian Zone of Mali, Upper Volta, and Niger Prepared on behalf of the Office of Science and Technology, Agency for International Development, U .S . Department of State GEOLOGICAL SURVEY PROFESSIONAL Application of Landsat Products in Range- and Water-Management Problems in the Sahelian Zone of Mali, Upper Volta, and Niger By M. E. COOLEY and R. M. TURNER GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 Prepared on behalf of the Office of Science and Technology, Agency for International Development, U.S. Department of State Landsat imagery can aid in solving problems related to natural phenomena and human activity UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1982 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES C. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging In Publicatlon Data Cooley, Maurice E. Application of Landsat products in range- and water-management problems in the Sahellan Zone of Mali, Upper Volta, and Niger. (Geological Survey professional paper; 1058) Bibliography: p. 1. Range management—Remote sensing. 2. Range management—Sahel. 3. Remote sensing—Sahel. 4. Water- shed management—Remote sensing. 5. Watershed management—Sahel. 6. Landsat satellites. 7. Sahel. I. Turner, Raymond M., jolnt author. II. United States. Agency for International Development. Office of Science and Technology. III. Title. IV. Series: United States. Geological Survey. Professional Paper; 1058. SF85.6.R45066 333.7 78—25686 For sale by the Distribution Branch, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 CONTENTS Abstract Introduction Acknowledgments General procedure Onsite investigation Selection of imagery Geohydrol Savanna vegetation Landsat imagery in relation to range and water " sments River- Tse—tse fly control Bush- Factors affecting the availability of arable land Alluvial flats and small valleys Channel and flood-plain alluvium along the Niger River Laterite duricrusts Accelerated erosion Annual flood of the Niger River Ground-water development in fractured rocks Evaluation and utilization of Landsat imagery Landsat imagery with explanations References cited ogic setting blindness control burning monitoring ILLUSTRATIONS Map of the Liptako—Gourma Authority region and adjacent area in Mali, Niger, and Upper Volta showing principal FIGURE 1. 2. GD 00 ‘4 (D (h 35 co physical features and localities visited during onsite inspections Mean annual precipitation, in millimeters, in parts of Mali, Niger, and Upper Volta (taken from Archambault, 1960, fig. 2) . Vegetation zones in parts of Mali, Niger, and Upper Volta (taken from Keay, 1959) . Photographs taken along the White Volta River showing influence of man’s activities on vegetation and terrain . Photograph showing west side of the Niger River valley near Niamey, Niger . Photographs showing effects of man’s activities around small villages . Photograph of the White Volta River east of Ouagadougou, Upper Volta . Photograph of unattended unchecked brush fire northwest of Bamako, Mali, April 24, 1974 ______________________ . Diagramatic sections of small valleys near Ouagadougou, Upper Volta, and Niamey, Niger, showing distribution of laterite, alluvial deposits, areas of accelerated erosion, vegetation, and ground-water conditions __________ of laterite, alluvial deposits, terraces, and vegetation zones . Photograph of a profile of the gray alluvium exposed in a steep-sided channel near Bamako, Mali ________________ . Generalized profiles across the valley of the Niger River near Bamako, Mali, and Niamey, Niger, showing distribution . Photograph of small bucket-irrigated vegetable gardens along the bank of the Niger River at Niamey, Niger ________ . Photographs of laterite in road cuts near Bamako, Mali . Photographs showing accelerated erosion in Mali and Upper Volta . Low-altitude oblique aerial photograph showing fractures, indicated by arrows, in the Gres Ordovicien (Ordo- vician sandstone) near the Baoulé River northwest of Bamako, Mali . Diagrammatic cross section of Dallol Bosso near Niamey, Niger . lndex map showing the areas represented by the six selected Landsat frames in Mali, Niger, and Upper Volta that are evaluated in this report Landsat Frames: S-1. False-color composite Landsat image (MSS bands 4, 5, and 7 of 1117-10232, November 17, 1972) of the region near Bamako, Mali S-2. False-color composite Landsat image (MSS bands 4, 5, and 7 of 1095—10000, October 28, 1972 near Ouagadougou, Upper Volta S-3. False color composite (MSS bands 4, 5, and 7 of Landsat image 1262—10290, April 11, 1973) of the Baoulé River region northwest of Bamako, Mali S-4. False color composite (MSS bands 4, 5, and 7 of Landsat image 1111-09483, November 11, 1972) of the region near Tillabery, Niger 3-5. Part of Landsat frame 1110~09424, MSS band 5, showing allluvial deposits of the Dallol 80550 and the Niger River valley near Niamey, Niger S—6. False color composite Landsat image (MSS bands 4, 5, and 7 01.1079-10102, October 12, 1972) showing part of the Inland Delta of the Niger River near Tombouctou, Mali , TABLES TABLE 1. Brief description of the stratigraphic units and their utilization by man in areas near Bamako, Mali, Niamey, Niger, and Ouagadougou, Upper Volta 2. Tentative assessment for relating Landsat imagery to selected problems in range and water problems in the Liptako- Gourma countries 3. Distribution of arable land and its relationship to accelerated‘erosion and gray alluvium ________________________ 4. Mean annual discharge at two gaging stations in the Niger River system, southern Mali _________________________ 46 Page 6 14 22 27 Application of Landsat Products in Range- and Water-Management Problems in the Sahelian Zone of Mali, Upper Volta, and Niger By M. E. COOLEY and R. M. TURNER ABSTRACT A brief field investigation during April and May 1974 to evaluate the application of Landsat (formerly ERTS) imagery to range- and water-management problems in Mali, Upper Volta, and Niger shows that imagery can provide general overviews of regions or even entire countries, can be used in areas where few or no good ground surveys exist, can provide a basis for repetitive inventorying and monitoring transient environmental changes on the Earth’s surface, and can aid in solving special problems of disease-vector control or human activity. Specific potential applications of Landsat imagery were identified in river-blindness control, tsetse fly control, bush-burning evalua- tion, distinction of arable from nonarable lands, analysis of problems of accelerated erosion, and monitoring of the annual flood of the Niger River, and of ground-water development in fractured rocks. Introduction As increasing pressures from drought, overgraz- ing, and human population have developed in West Africa, especially in the Sahelian countries (Dalby and Church, 1973; Wade, 1974; Sterling, 1974), the need for repetitive inventory and surveillance of natural resources is becoming more critical. Land- sat imagery provides a valuable tool for detecting, evaluating, and cataloging fixed Earth-resources information as well as for monitoring transient seasonal changes in the environment. Because of the large area (34,000 square kilometers) encom- passed by each frame, Landsat imagery is well suited for obtaining a general overview of a region and is helpful in solving certain problems not re- quiring large-scale imagery. Landsat capability to view the Earth simultaneously and repetitively in four spectral bands chosen to emphasize water and land resources is further reason for anticipat- ing that this satellite can yield valuable informa- tion for managing the resources of the Sahelian region south of the Sahara in West and Central Africa and of other comparable arid regions of the world. Because the data-recording instrument aboard Landsat 1 had ceased operating, images of Africa were not recorded for several months before June 1974. Nevertheless, imagery recorded during 1972 and 1973 proved to be entirely adequate for the objectives of the present work. Landsat 2, however, was launched in January 1975. This satellite could be employed to continue studies such as those undertaken in this project. In the short time since Landsat 1 was placed in orbit in July 1972, considerable interest has been directed to using imagery from the satellite to study the Sahelian region lying to the south of the Sahara in West and Central Africa. The Office of Science and Technology of the Agency for Interna- tional Development (AID), US. Department of State, began a program in 1973 to determine the utility of Landsat products in resource-manage- ment problems of the Sahel. In February 1973, Maurice Grolier, US. Geological Survey, visited Mali, Niger, the Ivory Coast, Senegal, and Mauritania to make preliminary arrangements for a regional remote-sensing workshop planned by AID for later that year. The workshop was held in Bamako, Mali, during April 1973 (Grolier and others, 1974). That same spring, AID sponsored a Landsat-oriented demographic study in Upper Volta and Niger (Reining, 1973). In addition, the Na- tional Aeronautics and Space Administration has supported at least two Landsat investigations of the Sahelian region; N. H. MacLeod, American Uni- versity, has been studying plant growth and annual flooding in the Niger Fliver, and the Republic of Mali has been conducting natural-resources in- vestigations using Landsat imagery. Also under AID sponsorship, a two-man team of Landsat specialists (Jones and Miller, 1974) made a visit during September and October 1973 to assess the possibilities of expanding and strengthening Land- sat applications programs in the three Liptako- Gourma Authority (LGA)1 countries of Mali, Upper Volta, and Niger (fig. 1). The present investigation is an outgrowth of this visit and of additional plan- ning sessions between African and US. officials. As a continuation of its program for furthering the utilization of Landsat products in this study ‘The LGA (more fully, Authority for Integrated Development of the Region of Liptako-Gourme) has the objective of promoting the develop— ment of minerals, energy, water, agriculture, livestock, and fish culture in Mali, Niger, and Upper Volta in the region near the Niger River known as Liptako-Gourma (fig. 1). 2 APPLICATION OF LANDSAT PRODUCTS, MALI. UPPER VOLTA, AND NIGER UPPER VOLTA OCEAN GULF o GUINEA 18° 16 MAURITANA \/__TIL ____~_. / Nioro du Sahel Names and boundary representation are not necessarily authoritative ( "I l} @RY’ ere/1&4 "‘. I Tombouctou 20 00 20 ?° 6° l I l 1 ;I \P~ LGER” \f/r BASSIN DU .. a: sou DAN fi/’ 2 "<3 \ 2 E ‘— \ Dallol Bosso Tillabéry _' ;\ 10° 0 100 200 300 490 590 KILOMETERS If I I I I I I I I o 100 200 300 400 500 MILES EXPLANATION Boundary of Liptako-Gourma Authority (LGA) region lllllIl|IllllllllllllllllllllIlllllllll Route of onsite ground inspection Route of aerial inspection near Bamako by light plane FIGURE 1.—Map of the Liptako-Gourma Authority region and adjacent areas in Mali, Niger, and Upper Volta showing principal physical features and localities visited during onsite inspections. and evaluation of the natural- and human- resources problems of the Sahel, AID requested the US. Geological Survey undertake a project for identification of significant range- and water- management problems that could be studied and evaluated from Landsat imagery. Accordingly, M. E. Cooley, geohydrologist, and R. M. Turner, botanist, both of the Geological Survey, were assigned to Mali, Upper Volta, and Niger from April 12 to May 27, 1974, to carry out the work. The prob- lems evaluated during the writers’ fieldwork includ- ed those associated with use and development of arable land, bush burning, location of villages and heavily grazed stock trails, tse-tse fly and river- inndness control, extent and duration of inunda- tion by the annual floods of the Niger River, and identification of localities favorable for accumula- tion and production of ground water. The results are presented in part in a series of illustrations (figs. S-1—S—6) located at the end of this report showing specifically what can be done with the Landsat imagery in evaluating some of these problems. Acknowledgments The cooperation of many individuals who willing- ly gave of their time and knowledge of the regional problems contributed much to the success of the project. Before departing from the United States, the writers met with Norman H. MacLeod, American University, who shared with them the reSults of his ongoing work with Landsat imagery in West Africa. Charles F. Withington, Geological Survey in Reston, Va., gave freely of his time and office space while the writers were applying enhancement procedures to Landsat imagery of Africa. Many individuals assisted the writers dur- ing their stay in Africa with technical aspects of the project. They are grateful for the help given in Bamako in the fields of botany and geohydrology by Abdoulaye Sow, agrostologist with the National Center of Zootechnological Research. Among others in Bamako with whom they conferred were K. J. R. MacLennan and Eric Carver, who shared with them their knowledge of tse-tse fly life cycles in relation to the vegetation and livestock of the area. In Ouagadougou, John Buursink and Phillip Roark, Comité lnterafricain d’Etudes Hydraulique (CIEH), were helpful in arranging meetings with several informed individuals, in providing pertinent publications, and, particularly Buursink, in con- tributing their knowledge of the area. In addition, the writers conferred with D. A. T. Baldry and Frank Walsh, entomologists with the River- Blindness Control Program; William Morris, Regional Economic Development Service Office, AID, Abijan; Robert Helmhols, CIEH; and Quétian Bognounou, botanist with the Parc Botanique, Centre Voltai'que de la Recherche Scientifique. In Niamey, they conferred with Ian Pattinson, regional officer of the Entente Fund, who gave them valuable information concerning agricultural practices in Niger. During the writers’ stay in the three capital cities, they were briefed and accommodated in numerous ways by the following members of the American Embassy staffs and AID officials who provided amenities and advice that contributed to a successful program: in Bamako, Ambassador Ralph J. McGuire, Vice-Consul David Peashock, Ray Denacourt, and John Garner; in Ouagadougou, Mark Johnson and Don Atwell; and in Niamey, Eugene Chiavaroli, James Hill, and Albert Baron. In addition, Howard B. Helman, American Embassy, Paris, kindly interrupted his schedule at Bamako to confer with the writers and to act as a translator. He also provided the opportunity for one of the writers to fly over an area being examined by tse- tse control specialists. Also in Bamako, Adama Timbo, acting as an interpreter, quickly perceived many of the technical aspects of the work and was able to cope immediately with its complicated ter- minology and concepts. To their African colleagues, the writers express special thanks. Many were already greatly over- worked and yet they received the writers gracious- ly. To the following, the writers are especially in- debted: in Ouagadougou, to Cyr Mathieu Samaké, Director General, LGA,and to Phillipe Kaboré, Chief of the Documentation Center, LGA; and in Bamako, to Aly Dembele, Service de I’Hydraulique, to Sidy Zouboye, National Society for Research and Development of Mining, and to Bakary Touré, Director General Direction Nationale des Mines et de la Géologie. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 3 General procedure As originally conceived, the project was to rely substantially on contributions from those Africans knowledgeable in the land, water, and demographic problems of the Sahelian region. Africans representing the three Liptako-Gourma countries were to meet with the U.S. Landsat specialists, to examine the imagery, and.through basic photointerpretation techniques, to draw ten- tative conclusions concerning various features noted on the images. After this preliminary evalua- tion, onsite examination was to be made of as much terrain as feasible to check earlier inter- pretations and to refine the investigators’ ability to recognize significant terrain features. The writers’ contacts with the Africans, however, proved to be limited, and insufficient time was available for set- ting up suitable joint schedules to examine the im- agery or to make onsite investigations. Conse- quently, the writers proceeded with the Landsat in- vestigation without the level of direct participation by Africans that was originally anticipated. Onsite investigation Because of the short-term scope of the project, the areas selected for study were those easily ac- cessible from the larger cities of the region. These cities are served by air passenger service and by good roads. Six main target sites near Bamako, Mopti, Tombouctou, and Gao in Mali, Niamey in Niger, and Ouagadougou in Upper Volta were selected in advance of the writers’ departure for Africa, and imagery covering the sites was ordered from the EROS Data Center at Sioux Falls, S. Dak. The main effort was concentrated near the three national capitals and on part of the Inland Delta of the Niger River between Tombouctou and Mopti. Of these localities, field checking was done only near the national capitals, where trips of more than 100 kilometers into the countryside were made in vehicles rented locally (fig. 1). Of necessi- ty in a region of limited accessibility, the areas in- spected were along the main highways that lead out from the capital cities. Additional onsite checking was made from the air by means of light planes and during commer- cial jet travel. The area west and north of Bamako, including the Baoulé River and Parc National de la Boucle de Baoulé, was inspected at altitudes be- tween 150 and 200 meters above the ground from a light aircraft. Another flight, made in conjunction with an AID tse-tse control project, permitted view- ing of an area south and east of Bamako. Also, useful information that aided in interpreting the 4 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER imagery was obtained from high-altitude jet air- craft in regularly scheduled flights between the na- tional capitals. These included the flight from Dakar to Bamako, two flights between Bamako and Ouagadougou, a flight from Ougadougou to Niamey, a flight upstream along the valley of the Niger River from Niamey to Bamako with stops at Gao, Tombouctou, and Mopti, and the final flight from Ouagadougou northward across the Sahara to Marseilles, France. Visibility was hindered on parts of these flights by the haze which prevails near the end of the dry season and by high clouds that herald the beginning of the rainy season. Mapping by use of the Landsat imagery was done only at the scale of 1:1,000,000. For further field use, however, scales of 1:500,000 or 1:250,000 are recommended. (The latter scale is the maximum for bulk Landsat imagery.) Selection of imagery Selection of imagery was made from computer printouts obtained from the EROS Data Center. Sufficient time was not available before departure from the United States for the writers to visit the Data Center and to make selections directly from its files, although this would have been the pre- ferred procedure. Approximately 30 different scenes were finally selected providing coverage by several frames around each of the six cities in the LGA region. In some instances, the same areas were covered on two successive dates. Such se- quential views provided opportunity to evaluate ap- plications of Landsat imagery to seasonal changes on the land surface. Most of the Landsat images used were 9- by 9-inch positive transparencies (scale 1:1,000,000). All four spectral bands were utilized, and, in some instances, scene features were enhanced by using diazochrome overlays where band 4 (0.5—0.6 micron) was reproduced in yellow, band 5 (0.6—0.7 u) in magenta, and band 7 (0.8—1.1 u) in cyan. This technique was particularly useful for examining details of the vegetation and for mapping surficial geologic features. Two other types of Landsat data were also employed; they were 9- by 9-inch false-color infrared red com- posites and 18- by 18-inch black-and-white prints of band 5 only (scale 1:500,000). Geohydrologic Setting Mali, Niger, and Upper Volta occupy part of a large relatively stable structural platform that ex- tends across most of northern Africa. The platform is formed principally by Precambrian basement rocks which are discontinuosly mantled by thin sedimentary rocks of Paleozoic to Cenozoic age. imposed upon this broad platform are several gent- ly downwarped sedimentary basins which are bor- dered by low uplands and plateaus (Archambault, 1960). The basins are major features, about 600 km or more across. Mali lies in parts of two of these basins, the Bassin du Soudan and the Bassin du Niger (fig. 1). Niger lies mainly in the Bassin du Niger, and Upper Volta lies in low uplands along the southern flanks of both basins. The Precam- brian basement rocks, including a variety of gran- itic and foliated metamorphic rocks, are exposed mainly in the uplands and plateaus (Marvier, 1952). The Paleozoic and Mesozoic sedimentary rocks crop out along the flanks of the structural basins or lie at relatively shallow depth beneath Cenozoic sedimentary rocks which occupy the central parts of the basins (Archambault, 1960). Mesozoic strata, however, are not recognized southwest of a line trending roughly northwestward through Niamey and Tombouctou. Surficial deposits, principally of Quaternary age, are thin but widespread— occurring mainly as stabilized and active dune- sand deposits, as stream alluvium, including de- posits of the Inland Delta of the Niger River, as scattered terrace deposits, and as widespread Iaterite duricrusts. The Iaterite forms surficial fer- ruginous crusts 1 to 10 m thick over more than 80 percent of Upper Volta, southern Mali, and south- ern Niger and lends a harsh reddish-brown aspect to the landscape. All the consolidated rocks and unconsolidated deposits yield water to some ex- tent, but the principal ground-water reservoirs are in the coarse facies of the Mesozoic and Tertiary sedimentary rocks occupying the central parts of the downwarped basins and in the unconsolidated alluvium, especially the deposits along the Niger River. Additional descriptions of thickness and lith- ology and the associations of the rocks with vege- tation, with ground-water supplies, and with farm and range parameters are summarized in table 1. The LGA countries lie principally in the low (200—650 m above mean sea level) semiarid Sudan and Sahel Savanna and the arid Saharan regions of West Africa where rainfall occurs only during the high-sun months of May to October. The southern parts of these countries receive more than 1,000 millimeters of rainfall annually (fig. 2). Rainfall during the high-sun period has to sustain plant and animal needs throughout the long dry season that lasts roughly from October to May. Bamako and Ouagadougou commonly have a dry season of 5 to 7 months and receive less than 25 mm of rain during this time. At Niamey, Gao, and Mopti, the dry season lasts from 7 to 9 months; at Tombouctou, the dry season is longer than 9 months (Church, 1968). Thus, any prolongation of the dry season or shortening of the rainy season U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 5 18° _p_ _ _ MAURITALVLA/ 'Nioro du Sahel MALI 73> ‘ \ __ __ _ __ __ a,” Didieni Nigel \ ‘3’. Q 1] Tributary l of A Senegal River) Names and boundary Boundary of Liptako-Gourma ’ Authority (LGA) regior>,/ \ representation are not ¢ ( d necessarily authoritative f“ '5" 10° )r IVORY COAST 1 l l 0 100 200 300 400 500 KILOMETERS (7 I l I I l I I I l I 0 100 200 300 400 500 MILES FIGURE 2.——Mean annual precipitation, in millimeters, in parts of Mali, Niger, and Upper Volta (taken from Archambault, 1960, fig. 2). has disastrous effects on the farming and grazing economy of the region. The precipitation decreases northward, and, in northern Niger and in Mali north of Gao, precipitation is less than 200 mm annually. There, rains fall mainly during July and August. Because of prevailing high mean an- nual temperatures (27°—29 °C), evapotranspiration is also high. Therefore, during the dry season, most streams and small reservoirs dry up, soil moisture and shallow ground-water supplies are depleted, and the range vegetation becomes dor- mant. The Niger, the Red, White, and Black Voltas, and the Senegal Rivers draining the Sahelian region of West Africa receive most of their runoff from pre- cipitation that falls on a rather low but broad high- land that extends east-west across northern Guinea, southern Upper Volta, northern Dahomey, and southern Mali. Annual rainfall in this highland commonly ranges from 1,000 to more than 1,250 mm (fig. 2). The Niger and Volta Rivers all empty into the Gulf of Guinea. The Volta Rivers enter the Gulf through Lake Volta in Ghana, but the Niger takes a long circuitous route northward to the edge of the Sahara near Tombouctou, where it bends eastward and then southeastward past Gao and Niamey (fig. 1) on its course to the Gulf of Guinea. The Senegal River flows generally north- westward to the Atlantic Ocean north of Dakar. These three great rivers and their main tributaries are in flood stage during the rainy season; this flooding is commonly referred to as the annual flood. In central Mali, the annual flood of the Niger Fliver spreads spectacularly over much of a vast In- land Delta where flood-retreat farming is practiced extensively (fig. 1). Savanna Vegetation The semiarid savanna vegetation of West Africa, from its southern limit at the Tropical Forest Zone, grades progressively through open woodland to shrubland to its northern limit at the Sahara. The major vegetation communities are oriented as a series of east-west parallel bands in response to the dominant rainfall gradient across Africa. The gradient of decreasing precipitation toward the north is accompanied by a progressive change in the character of the vegetation. To the south, where rainfall is highest, the vegetation comprises tall trees with large evergreen leaves; there is vir- tually no grass understory. This is the true forest. Proceeding northward through 10 or 15 degrees of latitude, these large-leaved forms are gradually replaced by short trees and shrubs which have small often finely divided drought-deciduous 6 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER TABLE 1,— Brief description ofthe stratigraphic units and their utilization by man in the areas near Bamako, Mali, Niamey, Niger, and Ouagadougou, Upper Volta 3 Period Epoch Stratigraphic Distribution and thickness U I Dune deposits near , _ . _ Niamey (dunes were Small discontinuous areas on terraces and slopes nearthe Niger River not inspected in and on broad gentle slopes underlain principally by laterite away other areas) from the river; generally less than 10 m thick. Channel alluvium (otafxtIllgaIrigRlver In wide and braided channels of the Niger River and in adjacent low deposits of the terraces inundated by the annual flood. Inland Delta) Flood-plain Forms terraces generally not inundated by the annual flood; terrace is Holocene aIIUVlUm along 3 to 6 m high (above low flow stage of the river) and from a few Niger B'Ver meters to more than 2 km wide; unit generally thin, in places less (eXClUdlng than 6 m thick, particularly near Bamako where older consolidated deposns 0‘ the rocks are exposed in the river. lnland Delta) Quaternary g Underlies central areas and much of gentle slopes of broad flats and 8 Gray alluvium narrow flood plains along streams in small valleys in uplands away 8‘ from the Niger River; unit is thin and is less than 1 m thick in much (3; of the broad flats; locally unit is more than 3 m thick along streams. .9 ._ 8 E 8 z (1) U i— — — — — Yellowish_buff Exposed on gentle slopes forming broad flats; at many localities, it Pl . (7) alluvium and comprises bulk of alluvium of the broad flats; unit forms conspicu- eistocene ' equivalents ous terrace 5 to 15 m high along the Niger, Senegal, and White Volta Rivers and a lower terrace along some of their tributaries; thickness varies locally, but in places the unit probably is greater than 20 m thick, ‘_ “" —‘ _ '—l Brown alluvium Exposed mainly in the perimeter area of broad flats; thickness is in vicinity unknown. of O a adou ou Pleistocene u g 9 Exposed over about 80 percent of the area on ridges and mesas, on Quaternary Pleistocene Laterite steep slopes, on colluvium or consolidated rocks, over broad plains, and and and on river terraces; also present beneath alluvial deposits; 1.5 to Tertiary(?) Pliocenei?) 10 m thick. Continental Terminal Present only near Niamey (in Bassin du Niger) where it underlies _ Miocene (Archambault 1950) laterite capped buttes, ridges, and broad slopes; 100 to 200 m Tertiary ' thick. Eocene f9 __ — _— ~— _ Cretajceous—Eocen: Not exposed, present only in subsurface of Bassin du Niger near 3 se Wemafv roc s Niamey; more than 400 m thick. 8 Cretaceous undifferentiated Q) E .9 g Ordovician GréS Ordovicien Forms uplands in Bamako area; not present or not recognized in the ,1; (Archambault,1960) other areas; unit generally capped by laterite; 50 to 200 m thick. 0. Precambrian Basement complex Few small isolated outcrops in area. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 TABLE 1 .— Brief description of the stratigraphic units and their utilization by man in the areas near Bamako, Mali, Niamey, Niger, and Ouagadougou, Upper Volta —Continued 7 General lithologic description Utilization by man Ground-water supplies Farm and range Consists of active and stabilized sand dunes; includes many composite dunes and a few climbing and falling dunes; older dunes show a slight amount of consolidation and development of soil. Generally too thin and of too small an areal extent to be a source of ground water; highly permeable sand allows much infil- tration and little runoff from precipitation Extensive local use for crops; main unit farmed between Niamey and Dallol Bosso; when soil and vegetation cover of stabilized dunes are disturbed by cropping, overgrazing, or by natural causes, the dunes are liable to severe wind erosion and blowout activity. Consists chiefly of unconsolidated sandy and silty alluvium; many large sand bars show huge current marks. Deposits are permeable and yield water to shallow temporary dug wells during low flow periods, but annual flooding prohibits development of the unit by permanent wells. Partially utilized in flood-retreat farming and for grazing; unit can be farmed much more intensively Consists of unconsolidated sand and silt con- taining a minor amount of gravel. Yields dependable supplies of ground water to wells because of its proximity to the river; well yields probably are not large be- cause of the general thinness of the unit; larger quantities of water, perhaps suffi» cient for some irrigation, can be obtained by construction of collector wells in the unit. Partially used for farming and for orchards; grass and brush foliage supports consider- able stock; unit comprises best arable land in the Bamako and Niamey areas and can be more intensively developed for farming, with water diverted from the Niger River. Consists of unconsolidated to very slightly consolidated light—gray to grayish-buff clay and silt; contains some sand, little gravel—mainly of grit and small pebbles; contains considerable organic material especially along streams. One of the alluvial deposits supplying small amounts of water to dug wells of villages and fields along small streams; unit proba- bly lies above the watertable in most of the broad flats. Unit is widely cultivated everywhere, but it comprises the only arable land in the up- lands near Bamako and Ouagadougou; in many places, the unit is 30 cm thick, thereby limiting its usefulness for farming, especially to deep plowing even if farm machinery would become available; many villages are situated on the unit because they are clustered in areas where there are shallow water supplies and arable land. Consists of slightly consolidated yellowish- gray, light-brown, or buff clay to silt con- taining considerable sand and little pebble-sized gravel; unit generally is yel- lowish in the Bamako and Ouagadougou areas and brownish near Niamey; as much as uppermost 2 m of unit may show weak development of laterite. Consists of weakly to moderately consoli- dated brownish-gray silt to mainly pebble- sized gravel composed of laterlte detritus; gravel concentrated mainly near the later- ite outcrops;silty and sandy parts are in the downslope areas; at many places, unit is overlain by moderately hard laterite form- ing a layer more than 1.5 m thick. Probably supplies a small amount of ground water to many shallow dug wells con structed in the broad flat areas. Yields small amounts of water to dug wells. Development of laterite in the topmost beds of the unit precludes its use for farming of crops, although the unit supports range grass and browse vegetation; unit proba- bly can support orchards and shade trees; unit is severely sheet eroded especially near villages where land has been sub- jected to extreme overuse by man‘s ac- tivities. Used as rangeland even though many expo- sures are nearly denuded of vegetation and are subjected to severe sheet erosion; lat- erite detritus in unit and associated laterite is excellent for road metal. Consists of several units; each unit has dif- ferent thicknesses, composition, amount of cementation, bedding features, and in- cluded alluvial detritus; generally hard to very hard; more ferruginous near Niamey and Gao than in other areas; older units may be siliceous and contain fractures formed along joints. Part of laterite underlying alluvial deposits apparently yields small amounts of water Figure 9 shows two typical conditions of occurrence of some of the dug wells that have become dry during the past few years. to dug wells; fractures aid infiltration from precipitation through the laterite and into the underlying rocks. Because of extensive distribution, unit forms principal rangeland of the area; excellent as building stone and makes attractive walls; when crushed, used as road metal. In a few exposures that were inspected, unit consists of silty to sandy deposits modified or partly altered during formation of the overlying laterite. Where saturated, unit should yield dependa- ble small to moderate supplies of water to drilled wells. Generally exposed only in steep slopes that are undergoing severe erosion; forms a minor part of the rangeland. Includes, in descending order, the Eocene, Middle and Upper Cretaceous, and Conti— nental Intercalaire (Archambault, 1960); consists of clay to gravel deposits; upper part mainly clay and sand, lower part mainly sand and gravel. Where saturated, unit should yield dependa- ble small to moderate supplies of water to drilled wells. Consists mainly of firmly cemented sandstone that can be divided into several distinct units; units are fractured exten- suvely along joints and small faults. Where saturated, probably would yield small amounts of water to drilled wells; where unit is highly fractured, well yields would be greatly increased. Mainly used for grazing; insufficient amount of soil developed on unit restricts farming. Consists of granitic and metamorphic rocks; some of metamorphic rocks are standing on end; rocks are deeply weathered to more than 15 m in the few exposures in— spected. Weathered part of unit is known to yield small amounts of water to dug wells near Ouagadougou; where rocks are highly fractured, they probably would yield some ground water to drilled wells. Small exposures form minor part of range— land. 8 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGEFI leaves. The changes in leaf morphology and plant stature are accompanied by an increased open- ness of the woody components, the openings bet- ween the woody plants occupied by grasses. The number of thorny species also increases. Terms widely used in West and Central Africa for the dominant transcontinental vegetation zones from south to north are Guinea Savanna, the Sudan Savanna, and the Sahel Savanna (fig. 3). A vegetation gradient comparable to the south- to-north cline of vegetation types can be seen locally within the Guinea and Sudan Zones in changes that proceed from moist river terraces to the relatively dry uplands. River terraces within these regions contain more moisture for the plants than local precipitation alone provides, and the rivers are bordered in many places by narrow strips of tall large-leaved trees whose main areas of distribution lie hundreds of kilometers to the south. The term “fringing forest” has been applied to these narrow strips of dense vegetation. This type of forest is comparable to the “gallery forest” of North America. The present savanna vegetation in West Africa has been exposed to more or less continuous heavy use by man for centuries and perhaps millenia (Hopkins, 1965) and consequently has been altered greatly (fig. 4). Since the late 1960’s 12° 20° 10° 8° l 18" l/\\/.___[L_____~ .Nioro du Sahel 14° ,( Tgibutary Senegal River SENEGAL 12° Names and boundary representation are not necessarily authoritative 10° 0 100 200 300 I l l I I l l O 100 200 SAHARA ./' \ \ 4 v {\kfln/COAST/J: I 400 500 KILOMETERS L I and early 1970’s, all zones of the savanna have been under severe stress from intensified drought conditions, coupled with increased population pressures of man and proliferating domestic herds built up during the 1950’s and early 1960’s, largely with inadequate regard to proper management practices. (A wet cycle prevailed in the region from about 1955 to 1966.) Where lands are cultivated, a combination of cutting, burning, and fallowing is also practiced. This swidden (slash-and-burn) form of agriculture has changed the area of earlier ex- isting dense forest vegetation to its present form of open forest or shrubland. These practices have increased the availability of farmland and rangeland for man’s use but have greatly modified or obliterated the original vegetation of the Sudan and Guinea Zones. Contrary to much of popular opinion, the Sahel vegetation (north of the 450-to 640-mm isohyets) has been less affected by man’s activities than that of the two southern zones where rainfall is greater (Church, 1968). in the Sahel, there is less grass to carry fires, population levels are low, and possibilities for cultivation without irrigation are slight, especially in areas ad- jacent to the Sahara; consequently, the natural vegetation has been modified only by grazing. Ac- cordingly, the savanna areas of most critical con- cern for maintaining a proper balance between the 4° 6° Boundary of Liptako-Gourma Authority (LGA) regicb’ _UPPER _\_ GHANA— h ANINA I I 300 400 I 500 MILES FIGURE 3.—Vegetation zones in parts of Mali, Niger, and Upper Volta (taken from Keay, 1959). U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 9 FIGURE 4.—Photographs taken along the White Volta River showing influence of man’s activities on vegetation and terrain. i“ .g X .g . -, ‘l. A. Vegetation and terrain show little effect of man’s activities during the year ending May 1974. Grass has been moderately grazed, and some branches have been cut from the tree in center middle ground. B. Grass understory vegetation has been somewhat altered by burning. The general absence of soil-holding vegetation allows for minor sheet erosion. 10 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NlGER FIGURE 4.—Photographs taken along the White Volta River showing influence of man’s activities on vegetation and terrain—Continued. ,. «. ‘; . .... ' W» - . f" ,. a” j .1 AG mg} ' _ ex .t‘. j' C. Burning has removed the grass and woody understory vegetation. A few trees have been cut for firewood; trunks and branches larger than about 10 centimeters in diameter are not utilized. The bark on some of the living trees is charred but is thick enough so that the trees are not injured by tires. This area, stripped of its ground cover, is susceptible to accelerated sheet erosion. . . I. l: D. Wood cutting and burning have removed all the vegetation on a low terrace formed from easily erodable yellowish-buff alluvlum. A small village lies just to the left of the picture. The White Volta River lies just off the photograph to the right. Denudation per- mits development of accelerated sheet erosion which soon will be accompanied by severe gullying. natural vegetation and man’s use of the land are to the south, where woodland is constantly being re- placed by grassland, rather than to the north, where the original vegetation has been less detrimentally affected by man. The Sudan Savanna, which lies in a belt 200 to 400 km wide north of the Guinea Savanna, in- cludes trees 8 to 16 m high, many of which belong to the same species found in the zone to the south. Especially common are the doum palm (Hyphaene thebaica), danya (Sclerocarya birrea), and soapberry tree (Balanites aegyptiaca), all of which increase in dominance northward toward areas of increasing aridity and are represented lit- tle or not at all in the Guinea Savanna. Grasses grow 1 to 1.75 m high. Because the grass species in the Sudan Savanna are less course than those to the south, they are more valued as forage and less often deliberately burned (Church, 1968). In the region of Bamako, which lies on the bor- der between the Guinea and Sudan Zones, and Ouagadougou, which is in the central part of the Sudan Savanna (fig. 3), the following geobotanical categories are recognized: (1) alluvial flats and valleys (generally containing ground water with a shallow water table), (2) uplands, (3) slopes of buttes and ridges underlain by laterite and (or) sandstone, and (4) the riverine fringing forest. In each of these categories, the vegetation has been greatly altered by man’s activities. For example, villages in the vicinity of Bamako occur at regular intervals of about 5 to 15 km. The land is heavily cultivated around the villages, and areas between villages usually are cultivated as well. All the un- cultivated vegetation is in some stage of recovery from burning or clearing. Presence of grasses is variable in the Bamako area, as elsewhere in the savanna zones, largely because of local dif- ferences in environment that affect moisture availability for plant growth, differences in the in- tensity of grazing, and in the frequency and timing of bush fires. On the alluvial flats, provided that destruction of the vegetation is not extreme, the first category of vegetation comprises such trees as the shea but- ter tree (Butyrospermum parkil), locust bean tree (Parkia big/obosa), dry-zone mahogany (Khaya senega/ensis), African rosewood tree (Pterocarpus erinaceus), and species of Combretum. Some of these trees, such as the shea butter, are of economic importance and are preserved even in areas of heavy disturbance. Another economically important tree that is closely associated with villages and can be seen standing sentinellike in fields is the baobab (Adansonia digitate). Many of U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 11 the same species that grow on the flats grow on the laterite-capped ridges and buttes (vegetation category 2), where edaphic conditions are drier than on the alluvial flats, but the plants are re- duced in size. In addition, the kapok tree (Bombax costatum), harike (Anogeissus Ieiocarpus), and figs (Ficus species) are present. Along the slopes of scarps, particularly of the buttes and hillslopes, where edaphic conditions are intermediate be- tween the ridge and butte surfaces and the alluvial flats, the vegetation (category 3) is usually denser than that above or below and probably attains 75-to100-percent foliar coverage during the rainy season. Here may be the most northerly habitats for the tse-tse fly. These hill-slope forests, where especially dense, stand out sharply on properly enhanced Landsat imagery (fig. S—1A). The fourth category of vegetation in the Bamako and Ouaga- dougou regions is the riverine fringing forest. A partial listing of the trees in this forest includes a palm (Raphia sudanica), a fig (Ficus capensis), a cola (Cola cordifolia), and malmo (Syzygium guineense). The driest area the writers were able to examine in detail was in the region of Niamey, Niger, which is near the northern limit of the Sudan Savanna (fig. 5). One of the striking differences between the vegetation in this region and that toward the southern limit of the Sudan Savanna near Bamako is the increase in small-leaved species such as the Acacias and in the spiney plants. One of the most common spiney trees is African myrrh (Com- miphora africana). Shrub communities grow on dry sites, dominated by a species of Combretum. The shrub canopy grows to about 2 m in height and is interrupted irregularly by a low tree, the soapberry. In general, the grasses are shorter and much less abundant in the vicinit” of Niamey than in the region of Bamako and Duagadougou. Fringing forests of evergreen erad-leaved trees are absent from this region (and northward), the watercourses being lined by certain drought-deciduous Acacias. As a consequence, intermittent stream courses do not stand out sharply on Landsat imagery taken during the dry season. Landsat Imagery in Relation to Range and Water Assessments In the following sections the writers describe the main applications they discerned for use of Landsat imagery in resolving land-resources pro- blems affecting the people of the LGA countries. In addition, tentative answers to some pertinent questions relative to the use of Landsat imagery in range and water management are given in table 2. 12 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER FIGURE 5.—Photograph showing west side of the Niger River valley near Niamey, Niger. In the foreground, a species of Combretum (dominant) and Pterocarpus (left) on detritus formed from a terrace capped by laterite. This photograph, taken on May 18, 1974, near the end of the dry season, shows many leafless plants, a typical condition for this time of year. Doum palm, soapberry tree, shea butter tree, among other trees, grow on the light-colored sandy terrace deposits and dunes in the background. This area is in the northern (dry) part of the Sudan Savanna zone. Two buttes along the horizon consists of fine-grained “Continental Terminal” semiconsolidated sand and clay capped by resistant laterite duricrust. Three main factors are important in the use of the imagery and to its interpretation: 1. Adequate onsite investigation is essential for accurate identification, mapping, or monitor- ing of geohydrologic, vegetative, and agricul- tural phenomena. 2. Many conclusions concerning hydrologic fea- tures, disease, and insect control must be deduced indirectly from the imagery by ob- serving geologic and vegetational features. For example, shallow ground-water zones and tse-tse fly habitats are not identified by mak- ing direct observations of water and flies; the presence of these is inferred by correlation of conditions observed in the imagery with geo- logical and vegetational features known to be associated with water and flies. Similarly, the extent of arable soils can be determined prin- cipally by relating the occurrence of such soils with geologic features that are readily discernible on the images. 3. The effects of man’s use of the land must also be considered when interpreting Landsat im- agery. In areas visited by the writers, the land around most villages is denuded of grass and forbs as a result of trampling by men and livestock, overgrazing, brush burning, and cultivation (fig. 6). These activities produce ac- celerated sheet erosion and wind deflation, both of which exert a profound effect on the distribution and thickness of arable soils. Lastly, so much of the rangeland has been burned each year or heavily grazed or cleared during the past centuries that no vegetation is left that can be considered as unmodified. River-blindness control River blindness (Onchocerciasis) is a disease of man caused by a filarial worm (Onchocera vol- vu/us). The causative organism is transmitted by a black fly (Simu/ium damnosum). Outbreaks of this disease, which ultimately causes blindness, are common along rivers because the riparian habitat is essential for fly reproduction. Simu/ium eggs are laid in streams or ponds where they hatch. The lar- vae feed by straining microorganisms out of the water; however, slowly moving water carries too lit- tle food to the sedentary larvae, and they starve. Therefore, larvae survive most successfully at sites of fast-flowing water such as rapids or dam spillways (fig. 7). Recently, a multinational effort was initiated to control river blindness (Tomiche, 1974). The ap- proach taken is to kill the larvae at all the breeding sites in an area of 700,000 square kilometers in the Volta River basin. The larvae are killed by dropping U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 13 from the air a specially formulated pesticide into streams at all known breeding sites. Accurate maps are necessary when preparing detailed flight plans for reaching known fly-breeding sites, and the absence of appropriate maps is hampering the programs along the Black Volta River (Frank Walsh, oral commun., 1974). Although Landsat im- agery, because of its lack of sufficient resolution, does not appear useful in locating specific sites of fast water or rapids, it does have potential applica- tion for correctly locating a river system in regions for which maps are poor or incomplete and for identifying small reservoirs that may be breeding sites. The location of dams has become a critical step in the control program because dam spillways often harbor large populations of the fly larva (Tomiche, 1974). The stockwater dams are difficult to keep track of because they may last only a few years and because new dams are constantly being built (fig. S—ZB). Landsat band 7 imagery or color- composite imagery can be especially suited to lo- cating these bodies of water if the reservoirs are larger than about 200 m in diameter (30 hectares in area). For elongate reservoirs, the total area may even be smaller. FIGURE 6.—Photographs showing effects of man’s activities around small villages. A. Newly hand-cultivated field adjacent to a recently dug well (indicated by circular concrete ring) near Ouagadougou, Upper Volta, May 14, 1974. The well obtains ground water from weathered granite, which in this area underlies a surficial man- tle of alluvium and laterite. B. Accelerated erosion along pathway leading through newly planted fields near Ouagadougou, Upper Volta. Erosion was caused by early rains of the 1974 wet season. 14 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER TABLE 2—Tentative assessment for relating Landsat imagery to selected problems in range and water management in the Liptako-Gourma countries (1) Can shallow water tables and zones of ground-water discharge be identified and their areal extent mapped? Shallow water tables are difficult to separate from zones of ground-water discharge on Landsat images because both occur at or near the land surface and both are associated with dense growths of vegetation. Discharge of ground water, however, maintains flow of streams and ponds in stream channels well after the end of the rainy season. Dense growths of vegetation are shown on the imagery along some streams, principally in alluvial valleys, near Bamako and Ouagadougou (figs. 8—1, 8—2; frames 1117—10232 and 1095—10000 taken in October and November 1972, respectively). The heavy growth suggests the presence of a shallow water table and probably ground—water discharge into the stream channels at the time the imagery was taken. For best results in differentiating between the two conditions, imagery taken periodically throughout the dry season should be examined for changes in vegetated areas affected by shallow ground-water discharge zones. (2) Can weathered or fracture zones in the Precambrian crystalline basement rocks, likely to be productive of ground water, be identified? Generally, the Precambrian basement rocks are concealed by laterite duricrust or by a thin surficial mantle of alluvium. Near Ouagadougou, hand-dug wells, penetrating through the laterite, yield small amounts of water (enough for stock, villages, and bucket irrigation of small cultivated plots) from deeply weathered regolith developed in the upper part of basement rocks. This area of low relief is identifiable on the imagery because of the generally light, rather even color tone and general lack of conspicuous drainage features (fig. S-2). Linears identifiable in the imagery in areas of consolidated rocks may be related to faults, fractures, and joints along which water movement and accumulation are facilitated. Weathering in such zones, and especially at points of intersection, would improve the potential for accumulation of important sources of water. (3) Can good sites for surface-water catchments be identified? Sites favorable for small surface-water catchments are widely distributed because of the general low permeability of the older consolidated rocks as well as the younger surficial deposits. Ephemeral lakes and ponds, which are discernible with repetitive imagery coverage, give clues as to locations for potential catchment sites that can be improved by artificial excavation and (or) low earth dams. Constrictions or narrows in stream channels in areas of outcropping consolidated rocks can also be identified to give clues for the location of small dams for surface-water catchments. Larger areas that generally are unfavorable for surface-water catchment sites are mainly those mantled by thick, relatively permeable, dune—sand deposits or those in areas of intensively fractured rock where the water table is at considerable depth. The main dune-sand and principal fractured areas are identified readily on the images (figs. 3—4, 8—63). The smaller areas, where surface-water catchments may not be successful, are on sandy terraces and slopes of the Niger River valley, on the sandy alluvium of at least part of the dallols, and on sandy alluvium along small streams that drain principally dune-mantled areas. The Landsat imagery aids in recognizing these areas, which generally appear light-colored in comparison to adjacent laterite duricrust, consolidated rocks, or the Continental Terminal where capped by laterite duricrust. (4) Can land potentially useful for irrigated crop production be identified? The Niger River valley is, of course, the most obvious choice. Much of the arable land is identifiable on the Landsat imagery and, with onsit inspection, can be mapped in considerable detail using La dsat imagery at a scale of 12250.000. (See section on "Factors affecting availability of arable land.") Only the flood plain ofthe Niger River and the Inland Delta, however, are capable of supporting large-scale farming operations. In these areas, large amounts of water are available for irrigation by diversion from the Niger River and, in the Inland Delta, from the Niger and the Bani Rivers. Supplemental ground water can also be obtained for irrigation in these areas from properly constructed wells. Small vegetable plots can be farmed along the various segments of the braided channel of the Niger River, as for example near Niamey (fig. 12). The braided channel is easily mapped by the imagery (figs. 3—4, 8—5). Analysis of Landsat imagery is useful for inspection, leading to final selection of the channel reaches most suitable for farming throughout the Niger River valley. Flood-retreat cultivation is the principal farming technique practiced by the people living along the Niger River in Mali. It is practiced to a lesser extent in Niger, where this method of cultivation is not well developed (Church, 1973). The lands near the river are seasonally flooded, and, as the floodwaters recede, the farmers use the wetted lands to cultivate a definite sequence of crops: maize, grain sorghum, sweet potatoes, cucurbits, tomatoes, and beans in order from top to bottom on the slopes. Grain sorghum is sown on the gently sloping outer valley floors and rice is sewn on the flattest areas of maximum depth of inundation. Landsat imagery and the capability Landsat provides for repetitive observation make it well suited for determining the maximum limit of flooding, thereby providing a means of predicting crop size in advance of harvest. By knowing a crop yield potential in advance, impending needs and requests for assistance can be tailored accordingly. (5) Can distinctions in the relative seasonal productivity of grass and browse vegetation be made from the imagery? The Landsat imagery is ideally suited for detection of seasonal trends in rangeland plant growth. Qualitative differences can be observed on sequential imagery provided observations are made on enhanced images; for example, color composite photographs or diazochrome overlays. To obtain quantitative data showing seasonal trends, sophisticated ratioing techniques can be used to eliminate the undesirable effects of variables such as haze and sun angle. These techniques require the use of computer-compatible tapes or, if images are used, a video system with a capacity for ratioing and electronic slicing. The ability to detect the density of crops in fields as a measure of crop success and crop yield would be extremely useful (W. Morris, oral commun., 1974) , although the main crops, such as millet and sorghum produce a sparse cover that might be difficult to detect. The time for analysis and degree of sophistication required to assess the applicability of the data for crop-yield estimate was beyond the scope of this project. Work by others, however, indicates that the data can be used to aid in identifying crop types and estimating yields for fields with areas of 32.4 hectares or greater (Wigton and Von Steen, 1973; Morain and Williams, 1973). U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 15 TABLE 2—Tentative assessment for relating Landsat imagery to selected problems in range and water management in the Liptako-Gourma countries—Continued (6) Can areas of relative overgrazing and undergrazing be identified from the imagery? Overconcentration of livestock around existing water points has led to complete denudation of vegetation in many localities. Landsat images clearly show some trails leading to water points as elongate light-colored streaks (fig. 5—3). These were not examined in the field, but it is apparent that the trails appear light colored on the images because of denudation through overgrazing. In support of this, villages are often clearly discernible as light areas (fig. 8-3). The high reflectance at the village sites does result from denudation by overgrazing, wind deflation, and sheet erosion, as well as perhaps other causes. (7) What is the relationship between the laterite duricrust of interfluvial upland surfaces versus grass and browse density? In the absence of perennial water, soils derived from what types of geologic terrains are most conducive to productive grazing and browse lands? Alluvial soils (mainly those derived from the gray alluvium) are the most productive grazing and browse lands. (See section on “Factors affecting availabilityofarable|and.”)Grass and shrub foliage is far denser there than on the adjoining laterite terrain. At many places, the laterite duricrusts form bare wind-swept surfaces nearly devoid of soil and vegetation. The Landsat imagery has been demonstrated to be highly useful in the distinction between alluvium and laterite in the Ouagadougou area (fig. 8—23) and near Niamey and Tombouctou (figs. 8—5, 8—6). More subtle distinctions between the three types of alluvia (brown, yellowish-buff, and gray) will require special Landsat false-color composites. (8). What do Landsat data tell us about desert encroachment as indicated by migrating sand dunes and wind and sheet erosion, accelerated in either the current drought cycle or by antecedent drought conditions? Migrating or active sand dunes do not extend as far south from the Saharan region as do stabilized dunes (fig. S—GB). Stabilized west-southwest—east—northeast longitudinal dunes near Tombouctou are covered by weakly developed slightly reddish-brown soils. These dunes are not now impeding the flow of the Niger River, although they have doubtless influenced the river’s course and flow regime in the past. At present, the river flows through these dunes in one wide main channel as well as in a system of tributary channels, many of which carry water only during the flood seasons. Both the active and stabilized dunes are easily mapped by the Landsat imagery. Denudation of vegetation and concommitant blowout activity can also be recognized on the images. To define and to separate the natural from the man-induced effects—and to determine whether these phenomena are a result of the current drought or the aggregate effects of man’s abuse of the land during previous decades or even centuries—would, of course, require much onsite investiga- tion. Accelerated sheet erosion, including severe gully erosion, is commonly observed in all the areas the writers were able to visit or to discern on the images. (See section on “Accelerated Erosion.”) The present advanced stage ofgully dissection and the large area involved in accelerated erosion strongly suggest that these processes have been in progress for several decades. In the localities visited by the writers, man’s activities in recent decades appear to have aggravated these processes more than have adverse effects of the present drought cycle. Continuous monitoring by Landsat can provide additional information that may be useful in the River-Blindness Control Program. Seasonal changes noted in the flow regime of rivers might indicated conditions favorable for growth of the black fly larvae. According to Malian officials, con- siderable relocation of the village peoples takes place in West Africa, principally because of (1) disease (including river blindness), (2) water prob- lems (from drought and pollution), (3) changing cultivation practices, and (4) superstitions. Large villages are readily discernible on the images, and areas having or lacking small villages are visible (fig. S-3). Thus, repetitive Landsat observations could be made to locate new villages and aban- doned old ones. Tse-tse fly control The life cycle of the tse-tse fly, which is the main carrier of bovine encephalitis (Nagana), has a relationship to the density of vegetation. This rela- tionship is being exploited in a program to eliminate this disease from large tracts of land in Mall. The tse-tse fly is inactive at midday, during which time it seeks shade within nearby forests. The fly can be controlled by spraying small clumps of these forests with insecticides or, where large areas of sheltering forest occur, by Spraying the forest peripheries. The tse-tse fly moves over rather short distances, probably spending its entire life within an area as small as 1 km’. The fly is viviparous, producing a single fully grown larva which crawls to a sheltered spot and then pupates directly without feeding. The pupal stage lasts for several weeks. Spraying with one insecticide ap- plication does not effect control because the killed adult flies are shortly replaced by a new genera- tion that develops from the sheltered pupae. A sec- ond spraying soon after the new crop of offspring emerges is usually effective, however (K. J. R. Maclennan, oral commun., 1974). In attempts to eradicate the fly permanently, a two-step scheme is being practiced. First, a patch of infested forest is isolated by clearing the land around the target area. The barrier of cleared land needs to be wider than the distance the fly normal- ly migrates, or roughly 1 km. After construction of the barrier, the isolated forest patch is sprayed with pesticide in the manner noted above. Hopeful- ly, the combination of these two steps will make areas of forest habitable that must now be avoided. 16 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER Landsat imagery can be used to locate the dense stands of trees, especially in areas where much of the vegetation has been thinned out by human activity. Here, the clumps of dense forest are clearly distinguishable from the surrounding vegetation if viewed at a season when the open mainly cultivated lands are inactive. Figure S—1A shows several areas of dense forest where insec- ticide spraying might be appropriate. Bush-burning monitoring The prime human force in altering vegetation in the Sahel appears to be bush burning, especially in the areas where annual rainfall exceeds 450 to 640 mm. The favorite period for burning is during the terminal stage of the dry season when, with vegetation at maximum dryness, combustion is more rapid and less controllable. Fires also burn hotter and cause greater damage to woody plants and perennial grasses during this period than they do at other times (fig. 8). The burning is wide- spread—from the arable alluvial flats to boulder- strewn slopes and laterite-capped ridges—and contributes to the overall harshness of the country- side. Proposals have been made to abolish or at least to limit bush burning to the early part of the dry season before the vegetation becomes overly dry. Such proposals, however, have not been ac- cepted by the pastoral population because they use the fires primarily to stimulate early leafing of trees and other plants when the livestock are in most critical need of green forage after the long dry season. This is done in spite of the fact that the burning obviously eliminates or reduces the availability of dry grass and forbs and the food supply during the dry season’s crucial terminal stage. FIGURE 7.—-Photograph of the White Volta River east of Ouagadougou, Upper Volta. Small rapids such as those in the middle ground and at the base of the stick dam are a possible habitat for black fly (Simu/ium damnosum) larvae, the insect vector responsible for spreading river-blindness disease (Onchocerciasis). Entire adult human populations over 30 years of age may become blind from this disease. Mud bricks are dry- ing in the sun in the lower right of the picture. An earthen dam extending across the middle ground has been breached by the river. Bush burning evidently has been practiced in Africa for 2,500 years or more (Hopkins, 1965; Church, 1968), and it was used widely during the dominance of the Bali, Songhai, and Ghana Em- pires as long ago as 1,000 years (Church, 1968). The reasons for burning the vegetation are varied: (1) man enjoys watching fire, especially at night, (2) man is negligent, allowing camp and cooking fires to burn unattended, (3) fires are thought to rid areas of parasites such as ticks and, through the clearing of the vegetation, of tse-tse flies, (4) clear- ing sections of the vegetation by burning makes cultivation and travel easier, (5) burning drives game animals from cover, and their capture is made easier, (6) burning stimulates early plant growth, (7) burning makes it easier for stock to graze on new sprouts, which otherwise would be obscured by the old growth, and (8) burning is thought to make it easier for the minerals con- tained in the plants to be returned to the soil. (See section on “Accelerated Erosion”; also, Hopkins, 1965, p. 56). Landsat imagery has several applications to problems where knowledge of the location of re- U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 17 cently burned areas is important. For example, in the event that attempts are made to limit bush burning or to control the season in which it oc- curs, Landsat imagery could be used during the establishment of such programs to detect fire fre- quency (figs. 8—23, 3—3). Bush burning is forbidden by law in some areas, and Landsat imagery could be used to monitor the effectiveness of fire- suppression policies. FIGURE 8.—Unattended unchecked brush fire northwest of Bamako, Mali, April 24, 1974. This small fire, burning through an area where grassy fuel is sparse, probably has a minimal effect on the ecosystem. In other areas where grass is dense, dry- season fires would burn intensely, eliminating much of the woody vegetation. Both lightly and severely burned areas probably would be visible on Landsat imagery. at < I 18 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER FIGURE 9—Diagrammatic sections of small valleys near Ouagadougou, Upper Volta, and Niamey, Niger, showing distribution of laterite, alluvial deposits, areas of accelerated erosion, vegetation, and ground-water conditions. Vegetation F I T ’l Wind deflation near village Accelerated sheet erosion l Dug well Dug well (Marginal to dry) (Permanent water) Water table Deeply weathered—basement rocks A. Diagrammatic section of one of the alluvial flats or of a small valley not having terraces near Ouagadougou. I 1 J Vegetation 2 J F ’l‘ 7) Accelerated erosion (includes wind deflation near village) Gully . erosion Sheet erasuon Accelerated gully Dug well and sheet erosion (Marginal to along edge of terrace Dug well Permanent) Du well Dug well (Permanent water) 9 (Marginal \ to dry) Steep-sided channel Laterite duricrust over consolidated rocks B. Diagrammatic section of a small terraced valley near Bamako. EXPLANATION Nonarable fl :EEIIEEIZEEEEEEEI: Arable gray alluvium, represents extent of Yellowish-buff alluvium and equivalents, Laterite duricrust, generally 1 to 0.5 m arable soil minus the areas mainly un- weakly developed laterite at top of unit thick dergoing sheet erosion where the soil is ‘l‘l‘r‘r‘r‘i’l‘l‘l‘l'i' too thin for cultivation KEY TO VEGETATION Figure 9A Figure 93 (1) Vegetation a low open forest; variable composition depending (1) Many ofthe sametrees asin areas with gray alluvium,but canopy on history of cultivation and burning; trees both evergreen and here more open and height lower. drought deciduous; grasses important element. (2) Where cultivated, scattered baobab, shea butter, and mango (2) Ground cover of grass all but eliminated where erosion is se- trees remain; on fallow land,vegetation highly variable depend- vere; trees and shrubs of original forest less affected. ing on burning and clearing history; trees, both large-leaved (3) Vegetation a low sparse version of that on the alluvial area; evergreen and small-leaved decuduous, dominate; grasses 'm' grasses sparse or only locally abundant. portant. Factors affecting availability of arable land In the LGA countries, arable soils are developed chiefly on deposits of alluvial flats and in small valleys (including the ancient dallols, which are drainage systems developed during the Pleistocene Epoch), bordered mainly by uplands capped by Iaterite duricrusts, on flood-plain deposits along the Niger and Volta Rivers, on alluvium of the Inland Delta of the Niger River, and on eolian deposits of northern Mali and Niger (figs. 8-4, 8—6; table 1). Alluvial flats and small valleys The Ouagadougou area was selected to il- lustrate that mapping of alluvium and Iaterite is feasible through use of Landsat imagery (fig. 8—28). In an area of gentle planar topography at Ouagadougou, the alluvial deposits are thin and lie as discontinuous mantles over Iaterite which is ex- posed mainly on low ridges and stream channels FIGURE 10.——A profile of the gray alluvium exposed in a steep-sided channel near Bamako, Mali. The upper deposit, A, is modern U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 19 (fig. 9A). To the west of the city is a moderately dissected region of flat-topped ridges and interven- ing small valleys containing thin alluvium. Laterite caps the ridges, is present along the slopes of the ridges, and extends across the valleys beneath the alluvium. Because of conspicuous tonal contrasts, the alluvium and Iaterite in the ridge and valley areas are easily distinguished in the imagery. However, tonal contrasts between the alluvium and Iaterite are rather indistinct in the gentle flats to the east near Ouagadougou and are much more difficult to map from the imagery. Admittedly, the mapping would be facilitated by the use of a high- quality Landsat false-color composite instead of the diazochrome overlay with which the writers worked. The writers’ brief field study indicates that the alluvium in the Ouagadougou area consists of an ascending stratigraphic succession of three units referred to informally in this report as the brown, yellowish-buff, and gray alluvia on the basis of sediment deposited during floods. The middle deposit, B, is represented by an immature soil containing considerable plant material as indicated by the dark color. The lower deposit, C, is a slightly consoldiated silt to silty sand which forms the bulk of the gray alluvium. The depth of the channel is about 1.5 m. The channel shows fresh scars from recent cutting. 20 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, their characteristic colors. Where the yellowish- buff and gray alluvia are adjacent to the hard laterite, they contain only a minor amount of coarse detritus derived from the laterite. However, the brown alluvium contains a considerable amount of coarse material near outcrops of the hard laterite and basement rocks. In all localities inspected, the yellowish-buff and gray alluvia are fine grained, have seemingly consistent lithology, and show little variation in grain size. Only the gray alluvium is not altered appreciably by lateriza- tion, and it is the only one of the three types of alluvium that is arable. The other alluvia show enough laterization to preclude cultivation. The gray alluvium, where exposed along many channels and gullies, in partially dissected flood plains near Ouagadougou and Bamako, consists of as least three deposits (fig. 10) which are separated by discrete erosion surfaces that prob- ably represent broad channel cutting. All the deposits are fine grained, except that the upper- most, deposit A, laid down during the past few decades in thicknesses of 0.3 to 0.5 m, is sandier than the underlying medial deposit B. Deposit B, which generally is less than 1 m thick, consists mainly of silt and clay containing some sand and AND NIGER considerable organic material. it appears to repre- sent deposition in a well-watered flood-plain en- vironment, under somewhat moister conditions than those prevailing at present. The lower de- posit, C, is more than 3 m thick, is slightly con- solidated, and consists of layers ranging from silt to silty sand. These layers, in places, show some slight development of laterite. Along many drainageways, deposit C forms a low terrace a few meters high. The gray and yellowish-buff alluvia and their equivalents are widely distributed in the LGA coun- tries, but the brown alluvium was recognized only in part of the area near Ouagadougou. In contrast, deposits correlative with the gray alluvium are present as the uppermost alluvial layer in small valleys and alluvial flats throughout the region. The yellowish-buff alluvium is recognized along the White Volta, Red Volta, and other rivers in Upper Volta. Near Bamako, light-brown to yellowish-gray alluvium—believed equivalent with the yellowish- buff alluvium—occurs along the Niger River (fig. 11A), along the Baoulé River and in small upland valleys between these rivers (fig. 93). The alluvium along these rivers forms a terrace from 3 m to about 5 m high and, except along the Niger River, FlGURE 11,—Generalized profiles across the valley of the Niger River near Bamako, Mali, and Niamey, Niger, showing distribution of laterite, alluvial deposits, terraces, and vegetation zones. Northwest Vegetation 1 ,1 2 Very hard laterite cap containing considerable siliceous material Laterite duricrust on colluvium / Consolidated rocks Laterite duricrust buried by younger deposits Southeast J 3 _J_ Arable land Flood-plain alluvium not now inundated by annual flood Channel and flood-plain alluvium in zone inundated by annual flood Laterite duricrust on terrace deposits . Niger River‘i—l A, Profile of the valley of the Niger River near Bamako. Maximum relief is about 175 m. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 21 FIGURE 11.-Generalized profiles across the valley of the Niger River near Bamako, Mali, and Niamey, Niger, showing distribution of laterite, alluvial deposits, terraces, and vegetation zones—Continued. West Vegetation l<-—1——>l teal l<—1 + 2 + a 4 Ea“ Arable land Flood-plain alluvium Channel and flood-plain not now inundated alluvium in zone inundated by annual flood by annual flood Laterite generally 1 m Laterite covering terrace of thick extends along steep Hard ferruginous cap about rounded gravel deposited by slope as low as 15 m above 1 m thick over porous Niger River. Niamey is river level earthy material (ochre) Sltuated on terrace 9 t010 m thick Side channel of Niger Discontinuous eolian deposits, givergndgy '2‘:- f|1r3t74 farmed at many places me p g Niger River main channel Dike protecting crops from annual flooding Continental Terminal - ....,/' Weathered basement rocks 8, Profile of the valley of the Niger River near Niamey. Maximum relief is about 100 m. EXPLANATION Nonarable I A Arableflood—plain andchanneldepositsof Equivalents of the yellowish-buff al- Preyellowish-buff alluvium terrace de- Niger River luvium; weakly cemented laterite at top posits of unit 1.25 to 2 m thick Laterite duricrust About 10 m thick KEY TO VEGETATION Figure 11A Figure 113 (1) Where soilmantleisthin, plants are confined to fractures and (1) Vegetation in clumps is broken by irregular barren areas; pockets of soil; low forest of kapok, shea butter, danya, and dominant plants are drought deciduous shrubs, trees, and other trees; grasses are less prevalent than in alluvial areas. vines that grow about 6 m maximum height. (2) Vegetation is more dense than on alluvial flats or on mesa (2) Shrubs t0 2 m high dominate; scattered doum palms and tops of buttes; vegetation not as tall as on the flats; trees soapberry trees. include kapok, fig, and many others. (3) Vegetation of areas not now cultivated in various states of (3) Scattered baobab and mango trees on cultivated lands. recovery from farming and clearing; open forest of shea butter, locust bean, and many other trees; grasses are preva- lent. 22 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER Table 3.— Distribution ofarable land and its relationship to accelerated erosion and gray alluvium Physiographic position Distribution of gray alluvium Broad flats Forms a thin mantle on yellowish-buff alluvium and on laterite; gener— ally is less than 1 m thick, but over wide areas is less than 0.3 m thick. Small valleys without terraces Forms a thin mantle on yellowish—buff alluvium; unit is greater than 1.5 m thick in central parts of 'valleys, but is less than 0.3 m on much of the gentle slopes along the sides of valleys. Small valleys with terraces Upland areas near Ouagadougou and Bamako Forms a generally thin somewhat discontinuous deposit on the sur— faces of low terraces and on slopes behind low terraces eroded from the yellowish-buff alluvium; unit usually underlies narrow flood plains that are in front of the low terraces. Reaches of White Volta and Baoulé Rivers and other streams with conspicuous terraces (not including the Niger River) Generally forms thin and discontinuous outcrops on the top of a well—developed terrace which is eroded from the yellowish-buff alluvium or its equivalents; unit underlies a narrow flood plain in front of the terraces, but, at many places, the channel occupies nearly all the bottom lands between the terraces. Valley of Niger River near Bamako and Niamey Generally forms thin discontinuous outcrops on terraces eroded from the yellowish—buff alluvium and equivalents and on higher terraces and slopes; unit covers part of slopes adjacent to the flood—plain deposits of the Niger River. comprises the only conspicuous terrace along these streams. The deposits along the Baoulé River may also be an upstream equivalent of sandy clays, 15 m thick along the Senegal River, de- scribed by Grove and Warren (1968, p. 196). Near Niamey, a light reddish-brown fine-grained alluvi- um, which is believed to be correlative with the yellowish-buff alluvium in the Ouagadougou and Bamako areas, forms terraces roughly 8 to 15 m above the Niger River. At Niamey, the upper part of this alluvium lies on rounded pebble-sized river gravels cemented by ferruginous material. Collectively, the alluvial deposits appear light and the laterite appears dark on both Landsat black-and-white images and on false-color com- posites. The younger gray alluvium has a slightly lighter tone than the other alluvial units on black- and-white images and is light gray to nearly white on the color composites. Thus, its extent, which also represents the maximum extent of arable land, can be roughly delineated. Unfortunately, the scale of 1:1,000,000 is too small to permit showing the gray alluvium as a separate unit on figure 8—28. In areas where the gray alluvium can be differen- tiated from the underlying yellowish-buff alluvium, a fair estimate of the amount and distribution of arable soil can be made, if a sufficient amount of field checking is done. Table 3 summarizes some of the relationships between the amount of arable land and different physiographic occurrences of the gray alluvium. ln localities where the alluvial deposits are not easily distinguishable, only a rough estimate can be made of the distribution of arable soil. In areas where arable soil maps are unavailable, however, any maps, even if only roughly defining the areal extent of the soil, would have some value. Landsat data could be useful in the preparation of such maps. u.s. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 23 TABLE 3.—Distribution ofarable land and its relationship to accelerated erosion and gray alluvium —Continued Distribution of arable land Effects of accelerated erosion Area favorable for cultivation may be small with respect to total area covered by the gray alluvium. Slight sheet erosion and wind deflation around villages and in culti» vated or abandoned fields. Arable land is restricted mainly to central parts of valleys because cultivation is limited in areas where the arable soil is greaterthan 0.3 m thick. Predominantly sheet erosion; severe erosion already has taken con» siderable land out of cultivation; locally, wind deflation is moderate. Arable land is limited mainly to the flood plains, but part or all of the flood plains are inundated by flood flow during the rainy season; in other areas, the arable soil is too thin or discontinuous to be Of much use for farming. Sheet and gully erOsion; gullying and channel dissection locally se- vere; sheet erosion locally severe accompanied by minor wind deflation on top of and on slopes behind the low terraces; the accelerated erosion has taken some land out of cultivation. Little arable soil is available because Of generally limited distribution Of the gray alluvium; reaches of some streams such as the Baoulé River contain almost no arable soil. Severe gullying accompanied by sheet erosion has removed much of the alluvium and locally forms sharply defined badlands. Area of arable soil on the gray alluvium is limited, but adjacent flood- plain deposits Of the Niger River are fertile and are cultivated exten- sively. Sheet erosion generally slight to moderate on slopes underlain by the gray alluvium; erosion generally slight on the flood-plain deposits of the Niger River, except for some gullying along the edges of low terraces formed from these deposits. Channel and flood-plain alluvium along the Niger River Arable alluvial deposits in the valley of the Niger River, excluding deposits of the inland Delta, cover thousands of hectares that are easily discerned on the Landsat imagery. The deposits comprise two broad groups: annually inundated channel and flood-plain deposits and earlier flood-plain deposits normally not flooded by the Niger River. The first group includes silty and sandy alluvium that occurs along the channel and on adjacent flood plains within the zone covered by the annual flooding. On some of the flood plains, fields sur- rounded by dikes to restrain the flood water are being cultivated. In the Gao-Niamey area, the river channel is braided, consisting of a main channel with one or more subchannels. Near Bamako, the river occupies one principal channel which is flanked by broad sandy flats or beveled bedrock slopes, both nearly free of vegetation. The chan- nels are conspicuous features on the Landsat im- ages and are easily mapped on any transparent overlay (fig. 8—4, 8-5). Some farming, mainly of small vegetable gardens, is practiced along the channels during the recession of the annual flood and during the low-flow periods (fig. 12). Such farming is now minor compared to the amount that would be possible if the entire channel system was developed systematically. The small garden plots have the advantage of being easily developed without use of heavy earth-moving equipment. The second group comprises flood-plain alluvium that forms a low terrace (or terraces) not now subject to inundation by annual flooding of the Niger River. These terraces are broad features that extend nearly continuously throughout the Gao-Niamey and Bamako areas. The fertile alluvium forming the terraces is being utilized for 24 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER field cultivation and tree crops, principally mangoes, but it has the potential for more inten- sive development with water diverted from the nearby river. The distribution of this alluvium was successfully mapped from Landsat imagery near Niamey (fig. 8-4, 8—5) and Gao; its general distribution could be easily mapped from the im- agery of other parts of the Niger River basin. Laterite duricrusts Hard reddish-brown to blackish-red laterite, in which iron oxides or hydrates are the most characteristic cementing materials (Cooke and Warren, 1973), has formed nearly everywhere in Up- per Volta and in the southern parts of Niger and Mali. It is present on the summits and slopes of tablelands and ridges, on stream terraces, on gen- tle plains, and beneath alluvial and eolian deposits. The laterite is so prevalent that Ab- doulaye Sow stated that in Mali “any well having a depth of 15 m or more penetrates laterite” (oral commun., 1974). The laterite varies widely from place to place in hardness, thickness, presence of detrital material, and composition. In places, it is thinly bedded, but, in others, it is massive. The detritus incorporated in the laterite is mainly com- posed of fragments of older laterite deposits, but, locally, it also includes rounded pebbles and cob- bles of quartz and other dense siliceous rocks. In the areas visited by the writers, the laterite duricrust is present on Precambrian basement rocks near Ouagadougou, on Gres Ordovicien (Or- dovician sandstone) near Bamako, on Continental Terminal sedimentary rocks near Niamey, on col- luvium and alluvium throughout the region, and on terrace gravels of rounded siliceous pebbles transported by the Niger River near Niamey and Gao. In general, the laterite near Niamey has a greater density, presumably because of a larger amount of iron oxides or hydrates than that near Ouagadougou and Bamako. Brief studies indicate differences in the develop- ment of the laterite duricrust on the alluvial deposits and on the terraces and slopes above the Niger River near Bamako and Niamey (fig. 13). The flood-plain alluvium of the Niger River and the gray ‘9' . y.“ .‘ .. ., , FIGURE 12.—Sma|l bucket-irrigated vegetable gardens along the bank of the Niger River at Niamey, Niger. alluvium in small valleys of the uplands do not show effects of laterization, whereas the yellowish- buff alluvium and its equivalents are associated with a slightly developed laterite that is generally weakly cemented and readily erodable. in contrast, the laterite comprising the main part of the duricrust that mantles slopes and terraces adja- cent to or underlying these alluvial deposits is well indurated and is resistant to erosion. Near Bamako and Niamey, the best developed, most indurated, and thickest (about 10 m) laterite occupies the summits of the highest buttes and ridges border- ing the valley of the Niger River. The physiographic association of the different laterite deposits with buttes, ridges, tablelands, and valleys makes it possible to differentiate and to map many of the deposits by use of Landsat im- agery (figs. S-1A, 3-28). The thickest and most in- durated laterite generally is on the summits of topographic highs—ridges, buttes, and tablelands. These areas appear much darker on the images than the areas of laterite on the slopes of these features but not as dark as areas where the vegetation has been burned recently. The laterite areas on the slopes are partly covered by col- luvium or alluvium, and, collectively, they have a reflectance intermediate between that of the dark- appearing topographic highs and the light-appear- ing alluvial deposits in nearby valleys. Except for those areas underlain by con- solidated rocks, all dark areas on the Landsat im- ages that the writers studied are underlain by laterite. The dark laterite is easily distinguishable from the light tonal expanses typical of alluvial deposits but less easily distinguishable from many exposures of consolidated rocks, even if a con- siderable amount of ground-truth information is available. in general, the consolidated rocks are slightly lighter than the laterites but darker than the alluvial deposits. The consolidated rocks also show much more structural deformation than the laterite surfaces. Many exposures of the con- solidated rocks appear to be “etched” by a pattern of closely spaced fractures. Locally, the rocks are tilted, and the tilted layers may appear as linear and arcuate patterns in Landsat images such as that showing a small area near Tombouctou (fig. S—6A). An intensive and detailed examination prob- ably would reveal other diagnostic features that would aid in distinguishing the laterite from the consolidated rocks in Landsat images. Accelerated erosion Many of the areas underlain by alluvial deposits are undergoing severe sheet and gully erosion ac- u.s. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 25 FIGURE 13.—Laterite in road cuts near Bamako, Mali. ‘ ‘.~~. . b 1. ~ ‘1.- <. A, Portion of a 10-m-thick laterite layer on the summit of a butte 175 m above the Niger River. The cut shows layering with in- dividual layers ranging from about 1 to 30 cm thick. Some layers are very hard and contain much siliceous material. B, Laterite formed on coarse colluvium on the slope of a butte about 20 m lower than the laterite shown in figure 13A. Includ- ed detritus consists of laterite fragments as much as 30 cm in diameter. 26 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER FIGURE 14.——Accelerated erosion in Mali and Upper Volta. A, Advanced sheet erosion in the yellowish-buff alluvium near Ouagadougou, Upper Volta. companied by wind deflation. This erosion unfor- tunately has resulted in the irreplaceable loss of much fertile soil (figs. 63, 10, 14) and already has taken from production considerable tracts of crop- land and rangeland. The principal areas of acceler- ated erosion lie in small valleys of the upland regions and along stretches of the larger rivers. The use of Landsat imagery for identifying such severely eroded areas (fig. 8—20) is an important tool in analyzing environmental problems confront- ing the LGA countries. Gentle slopes of small valleys without terraces (fig. 9A; table 3) have been subjected to severe sheet erosion during the past several decades. The sheet erosion has removed much of the most fer- tile part of the gray alluvium. In places, erosion has removed this alluvium altogether, thereby enlarging the exposures of the nonarable deposits. Man’s activities, especially near the villages, have aided and accelerated the erosion by destroying the natural vegetation through excessive grazing, trampling (fig. 143), cultivation, and bush burning. The removal of the vegetation aids wind deflation which is manifested by accumulations of dust around small clumps of brushy vegetation growing on the nearby slopes and ridges underlain by laterite. In the well-drained terraced valleys (figs. QB, 14A, table 3), gully and sheet erosion takes place on the slopes of the valleys and along stream channels and low terraces toward the centers of the valleys. At many places near Ouagadougou and Bamako, the valleys are in the process of be- ing deepened by downcutting (figs. 10, 140). These large gullies and steep-sided channels are similar B, Accelerated erosion along stock trails resulting primarily from trampling and browsing near Bamako, Mali. Straw hat toward upper right of photograph shows scale. Photograph taken on April 25, 1974, near the end of the 1973—74 dry season. C, Steep-sided channel (similar to arroyos trenched along many drainages in Southwestern United States) about 1.5 m deep cut in soft alluvium. Scour in channel forms a temporary water hole. Picture taken east of Ouagadougou, Upper Volta, on May 13, 1974, near the beginning of the rainy season. to the perpendicular walled arroyos or channels formed since about 1870 along many drainages in the Southwestern United States. The new channels display freshly cut scars, most ranging in depth from 1.5 to 2 m. Generally, the channels are dis- continuous and, fortunately, have not yet caused extensive damage to cultivated land. The channel downcutting would be more extensive if it were not for low stream gradients which tend to retard and localize the process. At places near Niamey, gullies and well-developed vertical walled channels are present along the sides of the Niger River valley. In this vicinity, the channels have been readily incised in loose sandy alluvial deposits. Many areas of badlands, scored by severe gully erosion, border the White Volta, the Baoulé, and other rivers in southern Mali and Upper Volta and are present at places near the Niger River in Niger. Groups of headward-cutting gullies are advancing into terraces and slopes formed principally of the easily erodible yellowish-buff alluvium and its equivalents. In places, the terraces have been nearly obliterated by the gullying. In most places, severe sheet erosion accompanies the gullying. The areas of accelerated erosion are large enough to be easily identified on black-and-white Landsat images or on false-color composites (figs. S-1A, 8—20). The color composites enhance the contrast between the severely and slightly eroded areas, thereby facilitating their mapping. From on- site inspection, the writers observed that the lightest areas on the images, appearing as “bright” areas within alluvium, indicate severe ero- sional activity. The bright areas generally appear as spots or blotches or combine in a somewhat elongate or linear pattern along the eroded edges of terraces. Annual flood of the Niger River The Niger River, the lifeline of Mali, Niger, and much of Nigeria, heads in the highlands of Guinea and the Ivory Coast. Its flow is sustained by pre- cipitation that occurs only during the rainy high- sun months (May-October). The river flows through a wide plain stretching from Mopti to the Detroit Soudanis (Sudanese Narrows) near Gao. This plain of low relief is laced with waterways and is called the Inland Delta of the Niger. The Niger River within the Inland Delta includes a main channel and many anastomosing distributary channels (fig. S-6A), some of which carry water only during high flows. Near Tombouctou, several distributary or overflow channels extend northward and ter- minate in a maze of active sand dunes along the southern margin of the Sahara (fig. S-6B). Throughout the centuries, the shifting of flood- waters in these distributaries has determined where people live and the use they made of the land in the Inland Delta. The flow of the Niger River is sustained during the long dry season (10 months at Tombouctou) by us. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 27 the precipitation that fell during the previous rainy season. Part of this precipitation does not run off immediately and is not evaporated but directly in- filtrates the land surface to recharge the ground- water reservoir. Another important recharge to the ground-water reservoir occurs during the annual flood when large areas are inundated by the Niger for weeks at a time. Slow drainage from the ground-water reservoir helps maintain the river’s flow during the dry season. The time of minimum flow of the river is in April at Bamako and in June at Niamey. From 1954 to 1972, the mean annual discharge ranged from a high of 2,063 cubic meters per second in 1969 to a low of 1,083 m3/s in 1972 (table 4). Beginning in 1970, the mean annual flow of the river has been consistently lower, a manifestation of the major drought cycle that has affected much of Sub-Saharan Africa for the past 5 years. The Niger River has a large annual flood that moves slowly downstream and takes several months to travel from Bamako to Gao, an airline distance of about 1,300 km. The crest of the 1972-73 annual flood after the 1972 rainy season passed Bamako in September, Mopti in October, Tombouctou at the end of November and the beginning of December, and Gao near the end of December 1972 (data from RAF/71-1283, Flood and Drought Forecasting and Warning System in the TABLE 4.—Mean annual discharge at two gaging stations in the Niger River System, southern Mali [Data from RAF/714283, Flood and Drought Forecasting and Warning System In the Niger Rlver Basin, World Meteorological Organlzatlon, Bamako, Mall] Mean annual dlacharge (cubic meters per second) Year Niger River Banl River at at Bamako Mopti 1972 1 ,083 694 1971 1 ,261 1 ,196 1970 1,157 1,139 1969 2,063 1,620 1968 1 ,459 1 ,1 73 1967 1,912 1,333 1966 1 ,438 1 ,472 1965 1,502 1,316 1964 1 ,566 |,622 1963 1 ,559 1 .328 1 962 1 ,832 1 ,61 7 1961 1 ,275 1 ,194 1960 1,657 1,250 1959 1,539 1,284 1958 1 ,502 1 ,483 1957 1,978 1,427 1956 1 ,365 1 ,264 1955 1,981 1,693 1954 1 ,969 1 ,636 28 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, Niger River Basin, World Meteorological Organiza- tion, Bamako, Mali). The progress of the flood crest is especially slow through the Inland Delta where the waters spread across an area about 100 km wide. Many investigators familiar with the Niger River have suggested that its annual flood could be monitored by the use of the Landsat imagery. Figure S-6A was prepared to show the feasibility of monitoring and mapping the annual flood from images. This image shows part of the Inland Delta near Tombouctou and the extent of the flood on October 12, 1972, a few weeks before the max- imum flood stage or extent in this area. Ground-water development in fractured rocks Many consolidated rock terrains in the LGA region are crisscrossed by extensive networks of linear features that can be mapped from aerial photographs as well as from Landsat imagery (fig. S-1B). These linear features indicate that the rocks are fractured intensively in places, such as at the intersections of the main linear features. In such places, the consolidated rocks may have a suffi- cient secondary permeability to contain depend- able supplies of ground water that could be tapped by drilled wells. In the area shown on figure 8—1 of Bamako vicinity, the consolidated rocks are composed mainly of tightly cemented sandstone referred to by Archambault (1960) as the Gres Ordovicien (table 1). These rocks are nearly horizontal or dip gently to the north and northeast. Some of the sandstone members contain a few rounded quartz pebbles, and, at one exposure about 48 km north of Bamako on the road leading to Didieni, the sandstone contains some coarse pebble conglom- erate. At Bamako, part of the sandstone shows some ripple marks and well-formed generally medium-scale current-bedding dipping to the east and northeast that indicates that it was laid down in generally eastward-flowing streams. At Kouli- koro, a sandstone member that also has east- dipping current beds and that probably is the same unit as the one at Bamako is exposed at the base of a high bluff. Above this sandstone member is another sandstone that has large-scale high-angle crossbedding dipping westward. The crossbedding and the generally uniform fine to medium grain size suggest that the sandstone was deposited by winds blowing generally from the east. Yields of wells penetrating the relatively unfrac- tured parts of the Gres Ordovicien probably would be small at best and sufficient only for supplying AND NIGER stock and small villages, but the yields of wells drilled into the fractured zones of the sandstone would be considerable and perhaps could supply comparatively large communities with water. Evidence that fractures locally influence the occur- rence and movement of ground water is demon- strated in two ravines at Bamako. Ground water discharging from fractures in the sandstone sus- tains springs in the Ledo Canyon ravine and, as recently as 20 years ago, sustained a small flow in the shallow ravine near the Bamako Zoo (Abdou- laye Sow, oral commun., 1974). Storage and movement of ground water is clear- ly indicated along the large linear features in the Baoulé River area northwest of Bamako (north- western part of fig. 8—13). The writers inspected this area from a light plane flying less than 200 m above land surface on May 2, 1974, near the end of the 1973—74 dry season. The specific trace of some of the linear features was observed to extend for more than 30 km. Differential erosion of the frac- tured rocks along the linear features has carved small narrow somewhat wedge-shaped canyons along the edges of buttes and ridges. At other places that have a gentle topography, many of the linear features support a growth of vegetation denser than that on the relatively unfractured rocks away from these features (fig. 15). Patches of verdant vegetation were observed at intersec- tions of the large linear features. Inspection from the air disclosed that the channel of the Baoulé River above its confluence with the Bakoye River in the area of Parc National de la Boucle de Baoulé contains large pools of water and short reaches of seemingly perennial flow downstream from the points where the river crosses large linear features; the other reaches of the river were dry at this time. As far as could be ascertained from air reconnaissance, the water in the river’s channel is maintained by the discharge of ground water from the fractured rocks along linear features. Landsat images are especially useful for map- ping the main linear features (fig. 8—18). In areas of high relief, where differential erosion of the rocks is great, the linear pattern is easily dis- cerned, but, in other areas, such as plains underlain by laterite, lineation is much fainter. The linear network provides a key to fracture trends and thus to the possible paths of ground-water movement in the consolidated rocks. Study of the lineations may point to favorable places where ground-water supplies in the consolidated rocks could be developed. Most favorable places would be along lineations representing fractured zones and especially at points of intersecting lineations. u.s. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 29 FIGURE 15.—Low-altitude oblique aerial photograph showing fractures, indicated by arrows, in the Gres Ordovicien (Ordivician sand- stone) near the Baoulé River northwest of Bamako, Mali. The photograph was taken from a light aircraft on May 2, 1974, near the end of the 1973—74 dry season. Dense vegetation in the niche carved in the large fracture suggests presence of permanent ground water at shallow depth. Evaluation and Utilization of Landsat Imagery Landsat imagery provides a valuable source of information required for solving important resource problems of the developing countries in semiarid and arid regions. It displays a view that is unique in its comprehensiveness and its repeatability and gives a quick, convenient, and inexpensive means of examining the Earth’s surface—a means that otherwise is not available to investigators and planners in the Sahelian countries. In essence, the imagery extends the vision of the investigator or planner by furnishing him a synoptic picture of the terrain, drainage network, vegetation, and geo- hydrology of a particular region. Given this general framework of information, the investigator may then choose, if warranted, more detailed methods of examination. Proper interpretation of the im- agery depends, in considerable measure, upon adequate onsite verification and upon the investi- gator’s knowledge and experience in dealing with environmental problems. An important attribute of the imagery is its simplicity—interpretation of the imagery does not require sophisticated photogram- metric equipment or specially trained photo- interpreters. As with any remote-sensing technique, the use of Landsat imagery has certain limitations im- posed by environmental conditions. The most com- monly encountered conditions in West Africa that impose such limitations are as follows: 1. The general evenness of the West African land- scape and the lack of sharp tonal contrast in the imagery limit the usefulness of the im- agery for mapping detail, even with excellent ground control. 2. The imagery provides a view of the land surface only; thus, surficial features such as the wide- spread laterite duricrust or dune-sand 30 mantles may conceal the underlying rocks and obscure many geohydrologic details. 3. Activities of man such as clearing, overgrazing, bush burning, cultivation of fields, and con- struction near villages may obscure natural vegetative and geohydrologic boundaries. 4. In West Africa, the widespread atmospheric haze that is present during much of the dry season hampers Earth-observation studies to some extent. During the rainy season, exten- sive cloud cover poses an additional problem. In spite of these limitations, the imagery can be usefully applied (1) to provide a general overview of a region as well as to serve as base maps in regions where few or no good ground surveys ex- ist, (2) to provide a method for surveying, catalog- ing, and mapping Earth-resources information, (3) to provide a basis for repetitive inventorying and monitoring transient environmental changes, and (4) to aid in solving special problems of disease- vector control or human activity. The Landsat images give an excellent visual im- pression of the landscape, including cultural and environmental features. The images can be grouped in mosaics to provide broad regional or national coverage. Such image maps can be effec- tively used as base maps showing the major drain- age systems and reservoirs and the location and areal distribution of other natural and cultural features. Landsat images give excellent synoptic views of faults, fractures, and other linear geologic features and of the lithologies of older consolidated sedi- mentary and basement rocks, where they are ex- posed. Because of the concealment of these rocks APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER in much of the LGA region and of the generally low relief, the Landsat images are more applicable to mapping of younger surficial deposits. Accom- panied by onsite investigation, the images form an excellent means for preparing small-scale maps showing flood plains, dunes, alluvial deposits, lat- erite duricrust, and accelerated sheet and gully erosion. Areas of arable land can also be deter- mined because of the association of such areas with certain alluvial deposits. In some of the LGA countries, such as parts of Niger, where accurate and complete geologic maps are available, rela- tively little new information concerning rock distri- bution or composition will probably be obtained from the imagery. Nevertheless, in most places, re- gardless of the previous geologic map coverage, analysis of the imagery can contribute to the knowledge of the details of geologic features pre- viously identified by conventional methods. When identified in the imagery, these features provide additional insight into the broad geologic configu- ration of the region. Landsat imagery can be used directly and in- directly to examine hydrologic features of the Sahel. Streams, lakes, and reservoirs are examples of directly observed features. Other features can be largely inferred from the vegetation or geology. Some hydrologic features that may be indentified indirectly include presumed permeable zones along the main linear structural features and at the points of intersection of these features, areas of shallow ground water in flood plains and in dallols (ancient drainages, fig. 16), and sites suitable for surface-water storage or for catchments. ’(————— Arable land —————-)‘ Laterite duricrust of yellowish-buff alluvium dissected by gullies Continental Terminal Terrace formed from equivalent Low terrace formed from alluvium of Dallol Bosso Laterite duricrust Present stream channel of Dallol Bosso Continental Terminal Birni Ngaburé Grey alluvium FIGURE 16.—Diagrammatic cross section of Dallol Bosso near Niamey, Niger. The length of section is about 7 km. The width of alluvium of Dallol 80530 is about 5 km. This section shows about 100 m of vertical relief. Because of almost complete cultivation, the floor of the Dallol Bosso near Birni-Ngaburé supports only scattered trees that have been preserved in the clearing process. Prominent among these trees are the doum palm and the baobab tree. The uplands, only sparsely cultivated because of laterite duricrust, support an open forest of varying composition depending upon soils and history of burning and clearing. Many transient environmental features showing seasonal change can be observed with repetitive Landsat imagery. These features are principally vegetative, but they may have hydrologic implica- tions. Seasonal change in foliation of vegetation is a commonly observed phenomenon on Landsat im- agery. Seasonal differences are especially marked in regions that have fluctuating rainfall and tem- peratures. The use of Landsat imagery to measure regional crop yields during the early part of the rainy season is probably one of the most important applications. Transient hydrologic phenomena such as the stages of rivers in floods or at low flow, inter- mittent streams, fluctuating lake levels, reservoirs, or small ponds can all be identified and their general stages monitored by repetitive imagery. The annual floods of the Niger, Senegal, and Volta Rivers and their larger tributaries should be rather easy to follow as the floods progress slowly down- stream. Within the inland Delta of the Niger River, U.S. GEOLOGICAL SURVEY PROFESSlONAL PAPER 1058 31 knowledge of the exact area inundated by flood- water would be important information upon which to base yield estimates for crops grown after the flood. Repetitive imagery may help locate shallow ground-water bodies that could provide a water supply during part of the dry season. Patches of lush vegetation often indicate areas of shallow ground water, particularly along intermittent streams and in small alluviated valleys, where ground water is discharged. All dark spots or areas shown on bands 6 and 7 of Landsat imagery are worth checking to determine if they are “damp” areas, where the water table is near the land sur- face, or ephemeral lakes or ponds that may not be related to the presence or discharge of ground water. Landsat imagery can be used to assist in disease-vector control programs such as the tse- tse fly and river-blindness control programs. 32 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER Landsat Imagery With Explanations the analyses of the remaining four images were made by using diazochrome overlays for which The following section presents analysis of six band 4 was reproduced in yellow, band 5 in Landsat images 8—1 to 8—6 (fig. 17). The analyses magenta, and band 7 in cyan. Comparisons also of two images were originally made on false-color were made between the false-color composites or composites of multispectral scanner (MSS) bands diazochrome overlays and the black-and-white 4, 5, and 7 prepared at the EROS Data Center, but frames of all four MSS bands. 20°12° 10° 8° 6° 40 21: 00 I l I | I I I | I \ Boundary of Liptako—Gourma . 18° l Authority (LGA) regiony— I ,/’ \ Tombouctou ,/' RiVe’ Nioro du Sahel 16° r \\/ _ _ _ MAUEIIANIA / MALI ‘ ands“ 726240290 6;. , a go éfé300\e ‘ .Didieni 14 , LaWSatim Tributaryo age tsfmega/ ’34 "’740232 . ’Rlver} 9* Koulikoro ”I“ Bamako 9 1, fl 12° \ \J \ . GUINEA “9' 3‘1 SENEGAL Names and boundary ( representation are not MALI necessarily authoritative L P" I 4 10° )r/I\von’v coAST 1 I (Z 190 290 3(30 MPG 590 KILOMETERS [mag fig. 5-3 2&- Q‘ 037 t , A I l | I I I 0 100 200 300 400 500 MILES FlGURE 17.—Areas represented by the six selected Landsat images of Mali, Niger, and Upper Volta that are evaluated in this report. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 33 I 00 I we: N 8 l 3 B B lacuna-"5.2 W ’ l nae?— I 1m C Nia-eim-ae N M757 rss 45 R SUI fi47fi£l§§1lBZ7-R-l-N-D-2L P358 ERTS E-Hlfilm's 81 FIGURE S—1.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1117-10232, November 17, 1972) showing the region near Bamako, Mali. This image shows an excellent panorama of the geohydrologic setting; the drainage network, including the Niger River valley and adjoining ridges and buttes; the vegetation; and many features of the small valleys and alluvial flats. (Approximate scale Is 1:1,000,000.) nah-.2 IWDW too-m 34 APPLICATION OF LANDSAT PRODUCTS, MALII UPPER VOLTA, AND NIGER rm C Nl3~0tmen ”Em/“76? m :, 7 R SUN fiflfiirIfljmefi-PM-D-ZL PM ERTB Wiritmz‘a OI FIGURE S—t .—False-color composite Landsat images (MSS bands 4. 5, and 7 of 1117—10232. November 17. 1972) showing the region near Bamako, Mali. This image shows an excellent panorama of the geohydrologic setting; the drainage network, including the Niger River valley and adjoining ridges and buttes; the vegetation; and many features of the small valleys and alluvial flats—Continued. (Approximate scale is 1:1,000,000.) ”In—[oz u.s. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 35 EXPLANATION S-1A This overlay shows the general distribution of laterite, alluvium, and areas of accelerated erosion (see arrows and also figure 8—2) and illustrates how the imagery can aid the tse-tse fly control program. Alluvial deposits (the gray alluvium and equivalents of the yellowish-buffalluviu m) constitute the light areas ofthe image. In well-drained valleys, the gray alluvium occupies narrow flood plains and appears as a reddish-brown band of vegeta- tion. The lightest areas are those alluvial areas undergoing accelerated erosion. The laterite-capped buttes and ridges and the indurated Ordovician (Gres Ordovicien) sandstone that form these features appear dark. Laterite, partly covered by thin alluvial deposits on slopes and in areas of low relief, has an intermediate tone. The irregulardark areas, showing little rela- tion to the topography, are burned areas. Tse-tse flies require shade during the warm part of the day and seem to prefer large clumps oftrees orcontinuous forest rather than individual trees. Toward the northern edge of the fly’s range, dense groves of trees large enough to support tse-tse populations occur only in special habitats. In the Bamako area, one such habitat of dense groves is along the flanks of laterite- capped mesas. Here one might expect isolated pockets of tse— tse flies. Toward the lower left corner of the image, in an area where rainfall probably reaches a maximum forthe area of the frame, some of the buttes attain altitudes of more than 650 m. Hillslope forests, which developed because ofthe greater rain- fall ofthese elevated lands, are possible habitats of tse-tse flies and appear as thin red patches fringing the elevated laterite- capped summit areas (see arrows). In the vicinity of Bamako and northward, where altitudes are 250 to 300 m lower, the hillslope forests are not developed. EXPLANATION 8—1 B Landsat imagery is extremely useful for mapping linear struc- tural features. This overlay shows the linear features that may affect the movement and storage Of ground water in the con- solidated rocks (Gres Ordovicien) near Bamako. The linear fea- tures, indicating to a large extent valleys, drainage lines, and ridges, trend as straight or slightly curved lines. — _ _ _ _ Major linear structural features __ _ __ _ _ _ Minor linear structural features Intersections of the major linear structures seem to be the most promising places for obtaining adequate ground-water supplies from deeply drilled wells. Inq- rat—ox ICO'W louvre—.3 36 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER A" ‘ Fire Scar? I Lake (drfl‘ / Askeméar) m C Him-l5 N mz-m-n $2.5” R M 51.52 fiZl3l lU-IM'R'ImbmW'Im-S II FIGURE S—2.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1095—10000, October 28, 1972) showing the area near Ouagadougou, Upper Volta. This image was used to map lakes, reservoirs, laterite, alluvlum, and areas of accelerated erosion. (Approximate scale is 1:1,000,000.) ‘ U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 37 EXPLANATION S—2A In the southern part of image 1095—10000, several lakes or reservoirs appear blue, if muddy, and dark purple, if clear. Several lakes shown on a map of the area (Army Map Service map 1501XND3015; ground-checked from 1959 to 1964; scale 1:250,000) are not visible on the Landsat image, presumably because they were dry at the time of the satellite overpass. Other lakes seen on the image but absent from the map are presumably new or were missed at the time ground—checking for the map was done. To be visible on Landsat images, a lake must be more than about 250 m in diameter. Some of the lakes are ringed by white, indicating that grazing and erosion are probably severe near the lake. The large lake near Ouagadougou does not have a white ring because of the dense vegetation that grows along its shore. Spillways for lakes such as those seen on this image may be breeding sites for the fly, Simu/ium damnosum, which carries river-blindness disease (Tomiche, 1974). Because these bodies of water are often temporary and because new stock ponds are constantly being constructed, as for example, in a Peace Corps program in Upper Volta, Landsat imagery could serve as a means for locating these sites, which are potential loci for the spread of river blindness. The tonal contract between the laterite and alluvium is excellent in the northwestern two-thirds ofthe image where the land has moderate relief. In the area oflow relief in the southeastern part of the image near Ouagadougou, the contrast is poor, making differentiation between the areas underlain by laterite or alluvium difficult to discern with either the black-and-white images or with the false-color composite. Areas of low relief may be beyond the limit of Landsat capabilities because of the slight tonal differences in soil-surface color occurring there. The laterite appears dark on the false-color composite or on the black-and-white bands, ofwhich MSS band 7 is the most useful for distinguishing the laterite from the alluvium. The areas underlain by alluvium appear as different light tones, depending upon the amount of vegetation, the amount of foliage at the time of the overpass, the amount of accelerated erosion, and the distribution of the different alluvial deposits. The gray alluvium appears slightly lighter than the other alluvial deposits, but not as lightwhere it orthe other deposits are being subjected to accelerated erosion. Several recently burned areas are visible as dark splotches on the image. These splotches may be distinguished from clear lakes because the burned areas appear less blue and are not confined to low positions in the terrain. (See also figure 8-3.) The area underlain by the gray alluvium represents the only available arable land. In much of this area, however, the gray alluvium is too thin for extensive cultivation (table 3), partly as a result of accelerated erosion. The general distribution of the gray alluvium and of the arable land can be coarsely outlined from this image. In valleys where the gray alluvium underlies a narrow flood plain along the main streams and is subjacent to terraces formed from the yellowish-buff alluvium, the flood plain may support relatively lush vegetation that appears dark on MSS band 5 and reddish-brown on the false-color composite. In the alluvial flats and in valleys lacking terraces, the gray alluvium extends nearly across the alluviated area. toque—.1 Iulm Iwim 38 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER m C mam-15 N NIZ-W-il '21”?! R M m Mill mum-mm“ m mum-mum ll FIGURE S—2.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1095—10000. October 28. 1972) showing the area near Ouagadougou. Upper Volta. This image was used to map lakes. reservoirs, laterite, alluvium. and areas of accelerated erosion—Continued. (Approximate scale is 121,000,000.) 3}" a; -3, . “I'D-“I Ifilm [flim EXPLANATION 8—28 Figure S—2A shows the preliminary results of mapping of the laterite and alluvial deposits in a moderately to slightly dis— sected region shown in the east-central part of this image. Area underlain chiefly by laterite duricrust generally more than 2 m thick on summits of low narrow mesas and ridges and on their slopes. Most mesas and ridges are too small for the laterite on their summits to be separated from that on their slopes. Area underlain chiefly by the brown, yellowish-buff, and gray alluvia. Includes small outcrops of laterite too small to show separately. Area consisting of gentle slopes underlain by laterite duricrust and alluvial flats and valleys underlain by the brown, yellowish-buff, and gray alluvia. Locally, the alluvial deposits may exceed 25 percent ofthe total a rea. The outcrops of laterite and alluvia are too small or too irregular to show separately at this scale. Gentle plain near Ouagadougou underlain by laterite duricrust and thin alluvium consisting of the brown, yellowish-buff, and gray alluvia. Although the gray alluvium may cover more than 50 percent of the area, the deposit is as thin as 20 cm thick in some places. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 39 row-won Uni“: rumor-o: 40 APPLlCATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER m C Him-IS I IlZW-H $.53; R u 9.52 MIG! m-raza-n-mfigl. m m4”! .1 FIGURE S—2.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1095—10000, October 28. 1972) showing the area near Ouagadougou, Upper Volta. This image was used to map lakes, reservoirs, laterite, alluvium, and areas of accelerated erosion—Continued. (Approximate scale is 121,000,000.) calm-.8! loo-W I'd-m EXPLANATION S-2 C Areas of accelerated erosion can be recognized easily on the Landsat black-and-white images or false-color composites. O I." I”.- Dots represent areas undergoing severe sheet erosion. Includes small areas of headward gullying along terraces of the larger streams and areas of scattered severely sheet-eroded alluvium overlying laterite, both of which are too small to be shown at this scale. 'I‘H'l'H‘HH- Area of extensive headward gullying along channels and along terraces formed from the yellowish-buff alluvium. On this image, areas of accelerated erosion have the greatest reflectance and appear as light spots, white splotches, or as features that are irregular, somewhat elongated, or linear. The linear or elongate features represent areas of severe sheet and gully erosion along terraces, whereas the other features are principally areas of severe sheet erosion. The width, depth, or the distribution of the gullies cannot be determined from the Landsat images and must be obtained from onsite inspections or from large-scale aerial photographs. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 41 42 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER New villageh) fl ,1 3“» . , r e .C ‘ O Burned area « .- New village? DSefe . . Abandoned Village? 0 - ‘ Abandoned village? 0 Abandoned Village? ””73 C MAW-I5 N NM-QGW-OB 433‘ R M EL57 92097 lflrm'N-l-a: - m E876 54232-192904 OI FIGURE S—3.—False-color composite Landsat irnage (MSS bands 4, 5, and 7 of 1262-10290, April 11, 1973) showing the Baoulé River country northwest of Bamako, Mali. The image shows burned areas and the distribution of villages. (Approximate scale is 121,000,000.) U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 43 EXPLANATION S—3 Villages can be seen easily on this Landsat image, which shows the region near Nioro du Sahel and Séfé, Mali. The light areas are land from which much ofthe vegetation has been removed by farming and grazing. These denuded areas reflect light throughout all spectral bands to which Landsat is sensitive. Villages are usually somewhere within the denuded areas. Some trails also appear as light-colored strips, presumably because the vegetation along them has been thinned out. To verify that the pattern of light spots seen in the image is produced by villages, a map of all villages within the area shown in this image was drawn from Army Map Service map 130XN029 (scale 1:1,000,000). When compared with the Landsat image, the correspondence between the location of the villages shown on the map and light areas in the image is close, although several villages not on the map appear in the image. Conversely, several villages noted on the map appear from their appearance on the image to have been abandoned. Several large dark areas seen in this image were not in an August 1973 image 1028—10274 (not shown). Although the writers did not visit these areas, they are probably the result of bush fires. In comparing the April 11, 1973, image to an April 29, 1973, image (not shown), additional dark spots were found in the latter image. These spots are presumably areas which were burned over in the 18-day period between the two satellite overpasses. . If attempts are made to limit bushburning or to limit it to a given season, Landsat imagery could be used to detect and monitor fires. North of the area shown in this image, bushburning is forbidden by law in some places, and satellite imagery could be used to aid in administering the bushburning supression policy there. The Baoulé River is barely visible in this image, and inspection of the area revealed the reason. This, and many other streams in the area, lack the fringing forest that is typical of watercourses in the Sahara and other deserts of the world. Instead of a concentration of these typical plants, streamcourses in this region support vegetation that is little different from the vege- tation of the surrounding area. As a consequence, the streams are not accentuated on Landsat images and are difficult to detect. The absence of a concentration of characteristic plant types along watercourses is typical of many Savanna streams and may be the result of burning (Grove, 1973). 44 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER M! NO! zu mmM m 4&2: 7}: a an» em ham méflmm am my: FIGURE S-4.—False-co|or composite Landsat image (MSS bands 4, 5, and 7 oi 1111-09483, November 11, 1972) of the area near Tillabéry, Niger, showing arable alluvium along the Niger River, the principal gune deposits, and small dark areas (A) and drainage that may indicate sources of shallow ground-water supplies. (Approximate scale is 121,000,000.) EXPLANATION 5-4 'A Small dark areas showing on MSS bands 5, 6, or 7 indicate vegetation and possibly damp areas that may indicate shallow ground water. Images 1111—09483 (November 11, 1972) and 1271—09484(May10, 1973, which is not shown) were also used to compare conditions at the beginning and near the end of the 1972—73 dry season. Some of the damp areas, if present, may contain water too salty for human or livestock use because most potable shallow ground-water sources probably would already have been developed by the local inhabitants (John Buursink, oral commun., 1974). A cursory inspection from a commercial jetliner revealed that some of the dark areas appear to be depressions—lined or underlain by dark clayey deposits—which probably act as tanks holding water temporarily. A few of the dark areas contained ponds as of November 11, 1974, and are so noted on the figure. (r //’ —— ) Majordrainagewaysthatappearas darkstrips on MSS bands 5, 6, or 7 of images 1111—09483 and 1271—09484. The dark strips indicate mainly riparian vegetation whose growth is dependent upon ephemeral streamflow and bank and channel storage. In some places, shallow ground-water supplies might be developed along these drainages. ./.'.-/ I /-'--.='/ Channel and flood-plain alluvium undifferentiated along the Niger River. If developed intensively, farm products grown on these deposits could help in alleviating food shortages that occur from time to time in Mali and Niger. Braided channel of the Niger River. Area of extensive eolian deposits (including deposits forming sand stripes). Includes some alluvial deposits. Thickness not known. Area of alluvium, laterite, and consolidated rocks generally not overlain by extensive eolian deposits. Includes the Continental Terminal valley fill deposits. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 45 46 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER immea- ' I l: ' ”Magnum” mm“: ”*mhuwa as FIGURE S-5—Part of Landsat frame 1110-09424, MSS band 5, showing alluvial deposits of the Dallol 80550 and the Niger River near Niamey, Niger. (Approximate scale is 1:1,000,000.) U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 47 EXPLANATION S—5 Some of the most interesting features of the northern Savanna and southern Sahara, readily identified and mapped from the Landsat imagery, are the dallols, which represent ancient and now largely unused drainage systems developed during more humid climatic conditions ofthe Pleistocene Epoch. The dallols are well-known physiographic featu res; they are shown on the geologic map of Niger (Greigert and Pougnet, 1965) and on other maps. The Landsat data provide a convenient method for quickly obtaining information about the size, distribution, and, perhaps, the vegetation and soil cover of the dallols. Only Dallol Bosso, an ancient valley east of Niamey, was inspected during the present investigation (fig. 16). There the alluvium is extensively hand cultivated and grazed. The presence of dug wells indicates that considerable ground water occurs at a shallow depth along the floor of the dallol, although the amount of water in storage and its chemical quality is not known. Comprehensive investigations, including some test drilling, would determine the extent to which the dallols can be developed for agriculture. Alluvial deposits of Dallol Bosso drainage system. The dallols of West Africa drained generally southward toward the Niger River or interior lowlands during Late Pleistocene time. a?" -_./. 2 <4“ Channel and flood—plain alluvium undifferentiated along the Niger River. Braided channel of the Niger River. tuna—.2 “Inna-nu ¢ 1010'“: 48 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER ff”) If“, i Q A. , , x“ 100cm (2 HIS-mi N NIS'W-IT I153; S 7 m FIZIZS‘ Iw-IOS‘I‘NNWP-D-lfigliIMQ-S OI FIGURE S-6.—False-color composite Landsat Image (MSS bands 4, 5, and 7 of 1079-10102, October 10, 1972) showing part of the In- land Delta of the Niger River near Tombouctou, Mali. The image provides a spectacular view of the below-normal 1972—73 flood of the Niger River, lakes and ponds fed by overflow distributaries of the river, broad lowlands or depressions of the Inland Delta that are subject to inundation by normal or above-normal floods, and extensive dune tracts composed of stabilized and active dunes. ‘ (Approximate scale is 1:1,000,000.) ‘—-d— EXPLANATION S—6A An effective application ofthe Landsat imagery is the mapping of floods. From this image, the 1972 annual flood of the Niger River can be readily mapped. Muddy flood waters (blue) are especially conspicuous on the false-color composite and can also be seen clearly on black-and-white images of M83 bands 5, 6, or 7. Extent ofthe annual flood ofthe Niger River on October 10, 1972. The maximum width ofthe inundated area shown atthe bottom of the image is 85 km. W Small distributary channels of the Niger River. Main lowland areas of the Inland Delta subject to inundation when flood crest passes. Outside boundary is indicated by a long dash (——). Approximate area mainly underlain by unconsolidated surficial deposits of dune sand and alluvium of the Inland Delta. Approximate area mainly underlain by consolidated sedimentary rocks. Highly generalized contact between sedimentary rocks and surficial deposits as mapped from the Landsat imagery. ——.—~ I _/ Direction of strike of folded sedimentary rocks. Area masked by clouds and shadows. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 49 .4-|m 50 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER I-‘m ‘; ‘k‘x’g‘w .V. a. I a ‘ I . . "' 100cm c "IO-m2 N Nil-W47 m 5 7 W nzm lI-lm-N-l-N-D-Lhmll FIGURE S-6.—False-color composite Landsat image (MSS bands 4. 5, and 7 of 1079-10102, October 10, 1972) showing part of the Inland Delta oi the Niger River near Tombouctou, Mali. The image provides a spectacular view of the below-normal 1972—73 flood oi the Niger River, lakes and ponds fed by overflow distributaries of the river, broad lowlands or depressions of the inland Delta that are subject to inundation by normal or above-normal floods, and extensive dune tracts composed of stabilized and active dunes—Continued. (Approximate scale is 1:1,000,000.) 02-! .1 t_.__ U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 51 EXPLANATION S—GB Dunes and areas of other eolian deposit types can be identified easily on Landsat images from eitherfalse-color composites or black-and-white images, preferably of M38 bands 5 or 7. In- terpretation of imagery, accompanied by onsite checking, could probably furnish enough information to aid in studies of the southward encroachment of the Sahara and desertification in the Sahel. Stabilized longitudinal dunes trending east to east-northeast (solid-line contact). A reddish-brown soil is developed locally on these dunes. Main areas of sand sheets or sand stripes (dashed—line contact). ////. /// Modern longitudinal dunes trending approximately northeast (dashed-line contact). Erg (shifting sand); lines of the dune crests trend approximately north-northwest (dashed-line contact). .c Area masked by clouds and shadows. 52 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER References Cited Archambault, Jean, 1960, Les eaux souterraines de l’Afrique Cocidentale: Service de I’Hydraulique de l’Afrique OeSte Francaise, Imprimerie Berger- Levrault, Nef-jeg 137 p. Comité lnter-Africain d’Etudes Hydrauliques (CIEH), 1972, (La culture du sorgho de decrue: L’utilisation agricole des eaux de crue en Afrique: Part 3), Société Générale des Techniques Hydro-Agricoles, Ougadougou, Upper Volta, 50 p. Cooke, R. U., and Warren, Andrew, 1973, Geomorphology in deserts: University of California Press. Berkeley and Los Angeles, 374 p. plus index. Church, R.J.H., 1968, West Africa: 6th ed., John Wiley & Sons, Inc., New York, 543 p. 1973, The development of the water resources of the dry zone of West Africa, in Dalby, David, and Church, R. J. H., Drought in Africa, University of Lon- don, p. 62-66. Dalby, David, and Church, R. J. H., eds., 1973, Drought in Africa: Centre for African Studies, University of Lon- don, 124 p. Greigert, J., and Poygnet, R., 1965, Carte Geologique, Republique du Niger. Grolier, M. J., Fary, R. W., Jr., and Gawarecki, S. J., 1974, The Sahelian zone remote sensing seminar and workshop at Bamako, Mali, West Africa, April 17-28, 1973: US Geological Survey Open-File Report, p. 74—196. Grove, A. T., 1973, Desertification in the African environment, in Dalby, David, and Church, R. J. H., Drought in Africa: University of London p. 33-45. Grove, A. T., and Warren, Andrew, 1968, Quaternary landforms and climate on the south side of the Sahara: Geographical Journal, v. 135, June 1968, p. 194-208. Hopkins, Brian, 1965, Forest and savanna: lbadan and London, Heinemann, 100 p. Jones, J. R., and Miller, R. H., 1974, Application of ERTS technology in development programs for the Liptako-Gourma Authority countries (Mali, Niger, and Upper Volta): US. Geological Survey open-file report, 16 p., 1 fig. Keay, R.W.J., 1959, Vegetation map of Africa: Oxford University Press, London. Marvier, L., 1952, Series hydrogéologiques de l‘Afrique Occidentale (map), in Archambault, Jean, 1960, Les eaux souterraines de I’Afrique Occidentale: Service de I’Hydraulique I'Afrique Oeste Francaise, Nancy Imprimerie Berger-Levrault. Morain, S. A., and Williams, D. L., 1973, Estimates of winter wheat yield from ERTS-1, in ERTS-1 Sym- posium, 3d, Washington, DC, Dec. 1973: Pro- ceedings, p. 21-28. Reining, Priscilla, 1973, Utilization of ERTS-1 imagery in cultivation and settlement sites identification and carrying capacity estimates in Upper Volta and Niger: US. Agency for International Development, Contract Report No. AlD/CM/AFR-c-73-21. Sterling, Claire, 1974, The making of the Sub-saharan wasteland: The Atlantic, v. 233, no. 5, p. 98-105. Tomiche, F. J., 1974, Man versus blackfly: World Health, May 1974, World Health Organization, Geneva, p. 20-27. Wade, Nicholas, 1974, Sahelian drought: No victory for western aid: Science, v. 185, p. 234-237. Wigton, W. H., and Von Steen, D. H., 1973, Crop identification and acreage measurement utilizing ERTS imagery: 3d ERTS-1 Symposium, Dec. 10-14, Paper A5, Nat. Aeronaut. Space Agency, p. 87—92. GIRAS: A Geographic Information Retrieval and Analysis System for Handling Land Use and Land Cover Data By WILLIAM B. MITCHELL. STEPHEN C. GUPTILL. K. ERIC ANDERSON. ROBIN G. FEGEAS, and CHERYL A. HALLAM GEOLOGICAL SURVEY PROFESSIONAL PAPER 1059 UNITED STATES GOVERNMENT PRINTING OFFICE.WASI—IINGTON:1977 UNITED STATES DEPARTMENT OF THE INTERIOR Cecil D. Andrus, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 77—600047 For sale by the Branch of Distribution, US. Geological Survey 1200 South Eads Street, Arlington, VA 22202 FIGURE 1. 2 3 4 5 6. 7 8 9 0 1 . TABLE 1. 2. Federal land ownership .......................................................................................... 3. 4. Estimated data volumes, 1975—1981 .............................................................................. CONTENTS Abstract ........................................................................... General system description .......................................................... Source data ........................................................................ Land Use and Land Cover Map .................................................. Political Unit Map .............................................................. Census County Subdivision Map . . . . : ............................................ Hydrologic Unit Map ........................................................... Federal Land Ownership Map . . . . r .............................................. State Land Ownership Map ...... F .............................................. Data volumes ......... ' .............. L .............................................. Data structure ..................................................................... Data capture ....................................................................... Data retrieval ...................................................................... Data manipulation, analysis, and output ............................................. Data manipulation ............................................................. Data analysis .................................................................. Data output .................................................................... GIRAS II, current system design ..................................................... References ......................................................................... ~u ,_. HQU‘PCOWWCOWNNHHIE hi hi >4 hi #4 rd 6: OD be 53 rd hi ILLUSTRATIONS Page General system flow of GIRAS .................................................................................... 3 . Topological elements of a polygon map ............................................................................ 5 . GIRAS file structure ............................................................................................ 6 . Map header control points ....................................................................................... 7 . Graphic output procedures for GIRAS ............................................................................. 10 Arc-to-polygon program sequence ................................................................................. 11 . Island routines within the arc-to-polygon program ................................................................. 11 . Final arc-to-polygon error-checking sequence ...................................................................... 12 . Design features and contrasting capabilities of GIRAS I and GIRAS II .............................................. 14 System flow diagram of GIRAS I and GIRAS II .................................................................... 15 TABLES Page US. Geological Survey land use and land cover classification system for use with remote sensor data ..................... 2 4 Data volumes of a sample of digitized map overlays ................................................................ 4 5 In GIRAS: A GEOGRAPHIC INFORMATION RETRIEVAL AND. ANALYSIS SYSTEM FOR HANDLING LAND USE AND LAND COVER DATA By WILLIAM B. MITCHELL, STEPHEN C. GUPTILL, K. ERIC ANDERSON, ROBIN G. FEGEAS, and CHERYL A. HALLAM ABSTRACT The US. Geological Survey is currently producing land use and land cover maps and associated overlays (e.g., political units) for the United States. These maps are being digitized, edited, and incorpor. ated into a digital data base. The data will be available to the public in both graphic and digital form, and statistics derived from the data will be published. To accomplish these tasks the Geographic Infor- mation Retrieval and Analysis System (GIRAS) has been designed and developed. GIRAS is designed to accept digitizer input, provide comprehensive editing facilities, produce cartographic and statistical output, permit retrieval and analysis of data, and exercise data base management tasks. The editing and output procedures are currently operational and utilize an arc segment, polygon approach in a pro- duction mode. The system incorporates facilities for gridding the polygon data to make it compatible with grid-based data sources. Current system development is focused upon an interactive data base to enable immediate retrieval and display of map information. Users will be able to search for either locations or attributes and display results in a graphic or tabular form. GENERAL SYSTEM DESCRIPTION The accelerating need to facilitate the rational plan— ning, management, and utilization of natural resources and the environment in the United States has been linked, in recent years, with an accompanying need for improved techniques and methods for the storage, analysis, and display of large quantities of spatial en- vironmental data. Concomitant with these needs, rapid developments in the past decade in computer tech nology and in the applications of computers to environ- mental and natural resources data handling have pro- moted the creation of increasingly sophisticated spatially-oriented information systems. Understanda- bly, those agencies of the Federal Government, plan- ning bodies in the regions and States of the United States, and the private sector which are concerned with the planning and management of the nation’s environ- mental and natural resources are likely to be in the vanguard of those system developments. Early in 1976, for example, more than 50 system activities in the US. Geological Survey were specifically concerned with gathering and handling spatial information in the fields of geology, geography, topography, and water resources. The Geographic Information Retrieval and Analysis System (GIRAS) is one such system. It has been designed to input, manipulate, analyze, and output digital spatial data developed for the land use and land cover mapping and data compilation program of the US. Geological Survey. The program is designed to pro- vide systematic and comprehensive collection and analysis of land use and land cover data on a nation- wide basis. In addition to the land use and land cover maps at scales of 1:250,000 and 1:100,000, associated maps are compiled showing hydrologic units, political units, census county subdivisions, Federal land owner- ship, and in some instances, State land ownership. GIRAS comprises three basic subsystems to handle that data: (1) Data input, (2) data retrieval and manipulation, and (3) data output. It incorporates a data base structure designed specifically for handling spatial data and provides comprehensive facilities for data editing, data manipulation, and graphic and statistical output. The initial development and current production mode of GIRAS I uses standardized batch computer routines for input and output processing. The general system flow of GIRAS I is shown in figure 1. GIRAS I is a batch-oriented sequential system on which development began in 1973. Initial emphasis was on the editing and correction of digitized land use and associated data bases, the assemblage of simple archival data files based upon individual 1:250,000 topographic quadrangles, and the application of rudi- mentary data retrieval routines to produce “standard- ized” statistical listings and plotter graphics. The driv- ing force of that initial emphasis was the clear need to provide basic standard statistics to the cooperating agencies. These included the Louisiana State Planning Office, the Florida State Planning Office and ten regional planning councils in the State of Florida, the Ozarks Regional Commission, and various Kansas State agencies. The recognition of the relevance and ap- 1 2 GIRAS: A GEOGRAPHIC INFORMATION RETRIEVAL AND ANALYSIS SYSTEM plication of up-to-date land use, political, hydrologic, census, and Federal and State land ownership data which could be stored, manipulated, and retrieved through modern computer-aided techniques have developed in the direct relation to the sophistication of planning organizations, their exposure to geographic information systems, and the availability of new plan- ning data. The initial reaction— and the initial re- quirement — of cooperative users was for statistics and graphics that can be produced by the most basic of geographic information systems. Areal data and associ- ated attributes are transformed to a fixed grid system which can produce simple composites of graphic data and simple tabular listings. This report describes the facilities and procedures of GIRAS I, a batch-oriented operational system. Sections of this report that follow describe in more detail the source and characteristics of the data being processed in GIRAS I, the data structure being used, the pro- cedures for data capture and editing, data retrieval, data manipulation, and data output. The final section of the report describes the system design features that have been established for the interactive GIRAS II which has been under development in parallel with GIRAS I since 1975. SOURCE DATA The basic set of data presently produced in the program includes: Land Use and Land Cover Map, Political Unit Map, Hydrologic Unit Map, Census County Subdivision Map, Federal Land Ownership Map, and State Land Ownership Map (optional). 939999.10!" LAND USE AND LAND COVER MAP The basic purpose of this map is to provide land use and land cover data to be used as a data source in itself or in combination with the other data sets produced in the program. One of the basic sources for land use com- pilation is the NASA high-altitude U—2/RB —57 aerial photocoverage, usually at scales smaller than 1:60,000. The 1:250,000-scale topographic map series is used as the base map for the compilation of the land use and land cover and the associated overlays, with the excep- tion that the 1:100,000-scale topographic map base is used if that base map is available at the time the data set is released to the open file by the Geological Survey. Although compilation of land use and land cover is per— formed on a film—positive base enlarged to approx-~ imately 1:125,000, digitizing is performed at 1:250,000. The associated overlays are both compiled and digitized at 1:250,000. TABLE 1. —— US. Geological Survey Land Use and Land Cover Classification System for use with remote sensor data Level I Level II Residential Commercial and services 1 3 Industrial 1 4 Transportation, communications, and services 1 5 Industrial and commercial complexes 16 Mixed urban or built-up land 17 Other urban or built-up land 1 Urban or built-up land 11 12 2 Agricultural land 21 Cropland and pasture 22 Orchards, groves, vineyards, nurseries, and ornamental horticultural areas 23 Confined feeding operations 24 Other agricultural land 3 Rangeland 31 Herbaceous rangeland 32 Shrub and brush rangeland 33 Mixed rangeland 4 Forest land 41 Deciduous forest land 42 Evergreen forest land 43 Mixed forest land 5 Water 51 Streams and canals 52 Lakes 53 Reservoirs 54 Bays and estuaries 6 Wetland 61 Forested wetland 62 Nonforested wetland 7 Barren land 71 Dry salt flats 72 Beaches 73 Sandy areas other than beaches 74 Bare exposed rocks 75 Strip mines, quarries, and gravel pits 76 Transitional areas 77 Mixed barren land 8 Tundra 81 Shrub and brush tundra 82 Herbaceous tundra 83 Bare ground 84 Mixed tundra 9 Perennial snow ice 91 Perennial snowfields 92 Glaciers Land use and land cover compilation is based upon the classification system and definitions of Level 11 land use and cover as shown in table 1. All features are delineated by curved or straight lines which depict the actual boundaries of the areas (polygons) being described. The minimum size of polygons depicting all urban and built-up land (catego- ries 11—17), water (51—54), confined feeding (23), other agricultural land (24), and strip mine, quarry, and gravel pit (75) categories is four hectares. All other categories of land use and land cover have a minimum polygon size of 16 hectares. Those sizes are also con- sidered the minimum sizes to which polygons are digitized. In urban and water categories, the minimum width of a feature to be shown is 200 meters; that is, if a square with sides 200 meters in length is delineated, the area will be 4 hectares. Although this minimum- width consideration precludes the delineation of very SOURCE DATA 3 DATA CAPTURE \ DATA EDITING - STATISTICS \ / RUDIMENTARY DATA RETRIEVAL GRID DATA ARCHIVES COMPOSITING GRAPHICS FIGURE 1. — General system flow of GIRAS. narrow and very long 4-hectare polygons, triangles or other polygons are acceptable if the base of the triangle or minimum width of the polygon is 200 meters in length, and the area of the polygon is 4 hectares. For categories other than urban and water, the 16-hectare minimum size for delineation requires a minimum width polygon of 400 meters. Line weight for delineat- ing land use and land cover polygons and for neat lines is 0.10 mm at the production scales of 1:250,000 or 1:100,000. POLITICAL UNIT MAP The Political Unit Map provides a graphic portrayal of the county and State boundaries and is compiled using base maps at either 1:250,000 or 1:100,000. Source material for the Political Unit Maps is from Bureau of the Census unpublished maps entitled “County Subdivisions— Townships and Places” and from the “Geographic Identification Code Scheme” and the “County and City Data Book,” both Bureau of the Census publications (US. Bureau of the Census, 1972a and b). The “County Subdivisions— Townships and Places” maps are also used to separate Census County Subdivisions into Census Tracts. State and county political subdivisions are encoded with a five-digit num- ber in accordance with the Geographic Identification Code Scheme with the exception that nontracted “inde- pendent cities” in Maryland, Missouri, Nevada, and Virginia are given an eight-digit code reflecting the State and city codes. CENSUS COUNTY SUBDIVISION MAP This map provides a graphic depiction of Census Tracts in Standard Metropolitan Statistical counties and Minor Civil Division or equivalent boundaries in non—Standard Metropolitan Statistical Area (SMSA) counties. The overlay is digitized in the same manner as the other overlays and is based upon a Bureau of the Census publication entitled “Census Tracts” for the SMSA covered by the sheet being compiled (Bureau of the Census, 1972a) and a Bureau of the Census publica- tion entitled “Geographic Identification Code Scheme” (Bureau of the Census, 19720). Census tracts are en- coded with a four-digit number which is unique for each SMSA and a five-digit number which is unique for each census tract. Minor civil divisions are encoded with an eight-digit number: the first two digits are the State code, the next three are the county code, and the last three are the minor civil division identifier. HYDROLOGIC UNIT MAP The Hydrologic Unit Map provides a reference for statistics published by the US. Geological Survey and is based upon Hydrologic Unit Maps together with the list “Boundary descriptions and name of region, subregion, accounting units, and cataloging unit.” The hydrologic units are encoded with an eight-digit number which in- dicates the hydrologic region (first two digits), hy- drologic subregion (second two digits), accounting unit (third two digits), and cataloging unit (fourth two digits). FEDERAL LAND OWNERSHIP MAP The US. Geological Survey has the responsibility to research, obtain, and format maps, plots, and other descriptive data relating to Federal Land Ownership. Minimum size for the delineation is 16 hectares and ownership is encoded according to the agencies shown in table 2. STATE LAND OWNERSHIP MAP In some instances in which the US. Geological Survey has a cost-sharing cooperative agreement with a specific State, a map overlay showing an inventory of State-owned land is produced from data furnished by GIRAS: A GEOGRAPHIC INFORMATION RETRIEVAL AND ANALYSIS SYSTEM TABLE 2. — Federal land ownership selected samples of 1:250,000 map quadrangles. The Code Agency statistics show the numbers of arcs and digitizer coordi- Departmentongricultui-e nates input to the system as a result of digitizing as well 11 Agricultural Research Service as the numbers of arcs and coordinates output after a 1% 52:22: 32:31:: Iggggggl 2:22:52“) data reduction process in the editing stage. In addition, the number of polygons and the arc line lengths for the Department “Commerce quadrangles are shown. The high, low, and average 21 National Oceanic and Atmospheric Administration counts and measurements are also shown for each. The most dramatic variations indicated are the Department of Defense digitizer coordinates reduced in the editing process 3; 2“ Force while not basically affecting the number of arcs. The rmy . 33 Army (Corps of Engineers—Civil Works) greater complex1ty of the land use and land cover maps 34 Navy is demonstrated by the average number of polygons recorded for them as compared to those recorded for 41 B0 31°”:mem :3” ”“3"" other overlays. Equally instructive is the wide high and nnev1 e ower ministration - - - 42 Bureau of Indian Affairs (does not include Indian 19w vanatlons In the number 0f p01y gons and the are 43 B lands hfeLd 11:1 17131813) line length for quadrangles sampled. 44 33:22: 3f Mailies anagement Data volumes for the initial 9-year period of the land :2 gugeaugweglafmgéion (N 1W d f Re use and land cover mapping program have been esti- is an i i e rvice ationa il li e fu e) ' ' ‘ ' ‘ 47 National Park Service (National Monument, g mated by usmg the average length of are lines digitized 48 N Seashoripe, afilg Recreational Areas) for land use and land cover and the associated overlays a "ma ar emce (Natmnal Park) in conjunction With the mapping schedules presently Dewnmemowumce planned for the program. Another estimate of the data 51 Bureau of Prisons volume is provided by the numbers of input coordinate Department, 01'5“” TABLE 3. — Data volumes of a sample of digitized map overlay 61 International Boundary and Water Commission, US. categories and Mexico Number of maps in sample Average High Low Department of Transportation Land use ”“1 Land Cover 71 Federal Aviation Administration Input arcs .................... 24 6,333 17,778 980 . . . . 0 t t ................... 24 6,296 17,543 967 72 Federal Railroad Administration iniiliucoalirriisinaies . 24 780,415 1,627,464 97,768 0 t t d‘ t .i 24 131,136 305,916 15,954 73 US" Coast Guard Pdllypguoncso‘lll m is, .. 20 2,402 9,856 392 Arc line length (mm) 24 56,337 102,743 7,290 Other Agencies Political Units 81 Energy Research and Development Administration Input arcs .................... 20 34 78 5 82 General Services Administration _ glm‘ll’t‘figrffmé-‘és' """""""" 33 45 8?; 77 6;; 2 26; 83 National Aeronautics and Space Administration o‘fiput coordinate; ‘ ' 2o 3:049 7:458 '792 84 Tennessee Valley Authority Polygons ........... 18 13 27 3 85 Veteran’s Administration Arc line lengths (mm) 15 4,521 6,985 813 Census County Subdivisions Input arcs .................... 21 394 1,318 31 Output arcs .............. 22 5 fig: 23;,283 10 93%; ' ' ' I t d‘ t i . . . i . i . 22 11 , , , the State. Although this overlay is compiled to the same gagugz‘gggmgfes .1 22 9,462 19,226 2,036 P l . ........... ,. 20 14 . 81 2 base map as used for the other overlays, the polygons Aficyfiffe‘jengthmm, ,,,,,,,,,, 20 “£08 20576 1,753 are encoded according to the referencmg system used Hydrolofiwnm by the particular State. Input arcs .................... 21 30 52 10 Output arcs .............. 21 31 52 10 Input Coordinates .. ...... 21 55,566 82,480 10,582 Output coordinates i 21 9,469 7,084 714 Polygons ............. , . 20 11 17 5 DATA VOLUMES Arc line length (mm) ,,,,,,,,,, 16 5,140 7,889 940 Federal Land Ownership The digitizing operation of the GIRAS has been func- 3‘1“?“ -------------------- fig 3; 1:3 1 . , _ . . u pu arcs .............. tional s1nce mid-1975. The records of the data-editing Inputcoordirxates u ------ 18 43.109 68,168 20,552 _ Output coordinates . .. 18 4,189 13,754 932 procedures have been used to est1mate the data Polygons ------------ 18 27 109 4 , , , _ Arc line length (mm) .......... 16 4,064 13,919 1,753 volumes that Will be involved in future operations. Ta- State Land Ownership ble 3 shows some measures of data volumes for the Inputms ................. 11 136 213 _ 13 ' ' ' ‘ O t t .......... .. .i 11 l 6 1 categories of Land Use and Land Cover, Political Units, 1,135,113,“, 11 50,725 116,558 29,930 Census County SubdiViswns, Hydrologic Units, Federal 9;?g‘g‘n:°‘ff°l‘f‘j‘ffisg i}, 4’53; 8’333 2'2}? Arc line length lmm) .......... 7 4,013 5,486 2,743 Land Ownership, and State Land Ownership for DATASTRUCTURE 5 points by millions of points as they are received from the digitizing contractor. The two data volumes are shown in table 4 as they are distributed by category over the 9—year period. Since the beginning of the digitizing contract in early 1975, over 10 million output coordinates and over 5,000 meters of arc lines have been processed in the editing stage. That volume is the equivalent of over 80 million bytes of data. TABLE 4. — Estimated data volumes, 1975 7-1981 Category Arc line length Output coordinates 11975 —1981l Imetersl Land Use and Land Cover . . . . 37,408 37,000,000 Political Units .............. 3,002 2,000,000 Census County Subdivisions . . 7,708 6,250,000 Hydrologic Units ............ 3,592 3,250,000 Federal Land Ownership ..... 2,698 2,750,000 State Land Ownership ....... 2,665 3,000,000 Total ................ 57,073 104,250,000 IM¥FA.STTKU(TTLHRE The handling of spatial data, particularly in large quantities, is an area which has not been explored very thoroughly. Researchers have typically dealt with either small quantities of complex data or large quan- tities of simple data. Under these circumstances, ques- tions of data organization have not been critical, but as large sets of spatial data are compiled, the necessity of having an efficient, comprehensive data structure becomes apparent. The problems of data organization that appear minor to a researcher working with what he views as a man- ageable data set become large obstacles to someone who is operating in a production mode. The economics of the system are such that they are very sensitive to forms of data organization. A well-thought-out and optimized logical and physical structuring of the data may mean the difference between the success and failure of a large project. The GIRAS data structure is the latest in a series of evolving structures used to represent digital land use data. As such it reflects our (and our users’) biases con- cerning the information to be presented and its format. Since all maps compiled in the land use and land cover mapping and data program are polygon maps, the data structure was designed to expedite the handling of this data type. The topological elements associated with polygon maps are shown in figure 2. In the GIRAS structure, the common boundaries, or arcs, are digitized only once. The arcs are then linked together to form polygons. Arcs are line segments defined by a series of x, y coordinate pairs. Topologically the structure is similar to the DIME format used by the Bureau of the Census, (Cooke and Maxfield, 1968) and to the struc- ture described by Puecker and Chrisman (1975). In dealing with spatial data, it is often more desirable to store certain data rather than to recompute it. Thus, a large amount of ancillary data (e.g., polygon area, perimeter, etc.) is carried along in the data structure. The storage of such information not only eliminates re- dundant computations, but also facilitates data retrieval and analysis tasks. The general structure of a map file is shown in figure 3. The map header contains a substantial amount of in- 21 ll 12 4 2 o NCDDE '\_/. ARC POLYGON ISLAND I2 POLYGON LABE L FIGURE 2. — Topological elements ofa polygon map. GIRAS: A GEOGRAPHIC INFORMATION RETRIEVAL AND ANALYSIS SYSTEM .953 .5 1 ._ t fears of. 9:52:09 5620.; as. we 33:52 52 £0029. :23! “352:3 £53: ‘9 53:52 3.2 .:oux_oa ‘0 33:0. 5.25:0; .Ewm :0me .0 “20:53.3 xi 5:61:22 Lx1> .mxix .coaboa *0 «295203 x... E3552 AZ2> .LZix 609:3 $0 E:< (B: 553:3: :oax—OA .E.< ‘50.. 5:2... :0 *0 x... 3.051235 >U.xU .aE L x < o _ 38w; 2 2 i << (£2 E? U U ._ h z _ > x > x . _ ._ O¢0Umx 200:0: .va .0 fie. .0 53:5: ovoz Zn .08 mo 55:50.3 5 33:5: 0102 2» £2. £2.28” 5 £9... E< 2H? .05 :_ «29.558 x... 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E O E V V V V — E g V V V V 0 § Caetano Tuff § Age 34 m. y. (McKee and Silberrnan,1970) .29 K a > n: Welded tuff and pyroclastic rocks 5 ‘ t— a g a . q t i ’— §§o Granodiorite and altered granodiorite Lug Age 38 - 41 my. (Theodore and others, 1973) Granodiorite and monzonite (‘2) + + + + + + l :8 - Lu 0 Granodiorite g 8 Age 87 m. y. (Theodore and others, 1973) . _ z < z E S Antler sequence < 5 Consists of Middle Pennsylvanian Battle _ 3 E Formation, the Upper Pennsylvanian >- a. and Lower Permian Antler Peak 3 g Limestone, and the Upper Permian E < Edna Mountain Formation . D- m Havallah sequence Consists of Pennsylvanian and Lower Permian Havallah Formation GOLCONDA THRUST GOLCONDA THRUST PLATE i DEWITT THR UST P LATE Upper Cambrian Contact .A—A—A—A ...... Thrust fault Dotted where concealed or inferred. Sawteeth on upper plate High angle fault Dashed where approximately located; dotted where con- cealed or inferred I?) Pumpernickel Formation and Middle Pennsylvanian Harmony Formation DEWITT THR UST UNCONF OHM? TY ROBERTS MOUNTAINS THRUST PLATE PENNSY LVANIAN (.7) AND PERMIAN z 8 s Valmy n: 2 Formation _ O > THRUST CONTACT _ z v 5 § - g ~-. < :63 L U {a E Scott Canyon g5 Formation J >4 BASE NOT EXPOSED ROBERTS MOUNTAINS THRUST (not exposed) fleeting variations in mechanical response during deforn mation because of slight differences in lithology. These folds should be termed cylindroidal rather than cylindri- cal (Hansen, 1971). The uniform thickness of chert beds, especially in the hinge regions of the folds, strongly suggests that the concentric folds were formed by flexural slip; slip along bedding planes must have been the dominant mechanism of fold formation in chert of the Scott Canyon Formation. Angular folds are rare. A chevron-type fold, shown in fig. 3D, grades through an intermediate zone of thin— bedded chert showing abundant flowage into the more common concentric-type fold. Similar folds are rare; they were found in only one area, 50 m2, in SE14 sec. 26, T. 31 N., R. 43 E. Two of these structures are shown in figures 4A and B. Folds here are commonly tightly appressed t0 isoclinal, with very areally restricted hinge regions. Chert generally makes up less than 40 volume percent of the rock, argil- lite the rest (fig. 4A, B). Flowage toward the hinges of similar folds is common. Some folded layers display a disharmonic style of folding with polyclinal axial planes. Apparently brittle failure of some layers along micro- faults occurred contemporaneously with the develop- ment of the folds. Variability of attitudes of the outcrop—scale folds from one locality to another is apparent throughout the Scott Canyon Formation (pl. 1). Because of space limitations, only representative fold measurements from many of the studied localities are included on the map. It is readily apparent, however, that folds have a a fairly strong pre— ferred orientation throughout the area. They generally plunge at shallow angles in a northerly or southerly di- rection. Two areas show some marked scatter. In the western part of area 8 (pl. 1), the folds have somewhat more northwesterly trends, and in area 4, some steeply plunging folds have approximately east-west trends. These steeply plunging folds we described above as pos- sibly having formed before the larger ones. The style of all these folds whose attitudes are apparently aberrant from the norm is the same as the style of the northerly shallow-plunging folds predominant in the Battle Moun- tain area. Fabric diagrams of all measured fold axes reveal the strong preferred orientations of folds in the Scott Can- yon Formation (pl. 1). The fold axes define very strong single maxima in each of the four grouped data sets. Each of these maxima has about a 60° spread in both trend and plunge. In addition, they all have northeast- southwest trends. The centers of the maxima in areas 1, 2, and 4 plunge 15°, N. 15°—20° E.; in area 3. the center 6 DEFORMATION OF THE ROBERTS MOUNTAINS ALLOCHTHON FIGURE 3.—Folds in chert of the Scott Canyon Formation. A, Folded chert—argillite layers. Light-colored chert phacoids surrounded by appa- rently more ductile, organic-rich dark-colored argillite in drill core. 8, BNroad open fold. C , Concentric synform and antiform. See dime (right center) for scale. D, Angular chevron-type fold (right), which becomes concentric fold (left). Planar axial surface is approximately horizontal. Point of rock pick is 5 cm long. plunges 15°, S. 20° W. The low-density perturbations in fold—axis concentrations in areas 3 and 4 (pl. 1) are pro- duced by axes of northwest—trending and east-west- trending minor folds in these areas. These perturbations, however, are defined by the Zcr contour (pl. 1), which is the expected density for no preferred orientation. Ac- cordingly, because these deviations apparently fail to at- tain statistical significance, we conclude that they proba- bly have no geologic significance. About 50 percent of the minor fold structures whose axes we recorded were exposed such that their axial plane attitudes could be determined (pl. 1). These axial surfaces are generally planar; some are curviplanar. Fabric diagrams of these data reveal that the poles to the axial planes mostly define a single maximum for all four areas (pl. 1). Scatter in the data spread the maxima into girdles of various types. A high—density partial horizon- tal girdle (area 1) results from variations in strike of vertical or near-vertical axial planes. Areas 2, 3, and 4 are characterized by axial—plane attitudes whose maxima grade into low-density girdles defined predominantly by the 20 contour. Throughout the Scott Canyon Formation, profile views of the outcrop-scale folds suggest that they are not consistently overturned to either east or west. The ab- sence of uniformly overturned folds is reflected in fabric diagrams of the axial-plane data (pl. 1). A 40' concentra- tion of poles to axial planes plunges about 45° E, in areas 1 and 2; this suggests some statistically resolvable folds are overturned to the east. The high density (120-) of vertical axial planes in area 1, however, indicates their statistical prominence over the inclined ones. Further, the maximum in area 3 has a shallow plunge to the west which implies a dominance of folds slightly overturned to BATTLE MOUNTAIN AREA FIGURE 4—Folds of various styles in the Battle Mountain area. A. Complex. partly disharmonic similar folds in predominantly argillite—rich layered sequence of rock. with minor chert (light— colored layers). 8. Tight isoclinal folds in argillite—rich rock. C. ()pposed sense of overturning in thin—bedded sequence of chert (light-colored layers). bounded by thick—bedded chert (dark- colored layers). the west in this part of the Scott Canyon Formation. Yet over many outcrops there is no persistent sense of over- turning; some complex structures have axial surfaces in- clined to both east and west (fig. 4C). KINEMATIC IMPLICATIONS OF MINOR STRUCTURES From the geometry and types of structures in the Scott Canyon Formation, we can make some judgments concerning their tectonic implications. Since a summary diagram of the fold axes (B) and B axes in all four areas (fig. 5) indicates shear displacements on the bedding planes normal to the fold axes as the dominant type of fold development, the geometric fold axes must have coincided with their kinematic fold axes. The statistically determined mean attitudes for fold axes in the four areas can thereby be designated B axes (axes of rolling) for these areas. For three of the areas studied at Battle Mountain (areas 1, 2, and 4), fold axes (B) are statisti- cally parallel to one another. The B axes at Battle Moun- tain, however, are parallel to but one of their B axes determined from the plots of the bedding—plane at- titudes. This relation may in part reflect inaccurate plac- EXPLANATION 9 Area 1 0 Area 2 I Area 3 E! Area 4 FIGURE 5.—l“abric diagram showing statistically determined mean- outcrop—scale fold orientations (B) and B axis orientations for areas 1—4 ot'the Scott Canyon Formation (pl. 1). 8 DEFORMATION OF THE ROBERTS MOUNTAINS ALLOCHTHON ing of the pole-to-bedding girdles owing to their poorly defined character (pl. 1). From the axial-plane data (pl. 1), we infer that most folds have vertical or near-vertical axial planes. Ortho— rhombic folds are dominant throughout many outcrops of chert in the Scott Canyon Formation. Accordingly, we make no judgments about the sense of tectonic transport in the Roberts Mountains plate from these data. The apparent horizontal component of tectonic shortening, however, is remarkably uniform throughout these rocks and it trends N. 70°+ 75° W.; the mean azimuthal bearing for all folds here is 15° to 20°. The chert layers in the Scott Canyon Formation may have behaved more or less rigidly after initially buckling during early stages of de— formation; most of the strain probably was concentrated in the argillite during deformation. SOUTHERN TUSCARORA MOUNTAINS AREA GENERAL GEOLOGY The Roberts Mountains allochthon in the Rodeo Creek NE and the Welches Canyon quadrangles, southern Tus- carora Mountains area, is made up chiefly of Ordovician and Silurian chert, shale, and minor quartzite and lime- stone of the siliceous assemblage (pl. 2; Evans, 1974a, b). This assemblage is represented by at least 3,050 m of strata. Upper Devonian limestone assigned to the transi— tional assemblage (pl. 2) occurs within the allochthon and is at least 915 m thick. This limestone was assigned to the transitional assemblage because it contains angular grit, rounded cobbles of chert, and beds of siliceous shale up to 15 m thick. Autochthonous rocks are exposed in the Lynn window and consist largely of Cambrian through Devonian limestone, dolomite, and quartzite of the car— bonate assemblage (pl. 2). These strata total 2,720 m. In the southern Tuscarora Mountains area, as in the Battle Mountain area, fine to very fine grained rocks with delicate laminations in the Ordovician and Silurian siliceous assemblage of the allochthon are evidence of deposition in quiet water. Sets of laminations, as much as a few centimeters thick, locally folded or truncated indi— cate minor flowage. Coarse sand and grit composed of chert and shale clasts and angular limestone conglomer— ate suggest some penecontemporaneous deformation. Evidence of large—scale penecontemporaneous deforma- tion, such as angular uncomformities within the siliceous assemblage is absent. The extremely poor outcrops of the siliceous rocks, however, may not be adequate to permit conclusions to be drawn concerning the mobility of the sedimentary rocks prior to their more spectacular translation during the Antler orogeny. Chert clasts in the Upper Devonian transitional lime- stone in the southern Tuscarora Mountains area point to the beginning of the Antler orogeny somewhere west of the Tuscarora Mountains by Late Devonian. The Webb Formation of Early Mississippian (Kinderhook) age, de— scribed by Smith and Ketner (1968), unconformably overlies the allochthonous Ordovician and Devonian rocks and the autochthonous Ordovician and Silurian rocks in the northern Pinon Range, thereby giving an upper—age limit to the Antler orogeny in northeast Nevada. The, northeast trend of the Antler orogenic belt through the southern Tuscarora Mountains suggests that large folds and minor folds trending northeast in the Roberts Mountains allochthon of the study area could be correlated with the Antler orogeny. The allochthon in the southern Tuscarora Mountains could also have been af- fected by the late Paleozoic and Mesozoic folding and thrusting identified in the Adobe Range, 50 km east of the southern Tuscarora Mountains (Ketner, 1970a). These later folds also trend northeast. Clear evidence for some post—Antler deformation in the southern Tuscarora Mountains is the asymmetric antic- line in the carbonate assemblage (plunge 20°, trend N. 15° W.; fig. 6) in the Lynn window (pl. 2). This anticline lies at an angle to the northeast trend of the Antler orogenic belt and therefore presumably postdates the N ° 6: B(autoch) FIGURE 6. —Contoured fabric diagram showing poles to bedding in car— bonate assemblage in the Lynn window (pl. 2), southern Tuscarora Mountains area. 300 points. Contoured in 20 intervals where 227 is the expected number of data points within a counting area for a uniform distribution across the entire stereogram (see Kamb, 1959). Contours 20', 40', 80', 120', and pole—free area. Fold axis B plunges 20° in the direction N. 15° W. Great circle (dashed line) is distribution of poles to bedding and defines fold axis. SOUTHERN TUSCARORA MOUNTAINS AREA 9 Antler orogeny. In addition, on the west side of the range, the carbonate assemblage is thrust over the siliceous assemblage along the West Lynn thrust, clearly of post-Antler age. The Paleozoic rocks were intruded in the Mesozoic (granodiorite, 121:5 m.y., Hausen, 1967, p. 36; granite, 106:2 m.y., M. L. Silberman, written commun., 1971) and in the Tertiary (granodiorite, 37:0.8 m.y., M. L. Silberman, written commun., 1971; quartz latite, 36:0.7 m.y., McKee and others, 1971, p. 41). The present small exposures of the Mesozoic intrusions may be apophyses; of larger buried plutons, as the Paleozoic rocks surround— ing the intrusions have been metamorphosed (recrystal- lization resulting in coarsening of grains, partial destruc— tion of bedding features and fossils, bleaching, and neomineralization) in aureoles several thousand meters wide. Emplacement of one or more plutons could have been associated with a stage of post—Antler deformation of the Paleozoic rocks and may have resulted in uplift of the autochthon at the Lynn window (Roberts, 1966). ALLOCHTHON DESCRIPTION Most of the outcrops of the Roberts Mountains al- lochthon in the southern Tuscarora Mountains area are chiefly of chert and exhibit thin planar beds and laminae with little sign of the intense deformation seemingly im— plied by many kilometers of transport from the west. Many lithologic units are mappable for several hundred meters before being truncated by faults, or more com- monly, disappearing beneath thick Cenozoic regolith. To all appearances, much of the siliceous assemblage ar- rived in the southern Tuscarora Mountains in fault slices that were relatively little deformed internally, although disrupted bedding is present. Some of the intensely fragmented bedding could have been produced by penecontemporaneous deformation (fig. 7A). Minor bedding-plane thrusts, possibly of penecontemporaneous origin, occur locally (fig. 73). Some intricate folding and boudinage may be related to strains developed around small Mesozoic intrusions (fig. 7C). Locally, bedding fea— tures have been nearly obliterated by intense fracturing (fig. 7D), possibly associated with the Antler orogeny. Large folds in the siliceous assemblage trending north-northwest, north, and north-northeast (pl. 2), can be traced for 11/2 to 3 km. Profiles ofthe folds (pl. 2) show them to be generally open and apparently concentric in general form and to have steeply dipping or vertical axial surfaces. ' Minor folds subparallel to the larger ones plunge at low angles, chiefly to the northeast and southwest. Such folds are not common in the allochthon. In fact, minor folds were found in only 81 chert outcrops in the 125 km2 underlain by the siliceous assemblage in the study area. Fault-faceted phacoids of chert and quartzite as much as a few hundred meters long, some elongate parallel to the bedding, occur near the Roberts Mountains thrust and near other shear zones within the allochthon. The bedding in some of the phacoids is contorted, but the internal structure of the phacoids has little relation to the shape of the phacoid or to the structure of the surround- ing shale. The chert, after folding plastically in an early part of the deformation, thereafter behaved in a brittle manner; rigid pieces of the chert swim in relatively duc- tile shale. In some parts of the allochthon, much of the strain must have been taken up within the shale. As the outcrops are chert, however, the data of this study prin- cipally describe deformation in the chert beds, which are subordinate to shale in the allochthon. MINOR STRUCTURES IN AREAS 1—4 The Roberts Mountains allochthon in the southern Tuscarora Mountains area was divided into four areas of study. Areas 1, 2, and 3 are several square kilometers each and cover most of the allochthon in the southern Tuscarora Mountains area (pl. 2). Area 4 is smaller and is in the eastern assemblage. The bedding in areas 1 and 2 dips predominantly to the northwest (figs. 8A, C). In area 3, the bedding attitudes are more varied (fig. 8G), and the poles to bedding lie along a great circle, defining a ,8 axis, ['33, which plunges 15° in the direction S. 18° W. The minor folds of the allochthon are generally concen— tric and cylindrical. Antiformal hinges tend to have a smaller radius of curvature than the synformal ones (figs. 9A—E). The beds are slightly thicker in the an- tiformal hinges than on the fold limbs. A few folds are tightly appressed, nearly isoclinal. Some of these folds have narrow zones of breccia along the axial surface. Most folds in area 1 plunge at low angles to the north- northwest, north, and north—northeast (fig. 88). At a few localities, folds plunge at low angles to the west- northwest. The folds in the north~northeast and west- northwest directions will be referred to here as B (lznne) and B (1:wnw), respectively. At one locality the folds B (12wnw) are the dominant set. No evidence was found there to determine the relative ages of B (lznne) and B (1:wnw). In area 2, the folds plunge at low angles to the north— northeast and northeast (fig. 8D). At one locality, hori— zontal folds trending west-northwest were observed. The folds of northeast and west-northwest directions are designated B (22nne) and B (2twnw), respectively. In the western part of area 2 the bedding of several chert out— crops, concluded to be phacoids of chert, are intricately 10 DEFORMATION OF THE ROBERTS MOUNTAINS ALLOCHTHON folded, as shown in figures 9F and G. The folds in the western part of area 2 plunge principally at small angles in northeast and southwest directions with a wide scat- tering to the north—northwest and west (fig. 8E). The pattern is not greatly different from the pattern in the remainder of area 2 (fig. SD). The folds of area 3 are more varied in orientation than the folds in areas 1 and 2 (fig. 8H). Most of the folds in area 3 plunge at low angles to the northeast and south- west. Others are steep. These fold axes may be distri- buted along a great circle of the orientation diagram. The pole to a great circle that seems to fit this distribution plunges at a small angle to the east-southeast. This pole, possibly an axis of rotation of the folds, is designated P3. The subordinate west-northwest~trending folds of areas 1 and 2 are at high angles to the dominant, gener- ally north—northeast-trending group of folds. This angu— lar relation, B (nne), approximately perpendicular to B (wnw), may be fortuitous, or it could indicate a syngene- tic relation between the two sets of folds (fig. 10). The suggestion from the data of area 3 is that the north- FIGURE 7.~—Disrupted bedding in chert of Roberts Mountains al- lochthon, southern Tuscarora Mountains area. A, Fragmented bedding in chert 2.3 km north of Carlin mine (sec. 1, T. 35 N., R. 50 E.). Prominent band of dark chert across center is 7 cm wide. B, Minor thrust in chert (sec. 21, T. 34 N., R. 50 E.). C, Folding and boudinage in chert near large Mesozoic granodiorite (like 4 km north of Carlin mine (T. 36 N., R. 50 E., unsurveyed). Six-inch ruler in lower left of photograph. D, Faulted bedding in cherty shale 3 km south of Lynn window (sec. 21, T. 34 N., R. 50 E.). Six-inch ruler in upper right of photograph. SOUTHERN TUSCARORA MOUNTAINS AREA 11 northeast-trending folds, B (3znne), were rotated about however, and both could have occurred during the Ant- an axis, P3, plunging east-southeast subparallel to B ler orogeny. (3zwnw), and that therefore the two sets could represent In general, the axial planes of the minor folds in areas consecutive stages of deformation with northeast- 1, 2, and 3 are steeply dipping or vertical. A preferred trending minor fOIdS better developed in the initial stage. sense of overturning 0f the axial planes is not evident. In These stages 0011101 have occurred very (31059 in time, the western part of area 2, the axial planes of the folds in .. .X B(2 :nne) SB(2:wnw) ' FIGURE 8. ——Fabric diagrams showing poles to bedding, fold axes, and poles to axial planes in areas 1. 2, and 3 (pl. 2). See text for explanation. A, Contoured poles to bedding in area 1. 175 points. Contours 20. 40'. 80', and 160. Great circle (dashed line) represents a plane striking N. 28° E. and dipping 30° NW. 8, Fold axes at 27 localities in area 1. 27 points. C, Contoured poles to bedding in area 2. 176 points. Contours at 2a, 40', 80, and 120-. Great circle (dashed line) represents a plane striking N. 53° E. and dipping 30° NW. D, Average orientations of fold axes at 22 localities in area 2. E, Fold axes from 13 localities in western part of area 2. 55 points. Contours 2U, 40', 80, and pole-free area. F', Contoured poles to axial planes in folds in western part of area 2. 35 points. Contours 20, 4a, and pole-free area. G, Contoured poles to bedding in siliceous assemblage in area 3. 300 points. Contours 20, 40', 80-, 120', and pole-free area. Great circle (dashed line) is distribution of poles to bedding. B3 is pole to great circle. [3 axis plunges 15° in the direction S. 18° W. H, Fold axes at 24 localities in area 3. 27 points. P3 (circled dots) is pole to the great circle (dashed line). 12 DEFORMATION OF THE ROBERTS MOUNTAINS ALLOCHTHON East-southeast _.... «— West-northwest W B /\/\’\/ ~O 606m I___I 0 1 m L_______J Southeast —’ N orthwest North-northwest East-southeast —> D‘— F M 280 / 0 5 m L__—__.__—l East-southeast West-northwest ——> West‘northwest East-southeast ‘— ——-> /\/ W / 5 Fault 0 5 m I | 0 14 m FIGURE 9. —Sketched profiles of minor folds in chert in areas 1 and 2, southern Tuscarora Mountains area. A—C. area 1: 0—6, area 2. In A—C, E, and G, folds plunge at low angles to the north-northeast, in D and F, to the south—southwest. Arrow points in the direction of plunge and away from the number giving the azimuth of the trend in degrees related to a 360° compass. Zero degrees (north) is assumed to be at the top of the page. The angle of plunge is written at the point of the arrow. SOUTHERN TUSCARORA MOUNTAINS AREA 13 Iv, ,0, ,7, B(2:wnw) X B(l :wnw) X B(3:ne) .63 EXPLANATION X Mean orientation of fold set o Rotation axis or B axis FIGURE 10. —Summary fabric diagram for areas 1, 2, and 3. See text for explanation. chert phacoids are also mostly steeply dipping or vertical (fig. 8F). Some of the axial planes, however, are flat lying, occur adjacent to minor thrusts, and dip northwest and southwest (fig. 9G). The axial planes that dip at low to moderately steep angles in westerly directions in fig— ure 8F indicate that the sense of overturning in these folds had a large eastward component. Other axial sur- faces are folded around axes coincident with the domin- ant northeast-trending fold axes (fig. 9F). The most common fold—axis direction in areas 1, 2, and 3 is north-northeast. In folds of this orientation, predo- minantly of concentric form, slip took place on the bed- ding in a direction perpendicular to the fold axis. The b-fabric axis is identical to the B—kinematic axis, and the direction of tectonic shortening is generally N. 70° W. These fabric features are consistent with the accepted easterly direction of movement of the allochthon. As stated here, however, only part of the total deformation of the allochthon is revealed in the chert outcrops. Minor local shortening within the allochthon could have occur- red in the relatively ductile shale, while, for example, the allochthon glided eastward over an irregular thrust sur- face. Minor shortening could have occurred perpendicu- lar to the principal movement direction of the allochthon, possibly resulting in local development of west- northwest-trending folds in the chert. Area 4 is in the thin-bedded limestone member, about 120 m thick, of a 1,400—m-thick section of chert and shale west of the Lynn window (pl. 2). The limestone member is folded into an antiform and synform plunging north- northwest at low angles. Bedding generally dips steeply and strikes north—northwest. The poles to bedding define a [3 axis, [-34, plunging 35° in the direction N. 8° W. (fig. 11A). In the hinge zone of the major antiform, the folds are characteristically concentric although the beds are slightly thicker in the hinges than on the fold limbs (fig. 12). Folds are more conical than cylindrical. Many are faulted, and bedding in some is pinched off in the cores. The fold axes of area 4 appear to fall into two groups (fig. 113): (1) a set designated B (4:nnw) that plunges at low angles in northerly directions and (2) a set of more steeply plunging folds, designated B (4:sc), that varies in trend from northeast to northwest. Many of the folds of set B (4:sc) are more intricate and more tightly ap- pressed than the folds in set B (4znnw). The steeper folds B (4:sc) lie along a small circle about 45° from the center of the cluster of folds B (4znnw). These relations, possibly more apparent than real, suggest that the folds B (4:sc) have been rotated about an axis, A4, which is subparallel to B (4znnw), and that therefore the folds B (4:sc) are older than the set B (42nnw). Poles to the axial planes of all the minor folds of area 4 are shown in figure 11C . Most of the axial planes dipping northeast are from the more numerous folds of the set B (4:sc). The axial planes of folds B (4znnw) have nearly vertical axial planes. The asymmetry of the folds B (4:sc), with steeper southwest limbs, could be an original characteristic or a feature developed during a super- posed deformation. The small-circle distribution of the folds B (4:sc) around a north—northwest plunging axis, A4, and the subparallelism of that axis and the folds B (4znnw) with the large post—Antler anticline in the autochthon strongly suggest that area 4 was subjected to two episodes of deformation, the later stage occurring after the al- lochthon was emplaced. The early folds of area 4, B (4:sc), might have formed in the limestone at the time of the Antler orogeny. If these folds originated at that time, the evidence does not clearly indicate whether the origi— nal orientation of these folds was north-northeast or west-northwest, the two major fold directions developed 14 DEFORMATION OF THE ROBERTS MOUNTAINS ALLOCHTHON 1n the allochthon in areas 1, 2, and 3. Most of the folds B N (4zsc) trend northwest, and on the strength of that ob- servation, most of them may once have trended north- west and west-northwest. Folds B (4:sc), tentatively assigned to the Antler orogeny, may be correlative with the west-northwest folds of areas 1 and 2. This suggests that the deformation of area 4 was not typical of most of the allochthon during the Antler orogeny. The presence of the limestone member may have resulted in localized anomalous strain within the allochthon. Some of the local tectonic shorten— ing may have been at a high angle to the dominantly eastward direction of movement of the allochthon. AUTOCHTHON Minor folds are generally absent in the autochthon ex- cept near large thrust faults. An exceptionally inten- sively folded area, area 5 (pl. 2), is located about a half mile south of the Roberts Mountains thrust and is in the upper plate of a large thrust within the autochthon. Area 5 is chiefly in laminated siliceous siltstone, believed to be silicified Silurian and Devonian strata of the carbonate . / assemblage. 