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Geochemistry of Minor Elements in
the Monterey Formation, California:
Seawater Chemistry of Deposition

By D.Z. Piper and CM. Isaacs

 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1566

 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995

US. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

For sale by
US. Geological Survey, Map Distribution
Box 25286, MS 306, Federal Center
Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only
and does not imply endorsement by the U.S. Government.

Text and illustrations edited by George A. Havach

Library of Congress Cataloging-in-Publication Data

Piper, David Z.

Geochemistry of minor elements in the Monterey Formation, California: seawater chemistry of decomposition / by D.Z. Piper and

CM. lsaacs.
p. cm. — (U.S. Geological Survey professional paper; 1566)

Includes bibliographical references (p. 36—41)

Supt. ofDocs. no.: I 19.1611566

l. Geochemistry—Califomia—Monterey Formation. 2. Geology, Stratigraphic—Miocene. 3. Monterey Formation (Calif). l. lsaacs,
Caroline M. II.T1tle. III. Series.
QE515.P54 1995
551.46'083432—dc20 95-31300

CIP

MMPP’PI‘

CONTENTS

 
 
 
  
 

14
17
18

21
24

25

26
27
28
29
29
3 1
34

PPN?‘

Abstract ..................................................................................................................... 1
Introduction ................................................................................................................. 1
Analytical procedures ................................................................................................ 2
Review: Elemental sources—the modern ocean ..................................................... 2
Detrital source .................................................................................................... 7
Marine source ....................... 7
Biogenic source ............ 7
Hydrogenous source ..... 11
Diagenetic overprint ................................................................... 18
Results: Elemental host phases—the Monterey Formation ............ 19
Detritus ........................................................................................ 20
Carbonates .................................................................. 20
Sulfur phases ...................................................................................................... 20
Organic matter .................................................................................................... 20
Apatite ................................................................................................................. 23
Miscellaneous ..................................................................................................... 28
Discussion: Elemental sources—the Monterey ocean ............................................ 28
Terrigenous source ............................................................................................. 30
Marine source ..................................................................................................... 30
Paleoceanography ............................................................................................... 35
Conclusions ................................................................................................................. 35
References cited ......................................................................................................... 36
FIGURES
Stratigraphic sections of the Monterey Formation at Naples Beach and Lions Head, Calif .....................
Plots of intraelement ratios for Fe203, Cr, and Ba ........................................................................................
Schematic diagram illustrating seawater and sediment chemistry in shelf and basin environments ........
Chart showing generalized summary of elemental accumulation in marine sediment .............................
Zn:Cu interelement ratio in modern marine organic matter and sediment ..................................................
Plots of:
6. Contents of selected major—element oxides and minor elements versus detritus content .................
7. Contents of organic matter, Fe203, and Ba versus S content ..............................................................
8. Contents of selected minor elements versus organic-matter content, with samples grouped
by lithology ..........................................................................................................................................
9. Contents of selected minor elements versus organic-matter content, with samples grouped
by site ...................................................................................................................................................
10. Contents of selected minor elements versus apatite content ................................................................
11. Rare-earth-element patterns of samples .................................................................................................
12. La content and Ce anomaly versus apatite content ...............................................................................
13. Cr versus organic-matter contents ..........................................................................................................
14. Contents of selected minor elements versus Cu content ......................................................................
15. Cd versus Cu contents .............................................................................................................................
TABLES
Major-element—oxide contents in the Monterey Formation ...........................................................................
Minor-element contents in the Monterey Formation .....................................................................................
Correlation coefficients for major-element oxides in the Monterey Formation ..........................................

Correlation coefficients for selected minor elements in the Monterey Formation ......................................

Coo-Aw

I—lt-d
{"PEO?°>'

CONTENTS

End-member major-element-oxide and minor-element contents in sedimentary fractions of the

Monterey Formation in comparison with standards ..... ' ..........................................................................

Major components in sedimentary rocks of the Monterey Formation at Naples Beach and

Lions Head, Calif ......................................................................................................................................
Weight ratios of minor elements to Fe in fecal matter, shale, and plankton ...........................................
Minor-element contents in organic matter and seawater ...........................................................................
Half-cell reactions, assuming equilibrium conditions ................................................................................
Correlation coefficients for major components and minor elements in the Monterey Formation .............

Factor analysis for major components in sedimentary rocks of the Monterey Formation,

using the computer program Statview II (oblique-solution primary-pattern matrix) ..........................

11

12
12
12
15
22

23

Geochemistry of Minor Elements in
the Monterey Formation, California:
Seawater Chemistry of Deposition

By D.Z. Piper and CM. Isaacs

ABSTRACT

We have analyzed samples of the Monterey Formation
of southern California, collected at one site in the Santa
Barbara-Ventura Basin and at another in the Santa Maria
Basin, for maj or-element oxides and minor elements. Agree—
ment between the analyses by three different laboratories,
using three different methods, is excellent. These analyses
allow identification of the following host phases for minor
elements: terrigenous quartz, clay minerals, and other A1
silicate minerals (detrital fraction), and biogenic silica, cal-
cite, dolomite, organic matter, and apatite (marine fraction).
Part of the marine fraction of minor elements also might be
present as sulfides, but we have no evidence for the presence
of this phase, except for pyrite.

The current minor—element contents in the marine frac-
tion alone required, at the time of deposition of the sediment
in these two basins, a moderate level of primary productiv-
ity in the photic zone (Cd, Cu, Fe, Mo, Se, Zn) and denitrify-
ing bacterial respiration in the bottom water (Cr, V, and rare-
earth elements). We interpret the absence of any enrichment
in Cu, Cd, Se, Mo, and Zn above that provided by accumu-
lating organic matter to preclude the establishment of sul-
fate reduction in the water column.

INTRODUCTION

The geochemistry of sedimentary formations composed
of the four units organic-carbon-enriched mudstone, lime-
stone and dolomite, chert and porcellanite, and phosphorite
have been widely studied because of (1) their oil-source and
reservoir potential (Waples, 1983), (2) their source of phos-
phate for fertilizers, and (3) the information that their
geochemistry might shed on paleoceanography. For example,
Cook and Shergold (1986) and Donnelley and others (1988)
suggested that this suite of rocks accumulates during times
of oceanic anoxia (seawater sulfate reduction), a seawater
chemistry that may contribute to the preservation of organic
matter in marine sediment and, ultimately, to the formation

of major oil deposits (Demaison and Moore, 1980; Jenkyns,
1980; Schlanger and others, 1987).

The Miocene Monterey Formation in southern Califor-
nia, which is both a source rock and a reservoir rock for oil,
consists of these four units (Bramlette, 1946; Pisciotto and
Garrison, 1981; Isaacs and others, 1983) and has been inter-
preted as accumulating in an environment of intermittently
high primary productivity in the photic zone of the water
column (Blueford and Isaacs, 1989) and under anoxic con-
ditions in the bottom water (Bramlette, 1946; Govean and
Garrison, 1981). This interpretation was based largely on
the occurrence of finely laminated porcellanite and diato-
mite units in both the lower and upper parts of the formation
and on the exceptionally high organic-matter contents.

In this study, we examine the chemical composition
(major-element oxides, organic carbon, and minor elements)
of the Monterey Formation. The aim of our research is to
establish criteria, based on minor-element contents, for (1)
defining the approximate primary productivity in the seawa-
ter photic zone and (2) identifying the redox conditions of
the bottom water at the time of deposition, as opposed to the
redox conditions of the sediment pore water during early
diagenesis, Basically, we attempt to determine the source
phases of minor elements at the time of their deposition, as
opposed to their current host phases in the rocks. These
criteria may be applicable to other sedimentary formations.
The success of determining the seawater chemistry of depo-
sition from the current minor-element contents of a forma-
tion, however, depends largely on the degree to which the
marine fraction of minor elements is diluted by the detrital
fraction and on the extent to which this marine fraction was
retained in the sediment during early diagenesis, lithification,
and deep burial, at one extreme, and subaerial weathering, at
the other extreme. In the Monterey Formation, the rocks
consist of a large fraction of marine mineral components,
suggesting that the marine minor-element signal may not be
masked by terrigenous debris or erased by postdepositional
events. That is, the minor-element contents of this formation
might be interpretable in terms of the environment of depo-
sition, specifically the seawater chemistry.

2 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

Acknowledgments.—We thank S. Calvert, J. Domagal—
ski, and L. Balistrieri for their helpful reviews of the manu-
script. M. Medrano drafted many of the figures and tables.

ANALYTICAL PROCEDURES

A total of 22 samples were analyzed, representing splits
of rock samples distributed for the Cooperative Monterey
Organic Geochemistry Study. Of these samples, 13 (KG—1
through KG—13, tables 1, 2) are from the Naples Beach
section of the Miocene Santa Barbara-Ventura Basin, in-
cluding 9 samples from the Monterey Formation and 2
samples from each of the overlying Sisquoc Formation and
the underlying Rincon Shale; the other samples are from
stratigraphically equivalent strata of the Lions Head section
in the Santa Maria Basin (fig. 1). Although we refer to these
samples collectively, we note that they come from two
separate basins. Detailed descriptions of individual samples
and of the regional geologic setting of the two basins were
given by Isaacs and others (1992).

Analyses of major elements, reported as oxides (table
1) and referred to subsequently as such, and of minor ele-
ments (table 2) were performed by three separate laborato-
ries: the US. Geological Survey laboratories in Menlo Park,
Calif., and Denver, Colo., and the X-Ray Assay Laboratory
in Don Mills, Ontario, Canada (M, D, and X, respectively,
tables 1—3). The methods used were X-ray-fluorescence
(XRF) spectroscopy, inductively coupled plasma (ICP) spec-
troscopy, and instrumental neutron—activation analysis
(NAA). Although details of these methods vary between the
laboratories, the basic techniques are quite similar in all
three laboratories, and all use internationally accepted rock
standards for calibration. Complete descriptions of the pro-
cedures used at laboratories D and M were given by
Baedecker (1987).

Agreement between the different techniques used at the
three laboratories for major-element-oxide analyses is ex-
cellent (table 3); for example, for Fe, the agreement is within
3 percent (fig. 7A), and correlation coefficients are greater
than 0.985. Correlation coefficients for 93 of the 101 pairs
of analyses exceed 0.98. We elected to use the XRF analyses
for major-element oxides (tables 1—3) from laboratory D
(analyses D—XRF, fig. 2A).

Rather than discuss the precision and accuracy for each
minor element, we use the data for Cr (fig. 23) and Ba (fig.
2C) to establish the confidence level of the minor-element
analyses and to identify possible analytical problems. Our
reasons for selecting Cr are that we have four analyses of
each sample and Cr is an element that we discuss below
in some detail. The X-NAA and X—ICP analyses agree
closely about the 1-to-l line. The D—ICP analyses are uni-
formly higher than the X—NAA and X—ICP analyses, but
they otherwise correlate strongly with both sets of analyses;
that is, they have a high precision (table 4). This variation

likely results from a systematic bias, rather than from a
failure of the analytical methods in either laboratory, given
the excellent agreement between the X—NAA and X—ICP
analyses. Still, the disagreement is not insignificant and
needs to be resolved. The deviation of the X—XRF analyses
from both the X—ICP and X—NAA analyses cannot be ex-
plained in this way because all three analyses are from the
same laboratory. The agreement between the ICP and NAA
analyses suggests that both methods give superior results for
Cr. The XRF analyses for other minor elements may be
equally reliable, or even superior, to the NAA and ICP
analyses; we simply have not examined the XRF technique
thoroughly.

Incomplete dissolution of minor minerals, such as rutile
and sphene, can introduce serious analytical errors into the
ICP analyses (Gromet and others, 1984; Sholkovitz, 1990).
These minerals are extremely difficult to dissolve with the
acids used in conjunction with the ICP procedure. This
condition may have greatly affected the ICP analyses for Ba
in this study (fig. 2C). In sample KG—24 (table 2), the Ba
content is 2,500 ppm by NAA and only 61 ppm by ICP
analysis; the difference corresponds to a possible barite
content of about 0.40 weight percent, a mineral that also is
highly insoluble.

This problem might have biased the rare-earth-element
(REE) analyses, as well as the Ba analyses. Marine barite is
known to have exceptionally high REE contents (Guichard
and others, 1979). For example, in sample KG—24, the La
content by ICP analysis is 7.2 ppm (31 percent) lower than
by NAA analysis (table 2). If this discrepancy is a result of
incomplete dissolution of barite in the ICP procedure, then
the barite in this sample also has extremely high REE con-
tents. As discussed below, the REE pattern of sample KG—
24 lends some support to this interpretation. The Ba contents
of other samples are much less than that of sample KG—24,
and although there is a disagreement between the NAA and
ICP analyses for Ba, for La the two procedures show no
consistent differences (table 2).

Therefore, we elected to use the X—NAA analyses be-
cause this technique measures the bulk concentration of an
element without resorting to chemical pretreatment, similar
to the XRF technique. For those minor elements not mea-
sured by NAA, we used the X—ICP analyses. Agreement
between the X—ICP and D—ICP analyses for these minor
elements, an agreement not seen in the Ba analyses (fig. 2C),
supports the interpretation that the data are not biased by
incomplete dissolution of barite or other weakly soluble
minerals.

REVIEW: ELEMENTAL SOURCES—
THE MODERN OCEAN

Marine sediment is a complex mixture of detrital debris
and seawater-derived material (Goldberg, 1963a). The

4

ELEMENTAL SOURCES—THE MODERN OCEAN

REVIEW

 

 

   

 

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GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

 

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REVIEW: ELEMENTAL SOURCES—THE MODERN OCEAN 5

 

   
  
 
 
  
   

 

  
 
 

  
   
   
   
    
 
 
 
 
    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LEGEND
NAPLES BEACH SECTION "ms“mm‘“
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Age (Ma) @ Porcelanilemdmudnane
A5LM= Cale-noun diattxmccoul mudltone
E and Ihnle with inlerbcdthd porcelanitc
— 5.1 _' Phouphltic shale
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Swarm“
m Phaphorite m SCALE
2 ES: :2 a teccilm FEET
SISQXOSN :entom'te METERS 200
F RM TI - Minister: 50
LIONS HEAD SECTION
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with interbcdded dolomite
thphllicmul 0
with inlerbedchd dolomite
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- 5,5 -i with mined“ ddomite
Phosphor“: zone
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siliceous with imprbedded dolomite
membCr Ultnrnafic buement
Upper calcareous-
siliceous and
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Figure l. Stratigraphic sections of the Monterey Formation at Naples Beach (Santa Barbara-Ventura Basin) and Lions Head (Santa Maria
Basin), Calif., showing locations of samples. Ages compiled from Arends and Blake (1986), Barron (1986), and DePaolo and Finger
(1991). Stratigraphic positions revised from lsaacs and others (1992); Point Sal ophiolite from Hopson and Frano (1977).

6 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

detrital fraction consists mostly of terrigenous Al silicates
and quartz, introduced into the oceans by way of riverine
and eolian transport, and marine volcaniclastic debris. The
seawater-derived marine fraction is predominantly inorganic

 

 
  
 
 
    
     

7

6 _ EXPLANA'UON
0 Fe (D-ICP)
0 Fe (X-NAA)

5 - a Fe (X-XRF)
x Fe (X-ICP)

4 + Fe (M-XRF)

Fe203 CONTENT,
IN WEIGHT PERCENT

 

 

l l l

0 1 2 3 4 5 6 7
Fe203 CONTENT,
IN WEICIIT PERCENT (D-XRF)

 

 
 
  
    
 

EXPLANATION
. Cr(X-NAA)
n Cr (X-XRF)
o. Cr (D-ICP)

Cr CONTENT,
IN PARTS PER MILLION
W
o
o

   

 

 

I l

0 100 200 300 400 500
Cr CONTENT, IN PARTS PER MILLION (X-ICP)

 

 

700
X
z 600 EXPLANATION
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E 0 Ba (D-ICP)
EN; 500
i—
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a a: 400
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z
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o o x C
I I I ?

 

 

 

 

0
O 500 1000 1 500 2000 2500 3000
Ba CONTENT, IN PARTS PER MILLION (X-NAA)

Figure 2. Intraelement ratios for Fe203 (A), Cr (B), and Ba (C).
Analyses are identified by laboratory (D, US. Geological Survey,
Denver, Colo.; M, US. Geological Survey, Menlo Park Calif; X,
X—Ray Assay Laboratory, Don Mills, Ontario, Canada) and method
(ICP, inductively coupled plasma spectroscopy; NAA, instrumental
neutron-activation analysis; XRF, X-ray-fluorescence spectroscopy).

precipitates and adsorbates (hydrogenous fraction) and
CaCO3, opal, and organic debris (biogenic fraction). The
distribution and abundance of the detrital and marine frac-
tions, their composition and rates of accumulation, and their
alteration products vary widely within the oceans. Geochem-
ists have used the complex distributions and major-element-
Oxide and minor-element compositions of these fractions
to identify the past record of such phenomena as eolian
transport of terrigenous material, biologic productivity in
the photic zone, hydrothermal activity along midoceanic
ridges, and sediment diagenesis as it might relate to
metallogenesis.

An evaluation of the geochemistry of ancient deposi-
tional environments for marine sedimentary rocks must be
based on the major-element-oxide and minor-element com-
positions of their marine fractions alone. For major—element
oxides, the marine signal is commonly masked by the detri-
tal fraction, even in sediment for which the accumulation
rate of detrital debris is low. In modern sediment from the
central Pacific Ocean, where the accumulation rate is as low
as 0.1 mg/cm2 per year, the ratio of the marine to detrital
fraction of Fe is approximately 0.05 to 0.10 (Piper, 1988),
ferromanganese nodules aside. By contrast, this ratio is as
high as 2 to 10 for many minor elements in pelagic sediment
(Chester and Hughes, 1967; Fischer and others, 1986; Piper,
1988). In sediment from ocean-margin areas, however, where
accumulation rates are as much as 105 times higher, the
marine fraction of minor elements also can be masked by the
detrital fraction, making identification of the marine fraction
uncertain, if not impossible.

Two procedures are commonly used to partition minor
elements among the different sedimentary fractions. One
procedure uses a chemical leaching procedure (Chester and
Hughes, 1967; Bruland and others, 1974; Bowser and oth-
ers, 1979; Lyle and others, 1984; Tessier and others, 1984;
Boust and others, 1988); the other involves modeling the
sediment on the basis of end-member compositions of the
major fractions (Leinen, 1977; Isaacs, 1980; Dymond, 1981;
Calvert and Price, 1983; Isaacs and others, 1983; Medrano
and Piper, 1992)——a stoichiometric approach—or on the
basis of factor analysis or other similar statistical approaches.

Both the leaching and modeling procedures are not
without problems. For the leaching procedure, sample treat-
ment can introduce a bias (Belzile and others, 1989;
Sholkovitz, 1990; Tessier and Campbell, 1991; Piper and
Wandless, 1992). Among the problems are incomplete iso-
lation of a fraction at any single step of the procedure, which
then imposes an operational rather than genetic interpreta-
tion on the origin Of the varyingly soluble fractions. For the
modeling procedure, a major uncertainty can be introduced
by selecting a single end-member composition for each of
the different fractions (Leinen and Pisias, 1984). Multiple
and varying detrital sources (BOStrom and others, 1969;
Calvert, 1990), as well as marine sources, can impart a
complex chemistry to both the detrital and marine fractions.

REVIEW: ELEMENTAL SOURCES—THE MODERN OCEAN 7

Despite these and other problems, both procedures have
been used with some success (Chester and Hughes, 1967;
Bruland and others, 1974; Dymond, 1981; Isaacs and others,
1983; Leinen and Pisias, 1984; Tessier and others, 1984;
Piper, 1988; Belzile and others, 1989; Calvert, 1990). We
use a modeling procedure in this study, although the leach-
ing procedure might be the only way to collect information
about the marine fraction of the several minor elements
whose bulk contents are strongly dominated by the detrital
contribution.

DETRITAL SOURCE

Studies using a stoichiometric, or normative, scheme to
evaluate the detrital input of elements to the marine environ-
ment typically use A1203 to estimate the abundance of the
detrital fraction (Isaacs, 1980; Dymond, 1981; Leinen and
Pisias, 1984; Medrano and Piper, 1992). Implicit in the
calculations is the assumption that the sum of the compo-
nents of the detrital fraction (quartz, feldspar, clay minerals,
and other A1 silicate minerals) has a constant major-ele-
ment-oxide and minor-element content (table 5), that is, that
the interelemental ratios with A1203 are constant between
samples, which is clearly a more reasonable assumption for
any single formation than it is for formations separated both
temporally and areally.

The detrital contribution of $0; P205, MgO, and CaO
to each sample is calculated on the basis of their ratios to
A1203 in a standard. The standard most often referenced is
the World Shale Average (WSA; Wedepohl, 1969—78). The
major-element-oxide contents in excess of the detrital con-
tribution then give the amounts of biogenic silica, apatite,
dolomite, and calcite (also adjusted for CaO content in
apatite and dolomite) by using appropriate stoichiometric
factors. The determination of organic-carbon content gives
the abundance of organic matter present (table 6). The
K20:A1203 and Ti02:A1203 ratios can evaluate the degree
to which the selected composition of WSA is representative
of the detrital fraction because K20 and TiOz, along with
A1203, occur virtually totally in the detrital fraction of many,
though certainly not all, sedimentary rocks.

The same procedure determines the contribution of
minor elements by the detrital fraction. That is, minor-
element:detritus ratios are assumed to be constant and simi-
lar to those in the WSA, or another, standard. In this study,
we used the REE contents of the North American Shale
Composite (NASC; Gromet and others, 1984), except for
Ce. The contents of other minor elements in detritus (table
5) are from Wedepohl (1969—78). Previous studies have
shown that C0:A1203, GazAIZO3, Li2A1203’ Sc2A1203, and
Tth1203 ratios may be used to evaluate this procedure for
the minor elements (Piper, 1991; Dean and Arthur, 1992)
because they, like K20 and TiOz, are present predominantly
in this fraction.

MARINE SOURCE

Within the modern open ocean, the bulk of the marine
fraction of Cu, Cd, Se, Zn, and, possibly, Cr, Mo, and V
accumulating in the sediment may be transported to the sea
floor by organic debris, whose minor-element stoichiometry
(table 5) has been estimated from field studies (Martin and
Knauer, 1973; Bruland, 1983; Collier and Edmond, 1984;
Brumsack, 1986). Organic matter is most important to mi-
nor-element budgets in shelf—slope environments (Collier
and Edmond, 1984), which have high rates of accumulation
of organic matter.

In addition to organic matter, biogenic silica and calcite
contribute to the marine flux of minor elements to the sea
floor. Silica may be an important carrier of Ni (Sclater and
others, 1976) and Zn (Bruland, 1983), and its content of Cu,
on the basis of the analyses by Martin and Knauer (1973), is
slightly higher than that of Zn. Conversely, biogenic carbon-
ate contributes little to the minor—element contents of sedi-
ment other than Sr (Palmer, 1985). If the biochemical
pathways of minor elements in ancient oceans were similar
to those in the modern ocean, organic debris would have
provided a major flux of several minor elements to ancient
marine sediment.

Many minor elements in sediment have a marine hy—
drogenous source, as well as a biogenic source. Under oxic
seawater conditions, such elements as Fe and Mn and, less
so, REE’s, Co, Cu, Ni, and Zn are transported to the sea
floor as hydroxides and oxides or as adsorbates on other
particulates. Under sulfate-reducing conditions, Fe, Cd, Cu,
and Zn precipitate as sulfides. Cr, Mo, and Se precipitate, or
are adsorbed onto other particulate matter, owing to their
reduction to less soluble valence states. Under intermediate
redox conditions of denitrification, Cr and REE’s are ex-
tracted from sea-water, either by precipitation or adsorption.
The accumulation of U and V requires some special atten-
tion because their distributions in the natural environment
seem to conflict with their behavior as predicted by their
thermodynamic properties.

Thus, the accumulation of minor elements within the
marine fraction of sediment may reflect the level of primary
productivity in the photic zone, assuming a stoichiometry
for the biogenic fraction of minor elements preserved in the
sediment. The suite of minor elements that show an enrich-
ment in excess of that due solely to the rain rate of organic
matter onto the sea floor defines the redox conditions of
bottom water under which the sediment accumulates.

BIOGENIC SOURCE

The minor-element contents of modern plankton have
been measured by several researchers. Measurements vary
considerably (Martin and Knauer, 1973; Collier and Edmond,
1984), owing to inconsistencies introduced during sample

GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

 

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2 8. 8 : 2 : 8 : 2 : 8 - 8.: 8 : 8.: 8 : 8 - 8 - 222 - 28 - 8.: “202-0“ ..... 06

2 8.: 8: 8.: 8.: 8.- 8.- 8.: 8.: 8.: 8.: 8.: 222.: 28: :2.- <<z¢2 ..... 05

2 2 2 8. 2 2 2o. 8 2m. 8. 8 2.. 2. 3. "257: 58088

2 2 2 2 2 2m 8 a. 8. 8 8. 8 2.. “Ex-o i392

2 8 8 2 8 8 8. 8. 8 8 8 3.. “Ex-x £888

2 8 8 8 222 8, 8 8 t. S 8. “22:2 28080".

2 2 8 8 8. 8. 22... 8 8 3.. <<z-x 38092

2 8 8. 8 8. 8 S. S. 8. 202-2 28088

2 2.... 2 2 8. 8. 8. 8. 202-2 {8082

2 8 8. 8. 8 8 8. "258-: :.no~2<

2 2 8. 8. 8. 8. ”Ex-n2 38082

2 8. 8. 8. 8. "Ex-x 38082
2 8. 8. 8. 202-2 58082

2 2 2 "25?: I808

2 2 2522 .3808

2 "2532 5.808

 

<<z:x 52-9 "252-: “Ex-o max-x .202:x .202:n2 25?: “Ex-n "Ex-x ,202-x <<z-x "257: 252A. max-x “202-0“ <<z:x 52-0 82-9 "252-: ”Ex-n "Ex-x “202-0" 58:: ”Ex-n "Ex-x 85!.
082 0»: 0»: 0»: 0»: 0»: 06 06 06 06 06 06 59m 8088 8092 808". 808". 8092 8082 8082 8082 8082 8082 ~08 ~08 ~08 $3333

 

$380.28on oo=oUmu20=c.>E-x MEX ”22388 2223320952220:
5222223285 .<<Z ”3080220on «Ema—n 2.29.200 bu>zo=u5 in: 800502 .25 huh—E22: .3 2:0 32.222283 80202832 2: 02222222200 33 OOH .2850 62.8225 8:22 2200 502833 88¢. 8“
-X .X £230 Jan— 22202 #9226 1880280 .m.D .2 2.0200 .8280 $9.225 2885—000 .w.D d 80220820923 22828-0 22890 2502 .002. 220222.82 220 .80— 20:2 528.2222: 82$: 02 3922202 mo=2§ 5;

22028222292 882202 05 E 80288 220820-20.qu .28 8222305000 220222880 .n 933.

TOC

L01 L01 L01 TOC TOC
D— M— “’26 #15 #36

x-

Ti02 no;

1102 no; no;

P205

P205 P205

K20 K20 K20 P205 P205

K20

X—ICP X—XRF D—XRF M—XRF D—lCP X-ICP X-XRF D—XRF M—XRF D—lCP X—ICP X—XRF D—XRF M-XRF D—lCP X—lCP X-XRF D—XRF M—XRF D—lCP

NazO NazO Na20 Na20 Nazo K20

method

laboratory—

........
nnnnnnnn
..........
lllllllll

Table 3. Correlation coefficients for major-element oxides in the Monterey Formation—Continued.

 

 

 

REVIEW: ELEMENTAL SOURCES—THE MODERN OCEAN 9

collection and analysis, but also to such natural factors as
variations among species, geography, and growth rates
(Eisler, 1983). Also, waste products (such as molts and fecal
material of zooplankton), which constitute a major contribu-
tion of organic matter to the sea floor, commonly have
minor-element contents significantly greater than those of
plankton itself (table 7).

The distributions of Cd, Cu, Cr, Ni, Se, V, and Zn in
the water column, relative to those of P03", N05, and
Si(OH)4, indicate that organic detritus is the major carrier
of many minor elements from seawater to the sea floor.
NO; and P02“ are the limiting nutrients for phytoplankton
productivity in the ocean today (Sverdrup and others, 1942;
Broecker and Peng, 1982; Codispoti, 1989), and Si(OH)4
may be a limiting nutrient in some ocean-margin areas
(Nelson and others, 1981). These nutrients are extracted
from seawater in the photic zone during photosynthesis
and returned to the ocean at depth by way of bacterial
respiration. As much as 15 to 40 percent of the initial
particulate organic matter survives to the sea floor, a func-
tion largely of sea-floor depth and primary productivity
(Sarnthein and others, 1988; Baines and others, 1994). Thus,
concentrations of P09; and NO; in surface water are
relatively low and even can closely approach zero; they
increase sharply below the photic zone to the thermocline
and then remain relatively constant below approximately
SOO—m depth.

Cd, Cu, Cr, Ni, V, and Zn all show a similar depth
profile. Cd parallels POZ‘ (Boyle and others, 1976), more
so than other minor elements. Zn and Ni profiles resemble
that of Si(OH)4 (Sclater and others, 1976; Bruland, 1983).
For Zn, the Zn:Si(OH)4 ratio in seawater (Broecker and
Peng, 1982) corresponds to a Zn content in opal of approxi-
mately 60 ppm; however, the measured content averages
only 5 to 10 ppm (Martin and Knauer, 1973), much less
than its bulk content in plankton of 110 ppm (table 5). Thus,
the high measured content of Zn in organic detritus (Collier
and Edmond, 1984) and its much lower measured con-
tent in the siliceous fraction of plankton (Martin and
Knauer, 1973) indicate that it and, probably, Ni are associ-
ated dominantly with the soft parts of organisms, similar to
Cd.

Se is unique among this group of elements; significant
amounts exist in two valence states, with SeOfi" somewhat
more abundant than Seog‘ (Measures and others, 1980).
The distribution of Seog' approaches zero in the photic
zone, similar to that of Cd. Although SeOfi‘ also shows a
nutrient-type profile, it does not approach zero in the photic
zone, similar to Si(OH)4.

The depth profiles of nutrients and minor elements in
seawater can be used to evaluate the interpretation that the
average measured minor-element composition of plankton
(table 8) approximates the composition of organic matter
settling through the water column and onto the sea floor. For
example, the concentration ratio of NO; and P02",

10 REVIEW: ELEMENTAL SOURCES—THE MODERN OCEAN

Table 4. Correlation coefficients for selected minor elements in the Monterey Formation.

[All values rounded to nearest hundredth. Laboratories: D, US. Geological Survey, Denver, Colo.; X, X-Ray Assay Laboratory, Don Mills, Ontario,
Canada. Methods: ICP, inductively coupled plasma spectroscopy; NAA, instrumental neutron-activation analysis; XRF, X-ray-fluorescence spectroscopy]

 

Laboratory— Ba Ba Ba Co Co Co Cr Cr

Cr Cr M0 M0 M0 Sc Sc Sc Zn Zn Zn

method X—NAA X—ICP D—ICP X—NAA X—ICP D—lCP X—NAA X—lCP X-XRF D—ICP X—NAA X-ICP D—ICP X—NAA X—lCP D—ICP X—NAA X—ICP D—ICl>

 

Ba ------- X—NAA 1

Ba ------- X—1C1> —.37 1

Ba ------- D—ICP —.39 .08 1

Co ------- X—NAA .34 .51 —.30 1
29 42 —.18 95 l
.34 .44 —.19 .96 .96 1
.80 —.08 —.49 .67 .57 .62 1
.80 -.ll — 52 .64 .55 .58 .99 1
.77 —.01 -.47 .68 .60 .61 .98 .97
.79 —.10 —.48 .62 .52 .56 .99 1.00
.86 —.32 -.40 .31 .28 .34 .75 .77
.83 —.28 —.44 .31 .28 .32 .75 .78
84 —- 28 - 43 .31 .27 .32 .75 .78
.23 .51 —.14 .94 .96 .97 .52 .48
.23 .54 — 16 .93 .96 .96 .53 .50
.20 .55 —.10 .93 .95 .96 .50 .46
.81 —.23 —.53 .42 .32 .40 .89 .91
.81 —. 13 —.58 .53 .44 .48 .94 .96
78 —. l 4 —.55 48 .37 44 92 94

 

72 .75 1

73 .76 .98 l

72 .76 .99 1.00 l

54 46 .18 .16 .15 1

56 47 .21 .20 .19 99 l

52 44 17 . 15 .14 99 99 1

83 91 82 .83 .83 27 27 .23 1

91 96 84 86 .86 36 39 .34 .97 1

88 94 82 84 .84 31 33 .29 .98 99 1

 

5—seawater[NO§] =

NO§(deep ocean) — NO§(photic zone)
POE—(deep ocean) — POZ'(photic zone), (1)

 

based on chemical analyses of seawater, should equal the
average atomic ratio in plankton of 15:1, if only metabolic
and advective processes determine their distributions in the
oceans. Although there is considerable scatter in the mea-
surements of the composition of plankton, the average N:P
ratio approaches the 8—seawater value. The ratios of minor
elements in plankton also should equal their S-seawater
values. This relation seems to be true for Cd, but the 8-
seawater values for Cu, Cr, Ni, Se, and V are higher, and for
Zn lower, than the mean element:P ratios in plankton. Boyle
and others (1977) explained the distribution of Cu in the
deep ocean by a combination of biologic and nonbiologic
processes, whereby the nonbiologic processes involve scav-
enging of Cu throughout the water column by settling par-
ticles and recycling of Cu into the bottom waters from oxic
pelagic sediment. These and other nonbiologic processes
also might explain the high 8—seawater values for Cr, Ni, Se,
and V, although their marine chemistries have not been
examined as thoroughly as that of Cu. Nonetheless, the
similarities of the seawater-concentration—versus-depth pro—
files of many minor elements to those of NO; and P03" and
the fact that their 8—seawater values are within ,a factor of 5
of the average compositional ratios of plankton (table 8),
suggest that the elemental composition of plankton approxi—
mates the average composition of marine organic detritus
settling into the deep ocean and, presumably, onto the sea
floor.

Nonbiologic processes might influence the distributions
of many minor elements in the deep ocean. Their influence
can be demonstrated for Cu if we consider the similarity of
its 8—seawater value based only on the uppermost 2,000 m of
seawater (1.6x10‘3) to the Cu:P ratio in plankton (1.4x10'3)
and its 5-seawater value based on bottom water (3.5x10‘3).
Thus, nonbiologic processes might contribute relatively little
to the minor-element distributions in shallow-basin and con-
tinental-shelf environments along the margins of the oceans.

The distributions of REE’s, Mo, and U are little influ-
enced by the biologic cycle. Mo and U concentrations are
constant with depth (Broecker and Peng, 1982; Emerson
and Huested, 1991). M0 is mildly bioreactive (table 5), but
its uptake by plankton in the photic zone and remineralization
at depth by bacteria are simply insufficient to affect measur-
ably its vertical distribution in the water column. REE con-
centrations increase continuously with depth in the ocean,
an observation that has been explained in terms of nonbio-
logic processes (de Baar and others, 1985). Although REE
contents are relatively high in handpicked biogenic siliceous
tests (Elderfield and others, 1981), indicating that REE’s
might be incorporated into the biogenic-silica fraction, their
low concentrations in bulk organic matter (table 5) suggest
that the REE contents are very low in silica, possibly similar
to those in biogenic calcite (Palmer, 1985).

Throughout the rest of this report, we present the con-
tent of each minor element in plankton as a single value that
we consider to be best defined by average plankton, although
it is unlikely to be a single value, nor is it well defined. We
note that whereas the absolute content of a single minor
element can vary by several orders of magnitude, the inter-
element ratios vary by no more than a factor of approxi-
mately 20; therefore, we focus our attention on these ratios.

REVIEW: ELEMENTAL SOURCES—THE MODERN OCEAN

Table 5. End—member major-element-oxide and minor-element contents in
sedimentary fractions of the Monterey Formation in comparison with standards.

[Major-element-oxide contents in weight percent; minor-element contents in parts per million.
Dashes, not available. NASC, North American Shale Composite (Gromet and others, 1984);
WSA, World Shale Average (Wedepohl, 1969—78). Values for detrital fraction of the Monterey
Formation (in parentheses) represent minimums or single trends, calculated from plots of
element or element oxide versus detritus; neither a minimum nor a single trend was recognized
in several plots, in which case no value is listed. Contents of other minor elements in WSA and
in detrital fraction (in parentheses) are as follows: Ag, — (0.5); As, 10 (10); Ba, 640 (670); Cs,
5.2 (5.4); Ga, 21 (22); Hf, 3.8 (4.0); Li, 60 (50); Se, 13 (16); Sr, 125 (220); Th, 12 (10.5); Y, 26
(32). Data sources: Biogenic SiOz, Elderfield and others (1981); calcite, Palmer (1985);
organic matter, Sverdrup and others (1942), Elderfield and others (1981), and Brumsack
(1986)]

 

 

 

 

 

 

 

 

 

 

11

Detrital fraction Marine biogenic fractions Authigenic
fraction
WSA or NASC
(Monterey Biogenic Si02 Calcite Organic matter Apatite
Formation)
Major-element oxides
0.16 - — 1.74 40.7
.77 (0.81) - — — —
3.2 (3.2) — — — —
3.09 — 56.0 -— 55.5
6.75 (6.33) - — .050 —-
17.1 (17.4) — — - —
58.4 100.0 — — —
Minor elements
312 (31) 5.80 .128 .14 —
66.7 (61) 8.21 .105 .23 -
27.4 (24) 6.71 .106 .30 —
5.59 (5.3) 1.56 .019 — —
1.18(1.12) .40 .004 — -
— 1.78 .022 —
.85 — — — _
—— 1.69 .024 .01 —
3.06 (3.0) 0 86 015 — —
Lu—-————--——- .456 (0.45) — — — —
35.0 ¢ 700 11.0 -
.2 - — 12.0 —
19.0 — — 1.0 —
83.0 — — 2.0 —-
2.6 — — 2.0 —
44.0 -— — 7.5 —
1.0 — - 3,0 _
3.0 — — _ ._
1 10 - — 3‘0 _
100 — - 110.0 —
HYDROGENOUS SOURCE the incorporation of seawater-undersaturated minor elements

Two mechanisms have been invoked by geochemists to
account for the accumulation directly from seawater of mi-
nor elements in marine sediment. One mechanism involves
equilibrium thermodynamics, first treated in depth by
Krauskopf (1956) and Garrels and Christ (1965). The sec-
ond mechanism, proposed by Goldberg (1954) to explain

into the inorganic phases of pelagic sediment, promotes
seawater scavenging throughout the water column by both
organic and inorganic particulate matter.

The major seawater redox reactions that drive the pre-
cipitation-dissolution reactions of individual minor com-
pounds can be written in a simplified form as follows
(Froelich and others, 1979):

GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

Table 6. Major components in sedimentary rocks of the Monterey Formation at Naples Beach and
Lions Head, Calif.

[All values in weight percent, calculated from major-element-oxide contents]

 

 

Sample (fig. 1) Silica Detritus Apatite Dolomite Calcite Organic matter
KG—l 3.35 31.92 5.16 1.43 37.76 15.03
KG—2 6.49 35.06 8.25 2.88 14.54 23.85
KG—3 4.85 64.40 6.30 7.01 .02 9.77
KG—4 5.11 55.66 1.54 1.40 2.60 24.60
[(6—5 34.85 36.40 1.35 1.80 11.06 5.00
KG—6 9.70 64.96 .82 1.66 3.84 8.25
KG—7 36.07 49.34 .09 .46 .31 5.96
KG-8 12.50 61.60 1.53 2.24 1.27 8.69
KG—9 3.15 70.00 3.09 9.79 2.60 6.18
KG—lO 20.46 30.46 .60 5.81 32.44 6.23
KG—l 1 45.82 18.37 .27 3.24 24.47 3.85
KG—12 28.3 57.12 .20 2.37 O 1.34
KG—13 32.51 51.18 0 1.85 0 1.34
KG—14 18.05 59.92 .16 5.72 7.58 3.53
KG—15 32.67 39.09 .68 6.17 13.02 5.88
[(6—16 17.17 24.70 2.17 41.30 4.98 8.40
KG—17 30.18 19.71 8.60 .65 28.83 10.28
KG—l 8 11.52 19.66 .23 53.03 11.02 . 1.35
KG—19 2.32 2.07 .63 91.14 3.77 1.40
KG—20 15.45 67.76 .50 5.47 O 6.44
KG—22 24.45 24.25 4.34 6.36 29.30 9.84
KG—24 26.91 43.34 3.52 O .55 22.20

 

Table 7. Weight ratios of minor elements (in parts per million) to Fe (in weight percent) in fecal
matter, shale, and plankton.

[Data on fecal matter from Fowler (1977); data on shale are for World Shale Average (WSA) from Wedepohl
(1969—79) or, for rare-earth elements, for North American Shale Composite (NASC) from Gromet and others
(1984). Fe contents (in weight percent): fecal matter, 2.4; WSA, 4.72; NASC, 4.43; plankton, 0.034]

 

Cu Zn Cd Sc Cr Mn Co Ni Ce Eu

 

Fecal material--- 94 400 4.0 1.2 16 100 1.5 8.3 83 .28
Shale ------------- 6.8 20 .06 2.5 16 112 3.6 8.2 17 .30
Plankton --------- 315 2,860 340 -- 58 —- 29 210 -- --

 

Table 8. Minor-element contents in organic matter (plankton) and seawater.

 

 

 

Seawater
Organic matter E1ement:P ratio S-seawater concentration
(ppm) (organic matter) (weight ratio) at ~2,000-m depth
(ppb)
12 1.6x10‘3 1.3x10-3 .078
<1 — — .0012
20 .26x10-3 1.6x1o-3 21
1 l 1.40x10‘3 1.6x10-3 .23
2 .26x1o-3 — 10.60
75 1.0><10-3 5.3x1o-3 .47
3.0 .40x1o-3 1.5x10-3 .13
<1 — —- 3.00
3-0 .39x10'3 1.1><10—3 1.80
110 14.00x10’3 6.1x1o-3 .39
REE's (La)--- <1 — — .0052

 

REVIEW: ELEMENTAL SOURCES—THE MODERN OCEAN 13

Oxygen respiration:
10CH2 O +1002+10CaCO3=

20HC0; + 130Ca2+ (2)
Denitrification:
10CH30 + 8No3 + 2Caco3
4N2 + 12Hco§ + 411:0 + 2Ca2+ (3)

Sulfate reduction:
IOCHZO + 5502- + 5Caco3 =
5HS + 15Hco§ + 5Ca2+ (4)

Organic matter, expressed here as CHZO but better
represented by the formula (CHZO)106(NH_3)15(H3 P04) (mi-
nor elements)o OX’ is the most important electron donor 1n
the oceans, and 02, N03, and 802‘ are the most important
electron acceptors. The hierarchy of these reactions is deter—
mined by the one yielding the greatest free energy (Froelich
and others, 1979). Thus, reaction 2 proceeds until 02 de-
creases to a concentration such that denitrification yields
equal free energy, and so on.

Within several ocean—margin basins, advection is weak
enough, and the flux of settling organic matter great enough,
to allow depletion of successively more favored electron
acceptors with depth in the water column. These basins
include the Gulfo Dulce (Costa Rica), Baltic Sea, Black Sea,
Cariaco Trench (Venezuela Shelf), and several fiords at
high latitudes (Richards, 1965; Emerson and others, 1979;
Jacobs and others, 1985, 1987; Emerson and Huested, 1991).
Profiles of 02, NOE, and H28 show that 02 is abundant in
the surface mixed layer, owing to mixing with atmospheric
02 and to photosynthesis, but decreases in the water column
below the mixed layer, in response to oxygen respiration;
O2 is present at a very low concentration at intermediate
depths (Emerson and others, 1979) under conditions of deni-
trification, the depth interval over which NO; shows a sharp
decrease in concentration, and both 02 and N03 are virtu—
ally absent in the bottom water, under conditions of sulfate
reduction (eq. 4), 1n the presence of H28. Sulfate reduction
continues into the sediment until 803‘ is depleted in the
pore water, at which depth the residual labile organic matter
begins to be broken down through methanogenesis and fer-
mentation reactions (equations not shown). In the Santa
Barbara Basin (California Continental Borderland) and Dar-
win Bay (Galapagos Islands), bacterial respiration in the
bottom water does not proceed beyond denitrification.

In contrast, the open ocean exhibits oxygen respiration
virtually throughout the water column. Denitrification oc-
curs in the oxygen-minimum zone (OMZ, fig. 3), but only
along the Peru and Mexico Shelves in the eastern Pacific
Ocean (Codispoti, 1980) and at a few other localities of
limited areal extent in the Atlantic and Indian Oceans. Al-
though the OMZ is present at intermediate depth throughout
most of the oceans, only in these relatively small areas is the
balance between advection in the OMZ and primary produc-

tivity in the photic zone such that bacterial oxidation of
settling organic matter drives down the 02 content of the
water column within the OMZ to a value that promotes
denitrification.

Several minor elements also serve as electron accep—
tors, including CrOZ‘, Fe(OH)_3 MnOz, M002: SeOfi‘,
U02(CO3)2 , H2V04, and other components of seawater
that might be reduced by way of oxidation of organic matter
(table 9). By including the half-cell reaction for the oxida—
tion of organic matter, as we did in equations 2 through 4,
Fe(III) reduction can be written in the following form:

10CH 20 + 4OFe(OH)3 + 60HCO3 + 70Ca2+=
70Caco3 + 40Fe2+ + 1001120 (5)

Its reduction occurs before that of sulfate (table 9) and
toward the end of denitrification (Berner, 1980; Bender and
others, 1989); SeOfi‘ and CrOfi‘ also are reduced under
conditions of denitrification (table 9; Measures and others,
1983; Murray and others, 1983).

These minor elements contribute insignificantly to the
actual oxidation of organic matter, owing to their low con-
centrations in seawater, but their accumulation on the sea
floor, as a result of their reduction and (or) precipitation,
contributes in a major way to our identification of past redox
conditions in the water column. Under conditions of oxygen
respiration, inorganic precipitates consist mostly of Fe and
Mn oxyhydroxides (Landing and Bruland, 1987). Other mi~
nor elements are undersaturated in oxic seawater, but high
concentrations of several minor elements in deep-ocean
ferromanganese nodules indicate that a fraction coprecipitates
with Fe and Mn oxide phases or is scavenged by these
oxides. Pelagic sediment, however, is a minor sink for many
minor elements, except Mn (Lyle and others, 1984). Its high
metallic—element contents reflect very low bulk-sediment-
accumulation rates rather than high minor-element-accumu-
lation rates.

Within basins that exhibit sulfate reduction in bottom
waters, Fe2+, Cu+, Cd2+, and Zn2+ exhibit reduced concen-
trations in the bottom water (Brewer and Spencer, 1974;
Jacobs and others, 1985, 1987), possibly owing to precipita—
tion as sulfides; CrOfi‘ is reduced and precipitates as Cr(OH)3
(Emerson and others, 1979); and HZVOZ should be reduced
to V204, or, possibly, V(OH)3 (Wanty and Goldhaber, 1992).
Mo, Se, and U also show lower concentrations in the bottom
water than in the oxic surface water (Bruland, 1983; Ander-
son and others, 1989a; Emerson and Huested, 1991); they
too might precipitate, possibly by some form of the reac-
tions listed in table 9.

Minor elements in the modern environment, however,
seldom behave ideally, or simply. For example, the thermo-
dynamic properties of U require that it is present in seawater
as U03(c03)§- (Langmuir, 1978) and U02(Co_3)f3‘~; the one
should be reduced under conditions of denitrification and
the other under conditions of sulfate reduction (table 9). The

14 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

distribution of U in the Black Sea (Anderson and others,
1989) supports its reduction under conditions of sulfate
reduction. It exhibits no variation through the intermediate
zone of denitrification but shows a strong decrease in the
bottom water. Isotopic evidence further suggests that reduc-

—.° .—

tion and precipitation of U actually occur in the sediment
pore-water environment (Anderson and others, 1989a). This
distribution indicates that the complex U02(CO3)‘3“ is the
stable seawater species. Similarly, V should be reduced
under strongly denitrifying conditions (table 9), but its dis-

Sea level

 

_% 92 .
respiration

""""'—" v)»

Aj

 

1‘ Phofic zone / ”‘°
, J

  
  

Sulfate reduction

   

 

 

 

 

OCEAN DEPTH, IN METERS

 

 

/ \
\
/ \ a
\ a
/ \ _
[Methanogenesis g E
l I—
p.
Z
| m
A D
Z
fl
E
H
Sea level D
_ E-'
02 respiration PhOfic zone 4 __ e E
. ,/ —a a
3 U)

  

8042‘ reduction

  

5042' reduction /
/

\_.._

Methanogenesis
B

 

Figure 3. Schematic diagram illustrating seawater and sediment chemistry in a marine-shelf
environment with high primary productivity and weak advection at intermediate depth (top), and in
a shallow-silled basin with low to moderate primary productivity and extremely weak advection
(bottom). Modem examples of shelf environment are the Peru and Namibia Continental Shelves,
and of basin environment the Black Sea and the Cariaco Trench. Fundamental difference between
these two environments is depth of most intense reduction in water column: at intermediate depth
on shelf and at maximum depth in basin. Shaded area, oxygen-minimum zone (OMZ).

REVIEW: ELEMENTAL SOURCES—THE MODERN OCEAN

Table 9. Half—cell reactions, assuming standard-state conditions.

[Boldface, major reactions in oxidation of organic matter. Activity coefficients calculated by using the Debye-Hiickel equation (Wagman and
others, 1982); 5, effective ionic diameter used in the Debye-Hiickel equation (from Nordstrom and Munoz, 1985, or estimated from their table
7—4). Seawater concentrations of dissolved species (in moles per kilogram) are those at approximately 2,000—m depth. The pH was taken to
be 7, although it is closer to 8 under conditions of oxygen respiration and 7.5 under denitrification. Data sources for thermodynamic constants
and species concentrations in seawater: 1, Bruland (1983); 2, Latimer (1953); 3, Wagman and others (1982); 4, Landing and Bruland (1987);
5, Broecker and Peng (1982); 6, Murray and others (1983); 7, Elderfield (1970); 8, de Baar and others (1985); 9, Langmuir (1978); 10, Jacobs
and others (1985); 11, Collier (1984); 12, Boyle and others (1976); 13, Collier (1985); 14, Emerson and Huested (1991); 15, Anbar and others
(1992); 16, Koide and others (1986)]

 

water concen ' i
Sea tratlon, nmoles Reference

 

Eh Half-cell reaction per kilogram or partial pressure
1.099 3C02+(aq) + 41-1200) -) C03O4(S) + 26' + 8H+(aq) 6 C02+ = 2.04><10‘ll 1, 2
.805 211200) -—) 02(g) + 4e‘ + 4H+(aq) -- 02 = 0.2 atm 3
.704 Mn2+(aq) + 2H200) —) Mn02(s) + 26‘ + 4H+(aq) 6 Mn2+ = 2.5)(10"10 3, 4
.702 I—(aq) + 311200) —> 103—(aq) + 6e‘ +6H+(aq) 3 I_ = 5.0X10'9, 1, 3
4 103— = 4.5X10‘7
.698 N2(g) + 61-1200) —) 2N03—(aq) + 10e‘ + 12H+(aq) 3 N03_ = 3.9X10‘5, 3, 5
N2(g) = 0.8 atm
.545 Cr(OH)3(S) + H200) —) Cr042‘(aq) +3e‘ + 5H+(aq) 4 Cr042‘ = 4.04X10‘9 2, 6, 7
.320 Ce3+(aq) + 21-1200) —) C602“) + e‘ + 4H+(aq) 9 Ce3+ = 1.0X10‘11 3, 8
.296 Fe2+(aq) + 3H200) —> Fe(OH)3(s) + e' +3H+(aq) 6 1362+ = 1.20><10‘9 3, 4
.153 Cu+ —> Cu2+ + e- -- ZCu = 3.59x10-9, 1, 3
Cu+ = 1.80X10"9
.013 U02“) + 2HCO3_(aq) —) U02(CO3)22‘(aq) + 26‘ + 2H+(aq) 4.0 HC03— = 2.47X10“3, 3, 5, 9
4.5 U02(CO3)22‘ = 1.26)<10‘8
—.018 2Fe2+(aq) + 311200) —> 176203“) + 26‘ + 6H+(aq) 6 See above
—.040 V2040) + 4H200) —-> 2H2VO4_(aq) + 26‘ + 4H+(aq) 5.6 H2VO4_ = 4.0><10‘8 2, 11
—.055 PIS—(ml) + 411200) —> SO42'(aq) + 8e" + 9H+(aq) 35 HS- = 7.75X10‘25, 3, 5
4 SO42— = 2.8><10‘2
—.055 Cqu(5) + 4H200) —) SO42‘(aq) + 2Cu+(aq) + 8e' + 8H+(aq) 4 SO42— = 2.8X10‘2, 1, 3, 10
2.5 Cu+ = 3.59X10‘9
—.l37 CdS(s) + 4H200) —-) SO42“(aq) + Cd2+(aq) + 8e‘ + 8H+(aq) 4 SO42— = 2.8X10‘2, 1, 3, 5, 12
6 Cd2+ = 6.94X10‘10
—.162 ZnS(s) + 41-1200) —) SO42‘(aq) + Zn2+(aq) + 86’ + 8H+(aq) 4 SO42‘ = 2.8X10‘2, 1, 3, 5
6 Zn2+ = 5.97X10‘9
—.170 M002“) + 21-1200) —) M0042'(aq) + 26‘ + 4H+(aq) 4.5 M0042‘ = 1.1><10‘7 3, 13
—.175 MoS2(s) + 12H20(1)—) M0042”(aq) + 18e- + 250427,,” + 4.5 5042- = 2.8x10-2, 3, 13, 14
24H+(aq) 5 M0042‘ = 1.1><10”7
—.188 NiS(S) + 4H200) —) SO42‘(aq) + N12+(aq) + 86‘ + 8H+(aq) 4 SO42- = 2.8X10‘2, 1, 3, 5, 10
6 Ni2+ = 8.01x10-9
—.209 1368(5) + 411200) —> SO42‘(aq) + Fe2+(aq) + 86‘ + 8H+(aq) 4 SO42” = 2.8X10‘2, l, 3, 4
6 Fe2+ = l.20><10‘9
—.210 U02“) + 3CO3_(aq) -> U02(CO3)34‘(aq) + 26‘ 4.5 CO3_ = 1X10‘4, 3, 5, 9
5.5 U02(CO3)34“ = 1.26><10—8
—-.25() R6020) + 21-1200) —) ReO4_(aq) + 36‘ + 4H+(aq) 4.5 ReO4_ = 4.5X10‘ll 3, 15, 16
—.250 HS_(aq) + 41-1200) —-> 8042—0”) + 8e‘ + 9H+(aq) 35 HS_ = 2.8X10‘2, 3, 5
4 SO42— = 4.3X10‘6

 

15

16 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

tribution in several basins (Emerson and Huested, 1991)
suggests it is reduced only under sulfate-reducing condi-
tions.

The concentration of Ni in seawater and the Eh condi-
tions established in sulfate-reducing environments predict
that Ni too should precipitate as a sulfide (table 9). At first
glance, its depth profile in the water column, which shows
no depletion in the bottom water relative to the surface
water (Jacobs and others, 1985, 1987), suggests that it does
not. However, the profile simply requires that Ni removal
from bottom water is limited to the amount added to bottom
water by way of bacterial oxidation of organic matter. Still,
Ni should exhibit a depth profile similar to those of Cu and
Cd. Several reasons likely account for its apparent nonideal
behavior and the nonideal behavior of other minor elements.
First, our calculations of stable species (table 9) are limited
to those for which we have equilibrium constants, and these
may not necessarily be the species that actually control the
solubility of, for example, Ni and U. Second, the therrnody—
namic constants used in our calculations are from one of
several recently published lists of values, which do not
always agree. Third, we have not fully evaluated the effects
of complexation (Kremling, 1983; Jacobs and others, 1985;
Landing and Lewis, 1991), which would increase solubili-
ties. Fourth, we have not considered diffusion across the
benthic boundary layer (see below).

Under the intermediate redox condition of denitrifica-
tion, metallic sulfides will not precipitate. Cr(OH)3, however,
is stable (Murray and others, 1983), and the thermodynamic
properties of V (table 9) allow for its reduction from HZVO,‘1
to the more reactive ionic state VO2+ (Sadiq, 1988) and to
V204 near the NOE-sogireduction boundary (table 9). The
higher concentration of V in sea-water than of Cr (table 8)
and the possible removal of V from the water column during
denitrification make V a more conspicuous index of sedi-
ment from this environment than is Cr.

REE’s respond still differently in seawater. They are
adsorbed onto seawater particulate phases under oxic and
denitrifying conditions and returned to seawater under sul—
fate—reducing conditions. Within the open ocean, acetic—
acid-soluble particulate phases show an increase in REE
content and increasingly positive Ce anomaly with depth
(Sholkovitz and others, 1994); however, sediment—accumu-
lation rates suggest the flux is quite low. Within the denitri-
fication zone of the Cariaco Trench and the Black Sea,
above the zone of sulfate reduction (Hashimoto and others,
1983; Codispoti and others, 1991), the 3+—valence-state
(within the marine environment, all REE’s except Ce) light
REE’s La, Pr, Nd, and Sm show strong concentration mini-
mums, requiring their removal onto particulate phases (de
Baar and others, 1988, German and others, 1991; Schijf and
others, 1991). Toward the NO;—SO§‘-reduction interface
and into the sulfate-reducing water in both basins, their

concentrations increase sharply. Within the denitrification
zone of the OMZ in the eastern Pacific Ocean, the 3+-

valence—state REE’s also show concentration minimums.
They are scavenged by particulate phases, most likely
oxyhydroxides of Mn (German and others, 1993) and Fe
(Sholkovitz, 1993), more so under denitrifying than oxic
conditions, and released to solution under sulfate-reducing
conditions. The carrier phase in the denitrification zone in
the OMZ of the eastern Pacific is unlikely to be an Mn
phase. Dissolved Mn shows a concentration maximum,
whereas REE’s exhibit concentration minimums (Klinkham-
mer and Bender, 1980; de Baar and others, 1985; German
and others, 1991). Particulate Mn is reduced, possibly by
some form of the reaction

2Mn304 + CHZO + 10HC03‘ + 11Ca2+ =
6Mn2+ + llCaCO3 + 6H20. (6)

Thus, although the mechanism whereby the 3+-valence-
state REE’s are transferred to the sea floor within the hy-
drogenous fraction remains problematic, the redox conditions
under which it is enhanced or diminished are well estab-
lished.

Ce is somewhat more complex than the other REE’s. Its
occurrence as insoluble Ce(OH)4 under oxic conditions (table
9) accounts for the negative Ce anomaly (see fig. 4 for
definition) of seawater. Reduction back to a 3+ valence state
under denitrifying conditions accounts for the increase in Ce
concentration and for the more positive Ce anomaly of the
OMZ in the eastern Pacific Ocean and the Cariaco Trench
(de Baar and others, 1988). In the Black Sea, this trend is
reversed (German and others, 1991 ; Schijf and others, 1991):
In the denitrification zone, the Ce concentration decreases to
a minimum, as does the Ce anomaly, paralleling the trends
of the 3+-valence-state REE’s.

Scavenging by the seawater particulate phases of other
minor—element ions (Balistrieri and others, 1981; Li, 1981;
Whitfield and Turner, 1987; Clegg and Sarmiento, 1989)
probably is equally complicated by such geochemically com-
plex water columns as that in the Black Sea and Cariaco
Trench, but the results of research into metallic—ion adsorp-
tion under oxic conditions clearly identify the importance of
scavenging for many minor elements. Evaluating the impor—
tance of minor-element scavenging in the Monterey Forma-
tion, or in any ancient rocks, however, is hampered by the
difficulty of identifying a marine fraction for those minor
elements that have been well studied, are nonbioreactive,
and are strongly scavenged. Th is the most intensively ex-
amined element in this group, but its high content in the
detrital fraction of sediment and sedimentary rocks, relative
to its concentration in seawater—that is, relative to a pos-
sible seawater contribution—makes it unlikely that we might
identify a marine fraction for Th in the Monterey Formation
from bulk analyses. Of the other minor elements for which
we have analyzed, Zn and Cu also are likely to be scav-
enged, and Ni and Cd should not be, or much less so (Clegg

REVIEW: ELEMENTAL SOURCES—THE MODERN OCEAN 17

and Sarmiento, 1989; Balistrieri and Murray, 1984). Thus,
within the group of minor elements for which we have
analyzed, hydrolytic scavenging should enrich Zn over Ni
and Cd, owing to the greater tendency for Zn to be adsorbed
onto particulate matter (under seawater oxic conditions) and
its higher concentration in seawater (for example, 5 times
that of Cd). The distributions of Zn, Ni, and Cd in the marine
fraction of sediment of the Gulf of California (Brumsack,
1986), however, reflect a strong, possibly solely, biogenic
input, suggesting that scavenging is a minor process under
conditions of high primary productivity.

Interpretation of the accumulation of metallic elements
in ancient rocks on the basis of their accumulation in mod—
ern sediment is further complicated by diffusion across the
benthic boundary layer. Where 02-depleted pore waters of
organic—matter-enriched sediment are present close to the
sea floor, Mo, U, V, and Cr can diffuse from seawater across
the seawater-sediment interface and be retained in the sedi—
ment (Calvert, 1976; Manheim and Landergren, 1978;
Brumsack, 1983, 1986; Francois, 1988; Pedersen and oth-
ers, 1989; Emerson and Huested, 199]; Klinkhammer and
Palmer, 1991), possibly independently of redox conditions
of the bottom water. Near—surface sediment in the Gulf of
California exhibits increasing concentrations of Mo, Cr, and
V with depth. In absolute terms, however, this enrichment
mechanism results in only slightly elevated minor-element
contents (Brumsack, 1986); sediment on the Peru Shelf,
which also accumulates under denitrifying conditions, shows
no evidence of minor-element diffusion across the benthic
boundary layer—minor—element concentrations are relatively
constant in the uppermost 35 to 40 cm of sediment (Dean
and Arthur, 1992).

The relative accumulation rates of metallic elements
under these different redox conditions, in an area of high
primary productivity, are summarized in figure 4. This dia-
gram should be considered only in general terms because
the elemental contribution of any single source changes
with primary productivity, water depth, bulk-sediment—ac-
cumulation rate, and residence time of the bottom water, to
name but four factors. Also, we exclude scavenging and
diffusion as major mechanisms of minor-element enrich-
ment under conditions of O2 depletion in the bottom water,
except for REE’s, although scavenging could be important
for some metallic elements, however difficult it is to evalu—
ate. Figure 4 is intended to show that the hydrogenous flux
of minor elements to the sea floor will be low under oxic
conditions, except for Mn and Fe, with REE’s exhibiting a
widely varying, but commonly positive, Ce anomaly; it will
be virtually zero for Mn and high for REE’s (negative Ce
anomaly), Cr, and V under denitrifying conditions; and it
will be zero for Mn and REE’s and high for Cr, V, Mo, Se,
Fe, Cu, Cd, and Zn under sulfate-reducing conditions. Al—
though Fe precipitates as a sulfide under sulfate-reducing
conditions, detection of a hydrogenous fraction is hampered
by detrital and organic inputs, even under conditions of the

lowest bulk—sediment-accumulation rates, as noted above
for pelagic deposits.

The failure of seawater profiles of several minor ele—
ments in modern basins to reflect the geochemistry of the
bottom water—that is, the apparent absence of approach
toward equilibrium between dissolved and solid phases

 

Particulate element fluxes to the sea floor

 

 

Marine fractions Non-

marine

Hydrogenous Biogenic fraction

Oxic Denitri- Sulfate ‘ ' Organic Detrilal
respiration ficatinn _reduction Carbonate Opal _ matter

Fe . o . I o .

M...

2
O
O
. o
I
D

O
o O
. .
Co . . . . . O .
Cr . . . . . o .
Cu O - . ° 0 . .
M0 , . . . . o -
N, . . Q . o O .
Se . — O — '— ° '
U . O . . . - o
v , O . . . O .
Zn 0 . . - 0 . .
REE . . ° ' ' .
Ce * Pos. to Zero Zero Neg. Neg. Neg. Zero

neg. to neg.

 

 

 

 

. Very high . High . Moderate . Low 0 Absent to very low

 

Figure 4. Generalized summary of elemental accumulation in
marine sediment under conditions of high primary productivity in
photic zone, where seawater (hydrogenous and biogenic) sources
are not totally masked by detrital (terrigenous) source. Chart should
be read across rather than down; for example, dominant sediment
source of Cd under conditions of high primary productivity is
organic matter. Under conditions of sulfate reduction in bottom
water, as well as high primary productivity in photic zone, Cd also
accumulates as an inorganic precipitate, CdS; its accumulation as
an inorganic precipitate under bottom-water redox conditions of
oxic respiration, or denitrification, is minor, as is its accumulation
within detrital fraction of sediment under all conditions. Sizes of
circles in any one row are unrelated, in absolute terms, to those in
any other row; open circles are used in those cases for which
theoretical considerations seem to conflict with observations. Ce*,
Ce anomaly, defined as log [3Ce/(2La+Nd)], in which all three
REE’s have been normalized on an element-by-element basis to
North American Shale Composite (see table 1). Dashes, no
information available on which to estimate accumulation rate.

18 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

(Cutter, 1982; Anderson and others, 1989a, b; Emerson and
Huested, l991)—urges further caution in the application of
figure 4 to natural systems. One possible explanation for
this apparent nonideality is suggested by the strong correla-
tions in many samples of modern and ancient sediment
between organic matter, albeit the residual fraction, and
several minor elements, which should otherwise behave
quite differently. We have stressed the transport of minor
elements to the sea floor by organic matter, whose inter-
element ratios approach those of plankton. A second major
role of organic matter is to supply minor elements to bottom
waters by way of oxidized organic matter (Piper and Isaacs,
1995), again in the ratios of plankton. A third role of settling
organic matter may be to provide a surface on which the
actual reduction and (or) precipitation of minor elements
occurs. The presence of the oxidized species U(VI) in the
sulfate-reduction zone of water column in the Black Sea
(Anderson and others, 1989a) might be explainable by this
mechanism. If, as we suggest, reduction and precipitation of
seawater-dissolved elements partly depend on reactions at
the surfaces of organic debris, then the rate of minor-ele-
ment accumulation in the sediment would depend on the
settling rate of organic matter—again, primary productivity.
The degree to which minor-element removal from the water
column then reflects equilibrium depends on a balance be-
tween primary productivity in the photic zone and residence
time of the bottom water, as well as on the physical chemical
properties of the dissolved species. In possible support of
this interpretation, Mo, U, and V are strongly depleted in the
bottom water of the Black Sea (long residence time) but
very weakly depleted in the bottom water of Saanich Inlet
(short residence time). Still, the distributions of Mo and V in
the bottom water of Framvaren Fiord demonstrate the full
complexity of our problem: M0 is depleted, whereas V is
not (Emerson and Huested, 1991). Thus, the enrichments of
minor elements, as illustrated in figure 4, represent idealized
cases of marine shelf-slope and basin environments for which
the detrital contribution of minor elements does not totally
mask that of the marine environment, and equilibrium be-
tween particulate and dissolved species in seawater is ap-
proached, if not actually attained.

DIAGENETIC OVERPRINT

The depth profile of Eh in sediment of the ocean mar-
gins resembles that in the water column of anoxic basins,
such as the Black Sea (see eqs. 2—5). The pore water of the
surface veneer of sediment has the same redox properties as
that of the immediately overlying bottom water, and the
pore water becomes more reducing with depth. Burial ex-
poses each parcel of sediment to ever more reducing condi-
tions than that under which it accumulated. Thus, deciphering
the marine fraction of metallic elements in sedimentary
rocks is further complicated by the changing redox condi-

tions to which the rocks were exposed immediately after
deposition. The loss of a minor element from a sediment
during early diagenesis can mask its source if its loss is
substantial and differs from the relative loss of other ele-
ments. Sholkovitz (1973) reported a difference between the
OP ratio of sedimentary organic debris in the Santa Barbara
Basin and that of plankton of 10621 (Redfield and others,
1963). Interelement ratios of minor elements may be simi-
larly decoupled from those in settling organic matter, through
diagenesis (Shaw and others, 1990).

Within fully oxygenated sediment, Cu, as well as Cd,
Cr, V, Zn, Ni, and organic P, are, indeed, recycled into the
overlying water column during early diagenesis. Sediment-
trap studies (Fischer and others, 1986) and pore-water stud-
ies of pelagic sediment (Callender and Bowser, 1980;
Klinkharnmer and others, 1982) reveal that as much as 90
percent of the Cu is recycled at the sediment surface. The
absence of Cr and U in excess of a terrigenous contribution
in oxic sediment (Piper, 1988) requires that virtually all of
the seawater-derived fractions of these elements also are
recycled. Even with this loss, the albeit-slight retention of
several minor elements by the sediment in oxic environ-
ments, largely associated with Fe and Mn oxides in both
concretions (Mero, 1965) and finely dispersed phases (Piper,
1988), is notable, owing to the very low rate of sediment
accumulation in the pelagic environment rather than to a
high flux of minor elements or a high retention efficiency on
the sea floor of the deep ocean. Thus, different interelement
ratios in the marine fraction of this sediment from those in
marine organic matter and in the marine fraction of modern

_.
M
O

 

.s
O
O

on
0

Zn CONTENT,
IN PARTS PER MILLION
A 0')
O O

N
O

        

 

 

   

 

I l l l
0 50 100 150 200 250
Cu CONTENT, IN PARTS PER MILLION

Figure 5. Zn1Cu interelement ratio in modem marine organic
matter (shaded area on left), based on this ratio in plankton, in
sediment from the Peru Shelf (circles), the Namibia Shelf, and the
Santa Barbara Basin of the California Continental Borderland, and
in fully oxic sediment (shaded area at bottom right) from a pelagic
environment (diamonds). Labeled curves represent averages. See
text for data sources.

RESULTS: ELEMENTAL HOST PHASES—THE MONTEREY FORMATION 19

sediment in ocean-margin areas (fig. 5), as discussed below,
might allow for the identification of sedimentary rocks that
accumulated under oxic conditions, on the basis of their
current minor-element contents.

Profiles of the major oxidants (02, N05, and 802‘) in
sediment on ocean margins are greatly steepened (Froelich
and others, 1979; Berner, 1980; Claypool and Threlkeld,
1983; Bender and others, 1989; Shaw and others, 1990) over
those in pelagic and hemipelagic sediment, somewhat inde-
pendently of the organic-matter content. At one extreme is
sediment on the Peru and Namibia Continental Shelves
(Baturin and others, 1972; Calvert and Price, 1983; Burnett
and Froelich, 1988), which contains as much as 20 weight
percent organic carbon (30—40 weight percent organic mat-
ter). The surface sediment is exposed to oxic seawater con-
ditions, or to denitrification over that area of the sea floor
impinged by the core of the OMZ (fig. 3), and sulfate-
reducing conditions extend upward to the surface of the sea
floor in some areas (Froelich and others, 1988), owing to the
high content of labile organic matter in the sediment and the
low 02 content in the overlying bottom water. Sediment of
the Santa Barbara Basin shows a similar redox profile. The
sulfate-reduction zone extends to within 2 cm of the surface
(Sholkovitz, 1973), yet the sediment contains as little as 3
weight percent organic carbon.

Cu, Cd, Cr, Zn, and V are likely to be retained in this
type of sediment, a conclusion supported by their behavior
in sulfate—reducing seawater and in sediment pore water.
Douglas and others (1986) and Shaw and others (1990)
showed that Cu tends to be retained in the solid phases of
such sediment. Cd and Zn are expected to behave similarly
because of the low solubility of CdS and ZnS. The distribu-
tions of Cr and V in surface and near-surface sediment of the
Gulf of California (Brumsack and Gieskes, 1983) reflect not
merely their retention by, but their slight addition to, the
sediment of 02-depleted environments, possibly owing to
the reduction of Cr and V under denitrifying and more
negative redox conditions (table 9). Their reduction, CrOfi‘
to Cr(OH)3 and H2V02‘ to VO2+ or V204, results in their
greater stability under reducing than oxidizing conditions
(Sadiq, 1988), although the formation of metal-organic com-
plexes (Douglas and others, 1986; Heggie and others, 1986;
Breit and Wanty, 1991) and various other possible reactions
greatly complicate their geochemical behavior.

Minor-element contents and interelement ratios in sedi-
ment on the Peru and Namibia Shelves and the California
Continental Borderland (fig. 5) support our interpretation
that minor elements are efficiently retained in mildly to
strongly reducing sediment. Average interelement ratios of
several elements in the marine fraction of sediment from
these areas are comparable and similar to those in average
plankton. Equally important, minor—element ratios in sedi-
ment from all of these environments differ significantly
from those in the marine fraction of oxic pelagic sediment
(fig. 5).

REE’s are remobilized within sulfate-reducing sedi—
ment (Elderfield and Sholkovitz, 1987), an observation in
agreement with their behavior in sulfate-reducing seawater
(de Baar and others, 1988; German and others, 1991). Sig-
nificant loss of REE’s from the sediment, however, may not
occur. Their incorporation into a stable solid phase, such as
apatite, before the onset of sulfate reduction might enhance
their retention in the sediment. In sediment on the Peru
Shelf, pelletal carbonate—fluorapatite accretes in the surface
and near-surface sediment (Burnett and others, 1988) and
has a high REE content (Piper and others, 1988). A slightly
negative Ce anomaly in several, but certainly not all, bulk-
sediment samples (Piper and others, 1988; Dean and Arthur,
1992), similar to that in apatite pellets (Piper and others,
1988) and in seawater (de Baar and others, 1985), also
requires retention of a seawater fraction, possibly within
very fine grained apatite that is dispersed throughout the
sediment (Burnett, 1977). Sulfate reduction in the water
column and in the surface sediment would have prevented
the retention of REE’s in all marine fractions of the sedi—
ment, if not their initial accumulation (fig. 4).

This discussion of the behavior of minor elements within
widely varying redox environments of the modern ocean—
from seawater through the sea floor to burial—has allowed
us to introduce a stoichiometric model for the minor-
element contents of ancient sediment and, at the same time,
to outline many of the limitations of this model. Though
none too brief, our discussion is little more than a cursory
summary of a vast literature that, even so, has yet to define
fully this extremely complex environment. Our discussion
can serve only as an introduction to the subjects of the
sources of minor elements in marine sediment and of the
behavior of minor elements during burial. It is surely but
one small step, hopefully, in the right direction.

RESULTS: ELEMENTAL HOST
PHASES—THE MONTEREY
FORMATION

Rocks of the Monterey Formation consist of the follow-
ing major components (Isaacs, 1980): biogenic silica (opal-
A, opal-CT, and diagenetic quartz), calcite, dolomite, organic
matter, and minor amounts of apatite and metallic sulfides—
the marine fraction—and quartz, clay, and other Al silicates,
such as feldspar and heavy minerals—the detrital fraction.
Their abundances (table 6) were calculated by using the
normative scheme for which A1203X5.7 gives the amount of
the detrital fraction. Comparison of the contents of other
major—element oxides with those in WSA defines the contri—
bution of these oxides by the detrital fraction in the Monterey
Formation. The combination of “excess” SiOz, MgO, and
P205 in each sample identifies the amounts of biogenic
silica, dolomite, and apatite, respectively. The CaO in

20 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

excess of that present in detritus, dolomite (assuming sto-
ichiometric dolomite), and apatite gives the amount of ca]-
cite present. The abundance of organic matter is calculated
from the organic-carbon content (organic matter=organic
carbonx 1 .5).

DETRITUS

Fe203, TiOz, and K20 correlate with A1203 (table 3).
On a plot of these elements versus detritus (A1203x5.6), the
trends approximate those of WSA (figs. 6A—6C) and ex-
trapolate to the origin. The agreements are especially close
when we consider the range of rock compositions used to
determine the composition of WSA (Wedepohl, 1969—78;
Medrano and Piper, 1992) and the heterogeneity of the
Monterey Formation. Several of the plots (fig. 6) suggest
that the average composition of NASC (Gromet and others,
1984) more closely approaches that of the detrital fraction of
the Monterey Formation than does that of WSA. Relative to
the NASC standard, the Monterey Formation contains a
slight excess of Fe203. Regardless of the standard used for
comparison, however, the detrital fraction of the Monterey
Formation appears to be uniform in composition. More
analyses of the Rincon Shale and Sisquoc Formation are
needed to fully evaluate their compositions relative to both
the Monterey Formation and the two shale standards, but
the two analyses of each unit suggest no significant differ-
ences.

Several minor elements, similar to K20 and TiOz, cor-
relate strongly with detritus (tables 10, 11). The trends of
elements versus detritus also approach those of WSA (figs.
6D—6F) and extrapolate to or near the origin. These ele—
ments include Li, Ga, and Co; additional elements that show
this same strong trend with detritus (tables 10, 11) and with
WSA are Hf, Sc, and Th (not shown) and the REE’s La
through Eu (figs. 60—61). The strength of these trends sup—
ports our use of WSA as a standard for the detrital host of
minor elements in the Monterey Formation and our assump-
tion that its composition is uniform. We can use the compo—
sition of WSA and the A1203 content in the Monterey
Formation to estimate the detrital contribution of minor
elements to their total inventory, even for those elements
that do not correlate with detritus, including Cd, Cr, Cu, M0,
Ni, Se, U, V, and Zn; we consider below REE’s as excep-
tions to this interpretation.

CARBONATES

Calcite has negligible contents of minor elements, ex-
cept Sr (tables 10, 11), as also may be true for dolomite
(table 11). These conclusions are supported by the sparse
minor-element content in modern biogenic calcite (Palmer,
1985).

SULFUR PHASES

Sulfur is present in the Monterey Formation in amounts
as high as 8 weight percent (table 1) but less than 4 weight
percent in most samples (Leventhal, 1989; Zaback and Pratt,
1992). It exhibits a positive correlation with organic matter
(fig. 7A), similar to the relation in core samples from the
Santa Maria Basin near Orcutt, Calif. (Leventhal, 1989). A
slight excess of 0.5 weight percent S at 0 weight percent
organic matter was reported in samples from the Santa
Maria Basin, as inferred by extrapolation of the trend of S
versus organic matter; Leventhal (1989) attributed this ex-
cess to the presence of metallic sulfides, mostly pyrite. A
similar trend is seen in our data (fig. 7A); however, by
merely interchanging the axes, the curve defining the rela-
tion in the samples used in this study extrapolates onto the
organic-matter axis at 0 weight percent S. Going through
this same exercise with the data of Leventhal (1989) reduces
the excess S in samples from the Santa Maria Basin virtually
to zero, a reflection of the weakness of the correlation, plus
very low pyrite.

The presence of pyrite was evaluated by comparing
excess Fe203—that is, relative to NASC (fig. 6A)—with
sulfur. Although the curve for pyrite (fig. 73) defines a
maximum for excess iron in the Monterey Formation, we
are unable to say whether pyrite is actually present, although
certainly it averages less than approximately 1.0 weight
percent. Pyrite has been reported by researchers investigat-
ing the Monterey Formation, and it was observed in several
of the samples in this study, in the range 1—2 volume percent
(J. Rullkotter, verbal commun., 1993). Such a low concen-
tration of pyrite likely hosts a minor fraction of minor
elements.

Ba also correlates weakly with S (fig. 7C; table 10). The
occurrence of Ba as barite (BaSO4) is more strongly sug—
gested by the much-reduced Ba content in samples analyzed
by ICP versus those analyzed by NAA (fig. 2C). The lower
La content in the ICP-analyzed than in the NAA-analyzed
sample (KG—24, table 2) with the highest Ba content sup-
ports this interpretation of barite occurrence; marine barite
is known to have an REE content of hundreds of parts per
million (Piper, 1974; Church, 1979; Guichard and others,
1979). The barite (present in only 0.5 weight percent) and
apatite in these samples likely represent the major hosts of
the marine REE inventory.

ORGANIC MATTER

Several minor elements that do not correlate with detri—
tus correlate strongly with organic matter (table 10), and the
correlations are enhanced, albeit slightly, by subtracting the
detrital contribution from their bulk contents (figs. 8, 9).
Strong partitioning of minor elements into organic matter

I
2

RESULTS: ELEMENTAL HOST PHASES—THE MONTEREY FORMATION

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22

GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

Table 10. Correlation coefficients for major components and minor elements in the Monterey Formation.

 

Organic

 

  

 

 

 

 

 

Silica Detritus Apatite Dolomite Calcite matter Sulfur Mn As Ba Be Cd Ce Co Cr Cu Eu Ga
Silica- l
Detritu —.196 l
Apatite -.276 —.143 1
Dolomite- —.355 “.565 —.204 1
Ca1cite--—- - .138 —.578 .371 —.l32 1
Organic matter--- —.321 .084 .592 —.341 .097 1
-- —.089 .125 .408 -—.288 O .687 1
- —.221 .027 —.246 .310 —.156 —.256 —.087 1
—.238 .462 .464 —.447 —.150 .643 .704 —.163 1
- —.065 .120 .336 —.279 —.083 .665 .804 —.066' .591 1
- —.571 .636 .375 —.407 —.127 .443 .207 —.031 .568 .25 1
—.133 .106 .406 —.168 —.080 .491 .407 -.148 .675 .461 .387 1
- —.172 .928 —-.126 —.539 —.574 .116 .084 —.035 .347 .117 .671 .129 1
—.305 .904 .047 —.564 —.432 .333 .372 .009 .677 .320 .751 .270 .823 1
-- —.316 .333 .517 —.419 -.083 .888 .771 —.177 .825 .794 .547 .504 .273 .590 1
- —.200 .130 .452 —.341 0 .910 .857 —.216 .720 .863 .365 .511 .146 .377 .916 1
—.022 .722 —.158 —.525 —.287 .162 .439 —.033 .539 .285 .445 .059 .648 .758 .411 .32 1
—.248 .982 —.105 —.531 —.565 .115 .160 .066 .501 .159 .700 .213 .932 .920 .371 .166 .699 1
- —.055 .916 -.199 —.578 —.493 .016 .184 .053 .342 .115 .480 .011 .873 .760 .217 .104 .777 .877
—.21 1 .881 .052 —.603 —.479 .357 .336 —.090 .543 .315 .693 .242 .933 .862 .519 .402 .695 .904
~.313 .882 .081 —.466 —.555 .177 .009 —.054 .516 .071 .677 .280 .830 .774 .355 .148 .468 .878
- —.065 .616 .152 —.529 —.285 .461 .724 —.092 .717 .561 .439 .265 .579 .759 .681 .625 .815 .632
- —.126 .073 .437 -.263 .004 .725 .717 —.182 .708 .833 .348 .790 .096 .275 .763 .860 .174 .150
—.143 .875 .072 —.613 —.469 .267 .318 —.131 .509 .231 .647 .208 .936 .836 .425 .317 .720 .888
—.229 .210 .516 —.425 —.002 .951 .805 —.229 .754 .795 .455 .507 .204 .473 .960 .969 .351 .239
—.052 .039 .464 —.318 —.020 .851 .788 —.249 .584 .684 .270 .378 .121 .281 .776 .887 .308 .055
—.146 .920 —.089 —.530 —.485 .063 .261 .073 .585 .175 .580 .139 .775 .929 .403 .158 .802 .916
—.188 .053 .493 —.296 .017 .946 .827 —.227 .698 .771 .285 .51 .063 .300 .894 .972 .256 .079
—.186 .901 .057 —.628 —.463 .345 .416 —.086 .600 .334 .672 .249 .915 .899 .536 .414 .775 .916
~.152 —.349 .625 —.233 .856 .334 .013 —-.181 .083 .059 .269 .144 —.358 —.164 .187 .147 —.295 —.319
—.250 .923 —.131 —.517 —.555 .168 .047 —.032 .352 .114 .702 .126 .984 .843 .312 .166 .608 .927
—.335 .337 .549 —.346 —.187 .780 .540 —.177 .720 .578 .651 .717 .456 .515 .770 .755 .233 .423
—.075 .230 .334 —.385 —.153 .826 .768 —.234 .698 .740 .383 .517 .274 .465 .833 .892 .447 .255
—.235 .526 .477 —.540 —.130 .677 .735 —.175 .819 .583 .574 .421 .480 .705 .837 .733 .606 .568
—.1 10 .642 .225 —.594 —.217 .512 .722 —.130 .761 .529 .529 .326 .606 .796 .701 .633 .818 .662
~.253 .278 .517 —.392 -.102 .893 .844 —.213 .849 .805 .482 .637 .262 .521 .951 .951 .400 .330
Hf La Li Lu Mo Nd Nl Sb Sc Se Sm Sr Th U V Y Yb Zn
1
.816 1
.779 .467 1
.297 .159 .438 1
.976 .791 .777 .214 1
.455 .228 .651 .788 .375 1
.327 .026 .570 .667 .306 .891 1
.785 .754 .734 .082 .794 .253 .072 1
.321 .093 .555 .807 .248 .964 .917 .081 1
.984 .788 .838 .302 .979 .471 .347 .847 .337 1
—.261 —.214 ——.230 .173 -.295 .205 .055 —.307 .149 —.277 1
.921 .843 .541 .103 .899 .235 .1 15 .758 .087 .891 —.304 1
.643 .496 .572 .753 .584 .787 .687 .290 .738 .600 .114 .471 1
.444 . 175 .624 .770 .394 .899 .926 .248 .899 .472 -.025 .289 .719 1
.744 .529 .897 .571 .712 .785 .622 .622 .691 .774 .058 .465 .751 .636 1
.802 .507 .986 .457 .805 .676 .582 .747 .572 .862 —.128 .572 .616 .638 .919 1
.527 .333 .721 .843 .454 .960 .832 .337 .933 .547 .112 .273 .838 .865 .858 .745 1

 

 

was also reported by Leventhal (1989) and Odermatt and
Curiale (1991) for the Monterey Formation and by Swanson
(1961) and Nissenbaum and Swaine (1976) for other rocks
and modern sediment. Lewan (1984), Odermatt (1986), and
Moldowan and others (1986) further examined fractionation
of metallic elements between the various phases of organic
matter. The actual slopes of the plots for minor elements and
organic matter, however, bear no relation to the composition
of the organic matter in marine plankton.

