Stratigraphy, Age, and 

Paleotectonic Significance of the 

Cottonwood Canyon Member 

of the Madison Limestone 

in Wyoming and Montana

GEOLOGICAL SURVEY BULLETIN 1251-B

Stratigraphy, Age, and 

Paleotectonic Significance of the 

Cottonwood Canyon Member 

of the Madison Limestone 

in Wyoming and Montana

By CHARLES A. SANDBERG and GILBERT KLAPPER

CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1251-B

A comprehensive study of the fades 

relations and conodont zonation of 

transgressive marine beds that straddle 

the Devonian-Mississippian boundary 

in the Northern Rocky Mountains

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1967
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 30 cents (paper cover)
CONTENTS

Page

Abstract_______________________________________________________ Bl

Introduction..-___________________________________________________ 2

Purpose and scope of report___--_-___-_-__-_____-_-___________ 2

Previous work_______________________________________________ 3

Sources of data______________________________________________ 6

Acknowledgments. ____________________________________________ 7

Age and stratigraphic relations of underlying units___________________ 7

Cottonwood Canyon Member_----------------------------_-_-_-_-_- 14

General discussion.____________________________________________ 14

Type section._________________________________________________ 16

Reference sections.-___________________________________________ 20

Distribution and thickness____________________________________ 25

Lithologic and physical character________________________________ 27

Facies and facies relations._____________________________________ 30

Tongues______________________________________________________ 33

Age___--.______________________.______.______._ 36

C orrelation ___________________________________________________ 37

Madison Limestone (lower part)_____________________________________ 39

General features.______________________________________________ 39

Age_____-_-______-_____-_--_--___--_-__---__-------__-___-___ 41

Lodgepole Limestone (lower part)_________________________________ 42

General features.._____________________________________________ 42

Age__________________________________________________________ 43

Conodont zones.__________________________________________________ 44

Upper Devonian zones_____----_-------------------_----------- 44

Scaphignathus velifera Zone (upper iolllo-lower £oIV)__________ 44

Upper Polygnathus styriaca Zone (lower toV)_____--________--_ 45

Lower Spathognathodus costatus Zone (upper £oV)______________ 45

Lower Mississippian zones_-____-_----__--_----_------__-------- 46

Siphonodella sulcata Zone (lower cuT) _______________________ 47

Siphonodella sandbergi-Siphonodella duplicata Zone (upper cuT) _ _ 47

Lower Siphonodella crenulata Zone (lower culla) _______________ 48

Representative conodont collections_______________________________ 48

Trident Member of Three Forks Formation._____---_---___-_----_ 49

Sappington Member of Three Forks Formation.-____--___________- 49

Lower tongue of Cottonwood Canyon Member._______-_-_-__-_-_- 50

Upper tongue of Cottonwood Canyon Member.___________________ 51

Madison Limestone.___________________________________________ 57

Lodgepole Limestone..-.__________-__-__---_---_------____-_--- 60

Paleotectonic interpretations._______________________________________ 61

References cited_______________-_____-_-___--_-_-___-----_-_-----_- 68

in
IV CONTENTS

ILLUSTRATIONS

FIGURE 1. Isopach and facies map showing location of measured sections of 

Cottonwood Canyon Member.__________________________

2. Map showing distribution of geologic units directly underlying 

Cottonwood Canyon Member.__________________________

3. Diagram showing age, conodont zones, and stratigraphic relations of Lodgepole and Madison Limestones, Cottonwood 

Canyon Member, and Three Forks Formation____________

4. Cross section of Cottonwood Canyon Member between Bridger 

Range, Mont., and Bighorn Mountains, Wyo____________

5. Photograph of type section of Cottonwood Canyon Member_ _

TABLES

Page

B4

15

17

Page

TABLE 1. Representative conodont collections from the Lower Spathognathodus costatus Zone (upper toV) in the lower tongue of the 

Cottonwood Canyon Member in Wyoming.______________ B51

2. Representative conodont collections from the upper part of the 

Siphonodella sandbergi-Siphonodella duplicate Zone (upper 

cuT) in the upper tongue of the Cottonwood Canyon Member 

in Montana and Wyoming______________________________ 54

3. Representative conodont collections from the Lower Siphonodella crenulata Zone (lower culla) in the basal part of the 

undifferentiated Lodgepole Limestone in Montana._______ 61
CONTRIBUTIONS TO GENERAL GEOLOGY

STRATIGRAPHY, AGE, AND PALEOTECTONIC

SIGNIFICANCE OF THE COTTONWOOD CANYON

MEMBER OF THE MADISON LIMESTONE IN

WYOMING AND MONTANA

By CHARLES A. SANDBERG and GILBERT KLAPPER

ABSTRACT

The dark shale unit of Devonian and Mississippian age is herein named the 

Oottonwood Canyon Member of the Madison Limestone in Wyoming and of -the 

Lodgepole Limestone in Montana and extreme western Wyoming, where the 

Lodgepole is the basal formation of the Madison Group. The type section is 

described from excellent exposures on the north wall of Cottonwood Canyon on 

the west side of the northern Bighorn Mountains, near Lovell, Wyo. A reference 

section is established in the Beartooth Mountains and a subsurface reference 

section, based on core descriptions, is established in the Bighorn Basin.

The Cottonwood Canyon Member, which ranges in thickness from 0 to 80 

feet, is recognized to be largely continuous in a 50,000-square-mile area of 

northern and western Wyoming and southern and central Montana. In Wyoming 

the member grades into and intertongues with other strata in the lower part 

of the Madison Limestone, whereas in Montana and extreme western Wyoming 

it generally lies at the base of the Lodgepole Limestone. The Cottonwood Canyon 

generally overlies an irregular erosion surface that represents part of an interregional unconformity. In the report area it rests on rocks ranging in age from 

earliest Mississippian to Late Cambrian, but farther south it rests on the 

Precambrian.

The Cottonwood Canyon Member is divided into a lower and an upper tongue, 

each of which is further divisible into an eastern, dolomitic facies and a western, 

shale and siltstone facies. Both tongues are characterized by basal conglomeratic 

lag deposits containing abundant phosphatic nodules and coprolites, conodonts, 

fish remains, and glauconite grains. The lag deposits are continuous between the 

facies of each tongue, and the lag deposit of the upper tongue also continues 

at the base of the Lodgepole Limestone, even where the upper tongue is too 

thin to be differentiated.

Four conodont zones are recognized within the Cottonwood Canyon Member. 

