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 STATE OF ILLINOIS 
 
 
 WILLIAM G. STRATTON, Governor 
 
 
 DEPARTMENT OF REGISTRATION AND EDUCATION 
 
 
 VERA M. BINKS, Director 
 
 
 Geochemistry of 
 
 
 Carbonate Sediments 
 
 
 and Sedimentary 
 
 
 Carbonate Rocks 
 
 
 Part II 
 
 
 Sedimentary Carbonate Rocks 
 
 
 Donald L Graf 
 
 
 DIVISION OF THE 
 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 
 JOHN C. FRYE, Chief URBANA 
 
 
 CIRCULAR 298 1960 
 
 
 ILLINOIS Gl 
 
 
 SUtfVhY LJBKakY 
 
 
 AUG 22 ^ Q 
 
ILLINOIS STATEGEOLOGICAl SURVEY 
 
 3 3051 
 
 00004 1206 
 
GEOCHEMISTRY OF CARBONATE SEDIMENTS 
 AND SEDIMENTARY CARBONATE ROCKS 
 
 Part II — Sedimentary Carbonate Rocks 
 
FOREWORD 
 
 Detailed knowledge of the chemical and mineralogical varia- 
 tions that exist in the carbonate rocks limestone and dolomite and of 
 the processes responsible for this diversity is fundamental to the Il- 
 linois State Geological Survey's program of furthering the practical 
 utilization of these natural resources of the state. Chemical com- 
 position is particularly important when the rocks are used as agricul- 
 tural limestone and fluxing stone or in the manufacture of dolomite 
 refractories, lime, calcium carbide, sodium carbonate, glass, and 
 other products . 
 
 The invitation extended to Dr. Graf by the United States Geo- 
 logical Survey to prepare the chapter on sedimentary carbonates for 
 their revision of F. W. Clarke's "Data of Geochemistry" has afford- 
 ed a valuable opportunity for the state and federal geological surveys 
 to cooperate in a basic review of selected topics in carbonate geo- 
 chemistry. The resultant material is presented in five Illinois State 
 Geological Survey Circulars and subsequently will serve as the basis 
 for a condensed treatment in the revised "Data of Geochemistry. " 
 
 Part I, published as Circular 297, includes an introduction 
 and sections on carbonate mineralogy and carbonate sediments. 
 
 Part II, Circular 298, includes the section on sedimentary 
 carbonate rocks. 
 
 Part III will deal with the distribution of minor elements. 
 
 Part IV will discuss isotopic composition, present chemical 
 analyses, and also will contain the bibliography for the first four cir- 
 culars. 
 
 Part V, concerned with aqueous carbonate systems, will be 
 published at a later date. 
 
 John C. Frye, Chief 
 
Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of Illinois Urbana-Champaign 
 
 http://archive.org/details/geochemistryofca298graf 
 
GEOCHEMISTRY OF CARBONATE SEDIMENTS 
 AND SEDIMENTARY CARBONATE ROCKS 
 
 Part II -Sedimentary Carbonate Rocks 
 
 Donald L. Graf 
 
 ABSTRACT 
 
 The distribution of major and minor elements in sedimentary 
 carbonate rocks and the mechanisms responsible for this distribution 
 are considered on the basis of published information contained in geo- 
 logic studies, and in studies of present-day environments of carbon- 
 ate deposition, isotopic composition of carbonates, and experimental 
 aqueous and nonaqueous carbonate systems. There are five parts in 
 the series and an extensive bibliography for the first four parts ap- 
 pears in Part IV. Part V carries a separate bibliography. 
 
 DEPOSITS FORMED BY CARBONATE ENRICHMENT 
 OF PRE-EXISTING MATERIALS 
 
 Caliche 
 
 More or less indurated, single or multiple carbonate-rich zones as much 
 as 150 feet thick lie just under present-day soils in much of the semiarid western 
 United States. On the northeastern Llano Estacado of Texas, this caliche consists 
 of roughly equal parts by volume of CaC03 and Si02 in the form of calcite and opal 
 or chalcedony (Brown, 1956). On the Southern High Plains of Texas, Sidwell (1943) 
 reported as much as 90 percent CaC03, mixed with silica and clays. Rounded and 
 frosted sand grains, volcanic ash, and glass fragments suggested to Sidwell that 
 an appreciable part of the original material in these deposits is of eolian origin. 
 Nine samples of lithified caliche caprock from southeastern New Mexico (Bretz and 
 Horberg, 1949b) contained from to 8.7 percent insoluble residue and "only a small 
 percentage of magnesium oxide. " Analysis 33 (Part IV) is of caliche from Mexico. 
 
 The caliche results from leaching of CaC03 and Si02 by downward percola- 
 tion of rainwater and their subsequent deposition when the water evaporates long 
 before it reaches the deeply buried water table (Brown, 1956). Sidwell (1943) noted 
 that the deposits in his area seem to be especially carbonate-rich below surface 
 drainage or shallow-water depressions that fill during rains. The distribution of 
 CaC03-enriched zones in some of the thicker caliche sections is a function of both 
 rate of leaching and rate of aggradation of eolian material on the surface, which 
 together determined the amount of time available for leaching a given vertical por- 
 tion of the deposit and the consequent degree of lithification of the CaC03~ and 
 Si02~enriched zone just below. 
 
 The operation of the process of calichification has been followed by Bretz 
 and Horberg (1949b) and by Frankel (1957). Frankel found that loess from Nebraska 
 had a variable content of snail shells. The relative rates of leaching and loess 
 deposition at a given point in the section may be inferred by noting the extent to 
 
 [5] 
 
6 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 which the shells are etched and the size and number of lime concretions formed by 
 precipitation of CaCOg leached out higher in the section. Bretz and Horberg de- 
 scribed a locality in southeastern New Mexico where downward-moving waters had 
 by dissolution formed cup-like depressions in limestone pebbles in the upper part 
 of a limestone conglomerate bed and deposited laminated CaCO^ on the undersides 
 of the pebbles. Pebbles in the lower part of the bed were unaffected. 
 
 The pisolitic, Tertiary cappirig-caliche of the Great Plains is apparently sim- 
 ilar in origin to the older caliche described by Bretz and Horberg (Swineford et al., 
 1958). Superficial textural similarity to algal pisolites had earlier led to other 
 explanations . 
 
 Loess in the Middle West often shows a weak development of caliche in the 
 subsoil. In this relatively humid area with a well developed organic cover, it ap- 
 pears likely that the precipitating mechanism is not evaporation but a partial loss 
 of the large amount of CO2 picked up in passing through humus-rich soil. 
 
 Some underclays in the Pennsylvanian cyclothems of Illinois contain, in 
 their lower parts, concentrations of limestone nodules. Obviously concretionary 
 in origin, these nodules have been attributed by some to superficial downward 
 leaching of calcareous clay (see Grim and Allen, 1938; Wanless, 1957; Schultz, 
 1958). They are not to be confused with nodules and solid limestone benches that 
 may occur in the same stratigraphic position but which contain fresh and brackish 
 water fossils, and sometimes even marine fossils. 
 
 Surface Concentration 
 
 The carbonate concentrations described above are attributable to descending 
 solutions. However, there are cases of carbonate cementation essentially at the 
 surfaces of carbonate sediments and rocks, analogous to the surficial case-harden- 
 ing of some carbonate rocks by silica. 
 
 Dapples (1941) believed that extensive cementation of Near East surficial 
 desert sands by CaCOo results from evaporation of ground water charged with cal- 
 cium carbonate from numerous local limestones and then carried to the surface by 
 capillarity. Natural walls of dense limestone occur on Okinawa at places where 
 there are nearly vertical exposures. On flat areas, organic acids from vegetation 
 dissolve underlying limestone, but secondary cementation from the surface inward 
 occurs at the steep exposures (Flint, 1949). 
 
 A surface limestone of Recent age from Natal, South Africa, the analysis of 
 which is included in Hall's (1938) compilation of analyses, is probably typical of 
 so-called calcretes found in many arid regions. The rock contained 0.63 percent 
 soluble silica, 1.14 percent alumina, 0.73 percent total iron as Fe20~, 74.84 per- 
 cent CaCOg, 4.26 percent MgCOg and 16.56 percent insoluble material. Calcareous 
 crusts such as those in the eastern and southeastern coastal area of Spain require 
 for their formation a climate with periods of precipitation, the amount not being crit- 
 ical, followed by relatively longer, dry, hot periods during which the water can evap- 
 orate (Rutte, 1958). A number of attempts have been made to correlate crust forma- 
 tion with the warmer interglacial periods of the Pleistocene. 
 
 Crusts containing CaCOg and other materials have formed after periods of 
 heavy rainfall in the semiarid Nebraska Sand Hills, when the water table has risen 
 close to the surface (J. C. Frye, personal communication). 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 7 
 
 Redistributed and Enriched CaCOg in Siliceous Rocks 
 
 Post-depositional activity of ground water may markedly alter the CaC03/ 
 SiOo ratio of sedimentary rocks. It is evident in many places where the Dover Lime- 
 stone of Pennsylvanian age in Lyon County, Kansas, is particularly high in silica 
 (as sand) that it overlies massive beds of sandstone in the Langdon Shale, and that 
 large sand-calcite crystals in the shale have been redeposited after ground-water 
 leaching from the Dover Limestone (O'Connor, 1953). Sand-calcite crystals from 
 Fontainebleau, France, contain as much as 50 percent calcite cement (Clarke, 
 1924). Calcite cement in calcareous sandstones of late Cretaceous age in the 
 eastern Carpathians is preserved where the formation is contained by shales, but 
 elsewhere the cement has been dissolved and reconcentrated in masses ten to twelve 
 feet in diameter (Sujkowski, 1958). 
 
 Petrographic studies show that partial to complete calcite and dolomite re- 
 placement of detrital quartz and feldspar grains is not uncommon (Walker, 1957, 
 1960; Carozzi, 1960, p. 38-39; Alimen, 1944; Alimen and Deicha, 1958). The 
 phenomenon has been observed even in Recent age calcarenite beachrock. Swine- 
 ford et al. (1958) similarly explained the development of the late Tertiary capping- 
 caliche of the Great Plains from calcareous feldspathic quartz sands and silts. The 
 caliche contains only a few percent of acid-insoluble material. They believed that 
 silica has been replaced by CaCOo and then redeposited to form the opal that occurs 
 lower in the section. 
 
 Cayeaux (1935) mentioned a Pliocene age diatomite from Sendai, Japan, that 
 has been completely calcified, with microstructures preserved. Radiolaria in the 
 limestones of Barbados are preserved in some places and calcified remains are left 
 in others. Lowenstam (1948) described an atypical case for the Racine Formation 
 of Silurian age near Chicago in which beds consisting largely of remains of the 
 siliceous sponge Astraeosponiia meniscus Roemer have been replaced by carbonate. 
 
 CAVE DEPOSITS 
 
 No detailed chemical analyses of stalactites and other CaCOo-rich cave 
 deposits were found in the literature. The mechanisms and rates of solution and 
 precipitation of CaCO„ in such environments will be discussed in Part V. 
 
 Collophane has been described by Proudfoot (1956) as a component of sta- 
 lagmites and as a cement in a cave stratum of Tornewton Cave, Devon, England. 
 It was formed under normal weathering conditions by percolating solutions that had 
 access to bat and hyena dung. Stalactites from 14 different cave deposits contain- 
 ing an average of 38.64 percent Ca (range, 25.24 to 42.42 percent) had an average 
 of 4.88 percent P (range, 0.674 to 10.70 percent) (Neuberg and Grauer, 1957). An 
 extensive discussion of cave guanos is given by Hutchinson (1950). 
 
 Gypsum excrescences of inorganic origin are not uncommonly found along 
 with the calcareous deposits in caves (see Pohl and Born, 1936; McGill, 1933; 
 Davies, 1949), and in two instances the growth rate during historical time, about 
 2 mm/100 years, is known from the thickness of overgrowth on dates scratched in 
 cave walls. The sulfate at Crystal Cave, Kentucky, is believed to have been de- 
 rived from abundant marcasite in a zone in the lower part of the Golconda Formation 
 of Mississippian age that nearly everywhere caps the cavernous ridges in Kentucky. 
 Merrill (1894) noted that gypsum incrustations were found in the old, dry chambers 
 of Wyandotte and Mammoth Caves. 
 
8 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 SPRING DEPOSITS 
 
 Dense, laminated travertine and the more spongy rock known as calcareous 
 tufa are deposited from both cold and hot spring waters that lose CO ? upon coming 
 in contact with the air (analyses 15, 34-36, Part IV). The ferrous and manganous 
 bicarbonates in solution in many of these waters are oxidized and precipitated as 
 the accessory oxides commonly found in spring deposits. 
 
 Dickey (1923) found only from 0.5 to 2 percent MgCO~ in the material from 
 spring-deposited terraces along the sides of valleys in Pennsylvania. Stout (1940) 
 noted that travertine deposited to a depth of as much as 4 feet in the pond main- 
 tained by overflow from the Castalia spring in Ohio reaches a purity of 99.4 per- 
 cent in places. 
 
 ALGAL LIMESTONES 
 
 The areally extensive Curley Limestone in central Utah is a fine-grained 
 laminated bed with wave to domelike structures superimposed on the laminae, and 
 contains.at some places, branching threads and leaf-like forms that Proctor and 
 Clark (1956) believed to be algal in origin (analysis 40, Part IV). Wayland and 
 Ham (1955) described a fine-grained limestone from the Baum Member of the Paluxy 
 Formation of early Cretaceous age in Oklahoma that contains ostracodes, charo- 
 phyte oogonia, and abundant remains of blue-green algae, and is believed to be a 
 brackish water facies deposited in a protected bay (analysis 42, Part IV). 
 
 Eardley (1932) described a limestone bed as much as 300 feet thick with 
 pisolitic texture and a freshwater fauna {Goniobasis simpsoni, G. tenera ) that occurs 
 interbedded in very coarse, poorly sorted alluvial fan deposits in the southern 
 Wasatch Mountains of Utah. The matrix of the rock contains less than 0.03 per- 
 cent insoluble material, mainly small well rounded quartz grains, but the limestone 
 as a whole grades into conglomerate with increase in the number of quartzite and 
 sandstone pebbles that form pisolite centers. The limestone is believed to be a 
 lake deposit, and spongy structures within the pisolites, together with recurrent 
 thin, dark bands therein, suggest algal origin. 
 
 Rezak (1957) attributed the stromatolites of the Belt Series in Montana to 
 Cyanophyta and, possibly, unicellular Chlorophyta. Rutte (195 3) described con- 
 cretions, rhythmic incrustations, reefs, and detrital material, all attributable to 
 blue-green algae, in the lacustrine limestones of Miocene age in the Engelwies 
 region, Baden, Germany. 
 
 STREAM DEPOSITS 
 
 Conglomerates made up of stream-transported carbonate rock particles, 
 although a relatively uncommon rock type, are known from a number of localities. 
 Erosional remnants remain of a once continuous, indurated limestone conglomerate 
 in the Ogallala Formation of New Mexico, a former river gravel supplied largely 
 from the western uplands (Bretz and Horberg, 1949b). Ham (1954) described a 
 limestone conglomerate from the late Pennsylvanian of Oklahoma, and Wayland 
 (1954) one from the Lower Cretaceous of southern Oklahoma (see also Folk, 1959). 
 
 Streams receiving considerable volumes of calcium-bicarbonate-rich waters 
 from springs and underground drainage through carbonate rocks may form extensive 
 travertine deposits at falls and rapids where agitation accelerates equilibration of 
 CO9 between air and water. Masses as much as 100 feet thick and nearly half a 
 mile in extent are described from creeks in the Arbuckle Mountains of Oklahoma 
 (Emig, 1917); alternating periods of erosion and deposition are shown to have oc- 
 curred (see Dickey, 1923). 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 9 
 
 TURBIDITES 
 
 Relatively few occurrences of calcareous turbidites are known (ten Haaf, 
 1959). They include the Teschen Limestone of the Polish Carpathians (Dzulynski 
 et al., 1959), several coarsely clastic beds in nappes near Geneva (Carozzi, 1952; 
 Kuenen and Carozzi, 1953), incidental intercalations in other noncalcareous forma- 
 tions (Kuenen and Migliorini, 1950), and a few graded calcarenitic turbidites in the 
 Apennines regularly interbedded with homogeneous, fine-grained limestones (Kuenen 
 and ten Haaf, 1956). 
 