The different units of the Monterey Formation and the
Rincon Shale exhibit nearly identical minor-element/organic-

matter trends (fig. 8), except possibly for slightly lower
concentrations of several minor elements in the phosphatic
shale unit of the Monterey Formation. Mere dilution by
apatite alone is insufficient to account for these lower con-
centrations, although more analyses are required to confirm
the trends. The two samples from the Sisquoc Formation
contain less than 1.5 weight percent organic matter (table 6)
and have low minor-element contents; data for these samples
plot near the origin. Thus, we are unable to evaluate a
partitioning of minor elements into a marine fraction, possi-
bly organic matter, in these two samples.

RESULTS: ELEMENTAL HOST PHASES—THE MONTEREY FORMATION 23

Table 11. Factor analysis for major components in sedimentary rocks of the Monterey Formation,
using the computer program StatView II (oblique-solution primary-pattem matrix).

 

 

 

Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 Factor 6

Silica ---------------- —0.133 —0. 147 -0. 108 —0.843 —0.231 —0.082
—.054 .976 —.065 .017 .033 .017
.348 —.074 .586 .067 .026 .252

—. 127 —.662 —.424 .585 —.061 .127
—.063 -.371 .827 —.187 -.077 —.225
Organic matter--- .874 .005 .129 .066 .331 —.013
Sulfur-—------------- .928 .050 .013 .037 —.303 —. 170
—.090 —.023 —.l38 .664 —.218 -.217
.599 .395 .163 .042 —.292 .298
.882 —.021 —.123 .006 —.073 .001
.117 .685 .355 .279 .222 .194
.186 .163 .185 —.015 .897 —.167
.382 .028 —.01 3 -.081 —. 173 .779
—.039 .929 —. 157 -.047 .222 .056
.217 .889 .074 .120 —.046 —.008
.855 .261 .084 .1 17 .026 .042
.992 .016 —.029 .012 .087 —.031
.277 .759 .029 —.070 —.299 —.326
—.035 .958 -.O75 .089 .001 .115
—.029 .917 —.089 —.076 —.055 —.150
.225 .891 —.062 —.034 . 129 .024

—. 104 .848 —.024 .056 .149 .339
.584 .646 .031 —.061 —.3 13 —. 196
.790 —.074 —.070 —. 102 —.1 12 .332
.148 .909 —.052 —.091 .061 .026
.942 .119 .071 .018 .133 —.044
.966 —.042 —.095 —.088 .162 —. 152
.021 .926 .057 .059 —.285 —.029
.999 —.073 —.048 .012 . 127 —.034
.254 .913 —.024 -.047 .005 —.022
—.026 -.181 .914 —.022 .141 .012
—.027 .913 —. 138 .007 .306 .050
.619 .289 .000 .053 . 195 .404
.929 .104 -—.177 —.098 .125 —.020
.623 .551 .234 .025 -. 190 —.008
.561 .680 . 125 —.058 —.276 —. 156
.902 .184 .026 .036 —.025 .125

 

 

For the samples from the Monterey Formation alone,
those from the Lions Head section have slightly higher
ratios of Cr, Cu, Se, V, and Zn to organic matter than those
from the Naples Beach section (fig. 9). We can attach no
significance to these differences, given the number of samples
we examined and the magnitude of the differences.

APATITE

On a plot of the marine fraction of heavy metals against
apatite (fig. 10), the samples follow two trends, a relation
suggested by the organic-matter plots (fig. 8). The first trend
is defined by the minimum of the plot of minor elements
versus organic matter (curves labeled “organic matter,”
fig. 9). This trend was plotted in figure 10 by converting
organic—matter to P content, on the basis of the C2? ratio in
plankton of 0.019 to 0.0225 (Collier and Edmond, 1984;
Brumsack, 1986), and then converting P to apatite content
by assuming 17.7 weight percent P in apatite (table 5). The

success of this calculation in defining the organic-matter
trend, particularly for Cr, Cu, Ni, and Zn, suggests that
much of the P in excess of the detrital contribution might be
organically bound, even though we have expressed it in
figure 10 as an apatite equivalent. The second trend, referred
to as the apatite trend (curves labeled “apatite,” fig. 10),
identifies samples with reduced minor-element contents.
These same relations have been observed for the San Gregorio
Formation (Piper, 1991), a phosphatic deposit of Oligocene
to Miocene age in Baja California.

The degree of minor-element enrichment between these
two trends, expressed by the relation

[metal/P] :[metal/P]

apatite organic matter’ (7)

is surprisingly similar for all minor elements; it varies over
the limited range 0.16 (Cd)——0.22 (Cr). Although it is tempt-
ing to conclude that minor elements are incorporated into

24 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

these two major phases, organic matter and apatite, they also
are probably present in minor phases, such as metallic
sulfides. Otherwise, we might have expected such an ele-

 

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ORGANIC-CARBON CONTENT,
IN WEIGHT PERCENT
m o

 

 

 

Fe203 CONTENT,
IN WEIGHT PERCENT

 

 

 

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S CONTENT, IN WEIGHT PERCENT

Figure 7. Organic-carbon content (A), Fe203 content in excess of
a detrital contribution (B), and Ba content (C) versus S content in
sedimentary rocks of the Monterey Formation. Two curves in 7A
are best-fit lines, obtained by interchanging axes; they have same
standard deviation (SD) of 0.65 and center of mass. SD. of curve
in figure 7C is 0.80.

ment as Cd, similar in ionic charge and radius to Ca2+, to be
the most strongly enriched of the minor elements in the
phosphatic samples. If anything, the opposite is true: The
ratio

[Cd/P] {Cd/P]

apatite' organic matter (8)
is smaller than those for other minor elements, which should
substitute less strongly into the apatite phase.

The REE patterns (fig. 11) of the samples indicate that
REE’s are present in excess of a detrital contribution, de-
spite strong correlations of individual REE’s with detritus
(fig. 6; table 1 l). The depletion of Ce relative to La and Nd
in most samples, and a heavy-REE enrichment in several
samples (for example, 2, 17, 22, 24, fig. 11), resemble the
REE pattern of seawater (Goldberg and others, 1963;
Hegdahl, 1967; de Baar and others, 1985). This pattern,
which is unique to the marine environment, represents un-
equivocal evidence of a marine origin for some of the REE’s
in the Monterey Formation. Although apatite is known to
host REE’s in phosphate deposits (Altschuler and others,
1967; McArthur and Walsh, 1984; Wright and others, 1987;
Piper, 1988, 1991; Piper and Medrano, 1991) and in modern
sediment (Piper and others, 1988), its low content in these
samples, the low content of REE’s in the marine fraction of
sediment, and the likely partitioning of some of this fraction
in barite preclude our ascertaining the importance of apatite
as REE host in the Monterey Formation.

An Eu anomaly exhibited by several samples (fig. 1 1) is
possible further evidence of a marine fraction of REE’s.
Plots of this Eu anomaly against major components and
minor elements, however, give no clue as to a possible phase
that might be responsible for its occurrence.

Apparently, the REE contents in WSA overestimate the
detrital contribution of REE’s to the Monterey Formation.
NASC also might not be totally representative of the detrital
fraction. Although it defines a minimum for La and Yb
contents (fig. 60), a Ce content even lower than that in
NASC (fig. 6H) is needed to define the minimum detrital Ce
content. Using these minimums for the REE content in
detritus—for La (31 ppm), Ce (61 ppm), and Nd (29 ppm)—
we can calculate the REE content and Ce anomaly in the
marine fraction alone (fig. 12). The Ce anomaly correlates,
albeit weakly, with apatite, and the correlation is stronger
than that between apatite and the Ce anomaly calculated by
using bulk REE contents. Given the large error in this calcu-
lation due to the dominance of the detrital contribution to
the light-REE inventory (figs. 6G, 6H), the improvement in
the apatite trend is rather remarkable and seems to support
our method of selecting Ce, La, and Nd contents in the
detrital fraction of the Monterey Formation.

U correlates with organic matter (fig. 8) and weakly
with apatite (tables 10, ll).

25

RESULTS: ELEMENTAL HOST PHASES—THE MONTEREY FORMATION

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28 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

MISCELLANEOUS

Several sample pairs, representing associated finely lami—
nated versus massive units, were included in the samples
analyzed (Isaacs and others, 1992). Although each massive
unit has a higher metallic-element content within the marine
fraction than its laminated pair (fig. 13), both plot close to a
single organic-matter trend.

DISCUSSION: ELEMENTAL SOURCES——
THE MONTEREY OCEAN

Two slightly different approaches to the partitioning of
minor elements between multiple marine sources offer a
possible check on our determination of elemental sources to
the Monterey Formation. Both approaches assume that the
detrital fraction has a uniform composition comparable to

 

 

CONCENTRATION RATIO
/
\
I
I
I
I
\
CONCENTRATION RATIO

 

 

 

 

 

CONCENTRATION RATIO
'0
5:
2
I
l
CONCENTRATION RATIO

 

 

 

 

 

   

CONCENTRATION RATIO
CONCENTRATION RATIO

 

 

 

Sm Eu G Yb Lu La Ce Nd Sm Eu Gd Yb Lu
RARE-EARTH ELEMENTS RARE-EARTH ELEMENTS

l

J

 

 

I I I 1 I l I I 0.1 I I I 1

011

 

La Ce Nd
Figure 11. Rare—earth-element patterns for samples from the Monterey Formation. A, Sisquoc Formation. B,
Siliceous shale (upper part). C, Phosphatic shale. D, Clay-shale. E, Siliceous shale (lower part). F, Rincon Shale.
Patterns represent elemental contents normalized on an element-by-element basis to World Shale Average (Wedepohl,
1969—78; Piper, 1974) and plotted against atomic number. Normalizing values (in parts per million): La, 41; Ce, 83;
Nd, 38; Sm, 7.5; Eu, 1.61; Yb, 3.53; and Lu, 0.61. Samples are grouped according to lithology, as in figure 8.
Although data for Gd are unavailable, curves are drawn through a Gd value estimated by interpolation between Sm
and Yb values. Purpose of interpolation is to emphasize anomalous behavior of Eu; however, we have made no
attempt to evaluate Eu anomaly without actual Gd data.

DISCUSSION: ELEMENTAL SOURCES—THE MONTEREY OCEAN 29

that of some sedimentary-rock standard. The first approach
computes the rate of accumulation of each element in the
marine fraction by using the rate of accumulation of the
rocks, which is determined by one of various methods. By

 

La CONTENT,

IN PARTS PER MILLION

 

 

 

 

 

 

 

 

 

 

 

 

 

_ 1 L x 1 1
0.350 2 4 6 8 10

APATITE CONTENT, IN WEIGHT PERCENT

Figure 12. La content (A) and Ce anomaly (B) of marine fraction,
and Ce anomaly in bulk sediment (C), versus apatite content in
sedimentary rocks of the Monterey Formation. Curves in figure
12A represent apparent trends; curves in figures 12B and 12C are
least-squares best-fit lines, with standard deviations of 0.65 (fig.
128) and 0.54 (fig. 12C)

assuming a minor-element stoichiometry for Miocene or-
ganic matter, based on the minor-element content of modern
plankton, the rate of accumulation of organic matter re-
quired to supply each minor element to the Miocene sea
floor can be calculated. These values are compared with the
rate of accumulation of organic matter on the sea floor of the
modern ocean. Those elements that give higher rates than
probable organic fluxes are interpreted to have accumulated
directly from seawater as a hydrogenous fraction, in addi-
tion to having accumulated as a biogenic fraction. Their rate
of accumulation within the hydrogenous fraction depends
on such factors as water-column advection, metallic-ele-
ment concentrations in seawater, and bottom-water redox
conditions; and their rate of accumulation within the bio-
genic fraction depends mostly on primary productivity in
the photic zone.

The varying rate of accumulation of sediment in the
Monterey Formation (Isaacs, 1985) and the small number of
samples analyzed in this study, alone, dissuaded us initially
from emphasizing this first approach. However, the range of
concentrations and average values measured in these samples
agree closely with those of cored (max 3,320 m deep) rock
samples from the Santa Maria Basin (Leventhal, 1989) and
35 additional surface samples from the Santa Barbara-
Ventura Basin (C.M. Isaacs, unpub. data, 1993). Also, ratios
of the maj or-element oxides and minor elements to A1203 in
the detrital fraction and minor-element:minor-element ra-
tios in the marine fraction are virtually identical in the three
sets of samples. Agreement with the Santa Maria Basin
samples further precludes major alteration by surficial weath-
ering of the rocks examined in this study.

The second approach compares the relative contents of
minor elements in the marine fraction of the rocks with their
contents in modern plankton. This approach is greatly facili-
tated when the minor elements exhibit strong interelement

 

400 ,

(A)

0|

0
I

§

Phosphatlc shale

    
 

N

U1

0
l

Clay-shale

’ 11-10 D
° Sillceous shale
100 ' o
«gtl

5-6 7-8

 
 
 
 

Cr CONTENT,
IN PARTS PER MILLION
- N
‘6 8
I

 

 

 

0 5 10 1 5 20 25
ORGANIC—MATTER CONTENT, IN WEIGHT PERCENT

Figure 13. Cr versus organic-matter content of marine fraction in
sedimentary rocks of the Monterey Formation (see fig. 8B).
Numbered data points represent closely associated, finely
laminated/massive sample pairs (see fig. 1 for locations).

30 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

correlations. From simple x-y plots, minor-element:minor-

element ratios give the elements that are enriched above a

biogenic contribution. This procedure, which is used in the

absence of information on sediment-accumulation rates,
points up the desirability of a master variable, or a single
element, that defines the marine organic source, just as

A1203 defines the terrigenous source. In this discussion, we

resorted to using Cu as the master variable for the marine

biogenic fraction. Several aspects of its chemistry recom-
mend it.

1. It is a bioreactive element, with a concentration in plank-
ton (table 5) that exceeds those of most other bioreactive
minor elements (Martin and Knauer, 1973; Broecker and
Peng, 1982; Bruland, 1983; Collier and Edmond, 1984;
Brumsack, 1986). Thus, its biogenic signal should be
strongly imprinted in rocks that were initially rich in
organic matter.

2. Although it accumulates from oxic seawater (fig. 5) by a
small fraction of its dissolved load being adsorbed onto
other particulate matter (Boyle and others, 1977), more
importantly, it precipitates under seawater sulfate-reduc-
ing conditions as a sulfide (Jacobs and others, 1985)
virtually quantitatively. Its concentration in seawater
should make this hydrogenous input to any sediment
distinguishable from a biogenic or a detrital input. If we
assume redox and advection conditions similar to those
in the Cariaco Trench (Jacobs and others, 1987); a Cu
concentration in seawater advecting into the basin equal
to that of seawater at 2,000-m depth (table 8), and a bulk-
sediment-accumulation rate of 3 mg/cm2 per year, simi-
lar to that of the Monterey Formation in this area (Isaacs,
1985), then the content of Cu, which would have precipi-
tated as a sulfide, would be approximately 30 ppm.

3. The organic-matter content of the Monterey Formation
(table 6) is similar to that of surface and near-surface
sediment accumulating currently on the Peru Shelf, in
which sulfate-reducing conditions in the sediment pore
water extend close to the benthic boundary layer in many
areas (Froelich and others, 1988). Although Cu is quickly
recycled into the overlying water under oxic conditions
(Boyle and others, 1977; Fischer and others, 1986), it
should be retained under sulfate-reducing conditions,
owing to the low solubility of CuZS, as reflected by its
precipitation under seawater sulfate-reducing conditions
(table 9; Jacobs and others, 1985) and the immobility of
Cu in sulfate-reducing sediment (Douglas and others,
1986).

4. The marine fractions of most minor elements in the
Monterey Formation correlate strongly with Cu (fig. 14;
table 10), allowing a precise comparison of the minor-
element contents through simple x-y plots. The absence
of such correlations, however, does not preclude the use
of this approach, inasmuch as the strength of present
correlations should depend more on the composition of
host phases than of source phases. The compositions of

the host phases likely reflect diagenetic processes and
(or) recent rock alteration, rather than depositional pro-
cesses. For those minor elements for which such correla-
tions are weak, more samples must be analyzed to fully
document the interelement ratios.

We should add that both approaches are stoichiometric.
They assume that the composition of detritus was the same
as that of standard shale (WSA or NASC), the composition
of deposited organic matter was the same as that of modern
organic matter, and the metallic-element content in excess
of these two sources is attributable to a hydrogenous source.

TERRIGENOUS SOURCE

Ratios of major-element oxides to detritus strongly in-
dicate that the detrital fraction in the Monterey Formation
has a uniform composition in the two sections sampled.
They furthermore indicate that the detrital fraction had a
predominantly terrigenous source, as opposed to a marine
volcaniclastic source. Plots of the detrital fraction
(5.6XA1203) versus Ti02 and K20 (figs. 68, 6C) fall along
single trends, have slopes approaching those for WSA, and
extrapolate to zero. Thus, this fraction is both a current host
phase and a source phase.

This interpretation extends to several minor elements.
The CozA1203 ratio in WSA is 1.13X10‘4, virtually the same
as in the Monterey Formation (fig. 6F). The scatter of the
data about the WSA line likely reflects uncertainties in the
analytical procedures at low Co contents (table 4), rather
than significant deviations in the Co content of any sample.
This same relation extends to Li and Ga (fig. 6) and to Hf,
Sc, and Th (table 10). Extrapolation of the curves to zero
also supports the conclusion that the detrital fraction is the
sole source of these minor elements. These relations support
our use of WSA as a representative of the detrital source of
the other minor elements under consideration, except REE’s.

For those minor elements that correlate with organic
matter (figs. 8, 9), their bulk content in most samples is large
relative their content in the detrital fraction. Thus, a slight
error in our estimate of the detrital contribution, based on
the minor-element content in WSA and the A1203 content in
the Monterey Formation samples, introduces a small error in
our calculation of the marine fraction of minor elements.

MARINE SOURCE

Strong correlations between many minor elements (fig.
14; tables 10, 11) and the similarity in the partitioning of all
minor elements into the organic-matter and apatite trends
(fig. 10) suggest that the minor elements have undergone
only limited remobilization since their initial accumulation
on the sea floor. Adsorption onto residual organic matter,
apatite, and, possibly, sulfide precipitates within the fine

DISCUSSION: ELEMENTAL SOURCES—THE MONTEREY OCEAN 31

 

 

     

     

 

 

 

 

    
  
   
     
 
   
      

 

 

 

 

     
 
 

  

 

 

 

 

    
 
   
    

 

 

 

 

 

 

35 60
E Plankton x 1.5 0
Z 30 _
Q g 50
.— o
[4" 25 j
Z E o E E 40 - Seawater Plankton
E a: 20 {E m
52 2a so—
0 a, 1 5 EXPLANATlON 8 m
u E X Sisquoc Formation. u I"
L) < Naples Beach (A 9‘ 20 ..
n. 10 + Rincon Shale. g
z Naples Beach Z
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5 Naples Beach
0 Monterey Formation,
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0 I 0 1
0 50 100 150 200 0 50 100 150 200
400 u 25
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350 ' Z 0
E Plankton x 15 Q 20 - + o
3 300 -
F: P; Seawater
2 E250 - z
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E E 200 — o a 2,. °
0 ([2150 - :5 1° °
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E Seawater E 5 _
50 ‘ Plankton ° 0
o
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o 50 100 150 200 0 50 100 150 200
100 600
G
C o o
500 " PI [do 20
a 80 ‘ Seawater 6 an n x
.l—l '-‘ Senwa r
l- d Plankton x 2.5 j 400 -
Z 2 I— .—
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8:: 6533”
° 5 40 - 0 fl 200
E < > %
9" Plankton 9‘
5 2° E 100 —
Plankton
o I l I 0 I I I
0 50 100 150 200 0 50 100 150 200
350 500
H
Z 300 ' Plankton x 3'5 z Plankton
9 o 400 — °
.r—I Seawater E
E: 250 ‘ Era Plankton x 0.35
2 -
E M 200 - E M 300
Z E z Lu
0 o D.
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z 3“ [5 m
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E Plankton E 100 -
50 r
o l I o I l I
0 50 100 150 200 0 50 100 150 200
Cu CONTENT, IN PARTS PER MILLION Cu CONTENT, IN PARTS PER MILLION

Figure 14. Contents of Cd (A), Cr (B), Mo (C), Ni (D), Se (E), U (F), V (G), and Zn (H) versus Cu content of marine
fraction in sedimentary rocks of the Monterey Formation. Samples are grouped by site. Curve labeled “plankton”
represents our best estimate of trend for modern plankton, extrapolated into field of the Monterey Formation; curve
labeled “seawater” represents ratio for seawater (table 8), also extrapolated into field of the Monterey Formation;
curve labeled “planktonx...” represents data for the Monterey Formation, along with its deviation from plankton.

32 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

unconsolidated sediment apparently removed minor elements
from pore water as they were released during diagenesis
from the labile fraction of organic matter and any labile
hydrogenous fractions.

Although the marine fraction of several minor elements
correlates strongly with organic matter (fig. 8), a curve that
defines the approximate average minimum minor-element
content in organic matter (curves labeled “organic matter,”
fig. 9) lies well above that for modern plankton in all cases,
by approximately 3- to 300-fold. If the sedimenting organic
matter had the same stoichiometry as modern plankton, then
clearly a major readjustment to the minor-element:organic-
carbon ratio occurred during sedimentation and burial. Depth
profiles of organic carbon in modern sediment (Douglas and
others, 1986; Froelich and others, 1988; Calvert, 1990),
which has an organic—matter content similar to that of the
Monterey Formation, strongly suggest that some organic
matter was lost during early diagenesis as HCOg, rather than
that minor elements were gained. Possible exceptions are
Cr, Mo, U, and V, which might have diffused across the
benthic boundary layer (Brumsack, 1983; Francois, 1988;
Emerson and Huested, 1991).

Sediment-trap studies of pelagic environments further
support the loss of organic matter during early diagenesis
(Fischer and others, 1986). Settling particulate matter col-
lected at greater than 3,000-m depth contains approximately
5 times more organic matter than detritus, whereas surface
sediment at the same sites contains approximately 100 times
more detritus than organic matter. Approximately 95 to 99
percent of the organic matter that rains out of the water
column is, thus, oxidized at and very near the surface.
Ocean-margin areas will have an even larger flux of organic
matter to the sea floor, owing to shallower sea floor (Sarnthein
and others, 1988), higher primary productivity (Berger and
others, 1988; Pedersen and Calvert, 1990), and a positive
relation between the relative rain rate of organic matter from
the photic zone and primary productivity (Baines and oth-
ers, 1994).

To differentiate between minor-element contributions
to the Monterey Formation by (1) a biogenic source and (2)
a hydrogenous source, we first ascertain the biogenic contri-
bution. The minor-element contribution by organic matter
(plankton) alone can be evaluated by comparing the rate of
accumulation of organic matter necessary to deliver the
now-observed metallic—element contents in the Monterey
Formation with modern sedimentary environments. The rate
of primary productivity of organic matter in the photic zone
of the Peru Shelf today, an area of exceptionally high pri-
mary productivity, is approximately 200 mg/cm2 per year
(Chavez and Barber, 1987), of which approximately 15 to
45 percent settles out of the photic zone (Dugdale and
Goering, 1970; Von Bockel, 1981). As much as 8 percent
escapes oxidation in the water column and benthic boundary
layer altogether and accumulates within the sediment
(Reimers and Suess, 1983). An even larger amount must

settle (that is, rain) onto the sea floor, as is the case in the
pelagic environment (Fischer and others, 1986; Sarnthein
and others, 1988). For the Monterey Formation, Isaacs (1985)
estimated a bulk-sediment-accumulation rate of 3 to 5 mg/
cm2 per year, although this rate varied spatially and tempo-
rally. By considering that (1) the average Cu content in the
marine fraction of the Monterey Formation is 37 ppm (fig.
14) and (2) the stoichiometry of accumulating organic mat-
ter was the same as that of modern plankton (table 5), we
calculate the rate of accumulation of organic matter required
to deliver Cu to the sea floor at 10 to 15 mg/cm2 per year. A
calculation based on the Fe content (fig. 7B) in excess of the
terrigenous contribution (NASC curve, fig. 6A) and the Fe
content of plankton (table 5) gives a similar accumulation
rate for organic matter. Cd and Zn require slightly lower
rates, and M0 and Se slightly higher rates. Thus, the sedi-
ment raining onto the sea floor consisted of approximately
80 percent organic matter. Our interpretation is that primary
productivity significantly lower than the current rate on the
Peru Shelf could have provided this amount and the total
marine fraction of Cu, Cd, Mo, Se, Zn, and Fe to the Monterey
sea floor.

If the sole source of these minor elements was organic
matter and minor elements were retained in the sediment
after deposition, then a projection of the interelement ratio
for any pair of minor elements in plankton should extend
into the field of concentrations for the Monterey Formation.
In fact, all the values are displaced slightly from the minor-
elementzCu trend of plankton (fig. 14). The shift in trends
away from the ratios in plankton is toward the seawater—
concentration ratios, suggesting that a small part of the
marine fraction may be attributable to the accumulation of a
hydrogenous fraction.

Unlike the Cd:Cu, MozCu, SezCu, Zn:Cu, and Fe:Cu
trends, the shifts in minor-element:Cu trends for Cr, V,
REE’s (not shown), and U away from the organic-matter
trends are extreme and must be explained largely by inor-
ganic processes. For Cr, U, and V, their diffusion across the
benthic boundary layer into a pore-water system that was 02
depleted offers one possible explanation (Brumsack and
Gieskes, 1983; Brumsack, 1986; Emerson and Huested,
1991; Klinkhammer and Palmer, 1991). This same explana-
tion might also account for the slight enrichment of Mo
relative to Cu (fig. 14). All else being equal, we might have
expected the order of enrichment in the rocks to reflect, in
part, their seawater concentrations: Mo>>U>V>>Cr; but
this is not the case. In absolute terms, V is somewhat more
enriched in rocks of the Monterey Formation than is Cr, and
both elements are much more strongly enriched than are Mo
and U (fig. 8). Their enrichments, over and above a biogenic
contribution and relative to their seawater concentrations,
follow the trend Cr>V>>U=Mo.

The thermodynamic properties of these elements (table
9) allow Cr and V to precipitate under conditions of denitri-
fication in the OMZ of the water column, as well as under

DISCUSSION: ELEMENTAL SOURCES—THE MONTEREY OCEAN 33

lower redox conditions, but these same properties restrict
Mo precipitation to sulfate-reducing conditions. Thus, bot—
tom-water conditions of denitrification can explain the much
greater enrichments of Cr and V. These two metallic ele-
ments would have been strongly enriched in sediment un-
derlying such an OMZ, more so than other minor elements,
by precipitation as oxyhydroxides and (or) adsorption onto
particulate phases within seawater, but unlikely by diffusion
across the benthic boundary layer. The absence of a strong
enrichment of U apparently is due to its occurrence in sea-
water as U02(CO3)§‘, rather than as U02(CO3)%‘. The slight
Mo enrichment probably reflects diffusion across the benthic
boundary layer, but we cannot dismiss the possibility of
brief periods of sulfate reduction in the bottom water, as
occur on the Peru Shelf (Dugdale and others, 1977).

Establishment of denitrification in the bottom water
constrains bottom-water advection. If we assume that the
denitrifying part of the water column was 250 m thick and
that approximately 25 percent of surface productivity was
oxidized in the bottom water—conditions similar to those
on the Peru Shelf today—a residence time for the bottom
water of approximately 5 yr would be required to establish
denitrification. Although this value will change by adjusting
the various parameters, the instability of the water column
of the present-day Santa Barbara Basin (Sholkovitz and
Gieskes, 1971) clearly suggests a residence time in this
modern, open-oceanic, denitrifying basin on the order of
years. This calculation should apply to “bottom” waters,
whether we are considering a basin environment or an open—
shelf environment, as illustrated in figure 3.

The Cr content of the Monterey Formation also limits
the residence time of the bottom water at the time of deposi-
tion. Assuming that (1) the thickness of denitrifying water
was 250 m, as above; (2) the initial Cr concentration in the
water advecting into the basin was 0.21 ppb (table 8), 25
percent of which was removed to the sea floor, the approxi-
mate maximum amount of Cr(III) in the DMZ of the eastern
Pacific Ocean (Murray and others, 1983); (3) the average Cr
content in the marine fraction of the Monterey Formation
is 102 ppm, 90 percent of which accumulated as a hydrog-
enous fraction (fig. 8); and (4) the sediment—accumulation
rate was 3 mg/cm2 per year (Isaacs, 1985), then the maxi-
mum residence time for bottom water in the basin is also
calculated at 5 yr. Adjusting the thickness of the denitrifying
section of the water column changes the residence time
proportionally but does not alter the agreement between
the calculation based on the accumulation of Cr and the
above calculation of the oxidation of organic matter. Al-
though this calculation is simplistic, the result is consistent
with our interpretation of bottom-water denitrification.

The residence time for bottom waters in permanently
sulfate reducing basins is considerably greater than this: in
the Black Sea about 375 to 1,000 yr (Ostlund, 1974; Murray
and others, 1991) and in the Cariaco Trench 100 to 200 yr
(Jacobs and others, 1987). Although sulfate reduction in the

bottom waters of such fiords as Saanich Inlet can be sea-
sonal (Anderson and Devol, 1973), several aspects of these
small inland basins suggest that they are unlikely to be
analogs of a large, open-ocean basin. For example, much of
the organic matter settling into the bottom water might be
terrigenous rather than marine, forcing sulfate reduction at
a much greater rate than that predicted by surface-water
productivity alone. Also, flushing apparently reestablishes
denitrification, rather than oxygen respiration, in the bot—
tom water of Saanich Inlet. Thus, the mean residence time
of the bottom water is more than merely 1 yr, and the water
is poised to almost immediately reestablish sulfate reduction
with the secession of flushing. Although we cannot dismiss
the dynamics of this basin as one possible explanation, the
longer bottom-water residence time required for the estab-
lishment of sulfate reduction in such larger basins as the
Black Sea, and the significantly shorter residence time for
bottom water of the Miocene basin (or open shelf), seems to
preclude sulfate reduction in the bottom water of the Santa
Barbara-Ventura Basin during Miocene time.

Field studies of REE’s have established their removal
from denitrifying seawater and their dissolution under con-
ditions of sulfate reduction (de Baar and others, 1988; Ger-
man and others, 1991). Sulfate reduction in the bottom
water would have required sulfate reduction in the pore
water of the surface sediment as well. Such a system should
have precluded any enrichment of REE’s above a detrital
contribution, and yet REE’s are enriched in the sediment,
although this conclusion is based more on the seawater-type
pattern of several samples (fig. 11) than on their absolute
contents (fig. 6). Nonetheless, denitrification in the bottom
water and sulfate reduction restricted to the near-surface
pore water could have allowed the accumulation of REE’s
from the water column. The content of marine La (fig. 12A)
supports this interpretation: Its content in the marine frac-
tion of the Monterey Formation and its content in seawater
(table 8) give a bottom-water residence time of 5 yr, the
same as did Cr. Thus, REE’s should have been no more
enriched than by the slight amount we observe.

Scavenging of additional minor elements in the water
column, particularly Th, Sc, Be, Ga, and Hf, by particulate
phases is clearly an important process on a global scale (Li,
1981; Balistrieri and Murray, 1984; Clegg and Sarmiento,
1989). The mere absence of these elements in the marine
fraction of the Monterey Formation, however, may not al-
low us to dismiss scavenging as an important minor-ele-
ment-enrichment mechanism in the Monterey Formation.
The low concentrations of Th and other elements of this
group in seawater should preclude our identification of a
hydrogenous fraction within bulk analyses. Leaching ex-
periments, which we have not pursued to date, might iden-
tify such a fraction.

Although Cd, Cu, Ni, and Zn are slightly enriched
above their biogenic input, scavenging cannot explain the
slight shifts in minor~elementzCu ratios toward their values

34 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

in seawater (fig. 14). Ni should be only weakly scavenged
from seawater, whereas Cu and Zn should be scavenged
more efficiently (Clegg and Sarmiento, 1989); yet Ni is the
more strongly enriched above a biogenic source. Also,
scavenging should have shifted the Zn:Cd ratio away from
the stoichiometric value in organic matter of about 9.2 (table
5), which is not observed (compare figs. 14A and 15 with
fig. 14H). Evidence against scavenging is also provided by
the metallic-element content of fecal material (table 7). Its
high Cd, Cu, and Zn contents indicate these minor elements
are strongly scavenged by fecal debris, but an NizFe ratio
approximating that in WSA suggests a detrital origin for Ni
(Piper, 1991). The low organic-carbon content (approx 5
weight percent; Youngbluth and others, 1989), and high
clay content (approx 85 weight percent; Dunbar and Berger,
1981) in fecal material emphasize the need for a complete
chemical analysis to fully account for the partitioning of
metallic elements between the various fractions of fecal
material. Even in the absence of such data, the enrichment
of Ni in the Monterey Formation over both Zn and Cu is
evidence against a major role for seawater scavenging in the
enrichment of minor elements in these rocks.
Accumulation within biogenic silica, in addition to or-
ganic matter, might account for the displacement of these
minor-element ratios away from the plankton value. The
enrichment of Zn in biogenic silica is supported by the
similarity of the distribution of Zn in seawater to that of
Si(OH)4 (Sclater and others, 1976). Analyses of biogenic
silica (Martin and Knauer, 1973), however, show that Cu is
even more enriched in this phase, which has a Zn:Cu ratio of
about 0.7. Accumulation of this phase on the sea floor, then,
followed by its dissolution and the retention of Cu and Zn
could explain the shift in the Zn:Cu trend in the rocks away

(A
(II

 

Siliceous
shale

   
 

(a)
O
I

  
  
 
   

Plankton O

Seawater

M
01
l

N
O
r

Phosphatic
shale

.4
(II
I

Cd CONTENT,
IN PARTS PER MILLION
8

 

 

0 50 1 60 1 I50 200
Cu CONTENT, IN PARTS PER MILLION

Figure 15. Cd versus Cu contents of marine fraction in sedimentary
rocks of the Monterey Formation. Labeled curves represent
averages. Data sources: circles, this study; squares, Leventhal
(1989); dots, C.M. Isaacs (unpub. data, 1993).

from the ratio in plankton of 10 (fig. 14H). The Zn:Cu ratios
in plankton, silica, and the Monterey Formation actually
suggest that silica supplied a major part of minor elements
to the sediment. This same mechanism might also contribute
to the low Cd contents, but a sampling bias also contributes
to the lower than expected average Cd content. The Cd-Cu
relation has two separate trends (fig. 9A). The samples with
the lower Cd:Cu ratios (phosphatic samples) seem to be
disproportionately represented. Additional analyses for the
Santa Barbara-Ventura Basin (C.M. Isaacs, unpub. data,
1993) and the analyses by Leventhal. (1989) for the Santa
Maria Basin (fig. 15) also show these two trends, but most
samples plot along the siliceous-shale trend.

An Ni content in biogenic silica needed to explain the
shift in the Ni2Cu ratio (fig. 14D) seems to be much higher
than we might expect to observe. Thus, the strong enrich-
ment of Ni in these rocks must remain enigmatic until its
distribution in biogenic phases is more fully evaluated. Its
behavior during early diagenesis (Shaw and others, 1990)
seems only to add to the problem; it is apparently remobi-
lized under 02-depleted pore-water conditions.

The slight shift of Cd:Cu, Mo:Cu, Se:Cu, UzCu, and
Zn:Cu ratios all away from their plankton values, toward
seawater values (fig. 14), might also be explained by a very
brief excursion of bottom-water redox conditions into the
field of sulfate reduction, as mentioned above. Just as the
DMZ on the Peru Shelf can become sulfate reducing for
brief periods of time (Dugdale and others, 1977), so might
have the bottom water of this Miocene sea. A simple calcu-
lation, similar to that made for Mo accumulation in early
Quaternary sediment from the Sea of Japan (Piper and Isaacs,
1995), limits sulfate-reducing conditions in the bottom wa-
ter considered here to less than about 1 percent of the time.
Thus, accumulating organic matter remains the dominant
source of these elements.

The variation in bottom-water redox is expressed by the
difference in V contents in the phosphatic unit and the shale
units (fig. 146). The higher values in the shale units require
accumulation under more strongly reducing bottom-water
conditions (table 9), an interpretation that seems to conflict
with the sulfur-isotopic data (Zaback and Pratt, 1992).

Our stoichiometric approach clearly has many prob-
lems because it is a simplified representation of an extreme-
ly complex system. Froelich and others (1979, 1988), Bender
and others (1989), J ahnke (1990), and Ingall and Van
Cappellen (1990) revealed the complex geochemistry of
major nutrients during diagenesis, from oxygen respiration,
through manganese reduction, denitrification, Fe(III) reduc-
tion, and sulfate reduction, to methanogenesis. The behavior
of minor elements during early diagenesis is likely to be
equally complex (Shaw and others, 1990). As future re-
search better defines the geochemistry of minor elements
in the modern marine environment, our interpretation of
their distributions in sedimentary rocks will surely require
adjustment.

CONCLUSIONS 35

PALEOCEANOGRAPHY

The late Miocene ocean is commonly considered as
representative of an ocean that underwent a global anoxic
event—that is, sulfate—reducing conditions much more wide-
spread in bottom water of the ocean than they are today.
Evidence generally cited for this representation is the seem-
ingly vast areal extent of formations of this age with high
organic-matter and minor—element contents, similar to those
of the Monterey Formation, and on the interpretation that
sedimentary rocks of this composition accumulated under
seawater sulfate—reducing conditions. This environment has
a very limited areal extent in the ocean today, and yet its
accumulating sediment represents a major sink for several
minor elements (Kolodny and Kaplan, 1970; Bertine and
Turekian, 1973; Cutter, 1982; Jacobs and others, 1987;
Emerson and Huested, 1991; Klinkhammer and Palmer,
1991). Sediment within this environment may or may not
have high minor-element contents, depending on the rate of
accumulation of the detrital fraction (dilution), but it will
have high minor—element-accumulation rates. The Monterey
Formation has high minor—element contents but minor-
element-accumulation rates that were typical of the modern
shelf environment.

The effect of a global anoxic event on the distribution
of minor elements in seawater would be drastic. In response
to their accumulating over a much larger area of the sea
floor, minor—element residence times and concentrations in
the ocean would decrease sharply. The decrease would be
felt worldwide and virtually instantaneously, owing to the
very short residence times of most minor elements (Goldberg,
1963b). Piper and Codispoti (1975) suggested that NO;
might have the same fate, with the somewhat-unexpected
consequence that if organic-matter enriched sedimentary
rocks represent periods of global anoxia, they must also
represent times of reduced global primary productivity.

The geochemistry of the Monterey Formation suggests
another interpretation for its high contents of organic matter
and minor elements. The high organic-matter content of this
formation and, possibly, of rocks of correlative age results
from low bulk-sediment-accumulation rates, that is, slight
dilution by detrital phases and biogenic carbonates and silica,
not from any significant change in primary productivity or
in the geochemistry of the world’s ocean. Locally, primary
productivity during much of the time represented by the
Monterey Formation was probably no higher than it is today
in the California Current. Similarly, high minor-element
contents reflect this moderate primary productivity and low
accumulation rate of diluting sediment fractions. The accu-
mulation rates of Cr and V, alone, required a somewhat-
expanded distribution of denitrifying bottom water, from its
current restricted distribution in the Santa Barbara Basin.
This local expansion of 02-depleted bottom water, however,
probably had no global significance. Interelement ratios of
all minor elements in the Monterey Formation can be ex-

plained by accumulation from a seawater with minor-ele-
ment contents similar to those in the North Pacific Ocean
today; in fact, interelement ratios in the Monterey Forma—
tion require such an ocean.

CONCLUSIONS

Analysis of 9 major-element oxides and 33 minor ele-
ments in 22 samples of the Sisquoc and Monterey Forma-
tions and Rincon Shale were carried out in three laboratories
by ICP, NAA, and XRF methods. The precision of most
analyses, on the basis of agreement of the results between
laboratories, was better than 5 percent, allowing us to iden-
tify contributions of the minor elements by terrigenous de-
bris, marine-biogenic matter, and marine hydrogenous
phases.

The interelement ratios between major-element oxides
(A1203, K20, Ti02) and minor elements (Co, Cs, Ga, Hf, Li,
Sc, Th) closely approach those of NASC and (or) WSA
standards. These ratios indicate that the detrital fraction was
the sole source for these elements and that it itself had a
terrigenous source. The strength of these relations allows us
to determine the detrital contribution to the total inventory
of other minor elements (Cd, Cr, Cu, Mo, Ni, Se, U, Zn,
REE’s) and Fe203 from the A1203zminor-elemental ratios
in the standards and the A1203 content of each individual
sample. The residual content of this group of minor ele-
ments and Fe203 represents, then, the marine contribution.

The interelement ratios between Cd, Cu, Mo, Se, Zn,
and Fe in this marine fraction of the rocks approximate the
corresponding interelement ratios in modern plankton, sug-
gesting that these minor elements had a predominantly bio-
genic source. During Monterey time, the rate of accumulation
of organic matter on the sea floor of the Miocene Santa
Barbara-Ventura and Santa Maria Basins necessary to pro-
vide these elements to the sediment was approximately equal
to that on the present-day California Continental Shelf, an
area of moderately intense coastal upwelling and primary
productivity in the photic zone of the water column.

The enrichments of Cr, V, and REE’ 5 required accumu-
lation directly from seawater, a hydrogenous input. On the
basis of their chemical properties and distributions in 02-
depleted environments of the ocean today, their accumula-
tion from seawater would have been enhanced by conditions
of denitrification in the bottom water. Their rates of accu-
mulation in Monterey sediment limited the residence time
of bottom water in the basin to a maximum of approximately
5 yr. This residence time is the same as that necessary to
establish denitrification in the bottom water by way of the
oxidation of settling organic matter.

Sulfate reduction was not established in the bottom
water through bacterial respiration, an interpretation based
on the preservation of a seawater-derived enrichment of
REE’s in the Monterey Formation, the absence of a strong

36 GEOCHEMISTRY OF MINOR ELEMENTS IN THE MONTEREY FORMATION, CALIFORNIA

marine input of U, and the absence of enrichments of Cu,
Cd, Se, Zn, and, particularly, Mo above a biogenic input.
Otherwise, Cu, Cd, Se, Zn, and Mo would have accumulated
as inorganic sulfides, in addition to accumulating in an
organic fraction, and REE’s would not have accumulated
from seawater at all but would have had solely a terrigenous
source. A hydrogenous input of Mo, which is 5 to 50 times
more abundant in seawater than V and Cr and 2,000 more
abundant than REE’s (La), would have been easily detected.
Sulfate reduction was restricted to the sediment pore water;
it likely closely approached the benthic boundary layer but
did not extend into the overlying water column.

In the ocean today, no single environment represents a
perfect analog of the Monterey Formation. The chemical
and biologic processes and bathymetry that controlled the
overall composition of these rocks do occur, but only within
several shelf-slope environments. Also, the Monterey For-
mation was deposited over several million years, during
which time the rocks recorded significant local oceano-
graphic changes. The minor—element content of the Monterey
Formation, however, requires that the chemistry of the open
ocean during late Miocene time was identical to that of
today.

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QE

’ 75
P6 U-Q. DEPOSlTCRY
no. 1567
BART MAY 2 2 1995
7-DAYS

Ecoregions of Alaska

 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1567

Prepared in cooperation with Colorado State University
and the Environmental Protection Agency

>UW§#4Wafififi$%fl&EMHflflfig

The Librarv - UC BerkeleV
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Geoloqical SurveV
professional paper

 

h Ecoregions of Alaska

By Alisa L. Gallant, Emily F. Binnian, James M. Omernik, and Mark B. Shasby

 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1567

Prepared in cooperation with
Colorado State University and the
Environmental Protection Agency

 

A spatial analysis of regional
ecological patterns in Alaska
using analog and digital maps
and descriptive information

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CONTENTS

Abstract ......................................................................................................................... 1
Introduction ................................................................................................................... 1
Background ................................................................................................................... 1
Methods ......................................................................................................................... 3
Materials ........................................................................................................................ 5
Ecoregion Descriptions ................................................................................................. 7
Arctic Coastal Plain ................................................................................................ 8
Arctic Foothills ....................................................................................................... 11
Brooks Range .......................................................................................................... 15
Interior Forested Lowlands and Uplands ................................................................ 17
Interior Highlands ................................................................................................... 20
Interior Bottomlands ............................................................................................... 23
Yukon Flats ............................................................................................................. 25
Ogilvie Mountains .................................................................................................. 28
Subarctic Coastal Plains .......................................................................................... 30
Seward Peninsula .................................................................................................... 32 '
Ahklun and Kilbuck Mountains .............................................................................. 34
Bristol Bay—Nushagak Lowlands ........................................................................... 38
Alaska Peninsula Mountains ................................................................................... 41
Aleutian Islands ...................................................................................................... 43
Cook Inlet ................................................................................................................ 45
Alaska Range .......................................................................................................... 48
Copper Plateau ........................................................................................................ 51
Wrangell Mountains ................................................................................................ 53
Pacific Coastal Mountains ...................................................................................... 55
Coastal Western Hemlock—Sitka Spruce Forests .................................................... 56
Summary ....................................................................................................................... 59
Acknowledgments ......................................................................................................... 59
References ..................................................................................................................... 60
Appendix 1 .................................................................................................................... 64
Appendix 2 .................................................................................................................... 70
Appendix 3 .................................................................................................................... 71
PLATES
1. Ecoregions of Alaska ........................................................................................................................................... In pocket

III

IV CONTENTS
ILLUSTRATIONS

1. Map of Alaska ............................................................................................................................................................... 9
2. Arctic Coastal Plain thaw lakes .................................................................................................................................... 9
3. Arctic Coastal Plain vegetation .................................................................................................................................... 10
4. Arctic Coastal Plain vegetation .................................................................................................................................... 10
5. Arctic Foothills physiography and drainage pattern ..................................................................................................... l3
6. Arctic Foothills beaded stream drainage ...................................................................................................................... 13
7. Arctic Foothills vegetation ............................................................................................................................................ 14
8. Brooks Range physiography ......................................................................................................................................... 14
9. Brooks Range unstable slopes ...................................................................................................................................... 16
10. Brooks Range vegetation .............................................................................................................................................. 16
11. Interior Forested Lowlands and Uplands forest vegetation ......................................................................................... 18
12. Interior Forested Lowlands and Uplands burned area ................................................................................................. 18
13. Interior Highlands physiography .................................................................................................................................. 22
14. Interior Bottomlands physiography, surface water, and vegetation ............................................................................. 22
15. Yukon Flats physiography and surface water ............................................................................................................... 25
16. Yukon Flats physiography and vegetation .................................................................................................................... 26
17. Yukon Flats vegetation ................................................................................................................................................. 26
18. Ogilvie Mountains physiography and vegetation ......................................................................................................... 29
19. Subarctic Coastal Plains physiography, surface water, and vegetation ........................................................................ 29
20. Subarctic Coastal Plains forest vegetation ................................................................................................................... 31
21. Seward Peninsula physiography and vegetation .......................................................................................................... 33
22. Seward Peninsula gelifluction lobes ............................................................................................................................. 33
23. Seward Peninsula low scrub and dwarf scrub—graminoid communities ...................................................................... 35
24. Ahklun and Kilbuck Mountains physiography ............................................................................................................. 35
25. Ahklun and Kilbuck Mountains vegetation .................................................................................................................. 36
26. Ahklun and Kilbuck Mountains vegetation .................................................................................................................. 37
27. Bristol Bay—Nushagak Lowlands physiography ......................................................................................................... 37
28. Bristol Bay—Nushagak Lowlands vegetation ............................................................................................................... 40
29. Alaska Peninsula Mountains physiography, soils, and vegetation ............................................................................... 40
30. Alaska Peninsula Mountains vegetation ....................................................................................................................... 42
31. Aleutian Islands physiography and vegetation ............................................................................................................. 42
32. Cook Inlet vegetation .................................................................................................................................................... 44
33. Cook Inlet vegetation .................................................................................................................................................... 44
34. Cook Inlet vegetation .................................................................................................................................................... 47
35. Alaska Range physiography and glaciation .................................................................................................................. 48
36. Alaska Range vegetation .............................................................................................................................................. 50
37. Alaska Range vegetation .............................................................................................................................................. 50
38. Copper Plateau surface water and vegetation ............................................................................................................... 52
39. Wrangell Mountains physiography and glaciation ....................................................................................................... 53
40. Wrangell Mountains glacial till .................................................................................................................................... 54
41. Pacific Coastal Mountains physiography ..................................................................................................................... 55
42. Coastal Western Hemlock—Sitka Spruce Forests physiography and vegetation .......................................................... 57

ECOREGIONS OF ALASKA

By Alisa L. Gallant‘, Emily F. Binnianz, James M. Omernik‘, and Mark B. Shasby4

ABSTRACT

A map of ecoregions of Alaska has been produced as a
framework for organizing and interpreting environmental data
for State, national, and international inventory, monitoring,
and research efforts. The map and descriptions of 20 ecolog-
ical regions were derived by synthesizing information on the
geographic distribution of environmental factors such as cli-
mate, terrain (including information on physiography, geolo-
gy, glaciation, permafrost, and hydrologic features), soils, and
vegetation. A qualitative assessment was used to interpret the
distributional patterns and relative importance of these factors
for influencing the character of the landscape from place to
place. The specific procedures and materials used to delineate
the ecoregion boundaries are documented, and the environ-
mental characteristics in each ecoregion are described. An
accompanying map shows the distribution of the ecoregions
and the transitional areas along their boundaries.

INTRODUCTION

A map and descriptions of ecological regions (ecore-
gions) of Alaska have been produced as a framework for
organizing and interpreting environmental data for State,
national, and international inventory, monitoring, and
research efforts. Ecoregions have been defined by Wiken
(1986) as ecologically distinct areas resulting from “... the
mesh and interplay of the geologic, landform, soil, vegeta-
tive, climatic, wildlife, water and human factors which may
be present. The dominance of any one or a number of these
factors varies with the given ecological land unit.” The map
of Alaskan ecoregions was derived by synthesizing informa—
tion on the geographic distribution of environmental factors
such as climate, terrain (including information on physiogra-
phy, geology, glaciation, permafrost, and hydrologic fea-

|Forest Sciences Department, Colorado State University, Fort Collins.
Work performed under US Geological Survey Cooperative Agreement
#1434-93—A—00760

2Hughes STX Corporation, US. Geological Survey, EROS Alaska Field
Office, Anchorage. Work performed under US. Geological Survey
Contract #1434—92—C—4004

3Environmental Protection
Laboratory, Corvallis.

4US. Geological Survey, EROS Alaska Field Office, Anchorage.

5The term “framework” will be used throughout this report to represent the
ecoregion map and accompanying descriptions as a package. The descriptions
are an important component because they allow the user to assess the charac—
teristics that are representative of each ecoregion and the relative amounts of
within—region environmental variability. Use of the map without the descrip-
tions restricts the selection of representative field sites for regional analyses.

Agency, Environmental Research

tures), soils, and vegetation. This synthesis was a qualitative
assessment of the distributional patterns and relative impor-
tance of these factors for influencing the character of the
landscape from place to place.

The ecoregion map has been designed to accommodate
a wide range of regional concerns, basically any that affect,
or are affected by, the environmental factors analyzed to
develop the map. Examples of applications for the map
include the assessment of natural resources (regional chemi-
cal, physical, and biological characteristics of surface
waters, soil erosion potential, wildlife habitat diversity, and
ecological risk assessment) and effects research (potential
regional ecological effects from environmental contaminants
or climate change). The map can also be used to evaluate
how well research sites are distributed across ecoregions or
along regional environmental gradients, and the regional
descriptions can be used to infer the relative density of sam-
ple sites needed to represent the ecological variability occur-
ring within each ecoregion so that site—level information can
be extrapolated to larger areas. Given national trends toward
more holistic monitoring and management of ecosystems,
the ecoregion map and descriptions provide an ecological
frameworks to help integrate efforts among different envi-
ronmental disciplines and agencies.

Sections in this report describe the origin of the need and
philosophy for delineating ecoregions of Alaska
(Background), general procedures (Methods) and references
(Materials) used, and environmental characteristics occurring
in each ecoregion (Ecoregion Descriptions). The accompany-
ing map (pl. 1) shows the distribution of Alaskan ecoregions.
Environmental characteristics that typify each ecoregion are
tabulated in appendix 1 and also appear on the reverse side of
the map. Specific methods used to delineate each ecoregion
are discussed in the descriptions of the individual regions.

BACKGROUND

Interest in developing the map of Alaskan ecoregions
evolved from the need to have an ecological framework that
is based on a variety of environmental characteristics of
interest to different State, Federal, and international agen-
cies. Single—theme frameworks have traditionally been pop-
ular because they are customized for specific concerns, such
as forest resources, soil characteristics, or agricultural poten-
tial. However, use of different frameworks by different
administrative agencies results in duplication of effort and
inability to integrate and co—reference data across agencies
and disciplines (Rubec, 1979). An ecological framework

1

2 ECOREGIONS OF ALASKA

that can integrate many environmental characteristics dimin-
ishes these problems and assists in the exchange of informa-
tion (Bailey and others, 1985). The utility of multipurpose
ecoregion frameworks, such as those developed for the con-
terminous United States (Omernik, 1987, 1995) and Canada
(Wiken, 1986), has been successfully demonstrated in vari-
ous projects (for example, Hughes and others, 1986; Rubec,
1979; Whittier and others, 1988; Whittier and others, 1987).
Work is under way to combine the frameworks for Canada
and the conterminous United States into one covering all of
North America (James Omernik and Ed Wiken, oral commun,
1993, 1994). Delineation of Alaskan ecoregions is a step to
furthering this work. Additionally, a growing interest in the
effects of potential global environmental change on ecosys-
tems, particularly on arctic systems,6 has promoted an effort to
expand the ecoregional frameworks developed for Alaska and
Northern Canada to all the northern circumpolar area.

The ecological frameworks developed for Alaska, the
conterminous United States, and Canada reflect a common
philosophy and methodology, making it possible to combine
these frameworks across international borders. The
approach and objectives of these frameworks differ from
those used to develop other, multipurpose7, regional schemes
covering Alaska, such as the “Land Resource Regions and
Major Land Resource Areas of the United States” (common-
ly referred to as MLRA’s; U.S. Soil Conservation Service,
1981), the “Major Ecosystems of Alaska” (Joint Federal-
State Land Use Planning Commission for Alaska, 1973), and
the “Ecoregions and Subregions of the United States”
(Bailey and others, 1994).

The map of MLRA’s depicts two levels of classification
hierarchy that were developed by considering a number of
environmental characteristics similar to those used to delin-
eate the ecoregions of Alaska. However, the main focus of
the Soil Conservation Service in developing MLRA’s was
land management concerns; the identification of regions was
based on their land use potential. In addition, the Soil

6This interest is evidenced in the escalating number of international
meetings and symposia on arctic ecological concerns, such as those includ—
ed in this list of recent meetings: (1) The Panarctic Biota Project (Moscow,
Russia, February 1991), (2) the Arctic Monitoring and Assessment
Program (Tromso, Norway, December 1991), (3) the Classification of
Circumpolar Arctic Vegetation (Boulder, Colorado, USA, March 1992),
(4) the Second Circumpolar Symposium on Remote Sensing (Tromsta,
Norway, May 1992), (5) Global Change and Arctic Terrestrial Ecosystems
Conference (Oppdal, Norway, August 1993), (6) the Arctic Environmental
Reference Database Workshop (Arendal, Norway, September 1993), (7)
the International Symposium on the Ecological Effects of Arctic Airborne
Contaminants (Reykjavik, Iceland, October 1993), and (8) the Third
Circumpolar Symposium on Remote Sensing of Arctic Environments
(Fairbanks, Alaska, USA, May 1994).

7The term “multipurpose” refers to regions that reflect general patterns
of many ecosystem characteristics, therefore providing an ecological
framework that should be generally useful for many environmental pur-
poses.

8The ecoregional maps delineated for the conterminous United States
(Omernik, 1987) and Canada (Wiken, 1986) were developed using this
approach.

Conservation Service did not have access to several
statewide references that have since become available.
These references improve the data base for interpreting
ecoregion patterns.

The map of “Major Ecosystems of Alaska” (Joint
Federal-State Land Use Planning Commission for Alaska,
1973) shows the distribution of nine classes of ecosystems
within a single hierarchic level. The focus of the ecosystems
map is on the regional distribution of vegetation community
type and structure. Information relating to other landscape
characteristics, such as topography, hydrology, and climate,
is considered only so far as it influences ecosystem type.
The resultant classes contain much variability in environ-
mental characteristics that are not reflected in the ecosystem
type. For example, the “Alpine Tundra” ecosystem class
encompasses mountain formations of different geologic ori-
gin and climatic regime. Therefore, the map may not be use-
ful for addressing concerns related to soil or surface water
characteristics.

The map “Ecoregions and Subregions of the United
States” (Bailey and others, 1994) depicts four hierarchic lev-
els of terrestrial ecological units. The authors explain that,
“At each successive level [of the hierarchy] a different
ecosystem component is assigned prime importance in the
placing of map boundaries.” Climatic characteristics are
used to delineate regions at the broadest level; vegetative
features are used at the second level; the distinction between
montane and nonmontane areas distinguishes the third level;
and physiographic units define the finest level.

The “Ecoregions of Alaska” map depicts a single level
of resolution (although the ecoregions are being aggregated
to conform with the coarser level of resolution planned for
the map of North American ecoregions that was discussed
earlier). Unlike the method used by Bailey and others (1994)
in defining the ecoregions for Alaska, our approach is to con-
sider a suite of environmental characteristics, regardless of
the level of hierarchic resolution, rather than assigning
importance to a single environmental characteristic per level
of classification hierarchy.8 There are at least three reasons
for this approach. First, the degree of influence of any one
environmental characteristic changes from region to region,
and even within regions (Omernik, 1987, 1995; Wiken,
1986); that is, there is no single, consistently reliable predic—
tor of where boundaries should be drawn for multipurpose
regions. An example is the popular use of “climate” at glob-
al, regional, and finer scales to predict the distribution of
ecosystems. The predictions have been disappointing in
light of the actual distribution of ecosystems. The reason for
this poor performance is that vegetation is also strongly
affected by other characteristics, such as interspecific com-
petition, factors affecting soil temperature and moisture, rate
of seed dispersal and establishment of propagules, and land
management practices (Barbour and others, 1987; Davis and
others, 1986 in Prentice, 1992; Prentice, 1992;), so consider-
ation of interrelationships among several environmental

METHODS 3

variables is necessary to understand distributional patterns.

Second, if emphasis is placed on a single factor at a par-
ticular hierarchic level, the resultant regions may not reflect
the distribution of other important features that have only a
weak association with that factor. Recall that in the example
described for the map of “Major Ecosystems of Alaska,”
regional patterns related to soil type or surface water charac-
teristics were not adequately recognized when the single fac-
tor of vegetation community type was emphasized for delin-
eating the regions.

Third, the data set representing the distribution of the
single factor includes varying degrees of informational reso-
lution and accuracy. For example, weather stations are not
distributed in a systematic network. The quality of interpo-
lation of data among stations is affected by the methods of
measurement at each station, the distance between stations,
and the intervening orographic (or other) effects. Similar
problems arise with soil or geology references, where con-
tinuous map surfaces have been generated from differential-
ly distributed observations. Therefore, weaknesses in a sin-
gle information source can have a heavy impact when that
source is emphasized in delineating regions. Incorporating a
suite of independently derived references into the delineation
process helps to counter the influence of weak information
from a single data source.

The multihierarchic maps so far discussed (the MLRA’s
and “Ecoregions and Subregions of the United States”) pri-
marily represent a “top down” approach toward delineating
ecological units. Information is first analyzed to delineate
the coarsest level of classification in a hierarchy (on the
order of 104 km2 for our purposes). Successively more
detailed information is then analyzed to subdivide the class-
es into more detailed subunits. An alternate approach is
described by Walker and Walker (1991) in their work on
Alaska’s North Slope. Data are gathered and patterns ana-
lyzed beginning at the microscale level (100—106 m2). A hier-
archy of units is then constructed upward (“bottom up”)
through mesoscale (10—104 km) and macroscale (104—106 kmz)
levels of information. The objectives of the approach taken by
Walker and Walker (1991) were to define the types of eco-
logical processes, questions, data, and linkages appropriate
to different hierarchic scales of regional analysis. Such an
approach requires a very long—term, intensive effort for map-
ping regions. Since our objective was to develop an ecore-
gion framework for the state of Alaska, a “top down”
approach was more appropriate because it directly addressed
the landscape scale of interest, with little dependence on
intensive, detailed ecosystem studies. This top—down
approach not only resulted in a product within a relatively
short time, but also provided an overall ecological context
for further subdivision of regions as interest and availability
of more specific data emerge.

When ecoregions are being mapped, errors can be intro—
duced into the process in several ways. Boundaries and
other map components may be inaccurately located; classes

can be incorrectly assigned or may not be informationally
discrete; the spatial or informational resolution of classes
may be misrepresented; data may not be available for some
areas; and data accuracy may change because of temporal
aspects in the landscape (for example, water level changes).
These factors pertain to the reference maps used to derive the
ecoregion map, as well as to the process used to delineate the
ecoregions. This makes it difficult to determine the accura-
cy of the map.

Other problems with determining the accuracy of an
ecoregion map relate to field sampling logistics,
within—region heterogeneity, and field and map differences
in informational resolution.

Field Sampling Logistics. — Because each ecoregion has
been defined on the basis of a number of ecological charac-
teristics, field verification of the ecoregion map would entail
collecting information on climate, physiography, geology,
soils, permafrost, glaciation, hydrology, and vegetation for
each sample site. Some of these variables are readily evalu—
ated in the field, but others are not. The difficulty of col-
lecting information for all of these variables at each site, plus
the problem of site accessibility (most sites are not accessi-
ble by ground transportation, and many are not accessible by
air), makes accuracy assessment from the field infeasible.

Within—Region Heterogeneity. — The array of combina-
tions of environmental characteristics that could be expected
within each ecoregion would have to be represented in the
field verification data set. This requires a more detailed level
of within—region analysis than that used to delineate the
ecoregions because of the top—down approach that was used.

Field and Map Informational Resolution. — The ecore—
gions have been delineated at a very general level of informa-
tional resolution. It would be necessary to design the collec-
tion of field data so that the same level of generalization is rep-
resented. This is difficult because the surrounding environ-
mental context for an ecoregion may be lost at the site level.

Because of the multipurpose nature of the ecoregion
map, it may be inappropriate to attempt to assess its accura-
cy. Boundaries between regions are expected to be “gener-
ally” correct for a number of purposes, but are not expected
to precisely fit the distribution of any singular variable.
Therefore, there is not even a conceptual set of boundaries
that will be perfect for all uses of the map. It is more perti—
nent to assess whether stratification of sample data by ecore-
gion helps to explain spatial variation of particular variables
of interest (an assessment of the utility of the map).

METHODS

A number of environmental references were examined for
this analysis, including statewide information on climate (sea-
sonal and annual temperatures, rain, and snow), physiography
(landsurface forms, topography, elevation, amount of local
relief, and local surface irregularity), surficial and bedrock

4 ECOREGION S OF ALASKA

geology, soils, permafrost, glaciation, hydrology, and current
and potential vegetation. Previous work (Gallant and others,
1989; Omernik, 1987; Oswald and Senyk, 1977; US. Soil
Conservation Service, 1981; Wiken, 1979, 1986) has shown
that these factors are of primary importance for delineating
ecoregional patterns. The steps for mapping ecoregions have
been described in Gallant and others (1989) and involve delin-
eating areas where unique combinations of different environ-
mental factors coincide. In Alaska, for example, topographic
data and physiographic maps show several extensive flat
coastal plain areas that coincide with areas depicted as wet tun-
dra on a map of major ecosystems. Among these coincidental
areas, one occurs where arctic climate prevails, while several
occur where subarctic climate prevails. Different climatic
regimes result in different growing season lengths, different
hydrologic cycles, and some variation in occurrence of plant
species. Such differences led us to distinguish the Arctic
Coastal Plain Ecoregion from the Subarctic Coastal Plains
Ecoregion. Another example includes the montane areas in
Alaska. All of these areas are mapped as having steep, high,
rugged mountains and alpine tundra ecosystems. Within these
areas of coinciding terrain and vegetation components are
areas subject to arctic, continental, transitional, or coastal cli-
matic influences that affect hydrologic characteristics and plant
species distributions. Additionally, there are different geologic
formations and soil parent materials that affect soil chemistry
and moisture holding capacity and the physical and chemical
characteristics of surface waters. These variations in condi-
tions resulted in our recognition of several different montane
ecoregions.

We used a predominantly qualitative approach for eval-
uating and delineating ecoregions. It would have been
quicker and easier to duplicate a product derived from a
strictly quantitative approach; however, we thought that the
product would have been less accurate in its representation
of ecoregions. It is difficult to apply strict quantitative
weightings to represent the importance of different environ-
mental factors for delineating ecoregions because the impor—
tance of these factors, and the accuracy with which they are
mapped, vary within and among ecoregions. An example
occurs within the Yukon—Kuskokwim lowland portion of the
Subarctic Coastal Plains Ecoregion. The importance of a
particular vegetation type for defining the extent of the
ecoregion varies across the region. Areas north of the Yukon
River include both wet and moist tundra communities and
exclude forests, while areas south of the Yukon River include
only wet tundra because moist tundra is more indicative of
the adjacent region to the south. A qualitative, interactive
approach allows the human interpreter to recognize the need
for changing the delineation criteria along the border of adj a-
cent ecoregions. A more mechanical approach would simply
delineate the ecoregions using prescribed factor weightings.
The question of whether a factor’s importance varied
throughout a region would most likely be overlooked.

The decision of when to delineate an area as an ecore-

gion is a judgment call that depends on (1) the combination
and pattern of environmental characteristics occurring in that
area versus those in the surrounding areas, (2) the size of the
area, (3) the informational resolution and accuracy of the ref-
erence material used in delineating regions, and (4) the infor-
mational resolution and scale intended for the final frame-
work. These four aspects are further described below.

1. There is more variation in the combination of envi-
ronmental characteristics within some regions than between
others. The size and distribution of the components that
make up a landscape pattern are important for deciding
whether areas should be classified as separate regions or
consolidated within a single region at a given level of region-
al resolution. For example, the Ahklun and Kilbuck
Mountains Ecoregion consists of clusters of steep, jagged
peaks separated by broad valleys. At the informational res-
olution depicted on our map, it is more appropriate to aggre—
gate these mountains and valleys into a single ecoregion.
However, the ecoregion could then be subdivided to separate
the mountains from the valleys at a finer level of resolution.

2. There are no hard and fast rules for designating a min-
imum—area criterion for ecoregions. Generally, 10,000 km2
or larger is a good size for regions of State—level frameworks
because the area is large enough both to be distinctive on
statewide maps of environmental variables and to be recog-
nized as a management unit for State resources. However, in
some circumstances this “rule” is not suitable. For instance,
an extensive ecoregion might have many small outliers that
are easily distinguishable on the reference materials, as in
the Interior Highlands and the Interior Bottomlands
Ecoregions in Alaska. The outliers, alone, are too small to
be considered as a separate ecoregion; but in the context of
mapping the larger, more extensive part of the ecoregion, it
makes sense to delineate associated outliers that are still dis-
cernible at the statewide scale. Another exception to a size
criterion arises when an ecoregion is broken up by a water-
body, as in the Aleutian Island Ecoregion. All of the indi-
vidual islands may be smaller than the minimum—size crite-
rion, but they are distinctive enough to be recognized as a
region in the context of their grouping and their location, and
their total area exceeds the minimum—size criterion.

3. The informational resolution and accuracy of the ref-
erence materials used for delineating ecoregions impose
implicit limits on the level of detail that can be depicted in
the resultant ecoregion map. It is misleading to delineate
regions that are more detailed than the bulk of the reference
material from which they were defined; rather, regions
should be less detailed than the components that were used
to define them.

4. The intended use of the final framework affects the
size and level of detail that is delineated for the regions. A
very general framework will have relatively large regions
separated by smooth boundaries. Accompanying regional
descriptions will also be fairly general, listing only the major
characteristics that typify each region. A very refined frame-

 

MATERIALS 5

work will have small regions (or one or more levels of
regional hierarchy) with more intricate boundaries and
detailed descriptions of regional characteristics. The pur—
pose for creating the framework governs the level of detail
that should be shown on the final product.

The general procedures used to produce the map of
ecoregions of Alaska involved an iterative cycle of steps. The
initial delineation of ecoregions was based on analysis of
hardcopy maps and descriptive text. Maps representing the
environmental variables listed earlier were examined to
locate concurrent spatial patterns of the different variables.
Also considered were the ecological processes associated
with these factors. An early draft map of ecoregions was pre—
pared by outlining areas (that met the minimum size criteri-
on) of unique combinations of factors. This initial draft map
was used to plan an itinerary for summer field reconnais—
sance. The purpose of the reconnaissance was to compare
ecosystems on the ground with the variables that represented
them on the reference maps. Prospective ecoregions were
visited by means of low—altitude flyovers and, where acces-
sible, by ground. The draft map of ecoregions was then mod—
ified on the basis of field reconnaissance, and a second ver-
sion was prepared and circulated to a number of regional
experts for review. Reviewers were asked to comment, based
on their field experience, on whether the set of ecoregions
depicted on the map corresponded with their understanding
and general knowledge of ecological patterns in Alaska.
Review comments provided guidance toward modifications
for a third draft map. This third map was circulated to the
reviewers, and their comments were incorporated. Final
boundary placement involved manipulating of digital files in
a geographic information system (GIS) to reduce errors intro-
duced by estimating the location of landscape patterns from
the variety of scales and projections used in the reference
maps. The GIS also was helpful for creating new maps
derived by combining information from different reference
maps (for example, mapping the coincidence of the distribu-
tion of major ecosystem types with different terrain features
or with patterns on images developed from satellite data).

The final map of ecoregions was further augmented to
show the approximate transitional zones between regions.
The zones are depicted as cross—hatched areas overprinted on
the ecoregions. A transitional zone represents an area that
shares the characteristics of adjacent regions. For example, a
transitional zone between a mountainous region and a plains
region might consist of widely scattered mountains separated
by broad plains. Within each ecoregion are areas that are not
indicative of the environmental characteristics that typify the
region. These areas are not shown as transitional zones.
Transitional zones distinguish land that is adjacent to, and
shares the characteristics of, two or more ecoregions.
Because of the relatively small scales of the ecoregion map
and the references used to develop the map, it is not possible
to depict transitional zones along all of the ecoregion bound-
aries. It is important to remember that a line on the ecoregion

map already represents an area (swath) on the ground, even
when no additional transitional zones are indicated.

When selecting names for ecoregions, we generally
tried to include information on the location of the region, as
well as a dominant distinguishing feature. Some examples
of names are: (1) Arctic Coastal Plain Ecoregion, which
confers climatic, physiographic, and location information,
(2) Interior Forested Lowlands and Uplands Ecoregion,
which confers information on physiography, vegetation com—
munity structure, and location, and (3) Coastal Western
Hemlock—Sitka Spruce Forests Ecoregion, which indicates
maritime climate, forest type, and coastal location attributes.
Most of the mountainous regions simply bear the name of
their respective physiographic units, because this information
conveys both location and terrain characteristics. Regions
encompassing a large variety of ecological characteristics,
such as the Seward Peninsula and Cook Inlet Ecoregions,
have names that denote only location. Attempts to make the
names more descriptive would have made them long and
unwieldy. We also avoided locational adjectives that are
Alaska—centered, such as northern or southeastern, because
eventually Alaskan regions will be included in North
American and Northern Circumpolar regional frameworks.

MATERIALS

Statewide and regional data sets and reports were
acquired for climate, physiography, elevation, geology and
geomorphology, soils, permafrost, glaciation, vegetation,
hydrology, wildfire occurrence, land use, and wildlife char—
acteristics. These references are itemized below by topic.

Climate. — Weather station data were obtained primarily
from two sources: (1) the World WeatherDisc (WeatherDisc
Associates, Inc., 1990, US. Monthly Normals and
Worldwide Airfield Summaries data sets), a data base con-
taining data acquired from the archives of the National
Climatic Data Center and the National Center for
Atmospheric Research and (2) a six—volume set of Regional
Profiles of Alaska (Selkregg, 1974). Climatic information
was also compiled from regional descriptions in several pub-
lications (Black, 1955; Hopkins, 1959; Kimmins and Wein,
1986; Oswald and Senyk, 1977; Reiger and others, 1979;
Slaughter and Viereck, 1986).

Terrain. — A number of references provided information
on physiographic characteristics (Black, 1955; Drury, 1956;
Oswald and Senyk, 1977; Reiger and others, 1979;
Spetzman, 1959; US. Geological Survey, 1964; Wahrhaftig,
1965). The US. Geological Survey (USGS) Map E shad-
ed—relief map (1987a) was also useful. USGS digital eleva-
tion data at a l—km2 resolution were used to determine ele—
vation, slope gradient, and terrain roughness. Terrain rough-
ness is an evaluation of the variability of local (within 5 km)

6 ECOREGIONS OF ALASKA

topographic relief. A terrain roughness map was derived
using the steps identified in appendix 2. Classes of local ter-
rain roughness include very low, low, moderate, high, and
very high (see appendix 2 for a definition of these classes).

Information on geology was obtained from maps and
reports by Beikman (1980), Black (1951, 1955, 1969), Drew
and Tedrow (1962), Karlstrom and others (1964), Oswald
and Senyk (1977), Reiger and others (1979), Selkregg
(1974), Spetzman (1959), US. Geological Survey (1964,
1987a), and Wahrhaftig (1965).

A map showing the extent of Pleistocene glaciation in
Alaska (Coulter and others, 1962) was the main source of
information on glaciation. Several reports (Oswald and
Senyk, 1977; Reiger and others, 1979; US. Geological
Survey, 1964; Wahrhaftig, 1965) were also helpful.

Information on permafrost came from a map classifying
the distfibution of permafrost in Alaska (Ferrians, 1965). Other
publications (Black, 1955; Ferrians and Hobson, 1973; Reiger
and others, 1979) were used to augment this information.

Several publications were helpful for characterizing sur-
face waters and other hydrologic features (Drury, 1956;
Reiger and others, 1979; Selkregg, 1974; Wahrhaftig, 1965;
US. Geological Survey, 1987a). A map showing the distri~
bution of wetlands in Alaska (Hall, 1991) was helpful in
depicting general areas of wetlands, but it included no fur-
ther classification of wetland types.

Soils. — A series of draft maps of various soil components,
derived from information published in the Exploratory Soil
Survey of Alaska (Reiger and others, 1979), was provided by
the USGS (Larson and Bliss, written commun., 1992). Several
published references were also used (Drew and Tedrow, 1962;
Reiger and others, 1979; Selkregg, 1974). More recent soil
information (since the publication of the Exploratory Soil
Survey) was provided by soil scientists (Moore, written com~
mun., 1993 and Ping, written commun., 1993).

Vegetation. — No statewide vegetation map has been
completed for Alaska, although parts of the State have been
mapped by different agencies. A subset of these maps
(Fitzpatrick—Lins and others, 1989; Markon, 1992; Powell
and others, 1993; Talbot and Markon, 1986, 1988; Talbot
and others, 1986; US. Geological Survey, 1987b), along
with other descriptive information and species lists (Drury,

gThe AVHRR, mounted on National Oceanic and Atmospheric
Administration (NOAA) satellites, has a polar, sun—synchronous orbit. The
AVHRR sensor offers spatial resolution of approximately 1 km2 (after geo—
graphic correction) and collects data in the red—visible, near—infrared,
mid—infrared, and thermal—infrared wavelengths.

l0An NDVI value is calculated for each pixel by using the following
equation: (Near IR — Visible)/(Near IR + Visible). This ratio relates to a
measure of relative photosynthetic activity; that is, the higher the NDVI
value, the greater the level of photosynthetic activity (Eidenshink, 1992).
However, NDVI values can be misleading because of the effects that
clouds, background soil color, and surface texture have on the original vis—
ible and near—IR reflectance values (Huete and Jackson, 1988; Huete and
others, 1985).

1956; Fleming, written communication, 1993; Reiger and
others, 1979; Selkregg, 1974; Shasby, unpub. mapping,
1985; Spetzman, 1959; US. Fish and Wildlife Service,
1987a, 1987b; US. Forest Service, 1992; Viereck, 1989;
Viereck and Little, 1972; Viereck and others, 1986, 1992;
Wibbenmeyer and others, 1982) were used for this project.
Descriptive information on vegetation for Alaskan ecore-
gions that border Canada was augmented using a publication
by Oswald and Senyk (1977).

We also used surrogate information regarding the distri-
bution of vegetation, such as statewide maps of major ecosys-
tem types (Joint Federal-State Land Use Planning
Commission for Alaska, 1973; Viereck and Little, 1972) and
maps of characteristics related to photosynthetic activity
(Markon and others, 1995). The latter refers to a collection
of data sets derived from twice—monthly composites of
advanced very high resolution radiometer (AVHRR)9 sensor
data that were available for the 1991 (Binnian and Ohlen,
1992) growing season. Each twice—monthly composite rep-
resents the five—band sensor data for the acquisition date hav-
ing the highest Normalized Difference Vegetation Index'0
(NDVI) value for each pixel. The conceptual basis for the
composite is that the highest NDVI value represents condi-
tions of least atmospheric interference during data acquisition
(Loveland and others, 1991). The products derived from
these composites (hereafter referred to as the “derivative
products”) include maps of the (1) temporal classification of
composite NDVI values over a growing season (resulting in
80 “greenness” classes; methodology for deriving this type of
classification has been described in Loveland and others,
1991), (2) duration of greenness (number of days, per green-
ness class, that the NDVI value exceeded a threshold value of
0.10), (3) yearly maximum NDVI (maximum NDVI per pixel
for a growing season), (4) mean NDVI (the average
twice—monthly composite value per pixel), (5) onset of green-
ness (the composite period during which the NDVI value for
a given pixel rose above 0.10), and (6) period of peak green-
ness (the composite period during which the maximum NDVI
value occurred for each pixel). Another derivative product
that proved particularly useful for capturing spatial trends in
vegetative characteristics is a relative color—infrared repre-
sentation (hereafter referred to as the “relative CIR image”)
of the 80 greenness classes (Fleming, 1994).

The AVHRR data products were not used to delineate the
actual boundaries of ecoregions because these data represent
characteristics detected over a single growing season. The
annual variation in these characteristics has not been ana-
lyzed, so it is difficult to determine how well a single grow-
ing season represents long—term landscape patterns. We used
the AVHRR data products to aid in the interpretation of the
spatial patterns shown on the rest of the reference maps.

Wildfire. — Although not used to delineate ecoregions,
information on wildfire has been included in the descrip—
tions. Wildfire information in this report is limited to fires

ECOREGION DESCRIPTIONS 7

started by natural causes. Human—caused fires are not dis-
cussed because they are concentrated primarily along high-
ways and in settled areas and are not necessarily indicative
of natural regional ecological processes. Information on the
occurrence of lightning fires was obtained from Gabriel and
Tande (1983), and somewhat augmented from Selkregg
(1974). The report by Gabriel and Tande summarized data
from a 23—year span (1957—1979). Information in the cur-
rent report, therefore, does not represent wildfires outside of
this interval.

Land use. — Although not used to delineate ecoregions,
information on extractable resources and subsistence land
use has been included in the descriptions. Extractable
resource information was compiled from the US. Bureau of
Mines (1992a; 1992b), Selkregg (1974), and Pittman (1992).
Information on subsistence land use came from Langdon
(1993), Morgan (1979), and Selkregg (1974).

Wildlife. — Information on wildlife was not used to
delineate ecoregions. Wildlife is an important component of
the Alaskan landscape; however, it was beyond the scope of
this report to describe the distribution and density of impor-
tant species across individual ecoregions.

ECOREGION DESCRIPTIONS

Ecoregion descriptions have been compiled from the
references listed in the Materials Section. An attempt has
been made to provide consistent types of information for
each ecoregion, but variations in the quality and quantity of
information available have sometimes hindered this objec-
tive. A State map of selected features (fig. 1) precedes these
descriptions to assist readers unfamiliar with locations that
are mentioned.

The description of each ecoregion has been divided into
the following topics: Distinctive Features, Climate, Terrain,
Soils, Vegetation, Wildfire, Land Use and Settlement,
Delineation Methods, and References. The general contents
of each topic are described below.

Distinctive Features. — Approximate location and size
of the ecoregion are described. Information on the primary
factors that distinguish it from the rest of the ecoregions has
been extracted from the subsequent paragraphs describing
that ecoregion.

Climate. — Overall climatic regime is described in terms
of major influencing factors (coastal, continental, transition-
al, arctic), winter and summer temperatures, and annual pre-

l'Wildfire information was obtained from Gabriel and Tande (1983).
Because their reporting units did not coincide completely with ecoregion
boundaries, data were summarized (using the actual frequency values pro—
vided in the original report) to a coarser class of information.

cipitation. Annual precipitation refers to the water equiva-
lent (for both rain and snow) per year, and annual snowfall
refers to cumulative depth. Weather stations are poorly dis-
tributed across most ecoregions. Because the available data
provide an imprecise representation of regional climate in
most ecoregions, we have rounded the figures to the nearest
10 mm for total annual precipitation and 5 cm for total annu-
al snowfall.

Terrain. — Information about physiography, geology,
extent of glaciation and permafrost, and hydrologic features
is provided. Elevation information is based on height
(meters) above mean sea level.

Soils. — Principal soils are listed and parent materials are
described.

Vegetation. — Major community types are described and
common or typifying species are listed. Names of communi-
ty types and species closely follow those described by
Viereck and others (1992). For the purposes of this report,
Equisetum (horsetail) species are considered herbaceous veg-
etation in the sense that they are nonwoody. Appendix 3 is a
list of Latin and common names for plant species mentioned
in this report.

Wildfire. — Frequency of lightning fires for each ecore-
gion has been classified based on the following cate—
gories”: very low (<1 fire/yr), low (1—5 fires/yr), common
(6—10 fires/yr), very common (11—20 fires/yr), and fre-
quent (>20 fires/yr; the only region in this last category
averages more than 80 fires per year). The range and the aver-
age area bumed are also provided. Other descriptive inforrna—
tion is included where available.

Land Use and Settlement. — Information is provided
regarding native human subsistence and selected commodi-
ties, such as resource extraction, agriculture, and timber har-
vest. Listings of extractable resources for an individual
region generally follow the frequency of occurrence (from
high to low) in the Bureau of Mines data base .

Delineation Methods. — Specific materials used to
decide boundary placement on the basis of synthesized char-
acteristics typifying each ecoregion are discussed. Although
nearly all information described above (except land use) was
assessed to evaluate regional patterns, only a small subset of
the material was used to delineate the boundaries. This sub-
set represents maps that best integrate the spatial patterns of
the full set of characteristics defining each ecoregion.
Scientists from Environment Canada and Agriculture
Canada assisted in the delineation of regional boundaries
that cross the international border into Canada.

References. — A list of specific references used to com-

8 ECOREGIONS OF ALASKA

pile each ecoregion description is included.

101.”, ARCTIC COASTAL PLAIN

Distinctive Features. — As the northernmost ecoregion
in Alaska, the 50,000—km2 Arctic Coastal Plain Ecoregion is
bounded on the north and the west by the Arctic Ocean and
stretches eastward nearly to the international boundary
between Alaska and the Yukon Territory, Canada. The poor-
ly drained, treeless coastal plain rises very gradually from
sea level to the adjacent foothills. The region has an arctic
climate, and the entire area is underlain by thick permafrost.
Because of poor soil drainage, wet graminoid herbaceous
communities are the predominant vegetation cover, and
numerous thaw lakes dot the region (fig. 2).

Climate. — The coastal plain has arctic climatic condi-
tions, with very low mean annual temperatures and very low
annual precipitation. Although July and August are general-
ly frost—free, freezing temperatures can occur in any month
of the year. Winds are persistent and strong. The few weath-
er stations in this region are primarily located along the
coast, but the data are fairly consistent from station to sta-
tion. Average daily minimum winter temperatures are about
-30°C, and average daily maximum winter temperatures are
about —21°C. Daily minimum summer temperatures average
just above freezing, and daily maximum summer tempera-
tures average 8°C. Continuous sunlight during the summer
months yields diurnal temperature fluctuations of only about
5°C. Cloud cover or fog prevails during the summer months,
although fog decreases (and temperature rises) with increas—
ing distance from the coast. The ecoregion receives approx-
imately 140 mm of precipitation13 annually. Average annual
snowfall varies among weather stations, ranging from 30 cm
to 75 cm.

Terrain. — The ecoregion is mainly a smooth plain ris-
ing very gradually (slope gradients 31°) from the Arctic
Ocean to the foothills of the Brooks Range, 180 m above sea
level. Locally, permafrost—related features mark the terrain
surface. Pingos rise 6 m to 70 m above the surrounding area,
and other ice—related features, such as extensive networks of
ice—wedge polygons, oriented lakes (ranging from a few
meters to 15 km in length), peat ridges, and frost boils are
common. Northeast—trending sand dunes, 3 m to 6 m high,
occur between the Kuk and Colville Rivers.

The coastal plain is mantled with Quaternary deposits of
alluvial, glacial, and aeolian origin. Siltstone and sandstone
lie beneath the unconsolidated materials at depths of several

12Numbers in front of ecoregion headings correspond with those used
on the map “Ecoregions of Alaska.”

13The average annual precipitation figure for all ecoregion descriptions
includes the snow water equivalent.

meters to tens of meters. The ecoregion was not glaciated
during the Pleistocene epoch, but the arctic climate is
responsible for permafrost to depths of more than 300 m.
The permafrost table is at or near the ground surface, with an
active layer of less than 0.50 111 (except beneath the larger
rivers, where thawing may be deeper).

The Arctic Coastal Plain is very poorly drained. Thaw
lakes cover 20 percent to 50 percent of the land surface
across the region. In many areas, for example, near
Teshekpuk Lake, lakes are rectangular and oriented
north—northwest. This orientation is related to the effects of
predominant winds on the permafrost shorelines of thaw
lakes. Thaw lakes expand approximately 1 m per year in
places and range from less than 1 In to 7 In in depth. Lake
bottoms are usually covered by organic muck. Streams orig—
inate in the highlands of ecoregions to the south. Streams
west of the Colville River tend to be sluggish and meander-
ing; those east of the Colville River are more braided and
distributary, building deltas into the Arctic Ocean. Most of
the smaller streams dry up or freeze during the winter and
have clean sand or gravel beds.