They are, in ascending order, the Lower Spathognathodus costatus (upper 

toV) Zone, which indicates a very late Devonian age for the lower tongue, and

1 Pan American Petroleum Research Center.

Bl
B2 CONTRIBUTION® TO GENEKAL GEOLOGY

the Siphonodella sulcata (lower cul), 8. sandftergi-S. duplicate, (upper cul), and 

Lower S. crenulata (lower cwlla) Zones, which indicate an Early Mississippian 

(Kinderhook) age for the upper tongue. The $. sandbergi-S. duplicata Zone, 

which is named herein, contains a succession of two distinct faunas. The older 

of the two faunas is recognized at only two localities, however, and no formal 

subdivision of this zone is proposed at present.

All the conodont zones that are present in the Oottonwood Canyon Member, 

except for the Siphonodella sulcata Zone, also have been found in the lower, 

undifferentiated part of the Madison or Lodgepole Limestone. Because the undifferentiated lower part of the Madison contains the Lower Spathognathodus 

cost'atus Zone in some areas of Wyoming, its age there must now be regarded as 

Mississippian and Devonian.

Two conodont zones are recognized in the Three Forks Formation, which 

unconformably underlies the Cottonwood Canyon Member, in Montana. These 

are, in ascending order, the ScapMgnathus velifera (upper tollla-lower JoIV) 

Zone, which is widespread in the top of the Trident Member of Late Devonian 

(Famennian) age, and the Upper Polygnathus styriaca (lower tfoV) Zone, which 

is found in the base of the overlying Sappington Member. The presence of this 

zone at the base and of a spore flora containing Leiosonotriletes naumovae near 

the top indicates a very late Devonian age for the bulk of the Sappington. 

Although the uppermost unit of the Sappington may be partly Mississippian, 

a reevaluation of previously cited conodont evidence provides no support for a 

Mississippian age designation.

Representative conodont collections are listed from all the described units 

to document the conodont zonation.

The tongues of the Cottonwood Canyon Member are interpreted to represent 

the basal deposits of two separate eastward transgressions of a Madison sea from 

the Cordilleran miogeosyncline. The earlier transgression in very late Devonian 

time was initially confined to narrow embayments and was less widespread. 

The later transgression in Early Mississippian time was much more widespread, 

and the report area and areas to the north and east were inundated. A mild 

orogenic episode, probably related to the Antler orogeny of Nevada and Idaho, 

intervened between the two transgressions in latest Devonian and earliest 

Mississippian time.

INTRODUCTION

The name Cottonwood Canyon Member of the Madison Limestone 

(or of the Lodgepole Limestone in areas where the Lodgepole is the 

basal formation of the Madison Group) is here applied to the informal 

dark shale unit of Sandberg (1963). The member is largely continuous in an area of about 50,000 square miles in northern and western 

Wyoming and in southern and central Montana (fig. 1). The units 

directly underlying the member are shown in figure 2.

PURPOSE AND SCOPE OF REPORT

The report demonstrates that the Cottonwood Canyon Member 

contains two tongues separated by a disconformity and that it is 

characterized by conglomeratic lag deposits related to two transgressions of a Madison sea. Four distinct conodont zones in the member
COTTONWOOD CANYON MEMBER, MADISON LIMElSTONE B3

and laterally equivalent beds of the Madison Limestone (or Group) 

are recognized and described. On the basis of these zones, the age of 

the Cottonwood Canyon Member and of equivalent beds in the basal 

part of the Madison is shown to range from very late Devonian 

(Clymenia-Stnfe,,2 upper toV 3 ) to Early Mississippian (PericyckisStufe, lower cuTLa) .

PREVIOUS WORK

Many published reports have described the stratigraphy or paleontology of the Madison Limestone (or Group) in small areas of Montana and Wyoming, and several have treated these subjects regionally. 

Few papers, however, have discussed the basal beds, their conodont 

faunas, or the lower contact of the Madison in the area of the present 

report, and only these are cited here.

The clastic content of basal deposits of a transgressive Madison sea 

in Wyoming was mentioned by Andrichuk (1955) in one of the first 

modern regional studies of the Madison Group. On the east side of 

the Bighorn Mountains, near North Crazy Woman Canyon (fig. 1), 

Hose (1955) noted that the lower 3 feet of the Madison is slightly 

sandy and locally conglomeratic. In the Teton Range, Wyo. (fig. 2), 

a black shale at the base of the Lodgepole was recognized by Sando and 

Dutro (1960), but they regarded it as a part of underlying formations. 

Similarly, Blackstone and McGrew (1954), at Cottonwood Canyon, 

and Klapper (1958), at Bull Lake and Dinwoody Canyons in the Wind 

River Range, Wyo. (fig. 1), recognized thin beds of black shale near 

the base of the Madison but included them in the top of underlying 

Devonian formations.

Sandberg (1963) advanced the present concept of a single widespread clastic unit that is comprised of shale and siltstone in some 

areas and of silty or sandy dolomite in others and that incorporates 

all the above-mentioned occurrences as well as many others. The 

stratigraphy of the various Devonian formations that successively 

underlie this unit unconformably was described by Sandberg (1965).

Conodonts in beds of black shale at Cottonwood Canyon were first

3 As the term "Stufe" (plural, "Stufen") is in good standing in Germany and elsewhere, 

it is not desirable to translate it.

3 These letter-numeral designations are standard map symbols in Germany. The first letter 

* is applied arbitrarily to Devonian (to avoid confusion with Diluvium), and the first letter 

c is applied to Carboniferous. The second letter o stands for "ober," or upper, and the 

second letter u stands for "unter," or lower. Thus to is Upper Devonian and cu is Lower 

Carboniferous. Roman numerals used in this report stand for the following Devonian and 

Carboniferous ammonoid Stufen: Manticoceras (tol), Cheiloceraa (toll), Platyclymenia 

(*oIII-IV), Glymenia (tov), WocJclumeria (*oVI), Gattendorfla (cul), and Perlcyclus 

(cull). Lowercase Greek letters o, fl, 5 are used in ascending order for subdivisions of 

these Stufen.
B4 'CONTRIBUTIONS TO GENEIRAL GEOLOGY

50 

I

75 100 MILES 

I______1

FIGURE 1. Isopach and facies map of Cottonwood Canyon Member of Madison 

limestone. Only critical (0-, 5-, 10-, 20-, 40-, and 60-ft.) isopachs are shown. 