 BEACHROCK AND DUNE LIMESTONE 
 
 Formation of beachrock and dune limestones by secondary CaCO- cementa- 
 tion of calcareous sediments has been reported throughout the tropic zone, in which 
 sea water is apparently saturated with CaCO- and there is extensive organic and 
 possibly chemical precipitation of CaCO„. Tne bedrock, exposed in cliffs and ledges 
 of the Bermuda Islands is made up of lithified calcareous dune sands blown together 
 during a low stand of sea level during Pleistocene time, and is now disaggregating 
 and contributing to present-day beaches (Todd, 1939; Dunbar and Rodgers, 1957). 
 
 Calcareous beach sands along the Mediterranean coast of Egypt gradually 
 change, away from the beach, to fairly well consolidated limestone ridges. Dune 
 limestones in Victoria may contain up to 98.75 percent CaCO^ (Coulson, 1940). 
 Similar rocks have been described from Puerto Rico (Guillou and Glass, 1957), the 
 northern Marshall Islands (Fosberg, 1954), and Kathiawar, some 30 miles inland 
 from the present margin of the Arabian Sea (Chapman, 1900; Evans, 1900; Crickmay 
 et al., 1941). The narrow zone of coquina along the east coast of Florida, formed 
 on an old beach, shows at various points all gradations from pure shell rock to car- 
 bonate-cemented quartz sand grains (Mossom, 1925). 
 
 A similar phenomenon is observed at Mono Lake, California, and at Pyramid 
 Lake, Nevada, where ordinary detrital minerals making up the beach sand are ce- 
 mented by CaC0 3 (Emery and Stevenson, 1950). 
 
 CHALKS AND FORAMINIFERAL LIMESTONES 
 
 Chalks are poorly consolidated, relatively pure limestones consisting prin- 
 cipally of fine-grained calcite and calcareous microfossils such as foraminifera, 
 coccoliths, coccospheres, rhabdoliths, and rhabdospheres. Although some chalks 
 are foraminiferal limestones, rocks such as the bed in the Comanchean of south 
 central Texas that consists of abundant miliolid foraminifera embedded in clear 
 calcite (Hanna, 1931) are certainly not chalks. 
 
 The foraminiferal assemblages of limestones may be quite indicative of dep- 
 ositional environments. Sediments in which planktonic foraminifera such as Glob- 
 iierlna sp. and Globorotalia sp. dominate probably were formed in at least moder- 
 ately deep water for, although these foraminifera are more abundant in lagoonal 
 waters, their contribution there is frequently masked by the high benthonic sedi- 
 mentation rate (Forman and Schlanger, 1957). 
 
 Well sorted, foraminiferal-algal calcarenites, such as the limestones rich 
 in benthonic foraminifera of the genus Beterosteiina found. at Guam and in southern 
 Louisiana, may be associated with reefs but could have formed in a shoaling bank 
 environment lacking a definite reef wall (Forman and Schlanger, 1957; Houbolt, 
 1957). Limestones containing abundant, thin-walled miliolid foraminifera in a 
 fine-grained carbonate matrix, such as described by Henson (1950) from Iraq, are 
 formed in back-reef and lagoonal environments. 
 
10 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 Crickmay et al. (1941) discussed the probable depositional environments of 
 various foraminiferal limestones, some of which (including the Upper Cretaceous 
 chalks of England) were once thought to be the consolidated equivalents of deep- 
 sea pelagic oozes. The siliceous tests of pelagic organisms and the finely divided 
 terrigenous and volcanic detritus present universally in small amount in the Globi- 
 ierina oozes are missing from many of these rocks, some of which are interbedded 
 with oolitic deposits. Most of the foraminifera in chalks (see Dunbar and Rodgers, 
 1957), such as those of Cretaceous age in Europe, are benthonic and the associa- 
 tions are not characteristic of the deep sea. Moderately shallow depths, perhaps 
 50 to a few hundred fathoms, are suggested. The Globigerina beds of the Oceanic 
 Series of Barbados, which are interbedded with radiolarian oozes and red earths, 
 may have been formed at somewhat greater depths. The thick, areally extensive 
 Globigerina limestones of the La Luna Formation and equivalent beds of Cretaceous 
 age in South America are highly bituminous and contain fish remains and phosphate 
 pellets (Smith, 1951). Deposition may have taken place in the deeper parts of a 
 seaway with impaired circulation. 
 
 Coccoliths occur in great variety and vast numbers in Cretaceous chalk 
 formations, are even more abundant in Tertiary calcareous deep-sea deposits, and 
 become successively less important in late Tertiary and Recent calcareous oozes 
 (Bramlette, 1958). The dissolution and recrystallization that are apparent in Creta- 
 ceous chalks, especially in the more permeable nonclayey ones, may lead to low 
 estimates of coccolith abundance. 
 
 Many of the minor but widespread carbonate beds interbedded in the siliceous 
 rocks of the Monterey Formation of California (Bramlette, 1946) consist largely of 
 foraminiferal remains. Current drifting of buoyant diatom and foraminiferal shells 
 is believed by Bramlette to explain the uniformity of depth facies apparent in the 
 foraminiferal zones over wide areas, as well as the remarkable thickness of diato- 
 maceous rocks. 
 
 The Fort Hays Chalk of Kansas, the lower member of the Niobrara Formation 
 of Cretaceous age, contains from 88.7 to 98.2 percent CaC03 (Runnels and Dubin, 
 1949) and consists of 60 to 80 percent very fine-grained material. There are also 
 microfossils such as Gumbelina, Globorotalia, Glob iter ina , and Textularia. P 2 5 
 in 30 samples ranges from a trace to 0.56 wt percent, mean 0.07 percent; S in 19 
 samples ranges from a trace to 0.23 wt percent, mean 0.05 percent. 
 
 SHALLOW-WATER MARINE LIMESTONES 
 
 Intraformational carbonate conglomerates are common in the geologic record, 
 and at some places such reworking has produced unusual rock types. Thus, an 
 intraformational conglomerate in the Upper Cretaceous of Haute Savoy, France, 
 marking the transition from calcareous glauconitic sandstone to lithographic lime- 
 stone, consists of wispy, streaked-out limestone pebbles, glauconitic micaceous 
 sandstone, and occasional phosphatic nodules. Rather vigorous shallow-water 
 wave action leading to mixing of glauconitic sand and still-plastic lime mud is 
 indicated (Carozzi, 1956). Hobbs (1957) described intraformational limestone con- 
 glomerates from the Ordovician of Virginia, some of which contain limestone peb- 
 bles and quartz sand in a matrix of dolomite. 
 
 Lithified equivalents of the suite of rock types now forming in the Bahama- 
 Florida area can be recognized. Bioherms in a number of areas were formed on 
 broad carbonate platforms, such as the Cooking Lake Formation of central Alberta 
 (Andrichuk, 1958). In this area sorted bioclastic and oolitic limestones formed in 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 11 
 
 agitated waters are associated with fine-grained, presumably precipitated limestones. 
 Environments inferred from the lithofacies and biofacies paralleling the reef front 
 correlate with those described by Ginsburg (1956) in the Florida area, allowing for 
 the differences in available Devonian and Recent organisms. 
 
 Four laterally successive environments of carbonate deposition are shown by 
 the Mission Canyon Formation and the lower part of the Charles Formation, both of 
 Mississippian age, in Saskatchewan: (1) basinal, dark gray-brown, argillaceous 
 limestones containing bituminous shale partings, and dark gray, dense, siliceous 
 limestones, both containing finely disseminated organic matter and iron sulfides; 
 (2) highly fossiliferous, open-shelf, marine limestones; (3) oolitic and lithographic 
 limestones containing only the remains of algae and a few scattered brachiopods; 
 (4) chalky, ostracodal, argillaceous limestones, anhydrite, and fine-grained dolo- 
 mite (Edie, 1958). Plots of the ratios of bioclastics to fine-grained limestone and 
 of true evaporites plus fine-grained dolomite to fine-grained limestone for these 
 beds show abrupt lateral transitions. The massive Mission Canyon Limestone in 
 the Little Rocky Mountains and at other Montana localities is a cross-laminated, 
 calcareous sand whose grains are saccharoidal crystal aggregates or, more rarely, 
 oolites (Sloss and Hamblin, 1942). 
 
 The granular cross-laminated "Bedford Oolite" of Mississippian age in 
 Indiana (Spergen Formation, according to U. S. Geological Survey usage) is made 
 up of small fossils and fossil fragments of similar particle size, apparently size- 
 sorted by marine currents or waves (Patton, 1953). Calcite and dolomite cements, 
 the latter microcrystalline, are noted (analysis 37, Part IV). 
 
 Frequently there is a close geographical association in lithified rocks 
 between reefs, euxinic basin deposits, and evaporite deposits, with abrupt lateral 
 facies changes (see Myers et al., 1956; Newell et al., 1953; Sloss, 1947; Gins- 
 burg and Lowenstam, 1958). This association has not been reported from present- 
 day environments. The basin margins between tectonically neutral platforms and 
 tectonically negative basins, some of which were euxinic, are the loci for narrow 
 but fairly persistent zones of such reef limestones (Sloss, 1947; Lowenstam and 
 DuBois, 1946; Parkinson, 1957). The reefs themselves, by physically changing 
 the amounts and directions of water flow, must have been to a considerable extent 
 responsible for development of evaporite basins on the platforms. 
 
 The intracratonic Michigan and Willi ston evaporite basins of Silurian age 
 owed their evaporite character at least in part to reefs (Krumbein, 1951). The rocks 
 of Niagaran age in northeastern and northwestern Illinois consist of reef and inter- 
 reef deposits that formed in the southwestern portion of the belt around the Michigan 
 Basin. The interreef deposits consist of variable mixtures of locally derived reef 
 detritus and regionally derived fine-graine'd terrigenous material deposited under a 
 range of water turbulences and degrees of aeration (analyses 79, 80, Part IV) 
 (Lowenstam, 1949). Normal shelf deposits including many coquinas are found in 
 west-central Illinois, and the section in southwestern Illinois is made up mostly of 
 quiet-water, muddy bottom deposits containing about 40 percent terrigenous elastics. 
 
 The Capitan Limestone in Texas is a great barrier reef 70 miles long and 
 more than 2000 feet high in its exposed portion alone. It separated a normal marine 
 sea to .the south from a restricted sea to the north, which in later stages became 
 highly saline and deposited salt and gypsum (Lloyd, 1929). A biohermal barrier in 
 the Travis Group of Devonian age in western Michigan separates shallow-water facies 
 to the east from evaporite-facies dolomites and anhydrites to the west (Jodry, 
 1957). 
 
12 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 FINE-GRAINED LIMESTONES 
 
 Illing (1954) noted that recrystallization to microcrystalline limestone, 
 obliterating fossils and ooliths, is already taking place in the Bahamas early in 
 diagenesis. One broad type of source area that can produce microcrystalline lime- 
 stone is thus defined. 
 
 The Upper Jurassic lithographic limestone of Solenhofen, Bavaria (analysis 
 49, Part IV) contains abundant marine fossils, dinosaur and Archeopteryx remains, 
 and many insects. It appears to have been formed from mud laid down on a shelf 
 area within the lagoon of an atoll, into which remains of the land dwellers were 
 blown or drifted out (Dunbar and Rodgers, 1957). 
 
 An eight-inch layer of fine-grained, argillaceous limestone with shrinkage 
 cracks, found in the Upper Pennsylvanian nonmarine, coal-bearing Uniontown 
 Formation of West Virginia, is probably a shallow marl-lake deposit (Dunbar and 
 Rodgers, 1957). The thin, fine-grained Carmel Limestone of Utah, which occurs 
 between nonmarine formations and contains some pellets, may represent recrystal- 
 lized CaC03 that was originally a shallow-water precipitate or disintegrated algal 
 debris (Bramlette, 1958). 
 
 Very fine-grained limestones in especially thin thin-sections are seen to 
 consist of interlocking crystals, commonly only a few microns in size, that must 
 have recrystallized from original particles of some sort (Bramlette, 1958). Bramlette 
 suggested that the coincidence between the first appearance of coccoliths in abun- 
 dance and the earliest occurrences of the relatively unlithified deposits known as 
 chalk indicates that earlier fine-grained limestones may have been coccolith-rich 
 and subsequently recrystallized. The fine-grained Upper Cretaceous chalk of 
 central Tunisia consists of foraminifera, mostly pelagic, scattered among interlock- 
 ing calcite crystals a few microns in size. In the less deformed stratigraphically 
 equivalent formation to the south, these foraminifera are scattered among abundant 
 coccoliths. Very fine-grained Tithonian (Upper Jurassic) and younger (Cretaceous) 
 geosynclinal limestones of the sub-Alpine region of France consist of interlocking 
 grains little larger than the coccoliths that occur in the somewhat older, though 
 much less lithified, Oxfordian age marl of northern France. 
 
 Pre-Cretaceous fine-grained limestones in which comparatively robust micro- 
 fossils are preserved also are known, indicating the original absence of planktonic 
 foraminifera, but the finer matrix is recrystallized. 
 
 LIMESTONES AND DOLOMITES FROM EVAPORITE SEQUENCES 
 
 Briggs (1958) calculated the theoretical distribution of evaporite minerals 
 in an ideal basin receiving an equilibrium influx of sea water and predicted that a 
 carbonate-anhydrite-halite sequence should be found from the inlet and edges of the 
 basin toward the center. This is a sequence recorded repeatedly in descriptions of 
 evaporite deposits (Sloss, 1953). 
 
 Briggs' evaporite facie s map for the Salina Formation of Upper Silurian age 
 in the Michigan Basin and the Ohio — New York Basin, based on proportions of car- 
 bonate, halite, and anhydrite (or gypsum) in samples from 56 wells studied visually, 
 is shown here as figure 1. The marginal position of the carbonate-rich zone agrees 
 with that predicted by his model. His plot of limestone to total carbonate ratios, 
 here reproduced as figure 2, shows dolomite to be the predominate carbonate rock 
 within the area studied, except in the region of the inferred principal Salina connec- 
 tion to the open sea where the normal marine environment is believed to have pro- 
 jected into the basin. 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 
 
 13 
 
 Fig. 1 - Proportions of carbonate, anhydrite (or gypsum), and halite in the 
 Upper Silurian age Salina Formation in the Michigan Basin and the Ohio- 
 New York Basin (Briggs, 1958; reproduced with permission of the "Journal 
 of Sedimentary Petrology"). 
 
 The argillaceous dolomite facies of the Florena Shale of Permian age in 
 Kansas (Imbrie, 1957; personal communication) is surrounded by limestone. Shal- 
 low-water fossils are present in the limestones but gradually disappear as the 
 dolomite is approached, suggesting a salinity control over the formation of dolomite. 
 
 Folk. (1958) cited a diminution in fauna as the dolomite facies is approached 
 in the Beekmantown rocks of Pennsylvania, and believed that the presence of fresh, 
 detrital K-feldspar indicates an arid coast to the west and a salinity control of dolo- 
 mite formation. He pointed out (see also Strakhov, 1956) that the decrease in fos- 
 sil content from limestone to dolomite is not solely due to destruction by dolomiti- 
 zation, inasmuch as large fossils are still recognizable in thin section because they 
 differ from the matrix in organic content and the crystal size of the dolomite that has 
 replaced them. 
 
 Ronov (1956) showed that the carbonate rocks of the Russian Platform have 
 a similar distribution pattern throughout much of the Paleozoic: highly dolomitic 
 rocks in a central area, which shifts about somewhat in different geologic periods, 
 
14 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 
 Fig. 2 - Ratios of limestone to total carbonate for the Upper Silurian age 
 Salina Formation in the Michigan Basin and the Ohio-New York Basin 
 (Briggs, 1958; reproduced with permission of the "Journal of Sedimen- 
 tary Petrology") . 
 
 surrounded by partly dolomitized rocks and then by limestones. This pattern would 
 result from Briggs' model if the salinity of the water in the basin of deposition never 
 became quite high enough for anhydrite precipitation. Strakhov (1956) and Ronov 
 debated the relative effect of fresh water from streams and from rains on salinity 
 and the resultant chemical precipitation in such a body of water. Briggs suggested 
 that occasional rains would merely stop the deposition of evaporite minerals until 
 the rainfall layer had evaporated, since the rainwater could not sink into the denser 
 underlying layer and would add little or no mineral matter. 
 
 The extensive development of biostromal shoals on a relatively stable shelf 
 area in the Stettler region of Alberta during late Devonian time resulted in the forma- 
 tion of dark bituminous limestones and then of interbedded anhydrite-dolomite and 
 local halite (Andrichuk and Wonfor, 1954). Evaporite ratio maps show an area to 
 the north in which there is only secondary dolomitization. Southward an evaporitic 
 anhydrite-dolomite section in which halite locally becomes a significant component 
 is followed by another area of secondary dolomitization. Reefs to the north are not 
 dolomitized. 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 15 
 
 The St. Louis Limestone of Mississippian age in southwestern Indiana, nor- 
 mally a marine limestone, in places contains nonfossiliferous, saccharoidal, dolo- 
 mitic limestone units that are succeeded by gypsum and anhydrite. The evaporite 
 part of the formation contains a higher percentage of evaporite beds and is thickest 
 in several intrasilled basins that have been outlined by isopach studies. There is 
 a correlation between increasingly saline units and an increasing segregation into 
 recognizable tectonic units (shelves, basins, and hinge lines) (McGregor, 1954). 
 