7"—_'1'»/.’// B(5.sc) O / C D FIGURE 13. —Fabric diagrams showing poles to bedding, fold axes, and poles to axial planes in area 5. A, Poles to bedding. 57 points. Contours 20, 40', 60-, and 80'. Great circle (dashed line) is distribution of poles to bedding. B5 is pole to great circle. B axis plunges 40° in the direction N. 55° E. B, Fold axes. 81 points. Contours 20', 40', and 60'. C, Fold axes. 18 points. Triangle with dot lies at center of 50° small circle (dashed line). A5 is rotation axis of small circle. D, Poles to axial planes. 48 points. Contours 20, 4a, 6a, and 80-. 3. Most of the minor folds in the chert plunge at low therefore the apparent horizontal component of tectonic angles to the north—northeast and south—southwest and shortening of the allochthon is N. 70°—75° W. in the have steeply dipping or vertical axial planes. Battle Mountain area and in the southern Tuscarora 4. The b—fabric axis, parallel to the north-northeast- Mountains area (figs. 5, 14). This direction is consistent trending folds, is identical to the B—kinematic axis and with the eastward direction of movement accepted for REFERENCES CITED 17 B (11:03,!) ' >4 qu to Contact / / Qal / 34: _._ 8 ....... T / l0 Alluvium Z Quartz monzonite 8 Q S l (0/ 20 // /5 .~ ‘ g " < Fault / 20 2 5 / / ' ' f E K d E Dotted where concealed \ / ro/I / Q I3 g 5 T—V" ...... O . . \\ ll SO // :' Fanglomerate A Granodlorlte _ Thrust fault ’ 5 5 2 Q >-‘ z Dotted where concealed. SO Qal K\5 l QTs <2: ‘3: Di 0 S Sawteeth on upper plate : > z 7 Z x l - 0 SO . : - F 9‘ '3‘ ‘80 Q? l’ 25 ‘ 5 Qf swanalggiirgcgfs E E Transitional assemblage L E _$_.I_ ..... .-' . z - - ll; LL Tuscarora Mountains ‘34 D I A < Antlform showmng trace m z \— / \ [L O E Z A.— Of crest gKgd - DC < 5 fig Dotted where concealed Qal / TC C b t bl — S: ; E Z l ar ona e assem age 7 ‘ ¥ _ ..... e I f / Carlin Formation of Regnier (1960) E. 2.3 Q Qal \ L:::::__=7_—=—:?’— _ U 90‘"); Synform showing trace of f V 3 Q81 Trt SO <0 nadir of trough \ 20 x / SOC <2: Z Dotted where concealed \/5‘ Siliceous assemblage ; g E a :5 > ,5/ /l Trd g 50c, chert. Shown in 0 <2 3 Minor fold or folds showing " ROBERTS MOUNTAINS THRUST (§3% / 7 E cross section only S g (7, trend and plunge \ Rhyodacite flows m H 5 H / f I SO \ Horizontal minor fold or 5 E qu folds showing trend Qal / f I / f 270 lfo ? 5 15 E Quartz latite l f 1 r 3 6:3 l \ :' d Tailings pond and earth dam MOUNTAINS THRUST A5 ) 3 TE [0 20 : \uHHllHU/ l '34 / [5 S) Granodiorite L immums Qal :‘ 8 / 1 f 5 Qf Mine dump (\LJ 1 ,0 '0 (l 5_ /§\ ROBERTS / \ 3 K_J MOUNTAINS K ‘ Numbered area discussed Qal THRUST \\ ‘iffixj' in text \ l0 ‘. Qal ': 30 V w l5 L Qd ' nn In W Qal DG 5 =_ y W 0 \\\ \ > W -ROBERTSINS so \ (j l A f l t b d EMOUNTA 5““: l , :f tea 0 p0 es 0 e - Trt “ ." THRUST 1N Carlm mme \ (<—) ,-' ding of figure 6 50 ‘- lD€ r\\ \ \ :- Qal DC .Qal l \ \\ \.\,/ 3" a \\ l 0 \ \ ”a. [I Qal ’3' DE: \ ,' I g :' \ 5 \\ :' ROBERTS MOUNTAINS THRUST METERS A A FEET E \\ 5Q25\ X‘ 2500 8000 .m ‘ 5'33 \\ \35\ 7000 " ‘- 2000 \\_/> “.I 6000 al Q 1500 5000 4000 1000 RODEO CREEK NE 5230" 52,30” WELCHES CANYON Trt I é]? METERS C C FEET 2500 8000 B’ 7000 \ METERS B FEET 2000 2500 8000 6000 0 7000 1500 5000 2000 6000 4000 1000 \ 1500 5000 3000 4000 2000 ROBERTS 1000 500 MOUNTAINS T 1000 THRUST SEA LEVEL SEA LEVEL Qal ' Tc ,_ . Qal FEET / \ /eTa)70 \ , 6000 SO I / \ Qal 5000 / ,0 . t _ 4 i 4000 METERS E E FEET 2500- 8000 T 7000 2000 Qal SO \ 6000 M \ \ 1500 4‘ 4 (”0/ \\\\ \ \ \\ \ \ \\\ \ \\\ /§/ 5500 ,, \\_ ;/ e/ — 4000 1000 . . filnterior~Geolog1calSurvey, Reston, Va.—1978EG77314 1 2 3 4 KILOMETERs 0 l.KHII.IHl l l l l IIIIIIIII l o 1 2 MILES GENERALIZED GEOLOGIC MAP AND SECTIONS OF THE SOUTHERN TUSCARORA MOUNTAINS AREA 40°45' I 116°22'30" Clay Mineralogy of Pleistocene Lake Tecopa, Inyo County, California By HARRY C. STARKEY and PAUL D. BLACKMON GEOLOGICAL SURVEY PROFESSIONAL PAPER 1061 In a saline lake with pH above 8.5 authigenle sepiolz‘te ana’ detrital lithium-bearing saponite were deposited in mudstones which were z'nterlayerea’ with volcanic tufls UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON21979 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. AN DRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Starkey, Harry C. Clay mineralogy of Pleistocene Lake Tecopa, Inyo County, California. (Geological Survey Professional Paper 1061) Bibliography: p. 33 Supt. of Docs. no.2 I 19.l6:106l 1. Clay minerals—California—Inyo Co. 2. Meerschaum—California—Inyo Co. 3. Saponite—California—Inyo Co. 4. Saline waters-California—Inyo Co. 1.. Blackmon, Paul 1)., joint author. II. Title. 111. Series: United States Geological Survey Professional Paper 1061. QE389.625.S73 549'.6 77—608318 For sale by the Superintendent of Documents. US. Government Printing Office Washington, DC. 20402 Stock Number 024—001—03185—0 CONTENTS Page Page Abstract .................................................... 1 Nonclay minerals—Continued Introduction ................................................ 1 Other minerals .......................................... 18 Location and geographic setting ............................ 1 Clay minerals ............................................... 20 Acknowledgments ....................................... 1 Chlorite and chlorite-mica ................................ 20 Scope of investigation .................................... 3 Mica and illite .......................................... 20 Previous work ........................................... 3 Lithian saponite ........................................ 23 Montmorillonite ........................................ 25 Geology of the basin .......................................... 3 Sepiolite ............................................... 25 Description of the mudstones and siltstones .................... 4 Tecopa basin occurrence ............................. 25 Laboratory methods ......................................... 5 Previous work on sepiolite ........................... 26 Nonclay minerals ............................................ 9 Modes of sepiolite formation ......................... 26 Quartz and plagioclase feldspar ........................... 9 Sources of magnesium and silica ...................... 27 Potassium feldspar ...................................... 16 Sepiolite formation in Lake Tecopa ................... 30 Carbonates ............................................. 16 Discussion ................................................. 31 Magadiite .............................................. 17 Sequence of events ...................................... 31 Zeolites and amorphous material ......................... 18 Conclusions ................................................ 31 Saline minerals ......................................... 18 References cited ............................................ 33 ILLUSTRATIONS Page FIGURE 1. Index and sample locality maps, Pleistocene Lake Tecopa drainage basin, Calif. . . . . . . . . . . . . . . . . . . . . .- ............. 2 2. Photograph from sample locality 54 looking northeast toward Shoshone, Calif .................................... 4 3. Generalized stratigraphic section of the Pleistocene Lake Tecopa deposits ....................................... 4 4. Photograph of sample locality 44 showing gravel mixed with clay ............................................... 5 5. Flow sheet for laboratory procedures used for mineral identification of Pleistocene Lake Tecopa deposits ........... 9 6—11. Transmission electron micrographs: 6. Suspended sepiolite ..................................................................................... 14 7. Sepiolite fibers more than 2pm long ..................................................................... 14 8. Surface replica of sepiolite ............................................................................... 15 9. Suspended saponite ..................................................................................... 15 10. Suspended crystals of magadiite from Lake Tecopa basin .................................................. 19 11. Suspended crystals of magadiite from Trinity County. Calif ................................................. 19 12. Vertical distribution of clay-mineral content in stratigraphic section ............................................ 21 13. X-ray diffraction curves of typical gradation from mica to mixed-layer mica-saponite ............................. 22 14. Photograph of mud cracks in saponite at sample locality 57 ..................................................... 24 15. Map of samples taken within 1 m of tuff A and their clay mineral content ........................................ 28 16. Map of samples taken within 1 m of tuff B and their clay mineral content ........................................ 29 Ill IV TABLE CONTENTS TABLES Page Localities and particle size distribution of samples .................................................................... 6 Mineral content of samples ........................................................................................ 10 X-ray diffraction data for magadiite ................................................................................ 18 Comparison of X-ray diffraction spacings of sepiolite and saponite from Pleistocene Lake Tecopa with those of previously reported occurrences ................................................................................ 20 Chemical comparison of Pleistocene Lake Tecopa saponite with other smectites ........................................ 23 Weight percent of Mg, Li, and F in samples from Pleistocene Lake Tecopa mudstones and siltstones ..................... 24 Li and F in samples outside of lake beds in local drainage ............................................................. 26 CLAY MINERALOGY OF PLEISTOCEN E LAKE TECOPA, INYO COUNTY, CALIFORNIA By HARRY C. STARKEY and PAUL D. BLACKMON ABSTRACT Pleistocene Lake Tecopa in southeastern Inyo County, Calif., was formed when the Amargosa River was blocked at the southern end of its valley. The lake acted as a settling basin for detrital material being transported by the river. This detritus consisted of clays, quartz, feldspars, and micas which became mudstones and siltstones. These mudstones and siltstones, much eroded and dissected after the draining of the lake, extend over the entire basin and are interbedded with tuffs formed by the intermittent deposi- tion of volcanic ashfalls in the former lake waters. These light- colored mudstones and siltstones are tough and well indurated and break with a conchoidal fracture. The predominant clay mineral in these detrital beds is a lithium- bearing saponite, which is found not only in the lake beds but also in the area beyond the boundaries of the lake, especially in fluvial deposits in the drainage basin of the Amargosa River to the north. This saponite does not contain enough lithium to be classified as a hectorite, and we have observed no indications that this clay con- sists of a mixture of two phases, such as hectorite and a diluent. Some authigenic dioctahedral montmorillonite, found only in small quantities close to the tuffs, was formed by alteration of the volcanic glass of the tuffs and was then admixed with the overlying or underlying detrital clays. The only authigenic clay-type mineral found in any significant quantity is sepiolite. found near the edges of the lake basin and stratigraphically located mainly within a meter of the two upper- most tuffs. This sepiolite probably was precipitated when silica became available to the magnesium-bearing lake water through dissolution of the volcanic ash. Precipitation of sepiolite probably did not occur within the tuffs owing to the presence of alumina in solution. Zeolites were produced there and sepiolite formed outside the margins of the tuffs. Also formed by the high-pH lake waters were water-soluble minerals, which were found widely dispersed in crusts or streaks on the clays. Much of the calcite was likely precipitated from the lake waters. especially near the north end of the lake where calcium- bearing fresh water came into contact with the cog-rich lake waters. Magadiite, a sodium silicate mineral reported only twice previous- ly in the United States, was found in small quantities in the southern end of the basin. This mineral is indicative of a minimum pH of 8.5. The authigenic minerals formed in the lake reflect the presence of silica-rich tuffs and the high-pH, alkaline character of the lake waters. INTRODUCTION LOCATION AND GEOGRAPHIC SETTING The basin of former Pleistocene Lake Tecopa, in southeastern Inyo County, Calif, is located in the Mo- jave Desert about 32 km east of Death Valley National Monument within Tps. 20, 21, and 22 N ., and Rs. 6 and 7 E. The area is shown in figure 1. The nearest large ci- ty is Las Vegas, N ev., which is located about 97 km to the east. The town of Shoshone is located in the northern part of the basin, and the town of Tecopa is located in the southern part; Shoshone is on State Route 127 , which runs generally north-south through the basin. The lake basin is bounded on the west by Dublin Hills, Ibex Hills, and the southern part of the Green- water Range and on the east by the southern parts of the Nopah Range and Resting Spring Range. To the south are the Sperry Hills through which the Amargosa River flows, draining the study area. The lake beds cover an area about 18 by 23 kilometers. The elevation of lowest exposures of the beds is at about 396 m near the south end of the lake, and the highest beds are at about 549 m at the margins of the lake. The hills and mountain ranges to the east and west of the basin have elevations of about 914—1,219 m. Sperry Hills to the south are about 610—762 In above sea level. ACKNOWLEDGMENTS We gratefully acknowledge the help of those members of the US. Geological Survey who furnished technical assistance during this study. Elaine L. Brandt, (Mrs.) Johnnie Gardner, John C. Hamilton, Violet Merritt, Wayne Mountjoy, and Daniel R. Nor- ton supplied the various chemical analyses. Toribio G. Manzanares did most of the fractionations and ran 1 36° 00' 35° 116°20’ CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA 50' _ 15’ 116°10' | I F | 116" Death Valley J11 “a ’9‘? 48% "<9 ‘9 ’12,? 101 a ’6» 4:» \ 1e ’2; q \ a,“ 4’06 \ 6‘4 1,, 7. K “be, 9;; _ "4 Shoshon <2 \ Q‘» ~ E? g a“ DUBLIN HILLS— Q8 E1 \ Pleistocene '“ _\ LakeTeoopa _ __\ __ :__ _ \i @ l] 10 20 30 KILDMETERS 51. . .52 53 Edge of Pleistocene Lake Tecopa 45 PLEISTOCENE '45 LAKE TECOPA _ T5423 - . T5—l 18 . T5419 EXPLANATION _ '47 Sample locality and number Spillway of _ Pleistocene Lake r—l Line of measured section Tecopa a Island in Pleistocene Jig Lake Tecopa 0 l 2 3 4 5 KILOMETEHS l_l_;l_l_l l l FIGURE 1.—Index and sample locality maps, Pleistocene Lake Tecopa drainage basin. California. GEOLOGY OF THE BASIN 3 most of the X-ray patterns. Donald C. Noble, now at Michigan Tech University, provided data on unaltered glasses from Nevada. SCOPE OF INVESTIGATION This report is concerned primarily with the iden- tification, distribution, and origin of the clay minerals found in the Lake Tecopa basin. It also discusses the types and amounts of other minerals present. The Lake Tecopa basin is suited for this type of study because: (1) it covers a relatively small area of about 18 by 23 km, (2) the clay beds are separated by tuffs which can be followed easily and, (3) the clay beds are dissected by gullies so that a few tens of meters of clays can be sampled without drilling. A total of 158 samples from 94 sample sites were examined, the loca- tions of which are shown in figure 1. Samples that were collected from the area outside the basin are shown in the area covered by the map in the inset. The word “basin” is used in this report to mean only the area ac- tually covered by the waters of Pleistocene Lake Tecopa. PREVIOUS WORK Numerous geologic investigations have been carried out in the Lake Tecopa area. Melhase (1926) described the geology and the mining operations of “amargosite,” which he claimed to have named in 1920. This clay, which is actually montmorillonite, at the time was known also as “soap rock” or “natural soap.” Noble, Mansfield, and others (1922) described the mudstones and saline deposits in their investiga- tions of the nitrate beds. Noble (1926) gave a brief description of the geology of part of the Amargosa valley in his investigation of a colemanite deposit near Shoshone. Later (1934) he gave a more complete description of the rock formations in the area. Dietrich (1928, p. 88) described the clay beds as trending north and south, as being 1.8—2.4 m thick, and as being overlain by 1.2—1.8 m of volcanic ash. Blackwelder (1936, 1954) gave brief outlines of the general geology and history of the Lake Tecopa area, pointing out that the deposits on the lake floors had been deeply entren- ched and eroded after the lake drained. Wright and Troxel (1954) described the lake beds as mostly siltstone with subordinate layers of volcanic ash and bentonite clay. Although in the past the clays in the beds of Lake Tecopa have been described by several authors, the scope of the work often was limited by the available analytical methods. Identifications and con- clusions were based on physical and chemical proper- ties and upon the commercial uses to which the clays could be put. Sheppard and Gude (1968), in their study of the authigenic silicate minerals in the tuffs of Lake Tecopa, described those tuffs in detail and we will use them as stratigraphic markers for the present study. They reported the occurrence of sepiolite in two of their samples, but they noted that neither Droste (1961) nor Kerr and Langer (1965) had reported sepiolite in their studies of other playa clays of the Mo- jave Desert. Sepiolite, however, is known to occur in desert lakes of high salinity (Bradley, 1930; Schroter and Campbell, 1942; Hardie, 1968; Parry and Reeves, 1968). The nearest probable occurrence of sepiolite to Lake Tecopa, known to the present authors, is that reported by Foshag and Woodford (1936). They state, “In the bentonitic clay of Ash Meadows near Shoshone, Calif., there are numerous lumps of mixed lime, magnesium carbonates and a magnesium silicate close to sepiolite,” but they do not give an exact sam- ple site location. Ash Meadows is about 40 km north of Shoshone (fig. 1). GEOLOGY OF THE BASIN Most of the geologic investigations that have been made of Lake Tecopa in the past have been primarily concerned with the saline deposits and especially with the possiblity of finding nitrate deposits. The reports of these investigations have also described the general geology of the area surrounding Lake Tecopa. Sheppard and Gude (1968) gave a detailed report on the mineralogy of the tuffs associated with the mudstones, and an excellent review of the previous geologic work in the area. Therefore, only a brief description will be given here to acquaint the reader with the mudstones in the basin. For a more complete understanding of the geology, the works of Bailey (1902), Campbell (1902), Thompson (1929), Miller (1946), Mason (1948), and Blanc and Cleveland (1961a,b) should also be consulted. The Amargosa River, the headwaters of which arise in Pahute Mesa, about 45 km north of Beatty, Nev., is the principal surface drainage of the Death Valley region. Its channel extends southward across the California-Nevada State line and through the area under study before it turns northwest into Death Valley. The river is mostly dry except for short distances where water is supplied by the springs located at Shoshone and Tecopa, Calif., and by infre- quent heavy rains. The Greenwater Valley enters the Lake Tecopa basin from the west, and the Chicago Valley enters from the east. Both, however, have small drainage areas. The Amargosa River has eroded the mudstones which were deposited in Lake Tecopa when, during 4 CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA Pleistocene time, the river was blocked south of the site of the present town of Tecopa. These mudstones appear to be almost horizontal but have a definite slight dip toward the center of the basin. This dip was probably produced by the original slope of the basin floor and by postdepositional compaction. Toward the center of the basin, near the river, the clay beds have been eroded to a low, hummocky surface. Away from the center of the basin, the hummocks become pro- gressively higher and then become buttes capped with gravel which, near the margins of the basin, coalesce to form gravel-capped pediments dissected by steep-sided washes with gravelly alluvium covering the bottoms (fig. 2). The washes, which are as much as 9 m deep make traverse difficult but provide excellent exposures for the study of the mudstones. The gravel covering the buttes, mesas, and pediments has developed a thin covering of desert varnish. FIGURE 2,—View from sample locality 54, looking northeast toward Shoshone. Washes in foreground and middle distance are eroding gravel-capped pediments covered with desert varnish. Light area in the middle distance is central portion of the Pleistocene Lake Tecopa basin where surface is eroded away exposing clays beneath. DESCRIPTION OF THE MUDSTONES AND SILTSTONES A generalized section of the stratigraphy is shown in Figure 3. The uppermost sample collected in the lake beds for this study was located about 12 m above tuff A. The lowest lake beds are not exposed. The beds have a more or less uniform gentle dip toward the center of the basin. The distances between the bottom of tuff A and the top of tuff B ranged from 6 to 8.5 m and the distance between the bottom of tuff B and the top of tuff C was approximately 23 In. The lowermost sample was collected from 7.6 m below tuff C.The tuffs range in thickness from several centimeters to about 4 m. ,\,~,.gfl _ {4: EXPLANATION Sa n dsto ne M udsto n e Xxxxx XXXXXX Tuff xxxxxxxx TMfA xxxxxxx C;::;::; xxxxxxxX TUHB xxxxxxxx r_—_*_—_—_- ______ AAETERS L____—_—_—_ _ 0 :—:—:—:—:—: _. Intermediate :-_— X X K A x Tuff _—_—X_X—X_X—X_X—§ X7 X7 X______ — 10 _—_—_:_:_:_ _,5 X [X i X_X X_X_ 7}} X3 XXX m c We} {xi E: X] {XX X: ——_-_—>onm HHw3 .HmemumE mxHHIHHom IIIII Hm MmowumE< we ummB sz mmem IIIII o q Hm Cq m IIonm Eu oq no wwzu 30Hwn E N.m mucumnsE NHAEEMU IIIIIU q RN oH H u wwau BOan Eu 0N ou 0H wEOumcaE vaumustH IIIIIm q we mN N IIu mwsu m>opm Eo Om mEOuwvse EmumusucH IIIIIonm Eu ON .0 wwsu EH mc0umv=E quauIEoIHH IIIIIo m mm mH m IIo wwnu Sonn Eu Ho mucumvpz IIIIIm n mc mN N 0 Hana w>onm Eu Om accumwaE uwuwhawEH IIIIIoam HmHEwumE mumwusm :Epouaom: IIIIIm m Nu mN mumuh IIIIIII IIIIIIIIII < stu Bonn Eu mH Mm wwzu Bonn wwsu mumvaEumucH m>onm Eu 0m IIIIIonm Eu om accumsz msouom IIIII m H on Hm m m wwnu w>oam E N.H accuwvze msouom IIIII D H mm HN H III II< wwsu BOHma E m.m IIIII o H 2 mN 8m: l- II< ES 322 E 5H lllll m c um oN q IIIII uuuuuuuuuuu I llllllll ¢ muau Emacs NHuumpr umme cmumnHHomcouE: .chmw Eu w IIII<< N Cm cN mcmgk IIIIIIIII I< wmsu BOHwn Eo oq uaoam vacuwsz upmm IIIII onm Eu Ho uzon< IIIIIIHH «umue cH Nm mN IIIIIIIII IIIIIIIIIIIIIIIIIIII a mun Eogw Emen cgm30u .< stu w>onm EwNmH zvcmm IIIIII oH H m Hm mq II II< wwsu m>onm HHmz .mnmn mme we mUHEHH Emuso IIIII I@ a mo «N m III III¢ wwnu sonn E m.H mucumusE anprm IIIII N c H» MN mange II < wwzu 30Hwn E H mc0umvzz IIIII r HN mm CN H II II II< wmau BOHmn E m.N wEOumsz vpmm IIIIIx oH qq mm o IIIIIIIIIIIIIIIII < wwsu Bonn E q.q .mxume BoHHm» new Esopn cuHB mcoumwsE cum: IIIII 3 Hq Nm cH o IIIIIIIIIIIIIIIIIIIII m «wag w>onm E N.H uaonm .< wwsu onma E m.n wcoumuze cum: IIIII > m mm em m I IIIuw ZOHmL uwme EBOMntxmuw IIIII a 0 cm mN HH IIIIIIIIIIIIIIIIIIIIIIIIIIII m stu sonn Eu mm “scam .onm Eu m .mEOEmvaz IIIII o N oH qm we I II< wwsu m>onm Eu Hm .uEOumvzz IIIII m q 0m cm NH IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII < wmsu w>onm Eu Ho ,mEOumUEE xUHsuIEIN.H EH IIIIIonm E N.mH usonm wcou Nmenu .wzowEQUHmu IIIIII o N m Nm Nc III IIIonm E eIm .quEu Eu Ho “scam mEON asepnlzmHonmelxumo IIIII onm E H.0Io ~30n< IIIIII q q me cN c IIIIIIIIIIIIIIIIII pmNmH chmm .emumOL quzu EmIOm sonn cam .< wwzu sonn Eu me IIIIII m H w ON ON IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII < wwau w>onm E N.NHIH.m .qucu E o uson< IIIIII N H q Nm mq IIIIIIIIIIIIIIIII < szu m>onm .Hm>mgm Eu w Na :HmHuv>o wEoN HHom Eu Ho mHnHmmom IIIINm m c Nq Hm IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII < wwau 3cHon .Eg NH :oNHEOL qunuIEUIom.o IIIII m m 0N cm x IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII .< EH2“ onon uwsn .EoNHEos qucuIEquH IIIII wuwu Hmflumuma zucwm vwflwfiumnum tnfimcnmzu Emwuum Eouw Hmwumumfi zuafim Hmfiuwume zuaww IIIIIIIIIIIIIIIIIIIIIIIIII can Emmuum haw Eouw HmflumumE mumwusm wxfiazmau .wwagzu maumm: wummusw :cuouaon: .nouaawz Ecum zmHu zufiflm smms Eouw Ewan zuawm we muww mHuEwm “mm: .sme we awn Eouu vaE zuawm IIIIIIIIIIIIIIIIIIIIIII momwunm wcmfi zomwn E N.H .mEOuman wwumuawcw xUHLuIEUION Ilowmzfimuv Ewumsnwmuo EH wonpsm Eouw vEMm zuawm llllllllllllllll >wa~m> umumzcmmgu cuafl mvcmuxw umcu wwku Eoum xuou nmuwzummscs >m-m> we wuwm co AcmmBusoV Hw>mum mvcwm zwafim> we mvwm ummw co HmflpmumE oumwunm IIIII |¢ mung sofiwn mucumnse EHnE=uu < wmau w>onm E H .wEOumuDE zmuo ||onm Eu om uncuwuzz I I< wwzu w>onm mucumsz wsomhmuamo I m wwsu scams Hmwuoums zuawm umumpzwcH < wwnu Bona Eu Om zmfio wwumhzvcm I< mus» m>onw E m usonm .wwn zEfiH mvcmw Cu muaflm IIIIIIII 9cm mHnEmm uwvc: cam wumwusm vama Seams Eu mNION .mcoumusE wquHsucw :H IIIIIIIIIIIIIIIIIIIIIIIIIII m uwsu w>onm E ~.H unonm .HmwuwumE wommusm :cuoumom: IIIIIII m “man xUHJuIElq.m «0 meL m>onm E N .m wwsu aw wafluumn Emao xuwzuIEUION Ilm «may Bofimn 0:0umU3E umuMEDvcH m wwsu w>onw E H .Hmwuwuwe xuflwm I< wwsu Beams Eu ma usonm .wEOumwaE cwumwwaowcoo < wmau w>onw Eu ma usonm wcoumnsE nwumwflaomcoo Ilt< mmsu w>oam E N .HmwuwumE zufifiw IIU mwsu scams HmHuwumE uwumvHHOmnouc: .aEmQ Ilo mwsu Scams Eu mm .wEOumnzz lino wwnu 30am: uwsu xuwzulEuxw Beamn Eu ma uzonm .o wwau Boawn Eu mm .wEOUmvsz IIU wwsu soawn umsfl zmau kumvwfiomcou IIIIIIIIIIIIIIII o wwzu sonn Eu mm waou wEHH w>onm umzn HmfiumumE nmumufifiowcouab ¢Nm wHaEmm Boamn Eu maxoa HmwumumE zuawm IIIIIIIIIIIIIIIIIIIIIIIIIIIII u wwsu w>onm E N.H wwau mmymunmwcmmhm .xOHnunEo ma IIIIIIIIIIIIIIIIIIIIII < wwzu Beams AHuumuHU mEOuvaE kuMMSUEHIHHwB ImDOQHMUHmU II d wwsu onmQ zfiuuwpfiv acmm zuawm [I . umzuu uamm scams Eu ma uzonm ccmm zuaflm mEmQ Ilmzmaa co umzuu uamm m wmzu 30am; E m.~ HmwumumE umumuaucH I: m wwau Beams Eu mq .wEOumuza AHQEsuo II< mwzu Bonn Eu Om .wEOumudE kuwuzucH II< wwsu m>oam Eu on .wEOuman mzouom < wwzu 30Hm£ Eu malw .wEOuwzmHo wwumuzvcH IIoam HwflhwumE momthm llllllllllllllllllllllllllll Emwuuwzsou E ma usonm uan uwumzcmwuo .wwws mxma w>onm Hm>mhm zvcmm Ilcwwum was <onm E N.H mucumvsz lumNH q m Ho mm u was” we moa uQNNH H mm mm wH o wmau 3onn E 0.5 In N mm mm mm 1:0 HHSH EOHmn E H.N nmmHH m «m mq 0H 0 wwsu w>onm E m.H IIwHH H MH Hm mm o Huau we may ImmoHumH H wH Ho mH :vcmeH: so qua muHvammE we uumn Ewan: Illmmm H m Nq mq m was“ we uuma Ewan: u< nlunmm H q Hq mm ¢ Hung mo wHusz Illmow H «H we mm m wwsu Ho wmmn m>onm E q.H Iliumn N NH Ho «N < stu H0 puma Ewan: Illlmm H mo mm N fl wwau 30Hwn Eu Ho wEOuwnDE IIIUON NH mm Hm mm m stu we mHnnHE «Lu uwmz nulm m mH «o HH < Hus“ we “Ema Moan: lulmoo H mm «0 HH m wmzu mo manHz nulonm E w.a .< «use Illuwm H mH Om pm « Hus» we uumm ummab llnumq H m mH mm « wwzu w>onm waoumuse anmHuHHHw Illa N aw EH mm --< “may we now -unoom H mH Hq Hm --m Hus“ Ho wmmm -uu¢Hm H 0H mm mm Jmmn m>onm E H ‘< wwss Illuom H NH mm oo awn m>onm a H .m Hung ulqu 0 m qq mq m menu mo anuHE ummz IIIINH H H mm sq Ilm wwau Ho ace Illa H m on mm IIIIIIIIIII unmn w>onw E H .m muse lulu m n we mm nwmmn w>onm Eu om .m Hush Illm H wH Nm wN In: Inm wmau BOHmp «Ecuwcaz Illoam Eu Hm .< mwae IIIQ¢I¢H ¢ cc wq c |I< mun“ sonn mHmumHuweEH mc0umc3E JOHsuIEolHo II1N|¢ c we «Q m u mung m>onm umzm mucumwafi E n.~ IIOHlm H mm mm q u wwsu m>onm E o u303m mucummmHU Ilmmlm H mm cm m II< wwau BOHQQ umafl wEOumvnz IIIMIN q mq Hq m m wwzu m>onm meumemEEH wEOummEHH IIImIHHm o H AH Hm Edwuuw uzmuuHEnmucH Ho vwn wnon HmHuwumE zuHHw IIIIII N@ N HH mm mm IIIIIIIIIIIIIIIIIIIIIIIII xumn EH wumwusm uw>Hu w>onm Eu Ho unonm HmHuwumE quHw lllll m m mm am HH Ivmn Emwuuw EH ucwEchm oumwunw vwxomnolusz IIIII ¢Hw H N NN mm IIEmwuum we vwn EH uEmEHnwm NSHHm IIIIII oo o N mm mm awn Emwuum mo xcma EH ucmEHuwm NSHHm IIIIII mm H N wH on uwn um>Hu w>onm a w.q .UHHm llllll mm H m mm mm awn Hm>Hu m>onm Eu 0m ucwEHumm muHHm IIIII m H 0H Nq we IIIIIIIIIIIIIIIIIIIIIIIIIII wma um>Hm mmowme< Eonw HmHuwumE mumwnsm wwxuNHUInnz lllll <~m m NH Hq we uuuuuuuuuuuuuuuuuuuuuuuuuuuu < stu m>onm E NHIm cam wumuusm 3OHmn e a nwn EUHHm IIIIII on o m «H mm mHHHm EHHnao Eouw wcoumeHH NHwho IIIII < 0 quHH oH om mHHH= EHHnsa Eouw wcoumeHH xumHm IIIIII mm HmHuwumE Enwv Eamwlm EnwoA .oz mHasHom zmHu uHHm vcmm mEOHunHuommn tam mcoHumooH UHnamuwHumuuw mHaEmm wwchucooulmmmcwwuu ucm :Hmmn mmoows mkmu mumUOHmmem EONM cmkmu mmHmEmm No \uszhmm 2w :oHu3QHEumww mnwm mwowuwmm him EMEOHuQHHommw ~mEOHumuoH UHEQmHmquMHMII.H mam62 ,u) Silt (2-62,u) Clay (<2/.L) Specific conductance Gravimetric measurements l l of leachates of evaporated leachates X-ray diffraction, X-ray diffraction, X—ray diffraction, Oriented X-ray of random orientation random orientation random orientation aggregate total sample, random Air drying orientation l l X-ray diffraction X—ray diffraction l l Glycol treatment Heat to 400° C l l X-ray diffraction X-ray diffraction l Heat to 550° C 1 X-ray diffraction Glycerine treatment J. 1 X—ray diffraction X—ray diffraction l l MgCIz-saturated KCl-saturated _ ' fraction fraction l X-ray diffraction X-ray diffraction l l Glycerine treatment l l X-ray diffraction X-ray diffraction FIGURE 5.—Flow sheet illustrating procedures used for mineral identification. sampling irregularities make comparisons of small amounts subject to error. Chemical determinations were made as needed when X-ray determinations were inconclusive. For instance, when single small peaks at 30.4° 29 on the diffraction patterns indicated possible manganocalcite, the car- bonates were removed by dilute hydrochloric acid. Qualitative manganese determinations were made on the resulting solutions. The amount of amorphous material in the clay-size fraction was difficult to estimate either optically or from X-ray patterns. Therefore, samples appearing to contain more than two parts in ten of amorphous material were boiled for 21/2 minutes in 0.5 N sodium hydroxide, according to Mallory’s (1965) method, and the weight loss sustained was reported as amorphous material, after the percentages of previously determin- ed water-soluble material were subtracted. Transmission electron micrographs (figs. 6-9) were made to illustrate the morphology and to confirm the presence of the different types of clay minerals. X-ray diffractograms and chemical analyses were made of concentrations of individual minerals to better deter- mine their characteristics. N ONCLAY MINERALS Although this investigation is primarily concerned with clay mineralogy, identification of the nonclay minerals is needed, because they may be either a source of materials necessary for the formation of authigenic clays or indicators of detrital origins. QUARTZ AND PLAGIOCLASE F ELDSPAR Quartz, which is mainly detrital, is found in most samples but only in small quantities, the largest amount being the 3 parts in 10 found in sample 47. This sample was taken in the area where sediments from Chicago Valley were brought into the lake basin. In general, the amounts of quartz are highest near the edges of the basin, at the northern end where the Amargosa River enters the basin, and near the junc- tions of the basin with Greenwater Valley and with Chicago Valley. Stratigraphically, the greatest amounts of quartz are found in the youngest sediments above tuff A. Bet- ween tuff A and tuff B (fig. 3) there appears to be a general decrease in quantity of quartz, but in the 7.6 meters between tuff B and the intermediate tuff still CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA 10 JII I4 I. 1 I .HH III Hv N III .MH III III III Hv +H +N III III Hv III III +H .MH .HH H IIIII m ..H III N ..H III .MH III III III H +H +N III III +H H III +N ..H ..H ..H ..... o ..H III Hv III III H III III III Hv +N m III ..H III H III +H ..H ..H .HH ..... 0 .HB w .MH III III III III III III +H Hv +H III III +N III N +N III .HH .HH IIIII m Hv III Hv III III Hv ..H III III +H H +~ III III +H III III Hv III ..H ..H IIII<< .MH III .HH m III III III III III +H +H +H III III +N III III +H III .HH HV IIIII Hv III +H .MH III .HH III III III III +H +N III .HH III N Hv +H .MH .HH Hv IIIII D Hv III H .HH III .HH III III III III +H m III III III III Hv Hv .HH Hv +H IIIII 0 .HH III H ..H III N III III III .pH +H +H N III III ..H ..H +H ..H +H H IIIII m NH 6 III .HH III .HH III III III III +m +N .HH III III N m +H .MH Hv .HH IIIII HuHmoa How Hwnfisc wzu cmwzumn wsHm> .mcowumcflskwumv uwuumEH>MHw Ho \cwmmn mmoomB mxmu m2®00umHmHm EOHM mmHQEmm m0 «Emu Cw wuxmm EH» COHuHmOQEOU uHmonumcwEII.m mqmdfi . HHmEm OOu ucsoEm m m mwumUchH .+ mucmupma cmzu mme mucmEmuammmE oocmuoavcoquHwHuwaw kn nwcHEHmumU wwa mHmHkumE ansHomH HUCJOW uo: .AIIIV muwwmmg ”Honssc pwszL uxm: mzu cum HOQEAm wzu mchmumHa ..HH .ucwuuma OH vcm m cwwsumn .Hv muczoE mmHo wmucmwko m0 wcm .mEOHuomxm m:0whm> mag MO muzzoE @mucmwno mmEowcmM M0 mummuumm EOHHUMwaHw mmme EOMM wmumeumm 11 NONCLAY MINERALS .MH Hv .HH .hH Hv Hv .HH .HH .uH .HH +N .HH .MH .HB .HH .HH .HH .HH HV .HH .HH .MH .MH .HH .HH .HH .HH .HH Hv .HH .HH .MH .HH .HH Hv .HH .MH .HH Hv Hv Hv Hv +H Hv Hv Hv .hH .MH (s. o. .MH .MH .HB .HH .98 .HH Hv .HH .MH .HH .MH .HH .HH .MH .HH .HH .MH .uH .HH +H Hv .HH Hv .mv +H Hv .MB +H Hv Hv +H +H +H HV +H +H +N +N +N Hv +m +N +H +H +H +N +N Hv +H +H +H +H +m . My +N +m +N +m +N +m +m +N +N +m . um. +N +m +m +H .HH .HH . HE +H +H +H +H +H +H .HH .HH .HH .HH Hv Hv +N +N +N +H Hv .uH .HH Hv Hv Hv Hv +H Hv +H +H Hv +H Hv (.5 .5. .5. +H Hv Hv .HH +H .HH .MH .uH “0-6‘ .uH +H .MH .MH .MH .HH +H Hv 3:. av .HH +H Hv .uH +~ +H +N .HH .uB .HH .HH Hv +H +H .MH Hv .HH .MH .HH .HH .HH QH +H CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA 12 .HH III HV III III III Hv III III .MH .HH N .MH .MH III III .uH Hv III m +H IIIII m .HB III HV 6 III III .uH III III III .uH +N Hv Hv III III .uH Hv III +N +N IIIII mflu mo mumzofi umutmwuo mHEOEEMH MO mmhmuumm :OHuomuwwww mmNIN EONM wmumeumm ~2Hmmn mQOUma mama mumUOHMHmHm EOHM mmHQEmm No «Emu 2H muhmm EH» :oHuHmOQEOU UHmOHMchwEII.N mqm<fi 13 NONCLAYLHNERALS .wuHmmemwm: .wUfiwwmmmZm duo :m mufiHmQOUw. N .wuHE%vHuu v.moHHHw wCHHmaoH .MH .HH .MH Hv .ue .uH .uH .MH .HH .HH .HH .HH .HH .MB +H .MH .HB US. .5 .5. .5 .HH QB .HH .HH .MH .uH .HH .HH .MH Hv +n .MH .uH .MH .MH .uH Hv .uH +0 .uH .HH .HH .‘HH .MH CC. .ME .MH .HH Hum. .HH Hv Hv Hv Hv Hv +N +H +H Hv +H +H +N +m +H +H +H +N +N +H +H HV .MH Hv Hv .gH .MH .HB .uH .uH .HH .MH +H Hv .MH av Hv +H Hv Hv .MH .HH .uH .HH .ua av +H CC. .HH Hv +H .MH .MH +m +H Hv +H +H Hv av Hv .MB 3C. .MH .35 .MH .uH Hv Hv +H Hv Hv Hv +H ImHmH I. E D E =' L: S 482 5’ A 2 o 0"“: L: 0 350: u. 9 -’ 0: u.Lu m :9 E 2 0 I: 5 E 02”: LLI _ < E I — — _| 0: m —' l— 2 o 0: I-z L“ 5 Q < z O m 0 << 5 D E 9 0 fi 35 2’ E E 2 m 2 E w 2 o to I i i _ < __ _ _ LL _ _ — 5 —1o:— 2— — — Lu 2'— _ > _ O _ m _58 — <2: _ '— 2 _ 2 3\ Q 6\._ _ _ ‘ 3; — 2L _ £11315? : _U, Q 2 —EE2 2 —LT”< — ‘ -2E< — — mm 2 _"th 3x _00 D \_ — 2‘ — _ _ l—4§/_ _ - 2— ' :2 _ 2/— — _ : co LL 2— — V _ 5 _ —5 l- 2— 3" — 5 ‘ fi LVWL WWW \f NW —20 e s _ l) c: 3—— : _ 3— ' ' —25 r30 R 0 50100 0 50100 0—50 0 50100 0 50 0—50 CLAY MINERALS, AS PERCENT OF CLAY FRACTION FIGURE 12.—Vertical distribution of clay minerals, in percent. If more than one sample was taken at a given level, the data from the number of samples shown in the second column were averaged. No samples were taken between 9.45 and 18.29 m below tuff B. 21 22 CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA RANDOM MOUNTS Mica- saponne K‘Afi IIIJ\;J_J 1110987654 DEGREES 20 COPPER K0 FIGURE 13.—X-ray diffraction curves showing typical gradation from mica to mixed-layer mica-saponite. 3 | 1 1 ORIENTED CLAY AGGREGATE MOUNTS llllll 1098765 DEGREES 20 COPPER Ka l 4 CLAY MINERALS 23 LITHIAN SAPONITE The most widespread clay mineral in the area is lithian saponite, which is found not only within the Lake Tecopa basin but also in Chicago Valley and along the Amargosa River upstream. Electron micrographs (fig. 2) of some of the purified clays from the Lake Tecopa clay beds show a fibrous character. There may be some sepiolite in the sample which was otherwise undetected, but as can be seen in figure 8, the sepiolite fibers are about twice as long as the fibers in the clay which has been identified as saponite. Saponite, as well as sepiolite, may be fibrous as reported by Midgely and Cross (1956), and Caillére and Hénin (1957). The chemical analysis (table 5) shows that the mineral is high in magnesium, has a lit- tle more iron and aluminum than is usual for saponite, and contains lithium. Although the sample was purified as much as possible (no impurities detected by X-ray diffraction) there could be a slight excess of silica due to the amorphous material which is common in the area. The amount of lithium is less than has been reported for hectorite from Hector, Calif. (Ross and Hendricks, 1945; Ames and others, 1958), and the alumina content is greater than in hectorite; therefore, we term this clay a saponite, recognizing the possibili- ty that instead of being a lithian saponite, the clay ac- tually may be a mixture of saponite and hectorite. The position of the 060 diffraction peak near 1.51 A in- dicates that almost all the smectite minerals in the Lake Tecopa mudstones are trioctahedral. Lithium, magnesium, and fluorine analyses of 12 samples from various parts of the lake beds (table 6) demonstrate that these elements are present throughout the area. Fluorite was found in none of the samples: small amounts would have been easily detected by X-ray dif- fraction. Fluorine was not determined in the purified sample because the purified sample was depleted by other analyses. Lithium in clays has been found in other locations in the arid southwestern part of the United States as reported by Kesler (1960), Norton (1965), and Shawe, Mountjoy, and Duke (1964). Foshag and Woodford (1936) reported that a clay from 5 km south of Hector, Calif., was a hydrous magnesium silicate containing appreciable lithia and related to saponite. They stated that similar clays were widespread in the Mojave Desert region of California and Nevada. Strese and Hofmann (1941) named the mineral hectorite. TABLE 5.--Chemical comparison of Pleistocene Lake Tecopa saponite with other smectites [Values in percent. Leaders (——-), not found; n.d., not determined] Lake San Tecopa, Hector, Bernadino, Clay Spur, Calif. Calif. Calif. Wyo. Sample ————— 1 2 3 4 Si02 ——————— 55.82 55.86 44.00 60.96 A1203 —————— 4.61 .13 10.60 18.27 Fe203 —————— 2.04 .03 Trace 2.83 FeO -------- .21 ——— --— .14 MnO ———————— .04 None --- -—— MgO ———————— 21.11 25.03 24.30 2.96 CaO ———————— 1.42 Trace 2.00 .10 K20 ———————— 1.50 .10 ——- .31 N320 ——————— .47 2.68 ——— 1.44 Li20 ——————— .34 1.05 --- --— T102 ——————— .19 None ——— .08 F —————————— n.d. 5.96 --— ——— P205 ——————— .03 ——— --- -—- H20+ ------ 5 76 2.24 6.20 6.56 H20- —————— 5 26 9.90 12.60 6.78 Total— 98 80 102.98 99.70 100.43 0 = F —————— ——— —2.51 --— ——— Total —————— 98.80 100.47 99.70 100.43 SAMPLE DESCRIPTIONS l. Lithian saponite, acetic acid—leached clay fraction. 2. Hectorite (Ross and Hendricks, 1945). Saponite (Ross and Hendricks, 1945). Montmorillonite (Kerr and others, 1950). DB) Ames, Sand, and Goldich (1958) described hectorite as being formed by the alteration of silica tuffs by solu- tions containing lithium and fluorine in the last stages of hot-spring activity and by lake waters that furnish- ed magnesium. Sand and Ames (1958) said, in their in- vestigation of altered silica volcanics for a source of refractory clay, that saponite is often formed as a result of hot-springs activity where pyroclastics are deposited in alkaline lakes. Their investigation includ- ed the Hector, Calif., area. Later, Sand and Regis (1960), reporting on a lithium- and fluorine-bearing montmorillonite from Tooele County, Utah, questioned whether the magnesium in hectorite was furnished by lake waters. Although hot springs are found in the area at the present time, it does not appear that the lithium and fluorine in the saponite were due to hot-springs activi- 24 CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA TABLE 6.—-Weight percent of magnesium, lithium and fluorine in total samples from scattered locations in clay beds of Pleistocene Lake Tecopa [Mg and Li determined by atomic absorption by Violet Merritt. F determined volumetrically by (Mrs.) Johnnie Gardner] Sample No. Mg Li F 8A ———————— 10.1 0.082 0.50 9 ————————— 3.00 .021 .11 12C ------- 13.4 .080 .74 D ——————— 7.00 .041 .29 16B ——————— 8.80 .042 .10 17A ——————— 8.80 .044 .37 B ——————— 13.4 .058 .35 25A ——————— 4.00 .010 .04 32C ——————— 10.1 .034 .31 36B ——————— 10.6 .056 .43 36E ——————— 13.6 .078 .78 41 ———————— 8.80 .060 .50 ty. Analyses of the clay-sized fractions (table 7) of sam- ple 53 from Chicago Valley and of sample 61A from the bed of the Amargosa River (fig. 14) about 29 km upstream from Lake Tecopa show that lithium and fluorine are both present outside the lake basin as well as within the basin, and in the same order of magnitude. The presence of lithium and fluorine in the present-day drainage suggests that these elements came from some other source than hot springs within the lake basin. Noble, Smith, and Peck (1967) presented fluorine analyses of 164 volcanic rocks of late Miocene or Pliocene age from southern Nye County, Nev., about 160 km north of the area under present study. The largest amount of fluorine in any sample was 1.40 per- cent with the average value being about 0.13 percent. Noble (Written Commun., 1970) supplied the authors with analyses of glasses from the same area that con- tained about 10—40 ppm lithium. Livingston (1963) reported 0.16 ppm lithium in the waters of the Amargosa River at Beatty, Nev., which is approx- imately 120 km upstream from Lake Tecopa. The occurrence of lithium in such a wide area demonstrates that there is sufficient lithium available FXGURE 14.—Polygonal mud cracks in bed of the Amargosa River at sample locality 57. The clay mineral crusting the entire surface is saponite. without relying on hot springs as a source. Lithium could have been introduced into the lake by the waters of the Amargosa River. Although hectorite has been thought to be of hydrothermal origin (Ames and others, 1958), ghassoulite from Morocco, which Faust, Hathaway, and Millot (1959) equated with hectorite, was said by Millot (1949) and Jeannette (1952) to be authigenically formed in a lake environment. Papke (1969, 1970), in studies of the montmorillonite-type clay deposits in Nevada, reported that montmorillonite is the predominant clay mineral in all the deposits studied except at Ash Meadows where saponite, formed by the sedimenta- tion and alteration of volcanic ash in lakes, is present. He did not determine if lithium was present in the samples. The presence of other detrital minerals, such as quartz, plagioclase feldspar, and mica, in the clays plus the presence of saponite in the drainage area outside the basin indicates that the saponite is detrital. However, we cannot rule out the possibility that some saponite may have formed authigenically in the basin sediments under conditions similar to those described by Papke (1969, 1970) in the Ash Meadows area north of Shoshone in the Amargosa River drainage. CLAY MINERALS 25 MONTMORILLONITE Montmorillonite, in the Lake Tecopa area, appears as an authigenic mineral that has two types of origin. “Amargosite,” found just west of Shoshone, is a soft, sticky, white montmorillonite which, despite the desic- cating effect of the present climate, is moist. This clay was formed by the hydrothermal alteration of a volcanic ash by warm springs laden with salts (Melhase, 1926). The warm springs found in the Shoshone area today may be relicts of the springs that produced the alteration. The other type of montmorillonite is found in or very close to the tuffs deposited in the lake itself and was formed by the action of the saline lake waters on the siliceous glass of the tuff. Sheppard and Gude (1968) reported that they observed glass shards, which had been altered to zeolites, that were coated with mont- morillonite. This montmorillonite is restricted and composes only a small fraction of the clay minerals. Montmorillonite is readily formed by the alteration of volcanic ash when alkalis and alkaline earths, par- ticularly magnesium, are present (Papke, 1969). A possible reason for the small amount of mont- morillonite could be that it was formed immediately after deposition of the ash (Grim, 1968) when the Na*+K*:H+ activity ratio was low. Alteration of silica glasses to montmorillonite was viewed by Hay (1963) as a hydrolysis reaction releasing silica and alkali ions into solution and raising the pH, producing conditions more favorable to formation of clinoptilolite than to formation of more montmorillonite. Several samples taken high above tuff A contained montmorillonite even though the site was not near any known tuff. These montmorillonites are usually associated with clinoptilolite. Inasmuch as these two minerals are commonly derived from volcanic ash, their presence indicates that an ash fall may have been deposited after that which formed tuff A. This evidence supports the conjecture of an ash fall as a source of silica for the sepiolite found above tuff A. SEPIOLITE TECOPA BASIN OCCURRENCE The Tecopa basin sepiolite is most prevalent in a nar- row band near the upper limit of the lake beds at about 488-m elevation. This elevation coincides with the stratigraphic level of tuff A (fig. 15); most of the sepiolite is found within a meter or two of the tuff, usually just below its base. A few other, scattered, sepiolite-bearing sediments were detected near tuff B (fig. 16), and occasionally throughout the stratigraphic column above tuff B (fig. 12), especially near the lake margins (fig. 15). One sample (25 SB), located near an intermediate tuff deposited 5 m below tuff B, also con- tained sepiolite, as did several samples in an anomalous occurrence 7.6—12 m above tuff A. Sepiolite is one of the most abundant of the possibly authigenic clay minerals found in the mud and siltstone beds adjoining the tuffs in the Tecopa basin. Little or no sepiolite has formed directly in the tuff for- mations, except occasionally in clay partings which were deposited in the tuffs. The only other probable authigenic clay mineral identified in or near the tuffs is the small amount of montmorillonite mentioned in the preceding section. The sepiolite of Tecopa basin does not occur in bulk form or in pure beds. Electron micrographs of the suspended material, and X-ray diffraction patterns of the total samples show the sepiolite fibers to be dispersed among the detrital and zeolitic minerals. As shown in the electron micrograph (fig. 6) of the clay fraction of sample 21, most sepiolite fibers are about 1 a or less long. However, some sepiolite fibers more than 2 )4 long have been observed in sample 1A (fig. 7). The electron micrograph of a surface replica of some of the sepiolite-bearing sediment (fig. 8) shows that the fibers may occur in very small randomly oriented bundles. An attempt was made to separate and purify the ap- proximately 50 percent of sepiolite from sample 21, but we were unable to remove all the saponite, illite, and poorly crystalline feldspar. An X-ray diffraction pattern of the impure sepiolite displays the broad peaks typical of many poorly crystalline sedimentary- type sepiolites. The diffraction pattern is compared in table 4 to that of a well-crystallized sepiolite. Ap- parently no rapid, large-scale accumulation of sepiolite has taken place at any time in this area, but rather a localized deposition in small amounts. Some sepiolites have been found in arid, alkaline en- vironments similar to the environment of the Lake Tecopa beds. Grim (1953) stated that sepiolite is par- ticularly prevalent in sediments accumulating in desert lakes containing alkaline waters with slight cir- culatory movement. Alternatively, Parry and Reeves (1968), after noting that others (Giiven and Kerr, 1966; Grim and others, 1960; Eardley and Gvodestsky, 1960; and Droste, 1961) had reported no sepiolite in their various reports on desert lakes and playas, suggested that sepiolite apparently was not as common as Grim (1953) had previously indicated. They did conclude, however, that the sepiolite found at Mound Lake, Tex., was formed in a saline, lacustrine environment by the alteration of preexisting montmorillonite. Others who have reported occurrences of sepiolite in saline, lacustrine environments include Bradley (1930), Yar- 26 CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA TABLE 7.—-Lithium and fluorine in samples outside the boundaries of Pleistocene Lake Tecopa [F determined by electrode method by D. R. Norton and (Mrs.) Johnnie Gardner; Li determined by atomic absorption by Wayne Mountjoy] Sample Localities F Li 0 (percent) (ppm) 53———— Chicago Valley 0.48 330 6lA——— Amargosa River, .58 440 29 kilometers upstream of Pleistocene Lake Tecopa. zhemshkii (1949), Hardie (1968), and Papke (1972). In- asmuch as sepiolite is found in some saline, lacustrine environments but not in others. apparently a par- ticular set of circumstances other than the basic en- vironment is necessary for its formation. PREVIOUS WORK ON SEPIOLITE Siffert and Wey (1962) produced at room temperature a fibrous clay of the sepiolite type by reac- ting Mg‘2 ions with silica in solution. The initial pH of the silica-magnesia solution was 1 1.20 and the final pH was 8.73. Wollast, Mackenzie, and Bricker (1968) reacted sea water with aqueous silica and produced a hydrated magnesium silicate compositionally and structurally similar to sepiolite. They also demonstrated that with a rise in pH of alkaline lake waters that have been concentrated by evaporation sepiolite may be precipitated if sufficient sources of magnesium and silica are available and if the dissolved silica is not removed from the waters by diatoms through biochemical processes. However, even if the silica is available, if the pH doesn’t rise above 8.0, sepiolite doesn’t form, even matastably, but the waters tend to become saturated with amorphous silica. Conversely, if silica activity is below the sepiolite saturation level and the pH is near 10, the magnesium may precipitate as brucite or hydromagnesite, or, under the proper conditions, even as dolomite. At a later time, if silica is reintroduced to the interstitial waters by dissolution of diatoms or nearby volcanic ash and dispersion of the resulting silica by circulating waters, then sepiolite may form as an authigenic mineral when the silica combines with the earlier form- ed magnesium mineral or with magnesium in solution. Another determinative factor is the presence or absence of reactive aluminous phases in the waters or sediments. If ionic alumina is present, the silica and magnesium are more likely to combine with it to form alumino-silicates, such as chlorite or montmorillonite, rather than sepiolite. In an attempt to synthesize sepiolite, Mumpton and Roy (1958) experimented with gel mixtures of the ap- proximate composition of the average sepiolite using MgO (38.1 percent), Si02 (59.6 percent), A1203 (2.3 per- cent), and H20. In about 100 runs at various temperatures and water pressures, they produced only montmorillonoids, talc, silica, or chloritic phases, but no sepiolite. They had started with the essential ingre- dients with which Hast (1956) and later Wollast, Mackenzie, and Bricker (1968) synthesized sepiolite, except that Mumpton and Roy added A1203 to the system. This would indicate that the presence of alumina in the mixture inhibits the formation of sepiolite from solution. Millot (1960), Isphording (1973), and Heron and Johnson (1966) have proposed an authigenic origin by direct precipitation for sepiolite in the natural sediments that they have studied. Precipitation could occur where the pH and MgO contents were high but A1203 was low or absent. In addition, Wollast, Mackenzie, and Bricker (1968) pointed out that sepiolite was commonly associated with carbonate sediments where alumina was low at the time of their sedimentation but not associated with shales where alumina was high. Therefore, it is evident that in order to form sepiolite authigenically, we need a source of magnesium, a source of silica, a pH higher than 8.0, and little or no reactive alumina present. MODES OF SEPIOLITE FORMATION Several possible sources were considered for the sepiolite in the Tecopa basin sediments: _ 1. Clastic deposition was ruled out because most of the sepiolite was concentrated in the vicinity of the ash beds; a more uniform distribution throughout the strata would be expected if the sepiolite were of elastic origin. Also, no sepiolite was found in the sediments surrounding the basin. 2. Direct diagenesis from the volcanic ash is unlikely. Little or no sepiolite was found within the tuff for- mations. It occurred most frequently within a few feet above or below the ash beds. Furthermore, none of the optically examined volcanic glass shards showed any alteration to sepiolite. CLAY MINERALS 27 3. A transformation of a parent smectite clay to a sepiolite, as suggested by Parry and Reeves (1968) for sediments in pluvial Mound Lake, Tex., was also considered. The dominant smectite mineral, a high- magnesian trioctahedral saponite, is found in all sec- tions and stratigraphic levels of the sediments of Tecopa basin whereas sepiolite is not, the sepiolite being principally detected near the tuff beds. Although we do not believe that the saponite was transformed directly to sepiolite, we do not rule out the possibility that slight dissolution of the mineral in a high-pH environment may have supplied some of the silica and magnesium necessary to authigenically form the sepiolite. 4. The sepiolite may have been precipitated directly from solution. We contend that the principal mode of sepiolite precipitation involved postdepositional fac- tors as well. Silica, in solution or in the form of a natural gel, may have combined with a previously formed magnesium mineral in solid or colloidal form, or may have possibly reacted with magnesium in solution in a high-pH, postdepositional environment. The latter possibility seems the most probable. One way in which sepiolite precipitation might occur involves the direct combination of silica and magnesium as they mix in solution in the lake waters after being brought in from the lake’s drainage basin. Papke (1972) suggested a sequential precipitation of dolomite and sepiolite in the Amargosa Flat, north of the study area. In this playa basin the magnesium in solution probably increased in concentration through evaporation until it began to precipitate out as dolomite. Then slowly increasing silica in solution com- bined with the magnesium and also precipitated sepiolite to form a combined bed about 1.2 m thick. A small percentage of detrital minerals was also included in the bed, and this, combined with a lack of internal bedding in the formation, indicates “rapid accumula- tion or, at least, constant conditions during deposition.” Apparently this did not occur in the Lake Tecopa basin as no massive beds of this sort, contain- ing sepiolite, were identified in its sediments. Jones and VanDenburgh (1966) have shown that even though the waters of Lake Abert, a closed basin lake in southern Oregon, contained high concentra- tions of magnesium and silica in solution, no sepiolite or even dolomite was spontaneously precipitated therein. Droste (1961) has also found that many of the playa and closed basin lakes of southern California contain no sepiolite in their sediments. Therefore, even though the ingredients may be there, sepiolite isn’t necessarily formed in these lakes in the manner described by Papke. Because of the formation in Lake Tecopa of only small quantities of sepiolite, most of which was adjacent to the tuff beds, widespread precipitation in open water seems unlikely. SOURCES OF MAGNESIUM AND SILICA Sheppard and Gude (1968) have reported the presence of thin beds of dolomite in the Tecopa sediments: one below tuff B and one between tuffs B and A, both toward the central part of the basin. If there were any dolomite beds in the younger strata they have since been removed by erosion. The presence of the two thin beds would indicate that at various times the lake waters had a high concentration of magnesium in solution and a pH of well over 8.0 in order to precipitate the dolomite (Peterson and others, 1963, and Skinner, 1963), or to convert calcite to dolomite. In addition, chemical analyses of the unaltered shards of the tuffs A and B showed a magnesium oxide content of 0.5 to 0.8 percent, which could become available on dissolution of the ash (Shep- pard and Gude, 1968). A magnesium content of 22 ppm was also determined in the spring water of the basin (Sheppard and Gude, oral commun., 1976). Additional magnesium in solution or as detritus was probably brought in from the north through the Amargosa River drainage areas which contains dolomite forma- tions and significant quantities of the high-magnesium smectite, saponite. When the ash and clay beds were deposited, this magnesium from all these sources was incorporated into the sediments and interstitial water, possibly as brucite or hydromagnesite in solid or col- loidal form if the pH became high enough, or as solu- tion with a high concentration of Mg ions and a fairly high pH. Further concentration of magnesium would occur during periods of evaporation of the lake waters. It is evident that a sufficient supply of magnesium was available for the precipitation of sepiolite if other en- vironmental conditions were propitious. An adequate source of silica in solution is also readi- ly available in the ash beds which were deposited at in- tervals in the lake basin and surrounding countryside. Alexander, Heston, and Iler (1954) have shown in laboratory experiments that different forms of amor- phous silica, including colloidal silica, will approach a constant solubility concentration in water in the range of 100 to 140 ppm at a temperature of 25°C. The solu- ble silica is in the form of the monosilicic acid Si (OH)4. The solubility of the silica is almost unaffected by pH’s below 9 but increases rapidly as the pH climbs, reaching about 400 ppm at a pH of 10 and about 3,600 ppm at a pH of 1 1. An increase in temperature will also increase the amount in solution and the rate of solubili- ty of silica. They also noted, as did Krauskopf (1956), 28 36° 00’ 55’ 35° 50’ CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA 116°20’ 15’ 115°10’ l | l EXPLANATION Clay mineral I: Sepiolite — Mica V/l/l/l/l/l/lA Montmorillonite Saponite Mixed-layer clay Chlorite Sample taken . In tuff A 4 Above tuff A ; Below tuff A .—a Measured section 0 I 2 3 4 5 KILOMETERS |_;l_l_l_J J l FIGURE 15.—Loca].ity map of sample taken within 1 In of tuff A. Clay mineral content expressed as proportion of length of bar. 36° 00’ 55’ 35° 50’ CLAY MINERALS 116°20’ 15’ 116°10’ 29 I l I | EXPLANATION Clay mineral Sepiolite Mica Saponhe Mixed-layer clay Chlorite Sample taken . In tuff B Above tuff B l Below tuff B .—. Measured section $5427 B l T5449 A Edge of Pleistocene Lake Tecopa 0 l 2 3 4 5 KILOMETERS L__‘L_I_L__L_l | l FIGURE 16.—Samples taken within 1 m of tuff B. Clay minerals expressed as proportion of length of bar. 30 CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA that at a pH over 9.0, colloidal, low-molecular-weight polysilicate ions are in equilibrium with the soluble monosilicic acid. As the soluble silica is removed from the solution by precipitation, the colloidal polysilicate spontaneously reverts to the soluble form and replenishes the supply of available silica in solution. Therefore, we postulate a constantly renewable source of soluble silica available in the vicinity of the ashfalls in the beds of Lake Tecopa when the pH was high ow- ing to evaporative concentration. We do not know the ultimate concentration of the silica in the lake but some recent studies of alkaline carbonate brines in closed basins have determined natural waters to con- tain as much as 2,700 ppm silica (Jones and others, 1967). SEPIOLITE FORMATION IN LAKE TECOPA As previously indicated, sepiolite is not found within the tuffs of the Tecopa basin but is most prevalent in sediments immediately adjacent to both the unaltered ash and the zeolitized ash. The question arises as to why sepiolite is absent from the ash but present in the other two environments. The mudstones, siltstones, and volcanic ash were probably deposited in waters with a pH of 9 or higher. Some intermixing of the ash and the previously deposited detritals occurred at their interface. Subse- quent evaporation and concentration tended to in- crease the salinity and pH in a downdip direction toward the center of the basin. However, owing to rain, snow, or the inflowing waters of the Amargosa River, incursions of fresher water into the lake basin flushed out the excess alkaline cations and lowered the pH of the outer, more-exposed, edges of the ash beds. This left the outer edges unaltered even as zeolitization started in downdip parts of the bed. In addition, there were periods of time when evaporation of the lake limited the waters to the central part of the basin so that the edges of the ash bed were not immersed in high-pH waters. Authigenic sepiolite, however, was still able to form beneath the unaltered ash. Undoubtedly, in times of fairly high pH (about 8) some dissolution of the ash occurred and silica and the alkalis were disseminated, by circulating waters, downdip and into the detrital beds below and above the ash bed. The concentration of silica increased to saturation in the ash but the pH was not high enough nor the concentration of the magnesium great enough to precipitate sepiolite. With an influx of fresh water the pH dropped throughout the system. The soluble silica was then in a supersaturated state so it began to precipitate out as a colloid or as sepiolite when it came in contact with the magnesium-saturated, high-pH pore waters in adjacent detrital beds. Some sepiolite also may have formed over long periods of time when initially admixed ash dissolved in the high-pH, original pore waters of the adjacent beds and combined there with magnesium in solution to precipitate out. Inasmuch as alumina does not readily go into solu- tion at a pH of less than 9.5, probably insufficient alumina was present to precipitate zeolites either in the unaltered tuff or in any significant quantity in the adjacent beds where sepiolite occurred, as seen in the table of mineral analyses (table 2). What small amounts of zeolite were formed with the sepiolite pro- bably were precipitated from the original pore waters which dissolved the admixed volcanic glass to provide the necessary alumina, silica, and the alkali cations. Phillipsite was most commonly found in the zeolitized tuffs or at their interface with the siltstones and claystones of the adjacent beds. Clinoptilolite was the zeolite most often found with sepiolite, sometimes with and sometimes without phillipsite. Downdip in the basin the ash beds were zeolitized owing to more constant exposure to high-pH waters. Dissolution of the ash (and concentration of the waters) had produced a pH of 9—10 and the necessary soluble ingredients, silica, alumina and the alkalis, for formation of the various zeolites; but sepiolite didn't form in the ash bed owing to the presence of alumina. All or most of the alumina was used in forming zeolites or other aluminosilicates within the tuffs, or at the in- terface of the tuffs and the adjacent beds, as shown by Sheppard and Gude (1968). After removal of the alumina the waters disseminating into the adjacent beds were still supersaturated with silica. A drop in pH then caused the silica to form a colloid or to combine with the available magnesium and precipitate out as sepiolite in the pore waters near the zeolitized tuff. An alternative method to direct precipitation of the mineral from solution is as follows: Silica has a great affinity for magnesium which would tend to adsorb on the colloidal silica .surface to form a hydrated magnesium silicate. Later desiccation could remove some of the water to form sepiolite. Sepiolites found in sediments near other tuffs in the basin sequence probably were formed in the same man- ner as those described above. However, some sepiolite detected in other parts of the basin may have a dif- ferent genesis. Several samples, taken from sediments approximate- ly 7.6—9.1 m, and one at 12 m above tuff A, also con- tained sepiolite. Sample 4, containing approximately 40 percent sepiolite was taken about 1.3 km southwest of Shoshone, in the northern part of the basin and 7.6 m above the tuff A. It is possible that a thin ash bed CONCLUSIONS 31 might have been deposited in the lake waters at that time, to act as a silica supply for sepiolite. N o trace of one was found by the authors at this location or at the other locations around the basin at that altitude where the samples containing sepiolite were collected. However, several nonsepiolite-bearing samples taken at those altitudes, 2, 20A, 20B, and 24, contained dioc- tahedral montmorillonite and clinoptilolite, both of which are products of ash devitrification. Under the proper conditions of pH, magnesium con- centration, and silica saturation, it is possible that at the locations listed in the preceding paragraph and other anomalous locations far from ash beds a direct precipitation from solution may have occurred as described by Papke (1972). However, no real evidence of this was found. An alternative possibility for a silica source for sepiolite precipitation would be the presence of abundant diatom colonies in the lake. Sheppard and Gude (1968) have stated that 42 species of diatoms were identified in their fossil locality 5 about 1.6 km northeast of the site of sample 4, at about 488+ m altitude. Some of the diatoms were identified as “fresh water” types which would correlate with their location in the north end of the basin where the Amargosa River entered, supplying fresh water from a con- siderable drainage area to the north. A flourishing colony of diatoms might remove a con- siderable quantity of silica from solution in the lake waters (Phillips and VanDenburgh, 1971). If the supp- ly of fresh water diminished radically, the salinity would rise and kill off the colony causing decay of the organisms and a rapid return of silica to the environ- ment. With a high enough pH and source of magnesium, a localized precipitation of sepiolite might occur wherever a colony had been located. Sample 37 in the same approximate area as diatom fossil locality 5, and altitude as sample 4 (7.6 m above A tuff), has an ostracode bed that indicates a fresh-water environ- ment. Sample area 39 on the east side of the basin at approximately the same altitude as sample area 4 also contains fresh water ostracodes, as well as a small amount of sepiolite. Two other sample sites, 50 and 56, containing sepiolite, are in an area where fresh water would intermittently incur and are at about the same altitude as the site of sample 4. Therefore, although diatoms were not actually found at the sepiolite sites at that lake level, 7 .6—9.1 m above tuff A, we cannot rule out the possibility that they were a source of the necessary silica for sepiolite precipitation in the high- pH, magnesium-concentrated pore waters of a later lake phase. On the basis of our laboratory experimentation and field evidence we conclude that the sepiolite found in the Tecopa basin is of authigenic origin. The volcanic ash beds, and possibly in some cases fossil diatoms, supplied the necessary silica in solution or colloidal form to combine with magnesium in a high salinity, high-pH lake-water environment. Sepiolite may have precipitated directly from solution in open lake waters at various times after the deposition of tuff A but no proof is available. DISCUSSION SEQUENCE OF EVENTS During the middle to late Pleistocene, the Amargosa River was dammed by alluvial fan deposits south of the present-day site of Tecopa, Calif. (Sheppard and Gude, 1968). Waters began to accumulate behind the dam with simultaneous deposition of fine-grained detritus. Figure 12 shows that the clay minerals deposited below the tuff C were mostly micas (or illites), saponite, and mixed layered material. Some small beds of volcanic ash were laid down at this time also. Later, the ash fall which subsequently produced tuff C was laid down, followed by the deposition of more detrital mudstones. The deposition of these mudstones was also interrupted periodically by light ash falls, one of which was large enough that it has been termed the “intermediate tuff”. The ash fall which produced tuff B was next deposited. By this time the concentration of the magnesium and the pH of the lake waters had increas- ed to the point that some sepiolite was being formed by the reaction of the magnesium-rich waters and the silica from the ash falls which had been taken into solu- tion by the lake waters. The salinity of the water would not have increased very rapidly at first but as the lake grew and covered a greater area, the enlarged surface area would have increased evaporation to produce greater salinity. More detrital material was deposited as mudstones, followed by another ash fall which produced tuff A. Again, magnesium-bearing waters of the lake combin- ed with the plentiful silica to produce even more sepiolite than was produced in associaton with tuff B. This was the last major ash fall although the presence of montmorillonite and sepiolite above tuff A indicates that there later was at least one minor ash fall. Detrital material was deposited as long as the lake existed. CONCLUSIONS Most of the minerals which make up the mudstones of the Tecopa basin are detrital in origin. They consist of quartz, plagioclase feldspar, some of the calcite and dolomite, and the clay minerals mica, illite, chlorite, 32 CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA the lithian saponite and mixed layered combinations of these. All these minerals are found areally throughout, and at all stratigraphic levels of, the Tecopa sediments as well as in the basin drainage area. This would tend to preclude an authigenic origin for them in the basin. The clay minerals brought into the lake as detritus from the drainage area were not affected by diagenesis. No differences can be detected between them and the clay minerals found along the tributaries. If there were any dissolution or alteration of the clays, the amount was negligible. This corroborates the findings of Droste (1961) who, after comparing the clay minerals from 45 playas in the Mojave Desert with the clay minerals from surrounding areas, concluded that clays deposited in alkaline lakes reflected the source rocks rather than diagenesis. Possibly some of the lithian saponite was formed by diagenesis of montmorillonite, as suggested by Papke for the Amargosa Flat sediments; however, most of it is considered to be detrital. The minerals that we consider to be authigenic in- clude much of the calcite and dolomite, sepiolite, magadiite, potassium feldspar, montmorillonite, zeolites, and the saline minerals. During this entire process, the calcium and C02 in the lake waters were combining to precipitate the calcite which is almost ubiquitous. It is especially abundant at the north end of the lake where the calcium-bearing waters of the Amargosa River came into contact with the carbonate waters of the lake. The calcite is less abundant in the southwestern part of the lake near the entrance of Greenwater valley. Only small amounts of dolomite are found in the lake beds although magnesium was probably present in its waters throughout the life of the lake and became more concentrated as the salinity of the waters increased. Dolomite is not readily precipitated from magnesium- rich solutions (Peterson and others, 1963, Peterson and others, 1966, Clayton and others, 1968), although calcite is readily precipitated if calcium is present. Any dolomite that was precipitated would have been form- ed very slowly. The thin beds of finely crystalline dolomite recognized in the basin by Sheppard and Gude (1968) probably are authigenic in origin. Their presence would imply water conditions of high salinity and pH and a good concentration of magnesium. The formation of authigenic sepiolite also requires a special environment as shown in experimentation by Siffert and Wey (1962), Wollast, Mackenzie, and Bricker (1968), and Mumpton and Roy (1958). It needs a source of silica and of magnesium in high-pH waters but with the absence of reactive aluminous phases. In the closed basin of Tecopa, the pH of the lake waters reached at least 8.0, owing to evaporation and the con- centration of magnesium and silica and various salts. The dissolution of volcanic ash, which periodically was deposited in the lake, then supplied the necessary silica to combine with magnesium in forming the sepiolite. The reactive alumina, which was also released by dissolution of the ash, served a twofold purpose. First, it was essential in the formation of the zeolites within the tuff beds and at their interface with the detrital beds. Second, the alumina prevented the precipitation of sepiolite within the tuffs but did not inhibit the dissemination of the silica-supersaturated, and by then alumina-depleted, waters into the surrounding sediments where sepiolite formed in the high-pH, magnesium-saturated pore waters. The dissolution of diatoms may have supplied the necessary silica for some sepiolite formation where volcanic ash was not available. Grim, Kulbicki, and Carozzi (1960) stated that the clay minerals rich in magnesium, such as sepiolite, pro- bably would not form in an environment of high- sodium content. However, in the mudstones of Lake Tecopa the sepiolite content is well established, dolomite is present in small quantities, and yet magadiite, a hydrous sodium silicate which is precipitated from silica-rich sodium waters (Eugster, 1969), is found in one area at about the same stratigraphic level as the sepiolite. Determination of how widespread the magadiite for- mation was in the basin because of subsequent erosion and leaching action is impossible; but, because of the magnesium content of the lake waters and because of the occurrence of magadiite only in one part of the basin, we conclude that this was a local occurrence caused by the presence of sodium-rich springs in this area making contact with the silica-bearing lake waters. Authigenic, dioctahedral montmorillonite is not as widespread in basin sediments as detrital, trioc- tahedral smectite saponite. It is found in a few localities where diagenesis of the volcanic ash has oc- curred to form clinoptilolite and montmorillonite. Sheppard and Gude (1968) also reported some mont- morillonite coatings on shards associated with other zeolites such as phillipsite. The other occurrence of montmorillonite, “amargosite,” is caused by the hydrothermal alteration of volcanic ash by hot-spring waters. This unique mineral formation was found in the vicinity of the town of Shoshone. Other authigenic minerals, such as the zeolites and potassium feldspar, are found scattered throughout the basin in small quantities in the detrital sediments, and larger more concentrated amounts are found in or near the tuffs. Sheppard and Gude (1968) have describ- ed the formation of these minerals in their paper on the REFERENCES CITED 33 authigenic silicates in the tuff formations of Tecopa basin. REFERENCES CITED Alexander, G. B., Heston, W. M., and Iler, R. 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Skinner, H. C. W., 1963, Precipitation of calcian dolomites and magnesian calcites in the southeast of South Australia: American Journal of Sciences 261, p. 449—472. Strese, H., and Hofmann, Ulrich, 1941, Synthesis of magnesium silicate gels with two-dimensional structure: Zeitschrift fiir anorganische und allgemeine Chemie, v. 247, p. 65-69 [Chemistry Abstracts, v. 36, 5073—4 (1942)]. Thompson, D. G., 1929, The Mohave Desert region, California: US. Geological Survey Water-Supply Paper 578, 759 p. Wollast, Roland, MacKenzie, F. J ., and Bricker, O. P., 1968, Ex— perimental precipitation and genesis of sepiolite at earth- surface conditions: American Mineralogist, v. 53, nos. 9—10, p. 1645—1662. Wright, L. A., and Troxel, B. W., 1954, Western Mojave Desert and Death Valley region, Geologic Guide no. 1 of R. H. J ahns, ed., Geology of southern California: California Department Natural Resources Division Mines Bulletin 170, 50 p. Yarzhemskii, Ya. Ya., 1949, Petrographic character of recent salt sediments (in Russian): Doklady Akad. Nauk., SSSR., v. 68, p. 1085—1088 [Chem. Abs., v. 44, 29011) (1950)]. aU.S. GOVERNMENT PRINTING OFFICE: 1979—677-026/46 flW/dhfl‘g%v /&é/, rm; w, m. .u N9 a,“ . :2 as»? Jurassic Paleobiogeography 0f the Conterminous United States in Its Continental Setting By RALPH W. IMLAY GEOLOGICAL SURVEY ‘PROFESSIONAL Paleogeographic changes in the United States during Jurassic time are revealed by the distribution, succession, and differentiation of molluscan faunas; by gross stratigraphic changes; by the position, extent, and duration of unconformities; and by comparisons with Jurassic data elsewhere in North America I 1 UNITED STATES GOVERNMENT PRINTING OFFICE, PAPER 1062 WASHINGTON : 1980 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Catalog—card No. 80—600017 For sale by the Superintendent of Documents, US. Government Printing Office Washington, D.C. 20402 Stock Number 024—001—03105—1 CONTENTS Abstract Introduction Acknowledgments Paleobiogeographic setting Atlantic Coast Gulf of Mexico and nearby regions -------------------------------- Pacific Coast Western interior region Arctic region Succession of ammonites and buchias by stages --------------------- Hettangian Sinemurian Pliensbachian Toarcian Bajocian Bathoniar Callovian Oxfordian Kimmeridgian Tithonian Definition and correlations -------------- Lower Tithonian of the Gulf region-—— Upper Tithonian of the Gulf region -------------------------- Ammonite sequences -------------------------------------- Kossmatia-Durangites ammonite assemblage ----- Substeueroceras-Proniceras ammonite assem- blage Tithonian of California and Oregon -------+ ---------------- Tithonian of Canada and Alaska-—----------—----------------- Intercontinentalfaunal relationships ------------------------------------ 35 36 36 37 Comparisons of lithologic and stratigraphic features --------------- Gulf of Mexico and nearby regions --------------------------------- Cuba Gulf region of the United States ----------------------------- Central and northeastern Mexico ---------------------------- East-central Mexico Southeastern Mexico -------------------------------------------- Eastern Chihuahua and west Texas------————-—------------ Pacific Coast region Western Mexico Western Nevada to central/California -------—---—---------- Western California and southwestern Oregon ------------ Eastern Oregon and western Idaho -----—--------—--- Northern Washington-------------------------------------------- British Columbia to southern Alaska——----—--------—------—— Western interior region of the United States Montana and North Dakota-----------------—----------------—- Southeastern Idaho to western South Dakota ------------ Northern Utah to northern Colorado -----------—---- North-central Utah to southwestern Colorado ----------- Southwestern Utah and northern Arizona—-------——------- Midcontinent region Jurassic unconformit'n“ Jurassic geologic history Atlantic Coast region Gulf of Mexico and nearby regions--------------------------------- Pacific Coast region Western interior region References cited Index ILLUSTRAITONS FIGURE 1. Jurassic basins of deposition in North America 2—12. Maps showing distribution of Jurassic fossils and inferred seas in North America: Hettangian Sinemurian Pliensbachiar Toarcian Bajociar. Bathonian Callovian Early to early middle Oxfordian pmfleweww 10. Late middle Oxfordian to early Kimmeridgian 11. Late Kimmeridgian to early Tithonian 12. Late Tithonian l3. Succession and correlation of Hettangian to Toarcian ammonites in North America: A. Mexico to southern British Columbia B. Northern British Columbia to East Greenland III IV FIGURE 14. 15. 16. 17. 18. 19. 20. 21. 22. 25. 26. 27. 28. 29. 30. 31. 32. 33. TABLE 1. CONTENTS Succession and correlation of Bajocian to Callovian ammonites in North America: A. Mexico to western interior region B. British Columbia to East GreenlanrI Succession and correlation of Oxfordian to 'I‘ithonian ammonites in North America: A. Gulf of Mexico, Pacific Coast, and western interior region B. Southwestern Canada to Greenland Comparisons of the Tithonian and Volgian Stages and the suggested subdivisions of the Tithonian — ----------------------------- Index map of Jurassic areas in the Gulf of Mexico and nearby regions Index map of Jurassic areas in the Pacific Coast region from California and Nevada to Washington ------------------------------ Index map of Jurassic areas in the Pacific Coast region from British Columbia to southern Alaska ------------------------------ Index map of Jurassic areas in the western interior region Correlations and comparisons of Jurassic rocks in the Gulf of Mexico and nearby regions: A. Western Cuba to Victoria, Mexico B. Huasteca area, Mexico, to Malone Mountains, Tex ‘ Correlations and comparisons of Jurassic rocks in the Pacific Coast region in California, Nevada, and western to east- central Oregon: A. Western Nevada and eastern California ‘B. Western California to east—central Oregon Correlations and comparisons of Jurassic rocks in the Pacific Coast region from eastern Oregon and western Idaho to north- western Washington Correlations and comparisons of Jurassic rocks in the Pacific Coast region in British Columbia, Yukon Territory, and south- ern‘ Alaska: A. Southwestern to central British Columbia B. Northwestern British Columbia to southern Alaska Correlations and comparisons of Jurassic rocks in the western interior region from southwestern Alberta through central Montana to southern Saskatchewan: A. Southwestern Alberta to central Montana E. Central Montana to southern Saskatchewan Correlations and comparisons of Jurassic rocks in the western interior region from southeastern Idaho to southwestern South Dakota: A. Ammon area, Idaho, to Red Creek, Wyo B. Hyattville area in north-central Wyoming to Minnekahta area, South Dakota Correlations and comparisons of Jurassic rocks in the western interior region from north—central Utah to north—central Colorado: A. Burr Fork to Whiterocks Canyon, Utah B. Dinosaur Quarry, Utah, to Hahns Peak, Colo Correlations and comparisons of Jurassic rocks in the western interior region from north-central Utah to southwestern Colorado: A. Monks Hollow to Black Dragon Canyon, Utah B. San Rafael River, Utah, to McElmo Canyon, Colo Correlations and comparisons of Jurassic rocks in the western interior region from southwestern Utah to northeastern Arizona: A. Gunlock to Brown Canyon, Utah B. Little Bull Valley, Utah, to Cow Springs, Ariz , Jurassic unconformities in Gulf of Mexico and Pacific Coast regions Jurassic unconformities in western interior region Inferred extent of Jurassic seas of early Bajocian to earliest Callovian Age in western interior region ----------- Inferred extent of Jurassic seas of late early Callovian to early Kimmeridgian Age 1n western interior region ----------------- TABLE Thickness of the Piper and underlying Gypsum Spring Formations in parts of north-central Wyoming and south- central Montana 44 45 54 56 58 59 112 79 CONTENTS CONVERSION FACTORS Metric unit Inch-Pound equivalent Metric unit Inch-Pound equivalent Length Specific combinations—Continued millimeter (mm) = 0. 03837 inch (in) liter per second (L/s) = .0353 cubic foot per second meter (11]) : 3. 28 feet (ft) cubic meter per second : 91.47 cubic feet per secondp kilometer (km) : .62 mile (mi) per square kilometer square mile [(ftB/s)/mi”] A [gala/”GRID? /d) 328 f t d (h d 11 me er per ay m : . ee per ay y rau c rea conductivity) (ft/d) square meter (in?) = 10.76 square feet (ft!) meter per kilometer = 5.28 feet per mile (ft/mi) square kilometer (km?) = .386 square mile (mi2) (m/ m hectare (ha) = 2“” acres kiloinetir) per hour = .9113 foot per second (ft/s) olume m/ , V meter per second (m/s) = 3.28 feet per second cubic centimeter (cm3) : 0.061 cubic inch (ins) . meter squared per day = 10.764 feet squared per day (ftz/d) litre); (L)t ( a) = gégfi cugic cheffta) ’ (mB/d) (transmissivity) cu cme er m = . cu c ee __ cubic meter : .00081 acre-foot (acre- ft) cubignngeter per second _ 22'826 111115135711? ns per day cubic hectometer (hma) = 10.7 acre- -feet . 9 lit er = 2.113 pints (pt) cubic‘met‘er per minute =264.- gallons per minute (gal/min) liter : 1.06 quarts (qt) (m/min) liter : .26 gallon (gal) liter per second (L/s) = 15.85 gallons per minute cubic meter : 00026 “111110,“ ggaillons (Mgal or liter per second per = 4.83 gallons lper minute per foot ter [(L/s)/m] [(ga /mln)/ftl bi = 6.29 b b1 1: .m" . cu c meter 0 arrels 3(1) ) (1 bb 42 gal) kilometer per hour = .62 mile per hour (mi/h) Weight (km/h) meter per second (m/s) 2 2.287 miles per hour gram (g) = 0.035 ounce, avoirdupois (oz avdp) gram per cubic = 62.43 ounds e c bi f t 3 gm ti t (t) = 1.0332 goundmavtéilégu§ggsl b()lb avdp) centimeter (g/cms) p p r u c 00 (JD/ft) me rc ons = . ons s or . a . metric tons : 0.9342 ton, long (2, 240 lb) g’cggzgefgr“fi§/Cm2, 2 048 ”was per square f°°t (lb/ft”) . - - gram per square 2 .0142 ound er s uare ‘ ch lb i 9 Specific combmatlons ‘ centimeter n p a 1n ( / n ) kilogram per square : 0.96 atmos here atm) klcentimeter (kg/Clue) p ( Temperature 1 ogram per square .98 bar (0.9869 atm) ,, centimeter ngI‘ee Celsius ( C) = 1. 8 degrees Fahrenheit (°F) cubic meter per second 2 35.3 cubic feet per second (fits/s) degrees Celsius : (ma/S) (temperature) [ (1. 8 X °C) +32] degrees Fahrenheit JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES IN ITS CONTINENTAL SETTING By RALPH W. IMLAY ABSTRACT During Jurassic time, marine sediments of considerable thickness in- cluding bedded salt were deposited on the outer part of the Atlantic Continental Shelf of the United States. The inner part of the shelf may have been inundated also during Oxfordian to Tithonian time, coinci- dent with extensive flooding elsewhere in the Atlantic Ocean and in the Gulf of Mexico. During the Early Jurassic, neither marine nor continental sediments seem to have been deposited within the area now covered by the Gulf of Mexico. Nonetheless, a marine embayment of Sinemurian to possibly early Pliensbachian Age did extend northward from the Pacific Ocean to east-central Mexico, where it terminated against a mass of meta- morphic and granitic rocks in eastern Veracruz. The marine sediments deposited are carbonaceous, contain much plant material and some coal, and evidently were laid down in a warm humid climate. During the later Early Jurassic, they were strongly folded, faulted, intruded by igneous rocks, slightly metamorphosed, and then eroded. Presum- ably, erosion took place mostly in Toarcian time after tectonic move- ments in Pliensbachian time. During the Middle Jurassic, marine sediments apparently were not deposited within the Gulf region until the late Bathonian. Continental sedimentation, however, took place in both Mexico and Cuba. In east- central Mexico, plant fossils show that continental deposition began in the early Bajocian. Such deposition took place over a larger area than that covered by the Lower Jurassic marine beds, continued until some- time in the Bathonian, but was followed by erosion before the early Callovian. In Cuba thousands of feet of carbonaceous plant—bearing beds were deposited during the Bajocian and Bathonian and possibly a little earlier. These plant-bearing beds show that the climate was warm and humid throughout the Gulf region during most of the Middle Jur- assic. During Callovian to early middle Oxfordian time, the Gulf region subsided and received some marine waters from the major oceans, which deposited thick masses of salt at various places. One marine em- bayment apparently extended westward into Cuba and was probably the major source of the salt. Another embayment extended from the Pacific Ocean into the Huasteca area of east-central Mexico, where it was separated from the Gulf at least in part by a land barrier located near the present Gulf coast. Salt was deposited mainly during late Cal— lovian to early middle Oxfordian time, but deposition may have started in middle Callovian time. At about the same time in nearby areas in east-central and northeastern Mexico, varicolored continental beds and some red-weathering lava were deposited. The climate during deposi- tion of the salt and nearby varicolored continental beds was probably hot and dry in the Gulf region. The red silt and sand were probably derived from upland areas to the west or north where the climate was hot and seasonally rainy. Near the middle of the Oxfordian, major portals to the oceans were opened abruptly by major structural movements, and as a result sea- water of normal salinity flowed quickly across the saline deposits and far beyond. Subsequently, during the later Jurassic, the Gulf of Mexico gradually deepened and widened; landmasses arose north of the Gulf basin and shed considerable sediment southward; and deposition pre- vailed in open marine water from Cuba and Florida westward to central Mexico. Deposition continued into the Cretaceous in most parts of the Gulf region except in some northern nearshore areas. The climate in the Gulf region during Oxfordian to Tithonian time was probably hot and moderately humid. Rainfall apparently became greater after the early Kimmeridgian and was greater in eastern Mexico than in the southeastern United States, as shown by the presence of coal beds in Mexico. On the whole, the climate was probably similar to that in the western interior region during deposition of the Morrison Formation. 0n the Pacific Coast during Jurassic time, marine deposition took place at depths ranging from very shallow to very deep, involved tre- mendous thickness of sediment, included much volcanic material, and gradually shifted westward. ' During the Early Jurassic, a sea extended from the Pacific Coast as far east as the Snake River in easternmost Oregon and a similar dis- tance east in Nevada. The deepest part of the sea probably trended northward through westernmost Nevada into eastern Oregon and be- yond, as indicated by continuous deposition of fine—grained sediments from the Triassic into the Jurassic. By contrast, in eastern California. Jurassic sedimentation apparently did not begin before the Sinemurian. During Bajocian time, a shallow sea covered nearly the same area as the Early Jurassic sea, except for an eastward extension into the west- ern interior region. This sea received a great variety of sediments that included much volcanic material, except in Nevada. Deposition of beds of Bathonian Age in the Pacific Coast region of the conterminous United States has been demonstrated by fossils only in eastern Oregon. The absence of Bathonian fossils elsewhere could be explained by col- lecting failure; it could also reflect the beginning of intense volcanism which lasted into the early Oxfordian and which may at first have pro- duced conditions on the sea bottom that were unfavorable for the pres- ervation of fossils. During the Callovian, marine waters covered most of the present area of California, Oregon, and Washington, and during earliest Callov- ian they also extended eastward into the western interior region. Enor- mous amounts of coarse to fine volcanic debris were ejected from vol- canoes and fissures into the sea, where they became mixed with sediments derived from islands and larger landmasses. Apparently deposition continued throughout the epoch, except in'eastern Oregon. The formation of oceanic crust during the Bathonian or Callovian ep- ochs, or both, is suggested by the characteristics of the Rogue Forma— tion in western Oregon. Marine sedimentation persisted in the Pacific Coast region without any apparent interruption, from Callovian to early Kimmeridgian time, over alarge area including California, western Oregon, and probably northwestern Washington. During the early Oxfordian, deposition of highly volcanic sediments continued just as during the Callovian. By contrast, from late Oxfordian to early Kimmeridgian, the most common sediments deposited were dark clay and silt, which in most places in- cluded only fine volcanic material. At the end of the early Kimmeridgian. marine deposition ceased in areas underlain by the Mariposa Formation in eastern California, and by the Galice Formation in western Oregon and in nearby California. 