Location of measured sections (x), type section (X), subsurface reference 

section (Pan American BBMU 72), and control wells ( ). Mountain ranges 

are outlined; names of mountain ranges and basins are shown in figure 2.

reported by Blackstone and McGrew (1954) and were described and 

illustrated by Ethington, Furnish, and Wingert (1961). A second and 

younger fauna from higher beds of the same unit at Cottonwood 

Canyon was reported by Sandberg (1963) and described and illustrated by Klapper (1966).
COTTONWOOD CANYON MEMBER, MADISON LIMESTONEi B5

111° 110° 109° 108° 107° 106°

MONTANA

WYOMINCN 

0 Sheridan

FIGURE 2. Distribution of geologic units directly underlying main body of 

Cottonwood Canyon Member of Madison Limestone. MDts, Sappington Member of Three Forks Formation; Dtt, Trident Member of Three Forks Formation; Dtl, Logan Gulch Member of Three Forks Formation; Djb, Birdbear 

Member of Jefferson Formation (surface) or equivalent Birdbear Formation 

(subsurface) ; Djl, lower member of Jefferson Formation (surface) or 

equivalent Duperow Formation (subsurface); Dd, Darby Formation; Ob, 

Bighorn Dolomite; Or, Red River Formation; O-Cr, undivided Upper Cambrian 

and Lower Ordovician rocks; g, Gallatin Limestone.

Conodonts from beds that are now included in the Cottonwood 

Canyon Member at other localities in Montana and Wyoming were 

reported by Koucky, Cygan, and Khodes (1961), Koucky and Khodes 

(1963), and Sandberg (1963) and were described and illustrated by 

Klapper (1958,1966).
B6 CONTRIBUTIONS TO GENEIRAL GEOLOGY

SOURCES OP DATA

This report is a product of close cooperation between the two authors 

since 1960. Because of obligations to their respective organizations or 

institutions, they have hitherto published their related findings independently, while freely exchanging new concepts and advance data 

and coordinating their investigations to prevent duplication of effort.

Since 1954, Sandberg has been engaged in a regional study of the 

lowermost Mississippian, Devonian, and older Paleozoic rocks of the 

Williston basin and Northern Rocky Mountains. In correlating newly 

established lithologic units throughout this region, emphasis was 

placed on the recognition and delineation of widespread unconformities. Two major interregional unconformities, whose criteria for recognition had previously not been well established in this region, were 

discerned. One of these, which is locally at the base of Upper, Middle, 

or Lower Devonian rocks, has been discussed in previous reports. The 

other, which is more complex and lies near the Mississippian-Devonian 

boundary, is considered in detail here.

Early in his investigation, Sandberg realized that conodonts, which 

are highly abundant above and less abundant below this latter unconformity, might be the most useful single group of fossils for dating the 

unconformity and for precisely locating the Devonian-Mississippian 

boundary. Megafossils were found to be relatively scarce and commonly poorly preserved in the largely dolomitic rocks of the region, so 

that phylogenetic sequences of individual groups across the unconformity could not be established. Sandberg also realized that age 

determinations based on the indiscriminate use of different, locally 

abundant groups of megafossils might provide conflicting age 

determinations.

Klapper became interested in conodont zonation of Devonian and 

lowermost Mississippian rocks as a result of his study of conodont 

faunas from the Wind River Range (Klapper, 1958). During his investigations toward a doctoral dissertation at the University of Iowa, 

Klapper was directed by Sandberg to several important conodont 

localities at previously measured sections. In return, Klapper provided 

many useful conodont determinations and information about newly 

discovered localities. This exchange of information continued after 

completion in 1962 of Klapper's thesis on Upper Devonian and Lower 

Mississippian conodont zones in Montana, Wyoming, and South 

Dakota.

During the 1965-66 field seasons, the authors spent several weeks in 

Montana and Wyoming resolving their minor differences and searching for new conodont localities in critical areas. This collaboration 

proved so successful that the preliminary reports (Sandberg, 1963;
CGTTONWOOD CANYON MEMBER, MADISON LIMESITONE B7

Klapper, 1966) became outdated. Consequently, the present report was 

written to make the necessary corrections and to present the latest 

findings.

ACKNOWLEDGMENTS

The contributions of many U.S. Geological Survey personnel are 

gratefully acknowledged. W. H. Hass provided determinations of several conodont collections during the early phase of investigation until 

his death in 1959. J. W. Huddle provided many determinations of 

conodont collections beginning in 1964. R. F. Gantnier and J. A. 

Thomas made the calcium-magnesium analyses for the type section 

and Clarks Fork Canyon reference section of the Cottonwood Canyon 

Member. W. R. Keefer, M. R. Mudge, J. F. Murphy, W. G. Pierce, 

A. E. Koberts, G. D. Kobinson, B. A. L. Skipp, and I. J. Witkind, all 

experienced in mapping in the Northern Rocky Mountains, constructively criticized the preliminary nomenclature. Special thanks are 

expressed to J. F. Murphy, J. T. Dutro, Jr., and W. J. Sando, who 

visited many of the measured sections with the authors during the 

summer of 1965, critically reviewed the field evidence, and enthusiastically supported the preparation of this report.

The authors are also grateful to A. L. Benson, who freely exchanged 

ideas and information during the preparation of his doctoral dissertation at the Ohio State University. A condensed version of Benson's 

thesis (1966) includes a description of the stratigraphy of the Cottonwood Canyon Member in western Wyoming.

The authors express their thanks to the Pan American Petroleum 

Corp. and other operators of the Elk Basin, oil field for permission 

to examine cores of the Pan American 72 Elk Basin Madison Unit 

well and to publish the lithologic descriptions that establish a subsurface reference section for the Cottonwood Canyon Member. J. A. 

McCaleb, Pan American Petroleum Corp., accompanied the authors 

during the 1965 field season and later facilitated examination of the 

cores.

AGE AND STRATIGRAPHIC RELATIONS OF 

UNDERLYING UNITS

The Cottonwood Canyon Member rests unconformably, and locally 

with marked angularity, on rocks ranging in age from Mississippian 

to Cambrian within the report area (fig. 2) and on Precambrian 

rocks in isolated areas in southeastern Wyoming.

The youngest unit that lies directly below the Cottonwood Canyon 

Member is the Sappington Member of the Three Forks Formation 

in the vicinity of the Bridger Range in southwestern Montana (fig. 

2). The precise age of the top of the Sappington has not yet been
B8 CONTRIBUTIONS TO GENERAL GEOLOGY

firmly fixed in terms of the conodont zonation (fig. 3), but it is possibly Early Mississippian.

The age and stratigraphic relations of the Sappington are important 

not only to the dating of the regional unconformity but also to the 

correlation of the Cottonwood Canyon Member. Consequently, they 

are evaluated in more detail than the ages and stratigraphic relations 

of the other unconformably underlying rocks.

The Sappington Member is largely a regressive marine deposit 

consisting mostly of calcareous and dolomitic siltstone, in which conodonts are relatively scarce and generally poorly preserved. The Sappington was divided into five units, numbered from base to top, by 

Sandberg (1965). Its lowermost unit (1) is a thin brownish-gray to 

black carbonaceous shale locally containing a very thin transgressive 

sandstone at or near the base. A poorly preserved conodont fauna 

was obtained by Klapper (1966) from a sandstone within this shale 

at a locality 1% miles north of Peak 9559 in the Bridger Kange 

(fig. 1). More recently, a large diverse well-preserved conodont fauna 

was found by Sandberg in a conglomeratic lag deposit at the base of 

the Sappington at Bandbox Mountain in the Little Belt Mountains 

(ng.l).