 Evaporite cycles in which dolomite, CaSO^ NaCl, and KC1 were success- 
 ively deposited are described from the Permian rocks of northeast Yorkshire (Ray- 
 mond, 1953). The basinal Zechstein beds of Permian age in north Germany include 
 four evaporite cycles, each showing a clay-carbonate-anhydrite-halite-sylvite 
 succession. Best shown by the second cycle, the facies in the carbonate horizon 
 are massive dolomite (containing oolite and algal [?] grains) along the basin rims 
 and atop linear ridges near the rim, and, basinward, dark, fetid, better stratified 
 dolomite; darker, thin-bedded, fetid limestone; and,finally,very dark, thinly bedded, 
 fetid, clayey limestone (Fiichtbauer, 1956; Andres et al., in press). The mineralog- 
 ical composition of the last named bed as determined from optical and X-ray diffrac- 
 tion data is 77 percent calcite, 7.5 percent albite (authigenic), 6.5 percent quartz 
 (detrital), 5.5 percent muscovite, 2.3 percent K-feldspar (detrital), 1.8 percent 
 pyrite, and 0.2 percent anhydrite. 
 
 Limestones and dolomites occurring in evaporite sequences may contain con- 
 siderable amounts of halite, gypsum, and anhydrite. Schwade (1947) described, from 
 the upper Yeso Formation of Permian age in New Mexico, varve-like layers of salt- 
 free dolomite alternating with layers of salt-dolomite intergrowths . Secondary salt 
 occurs as fracture fillings, primary salt as discrete crystals. Martens (1943) 
 studied cores from the Silurian of eastern Ohio that contained porous dolomite from 
 which salt had been dissolved; one five-foot section of such material that was still 
 intact contained 18 percent salt,well mixed with the less soluble ingredients. Sec- 
 ondary salt filling of porous Devonian limestones and dolomites underlying a salt 
 bed at Dawson Bay, Saskatchewan, was described by Edie (1959). 
 
 Anhydrite commonly occurs as pore fillings and porphyroblasts in Mississip- 
 pian age limestones underlain or overlain by evaporite units, described by Edie 
 (1958) from Saskatchewan. Dense, nonfossiliferous, nonporous, thinly laminated 
 dolomites contain intermixed salt casts and anhydrite. Edie noted that a complete 
 gradation between cryptocrystalline anhydrite and cryptocrystalline dolomite exists 
 in the Mission Canyon Formation. Brecciated fragments of anhydrite layers are 
 sometimes found in a dolomite matrix in the Salina Formation of Michigan (Dellwig 
 and Briggs, 1953). The Middlebury Limestone of early Permian age shows a gypsum- 
 crystal-bearing zone that grades into a gypsum bed in the Early Creek Shale (Kulstad 
 et al., 1956). Mixed carbonate-anhydrite rocks occur in the Zechstein of Permian 
 age of northern Germany (Fiichtbauer, in press). There are, for example, anhydrite- 
 filled oolites in dolomite, and algal pebbles in anhydrite beds. 
 
 Some dolomitic parts of the St. Louis Formation of Mississippian age in 
 southwest Indiana contain porphyroblastic anhydrite in extensive lenticular beds, 
 as well as later veins of anhydrite (Bundy, 1956). Saxby and Lamar (1957) made 
 closely-spaced visual estimates, spotchecked by microscopic and X-ray analyses, 
 of the mineralogy of cores through this formation in southern Illinois. Limestones 
 containing as much as 40 percent gypsum and 15 percent anhydrite are noted, as 
 are dolomites with up to 30 percent gypsum and 10 percent anhydrite. 
 
 Dolomite generally is subordinate in the compact dolomite-anhydrite layers 
 of the halite-anhydrite zone in the Permian of northeast Yorkshire (Stewart, 1951a) 
 
16 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 but locally may reach 70 percent. Mixed dolomite-anhydrite rocks of Permian age 
 in South Cumberland and Furness consist of anhydrite crystals up to 0.5 mm long 
 with interstitial fine-grained dolomite particles averaging 0.02 mm diameter. An- 
 hydrite-calcite rocks also occur, including one in which spherical calcite aggregates 
 about 0.04 mm in diameter are scattered throughout a matrix of anhydrite crystals 
 0.005 to 0.1 mm long (Dunham and Rose, 1949). 
 
 The replacement of dolomite by anhydrite in the Permian of Yorkshire can be 
 demonstrated particularly well when carbonaceous impurities, originally present in 
 the dolomite but not in the adjoining anhydrite, are present to serve as markers 
 (see Stewart, 1951a). Scattered remnants of a single dolomite grain in optical con- 
 tinuity also occur (Carozzi, 1960, p. 436). Magnesite, anhydrite, and dolomite 
 are sometimes found together, and Stewart (1949) concluded from petrographic 
 evidence that the first two may have formed at the expense of the dolomite. 
 
 There is a considerable variety of thinly interlaminated carbonate rocks 
 from evaporite sequences. Delicate laminae in the fine-grained dolomite of the 
 Mission Canyon Formation of Mississippian age in Saskatchewan, associated with 
 anhydrite, result from intermixing of small amounts of argillaceous, dark gray ma- 
 terial in some layers, as well as interlayering of paper-thin shale partings (Edie, 
 1958). These laminae presumably resulted from fluctuations in the amount of detri- 
 tus carried in by freshwater; most of the other known examples of interlaminated 
 beds involve chemical precipitates and are believed by Briggs (1958) to indicate a 
 nonconstant rate of sea-water influx. Yarzhemskij (1955) described almost sheet- 
 like interlayering of dolomite and anhydrite, and noted that in the same small dolo- 
 mite interlayers there are marked facies changes into anhydrite, NaCl, and even 
 KC1. 
 
 In places in the Blaine Formation of Permian age in Oklahoma, dolomite beds 
 0.25 inch thick alternate with gypsum in beds 1.5 inches thick (Muir, 1934). Thin 
 dolomite bands alternating with those of anhydrite in the Salina Formation of Michi- 
 gan are believed by Dellwig (1955) to have resulted from water influxes from outside 
 the evaporite basin. The bituminous material found in the dolomite laminae (but 
 not in the anhydrite) is thought to have been formed from the remains of organisms 
 that grew in the less saline surface layer of influx water, fell to the bottom on 
 death, and were preserved there by reducing conditions. Von Hoyningen-Huene 
 (195 7) described a similar localization of organic matter in gray-black, thinly 
 bedded, dolomite layers in the anhydrites of the Zech stein of Permian age of Ger- 
 many. Fine interlaminations of anhydrite and bituminous calcite in the Castile 
 Formation are attributed by Scruton (195 3) to short-term fluctuations in water salin- 
 ity (see also Stewart, 1954). 
 
 Hobbs (1957) described Ordovician carbonate rocks from Virginia containing 
 millimeter-laminated alternations of limestone and dolomite (see also Sander, 1951), 
 but an interpretation of variable salinity does not appear to have been attached to 
 these alternations. 
 
 OTHER DOLOMITES 
 
 Some apparently lacustrine dolomites that formed in bodies of water of un- 
 known salinity are described below. Sedimentary dolomites other than these and 
 the evaporite dolomites described earlier are evidently replacive because individual 
 dolomite rhombohedra cut pre-existing textures and fossil outlines. In completely 
 dolomitized rocks of this type, the outlines of the larger fossils generally can still 
 be identified. Inasmuch as no organism is known that forms its hard parts of dolo- 
 mite, at least the dolomite of the large-fossil component of such rocks must be 
 replacive. 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 17 
 
 Lacustrine Dolomites 
 
 Drill cores near Ipswich, Queensland, cut the Silkstone Series of Tertiary 
 age, which includes four basalt layers and six beds of fine-grained dolomite with 
 accessory chert, palygorskite (attapulgite), and montmorillonite (Rogers et al., 
 1954). There are also freshwater limestones containing Planorbis sp. The weather- 
 ing of the basalts is believed to have produced Ca, Mg, and Si that were deposited 
 in lakes as dolomite, chert, and sepiolite . The latter mineral can be seen as cores 
 in the bands of palygorskite, which probably formed by subsequent addition of alu- 
 minum. 
 
 Dolomitized Shallow-Water Limestones 
 
 The dolomite that replaces in mottled fashion certain very pure, shallow- 
 water limestones of Devonian age from Alberta, which are made up of fine-grained 
 fossil debris and well rounded lime sands, typically constitutes 10 to 40 percent of 
 the rock, rarely almost 100 percent (Beales, 1953). The fossils are shallow-water, 
 marine pelagic and benthonic forms, not present in great numbers. The dolomite 
 distribution is controlled by bedding laminations and not by joints or faults. These 
 rocks appear to be lithified equivalents of the material being deposited today in the 
 central portion of the Bahama Banks, where fine-grained carbonate exceeds the skel- 
 etal carbonate contribution. Erosion to the west and dolomitization to the east made 
 it impossible for Beales to locate the equivalents of the sediments rich in skeletal 
 debris found on the edge of the Bahama Banks. 
 
 Dolomitization of shallow-water limestones in some instances is known to 
 have occurred very early in the history of the rock. The Arbuckle Limestone of 
 Upper Cambrian — Lower Ordovician age in Oklahoma contains detrital, sand- sized 
 fragments of dolomite rock, dolomite crystals, and dolomitic limestone associated 
 with limestone fragments derived from penecontemporaneous or slightly older beds, 
 indicating the very early origin of the dolomite (Ham, 1951). Folk (1958) described 
 cross-bedding and reworked dolomite pebbles in the dense Nittany Dolomite of the 
 Beekmantown Group in Centre County, Pennsylvania. The Precambrian age Rand- 
 ville Dolomite of Dickinson and Iron Counties, Michigan, includes sandy dolomite 
 and dolomitic sandstone lithologies (Greenman, 1951). Conglomeratic and oolitic 
 facies suggest shallow, wave-agitated, near-shore waters. The conglomerates 
 contain, in a sandy dolomite matrix, pure dolomite fragments that could have come 
 only from reworked Randville Dolomite. This evidence is analogous to that cited 
 by Greenman (1951) for the Shakopee Dolomite, in which sandy dolomites contain- 
 ing dolomite pebbles grade down into undisturbed dolomites that obviously gave 
 rise to the pebbles. 
 
 A diagenetic origin appears likely for the zoned ferroan dolomite rhombohedra 
 observed by Biggs (1957) only inside or within a one-inch distance from chert nod- 
 ules in certain Paleozoic limestones from Illinois. 
 
 Structurally-Controlled Dolomitization 
 
 Where replacive dolomite has been localized by post-depositional structural 
 elements, it generally has not been possible to define the nature of the replacing 
 solution, which might have been low-temperature hydrothermal or merely ground 
 water or connate water of a more or less saline nature. The Carboniferous age 
 limestone of the Pennines has been invaded along planes of weakness — faults, 
 joints, bedding planes, fractures — by secondary dolomite (Hatch et al., 1938). 
 
18 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 Geikie (1903) described dolomitization of limestones of Carboniferous age in Ireland 
 and northern England for a few feet or yards away from joints. Hobbs (1957) ob- 
 served in the Ordovician carbonate rocks of Virginia that dolomitization may occur 
 along stylolites and permeable zones in cross-bedded laminae and scour-and-fill 
 structures, just as along joints and faults. 
 
 Dolomite masses which extend along faults in the Arbuckle Limestone of 
 Oklahoma, through as much as 1200 feet of beds and for as much as three miles 
 away from the faults, are in part ankeritic, containing up to 8 percent FeO. Ham 
 (1951) believed they were introduced during one or more of the strong orogenic 
 pulses that deformed the Arbuckle Mountains in Pennsylvanian time. Cayeux 
 (1932) described several places in which the chalk of the Paris Basin contains 
 dolomitic zones localized along anticlinal folds. Jodry (1955) showed a distinct 
 grading-off of dolomite content in a normally fossiliferous limestone of the Michigan 
 Basin, the Rogers City Formation of Middle Devonian age, away from apices of 
 folded structures and from certain long, narrow dolomite zones not related to fold- 
 ing. He believed that tension fractures and faults localized the ascent of high-Mg 
 brines from underlying evaporite beds. Tinklepaugh (1957) chemically analyzed 
 250 samples of this formation from 95 cores and found a highly significant differ- 
 ence, beyond the 1 percent level, for the Mg/Ca ratio of sets of cores from struc- 
 tural highs and those from troughs. The Fe content ranges from 0.01 percent to 
 8.50 percent, typically 1 or 2 percent, and is higher in the troughs, again giving 
 a difference significant beyond the 1 percent level. 
 
 Dolomitized Reefs 
 
 Maximum dolomitization of reef cores, with lesser amounts farther away 
 from the reefs, is noted for the Cooking Lake Formation of Alberta (Andrichuk, 
 1958). Illing (1956) noted that reefs form a zone of relatively high permeability 
 through which connate water expressed by compaction or tectonic activity would 
 tend to be funneled, and suggested that these fluids were the agents of secondary 
 dolomitization. It should be emphasized that the reverse also occurs: Carozzi 
 and Lundwall (1959) described a Middle Devonian bioherm in Indiana that is made 
 of limestone and is both overlain and underlain by dolomite. Numerous bioherms 
 in the northern Delaware Basin of New Mexico are limestone (Motts, 1960), with 
 dolomite in areas between bioherms. Newell et al. (1953), noting that the Goat 
 Seep reef mass of the Permian reef complex of New Mexico is completely dolomitized 
 whereas the Capitan Reef is dolomitized only slightly, along sandstone dikes, sug- 
 gested that the critical factor may have been availability of shelf brines enriched 
 in Mg after deposition of anhydrite. 
 
 The dolomitized reefs in the Racine Formation of Silurian age in the Chicago 
 area are exceptionally pure (Willman, 1943), often with less than 0.3 percent Si0 2 , 
 0.1 to 0.4 percent iron oxides, less than 0.01 percent Na 2 + K 2 0, no detectable 
 P 2 Or in a 5-gram sample, and 0.1 to 0.4 percent SO3 (analysis 77, Part IV). The 
 argillaceous interreef strata typically contain from 80 to 95 percent acid- soluble 
 material, but may have as little as 60 percent (analysis 78, Part IV). 
 
 "Dolomite Sands" 
 
 Rocks consisting of a mixture of dolomite and calcite may be enriched in 
 dolomite content by the preferential solution of calcite during weathering. The 
 resulting material is frequently an unconsolidated sand made up of dolomite par- 
 ticles from the original rock. Bevan (see Murray, 1930) found cavities in dolomitic 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES 
 Table 1. 
 
 II 
 
 19 
 
 - Calculated Contents, in Weight Percent, of MgCO- and Ca (P0.) 2 in 
 
 Marine Invertebrates 
 (Compiled from Clarke and Wheeler, 1922. Analyses by W. C. 
 Wheeler, A. A. Chambers, R. M. Kamm, B. Salkover, and 
 George Steiger of the U. S. Geological Survey.) 
 
 
 
 Number of 
 
 Classification 
 
 
 analyses 
 
 Foraminif era 
 
 
 6 
 
 Calcareous sponges 
 
 
 4 
 
 Madreporian corals 
 
 
 30 
 
 Alcyonarian corals 
 
 
 22 
 
 Coralline hydroids 
 
 (Millepora 
 
 
 and Distichopori 
 
 3) 
 
 6 
 
 Annelid tubes 
 
 
 3 
 
 Echinoderms 
 
 
 
 Recent crinoids 
 
 
 24 
 
 Fossil crinoids 
 
 (Eocene 
 
 
 to Lower Ordovician) 
 
 10 
 
 Sea urchins 
 
 
 12 
 
 Starfishes 
 
 
 29 
 
 Ophiurans 
 
 
 17 
 
 Holothurians 
 
 
 1 
 
 Bryozoa 
 
 
 13 
 
 Calcareous brachio 
 
 pods 
 
 5 
 
 Phosphatic brachio 
 
 pods 
 
 4 
 
 Mo Husks 
 
 
 
 Pelecypods 
 
 
 11 
 
 Scaphopods and 
 
 
 
 amphineurans 
 
 
 2 
 
 Gastropods 
 
 
 20 
 
 Cephalopods 
 
 
 3 
 
 Crustaceans 
 
 
 
 Barnacles 
 
 
 7 
 
 Others 
 
 
 13 
 
 Calcareous algae 
 
 
 
 Lithothnmnium, . 
 