1 2 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Those areas were then uplifted, and the rocks were folded, intruded locally by igneous rocks, and strongly eroded before the end of the Jurassic. In some other places near the present Pacific Coast, marine sedi- ments were deposited from the late Kimmeridgian to the Tithonian, but in many other places such deposition apparently only took place during the Tithonian. Some of the sediments, now represented by the Knoxville and Riddle Formations, consist mostly of nonvolcanic ter- rigenous clastic materials which locally contain limestone lenses and which were deposited in shallow waters. Other sediments, represented by the Dothan and Otter Point Formations and by the Franciscan as- semblage, consist of volcanic clastic materials, breccia, lava, and chert and were deposited in deep waters. All available evidence indicates that the volcanic sediments were deposited far west of the nonvolcanic sediments and in much deeper waters, but that deposition of both be- gan at about the same time on oceanic crust of late Oxfordian to early Kimmeridgian Age. Evidently, the oceanic crust was formed at the same time at which the Galice and Mariposa Formations were being deposited in areas far to the east. That the climate in California and Oregon during Jurassic time was probably warm is indicated by the presence of ammonites of Mediter- ‘ ranean (Tethyan) affinities in those States and by the lack of certain ammonites that are common in the Arctic region and along the Pacific Coast as far south as British Columbia. The change is similar to that found in Jurassic ammonite faunules between northwest Europe and the Mediterranean region. During the Early Jurassic, the western interior region south of Mon- ‘ tana received as much as 3,000 feet (915 m) of continental sediments deposited under fluviatile and eolian environments. During the late Ox- fordian, Kimmeridgian, and probably early Tithonian, the region re- ceived hundreds of feet of continental sediments deposited under flu- viatile, lacustrine, and swampy environments. Between these two episodes, the area was invaded five times by marine waters that en- tered from the west through Idaho, Washington, or Alberta. Three of the invasions were followed by complete withdrawals of the sea from the region and two by partial withdrawals. The sea first invaded southeast Idaho early in the Bajocian, extended from there northeast into the Williston basin and southward into south- west Utah, and then withdrew completely at about the beginning of the middle Bajocian. That sea left deposits of gypsum, red silt, limy mud, some chert, and locally in the Williston basin, a little salt. The characteristics of these sediments show that the sea was very shallow, that its initial sediments were laid down in highly saline waters, that later sediments were deposited in slightly deeper waters which sup- ported some marine organisms, and that the sea deepened a little in southeastern Idaho. The second and greatest marine invasion of the western interior re- gion started in the late middle Bajocian and lasted until the early Cal- lovian. The sea underwent marked shallowing in the middle Bathonian and then withdrew nearly completely in late early to middle Callovian. It entered across northern Utah, eastern Idaho, and southern Alberta, surrounded a large island in central Montana, and was much more ex- tensive than the seaof the earlier Bajocian except in eastern and south- ern Wyoming during late Bajocian to early Bathonian. From late Bath- onian to early Callovian, however, it advanced across Wyoming into South Dakota beyond the erosional eastern limit of beds of early Bajo- cian Age. In this sea were deposited clayey to dense to oolitic lime mud, limy clay and silt, gray to yellow limy sand, and some red silt and gyp- sum. The sediments deposited at any one time were similar over great distances, except for the initial deposits that filled irregularities on the underlying erosion surface. Most of the sediments were deposited as the sea transgressed. Regressive deposits include the Boundary Ridge and Giraffe Creek Members of the Twin Creek Limestone and their equivalents. L The second marine invasion was terminated near the middle of the Callovian by the rise and enlargement of a large island in Montana that cut off marine waters from the north. South of this island in very shal- low, probably highly saline waters were deposited unfossiliferous, red, even-bedded, fine-grained sand that thickens westward from 100 to 1,000 feet (30 to 300 m) or more, and that extends from the Black Hills area southwestward through southern Wyoming and northernmost Utah into southeastern Idaho. Near Idaho Falls, the lower part of the sand was deposited along with some marine lime mud and sand. This marine facies thins eastward to an area near the western boundary of Wyoming where bedded salt and gypsum were deposited at about the same stratigraphic position over a distance of several hundred miles (several hundred kilometers) from north to south. Evidently, marine and lagoonal conditions persisted to the west in Idaho at the same time that red sand was being deposited farther east in highly. saline or pos- sibly brackish waters and at the same time that light-colored, crossbed- ded sand was being reworked by winds in the Colorado Plateau. The third marine inVasion into the western interior region appar- ently happened during the late middle to early late Callovian, in some places immediately after deposition of red even-bedded sand and equiv- alent eolian sand and in other places after a brief interval of erosion. The sea extended eastward across northern Utah, southern Idaho, northern Colorado, and southern Wyoming into South Dakota. It may have also extended northward from the Black Hills area into southern Saskatchewan, where it could be represented by all or part of the glau- conitic deposits called the Roseray Formation (equals middle member of the Vanguard Formation). In this sea, highly glauconitic limy sand, sandy silt, some gypsum, and some limy mud (Curtis Formation and Pine Butte Member of the Sundance Formation) were deposited in very shallow water, as shown by the presence of Ostrea, Lopha, Lingula, and Meleagfinella. Such sediments in the San Rafael swell were overlain conformably by, and passed laterally southeastward into, unfossiliferous chocolate-brown, red, or gray even—bedded sand, silt, and clay, and, locally, some gyp- sum. Such sediments were probably deposited in highly saline water in marginal areas of the sea. Deposition of both the marine, brackish-, and saline-water sediments was followed rather quickly by withdrawal of the sea completely from the western interior region and by an interval of erosion that lasted until early Oxfordian time. The fourth marine invasion into the western interior region entered central Montana east of the Sweetgrass arch during the latest Callovian and possibly entered the Williston basin even earlier. During the early Oxfordian, the sea spread widely, but did not advance as far south in Utah as the preceding sea, and apparently did not spread west of the Sweetgrass arch. At the end of the early middle Oxfordian, the sea withdrew northward into northern Wyoming and the Williston basin but spread westward in Montana at least as far as the Sawtooth Range south of Glacier Park. It persisted in Montana at least to the end of the Oxfordian. The sea was bounded on the west in central Idaho and pos- sibly in westernmost Montana by a landmass that shed considerable clastic sediment eastward. This is shown by a change from'mostly glau- conitic, calcareous sand, sandy lime, and sandy silt in the west to mostly silt and clay farther east. The sea was shallow, as shown by the presence of Ostrea, Mytilus, and Meleagrinella, and by abundant rip- ple marks and crossbedding. The climate was probably warm and hu- mid, as shown by the presence of many wood fragments in the Swift Formation in western Montana. The northward withdrawal of the sea in Montana during the early middle Oxfordian was followed by a brief fifth marine invasion south- ward from Montana and northern Wyoming as far as northwestern Col- orado and northeastern Utah. In this sea was deposited a thin unit (Windy Hill Sandstone Member of the Sundance Formation) of yellow— ish-gray, limy, locally oolitic, ripple-marked sand, and a little gray to green mud that contains a few mollusks, such as Ostrea. These marine ACKNOWLEDG ME NTS 3 sediments were deposited unconformably on the Redwater Shale Mem- ber of the Sundance Formation and conformably below the continental Morrison Formation. As they are not recognizable as a lithologic unit north of the Wind River Basin in central Wyoming, they presumably pass northward into the upper part of the Redwater Shale Member in northern Wyoming. During later Jurassic time, continental sediments (Morrison For- mation) were deposited on flood plains and in lakes throughout much of the western interior region and in coal—forming swamps in Montana. Continental deposition began during the early or late Oxfordian in the southern part of the region, definitely during the late Oxfordian in the central part, and probably as late as the Kimmeridgian in northern Montana. It persisted in all parts at least through the Kimmeridgian. Sediments in the southern and central parts of the western interior region were derived from the south and west. In the northern part, they were derived from the east and west. Evidently, continental sedi— mentation began at about the same time as deposition of the marine Norphlet and Smackover Formations of the Gulf region. Uplift of land areas from which the continental sediments were derived apparently occurred at the same time as uplift of the land areas that shed sediment southward into the Gulf of Mexico during late Oxfordian to Tithonian time. The Jurassic ammonite succession in North America from Hettan— gian through early Bajocian time is essentially the same as elsewhere in the world. Ammonite assemblages of late Pliensbachian Age are dif- ferentiated from north to south, just as they are in Europe. Ammonite assemblages of middle Bajocian Age in the Pacific Coast region contain some genera that are known only from areas bordering the Pacific Ocean, but overall their generic resemblances to European ammonites are striking. In contrast, from late Bajocian time until the end of the Jurassic, marked differentiation of ammonite faunas took place from north to south. The ammonite successions in the Gulf region and in the Pacific Coast region as far north as southern California remained closely simi- lar to those in the Mediterranean region. The succession from northern California to northern Alaska became similar to that in northern Eu- rasia, although some mingling of genera of Boreal and Mediterranean affinities occurred in California and Oregon. Such mingling and the presence of genera known only from the Western Hemisphere or from areas bordering the Pacific Ocean have aided greatly in making fairly accurate correlations of rocks in widely separated areas. The differentiation of ammonite faunas from north to south can be reasonably ascribed to partial isolation of an arctic sea from the Pacific Ocean, except for at least one connection through Yukon Territory dur- ing Middle and most of Late Jurassic time, and another connection from East Greenland to northwest Europe from the beginning of Callovian time. INTRODUCTION This report is a successor to that written by Imlay and Detterman (1973) on the Jurassic Paleobiogeogm- play of Alaska. It is more detailed because much more information is available concerning the conterminous United States. It deals in a broad way with changes in Jurassic geography, stratigraphy, and ammonite assem— blages. It‘ presents paleogeographic maps depicting the main areas of Jurassic marine deposition and most of the marine Jurassic megafossil occurrences in North Amer- ica (figs. 1-12). It presents charts depicting the succes- sion of ammonite taxa and Buchia species in North America (figs. 13—16), the locations of some of the best known Jurassic sequences (figs. 17—20), the gross strat- igraphic and lithologic changes in space and time (figs. 21—29), and the position, extent, and duration of uncon- formities during Jurassic time (figs. 30, 31). In addition, the report discusses most existing published strati- graphic, lithologic, and faunule knowledge in sufficient detail to substantiate the interpretations presented on the maps, on the charts, and in the section on Jurassic geologic history. Most of the geographic features, areas, and towns mentioned in this report are shown on figures 17-20. Further locality data concerning such features in the Gulf of Mexico region are shown in papers by Imlay (1943a, p. 1408, 1409, 1412, 1496, 1503, 1509; 1952a, p. 954; 1953c, figs. 2—4), Swain (1944, p. 583), K. A. Dick- inson (1968, p. E2), and Lopez Ramos (1974, p. 382, 385, 388, 391). Such data for the Pacific Coast region of the United States and Canada are shown in papers by Imlay (1952a, p. 956; 1961, p. D15; 1973, pl. 48; Imlay and Jones, 1970, p. B19); Frebold and Tipper (1970), and Imlay and Detterman (1973, p. 7). Such data for the western interior region are shown in papers by Baker, Dane, and Reeside (1936), Imlay (1952a, p. 956; 1953a, p. 12; 1956a, p. 563; 1957, p. 472; 1962b, p. C8, C9; 1967b, p. 5, 63—65), Frebold (1957, figs. 1, 2; 1969, fig. 1), Brooke and Braun (1972, fig. 1), J. A. Peterson (1957, p. 402, 403), and Pipiringos and O’Sullivan (1975). ACKNOWLEDGMENTS For the data published herein, the writer is indebted to many geologists from Canada, the United States, and Mexico. Canadians who contributed include Hans Fre- bold, J. A. Jeletzky, and H. W. Tipper of the Canadian Geological Survey; M. M. Brooke, W. K. Brown, J. E. Christopher, and D. F. Paterson of the Saskatchewan Geological Survey; and L. W. Vigrass of the University of Saskatchewan. In the United States, information was provided by George Gryc, K. A. Dickinson, Arthur Grantz, D. L. Jones, J. D. Love, W. J. Mapel, A. A. Baker, W. A. Cobban, E. M. MacKevett, Fred Peterson, G. N. Pipiringos, Donald Richter, E. H. Bailey, W. P. Irwin, L. D. Clark, R. L. Detterman, and Robert Sharp of the U.S. Geological Survey; George Herman and Jules Braunstein of Shell Oil 00.; W. E. Humphrey of Ameri- can International Oil Co. (Amoco); R. T.'Hazzard of Gulf Oil 00.; W. B. Weeks of Phillips Oil Co.; F. M. Swain of the University of Minnesota; W. R. Dickinson of Stan- ford University; J. A. Peterson of the University of Mon- tana; and many others. In Mexico, those providing data included Gloria Alencaster de Cserna, Manuel Alvarez, Jr., Abelardo Cantu Chapa, Edmundo Cepeda, D. A. 4 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Cordoba, Zoltan de Cserna, Teodoro Diaz-Gonzalez, E. J. Guzman J iménez, Ernesto Lopez Ramos, Roberto Flo- res Lopez, G. P. Salas, Hector Ochoterana F., Francisco Viniegra 0., and J. P. Alor, all of whom are affiliated with either Petroleos Mexicanos or the Instituto Geolo- gico de Mexico. Special thanks are due George Pipiringos and Fred Peterson of the US. Geological Survey for sharing infor- mation and exchanging interpretations concerning the stratigraphic relationships of Jurassic formations in the western interior region. The writer is much indebted to John H. Callomon of University College, London, England, and to Tove Birk- elund of the University of Copenhagen, Denmark, for ammonite biostratigraphic data concerning the position of the Bathonian—Callovian boundary in East Greenland and its probable position in Alaska and Montana. PALEOBIOGEOGRAPHIC SETTING ATLANTIC COAST Jurassic marine beds have not been identified defi- nitely along the Atlantic Coast of the United States, al- though 45 feet (13.7 m) of limy beds of possible Late J ur- assic age have been penetrated in two wells at Cape Hatteras, N.C. Three species of ostracodes have been found, of which two, belonging to the genus Schuleridea, have been found elsewhere in the Schuler Formation (Upper Jurassic) of the southeastern United States; one belongs to the genus Octocythere, which is known only from the Jurassic (Swain, 1952, p. 59, 60; Swain and Brown, 1972, p. 8, 9; Brown and others, 1972, p. 38). These possible Jurassic beds are about 370 miles (600 km) west of the marine Upper Jurassic sequence about 560 feet (170 m) thick that was cored at JOIDES Site 105 in the Hatteras Abyssal Plain (Hollister and others, 1972). It is about 60 miles (100 km) west of the western margin of Jurassic beds suggested by Emery and Uchupi (1972, p. 95). No drilling reports have yet been published that prove the presence of Jurassic beds along the Atlantic Continental Shelf of the United States. Nonetheless, seismic data suggest the presence of thousands of feet of both Jurassic and Lower Cretaceous beds along the en- tire shelf area from Maine to Florida (Ballard and Uchupi, 1974, p. 1158; Schultz and Grover, 1974, p. 1164, 1165; Minard and others, 1974, p. 1172, 1176; Olson, 1974, p. 1196, 1197). Furthermore, salt concentrations in pre-Up- per Cretaceous rocks in coastal areas between Delaware and Florida suggest that evaporitic facies of possible J ur- assic age may be present seaward from the present coastline (Mattic and others, 1974, p. 1182, 1183). Ma- rine Jurassic sedimentation along the Atlantic Coast was probably influenced in places by the Palisade disturb- ance, which is now definitely dated as Jurassic, rather than Triassic, by the presence of palynofloras of Early Jurassic age from the top of the Newark Group (Cornet and others, 1973; Cornet and Traverse, 1975, p. 25—27). This evidence is supported by some K—Ar dates for the Palisades sill that intrudes the Newark Group in New Jersey (Dallmeyer, 1975) and by K—Ar dates for lava flows in the middle of the Newark Group in the Hartford basin of Connecticut and the Deerfield basin of Massa- chusetts (Armstrong and Besancon, 1970). Jurassic beds of considerable thickness have been identified by means of microfossils found in deep wells drilled along the Atlantic Coast of eastern Canada (Sher- win, 1973, p. 529, 534—537; Upshaw and others, 1974, p. 1132). For the Nova Scotia shelf, the fossil evidence shows that the marine Lower and Middle Jurassic beds are about 6,600 feet (2,012 m) thick, and those for the Upper Jurassic are at least 8,200 feet (2,500 m) thick (McIver, 1972, p. 56-62). The sequence includes a basal salt unit about 2,500 feet (760 m) thick that is dated as probably earliest Jurassic on the basis of its microflora and its stratigraphic continuity with overlying marine beds that are dated as Early Jurassic (Pliensbachian). The Jurassic sequence may also include several hundred feet of red beds that are gradational upward into the main salt mass and that rest on metamorphosed sedimen- tary rock. In the Grand Banks of Newfoundland, microfossils of Early to Late Jurassic age have been reported through- out at least 20,000 feet (6,100 m) of beds penetrated by drilling (Upshaw and others, 1974, p. 1132). These beds consist of elastic oolitic to dense limestone, gray to red siltstone and mudstone, and limy fine—grained sandstone. In the Murre well, the Lower Jurassic is represented by 1,120 feet (341 m) of limestone whose basal 600 feet (183 m) contains bedded anhydrite and some salt. In addition, some salt, penetrated in two salt domes, has been inter- preted as of Early Jurassic age or older (Bartlett and Smith, 1971, p. 67—69; Amoco, 1974, p. 1112—1115; Up- shaw and others, 1974, p. 1127—1129). Studies of Foraminifera, ostracodes, dinoflagellates, spores, and pollen, obtained from well cutting on the Sco- tian Shelf and the Grand Banks, show that the oldest dated beds are of Bathonian to Callovian Age (Ascoli, 1974, p. 132, 133; Williams, 1974). The underlying salt- bearing beds are referred to the Early Jurassic, how- ever, although the evidence for such dating is not yet published (Jansa, 1974, p. 141). GULF OF MEXICO AND NEARBY REGIONS Thick Jurassic deposits are widespread in Mexico, the southern United States, and Cuba. Marine beds of PALEOBIOGEOGRAPHIC SETTING 1 50° 1 40° 130° 30° 20° 1 0° 0° 160° ' .5 ’1 s 170° 1 80° 170° 1- 1 60° 150° 140° 130° FIGURE 1.—Jurassic basins of deposition in North America. Note small basins of continental deposition in central Michigan, northern New Jersey, and Connecticut to southern Massachusetts. Land areas are ruled. FIGURE 2.—Distribution of Hettangian fossils (X) and inferred seas in North America. Land areas are ruled. 6 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 150° 140° 130° 30° 20° 10° 0° 160°r ' $4 .° » 4 q, // . 0 v ° 3; 170° 1 '1" ‘ “ 10° 0 ' » % , 180° ' «)7 .7 20., ~ , 4/ \ t / ‘ 1; . 170° \n .P )00 . 1 \\ 30¢ , fl :2 N X //’ 160° 3 ‘0 <57 E 40° 60° 41 T L p, q ‘ '44 1500 <3 ‘ / 9 \ X X Q ’\. Q 50° x 1 ‘n 50° / \ .3 9 140° 0 , x \ 40 ‘ l\ 0 Q3 60° X x Q Q / \I /\ 0 30° Y- T“ \a 0 7 130° \ ' > a 7 Z 700 20° ? / 7- 0 500 1000 MILES ' 0 500 1000 KILOMETERS 700 7 7 % 120° 110° 100° 90° 80“ 160° 170° 1 80° 170° ‘ 160° 1 50° 140° 130° PALEOBIOGEOGRAPHIC SETTING 30° 20° 3 10° , /. 1' 4" = Vffizfgg‘.‘ v , figh‘ve)’ '1 - l ‘ f%)" i ’ fiW~ “’3'“ MI 1):»! 0“» / 3’; lg, \ ° 1 J > 7 I . ‘V ’0‘ ? a V / a 2 1 VA: STAT EOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED 140° 130° ASSIC PAL 150° JUR PALEOBIOGEOGRAPHIC SETTING 9 150° 140° 130° 30° 20° 10° 0° 160° V \ ' SEA .° K4: . ~ 0 .. \1 ° ° C; 5 a 170° 1 a -1- ’ 10 f % 180" /<“ _7 20° ./ 74/ ‘ V .l‘ . / . Q 1; / 170° ‘V; / xx 00 / 30° ‘9 X ‘3‘ 160° C E . 40° Q L I) § 50° 4’ J T Q In X ‘ f 1 LL] \ \ 150° “ 6 fl 9 "1 " 0 50° \ )§( I ° 4 0 x 50°’$( x / A. /‘ / x // (.1 /,/ 140° 4, \ \ K 400 600 X f\ x" % 0 VI / o V s .4 I\ 111 30° ' / 0 » Y 0-- 1 / R > 130° b 1 ° ’ 7 Z ” a ' O 70° 20° I ,3 o 500 1000 MILES 1. o 500 1000 KILOMETERS -’ 2 70° \ 7 ”\‘fi 120° 110° 100° 90° 80° FIGURE 5.——Distribution of Toarcian fossils (X) and inferred seas in North America. Land areas are ruled. 10 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 150° 140° 130° 30° 20° 10° 0., 160° \j SEA .1: 6 0 - \ 9 0 \ I % 10° 170° 4‘3 ‘.‘ I o ,f // 0 180° // /<<\ 7 20° . '7 _. / ¢ T ’ / . ° 0 . o ‘ 170° \‘b x )00 300 O / w x / 160° . 2 .‘o \ .. q 40 X ‘ o J L fl x 1 Lu o 0 x x 150 \ x x 6 fl 1. x x x 0 50° ’5‘ Xx \ \ 50° § . . . . ' x 0 .. 9 \ 1400 x ,5. \ ' .. Ix \ 40° 0 tax 60 / x ~ * ' x ¥ 1 , V x , Q 300 \ Ix ° v . \ / 0 130° m 1 o 7 , /? . 1 . 7 / CONTINENTAL PLANT-BEARIN 2 BEDS IN CUBA AND IN » = 70° 20° 7 EAST-CENTRAL MEXICO 0 500 1000 MILES 0 500 1000 K|LOMETERS ‘? 70° 7 ' Y1 120° 1 10° 100° 90° 80° FIGURE 6.—Distribution of Bajocian fossils (X) and inferred seas in North America. Land areas are ruled. Extent of early Bajocian sea in western interior region is indicated by dotted line. Extent of late middle to late Bajocian sea in western interior region is indicated by solid line. 11 PALEOBIOGEOGRAPHIC SETTING 10° 150° 30° 20" I 140° 130° 1000 MILES 500 500 1000 KILOMETERS 0 #00 160° 140° 1 50° 110° 120° a. mm 1 om my ab Hm .Ilt mm em Mm mm 8 mm Em .r mm ma em mm m t S e w .m in North America. Land areas fossils (X) and inferred seas is indicated by dotted line. Extent of late Bathonian sea tidal flat and continental deposits is indicated by dashed line. H .m n 0 h m Bmm mwm nrm .mrt mma .me mmm .mml D of. _mm 7.8% Ewm .mE b'IGUR 12 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 150° 140° 130° 30° 20° 10° 0° 160° V 634 .- 7 /,.// ‘ 4) /» / ‘ . \ ‘3 /. , / c — a 1 v 6;» . _vg _,,_ 7 _ 7, - 10° 170° , A -1- /% \ 59x0 180° V/L ?\ s 1 ~ / ' z & / °\\ :\_ 170° ‘3‘ / )00 Q \_ ,\ 30° \\¥ \_\ ‘b‘ x7 \_ \ 160° \ ~O , e n e 400 L / o 60" J 7 T a XX / [LI 0 \ ' 150° ’3‘: Q \ ? o ‘1 Xx X 50 x x \ - X 50° X ’ ‘ a: \ .X\ X b O \X XX .I! ,//‘ ‘ \- I ./- \ \ 140° ' . v." \\ / 4o ' ' J .7 ‘ a ’\ / ° '60° / 95 Q3 .3 \, Q \4 \' . \ . II { / n 1T1 130 > 2 . 20° ? o 500 1000 MILES o 500 1000 KILOMETERS 70o 120° 110° 100° 907 FIGURE 8.—Distribution of Callovian fossils (X) and inferred seas in North America. Land areas are ruled. Extent of earliest Callovian sea in western interior region is indicated by solid line. Extent of late middle Callovian sea (Curtis and Summerville time) is indicated by dotted line. Extent of Callovian continental beds is indicated by dashed line. Possible extent of latest Callovian sea is indicated by alternating dots and dashes. 160° 170° 1 80° 170° 3- 1 60° 1 50° 140° 130° PALEOBIOGEOGRAPHIC SETTING 150° 140° 130° 10" 500 1000 MILES 0 500 1000 KILOMETERS N I '5 Ar 5° I .c. 1 < "é/flé " III A v 30° 20° B " \ -1- “(4715,: k, ’31 ‘32; "{\‘« ” ' “@384? b - '9 9 é 8*! v’. y S": I“?! ~11} V'I% A 6% \ 2 <( \lu D O 45 r -i «’4! C25 6 50° 120° 110° 100° 90° 80" FIGURE 9.—Distribution of early to early middle Oxfordian fossils (X) and inferred seas in North America. Land are areas ruled. 14 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES L 1 60° 170° 180° 170° 1 60° 1 50° 140° 130° 0 500 1000 MILES I; ‘6 . o 500 1000 KILOMETERS 120° 110° 100° FIGURE 10.—Distribution of late middle Oxfordian to early Kimmeridgian fossils (ammonites and buchias) (X) and inferred seas in America. Land areas are ruled. North 160° 170° 180° 170° 1 60° 150° 140° 1 30° PALEOBIOGEOGRAPHIC SETTING 500 1 1000 MILES 0 1000 KILOMETERS V‘KL 110° 100° 15 FIGURE 11.—Distribution of late Kimmeridgian to early Tithonian fossils (ammonites and buchias) (X) and inferred seas in North America. Land area s are ruled. 16 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 1 60° 170° 1 80° 170°7 s 1 60° 1 50° 140° 130° 1 20° 1 1 0° 1 00° 8, FIGURE 12,—Distribution of late Tithonian fossils (ammonites and buchias) (X) and inferred seas in North America. Land areas are ruled. PALEOBIOGEOGRAPHIC SETTING Early Jurassic age occur in southern and east-central Mexico and perhaps as far north as Catorce (Burckhardt, 1930, p. 8—44, 91—93; Erben, 1957a, 1957b). In east- central Mexico, these beds contain ammonites of Sine- murian and early Pliensbachian Age and Were deposited in an embayment (Huayacocotla) that opened only to the Gulf of Mexico, according to Erben (1957b, p. 38), but only to the Pacific Ocean aCcording to Viniegra O. (1971, p. 484) and Lopez Ramos (1974, p. 381—386). In south— ern Mexico, one ammonite of Early Jurassic agey(late Pliensbachian) from the state of Guerrero (Erben, 1954, p. 5—12, pl. 1, figs. 4, 5) is the sole evidence for beds of that age near the Pacific Coast. Beds of Early Jurassic age have not been identified in Cuba or in the subsurface of the southern United States. Marine beds of Bajocian and Bathonian Age have been identified definitely in Mexico only in northwestern Oaxaca and northeastern Guerrero (Burckhardt, 1927; 1930, p. 25, 26; Erben, 1957a, p. 49, 50). They were de- posited in an embayment (Guerrero) that probably opened into the Pacific Ocean rather than into the Gulf of Mexico (Erben, 1956b, p. 122—124, pl. 17; 1957b, p. 39, fig. 2; Viniegra 0., 1971, p. 484, 492). Marine beds of late Bath- onian Age may occur also in the subsurface of east-cen- tral Mexico near Tampico, as shown by the presence of some small ammonites similar to the late Bathonian Wag- nericeras (Cantu Chapa, 1969, p. 5). Elsewhere in the Gulf region, a Bajocian to Bathon- ian Age seems probable for part of the San Cayetano Formation of Cuba (Meyerhoff, 1964, p. 152—153; Krom- melbein, 1956; Khudoley and Meyerhoff, 1971, p. 37, 38) but most unlikely for the Louann Salt of the southern United (States or for similar bedded salt deposits of southeastern Mexico (Imlay, 1943a, p. 1438; 1953c, p. 7; Viniegra 0., 1971, p. 482). Marine beds of Callovian Age have been found in Mexico only in its east-central and southern areas (Burckhardt, 1927; 1930, p. 26, 32—36, 43; Erben, 1956b, p.12—16, 31, 38; 1957a, p. 46—50; Cantu Chapa, 1969, p. 5, 6; 1971, p. 21—24, 36—38). Those beds in the east- central area may have been deposited in an arm of the Gulf of Mexico (Erben, 1957b, fig. 2) but more probably represent a transgression from the Pacific Ocean (Vinie- gra 0., 1971, p. 484, 492). Those beds in the southern area were deposited in waters that definitely connected with the Pacific Ocean (Erben, 1957b, p. 39—40, fig. 2). Marine beds of Callovian Age probably are also present in Cuba (Meyerhoff, 1964, p. 151, 152; Khudoley and Meyerhoff, 1971, p. 60), but the fossil evidence has not yet been published. _ Later Jurassic beds of Oxfordian to Tithonian Age are widely distributed throughout the lands bordering the Gulf of Mexico (Burckhardt, 1930; Imlay, 1940b, 17 1943a, p. 1411—1422; 1953a, p. 20—61, figs. 4, 5; Mur— ray, 1961, p. 287—297; Khudoley and Meyerhoff, 1971, p. 59—67; Maher and Applin, 1968, p. 9—11; Rainwater, 1967). The Gulf of Mexico of that time must have had marine connections with the Atlantic Ocean via Cuba and southern Florida. It must also have been connected with the Pacific Ocean either through southern Mexico or Central America, or both (Viniegra 0., 1971, p. 484, 486, fig. 10), judging from the similarities between the marine faunas in Mexico and California. The Gulf of Mex- ico during Late Jurassic time was separated from the seas in the western interior region by highlands that ex— tended across parts of central Arizona and New Mexico (Harshbarger and others, 1957, p. 43, 44). PACIFIC COAST Jurassic rocks near the Pacific Coast of Mexico have been found only in the states of Oaxaca and Guerrero, as discussed above, and in northwestern Sonora (Burck- hardt, 1930, p. 23, 24, 41, 42; Erben, 1957b, p. 36; King, 1939, p. 1645—1659; Imlay, 1952a, p. 972). Farther north in the Pacific Coast region, many Jurassic outcrops are found between southern California and westernmost Alaska. . Northward through Nevada and California into southwestern Oregon, the distribution of outcrops of the various stages indicates that the Jurassic seaways grad- ually shifted westward (Taliaferro, 1942, fig. 2 on p. 80; Imlay, 1959a, p. 103—106). Thus, in the Sierra Nevada, beds of Callovian Age extend westward beyond beds of Bajocian and Early Jurassic age. Beds of Oxfordian to early Kimmeridg'ian Age occur with beds of Callovian Age in the foothills of the Sierra Nevada but crop out also at two places west of the Callovian beds (Santa Mon- ica Mountains and Klamath Mountains). Beds of Tithon- ian Age crop out only in western California and in south- western Oregon. Only in southwestern Oregon have they been found in the same sequence with beds of Oxfordian to early Kimmeridgian Age. In east-central Oregon is a thick Jurassic sequence (Dickinson and Vigrass, 1965), ranging in age from Het- tangian to early Callovian (Imlay, 1964a, 1968, 1973), that correlates faunally with thick Jurassic sequences in the Sierra Nevada, California, and in the Cook Inlet re- gion, Alaska. In extreme northeastern Oregon and in the adjoining part of Idaho, along the Snake River, are beds of early Oxfordian Age containing Cardiocems (Imlay, 1964a, p. D6, D15). Of paleogeographical interest is the fact that rocks of that particular age have not been iden- tified in California or in southwestern Oregon but have been identified faunally at various places in British Co- lumbia, Alberta, Montana, and Alaska. 18 In Washington, Upper Jurassic beds have been found only in three areas in the northern part of the State. N orthward from Washington into Alaska, beds of Early, Middle, and Late Jurassic age are widespread, although in some areas certain stages are not represented or have not been identified faunally. WESTERN INTERIOR REGION Marine beds of Early Jurassic age have been identi- fied in the western interior region of Canada as far east as westernmost Alberta (Frebold, 1957, p. 5—12; 1964d, p. 24—26; 1969). They “probably were never deposited much farther east or southeast, and they have not been found in the western interior of the United States. Faun- ally, they represent only parts of the Sinemurian, Pliens— bachian, and Toarcian Stages. Marine beds of earliest Bajocian Age have not been identified definitely by fossils in the western interior of the United States or Canada. In fact, they have not even been found in the eastern half of British Columbia along a line drawn from Whitesail Lake southeastward to Ta- seko Lakes (Frebold, 1951b, p. 18, 19; 1964d, p. 26; Fre- bold and Tipper, 1970, p. 9, 10). The projection of this line farther southeast coincides approximately with the easternmost occurrence of lower Bajocian beds in east- ern Oregon. Nonetheless, an early to early middle Bajo- cian Age for the Gypsum Spring Formation (or member) in the western interior region is indicated by its position unconformably below a limestone whose middle and up- per parts contain late Bajocian ammonites (Imlay, 1967b, p. 19, 26, 27). By contrast, marine Jurassic beds of middle Bajocian to late Oxfordian or early Kimmeridgian Age are wide- spread in the western interior of the United States, and, with the exception of the late Bajocian, are equally wide- spread in Canada. These beds were deposited in an em- bayment that spread eastward from the Pacific Coast re— gion across the northernmost part of the United States and adjoining parts of Canada. At one time it was thought that the embayment in the western interior of Canada was partially separated from the Pacific Ocean by a land- mass (Schuchert, 1923, p. 226, fig. 14; Crickmay, 1931, p. 89, map 10) whose position coincided approximately with the present Rocky Mountain trench. Recently, how- ever, Frebold (1954; 1957 , p. 37—41; Frebold and others, 1959, p. 12—16) has presented evidence showing that such a landmass did not exist. In contrast with conditions in Canada, however, ample evidence exists that at least the southern part of the embayment in the western in- terior of the United States was bounded on the west by low landmasses or islands, or both, which furnished some sand and pebbles from late Bajocian until Oxfordian time (Imlay, 1950, p. 37—42; 1952c, p. 79—82; 1953d, p. 54— JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 59). The position of these landmasses coincides fairly well with that of the Paleozoic Antlers uplift (Roberts and others, 1958, p. 2825, 2850, 2851). Similarly, other landmasses surrounding the Jurassic embayment on its southern, eastern, and northern sides furnished most of the clastic sediment that was deposited in the embay- ment. Major marine transgressions took place during mid- dle to late Bajocian, late Bathonian to early Callovian, and early Oxfordian time. Regressions occurred during early Bathonian, middle Callovian, and middle Oxfordian to early Kimmeridgian time. Sedimentation was inter- rupted marginally during the Bathonian (Imlay, 1956a, p. 564, 579—580) and regionally during the late Callov- ian (Imlay, 1952b, p. 1747—1752; 1956a, p. 591; 1957, p. 475; 1967b, p. 53—57). . The latest Jurassic marine regression began near the middle of Oxfordian time, as shown by the presence of . the early Oxfordian ammonite Cardioceras less than 20 feet (6 m) below the base of the continental Morrison Formation of Late Jurassic age in the Wind River and Bighorn Basins. Farther north [in northwestern Montana and in Can- ada, marine deposition continued into late Oxfordian or early Kimmeridgian time, as shown by the presence of Buchz'a concentrica (Sowerby) (Imlay, 1954, p. 60; 1956a, p. 595; Frebold, 1953, p. 1238, 1239; 1957, p. 68, Frebold and others, 1959, p. 10, 11) considerably below the top of the marine sequence. Furthermore, near Fernie, British Columbia, a large ammonite, Titanites, of early late Ti- 'thonian Age has been found (Frebold, 1957, p. 36, 66, 67; Frebold and Tipper, 1970, p. 14—17; Westermann, 1966). It appears, therefore, that marine waters disappeared from most of the western interior region of the United States by the end of early Oxfordian time but persisted in northern Montana into late Oxfordian time, and in the western interior of Canada, until late Tithonian time. The characteristics and distribution of the Jurassic sediments were greatly influenced by tectonic features in the Jurassic embayment (Imlay, Gardner, and others, 1948; Nordquist, 1955; McKee and others, 1956, pl. 8; Imlay, 1957, p. 470—477; J. A. Peterson, 1957, p. 401— 404; 1972, p. 177). These include broad gentle uplifts in north-central Montana (Belt Island) and west-central Colorado (Uncompahgre uplift); the large Williston basin in eastern Montana, western North Dakota, and adjoin- ing parts of Canada; the Alberta trough extending north- ward from Belt Island across northwestern Montana far into Canada; the Twin Creek trough extending south from Belt Island along the Wyoming-Idaho border into north-central Utah; the Sheridan arch extending north- east from north-central Wyoming into southeastern Montana and separating the Williston basin from the Powder River basin (J. A. Peterson, 1954a, p. 474, 477, SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 489); and the Hardin trough (J. A. Peterson, 1954a, p. 474; 1957, p. 403), which connects the Williston basin with the Twin Creek trough across northwestern Wyo- ming. Of these tectonic features, Belt Island had the greatest influence on the marine currents, salinities, and temperatures because of its geographic position and its large ,size, but it supplied very little clastic sediment (Im- lay, Gardner, and others, 1948; J. A. Peterson, 1957, p. 403). ARCTIC REGION Beds of Early to Late Jurassic age in northern Alaska (Imlay, 1955) bear a succession of ammonites similar to that in northern Canada (Frebold, 1958; 1960; 1961, p. 6—24; 1964a, c; Tozer, 1960, p. 9—12, 15, 19, 20). The ‘ ammonite successions of these regions do not include any ammonite faunules resembling those of middle to late Ba- jocian, Bathonian, or late Callovian Age in northwest Europe. The Bathonian is represented faunally, how- ever, by the ammonite genera Arcticocems, Arctoce- phalites, and Cranocephalites, as in East Greenland and arctic U.S.S.R. This age determination is based on their stratigraphic position below beds of early Callovian Age in Greenland (Callomon, 1959). g In southern Alaska, the basal Hettangian is repre- sented by the ammonite Waehnerocems at Wide Bay and Puale Bay on the Alaska Peninsula, in the Seldovia area south of Cook Inlet, and in the southern part of the Wrangell Mountains. Psilocems occurs in those same mountains and also north of Old Rampart near the Por- cupine River in northeastern Alaska. The Hettangian is probably represented also on Hagermeister Island and in the Kuskokwim area by pelecypods identical with species found in the basal Jurassic near Seldovia (Imlay and Det- terman, 1973, p. 22). The lack of Hettangian ammonites in most of northern Alaska is matched by a similar lack in arctic Canada and in East Greenland. To date, the presence of Hettangian deposits in northern Alaska is based on one specimen of Psiloceras (Franziceras) ob- tained from a core at the depth of 2,170.5 feet (661.6 m) in the South Barrow test well 12, about 10 miles (16 km) southeast of Point Barrow. SUCCESSION 0F AMMONITES AND BUCHIAS BY STAGES HETTANGIAN In Mexico, the Hettangian Stage has not been iden- tified faunally. The presence of one ammonite similar to. the Hettangian genus Psiloceras is not valid evidence of such an age because of its association with the early Si- nemurian ammonite Corom'cems (Flores Lopez, 1967, p. 26, 29, 30, pl. 8, fig. 1). 19 In western Nevada and eastern Oregon, the basal Jurassic has furnished ammonite genera that specifically and stratigraphically correspond close to Hettangian am- monites in Europe (Muller and Ferguson, 1939, p. 1611, chart opposite p. 1590; Corvalan, 1962; Hallam, 1965, p. 1485—1487, 1494). These include, in particular, the gen- era Waehnerocems and Psiloceras in the lower part of the Hettangian sequence and the genera Schlotheimia, Calocems, and Alsatites in the upper part. SINEMURIAN In east-central Mexico, the highest and lowest parts of the Sinemurian are represented by ammonites closely similar to or identical with ammonites in Europe (Burck— hardt, 1930, p. 8—23; Erben, 1956a, p. 124—149; 1957a, p. 44; Flores Lopez 1967, p. 29, 30). No evidence exists, however, for the presence of the European zones of Caenisites turneri and Asteroceras obtusum (Hallam, 1965, p. 1491—1493). In northwestern Mexico near El Antomonio, Sonora, the early Sinemurian is represented by Amioceras (Im- lay, 1952a, p. 973). Pelecypods of Hettangian or Sine- murian Age are present in west-central and southern Sonora (Burckhardt, 1930, p. 23, 24, 41, 42; King, 1939, p. 1655—1659, pl. 5). The late Sinemurian is probably represented by Crucilobiceras about 25 miles (40 km) south-southeast of Caborca, on the basis of collections made by L. T. Silver (California, Inst. Technology). In western Nevada, the Sinemurian succession is nearly the same as that in eastern Mexico; it has the same faunal gaps and includes similar species, some of which may be identical with species in Mexico and Eu- rope (Muller and Ferguson, 1939, p. 1611, 1612, table 3). Similar faunal successions have been found also in east- ern Oregon, western and northwestern Canada, and southern and northern Alaska. (See fig. 13.) Nearly all successions contain ammonites representing the highest and lowest parts of the Sinemurian (Frebold, 1957, 1959, 1966, 1975; Frebold and Tipper, 1970) but lack any evi- dence for much of the middle part of the stage. Thus, the European Caem'sites turneri zone has been identified only in the Wrangell Mountains, Alaska (Imlay and Det— terman, 1973, p. 22); the Asterocems obtusum zone, only in southern British Columbia (Frebold, 1964d); and the Oxynoticems oxynotum zone, only in the Richardson Mountains of northwestern Canada (Frebold, 1960, p. 16, pl. 4, figs. 1—5). PLIENSBACHIAN Ammonites of Pliensbachian Age have been found in southeastern and south-central Mexico, western Nevada (Muller and Ferguson, 1939, p. 1621, 1622; Silberling, 20 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES . British Columbia. ., Eastern and Canadian Rocky Northwest European southern Mexico Wegfltzrlgygxgda East-central Mountains infiii‘di‘nem‘ Tand ammonite zones - 9 '53" s 513995 (Erben, 19563: Ferguson 1939' 0’990" (Frebold,19§9, (Frebold 19643 d' (after Dean and others. 1961) 1957a; Hallamjgss, ' (Imlay, 1968) Frebold and Tipper: Frsbcild and' ' Hallam, 1965) 1970) Tipper, 1970) . . . Catulloceras Dumartler/a /9V95 “". ”I B. (immense, and o. Cadocsras cf. C. septontr/ana/e E Effigffggcgfaflfm Lil/0min buckmani l g 7 7 2 Cadooem p- 813- s " 1 . . Disconfo Y In iskin ires Cadaceras calyx i. Cadoceras variablle n. 7 Arctiooceras n. sp. 3 c r . , .2 Ar’ aa'L Aru' ...'L Ar' as» Ar as . g g -. 3 S - ' Zrctocephalites ”cf. - . ArctocephanIFs reenland/cus E '5 Armocepha/Ites? cf. A. slogans A. elegans Arctocephalrtes spp. Arctacepha/Itas spp. A rota c9 halites graicus 2 m Cranocephalites spn . Cranocephalnes C. .- 3 " C, ‘- liles ,. ,. ‘;" " ~ 7 ~ . u. .. a 7 \ vulgar» ’ S Cranacepha/Ites cosudansus C. castrdensus Cranacepha/ites‘ sp. ? Cranacephalites indistinctus 3 I An ular unconfom ity on Cranacephalites bares/is Cranocapha/ites bores/is lnis in Peninsula 7 ’ 3-, 7 E lam/flaphflnUSICDDbanflOS. Megasphaeroceras ratundum , D and Megasphaeraceras? Loptasphinctes, and Normannites Narmanmtes one/(ma I, Chondraceras allani, Te/aceras runs“, an Norma/mites crickmayi. Zemiszaghanus r/chardsoni and Telecoms iiinsae Stephanaceras kirsclmeri ? 7 7 a f! . . . 1: :ggafiflg%ecsef$ss1costatus Arke/loceras Arkalloceras Arkelloceras g g: 7 Witchellia lLatiwitcha/Iia?), Docidacaras widebayensa Guhsania bel/amnd Sanninia and Sonm'nia Erycitoides hows/Ii, Erycitoides howelli, - . Erycites and Tmaroceras Pseudo/iocsras whiteavesi, Pseudo/iaceras' Egyfigwgfi c" .. ’ and Tmetaceras scissum whitaav'esi ' 7 g Pseudp/ioceras ”fizz/$1527.75...) A mac/[mach Leioceras opalinum B. British Columbia to East Greenland. BAJOCIAN TO CALLOVIAN AMMONITES IN NORTH AMERICA. BAJOCIAN The only Bajocian ammonites found in southern Mex- ico are from upper Bajocian strata in northeastern Guer- rero and northwestern Oaxaca. Of these, Normanm'tes (Burckhardt, 1927, p. 22, pl. 12, figs. 1—4), in association with Stephanoceras, could represent the Stephanocems humphfiesianum zone of Europe, or the next younger zone. Leptosphinctes? (Burckhardt, 1927, pl. 11, figs. 11, 12) could represent the early late Bajocian. Parastreno— ceras mixteca Ochoterena F. (Ochoterena F., 1963, p. 7, pl. 1; Burckhardt, 1927, pl. 16, figs. 10, 11, 16) probably represents some part of the late Bajocian younger than the beds containing N ormmmites. Fairly complete and closely similar ammonite succes- sions of Bajocian Age have been found in east-central Or- egon (Imlay, 1973, p. 16—31, figs. 3—8) and in southern Alaska (Westermann, 1964, 1969; Imlay, 1962a, 1964b; Imlay and Detterman, 1973, p. 23—24). In neither area is there any faunal evidence for the earliest Bajocian (Lioceras opalinum zone). Otherwise, in both areas, the succession of ammonite genera from Tmetoceras at the base up to Teloceras is remarkably similar to that in Eu- rope and in other parts of the world. Exceptions include a few genera that have been found only in areas border— ing the Pacific Ocean (Imlay, 1965, fig. 1 on p. 1024). Among such genera are Pseudotoites, Parabigotites, and Zemistephanus, which occur in stratigraphic succession associated respectively with the genera. Docidocems, Otoites, tand Telocems. In both southern Alaska and Oregon, beds of late Ba— jocian Age are identified by the presence of Leptos- phinctes and Sphaerocems. In Oregon, associated am- monites include Spiroceras, Normanm'tes, and Megas- phaeroceras. In southern Alaska, associated ammonites include Megasphaeroceras, Oppelia (Lyroxyites), and N armamtites (Imlay, 1962a). Of these, Megasphaero- ceras and the subgenus Lyroxyites are known only from North America. The presence of N ormanm'tes suggests that the fauna is not younger than the earliest late Bajocian. 24 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Northwest European ammonite Cgsbza (lgilayk I19132, 1133?); . (E'afitern'lgzg ngrgggrzn 11:3;3300 zones(Arkell, 1956; Callomonn 964; 1 m We 3' ‘1 1 Gulf r ion of United m 3Y1 ‘1 . a! , °1 CaIifornia, Or omend Western interior United Stages Enay, 1964,1971, 1972; Cope, 111131215111, 194015 Judg'fY Statesefimlay, 19433, 1945) 361: Em": 1951311???“ western Idaho Imlay, States (Imlay, 1947, 1948. 1967; Em: and. others. 1971; 3‘" $6339; “Cg“ :36 , 1 $811963'1PG ' 9 . 1961, 1964a; lmlay and 1952a, b, c. 19563. b; Saks and hulgma, 1972) 965, . ermu OZ, 1. Br: gee, 1965, Burckhardt, Jones, 1970) Reeside 1919) Arkell, 1956) 1906, 1912.1919,1927,1930) , ' Berriasella é'u ignslggzgacerae, Buchia Substeueroceras, o S > S iticeras ' 81f, Substaueraceras Aulacosphing‘tes. ?oav? Pgrodantdceras B.akensis F: L ' 7 e we. . Pron/ceras.and .13 k” - ~ 5‘10”" _ Protancyc/aceras 13% £323,730,,” £5)?"' a ‘ - g . . _ Durangites vulgar/s, Kossmafia victoris, SE 3’ :) Tnamtes giganteus Parodontoceras bum, Durang/tes vulgans“ g ”g K a 5 5m aria Bye/via Carongaceras, Simoceras, Parodontqceras bum, Sfio Plat/"7 Glauco/ithites gorei Pfatancy/oqeras, Lytohop/ites, D{ck9rsanla, Slmoceras, 5: 73335122632252? ’0 'ckersom’a Yfi’ifiifle‘lw’“ E s ? . . . , I . 1 g Zara/sk/tes albam Mlicracanthocera/s, and Pseudo- Prs‘gtgioéfigoceras zittefl, Efi ~— I a.) zittei U ’ w E Pavlovia pal/asioides ? L? —/ i5 Virgatosphinctes and Pavlovia rotunda Su plan/res a Xir atasphi'nuesa,’ Pocrinatites pectinatus Tgrgggjggrlggtgs, A I 5.,- Subplanites, "9U 8' . Continental beds 3 ArkeI/ires hudlestani Pseudo/issoceras Unwnfo'mflv 3 (rare),_a_nd Virgatasphinctoides wheat/eyensis Mazap/I/tes Virgatosphinctoides scitulus Virgarasphinctoides slogans Hybongn‘ceras Au/acosrephanoceras acutissiodorensis E “9-; Aulamstephanus eudoxus Gloch/‘ceras fie/8r Ggglggzreajsgs/aanragzcclgg 3 3 p ? conwmrim7 '3 Rasenia mutabilis Id f / d ' a. aceras c. . uran ense E ldoceras cf. I. ba/defgum Idaceras cf. /. ba/derum 7099,55 and 52 5% flasenia cymadoce '7 A I: _ d (Amoebitegl, g . taxioceras, asenla, an dub/um "t A Pictonia baylei Ataxmceras Sutneria cf. S. p/atynota E . = .' - J . I" ,. *‘ 1.1m 'L . I" *' cf. D. Discasphinctes carribeanus, ° _ ”I dim ’ "a” Ochetaceras canalicu/atum D carrfiaeanus. [QC/retoceras canalicu/atum, : _ _ . , var. ' L r" -‘ ,. ' f ‘ ,_" “a. P‘ r" E Bach/a concentrica in § Damp/a damp/ens Dicqatqmpsphinctes onhosphincfgsr plicafl/azdasmnd virgu/atifarmis g northwestern Montana 3. plan/01119.9, ‘ _ Ochetoqeras . Euasp/daceras and a: c Perisphinctes camisnigrae Otrhafphmctes, Qech/a, cans/Lculatummnd Dichotomosphincres g r r . “ ,Per/zrhmctes, '5 r ae “L L' 13 . Euaspldoceras, an Dichatomosphinctes % % Gregoryceras transversarlum Aspidoceras durangensis 7 '0 ’ . o 5 Perisphinctes p/icati/is Card/aceras spp. g Cardioceras cardatum , Card/oceras cordilorme 3 . Card/:aqeras(Sparburgiceras) Scarburgiceras and Ouenstedloceras mar/3e 7119mm (only In Idaho) Pavlovicaras A. Gulf of Mexico, Pacific Coast, and western interior region. The Bajocian is poorly represented in the western interior of the United States. A middle Bajocian Age, probably corresponding to the European zone of Ste- phanocems humphm'esianum, is shown by one specimen of Chondroceras and several fragments of Stemmato- cems from the basal part of the shale member of the Sawtooth Formation exposed at Swift Reservoir in northwestern Montana (Imlay, 1948, p. 19, pl. 5, figs. 1—5; 1967b, p. 28). A late Bajocian Age is shown by an association of Spiroceras, Stemmatocems, Stephano- cams, and Megasphaeroceras in the upper part of the lowermost limestone (Sliderock Member) of the Twin Creek Limestone near the border of Wyoming and Idaho (Imlay, 1967b, p. 28, 29). The association of the first three genera in the Twin Creek Limestone, by compari- son with the European fauna] succession, indicates a correlation with the basal part of the upper Bajocian. FIGURE 15.—SUCCESSION AND CORRELATION OF The presence of Megasphaerocems furnishes a correla- tion with lower upper Bajocian beds in southern Alaska. The overlying beds (Rich Member) of the Twin Creek, containing Parachondrocems and Sohlites (Imlay, 1967b, p. 31), are correlated with the uppermost Bajocian on the basis of stratigraphic position and the resemblances of the ammonites to genera of Bajocian Age. In northern Alaska, only the lower Bajocian and part of the middle Bajocian have been identified. The Euro- pean zone of Liocems opalinum is probably represented by Pseudolioceras maclintochi (Haughton) (Wester- mann, 1964, p. 422—424; Imlay, 1955, p. 89, pl. 12, figs. 15, 16), which in arctic Canada has been found with Lio- cems opalmum (Reinecke) (Frebold, 1958, p. 23; 1960, p. 28). The European zone of Tmetocems scissum is probably represented by one fragment of Tmetoceras ob- tained from‘a test well (Imlay, 1955, p. 89, 90) and by SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 25 Canadian Roe Mountains British Columbia and Southern Alaska (Imlay, Northern Alaska (Imlay, Arctic Canada (Frebold. East Greenland (After Spath. Stages (Frebold, 1964?; Frebold and southern Yukon (Frebold, 1953b, 1961; lmlay and 1955; lmlay and 19648; Jeletzky, 1965, 1966) 1935. 1936: Arkell, 1956; others, 1959; Frebold and 1964a; Frebold and Tipper. Denerman, 1973) Dmerman, 1973) Donovan, 1957) Tipper, 1970) 1970; Jeletzky. 1965) Cras dites aff. Chetatires chetae ganzdenslls nd _ S [7 ed f S . , , . . . . . acrqun ‘nIs ucrasp itesc.. Buchla cf. 8. fischerlana Buchla Ilscherlana $11225: #351733; r1233 uc [a {Isobar/ans p/icampha/us . . , and Dorsoglamtes Bus/Ha fischenana and B . . . ? , Buchia piachii , uch/a nchardsanenSIs i D. T' ' " " ° ‘-‘ , L"and n i.~ - 1. 3 and Buchia piochii Buchia b/anfordiana " . . Laugeltes vagu/Icus .’ 7 ’ 7 ’ lo \ Glauca/ithites .3 c = .._ .‘2 ‘r‘ 8 Pavlovia and Buchia g g ,, mosquensis S v- Q Pectinatites . a Buchia Euchia gch/y rugosa and 51102123 rugasa and Buchla masquensis ’ g ' ' ' uc Ia mos uensis uc ia mos uensis .I mosquensm mosquenws q q Subp/anites ? . ‘é ? ‘ . .. ' wow... 3 fi’ Amoebites r . _ ‘E’ m 3 and Eupr/anoceras ._ E , 5g '5 Buchia g "g / E E cancentrica Rasenia 3 3 2 Amaeboceras and Amaebaceras and Amoebaceras '5 Amaeboceras 3 Amoeboceras and Buchia concentrica Buchia cancemn'ca (Pnlbirfgzdocerag) : (Prionodoceras) .2 Buchla concentrlca spm rum an N a h chhotamosphinctes E g Arnoeboeeras g m 0: (Pnonodaceras) g, and 3 Ringsteadia c — .‘S 2 E E ~S 7 7 2 0 Cardioceras and Cardioceras . . . T Goliathiceras (Subvenebriceraswanadense Card/oceras drstans Card/oceras g Cardiocerasng’cr'alrlgurglceras) Cardincerazyiafi‘afiburgiceras) Cardioceras (Scarburgiceras) Cardioceras (Scarburgiceras) 3 In] , / B. Southwestern Canada to East Greenland. OXFORDIAN TO TITHON IAN AMMONITES IN NORTH AMERICA. several specimens of E'rycitoides obtained from outcrops (Imlay, 1955, p. 90, pl. 13, figs. 12, 13). The middle Ba- jocian is represented only by Arkelloce'ras, whose age is based on stratigraphic occurrences on the Alaska Penin— sula (Imlay, 1964b, p. B18, B53) and in the Canadian Rocky Mountains (Westermann, 1964, p. 405—409; Fre- bold and others, 1967, p. 20). Bajocian ammonites in the Canadian Rocky Moun- tains, British Columbia, and southern Yukon bear close resemblances specifically and stratigraphically to the Ba- jocian ammonites in eastern Oregon and in southern Alaska. The main difference is the rarity in western Can; ada of ammonites of early and late Bajocian Ages and of the Otoites sauzei zone of the middle Bajocian. In arctic Canada, the Bajocian ammonite sequence is identical with that in northern Alaska, except for the presence of Leiocems opalinum near the base. As in northern Alaska, the only middle Bajocian ammonite present is Arkellocems. BATHONIAN Lowermost and uppermost Bathonian sediments have been identified in northeastern Guerrero and northwest- ern Oaxaca, Mexico, on the basis of ammonite evidence. These beds were deposited in an embayment (Guerrero) from the south that apparently connected with the Pa- cific Ocean and did not extend to the Gulf of Mexico (Er- ben, 1957b, p. 35, 39, fig. 2). The earliest Bathonian is represented by Zigzagiceras floresi Burckhardt (Burck— hardt, 1927, p. 25, pl. 12, figs. 14—16, 18—20; Arkell, 1956, p. 564; Erben, 1956b, p. 110, 122; 1957a, p. 50) and the latest Bathonian, by Epistrenoceras paracontmn’um 26 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES (Burckhardt) (Burckhardt, 1927, p. 80, 94, 95, pl. 16, figs. 14, 15; Arkell, 1956, p. 564; Erben, 1956b, p. 119; 1957a, p. 50). The latest Bathonian is probably also represented in the subsurface of northern Veracruz by some small am- monites resembling Wagnericeras (Cantu Chapa, 1969, p. 5). This occurrence is in the Huayacocotla embayment, which may have been connected eastward with the At- th set E Southern Europe Argentina W l-II'ODS Garth, 1925; Weaver Stage (Enay, 1971' 1972) (Enay, 1971' 1972’ (Leanza, 1945; Arkell, Substauerocere: kaeneni Pareu/acosphinctes transitorius ' 7..— Corongoceras alts; a 5: Titenites giganteus 7 _. G/a uco/ithites gorei Pseudo virgatites . scruposus Windhausenice/ interspinosum Zaraiskites albani 3 : Pavlov/a pallisioides H 5 Psaudolissaceras PSWWVSS‘F-‘e’ E bavaricum ”"9” Pa v/a via rotunda 7 Sublit/vacoceras peniciI/atum Iii—.4 ‘ 1' 1;, L . pact/hams mendozanus Frenbonites vimineus 7— ; Arke/Iitas 4 hud/estom L‘ P. . u triplicatus Virgatosphinctoides wheat/eyensis Virgatasphinctaides / sciru/us » Hybonoticeras hybonotum and G/ochiceras Virgatosphinctaides Iithographicum elegens FIGURE 16.—COMPARISONS OF THE TITHONIAN lantic Ocean (Erben, 1957b, p. 35, 39, fig. 2), or west- ward with the Pacific Ocean, or both. In the United States, the assignment of certain beds to the Bathonian is based mainly on stratigraphic posi- tion, as the ammonites present are mostly generically different from those in the typical Bathonian of Europe. In eastern Oregon, southweSt of John Day, the Bath- onian is represented by beds containing Cobbam'tes, Par- smsgg‘ggssigggnog AMMONITES AND BUCfitfiflmfifiéGEs 27 Iexioo (Imlay, 1952:,- (Geres'imov and. , Emn' 1957'; can“ cm"; 2““ Jugg‘l’w Trina Enay Salaam?!1 3139333759“ Sm. Cha 8, Furrazola- ‘ ' . . Chaps, 1967. 1971) Enay, 1964 19:7. 1968 Bermadez, Jones. EnaY. 1971 1972 Saks and others, 1968) 1971 138 1970 Craspeditu nodiger Substeuergceras Upper Upper Upper Craspedites subditus é an 3 Proniceras Upper Kachpuritos fulgens Upper Upper ? Upper Upper Upper ’ Epivirgatitas nikitini _._.7_ Kossmalia. , Dumngites, . . . Lytahop/ites,and Vlrgames wrgatus oudolissaceras zine/i M'ddl Z . Ir' 2 I e . era/s nos M'ddle zaraiskensis E 7 Middle Dors Ianites Middle mofdw .§ . , Pavlovia % Subplanites, Mlddle pavlovi > Psaudo/issoceras. , . and Middle V/rgatosphinctes —? Subp/anites 7 —7— —? I=llawaiskyel pseudosycthica Lower L Mazapi/ites, ower Lower Virgatasphinctes, and L ubdichoromoceras Subp/anites g Lower Lower Lower ’=”°W”"kyal 3 soka/ovi Lower Lower Lower : Hybanoticeras Subp/anites klimavi AND VOLGIAN STAGES AND THE SUGGESTED SUBDIVISIONS OF THE TITHONIAN. areineckeia, and Choffatia beneath beds containing Lil— loettia buckmam' (Crickmay) and Reineckeia. In the western interior of North America, the early to middle Bathonian is probably represented by the am- monites Paracephalites (Frebold, 1963, p. 5, 8—13, 27— 29) and Cobbanites. In western Montana, Paracephalites includes the species formerly referred to as Arctocephal- ites (Cranocephalites) (Imlay, 1962b, p. C24, 025). Par— acephalites differs from Arctocephalites and Cranoce- phalites, according to Frebold (1963, p. 8), by having a wider umbilicus that opens up at a later growth stage and by retaining ribbing later on the adult body cham— ber. Its Bathonian Age is based primarily on strati- graphic position beneath beds containing Cadocems and Kepplem'tes, of early Callovian Age (Frebold, 1963, p. 29—31; Imlay, 1962b, p. 019). The age of Paracephalites 28 must be about the same as that of Cranocephalites in Alaska, as both are associated with Gryphaea impressi- margimta McLearn and with the lowest occurrences of Cobbanites (Imlay, 1962b, tables 5 and 6). The late Bathonian in the western interior of North America is represented by species that were once as- signed to Arcticocems by Imlay (1953a, p. 19—22) be- cause of their general resemblance to that genus in shape and rib pattern. They were subsequently assigned to a new genus, Wawenoceras (Frebold, 1963, p. 13, 14), that differs from Arcticocems in its narrower umbilicus, less sharp ribs, absence of constrictions, and broader ele— ments of the suture line, and by becoming smooth at a much earlier growth stage. These differences do not jus- tify more than a subgeneric status for Warrenocems un- der Arcticocems, according to J. H. Callomon (written commun., 1972). The exact age of Warrenocems is not known. Its general resemblance to Arcticocems suggests, however, that it is either a provincial time equivalent of Arctico- ceras or is a descendant. If so, it could be of the same age or could be younger. Its association with Cadocems suggests that it is younger than the typical Arcticocems of the Arctic region. Against such a suggestion, how- ever, is the fact that all species of Cadoceras in the west- ern interior of North America have a rounded instead of a sharp umbilical edge (Imlay, 1953a, p. 3; 1953b, p. 45) and hence may not have the same age significance as Ca- docems proper. Furthermore, the exact time relation- ships of Warrenocems to the older Paracephalites are uncertain because of the presence of a disconformity of unknown magnitude at the base of the Wawenocems- bearing beds in Montana, northern Wyoming, and west- ern South Dakota (Imlay, 1962b, p. 09). Nonetheless, the association of Cobbam'tes with Warrenoce'ras in Al- berta (Frebold, 1963, p. 5) indicates a Bathonian Age, because Cobbanites in southern Alaska has not been found above beds of Bathonian Age and is closely related to the late Bajocian genus Vermisphinctes. The late Bathonian 1n the northern part of the west- ern interior region may be represented also by species of Kepplem’tes that were assigned previously to “Goweri- cems” costidensus Imlay, “G.” subitum Imlay, and Kepplerites cf. K. tychom's Ravn (Imlay 1953a, p. 7, 8). This age is indicated by the close resemblance of K. cos- tidensus to an undescribed species (N0. 3149 in Geologi- cal Museum, Univ. Copenhagen) from the Kepplem'tes ty- chom's zone on Fossil Mountain, East Greenland; by the resemblance of K. cf. K. tychom's Ravn (Imlay, 1948, p. 16, 25, pl. 8, figs. 3, 4, 6) to K. tychonis (Ravn) (Ravn, 1911, p. 490, pl. 37, fig. 1) from East Greenland; and by the occurrence of these ammonites in Montana below beds characterized by K. maclearm' Imlay in association JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES with Lilloettz'a and Xenocephalites (Imlay, 1953a, p. 8, 18, 19, 25, pls. 1, 15, 16, and part of 17). Such an associ- ation by comparison with ammonites of southern Alaska (Imlay, 1975, p. 6, 14) is definitely of early Callovian Age. In fact, with one exception, Xenocephalites in Alaska is not known above the basal part of the range of Lilloettia or Kepplem'tes. In southern Alaska between Cook Inlet and the Wrangell Mountains the early to early middle Bathonian is probably represented by Cranocephalites, Arctoce- phalites, Pararemeckeia, and Cobbam'tes (Imlay, 1962b, p. C20). The sequence containing these ammonites rests unconformably on beds of early late Bajocian Age and 1s overlain disconformably by beds of early Callovian Age (Imlay, 1962b, p. C2, C3, Detterman and Hartsock, 1966, p. 35, 40, 42). Arcticoceras has not yet been found In the sequence, but the time during which it lived could be rep- resented locally near the top of the sequence or by the disconformity at the top. In northeastern Alaska, the Bathonian is repre— sented, in ascending order, by Cranocephalites spp., Arctocephalites cf. A. elegans Spath, and Arcticoceras ishmae (Keyserling) (Imlay and Detterman, 1973, p. 18, 24, fig. 14). These fossils should represent. most of the stage, because the ammonite sequence is similar to that in East Greenland (Callomon, 1959, p. 507, 508). Concerning the age ranges of these genera in the arc- tic region, Spath (1932, p. 145) placed Arcticoceras in the Callovian and Arctocephalites in the Bathonian. Arkell (1956, p. 527) placed both genera as well as the somewhat older Cranocephalites in the Callovian. Callomon (1959), on the basis of field studies in East Greenland, assigned all three genera to the Bathonian and suggested that the earliest occurring species of Cranocephalites might be as old as latest Bajocian. He based these age assignments on the position of the Arcticocems-bearing beds in East Greenland directly beneath beds that, according to him, contain a varied ammonite fauna closely similar to and in part identical with the fauna in the M acrocephalites ma- crocephalus zone of earliest Callovian Age in northwest— ern Europe. He discounted the presence of Cadocems and Kepplerites at the top of the range of Arcticocems, although both Cadoceras and Kepplerites are normally considered good evidence for a Callovian Age. Subse— quently, Callomon (written commun., August 1972) de- termined that 1n Greenland the ranges of Cadocems and Arcticoceras do not overlap but that Kepplemtes does occur as low as the upper part of the range of Arctico- Gems above Arcticocems ishmae (Keyserling) (Callomon and others, 1972, p. 18, 19; Donovan, 1957; Surlyk and others, 1973). In arctic Canada, the Bathonian is represented by an ammonite sequence that is nearly identical with that in SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES Bathonian beds in East Greenland but that contains dif- ferent species of Cranocephalites from those known in northern Alaska. These differences probably reflect in- adequate collecting. CALLOVIAN In Mexico, Callovian ammonites have been found in the south-central part (Guerrero embayment) and in the east-central part (Huayacocotla embayment) (Erben, 1957b, fig. 2). In the east-central part, the early Callov- ian is represented by Kepplerites (Cantu Chapa, 1969, p. 3) from a well core in Veracruz; the late early Callovian, by Neuquenicems neogaeum and Reineckeia (Imlay, 1952a, p. 970; Erben, 1956b, p. 39; Cantu Chapa, 1971, p. 21) from the Necaxa area of Puebla; and the middle Callovian, by Erymnoceras cf. E. mixtecorum from slightly higher beds in the Necaxa area (Erben, 1957a, p. 47). In south-central Mexico (Oaxaca and Guerrero), the Callovian ammonite sequence is essentially the same, but also includes Peltoceras at the top, and Eurycephal- ites and Xenocephalites at the base. The Callovian ammonite sequence in Mexico (see fig. 14) is similar to that in the Callovian of Chile (Hille— brandt, 1970, p. 176, 190, 202) and likewise includes taxa, characteristic of the Pacific Realm, such as Xenocephal- ites, Eurycephalites, and Neuquenicems. The presence of Xenocephalites and the close resemblance of Euryce- phalites to Lilloettia (Hillebrandt, 1970, p. 202) show that the lower Callovian of Mexico contains some am- monites similar to those in the lower Callovian of Ore- gon, British Columbia, and southern Alaska. Ammonites of Callovian Age have been found in the United States in southern and northeastern California, east-central Oregon, western Idaho, Alaska, and in the northern part of the western interior region. A few ammonites found in Callovian beds in Califor- nia are closely related to ammonites from Mexico and the Tethyan Realm. These California specimens includethe early Callovian genera Macrocephalites and Hectico- Gems from the Santa Ana Mountains in southern Califor- nia (Imlay, 1963; 1964c, p. 508) and the late Callovian genus Peltoceras from the Sierra Nevada in east-central California (Imlay, 1961, p. 27, pl. 6). None of these have been found farther north in the Pacific Coast region. Most of the Callovian ammonite faunas in the Pacific Coast region from British Columbia northward to Alaska are dominated by genera of the Boreal families Cardi- oceratidae and Kosmoceratidae, including Im'skz'nites, Cadocems proper, Stenocadocems, Paracadoceras, Pseudocadoceras, and Kepplerites (Imlay, 1953b, 1961, 1964a; Crickmay, 1930, 1933a, b; McLearn, 1929, 1949; Frebold and Tipper, 1967). Of these, only Im'skim'tes, 29 Pseudocadoceras, and Kepplem'tes are definitely identi- fied south of British Columbia. The family Phyllocerati- dae is fairly common throughout the region and is rep- resented by several genera or subgenera that occur nearly worldwide. With these occur some genera of en— demic or Pacific affinities, including Lilloettia, Xenoce- phalites, and Parareineckeia. In addition, a few ammo- nites present belong to the genera Oppelz'a, Grossouvria, Procem'tes, and Choffatia, all of which are nearly world- wide. The succession of genera and species is similar throughout the Pacific Coast region. Fauna] evidence for beds of late Callovian Age is completely lacking north of east-central California, except for one occurrence in Brit- ish Columbia (Frebold and Tipper, 1975, p. 149, 156). In the western interior region, only the early and very latest Callovian is represented by ammonites (Fre- bold, 1957, p. 19—27; 1963; Imlay, 1953a). The early Cal— lovian ammonites include Imlayocems, Lilloettia, Xeno— cephalites, and Grossouvria and are dominated by the families Cardioceratidae, Macrocephalitidae, and Kos- moceratidae. Despite some generic resemblances with ammonites from the Pacific Coast region, there appear to be no species in common; the families Phylloceratidae and Lytoceratidae are unknown from the western inte- rior, and the genus Imlayoceras Frebold (Frebold, 1963, p. 20) has been found only in that region. The latest Callovian in the western interior region is represented by Quenstedtocems (Lamberticeras) colliem’ Reeside from the Little Rocky Mountains and Bearpaw Mountains in north-central Montana. Recent collecting shows that it underlies and does not occur with Cardi- oceras as previously stated (Imlay, 1948, p. 16, 17). In the arctic region of Alaska and Canada, the Cal- lovian is represented by typical species of Cadocems that are associated with C. (Stenocadoceras) and Phyllocems bakeri Imlay in the Richardson and British Mountains, Yukon Territory, Canada. This association, plus the ab- sence of Kepplerites, favors correlation with the upper part of the Paveloff Siltstone Member of the Chinitna Formation in southern Alaska (Detterman and Hartsock, 1966, p. 48). That upper part is dated as middle to early late Callovian on the basis of the European range of C. (Stenocadoceras), the presence of C. (Longaeviceras?) pomeroyense (Imlay) near the top of the member, and the absence of Kepplerites in its upper half. Similarly, the Cadoceras-bearing beds in arctic Alaska and Canada are probably of middle Callovian Age because Keppler- ites is unknown above the lower Callovian (Callomon, 1964, p. 274, 275), Cadocems proper is unknown above the middle Callovian (Callomon, 1955, p. 255; 1964, p. 273—278), and C. (Stenocadocems) is unknown below the uppermost part of the lower Callovian (Arkell, 1956, p. 26). 30 OXFORDIAN In the subsurface of the southern United States, a few fragmentary ammonites of late Oxfordian Age have been found in the Smackover Formation (fig. 15). They include species of Perisphinctes (Dichotomosphinctes), P. (Discosphinctes), Euaspidoceras, and Ochetocems (Imlay, 1945, p. 274, pl. 41, figs. 7—14), which appear to be identical with species from beds of late Oxfordian Age in Mexico (Burckhardt, 1912, p. 1—40, 203—312, pls. 1— 7; Cantu Chapa, 1969, p. 6; 1971, p. 22, 37) and Cuba (S‘anchez Roig, 1920, 1951; O’Connell, 1920; Jaworski, 1940; Judoley and Furrazola—Bermudez, 1965, 1968, p. 5, 18, 22). The late middle Oxfordian is probably repre- sented at San Pedro del Gallo, Mexico, by the lower part of the Oxfordian sequence, which is below an upper part characterized by Ochetocems canaliculatum (von Buch) and Discosphimtes carribbeanus (Jaworski). In the lower part, Dichotomosphinctes occurs in association with Taramelliceras (Proscaphites) (Burckhardt, 1912, p. 211, 212; Arkell, 1956, p. 563) and Creniceras cf. C. crenatum (Bruguiére) (Burckhardt, 1912, p. 15, 16, pl. 7, figs. 15—17). Amoebocems cf. A. altemans (von Buch) is reported by Burckhardt (1930, p. 66) from probable equivalent beds at another locality near San Pedro del Gallo. Early Oxfordian ammonites have not been found in the Gulf of Mexico region, except for unconfirmed re— ports of Crenicems renggeri (Oppel) at Huayacocotla in . Veracruz,iMexico (Erben, 1957a, p. 47), and Fehlman- nites at rXochapulco in Puebla, Mexico (Cantu Chapa, 1971, p. 23). Most of these ammonites in the Gulf region have Tethyan affinities. In California and southwestern Oregon, as in the southern United States, the late Oxfordian is repre- sented by species of Pem'sphinctes (Dichotomosphinctes) and P. (Discosphinctes) that are similar to species in Mexico and Cuba (Imlay, 1961, p. D7—D8, D10, D23— D25, pl. 3, figs. 1—10, pl. 4, figs. 4, 7, 8). In west-central Idaho, the early Oxfordian is represented by Cardi- ocerasv (Scarburgicems) martini Reeside (Imlay, 1964a, p. D15, pl'. 2, figs. 1—5); which has Boreal affinities. In the western interior of the United States, cardi- oceratid ammonites of early to early middle Oxfordian Age are fairly widespread, but ammonites of late Oxford- ian Age have not been found (Reeside, 1919; Imlay, 1947, p. 264; 1948, p. 16, 17, 25, pl. 7, figs.- 12, 14, 15, 18; Arkell, 1956, p. 548). The presence of upper Oxfordian beds in northwestern Montana is shown, however, by the presence of Buchia concentrica (Sowerby) (Imlay, 1956a, p. 595). The oldest Oxfordian ammonites have been collected only in the lower part of the Swift For- mation in north-central Montana, and belong to Quen- stedtocems (Pavlovicems), Prososphinctes, Cardioceras '(Maltom'ceras), and C. (Scarburgicems). This assem- JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES blage probably corresponds to the basal Oxfordian (zone of Quenstedtoce’ras mariae) of northwest Europe. , The next oldest ammonites of the marine lower Ox- fordian have been found in north-central Montana di- rectly above the beds containing an association of Car- dioceras and Quenstedtocems (Pavlovicems). They also occur at many other places in the western interior re- gion. These ammonites apparently represent a single faunal zone (Cardioceras cordiforme), although by Eu- ropean standards they probably correspond to the zones of Cardioceras cordatum and Perisphinctes plicatilis. They are closely related specifically to ammonites in British Columbia, Alaska, and the arctic region, but have nothing in common generically with Oxfordian ammo- nites in the Gulf of Mexico region. In Alaska, both the'early and the late Oxfordian are represented mostly by genera of the Cardioceratidae. Cardioceras is the most common genus in the lower Ox- fordian, as is Amoebocems in the upper Oxfordian. In the basal part of the Cardioceras-bearing beds, the subgenus Scarburgicems is locally common. Peris- phmctes (Dichotomosphinctes) is associated with Buchia concentm'ca (Sowerby), of late Oxfordian to early Kim- meridgian Age,on the Alaska Peninsula (Imlay, 1961, p. D11, pl. 4, fig. 6). The presence of Phyllocems and Ly- toceras in fair abundance contrasts with their complete absence in Oxfordian beds in the western interior of the United States. The Oxfordian ammonite sequences in western and arctic Canada are nearly the same as those in Alaska (Frebold, 1961, p. 22—24, 29, 30, table 1 opposite p. 26; 1964a, p. 4; Frebold and Tipper, 1970, p. 13, 14, 17; Fre- bold and others, 1959). Likewise, few ammonite taxa are present, and an exact faunal boundary between Oxford- ian and Kimmeridgian cannot be drawn. KIMMERIDGIAN The Kimmeridgian Stage as used herein follows the recommendation of Enay and others (1971, p. 97). It is equivalent to the lOwer Kimmeridgian of Arkell (1956, p. 21, 22) and to the lower part of the Kimmeridge Clay of England below the ammonite zone of Pectinatites (V ir— gatosphinctoides) elegans (Cope, 1967, p. 66). In eastern Mexico, the Kimmeridgian ammonite se- quence from the base up, according to Cantu Chapa (1971, p. 25, 26, 36), is characterized by (1) Ataxioceras associated with Rasenia, (2) Idoceras, and (3) the Glo- chicems group of G. fialar. In northern Mexico, the se- quence recognized by Burckhardt (1930, p. 64, 66, 91, 92) is nearly the same, except for the presence of Sutneria cf. S. platynota (Reinecke) at the base. Also, in the lower part of the bed containing Glochicems cf. G. fialar are species of “Aucella” (Burckhardt, 1906, p. 144, 155; SUCCESSION OF‘ AMMONITES AND BUCHIAS BY STAGES 31 1912, p. 50, 67, 80) that are now referred to as Buchia concentrica (Sowerby) and B. mosquensis (von Buch) (Imlay, 1955, p. 85). This faunal sequence was modified slightly by Imlay (1939, p. 21, tables 4, 5; 1943a, p. 1471) because of an apparent association of the Idocems group of I. dumm- gense Burckhardt with Glochiceras cf. G. fialar at some localities. Still later, studies by Cantu Chapa (1970, p. 42; 1971, p. 26), dealing with both subsurface cores and outcrops, showed that Idocems invariably occurs in a lower bed than does Glochicems cf. G. fialar. A few ammonites of Kimmeridgian Age have been found in the southern United States (figure 15) in the subsurface of northwestern Louisiana (Imlay, 1945, p. 271—274, pl. 41, figs. 15—28) and east Texas and in out- crops in west Texas (Cragin, 1905; Albritton, 1937; 1938, p. 1761—1764). Well cores in Louisiana have yielded spe- cies of Idoceras, Ataxioceras, Metahaploceras, and Glo- chiceras that appear to be identical with species from beds of early and middle Kimmeridgian Age in Mexico (Imlay, 1943a, p. 1471—1472); Burckhardt, 1906, p. 2— 106). From the Malone Mountains in west Texas, early Kimmeridgian ammonites have been obtained that be- long to the genera Haplocems, Idoceras, Nebrodites, Physodocems, and Aspidoceras. Some of these are iden— tical specifically with ammonites from beds of Kimmer- idgian Age in northern Mexico. The ammonite species and genera of Kimmeridgian Age that have been found in the southern United States are only a small part of the assemblages of Kimmeridgian Age that are known in Mexico (see Burckhardt, 1930, p. 66—68; Imlay, 1939, tables 4—6, 10). In California, the lower to middle Kimmeridgian has been identified faunally. This identification in California is based on an abundance of the pelecypod Buchia con- centrica (Sowerby) in association with the boreal am- monite Amoeboceras (Amoebites) and the nonboreal am- monites Subdichotomoceras? and Idoceras (Imlay, 1961, p. D8, D22, D25, D26; pl. 2, figs. 24~28; pl. 5, figs. 1—3, 9, 12-16). In northwest Sonora, on Rancho Cerro Pozo Serna, the Kimmeridgian is represented by an association of I doceras, Amoeboceras, and Aulacomyella (T. E. Stump, Univ. Calif. at Davis, written commun., Apr. 1973). Of these ammonites, Idoceras ranges through about 565 feet of beds; Amoeboceras occurs in the lower 510 feet of that range; and Aulacomyella is associated with the highest occurrence of Amoeboceras. Aulacomyella oc- curs elsewhere in Mexico in beds characterized by I do- ceras and Glochiceras cf. G. fialar (Burckhardt, 1930, p. 51, 67, 86, 90, 92, 96, 97; Imlay, 1940a, p. 399; 1943a, p. 1472) but ranges higher into beds containing the lowest occurrences of Virgatosphmctes (Cantu Chapa, 1971, p. 27, 28, 36). The occurrence of Amoebocems with Ido- ceras in Sonora is considerably younger than its reported occurrence with Dichotomosphinctes durangensis Burckhardt near San Pedro del Gallo, Durango (Burck- hardt; 1930, p. 66). Marine Kimmeridgian beds have not been identified in the western interior of the United States or east of the Canadian Rocky Mountains. Throughout western and arctic Canada and Alaska, the identification of beds of Kimmeridgian Age is based mostly on the ranges of spe- cies of Buchia (Imlay, 1955, p. 83—86), because ammon- ites of definite Kimmeridgian Age have not been found. Some of the specimens of Amoeboceras from Alaska (Reeside, 1919, p. 30, pl. 18, fig. 4, pl. 19, figs. 1—3; Imlay, 1955, p. 90, pl. 12, figs. 2—6) could be of early Kimmeridgian Age, but their resemblance to the subgenus Prionodoceras favors a late Oxfordian Age, judging by the range of that subgenus in northwest Eu- rope (Arkell and others, 1957, p. L307). TITHONIAN DEFINITION AND CORRELATIONS The Tithonian Stage is now defined (Enay, 1964, 1971) so that it correlates at its base with the Volgian Stage of the Boreal Realm (Saks and Shulgina, 1964; Saks and others, 1968 and 1972; Gerasimov and Mikhai- lov, 1967) (equals North Temperate Realm of Kauffman, 1973, p. 367). This correlation is based primarily on the local association in Europe of the subboreal ammonite Gravesia with the Tethyan ammonite Hybonoticeras, which is widespread in southern Europe, Madagascar, India, and Mexic0.(Enay, 1972, p. 370; Zeiss, 1968, p. 137, 143—146). The Tithonian is commonly divided into three parts, on the basis of the stratigraphic ranges and associations of certain ammonites (fig. 16). As thus divided, the lower Tithonian is equivalent to the middle and part of the up- per Kimmeridgian of England as defined by Arkell (1956, p. 21) and to most of the upper Kimmeridgian as rede- fined by Cope (1967, p. 4, 70, 74). The middle Tithonian as defined by Enay in 1964 (p. 365) is equivalent to the remainder of the Kimmeridgian of England plus an in- definite part of the Portlandian. The middle Tithonian as defined by Zeiss (1968, p. 137) includes only the zones of Pavlovia rotunda and P. pallasioides of northwest Eu- rope. As redefined by Enay (1971, p. 99, 100), it includes those zones plus part of the underlying zone of Pectina— tites pectinatus; it does not include any faunal zone as young as the Portlandian. The middle Tithonian as used by Judoley and Furrazola-Bermtidez (1968, p. 5) and by Imlay and Jones (1970, p. B8—B9) is nearly the same as that used by Enay in 1964. The upper Tithonian of these 32 various authors includes all Jurassic beds above the mid- dle Tithonian. The Tithonian has also been divided into two parts by Enay (1964, p. 363, 364; 1971, p. 99, 100) who consid- ers a threefold division impractical except in those areas where Pseudolz'ssoceras and Semiformicems are present (Enay, 1972, p. 371). Also, the association of Pseudolis- socems with the typical late Tithonian ammonite Prom- ceras in Kurdistan (Spath, 1950, p. 125) suggests that Pseudolissoceras may range higher than recorded in Eu- rope. Therefore, a twofold division is favored by Enay (1971, p. 99; 1972, p. 382), who has correlated the lower Tithonian with the upper part of the Kimmeridge Clay of England above the zone of Aulacostephanocems acutis— siodorensis (Cope, 1967, p. 4, 70). He correlated the up— per Tithonian with the remainder of the overlying Jur- assic above the zone of Pavlovia pallasioides. As thus defined, the base of the upper Tithonian corresponds to the first appearance of the calpionellid microfossils and to the first appearance of such ammonites as Kossmatia, Durangites, Corongoceras, Micracanthoceras, Lytoho- plites, and Hildoglochiceras. A threefold faunal division of the Tithonian within the Gulf region is feasible and useful, as discussed by Cantu Chapa (1967, p. 18—22, table 1; 1971, p. 27—31), but there is no assurance that the middle part is even approximately the same as the middle Tithonian as used in Eurasia. For correlations between the continents, preference is given herein to a twofold division of the Tithonian because the faunal boundary between the two divisions is much sharper than are the boundaries within the threefold division. LOWER TITHONIAN OF THE GULF REGION In the Gulf of Mexico and bordering areas, early Ti— thonian fossil sequences are well known only in northern, north-central, and eastern Mexico (fig. 15). In north-cen- tral Mexico near Mazapil, Zacatecas, the early Tithonian ammonite sequence from the base upwards apparently consists of (1) Hybonoticeras ( = Waagenia); (2) Maza- pilites in association with Virgatosphinctes aguilam’ (Burckhardt), V. spp., Subdichotomocems cf. S. m'kitim' (Michalski), Aulacosphinctoides and Aspidoceras; and (3) Virgatosphmctes mexicanus Burckhardt, V. spp., Subplam'tes cf. S. danubiensis (Schlosser), Parastre- blites mazapilensis (Burckhardt) and Pseudolissocems submsile Burckhardt (Burckhardt, 1906, p. 110, 147— 149; 1930, p. 68—71, tables 6—9; Imlay, 1939, p. 27—30, 38, 39, tables 7—10). Of these, only the relative posi- tions of M azapilites and Virgaltosphinctes mexicanus are questionable, because those taxa have not yet been col— lected in the same stratigraphic sequence in central or JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES northern Mexico. At first, Burckhardt (1906, p. 168— 170) considered them to be of the same age because they both occur in similar phosphatic limestone in areas near Mazapil. Later, he decided that Mazapilites must be older because near Symon, Durango, about 70 miles (112 km) west of Mazapil, the lowest occurrence of Mazapi- lites is in the same bed with H ybonoticems (Burckhardt, 1919, p. 74; 1930, p. 56). This association was confirmed by Imlay (1939, p. 10, 11). The early Tithonian ammonite sequence near Sy- mon, Durango (Burckhardt, 1919, p. 61—66; 1930, p. 56, 57, 68, 69; Imlay, 1939, p. 9—11), resembles that near Mazapil except that its upper part above Mazapilites contains only rare specimens of Subplam'tes? (Blanchet, 1923, p. 74; Burckhardt, 1919, p. 39; 1921, pl. 14, figs. 1— 3) and Virgatosphinctes? (Imlay, 1939, p. 10). Also, all the beds above Hybonoticems and below Kossmatia con- tain an abundance of ammonites that generally have been assigned to Torquatisphmctes rather than to Aulacos- phinctoides (Spath, 1931, p. 466, 484, 1933, 865; Imlay, 1939, p. 22, table 7; Arkell, 1956, p. 562; Enay, 1972, p. 382). Mazapilites has been found elsewhere in north-cen- tral Mexico only in the Sierra de Catorce, northern San Luis Potosi, about 75 miles (120km) southeast of Maza- pil. In this mountain, the early Tithonian is represented only by one ammonite assemblage consisting of Phyllo- ceras, Virgatosphinctes (rare), Aulacosphinctoides, Sub- dichotomocems, Andicems, Aspidocems, Simoceras, Haplocems, Pseudolissocems zitteli (Burckhardt), and Mazapilz'tes (rare). Most of these occur in 10 feet (3 m) of limestone (Verma and Westermann, 1973, p. 148) and do not occur in the higher (early late Tithonian) assemblage characterized by Kossmatia and Durangites. Mazapi- lites itself was obtained from just 2 feet (0.6 m) of lime- stone at only one place, in association with Pseudolisso- ceras zitteli, Aulacosphmctoides, Subdichotomoceras, and ‘Virgatosphinctes” sanchezi Verma and Wester- mann (Verma and Westermann, 1973, 10c. 23B on p. 141, 148, 186). The last named species was described as sim- ilar to Subplanites? sp. in Imlay (1939, p. 36, pl. 9, figs. 1—3). Burckhardt (1919, p. 39; 1921, p. 14, figs. 1—3) found it similar to Virgatites sp. ind. , which was renamed Perisphinctes burckhardti by Blanchet (1923, p. 74) and referred questionably to as Subplam'tes by Arkell (1956, p. 562). Another early Tithonian ammonite sequence occurs near Placer de Guadalupe and Plomosas in east-central Chihuahua, about 450 miles (700 km) north-northwest of the one at Mazapil (Bridges, 1965, p. 66—77, 105, 118— 120, 132-134; Imlay, 1943b). The oldest Tithonian is rep- resented by Hybonoticeras ( = Waagem'a) (Imlay, _ 1943b, p. 527-529), which was found about 15 miles (24 SUCCESSION 0F AMMONITES AND BUCHIAS BY STAGES km) south-southeast of Placer de Guadalupe. The re- mainder of the early Tithonian ammonite sequence is well exposed in a fairly thick section (Bridges, 1965, fig. 15 on p. 76, p. 133—134) that was measured northeast- ward, starting from a point about 1.2 miles (2 km) N. 42° E. of Placer de Guadalupe. In that section, some conglomerates that are proba- bly Paleozoic are overlain by shale 152 feet (46 m) thick that contains I docems from 66—100 feet (20-30 m) above its base, and Idocems? throughout its lower 126 feet (38 m). Above this shale is about 160 feet (49 m) of unfossiliferous sandstone. Next higher is 1,075 feet (328 m) of dark shale and shaly limestone that contains spe- cies of Virgatosphinctes, Subplanites, and Pseudolisso- cems, which are like those found with V. mexicanus in southern Zacatecas, in 3—6 feet (1—2 m) of limestone. Above the dark shale and limestone is 565 feet (172 m) of shale that contains Virgatosphmctes cf. V. densiplicatus (Waagen). At the top of the section is 465 feet (142 m) of shale and sandstone that contains Kossmatia. Mazapi- lites has not been found in the sequence, but the time during which it lived could be represented by any one of several 50- to 60-foot (15- to 18—m) units that have not furnished any ammonites. ‘ ' The lowest of these faunules is definitely of early Ti- thonian Age, judging by an association of Subplam'tes, Virgatosphinctes and questionable Pseudolissocems (Arkell and others, 1957, p. 329, 330; Bridges, 1965, pl. 3 on p. 76). It may be correlated with a faunule near Ma- zapil that is characterized by Virgatosphinctes maxi- canus Burckhardt, Pseudolissoceras subrasile (Burck- hardt), and Subplam'tes (Burckhardt, 1906, p. 155, 156; 1930, p. 69). Thus, Subplam'tes aff. S. 'reise (Schneid) (Imlay, 1943b, p. 533, pl. 91, fig. 1) from Chihuahua is probably identical with Perisphinctes cf P. danubiensis (Schlosser) in Burckhardt (1906, p. 112, pl. 32, fig. 1) and Virgatosphi’nctes chihuahuensis Imlay (Imlay, 1943b, p. 534, pl. 91, figs. 2—5) is probably the same as Peris- phinctes aff. P. transitorius Oppel in Burckhardt (1906, p. 113, pl. 30, fig. 8). Above this lowest faunule is a finely ribbed species of Virgatosphinctes (Imlay, 1943b, p. 535, pl. 89, figs. 1—4), whose resemblance to V. densiplicatus (Waagen) suggests correlation with the basal upper Tithonian (Enay, 1972, p. 377, 378). Still higher are species of Kossmatia that represent the lower part of the upper Tithonian of Enay. A much different early Tithonian ammonite sequence is present in the Huasteca area of east-central Mexico, according to Cantu Chapa (1971, p. 24—30, 33, 36, 38), whose conclusions are based on both surface and subsur- face studies. That sequence is distinguished from all those just discussed by the local absence or scarcity of 33 H ybonoticems at the base of Tithonian and by the pres- ence of Mazapilites above instead of below Virgatos- phinctes mexicanus (Burckhardt). Of these differences, the rarity of Hybonoticeras is probably related to sparse occurrences in very thin beds, as suggested by Cantu Chapa (1971, p. 28). Hybonoti- cents is present, however, at two localities in eastern Mexico. One specimen was obtained at the base of the Corona-San Manuel well 82, about 30 miles (48 km) southwest of Tampico, Tamaulipas (USGS Mesozoic 10c. 20854). Another was found in chalky limestone in Arroyo La Mula at the west end of the Huizachal anticline, west of Victoria, Tamaulipas (USGS Mesozoic 10c. 20836). The occurrence of Mazapilites above Virgatosphinctes mexicanus in eastern Mexico but below it elsewhere could be explained if one or both of those taxa had longer or different stratigraphic ranges than those shown by studies in north—central Mexico, or if the Mazapilites- bearing beds in eastern Mexico were separated from overlying Kossmatia-bearing beds by a disconformity, or by a nonsequence, reflecting lack of deposition. In summation, the biostratigraphic record, as dis- cussed above, shows that Virgatosphinctes in northern and north-central Mexico ranges through the lower Ti- thonian above the beds containing Hybonoticeras. Lo- cally, in north-central Mexico near Mazapil, species of Virgatosphinctes occur in two faunules, of which only the lowest contains Mazapilites and only the highest con— tains Pseudoliocems. The higher faunule is represented elsewhere in northern Mexico near Symon, Durango, and in east-central Chihuahua by identical or closely sim- ilar species of Virgatosphinctes and Subplanites. Against such a faunal division is the association of Mazapilites with Pseudolissocems in the Sierra de Catorce of San Luis Potosi. That association may not be of stratigraphic value, however, if the 2 feet (0.6 m) of limestone in which the ammonites occur represents a condensed deposit that formed so slowly that organisms of different ages occur together. Much better evidence against the faunal divi- sion recorded for north-central Mexico is the presence of Mazapilites above Virgatosphinctes mexicanus in east- central Mexico. Evidently, more stratigraphic collecting is needed in order to determine the total range of M aza- pilites and the correct ammonite succession in the lower Tithonian beds of Mexico. Nonetheless, the range of Ma— zapilites into the middle part of the lower Tithonian is favored by its association with Pseudolissocems and Protancyloceras in Cuba below beds containing Torqua- tisphinctes and Pampallasicems (Housa and de La Nuez, 1975). Elsewhere in the Gulf region, lower Tithonian beds may be represented in Cuba by an association of Virga- tosphinctes and Subplanites? beneath beds containing 34 typical upper Tithonian ammonites such as Durangites, Corongoceras, and Micracanthoceras (Judoley and Fur- razola-Bermudez, 1968, p. 5, 19, 23, 109—111). The lower Tithonian assignment is based on two facts: Vir- gatosphinctes is unknown from beds older than the Ti- thonian (Arkell and others, 1957, p. L330), and Subplcm- ites is characteristic of the entire lower Tithonian (Enay, 1964, p. 365; 1971, p. 99, 100; 1972, p. 382). One trouble with this correlation is that the species of Subplam'tes? and Virgatosphinctes in question are reported by Judo- ley and Furrazola-Bermudez (1968, p. 19) to be associ- ated with Tintinids as well as with the ammonite Paro- dontocems butti Imlay, which are not known below the upper Tithonian. UPPER TITHONIAN OF THE GULF REGION AMMONITE SEQUENCES Upper Tithonian ammonite sequences are well known in lands bordering the Gulf of Mexico (Burckhardt, 1906, p. 125—141, 148, 149, 170, 171; 1912, p. 127—172, 220— 226; 1930, p. 70, 71, tables 6, 8, 9; Imlay, 1939, p. 23, 24, tables 8—10; 1942; Cantu Chapa, 1963, p. 27—29, 33, 37—41, 70; 1967; 1968; 1971, p. 28—31, 37—39). They are divisible into two assemblages, of which the lower is characterized by Kossmatia, Durangites, Lytohoplites, Simoceras, Metahaploceras, Dickersom'a, and Pseudo— lissoceras. The upper assemblage is characterized by Be’rriasella, Substeueroceras, Aulacosphinctes, Prota- canthodiscus, Proniceras, and rarely Himalayites. With both assemblages occur Parodontocems, Hildoglochi- ceras, Micracanthocems, and Corongocems. Virgatos- phinctes occurs rarely in the lower assemblage in Cuba and in the upper assemblage in Mexico. The ages of these ammonite assemblages have been discussed sufficiently elsewhere (Cantu Chapa, 1967, p. 17.22; 1971, p. 30, 31; Imlay and Jones, 1970, p. B11— , B12; Enay, 1972, p. 361, 371, 376, 382). Substeueroceras and Prom'ceras must represent the latest Tithonian. Kossmatia and Durangites must represent slightly older Tithonian, but their exact ranges relative to the standard zones of Europe are difficult to determine. Nonetheless, the presence of calpionellid microfossils in the Kossma- tia-bearing beds indicates an age not older than late Ti- thonian as defined by Enay (1971, p. 99). Also, the pres- ence of Buchia mosquensis (von Buch) locally in those beds at San Pedro del Gallo, Durango (Burckhardt, 1912, p. 206, 221) shows that some of those beds are at least as old as the Zaraiskites albam' zone of northwest Eu- rope and the equivalent upper part of the Dorsoplanites panderi zone in Russia (Imlay, 1955, p. 74, 75, 85; 1959b, JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES p. 157; Imlay and Jones, 1970, .;B11 Gerasimov and Mikhailov, 1967, p. 9, 19, 20; Saks and others, 1963, table 5). Both of these assemblages are associated with calpi- onellid microfossils of late Tithonian Age. Such microfos- sils occur with the higher assemblage characterized by Substeueroceras in Puebla, Mexico (Cantu Chapa, 1967 , table 1 opposite p. 22) and also throughout the lower assemblage in Cuba (Bronnimann, 1954; Bermtidez, 1961; Judoley and Furrazola-Bermudez, 1968, p. 14—19). In Mexico, they are reported from La Casita and Pimienta Formations (Bonet, 1956, p. 417—419, 462, 463, 468, ta- ble opposite p. 398), and they occur also in the Sierra Cruillas, Tamaulipas (Bonet, 1956, localities 44, 45, and 48 on p. 468), just below a sequence containing Kass- matia and Durangites. KOSSMATIA-DURANGITES AMMONITE ASSEMBLAGE The lowermost upper Tithonian ammonite assem- blage in Cuba is dated confidently as Late Jurassic, but not the very latest, for reasons that have been discussed in detail elsewhere (Imlay, 1942, p. 1433, 1434; Arkell, 1956, p. 572; Judoley and Furrazola—Bermudez, 1968, p. 24, 25). It is rather peculiar, however, that Protcmcylo- ceras, with is common in the assemblage in Cuba, is un- known in Mexico below the uppermost upper Tithonian. It is also peculiar that Protancylocems has not been found in Cuba in association with Durangites (Imlay, 1942, p. 1428), an ammonite characteristic of the lower- most upper Tithonian in Mexico. These peculiarities are probably unimportant stratigraphically because Protcm- cylocems hondense Imlay (written commun. to Paul Bronniman, March 1953) occurs on Lorna Sabinilla, Las Villas Province (Gulf Oil Co. locs. 21141 and 21142), at about the same place where Durangites was collected (Atlantic Refinery Co. locs. 268, 269, and 7539), and be- low the lowermost occurrences of calpionellas (Paul Bronniman, written commun., 1953). Also, Protancylo- ceras has been recorded in central Europe and in Kurdis- tan in beds that are slightly older than latest Tithonian (Wiedmann, 1973, p. 309, 310, 313, 314). Durangites vulgaris Burckhardt in Cuba, in addition to the occurrences in Camagfiey and Las Villas Provinces previously listed (Imlay, 1942, p. 1428, 1453), occurs at Finca Ancon, 3 miles (5 km) west of Balneario San Vi- cente in Pinar del Rio Province (Gulf Oil Co. loc. 24976). It is associated there with D. cf. D. incertus Burckhardt, Hildoglochicems? ecarinatum Imlay, and an ammonite fragment whose venter bears chevron-shaped ribs, as would Kossmatia or Pronicems. That species of Hildog- lochiceras? or Glochiceras (Cantu Chapa, 1968, p. 20) occurs elsewhere in association with Durangites (Imlay, 1939, p. 5, 28). SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES The earliest late Tithonian assemblage, present in the subsurface of eastern Mexico and in the mountains and plateau to the west, contains many species in com- mon with Cuba (Imlay, 1942, p. 1428, 1432). This is well illustrated by the ammonites present in the upper 394 feet (120 m) of a 722-foot-thick (220-m) Jurassic sequence exposed on the Sierra Cruillas, southwest of Cruillas, in north-central Tamaulipas. That fossiliferous part of the sequence from top to bottom is as follows: Partial Jurassic sequence on Loma Rinconada in the northeast— ern part of Sierra Cruillas, Tamaulipas, Mexico [Measured and collected in June 1954 by William E. Humphrey, Raul Perez F., and Teodoro Dlaz G. Fossils identified by Ralph W. imlay] Measured interval Feet Meters ' 12. Limestone, thin-bedded, tabular, laminated dark-gray to black; lenses of black chert; intercalated gray shale. Contains Micracanthoceras acanthellum Imlay --------- Limestone, thin-bed e , am nated; intercalated gray shale. Contains Corongoceras filicostatum, Metahgploceras? an noceramus ----------------------------- Mostly covered. Some tuffaceous limestone. Contains Kossmatia victoris Burckhardt. Probable Float also contains Corongoceras 9. Limestone, black, laminated, thin-bedded; lenses of black chert. Contains Kossmatia victoris (Burckhardt). Float con ains L toho lites caribbeanus Imlay and oron oceras filicostatum Imlay ------------ 8. Tuff, sandy, thin-Beaded, platy, laminated. Contains perisphinctid anmonites ----------- Tuff, sandy, medium-bedded, siliceous -------- Limestone, dark-gray, thin-bedded, laminated, siliceous; limestone concretions and chert bands. Contains Ph sodoceras and Metahaglocerasi. Float, proEably from same unit, contains Duran ites, Parodontoceras?, and Simoceras? ------------ Mostly covered -------------- ' ----------------- Limestone, siliceous, thin-bedded, shaly, flaggy; gray limestone concretion. Contains Corongoceras? --------------------- Tuffs and black siliceous limestone ---------- Mostly covered ------------------------------- Limestone, gray to black, siliceous, banded, laminated, medium- to thin-bedded; some tuffaceous shale. Contains Micracanthoceras acanthellum Imlay and Simoceras lVirgatosimoceras.) Float contains Corongoceras filicostatum Imlay -------------------------------------- 43 11. 