Soils. — The principal soils of the Arctic Coastal Plain
are Histic Pergelic Cryaquepts and Pergelic Cryaquepts.
Soils are poorly drained and have developed under thick
vegetation cover. Very poorly drained fibrous peat soils
occupy broad depressions, shallow drainages, and lake bor-
ders, commonly under a thick cover of sedges. Pergelic
Cryopsamments have developed on low, stabilized sand
dunes. Very gravelly soils form from stream deposits in
braided and distributary channels of streams west of, and
including, the Sagavanirktok River. Lower parts of the ter-
rain are subject to annual flooding from runoff of spring
snowmelt and heavy summer rainstorms in the upper,
mountainous reaches of their watersheds. East of the
Colville River are extensive areas of loamy and poorly
drained soils that have formed beneath a cover of sedge tus-
socks, mosses, and low shrubs in nonacid and calcareous
sediments.

Vegetation. — The distribution of vegetation communi—
ties is strongly related to microtopographic features that
affect soil drainage. Wet soil conditions are most typical of
this ecoregion, supporting wet graminoid herbaceous com-
munities dominated by sedges or grasses (fig. 3). Dryer soil
conditions occur where slight rises in microtopographic
relief provide a rooting zone above the standing water table,
such as along the rims of old lake basins, on river, lake, and
coastal bluffs, and on pingos. Dwarf scrub communities
grow in these better drained areas (fig. 4).

Sedge communities are generally dominated by Carex
aquatilis and Eriophorum angustifolium. Various herba-
ceous species may share dominance with sedges in some
areas. Mosses (usually Scorpidium spp. or Drepanocladus
spp.) may be common.

ARCTIC COASTAL PLAIN

180° 70" 172° 164° 156° 148° 140° 132° 124° 70°

 

   
    
 

Barrow .
D

ARCTIC OCEAN

62"

nchor

 

58°

    

OF ALASKA i
\ l
' " Sitka
54° ‘ . an
“} , Dafl 0 100 200 300 400 MILES
("g 0 100 200 300 400 501 KILOMETERS

/”

Bass adapted from US. Geological Survey Map 0

 

 

 

Figure 1. Locational map of Alaskan features.

 

Figure 2. Thaw lakes scattered over the treeless Arctic Coastal Plain Ecoregion. Many are oriented north-northwest, as in
this area east of the Kuparuk River.

ECOREGIONS OF ALASKA

 

Figure 3. Wet graminoid herbaceous community dominated by sedge (Carex and Eriophomm species) in the Arctic Coastal

Plain Ecoregion. (Photo taken by Carl Markon, Hughes STX Corporation, US. Geological Survey, EROS Alaska Field
Office, Anchorage.)

 

Figure 4. Dwarf scrub community indicative of dryer soil conditions occurring on raised topographic features (approxi-
mately 10 cm or more above the surrounding plain) in the Arctic Coastal Plain Ecoregion. (Photo taken by Carl Markon,
Hughes STX Corporation, US. Geological Survey, EROS Alaska Field Office, Anchorage.)

ARCTIC FOOTHILLS 11

Grass communities are generally dominated by Dupontia
fischeri and Alopecurus alpinus, but Arctophilafizlva dominates
where surface water is 15 to 200 cm deep. Various herbaceous
species may share dominance with grasses in some areas.

Dwarf scrub communities commonly include entire—leaf
mountain—avens (Dryas integrifolia), mountain—cranberry
(Vaccim'um vitis—idaea), four—angled cassiope (Cassiope
tetragona), bearberry (Arctostaphylos alpina and A. rubra),
and willows (Salix reticulata and S. phlebophylla).

Wildfire. — Occurrence of wildfires in the Arctic Coastal
Plain Ecoregion is very low. Fire records show a range in size
from 1 ha to 3,400 ha, with an average size of 1,135 ha.

Land Use and Settlement. — Native inhabitants of this
region are Inuit (Taremiut) who have traditionally depended
heavily on large marine mammals (for example, bowhead
whales, beluga whales, and walrus) for food and materials.
Winter ice fishing and seal hunting supplement these food
supplies. Caribou are hunted during late spring, following
the conclusion of the major whale hunts. Edible plant roots
and summer waterfowl and their eggs add variety to the diet.

The ecoregion is rich in energy related commodities,
including oil, gas, and coal. The Prudhoe Bay area has
played a major role in providing these commodities. A num—
ber of sand and gravel operations support construction and
road maintenance.

Delineation Methods. — The reference that best depict-
ed the integration of important regional characteristics was
the terrain roughness map. The ecoregion boundary corre-
sponds with the pattern of continuous, very low terrain rough-
ness. This boundary encompasses the full extent of “Wet
Tundra” ecosystems shown on the arctic portion of the
“Major Ecosystems of Alaska” map, as well as the thaw lakes
shown on the USGS Map E base map. Some inclusions of
“Moist Tundra” from the map “Major Ecosystems of Alaska”
also occur, and are depicted as transitional gray tones on the
ecoregion map. Patterns on the relative CIR image reflect a
combination of those shown on the surface roughness map
and those shown on the ecosystems map; so the image is gen-
erally in agreement with the ecoregion boundary.

References. — The information provided in this regional
description has been compiled from: Beikman (1980), Black
(1951, 1955, 1969), Coulter and others (1962), Ferrians
(1965), Gabriel and Tande (1983), Joint Federal—State Land
Use Planning Commission for Alaska (1973), Karlstrom and
others (1964), Langdon (1993), Larson and Bliss (written
commun., 1992), Moore (written commun., 1993), Morgan
(1979), Ping (written commun., 1993), Reiger and others
(1979), Selkregg (1974), Spetzman (1959), US. Bureau of
Mines (1992a, 1992b), U.S. Geological Survey (1964,
1987a),Viereck and Little (1972), Viereck and others (1992),
Wahrhaftig (1965), and WeatherDisc Associates, Inc. (1990).

102. ARCTIC FOOTHILLS

Distinctive Features. — The 124,000—kmZ Arctic
Foothills Ecoregion consists of a wide swath of rolling hills
and plateaus that grades from the coastal plain on the north
to the Brooks Range on the south. The east—west extent of
the ecoregion stretches from the international boundary
between Alaska and The Yukon Territory, Canada, to the
Chukchi Sea. The hills and valleys of the region have better
defined drainage patterns than those found in the coastal
plain to the north and have fewer lakes (fig. 5). The Arctic
Foothills Ecoregion is underlain by thick permafrost and has
many ice—related surface features. The region is predomi-
nantly treeless and is vegetated primarily by mesic
graminoid herbaceous communities.

Climate. — Arctic climate prevails in this ecoregion.
The foothills are somewhat warmer in winter than the
adjacent regions to the north and south, and gain some
ameliorating effects from the Chukchi Sea to the west.
Weather stations are rare in the Arctic Foothills Ecoregion,
and information from the few data locations and anecdotal
accounts may not be representative. Annual precipitation
mirrors that of the Arctic Coastal Plain (2140 mm). As
much as 50 mm of additional precipitation is intercepted
near the boundary with the Brooks Range Ecoregion. The
Noatak Valley, in the western portion of the Arctic
Foothills Ecoregion, receives approximately twice as
much annual precipitation as the rest of the region.
Snowfall patterns are similar to overall annual precipita-
tion patterns in that more snowfall occurs near the Brooks
Range (up to 130 cm) and in the Noatak Valley (up to 150 cm)
than throughout the rest of the region (75 cm to 100 cm).
Average daily winter temperatures range from a minimum
of -29°C to a maximum of —20°C. Average daily summer
temperatures range from a minimum of 1°C to a maximum
of 11°C to 15°C, although maximum temperatures of 24°C
are not uncommon in some areas. Freezing can occur in
any month of the year, but July and August are usually
frost—free.

Terrain. — The Arctic Foothills Ecoregion can be topo-
graphically and geologically separated into northern and
southern sections. The northern section consists of broad,
rounded east—west ridges and mesa—like uplands built from
unconsolidated Quaternary materials (glacial, alluvial, and
aeolian in origin) over Lower Cretaceous continental
deposits. Elevations are generally less than 600 m above sea
level. The southern section has undifferentiated alluvial and
colluvial deposits overlying Jurassic and early Cretaceous
graywacke and chert formations. Elevations are higher than
in the northern section (up to 800 m) and consist of irregular
buttes, mesas, and long linear ridges with intervening undu-
lating plains and plateaus.

The ecoregion was free from Pleistocene glaciation

12 ECOREGIONS OF ALASKA

(except for some areas directly north of the Brooks Range)
but is currently underlain by thick permafrost. The active
layer of the permafrost is generally less than 1 m, except
beneath large rivers, where thawing may be deeper. Many
ice—related features are present, such as pingos, gelifluction
lobes, ice—wedge polygons, stone stripes, and beaded
drainage (fig. 6). Although regional slope gradients general-
ly vary from 0° to 5°, they may be steeper in some areas.

Drainage in the Arctic Foothills Ecoregion is integrated.
Major streams originate from the Brooks Range and are
structurally controlled by the bedrock. Most streams are
swift, but portions may be braided across gravel flats.
Smaller streams dry up or freeze to the bottom in winter;
these streams typically have clean sand or gravel bottoms.
Perennial streams have algae—covered rocky bottoms.
During spring snowmelt and breakup of river ice, flooding
and channel shifting are common. Oxbow lakes along major
stream valleys are the predominant type of lake in this
ecoregion. Most lake beds are organic muck, but some are
sandy. Lake shores are surrounded by ice—push ridges (as
much as 2 m high). Plant communities in lakes are general-
ly arranged in concentric bands that correspond with water
depth; aquatic vegetation is usually limited to water that is
less than 1.5 m deep.

Soils. — Principal soils are Histic Pergelic Cryaquepts,
Pergelic Cryaquepts, and Pergelic Ruptic—Histic Cryaquepts.
Dominant soils in valleys and on long slopes formed in silty
or loamy colluvial sediments. On hills and ridges, most of
the soils are composed of very gravelly materials eroded
from sedimentary rock. The dominant soils in the Noatak
Valley are poorly drained and are derived from very gravel—
ly glaciofluvial material from limestone rock in the sur-
rounding mountains. Well drained soils occur on hilly
moraines of the valley, formed from very gravelly, nonacid
and calcareous drift. Shallow depressions on terraces
accommodate fibrous peat soils.

Vegetation. — Vegetation over most of the region con-
sists of mesic graminoid herbaceous (fig. 7) and dwarf scrub
communities. Open low scrub occurs along drainages.
Forest communities occur in the Noatak River Valley, a
somewhat anomalous area of this ecoregion.

Mesic graminoid herbaceous communities dominated by
tussock—forming sedges are widespread. Typical species are
Eriophorum vaginatum and Carex bigelowii. Low shrubs,
such as dwarf arctic birch (Betula nana), crowberry
(Empetrum nigrum), narrow—leaf Labrador—tea (Ledum
decumbens), and mountain—cranberry (Vaccinium vitis—idaea)
often occur and may codominate with sedges. Mosses (for
example, Hylocomium splendens and Sphagnum spp.) and
lichens (for example, Cetraria cucullata, Cladonia spp., and
Cladina rangiferina) are common between tussocks.

Dwarf scrub communities are dominated by mat—form-
ing Dryas species accompanied by ericaceous species (for

example, Vaccinium spp., Cassiope tetragona, Arctostaphylos
spp.) and prostrate willows (Salix reticulata and S. phlebo-
phylla).

Open low scrub communities are codominated by alders
(Alnus crispa) and willows (for example, Salix lanata, S. plan-
ifolia, and S. glauca). Mosses (for example, Tomenthypnum
nitens and Drepanocladus spp.) are usually abundant.

Forest vegetation is common along river terraces of the
lower Noatak Valley (as far inland as the Kugururok River).
White spruce (Picea glauca) occurs in either pure stands or
with balsam poplar (Populus balsamifera). The spruce grows
in open stands along the riverbanks, with an understory dom-
inated by willows (for example, Salix alaxensis, S. planifolia,
and S. lanata). Away from the river, forest canopies are
closed and stands have few understory species (for example,
ericads such as Ledum spp., Arctostaphylos spp., and
Vaccinium spp.). A thick layer of featherrnosses (for exam-
ple, Hylocomium splendens) is common. Balsam poplar
stands grow all along the river, occurring farther upriver than
white spruce stands. Typical understory species are alpine
bearberry (Arctostaphylos alpina), buffaloberry (Shepherdia
canadensis), and bush cinquefoil (Potentilla fruticosa).

Wildfire. — Occurrence of wildfires in the Arctic
Foothills Ecoregion is very low. Fire records show a range in
size from <1 ha to 1,600 ha, with an average size of 185 ha.

Land Use and Settlement. — The ecoregion has tradi-
tionally been home to the Inuit (Nunamiut). Caribou is the
primary subsistence resource. Moose, bear, hare, ground
squirrel, and ptarmigan are also hunted. Edible plant roots
and berries supplement the diet.

Subsistence and recreational fishing and hunting remain
the primary human activities in this ecoregion. A number of
potential extractable resources have been investigated,
including coal, barium, lead, chromium, zinc, and silver.
Sand and gravel operations have supported construction of
the trans—Alaska pipeline service road.

Delineation Methods. — Typical characteristics of the
Arctic Foothills Ecoregion are integrated within the area of low
terrain roughness on the arctic portion of the terrain roughness
map. The ecoregion boundary shared with the Arctic Coastal
Plain was delineated on the basis of a distinct boundary between
very low terrain roughness and low terrain roughness. The
ecoregion boundary shared with the Brooks Range was delin—
eated along a generalized 600—m elevation contour, an elevation
coinciding with the northern extent of “Alpine Tundra” in the
Brooks Range, as depicted on the “Major Ecosystems of
Alaska” map. This contour line corresponds well with regional
pattems shown on the relative CIR image. The ecoregion
boundary shared with Interior Forested Lowlands and Uplands
was based on the interface of the forest ecosystems of the inte—
rior and the tundra (graminoid herbaceous) ecosystems of the
Arctic. Transitional areas adjacent to the Brooks Range indicate

ARCTIC FOOTHILLS

Figure 5. Rolling hills of the Arctic Foothills Ecoregion showing better defined drainage patterns than those found in the
coastal plain to the north. (Photo courtesy of Skip Walker, Institute of Arctic and Alpine Research, University of Colorado,

Boulder.)

 

Figure 6. Beaded stream drainages controlled by the pattern of ice wedges formed in permafrost environments of the Arctic
Foothills Ecoregion. (Photo courtesy of Skip Walker, Institute of Arctic and Alpine Research, University of Colorado, Boulder.)

 

ECOREGION S OF ALASKA

Figure 7. Mesic graminoid herbaceous-dwarf scrub community near Umiat in the Arctic Foothills Ecoregion. (Photo cour-
tesy of Skip Walker, Institute of Arctic and Alpine Research, University of Colorado. Boulder.)

 

Figure 8. The Brooks Range Ecoregion is composed of deeply dissected mountains formed from uplifted, stratified
Paleozoic and Mesozoic sediments.

 

 

 

BROOKS RANGE 15

alpine tundra ecosystems, areas greater than 600 m in elevation,
and areas of medium to high terrain roughness. Transitional
areas adjacent to the Arctic Coastal Plain indicate inclusions of
areas of very low terrain roughness.

References. — The information provided in this regional
description has been compiled from Beikman (1980), Black
(1951, 1955, 1969), Coulter and others (1962), D. Binkley
(oral commun., 1994), Ferrians (1965), Gabriel and Tande
(1983), Joint Federal-State Land Use Planning Commission
for Alaska (1973), Karlstrom and others (1964), Langdon
(1993), Larson and Bliss (written commun., 1992), Moore
(written commun., 1993), Morgan (1979), Ping (written
commun., 1993), Reiger and others (1979), Selkregg (1974),
Spetzman (1959), US. Bureau of Mines (1992a, 1992b),
US. Geological Survey (1964, 1987a), Viereck and Little
(1972), Viereck and others (1992), Wahrhaftig (1965), and
WeatherDisc Associates, Inc. (1990).

103. BROOKS RANGE

Distinctive Features. — The 134,000—km2 Brooks
Range Ecoregion consists of several groups of rugged,
deeply dissected mountains carved from uplifted sedimenta-
ry rock (fig. 8). The ecoregion traverses much of the
east—west extent of northern Alaska, from the Canadian bor-
der to within 100 km of the Chukchi Sea. Elevation of
mountain peaks ranges from 800 In in the relatively low
Baird Mountains in the west to 2,400 m in the central and
eastern Brooks Range. Pleistocene glaciation was extensive,
and small glaciers persist at elevations above 1,800 In. An
arctic climatic regime and unstable hillslopes maintain a
sparse cover of dwarf scrub vegetation throughout the moun-
tains, though some valleys provide more mesic sites for
graminoid herbaceous communities.

Climate. — The ecoregion is influenced by arctic cli-
mate. The only perennial weather station, located at
Anaktuvuk Pass, sits at an elevation of 770 m, where winter
temperatures average a daily minimum of -30°C and a daily
maximum of -22°C, and summer temperatures average lows
of 3°C and highs of 16°C. In most years, freezing tempera-
tures occur each month. In general, temperatures decrease
with elevation, but hillslope aspect, strong and persistent
winds, and convective currents result in climate that is high-
ly variable. Mean annual precipitation at Anaktuvuk Pass is
280 mm, with 160 cm of annual snowfall. Precipitation is
heaviest on south—facing slopes and near mountain summits.

Terrain. — The Brooks Range Ecoregion represents the
Alaskan extension of the Rocky Mountains. The steep,
rugged mountains consist of folded and faulted stratified
Paleozoic and Mesozoic sedimentary deposits (including
sandstone, shale, and limestone marine and nonmarine

deposits, and some metamorphic rocks) that were uplifted
during the Cretaceous period. Elevations range from 500 m
in the lower valleys to 2,400 m on the higher peaks. Slope
gradients of 5° to 15° are common. The ecoregion was
extensively glaciated during the Pleistocene epoch, but only
small, scattered glaciers persist. Continuous thick per-
mafrost underlies the region. The interplay between water
(frozen and thawed) and sediments is evidenced by moraine
and gravel outwash terraces in most valleys, by gelifluction
lobes on hillslopes, by ice—push ridges around lakes, and by
polygons, stripes, and circular frost scars on many surfaces.
Rubble and exposed bedrock cover the mountain slopes.

Lakes are sparse for such a glacially influenced region,
occurring primarily in rock basins at the mouths of large
glaciated valleys, in areas of ground and end moraine, and on
the floodplains of major streams. Streams often have a trel-
lis drainage pattern, with major streams draining north or
south and their tributaries draining east or west. Extensive
alluvial fans of loose material carried down from mountain
slopes have formed in broad valleys at the base of streams.
Hot springs are known to occur in several areas.

Soils. — The principal soils of the Brooks Range
Ecoregion are Pergelic Cryaquepts, Pergelic Cryumbrepts,
and Lithic Cryorthents. Hillslope soils formed from local
colluvium, while most valley soils generally developed from
glacial till. Soils are often gravelly, but are covered in many
places with silty colluvial and residual material from
fine-grained sedimentary rocks. Because of glaciation, frost
action, and rapid erosion of steep slopes, there is little soil
accumulation on hillslopes. Soils throughout this ecoregion
typically have poor drainage because of the shallow depth to
permafrost.

Vegetation. — Because of highly erodible hillslope sed-
iments, shallow soils, high winds, and harsh climate in this
ecoregion, vegetation cover is sparse (fig. 9) and generally
limited to valleys and lower hillslopes. Drier sites support
dwarf scrub communities. Wet to mesic sites support mesic
graminoid herbaceous communities.

Dwarf scrub communities are dominated by ericaceous
species (for example, Arctostaphylos alpina, A. rubra,
Vaccinium spp., Ledum decumbens, Empetrum nigrum, and
Cassiope tetragona), mountain—avens (Dryas octopetala and
D. integrifolia), and willow (Salix rotundifolia, S. arctica, and
S. polaris). Herbaceous species (for example, Carex spp.) and
fruticose lichens (for example, Cladina spp. and Cetraria
spp.) may codominate with shrubs in some areas (fig. 10).

Graminoid herbaceous communities are dominated by
sedges (Carex aquatilis and C. bigelowii) and willows (Salix
planifolia and S. lanata). Mosses (for example, Tomenthypnum
nitens, Distichium capillaceum, Drepanocladus spp., and
Campylium stellatum) are often abundant.

Wildfire. — Occurrence of wildfires in the Brooks Range

ECOREGION S OF A SKA

‘ u waif? Mil?“

.ae'

Figure 9. Steep, unstable slopes of the Brooks Range Ecoregion. Physiography and an arctic climate restrict vegetation.

 

Figure 10. Dwarf scrub community dominated by mountain-avens and lichen growing on a windswept site of the Brooks
Range Ecoregion. (Photo courtesy of Skip Walker, Institute of Arctic and Alpine Research, University of Colorado, Boulder.)

 

INTERIOR FORESTED LOWLANDS AND UPLANDS 17

Ecoregion is common. Fire records show a range in size from
<1 ha to 109,265 ha, with an average size of 1,790 ha.

Land Use and Settlement. - The Brooks Range has
historically been used by nomadic groups of the Interior
North Alaska Coast Inuit (Nunamiut) and by the Kutchin and
Koyukon Athabascans. Salmon fishing and hunting for cari—
bou and moose are the major means of subsistence. Small
fur—bearing mammals are hunted secondarily. Edible plants
are also gathered.

The fact that Anaktuvuk Pass is the only year—round set-
tlement in this ecoregion underscores the harsh environment
and difficulty of transportation associated with the moun-
tains. The region is little developed and provides subsistence
hunting and fishing, as well as recreational uses. Many
extractable resources have been investigated and, in some
cases, mined. These include gold, silver, copper, tungsten,
zinc, lead, chromium, vanadium, antimony, barium, molyb—
denum, phosphate, and rare earth elements. Numerous sand
and gravel operations have supported construction of the
trans-Alaska pipeline service road.

Delineation Methods. — The ecoregion boundary pri-
marily follows a generalized 600—m elevation contour. An
exception occurs in the southeastern part of the ecoregion,
where a 900—m contour was used. This is because the moun-
tains at the 600—m level in the southeast are more widely
spaced, have climatic characteristics more similar to those of
interior regions, and have a different geologic origin than the
rest of the Brooks Range. The boundary delineated general-
ly corresponds with patterns shown on the relative CIR
image. The transitional zones on the northern side of the
ecoregion distinguish areas of “Moist Tundra,” as depicted
on the map “Major Ecosystems of Alaska,” and lower eleva-
tion valleys penetrating from the Arctic Foothills Ecoregion.
Transitional zones on the southern side distinguish “Upland
Spruce—Hardwood Forest” ecosystems, as depicted on the
map “Major Ecosystems of Alaska,” along drainages adja-
cent to interior ecoregions.

References. — The information provided in this region—
al description has been compiled from Beikman (1980),
Black (1955, 1969), Coulter and others (1962), Ferrians
(1965), Ferrians and Hobson (1973), Gabriel and Tande
(1983), Joint Federal-State Land Use Planning Commission
for Alaska (1973), Karlstrom and others (1964), Langdon
(1993), Larson and Bliss (written commun., 1992), Moore
(written commun., 1993), Morgan (1979), Ping (written
commun., 1993), Reiger and others (1979), Selkregg (1974),
Spetzman (1959), US Bureau of Mines (1992a, 1992b),
US. Geological Survey (1964), Viereck and Little (1972),
Viereck and others (1992), Wahrhaftig (1965), and
WeatherDisc Associates, Inc. (1990).

104. INTERIOR FORESTED LOWLANDS
AND UPLANDS

Distinctive Features. — The 269,000—km2 ecoregion rep-
resents a patchwork of ecological characteristics. Regionwide
unifying features include a lack of Pleistocene glaciation, a
continental climate, a mantling of undifferentiated alluvium
and slope deposits, a predominance of forests dominated by
spruce and hardwood species, and a very high frequency of
lightning fires. On this backdrop of characteristics is super-
imposed a finer grained complex of vegetation communities
resulting from the interplay of permafrost, surface water, fire,
local elevational relief, and hillslope aspect (fig. 11).

Climate. — The ecoregion has a continental climate,
with short, warm summers and long, very cold winters.
Because the ecoregion is so large, there is much variation in
temperature and precipitation from west to east. Total annu-
al rain and snow generally increase with elevation.
Temperature, while affected by elevation, is also influenced
by distance from the ocean; maximum summer temperatures
increase from west to east, and minimum winter tempera-
tures decrease in the same pattern. Accordingly, variation in
diurnal temperature increases from west to east.

Mean annual precipitation over most of the region
ranges from 250 mm to 550 mm, with contribution from
snowfall averaging from 125 cm to 205 cm. Most precipita—
tion occurs during summer, mainly as a result of convective
storms. Snow covers the landscape for half the year, linger-
ing at higher altitudes, on north—facing slopes, and on shad-
ed aspects. Average minimum winter temperatures vary from
-18°C in the west to -35°C in the east; average maximum
winter temperatures vary from -11°C in the west to -22°C in
the east. Strong, stable temperature inversions are common
in winter due to low sun angle and corresponding long—wave
radiation cooling. Summer temperatures, averaging a mini-
mum of 8°C to 11°C and a maximum of 17°C to 22°C, have
less regional variation than winter temperatures. At lower
elevations, temperatures usually remain above freezing from
June through mid—September.

Terrain. — The Interior Forested Lowlands and Uplands
Ecoregion consists of rolling lowlands, dissected plateaus,
and rounded low to high hills. Most of the region lies
between elevations from sea level to 500 m, but some hills
rise over 700 m. Slope gradients are generally from 0° to 5°.
The predominant geologic formations are derived from
Mesozoic and Paleozoic sedimentary rocks, but extensive
areas of volcanic deposits also occur. The region is surfi-
cially mantled by undifferentiated alluvium and slope
deposits. There is little exposure of bedrock. Streams orig-
inating from within the ecoregion tend to be short, with the
larger and longer streams originating from adjacent glaciat—
ed mountainous regions. Although thaw lakes and oxbow
lakes occur throughout the ecoregion, lakes are not a pre-

ECOREGION S OF ALASKA

 

Figure 11. Forest plant communities typical of the Interior Forested Lowlands and Uplands Ecoregion. The patterns and
species composition of the communities are often controlled by the effects of permafrost, surface water, fire, relief, and hill-
slope aspect.

 

Figure 12. Initial recolonization by fireweed within recent burn, east of Tok in the Interior Forested Lowlands and Uplands
Ecoregion. High frequency of lightning fires is a common characteristic.

 

INTERIOR FORESTED LOWLANDS AND UPLANDS 19

dominant landscape feature. The western portion of the
ecoregion is underlain by thin to moderately thick per-
mafrost, and the eastern portion has a discontinuous distrib-
ution of permafrost. The region was not glaciated during the
Pleistocene epoch.

Soils. — Dominant soils of this ecoregion are Histic
Pergelic Cryaquepts, Pergelic Cryaquepts, Aquic
Cryochrepts, Pergelic Cryochrepts, Typic Cryochrepts, Typic
Cryorthents, and Pergelic Cryumbrepts. Many upland soils
were formed in silty, micaceous loess and colluvial material.
Where mantles of loess are lacking, upland soils formed in
stone and gravel weathered from local rock. Lowland soils
were formed in silty alluvium and loess derived from the
floodplains of large rivers. Soils are generally shallow, often
overlying ice—rich permafrost. Those soils with permafrost,
especially in the eastern portion of the ecoregion, are very
susceptible to alteration upon disturbance of the organic mat.
This is due to the relatively warm (>-1.5°C) permafrost tem—
perature. Organic mat disturbance, as by wildfire, can result
in warmer soil temperatures, lowered permafrost tables, and
significant changes in soil physical properties and hydrology.

Vegetation. — Interrelationships among permafrost, sur—
face water, fire, hillslope aspect, and soil characteristics result
in a finely textured, complex pattern of vegetation across the
ecoregion. Soil temperatures may differ greatly from air tem—
peratures, so patterns in vegetation may not correspond with
expected site conditions. Needleleaf, broadleaf, and mixed
forests occur over a variety of sites. Tall scrub communities
grow in areas of newly exposed alluvium, such as flood-
plains, strearnbanks, drainageways, and lake margins, on
burned or otherwise disturbed areas, and near timberline.
Low scrub communities occur in moist areas and on
north—facing slopes. The wettest sites support tall scrub
swamps, low scrub bogs, or scrub—graminoid communities.
Recently burned areas (fig. 12) display a succession of recov—
ery stages that include mesic forb herbaceous communities,
mesic graminoid herbaceous communities, scrub communi-
ties, and broadleaf, needleleaf, and mixed forests.

Needleleaf forests are dominated by spruce and occur
over a variety of site conditions. White spruce (Picea glau-
ca) occurs on warm, dry, south—facing hillslopes, along rivers
where drainage is good and permafrost is lacking, and on well
drained timberline sites. Dominant components of the under-
story include shrubs, such as resin birch (Betula glandulosa),
prickly rose (Rosa acicularis), alder (Alnus spp.), willow
(Salix spp.), buffaloberry (Shepherdia canadensis), high
bushcranberry (Viburnum edule), and bearberry
(Arctostaphylos spp.); herbs, such as twinflower (Linnaea
borealis); and mosses, such as Hylocomium splendens,
Pleurozium schreberi, and Cladonia spp.

Black spruce (Picea mariana) forests are found on
floodplain terraces and flat to rolling uplands in well drained
to poorly drained soils. Tamarack (Larix laricina) may be

associated with black spruce in wet bottomland areas. Low
shrubs, such as Labrador—tea (Ledum groenlandicum and L.
decumbens), prickly rose (Rosa acicularis), blueberry/cran-
berry (Vaccinium spp.), and resin birch (Betula glandulosa)
are typically dominant in the understory. The ground has a
patchy to continuous layer of mosses (for example,
Pleurozium schreberi, Hylocomium splendens, Polytrichum
spp., and Sphagnum spp.), and lichens (for example,
Peltigera spp. and Cladonia spp.).

Broadleaf forests of balsam poplar (Populus balsam-
ifera), quaking aspen (Populus tremuloides), or a mix of the
two develop on the floodplains of meandering rivers. These
forest stands follow the establishment of alder and willow
thickets. The stands are subsequently replaced by white
spruce (Picea glauca). Dominant understory species of
broadleaf forests are alder (Alnus spp.), willow (Salix spp.),
prickly rose (Rosa acicularis), and herbaceous species (for
example, Equisetum spp., Calamagrostis canadensis, and
Heracleum lanatum).

Mixed forests are dominated by combinations of spruce,
paper birch, and quaking aspen. Dominant understory
species include bluejoint (Calamagrostis canadensis), alder
(Alnus spp.), bearberry (Arctostaphylos spp.), and
Labrador—tea (Ledum spp.).

Most tall scrub communities are dominated by willows
(Salix alaxensis, S. glauca, and S. lanata) and alders (Alnus
crispa, A. tenuifolia, and A. sinuata), though communities
near timberline may be dominated by birch (Betula glandu-
losa and B. papyrifera). Understory shrubs are usually sparse,
but mosses (for example, Polytrichum spp., Hylocomium
splendens, and Drepanocladus uncinatus) may be abundant.

Low scrub communities are dominated by open stands of
willow (for example, Salix glauca, S. planifolia, and S. lana-
ta), birch (Betula glandulosa and B. nana), alder (Alnus
crispa), or mixes of these genera. Dominant understory
shrubs may include cranberry/blueberry (Vaccinium spp.),
bearberry (Arctostaphylos spp.), and Labrador—tea (Ledum
spp.). The ground is covered by a patchy to continuous layer
of moss (for example, Hylocomium splendens, Pleurozium
schreberi, Tomenthypnum nitens, and Aulacomnium palustre).

Tall scrub swamps are dominated by alder (Alnus
tenuifolia and A. crispa) and willow (Salix planifolia and S.
lanata). Low shrubs may be present in the understory,
including leatherleaf (Chamaedaphne calyculata), high
bushcranberry (Viburnum edule), sweetgale (Myrica gale),
and spirea (Spiraea beauverdiana). Mosses (for example,
Sphagnum spp.) are usually present.

Bogs support open low scrub or scrub—graminoid com-
munities. The shrub component includes a number of wil—
low species (for example, Salix planifolia, S. reticulata, S.
barclayi, S. commutata, and S. fuscescens), birch (Betula
glandulosa and B. nana), Labrador—tea (Ledum decumbens),
blueberry/cranberry (Vaccinium uliginosum, V. vitis—idaea,
and V. oxycoccos), bush cinquefoil (Potentilla fruticosa),
sweetgale (Myrica gale), alder (Alnus tenuifolia), and bog—

20 ECOREGION S OF ALASIQA

rosemary (Andromeda polifolia). Sedge tussocks
(Eriophorum vaginatum and Carex bigelowii) or other
graminoids (for example, Calamagrostis canadensis, Carex
aquatilis, and C. pluriflora ) are codominant with shrub
species in some bogs. A continuous moss layer, commonly
consisting of Sphagnum spp., Pleurozium schreberi,
Hylocomium splendens, Dicranum spp., and Polytrichum
51211., is present.

Recent burn areas are initially colonized by mesic forb
herbaceous communities dominated by fireweed (Epilobium
angustifolium). Mesic graminoid herbaceous communities
develop when bluejoint (Calamagrostis canadensis) becomes
dominant. The scrub communities that follow consist mainly
of willows (Salix arbusculoides, S. barclayi, S. bebbiana, and
S. scouleriana), accompanied by prickly rose (Rosa acicu-
laris), buffaloberry (Shepherdia canadensis), and ericaceous
species (for example, Ledum decumbens, L. groenlandicum,
Vaccinium caespitosum, and V. vitis—idaea). Broadleaf forests
dominated by quaking aspen (Populus tremuloides) often suc-
ceed the willow stage in upland areas on south—facing slopes,
or on well drained river terraces. Paper birch (Betula
papyrifera) stands succeed the willow stage on east—, west—,
and occasionally north—facing slopes and flat areas. Mixed
forest stands occur when spruce becomes established in the
broadleaf stands. Needleleaf forests dominated by spruce
eventually replace the mixed stands on many sites.

Wildfire. — Wildfires occur frequently in the Interior
Forested Lowlands and Uplands Ecoregion. Fire size has
ranged from less than 1 ha to 260,800 ha (the largest occur-
ring in the Kuskokwim Mountains), with an average size of
1,630 ha. Low annual precipitation, high summer tempera-
tures, low relative humidity, frequent lightning storms, and
trees having branches low to the ground are factors that make
this ecoregion especially prone to wildfire. The fire season
usually lasts from June through the beginning of August.

Land Use and Settlement. — The region is used primar-
ily for subsistence and recreational hunting and fishing.
Native inhabitants have descended from a number of
Athabascan groups, such as the Koyukon, Kutchin, Tanana,
Han, Tanacross, Upper Tanana, Upper Kuskokwim,
Holikachuk, and Ingalik. Upland dwellers rely on large game
(caribou and moose) as important sources of food and materi-
als. Riverine groups depend heavily on salmon and freshwa-
ter fish (for example, Whitefish, blackfish, and pike). Smaller
mammals and ptarmigan provide secondary subsistence
sources. Edible and medicinal plant parts are also collected.

Investigation and extraction of metals (for example, gold,
silver, tin, tungsten, mercury, lead, platinum, nickel, zinc,
chromium, cobalt, columbium, and copper) occur in many
areas. Energy—related resources in the region include uranium
and coal. Other extractable resources are antimony, bismuth,
molybdenum, thorium, and rare earth elements. Sand and grav-
el operations have supported construction and road building.

Delineation Methods. — The ecoregion boundary abut—
ting the Arctic Foothills in the northwest delineates where
the forest ecosystems meet the arctic tundra ecosystems, as
depicted on the map “Major Ecosystems of Alaska.” The
boundaries adjacent to the Brooks Range, the Ogilvie
Mountains, the Ahklun and Kilbuck Mountains, the Alaska
Range, and the Wrangell Mountains Ecoregions are based on
a generalized 600—rn elevation contour. The boundary adja-
cent to the Interior Highlands is based on a generalized
500—m elevation contour. The boundary shared with the
Interior Bottomlands and Yukon Flats Ecoregions eliminates
from the Interior Forested Lowlands and Uplands Ecoregion
those areas of low and very low terrain roughness that have
“Bottomland Spruce—Poplar Forest,” “Lowland
Spruce—Hardwood Forest,” or “Low Brush, Muskeg Bog”
ecosystems, as shown on the map “Major Ecosystems of
Alaska.” The boundary adjoining the Subarctic Coastal
Plains Ecoregion was based on where the coastal “Wet
Tundra” and “Moist Tundra” ecosystems meet the interior
forest ecosystems, also as shown on the map “Major
Ecosystems of Alaska.” Likewise, the boundary adjoining
the Seward Peninsula was based on the extent of the forest
ecosystems of the interior versus the brush and tundra
ecosystems shown for the peninsula. The boundary shared
with the Bristol Bay— Nushagak Lowlands Ecoregion is
based on separating the coastal tundra and “Lowland
Spruce—Hardwood Forest” of the Lowlands from the
“Upland Spruce—Hardwood Forest” and small, scattered
“Alpine Tundra” areas of the Interior. Transitional zones
shown in the Interior Forested Lowlands and Uplands
Ecoregion depict areas of isolated peaks greater than 600 m
in elevation that are near borders of montane regions, and
moist tundra ecosystems that are adjacent to coastal and bot-
tomland regions.

References. — The information provided in this region-
al description has been compiled from Beikman (1980),
Coulter and others (1962), Ferrians (1965), Gabriel and
Tande (1983), Joint Federal-State Land Use Planning
Commission for Alaska (1973), Karlstrom and others
(1964), Kimmins and Wein (1986), Langdon (1993), Larson
and Bliss (written commun., 1992), Moore (written com-
mun., 1993), Morgan (1979), Ping (written commun.,1993),
Pittman (1992), Reiger and others (1979), Selkregg (1974),
Slaughter and Viereck (1986), Viereck (1989), US. Bureau
of Mines (1992a, 1992b), US. Geological Survey (1987a),
Viereck and Little (1972), Viereck and others (1986, 1992),
Wahrhaftig (1965), and WeatherDisc Associates, Inc.
(1990).

105. INTERIOR HIGHLANDS

Distinctive Features. — The 115,000—kmz discontinu-
ous Interior Highlands Ecoregion is composed of rounded,

INTERIOR HIGHLANDS 21

low mountains, often surmounted by rugged peaks (fig. 13).
The highlands primarily sustain dwarf scrub vegetation and
open spruce stands, though graminoid herbaceous communi-
ties occur in poorly drained areas. Mountains in most parts
of this region rise to at least 1,200 m, and many rise higher
than 1,500 m. Most of the higher peaks were glaciated dur—
ing the Pleistocene epoch.

Climate. — The ecoregion has a continental climate.
Although no long-term weather data are available, certain
generalizations can be made regarding temperature and pre—
cipitation. First, an orographic effect on precipitation caus-
es the highlands to receive more precipitation than the sur-
rounding, lower elevation areas. Second, summer tempera-
tures probably decrease with elevation. Because of steep and
persistent winter temperature inversions at lower elevations,
it is difficult to generalize the relative pattern of winter tem-
peratures in the highlands versus in the surrounding areas.

Terrain. — The ecoregion consists of steep, rounded
ridges, often capped by rugged peaks. Elevations range from
500 m in the valleys to greater than 1,500 m on the peaks
(some peaks rise above 1,800 m). Slope gradients commonly
range from 5° to 15°, but lower gradient slopes are typical
around the margins of the ecoregion. The mountains have
much more exposed bedrock than the surrounding hills of the
Interior Forested Lowlands and Uplands Ecoregion. Geologic
formations of the Interior Highlands consist of Paleozoic and
Precambrian metamorphic rocks, felsic volcanic rocks, and
intrusive rocks. Outlying parts of the ecoregion, in the
Kuskokwim Mountains and Nulato Hills, have Cretaceous
and Lower Paleozoic sedimentary rocks. The northern por—
tions of the ecoregion are underlain by continuous permafrost,
and the central and southern portions are underlain by discon-
tinuous permafrost. Permafrost and frost—related ground fea-
tures are evident, including low mounds, gelifluction lobes,
frost boils, and stone stripes. Many of the peaks were glaciat-
ed during the Pleistocene epoch.

Soils. — Dominant soils are Histic Pergelic Cryaquepts,
Typic Cryochrepts, Pergelic Cryumbrepts, Lithic
Cryorthents, and Typic Cryorthods. Most soils are shallow,
formed in very stony or gravelly material weathered from
local rock. The permafrost table is shallow and soils are
poorly drained; however, they are generally too shallow over
bedrock for ground-ice to form. Barren, rocky peaks and
stony and bouldery slopes are common. Alluvium and col-
luvium cover the valley floors. Soils with permafrost are
very susceptible to alteration upon disturbance of the organ-
ic mat because of the relatively warm (>-1.5°C) permafrost
temperature. Organic mat disturbance, as by wildfires, can
result in warmer soil temperatures, lowered permafrost
tables, and significant changes in soil physical properties and
hydrology.

Vegetation. — The highest elevations are barren of veg-
etation. Dwarf scrub communities, dominated by species of
mountain—avens, ericads, and willow, are widespread in sites
exposed to wind. Lower elevations are generally more pro—
tected from wind and have a denser vegetation cover that can
include open needleleaf forests and woodlands. Areas of
poor soil drainage support mesic graminoid herbaceous
communities.

Mountain—avens dwarf scrub communities are dominat-
ed by several species of Dryas (for example, D. octopetala,
D. integrifolia, and D. drummondii). Sedges (for example,
Carex scirpoidea, C. misandra, C. bigelawii and Kobresia
myosuroides) and lichens (for example, Alectoria spp.,
Cetraria spp., and Cladina spp.) may codominate with
Dryas. Also common are prostrate willows (Salix reticulata
and S. phlebophylla) and ericaceous species (for example,
Vaccinium spp., Cassiope tetragona, Arctostaphylos spp., and
Empetrum nigrum). Mosses (for example, Tomenthypnum
nitens, Rhytidium rugosum, and Hylocomium splendens) are
abundant in Dryas—sedge communities.

Ericaceous dwarf scrub communities are also wide-
spread. Bearberry (Arctostaphylos alpina or A. rubra) and
cranberry/blueberry (Vaccinium spp.) are the common dom-
inants, though other ericaceous shrubs (for example, Ledum
decumbens, Empetrum nigrum, and Cassiope tetragona),
prostrate willows (Salix phlebophylla and S. rotundifolia),
and fruticose lichens (for example, Cladina spp., Cetraria
spp., and Stereocaulon tomentosum) may be common or
codominant. Mosses (for example, Dicranum spp.,
Rhacomitrium lanuginosum, Tomenthypnum nitens, and
Hylocomium splendens) are common.

Willow dwarf scrub communities are dominated by wil-
low (for example, Salix polaris, S. reticulata, and S. arctica).
Other dwarf shrubs (for example, Empetrum nigrum,
Cassiope lycopodioides, Dryas spp., Vaccinium spp., and
Ledum decumbens) are common and may codominate with
willows. Mosses (for example, Dicranum spp. and
Aulacomnium spp.) can be common.

Open needleleaf forests and woodlands are often domi-
nated by white spruce (Picea glauca) or codominated by
white spruce and black spruce (P. mariana). Other tree
species in these communities include paper birch (Betula
papyrifera) and quaking aspen (Populus tremuloides). The
open shrub layer commonly includes resin birch (Betula
glandulosa), alder (Alnus crispa and A. sinuata), willow
(Salix planifolia and S. lanata), prickly rose (Rosa acicu-
laris), buffaloberry (Shepherdia canadensis), and other eri-
caceous shrubs. The ground is covered by a continuous layer
of mosses (for example, Pleurozium schreberi, Hylocomium
splendens, Polytrichum spp., and Dicranum spp.). Lichens
(for example, Cladonia spp.) provide significant cover at
some sites.

Mesic graminoid herbaceous communities consist of
sedge tussocks (for example, Eriophorum vaginatum and
Carex bigelowii) surrounded by mosses. Low shrubs (for

22

ECOREGIONS OF ALASKA

 

Figure 13. Rounded mountains, often surmounted by rugged peaks, are typical of the Interior Highlands Ecoregion.
Vegetation communities consist of alpine tundra and open spruce stands.

 

Figure 14. Relatively flat terrain of Interior Bottomlands Ecoregion. Soil drainage is usually poor. Black spruce and low
ericaceous shrubs are common on slightly raised peat deposits. Various forbs and graminoid species occur in vegetated wet—
lands. Vegetation communities are subject to periodic flooding from local rivers.

INTERIOR BOTTOMLANDS 23

example, Betula mum and several ericaceous species) may
also grow between tussocks.

Wildfire. — Occurrence of wildfires in the Interior
Highlands Ecoregion is very common. Fire records indicate
a range in size from less than 1 ha to greater than 82,000 ha,
with an average size of 640 ha. The occurrence of fires can
be related to the relatively warm and dry summer climate of
interior Alaska and frequent lightning storms. Fire season is
usually from June through the beginning of August.

Land Use and Settlement. — The ecoregion primarily
provides resources for subsistence and recreational hunting
and fishing. The highlands have historically been used by a
number of Athabascan groups. Hunting for large game (for
example, moose, caribou, and sheep) is supplemented by
hunting for smaller mammals (such as ground squirrels).
Streams supporting salmon and freshwater fish provide addi-
tional food and materials. Plants are collected for edible and
medicinal purposes.

Many minerals have been mined, although most opera-
tions have ceased production. Important mining elements
have included gold, silver, tin, tungsten, lead, copper, mer-
cury, zinc, platinum, chromium, antimony, asbestos, molyb-
denum, and rare earth elements. Energy—related resources
have included uranium and coal.

Delineation Methods. — The ecoregion boundary was
delineated based on a generalized 500—m elevation contour.
This elevation often, but not always, coincides with areas of
“Alpine Tundra” on the map of “Major Ecosystems of Alaska.”
“Upland Spruce—Hardwood Forest” covers the rest of the
region. Patterns on the relative CIR image generally agree with
the boundary depicted on the ecoregion map. Transitional
zones represent areas where upland peaks are widely scattered
(approximately 10 km or farther from other peaks).

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Ferrians (1965), Ferrians and Hobson
(1973), Gabriel and Tande (1983), Joint Federal-State Land
Use Planning Commission for Alaska (1973), Karlstrom and
others (1964), Langdon (1993), Larson and Bliss (written
commun, 1992), Moore (written commun., 1993), Morgan
(1979), Ping (written commun, 1993), Reiger and others (1979),
Selkregg (1974), Slaughter and Viereck (1986), US. Bureau of
Mines (1992a, 1992b), US. Geological Survey (1964, 1987a),
Viereck and Little (1972), Viereck and others (1992), Wahrhaftig
(1965), and WeatherDisc Associates, Inc. (1990).

106. INTERIOR BOTTOMLANDS

Distinctive Features. — The 103,000—km2 ecoregion is
composed of flat to nearly flat bottomlands along larger

rivers of interior Alaska. The bottomlands are dotted with
thaw and oxbow lakes (fig. 14). Soils are poorly drained and
shallow, often over permafrost. Predominant vegetation
communities include forests dominated by spruce and hard-
wood species, tall scrub thickets, and wetlands.

Climate. — The ecoregion has a continental climate.
The bottomlands in the west receive more annual precipita-
tion than those in the east. Annual precipitation ranges
from 280 mm to 400 mm, and annual snowfall from 95 cm
to 205 cm. Average daily minimum temperatures in winter
range from -33°C to -26°C. Average daily maximum winter
temperatures range from -22°C to -17°C. Summer tempera-
tures have lows of about 7°C and highs of about 22°C.
Summer maximum temperatures generally increase from
west to east. Temperatures usually remain above freezing
throughout the summer (June through August), though they
may dip below freezing during this time.

Terrain. — The ecoregion is typified by flat to nearly flat
bottomlands, with some inclusions of local hills. Most areas in
the bottomlands have a slope gradient of less than 1°.
Elevations range from 120 m in the west to 600 m in the east.
Fluvial and aeolian (for example, large areas of stabilized
dunes) deposits of mixed origin cover most of the region, but
outwash gravel and morainal deposits occur in some areas, such
as the Northway—Tanacross lowland. Permafrost is widespread,
but it ranges from isolated masses to a continuous thin layer.
The ecoregion is strongly associated with riparian features;
meandering streams and side sloughs are prevalent. Oxbow
lakes and thaw lakes are numerous. Morainal lakes occur in a
few areas, where Pleistocene glaciers from the Alaska Range
reached the edge of this ecoregion. The Interior Bottomlands
Ecoregion was not glaciated during the Pleistocene epoch.

Soils. — Principal soils are Histic Pergelic Cryaquepts,
Pergelic Cryaquepts, Aquic Cryochrepts, Typic Cryochrepts,
and Typic Cryofluvents. Most soils formed in micaceous
loess and alluvial materials. On flat areas away from the
main river channels, soils are shallow over permafrost, poor-
ly drained, and nearly always wet. On the slightly higher lev-
ees, soils are well drained and permafrost is deep or absent.
Soils with permafrost are very susceptible to alteration upon
disturbance of the organic mat because of the relatively warm
(>-1.5°C) permafrost temperature. Organic mat disturbance,
as by wildfire, can result in warmer soil temperatures and
lowered permafrost tables. Soil physical properties may
change, as well as hydrology, on any upland position.

Vegetation. — Needleleaf, broadleaf, and mixed forest
stands occur on a variety of sites in the Interior Bottomlands (
Ecoregion. Tall scrub communities form thickets on flood—
plains. The wettest sites support a variety of wetland com-
munities, such as low scrub bogs, wet graminoid herbaceous
meadows, and wet forb herbaceous marshes and meadows.

24 ECOREGIONS OF ALASKA

Needleleaf forests are dominated by white spruce (Picea
glauca), black spruce (Picea man'ana), or a combination of the
two. Closed stands of white spruce occupy young river terraces
where soil drainage is good. Understory vegetation consists pri-
marily of low and dwarf scrub, such as ericaceous species (for
example, Vaccinium vitis—idaea and V. uliginosum, Ledum
groenlandicum, and Empetrum nigrum) and dwarf arctic birch
(Betula nana). Herbaceous species, such as twinflower
(Linnaea borealis) and horsetail (Equisetum sylvaticum and E.
arvense), are common. A well—developed moss layer (mainly
of feathermosses, such as Hylocomium splendens, Pleurozz'um
schreberi, and Rhytia'iadelphus triquetrus) is typical.

Closed stands of black spruce occur on well—drained to
poorly drained floodplain soils. Associated woody species
include white spruce (Picea glauca), paper birch (Betula
papyrifera), American green alder (Alnus crispa), prickly
rose (Rosa acicularis), willow (Salix spp.), Labrador—tea
(Ledum groenlandicum), bog blueberry (Vaccinium uligi-
nosum), and mountain—cranberry (V. vitis—idaea). The moss
layer varies from patchy to continuous and generally includes
Hylocomium splendens and Pleurozium schreberi.
Sphagnum species may occur on wetter sites. Foliose lichens
(for example, Peltigera aphthosa and P. canina) are common.

Stands codominated by white spruce and black spruce
have a tall shrub understory of alder (Alnus crispa) and wil-
low (Salix bebbiana and S. scouleriana). Other understory
components are similar to those found in white spruce stands
and black spruce stands.

Colder, wetter soils support black spruce woodlands,
where the tall shrub (for example, Alnus crispa, Betula glan-
dulosa, Salix lanata, S. planifolia, and S. glauca) understory is
a much more important component of the ecosystem than in
the closed forest stands. Ericaceous shrubs (for example,
Vaccinium uliginosum, V. vitis—idaea, Ledum decumbens, L.
groenlandicum, and Empetrum nigrum) are common, and
herbaceous cover, dominated by sedges (Carex spp. and
Eriophorum vaginatum) and grasses (for example,
Calamagrostis canaa'ensis), ranges from sparse to dense.
Mosses (Hylocomium splendens, Pleurozium schreberi, and
Sphagnum spp.) and lichens (Nephroma arcticum, Cladonia
spp., Cladina spp., Cetraria spp., and Peltigera spp.) provide
continuous ground cover.

Broadleaf forests consist of closed stands of Balsam
poplar (Populus balsamifera). The understory consists of
shrubs, such as alder (Alnus crispa and A. tenuifolia), willow
(Salix spp.), prickly rose (Rosa acicularis), high bushcran-
berry (Vzburnum edule), and red—osier dogwood (Cornus
stolonifera), as well as a dense herb layer of species such as
northern bedstraw (Galium boreale), dwarf dogwood
(Cornus canadensis), and bluebell (Mertensia paniculata).

Mixed forests form where paper birch codominates in
stands with black spruce and white spruce, and where white
spruce codominates in stands with balsam poplar.

Tall scrub communities are dominated by willow (for
example, Salix alaxensis and S. glauca) or alder (Alnus crispa

or A. sinuata). The understory is usually sparse, though
mosses (for example, Polytrichum spp., Hylocomium splen-
dens, and Drepanocladus uncinatus) may be common. Herb
cover ranges from sparse to dense, including bluejoint
(Calamagrostis canadensis), horsetail (Equisetum arvense),
monkshood (Aconitum delphinifolium), fireweed (Epilobium
latifolium and E. angustifolium), bluebell (Mertensia panicu-
lata), and lady fern (Athyriumfilix—femina).

Low scrub bogs are characterized by open, low mixed
shrubs and tussock—forming sedges. Resin birch (Betula glan-
dulosa), dwarf arctic birch (B. nana), narrow—leaf
Labrador—tea (Ledum decumbens), bog blueberry (Vaccinium
uliginosum), mountain—cranberry (V. vitis—idaea), and sedge
tussocks (for example, Eriophorum vaginatum) are the most
common species. Mosses (for example, Sphagnum spp.,
Pleurozium schreberi, and Hylocomium splendens) form a
continuous mat between tussocks.

Wet graminoid herbaceous meadows are typically domi-
nated by tall sedges (for example, Carex aquatilis, C. rostra-
ta, C. saxatilis, and C. sitchensis). Woody plants are scarce.
Mosses (for example, Sphagnum spp.) can be common.

Wet forb herbaceous marshes are characterized by an
open cover of wetland emergent species. Horsetail
(Equisetum fluviatile) typically dominates the communities,
though buckbean (Menyanthes trifoliata) and marsh fivefin-
ger (Potentilla palustris) are common associates. Aquatic
mosses often are present.

Wet forb herbaceous meadows are dominated by non-
graminoid herbaceous species, (for example, Equisetum
arvense, E. variegatum, Caltha palustris, and Juncus arcti-
cus,), though grasses and sedges may be present.

Wildfire. — Occurrence of wildfires in the Interior
Bottomlands Ecoregion is very common. Fire records indi-
cate a range in size from less than 1 ha to 325,150 ha (the
largest in Kanuti Flats), with an average size of 2,260 ha. A
high occurrence of lightning storms, a warm and dry summer
climate, and stands of vegetation with branches low to the
ground aid the ignition and spread of wildfire. Fire season
generally lasts from June through the beginning of August.

Land Use and Settlement. — Most of the settlements in
the Alaskan interior occur in the bottomlands because of the
food sources and transportation routes provided by rivers.
The ecoregion is used for subsistence and recreational hunt-
ing and fishing. Native inhabitants include several
Athabascan groups (for example, lngalik, Koyukon, Tanana,
and Holikachuk). The riverine systems of the bottomlands
provide salmon and other fish that are important sources for
subsistence. A variety of mammals (for example, caribou,
moose, beaver, and muskrat) and birds (for example, geese
and ducks), drawn to the water, are also hunted for food and
materials. Edible greens, roots, and berries round out the diet.

Extractable metals are found in certrain areas, such as
near the confluence of the Yukon and Tanana Rivers, where

YUKON FLATS 25

 

Figure 15. Water-worked basin of the Yukon Flats Ecoregion covered by numerous thaw and oxbow lakes. Annual precip—
itation is insufficient to maintain many lakes, which are replenished by yearly flooding of the Yukon River (center, flowing
from east to west) during spring breakup of river ice.

gold and silver occur. An assortment of other metal and non-
metal resources have also been mined, but to a much small-
er degree. There is some logging activity. Limited agricul-
tural efforts have occurred along the Tanana River.

Delineation Methods. — The ecoregion boundary was
based on areas where low and very low terrain roughness
coincide with the distribution of the “Bottomland
Spruce—Poplar Forest,” “Lowland Spruce—Hardwood Forest,”
and “Low Brush, Muskeg—Bog” classes shown on the map
“Major Ecosystems of Alaska.” Transitional areas are not
indicated because areas not consistent with the above criteria
were not included in the ecoregion.

References. — The information provided in this region-
al description has been compiled from Beikman (1980),
Coulter and others (1962), Drury (1956), Fenians (1965),
Gabriel and Tande (1983), Hall (1991), Joint Federal-State
Land Use Planning Commission for Alaska (1973),
Karlstrom and others (1964), Langdon (1993), Larson and
Bliss (written commun., 1992), Markon (1992), Moore
(written commun., 1993), Morgan (1979), Ping (written
commun., 1993), Reiger and others (1979), Selkregg (1974),
Shasby (unpub. mapping 1985), Talbot and Markon (1988,
1986), Talbot and others (1986), US. Bureau of Mines

(1992a, 1992b), US. Fish and Wildlife Service (1987a),
US. Geological Survey (1964, 1987a), Viereck (1989),
Viereck and Little (1972), Viereck and others (1992),
Wahrhaftig (1965), and WeatherDisc Associates, Inc. (1990).

107. YUKON FLATS

Distinctive Features. — The 33000—ka Yukon Flats
Ecoregion is a relatively flat, marshy basin floor in east cen-
tral Alaska that is patterned with braided and meandering
streams, numerous thaw and oxbow lakes, and meander scars
(fig. 15). Surrounding the basin floor is a variable band of
more undulating topography with fewer water bodies (fig. 16).
In many respects, the ecoregion is similar to the Interior
Bottomlands Ecoregion. However, the Yukon Flats
Ecoregion differs in climatic characteristics. Temperatures
in the Flats tend to be more extreme than in the Bottomlands.
For example, summers in the Flats are warmer and winters
are colder than in other areas of comparable latitude. The
Flats also receive less annual precipitation than the
Bottomlands. Forests dominated by spruce and hardwood
species, tall scrub communities, and wet graminoid herba-
ceous communities are the predominant vegetation types.

ECOREGIONS OF ALASKA

Figure 16. Undulating topography covered by dense forests of black spruce interspersed with small lakes along the periph—
ery of the Yukon Flats Ecoregion.

Figure 17. Widespread forests of the Yukon Flats Ecoregion occupying sites representing an array of soil drainage charac-
teristics often formed by changes in river courses. Tall scrub thickets occur on alluvial deposits subject to periodic flooding.
Tall scrub swamps and wet gramino d herbaceous communities occupy the wettest sites.

 

YUKON FLATS 27

Climate. — The Yukon Flats Ecoregion has a continental
climate. The mountains surrounding the ecoregion isolate it
from the weather systems affecting the neighboring regions.
Consequently, summer temperatures tend to be higher than
at other places of comparable latitude and winter tempera-
tures tend to be colder. Average daily temperatures in win-
ter range from lows of about -34°C to highs of about -24°C.
Average daily temperatures in summer range from lows of
just above freezing to highs of about 22°C (the ecoregion is
the only place north of the Arctic Circle where a temperature
of 38°C has been recorded). Although temperatures usually
remain above freezing from June through August, freezing
can occur in any month.

Annual precipitation is low, averaging 170 mm.
Average annual snowfall is 115 cm. Precipitation is not suf—
ficient to maintain water levels in many lakes. Levels are
primarily maintained by the yearly flooding of the region
that accompanies spring breakup of ice on the Yukon River.

Terrain. — The central portion of the ecoregion is flat,
becoming more undulating along the edges. Elevations range
from 90 m to greater than 250 m. Slope gradient is general-
ly less than 1° in the center of the ecoregion, and 1° to 2° at
the edges. The region is mantled by Quaternary alluvial
deposits. Aeolian silt and sand deposits cover some areas.
The Yukon River drains the ecoregion, assisted by numerous
meandering and braided tributaries and side sloughs.
Permafrost is present in most areas, except beneath rivers and
large thaw lakes. Thaw lakes are abundant, as are oxbow
lakes. The region was free from glaciation during the
Pleistocene epoch.

Soils. — Principal soils are Histic Pergelic Cryaquepts,
Pergelic Cryaquepts, Aquic Cryochrepts, and Pergelic
Cryochrepts. Most soils formed from silty alluvium and
loess from the floodplains of the large rivers. On flat areas
away from the main river channels, soils are poorly drained,
commonly overlain by peat, and have a shallow permafrost
table. Soils on the natural levees are better drained and con-
sist of silty and sandy sediments. Many of the soils are sub-
ject to flooding. Soils with permafrost are very susceptible
to alteration upon disturbance of the organic mat, due to the
relatively warm (>-l.5°C) permafrost temperature. Organic
mat disturbance, as by wildfire, can result in warmer soil
temperatures and lowered permafrost tables. Soil physical
properties may change, as well as hydrology, on any upland
position.

Vegetation. — Needleleaf, broadleaf, and mixed forests
are widespread and occupy sites representing an array of soil
drainage characteristics. Tall scrub thickets occur on alluvial
deposits subject to periodic flooding. Tall scrub swamps and
wet graminoid herbaceous communities occupy the wettest
sites (fig. 17).

Needleleaf forests of white spruce (Picea glauca) are

found on well drained sites. Willow (for example, Salix beb-
biana) commonly dominates the understory shrub layer.
Foliose lichens (for example, Parmelia spp. and Peltigera
spp.), along with feathermosses, cover the ground.

Needleleaf forests dominated by black spruce (Picea
mariana) grow in open stands where drainage is poor.
Common understory shrubs are resin birch (Betula glandu-
losa), narrow—leaf Labrador—tea (Ledum decumbens), crow-
berry (Empetrum nigrum), and bog blueberry (Vaccinium
uliginosum). Feathermosses are common.

Broadleaf forests dominated by quaking aspen (Populus
tremuloides) and balsam poplar (Populus balsamifera) occur
on floodplains. Common understory shrubs include willow
(Salix spp.), prickly rose (Rosa acicularis), and buffaloberry
(Shepherdia canadensis).

Mixed forests consist of closed stands of white spruce
and paper birch (Betula papyrifera) or white spruce and bal—
sam poplar (Populus balsamifera) on the better drained allu-
vial soils; poorly drained soils support stands of black spruce
(Picea mariana) and paper birch.

Understory constituents of the broadleaf and mixed for—
est communities generally include a tall shrub layer of alder
(for example, Alnus crispa and A. tenuifolia) and willow
(Salix spp.) and a low shrub layer of prickly rose (Rosa aci-
cularis) and high bushcranberry (Viburnum edule). An herb
layer is common and typically includes bluejoint
(Calamagrostis canadensis), bluebell (Mertensia
paniculata), and horsetail (Equisetum spp.).

Tall scrub communities are dominated by willows (gen-
erally Salix alaxensis, S. arbusculoides, S. barclayz', S. lana-
ta, and S. sitchensis), alders (Alnus crispa, A. sinuata, and A.
tenuifolia), or a mix of willows and alders. Herbs (for exam-
ple, Calamagrostis canadensis, Epilobium angustifolium,
Geranium erianthum, and Aconitum delphinifolium) and
mosses (for example, Hylocomium splendens, Polytrichum
spp., and Drepanocladus uncinatus) may be abundant or
sparse.

Tall scrub swamp communities are dominated or
codominated by alder (Alnus tenuifolia) and willow (Salix
planifolia and S. lanata). The low shrub layer typically
includes currant (Ribes spp.), high bushcranberry (Viburnum
edule), and prickly rose (Rosa acicularis). Bluejoint
(Calamagrostis canadensis), sedge (Carex aquatilis), horse—
tail (Equisetum spp.), and marsh fivefinger (Potentilla palus-
tris) are common herbs. Mosses (for example, Sphagnum
spp., Mnium spp., and feathermosses) are usually present.

Wet graminoid herbaceous communities are dominated by
sedges (for example, Carex aquatilis, C. rostrata, C. saxatilis,
and C. sitchensis). Other herbaceous vegetation, such as horse—
tail (Equisetum arvense), may codominate with sedges.
Mosses (for example, Sphagnum spp.) can be common.

Wildfire. — Occurrence of wildfires in the Yukon Flats
Ecoregion is common. The recorded range in size has been
from less than 1 ha to 32,370 ha. Mean fire size is 685 ha.

28 ECOREGION S OF ALASKA

Land Use and Settlement. — The region is populated by
several small villages. The primary land use is subsistence
and recreational hunting and fishing. The Kutchin
Athabascans have historically inhabited the Yukon Flats basin.
They depend on the rivers to provide salmon and freshwater
fish, a main dietary staple. Hunting for caribou and moose is
also important, supplemented by hunting for smaller mam-
mals. Edible and medicinal greens, roots, and berries are col-
lected. Gold has been the only major mined commodity.

Delineation Methods. — The ecoregion boundary was
based on areas where low and very low terrain roughness
coincide with the “Bottomland Spruce—Poplar Forest,”
“Lowland Spruce—Hardwood Forest,” and “Low Brush,
Muskeg—Bog” classes shown on the map “Major Ecosystems
of Alaska.” Transitional zones separate the central core of the
region, where very low terrain roughness occurs, from the
peripheral, low surface roughness areas. The “core” area cor-
responds with patterns evident on the relative CIR image.

References. — The information provided in this region-
al description has been compiled from Beikman (1980),
Coulter and others (1962), Ferrians (1965), Gabriel and
Tande (1983), Joint Federal-State Land Use Planning
Commission for Alaska (1973), Karlstrom and others
(1964), Langdon (1993), Larson and Bliss (written com—
mun., 1992), Moore (written commun., 1993), Morgan
(1979), Ping (written commun., 1993), Reiger and others
(1979), Selkregg (1974), US. Bureau of Mines (1992a,
1992b), US. Fish and Wildlife Service (1987b), US.
Geological Survey (1964, 1987a), Viereck and Little (1972),
Viereck and others (1992), Wahrhaftig (1965), and
WeatherDisc Associates, Inc. (1990).

108. OGILVIE MOUNTAINS

Distinctive Features. — The 11,000—km2 Ogilvie
Mountains Ecoregion, along the eastern edge of Alaska, con—
sists of flat—topped hills eroded from a former plain (fig. 18)
and broad pediment slopes built up from mountains that are
much subdued from their former stature. Karst topography is
common. Mesic graminoid herbaceous communities and tall
scrub communities are widespread throughout the region.
Forest communities occupy lower hillslopes and valleys.

Climate. — The Ogilvie Mountains have a continental cli—
mate. No perennial weather stations are located in this region.
Precipitation and temperature characteristics, interpolated
from stations outside the region, include an annual precipita-
tion of about 500 mm in the hills to 650 mm in the higher
mountains, annual snowfall from 130 cm to 205 cm across the
region, daily winter temperatures ranging from lows of —32°C
to highs of -22°C, and daily summer temperatures ranging
from lows of 8°C to highs of 22°C.

Terrain. — The ecoregion consists predominantly of
flat—topped hills eroded from a former plain. Pediment
slopes, extending across broad valleys to the foothills of the
current, subdued mountains, are characteristic of the
plateaus. Erosional scarps in sedimentary rock occur in
many localities. Weathered limestone is exposed at higher
elevations, and talus and rubble mantle the lower mountain—
sides. Elevations range from 900 m to greater than 1,300 m.
Slope gradients are generally less than 5°. The region is
composed of metamorphic and sedimentary rocks, primarily
dolomite, phyllite, argillite, limestone, shale, chert, sand-
stone, and conglomerate. Karst topography is common.
Most of the region is underlain by permafrost; related fea-
tures include pingos, earth hummocks, peat polygons, stone
stripes, and beaded streams. Ponds and thermokarst basins
occur in valley bottoms. The Ogilvie Mountains Ecoregion
was not glaciated during the Pleistocene epoch.

Soils. — Principal soils of the Ogilvie Mountains
Ecoregion are Histic Pergelic Cryaquepts, Typic
Cryochrepts, and Pergelic Cryorthents. Soils formed in
gravelly or stony material weathered from local rock. Soils
in valleys formed from deep, loamy, alluvial sediments from
the surrounding uplands. Areas near large floodplains are
commonly mantled with silty loess. Rock fragments cover
the lower mountainsides.

Vegetation. — Mesic graminoid herbaceous communi-
ties dominated by tussock—forming sedges are widespread
and occur on sites exposed to wind. Needleleaf, broadleaf,
and mixed forest communities occupy lower hillslopes and
valleys. Tall scrub communities occur extensively at lower
elevations and can extend above the timberline.

Mesic graminoid herbaceous communities are dominat-
ed by sedges (for example, Eriophorum vaginatum and
Carex bigelowii). Mosses (for example, Drepanocladus spp.
and Sphagnum spp.) commonly occur between sedge tus-
socks. Dwarf shrubs, such as dwarf arctic birch (Betula
nana) and ericaceous species (for example, Ledum decum-
bens, Vaccinium vitis—idaea, V. uliginosum, and Empetrum
nigrum), are often present.

Needleleaf forests dominated by white spruce (Picea
glauca) occur in well drained valleys and on protected sites.
The more open forest stands typically have a tall shrub layer
of alder (Alnus crispa and A. sinuata) and willow (Salix
plam'folia and S. lanata), and a low shrub layer dominated by
buffaloberry (Shepherdia canadensis) and prickly rose (Rosa
acicularis). The ground supports a continuous mat of feath-
ermosses (for example, Pleurozium schreberi and
Hylocomium splendens). Closed forest stands generally lack
a tall shrub layer but have a low shrub layer of bog blueber-
ry (Vaccinium uliginosum), mountain—cranberry (V.
vitis—idaea), bearberry (Arctostaphylos rubra), Labrador—tea
(Ledum groenlandicum), crowberry (Empetrum nigrum),
and resin birch (Betula glandulasa).

 

OGILVIE MOUNTAINS

 

Figure 18. The Ogilvie Mountains Ecoregion consists of flat—topped hills and broad pediment slopes vegetated by tussock
tundra communities, alpine shrubs. mosses, and lichens. Forest communities occupy lower hillslopes and valleys. (Photo
courtesy of Ken Winterberger, Forest Service. Forestry Sciences Laboratory, Anchorage.)

 

Figure 19. The Subarctic Coastal Plains Ecoregion is typified by numerous lakes surrounded by wet tundra communities,
resulting from a shallow permafrost table and wet soils. The climate is affected by both maritime and continental influences.

29

30 ECOREGIONS OF ALASKA

Broadleaf forests of quaking aspen (Populus tremu-
loides) and balsam poplar (Populus balsamifera) occupy
well—drained warmer sites and recently exposed alluvial
deposits. A tall shrub layer of willow (Salix spp.) is com-
mon. A low shrub layer generally includes prickly rose
(Rosa acicularis) and buffaloberry (Shepherdia canadensis).

Mixed forests on poorly drained lowlands are dominat-
ed by black spruce (Picea mariana) and paper birch (Betula
papyrifera). The understory consists of tall shrubs (for
example, Alnus crispa, Salix bebbiana, and S. scouleriana)
and low shrubs (for example, Rosa acicularis, Viburnum
edule, Ribes triste, and Spiraea beauverdiana).

Mixed forests of well drained sites result from the inva-
sion of white spruce into stands of aspen and balsam poplar
(see broadleaf forest description above).

Tall scrub communities form dense thickets dominated
by birch (Betula glandulosa) and willow (for example, Salix
alaxensis, S. arbusculoides, S. planifolia, and S. lanata).

Wildfire. — Occurrence of wildfires in the Ogilvie
Mountains Ecoregion is low. Size of burn ranges from less
than 1 ha to 18,650 ha, with an average of 1,050 ha.

Land Use and Settlement. — There are only a few per-
manent settlements in this ecoregion. The region has tradi-
tionally been used for subsistence hunting and fishing by
descendants of the Kutchin Athabascans. Larger streams are
fished for salmon and freshwater species. Caribou, moose,
and small mammals are the major terrestrial game. Edible
and medicinal plants are also collected.

Gold, silver, platinum, and tin have been mined in this
region, though mining is not extensive. Prospective sources
of other metals and of energy—related commodities (coal,
petroleum, and uranium) have been investigated.

Delineation Methods. — The ecoregion boundary was
delineated using a generalized 600—m elevation contour,
which somewhat corresponded with patterns shown on the
relative CIR image. Information was insufficient to map
transitional areas.

References. — The information provided in this region—
al description has been compiled from Beikman (1980),
Coulter and others (1962), Ferrians (1965), Gabriel and
Tande (1983), Joint Federal-State Land Use Planning
Commission for Alaska (1973), Karlstrom and others
(1964), Langdon (1993), Larson and Bliss (written com-
mun., 1992), Moore (written commun., 1993), Morgan
(1979), Ping (written commun., 1993), Oswald and Senyk
(1977), Reiger and others (1979), Selkregg (1974), US.
Bureau of Mines (1992a, 1992b), US. Geological Survey
(1964, 1987a), Viereck and Little (1972), Viereck and others
(1992), Wahrhaftig (1965), and WeatherDisc Associates, Inc.
(1990).

109. SUBARCTIC COASTAL PLAINS

Distinctive Features. — The 91,000—km2 ecoregion main—
ly includes coastal plains of the Kotzebue Sound area and the
Yukon and Kuskokwim River delta area. Flat, lake—dotted
coastal plains and river deltas are characteristic of the region
(fig. 19). Streams have very wide and serpentine meanders.
Soils are wet and the permafrost table is shallow, providing
conditions for wet grarninoid herbaceous communities, the
predominant vegetation type. The region is affected by both
maritime and continental climatic influences.

Climate. — Climate is transitional between maritime and
continental influences. In general, the southern portion of
the region has warmer temperatures and receives more pre-
cipitation than the northern portion. Average annual precip—
itation varies from about 250 mm around Kotzebue Sound to
500 mm in the Yukon—Kuskokwim lowlands. Annual snow—
fall is approximately 100 cm in the north and ranges from
105 cm to 150 cm in the south. Temperatures in winter range
from average daily lows of -25°C in the north and -20°C to
—15°C in the south, to average daily maximums of -16°C in
the north and -10°C in the south. July and August are usual-
ly frost—free months over most of the region. Average daily
minimum temperatures in summer range from 6°C in the
north to a couple of degrees warmer in the south. Average
summer daily maximum temperatures vary from 13°C to
17°C in both the northern and southern sections of the ecore-
gion, generally increasing inland from the coast.

Terrain. — The ecoregion is comprised mainly of flat,
poorly drained coastal plains with shallow permafrost
tables. Low hills of basalt surmounted by cinder cones and
broad shallow volcanic craters occur in some locations, cre-
ating a range in regional elevation from sea level to greater
than 120 m. Slope gradients in the plains are generally less
than 1°. The region is predominantly covered by older
coastal deposits of interstratified alluvial and marine sedi-
ments. Quaternary mafic and undifferentiated volcanic
rocks occur in the western part of the Yukon—Kuskokwim
lowlands and on Nunivak and St. Lawrence Islands.
Cretaceous intermediate volcanic rocks occur in the
Selawik Wildlife Refuge area. Only the northernmost por-
tion of the ecoregion, around Kotzebue, was subject to
Pleistocene glaciation. Continuous thin to moderately thick
permafrost underlies the entire region. Thaw lakes and
thaw sinks are numerous. Pingos are common around the
Selawik River area. Streams are sluggish and have very
wide meanders.

Soils. — Dominant soils are Histic Pergelic Cryaquepts
and Pergelic Cryofibrists. Soils are shallow over permafrost
and are constantly wet. Soils have formed from stratified
silty and sandy alluvial deposits that, in many areas, have
additionally incorporated deposits of volcanic ash and loess.

SUBARCTIC COASTAL PLAINS 31

 

White and black spruce stands growing on old river
meander scars in the southern portion of the Subarctic Coastal
Plains Ecoregion.

Figure 20.

Soils on Nunivak Island formed in very gravelly and stony
materials derived from basaltic rock.

Vegetation. — Standing water is almost always present
in this ecoregion. Wet graminoid herbaceous communities,
such as wet meadows and bogs, predominate in saturated
soils. Peat mounds, barren sand dunes, and volcanic soils
support dwarf scrub communities dominated by ericaceous
species. In areas where peat or alluvium accumulation and
growing season temperatures are sufficient, as in the south-
ern section of the ecoregion, invasion by trees is possible,
and stands of needleleaf forests occur (fig. 20).

Wet meadows are typically dominated by sedges (for
example, Eriophorum angustifolium and Carex spp.).
Mosses (for example, Sphagnum spp.) are common and may
codominate with sedges.

Bogs develop where peat mounds and polygonal ridges
provide drained substrates for woody plants, such as erica-

ceous shrubs (for example, Empetrum nigrum, Ledum
decumbens, Loiseleuria procumbens, Vaccinium vitis—idaea,
and Andromeda polifolia). Sedges are common or codomi—
nant with woody species. Sphagnum species usually domi-
nate the moss layer.

Dwarf scrub communities are typically dominated by
crowberry (Empetrum nigrum). Many other ericaceous
species (for example, Vaccinium vitis—idaea, V. uliginosum,
Ledum decumbens, Loiseleuria procumbens, and
Arctostaphylos alpina) and dwarf willows are common in
these communities. Fruticose lichens (for example,
Alectoria spp., Cladina spp., and Cetraria spp.) often
codominate with shrubs. Mosses (for example,
Rhacomitrium spp., Hypnum spp., Polytrichum spp.,
Sphagnum spp., and Dicranum spp.) are also common.

Needleleaf forests consist of black spruce (Picea mari—
ana) and white spruce (P. glauca). Alder (Alnus spp.), wil-
low (Salix spp.), birch (Betula glandulosa and B. nana), and
ericaceous shrubs (Vaccinium vitis—idaea, Ledum decum-
hens, and Empetrum nigrum) may be found in the understo-
ry. Mosses (for example, Sphagnum spp., Dicranum spp.,
Hypnum spp., Polym'chum spp., Hylocomium splendens, and
Pleurozium schreberi) cover the ground.

Wildfire. — Occurrence of wildfires in the Subarctic
Coastal Plains Ecoregion is low. Fires generally range in size
from less than 1 ha to 4,050 ha. Mean burn size is 280 ha.

Land Use and Settlement. — Small permanent and sea-
sonal settlements occur throughout the region, primarily
adjacent to rivers or along the coast. The eastern end of
Kotzebue Sound was settled by the Kotzebue Sound Inuit,
who rely on small ocean mammals (for example, seals),
land mammals (for example, caribou), fish (for example,
pink and chum salmon), and migratory birds and their eggs
as important sources of food and materials. The western
end of Kotzebue Sound and the northeastern portion of
Norton Sound were settled by the Bering Strait Inuit, who
depend more heavily on large marine mammals (for exam-
ple, beluga whale, bowhead whale, and walrus). The
remainder of the ecoregion was settled by the Yup’ik. The
Yup’ik of St. Lawrence Island rely on walrus as a main
source of food and materials. Bowhead whales and seals
are also important. The Yukon—Kuskokwim Delta Yup’ik
depend primarily on salmon, but other fish, seals, beluga
whales, and terrestrial mammals are also important.
Migratory waterfowl and their eggs provide resources dur-
ing the spring. Edible and medicinal greens and berries are
collected during summer.

Though mining is not extensive in this region, gold and
silver have been extracted.

Delineation Methods. — The ecoregion boundary repre-
sents the coincidence of low and very low terrain roughness
and the “Wet Tundra” and “Moist Tundra” ecosystems por-

32 ECOREGIONS OF ALASKA

trayed 0n the map “Major Ecosystems of Alaska.” In the
Yukon—Kuskokwim portion, areas that are north of the
Yukon River include both “Wet Tundra” and “Moist Tundra”
and exclude the forests of the interior regions. South of the
Yukon River, only “Wet Tundra” is included because the
“Moist Tundra” grades into the adjacent Ahklun and Kilbuck
Mountains Ecoregion. Transition zones eliminate “Moist
Tundra” from the periphery of the Subarctic Coastal Plains
Ecoregion.

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Ferrians (1965), Fleming (written commun.,
1993), Gabriel and Tande (1983), Joint Federal-State Land Use
Planning Commission for Alaska (1973), Karlstrom and others
(1964), Langdon (1993), Larson and Bliss (written commun.,
1992), Moore (written commun., 1993), Morgan (1979), Ping
(written commun., 1993), Reiger and others (1979), Selkregg
(1974), US. Bureau of Mines (1992a, 1992b), US. Geological
Survey (1964, 1987a), Viereck and Little (1972), Viereck and
others (1992), Wahrhaftig (1965), WeatherDisc Associates,
Inc. (1990), and Wibbenmeyer and others (1982).

110. SEWARD PENINSULA

Distinctive Features. — Some of the oldest geologic for-
mations in Alaska provide a backdrop for the 47,000—km2,
predominantly treeless Seward Peninsula Ecoregion (fig. 21).
Mesic graminoid herbaceous communities and low scrub
communities occupy extensive areas. The ecoregion is sur-
rounded on three sides by water, yet this has little ameliorat-
ing effect on the climate. Winters tend to be long and harsh
and summers short and cool.

Climate. — Long, severe winters are typical of this ecore—
gion. Overall climatic characteristics range from maritime (a
narrow strip along the coast), to transitional between mar-
itime and continental influences (most of the region), to con-
tinental (in the eastern portion). Winds are persistent and
strong throughout the region. Approximately 10 weeks are
frost—free each summer. All weather stations in the region are
located at the lower elevations. Annual precipitation is heav-
iest in late summer and early fall, occurring as rain. Mean
annual precipitation ranges from 250 mm to 510 mm at lower
elevations, with 100 cm to 190 cm of snowfall occurring.
Mean annual precipitation for the highlands, interpolated
from lowland data, exceeds 1,000 mm, and snowfall may be
as much as 250 cm. Average daily minimum temperature in
winter ranges from -24°C to -19°C, and average daily maxi-
mum from -16°C to —11°C. Average daily minimum temper-
ature in summer ranges from 1°C to 6°C, and maximum from
13°C to 17°C. Temperatures are generally warmer in the
southern portions of the region.

Terrain. — The ecoregion has narrow strips of coastal
lowlands that grade into extensive uplands of broad convex
hills and flat divides. Small, isolated groups of rugged
mountains occur in a few locations. Elevation ranges from
sea level to 500 m for most of the region; the higher moun-
tains climb to 1,400 m. Slope gradients are generally from
0° to 5° in the lowlands and hills, but typically from 5° to 15°
in the mountains. Geologic parent materials include
Paleozoic sediments and metamorphosed volcanic rocks and
Precambrian volcanic rocks. Highland areas are possible
Cenezoic uplifts of these formations. An extensive area of
Quaternary or Tertiary volcanic rock occurs in the northeast-
ern part of the ecoregion.

Permafrost is continuous throughout the ecoregion,
ranging from a thin to a moderately thick layer. Related
features, such as gelifluction lobes (fig. 22) and stone
stripes on sloping areas, frost scars on low knolls, and poly-
gons in level valley bottoms, are common. Streams drain-
ing interior basins travel through narrow canyons across
broad uplands. Lowlands have numerous thaw lakes, but
lakes are rare in the highlands. Except for the highest ele-
vations, the region was unglaciated during the Pleistocene
epoch.

Soils. — Predominant soils are Histic Pergelic
Cryaquepts, Pergelic Cryaquepts, Typic Cryochrepts,
Pergelic Cryumbrepts, Lithic Cryorthents. and Pergelic
Cryorthents. Soils are generally poorly drained and shallow
over permafrost. Soils on hillslopes and ridges formed in
very gravelly residual materials over weathered bedrock.
Soils in valleys and on lower slopes formed mainly in collu—
vial and alluvial sediments.

Vegetation. — The coastal beaches, rolling hills, and
mountains in this ecoregion provide a variety of climate and
substrate characteristics. Mesic graminoid herbaceous com—
munities (fig. 23) and low scrub communities occupy exten—
sive areas on hills and lower mountain slopes. Saturated or
flooded soils sustain wet graminoid herbaceous communi-
ties. Tall scrub vegetation occurs along streams and on
floodplains. Ridgetops and higher elevations are barren or
support dwarf scrub communities.

Mesic graminoid herbaceous communities are dominat-
ed by tussock—forrning sedges. Low scrub communities
result when woody species colonize the area between tus-
socks. Principal sedges are Eriophorum vaginatum and
Carex bigelowii. Woody species include dwarf arctic birch
(Betula nana), resin birch (B. glandulosa), mountain—cran-
berry (Vaccinium vitis—idaea), bog blueberry (V. uligi-
nosum), diamondleaf willow (Salix planifolia), netleaf wil—
low (S. reticulata), and crowberry (Empetrum nigrum).
Mosses (for example, Pleurozium schreberi, Hylocomium
splendens, Aulacomnium spp., and Sphagnum spp.) are
prevalent, and lichens (for example, Cetraria cucullata, C.
islandica, Cladonia spp., Cladina rangiferina, and

SEWARD PENINSULA

 

Figure 21. Coastal plains, rolling hills, low mountains, and lava flats of the Seward Peninsula Ecoregion. A lack of trees is
noticeable across all terrain types.

 

Figure 22. Gelifluction lobes in the Bendeleben Mountains of the Seward Peninsula Ecoregion.

33

34 ECOREGIONS OF ALASKA

Thamnolia subuliformis) can be common.

Wet graminoid herbaceous communities consist of
sedges (for example, Carex aquatilis, C. lyngbyaei, C. ros-
trata, C. saxatilis, C. sitchensis, and Eriophorum angusti-
folium) and grasses (for example, Calamagrostis canadensis
and Arctophila fulva).

Tall scrub communities are dominated by willow (for
example, Salix alaxensis, S. glauca, S. planifolia, and S. lana-
ta). Birch (for example, Betula nana) may codominate with
willow in some areas. Other woody constituents include alder
(Alnus sinuata and A. crispa) and shrubby cinquefoil
(Potentillafruticosa). A dense herb layer may be present, typ-
ically including oxytrope (Oxytropis spp.), vetch (Astragalus
spp.), dwarf fireweed (Epilobium latifolium), worrnwood
(Artemisia spp.), and bluejoint (Calamagrostis canadensis).
Mosses (for example, Polytrichum spp., Hylocomium splen-
dens, and Drepanocladus uncinatus) can be abundant.