 Lithophyllum > 
 
 Goniol ithon, 
 
 etc. 
 
 23 
 
 Halimeda 
 
 
 4 
 
 m.% MgCO (range 
 and av. ) after 
 elimination of 
 organic matter 
 and water from 
 the analyses 
 
 m% ca 3 (po 4 ) 2 
 
 (range and av. 
 
 similarly 
 
 calculated 
 
 1.79-11.08(9.61) 
 
 4.61-14.10(8.02) 
 
 0.09-1.11(0.50) 
 
 *6. 18-15. 73(11. 12) 
 
 0.24-1.28(0.54) 
 0.00-9.72(3.35) 
 
 Trace 
 
 Trace-9.96(3.38) 
 Trace 
 Trace-8.57(2.34) 
 
 Trace 
 Trace-0.99(0.54) 
 
 7.86-13.74(10.86) Trace-1.12(0.21 
 
 0.80-20.23(3.43) 
 5.41-13.79(8.51) 
 7.79-14.35(10.94) 
 6.61-14.95(10.52) 
 
 13.84 
 0.17-11.08(5.41) 
 0.49-8.63(2.42) 
 0.79-6.68(2.97) 
 
 0.00-1.00(0.22) 
 
 0.20-0.45(0* 
 0.00-1.78(0. 
 0.16-6.02(2. 
 
 0.75-2.49(1. 
 3.65-15.99(8 
 
 32) 
 
 29) 
 60) 
 
 82) 
 .28) 
 
 10. 93-25. 17( 
 0.02-1.09(0. 
 
 17.74) 
 65) 
 
 Trace(one had 0.20) 
 
 Trace-1.85(0.28) 
 
 Trace-0.78(0.15) 
 
 Trace-1.14(0.17) 
 
 Trace 
 
 Trace-8.47(2.08) 
 
 Trace-0.57(0.19) 
 
 74.73-91.74(82.91) 
 
 Trace(two had 0.07, 
 0.40) 
 
 Trace 
 
 Trace-0.85(0.10) 
 
 Trace 
 
 Trace (one had 0.77) 
 6.57-49.56(17.12) 
 
 Trace-0.43(0.05; 
 Trace 
 
 * One value (Heliopora cerulea, Philippine Islands) of 0.35. 
 
 limestone of the Oregon Quadrangle, Illinois, that were partly filled by residual 
 dolomite sand, and Stout (1940) described local areas of the Peebles Dolomite of 
 Niagaran (Silurian) age in Pike, Adams, and Highland Counties, Ohio, that have 
 been rendered soft and porous through leaching. 
 
20 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 Table 2. - MgCO in Calcareous Skeletal Materials 
 
 (Compiled from Chave (1954a). The analyses include 43 from Clarke 
 
 and Wheeler (1922), for which water temperatures were known.) 
 
 
 Number of 
 
 Percent 
 
 Weight Percent 
 
 Classification 
 
 samples 
 
 arago 
 
 nite 
 
 MgC0 3 
 
 Foraminif era 
 
 23 
 
 
 
 
 <4-15.9 
 
 Sponges 
 
 3 
 
 
 
 
 5.5-14.1 
 
 Madreporian corals 
 
 10 
 
 100 
 
 
 0.12-0.76 
 
 Alcyonarian corals 
 
 14 
 
 
 
 
 6.05-13.87 
 
 Echinoids 
 
 25 
 
 
 
 
 4.5-15.9 
 
 Echinoid spines 
 
 12 
 
 
 
 
 <4-10.2 
 
 Asteroids 
 
 9 
 
 
 
 
 8.6-16.17 
 
 Ophiuroids 
 
 6 
 
 
 
 
 9.23-16.5 
 
 Crinoids 
 
 22 
 
 
 
 
 7.28-15.9 
 
 Annelid worms 
 
 12 
 
 0- 
 
 99 
 
 6.4->16.5* 
 
 Pelecypods 
 
 11 
 
 0- 
 
 100 
 
 0.09-2.80 
 
 Gastropods 
 
 7 
 
 5- 
 
 100 
 
 0.08-2.40 
 
 Cephalopods 
 
 3 
 
 0- 
 
 100 
 
 0.05-7.00 
 
 Decapod crustaceans 
 
 6 
 
 
 
 
 5.2-11.70 
 
 Ostracode crustaceans 
 
 6 
 
 
 
 
 <4-10.2 
 
 Barnacles 
 
 9 
 
 
 
 
 1.35-4.60 
 
 Calcareous algae 
 
 15 
 
 
 
 
 7.7-28.75 
 
 * The highest values cited apply to small amounts of calcite found in the 
 more aragonitic materials formed at higher temperatures. 
 
 MAGNESIUM DISTRIBUTION IN CARBONATE ROCKS 
 AND SEDIMENTS 
 
 Magnesium in Skeletal Carbonates 
 
 Clarke and Wheeler (1922) presented an extensive series of original chem- 
 ical analyses of invertebrate skeletal materials, summarized here as table 1, as 
 well as an evaluation of earlier literature on the subject. Some of the materials 
 contained more than 20 wt percent MgC03 . Even though the available data on 
 water temperatures at the points where the various organisms were collected were 
 incomplete, Clarke and Wheeler were able to show quite clearly that the percentage 
 of MgC03 in the skeletal material of alcyonarian corals and echinoderms increased 
 with water temperature. Fossil crinoids contained distinctly less MgCOo than their 
 present-day counterparts, the MgC03 content of sea urchin spines differed from that 
 of shells and teeth, and the magnesia and phosphorus contents differed for lobsters 
 of different ages . 
 
 Chave (1954a) showed by X-ray diffraction that the MgCO-, in invertebrate 
 skeletal materials is present in solid solution, and that the amount of solid solu- 
 tion in aragonitic materials (rarely more than 1 wt percent MgCOo) is in general 
 much less than that in calcific materials (rarely less than 1 to as much as 20 or 
 more wt percent MgC03) (see table 2) . 
 
 In all groups of calcitic organisms for which sufficient data were available, 
 a linear or nearly linear relation could be shown between Mg content of the skeleton 
 and water temperature. An increase in phylogenetic level of the organism is in 
 general accompanied by a decrease of MgC03 in the skeleton and by a decrease in 
 the slope of the wt percent MgC03 vs. temperature plot. Chave, like Clarke and 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 
 
 21 
 
 Table 3. - Mineralogical Classification of Foraminifera by Families 
 (after Blackmon and Todd, 1959) 
 
 Imperforate 
 
 Perforate 
 
 Highly magnesian 
 (>10 mol % MgC0 3 ) 
 
 Calcite low in magnesium 
 (<5 mol % MgCO ) 
 
 Aragonite 
 
 
 Single 
 crystal 
 
 Radial microstructure 
 
 Granular 
 microstructure 
 
 
 Alveolinellidae 
 
 Fischerinidae 
 
 Miliolidae 
 
 Ophthalmidiidae 
 
 Peneroplidae 
 
 Spiril- 
 linidae 
 
 Calcarinidae 
 
 Camerinidae 
 
 Discorbidae 
 Heterohelicidae 
 Homotremidae 
 Planorbulinidae 
 
 Buliminidae - — • 
 
 Anomalinidae — — 
 
 Elphidiidae 
 
 Globigerinidae 
 
 Globorotaliidae 
 
 Lagenidae 
 
 Polymorphinidae 
 
 Rupertiidae 
 
 Buliminidae 
 
 Pegidiidae 
 
 Anomalinidae 
 
 Cassidulinidae 
 
 Chilostomellidae 
 Nonionidae 
 
 Rotaliidae 
 
 Ceratobu- 
 liminidae 
 
 Rober- 
 tinidae 
 
 
 
 
 
 
 *Amphisteginidae 
 *Cymbaloporidae 
 
 
 * Indicates intermediate to low range 
 
 Wheeler, observed that the tests and spines of the same echinoid individuals fre- 
 quently showed different MgC03 contents. Lowenstam (1954b) showed that the 
 percentage of aragonite in serpulid worm tubes increases with increasing water 
 temperature, and Chave pointed out that the total MgC03 content of such tubes 
 should increase with temperature as more Mg is taken into the calcite, but decrease 
 with further temperature rise because of the increasing percent of aragonite. 
 
 In a still more detailed X-ray diffraction study, Blackmon and Todd (1959) 
 examined shells of 155 species of calcareous foraminifera, belonging to 29 Recent 
 families, and found that the mineralogy with few exceptions fitted the pattern re- 
 produced here as table 3. The calcite of some samples contains as much as 20 to 
 24 mol percent MgC03- The control of the carbonate mineralogy of these materials 
 is believed to be mainly biologic, although a depression of MgCO^ content, highly 
 variable in amount among different species, is observed in colder waters for all 
 foraminifera with shells of highly magnesian calcite. 
 
 Pilkey and Hower (1960) found that the percentage of MgC03 in specimens 
 of Dendraster excentricus collected from the coast between British Columbia and 
 Baja California ranges from 8.4 to 9.5 (215 analyses) and that the percentage of 
 SrC03 ranges from 0.296 to 0.354 (117 analyses). These authors conclude that 
 that Mg content is directly related to both water temperature and salinity, and that 
 Sr content is inversely related to water temperature and independent of salinity. 
 
22 
 
 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 Goldsmith et al. (1955) made additional spectrographic analyses and cell- 
 size measurements on some 25 of Chave's samples, and described one Mg-rich al- 
 gal calcite that contained several mol percent MgCOo in some form other than ideal 
 solid solution, as shown by a measurable cell-size change when homogenization 
 took place at high temperature. 
 
 In view of the several variables that affect the content of MgCOo in skeletal 
 materials, summaries such as presented here in tables 1, 2, and 3 are of only gen- 
 eral value in indicating skeletal MgCOj contributions to sediments. In apportioning 
 the total MgC03 content of a sediment among the several skeletal contributors, so 
 as to determine whether there has been a gain or loss of MgCOo to sea water, for 
 example, it is necessary to identify the organisms as closely as possible and to 
 refer to detailed information on the MgC03 contents of individual species or small 
 taxonomic groups. Chave (1954b) obtained reasonable agreement between total 
 and apportioned MgCOo in several sediments. He discussed earlier attempts by 
 Vaughan (1918), Bramlette (1926), Goldman (1926), and Thorp (1935), suggesting 
 that the use of average MgCO~ contents from Clarke and Wheeler's data and the 
 difficulty of distinguishing fine-grained fragments of aragonitic and calcitic algal 
 calcites limited the accuracy of their results. 
 
 Chave (1954b) found that calcitic fos- 
 sils in porous sandstones and oolites of 
 Pleistocene age had lost Mg, that some of 
 the fossils in silts and marls of intermed- 
 iate porosity had lost Mg, but that fossils 
 imbedded in relatively nonporous post- 
 Paleozoic shales had retained their Mg. 
 The Key Largo Reef and the Miami (back- 
 reef) Oolite of Pleistocene age in south 
 Florida have been above sea level most 
 of the time since they were formed, and 
 Mg has been leached by ground water. The 
 Miami Oolite, which contains about 15 per- 
 cent fossils originally high in Mg and mol- 
 lusks and oolites that originally contained 
 smaller amounts of Mg, now has only 0.37 
 percent MgCOo . 
 
 10,000- 
 
 8,000- 
 
 6,000- 
 
 4,000 
 
 2,000 
 
 (a) 
 
 30-| 
 
 20- 
 
 10- 
 
 (b) 
 
 DOLOMITE — 
 CALCITE 100 
 
 20 
 
 40 
 
 60 
 
 80 
 
 PERCENT 
 
 100 
 
 Mg 
 
 - 
 
 2.5 
 
 5 7.5 
 
 10 
 
 13.2 
 
 
 
 DOLOMITE - 
 
 - 
 
 19 
 
 38 57 
 
 76 
 
 100 
 
 
 CALCITE 
 
 100 
 
 81 
 
 62 43 
 PERCENT 
 
 24 
 
 
 
 Fig. 3 - The frequency of occurrence of various calcite-dolormte mixtures in 
 the Middle and Upper Paleozoic carbonate rocks of the Russian Platform 
 (Ronov, 1956): (a) computed from 23,101 individual analyses, and (b) 
 based on measurements of areas on maps contoured for Mg content. 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 
 
 23 
 
 480 
 
 420- 
 
 360 
 
 300- 
 
 Ll. 240- 
 
 180- 
 
 120- 
 
 hJ 
 c/> 
 >■ 
 _l 
 < 
 
 < 
 
 o 
 
 a: 
 
 00 
 
 DOLOMITE — 
 CALCITE 100 
 
 Relative Abundance of Various 
 Calcite-Dolomite Mixtures 
 
 Plots of the frequency distribution 
 of calcite-dolomite mixtures occurring in 
 carbonate rocks, made for large numbers 
 of samples (Steidtmann, 1917; Ronov, 
 1956; Nikolaev, 1956), show maxima 
 near both ends of the range (figs. 3, 4, 
 5) . If dolomitization in nature took place 
 by some one process (for example, sec- 
 ondary replacement by Mg derived from an 
 external source), this bimodal distribution 
 would suggest that a threshold of some sort 
 must be exceeded before dolomitization 
 can proceed, but that once the threshold 
 had been passed, dolomitization has a 
 good chance of going essentially to com- 
 pletion. It appears more likely, however, 
 that the two ends of the range are being 
 reinforced statistically by carbonate rocks 
 of special types, in the one case by fine- 
 grained, virtually pure, supposedly chem- 
 ically precipitated dolomite rocks from 
 evaporite sequences, in the other by the 
 weakly dolomitized rocks in which very 
 local redistribution of the Mg originally 
 in biogenic magnesian calcites is ade- 
 quate to account for the dolomite present. 
 
 When Ronov 's analyses are used to plot maps of the Mg concentration in 
 various parts of the Paleozoic sequence on the Russian Platform, and the areas of 
 various Mg concentrations on the maps are made the basis of a frequency distribu- 
 tion, the picture shown in figure 3b is obtained and is quite different from that in 
 figure 3a. Many of the intermediate mixtures in figure 3b must result from averag- 
 ing of analyses for sub-layers, some of which are rich in dolomite, others in cal- 
 cite. The frequency of intermediate mixtures in the plots of figures 3a, 4, and 5 
 probably is increased slightly by an analogous effect. Analyses of samples of 
 finely interlaminated dolomite and calcite would necessarily be an average of a 
 considerable number of such layers. Such an analysis may indeed be a perfectly 
 valid statement of rock composition, but it does not correspond to either of the two 
 depositional environments in which the successive laminations were formed. 
 
 PERCENT 
 
 Fig. 4 - Computed percentages of calcite 
 and dolomite for 1148 analyses of car- 
 bonate rocks from North America (Steidt- 
 mann, 1917; reproduced with permission 
 of the "Bulletin of the Geological Society 
 of America") . 
 
 Dolomitization Throughout Geologic Time 
 
 Daly (1909) compiled 900 chemical analyses of limestones and dolomites 
 from Belgium, Canada, and the United States and found that the average Ca/Mg 
 ratios were relatively constant for pre-Devonian rocks but rose steadily for Devonian 
 and Carboniferous samples and reached an apparent maximum during Cretaceous 
 time, although the number of samples of Tertiary and younger rocks was rather small. 
 The increase of Ca/Mg .ratios with geologic time for carbonate rocks of the Russian 
 Platform (Vinogradov et al., 195 2) is shown in figure 6. A number of explanations 
 have been put forth to explain this distribution, including the increased time the 
 
24 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 400 
 
 300 
 
 GO 
 
 Ld 
 CO 
 
 >- 
 
 L»- 200 
 O 
 
 cr 
 
 UJ 
 CO 
 
 100 
 
 fl 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i-l 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 n 
 
 1 
 
 
 
 
 
 
 
 J 
 
 f 1 
 
 
 V 
 
 
 
 
 
 
 
 y 
 
 j 
 
 T. 
 
 20 
 
 40 60 
 
 PERCENT DOLOMITE 
 
 80 
 
 100 
 
 Fig. 5 - The frequency of occurrence of various calcite-dolomite mixtures 
 
 in Upper Carboniferous rocks of the Samarov Valley. The rocks rarely 
 
 contain more than 2 percent insoluble residue (Nikolaev, 1956). 
 
 older rocks have had to undergo post-depositional replacement, the times at which 
 particular groups of lime-secreting organisms appeared, and the possibility that the 
 partial pressure of CO2 in the atmosphere was greater in earlier geologic periods 
 than more recently. 
 