Faunas from both localities are assigned to the Upper Polygnathus 

styriaca Zone (lower toV). This assignment dates the base of the 

Sappington Member as very late Devonian but unequivocally older 

than the base of the Cottonwood Canyon Member at any locality 

(fig. 3).

Although most workers would now agree that some part of the 

Sappington Member is Mississippian, the exact placement of the 

Devonian-Mississippian boundary on the basis of brachiopod assemblages continues to evoke considerable .controversy. (See Gutschick 

and Rodriguez, 1967.) Turning to another possible method of dating, 

Sandberg (1965) reported the 'occurrence in the Sappington of a large 

continental spore flora, which was dated as latest Devonian by R. H. 

Tschudy. The most significant element of this flora is LeiozonotrUetes 

naumovae Balme and Hassell (1962), which is apparently restricted 

to the Devonian and has a cosmopolitan distribution in beds of known 

latest Devonian age in Western Australia, Colombia, Libya, and western Canada (R. H. Tschudy, written commun., Feb. 14,1962) and in 

Belgium, Germany, Russia, Ohio, and New York.

In the Canning Basin of Western Australia, Leiozonotriletes naumovae is considered by Balme and Hassell (1962) to be the key species 

of the Upper Devonian. There, it occurs in beds of the Fairfield Formation with conodonts that are not younger than latest Devonian. In 

fact, the youngest conodont fauna recognized in the Fairfield is

BIO CONTRIBUTIONS TO OEiNElRAL GEOLOGY

slightly older than latest Devonian and was assigned by Glenister and 

Klapper (1966, p. 838, sample GSWA 3240) to either the Lower or 

Middle Spathognathodus costatus Zone (upper £0V-lower toVI).

Although the upper range limit of Leiozonotrttetes naumovae has 

not been established in terms of conodont zonation on a worldwide 

basis, it has been firmly fixed in Belgium as a result of a recent palynological study by Streel (1966). L. naumovae of the Sappington appears to be included in a phylogenetic sequence of spores that was designated by the key species Hymenozonotriletes lepidopJiytus Kedo 

sensu lato and used as a basis for zonation by Streel (1966). H. lepidopJiytus occurs throughout the Strunian (T'nla) of Belgium, which is 

equated by Streel (1966) and other workers to theWocklumeria-Stufe 

(toVI) of Germany. It occurs no higher than the top of the Devonian 

(Strunian) in Belgium, and its highest occurrence there is below the 

lowest recognized occurrence of the conodont Siphonodella (Streel, 

1966, p. 80).

The position of the spore flora of the Sappington has recently been 

established in terms of both ammonoid and conodont zonation in the 

classic Devonian section of Germany. The Sappington flora has been 

correlated through similar floras in Alberta to a spore flora, recognized by M. Streel in the Hangenberg Shale of the Honnetal section 

in Germany (H. S. Walton and David Mason, oral commun., Apr. 21, 

1967). The Hangenberg Shale, which is dated as latest Devonian 

( Wocklumeria-Stufe, toVI) , directly underlies the Hangenberg Limestone, whose base is Lower Carboniferous (Gattendorfia-Stufe, lower 

cul).

In Montana, the spore flora containing Leiozonotriletes naumovae 

occurs near the top of unit 4 in a bed of shale 23 feet below the top 

and 42 feet above the base of the Sappington Member at Peak 9559. 

The presence of this flora so close to the top of the Sappington suggests that the Sappington is almost entirely Devonian and that only 

its uppermost part, unit 5 of Sandberg (1965), may contain beds 

of Mississippian age.

Conodonts appear to be present in the top few inches of unit 5 of 

the Sappington Member at Logan, Mont. (Achauer, 1959), and at 

other nearby localities (fig. 1). They are absent, however, in lithologically similar underlying beds of the member. Although poorly 

preserved and difficult to separate from the rock, the conodonts that 

supposedly come from the top of the Sappington are unquestionably 

siphonodellids, which indicate an age younger than earliest Mississippian. A detailed reexamination of the upper contact of the Sappington 

at Mud Spring Gulch, 10 miles northwest of Logan, and at Ingleside 

Quarry, 12 miles west of Logan (fig. 1), revealed the presence of a
COTTONWOOD CANYON MEMBER, MADISON LIMESTONE' Bll

previously unrecognized very thin conodont-rich basal lag deposit of 

the Cottonwood Canyon Member at these localities. Because of the 

abundance of conodonts in this lag deposit and because of the absence 

of conodonts from lower beds of the Sappington, it seems more logical 

to refer all thin beds from which conodonts are reported at the top 

of the Sappington to the Cottonwood Canyon. However, even if some 

of the beds near the contact are indeed Sappington, the possibility 

that the conodonts have infiltrated downward through cracks from 

a lag deposit above an unconformity cannot be eliminated at present. 

Stratigraphic leak of conodonts into the top 1 inch of the Sappington 

has been observed at Beaver Creek (fig. 1) and, as will be discussed 

later, into other beds as low as 6 feet beneath the Cottonwood Canyon 

Member elsewhere. Consequently, in the absence of firm conodont evidence, the Early Mississippian age assignment of the top of the Sappington, although quite possible, is considered tentative and is so 

indicated in figure 3.

The Sappington is restricted largely to southwestern Montana (fig. 

2), owing to its eastward truncation beneath the Cottonwood Canyon 

Member. Because of this truncation, successively lower units of the 

Sappington cap the member as it thins toward its eastern limit. The 

overall thinning of the Sappington does not result from depositional 

thinning of its units nor from the disappearance of units at its base 

by onlap, as demonstrated by measured sections in the eastern Little 

Belt Mountains. There, at Bandbox and Grendah Mountains (fig. 1) 

and at several other localities close to it its eastern limit, the Sappington is 5-9 feet thick, and only its basal two units (1, 2) are preserved 

beneath a half-inch-thick lag deposit, related to the Cottonwood Canyon Member, at the base of the Lodgepole Limestone. Significantly, 

unit 2, which caps the Sappington at these localities, is 3-7 feet thick. 

This thickness range is the same as that of unit 2 in the vicinity of 

Logan, where the Sappington attains a maximum thickness and all 

five units are present (Sandberg, 1965 p. 14-15).