18 5.5 10. 28 8.5 39 H N O 18 33 1 ‘ow CDLn czcn 20 26 J50! mm 00 23 43 l-IN‘AJ 0'! \D i—u—n WCDV 000 44 13.5 Other Mexican ammonites of the earliest late Tithon- ian assemblage that are similar to species in Cuba, or that are of stratigraphic significance, include the follow- ing: 1. Parodontoceras cf. P. butti Imlay. Petroleos Mexicanos lot 20851 from the Pimienta Formation 3 km south of Jonotla on trail to Zacapoaxtla, Puebla (written commun. to M. R. Aguilar, 1948). 2. DickerSonia cf. D. sabam'llensis Imlay. Chocoy well 2 at depth of 3,195 feet (974 m), about 28 miles (45 km) northwest of Tampico, Tamaulipas. Associated ammonites include Parodontocems and 35 Corongoceras cf. C. altemans Gerth (written com- mun. to Federico Bonet, 1959). 3. Pseudolissoce'ras zitteli (Burckhardt) in associ- ation with Kossmatia victor-is (Burckhardt) and Grayz'ceras? mexicanum (Burckhardt), Mazatepec area, Puebla (Cantu Chapa, 1967, p. 4, 5, 21; 1971, ,- p. 30). 4. Prom'ceras sp. associated with Durangites, Par- odontoceras and Micracanthocems. Petroleos Mexicanos lot AC-1933 from Bolson de Judas in Candela district near boundary of Coahuila and Nuevo Leon (written commun. to Teodoro Diaz- Gonzalez, 1953). The mentioned association of Prom'ceras with Dur- angites, as well as a similar association reported by Cantu Chapa (1968, p. 23—25) from Galeana in southern Nuevo Leon, could mean either that Durangites ranges up into the uppermost Tithonian or that Pronice'ras oc- curs lower than previously recorded. . The earliest late Tithonian ammonite assemblage of north-central Mexico is dominated by species of Kass- matia and Durangites (Burckhardt, 1930, p. 70, 71) but also includes Micracanthoceras, Hildoglochiceras ( = Salinites Cantu Chapa, 1968, p. 20), Grayiceras?, Aulacosphinctes?, and Micracanthoceras (Imlay, 1939, p. 22, table 8). This lower faunule near Placer de Guad- alupe in east-central Chihuahua is represented mainly by species of Kossmatia near the top of the Jurassic se- quence. Of the species present, K. kingi Imlay is proba- bly identical with Perisphinctes sp. ind. in Burckhardt (1906, p. 130, pl. 37, figs. 9, 11, 12), and K. varicostata Imlay is closely similar to K. victoris Burckhardt (Burck- hardt, 1906, p. 131, pl. 26, figs. 1—6, pl. 27, fig. 1). An associated species, Kossmatia rancheriasensis Imlay, has been found elsewhere, in the Malone Moun- tains of Texas. R. T. Hazzard collected the species about 25 feet (7.6 m) below a conglomerate at the base of the Lower Cretaceous(?) Torcer Formation, approximately three-quarters of a mile (1.2 km) northwest of a cafe at a bend on U.S. Highway 80, 10 miles (16 km) west of Sierra Blanca, Tex. (USGS Mesozoic loc. 26956). An- other fragment of Kossmatia found in the conglomerate (Albritton, 1937, pl. 4, fig. 1) was probably derived from the underlying Malone Formation. SUBSTEUEROCERAS—PRONICERAS AMMONITE ASSEMBLAGE The latest late Tithonian ammonite assemblage in the Gulf region, characterized by Substeueroceras and Proniceras, is not known in Cuba. It is represented in the subsurface of the southeastern United States only by one occurrence of Substeueroceras at the depth of 17,403 feet (5,304 m) in the Humble Benavides well 1 in Webb 36 County, Tex. It is widespread in eastern and north-cen- tral Mexico in both the surface and subsurface, and is not represented in Chihuahua or in west Texas. In southeastern Mexico (Huasteca area), two faunal units, or zones in the uppermost upper Tithonian are rec- ognized by Cantu Chapa (1967, p. 22, table 1). Of these, the higher faunal unit is characterized by Parodonto- ceras cf. P. callistoides (Behrendsen) in association with Prom'ceras and Protacanthodiscus. The lower fauna] unit is characterized by Suam'tes bituberculatum Cantu Chapa in association with the genera Acevedites, Wich- mannicems, and Corongoceras (Cantu Chapa, 1967, p. 12—14, 18—20) and occurs below the lowest known occur- rences of calpionellid microfossils. Probably the most complete latest Jurassic ammon- ite sequence found in the subsurface in Mexico occurs at depths of 10,505 to 10,761 feet (3,202 to 3,280 m) in the San Javier well 1, Nuevo Leon (see location in Pérez Fer- nandez and Diaz-Gonzales, 1964, p. 232); it is described as follows: Latest Jurassic ammonite sequence in the San Javier No. 1 well, about 90 miles (145 km) south of Laredo and 70 miles (1 10 km) west of Reynosa in Nuevo Leon, Mexico [Core and depth data furnished by Teodoro Diaz G., of Petroleos Mexlcanos. Fossils Identlfled by R. W. lmlay (wrltten commun. to Dlaz G., 1957)] w Core Ni Feet Meters Fossil 47 ------------- 10,505 - 3,202 Himalaxitesl 47 ------------- 10,518 3,206 Promceras, Parodontoceras. 48 ------------- 10,728 3,270 Substeueroceras? an seu o issoceras?. 10,732 3,271 Virgatospfiincfesl 10,735 3,272 Perisphinctid ‘amnonite. 10,738 3,273 Substeueroceras. 10,741 3,274 SuEsteueroceras. 10,748 3,276 Substeueroceras?. 10,751 3,277 Perisphinctid amonite. 10,755 3,278 Himalayites. 10,758 3,279 Virgatosphincte57. 10,761 3,280 Substeueroceras. 11,065 3,272.5 er 5p incti ammonite. 11,065- 3,372.5— Exo ra cf. E_. virgula 11,216 3,418.5 (Defiance). In this well, the contact with the Cretaceous is not indicated by megafossils, but. cores from depths of 10,028 to 10,064 feet (3,056.5 to 3,067.5 m) contain the ammonites Olcostephanus, Bochianites, Thurmanni— cams, Sarasinella, and Kilianella of Valanginian to early Hauterivian Age. Occurrences of most of the latest Jurassic ammonite genera in Mexico are well documented. Occurrences of the uncoiled ammonite, Protancylocems, are listed be- low, however, because the presence of the genus in Mex- ico was not recognized until recent years, and because some species are similar to or identical with species in Cuba (lmlay, 1942, p. 1456, 1457, pl. 10, fig. 1 to 9, 11, 12). JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 1. Protancyloceras cf. P. hondense lmlay. Tantima well 2 at depths of 8,036 to 8,045 feet (2,449 to 2,452 m), near Tantima, Veracruz. Associated with Substeuerocems and Parodontoceras (written commun. to M. R. Aguilar, 1953). 2. Protancylocems cf. P. catalinense lmlay. Piedra de Cal well No. 8‘at depths of 5,837 to 5,850 feet (1,779 to 1,783 m), about 60 miles (100 km) south- west of Tampico, near Tantoyuca, Veracruz. As- sociated with Substeueroceras (written commun. to Federico Bonet, 1959). 3. Protancylocems anahuacense Cantu Chapa (1963, p. 28, 73, pl. 1, figs. 2—4) from the Anahuac well 1 at depths of 8,200—8,213 feet (2,499.3— 2,503.3 m), near Anahuac in northern Nuevo Leon (Perez Fernandez and Diaz Gonzales, 1964, p. 232). Associated with Proniceras, Substeueroceras? and Protacanthodiscus. 4. Protancyloceras barrancense Cantu Chapa (Cantu Chapa, 1963, p. 27, 73, pl. 1, fig. 5) from the Barranca 1 well at depths of 8,755 to 8,768 feet (2,668.5 to 2,672.5 m), Panuco-Ebano area, Veracruz. 5. Protancylocems alamense Cantu Chapa (Cantu Chapa, 1963, p. 28) for Aegocrioceras sp., in Imlay (1939, p. 5, 57, pl. 11, figs. 1, 2) from Canon Al- amo, SierraJimulco, Coahuila. Associated with Prom’ceras, Aulacosphinctes, Hildoglochiceras, Micmcanthocems, Parodontocems, and Sub- steue'roceras. 6. Protancyloceras ramirense Cantu Chapa (Cantu Chapa, 1963, p. 28) for Crioceras sp. incl. in Burckhardt (1919, p. 58, 69; 1921, pl. 21, fig. 3) from near the Jurassic-Cretaceous contact in the Sierra Ramirez, near Symon, Durango. Associ- ated with Parodontoceras (Burckhardt, 1921, pl. 20, figs. 1—3) and Substeuerocems. TITHONIAN OF CALIFORNIA AND OREGON In western California and southwestern Oregon, the upper Tithonian contains a sequence of ammonites simi- lar to those present in the Gulf region (Imlay and Jones, 1970, p. B6—B12). These are associated with species of Buchia that permit correlations with faunas to the north in Canada and Alaska. As Buchia mosquensis (von Buch) had not been found in California or Oregon, it is assumed that the base of the Kossmatia-bearing beds in those States is not as old as the base of the Kossmatia-bearing beds in Mexico (lmlay and Jones, 1970, p. B11). TITHONIAN OF CANADA AND ALASKA Tithonian beds are widespread in western and arctic Canada and in southern and northern Alaska, judging INTERCONTINENTAL FAUNAL RELATIONSHIPS from occurrences of certain species of Buchia that fur— nish correlations with those in Greenland and northern Eurasia (Jeletzky, 1965, p. 57; Imlay, 1965, p. 1034; Im- lay and Jones, 1970, p. B8, 9, 19; Frebold and Tipper, 1970, p. 17). Associated ammonites are rare and are gen- erally poorly preserved (Frebold, 1957, p. 35, 66, pls. 42-44; Frebold, 1961, p. 23, pl. 17, fig. 2; Jeletzky, 1966, p. 3—23, pls. 1—5, 8 in part; Frebold and Tipper, 1970, p. 14—16), in contrast with the situation in East Green- land. INTERCONTINENTAL F AUNAL RELATIONSHIPS The known Jurassic ammonite successions in North America from Hettangian through early Oxfordian time were in seas that were either extensions of the Pacific Ocean or of the Arctic Ocean. Nevertheless, the North American ammonite successions during Early Jurassic time were essentially the same as those in Europe and elsewhere in the world. The same statement applies to the early Bajocian, except for an apparent absence of any taxa typical of the Leiocems opalinum zone in the Pacific Coast region (Arkell, 1956, p. 607, 608; Imlay, 1965, p. 1029—1031; Frebold, 1964a, p. 5; Frebold and Tipper, 1970, p. 9, 17). After early Oxfordian time, the ammonite successions in the Gulf of Mexico region were in waters connected with both the Atlantic and Pacific Oceans. After early Bajocian time, the ammonite'successions along the Pacific Coast of North America became differ— entiated from north to south because of fairly complete separation of the Arctic Ocean from the Pacific Ocean and the Mediterranean. Similar differentiation took place in Europe and presumably elsewhere. During the middle to late Bajocian, the ammonite successions in western and northern North America be- came different from those in Europe and the Tethyan re- gion. For example, in the Arctic region, the sole known representative of middle Bajocian Age consists of Arkel- loce’ras, and there are no ammonites of definite late Ba- jocian Age. In the Pacific Coast region, the ammonite successions of middle Bajocian Age contain some genera and species identical with taxa in Europe and the Teth- yan region, but they differ in that they contain Alaska- cems, Pseudotoites, Parabigotites, Zemistephanus, and Arkelloceras (Westermann, 1964, 1969; Imlay, 1973, p. 1, 35, 36; Frebold and Tipper, 1970, p. 17). Of these, Pseudotoites is known elsewhere in Argentina, Chile, and western Australia (Westermann, 1967, p. 67, 68; 1969, p. 27, 28, 129, 130, 157; Arkell, 1954, p. 592; Hi]- lebrandt, 1970, p. 176, 187, 199). Ammonites of late Bajocian Age in the arctic region of North America have not been definitely identified but 37 could be represented by the lowermost occurrence of Cranocephalites. By contrast, in the Pacific Coast re- gion, the ammonite successions of late Bajocian Age are definitely represented by such widespread genera as Spirocems, Leptosphinctes, and Sphaerocems. These successions differ from those in most parts of the world outside of the arctic region by the presence of Mega- sphaeroceras, Eocephalites, Parachondroceras, Soh- lites, Lupherites, and Parastrenocera‘s and by lacking all genera of the Parkinsonidae. Of these ammonites, Mega- sphaerocems and Eocephalites are reported elsewhere only in Chile and western Argentina, where they are as- sociated with Spirocems, Normannites, Teloceras, and Cadomites but are not associated with the Parkinsonid genera (Hillebrandt, 1970, p. 176, 201). It appears, therefore, that the middle and late Bajo- cian ammonite faunas along the Pacific Coast of North and South America evolved in a similar manner. Both can be correlated fairly closely with sequences in Europe and in the Mediterranean region, but both include genera that appear to be restricted to areas bordering the Pa- cific Ocean. Apparently, this development was entirely different from that in the arctic region of North America during the same time interval. Bathonian ammonites belonging to genera character— istic of the Mediterranean (Tethyan) region and north- west Europe are present in the Pacific Coast region of southern Mexico and may occur in east-central Mexico. Elsewhere in North America, Bathonian ammonites have been found in the arctic region, southern Alaska, north- ern British Columbia, eastern Oregon, westernmost Idaho, and in the western interior region. The succession in southern Alaska and in the arctic region of Alaska and Canada consists, from bottom to top, mainly of the gen- era Cmnocephalites, Arctocephalites, and Arcticoceras. The succession in the western interior consists of Para- cephalites, which is similar to Arctocephalites, overlain by Warrenoceras, which is similar to Arcticoceras. Cob- banites, a genus similar to Vermisphinctes of late Bajo— cian Age, is associated with Cranocephalites in southern Alaska and with Paracephalites and Warrenocems in the western interior of the United States and Canada. In eastern Oregon, Cobbanites is associated with a species of Pamreineckeia that is similar to a species of Pararei- neckeia that occurs with Cranocephalites in southern Alaska. Both Wawenoceras in the western interior and Arcticoceras in southern Alaska are succeeded by spe- cies of Kepplerites similar to species in Greenland pres- ent below beds identified as earlier Callovian. These Bathonian ammonite successions, as far as is known, originated in the Arctic Ocean, had marine connections southward only through Yukon Territory and British Co- lumbia into the western interior region, and were unlike any other Bathonian succession outside the arctic region. 38 The Callovian ammonite succession in southern Mex- ico resembles that in Europe by containing Peltocems, Erymnocems, and Reineckeia and its subgenera. It also resembles that in western South America by containing Xenocephalites, Eurycephalites, and probably N euquen— icems. Similarly, the Callovian succession in southern and east-central California bears some resemblance to that in Europe, as shown by the presence of such genera as Macrocephalites, Hecticocems, and Peltocems. The successions in east-central and northeastern California and in eastern Oregon are characterized, however, by such genera as Kepplerites, Xenocephalites, Pseudoca- doceras, and Lilloettia. They do contain species in com- mon with successions in British Columbia and Alaska but differ from those successions by lacking Cadocems proper and its subgenera. In the western interior region, the earliest Callovian is represented by Kepplem'tes, Xeno- cephalites, Lilloettia, and Grossoum'ia, and the latest Callovian by a species of Quenstedtocems similar to Q. henrici R. Douville from the latest Callovian of Europe. In arctic Alaska and arctic Canada, the Callovian is rather poorly represented by species similar to those of middle Callovian Age in southern Alaska. Overall, the Callovian ammonite sequences from British Columbia northward are dominated by ammonites characteristic of the arctic region, such as Kepplerites, Cadocems, and Pseudocadocems, but include genera found only in the Pacific region, such as Xenocephalites, Lilloettia, and Parareineckeia. The Oxfordian ammonite sequences in the Gulf of Mexico region, in California, and in western Oregon con- tain the same genera found in beds of late middle to late Oxfordian Age in the Mediterranean region and are char- acterized by Perisphinctes (Dichotomosphinctes) and P. (Discosphinctes). They do not contain any ammonites of boreal origin, but in California and western Oregon they do contain Buchia concentrica (Sowerby) of such origin. These sequences have not yielded any ammonites of early to early middle Oxfordian Age, apparently because of the deposition at that time of highly saline deposits or red beds in the Gulf region and thick submarine volcanic materials in California and western Oregon. Elsewhere in North America, the Oxfordian ammon- ite sequences are very similar to those in areas bordering the Arctic Ocean. The early to early middle Oxfordian is characterized by Cardiocems in association with Quen- stedtocems (Pavloviceras) and Prososphinctes. The late middle to late Oxfordian is characterized by Amoeba- cems in association with the pelecypod Buchia concen- tm’ca (Sowerby). Like the Oxfordian sequences, the Kimmeridgian ammonite sequences in the Gulf of Mexico region com- prise genera typical of the Mediterranean region and southern Europe. They also do not contain ammonites of JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES boreal origin, but in central Mexico they do contain the boreal pelecypods Buchia concentm’ca (Sowerby) and B. mosquensis (von Buch) in association with Idocems and Glochicems. In northwest Sonora, in California, and in western Oregon, the Kimmeridgian sequences contain ammonites of Mediterranean or nonboreal origin, such as Subdichotomocems and Idocems, associated with the Amoebocems and A. (Amoebites) of boreal origin. Such ammonites in California and western Oregon are also as- sociated with the boreal Buchia concentrica (Sowerby). From British Columbia northward to arctic Alaska and Canada, the faunal sequences do not contain ammonites that are definitely Kimmeridgian, although some of the occurrences of Amoebocems could be of that age. None- theless, the top of the Kimmeridgian can be placed ap- proximately at the top of beds containing an association of Buchia mosquensis (von Buch) with B. concentrica (Sowerby) and B. rugosa (Fischer). The Tithonian ammonite sequences in the Gulf of Mexico region, in California, and in western Oregon in- clude mostly genera that are similar to those in the Med- iterranean (Tethyan) region and in South America, but they also include some ammonite genera that are found only, or mainly, in areas bordering the Pacific Ocean south of Oregon (Imlay, 1965, p. 1024, 1032). With these in California and Oregon are associated species of Buchia of boreal origin (Imlay ‘and Jones, 1970, p. B5, B8). In contrast, from British Columbia northward to the arctic region of Canada, age determinations are based mainly on species of Buchia because ammonites are exceed- ingly rare (Frebold and Tipper, 1970, p. 14—16; Frebold, 1964a, p. 4; Jeletzky, 1965‘, 1966; Imlay and Detterman, 1973, p. 21). This rarity contrasts markedly with the presence of a fair abundance of Tithonian ammonites in East Greenland and in the arctic region of Eurasia. Evi- dently the environmental conditions permitting the exis— tence or the preservation of ammonites in arctic Alaska and Canada became less and less favorable from Oxford- ian time to the end of the Jurassic. In summation, Jurassic ammonite successions in North America were essentially the same as elsewhere in the world from the Hettangian until the early Bajo- cian. Differentiation of ammonite faunas began in the middle Bajocian, continued through the remainder of the Jurassic, and was greatest during the Bathonian and Ti— thonian (Volgian). This differentiation was due to partial to fairly complete isolation of the Arctic Ocean. That ocean opened southward to the Pacific Ocean through the Yukon Territory after Early Jurassic time. It opened southward from the East Greenland area into western Europe and the Mediterranean region in early Callovian time and later. Also, from middle Bajocian time onward, some new ammonite genera evolved in the Pacific Ocean. Some of these are known only, or mainly, from the Pa- COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES cific Coast region of North and South America, or from parts of that region; some extended to New Zealand and beyond; a few spread into the Mediterranean region;rbut [none reached into the arctic region (Arkell, 1956, p. 608—618; Imlay 1965, p. 1024; Enay, 1972). COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES GULF OF MEXICO AND NEARBY REGIONS CUBA The Jurassic formations of Cuba have been discussed recently in detail by Khudoley and Meyerhoff (1971, p. 34—44, 59—67, 104—108). Their conclusions concerning the formations have been modified by certain Polish geolo- gists, as discussed briefly herein and depicted in figure 21. At the base in western Cuba is the tremendously thick San Cayetano Formation, which is characterized by dark-gray to black carbonaceous shale, siltstone, and fine-grained sandstone. Locally it is slightly metamor- phosed. It contains many carbonized plant stems and near the top contains marine pelecypods of probable Mid- dle Jurassic age (Meyerhoff, 1964, p. 152, 153). It could be equivalent to all or part of the plant-bearing beds of ' Toarcian to Bathonian Age in southern Mexico. Its upper part is now dated as early middle Oxfordian on the basis of its gradational contact with the overlying Francisco Formation, which is mostly of middle Oxfordian Age (Wierzbowski, 1976, p. 141). Such an age is supported by the presence of the Oxfordian ammonites Peris— phinctes (Dicha‘tomosphinctes?) and P. (Discosphinctes) in the upper 35 to 100(?) meters of the San Cayetano Formation in the Sierra del Rosario (Myczynski and Pszczolkowski, 1976). Conformably above the San Cayetano Formation in the Sierra del Rosario is the Francisco Formation, which ranges in thickness from 43 to 82 feet (13 to 25 m), con- sists of rather soft shale, marl, limestone, and some sandstone, and contains ammonites of middle to probable early late Oxfordian Age (Kutek and others, 1976, p. 300305; Wierzbowski, 1976, table 2 opposite p. 141, pf 152—159; Myczynski, 1976, p. 269, 292; Sénchez Roig, 1920, 1951; O’Connell, 1920; Jaworski, 1940; Burck- hardt, 1930, p. 61, 62; Spath, 1931, p. 400; Arkell, 1956, p. 572, 573). Conformably above the San Cayetano in the Sierra de los Organos is the Jagua Formation (Wierzbowski, 1976, p. 141—143; Hatten, 1967, p. 782), which consists of three members. The lower, or Azucar Member, ranges in thickness from 158 to 250 feet (48 to 76 m) and con- sists of gray to black thin-bedded limestone that varies 39 from dense t0 oolitic to sandy (Hatten, 1967 , p. 782). The middle, or Jagua Vieja Member, ranges in thickness from 164 to 198 feet (50 to 60 m), consists of dark—gray silty to sandy shale, marl, and limestone, contains many limestone concretions in the marly and shaly beds, and grades into the adjoining members. The upper, or Pi- mienta Member, ranges in thickness from 131 to 198 feet (40 to 60 m) and consists of gray, dense, platy thinébed- ded limestone. Ammonites present in all three members (Wierzbowski, 1976, table 2 opposite p. 141) show that the J agua Formation is of the same age as the Francisco Formation in the Sierra del Rosario. In particular, the presence in the Azucar Member of the ammonites Vina: lesphinctes, Perisphinctes, Discosphinctes, Cubaocheto- ceras, and Glochiceras shows that its age is not older than middle Oxfordian. The uppermost Jurassic in the Sierra del Rosario is represented by the Artemsia Formation, which consists mostly of thin- to medium-bedded, dense cherty lime- stone and tuffaceous shale. Its basal beds are of middle or late Oxfordian Age, as shown by the presence of the ammonites Mirosphinctes and Cubaochetoceras (Wierz- bowski, 1976, p. 145; Kutek and others, 1976, p. 302— 306, fig. 6 on p. 307). Most of the formation, however, contains ammonites of late early to early late Tithonian Age (Imlay, 1942; Judoley and Furrazola—Bermudez, 1968, p. 3, 17, 23—25) and perhaps also contains a later Tithonian assemblage characterized by Dalmasicems and Spiticems (Housa and de la Nuez, 1973). The earliest Tithonian fossils were found 165—230 feet (50—70 m) above the base of the for- mation near Cinco Pesos (Wierzbowski, 1976, p. 145; Ku- tek and others, 1976, p. 315; Judoley and Furrazola—Ber- mudez, 1965, p. 15), which means that the latest Oxfordian, all of the Kimmeridgian, and the earliest Ti- thonian must be accounted for by the basal 50 m of the Artemsia Formation. The uppermost Jurassic beds above the Jagua For- mation in the Sierra de los Organos are now placed in the Guasasa Formation of Herrera (1961, p. 11—14) by Cu- ban and Polish geologists (Wierzbowski, 1976, p. 144; Kutek and others, 1976, p. 312). These geologists aban- - doned the term Viriales Limestone because it was poorly defined and had been used for different rock units in dif- ferent areas. Thus, the term Vifiales Limestone as used by Imlay (1942) includes both the Artemsia Formation in the Sierra del Rosario and the Guasasa Formation in the Sierra del Organos. The Vinales Limestone as used by Khudoley and Meyerhoff (1971, p. 10—11) and by Judo- ley and Furrazola—Bermudez (1968, p. 17) represents the lower member of the Guasasa Formation. The Guasasa as used by these geologists ranges in thickness from about 4,265 to 4,600 feet (1,300 to 1,400 m) and consists of two members. Its upper member is 40 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 98° 92° 86° \- l l \ \ LO\_\/\~-~~~\l ARKANS2 ‘ ! ‘\ \\ I , I \ —— —( l7; 2 ' EMISSISSIPPI! ,' GEORG'A ) ' ' ALABAMA \ \ / l _ .1 r TEXAS \ L" ‘ I. 4’” _ _____ _\, ' 30° ) LOUISIANA ”L » «I i A '— "o ‘ ‘8 as; . ‘ 7 45? «V CHIHUAHUA ‘9 Laredo Q , é” \ / \w\, \ .I/L i. be GULF 7/ < 3X K San Pedro’ X ”Monterrey NUEVO‘ Reynosa 0 del Gallo d2" \ Galean'a EDP”, 9 24° DURANGO Symon' . , .Cruillasfis Rf Mazapilr \l 5 I . 61\ ‘\ 1,)2ACATECA3’/\x ’4 \‘thonLI o 100 200 300 MILES CUBA x1 ‘ ' TAMAULIPAS ‘L\ l7, share; \{9 s\ o 100 200 300 KILOMETERS ¢ 7 Is “A _ Tampico 7 ,J UAS .I‘ ‘ . A \ r g CALIENTES 0.5:, J anuco 7 l x \ l a F) J / \/\"V ‘) I: ‘ 4,..2‘ , ”OPE-94“ Tantoyuca YUCATAN/ 7 e / q, I _ z \‘ I «3* I 5c ‘ 58 / JALISCO ”)8? ‘ ° #104, {202a Rica \v/ (2 ""\-’ (’13) 5b; ‘oUINTAN (>MlCHOACAN MEXICg 6‘ kg? \ R00 ’0. Veracruz CAMPECHEI ° J MOIRELoifl-I-LAXCAI 09:9 .1 l l 5 18, {\msjb‘ «(3 PUEBLA ‘P\ Té‘BASCO x , ___... BELIZE 1. Western Cuba 6. Sierra de Catorce, San Luis PotOSI’, central Mexico 2. Gulf region of United States 7. Villa Juarez area, eastern Durango, central Mexico . 3- Monterrey area, northeastern MGXIGO 8. Placer de Guadalupe and Plomosas areas, east-central ChIhuahua 4. Mountains west of Ciudad Victoria, Tamaulipas, eastern Mexico 9_ Malone Mountains, southeast of El Paso, west Texas 5. Huasteca area, northern Hidalgo to southern San Luis Potosi, east- ern Mexico (53= Huehuetla; 5b= Huauchinango; 5c= Huay- acocotla) FIGURE 17.——Index map of J urassic areas in the Gulf of Mexico and nearby regions. Numbers 1 to 9 refer to stratigraphic sequences shown in figure 21. 990—1,320 feet (300—400 m) thick and consists of hard, compact, gray to black, highly fossiliferous thin- to thick- bedded limestone. Its lower member, the San Vicente Member (Herrera, 1961, p. 11), is at least 3,280 feet (1,000 m) thick. It consists of gray to black, mostly thick— bedded to massive limestone, some dolomite, and in places lentils and concretions 0f chert. It is marked bas- ally by a breccia composed of rounded to angular black limestone fragments that have been interpreted as evi- dence for a disconformity (Herrera, 1961, p. 11; Judoley and Furrazola—Berrmidez, 1965, p. 20; Khudoley and Meyerhoff, 1971, p. 10—11). The upper member of the Guasasa Formation has furnished ammonite assemblages at several levels, ac- cording to Housa and de la Nuez (1975). Of these, the lowermost, collected directly above the massive lime- stone of the lower member, contains Mazapilites, Pro- tancylocems, and Pseudolissocems, of middle early Ti- thonian Age; the next higher contains Torquatisphinctes and Pampallasicems of late early Tithonian Age; and the uppermost, obtained near the top of the Guasasa Formation, contains some early late Tithonian ammon- ites, which were described by Imlay (1942) as late Port- landian. COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 4]. 124° 120° 116° 112° 108° b ‘ ‘12 __""'"'—‘—'T—'l "—— 03 I 48° . A ‘ I ll 1’ WASHING f , l I \ 13 ' -/-"’ _ a 12 V ’ _ f I 1 1 / I! 10 John Day 10 . o 0 x Mineral 44 l OREGON 9x/Br/ogzan 10 ( 1 . I 8 l 8 ays Creek || i _ _ _ _ _ _ _ _ _ .1__.| _ l *‘7 1 l 5 Big Bend NEVADA | 40° \/ 2‘3’.Taylolrsv1lle | 6 x . | Westgate LOCATION OF STRATIGRAPHIC SEOUENCES O . r0v1l|e I 2 1. Santa Ana and Santa Monica Mountains,southern California Colfax X 2. Western Nevada 3. Taylorsville area, northeastern California 4 \ 4. Gold-belt area, east-central California X\ \ 5. Big Bend area, north-central California 4 6. Western California from San Diego northward '° X \ 7. Parts of northwestern California and southwestern Oregon ‘y 4 §. Sonora \ 8. Parts of southwestern Oregon \ 9. Suplee and lzee-Seneca areas, east-central Oregon 0 x 10. lronside-Brogan-Huntington area, eastern Oregon, and Mineral 4 11 Wafiea, ldnanho ' rth st 0 . a owe ountains, no ea ern r on CALIFORNIA \\ 12. Snake River Canyon, 32 miles south ofergortheast comer of Oregon 13. Snake River Canyon, northeast corner of Oregon ’ 14. Cascade Mountains, northwestern Washington 36C 0 O O t“ 0 50 ’ 100 150 200 MILES 7 |'—l_LlflJfi—l—J ¢ x1 0 50 100 150 200 KILOMETERS 0 Los Angele \ ( d San Diego __ ___/ .— I 1 FIGURE 18.—Index map of Jurassic areas in the Pacific Coast region from California and Nevada to Washington. Numbers 1-9 refer to strati- graphic sequences illustrated in figure 22. Numbers 10—14 refer to stratigraphic sequences shown in figure 23. 42 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES , 148° 144° 140° 136° 132° 128° 124° 120° 116° \ K as \ \ YUKON Kx , a 60° . \x 7 / ’/ Whitehorse .- / ’ 0 50 100 150 MILES 0 50 100150 KlLOMETERS QUEEN CHARLOTTE ISLANDS . Harrison Lake area, British Columbia . Taseko Lake area, British Columbia . Vancouver Island, British Columbia . Queen Charlotte Islands, British Columbia . Smithers area-Tenas Creek-McDonell Lake, British Columbia . Tulsequah area, British Columbia . Whitehorse area, Yukon Territory . Eastern Alaska Range and Nutzotin Mountains, Alaska . Wrangell Mountains, Alaska . Talkeetna Mountains (Nelchina area), Alaska O‘DQNQUI-th—I .1 , “N 4 r% 0 COLUMBIA .X §0 52° \ % $ « ‘ l l \ 58° 56° \ 54° 500 VANCOUVER ISLAND FIGURE 19,—Index map of Jurassic areas in the Pacific Coast region from British Columbia to southern Alaska. Numbers 1—10 refer to strati- graphic sequences shown in figure 24. This lower member of the Guasasa Formation has not been dated by fossils. Its age, however, must be mostly Kimmeridgian on the basis of its disconformable relationship with the underlying Jagua Formation of middle to late Oxfordian Ageand on the presence of M a- zapilites in the basal beds of the upper member. The dis- conformity at the base of the lower member could be of latest Oxfordian or earliest Kimmeridgian Age, or both, and could be contemporaneous with deposition of the Buckner Formation in the Gulf of Mexico region. The Jurassic may also be represented in north-cen- tral Cuba by the Punta Alegre Formation, which consists of 2,000 feet (610 m) or more mostly of salt and anhy- drite, but includes some red to gray shale and siltstone, and is known only from four salt domes (Khudoley and Meyerhoff, 1971, p. 40, 41). Some red silty shale in the COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES 116° 112" 108° 104° 1mr a? \ \0 Ba nff \ ALBERTA \ LBlairmore O Fernie \\ m --: 5‘ —é m GLACIER I NAJIONAL r“ A '7 3% 44°~ °Sweet Grass Hills BEAR PAW MT 8 Big Snowy\R\ 9 I 6‘ .Columbus X/Wlill'hermopolis I I SASKATCHEWAN X CANAD_A L-- ’-——-‘ WILL|ISTON BASIN MONTANA | OBillings NS» 0 ,9 m 38. Dewe Bridge, east—central Utah LBHGBI’. [V59 0" Glendq 39. John rown Valley, southwestern Colorado 948 ‘ o | 40. Slick Rook area, southwestern Colorado Blsqn 0 I4, 41. McElmo Canyon, southwestern Colorado. asrn Medicine Bow 42. Gunlock, southwestern Utah Rawlins . ° . NEBR 43. Danish Ranch, southwestern Utah I 44. Kanarraville-Cedar City, southwestern Utah WYOMING I 45. Mount Carmel Junction, southwestern Utah I 46. Brown Can on, southwestern Utah -- - - —- - 1 47. Little Bull alley, southwestern Utah x 31 48. Pine Creek, south-central Utah \ I 49. Sand Valley, north-central Arizona 30 I 50. Page, north-central'Arizona 1‘ 51. Big Hollow Wash, southeastern Utah 29 . Denver 52. Cow Springs, northeastern Arizona °Grand Junction I COLORADO ‘ I I I X41 l _ ' r— __. __ ______l__.L__——————-——————" q —— - — - 1 36°4:J I I . NEW MEXICO I I ’ l 0 Santa Fe | l i u‘nfiTEO [STATES 10 | NORTH DAKOTA L_______.. ' SOUTH I DAKOTA .Spearfish I __-".— _- I I . Rocky Mountains of southwestern Alberta Swift Reservoir, Sun River area, northwestern N.- Montana Southwest of Craig.Mont. Smith River, south of Great Falls, Mont. Belt Creek, southeast of Great Falls, Mont. Near Utica on Judith River, Mont. . Big Snowy Mountains near Heath,Mont. Button Butte, Mont- . Porcupine Dome, Mont; Northeastern Montana and northwestern North Dakota . Southwestern Saskatchewan . Ammon Ctuad., southeastern Idaho . Red Mountain, southeastern Idaho . Lower Slide Lake, Wyo. . Green River Lakes, northwestern Wyoming . Red Creek, northwestern W oming . Near Hyattville.north—oentra Wyoming . Mudd Creeklnorth' —Tuffaceou_—fls shale Ca ban/tee talkeetnanus '7 . :32; IsteIggsItToIne Sm ithers Form etion Tel ”w’gwgma‘figfig’sa" % Shale, sIItstone, La if t ff 600- 985-2625ft Be‘ocian u argillite.and some ”I; ”3'34,“ m) (300-800 ml ‘ E graywacke Gray ' tuff, Echo Island 1000 ft (305 m) YT/r'? sarIIIdstomIa, breoitiie. Sonninia and LatiwitcheI/ia __ FormatIon Base not exposed Erosion and igneous an cong omer e Erycites and Tmetoceras E 7 L intrusions o . 7 L‘ W " 7 «xi/\wc/K, . -| I L ' ' Gremmoceras, Catu/loceres. 3. and Ph/yseogrammoceras n D Gravwacke. dark gray. MW“ F°""'“°" Ph matoceras and Toercian — Basal part contains 600—700 fl Peénoceras S pebble con lomerate “32-210 m) 5,, 1000-3000 (305—91 5 m) MOSW 9’BY Harpoceras cf. H. lexaratum, _l Disconfom'Iity may erg-Hue.- shale. Prodaqtylloceramnd occur at base and sanqstone. Dect [laceras 5 ' Same ""n beds Amaltheus, Pa/tarpites, & ° dlmesItIIone Aristiceras, P/euroceras, .9 D 7 an 58" stone. and Lepreleoceras 3 '_ Harrison Lake ' - Grades Into II, I I Lava and News underlying Prodactylioceras 5 Pliansbachien 5 WWW" 300-400 a (91—122 m) mmaIIon 2 g Argillite 150 ft (45 m) g -' Volcanic breccia Upton/a, Tropidoceras, _I 7 600 ft (182 m) 7 Telkwa Formation and Acanthag/euraceras ' ' 3200—8200 ft (1000- Eamon,” 5 Kunga Formation 2500 m) Volcanics. g gnosfly grey ar illitIeI.d ugperftngbe') marine and 3 _ I ome graywac e a m nonmarine Sinem r'e —— She" S."‘.s‘°"°' limestone Some tuff Black argillite, 7 Asteroceras u ' n L and argIllIte in middle. siltstone.and shale. ‘ ; 720—1350 ft (219-411 ml Lower contact abrupt Arnioceras, Caroniceras, 3 but conformable Ian-9mg; .and 7 WELL I ? Graywacke, gray-green. Volcanic breccia ' , Psi/oceras canadense Hettangian :03“ green pebbly gagolave. ft e s 9000 . 30-35 a (9—11 m) ' (2133—2742 m) Ps’me’” WWW Underlying beds Upper Paleozoic(?) Upper Triassic Upper Triassic Upper Triassic A. Southwestern to central British Columbia. COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 59 Tulsequah area, 6 )clllitehgse area, 7 rEastern Alaskanlianges Wrarriigell Mountains, 9 10 northwestern u on erritory utzotin cu ains sout -oentra part Talkeetna Mountains, C - - . . British Columbia (Wheeler, 1961; (Richter and Jones, McCarthy 0—4 to 6 NeIchina area garfigfirfla'gggss“ ‘" (Souther, 1971; Frebold and Tipper. 1973; Berg, Jones,and Quadrangles (Grantz, 1960. 1951) ‘ Frefiold, 1964a) 1970) Richter, 1 72) (Mackevett, 1969, 1971) U )e C et . C etaceous Lo at co 5 A/‘MfiBN’. r :fieous NArl/‘QVOQK/ V war Cretaceous . Lower Cr at: u /\Lowar Cretaceous 3000 ft (914 m (Basal part onl)y) Buchia fischariana and Mostly argillite. Bach/a plochu Mostly not graded 7 7 5000 ft (1524 m) Conglomerate, graywacke, argillite, ' massive, graded iBuchia rugosa and Such/a mosquensis Sandstone and : siltstone (goat Glacier ,9 ? 30 fl 1 ormatio "’ " ‘5" M33” $3, 3})” o—aeoo ft (1158 m) E: E argilli‘te. Mudstone, sllmone, as c Some sflmone' graywacke, limestone xv . Amoebaceras g mudstone, graywacke, and conglomerate g»: Sri‘ltstone and (Prionodoceras) o and limestone fig 9 3° and : ‘\./'\ V Z 8 Dichotomosphinctes 3E I K'N Q Conglomerate , j Cardioceras distans Cardiaceras martini / Cédoceras (Stenocadacelas) stena/obaida g goglitna Formation Simfif’fig 3,93%]:2 m Cadaceras carostarna and Some sandstone or Lil/acme buckmam c glo er to ba e Kegg/erites Arctoce haiir‘es 244 m ._—L.,__ ’ ? %andst)one1silt» at Cranocephallres s °"°' cong mm" a, Cranocepha/itas costidensus Nizina Mountain a co ly eds Formation ? (31500 ft (457 m) _raywa. e, _ VAUN/VJ’J/‘JVN‘N/JVNN/‘e/N fine-grained Tuxedni Group Megasphaeroceras, Leptasphmctes . I H. 7 700—1200 n (213-366 m) WW 3:322:21 £3,381,” 2500 ft (762 m) ' Egfisne anld I iStephanaceras kirschneri 11,000 ft 10.000 1“ Conglomerate, some 02:5. 008 IV Parabigotites crassicastatus (3352 ml (3048 m) quartz“, shell ineds Y or arglllite,and y Sonninia and Docidoceras some graywacke. _ . . Age uncertain , _ Eryc/tmdes hOWGWI, Tmetoceras Not identified Uplift, folding, erosron,and ? dior' e intr sio s Grammoceras yHaugia and Phymatoceras Graywacke, Interbedded m Talkeetna Dacryliaceras cf. D. commune 3000 ft (914 ) 7 n siltstone, graywacke, a, Arginite, Formation . 7 J and shale. stltstone, = sil t n d 6000-8000 ft . ° l t b dd d sa dst 9 ‘3 ° 9"“ ‘ (1828-2438 m) (5 i: aw; a anrd 50%}: ‘5 graywacke Lubbe Creek Formation Upper part: P/eiiroceras, Ama/rheus, Paltarpites 8, part with conglomerate 3; 109-390 1“ (30191 m) sandstone 3 conglomerate of volcanic, b Spiel-”I18. coqulna. and argillita. g cgntainirlt) l raniticbglr E and chart _icerteesimees. ., or graemic y p Middle. part: boulders. lntertongues volcanic "0W9: southwest , and pyroclastlcs. Uprania and Apoderoceras Volcanic rocks with the 7 , _ , present only Takwahoni Lower part: Cruel/ob/ceras near base Formation $000 lft (1219 m) {.VloCartgiy Formation argillite and ong omerate in part , u er :vith granitic Egberg§00 ft sandstone ragments. m ert, . . Grades laterally spiculite, shale, M’” ”de)’ ”‘9’ as into graywacke and limestone . Ami ceras 7 Corom'ceras \ Present near Not/ex e/ Laber a. pos J g - [\J L/ Waehnerocaras and Psi/oceras PreCarnian Upper Triassic Upper Triassic Upper Triassic Upper Triassic B. Northwestern British Columbia to southern Alaska. FIGURE 24.—CORRELATIONS AND COMPARISONS OF J URASSIC ROCKS IN THE PACIFIC COAST REGION IN BRITISH COLUMBIA, YUKON TERRITORY, AND SOUTHERN ALASKA. Vertical. lines indicate that strata are missing; right diagonal lines indicate strata not exposed; left-diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column numbers refer to locations shown on figure 19. 60 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES The overlying Moonshine Conglomerate is dated as early late Bajocian because it contains several fragments of loosely coiled ammonites (USGS Mesozoic 10c. 27322) belonging to the family Spiroceratidae and closely resem- bling specimens of Spiroceras bifurcatum (Quenstedt) from eastern Oregon (Imlay, 1973, pl. 1, figs. 3—8). Next higher in the Mount Jura Jurassic sequence is an unnamed dacite tuff of McMath (1966, p. 182), which is overlain by the Hull Meta-andesite. These units have not furnished fossils but could represent any time be- tween latest Bajocian and earliest Callovian. They are herein provisionally assigned a Bathonian Age mainly on the basis of stratigraphic positions but partly because the early Callovian appears to be accounted for by the overlying formations. The lower to middle Callovian is represented on Mount Jura by ammonites from the Hinchman Sand- stone, the North Ridge Agglome‘rate, and the Foreman Formation (Imlay, 1961, p. D9). The next three overly- ing formations have not furnished any identifiable fossils and could be in part younger than Callovian. They are herein provisionally assigned to the Callovian because the thickness of the sequence from the Hinchman Sand- stone to the Trail Formation is not much greater than that of the Logtown Ridge Formation in the western part of the Sierra Nevada and is much less than that of the Callovian beds in eastern Oregon. Jurassic sequences exposed in the western part of the Sierra Nevada consist of partially metamorphosed sedimentary and volcanic rocks that differ from those ex- posed in the higher part of the Sierra in the following ways: (1) none is older than Callovian; (2) they are, in part, of early Oxfordian to early Kimmeridgian Age; (3) they are much more extensive; and (4) they contain more slaty beds. They have been divided into many forma- tional units based generally on local lithologic and strati- graphic features (Turner, 1894, 1897; Lindgren, 1900; Lindgren and Turner, 1894; Becker, 1885, p. 18, 19; Taliaferro, 1942, p. 98, 99; 1943a, p. 282—284; Heyl and Eric, 1948, p. 51—53; Eric and others, 1955, p. 10—12; Imlay, 1961, p. D2—D9; Clark, 1964, p. 15—41; Sharp and Duffield, 1973, p. 3971—3974). Apparently most for- mational boundaries have been difficult to trace laterally because of complicated and extensive faulting, lithologic changes laterally within short distances, and scarcity of fossils. Thus, the sequence exposed in a central fault block near the Cosumnes River (Clark, 1964, p. 17—21,‘23— 26, pl. 9) was dated by Imlay (1961, p. D3—D8) as Cal- lovian to early Kimmeridgian. Within this age span, the Mariposa Formation was dated as late Oxfordian to early Kimmeridgian on the basis of the presence of the ammo- nites Discosphimtes, Dichotomosphinctes, and Amoeba- cems (Amoebites), in association with the pelecypod Buchia concentrica (Sowerby). The underlyingLogtown Ridge Formation was dated as late early Callovian to late Oxfordian on the basis of the presence of Pseudoca- docems in its lower 600 feet (180 m) and Idocems cf. I. planula (Heyl) near its top. The underlying “Cosumnes . Formation” (of former usage) was dated as early Cal- lovian because of its gradational relationship with the Logtown Ridge Formation. Subsequent studies by Sharp and Duffield (1973, p. 3971—3974; Duffield and Sharp, 1975, p. 1, 5, 8, 22, 29) showed, however, that the “Cos- umnes Formation” is not a mappable unit, because it consists of scattered blocks of graywacke, clay slate, and conglomerate that are bounded by faults and are part of a melange. This melange is separated from the Logtown Ridge Formation by a major fault involving considerable displacement and brecciation of beds. The melange may involve beds of several ages but is not younger than Late Jurassic, because it bears foliation that predates intru- sions of Upper Jurassic granitic rocks. Marked lateral variation within the Jurassic beds of the central fault block has been demonstrated by Clark (1964, p. 22, 23, pl. 9), who showed that the Logtown Ridge Formation passes southward near the Merced River into at least 15,000 feet (4,570 m) of volcanic rocks called the Penon Blanco Volcanics. Also, the Mariposa Formation locally contains thick volcanic members that consist mostly of breccia. The Jurassic rocks exposed in a western fault block have been described by Clark (1964, p. 27—33) under formational names different from those used for the cen- tral block. These rocks are called, from youngest to old- est, the Copper Hill Volcanics, the Salt Spring Slate, and the Gopher Ridge Volcanics, Of these, the Salt Spring Slate resembles the slaty part of the Mariposa Forma- tion, has been mapped previously under that name (see list of names in Clark, 1964, p. 29), and contains Buchia concentrica (Sowerby), a fossil common in the Mariposa Formation (see Imlay, 1961, p. D14). Presumably the Gopher Ridge Volcanics is roughly equivalent to the Logtown Ridge Formation, and the Copper Hill Volcan- ics, to the upper part Of the Mariposa Formation. In comparison with the Jurassic sequence near Tay- lorsville, the lower part of the Logtown Ridge, which contains Pseudocadoceras grewingki (Pompeckji), is cor- related with the Foreman Formation. The lowest part of the Logtown Ridge Formation, which was separated from the “Cosumnes Formation” by Sharp and Duffield (1973, p. 3971, 3972) should be equivalent to the Hinch- man Sandstone and the North Ridge Agglomerate. The middle to upper parts of the Logtown Ridge Formation are possibly equivalent to some or all of the three upper- most Jurassic formations near Taylorsville (see fig. 22). COMPARISONS 0F LITHOLOGIC AND! STRATIGRAPHIC FEATURES The Mariposa Formation may be correlated by the presence of Buchia concentrica (Sowerby) with the Santa Monica Slate just north of Los Angeles (Imlay, 1963, p. 103, pl. 14, figs. 14—19), with the Monte de Oro Forma- tion exposed northeast of Oroville in Butte County, Calif. , and with the GaIice Formation in northwest California and adjoining parts of southwest Oregon. All these are characterized by dark-gray to black slaty to phyllitic beds that contain Buchia in places. Failure to find Buchz'a in slaty beds in the uppermost Jurassic formations near Tay- lorsville suggests that those formations are older than late Oxfordian. Jurassic rocks older than Callovian occur at only two places in California outside the eastern and middle Jur— assic belts in the Sierra Nevada. One of these is along the Pit River in the eastern Klamath Mountains about 30—40 miles (48—64 km) northeast of Redding. It ap- pears to be a northwestward extension of the Jurassic beds exposed near Taylorsville, although the two se- quences are separated by about 75 miles (121 km) of vol- canic rocks exposed at the south end of the Cascade Range. The other occurrence is in the Santa Ana Moun- tains southeast of Los Angeles. It could represent a southward extension of the metamorphosed Jurassic rocks of the central part of the Sierra Nevada, just as the Santa Monica Slate near Los Angeles could represent a southern extension of the Mariposa Formation of the western Sierra Nevada. The Jurassic sequence exposed along the Pit River in north-central California is about 8,000 feet (2,440 m) thick. At its base is the Arvison Formation, which is about 6,000 feet (1,830 m) thick, consists mostly of vol- canic flows, breccia, agglomerate, and tuff, and contains some conglomerate and tuffaceous sandstone. The Arvi- son rests unconformably on Triassic beds and at one place has yielded the Sinemurian ammonites Asterocems and Arm'ocems (Sanborn, 1960, p. 11-14). The overly- ing Potem Formation (Diller, 1906, p. 5), which is 1,000— 2,000 feet (305-610 m) thick, passes laterally in its lower part into the Bagley Andesite. The Potem consists mostly of argillite and calcareous tuffaceous sandstone but in- cludes some conglomerate and limestone lentils and ap- parently is conformable with the Arvison Formation of Sanborn (1960, p. 6, 14—16, pl. 1). The age of the lower part of the Potem Formation is definitely Early Jurassic, not younger than early Toarcian, as shown by the occur- rence of Weyla aff. W. alata (von Buch) (S. W. Muller, oral commun., 1958). The age of the upper part is not older than late Toarcian, as shown by the occurrence of Bositra buchii (Romer) (Guillaume, 1928), and could be as young as Bajocian, according to Sanborn (1960, p. 16). The Jurassic beds cropping out in the Santa Ana Mountains of southern California are all included in the 61 Bedford Canyon Formation, which consists mostly of dark-gray to black slates and argillite, includes some quartzite and fossil‘iferous limestone lentils, and is esti- mated to be 20,000 feet (6,100 m) thick (Larsen, 1948, p. 18—24; Engel, 1959, p. 16—25). Fossils from the lime- stone lentils were once considered to be of Triassic age (Engel, 1959, p. 22—24) but are now dated as Jurassic on the basis of ammonites (Silberling and others, 1961, p. 1746, 1747). Thus, the pelecypod originally described as Daonella sanctea-anea Smith (Smith, 1914, p. 145) is now assigned to the genus Silberlingia (Imlay, 1963, p. 100) and dated as early Callovian because it occurs with M acro- cephalites and Hecticocems (Imlay, 1963, p. 98, 99, pl. 14, figs. 1—9, 26—36; 1964c, p. 506, 508, pl. 78, figs. 22—26). Also, some brachiopods that were once considered to be of Triassic age (G. A. Cooper, cited in Larsen, 1948, p. 18), were apparently collected at the same stratigraphic level as some middle Bajocian ammonites identified as Dorsetensia and Telocems? sp. juv. (Imlay, 1964c, p. 506—508, pl. 78, figs. 3—18). WESTERN CALIFORNIA AND SOUTHWESTERN OREGON Jurassic marine sequences exposed in and near the Coast Ranges in California and in the western Klamath Mountains in northwest California and southwest Ore- gon have the following characteristics, geologic relation- ships, and historical developments: 1. They are entirely of Late Middle to Late J uras- sic age (Callovian and younger). 2. They are generally many thousands of feet thick. 3. They include sequences of two or three different age ranges that are associated only in the western Klamath Mountains and are therein separated by thrust faults. 4. Some sequences are of Callovian to early Kim- meridgian Age; contain a great deal of volcanic ma- terial; were deposited in deep to fairly deep waters, on the basis of lithologic characteristics; were uplifted, folded, metamorphosed, intruded, and eroded during late Kimmeridgian to Tithonian time; and were then overlain unconformably in places by shallow-water marine Cretaceous beds. These se- quences include the Logtown Ridge-Mariposa se- quence in the Sierra Nevada and the Rogue-Galice sequence in the Klamath Mountains. 5. Other sequences are of late Kimmeridgian to late Tithonian Age; are mostly nonvolcanic; originated in shallow to fairly shallow water, on the basis of fossils and lithologic features; and pass conforma- bly upward into shallow-water marine sediments 62 of earliest Cretaceous age. They include the Knox- ville Formation of California and possibly the Rid- dle Formation of Oregon, although the last named has not furnished fossils older than the late Tithon- ian. They are underlain by unfossiliferous meta- volcanic rocks that, on the basis of stratigraphic position, should be at least of early Kimmeridgian and Oxfordian Age. 6. Still other sequences are only of late Tithonian Age, are volcanic, pass conformably upward into beds of earliest Cretaceous age, and appear to be of fairly deep to deep-water origin, on the basis of lithologic features. They include the Dothan For- mation and most of the Otter Point Formation of Oregon and the Franciscan assemblage of Califor- ma. 7. The sequences of Callovian to early Kimmeridg- ian Age were deposited in different areas from those of later Jurassic age and are now juxtaposed in the Klamath Mountains by eastward under- thrusting of the younger sequence. In the Dayville-Riddle area of southwestern Oregon, the slaty Galice Formation overlies the metavolcanic Rogue Formation. These rocks crop out in an arcuate belt 10—30 miles (16—48 km) wide that extends about 190 miles (306 km) south into southern Trinity County in northwest California, where they are all included in the Galice Formation. The Galice ranges from Oxfordian to early Kimmeridgian time. Along the west side of the belt, these rocks are in contact with the Josephine ultra- mafic mass, the South Fork Mountain Schist, and the‘Do— than Formation. Along the east side, they are in fault contact with upper Paleozoic rocks in California and Triassic(?) rocks in Oregon (Diller, 1907, p. 403; Wells and others, 1949, p. 47; Cater and Wells, 1953, p. 84; Wells and Walker, 1953; Irwin, 1960, p. 27, 28; Dott, 1971, p. 9, 10; Beaulieu, 1971, p. 3, 15, 19, 20, 38). Thick- nesses cannot be measured owing to intense crumpling, faulting, and intrusions, but estimates range from 10,000 to 30,000 feet (3,050 to 9,140 m) (Irwin, 1960, p. 27). At the top of the Galice Formation, a normal sedi- mentary contact, instead of a faulted contact, has only been found near the Oregon coast on Barklow Mountain in northwestern Curry County. On that mountain, the formation is overlain unconformably by a conglomerate that contains Buchia pacifica Jeletzky (USGS Mesozoic loc. M5006) of early to middle Valanginian Age (Dott, 1966, p. 94; 1971, p. 11). This relationship, plus the fact that no Upper Jurassic beds have yet been found above the Galice Formation or the equivalent Mariposa For- mation, suggests that both these formations were above sea level and that they provided sediment during depo- sition of the Knoxville Formation and the older part of the Franciscan rock assemblage (Bailey and others, 1964, p. 126, 146, 147). JURASSIC PALEOBIOGEOGRAI’HY OF THE CONTERMINOUS UNITED STATES The Galice Formation is correlated with the Mari- posa Formation of the western Sierra Nevada because it is strikingly similiar lithologically and likewise contains ° the pelecypod Buchia concentrica (Sowerby) and the am- monite Perisphinctes (Dichotomosphinctes) (Imlay, 1961, p. D10). The underlying Rogue Formation, which appar- ently is gradational with the Galice, consists of many kinds of volcanic rocks similar to those in the Logtown Ridge Formation of the western Sierra Nevada. It may be of the same age, but to date it has not yielded any fossils. These facts show that the Galice Formation is a northward extension of the Mariposa Formation and was deposited under the same environmental conditions. Similarly, the Rogue Formation may be the northern ex- tension of the Logtown Ridge Formation, but the Rogue was deposited under somewhat different environmental conditions, as shown by its lack of some ammonites that are present throughout the Logtown Ridge Formation. Upper Tithonian beds crop out in the Coast Ranges of western California as far south as San Diego, in the Klamath Mountains of northwestern California, and in southwestern Oregon (fig. 22). In California, they occur in the Franciscan rock assemblage and in the Knoxville Formation (Taliaferro, 1943b). In Oregon, they occur in the Otter Point, Dothan (Taliaferro, 1943b), and Riddle Formations. Among these rock units, the Franciscan assemblage and the Dothan and Otter Point Formations closely re- semble each other. The Franciscan consists mostly of graywacke but includes some dark shale, altered v‘olcanic rock (greenstone), chert, limestone, and blue schist and is estimated to be at least 50,000 feet (15,240 m) thick (Bailey and others, 1964, p. 5, 20—122). The Dothan con- sists mostly of massive hard graywacke but includes black mudstone, chert, and conglomerate. It is estimated to be at least 18,000 feet (5,490 m) thick and passes southward into the Franciscan assemblage in California (Beaulieu, 1971, p. 15; Dott, 1971, p. 43—46; Wells and Walker, 1953). The Otter Point consists of graywacke, black mudstone, argillite, altered volcanic breccias and flows (greenstone), much conglomerate, chert, and some limestone lentils and appears to be thousands of feet thick (Koch, 1966, p. 36—43; Beaulieu, 1971, p. 30; Dott, 1971, p. 27—31). It greatly resembles the Dothan For- mation but is distinguished lithologically by being darker and more sheared, by containing more volcanic frag- ments, pillow lavas, and fossils, and by its graywacke being less indurated (Dott, 1971, p. 46). All contacts of _ these formations are marked by thrust faults. Resemblances between the Knoxville and Riddle Formations are not nearly as close as those among the three formations just described. The Knoxville Forma- tion consists of gray shale, siltstone, thin—bedded sand- stone, conglomerate lenses, and some limestone concre- tions in shale units and is 2,000—13,000 feet (610—3,960 m) thick. The Riddle Formation consists of gray silt- COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES stone, thin-bedded graywacke, lenses of conglomerate, and some limestone lentils and is at least 1,100 feet (335 m) thick. Most of that thickness, however, involves beds of Berriasian Age, which are younger than any part of the Knoxville Formation as now defined. Comparisons between the two formations are difficult to make because the Riddle Formation is much broken by faults and has not been studied as thoroughly as the Knoxville Forma- tion. On the basis of fossils, the Franciscan assemblage is dated as late Tithonian to Turonian and possibly Cam- panian (Bailey and others, 1964, p. 115—122, table 16). A late Tithonian Age is based mainly on four occurrences of Buchia piochii (Gabb) in the northern Coast Ranges, including one at the south end of Lake Pillsbury. This age is supported by the occurrence of B. piochii with Au- lacosphinctes? sp. juv. near Stanley Mountain in the southern Coast Ranges. ’ The upper part of the Knoxville Formation is dated as late Tithonian on the basis of both ammonites and buchias at many levels, as recently documented in detail (Bailey and others, 1964, p. 124—130; Jones and others, 1969, p. A9—A12; Imlay and Jones, 1970, p. B5—B12, B17—BlQ). The lower part is dated as late Kimmeridg- ian to early Tithonian by the presence of Buchia mgosa (Fischer) about 50—100 feet (15-30 m) above the base of the formation in the Paskenta area (Jones, 1975). As- signment to the late Kimmeridgian is also favored by the presence of a few specimens that bear very fine ribs, as on B. concentrica (Sowerby), and by the absence of B. mosquensis (von Buch) (D. L. Jones, oral commun., 1975), an associate of B. mgosa, which becomes more common upward. This occurrence does not imply thatft'he basal part of the Knoxville Formation is of late Kimmer- idgian Age throughout its extent. A late Tithonian Age for the Otter Point Formation in southwestern Oregon is proven by the presence of Buchia piochii (Gabb) at many localities (Koch, 1966, p. 42, 43). However, a Berriasian Age for part of the for- mation is shown by the presence of many specimens of B. uncitoides (Pavlow) (USGS Mesozoic loc. 2074) in as- sociation with the ammonite Neocosmocems, a genus that is much more common in Berriasian than in Tithon- ian beds. With these occur one immature specimen of Prom'ceras and a few specimens of B. piochii (Gabb), both of which are good evidence of :a late Tithonian Age and both of which have a different colored matrix from the specimens of Neocosmocems and B. uncitoides. Therefore, the fossils were probably collected from dif- ferent beds of different ages (Imlay and Jones, 1970, p. B5, B32, B51, B52). A late Tithonian Age for part of the Dothan Forma- tion is proven only by the occurrence of Buchia piochii (Gabb) at oneplace on the Chetco River in Curry County, Oreg. (Ramp,'1969, p. 245). The probability that the for- mation is partly of younger age is suggested by its great 63 thickness and by its close lithologic similarities to the Ot- ter Point Formation and to the Franciscan assemblage, both of which have yielded fossils younger than Tithon- ian. The Riddle Formation is definitely of Tithonian to Berriasian Age in its type section near Days Creek, Oreg. Buchia fischeriana. (Keyserling) and Aulac‘os- phinctes of late Tithonian Age occur just above the basal conglomerate. B. uncitoides (Pavlow) of Berriasian Age occurs from 20 to 1,004 feet (6 to 306 m) above the basal conglomerate (Imlay and others, 1959, p. 2775—2778; Im- lay and Jones, 1970, p. 313, B17). The late Tithonian Age for the lower part of the Riddle Formation is con- firmed by the presence of B. fischen'ana with Prom‘cems on Cow Creek near the mouth of Iron Mountain Creek in the NE% sec. 4, T. 31 S., R. 7 W., Dutchman Butte Quadrangle, Douglas County, Oreg. In addition, the ammonite Durangites, obtained from a limestone lentil in the Dillard area south of Roseburg, Oreg. (Imlay and others, 1959, p. 2778; Imlay, 1960, p. 169, pl. 31, figs. 11, 12), could be from either the Riddle or the Dothan Formation. EASTERN OREGON AND WESTERN IDAHO The stratigraphic and lithologic features and corre- lations of the Jurassic formations exposed in an inlier in Tertiary volcanic rocks south and southwest of John Day, Oreg. have been described in considerable detail. (Lupher, 1941; Dickinson and Vigrass, 1965, p. 30—64; Buddenhagen, 1967; Brown and Thayer, 1966a, b; Imlay, 1964a, p. D2—D9; 1968, p. C4-C2]; 1973, p. 8—25) and .are summarized on figure 22. As a whole, the Jurassic sequences in that inlier are characterized by enormous thicknesses, by rapid facies changes, and by consisting mostly of volcanic ejecta, flows, and breccias. They also include some sedimentary material that was derived mostly from a landmass to the west Where Triassic and Paleozoic rocks were exposed but that was derived in part from a landmass to the north where only Triassic rocks were exposed. Overall thicknesses of the Jurassic sequenoes range from about 1,800 feet (550 m) on the west to about 24,000 feet (7,300 m) on the east. Lower Jurassic beds thicken eastward from about 400 to 1,600 feet (120 to 490 m), to which may be added about 8,000 feet (2,400 m) of Het- tangian and Sinemurian beds exposed in the northeast- ern part of the Izee Quadrangle, the northern parts of the Logdell and Seneca Quadrangles, and the southern part of the Mount Vernon Quadrangle. Bajocian and Bathonian beds vary in thickness from about 1,800 to 2,750 feet (550 to 838 m) and are thinnest inthe central part of the inlier. Callovian beds vary in thickness from about 1,000 feet (300 m) on the west to about 14,000 feet (4,300 m) on the east. 64 These variations in thickness are related to nearness to volcanic sources, to positions relative to land areas, upwarps, and basins, and to the presence and extent of unconformities (Dickinson and Vigrass, 1965, pl. 3). Widespread angular unconformities, involving intense folding, some faulting, erosion, and changes in direction of folding, developed in early Pliensbachian time (Brown and Thayer, 1966a, b) and after middle Callovian time. A local unconformity involving folding, uplift, and ero- sion developed in the Suplee area in Toarcian to early Bajocian (Aalenian) time. Another unconformity, involv- ing some warping and erosion, formed in the Suplee-Izee area between deposition of the Snowshoe Formation and the Trowbridge Shale but within beds of early Callovian Age, according to DiCkinson and Vigrass (1965, p. 83, pl. 3). Nonetheless, the presence of the early Callovian am- monites Iniskimtes and Lilloettia 300—500 feet (90—150 m) below the top of the upper member of the Snowshoe Formation suggests that the exact stratigraphic position and age of the unconformity needs confirmation. The fact that the Suplee Formation of late Pliens- bachian Age rests on the Graylock Formation of Het- tangian Age at one place and on the much thicker Keller Creek Shale of early to late Sinemurian Age only 6 miles (9.6 km) away suggests considerable erosion locally dur- ing early Pliensbachian time. It is not proof, however, because the two occurrences are separated by a major fault of unknown displacement. Before faulting they could have been much farther apart, could have been parts of different structural plates, and could have had a different sedimentary history. Perhaps the best evidence for ero— sion is the presence of an angular unconformity between the Keller Creek and Suplee Formations (Brown and Thayer, 1966a). This unconformity is well exposed on a road near fossil locality D66 (Dickinson and Vigrass, 1965. pl. 1) in the NE% NE% sec. 2, T. 17 S., R. 28 E., in the Izee Quadrangle. Beds of early Sinemurian to early late Bajocian Age and of possible Callovian Age are present in southern Baker County and northern Malheur County in east-cen- tral Oregon (fig. 23) from the Snake River westward at least 50 miles (80 km). Beds of early Callovian Age and of probable older Jurassic age are present nearby, east of the Snake River near the abandoned mining town of Mineral, Idaho. From Juniper Mountain, about 10 miles (16 km) west-southwest of Brogan, Oreg., the eastern (lower- most) boundary of the Jurassic extends northeastward about 25 miles (40 km), crosses the Snake River about 64 miles (104 km) north-northeast of Huntington, and con- tinues another 10 miles (16 km) in Idaho to Dennett Creek, where it curves eastward just south of the old mining town of Mineral (abandoned). JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES The lower boundary of the Jurassic in the Hunting- ton area, Oregon, is marked by 30—800 feet (9—240 m) of red, purple, and green conglomerate that rests uncon- formably on Upper Triassic beds (Brooks, 1967, p.‘ 114— 118) and consists of clasts derived from those beds. These clasts are typically compressed and sheared ex- cept for certain discontinuous rock bodies of late Pliens- bachian Age that occur in the lower part of the conglom- erate. Within these bodies, such fossils as ammonites, pelecypods, and corals occur in thin calcareous gray- wacke that is associated with mostly round, nonsheared clasts that are a peculiar dark green (H. C. Brooks, writ- ten commun., April 1974). In the Mineral area, Idaho, similar coarse conglomerate beds grade downward into tuffs that overlie a quartz diorite sill (Livingston, 1932, p. 33). In the Juniper Mountain area of Oregon, the lower boundary is marked by a thin unit of reddish sandstone and shale that rests on massive limestone of possible Early Jurassic, Triassic, or late Paleozoic age. The late Pliensbachian ammonites in the basal con- glomerate are not proof that the conglomerate is of that age, because the conglomerate is overlain by graywacke that basally contains ammonites of early to late Sinemur- ian Age. It appears, therefore, that rock bodies of late Pliensbachian Age in the lower part of the conglomerate must have attained that position as a result of southeast— ward thrusting after Pliensbachian time or by deposi- tion in channels or pockets that were cut into the con- glomerate or into the Triassic beds during early Pliensbachian time. The possibility of erosion during that time is suggested by the lack of fossils of that age any- where in eastern Oregon and by the fact that consider- able erosion took place during early Pliensbachian time in the Suplee-Izee area farther west. Above the basal conglomeratic unit in the Hunting- ton area are some thousands of feet of beds that contain fossils of Sinemurian to early late Bajocian Age (fig. 23). This sequence consists mostly of sheared and slightly metamorphosed gray to yellowish-gray, green, brown or black massive to thin-bedded graywacke, tuffaceous sandstone and siltstone, but it also includes some beds of water—laid tuff, conglomerate, quartz sandstone, lime— stone, and lava flows. AbOVe the thin basal unit of reddish sandstone and shale in the Juniper Mountain area is at least 5,000 feet (1,500 m) of gray shale, siltstone, graywacke, and con- glomerate (Wagner and others, 1963, p. 688). Within this sequence, the upper 2,000 feet (600 m) has been dated as early to early late Bajocian on the basis of am- monites (Imlay, 1973, p. 30), and the lower 3,000 feet (900 m) has been dated as Early Jurassic on the basis of stratigraphic position and the presence of Crucilobi- ceras? 75—100 feet (23—30 m) above the base. COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES In the Mineral area, Idaho, a coarse conglomerate unit is overlain by some 100 feet (30 m) or more of dark- gray, sandy, thin- to medium-bedded tuff, which con- tains a species of Gryphaea (Imlay, 1964a, p. D13). This species has been found elsewhere about 64 miles (104 km) north-northwest of Brogan, Oreg., in association with the early Bajocian ammonites Tmetoceras and Eryci- toides (USGS Mesozoic loc. 30142). Still younger beds of early Callovian Age are ex- posed along Dennett Creek and its tributaries near Min- eral, Idaho. These beds are probably several hundred feet thick and consist of dark-gray calcai “‘s shale that contains many black concretions (Livingston, 1932, p. 33, 34; Imlay, 1964a, p. D3). From a few concretions have been obtained such ammonites as Lilloettia buckmam' (Crickmay), Xenocephalites vicarius Imlay, and evolute Kepplerites apparently identical with K. snugharborense (Imlay) (1964a, p. D6, D7). This shale contains the same ammonites as the lithologically similar Trowbridge Shale in the Suplee-Izee area southwest of John Day, Oreg. (Lupher, 1941, p. 263; Dickinson and Vigrass, 1965, p. 60—64). Faunally, it correlates with the lower part of the Tonnie Siltstone Member of the Chinitna Formation in southern Alaska (Imlay, 1975, p. 3, 6, 14). Similar dark-gray to black shale, slightly to strongly metamorphosed locally, occurs at several places in Baker and Malheur Counties, Oreg., above beds of late Bajoc- ian Age. It is represented (1) in the northern part of the Huntington Quadrangle near Dixie Creek and farther northeast near Morgan, Hibbard, and Connor Creeks by thick, tightly folded, gray to black phyllite and slaty beds (Brooks, 1967, p. 118, location map on p. 114); (2) on the northern side of Juniper Mountain (T. 15 S., R. 41 E., secs. 30—32), southwest of Brogan, by 1,000 feet (300 m) or more of black phyllitic shale that contains limestone lentils and concretions (Wagner and others, 1963, loca- tion map on p. 689); and (3) by dark-gray to black slate and phyllitic shale exposed southwest of Ring Butte in the northeast part of T. 16 S., R. 37 E., in the Ironside Mountain Quadrangle (W. D. Lowry, unpub. data, 1968). No fossils have been found in any of these dark shales, phyllites, or slates in easternmost Oregon, but a Callov- ian Age for them is indicated by their lithologic resem- blance to the Trowbridge Shale in the Suplee-Izee area and to the unnamed black shale near Mineral, Idaho, and by their superpositions on Bajocian beds. Lower Jurassic beds are represented in the upper 2,000 feet (600 m) of the Hurwal Formation (Smith and Allen, 1941, p. 6, 13, 14) exposed in the Wallowa Moun— tains south of Enterprise in northeast Oregon. They con- sist of partially metamorphosed dark—gray to black clay- stone and siltstone that weathers brownish red and contains Sinemurian and Pliensbachian fossils (Imlay, 65 1968, p. C7, 015, 016). The most complete sequence is exposed in the northeast part of the mountains (NW% NW% sec. 19 (unsurveyed), T. 2 S., R. 44 E.), is 980 feet (299 m) thick, is covered by debris basally, and con- tains ammonites of late Sinemurian to late Pliensbachian Age. Elsewhere in the mountains, early Sinemurian am- monites are known at five places. At one of these places, near Twin Peaks (center of SW% sec. 17 , T. 3 S., R 44 E.), the beds of that age grade downward into unfossili- ferous beds that, in turn, grade downward into Upper Triassic beds. On the basis of these occurrences, the thickness of the Pliensbachian beds is about 680 feet (207 m), of the upper Sinemurian beds, at least 300 feet (90 m), of the lower Sinemurian beds, 700—800 feet (210—240 m), and of the beds of possible Hettangian Age, 200-300 feet (60—90 m). Within the Lower Jurassic sequence exposed in the Wallowa Mountains, the early Sinemurian is represented by crushed and deformed ammonites of the family Arie- titidae that probably include Corom'cems, Memphi- oceras, and Megarietites. The late Sinemurian is repre- sented by Glevicems, Cmcilobicems, Eoderoceras, Oxynoticeras?, Echiocems?, Coelocems?, and Arctoas- terocems. The early Pliensbachian is either absent or is represented by 60 feet (18 m) of unfossiliferous beds. The late Pliensbachian is identified throughout about 620 feet (189 m) of beds by such genera as Canavaria, Har- pocems (Harpocemtoides), Arieticeras, Prodactyli- 'oce'ras, Protogrammoceras, and Fuciniceras. Fannino- ceras was collected from the lower 350 feet (107 m) of these beds (USGS Mesozoic locs. 28809, 28810) in as- sociation with the ammonites listed. This association of Fanninocems with ammonite genera of late Pliensbachian Age is confirmed by a simi- lar association in the Izee-Suplee area southwest of John Day, Oreg. In that area, Fanninoceras has been col- lected with Fucim'cems in concretions and beds in the upper third of the Suplee Formation (USGS Mesozoic loc. 29223) and with Leptaleoceras and Arieticeras, from a 6-inch (15—cm) layer about 15—20 feet (4.5—6 m) above the base of the Nicely Formation (Lupher’s 10c. 125 in Imlay, 1968, p. 013, 015). Arieticems, Paltarpites, and Liocemtoides are about 54 feet (16.5 m) above the base of the Nicely (USGS Mesozoic loc. 29218), and Leptaleo— cems, Fucinicems, Reynesocems, and Am’eticems are about 20 feet (6 m) below the top of the Nicely (USGS Mesozoic 100. 27360). In that area, as well as in the Wal- lowa Mountains, Fanninocems is associated with Pro- dactylioceras but not with Dactyliocems. The presence of Fanninocems in beds of late Pliensbachian Age has recently been confirmed by Hans Frebold (written com- mun., 1975), who has found Fanninocems associated with ammonites of early Pliensbachian to early Toarcian 66 Age on Maude Island in the Queen Charlotte Bsfands of British Columbia. The Jurassic is represented in the Snake River Can— yon at Pittsburg Landing, about 32 miles (52 km) south of the northeast corner of Oregon, by at least several hundred feet of tightly folded soft black shale, dark- brown graywacke, and some limestone, which rests un- conformably on Upper Triassic clastic rocks (Vallier, 1968, p. 247). An early to middle Callovian Age is shown by the presence of Lilloettia, Xenocephalites vicarius Imlay, and probable Grossoum'ia. Correlation with the Trowbridge Shale instead of the Lonesome Formation of the Suplee—Izee area of eastern Oregon is suggested by the absence of Pseudocadoceras. Upper Jurassic beds that are lithologically and faun- ally distinct from any known elsewhere in Idaho and Or- egon are exposed along both sides of the canyon of the Snake River for about 4 miles (6.4 km) just south of the northeast corner of Oregon (Morrison, 1961). These beds, named the Coon Hollow Formation by Morrison (1964), are about 2,000 feet (610 m) thick and consist mostly of hard, splintery, thin-bedded, black noncalcareous mud- stone. They include also some beds of graywacke and chert-pebble conglomerate that are most common in the upper 400 feet (120 In). Their base is marked by a crossbedded sandstone that contains some pebbles de- rived from plutonic rocks and some large rounded lime- stone boulders. Their age is early Oxfordian, at least partly, as shown by the presence of Cardioceras (Scar- burgiceras) martini Reeside about 400 feet (120 m) above their base (Imlay, 1964a, p. D6, D15, D16). NORTHERN WASHINGTON In the Cascade Mountains of northwestern Washing- ton, the Upper Jurassic is represented in the lower part of the Nooksack Formation by Buchia piochii (Gabb) (USGS Mesozoic locs. 26253, 26267), by B. rugosa (Fischer) associated with B. mosquensis (von Buch) (USGS Mesozoic locs. 26249, 26265) (Popenoe and oth- ers, 1960, p. 1533), and by Buchria fische’r’iana (d’Orbigny) and B. cf. B. blanfordiana (Stoliczka) (Univ. California, Berkeley, Nos. 34709—11; Jeletzky, 1965,’pl. 3, figs. 2—4). In addition, B. concentrica (Sowerby) may be represented by specimens identified as Aucella er- ringtom' Gabb by T. W. Stanton (in Smith and Calkins, 1904, p. 27). The presence of B. rugosa and B. mos- guensis is significant because they are Widely distributed from Washington northward to Alaska and the arctic re- gion (Frebold and Tipper, 1970, p. 14—21; Frebold, 19643, p. 4; Imlay and Detterman, 1973, p. 11, 13, 19, 26, 27). They are unknown, however, in the United States south of northern Washington, except for one 0c- currence of B. rugosa at the base, of the Knoxville For- mation near Paskenta, Calif. JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Disconformably beneath the Nooksack Formation in the Mount Baker area of Washington, about 3,500 feet of volcanic beds and some interbedded marine slate and graywacke is exposed that Misch (1966, p; 103, 118) named the Wells Creek Volcanics. In the lower part of these volcanic rocks, a few fossils were obtained that were identified as Middle Jurassic or younger by J. A. Jeletzky (cited in MisCh, 1966, p. 118). Lower Jurassic beds have not yet been identified faunally in northwest- ern Washington, but they may be represented near the Canadian border by nonvolcanic shaly to silty sandstone that Misch, (1966, p. 103, 117) named the Bald Mountain Formation. The Lower Jurassic is possibly represented in north- central Washington by a fairly large ammonite that has evolute coiling and straight simple ribs, as does the Ar- ietitidae of Sinemurian and Pliensbachian Age. This am- monite (USGS Mesozoic loc. 17460) was collected in the SE%NE%NE% sec. 21, T. 35 N., R. 26 E., about 2 miles northwest of Riverside in Okanogan County. This local- ity is nearly due south of Amy Lake, a little above the 2,000—foot contour on a northward-draining slope. The specimen is preserved in a black, thin-bedded phyllitic noncalcareous rock that was obtained, from a limestone unit 300 feet (90 m) thick. That unit underlies 200 feet , (60“ m) of gray limestone and dolomite and overlies the ' same thickness of amphibole-pyroxene. The Jurassic is possibly represented about 30 miles (48 km) west-southwest of Riverside near Twist and Winthrop by the Twist Formation of Barksdale (1975, p. 22—24, 65, 66, figs. 4, 8, 14, 15). That formation consists mostly of argillitic black shale that is interbedded with some dark volcanic siltstone and volcanic sandstone. It is at least 4,000 feet (1,220 m) thick, but its total thickness cannot be determined because of tight folding. It rests unconformably on gneiss, schist, and coarse-grained ig- neous rocks and is overlain unconformably by the Buck Mountain Formation of Early Cretaceous (Hauterivian to Barremian) age. Its exact age is uncertain because it has yielded only molds of belemnites and of fragments of cycads. Barksdale (1975, p. 22—24) suggested, however, that the Twist Formation is possibly of Early to Middle Jurassic age. Such an age is supported by the presence of an Early Jurassic ammonite in similar black rock near Riverside. BRITISH COLUMBIA TO SOUTHERN ALASKA Reasonably accurate interpretations of Jurassic his- /tory in California, Nevada, Washington, and Oregon re- quire that the Jurassic sequences exposed there be com— pared and‘ correlated with some of the best known sequences in westernmost Canada (Brown, 1968; Crick- may, 11930, 1962; Frebold, 1951a, b; 1964a, l964d, 1966, 1967a, 1967b; Frebold and Tipper, 1967, 1970, 1973; Fre- COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES bold, Tipper and Coates, 1969; J eletzky, 1950, 1953, 1965; Jeletzky and Tipper, 1968; McLearn, 1929, 1932, 1949; Tipper and Richards, 1976) and southern Alaska (Berg, Jones, and Richter, 1972; Grantz, 1960, 1961; Im— lay and Detterman, 1973, p. 10, 11; MacKevett, 1969, 1971; Richter and Jones, 1973). Such comparisons (fig. 24) aid greatly in determining the time, duration, and geographic extent of major events in the Pacific Coast region during Jurassic time. These sequences show that the Jurassic beds of Brit- ish Columbia resemble those of southern Alaska in many respects. First, they contain essentially the same succes- sion of ammonites and buchias. Second, they contain enormous amounts of volcanic sedimentary rocks of Si- nemurian to middle Callovian Age but generally only mi- nor amounts of volcanic sedimentary rocks of older and younger Jurassic age. Third, they include unconformities of early Bajocian, late Bathonian, and late Callovian Age. Fourth, the early Bajocian unconformity coincides in time with igneous intrusions, as in parts of southern Alaska (Detterman and Hartsock, 1966, p. 63, 64, 69, 71; Grantz and others, 1963, p. B58). Fifth, an unconformity of possible late Oxfordian to latest Tithonian Age in Brit- ish Columbia coincides partly in time with an unconform- ity at the top of the Jurassic in the Cook Inlet region in southern Alaska (Imlay and Detterman, 1973, p. 10, 11, 15, 16). Sixth, granitic intrusions that cut lower Oxford- ian rocks in the Harrison Lake area of British Columbia could be of the same age as a granodiorite intrusion in Alaska’s Wrangell Mountains (Imlay and Detterman, 1973, p. 11). The Jurassic sequences in British Columbia are like- wise similar to those to the south in certain respects. Se- quences in these two areas have the same general succes- sion of ammonites and of species of Buchia, enormous amounts of volcanic material, granitic intrusions younger than early Oxfordian and possibly of Tithonian Age, and unconformities, or disconformities, of earliest Bajocian, Bathonian, late Callovian, and locally of late Kimmeridg— ian to Tithonian Age. The Jurassic sequences in the westernmost conter- minous United States differ from those in British Colum- bia in several respects. Faunally, they lack the pelecypod Buchia mosquensis (von Buch) except in northwestern Washington; lack ammonites of Bathonian Age except in eastern Oregon; lack the Callovian ammonite Cadoceras; contain the ammonites Macrocephalites and Peltoceras of earliest and latest Callovian Age, respectively; and contain ammonites of Tethyan affinities in beds younger than early Oxfordian. Lithologically, they contain much greater thicknesses of volcanic beds of Callovian Age and much more volcanic material in beds younger than Ca1- lovian. Orogenically, they include a widespread uncon- formity of early Pliensbachian Age that is not recognized in British Columbia except possibly in the western part 67 of Vancouver Island (J eletzky, 1970, p. 22, 23). The most striking difference is that Tithonian beds in California and Oregon occur only in the westernmost parts of those States and represent mainly the upper part of that stage. In contrast, on the mainland of British Columbia, beds of Tithonian Age locally pass conformably down- ward into beds of Kimmeridgian and Oxfordian Age (J e- letzky and Tip, 1968) and occur at many places through- out the central and southern part of the province as far east as westernmost Alberta (Frebold and Tipper, 1970, p. 15). Evidently, in latest Jurassic time, marine waters spread much farther east in British Columbia and ap- parently also in Washington than in areas to the south. This eastward spread is related to the presence of certain major structural features (Jeletzky, 1970; Jeletzky and Tipper, 1968, p. 3—5, 71—83, fig. 7 on p. 76). These fea- tures include several , southeast trending sedimentary troughs separated by land areas (Tippe‘r and Richards, 1976, p. 8, 41). Presumably, the sea that occupied these troughs once extended eastward to the sea that occupied the western interior region from early Bajocian to late Oxfordian or early Kimmeridgian time. WESTERN INTERIOR REGION OF THE UNITED STATES MONTANA AND NORTH DAKOTA Marine Jurassic beds in Montana and North Dakota (fig. 25) are of early or middle Bajocian to late Oxfordian Age (Reeside, 1919; Crickmay, 1936; Imlay, 1948, 1953a, 1954, 1962b, 1967b; J. A. Peterson, 1954a, 1954b; Swain and Peterson, 1951, 1952; Loeblich and Tappan, 1950a, 1950b; Carlson, 1968, p. 1973—1979; Schmitt, 1953). They rest unconformably on beds of Mississippian to Triassic age (Imlay, Gardner, and others, 1948; McKee and others, 1956; J. A. Peterson, 1972, p. 186); and are overlain gradationally by the continental Morrison For- mation of Kimmeridgian to possible early Tithonian (Portlandian) Age (Yen, 1952; Peck, 1956; Mitchell, 1956). The Morrison Formation thins northward, disappears near the Canadian border, and is overlain unconforma- bly by the Kootenai Formation of Aptian and possibly also Neocomian Age (Cobban and Reeside, 1952, p. 1016; McGookey and others, 1972, p. 192, 193, 195). The Nesson Formation is the oldest known Jurassic formation in Montana and North Dakota. It occurs only in the subsurface of the Williston basin between central Montana and central North Dakota and consists of three lithologically distinct members (N ordquist, 1955, p. 104— 106; Rayl, 1956, p. 36—38). The oldest, the Poe Evapor- ite Member, averages about 120 feet (36 m) in thickness and consists of massive salt or gypsum overlain by in- terbedded gypsum, dark-red shale and some beds of 68 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Rocky Mountains of 1 Swift Reservoir- 2 Southwest of Craig 3 Smith River 4 BB" Creek 5 SOtheSi of Utica 6 .3 St a southwestern Alberta Rierdon Gulch-Sun River 2‘/2 miles,in north bank, 22 miles 24 miles southeast 3 miles. on north side a “9 and southeastern sections, northwestern west-central Montana south of Great FaIIS. of Great Falls, ofJudith River, w British Columbia Montana Mont. Mont. central Montana Overlying beds Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous W _ Kootenay Formation a (lower part) 3. Mofily nonrgarine l sen stone. ? ome coa ? 7 _? 7 7 '—" Passage beds Tithonian 100430 fl Morrison Formation Morrison Formation Morrison Formation Morrison Formation Morrison Formation (30—68 m) Mostly green to Varicolored beds. Varicolored beds. 130 ft (55 m) Coalv beds at 10i)- la Upper part: gray shale. Coaly at top Coaly at top Upper 120 it bears Varicolored beds 3 Sandstone and ome sandstone coal, carbonaceous below a _. shale gray to and freshwater shale, alltstone,end m b ’ B limestone sandstone. 5 5:322} ‘g‘cflzr'rées Lower part bears 3, .. top varicolored shale g and some silty h 3 limestone g Kimmeridgian —r-‘ Lower part: :1 ° Mostly dark 3 E gray shale. 7 7 7 7 7 a; 0:13:33:ng Swift Formation Swift Formatlon Swifi Formation Swifi Formation SWI orrrietlon & 106-135ft(32—41m) l10ft(33 m) _. 72n(22 m) 82ft(25 m) . 60ftl18m . :> Sandstone overlying Sandstone, glauconltlc, Sandstone and Sandstone, thln-to Sandstone,'thlck-to T silty shale. Pebbly 320v? sandv‘ agele-l con lornerate. Pebbles . 21i°k'i’°dd°:{ b Ilv thm'liwdedi b ‘IIy — ‘ ' n ome a ' o omer e asa n mere e asa . 3 (gen beds and glauconltlc asal ’\ {figsfii/v‘\/flll ){p/lfiolevxw nk/‘WN/ g Oxfordlan -— 7 ? 7 ? 2 (1.5—20 m) . 5 Glauconitic ; shale, siltstone, o and sandstone _l '5 D. a. _D_ 2 o :9 , Callovian 2 5 A 7 g E Shale, gray -‘ n (30—120 ft) ; (9-36 m) _ Rlerdon Formation s animals-.43“ * ”‘ Sandstone an a 9 an S a y‘to Rierdon Formation 9 §m - thin-bedded limestone h r 3 n 3’ Bmh°nian ‘2 2’3".” “1 c . Al,» . \K/‘g/K.’ . AL/LLN . my L.\/7L/v\.> 5 ae,gray 5% . a 8, WW. 2A Slltstone , leestone,sandy SSMOOih Formation .; leestone, sandy, : Limestone, sandy 5.. Slltv- Some 5 E and silty 5 c to silty, partly 57 ft (32 m) .2 thln-bedded. .9 to shah, my, _. sandstone E.— limestone, yello . g oolitic Lmestone, sandy. a“ pebbly. 3A 20 ft (6 in a: 25-58ft(7.5m) §w 45ft(l4rn) Pebbl atbase gs 23ft(7m) EE 3 _ “5 Dark shale and § E Dark shale \RK/v-y ”3:: .2 v Red silty shale. g g g. .5 c basal sandstone. r 0,8 and limestone 5“ Red shale, gypsum, h: Limestone at base 5 D- o o m Thlns south 35 ft (10 ml at: some limestone. g3: 15 ft (4.5 m) 3 5 °93 18—132ft VA /‘¢'\./'\.1/'\_/ Em Pebbly at base a"; Green to red __ it (55-40 9‘, \ 72 ll (22 m) 312m :2 n Member40-215ft 5” w" / \ - 'm . . é (12-63m)Shale J \A/VN" xv‘vp/‘J Batocwn ._ 2 Locally present ’— .2 h c 2 s .Nm .. 0 w .1 5 . 3 Poker Chip Shale D 100 ft (30 m) Toarcian — Paper shale , L overlaln ln ° places by E platy sandstone " ? o ‘- Red Deer Mernbe ‘3 § 3 l} (75"m) f is a a, at 2 L V l Pliensbachian g 0 _J F - Shale, llmy g 8 8—12 h (3.5 m) _. S Sinemurian — 5 Phosphate, g pebbl locally _, 2—14 4 m) Hettangian LL L L . , , \. ns/JKAL/‘NLA/‘u/Ke L\/\/l K/xmt/‘VK, AL/k/le/‘L/Kr W/ K/\/\ \ Underlylng beds Paleozoic Trlassu: Mississippian Pennsylvanian ”' ' ’rr' r Mississmplen Pennsylvanlan ‘Piper Formation divided into (ascending): Tampico Shale Member (Baioc'an), F‘remoon Limestone 'Nesson Formation of Nerdquist (1955) with Nordquisfs three members (ascendlnai. P09 EVIPOI'M Member (Baioc'enl,end Bows: Member (Bathoniln) of Nordquist (1955), all herein adopted for Member, Picard Shale “ L , and Kline “ ‘ .l'lerain ‘ ‘ (or us. r: ' ,' ' Survey U.S. Geological Survey usage. usage. A. Southwestern Alberta to central Montana. COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 69 Big Snowy Mountains 7 North side Button Butte, 8 Porcupine Dome, 9 Northeast Montana and10 Southwestern 11 Characteristic fossils near Heath and Piper, sec. 18, T. 14 N., R. 24 E.. sec. 26, T. 10 N., Fl. 39 E., northwestern North Dakota, Saskatchewanin In western Interror of 7 miles southeast of 32 miles east of 50 miles west-nonhwest in subsurface subsurface UnIted 5m” Lewistown, Mont. Lewistown, Mont. of Miles City, Mont. Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous Id / Morrison Formation Morrison Formation Morrison Formation 220ft(67 m) 220ft(61 m) 155ftl47 m) Mostly varicolored Varicolored shale Shale, gray 95 ft. shale. and thin beds Shale, varicolored 30 ft. Some gray to butt of sandstone Limestone 30 ft sandstone beds. I Coal beds at top. florihliggn Freshwater limestone Varicolored at base shale 7 7 7 ? A magma" 3mm“ stigma" Ind“ n1 1 rn m . . Sandstone, shalv to Mostly sandstone, Sandstone, glauconitic Swift Formation ‘Masefield N’\— 5"""a ”New” medium— bedded. thin-to medlum- ray 65 ft 230 ft (64 m) Shale glauoonitic. e . Iltstone, sandstone, SIltstone and 175400 (54_91 ml t base 6 ft of sandy, Some sandy shale and some shale sandstone, limy, Greenish— ray lower Cardiooeras spp. pebbly limestone ‘20 1“ glauconItIc, part calcaIgeou's - ' overlying shale Upper part becomes Card/oceras card/forms and IImestone a sandy southward Scarburg/ceras and 7 g Pavlov/cares ? 5 Ouensledtoceras collieri ‘3 ‘ W 3 at C (D > Rierdon Formation Rierdon Formation Rierdon Formation 152.370 «0(r4rBai-i102'rln) K9PP/9rl't95 madeaffll' G 90 ft (27 m) _ , 205 ft (62 m) 50-350 ft (15-105 ml Sham “my my , ”Phat” léilemorie' sang; .1921, ffi. Rzigrgtig IZ‘lTiIZ'IE’" ”mam“: °°""‘° Shale. gray. most ebbrés baéaly ' K' 3”" K‘ ”Chan's 2:55:- a 6 SI ty-san 95 ft thin-bedded. Iimy at top K. sub/'tus Shale and limestone 18 ft. ”wa/VV’ Shale. gray 120 it s ”’3" poart bweooénes ‘W Shale, soft, gray 10 ft erestone basally X: Warrenocerascodyanss G Sandstone K ‘ Bowes Memberl 50ft Ups , ryphaea c and sandy to E B°w°3 Member1 : (15 m) Red shale E S 7gfirm (23 m)Shale, Paracephalites Impresse .g silty shale ‘3; 2202111}??? "1) .9 passes westward into III'15 cuquina, lime- saMoothensls margmata «IE 43 ft 5'; E F e S a e a? sandy limestone g E stone, sandstone E8 Shale, limestone, .35 Firemoon Limestone Em Firemoon Limestone .2 a 83'3" 29mm or Sohlites, Parachondrooeras. 3' dolomite 95 ft Memberl 55 fl (17 m) 32 Member1 70ft (21 ml ‘0 Limestone, ”glam and Gryphaea p/anoconvexa 5‘ VNA fVNA/‘v ._ Limestone, oolitic gm Gypsum 17 ft 7 0-: hale, ray, Me asphaeroceras, Spiroceras, a“ Limestone and shale, .93 Tam Dim ShflleMembe Grevel- limyc Stemm‘atoceras ‘ N pebbly at base 65 fl em: 85 ft_(26 m) Red shale our pebb es 1basally Wondmceras a Iani VA~/\J\?1’\/\/ and GYPSUM (15m) and Stemmatoceres N PossIbly absent 140 ft ' c 5 Kline Member- 8': ft (94 m) 82 Dolomrte.LImestone 2'5 Picard Shale Member Watrous Formation(in part) u. Red shale 40 ft (12 m) (upger member) °°7nggmi ‘Mrrergregrgfo A h gaitmiited shale / K JpxxVA/Lé waxy/N ' EVVNA,’ 7 ? VN/‘N/‘VVNA JVNA/‘s/vNA/‘JVN/s/‘f \JA/‘JVN/x/ A/JV‘ Mississippian Pennsylvanlan Pennsylvanian Triassic Mississippian Triassic Mississippian B. Central Montana to southern Saskatchewan. FIGURE 25.——CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM SOUTHWESTERN ALBERTA THROUGH CENTRAL MONTANA TO SOUTHERN SASKATCHEWAN. Vertical lines indicate that strata are missing; diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column numbers refer to locations shown on figure 20. JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Ammon 0uad.,ldaho.12 - ' 13 - 14 Green RM?" LBRES. 15 Red Creek, 16 3 Wolverine Canyon,in secs. Red Mountainnldaho. "entry/“gr Emaagniles sac. 29' T' 39 N" R2108 W" NE% sec. 7, T. 6 N., R. 3 W., 50mm”! S'der . northwest and of w d n 5:; Stage vaugwgféel' :1 B'gfiégrf’dfin swv. sec. 33, T. 4 N., n.44 5., northeast of Mountains Sublene'goux' Fremont County Wyo , secs 1740 T 1 N R 40 E. Teton County Jackson,Wyo. Wyo. overlying beds Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous “é D 7 7 Tithonian L I) 5 J Probably absent Not identified Morrison Formation Morrison Formation 3 ' 370 ft (112 m) Varicolored to grey ,3 u Probably absent Varicolored shale. silty shale and 9 3. Contact shown Some beds of sandstone sandstone. Changes 3 g as a fault and dense limestone laterally into white ‘6 Kinmeridgian l-c— by Mansfield sandstone & g 1952, pl. 1) 3 3 5 E D J .zNN/Jx/Vm 7 ‘,' 7 . % GI - ~ Sandstone green ra , Redwater Shale Member OxfordIan 33 g reguggrgtzel sag-(fistone, glauoonitiozoo «(£1 ’Yfi)’ 5:31;, (srlty,gr;en to gray 148 fl (45 m) Sandstone, 5 o . , , 1 30 m). andstone, Iauoonite, some L" %. 5"‘5‘9'1: 9'3“??vi b£°tsgm°:° Bantonite green, ebbly at base. lgImestone, overlying g g E greenis ’9'“ (7 m) a “5" 48 ft (’63 m silty to sandy shale a ‘33. . c 5 r’N/vamwv E": 8 a. : «3 u n /Stump Sandstone \ an . E D Shale 65 ft (20 m). ‘0 F “"1999“ “we ‘5‘ % Sandstone 145 it (44 m) quanzIta 53 f‘ “5 m) Sandstone, silty, : (Lg Callovian .12 Preuss Sandstone 1043 ftl318m Preuss Sandstone .5 '99" 13- 5 L._f‘___/( (4 l") 9 ég 2 Sandstone, rod 600 ft (183 ml- 68 ft (21 m) Siltstone, 5 Siltstone, sandy, green 1; 7 3.. T Limestone, sandy 193 ft (59 m). red. IImy, above grey g ‘0 pink 2&5 fl (8m) E c: g Sandstone red 250 ft (76 m) sigma: C b '2? 8E (3 g , Giraffe Creek Member Ira reek Mern er _. ' 295 n so m) 26 n (5 5m 5?; Shale, g3”, “my 33 23:61:32}: ems" Member 20 n (s m) Leeds Creek Member Leeds Creek Member a; 63 fl ( m) 5: 230 h (70 ml |§tockade Beaver Shale , 1145ft(349m) 471M144m) ‘3, Kg: \ {Membersah(27m) N -‘-’ / 3 Limestone, oolitic : " Limestone dense to imestone oolitic and E YvéalttonifiCanyon Membe) ganga Crann)yon Mambo} 108 57 ft (17 m) ‘08 oolitic 20 ft (6 m) sand shale. 67 ft 21 m) " Bath ' - - g omen 2 Boundary Ridge Member 3 BoundaryRidge Member Mostly red siltstone. Sh l ed griffigrmfnon ° A87 n 557'“ b0 0 36 ft (11 m) Siltstone. Grey, shal limestone wafte('1r2m) Shale, red. Pebbly % E“ silo; $11133: vs E '9“ ‘° 9'99" at top. 38. (12 m) limestone lens at base E L I-‘E Rich Member 330 ft 3? Rich Member 208 ft Shfllv limestone Shale and limestone S. 353 (116 m) Limestone, shaly-ti: (62 m) shaly limestone gray. 85 ft (26 m‘) 33 ft (10.5 m) ‘31 5E Sliderock Member 140 ft 58 Sliderock Member Limestone, oolitic, Limestone, massive, . . __ c a, (33 m) Limestone, ca 59 fl (21 myLimegmne, medIum-beddad to dense, gray, glauconItIc E g massive at base 3" medium-bedded shaly 21 ft (7 m) 14 ft (4 m) g P- “ l- g Baiocian g m . prin Forrnet avgfirr‘la‘p'r‘rng Member Gypsum sering Formation Gypsum 3Ssiring Formation 25y: ft "(80 ml 9 (on .. L' 51 no | minated . h (14 "1 Z‘SfH 12 Gypsum, dolomitic limestone, me o . a , Gypsum s’pmg Member sInsIone, red 15 n. ed 8' 35‘0" and 3"“ and red shale 107 n. g ""V “"‘Y “"59' 12 ft (35 m) Limestone, brecciated 28 ft. Gypsum masses and some Gypsum mailsssitve 114 3 grlvuggy 23% “60 Limestone areccia Siltstone. red,soft 3 ft dense limestone stone 33m itst ne. r I hf“ ”VMNAFAVH’W/ x/x/\/\(\/~e/\/\./s\an /'\/‘ " 7 § 7 7 7 7 ' D Toarcian —— "3‘ _l a o. L3.— '3 PlIensbachIan g Nugget Sandstone1 g c 1000-1500 ft (305-457 m) i _J . 5 .. 5 § -‘ :3 7 7 7 ./J , Sinemurian ._ A/VNA/VNN/‘JVVA/‘VV \A/‘VVNA VNN/‘c/VNA/v r 5 Nugget Sandstonei Nugget Sandstone1 Nugg et SSandstone" gllugget Sandstone1 5 255—300 (I (73—92 m) (46 m) 300% (9 m) _J \ WV Hettangian b I“ Underlying beds Triassic Triassic Triassic Triassic Triassic ‘ln this author's opinion. A. Ammon area, Idaho, to Red Creek, Wyo. COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES ’ 71 S h of H H17 18 19 SEEast of Newoastle, 20 Minnekahte area out east yattvi e Mudd Creek area. I - ‘/ sec. 7.T. 45 N.. . . _ , 3V; miles,in sec. 16. secs. 2 and 11, T. 49 N., B“‘“,,§:Wg;‘g4fignm"“ R_ so W, Swy. sec. 23, “Cl 11. 33:3“ 34, Characteristic fossrls T. 49 N., R. as w., n. 83 W..Johnson County, o ok Conn, w' T. 43 N., n. 61 w., T- 7 5" R‘ 3 5" Fa“ “W I" W951“? Big Horn County,Wyo. Wyo. ro y, yo. Weston County-Wyo. County, S.Dak.. "“9"” region Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous 7 7 7 7 Morrison Formation Morrison Formation. Morrison Formation Morrison Format‘ Morrison Formation 180ft(55 m) 185M55 ml 100fll3° "0 1103(34 m) '0" 65-100ft(20—80 m) Mostly claystone, Claystone, greenish-gray. . greenish~grey to limy. Upper part: Th'" beds °f sandstone M°3“Y chi/31°“! grayish-red. Meny limestone beds. gray pebblylsandstone,d 913' £1133:sz QFEGNSN'QFBY Some beds of limestone A few sandstone beds rown con omerate,an In carbonacetgus shale varicolored claystone and sandstone Lower part: Varicolored shale 7 anddbrown to grey 7 ? W ' san stone ‘ . / ind Hill \ ’WindyHIllSandstoné indy Hill Sandstone Sandstoney Member ‘ _ .7 ? Member 30 ft (9 m) M ber 1-5 ft (ll/2m) __ 10-15 m34,5m) Buchla cancentnca gedv‘ilrgzegfiggle lVlem- Eeo‘uaterShaleMem- er m er 175 ft 53 m . _ ~ gissile day-fiche. . glostly sil shale. . 56:33:13???“ ml fimfi‘g :33“ Member Eflfiefrt (8:33:le carding,” spp. ome san °"° '" ome 33" stone in Mostly ray shale. Mostl ray shele.Some Mostly siltstone and Cerdioceras cordiforme “999' 41 fl “3 m) “We" 13 fl (4 m) Some [ignestone sandstyoge and limestone shele.Some limes-one , P . c .: : c c Scarburgrceras and av/owceres . g I??? g 3% lg Ouenstedtoceras collieri E... E E... pine Butte Member E Pine Butte em an EA ine Butte Member .25 8: 35 5ft(l.5m) £5 7ft(2ml BE 27ft(8m) 35 3B 3“ Lek Member 42ft 3“ L k 3“ c: c z: :" a Member75ft =:; Lk M b 60ft e 5" a (13m) Red siltstone e' (23m) Red siltstone or: a 9'" °' g; g: g: and sandstone 2E and sandstone §§ “8 m) Red beds um ulett Sandstone m3 Hu ett an stone (09 Huletl Sandstone can: Hu ett Sandstone tn Hulett Sandstone K I it . Member 27 ft (9 m) Member 62 ft (19 ml Member 82 ft 25 m) Member 71 ft (22 m) Member 32 ft 10 m) app 5’ es mac/9”” Stockade Beaver lStockade Beaver Shale Eockade Beaver hale Stockade Beaver Shale Stockade Beaver Shale . eff. K. tychanis Glyphs“. Shale Member 21 ft Member 23 ft (7 ml Member 90 ft (27 ml Member 63 ft (20 m) Member 48 ft (15 m) K. subitus "W' ' r ' \ anyon n s a h rt ebbl ‘ ‘ Canyons In 5 Ba / 8W0" 59""95 \JMM liwfigrm) 00 mo 1°" Meg‘brég' 2 R C trasa‘isandgiolr‘i‘e 31"“ M pt; 9°33an :nd4mone1Mm ' Warrinaceras \fT/‘v g‘Q/a V co ense Cryphaea Paracaphalites ”'7”,er sawtoothensis margmate Sohlires, Parechondraceres. and Gryphaea planaconvexa M as haeraceras,$ iroceris, 99 ered'sremmato p Chandroceras of: C. a/Iani and Stemmatoceras 7 if; #:215ng Formation gigspzugzsraglng Formation 6%;er airing Form etion Red shale, dolomitic Limestone and red shale ' s ’ limestone.and chart above limestone, Erfirfis‘gfli fiflmaaagiifid Fgrllj'rsigtgng—lzl‘gft (3.7 m) above massive gypsum breccia,and gypsum gypsum y g Gypsum, massive / f A/Tv‘fl ’\ JV /' \z ' J lfinnnn was ens Mn e Winn an Triassic Triassic Triassm Triassic Triassic B. Hyattville area in north-central Wyoming to Minnekahta area, South Dakota. FIGURE 26.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM SOUTHEASTERN IDAHO T0 SOUTHWESTERN SOUTH DAKOTA. Vertical lines indicate that strata are missing; diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column numbers refer to locations shown on figure 20. JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 21 B 2i k 23 H 24 25 / 26 __ urr or . Near Peoa and 0a ey, Duchesne River near Hanna, k Whiterooks Can on, g 3‘99 3%“2‘, I251. $532130; 1tN.. secs.‘lla:td1'_l4i'l:é 1 RS'ERE' 5 E.. 5?? vav 4139' and 10g. 1 3. secs. 1 anldaZfoqlflii, a.5w., seee.1a and 19.12117, 11. 1 5., . ., a un y, sec. , . .. ., . ., uchesne oun , "m h C , Utah Utah Summit County,Utah Utah 11! Duchesne County, Utah U1 a ounW Overlying beds Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous a D. o. D I _ .7 .7 ? Tithonian Not exposed 5 Not identified 3 3 g Morrison Formation Mogrgsan gormation 1 m E 440 (mu m) Variegated s - 'P :1 .. . andstone, siltstone, - - - -: 8. shale and white and shale. Mostly %%rias(ozr: go'nination 5 ' 3 ifel‘if‘r‘r’g‘l'rsififione “wish-Wm- Q . . . _ . 3Q Kimmeridgian 56 ? 83:: bzgilvalgzgsgged. Morrison Formation g Morrisoanormation p y Gray siltstonbeed, ssandstone, .1 102 fl3 (3 m) and ebblyb 5 d.beds Some algal 00" 0°Y exposeds a limestone. Conglomerate 3 at base 2 ? 7 7 7 Oxfordian B ' ' ‘ Redwater Member 5 g Redwater Member 2 Redwater Member g Redwater Membersh | g 113 ft (34 m) Limestone, T“ 3 ‘32 h (55 m) 0 137 ft (45 m) 5;, 98 ft (30 m) Gray 3° ,9 sandy.oolitic, glauconitic . o 3 Mostly gray shale. fg Mostly gray shale. Some .0 Some glauoonitic um Lower third mostly g 5 Some green sandstone 5 limestone and sandstone g sandstone 5 shale. Pebbles at base -| w m (a (n a; o a o g e 1% .._ (n “ - U) "‘ .9 Cums Mern er 41 "’ Cums Mem er 72 f1 Cums Member 32 f' ‘0 Curtis Member 55 h Callovian 3 En’ rada Sands—tone 5— PI’ 58 5‘0" . Pr 35 San stone reuss andst no 240 ft (73 m). Sandstone *6 1920 ft (311 m). Red, Silty. 1196“ 365 m")d RE esofl 669 ft (204 m). Red, silty, 858 ft (262 m). Red, soft crossbedded, fine-grained. g Limestone unit near base s1|ty,( evan- -bed 6 - ‘ r tomav _‘ Giraffe Creek Member Giraffe Creek E Giraffe Creek Member —— Giraffe Creek Member Siltstone, greenish- gray zooft(61m) Memberszrtgzs mi 0, 165ft(50 ml E 49ft(15m) 7611(23 rn) Leeds Creek Member ’E‘ Leeds Creek Member 3 Leeds Creek Member S Leeds Creek Member 5 vasurn- Red “1 9'99" A 1520 ft (464 m) ._ 776 ft (237 m) E 200 ft (85 m) E 114 (t (35 m) as? s1|tstone.191ft(58 ml E 'Watton Canyon 9 tt Watton Canyon W W tt c M E '/ Limestone, shal at \ -% Bathonian ,9 Member 348 ft (107 m) E ‘wzim °" “scam?" Mem’e' E Member 104 (1 (32 m) 3 was £73333!” “mm" 38. base. 17 11(5 mi U! a 5’, Boundary Ridge 01 Boundary Ridge Member G’ unda Rid 9 Member ° ~ __3: ' E; 5 Member 102 Mi" ml 8 107 ft (33 m) Limestone, 8 ft (21Wm) Rgd S og‘ngarvmgges 34:12:: E3 Eggdv'ffin‘igéfgm ea Yellow. siltY "‘ shaly to sandy. '05 siltstone and yellow. 5 m - In m 1» N . . . a: o o and sandy limestone 21 ft (6 m) .5 o or oolitic limestone 5 Some redbeds g sandy limestone E r, U E ,_ 5 Rich Member 391 ft 15 Rich Member 125 it '—| Rich Member 91 ft 3 Rich Member 109 ft Shaly limestone 8. g (119 m).Shaly limestone E (38 ml Shaly limestone E 28 m) Shaly Limestone § (33 m) Shaly limestone 40 ft 12 ml 3 E Sliderock Member ‘3 Sliderock Member 6 Sliderock M- _ 5 iderock Member ._( '_'i 150ft(46 m) Limestone, at 47 it (14 m) Limestone, : (13 m) Lime- 3 e c 32 fl “0 m) Limestone f, medium-bedded. E medium-bedded, '§ stone, sandy andstone 1; medium bedded, sandy g g iticb ally to s dyb lly l— 291: :bed d: Bajocian g \ o E E g i- — '- Gypsum Spring 5 glirmber 140flft (33 ml ‘tstone, so , E reddish-brown Gzypsu7rnm Spring Member 8 3 ? 7 Toarcian B / s O _l 8 G. D .2 —' 3 Pliensbaohian ._ E o 3 Nu et Sandstone1 Glen Canon Sandstonel Glen Canyon Sandstone1 Glen Canyon Sandstone1 Glen Canyon Sandstone‘ 2 E 8309g(253 3m 1290ft (3E4m) 2030ft( 66 "1) 1190ft(363m) 970ft(326ml § _l L 0 D. D. D Sinemurian __ 5 E _l Hettangian I'll ? Underlying beds Triassic Triassic Triassic Triassic Triassic ‘In this author's opinion. A. Burr Fork to Whiterocks Canyon, Utah. COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 73 - 29 30 31 cmg'Wfif‘Q‘fig' '4257 Milleggreek, Elk Creek area.SW‘/. sec. Frantl Creek“ Hahns Peak,NE% sec. 9, Characteristic fossils R. 23 E.. Uimair c'orinty." swv. sec. 27, fl 4 N., 33;; ‘45; 2884:1ng“ ng'zfiwjeg iflefifia T. 10 N., R. as w., in waste". 5" ' ‘ . . , . ., . ., _ ., r , ‘ - . . U‘thi. P'Pgagz) R- 10“ Wallégg?‘ County, Routt County, Colo. Colo. Routt County, Colo Interior region Cretaceous Cretaceous Cretaceous Cretaceous Cret -s M F at' lleegngso‘g 1Formation orrison orm Ion _ , 1 m 3350 —w0df;t(244 ml Monisciqaorrnation gag'g’fl: 1F; matron vaaiegatfid claystone ra sen one, . . 400 ft: m - ‘ an res water “#139“? “as“ ”°""°"‘°'"""“’" varieaarwbeds zmmmm- gmegtonemmwml s a e an san one, , an stone. r and some pebbly lenses limestone beds. 75 ft (23 m)9 ay ,_ ' - W‘ H“ Sandstone Windy Hill Sandstone Win Hill Sandstone Windy Hill Sandstone BUM/'5 cancentrica mmnflkscg'ifimifixm if MMdlyaerIB ft (2.4 \[ Member 9 ft (2.7 m) \/ ember 1ft \/ Member \ .9 “ '7 o E E 1 Cardiaceras spp. C ' . . t M bar " Hedwater Shale Card aceras card/forms ‘3 imigar mlem ‘2 E Member 179 ft (54 ml 3; A edwater Shale Men-5m ' , , 2 8g : a E ft (11 m) Scarburgicaras and Pavlowcaras a c . .- ‘3 fig E E 3 Ouenstedtoceras callieri A 41' E 3 . = - " E - ' Bun M be in HM Butte Mamba Pine Butte Member 0 Pine Button) In Pine e an r 5 12n(3.s m) r 3% 62ft(19m) 2?; Member 28fl(9 m) .‘1‘ aoms m) Entrada Sandstone E =3 LIN?) Member '5 137 ft (45 m) Entrada Sandstone ,2 we 47 f‘ 14 ml 6 Canyon Spfings Crossbedded, white 120 ft (36 m) E Canzon 50395 b EN 3:8 sandstone and g 33%??? Member ' . S stone em er. (I) , m . . Cagnafilomatlon Canmal Formation 8 133 n (50 m) Massive, Canyon Sprmgs E Massive, 9”! to Kepp/entes mac/earn: Gr haea Red beds soft ‘33? (991 M v E pink to grey. Chen 58mm“ MWW- 2 pink, lino rained. K a“ K who” ages 3_ C"°" ”5"” mm” 1 \i T T w pebbles basaw' ($35353er to § ‘7be“ ”3.5" ' K. .su'bitus gensis “'1 N1? 17 fi- ink. Chen pebbles ‘3 p ‘ K. cost/densus ‘ ”am/\‘flfi/ ”7-41 q\1 Warrenaceras codyens-eG h Urey /‘ 4‘s“ P‘fi T . ryp sea TE 7 W Paracephalites ”71pm”,— . mar inata sawtoothens/s g Sch/free, Parachondrooeras, and Gryphaea planocanvexa Megasphaemcara , Spiroceras, r a Chondroceras of. C. allani er s Glen Canyon Sandstone‘l Glen Canyon Sandstonel 670fl(204 m) MOft(256 m) ? I'll \i/LNL/KDALL-\(/LL,A~/\/Lrt/’\L~Vfik \ Triassic Triassic Triassic . Tr iassic-Perm ian Triassic B. Dinosaur Quarry, Utah, to Hahns Peak, Colo. FIGURE 27.—CORRELATIONS AND COMPARISONS OF J URASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM NORTH—CENTRAL UTAH TO NORTH—CENTRAL COLORADO. Vertical lines indicate that strata are missing; right-diagonal lines indicate strata not exposed; left-diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column numbers refer to locations shown on figure 20. JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 33 36 8 Monks Hollow, Ne hi-Levan area. Gunnison-Salina— Buckhorn Wash area, -5 Stage sec. 32, r. 4 s., R. 5 E., and west gide of Gunnison Richfield area. 800‘" °' Cedar M°“""‘" ELifé‘Er' 31-“??2'2 0, sec. 5, T. 5 s., R. 5 5., Plateau, Juab County, Savior and Sanpete 1" T- 19 3-: R ‘1 5., m‘g be m "u:' h " Utah County. Utah north-central Utah Counties, Utah Emery County, Utah mew u v. a Overlying beds Upper Cretaceous Cretaceous P Tertiary Tertiary Lower Cretaceous Lower Cretaceous ~\KF\ rhr 2 D. D 7 ? ? —d ' Tithonian g Mm’ifisogggrrnation 12 m . . " Yariegated shale Morrison? Formation 9A5%"f(s(’2t129F:?anon Morrison Formation .9 tnterbeddad wrth "“1 ft (259 ml Variegated mudstone. 600,“ ('83 m) ‘ g _ "1063”“ and sandy lnterbedded, gray to siltstone,and sandstone VP'WGIN“ "WWW“ g a shale and fed to grey white conglomerate siltstone and sandstone- g a sandmme and sandstone and . Becomes less sandy upward s Kimmeridgian 5-3- red to gray shale 3?,” some thin Massive gypsum at base a g s 01 limestone D. D 3 Some conglomeratic .5 sandstone at top a. :‘t‘ T ? ,7 ? ? Oxfordian 33 i B 3 o i L ‘ht brown siltstone g omt’ag gray sandstone and 3. shale 250 M761") mm s . . 2‘ unis Formation 260 ft (79 m) J r W} 1: Callovian 33 # A4 .’~‘.‘-- .5. Preuss Sandstone TWIst Gum: Mam er o Tw‘ Gulch ember ntra-a Sen-stone ntrada andstone _ 1270 24333:). Bdrown . E 1730 ft (528 m 425 ft (129 m). Red, earthy 405 ft (123 m). Red,earthy sven- san stone ' n ' g . Sandstone, shale.and w . 3 Glrafie Creek Member limestone 1500 _tt (457 ml g mmi'gofiisigg n Variegated shale and Red shale and Itmeaone 'o (823 m) Rad to gray sandstone. 50""9 . : Sandstone, silutone, Leeds Creek Member ”0 ft (228 m) 2 shale. salt at top 5 gypsum.182 ft (56 m) 3 and shale, rod 275 ft (84 mi Limestone, gray 800 ft < 35 S 125 h (38 m) Watton Canyon i A E i’Limestone, medium-\ ’ E? S_andstone and ' E? .g Whom Member 305 ft (93 m) g; 5; bedded. 100 ft (30 m) .2» limestone. 29 ft (9 m) ‘2 2 s h I “’ n Boundary Rid 6 ‘3 L' esto d t 5"— Sandy shale and -5~— andstone, 5 a ‘° 2 2 Member 57 ft 17 m) 2‘3 : oinlimc "Sign y 0 at ”Mm“, gray, s: thin-bedded.“ :: o . .— 0 . Y E . E a. mudstone ra to 5 ,5 Red stltstone above 8: ‘1' Some red siltstone. .§ rigpIe-marked a 0, ed S I z“ 2 a: silty-sandy limestone v 8 100 ft (30 m) on 4 ft (14) U N " - 0"‘9 '7“ °"°.' 1: E .. u, 105 ft (32 ml .13 3 E Rich Member 123 ft g m Limestone, shaly Limestone, sandy and 2 i .g N ' o 5 sandstone. 66 ft (20 m) a EE Sliderock Member 91 ft Ta g L(Eli‘es‘ona. medium- Page Sandstone P399 53””me . 3 u a: (28 m). Limestone, f, thlck;bedded, sandy, 100 ft (31 m) Mafia”, 30-35 ft (11 m). “an: —' ,g 3 thin to medium-bedded, c 5 oolmc. 50-80ft c: any. Chen °'°s’b°dd°d' 9"“ ‘ O E .. oolit' . nd all .2 g 15—24 -- mum at base Pabb'e' 3‘ hm _ - o. Bajocian E 3 E 2 . _ 5 Gypsum Sprin g - T Member 48 ft (115 m) E 0 Had to green siltstone :- g and brecciated or 3‘ _i laminated limestone i \37 ‘6 a. . S 7 Not ex sed Toarcian __ ' /‘\.. 9° 7 5 g Nugget Sandstone1 " 100 ft (30 n1) Navajo Sandstone1 Navajo Sandstone1 S Incomplete 380 ft (116 m) 520 ft (159 m) 3 i -% Pliensbachian h "‘ ° K nta Formation'l Ka enta Formation1 5 3 Nu et sandstone‘ aye Y a 3 1&9“ (442 m) 190 ft (88 ml 240 7! (103 m) ‘5 g L 3 a D. 3 Not exposed Win%ate Sandstone1 Win ate Sandstone‘ Sinemurian — 320 (98 m) 323 (99 m) § . _l Hettangian :7 IIIII ‘ Underlying beds Triassic Triassic Triassic Triassic ‘In this author's opinion. A. Monks Hollow to Black Dragon Canyon, Utah. COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 75 , 37 38 3 Slick Rock area, 40 41 s n f, I R. a, Dewey Bridge. “”9" °“°’"‘ Emma“? . secs. 13.25.32 and 36, McEImo Canyon area, Charmermk «mus 532s :Seandvlé sec. 3, T. 23 s., R. 24 E.. “35-139‘vend 33' T‘ 5‘5”" T. 44 N., n. 19 w., and 896-26136 N-v R- 13 w.. in western 1. 24's.’, r't. 16 E..' Grand CoumVIUtnh ‘T_ 50 fig. 133%,] sec. 30,_T. 44 N., R. 18 w., M°m°lugfoc°umv interior region Emery County. Utah ' Mesa County, COLO- San Miquel County.Colo. ' Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous ?' 7 7 ? ? Brushy Basin Shala . , Brushy Basin Shale Brushy Basin Shale Member Morrison Formation Member 333ftfi04m) Member 150—300 ft (91 ml 650 ft:(2o1 m) Mo’stl'y siltstone 350“ (110 m) . _ i i: an o aystone, : Vari' ated Morrison Formation Upper part: .9 soft, bentonitic. 9 b e ngnitic .5- \évamzatae fianygn 50°.“fl133 m) Variegated silty to s and variegated 5- mudstone as E 72 200°; 6 °"‘ °' Variegated shale, limy shale. Some g“ E E E " — ( 1 m) ssiltstonaaqd sandtstone. thin dense limestone (BE .2 v- “63. ome cong omera e. and chart ebble o 8 a Race ure Shel L.°°""V gypsum “db", conglomerates. §S Magnvggfg 33%;? é‘f Salt Wash Sandstone 5% Memg‘er e “manor“? 3‘ base "E c SandmnBIbdgv '5‘ Member 300 mm m) .95: 0—200 ft (61 m, I borer part: £5 browgmo pink, fig 3:333ng 28 ' - its to are cross- inter added with bedded san stone and soft siltstone 5?:YT:2?$:I 58:"th Sandstone red to gray claystona, and claystone 0—200 ft (61 m) Buchia concentrica 7 7 l ? z . Contact local ' . ontact sharp Contad gradational ontact discontormabl dis conform ab e an d Cardiacaras spp and irregular at most places ' most p 8°95 locally gradational Cardioceras cordiforme I Scerbur iceras and 7 ? 7 ‘ Egylgvtémg Summerville Formation ummerville Formatio Summervilla Formation si‘ffid'ggecieek Ouenstedmceras col/ieri 82ftl25 m) W 80fll24ml 109ftl33 m) 1 . . O 0 . A l k R k M b Cums Formation 75 ft 5 Mamba 51 ft (1 m) g Slick Rock Member w E Sandstone 31 ft E Sic foo” mean or g- m k & EA 225h.(69 m) 3 g m Slick Rock Member 2 n Sandstone, pink £31;th;t 183:5; 83'9"" : E Slick Rock Member = E Massive sandstone , gov-38 103 ft (31 ml 1. on brown, white mm» as": n (as m, ‘33 to W E2: mm as: a: '- 3- . "" a In . ‘- : . . ‘ v . 3 e (v) Dewey 3"ng ~ 2 ewe B d M ber - ' “9“ "“V “"dmne- 3‘ awglntlgmmw ‘35 Meflwzséifimr ‘0- JMember 32 n (10 m) (5%.. 30 fl (1:. ,3, 9° em Kemp/ems mac/earn! G h sandshaleland 50,3 Chm ebb.“ base" «5.. than ebb,“ bannyxx \MAHK-\/'\.’ \/\/\_, K. off. K. tychonls WP 898 ‘3 mudstone. Some A m p y )“Q 9 ,- A , , nabras- §—E~ gypsum 71 ft (22 m) \-— \/"\—/-‘-— -/"\/ V K. subrtus cons/1s K. costidensus E5 ‘ -'...e.,.,..,...wd,m.. 1'8: Sandstone, red to Gryphaee Ea ray, thin~bedded. Paracepha/ites Impress: ' .. - e limestone. sawtomhensis margmata 8 Chart pebbles locally at base. 58 ft (18 m) Sahlitas, Parachondrooeras, and Gryphaea planocan vexa ”9° Sandstone 5‘10 fl . , i M asphaarocaras,Sp/roceras, Chen pebbles at base . a ' Chondroceres cf. C. a/Iani and Stemmatoceras 2 L 7 J 7 7 "V/‘\V\/'\v)\/ L”K/‘\4_z"\_/‘\l/'\_/“\/ “NV/JV/l Navajo Sandstone1 Navajo Sandstone‘ Navajo Sandstone1 Navzzgo Sandstone1 Navajo Sandstonel 100 (lgtm 215ft(66m) o-soonnsam) 0—4 ftl128m) 300mm ml mcomp e Kayenta Formation1 Kwenta Formation 1 Kayanta Formation1 Kayenta Formation‘ subsurface only 320 n (98 m) 180-220 n (55 -70 m) 160—300 “ (49-92 m) 50 n (9 m) Not exposed WM?“ Sandstonel Wingate Sandstone1 Win ate Sandstone1 Wingate Sandstone‘ 300 (91 m) ' 280-300 R ( 86-91 m) 275 (84 ml 775— 90 ft (236—241 ml Triassic Triassic Triassic Triassic B. San Rafael River, Utah, to McElmo Canyon, Colo. FIGURE ~28.-CORRELATIONS AND COMPARISONS 0F J URASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM NORTH-CENTRAL UTAH T0 SOUTHWESTERN COLORADO. Vertical lines indicate that strata are missing; right-diagonal lines indicate strata not exposed; left—diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column numbers refer to locations shown on figure 20. 76 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES v, Guniock. 42 Danish Ranch-l 43 Cedgncaiiragiggs 7 44 Mount Carmel Junaion. 45 46 .3 Sta 9 near center Sec. 32. NEV. sec. 34, T. 40 S.. d 18 T 38y's Fl '11 W' secs. 12, 13, 24,3nd 25, Brown Canyon. 3 9 w 11‘4013" 2' 1AM”! an R. 14 w., Washington 1;” g1 'and 1;; 1' 37 s" T. 41 5.. n. 8W., secs. 7.19.3111: 21.1.41 5., as "19 0" 0“ Y- COUMY. Utah R. 11 W., iron County. Utaii Kane County,Utah R. 5 W., Kane Coumy,Uteh Overiying beds Cretaceous Cretaceous Cretaceous Cretaceous Cretaceous \A/‘vxmr‘v\A/v‘ym/‘J\q'\/\/\/\er\/‘r/\J NA/wNmA/V \A/va/NJv E: I) Tithonian "3 o —l .2 a ._ 3 3% i Kimmeridgian T a. 3 3 3 § 9 D .5 Oxfordian E .5. i o _.1 8 D. D 2 Callovian E -B_ /\ \{VKW/V\/\i{\/\/‘\AL/‘K/\JNWJVNAL/VK 3 ’ WM” Memb‘" Winsor Member w M b Insor em er .-1 émfigg‘gfim’ 180 11 (55 m) 581 111172 mi A . Sandstone, gray 50 ft. , Sandstone, gray at top, E mudstone, redd1sh- 1: Sandstone, red 130 ft. 5 red at base c m brown to pale green .9- 3E 9?: Gypsum and shaly \ 15 E /Gypsum and \ E'- Gypsum and Bathonian Em Iimestone.80—140ft(42m) E3 limestone 50 ft (16 m) 53 limestone 52 ft 16 m) ‘69 Banded member 3: Banded member 2:; Banded member 4 ’\ .~/ MAL/mg: 155-225ft(47—69m) 71‘: 17011152 m) ”8 14511144m) g .9 Red Siltstone and Bo Siltstone and sandstone, E 5 iSandstone and siltstone, Ea, Sandstone and siltstone. 3 “JV Q E sandstone 40 ft (12 m) gg red. Some gypsum 5 gray to redSome gypsum 8 Some gypsum g ._ W . N“ E Limestone member 8 é Limestone member U Limestone member Limestone member _, g Carmel Fonnatlon610fti186mi a 627 ft (191 m) 544 ft(166 m) 235 ft (72 m). Mostly 168 ft (52 m) 2 3- S.hale, red to gray135 (t. 3 Shale-limestone 110 ft 9— Thin— bedded to shaly oolitic limestone. Red Red siitstone in u _ Limestone, 0° "'0 60 it E' Shale, gray— ink 123 ft Siltv, or oolitic 483 f1. pebbly shale at base lower 20 ft 39 LImeStOne and shale 351 11- ' Limestone-s ale 253 ft. Gy sum and sandstone, 2 % Sandstone, SIIW. red 64 fl- (3 Siltstone, red 141 ft. gritty at be e 6 ft. Bejocian :9 2 . Temple Cap Sandstone Tern a Ca Sandstone Temple Ca Sandstone __ 372mgle1$apm Sandstone :31; (eggpwfiandstone $032 a?” m) 125 (38 1:).111135 fl £11115" dug? gray, * . . . ' e is rown, even- ray, crossbedded.‘ cross e e 7 . 8 Pink even bedded, stity. PM S'Wlsha'Vfiven'bedded bedded, gritty at base gsilty beds in basal 16 11 silty to shaly 28 ft 3 Some mudstqne and gypsum ' § 3 ? ? Toarcien _"__ 3 ‘3 Navajo Sandstone‘I Navajo Sandstone1 Navajo Sandstone‘ Navajo Sandstone“ . _l v 2200 11 671 m 1700 11 (518 mi Navajo Sendstone‘ . l l 2100ft (640m) 210011 (640m) 1900“ (500 m, 8 Q 1—.— .2 13— 2 ? 3 Pliensbachian K 1 F 1 1 Kayenta Formation1 K t F t' 1 g 5 even a orma ion even a orma ion Ka . 1 . 1 yenta Formation Kayenta Formation 3 E 1000 ft (305 m) 1000 fl1305m) 1175 ft 1358 m) 715 ft (218 m) 270 ft (82 m) 0 E _ 7 7 ? ? r 8 o Sinemurian D Moenave Formation1 Moenave Formation1 Moenave Forma’tion‘| Moenave Formation1 Moenave Formation'i 5 250fli76 m) 355fli108fni 510fii155mi 600f11183 m) 450ft(137m E _l Hmangian 7 III“ Underlying beds I Triassic Triassic Triassic Triassic Triassic ‘In this author's opinion. A. Gunlock to Brown Canyon, Utah. COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES 77 1.1111 Bull v I 47 Pine Creek! Sand Valley. 49 50 B' Hollow w h. 51 - 52 sec, 27°“; 3331m'3gs,’ swv. sec. 29 and say. sees. so and 34, T. 42 N., sw'/ 59539;, 41 N secs_7',°11,and 12,819}. 39' s. fmfliagit “5,9,3 W 3 ”“3 ... $13,953.33 ssgc'l'rfnfé "Eatiaéil‘é'ig‘e ' R59 El ' " “16§§'§"% 87°“: 9' Comm“ 9°“ sage (soukhane 6:33;", It)??? e, Garfield County, Utah ' Coconino County, Ariz. C°°°"l"° CWMY' A“?- Kafig Cotlntz‘ Utah mno County An: Cretaceous Lower Cretaceous Cretaceous Lower ?Cretaceous Lower? Cretaceous Cretaceous -q-/V\lf\/l¢\ WxA/VNT/VNA/flwa A/v'\_/\/\/ 7 Tithonian E Upper member ‘5, 116 (1 (35 ml E L: ? L 52 E .3 Salt Wash kd/‘F/‘PN / 1: 3 7 E figritstrgne‘lgsetmber 18%"fisgle ”(firmsnon -§: .33” WaSh Kimmeridgian 5A ' a one, Sandstone, gray to green. ‘6 Sandstone ’ E crossbedded g ‘Ew pebbly ’ abble’lafigsmw s. Member 353 ft ‘22 Lower W I A (111m) g: member 140 f! Lower Amber 2 E Sandstone.flat- 10 ft (3 m) bedded 7 \. ' Oxfordian Sandstone at Romana andstone at Romana S d r81831ft L, Mesa 115 ft (35 m) Mesa 44 ft (13 m) L an stone (314 m). 'Crossbedded, JvNWf . ’\ VV\/‘K - {RAKE/NR white 228ft Flat-bedded, Emrada Sandstone \ Entrada Sandstone Entrada Sandstone Entrada Sandstone Callowan ’ n '3 a 5" SW"? shal 434 n. Fa 445 ft (135 m). Gray, 640 ft (195 ml. White to 830 ft (253 m). Upper 773 n (235 m) 493 ft 150 )FI bedd V l m at- 9 thick beds 359 ff mostly crossbedded red, mostly crossbedded 537 ft flat-bedded Mostly CFOSSbedded Winsor Member Carmel Formation Carmel Formation Carmel Formation Carmel Formation Carmel Formation 673 ft (205 nj). Mostly upper member, 372 ft upper member 433 ft upper member 255 ft 205 ft (61 m) I' member sargflstone-sultstone; (134 m). Gypsum and (137 m). Flat-bedded red (77 m). Sandstone and ft (59 m) g ‘6 °f 'lmes'm‘e red to grey, sil shale and sandstone 166 ft siltstone, flat— bedded Sandstone and mudstone. '3" Wm— sandstone 278 f1 Crossbedded sandstone to crossbedded, pink CehngShlz’rbclw" tobgrav. E E I esteneAs “(14 ml Limestone, gray 94 53ftSame as top unit214ft t0 Gray 11 99 es 5‘ “59 Bathonian . ’\/\./' A/ 123 Tongue of Page Thousand Pockets Tongue Thousand P061915 Tongue W“ .59. Sandstone of Pa e Sandstone of Page Sandstone Page Sandstone Page Sandstone E4: 25 ft8 m) 72 ft 22 m), Red to gray, 1041t (31 m). Light 183 ft (56 m) 84 ft (25 m all; Banded member flat-to cross-bedded gray. Crossbedded Crossbedded, orange to Crossbedded Um _46 ft 14 m) Judd HollowTengue of Judd Hollow Tongue btr‘gwn'sllfid- Pebb'Y Limestone mem er Carmel Formation of Carmel Formation 3 35° 138 ft (42 m) Basal 74 ft (23 m). Sandstone, \ 40 ft (12 m! / 8 ft is red shale I ma lime one Harris Wash Ten "6 of garrissWagh Tonggeflof e Sandstone 2 ft age an stone Cross-bedded Chart "cm“bedded . . bl ‘ BBJOCIGI‘I ? 7 7 R 7 ./‘\/\a ”“VN Toarcian N3V3l° Sandstonel Navajo SBDdStOHB1 Navajo Sandstone1 Navajo Sandstone1 Navajo Sandstone.l Navajo Sandstone1 1400ftl427 m) 1250ftl384 m) 1650110500 m) 1600ftl488 m) 1165fll355 m) 1150 ftl350 m) , 1’ Pliensbachian enta Formation1 Kayenta Formation1 Ka enta Formation‘ Ka enta Formation1 Kayenta Formation1 Kayenta Formation1 396’ 6 6 ftl113 m) 370ft(113m) ‘I fl(50 ml / 7 ft(51 m) 350ft(107 m) 300ft(92m) 7 7 Moenave Moenave Formation1 Win ate SandstoneI MoenaverFormation1 Moenave Formation‘I Win ate Sandstone1 Form t' 1 Wind ate - . 480 a (146 m) 160% (49 m) 400 ft (122 m) 350 n (107 m) 290% (as m) a '0" g 1 5'"°"‘“""" 250 ft Sandstone (76 m) 50 ft (15 m) Hettangian 7 7 ? 7 Triassic Triassic Triassic Triassic Triassic Triassic B. Little Bull Valley, Utah, to Cow Springs, Ariz. FIGURE 29.—CORRELATIONS AND COMPARISONS OF J URASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM SOUTHWESTERN UTAH T0 NORTHEASTERN ARIZONA. Vertical lines indicate that strata are missing; wavy lines indicate unconformity or disconformity; jagged lines indicate gradational or indefinite contact. Column numbers refer to locations shown on figure 20. 78 dense dolomite. It is overlain gradationally by the Picard Shale Member, which is about 40 feet (12 m) thick and consists mostly of dark-red shale but contains some gyp- sum at its base. The Picard is overlain rather sharply by the Kline Member, which ranges from 80 to 190 feet (24 to 58 m) in thickness, consists generally of an upper dense dolomitic unit and a thicker lower limestone unit that locally is oolitic, and also contains some beds of fine- grained sandstone and green to purple shale. The upper contact of the Kline with the Piper Formation is sharp but concordant. The possibility of a disconformity at the top of Kline Member is suggested by the presence of chert pebbles at the top of the equivalent lower member of the Gravelbourg Formation in Saskatchewan (Milner and Blakslee, 1958, p. 71; Springer and others, 1966, p. 144; Milner and Thomas, 1954, p. 257). . The exact age of the N esson Formation is not known. An early Bajocian or older age was suggested by Nord- quist (1955, p. 105) on the basis of stratigraphic position. An Early Jurassic age was suggested by Pocock (1970, p. 15) on the basis of pollen studies of the partially equiv- alent lower member of the Gravelbourg Formation in southern Saskatchewan. For the same lower member, an early to middle Bajocian Age“ was suggested by Brooke and Braun (1972, p. 4). Apparently no evaluation has been made of the many fossils reported from the Kline Member by Nordquist (1955, p. 105). The pOSSibility ex- ists that the subsurface Kline Member of the Nesson Formation and the overlying Firemoon Limestone and Tampico Shale Members of the Piper Formation are the expanded basinward subsurface equivalents of the out- cropping middle member of Piper Formation in the Big Snowy Mountains, as proposed by J. A. Peterson (1957, p. 435). It is more probable, however, that the Nesson Formation is the time equivalent of the Gypsum Spring Formation of northern Wyoming (fig. 26), as originally defined by Love (1939, p. 42, 45; Love and others, 1945) and as proposed by Francis (1956, p. 22—26, 46, fig. 4). Correlation of the subsurface Nesson Formation with the Gypsum Spring Formation rather than with parts of the surface Piper Formation is favored by the greater stratigraphic and lithologic resemblances of members of the Nesson to the successive units of the Gypsum Spring Formation and by the fact that the upper limestone member of the N esson Formation is more dolomitic and much less fossiliferous than the middle limestone mem- ber of the Piper Formation. Also, the Gypsum Spring Formation extends northward into Montana unconform- ably beneath the Piper Formation along the flanks and northern ends of the Pryor and Bighorn Mountains. Recognition of the presence of the Gypsum Spring Formation beneath the Piper Formation was made pos- sible by joint field studies in 1964 and 1971 by G. N. Pi- piringos and the writer, who traced typical exposures of JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES the Gypsum Spring Formation northward from the Wind River Basin. These studies showed that the limy units in the Gypsum Spring Formation are commonly dolomitic, dense, white to light gray, are locally pinkish or green- ish, are nonoolitic, poorly fossiliferous, and contain blocky or banded chert in some beds. By contrast, the limy units in the Piper Formation are shaly to thin-bedded, com- monly oolitic, highly fossiliferous, do not contain chert, and are not dolomitic. Also, the base of the Piper For- mation at some localities contains small chert pebbles that are lithologically identical with the bedded chert in the Gypsum Spring Formation. Such pebbles were noted along the Pryor Mountains at the head of Gypsum Creek, at Red Dome, and at Grapevine Creek. Their strati- graphic occurrence should not be confused with that of much larger pebbles consisting of both chert and quartz- ite near the top of the limestone member of the Piper Formation in the Pryor Mountains (Imlay, 1956a, p. 572— 574). On the basis of the criteria cited, the thicknesses of the Piper and the underlying Gypsum Spring Formation have been determined for the area of the Pryor and Big- horn Mountains (table 1). Evidently, the Gypsum Spring is thinnest along the west side of the Pryor Mountains and thickens eastward from 17 feet (5 m) at Red Dome to about 150 feet (46 m) at the Montana-Wyoming State line on both sides of the Bighorn Mountains. Also, the Piper Formation is thickest on the west side of the Pryor Mountains and thins eastward from 163 feet (50 m) at Red Dome to about 55 feet (17 m) at the State line north of Cowley, Wyo., and to about 40 feet (12 m) at Lodge Grass Creek, near the State line on the east side of‘ the Bighorn Mountains. Lithologically, the thickest sequences of the Gypsum Spring Formation in the Pryor Mountains greatly resem- ‘ ble sequences typical of that formation in the Wind River Basin. At the base is a unit of massive gypsum and some red siltstone, or a unit of red siltstone that contains brec- ciated beds. Above this unit is one of soft red claystone. At the top is a unit consisting of interbedded gray lime- stone, white to light-gray dolomitic limestone, and some varicolored claystone. As the formation thins toward the west in the Pryor Mountains, the upper units disappear from the top downwards so that only the basal gypsifer— ous unit is present along the west side of the mountains. Evidently, the Gypsum Spring Formation was truncated by erosion before the Piper Formation was deposited. Similarly, the thickest sequences of the Piper For- mation in the Pryor Mountains contain all the units typi- cal of the Piper elsewhere in Montana. For example, at Red Dome in Carbon County, Mont., the formation con- sists of a basal red claystone about 24 feet (7 m) thick, overlain by interbedded, fossiliferous gray shale and limestone about 60 feet (18 m) thick, which is overlain by COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES TABLE L—Thickness of the Piper and underlying Gypsum Sprigg Formations in parts of north-central Wyoming and seat central Montana [3, indicates the presence of breccia instead of massive gypsum] Piper Formation Gypsum Location Spring Formation Thickness Feet Meters Thickness Feet Meters 1 Lodge Grass Creek, sec. 8, T. 9 S, R. E., Big Horn County, Mont ----------------------------- 43 2 Grapevine Creek, center sec. 6, 5., R. 31 E., Big Horn County, Mont --------------------- 20 6.1 130 39.5 3 Shively Dane, west-central part sec. 23, T. 5 S., R. 27 E., Big Horn County, Mont ———————————————— 66 20.1 (B) 53 4 Fivemile Creek, sec. 36 T. 5 S., R. 24 E., Carbon County, Mont ----------------------------- 90 27.4 (B) 46 5 Red Dome, west flank, sec. 19, T. 7 5., R. 24 E., Carbon County, Mont --------------------- 163 49.7 17 5.2 6 South of Bowler 1-1/2 mi, sec. 1, T. B S., R. 24 E., Carbon County, Mont -------------- 95 29.0 (B) 64 7 South side of Pryor Mountains, S-l/2 sec. 14, T. 9 5., R. 26 E., Carbon County, Mont ---------- 91 27.7 43 13.1 8 East side of Gypsum Creek, SE-1/4 sec. 33, T. 9 S., R. 27 E., Carbon County, Mont ---------- 64 19.5 107 32.6 9 East side of Red Gulch, sec. 22, T. 58 N., R. 89 N., Sheridan County, Hyo ---------------------- 46 14.0 150 (B)45.7 10 Hoif Creek, NH-1/4 sec. 9, T. 55 N., R. 86 N., Sheridan County, Hyo ---------------------- 5 1.5 (B) 143 11 Big Goose Creek, NE—1/4 sec. 2, T. 54 N., R. 86 N., Sheridan County, Hyo ---------------------- 5 1.5 (B) 142 12 LittTe Goose Creek, N-1/2 sec. 36, T. 54 N., R. 85 N., Sheridan County, Nyo ------------- 59 18.0 (B) 146 13 North side of Sykes Mtn., NE-1/4 sec. 12, T. 57 N., R 95 N., Big Horn County, Nyo ------ 86 26.2 164 50.0 14 Northwest end of Littie Sheep Mtn. NH-1/4 sec. 28, T. 56 N., R. 95 N., Big Horn County, Nyo--- 44 13.4 152 46.3 15 Northwest end of Spence Dome, north—centraT part sec. 6, T. 54 N., R. 94 N., Big Horn County, Hyo ---------------------- 36 16 Southeast end of Sheep Mtn., . east-centraT part sec. 16, T. 13.1 (B) 120 (B) 36.6 (B) 19.5 210 64.0 53 N., R. 93 N., Big Horn Count . Hyo ---------------------- 44 13.4 110 33.5 17 About mi north-northwest of Shell, south-centraT sec. 21 and north-central sec. 28, 54 N. R. 91 N., Big Horn County, Hyo ---------------------- 34 18 About 8 mi south of Shell, east-central part sec. 3, T. 51 R. 91 N., Big Horn County. My 0 ------------------------------ 22 19 About 9 mi north- northwest of Hyattvilie, SH-1/4 sec. 21, T. 51 N., R. 90 N., Big Horn County, Hyo ---------------------- 30 9.1 20 2 mi northeast of Hyattville, centrai sec. 29, T. 50 N., R. 89 E., Big Horn County, Nyo ---------------------- 11 3.4 174 53.0 21 1 mi north of mouth of . Ciarks Fork Canyon, sec. 5, T 10.4 162 49.4 6.7 216 65.8 192 58.5 56 N, R. 103 N., Park County. Hyo ------------------------------ 223 68.0 0 0 22 Trail Creek, about 8 mi northwest of Cody, center sec. 12, T. 53 N., R. 103 N., Park County, Hyo ---------------------- 206 62.8 0 0 79 TABLE 1.—Thickness of the Piper and underlying Gypsum Spring Formations in parts of north-central Wyoming and south-central Montana—Continued Piper , Gypsum Location Formation Spring Formation Thickness Thickness Feet Meters Feet Meters 23 Shoshone Canyon 2 mi west of Cody, NE-1/4 sec. 4, T. 52 N , R. 102 N., Park County, Hyo ------------------------------ 196(8) 59.7 0 0 24 Six miles south of Cody aiong line between secs. 5 and 6, T. 51 o.,N R. 101 N., Park County, ------------------------------ 277 84.4 0 0 25 Red0 Creek, SE- 1/4 sec. 6, T. 6 N., R. 3 N., Fremont County, Nyo ------------------------------ 40 12.2 220 67.1 26 Mavericks Spring anticline, secs., 23 and 26, T. 6 N., R. 2 N., Fremont County, Hyo ---------- 20 6.1 173? 52.7? 27 Tributary to East Fork of Sheep Creek, SH-1/4 sec. 2 to NN-1/4 sec. 11, T. 6 N., R. 2 E., Fremont Count , Hyo -------------- 10 3.0 165 50.3 28 Bu11 Lake, SEX/4 sec. 36, T. 3 N., R. 4 N., Fremont County, Hyo— 9 2.7 196 59.7 29 SweCmfl mfich,SDU4sa. 16, T. 1 N., R. 1 N., Fremont County, Hyo ---------------------- 13 4.0 121 36.9 30 Mill Creek, NH-1/4 sec. 5, T. 2 5., R. 1 N., Fremont County, ’ Hyo ------------------------------ 12 3.7 212? 64.67 77 feet (23 m) of brownish-red claystone and siltstone that contains some thin layers of gypsum. As the forma- tion thins toward the east, the units disappear from the base upwards, and at the State line east of the Bighorn Mountains, only the highest redbed unit is present. ' Thus, the Piper Formation overlaps eastward and south- eastward over the Gypsum Spring Formation. The Piper Formation consists of three members, is more widely distributed in the subsurface than is the N esson Formation, and crops out at many places in north-central, central, and southern Montana. The 01-d- est, or Tampico Shale Member (Nordquist, 1955, p. 101), is about 85 feet (26 m) thick in the subsurface and as much as 100 feet (30.5 m) thick on the surface. It consists mostly of red shale but includes some green to gray shale and siltstone, some thin beds of red to white sandstone, and some gray to brown dolomite and dolomitic lime- stone, and in places its lower part bears thick masses of gypsum (Imlay, Gardner, and others, 1948). It is overlain by the middle, or Firemoon Limestone , Member (Nordquist, 1955, p. 101), whose thickness av- erages about 75 feet (23 m) in the subsurface and ranges from 15 to more than 100 feet (4.5 to 30.5 m) on the sur- face. It consists mostly of gray shale and limestone, which may be shaly, oolitic, dense, or dolomitic. Its boundaries with adjoining members are transitional within narrow intervals (Imlay, Gardner, and others, 1948b; Sandberg, 1959). 80 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES The youngest, or Bowes Member, of the Piper For- mation (Nordquist, 1955, p. 102) averages about 50 feet (15 m) in thickness in the Williston basin and from 20 to 130 feet (6 to 40 m) in thickness in outcrops. It consists mostly of red to varicolored shale and siltstone in the subsurface east of the Big Snowy and Bearpaw Moun- tains, as well as on the surface in southern Montana as far west as the Gallatin Range north of Yellowstone N a- tional Park. It passes westward and northward in Mon- tana into yellowish silty to sandy limestone and calcar- eous sandstone that characterize the upper member of the Sawtooth Formation in western and north-central Montana. Northward from the Williston basin, the Piper For- mation continues into southern Saskatchewan, Where its Tampico Shale Member passes into gray calcareous shale at the top of the Gravelbourg Formation, its Firemoon Limestone Member passes into the nearly identical lower member of the Shaunavon Formation, and its Bowes Member passes into shale, limestone, and sandstone in the upper member of the Shaunavon Formation (Chris— topher, 1964, p. 16; Brooke and Braun, 1972, p. 4; Milner and Thomas, 1954, p. 258—262). The middle limestone member of the Piper Forma- tion is dated as late Bajocian because in both the surface and subsurface in Montana it contains certain mollusks (Hearn and others, 1964, p. B8; Imlay, 1967b, p. 33—35) that also characterize the upper Bajocian Rich Member of the Twin Creek Limestone (Imlay, 1967b, p. 31, 32). These include particularly the ammonites Sohlites and Parachondroceras and the pelecypods Gryphaea plana- convexa Whitfield and Gemillia? montanaensis Meek. Dating the Rich Member as latest Bajocian is based on its gradational relationship with the underlying Slide- rock Member, whose upper half contains the ammonites M egasphae’rocems, Spiroceras, Stemmatocems, Ste- phanocems, and questionable Normannites. These in as— sociation can only be of early late Bajocian Age (Imlay, 1967b, p. 26, 27; 1973, p. 29, 34). Elsewhere, the mollusks that characterize the mid- dle limestone member of the Piper Formation are widely distributed. They occur in the middle of the Sawtooth Formation south of Belt Island in Gallatin and Madison Counties, southwestern Montana (Imlay, 1967b, p. 33, 34, 65). They occur throughout 27 feet (8 m)‘0f black limestone and shale in the middle of the Sawtooth For- mation exposed on East Butte in the Sweet Grass Hills, Liberty County, Mont. They occur in the lower mem- ber of the Shaunavon Formation in southern Saskatche- wan (Paterson, 1968, p. 15, 16) along with the coral Ac— tinastrea cf. A. hyatti (Wells) (Wells, 1942, p. 2, pl. 2, figs. la—c, 2a, b). That coral is Widespread in the middle limestone member of the Piper Formation in southern Montana, in the middle limestone member of the Saw— tooth Formation in southwestern Montana, in the middle limestone member of the Sawtooth Formation in the Bearpaw Mountains, and in equivalent limestone beds in the northern part of the Bighorn Basin (Imlay, 1956a, p. 567, 568, 577). Dating the middle limestone member of the Piper Formation as latest Bajocian means that the upper mem- ber must be of Bathonian Age and that the lower mem- ber must be at least in part of early late Bajocian Age, equivalent to the ammonite-bearing upper part of the Sliderock Member of the Twin Creek Limestone. This dating for these three members holds also for the three members of the Sawtooth Formation in southwestern Montana. However, the basal part of the lower member of the Piper Formation may be as old as the late middle Bajocian (Stephanoceras humphm'esianum zone) be- cause ammonites of that age occur near the base of the Sawtooth Formation (Imlay, 1967b, p. 50, 91—94) in northwestern Montana, because the lower part of the Sliderock Member could be of that age, and because ma- rine invasion from the west probably took place at about the same time in eastern Idaho as in western Montana. Nonetheless, it is doubtful whether marine waters older than latest Bajocian ever crossed the Sweetgrass arch or Belt Island, because the members of the Sawtooth For- mation thin considerably where they cross the arch (Cob- ban, 1945, p. 1271; Weir, 1949, p. 551, 552) and because the middle member of the Sawtooth Formation on East Butte in the Sweet Grass Hills correlates faunally with the upper Bajocian Rich Member of the Twin Creek Limestone (Imlay, 1967b, p. 35). A The Sawtooth Formation, in western and north-cen- tral Montana, is 230 feet (70 m) or less in thickness, con— sists of normal marine shale, sandstone, and limestone, and passes eastward gradually into the Piper Formation. Most of the gradation is near a line drawn northward from the northwest corner of Yellowstone National Park, although in north—central Montana the upper member of the Sawtooth Formation is represented by sandstone and silty limestone as far east as the‘Bearpaw Mountains in south-central Blaine County. In northwestern Montana, north of Belt Island, the westernmost exposures of the Sawtooth Formation con- sist typically of a thin lower sandstone member, a middle shale member, and an upper calcareous siltstone-sand— stone member. The lower sandstone member ranges from 8 to 30 feet (2.4 to 9 m) in thickness, is ripple marked, and locally bears a basal conglomerate. The middle shale member thickens northward from about 18 feet (5 m) at the Sun River to about 170 feet (52 m) near Glacier National Park and consists mostly of poorly fos- siliferous gray to black shale that contains lenses and nodules of phosphate throughout and some glauconitic sandstone at its base. The upper member thickens north— COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES ward from 25 to 65 feet (7.6 to 20 m) and consists of gray to yellowish—gray siltstone, sandstone, and silty to sandy limestone. All these members thin eastward and locally pinch out on the Sweetgrass arch. East of the arch, the middle member passes into highly fossiliferous black thin- to thick-bedded limestone typical of the middle member of the Piper Formation. The upper boundary of the Sawtooth Formation with the Rierdon Formation is sharp but apparently not disconformable except possibly on the Sweetgrass arch, where the top of the Sawtooth Formation bears chert pebbles and broken and worn be- lemnite guards (Cobban 1945, p. 1273; Weir, 1949, p. 551). The Sawtooth Formation in southwestern Montana west of the Gallatin Range is also represented by three members which are well exemplified by the sequence on Indian Creek in the Madison Range (Imlay, Gardner, and others, 1948). At that place, the lower member rests on Triassic sandstone, is 79 feet (24 m) thick, and consists of interbedded green to brown siltstone and mudstone. The middle member is 67 feet (20.4 m) thick, consists of light-gray thin— to thick-bedded limestone and contains Gryphaea planoconvexa Whitfield. The upper member is 84 feet (25.6 m) thick and consists of interbedded papery siltstone, sandy siltstone, thin- to medium-bedded sand- stone and thin- to thick-bedded sandy limestone. The siltstones are greenish gray to greenish brown, and the other rock types are gray to brown. This sequence con- trasts with those in the Gallatin Range to the east, be- cause it has no red beds in its upper and lower members (Imlay, Gardner, and others, 1948; Ruppel, 1972, p. A25; Moritz, 1951; Scholten and others, 1955, p. 367, 395, 396). The westernmost sequence of the Sawtooth Forma- tion in Montana, exposed in Little Water Canyon in the NE%SW% sec. 10, T. 13 S., R. 10 W., Beaverhead County, is also divisible into three members. The lower member consists of 58 feet (17.7 m) of gray sandstone and sandy limestone that bears oysters and Campto- nectes. The middle member consists of 120 feet (36.5 m) of fossiliferous gray calcareous shale and ‘shaly lime- stone. The upper member consists of 14 feet (4.2 m) of interbedded oolitic limestone, fissile shale, and sand- stone. Throughout southern Montana, exposures of the highest parts of the Sawtooth and the Piper Formations are overlain abruptly by an oolitic limestone bed at the base of the Rierdon Formation. The base of the Sawtooth Formation in northwestern Montana is dated as late middle Bajocian (Imlay, Gard- ner, and others, 1948; Imlay, 1948, p. 19, pl. 5, figs. 1— 5; 1967b, p. 35, 90, 93, pl. 6, figs. 1-3, 7, 8) because of the presence of Chondroce’ras in close association with Stemmatoceras. The upper member is dated as early to middle Bathonian on the basis of the resemblance of the 81 ammonite Paracephalites (Frebold, 1963, p. 5, 8—13, 27—29) to Arctocephalites and Cranocephalites of the arctic region. The middle shale member in the Sweet Grass Hills is dated as late Bajocian because it contains a pelecypod fauna identical with that in the Rich Member of the Twin Creek Limestone and the Firemoon Lime- stone Member of the Piper Formation (Imlay, 1967b, p. 35). The Sawtooth Formation in southwestern Montana is dated only by the presence of the ammonites Sohlites and Parachondroceras in its middle member. Those am- monites in the Twin Creek Limestone are dated as latest Bajocian because they occur just above beds containing an association of Stemmatocems, Spirocems, and Me- gasphaeroce’ras (Imlay, 1967b, p. 26, 27, 31). The Rierdon Formation occurs widely throughout Montana and North Dakota except in the area of Belt Island, ranges in thickness from a featheredge to 180 feet (55 m) on the surface and to about 350 feet (107 m) in the subsurface, and consists mostly of calcareous gray shale and shaly to thin-bedded limestone. Shale predom- inates over limestone except in the Little Rocky Moun- tains and in the subsurface of south-central Montana. Some silty to sandy beds occur locally near the base of the formation near Belt Island. The basal unit in south— ernmost Montana from the Pryor Mountains westward consists of oolitic limestone that ranges from a few inches to about 30 feet (9 m) in thickness and represents the northern edge of the Canyon Springs Sandstone Member of the Sundance Formation. At the top of the Rierdon Formation in south-central Montana is an oolitic to sandy limestone that represents the northern extension of the Hulett Sandstone member of the Sundance Formation (Cobban, 1945, p. 1279, 1280; Imlay, 1945, p. 255; 1956a, p. 585—587; Imlay, Gardner, and others, 1948; J. A. Peterson, 1957, p. 408, 409; Richards, 1955, p. 40, 41). This limestone passes northward into chalky limestone at the top of the Rierdon Formation. The Rierdon Formation extends from the Williston basin into southern Saskatchewan, where its upper part gradually becomes sandy to the north and northwest. In the subsurface of southern Saskatchewan, beds equiva- lent to this sandy upper part are called the Roseray For- mation, which is much less extensive than the overlying and underlying subsurface formations. The Roseray con- sists mostly of even-bedded fine-grained sandstone but has some shaly beds near its tip and bottom (Christo- pher, 1974, p. 4, 8, 9, 13, 14, 49, 101). In those shaly beds are Foraminifera and ostracodes suggestive of ages intermediate between those of the Rierdon and Swift Formations of Montana (Brooke and Braun, 1972, p. 8, 13, 20, pls. 23, 24). The age of the Rierdon Formation in Montana has ‘ previously been considered as early Callovian (Imlay, 82 Gardner, and others, 1948; Imlay, 1948, p. 14—16; 1953a, p. 5—8; 1967b, p. 60). However, the lowermost part of the formation, which is characterized by Warren- oceras (formerly called Arcticocems), should be of late middle to early late Bathonian Age on the basis of the close resemblance of Warrenoceras to Arcticoceras; the latter genus in East Greenland occurs below ammonites characteristic of the earliest Callovian Macrocephalites macrocephalus zone of Europe, according to Callomon (1959) and Birkelund and others (1971, p. 254). Also, most of the overlying beds, characterized by Kepplerites costidensus (Imlay), K. subitus Imlay, and K. aff. K. tychom‘s (Ravn), should be of latest Bathonian Age on the basis of comparisons with East Greenland. Only the uppermost part of the Rierdon Formation, characterized by Kepplerites maclearni Imlay in association with Lil- loettia and Xenocephalites, is definitely early Callovian. The age of the Rierdon Formation in southern Sas- katchewan is apparently the same near its top as that of 'the Rierdon Formation of Montana, as shown by the presence of certain species of Kepplerites (Frebold, 1963, p. 23-26, pl. 10, fig. 3, pl. 12, fig. 1; Paterson, 1968, p. 35, 36, pl. 8, pl. 9, figs. 1—3). The Swift Formation is more widespread than the underlying Jurassic formations. It ranges in thickness from a few feet to about 165 feet (50 m) in outcrops, and to more than 400 feet (122 m) in the subsurface. It con- sists of glauconitic sandstone, siltstone, and shale, and in surface sequences generally has a basal conglomerate. In the Sawtooth Range of northwestern Montana, the Swift is divisible into two transitional members. The upper member consists of thin-bedded, ripple—marked sand- stone that contains partings of dark micaceous shale. The lower member consists of dark fissile micaceous noncal- careous shale. To the east, one or both members locally pinch out on the Sweetgrass arch but reappear farther east and gradually become much shalier eastward (Cob- ban, 1945, p. 1281—1286). By contrast, the Swift Formation in southwestern, southern, and central Montana consists mainly of me- dium— to thick-bedded, glauconitic ripple-marked sand- stone that persists as far east as the Big Snowy Moun- tains and the western part of the Pryor Mountains. Shale appears in these mountains at or near the base of the formation and gradually thickens eastward as the over- lying sandstone thins (Imlay, Gardner, and others, 1948; Imlay, 1956a, p. 598, fig. 2 on p. 566; Moritz, 1951, p.‘ 1804—1810). The age of the basal beds of the Swift Formation var- ies considerably from place to place. In the Bearpaw and Little Rocky Mountains, the basal beds contain Quen- stedtocems (Lamberticeras) collieri Reeside, which by comparison with Europe should represent the latest Cal- lovian. Directly above in the lower part of the formation JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES is shale containing Cardioceras and Q. (Pavlovicems) of early Oxfordian Age. By contrast, in the Sawtooth Range of northwestern Montana, one specimen of Buchia con- centn‘ca (Sowerby) (USGS Mesozoic 10c. 27058) of late Oxfordian Age was obtained from the base of the Swift Formation at the south end of Diversion Ridge south of the Sun River (NW%SW¥; sec. 12, T. 21 N., R. 9 W., Sawtooth Ridge Quad) The same species was also ob- tained from sandy shale above a thick sandstone ledge in the upper part of the lower member of the Swift Forma- tion on the north side of the Great Northern Railway about 3 miles (4.8 km) southwest of Marias Pass (Imlay, 1956a, p. 595). The age of the upper part of the Swift Formation is uncertain because that part has not furnished any diag- nostic fossils. It should be late Oxfordian to possibly early Kimmeridgian on the basis of its stratigraphic po- sition. The Morrison Formation in Montana rests conform- ably on the Swift Formation; ranges in thickness from 250 to 400 feet (76 to 122 m); thins northward and disap- pears near the U.S.-Canadian border; consists mostly of clay shale, mudstone, dense limestone, and fine-grained sandstone; and at its top contains coal beds or carbona- ceous beds (Cobban, 1945, p. 1268; Reeside, 1952, p. 25; Gardner and others, 1945; Hadley and others, 1945). The lowermost part of the Morrison Formation in western Montana should be of Kimmeridgian Age, as shown by the presence of the late Oxfordian to early Kimmeridgian Buchia concentrica (Sowerby) in the lower member of the underlying Swift Formation. SOUTHEASTERN IDAHO TO WESTERN SOUTH DAKOTA Marine Jurassic sequences in Wyoming and adjoin- ing parts of Idaho and South Dakota (fig. 26) closely/re- semble the equivalent marine sequences in Montana and North Dakota at their top and bottom. At the top of the Jurassic, the Stump Sandstone, as exposed along the Idaho-Wyoming border, resembles the Swift Formation of western Montana and likewise passes eastward into shale (Redwater Shale Member of the Sundance Forma- tion) that becomes shalier from the base upward and is predominantly shale east of the center of the Bighorn Basin. At the bottom of the Jurassic, the Gypsum Spring Formation (or Member of the Twin Creek Limestone), resembles the Nesson Formation of the Williston Basin. The lithologic units between the Stump and the Gypsum Spring show some resemblances to the units between the Swift and N esson Formations but also show many differ- ences. \ The Gypsum Spring Formation, as originally defined by Love (1939, p. 42—46; Love and others, 1945), crops out in the northwestern part of the Wind River Basin COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES west of long 108" W., in the Teton and Gros Ventre areas of northwestern Wyoming, along the east and west sides of the Bighorn Mountains, in the northwestern part of the Black Hills in eastern Wyoming and western South Dakota, and around the northern parts of the Bighorn and Pryor Mountains in south-central Montana. Also, the equivalent Gypsum Spring Member of the Twin Creek Limestone occurs near the Wyoming-Idaho border and in north-central Utah. In the Wind River Basin, the Gypsum Spring For- mation ranges in thickness from 250 feet (76 m) to a featheredge and consists of three lithologic units. At the base is 20 to 40 feet (6—12 m) of red, slightly sandy silt- stone that is overlain by 13—95 feet (4-30 m) of massive white gypsum. At the top is 65—135 feet (20—41 m) feet of interbedded red siltstone, red claystone, slabby lime- stone, ribboned chert-bearing dolomite or dolomitic lime- stone, and some gypsum (Love and others, 1945; Love and others, 1947; Pipiringos, 1968, p. D18). The Gyp- sum Spring Formation rests unconformably on the Nug- get Sandstone and is overlain unconformably by the Piper Formation or by sandy oolitic beds at the base of the Sundance Formation. In northwestern Wyoming east of the belt of thrust faulting, the Gypsum Spring Formation is essentially the same as in the Wind River Basin except that the massive gypsum is locally replaced on the surface by a brecciated unit consisting of red siltstone and limestone. Here, as in the Wind River Basin, the formation is underlain uncon- formably by the Nugget Sandstone and overlain uncon- formably by normal marine limestone equivalent to the Piper Formation of Montana and north-central Wyoming (Imlay, 1956b, p. 70; 1967b, p. 6, 7, 19; Foster, 1947, p. 1566; Wanless and others, 1955; Love and others, 1973). Along the Idaho-Wyoming line and in north-central Utah, the Gypsum Spring member of the Twin Creek " Limestone thickens westward from 12 to 400 feet (3.6 to 122 m) and consists mostly of soft red to yellow clay- stone and siltstone that is interbedded with brecciated or vuggy limestone, or with chert-bearing limestone. The chert-bearing limestone thickens westward from a few feet to 70 feet (21 m). The brecciated limestone marks the position of thick masses of gypsum that are exposed about 32 miles (51 km) south-southeast of Jackson, Wyo. (Imlay, 1967b, p. 3, 17—19). Both lower and upper con— tacts of the member are sharp and presumably uncon- formable. The Gypsum Spring Formation exposed along the flanks of the Bighorn Mountains and at the south end of the Bighorn Basin is similar lithologically to the forma- tion in the Wind River Basin. Along the western flank of the mountains, the lower part of the formation consists of 25—100 feet (7.6-30.5 m) of massive white gypsum interbedded with some dark-red claystone, red siltstone, 83 and gray limestone and overlain by 20—40 feet (6—12 m) of dark-red claystone containing nodules and lenses of gypsum (Imlay, 1956a, p. 578). Along the eastern flank of the mountains, the lower 40—70 feet (12—21 m) or more of the formation at more places consists of dark-red claystone and siltstone whose basal 10—50 feet (3—15 m) contains some thin beds of gypsum, and some units of limestone breccia. At a few places, however, the basal beds consist of gypsum masses as much as 50 feet (15 m) thick (Hose, 1955, p. 52—54, 106, 107; Mapel, 1959, p. 28—32, pl. 5). Along both‘ flanks of the Bighorn Mountains, the up- per part of the Gypsum Spring Formation consists mostly of 70—110 feet (21—33.5 m) of alternating units of lime- stone and dark-red claystone. The lower limestone unit consists mostly of gray, dense, shaly to thin-bedded lime- stone, is locally dolomitic, locally contains blocky chert, and in some beds contains external molds of tiny gastro- pods. The middle limestone unit is similar, but some beds are mottled pink to light green, and some bear many poorly preserved molds of pelecypods. The upper lime- stone unit is white, dense, and partly dolomitic, contains many beds and lenses of blocky chert, and forms a prom- inent ledge. Above these limestone units on both flanks of the Bighorn Mountains is 10—50 feet (3—15 m) or more of dark-red to pale-green siltstone and claystone (Imlay, 1956a, p. 578, Mapel, 1959, p. 29). These beds could rep- resent the uppermost part of the Gypsum Spring For- mation, but they are herein considered to represent the southern pinch-out of the upper red-bed member of the Piper Formation. The Gypsum Spring Formation pinches out south: ward along the flanks of the Bighorn Mountains. It rests sharply and unconformably on the Triassic part of the Chugwater Formation (Hose, 1955, p. 53; Mapel, 1959, p. 29; Imlay, 1956a, p. 579). The Gypsum Spring is overlain with angular unconformity by the lower part of the Sundance Formation south of a line extending north- east from Hyattville to Banner, Wyo. North of that line, it is overlain sharply by red claystone, herein assigned to the Piper Formation, which in turn is overlain sharply by gray sandstone or calcareous shale at the base of the Sundance Formation. In the Black Hills area, the Gypsum Spring Forma- tion is exposed only in the northwestern and northern parts, where it ranges in thickness from a featheredge to 125 feet; it attains its greatest thickness 10 miles north- east of Hulett, Wyo. At that place, its lowermost 75 feet (23 m) consists of massive gypsum and red claystone that rests sharply on the Triassic part of the Spearfish For- mation. Its uppermost 50 feet (15 m) consists of interbed- ded limestone and red to gray claystone. . Its upper con- tact is truncated and channeled in places by chert pebbles 84 in the basal bed of the overlying Sundance Formation (Mapel and Bergendahl, 1956). The upper part of the Gypsum Spring Formation is definitely of Jurassic age, on the basis of an association of the pelecypods Grammatodon, Myophorella, Opis (Trigonopis), and Quenstedtia. with the gastropods Ner- itina, Tylostoma?, Nododelphinula?, Procerithium, and Lyosoma powelli White. These fossils were collected near Mill Creek, about 30 miles (48 km) northwest of Lander, Wyo., in a limestone bed about 20 feet (6 m) below the top of the formation, which is 224 feet (68 m) thick at that place (Love and others, 1945; Sohl, 1965, p. D10). The Gypsum Spring Formation must be older than late Bajocian, because it underlies limestone of that age at Lower Slide Lake northeast of Jackson, Wyo. (Imlay, 1967b, p. 567, 577, 583; 1967b, p. 19, 33, 34, 59), and because the equivalent Gypsum Spring Member of the Twin Creek Limestone underlies limestone of late Bajo- cian Age and probably late middle Bajocian Age along the Idaho-Wyoming border (Imlay, 1967b, p. 28). The Gypsum Spring cannot be much older than late Bajocian, however, because it contains the gastropod Lyosoma powelli White, which occurs elsewhere mostly in upper Bajocian beds such as the Sliderock and Rich Members of the Twin Creek Limestone, the middle limestone member of the Piper Formation near Cody, Wyo., and the basal limestones of the Carmel Formation in central Utah. That species also occurs in somewhat younger Canyon Springs Sandstone Member of the Sundance Formation in the Bighorn Basin (Sohl, 1965, p. D5, D10, D11, D18). This evidence definitely favors an early to middle Bajocian Age for the Gypsum Spring Formation. The Piper Formation is exposed in Wyoming along the northwest side of the Bighorn Basin from about 30 miles (48 km) southwest of Cody northward to the Mon- tana border, in the northwestern part of the Wind River Basin nearly as far east as Lander, and along the flanks of the Bighorn Mountains north of Hyattville and Banner. The Piper Formation exposed along the northwest side of the Bighorn Basin is of special interest because it consists of three members that are essentially identical with the three members of the Piper Formation in Mon- tana (Imlay, Gardner, and others, 1948; Imlay, 1954, 1956a) and that rest directly on the Triassic part of the Chugwater Formation. The sequence exposed at Clarks Fork Canyon near the Montana border (Imlay, 1956a, p. 567) is essentially identical with that exposed 30 miles (48 km) southwest of Columbus, Mont. (Imlay, Gardner, and others, 1948). The sections exposed near Cody are essentially identical with the section exposed at Red Dome about 10 miles (16 km) southeast of Bridger, Mont., as well as closely similar to the Piper Formation in the subsurface in southern Montana and in the Williston JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES basin (Nordquist, 1955, p. 99—103; Ray], 1956, p. 38— 43; Imlay, Gardner, and others, 1948). The absence of the Gypsum Spring Formation along the northwest side of the Bighorn Basin is shown by the lack of any dolomi- tic beds, by the presence of much highly fossiliferous shaly limestone, and by the basal beds of the Piper For- mation containing chert pebbles that are identical litho- logically with chert beds or lenses in the Gypsum Spring Formation. The Piper Formation elsewhere in north-central Wy- oming is represented mainly by its upper red-bed mem- ber. In the Wind River Basin thatmember ranges from about 50 feet (15 m) to a featheredge, consists of red silt- stone and claystone that becomes sandy near its eastern margin, and rests sharply on dolomitic beds or limestone at the top of the Gypsum Spring Formation (Love and others, 1945; Pipiringos, 1968, p. D10). The thickest sec- tion, exposed at Red Creek on the north side of the Wind River Basin, is of special interest because its base is marked by a chert conglomerate and at one place by a lens of pebbly limestone resembling that which occurs near the top of the middle limestone member of the Piper Formation along the western and southern sides of the Pryor Mountains, Mont. (Imlay, 1956a, p. 572—574). Near the northern border of Wyoming, the upper red-bed member of the Piper Formation is represented by 10—86 feet (3—26 m) of red claystone and some gyp- sum, which is beneath the Sundance Formation and above dolomitic beds typical of the Gypsum Spring For- mation (Imlay, 1956a, p. 578). This claystone and gyp- sum unit crops out nearly continuously along the east side of the Bighorn Mountains north of Banner, and along the west side of the Bighorns north of Hyattville. It correlates with, and is continuous with, the upper red- bed member of the Piper found in south-central Mon- tana. This correlation is supported by comparisons be- tween sequences at Sykes Mountain, Wyo., and Gypsum Creek, Mont. (Imlay, 1956a, p. 568, 569), and between sequences at Red Gulch, Wyo., and Lodge Grass Creek, Mont. (see table 1 for exact locations)(Imlay and others, 1948, columnar sections along line D—D’; Mapel, 1959, pl. 5). A basal unconformity is indicated by the presence of chert pebbles found as float near the base of 43 feet (13 m) of red claystone exposed at Lodge Grass Creek. This unconformity is further substantiated by the presence of dark-gray wind—polished chert pebbles at the base of 86 feet (26 m) of dark-red claystone that underlies the Sun- dance Formation near the east end of Sykes Mountain. These pebbles, collected by G. N. Pipiringos and the writer, consist of chert identical with that in the under- lying Gypsum Spring Formation. The middle limestone member of the Piper Forma- tion in the Cody area contains the same characteristic mollusks that occur (1) in that member in Montana, (2) in COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES the Rich Member of the Twin Creek Limestone near the Wyoming-Idaho border, and (3) on the north side of Lower Slide Lake, Teton County, Wyo., in 85 feet (26 m) of shaly limestone that represents a thin eastern ex- tension of the Rich Member (Imlay, 1956b, p. 70; 1967b, p. 31). Accordingly, on the basis of stratigraphic posi- tion, the upper red-bed member of the Piper Formation in the Bighorn Basin is correlated with the similar-ap- pearing Boundary Ridge Member of the Twin Creek Limestone and with the eastward extension of that mem- ber at Lower Slide Lake and at Green River Lakes (Im- lay, 1967b, p. 39). Similarly, the lower red-bed and gyp- sum member of the Piper Formation from the Cody area northward to Montana is correlated with the Sliderock Member of the Twin Creek Limestone and with eastern extensions of that member, which underlies the Rich Member (Imlay, 1967b, p. 27, 29, 30). The Sundance Formation comprises seven members in the Black Hills region of Wyoming and South Dakota and in southeastern and central Wyoming as far north as the southern side of the Wind River Basin (Imlay, 1947; Pipiringos, 1953, 1957, 1968, p. D18—D24). These members, from the base upward, are Canyon Springs Sandstone, Stockade Beaver Shale, Hulett Sandstone, Lak, Pine Butte, Redwater Shale, and Windy Hill Sand— stone. Regional unconformities occur at the base of the Canyon Springs, the Redwater, and the Windy Hill. The Canyon Springs Sandstone Member represents the initial deposits of a transgressing sea. It rests on an irregular surface of erosion, varies considerably in thick- ness within short distances, becomes thicker to the south, and in many places is marked basally by pebbles, most of which consist of chert. As a lithologic unit it extends westward from the Black Hills to the Bighorn Mountains and northward from north-central Colorado to Sheep Mountain, about 18 miles (29 km) southeast of Lander, Wyo. Westward or northward from those mountains, it passes into sandy oolitic limestone that becomes less sandy away from the source. 7. In the Black Hills, the member is present only along the southern and western margins, ranges in thickness from a featheredge to 92 feet (28 m), and consists mostly of light-gray thin- to thick-bedded sandstone. Locally, the sandstone may be ripple marked, oolitic or massive, and red to white. Locally, the member includes beds of maroon to gray shale or siltstone (Imlay, 1947, p. 247— 251; Gott and Schnabel, 1963, p. 139—140; Mapel and Bergendahl, 1956, p. 87). In southern Wyoming, the Canyon Springs Sand- stone Member consists of a lower unit of yellowish-white massive or crossbedded sandstone overlain by a unit of ripple-marked, oolitic fossiliferous sandstone (Pipirin- gos, 1968, p. D18—D21). It thickens southward from a featheredge to 65 feet (20 m) in Wyoming and to about 85 165 feet (50 m) in north-central Colorado (Pipiringos and others, 1969, p. N10). The Canyon Springs Sandstone Member is probably of Bathonian Age because it contains Warrenocems (USGS Mesozoic locs. 20496, 20497, 20503) in the Hart— ville uplift of southeastern Wyoming and in the type sec- tion of the member (USGS Mesozoic 10c. 20337) about 4 miles west of Horton, Wyo. (Imlay, 1947, p. 250; 1953a, p. 17, 22). Warrenoceras, formerly classified with Arcti- coceras (Imlay, 1953a, p. 5, 19—23), is either a subgenus of Arcticocems or a provincial time equivalent. Its re- semblance to Arcticoceras suggests that it is of about the same age and probably early late or late middle Bathon- ' ian on the basis of the ammonite sequence in East Green- land (Callomon, 1959). Similarly, a late Bathonian Age is indicated by the presence of Wawenocems in an oolitic limestone unit at the base of the Sundance Formation at Red Creek (USGS Mesozoic loc. 21635) in the Wind River Basin and in the Cody area of the Bighorn Basin (USGS Mesozoic loc. 17106). This oolitic limestone unit correlates, therefore, both stratigraphically and faunally with the Canyon Springs Sandstone Member. The Stockade Beaver Shale Member of the Sundance Formation grades into the adjoining members and passes laterally southward entirely into the underlying Canyon Springs Sandstone Member in south-central Wyoming. In the Black Hills, the shale member consists ‘of 5—90 feet (1.5—2.7 m) of greenish-gray, fissile, calcareous shale that includes some limestone beds and nodules near its base and some siltstone and sandstone near its top (Imlay, 1947, p. 251, 252). In south-central Wyoming, the member consists of 12-110 feet (3.6—34 m) of greenish-gray shale and siltstone (Pipiringos, 1968, p. D21). In the Bighorn Basin, the shale member consists mostly of soft, gray fissile calcareous shale that is locally sandy toward its top, ranges in thickness from a feath- eredge to about 80 feet (24 m), is thickest in the northern part of the basin, and contains an abundance of Gry- phaea, which genus is uncommon in the shale member in the Black Hills (Imlay, 1956a, p. 588-595). The Hulett Sandstone Member of the Sundance For- mation grades into the adjoining members. It consists mostly of light-gray, fine-grained, calcareous, fossilifer- ous, thin- to thick-bedded, ripple-marked, slightly glau- conitic sandstone that is interbedded with some green- ish-gray shale and siltstone. In the Black Hills, the thickness of the Hulett Sandstone Member ranges from 20 to 120 feet (6 to 36.5 m) (Imlay, 1947, p. 255; Robinson and others, 1964, p. 15); in southern Wyoming, from 4 to 40 feet (1.2 to 12 m) (Pipiringos, 1968, p. D22); along the east side of the Bighorn Mountains, from 27 to 70 feet (8 to 21 m) (Mapel, 1959, p. 33; Hose, 1955, p. 106; J. A. Peterson, 1954a, p. 477); along the west side of the Big- horn Mountains, from 16 to 104 feet (5 to 32 m); and around the Pryor Mountains and the northern end of the 86 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Bighorn Mountains, from 0 to 48 feet (0 to 14.6 m) (Im- lay, 1956a, p. 589). Farther west, the Hulett Sandstone Member is possibly represented by about 8 feet of sand- stone and oolitic Limestone at the top of the “Lower Sundance” Formation at Red Creek in the Wind River Basin (T. 6 N., R. 3 W.) (Love and others, 1945). It is also possibly represented at the same stratigraphic po— sition in the gorge, of the Shoshone River west of Cody by 24 feet (0.8 m) of gray sandstone and by the overlying 14 feet (4.2 m) of sandy claystone and sandy oolitic lime- stone (Imlay, 1956a, p. 592). The Lak Member of the Sundance Formation grades into the adjoining members. In the Black Hills, it con- sists of 25—100 feet (7.6—30.5 m) of dark-brownish-red to pink to yellowish-gray, very fine grained, generally massive sandstone and sandy siltstone (Imlay, 1947, p. 257; Robinson and others, 1964, p. 15; Gott and Schnabel, 1963, p. E141, E142). In southeastern Wyoming near Glendo, the member consists of 50 feet (15 m) of fine- grained nonglauconitic sandstone that is commonly red (Love and others, 1949). In south-central Wyoming, the member consists of 7-70 feet (2—21 m) of reddish-brown siltstone, sandy siltstone, and silty sandstone that changes southward to pale gray or pale yellow near Medicine Bow and Rawlins (Love and others, 1945; Love and others, 1947; Love and others, 1949; Pipiringos, 1968, p. D22, D23). The Lak Member pinches out to the west in the Powder River Basin and to the north about 20 miles (32 km)\west of Lander. It is absent around the Bighorn Mountains and the Bighorn Basin, along the north side of the Wind River Basin, and apparently also at Green River Lakes at the northwest end of the Wind River Mountains. The Pine Butte Member of the Sundance Formation in southern Wyoming (Pipiringos, 1968, p. D22—D23) consists of 60 feet or less of greenish-gray to white, thin- bedded, glauconitic, limy, ripple»marked sandstone that is interbedded with gray to green limy siltstone and clay- stone and that near its middle generally contains 1—18 feet of red sandstone and siltstone. Surfaces of sandstone beds are characterized by the presence of raised fur- rowed trails (Gyrochorte?) Marine fossils are not com- mon in the Pine Butte Member, but Pentacrinus colum- nals, echinoid spines, and pelecypods have been found. The member passes southward into north-central Colo- rado, where it intertongues with the underlying Canyon Springs Sandstone Member (Pipiringos, 1972, p. 27). It thins northward in Wyoming and pinches out about 17 miles (27 km) southeast of Lander. It is overlain sharply by the Redwater Shale Member and is locally truncated by that member. The contact is marked by the presence of many belemnites in the basal beds of the Redwater Shale Member and by their absence in the Pine Butte Member. Sandstone beds at or near the base of the Red- water Shale Member can be distinguished from sand- stone beds in the Pine Butte Member by the presence of belemnites and the absence of furrowed trails. The Pine Butte Member in the Black Hills area was identified by G. N. Pipiringos in 1964 while on a field trip with the writer. At that time he noted that a sandstone unit 5—32 feet (1. 5—10 m) thick at the base of the Red- water Shale Member (Imlay, 1947, p. 245, 260, 267—273; Robinson and others, 1964, p. 16—18) had all the char- acteristics of the Pine Butte Member of southern Wyo- ming. It graded downward into or was conformable with the Lak Member, contained raised furrowed trails, did not contain belemnites, and was overlain sharply by silt- stone containing many belemnites. He found that the thickest section of the Pine Butte Member was exposed northeast of Spearfish, S. Dak., in the standard refer~ ence section of the Sundance Formation (Imlay, 1947, p. 245). The characteristics of the member at that locality, as shown In a diagram by Pipiringos (1968, p. D12), are described as follows: Stratigraphic section of the Pine Butte Member of the Sundance Formation [Located in the Jolly Quadrangle, about three-quarters of a mlle (1.2 km) northeast of Spearfish, S. Dak., in the SEVANWIIASEl/aSEl/a sec. 3, T. 7 N., R. 2 E. Measured by G. N. Plplrlngos, September 1964] Thickness Feet Meters Sundance Formation: Redwater Shale Member (in part): 8. Siltstone, medium-gray, clayey, sandy, calcareous,, glauconitic, fossiliferous; r basal few inches contains abundant belemnites; makes slope; basal contact is sharp; no belemnites were found below this contact ------------------------------ 25 7.6 Partial thickness of Redwater Shale Member ------------------------- 25 7_5 J- 4 unconformity Pine Butte Member: .Siltstone, greenish- gray, clayey, sandy, and some thin beds of light- olive-gray silty clay shale; unit makes slope ------ 8 2.4 6. Sandstone, greenish-gray, weathers dusky yellow at the top; very fine grained, calcareous, clayey; contains worm borings filled with gray clay; iron oxide nodules about one-half inch (1.3 cm) in dianeter near middle of unit, and some olive gray mudstone partings; unit makes rounded ledge ----------------------------------- 2.5 0.8 5. Sandstone, siltstone, and clay shale; the sandstone is light gray, very fine grained, silty, clayey, structureless, calcareous, finely glauconitic, fossiliferous, and makes weak ledge in middle; upper and lower parts of unit consist of about equal parts of light-greenish-gray clay shale and light-gray clay siltstone --------------- B 2.4 4. Sandstone, light-gray, very fine grained, calcareous; middle part makes rounded weak ledge overlain by a 1-foot bed of light-greenish-gray, noncalcareous clay shale; upper and lower parts of unit are soft, structureless, clayey, and make slopes ---------------------------------- 7.5 2.3 3. Clay shale, pale-olive to light-olive-gray; contains a zone of pale-red clayey siltstone about 2- 3 feet above base; unit makes slope ------------------------ 5 1.5 COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES Stratigraphic section of the Pine Butte Member of the Sundance Formation—Continued Sundance Formation--Con. Pine Butte Mernber—-Con. 2. Sandstone, yellowish-gray, very fine grained, calcareous; obscure low-angle crossbedding gives faintly varved appearance; fine grains of glauconite are alined along bedding; also some biotite muscovite flakes present; unit makes weak ledge in sharp contact with the underlying red beds. At an isolated exposure of this contact about 30 feet (9 m) east of this section, the basal few inches of the Pine Butte consists of yellow-orange to rusty-brown siltstone and green clay shale that contains thin stringers of vitrain midnfls Feet Meters I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I l I I I I I I H woo mm oa Thickness of Pine Butte Member -------- 32 Lak Member 1. Sandstone, pale-reddish-brown, silty; makes soft slope; not measured. The Pine Butte Member is considered to represent the upper part of the “Lower Sundance” Formation on the basis of its conformable relationship with the under- lying member, its unconformable relationship with the overlying Redwater Shale Member, and the presence of the pelecypods Vaugonia conmdi (Meek and Hayden) and Quenstedtia cf. Q. sublaem's (Meek and Hayden). These species were originally described from the various members of the “Lower Sundance” Formation in the Black Hills and are widely distributed in the western interior region, but they are not known from the Red- water Shale Member or its equivalents. In addition, in the section of the Pine Butte Member described above, the fossiliferous ledge in the middle of unit 5 contains Myophorella montamtensis Meek (USGS Mesozoic locs. 29128 and 29518). In Montana this species ranges from the middle limestone member of the Piper Formation into the lower part of the Rierdon Formation; along the Idaho-Wyoming border it ranges from the Sliderock Member of the Twin Creek into the Watton Canyon Member of the Twin Creek; and in Utah it occurs in the lower part of the Carmel Formation (Imlay, 1964d, p. C4, C31—C33; 1967b, p. 82). The Redwater Shale Member of the Sundance For— mation in south-central Wyoming, as defined by Pipirin- gos (1968, p. D23), consists of four units, which from the base to top are alternately siltstone and shale. Of these, the siltstone units contain beds of shelly coquinoid sand- stone or limestone, and the shale beds contain limestone concretions. To the northwest, the upper two units pass into cliff-forming sandstone, and the lower two units pass into somewhat softer silty or clayey sandstone. This two- fold division exists in the Bighorn Mountains and Big— horn Basin and in west-central Wyoming west of Sheep Mountain, which is about 20 miles (32 km) southeast of Lander (Pipiringos, 1968, fig. 2 on p. D3). The Redwater Shale Member ranges in thickness from about 75 to 165 feet (23 to 50 m) in the Black Hills, from 50 to 120 feet (15 to 37 m) in southern Wyoming, from 130 to 160 feet 87 (40 to 49 m) in the Wind River Basin, and from 120 to 175 feet (37 to 53 m) in the Bighorn Basin and Bighorn Mountains. The age of the Redwater Shale Member is probably entirely early to early middle Oxfordian, on the basis of the presence of the cardioceratid ammonites Cardioceras and Goliathiceras throughout most of the member. Low- ermost occurrences range throughout the basal 15 feet (4.5 m) (Mesozoic locs. 19359, 2434, 24736). The upper- most occurrence is 20 feet (6 m) below the top of the member where it is 230 feet (70 m) thick on Little Sheep Mountain southeast of Lovell, Wyo. (Mesozoic 10c. 26717). At Horse Creek near the northwest end of the Wind River Basin (Love and others, 1945), Cardioceras occurs 25 feet (7.6 m) below the top of the member where the member is 130 feet (40 m) thick (Mesozoic loc. 19398). On the Johnson Ranch about 117 miles (27 km) southeast of Lander, Wyo., Cardioceras occurs 29 feet (9 m) below the top of the member, which is 127 feet (39 m) thick ‘ (Mesozoic 10c. 28400). The Windy Hill Sandstone Member of the Sundance Formation in southern Wyoming (Pipiringos, 1968, p. D23—D25) consists of 5—57 feet (1.5—17 m) ledge-form- ing sandstone that is yellowish-gray, limy, ripple marked, weathers .bright yellow to orange to brown, and contains a few specimens of Ostrea and Camptonectes. Its upper part grades into and locally intertongues with {the Mor- rison Formation. Its basal part rests sharply on and lo- cally truncates the Redwater Shale Member. It pinches out northwestward a little west of Hanna, Utah, and a little west of Lander, Wyo. (G. N. Pipiringos, oral com— mun., 1974). It is not present along the north side of the Wind River Basin, or around the Bighorn Mountains, or anywhere in northwestern Wyoming or in Montana. The Windy Hill Sandstone Member is represented in the Black Hills area, according to Pipiringos (1968, p. D24), by a bright yellow sandstone that is lithologically similar to the typical exposures of the member elsewhere and that occupies the same stratigraphic position. These similarities were recognized previously by Mapel and Pillmore (1963, p. N16) before the member was named. For mapping purposes, they placed the yellow sandstone in the top of the Redwater Shale Member because it was too thin to map separately but formed an easily recog- nizable formation boundary. They did not see any evi- dence that the yellow sandstone might rest unconform- ably on the underlying shale. They did note, however, that the yellow sandstone contained some thin seams of chert and some thin beds of gypsum and that locally beds of gypsum occurred both above and below the sand- stone. The exact age of the Windy Hill Sandstone Member is not known. Nonetheless, its unconformable relation- ship with the underlying dated Redwater Shale Member 88 in southern Wyoming suggests that it is younger than early Oxfordian and probably represents a small part of middle Oxfordian time. Its absence north of central Wy- oming may be due to distance away from a source of sand, to its merging northward into deeper water marine deposits, or to both. The Twin Creek Limestone, exposed along the Wy- oming-Idaho border in an area of thrust faulting and in north-central Utah, has recently been described in detail and correlated member by member with marine beds elsewhere in the western interior region (Imlay, 1967b, p. 2—52). As this information is readily available, only the most essential is discussed here and is shown on fig- ures 26, 27, and 28. East of the area of extensive thrust faulting, beds equivalent to the Twin Creek Limestone crop out in the south-central part of Yellowstone National Park, near the Gros Ventre River northeast and east of Jackson (Foster, 1947, p. 1565, 1566; Imlay, 1956b; 1967b, p. 6), and at the west end of the Wind River Mountains near Green River Lakes (Richmond, 1945). In those areas, however, the marine Jurassic beds above the Gypsum Spring Formation are referred to the Sundance Forma— tion because they are much thinner, much less calcar- eous, and more fossiliferous than the typical Twin Creek Limestone. Nonetheless, the lower part of the Sundance Formation in those areas consists of units that are lith— ologically, stratigraphically, and faunally equivalent to the Sliderock, Rich, Boundary Ridge, Watton Canyon, and Leeds Creek Members of the Twin Creek Lime- stone. Also, the first three members are not represented in the typical Sundance Formation farther east but are represented in the Piper Formation. Thus, at Bacon Ridge, in secs. 13 and 14, T. 40 N., R. 111 W. Teton County, Wyo., 125 feet (38 m) of soft limy shale resembles both the Stockade Beaver Shale Member of the Sundance Formation and the Leeds Creek Member of the Twin Creek Limestone. Above this shale is 8 feet (2.4 m) of gray, fine-grained, hard, ripple- marked sandstone (Love and others, 1948, p. 48) that could be interpreted either as an extension of the Hulett Sandstone Member of the Sundance or of the Giraffe Creek Member of the Twin Creek Limestone. Next higher is 4 feet of soft, gray, nonglauconitic siltstone that most probably is the bleached lateral extension of the Preuss Sandstone or of the Lak Member of the Sundance Formation. Sharply overlying is highly glauconitic sand- stone and shale typical of the Stump Sandstone or of the “Upper Sundance” Formation in nearby parts of Wyo- ming. Also, a section measured by G. N. Pipiringos and the writer north of Lower Slide Lake (see below) contains five well-exposed units that greatly resemble the named members of the Twin Creek Limestone from the Slide- JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES rock Member to the Leeds Creek Member. The upper- most of these, the Leeds Creek equivalent, also reseme bles the Stockade Beaver Shale Member'of the Sundance Formation lithologically and faunally. This unit is over- lain by 41 feet (12.5 m) of partially covered beds (units 23 to 30 in the section below), which were exposed in a trench made when the section was measured. These beds extend up to an unconformity at the base of the “Upper Sundance” formation (equivalent to the Stump Sand- stone, or the Redwater Shale Member of the Sundance): Stratigraphic section of the Sundance Formation and its mem- bers with its Twin Creek Limestone member equivalents and Gypsum Spring Formation [Exposed on the north side of Lower Slide Lake in sec. 4, T. 42 N., R. 114 W., Teton County, Wyo.] Thickness Feet Meters Sundance Formation: Redwater Shale Member: 35. Sandstone, gray, fine- to medium-grained, limy, glauconitic; basal 20 feet pebbly; overlain by Morrison(?) and Cloverly Formations; estimated thickness ---------- 100: 30.4: 34. Sandstone, green, fine-grained, glauconitic; forms vertical reentrant under cliff ----- 17 5.2 33. Sandstone, dark—gray to black, clayey to silty, highly glauconitic; forms slope——- 7 2.1 32. Siltstone, dark-gray, clayey, glauconitic; contains 4-inch (IO-cm) bed of siliceous nodules; contains many belemnites and ostracodes near base --------------------- 7 2.1 31. Bentonite, yellowish-white to gray, fissile ---------------------------------- 1 0.3 Total Redwater Shale Member ------------ 132: 40.2+ Pine Butte(?) Member 30. Sandstone, greenish-gray, very fine grained, limy, ripple-marked; forms prominent ledge -------------------------- 2 0. 29. Sandstone, greenish-yellow, soft, silty; includes some thin sandstone beds that 01 form weak ledges ------------------------- 9-5 2-9 28. Sandstone, greenish-gray, very fine grained, platy, nonglauconitic; forms ledge ------- 1 0.3 27. Siltstone, pink, soft ---------------------- 1 0.3 26. Sandstone, greenish-gray, very fine grained, platy, nonglauconitic; forms ledge ------- 1 0.3 Total Pine Butte(?) Member ------------- 14.5 4-4 Lak Member: 25. Siltstone, greenish- to yellowish-gray, sandy, soft ------------------------------ 5 1.5 24. Siltstone, reddish- pink, sandy, soft ------- 19.5 5.9 23. Siltstone, greenish- to yellowish- gray, sandy, soft ------------------------------ 12 3.7 Total Lak Member ----------------------- 36.5 11.1 Stockade Beaver Shale Member: 22. Shale, limy; several thin beds of limestone 30-40 feet (9-12 m) above base. Contains m and arm nebrascensis ---------------------------- 163 49.7 Total Stockade Beaver Shale Member-—-- 163 49.7 Canyon Springs Sandstone Member. 21. Limestone, yellowish- gray, oolitic, thin- to thick- bedded ------------------------- 7 2.1 20. Shale, medium-gray, limy; contains Gryghaea nebrascensis ------------------- 20 6.1 19. Shale, medium-gray, limy, and thin beds of soft brownish—gray limestone; contains Harrenoceras ---------------------------- 10 3.0 18. Limestone, medium-gray, oolitic, massive—— 3.5 1 1 17. Limestone, yellowish—gray, crumbly, medium- to thin-bedded -------------------------- 4.5 1.4 16. Limestone, yellowish-gray, oolitic, medium- to thin-bedded -------------------------- 12 3.7 Total Canyon Springs Sandstone Member -------------------------------- 57 17.4 Boundary Ridge Member of Twin Creek Limestone equivalent: 15. Limestone, yellowish-gray, soft, shaly---- 3.5 1.1 14. Limestone, olive-green to gray, soft, shaly ----------------------------------- 1.5 0.5 COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 89 Stratigmphic section of the Sundance Formation and its mem- bers with its Twin Creek Limestone member equivalents and Gypsum Spring Formation-Continued Thickness Feet Meters Sundance Formation--'Con. Boundary Ridge Member of Twin Creek Limestone equivalent—Con. 13. Siltstone, brownish-red, soft; lower contact sharp ----------------------- Total Boundary Ridge Member of Twin Creek Limestone equivalent ------- Rich Member of Twin Creek Limestone equivalent: 12. Limestone, medium-gray, shaly, partly coquinoi'd----' --------------------------- Z3 7. 11. Limestone, medium-gray, soft, shaly ------- 27 8. 10. Limestone, dark-gray to nearly black, mostly soft and shaly; some beds 4 -10 inches thick; contains Parachondroceras and Gryphaea —T——_—_2anOC0nVEXa---- ------------------------ 35 Total Rich Member of Twin Creek Limestone equivalent ---------------- 85 Sliderock Member of Twin Creek Limestone equivalent: 9. Limestone, gray, partly oolitic, medium— to thin-bedded -------------------------- 16 8. Limestone, medium-gray, soft, shaly ------- 4 7. Shale, yellowish-gray, soft --------------- 1 Total Sliderock Member of Twin Creek Limestone equivalent ---------------- 21 Gypsum Spring Formation: . Siltstone, brownish-red, soft ------------- 15 Limestone, pinkish-yellow; forms top of cliff ----------------------------------- 8 Limestone, gray to yellow, brecciated; forms cliff Limestone, purple, yellow. gray, brecciated, silty ----------------------------------- 2 Limestone, yellou to pink, soft, silty---- 1-2 0. Siltstone, brownish—red; rests sharply on Nugget Sandstone ------------------------ 3 0. Total Gypsun Spring Formation --------- 46 14. 