 Strakhov (1956) pointed out that aridity and concomitant high evaporation 
 rates seem to have played an important part in adjusting water composition for dolo- 
 mite formation, both in present-day lacustrine deposits and in the Paleozoic rocks 
 of the Russian Platform. Until comparisons of carbonate rocks of different geologic 
 ages from similar climates can be made, the possibility remains that the compilations 
 mentioned above are influenced by average past climates in the countries from which 
 the samples came. 
 
 Some Empirical Generalizations 
 
 Fairbridge (1957) showed a correlation between dolomite content and the per- 
 centage of insoluble residue in the analyses of "Cambro-Ordovician" rocks from near 
 Harrisburg, Pennsylvania, published by Lesley (1879). However, the Ellenburger 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 
 
 25 
 
 36 r 
 
 32 
 
 28 
 
 24 
 
 20 
 
 16 
 
 12 
 
 PCm 
 
 Cm 
 
 510 
 
 430 
 
 S, I S 2 iDjbjl IJCjCglCjl P, IP 2 I T 
 310 — 275 225 150 
 
 1 Cr I T> lol 
 
 1 10 - 
 
 •70- 
 
 ABSOLUTE TIME IN MILLIONS OF YEARS 
 
 Fig. 6 - The change with geologic time of the Ca and Mg content of the car- 
 bonate rocks of the Russian Platform (after Vinogradov et al . , 1952). 
 (I) Based on analyses of 97 composites of 3569 samples. (II) Based on 
 2826 published analyses for Ca, 2583 for Mg. 
 
 limestones and dolomites analyzed by Goldich and Parmalee (1947), virtually all of 
 which contain less than 7 percent insoluble residue, show no evident correlation 
 between the calculated normative percentage of dolomite and weight percent insol- 
 uble residue. 
 
 Folk. (1958) found an average of 12.56 percent insoluble residue in the nine 
 dolomite beds of the Axemann Formation of the Beekmantown Group in Centre County, 
 Pennsylvania, but an average of only 6.52 percent in nineteen limestones and dolo- 
 mitic limestones in that formation. The difference lies in the kind and amount of 
 authigenic silica; euhedral quartz crystals and overgrowths in limestones are out- 
 weighed by the large amount of disseminated chert in the dolomites, which also con- 
 tain some quartz overgrowths and aggregates. It is possible that a similar explana- 
 tion applies to Lesley's analyses. 
 
26 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 When the Funafuti core was the only one available from the Pacific, the 
 specific distribution of dolomite with depth in that core was made the basis for con- 
 siderable speculation. It is now known that the distribution of dolomite with depth 
 on Pacific islands is extremely variable (Ladd et al . , 1948). On Kita Daito Jima 
 there is strong dolomitization from the surface down to 103.5 meters, and then only 
 a small MgO content except for a few intervals (Hanzawa, 1940); at Funafuti, dolo- 
 mite is found below 637 feet (Cullis, 1904); at Bikini, there is no dolomitization 
 down to the bottom of the hole at 2556 feet depth; two Great Barrier Reef bores to 
 600 feet and 732 feet showed no dolomite (Richards and Hill, 1942). Appreciable 
 dolomite was found at Eniwetok in only four samples of Eocene age at depths below 
 4300 feet (Ladd et al . , 1953). The MgCOg values do not appear to have been re- 
 ported in detail for two holes drilled on Maratoea Atoll northeast of Borneo to depths 
 of 856 and 1407 feet (Kuenen, 1947). The dolomite discussed above is inferred 
 from chemical analyses; small percentages of MgO that, particularly in the upper 
 parts of the cores, could be present in magnesian calcites have been ignored. In' 
 the Mg-rich horizon near the top of the Funafuti core, X-ray diffraction measurements 
 (Schmalz, 1956; Graf and Goldsmith, in press) have shown that the Mg occurs in 
 magnesian calcite and not in dolomite. 
 
 IMPURE CARBONATE ROCKS 
 
 Arenaceous and Cherty Carbonate Rocks 
 
 The silica in carbonate rocks occurs as detrital and authigenic quartz, 
 chert, and the so-called amorphous silica. The last of these forms the shells of 
 siliceous organisms such as diatoms, radiolaria, and siliceous sponges. It may be 
 hydrated and consists of a disordered association of cristobalite crystallites very 
 little larger than one unit cell and therefore not properly called crystalline cristo- 
 balite (Warren and Biscoe, 1938). 
 
 Although angular chert fragments have been described from the siliceous 
 limestone portion of the Zesch Formation (Barnes et al., 1947), it is generally 
 quartz that is encountered as a detrital contribution. The variation this contribu- 
 tion may show with change in depositional environment is well illustrated by the 
 Ballyshannon Limestone of early Carboniferous age. In the Donegal Syncline this 
 limestone shows rapid facies changes between deltaic sandstone members to the 
 north and shallow-water oolites and fragmental bioclastic limestones with a grad- 
 ually decreasing content of smaller and smaller quartz and feldspar grains to the 
 south (George and Oswald, 1957). Unusual rock types in the Ballyshannon include 
 an oolite made up of angular quartz grains with oolitic skins, and a fine-grained 
 limestone containing an abundance of both fine silt and sponge spicules. Such 
 fine-grained quartz-carbonate mixtures may be difficult to classify in the field. 
 Two samples from the Paradox Member of the Hermosa Formation of Pennsylvanian 
 age in southeast Utah which would routinely have been called calcareous shales 
 were shown by X-ray diffraction analysis to consist of 50 percent calcite and dolo- 
 mite, 40 to 45 percent quartz, and 5 to 10 percent illite, montmorillonite, and chlor- 
 ite (Merrell, 1957). 
 
 The chert in carbonate rocks commonly occurs as beds and as nodules. The 
 replacement origin of the latter is shown by, among other things, residual particles 
 of organic matter outlining oolites and other replaced textural features (see Biggs, 
 1957; Folk, 1958). All gradations between pure limestone and pure chert occur. 
 Ver Wiebe (1946), for example, described several wells in Sedgwick County, Kansas, 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 27 
 
 in which dolomitic layers in the Kinderhook Limestone of Mississippian age contain 
 40 to 50 percent chert; Dott (1958) found many limestone units in the Pennsylvanian 
 rocks of northeastern Nevada that contain more than 30 percent chert. Porcelanite 
 of the Lower Triassic Thaynes Formation of west-central Utah is seen in thin-section 
 to contain about 50 percent disseminated quartz present in a fine mosaic in calcite 
 and dolomite (Hose and Repenning, 1959). Chert generally does not, however, re- 
 place collophane (Carozzi, 1960, p. 323) or dolomite, which exists as euhedral 
 crystals in chert nodules and passes through them as unreplaced laminae (Folk, 
 1958; Biggs, 1957; Hatch et al . , 1938). The chert in most dolomites is a uniform- 
 ly impalpable powder, which in the Beekmantown Group of Centre County, Pennsyl- 
 vania, makes up 5 to 10 percent of the rock (Folk, 1958). Dolomites of the Ellen- 
 burger Group of early Ordovician age in central Texas at many places contain highly 
 disseminated chert which seldom is visible on fresh rock surfaces but which on 
 weathering yields spongy masses containing abundant holes of rhombic shape 
 (Cloud et al., 1946). 
 
 Attempts have been made to distinguish the relative amounts of chert found 
 in limestones of different types and origins. Vishnyakov (1953) claimed that chert 
 is more common in fine- to medium-grained deeper water limestones and deep-water 
 foraminiferal limestones than in shallower water brachiopod facies, and Teodoro- 
 vitch (1950) stated that oolitic limestones are poor in chert. Hattin (1957) noted 
 that chert usually is not found in purely molluscan or purely algal limestones. 
 
 Reef cores and reef-like accumulations of skeletal remains are not entirely 
 free of silica. There are, for example, small amounts of secondary chert and a 
 little drusy quartz in the cores from the Horseshoe Atoll, of Pennsylvanian and 
 early Permian age, in west Texas (Myers et al . , 1956). However, there is typical- 
 ly a much greater amount of silica in the interreef limestones (see Pray, 1958). 
 These estimates seem to indicate that limestones formed in waters agitated enough 
 to winnow out the finer grained detrital silica and the invariably small and relative- 
 ly buoyant siliceous shells, if indeed these materials enter the environment in sig- 
 nificant amounts, are less likely to contain chert. 
 
 Nature and Origin of Chert in Carbonate Rocks 
 
 Jensen et al. (1957) made an X-ray diffraction study of 42 Danish "flints" 
 and other siliceous rocks (all but one derived from chalk deposits of Cretaceous 
 age) and found they contained from 4 to 95 percent fine-grained a- quartz, typical- 
 
 o 
 
 ly of 300 to 500 A particle size. The remainder consisted principally of flaky, crypto- 
 crystalline material having a two-dimensional cristobalite arrangement. These authors 
 were able to correlate with fair to moderate accuracy estimates made by X-ray and 
 petrographic methods of the amount of cristobalite-like material, which would be 
 called opal by a petrographer. Chert in lacustrine dolomite beds of Tertiary age 
 near Ipswich, Queensland, gives an X-ray diffraction pattern "similar but not iden- 
 tical to" that of (3 -cristobalite (Rogers et al . , 1954). Significantly, Folk (1958) 
 failed to detect by petrographic means any opal in the chert contained in the much 
 older carbonate rocks of the Beekmantown Group of early Ordovician age, and Biggs 
 (195 7) detected no "amorphous silica" or opal, only microcrystalline quartz, on 
 microscopic examination of chert from 18 Illinois limestone and dolomite formations 
 ranging from Cambrian to Mississippian in age (see also Rubey, 1952, on the chert 
 of the Burlington Limestone of Mississippian age in Illinois). Fibrous quartz ("chal- 
 cedony"; see Pelto, 1956) generally is restricted to places where a free surface is 
 available as a starting point for its growth (Folk and Weaver, 1952; Biggs, 1957). 
 
28 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 The "amorphous silica" in the siliceous tests of organisms is metastable, 
 c-quartz being the stable form of SiO? at room temperature, and it is known from 
 experimental studies of reactions in concrete to be highly reactive toward alkalis. 
 Jensen et al. (195 7) suggested that weakly alkaline waters saturated with CaCOg 
 in the chalks apparently are sufficient to induce concentration and transformation 
 of disseminated "amorphous silica" (see also Correns, 1950). CaC03~saturated 
 water in chalk, not in contact with air, would have a pH of about 9.9; in contact 
 with air, it would have a pH of about 8.3 (R. M. Garrels, personal communication). 
 The first of these figures is significantly above the value of 9, which Krauskopf 
 (1956) found to be the upper limit of the range in which silica solubility is essen- 
 tially independent of pH. The water and residual CaCOg found in many chert nod- 
 ules, as well as the very small particle size of the c-quartz therein, indicate the 
 difficulty of obtaining the truly stable end product, macrocrystalline a-quartz. 
 
 There is additional support for the origin of at least some chert by reorgan- 
 ization of organic silica. Extensive solution of the silica of diatom shells in the 
 Monterey Formation and its reprecipitation as a cement and as chert masses and 
 beds are shown by lateral transitions within short distances between the cherty 
 or porcelaneous beds and soft diatomites. Significantly, Bramlette (1946) sug- 
 gested that the unaltered diatomites may be poorer in carbonate than the porcelane- 
 ous and cherty parts. Cayeux {in Newell et al. , 1953) and others believed that 
 the principal source of silica for chert in European chalks is the siliceous spicules 
 of sponges. Nodular chert in the Helderberg Limestone of West Virginia contains 
 sponge spicules and is clearly of replacement origin. All stages, from normally 
 calcareous oolites and fossils to their completely silicified equivalents, can be 
 observed. The sponge spicules in the limestone outside the nodules have been 
 largely calcified, indicating at least a partial source for the silica of the nodules 
 (Heald, 1952). Black, silica-rich concretions in a sponge-bearing Onondaga Lime- 
 stone, found by Schwartz and Mathiasen (1934) to contain 0.38 percent finely sub- 
 divided free carbon, are believed by them to be recrystallized and calcite-enriched 
 concentrations of siliceous sponge remains (analysis 55, Part IV). Limestone of 
 the Rauracian Formation of Upper Jurassic age in southern Poland contains very 
 abundant calcified sponge spicules, whereas many of the spicules in adjoining 
 chert-rich beds seem to have served as nuclei for chert growth (Sujkowski, 1958). 
 A similar situation exists for the Turonian white chalk of Polish Volhynia. In the 
 Phosphoria Formation of northwestern Wyoming there are all gradations between 
 chert farily rich in organic matter, which outlines relict sponge spicules, and chert 
 recrystallized to spherulites that contain no carbonaceous matter and no relict 
 sponge spicules (Sheldon, 1957). 
 
 At several localities chert is restricted to interreef facies rich in siliceous 
 sponge remains, from which it apparently formed. For example, an unusually 
 large amount of biogenic silica is contained in the sooty, black, thin-bedded lime- 
 stone of the Marble Falls Formation of Pennsylvanian age, Lampasas County, Texas, 
 which has from 20 to 45 percent siliceous residue consisting largely of sponge 
 spicules (Damon, 1943; Barnes, 1952). It can be followed laterally into spiculite 
 that contains some 88 percent siliceous residue, is hard, and appears under the 
 microscope to have been partly cemented by silica. This altered spiculite in places 
 passes into chert that is interbedded with the limestone. Nearby reef rock is of 
 very high purity (analysis 44, Part IV) and the small amount of chert it contains is 
 the porous, friable kind that replaces fossils. 
 
 In the post-Joliet formations of the Niagaran Series in northeastern Illinois, 
 chert is confined principally to the biostromes, composed mainly of siliceous sponges, 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 29 
 
 that occur in the dolomites of the interreef facies (Lowenstam, 1942, 1948). The 
 nearby dolomitized reefs are extremely pure (analyses 79 and 80, Part IV). Chert 
 in zones now devoid of sponge remains apparently also was sponge-derived, for a 
 gradation exists between spiculeless chert in such zones and nearby chert contain- 
 ing completely preserved sponge skeletons, and the specialized fauna of the sponge 
 biostromes also is found in the spiculeless chert zones but not in chert-free areas. 
 Lowenstam found that well shaped chert nodules typically contained a complete 
 siliceous sponge skeleton, whereas bedded cherts and incompletely chertified areas 
 with poorly defined boundaries contained abundantly distributed flesh and tuft 
 spicules that had served as centers for chertification. The relative rates of sedi- 
 mentation, decomposition of soft parts, and reorganization of silica were presumably 
 critical in determining whether recognizable sponge remains persisted or were dis- 
 aggregated. Localized solution of isolated spicules and margins of already formed 
 chert nodules has resulted in the silicification of fossils other than sponges. The 
 remarkable preservation of morphologic details in chertified fossils and the poor de- 
 tail in dolomitized and silicified fossils were taken by Lowenstam to indicate that 
 chertification is pre-dolomitization in this area. Apparently assuming that the 
 preservation of detail in silica replacements is relatively constant, he further con- 
 cluded the silicified fossils must be replacements of already dolomitized ones. 
 
 Sponge spicules are absent in the core of the Wabash Reef, Wabash, Indi- 
 ana (Carozzi and Zadnik, 1959), very scarce in the adjoining reef detritus, and 
 abundant in the interreef area. 
 
 The relatively early formation of at least some chert is indicated by its 
 occurrence as nodules in some of the desiccation polygons in the Hardy Creek 
 Limestone of middle Ordovician age in southwest Virginia (Harris, 1958). The size 
 and shape distribution of the polygons is distorted according to the size and shape 
 of the contained nodules. An early age also is indicated by occurrences like those 
 cited by Poor (1925) and Rubey (1952) in which chert pebbles of Mississippian age 
 are found in the basal conglomerate of the Pennsylvanian in Illinois (see also 
 Cayeux, 1941). Dolomite-free calcareous inclusions frequently found in cherts 
 contained in dolomitized rocks indicate that chert formation usually precedes sec- 
 ondary dolomitization (Carozzi, 1960). 
 
 Silicification of exposed surfaces (Moore, 1955, Crystal River Formation of 
 northwest Florida; Dott, 1958, Pennsylvanian limestones of northeast Nevada) and 
 of the exposed portions of fossils (Howell, 1931; Lowenstam, 1948; Dott, 1958) 
 generally is taken as evidence for continuing present-day redistribution of silica in 
 carbonate rocks. However, Newell et al . (195 3) noted that frequently only parts of 
 fossils are silicified, whetherthey are collected from the surface or well within large 
 blocks, and suggested that a portion of such a partly silicified fossil which stands 
 in relief on the weathered surface of a carbonate rock would naturally be the silici- 
 fied portion . 
 