The Sappington is underlain by the Trident Member of the Three 

Forks Formation in southwestern Montana. There, at Peak 9559, Sheep 

Mountain, and probably at Mud Spring Gulch, the uppermost beds of 

the Trident contain <a conodont fauna assigned to the Scaphignathus 

veil/era Zone (fig. 3). This fauna is Upper Famennian (Bouckaert 

and Ziegler, 1965) and confirms previous age determinations of the 

Trident based on ammonoids and brachiopods from lower beds.

Two conodont zones, the Lower Polygnathus styriaca and the Middle P. styriaca Zones of Ziegler (1962), are as yet unrecognized between conodont zones in the top of the Trident and in the base of the 

Sappington Member. As the Sappington does not overstep rocks older
B12 COGSTTRIBUTIONlS TO GENERAL GEOLOGY

than the Trident, the break below the Sappington (fig. 3) is interpreted as a disconformity in southern Montana. This disconformity 

may have some regional significance, however, because it extends 

northward into Alberta, where it underlies the Exshaw Formation.

East of the limit of the Sappington, the Cottonwood Canyon Member rests unconf ormably on the Trident and Logan Gulch Members 

of the Three Forks Formation in descending order (fig. 3). The 

weakly resistant Trident Member, which is largely greenish-gray calcareous shale, is truncated in a belt 10-50 miles wide. It extends only 

about 25 miles into Yellowstone National Park in the northwest corner 

of Wyoming (fig. 2). Farther east, the Logan Gulch, which comprises silty dolomite, dolomitic siltstone, and eyaporite-solution breccia 

in Wyoming, is truncated in a belt about 65 miles wide. It underlies the Cottonwood Canyon at Meridian Ridge in the northeast corner 

of Yellowstone Park (fig. 1) and is the only member of the Three 

Forks that is widespread in western Wyoming. The eastern limit of 

the Logan Gulch lies along the west side of the Bighorn Basin, as 

shown in figure 2. The contact with the overlying Cottonwood Canyon 

is well exposed at the Clarks Fork Canyon reference section on the 

east side of the Beartooth Mountains (fig. 1), where the Logan Gulch 

is only 15 feet thick close to its wedge edge.

Beyond the limit of the Three Forks Formation, the Cottonwood 

Canyon Member unconformably overlies the resistant but thin subsurface Birdbear Formation (or the exactly equivalent outcropping 

Birdbear Member at the top of the Jefferson Formation). The Birdbear consists uniformly of dolomite and pseudobrecciated dolomite. 

The subcrop of the Birdbear is a belt only about 10-20 miles wide 

except near the Pry or Mountains, where it is as much as 65 miles wide 

(fig. 2). At the subsurface reference section of the Cottonwood Canyon 

Member in the Pan American 72 Elk Basin Madison Unit well, which 

is within this belt, the Birdbear is only 19 feet thick, whereas 22 miles 

to the southwest, where overlain by the Three Forks Formation at 

Clarks Fork Canyon, it is 27 feet thick (fig. 1).

A common misconception among some geologists is that the Three 

Forks Formation extends farther east than is shown in figure 2 and 

is present in the subsurface at the Elk Basin oil field and elsewhere in 

the Bighorn Basin, Wyo. This fallacy, which results partly from incorrect placement of the pre-Mississippian unconformity, is repudiated 

by a comparison of units below the Cottonwood Canyon Member at 

the subsurface and Clarks Fork Canyon reference sections, which are 

described later in this report. The so-called Three Forks of subsurface 

usage is a sequence, 62-69 feet thick, of brownish dolomite interbedded 

with varicolored shale and siltstone, which supposedly underlies the
COTTONWOOD CANYON MEMBER, MADISON LIMEiSITONE B13

Madison Limestone in the Elk Basin field, according to Rea (1962). 

Correlation from the Pan American 189 Pre-Madison Unit well, where 

this unit was identified by Kea (1962, fig. 1), to the reference well only 

7,000 feet to the southeast clearly demonstrates that there the so-called 

Three Forks lies directly below the Birdbear Formation, not the Madison Limestone, at a depth of 5,832.2 feet and that it is capped by a bed 

of greenish-gray dolomitic siltstone. The Birdbear and the underlying 

siltstone at the reference well are readily correlated with the same 

two units at the Clarks Fork Canyon section, which was further correlated with a measured section at Logan, Mont., by Sandberg (1967). 

As the Birdbear is the upper member of the type Jefferson at Logan 

(Sandberg, 1965), the Three Forks of Kea (1962) must be the upper 

part of the lower member of the Jefferson or the upper part of the 

equivalent subsurface Duperow Formation. The true Three Forks, 

which overlies the Birdbear and as previously mentioned is only 15 

feet thick at Clarks Fork Canyon, and the upper 8 feet of the Birdbear are truncated beneath the Cottonwood Canyon Member between 

Clarks Fork Canyon and the reference well.

The description of cores from the reference well demonstrates the 

unconformity at the base of the Cottonwood Canyon Member, the 

deep weathering of underlying beds, and the stratigraphic leak of 

conodonts downward into the weathered part of the Birdbear. Beneath 

a sharp contact at a depth of 5,819.2 feet is a regolithic zone, 1.6 feet 

thick, composed largely of disoriented pebbles of silty dolomite. These 

pebbles were derived from and grade into an underlying highly weathered zone, 0.8 foot thick. This zone, where the rock is highly fractured 

but incipient pebbles are oriented and largely in place, is transitional 

between the regolithic zone above and the weathered zone below. The 

underlying weathered zone, 9 feet thick, consists of brecciated dolomite 

that becomes progressively less brecciated downward. Solution crevices, fractures, and vugs in all three zones apparently were open when 

the Cottonwood Canyon Member was deposited, although they were 

later sealed by anhydrite. They contain identifiable infiltrations of 

quartz silt and sand, glauconite grains, fish remains, and conodonts. 

The effects of weathering are clearly recognizable for about 11.4 feet 

below the unconformity. A few related hairline fractures without fillings extend downward for an additional 7 feet into largely unweathered dolomite in the basal part of the Birdbear. Conodonts from the 

Cottonwood Canyon Member are found at a depth as low as 5,825.3 

feet, or about 6 feet below the unconformity. Similar infiltrations of 

conodonts in the top few inches of the Birdbear were noted at Little 

Dry head Canyon on the east side of the Pryor Mountains (fig. 2).

266-133 O 67 2
B14 OONTBIBUTIONlS TO GEOSTEIBAL GEiOLOGY

These observations make the authors hesitant to unequivocally accept evidence for dating provided by broken or abraded conodonts in 

the top of the Sappington Member or in any other units where they 

directly underlie an unconformity.