Dwarf scrub communities are composed of low shrubs,
grasses, and lichens. Communities are dominated by moun-
tain—avens (Dryas octopetala and D. integrifolia) or codom-
inated by a combination of mountain—avens and sedge (for
example, Carex scirpoidea, C. misandra, and C. bigelowii)
or mountain—avens and lichens (for example, Alectoria spp.,
Cetraria spp., and Cladina spp.). Other typical shrubs
occurring in these communities are willows (Salix reticulum
and S. phlebophylla) and ericads (for example, Cassiope
tetragona, Empetrum nigrum, Arctostaphylos spp.,
Vaccim'um vitis—idaea, and V. uliginosum). Mosses (for
example, Tomenthypnum nitens, Rhytidium mgosum, and
Hylocomium splendens) can be common.

Wildfire. — Occurrence of wildfires in the Seward
Peninsula Ecoregion is common. Burns range in size from
less than 1 ha to 109,260 ha, with an average size of 2,815 ha.
Mosses and lichens dry out during summer, allowing fire to
spread readily through the tundra. Fire season is usually from
June through August.

Land Use and Settlement. — Population is low and small
settlements are scattered throughout the region. The land has
been historically used for subsistence hunting and fishing by
the Bering Strait Inuit. Their livelihood has depended on large
marine mammals, such as bowhead whales, beluga whales,
and walrus. Winter ice fishing and seal hunting are important
to supplement spring and summer ocean catches. Away from
the coast, streams provide salmon and freshwater fish. Large
game (for example, caribou) and smaller mammals (for exam-
ple, rabbits, squirrels, muskrats, and beaver) are also taken.
Reindeer herding is unique to this area.

A number of metallic elements, including antimony,
barium, gold, lead, silver, tin, tungsten, and zinc occur in the
region. Numerous mines, including many gold mines, are
scattered throughout large parts of the region. Other impor-
tant metals include copper, mercury, platinum, and uranium.
Antimony, bismuth, and coal have also been mined.

Delineation Methods. — The ecoregion boundary delin—
eates a break between the forested ecosystems of interior
Alaska and the nonforested peninsula. One of the character-
istic features of the Seward Peninsula is the age of the
bedrock geologic formations; the transitional area on the
ecoregion map excludes the more recent geologic formations
along the eastern portion of the ecoregion from the older for-
mations throughout the core of the region.

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Ferrians (1965), Gabriel and Tande (1983),
Joint Federal-State Land Use Planning Commission for
Alaska (1973), Karlstrom and others (1964), Langdon
(1993), Larson and Bliss (written commun., 1992), Moore
(written commun., 1993), Morgan (1979), Ping (written
commun., 1993), Pittman (1992), Reiger and others (1979),
Selkregg (1974), US. Bureau of Mines (1992a, 1992b),
US. Geological Survey (1964, 1987a), Viereck and Little
(1972), Viereck and others (1992), Wahrhaftig (1965), and
WeatherDisc Associates, Inc. (1990).

111. AHKLUN AND KILBUCK MOUNTAINS

Distinctive Features. — Located in southwestern Alaska
off Bristol and Kuskokwim Bays, the 51,000—km2 ecoregion
is composed of steep, sharp, often ringlike groupings of
rugged mountains separated by broad, flat valleys and low~
lands (fig. 24). The mountains were glaciated during the
Pleistocene epoch, but only a few small glaciers persist.
Dwarf scrub communities are the predominant vegetation
cover in the mountains. Tall scrub and graminoid herba-
ceous communities are common in valleys and on lower
mountain slopes. Valley bottoms may support stands of
spruce and hardwood species.

Climate. — Climate is affected by both maritime and
continental influences. Average annual precipitation
ranges from 1,020 mm in the lowlands to 2,030 mm in the
higher mountains. Average annual snowfall ranges from
205 cm to 510 cm, with a similar distribution pattern.
Winter temperatures have an average daily minimum of
-16°C and a maximum of -8°C. Mean summer tempera-
tures have daily lows averaging about 8°C and daily highs
of about 16°C to 19°C.

Terrain. — This mountainous ecoregion is composed of
strongly deformed sedimentary and volcanic rocks of late
Paleozoic and Mesozoic age and includes some bodies of
older schist. Ringlike mountain groupings have resulted
from small granitic masses surrounded by more resistant
homfels. Slope gradients over most of the region are from
0° to 8°, but steeper slopes are not uncommon (occurring
across 7 percent of the area), and summits are very steep and

‘4‘

AHKLUN AND KlLBUCK MOUNTAINS

 

Figure 23. Mesic graminoid herbaceous communities often occupy hills and lower mountain slopes of the Seward Peninsula
Ecoregion.

 

Figure 24. Typical sharp mountain ridges encircling glacial lakes of the Ahklun and Kilbuck Mountains Ecoregion.
Mountain groupings are separated by broad valleys.

35

36 ECOREGIONS OF ALASKA

 

Figure 25. Ericaceous‘ dwarf scrub-graminoid community of the
Ahklun and Kilbuck Mountains Ecoregion. Prostrate dwarf scrub-
lichen vegetation grows on the hilltop in the background. (Photo
taken by Carl Markon, Hughes STX Corporation, U.S. Geological
Survey, EROS Alaska Field Office, Anchorage.)

sharp. Broad lowlands separate mountain groups. Regional
elevations rise from sea level to more than 1,500 m. Streams
are generally shallow and have radial drainage patterns; most
are incised in bedrock gorges. A number of long, narrow,
and often deep glacial lakes have formed in U—shaped val-
leys. The region was heavily glaciated during the
Pleistocene epoch, and a few small cirque glaciers persist on
higher mountains. Permafrost is discontinuous at higher ele-
vations, and isolated masses occur at lower elevations.

Soils. — Principal soils are Histic Pergelic Cryaquepts,
Pergelic Cryaquepts, Typic Cryochrepts, Lithic
Cryumbrepts, Pergelic Cryumbrepts, Pergelic Cryorthods,
Typic Haplocryods, and Typic Humicryods. Mountain soils
formed in very stony and gravelly colluvial material over
bedrock. Valleys soils formed in glacial till.

Vegetation. — Upper slopes and summits of mountains
are exposed to harsh climatic conditions. Lower slopes and
valleys offer more protected sites for vegetation establish-
ment. Dwarf scrub communities are widespread in the
mountains (fig. 25). Valleys provide an array of soil
drainage conditions that support different vegetation com-
munities (fig. 26). Sites with better drainage support needle-
leaf, broadleaf and mixed forest stands, and tall scrub com—
munities. Mesic graminoid herbaceous communities occur
over a range of dry to wet soils. The wettest sites are colo-
nized by low scrub communities and wet graminoid herba—
ceous communities.

Dwarf scrub communities are dominated either by erica-
ceous shrubs (for example, Arctostaphylos alpina, Vaccim'um
vitis—idaea, V. uliginosum, Empetrum nigrum, and Ledum
decumbens), or by a mix of mountain—avens (Dryas octopeta-
la) and dwarf arctic birch (Betula nana). Lichens (for exam-
ple, Cladina spp., Cetraria spp., Stereocaulon tomentosum,
Thamnolia vermicularis, Cladonia spp., and Alectoria spp.)
may be sparse or may codominate with shrubs.

Valley bottoms may support needleleaf forests dominat-
ed by white spruce, broadleaf forests dominated by balsam
poplar (Populus balsamifera), or mixed forests of white
spruce and paper birch (Betula papyrifera). White spruce
forests are dominated by Picea glauca. Resin birch (Betula
glandulosa) dominates the low shlub layer. Common herbs
include Linnaea borealis, Calamagrostis canadensis, and
Equisetum spp. A nearly continuous cover of feathermosses
(for example, Pleurozium schreberi and Hylocomium splen-
dens) is typical. Lichens (for example, Cladonia spp.) are
particularly common in open areas.

Balsam poplar forests are dominated by Populus bal-
samifera in the overstory. Understory composition varies,
usually including willow (Salix spp.), alder (Alnus spp.), high
bushcranberry (Viburnum edule), prickly rose (Rosa acicu-
laris), bluejoint (Calamagrostis canadensis), and feather-
mosses (Hylocomium splendens and Pleurozium schreberi).

Spruce—paper birch forests are dominated by white
spruce (Picea glauca) and paper birch (Betula papyrifera).
Shrubs, such as willow (Salix bebbiana and S. scouleriana),
alder (Alnus crispa), prickly rose (Rosa acicularis), and high
bushcranberry (Viburnum edule), are common. Typical
herbs are bluejoint (C alamagrostis canadensis) and horsetail
(Equisetum arvense). Cover by mosses (for example,
Hylocomium splendens, Dicranum spp., Hypnum spp., and
Rhacomitrium spp.) is patchy.

Tall scrub communities are dominated by willow (for
example, Salix alaxensis, S. planifolia, and S. glauca), alder
(for example, Alnus crispa and A. sinuata), or a mix of eri-
caceous shrubs (for example, Empetrum nigrum, Ledum
decumbens, Vaccim'um vitis—idaea, V. uliginosum, and
Arctostaphylos alpina), dwarf arctic birch (Betula mum), and
sedges (for example, Carex spp.). Mosses (for example,
Hypnum spp., Dicranum spp., and Polytrichum spp.) may be
common or absent.

AHKLUN AND KILBUCK MOUNTAINS

 

Figure 26. Vegetation communities showing patterns related to slope position and drainage characteristics in the Ahklun and
Kilbuck Mountains Ecoregion. Low scrub communities grow in drainage tracks. Dwarf scrub—lichen communities grow on
better drained sites that are more exposed to wind, such as on the tops of lower rounded summits and at middle and upper

slopes. Low and dwarf scrub communities occur in open, low, flat areas.

.\

Figure 27. Subtly rolling terrain of the Bristol Bay—Nushagak Lowlands Ecoregion. The region has better drainage than
other coastal lowlands.

 

38 ECOREGIONS OF ALASKA

Mesic graminoid herbaceous communities are dominat—
ed by bluejoint (Calamagrostis canadensis), which forms
meadows that may include other herbaceous species (for
example, Carex spp., Eriophorum spp., and Epilobium
angustifolium).

Low scrub communities include low scrub—sedge tussock
bogs, ericaceous scrub bogs, and low sweetgale—graminoid
bogs. Low scrub—sedge tussock bogs are codominated by low
woody plants (for example, Betula glandulosa, B. nana, and
Vaccinium vitis—idaea) and tussock—forming sedges (for
example, Eriophorum vaginatum). Mosses (for example,
Sphagnum spp. and Rhacomitrium spp.) provide a nearly con-
tinuous mat between tussocks.

Ericaceous scrub bogs are dominated by Empetrum
nigrum, Vaccinium vitis—idaea, V. uliginosum, V. oxycoccus,
and Ledum decumbens. Sedges (for example, Carex spp.
and Trichophorum caespitosum) are common or codomi-
nant. The moss layer is usually dominated by Sphagnum
species, though other species (for example, Dicranum spp.)
may be common. Lichens (for example, Cladina spp.) are
present on mounds.

Sweetgale—graminoid bogs are dominated by sweetgale
(Myrica gale), bluejoint (Calamagrostis canadensis), sedges
(Carex spp.), and clubrush (Trichophorum caespitosum).
Other woody and herbaceous species may be present.
Mosses (for example, Sphagnum spp., Rhacomitrium spp.,
and Hypnum spp.) are abundant.

Wet graminoid herbaceous communities include sedge
wet meadows and sedge—moss bogs. Several species of
sedge (for example, Carex aquatilis and C. lyngbyaei) dom-
inate sedge wet meadows. Sedge—moss bogs are dominated
by mosses (principally Sphagnum spp.) and low sedges (for
example, Eriophorum russeolum, Carex spp., and
Trichophorum caespitosum).

Wildfire. — Occurrence of wildfires in the Ahklun and
Kilbuck Mountains Ecoregion is very low. Recorded burns
have ranged in size from less than 1 ha to 80 ha, averaging
about 20 ha.

Land Use and Settlement. — Permanent settlements are
limited to the coastal margins of the ecoregion. The region
has traditionally provided hunting and fishing resources to
the people of the Bristol Bay and Yukon—Kuskokwim Delta
Yup’ik groups. Their primary resources for subsistence have
been salmon and freshwater fish, seals, and beluga whales.
Terrestrial mammals, particularly caribou, provide a sec-
ondary resource. Migratory waterfowl and their eggs are an
important source of food in early spring. Edible and medic—
inal plants are collected. Gold, silver, platinum, lead, mer-
cury, zinc, and borax have all been mined in this ecoregion.

Delineation Methods. — The ecoregion boundary outlines
a group of mountains that exceed 600 m in elevation, with
some adjustment in order to include areas shown as “Moist

Tundra,” “Alpine Tundra,” “Upland Spruce—Hardwood
Forest,” and “High Brush” on the map “Major Ecosystems of
Alaska.” These latter two ecosystem types are considered tran-
sitional with adjacent regions. Also transitional are areas of
very low terrain roughness on the west side and of low and
very low terrain roughness on the east side. Excluded from the
Ahklun and Kilbuck Mountains Ecoregion are areas of
“Lowland Spruce—Hardwood Forest” and “Wet Tundra.”

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Ferrians (1965), Gabriel and Tande (1983),
Joint Federal-State Land Use Planning Commission for
Alaska (1973), Karlstrom and others (1964), Langdon
(1993), Larson and Bliss (written commun., 1992), Moore
(written commun., 1993), Morgan (1979), Ping (written
commun., 1993), Reiger and others (1979), Selkregg (1974),
US. Bureau of Mines (1992a, 1992b), US. Geological Survey
(1964, 1987a), Viereck and Little (1972), Viereck and others
(1992), Wahrhaftig (1965), WeatherDisc Associates, Inc.
(1990), and Wibbenmeyer and others (1982).

112. BRISTOL BAY—NUSHAGAK LOWLANDS

Distinctive Features. — This 61,000—km2 lowland
ecoregion is located in southwestern Alaska off Bristol Bay.
The region has rolling terrain, formed from morainal
deposits (fig. 27). Soils of the lowlands are somewhat better
drained than soils of the Subarctic Coastal Plains Ecoregion.
Dwarf scrub communities are widespread, but large areas of
wetland communities occur. Lakes are scattered throughout
the lowlands, but are not nearly as numerous as in the
Subarctic Coastal Plains.

Climate. — Climate is transitional between maritime and
continental influences. Average annual precipitation varies
greatly from location to location, ranging from 330 mm to
860 mm, with contributions from annual snowfall ranging
from 75 cm to 250 cm. There is less geographic variation in
temperatures. Daily winter low temperatures average -15°C
in the Nushagak Lowlands and -10°C along the Alaska
Peninsula. Daily winter highs average near freezing
throughout the region. Daily summer low temperatures
average just above freezing, and highs average about 18°C.

Terrain. — The Bristol Bay—Nushagak Lowlands
Ecoregion consists of rolling lowlands, with elevations rang-
ing from sea level to 150 m and slope gradients of generally
less than 2°. The region was glaciated during the Pleistocene
epoch and is covered by glacial moraine and outwash.
Deposits tend to be coarse near the mountains of adjacent
ecoregions, grading to fine sand along the coast. Sand dunes
are found along sea bluffs, river bluffs, and past and current
shorelines of larger lakes. Parts of the lowlands are mantled

BRISTOL BAY—NUSHAGAK LOWLANDS 39

by silt and peat. Most streams arise from nearby mountain-
ous ecoregions, and many are headwatered in lakes in
ice‘carved basins. The lowland is dotted with morainal and
thaw lakes. Isolated masses of permafrost occur in the
Nushagak Lowland area. The southern half of the region is
generally free from permafrost.

Soils. — Dominant soils are Typic Haplocryands, Typic
Vitricryands, Fluvaquentic Cryofibrists, Histic Pergelic
Cryaquepts, Pergelic Cryaquepts, and Typic Cryochrepts.
Most soils formed in volcanic ash deposits of various thickness
underlain by gravelly glacial till, outwash deposits, or silty
alluvium. Coastal plain soils formed in gravelly alluvium, cin-
ders, or weathered rock blanketed with thick sedge peat.

Vegetation. — Dwarf scrub communities grow on rela-
tively well drained mineral soils and are the dominant vege-
tation type in this ecoregion (fig. 28). Wetland communities
vegetate large areas; poorly drained slopes and terraces are
colonized by low scrub bog communities, and poorly
drained lowlands are colonized by wet graminoid herba-
ceous communities and wet forb herbaceous communities.
Of more limited distribution are broadleaf and mixed forest
stands that grow on the floodplains of major rivers.

Dwarf scrub communities are dominated by ericaceous
species (typically Empetrum nigrum). Lichens (for example,
Alectoria spp., Cetraria spp., and Cladonia spp.) may be
codominant. A number of other woody species (for example,
Ledum decumbens, Loiseleuria procumbens, Arctostaphylos
alpina, Salix spp., and Dryas octopetala) may be present.
Mosses (for example, Sphagnum spp. and Dicranum spp.)
are common in most stands. Dwarf arctic birch (Betula
nana) may invade these communities when peat accumula—
tion provides a deeper rooting zone.

Low scrub bog communities are codominated by woody
species (for example, Betula glandulosa, B. nana, Ledum
decumbens, Vaccinium vitis—idaea, V. uliginosum, and
Empetrum nigrum) and tussock—forming sedges (for exam-
ple, Eriophorum vaginatum). Mosses (primarily Sphagnum
spp.) form a nearly continuous mat.

Wet graminoid herbaceous communities include fresh
sedge marshes, wet sedge meadows, sedge—moss bog mead—
ows, and halophytic sedge wet meadows. Fresh sedge marsh-
es are comprised almost entirely of tall emergent sedges (for
example, Scirpus validus or Eleocharis palustris). As plant
detritus and sediments accumulate, these communities may
be replaced by wet sedge meadows dominated by Carex
species. Mosses (for example, Dicranum spp., Polytrichum
spp., and Sphagnum spp.) may be abundant in meadows.

Sedge—moss bog meadows occur in peat—filled depres-
sions. Low sedges (for example, Eriophorum russeolum,
Carex spp., and Trichophorum caespitosum) are dominant
and are rooted along with other herbs (for example,
Potentilla palustris) in a mat of Sphagnum mosses.

Halophytic sedge wet meadows occur in coastal areas

and are dominated by Carex lyngbyaei. Other important
graminoid constituents include Eriophorum spp. and
Calamagrostis canadensis.

Wet forb herbaceous communities mainly include fresh
herb marshes colonized principally by emergent herbs (for
example, Menyanthes trifoliata, Potentilla palustris, and
Equisetum fluviatile). Aquatic mosses (for example,
Sphagnum spp.) are common.

Broadleaf forest communities are dominated by birch
(Betula papyrifera) or codominated by birch and other tree
species (for example, Populus balsamifera). A tall shrub
understory is common, consisting of willow (for example,
Salix bebbiana and S. scouleriana) and alder (Alnus crispa
and A. sinuata). A low shrub understory typically includes
prickly rose (Rosa acicularis), high bushcranberry
(Viburnum ea’ule), and resin birch (Betula glandulosa).
Dwarf dogwood (Camus canadensis) and fireweed
(Epilobium angustifolium) are common forbs. Mixed forest
communities result where white spruce (Picea glauca)
codominates with birch.

Wildfire. — Occurrence of wildfires in the Nushagak
Lowlands portion of the ecoregion is low. The range in
recorded burn size is from less than 1 ha to 1,820 ha, aver-
aging 870 ha. Fire data are not available for the portion of
the ecoregion along the Alaska Peninsula.

Land Use and Settlement. — Permanent settlements
occur primarily along the coast or adjacent to the larger
rivers. The region is used primarily for commercial fishing
and processing and for subsistence and recreational hunting
and fishing. The northern half of the region was settled by
the Bristol Bay Yup’ik, and the southern half was settled by
the Koniag. These two groups are descended from the
Bering Sea Yup’ik and the Pacific Yup’ik, respectively.
Coastal communities rely primarily on marine resources (for
example, whales, seals, salmon, halibut, sea lions, sea otters,
clams, mussels, and seaweed). Away from the coast, salmon
and terrestrial mammals (for example, caribou and moose)
are more important. Edible and medicinal greens, roots, and
berries are also collected.

Delineation Methods. — The ecoregion boundary is
generally based on inclusion of the “Moist Tundra,” “Wet
Tundra,” and “Lowland Spruce~Hardwood Forest” ecosys—
tems and an exclusion of “High Brush,” “Alpine Tundra,”
and “Upland Spruce—Hardwood Forest” ecosystems, as
depicted on the map “Major Ecosystems of Alaska.”
Transitional zones occur where “Upland Spruce—Hardwood
Forest” penetrates from the Ahklun and Kilbuck Mountains
Ecoregion to the west, and in areas having moderate to high
terrain roughness, as shown on the terrain roughness map.

References. — The information provided in this region-
al description has been compiled from Beikman (1980),

40

 

ECOREGIONS OF ALASKA

.4.

Figure 28. Distribution of vegetation communities indicates a relationship with hillslope position and drainage characteris-
tics in the Bristol Bay-Nushagak Lowlands Ecoregion. Dwarf shmbs, graminoid species, and lichens grow in well drained
areas. Scattered small communities of alder occur on hillslopes. Graminoid marsh communities grow in depressions.

 

Figure 29. Alaska Peninsula Mountains Ecoregion typically shrouded in clouds. Soils, formed from volcanic ash and cin-
der, are highly erodible and restrict the development of vegetation.

ALASKA PENINSULA MOUNTAINS 41

Black (1951), Coulter and others (1962), Ferrians (1965),
Gabriel and Tande (1983), Joint Federal-State Land Use
Planning Commission for Alaska (1973), Karlstrom and others
(1964), Langdon (1993), Larson and Bliss (written cornmun.,
1992), Moore (written commun., 1993), Morgan (1979), Ping
(written commun., 1993), Reiger and others (1979), Selkregg
(1974), US. Bureau of Mines (1992a, 1992b), US. Geological
Survey (1964, 1987a), Viereck and Little (1972), Viereck and
others (1992), Wahrhaftig (1965), WeatherDisc Associates,
Inc. (1990), and Wibbenmeyer and others (1982).

113. ALASKA PENINSULA MOUNTAINS

Distinctive Features. — The 48,000—km2 ecoregion is
composed of rounded, folded and faulted sedimentary ridges
intermittently surmounted by volcanoes. The mountains
were heavily glaciated during the Pleistocene epoch. A mar-
itime climate prevails, and the region is generally free of per-
mafrost. Many soils formed in deposits of volcanic ash and
cinder over glacial deposits and are highly erodible (fig. 29).
Vegetation cover commonly consists of dwarf scrub commu—
nities at higher elevations and on sites exposed to wind, and
low scrub communities at lower elevations and in more pro-
tected sites.

Climate. — Climate has a predominantly maritime influ-
ence, as is evident from the higher precipitation and lower
seasonal and diurnal fluctuations in air temperatures than in
ecoregions having continental or transitional climates.
Annual precipitation varies greatly from location to location
along the coast, with coastal areas receiving from 600 mm to
3,300 mm. High elevations in the mountains average more
than 4,060 mm of precipitation each year. Mean annual
snowfall ranges from 55 cm to 150 cm along the coast and
exceeds 510 cm in the higher mountains. Winter daily min—
imum temperatures average from -11°C to -6°C throughout
the region; daily maximum temperatures average from -2°C
to 1°C. Summer temperatures range from lows of about 6°C
to highs of about 15°C.

Terrain. — The region is characterized by rounded
ridges, 300 m to 1,200 m high, surmounted at varying inter-
vals by rugged volcanic peaks, 1,400 m to 2,600 m high.
The mountains are dissected by many drainageways. Slope
gradients are usually from 0° to 11°, but steeper slopes occur
across 7 percent of the region. Geological formations con-
sist of stratified Jurassic, Cretaceous, and Tertiary sediments,
and undifferentiated Quaternary volcanic rocks. The region
was heavily glaciated during the Pleistocene epoch. Most of
the volcanoes reached their acme following Pleistocene
glaciation. Glaciers persist on volcanoes. Many features of
glacial erosion are present, such as cirques and U—shaped
valleys. The ecoregion is generally free from permafrost.

Streams draining to the Pacific Ocean are short and have

steep gradients. Streams draining to the Bering Sea become
braided when they reach the rolling lowlands of the Bristol
Bay—Nushagak Lowlands Ecoregion to the north. Many
streams are glacier fed. Lakes have been formed by
moraines, or have formed in ice—carved basins.

Soils. — Dominant soils are Typic Haplocryands and Typic
Vitricryands. Glacial deposits cover all but the highest parts of
ridges. Soils, formed in deposits of volcanic ash and cinder
that mantle the glacial deposits, are highly erodible. Mountain
peaks, rock escarpments, and talus slopes have little or no soil
cover. Some depressions are filled with fibrous peat.

Vegetation. — Dwarf scrub communities are widespread
in this ecoregion, occurring at higher elevations and on
windswept areas (fig. 30). Low scrub communities grow on
sites more protected from wind and at lower elevations. Tall
scrub communities grow at lower elevations and along hill-
slope drainages. Floodplains and south—facing slopes sup-
port broadleaf forest stands. Poorly drained areas are colo-
nized by low scrub bog communities and mesic graminoid
herbaceous communities.

Dwarf scrub communities are generally dominated by
crowberry (Empetrum nigrum). Accompanying shrubs
include other ericads (for example, Vaccinium vitis—idaea, V.
uliginosum, and Arctostaphylos alpina), arctic willow (Salix
arctica), and white mountain—avens (Dryas octopetala).
Mosses (for example, Dicranum spp., Hypnum spp.,
Polytrichum spp., and Rhacomitrium spp.) and lichens (for
example, Alectoria spp., Cladom'a spp., Cladina spp., and
Cetraria spp.) are common.

Low scrub communities are dominated by willow (for
example, Salix glauca, S. lanata, and S. planifolia). Dwarf
shrubs (for example, Betula nana, Vaccinium vitis—idaea, V.
uliginosum, Ledum decumbens, Dryas spp., and Salix reticu-
lata) and forbs (for example, Calamagrostis canadensis,
Festuca altaica, Carex bigelowii, and Artemisia spp.) colo—
nize the understory. Mosses (for example, Polytrichum spp.
and Hypnum spp.) form a patchy to continuous mat cover.

Tall scrub communities consist primarily of alder (for
example, Alnus sinuata) or a mix of alder and willow (Salix
alaxensis, S. barclayi, S. planifolia, and S. glauca). Low
shrubs (for example, Betula glandulosa, B. nana, Vaccim'um
vitis—idaea, V. uliginosum, and Ledum decumbens) may be
common or absent in the understory.

Broadleaf forests are dominated by balsam poplar
(Populus balsamzfera). A tall shrub understory of alder and
willow is usually present. Bluejoint (Calamagrostis canaden-
sis) is important in the herbaceous layer. Mosses (commonly
featherrnoss species) provide extensive ground cover.

Low scrub bogs are typically dominated by ericaceous
species, such as crowberry (Empetmm nigrum), narrow—leaf
Labrador—tea (Ledum decumbens), mountain—cranberry
(Vaccinium vitis—idaea), bog blueberry (V. uliginosum), and
bog cranberry (V. oxycoccus). Sedges (for example,

42

ECOREGIONS OF ALASKA

 

Figure 30. Dwarf scrub communities are common on the middle slopes and some of the higher slopes of the Alaska
Peninsula Mountains Ecoregion. Willow grows along the lower slopes. The beach ridges along the shore are vegetated by
willow and alder. (Photo courtesy of Keith Trexler, National Park Service, Anchorage.)

 

Figure 31. Typical landscape of the Aleutian Islands Ecoregion, composed of a chain of sedimentary islands overtopped by
steep volcanoes. Bare rock and rubble occur on volcanic cones, peaks, and high ridgetops. Dwarf shrub tundra communities
occur at higher elevations and in windswept areas. Moist tundra communities are found at lower elevations and in protected
sites. (Photo courtesy of Leslie Kerr, Fish and Wildlife Service, Anchorage.)

ALEUTIAN ISLANDS 43

Eriophorum spp. and Carex spp.) and forbs (for example,
Potentilla palustris and Menyanthes trifoliata) are common.
Sphagnum mosses are always present and are usually the
dominant mosses. Lichens (for example, Cladina spp. and
Cetraria spp.) occur on mounds.

Mesic graminoid herbaceous communities primarily
consist of meadows dominated by bluejoint (Calamagrostis
canadensis) or a mix of bluejoint and various herbs (for
example, Epilobium angustifolium, Heracleum lanatum,
Athyrium filix—femina, and Equisetum arvense).

Wildfire. — No fire data are available for the Alaska
Peninsula.

Land Use and Settlement. — Settlements are located
mainly along the coastline. The region is used primarily for
commercial fishing and processing and for subsistence and
recreational hunting and fishing. The area was historically
occupied by the Koniag, of the Pacific Yup’ik people.
Marine resources, such as whales, seals, salmon, halibut,
cod, rockfish, sea lions, sea otters, porpoises, shellfish, sea
urchins, bivalves, and seaweed, have been the basis for sub-
sistence. Terrestrial mammals (for example, caribou, moose,
ground squirrel, and hare) are of secondary importance.
Plant greens, roots, and berries are collected for food and
medicinal purposes.

Several metals have been mined in this ecoregion, includ-
ing gold, silver, lead, and copper. Energy—related resources,
such as coal and petroleum, have also been extracted.

Delineation Methods. — The boundary separating the
Alaska Peninsula Mountains from the Bristol Bay—Nushagak
Lowlands is based on the inclusion of “Alpine Tundra” and
“High Brush” ecosystems and on the exclusion of “Moist
Tundra” and “Wet Tundra” ecosystems, as shown on the map
“Major Ecosystems of Alaska.” The boundary separating the
Alaska Peninsula Mountains from the Aleutian Islands is
based on general climate information; the exact placement of
the line is somewhat arbitrary. Because the Alaska Peninsula
Mountains Ecoregion is narrow and environmental gradients
are steep, it is not possible to delineate transitional areas at the
current scale of mapping.

References. — The information provided in this region—
al description has been compiled from Beikman (1980),
Coulter and others (1962), Ferrians (1965), Joint Federal-
State Land Use Planning Commission for Alaska (1973),
Karlstrom and others (1964), Langdon (1993), Larson and
Bliss (written commun., 1992), Moore (written commun.,
1993), Morgan (1979), Ping (written commun., 1993),
Reiger and others (1979), Selkregg (1974), US. Bureau of
Mines (1992a, 1992b), US. Geological Survey (1964,
1987a), Viereck and Little (1972), Viereck and others
(1992), Wahrhaftig (1965), WeatherDisc Associates, Inc.
(1990), and Wibbenmeyer and others (1982).

114. ALEUTIAN ISLANDS

Distinctive Features. — The 12,000 km2 Aleutian
Islands Ecoregion in southwestern Alaska is composed of a
chain of sedimentary islands (eroded from older volcanic
formations) that are crowned by steep volcanoes (fig. 31).
Maritime climate prevails. The region is south of the winter
sea ice pack and is generally free from permafrost.
Vegetation cover mainly consists of dwarf scrub communi-
ties at higher elevations and on sites exposed to wind, and of
graminoid herbaceous communities in more protected sites.

Climate. - The Aleutian Islands have a maritime climate.
Annual precipitation varies greatly from place to place, from
as little as 530 mm to as much as 2,080 mm at sea level weath-
er stations. Annual snowfall averages from 85 cm to 250 cm
at the same stations. In general, smaller islands receive less
precipitation than larger islands. Winter daily low tempera-
tures average from -7°C to -2°C, and daily highs average from
2°C to 5°C. Summer daily temperatures average from lows of
4°C to highs of 10°C to 13°C. The frost—free season usually
lasts from May through mid—September.

Terrain. — The ecoregion is composed of a chain of
islands exposed along the crest of a submarine ridge. Most
of the islands, formed of blockfaulted Tertiary sediments
derived from earlier igneous processes, are surmounted by
volcanoes of Tertiary and Quaternary Age. Regional eleva-
tions range from sea level to greater than 1,900 In. Most
high volcanoes have icecaps or small glaciers. Lowlands
have slope gradients less than 1°, but mountains are steep,
with gradients almost always greater than 5°. The islands
have been intensely glaciated (though only the easternmost
portion was glaciated during the Pleistocene epoch), and evi-
dence of glacial erosion is common. The region is generally
free from permafrost, but periglacial erosional processes are
active because of the cold, wet climate.

Streams are short and swift. Many enter the sea as
waterfalls. In areas of porous volcanic rock, stream courses
are widely spaced and are filled with water only during
exceptionally heavy rains. Many small lakes occupy irregu-
lar ice—carved basins in rolling topography on the glaciated
islands. Lakes fill a few volcanic craters and calderas.

Soils. — Dominant soils are Typic Haplocryands and
Typic Vitricryands. Most soils formed in deposits of vol-
canic ash or Cinders over basaltic bedrock. Bare rock and
rubble occur on volcanic cones, peaks, and high ridgetops.
Volcanic material generally grades from coarse to fine with
increasing distance from active volcanoes. Organic soils
occupy depressions and some broad valley bottoms.

Vegetation. — Vegetation cover at higher elevations and
on windswept areas consists of dwarf scrub communities
dominated by willow or crowberry. Mesic graminoid herba-

ECOREGIONS OF A ASKA

Figure 32. Spruce—hardw )od forests. the most widespread vegetation co nunity of the Cook Inlet Ecoregion. The area has
one of the mildest climates in Alaska and. consequently. is generally free liom permafrost.

Figure 33. Forest stand with pockets of white spruce or hite spruce mixed with birch in the Cook Inlet Ecoregion.

 

 

COOK INLET 45

ceous and dry graminoid herbaceous communities occur at
lower elevations and in protected sites. Low scrub commu—
nities grow in bogs having thick peat deposits.

Willow dwarf scrub communities are dominated by
Salix arctica, S. rotundz'folia, and S. ovalifolia. Other com-
mon shrubs are crowberry (Empetram nigrum),
mountain—cranberry (Vaccim'am vitis—idaea), bog blueberry
(V. uliginosam), mountain—avens (Dryas spp.), cassiope
(Cassiope lycopodioides), and narrow—leaf Labrador—tea
(Ledum decumbens). Herbs, (for example, Carex spp. and
Saxifraga spp.) and mosses (for example, Dicranam spp. and
Aulacomniam spp.) are common.

Crowberry dwarf scrub communities are dominated by
Empetrum nigrum. Aleutian mountain—heath (Phyllodoce
aleutica), cassiope (Cassiope stelleriana), dwarf blueberry
(Vaccinium caespitosam), and meadow—spirea (Luetkea
pectinata) are typical constituents of these communities.
Mosses are common. Lichens (for example, Cladom'a spp.)
are common in many stands.

Mesic graminoid herbaceous communities primarily
consist of meadows, where bluejoint (Calamagrostis
canadensis) is codominant with a variety of other herbs (for
example. Epilobium angusttfolium, Equisetum arvense,
Carex spp., and Festuca spp.).

Dry graminoid herbaceous communities occur in coastal
areas, such as near coastal marshes and at the bases of cliffs.
Hair—grasses (Deschampsia spp.) provide nearly all of the
vegetation cover.

Low scrub bog communities are dominated by erica—
ceous species (for example, Empetrum nigrum, Vaccinium
uliginosum, V. vitis—idaea, V. oxycoccus, Andromeda polifo-
Zia, and Ledam decumbens). Sedges (for example,
Eriophoram angustifolium, Trichophorum caespitosum,
Carex pluriflora, and C. pauciflora) are common or codomi-
nant. Sphagnum species are always present and are usually
the dominant mosses. Feathermosses may be common.
Lichens may occur on mounds.

Wildfire. — No fire data are available for the Aleutian
Islands.

Land Use and Settlement. — Settlements are sparse and
are primarily located along the coastline. The native popu-
lations of the islands are Aleut. They depend on marine
resources (for example, Steller sea lions, seals, otters, and
whales) for subsistence. Caribou and salmon are important
sources of food and materials in the eastern part of the
region. Tidal waters provide additional resources, such as
algae, chitons, fish, mussels, urchins, octopus, and sea otters.
Birds (for example, cormorants, gulls, murres, and puffins)
and their eggs augment the traditional diet. Edible and med-
icinal plants are also collected.

Delineation Methods. — The ecoregion boundary sepa—
rates the islands of the Aleutian chain from those immediately

south and west of the Alaska Peninsula. The boundary is based
primarily on climate information. A lack of sufficient infor-
mation detail prohibits the delineation of transitional areas.

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Ferrians (1965), Joint Federal-State Land
Use Planning Commission for Alaska (1973), Karlstrom and
others (1964), Langdon (1993), Larson and Bliss (written
commun, 1992), Moore (written commun, 1993), Morgan
(1979), Ping (written commun., 1993), Reiger and others
(1979), Selkregg (1974), US. Bureau of Mines (1992a,
1992b), US. Geological Survey (1964, 1987a), Viereck and
Little (1972), Viereck and others (1992), Wahrhaftig (1965),
and WeatherDisc Associates, Inc. (1990).

115. COOK INLET

Distinctive Features. — Located in the south central part
of Alaska adjacent to the Cook Inlet, the 28,000—km2 ecore—
gion has one of the mildest climates in the State. The cli-
mate, the level to rolling topography, and the coastal prox-
imity have attracted most of the settlement and development
in Alaska. The region has a variety of vegetation communi-
ties (fig. 32) but is dominated by stands of spruce and hard-
wood species. The area is generally free from permafrost.
Unlike many of the other nonmontane ecoregions, the Cook
Inlet Ecoregion was intensely glaciated during the
Pleistocene epoch.

Climate. ~ The climate is affected by both maritime and
continental influences. Average annual precipitation ranges
from 380 mm to 680 mm across the region. Annual snow-
fall averages from 160 cm to 255 cm. Winter temperatures
range from lows of -15°C to highs of —5°C, and temperature
inversions are common. Summer temperatures vary from
lows of about 5°C to highs of about 18°C. May through
September are usually frost—free.

Terrain. — The level to rolling terrain of this ecoregion
is shaped by ground moraine, drumlin fields, eskers, and out-
wash plains, remnants of Pleistocene glaciation. Elevations
range from sea level to 600 m. Slope gradients are general-
ly less than 3°. Bedrock consists of poorly consolidated
Tertiary coal—bearing rocks. Marine and lake deposits man-
tle portions of the region, and a considerable part of the low-
lands has been blanketed by aeolian materials. Hundreds of
small lakes, swamps, and bogs have developed in areas of
stagnant ice topography and on ground moraines. The
region was intensely glaciated during the Pleistocene epoch.
There is currently little permafrost.

Soils. — Dominant soils are Haplocryands, Sphagnic
Borofibrists, Terrie Borosaprists, Typic Borohemists, Andic

46 ECOREGIONS OF ALASKA

Haplocryods, and Andic Humicryods. Surface soil layers
formed in loess blown from the floodplains of glacial
streams and in volcanic ash blown from mountains to the
west. Subsurface soil layers formed predominantly in
glacial deposits, and range from gravelly clay loam to very
gravelly sandy loam. The subsurface soil layers on alluvial
terraces and outwash plains are waterworked, very gravelly
sand. Soils in depressions holding fens and bogs are organ-
ic and consist of peat.

Vegetation. — A variety of vegetation communities
occur in the ecoregion. Needleleaf, broadleaf, and mixed
forests are the most widespread (fig. 33). Tall scrub com-
munities form thickets on periodically flooded alluvium,
such as occurs on floodplains, along streambanks, and in
drainageways. Mesic graminoid, graminoid herbaceous, and
low scrub graminoid communities occur over a range of
moist to dry sites. Poorly drained lowlands support low
scrub communities. The wettest sites are colonized by tall
scrub swamp, low scrub bog, wet forb herbaceous, and wet
graminoid herbaceous vegetation (fig. 34).

Needleleaf forests are dominated by white spruce (Picea
glauca), black spruce (P. mariana), and Sitka spruce (Picea
sitchensis). Broadleaf forests are dominated by quaking
aspen (Populus tremuloides), balsam poplar (P. balsam-
ifera), black cottonwood (P. trichocarpa), and paper birch
(Betula papyrifera). Mixed forests are codominated by com-
binations of these needleleaf and broadleaf species.

White spruce forests grow on well drained soils. Black
spruce, paper birch, balsam poplar, and aspen may codomi—
nate with white spruce. A low shrub layer is typical, includ—
ing birch (for example, Betula glandulosa and B. nana), eri-
caceous species (for example, Vaccinium vitis—idaea, V. ulig-
inosum, Ledum groenlandicum, and Empetrum nigrum), buf—
faloberry (Shepherdia canadensis), and prickly rose (Rosa
acicularis). Herbaceous cover varies, depending upon open-
ness of stands. Common species are Equisetum spp.,
Linnaea borealis, and Calamagrostis canadensis.
Feathermosses (for example, Hylocomium splendens and
Pleurozium schreberi) form a nearly continuous layer.

Aspen forests grow on relatively warm, dry slopes.
Stands may also contain balsam poplar (Populus balsam-
ifera), spruce (Picea glauca and P. mariana), and paper birch
(Betula papyrtfera). Alder (Alnus crispa) and willow (Salix
bebbiana) commonly provide a tall shrub layer. The low
shrub layer includes prickly rose (Rosa acicularis), buf-
faloberry (Shepherdia canadensis), and high bushcranberry
(Viburnum edule). The herb layer is patchy, and mosses and
lichens provide little cover.

Paper birch forests are common on moderately well to
well drained upland sites. White spruce and black spruce
may be present. Alders (Alnus crispa and A. sinuata), wil-
lows (Salix spp.), and, in open stands, resin birch (Betula
glandulosa) occur as a tall shrub layer. Prickly rose (Rosa
acicularis), high bushcranberry (Viburnum edule), and erica-

ceous shrubs provide low shrub cover. In closed forest
stands, Calamagrostis canadensis dominates the herb layer,
and mosses and lichens are rare. In more open stands, the
ground is covered by feathermosses (for example,
Hylocomium splendens and Pleurozium schreberi).

Forests dominated by black spruce or a mixture of black
spruce and paper birch colonize poorly drained areas. Alders
(Alnus crispa) usually provide a tall shrub layer. Common
lower shrubs are prickly rose (Rosa acicularis), willow
(Salix spp.), Labrador—tea (Ledum groenlandicum), and eri-
caceous species. Feathermosses (for example, Pleurozium
schreberi and Hylocomium splendens) form a patchy to con-
tinuous moss layer. Sphagnum mosses may occur on the
wetter sites. Foliose lichens (for example, Peltigera aph-
thosa and P. canina) are common.

Floodplains and active alluvial fans support relatively
pure or mixed stands of Sitka spruce (Picea sitchensis), black
cottonwood (Populus trichocarpa), balsam poplar (P. bal-
samifera), and paper birch (Betula papyrifera). When pre—
sent, the tall shrub component consists of alder and willow.
Lower shrubs typically include prickly rose (Rosa acicu-
laris), high bushcranberry (Viburnum edule), and devilsclub
(0plopanax horridus). Herbaceous species vary with forest
type. Gymnocarpium dryopteris, Athyrium filix—femina, and
Tiarella trifoliata occur in Sitka spruce stands; Calamagrostis
canadensis and Equisetum spp. occur with black cottonwood;
Calamagrostis canadensis, Mertensia paniculata, and
Epilobium angustifolium occur with balsam poplar.
Feathermosses are found in some of these communities.

Tall scrub thickets are dominated by alders (Alnus
crispa, A. tenuifolia, A. sinuata), willows (Salix alaxensis, S.
brachycarpa, and S. planifolia), or a combination of alders
and willows. Mosses (for example, Hylocomium splendens,
Drepanocladus uncinatus, and Polytrichum spp.) may be
abundant.

Dry to mesic sites support mesic graminoid, graminoid
herbaceous, and low scrub graminoid communities.
Examples are communities dominated by dry fescue
(Festuca altaica), communities codominated by midgrasses
(Festuca altaica, F. rubra, Deschampsia beringensis, and
Poa eminens) and forbs (for example, Aconitum delphini-
folium and Mertensia paniculata), and communities codom—
inated by midgrasses (Festuca altaica, Calamagrostis pur-
purascens, Agropyron spicatum, Poa spp., Bromus pumpel—
lianus) and low shrubs (for example, Vaccinium vitis—idaea,
Empetrum nigrum, Salix reticulata, and S. lanata), respec—
tively. Nonsphagnaceous mosses are common in all of these
community types. Lichens may be common or absent.

Mesic to moist sites support mesic graminoid communi—
ties dominated by bluejoint (Calamagrostis canadensis),
graminoid herbaceous communities codominated by blue-
joint and herbs (for example, Epilobium angustifolium,
Angelica lucida, Athyrium filix—femina, Equisetum arvense,
and E. fluviatile), or low scrub graminoid communities dom-
inated by bluejoint and low shrubs (for example, Alnus sinu-

 

 

COOK INLET 47

 

Figure 34.

am). Feathermosses form a patchy layer on the ground.

Low scrub communities are dominated by willows (for
example, Salix glauca and S. lanata) or a mixture of willows
and birch (for example, Betula glandulosa). The herbaceous
layer typically includes graminoid species (for example,
Calamagrostis canadensis, Carex spp., and F estuca altaica).
Mosses (for example, feathermosses) form a patchy to con-
tinuous mat.

Tall scrub swamps are dominated by alder (for example,
Alnus tenuifolia) or combinations of alder (A. tenuifolia) and
willow (Salix planifolia and S. lanata). Cover by low shrubs
varies, but typical constituents are high bushcranberry
(Viburnum edule), currant (Ribes spp), prickly rose (Rosa
acicularis), and Pacific red elder (Sambucus callicarpa).
Sedges (Carex spp), bluejoint (Calamagrostis canadensis),
dwarf dogwood (Cornus canadensis), and horsetail
(Equisetum spp) are typical herbaceous species. Mosses (for
example, feathermosses and Sphagnum spp.) are common
but discontinuous.

Low scrub bog communities include those dominated
by low mixed shrubs (for example, Betula glandulosa, B.
nana, Ledum decumbens, Vaccinium vitis—idaea, and V. ulig-
inosum) and tussock—forming sedges (for example,
Eriophorum vaginarum), ericaceous species (for example,
Vaccinium vitis—idaea, V. uliginosum, Ledum decumbens,
Empetrum nigrum, and Andromeda polifolia), a mixture of

Wet graminoid herbaceous communities, such as this sedge meadow, commonly occur in shallow basins in the
Cook Inlet Ecoregion.

birch (for example, Betula glandulosa and B. nana) and eri-
caceous species, and a mixture of willow (for example, Salix
barclayi and S. commutata) and graminoid species (for
example, Calamagrostis canadensis and Carex spp). Other
low shrubs (for example, C hamaedaphne calyculata and
Andromeda polifolia) may be present in any of these bog
communities. A nearly continuous mat of mosses (for exam—
ple, Sphagnum spp. and feathermosses) occurs in low
scrub—sedge tussock communities.

Wet forb herbaceous communities are dominated by
nongraminoid species, including horsetail (for example,
Equisetum fluviatile), buckbean (Menyanthes trifall’ata),
marsh fivefinger (Potentilla palustris), and marsh—marigold
(C altha palustris). Mosses and floating 0r submerged aquat—
ic plants may be abundant.

Freshwater wet graminoid herbaceous communities are
dominated by sedges (Carex spp.) or a mixture of sedges and
low shrubs (for example, Myrica gale and Salix spp). Mosses
are common. Coastal areas may be dominated by salt—toler—
ant grasses (for example, Puccinellia spp), sedges (for exam—
ple, Carex lyngbyaei), and forbs (for example, Honckenya
peploides, Triglochin maritimum, and Plantago maritima).

Wildfire. — Occurrence of wildfires in the Cook Inlet
Ecoregion is low. The size of burns varies from less than
1 ha to 2,270 ha, averaging 160 ha.

48 ECOREGIONS OF ALASKA

Figure 35. Extensive systems of valley glaciers in the Alaska Range Ecoregion. Features of glacial erosion, such as cirques
and U-shaped valleys, are common.

Land Use and Settlement. — The Cook Inlet Ecoregion
is the most populated region in Alaska. Summer and winter
recreational activities occur extensively throughout the region.
Agricultural activities are limited largely to the Susitna Valley,
but they also occur on the Kenai Peninsula. Numerous gas
and oil wells dot the Trading Bay area, and some are scattered
about the Kenai Peninsula. Many oil platforms occupy the
Cook Inlet. Timber production occurs on the west shore of
Cook Inlet and in some areas along the Susitna River.

The Tanaina, a group of Pacific Athabascans, were the
native inhabitants of the ecoregion. Their traditional diet
included salmon, moose, and caribou, although these were
supplemented by beaver, hare, ground squirrel, grouse,
ptarrnigan, migratory waterfowl, Whitefish, blackfish, and
pike. Edible greens, berries, and roots were also collected.

Extractable resources have included metals (for exam-
ple, gold, silver, platinum, tin, copper, and tungsten) and
energy—related commodities (for example, coal and urani-
um). Numerous sand and gravel operations support con—
struction and road building activities.

Delineation Methods. — The ecoregion boundary repre—
sents areas less than 600 m in elevation. The boundary cor-
responds well with patterns on the relative CIR image.
Transitional areas include the “Upland Spruce~Hardwood
Forest" areas, depicted on the map “Major Ecosystems of
Alaska,” that occur along the interface with the surrounding
mountainous ecoregions.

 

References. — The information provided in this regional
description has been compiled from Beikrnan (1980), Black
(1951), Coulter and others (1962), Ferrians (1965), Gabriel
and Tande (1983), Joint Federal-State Land Use Flaming
Commission for Alaska (1973), Karlstrom and others (1964),
Langdon (1993), Larson and Bliss (written commun., 1992),
Moore (written commun., 1993), Morgan (1979), Ping (writ-
ten commun., 1993), Reiger and others (1979), Selkregg
(1974), U.S. Bureau of Mines (1992a, 1992b), U.S.
Geological Survey (1964, 1987a), Viereck and Little (1972),
Viereck and others (1992),Wahrhaftig (1965), and
WeatherDisc Associates, Inc. (1990).

116. ALASKA RANGE

Distinctive Features. — The mountains of south central
Alaska, the Alaska Range, are very high and steep. The
117,000—km2 ecoregion is covered by rocky slopes, icefields,
and glaciers (fig. 35). Much of the area is barren of vegeta-
tion. Dwarf scrub communities are common at higher ele-
vations and on windswept sites where vegetation does exist.
The Alaska Range has a continental climatic regime, but
because of the extreme height of many of the ridges and
peaks, annual precipitation at higher elevations is similar to
that measured for some ecoregions having maritime climate.

Climate. — Climate is influenced by continental factors.

 

 

ALASKA RANGE 49

Weather data for the region are from lower elevation sta—
tions. Daily winter low temperatures average about —25°C
and daily highs about -3°C at these stations. Daily summer
low temperatures for the same areas average about 2°C and
daily highs about 18°C. Mean annual precipitation in the
lowlands is approximately 380 mm, with snowfall ranging
from 150 cm to 305 cm at various stations. Estimated aver—
age annual precipitation for the higher mountains peaks is
2,030 mm, with estimated snowfall at 1,015 cm.

Terrain. — The ecoregion consists of steep, rugged moun-
tain ridges separated by broad valleys. Elevations are 600 m in
the lower valleys (sea level in the southwestern portion of the
ecoregion), often rising to greater than 3,900 m on mountains
peaks (Mt. McKinley is higher than 6,100 m). Slope gradients,
which are almost always greater than 5° on hillslopes, exceed
25° on some mountains. The southern portion of the ecoregion
is underlain by granitic batholiths intrusive into moderately
metamorphosed, highly deformed Paleozoic and Mesozoic
volcanic and sedimentary rocks. Large active volcanoes occur
in this area. The central and eastern portions of the ecoregion
are part of a broad syncline having Cretaceous rocks in the cen-
ter and Paleozoic and Precambrian rocks on the flanks.

The ecoregion was heavily glaciated during the
Pleistocene epoch, and extensive systems of valley glaciers
still radiate from the higher mountains. Rock glaciers are com-
mon. Gelifluction features are well developed. Permafrost is
discontinuous in this ecoregion; however, its full extent is
unknown. Streams are swift and braided, and most are head-
watered in glaciers. Many large lakes occupy the glaciated val-
leys within the southern part of the ecoregion. Lakes in the
central and eastern part of the ecoregion are relatively rare for
a glaciated area; most occur either as rock—basin lakes or as
collections of small ponds in areas of ground moraine.

Soils. — Much of the ecoregion consists of rocky slopes,
icefields, and glaciers. Where soil development has
occurred, principal soils are Lithic Cryorthents, Pergelic
Cryaquepts, Pergelic Ruptic—Histic Cryaquepts, Typic
Cryochrepts, Pergelic Cryumbrepts, and Typic Cryumbrepts.
Most soils are stony and shallow over bedrock, or bouldery
colluvial or glacial deposits. Soils on lower slopes and in
valleys are typically poorly drained, with a shallow per—
mafrost table. Soils on upper hillsides and ridgetops are
often well drained, very gravelly, and shallow over bedrock.
These soils usually do not retain sufficient moisture for
ice—rich permafrost.

Vegetation. — Much of the ecoregion is barren of vege-
tation. Dwarf scrub communities are most common where
vegetation does occur, growing on well drained, windswept
sites. More protected slopes provide moist to mesic sites
that support low or tall scrub communities (fig. 36). Open
needleleaf forests and woodlands occur on well drained sites
in some valleys and on lower hillslopes (fig. 37).

Dwarf scrub communities are typically dominated by
mountain—avens (Dryas octopetala, D. integrifolia, and D.
drummondii), ericaceous species (for example, Vaccinium
vitis—idaea, V. uliginosum, Cassiope tetragona,
Arctostaphylos alpina, and A. rubra), or combinations of
these species. Grarninoid species, such as sedges (for exam-
ple, Carex scirpoidea and C. bigelowii) and alpine holygrass
(Hierochloé‘ alpina), may be present and may even codomi-
nate with shrubs, as may lichens (for example, Alectoria spp.,
Cetraria spp., Cladonia spp., and Thamnolia spp.). Forbs
(for example, Oxytropis nigrescens, Hedysarum alpinum,
Minuartia spp., Anemone spp., and Saxifraga spp.) and moss—
es (for example, Tomenthypnum nitens, Hylocomium splen-
dens, and Polytrichum spp.) typically form the ground layer
of these communities.

Low scrub communities are dominated by birch (Betula
glandulosa and B. nana) and ericaceous shrubs (for example,
Vaccim'um vitis—idaea, V. uliginosum, Ledum decumbens,
Arctostaphylos spp., and Empetrum nigrum), or by willows
(for example, Salix glauca, S. planifolia, and S. lanata). Other
shrubs commonly found in these communities include
red—fruit bearberry (Arctostaphylos rubra), bog blueberry
(Vaccinium uliginosum), mountain—avens (Dryas spp.), netleaf
willow (Salix reticulum), and arctic willow (S. arctica).
Common herbs are fescue grass (F estuca altaica), alpine holy-
grass (Hierochloé alpina), Bigelow sedge (Carex bigelowii),
arctic sweet coltsfoot (Petasites frigidus), and arctic worm-
wood (Artemisia arctica). Mosses (for example, Hylocomium
splendens and Pleurozium schreberi) form patchy to continu-
ous mats. Lichens (for example, Cetraria spp. Stereocaulon
tomentosum, and Cladom'a spp.) can be abundant.

Tall scrub communities occur at altitudinal treeline,
along streambanks, in drainages, and on floodplains. These
communities are dominated by willow (Salix alaxensis, S.
arbusculoides, S. planifolia, and S. lanata), alder (Alrms sin-
uata and A. crispa), a mixture of willow and alder, or a mix-
ture of willow and birch (Betula glandulosa). Low shrubs,
such as Alaska bog willow (Salix fizscescens), Beauverd
spirea (Spiraea beauverdiana), narrow—leaf Labrador—tea
(Ledum decumbens), and bog blueberry (Vaccinium uligi-
nosum), occur in the more open stands. Understory herbs
include polar grass (Arctagrostis latifolia), fescue grass
(Festuca altaica), Bigelow sedge (Carex bigelowii), and
large—flowered Wintergreen (Pyrola grandiflora). Mosses
(for example, Polytrichum spp., Hylocomium splendens, and
Drepanocladus uncinatus) may be abundant in wetter stands.
Lichens (for example, Cladonia spp. and Stereocaulon
tomentosum) are locally abundant in drier stands.

Needleleaf forests and woodlands are dominated by
white spruce (Picea glauca) or white spruce mixed with
black spruce (P. mariana). The understory typically consists
of low woody vegetation, such as white mountain—avens
(Dryas octopetala), red—fruit bearberry (Arctostaphylos
rubra), arctic willow (Salix arctica), crowberry (Empetrum
nigrum), and mountain—cranberry (Vaccinium vitis—idaea).

50

ECOREGIONS OF ALASKA

 

Figure 36. Mountains with middle to lower slopes blanketed with low and tall scrub communities in the Alaska Range
Ecoregion. Deciduous (for example, Populus spp.) and coniferous (Picea spp.) trees often follow water tracks downslope.
(Photo courtesy of Beverly Friesen, Saint Mary’s College of Minnesota, Winona.)

 

Figure 37. White spruce woodlands on well drained lower slopes and valleys in the Alaska Range Ecoregion. The under-
story is resin birch.

COPPER PLATEAU 51

Mosses (for example, Pleurozium schreberi and Rhytidium
rugosum) grow in moist depressions. Fruticose lichens (for
example, Cetraria spp.) are scattered throughout the under-
story vegetation mat.

Wildfire. — Occurrence of wildfires in the Alaska Range is
low. Fires have ranged in size from less than 1 ha to 3,290 ha,
with the majority of the largest fires occurring in the central and
eastern portion of the ecoregion. Average area burned per fire
over the entire region is about 90 ha.

Land Use and Settlement. — The few permanent settle-
ments in this ecoregion are below 750 m elevation. The
region is used primarily for recreation and subsistence hunt-
ing and fishing. Native inhabitants of the Alaska Range
belong to several Athabascan groups, primarily the Tanaina,
Ahtna, and Tanacross. Their livelihoods depend on salmon
and freshwater fish (for example, Whitefish, blackfish, and
pike), large mammals (caribou, moose, and dall sheep),
smaller fur—bearing mammals (for example, beaver, hare,
and ground squirrel), and edible plants. Many extractable
resources occur in this ecoregion; these include metals (for
example, gold, silver, lead, copper, tungsten, platinum, zinc,
chromium, mercury, and tin), energy-related commodities
(for example, coal and uranium), and other commodities (for
example, antimony, bismuth, and molybdenum).

Delineation Methods. — The ecoregion boundary fol—
lows a generalized 600—m elevation contour for separating
the Alaska Range from the interior forested ecoregions. A
generalized 900—m elevation contour was used to separate the
Alaska Range Ecoregion from the Copper Plateau Ecoregion.
The Matanuska River is the boundary between the geological
formations of the Alaska Range and those of the Chugach
Mountains. The mountain pass along Jack Creek and the
upper Nabesna River forms the boundary between the Alaska
Range and Wrangell Mountains Ecoregions. Transitional
zones are areas less than 600 m in elevation along river
drainages, areas where mountains higher than 600 m become
more widely spaced (approximately 210 km apart), and areas
having upland spruce—hardwood forest vegetation.

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Ferrians ( 1965), Gabriel and Tande (1983),
Joint Federal-State Land Use Planning Commission for
Alaska (1973), Karlstrom and others (1964), Langdon
(1993), Larson and Bliss (written commun., 1992), Moore
(written commun., 1993), Morgan (1979), Ping (written
commun., 1993), Reiger and others (1979), Selkregg (1974),
US. Bureau of Mines (1992a, 1992b), US. Geological
Survey (1964, 1987a), Viereck and Little (1972), Viereck and
others (1992), Wahrhaftig (1965), WeatherDisc Associates,
Inc. (1990), and Wibbenmeyer and others (1982).

117. COPPER PLATEAU

Distinctive Features. — The 17,000—km2 Copper
Plateau Ecoregion in south central Alaska occupies the site
of a large lake that existed during glacial times. The nearly
level to rolling plain has many lakes and wetlands (fig. 38).
Soils are predominantly silty or clayey, formed from glacio-
lacustrine sediments. Much of the region has a shallow per-
mafrost table, and soils are poorly drained. Black spruce
forests and tall scrub, interspersed with wetlands, are the
major types of vegetation communities.

Climate. — The ecoregion has a continental climate.
Weather stations are located along the eastern side of the
region. There, winter temperatures range from lows of about
-27°C, to highs of about -16°C. Summer temperatures are
more consistently distributed throughout the area, with aver-
age lows of about 4°C and average highs of about 21°C.
Annual precipitation is lowest in the south and highest in the
north, ranging from 250 mm to 460 mm. Snowfall distribu-
tion patterns are comparable, ranging from 100 cm in the
south to 190 cm in the north. Although frost can occur in any
month, temperatures warm enough for plant growth general-
ly occur over a period of 11 weeks.

Terrain. — The ecoregion has smooth to rolling terrain.
Elevations vary from 420 m to 900 m, with slope gradients
generally less than 2°. The region is mantled in Pleistocene
proglacial lake deposits that are tens to hundreds of meters
thick. Most rivers head in glaciers from the surrounding
mountains. Wind—blown deposits from local floodplains
have developed into dunes along most of the glacial streams.
The overall drainage pattern is poorly defined, but the lower
stretches of the larger rivers are deeply incised in narrow val—
leys. The continuous permafrost layer ranges from thin to
moderately thick. The permafrost table is close to the
ground surface, resulting in abundant thaw lakes. The per-
mafrost table is deep or absent in some of the very gravelly
and sandy material. Lakes have formed in abandoned melt-
water channels and morainal depressions.

Soils. — Principal soils are Histic Pergelic Cryaquepts,
Aquic Cryochrepts, Typic Cryochrepts, Pergelic Cryaquolls,
and Typic Cryoborolls. The major soils formed in silty aeo-
lian mantles overlying calcareous silty and clayey glaciola-
custrine sediments and, in places, gravelly glacial drift.
Organic soils occupy some depressions. Most of the soils
have a shallow permafrost table and are poorly drained.
Well drained soils occur in upland areas disturbed by wild—
fire or in very gravelly deposits where permafrost is deep or
absent. Soils with permafrost are very susceptible to alter—
ation upon disturbance of the organic mat, because of the rel—
atively warm (>-l.5°C) permafrost temperature. Organic
mat disturbance, as by wildfire, can result in warmer soil
temperatures, lowered permafrost tables, and significant

52 ECOREGIONS OF ALASKA

 

Figure 38. Widespread black spruce forest and small lakes typically encircled by bog communities are common in the
Copper Plateau Ecoregion. The area is mantled with fine—textured glaciolacustrine sediments. Depth to permafrost is shallow
and soils are poorly drained.

changes in soil physical properties and hydrology.

Vegetation. — Vegetation communities in the ecoregion
reflect characteristics of the poor soil drainage and shallow
permafrost table. Needleleaf forests and woodlands domi-
nated by black spruce are the most common communities.
Better drained sites, such as those occurring along streams,
on the larger floodplains, and on south—facing slopes of very
gravelly moraines, support needleleaf forests dominated by
white spruce, broadleaf forests dominated by black cotton—
wood or aspen, and tall scrub communities. Wetlands are
common and support low scrub bogs and wet graminoid
herbaceous communities.

Black spruce (Picea mariana) forests and woodlands
may include a tall shrub layer dominated by willow (for
example, Salix planifolia and S. glauca) and resin birch
(Betula glandulosa), a low shrub layer of ericaceous species
(for example, Ledum groenlandicum, Vaccinium vitis—idaea,
and V. uliginosum), and herbs (for example, Eriophorum
spp., Carex spp., and Equisetum spp.). Moss cover (for
example, feathermosses and Sphagnum spp.) is patchy to
continuous. Lichens (for example, Cladonia spp., Cladina
spp., and Cetraria spp.) are often present.

White spruce (Picea glauca) and balsam poplar
(Populus balsamifera) stands commonly have a low shrub
layer that includes prickly rose (Rosa acicularis) and buf-
faloberry (Shepherdia canadensis). Species of

Calamagrostis and Equisetum are typical of the herb layer.

Quaking aspen (Populus tremuloides) stands have a low
shrub understory that typically includes prickly rose (Rosa
acicularis), a number of ericaceous species (for example,
Vaccinium vitis—idaea, V. uliginosum, and Arctostaphylos
uva—ursi), and buffaloberry (Shepherdia canadensis). The
ground cover usually consists of herbs (for example, Cornus
canadensis and species of Calamagroslis and Pyrola) and
mosses (for example, Drepanocladus spp., Hylocomium
splendens, and Polytrichum 3121).).

Low scrub bogs are dominated by birch (Betula glandu-
losa and B. nana) and ericaceous shrubs (for example,
Vaccinium vitis—idaea, V uliginosum, Ledum decumbens,
Empetrum nigrum, and Andromeda polifolia). Sedges
(Carex spp.) and other herbs are common in the understory.
Sphagnum mosses are abundant at most sites.

Wet graminoid herbaceous communities are typically
dominated by sedges (for example, Eriophorum angustifoli-
um and Carex spp.) or codominated by sedges and herbs (for
example, Menyanthes trifoliata, Petasites frigidus, and
Potentilla palustris). Mosses (for example, Sphagnum spp.)
are common.

Wildfire. — Occurrence of wildfires in the Copper
Plateau Ecoregion is low. Size of burn typically is small, rang-
ing from less than 1 ha to about 40 ha, with a mean of 5 ha.

 

WRANGELL MOUNTAINS 53

 

Figure 39. The Wrangell Mountains Ecoregion is extensively covered by ice fields and glaciers. Most slopes are barren of
vegetation; however, dwarf scrub communities predominate where vegetation does occur. (Photo courtesy of M. Woodbridge
Williams, National Park Service, Anchorage.)

Land Use and Settlement. — A few small settlements
occur in the region. The region has traditionally been used
for subsistence hunting and fishing by the Ahtna
Athabascans. Their principal resources for food and materi—
als are salmon and freshwater fish, large game (for example,
caribou and moose), small fur-bearing mammals (for exam—
ple, beaver, hare, and ground squirrel), and edible plants.
Some mining activities have occurred, such as those related
to extraction of gold and selenium.

Delineation Methods. — A generalized 900—m elevation
contour was used to delineate the boundary of the Copper
Plateau Ecoregion. This boundary corresponds with patterns
on the relative CIR image. Because the ecoregion is typified
by features that relate to low and very low terrain roughness,
steeper, more variable terrain has been depicted as transitional.

References. — The information provided in this region—
al description has been compiled from Beikman (1980),
Black (1951), Coulter and others (1962), Ferrians (1965),
Gabriel and Tande (1983), Joint Federal-State Land Use
Planning Commission for Alaska (1973), Karlstrom and oth-
ers (1964), Langdon (1993), Larson and Bliss (written com-
mun., 1992), Moore (written commun., 1993), Morgan
(1979), Ping (written commun., 1993), Reiger and others
(1979), Selkregg (1974), US. Bureau of Mines (1992a,
1992b), US. Geological Survey (1964, 1987a), Viereck and

Little (1972), Viereck and others (1992), Wahrhaftig (1965),
and WeatherDisc Associates, Inc. (1990).

118. WRANGELL MOUNTAINS

Distinctive Features. — The 29,000—km2 Wrangell
Mountains Ecoregion consists of steep, rugged mountains of
volcanic origin that are extensively covered by ice fields and
glaciers (fig. 39). Most slopes are barren of vegetation. Dwarf
scrub tundra communities, consisting of mats of low shrubs,
forbs, grasses, and lichens, predominate where vegetation does
occur. The climate has harsh winters and short summers.

Climate. — Climate is primarily affected by continental
influences. The only weather station within the region is
located at McCarthy. There, winter low temperatures aver-
age -34°C, and winter highs average -9°C. Mean summer
low temperature is 3°C, and mean summer high is 22°C.
The average number of frost—free days each year is some-
what less than 2 months. McCarthy receives an average of
410 mm of precipitation per year, of which 175 cm is snow.
Higher elevations may receive 2,030 mm of precipitation
annually, including 255 cm of snow.

Terrain. — The ecoregion represents a large group of
shield and composite volcanoes of Cenezoic age; Mount

54 ECOREGION S OF ALASKA

 

Figure 40. Typical glacial till parent material in valley soils of the Wrangell Mountains Ecoregion. Deposits, such as these
left by the receding Kennicott Glacier, can deeply mantle valley floors and provide considerable sediment loading to streams.

Wrangell remains an active volcano. These volcanic forma-
tions lie over Paleozoic and Mesozoic sedimentary and vol-
canic rocks. The terrain is steep and rugged, with most slope
gradients exceeding 7° and many (15 percent of the come-
gion) surpassing 15°. Elevations start at 600 m, and most of
the largest peaks are 3,900 m or more, with a couple of peaks
exceeding 4,880 m. The mountains were glaciated during
the Pleistocene epoch, and extensive glaciation persists.
Permafrost is discontinuous. Streams headwater in glaciers,
and their drainages radiate outward from the region. There
are few lakes.

Soils. — Much of the landscape consists of steep rocky
slopes, icefields, and glaciers. Soil development has result-
ed in thin, stony soils that are shallow over bedrock or boul-
dery deposits. Most soils have formed in very stony and
gravelly colluvial material. Soils in valleys and on foot-
slopes have formed in glacial till (fig. 40), with a thin man-
tle of volcanic ash or loess in some places. Most soils are
poorly drained, but well drained soils do occur in very grav-
elly material at the foot of high ridges, on some south—facing
slopes, and on hilly moraines at lower elevations. Principal
soils are Lithic Cryorthents, Typic Cryorthents, Pergelic
Cryochrepts, and Pergelic Cryumbrepts.

Vegetation. — Most slopes in the mountains are barren of
vegetation. Dwarf scrub communities dominate where vege—

tation does occur, growing on well drained, windy sites. Tall
scrub communities occur along drainages and on floodplains.
Broad ridges, valleys, and hilly moraines at lower elevations
support needleleaf forests dominated by white spruce or
broadleaf forests dominated by paper birch or aspen.

Dwarf scrub communities are dominated by moun-
tain—avens (Dryas drummondii, D. integrifolia, and D.
octopetala), ericaceous shrubs (for example, Vaccim’um
vitis—idaea and V. uliginosum), or willow (for example,
Salix rotundifolia, S. polaris, S. reticulata, and S. arctica).
Typical herbaceous vegetation includes Carex spp., F estuca
spp., Anemone spp., and Saxifraga spp. Lichens (for exam-
ple, Cladina spp., Cetraria spp., and Cladom'a spp.) may
provide substantial cover and may codominate with shrubs.

Tall scrub communities are dominated by willow (for
example, Salix lanata, S. alaxensis, S. barclayi, and S. plani-
folia) and alder (for example, Alnus sinuata). The understory
consists of herbs, typically including both graminoid and
broad—leaved species, and mosses (primarily feathermosses).

Forests dominated by white spruce (Picea glauca) typi—
cally include understory shrubs, such as willow (Salix spp.),
alder (Alnus spp.), and birch (Betula spp.). A nearly continu-
ous layer of featherrnosses covers the ground. .

Forests dominated by paper birch (Betula papyrifera) or
quaking aspen (Populus tremuloides) are typically accompa-
nied by an understory shrub layer, including alder (Alnus
spp.), willow (Salix spp.), prickly rose (Rosa acicularis), and

 

 

PACIFIC COASTAL MOUNTAINS 55

high bushcranberry (Viburnum edule). Herbaceous cover is
variable, often including species such as bluejoint
(Calamagrostis spp.), horsetail (Equisetum spp.), and twin—
flower (Linnaea borealis). A layer of mosses (primarily
feathermosses) or, on drier sites, lichens is common under
open stands of paper birch.

Wildfire. — Occurrence of lightning fires in the Wrangell
Mountains is very low. Gabriel and Tande (1983) report no
fires during the 22—year period of record examined.

Land Use and Settlement. — Perennial settlements are
rare, mostly located in the lower valleys. The region has tra-
ditionally provided subsistence resources for Athabascans of
the Upper Tanana and Ahtna groups. Salmon and freshwa-
ter fish, caribou, moose, dall sheep, beaver, hare, and ground
squirrels are typical sources of food and materials. Edible
and medicinal plants are also collected.

A belt of copper deposits lies on the south side of the
region and has been economically important. Other impor-
tant metals have included silver, gold, lead, and zinc.

Delineation Methods. — The Chitina River, up through
Logan Glacier, was used to separate the geologic formations
of the Wrangell Mountains Ecoregion from those of the
Pacific Coastal Mountains Ecoregion. The mountain pass
along Jack Creek and the upper Nabesna River forms the
boundary between the Wrangell Mountains and the Alaska
Range Ecoregions. A generalized 900—m elevation contour
was used to separate the Wrangell Mountains from the
Copper Plateau. Moderate to very high terrain roughness
was used to distinguish the mountains from the bottomlands
of the Tetlin National Wildlife Refuge, to the north. The
boundary between the Wrangell Mountains and the Interior
Highlands Ecoregions was based on a generalized 600—m
elevation contour. Transitional areas are those having vege—
tation other than alpine tundra ecosystems.

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Ferrians (1965), Gabriel and Tande (1983),
Joint Federal-State Land Use Planning Commission for
Alaska (1973), Karlstrom and others (1964), Langdon
(1993), Larson and Bliss (written commun., 1992), Moore
(written commun., 1993), Morgan (1979), Reiger and others
(1979), Selkregg (1974), US. Bureau of Mines (1992a,
1992b), US. Geological Survey (1964, 1987a), Viereck and
Little (1972), Viereck and others (1992), Wahrhaftig (1965),
and WeatherDisc Associates, Inc. (1990)

119. PACIFIC COASTAL MOUNTAINS

Distinctive Features. — The steep and rugged moun-
tains along the southeastern and south central coast of Alaska

receive more precipitation annually than either the Alaska
Range or Wrangell Mountains Ecoregions. Glaciated during
the Pleistocene epoch, most of the 106,000—km2 ecoregion is
still covered by glaciers and ice fields. Most of the area is
barren of vegetation (fig. 41), but where plants do occur,
dwarf and low scrub communities dominate.

Climate. — Climate for most of the ecoregion is transi—
tional between maritime and continental influences. There are
no long—term weather stations in this ecoregion. Climatic pat-
terns within the region are affected by elevation, latitude, and
geographic position. Interpolation of data from the low—ele—
vation stations of the adjacent coastal ecoregion estimates an
annual precipitation ranging from 2,030 mm to greater than

 

Figure 41.
Pleistocene epoch, are typical of the Pacific Coastal Mountains
Ecoregion. The ecoregion is predominantly barren of vegetation,
but alpine tundra communities occur where conditions permit.
(Photo courtesy of Ray Koleser, Forest Service, Forestry Sciences
Laboratory, Anchorage.)

Glaciers and ice fields, remaining since the

56 ECOREGIONS OF ALASKA

7,000 mm, increasing with elevation and in a south—to—north
direction. Estimated annual snowfall ranges from 510 cm to
2,030 cm and follows the same distribution pattern.

Terrain. — Steep, rugged mountains covered by many
active glaciers are typical of this ecoregion. Elevations
range from sea level to more than 4,500 m. Higher parts of
the ecoregion are buried in ice fields, from which valley and
piedmont glaciers radiate. Slope gradients for most of the
region are greater than 7°; slope gradients for 5 percent of
the region exceed 20°. Geologic formations of Cretaceous
and Upper Jurassic sediments occur extensively throughout
the Chugach Mountains. Tertiary to Cretaceous (Paleozoic
in some places) intrusive rock occurs throughout the south-
eastern portion of the ecoregion. The Chugach Mountains
are underlain by isolated masses of permafrost. The moun-
tains of the southern half of the region are generally free of
permafrost. The ecoregion was extensively glaciated during
the Pleistocene epoch, and many glaciers remain. Features
typical of glaciated terrain, such as arétes, horns, cirques, U—
shaped valleys, and morainal deposits in valleys and on
lower hillslopes, are abundant. Streams are short and swift,
and headwatered in glaciers. Lakes lie in ice—carved basins.

Soils. — Most areas are covered by glaciers, ice fields, or
rock outcrops. Where soil development has occurred, soils
have formed in gravelly till and colluvium. Soils on steep
ridges are shallow over bedrock. Dominant soils are Lithic
Cryorthents, Andic Cryumbrepts, Pergelic Cryumbrepts,
Typic Cryumbrepts, Typic Haplocryods, Andic Humicryods,
Lithic Humicryods, and Typic Humicryods.

Vegetation. — The principal nature of this ecoregion is
alpine slopes barren of vegetation or dwarf and low scrub
communities in areas where vegetation does occur. There
are many areas where needleleaf forests, originating in adja-
cent, lower elevation ecoregions, colonize mesic sites along
drainageways.

Dwarf scrub communities are typically dominated by
mountain heath (Phyllodoce aleutica). Associated shrubs
include cassiope (Cassiope mertensiana and C. stelleriana),
meadow—spirea (Luetkea pectinata), bog blueberry (Vaccinium
uliginosum), and dwarf blueberry (V. caespitosum).

Low scrub communities dominated by ericaceous
shrubs (for example, Cladothamnus pyrolaeflorus) form
dense thickets at lower elevations in the ecoregion where
snow cover persists until late spring.

Needleleaf forest stands are dominated by hemlock
(Tsuga heterophylla or T mertensiana) and subalpine fir
(Abies lasiocarpa) or by Sitka spruce (Picea sitchensis). The
understory layer consists of ericaceous shrubs (for example,
Vaccinium alaskaense, V. ovalifolium, and Menziesiaferrug-
inea), raspberry (Rubus spp.), currant (Ribes spp.), and dev-
ilsclub (Opiopanax horridus). The forest floor is typically
covered by herbs (for example, Tiarella trifoliata and

Streptopus spp.) and a number of fern species.

Wildfire. — Wildfire information is only available for
the northern portion of the ecoregion, in the Chugach
Mountains, where occurrence is very low. Burn areas have
ranged in size from less than 1 ha to 40 ha, averaging 4 ha.

Land Use and Settlement. — Permanent settlements are
rare in this ecoregion, primarily occurring at the lower ele-
vations. The eastern half of the region has historically been
used by the Tlingits, and the western half has been used by
the Chugach and Eyak peoples. Moose, mountain goat, and
smaller mammals are hunted in the mountains. Streams
yield salmon and freshwater fish. Coastal areas provide
marine resources as well as coastal birds and their eggs.
Edible greens, roots, and berries are also collected.

In addition to subsistence and recreational hunting and
fishing, the region has supplied a variety of metallic elements
(for example, gold, silver, copper, zinc, lead, tungsten, iron,
nickel, platinum, barium, and chromium), nonmetallic ele-
ments (for example, antimony, arsenic, and molybdenum), and
energy—related commodities (coal, petroleum, and uranium).

Delineation Methods. — The boundary of the southern
section of the ecoregion excludes the western hemlock—Sitka
spruce forests of the Pacific Coast. The northern boundary
is based on Logan Glacier, along the interface with the
Wrangell Mountains; a generalized 900—m elevation con-
tour, along the interface with the Copper Plateau; the
Matanuska River, along the interface with the Alaska Range;
and a generalized 600—m elevation contour, along the inter—
face with the Cook Inlet Ecoregion. Transitional areas are
those having forests.

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Ferrians (1965), Gabriel and Tande (1983),
Joint Federal-State Land Use Planning Commission for Alaska
(1973), Karlstrom and others (1964), Langdon (1993), Larson
and Bliss (written commun, 1992), Moore (written commun,
1993), Morgan (1979), Ping (written commun, 1993), Reiger
and others (1979), Selkregg (1974), US. Bureau of Mines
(1992a, 1992b), US. Forest Service (1992), US. Geological
Survey (1964, 1987a), Viereck and Little (1972), Viereck and
others (1992), Wahrhaftig (1965), and WeatherDisc Associates,
Inc. (1990).

120. COASTAL WESTERN HEMLOCK—SITKA
SPRUCE FORESTS

Distinctive Features. — Located along the southeastern
and south central shores of Alaska, the terrain of this
61,000—km2 ecoregion is a result of intense glaciation during
late advances of the Pleistocene epoch. The deep, narrow

 

 

 

COASTAL WESTERN HEMLOCK—SITKA SPRUCE FORESTS 57

 

 

   

 

Figure 42.

peratures of all ecoregions in Alaska.

bays, steep valley walls that expose much bedrock, thin
moraine deposits on hills and in valleys, very irregular coast—
line, high sea cliffs, and deeply dissected glacial moraine
deposits covering the lower slopes of valley walls are all evi-
dence of the effects of glaciation. The region has the mildest
winter temperatures in Alaska, accompanied by large
amounts of precipitation. Forests of western hemlock and
Sitka spruce are widespread (fig. 42).

Climate. — The ecoregion has a maritime climate, with
cool summers and mildly cold winters. Moderate to heavy
precipitation occurs throughout the year, though storms are
most frequent and heavy during the winter. Surface winds
are moderate to strong, with prevailing winds coming from
the south or southeast. The average frost—free season is
about 7 months. Mean annual precipitation ranges from
1,350 mm to 3,900 mm, depending on location. Mean annu-
al snowfall ranges from 80 cm to 600 cm. Daily minimum
temperature in winter is about -3°C at many weather sta-
tions, and daily maximum temperature averages about 3°C.
Mean daily minimum temperature in summer is about 7°C,
and maximum temperature is about 18°C.

Terrain. — The ecoregion includes the steep footslopes,
alluvial fans, floodplains, outwash plains, scattered

The Coastal Western Hemlock-Sitka Spruce Forests Ecoregion has deep, narrow bays and steep, dissected valley
walls covered by highly productive forests. The ecoregion receives large amounts of precipitation and has the mildest winter tem-

(Photo courtesy of Ken Winterberger, Forest Service, Forestry Sciences Laboratory,

moraines, river terraces, and river deltas of the Pacific
coastal mountains. Elevations climb from sea level to 500 m
(including some local mountains up to 1,000 m). Slope gra-
dients range from 0° to 28°, with a median of 5°. Geologic
formations are Lower Tertiary interbedded sedimentary, vol-
canogenic, and volcanic rocks in the Prince William Sound
area, Upper Cretaceous sandstone and slate on Kodiak
Island, and Mesozoic volcanic and intrusive rock along with
Mesozoic and Paleozoic sediments in the southeastern por-
tion of the ecoregion. More recent formations are dunes of
aeolian sand that border some of the floodplains throughout
the ecoregion. Nearly all of the ecoregion was subject to late
glacial advances during the Pleistocene epoch, although no
glaciers remain. The region is generally free from per-
mafrost. Most streams originate from the mountain glaciers
of adjoining ecoregions; exceptions are streams on islands.
Lakes are plentiful in some areas and absent in others.

Soils. — Dominant soils are Terric Cryohemists, Andic
Cryaquods, Andic Humicryods, Lithic Humicryods, and
Typic Humicryods. Soils near the mountains formed in
gravelly and stony moraine deposits or in a mantle of vol-
canic ash over the morainal deposits. Soils of river deltas,
terraces, alluvial fans, and floodplains formed in waterlain
silts and clays. Poorly drained depressions are filled with

58 ECOREGIONS OF ALASKA

fibrous peat. Many parts of the ecoregion are susceptible to
flooding or to inundation by tidewater. Ash—influenced soils
are located on Kruzof Island and areas of Baranof Island.

Vegetation. — The relatively long growing season, high
annual precipitation, and mild temperatures of this ecoregion
support a large variety of coastal forest, scrub, and wetland
communities. Forests, which may be dominated by needle-
leaf or broadleaf species, or a mixture of both, predominate.
Scrub communities are dominated by tall shrubs, low shrubs,
or dwarf shrubs. Wetland sites support tall scrub swamps,
low scrub bogs, wet graminoid herbaceous communities,
and wet forb herbaceous communities.

A large variety exists in the dominant and codominant
constituents of forested communities. Western hemlock
(Tsuga heterophylla) and Sitka spruce (Picea sitchensis) are
the two most typifying species of the region, but a variety of
other trees also occur, including silver fir (Abies amabilis),
subalpine fir (A. lasiocarpa), lodgepole pine (Pinus contor-
ta), Pacific yew (Taxus brevifolia), alder (Alnus rubra), and
black cottonwood (Populus trichocarpa). Understory vege-
tation varies somewhat with forest type. Typical woody
species include alder (Alnus spp.), willow (Salix spp.), cur-
rant (Ribes spp.), salmonberry (Rubus spectabilis), prickly
rose (Rosa acicularis), red—fruit bearberry (Arctostaphylos
rubra), cranberry/blueberry (for example, Vaccim'um
alaskaense, V. ovalifolium, and V. parvifolium), high
bushcranberry (Viburnum edule), dwarf dogwood (Cornus
canadensis), devilsclub (Opiopanax horridus), and five—leaf
bramble (Rubus pedatus). Herbaceous cover is supplied by
bluebell (Mertensia paniculata), false lily—of—the—valley
(Maianthemum dilatatum), laceflower (Tiarella trifoliata),
deer cabbage (Fauria crista—galli), twisted stalk (Streptopus
spp.), goldthread (Coptis aspleniifolia), sedge (Carex spp.),
reed—grass (Calamagrostis spp.), and ferns (for example,
Gymnocarpium dryopteris, Dryopteris dilatata, Athyrium
filix—femina, and Blechnum spicant). Mosses (for example,
Hylocomium splendens, Pleurozium schreberi, and
Drepanocladus uncinatus) are common.

Scrub communities range from tall scrub to dwarf scrub.
Tall scrub communities are dominated by willow (for exam-
ple, Salix alaxensis, S. planifolia, S. lanata, and S. sitchen-
sis), alder (Alnus tenuifolia), or a mix of willow and alder.
An understory scrub layer is typically absent, but cover by
herbs (for example, Calamagrostis canadensis, Festuca
altaica, Equisetum spp., Epilobium spp., Mertensia particu-
lata, Aconitum delphinifolium, and Athyrium filix—femina)
may be dense. Mosses (for example, Polytrichum spp.,
Hylocomium splendens, and Drepanocladus uncinatus) form
a patchy to continuous mat.