 Available data on the solubility of "amorphous silica" and quartz and on the 
 silica content of natural waters suggest that most natural waters are undersaturated 
 with respect to "amorphous silica, " but that solutions supersaturated with regard to 
 quartz are not rare and may persist in that condition for years (Siever, 1957; Kraus- 
 kopf, 1956). Synthetic crystalline quartz has not been formed directly from solu- 
 tion at anywhere near room temperature and pressure, and the mechanism of forma- 
 tion of authigenic quartz crystals in limestones and elsewhere is not yet under- 
 stood . 
 
 The amount of silica dissolved in alkaline lakes with a pH above 9 increases 
 markedly because of the formation of silicate ions, so that a subsequent pH drop 
 
30 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 might be expected to result in inorganic precipitation of "amorphous silica" (Siever, 
 1957). The chert in the dolomite-rich, lacustrine Green River Formation of Eocene 
 age in Wyoming, Colorado, and Utah might represent such a product. However, 
 diatoms flourished in the Green River lake during at least part of its history, and 
 they may have succeeded in keeping the silica concentration well below saturation. 
 
 Argillaceous and Glauconitic Limestones 
 
 Robbins and Keller (195 2) examined the less than 2\± fraction of insoluble 
 residues from 271 limestones and dolomites and found illite to be the dominant clay 
 mineral in both marine and nonmarine carbonate rocks. However, they used 6N 
 HC1, which could have deteriorated a good deal of chlorite. Weaver (1958) con- 
 cluded from several thousand clay mineral determinations that illite is the predom- 
 inant clay mineral in carbonate rocks, as Grim et al . (1937) and Millot (1953) had 
 said earlier. However, he also found clay suites commonly composed entirely of 
 montmorillonite and of mixed-layer materials. Occurrences of chlorite and kaolinite 
 in carbonate rocks are not uncommon, but these minerals are seldom dominant in the 
 clay mineral suite. Weaver found no particular clay mineral restricted to a particular 
 environment. In another study, Degens et al . (1958) found that the illite/kaolinite 
 ratio of 18 samples of marine and freshwater limestones of Pennsylvanian age did 
 not reflect differences in depositional environment. The relative importance of the 
 original character of detrital clay minerals and of diagenetic changes in depositional 
 environments is at present under intensive study by many workers. 
 
 Myers et al . (1956) described a zone at the top of the reef limestone of the 
 Pennsylvanian and early Permian Horsehoe Atoll of west Texas that lies under dark 
 pyritiferous shale. The pores of the limestone have been filled with dark gray to 
 black clay and, in a few places, with pyrite thought to have been precipitated from 
 connate water originally contained in the shale. 
 
 Alternating laminae of relatively pure limestone and more argillaceous lime- 
 stone were reported by Brill (1956) in the Berriedale Limestone of Tasmania. Hadding 
 (1958, p. 37-40) described a similar alternation in which the individual layers are 
 about 100 mm thick. 
 
 The small green pellets called glauconite are shown by X-ray examination to 
 consist of a variety of layer-lattice materials (Burst, 1958a, b) in addition to the 
 carefully defined glauconite of Gruner (1935) and Hendricks and Ross (1941). Burst 
 believed that degraded layer-lattice silicates surrounded by local environments of 
 reduction are nucleation centers to which Fe and K migrate, and he noted that glau- 
 conite formation in fecal pellets and inside foraminiferal shells fulfills these con- 
 ditions. The argillaceous minerals of Recent age in Gulf Coast fecal and cavity-fill 
 material are considerably degraded. 
 
 Hadding (1932) concluded from his study of Swedish glauconite rocks that 
 glauconite formation is favored in agitated waters under conditions of limited dep- 
 osition, an opinion strengthened by the glauconite deposition actually observed off 
 southern California (Emery, 1960). 
 
 Some mica-booklet type of glauconite occurs in the Senonian age limestones 
 of Sweden, in addition to that which impregnates sponges, porous fossil fragments, 
 and gastropod shells (Hadding, 1932). Herzog et al . (1958) mentioned a richly 
 fossiliferous, pyritic limestone of lowermost Ordovician age from a quarry at Sten- 
 brottet, Sweden, from which chips containing more than 50 percent glauconite in 1 
 to 2 mm pellets can be selected. Many of the Eocene marls and chalks of the Gulf 
 Coast are glauconitic and are likely to contain phosphatic concretions and internal 
 molds of mollusks as well (Monroe, 1941; Burst, 1958a, b) . The glauconitic chalks 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 31 
 
 of the Paris Basin all carry variable amounts of phosphate granules (Cayeux, 1935). 
 A dense, nodular, black limestone described by Cayeux from the boundary zone be- 
 tween the Upper and Lower Cretaceous at Interlaken, Switzerland, contains abun- 
 dant quartz, glauconite, and phosphate. The lower twenty feet of the Colon Lime- 
 stone in Venezuela (Smith, 1951) is glauconitic, asphaltic, and highly pyritiferous. 
 Pfefferkorn and Urban (1957) noted that the "Grunsandstein" of Westphalia is actual- 
 ly a limestone containing about 10 percent quartz and 10 percent glauconite. 
 
 Tuffaceous Limestones 
 
 The Tertiary limestones of Saipan include relatively pure reef and detrital 
 bioclastic limestones, calcite-cemented conglomerates consisting of limestone 
 pebbles and cobbles and material of volcanic origin, and rocks containing from 20 
 to 80 percent bioclastic carbonate fragments set in a matrix of tuffaceous material, 
 quartz sand, and crystalline calcite (Cloud et al . , 1956; Schmidt et al . , 1957). 
 Volcanic material typically makes up 3 to 5 percent of the Saipan limestones, but 
 may reach 12 to 15 percent. When these rocks are exposed to weathering, recrys- 
 tallization starts in the groundmass and the volcanic ash is altered to clay. 
 
 Ladd and Hoffmeister (1945) found at Lau, Fiji, all gradations between lime- 
 stone, limestone containing water-worn grains of volcanic detritus and clay derived 
 from weathering of volcanic material, and pyroclastic rocks. 
 
 Pyritic Limestones 
 
 Although many argillaceous and bituminous limestones contain some pyrite, 
 in other less common limestones it is a substantial constituent. The Top Jet Dogger 
 of the Upper Lias succession in Yorkshire is a thin, platy, argillaceous limestone 
 with coarsely crystalline lenses of calcite separated by irregular but laminated 
 layers of pyritic shale. Hemingway (1951) considered the bed to be a diagenetically 
 altered analog of the calcareous mud now forming in the western basin of the Black 
 Sea (see Archanguelsky, 1927). 
 
 The basal pyritic limestone bed of the Greenhorn Formation of- Upper Creta- 
 ceous age in the Black Hills, South Dakota (Rubey, 1930; analysis 72, Part IV), 
 contains, principally, Inoceramus shells and fine-grained calcite, pyrite (some 
 25 percent), and secondary gypsum and iron oxides probably derived from the pyrite. 
 The pyrite is minutely crystalline, forms nodules and coatings, and is intimately as- 
 sociated with unreplaced shell fragments and fine-grained CaC03. Rubey suggested 
 that water escaping upward from immediately underlying black shale during compac- 
 tion may have formed the pyrite. He noted that present-day oceanic blue muds con- 
 tain up to 35 percent CaCO^ but are reducing in character and contain sulfides and 
 H2S below the sediment-water interface (Murray and Renard, 1891; see also Murray 
 and Irvine, 1895, concerning the processes involved), so that the calcite-pyrite 
 association is not inconsistent. 
 
 The Pumpherston Shell Bed and the Pumpherston Oil Shales of Lower Carbon- 
 iferous age in Scotland contain large numbers (~1 x 10^/cm^) of pyrite grains 2 to 
 30 microns in size (Love, 1958). Microfossils, found only in pyrite grains, are 
 obtained by treating a concentrate of the pyrite grains with nitric acid. The size 
 distribution of pyrite grains virtually coincides with that of the microfossils, which 
 are believed to be actinomycetes rather than bacteria. The even lamination of the 
 oil shales indicates an anaerobic depositional environment free of bottom scaven- 
 gers, and the carbonate cementation that has occurred suggests a late-diagenetic 
 rise in pH . 
 
32 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 Phosphatic Limestones 
 
 The small percentages of phosphate found in most limestones are contributed 
 by detrital apatite, by either replaced or originally phosphatic fossils, and by detri- 
 tal phosphate grains and pebbles. The weakly phosphatic limestones are composi- 
 tionally quite distinct from phosphorites, for highly phosphatic limestones are rare. 
 This rarity is believed to result from the fact that carbonate can precipitate in the 
 ocean (with its present composition) only above a pH of 7.8, whereas apatite is 
 stable above a pH of 7 . (see discussion by Sheldon, 1959, p. 93). Carbonate- 
 poor phosphorites thus presumably form at a lower pH than phosphatic carbonate 
 rocks. Furthermore, the ratio of carbonate to apatite should be high when these 
 two materials coprecipitate (Krumbein and Garrels, 1952). 
 
 Fish remains and the shells of certain inarticulate brachiopods {Liniula sp., 
 Discina sp., Glottidia sp.) are the most important sources of organically deposited 
 phosphate, with lesser contributions from vertebrate bones, alcyonarians, crusta- 
 ceans, and conodonts (see also table 1). C. W. Collinson (personal communication) 
 estimated that there is a 50 percent chance of recovering 15 or more conodonts in 
 any 1000 grams of marine limestone of Ordovician through Pennsylvanian age in the 
 midwestern United States. Fifteen conodonts would correspond to about 1 ppm 
 Ca 3 (P0 4 ) 2 . 
 
 An original ecological control of phosphate content appears probable in some 
 limestones. The number of conodonts is greater in sponge-crowded habitats of the 
 interreef beds of Silurian age near Chicago than it is in sponge-poor areas (Lowen- 
 stam, 1948), and Liniula are restricted to the sponge-crowded areas. Lowenstam 
 suggested that putrification of inter-sponge passages by metabolism products of 
 sponges may have kept the number of sessile benthos associates lower than the 
 number of anchorage sites, allowing Liniula to move in. Willman (1943) stated 
 that the PoOc content °f the nearby reefs is often so slight as to be undetectable 
 in a 5-gram sample by conventional analytical methods. 
 
 Phosphate in the Cambrian and Ordovician limestones of Sweden occurs 
 almost always in beds that contain glauconite (Hadding, 1958). Hadding contrasted 
 these limestones with others rich in organic matter and clay that usually do not 
 contain phosphate. He supposed that relatively agitated water in the depositional 
 environment had removed bituminous muds from the phosphatic-glauconitic lime- 
 stone sediment. This concept has been substantiated by the recent oceanographic 
 work of Emery (1960) and others (see discussion of carbonate sediments). 
 
 Determinations of phosphorus (0.005 to 0.136 percent) and iron (0.15 to 
 3.22 percent) in some 380 argillaceous limestone samples from the Lower Malm of 
 southern Germany (Seibold, 1955) show a pronounced negative correlation between P 
 and CaC03 and between Fe and CaC03. There is a distinct positive correlation 
 between P and Fe. The P/Fe ratio has a mean value of 0.046 but shifts progressive- 
 ly to higher values as CaC03 content increases. Part of the iron is present as 
 sulfide, but an iron content in the clay minerals and the presence of iron carbonate, 
 silicate, or oxide are suggested to account for the remainder. 
 
 Erosion remnants of the phosphatic, glauconitic chalk of Senonian age at 
 Taplow, England, contain phosphate as bones, teeth, fish scales, and phosphatized 
 coprolites and foraminiferal tests, and as a veneer coating nodules and rock bands 
 (Willcox, 1952). The fossils are like those in normal chalk but much more abundant. 
 Petrographic evidence argues against the deposit's being merely current- sorted 
 phosphatic debris. A locally flourishing community of organisms is postulated in 
 a nutrient-rich zone where the bottom currents were deflected upward by a sub- 
 marine ridge, and where a trough provided tranquillity for phosphate accumulation. 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 33 
 
 Two thin, areally extensive beds in the limestone of the Delaware Forma- 
 tion of Middle Devonian age in central Ohio contain abundant crinoid fragments and 
 fish teeth and plates, often worn and rounded (Westgate and Fischer, 1933). An 
 analysis of one of the beds gave 16.80 percent Ca^{PO^)2> 73.27 percent CaC03, 
 4.97 percent MgCOo, 2.46 percent iron oxides, and 2.14 percent SiO^, for a total 
 of 99.61 percent (Orton, 1878). 
 
 Both bone beds and phosphate pebble concentrations often occur as basal 
 conglomerates on old erosion surfaces, and are accompanied by pyrite and Mn- 
 oxide stain (Pettijohn, 1926). Phosphate pebbles occur in carbonate rocks, above 
 and below the phosphate zone, near the Quadrant-Phosphoria boundary in southern 
 Montana . Many are found in the Noix Oolite Member of the Edgewood Formation 
 of Silurian age in Illinois (Rubey, 1930). Phosphate pebbles and grains occur scat- 
 tered throughout the Middle Miocene Hawthorn Formation of Alachua County, Florida 
 (Pirkle, 1957), which is a variable mixture of sand, clay, and carbonate, any one 
 of which may predominate locally. The phosphate particles include replaced fossils 
 and fragments of impure limestone, aggregated masses and concretionary oolites, 
 and phosphate filling organic cavities, such as bryozoan chambers. 
 
 A Cretaceous chalk near Mons and Liege in south Belgium contains numerous 
 small phosphatic concretions "no larger than a mustard seed" that in many places 
 form 10 percent of the rock (McCallie, 1896). The phosphatic limestone of the 
 Bigby Formation of Tennessee contains worn and rounded fragments of small bryozoa 
 and perhaps crinoid stems, in all stages of replacement by phosphate, set in fine- 
 grained calcite (Whitlatch and Smith, 1940). Partial replacement of the fossils in 
 a phosphate-rich environment before consolidation of the rock is indicated. In 
 two areas the Bigby Limestone and part of the Leepers Limestone average 15 to 20 
 percent Ca3(PO^)2; darker streaks have 40 percent or more. Thin beds of dark, 
 greenish gray, silty dolomite in the Plympton Formation of Permian age in west- 
 central Utah contain as much as 20 percent collophane as minute pellets and inter- 
 stitial fillings (Hose and Repenning, 1959). 
 
 In cherty argillaceous limestone layers in the La Caja Formation of Jurassic 
 age in Zacatecas, Mexico, containing 10 to 15 percent P2O5, the chert appears 
 mainly to be replacing the phosphate (see also analysis 69, Part IV). This forma- 
 tion shows marked variation in thickness and contains terrestrial reptile remains, 
 conglomerate units, and, in some units, cup-shaped gastropods and abundant 
 ammonites; benthonic mollusks are rather scarce. A muddy environment and not 
 too great a depth of water are suggested (Rogers et al., 1956) . 
 
 Unconsolidated lime sands and gravels in the northern Marshall Islands 
 are overlain locally by a consolidated 5 to 15 cm bed containing from 2.7 to 14 
 percent P (Fosberg, 1957). X-ray diagrams show the presence of an apatite that 
 both fills interstices and replaces CaC03. The phosphatic limestone occurs only 
 under humus-producing Pisonia grandis trees, which are a favorable nesting site 
 for sea birds. Finely divided calcium phosphate in the guano is dissolved by rain- 
 water enriched by humic acids and then precipitated when the solution is neutral- 
 ized by the limestone below. McConnell (1943) described replacement of bio- 
 clastic limestone at Malpelo Island, Colombia, by phosphatic solutions derived 
 from the leaching of superficial guano deposits. 
 
 Hutchinson (1950) concluded after a broad survey of guano deposits that 
 rainfall must be less than 1500 mm a year to allow a consolidated phosphatic zone 
 to form in underlying rock or soil, and less than 1000 mm a year to permit the 
 formation of a major deposit. 
 
34 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 Carbonate Rocks Containing Organic Material 
 
 The Avon Park Limestone of Eocene age in Citrus and Levy Counties, Flori- 
 da, is a virtually unaltered sediment of unconsolidated calcareous mud with lamina- 
 tions of carbonaceous matter, much of which appears to be branches of land plants 
 (Fischer, 1949). Sediments like this are found today in shallow, protected waters 
 around mangrove islands in Florida Bay. 
 
 The rather common, dense, sparingly fossiliferous limestones rich in organic 
 matter and often in pyrite are interpreted by Sloss (1947) as having formed at depth 
 in areas where impeded circulation inhibited bacterial decay and was inhospitable 
 to the existence of benthonic organisms. These rocks, according to Sloss, contain 
 abundant chert but are rarely dolomitized. Pennsylvanian and Permian limestones 
 of this type, such as the Bone Spring Limestone of the Permian age Leonard Series, 
 occur interbedded with dark shales and silts in basinal off-reef areas in west Texas 
 (King, 1942; Adams, 1951). The fauna in the Bone Spring Limestone is a character- 
 istic pelagic one consisting mainly of ammonites, which could float at the surface 
 and whose shells could float and drift after death. These basins were surrounded 
 by epicontinental shelves furnishing but little sediment. 
 