Most of the eastern half of the Cottonwood Canyon Member transects a single body of moderately thick cyclically deposited marine 

carbonate rocks of early Late Devonian (Frasnian) age (fig. 2), to 

which three names are locally applied. This body of rocks comprises 

the lower member of the Jefferson Formation in outcrops in Montana 

and Wyoming, the exactly equivalent Duperow Formation in the subsurface of the same area, and the largely equivalent Darby Formation 

in the Wind Kiver Basin and adjacent outcrops. The contact with the 

lower member of the Jefferson is well exposed at the type section of 

the Cottonwood Canyon Member and at several other measured sections in northern Wyoming (fig. 4, cols. 5-7; Sandberg, 1967).

In the subsurface of central Montana, the Duperow Formation is 

deeply eroded on the margins of the ancestral Central Montana uplift. 

In the core of this latest Devonian to earliest Mississippian uplift, the 

Duperow is truncated and in a narrow belt the Cottonwood Canyon 

Member rests on the Red River Formation of Late Ordovician age 

(fig. 2). In a small area at the probable apex of this ancestral uplift, 

the Cottonwood Canyon unconformably overlies undivided rocks of 

Late Cambrian and Early Ordovician age. This contact was penetrated 

at a depth of 8,265 feet in the Texas 1 Manion well on the Ragged 

Point anticline.

In the southern Bighorn Mountains, the Cottonwood Canyon Member truncates the lower member of the Jefferson Formation and rests 

successively on the Bighorn Dolomite of Ordovician age and the Gallatin Limestone of Cambrian age (fig. 2). Southeastward from the Bighorn Mountains, small thin discontinuous patches of the Cottonwood 

Canyon, not shown in figures 1 and 2, rest on progressively older Cambrian rocks in the subsurface of the southern Powder River Basin. In 

the Hartville Uplift, southeast of the report area, a thin conodontbearing sandstone related to the Cottonwood Canyon rests with 

marked angularity on Precambrian schist and gneiss.

COTTONWOOD CANYON MEMBER 

GENERAL DISCUSSION

The name Cottonwood Canyon Member is here applied to a thin but 

complex well-dated sequence of clastic transgressive-marine rocks that 

lies at or near the base of the Madison Limestone of Mississippian 

and, locally, Devonian age in Wyoming and at the base of the Lodgepole Limestone of Early Mississippian age in Montana (fig. 3). This
Peak 9559

SEy4 SE'/, sec. 21,

T. 2 N , R. 6 E.,

Gallatin County,

Mont.

Meridian Ridge 

Ny2SW'/4 sec. 29,

darks Fork Canyon 

NE>/4 NEi/4 sec. 7,

T 56 N., R 103 W , 

Park County, Wyo.

Baker Mountain 

SW'/,NWy4 sec. 35,

T 3 S., R. 12 E.,

Sweetgrass County,

Mont.

Gtadational 

contact

FIGURE 4. Cross section of Cottonwood Canyon Member and adjacent roc

Mountains, Wyo. 
B16 CONTRIBUTIONS TO GENERAL GEOLOGY

name replaces the informal "dark shale unit of Devonian and Mississippian age," which was proposed by Sandberg (1963) and subsequently used by Sandberg (1965; 1967), Klapper (1966), and Benson (1966). The contact between the Cotton wood Canyon Member and 

the undifferentiated carbonate rocks in the lower part of the Madison 

is now recognized to be generally conformable, and is not disconformable as stated by Sandberg (1963). At some localities the contact 

is gradational or intertonguing (figs. 3, 4). In Montana, the contact 

between the member and the undifferentiated carbonate rocks in the 

lower part of the Lodgepole may locally appear to be disconformable 

because of an abrupt lithologic change.

The Cottonwood Canyon Member is divided into an upper tongue 

and a lower tongue, both of which have basal conglomeratic lag deposits characterized by abundant phosphatic nodules and coprolites, 

conodonts, fish remains, and glauconite grains. These tongues are not 

similarly distributed, but where both tongues are present and can be 

differentiated, they are separated by a physical disconformity as well 

as by a hiatus in conodont faunas. The member is also divided areally 

into a western, shale and siltstone facies and an eastern, dolomitic 

facies. These facies interfinger, and both may be present within a single 

tongue at a given locality for example, Clarks Fork Canyon (fig. 4, 

col. 4). Consequently, only the eastern limit of the shale and siltstone 

facies is shown in figure 1.

TYPE SECTION

The Cottonwood Canyon Member is well exposed in the canyon 

after which it is named on the west side of the northern Bighorn 

Mountains, 16 miles east of Lovell, in northern Wyoming. The type 

section is on the north wall of Cottonwood Canyon, about 1 mile east 

of the mouth, in sec. 34, T. 57 N., R. 93 W., Big Horn County, Wyo., 

as shown on the Cody 1 : 250,000 Army Map Service sheet NL 12-12. 

From Lovell, the canyon is approached in a passenger car by driving 

1(% miles east on Wyoming State Highway 14 to the east side of the 

bridge across the Bighorn River. A wide graded dirt road extends 

51/2 miles from the north side of the highway to a quarry, which supplied riprap used in constructing the bridge approaches, at the mouth 

of the canyon. From the canyon mouth, an automobile can be driven 

for about half a mile on a passable trail through the narrow formed 

by a cliff of Madison Limestone to a wide part of the canyon, where 

dipping brown-weathering thick ledges of the Jefferson Formation 

lie about 100 feet above trail level at a burned grove of cottonwood 

trees. From this trail the type section is approached on foot by climbing a talus slope across dipping ledges of Jefferson to the base of 

the high cliff of Madison, about 500 feet above the trail. From there
CGTTONWOOD CANYON- MEMBER, MADISON LIMESTONE B17

it is necessary to follow the orange-weathering Cottonwood Canyon 

Member for about three-eighths mile eastward to a point where its 

contact with the Jefferson is not concealed by talus and the westward 

dip has decreased to about 20°. Here the type section is well exposed 

in the base of the cliff of Madison Limestone (fig. 5).

The type section of the Cottonwood Canyon Member comprises both 

tongues of the member in their dolomitic facies and contains a succession of diagnostic well-preserved conodont faunas. It was selected 

not only for the excellence of the exposure but also because it demonstrates a well-developed basal lag deposit, a disconformity between

FIGURE 5. Type section of Cottonwood Canyon Member of Madison 

Limestone on north wall of Cottonwood Canyon, west side of Bighorn 

Mountains, Wyo. Member lies between lower member of Jefferson 

Formation (Dp) and undifferentiated lower part of Madison Limesone (MDm). Numbers (1-8) correspond to numbered units in 

measured section.
Bl,8 CONTRIBUTIONS TO GEiNEIRAL, GEOLOGY

the two tongues, and an almost imperceptible gradation into overlying 

beds of the Madison Limestone, as described in the following measured 

section.

Type section of the Cottonwood Canyon Member of the Madison Limestone at Cottonwood Canyon in sec. 34, T. 67 N., R. 93 W., Big Horn County, Wyo.