33-43 10.1-13.1 38-48 11.6—15.6 0 Z D-‘N w :- 010‘ The Preuss Sandstone crops out in the same area as the Twin Creek Limestone, thickens westward from 70 feet (21 m) or less to about 1,300 feet (400 m), and con- sists mostly of pale- to dull-red, even-grained, fine- grained, plane-bedded, locally ripple-marked sandstone. In addition, its lower part contains considerable bedded salt along the Idaho-Wyoming border, and a marine lime- stone member attains nearly 200 feet (61 m) in the area east of Blackfoot and Idaho Falls, Idaho. The formation grades downward into the Twin Creek Limestone and is overlain sharply and unconformably by the Stump Sand- stone or by the Curtis Formation in Utah (Mansfield, 1927, p. 98, 99, 338—340; Baker, 1947; Thomas and Krue- ger, 1946, p. 1277, 1278; Imlay, 1952b). A marine origin for the Preuss Sandstone is shown by the presence of salt, marine limestone, even grain size, even bedding and oscillation ripple marks. Marine fossils, including pelecypods, gastropods, and corals, are common only in exposures east of Blackfoot and Idaho Falls, Idaho, but oysters and crinoid columnals are found as far east as sec. 17, T. 31 N., R. 119 W._, about 7 miles (11 km) southwest of Afton, Wyo. The age of the Preuss Sandstone must be mostly middle Callovian, because it conformably overlies beds of early Callovian Age and unconformably underlies beds of early Oxfordian Age. The Wolverine Canyon Lime- stone Member of the Preuss (Imlay, 1952b, p. 1742) can- not be much younger than early Callovian, as it contains the coral Actinastrea kyatti (Wells) (Imlay, 1967b, p. 35) and the gastropod Lyosoma cf. L. powelli White (Sohl, 1965, p. D11, D17, D18, pl. 2, fig. 4). Of these fossils, A. hyatti (Wells) has been recorded elsewhere only in beds of late Bajocian Age. Lyosoma cf. L. powelli White has been recorded from the Hulett Sandstone Member of the Sundance Formation in the Badwater area, Fremont County, Wyo., and from the Rierdon Formation in northern Yellowstone National Park, Mont. The term Stump Sandstone has been applied to the uppermost Jurassic marine sandstone and sandy shale overlying the Preuss Sandstone in westernmost Wyo- ming, southeastern Idaho, and parts of north-central and northeastern Utah. Within that area, the Stump Sand- stone ranges in thickness from 130 to 500 feet (40 to 152 m). It is thickest in southeastern Idaho and thins irreg- ularly northward and eastward (Mansfield and Roundy, 1916, p. 76, 81; Mansfield, 1927, p. 99—101; 1952, p. 38; Gardner, 1944; Rubey, 1958; Cressman, 1964, p. 52, 53; Staatz and Albee, 1963, 1966; Pampeyan and others, 1967; Albee, 1968; Schroeder, 1969; Thomas and Kreu- ger, 1946, p. 1269, 1276, 1278, 1285). The Stump Sandstone exposed along the Idaho-Wy— oming border consists mostly of sandstone and sandy shale units and has not hitherto been considered divisi- ble into members. As described by Mansfield (1927, p. 99—101), the sandstone is fine to medium grained, thin bedded to massive, ripple marked, calcareous, glaucon- itic, greenish-gray to gray, and locally crossbedded. In- terbedded with the sandstone are some beds of calcar- eous, greenish-gray shale and sandy siltstone and some beds of glauconitic, greenish-gray, shaly, thin-bedded to massive limestone that may be sandy, oolitic, and ripple marked. Apparently all gradations between sandy lime- stone and calcareous sandstone are represented. The base is generally marked by a bed of fossiliferous coarse— grained sandstone or grit, according to Mansfield (1927 , p. 99-101). Recent field studies by George Pipiringos and the writer have shown that the Stump Sandstone exposed along the Idaho—Wyoming border includes members that are lithologically, stratigraphically, and faunally equiva- lent to the Curtis Formation of Utah and to the younger sandy facies of the Redwater Shale Member of the Sun- dance Formation of northern Utah and western Wyo- ming. As the Stump Sandstone at present is the most practical unit for mapping purposes, it is herein retained as a formation and is divided into the Curtis Member be- low and the Redwater Member above. This terminology applies to an area extending eastward from the Black— foot Mountains east of Blackfoot and Idaho Falls in Idaho 90 to the Wyoming and Hoback Ranges in western Wyo- ming; extending southward from the Teton Range in the western part of the Jackson Hole area at least as far as Woodruff and Peoa in north-central Utah, Evanston in southwestern Wyoming; and eastward from Peoa along the length of the Uinta Mountains. The Curtis Member near the Wyoming-Idaho border ranges in thickness from 30 to at least 395 feet (9 to 120 m), thins eastward and northward, and extends consid- erably farther south and southwest than the Redwater Member. Its lower contact with the underlying Preuss Sandstone is sharp on McCoy Creek, Idaho (sec. 6, T. 37 N., R. 46 E.), is gradational elsewhere within a few inches or a few feet, and is not marked by pebbles or by irregularities suggestive of a disconformity. The/ Curtis Member is distinguished from the Preuss Sandstone by a fairly abrupt color change upward from red to gray and by the presence of tracks and trails in abundance. These differences probably indicate a slight deepening of the sea that caused a change from hypersalinity to almost normal marine salinity. The change must have been very slight because the Curtis Member on Tincup Creek in Idaho (sec. 9, T. 5 S., R. 46 E., and sec. 10, T. 5 S., R. 45 E.) and on Fish Creek in Wyoming (SE14 sec. 32, T. 30 N., R. 118 W.) contains a unit of red sandstone and siltstone that is nearly identical lithologically with red units in the Preuss Sandstone. The Redwater Member of the Stump near the Idaho- Wyoming border is well developed along both sides of the Snake River and farther east, ranges in thicknesses from a featheredge to 175 feet (0433 m), and thins east- ward and southward. It differs from the underlying Cur- tis Member by being much more fossiliferous, by contain— ing belemnites and ammonites, by its shale being chunky instead of fissile, by being more glauconitic, and by its bedding surfaces being marked only rarely by tracks and trails. Unlike the Curtis Member, it does not bear clay- pebble impressions or cube-shaped imprints indicative of salt crystals. Its upper and lower contacts are marked by sharp lithologic changes that reflect unconformities. It has not yet been identified lithologically or faunally in southeastern Idaho or along the Idaho-Wyoming bor- der south of the Caribou Range, which is just south of the Snake River. The Redwater Member is definitely not present in the type area of the Stump Sandstone cut or near Stump Peak. ‘ The Redwater Member of the Stump Sandstone in southeastern Idaho and western Wyoming is correlated with the Redwater Shale Member of the Sundance For- mation elsewhere because it contains belemnites in fair abundance from bottom to top (USGS Mesozoic locs. 12125, 112126, 16024, 16028, 17897, 18183, 18185, 30393, 18187, 30395) and contains Cardiocems near its base at Telephone Creek, Wyo. (USGS Mesozoic loc. JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 16024), and at McCoy Creek, Idaho (Mesozoic loc. 17897), as well as in the lower part of its upper third at McCoy Creek (USGS Mesozoic loc. 30395). In addition, the for- mation at its base at Telephone Creek contains the pele- cypods Vaugom'a quadrangular-is (Hall and Whitfield) and Oxytoma wyomingensis (Stanton) along with Car- diogems and belemnites (USGS Mesozoic loc. 16024) and at its top on McCoy Creek contains 0. wyomingensis (Stanton) (USGS Mesozoic 10c. 12125). The presence of these bivalves is important for correlation purposes be- cause they occur elsewhere in the Redwater Shale Mem— ber of the Sundance Formation and in the Swift Forma- tion, but they do not occur in older formations or members. The presence of Cardioceras shows that the Redwater Member is of early to early middle Oxfordian Age. These facts show that the Curtis and Redwater Members of the Stump Sandstone were deposited in dif- ferent seas that covered somewhat different areas, that erosion took place at the end of Curtis deposition and again after Redwater deposition, and that the present changes in thicknesses of the members is in part deposi- tional as well 'as erosional. The continental Morrison Formation in Wyoming, western South Dakota, and northernmost Utah and Col- orado was deposited conformably on the Windy Hill Sandstone Member or on the Redwater Shale Member of the Sundance Formation. The Morrison attains thick- nesses of 125—370 feet (38—113 m) in Wyoming and South Dakota and more than 800 feet (244 m) in north- eastern Utah (Reeside, 1952, p. 24, 25; Craig and others, 1955, p. 159; Hansen, 1965, p. 85). Westward increases in thickness and certain changes in lithologic character- istics (Mirsky, 1962, p. 1675—1678) indicate that its source was to the west in Utah and Idaho. On the basis of fresh-water mollusks, it should be older than the Pur- beck Beds of England (Yen, 1952, p. 31—34), which are now correlated with the upper part of the upper Tithon~ ian (Yen, 1952, p. 31—34). On the basis of vertebrates and stratigraphic position, its age should be mostly Kim- meridgian (Imlay, 1952a, p. 953, 958; Reeside, 1952, p. 25). The basal beds of the Morrison, however, where they overlie the Redwater Shale Member, should be of late Oxfordian Age, as shown by the presence of Cardi- oceras and Quenstedtocems throughout most of that member. The continental Nugget Sandstone, as exposed in southeastern Idaho, western and central Wyoming, and north-central Utah, lies unconformably below the Gyp- sum Spring Formation, or the Gypsum Spring Member of the Twin Creek Limestone, of early to early middle Bajocian Age. Regionally, the Nugget rests unconform- ably on beds of Late Triassic age (Reeside, 1957, p. 1480, 1482; Pipiringos, 1968, p. D16; Pipiringos and COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 116° 112" 104° 108° 43 100° 96: 92° I l §1 \\o Ba nff \ l ALBERTA SASKATCHEWAN .0 . Blairmore \ ___-§AEAQA__ UNITEDfSTATES BEAR PAW MTS I WILLISTON OBillings /‘ Columbus 9‘ l Brid P353 SOUTH . ger PRYOR _—___._.._ Lovell. MTS 6 to o 0 Banner 5 C°dy 13%-,5/ '{gn S eep. ‘Sv 15 /o ‘9 / . on [1” Thermopolis Lander. “6’52? 19 S O ’\ a x 20 bx? 212 pearfish S 9 5i I IDAHO ”Ii/5,? 1‘» . 94 8 32:32- W Rawlins . WYOMING 0 Medicine Bow l C k 'll If 0 evr e NEBR 27[ .‘ UIN_TA 22 23 MT§ . Denver __ -im __ 28 \130 29 'GrandJunction ‘ COLORADO /x # O X X'—"' h ..a l 36°pJ l ARIZONA NEW MEXICO 0 Santa Fe ____1___ 0 Laguna fifiMsac I ’0 1w NOMKE x) 100 zoo KILOMETERS / l LIMITS l l __i L_______.__ $____| DAKOTA I . Rocky Mount Swift Reserve Montana . Southwest of Craig,Mont. Smith River, south of Great Falls, Mont. Belt Creek, southeast of Great Falls, Mont. Near Utica on Judith River, Mont. . Big Snowy Mountains near Heath,Mont. Button Butte, Mont. Porcupine Dome, Mont; . Northeastern Montana and northwestern North Dakota . Southwestern Saskatchewan . Ammon Quad, southeastern Idaho . Red Mountain, southeastern Idaho . Lower Slide Lake, Wyo- . Green River Lakes, northwestern Wyoming . Red Creek, northwestern W oming . Near Hyattvillemorth~centra Wyoming . Mudd Creek,north-central Wyoming . Bush anyonmortheastern Wyoming . East of Newcastle, northeastern Wyoming . Minnekahta area, southwestern South Dakota . Burr Fork, east of Salt Lake City, Utah 23. Peoa-Oakle area.north-oentral Utah . Duchesne iver near Hanna, Utah . Lake Fork, northeastern Utah ' . Whiterocks River canyon, northeastern Utah . Dinosaur Quarry, northeastern Utah Miller Creek, northwestern Colorado . Elk Creek area, northern Colorado Frantz Creek, northern Colorado Hahns Peak, northern Colorado Monks Hollow, north-central Utah Nephi-Levan area, central Utah Gunnison—Salina area, south-central Utah Buckhorn Wash, east-central Utah . Black Dragon Canyon ,, east-central Utah San Rafael River, east-central Utah Dewe Bridge, east-central Utah John rown Valley, southwestern Colorado Slick Rock area, southwestern Colorado McElmo Canyon, southwestern Colorado. Gunlock, southwestem Utah Danish Ranch, southwestern Utah Kanarraville-Cedar City, southwestern Utah Mount Carmel Junction, southwestern Utah Brown Can on, southwestern Utah Little Bull alley, southwestern Utah Pine Creek, south-central Utah Sand Valley, north—central Arizona Page, north-central Arizona Big Hollow Wash, southeastern Utah Cow Springs, northeastern Arizona I ains of southwestern Alberta ir, Sun River area, northwestern cppsewsw N- 1 $3858?$6$$fi$888§88383388 KANSAS — —_——-——._.——.———-T— FIGURE 20.—-Index map of Jurassic areas in the western interior region. Numbers 1-1 1 refer to stratigraphic sequences shown in figure 25; numbers 12—21 refer to sequences shown in figure 26; numbers 22-31 refer to sequences shown in figure 27; numbers 32—41 refer to sequences shown in figure 28; and numbers 42—52 refer to sequences shown in figure are indicated by a solid line. 29. Western and southern limits of Jurassic deposition COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES 91 O’Sullivan, 1978). It consists characteristically of red to brown, or yellowish-gray to white, massive highly crossbedded sandstone, but in some places it includes considerable even-bedded, thin-bedded, ripple-marked, red to gray sandy shale, silty sandstone, and siltstone, which are most common in its lower 200 feet (Mansfield, 1927, p. 96; Love and others, 1945; Pipiringos, 1968, p. D17; Poole and Stewart, 1964, p. D38; Cressman, 1964, p. 45; Rubey, Oriel, and Tracey, 1975, p. 4). The Glen Canyon Sandstone, as exposed in the Uinta Mountains of northeastern Utah and northwestern Colorado, occu- pies the same stratigraphic position as the Nugget Sand- stone, is bounded by the same unconformities, and is reddish in the western part of the Uinta Mountains and white in the eastern part. Both of these formations on the basis of stratigraphic position could be of Late Trias- sic and (or) Early Jurassic age. NORTHERN UTAH TO NORTHERN COLORADO The Twin Creek Limestone and Preuss Sandstone in the Wasatch and Uinta Mountains of north-central Utah are nearly identical lithologically with the same forma- tions exposed farther north, along the Wyoming-Idaho border. Eastward in the Uinta Mountains, however, the lower five members of the Twin Creek Limestone grad- ually wedge out from the base upwards (see fig. 27). Thus, the Gypsum Spring Member wedges out between Oakley and the Duchesne River; the Sliderock Member, between Lake Fork and Whiterocks River canyon; the Rich Member, between Whiterocks River canyon and Vernal; and the Boundary Ridge and Watton Canyon Members, eastward near Vernal. The two uppermost members of the Twin Creek Limestone change markedly east of Lake Fork into a sequence of gypsum, red sand— stone and siltstone, and green claystone. This sequence closely resembles the Carmel Formation of the San Ra- fael Swell and persists eastward into Colorado. The eastward lithologic changes from the Twin Creek Limestone to the Carmel Formation are well shown by the sequence at Whiterocks River canyon as described below: Stratigraphic section of the Carmel Formation [Exposed in the canyon of Whiterocks River In Nwl/a sec. 19 and SE1/4$E|/4 sec. 18, T. 2 N., R. 1 E., Uintah County, Utah] Thickness Feet Meters Entrada Sandstone. — "’_ Carmel Formation: Giraffe Creek equivalent: 25. Siltstone, greenish-gray, soft, mostly covered -------------------------- 64 19.5 24. Shale, greenish-gray, soft ---------------- 12 3.7 _Leeds Creek equivalent: 23. Siltstone, red, interbedded with red fine-grained sandstone containing thin streaks of gypsum ....................... 9 2.7 Stratigraphic section of the Carmel Formation—Continued Thickness Feet Meters Carmel Formation--Con. 22. Gypsum, white ----------------------------- 2 .6 21. Sandstone, red; some gypsum streaks ------- 3 .9 20. Gypsum, white ----------------------------- 2 .6 19. Shale, light~greenish-gray, finely sandy to papery ------------------------------- 6 1.8 18. Gypsum, white ----------------------------- 1 .3 17. Siltstone, red; some green lenses --------- 12 3.7 16. Shale, light-green, sandy ----------------- 23 7.0 15. Shale, light-green, soft; sane streaks of red siltstone; poorly exposed ----------- 86 26.2 14. Siltstone, red, interbedded with gypsum--- 20 6.1 13. Gypsum, massive --------------------------- 12 3.7 12. Shale, greenish, soft --------------------- 15 4.6 Watton Canyon equivalent: . 11. Limestone, grayish-white, lithographic---- 11 3.4 10. Limestone, light-gray, shaly -------------- 6 1.8 Boundary Ridge equivalent: 9. Limestone, light-yellowish-gray, oolitic, thin-bedded, slightly sandy, ripple marked ---------------------------------- 4 1. 8. Siltstone, red, soft ---------------------- 17 5.2 Rich equivalent: 7. Claystone, greenish-gray, soft, bentonitic 2 .6 6. Sandstone, white, fine-grained, soft ------ 2 .6 5. Claystone, greenish-gray, very soft ------- 6 1.8 4. Limestone, yellowish gray; thin—bedded in middle, oolitic at top and bottom; contains Pleuro a and Cgmp%%flggtg% ----- 4 1.2 3. Claystone, ye owis -gray, so ; con ains thin beds of nodular yellow limestone containing oysters ---------------------- 12 3.7 2. Claystone and sandy shale, light-gray, soft; contains a 6-inch (15 cm) bed of brown, sandy, oolitic limestone at base containing Cagptonectes ----------------- 9 2.7 1. Claystone, yellowish—green, soft;’ contains many very thin beds (0.2-0.5 in.; 0.6-1.3 cm) 1/4-1/2 inch of light—yellowish ray shaly sandstone. ------- Total thickness Sharp unconformity. Glen Canyon Sandstone (not measured). 345 105.2 The Sliderock Member of the Twin Creek Lime- stone, as exposed in the Uinta Mountains, is of particular interest stratigraphically because its lower beds are sandy, some are slightly crossbedded, and much of the member locally ,passes laterally into gray massive crossbedded sandstone that rests sharply on the brown- ish-red Glen Canyon Sandstone. Thus, in an exposure on the south side of the Duchesne River near Hanna (Imlay, 1967b, p. 23), the member consists from bottom to top of 5 feet (1.5 m) of fine-grained yellow sandstone, 25 feet (7.6 m) of fine-grained, sandy, medium- to thin-bedded limestone, and 12 feet (3.6 m) of gray massive oolitic limestone. Two miles to the west on Sand Creek, in the NW% sec. 7, T. 1 S., R. 8 W., the same member from its base upward consists of 4 feet (1.2 m) of deep-red, fine- grained sandstone, 25 feet (7.6 m) of yellowish-gray, massive crossbedded sandstone that contains Gryphaea and Camptonectes, and then 12 feet (3.6 m) of gray, mas- sive oolitic limestone. Except for this uppermost lime— stone, the member at Sand Creek is similar lithologically to the Page Sandstone of central and southern Utah (Fred Peterson and G. N. Pipiringos, unpub. data, 1977; 92 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Pipiringos and O’Sullivan, 1975) and occupies the same stratigraphic position just below limestone that contains mollusks characteristic of the Rich Member of the Twin Creek Limestone (Imlay, 1967b, p. 31, 33). These sand- stone beds were first recognized by G. N. Pipiringos (oral commun. , 1974) as a northern extension of the Page Sandstone. The Preuss Sandstone in the Wasatch Mountains re- sembles the same formation as exposed along the Wyo- ming-Idaho border by consisting mostly of red fine- / grained sandstone, by containing saline deposits in its lower part, and by containing locally near its base a sandy limestone member (Granger, 1953, p. 11) that could be equivalent to the Wolverine Canyon Limestone Member of the Preuss of southeastern Idaho (Imlay, 1952b, p. 1740—1743). The exposures in the Wasatch dif- fer from the others, however, by being softer, siltier, and darker red. This dark-red facies persists eastward into the Uinta Mountains as far as Lake Fork, but be- tween Lake Fork and Whiterocks River canyon, it passes into light-colored, clean, crossbedded sandstone that is called the Entrada Sandstone and that extends eastward into Colorado. Marine beds overlying the Preuss Sandstone, or the 1 equivalent Entrada Sandstone, in the Uinta Mountains are commonly referred to the Curtis Formation (Huddle and McCann, 1947; Kinney and Rominger, 1947; Baker, 1947; Kinney, 1955, p. 85—89) or to the Stump Sand- stone from Lake Fork westward and to the Curtis For— mation from the Whiterocks River canyon eastward (Thomas and Krueger, 1946, p. 1278—1290). All authors cited hereagree that the formation is readily diVided into two distinct members. Recent studies by G. N. Pipirin- gos (oral commun., 1974) show that the lower member is identical lithologically and stratigraphically with the type Curtis Formation of central Utah (Gilluly and Reeside, 1928, p. 78, 79) and with the Pine Butte Member of the Sundance Formation in southern Wyoming (Pipiringos, 1968, p. D23). Assignment to the Curtis Formation (or Member) rather than to the Pine Butte Member is fa- vored=by the presence of basal unconformity. The Pipi- ringos studies also show that the upper member is iden- tical with the Redwater Shale Member of the Sundance Formation of Wyoming and South Dakota (Imlay, 1947, p. 259—264; Pipiringos, 1968, p. D23) and is likewise characterized by an abundance of belemnites. Recent studies by Pipiringos and Imlay (unpub. data) show also that the Redwater Member is widespread in the upper part of the Stump Sandstone, as exposed along the Wyoming-Idaho border, and that it overlies a lower member that is nearly identical with the Curtis Forma- tion, or Curtis Member of Utah. These relationships show that the term Stump Sandstone was correctly ap- plied by Thomas and Krueger (1946, p. 1278—1290) for the western part of the Uinta Mountains at least as far east as LakeFork north of Duchesne, Utah. Usage of the term Stump Sandstone farther east in the Uinta Mountains is justified because the Curtis and Redwater Members are fairly continuous, because of their strati- graphic relationships with each other, because the Mor- rison Formation is the same throughout the mountains, and because geologists to date have not found it practical to map the two members separately. As thus defined, the Curtis Member of the Stump Sandstone in the Uinta Mountains ranges from 30 to 110 feet (9 to 33.5 m) in thickness; consists mostly of glauco- nitic, fine-grained to very fine grained, thin- to thick- bedded sandstone that may be even-bedded and ripple marked, or crossbedded; contains glauconite grains of the same size as the surrounding sand grains; locally con- tains minor amounts of green fissile or sandy shale; is characterized by furrowed trails, by round, flat shale pebble impressions, and by salt casts on bedding plane surfaces; generally rests sharply on the underlying En- trada or Preuss Sandstone; is locally marked basally by a chert pebble conglomerate; and in places contains the pelecypods Meleagm'nella and Camptonectes (Thomas and Krueger, 1946, p. 1279; Kinney, 1955, p. 87—88; Untermann and Untermann, 1954, p. 51; Pipiringos, oral commun., 1975). The overlying Redwater Member of the Stump Sandstone ranges from 115 to 140 feet (35 to 43 m) in thickness; contains much soft greenish-gray shale and thin beds of glauconitic limy sandstone and sandy to ooli- tic limestone, which are especially common near its top and in the northern and eastern parts of the Uinta Moun- tains; is characterized by an abundance of belemnites and braciopods; rests sharply on the Curtis Member; and is locally marked basally by a pebble conglomerate (Thomas and Krueger, 1946, p. 1287). From Duchesne eastward, the Redwater Shale Member of the Sundance is overlain by the Windy Hill Sandstone Member of the Sundance (G. N. Pipiringos, oral commun., 1974). Elsewhere in the Uinta Mountains, the contact with the overlying Morri- son Formation is generally drawn at the top of a unit of hard sandstone or oolitic limestone and is reported to be conformable but not gradational. The Redwater Member of the Stump Sandstone in ’ the Uinta Mountains is distinguished from the underly- ing Curtis Member by being generally much shalier and less glauconitic, by containing belemnites and brachio— pods, by 10cally containing the ammonite Cardiocems, and by lacking furrm red trails. Evidently the sequence near Manila. Utah, that Hansen (1965, p. 82) assigned to the Curtis Formation actually belongs entirely to the Redwater Member, although the presence near Manila COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES of a few feet of the Curtis Member is reported by G. N. Pipiringos (oral commun., 1967). All these formations and members extend eastward along the margins of the Uinta Mountains into the west- ern part of Moffat County, in the northwestern corner of Colorado (G. N. Pipiringos, oral commun., 1974). The Camel Formation, however, wedges out east of Miller Creek (sees. 27 and 34, T. 4 N., R. 101 W.). The Red— water Shale Member of the Sundance Formation is ab- sent east of Uranium Peak (sec. 28, T. 2 N., R. 92 W.) in the northeastern part of Rio Blanco County, Colo. The Curtis Formation and the equivalent Pine Butte Member of the Sundance Formation are locally absent at several places within their area of outcrop, even though the un- derlying Entrada Sandstone and the overlying Redwater Shale Member are present. In north-central Colorado along the margin of the Park and Gore Ranges in Eagle, Routt, and Grand Counties, the marine Jurassic is represented near Kremmling, State Bridge, and Burns by the Canyon Springs Sandstone, Lak(?), Pine Butte(?), and Windy Hill Sandstone Members of the Sundance Formation (Pi- piringos and others, 1969, p. N9—N35). The lower three of these members are transitional into each other, as at Frantz Creek (fig. 27), but locally the Canyon Springs grades upward into the Pine Butte, as at Elk Creek (fig. 27). This relationship shows that the upper part of the Canyon Springs must locally be as young as the Entrada Sandstone of other areas. Its lower part, which is unfos- siliferous, may or may not be as old as the typical mem- ber in Wyoming. The identification of both the Lak and the Pine Butte Members is tentative (Pipiringos and oth- ers, 1969, p. N12, N15). Farther north along the Park Range in the Hahns Peak area of northern Routt County, the marine Sun- dance Formation is represented by the Canyon Springs Sandstone Member, the Pine Butte Member, the Red- water Shale Member, and the Windy Hill Sandstone Member (Pipiringos, 1972, p. 25-29). Of these, the Can- yon Springs consists of about 60 feet (18 m) of gray to pink crossbedded sandstone and rests unconformably on Triassic rocks. The Pine Butte Member consists of about 30 feet (9 m) of greenish—gray shale and some thin beds of ripple-marked sandstone that intertongues downward with the Canyon Springs. The Redwater Shale Member consists of 35 feet (10.6 m) of glauconitic siltstone and sandstone that correlates with only the lowermost of four units of that member exposed in south-central Wyoming . (Pipiringos, 1968, p. D23). The Redwater Shale Member rests unconformably on the Pine Butte Member, is trun- cated by the Windy Hill Sandstone Member, and is un- known south of Corral Creek (sec. 18, T. 8 N., R. 84 W.). This unconformable relationship and the wide- 93 spread occurrence of the Windy Hill beyond the boun- daries of the Redwater Shale Member demonstrates that these two members represent separate marine inva— slons. The Jurassic exposed along the east side of the Front Range in northern Colorado is represented, from bottom to top, by 20 to 50 feet (6 to 15 m) of the Entrada Sand- stone, by thinner marine units belonging to the Pine Butte Member and the Windy Hill Sandstone Member of the Sundance Formation, and by the Morrison Forma- tion (G. N. Pipiringos, oral commun., 1974). All contacts between these units are conformable except that be- tween the Windy Hill and the Pine Butte. The conform- able relationship of the Entrada Sandstone with the Pine Butte Member shows that it is equivalent at least at its top to the Lak Member of the Sundance Formation in eastern Wyoming. It is probably equivalent also to the Canyon Springs Sandstone Member in the Park Range in north-central Colorado but may be younger than the typical Canyon Springs Sandstone Member in southern Wyoming and the Black Hills. NORTH—CENTRAL UTAH TO SOUTHWESTERN COLORADO The Jurassic sequence exposed in Monks Hollow (Baker, 1947; Imlay, 1967b, p. 11), about 18 miles (29 km) southeast of Provo, Utah, is essentially the same as that exposed in the western part of the Uinta Mountains. A possible difference is in the 510 feet (155 m) of beds between the Preuss Sandstone and the Morrison For- mation. The lower 260 feet (79 m) of these beds consists mostly of greenish-gray sandy shale interbedded with some gray to greenish-gray glauconitic sandstone and greatly resembles the unit in the Uinta Mountains that is identified with the typical Curtis Formation of central and northeastern Utah. The upper 250 feet (76 m) con- sists mostly of light-brown siltstone that contains a few beds of gray sandstone and greenish-gray shale and that was compared by Baker (1947) with the Summerville Formation. These identifications have now been con— firmed by G. N. Pipiringos and the writer. The lower 260 feet (79 m) of beds overlying the Preuss Sandstone at Monks Hollow occupies the same stratigraphic position as the Curtis Formation, resem- bles it lithologically, and likewise contains an abundance of M eleagrinella. These beds differ from the type Curtis Formation on the San Rafael Swell mainly by containing more soft clay shale and fewer hard sandstone beds and by the presence of a few cephalopods. Meleagrinella was collected throughout about 40 feet (12 m) of beds ranging from about 180 to 220 feet (55 to 67 m) above the top of the Preuss Sandstone. With these were found external and internal molds of the ammonite Lytocems (USGS 94 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Mesozoic loc. 30718). Also, four belemnites were ob- tained from the upper 10 to 15 feet (3 to 4.5 m) of the M eleagfinella-bearing beds. The next higher 250 feet (76 m) of beds is definitely similar lithologically to the Summerville Formation of the San Rafael Swell. Like that formation, these beds are unfossiliferous and are gradational downward into the un- derlying Curtis Formation. These upper beds cannot rea- sonably be correlated with the Redwater Shale Member of the Stump Formation, as exposed nearby in the Uinta Mountains, because that member consists mostly of greenish-gray shale, rests unconformably on the Curtis Member, and contains a fair abundance of fossils. The presence of belemnites in the Curtis Formation at Monks Hollow is not evidence that the Redwater Shale Member is present there, because in Montana, bel- emnites are in beds of middle Bajocian to late Callovian Age (Imlay, 1948, p. 17; 1962b, p. C11, 021) and in the Pacific Coast region, they range throughout the Jurassic. Their presence along with Lytoceras, however, is evi- dence that the marine waters that deposited the Curtis Formation at Monks Hollow were deeper than those far- ther east in Utah and that the sea of Curtis time must have entered the western interior region from the west. Marine Jurassic beds exposed on the west side of the Gunnison Plateau near Nephi and Levan, Utah, are de- fined as the Arapien Shale and are divided into two mem- bers (Spieker, 1946, p. 123—125; Hardy and Zeller, 1953, p. 1264—1266; Hardy, 1962, p. 52-54). The lower of these, the Twelvemile Canyon Member, greatly resem- bles the Twin Creek Limestone. It differs by being in- tensely folded, crinkled, and fractured and by containing more shale, more red units, and some gypsum in its upper part. Nonetheless, the lower part of the Twelvemile Can- yon Member, as exposed on the south side of Red Canyon, about 2 miles (3 km) north of Nephi, contains units that resemble the members of the Twin Creek Limestone from the Gypsum Spring Member up to the basal part of the Leeds Creek Member (Imlay, 1964d, p. C6; 1967b, p. 30, 40, 44). The Twelvemile Canyon Member is overlain along the Gunnison Plateau by the Twist Gulch Member, which consists of red siltstone and sandstone more than 1,800 feet (550 m) thick. This member is similar lithologically to the Preuss Sandstone in northern Utah, except for the presence of some gritty or pebbly beds. Marine Jurassic beds exposed along the west side of the Wasatch Plateau near Gunnison and Salina are also referred mostly ‘to the Arapien Shale (Hardy, 1952, p. 14-24, 67—95). The Twelvemile Canyon Member, how- ever, is represented only by its upper part, which con- sists mostly of much crinkled, gypsiferous red to gray shale, siltstone, and sandstone. At its very top, it also includes 165—200 feet (50—61 m) or more of red silty shale and interbedded salt (Hardy, 1952, p. 21, 22, 91). It is conformably overlain by the Twist Gulch Member, which consists of 1,670—1,730 feet (509—527 m) of in-, terbedded red calcareous siltstone and claystone, red- dish-gray to red sandstone, and some conglomerate. Above the Arapien Shale in the Salina Creek canyon east of Salina is 177 feet (54 m) of gray to green shale in- terbedded with and overlain by thin beds of gray sand- stone. This shale contains 17 feet (5 m) of gray grit and some brown to red shale at its base (Hardy, 1952, p. 78). Fossils in the thin sandstone beds include Meleag'm'nella curta (Hall) and Ostrea. Of these units, the upper 177 feet (54 m) of fossilifer- ous shale and sandstone is identical with the typical Cur- tis Formation of central Utah and is herein referred to that formation. The underlying Twist Gulch Member is similar to the Preuss Sandstone of northern Utah but differs in that it contains some pebbly beds and in that some of the sandstone beds are coarse grained or gritty, or crossbedded. The salt-bearing red silty shale, which is defined as being at the top of the Twelvemile Canyon Member, corresponds lithologically and stratigraphically with the salt-bearing red beds in the lower part of the Preuss Sandstone along the Idaho-Wyoming border (Mansfield, 1927, p. 99, 338—340; Imlay, 1952b, p. 1746). The underlying upper part of the Twelvemile Canyon Member probably correlates with the Leeds Creek and Giraffe Creek Members of the Twin Creek Limestone but differs by containing more red units, more sand- stone, and more gypsum. The described Jurassic sequences present on the west side and north end of the San Rafael Swell are typified by the sequence near Buckhorn Wash (Gilluly, 1929, p. 99—114; Gilluly and Reeside, 1928, p. 97—106, chart opposite p. 74). On the east side of the swell, they are typified by the sequences at the Black Dragon Can- yon and at the San Rafael River (Baker, 1946, p. 69—90). Lithologic units within those sequences are described, correlated, and dated in various papers (Baker and oth- ers, 1936, p. 11, 25, 26, 31, 58—63; Imlay, 1952a, p. 961— 964; Wright and others, 1962; and Cater and Craig, 1970) and are summarized in figure 28, except for the Curtis, Summerville, and Morrison Formations discussed below. Of these three, the Curtis Formation consists mostly of greenish shale, glauconitic sandstone, and shale. Sand- stone is most common and is generally thin bedded, rip— ple marked, and crossbedded. Shale beds are generally sandy and some are red or lavender. Conglomeratic beds occur in the lower part of the formation in the northern and northwestern parts of the swell. The contact of the Curtis Formation with the underlying Entrada Sand- stone is sharp, locally angular, and is locally marked by conglomerate (Gilluly, 1929, p. 105—108; Gilluly and COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES Reeside, 1928, p. 78—106; Baker, 1946, p. 80—84). The Curtis Formation contains echinoid fragments, cri- noid columnals, Ostrea strigilecula White, Meleagrinella curta (Hall), Tamredia, and Camptonectes. The Summerville Formation on the San Rafael Swell consists mainly of thin-bedded, even—bedded shale and sandstone and locally contains considerable gypsum. Generally the shales are chocolate brown to maroon, and the sandstones are reddish brown. Ripple marks are common in the sandstones. The formation grades down- ward into the Curtis Formation, replaces the Curtis gra- dationally near the Green River, and is overlain with angular unconformity by the Morrison Formation (Gil- luly, 1929, p. 108—110; Gilluly and Reeside, 1928, p. 79— 106; Baker, 1946, p. 84-86). The Morrison Formation in the southern part of the western interior region attains maximum thicknesses of 800—900 feet (240—270 m) (Craig and others, 1955, p. 159) and was derived mainly from source areas in the west-central parts of New Mexico, in Arizona, in west- ern and northwestern Utah, and in southeastern Califor- nia (Craig and others, 1955, p. 126, 150, 151, 159). Its base cannot be dated as precisely here as in areas to the north where the formation rests conformably on the Red- water Shale Member of the Sundance Formation. Pre- sumably the Morrison Formation south of northern Utah and northern Colorado is also of late Oxfordian to early Tithonian Age. However, the basal part of the Morrison may be of early Oxfordian Age, equivalent to the Redwater Shale Member. Such is suggested by the presence of massive gypsum at the base of the Morrison Formation in the San Rafael Swell (Gilluly, 1929, p. 114, 117; Baker, 1946, p. 87, 89, 90). As that gypsum rests unconformably on the Summerville Formation, it cannot be as old as that for- mation. Instead, its presence suggests deposition in la- goons at the margin of a shallow sea, such as existed in early Oxfordian time north of the San Rafael Swell. Recent refinements in dating the Jurassic formations in the San Rafael Swell are based on three discoveries. First, G. N. Pipiringos (oral commun., 1974) recognized that the Curtis Formation in the San Rafael Swell is identical with the Pine Butte Member of the Sundance Formation in Wyoming (Pipiringos, 1968, p. D23) and with the lower member of the so-called Curtis Formation and Stump Sandstone of northern Utah, as used by Thomas and Krueger (1946, p. 1278, 1279). All these units occupy the same stratigraphic position above the Entrada Sandstone, or equivalent units. This identifi- cation means that the Curtis Formation of the San Rafael Swell must be older than early Oxfordian, because the equivalent beds in Wyoming and in northern Utah dis- conformably underlie the lower Oxfordian Redwater Shale Member of the Sundance Formation and of the 95 Stump Sandstone. Faunally, the Curtis Formation of the San Rafael Swell is distinguished from the Redwater Shale Member by its lack of belemnites and brachiopods. These taxa are also absent in the Pine Butte Member of the Sundance Formation and in the Curtis Member of the Stump Sandstone. Second, the lowest limestone unit in the Carmel For- mation on the west side of the San Rafael Swell was dated by Imlay (1967b, p. 32, 33) as latest Bajocian, be- cause it contains certain pelecypods and ammonites that elsewhere are characteristic of the Rich Member of the Twin Creek Limestone and that do not range higher. In particular, the ammonite Sohlites spinosus Imlay was obtained 6—12 feet above the base of the Carmel For- mation on The Wedge near Buckhorn Wash (Imlay, 1967b, p. 92, pl. 11, fig. 24). . Third, 100 feet (30 m) or less below the base of the Carmel Formation on the San Rafael Swell, Pipiringos and O’Sullivan (1975) recognized an unconformity that is marked by chert pebbles and that probably correlates with the unconformity at the top of the Gypsum Spring Formation in Wyoming. These pebbles are overlain by massive, crossbedded gray sandstone, which was pre- viously assigned to the Navajo Sandstone (Gilluly, 1929, p. 98; Gilluly and Reeside, 1928, p. 72; Baker and oth- ers, 1936, pls. 13, 14; Baker, 1946, p. 68, 69) but which has now been renamed Page Sandstone (Peterson and Pipiringos, unpub. data, 1977). This sandstone has been recognized above chert pebble beds at many places in southern Utah, where it is as much as 250 feet (76 m) thick and where it conformably underlies and laterally intertongues with the lower part of the Carmel Forma- tion (Pipiringos and O’Sullivan, 1975, 1978). Therefore, inasmuch as the lower part of the Carmel has. been cor- related with the Rich Member of the Twin Creek Lime- stone (Imlay, 1967b, p. 33), the underlying Page Sand- stone on the swell should be equivalent to the Sliderock Member of the Twin Creek. On the basis of these discoveries, the Curtis For- mation on the San Rafael Swell is considered to be of late middle Callovian Age. The overlying Summerville Formation is considered to be only slightly younger, as shown by its gradation downward and laterally into the Curtis Formation (Baker, 1946, p. 86) and by the an- gular unconformity at its top. This unconformity presum- ably correlates in part with the regional unconformity at the base of the Redwater Shale Member of the Sundance Formation. The basal limestone of the Carmel Formation on the \San Rafael Swell is dated as latest Bajocian on the basis of fossils. Consequently, the beds overlying this unit, but below the Curtis Formation, are dated as Bath- onian to early or early middle Callovian on the basis of stratigraphic position. Furthermore, the lower part of the Carmel Formation, between its basal limestone beds 96 and its varicolored gypsiferous beds, bears lithologic re- semblances to the Boundary Ridge and Watton Canyon Members of the Twin Creek Limestone (Imlay, 1967b, p. 40, 44, 49), which members are now dated as early to middle Bathonian. The Jurassic formations exposed east of the San Ra— fael Swell, in easternmost Utah and westernmost Colo— rado, have been studied in considerable detail (Mc— Knight, 1940; Dane, 1935; Baker, 1946; Wright and others, 1962; Craig and others, 1955; Cater and Craig, 1970; Shawe and others, 1968, Ekren and Houser, 1965) but are difficult to correlate and date precisely because fossils are scarce in all of them except the continental Morrison Formation. Lateral tracing of beds shows, however, that the lower, limestone-bearing part of the Carmel Formation thins eastward and pinches out a little east of the mouth of the San Rafael River (Baker, 1946, p. 71; McKnight, 1940,-p. 87; Wright and others, 1962, p. 2058). The upper varicolored gypsiferous part of the Carmel Formation also thins gradually eastward, and "east of the Green River in east-central Utah, it passes into reddish-brown siltstone and silty sandstone that most geologists have mapped as the eastern part of the Carmel Formation but that are now called the Dewey Bridge Member of the Entrada Sandstone (Wright and others, 1962, p. 2059). This member pinches out near the State line west of Grand Junction, Colo., but persists southeastward as a thin unit into southwestern Colo— rado. East of the San Rafael Swell, the Entrada Sandstone consists of three members (fig. 28). The basal Dewey Bridge Member is conformably overlain by the Slick Rock Member, and the Moab Member is locally present at the top of the formation. The Entrada Sandstone of the San Rafael Swell extends eastward as the Slick Rock Member, a massive, crossbedded sandstone that thins to the east and southeast (Wright and others, 1962, p. 2062). The overlying Moab Member consists of massive, white, crossbedded sandstone that is at least 100 feet thick near Moab but that thins laterally away from there into ledge-forming sandstone (Baker and others, 1927, p. 804; Dane, 1935, p. 94). It is reported to intertongue laterally in places with the Summerville Formation, in places to grade downward or laterally into the Slick Rock Member, and in other places to rest on an erosion surface at the top of the Slick Rock Member (McKnight, 1940, p. 89-97; Wright and others, 1962, p. 2063—2067; Cater and Craig, 1970, p. 30). In places where the Moab Mem- ber is absent, the Slick Rock apparently is overlain con- formably by the Summerville Formation. The Summerville Formation east of the Green River in eastern Utah and in westernmost Colorado includes beds that are probably equivalent to the Curtis Forma— JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES tion, but otherwise it maintains its lithologic character- istics, except for the presence of a few sandstone lenses. Such lenses occur (1) at its base where the Moab Member intertongues, (2) in a fairly persistent marker bed a little above its middle (Wright and others, 1962, fig. 2, 3; Shawe and others, 1968, p. A45), (3) at its top in south- western Colorado where the Junction Creek Sandstone intertongues (Shawe and others, 1968, p. A49, A50; Ek- ren and Houser, 1965, p. 12, 13; Stokes, 1944), and (4) where a similar sandstone called the Bluff Sandstone in- tertongues in southeastern Utah. (See summary in Craig and others, 1955, p. 132—134.) Considerably different statements have been made concerning the nature of the boundary between the Mor- rison Formation and the underlying Summerville For- mation, or equivalent units, as exposed along the Utah- Colorado border (fig. 28). Northeast of Moab, Utah, in the Salt Valley anticline area, as at Dewey Bridge, the contact is sharp, slightly irregular, and persistent (Dane, 1935, p. 112). In the adjoining area in western Colorado, as at John Brown Valley, the contact as mapped is re— ported to be gradational within 15 feet or less (Cater and Craig, 1970, p. 40). Nonetheless, the absence of the Sum- merville Formation locally along crests of some salt an- ticlines could be due to erosion during early Morrison time (Cater and Craig, 1970, p. 34) or to nondeposition during Summerville time. To the southeast in the Slick Rock area, the same contact is disconformable at most places (Shawe and others, 1968, p. A58). Still farther south in the Ute Mountains area, as at McElmo Canyon, the contact of the Morrison Formation with the Junction Creek Sandstone is locally disconformable and locally gradational (Ekren and Houser, 1965, p. 13). If these statements are correct, then deposition of the Summer- ville Formation was succeeded in places directly by dep- osition of the Morrison Formation while erosion took place in other places nearby. SOUTHWESTERN UTAH AND NORTHERN ARIZONA Along the Utah-Arizona border the lowermost Ju- rassic may be represented by units of continental origin that from the base up include the Moenave Formation, the Kayenta Formation, and the Navajo Sandstone (fig. 29). The Moenave Formation rests unconformably on the Chinle Formation, is mostly of fluvial origin, comprises three members, and drained southwestward. Of these members, the lowermost, or Dinosaur Canyon Sand- stone Member, consists of reddish—orange to brown sand- stone and siltstone (Harshbarger and others, 1957, p. 13; Wilson, 1965, p. 39); the middle, or Whitmore Point Member, consists mostly of gray to red siltstone and claystone but includes some limestone (Wilson, 1967); COMPARISONS 0F LITHOLOGIC AND STRATIGRAPHIC FEATURES and the upper, or Springdale Sandstone Member, con- sists mostly of pale—red to brownish-red sandstone but includes some siltstone and conglomerate. The Kayenta Formation consists of light-gray to reddish-orange sand- stone and siltstone that becomes finer grained and thicker southwestward, intertongues southwestward with the adjoining members, is mostly of fluvial origin (Wilson, 1965, p. 40, 42), and drained southwestward. The Navajo Sandstone consists mostly of highly crossbedded sand- stone, includes some beds of cherty limestone, and is mostly of eolian origin (Harshbarger and others, 1957, p. 19—25; Wright and Dickey, 1958, p. 173; Stokes, 1963, p. 61; Wilson, 1965, p. 41, 42; Averitt, 1962, p. 17, 18). The Moenave Formation occupies the same strati- graphic position as the Lukachukai Member of the Win- gate Sandstone, which lies to the east and northeast and which consists mostly of eolian, large-scale crossbedded sandstone (McKee and MacLachlan, 1959, p. 22, pl. 8, figs. 5, 6, table 1; Wright and Dickey, 1958, p. 172, 173). The change from the eolian Wingate Sandstone to the fluvial Moenave Formation in southern Utah takes place within a few miles along a northwest-trending zone, which is an extension of that mapped by Harshbarger and others (1957, p. 3, 10) in the Navajo Indian Reser- vation in northern Arizona. These formations are possibly of Early Jurassic age, as suggested (1) by the presence of an unconformity be- tween the Moenave and the underlying Chinle Forma- tion of Triassic age; (2) by an unconformity between the Navajo Sandstone and the overlying Temple Cap Sand- stone of early to early middle Bajocian Age; and partic- ‘ ularly (3) by palynomorphs dated as of late Sinemurian to early Pleinsbachian Age in the basal 15 feet (5 m) of the Whitmore Point Member of the Moenave Formation (Peterson and others, 1977, p. 755). Acceptance of this dating must await adequate description and illustration of the fossils and confirmation by other paleontologists. At present, the formations in question are dated by the US. Geological Survey as Triassic (or Triassic?) and (or) Jurassic (or Jurassic?) This evidence suggests that the unconformity at the base of the Moenave Formation is possibly of Hettangian Age, that the unconformity at the top of the Navajo Sandstone is at least partly of late Toarcian Age, and that the Kayenta Formation and Navajo Sandstone may have been deposited during Pliensbachian and Toarcian time. Furthermore, the Navajo Sandstone may be cor- related with the Dunlap Formation of western Nevada on the basis of the presence in common of nearly identical crossbedded quartz sandstone (Stanley, 1971, p. 467- 475), on a similar stratigraphic position, and on the main source area of both formations being an uplifted north- ward-trending area in central Nevada. However, the 97 sand in the Dunlap Formation may have been derived from the Navajo Sandstone by erosion. If this premise is correct, the Navajo should be at least as old as Sinemu— man. The Temple Cap Sandstone was originally described by Gregory (1950) as a member of the Navajo Sandstone. It was subsequently made a separate formation (Fred Peterson and G. N. Pipiringos, unpub. data, 1977). It consists of two facies, or members, which extend about 75 miles (120 km) to the east from Gunlock, Utah, and which pinch out between the Carmel Formation and the Navajo Sandstone (fig. 29) a few miles east of Johnson Canyon. One facies, called the White Throne Member, consists of 170 feet (52 m) or less of pale-red to gray crossbedded sandstone that is identical with the sand- stone of the underlying Navajo Sandstone but that is separated from it by 5 to 25 feet (1.5 to 7.6 m) of softer red or gray siltstone and silty sandstone. The other fa— cies, called the Sinawava Member, consists of 372 feet (113 m) or less of red to gray, flat-bedded sandstone, silty sandstone, mudstone, and some bedded gypsum. This facies changes eastward from red to gray at Mount Carmel Junction. To the west, the White Throne Mem- ber intertongues with the Sinawava Member near the Hurricane Cliffs on the west side of Zion National Park, and to the east it overlies a thin extension of the Sina- wava Member as far east as their pinchout near Johnson Canyon, about 10 miles (16 km) east of Mount Carmel. The formation contains small, rounded chert granules at its base, and rests sharply on the Navajo Sandstone. Criteria that suggest an unconformity at the base of the Temple Cap, according to Peterson and Pipiringos (unpub. data, 1977), are (1) lack of interfingering be— tween the Temple Cap and Navajo Sandstones; (2) clear separation of these formations by a continuous surface; (3) broad irregularities at the base of the Temple Cap that are interpreted as an expression of erosional relief developed on the Navajo prior to Temple Cap deposition; and (4) a thick bleached zone at the top of the Navajo at most places, which is interpreted as alteration product of ground-water seepage into the upper part of the Navajo during a long erosion interval. These criteria and rela- tionships show that the Temple Cap Sandstone is not a tongue of the Navajo Sandstone and should not have been considered a member of that formation by Gregory (1950, p. 89) and later workers (Wright and Dickey, 1963a, b; Thompson and Stokes, 1971; Lewis and others, 1961). The Carmel Formation of southwestern Utah be- tween Gunlock and Johnson Canyon consists of four members (fig. 29) that from base to top were called the limestone member, the banded member, the gypsiferous member, and the Winsor Member by Cashion (1967). The 98 same members were also described by Gregory (1950, p. 92—98) under the names Carmel Formation, Entrada Sandstone, Curtis Formation, and Winsor Formation, respectively. We now know, however, that rocks called the Entrada Sandstone and the Curtis Formation by Gregory are much older than those formations at their type localities in central Utah (Imlay, 1967b, p. 20, 33, 40, 44). Of the four members, the limestone member is of most importance for age determinations because it is the only Jurassic member in southern Utah that contains datable marine fossils. Also, its lower 20—120 feet (6- 36.5 m) of pink to red siltstone and claystone basally con- tains angular chert pebbles from Zion National Park eastward, but west of the park, the same unit contains granules of rounded chert and quartz. Its lower contact, according to Fred Peterson and Pipiringos (unpub. data, 1977) is sharply defined and bevels out the Temple Cap Sandstone to the east near Johnson Canyon. The fourfold division of the Carmel Formation per- sists eastward across southwestern Utah for about 90 miles (144 km) with little change except for thinning of the lower three members. East of the Little Bull Valley area, however, the Winsor Member grades into the mid- dle and upper parts of the upper member of the Carmel Formation, as described by Fred Peterson and Pipirin- gos (unpub. data, 1977). Near the Paria River, the gyp- siferous member grades into the lower part of the upper member. Also near Little Bull Valley, 8 miles (13 km) south- west of Cannonville, the banded member grades into crossbedded to flat-bedded sandstone of the Thousand Pockets Tongue of the Page Sandstone (Wright and Dickey, 1963a, p. E65, E66; Phoenix, 1963, p. 32, 33; Fred Peterson and Pipiringos, unpub. data, 1977). East of the Paria River near Cannonville, the lower limestone member is termed the Judd Hollow Tongue of the Car- mel Formation (Phoenix, 1963). Farther east, this ton- gue grades into flat-bedded sandstone and siltstone that disappears eastward between two tongues of the Page Sandstone. Evidently, the Page Sandstone, where fully developed, as at its type locality near Page, Ariz., is equivalent to both the limestone member and to the banded member of the Carmel Formation farther west. The Page sandstone, as defined by Fred Peterson and Pipiringos (unpub. data, 1977), is as much as 291 feet (89 m) thick about 10 miles (16 km) south-southwest of Page, Ariz. It consists mostly of gray, cliff-forming, crossbedded sandstone, contains angular, red to gray chert pebbles at its base and, locally, higher, and rests sharply and unconformably on the Navajo Sandstone along a surface that locally has a relief of as much as 37 feet (11 m). According to Fred Peterson and Pipiringos (unpub. data, 1977) the evidence for an unconformity is strengthened by two facts: (1) the angular pebbles con- JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES sist of the same kinds of chert that are formed in authi- genic chert nodules in the Navajo Sandstone; and (2) the upper few feet of the Navajo Sandstone at many places contains crevices that they interpret as fossil joints weathered out prior to deposition of the Page Sandstone. The Entrada Sandstone of south-central Utah, where fully developed, as at Pine Creek near Escalante, con- sists of three members, according to Fred Peterson and Pipiringos (unpub. data, 1977). At Pine Creek, the upper member consists of white crossbedded sandstone, the middle, of red to white to light-green flat-bedded silty sandstone and mudstone, and the lower, of red, thick- bedded, flat-bedded silty sandstone. The upper member becomes truncated southward in Utah, but the middle and lower members persist considerably beyond the lim- its of the upper member and become sandier and more crossbedded both westward in Utah and southward in Arizona. At some places, as at Big Hollow Wash, Utah, and Page, Ariz., the middle member of the Entrada is overlain unconformably by a light-gray sandstone unit 0—44 feet (0—13.4 m) thick, which has a thin red mud- stone bed at its base, and which apparently occupies the same stratigraphic position as the Summerville Forma- tion of central Utah (Fred Peterson, 1974, 1973; Fred Peterson and Barnum, 1973). The Morrison Formation unconformably overlies the light-gray sandstone at Page and Big Hollow Wash (fig. 29). In areas where the light-gray sandstone is missing, the Morrison rests unconformably on the upper or middle member of the Entrada Sandstone. The Morrison For- mation is highly variable in thickness, comprises three members of which the lower and upper may be locally absent, and is overlain unconformably by Cretaceous beds (Fred Peterson and Barnum, 1973; Fred Peterson, 1973, 1974; Zeller and Stephens, 1973). The Jurassic formations of southern Utah are corre- lated with formations farther north by some lithologic re- semblances, by their relative stratigraphic positions, and by the presence of certain species of mollusks in the mid- dle to upper parts of the limestone member of the Carmel Formation. These mollusks have been found in expo- sures between Gunlock and the Mount Carmel-Glendale area and also in a thin limestone unit 12—20 feet (3.6— 6 m) above the base of the Carmel Formation at Deep Creek north of Escalante and at Hells Backbone north— west of Boulder, Utah. At least the upper three-fourths of the limestone member of the Carmel Formation between Gunlock and Mount Carmel is dated as late Bajocian. That age is shown by the presence or association of certain species of pelecypods that in Idaho and Wyoming are character- istic of the Rich Member of the Twin Creek Limestone and are not known from higher or lower members (Im- lay, 1964d, p. C3; 1967b, p. 14, 15, 31, 33). Near Gunlock, JURASSIC UNCONFORMITIES for example, correlation with the Rich Member is shown by the presence of Gervillia? montamensis Meek, which occurs about 150 feet (46 m) above the base of the lowest limestone beds and also about 323 feet (98 m) higher, or 50 feet (15 m) below the eroded top of the member. Vau- gom'a conmdi Meek, not known below the Rich Member, was found 74 miles (12 km) east of Gunlock in the Dia- mond Valley sequence 60—80 feet (18—24 m) above the lowest limestone bed, and 9 miles (14.5 km) northwest of Hurricane near the Danish Ranch about 60 feet (18 m) above the lowest limestone bed. These fossil occurrences and others, as listed previ- ously (Imlay, 1964d, p. C8, C9, C13; Sohl, 1965, p. D5, localities 8—12, 33-38 on p. D6, D7), show that only the lower one-fourth to one-fifth of the limestone mem- ber could be older than the Rich'Member. Beds equiva- lent to the Sliderock Member of the Twin Creek Lime- stone could only be represented by the lowest 50-150 feet (15—46 m) of unfossiliferous limestone of the lime- stone member and by the underlying gypsiferous red sandy siltstone beds at the base of the Carmel Forma- tion. Such a correlation seems most likely for the thickest sequences of the member as exposed from Gunlock east- ward to Pintura and thence northeastward to Shurtz Creek about 6 miles (10 km) south of Cedar City. If this correlation is correct, then the unconformably underly— ing Temple Cap Sandstone should be of about the same age as the Gypsum Spring Formation of Wyoming and adjoining States, which is of early to early middle Bajo— cian Age, only a little older than the Sliderock Member. Similarly, on the basis of stratigraphic position, the banded member of the Carmel Formation, and its equiv- alent Thousand Pockets Tongue of the Page Sandstone, ' should correlate with the Boundary Ridge Member of the Twin Creek Limestone and should be of early Bathonian Age. The overlying upper part of the Carmel Formation in southwestern Utah should correlate with the higher members of the Twin Creek Limestone and should be of middle Bathonian to early Callovian Age. Southeastward from Page, Ariz., according to Fred Peterson (1974, p. 467; oral commun., 1974), the Page Sandstone pinches out in about 15 miles (24 km), the Morrison Formation, in about 30 miles (48 km), and the underlying gray sandstone of Romana Mesa, in about 45 miles (72 km). As a result, at Cow Springs, about 50 miles (80 km) southeast of Page, the Jurassic is repre- sented only by the Carmel Formation and the Entrada Sandstone. Peterson noted that the Carmel Formation at Cow Springs is 188 feet (57 m) thick, consists of flat- bedded sandstone, silty sandstone and mudstone, is mostly reddish brown, includes some angular chert/peb- bles at its base, and rests unconformably on the Navajo Sandstone. At the same place, the Entrada Sandstone is 773 feet (236 m) thick. Its lower 197 feet (60 m) consists 99 mostly of light-gray crossbedded sandstone but includes some thin beds of dark-brownish-red mudstone or sand— stone. Its middle 274 feet (84 m) consists mostly of or- ange—brown to reddish-brown or white flat-bedded sand- stone but includes some crossbedded sandstone. Its upper 302 feet (92 m) consists mostly of light-gray to greenish- gray crossbedded sandstone but includes some fairly thin beds of flat-bedded sandstone and is overlain unconform- ably by the Dakota Sandstone. This upper unit repre— sents the Cow Springs Sandstone of Harshbarger and others (1957, p. 49—51), but it is considered by Fred Pe- terson (1974, p. 467) to be a bleached-out upper part of the Entrada Sandstone, such as occurs in many sections in northern Arizona and southern Utah. MIDCONTINENT REGION The only Jurassic deposit identified to date in the middle part of the continent is in the center of the Mich- igan basin. It consists of 100-400 feet (30-120 m) of red clay, shale, sandstone, and some gypsum. The deposit has lenticular bedding, rests on Pennsylvanian and Mis— sissippian rocks, contains spores identified as Kimmer- idgian in age, and presumably is entirely continental (Cohee, 1965). Its age apparently coincides with that of the Morrison Formation in Montana and the Dakotas. JURASSIC UNCONFORMITIES A major unconformity representing more than the lower half of Jurassic time occurs throughout the north- ern and western parts of the Gulf region as far south as Victoria, Tamaulipas, Mexico (figs. 21, 30). This uncon- formity probably continued into early Callovian time, on the basis of the probability that the overlying saline beds (Louann Salt, Werner Formation, and Minas Viejas For- mation) were deposited at the same time as similar saline beds in southeastern Mexico, where conditions were un- favorable for salt deposition before late Callovian time (Imlay, 1943a, p. 1438, 1508—1510; 19530, p. 31; Vinie- gra 0., 1971, p. 480, 484). Farther south, in the Huasteca area of eastern Mex- ico, an unconformity of such magnitude is not recogniz- able except locally on certain uplifts. Instead, the same time interval is represented by (1) an unconformity of Hettangian Age, (2) marine and plant-bearing deposits of Sinemurian and questionably of early Pliensbachian Age, (3) an unconformity of Pliensbachian to Toarcian Age caused by orogenic activity, (4) continental beds of Bajocian to Bathonian Age, (5) an unconformity of latest Bathonian and earliest Callovian Age, and (6) marine beds of late early Callovian and younger ages. Bajocian 100 i J URASSIC PALEOBIOGEOGRAPHY OF THE CONTERMlNOUS UNITED STATES Gulf of Mexico region Pacific Coast region I Southwest Oregon and _ I .28. Sgauéth' Nonh- Mountains Huasteca area, W 3‘ rn TaylorsVIlle area Western part of northwest California East centre Oregon 35) 5'399 United east west of Victoria, gaspcentral Ne ed in northern the G t ' ‘ - 9V3 a ' S'er N da alioe- ‘ States Mexuco eastern Mexuco Mexuco Slerra Nevada I re eve Rogue figflmlilg Suplee Izee area sequence sequence 3'93 Tithonien .2 i2 8 3 2 Kimmeridgian a . Q 2) Oxfordian l I I I I I 7 I 1 "IV L? , 7 Non- marine Callovian —? 1 ___7__ '3 No fossil\ 3 Bethonian evudonoe 5 _, 2 3 Non- : marine ? Bajocian Non- ' ‘ marine 7 7 in subsurface ? '1— Not expose Toarcian ? .9 ‘ ’ 3 Pliensbachian fl 3» 7 E’ _l Partly ‘ Sinemurian nonmarine ? ? Hettangian \\ . FIGURE 30.—Jurassic unconformities in Gulf of Mexico and Pacific Coast regions. Blank spaces indicate that marine strata are present; vertical lines indicate that strata are missing; left—diagonal lines indicate that strata are not exposed; right-diagonal lines indicate lack of fossil data. ' JURASSIC UNCONFORMITIES 101 Western interior region Sw'ft s Reserlvoir Williston Ammo" n dCreek Bus" PeoarOakley Dinosaur Buckhorn Mount Carmel Pine Creek P a 'g 5‘399 and basin, uadrangle, ecentral ’ Canyon, area, Quarry, Wash, Junction, so uth- entr'l 0:9: ”net" to Sun River, northeast southeast Wyoming “3‘97." north-central "0'1“985‘ central 30““19'" Utah 3 n “has” northwest Montana Idaho Wvommfl Utah Ulah Utah Utah Montana ? ? 7 7 7 ‘ ? \ Tithonian .2 ID . ‘3; Nonmarrne Nonmarine Nonmarine Nonmarine Nonmarine Nonmarine 7 ? g ‘ ‘ 'n a Krmrneridgla Nonmarine Nonmarine 3 Nu.......;..= Oxfordian I I l I I I Callovian I I l I l I I J Nonmarins ' Partly nonmarine nonranriaying .2 8 g Bathonian 3, (I Partly 2 ’ nonmarine E Nonmarine E / / Nonmarine / Nonmarine 7 7 Bajocian / I l l l | | | J Mostly nonmarlne 7 ? 7 7 ? 7 ' 7 7 l 7 7 7 7 Toarcian .9 \ a Pliensbachian .. 3: Nonmarine Nonmarine Nonmarine Nonmarine Nonmarine Nonmarine Nonmarine E E» Sinemurian . 7 7 7 7 7 ? 7 Hernanglan FIGURE 31.—Jurassic unconformities in western interior reg-ion. Blank spaces indicate that marine strata are present; vertical lines indicate that strata are missing. 102 and Bathonian continental beds in the Huasteca area cor- relate fairly well in time with similar plant-bearing beds in the States of Guerrero and Oaxaca in southern Mexico and with the plant-bearing San Cayetano Formation in Cuba. The fact that beds of Kimmeridgian Age locally rest on beds of Sinemurian to possible earliest Pliensbachian Age suggests that certain areas were is- lands from Middle Pliensbachian to late Oxfordian time, or that erosion occurred in late Oxfordian time, or that both things may have happened. The orogenic activity associated with the unconform- ity of Pliensbachian to Toarcian Age (Imlay, Cepeda and others, 1948, p. 1750—1753; Carrillo Bravo, 1965, p. 85, 87, 92—95) suggests that the unconformity developed mainly during Pliensbachian time and may be areally more extensive in the Gulf region than is now realized. Also, it may correlate roughly with an unconformity of early Pliensbachian Age in eastern Oregon, southwest- ern Alberta, arctic Canada, and Alaska (see fig. 13); with uplift of an area in eastern Nevada from which the sands of the Dunlap Formation were derived (Muller and Fer- guson, 1939, p. 1616-1622); and with intrusion of dia- base sills (Palisade disturbance) into continental beds of Sinemurian Age in New Jersey (Dallmeyer, 1975). In addition, several minor unconformities of Late Jurassic age have been recognized in the northern and western parts of the Gulf region. These include (1) a probable minor disconformity of middle Oxfordian Age formed after deposition of the main saline beds (Louann Salt) by a swiftly transgressing sea (Norphlet Forma- tion) which reworked the surface of the saline beds and transgressed beyond; (2) a minor disconformity of early Kimmeridgian Age formed locally in Mexico and possibly also in the southeastern United States, at the same strat- igraphic position as a nearby gypsiferous red-bed unit (Olvido Formation and Buckner Formation); and (3) a disconformity formed locally at the top of the Jurassic in the Gulf region of the United States. In the Pacific Coast region, the entire Jurassic is rep- resented by unconformities at one place or another (fig. 30). Of those unconformities found in two or more places, some represent Hettangian, early Pliensbachian, Bath- onian, early Callovian, and late Callovian time. Others begin in middle Bajocian, middle Callovian, and late Kimmeridgian time and continue through the remainder of the Jurassic. These unconformities lack continuity over large distances, owing to westward shifting of dep- ositional troughs during Jurassic time, to deposition in waters ranging from very shallow to very deep, to dis- tances from sources of sediment, and to the presence of islands rising from waters of different depths. Thus, the unconformable relationships noted in the Suplee—Izee area of eastern Oregon (fig. 30) were produced by west- ward onlap of a sea across an island composed of Paleo- JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES zoic and Triassic rocks and by periodic uplift of that is- land in early Pliensbachian time and later, perhaps accompanied by variations in sea level. Six unconformities have been definitely identified in the Jurassic sequences of the western interior region (fig. 31) (Pipiringos, 1968, 1;). D10, D11). These, from old- est to youngest, represent (1) the later part of the Early Jurassic, (2) the middle part of the middle Bajocian, (3) a small part of the middle Callovian locally in Utah, (4) most of the late Callovian and locally some of the Oxford— ian, (5) a small part of late early or early middle Oxford— ian locally in the middle part of the region, and (6) at least part of the later Tithonian. Complete withdrawal of marine waters took place during the development of the first, second, fourth, and sixth unconformities listed. The lowest unconformity formed during the late Early Jur- assic, as shown by its position below marine beds of early Bajocian Age and above the continental Navajo Sand- stone, which is now dated as probably Early Jurassic (Fred Peterson, written commun., 1976) on the basis of the palynoflora present in the older Moenave Formation. The highest unconformity formed during the latest Jur- assic, and it could represent all or only part of the Ti- thonian. Because it formed on continental beds, it prob- ably represents more time than the unconformity at the top of some marine Jurassic sequences in the southeast- ern United States and in west Texas. It represents con- siderably less time than the unconformity (Nevadan or- ogeny) formed after deposition of the Mariposa and Galice Formations in parts of California and Oregon. All these Jurassic unconformities in the western in- terior region could result from lowering of sea level by a few hundred feet or less, or from a slight elevation of the region, or from a rise of landmasses in eastern Nevada, western Utah, and central Idaho that blocked the en- trance of marine waters from the west. Of these uncon— formities, only that of late Callovian Age can be matched definitely in the Pacific Coast region. In addition, the un- conformity of middle Bajocian Age, corresponding roughly to the European zone Otoites sauzei, may be present locally in British Columbia and southwestern Al- berta, as suggested by the rarity of ammonites charac- teristic of that zone (Imlay, 1973, p. 34). JURASSIC GEOLOGIC HISTORY ATLANTIC COAST REGION Deposition of marine Jurassic sediments along the Atlantic Continental Shelf of the United States has not been demonstrated by fossils. Nonetheless, seismic evi- l dence suggests that fairly thick Jurassic sequences were JURASSIC GEOLOGIC HISTORY deposited at least on the outer part of the shelf. This con- clusion is supported by the presence of (1) about 6,500 feet (1,980 m) of Lower to Upper Jurassic beds in the Scotia Shelf area and at least 20,000 feet (6,100 m) of such beds in the Grand Banks of Newfoundland, (2) 8,000.16,000 feet (2,440 to 4,880 m) of Middle to Up- per Jurassic beds in Cuba, and (3) a thin Upper Jurassic sequence in the Hatteras Abyssal Plain. As the last men- tioned sequence contains organisms characteristic of fairly deep waters (Luterbacher, 1972, p. 575; Bernoulli, 1972, p. 813; Bernoulli and Jenkyns, 1974, p. 145, 146), the Jurassic sea probably extended considerably farther west. Also, the marked lithologic and stratigraphic differences among these sequences suggest that the history of Ju- rassic sedimentation probably differed considerably from place to place. All available evidence indicates that the North Atlantic formed near the end of the Triassic, was much smaller during the Jurassic than today, was the site of salt deposition at one or more times, and was flooded extensively by marine water of normal salinity from Oxfordian to Tithonian time, coincident with exten- sive flooding in the Gulf of Mexico region (Gordon, 1974, p. 138; Berggren and Hollister, 1974, p. 130, 131, 176). GULF OF MEXICO AND NEARBY REGIONS Jurassic marine sedimentation in or near the Gulf re- gion began at different times in different places. Marine \ sedimentation in Cuba probably began during the Bath- onian, but possibly as early as Bajocian. In the southern United States and northeastern Mexico, deposition prob- ably began during the Callovian, but possibly a little ear- lier. Sedimentation started in north-central Mexico dur-‘ ing the middle Oxfordian, in northern Chihuahua and western Texas during the Kimmeridgian, and in the ’ Huasteca area of east-central Mexico during the Sine- murian. In eastern Veracruz in east-central Mexico, ma- rine deposition probably began as early as late Bathon- ian and definitely as early as Callovian. In south—central Mexico in the State of Guerrero, deposition definitely be- gan as early as Pliensbachian and probably much earlier. During Early Jurassic time, marine sedimentation probably did not take place within the drainage basin of the Gulf of Mexico. Field studies in southern Mexico and drilling in the region of Veracruz both show that an Early Jurassic sea entered southern Mexico from the Pa- cific Ocean and extended north or northeast but did not quite reach the area of the present Gulf of Mexico. Con- sequently, marine Sinemurian and questionable lower Pliensbachian beds exposed in the Huasteca area pinch out eastward in the subsurface against ancient schist, gneiss, and granite in eastern Veracruz (Viniegra 0., 1971, p. 484; Lopez Ramos, 1972, sections A—A’ and B—B’; 1974, p. 381—386). Earlier studies favoring a 103 marine connection eastward with the Atlantic Ocean dur- ing Early Jurassic time were based on the close similari- ties between the Sinemurian ammonite faunules in southern Mexico and those in Europe (Burckhardt, 1930, p. 20; Erben, 1957b, p. 37, 38). It is now known, how- ever, that the Early Jurassic ammonite succession is re- markably similar throughout the world from Hettangian to early Pliensbachian time (Imlay, 1971, p. 712—713; Im- lay and Detterman, 1973, p. 21) and is fairly similar until Bajocian time. Likewise, continental sedimentation may not have taken place within the Gulf of Mexico drainage area dur- ing Early Jurassic time. The best evidence for its occur- rence consists of plant-bearing black shale within and di- rectly overlying Sinemurian marine beds in the Huasteca area of east-central Mexico (Burckhardt, 1930, p. 20; Er- ben, 1956a, p. 129—132; 1957a, p. 45). That area, how- ever, may have drained southward or southwestward rather than eastward, because the associated marine beds were deposited in an arm of the Pacific Ocean. If that is true, then at least the western part of the Gulf of Mexico may not have existed during Sinemurian and early Pliensbachian time. Such a possibility is supported by the fact that the Jurassic beds in the Huasteca area were folded, faulted, intruded by igneous rocks, meta- morphosed, and then partially eroded away before dep- osition of the overlying continental Cahuasas Formation of Bajocian to Bathonian Age (Carrillo Bravo, 1965, p. 85—87, 92—95). During Bajocian time, and most or all of Bathonian time, marine sediments were not deposited within the drainage basin of the Gulf of Mexico, as far as is known. Well outside that basin, however, those stages are rep- resented in part in western Oaxaca and northeastern Guerrero by marine beds deposited in an embayment of the Pacific Ocean (see fig. 6, 7, 14, and 21). Within the Gulf drainage basin, the latest Bathonian is possibly rep- resented by some small undescribed ammonites resem- bling Wagnem'ceras, which were obtained from the sub- surface near Tampico in east-central Mexico (Cantu Chapa, 1969, p. 5). Also, in western Cuba, the upper 2,000 feet (610 m) of the enormously thick San Cayetano Formation has furnished a few marine pelecypods that could be of Bathonian Age, providing the overlying Azu- car Member contains Callovian microfossils as reported (Meyerhoff, 1964, p. 151). During Bajocian and Bathonian time, continental sed- iments were deposited widely in the Gulf region and in nearby areas. In the Tampico and Huasteca areas of east— central Mexico, some thick red to gray clastic non-marine beds, called the Cahuasas Formation, were laid down from middle Bajocian to at least middle Bathonian time on top of plant-bearing beds of early Bajocian Age (Car- rillo Bravo, 1965, p. 87—88; Erben, 1956a, p. 137; 104 1956b, p. 43). In Cuba, those stages are probably repre— sented by thousands of feet of plant-bearing beds in the San Cayetano Formation. Outside the Gulf region, in northeastern Guerrero and western Oaxaca, some dark-gray to black carbona— ceous plant-bearing shale and coaly beds were deposited during Toarcian to early middle Bajocian time and again during middle Bathonian time (Erben, 1957a, p. 49—50), as dated by marine fossils in adjoining beds. Studies of the plant fossils have made it possible to assign an early Bajocian date to the basal part of the Cahuasas Forma- tion of east-central Mexico, as mentioned above. The presence of plant fossils and carbonaceous material in both east-central and southern Mexico suggests that the climate was generally warm and humid throughout the Gulf region during most of the Early and Middle Ju- rassic. During Callovian time, marine sediments probably were deposited in Cuba (Meyerhoff, 1964, p. 151; Mey- erhoff and Hatten, 1974, p. 1211), but the evidence has not yet been published. Marine sediments of early to middle Callovian Age were definitely deposited in east- central Mexico near the present Gulf of Mexico and may represent an embayment of the Gulf (Erben, 1957b, fig. 2). Recent studies, however, strongly favor the theory that deposition took place in an embayment that ex- tended northeastward from the Pacific Ocean and that was separated from the Gulf at least in part by a land barrier (Viniegra O., 1971, p. 484, 492; Lopez Ramos, 1974, p. 388). Thick masses of salt and associated anhydrite prob— ably were deposited during middle or late Callovian to early Oxfordian time in various parts of the Gulf region. Such an age is suggested by (1) the stratigraphic position of the salt and anhydrite below normal marine beds of middle Oxfordian to early Kimmeridgian Age, (2) lack of evidence of any appreciable erosion before the overlying normal marine beds were laid down, and (3) lack of any fossils that are definitely of late Callovian to early Oxfordian Age either above or below the saline deposits. In particular, the Santiago Formation of east-central Mexico contains early to middle Callovian ammonites in its lower part, late Oxfordian ammonites in its upper part, but apparently no fossils of any kind in its middle part. Considering the distribution and stratigraphic posi- tions of the main saline masses in the Gulf region, some marine waters from both the Atlantic and Pacific Oceans probably entered the Gulf at about the same time. The entrance of seawater into the Gulf during salt deposition probably resulted from some structural movement that either caused a rise in sea level, or a downwarping of landmasses in southern Mexico and between Cuba and JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Florida. The fact that the Callovian sea in east-central Mexico was bounded on the east by a barrier or uplift suggests that most of the marine water that furnished the salt came from the east. Some red to varicolored continental beds, called La Joya Formation, were probably deposited during Callo- vian time in northeastern and north-central Mexico. These beds differ from the Cahuasas Formation by containing some red-weathering lava, by being much thinner and redder, and by not passing downward into plant-bearing beds. They could be the same age as that formation, but their close geographic proximity in northeastern Mexico to thick salt and gypsum masses, called the Minas Viej as Formation, suggests that they were formed at the same time as the saline beds. Presumably, the red sand and silt in the red beds were derived from areas to the west or north, where red lateritic soil accumulated under a hot and seasonably rainy climate. The salt and the red beds probably were deposited under a hot and very dry cli- mate. The sequence of marine sediments deposited during Late Jurassic time were remarkably similar from Ala- bama westward to north-central Mexico. During the late middle to late Oxfordian in offshore areas, the deposits were mostly limy mud; in nearshore areas, they were limy mud or sand or both, and locally in nearshore areas they were limy sand and gravel. The upper part of the limy mud sequence was deposited in shallow agitated water, and the lower part, apparently in deeper and rather quiet water. Seas having unrestricted circulation and normal sa- linity suddenly became widespread in the Gulf region near the middle of the Oxfordian and gradually expanded until near the end of the Jurassic. At the beginning of that time interval, the portals from the Atlantic Ocean, or the Pacific Ocean, or both, suddenly widened and deepened, allowing huge quantities of sea water to flood abruptly inland over older Jurassic saline and continental beds onto Triassic red beds and Paleozoic rocks. The ex- tent of the late Oxfordian sea (fig. 10), far beyond the present Gulf of Mexico, suggests that either the older evaporite basins within the Gulf were dead seas consid- erably lower than ocean levels, or that the entire Gulf basin sank fairly rapidly during the Oxfordian, or that both conditions existed. The first possibility is favored because the sea spread quickly over an area extending at least 1,500 miles (2,400 km) from east to west, because it reworked the saline beds only slightly as it advanced and because it then quickly covered those beds with a protective blanket of red to gray mud and sand (Norphlet Formation) that prevented further erosion. Nonetheless, the fact that considerable sand and pebbles were shed into the sea from the north during most of Late Jurassic JURASSIC GEOLOGIC HISTORY time shows that land areas to the north were rising as the Gulf basin itself was sinking. The fact that the saline deposits of the Gulf region extended at least as far east as Cuba and probably considerably farther east suggests that major tectonic movements allowed normal marine waters from the major oceans to flood smaller basins such as the Jurassic Atlantic basin and the Gulf of Mexico. In the Gulf region of the southeastern United States, the initial deposits of the rapidly advancing middle 0x- fordian sea were derived mostly from pre-Jurassic rocks and from Jurassic saline beds across which the sea trans- gressed. These deposits (Norphlet Formation) were suc- ceeded rather abruptly in offshore areas by dense, finely laminated, silty to shaly, calcareous muds (lower part of the Smackover Formation) that contain well-preserved specimens of the fragile-shelled pelecypod Bositra (not Posidom'a). Such muds must have been deposited in quiet, toxic waters, as indicated by the fine laminations and by the good preservation of the fragile pelecypod shells. However, these waters were not necessarily deeper than the lower part of the neritic zone. Also, rapid deepening of the sea at the beginning of Smackover time is indicated by the abrupt change from deposition of red mud, sand, and some pebbly beds to the deposition of laminated beds. In offshore areas in the southern United States, these laminated limy beds in the lower part of the Smackover Formation were overlain by gray to black mud of the Bossier Formation in late Oxfordian to late Kimmeridgian time. In some nearshore areas, though, the laminated beds were succeeded by limy dense to 00- litic mud and sand representing the middle and upper parts of the Smackover, which was in turn overlain by the Buckner Formation in early Kimmeridgian time. The Buckner consists of red to greenish-gray mudstone, an- hydrite, dolomite, oolitic carbonate, and, locally, salt, which were deposited as a rather narrow lens-shaped body now extending from east Texas through Arkansas to Alabama. Deposition of the Buckner and Smackover Forma- tions was succeeded conformably in most nearshore (up- dip) areas by deposition of red to gray fine-grained sand and mud (Schuler Formation), which may have been de- posited in brackish or nonmarine waters. However, the local thinning or absence of the Buckner Formation over the crests of some salt anticlines may indicate a local dis- conformity at the base of the Schuler Formation (Weeks and Alexander, 1942, p. 1475; K. A. Dickinson, 1968, p. E13, E23). The Bossier Formation is overlain by marine shale and gray sandstone (marine facies of the Schuler Formation) that become more shaly basinward, suggest- ing deeper waters offshore. Deposition apparently con- 105 tinued to the end of Jurassic time offshore but not in nearshore areas. In summation, the Smackover Formation was depos- ited in a transgressive sea that was very shallow and ag- itated nearshore and apparently deeper than wave base offshore. The Buckner Formation was deposited in evap— oritic basins partially blocked off from the sea by salt anticlines or by local uplifts. The Bossier Formation was deposited in moderately shallow waters in offshOre areas. The Schuler Formation was deposited in shallow water that was brackish in part, or perhaps nonmarine in near- shore areas. It has been interpreted as a mostly regres- sive deposit. Nonetheless, the fact that it extends north of the Smackover and Buckner Formations in Arkansas (K. A. Dickinson, 1968, p. E10, E14, E23) shows that its lower part, at least, is transgressive with respect to those formations. In north-central and northeastern Mexico, deposits of limy mud or sand of late middle to late Oxfordian Age were overlain by dark limy mud or clay (La Caja For- mation), or by gray to black sand, limy mud, gravel, and some coaly beds (La Casita Formation), or by gypsifer- ous red beds and gypsum (Olvido Formation). These gypsiferous beds crop out only in the high mountains of eastern Mexico from Victoria, Tamaulipas, northward to eastern Coahuila. They are of particular interest because they were deposited at the same time as the Buckner Formation of the southern United States, they are nearly identical lithologically, and they also were deposited as a narrow lens-shaped body. They must represent a time of uplift and slight folding, because in areas where they are absent, the Oxfordian beds are generally overlain discon- formably by La Casita Formation or by La Caja Forma- tion, which were laid down during the remainder of the Jurassic. Of these lithologic units, the Olvido and La Caja For- mations were probably deposited under conditions simi- lar, respectively, to those of the Buckner and Bossier Formations in the southern United States. La Casita Formation was deposited in shallow water or under non- marine conditions, as was the Schuler Formation. None- theless, the dark~gray to black color of the La Casita and the presence of coal beds and considerable carbonaceous material within it contrast with the red to gray colors of the Schuler Formation and show that the climate on nearby landmasses must have been much more humid during deposition of La Casita Formation. Also, the fact that La Casita Formation in Chihuahua and equivalent beds in west Texas lap considerably beyond older J uras- sic beds onto Permian rocks shows that the formation is distinctly transgressive. Farther south, in the Tampico and Huasteca areas of east-central Mexico (fig. 21), the lithologic units of 106 Oxfordian to Tithonian Age differ considerably from those of the same age in northern Mexico. They consist almost entirely of dark-gray to black normal marine shale and shaly to thin-bedded limestone. Sandy beds and pebbles are uncommon, and the highest unit (Pi- mienta Formation) contains thin lenses of chert. Evij dently these beds were deposited as soft limy mud in an open, shallow or fairly shallow sea that received very lit- tle sandy material. Locally within this sea, on platform areas or nearshore, were deposited bioclastic, oolitic, and coralline reef carbonates (San Andrés Member of Ta- man Formation) (Cantu Chapa, 1969, p. 8; 1971, p. 34—- 36). Still farther south, drill cores from near Chinameca and Cerro Pelon, Veracruz, in the Chiapas salt basin, show that deposition of considerable salt and some asso- ciated red to black mud was followed by deposition of a thin unit of red mud and some salt. That in turn was fol- lowed by deposition of normal marine beds of early Kim- meridgian to early Neocomian Age. Elsewhere in south- east Mexico, the Upper Jurassic deposits outside the salt basin apparently were mostly red mud. On the Chiapas massif, however, the deposition of red mud was inter- rupted briefly by a marine incursion during early Kim- meridgian time. The deposition of red beds and salt masses implies arid conditions during Late Jurassic time, which was a marked climatic change from Early and Mid- dle Jurassic time when considerable coal and carbona- ceous material was deposited in nearby parts of southern , Mexico. Furthermore, the characteristics of the marine ' beds of Kimmeridgian and Tithonian Age in the Chiapas basin indicate that water depth was generally shallow , and that bordering land areas were very low (Viniegra 0., 1971, p. 485—487). PACIFIC COAST REGION The Jurassic marine sequences deposited in the Pa- cific Coast region of the United States differ markedly lithologically within fairly short distances, attain enor- mous thicknesses, and contain a great deal of volcanic material. In addition, some represent different ages from others that are nearby. These differences are attribut- able to deposition under changing environmental condi- tions; to the relative positions of the sequences within rapidly sinking basins; to differing distances from vol- canic vents, from islands, or from landmasses composed of pre-Jurassic rocks; to westward shifting of deposi- tional sites during Jurassic time; and to major post-Ju- rassic thrust faulting that has brought together se- quences that were originally deposited far apart under very different environmental conditions. Evidently, the changing environmental conditions reflect the gradual JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES westward shift in depositional sites, which in turn re- flects major orogenic movements along the western mar- gin of the continent. During the Early Jurassic, a shallow to very shallow sea existed as far east as the Snake River in eastern Or- egon and nearly as far east in Nevada. Fossil mollusks from this sea have been found as far west as the Suplee? Izee area in east-central Oregon, the Big Bend area in north-central California, and the Sailor Canyon area a lit- tle west of the crest of the Sierra Nevada on the North Fork of the American River in eastern California. The sea in Nevada and eastern Oregon continued from latest Triassic time and during Hettangian to Sinemurian times received sediment similar to that deposited during the Triassic. In contrast, the lowermost Jurassic sediments deposited in the Sailor Canyon and Big Bend areas are of Sinemurian Age and were deposited unconformably on Triassic rocks or locally in Sailor Canyon on older rocks. These relationships suggest that the center of the Early Jurassic seaway was in western Nevada rather than in eastern California and probably trended northward through eastern Oregon. The fact that no Lower Jurassic beds are known in western California and western Ore- gon does not mean necessarily that an Early Jurassic sea did not also exist there. The absence of these beds, as well as the absence of Bajocian and Bathonian beds in those areas, could be a consequence of major tectonic events during Bathonian to early Kimmeridgian time that resulted in the formation of oceanic crust and that either altered or destroyed preexisting sediments. During Bajocian time, the sea covered nearly the same area as it did during earlier Jurassic time, and as before, it had marine connections both northward into Canada and southward into Mexico. In addition, during the later Bajocian, this sea had marine connections east- ward through Idaho into the western interior region. The marine sediments deposited near Westgate, Nev., consisted of limy mud and quartz sand; those de- posited in the Santa Ana Mountains of southern Califor- nia consisted of mud, sand, gravel and some limestone lenses; those deposited in the northern Sierra Nevada near Taylorsville consisted of volcaniclastic materials and some limy lenses; those deposited in the big Bend area of north-central California consisted of volcaniclas- tic materials, lava flows, and some clastic lime muds; and those deposited in eastern Oregon consisted of volcani- clastic materials, some silty to sandy lime mud, and much dark clay and silt associated with much fine volcanic ma- terial. Most of these sediments, as shown by their fossil content and lithologic features, were deposited in normal shallow marine waters that were much agitated in some places and were quiet in others. The shallowness of the sea in the Taylorsville area during Bajocian time is at- J URASSIC GEOLOGIC HISTORY tested to by the fauna] content of the Mormon Sandstone (Crickmay, 1933b, p. 898, 899) and by the presence of a disconformity below the Mormon. Marine beds of Bathonian Age have not been found in the Pacific Coast region south of eastern Oregon, but neither has any physical evidence been found for an un- conformity of that age. In the Taylorsville area in east- ern California, the Bathonian could be represented by about 1,300 feet (396 m) of volcanic breccia and tuff be- tween the Moonshine Conglomerate of early late Bajo- cian Age and the Hinchman Sandstone of early Callovian Age. In the Izee area of eastern Oregon, the Bathonian is represented within a mudstone-siltstone'unit 1,250— 2,000 feet (381—610 m) thick that is called the upper \. member of the Snowshoe Formation. In that member, early Callovian ammonites have been collected from its highest 300—500 feet (91—152 m), Bathonian ammonites, from its next lower 300—400 feet (91—122 m), and one late Bajocian ammonite (Leptosphinctes), from near its base. That leaves hundreds of feet of beds that could also rep- resent the Bathonian and uppermost Bajocian. As ma- rine Bathonian beds containing ammonites of boreal af- finities occur in central British Columbia, southern Alberta, and western Montana, a Bathonian seaway probably extended from British Columbia southward and southeastward across parts of Washington and Idaho. During Callovian time, a sea apparently covered most of California, all of Oregon, part of western Idaho, and probably most of Washington. During early Callov- ian time, it also extended eastward through southern Alberta and probably also through northern Idaho into the western interior region of the United States and Canada. That sea, so far as is known, didznot extend into Nevada as did the Bajocian sea but did extend into north- eastern Oregon where Bajocian beds are'unknown. Sediments deposited in this Callovian sea in the Pa- cific Coast region are very thick and contain a great deal of volcanic ejecta such as agglomerate, breccia, lava flows, and ash (see figs. 22, 23). Even the finer sediments ' deposited as sand, silt, and clay contain much fine vol- , canic material. Deposition was nearly continuous from early to middle Callovian time in eastern Oregon and apparently continued through the entire Callovian intoj early Oxfordian time imparts of California and southwest Oregon. One exception'occurs, however, in the Izee area of eastern Oregon, where an unconformity has been found near the middle of beds of early Callovian Age (W. R. Dickinson and Vigrass, 1965, p. 84). The presence of an unconformity at that position is supported by the much wider distribution of the beds above than below that position. Thus, the Trowbridge Shale overlaps west- ward onto beds of middle Bajocian Age (Imlay, 1973, p. 9, 14). 