Low scrub communities are dominated by copperbush
(Cladothamnus pyralaeflorus) or by a mix of willow (for
example, Salix glauca, S. planifolia, and S. lanata) and alder
(for example, Alnus sinuata). Although copperbush commu-
nities generally have no significant associated species, com-

munities dominated by willow and alder are often accompa-
nied by ericaceous shrubs (for example, Arctostaphylos
alpina, Empetrum nigrum, and Vaccinium vitis—idaea) and
nonsphagnaceous mosses.

Dwarf scrub communities occur at higher elevation,
where sites are exposed to harsh climatic elements.
Mountain—heath (Phyllodoce aleutica) is the dominant
species. Associated dwarf shrubs include cassiope (Cassiope
mertensiana and C. stelleriana), meadow—spirea (Luetkea
pectinata), bog blueberry (Vaccim'um uliginosum), dwarf
blueberry (V. caespitosum), Nootka lupine (Lupinus
nootkatensis), Sitka valerian (Valeriana sitchensis), and rose—
root (Sedum rosea). Mosses and lichens can be common.

Tall scrub swamps are usually dominated by alder
(Alnus tenuifolia) but are sometimes dominated or codomi-
nated by willow (for example, Salix planifolia or S. lanata).
Typical herbs are bluejoint (Calamagrostis canadensis) and
horsetail (Equisetum spp.).

Low scrub bogs are dominated by low ericaceous shrubs
(for example, Empetrum nigrum, Vaccinium oxycoccus,
Andromeda polifolia, and Kalmia Polifolia), a mixture of
willow (Salix spp.) and graminoid species (for example,
Calamagrostis canadensis, Carex aquatilis, and C. pluriflo-
ra), or a mixture of sweetgale (Myrica gale) and graminoid
species (Calamagrostis canadensis, Trichophorum spp., and
Carex spp.). Mosses (usually including Sphagnum spp.)
occur at most sites.

Wet graminoid herbaceous communities are dominated
by sedges (for example, Scirpus validus, Eleocharis palus-
tris, and Carex spp.), a mixture of sedges and mosses (princi~
pally Sphagnum spp.), or a mixture of sedges and shrubs
(Myrica gale or Salix spp.). Woody plants are lacking from
the first two community types, and lichens are lacking from
all three.

Wet forb herbaceous communities are typically dominat—
ed by one or more of the following: swamp horsetail
(Equisetum spp.), yellow marsh—marigold (Caltha palustris),
buckbean (Menyanthes trifoliata), and marsh fivefinger
(Potentilla palustris). Woody plants and lichens are lacking
from these communities, though aquatic mosses are common.

Wildfire. — Lightning fires are rare in this ecoregion;
however, no data have been recorded regarding the frequen-
cy and size of burns.

Land Use and Settlement. — Population is concentrat-
ed along small stretches of flat coastal areas. Timber harvest
and mining are the primary economic activities. A variety of
metallic elements occur in this ecoregion, including gold,
copper, silver, zinc, lead, iron, platinum, titanium, barium,
nickel, cobalt, and chromium. Nonmetallic elements include
antimony, arsenic, calcium, molybdenum, and sulfur.
Energy—related commodities, such as coal, uranium, and
petroleum, have also been investigated and mined.

The ecoregion has traditionally been populated by

 

SUMMARY 59

Tlingit and Haida groups in the eastern half and by Eyak,
Chugach, Uneqkurmuit, and Koniag peoples in the western
half. Mainland dwellers base their subsistence on salmon,
eulachon (an important source of oil), moose, and mountain
goat. Because island dwellers have access to smaller salmon
runs, they make more use of marine resources, such as her—
ring, halibut, and seaweed. Both mainland and island groups
supplement their diets with deer, birds (for example, cranes,
ducks, geese, grouse, and ptarmigan) and their eggs, seals
(hunted at rookeries), intertidal resources (for example,
clams, cockles, and chitons), and edible plants.

Delineation Methods. — The ecoregion boundary is
based on the extent of “Coastal Western Hemlock—Sitka
Spruce Forest,” as shown on the maps “Major Ecosystems of
Alaska” and forest types (Powell and others, 1993). This
boundary corresponds with patterns on the relative CIR
image. Because individual land units are small and environ-
mental gradients are steep, it is not possible to delineate tran-
sitional zones at the current scale of mapping.

References. — The information provided in this regional
description has been compiled from Beikman (1980), Coulter
and others (1962), Fenians (1965), Joint Federal-State Land
Use Planning Commission for Alaska (1973), Karlstrom and
others (1964), Langdon (1993), Larson and Bliss (written
commun., 1992), Moore (written commun, 1993), Morgan
(1979), Ping (written commun., 1993), Powell and others
(1993), Reiger and others (1979), Selkregg (1974), US.
Bureau of Mines ( 1992a, 1992b), US. Forest Service (1992),
US. Geological Survey (1964, 1987a), Viereck and Little
(1972), Viereck and others (1992), Wahrhaftig (1965), and
WeatherDisc Associates, Inc. (1990).

SUMMARY

We have mapped and described 20 ecoregions of Alaska
to serve as a framework for organizing and interpreting envi—
ronmental data relevant to a wide range of regional ecologi—
cal concerns. Examples of applications for the map include
the assessment of natural resources (for example, regional
chemical, physical, and biological characteristics of surface
waters, soil erosion potential, and wildlife habitat diversity)
and effects research (for example, potential regional ecolog-
ical effects from environmental contaminants or climate
change). The map can also be used in developing strategies
for locating field sites or in evaluating how well existing
research sites are distributed across ecoregions or along
regional environmental gradients.

The regional descriptions accompanying the map indi-
cate the degree of ecological variability occurring within
each ecoregion. This information can be used to infer the
relative density of sample sites needed to represent each
ecoregion and the within—region areas over which field sam—

ple information can be extrapolated.

The ecoregion map was compiled by synthesizing infor-
mation on the geographic distribution of environmental fac-
tors such as climate, physiography, geology, soils, per-
mafrost, glaciation, hydrology, and vegetation. The synthe-
sis was a qualitative assessment of the distributional patterns
of these factors and their relative importance in influencing
the nature of the landscape from place to place. The actual
placement of ecoregion boundaries was achieved by follow—
ing boundaries from a selected subset of mapped references
that best integrated the patterns of the major factors of inter—
est for each ecoregion.

An accuracy assessment was not performed on the map of
Alaskan ecoregions. There are several problems associated
with determining map accuracy, such as inability to sufficient-
ly field sample the number of variables that define each ecore—
gion, inability to sample a sufficient number of (largely inac-
cessible) field sites to represent the range of within—region
ecological variability, and difficulty in designing a sampling
strategy that reconciles the differences in informational reso-
lution between field samples and the ecoregion map. It may
be more appropriate to assess the utility of the ecoregion map
for different needs than to assess its accuracy. This is because
the ecoregion boundaries have been delineated to be general-
ly correct for a number of purposes but not necessarily precise
for any singular purpose or variable.

The 20 ecoregions of Alaska are being aggregated into
coarser ecological units for developing a North American
map of ecoregions. A map of ecoregions has already been
developed for Canada and has been integrated across the
international border with the map of Alaskan ecoregions.
Also under way are efforts to delineate ecoregions of other
northern circumpolar areas to promote international programs
involved with assessing and monitoring global resources.

ACKNOWLEDGMENTS

We are grateful to the many people who contributed
their expertise, materials, and general support for this pro-
ject. Carl Markon, Hughes STX Corporation, USGS EROS
Alaska Field Office, coordinated field reconnaissance, fur-
nished extensive information on Alaskan ecosystems, and
provided review and discussion on draft versions of the
ecoregion map and text. A number of people donated an
assortment of unpublished information. Thomas Loveland,
USGS EROS Data Center, Donald Ohlen, Hughes STX
Corporation, USGS EROS Data Center, and Michael
Fleming, Hughes STX Corporation, USGS EROS Alaska
Field Office, provided unpublished maps derived from vari-
ous methods of synthesizing Advanced Very High
Resolution Radiometer satellite data to depict relative pat-
terns in photosynthetic activity across Alaska. Norman Bliss
and Kevin Larson, Hughes STX Corporation, USGS EROS
Data Center, provided a series of maps based on soil compo-

60 ECOREGIONS OF ALASKA

nents, textures, and slopes. Joseph Moore, Soil
Conservation Service, edited the discussions on regional soil
characteristics to reflect more recent field information than
that published in the 1979 Alaska Soil Survey; Chien—Lu
Ping, Agricultural and Forestry Experiment Station,
University of Alaska, Palmer Research Center, provided cor-
rections for the soils information in an early draft of the table
of major ecoregion characteristics. Douglas Brown, Forest
Service, Rocky Mountain Forest and Range Experiment
Station, supplied a digital data base showing the type, loca-
tion, and status of mines in Alaska. Daniel Binkley, Forest
Sciences Department, Colorado State University, and Sara
Wesser, National Park Service, provided information on veg-
etation of the Noatak River Valley. Ian Marshall, Ed Wiken,
and Denis DeMarchi, all of Environment Canada, and Scott
Smith, Agriculture Canada, helped to integrate the ecore-
gional boundaries delineated for Alaska with those delineat-
ed for Canada. Valuable reviews were contributed by: Leslie
Viereck, Forest Service, Pacific Northwest Research Station,
Institute of Northern Forestry, Robert Lipkin and Gerald
Tande, Alaska Natural Heritage Program, The Nature
Conservancy, Ken Winterberger, Forest Service, Pacific
Northwest Research Station, Anchorage Forestry Sciences
Laboratory, Walt Stieglitz and Anthony DeGange, US. Fish
and Wildlife Service, Torn Newbury, Minerals Management
Service, Dave Carneggie, USGS EROS Data Center, Page
Spencer, National Park Service, David Swanson, Soil
Conservation Service, and Jim Hawkings, Canadian Wildlife
Service. Roger Hoffer, Forest Sciences Department,
Colorado State University, administered Colorado State
University’s cooperative participation in this project and
provided critical reviews of this report and of all proposals
leading up to this report. We gratefully acknowledge the sig-
nificant contributions in production of this report by Sablou
Gabriel and Darla Larsen, and the cartographic work by John
Hutchinson, all of Hughes STX Corporation, USGS EROS.
This work was partially funded under Environmental
Protection Agency Cooperative Agreement #CR820070.

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65

APPENDIX 1 — Table of major environmental characteristics.

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66

 

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APPENDIX 1 — Table of In

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69

APPENDIX 1 — Table of major environmental characteristics.

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70 APPENDIX 2.—Methodology for deriving the terrain roughness map

The terrain roughness map was derived from l—km2 resolu—
tion digital elevation model (DEM) data using a raster based
GIS. Procedures are listed below; common GIS terminolo-
gy appears in italics.

1. The maximum change in local terrain elevation was
calculated within a 5—kma radius around each pixel of the
DEM data (an 11x1] diflerencing filter was applied over the
DEM raster map). This resulted in a new map where the
original DEM data values were replaced by maximum ele-
vation difference values. The maximum amount of local
relief measured was 4,310 m.

2. Values on the maximum local relief map were then
sorted (sliced) into consecutive classes so that each class rep-
resented a change in elevation of 10 m. This resulted in a
map of 431 “relief change” classes.

3. The number of different relief change classes occur—
ring within 25 km2 around each pixel was used to calculate
local terrain variability (a 5x5 diversity filter was passed

a Five kilometers was selected as an appropriate resolution for defining
“local” relief based on the level of generalization represented by the ecore—
gions.

over the pixels of the relief Change class map). The resultant
map depicted values representing the number of different
classes that occurred in the vicinity of each pixel. The max-
imum number of classes recorded for a single pixel was 25,
which was also the theoretical maximum.

4. The values on the local terrain variability map were
sorted (reclassified) into five classes of terrain roughness:
very low (0—2 terrain change classes within the 5 km2 vicin-
ity of a pixel), low (3—5 change classes), moderate (6—10
change classes), high (11—15 change classes), and very high
(16—25 change classes).

5. The average terrain roughness class within 25 km2 of
each pixel was determined (a 5x5 low—pass, averaging filter
was applied to the raster map of the five classes of local ter-
rain roughness). This effectively smoothed the local “noise”
on the map of terrain roughness classes so that broad—scale
patterns of the variability in local relief were more dis-
cernible on the final terrain roughness map.

 

APPENDIX 3.—List of Latin and common names of plant species mentioned in this report 71

TREESa

Abies amabilis
Abies lasiocarpa
Alnus rubra
Betula papyrifera
Larix laricina
Picea glauca
Picea mariana

Pacific silver fir
Subalpine fir

Red alder

Alaska paper birch
Tamarack, larch
White spruce
Black spruce

Picea sitchensis
Pinus contorta
Populus balsamifera
Populus tremuloides
Populus trichocarpa
Taxus brevzfolia
Tsuga heterophylla
Tsuga mertensiana

Sitka spruce
Lodgepole pine
Balsam poplar
Quaking aspen
Black cottonwood
Pacific yew
Western hemlock
Mountain hemlock

 

SHRUBSb

Alnus crispa

Alnus sinuata

Alnus tenuifolia
Andromeda polifolia
Arctostaphylos alpina
Arctostaphylos rubra
Arctostaphylos uva—ursi
Betula glandulosa
Betula nana

Cassiope lycopodioides
Cassiope mertensiana
Cassiope stelleriana
Cassiope tetragona
Chamaedaphne calyculata
Cladothamnus pyrolaeflorus
Cornus canadensis
Cornus stolonifera
Dryas drummondii
Dryas integrifolia
Dryas octopetala
Empetrum nigrum
Kalmia polifolia

Ledum decumbens
Ledum groenlandicum
Loiseleuria procumbens
Luetkea pectinata
Menziesia ferruginea
Myrica gale

Oplopanax horridus
Phylloa'oce aleutica
Potentilla fruticosa

aNomenclature from Viereck and Little (1972), as cited in Viereck and others

(1992).

b Nomenclature from Hultén (1968) and Welsh (1974), as cited in Viereck and oth-

ers (1992).

American green alder
Sitka alder

Thinleaf alder
Bog—rosemary

Alpine bearberry
Red—fruit bearberry
Bearberry, kinnikinnik
Resin birch, bog birch
Dwarf arctic birch

Alaska cassiope

Mertens cassiope

Starry cassiope
Four—angled cassiope
Leatherleaf

Copperbush

Bunchberry, dwarf dogwood
Red—osier dogwood
Drummond mountain—avens
Entire—leaf mountain—avens
White mountain—avens
Crowberry

Bog kalmia

Narrow—leaf Labrador—tea
Labrador—tea
Alpine—azalea

Luetkea

Rusty menziesia
Sweetgale

Devilsclub

Blue mountain—heath
Bush cinquefoil

Ribes triste

Rosa acicularis
Rubus spectabilis
Salix alaxensis

Salix arbusculoides
Salix arctica

Salix barclayi

Salix bebbiana

Salix brachycarpa
Salix commutata
Salixfuscescens

Salix glauca

Salix lanata

Salix ovalifolia

Salix phlebophylla
Salix planifolia

Salix polaris

Salix reticulata

Salix rotundifolia
Salix scouleriana
Salix sitchensis
Sambucus callicarpa
Shepherdia canaa’ensis
Spiraea beauverdiana
Vaccinium alaskaense
Vaccinium caespitosum
Vaccinium ovalifolium
Vaccinium oxycoccos
Vaccinium parvifolium
Vaccinium uliginosum
Vaccinz'um vitis—idaea
Viburnum edule

American red currant
Prickly rose
Salmonberry
Feltleaf willow
Littletree willow
Arctic willow
Barclay willow
Bebb willow
Barren—ground willow
Undergreen willow
Alaska bog willow
Grayleaf willow
Richardson willow
Ovalleaf willow
Skeletonleaf willow
Diamondleaf willow
Polar willow
Netleaf willow
Least willow
Scouler willow
Sitka willow

Pacific red elder
Buffaloberry
Beauverd spirea
Alaska blueberry
Dwarf blueberry
Early blueberry
Bog cranberry

Red huckleberry
Bog blueberry
Mountain—cranberry
High bushcranberry

72

HERBSC

Aconitum delphinifolium
Agropyron spicatum
Alopecurus alpinus
Anemone spp.

Angelica lucida
Arctagrostis latifolia
Arctophila fulva
Artemisia arctica
Astragalus spp.
Athyriumfilix— emina
Blechnum spicant
Bromus pumpellianus
Calamagrostis canadensis
Calamagrostis purpurascens
Caltha palustris

Carex aquatilis

Carex bigelawii

Carex lyngbyaei

Carex misandra

Carex pauciflora

Carex pluriflora

Carex rostrata

Carex saxatilis

Carex scirpoidea

Carex sitchensis

Coptis aspleniifolia
Deschampsia beringensis
Dryopteris dilatata
Dupontia fischeri
Eleocharis palustms
Epilobium angustifolium
Epilobium latifolium
Equisetum arvense
Equisetumfluviatile
Equisetum sylvaticum
Equisetum variegatum

CNomenclature from Viereck and Little (1972), as cited in Viereck and others

(1992).

ECOREGIONS OF ALASKA

Monkshood
Bluebunch wheatgrass
Alpine foxtail
Anemone

Sea coast angelica
Polar grass

Pendent grass
Wormwood

Milk vetch

Lady fern

Deer fern

Brome grass

Bluejoint

Purple reed—grass
Yellow marsh—marigold
Water sedge

Bigelow sedge
Lyngbye sedge
Short—leaved sedge
Few—flowered sedge
Many—flowered sedge
Beaked sedge

No common name
Northern single—spike sedge
Sitka sedge
Goldthread

Bering hair—grass
Spinulose shield—fern
Tundra grass, dupontia
Spike rush

Fireweed

Dwarf fireweed
Meadow horsetail
Swamp horsetail
Woodland horsetail
Variegated scouring-rush

Eriophorum angustifolium
Eriophorum russeolum
Eriophorum vaginatum
Fauria crista—galli
Festuca altaica

F estuca rubra

Galium boreale
Geranium erianthum
Gymnocarpium dryopteris
Hedysarum alpinum
Heracleum lanatum
Hierochloe' alpina
Honckenya peploides
Juncus arcticus
Kobresia myosuroides
Linnaea borealis
Lupinus nootkatensis
Maianthemum dilatatum
Menyanthes trifoliata
Mertensia paniculata
Minuartia spp.
Oxytropis nigrescens
Petasites frigidus
Plantago maritima

Poa eminens

Potentilla palustris
Puccinellia spp.

Pyrola grandiflora
Rubus pedatus
Saxifraga spp.

Scirpus validus

Sedum rosea

Streptopus spp.

Tiarella trifoliata
Trichophorum caespitosum
Triglochin maritimum
Valeriana sitchensis

Tall cottongrass
Russett cottongrass
Tussock cottongrass
Deer cabbage

Fescue grass

Red fescue

Northern bedstraw
Northern geranium
Oak fern

Alpine sweet—vetch
Cow parsnip

Alpine holygrass
Seabeach sandwort
Arctic rush

No common name
Twinflower

Nootka lupine

False lily—of—the—valley
Buckbean

Bluebell

Sandwort

Blackish oxytrope
Arctic sweet coltsfoot
Goose—tongue
Coastal bluegrass
Marsh fivefinger
Alkali grass
Large—flowered Wintergreen
Five—leaf bramble
Saxifrage

Great bulrush
Roseroot
Twisted—stalk

Lace flower

Tufted clubrush
Maritime arrow grass
Sitka valerian

 

ALL- _

MOSSES d

Aulacomnium palustre
Campylium stellatum
Dicranum spp.
Distichium capillaceum
Drepanocladus uncinatus
Hylocomium splendens
Hypnum spp.

Mnium spp.

APPENDIX 3 — List of Latin and common names of plant species.

No common name
No common name
No common name
No common name
No common name
Feathermoss

No common name
No common name

Pleurozium schreberi
Polytrichum spp.
Rhacomitrium lanuginosum
Rhytidiadelphus triquetrus
Rhytidium rugosum
Scorpidium spp.

Sphagnum spp.
Tomenthypnum nitens

Feathermoss

No common name
No common name
No common name
No common name
No common name
Sphagnum moss
No common name

73

 

LICHENSe
Alectoria spp.
Cetraria cucullata
Cetraria islandica
Cladina rangiferina
Cladom'a spp.
Nephroma arcticum

dNomenclature from Crum and others (1973), as cited in Viereck and others

(1992).

e Nomenclature from Egan (1987), as cited in Viereck and others (1992).

No common name
No common name
N 0 common name
Reindeer lichen

N0 common name
No common name

Parmelia spp.

Peltigera aphthosa
Peltigera canina
Stereocaulon tomentosum
Thamnolia subuliformis
Thamnolia vermicularis

No common name
No common name
Dog lichen

No common name
No common name
Worm lichen

US. DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY

ECOREGIONS OF ALASKA

By Alisa L. Gallantl, Emily F. Binnianz, James M. Omernik3, and Mark B. Shasby4
1995

 

U.s. DEPOSITORV «I,

MAY 22 1995 "

11:»-
Professional Paper 1567
Plate 1434 /

 

 

 

 

   
 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

0 175° 170° 165° 160° 155° 150° 145° 140° 135° 130° 125° 120°
70 / / I / l l \ \ , , , . _ , ,
B E A U F 0 R T S E A
65°
g: This map of ecoregions has been produced for Alaska as a framework for organizing
c7) and interpreting environmental data for State, national, and international level inven-
$0160 tory, monitoring, and research efforts. The map and descriptions for 20 ecological
q- E, regions were derived by synthesizing information on the geographic distribution of
I: environmental factors such as climate, physiography, geology, permafrost, soils, and
I32 vegetation. A qualitative assessment was used to interpret the distributional patterns
I and relative importance of these factors from place to place.
Numeric identifiers assigned to the ecoregions are coordinated with those used on
the map of “Ecoregions of the Conterminous United States” (Omernik 1987) as a
continuation of efforts to map ecoregions for the United States. Additionally, the
I, ecoregions for Alaska and the conterminous United States, along with ecological
650\ . regions delineated for Canada (Wiken 1986), have been aggregated at a coarser
/ level into a map of North American ecological regions (Omernik 1995).
/ References
7L / Omernik, J.M., 1987, Ecoregions of the Conterminous United States: Annals of the Association of Ameri-
/ can Geographers, v. 77, no. 1, p. 118-125.
/ ' 1995, Ecoregions: a Framework for Managing Ecosystems: The George Wright Forum, v. 12, no. 1,
p. 35-51.
/
J Wiken, E.B., 1986, Terrestrial Ecozones of Canada: Lands Directorate, Environment Canada Ecological
__ - Land Classification Series 19, 26 p. ,
/ , For table of major environmental characteristics occurring in each ecoregion, see reverse side. ,
St. Lawrence H I I I L I: , r ' i L ‘4 I L ' I i I l i ' L i
’S’and NORTON SOUND
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<7 ,
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+ ,3 “Q . (same scale as main map) :63 r
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1 65° 160° 1 55° 150° 145° 1 400 INTERIOR~GEOLOGICAL SURVEY, RESTON,VIRGINIA—-1995 1 35°
AUTHOR AFFILIATIONS SCALE 1:5 000 000 ROADS
lForest Sciences Department, Colorado State University, Fort Collins, Colorado.
Work performed under USGS Cooperative Agreement #1434-93-A-00760. 100 O 100 200 300 400 500 KILOMETERS TRAN S-ALASM PIPELINE
2Hughes STX Corporation, US. Geological Survey, EROS Alaska Field Office, Anchorage, Alaska.
Work performed under USGS Contract #1434—92-C-4004. 100 o 100 200 300 MILES — — - —— — — INTERNATIONAL BOUNDARY

3Environmental Protection Agency, Environmental Research Laboratory, Corvallis, Oregon.
4U.S. Geological Survey, EROS Alaska Field Office, Anchorage, Alaska.

Prepared by USGS in cooperation with Colorado State University and Environmental Protection Agency

 

 

Albers Equal Area Projection

Standard Parallels: 55°N, 65°N

_:

 

 

 

Arctic Coastal Plain 50,000 sq km

The northernmost ecoregion is bounded on the north and the west by the Arctic Ocean and stretches
eastward nearly to the international boundary between Alaska and the Yukon Territory, Canada.
The poorly drained, treeless coastal plain rises very gradually from sea level to the adjacent foothills.
The region has an arctic climate, and the entire area is underlain by thick permafrost. Because of
poor soil drainage, wet graminoid herbaceous communities are the predominant vegetation cover,
and numerous thaw lakes dot the region.

124,000 sq km

This ecoregion consists of a wide swath of rolling hills and plateaus that grades from the coastal plain
on the north to the Brooks Range on the south. The east-west extent of the ecoregion stretches from
the international boundary between Alaska and the Yukon Territory, Canada, to the Chukchi Sea.
The hills and valleys of the region have better defined drainage patterns than those found in the
coastal plain to the north and have fewer lakes. The area is underlain by thick permafrost and many
ice-related surface features are present. The region is predominantly treeless and is vegetated
primarily by mesic graminoid herbaceous communities.

 

 

134,000 sq km

: This ecoregion consists of several groups of rugged, deeply dissected mountains carved from uplifted

sedimentary rock. The region traverses much of the east-west extent of northern Alaska, from the
Canadian border to within 100 km of the Chukchi Sea. Elevation of mountain peaks ranges from 800 m
in the relatively low Baird Mountains in the west to 2,400 m in the central and eastern Brooks Range.
Pleistocene glaciation was extensive, and small glaciers persist at elevations above 1,800 m. An
arctic climatic regime and unstable hillslopes maintain a sparse cover of dwarf scrub vegetation
throughout the mountains, though some valleys provide more mesic sites for graminoid herbaceous
communities.

Interior Forested Lowlands and Uplands 269,000 sq km

This ecoregion represents a patchwork of ecological characteristics. Regionwide unifying features
include a lack of Pleistocene glaciation, a continental climate, a mantling of undifferentiated alluvium
and slope deposits, a predominance of forests dominated by spruce and hardwood species, and a
very high frequency of lightning fires. On this backdrop of characteristics is superimposed a finer
grained complex of vegetation communities resulting from the interplay of permafrost, surface water,
fire, local elevational relief, and hillslope aspect.

  

nterior Highlands 115,000 sq km

This discontinuous ecoregion is composed of rounded, low mountains, often surmounted by rugged
peaks. The highlands primarily sustain dwarf scrub vegetation and open spruce stands, though
graminoid herbaceous communities occur in poorly drained areas. Mountains in most parts of this
region rise to at least 1,200 m, and many rise higher than 1,500 m. Most of the higher peaks were
glaciated during the Pleistocene epoch.

- Interior Bottomlands 103,000 sq km

This ecoregion is composed of flat to nearly flat bottomlands along larger rivers of interior Alaska.
The bottomlands are dotted with thaw and oxbow lakes. Soils are poorly drained and shallow, often
over permafrost. Predominant vegetation communities include forests dominated by spruce and
hardwood species, tall scrub thickets, and wetlands.

- Yukon Flats 33,000 sq km

This ecoregion is a relatively flat, marshy basin floor in east central Alaska that is patterned with
braided and meandering streams, numerous thaw and oxbow lakes, and meander scars. Sur-
rounding the basin floor is a variable band of more undulating topography with fewer water bodies. In
many respects, the ecoregion is similar to the Interior Bottomlands Ecoregion, but differs in climatic
characteristics. Temperatures tend to be more extreme; summers are warmer and winters are colder
than in other areas of comparable latitude. The ecoregion also receives less annual precipitation than
the Interior Bottomlands. Forests dominated by spruce and hardwood species, tall scrub com-
munities, and wet graminoid herbaceous communities are the predominant vegetation types.

A Ogilvie Mountains 11,000 sq km

This ecoregion, along the eastern edge of Alaska, consists of flat—topped hills eroded from a former
plain and broad pediment slopes built up from mountains that are much subdued from their former
stature. Karst topography is common. Mesic graminoid herbaceous communities and tall scrub
communities are widespread throughout the region. Forest communities occupy lower hillslopes and
valleys.

u Subarctic Coastal Plains 91,000 sq km

This ecoregion mainly includes coastal plains of the Kotzebue Sound area and the Yukon and
Kuskokwim River delta area. Flat, lake—dotted coastal plains and river deltas are characteristic of the
region. Streams have very wide and serpentine meanders. Soils are wet and the permafrost table is
shallow, providing conditions for wet graminoid herbaceous communities, the predominant vegetation
type. The region is affected by both marine and continental climatic influences.

  

Seward Peninsula 47,000 sq km

Some of the oldest geologic formations in Alaska provide a backdrop for this predominantly treeless
ecoregion. Mesic graminoid herbaceous and low scrub communities occupy extensive areas. The

‘1 ecoregion is surrounded on three sides by water, yet this has little ameliorating effect on the climate.
, Winters tend to be long and harsh and summers short and cool.

7%7% Transitional Areas

Cross-hatched portions along the ecoregion boundaries represent transitional areas sharing charac-
teristics of two or more adjacent ecoregions. Due to the map scale and resolution, as well as to the
resolution of the information used to derive the map, not all transition zones can be represented.

 

 

Ahklun and Kilbuck Mountains 51,000 sq km

Located in southwestern Alaska off Bristol and Kuskokwim Bays, this ecoregion is composed of
steep, sharp, often ringlike groupings of rugged mountains separated by broad, flat valleys and
lowlands. The mountains were glaciated during the Pleistocene epoch, but only a few small glaciers
persist. Dwarf scrub communities are the predominant vegetation cover in the mountains. Tall scrub
and graminoid herbaceous communities are common in valleys and on lower mountain slopes.
Valley bottoms may support stands of spruce and hardwood species.

 

 

   

Bristol Bay-Nushagak Lowlands 61,000 sq km

, This lowland ecoregion is located in southwestern Alaska off Bristol Bay. The region has rolling
terrain, formed from morainal deposits. Soils of the lowlands are somewhat better drained than soils
of the Subarctic Coastal Plains Ecoregion. Dwarf scrub communities are widespread, but large areas
of wetland communities occur. Lakes are scattered throughout the lowlands, but are not nearly as
numerous as in the Subarctic Coastal Plains.

 

 

 

 

  

Alaska Peninsula Mountains 48,000 sq km

., This ecoregion is composed of rounded, folded and faulted sedimentary ridges intermittently
surmounted by volcanoes. The mountains were heavily glaciated during the Pleistocene epoch. A
' marine climate prevails, and the region is generally free of permafrost. Many soils formed in deposits
of volcanic ash and cinder over glacial deposits and are highly erodible. Vegetation cover commonly
consists of dwarf scrub communities at higher elevations and on sites exposed to wind, and low scrub
communities at lower elevations and in more protected sites.

' Aleutian Islands 12,000 sq km

, This ecoregion in southwestern Alaska is composed of a chain of sedimentary islands (eroded from
older volcanic formations) that are crowned by steep volcanoes. Maritime climate prevails. The
region is south of the winter sea ice pack and is generally free from permafrost. Vegetation cover
mainly consists of dwarf scrub communities at higher elevations and on sites exposed to wind, and of
graminoid herbaceous communities in more protected sites.

- Cook Inlet 28,000 sq km

, i, Located in the south central part of Alaska adjacent to the Cook Inlet, the ecoregion has one of the
mildest climates in the State. The climate, the level to rolling topography, and the coastal proximity
have attracted most of the settlement and development in Alaska. The region has a variety of
vegetation communities but is dominated by stands of spruce and hardwood species. The area is
generally free from permafrost. Unlike many of the other nonmontane ecoregions, the Cook Inlet
Ecoregion was intensely glaciated during the Pleistocene epoch.

 

Alaska Range 117,000 sq km

The mountains of south central Alaska, the Alaska Range, are very high and steep. This ecoregion is
' . covered by rocky slopes, icefields, and glaciers. Much of the area is barren of vegetation. Dwarf
scrub communities are common at higher elevations and on windswept sites where vegetation does
‘ exist. The Alaska Range has a continental climatic regime, but because of the extreme height of

many of the ridges and peaks, annual precipitation at higher elevations is similar to that measured for
some ecoregions having maritime climate.

 

 

 

- Copper Plateau 17,000 sq km

This ecoregion in south central Alaska occupies the site of a large lake that existed during glacial
times. The nearly level to rolling plain has many lakes and wetlands. Soils are predominantly silty or
clayey, formed from glaciolacustrine sediments. Much of the region has a shallow permafrost table,
and soils are poorly drained. Black spruce forests and tall scrub, interspersed with wetlands, are the
major types of vegetation communities.

 

Wrangell Mountains 29,000 sq km

This ecoregion consists of steep, rugged mountains of volcanic origin that are extensively covered by
ice fields and glaciers. Most slopes are barren of vegetation. Dwarf scrub tundra communities,
consisting of mats of low shrubs, forbs, grasses, and lichens, predominate where vegetation does
occur. The climate has harsh winters and short summers.

 

 

 

- Pacific Coastal Mountains 106,000 sq km

The steep and rugged mountains along the southeastern and south central coast of Alaska receive
more precipitation annually than either the Alaska Range or Wrangell Mountains Ecoregions.
Glaciated during the Pleistocene epoch, most of the ecoregion is still covered by glaciers and ice
fields. Most of the area is barren of vegetation, but where plants do occur, dwarf and low scrub
_ communities dominate.

- Coastal Western Hemlock-Sitka Spruce Forests 61,000 sq km

Located along the southeastern and south central shores of Alaska, the terrain of this ecoregion is a
result of intense glaciation during late advances of the Pleistocene epoch. The deep, narrow bays,
steep valley walls that expose much bedrock, thin moraine deposits on hills and in valleys, very
irregular coastline, high sea cliffs, and deeply dissected glacial moraine deposits covering the lower
slopes of valley walls are all evidence of the effects of glaciation. The region has the mildest winter
temperatures in Alaska, accompanied by large amounts of precipitation. Forests of western hemlock
and Sitka spruce are widespread.

 

 

 

 

Major Environmental Characteristics Occurring in each Ecoregion

 

Major Environmental Characteristics Occurring in each Ecoregion

 

 

 

 

Ecoregion

101. Arctic Coastal
Plain

(50.000 km:)

(1. 2. 4.6)

102. Arctic Foothills
( 124.000 knr‘)

(1.2.4.6)

103. Brooks Range
(134.000 kml)

(1.2.3.4.6. 7)

104. lntcrior Forested
Lowlands and
Uplands

(269.000 km:)

(2. 3. 6. 7)

105. Interior
Highlands

(115.000 knr)

(2.6.7)

106. lnterior
Bottomlands

(103.000 knr)

(2.3.6)

107. Yukon Flats
(33.000 km")

(2. 3. 4. 6)

Cli matc‘
(t )‘i

Arctic. Ann. precip."
Z140 mm. Ann. snow-
fall 30 cm to 75 cm.
Avg. daily min. temp.
in winter is »30“‘C:
avg. daily max. in
summer is Z8°C.

Arctic. Ann. precip.
Z140 mm. up to

190 mm near
Brooks Range. Ann.
snowfall 75 cm to

130 cm. Avg. daily
min. temp. in winter
is —29"C: avg. daily
max. in summer is
11C to 15°C.

Arctic. Ann. precip. at
Anaktuvuk Pass (the
only long—term weath—
er station in the
region) 280 mm. Ann.
snowfall 160cm.

Avg. daily min. temp.
in winter at
Anaktuvuk Pass is
»30“C: avg. daily
max. in summer for
same location is l6“C.

Continental. Ann.
precip. 250»550 mm.
usually increasing
with elevation. Ann.
snowfall 125 cm to
205 cm. Avg. daily
min. temp. in winter
is —35"C to ~18'7C:
avg. daily max. in
summer is 17C to
22"‘C.

Continental. No
long»term weather
data available. Likely
increasing precip. and
decreasing temp. with
rise in elevation.

Continental. Ann.
precip. 280 mm to
400 mm. Wetter in
west. drier in east.
Ann. snowfall 95 cm
to 205 cm. Avg. daily
min. temp. in winter
is »33“C to »26°C:
avg. daily max. in
summer is 22"C.

Continental. Ann.
precip. 170mm. Ann.
snowfall l 15 cm.
Avg. daily min. temp.
in winter is :234vc;
avg. daily max. in
summer is ~22 C.

 

Pliysiography
(2)

Nearly level plain.
Elevations from sea
level to 180 ms.
Slope gradients 51°.

Broad. rounded ridges
and rnesas in northern
section; irregular
btrttes. rnesas. long.
linear ridges. and
undulating plains and
plateaus in southern
section. Elevations
from sea level to 800
m. Slope gradients
generally 0” to 5".

Steep. rugged moun»
tains. Elevations
from 500 m to
>2.400 1n. Slope gra»
dients generally 5" to
15‘”.

Rolling lowlands. dis»
sccted plateaus. and
low to high hills.
Elevations from sea
level to 500 In. Slope
gradients generally 0”
to 5".

Steep. round ridges
often capped by
rugged peaks.
Elevations from 500 in
to >1 .500 m. Slope
gradients generally 5°
to 15". lower gradients
typical around margins
of ecoregion.

Flat to nearly flat bot»
tomlands. inclusion of
local hills. Elevations
from 120 in to 600 in.
Slope gradients gener»
ally <1 ".

Flat to undulating
basin floor.
Elevations from 90 m
to >250 111. Slope
gradients generally
<1 1".

Geologv

(3)

Quaternary deposits
of alluvial. glacial.
and aeolian origin.

Northern section has
unconsolidated
Quaternary deposits
of glacial. alluvial.
and aeolian origin.
Southern section has
undifferentiated allu-
vial and colluvial
deposits over Jurassic
and early Cretaceous
formations.

Stratified Paleozoic
and Mesozoic sedi»
mentary deposits.
.Vluch exposed
bedrock and rubble.

Predominantly
Mesozoic and
Paleozoic sedimentary
rocks. but also exten»
sive areas of volcanic
deposits. Region is
covered by undiffer-
entiated alluvier and
slope deposits. Little
bedrock exposure.

Paleozoic and
Precambrian metamor»
phic rocks. felsic vol»
canic and intrusive
rocks. Kuskokwim
Mountains and Nulato
Hills have Cretaceous
and Lower Paleozoic
sedimentary rocks.
Much more bedrock
exposure than lntcrior
Forested Lowlands and
Uplands Ecoregion.

Fluvial and aeolian
deposits of mixed ori»
gin. Outwash gravel
and morainal deposits
in some areas.

Quaternary alluvial
(and some aeolian)
deposits.

Permafrost
(4)

Underlain by continu»
ous thick permafrost.

Underlain by continu-
ous thick permafrost.

Underlain by continu»
ous thick permafrost.

Western portion
underlain by thin to
moderately thick per-
mafrost. Eastern por»
tion underlain by dis-
continuous per-
mafrost.

Northern portions are
underlain by continu-
ous permafrost.
Central and southern
portions are underlain
by discontinuous per-
mafrost.

Ranges from isolated
masses of permafrost
to continuous thin
permafrost.

Permafrost wide»
spread but discontinu»
ous.

Soils
(5)

Histic Pergelic
Cr‘yaquepts and
Pergelic Cryaquepts.

Histic Pergelic
Cryaquepts. Pergelic
Cryaquepts. and
Pergelic
Ruptic»Histic
Cryaquepts.

Pergelic Cryaquepts.

Pergelic Cryumbrepts.

and Lithic
Cryorthents.

Histic Pergelic
Cryaquepts. Pergelic
Cryaquepts. Aquic
Cryochrepts. Pergelic
Cryochrepts. Typic
Cryochrepts. Typic
Cryorthents. and
Pergelic Cry umbrepts.

Histic Pergelic
Cryaquepts. Typic
Cryochrepts. Pergelic
Cryumbrepts. Lithic
Cryorthents. and
Typic Cryorthods.

Histic Pergelic
Cryaquepts. Pergelic
Cryaquepts. Aquic
Cryochrepts. Typic
Cryochrepts. and
Typic Cryofluvents.

Histic Pergelic
Cryaquepts. Pergelic
Cryaquepts. Aquie
Cryochrepts. and
Pergelic Cryochrepts.

Vegetation
(6)

Wet graminoid herba-
ceous communities
predominate. Dwarf
scrub communities in
areas where micr‘otO»
pography provides
deeper rooting zone.

Mesic graminoid
herbaceous communi»
ties predominate.

Dvy arf scrub on other
well—drained sites.
Open low scrub along
drainages.

Much of region is
barren of vegetation.
Dwarf scrub commu»
nities on drier sites.
Mesic graminoid
herbaceous communi»
ties on wet to moist
sites in lower valleys.

Needleleaf, broadleaf.
and mixed forests pre-
dominate. Tall scrub
communities on newly
exposed alluvium.
burned or disturbed
areas. and at treeline,
Lovv scrub in moist
areas and on nortb»fac»
ing slopes. Tall scrub
swamps. low scrub
bogs. and scrub»
graminoid communi»
ties in wettest areas.

Dwarf scrub on sites
exposed to harsh eli»
matic elements.

N eedleleaf forests and
woodlands at lower
elevations. Mesic
graminoid herbaceous
communities in poor»
1y drained areas.

Needleleaf. broadleaf.
and mixed forest com»
munities are wide-
spread. Tall scrub
communities on flood»
plains. Low scrub
bogs. wet graminoid
herbaceous meadows.
and wet forb herba—
eeots meadows and
matches in wettest
sites

N eedleleaf. broadleaf.
and mixed forest
communities wide—
spread. Tall scrub
communities on allu»
vial sites subject to
periodic flooding.
Tall scrub swamps
and wet graminoid
herbaceous communi-
ties in wettest areas.

Pleistocene Glaciation
(.7)

None.

None. except for
some areas directly
north of the Brooks
Range.

Extensive.

None.

On higher peaks.

None.

N one.

Ecoregion
112. Bristol Bay»
Nushagak Lowlands
(61.000 km:)

(2. 3. 6. 7)

113. Alaska Peninsula
Mountains

(48.000 kml)

,_\

2. 3. 4. 6. 7)

114. Aleutian Islands
(12,000 km*')

(1.3.4.6. 7)

Climate
( l )

Transitional. Ann.
precip. 3.30 mm to
860 mm. Ann. snoW»
fall 75 cm to 250 cm.
Avg. daily min. temp.
in winter is »15°C to
»10“C (higher in
south. lower in north):
avg. daily max. in
summer is 18°C.

Maritime. Ann. pre—
cip. 600 mm to

3.300 mm in coastal
lowlands. >4.060 mm
at higher elevations.
Ann. snowfall 55 cm
to 150 cm in lovv»
lands. >510 cm in
mountains. Avg.
daily min. temp. in
winter is »| 1°C to
»6"‘C; avg. daily max.
in summer is z15°C.

Maritime. Ann. pre»
cip. 530 mm to

2.080 mm at sea level
locations (smaller
islands may have
much less precip.).
Ann. snowfall 85 cm
to 250 cm at same
locations. Avg. daily
min. temp. in winter
is —70C to —25C; avg.
daily max. in summer
is 10C to 13C.

Physiography
(2)

Rolling lowlands.
Elevations from sea
level to 150 m. Slope
gradients generally
0—2“.

Rounded ridges over—
toppcd by steep.
rugged mountains.
Elevations from sea
level to 2.600 m.
Slope gradients gener-
ally 0“ to 11“. steeper
slopes not uncom»
mon.

Low mountains. often
overtopped by steep.
rugged mountains.
Elevations from sea
level to >1.900 m.
Slope gradients <1“ in
lowlands. >5“ in
mountains.

Geology
(3)

Quaternary glacial
outvvash and morainal
deposits. mantled in
part by silt and peat.

Stratified Jurassic.
Cretaceous. and
Tertiary sediments
and undifferentiated
Quaternary volcanic
rocks.

Blockfaulted Tertiary
sediments surmounted
by undifferentiated
Quaternary and
Tertiary volcanic
rocks.

Permafrost
(4)

Ranges from isolated
masses of permafrost
to areas free from per»
mafrost.

Generally free from
permafrost.

Generally free from
permafrost.

Soils

(5)

Typic Haplocryands.
Typic Vitricryands.
Fluvaquentic
Cryofibrists. Histic
Pergelic Cryaquepts.
Pergelic Cryaquepts.
and Typic
Cryochrepts.

Typic Haplocryands
and Typic
Vitricryands.

Typic Haplocryands
and Typic
Vitricryands.

Vegetation
(6)

Dwarf scrub commu-
nities most common
on better drained
sites. Low scrub
bogs, wet graminoid
herbaceous communi»
ties. and wet forb
herbaceous communi-
ties on poorly drained
sites. Broadleaf and
mixed forest commu»
nities on floodplains
of major rivers.

Dwarf scrub commu-
nities at higher eleva»
tions and on
windswept areas. Low
scrub communities in
more protected sites.
Of less extensive dis»
tribution are tall scrub
communities (in
drainages and at low
elevations). broadleaf
forests (on floodplains
and south»facing
slopes). and low scrub
bogs and mesic
graminoid herbaceous
communities (in poor»
1y drained areas).

Dwarf scrub commu»
nities at higher eleva»
tions and on
windswept areas.
Mesic graminoid
herbaceous commu—
nities and dry
graminoid herba»
ceous communities at
lower elevations and
on sites protected
from wind. LOW
scrub bogs in moist
areas.

Pleistocene Glaciation

(7)

Extensive.

Extensive.

Only the easternmost
portion glaciated.

 

115. Cook Inlet
(28.000 kml)

(1.3.4.5.6. 7)

Transitional. Ann.
precip. 380 mm to
680 mm. Ann. snow»
fall 160 cm to

255 cm. Avg. daily
min. temp. in winter
is 45°C; avg. daily
max. in summer is

18°C.

Level to rolling ter—
rain. Elevations from
sea level to 600 m.
Slope gradients gener»
ally 0” to 3".

Poorly consolidated
Tertiary coal»bcaring
rocks mantled by
glacial moraine and
outwash. aeolian
deposits. and marine
and lake deposits.

Generally free from
permafrost.

Haplocryands.
Sphagnic Borofibrists.
Terrie Borosaprists.
Typic Borohemists.
Andie Haplocryods.
and Andie
Humicryods.

Needleleaf. broadleaf.
and mixed forests
widespread. Mesic
graminoid, graminoid
herbaceous. and low
scrub graminoid corn—
rntrnities in dry to
mesie sites. Tall
scrub communities on
periodically flooded
alluvium. Low scrub
communities on poor-
ly drained lowlands.
Tall scrub swamps.
low scrub bogs. wet
forb herbaceous com»
munities. and wet
graminoid herbaceous
communities on
wettest sites.

Extensive.

 

 

108. Ogilvie
Mountains

(1 1.000 kml)

(Region is most dis-
tinguishable on vege-
tation greenness
images. Other impor-
tant characteristics are
distinctive mainly in
Canada.)

109. Subarctic Coastal
Plains
(91.000 km:)

(2. 3. J 5. 6)

l 10. Seward
Peninsula

(47.000 km:)

(3. 6)

11 1. Ahklun and
Kilbuck Mountains

(51.000 km:)

(2. 3. 6. 7)

Continental. No
longAtcrm weather
data available. Ann.
precip. probably from
500 mm to 650 mm.
Ann. snowfall proba»
bly from 130 cm to
205 cm. Estimated
avg. daily min. temp.
in winter is »32”C:
estimated avg. daily
max. in summer is
22C.

Transitional Ann.
precip. 250 mm to
500 mm. Ann. snow-
fall 100 cm in north.
105 cm to 150 cm in
south. Avg. daily
min. temp. in winter
is —25"‘C for the
Kotzebue Sound area
and »20°C to »15"C
for the Cape Denbigh
and Yukon—
Kuskokwim Lowland
areas; avg. daily max.
temp. in summer is
13"C to 17"C.

Maritime to continen-
tal. Ann. precip.

250 mm to 510 mm in
the lowlands. >1 .000
mm estimated for the
mountains. Ann.
snowfall 100 cm to
190 cm in the low'»
lands. probably up to
250 cm in the moun-
tains. Avg. daily min.
temp. in winter is
—24°C to —190C; avg.
daily max. in summer
is 13C to 17C.

Transitional. Ann.
precip. 1.020 mm in
lowlands to 2.030 mm
in highlands. Ann.
snowfall 205 cm in
lowlands to 510 cm in
highlands. Avg. daily
min. temp. in winter
is »16”C; avg. daily
max. in summer is
16°C to 19C.

Predominantly
11at~topped hills.
sometimes overtoppcd
by mountains. eroded
from a former plain.
Elevations from

900 m to >1.300 1n.
Slope gradients gener»
ally 00 to 5"".

Flat plains.

Elevations from sea
level to >120 111.
Slope gradients gener-
ally <1".

Narrow strips of
coastal lowlands.
extensive uplands of
broad convex hills
and flat divides.
small. isolated groups
of rugged mountains.
Elevations from sea
level to 500 m for
most of region.
>1.400 m on high
mountains. Slope
gradients generally 00
to 5”. tip to 15" typi—
cal in the mountains.

Steep. rugged moun—
tain groupings sepa-
rated by broad low-
lands. Elevations
from sea level to

>1 .500 m. Slope gra—
dients generally 00 to
8”. steeper slopes not
uncommon.

Metamorphic and sed»
irnentary rocks, pri—
marily dolomite. phyla
lite. argillite. lime-
stone. shale. chert.
sandstone. and con—
glomerate. Karst
topography common.

Older coastal deposits
of interstratified allu»
vial and marine sedi»
ments. Includes areas
of Quaternary mafie
and undifferentiated
volcanic rocks in
western part of
Yukon»Kuskokwim
Lowlands and on
Nunivak and St.
Lawrence Islands.
Cretaceous intermedi—
ate volcanic rocks in
Selawik Wildlife
Refuge Area.

Paleozoic sediments
and metamorphosed
volcanic rocks and
Precambrian volcanic
rocks. Highlands may
be Cenozoic uplifts of
these formations.
Extensive Quaternary
or Tertiary volcanic
rock formations in
northeastern portion
of ecoregion.

Strongly deformed
sedimentary and vol»
canic rocks of late
Paleozoic and
Mesozoic age. Small
granitic masses sur»
rounded by more
resistant hornfels have
formed ringlike
mountain groups.

"Climate information for nearly all ecoregions represents interpolations from very few weather stations.
“Numbers below headings of environmental characteristics correspond with those listed in footnote c.

‘Numbers indicate the mapped environmental characteristiCs most useful for distinguishing the ecoregion and do not necessarily reflect the primary

l=climate. 2=physiography 3=geology. 4=permafrost. 5=soils. 6=v egetation. and 7=Pleistocene glaciation.

t .
‘lncludes snovt water equrvalent.
“Elevation is in meters above mean sea level.

Permafrost wide-
spread but discontinu»
ous.

Continuous thin to
moderately thick per»
mafrost.

Continuously thin to
moderately thick per-
mafrost.

Discontinuous per-
mafrost at higher ele»
vations. isolated
masses at lower ele-
vations.

Histic Pergelic
Cryaquepts. Typic
Cryochrepts. and
Pergelic Cryorthents

Histic Pergelic
Cryaquepts and
Pergelic Cryofibrists.

Histic Pergelic
Cryaquepts. Pergelic
Cryaquepts. Typic
Cryochrepts. Pergelic
Cryumbrepts. Lithic
Cryorthents. and
Pergelic Cryorthents.

Histic Pergelic
Cryaquepts. Pergelic
Cryaquepts. Typic
Cryochrepts. Lithic
Cryumbrepts. Pergelic
Cryumbrepts. Pergelic
Cryorthods. Typic
Haplocryods. and
Typic Humicryods.

ecological driving factors:

Mesic graminoid
herbaceous communi-
ties widespread on
exposed sites.
Needleleaf. broadleaf,
and mixed forest
communities on lower
hillslopes and in val-
leys. Tall scrub corn-
rnunitics mainly at
lower elevations.
sometimes extending
above timberline.

Wet graminoid herba»
ceous communities
predominate. Dwarf
scrub communities in
better drained areas.
Needleleaf forests in
southern portion of
region. where
drainage and warm
temperatures suffi»
cient .

Mesic graminoid
herbaceous communi—
ties and low scrub
communities wide»
spread on hills and
lower mountains.

Wet graminoid herba-
ceous communities in
wettest areas. Tall
scrub communities
along drainages and
on floodplains.
Dwarf scrub commu»
nities in highlands.

Dwarf scrub commu-
nities in mountains.
Mesi graminoid
herbaceous communi»
ties on mesie valley
sites. Wet graminoid
herbaceous communi»
ties and low scrub
herbaceous bogs on
wettest valley sites.
Needleleaf, broadleaf.
and mixed forest
stands on better
drained valley sites.

 

None.

Only northernmost
portion glaciated.

Only highlands were
glaciated.

Extensive.

116. Alaska Range
(117.000 km“)

(1.2.3.467)

Continental. Weather
data available only for
low elevations. Ann.
precip. 380 mm at
low elevations. proba-
bly z2.030 mm at
high elevations. Ann.
snowfall 150 cm to
305 cm at low eleva—
tions. probably

z1.015 cm at high
elevations. Avg. daily
min. temp. in winter
is —250C at low eleva-
tions; avg. daily max.
in summer is 18‘7C at
same locations.

Steep. rugged moun—
tains and broad val~
leys. Elevations from
600 m (sea level in
southwest portion of
eeoregion) to

>3,900 in (Mt.
McKinley >6.100 m).
Slope gradients gener»
ally 5° to 25’“. >25Oon
some mountains.

Southern portion
underlain by granitic
batholiths intrusive
into moderately meta»
morphosed. highly
deformed Paleozoic
and Mesozoic volcanic
and sedimentary rocks.
This area includes
active volcanoes.
Central and eastern
portions of ecoregion
are a broad syneline
having Cretaceous
rocks in the center and
Paleozoic and
Precambrian rocks on
the flanks. Rocky
slopes. ieefields. and
glaciers cover much of
region.

Discontinuous per-
mafrost.

Lithic Cryorthents.
Pergelic Cryaquepts.
Pergelic Ruptie»
Histic Cryaquepts.
Typic Cryochrepts.
Pergelic Cryumbrepts.
and Typic
Cryumbrepts.

Much of region is bar—
ren of vegetation.
Dwarf scrub commu»
nities on drier,
windswept sites. Low
scrub communities
and tall scrub commu—
nities on moist to
mesie sites. Needleleaf
forests and woodlands
on well»drained sites
of valleys and lower
slopes.

Extensive.

 

1 17. Copper Plateau
( 17.000 km:)

(2. 3. 4. 5. 6. 7)

Continental. Ann.
precip. 250 mm to
460 mm. Ann. snow»
fall 100 cm to

190 cm. Avg. daily
mrn. temp. in vvrnter
is z»27“C: avg. daily
max. in summer is

=210C.

Level to gently rolling
plain. Elevations
from 420 in to 900 m.
Slope gradients gener-
ally 00 to 2°

Pleistocene proglacial
lake deposits.

Thin to moderately
thick permafrost.

Histic Pergelic
Cryaquepts. Aquic
Cryochrepts. Typic
Cryochrepts. Pergelic
Cryaquolls. and Typic
Cryoborolls.

Needleleaf forests and
woodlands predomi»
nate. Broadleaf
forests. tall scrub
communities, and
needleleaf forests
dominated by white
spruce on better
drained sites. Low
scrub bogs and wet
graminoid herbaceous
communities in
wettest areas.

Extensive.

 

118. Wrangell
Mountains

(29.000 kml)

(1.2.3.4, 6, 7)

119. Pacific Coastal
Mountains

(106,000 km:)

(1,2. 3.6.7)

Continental. Ann.
precip. 410 mm at
McCarthy (the only
long—terrn weather
station in the ecore»
gion). probably
z2,030 mm at higher
elevations. Ann.
snowfall 175 cm at
McCarthy, probably
z255 cm at higher ele»
vations. Avg. daily
min. temp. in winter is
»34°C at McCarthy:
avg. daily max. in
summer at same loca-
tion is 22")C.

Transitional. No
long—terrn weather
data available. Ann.
precip.. interpolated
from low elevation
coastal station data.
2.030 mm to

>7.()()() mm. Ann.
snowfall 510 cm to
2.030 cm. Ann. pre-
cip. generally increas—
es with elevation.

Steep. rugged moun-
tains. Elevations
from 600 m to
>3.900 m. Slope gra»
dients usually >7“.
>150 for many areas.

Steep. rugged moun—
tains. Elevations
from sea level to
>4.500 m. Slope gra»
dients generally >7",
>200 on some moun-
tains.

Shield and composite
volcanoes of
Cenozoic age. Rocky
slopes. ieefields. and
glaciers cover much
of region.

Cretaceous and Upper
Jurassic sediments
extensively through-
out Chugach
Mountains. Tertiary
to Cretaceous
(Paleozoic in some
places) intrusive rock
primarily throughout
southeastern coastal
mountains. Rocky
slopes. ieefields. and
glaciers cover much
of region.

Discontinuous per»
mafrost.

Chugach Mountains
have isolated masses
of permafrost. The
remainder of the
ecoregion is generally
free from permafrost.

Lithic Cryorthents,
Typic Cryorthents.
Pergelic Cryochrepts.
and Pergelic
Cryumbrepts.

Lithic Cryorthents.
Andie Cryumbrepts.
Pergelic Cryumbrepts.
Typic Cryumbrepts.
Typic Haplocryods.
Andie Humicryods.
Lithic Humicryods.
and Typic
Humicryods.

Much of region is
barren of vegetation.
Dwarf scrub commu—
nities on drier.
windswept sites. Tall
scrub communities
along drainages and
on floodplains.
Needleleaf and
broadleaf forests at
lower elevations on
broad ridges, valleys,
and hilly moraines.

Much of region is
barren of vegetation.
Low and dwarf scrub
communities are com—
mon where vegetation
does occur.
Needleleaf forests in
some lower drainages.

Extensive.

Extensive.

 

 

 

Gallant. A.L.. Binnian. E.F.. Omernik. J.M.. and
Shasby. M.B.. 1995. Ecor‘zions ofAlaska:
U.S.Geo|ogical Survey Professional Paper 1567.

 

 

120. Coastal Western
Hemlock»Sitka
Spruce Forests

(61.000 kml)

(1.4.5.6.7)

Maritime. Ann. pre»
cip. 1.350 mm to
3,900 mm. Ann.
snowfall 80 cm to
600 cm. Avg. daily
min. temp. in winter
is »3"C; avg. daily
max. in summer is
180C.

Level to irregular ter—
rain to steep foothills
of coastal mountains.
Elevations from sea
level to 500 m
(includes some local
mountains up to
1.000 m). Median
slope gradient 5”.
range is from 0" to
28”.

Lower Tertiary
interbcdded sedirnen»
tary, volcanogenic.
and volcanic rocks in
Prince William Sound
area. Upper
Cretaceous sandstone
and slate on Kodiak
lsland. Mesozoic vol»
canic and intrusive
rock. and Mesozoic
and Paleozoic sedi-
ments in the south»
eastern portion of the
ecoregion.

Generally free from
permafrost.

Terrie Cryohemists,
Andic Cryaquods.
Andie Humicryods.
Lithic Humicryods.
and Typic
Humicryods.

Needleleaf. broadleaf,
and mixed forests pre-
dominate. Tall scrub
swamps, 10w scrub
bogs. wet graminoid
herbaceous communi»
ties. and wet forb
herbaceous communi-
ties on wet sites.

Extensive.

 

‘ U.S. DEPOSITORY
no. 1568
EART

7mm » JUL 0 11996

Lithostratigraphy, Mierolithofacies, and COnOdont
Biostratigraphy and Biofacies of the Wahoo
Limestone (Carboniferous), Eastern Sadlerochit
Mountains, Northeast Brooks Range, Alaska

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1568

 

 

    

   

The Library - UC Berkele}
Received on: O7—18w96
Geological Survey
professional paper

Cover: Angular unconformity separating steeply dipping pre-Mississippian
rocks from gently dipping carbonate rocks of the Lisbume Group near Sunset
Pass, eastern Sadlerochit Mountains, northeast Brooks Range, Alaska. The
image is a digital enhancement of the photograph (fig. 5) on page 9.

Lithostratigraphy, Mierolithofacies, and Conodont
Biostratigraphy and Biofaeies of the Wahoo
Limestone (Carboniferous), Eastern Sadleroehit
Mountains, Northeast Brooks Range, Alaska

By Andrea P. Krumhardt, Anita G. Harris, and Keith F. Watts

 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1568

Description of the lithostratigraphy, microlithofacies, and
conodont biostratigraphy and biofacies in a key section of
a relatively widespread stratigraphic unit that straddles
the M ississippian-Pennsylvanian boundary

 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1996

US. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY
GORDON P. EATON, Director

For sale by US. Geological Survey, Information Services
Box 25286, Federal Center, Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and

does not imply endorsement by the US. Government.

Published in the Eastern Region, Reston, Va.
Manuscript approved for publication June 26, 1995.

Library of Congress Cataloging in Publication Data

Krumhardt, Andrea P

Lithostratigraphy, microlithofacies, and conodont biostratigraphy and biofacies 0f the
Wahoo Limestone (Carboniferous), eastern Sadlerochit Mountains, northeast Brooks
Range, Alaska / by Andrea F. Krumhardt, Anita G, Harris, and Keith F. Watts.

p, cm. — (US Geological Survey professional paper ; 1568)

Includes bibliographical references.

Supt. of Docs. n0.:l 19.16:1568

1. Geology, Stratigraphic—Pennsylvanian. 2. Geology, Stratigraphic—Mississippian.
3. Geology—Alaska—Sadlerochit Mountains Region. 4. Conodonts—Alaska—
Sadlerochit Mountains Region. 5. Paleontologwaennsylvanian. 6. Paleontology—
Mississippian. 7. Wahoo Limestone (Alaska). 1. Harris, Anita G. ll. Watts, Keith F.
111. Title. W. Series.

QE673.K77 I996

551.7'5'097987—d020 95—3128l
ClP

CONTENTS

Abstract ........................................................................................................................... 1
Introduction ..................................................................................................................... 2
Acknowledgments ................................................................................................... 2
Previous Studies .............................................................................................................. 4
Regional Geologic Setting .............................................................................................. 5
Lisburne Group, Northeast Brooks Range .............................................................. 5
Alapah Limestone ........................................................................................... 7
Alapah Limestone-Wahoo Limestone Boundary, Northeast Brooks Range ........... 7
Wahoo Limestone ............................................................................................ 7
Lithostratigraphy of the Wahoo Limestone, Eastern Sadlerochit Mountains ................. 9
Lower Member of the Wahoo Limestone ............................................................... 10
Upper Member of the Wahoo Limestone ................................................................ 10
Conodont Biostratigraphy of the Wahoo Limestone, Eastern Sadlerochit
Mountains ........................................................................................................... 12
muricatus Zone ....................................................................................................... 13
Lower muricams Subzone .............................................................................. 13
Upper muricatus Subzone ............................................................................... l3
noduliferus-primus Zone ......................................................................................... l4
minums Fauna ......................................................................................................... 15
Lower minums Fauna ...................................................................................... 15
ldiognathoa’us Fauna ............................................................................................... 16
The Mid-Carboniferous Boundary—An Approximation of the Mississippian-
Pennsylvanian Boundary .................................................................................... 17
Biostratigraphic Criteria .......................................................................................... 17
Conodont-Based Boundary in the Eastern Sadlerochit Mountains ......................... 18
Foraminiferan-Based Boundary in the Eastern Sadlerochit Mountains ................. 18
Morrowan-Atokan Boundary .......................................................................................... 2O
Conodont Biofacies ......................................................................................................... 21
Conodont Biofacies and Associated Microlithofacies, Wahoo Limestone,
Eastern Sadlerochit Mountains ................................................................... 21
Mississippian Part of the Wahoo Limestone ................................................... 22
Cavusgnathid Biofacies .......................................................................... 22
Near-Restricted to Open-Platform Environments ........................... 22
Cavusgnathid-Kladognathid Biofacies ................................................... 25
Open—Platform to Open-Marine Environment ................................ 25
Gnathodid—Hindeodid Biofacies ............................................................. 26
Low-Energy, Open~Marine Environment ....................................... 26
Pennsylvanian Part of the Wahoo Limestone .................................................. 26
Lower Member of the Wahoo Limestone ....................................................... 27
Adetognathid-Related Biofacies ............................................................. 27
Near-Restricted to Open-Platform Environment ............................ 27
Low-Energy, Open-Marine Environment ....................................... 27
Upper Member of the Wahoo Limestone ........................................................ 27
Adetognathid—Rhachistognathid Biofacies ............................................. 27
Restricted to Near Open-Platform Environment ............................. 27
Open—Platform to Near-Shoal Open—Platform Environments ......... 28
Tidal-Channel(?) Environment ....................................................... 28

Ill

IV

CONTENTS
Rhachistognathid Biofacies .................................................................... 28
Near—Shoal, Open-Platform Environment ...................................... 28
Shoal or Tidal-Channel Environments ............................................ 28
Near-Shoal, Open-Marine Environment ......................................... 29
Deelinognathodid-Related Biofacies ...................................................... 30
Near~Shoal, Open-Marine Environment ......................................... 30
Low—Energy, Open-Platform and (or) Open—Marine
Environment ........................................................................ 30
Biofacies Summary ................................................................................................. 3O
Conodont Preservation and CAI Values ......................................................................... 3]
Systematic Paleontology ................................................................................................. 32
References Cited ............................................................................................................. 50
Appendix 1. Conodont Faunas, Biofacies, and Age and Lithology of Collections
Mentioned in Text but not Described Elsewhere in this Report ......................... 59
PLATES

[Plates 1—5 follow appendix 1; plate 6 in pocket]

1—3, 5. Conodonts from the Wahoo Limestone, eastern Sadlerochit Mountains, Alaska.

4. Conodonts from the Wahoo Limestone, eastern Sadlerochit Mountains, and Pogopuk Creek, Franklin
Mountains, Alaska.

6. Conodont zones, faunal intervals, and species distribution and lithologies of the Wahoo
Limestone in the study section, eastern Sadlerochit Mountains, northeast Brooks Range, Alaska.

FIGURES

Map showing distribution and tectonic affinities of the Lisburne Group in the Brooks Range .................................... 3

Map showing distribution of the Lisburne Group, major structural features, and location of study section,

northeast Brooks Range ................................................................................................................................................ 4

Diagram showing generalized stratigraphic succession, northeast Brooks Range and northeast coastal plain ............ 6
. Schematic diagram showing stratigraphic relationships, lithologies, and inferred depositional environments

of the Lisburne Group, northeast Brooks Range ........................................................................................................... 8

Photograph of study section, eastern Sadlerochit Mountains ....................................................................................... 9

Photograph of Mississippian-Pennsylvanian boundary beds in upper part of lower member of the Wahoo

Limestone at study section ............................................................................................................................................ 11

Diagram showing conodont zonation/fauna] succession recognized in the Wahoo Limestone at study section

compared to the North American middle Carboniferous conodont zonation of Baesemann and Lane ........................ 12

Diagram comparing lithostratigraphic, biostratigraphic, and time—rock boundaries between study section and

nearby Sunset Pass section ............................................................................................................................................ 19

Schematic diagram showing depositional model for and sediment characteristics of the Wahoo Limestone .............. 23
. Schematic diagram showing generalized paleogeography, biofacies, and distribution of conodont genera,

Wahoo Limestone, eastern Sadlerochit Mountains ....................................................................................................... 24

TABLES

[Tables 1 and 2 are in pocket]

Conodont species distribution in the Wahoo Limestone in the study section, eastern Sadlerochit Mountains, northeast
Brooks Range, Alaska.

Depositional environments interpreted from carbonate-micro]ithofacies and conodont—biofacies data, Wahoo Limestone,
eastern Sadlerochit Mountains, northeast Brooks Range, Alaska.

Lithostratigraphy, Microlithofacies, and Conodont Biostratigraphy
and Biofacies of the Wahoo Limestone (Carboniferous),
Eastern Sadlerochit Mountains, Northeast Brooks Range, Alaska

By Andrea P. Krumhardt,l Anita G. Harris,2 and Keith F. Watts3

ABSTRACT

The Lisburne Group (chiefly Carboniferous) is a wide-
spread succession of platform carbonate rocks that appar-
ently developed along a south-facing passive continental
margin in northern Alaska. Marine transgressions onlapped
northward across northeast Alaska allowing the Lisburne
platform to extend over terrigenous deposits of the Endicott
Group and local pre-Mississippian paleotopographic highs.
The Wahoo Limestone is the youngest formation of the
Lisburne Group in northeasternmost Alaska, ranging from
latest Mississippian (latest Chesterian) to Middle Pennsyl-
vanian (at least early Atokan) in age. The Wahoo Limestone
was systematically sampled for lithostratigraphy and con—
odont biostratigraphy and biofacies at a relatively continu-
ous section (about 262 m in thickness) in the eastern
Sadlerochit Mountains.

Existing Carboniferous conodont zonations could not
be readily applied to the study section because most zonal
indicators are absent. Species diversity is low for a section
that spans at least 10 million years. Twenty-four species,
distributed among 14 genera, were identified in 72 produc-
tive samples; no new species were distinguished. The fol-
lowing biostratigraphic zones and fauna] intervals were
recognized: Upper muricams Subzone (latest Chesterian);
noduliferus—primus Zone (earliest Morrowan); minutus
Fauna (Morrowan) containing a lower subdivision (lower
minutus Fauna of early to middle? Morrowan age); and an
Idiognathodus Fauna (Morrowan? to early Atokan). The
presence of Idiognathoa'us incurvus? and Rhachistognathus
minutus subspp. above the first occurrence of the foramini-
fer Pseudostafiella sp. in the uppermost part of the Wahoo
Limestone indicates that the youngest beds are early Atokan
in age. The Mississippian-Pennsylvanian boundary is

1Department of Geology and Geophysics and Geophysical Institute,
University of Alaska Fairbanks, Fairbanks, AK 99775.

2us. Geological Survey.

3Geophysical Institute. University of Alaska Fairbanks, Fairbanks,
AK 99775.

placed at 56 m above the base of the lower member of the
Wahoo Limestone on the basis of the lowest occurrence of
Declinognathodus noduliferus japonicus above forms tran-
sitional from Gnarhodus girtyi simplex.

Established foraminiferan biostratigraphy is somewhat
inconsistent with respect to conodont-based time—rock
boundaries and conodont zones in the study section and in
northern Alaska in general. This indicates that the standard
foraminiferan and (or) conodont zonations are not locally
applicable without modification.

Conodont collections from the Wahoo Limestone
across the northeast Brooks Range (from Wahoo Lake to the
Clarence River) show remarkably similar faunal succes-
sions but even less species diversity than that found in the
study section. Fifty-six biostratigraphically significant col—
lections documenting the distribution of faunal units recog—
nized in the study section are described in appendix 1.

The Wahoo Limestone formed in a range of chiefly
open-platform, near-shoal, and open-marine environments
on the shallow, inner part of a high—energy carbonate ramp.
In the uppermost Mississippian and lowermost Pennsylva-
nian part of the formation, shoal facies were uncommon so
that open-platform and open-marine microlithofacies and
conodont biofacies were not clearly separated. Grain types
and, to a lesser extent, conodonts were hydraulically spread
beyond their original settings making some paleoenviron-
mental interpretations equivocal. The use of conodont bio-
facies and microlithofacies in concert clarifies some of the
environmental ambiguities. In the Pennsylvanian part of the
Wahoo Limestone, extensive ooid and skeletal shoal tracts
separated open-marine and open—platform environments
producing more distinct biofacies and diagnostic microli-
thofacies. Rhachistognathids thrived in and adjacent to the
shoal facies. After death, many of their skeletal elements
remained in place; however, a substantial number were
washed into surrounding environments, masking natural
species associations. Similarly, mixing of carbonate grains
obscures microlithofacies interpretations. The vertical suc-
cession of conodont biofacies substantiates microlithofacies
interpretations that indicate that the upper part of the Wahoo

2 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

Limestone represents a transgressive—regressive sequence
passing from restricted platform to shoals and, finally, back
to restricted platform. Conodont species associations,
abraded conodonts and bioclasts, and grain-type associa-
tions indicate a high degree of postmortem hydraulic
mixing across the carbonate platform supporting the inter-
pretation that it represents a high-energy carbonate ramp.

Conodont color alteration indices (CAI) in the study
section are chiefly 4 and 6, rarely 3, and very rarely 3.5 and
4.5. Most conodont elements have a sugary and (or) cor-
roded texture. The anomalously high CAI values of 6 have
positive correlation with grainstones and dolomitized inter-
vals and negative correlation with quartz-rich and poorly
washed carbonate rocks. The range of CAI values and tex—
tures and the distribution of high CAI values suggest local,
probably low-temperature hydrothermal alteration of the
Wahoo Limestone.

INTRODUCTION

The Lisburne Group (chiefly Carboniferous) is a thick
sequence of predominantly carbonate rocks that extends
across the Brooks Range and into the subsurface of the
North Slope (fig. 1). In the northeast Brooks Range, the Lis—
burne Group is at least 500 m thick and is subdivided into
the Alapah Limestone and overlying Wahoo Limestone.
The northeast Brooks Range is the area east of the
Trans-Alaska Pipeline and north of the Continental Divide,
which trends east-northeast between lat 68° and 69° N. and
long 139° to 147° W.

The Wahoo Limestone in the eastern Sadlerochit
Mountains, Arctic National Wildlife Refuge (ANWR), was
measured and systematically sampled for conodonts, fora—
minifers, and microlithofacies (figs. 1, 2). The study section
is well exposed, contains some of the youngest beds of the
Wahoo Limestone in the area, and is similar to the Wahoo
Limestone in the subsurface at Prudhoe Bay (Reiser, 1970;
Armstrong and Mamet, 1974). It is accessible from Kakto—
vik, a major embarkation point for ANWR (fig. 1).

This study was undertaken to (1) establish a conodont
biostratigraphic framework for the Wahoo Limestone in
ANWR, (2) determine the position of the Mississippian-
Pennsylvanian boundary in the formation, (3) integrate con-
odont biofacies with microlithofacies studies (for example,
Armstrong, 1972; Armstrong and Mamet, 1977; Watts,
1990; Gruzlovic, 1991; Krumhardt, 1992), and (4) compare
conodont and foraminiferan biostratigraphic data. Previ-
ously, foraminifers provided the primary biostratigraphic
control for the Lisburne Group in ANWR. Inconsistent
assignment of foraminiferan zones and lithologic bound-
aries by previous researchers in our study area, however,
indicates unresolved stratigraphic problems (see fig. 8).
More recently, conodonts have been used to refine, confirm,
or as an alternative to foraminiferan age determinations
(>500 conodont collections from the Lisburne Group were

analyzed by AG. Harris from 1979 to 1994 and by Harris
and AP. Krumhardt from 1989 to 1994; published and
unpublished written communs.). Many of these samples
indicate that conodonts have greater biostratigraphic resolu-
tion than foraminifers in the uppermost Mississippian and
Lower Pennsylvanian part of the Lisburne Group. In addi-
tion, the conodont Declinognathodus noduliferus is the pri-
mary micropaleontologic indicator for the base of the
Pennsylvanian (Lane and Manger, 1985). Thus, conodonts
are the preferred microfossils for locating the mid-
Carboniferous (Mississippian—Pennsylvanian) boundary.

ACKNOWLEDGMENTS

We are grateful to many people and organizations for
their time, help, knowledge, and support during this study.
Much of this investigation was part of a Master’s thesis by
AP. Krumhardt at the University of Alaska Fairbanks
(Krumhardt, 1992). Krumhardt is indebted to the US Fish
and Wildlife Service and the helicopter pilots who provided
safe and timely transport throughout ANWR. Special
thanks are due Kurt (“Stretch”) Johnson, who wounded his
knees and destroyed several pairs of boots collecting and
hauling conodont samples. Her colleague, P.D. Gruzlovic,
provided invaluable advice on thin section interpretations.
Krumhardt acknowledges the aid of her advisors (exclusive
of co-authors), R.K. Crowder and RA. Gangloff. Funding
for Krumhardt and Watts was provided by (1) the Tectonics
and Sedimentation Research Group, University of Alaska
Fairbanks, from contributions by Amoco, ARCO Alaska,
ARCO Research, BP Alaska, Chevron, Conoco, Elf Aquita-
ine, Exxon, Japan National Oil Corporation, Marathon,
Mobil, Murphy, Phillips, Shell, Texaco, and UNOCAL,
(2) the US. Department of Energy (contract no. DE—AC22—
89BC14471), and (3) the University of Alaska Museum
Geist Fund to partly cover field and thin section expenses.
Watts also acknowledges partial support from the Petroleum
Research Fund, administered by the American Chemical
Society, and the Geophysical Institute and College of Natu-
ral Sciences of the University of Alaska Fairbanks.

Special thanks are extended to J.F. Baesemann, H.R.
Lane, and PL. Brenckle, Amoco Production Company,
Houston, Tex.; Sylvie Pinard, Geological Survey of Can—
ada; and RC. Grayson, Jr., Baylor University, Waco, Tex.,
for their expert consultation on conodont and Foraminifera
specimens. Many collections listed in the appendix were
submitted to us for conodont analysis by other investigators
identified in the appendix. We are indebted to them for
providing stratigraphically well—positioned samples that
yielded important data for our understanding of the bios-
tratigraphic and paleoenvironmental distribution of con-
odonts in the Lisburne Group. Particular thanks are
extended to S.K. Morgan and MK. Eckstein, University of
Alaska Fairbanks, for collecting many samples from their

INTRODUCTION

       

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4 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE
145° 30' w.
EXPLANATION
El Coastal-plain deposits (Quaternary to
Cretaceous)

Sedimentary rocks (Cretaceous to
Precambrian)--Mainly Permian to
Cretaceous sedimentary rocks and
subordinate pre-mid-Caboniferous
sedimentary, metamorphic, and
igneous rocks

Lisburne Group (Carboniferous)--

Carbonate rocks

— Contact

.A....L Thrust fault--Sawteeth on
upper plate

—¢—> Anticline--Showing plunge

. Measured section or

sample locality

o 10 MILES

 

 

0
$00 .
g ‘22“.
0 FOURTH
’33; RANGE
0»

 

    

10 KILOMETERS

Figure 2. Distribution of the Lisburne Group, major structural
features, and locations of study section (1A) and selected mea-
sured sections discussed in this report, northeast Brooks Range
(geology modified from Bader and Bird, 1986; see fig. 1 for
regional setting). Numbered localities refer to measured sections
and (or) conodont collection sites described in appendix 1. Let-
tered and some numbered localities are sections described by other

measured sections and providing us with microlithofacies
analyses of their samples. We are most grateful to J.A.
Dumoulin, US. Geological Survey; P.H. von Bitter, Royal
Ontario Museum and University of Toronto; L.M. Brown,
Lake Superior State University; and GD. Webster,
Washington State University for their heroic, timely, and
thorough reviews of the manuscript. This paper was consid-
erably improved by their technical reviews.

PREVIOUS STUDIES

Schrader (1902, p. 241) first used the name “Lisburne
formation” for limestone and shale exposed in the vicinity
of Anaktuvuk Pass in the central Brooks Range (fig. 1). The
regional extent and character of the formation were more
fully described by him in a later paper in which he states
that the Lisburne extends from Cape Lisburne to Anaktuvuk
Pass and eastward “nearly to the international boundary and

 
 
 
 
 
   
  
  

STUDY

SECTION
K
. E
Moo“ 5'5
69 KIKIKTAT E
MOUNTAIN g — 59° 30' N.
I

 

  
    

workers referred to in text: 18, Armstrong and co-workers (Arm-
strong and others, 1970; Armstrong, 1972; Armstrong and Mamet,
1975, 1977; Mamet and Armstrong, 1984; Wood and Armstrong,
1975); C, 18, and 1C, Carlson (1987); 2, Clough and Bakke (1986)
and Imm (1986); G, 6, and 7, Gruzlovic (1991); and 5, Morgan
(1992).

probably beyond it” (Schrader, 1904, p. 67). Subsequently,
in the central Brooks Range, Bowsher and Dutro (1957)
raised the Lisburne to group rank and subdivided it into two
new formations, the Wachsmuth Limestone and overlying
Alapah Limestone. Brosgé and others (1962) distinguished
a third and the youngest formation of the group, the Wahoo
Limestone, in the eastern Brooks Range.

Detailed regional biostratigraphic and microlithofacies
analyses of the Lisburne Group accompanied the expansion
of hydrocarbon exploration of the North Slope during the
1970’s. Armstrong and others (1970) first applied Mamet’s
Carboniferous foraminiferan zonation to the Lisburne
Group in the northeast Brooks Range. and, later, Armstrong
(1972) described the carbonate lithology, coral biostratigra-
phy, and paleoecology. Mamet and Armstrong (1972)
examined sections in the Franklin and Romanzof Moun-
tains (fig. 1) and later Armstrong and Mamet (1974) tied the
Lisburne Group in the subsurface at Prudhoe Bay to expo—
sures in ANWR. Wood and Armstrong (1975) described the

REGIONAL GEOLOGIC SETTING

diagenesis and stratigraphy of the Lisburne Group in the
Sadlerochit Mountains and adjacent areas while Armstrong
and Mamet (1975) extended their biostratigraphic studies to
other sections in the northeast Brooks Range. Ultimately,
Armstrong and Mamet (1977) produced a regional synthe-
sis of their investigations for the entire northern Brooks
Range. Armstrong and Mamet (1978) extended their work
to the Lisburne Group in the allochthonous thrust sheets in
the central and western Brooks Range. Mamet and Arm-
strong (1984) discussed the Mississippian—Pennsylvanian
boundary in the Sadlerochit, Franklin, and Romanzof
Mountains and placed the boundary at the contact between
the Alapah and Wahoo Limestones. A revised megafossil
‘zonation for the Carboniferous of the northern Brooks
Range and its relation to Mamet’s foraminiferan zonation is
given in Dutro (1987). As in Mamet and Armstrong (1984),
Dutro (1987) placed the Mississippian-Pennsylvanian
boundary at the contact between the Alapah and Wahoo
Limestones.

Since 1985, many reports have been produced on the
geology of ANWR by investigators at the University of
Alaska Fairbanks (for example, Crowder, 1990; Wallace
and Hanks, 1990; Watts, 1990). Of particular importance to
our study are reports on the depositional environments,
cyclicity, and diagenetic history of the Wahoo Limestone in
the eastern Sadlerochit Mountains and the stratigraphic evo-
lution and lateral facies changes of carbonate cycles
(parasequences) across the Lisburne Group carbonate plat-
form (fig. 2; Carlson, 1987; Gruzlovic, 1991). Additional
studies describing the geology of ANWR are included in
Bird and Magoon (1987), Tailleur and Weimer (1987), and
Grantz and others (1990).

REGIONAL GEOLOGIC SETTING

The parautochthonous rocks of northeastern Alaska
are part of the tectonically complex Arctic Alaska terrane
that also includes allochthonous thrust sheets of the south-
ern Brooks Range and the relatively little deformed autoch-
thonous rocks beneath the North Slope (fig. 1; Reiser, 1970;
Mull, 1982; Crowder, 1990). The rocks in the Arctic Alaska
terrane have been subdivided into the Franklinian, Ellesme-
rian, and Brookian tectono-depositional sequences (fig. 3;
Grantz and May, 1983; Bird and Molenaar, 1987; Hubbard
and others, 1987) using terminology established by Lerand
(1973) in the Canadian Arctic.

The Franklinian sequence in the northeast Brooks
Range includes Precambrian to Devonian sedimentary,
metamorphic, and igneous rocks. Erosion of these rocks fol-
lowing orogenic uplift during the middle Paleozoic pro-
duced a paleotopography that considerably influenced
subsequent depositional patterns and structural deformation
(Watts and others, 1988; Wallace and Hanks, 1990).

Mississippian to Lower Cretaceous sedimentary rocks
of the Ellesmerian sequence unconformably overlie the
Franklinian sequence (fig. 3). The Ellesmerian sequence
documents a long interval of sedimentation from a northerly
source onto a broadly subsiding, passive continental mar-
gin. In the Carboniferous part of the sequence, terrigenous
elastic sedimentary deposits of the Endicott Group (Missis-
sippian in age in the Sadlerochit Mountains) are succeeded
by carbonate-platform deposits of the Lisburne Group. A
major unconformity with a hiatus of about 40 my. separates
the Lisburne Group from the overlying terrigenous elastic
deposits of the Sadlerochit Group (Permian and Triassic)
(Crowder, 1990). The upper part of the Ellesmerian
sequence (Triassic to Lower Cretaceous) is dominated by
terrigenous shale of the Kingak Shale (primarily Jurassic)
with lesser amounts of sandstone and rare phosphatic lime-
stone and calcareous sandstone to siltstone of the Shublik
Formation (Triassic). This report concerns the Carbonifer-
ous part of the Ellesmerian sequence.

LISBURNE GROUP, NORTHEAST
BROOKS RANGE

The Lisburne Group (chiefly Carboniferous) is a thick
succession (>500 m) of platform-carbonate rocks that
apparently developed along a south-facing passive conti-
nental margin in northern Alaska (relative to present coordi-
nates). Marine transgressions onlapped northward across
northeast Alaska so that eventually the Lisburne platform
extended over much of Arctic Alaska. In most of the north-
east Brooks Range, the Lisburne Group gradationally over-
lies the fluvial to marginal—marine deposits of the Endicott
Group (fig. 4). In the Sadlerochit Mountains, however, the
pre-Mississippian rocks formed a paleotopographic high so
that the Endicott Group is thin or absent (Armstrong and
Mamet, 1975; Watts and others, 1988). Where the Endicott
Group is absent, the Lisburne Group rests with angular dis-
cordance on southward-dipping, pre-Mississippian rocks
(fig. 5); this relationship influenced the structural develop-
ment of northeastern Alaska (Wallace and Hanks, 1990).
South of the Sadlerochit Mountains, the Kayak Shale of the
Endicott Group provides a major detachment surface.
Because the Kayak Shale is absent or thin in the Sadlerochit
Mountains, Ellesmerian rocks (fig. 3) remained attached to
the underlying Franklinian rocks, and both deformed as a
unit (Wallace and Hanks, 1990). Thus, the Lisburne Group
here is parautochthonous and has undergone little north-
ward tectonic transport.