 Newell et al. (195 3) presented a monographic study of the Permian reef 
 complex of Texas and New Mexico, with references to other fossil reefs in England, 
 Greenland, and the Italian Tyrol that lie along the borders of euxinic basins. Some 
 95 percent of the black, pyritic, bituminous limestones of the Delaware Basin, such 
 as the Bone Spring, are divided into light and dark laminae 0.1 to 3.0 mm thick. 
 Some of the finer grained dark laminae contain up to 30 percent by volume of siliceous 
 sponge spicules, many of which have been replaced by calcite . Spicule sorting is 
 indicated by parallel alignment of spicules and by the fact that adjacent laminae 
 show differences in mean spiculite size. Organic matter is tightly sealed in voids 
 and is believed to have been emplaced before the matrix lost its connate water. The 
 content of organic matter insoluble in organic solvents ranges from 0.10 to 1.76 
 percent. 
 
 Newell et al. believed that fluids driven out of the basin sediments by cal- 
 cite cementation played a role in the several marginward diagenetic effects observed. 
 Macroscopic fossils toward the basin margin, near the outer edge of the reef talus, 
 are replaced by silica. Chert is very frequently associated with spiculites and is 
 localized along noses of primary fold structures. The preferential replacement by 
 silica of fossils rather than mud, and of certain types of fossils rather than others, 
 does not appear to be a simple function of porosity or of the original content of 
 aragonite. Dolomitization is significant only toward the basin margins, and in 
 some horizons there is a marked replacement of foraminifera and bryozoa in prefer- 
 ence to the matrix. A flood of secondary calcite cement also occurs toward 
 the basin margin. 
 
 Another carefully studied suite of bituminous carbonate rocks is that con- 
 tained in the Green River Formation, a series of lacustrine beds of Eocene age some 
 1500 to 2000 feet thick that today occupy several basins in Colorado, Wyoming, 
 and Utah. Deltaic and fluvial sands and shales are followed basinward in turn (1) 
 by a freshwater shore facies of reefs and algal limestones containing caddis fly 
 larval cases, freshwater mollusks, and an abundance of ostracodes (Bradley, 1925); 
 (2) by muddy limestones and limy mudstones; (3) by the so-called oil shale and its 
 somewhat more saline facies. All of these rocks have high carbonate contents; 
 Hunt et al. (1954) estimated that the limestones typically contain 82 percent car- 
 bonate as calcite, the saline "oil shales" and the marlstones of the "oil shales" 
 have 52 to 55 percent as dolomite (analyses 73, 74, Part IV), and the platy and 
 so-called Mahogany oil shales, 42 to 43 percent as dolomite. 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 35 
 
 The marl stones of the Green River Formation are varved and contain light 
 colored layers rich in microgranular carbonate and dark colored layers with abundant 
 organic matter. Studies of modern varved sediments from Lake Zurich (Nipkow, 1927) 
 and other localities described in Circular 297, the first of this series, indicated that 
 the Green River varves probably are annual, with carbonate precipitated at the sur- 
 face by summer warming and photosynthesis. The presence of perfectly preserved 
 fossil fish in the varved sediments, contrasted with the broken and chewed-up bones 
 in the nonvarved sediments, indicates that the former were deposited in a stagnant 
 bottom zone free of scavengers or bottom feeders. The remarkable suite of authigenic 
 minerals in the "oil shale, " described in Part III of this series, indicates that the 
 lake waters at times must have been highly mineralized. 
 
 The organic matter in these beds, which at places is as much as 80 percent, 
 is relatively rich in fatty and waxy matter, high in C and H and low in O. Bradley 
 (1925) believed that it was derived almost entirely from plankton, for peat bogs are 
 inconspicuous around the shore and there are no remains of large plants. The summer 
 temperature maximum indicated by the larger land plants, insects, and animals would 
 have been high enough to support a bloom. 
 
 "Oil shale" has been described from various other localities. That from Um 
 Barek, Israel, is of Senonian age and contains 50 to 60 percent carbonates, mostly 
 calcite, 15 to 20 percent silica and silicates, 1 to 4 percent P„0 , 2 to 7 percent 
 R2O0 (mainly AUO3), 1 percent pyrite, 0.002 to 0.003 percent uranium, and from 4 
 to 25 percent total organic matter, mostly kerogen. The ultimate composition of the 
 kerogen, estimated from total organic content and amount and elemental analysis of 
 the assay products is C, 69.1; H, 8.6; N, 1.9; S, 11.0; O, 9 . 4 percent by differ- 
 ence. The more calcareous beds (Stinkschiefer) of the Posidonia bituminous shales of 
 Liassic age in Swabia, Germany, consist of alternate light and dark units 1 mm 
 thick, and contain 70 to 86 percent CaCO~ and as much as 7 percent organic matter 
 (Einsele and Mosebach, 1955; Wunnenberg, 1950). 
 
 The occurrence of free bitumens in carbonate rocks has been recorded from 
 widely separated localities. Petrographic descriptions of chemically analyzed 
 Scottish carbonate rocks (Geol. Survey Great Britain, 1956) include numerous cases 
 in which there is observable bituminous matter interstitial to carbonate grains or 
 mixed with accessory clay. Henson (1950) mentioned two fossil reefs of the Lower, 
 Middle, and Upper Cretaceous in the Middle East that are highly bituminous at their 
 outcrops. Reefs in this area pass through transition beds of reef detritus, which are 
 bituminous if porous, into basinal anhydrites and Globiierina facies that are in part 
 bituminous . 
 
 The organic material in Upper Jurassic bituminous limestones in the southern 
 Jura region of eastern France consists principally of pseudoasphaltenes and resins 
 and has high acidity and sulfur content (Gubler and Louis, 1956). The Seefelder 
 marls of the Tyrol region are a sapropel facies with some layers containing up to 20 
 percent by weight of organic substances (Fischer, 1957). Swain (1958) gave detail- 
 ed information about extracts, obtained by leaching of Middle Devonian limestones 
 of the Mount Union area, Pennsylvania, with various solvents. 
 
 Viscous to solid organic matter has been observed coating cavities of var- 
 ious sorts in Mississippian and Pennsylvanian limestones of western Missouri 
 (Searight, 1957), Niagaran age limestone at Monon, Indiana, and the South Canyon 
 Creek Dolomite Member of the Pennsylvanian and Permian (?) Maroon Formation at 
 Glenwood Springs, Colorado (Bass, 1950). Schoch (1918) gave partial chemical 
 analyses of a porous coquina, the Anacacho Limestone of Uvalde County, Texas, 
 and of a Comanchean age limestone of Burnet County, Texas, which were impregnated 
 
36 
 
 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 with 14.00 and 10.30 percent bitumens, respectively. Anthraxolite, a carbonaceous 
 material similar to anthracite, occurs disseminated or in vugs, fractures, and within 
 quartz crystals in the Upper Cambrian and Lower Ordovician dolomites of the Mohawk 
 Valley, New York (Dunn and Fisher, 1954). A typical ultimate analysis is C, 90.42 
 percent; H, 3.94 percent; O, 3.42 percent; N, 1.30 percent; S, 0.57 percent; and 
 ash, 0.35 percent. The occurrence of asphalt in porous areas of the reefs of the 
 Chicago area is common (Willman et al . , 1950). 
 
 Table 4. -" Organic Content of Some Carbonate Rocks 
 [After Hunt and Jamieson, 1956. The values of barrels per 
 acre foot originally reported have been converted to ap- 
 proximate values of parts per million by multiplying by 
 the factor 41.7. ) 
 
 Stratigraphic 
 
 Hydrocarbons 
 
 Asphalt 
 
 Kerogen 
 
 Age and 
 
 unit 
 
 (ppm) 
 
 (ppm) 
 
 (ppm) 
 
 location 
 
 Amsden (limestone) 
 
 8.3 
 
 8.3 
 
 290 
 
 Mississippian-Penn- 
 sylvanian, Wyoming 
 
 Smackover (limestone) 
 
 87. 
 
 83. 
 
 460 
 
 Jurassic, Arkansas 
 
 Dundee (dolomitic lime- 
 
 87. 
 
 100. 
 
 1900 
 
 Devonian, Michigan 
 
 stone) 
 
 
 
 
 
 Greenfield (argillaceous 
 
 120. 
 
 150. 
 
 1200 
 
 Silurian, Michigan 
 
 dolomite) 
 
 
 
 
 
 Reed City (dolomite) 
 
 280. 
 
 170. 
 
 960 
 
 Devonian, Michigan 
 
 Phosphoria (carbonaceous 
 
 290. 
 
 580. 
 
 2400 
 
 Permian, Wyoming 
 
 dolomite) 
 
 
 
 
 
 More finely distributed organic matter, however, has been found in carbon- 
 ate rocks. Hunt and Jamieson (1956) found that organic matter and, in most cases, 
 elemental sulfur could be extracted from nonreservoir rocks showing no evidence of 
 oil under close microscopic examination, by micronizing the samples to a particle 
 size of 15 microns and refluxing with selected mixtures of solvents. The results for 
 carbonate rocks are given here as table 4, in which hydrocarbons are defined as that 
 part of the total refluxed extract eluted from an activated alumina column with hep- 
 tane and benzene, minus free sulfur. The nonhydrocarbons (asphalt) are the total 
 extract minus hydrocarbons, sulfur, and ash. The organic matter insoluble in the 
 reflux mixtures (kerogen) is estimated as the organic carbon in the extracted rock 
 times an empirical factor, 1.22. The hydrocarbons are similar in physical and chem- 
 ical properties to natural crude oils, differing only in that their initial boiling point 
 is 400° to 500°F. The kerogen from the Madison Dolomite has a H/C ratio of 0.68, 
 within the range for coals. Age and depth of burial do not seem to have affected the 
 distribution of types of organic matter present. Further work by Forsman and Hunt 
 (1958) showed that there are two kinds of kerogen, one coal-like and the other more 
 like the material from oil shale, as well as gradations between these types (see 
 table 5). These kerogens are found in marine shales and limestones of various ages. 
 The kerogen type appears to be controlled by depositional environment and by sub- 
 sequent metamorphism. 
 
 Philippi (1957) found small amounts of hydrocarbons, generally ranging from 
 5 to 5000 ppm, in dense sediments, including marls and argillaceous limestones. 
 He stated that the indigenous hydrocarbon content can be recognized by the pro- 
 portionality between it and the total organic content and that apparently only a small 
 part of the oil generated by the source beds is released to reservoirs. 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 
 
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38 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 Lucas (1952) isolated from fetid limestones a volatile, water-soluble sub- 
 stance containing phosphate and ammonia, but no sulfur, which he believed to be 
 similar to the phosphenates . 
 
 The principal carbohydrate that has been isolated from fossils is cellulose 
 (Abelson, 1959b). Abderhalden and Heyns (1933) also identified chitin in a fossil 
 coleopteron from the Middle Eocene. It appears that relatively impermeable bio- 
 genic carbonate rocks that have had a sufficiently mild thermal history may still 
 contain measurable amounts of the amino acids originally present in skeletal ma- 
 terials. The various amino acids, following breakdown of the protein structure, 
 undergo thermal degradation even at earth-surface temperatures. The process is 
 accelerated by exposure to bacterial action, water, oxygen, and the aragonite-to- 
 calcite transformation or other recrystallization. 
 
 Conway and Libby (1958) measured the half-life for decarboxylation of 
 alanine, one of the thermally most stable amino acids, at temperatures down to 
 373 °K, using radioactive labeling and low-level counting techniques. The indicated 
 half-life at room temperature is about 10 10 years. Abelson (1954) obtained a value 
 of about 2 x 1()9 years by extrapolation of the decomposition rate of alanine in 
 aqueous solutions at a series of higher temperatures. If oxygen is present, carboxyl 
 carbon is released at a rate corresponding to a half-life of about 2x10^ years at 
 the same temperature . 
 
 The thermally more stable amino acids have been found in suitably preserved 
 fossils as old as Ordovician. An Ordovician brachiopod, Plaesiomys sub quadrat a , 
 from Wayne sville, Ohio, had 0.005 percent amino acids, and a plate from the armor 
 of the Devonian fish Dinichthys terellihad 0.03 percent (Abelson, 1957). Although 
 there are amino acids in ground water and it has been shown by Abelson that aspartic 
 and glutamic acids in particular are adsorbed by CaC03, differences in amino acid 
 content of different fossils from the same locality indicate that adsorption is prob- 
 ably only a minor contributing factor. 
 
 The organic matter, found in some stylolites mixed with clay (analysis 75, 
 Part IV) has been considered a concentrate of material originally disseminated in 
 the limestone, in view of the difficulty of introducing it later into such an impene- 
 trable host (Myers et al., 1956). 
 
 Intimately distributed organic matter is expelled into intercrystalline spaces 
 during calcium carbonate recrystallization and during dolomitization. Contacts be- 
 tween dolomitic rock and embedded algal nodules in the Lockport Dolomite of Silur- 
 ian age in Orleans County, New York, are marked by a zone of dolomite grains two 
 or three times the normal size, as well as by a band of organic matter expelled 
 during crystallization of the large grains (Cannon, 1955). Organic matter in dolo- 
 mitic rocks of the Phosphoria Formation in northwestern Wyoming is concentrated 
 into inclusions in the dolomite grains and crusts around these grains (Sheldon, 1957). 
 Folk (1958) observed 0.002-inch rims of organic matter around dolomite crystals 
 from rocks of Ordovician age in Pennsylvania. During the dolomitization of the 
 Metaline Limestone in northeastern Washington, the organic coloring matter was 
 expelled and, in places, it accumulated in vugs as rounded globules of anthracite 
 composition less than half an inch in diameter (Park, 1938). Some dolomites have 
 light and dark bands, generally less than half an inch thick. Analyses by R. C. 
 Wells of fine-grained black dolomites versus relatively coarser grained, lighter 
 colored dolomites are almost identical except for a small amount of organic matter 
 in the darker bands. Rejection of bituminous and argillaceous material during the 
 secondary growth of macroscopic calcite crystals in the Swedish anthraconites 
 (bituminous argillaceous limestones) has resulted in the interstitial concentration 
 of these materials (Hadding, 1958). 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 39 
 
 Oolites enclosed in a layer of dolomitic calcilutite described by Wherry 
 (1916) have light upper portions and dark lower portions rich in organic matter, with 
 nuclei occurring toward the bottom. Post-lithification solution of the aragonite of the 
 oolites apparently left a solution residue at the bottom of the voids, which were sub- 
 sequently filled by fine-grained secondary dolomite. 
 
 Chemical analyses show that the organic matter in siliceous Cretaceous 
 limestones from two localities in the French Pyrenees was not expelled or destroyed 
 during metamorphism of the limestones to hornstones. Small granules of organic 
 matter are enclosed in wernerite and diopside crystals. Louis and Ravier (1952) 
 found 1.43 percent organic carbon and 0.036 percent total nitrogen in a hornstone, 
 compared with 0.98 percent organic matter and 0.065 percent total nitrogen in the 
 unmetamorphosed equivalent. 
 
 Hunt (1953) attempted to correlate differences in crude oil types in Wyoming 
 with differences in depositional environment and thus of organisms contributing or- 
 ganic compounds to the sediment, but the problem in that area may be complicated 
 by migration, by differences in depth of burial, and by other post-depositional 
 changes. More positive results were obtained for the lacustrine carbonate rocks of 
 Eocene age in the Uinta Basin. The change in mineralogy of the basinward facies 
 in the Uinta Basin from calcite through dolomite to the sodium carbonates, proceed- 
 ing through the increasingly younger Wasatch, Green River, and Uinta Groups, was 
 taken by Hunt et al. (1954) to indicate a progressive change in salinity. The pro- 
 gressive change in hydrocarbons in these beds, from ozocerite to albertite to gilson- 
 ite to wurtzilite, represents an increase in N and S and in condensed ring structures 
 as opposed to chains. The parallel changes in the composition of organic and in- 
 organic materials indicate that the hydrocarbons have not migrated appreciably and 
 that progressive changes in the composition of the lake, and perhaps of the kinds 
 of organisms inhabiting it, are reflected in the hydrocarbon compositions now ob- 
 served, in spite of whatever post-depositional alteration may have occurred. 
 
 The median organic carbon content of 461 limestones from the United States 
 examined by Trask and Patnode (1942) was 0.49 percent, compared with 0.75 percent 
 for 2245 clastic rocks. The median C/N value for 492 limestones was 19.3, and for 
 2105 clastic rocks was 15.5. 
 