[First number in parentheses is Ca: Mg molal ratio; second number is percentage of total carbonate by weight]

n, ,. T . , Thickness Madison Limestone: (ft)

Undifferentiated lower part:

8. Dolomite, calcitic, (1.36, 90), light-gray, yellowish-gray, and 

very pale yellowish brown, microcrystalline, microsucrosic, 

finely to coarsely fossil-fragmental, crinoidal, slightly silty. 

Contains crinoid columnals and leached fossil molds, mostly 

of crinoids. Weathers to yellowish-gray rough, pitted surface; 

massive; resistant; cliff forming______________________ 21 +

7. Limestone, dolomitic, (8.62, 93), medium-light-gray, mediumgray, and light-olive-gray, microcrystalline, finely to coarsely 

fossil-fragmental, crinoidal. Grades laterally to calcitic dolomite. Contains Kinderhook (cul-lla) conodont fauna and 

Syringopora sp. and Vesiculophyllum sp. corals in lower 3 ft. 

Weathers medium gray; medium to thick bedded; resistant; 

forms 3 slightly reentrant ledges-_______________________ 7

6. Dolomite, calcitic, (2.25, 89), medium-gray, medium-lightgray, and light-olive-gray, microcrystalline, very finely to 

finely fossil-fragmental, slightly silty. Bottom 2 in. is slightly 

hematitic silty calcitic dolomite (1.72, 77). Unit contains 

scattered crinoid columnals, small brachiopods, and Kinderhook conodonts. Weathers medium gray; thin to medium 

bedded; moderately resistant; forms 2 reentrant ledges____ 2

Total described undifferentiated lower part of Madison 

Limestone_______ ________-____-____--___-_------- 30+

Gradational contact. 

Cottonwood Canyon Member: J

5. Dolomite, calcitic, silty, (1.46, 84), yellowish-gray and lightolive-gray mottled with yellowish-orange, microcrystalline, 

microsucrosic, slightly argillaceous, containing scattered 

limonite nodules and leached fossil molds mostly of crinoids. 

Contains Lower Carboniferous (upper cul) conodont fauna 

throughout. Weathers to yellowish-gray and pale-yellowishorange minutely pitted surface; thin to medium bedded; 

moderately resistant; forms reentrant ledge. 3

Disconformity.

4. Dolomite, calcitic, (1.29, 90), grayish-orange to pale-yellowishbrown and medium-light-gray to light-olive-gray, very 

finely crystalline, rhombic, sucrosic, vuggy, slightly sandy, 

slightly silty, slightly limonitic. Silt is subangular grains of 

quartz, slightly smaller than very fine grained sand. Sand is 

fine to medium rounded frosted grains of quartz. Contains 

fish fragments and very late Devonian (upper toV) conodont 

fauna in lower 1 ft. Weathers to grayish-orange, yellowishorange, and light-yellowish-brown pitted surface; medium 

bedded; moderately resistant; forms reentrant ledge._____ 2
COTTONWOOD CANYON MEMBER, MADISON LIMEISITONE B19

Type section of the Cottonwood Canyon Member of the Madison Limestone at 

Cottonwood Canyon Continued

Madison Limestone Continued Thickness 

Cottonwood Canyon Member Continued

3. Dolomite, calcitic, silty (1.28-1.75, 72-77), grayish-orange, 

dark-yellowish-orange, yellowish-orange, pale- to moderateyellowish-brown, and medium-light-gray, very finely crystalline, rhombic, sucrosic, limonitic, slightly sandy, containing wisps and laminae of dark-gray to black carbonaceous 

dolomitic quartzose shale and nodules of limonite. Silt is 

subangular grains of quartz, slightly smaller than very 

fine grained sand. Sand is fine to coarse rounded frosted 

grains of quartz. Fucoids and Zoophycus markings on bedding 

planes. In 3 ledges, l-in.-thick reentrant at top and two 2-in.- 

thick reentrants that separate ledges are black and mottled 

greenish-gray, yellowish-gray, and dark-gray carbonaceous 

dolomitic quartzose shale (1.10, 26). Dolomite ledges contain 

abundant conodonts and fish fragments. Shale interbeds 

also contain conodonts, which were determined to be very 

late Devonian (upper toV) by Ethmgton, Furnish, and 

Wingert (1961). Dolomite weathers to dark-yellowishorange smooth surfaces except upper 1-ft-thick ledge which 

weathers yellowish orange; shale weathers yellowish gray; 

thin to medium bedded; moderately resistant; ledge forming. 7

2. Dolomite, calcitic, very silty, very sandy, conglomeratic 

(1.44, 58), 4 pale-yellowish-brown, grayish-orange, mediumgray, and medium-dark-gray, grading to subangular to 

subrounded very fine grained very dolomitic siltstone and 

sandstone. Contains laminae of black carbonaceous dolomitic 

quartzose shale, granules and rounded pebbles of yellowishgray and greenish-gray microcrystalline silty dolomite, fine 

to coarse rounded frosted grains of quartz, and limonitic and 

phosphatic nodules. Also contains abundant very late 

Devonian (upper foV) conodont fauna and fish bones, plates, 

teeth, and scales. Weathers light brown and dark yellowish 

orange; medium bedded; moderately resistant; forms ledge at 

base of cliff_________________________________________ 1

Total Cottonwood Canyon Member___________________ 13

Unconformity. 

Jefferson Formation:

Upper part of lower member:

1. Siltstone, very dolomitic, (1.12, 40), light-greenish-gray, 

greenish-gray, and grayish-yellow-green, glauconitic; partly 

sandy. Weathers yellowish gray; thin bedded to thinly 

laminated; nonresistant; slope forming_________________ 26

* High Ca:Mg molal ratio is attributed to excess calcium, largely from fluorapatite and collophane and 

due to presence of 4-6 percent by weight of conodonts, fish remains, and phosphatic nodules. Reanalysis 

of same powdered sample after removal of clay-size fines by washing and of conodonts and other phosphatic 

grains by heavy liquid and magnetic separation techniques: (1.26, 74).
B20 CONTRIBUTIONS TO GEJsTElRAL GEOLOGY 

REFERENCE SECTION'S

The reference section for the shale and siltstone facies of the Cottonwood Canyon Member is in the Beartooth Mountains at Clarks Fork 

Canyon, north of the river in the NE^NE^ sec. 7, T. 56 N., K. 103 

W., Park County, Wyo., in the Deep Lake 15-minute quadrangle. 