107 Early Callovian sediments in the Izee-Suplee area of eastern Oregon were deposited on beds of late Bajocian to Bathonian Age. In the Taylorsville area of northeast- ern California, they were deposited on beds of probable Bathonian Age. Elsewhere in California and in western Oregon, the age of the beds underlying Callovian sedi- ments is not known, either because of lack of fossils or because of thrust faulting. As the age of the Rogue For- mation in southwestern Oregon is based on its strati- graphic position gradationally beneath beds of late Ox- fordian Age, its lower part could be as old as Bathonian. Similarly, the lower part of the Logtown Ridge Forma- tion, or the equivalent Gopher Ridge Volcanics, as ex- posed along the foothills of the Sierra Nevada, could lo- cally be of Bathonian Age. The Callovian sediments in California and Oregon were deposited in rapidly sinking basins, which were re- ceiving quantities of lava and coarse volcanic material from vents and volcanoes. Some of the Rogue Formation may represent newly formed oceanic crust, as indicated by the presence of lava flows, agglomerates, breccias, tuff, serpentine, and gabbro intrusive rocks. The Log- town Ridge Formation or the Gopher Ridge Volcanics could also locally repnesent oceanic crust, although a somewhat different environment of deposition is indi- cated by the presence of ammonites at various levels. During the Oxfordian to early Kimmeridgian, a sea covered much of California west of the crest of the Sierra Nevada, extended northwestward into Oregon, covered at least the northwestern part of Washington, and re- ceived much volcanic sediment. Another sea of early Ox- fordian Age extended southward from easternmost Washington a short distance into Idaho and Oregon near the present site of the Snake River and received non- volcanic mudstone, graywacke, and pebbles. Except for the area near the Snake River, highly volcanic marine sedimentation continued from the Callovian into the early Oxfordian. By contrast, the marine sediments de- posited from late Oxfordian to early Kimmeridgian time were mostly dark clay but included some silt, sand, and gravel and only in places included appreciable volcanic material. Apparently near the middle of Oxfordian time, volcanism either decreased markedly or shifted far to the west of its position during Callovian or earlier Ox- fordian time. Such .a shift is indicated by the presence near Paskenta, Calif, of thousands of feet of mafic vol- canic rocks (mostly breccias and flows) (Bailey and oth- ers, 1970, p. 072—074) eonformably below the Knoxville Formation, the base of which is dated as late Kimmer— idg'ian at that place (Jones, 1975). At the end of the early Kimmeridgian, marine sedi- mentation ceased for the remainder of the Jurassic in areas underlain by the Galice and Mariposa Formations, 108 as well as in areas a little farther east. Such areas during the remainder of the Jurassic were subjected to uplift, folding, igneous intrusion, and much erosion associated with the Nevadan orogeny. Orogenic activity ceased, however, by the end of the Jurassic in western Oregon, where the Galice Formation locally was overlain by ma- rine sediments of earliest Cretaceous age. / During the late Kimmeridgian, marine sediments were deposited in areas of northwestern Washington and northwestern California. During the Tithonian, deposi- tion took place along a narrow belt whose position is now shown by fossiliferous beds near the present coast from Baja California to northwest Washington. All this depo- sition took place at least 100 miles (160 km) west of areas in which the Mariposa and Galice Formations were de- posited during the late Oxfordian to the early Kimmer- idgian. Evidently, the deposition of sediments of early Kimmeridgian Age coincided with the beginning of the Nevadan orogeny in areas underlain by the Mariposa and Galice Formations and in the Sierra Nevada. Marine sedimentation during late Kimmeridgian to late Tithonian time'varied considerably from place to place, apparently depending on the depth of the sea, the distance from shore, and the presence or absence of vol- canoes or volcanic vents. Some sediments, now repre— sented by the Knoxville and Riddle Formations, were deposited in shallow to fairly shallow waters as mostly nonvolcanic, highly fossiliferous mud, silt, sand, and gravel and locally as limestone lenses. Other sediments, now represented by the Dothan and Otter Point For- mations and by the lower part of the Franciscan assem- blage, were deposited in moderately deep to deep waters as highly volcanic, rather poorly fossiliferous mud, silt, sand, gravel, chert, volcanic breccias, and lava flows. Deposition of all these sediments continued into Creta- ceous time. All available evidence suggests that the vol- canic sequences were deposited at least several hundred miles west of the nonvolcanic sequences and in much deeper water but that all marine deposition began at about the same time, after the formation of oceanic crust in late Oxfordian to early Kimmeridgian time. In summation, Jurassic marine sediments in the Pa- cific Coast region were deposited in waters ranging from very shallow to very deep; involved tremendous thick- nesses; included a great deal of volcanic material, except in the Knoxville Formation of California and the Riddle Formation of Oregon; and were deposited in troughs whose positions gradually shifted westward. Further— more, the scarcity of red sediments suggests that dep- osition took place mainly under reducing conditions. The absence of gypsum and salt deposits implies that lagoonal conditions did not last long and that shorelines shifted frequently. The fact that no sediments were derived from the east, except for the Dunlap Formation of Ne- JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES vada, implies that the landmass in central Nevada was generally low or shed most of its sediment eastward. These conclusions are of little help in evaluating the kind of climate that existed in the Pacific Coast region during Jurassic time. However, the presence of ammo- nites that have Mediterranean affinities indicates that the waters were fairly warm. Thus, the Pliensbachian ammonite faunain eastern Oregon is characterized by the families Hildoceratidae and Dactylioceratidae but lacks the Amaltheidae, which is common in northwest Europe and from British Columbia northward (Imlay, 1968, p. Cl, C21, 022). The Bajocian ammonites in Or- egon and California include certain genera that are com- mon in Europe but, that are as yet unknown in Alaska (Imlay, 1973, p. 31, 36). The Callovian beds in those States lack Cadocems, which is very common from Brit- ish Columbia northward. Finally, the Tithonian beds of those States contain many ammonites of Mediterranean and South American affinities that are unknown from British Columbia northward (Imlay and Jones, 1970, p. B17—B19). WESTERN INTERIOR REGION During the Jurassic, most of the sediments deposited in the western interior region were derived from border- ing areas on the southeast and north and from a persist- ently rising area in south—central Colorado. Some sedi- ments were also derived from the west at certain times. Thus, during late middle to late Bajocian time, and again during earliest Callovian time, sand and pebbles derived from a landmass in south—central Idaho were deposited respectively as part of the Sliderock and Giraffe Creek Members of the Twin Creek Limestone (Imlay, 1967b, p. 22, 23, 26, 30, 50—53). Later, in the early Oxfordian, a northern extension of this landmass was the main source of sand deposited as parts of the Swift Formation and the Stump Sandstone (Imlay, 1957, p. 481—482; Imlay, Gardner, and others, 1948). Similarly, the sediments composing the Morrison Formation were derived from the west as well as from the south and northeast. During Early Jurassic time, marine sediments were not deposited in the western interior of the United States or east of the foothills of the Canadian Rocky Mountains, so far as is known. A southeastward extension of marine waters into northwestern Montana is suggested by the presence of marine beds of Sinemurian and Toarcian Age near the International Boundary in southeastern British Columbia and in southwestern Alberta, but the facies present indicate deposition in very shallow waters near a southeastern shoreline (Frebold, 1969, p. 76, 78, 82, 84). In contrast, continental sediments may have been deposited, in my opinion, during earliest Jurassic time over fairly wide areas in the southern and central parts J URASSIC GEOLOGIC HISTORY of the western interior region. Near the border of Ari- zona and Utah, the earliest deposits (Moenave Forma- tion) of possible Early Jurassic age were mostly fluviatile sand and silt. These sediments were succeeded from that border area northward to east-central Utah and to south— western Colorado by fluviatile sand and silt (Kayenta Formation), which were interbedded with some eolian sand. Next followed deposition of buff to white, conspic- uously crossbedded sand (Navajo Sandstone) of eolian origin over the same area as well as in eastern Nevada and northern Utah. Similar crossbedded sand (Nugget Sandstone and Glen Canyon Sandstone) was deposited at least in part at the same time in northernmost Utah, northwestern Colorado, southeastern Idaho, and west- ern and central Wyoming. Its lower part, however, which contains some thin beds of ripple-marked, flat-bedded sand and silt, was probably deposited earlier than the Navajo Sandstone (Reeside, 1957, p. 1480, 1482; Pipi- ringos, 1968, p. D16, D17; Poole and Stewart, 1964, p. D38). Early in Bajocian time, a very shallow sea entered the western interior region from the west across south- eastern Idaho, western Wyoming, and northern Utah (fig. 32). It then enlarged itself northeastward through north-central and northeastern Wyoming into the Willis- ton basin of eastern Montana, western North Dakota, and adjoining parts of Saskatchewan and Manitoba. The sediments it deposited now comprise the Nesson For- mation of the Williston basin, the Gypsum Spring For- mation farther south, and the Temple Cap Sandstone of southwestern Utah. Those sediments consist mostly of gypsum, even-bedded red to green silt and mud, lami- nated or dolomitic lime mud, and some chert nodules and layers. During the advance of the sea across Wyoming and Montana, the initial deposits were mainly gypsum interbedded with red silt and a little limy mud, but in the Williston basin they included some salt. These deposits are overlain by limy beds, some dark-gray chert, and some red silt. In southeastern Idaho, the sediments de- posited in the same sea contained much less gypsum and much more limy mud and siliceous material (Imlay, 1967b, p. 21). A southward extension of the same sea into south- western Utah deposited red, even-bedded silt and gyp- sum that to the east passed rather abruptly into crossbedded sand. Evidently the sea deepened toward the west both in Idaho and in Utah. The initial sediments of the early Bajocian sea, were deposited in very shallow, highly saline waters, as shown by an association of gypsum, red mud, silt, and locally some salt, and by an absence of any marine fossils. More limy sediments were deposited later in slightly deeper waters, as shown by the presence of some pelecypods, gastropods, echinoid spines, crinoid columnals, and worm tubes. An absence of ammonites in the limy rocks, how- 109 ever, suggests that the sea waters were either very shal- low or were more saline than normal. The characteristics of the sediments indicate that the landmasses bordering the sea were low and that the climate was warm to hot and seasonally humid. Near the middle of the middle Bajocian, the sea with- drew westward completely from the western interior re- gion. It returned to some areas, however, by the late middle Bajocian (Stephanocems humphriesianum zone), and by late Bajocian time, it spread over a larger area than in the early part of the epoch. This rapid retreat and readvance of marine waters over such a large area dur- ing part of middle Bajocian time suggests that the west- ern interior region had little relief, was near sea level, and consequently was flooded or drained in response to minor vertical movements of landmasses or of ocean ba- sins. The unconformity that developed between flood- ings, although representing only a small part of middle Bajocian time, could have represented 1 million or 2 mil- lion years. It was sufficiently long for erosion and local removal of the Gypsum Spring Formation and equivalent beds and for the accumulation of a lag deposit of weath- ered, dark-gray chert nodules on the surface of that for- mation. Such nodules were then reworked by the incom- ing sea and scattered widely. The shallow sea that entered the western interior region in late middle to late Bajocian tinie lasted into earliest Callovian time and even then did not completely Withdraw from the region. During the late Bajocian and early Bathonian, it extended eastward across about two- thirds of Utah, across the western third and north-cen— tral part of Wyoming, and across most of Montana into the Williston basin, except for some islands in central Montana. During late Bathonian time, the sea deepened and extended even farther east across northern Utah and Colorado and across Wyoming into western South Dakota. It shallowed somewhat during the earliest Cal- lovian. It was also shallower in Utah than farther north, as shown by a southward increase in red beds and gyp- sum, a southward decrease in molluscanspecies, an ab- sence of ammonites south of the northwestern part of the San Rafael Swell in central Utah, and an absence of Gry- phaea south of Thistle in north-central Utah. The first sediments deposited in the advancing sea during late middle to early late Bajocian time filled in the irregularities of the underlying erosion surface and consequently/varied lithologically within moderate dis- tances. The initial deposits include normal shallow—water marine shale and limestone containing Gryphaea and am- monites (Sliderock Member of the Twin Creek Lime— stone), gypsiferous shale (lower member of the Piper Formation), and massive crossbedded sand (Page Sand- stone near Hanna, Utah). Succeeding sediments of latest Bajocian Age were deposited in slightly deeper water in / x’/ v \N {213‘ u‘fi .\\ _ ’\\ LA THONIAN TO EARLIEST CALLOVIAN ///f//////////////, JURASSIC GEOLOGIC HISTORY broad, fairly uniform basins. Consequently, they main- tain their lithologic and stratigraphic characteristics over considerable distances. Thus, during latest Bajocian time, oolitic to dense highly fossiliferous gray lime mud was deposited over nearly the entire seaway from Idaho to South Dakota and from Saskatchewan to southwestern Utah. During early Bathonian time, the sea became shal- lower and a little more restricted than in latest Bajocian time. It was definitely hypersaline in southernmost Utah, as shown by an association of red silt and considerable gypsum (banded member of the Carmel Formation). It was definitely of normal salinity in western and north- central Montana, as shown by an association of fossilifer- ous sandstone, siltstone, and limestone. It probably var- ied elsewhere from shallow marine to littoral or lagoonal, as shown by an association of variegated siltstone with silty to sandy limestone and locally a little gypsum. During late Bathonian time, limy mud was deposited in shallow to moderately shallow marine waters over most of the western interior seaway as far south as the western part of the Uinta Mountains in northern Utah. Farther south in Utah, the limy mud (Watton Canyon "‘ and Leeds Creek Members of the Twin Creek Lime- stone) passes laterally into variegated sand, silt, lime- stone, and gypsum (Winsor Member and gypsiferous member of the-Carmel Formation), which in places were deposited under hypersaline conditions. Southeastward from the Wind River Basin across south-central and southeastern Wyoming, the limy mud (Stockade Beaver Shale Member of the Sundance Formation) was gradu- ally replaced entirely from the base upward by oolitic sand (Canyon Springs Sandstone Member of the Sun- dance Formation), which was deposited by the south- eastward advancing sea partly in very shallow water and partly in intertidal and supratidal environments. Deep- ening of the sea northwestward across Wyoming is at- tested by the pelecypod G’ryphaea being rare throughout central and eastern Wyoming but abundant from the Bighorn Basin northward. This change in abundance co- incides roughly with the position of the northeastward- trending Sheridan arch, as discussed by Wright (1973, p. 13). During earliest Callovian time, the sea became shal- lower than during late Bathonian time, as shown by dep- osition of fossiliferous ripple-marked sand throughout most of the central part of the western interior region and of nonfossiliferous variegated clay, silt, sand, and some gypsum in central and northern Utah. The deposi- tion of fossiliferous chalky limestone in north-central Montana at that time shows that marine circulation in the Williston basin was unrestricted. Near the middle of the early Callovian, a large island arose in Montana and northwestern Wyoming that even- 111 tually cut off the southern part of the sea from marine waters to the north but not from those to the west (fig. 33) (Imlay, 1952b, p. 1745, 1751—1753; 1957, p. 487, 490). Southeast, south, and southwest of this island, red, even-bedded, fine-grained sandstone, silty sandstone, and shale were deposited in very shallow waters along a strip 100—150 miles (160—240 km) wide. Beds generally less than 100 feet (.30 m) thick were deposited (Lak Mem- ber of Sundance Formation) in the eastern and southern parts of the strip; beds 400—1,800 feet (122—549 m) thick (Preuss Sandstone), in the Twin Creek trough in the western part of the strip; and beds more than 400 feet (122 m) thick (Entrada Sandstone), along the west side of the San Rafael Swell in central Utah. Red beds deposited along the Idaho-Wyoming bor- der and as far south as the N ephi area in Utah differ from those to the east and west by having bedded salt and a little gypsum in their lower third (Mansfield, 1927, p. 99, 338—340; Spieker, 1946, p. 124; Eardley, 1933, p. 330— 334; Hardy, 1952, p. 21, 22, 91,). To the west, red beds near Blackfoot and Idaho Falls, Idaho, differ from those farther east by having nearly 200 feet (61 m) of fossilifer- ous marine limestone and red sandstone at about the same stratigraphic position as the salt. These fossilifer- ous limestone and unfossiliferous red sandstone beds ex- tend eastward as a thin unit to within a few miles of Af- . ton, Wyo. (Imlay, 1952b, p. 1739—1746; 1957, p. 497). These red beds were deposited at the same time as some light-colored, crossbedded sands (Entrada Sand- stone) in the Colorado Plateau area, as is shown by inter- tonguing and interbedding of the two facies over large areas (Imlay, 1957, p. 480—490). These relationships show that deposition took place alternately on land and in shallow waters and imply that the bordering land areas were low. These relations and the lithologic character of the rocks deposited show that a shallow sea of normal salin- ity existed in eastern Idaho during late early Callovian time and perhaps during part of middle Callovian time. The salt and gypsum were deposited a little farther east in lagoons or in stagnant water near the shore; the unfos- siliferous, red, silty to fine-grained sandstones were de- posited still farther east in Utah, Wyoming, and western South Dakota in highly saline rather than in brackish waters. The red sediments were probably derived mostly from an island in Montana on which lateritic soils had developed under a warm and seasonally rainy climate. The light-colored crossbedded sands that were deposited at the same time in the Colorado Plateau area presum- ably were derived from an uplift in west-central or south- ern Colorado, are at least partly eolian in origin, and formed under a hot and arid climate. This red, even-bedded fine-grained sand and silt of late early to possible middle Callovian Age was overlain 112 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES v I 9’4 191’ II II ' I .5 k. I? I f/ MI, ’/¢/’{§ ~ —CLLI|QV1’W_DEP9£§ . I; xx // Km; ‘> LATE EARLY CALLOVIAN TO EARLY MIDDLE dALLOVIAN . V .- [EN] g,“ x% ORMAL MARINE I HYPER— / SALINE/ 77 4L FLATS! _7 —-—__ .— 1LATE MIDDLE CALLOVIAN / .- I _ / ' , LATE CALLOVIAN/ 1»)!er \ I / “3 , .agses EARLY TO EARLY MIDDLE OXFORDIAN (SOLID LINE) / LATE OXFORDIAN TO EARLY KIMMERIDGIAN/ XIDASHED LINE) / A h r‘,/" l I? 0 100 200 300 400 500 MILES 0 200 400 600 KILOMETERS FIGURE 33.—Inferred extent of Jurassic seas of late early Callovian to early Kimmeridgian Age in western interior region. Land areas are ruled. Modified from McKee and others (1956), Frebold (1957), Imlay (1957), J. A. Peterson (1957), and Springer and others (1966). JURASSIC GEOLOGIC HISTORY by shallow-water marine, green to gray glauconitic sand, silt, and clay. In western South Dakota, southern Wyo— ming, and northern Colorado, these glauconitic sedi- ments (Pine Butte Member of the Sundance Formation) were deposited gradationally on the red Lak Member of the Sundance Formation. In north-central and north- eastern Utah, these glauconitic sediments (Curtis For- mation) were deposited unconformably in most places on the Preuss Sandstone or on the red earthy facies of the Entrada Sandstone. Similar glauconitic sediments in southeastern Idaho and in bordering parts of Wyoming and Utah (Curtis Member of the Stump Sandstone) were deposited conformably and gradationally on the Preuss Sandstone. The sea of Curtis-Pine Butte time must have been very shallow except in its westernmost part. This conclu- sion is based on the presence of Ostrea, Lopha, Lingula, and Meleagm'nella in the Pine Butte Member of the Sundance, the presence of Ostrea and Meleagm'nella in the type section of the Curtis Formation on the San Ra— fael Swell, and the general scarcity of other pelecypods. It is based also on the fact that the glauconitic sediments of the Curtis Formation on the swell pass laterally south- eastward and grade vertically into unfossiliferous, brown or gray, locally gypsiferous, even-bedded sandstone, silt- stone, and clay (Summerville Formation) that probably originated under lagoonal to highly saline conditions. The westernmost occurrences of the Curtis Formation were deposited in slightly deeper waters, as shown by (1) the presence of Gryphaea with Ostrea and Meleagm‘malla in Salina Creek Canyon east of Salina, Utah (USGS Meso- zoic loc. 21646) and (2) the presence of belemnites and the ammonite Lytoceras in Monks Hollow, about 18 miles (29 km) southeast of Provo, Utah. The distribution of these cephalopods indicates that the sea entered from the west. The age of the Curtis-Pine Butte beds is not pre- cisely known. It is considered to be middle Callovian be- cause those beds are overlain unconformably by beds of early Oxfordian Age, grade downward into the Preuss Sandstone of early to possibly early middle Callovian Age, and contain the pelecypods Vaugom’a conradi (Meek and Hayden) and Myophorella montanaens'is (Meek), which occur elsewhere only in older Middle Jurassic beds (Imlay, 1967b, p. 14). During Curtis-Pine Butte time, the climate was warm and presumably more rainy than during deposition of the underlying red beds. Marine waters withdrew from the western interior region at about the end of the middle Callovian. This withdrawal was followed by erosion during the late Cal- lovian at least as far south as the San Rafael Swell in northeastern Utah (Pipiringos and O’Sullivan, 1978) a d probably as far south as northern Arizona (Fred Pe- terson, 1974, p. 466). Erosion apparently was slight in 113 the central and southern parts of the region and was greatest in central and northwestern Montana in the Belt Island area. Near the end of the Callovian, a sea entered central Montana and the Williston basin area from the northwest across southern Alberta. During the early Oxfordian, this sea spread eastward into South Dakota, southward into northwestern Colorado and northern Utah, west- ward across Wyoming into southeastern Idaho, and westward in Montana at least as far as the eastern side of the Sweetgrass arch. At the end of the early middle Oxfordian (Pem'sphinctes plicatilis zone), the sea with- drew northward at least as far as the Williston basin area, but it expanded westward in Montana as far as the Sawtooth Range south of Glacier Park, as shown by the presence of Buchia concentrica (Sowerby) near the base of the Swift Formation in that range. The fossil evidence suggests that the sea in northern Montana persisted un- til at least the end of the Oxfordian and possibly into the early Kimmeridgian. The initial retreat of the sea near the middle of the Oxfordian was followed in western South Dakota, east- ern and southern Wyoming, northwestern Colorado, and northeastern Utah by a brief readvance, during which a very thin marine unit (Windy Hill Sandstone Member of the Sundance Formation) was deposited disconformably on middle Callovian to lower Oxfordian marine beds (Pi- piringos, 1968, p. D23, D25). As this thin marine unit has not been recognized in north-central Wyoming or in Montana, it is assumed to have been deposited at the same time as the upper part of the Oxfordian marine beds lying conformably below the Morrison Formation in that area. The sea of latest Callovian to Oxfordian Age did not extend south of northern Colorado or northern Utah, so far as is known. It probably did not enter the western interior region through either southern Idaho or western Montana, because the sediments deposited become coarser westward and in western Montana they contain many wood fragments. Also, the age of the basal sedi- ments in Montana changes westward from latest Callo— vian in the Little Rocky Mountains of central Montana to late Oxfordian in the Sawtooth Range of northwestern Montana. This evidence indicates the presence of a land- mass to the west that shed considerable elastic sediment into the sea. In western Montana at least, this landmass was gradually submerged during the late Oxfordian. The marine sediments deposited in the western in— terior during latest Callovian and Oxfordian time changed from mostly silt and clay on the east topmostly glauconi- tic, calcareous sand, sandy coquinoid lime mud, and sandy silt on the west (Cobban, 1945, p. 1281—1286; Imlay, Gardner, and others, 1948; Imlay, 1956a, p. 595— 597; Pipiringos, 1968, p. D23; Brenner and Davies, 1974). The basal contact of sediments deposited in the 114 eastern part of the sea is sharp and is characterized by an abundance of belemnites (some of which are water worn), or by a few pebbles, or by a grit bed. The basal contact of sediments deposited in the western part of the sea is similar but is generally marked by pebbles of lime— stone, chert, or quartzite or by highly glauconitic sand in addition to many belemnites. Deposition of the sedi- ments in shallow water is shown by the presence of a varied pelecypod fauna including Ostrea and Mytilus. The climate was probably warm and rainy. The Morrison Formation was deposited during Late Jurassic time in fluviatile and lacustrine environments throughout much of the western interior region (Ree- side, 1952; Craig and others, 1955, fig. 30, p. 159). In Montana, as far north as the Great Falls area, its upper part was deposited in coal-forming swamps. Deposition began during the late Oxfordian in Wyoming and border- ing parts of Utah and Colorado, probably began at the same time or slightly earlier in areas farther south, but probably began in the Kimmeridgian in northern Mon- tana. This northward change in age of the basal Morrison coincides with northward thinning of the formation across Montana to a pinch-out near the Canadian boundary. These relations, especially including the persistence of coaly beds at the top of the Morrison in Montana, sug- gest that continental deposition in the south coincided with marine deposition in the north during late Oxford— ian time and that the northward pinch-out of the conti- nental Morrison is not primarily due to post-Morrison erosion. 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Page \ A Aalenian time ________________________ 64 Abstract ______________________________ 1 Acanthopleu'rocerac _ 20, 21, 58 A cevediteo __________ _ _ - 36 Acknowledgments _. -_ .9 Actinaatrea hyatti _____________________ 80, 89 Aeyute'roceraa ________________________ 52 Afton, Wyo __________________________ 111 Agassiz Prairie Formation (Canada) __ 58 Alabama _________________ 46, 47, 48, 104, 105 Alaska ________ 19, 20, 21, 22, 23, 24, 25, 28, 2.9, 30, 31, 37, 38, 59, 66, 67 Alaska Range, Alaska _________________ 59 Alaakoceraa ___________________________ 37 Alberta _____________________ 18, 107, 108, 113 Alberta trough, Montana, Canada _____ 18 Alsatites __________________________ 19, 20, 55 liaaicua none - ____________ 20 Amalthe‘us _________ _ 20, 21, 58, 59 maraaritatua _____________________ 21 zone _________________________ 20 atokeu‘ ___________________________ 21 American River, Calif _______________ 57 , 106 Ammon, Idaho ________________________ 70 Ammonite sequence, Gulf of Mexico region .................... .94 Ammonite zones, northwest Europe. See name of particular zone. Ammonites, succession of ________ 19, 37, 103 Amoebitea ____________________________ 25 (Amoebites) , Amoeboceraa ___- 31, 38, 55, 60 dubium, Amoeboceraa ____________ 24 Amoebocertu ______ \ ______ 25, 30, 31, 38, 52, 58 alternana ___ (Amoebites) dubium (Primwdoceras) __________________ 25, 59 spiniferum _..__ __ 25 Amy Lake, Wash ________ __ 66 Anahuac, Nuevo Leon - 36 Andiceraa ____________________________ 32 Androgynocema _______________________ 21 Anhydrite __________ 44, 46, 47, 49, 51, 1'04, 105 Antlers uplift _________________________ 18 Apoderoceraa ___________________ _- 21, 59 Aptian Age _____________________ __ 6‘7 Arapien Shale ________________________ 74, 94 Arctic region, paleobiogeographic set- ting of ___________________ l9 Arcticocema ______________ 19, 23, 28, 37, 82, 85 ishmae ___________________________ 23, 28 Arctoaaterooerasr _-_ ______________ 65 Arctocephalites _____ __ 19, 23, 28, 37, 59, 81 arcticua ___ ______________ 23 elegana ___________________________ 23, 28 greenlandicus _____________________ 23 (Cranacephalites) _ _ _ , _____________ 27 Argentina ____________________________ 26, 50 Arietioe'ras __ _ 20, 21, 45, 55, 56, 57, 58, 65 Arietites __________ -- 20, 21, 52, 55, 58 bucklandi zone ____________________ 20 “INDEX [Italic page numbers indicate major references] Page Ariaphinctea __________________________ 24 Arizona _____________________ 17, 96, 109, 113 Arkansas ______________________ 46, 47, 48, 105 Arkellites hudleatoni zone ____________ 24, 26 Arkelloceras ___________________ 22, 23, 25, 37 Arniocema __ 19, 20, 21, 45, 52, 55, 56, 58, 59, 61 aemicostutum zone ................ 20 Arniotites ____________________________ 21 Arroyo de San Jose, Baja California ___ 51 Arroyo La Mula, Tamaulipas _________ 33 Artemsia Formation (Cuba) ______ 39, 44, 46 Arvison Formation _____________ ___ 54, 61 Ashman Formation (Canada) - -__ 58 Aspidocema ____________________ -_ 24, 31, 32 Asteroceras ________________________ 20, 58, 61 obtusum zone _____________________ 19, 20 Anthenaceras delicatum Ataxioce'ras ________________ Atlantic Coast region _ Aucella eringtoni _____________________ Aulacomuella _________________________ Aulacaaphinctes __________ 24, 34, 35, 36, 45, 63 Aulacosphinctaidea _‘ _______________ 24, 32, 57 Aulacoatephanacems acutissiodorensia zone _____________________ fi, 32 Aulacostephanus eudoxus zone _ Aztec Sandstone ______________________ Azucar Member, Jagua Formation (Cuba) _________________ 39, 103 B Bacon Ridge, Wyo ___________________ 88 Bagley Andesite _______ Baja California, Mexico _- ______ 51, 108 Bajocian Stage, Alaska ________ 19, 23, 24, 67 ammonite and buchias succession in _ 2.1, 37 arctic region ____________________ 37 Arizona __________________________ 97, 99 California ___17, 52, 57, 60, 61, 106, 107, 108 Canada __________ 18, 25, 67, 1'02, 106, 109 Cuba -- 17, 103, 104 Gulf of Mexico region ____________ 47, 48 Idaho ________________ 24, 65, 106, 108, 109' Mexico __ 17, 23, 39, 49, 52, 99, 103, 104, 106 Montana ___________ 24, 67. 68, 80, 81, 109 Nevada ___________________________ 53 North Dakota ________________ 67, 78, 109 Oregon _____ 17, 18, 23, 64, 65, 106, 1017, 108 Pacific Coast region __________ 37, 102, 1106 Utah __________________ 95, 97, 98, 99, 109 western interior region ________ 18, 24, 67, 102, 106, 108, 111 Wyoming _________________ 24, 84, 99, 109 Baker County, Oreg __ ________ 64, 65 Bald Mountain Formation ____________ 66 Balsas Portal (Mexico) ______________ 52 Banner, Wyo _________________________ 83, 84 Barklow M0untain, Oreg _____________ 62 Barranca Formation (Mexico) ________ 52 Basey Member, Snowshoe Formation __ 55 Page Bathonian Stage, Alaska __________ 19, 28, 37 ammonites and buchias succession in ________________________ 25, 37 ammonites of _ ____________ 28 arctic region _- ......... 19, 28. 37 Atlantic Coast ____________________ 4 California ________________ 57, 60, 106, 107 Canada _____________ __ 28. 37, 67, 107 Colorado _________________ 85, 109 Cuba _________________ _ 17, 103, 104 Gulf of Mexico region _____________ 47 Idaho __________________________ 37, 107 Mexico ________________________ 17, 25, 37, 39, 49, 5'0, 51, 52, 99, 103, 104 Montana _______ 27, 67, 81, 82, 107, 109, 111 North Dakota ____________________ 67 Oregon ____________ 17, 26, 37, 67, 106, 107 Pacific Coast region ____________ 102, 107 South Dakota ____________________ 85, 109 Utah _________________ 95, 96, 99, 109, 111 western interior region ---- 18, 27, 37, 67 Wyoming ____________________ 85, 109, 111 Bearpaw Mountains, Mont ________ 29, 80, 82 Beaverhead County, Mont _-_- ___- 81 Becheicems ______________________ 21 (Becheiccras) , Liparoceras __ _______ 20 Bedford Canyon Formation ___________ 54, 61 Belt Creek, Mont _____________________ 68 Belt Island uplift __________ 18, 19, 80. 81, 113 Berriasello ____________________________ 24, 34 Berriasian Age _ 63 Bibliography ___ 114 Big Bend, Idaho ' 7o Big Bend area, California ___- 52, 53, 54, 106 Big Hollow Wash, Utah ______________ 77,98 Big Horn County, Wyo ________________ 71 Big Snowy Mountains, Mont ___ 69, 78, 80, 82 Bighorn Basin, Wyo ______________ 18, 80, 82, 83, 84, 85, 86, 87, 111 Bighorn Mountains, Wyo., Mont ______ 78, 8.9. 84, 85, 86, 87 Billhook Formation (Canada) ________ 58 Black Dragon Canyon, Utah __________ 74,94 Black Hills, Wyo., S.‘ Dak _______ 83, 85, 86, 87 Blackfoot, Idaho ______________________ 89, 111 Blackfoot Mountains, Idaho ____________ 89 Blaine County, Mont _______ __ 80 Bluff Sandstone ______________ 96 Bochianitea ___________________________ 36 Bolson de Judas, Candela district, Mexico 35 Boaitra. _________________ 105 buchii ______________ 61 Bossier Formation _ ._ 44, 47, 105 Boulder, Utah ________ __ _______________ 98 Boundary Ridge Member, Twin Creek Limestone ____________ 70, 72, 74, 85, 88, 91, 96, 99 Bowas Member, Piper Formation ___ 68, 69, 80 Boyden Cave pendant __ _- _____ 53 Bridger, Mont _________________ 84 British Columbia _______________ 20, 21. 23, 25. 29, 58, 59, 66, 67, 68, 107, 108 127 128 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Page British Mountains, Yukon Territory- 21, 23, 29 Brogan, Oreg ______________________ 56, 64, 65 Brown Canyon, Utah ________________ '76 Brushy Basin Shale Member, Morrison Formation ________________ 75 Buchia. ____________________ 3, 36, 37, 88, 61, 6'7 blanfordiana __________________ 25, 58, 66 cancentrica ______ 18, 24, 25, 30, 31, 38, 55, 56, 58, 59, 60, 62, 63, 66, 69, 71, 73, 75, 82, 113 ficchen'ana ________ 24, 25, 55, 58, 59, 63, 66 moaquemia ______ 24, 25,31, 34, 36, 38, 56, 58, 59, 63, 66, 67 okenaia ___________________________ 24, 55 pacifica ___ 62 piochii ________ 2‘4, 25, 51, 56, 58, 59, 63, 66 richardaonensis ___________________ 25 rugocu. ___________ 25, 38, 55, 56, 59, 63, 66 terebratuloides ____________________ 58 uncitoidea ________________________ 63 umchenais ________________________ 25 Buchias, succession by stages __‘ ________ 19 Buck Mountain Formation ____________ 66 Buckhorn Wash, Utah .............. 74, 94, 95 Buckner Formation _ 42, 44, 46, 47, 48, 102, 105 Burr Fork, Utah _____________________ 72 Bush Canyon, Wyo ____________________ 71 Butte County, Calif ___________________ 57 Button Butte, Mont ___________________ 69 C Caborca, Sonora ______________________ 19, 52 Cadoceras ________ 23, 27, 28, 29, 38, 67, 88, 108 calyx __________________________ 23 catostoma _____ _ 23, 58, 59 septentrionale _ _ - _ _ 23 variabile _________________________ 23 (Longaeviceras) pomeroyemz _____ 29 (Paracadocerus) tonnienae _____________________ ( S tenocadoceraa ) canmiense ________ atenolaboidc striatum _____________________ 23, 58 Codmm'tes ____________________________ 37 Caeniaites turncri zone ________________ 19,20 Cahuasas Formation (Mexico) _ 45, 49, 103, 104 California ______ 20, 22, 24, 29, 30, 31, 36, 38, 52, 54, 55, 61, 1‘06, 107, 108 Callovian Stage, Alaska ____________ 19, 29, 38 ammonite and buchia succession in __ 29, 38 ammonites of _____________________ 28 arctic region ___ ________ 28, 29, 38 Arizona __________________________ 113 Atlantic Coast region _____________ 4 California _______ 17, 29, 38, 53,57, 60,61, 62, 106, 107 Canada ___________ 29, 38, 67, 107, 108, 113 Colorado ________________________ 111, 113 Cuba ___________________________ 103, 104 Gulf of Mexico region __-_ 47, 48, 103, 104 Idaho ________ 65, 66, 89, 107, 108, 111, 113 Mexico 17, 29, 38, 49, 50, 51, 52, 99, 103, 104 Montana ______________ 29,67, 81,111, 113 North Dakota ____________________ 67 Oregon ______ 17, 38, 60, 64, 65, 66, 1'06, 107 Pacific Coast region ____________ 102, 107 South Dakota __________________ 111, 113 Utah ________________ 95, 99,102, 111, 113 western interior region ________ 18, 29, 67, 102, 107, 108, 109, 111 Wyoming ____________________ 89, 111, 113 Caloceras _____________________________ 19 Camagiiey Province, Cuba _____________ 34 Campian Age _________________________ 63 Camptonectes _______________ 81, 87, 91, 92, 95 Page Canada, arctic ____________________ 21, 22, 23, 25, 28, 29, 30, 31, 36, 87, 38 eastern ___________________________ 4, 103 western ________________ 19, 22, 31, 36, 106 Contwan‘a, ___________________ 20, 65 Cannonville, Utah ____________________ 77, 98 Cafion Alamo, Sierra J imulco _________ 36 Cantu Chapa, Abelardo, quoted _______ 51 Canyon Springs Sandstone Member, Sundance Formation ______ 71, 73, 81, 84, 85, 86, 88, 93, 111 Cape Hatteras, N.C. __________________ 4 Carbon County, Mont _________________ 78 Cardioceras __________ 17, 18, 24, 25, 29, 38, 58, 69, 71, 73, 75, 82, 87, 90, 92 oanadenae ________________________ 58 cordatum zone __________ 24, 30, 50 cmdiforme _ __ 24, 30, 69, 71, 73, 75 distorts ___________________ 25, 59 martini __________________________ 58, 59 ( M altom‘c eras ) ___________________ \30 (Scarburgiceras) _________________ 25, 30 martini __________ 24, 25, 30, 55, 56, G6 (Subvertebrice’ras) canadenae 25 Caribou Range, Idaho 90 Carmel Formation __________ 72, 73, 74, 75, 76, 77, 84, 87, .91, 93, 95, 96, 97, 99, 111 Cascade Mountains, Wash ____________ 56, 66 Catacoeloceras _____________________ 20, 21, 55 Catulloceraa _________________ 20, 21, 22, 55, 58 Cedar City, Utah __________________ 76, 99 Cedar Mountain, Utah _-_ -_ 74 Cerro Pelon, Veracruz __ __ 106 Challenger Knoll ______________________ 47 Charcas, San Luis Potosi ______________ 49 Charmasscicems ______________________ 20, 21 Chetatites chetae ______________________ 25 Chetco River, Oreg ______ __ 63 Chiapas massif, Mexico - _ __ 51, 1‘06 Chiapas salt basin (Mexico) _________ 51, 106 Chihuahua, Mexico _ 32, 33, 35, 45, 51, 103, 105 Chinameca, Veracruz __________________ 106 Chinitna Formation ________________ 29, 59, 65 Chinle Formation _____________________ 96, 97 Chofiat‘ia ________ ___ 27, 29, 50 Chondroceraa __________________ 2A, 55, 58, 81 allam‘ _____________ 22, 23. 59, 69, 71, 73, 75 Chugwater Formation ________________ 83, 84 Cinco Pesos, Cuba ____________________ . 39 Clarke County, Miss ________ 46 Clarks Fork Canyon, Wyo _____________ 84 Climate, Jurassic __ 104, 108, 109, 111, 113, 114 Cloverly Formation ___________________ 88 Clydoniceraa discus zone ______________ 22 Coahuila, Mexico _______________ 36, 44, 48, 105 Coahuila Peninsula, Mexico ___________ 48 Coast Ranges, Calif ________________ 53, 61, 63 Cobbam‘tes ______ __ 22, 23, 216, 27, 28, 37, 55 talkeetnanus ______________________ 58 Coconino County, Ariz ________________ 7'7 Cody, Wyo ________________________ 84, 85, 86 Coeloceraa ____________________________ 65 Colebrook Schist ______________________ 55 Colfax, Calif _________________________ 53, 57 Colorado ________ 73, 85, 90, 9.9, 96, 109, 113, 114 Colorado Plateau _____________________ 111 Columbus, Mont ______________________ 84 Combe Formation _____________________ 57 Connor Creek, Oreg ___________________ 65 Cook Inlet region, Alaska _________ 17, 19, 28 Cooks Canyon Agglomerate ___ ______ 54 Coon Hollow Formation _____ Copper Hill Volcanics ___ Corongoceras ________________ 24, 32, 34, 35, 36 alternam _________________________ 26, 35 filicostatum _______________________ 35 Coroniceras _______ 19. 20, 21, 45, 55, 58, 59, 65 bisulcatum ________________________ 20 Page Corral Creek, Colo ____________________ 93 Cosumnes Formation _________________ 60 Cosumnes River, Calif ________________ 60 Cotton Valley Group ______________ 44, 47, 48 Cow Creek, Oreg _____ __-_ 63 Cow Springs, Ariz __ _ 77, 99 Cow Springs Sandstone --_ _ 99 Cowley, Wyo _________________________ 78 Craig, Mont _________________________ 68 Cranocephalites ______ 19, 23, 28, 29, 37, 59, 81 borealis __________________________ 23 costidensus ___ _ 23, 58, 59 indistinctus __ _-_- 23 pompeckji -_ _ 23 uulgaris __________________________ 23 (Cranocephalitea), Arctocephqlitea _____ 27 Craspedites canadensis ________________ 25 nodiger __________________________ 27 aubditus ___ _ 27 Creniceras ___________________________ 45, 50 crenatum _________________________ 30, 50 dentatum _________________________ 50 rengyeri _________________________ 30, 50 Crioceras ___________________ 36 Crook County, Wyo _ _______________ 71 Crucilobiceras ___________ 19, 20, 21, 52, 55, 56, 57, 59, 64, 65 Cuba _______ 17, 24, SS, 34, 89, 44, 103, 104, 105 Cubaochetoceraa ______________________ Cucurpe, Sonora _____________________ Curry County, Oreg _ Curtis Formation __________________ 74, 75, 89, 92, 9.9, 94. 95 96, 113 Curtis Member, Stump Sandstone __ 72, 73, 89, 90, 92. 95, 113 D Dactylioceras _ _ 20, 21, 22, 58, 65 commune _-__ ....... 21, 55, 59 semicelatum ______________________ 21 tenuicoatatum zone _______________ 20 Dalmaaiceras _________________________ 39 Danish Ranch, Utah __________________ 76 Doonella sancteo—anea _ _ 61 Days Creek, Oreg __ _ 63 Dayville, Oreg ___- _ 62 Decipia. ______________________________ 24 decipiena zone ____________________ 24 Deep Creek, Utah ____________________ 98 Deerfield basin (Massachusetts) _______ 4 Dennett Creek, Idaho ___________ Dewey Bridge, Utah ________________ 75, 96 Dewey Bridge Member, Entrada Santktone ________________ 75, 96 Diamond Valley, Utah ________________ 99 Dichotomosphinctea ___- 24, 25, 30, 52, 55, 59, 60 durangensis ___________________ 24, 31, 45 muhlbachi ___- _ 24 plicatiloides __ __ 24 (Dichotomosphinctes), Perisphinctes __ 30, 38, 39, 62 Dickersonia, _________ / _________________ 24, 34 sabanillenaia ______________________ 35 Dillard, Oreg _________________________ 63 Dinosaur Canyon Sandstone Member, Moenave Formation -- 96 Dinosaur Quarry, Utah _______________ 73 Discosphinctes __________________ 39, 52, 55, 60 carribezmus ____________________ 24, 30, 45 virgulatiformis ___________________ 24 (Diacosphinctes) , Periaphi‘nctes _______ 30, 38 Divesian (term) _______________ _ 47 Dixie Creek, Oi'eg ___________ 65 Docz‘doceraa _______ - 22, 23, 55, 56, 59 widebayense ______________________ 23 Donetenaia ___________________________ 61 oregonemis _--_._.______--____-.___ 22, 55 Doraoplam’tee panderi Donoplanitoidea triplicatua ____________ 26 Dothan Formation _____________ 55, 62, 6.9, 108 Douglas County, Nev __ ________ 53 Douglas County, Oreg __ _ 63 Duchesne County, Utah __ __ 72, 92 Duchane River, Utah ________________ 72,91 Dufrenoya ____________________________ 47 Dumo'rtieria __________________________ 20, 22 leveaauei zone _____________________ 20 Dunlap Formation _ _ 5.9, 54. 97, 102, 108 Duranaitea ___ _- 27, 32, 34. 35, 63 incertua ___ __________ 34 vulgaria _______________________ 24, 34, 45 Durango, Mexico ___________ 32, 33, 34, 36, 45 E Eagle County, Colo ___________________ 93 Eagle Mills Formation ________________ 46, 47 East Butte, Mont ____________________ 80 Echioceraa ______________ 210, 21, 45, 57, 58, 65 arcticum __________________________ 21 raricostatum zone ________________ 20 Echo Island Formation (Canada) ______ 58 El Antomonio, Sonora ................ 19, 52 Elk Creek, Colo ______________________ 73, 93 Embayment, Gulf of Mexico - _ 104 western interior region __ _ 18 Emery County, Utah ____________ 74, 75 England, Jurassic formations _______ 44, 54, 90 Enterprise, Oreg _____________________ 56, 65 Entrada Sandstone _________ 72, 73, 74, 75, 77, 92, 93, 94, 95, 96, 98, 99, 111, 113 Eocephalites _________________________ 37 Eoderoceras _________ __ 2.0, 55, 65 Epistrenoceras _____ - _ _ _ 45 paracmtrarium ___________________ 22, 25 Epivirgatites 'nikitini __________________ 27 E'rycites _____________________________ Erycitoidec ________________________ 25, howelli __________ Erymnoceraa \ _______ coronatum zone __ mixteco'rum ___________________ 22 Escalante, Utah _____________________ Euaapidace'raa ________________________ Eudmetoceras _____________________ 22, 55, 56 Eugeosynclines __________ Euhoplaceras _____________ Modesto. ______________ (Euhoplocems), Sonninia Euprionocema ________________________ Europe, northwest, ammonite zones. See name of particular zone. Europe, southern, subdivisions of the Tithonian in ______________ 26 Eumcephalitee __________________ 29, 38, 45, 50 boeaei 22 Evanston, Wyo _______________________ 90 Evaporitic sequences __________________ 4, 50 Exog'y'ra virgula ______________________ 36 F Fall River County, S. Dak ____________ 71 Fannimceras Fant Andesite _____ Fauna] relationships, intercontinental __ 37 Fehlmanm’tes _________________________ 30, 50 Ochetocems _______________________ 50 Fernie, British Columbia _____ __ 18 Fernie Group (Canada) ______________ 68 Finca Ancon, Pinar del Rio Province, Cuba _____________________ 34 INDEX Page Firemoon Limestone Member, Piper For- mation _______ 68, 69, 78, 79, 80, 81 Fish Creek, Wyo __ .............. 90 Florida ___________________ 47 Fontanelliceras __ ______________ 20 Fontannesia __________________________ 22, 5 Foreman Formation __________________ 54, 60 Fort Pierce Formation ___________ __ 47 Fossil Mountain, East Greenland __ __ 28 Fossils, characteristic _________________ 45, 55, 56, 58, 59, 69, 71, 73 Franciscan assemblage ________ 55, 62, 6.9, 108 Francisco Formation (Cuba) _________ 39, 44 Franconiteo vimineus _________________ 2‘6 Frantz Creek, Colo ____________________ 73, 93 (Franziceras), Pailoceras ______________ 19 Fremont County, Wyo -- __ 70,89 Front Range, Colo ___ ___- 93 Fuciniceras ________________________ 20, 56. 65 G Galeana, Nuevo Leon _________________ 35 Galice Formation _____ 55, 61, 6‘2, 102, 107, 108 Gallatin County, Mont ________________ 80 Gallatin Range, Mont _________________ 80, 81 Garantiuna garantiana zone ___________ 22 Garfield County, Utah ________________ 77 Geologic history, Jurassic ____________ 102 Germ’llia montanaemia ________________ 80, 99 Giraffe Creek Member, Twin Creek Limestone _._ 70, 72, 74, 88, 94, 108 Glacier National Park, Mont _________ 80, 113 Gluucolithites _________________________ 25 ga'rei zone ________________________ 24, 26 Glen Canyon Sandstone _______ 72, 73, 91, 109 Glendale, Utah ________________________ 98 Gleviceraa ______ _ _ _ 20, 65 plauchuti _ _________ 21 Glochiceras _. ___ 31, 34, 38, 39 fialar ______________________ 24, 30, 31, 45 lithographicum ___________________ 26 Gold-belt area, Sierra Nevada, Calif ___ 54 Goliathice’ras __________________________ 25, 87 Gopher Ridge Volcanics _ 60, 107 Gore Range, _Colo _______ ___- 93 Gowericeras castidensus _ ___- 28 subitu'm __________________________ 28 Gracilisphinctes progracflis zone ______ 22 Grammatodon _________________________ 84 Grammoceras ____________ 20, 21, 22, 55, 58, 59 thouarsense zone __________________ 20 Grand Banks, Newfoundland __ ___ 4, 103 Grand County, Colo ___________ ___ 73, 93 Grand County, Utah __________________ 75 Grand Junction, Colo ________________ 96 Grapevine Creek, Mont _______________ 78 Graphoceraa concaoum zone __________ 22, 57 Gravelbourg Formation (Canada) __ 69, 78, 80 Gravesia _______________ __ ‘ 31 Grayiceras ___- __ 35 mexicanum _______________________ 35 Graylock Formation __________________ 55, 64 Great Falls, Mont ____________________ 68, 114 Green River, Utah ___________________ 95, 96 Green River Lakes, Wyo ________ 70, 85, 86, 88 Greenland, East ___- 19, 21, 22, 23, 25, 28, 82, 85 Gregorycems transversarium zone ___- 24, 50 Gros Ventre River, Wyo ______________ 83, 88 Grossouvria ________________________ 29, 38, 66 Gmphaea _____________ 65, 85, 91, 109, 111,113 culebra ___________________________ 56 impressimarginata ___ 22, 28, 69, 71, 73, 75 nebraacensis __ ___- 22, 69, 71, 73, 75, 88 planocon'vexa ______ 69,71, 73, 75, 80, 81, 89 Guasasa Formation (Cuba) ___________ 3.9, 44 Guerrero, Mexico ___- 17, 23, 25, 45, 51, 52, 102, 103. 104 129 Page Guerrero embayment (Mexico) ________ 17, 20, 25, 29, 52, 1.03 Guhacm‘a bella ________________________ 23 Gulf of Mexico, Jurassic connections with Pacific and Atlantic Oceans ___________________ 17, 51 Gulf of Mexico region, ammonite suc- cession and correlation in __ 24, 38 characteristic fmils of __-..; ______ 45 geologic history of ________________ 10.9 Jurassic formations in ___________ _ 44 lithologic and stratigraphic features of ________________________ .19 locality bibliographic references _-_ 3 paleobiogeographic setting ________ 4 Tithonian Stage in ____________ ..-_ 82, 34 United States, stratigraphic and lithologic comparisons in -_ 46 unconformities in _________________ 99 Gunlock, Utah ________ 76, 97, 98, 99 Gunnison, Utah _____________ 74, 94 Gunnison Plateau, Utah -_ __- 74, 94 Guphaea planoconvexa ________________ 22 plunoconvewa fraterna ____________ 22 Gypsum ________ 67,79, 83, 87, 95, 104, 109, 111 Gypsum Creek, Mont _________________ 78,84 Gypsum Spring Formation ____________ 18, 70, 71, 78, 82, 84, 88,89, 90, 95, 99, 109 Gypsum Spring Member, Twin Creek Limestone ________________ 18, 70, 72, 74, 82, 8.9, 9-0, 91, 94 Gurocho-rte ___________________________ 86 H Hagermeister Island, Alaska __________ 19 Hahns Peak, Colo ____________________ 73, 93 Hanna, Utah _________________ 72, 87, 91, 109 Haplocems ___________________________ 31, 32 Hardgrave Sandstone _________________ 54,57 Hardin trough, Wyoming _ _ 19 Harpoceras _________ __ 21. 53 exaratum _____ _ 20, 21, 22, 58 falcifer zone ______________________ 20 ( H arpocerataidea) ________________ 65 ( H arpoceratoides ) , H arpoceras ________ 65 Harris Wash Tongue, Page Sandstone _ 77 Harrison Lake, British Columbia _____ 58, 67 Harrison Lake Formation (Canada) ___ 58 Hartford basin (Connecticut) _______ 4 Hartville uplift _______________________ 85 Hatteras Abyssal Plain _______________ 4, 103 Haum‘a ______________________ 20, 21,22, 55, 59 variabilia zone ____________________ 20 Haynesville Formation _ 46 Heath, Mont ___- 69 Hecticoceraa ____________ - 29, 38, 61 retrocostatum zone _______________ 22 Hells Backbone, Utah _________________ 98 Hettangian Stage, Alaska _____________ 19 ammonites and buchias succession \ in ________________________ 19 Arizona __ 97 Mexico __ ___ 19, 52, 99 Nevada _______________________ 19, 53, 106 Oregon _____________ 17, 19, 63, 64, 65, 106 Pacific Coast region ______________ 102 Utah _____________________________ 97 Hibbard Creek, Oreg -__ - 65 Hidalgo, Mexico ______ ._ 45, 50 H ildaites _______________ _- 21 Hildaceraa bif'rona zone _______________ 20 Hildoglochiceras _____________ 24, 32, 34, 35, 36 ecarinatum ______________________ 34 Himalauites __________________________ 34, 36 Hinchman Sandstone __ 54, 60, 107 Hoback Range, Wyo _ ___- 90 Hoplocardioce'ras ______________________ 25 130 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Page Home Creek, Wyo ____________________ 87 Horton, Wyo _________ 85 Hosston Formation _- 48 Huasteca, Mexico _________ 33, 45, 99, 103, 105 Huauchinango, Hidalgo ________________ 45 Huayacocotla, Veracruz _______________ 30 Huayacocotla embayment (Mexico) _ 17,26, 29 Huayacocotla Formation (Mexico) ___- 45,49 Huehuetla, Hidalgo ___________________ 50 Huizachal anticline (Mexico) _____ 33 Huizachal Formation (Mexico) _______ 49 Hulett, Wyo ______________________ 71, 83, 85 Hulett Sandstone Member, Sundance Formation _____ 70, 71, 81, 88, 89 Hull Meta-andesite ___. ‘ .......... 54, 60 Huntington, Oreg ____________________ 64 Hurricane, Utah ______________________ 99 Hurwal Formation ___ _____ 56, 65 Hyatt‘ville, Wyo ___________________ 71, 83, 84 Hybbmticerm ____________ 24, 27, 31, 32, 9.9, 45 hybimotum __ 26 Hyde Formation 55 y I Idaho _______ 17, 24, 30, 52, 68, 70, 80, 82, 83, 89, 90. 92, 106, 107, 108, 109, 111, 113 Idaho Falls, Idaho ___________________ 89, 111 Idoce‘raa ___________ 24, 30, 31, 32, 38, 45, 52, 55 bulderum __ duramaeme planula ___________________________ (IL, ‘ ' ) , " ‘M-‘n Sub,’ "0‘ 27 (Ilowaiakya) aokolom‘, Subplam'tes _____ 27 Imlayocems __________________________ 29 miettense _________________________ 22 Indian Creek, Mont ___________________ 81 Iniskinitea ........... __ 23, 29, 64 intermediua ___ _.-_,_ 22 Inkin Formation (Canada) __ __ 59 Inocemmua ___________________________ 35 Interior region. See Western interior region. Introduction __________________________ 9 Iron County, Utah ................... 76 Iron Mountain Creek, Oreg _- 63 Ironside, Oreg ________________________ 56 Islands, Jurassic -0- 18, 52, 102, 106, 109, 111 Isthmus of Tehuantepee .............. 50 IzeE, Oreg ________ 55, 64, 65, 66, 102, 106, 107 J Jackson, Wyo __________________ 70, 83, 84, 88 Jackson Hole, Wyo ___________________ 9'0 Jagua Formation (Cuba) --__ 89, 42, 44, 48, 50 Jagua Vieja Member, Jagua Formation (Cuba) __________________ 39 Japan ________________________________ 50 John Brown Creek valley, Colorado ___ 75, 96 John Day, Oreg _________________ 21, 26, 63, 65 Johnson Canyon, Utah _______________ 97, 98 Johnson County, Wyo 71 J onotla, Puebla ______________ 35 Josephine ultramafic mass ____________ 62 Juab County, Utah ____________________ 74 Juarez, Durango _____________________ 45 Judd Hollow Tongue, Carmel Formation 77, 98 Judith River, Mont ___________________ 68 Junction Creek Sandstone ........... 75, 96 Juniper Mountain, Oreg ............. 64, 65 K Kachpm‘iteo fulaem .................. 27 Kanarraville, Utah ____________________ '76 Kane County, Utah .................. ' 76, 77 Page Kayenta Formation __ 74, 75, 76, 77, 96, 97, 109 Kellawayaitea __--______-; _____________ (Kellawavaitea), Reineckia _-- Keller Creek Shale __________ Kent Formation (Canada) ____________ Keppleritee ___________ 22, 23, 27, 28, 29, 37, 38, 45, 50, 55, 56, 58, 59. 82 coatidenaus ________ 22, 28, 69, 71, 78, 75, 82 maclearni ________ 22, 28, 69, 71, ‘73, 75, 82 anugharboreme ___________________ 65 aubitua _________ __ 22, 69, 71, 73. 75, 82 torrensi _- _________________ 22 ”10th __________ 22, 28, 69, 71, 73, 75, 82 Kilianella _____________________________ 36 Kimmeridge Clay (England) 32 Kimmeridgian Stage, Alaska __________ 31, 38 ammonite and buchia succession in _ so, 38 Atlantic Coast region ............ 103 California 17, 31, 38, 60, 61, 63, 106, 107, 108 Canada ____________________ 18, 31, 88, 67 Colorado ._ _______ 90 Cuba ________ __ 39, 42 definition of _ _ 30 England __________________________ 31 Gulf of Mexico region ___________ 17, 38, 48, 102, 104, 105 Louisiana _________________________ 31 Mexico _____ 30, 38, 49, 51, 52, 102, 103, 106 Michigan ,- ________________________ 99 Montana __________ 18. 67, 82, 99, 113, 114 North Dakota ___ ------------,--- 67. 99 Oregon _______________ 17, 38, 62, 106, 107 Pacific Coast region ____________ 102. 108 South Dakota _____ 90, 99 Texas _______________________ 31, 103, 105 90 _- 107, 108 western interior region _____ ___ 18, 114 Wyoming ______________ 90 Kings River, Calif ____________________ 53 Klamath Mountains, Calif., Oreg _ 17, 53, 61, 62 Kline Member, Nesson Formation ___- 69, 78 Knoxville Formation ___ 55, 6‘2, 6'8, 66, 107, 108 Kootenai Formation .................. 67, 68 Kosmoceraa __________ 23 jason zone ________________________ 22 Kosamatia, _____ 24, 27, 32, 33, 94, 35, 36, 51, 55 kingi _____________________________ 35 rancheriaaensia .0 35 varicoatuta, ______ 35 victoris ________________________ 24, 35, 45 Koaamatiq-Dura’ngites ammonite assem- blage ..................... J4 Kremmling, Colo ______________________ 93 Kunga Formation (Canada) __________ 58 Kuskokwim, Alaska ___________________ 19 L La Boca Formation (Mexico) _______ 49 La Caja Formation (Mexico) _____ 45, 48, 105 La Casita Formation (Mexico) ______ 34, 44, 45, 48, 105 La Gloria Formation (Mexico) __ 45, 48, 49, 50 La Joya Formation (Mexico) __ 44, 45, 49, 104 La Punta de San Hipolito, Baja Califor- nia ______________________ 51 Laberge Group (Canada) 59 Lak Member, Sundance Formation ___- 71. 73, 85, 86, 88, 93, 111,113 Lake Fork, Utah _________________ 72, 91, 92 Lake Pillsbury, Calif __________________ 63 (Lamberticeraa) collieri. Quensted- toceras ___________________ 29, 82 Lander, Wyo _______________ __ 84, 85, 87 Las Villas Province, Cuba __ ..... 34 Latiwitchellia ____________________ 58 gracilis ___________________________ L 22 Page (Latiwitchellia), Witchellia ___________ 23 Laugeitea uogulim ____________________ 25 Leeds Creek Member, Twin Creek Lime- stone _______ 70, 72, 74, 88, 94, 111 Let'oceras opalinum _______________ 23, 24, 25 opalinum zone ____________ 22, 23. 24, 37 Leptaleoceras ______________ 20, 21, 55, 58, 65 Leptoaphinctes ___- 22. 23, 37, 45, 55, 56, 59. 107 Levan, Utah .......................... 74, 94 Lewistown, Mont _____________________ 69 Liberty County, Mont ............. .---- 80 Lilac Argillite ________________________ 54. 57 Lilloettia _____________ 28, 29, 38, 50, 64, 66, 82 buckmani ...... 22, 23, 27, 55, 56, 58. 59, 65 atantom' _- __________________ 22, 23, 55 Linaulu ______________________________ 113 Lioceratoides _________________________ 65 Liparoceras (Becheicerua) _____________ 20 Lithologic and stratigraphic features, comparisons of ___________ 99 Little Bull Valley, Utah .............. 77, 98 Little Rocky Mountains, Mont __ 29, 81, 82, 113 Little Sheep Mountain, Wyo .......... 87 Little Water Canyon, Mont ___________ 81 Locality data, bibliographic references to 3 Lodge Grass Creek, Mont _____________ 78, 84 Logtown Ridge Formation __ 54, 60, 61, 62, 107 Loma Rinconada, Sierra Cruillas ______ 35 Loma Sabinilla, Las Villas, Cuba ______ 34 Lonesome Formation .................. 55. 66 Longuem‘cerac ________________________ 23 (Lonaaevicerao) pomeroyeme, Cadoce'raa 29 Lopha ................................ 113 Louann Salt- 17, 44, 46, 47, 48, 49, 50, 51, 99, 102 Louisiana ______________________ 31, 46, 47, 48 Lovell, Wyo ___________________________ 87 Lower Slide Lake, Wyo __ _ 70, 84, 85, 88 Lubbe Creek Formation __ __ 59 Lucky S Argillite _________ _ 54 Ludwiaia, murahiaomw zone ............ 22 Lukachukai Member, Wingate Sandstone 97 Lupheritea ____________________________ 37 Lyoaoma. powelli ______________________ 84, 89 (Lyroa'yitee), Oppelia _________________ 23 Lytoceras ____________ .- 30, 93, 94, 113 Lytohoplitea _____________ _-- 24, 27, 32, 34 caribbeanua _______________________ 35 M McCarthy Formation .................. 59 McCoy Creek, Idaho _____________ 90 McDonell Lake, British Columbia ...... 58 McElmo Canyon, 0010 _________________ 75, 96 Macrocephalitea __________ 29, 38, 50, 55, 61, 6'] macrocephalus zone -__ ..... 22, 28, 82 Madera County, Calif _____ ___- 57 Madison County, Mont _______________ 80 Madison Range, Mont ________________ 81 Malheur County, Oreg -_ Malone Formation ________________ Malone Mountains, Tex __________ 31. 35, 45 (Maltoniceraa) Cardioceraa _ _____ 30 Manila, Utah _____ _ 92 Manitoba - 109 Marias Pass, Mont ______---; __________ 82 Marine transgressions ___- 17, 18, 46, 47, 48, 51, 80, 85, 102, 103, 104, 105, 109, 113 Mariposa Formation 54, 60, 61, 62, 102, 107, 108 Masefield Shale (Canada) .............. 69 Maude Formation (Canada) ___________ 58 Maude Island, British Columbia ....... 66 Mazapil, Zacatecas ____________________ 32, 33 Mazapilitu ___________ 24, 27, 32, 98, 40, 42, 45 Mazatepec, Puebla .................... 85 Megarietitea _____________ ' ....... 2 0,55, 56, 65 Page Meaasphaeroceraa _____________ 22, 23, 24, 37, 58. 59, 69, 71, 73, 75, 80, 81 rotundum _________________________ 22, 23 Meleagrinella - 92, 93, 118 curta ______________ ,. .............. 94, 95 Merced River, Calif ................... 60 Mesa County, 0010 ____________________ 75 Metahaplocem ________________ 24, 31, 34, 35 (Metapeltoceraa), Peltoceras __________ 22, 55 Metaphioceras 65 Mexico _____ 17, 19, 20, 22, 23, 24, 25, 27, 29, 30, 31, .12, 34, 35, 36, 38, 44, 45, 48, 4.9, 51, 103, 105, 106 Mexico, Gulf of. See Gulf of Mexico. Michigan basin _______________________ 99 Michoacan, Mexico I- __________ 51 Micracanthoceras __ _ 24, 32, 34, 35, 36 acan thellum _ _ ___________ 35 Microderoceraa ________________________ 59 Midcontinent region (United States) __ 99 Miles City, Mont ______________________ 69 Mill Creek, Wyo ______________________ 84 Miller Creek, Colo ________________ Minas Viejas Formation (Mexico) ___. 44, 48, 50, 99, 104 Mineral, Idaho ____________________ 56, 64, 65 Minnekahta, S. Dak ___________________ 71 Miogeosyncline ..... _- 53 Miroaphi‘nctca ___ _ 39 Mississippi ___ __ 46, 48 Moab, Utah _- _____________________ 96 Moab Member, Entrada Sandstone ___- 75, 96 Moenave Formation __-_ 75, 76, 77, 96‘, 102, 109 Moffat County, Colo __________________ 73, 93 Monks Hollow, Utah ___________ 74, 93, 94, 113 Montana __________ 27, 28, 29, 30, 67, 68. 69, 78, 80, 81, 82, 84, 85, 87, 107, 108, 109, 111, 113, 114 Monte de Oro Formation ______________ 61 Monterrey, Mexico ____________________ 44 Montezuma County, Colo .............. 75 Moonshine Conglomerate _- 54, 57, 60, 107 Morgan Creek, Oreg __ ___. 65 Mormon Sandstone _______ 54, 57, 107 Morriaiceras mor'riai zone ______________ 22 Morrison Formation ______ 18, 67, 68, 69, 70—75, 77, 89, 87, 88, 90, 92, 93, 95, 96, 98, 99, 108, 113, 114 Mount Baker, Wash .................. 66 Mount Carmel, Mount Carmel Junction, Utah __________________ 76, 97, 98 Mount Jura, Calif ____________________ 57, 60 Muddy Creek, Wyo ____________________ 71 Murderers Creek Graywacke ___________ 55 Myophorella __________________________ 84 montamemis .................... 87, 113 Mysterious Creek Formation (Canada) _ 58 Mytilua _______________________________ 114 N Naknek Formation ____________________ 59 Navajo Indian Reservation, Ariz _____ 97 Navajo Sandstone ................. 53, 74—77, 95, 96, 97. 98, 99, 102, 109 Nebroditea ____________________________ 31 Necaxa, Puebla _______________________ 29 Nelchina, Alaska ______________________ 59 Neocomian Age ___ _ 51, 67,106 Neocoamoce’ras -__ ---. 63 Nephi, Utah __ _ 74, 94, 111 Nerinea. ______________________________ 57 Neritim ______________________________ 84 Nesson Formation ............ 67. 69, 82. 109 Neuquem'ceras __________________ 29, 38, 45, 50 neoaaeum _________________________ 22, 29 Nevada ___ 19, 20, 21,52, 53, 54, 97, 106, 108, 109 INDEX Page Nevadan orogeny ___________________ 102, 108 New Mexico _____________________ 17 Newark Group _____________ __ 4 Newcastle, Wyo ___ -- 71 Nicely Formation -_ ........... 55, 65 Nizina Mountain Formation ___________ 59 Nodicoeloceraa __________________ 20, 21, 22, 55 Nododelphinula _______________________ 84 Nooksack Formation __________________ 56, 66 Normannitea _-_ 22, 23, 37, 45, 55, 56, 57, 58, 80 crickmaui ________________________ 22, 23 undulatum ________________________ 22 Norphlet Formation _ 44, 46, 47, 48, 102, 104, 105 North Dakota ________________ 67, 69, 81, 109 North Ridge Agglomerate _____________ 54, 60 North Temperate Realm of Kaufiman __ 31 Nova Scotz‘a shelf __- ______ 4, 103 Nuevo Leon, Mexico ___________ 35, 36, 44, 48 Nugget Sandstone ______ 70, 72, 74, 83, 90, 109 Nutzotin Mountains, Alaska __________ 59 O Oakley, Utah _- Oaxaca, Mexico _____________ 23, 25, 45, 49, 51, 52, 102, 103, 104 Ochetoceras _______________________ 30 canaliculatum __________________ 24, 30, 45 (Fehlmannites) ___________________ 50 Octocythere ______________ _ - 4 Okanogan County, Wash ___ _- 66 Olcoatephanus ________________ 36 Old Rampart, Alaska __________________ l9 Olvido Formation (Mexico) ___ 44, 48, 102, 105 Opis (Trigonopis) ____________________ 84 Oppelia. ______________________________ 29 aspidoides zone ......... 22 (Lyroxuites) ______________ 23 Oregon ________ 17, 19, 20, 21, 22, 23, 24, 25, 26, 30, 36, 37, 38, 53, 55, 56, 61, 68. 106, 107 Orogenic activity ________________ 102, 106, 108 Orthoaphinctes ________________________ 24 Oatrea __________ -- 44, 87, 94, 113, 114 strigilewla. 95 Otapiria ______________________________ 51 tailleu'ri __________________________ 52 Otoites _______________________________ 23 sauzei zone _________ ' Otter Point Formation __ Oxfordian Stage, Alaska ________ 17, 30, 31. 67 ammonite and buchia succession in _ 90, 38 Atlantic Coast region _____________ 1103 California _______________________ 17, 30, 38, 53, 60, 61, 62, 106. 107 Canada ____________________ 17, 18, 30, 67 Colorado _ __ 95, 113, 114 Cuba __________________________ 30, 39, 42 Gulf of Mexico region ____________ 17, 30, 38, 47, 48, 102, 104, 105 Idaho _____________ 1'7, 30, 66, 90, 107, 113 Mexico ________ 30, 49, 50, 51, 52, 1'02, 103, 104, 105, 106 Montana nu. . . __ 17, 18, 30, 67. 82, 113 North Dakota ____________________ 67 Oregon _________ 17, 30, 38, 62, 66, 106, 107 South Dakota ___________________ 87, 113 Utah ________________________ 95, 113, 114 Washington ______________________ 107 western interior region ___________ 18, 30, 67, 102, 108, 113 Wyoming __________ 18, 87, 88, 90, 113, 114 Oxynoticems ___________________ 20, 45, 55, 65 oxunotum ________________________ 21 zone __________________________ 19, 20 Ozytoma wyomingemia _______________ 90 131 Page P Pacific Coast region, ammonite succes- sion in ___________________ 29, 87 characteristic fossils of __ - 55, 56, 58, 59 geologic history of ________________ 106 lithologic and stratigraphic features compared in ______________ 51 locality bibliographic references for _ 3 paleobz'ogeographic setting of ______ 17 unconformities in _________________ 102 Pacific Ocean Page, Ariz _________________________ 77, 98, 99 Page Sandstone _ 72, 74, 75, 77, 91, 95, 98, 99, 109 Paleobiogeography, setting of ........ 4 Palisade disturbance ________________ ‘__ 4, 102 Palo Blanco Formation (Mexico) _-__ 49, 50 Paltarpitea _______________ 20, 21, 55, 58, 59, 65 Panuco-Elbano area, Veracruz _________ 36 Papilliceraa stantoni __-- (Papilliceras) Sonninia - Parabigotitu ___________________ 23, 37, 55, 56 crasaicostatuu __________________ 22, 23, 59 Paracadoceras ________ , _______________ 29, 58 (Paracadocerac) , Cadoceras ___________ 23 tomu'ence, Cadoceraa _____ .- 23 Paracaloceras ___. ______ 20 Paracephalites -_ - 27, 28, 37, 81 glabreacens _______________________ 22 sawtoothemis ____________ 22, 69, 71, 73, 75 Parachondmceraa __ 37, 69, 71, 73, 75, 80, 81, 89 andrewsi _________________________ 22 Paracoroniceras _ _ - Parapallasiceras __-_ __ 33, 40 Parapecten acutiplicatas _ 57 praecm‘sor _______________________ 57 Parapeltoceraa ________________________ 50 (Parapeltoceraa) annulare, Peltaceras _ 50 Parareineckeia ________ 22, 26. 28, 29. 37, 38, 55 Parastreblitea muzupilenaia ____________ 32 Parastrenoceras _- -_ 37, 45 mixteca ___________________ __ 22, 23 Paraulacoaphinctes transitoriua ________ 26 Paris River, Utah ____________________ 98 Park Range, Colo ..................... 93 Parkimonia parkinaani zone ___________ 22 Parodontoceraa ____________ _ 24, 34, 35, 55 buttt __________ _ 24, 34, 35 calliatoides __ ______ 36 Paskenta, Calif ___________________ 63, 66, 107 Pavelofi Siltstone Member, Chinitna For- mation ................... 29 Pavlovia ______________________________ 25 pallasioidea zone _ - 24, 26, 31, 32 pavlom’ _____________ 27 rotunda zone _ ________ 24, 26, 31 Pavloviceras ________________ 24, 69, 71, 78, 75 (Pavlovicema), Quenstedtoceras ___- 30, 38, 82 Pectimztites ........................... 25 pectinatua zone ________________ 24, 26, 31 ( Viraatoephinctoidea) eleaam zone _ 30 Peltoceras _______ _. 29, 88, 45, 67 athleta zone _____________ 22, 47 (Metapeltoceraa) _________________ 22, 55 (Parapeltaceras) annulare ________ 50 Pefion Blanco Volcanics ______________ 60 Pentacrinua __________________________ 86 Peoa, Utah ___ ___- 72, 90 Perisphinctca __ _-.. 24, 35, 39 burckhardti _________ 32 cautionigrae zone _________________ 24 danubiensia ______________________ plicatilia zone _________ transitorius ____________ (Dichotomouphinctes) _ _ (Diacoaphinctea) .................. 30, 38 Peronoceras ___________________ 20, 21, 22, 58 Phn'codocerua _________________________ 20 132 JURASSIC PALEOBIOGEOGRAPHY OF Page Phylloceras ___________________________ 30, 32 bakeri ____________________________ 23, 29 Phylseogrammcceras _______________ 2'0, 22, 58 Phymatoceraa _______________ 20, 21, 22, 58, 59 Phyeodocerua _________________________ 31, 35 Picard Shale Member, Nesson Forma- tion ______________________ 69, 78 Pictom'a. baylei zone __________________ 24 Pimienta Formation (Mexico) 34, 35, 45, 49, 106 Pimienta Member, Jagua Formation (Cuba) __________________ 39 Pinar del Rio Province, Cuba _________ 34 Pine Butte Member, Sundance Forma- tion 71,73, 85, 86, 88, 92. 93, 95, 113 Pine Creek, Utah ____________________ 77, 98 Pintura, Utah ________________________ 99 Piper, Mont _____ 69 Piper Formation ______________________ 68, 69, 70, 78, 7.9, 81, 83, 84, 87, 88, 109 Pit River, Calif _______________________ 54, 61 Pittsburg Landing, Oreg _____________ 56, 66 Placer de Guadalupe,Chihuahua _ _ 32, 35, 45, 51 Platypleuroceras ______________________ 21 Pleuraceras _____________________ 20, 21, 58, 59 apinatum zone ____________________ 20 Pleuromya ________ - 91 Plicatoetylus _____________________ __ 53, 57 Pliensbachian Stage, Alaska ___________ 20 ammonite and buchias succession in 19 Arizona __________________________ 97 Atlantic Coast _ ________ 4 California ___- __________ 20, 57 Canada ________________ 18, 21, 65, 67, 108 Gulf of Mexico region _________ 102, 103 Mexico ___________ ,_ _____ 17. 20, 49, 99, 103 Nevada _______________________ 2'0, 53, 57 Oregon _________ 17, 20, 57, 64, 65, 102, 108 Pacific Coast region ______________ 102 97 Plomosas, Chihuahua _______________ 32, 45, 51 Poe Evaporite Member, Nesson For- mation ___________________ 67, 69 Point Barrow, Alaska _________________ 19, 22 Poker Chip Shale, Fernie Group (Canada) ________________ 68 Polyplectua ______________ __ 20, 22, 55 Porcupine Dome, Mont ___ __ 69 Porcupine River, Alaska ______________ l9 Pasidoniu _____________________________ 105 Potem Formation __________._______;__ 54, 6'1 Powder River Basin ___________________ 86 Poza Rica, Veracruz _ _- 49, 51 Praeatrigites _________________________ 22, 55 Preuss Sandstone _________________ 70, 72, 74, 88, 89, 90, 91, 92, 93, 94, 111, 113 Prionodoceras _________________________ 31 (Prionodocerac), Amoeboce'rua _________ 25, 59 spiniferum, Amoeboceras __________ 25 Procerites 29 Procerithium __________________________ 84 Productylioceras 1 ____________ 20, 55, 56, 58, 65 davoei ____________________________ 21 dtwoei zone ______________________ 20 P’rom'ce'ras ________ 24, 27, 32, 34, 35. 45, 55, 63 (Proacaphitea) , Taramelliceras _ _ _ _ _ 30 Prososphinctes _________________ _ _ - 30, 38 Protacanthodiacuc _________________ 24, 34, 36 Protancyloceraa ______________ 24, 33, .94, 36‘, 40 alamense _________________________ 36 anahuacenae ______________________ 36 barrancense _____________ _ 36 catalinense _______________ 36 hondense ___ __ 34, 36 ramireme _ _ ______________ 36 Protogrammoceras ____________ 20, 56, 65 Provo, Utah ________________________ 93, 113 Pryor Mountains, Mont ___ 78, 81, 82, 83, 84, 85 Paeudoamaltheus _____________________ 21 Page Pseudocadoceras _________ 23, 29, 38, 58, 60, 66 grewingki _____________________ 22, 55, 60 Pseudolioceras _______________ 20, 21, 22, 33, 55 compactile ________________________ 21, 22 muclintocki _ __ 23, 24 whitezwesi __ ________ 23 Paeudoliuoceraa -_ 24, 27, 32, 33, 34, 36, 40 bavaricum ________________________ 26 aubmsile _________________________ 32, 33 zitteli ___________________ 24, 26, 27,32, 35 Paeudotoites __________________________ 23, 37 Pseudovirgatitea scruposus ____________ 26 Psilocema ________________ 10, 19, 20, 21, 55, 59 canadense crugatas planorbis zone (Franziceras) ____________________ 19 Puale Bay, Alaska _ ______ 19 Puebla, Mexico ___- ___________ 34, 35, 51 Punta Alegre Formation (Cuba) ______ 42 Purbeck Beds (England) _____________ ,90 Q Queen Charlotte Islands, Canada ___ 21,58, 66 Quenstedtia ___________________________ 84 sublaevia _________________________ 87 Qucnstcdtoceras _______________________ 90 collieri _________________ 22, 69, 71, 73, 75 henrz‘ci _________________________ 23, 38, 58 lamberti zone __________________ 22, 47, 50 marine zone _____________ ___- 24,30 (Lamberticeras) collieri _ __ 29, 82 (Pavloviceras) _________________ 30, 38, 82 R Ramona Mesa, Utah, Ariz ___________ 77 Rancho Cerro Pozo Serna, Sonora _____ 31 Rasenia ________________________ 24, 25, 30, 45 cymodace zone ____________________ 24 mutabilis zone ____________________ 24 Recapture Shale Member, Morrison For- mation ___________________ 75 Red Canyon, Utah ____________________ 94 Red Creek, Wyo ________________ 70, 84, 85, 86 Red Deer Member, Fernie Group (Canada) _________________ 68 Red Dome, Mont _____________________ 78,84 Red Gulch, Wyo ______________________ 84 Red Mountain, Idaho ___ 70 Redding, Calif _________ _ 61 Redwater Member, Stump Sandstone __ 72, 73, 89, 90, 9.2 Redwater Shale Member, Sundance For- mation __________ 70, 71, 73, 82, 85, 86, 87, 88, 89, 90, 92, 93, 94, 95 Reineckeia _______________ 22, 27, 29, 38, 45, 50 (Kellawayaites) 50 (Reineckeitea) 50 Reineckeitea __________________________ 22 (Reineckeites), Reineckeia _____________ 50 Rsynesoceras ____________________ 20, 55, 57,65 Rich Member, Twin Creek Limestone - 70, 72, 74, 80, 81, 84, 85, 88, 89, 91, 92, 95, 98 Richardson Mountains, Canada __ 19, 21, 23, 29 Richfield, Utah _______________________ 74 Riddle, Oreg __________________________ 62 Riddle Formation ___- 55, 62, 63, 108 Rierdon Formation ________ 68, 69, 81, 87, 89 Rierdon Gulch, Mont - 68 Ring Butte, Oreg ____________________ 65 Ringsteadia ___________________________ 25 pseudocordata zone ________________ 24 Rio Blanco County, Colo _______________ 93 Riverside, Wash ______________________ 66 THE CONTERMINOUS UNITED STATES Page Robertson Formation _________________ 55, 57 Rock Creek Member, Fernie Group (Canada) ________________ 68 Rocky Mountains, British Columbia, Alberta _____ 20, 21, 22, 25, 68, 1‘08 Rogue Formation ______________ 55, 61, 62, 107 Romana Mesa, Ariz __________________ 99 Root Glacier Formation _______________ 59 Rosario Formation (Mexico) __________ 49 Roseburg, Oreg ________________ 63 Roseray Formation (Canada) _ . 81 Routt County, Colo ____________ _ 73,93 Russian platform _____________________ 27 S Sabinas basin, Mexico ________________ 48,49 Sadlerochit River, Alaska _____________ 22 Sailor Canyon, Calif _______ 106 Sailer Canyon Formation 57 Salina, Utah ______________________ 74, 94, 113 Salina Creek Canyon, Utah _________ 94,113 Salina Formation (Mexico) __________ 50 Salinites ______________________________ 35 Salt ___________________ 4, 17, 46, 47, 49, 50, 67, 99, 103, 104, 105, 106, 109, 111 Salt domes ____________________________ 42, 47 Salt Lake County, Utah _______________ 72 Salt Spring Slate _____________________ 60 Salt Valley anticline __________________ 96 Salt Wash Sandstone Member, Morrison Formation ________________ 75, 77 San Andrés Member, Taman Formation (Mexico) ________________ 106 San Cayetano Formation (Cuba) _____ 17,39, 44, 1'02, 103, 104 San Luis Potosi, Mexico ________ 32, 33, 45,49 San Miguel County, Colo _____________ 75 San Pedro del Gallo, Durango ___ 30, 31,34, 48 San Rafael River, Utah ___________ 75, 94,96 San Rafael Swell, Utah ______________ 91,93, 94, 95, 96, 109, 111, 113 San Vicente Member, Guasasa Forma- tion (Cuba) __- _ 40 Sand Creek, Utah __________ 91 Sand Valley, Ariz ___________________ 77 Sanpete County, Utah ________________ 74 Santa Ana Mountains, Calif _________ 29, 52, 53, 54, 61, 106 Santa Monica Mountains, Calif ___- 17, 53, 54 Santa Monica Slate ___________ __ 54, 60, 61 Santiago Formation (Mexico) ________ 45, 48, 49, 50, 51, 104 Sarasinella ____________________________ 36 Saskatchewan ______ 69, 78, 80, 81, 82, 109, 111 Sawtooth Formation _______________ 24, 68, 80 Sawtooth Range, Mont _ _________ 82, 113 Scarbu'rgice'raa ______________ 24, 69, 71, 73, 75 (Scarburgiceras), Cardiooema _________ 25,30 martini, Cardioceras ______________ 24, 25, 30, 55, 56, 66 Schlitea apinoaua ______________________ 22 Schlothei’mia _______________________ 19, 20, 55 anyulata zone ___- __________ 20 Schuler Formation _-_ _ 4, 44, 47, 48, 105 Schulerideu ___________________ 4 Seaways, Jurassic ___________ 17, 106, 107, 111 Seldovia, Alaska ______________________ 19 Semiformicems _______________________ 32 Seneca, Oreg __________________________ 55 Sevier County, Utah ___________ _ 74 Shaunavon Formation (Canada) __ __ 69,80 Sheep Mountain, Wyo ________________ 85, 87 Sheridan arch, Wyoming, Montana ___ 18, 111 Shoshone River, Wyo _________________ 86 Shurtz Creek, Utah ___________________ 99 Sierra Blanca, Tex ___________________ 35 Sierra Cruillas, Tamaulipas ___________ 34, 85 Page Sierra de Catorce, San Luis Potosi __ 32, 33, 45 Sierra de Santa Rosa, Sonora __________ 52 Sierra del Rosario, Cuba _____ __ 39,44 Sierra do 10s Organos, Cuba _ .- 39, 44 Sierra Jimulco, Coahuila ______________ 36 Sierra Nevada, Calif __________ 17, 29, 52, 53, 54, 57, 60, 61, 62, 106, 107 Sierra Ramirez, Durango ______________ 36 Sigaloceraa cafloviense _-_- __ 23 callovieme zone __ _ 22, 50 Silberlingia ___________________________ 61 Silvies Member, Snowshoe Formation _- 55 Simoceraa ...................... 24, 32, 34, 35 ( Virgatoaimoceraa) _______________ 35 Sinawaya Member, Temple Cap Sand- stone _____________________ 97 Sinemurian Stage, Alaska 19 ammonites and buchias sucession in 19 Arizona ___________________________ 97 California ____________________ 57, 61, 106 Canada ____________________ 18, 19, 67, 108 Mexico ......... 17, 19, 49, 52, 99, 1'02, 103 Nevada ____ ' ______________ 19, 53, 106 New Jersey __ ______________ 102 Oregon ______________ 17, 19, 63, 64, 65, 106 Pacific Coast region ______________ 52 Utah _____________________________ 97 Slick Rock, Colo ______________________ 75,96 Slick Rock Member, Entrada Sandstone 75,96 Sliderock Member, Twin Creek Lime stone --__ 24, 70, ‘72. 74, 80, 84, 85, 87, 88, 89, 91, 95, 99, 108, 109 Smackover Formation ________________ 30, 44, 46, 47, 48, 50, 105 Smith River, Mont ____________________ 68 Smithers, British Columbia ____________ 58 Smithers Formation (Canada) 58 Snake River, 0reg., Idaho ____________ 17, 56, 64, 66, 90, 106, 107 Snowshoe Formation _______ 22, 55, 57, 64, 107 Sohlitea ______________ 37, 69, 71, 73, 75, 80, 81 spinosus __________________________ 95 Sonninia _______________________ 23, 57, 58, 59 dominana ____________ 53 lowerbyi zone __ __- 22, 57 (Euhoploceraa) _ _ _ 22 (Papillice'raa) _____________________ 57 Sonora, Mexico ______________ 17, 31, 38,51, 52 South Dakota ...... 71, 82, 86, 90, 109, 111, 113 South Fork Mountain Schist ___________ 62 Spearfish, S. Dak .......... __ 86 Spearfish Formation -- __ 83 Sphaeroceras ____________________ 23, 37 Spiroceraa _______________ 22, 23, 24, 37, 55, 56, 69, 71, 73, 75, 80, 81 bifurcatum _______________________ 22, 60 Spiticeras ____________________________ 24, 39 Springdale Sandstone Member, Moenave Formation __ -- 97 Stanley Mountain, Calif _ __ 63 State Bridge, Colo ____________________ 93 Stemmatoceras ____ 22, 24, 69, 71, 73, 75, 80, 81 arcicoatatum ______________________ 22 Stemcadoceraa ________________________ 29 (Stenocadoceraa), Cadaceraa _ ___ 23, 29 canadenae, Cadaceraa __- __ 23 stenolobaide, Cadocerua _ -__ 23, 59 striatum, Cadaceraa ______________ 23, 58 Stephanoceraa ____________ 22, 23, 24, 45, 57. 80 humphriesianum zone ____________ 22, 23, 24, 57, 80, 109 kirnchneri ________________________ 23, 59 Stockade Beaver Shale Member, Sun- dance Formation .70, 71, 85, 88, 111 Strenoceras subfurcatum zone _________ 22 Strigoceratidae ________________________ 22 Stump Sandstone ______________ 70, 72, 73, 82, 88, 89, 92, 95, 108, 113 INDEX Page Suarites bituberculatum _____ 36 Subcrrupedites plicomphalus _ 25 Subdichotomocems ______________ 27, 31, 32, 38 m‘kitini ___________________________ 32 Subgroseouvia _________________________ 50 Sublette County, Wyo ___________________ 70 Sublithacoceras penicillatum __________ 26 Subplam‘tes ____________ 24, 25, 27, 32, 33, 34,45 dunubiensis _ 32 Iclimovi 27 reiae ______________________________ 33 (Ilowaz'akya) pseudowcthica ______ 27 sokolom' ______________________ 27 Subateucraceras _______ 24, 27, 34, 85, 45, 52, 55 koeneni ___________________________ 26 Subs:eueroceras-Proniceras ammonite as- semblage __________________ .95 (Sub-vertebricema) canadense, Cardio- ceras _____________________ 25 Summerville Formation _______________ 74, 75, 93, 94, 95, 96‘, 98, 113 Summit County, Utah ____________ 72 Sun River, Mont _______ ___ 68,80 Sundance Formation .y ____________ 70, 71, 73, 81, 82, 83, 84, 85, 88. 93, 111, 113 Sunrise Formation ___________________ 53, 54 Suplee, Oreg ______ 55, 64, 65, 66, 102, 106, 107 Suplee Formation ________________ 55, 64, 65 Sutneria platynota ______________ __ 24, 30 Sweet Grass Hills, Mont ____ ________ 80, 81 Sweetgrass arch (Montana) _.._ 80, 81, 82, 113 Swift Formation _____________________ 30, 68, 69, 81, 82, 90, 108, 113 Swift Reservoir, Mont ________________ 24, 68 Sykes Mountain, Wyo _______ 84 Symon, Durango __________________ 32 33,36 T Takwahoni Formation (Canada) _____ 59 Talkeetna Formation _________________ 59 Talkeetna Mountains, Alaska _________ 22, 59 Taman Formation (Mexico) _____ 45,49, 106 Tamaulipas, Mexico -_- 17, 33, 34, 35, 44, 48, 49 Tamn, San Luis Potosi _______________ 45 Tampico, Tamaulipas __ 17, 33, 35, 49, 103. 105 Tampico embayment (Mexico) ________ 49, 51 Tampico Shale Member, Piper Forma- tion _ _ 68, 69, 78, 79, 80 Tancrcdia _____________________ 95 Tantima, Veracruz ____________________ 36 Tantoyuca, Veracruz __________________ 36 Taramelliceraa (Proacaphites) _________ 30 Taseko Lake, British Columbia ________ 58 Taylorsville, Calif ___ 53, 54, 57, 60, 61, 106, 107 Telephone Creek, Wyo .......... 90 Telkwa Formation (Canada) __________ 58 Teloceraa _________ 22, 23, 37, 55, 57, 58, 59, 61 itinaae ............................ 22, 23 Temple Cap Sandstone _____ 76, 97, 98, 99, 1‘09 Tenas Creek, British Columbia ________ 58 Tepexic Limestone (Mexico) _________ 45, 50 Tethyan Realm ..... _-_ 29, 30, 37, 38, 67 Teton County, Idaho _ __________ 70 Teton County, Wyo ________________ 83, 85, 88 Teton Range, Wyo ____________________ 90 Texas ________ 31, 45, 46, 47, 48, 49, 51, 103, 105 Thistle, Utah _________________________ 109 Thompson Limestone __- __________ 54, 57 Thousands Pockets Tongue, Page Sand- stone __________________ ‘77, 98, 99 Thurmanniceras _______________________ 36 Tincup Creek, Idaho ___________________ 90 Titanites ______________________________ 18 giganteus zone ____________________ 24, 26 occidentalia 25 133 Page Tithonian Stage, Alaska _______________ 36,38 ammonite and buchia succession in _ 31 arctic region ______________________ 38 Atlantic Coast region __ 103 California _____ 17, 36, 38, 53, 57, 61, 62, 63, 67, 108 Canada _____________________ 18, 36, 38, 67 Colorado __________________________ 95 Cuba ____________________ 33, .94, 35, 39. 4'0 definition and correlations of ______ 81 Gulf of Mexico region _________ 17, 82, 38 Mexico ____________ 82, 34, 35, 36, 106, 108 Montana __ 67 North Dakota _____________________ 67 Oregon __________ 17, 36, 38, 62, 63, 67, 108 Pacific Coast region _______________ 108 Russia ____________________________ 34 subdivisions of ____________________ 26, 32 Texas _________ __ 35, 36 Utah __________________________ 95 Washington _______________________ 108 western interior region _________ 102, 114 Tmetoceras ______________ 22, 23, 56, 57, 59, 65 scissum ________________ 22, 23, 24, 55, 58 Toarcian Stage, Alaska ______________ 22 ammonite and buchias succession in. 21 Arizona __ California Canada _________________ 18, 22, 65, 67, 108 Gulf of Mexico region ____________ 102 Mexico ____________________ 39, 52, 99. 104 Nevada ___________________________ 21, 53 Oregon Utah ____________________ Tonnie Siltstone Member, Chimtna For- mation ___________________ 65 Torcer Formation _____________________ 35, 51 Torquatisphinctes _______ '_ ______ 24, 32, 33, 40 Tragophyllacc'ras ______________________ 20 ibex zone 20 Trail Formation ______________________ 54, 60 Transgressions, marine. See Marine transgressions. Trinity County, Calif _________________ 62 Tropidocems _________________________ 20, 58 Trowbridge Shale ___________ 55, 64, 65, 66, 107 Tulites subcontractua zone ____________ 22 Tulsequah, British Columbia _____ 59 Tuxedni Group ________________________ 59 Twelvemile Canyon Member, Arapien Shale ____________________ 74, 94 Twin Creek Limestone __ 24, 70, 72, 74, 80, 81, 82, 83, 84, 85, 87, 88, 89, 91, 94, 95, 96, 99, 108, 109, 111 Twin Creek trough (Wyoming, Idaho, Utah) ___________________ 18, 111 Twin Peaks, Oreg _ --._ 65 Twist, Wash _______ __ 66 Twist Formation ______________________ 66' Twist Gulch Member, Arapien Shale" 74, 94 Tylostama ______1 _____________________ 84 U Uinta Mountains, Utah -_ 90, 91, 92, 93, 94, 111 Uintah County, Utah ______ ,- __________ 72,73 Uncompahgre uplift (Colorado) _______ 18 Unconformities, Jurassic ____________ 99, 107 United States, southern __-_ 17, 30, 31, 103, 105 Uptom'a __________________ 20, 21, 45, 55, 58, 59 jameaoni 21 zone 20 Uranium Peak, Colo ___________________ 93 Utah _______ 72, 73, 74, 75, 76, 87, 89, 90, 91, 93. .96, 109, 111, 113, 114 Utah County, Utah ____________________ 74 Ute Mountains, Colo _- 96 Utica, Mont _________ -_ 68 134 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES Page V Vancouver Island, British Columbia ___ 58. 67 Vanguard Group (Canada) ___________ 69 Vaugonia _____________________________ 44 canradi ______________________ 87, 99, 113 quadrangularia ____________________ 90 Veracruz, Mexico - 26, 29. 3‘0, 36, 49, 51, 103, 106 Vermiceraa ___________________________ 45 Vermiaphincteo _ _-_ 28, 37 Vernal. Utah --- -- - ___ 91 Victoria, Tamaulipas _-_ 83, 44, 48, 49, 99, 105 Viiiales Limestone (Cuba) ____________ 39 Vinalesphinctes _______________________ 39 Viraatites ____________________________ 32 'uimatus _____________ ' _____________ 2 7 Viraatosimoceras _____________ 24 ( Virgatosimoceraa) , Simocems 35 Viruatosphinctea _.- 24, 27, 31, 32, 33, 34, 36, 45 aguilari __________________________ 32, 45 chihuahuensis _____________________ 33 demiplicatus ______________________ 33 memdozanus _______________________ 26 mexicanua ________________________ aanchezi __________________________ Viruatoaphinctoides elegans zone _ scitulus zone ________________ wheadeuemia zone _______________ 24, 26 ( Virgatosphinctoides) elegam, Pectina- tiles, zone ________________ 30 Volcanism, Jurassic __ 52, 53, 64, 106, 107. 108 Volgian Stage _______________________ 27, 31 W Waagem'a _____________________________ 32 Waehneroceraa __/ ____________ 19, 20, 21, 55. 59 Wagnerz'ceras ______________ 17, 26, 45, 50, 103 Wallowa Mountains, Oreg _____________ 56, 65 Warm Springs Member, Snowshoe For- mation ___________________ 55, 57 Warrenocems ________ __ 22, 28. 37, 82, 85, 88 codyenae ________________ 22. 69, 71, 73, 75 Wasatch Mountains, Utah __________ 91, 92, 94 Washington ___________ 18, 52, 56. 66, 107, 108 Page Washington County, Utah _____________ 76 Watrous Formation (Canada) _________ 69 Watton Canyon Member. Twin Creek Lime- stone _ 70, 72, 74, 87, 88, 91, 96, 111 Webb County, Tex ____________________ 35 Weberg Member, Snowshoe Formation - 55 Wedge, The, Utah ____________________ 95 Wells Creek Volcanics ________________ 56,66 Werner Formation _____________ 44, 46, 47, 99 \ Western interior region (United States), ammonite succession and correlation in ___ 22, 24, 27. 37, 38 Bajocian Stage in ________________ 24 Callovian Stage in ________________ 29, 88 characteristic fossils of ___. 69, 71, 78, 75 geologic history of __________ 106, 107, 108 lithologic and stratigraphic features compared in .............. 67 locality bibliographic references for 3 Oxfordian Stage in _______________ 30 paleobiogeographic setting of _____ 18 unconformitia in _________________ 102 Westgate, Nev _______________________ 21, 1‘06 Westgate Formation -- Weston County, Wyo __________________ Westwater Canyon Sandstone Member, Morrison Formation ______ 75 Weyla ________________________________ 56 claim _____________________________ 57, 61 White Throne Member, Temple Cap Sandstone _________________ 97 Whitehorse, Yukon Territory __________ 59 Whiterocks River canyon, Utah ___- 72, 91, 92 Whitmore Point Sandstone Member, Moenave Formation ______ 96, 97 Wichmanniccras ______________________ 36 Wide Bay, Alaska _____________________ 19 Williston basin (Montana, North Dakota) _____ 18, 67, 80, 81, 82, 84, 109, 111, 113 Willow Creek,‘ Idaho __________________ 70 Wind River Basin, Wyo __ 18, 78, 82, 83, 84, 85, 86, 87, 93, 111 Wind River Mountains, Wyo _______ 70, 86, 88 Page Windhausenicems interspinosum _______ 26 Windy Hill Sandstone Member, Sundance Formation 71, 73, 85, 87, 9o, 92. 113 Wingate Sandstone _____________ 74, 75, 77, 97 Winsor Member, Carmel Formation _________ 76, 77, 97, 111 Winthrop, Wash ______ 66 Witchellia _____________________________ 56 (Latiwitchellia) ___________________ 23 Wolverine Canyon. Idaho ______________ 70 Wolverine Canyon Limestone Member, Preuss Sandstone _________ B9, 92 Woodrul’f, Utah ______________ 90 Wrangell Mountains, Alaska ___- 19, 28, 59, 67 Wyoming ___- 70, 71, 78, 82, 8.9, 90. 92, 109, 111, 113, 114 Wyoming Range, Wyo ______-_______;_- 90 X Xenocephalites ___- 22, 28, 29, 38, 45, 50, 55, 82 vicarius _________________ 22. 55, 56, 65, 66 Xochapulco, Puebla ___________________ 30 Y ‘ Yakoun Formation (Canada) _________ 58 Yellowstone National Park, Wyo ___. 8'0. 88, 89 Yukon Territory _____________ 21, 23, 25, 29, 59 Z Zacatecas, Mexico ..................... 32, 33 Zaraialcites albam‘ zone ____________ 24, 26. 34 zarajskensis ______________________ 27 Zemiatephanus ____________________ 22, 23, 37 richardaoni _______________________ 23 Zigzaaiceras _ _ _ _ ‘ _ _ 45 floresi ___- _- 22, 25 zigzag zone ___________ __ 22 Zion National Park, Utah _____________ 97, 98 Zuloaga Limestone (Mexico) __ 44, 45, 48, 49, 50. 52 Y} U15. 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