 Readily observable changes take place in the amount of organic matter and 
 FeO in limestones during weathering. In eastern South Dakota, black unweathered 
 chalk of the Niobrara Formation analyzed 10 to 11-j percent volatile matter, ex- 
 cluding CO2, and about 3 percent FeO. For the weathered white equivalent, the 
 comparable figures are about 1.5 percent and about 1 percent (Rothrock, 1931). 
 Partial analyses by W. A. Noyes (in Loughlin, 1930) of several samples of the well 
 known oolitic limestone at different quarries near Bedford, Indiana, gave for the 
 unweathered gray material 0.24, 0.21, and 0.22 percent organic matter; 0.067, 
 0.063, and 0.055 percent FeO; and 0.196, 0.044, and 0.089 percent Fe 2 3 . For 
 buff weathered equivalents at the same localities, the comparable values were 0.12, 
 0.11, and 0.13 percent organic matter; 0.050, 0.055, and 0.050 percent FeO; and 
 0.126, 0.150, and 0.119 percent Fe 2 3 . 
 
 Feldspathic Carbonate Rocks 
 
 Tester and Atwater (1934) found authigenic feldspar throughout all of the 
 Paleozoic, in shell-rich limestones as well as in recrystallized and dolomitized 
 rocks. Adularia, albite, and microcline were observed in various combinations, 
 either completely authigenic without cores, or overgrown upon detrital feldspar 
 
40 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 cores of the same or different minerals. Tiny secondary crystals of both albite and 
 potash feldspar were described by Trumpy (1916) from even younger rocks, the Ter- 
 tiary (Flysch) limestones of the western Rhatikon, Switzerland. 
 
 Authigenic feldspars from 40 localities, ranging in age from Precambrian to 
 Triassic, were studied by Baskin (1956), who found that these feldspars were ran- 
 domly distributed irrespective of fractures (see also Honess and Jeffries, 1940) and 
 rarely exceeded 2 percent of the rock. All carbonate rocks containing them had been 
 partially or completely recrystallized or dolomitized. Authigenic Na-feldspars were 
 found only in carbonate rocks (see also Flichtbauer, 1950), rarely had detrital cores, 
 unlike the K-feldspars, and were all low-temperature albite except for crystals 
 structurally intermediate between albite and analbite, which were found at one lo- 
 cality. The majority of the potash feldspars were monoclinic . 
 
 Authigenic feldspars have idiomorphic crystal shapes, are nonperthitic, and 
 show fourling twinning never observed in nonauthigenic microcline or in albite crys- 
 tals formed at higher temperatures than those at which authigenic feldspars crystal- 
 lize. They are remarkably pure, as would be expectable from the K-feldspar — Na- 
 feldspar immiscibility gap at low temperatures. Authigenic potash feldspars rarely 
 contain more than 0.3 percent Na20 (2 mol percent albite), and the K2O and CaO 
 contents of Na-feldspars rarely exceed 0.4 percent (3 mol percent K-feldspar) (see 
 also Honess and Jeffries, 1940) and 0.2 percent (1 mol percent anorthite), respec- 
 tively. These feldspar crystals cut single crystal outlines of the carbonates and 
 contain carbonate inclusions, usually rounded. 
 
 At least two localities have been reported where authigenic potash feldspar 
 is a major constituent of carbonate rocks. The so-called Kristalltuff of Monte San 
 Giorgio (Tessin) contains about 40 percent feldspar and 60 percent limestone (Flicht- 
 bauer, 1950). Daly (1917) described an apparently unmetamorphosed Precambrian 
 dolomite from theWaterton Formation of Alberta that contained about 40 percent by 
 volume of disseminated, glassy, clear crystals (analysis 85, Part IV). 
 
 Fuchtbauer (1956) noted a correlation between the amount of authigenic K- 
 feldspar in the Muschelkalk of GOttingen and the amount of illite that is available 
 to furnish K^O for the reaction. There is no correlation between amount of clay 
 minerals and amount of authigenic albite, which Fuchtbauer (1950) believed formed 
 before complete lithification at a time when sea water was still available to furnish 
 sodium. Carozzi (1953) and Topkaya (1950) described similar relations. 
 
 Arkosic limestone of the Baum Member of the Paluxy Formation of early 
 Cretaceous age in southern Oklahoma consists of soft, fine-grained limestone 
 cementing the quartz and feldspar that overlie Precambrian granite (Wayland, 1954). 
 
 SEDIMENTARY SIDERITES AND FERROAN DOLOMITES 
 
 A number of relatively thin but laterally extensive Pennsylvanian limestones 
 have been observed to contain ferroan dolomite in samples taken over large areas. 
 Siever and Glass (1957) observed this phenomenon in the Cutler (Piasa), Galum, 
 and Bankston Fork Limestones of the Illinois Basin in Illinois, using a differential 
 thermal analysis technique by which the ferrous iron substitution in the dolomite 
 could be determined as less than or greater than about l\ mol percent. No correla- 
 tion with depositional facies could be established. 
 
 Miles (1958) made some 350 X-ray diffraction runs to study further the car- 
 bonate composition of the Bankston Fork, which is a thin, argillaceous, relatively 
 discontinuous, marine limestone of Pennsylvanian age in southern Illinois. The 
 ferroan dolomite in most cases makes up from 20 to 60 percent of the rock, calcite 
 is responsible for 50 to 70 percent, and siderite is relatively uncommon, constituting 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 41 
 
 only 10 to 20 percent of portions of the cores examined. The siderite is present as 
 disseminated crystals, spherulitic masses 10 to 20 microns in diameter, and patches 
 of very fine mosaic. 
 
 Thin beds and thin nodular zones rich in siderite are in general not uncommon 
 in Carboniferous rocks (Lowe, 1914; Edwards and Stubblefield, 1948; Crane, 1912; 
 Singewald, 1909, 1911; Scheere, 1955). Hunt et al. (1954) found minor amounts of 
 siderite in the bituminous lacustrine beds of the Green River Formation in the Uinta 
 Basin, and commented that the dolomites of this formation are ferroan. Rubey (1930) 
 found abundant iron- stained concretions and thin beds of siderite in the Pierre Shale 
 of late Cretaceous age in the Black Hills region. He also described (1952) nodular 
 sideritic beds a few inches thick interlaminated with calcareous shales in the lower 
 and middle portions of the Maquoketa Formation of Ordovician age in Illinois. Re- 
 fractive index determinations show that the dolomite in a number of analyzed Scot- 
 tish carbonate rocks is ferroan (Geol. Survey Great Britain, 1956). Spherules of 
 kaolinite about 0.5 mm in diameter and containing small lenticular apatite crystals 
 occur in a microgranular siderite rock described by van Tassel (1955). 
 
 Lenticular and interbedded masses of siderite in irregularly shaped bodies 
 of bauxite in the Eocene age Ackerman Formation are thought (Burchard, 1924) to 
 have formed in a peat swamp environment (see also Mead, 1915). The iron carbonate 
 ore described by Burchard (1915) in northeast Texas, apparently derived from glauco- 
 nite in Eocene rocks, is one of a number of Tertiary glauconite- siderite ores on the 
 Gulf Coast. 
 
 Mansfield (1922) described a 6-foot bed of hardpan, composed largely of 
 iron carbonate and containing scattered grains of glauconite, from the Hornerstown 
 Formation of Upper Cretaceous age in New Jersey. Rolshausen (1934) encountered 
 a zone of siderite with minor impurities in the caprock at Carlos Dome, Grimes 
 County, Texas (analysis 93, Part IV), associated with quartz, sphalerite, and 
 galena . 
 
 The Mesozoic sedimentary iron ores of England and Western Europe include 
 a number of unusual rock types made up of varying proportions of chamosite, calcite, 
 siderite, and iron oxides formed by oxidation of the chamosite and siderite (analyses 
 94-96, Part IV). Well defined beds in which oolites and shell fragments are heavily 
 pyritized also occur there. The existence of current bedding, pebble beds, oolites, 
 and a normal shallow-water marine fauna, together with lateral transitions to sand- 
 stone, indicate marine deposition (the Yorkshire Lias, for example) in a basin or 
 lagoon of limited extent (Rastall and Hemingway, 1940; Hemingway, 1951; Rastall 
 and Hemingway, 1941; see, more generally, Hallimond, 1925; Cayeux, 1909, 1922). 
 The chamosite in such sedimentary ironstones has been shown to be a member of the 
 kaolin group having a virtually trioctahedral structure, typically with 2.9 octahedral 
 sites out of 3 occupied by Fe, Mg, or Al (see references in Youell, 1958). 
 
 The siderite widely distributed in Devonian rocks in the Bashkirian A.S.S.R. 
 (Florenskij and Bal'shina, 1948) also is mixed with chamosite oolites, in addition 
 to detrital minerals and lesser amounts of pyrite, marcasite, and sphalerite. Rocks 
 containing from 50 to as much as 70 percent siderite have been described (analysis 
 92, Part IV). 
 
 The preservation of fine bedding and slump structures, constancy of chem- 
 ical composition, and presence of fragments of each rock type in intraformational 
 breccias and clastic dikes argues for a primary rather than a replacement origin for 
 the interlaminated chert, siderite, and other rock types in the Precambrian of the 
 Iron River District, Michigan (James, 1951). The rocks have been intensely deformed 
 structurally but only slightly metamorphosed. 
 
42 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 298 
 
 SEDIMENTARY MAGNESIUM CARBONATE DEPOSITS 
 
 Longwell (1928) and Rubey and Callaghan (1936) described magnesium car- 
 bonate beds of limited lateral extent in the almost fossil-free Horse Springs Forma- 
 tion of Miocene age in the Muddy Mountains of Nevada. The 1- to 2-micron particles 
 of magnesium carbonate make up a dense, white rock that is interbedded with almost 
 indistinguishable dense, clayey dolomite, and is associated in the formation with 
 beds of gypsum and other salines, volcanic ash, colemanite-bearing clays, and 
 argillaceous sandstones. The exceedingly fine grain size of the carbonates, excel- 
 lent preservation of all details of depositional bedding, concordance and diverse 
 composition of successive beds, and uniform composition of individual beds traced 
 laterally argue for a sedimentary origin in an inland lake enriched in Mg. 
 
 Similar magnesium carbonate beds from Bissel, California (Gale, 1914; 
 Rubey and Callaghan, 1936) are limited to certain basinal areas and associated with 
 thin, hard beds of dolomite and dark, silty clay. Small surface deposits up to 18 
 acres in extent at Atlin, British Columbia (Gwillim, 1899; Young, 1916; Bain, 1924), 
 and Bannock County, Idaho (Yale and Stone, 1923), are made up of white, powdery 
 magnesium carbonate. Bedded magnesium carbonate at Needles, California, makes 
 up a thin lens enclosed in Tertiary volcanic and sedimentary rocks. These Tertiary 
 rocks include beds of dolomite, some of which contain uniform, continuous, cherty 
 layers up to a tenth of an inch thick (Vitaliano, 1950). 
 
 These several materials are surely sedimentary magnesium carbonates (anal- 
 yses 22, 23, 85, Part IV), although the possible effect of associated volcanic ac- 
 tivity on the composition of the waters in some of the lakes involved is not known 
 and the mineralogy remains to be worked out. The general failure of (MgO + CaO) 
 to balance CO2 in some of these analyses has led, depending upon the amount of 
 water present, to two assumptions: the magnesium carbonate is hydromagnesite, or 
 hydrous magnesium silicate is present. 
 
 Magnesite, identified by partial chemical analyses, indices of refraction, 
 and a positive reaction to the diphenylcarbazide test reaction, occurs as micro- 
 layers and isolated well defined masses in a number of Lower Permian anhydrites 
 of the Volga region (Frolova, 1955). The highest concentrations of magnesite are 
 restricted to anhydrite rocks containing chlorides. A thin-bedded, anhydrite-bear- 
 ing magnesite horizon having regional distribution contains up to 75 wt percent 
 magnesite, as computed by Frolova from the analytical data shown as analysis 88 
 in Part IV. The rock described by Hartwig (1955) from the Rhon region of West 
 Germany (analysis 91, Part IV) is, on the basis of chemical analysis and X-ray 
 diffraction data, about one-third halite and two-thirds magnesite, the latter apparent- 
 ly containing as much as 15 mol percent FeC03 in solid solution. 
 
 Brown layers a few millimeters thick and consisting largely of magnesite are 
 frequent in the Upper Evaporite Bed, Eksdale No. 2 boring, east Yorkshire (Stewart, 
 1951b). A carbonate, identified as magnesite by its refractive indices and difficult 
 solubility in acid, occurs in anhydrite and polyhalite of the Permian potash field of 
 New Mexico and Texas (Schaller and Henderson, 1932) as disseminated crystals and 
 layers up to an inch thick. All gradations between almost pure magnesite and almost 
 pure clay are present. Clear, glassy, authigenic crystals of magnesite several 
 millimeters long have been described from a dolomitic outcrop sample of the Eocene 
 age Green River Formation in Utah (Milton and Fahey, 1960). Magnesite crystals 
 1 by 5 mm in size, often stained with petroleum or asphalt, were described by 
 Lonsdale (1930) from a cherty dolomitic limestone of Permian age encountered in 
 drill cores. An analysis of the crystals by P. J. A. Zeller gave MgO, 47.24; CaO, 
 1.47; FeO, 1.67; CO2, 49.49; total, 99 . 87 percent . 
 
GEOCHEMISTRY OF SEDIMENTARY CARBONATES - II 43 
 
 Beds of magnesite several feet thick, interbedded with dolomitic shale, 
 chert, and tillite in the Lower Adelaide System of Precambrian age, are consistent 
 in thickness and composition over many miles of lateral distance in South Australia 
 (King, 1956). Aside from variable amounts of chert and minor quartz veins, impurities 
 in a typical case might be MnO, 0.06 percent; Fe^O.,, 0.8 percent; Al„Oo, 0.9 per- 
 cent; CaO, less than 1 percent. There is disseminated talc in some samples. 
 
 Well crystallized magnesite from the Pyrenees (Gomez de Llarena, 1950) 
 is now interbedded with limestone, dolomite, schist, and graywacke, but ripple- 
 marked surfaces are preserved and an original lacustrine precipitation of magnesium 
 carbonate is postulated. Donath (1957) described bitumen-containing magnesite 
 of the Bela Stena deposit, Serbia, which is interbedded with sandstones, marls, 
 and clays in a faulted basin. The magnesite at Ajani is associated with impure 
 dolomite in an essentially undisturbed young Tertiary sedimentary succession. 
 There is serpentine in both regions from which Mg-rich solutions in the depositional 
 basins could have been derived. 
 
 SEDIMENTARY MANGANESE CARBONATE DEPOSITS 
 
 The examples of sedimentary manganese carbonate that can be cited all 
 occur in beds that are now somewhat metamorphosed, but the authors who have 
 described the deposits do not believe that the metamorphism was severe enough to 
 mask the fundamentally sedimentary nature of the MnCO~ formation. 
 
 The MnCOo-rich beds in the nonfossiliferous Lower Cambrian of North Wales 
 (Mohr, 1956) are intercalated in blue-gray shales and have been subjected to low- 
 grade metamorphism. They typically contain subordinate quartz and 50 to 55 percent 
 spessartite, believed to have formed by reaction of clay and siliceous material with 
 fine-grained MnCOo (analysis 97, Part IV). 
 
 On the Avalon Peninsula of southeast Newfoundland, interbeds of mangan- 
 iferous carbonate, manganese oxide, and associated barite, hematite, and calcium 
 phosphate are found in Cambrian shales (analysis 98, Part IV) (Dale, 1915; Hanson, 
 1956). Similar thin layers are found in southeast New Brunswick, near Woodstock, 
 interbanded with sharply folded slate, clastic sedimentary rocks, and hematite of 
 Silurian age (Anderson, 1954). 
 
 Thinly laminated beds of Silurian (?) age including argillite, slate, hematitic 
 ironstone, and siliceous carbonate rocks containing ferrous chlorite, ferroan rhodo- 
 chrosite, and some calcic manganiferous carbonate are found in a belt some 65 miles 
 long in Aroostook County, Maine (Crittenden, 1956; White, 1943). Radugin (1940) 
 described a bed in the Cambrian section on the Usa River in the Kuznetsk Alatau 
 (Siberia) that is a white to gray, fine-grained, rhodochrosite marble containing 32 
 to 34 percent Mn. Crushed diabase dikes and massive porphyrite are present in 
 the section. 
 
 Illinois State Geological Survey Circular 298 
 43 p., 6 figs., 4 tables, 1960 
 
nnmni 
 
 CIRCULAR 298 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 URBANA