In the northeast Brooks Range, the Lisburne Group
consists of the Alapah Limestone and Wahoo Limestone.
Three large-scale transgressiveregressive (TR) sequences
are recognized in these strata (fig. 4; Gruzlovic, 1991).
Superimposed on these large-scale sequences are many
parasequences of variable thickness that record the response

CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EXPLANATION

 

Conglomerate

   

sandSt ne

  

SIItstone

 

E

Limestone

Sandy limestone

Q

Dolostone

 

Igneous rocks,
undivided

 

Metamorphic rocks,
undivided

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UJ
o
E
3 STRATIGRAPHIC UNIT LITHOLOGY AGE
8
(I)
SURFiCIAL DEPOSITS HOLOCENE
GUBIK FORMATION PLEISTOCENE
PLIOCENE
SAGAVANIRKTOK MIOCENE
FORMATION
<2: ________
i OLIGOCENE
8
II EOCENE
In
CANNING FORMATION PALEOCENE
LATE CRETACEOUS
HUE SHALE ________
PEBBLE SHALE UNIT EARLY CRETACEOUS
KEMIK SANDSTONE
EARLY CRETACEOUS(?)
KINGAK SHALE AND
JURASSIC
Z KAREN CREEK SANDSTONE
< SHUBLIK FORMATION
E I:
”g LI) 0. TRIASSIc
m g 8 |V|SHAK FORMATION
u.I Lu I:
j a 6
Lu 5, ECHOOKA FORMATION PERMIAN
E35 WAHOO LIMESTONE PENNSYLVANIAN
: O
m II
<2 <5 ALAPAH LIMESTONE
-' MISSISSIPPIAN
ENDICOTT ITKILYARIAK FORMATION _.
GROUP KEKIK‘FSIIQIOSECOEAERATE '-'
<2: MOUNT COPLESTON LIMESTONE
2 NANOOK LIMESTONE
g KATAKTURUK DOLOMITE PRE—MISSISSIPPIAN
<2); SEDIMENTARY, METAMORPHIC, AND :
E IGNEOUS ROCKS, UNDIVIDED

 

 

 

 

Contact or boundary--
Dashed where approxi-
mately located

Figure 3. Generalized stratigraphic succession, northeast Brooks Range and northeast coastal plain, Alaska (not to scale;
modified from Bird and Molenaar, 1987).

REGIONAL GEOLOGIC SETTING 7

of the platform to eustacy and (or) changes in carbonate
production and platform subsidence (fig. 4: Watts, 1990;
Gruzlovic, 1991). The Endicott Group (where present) and
the Alapah Limestone represent the first large-scale TR
sequence. The remaining TR sequences generally corre-
spond to the lower and upper members of the Wahoo
Limestone.

ALAPAH LIMESTONE

The age of the Alapah Limestone (~200 to >500 m in
thickness) is Meramecian and (or) Chesterian on the basis
of foraminiferan (Armstrong and others, 1970; Armstrong
and Mamet, 1977) and conodont biostratigraphy (this
report). In the Sadlerochit Mountains, Alapah deposition
began in the Chesterian (Mamet and Armstrong, 1984). The
age of the base of the Lisburne Group is progressively older
southward and westward. In the northern part of the north-
east Brooks Range, continued transgression during much of
the deposition of the Alapah Limestone is indicated by a
transition from algal limestone into cross-stratified skeletal
grainstone culminating in bryozoan-pelmatozoan limestone.
The upper member of the Alapah Limestone is dominantly
spiculitic dolostone and dolomitic lime mudstone-
wackestone containing lesser amounts of cryptalgal
laminite (fig. 4: Watts, 1990; Gruzlovic, 1991) indicating
restricted and (or) peritidal conditions associated with a
major regression. The uppermost part of the Alapah Lime—
stone is late Chesterian in age (Armstrong and Mamet,
1977; this report). The contact with the overlying Wahoo
Limestone is relatively sharp in the study area but is more
gradational and difficult to define farther to the south.

ALAPAH LIMESTONE-WAHOO LIMESTONE
BOUNDARY, NORTHEAST BROOKS RANGE

The base of the Wahoo Limestone is placed at the first
light-weathering, cliff-forming, fossiliferous limestone
above the slope-forming, darker limestone and dolostone
characteristic of the underlying Alapah Limestone (fig. 5).
A similar contact was chosen by Brosgé and others (1962),
Armstrong (1972, 1974), Wood and Armstrong (1975), and
Carlson (1987). Other authors were inconsistent in their
placement of the contact (see fig. 8) and used biostrati-
graphic rather than lithostratigraphic criteria so that their
contact approximated the Mississippian-Pennsylvanian
boundary (Armstrong and others, 1970; Armstrong and
Mamet, 1974, 1975, and 1977; and Mamet and Armstrong,
1984).

WAHOO LIMESTONE

The age of the Wahoo Limestone (O to >350 m in
thickness) is late Chesterian to Atokan on the basis of fora-

minifers (Armstrong, 1972, 1974; Wood and Armstrong,
1975; Carlson, 1987) and conodont biostratigraphy (this
report). Brosge’ and others (1962) named the Wahoo Lime—
stone and subdivided it into lower and upper members at its
type section near Wahoo Lake (fig. 1). They assigned the
formation a Pennsylvanian(?) and Permian age on the basis
of brachiopod-bryozoan assemblages in the basal part of the
lower member and brachiopods in the uppermost part of the
upper member. Our conodont collections from the forma-
tion, 1.5 km west of the type section, show that the lower
member is within the late Chesterian muricatus Zone at its
base, and the appearance of Adetognathus [autus 15 m
higher indicates the Upper muricatus Subzone (app. 1, locs.
4Ala, b). The first definitive Pennsylvanian strata are
marked by the appearance of Declinognathodus nodu—
liferus, the guide to the Pennsylvanian, at 155 m above the
base of the lower member (app. 1, loc. 4A1d). The youngest
bona fide Wahoo Limestone at the type locality is Mor-
rowan to early Atokan in age (Watts and others, 1992; app.
1, loc. 4E). At its type locality, Watts and others (1989)
referred the calcareous beds of Permian age to the Echooka
Formation in their examination of the upper member of the
Wahoo Limestone. A collection from 4.5 m below the top of
the formation, about 5 km west of the type section, helps
constrain the age of the uppermost beds to the late Mor-
rowan or early Atokan (app. 1, loc. 4D).

Grainstone makes up two-thirds of the Wahoo Lime-
stone at the study section indicating deposition under domi-
nantly high-energy conditions. We recognize two mappable
members of the Wahoo Limestone: light-gray, massive,
cliff-forming grainstone and packstone of the lower mem-
ber overlain by the heterolithic upper member that forms
ledge-and-slope topography. The lower member represents
a large-scale TR sequence (fig. 4) consisting primarily of
bryozoan-pelmatozoan grainstone and packstone that prob—
ably formed in an open-marine environment. Four to five
parasequences (each 10—20 m in thickness) are recognized
within the lower member (fig. 4; Carlson, 1987; Watts,
1990; Gruzlovic, 1991); these probably formed in slightly
deeper water than those of the upper member. Parase-
quences in the lower member are more difficult to distin-
guish in the field because they lack the marked lithologic
contrasts characteristic of the upper member; parasequences
of the lower member are best recognized by microlithofa-
cies analysis.

In the eastern Sadlerochit Mountains, the contact
between the lower and upper members of the Wahoo Lime-
stone appears to be planar but locally has erosional relief
(Carlson, 1987; Krumhardt and Harris, 1990). Farther to the
southwest, in the Fourth Range and at Plunge Creek (fig. 2),
this contact is gradational (Gruzlovic, 1991).

Most of the upper member of the Wahoo Limestone
represents a TR sequence containing many parasequences
(each 3—9 m thick) related to relative sea-level changes and
the migration of ooid shoals. The ooid shoals formed a

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE
DEPOSITIONAL
E % ENVIRONMENT
.. O STRATIGRAPHIC LITHOLOGY DESCRIPTION HAT- OPEN
9 03 UNIT FORM MARINE
< ”J 3% BASE
Q . . Q 5 0c:
8 i: IVishak Formation I- E E; _l m g
s I Quartzose sandstone and shale '1 ,_ Z :2 < > o
woe (part) “Jr/)LUEOOJ
i— o I) '— Lu 0. E0 I 03 LL]
? E 9: Z n: O 3 m < m
g 5' (5 EChOOka S'Itstone and la con'tic sandstone
- l u l .
35 5 Formation g Clastic shelf
0' wJWA-We ”'33:? ' MWGHéQ—flx/“V
Z Oncolitic and peloid <>
it ackstone and rainstone —=‘
z p g Cyclical, \
< Ooid and (or) Donezella alternating <>"
3 upper packstone and grainstone with \\
(>5 Wahoo member Ooid grainstone tart/0:03“- ‘\>
. T LU pe ma ozoan
E D. leeStone J: Cryptalgal and (or) limestone 3
UJ 8 . dolomitized mudstone .<;>
n. ,.
— 0: lower Bryozoan-pelmatozoan grainstone and <
8 member packstone
E u er Spiculitic dolostone and dolomitic
3 meprgber lime mudstone-wackestone,
m ' ' \\~ __
(L) cryptalgal laminite F.
_i
. ap middle “Mme” m Bryozoan-pelmatozoan limestone
<2: Limestone member /
-<
_ ; 3; Cyclical, crossbedded, skeletal grainstone ‘ x
D.
0_ lower E alternating with peloidal skeletal packstone. ‘
(7) member 'r Algal limestone and spiculitic dolostone and <\
(D limestone in lower part \>
(7) CL ltkilyariak .
(2 3 Formation Sandy limestone
E Q
g Fluvial
|_ Black shale, containing some sandstone to
l— Kayak Shale and limestone marginal
0 marine
9
D .
Z Keklktuk Quartzose sandstone and con lomerate
L” Conglomerate g
i WWW
Z Mount Cop eston Limestone
E Nanook Limestone
u-J g: ' Sedimentary, metamorphic, and igneous Variously deformed,
E a Katakturuk Dolomite rocks relatively south-dipping
(7) rocks
(—1-) Sedimentary, metamorphic, L,
E and igneous rocks, undivided

 

 

 

 

 

 

 

Figure 4. Stratigraphic relationships, lithologies, and inferred
depositional environments of the Lisburne Group, northeast
Brooks Range. At the study section, the Endicott Group is absent,

and the Alapah Limestone rests with angular discordance on

pre~Mississippian rocks (fig. 5). Only the Wahoo Limestone was
systematically analyzed for this study. See fig. 3 for explanation.
(Modified from Carlson, 1987; Watts, 1990; and Gruzlovic, 1991.)

LITHOSTRATIGRAPHY OF THE WAHOO LIMESTONE, EASTERN SADLEROCHIT MOUNTAINS 9

 

Figure 5. View of study section looking northeast, eastern Sadlerochit Mountains (see fig. 2 for location). Measured section follows
ridgeline and includes upper 3 m of the Alapah Limestone, the entire Wahoo Limestone, and lower 1 m of the Echooka Formation. Note
that the Endicott Group is absent and a marked angular unconformity separates the Alapah from underlying pre—Mississippian rocks.

broad, discontinuous belt trending westward from the north-
ern British Mountains, near the Canadian border, to the
Canning River and then possibly northwestward toward
Prudhoe Bay (fig. 1). The shoals pinch out southwestward,
down the depositional dip of the carbonate ramp
(Gruzlovic, 1991). The lithology of the upper member var-
ies vertically and laterally as a consequence of ooid shoal
migration through time (Carlson, 1987; Watts, 1990;
Gruzlovic, 1991).

A disconformity of considerable magnitude (~40 m.y.)
separates the Lisburne Group from the overlying Echooka
Formation of Permian age (fig. 4). Regionally, this discon—
formity is an irregular surface having as much as 200 m of
section removed by erosion locally and as much as 20 m of
local erosional relief (Crowder, 1990). The contact between
the Lisburne Group and Echooka Formation is typically
planar; carbonate rocks of the Lisburne Group are overlain
by terrigenous siltstone, shale, and (or) glauconitic quart-
zose sandstone of the Echooka Formation (Crowder, 1990).
Locally, erosional relief is most apparent beneath channel-
ized conglomerates in the basal part of the Echooka Forma-
tion. Clasts in the conglomerates include limestone and
chert derived from the Lisburne Group providing additional

evidence of erosion. Even though the Lisburne Group plat-
form was subaerially exposed, karst features are rare (Carl-
son, 1990; Watts, 1990; Watts and others, 1992). Erosion
along the disconformity produced some of the variation in
thickness of the Wahoo Limestone and significantly influ-
enced the age of the uppermost part of the formation. At the
study section, the formation is not as thick as at the type
section (262 m versus >330 m in thickness), but the upper—
most part of the formation is as young as or younger than
the highest beds at and near the type section (app. 1, locs.
4E, D). In some areas, such as near the Trans-Alaska Pipe—
line (fig. 1), the upper part of the Lisburne Group is no
younger than latest Mississippian (Watts, 1991).

LITHOSTRATIGRAPHY OF
THE WAHOO LIMESTONE,
EASTERN SADLEROCHIT MOUNTAINS

The study section is near the eastern limit of outcrops
of the Wahoo Limestone in the Sadlerochit Mountains (fig.
2). The base of the section is in the SE1/4SW1/4 sec. 5, T. 3
N., R. 31 E. (lat 69°38‘24" N., long 144°34‘45" W.), and the

10 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

top is in the center NW1/4 sec. 8, T. 3 N., R. 31 E. (lat
69°38'03" N., long 144°34'45" W.), Mt. Michelson C-1
quadrangle. This section was chosen because of (1) accessi—
bility by helicopter (65 km southwest of Kaktovik; fig. 1),
(2) proximity to measured sections described by previous
workers (Armstrong and others, 1970; Wood and Arm—
strong, 1975; and Carlson, 1987) that were less accessible
for conodont sampling, (3) excellent exposures of the
Wahoo Limestone (95 percent) and its boundaries (fig. 5),
and, in particular, (4) the relatively thick interval of upper
Morrowan and Atokan strata.

Our measured section includes the upper 3 m of the
Alapah Limestone, the entire Wahoo Limestone (262 m),
and the basal 1 m of the succeeding Echooka Formation (pl.
6). The lower 3 m of the Wahoo Limestone is massive—
bedded dolomitized bryozoan packstone that overlies a
0.5—m—thick interval of light-gray, fenestral, dolomitic mud-
stone at the top of the Alapah Limestone. The lower and
upper members of the Wahoo Limestone are readily distin-
guished; their boundary is placed at the change from
cliff-forming, light—gray packstone below to orange-
weathering, silty, cryptalgal(?) dolostone above (fig. 5). The
contact with the overlying Echooka Formation forms a
rubble-covered dip slope, but only a few meters of section
are concealed. The section was systematically sampled for
microlithofacies at 2-m intervals. Additional samples were
taken to document obvious lithologic changes and at all
conodont sample sites (table 1; pl. 6).

LOWER MEMBER OF THE WAHOO LIMESTONE

The lower member (Mississippian and Pennsylvanian)
of the Wahoo Limestone is 70 m thick and is chiefly
bryozoan—pelmatozoan grainstone and packstone. Rare beds
of wackestone and skeletal packstone occur particularly in
the basal part of the lower member and near the
Mississippian-Pennsylvanian boundary and contain minor
sponge spicules. Peloids, including completely micritized
bioclasts, are a common constituent of the lower member
and become abundant near the boundary. An interval of
oolitic grainstone, 62 to 64 m above the base of the lower
member, is the lowest occurrence of a lithology that typifies
the upper member. Dark-gray replacement chert nodules are
common throughout (pl. 6).

The lower member of the Wahoo Limestone formed on
a predominantly open—marine platform that developed
above restricted-platform carbonate deposits of the upper
part of the Alapah Limestone (see fig. 9). Muddy and spicu—
litic limestone in the lower several meters of the Wahoo
Limestone formed in partly restricted conditions during the
early phase of a major transgression. The upper 25 m of the
lower member primarily formed in normal-marine condi-
tions, but common to abundant peloids and minor spicules
suggest intermittent restriction; locally abundant ooids

imply proximity to shoals. These grain types indicate the
onset of regression.

Just below the Mississippian-Pennsylvanian bound-
ary, at 56 m above the base of the lower member of the
Wahoo Limestone, a distinct interval of peloidal-spiculitic
wackestone is partly replaced by reddish-brown and gray
nodular chert. This chert-bearing interval has variable thick-
ness (<0.5 to 1 m), sharp lower and upper contacts, and
appears to have been deposited above an irregular surface
with as much as 1 m of relief (fig. 6). The surface has been
interpreted to have formed during subaerial exposure (Carl-
son, 1990; Watts, 1990). The chert-bearing interval overlies
a skeletal grainstone that contains definitive Mississippian
conodonts within 10 cm of the contact and, in turn, is over-
lain by a peloidal-skeletal grainstone, the base of which pro-
duced the lowest definitive Pennsylvanian conodonts in the
study section (fig. 6). The chert—bearing interval was traced
1 km west to Carlson’s (1987) section where Declinogna-
thodus noduliferus japonicus, an index to the Pennsylva-
nian, occurs 1.5 m below the chert (app. 1, 100. lBlb),
suggesting at least 1.5 m of erosion at the study section.

A comparable chert-rich interval was noted in Lower
Pennsylvanian rocks (based on foraminiferan biostratigra-
phy) in the western Sadlerochit Mountains (Clough and
Bakke, 1986; Imm, 1986). Correlation of this interval with
the eastern Sadlerochit Mountains, however, has not been
verified with conodonts. A chert-rich interval has not been
noted in a similar stratigraphic position in sections to the
south or east.

The contact between the lower and upper members of
the Wahoo Limestone appears planar. Redeposited, latest
Mississippian conodonts occur sporadically in the Pennsyl-
vanian part of the lower member and increase in abundance
a meter below the contact with the upper member (table 1).
The redeposited conodonts indicate intermittent reworking
of slightly older deposits of the Wahoo Limestone.

UPPER MEMBER OF THE WAHOO LIMESTONE

The upper member of the Wahoo Limestone is 192 m
thick at the study section and contains many shallowing-
upward parasequences. These parasequences are superim-
posed on a major TR sequence.

The lower 24 m of the upper member is dominated by
peloidal-bryozoan packstone, dolomitized silty mudstone,
and wackestone. Cryptalgal laminites are poorly developed
in the study section but are present in nearby exposures.
Shallowing-upward parasequences in this interval begin
with peloidal-bryozoan packstone (minor grainstone) and
pass upward into dolomitized, silty, locally spiculitic, lime
mudstone. Detrital quartz is relatively abundant (as much as
40 percent), particularly in dolomitic mudstone. Signifi—
cantly, quartz sand increases from 3 to 4.5 percent in the
upper meter of the lower member and then abruptly rises to

LITI-IOSTRATIGRAPHY OF THE WAHOO LIMESTONE, EASTERN SADLEROCHIT MOUNTAINS 1 1

Figure 6. Mississippian-Pennsylvanian boundary beds in upper
part of lower member of the Wahoo Limestone at the study section
showing the distinct reddish-brown and gray, nodular chert-bear—
ing interval (arrows mark its top and bottom). Thickness of beds
shown is approximately 4 m. Conodont samples at locations A—D.
Sample A, 53 m above base of the Wahoo (table 1, USGS colln.
30757—PC), contains Gnathodus girtyi girtyi, G. g. simplex, and
forms transitional t0 Declinognathoa'us spp. as well as
G. bilineatus bilinealus, Hindeodus minutus, Vogelgnathus post-
campbelli, and Kladognathus sp. Sample B, 54.9 m above base of
formation (table 1, USGS colln. 31698—PC), contains Mississip-
pian species including G. g. girtyi, Kladognathus spp., and
Lochriea commutata as well as subadult Pa elements of G. g. sim-
plex transitional to D. noduliferusjaponicus and abundant Cavusg-

an average of 12 percent in the lower 20 m of the upper
member (percent quartz determined from acid-insoluble
residues of conodont samples). This sudden increase of ter-
rigenous sediment at and above the lower member-upper
member contact suggests considerable regression and some
exposure of the Wahoo platform. Indeed, exposure surfaces
in the lower part of the upper member and local channeliza—

 

nut/ms? tytlhus of Mississippian and Pennsylvanian age. Sample
C, 55.5 m above the base and within the cherty interval (table 1,
USGS colln. 31699—PC), produced only a few conodonts, chiefly
C? tytthus of Mississippian and Pennsylvanian age. In sample D,
56 m above base of formation, D. n. japonicus (pl. 3, figs. 4—8), an
index to the Pennsylvanian, occurs with several other species
known to range across the Mississippian-Pennsylvanian boundary
(table 1, USGS collns. 30758—PC and 31700—PC). Collections 1
km to the west yielded Pennsylvanian conodonts 1.5 m below
reddish-brown and gray chert-bearing interval suggesting that the
irregular surface at base of chert is a disconformity that probably
marks the Mississippian—Pennsylvanian boundary at the study sec-
tion.

tion of cryptalgal laminites at the lower member—upper
member contact have been described in the eastern Sadlero-
chit Mountains here and 1 km to the west (Carlson, 1987,
1990; Watts, 1991). In addition, relatively few conodonts
and foraminifers are found in this part of the upper member,
possibly due to inhospitable environmental conditions.
The lower 24 m of the upper member formed on a

12 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

predominantly restricted platform during a major regression
and contain some of the shallowest water deposits in the
Wahoo Limestone (Gruzlovic, 1991).

The succeeding 120 m of the upper member of the
Wahoo Limestone are characterized by oolitic grainstones,
particularly the upper part of the member (pl. 6). Bioclasts
and peloids are common and grapestone lumps, intraclasts,
and Archaeolithophyllum sp. (algae) are rare to minor in
these high-energy grainstones and associated packstones.
Oncolites are most common in the lower part of this interval
whereas Donezella sp. (algae) occur in the upper part, first
appearing at 167 m above the base of the Wahoo (P.L.
Brenckle, written commun., 1991) suggesting some envi-
ronmental restriction up section. Shallowing—upward
parasequences typically begin with dolomitic bryozoan
wackestone and pass upward into dominantly skeletal and
oolitic grainstone that may be capped by dolomitized,
locally spiculitic, lime mudstone. Repeated intervals of
oolitic grainstone represent migration of shoals across the
Wahoo platform. Oncoids, peloids, grapestone lumps, and
algae indicate that open-platform depositional environ-
ments developed shoreward of the shoals. Rare, isolated
colonial and solitary corals also occur and are locally asso-
ciated with spiculitic mudstone and peloids that suggest
proximity to partly restricted conditions. The abundant
ooid-shoal deposits in the upper part of this interval corre-
spond with the maximum transgression during deposition of
the upper member of the Wahoo (Watts, 1990; Gruzlovic,
1991).

The upper 48 m of the upper member of the Wahoo
Limestone are chiefly peloidal-oncolitic and bryozoan-
pelmatozoan packstone and grainstone (pl. 6). Ooids and
superficial ooids occur in the lower part of the member, rep-
resenting the last ooid-shoal deposits of the Wahoo.
Peloidal-spiculitic-oncolitic wackestone and spiculitic mud—
stone become prevalent approximately 13 m below the top
of the formation, marking a shift from primarily open-
platform to restricted—platform environments.

Persistent sea—level fluctuations during deposition of
the Wahoo Limestone produced a mosaic of shifting envi—
ronments that controlled biotic distribution. Conodont and
foraminiferan biofacies (species associations) reflect these
environmental changes. Biofacies, as well as postmortem
transport of skeletal remains, controlled the occurrence of
biostratigraphically significant species and, ultimately, the
biozonation of the Wahoo Limestone.

CONODONT BIOSTRATIGRAPHY OF
THE WAHOO LIMESTONE,
EASTERN SADLEROCHIT MOUNTAINS

The conodont zonation proposed by Lane and Straka
(1974) and subsequently revised by Lane (1977) and Baese-
mann and Lane (1985) for uppermost Mississippian and

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

STUDY SECTION CONODONT
CONODONT ZONATION
SYSTEM SERIES F%RE“:AAJégN/ ZONE/ (Baesemann
FAUNA and Lane,1985)
ECHOOKA
PERM'AN FORMATION
wmwmmez m)W‘\/W
First appearance Unzoned
ATOKAN of ldiognathodus \
Z ,
< Incurvus’? Idiognathoides
(246 m)
<2: 5 ouach/Iensis
g l—
< . ' '
g D: Id/ognathodus ld/ognathOIdes
a: LU convexus
0 g E Fauna
Z 2 9 C0 ldiognathadus
S E E 2 k/apperi
Z O. o g
< “-V ”J Id' m d
> Do 2 II (177 m) ’09“ ° “5
i <2: 0 Bi smuosus
g ('7) n_ Y First appearance N rh d
2 LL! 3 of Pseudostafie/la eogna 0. us
LIJ E w (171 m) bass/en
CL 3 c (162 m,
<2: 0 a Neognathodus
; g “0-) lower symmetricus
: .
8 < ‘5 minutus Idiognathoides
I g .5 Fauna Siriuatus-
E RhachIstognathus
CE) (84 m‘ minutus
nlodu/I'ferus Dec/ingglnfathodus
' I70 UI erus—
primus Zone Hhachistognarhus
CE \ pr/mus
2 E UJ (56 I“!
< <2: E tn (First appearance
E _ A E of G. buI/oides U
a. CC I— O L” (43 m) ‘pper
a M [I —' 2 Hhachrstognarhus
(I) 5 at Upper muricatus
(7, I:.IEJ v ALAPAH (0 m) muricatus Subzone
<2 0 LIMESTONE Subzone
2 (PART)

 

 

 

 

 

 

Figure 7. Conodont zonation/fauna] succession recognized in
the Wahoo Limestone at study section compared to the North
American middle Carboniferous conodont zonation of Baesemann
and Lane (1985). Zonal indicators of Baesemann and Lane not
found at study section include Neognathodus symmetricus, N.
bassleri, Idiognathodus klapperi, and ldiognathoides convexus.
Declinognathodus noduliferus first appears 13 m above Globival-
vulina bulloides, the foraminiferan secondary guide to the mid-
Carboniferous boundary (Lane and Manger, 1985). See figure 6
and table 1 for detailed information on the Mississippian-
Pennsylvanian boundary. Idiognathodus sinuosus first appears 6 m
above Pseudostafi‘ella sp., a foraminiferan guide to the Morrowan-
Atokan boundary in the Midcontinent and Cordillera of the conter-
minous United States (Lane and Manger. 1985; Groves, 1986).
The Morrowan—Atokan boundary is poorly constrained by con-
odonts and foraminifers. The foraminifer Pseudostaflella sp.
appears well below the lowest definitive Atokan conodont, [diag-
nathodus incurvus? (table 1). G, Glabivalvulina.

Pennsylvanian (Morrowan) rocks in North America only
applies to the conodont succession in the upper part of the
Alapah Limestone and the succeeding 84 m of the Wahoo
Limestone (fig. 7). The Upper muricatus Subzone (upper-
most Mississippian). the noduliferus-primus Zone (lower-
most Pennsylvanian), and the lower part of the succeeding

CONODONT BIOSTRATIGRAPHY OF THE WAHOO LIMESTONE, EASTERN SADLEROCHIT MOUNTAINS l3

minums Fauna (= sinuarus-minutus and symmetricus Zones
of Baesemann and Lane, 1985) are well documented in this
part of the section (table 1 and pl. 6). The remaining Penn—
sylvanian strata, however, could not be precisely dated by
using existing conodont zonal schemes (for example,
Baesemann and Lane, 1985; Grayson, 1990) because of a
persistent, chiefly rhachistognathid biofacies (high-energy,
shoal to near-shoal environments) in which most zonal indi—
cators are rare or absent. We have, instead, used a faunal
designation for this part of the Wahoo Limestone based on
possible local ranges of some rhachistognathids and what is
almost certainly a relatively late migration of Idiognathodus
into northeast Alaska. Some of the rhachistognathids that
appear before or originate in the lower 84 m of the Wahoo
Limestone disappear before the lowest occurrence of Idio—
gnathodus in the northeast Brooks Range; other rhachisto-
gnathids persist to the major unconformity that truncates the
formation (pl. 6). Rare, sporadic occurrences of generally
poorly preserved, nonrhachistognathid species are not origi-
nations but are clearly the result of postmortem hydraulic
admixture from other biofacies and can be used to roughly
tie the northeast Alaskan succession to successions in other
parts of North America.

Species diversity is rather low for a section that spans
at least 10 million years, from the latest Chesterian to at
least early Atokan. Only 24 species, distributed among 14
genera, were identified in 72 productive samples. Further
complicating establishment of a reliable conodont succes—
sion for part of the Wahoo Limestone is the menace of rede-
position. Several samples from the post—Mississippian part
of the study section (table 1 and pl. 6), as well as many
other spot samples from the uppermost part of the Wahoo
Limestone in the northeast Brooks Range, produced rede-
posited Mississippian and earliest Pennsylvanian conodonts
that cast some doubt on the biostratigraphic integrity of spe—
cies distribution in the upper part of the formation.

The conodont zones of Baesemann and Lane (1985)
and the conodont faunal succession established in the
Wahoo Limestone and upper part of the Alapah Limestone
at the study section and elsewhere in the northeast Brooks
Range are described below.

MURICA TUS ZONE

The muricatus Zone is defined by the first appearance
of Rhachistognalhus muricatus below the occurrence of
either Declinognathodus noduliferus or R. primus (Lane
and Straka, 1974; Baesemann and Lane, 1985). Baesemann
and Lane (1985) proposed a phylogeny for the rhachistog-
nathids of the middle Carboniferous in which R. prolixus is
the inferred ancestor. They suggested that R. prolixus proba-
bly gave rise to R. muricatus after the appearance of
Adetognarhus unicornis (= Cavusgnathus monocerus
[Rexroad and Burton] of Brown and others, 1990) the name

bearer of the preceding conodont zone. Baesemann and
Lane (1985) subdivided the muricams Zone into lower and
upper subzones. The muricams Zone is the most widely rec-
ognized conodont zone in the Chesterian part of the
Lisburne Group in the northeast Brooks Range. It is repre-
sented by a very thick sequence that may include much of
the Alapah Limestone and part of the Wahoo Limestone and
is well documented in nine sections between Atigun River
gorge and the Clarence River (fig. 1; AG. Harris and AP.
Krumhardt, unpub. data). At and near the study section, the
muricams Zone is at least 155 m thick and ranges from
about 24 m above the base of the Alapah Limestone (app. 1,
loc. 1A2) to 55.5 m above the base of the Wahoo Limestone
(table 1, USGS colln. 30757—PC). It is apparently thickest
(250 m) in the Romanzof Mountains (app. 1, locs. 9B1a, b).
In the area of the type section of the Wahoo Limestone, the
upper 70 m of the Alapah Limestone and lower 140 m of
the overlying Wahoo Limestone are within the muricams
Zone (app. 1, locs. 4A1a, c).

LOWER MURICATUS SUBZONE

The Lower muricams Subzone is defined by the first
appearance of the zonal indicator below the occurrence of
Adetognathus laums. This subzone has not yet been identi-
fied at the study section or in our other collections from
northern Alaska but may be present in the Alapah Lime-
stone. As proposed (Baesemann and Lane, 1985), the sub—
zone can be identified only in closely sampled sections of
appropriate shallow—water, relatively normal-marine biofa-
cies. Virtually all common associates of this biofacies in the
Lower muricatus Subzone, with the possible exception of
Hindeodus cristulus (Youngquist and Miller), extend or
likely extend into the Upper muricams Subzone (table 1;
Weibel and Norby, 1992). Thus, the only guide to this zone
is the presence of A. [autus in definitive pre-Pennsylvanian
strata above the occurrence of Rhachistognathus muricatus
with H. cristulus.

UPPER MURICA TUS SUBZONE

This subzone is defined by the overlapping ranges of
Rhachistognathus muricalus and Adetognathus [aunts
below the appearance of Declinognathodus noduliferus or
R. primus. As yet, R. muricams has not been found in the
upper 64 m of the Alapah Limestone or the succeeding
lower 5 m of the Wahoo Limestone in the eastern Sadlero-
chit Mountains. Representatives of the species were recov—
ered 6 m above the base of the formation and well below D.
noduliferus (table 1). Adetognathus lautw. although not
found in the lower 84 m of the Wahoo Limestone, was
recovered from the Alapah Limestone at 72 and 65 m below
the base of the Wahoo Limestone at the study section (app.
I, locs. lAla, b). Thus, the Upper muricams Subzone is

l4 CONODONT BlOSTRATIGRAPHY AND BIOFACIES OF THE WAl-lOO LIMESTONE

present at a level considerably below the base of the Wahoo
Limestone and is at least 127 m thick (from 72 m below the
top of the Alapah Limestone to 56 m above the base of the
Wahoo Limestone).

Species that occur within the Upper muricatus Sub—
zone in the Alapah and Wahoo Limestones in the study sec—
tion include, in order of decreasing abundance,
Cavusgnatlms unicornis Youngquist and Miller, Klado—
grim/ms spp., Gnatlzodus girtyi simplex Dunn, G. g. girtyi
Hass, Hindeodus minutus (Ellison), Rhachistognathus
muricatus (Dunn), Vogelgnathus postcampbelli (Austin and
Husri), C.? tytthus Brown and Rexroad, G. bilineatus bilin-
eams (Roundy), Idioprioniodus spp., Adetognathus lautus
(Gunnell) (see app. 1, locs. lAla, b), Lochriea commutata
(Branson and Mehl), G. girtyi subspp. transitional to Decli-
nognathodus spp., C. altus Harris and Hollingsworth, R.
prolixus Baesemann and Lane?, and Gnathodus defectus
Dunn?.

Cavusgnathus monocerus (Rexroad and Burton), 3 rel—
atively common component of the R. muricams Zone as
well as the name bearer of the preceding conodont zone, is
notably absent in the Brooks Range.

The Upper muricatus Subzone is recognized in the
upper part of the Alapah Limestone and lower part of the
Wahoo Limestone in six sections (including the study sec—
tion) between Wahoo Lake and the Clarence River. The sub—
zone is thickest (at least 133 m) at Clarence River and
includes at least the upper 53 m of the Alapah Limestone
and the lower 80 m of the Wahoo Limestone (app. 1, locs.
10A1a-e) and at least 124.5 m near Wahoo Lake (app. 1,
locs. 4A1b, c). The only other species found in the subzone
in the northeast Brooks Range, but not in the study section,
is Rhachistognatlzus websteri Baesemann and Lane (app. 1,
loc. 4Alc).

NODULIFERUS-PRIMUS ZONE

Baesemann and Lane (1985) modified the primus
Zone of Lane and Straka (1974) to the noduliferus—primus
Zone, the lower boundary of which marks the base of the
Morrowan Series and the Pennsylvanian System. Whereas
Rhachistognathus primus has not been found outside of
North America, Declinognathodus noduliferus has a world-
wide distribution and has been recommended as the primary
micropaleontologic guide for the base of the Pennsylvanian
(Lane and Manger, 1985). The noduliferus-primus Zone is
recognized by the occurrence of either D. noduliferus or R.
primus below the appearance of R. minutus or Idiogna-
thaia’es sinuams Harris and Hollingsworth. The zone was
subdivided into lower and upper subzones by Brenckle and
others (1977). The lower subzone is characterized by “the
overlap in the upper ranges of Gnathodus girtyi simplex and
G. cf. G. bollandensis with the lower ranges of R. primus
and D. noduliferus” (Baesemann and Lane, 1985, p. 100).

We assume that G. cf. G. bollana'ensis of Baesemann and
Lane (1985) is G. bilineams bollandensis of other workers
or a form close to it. Gnat/iodus girtyi simplex has been
reported together with D. noduliferus in Nevada (Baese-
mann and Lane, 1985). In our study section, G. g. girtyi and
G. g. simplex occur relatively consistently in the lower
54.9m of the Wahoo Limestone, 1.1 m below the first
occurrence of D. noduliferus japonicus (table 1). Neither
subspecies has been recovered from the succeeding 10 m,
but 4 and 5 In higher G. g. girtyi reappears together with G.
b. bilineatus and Kladognathus spp. as well as other species
(table 1). We believe that these typical Mississippian forms
are redeposited. Significantly, Carlson (1987) reported
channelization at this level about 1 km to the west. It is pos—
sible that other Pennsylvanian occurrences of G. g. girtyi
are also redeposited, as shown for the Granite Mountain,
Utah section, by Wardlaw (1984). Gnathodus bilineams
bollandensis has not been recognized in the study section
and G. g. simplex does not occur in the noduliferus-primus
Zone here. Thus, we cannot recognize the subdivisions of
the noduliferus-primus Zone at the study section. Elsewhere
in the northeast Brooks Range, G. g. simplex is a rare, possi—
bly indigenous constituent of the noduliferus—primus Zone
(app. 1, locs. 5b, lBle).

Species that occur in the noduliferus-primus Zone in
the study section include, in order of decreasing abundance,
Cavusgnathus? tyttlms, Declinognatliodus noduliferus
japonicus (Igo and Koike), Rhachistognathus muricalus,
Hindeodus minutus, D. n. noduliferus (Ellison and Graves),
Vogelgnathus postcampbelli, Idioprioniodus conjunctus
(Gunnell)?, R. websteri, and Gnathodus girtyi subspp. tran-
sitional to Declinognathodus spp. Rhachistognathus primus
has not been identified in this zone in our section but has
been found elsewhere in the zone in the northeast Brooks
Range (app. 1, loc. 4B). Additional guides for the
noduliferus—primus Zone in the northeast Brooks Range are
Cavusgnathus? tytthus and Vogelgnathus postcampbelli
with or above D. noduliferus (table 1). Cavusgnathus? [yt-
thus extends to near the top of the zone, is common, and
appears to occupy the habitat of Adetognathus lawns, which
is notably absent in this zone in collections in the northeast
Brooks Range; V. postcampbelli has a similar range but is
rare in the study section. Only 1 km to the west, V. post-
campbelli is relatively abundant (app. 1, loc. lBlg). Other
species found in the zone in the northeast Brooks Range,
but not in the study section, are G. girtyi simplex (app. 1,
locs. 4B, 4A1d, 5a) and R. prolixus (app. 1, loc. 5a).

Beds 56 to 84 m above the base of the Wahoo Lime-
stone in the study section are representative of the
noduliferus-primus Zone (table 1). The zone is recognized
within the lower member of the formation in three other
sections, as far west as Wahoo Lake. These are (1) the Sun-
set Pass section (app. 1, locs. lBlb—g); (2) the Pogopuk
Creek section (app. 1, locs. 5a, b), where the zone is thickest
in the northeast Brooks Range (at least 80 m) and where the

CONODONT BIOSTRATIGRAPHY OF THE WAHOO LIMESTONE, EASTERN SADLEROCHIT MOUNTAINS 15

highest sample in the zone contains Gnarhodus girtyi sim-
plex suggesting a level presumably within the lower part of
the zone; and (3) in the vicinity of the type section near
Wahoo Lake (app. 1, locs. 4A1d, 4B).

MINUTUS FAUNA

Considerable controversy surrounds the time of origin
of Rhachistognathus minutus. Baesemann and Lane (1985)
proposed a phylogeny for rhachistognathids in which R.
minutus evolved from R. muricatus some time after the
appearance of R. primus and Declinognathodus noduliferus.
Lane and others (1985b) noted that Higgins (1975) reported
R. minutus below the first appearance of D. noduliferus in
the Craven basin, northern England. In order to explain the
succession of rhachistognathids in chiefly shallow-water
carbonate rocks of North America, a hiatus was inferred in
the Craven basin succession encompassing the interval of
the North American unicornis, muricatus, noduliferus-
primus, and most of the sinualus—minums Zones (Lane and
others, 1985b). However, Riley and others (1987) demon-
strated persuasively that R. minutus appears substantially
later in North America than in northern England. Manger
and Sutherland (1992) support the interpretation of Riley
and others (1987) in their comprehensive summary of this
controversy. We agree that the appearance of R. minutus in
many areas of North America is a migration event, so that
the lower boundary of the sinuams-minutus Zone (based on
R. minutus) is diachronous from England to North America.
Rhachistognathus minutus has a very short range in
England but is relatively long ranging and widespread in the
Cordillera of North America (including Alaska) where it is
most abundant in high-energy, shallow-water deposits.
According to Baesemann and Lane (1985), R. minums
extends into at least the lower Atokan.

We are introducing a minutus Fauna to identify the
local range of Rhachistognathus minutus subspp. below the
range of ldiognathodus spp. The lower boundary of this
fauna undoubtedly varies within the northeast Brooks
Range because its distribution is biofacies dependent. The
sinuams—minutus Zone of Baesemann and Lane (1985) is
not used because Idiognathoides sinuatus (as defined by
Grayson and others, 1990) was found in only a single sam-
ple high in the study section (table 1). Furthermore, the suc-
ceeding symmetricus Zone (as used by Lane and Straka,
1974) cannot be recognized because of the apparent
absence of the zonal indicator in the Brooks Range. In the
western Canada sedimentary basin of the Canadian Cordil-
lera, Higgins and others (1991) recognize a minutus Zone
that includes the sinuams—minutus and symmetricus Zones
of Baesemann and Lane (1985) because of the absence of
Idiognathoides sinuams and Neognathodus symmetricus in
their sections. The minutus Zone of western Canada con-
tains diverse rhachistognathids and is probably equivalent

to the lower part of our minums Fauna. Indeed, we recog—
nize a lower subdivision of the minutus Fauna by the over—
lapping ranges of R. minutus subspp. and R. websteri. In our
section, R. websteri ranges slightly higher than R. murica-
ms. Baesemann and Lane (1985) indicate that R. websteri
does not occur above their symmetricus Zone in North
America, and they show R. muricatus extending into the
lower Atokan. According to J.F. Baesemann and HR. Lane
(oral commun., 1992), R. muricams may be absent from the
upper Morrowan part of the Wahoo Limestone and is rare in
the post-Morrowan part. These late forms of the species are
small and atypical of early R. muricatus. The only small
rhachistognathids from the highest part of the Wahoo Lime-
stone are juveniles of R. minutus that occur with adults of R.
minutus subspp. (table 1, USGS colln. 30800—PC).

In our section, the upper limit of the minutus Fauna is
defined by the first appearance of Idiognathodus sp., 177 m
above the base of the Wahoo Limestone (15 m above the
disappearance of Rhachistognathus websteri; table 1). The
upper 15 m of the minulus Fauna contains few conodonts;
most samples have a few specimens each of Declinognatho—
dus noduliferus subspp., R. minutus subspp., and Adeto-
gnathus laurus. These upper 15 m may be equivalent to part
of the Idiognathoa'us Fauna. Similarly, many other collec-
tions from single-sample localities or partial sections in the
northeast Brooks Range contain R. minums subspp. above
or with D. noduliferus subspp. and (or) R. primus and lack
R. muricatus, R. websteri, and idiognathodids. Such collec—
tions have been assigned to the minums Fauna although,
similar to the upper 15 m of the minutus Fauna in the study
section, they could be equivalent to the Idiognathodus
Fauna. For example, about 10 km north of Wahoo Lake,
samples from the upper 132 m of the Wahoo Limestone
contain R. minutus subspp., R. primus, D. n. noduliferus,
adetognathids, and idioprioniodids and are assigned to the
minums Fauna (app. 1, locs. 4C1a—c).

In the northeast Brooks Range, the minutus Fauna is
thickest (93 m) in the eastern Sadlerochit Mountains (table
1) and is at least 70 m thick at Katakturuk gorge, western
Sadlerochit Mountains (app. 1, locs. 2a—g).

The foraminifers Pseudostafiella sp. and Eoschuber-
tella sp. first appear in the upper part of the minutus Fauna
at 171 m and 175 m above the base of the Wahoo Lime-
stone, respectively (P.L. Brenckle, written commun., 1991).
These species are used to approximate the base of the Ato-
kan in much of North America (Groves, 1986). Their first
occurrence in Alaska relative to the Morrowan-Atokan
boundary remains uncertain, and conodonts provide no
additional control.

LOWER MINUTUS FAUNA

The lower subdivision of the minutus Fauna is defined
by the local overlapping ranges of Rhachistognathus

16 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

muricams, R. websteri, and R. minutus subspp. below the
range of Idiognathoa’us spp. (pl. 6). In the northeast Brooks
Range, this fauna] interval contains the greatest diversity
and abundance of rhachistognathids. Associated conodonts
within the lower minutus Fauna in the study section include,
in order of decreasing abundance. Rhachistognathus muri-
cams, R. minutus minutus (Higgins and Bouckaert), Adeto-
gnalhus lautus, R. m. havlenai Baesemann and Lane, R.
websteri, Declinognathodus noduliferus nodulzferus, R. m.
declinams Baesemann and Lane, A. spathus, D. n. japoni-
cus, Idioprioniodus spp., Hindeoa'us minutus, Gnathodus
defectus, and R. prolixus?. The interval contains a few spec-
imens of Kladognathus spp. in one sample, which we con—
sider redeposited. No additional species have been
recognized within the lower minutus Fauna in our many
collections from the northeast Brooks Range.

R/iac/iistognathus websteri and R. muricatus do not
occur above the lower minutus Fauna in the study section
(table 1). Rhachistognathids generally maintain their domi-
nance higher in the section, but with reduced diversity; R.
m. declinatus is the most abundant rhachistognathid above
the lower minulus Fauna. The lower minutus Fauna is likely
Morrowan in age because the foraminiferan guides to the
base of the Atokan occur in the upper part of the minutus
Fauna. The lower minutus Fauna roughly correlates with the
sinuams-minutus to symmetricus Zones of Baesemann and
Lane (1985; fig. 7, this report).

Rhachistognathus minums appears 84 m above the
base of the Wahoo Limestone (14 m above the base of the
upper member) and R. websleri disappears 78 in higher in
the study section (table 1). At Katakturuk River gorge, in
the western Sadlerochit Mountains (fig. 2, 10c. 2), at least
34.5 m of the Wahoo Limestone contain the lower minutus
Fauna (app. 1, locs. 2a—d). The fauna is also present in a
43.5—m-thick interval in the lower member of the formation
at Pogopuk Creek (app. 1, locs. 5c—e) and in a single sample
from the upper member in the Clarence River area (app. 1,
loc. 10A11‘).

IDIOGNA T HODUS FAUNA

This fauna is characterized chiefly by the association
of ldiognathodus spp., Rhachistognathus minums subspp.,
and Adetognathus lautus; the first appearance of
Idiognathodus spp. in the Wahoo Limestone marks its lower
boundary. The upper boundary cannot be defined biostrati-
graphically but is placed at the unconformity that separates
the Wahoo Limestone from the overlying Echooka Forma-
tion (Permian). The lower boundary could be as old as the
sinuosus Zone (late Morrowan) of Baesemann and Lane
(1985) or as young as early Atokan. At least half the idiog-
nathodids in our collections from the northeast Brooks
Range cannot be determined to species because of poor
preservation. Many of the rocks that produce abundant

Idiognathodus are high-energy oolitic to skeletal grain-
stones resulting in incomplete and moderately to extremely
abraded specimens. Most of the better preserved specimens
are assigned to I. sinuosus Ellison and Graves following the
species concept of Grayson and others (1989; 1990). This
species ranges from the base of the sinuosus Zone (upper
Morrowan) to at least the Upper Pennsylvanian; it ranges
from 187 to 243 m above the base of the Wahoo Limestone
in our section (table 1) and above the lowest occurrence of
Pseudostaflella sp. (fig. 7). If the latter approximates the
base of the Atokan in Alaska, then the first occurrence of
I. sinuosus (16 m higher in the study section) is in the early
Atokan and considerably later than its debut in the type
Morrowan in Arkansas. Two specimens from 246 to 250 m
above the base of the Wahoo Limestone are assigned to
I. incurvus Dunn? sensu Grayson and others (1989)
(table 1). ldiognathodus incurvus is restricted to the Atokan
and lower Desmoinesian (Grayson and others, 1989); there—
fore, the upper 16 m of the Idiognathoa’us Fauna in the
study section is probably no older than Atokan. In addition,
R. minutus subspp., identified in samples from the upper—
most part of the Wahoo Limestone, is not known to extend
above the lower Atokan (Baesemann and Lane, 1985).
Therefore, the top of the Idiognathodus Fauna in our section
is considered no younger than early Atokan in age.

Conodonts that occur in the [diagnathodus Fauna in
the study section include, in order of decreasing abundance,
Rhachistognathus minutus declinatus, Declinognaz‘hodus
noduliferus noduliferus, Idiognathodus sinuosus, Adeto—
gnathus laumr, D. n. japom'cus, R. m. havlenai, R. m. minu—
tus, A. spathus, Idioprioniodus spp., Hindeodus minutus,
Idiognathoides sinuatus (Harris and Hollingsworth), Idio-
gnathodus imam/145?, Diplognalhoa’us? ellesmerensis?, and
Neognathodus? sp. indet. Taken together, our many collec-
tions from the Idiognathodus Fauna from elsewhere in the
northeast Brooks Range have fewer species than the study
section (see app. 1).

The ldiognathadus Fauna is widespread in the upper—
most part of the Wahoo Limestone across the northeast
Brooks Range, from the Philip Smith Mountains to the
Yukon (fig. 1). Some of the localities (see app. 1) that pro-
duced this fauna include [samples are from the upper l m of
the Wahoo Limestone, except as noted] (1) northwestern
Philip Smith Mountains (locs. 3A, B), (2) 4.5 m below the
top of the Wahoo Limestone near its type section, Philip
Smith Mountains (loc. 4D), (3) Pogopuk Creek, Franklin
Mountains (loc. 5f), (4) central Fourth Range (100. 7b), (5)
central Shublik Mountains (10c. 8), (6) 6—m—thick interval in
upper part of the Wahoo Limestone (locs. 2h, i) and the
uppermost (loc. 2j) beds, Katakturuk River gorge, western
Sadlerochit Mountains, (7) eastern Sadlerochit Mountains
(10c. 1C), (8) central Romanzof Mountains (loc. 9A), (9)
upper 45 m of the Wahoo Limestone, Clarence River, north—
ern British Mountains, Alaska (locs. 10A1g, h), and (10)
near the top of Wahoo Limestone, northern British Moun-

THE MID-CARBONIFEROUS BOUNDARY 17

tains, Alaska—Yukon border (loc. 10B; figs. 1, 2). The Idio—
gnathodus Fauna may extend lower at localities that repre—
sent single collections

THE MID-CARBONIFEROUS
BOUNDARY—AN APPROXIMATION
OF THE MISSISSIPPIAN-
PENNSYLVANIAN BOUNDARY

BIOSTRATIGRAPHIC CRITERIA

Three major fossil groups, ammonoids, foraminifers,
and conodonts, have been used for zoning the Carbonifer-
ous and as guides to the mid-Carboniferous boundary
(Sutherland and Manger, 1984b; Manger and Sutherland,
1992). In 1983, the Subcommission on Carboniferous
Stratigraphy (SCCS) approved several recommendations
regarding the various biostratigraphic criteria for establish-
ing an international mid-Carboniferous boundary (Lane and
Manger, 1985). These include—

(1) The transition between the Eumorphoceras and
Homoceras ammonoid zones. Homoceras, however, is
geographically restricted and not useful for global cor-
relations.

(2) The first appearance of the conodont Declinagnarhodus
noduliferus, preferably together with its ancestor Gna-
thodus girtyi simplex.

Secondary guides to the boundary include the first
appearance of the conodonts Adetognarhus lautus, Rhachis-
tognathus primus, and R. minutus and the foraminifers
Globivalvulina sp. D of Brenckle (=G. moderata = G.
bulloia'es; P.L. Brenckle, oral commun, 1991), Millerella
pressa Thompson, and M. marblensis Thompson.

These recommendations are not yet ratified because a
stratotype has not been selected. Nevertheless, the recom-
mendations of the SCCS are useful for defining the
mid—Carboniferous boundary in marine successions (Lane
and others, 1985b; Riley and others, 1987) and are followed
here.

The fauna] succession across the mid-Carboniferous
boundary in North America and elsewhere has been exten—
sively documented (for example, Ziegler and Lane, 1985;
Brenckle and Manger, 1990; Sutherland and Manger, 1992).
The lithofacies and conodont succession in our section are
most like those described from Nevada, Utah, and Montana
(Wardlaw, 1984; Baesemann and Lane, 1985; Davis and
Webster, 1985; Morrow and Webster, 1991, 1992). These
studies, however, indicate significant inconsistencies in
conodont distribution and possible misinterpretations of
depositional continuity that affect zonal schemes. For
example, in the Arrow Canyon section, Nevada, Baesemann
and Lane (1985) place the Mississippian-Pennsylvanian
boundary at the simultaneous first occurrence of Declina-
gnathoa'us noduliferus, Rhachistognathus primus, and R.

websteri immediately above beds containing Adetognat/ms
laums, R. muricams, and Gnathodus girtyi simplex. Gna-
tlzodus girtyi simplex occurs in 10 samples taken through a
6-m-thick interval above the boundary (Baesemann and
Lane, 1985, fig. 2). Thus, beds representing the Upper muri-
cams Subzone are overlain by beds representing the Lower
noduliferus-primus Zone. Their lithic column shows a
2—m‘thick elastic—rich interval less than 1 m above the
boundary that occurs in a limestone. According to field
observations made by K.F. Watts in 1989, the systemic
boundary lies at a lithic change from crinoidal
packstone-grainstone to packstone having a greenish matrix
and sand-filled burrows in its uppermost part. The elastic
interval less than 1 m above the boundary contains a variety
of lithologies including mixed-pebble conglomerate in a
carbonate and lesser quartz sand matrix and flat-pebble con—
glomerate. These features suggest a change in depositional
regime, possibly beginning at the boundary but certainly
occurring less than 1 m above it. The first appearance of
Declinognathodus and new species of Rhachistognathus
may be a migration event related to Changing environmental
factors associated with the lithic changes. Conodont collec-
tions made by ER. Wardlaw and RC. Stamm (U.S. Geo-
logical Survey, unpub. data), at 0.5—m intervals from 14.5 m
below to 2 m above the boundary as designated by Baese—
mann and Lane (1985) reveal additional problems. In these
collections, R. primus is limited to one sample 4 m below
the only sample containing D. noduliferus (taken at the sys-
temic boundary). Thus, in Arrow Canyon, R. primus
appears before, rather than together with, D. noduliferus.

At Granite Mountain, Utah, Morrow and Webster
(1992) report the appearance of Rhachistogriathus primus 9
m below the first Declinognathodus noduliferus. They place
the Mississippian-Pennsylvanian boundary at the first
occurrence of D. noduliferiis on the basis of comparisons to
other localities where R. primus occurs below D. nodu-
liferus. We agree with Morrow and Webster (1991) that the
rarity of D. noduliferus and gnathodids at Granite Mountain
is biofacies related and that the first appearance of D. nodu-
liferus is a migration event. We do not, however, agree with
their placement of the primus Zone interval in the Missis—
sippian (Morrow and Webster, 1992), as it couldjust as well
be partly or entirely Pennsylvanian in age.

As documented above, our own and published data
suggest Rhachistognathus primus evolved shortly before
Declinognathodus nodulifems. Rhachistognathus primus is
relatively rare in the northeast Brooks Range. Only one col~
lection contains R. primus not constrained by D. nodu—
liferus; it is assigned to the nodulifems-primus Zone (app.
1, 10c. 4B)

The ancestry of Declinognathodus nodulifems, the
micropaleontologic guide to the base of the Pennsylvanian,
remains controversial with conflicting evidence indicating
ancestry from either Gnarhodus girtyi simplex or G. bilinea-
tus. Grayson and others (1985b), Grayson and others

18 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

(1990), and Grayson (1990) consider G. bilineatus ancestral
to D. noduliferus on the basis of apparatus comparisons.
Indeed, examination of chiefly Pa elements from a proposed
mid—Carboniferous stratotype section in middle Asia
strongly supports the G. bilinearus ancestry (Nigmadganov
and Nemirovskaya, 1992a, 1992b; Nemirovskaya and
Nigmadganov, 1994). Our data, however, are equally con-
vincing for a G. g. simplex ancestry (see below). The con-
troversy concerning the ancestry of D. noduliferus may be
the result of homeomorphy. Pa elements documenting the
evolution of G. bilineams bollandensis to G. postbilineatus
to D. praenoduliferus and, finally, to D. noduliferus nodu—
liferus (Nigmadganov and Nemirovskaya, 1992a;
Nemirovskaya and Nigmadganov, 1994) are just as con-
vincing as those documenting the evolution of G. girtyi sim-
plex to D. n. japonicus and (or) D. n. noduliferus (Dunn,
1970b; this report). It may be that the Pa elements presently
recognized as those of D. nodulzferus are polyphyletic.

Presently, the leading candidate section for the mid-
Carboniferous boundary stratotype is in Arrow Canyon,
Nev. (Baesemann and Lane, 1985). The first appearance of
Declinognathodus noduliferus inaequalis, D. n. japonicus,
or D. n. noduliferus in the section marks the mid-
Carboniferous boundary and will be used to mark the base
of the Pennsylvanian System.

CONODONT-BASED BOUNDARY IN THE
EASTERN SADLEROCHIT MOUNTAINS

Gnathodus girtyi simplex transitional to Declinogna-
thodus noduliferusjaponicus first appears at 53 m above the
base of the Wahoo Limestone (table 1). Additional speci-
mens were found at 54.9 m above the base of the formation,
immediately below a reddish-brown and gray chert-bearing
peloidal spiculitic wackestone interval (fig. 6). Declinogna—
thodus nodulifems japom'cus first appears immediately
above the chert-bearing interval, at 56 m above the base of
the Wahoo Limestone (table 1). The mid—Carboniferous
boundary may be no higher than 55 m above the base of the
Wahoo Limestone and below the chert-bearing interval at
the study section because 1 km to the west (app. 1, locs.
lBla—g) D. n. japonicus is common in a 1.5-m interval
below a reddish-brown and gray chert-bearing peloidal spi-
culitic wackestone. The chert-bearing interval can be traced
between the two localities. Collections from within it con—
tain similar conodont faunules (app. 1, loc. lBlf; table 1,
USGS colln. 31699—PC). Its base is a discontinuity and has
a relief of at least 1 m. It may be that the 1.5-m interval con-
taining D. n. japonicus below the discontinuity to the west
was cut out at the study section.

Other, less diagnostic guides to the mid-Carboniferous
boundary are either rare or absent in the boundary interval.
Adetognalhus [autus does not occur in this interval for envi-
ronmental reasons but does occur 121 m below it (app. 1,
loc. lAlb) and 28 m above it (table 1), and Rhachisto-

gnatlms primus has not been recognized. Additional guides
include the last appearance of Cavusgnathus spp. at 3 m
below the boundary and the continuation of C? tytthus and
Vogelgnathus postcampbelli to 20.5 m above the boundary.
A few representatives of species believed to be restricted to
the Mississippian occur sporadically above the boundary;
these are shown in table 1 as redeposited.

FORAMINIFERAN-BASED BOUNDARY IN THE
EASTERN SADLEROCHIT MOUNTAINS

The Mamet and Skipp (1970) foraminiferan zonation
has been used extensively to correlate the Lisburne Group
in northern Alaska (for example, Armstrong and others,
1970, Armstrong and Mamet, 1975. 1977; Dutro, 1987).
Mamet and Skipp (1970) and subsequent publications by
Mamet and his co-workers place the mid—Carboniferous
(Mississippian—Pennsylvanian) boundary coincident with
the boundary between foraminiferan Zones 19 and 20. The
base of Zone 20 is defined by the appearance of the
Lipinella—Millerella sensu stricto assemblage (Armstrong
and others, 1970). Later, Mamet (1975) amended Zone 20
to include the first diaphanotheca—bearing Globivalvulina.

Studies in the eastern Sadlerochit Mountains show
inconsistencies in lithostratigraphic and chronostratigraphic
boundaries with the foraminiferan zonation (fig. 8). Arm-
strong’s (1972) boundary between the Alapah Limestone

 

Figure 8. Comparison of lithostratigraphic, biostratigraphic, »
and time-rock boundaries between study section and the nearby
Sunset Pass section analyzed in previous reports. Prior to Carl—
son (1987; column 4), all interpretations for the Sunset Pass sec-
tion (fig. 2, loc. 1B) were based on one composite section
(Armstrong and others, 1970, sections 68A—4A, 4B); Carlson’s
section is along the same traverse. The Alapah Limestone—
Wahoo Limestone boundary is at the same stratigraphic level in
columns 2, 4, and 5 but differs from that in columns 1 and 3.
Foraminiferan zonal boundaries in columns 1—4 were deter-
mined by B.L. Mamet; foraminiferan data for column 5 are from
FL. Brenckle (b: written commun, 1991) and Sylvie Pinard (p;
written commun, 1991). In column 5, the first occurrence of the
diagnostic foraminifer that approximates the base of the Penn-
sylvanian, Globivalvulina bulloides, is at least 13 m below the
first Declinognathodus noduliferus. PL. Brenckle (written com—
mun., 1991) also noted the last occurrence of Brenckleina mg—
osa well above its known range in the conterminous United
States (at or very slightly above the base of the Pennsylvanian).
See figure 6 and table 1 for specific information on the
Mississippian—Pennsylvanian boundary. The Morrowan-Atokan
boundary is poorly constrained by conodonts. Pseudostaffella
sp. is used to approximate this boundary in the Midcontinent and
Cordillera of the conterminous United States (Lane and Manger,
1985; Groves. 1986). In the study section, it appears 14 in above
the lowest occurrence of its plectostaffellid ancestor and 75 m
below the first definitive Atokan conodont. NML. “No Man’s
Land” as used by BL. Mamet in Carlson (1987) and Gruzlovic
(1991).

Study section

THE MID-CARBONIFEROUS BOUNDARY

 

 

 

 

 

 

   
      
 

   
 

 

 

      
  
 

 

 

 

 

 

 
  
   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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20 CONODONT BlOSTRATlGRAPHY AND BlOFACIES OF THE WAHOO LIMESTONE

and Wahoo Limestone and his systemic boundary are simi—
lar to our results; however, Armstrong and Mamet (1975,
1977) subsequently changed the position of both boundaries
(fig. 8). Most of the reports cited in figure 8 use the original
section measurements and thin sections that were first used
by Armstrong and others (1970). Carlson’s (1987) section is
at or immediately adjacent to Armstrong’s original section
but was sampled in more detail. Analysis of Carlson’s sam—
ples by Mamet (in Carlson, 1987) produced results different
than those in previous reports. The reasons for changing
lithostratigraphic and chronostratigraphic boundaries, how-
ever, were not explained. It is likely that biostratigraphic
criteria changed, and the formation boundary was moved to
approximate the systemic boundary.

In the northeast Brooks Range, Mamet and Armstrong
(1984, p. 435) recognized an “...undetermined interval
between Zones 19 and 20 [which] represents a very small
amount of the sedimentation column but is a stratigraphic
break lacking any characteristic paleontologic association.”
Mamet called this interval “No Man’s Land” or NML (in
Carlson, 1987; in Gruzlovic, 1991; this report, fig. 8).
According to Mamet (in Clough and Bakke, 1986; in Carl-
son, 1987), the NML interval is correlative with the
Mississippian—Pennsylvanian regional unconformity of the
Midcontinent of North America.

Because foraminifers have been the principal fossils
used for correlating the Lisburne Group, we were eager to
tie our conodont biostratigraphy t0 Mamet’s foraminiferan
zonation. Unfortunately, the original Sunset Pass section
was not logistically suitable for conodont sampling, but our
study section, 1 km to the east, is close enough to assure
lithologic correlation and thus permit comparison of con—
odont and foraminiferan data. Microlithofacies samples
were taken every 2 m or less to coincide with conodont
samples and lithologic changes and were also used for fora—
miniferan analyses. The conodont-based Mississippian—
Pennsylvanian boundary generally does not agree with the
boundary determined by foraminifers. Figure 8 shows the
conodont—based boundary at about the same stratigraphic
level as given in columns I and 2, but about 25 In higher
than in column 3, and about 17 m lower than in column 4
(see fig. 8 caption for details). If the first appearance of the
foraminifer Globivalvulina bulloia’es is used as a guide to
the base of the Pennsylvanian in our section, the mid-
Carboniferous boundary would be 13 m lower than the
conodont—based boundary but would still not match other
levels determined by Mamet using his own zonation (fora-
miniferan analysis by PL. Brenckle, Amoco Production
Company, written commun., 1991). Sylvie Pinard (Geologi-
cal Survey of Canada) analyzed the foraminifers (written
commun., 1991) in the same thin sections as those exam-
ined by PL. Brenckle and placed the boundary 9 m higher
than his determination (fig. 8; 4 m below the conodont-
based boundary).

The last appearance of the foraminifer Brenckleina
rugosa may be an additional guide to the mid—
Carboniferous boundary in the Cordillera of the contermi—
nous United States where the species disappears at, or
slightly above, the base of the Pennsylvanian and before the
first occurrence of Globivalvulina (Brenckle and others,
1982). At the study section (fig. 8), however, 8. rugosa
extends at least 25 m above the first appearance of D. nodu—
lifems and 38 m above the first Globivalvulina (PL.
Brenckle, written commun., 1991).

It is obvious that taxonomic interpretations, biostrati-
graphic models, and paleobiogeography, as well as spacing
and selection of foraminifer and conodont samples, control
boundary placements. As taxonomic interpretations stabi-
lize and global biostratigraphic data increase for both fora—
minifers and conodonts, correlations should improve the
usefulness these groups separately and in concert.

MORROWAN-ATOKAN BOUNDARY

The foraminiferan zonation of Mamet and Skipp
(1970) has been used extensively to correlate the Lisburne
Group and to approximate the position of the standard
North American Midcontinent series boundaries within it.
Armstrong and Mamet (1977, p. 18) place the base of the
Atokan Series at the boundary between foraminiferan
Zones 20 and 21. They define the base of Zone 21 as the
“outburst of abundant Eoschubertella, Pseudostafiella, and
Globivalvulina of the group G. bulloides.” Groves (1986)
also uses Eoschubertella and (or) Pseudostaflella to define
the base of the Atokan in the southern Midcontinent and
Cordillera of the conterminous United States and to approx—
imate this boundary in northeast Alaska. Sutherland and
Manger (1984b) recommended that the base of the Atokan
Series in the southern Midcontinent be marked by the
appearance of the foraminifer Eoschubertella spp. and the
conodont Diplognathodus spp.

Diplognathodus? was found in only one sample in our
section (pl. 5, figs. 18, 19; pl. 6; table 1) and is rare in the
Lisburne Group in northern Alaska. Moreover, the proposal
to use Diplognathoa’us as a guide to the base of the Atokan
preceded the recognition of Morrowan diplognathodids
(von Bitter and Merrill, 1990). For now, Diplognathodus?
orphanus appears to be the only known diplognathodid
restricted to the Atokan. Consequently, other conodonts or
groups are needed to identify rocks of Atokan age. Grayson
(1990) and Whiteside and Grayson (1990), in their revision
of Idiognathodus sinuosus, I. klapperi, and I. incurvus, sug—
gest that the appearance of I. incurvus indicates an Atokan
or slightly younger Pennsylvanian age in the southern Mid-
continent, including the type area of the Atokan. Addition-
ally, ]. incurvus probably overlaps the upper range of its
ancestor I. klapperi within the lower Atokan (Grayson and
others, 1989). We were unable to confirm the phylogeny

CONODONT BIOFACIES 21

proposed by Grayson and his co-workers. Nearly all of the
idiognathodids recovered from our section are either too
poorly preserved for specific identification or are represen—
tatives of the long—ranging species, I. sinuosus. Two speci—
mens of I, incurvus? were identified. The first appearance
of I. sinuosus in the study section is probably unrelated to
its origin and could represent any level within the lower part
of its stratigraphic range. The occurrence of I. incurvus?
with Rhachistognathus minutus subspp. suggests an age no
younger than early Atokan for the uppermost part of the
Wahoo Limestone in the study section.

Foraminiferan data suggest that the first appearance of
ldiognalhoa’us sirmosus in the study section is within the
Atokan (figs. 7, 8). The foraminiferan guides to the Atokan,
Pseudostaflella and Eoschubertella, first appear 16 m and
12 m, respectively, below I. sinuosus (171 and 175 m above
the base of the Wahoo Limestone, P.L. Brenckle, written
commun., 1991). Furthermore, Plectostaffella, the ancestor
of Pseudostafi‘ella, first appears 14 m below its descendant
(157 m above the base of the Wahoo Limestone) and contin-
ues to 183 m above the base of the Wahoo Limestone. Plec-
tostaflella is unknown in North America except from
northern Alaska (Groves, 1986, 1988). The sudden appear-
ance of its descendant, Pseudostaffella, at the base of the
Atokan in the North American Midcontinent indicates its
migration from the Eurasian-Arctic Faunal Realm to the
Midcontinent-Andean Faunal Realm (Groves, 1988). Thus,
Pseudostaflella probably is not a reliable guide to the base
of the Atokan in northern Alaska. The base of the Atokan
could lie at some level between the first appearance of
Pseudostaflella and I. incurvus?. Figures 7 and 8 show the
relative position of the lower boundary of the Atokan on the
basis of conodonts versus foraminifers. A third fossil group
may be needed to distinguish evolutionary from migratory
patterns in foraminifers and conodonts.

CONODONT BIOFACIES

The distribution of conodonts was chiefly controlled
by the physical and chemical characteristics of the water
mass and its trophic resources and, on a grander scale, by
paleogeography. These factors influence biostratigraphic
analyses because most zonation is based on first appear-
ances. Thus, the presence or absence of a species is not only
related to evolution but also to a wide range of paleogeo—
graphic, paleoenvironmental, and postmortem factors (Mer-
rill and von Bitter, 1976; Rexroad and Horowitz, 1990;
Pohler and Barnes, 1990).

Studies that are useful for conodont biofacies analysis
of the Wahoo Limestone include Webster (1969), Merrill
(1973a), Merrill and Martin (1976), Merrill and von Bitter
(1976, 1979, 1984), Driese and others (1984), Davis and
Webster (1985), Wilson (1985), Sweet (1988), Rexroad and
Horowitz (1990), and Morrow and Webster (1991, 1992).

Of these, Davis and Webster (1985) and Morrow and Web-
ster (1991, 1992) best approximate the age, paleoenviron—
mental conditions, and species associations found in the
Wahoo Limestone. Davis and Webster (1985) proposed four
conodont biofacies for middle Carboniferous, shallow-
water, carbonate-shelf deposits in central Montana:
Declinognathodus-Idiognath0ides, Rhachistognathus,
Adetognathus, and Neognathodus biofacies. Morrow and
Webster (1991) recognized only the Rhachistognathus and
Adetognathus biofacies in offshore barrier—shoal and
nearshore-lagoon environments through the mid-
Carboniferous boundary interval in the Ely Limestone of
west-central Utah. All but the Neognathoa’us biofacies have
been recognized, with some modifications, in the Wahoo
Limestone. According to Davis and Webster (1985), the
Declinognathodus-Idi0gnath0ides biofacies (2
Idiognathodus-Strept0gnath0a’us biofacies of Merrill,
1973a, and Merrill and von Bitter, 1976, 1979) represents
an offshore, shallow, open-marine environment. The Rha-
chistognathus biofacies represents a higher energy regime
that is associated with shoals transitional between the open-
platform and open-marine environments (see fig. 10C). The
Adetognathus biofacies (2 Cavusgnathus biofacies of Mer-
rill and von Bitter, 1976, 1979) occupies the open- to
restricted-platform area behind a shoal, an area of variable
salinities represented by a variety of lithologies.

Like Morrow and Webster (1991, 1992), we relied on
regional stratigraphic relationships, field observations, such
as stratigraphic sequence and bedding characteristics, and,
most heavily, on microlithofacies to confirm and constrain
conodont paleoenvironmental interpretations.

CONODONT BIOFACIES AND ASSOCIATED
MICROLITHOFACIES, WAHOO LIMESTONE,
EASTERN SADLEROCHIT MOUNTAINS

Conodont biofacies and depositional environments of
the Wahoo Limestone in the eastern Sadlerochit Mountains
are intermediate between those presented by Davis and
Webster (1985) and Morrow and Webster (1991, 1992) for
sections in Montana and Utah. Rhachistognathus and
Adetognathus, however, are distributed across a wider range
of depositional environments in the Wahoo Limestone. This
probably resulted from hydraulic mixing of conodont ele-
ments from adjacent environments during periodic high-
energy conditions on the Wahoo carbonate platform. The
predominance of grainstone (65 percent, including oolitic
grainstone) in the Wahoo indicates deposition on the shal-
low inner part of a carbonate ramp. Lacking reefal barriers,
carbonate ramps are particularly susceptible to reworking
and redistribution of sediment by waves and storm surges
(Oslenger, 1991). Conodont elements in our section are
commonly abraded, further evidence of hydraulic transport.

22 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

Our data are from 72 samples. Initially, samples were
collected at about S—m intervals. Subsequently, intervals
containing important biostratigraphic boundaries and (or)
few conodonts were resampled at closer spacing. Because
the main focus of this study was biostratigraphic, some
lithologies, representing environments unfavorable for con-
odonts, were avoided. For example, rocks representing
restricted—marine and oolitic and oncolitic shoal environ~
ments were not sampled initially. After preliminary bios—
tratigraphic analysis, however, even rocks known or
inferred to be unfavorable for conodont recovery were col-
lected near lithostratigraphic and biostratigraphic bound-
aries. None of these samples were devoid of conodonts, but
predictably, they produced few if any biostratigraphically
significant species and, even worse, too few for biofacies
analysis (for example, tables 1 and 2; 62—808 m and 167—
182 m above the base of the Wahoo Limestone). Conse—
quently, 26 samples could not be used for biofacies analysis.
Ten of these contain common to abundant peloids and (or)
spicules, and another 12 contain common to abundant
ooids, superficial ooids, and (or) oncoids. Five samples that
contain common but not abundant ooids, superficial ooids,
and (or) oncoids did qualify for biofacies analysis. The pos-
itive aspect of these largely negative results is that most of
our prejudices about “offensive” rock types were rein-
forced, but, in a few cases, we learned not to suggest depo-
sitional environments using minimal conodont data (see
table 2, samples not qualifying for biofacies analysis).

Only generically identifiable conodonts, including all
apparatus elements, were used for biofacies analysis. Sam—
ples with fewer than 20 elements identifiable to genus and
genera represented by less than 5 elements were not used
for analysis. Cavusgnathus? tytthus, listed separately on
table 2, is combined with cavusgnathids in Mississippian
collections and adetognathids in Pennsylvanian collections.
Following Ziegler and Sandberg (1990), conodont biofacies
are designated using the name of one or two generic compo-
nents that make up about 70 percent of the fauna. If the two
most abundant genera do not reach this percentage, the con-
odont association is, with some exceptions, considered the
result of postmortem hydraulic transport, bioturbation, and
(or) unfortunate sampling. Although most of the samples
analyzed show evidence of some hydraulic transport and
mixing, those dominated by one or two genera are inter-
preted to represent a living association or an association
derived from laterally adjacent environments.

For the most part, biofacies are closely related to spe—
cific paleoenvironments. In some instances, however, the
associated biota and (or) degree of abrasion of conodonts
and grain types influenced environmental interpretations
(table 2). Biofacies and microlithofacies environmental
analyses agree in general but may differ in some details.

Paleoenvironments (fig. 9) were interpreted from
regional and local and vertical and lateral stratigraphic rela-
tionships, bedding characteristics, sedimentary structures,

carbonate lithology (megascopic and microscopic textural
classification of Dunham, 1962), carbonate grain types, and
fossil assemblages. The data set for this study is given in
tables 1 and 2 and plate 6.

MISSISSIPPIAN PART OF THE WAHOO LIMESTONE

Regional relationships suggest that the Mississippian
part of the lower member of the Wahoo Limestone was
deposited in a predominantly open-platform to open-marine
setting. Three major environments were sampled in this part
of the section: (1) near—restricted open platform4 to open
platform, (2) moderate- to high-energy (above wave base)
open marine, and (3) low-energy (below wave base) open
marine. The general characteristics and paleogeographic
setting of each are given in figure 9.

CAVUSGNATHID BIOFACIES

NEAR-RESTRICTED TO OPEN-PLATFORM ENVIRONMENTS

Six collections from the Mississippian part of the
lower member of the Wahoo Limestone represent the cavus-
gnathid biofacies. The samples are from moderate— to
well-sorted bryozoan grainstone, commonly containing
fenestrate bryozoans and fewer pelmatozoans. Minor to rare
grains include peloids, intraclasts, and bioclasts of algae,
foraminifers, brachiopods, gastropods, and trilobites
(table 2). Macrofossils, which are typically incomplete,
occur as abraded and commonly micritized bioclasts. Beds
are generally massive, bioturbated and, where preserved,
parallel bedded. Grainstones are better washed and slightly
coarser grained than those in the adjacent, lower energy
cavusgnathid-kladognathid biofacies. A seventh collection
qualified for biofacies analysis (table 1, USGS colln.
31698—PC) but could not be included here because no
microlithofacies sample was saved.

Conodonts are rare (<lO/kg) to common (lO—25/kg)
and average ll/kg in this biofacies. Only 43 percent of the
conodonts, however, are generically determinate, and rami-
form elements are rarely identifiable to genus or even ele-
ment type reflecting a relatively high—energy regime. Most
smaller and lighter elements were probably carried into
nearby lower energy regimes.

Cavusgnathus, dominantly C. unicornis, makes up 69
to 100 percent, averaging 84 percent, of all conodonts from
this biofacies (fig. 10A); C.? tytthus makes up less than 4
percent of the cavusgnathids. Kladognathus and Gnathodus
average 9 and 2 percent, respectively, and hindeodids,
lochrieids, and rhachistognathids, together, make up less
than 5 percent of conodonts from this biofacies. One sample

4We use near restricted to indicate proximity to restricted environ-
ments such as back shoals and tital flats (see fig. 9).

CONODONT BIOFACIES 23

     
 

TERRIGENOUS
CLASTIC INFLUX

Intertidal

Dolomitized mudstone
containing cryptalgal laminations,
nodular evaporites(?), mudcracks,

Restricted platform

Silty dolomitized mudstone
to wackestone containing
algae, foraminifers, ostracodes,

WAVE BASE

Open platform

Packstone and grainstone
containing algae, peloids, foraminifers,
bryozoans, pelmatozoans, oncolites, and

terrigenous clastic sediment calcispheres, peloids, spicules, and
quartz and rare ooids and superficial

ooids transported from adjacent shoals

Shoal Tidal channel

Grainstone, partly
crossbedded, containing
ooids, abraded skeletal
grains and (or) peloids

Grainstone containing a
transported mixture of
intraclasts, peloids, bioclasts,
bivalves, brachiopods,
foraminifers, ostracodes, ooids,
and superficial ooids

corals; partly bioturbated. Also ooids and
calcispheres transported from adjacent
environments. Common to minor calcispheres,
spicules, and peloids suggest proximity to
restricted platform (=near restricted)

Open marine

Above wave base, high to moderate
energy. bioclastic to bryozoan-
pelmatozoan grainstone and packstone
Below wave base, low energy.
pelmatozoan-bryozoan packstone to
wackestone and spiculitic mudstone

Figure 9. Depositional model for and sediment characteristics of the Wahoo Limestone. Terminology modified from Scoffin (1987) and
Wilson (1975). Carbonate platform upon which the Wahoo Limestone was deposited was probably a southward-dipping homoclinal ramp

(for example, Read, l982).

contains 12 percent Vogelgnathus and 11 percent Rhachis-
tognathus (table 1, 13.2 m above the base of the Wahoo
Limestone). The presence of rhachistognathids is compati-
ble with the high-energy, well-sorted microlithofacies inter-
pretation. All other collections from this biofacies are from
moderately sorted, lower energy grainstones and lack
rhachistognathids.

Cavusgnathus dominated this and, less commonly,
adjacent offshore environments. Most other genera were
minor components of the population and (or) postmortem
additions. We have not been able to identify the ecologic
preference of Vogelgnathus in the study section because of
its scarcity. Elsewhere. this genus is associated with
restricted marine environments (Purnell and von Bitter,

24 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

’////

///
////

 

 

9 v\
‘0 <2~
OQ’KQO

 
      

Cavusgnalhus
(including 0.? tynhus)

K/adagnathus

Gnathodus

Hindeodus
Rhachistognathus, Loom/ea

Voge/gnathus

ldioprioniodus

 

 

INTERTIDAL NOT SAMPLED
RESTRICTED

 

 

\ \
\2\\ N

Open‘ near\ 8 \
(estricled \ \
Open and 7 \
near shoal h
SHOALr \

\
TIDAL
Near \

CHANNEL
shoal

/

 

 

   
  
    
     

 

 

 

PLATFOHM

MAFllNE

 

energy N

   

Hhach/stognarhus

Adetognathus

\ \ Declinognathodus
\

Idiognalhodus
\ Hindeodus
\ . ‘
Idlognathwdes
\ Dip/ognathodus?
7 \
IO non/o us
ld' p ’ d

 

 

 

Partly
veslricled

PLATFORM

  
 

MAFllNE

\
\
\
Dec/inognathodus
\ Hindeodus
1
Below
wave
base

    
  
  
     

Cavusgnathus’? tytthus
+ Adelognathus

Flhachistognathus

ldioprl'oniodus +
Vogelgnathus

 

N

 

— 55%

 

- 100%

' 80

' 60

' 40

~ 20
0

Relative percem

of genus in each

enVIronmenl

 

 

CONODONT BIOFACIES 25

(— Figure 10. Generalized paleogeography, biofacies, and dis-
tribution of conodont genera at the study section, Wahoo
Limestone, eastern Sadlerochit Mountains (fig. 2, 100. 1A).
A, Mississippian part of lower member. B, Pennsylvanian part
of lower member. High—energy oolitic shoals that
dominate the upper member of the Wahoo had not fully devel—
oped during the earliest Pennsylvanian. Instead, lithologies and
biofacies of this time period reflect the normal-marine, low- to
moderate-energy conditions characteristic of an open-platform
environment. C, upper member (Pennsylvanian). N, number of
samples.

 

1992). Most of the rocks in our section that might represent
the habitat of Vogelgnathus were either not sampled or
formed in moderate- to high-energy regimes from which the
small skeletal elements of Vogelgnathus were probably win-
nowed. Vogelgnathus is abundant in a poorly washed peloi-
dal grainstone containing minor echinoderm debris and
spicules.

The conodont species association and taphonomy sug-
gest that the cavusgnathid biofacies occupied a near-
restricted to moderate—energy open-platform setting. The
predominance of Cavusgnathus strongly favors a nearshore,
relatively variable environment (Merrill and von Bitter,
1976, 1979). In addition, minor kladognathids and rare
hindeodids, gnathodids, and lochrieids support an open-
platform rather than an open-marine interpretation.

The Mississippian part of the lower member of the
Wahoo Limestone formed during the early phase of a major
TR sequence. Initially, circulation and depositional patterns
were not well established so that shoal facies and associated
environmental partitioning are absent. Without intervening
shoals, the depositional setting (open platform versus open
marine) of fossiliferous packstones and grainstones cannot
be reliably interpreted. Microlithofacies and conodont—
based interpretations of the environmental setting for sam-
ples from the cavusgnathid biofacies differ. The over-
whelming dominance of Cavusgnathus and the virtual
absence of open—marine conodont species point to an open-
to near-restricted platform environment. In contrast,
microlithofacies favor a moderate- to high—energy, open-
marine or open—platform environment containing a diverse
marine fauna. We believe that the conodonts favor the
open-platform interpretation because of the low-diversity
conodont fauna.

CAVUSGNATHID-KLADOGNATHI D BlOFACIES

OPEN-PLATFORM TO OPEN-MARINE ENVIRONMENT

Five samples from the lower 37 m of the Wahoo Lime-
stone contain subequal mixtures of Cavusgnathus and Kla-
dognat/ms. These samples are primarily from moderately
sorted grainstone and poorly sorted packstone that contain

bryozoans and pelmatozoans, minor peloids, and rare intra-
clasts. Other bioclasts include minor algae, brachiopods,
sponge spicules, and foraminifers and rare gastropods, cal-
cispheres, and ostracodes (table 2). Grains are moderately
abraded and variably micritized. The rocks are less well
sorted and slightly finer grained than those of the cavusg-
nathid biofacies. Massive bedding may have resulted from
extensive bioturbation, indicating oxygenated bottom
waters and (or) low sedimentation rates. Bryozoans and pel-
matozoans probably lived within or near this environment,
indicating normal-marine conditions. Mud—rich laminae and
burrow fills commonly contain peloids, spicules, and (or)
ostracodes that indicate partial derivation from adjacent
restricted-platform environments. The three samples in the
lower 7 m of the Wahoo Limestone are packstone and
grainstone-packstone interbedded with dolomitic spiculitic
mudstone; this association of lithologies further indicates
proximity to low-energy, intermittently-restricted platform
environments.

Samples from the cavusgnathid-kladognathid biofacies
contain relatively abundant conodonts (26/kg), but about 60
percent are generically indeterminate fragments, suggesting
considerable postmortem movement. Many elements,
including ramiforms, are complete; thus, postmortem
movement was probably within this and (or) from nearby
biofacies.

Four samples from the open-platform to open-marine
environment contain 40 to 57 percent Cavusgnathus unicor-
m's, 21 to 40 percent Kladognathus spp., and 9 to 24 percent
Gnathodus girtyi. Rhachistognathus, chiefly R. muricams,
makes up as much as 9 percent of two samples and idiopri—
oniodids, lochrieids, and vogelgnathids together make up
less than 5 percent (table 1). Cavusgnathus probably lived
within this environment. but many elements may have been
transported from the adjacent higher energy cavusgnathid
biofacies (fig. 10A). The ecologic preference of Cavus-
gnathus for nearshore, relatively variable environments
(Merrill and von Bitter, 1976, 1979) is consistent with its
distribution in the Wahoo Limestone. Kladognathus also
lived in this environment, as nearly all the components of its
apparatus are present (table 1). The percentage of Klado-
gnathus diminishes rapidly shoreward toward the cavus—
gnathid biofacies (fig. 10A). Gnathodus girtyi may have
lived in this environment in low to moderate numbers. Most
of our specimens, however, are incomplete and poorly pre—
served suggesting postmortem transport from the more off-
shore gnathodid-hindeodid biofacies (fig. 10A). During this
time interval, Gnathodus girtyi subspp. is the dominant gna-
thodid in collections from normal-marine, relatively
shallow-water deposits in the Brooks Range and elsewhere
in the Cordillera of the United States (unpub. USGS collec-
tions). This species had a variety of ecophenotypes
(included here in G. g. simplex) that successfully competed
in shallow water. Rhachistognathids, in addition to other
genera that make up less than 5 percent of the conodonts

26 CONODONT BIOSTRATIGRAPl-IY AND BIOFACIES OF THE WAHOO LIMESTONE

from this environment, are considered postmortem admix—
tures. Rhachistognathids were probably transported from
nearby higher energy regimes as representatives of the
genus generally occupy near—shoal and shoal-water
environments.

A sample from 37 m above the base of the Wahoo
Limestone contains conodonts of the cavusgnathid-
kladognathid biofacies and represents an open-marine envi—
ronment. Cavusgnathus and Kladognathus are equally
abundant (36 percent) and gnathodids make up 27 percent
of the faunule, a higher proportion than other samples in
this biofacies. On the basis of conodonts, we would inter—
pret the environment as open platform or possibly open
marine. Microlithofacies suggest an open-marine to open-
platform, moderate—energy environment, but the low diver-
sity and absence of shallow-water grain types favor the
open-marine setting. The gnathodids and grain types
together with slightly muddier lithologies convinced us to
extend the cavusgnathid—kladognathid biofacies into the
open-marine environment.

GNATHODID-HINDEODID BIOFACIES

LOW-ENERGY, OPEN-MARINE ENVIRONMENT

This biofacies is represented by a single sample (53 m
above the base of the Wahoo Limestone) that is the young—
est Mississippian collection used for analysis from the for-
mation (table 2). It is from a poorly sorted bryozoan
packstone containing common pelmatozoan, ramose bryo-
zoan, and brachiopod fragments, minor quartz grains, and
rare bioclasts of foraminifers, trilobites, and algae. Micro-
lithofacies indicate a low-energy, open-marine environment
(table 2 and fig. 9).

Conodonts are relatively common (IS/kg); 50 percent
are generically determinate, and many elements are com-
plete. We believe that Gnathodus (63 percent) and Hindeo-
dus (32 percent) were living in and probably seaward of this
environment, as these forms are rare or absent in adjacent
shoreward biofacies (fig. 10A). Hindeoa’us minutus (Elli-
son), the only hindeodid recovered from the Wahoo Lime-
stone, is a long—ranging (latest Chesterian to at least Early
Permian), cosmopolitan species that is generally a persistent
component in samples from most normal—marine environ-
ments. The gnathodids are represented chiefly by Gnatho-
dus girtyi simplex and G. g. girtyi (in a ratio of 3:2); rare,
but biostratigraphically significant G. girtyi simplex transi-
tional to Declinognathodus noduliferus as well as G. bilin-
eams bilineatus also occur. The species association and the
absence of nearshore conodont species confirm the micro-
lithofacies interpretation of a below—wave-base, open-
marine depositional setting (fig. 10A). This sample repre—
sents maximum transgression during deposition of the
lower member of the Wahoo Limestone.

PENNSYLVANIAN PART OF THE WAHOO LIMESTONE

The maximum transgression in the latest Mississip-
pian, represented by open-marine deposits that formed
below wave base (fig. 10A), was followed by rapid shallow-
ing in the earliest Pennsylvanian. Locally, uppermost Mis—
sissippian deposits were subaerially and (or) subaqueously
eroded as evidenced by paleotopography beneath an expo-
sure surface (local preburial banded caliche, Watts, 1990;
fig. 6). Rare, redeposited latest Mississippian conodonts
occur in basal Pennsylvanian deposits above this disconfor-
mity (table 1). Depositional patterns were more complex in
the Pennsylvanian than in the Mississippian. The lowest
part of the Pennsylvanian, however, is generally similar to
the Mississippian because it lacks the ooid grainstones that
typify the upper member of the Wahoo Limestone. Addi-
tionally, the upper member contains shorter and more
numerous shallowing-upward cycles, as reflected in its
characteristic ledge-and—slope topography (fig. 5).

The maximum duration of regression in the Wahoo
Limestone is the Mississippian—
Pennsylvanian boundary but is 14 m higher at the contact
between the lower and upper members of the formation
(fig. 4). Redeposited Mississippian conodonts are more
prevalent immediately below the contact, the shallowest
water deposits in the Wahoo Limestone occur immediately
above the contact, and quartz increases from an average of 3
to at least 12 percent in the lower 20 m of the upper mem-
ber. All these features indicate significant regression and
some exposure and erosion of older deposits. The duration
of this possible disconformity is unknown; it may be as
short as a diastem or as long as most of the Morrowan.

apparently not at

Six depositional environments—intertidal, restricted
platform, open platform, shoal, tidal channel, and open
marine—are recognized in the Pennsylvanian part of the
Wahoo Limestone. The general characteristics and paleo-
geographic setting of each are given in figure 9. Rocks rep-
resenting the intertidal environment were not sampled for
conodonts.

Greatly influencing conodont biofacies in the upper
member of the Wahoo Limestone is the ooid facies that
makes up 20 percent of the member. This high-energy
regime caused many conodont elements, particularly rha-
chistognathids, to be transported beyond their biofacies,
substantially disrupting and even obliterating original biofa-
cies patterns. Consequently, some samples representing the
same environment, as interpreted from microlithofacies and
stratigraphic relationships, produce significantly different
relative abundance of conodont genera. Postmortem mixing
of conodonts eradicated some biofacies and artificially cre-
ated others.

CONODONT BlOFAClES 27

LOWER MEMBER OF THE WAHOO LIMESTONE
ADETOGNATHlD-RELATED BlOFAClES

NEAR»RESTRICTED TO OPEN-PLATFORM ENVIRONMENT

Two samples from the Pennsylvanian part of the lower
member of the Wahoo Limestone represent an
adetognathid-declinognathodid biofacies (table 2). The first
is from 56 m above the base of the Wahoo Limestone and is
an interlaminated peloidal packstone-wackestone and mod-
erately sorted bryozoan-pelmatozoan grainstone; this mix-
ture of lithologies suggests hydraulic mixing of open— and
restricted-platform grain types. The second is from 59 m
above the base of the Wahoo Limestone and is a moderately
sorted bryozoan grainstone-packstone containing common
bioclasts of brachiopods and pelmatozoans and rare algae,
foraminifers, trilobites, and peloids. The microlithofacies
suggest a moderate-energy, open-marine setting.

Conodonts are relatively common in the adetognathid-
declinognathodid biofacies (13/kg); 50 percent are generi-
cally indeterminate indicating considerable postmortem
transport. Adetognathids and Cavusgnathus? tytthus,
together, account for 35 to 58 percent of the conodonts in
this biofacies. Adetognathids are a long-ranging (latest
Chesterian to Early Permian), relatively shallow-water,
eurytopic group that is a common to abundant component
of all our Pennsylvanian faunas. The group was competi-
tively successful in partly restricted and (or) variable envi-
ronments. Cavusgnathus? tytt/ms is relatively abundant
(22—35 percent) in the adetognathid-declinognathodid bio-
facies. It is a relatively rare, short-ranging, latest Mississip-
pian and very earliest Pennsylvanian species in the
northeast Brooks Range. Consequently, it is restricted to the
lower 20.5 m of the Pennsylvanian part of our section. The
species is known only from the northeast Brooks Range,
western Utah, and its type area in the Illinois basin. It
appears to extend from nearshore, possibly intermittently
restricted environments that typify the inner margins of
intracratonic basins to the shallower part of the open—
platform environment. Its presence in open-marine environ—
ments may be chiefly a consequence of postmortem hydrau—
lic transport (fig. 103). In the adetognathid-
declinognathodid biofacies, it occurs with Declinognatho—
dus noduliferus japonicus. Declinagnathodus noduliferus is
a cosmopolitan species that has a variety of ecophenotypes.
We assume that the most nodose form (D. n. japonicus)
occupied shallower and more variable environments than
the more delicately ornamented D. n. inaequalis. Indeed, D.
n. japonicus makes up about 90 percent of the declinogna—
thodids in this relatively shallow-water biofacies.

Rhachistognathids are few in the Pennsylvanian part of
the lower member of the Wahoo Limestone because their
principal habitat, the shoal-water environment, was rare
(fig. 108). Rhachistognathus muricatus, virtually the only
rhachistognathid in this part of the Wahoo Limestone,

makes up 8 to 21 percent of the conodont assemblage in the
two samples from the adetognathid-declinognathodid biofa-
cies. This species is morphologically variable, a characteris-
tic of conodonts that are successful in a variety of
shallow-water environments.

LOW-ENERGY, OPEN-MARINE ENVIRONMENT

A single sample of bryozoan packstone containing
common pelmatozoans, minor brachiopods and bivalves,
and rare bioclasts of foraminifers, gastropods, sponge spi—
cules, and trilobites produced conodonts of the hindeodid-
adetognathid biofacies (tables 1, 2; 69 m above the base of
the Wahoo Limestone). The microlithofacies indicates a
low-energy open-marine environment. Although the sample
qualifies for biofacies analysis, the species association sug—
gests a mixed assemblage. It is likely that Hindeodus minu—
tus occupied this environment as all elements of its
apparatus are present. This species is long ranging and con-
sistently appears in rocks representing the relatively deeper
depositional settings of the Wahoo Limestone (figs. 10A,
B). This biofacies may represent the outer limit of the
Cavusgnathus? tytthus and adetognathid habitats. More
likely, these forms are hydraulic admixtures. In addition,
rhachistognathids (18 percent) were probably carried here
from their shallow-water high-energy habitat.

UPPER MEMBER OF THE WAHOO LIMESTONE
ADETOGNATHID-RHACHISTOGNATHID BlOFAClES

RESTRICTED TO NEAR OPEN—PLATFORM ENVIRONMENT

Restricted platform conditions were prominent near
the base and top of the upper member of the Wahoo Lime-
stone when shoals had migrated farther south. Six samples
from the upper member were collected from restricted— to
near open-platform environments as determined by field
observations and microlithofacies (table 2).

Only two samples from the least restricted part of this
environment qualified for biofacies analysis. These pro—
duced nearly equal numbers of adetognathids and rhachis—
tognathids. One (246 m above the base of the Wahoo
Limestone) is a peloidal grainstone containing common
quartz and minor bioclasts of pelmatozoans, brachiopods,
foraminifers, sponge spicules, ostracodes, and calcispheres.
The other, at 261.5 m, is spiculitic mudstone containing
common peloids, oncoids, and a variety of bioclasts. Con-
odonts in these collections represent either the edge of the
rhachistognathid-adetognathid biofacies or, more likely,
storm-tossed skeletons, stranded voyagers, or fecal
droppings.

Four samples from the restricted platform did not qual-
ify for biofacies analysis; their microlithofacies are listed in
table 2. The conodonts that occur in these samples were

28 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

probably derived from the adjacent open-platform environ-
ment that hosted the rhachistognathid-adet0gnathid biofa-
cies (fig. 10C).

OPEN<PLATFORM TO NEAR-SHOAL OPEN—PLATFORM ENVIRONMENTS

Five samples from the adetognathid-rhachistognathid
biofacies occur in a variety of open-platform subenviron—
ments (table 2; 84, 118, 157, 203, 241 m above the base of
the Wahoo Limestone). These are variously sorted grain-
stones and one moderately sorted grainstone—packstone.
These rocks contain locally abundant bryozoans or pelma-
tozoans, as well as a variety of bioclasts such as brachio-
pods, gastropods, and algae. Peloids, ooids, superficial
ooids, oncoids, and intraclasts are common in several sam—
ples and grains are commonly micritized (table 2). Done-
zella algae are common to minor in two samples.

Conodonts are rare (6/kg) in these samples. About 50
percent are generically determinate, most are incomplete Pa
elements, and some are abraded. Many, particularly the rha-
chistognathids, were probably transported from the adja-
cent, higher energy, shoal—water environment. Adetognathus
forms 40 to 54 percent of the assemblage in open-platform
settings and shoal aprons. It probably lived in these settings
as its relative abundance generally decreases seaward (fig.
10C). Although rhachistognathids make up about half the
conodonts in open-platform to near-shoal deposits, they
become even more abundant shoalward. We cannot distin—
guish postmortem admixtures from in situ specimens but
suspect that a high percentage represent the former. Collec-
tions from this biofacies are remarkably free of other gen-
era. This may be the natural species association or an
artifice of winnowing and breakage. Both the microlithofa-
cies and the low diversity of conodonts favor an open-
platform to near-shoal interpretation.

TIDAL-CHANNEL(?) ENVIRONMENT

One sample of very well sorted grainstone containing
common highly abraded bioclasts of foraminifers, bryozo-
ans, and ostracodes and minor peloids, quartz, and other
bioclasts including algae suggests a high-energy, open—
platform to open-marine setting, possibly a tidal channel
(table 2; 113 m above the base of the Wahoo Limestone). It
produced 66 and 31 percent rhachistognathids and adetog-
nathids, respectively. The abundance of rhachistognathids
suggests a high-energy regime, either a shoal or tidal-
channel setting. The species association favors a tidal-
channel or near-shoal open—platform environment because
adetognathids are abundant and other conodonts are rare. In
combination, biofacies and microlithofacies data favor a
tidal-channel setting. This sample is plotted in the

rhachistognathid-dominated shoal or tidal channel environ—
ment on figure 10C.

RHACHISTOGNATHID BIOFACIES

Rhachistognathids are the most abundant conodonts in
a variety of high—energy environments including shoal and
shoal aprons in open-platform and open-marine settings.
The association of rhachistognathids and lesser adeto-
gnathids suggests a near-shoal, open-platform setting, par-
ticularly if the adetognathids are relatively intact. In shoal t0
tidal—channel environments, the number of rhachisto—
gnathids is generally much greater in the adjacent shoal
aprons (table 2). If typically open—marine forms, such as
declinognathodids or idiognathodids, occur with abundant
rhachistognathids and are nearly as common as adeto—
gnathids, we favor a near—shoal, open-marine setting.

NEAR-SHOAL, OPEN-PLATFORM ENVIRONMENT

Three samples (table 2; 95, 107, and 257.5 m above the
base of the Wahoo Limestone) from the rhachistognathid
biofacies referred to this environment contain adetognathids
as virtually the only other conodonts. Poorly to well-sorted
grainstone-packstone to grainstone contain a variety of
common to minor bioclasts (bryozoans, pelmatozoans, fora—
minifers, oncoids, and algae) and ooids, superficial ooids,
peloids, and intraclasts. Conodonts are relatively common
(12/kg); 73 percent are identifiable to genus. The abundant
rhachistognathids (71—80 percent) indicate a relatively
high-energy shoal to near-shoal environment. The virtual
absence of conodonts other than adetognathids (20—29 per-
cent) favors a back—shoal setting. Environmental interpreta-
tions, based on microlithofacies, generally match the
conodont-based interpretations. These three samples are
plotted with the adetognathid-rhachistognathid open—
platform to near-shoal biofacies on figure 10C .

SHOAL OR TIDAL—CHANNEL ENVIRONMENTS

High-energy shoal or tidal-channel environments
include oolitic-rich and skeletal-rich grainstones. Although
no tidal channels were distinguished in the field, some con—
odont and microlithofacies samples produce a well-sorted
mixture of grains derived from open-platform, open-
marine, and shoal environments that are compatible with a
tidal-channel setting.

Five samples qualifying for biofacies analysis are from
massive—bedded, very well to well—sorted grainstone con—
taining mixtures of common to minor bioclasts (foramini-
fers, bryozoans, pelmatozoans, algae, brachiopods, and
bivalves), ooids, superficial ooids, peloids, intraclasts, and

CONODONT BIOFACIES 29

quartz (table 2). Conodonts are common (21/kg) and
remarkably well preserved; 67 percent are generically
determinate suggesting the conodonts lived in and (or) adja-
cent to shoal and tidal-channel environments.

Rhachistognathids overwhelmingly dominate the shoal
and tidal—channel environments, making up 73 to 90 percent
of the collections. In the upper member of the Wahoo Lime-
stone, this group is probably as diverse as in any other suc-
cession thus far described (for example, Baesemann and
Lane, 1985). Specimens are abundant and extremely robust.
If Rhachistognathus minutus had been first described from
the Wahoo, its trivial name would have been gigantus. The
rhachistognathids include, in order of decreasing abun—
dance, R. muricatus, R. minutus subspp., and R. websteri.
The two lowest samples are dominated by R. muricatus, the
next higher two by R. websterz', and the stratigraphically
highest by R. minutus subspp. Species of Rhachistognathus
probably occupied different areas of the shoal and tidal-
channel environments. The replacement of R. muricatus by
R. websteri and subsequent replacement of R. websteri by
R. minutus subspp. generally parallel a major transgression
and the concomitant expansion of shoal facies in the upper
member of the Wahoo Limestone. The same species succes-
sion is found at similar stratigraphic levels in the near—shoal
open—platform environment (see tables 1 and 2). Morpho—
logically, R. muricatus and R. websteri are more variable
than R. minutus subspp., likely reflecting their adaptation to
variable environments. Rhachistognathus minutus subspp.
first appears in the study section 14 m above the base of the
upper member and eventually replaces other rhachisto-
gnathids as the dominant species in environments favorable
for the genus. The more uniform and symmetrical morphol-
ogy of R. minutus subspp. suggests its adaptation to more
uniform, normal-marine environments. Indeed, R. minutus
subspp. is the dominant rhachistognathid in seaward
settings.

Adetognathids, the only other group common to the
shoal and tidal-channel environments, make up 10 to 27
percent of the collections. Their relative abundance does not
appear to correlate well with any particular species of Rha-
chistognathus. The adetognathids are probably migrants
and (or) hydraulic admixtures from the open platform. Vir-
tually no other conodonts occur in this biofacies in these
environments (table 1).

NEAR-SHOAL,OPEN-MAR1NE ENVIRONMENT

Three samples from the rhachistognathid biofacies are
attributed to this environment (table 2). One sample (133.5
m above the base of the Wahoo Limestone) is from moder-
ately sorted, bryozoan grainstone containing common pel-
matozoans and a variety of minor bioclasts, peloids,
intraclasts, and quartz. Conodonts are abundant (34/kg);
62 percent are generically determinate. They include

rhachistognathids (77 percent), adetognathids (14 percent),
and declinognathodids (9 percent). The rhachistognathids
indicate proximity to a high-energy environment, and the
declinognathodids suggest a position seaward of a shoal or
tidal channel. Microlithofacies also suggest a near-shoal,
open-marine setting, but of moderate energy (table 2). An
open-marine shoal apron seems appropriate for a faunule
dominated by cosmopolitan Rhachistognathus minutus sub—
spp. The second sample (at 232 m) is a well-sorted bryo-
zoan grainstone containing common pelmatozoans and
minor bioclasts of gastropods, oncoids, foraminifers, algae,
bivalves, and brachiopods. Conodonts are relatively com-
mon (ll/kg), and 43 percent are determinable to genus.
These include rhachistognathids (54 percent), idiognathod-
ids (23 percent), adetognathids (12 percent), and declino-
gnathodids (10 percent). For convenience, this sample is
included in the rhachistognathid biofacies even though rha-
chistognathids make up less than 70 percent of the faunule.
Rhachistognathids indicate proximity to a high-energy envi-
ronment. The declinognathodids and idiognathodids sug-
gest open-marine conditions, and the adetognathids, in
particular A. spathus, may indicate proximity to an open-
platform high—energy regime. Taken together, this mix
favors a near-shoal, open—marine setting, assuming some of
the adetognathids are postmortem admixtures. Alterna-
tively, declinognathodids may have been carried over the
shoals and into the open platform. Microlithofacies support
either interpretation. In the overall TR sequence of the
upper member of the Wahoo Limestone, both samples occur
at the transition from open-platform to shoal conditions,
thus possibly favoring an open-platform interpretation. The
high percentage of declinognathodids and idiognathodids
influenced the choice of an open—marine near-shoal deposi-
tional environment.

A third collection, (187 m above the base of the Wahoo
Limestone) contains the greatest number of Rhachisto-
gnathus minutus declinams in our sample set and is ques-
tionably included in this environment. It is the most produc-
tive sample (SI/kg) and yields 62 percent generically
determinate conodonts. No other rhachistognathids occur in
this sample; other conodonts include 10 percent declinogna—
thodids and 3 percent each of idiognathodids and adeto-
gnathids. The association suggests an open-marine shoal-
apron to near-shoal environment. The collection is from a
moderately sorted bryozoan grainstone interbedded with
fine-grained foraminiferan packstone that could have
formed in open-platform and (or) open-marine environ—
ments. Perhaps R. m. declinatus occupied the open-marine
shoal apron. The unusual species association may have
resulted from sampling two lithologies with bryozoan
grainstone producing rhachistognathids and adetognathids
and the deeper(?) water foraminiferan packstone supplying
idiognathodids and declinognathodids.

30 CONODONT BIOSTRATIGRAPl-IY AND BIOFACIES OF THE WAHOO LIMESTONE

DECLINOGNATHODID-RELATED BIOFACIES

NEAR-SHOAL, OPEN-MARINE ENVIRONMENT

Two samples of moderately sorted bryozoan grain—
stone to packstone containing common pelmatozoans and
minor brachiopod bioclasts and ooids produced a declino-
gnathodid and declinognathodid-idiognathodid biofacies
(table 2; 197.5 and 207 m above the base of the Wahoo
Limestone). Conodonts are rare (6/kg); only 28 percent are
generically determinate suggesting an abundant influx of
fragments from high—energy environments. Declinognatho—
dus noduliferus, chiefly D. n. noduliferus, is most abundant
(62 percent), followed by idiognathodids (21 percent) and
Rhachistognathus minutus declinatus (9 percent). The spe—
cies association and microlithofacies suggest an open-
marine, near—shoal depositional environment. Both samples
are from strata that represent the maximum transgression
during deposition of the upper part of the Wahoo
Limestone.

One sample (table 2; 177 m above the base of the
Wahoo Limestone) representing a declinognathodid-
rhachistognathid biofacies is from a poorly sorted grain-
stone that contains a variety of bioclasts (for example,
algae, foraminifers, bryozoans, and oncoids) and peloids,
ooids, superficial ooids, and intraclasts. Conodonts are rare
(7/kg); 50 percent are generically determinate. Subequal
numbers of Declinognathodus noduliferus noduliferus and
Rhachistognathus minutus (chiefly R. m. declinams) sug~
gest a near-shoal, open-marine setting. The bioclasts and
lithoclasts are a mix of open-platform (particularly several
types of algae), shoal, and open-marine forms that might
represent a tidal—channel in proximity to ooid shoals. The
conodonts do not argue against this interpretation. This
sample has been included in the shoal to tidal-channel envi-
ronment on figure 10C.

LOW-ENERGY. OPEN-PLATFORM AND (OR)
OPEN-MARINE ENVIRONMENT

Seven samples produced declinognathodids with and
without other associated open-marine and shallow—water
genera (table 2). Three samples (table 2; 152, 178, and 250
m above the base of the Wahoo Limestone) indicate that the
low-energy, open-marine environment supported only low
numbers of declinognathodids (3/kg). The samples, from
lowest to highest, are lime mudstone, poorly sorted pack-
stone containing common bioclasts of bryozoans and pel-
matozoans, and a dolomitized mudstone to wackestone.
Microlithofacies and conodont biofacies both indicate an
open-marine depositional environment.

Only two samples from the declinognathodid-related
biofacies produced Declinognathodus noduliferus subspp.
together with [diagnathodus sinuosus (table 2; 217.5 and
237 m above the base of the Wahoo Limestone). Both are

poorly sorted packstone containing common bioclasts of
bryozoans. pelmatozoans, and brachiopods and minor
algae. Conodonts are rare to common (8—17/kg), and only
40 percent are generically determinate. The conodont spe-
cies associations indicate a low-energy, open-marine envi—
ronment; microlithofacies indicate the same environment
for one sample (at 217.5 m) and an open-platform to open-
marine environment for the other sample.

Microlithofacies and conodont biofacies of the final
two samples indicate a low-energy, open-platform or
open-marine depositional environment (table 2; I42 and
162 m above the base of the Wahoo Limestone). These are
included in the low-energy open-marine environment on
figure 10C. The lower sample is dolomitized packstone that
contains common bryozoans and minor quartz and bioclasts
of brachiopods and pelmatozoans. These constituents indi-
cate a low-energy open-platform or open-marine environ-
ment. The conodont biofacies is equally ambiguous.
Rhachistognathids (47 percent) suggest a relatively high—
energy near—shoal or shoal setting; adetognathids (31 per-
cent) suggest proximity to a back-shoal area, but declinog-
nathodids (22 percent) favor a more open—marine setting.
The sample could represent postmortem seaward transport
of adetognathids and probably rhachistognathids into an
open-marine habitat that contained low numbers of decli-
nognathodids. Alternatively, the declinognathodids could
have been transported to the open platform. The higher
sample is a dolomitized packstone-wackestone containing
some grains possibly derived from the open platform
(minor peloids and quartz and rare ooids, spicules, and
ostracodes). The conodonts are a mix of platform, shoal,
and open—marine forms (29 percent adetognathids, 40 per-
cent rhachistognathids, and 27 percent declinognathodids).

BIOFACIES SUMMARY

The Wahoo Limestone formed in chiefly open—
platform, near—shoal, and open-marine environments on the
shallow, inner part of a high—energy carbonate ramp. In the
uppermost Mississippian and lowermost Pennsylvanian part
of the Wahoo Limestone, shoal facies were uncommon so
that open—platform and open-marine microlithofacies and
conodont biofacies were not clearly separated. Grain types
and, to a lesser extent, conodonts were hydraulically spread
beyond their original settings making some environmental
interpretations equivocal. The use of conodont biofacies
and microfacies in concert clarifies some of these environ-
mental ambiguities. In the upper member of the Wahoo
Limestone, extensive ooid and skeletal shoal tracts sepa-
rated open-marine and open-platform environments produc—
ing more distinct biofacies and diagnostic microlithofacies.
Rhachistognathids thrived in and adjacent to the shoal
facies. After death, many of their skeletal elements
remained in place, however, a substantial number were

CONODONT PRESERVATION AND CAI VALUES 3]

washed into surrounding environments, masking original
species associations (see table 2). Similarly, mixing of car-
bonate grains obscures microlithofacies interpretations. The
vertical succession of conodont biofacies substantiates our
microlithofacies interpretations that indicate the upper part
of the Wahoo Limestone formed in a TR sequence passing
from restricted platform to shoals and, finally, back to
restricted platform. Additional studies are needed to further
integrate conodont biofacies and microlithofacies analyses.

CON ODONT PRESERVATION
AND CAI VALUES

Epstein and others (1977) and Rejebian and others
(1987) demonstrated in controlled laboratory experiments
that color alteration in conodonts is time and temperature
dependent. These color changes were assigned color alter-
ation indices (CAI) from 1 to 8. Conodonts visibly change
from pale yellow to brown and black (CAIs 1 to 5) from 50°
to 300°C as a result of carbonization of the trace amounts of
organic matter sealed within a conodont element. Con—
odonts change from black to gray, opaque white, and finally
crystal clear (CAIs 5 to 8) from 300° to >600°C as a result
of loss of carbon and water of crystallization and
recrystallization.

Conodonts altered during burial metamorphism have
consistent CAI values, locally and regionally, that reflect
depth and duration of burial; textural alteration related to
burial thermal regimes does not generally begin until a CAI
of 4.5 or greater. In contrast, conodonts recovered from
contact-metamorphosed or hydrothermally altered rocks
have a range of CAI values locally within an area and even
within a single sample; these can be texturally unaltered to
corroded and may be fractured or deformed. If a range of
CA1 values occurs in a small area, the minimum value is
used to estimate the regional background (burial metamor-
phic) temperature (Rejebian and others, 1987). Signifi-
cantly, CAI values of 6 and 7 can also be produced by
relatively low—temperature saline solutions. These solutions
corrode conodonts and oxidize their organic matter thereby
producing CAI values of 6 and 7 that are unrelated to the
thermal regimes that can also produce these values during
burial and contact metamorphism (Rejebian and others,
1987; Harris and others, 1990). Characteristically, con-
odonts from hydrothermally altered rocks tend to have low
to medium CAI values mixed with values of 6 and 7; CAI
values of 5, 5.5, and 8 are generally absent.

CAI values in Ordovician through Permian rocks in
the Sadlerochit Mountains range chiefly from 3 to 4 (Johns-
son and others, 1992) suggesting that regional burial tem-
peratures reached at least 150° to 200°C. None of the
samples reported by them have CAI values greater than 4.5.
Nine samples from a 102-m-thick section in the upper part
of the Wahoo Limestone at Katakturuk River gorge (fig. 2,

loc. 2), about 40 km west of the study section, produced
conodonts having consistent CAI values of 3 to 3.5 (app. 1,
locs. 2a—j).

In the study section, 71 of 73 samples could be ana-
lyzed for CAI; two samples contain conodonts that were too
few and (or) small for CAI analysis (table 1). CAI values of
3 to 4.5 and 6 were determined; no CAI values of 5 were
observed. Most samples (96 percent) contain conodonts of
CAI 4, but half of these have a mixture of CAI values
(chiefly 4 and 6, rarely 3, and very rarely 3.5 and 4.5). In
addition, most conodonts have a sugary and (or) corroded
texture (many are coated with dolomite crystals; pl. 5, figs.
18, 19). The range of CA1 values and textures suggest
hydrothermal alteration of the Wahoo Limestone. A section
1 km west of the study section (fig. 2, loc. 1B1b—e), pro-
duced CAIs of 4 and 6 in four samples taken immediately
above the Mississippian-Pennsylvanian boundary.

What caused the anomalously “high” CAI 6 values in
the study area? Nearly 50 percent of the samples produced
some conodonts having a CAI of 6. About 60 percent of the
anomalous samples are from grainstone or packstone-
grainstone and another 30 percent are from a variety of
dolomitized carbonate rocks. These data suggest positive
correlation between anomalous CAI and rock porosity and
permeability. However, not all grainstones or dolomitized
carbonate rocks produced conodonts having anomalous
CAIs. Some of the variability in CA1 values could be
related to occlusion of porosity and permeability by
cements that formed prior to deposition of the Permian
Echooka Formation (Watts, 1991). To date, the carbonate—
cement stratigraphy of the study section has not been ana-
lyzed. Carlson (1990) and Watts (1991), however, partly
analyzed the carbonate-cement stratigraphy of a section 3
km to the southwest (fig. 2, loc. 1C) and found that most of
the cements in the Wahoo Limestone formed prior to depo—
sition of the Echooka Formation. But, post-Permian
cements do form 20 to 80 percent of the cement in the low-
ermost 35 m of the Wahoo Limestone. Some of this porosity
may have still been open for fluid migration during orogen-
esis. The anomalous CAI values, at least in the lower mem-
ber at the study section, may have formed prior to or
concurrently with these late-stage cements, but other inter—
vals of anomalous CAIs may be related to still other factors.
For example, fracture porosity (related to Late Cretaceous
to Holocene regional orogenesis; Wallace and Hanks, 1990)
undoubtedly influenced hydrothermal circulation patterns.

Two intervals in our section lack conodonts having
anomalous CAIs: (1) an interval from 69 to 97 m above the
base of the Wahoo Limestone that approximates the quartz-
rich lower part of the upper member of the formation and
(2) a lO—m-thick interval at the top of the upper member
containing a higher than average percentage of undolo-
mitized spiculitic mudstone and wackestone. These data
suggest a negative correlation between anomalously high
CAI values and mixed mineralogy or poorly washed

32 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

deposits; such rock types tend to have low porosity and per-
meability. Much of the above data suggest that the anoma-
lous CAI values of 6 were produced by hydrothermal
solutions (probably low-temperature saline solutions) mov—
ing through relatively permeable channelways and possibly
elevating CAIs no more than one index value (from 3 to 3.5
or 4), as well as corroding and bleaching some specimens to
produce CAIs of 6. Additional samples from the uppermost
part of the Alapah Limestone at the study section are
severely bleached and corroded and approximate a CAI of
7, suggesting increased alteration at this level. Watts (1990)
also noted that porous dolostones and spar-filled caverns in
the upper part of the Alapah Limestone probably acted as
channelways for hydrothermal fluids. The hydrothermal
alteration occurred after the early Atokan, most likely after
the Permian. It is probably related to Brookian orogenesis
and occurred after maximum burial metamorphism that ele—
vated CAI values to 3 or 3.5 in Carboniferous and Permian
rocks.

SYSTEMATIC PALEONTOLOGY

We have used the element notation summarized by
Sweet (1988, fig. 2.10). Most of the generically and specifi-
cally determinate specimens in our collections are Pa ele-
ments. Wherever possible we have tried to identify other
elements of apparatuses, particularly for hindeodids, idio-
prioniodids, and kladognathids (table 1). Genera are listed
alphabetically. Many specimens are easily assignable to a
genus but are not well enough preserved for specific deter-
mination. Most conodonts in the collections have under—
gone extensive postmortem transport and are thus
incomplete and abraded; moreover, some are diagenetically
and hydrothermally altered.

All specimens shown on plates 1—5 are reposited in the
U.S. National Museum (USNM), Washington, DC. All
other specimens are in the collections of the conodont labor-
atory of the U.S. Geological Survey, Reston, Va., and are
cataloged by USGS collection number. Table l and plate 6
show the distribution and abundance of conodont elements,
and figure 10 and table 2 show their inferred paleoenviron-
mental distribution.

Genus ADE TOGNAT H US Lane, 1967

Type species.—Cavusgnathus lautus Gunnell, 1933
p. 286, pl. 31, figs. 67, 68
Adetognathus lautus (Gunnell, 1933)

Plate 1, figures 1345, 21—24
For synonymy to 1971, see Lane and Straka (1974, p. 64).

1971 Adetognathus gigantus (Gunnell). Lane and others,
pl. 1, fig. 6.
1971 Adetognathus laums (Gunnell). Lane and others, pl.

1, fig 5.

1971

1971

1972

1973

1973

1974

1974

1974

1974

1975

1975

1975

1979

1979

1980

1980

1980

1984

1984

1985b

1985a

1985

1985

1985

Cavusgnathus gigantus Gunnell. Merrill and King,
p. 654—655, pl. 75, figs. 9—22 (only).

Cavusgnathus [autus Gunnell. Merrill and King, p.
655, pl. 75, figs. 23, 24, 26—29 (only).
Cavusgnathus [autus Gunnell. von Bitter, p. 61—63,
pl. 4, figs. 3a—h; pl. 5, figs. la—h.

Adetognathus gigantus (Gunnell). Baesemann, p.
696—697, pl. 2, figs. 23?—28?, 32?, 33?, 35, 36. 37?.
3841.

Adelognathus [aunts (Gunnell). Baesemann, p. 697,
pl. 2, figs. 29—31, 34.

Adetognathus [autus (Gunnell). Lane and Straka,
p. 64—65, figs. 36: 17,21, 22, 25—31; figs. 38: 1—4,
6—8, 10—15, 20; figs. 39: 14, 15, 19, 20; figs. 40: 1—
3, 7—14?.

Cavusgnathus lautus Gunnell. Merrill, pl. 1, figs. 8,
9.

Adetognathus gigantus (Gunnell). Toomey and oth—
ers, pl. 3, fig. 15.

Adetognathus [autus (Gunnell). Toomey and others.
pl. 3, fig. 14.

Adetognathus gigantus (Gunnell).
p. 101, pl. 3, figs. 32, 33, 40,41, 46, 47.
Adetognathus lautus (Gunnell). Perlmutter, p. 101,
pl. 3, figs. 34—39, 42—45.

Cavusgnathus lautus Gunnell. Merrill, p. 44—46,
figs. 14: 8?, 9, (not figs. 14: 1, 2); figs. 15: 1, 2, 13—
16; figs. 16: 3, 4, 36, 37; (not figs. 17: 1, 2).
Cavusgnathus [autus Gunnell. Einor and others,
pl. 14, figs. l3a—c.

Adetognarhus giganms (Gunnell). Semichatova and
others, pl. 22, fig. 16.

Adetognathus [autus (Gunnell). Bender, p. 8, 9,
pl. 4, figs. 26—33.

Cavusgnathus lautus Gunnell. Merrill and Powell,
pl. 1, figs. 30—33.

Adetognathus [autus (Gunnell). Tynan, p. 1298,
1299, pl. 2, figs. 12, 13, 20, 21 (not fig. 22).
Adetognathus spp. Driese and others, pl. 1, figs. 1—
3.

Adetognathus [aunts (Gunnell). Grayson, pl. 3,
figs. 8, 9, 26, 27.

Adetognathus [autus (Gunnell). Grayson and others,
p. 124, pl. 1, figs. 22, 29.

Adetognathus [autus (Gunnell). Lane and others,
figs. 6D, E.

Adetognathus [autus (Gunnell). Rexroad and
Merrill, p. 45, 46, pl. 2, figs. 5, 6?, 28—39; pl. 3,
figs. 26—28; pl. 4, figs. 22—25.

Adetognathus gigantus (Gunnell). Skipp and others,
pl. 8, fig. 7.

Adetognathus [autus (Gunnell). Skipp and others,
pl. 8, fig. 6.

Perlm utter,

SYSTEMATIC PALEONTOLOGY 33

1985 Adetognathus lautus (Gunnell). Wardlaw, p. 400,
pl. 3, fig. 7.

1985 Adetognathus spathus (Dunn). Wardlaw, p. 400,
pl. 2, figs. 7, 8.

1989 Cavusgnathus lautus Gunnell. Merrill and Grayson,
pl. 1, figs. 31, 32, 33?, 34?; pl. 2, figs. 20—23, 24?,
257—297.

1991 Adetognathus lautus (Gunnell). Brown and others,
figs. 7: 8—11. ,

1991 Adetognathus lautus (Gunnell). Morrow and

Webster, pl. 1, figs. 4—11.
Adetognathus lautus (Gunnell). Nemirovskaya and
others, pl. 3, figs. 20—24.
Adetognathus lautus
Webster, pl. 1, fig. 12.
Adetognathus lautus (Gunnell) morphotype A.
Weibel and Norby, p. 44, 45, text-fig. 5, pl. 2,
figs. 1—35.
Cavusgnathus lautus Gunnell. Sutherland and Gray-
son, pl. 2, fig. 2.
Remarks—Rexroad and Merrill (1985) suggest that A.
spathus may be a recurrent ecophenotype of A. lautus. We
retain A. spathus, however, as a separate taxon to test this
concept; see remarks under A. spathus.

A few sinistral specimens (pl. 1, figs. 13—15) have a
short right-trending carinal extension of the blade.

The first appearance of Adetognathus lautus below
Deciinognathodus noduliferus defines the Upper muricatus
Subzone of the latest Chesterian. Adetognathus lautus
occurs in two collections from 72 and 65 m below the top of
the Alapah Limestone (app. 1, locs. lAla, b) but is repre-
sented by only one specimen in the Mississippian part of the
overlying Wahoo Limestone. This specimen is from a sam-
ple taken 53.4 m above the base of the Wahoo Limestone
(app. 1, 10c. lAlc), about 50 m along strike from USGS
colln. 30757—PC in the study section (table 1). Adet0g~
nathus lautus does not reappear in our collections from the
study section until 84 m above the base of the Wahoo
Limestone.

Distribution in the study section.—84 to 260.5 m
above the base of the Wahoo Limestone (Morrowan to
lower Atokan; lower minutus Fauna to Idiognathodus
Fauna).

Known stratigraphic range.—uppermost Chesterian
(base of Upper muricatus Subzone) to Lower Permian.

Materiai.—306 Pa elements.

1991

Morrow and

1992 (Gunnell).

1992

1992

Adetognathus spathus (Dunn, 1966)
Plate 1, figures 16—20, 25, 26

1966 Cavusgnathus spatha Dunn, p. 1297, 1299, pl. 157,
figs. 3, 7, 8.

1967 Adetognathuslauta(Gunne11). Lane, pl. 121, figs. 4,
5. 18.

1969 Cavusgnathus spathus Dunn. Webster, p. 28, 29,
pl. 4, figs. 1, 4, 5.
1970b Adetognathus spathus (Dunn). Dunn, p. 327, text—

fig. 10B, pl. 61, figs. 11—13.

1970 Adetognathus gigantus (Gunnell). Thompson,
pl. 139, fig. 26.

1971 Adetognathus spathus (Dunn). Lane and others,
pl. 1, fig. 25.

1971 Cavusgnathus gigantus Gunnell. Merrill and King,
p. 654, 655, pl. 75, figs. 30—32 (only).

1971 Cavusgnathus lautus Gunnell. Merrill and King,

p.655, pl. 75, fig. 25 (only).
?1973 Adetognathus gigantus (Gunnell).
p. 696, 697, pl. 2, figs. 36, 38—41.

Baesemann,

1974 Adetognathus spathus (Dunn). Lane and Straka,
p. 65, 66, figs. 38: 5, 9, 16—19; figs. 40: 4—6.

1975 Cavusgnathus lautus Gunnell. Merrill, figs. 14: 1, 2
(only); figs. 17: 1?, 2?.

1985 Adetognathus spathus (Dunn). Skipp and others,
pl. 8, figs. 1, 4.

1985 Adetognathus spathus (Dunn). Wardlaw, pl. 3,
figs. 8, 9'? (only).

1991 Adetognathus spathus (Dunn). Morrow and
Webster, pl. 1, figs. 12—16; pl. 2, figs. 14.

1992 Adetognathus spathus (Dunn). Morrow and

Webster, pl. 1, fig. 13.

Remarks—Specimens of Adetognathus spathus from
the Wahoo Limestone may have large, exaggerated antler-
like denticles on the posterior process (pl. 1, figs. 25, 26).
Biofacies analysis does not show significant environmental
separation in the distribution of A. spathus and A. lautus.
This may be a consequence of postmortem hydraulic mix-
ing. The Pa-element morphology suggests a very shallow
water, possibly high-energy environment (GD. Webster,
written commun., 1994, and unpub. US. Geological Survey
collections). We agree with Rexroad and Merrill (1985)
who believe that A. spathus may be a recurrent ecopheno-
type of A. lautus.

Distribution in the study section—113 to 257.5 m
above the base of the Wahoo Limestone (Morrowan to
lower Atokan; lower minutus Fauna to Idiognathodus
Fauna).

Known stratigraphic range—uppermost Chesterian
(base of Upper muricatus Subzone) to at least Upper Penn—
sylvanian. Webster (1969) reported Adetognathus spathus
from the uppermost Rhipidomella nevadensis Zone suggest—
ing a latest Chesterian age for the lowest part of its range.

Material.—54 Pa elements.

Adetognathus spp. indet.

Remarks—Included are chiefly broken, abraded, or
juvenile Pa elements.

Distribution in the study section—56 to 261.5 m
above the base of the Wahoo Limestone (Morrowan to

34 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

lower Atokan; nodnliferns—primns Zone to ldiognathodus
Fauna).
Known stratigraphic range—uppermost Chesterian
(base of Upper mnricatus Subzone) to Lower Permian.
Material.—277 Pa and 3 Pb elements.

Genus CAVUSGNATH US Harris and Hollingsworth,
1933

Type species.—Cavusgnathus alta Harris and
Hollingsworth, 1933
p. 201, 10a, b
Cavusgnathus altus Harris and Hollingsworth, 1933

Plate 1, figure 27

For synonymy to 1968, see Thompson and Goebel (1969).

1969 Cavusgnathus alta Harris and Hollingsworth.
Thompson and Goebel, p. 21, 22, pl. 1, figs. 19, 22.

1979 Cavusgnathns altus Harris and Hollingsworth.
Chaplin, p. 276, pl. 3, figs. 1-3.

1981 Cavusgnathus altus Harris and Hollingsworth.
Rexroad, p. 7, 8, pl. 1, figs. 28—34.

1985 Cavusgnathns altns Harris and Hollingsworth.

Wardlaw, p. 400, pl. 3, fig. 13.
1991 Cavusgnathus altus Harris and Hollingsworth.
Stone, p. 17, pl. 4, figs. 1?, 2?, 4, 5?.

Remarks.———Three specimens of Cavusgnathus altus
have a posterior process with 1 or 2 low denticles, a com-
mon characteristic of the species (see photograph of holo-
type in Rexroad and Lane, 1966).

Distribution in the study section—7 to 22 m above the
base of the Wahoo Limestone (uppermost Chesterian;
Upper mnricatus Subzone).

Known stratigraphic range—upper Meramecian to
uppermost Chesterian (Upper muricatus Subzone).

Material.—3 Pa elements.

Cavusgnathus? tytthus Brown and Rexroad, 1990
Plate 1, figures 7—12; plate 5, figure 20

1980 Adetognathns lautus (Gunnell). Tynan, p. 1298,
1299, pl. 2, fig. 22 (only).

1980 Adetognathns n. sp. Tynan, p. 1299, pl. 2, figs. 15—
17.

1990 Cavusgnathns tytthus Brown and Rexroad. Brown
and others, p. 81, 82, text-fig. 5 [part], pl. 1, figs. 1,
4—6, 10—12, 14, 18.

71991 Adetognathus sp. cf. Adetognathus n. sp. Tynan.
Morrow and Webster, pl. 2, figs. 5, 6.

Description—Three Pa-element morphotypes occur in

the Wahoo Limestone. The two most abundant morpho—

types are right sided. The first (pl. 1, figs. 7, 8; = (x morpho-

type of Brown and Rexroad, in Brown and others, 1990) has

a free blade with three to four denticles that joins the right

parapet (outer) and continues as a fixed blade bearing two

to three denticles; the posteriormost denticle is the largest;
therefore, the upper blade profile increases in height poste-
riorly. The left parapet intercepts the blade two to four den-
ticles behind its anterior margin. In lateral view, the outer
margin is slightly to considerably higher than the inner mar-
gin. The free blade of the second morphotype (pl. 1, figs. 9,
10; = [3 morphotype of Brown and Rexroad, in Brown and
others, 1990) joins the platform on or slightly left of the
right parapet; the very low posteriormost denticle may be
slightly to moderately offset to the left; a notch separates the
blade from the platform. The upper margin profile of the
blade forms a moderate asymmetric arch that is highest in
the middle, descends only slightly anteriorly, but steeply
posteriorly. In lateral view, the right parapet margin is
slightly to considerably higher than the left. The third and
rarest Pa morphotype (pl. 1, figs. 11, 12; = y morphotype of
Brown and Rexroad, in Brown and others, 1990) has a free
blade that joins the platform centrally or subcentrally
toward the right. The blade has the same upper margin pro-
file as the B morphotype; the two very low, posteriormost
denticles of the blade continue onto the platform as a short
carina. In lateral view, right and left parapet margins are
approximately equal in height.

Remarks—Characteristics of the OL morphotype do not
appear to change ontogenetically; the [3 morphotype devel—
ops a carinal extension of the blade ontogenetically; no
juveniles of the 'y morphotype were found. The collections
contain chiefly adult specimens. Specimens of Cavns—
gnathns? tytthus in the Wahoo Limestone differ slightly
from topotype material from the Kinkaid Limestone of the
Illinois basin. Carina] extensions of the blade in the [3 and y
morphotypes that are obvious in the material from the
Wahoo Limestone were not noted by Brown and Rexroad
(in Brown and others, 1990). This is probably because their
specimens are small; the name they chose for the species
reflects that condition. The trivial name is somewhat unsuit—
able for the material from the Wahoo Limestone in which
most representatives of the species are rather large.

Because no left-bladed specimens appear to occur in
Cavusgnathus? tytthus, it seems inappropriate to place the
species in Adetognathus, even though its fixed blade is short
and, in some morphotypes, may be absent. Presently, it
seems best to questionably retain it in Cavusgnathus. The
array of morphotypes that occur in C.? tytthus is reminis-
cent of morphotypes assigned to older Mississippian
species of Taphrognathns and Cloghergnathus that are
found in shallow—water, somewhat restricted depositional
environments.

Brown and Rexroad (in Brown and others, 1990) theo-
rized that Cavusgnathns? tytthus is the phylogenetic link
between C. unicornis and C. monocerus (2 Adetognathus
unicornis (Rexroad and Burton) of Lane, 1967). Cavns—
gnathus? tytthus occurs with abundant representatives of C.
unicornis in the lower part of its range in our section; C.
unicornis does not occur above the lower 51 m of the

SYSTEMATIC PALEONTOLOGY 35

Wahoo Limestone, and C. monocerus is absent at the study
section. Thus, our data neither confirm nor contradict
Brown and Rexroad’s phylogenetic hypothesis.

Distribution in the study section—22 to 76.5 m above
the base of the Wahoo Limestone (uppermost Chesterian to
lowermost Morrowan; Upper muricatus Subzone to within
noduliferus-primus Zone). Cavusgnathus? tytthus occurs in
the upper part of the Alapah Limestone and in many collec—
tions from the Wahoo Limestone in the northeast Brooks
Range including the type section at Wahoo Lake (app. 1,
loc. 4A1c), at Plunge Creek (app. 1, loc. 6), and as far east
as the Clarence River at the Canadian border (app. 1, locs.
10A1b, c).

Known stratigraphic range—upper Chesterian and
lower Morrowan (upper part of naviculus Zone (Brown and
others, 1990) into noduliferus-primus Zone).

Material.—99 Pa and 3 Pb (pl. 5, fig. 20) elements.

Cavusgnathus unicornis Youngquist and Miller, 1949
Plate 1, figures 28—31; plate 2, figures 1—17

For synonymy to 1987, see Rexroad and Horowitz (1990).
Additions and exceptions are noted below.

1979 Cavusgnathus unicornis Youngquist and Miller.
Aisenverg and others, pl. 6, fig. 8.

Cavusgnathus unicornis Youngquist and Miller.
Skipp and others, pl. 8, fig. 10.

Cavusgnathus unicornis Youngquist and Miller.
Armstrong and Purnell, pl. 1, figs. 11—13 (only).
Cavusgnathus unicornis Youngquist and Miller.
Wang and Higgins, p. 275, 276, pl. 13, figs. 2—4.
Cavusgnathus unicornis Youngquist and Miller.
Rexroad and Horowitz, p. 499, 500, pl. 1, figs. 5—20.

1985

1987

1989

1990

1991 Cavusgnathus unicornis Youngquist and Miller.
Morrow and Webster, pl. 3, figs. 1—3.

1992 Cavusgnathus unicornis Youngquist and Miller.
Morrow and Webster, pl. 1, fig. 1.

1992 Cavusgnathus unicornis Youngquist and Miller.
Purnell, p. 10, 11, pl. 2, figs. 1—5, 7.

1992 Cavusgnathus cf. unicornis Youngquist and Miller.
Purnell, pl. 2, fig. 6.

1992 Cavusgnathus unicornis Youngquist and Miller.

Weibel and Norby, pl. 1, fig. 18.

Remarks—Rexroad (1981) synonymized Cavus—
gnathus regularis ([3 morphotype) and C. convexus (y mor—
photype) under C. unicornis (0c morphotype). All specimens
have a right-sided free blade that is shorter than the fixed
blade. In the on morphotype, denticles decrease in size ante-
riorly; the largest denticle is posteriormost. The blade pro—
file of the B morphotype is uniform in height or may
decrease slightly anteriorly. The blade profile of the 'y mor-
photype is arched. In collections from the study section,
many of the blade denticles are broken so that morphotypes
are indeterminate. Of the complete specimens, 0L and B mor-
photypes are more common than 7 morphotypes.

Wardlaw (1985, pl. 2, figs. 9—11, 13) included robust,
digyrate elements in the apparatus of Cavusgnathus navicu-
[us that he claimed were vicariously shared by most species
of Cavusgnathus, including C. unicornis. We strongly dis-
agree with this reconstruction and concur with the element
morphotypes determined by Norby (1976) from natural
assemblages. The digyrate elements Wardlaw attributed to
Cavusgnathus belong instead to Kladognathus (see Merrill
and others, 1990). Armstrong and Purnell (1987) also
included an Sc element of Kladognathus as well as two
morphologically dissimilar M elements in the apparatus of
C. unicornis.

Distribution in the study section—0.4 to 50.5 m above
the base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone).

Known stratigraphic range.—upper Meramecian to
uppermost Chesterian (Upper muricatus Subzone).

Material.——415 Pa, 11 Pb, 26 M, and 6 Sc elements.

Cavusgnathus spp. indet.

Remarks.—Chiefly broken, abraded, or juvenile Pa
elements are included in this category.

Distribution in the study section—13.2 to 53 m above
the base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone).

Known stratigraphic range.—upper Meramecian to
uppermost Chesterian (Upper muricatus Subzone).

Material.—122 Pa elements.

Cavusgnathoids

Remarks—Included are posterior Pa-element frag-
ments of Cavusgnathus, Cavusgnathus?, or Adetognathus.

Distribution in the study section—0.4 to 137 m above
the base of the Wahoo Limestone (uppermost Chesterian to
Morrowan; Upper muricatus Subzone to lower minutus
Fauna).

Known stratigraphic range.—upper Meramecian to
Lower Permian.

Material.—-419 Pa element fragments.

Genus DE CLINOGNAT H GB US Dunn, 1966

Type species—Cavusgnathus nodulifera Ellison and
Graves, 1941
p. 4, 5, pl. 3, figs. 4, 6

Remarks—Dunn (1970b) expanded the concept of the
genus to include forms with a median longitudinal trough
and a long, slightly declined, medial carina (: Declinogna—
thodus lateralis (Higgins and Bouckaert)). Grayson and
others (1990) concurred with Dunn’s emendation but con-
sidered D. lateralis morphotypes as vertically persistent
species of Declinognathodus that are convergent with
Neognathoa'us.

36 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

Declinognathodus noduliferus (Ellison and Graves,
1941)

Grayson and others (1990) provide an extensive syn—
onymy for the species.

Remarks.—Declinognathodids in our collections are
assigned to Declinognathodus noduliferus noduliferus, D.
n. japonicus, or D. n. subspp. indeterminate. A few speci—
mens in a single collection (USGS colln. 30786—PC; pl. 3.
fig. 32), 187 m above the base of the Wahoo Limestone,
resemble forms assigned to D. lateralis (Higgins and
Bouckaert) by other workers. These specimens are the larg-
est declinognathodids in a sample that also contains the
most abundant and largest rhachistognathids in our collec-
tions. We suspect that these D. lateralis morphotypes are
ecophenotypic and (or) gerontic specimens. Consequently,
they are included in D. noduliferus.

Specimens identified as Declinognathodus noduliferus
japonicus, however, exhibit variation in ornamentation,
deflection of the carina, and spacing of posterior nodes
within each sample throughout the Wahoo Limestone.
Some specimens have transverse ridges on the anterior
inner margin (pl. 3, figs. 6, 7). All specimens of D. n.
japom'cus have one or two accessory nodes that are in con-
tact with or cleanly separated from the carina near the ante—
rior platform margin. Juvenile specimens tend to have more
widely spaced posterior nodes and a straighter carina. Spec-
imens with very nodose ornamentation (pl. 3, fig. 22) are
rare and considered ecophenotypes; Grayson (1984, p. 50)
erected a separate species (Idiognathoides marginodosus; =
Declinognathodus marginodosus of Grayson, 1990) for
such forms. We see no stratigraphic succession of D. nodu-
liferus morphotypes in our section and, therefore, retain
these forms in D. n. japom'cus.

Declinognathodus noduliferusjaponicus (Igo and Koike,
1964)

Plate 3, figures [—8, 19—22

1964 Streptognathodus japonicus Igo and Koike, p. 188,
189, pl. 28, figs. 5~10, 711—13.

1966 Declinognathoa'us
pl. 158, figs. 4, 8.

1967 Gnathodus nodulifera (Ellison and Graves). Koike,
p. 297, 298, pl. 3, figs. 9, 11 (only).

1967 ldiognathoides aff. l. nodulifera (Ellison and
Graves). Lane, p. 938, pl. 123, figs. 10, 13 (only).

1968 Gnathodus japonicus (Igo and Koike). Higgins and
Bouckaert, p. 35, 36, pl. 4, figs. 1,2,4.

1970b Declinagnalhoa’us noduliferus (Ellison and Graves).
Dunn, p. 330, pl. 62, fig. 1 only. text-fig. 9D,

1970 ldiognathoides noduliferus (Ellison and Graves).
Thompson, p. 1046, 1047, pl. 139, figs. 2?, 3?, 5, 6,
8, 16, 20.

nevadensis Dunn, p. 1300,

1971 Gnathodus noduliferus (Ellison and Graves). Lane
and others, pl. 1, fig. 32.

1971 Idiognathoides nodulifems (Ellison and Graves).
Lane and others, pl. 1, fig. 11.

1972 Idiognathoides noduliferus (Ellison and Graves)
transitional to Streptognalhodus lateralis Higgins
and Bouckaert. Austin, pl. 1, figs. 33, 40.

1972 Unnamed figured specimens. Austin, pl. 2, figs. 27,
28.

1974 Idiognathoides noduliferus (Ellison and Graves).
Lane and Straka, p. 85—87, figs. 35: 1—3, 5?, 6?, 10—
12, 13—15?.

1975 Idiognathoides noduliferus japom'cus (Igo and
Koike). Higgins, p. 54, pl. 14, figs. 7—10.

1979 Declinognathodus nodulzferus (Ellison and Graves).
Semichatova and others, pl. 22, figs. 12, 13.

1980 Idiognathoides noduliferus japonicus (Igo and
Koike). Metcalfe, p. 306, pl. 38, figs. 14?, 17?.

?1984 Declinagnalhodus noduliferus japonicus (Igo and
Koike). Orchard and Struik, pl. 2, fig. 9.

1984 Idiognathoides marginodosus Morphotype B, Gray—
son, p. 50, pl. 1, figs. 3, 4, 9—11 (pl. 2, fig. 17: pl. 1,
fig. 10),13, 14; pl. 3, fig. 19?; pl. 4, figs. 11, 12, 22.

1985 Declinognathodus nodulifems japonicus (Igo and
Koike). van den Boogaard and Bless, p. 140, 141,
fig. 9: 5.

1985a Declinagnalhoa’us noduliferus japonicus (Igo and
Koike). Grayson and others, p. 163—165, pl. 1, figs.
13, 18.

1985b ldiognathoides marginodasus Grayson. Grayson
and others, pl. 1, fig. 21.

?1985aDeclin0gnathoa’us noduliferus (Ellison and Graves).
Lane and others, figs. 7D—G [figs 7D, E, ?Decli-
nognathodus noduliferus; figs. 7F, G, D. noduliferus
japonicus?].

1985 Declinognathoa'us noduliferus (Ellison and Graves).
Sada and others, pl. 1, fig. 3.

1987 Declinagnalhodus marginodosus (Grayson). Gray-
son and others, pl. 8, figs. 8, 11.

1987 Declinagnathodus noduliferus japonicus (Igo and
Koike). Nemirovskaya, pl. 1, figs. 12, 15, 19.

1988 Declinognathodus noduliferus japonicus (Igo and
Koike). Dong and Ji, pl. 6, figs. 7, 8.

1989 Declinognathodus noduliferus japonicus (Igo and

Koike). Wang and Higgins, p. 276, pl. 1, figs. 6—9.

Declinognathodus marginodosus (Grayson). Gray—

son, p. 90, 91, pl. 4, figs. 9, 10?, 11—13.

1990 “Declinagnalhodus” marginodosus
Grayson and others, p. 365, pl. 1, fig. 28.

1990 “Declinognathodus” noduliferus (Ellison and
Graves). Grayson and others, p. 365, pl. 1, fig. 21.

19923 Declinognathoa'us noduliferus s.l. (Ellison and
Graves). Nigmadganov and Nemirovskaya, pl. 3,
figs. 6?, 7, 10.

1990

(Grayson).

SYSTEMATIC PALEONTOLOGY 37

1992 Declinognathodus marginodosus (Grayson). Suther-
land and Grayson, pl. 2. fig. 11.

Remarks—Most specimens are identical to the types
of Declinognathodus noduliferus japonicus. Several speci—
mens (pl. 3, fig. 22), however, have an undeflected carina,
relatively even-noded margin and carina, and a single,
prominent, round node that is cleanly separated from the
carina near the anterior margin of the outer lobe. Such
forms were included in D. marginodosus by Grayson (1990)
and Sutherland and Grayson (1992). We include these in D.
n. japonicus because some populations are intergradational
between D. n. japonicus and D. marginoa'osus (Grayson).
We regard D. marginodosus to be a possible shallower
water ecophenotype of D. n. japonicus. Partial division of
the anteriormost node produces an incipient third node in a
few specimens (pl. 3, fig. 9).

Distribution in the study section—56 to 250 m above
the base of the Wahoo Limestone (lowest Morrowan to
lower Atokan; noduliferus-primus Zone to ldiognathodus
Fauna).

Known stratigraphic range.—lowest Morrowan
(base of noduliferus-primus Zone) to at least lower
Desmoinesian(?).

Material.—144 Pa elements.

Declinognathodus noduliferus noduliferus (Ellison and
Graves, 1941)

Plate 3, figures 10—14, 32

1941 Cavusgnathus nodulifera Ellison and Graves, p. 4,
5, pl. 3, fig. 4 (only).

1960 Streptognathodus parallelus Clarke, p. 29, pl. 5,
figs. 6—8, 14, 15.

1967 Gnathodus nodulifera (Ellison and Graves). Koike,
p. 297, 298, pl. 3, figs. 10, 12? (only).

?1967 ldiognathoides aff. l. nodulzfem (Ellison and
Graves). Lane, p. 938, pl. 123, figs. 9, 11, 17 (only).

1968 Gnathodus noduliferus (Ellison and Graves).
Higgins and Bouckaert, p. 33~35, pl. 2, figs. 6, 12.

1968 Idiognathoides nodulifera (Ellison and Graves). Igo
and Koike, p. 28, 29, pl. 3, figs. 7, 8, 9?, 10 (only).

1969 Streptognathodus noduliferus (Ellison and Graves).

Webster, p. 48, 49, pl. 4, figs. 7, 8.
1970b Declinognathodus noduliferus (Ellison and Graves).
Dunn, p. 330, pl. 62, fig. 2 (only).

1971 Gnathodus noduliferus (Ellison and Graves). Lane
and others, pl. 1, fig. 32.

?1971 Idiognathoides noduliferus (Ellison and Graves).
Lane and others, pl. 1, fig. 11.

1972 Idiognathoides noduliferus (Ellison and Graves)

transitional t0 Streptognathodus lateralis Higgins
and Bouckaert. Austin, pl. 1, figs. 2, 4, 5, 7, 11, 12,
14, 15, 16?, 17?, 18, 19, 27, 29—32, 34—36?, 38, 39,
41, 44, 45, 49, 50, 53?, 54.

1972

1972

1974

?1974

1975

1975

1979

1979

1980

1980

1980

1984

1985a

1985

1985

1985

1985

?1985

1985

1987

1987

1987

1987

1987

1988

Streptognathodus lateralis Higgins and Bouckaert.
Austin, pl. 2, fig. 31.

Unnamed figured specimen. Austin, pl. 2, fig. 33.
Idiognathoides noduliferus (Ellison and Graves).
Lane and Straka, p. 85—87, pl. 35, figs. 11—13; pl.
41, figs. 15—17.

Gnathodus noduliferus (Ellison and Graves). Mer—
rill, pl. 1, figs. 28, 29.

Idiognathoides noduliferus noduliferus (Ellison and
Graves). Higgins, p. 54, pl. 14, figs. 15, 16.
Idiognathoides noduliferus inaequalis Higgins. Hig-
gins, pl. 12, figs. 3, 4.

Declinognathodus noduliferus (Ellison and Graves).
Aisenverg and others, p]. 6, figs. 17, 18.
Streptognathodus noduliferus (Ellison and Graves).
Einor and others, pl. 14, figs. 6, 7.

ldiognathoides noduliferus (Ellison and Graves).
Bender, p. 12, pl. 1, figs. 3?, 8—15, 16?.
Idiognathoides noduliferus inaequalis Higgins.
Metcalfe, p. 306 (part), pl. 38, fig. 15.
ldiognathoides noduliferus noduliferus (Ellison and
Graves). Metcalfe, p. 306, pl. 38, figs. 16. 18.
Idiognathoides marginodosus Morphotype A, Gray-
son, p.50, pl. 1, fig. 7.

Declinognathoa'us noduliferus japonicus (Igo and
Koike). Grayson and others, p. 163—165, pl. 1, figs.
9, 15, 25.

Declinagnathodus noduliferus inaequalis (Higgins).
Higgins, pl. 6.2, figs. 11, 14; pl. 6.3, figs. 1, 4.
Declinognathodus noduliferus noduliferus (Ellison
and Graves). Higgins, p. 220, p]. 6.2, figs. 13, 15; pl.
6.3, fig. 7.

Idiognathoides noduliferus (Ellison and Graves).
Plafker and others, figs. 48A, B.

ldiognathoides noduliferus (Ellison and Graves).
Savage and Barkeley, p. 1466, 1467, figs. 9: 1—8.
Declinognathodus noduliferus (Ellison and Graves).
Skipp and others, pl. 8, fig. 8 [form transitional from
Gnathodus girtyi to D. noduliferus].
Declinognathoa'us noduliferus (Ellison and Graves).
Wardlaw, p. 397, pl. 1, fig. 1.

Declinognathodus marginodosus (Grayson). Gray—
son and others, pl. 8, figs. 16?, 23, 28?.
Declinognathodus noduliferus (Ellison and Graves).
Nemirovskaya, pl. 1, figs. 7, 9, 11,20, 21.
Declinognathodus inaequalis (Higgins). Riley and
others, pl. 3, fig. 30?.

Declinognathodus noduliferus (Ellison and Graves).
Riley and others, pl. 3, figs. 41?, 42, 43, 44?, 46, 47.
Declinognathoa'us noduliferus noduliferus (Ellison
and Graves). Wang and others, p. 127, pl. 3, figs. 3—
5; pl. 7, fig. 1.

Declinognathodus noduliferus inaequalis (Higgins).
Dong and Ji, pl. 6, fig. 9.

38 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

1988 Declinognathodus noduliferus noduliferus (Ellison

and Graves). Dong and Ji, pl. 6, figs. 5, 6.

1989 Declinognathodus noduliferus noduliferus (Ellison

and Graves). Wang and Higgins, p. 276, 277, pl. 2,

figs. 5—9.

Declinognathodus noduliferus (Ellison and Graves).

Grayson, pl. 1, figs. 10, 13; pl. 3, fig. 29.

Declinognathodus noduliferus (Ellison and Graves).

Grayson and others, p. 362, 363, pl. 1, fig. 21.

1991 Declinognathodus noduliferus noduliferus (Ellison
and Graves). Gibshman and Akhmetshina, pl. 5,
figs. 7, 8.

1991 Declinognathodus noduliferus inaequalis Higgins.
Nemirovskaya and others, pl. 4, figs. 3, 5?, 15.

1990

1990

1992 Declinognathodus noduliferus (Ellison and Graves).
Morrow and Webster, pl. 1, fig. 5.
1993 Declinognathodus noduliferus inaequalis (Higgins).
Duan, p. 206, pl. 3, figs. 7, 8?, 9.
Remarks—Almost all specimens from the Wahoo
Limestone assigned to Declinognathodus noduliferus nodu-
liferus have nodose and (or) transversely ridged parapets, an
outwardly deflected carina, and three or more accessory
nodes on the anterior outer margin (pl. 3, fig. 12). The car-
ina merges with the outer parapet within or slightly poste-
rior to the anterior half of the platform (pl. 3, figs. 11, 12).
According to Higgins (1975, 1985), specimens of D. nodu-
liferus in which the carina merges with the outer parapet
within the posterior half of the platform should be referred
to D. n. inaequalis. None of our specimens are comparable
to the holotype of D. n. inaequalis, which has a carina that
extends well beyond the anterior half of the platform.
Distribution in the study section—~59 to 250 m above
the base of the Wahoo Limestone (lowest Morrowan to
lower Atokan; base of noduliferus-primus Zone to Idiogna~
thodus Fauna).
Known stratigraphic range—lowest Morrowan (base
of noduliferus-primus Zone) to lower Desmoinesian(?).
Material—285 Pa elements.

Declinognathodus noduliferus subspp. indet.

Remarks—Included are chiefly broken, abraded, and
juvenile Pa elements.

Distribution in the study section.——-65 to 243 m above
the base of the Wahoo Limestone (lower Morrowan to
lower Atokan; noduliferus-primus Zone to Idiognathodus
Fauna).

Known stratigraphic range—lowest Morrowan (base
of noduliferus—primus Zone) to lower Desmoinesian(?).

Material.——18 Pa elements.

Genus DIPLOGNATHODUS Kozur and Merrill, 1975

Type species.—Spathognath0dus coloradoensis Murray
and Chronic, 1965
p. 606, 607, pl. 72, figs. 11—13

Remarks—von Bitter and Merrill (1990) recommend
that only forms having a spatulate carina be included within
the genus. They admit that species presently assigned to the
genus are morphologically variable and probably polyphyl-
etic. A single specimen is tentatively assigned to Diplogna-
thodus? ellesmerensis, a species questionably included in
Diplognathodus because its Pa element has a denticulate
carina.

Diplognathodus? ellesmerensis Bender, 1980?
Plate 5, figures 18, 19

1980 Diplognathodus ellesmerensis Bender, p. 9, 10,

pl. 4, figs. 5—7, 11, 15—21,23—25.

1981 Diplognathodus coloradoensis (Murray and
Chronic). Landing and Wardlaw, p. 1257—1259,

pl. 1, figs. 1, 6, 7, 9, 10.

1983 Diplognathodus ellesmerensis Bender. van den
Boogaard, p. 23, 24, pl. 1, fig. a.

1985 Diplognathodus coloradoensis (Murray and
Chronic). Savage and Barkeley, p. 1473, figs. 12: 9—
16.

1990 Diplognathodus? ellesmerensis Bender. von Bitter
and Merrill, fig. 4: 16a—c.

1992 Diplognathodus sp. A. Sutherland and Grayson,
pl. 2, fig. 9.

?1993 Diplognathodus? orphanus Merrill. Lemos, pl. 4,
fig. 6.

Description—One poorly preserved juvenile(?) Pa
element has a free blade bearing eight partly fused denti-
cles. The upper margin profile of the blade gradually
increases in height from the anterior margin to midlength
and then descends abruptly at the intersection of the blade
and platform. A carina of eight mostly fused but distinct
denticles gradually decreases in height toward the posterior
tip of the platform. The platform margin is incomplete; the
lobes appear to be unornamented, oval, and possibly sym—
metrical. The basal cavity is gnathodontid.

Remarks—The single specimen resembles Diplogna-
thodus? ellesmerensis but has a few more denticles on the
carina than specimens illustrated by Bender (1980). More-
over, the upper margin profile of the posterior end of the
carina decreases abruptly in height and is adenticulate in
most of Bender’s specimens.

We agree with Bender (1980) and von Bitter and Mer-
rill (1990) that this species is closer to Diplognathodus?
orphanus (Merrill) than to other diplognathodids.

Distribution in the study section—203 m above the
base of the Wahoo Limestone (upper Morrowan or lower
Atokan; Idiognathodus Fauna).

SYSTEMATIC PALEONTOLOGY 39

Known stratigraphic range.—Diplognath0dus? elles—
merensis is known from the Canadian Arctic islands,
Yukon, southeast Alaska, Oklahoma, Michigan, and Spain
and apparently ranges from upper Morrowan to Desmoine—
sian (von Bitter and Merrill, 1990, fig. 4). Sutherland and
Manger (1984a) recommended that the first appearance of
Diplognathodus or the foraminifer Eoschubertella be used
as a guide to the base of the Atokan. This recommendation
preceded the recognition of diplognathodids in the Mor—
rowan (von Bitter and Merrill, 1990). Diplognathodus?
orphanus appears to be the only known species restricted to
the Atokan.

Material.—1 Pa element.

Genus GNATHODUS Pander, 1856

Type species.—P0lygnathus bilineatus Roundy, 1926
p. 13, pl. 3, figs. IOa—c

Remarks—Gnathodus bilineazus (Roundy) was desig—
nated the type species of Gnathoa'us by Tubbs (1986)
because the types of G. mosquensis, the oldest described
species of the genus, were lost and its type locality was
uncertain.

Gnathodus bilineatus bilineatus (Roundy, 1926)
Plate 2, figures 18, 19; plate 5, figure 23
Only a selected synonymy is given because this subspecies
is widespread, commonly figured and cited in the literature,

and relatively easily diagnosed. See Wang and others
(1987) for additional selected synonymy through 1983.

1926 Polygnathus bilineatus Roundy, p. 13, pl. 3,
figs. 10a—c.

1926 Polygnathus texanus Roundy, p. 14, pl. 3,
figs. 13a, b.

1953 Gnarhodus bilineams (Roundy). Hass, p. 78—80,
pl. 14, figs. 25—29.

1958 Gnathodus bilineatus (Roundy). Stanley, p. 464,
465, pl. 68, fig. 7.

1961 Gnathodus bilineatus (Roundy). Higgins, pl. 10,
fig. 5.

71965 Gnathodus bilineams (Roundy). Dunn, p. 1148,
pl. 140, figs. 7—9.

1967 Gnathodus bilineams (Roundy). Globensky, p. 440,
pl. 58, figs. 9?, 13.

1967 Gnathodus bilineatus (Roundy). Koike, p. 296,
pl. 1, figs. 9—11.

1968 Gnathodus bilineatus bilinearus (Roundy). Higgins
and Bouckaert, p. 29, pl. 3, fig. 9.

1971 Gnathodus bilineatus (Roundy). Rhodes and Austin,
pl. 2, fig. 1.

1974 Gnathodus bilineatus bilineatus (Roundy). Austin
and others, pl. 1, figs. 4, 5, 15, 19, 23.

1974 Gnathodus bilineatus (Roundy). Gromczakiewicz-

Lomnicka, pl. 1, fig. 1.

1974

1974

1974

1975

1979

1979

1985

1985

1985

1986

1986
1986

1986

1987

1987

1987

1987

1988

1989

1989

1990

1990

1990a

1990b

1991

1992a

Gnathodus bilineatus (Roundy). Matthews and
Thomas, pl. 50, fig. 19; pl. 51, figs. 12—15,21—24.
Gnathodus sp. Matthews and Thomas, pl. 50,
fig. 22.

Gnarhoa’us bilineams (Roundy). Rice and Langen—
heim, p. 27, pl. 1, fig. 11.

Gnathodus bilinealus bilineatus (Roundy). Higgins,
p. 28, 29, pl. 11, figs. 1—4, 6, 7.

Gnathodus bilineams bilinealus (Roundy). Aisen-
verg and others, pl. 6, fig. 12.

Gnarhodus bilineatus Morphotype B. Chaplin, p.
276, 279, pl. 3, figs. 8—11; pl. 4, figs. 1, 2; pl. 5,
fig. 2.

Gnathodus bilinearus bilineatus (Roundy). Higgins,
p. 218, pl. 61, figs. 1, 2.

Gnathodus bilineams (Roundy). Varker and Sevas-
topulo, p. 199, pl. 5.4, figs. 19,20.

Gnathodus bilineatus (Roundy). Wardlaw, pl. 1,
fig. 10.

Gnathodus bilinealus bilineams (Roundy). Ji, pl. 1,
figs. 1—4, 6, 8—10.

Gnathodus bilineatus (Roundy). Li, pl. 1, figs. 1, 8.

Gnathoa’us bilineatus (Roundy). Mapes and
Rexroad, p. 117, pl. 2, figs. 22—31.
Gnathodus bilineatus (Roundy). Ruppel and

Lemmer, p. 28, pl. 2, figs. 14, 15.

Gnarhodus bilineams (Roundy). Grayson and oth—
ers, pl. 3, figs. 11, 36; pl. 4, figs. 20—23.

Gnathodus bilineatus (Roundy). Merrill, p. 147—
151, pl. 11, figs. 1—6, 9-18.

Gnathoa'us bilineatus bilineatus (Roundy). Riley
and others, pl. 2, figs. 2, 4.

Gnathodus bilineams bilineams (Roundy). Wang
and others, p. 128, pl. 1, fig. 6.

Gnathodus bilineams bilineams (Roundy). Dong
and Ji, pl. 4, figs. 6—8, 10.

Gnathoa'us bilineatus (Roundy). Ellison and Powell,
pl. 2, figs. 1—6, 13—16.

Gnathodus bilineatus bilineatus (Roundy). Wang
and Higgins, p. 277, 278, pl. 6, figs. 7—11.
Gnathodus bilineatus (Roundy). Grayson, pl. 1,
figs. 25, 267—31.

Gnathodus bilineatus (Roundy). Grayson and oth-
ers, p. 361, 362, pl. 1, figs. 1, 3—6, 10—14, 18—20
[figs 2, 7—9 appear to include two different Pb
morphotypes and have thus been excluded].
Gnathodus bilineams (Roundy). Ramovs, p. 91, 92,
pl. 4, figs. 2, 4, 5, 9, l2.

Gnathodus bilineatus (Roundy). Ramovs, p. 109, pl.
1, figs. 1—3, 11.

Gnathodus bilineatus bilineatus (Roundy). Higgins
and others, pl. 3, fig. 19.

Gnathodus bilineatus bilineatus (Roundy). Nigmad-
ganov and Nemirovskaya, pl. 1, fig. 3.

40 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

1992a Gnathoa'us bilineatus bollandensis Higgins and
Bouckaert. Nigmadganov and Nemirovskaya, pl. 1,
figs. 1, 2.
Gnathoa'us bilineatus (Roundy).
Kononova, pl. 29, figs. 8, 10.
Gnathodus bilineatus (Roundy). Kolar-Jurkovsek
and Jurkovsek, p. 432, pl. 2, figs. 6—8.

Distribution in the study section—0.4 to 53 m above

the base of the Wahoo Limestone (uppermost Chesterian;

Upper muricatus Subzone) and 69 m above the base of the

Wahoo (lower Morrowan—redeposited?)

Known stratigraphic range—upper Meramecian into
lowermost Morrowan. Wang and Higgins (1989) report
Gnathodus bilineatus bilineatus from the lowermost upper
Carboniferous in China, but all their figured specimens are
from uppermost lower Carboniferous strata. Gnathodus
bilineatus bilineatus and (or) G. b. bollandensis have been
reported from lowermost upper Carboniferous strata (in
samples containing Declinognathodus noduliferus or other
late Carboniferous species) in many parts of the world (for
example, Malaysia, Metcalfe, 1980; South China, Wang and
Higgins, 1989; Texas, Grayson and others, 1990; Ukraine,
Nemirovskaya and others, 1991; south Tienshan, Uzbeki-
stan, Nigmadganov and Nemirovskaya, 1992a). We regard
the specimen of G. b. bilineatus (pl. 5, fig. 23) that occurs
13 m above the lowest D. n. japonicus in the Wahoo Lime-
stone to be redeposited.

Material.—8 Pa elements.

1993 Alekseev and

1994

Gnathodus bilineatus subsp. indet.

Remarks—A few small specimens can be identified
only as G. bilineatus.

Distribution in the study section—37 to 53 m above
the base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone).

Known stratigraphic range—upper Meramecian into
lowermost Morrowan.

Material.—3 Pa elements.

Gnathodus defectus Dunn, 1966
Plate 2, figures 23,24, 31—33; plate 4, figure 26

1966 Gnathoa’us defectus Dunn, p. 1300, pl. 158, figs. 1,
5.

1969 Gnathodus defectus Dunn. Webster, p. 32, pl. 5,
fig. 16.

1970a Gnathodus defectus Dunn. Dunn, text-fig. 4.

1970b Gnathodus defectus Dunn. Dunn, p. 331, pl. 62,
figs. 15, 16; text—fig. 9C.

1980 Gnathodus defectus Dunn. Tynan, pl. 1, fig. 20.

?1985a Gnathodus defectus Dunn. Grayson and others,
p. 166, pl. 1, fig. 21.

Gnathodus sp. of G. defectus Dunn. Higgins and
others, pl. 3, fig. 9.

?1991

1991 Gnathodus defectus Dunn. Morrow and Webster,
pl. 3, figs. 6, 7.

1992 Gnathoa’us defectus Dunn. Morrow and Webster,
pl. 1, fig. 2.

1993 Gnathoa'us defectus Dunn. Dumoulin and Harris,
fig. SB.

Remarks—Most specimens assigned to this species
are considerably smaller than those illustrated from Nevada
by Dunn (1966). Most, however, are like the specimen illus-
trated by Dunn (1970b) on plate 62, figure 16 and
text-figure 9C.

Distribution in the study section—54.9? to 157 m
above the base of the Wahoo Limestone.

Known stratigraphic range—From within the Cheste—
rian (from at least below the muricatus Zone) to at least the
lower Morrowan (lower minutus Fauna). Dunn (1966) indi-
cated that Gnathodus defectus extended into the lowest
Morrowan because it occurred in samples with Rhachistog-
nathus primus. Wardlaw (1984) and Morrow and Webster
(1992) considered G. defectus in Pennsylvanian samples
indigenous; however, it is possible that the sporadic
occurrence of G. defectus from 30 to 102 m above the
Mississippian—Pennsylvanian boundary in the study section
indicates redeposition. Some redeposited Mississippian
conodonts occur in the Pennsylvanian part of the section
(table 1). Gnathodus defectus occurs in four samples from
the lower member of the Wahoo Limestone between 157.5
and 100.5 m below the Wahoo Limestone and Echooka For-
mation contact at Pogopuk Creek (samples collected by
S.K. Morgan, University of Alaska Fairbanks). The con—
odont species association in the lowest collection indicates
the noduliferus-primus Zone, and the remaining collections
are indicative of the lower minutus Fauna (app. 1, loc. 5d).
The data from Pogopuk Creek and the study section indi-
cate that G. defectus extends well into the Morrowan (into
the lower minutus Fauna) in the northeast Brooks Range.

Material.——9 Pa elements.

Gnathodus girtyi Hass, 1953

Remarks—We recognize two subspecies of Gnatho-
dus girtyi in our collections, G. g. girtyi and G. g. simplex.

Gnathodus girtyi girtyi Hass, 1953
Plate 2, figures 20—22

Gnathodus girtyi Hass, p. 80, pl. 14, figs. 22—24.
Gnathodus girtyi Hass. Elias, p. 118, pl. 111, figs. 30,
31.

Gnathoa'us girtyi Hass. Bischoff, p. 24, 25 (part),
pl. 4. figs. 17, 22, 23.

Gnathodus clavatus Clarke, p. 25, pl. 4, figs. 4—8.

la'iognathoides nodulifera (Ellison and Graves). Igo
and Koike, pl. 3, fig. 11 (only).

1953
1956

1957

1960
1968

1969

1969

1969

1969

1970a
1970b

1970

1972
1973

?1974

1974

1974

1974

1974

1975

1979

1980

1980

1980

1981

1985

1985

1985
71987

1987

71987

1988

1988

1990

SYSTEMATIC PALEONTOLOGY 41

Gnathodus girtyi girtyi Hass. Rhodes and others,
p. 98, 99, pl. 17, figs. 9, 10.

Gnathoa’us girtyi simplex Dunn. Rhodes and others,
p. 100, 101, pl. 16, figs. 1—4.

Gnathodus girtyi subsp. nov. A. Rhodes and others,
p. 102, 103, pl. 17, figs. 1—3.

Gnathodus girtyi simplex Dunn. Webster, p. 32,
pl. 5, fig. 10.

Gnathodus girtyi girtyi Hass. Dunn, text-fig. 4.
Gnathodus girtyi girtyi Hass. Dunn, p. 331, text-
fig. 9A.

Gnathoa'us girtyi Hass. Reynolds, p. 10, pl. I,
figs. 10—12.

Gnalhodus girtyi Hass. Austin, pl. 2, figs. 11, 15.
Gnathoa'us girtyi Hass. Austin and Aldridge, pl. 1,
figs. 4 —6; pl. 2, figs. 2, 13?,14,15.

Gnathodus girtyi girtyi Hass. Gromczakiewicz-
Lomnicka, pl. 11, fig. 1.

Gnathoa'us girtyi simplex Dunn. Gromczakiewicz—
Lomnicka, pl. 1, fig. 4.

Gnathodus girtyi Hass. Matthews and Thomas,
pl. 51, figs. 16,17,28—31.

Gnathodus sp. Matthews and Thomas, pl. 51,
figs. 8, 9.

Gnatlzoa’us girtyi girtyi Hass. Rice and Langenheim,
pl. 1, figs. 15, 16.

Gnathodus girlyi girtyi Hass. Higgins, p. 31, pl. 10,
figs. 5, 6.

Gnathodus girtyi collinsoni Rhodes and others.
Aisenverg and others, pl. 6, figs. 1, 2.

Gnathodus girtyi simplex Dunn. Metcalfe, p. 304,

pl. 38, fig. 1.

Gnat/iodus girtyi rhodesi Higgins. Metcalfe, p. 304,
p]. 38, fig. 6.

Gnathodus girtyi girtyi Hass. Tynan, p. 1302, pl. 1,
figs. 16—18.

Gnathoa’us girtyi Hass. Metcalfe, p. 23, 25, pl. 4,
figs. 2, 4, 5, 7.

Gnarhoa’us girtyi girtyi Hass. Higgins, p. 220,
p1. 6.2, fig. 2.

Gnathodus girtyi rhodesi Higgins. Higgins, p. 220,
p1. 6.2, fig. 1.

Gnathodus girtyi girtyi Hass. Wardlaw, pl. 1, fig. 12.
Gnatliodus girtyi Hass. Armstrong and Purnell,
pl. 2, figs. 12, 13.

Gnathodus girtyi Hass. Grayson and others, pl. 7,
fig. 29.

Gnathodus girtyi girtyi Hass. Wang and others,
p. 128, pl. 7, figs. 9, 10.

Gnathodus girtyi girtyi Hass. Dong and Ji, pl. 5,
fig. 14.

Gnatlzodus girtyi simplex Dunn. Dong and Ji, pl. 6,
fig. 4.

(Ne0)Gnath0dus sp. aff. G. girtyi Hass. Grayson and
others, p. 376, 377, pl. 3, figs. 2—13.

1991 Gnathoa’us girtyi collinsoni Rhodes and others. Hig-

gins and others, pl. 3, fig. 2.

1991 Gnathodus girtyi girtyi Hass. Higgins and others,
pl. 3, figs. 3—5.
1991 Gnathodus girtyi girtyi Hass. Morrow and Webster,
pl. 3, fig. 9.
1992 Gnathodus girtyi girtyi Hass. Morrow and Webster,
pl. 1, fig. 3.
Remarks.——Gnath0dus girtyi girtyi has a well-

developed transversely ridged anterior inner parapet that
continues to or close to the posterior end of the platform
where it is noded and merges with the carina. The anterior
part of the inner parapet is as high as or higher than the car-
ina. The outer parapet begins posterior to and terminates
slightly to considerably anterior of the inner parapet and is
lower than the carina. The carina is central, straight or
slightly deflected, and continues to the posterior tip of the
platform where it expands to form split nodes or transverse
ridges in adult or gerontic specimens (pl. 2, fig. 20).

We are unable to evaluate the taxonomic position of
the specimens assigned to Gnathodus sp. cf. G. girtyi sub-
spp. by Grayson and others (1985a) as well as many speci—
mens assigned to G. girtyi by other workers without
examining the actual specimens and the conodont faunule
in which they occur.

Distribution in the study section—0.4 to 54.9 m above
the base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone) and 69 to 74 m (lower Mor-
rowan—redeposited?).

Known stratigraphic range—upper Meramecian to
uppermost Chesterian (Upper muricams Subzone).

Material—56 Pa elements.

Gnathodus girtyi simplex Dunn, 1965
Plate 2, figures 25—27

1965 Gnathodus girtyi simplex Dunn, p. 1148, pl. 140,
figs. 2, 3, 12.

Gnathodus girtyi simplex Dunn, text—fig. 4.
Gnathodus girtyi simplex Dunn, p. 331, 332, pl. 62,

fig. 17; text—fig. 9B.

1970a
1970b

1971 Gnathodus girtyi collinsoni Rhodes and others.
Rhodes and Austin, pl. 2, fig. 3.

71974 Gnatlzoa’us girtyi simplex Hass. Gromczakiewicz—
Lomnicka, pl. 11, fig. 3.

1974 Gnatlzodus girtyi simplex Dunn. Rice and Langen-
heim, pl. 1, figs. 17, 18.

1975 Gnathodus girtyi collinsoni Rhodes and others.
Higgins, p. 30, 31, pl. 10, figs. 1, 2.

1975 Gnathodus girtyi simplex Dunn. Higgins, p. 33,
pl. 9, figs. 6, 7, 11.

1980 Gnathodus girtyi collinsoni Rhodes and others.
Tynan, p. 1301, pl. 1, figs. 10, 11.

1980 Gnathodus girtyi simplex Dunn. Tynan, p. 1303.

pl. 1, figs. 5—7.

42 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

1982 Gnathodus girtyi girtyi Hass. Higgins and Wagner—
Gentis, p. 334, pl. 34, fig. 9.

1984 Gnathodus girtyi collinsoni Rhodes and others. Qiu,
pl. 2, figs. 17—19.

1984 Gnathodus girtyi simplex Dunn. Qiu, pl. 2,
figs. 15, 16.

1985a Gnathoa'us girtyi simplex. Lane and others,
figs. 7A, B.

1985 Gnathodus girtyi rhodesi Higgins. Wardlaw, pl. 1,
fig. 11.

1986 Gnathodus girtyi simplex Dunn. Ji, pl. 1, figs. 15—
17.

1988 Gnathodus girtyi simplex Dunn. Dong and Ji, pl. 5,
figs. 1—3.

1991 Gnathodus girtyi simplex Dunn. Higgins and others,
pl. 3, figs. 6, 12.

1991 Gnathodus girtyi simplex Dunn. Morrow and

Webster, pl. 3, fig. 8.

1992 Gnathodus girtyi simplex Dunn. Morrow and
Webster, pl. 1, fig. 4.
1993 Gnathodus girtyi simplex Dunn. Dumoulin and

Harris, fig. 8C.

Remarks.—Gnathodus girtyi simplex differs from G.
g. girtyi by having an outer parapet consisting of one or two
nodes that are restricted to the anterior half of the platform.

Specimens from the Wahoo Limestone below the
Mississippian—Pennsylvanian boundary are transitional to
Declinognathodus noduliferusjaponicus (pl. 2, fig. 30) con-
firming Dunn’s (1970b) concept of the phylogeny of D.
noduliferus.

Distribution in the study section—6 to 54.9 m above
the base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone).

Known stratigraphic range—Chesterian into
noduliferus-primus Zone. Lane and others (1985a) and
Baesemann and Lane (1985) reported Gnathodus girtyi sim—
plex from about the basal 5 m of the Pennsylvanian in their
Arrow Canyon section, Nevada. In the northeast Brooks
Range, G. g. simplex occurs in two sections with or above
Declinognathodus noduliferus, 1 km west of the study sec-
tion (app. 1, locs. 1B 1e, g) and at Pogopuk Creek, about 220
m below the base of the Echooka Formation (app. 1, loc.
5b).

Material—72 Pa elements.

Gnathodus girtyi subspp. indet.

Remarks—Included are chiefly broken, abraded, or
juvenile Pa elements.

Distribution in the study section—0.4 m above the
base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone).

Known stratigraphic range—upper Meramecian into
lowermost Morrowan (into noduliferus—primus Zone).

Material—54 Pa elements.

Gnathodus girtyi subspp. Hass transitional to
Declinognathodus spp.

Plate 2, figures 29, 30

1985a Gnathodus girtyi simplex transitional to Declino-
gnathodus noduliferus. Lane and others, fig. 7C.

Remarks—An array of gnathodontid Pa element mor—
photypes that range from Gnathodus girtyi subspp. to Decli-
nognathodus spp. appear close to the Mississippian-
Pennsylvanian boundary. These morphologic variations
make taxonomic assignment uncertain. Pa elements transi-
tional between G. g. simplex and D. n. japonicus (pl. 2.
fig. 30) in the highest Mississippian samples (53 and 54.9 m
above the base of the Wahoo Limestone and 2 and 0.1 m
below the base of the Pennsylvanian) support the sugges-
tion of Dunn (1970b) and Lane and Manger (1985) that
G. g. simplex is the ancestor to D. noduliferus. These speci-
mens are closer to G. g. simplex because the trough separat—
ing the inner parapet from the carina does not extend to the
posterior tip of the platform, and the node(s) forming the
outer parapet are not cleanly separated from the carina.
These specimens do show, however, a slight depression
between the inner parapet and carina near the posterior tip
of the platform. A few specimens from 13 m above the
Mississippian-Pennsylvanian boundary are transitional
between G. g. girtyi and D. inaequalis (Higgins) (pl. 2,
fig. 29).

Distribution in the study section—53 to 69 m above
the base of the Wahoo Limestone (uppermost Chesterian to
lowermost Morrowan; Upper muricatus Subzone into
noduliferus-primus Zone).

Material—9 Pa elements.

Gnathodus spp. indet.
Plate 2, figure 28

Remarks—Included are broken, abraded, or juvenile
Pa elements and one vicarious M element.

Distribution in the study section—0.4 to 53 m above
the base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone).

Known stratigraphic range.—Mississippian to lower-
most Pennsylvanian (upper Kinderhookian into lowermost
Morrowan).

Material—5 Pa and 1 M (pl. 2, fig. 28) elements.

Genus HINDEODUS Rexroad and Furnish, 1964

Type species.—Spathognath0dus cristula Youngquist and
Miller, 1949
p. 621, pl. 101, figs. 1—3

Remarks—See discussion of genus in Sweet (1977).

SYSTEMATIC PALEONTOLOGY 43

Hindeodus minutus (Ellison, 1941)
Plate 1, figures 1—6

Only a selected synonymy, chiefly for Chesterian and

Lower Pennsylvanian occurrences, is given for this

long-ranging, widespread species. For occurrences to 1971,

see Sweet (1973).

1941 Spathodus minutus Ellison, p. 120, pl. 20, figs. 50—

52.

Spathognathoa’us echigoensis Igo and Koike, p. 187,

pl. 28, figs. 24?, 25?.

1965 Spathognathodus minutus (Ellison). Dunn, p. 1149,

pl. 140, figs. 15, 21, 24.

Spathognathodus minutus (Ellison). Koike, p. 311,

pl. 3, figs. 39—42.

Spathognathoa’us minutus (Ellison). Palmieri, p. 9,

10, pl. 5, figs. 17, 18.

1973b Spathognathodus minutus (Ellison). Merrill, p. 305—

308, pl. 1, figs. 1—14; pl. 2, figs. 1—28.

Anchignathodus minutus (Ellison). Sweet, p. 15—17,

pl. 1, fig. 2.

Spathognathodus minutus

Straka, p. 101, figs. 44: 7, 12.

1974 Anchignathodns minutus (Ellison). Merrill, pl. 2,

fig. 8.

Hindeodus ex. pr. H. minutus (Ellison). Bender,

p. 10, pl. 4, fig. 22.

Anchignathodus minutus (Ellison). Tynan, p. 1300,

pl. 2, figs. 8, 9.

1981 Hindeodus minutus (Ellison). Landing and Wardlaw,

p. 1259, 1260, pl. 1, figs. 11, 12, 18, 23?.

Hindeodus sp. Driese and others, pl. 1, fig. 4.

Anchignathodus minutus (Ellison). Grayson, pl. 2,

figs. 3, 26.

1985b Hindeoa’us minutus (Ellison). Grayson and others,
pl. 1, figs. 47, 48.

1985 Hindeodus minutus (Ellison). Rexroad and Merrill,

pl. 3, figs. 21, 22.

Hindeodus sp. Sada and others, pl. 1, figs. 7—10.

Hindeodus minutus (Ellison). Savage and Barkeley,

p. 1472, figs. 12: 1—8.

1985 Hindeoa’us minutus (Ellison). Wardlaw, p. 400, pl. 3,

1964

1967

1969

1973

1974 (Ellison). Lane and
1980

1980

1984
1984

1985
1985

fig. 1.

1986 Hindeoa’us minutus (Ellison). Mapes and Rexroad,
pl. 1, figs. 7—15.

1987 Hindeodus minutus (Ellison). Grayson and others,
pl. 9, fig. 1.

1989 Hindeodus minutus (Ellison). Wang and Higgins, p.

279, pl. 13, figs. 6, 7.

1990 Hina’eodus minutus (Ellison). Grayson, pl. 2, figs. 6,
7, 8?.

1991 Hindeoa’us minutus (Ellison). Brown and others,
figs. 7: 12—19.

1992 Hina’eodus minutus (Ellison). Sutherland and Gray-

son, pl. 2, fig. 1.

1992 Hindeodus minutus (Ellison). Weibel and Norby,
pl. 1, fig. 21.
Hindeodus minutus (Ellison). Lemos, p. 87, 88,
pl. 4, figs. 1, 2; pl. 5, figs. 1, 2?, 3, 4 (fig. 3, Sb ele—
ment; fig. 4, Sc element).
Hindeodus minutus (Ellison). Rexroad, figs. 3: 14—
17, 19.
Remarks.—A11 specimens of the apparatus of Hindeo-
dus minutus in the collections from the Wahoo Limestone
conform to the multielement reconstruction shown in
Mapes and Rexroad (1986) and Brown and others (1991).

A Pa element figured by Rexroad and Horowitz (1990,
pl. 1, fig. 42) as Hindeodus cristula (Youngquist and Miller)
has the same anterior denticulation as H. minutus. We
assume this morphotype is a rare component of the H. cris-
tula population in the lower Chesterian and is appropriately
assigned to H. cristula.

Distribution in the study section—~27 to 237 m above
the base of the Wahoo Limestone (uppermost Chesterian to
lower Atokan?; Upper mnricatus Subzone to Idiognathodus
Fauna).

Known stratigraphic range.—upper Chesterian (from
within the Cavusgnathus monocerus Zone (= Adetognathus
unicornis Zone)) through at least the Lower Permian.

Material.—41 Pa, 10 Pb, 14 M, 3 Sa, 2 Sb, and 3 Sc
elements. “

1993

1993

Hindeodus spp. indet.

Remarks.—Included are broken or abraded Pa
elements.

Distribution in the study section—37? to 253 m above
the base of the Wahoo Limestone (uppermost Chesterian to
lower Atokan; Upper muricatus Subzone to Idiognathodns
Fauna).

Known stratigraphic range.—Mississippian to lower-
most Triassic (middle Kinderhookian to Dienerian).

Material.—14 Pa elements.

Genus IDIOGNATHODUS Gunnell, 1931

Type species.—Idiognath0dus claviformis Gunnell, 1931
p. 249—250, pl. 29, figs. 21, 22
Idiognathodus incurvus Dunn, 1966?

Plate 5, figure 21

For synonymy of the species through 1987, see Grayson
and others (1990).

1989 Idiognathodus incarvus Dunn Complex. Grayson
and others, p. 87, 88, pl. 1, figs. 21—25.
Idiognathodus incurvus Dunn. Grayson, pl. 4, figs.
4—7, 8?.

Idiognathodus incurvus Dunn. Whiteside and Gray-
son, p. 159, pl. 1, figs. 15, 20—23, 34.
Idiognathodas incnrvus Dunn. Sutherland and Gray—
son, pl. 2, figs. 4, 12.

1990

1990

1992

44 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

Remarks—Grayson and others (1989) revised the
diagnosis for ldiognathodus sinuosus, I. klapperi, and I.
incurvus on the basis of the position of the adcarinal ridges
and used this characteristic to establish a phylogeny. Idio—
gnathodus sinuosus (originating in the middle Morrowan)
has two adcarinal ridges, the inner of which extends slightly
anterior of the platform and parallel to the free blade; I.
klapperi (late Morrowan) has ridges that are restricted to the
platform; and I. incurvus (Atokan) has ridges that extend
anteriorly beyond the platform and intersect the free blade.
The poor preservation and apparent low diversity of idio-
gnathodids in the Wahoo Limestone do not allow us to test
the evolutionary model proposed for the genus by Grayson
and others (1989). Some specimens that Grayson and others
(1990) and Sutherland and Grayson (1992, for example, pl.
2, fig. 21) include in l. klapperi appear to be representatives
of the I. sinuosus complex (I. delicatus morphotype). We
did not recognize any specimens that we could confidently
assign to I. klapperi.

Two specimens, 16 and 12 m below the top of the
Wahoo Limestone, are questionably assigned to Idiognatho—
dus incurvus. One is ajuvenile and the other is a large adult.
Although the latter is abraded, the adcarinal ridges extend
beyond the anterior platform margin to intersect the rem-
nant of the free blade (pl. 5, fig. 21).

Distribution in the study section—246 to 250 m above
the base of the Wahoo Limestone (lower Atokan; Idiogna-
thodus Fauna). Idiognathodus incurvus? is used to indicate
a level no older than Atokan at the study section on the
basis of its distribution in the Atoka Formation in
Oklahoma.

Known stratigraphic range—From within the Atokan
(probably lower Atokan) to lower Desmoinesian.

Material.—2 Pa elements.

Idiognathodus sinuosus Ellison and Graves, 1941
Plate 3, figures 15—18, 23~25

For synonymy through 1987, see Grayson and others
(1990).
1990 Idiognathodus sinuosus Ellison and Graves. Gray—
son, pl. 4, figs. 36—39.
1992 Idiognathodus sinuosus Ellison and Graves. Suther-
land and Grayson, pl. 2, figs. 28, 29.
Remarks—See remarks under Idiognathodus incurv-
us? for Grayson and others’ (1989) concept of I. sinuosus.
In addition, Grayson and others (1990) synonymize I. deli-
catus Gunnell and I. sinuosus; we follow their concept here.
Many subadult and adult specimens included in Idiognatho-
dus sinuosus have nodes on only one side of the platform
but, uncharacteristic of I. sinuosus, have a relatively straight
platform. One subadult specimen (pl. 3, fig. 23) has rostral
ridges of equal length that extend slightly beyond the
anterior end of the platform. This specimen is included in I.
sinuosus and not in I. incurvus because similar size speci-

mens 0f the latter exhibit rostral ridges characteristic of that
species. Grayson (1990, pl. 4, figs. 37—39) includes similar
forms in I. sinuosus.

Distribution in the study section—187 to 243 m above
the base of the Wahoo Limestone (upper Morrowan and (or)
lower Atokan; ldiognathodus Fauna).

Known stratigraphic range.—upper Morrowan (sinuo-
sus Zone) to at least Upper Pennsylvanian.

Material.~—100 Pa elements.

Idiognathodus spp. indet.

Remarks—Included are broken, abraded, or juvenile
Pa elements.

Distribution in the study section—177 to 257.5 m
above the base of the Wahoo Limestone (upper Morrowan
to lower Atokan; Idiognathodus Fauna).

Known stratigraphic range—upper Morrowan (1. sin-
uosus Zone) to Lower Permian.

Material.—52 Pa elements.

Genus IDIOGNATHOIDES Harris and Hollingsworth,
1933

Type species.—Idiognathoides sinuata Harris and
Hollingsworth, 1933
p. 201—202, pl. 1, fig. 14
Idiognathoides sinuatus Harris and Hollingsworth, “I.
ouachitensis” morphotype

Plate 5, figure 22

For synonymy of Ia'iognathoides sinuatus to 1987, see
Grayson and others (1990).
1992 Idiognathoides sinuatus Harris and Hollingsworth.
Lemos, pl. 3, figs. 3, 8.
1992a Idiognathoia'es corrugatus (Harris and Hollings—
worth). Nigmadganov and Nemirovskaya, pl. 5,
figs. 6—11.
1992a ldiognathoides sinuatus Harris and Hollingsworth.
Nigmadganov and Nemirovskaya, pl. 5, figs. 4, 5.
Remarks—Grayson ( 1984) indicated that the length of
the trough of the dextral Pa element of Idiognathoides oua—
chitensis was diagnostic of this late Morrowan species.
Moreover, he inferred a phylogenetic succession, on the
basis of increasing trough length, from I. corrugatus to I.
ouachitensis. Subsequently, Grayson (1990) and Grayson
and others (1990) synonymized these species with the long-
ranging I. sinuatus and speculated that the character of the
trough was environmentally controlled. Wang and others
(1987) synonymized l. ouachitensis in l. corrugatus but
continued to recognize I. sinuatus as a separate species. We
follow the multielement concept implemented by Grayson
and others (1990) by including all three within 1. sinuatus.
Only three specimens of the genus were recovered
from the study section. All are from one sample and appear
to have troughs characteristic of the “I. ouachitensis” mor-

SYSTEMATIC PALEONTOLOGY 45

photype. Because of their rarity, we cannot evaluate the
environmental preference of these forms. Likewise, we can-
not evaluate their biostratigraphic utility.

Distribution in the study section—217.5 m above the
base of the Wahoo Limestone (upper Morrowan or lower
Atokan; Idiognathodus Fauna).

Known stratigraphic distribution—lower Morrowan
(sinuatus-minutus Zone) through at least Atokan.

Material.—3 Pa elements.

Genus IDIOPRIONIODUS Gunnell, 1933

Type species.—Idi0prioniodus typus Gunnell, 1933
p. 265, pl. 31, fig. 47

Remarks—For discussion of the genus see Stone
(1991).

Idioprioniodus conjunctus (Gunnell, 1931)?
Plate 5, figures 11, 14—17

For synonymy to 1975, see Higgins (1975) and Higgins and

Wagner—Gentis (1982).

1982 Idioprioniodus conjunctus (Gunnell). Higgins and
Wagner—Genus, p. 332, 333, pl. 34, figs. 18, 21, 23,
27—29.

?1985 Idioprioniodus cf. 1. conjunctus (Gunnell). Rexroad

and Merrill, pl. 3, figs. 15?, 16—20; pl. 4, figs. 17—

19.

Idioprioniodus conjunctus (Gunnell). Savage and

Barkeley, p. 1459, figs. 5: 1—14.

1987 Idioprioniodus conjunctus (Gunnell). Grayson and
others, pl. 2, figs. 1—6.

1987 Idioprionioa’us cf. conjunctus. Grayson and others,

pl. 5, 7—9; pl. 6, figs. 13—20.

Idioprioniodus conjunctus

pl. 2, figs. 15—24.

1991 Idioprionioa’us conjunctus (Gunnell). Brown and
others, pl. 7, figs. 23—25, 26?, 27—29.
ldioprioniodus conjunctus (Gunnell). Rexroad, figs.
4: 1?, 2—12, 13?, 14?.

Remarks.———Idiopri0niodid elements are relatively rare

in the Wahoo Limestone; all are incomplete. Elements

approximate the better preserved material illustrated by

Savage and Barkeley (1985, fig. 5). We have referred virtu-

ally all representatives of ldioprioniodus in the collections

from the Wahoo Limestone to I. conjunctus?.

Distribution in the study section—53 to 257.5 m
above the base of the Wahoo Limestone (uppermost Ches-
terian to lower Atokan; Upper muricatus Subzone to Idio-
gnathodus Fauna).

Known stratigraphic range—Within the Upper Mis-
sissippian to at least Desmoinesian.

Material.—6 Pb, 7 M, 5 Sa, 10 Sb, and 7 Sc elements.

1985

1990 (Gunnell). Grayson,

1993

Idioprioniodus cf. 1. healdi (Roundy, 1926)?
Plate 5, figure 13

For synonymy to 1987, see Stone (1991).

Remarks—Stone (1991) assigned many Mississippian
representatives of Idioprioniodus to 1. cf. 1. healdi, includ-
ing 1. paraclaviger (Rexroad). One Pb? element from the
Wahoo Limestone conforms to the Sb] element illustrated
by Stone for 1. cf. 1. healdi (1991, pl. 5, fig. 5). This ele—
ment, unlike similar elements of I. conjunctus, has a denti—
cle immediately anterior to the cusp that is fused to it, at
least near its base. Pb or Sb elements of forms we assign to
I. conjunctus? do not have an anterior denticle fused to or
impinging on the cusp.

Distribution in the study section—207 m above the
base of the Wahoo Limestone (Morrowan or lower Atokan;
Idiognathodus Fauna).

Known stratigraphic range—upper Osagean to at
least Chesterian. The specimen from the Wahoo Limestone
is from Pennsylvanian strata.

Material.—1 Pb? element.

Idioprioniodus spp. indet.
Plate 5, figure 12

Remarks—Broken and abraded robust digyrate ele—
ments, some of which are indeterminate to morphotype.

Distribution in the study section—0.4 to 241 m above
the base of the Wahoo Limestone (uppermost Chesterian to
lower Atokan?; Upper muricatus Subzone to Idiognathodus
Fauna).

Known stratigraphic range—Lower Mississippian
(upper Osagean) to at least Desmoinesian.

Material.——1 Pa, 3 Pb, 8 M, 6 Sa, and 7 Sb elements
and 9 elements indeterminate to morphotype.

Genus KLADOGNATH US Rexroad, 1958

Type species.—Cladognathus prima Rexroad, 1957
p. 28, 29, pl. 1, figs. 8—10
Kladognathus spp.

Plate 5, figures [—10

For synonymies of several species of Kladognathus, see
Rexroad (1981) and Rexroad and Horowitz (1990).

Remarks—Element notation for Kladognathus spp.
follows that of Purnell (1993). Purnell’s reconstruction is
based on a well-preserved bedding-plane assemblage in the
gut of a conodont predator. Except for some M elements, all
kladognathid specimens from the Wahoo Limestone are
incomplete. Thus, we could not distinguish Pa from Pb ele—
ments, and we have not attempted to identify the four mor—
photypes of the Sb-Sc transition series documented by
Purnell (1993). The end members of the Sb-Sc transition
series are illustrated (pl. 5, figs. 9, 10).

46 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

The lowest collection from the Wahoo Limestone con—
tains the greatest number of kladognathids (table 1, USGS
colln. 30745—PC). Most elements appear to be Kladog—
nathus tenuis (Branson and Mehl) as reconstructed by
Rexroad and Horowitz (1990).

Distribution in the study section—0.4 to 54.9 m above
the base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone). Specimens from 59 to 107 m
above the base of the formation are considered redeposited.

Known stratigraphic range.—upper Osagean to upper-
most Chesterian.

Material.—68 P, 52 M, 6 Sa, and 115 Sb-Sc elements.

Genus LOCHRIEA Scott, 1942

Type species.—Spathognathodus commutatus Branson
and Mehl, 1941b
p. 98, pl. 19, figs. 1—4
Lochriea commutata (Branson and Mehl, 1941b)

Plate 3, figures 26, 27

For synonymy to 1987, see Rexroad and Horowitz (1990).

Additions and exceptions are noted below.

1941a Spathognathodus commutatus Branson and Mehl,
p. 172, p1. V, figs. 19—22.

1941b Spathognathodus commutatus Branson and Mehl,
p.98, pl. 19, figs. 1—4.

1969 Gnathodus commutatus (Branson and Mehl).
Thompson and Goebel, p. 23, 24, pl. 4, figs. 4, 6, 7.

1979 Gnathodus commutatus (Branson and Mehl). Aisen—
verg and others, pl. 6, figs. 3, 4.

1979 Gnathodus commutatus commutatus (Branson and
Mehl). Einor and others, pl. 14, figs. 2, 3.

1986 Paragnathodus commutatus (Branson and Mehl). Ji,
pl. 2, figs. 1—4, 5?, 6.

1987 Lochriea commutata (Branson and Mehl). Arm-
strong and Purnell, pl. 3, fig. 1.

1987 Paragnathodus commutatus (Branson and Mehl).
Riley and others, pl. 2, figs. 1, 3.

1987 Paragnathodus commutatus (Branson and Mehl).
Wang and others, p. 130, 131, pl. 2, fig. 12.

1988 Gnathoa’us commutatus commutatus (Branson and
Mehl). Dong and Ji, pl. 5, figs. 1—3.

1989 Paragnathodus commutatus (Branson and Mehl).
Wang and Higgins, p. 285, pl. 8, figs. 4, 5.

1990 Lochriea commutata (Branson and Mehl). Grayson,

pl. 1, figs. 14—24.

1990a Lochriea commutata (Branson and Mehl). Ramovs,
p. 94, 95, pl. 4, figs. 6, 7,10,11.

1990b Lochriea commutata (Branson and Mehl). Ramovs,
p. 110, pl. 1, figs. 6, 7, 9, 12—14.

1990 Lochriea commutata (Branson and Mehl). Rexroad
and Horowitz, p. 508—510, pl. 2, figs. 10—24.
1990 Lochriea commutata. Whiteside and Grayson, pl. 1,

figs. 1, 2.

1991 Paragnathodus commutatus (Branson and Mehl).
Nemirovskaya and others, pl. 3, fig. 4.

1991 Paragnathodus commutatus (Branson and Mehl).
Varker and others, pl. 1, figs. 13—15.

?1992aParagnathodus aff. commutatus (Branson and

Mehl). Nigmadganov and Nemirovskaya, pl. 1,

fig. 5.

Lochriea commutata (Branson and Mehl). Weibel

and Norby, pl. 2, figs. 35?, 36.

Paragnathodus commutatus (Branson and Mehl).

Alekseev and Kononova, pl. 29, fig. 11.

1992

1993

1994 Lochriea commutata (Branson and Mehl). Kolar-
Jurkovsek and Jurkovsek, 432—433, pl. 1, figs. 3, 4.
1994 Lochriea commutata (Branson and Mehl).

Nemirovskaya and others, pl. 2, fig. 1.

Lochriea commutata (Branson and Mehl). von Bit-

ter and Norby, p. 861—869, figs. 2—7.
Remarks—A11 Pa and M elements conform to those
listed in the above synonymy.

Distribution in the study section—0.4 to 54.9 m above
the base of the Wahoo Limestone (uppermost Chesterian;
Upper muricatus Subzone).

Known stratigraphic range.——lower Meramecian
(lower Arundian in England according to Metcalfe, 1981)
into the lowermost Morrowan (noduliferus Zone or earliest
Bashkirian in the Donets basin, Ukraine (Nemirovskaya and
others, 1991), and South Tienshan, Uzbekistan (Nigmadga-
nov and Nemirovskaya, 1992a).

Material.——8 Pa and 2 M elements.

1994

Genus NEOGNATHODUS Dunn, 1970b

Type species.—Polygnathus bassleri Harris and
Hollingsworth, 1933
p. 198, 199, pl. 1, figs. 13a—e
Neognathodus? sp. indet.

Remarks—A single posterior Pa element fragment is
assigned to Neognathodus? sp. indet.

Distribution in the study section—257.5 m above the
base of the Wahoo Limestone (lower Atokan; Idiognatho-
dus Fauna).

Known stratigraphic range.—Morrowan (N. symmet—
ricus Zone) to Desmoinesian.

Material.—1 Pa element fragment.

Genus RHACHIS T OGNAT H US Dunn, 1966

Type species.—Rhachistognathus prima Dunn, 1966
p. 1301, 1302, pl. 157, figs. 1, 2
Rhachistognathus minutus (Higgins and Bouckaert,
1968)

Remarks.———Baesemann and Lane (1985) recognized
three subspecies of Rhachistognathus minutus—R. m.
declinatus, R. m. havlenai, and R. m. minutus—on the basis
of the position of the blade attachment and the degree of

SYSTEMATIC PALEONTOLOGY 47

curvature of the anterior part of the left platform margin.
They reported (p. 107) that “All specimens in our collec-
tions are comparatively small.” In contrast, adult to gerontic
specimens from the Wahoo Limestone are quite large (some
incomplete specimens are at least 1 mm long; pl. 4, figs. 5—
8). Many specimens exhibit transitional subspecies charac—
teristics so that subspecific assignment of such forms was
arbitrary. In addition, some specimens of R. m. minutus are
similar to R. muricatus (pl. 4, fig. 15; Higgins, 1985, pl. 6.2,
fig. 9). Regularly nodose specimens were cosmopolitan
(R. m. minutus) and probably lived in relatively uniform,
normal-marine shallow—water environments, whereas
increasingly asymmetrical forms (R. muricatus to R. pri-
mus) occupied more variable shallow—water environments
and were chiefly North American Cordilleran and southern
Midcontinent inhabitants.

We are unable to evaluate the biostratigraphic utility, if
any, of the subspecies of R. minutus from the Wahoo Lime-
stone. All subspecies appear between 84 and 85 m above
the base of the section and continue to near the top. We sup-
pose that any paleoecologic partitioning of these subspecies
was obliterated by hydraulic mixing across the Wahoo car-
bonate platform. The distribution of R. minutus subspp. in
the Arrow Canyon section, Nevada (Baesemann and Lane,
1985), is quite different from that of our section. At Arrow
Canyon, R. m. minutus and R. m. havlenai make their
appearance about 105 m below that of R. m. declinatus,
co-occur for about 90 m, and disappear about 15 m below
the first R. m. declinatus. R. m. declinatus continues as the
only rhachistognathid in the succeeding 75 m. Unfortu—
nately, Baesemann and Lane (1985) do not explain the
stratigraphic succession of these subspecies nor the pale-
oenvironmental implications. Varker and others (1991)
report all three subspecies together in several samples.

Rhachistognathus minutus declinatus Baesemann and
Lane, 1985

Plate 4, figures 1—9

For synonymy through 1975, see Baesemann and Lane
(1985).
1985 Rhachistognathus minutus declinatus Baesemann

and Lane, p. 108, 109, pl. 1, figs. 1—10.

1987 Rhachistognathus minutus declinatus Baesemann
and Lane. Nemirovskaya, pl. 1, figs. 1, 4.

1987 Rhachistognathus minutus declinatus Baesemann
and Lane. Riley and others, pl. 3, figs. 10?, 11.

1991 ?Rhachist0gnathus minutus declinatus Baesemann

and Lane. Nemirovskaya and others, pl. 4, figs. 1, 2.

1991 Rhachistognathus minutus declinatus Baesemann
and Lane. Varker and others, pl. 1, figs. 30, 31.

Remarks.—Rhachist0gnathus minutus declinatus is

the most abundant rhachistognathid in the Wahoo

Limestone. One sample from the upper member yielded 276

Pa elements of R. m. declinatus; some specimens are transi—

tional to R. m. havlenai (table 1, USGS colln. 30786—PC).
The free blade joins the platform subcentrally and, with few
exceptions, the anterior end of the left parapet is deflected
to the left. A few gerontic specimens have the anterior end
of the right parapet deflected to the right (pl. 4, fig. 6). The
inner platform margin of some gerontic Pa elements have
one or two nodes (pl. 4, figs. 7, 8); a transverse ridge may
extend from the node(s) to the parapet (pl. 4, fig. 7).

A form geometrically similar to R. m. declinatus was
described from Lower and Middle Pennsylvanian rocks in
southeast Alaska by Savage and Barkeley (1985). The plat-
form margin of their species, “Taphrognathus alaskensis,”
however, is ornamented by closely spaced, delicate trans—
verse ridges, whereas R. m. declinatus has noded or trans-
versely ridged and noded parapets. The new species may
represent a part of the R. minutus plexus that occupied
quiet, open—marine environments.

Distribution in the study section—85 to 261.5 m
above the base of the Wahoo Limestone (lower Morrowan
to lower Atokan; lower minutus Fauna to ldiognathodus
Fauna).

Known stratigraphic range.—lower Morrowan (base
of sinuatus-minutus Zone in North America, but below the
mid-Carboniferous boundary and within the lowermost
Chokierian in England; Varker and others, 1991) to lower
Atokan.

Material.—5 18 Pa elements.

Rhachistognathus minutus havlenai Baesemann and
Lane, 1985

Plate 4, figures 10—12

For synonymy through 1975, see Baesemann and Lane
(1985). Additions and exceptions are noted below.

1969 Streptognathodus lanceolatus Webster, p. 47, 48,
pl. 6, fig. 14 (only).

Rhachistognathus minutus havlenai Baesemann
and Lane, p. 109—111, pl. 2, figs. 1—6, 8, 9.
Rhachistognathus minutus havlenai Baesemann
and Lane. Riley and others, pl. 3, figs. 8, 9.

I991 Rhachistognathus minutus havlenai Baesemann

and Lane. Varker and others, pl. 1, figs. 26—29.

Remarks—According to Baesemann and Lane (1985),
the offset of the free blade from the left parapet distin-
guishes Rhachistognathus minutus havlenai from R. m.
minutus and R. muricatus. The anterior margin of the left
parapet in R. m. havlenai is straight as opposed to R. m. dec-
linatus in which it curves strongly outward (compare pl. 4,
figs. 1, 10).

Distribution in the study section—85 to 261.5 m
above the base of the Wahoo Limestone (lower Morrowan
to lower Atokan; lower minutus Fauna to Idiognathodus
Fauna).

Known stratigraphic range.—lower Morrowan (base
of sinuatus-minutus Zone in North America, but below the

1985

1987

48 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

mid-Carboniferous boundary and within the lowermost
Chokierian in England; Varker and others, 1991) to lower
Atokan.

Material.—-228 Pa elements.

Rhachistognathus minutus minutus (Higgins and
Bouckaert, 1968)

Plate 4, figures 13—15

For synonymy through 1975, see Baesemann and Lane

(1985). Additions and exceptions are noted below.

1969 Streptognathodus lanceolatus Webster, p. 47, 48,

pl. 6, fig. 15 (only).

Rhachistognathus minutus minutus (Higgins and

Bouckaert). Baesemann and Lane, p. 111, 112, pl. 2,

figs. 7, 10, 11; pl. 3, figs. 1—12.

Rhachistognathus minutus (Higgins and Bouckaert).

Higgins, p. 220, pl. 6.2, figs. 3—9.

?1985 Rhachistognathus minutus n. subsp. C. Skipp and

others, pl. 8, fig. 5.

Rhachistognathus minutus minutus (Higgins and

Bouckaert). Riley and others, pl. 3, figs. 1—7.

1991 Rhachistognathus minutus minutus (Higgins and
Bouckaert). Varker and others, pl. 1, figs. 16?, 17?,
20—22, 25.

Remarks—Specimens from the Wahoo Limestone
assigned to this subspecies conform to the diagnosis and
description given in Baesemann and Lane (1985). Also see
remarks above for Rhachistognathus minutus.

Distribution in the study section—84 to 260.5 m
above the base of the Wahoo Limestone (lower Morrowan
to lower Atokan; lower minutus Fauna to Idiognathodus
Fauna).

Known stratigraphic range.—lower Morrowan (base
of sinuatus-minutus Zone in North America, but below the
mid-Carboniferous boundary and within the lowermost
Chokierian in England; Varker and others, 1991) to lower
Atokan.

Material.—300 Pa elements.

1985

1985

1987

Rhachistognathus minutus subspp. indet.

Remarks—Included are broken, abraded, or juvenile
Pa elements.

Distribution in the study section—107 to 261.5 m
above the base of the Wahoo Limestone (Morrowan to
lower Atokan; lower minutus Fauna to Idiognathodus
Fauna).

Known stratigraphic range—lower Morrowan (base
of sinuatus—minutus Zone in North America, but below the
mid-Carboniferous boundary and within the lowermost
Chokierian in England; Varker and others, 1991) to lower
Atokan.

Material.—33 Pa elements.

Rhachistognathus muricatus (Dunn, 1965)
Plate 4, figures 27—30
For synonymy through 1980, see Baesemann and Lane
(1985). Additions and exceptions are noted below.

?1966 Cavusgnathus transitoria Dunn, p. 1299, pl. 157,
fig. 9.

1985 Rhachistognathus minutus minutus (Higgins and
Bouckaert). Baesemann and Lane, pl. 2, figs. 7, 10
(only).

1985 Rhachistognathus muricatus (Dunn). Skipp and oth-
ers, pl. 8, fig. 9.

1985 Rhachistognathus muricatus (Dunn). Wardlaw,
pl. 1, fig. 9.

1987 Rhachistognathus muricatus (Dunn). Grayson and

others, pl. 4, figs. 23, 30?, 32, 38.
?1987 Rhachistognathus aff. muricatus (Dunn). Wang and
others, p. 131, 132, pl. 7, figs. 5, 6.

1991 Rhachistognathus muricatus (Dunn). Higgins and
others, pl. 3, figs. 8, 13.

1991 Rhachistognathus muricatus (Dunn). Morrow and
Webster, pl. 4, figs. 1—5.

1992 Rhachistognathus muricatus (Dunn). Morrow and
Webster, pl. 1, fig. 6.

1993 Rhachistognathus muricatus (Dunn). Lemos, p. 88,

90, pl. 4, figs. 3, 4, 5?.

Remarks—This species is the most morphologically
variable rhachistognathid and is intermediate between
Rhachistognathus minutus and R. primus. Many specimens
in the collections from the Wahoo Limestone conform to the
species diagnosis, whereas others are transitional to
R. minutus, R. primus, or R. websteri. Transition forms are
discussed below.

Distribution in the study section—6 to 133.5 m above
the base of the Wahoo Limestone (uppermost Chesterian to
Morrowan; Upper muricatus Subzone to lower minutus
Fauna).

Known stratigraphic range—uppermost Chesterian
(base of muricatus Zone) to lower Atokan.

Material.—336 Pa elements.

Rhachistognathus muricatus (Dunn) transitional to
R. primus Dunn

Plate 4, figure 25

1974 Rhachistognathus muricatus (Dunn). Lane and
Straka, p. 97, 98, figs. 35: 16, 17.

1985 Rhachistognathus muricatus (Dunn) transitional to
R. primus Dunn. Baesemann and Lane, p. 115, pl. 4,
figs. 8, 9.

1987 Rhachistognathus minutus (Higgins and Bouckaert).

Grayson and others, pl. 4, fig. 31.
1991 Rhachistognathus minutus havlenai Baesemann
and Lane. Higgins and others, pl. 3, figs. 7, 11.

SYSTEMATIC PALEONTOLOGY 49

Remarks.—-The absence of a narrow, medial trough
distinguishes R. primus from R. muricatus. Specimens con-
sidered transitional between R. muricatus and R. primus
have a moderate trough on the anterior half of the platform
and a shallow trough containing a row of low nodes on the
posterior half.

Distribution in the study section—85 to 95 m above
the base of the Wahoo Limestone (Morrowan; lower minu-
tus Fauna).

Material.—4 Pa elements.

Rhachistognathus muricatus (Dunn) transitional to
R. websteri Baesemann and Lane

Plate 4, figure 16

Remarks.——Rhachist0gnathus websteri is distin-
guished from other rhachistognathids by a prominent mar-
ginal node that is distinctly offset from the posterior part of
the outer parapet. This node is only slightly offset in the fig-
ured specimen.

Distribution in the study section—6 m above the base
of the Wahoo Limestone (uppermost Chesterian; Upper
muricatus Subzone).

Material.—1 Pa element.

Rhachistognathus prolixus Baesemann and Lane, 1985?

Remarks—Two posterior platform fragments resem-
ble Rhachistognathus prolixus but are too incomplete for
positive identification.

Distribution in the study section—6 to 157 m above
the base of the Wahoo Limestone (uppermost Chesterian to
Morrowan; Upper muricatus Subzone to lower minutus
Fauna).

Known stratigraphic range.~—lower Chesterian to
middle Morrowan.

Material.—3 Pa element fragments.

Rhachistognathus websteri Baesemann and Lane, 1985
Plate 4, figures 17—21

For synonymy through 1980, see Baesemann and Lane

(1985).

1983 Rhachistognathus primus Dunn. Metcalfe, pl. 2,
fig. 18.

1985 Rhachistognathus websteri Baesemann and Lane,
p. 117—119, pl. 5, figs. 1,2, 8—12.

1985 Rhachistognathus muricatus (Dunn)-Rhachisto-
gnathus primus Dunn plexus. Plafl<er and others,
figs. 48C, D.

71985 Rhachistognathus minutus (Higgins and Bouckaert).
Wardlaw, pl. 1, fig. 7.

1991 Rhachistognathus muricatus (Dunn). Higgins and
others, pl. 3, fig. 13.

1991 Rhachistognathus websteri Baesemann and Lane.
Higgins and others, pl. 3, fig. 17.

1991 Rhachistognathus websteri Baesemann and Lane.
Morrow and Webster, pl. 3, figs. 14, 15.

1992 Rhachistognathus websteri Baesemann and Lane.
Morrow and Webster, pl. 1, fig. 8.
1992 Rhachistognathus cf. R. websteri Baesemann and

Lane. Weibel and Norby, pl. 2, fig. 37.

Remarks—The morphology of Pa elements agrees
with those synonymized above; most specimens are rela-
tively small. Rhachistognathus websteri may be an ecophe-
notype of R. muricatus. Collections containing abundant R.
muricatus generally contain relatively abundant R. websteri
and visa versa (compare table 1, USGS collns. 30770—PC
and 30773—PC). The same relationships persist in the north-
east Brooks Range (app. 1, 10c. 5d).

Distribution in the study section—59 to 162 m above
the base of the Wahoo Limestone (lowermost Morrowan;
noduliferus—primus Zone to lower minutus Fauna).

Known stratigraphic range.—uppermost Chesterian
(Upper muricatus Subzone; app. 1, loc. 4A1c) to lower and
possibly middle Morrowan (this report).

Material.——1 87 Pa elements.

Rhachistognathus spp. indet.
Plate 4, figures 22~24

Remarks—Included are broken, abraded, or juvenile
(pl. 4, figs. 22—24) nodose Pa elements, chiefly posterior
platform fragments.

Distribution in the study section—6 to 260.5 m above
the base of the Wahoo Limestone (uppermost Chesterian to
lower Atokan; Upper muricatus Subzone to Idiognathodus
Fauna).

Known stratigraphic range.—at least lower Chesterian
to lower Atokan.

Material.—396 Pa elements.

Genus VOGELGNAT H US Norby and Rexroad, 1985

Type species.—Spathognathodus campbelli Rexroad,
1957
p. 37, 38, pl. 3, figs. 13—15
Vogelgnathus postcampbelli (Austin and Husri, 1974)

Plate 3, figures 28—31

For synonymy to 1985, see Purnell and von Bitter (1992).
Additions and exceptions are listed below.

1967 Spathognathodus campbelli Rexroad, Koike, p. 310,
pl. 3, figs. 26, 27, 29, 32?.

1974 Spathognathodus campbelli Austin and Husri, p. 57.
pl. 5, figs. 1, 3, 4.

1985 Vogelgnathus n. sp. Norby and Rexroad, p. 11, 12,
pl. 1, figs. 3—5.

50 CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF THE WAHOO LIMESTONE

1985 Ozarkodina sp. (Spathognathodus campbelli
Rexroad). Sada and others, pl. 1, fig. 27 (only).
Vogelgnathus postcampbelli (Austin and Husri).
Purnell and von Bitter, p. 327, 328, figs. 13: 1—4,
fig. 14 (part).

Vogelgnathus n. sp. of Norby and Rexroad. Weibel
and Norby, pl. 1. fig. 23.
Remarks.—Purnell and von Bitter (1992, their table 1)
summarize the characteristics of species of Vogelgnathus
spp. Specimens of V. postcampbelli from the Wahoo Lime—
stone are poorly preserved Pa elements having 10 to 14 den-
ticles. The upper margin profile of most specimens
gradually increases in height posteriorly toward the cusp
and then sharply decreases from the cusp to the posterior tip

(pl. 3, figs. 28, 30). Some specimens have a cusp that is

slightly higher and wider than adjacent denticles.

Vogelgnathus postcampbelli is locally common to
abundant in beds above and below the Mississippian-
Pennsylvanian boundary in the northeast Brooks Range (for
example, app. 1, loc. 7a, 50 km southwest of the study sec-
tion in the Fourth Range, 20 m below the Mississippian-
Pennsylvanian boundary; app. 1, loc. lBlg, 1 km west of
the study section—53 Pa elements from 2.8 m above the
boundary, pl. 3. fig. 31). All specimens are nearly identical
to and some are even more poorly preserved than those
from the study section.

Distribution in the study section—0.4 to 76.5 m above
the base of the Wahoo Limestone (uppermost Chesterian to
lower Morrowan: Upper muricalus Subzone to noduliferus-
primus Zone).

Known stratigraphic range—At least Chesterian into
the lowermost Morrowan (no younger than noduliferus-
primus Zone).

Material.—l6 Pa elements.

1992

1992

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APPENDIX 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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PLATES 1—5

 

 

PLATE 1

Conodonts from the Wahoo Limestone, eastern Sadlerochit Mountains,

northeast Brooks Range, Alaska.

[Scanning electron microscope photomicrographs of specimens coated
with carbon and gold. Meters shown are above base of formation]

Figures 1—6. Hindeodus minutus (Ellison), X50, lower member.

1.

5—6.

Pa element, outer lateral view, 42 m (USGS colln. 30754—PC),
USNM 442115.
Pb element, inner lateral view, 69 m (USGS colln. 30762—PC),
USNM 442116.

. M and Sa elements, posterior and lateral views, 53 m (USGS colln.

30757—PC), USNM 442117-118.
Sb and Sc elements, lateral views, 69 m (USGS colln. 30762—PC),
USNM 442119—20.

7—12. Cavusgnathus? tytthus Brown and Rexroad, Pa elements, lower member.

7—8.

9—10.

11—12.

0t morphotype, oblique upper and upper views, 56 m (USGS colln.
30758—PC), USNM 442121—122; figure 7, X50 and figure 8, X35.
[3 morphotype, X50, upper and lateral views of specimen with
left-trending carinal extension of blade, 22 m (USGS colln. 30750—
PC), USNM 442123.

Y morphotype, X50, lower and upper views of specimen with
central free blade and carina, 50.5 m (USGS colln. 30756—PC),
USNM 442124.

13—15, 21—24. Adetognathus lautus (Gunnell), Pa elements, X50, upper member.

13.

14—15.

21.

22.

23.

24.

Left element with short, right-trending carinal extension of blade,
lateral view, 113 m (USGS colln. 30775—PC), USNM 442125.
Left elements with right-trending carinal extension of blade, upper
views, 107 m (USGS colln. 30774—PC), USNM 442126—27.

Right element, upper view, 85 m (USGS colln. 30768—PC), USNM
442130.

Right element, inner lateral View, 91 m (USGS colln. 30770—PC),
USNM 442131.

Left element, upper view, 133.5 m (USGS colln. 30778—PC),
USNM 442132.

Left element, upper View, 85 m (USGS colln. 30768~PC), USNM
442133.

16—20, 25—26. Adetognathus spathus (Dunn), Pa elements, upper member.

27.

28—3 1 .

16—18.

1 9—20.

25—26.

Right element, upper, lower, and inner lateral views, 157 m (USGS
colln. 30781—PC), USNM 442128; figure 16, X50 and figures 17—
18, X40.

Left element, upper and outer lateral views, X50, 157 m (USGS
colln. 3078l—PC), USNM 442129.

Left element, upper and oblique lower views, X50, 246 m (USGS
colln. 30795—PC), USNM 442134.

Cavusgnathus altus Harris and Hollingsworth, Pa element, X50, upper
view, lower member, 7 m (USGS colln. 30747—PC), USNM 442135.
Cavusgnathus unicorm's Youngquist and Miller, Pa elements, lower
member.

28—30.

31.

Y morphotype, upper, lower, and inner lateral views, X35, 22 m
(USGS colln. 30750—PC), USNM 442136.

0t morphotype, inner lateral view, X50, 50.5 m (USGS colln.
30756—PC), USNM 442137.

U‘S. GE OGICAL SUR Y PROFESSIONAL PAPER 1568 PLATE 1

ADETOGNATHUS, CAVUSGNATHUS, CAVUSGNATHUS?. AND HINDEODUS

 

PLATE 2

Conodonts from the Wahoo Limestone, eastern Sadlerochit Mountains,

northeast Brooks Range, Alaska.

[Scanning electron microscope photomicrographs of specimens coated
with carbon and gold. Meters shown are above base of formation]

Figures 1—17. Cavusgnathus unicorm's Youngquist and Miller, lower member.

18—19.

20-22.

23—24, 31—33.

25—27.

28.

29.

30.

1—2. Pa element, 7 morphotype, inner lateral and upper views,
X50, 6 m (USGS colln. 30746—PC), USNM 442138.
3. Pa element, juvenile, X50, upper view, 13.2 m (USGS colln.
30748—PC), USNM 442139.
4—7. Pa elements, upper and inner lateral views, 7 m (USGS
colln. 30747—PC).
4—5. on morphotype, X50, USNM 442140.
6—7. B morphotype, X45, USNM 442141.
8—9. Pa element, 0: morphotype, X40, outer and inner lateral
views, 42 m (USGS colln. 30754—PC), USNM 442142.
10—12, 14—17. 0.4 m (USGS colln. 30745—PC).
10—12. Pa elements, inner lateral, upper, and inner lateral views.
10—11. v morphotype, X45, USNM 442143.
12. 0t? morphotype, X50, USNM 442144.
14—15. Two Sc elements, X30, lateral views, USNM 442146—47.
16. Pb element, X40, lateral view, USNM 442148.
17. M element, X50, lateral view, USNM 442149.
13. Pa element, X45, upper view, 22 m (USGS colln. 30750—
PC), USNM 442145.
Gnathodus bilineatus bilineatus (Roundy), Pa elements, X50, upper views,
lower member.
18. Left element, 37 m (USGS colln. 30753—PC), USNM
442150.
19. Right element, 7 m (USGS colln. 30747—PC), USNM
442151.
Gnathodus girtyi girtyi Hass, right Pa elements, X50, lower member.
20—21. Upper and lower views, 53 m (USGS colln. 30757—PC),
USNM 442152.
22. Upper view, 32 m (USGS colln. 30752—PC), USNM
442153.
Gnathodus defectus Dunn, Pa elements, X75, upper member.
23—24. Left and right elements, upper views, 102 m (USGS colln.
30773—PC), USNM 442154—155.
31—33. Right element, upper, lower, and inner lateral views, 85 m
(USGS colln. 30768—PC), USNM 442160.
Gnathodus girtyi simplex Dunn, X50, right Pa elements, lower member.
25. Upper view, 32 m (USGS colln. 30752—PC), USNM
442156.
26—27. Upper and lower views, 37 m (USGS colln. 30753—PC),
USNM 442157.
Gnathodus sp. indet, M element, X50, inner lateral view, lower member, 53
m (USGS colln. 30757—PC), USNM 442158.
Gnathodus girtyi girtyi Hass transitional to Declinognathodus inaequalis
(Higgins), right Pa element, X40, upper view, lower member, 69 m (USGS
colln. 30762—PC), USNM 442159.
Gnathodus girtyi simplex Dunn transitional to Declinognathodus
noduliferur japonicus (Igo and Koike), left Pa element, X50, upper view,
lower member, 54.9 m (USGS colln. 31698—PC), USNM 483406.

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1568 PLATE 2

g 1.3

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«Sm;

CAVUSGNATHUS AND GNATHODUS

 

PLATE 3

All conodonts from the Wahoo Limestone at study section,
eastern Sadlerochit Mountains, northeast Brooks Range, Alaska,

except figure 31, which is from 1 km to the west.

[Scanning electron microscope photomicrographs of specimens coated

Figures 1—8, 19—22.

10—14,32.

15—18,23—25.

26427.

28—3 1.

with carbon and gold. Meters shown are above base of formation]

Declinognathodus noduliferus japom'cus (Igo and Koike), Pa elements.
1—8. Right Pa elements, lower member.

1—2. Upper and lower views, X40, 62 m (USGS colln. 30760—PC), USNM
442161.

3. Upper view, x50, 59 m (USGS colln. 30759—PC), USNM 442162.

4—8. Figures 4—6 upper views, 7—8 upper and lower views, x50, 56 m
(USGS colln. 30758~PC), USNM 442163—166.

19—22. Upper member.
19—20. Left element, X40, lower and upper views (blade broken during SEM
preparation), 207 m (USGS colln. 30789—PC), USNM 442175.
21. Right element, X50, upper view, 250 m, (USGS colln. 30796—PC),
USNM 442176.
22. Right element, X50, upper view, 207 m (USGS colln. 30789—PC),
USNM 442177.

. Declinognathaa'us noduliferus japonicus (Igo and Koike) transitional to D. n.

noduliferus (Ellison and Graves), right Pa element, X50, upper view, lower
member, 62 m (USGS colln. 30760—PC), USNM 442167.

Declinognathodus noduliferus noduliferus (Ellison and Graves), Pa elements,
upper views, X50, upper member.

10. Right element, juvenile, 113 m (USGS colln. 30775—PC), USNM
442168.

11. Left element, 85 m (USGS colln. 30768—PC), USNM 442169.
12. Right element, 133.5 m (USGS colln. 30778—PC), USNM 442170.
13. Left element, 177 m (USGS colln. 30785—PC), USNM 442171.
14. Right element, 250 m (USGS colln. 30796—PC), USNM 442172.
32. Left element (lateralis morphotype), 187 m (USGS colln. 30786—PC),
USNM 442184.
Idiognathoa’us sinuosus Ellison and Graves, Pa elements, X50, upper member.
15—16. Juvenile, upper and lower views, 207 m (USGS colln. 30789—PC),
USNM 442173.
17—18. Lower and upper views, 187 m (USGS colln. 30786—PC), USNM
442174. '
23—25. Upper and upper and lower views, 207 m (USGS colln. 30789—PC),
USNM 442178—179.
Lochriea commutata (Branson and Mehl), X50, lower member, 6 m (USGS
colln. 30746~PC).
26. Left Pa element, upper view, USNM 442180.
27. M element, lateral view, USNM 442181.
Vogelgnathus postcampbelli (Austin and Husri), Pa elements, lower member.

28—29. Lateral and lower oblique views, 13.2 m (USGS colln. 30748—PC),

USNM 442182.

30. Lateral view, 53 m (USGS colln. 30757—PC), USNM 442183.

3]. Lateral view, 55.3 m (USGS colln. 31836—PC, app. 1, loc. lBlg),
USNM 483407. From Mississippian-Pennsylvanian boundary section
1 km west of study section. Sample from 2.8 m above the first
appearance of Declinognathodus noduliferus japom'cus in the eastern
Sadlerochit Mountains.

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1568 PLATE 3

DECLINOGNATHOD US, IDIOGNATHOD US, LOCHRIEA, AND VOGELGNATHUS

 

PLATE 4

Conodonts from the Wahoo Limestone, eastern Sadlerochit Mountains,
northeast Brooks Range, Alaska, except figure 26 from Pogopuk Creek section,

Figures 1—9.

10—12.

13—15.

17—21.

22—24.
25.

26.

27—30.

Franklin Mountains (see text-fig. 2).
[Scanning electron microscope photomicrographs of specimens coated
with carbon and gold. Meters shown are above base of formation]

Rhachistognathus minutus declinatus Baesemann and Lane, Pa elements, X50,
upper member.
1. Right element, upper View, 107 m (USGS colln. 30774—PC), USNM
442185.
2. Right element, upper view, 177 m (USGS colln. 30785—PC), USNM
442186.
3—4. Right element, lower and upper views, with node on anterior part of inner
lobe, 187 m (USGS colln. 30786-PC), USNM 442187.
5—6. Left element, lower and upper views, 187 m (USGS colln. 30786—PC),
USNM 442188.
7. Right element, upper view, with transverse ridge connecting node on inner
lobe to parapet, 191.5 m (USGS colln. 30787—PC), USNM 442189.
8. Right element, upper view with node on inner lobe, 232 m (USGS colln.
30793—PC), USNM 442190.
9. Right element, upper view, 85 m (USGS colln. 30768—PC), USNM
442191.
Rhachistognathus minutus havlenai Baesemann and Lane, Pa elements, X50, upper
views, upper member.
10—1 1. Right elements, 107 m (USGS colln. 30774—PC), USNM 442192—93.

12. Left element, 162 m (USGS colln. 30782—PC), USNM 442194.
Rhachistognathus minutus minutus (Higgins and Bouckaert), Pa elements, X50,
upper member.

13—14. Right elements, upper and lower views, 85 m (USGS colln. 30768—PC),
USNM 442195—96.
15. Left? element, upper view, 107 m (USGS colln. 30774—PC), USNM
442197.

. Rhachistognathus muricatus (Dunn) transitional to R. websteri Baesemann and

Lane, X50, upper view, lower member, 6 m (USGS colln. 30746—PC), USNM
442198.
Rhachistognathus websteri Baesemann and Lane, Pa elements, X50, upper
member.
17—19. Upper, lower, and upper views, 91 m (USGS colln. 30770—PC), USNM
442199—200.

20—21. Upper and lower views, 122 m (USGS colln. 30777—PC), USNM 442201.
Rhachistognathus spp. indet., Pa elements, juveniles, lateral, upper, and lower
views, upper member, 260.5 m (USGS colln. 30799—PC), USNM 442202—203.
Rhachistognathus muricatus (Dunn) transitional to R. primus Dunn, Pa element,
X50, upper view, upper member, 95 m (USGS colln. 30771—PC), USNM 442204.
Gnathodus defectus Dunn, Pa element, X50, upper view, lower member, 154.5 m
below base of overlying Echooka Formation (USGS colln. 31860—PC, app. 1, loc.
5D), USNM 442205. In this collection, G. defectus occurs with three species of
Rhachistognathus, including R. minutus, indicating the lower minutus Fauna.
Rhachistognathus muricatus (Dunn), Pa elements, lower member.

27. Upper view, X50, 56 m (USGS colln. 30758—PC), USNM 442206.

28—29. Upper and lower views, X50, 7 m (USGS colln. 30747—PC),
USNM 442207.
30. Upper view, X40, 69 m (USGS colln. 30762—PC), USNM 442208.

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1568 PLATE 4

RHACHISTOGNATHUS AND GNATHODUS

 

Figures

PLATE 5

Conodonts from the Wahoo Limestone, eastern Sadlerochit Mountains,

northeast Brooks Range, Alaska.
[Scanning electron microscope photomicrographs of specimens coated
with carbon and gold. Meters shown are above base of formation]

1—10. Kladognathus spp. indet., lower member.

11.14—17.

12.

13.

18-19.

20.

21.

22.

23.

1. P element, X50, lateral View, 04 m (USGS colln. 30745—PC), USNM

442209.
2. P element, X50, lateral View, 6 m (USGS colln. 30746—PC), USNM
442210.
3. P element, X50, oblique view, 0.4 m (USGS colln. 30745—PC), USNM
442215.
4. P element, X50, oblique view, 42 m (USGS colln. 30754—PC), USNM
442216.
5. M element, X45, lateral view, 7 m (USGS colln. 30747—PC), USNM
442211.
6. M element, X30, lateral view, 6 m (USGS colln. 30746—PC), USNM
442212.
7. Sa element, X50, anterolateral View, 0.4 m (USGS colln. 30745—PC),
USNM 442213.
8. Sa element, X50, posterior view, 37 m (USGS colln. 30753—PC),
USNM 442214.
9. Sc element, X50, lateral view, 6 m (USGS colln. 30746—PC), USNM
442217.
10. Sb element, X50, lateral view, 0.4 m (USGS colln. 30745—PC), USNM
442218.

Idioprioniodus conjunctus (Gunnell)?, X50.
11. Pb element, lateral view, upper member, 162 m (USGS colln.
30782—PC), USNM 442219.
14—15. Sb? element, inner and outer lateral views, upper member, 207 m
(USGS colln. 30789—PC), USNM 442222.
16—17. M and Sc elements, lateral view, lower member, 53 m (USGS colln.
30757—PC), USNM 442223—24.
Idioprioniodus sp. indet., Pb element, X50, lateral view, lower member, 53 m
(USGS colln. 30757—PC), USNM 442220.
ldioprioniodus cf. 1. healdi (Roundy)?, Pb? element, X50, lateral view, upper
member, 207 m (USGS colln. 30789—PC), USNM 442221.
Diplognathodus? ellesmerensis Bender?, Pa element, X50, lateral and upper
views, upper member, 203 m (USGS colln. 31710—PC), USNM 442227.
Cavusgnathus? tytthus Brown and Rexroad, Pb element, X50, inner lateral
view, lower member, 54.9 m (USGS colln. 31698—PC), USNM 484526.
ldiognathoa’us incurvus Dunn?, Pa element, X40, upper view, upper member,
250 m (USGS colln. 30796—PC), USNM 442225.
Idiognathaides sinuatus Harris and Hollingsworth, Pa element, X40, upper
view, upper member, 217.5 m (USGS colln. 30790—PC), USNM 442226.
Gnathodus bilineatus bilineatus (Roundy), juvenile right Pa element, X90,
upper view, lower member, 69 m (USGS colln. 30762—PC), USNM 483408.
This specimen is possibly redeposited because it occurs 13 m above the base of
the Pennsylvanian and all other representatives of the species are restricted to
the Mississippian part of the Wahoo Limestone in the study section (table 1).

U,S‘ GEOLOGICAL SUR PROFESSIONAL PAPER [568 PLATE 5

CAVUSGNATHUS?, DIPLOGNATHODUS?, GNATHODUS. IDIOGNATHODUS, IDIOGNATHOIDES,
[DI OPRI ONIOD U S , AND KLADOGNA THUS

 

 

 

 

MlSSISSlPPlAN PENNSYLVANIAN PERMIAN SYSTEM
CHESTERIAN MORROWAN UPPER MORROWAN AND OR LOWER ATOKAN LOWER ATOKAN SERIES/SUBSERIES

Upper muricatus Subzone noduliferus - primus Zone minutus Fauna _ IdiognathOdUS Fauna 7 ZONE/”UNA

WAHOO L'MESTONE ECHOOKA FORMATION/MEMBER
LOWER MEMBER UPPER MEMBER FORMATION
3 USGS collection No. (30801 -PC)

Meters above base of Wahoo Limestone

9'9 S‘LLZ

[6

Sample weight (kg)
lautus
spathus

spp. indet.

Ca vusgnathus altus

0.? tyffhus

C. unicomis

spp. indet.
cavusgnathoids
noduliferus japonicus ‘

. n. nodu/iferus

umueoun uoxm 01 maumfi’rsse ‘51 fumueoun uoprsodepol ‘53 fpeusodopol ‘3]
I sumsewn 001mm 3111 u; uopnqmsip setoeds 1uopou03 '1 alqel

nodu/iferus subspp. indet.
ellesmerensis?

bilineatus bilineafus

bilineatus subsp. indet.

defectus

giITyi ginyi

girtyi simplex

girfyisubspp. indet.

girfyi subspp. trans; to Dec/inc. spp.

spp. indet.

minutus

spp. indet.

‘sumunow 1rq00191peg memes ‘uopoes Apms 9111 u

incurvus’?
sinuosus
spp. indet.

sinuafus

[emuruumeput 9d/{11u9u1919 ‘g, fumueoun cad/{1 memep 01 meumfirsse ‘qu f

conjuncfus?

cf. I. healdl?
spp. indet.

5
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W
H
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W
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5°
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m

commutata

sp. indet.
minufus declinafus
havlenai
minutus

subspp. indet.

trans. to Fl. primus

trans. to Fl. websteri

spp. indet.
postcampbelli
Pa element
Pb element
M element
Sa element
Sb element

Sc element

generically identifiable elements
per kilogram

bar, blade, and platform fragments

Alteration Index (CAI)

 

 

U.S. Department of the Interior Professional Paper 1568
U.S. Geological Survey Plate 6

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 
      

 

 

 
    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SYSTEM MISSISSIPPIAN PENNSYLVANIAN(?) PENNSYLVANIAN PERMlAN
SERIES CHESTERIAN (pART) MORROWAN(?) MORROWAN UPPER MORROWAN AND (OR) LOWER ATOKAN LOWER ATOKAN
APAH
FORMATION/MEMBER filme@ LOWER MEMBER OF WAHOO LIMESTONE UPPER MEMBER OF WAHOO LIMESTONE ECHFfAOKA
- (Globivalvu/I'na ' _ ' . minutus Fauna Pse dostalle/las . '
CONODONT ZONE/FAUNA Upper murIcatus Subzone / DUI/aides) 7 nodu/Iferus prImus Zone lower mInutusFauna l u\ , up I ldIognathodus Fauna
(Biostratigraphically significant _ ' __ ‘ K _ __ .
loramInIfer) -—l o . . . . O . ._.g 7: _ 9 T -l'
ROCK TYPE E” e 7
T Hit/jongEqSSE‘; o 50 100 150 200 250
l l l | | l l I | l l J l I l I l I I I I I I
CavusgnathOIds X XX X X X X X X X X XXX X X 4X
Cavusgnathus unicornls X XX X X X X X X X X X
Cavusgnathus spp. Indet. X X X X X X X X X—X
Cavusgnathu37lytthus X X X X HOOP—X—X— X? —X——)(-—)(
Cavusgnathus a/tus x———X
Gnamodus spp. indet. X X? X
Gnalhodus bl/Ineatus biI/neatus X X A X X — — —XR?
G. bilineatus subsp. indet. x———X
* Gnalhodus girty/ girlyi X X X X X X X — — -XR? — XR?
Gnathodus gIrtyI SImp/ex XX X X X X
Gnalhodus giltyisubspp, indet. X
G. glrty/ trans. to Dec/inognathodus spp. X—X—-X——X
Hindeodus minutus X X X X X X X X X in X X X
Hmdeodus spp. Indet. X'.‘ X X X X X X 3'
ldiopr/omodus conjunctus° I\ X X X X X X X X X
ldIoprI'onIodus spp, indet. X X X X X X X? "r X X X X X X X X X X
K/adognamus spp. X XX X X X X X X X X X - XR XR — XR —- — — — — — -—— — XR
Lochriea commutata Xi XX X X" X
* Rhach/stognathus mun'catus X X X A X X XX X X X X X X X X 4X
Rhachistognafhus spp, indet. X X X X X X H X X X X X V X X X X X X X X X X A X
R. mur/calus trans. to F1. websteri X
Flhach/slognathus prolixus’? X X
Vogelgnathus postcampbe/II X A A X 4X
EXPLANATION Adetognathus spp. Indel. X? ‘X ‘X X X X XX X X X X X X X X X X X X X X X XXX X X X X X X X 4X
* Dec/mognathodus nodu/Iferus Iapomcus Xi 7\ X X X X X X X X X X
I m - * Dec/inognathodus nodu/I'ferus nodu/iferus X X A A X X A X X X X XX X " X X 4X
I I WA * Declinognathodus nodu/iferus subspp. indet, X X X X? X? X A X X
Grainstone Packstone-wackestone Mudslone Gnathodus defectus X? X X X
* Hhachistognathus websleri X X X X X X X X X X X X X X X
I AdeIognamus Iaqus xx A A x X x x x A x x X x x x X x A x x A x x A x
l Adetognalhus spathus X X X X X X X X X X X X X X
Graipsttogg_ Wackeslone Siltstone * Flhachlstognathus mlnutus subspp. Indet. X X X? X X X
ac S O
p * Rhach/‘stognathus mlnutus minutus X X X X X X X X X X X X X X X X X X X X? ———X—X
I / / * Rhachistognathus minutus declinatus " X X X X X X X X X X X X XX XXX X X X X X X X X X X X XX
1 l * Rhachislognathus mmutus hav/ena/ X X X X X X X X X X n X X X X X X n X X XX
Packstone Wackestone-mudstone DOlO-mitizeC‘l Rhachistognamus muricatus trans. to R. primus x—x
(combIned WIth
other lithologies) -k Idiognalhodus spp. Indel. X X X X X X X X X X
X Species * Index species _ . V v v v v v
identified in _ - - * ldIognalhodus smuosus A A n X ,A X X X
sam '9 R RedepOSIted D l th (1 9 // ' 9 X
.. Ipo na 0 us 9 esmerenSIs,
p R? Redeposmon Chert nodules g , _
. - ldIoprIonIodus cl. /. healdI? x
X? ASSIgnment to uncertaIn (9
species or genus — '— _ 0 O IdlognalhOIdes s/nuaius x
questionable Redeposition or OOIds common * ldiognamodus Incurvus? x——x
probable redeposition to abundant
Neognalhodus? sp Indet, X

 

 

 

 

Conodont zones, faunal intervals, and species distribution and lithologies of the Wahoo Lirrestone in the study section, eastern Sadlerochit Mountains, northeast Brooks Range, Alaska

 

 

Table 2. Depositional environments interpreted from carbonate-nficrolithofacies and conodont-

 

Sadlerochit Mountains, northeast Brooks Range, Alaska

[Conodont genera: Ad., Adefognathus; C.?, Cavusgnathus?
Idid., ldiognathoides; Idp., Idioprioniodus; K/d., K/adognathus

\

(includes only 0.? tytfhus); Cav., Cavusgnafhus;’De., Dec/inognalhodus; Gn., Gnathodus; Hi.,
; Rh., Rhachisfognafhus; Vo., Vogelgnathus; 1?, assignment to taxon uncertain]

biofacies data, Wahoo Limestone, eastern

Hindeodus; Idg., ldiognalhodus;

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Meters Carbonate Abun- Common Minor Rare Sorting . Micrit- Abrasion Depositional Environment Conodont Genera ‘ ~ _
(abw)1 Texture dant (1o-50%) (140%) (<1%) ization (Microlithofacies) (Includes only genera having more Conodont Deposrtlonal Unlv. Alaska
(>50%) th< n 5 specimens in each sample) BiofaCIes EnVIronment Museum
MISSISSIPPIAN PART OF THE LOWER MEMBER OF THE WAHOO LIME STONE Q? Ca. Gn. Hi. Kld R11 V0. (Conodont-based) Sample No-
CAVUSGNATHID BIOFACIES (NEAR RESTRICTED TO OPEN PLATFORM )
13.2 Grainstone Y AOQ ”Q6 well A moderate open marine or open platform, 59 8 9 1o cavusgnathid open platform AK22M16.2
high energy
22 Grainstone, Yfl A NA<9>OQO 0% moderate M moderate open marine or open platform, 1 69 1 cavusgnathid open platform, near AK22M25
packstone moderate to high energy restricted(?)
32 Grainstone Y #7 A 00 NAcQJZQ moderate C moderate open marine or open platform, 53 6 9 cavusgnathid open platform AK22M35
moderate energy
42 Grainstone Y 177 A Mcfiflfi 0 moderate 0 strong open marine or open platform, 21 cavusgnathid open platform, near AK22M45
moderate to high energy restricted(?)
47 Grainstone Yr? A N03®0 A665 moderate C moderate open marine or open platform. 1 63 14 cavusgnathid open platform AK22M50
moderate to high energy
50.5 Grainstone Yr? A WQAOIQ (sax moderate C moderate open marine, near restricted 4 16 cavusgnathid open platform, near AK22M53.5
61)}. platform restricted(?)
CAVUSGNATHlD-KLADOGNATHID BIOFACIES (OPEN PLATFORM TO OPEN MARINE)
0.4 Packstone Y #7 We AX ® 7 Q poor 0 moderate open marine to open platform, 108 67 97 cavusgnathid- open platform to open AK22M3.4
moderate energy kladognathid manne
6 Grainstone, Yr? A @2an A880 moderate M moderate open piatfonn, near restricted 81 18 30 14 cavusgnathid- open piatforrn to open AK22M9
packstone platform kladognathid marine
7 Grainstone, Y #7 A NQAébO @680 well C moderate open marine near restricted 88 15 46 15 cavusgnathid- open piatfonn near AK22M10
packstone platform kladognathid open manne
27 Grainstone Y #7 NQAOA X. moderate C moderate open marine or open platform, 3 7 5 1o cavusgnathid- open platform to open AK22M30
moderate energy kladognathid marine
37 Grainstone, A Y 0 Mr?) moderate M moderate open marine or open platform, 8 6 7 cavusgnathid- open marine, near open AK22M40
mUddL___ moderate energy kladognathid platform
GNATHODlD-HINDEODID BIOFACIES (LOW ENERGY, OPEN MARINE)
53 Packstone Y \UQA Q wA&)R_flf poor C weak open marine, low energy 67 32 5 gnathodid- open marine, low AK22M56
hindeodid energy
Meters Carbonate Abun- Common Minor Rare Sorting Micrit- Abrasion Depositional Environment Conodont Genera
(abw)1 Texture dant (10-50%) (140%) (<1%) ization (Microlithofacies) (Includes only genera
(>50%) having more than 5 Conodont Depositional Univ. Alaska
spec‘mens in each sample) Biofacies Environment Museum
PENNElYLVANIAN PART OF THE LOWER MEMBER OF THE WAHOO LIMESTONE Ad. C.? De. Hi. Rh. (Conodont—based) Sample N0-
ADETOGNATHID-RELATED BIOFACIES (NEAR RESTRICTED PLATFORM TO LOW ENERGY, OPEN MARINE)
56 Packstone- 0 Y A NQAfl/fl aaafi'to moderate C weak open to restricted platform 1 15 19 1o declinognathodid- mixed: near restricted to AK22M59
wa9keSt°”°' @ ® 3 V 7Q adetognathid open platform near
gramstone shoal
59 Grainstone. Y 047' A NQAvm moderate C moderate open marine, moderate energy 61 37 58 14 adetognathid- open marine to open AK22M62
packstone declinoqnathodid platform
69 Packstone Y A O \0/ ($3 7(5)?) poor strong open marine, low energy 11 8 18 10 hindeodid- open marine AK22M72
(dolomitic) adetognathid
Meters Carbonate Abun- Common Minor Rare Sorting Micrit- Abrasion Depositional Environment Conodont Genera
(abw)‘ Texture dant (10-50%) (140%) (<1%) ization (Microlithofacies) (Includes only genera having
(>50%) more than 5 specimens in each Conodont Depositional Univ. Alaska
sample) Biofacies Environment Museum
PENNSYLVANIAN Ad. De. Hi. Idg. Idp. Rh. (Conodont-based) Sample No.
UPPER MEMBER OF THE WAHOO LIMESTONE
ADETOGNATHID-RHACHISTOGNATHID BIOFACIES(?) (RESTRICTED TO NEAR OPEN PLATFORM)
246 Grainstone 0 Q 0®66€A7§ 3 0 very poor A strong restricted to open platform 26 7 23 adetognathid- open platform, near AK22M249
rhachistognathid shoal
261.5 Packstone, N © 7% O YchV A AxO/Q very poor 0 restricted to open platform 15 18 adetognathid- restricted to open AK22M264.56
mudstone rhachistognathid platform
ADETOGNATHID-RHACHISTOGNATHID BIOFACIES (OPEN PLATFORM TO NEAR SHOAL AND SHOAL TO TIDAL C -|AN NEL
84 Grainstone Y 47 A@&3A \O/ZGOQ moderate C moderate open platform, moderate 27 31 adetognathid- open platform, near AK22M87
energy rhachistognathid shoal
113 Grainstone Yc9>€ MQOAO 0 very well A strong open platform to open marine, 66 7 142 adetognathid- shoal to tidal channel AK22M116
Q high energy, tidal channel(?) rhachistognathid
118 Grainstone A NYE 66309 QAW poor C moderate open platform, near shoal 11 11 adetognathid- open platform, near AK22M121
° rhachistognathid shoal
157 Grainstone Ge. NOY #7 fl 3 ® moderate A strong shoal, near platform 29 34 adetognathid open platform, near AK22M160
:9) © 7 0 X rhachistognathid shoal
203 Grainstone A0 iO® V well A strong open platform 12 18 adetognathid- open platform, near AK22M206
rhachistognathid shoal
241 Grainstone, MiG/Y @AX an moderate ‘ C moderate open platform 13 5 11 adetognathid- open platform, near AK22M244
packstone 127 © rhachistognathid shoal
RHACHISTOGNATHID BIOFACIES (NEAR SHOAL TO OPEN PLATFORM
95 Grainstone QOY V N777 (EBA © 7 (3 well C strong open platform, near shoal or 17 41 rhachistognathid open platform, near AK22M98
0 e o XQ tidal channel shoal
107 Grainstone, C 09 MQ0Y&>© W well strong open platform, near shoal, 36 147 rhachistognathid open platform, near AK22M110
packstone 7 AXQ. high energy shoal
257.5 Grainstone, Y #7 A 03 © 7X6 MMOQ poor C moderate open platform, moderate 7 26 rhachistognathid open platform AK22M260.5
ac 5 one energy
RHACHISTOGNAT HID BIOFACIES (SHOAL OR TIDAL CHANNEL)
85 Grainstone Yflc$A WOO/00 very well A strong opehn platform or tidal channel, 26 118 rhachistognathid shoal or tidal channel AK22M88
hig energy
91 Grainstone ($0 Nil/Y AQQ very well A strong open marine, near shoal, or 26 245 rhachistognathid shoal AK22M94
(d°'°m'"z°d) tidal channel, high energy
97 Grainstone AG) figchgg 3 75 ® well C strong shoal and (or) tidal channel 7 19 rhachistognathid shoal or tidal channel AK22M100
o
102 Grainstone NQO/A O Y<9>®e 0 Q very well C strong tidal channel or open marine, 30 130 rhachistognathid shoal AK22M105
near shoal, high energy
122 Grainstone NQO Y&>A To well A strong open platform, near shoal or 34 8 180 rhachistognathid shoal or tidal channel AK22M125
Q 0 tidal channel, high energy
RHACHISTOGNAT HID BIOFACIES (OPEN MARINE, NEAR SHOAL)
133.5 Grainstone Y A 6400/17? @ AO moderate C moderate open marine to open platform, 36 24 192 rhachistognathid open marine, near shoal AK22M136.5
<52>© 7 A X e ‘ near shoal, moderate energy
00
187 Grainstone, Yfl 649) 00/663 7 A 890 moderate C weak . open platform or open marine, 10 33 19 276 rhachistognathid open marine, near shoal AK22M190
packstone A 0 moderate energy
232 Grainstone Y #7 A WQOOflaé AEOQ well C strong - open marine to open platform, 8 7 16 37 rhachistognathid open marine, near shoal AK22M235
© moderate energy
Meters Carbonate Abun- Common Minor Rare Sorting Micrit- Abrasion Depositional Environment Conodont Genera
(abw)' Texture dant (10-50%) ( 1-10%) (<1%) ization (Microlithofacies) (Includes only genera having more than Conodont Depositional Univ. Alaska
(>50%) 5 sm time is in t ach sample Biofacies Environment Museum
PENNS YLVANIAN Ad. De. Hi. Idg. Idp. Idid. Rh. (Conodont-based) Sample No.
UPPER MEMBER OF THE WAHOO LIMESTONE
DECLINOGNATHODID-RELATED BIOFACIES (OPEN MARINE, NEAR SHOAL)
177 Grainstone NQOO Am A MO poor A moderate ' open platform, near shoal, or 23 20 declinognathodid- open marine, shoal AK22M180
Y 1% )3 G e tidal channel(?) rhachistognathid apron
197.5 Grainstone, Y A 00 age moderate C moderate open marine, near shoal 23 8 declinognathodid open marine, near shoal AK22M200.5
packstone
207 Grainstone, Y #7 @A 00 A3 580 moderate C moderate open marine, near shoal 30 15 8 declinognathodid- open marine AK22M210
packstone to oor idiognathodid
DECLINOGNATHODID-RELATED BIOFACIES (LOW ENERGY, OPEN PLATFORM AND (OR, OPEN MARINE)
142 Packstone Y 047 A0 NW poor 0 moderate open marine to open platform, 21 15 33 rhachistognathid- open platform or open AK22M145
(d°'°mi‘ized) =low energy adetognathid marine
152 Mudstone A not 0 not open marine, low energy 34 declinognathodid open marine AK22M155
ld°'°"‘"i15d) a Iicable a Iicable
162 Packstone, YA ()0. V X80 poor C strong ‘ open marine to open platform, 44 41 6 61 rhachistognathid- open platform or open AK22M165
wackestone low energy adetognathid- marine
(d°'°'“m25d) declinognathodid
178 Packstone Y A iOX O A&><§m poor C moderate 1 open marine, low energy 21 declinognathodid open marine AK22M181
217.5 Packstone \O/Y A NW 38 poor C moderate open marine, low energy 34 75 12 3 declinognathodid- open marine AK22M220.5
(dolomitized) idiognathodid
237 Packstone YA \0/ 6M poor 0 moderate open platform to open marine 17 8 declinognathodid- open marine AK22M240
idiognathodid
250 Wackestone, Yfll?’ A not 0 not , open marine, low energy 17 declinognathodid open marine Ak22M253
mudstone applicable applicable
(dolomltlzed)
CONODONT SAMPLES NOT QUALIFYING FOR BIOFACIES ANALYSIS
Meters Carbonate Abun- Common Minor Rare Sorting Micrit- Abrasion Depositional Environment Conodont Genera Univ. Alaska
(abw)1 Texture dant (1 O-50%) (1 -10%) (<1%) ization (Microtithofacies) Museum
(>50%) Sample No.
RESTRICTED PLATFORM Ad. 0.? Cav De. Gn, Hi. Idg. Idp. Idid Kld. Flh. V0.
76.8 Mudstone 0 intertidal to restricted; 1 AK22M79.8
(“minim“) conodonts confirm
80.8 Packstone Y to (9:8 56 well A strong restricted platform; conodonts 9 AK22M83.8
suggest open platform near
, 571033
253 Grainstone, 0 K @669 80 , very‘weII A strong restrided piatfonn; conodonts 1 4 AK22M256
mudstone suggest open platform near
shoal
260.5 Grainstone O 7Q very‘well A strong restricted platform; conodonts 8 9 AK22M263.5
. suggest near shoal, open
platform
OPEN TO RESTRICTED PLATFORM
55.5 Packstone, 7t 0 Y #7 r 0A0 poor 0 weak restricted to open platform; 3 2 AK22M58.5
bafflestone conodonts confirm
65 Grainstone, Y fl 7% 0 GAO 66/51? 0 [poor to A moderate open to restricted platform; 4 2 1 AK22M68
packstone weak to weak conodonts confirm
74 Wackestone, YA. 0 #7 @0X HA7 poor Ft weak to restricted to open platform, low '1 AK22M77
mudstone, moderate energy; rarity of cone-dents
packstone suggest restricted to open
. platform
76.5 packstone Y o #7 Q M@&)€Z 0 moderate A moderate restricted to open platform; 1 1 1 AK22M79.5
e to well to strong conodonts confirm
212 Grainstone, 0 Y6?” AX Q® AO very well I A strong restricted to open platform; 7 AK22|y1215
mudstone , conodonts suggest restricted
to near shoal
OPEN PLATFORM
88 Packstone, @ #7 A. NW8 poor M weak open platform; 14 AK22M91
wackestone Q conodonts suggest open
(dolomitized) platform near shoal
137 Grainstone Y #7 A 0? A 33 0 moderate R weak opefn platform; conodonts 3 9 2 7 AK22M140
con lrm
167 Grainstone, MQOY i@&>3 7)} 760 poor to C weak to open platform; conodonts 1 1? 1 7 AK22M169.9
packstone 417 Q *6 0 moderate moderate confirm
191.5 Grainstone, WQI© 0Y3 AW poor A moderate open platform; conodonts 12 5 AK22M194.5
bafflestone G) confirm
222 Grainstone 0 O O YWAX 0 well C strong open platform, behind shoal; 3 AK22M225
indet. conodont fragments
243 Grainstone, Y 0177 A @ N- O ’5‘ poor A weak open platform to open marine 3 5 3 1o AK22M246
packstone
OPEN PLATFORM OR OPEN MARINE TO SHOAL
62 Grainstone, 777 Y @Ae NWO Q16?) 5 Q poor to A moderate open platform near shoal; 5 2 2 12 AK22M65
packstone 0 moderate to weak conodonts confirm
169 Grainstone NQG 00Yfl ® a C m very well A strong open marine to shoal; 4 7 a AK22M172
(9,? *3 O o to well conodonts suggest open
marine to shoal
171 Grainstone G) © 0 HQ 777 3® well to A strong shoal to Open platform; 4 1 AK22M174
9 very well conodonts confirm
174 Grainstone N©XO Qifl/Yfl fi® to moderate 0 moderate open platform to shoal; 1 1 2 AK22M177
<9) 3 *® 9 o to poor conodonts suggest open
marine to shoal
181 Grainstone iN 6 Q C (BAG 0W®XO very well A moderate open platform to shoal; 2 AK22M184
to well conodont data inadequate
132 Grainstone im e 559 0 very well A moderate open platform to shoal; 2 AK22M185
to well conodont data inadequate
227 Grainstone <9>© 00 MY Q) A 57 moderate C strong open platform behind shoal or 6 1 AK22M230
tidal channel; conodonts
confirm
SHOAL
173 Grainstone 0 Ni Y&>Z{ QAO ©® well A moderate shoal; conodonts confirm 3 1 5 AK22M176
e o
179 Grainstone 0 © 0 \O/A very well A strong shoal; conodont data 1 AK22M182
inadequate
180 Grainstone O NQ®G i C @YW A well A strong shoal; conodonts confirm 2 16 AK22M183
A X 0
OPEN MARINE TO OPEN PLATFORM, LOW ENERGY
17.1 Packstone A Y MAO/[77 $6): poor to C moderate open marine to open platform, 9 AK22M20.1
@0 very poor low energy;
conodonts suggest open
platform
1abw, above base of Wahoo Limestone.
EXPLANATION
GRAINS MICRITIZATION
SKELETAL NONSKELETAL
Algae ® Calcisphere ® Grapestone 0 None
6M Undifferentiated é?) Foraminifer )3 Intraclast M Minor (140%)
Q Archaeolithophy/lum sp. 8 Gastropod O Ooid C Common (10-50%)
A Aspha/tina sp. © Oncoid e Superficial ooid A Abundant (>50%)
i Donezella sp. ¢ Ostracode o Peloid
C Bioclast, A Pelmatozoan Q Quartz
undifferentiated
O Bivalve 7Q Sponge spicule
\0/ Brachiopod 6) Trilobite
Bryozoans
Y Undifferentiated
#7 Fenestrate
@ Ramose