This section (fig. 4, col. 4) was formerly considered the reference 

section of the dark shale unit. As a detailed stratigraphic section and 

complete directions for visiting this locality were given by Sandberg 

(1963, p. 17), they are not repeated here. It should be noted, however, 

that the 48 feet of beds previously assigned to the dark shale unit 

is now assigned to the shale and siltstone facies there. An underlying 

sequence of silty dolomite 7 feet thick is now recognized to be included in the Cottonwood Canyon and is assigned to the dolomitic 

facies. Consequently, the member has a total thickness of 55 feet at 

this reference section. As a detailed description of the added part of 

the member was not given by Sandberg (1963), it is presented here; 

descriptions of three thin underlying units the Logan Gulch Member 

of the Three Forks Formation, the Birdbear Member of the Jefferson 

Formation, and the top bed of the lower member of the Jefferson 

Formation are given for comparison with their descriptions at the 

subsurface reference section.

Measured section of the dolomitic facies of the Cottonwood Canyon Member of the 

Madison Limestone and adjacent units at Clarks Fork Canyon

[Section measured in NEMNEM sec. 7, T. 56 N., E. 103 W., Park County, Wyo. First number in parentheses 

is Ca: Mg molal ratio; second number is percentage of total carbonate by weight]

Madison Limestone: Thickness 

Cottonwood Canyon Member: (/O 

Shale and siltstone facies (described by Sandberg, 1963, p.

C17)_ _____._.______ ---.---- ---- 48

Dolomitic facies:

Dolomite, silty, calcitic (1.52, 78), microcrystalline; dark 

yellowish orange in upper part, medium gray mottled with 

dark yellowish orange in lower part. Weathers to yellowishorange smooth surface with 1- to 2-in.-wide pits formed 

by weathering of calcite geodes; thick bedded; moderately 

resistant; ledge forming._______________--_--------___ 5

Dolomite, silty (1.16, 63), brownish-gray to medium-darkgray and yellowish-gray, microcrystalline. Lower 6 in. is 

medium-dark-gray very dolomitic quartzose shale (1.08, 

46). Black carbonaceous films on bedding planes resemble 

macerated plant or algae remains. Weathers yellowish gray 

and medium gray; platy; weakly resistant; forms reentrant__ _________________________-_-_---------__- 2

Total dolomitic facies._____________________________ 7

Total Cottonwood Canyon Member__________________ 55
COlTTONWOOD ANYON MEMBER, MADISON LIMElSrTONB B21

Measured section of the dolomitic fades of the Cottonwood Canyon Member of 

the Madison Limestone and adjacent units at Clarks Fork Canyon Continued

Unconformity.

Three Forks Formation: Thickness 

Logan Gulch Member: (/O 

Dolomite, silty (1.07, 65), mottled yellowish-gray, light-olivegray, light-brown, and greenish-gray, microcrystalline. Grades 

to silty dolomite evaporite-solution breccia (1.12, 64) containing 

angular fragments and flakes of light-greenish-gray dolomitic 

shale. Weathers to yellowish-gray and dark-yellowish-orange 

rough surfaces; in beds J_>- to 4-in. thick; moderately resistant; 

ledge forming.__________________________________________ 11

Dolomite, calcitic, silty (1.54, 87), yellowish-orange, yellowishgray, and light-brown with grayish-red hematitic laminae, very 

finely crystalline, fragmental, limonitic; partly nodular. Contains interbeds and scattered angular fragments of lightgreenish-gray dolomitic shale. Weathers yellowish gray and 

moderate yellowish brown; thin bedded to laminated; crossbedded; ripple marked; moderately resistant; ledge forming.__ 4

Total Three Forks Formation._______-______-_---___---- 15

Jefferson Formation: 

Birdbear Member:

Dolomite, calcitic (1.37, 96), pseudobrecciated, yellowish-orange, 

yellowish-gray mottled with light-gray, light-brownish-gray, 

and medium-light-gray, very finely crystalline, rhombic, 

sucrosic, porous. Stained by limonite and hematite. Fractures 

and vugs filled with white calcite. Weathers to mottled moderate-yellowish-brown and yellowish-gray rough pitted surface; 

massive; resistant; cliff forming__________________________ 27

Total Birdbear Member______________________________ 27

Lower member:

Shale, quartzose, dolomitic light-olive-gray, yellowish-gray, and 

dusky-yellow, glauconitic. Interlaimnated with light-gray to 

greenish-gray clay shale. Bottom 4 ft contains a few 1-ft-thick 

interbeds of dark-yellowish-orange silty dolomite. Weathers 

yellowish gray and dusky yellow; weakly resistant; slope 

forming,_______________________________________________ 13

The subsurface reference section of the Cottonwood Canyon Member 

is here designated the interval between core depths of 5,806.9 and 

5,819.2 feet in the Pan American 72 Elk Basin Madison Unit well 

of the Elk Basin oil field in the northwestern Bighorn Basin (fig. 1). 

This well is in the NW^SE^ sec. 30, T. 58 N., K. 99 W., Park 

County, Wyo. The thickness of the Cottonwood Canyon Member, on 

the basis of cores, is 12.3 feet. Adjustment to the gamma-ray log locates the member between well depths of 5,807 and 5,820 feet and gives 

it an apparent thickness of 13 feet. After this thickness is corrected 

for a dip of 30° and a borehole deviation of 11° from vertical in the
B22 CONTRIBUTIONiS TO GENERAL GEOLOGY

direction of dip, the true stratigraphic thickness rounded to the nearest 

foot is 12 feet. The subsurface reference section of the member is 

within the dolomitic facies of its upper tongue. The eastern limit of 

the shale and siltstone facies is projected to lie about 10 miles west 

of the well (fig. 1). Detailed lithologic descriptions of the cored 

interval between 5,798.4 and 5,846.5 feet from the lower part of the 

Madison Limestone to the upper part of the Duperow Formation, 

about £1/2 feet above the bottom of the well, are presented. They 

demonstrate not only the upward gradation of the Cottonwood Canyon 

into the overlying part of the Madison but also the previously discussed basal unconformity and deep weathering of underlying beds.

Subsurface reference section of the Cottonwood Canyon Member of the Madison

Limestone

[Section described from cores of the Pan American Petroleum 72 Elk Basin Madison Unit well, NW}£SE}£ 

sec. 30, T. 58 N., E. 99 W., Park County, Wyo. Numbers in parentheses are core depths, in feet]

Mississippian:

Madison Limestone: Thkknets 

Undifferentiated lower part: Tffi

Dolomite, light-olive-gray, finely microcrystalline, crinoidal. 

Contains conodonts and yellowish-gray ghosts of crinoids 

and other fossil debris, 1-2 mm in diameter (5,798.4- 

5,800.4)._-_-_-_---_-_--__-_-___-_-___-___---_--_--- 2.0

Dolomite, medium-gray, microcrystalline, microsucrosic, 

very slightly pyritic (5,800.4-5,801.6). _. ________ 1. 2

Dolomite, light-olive-gray and mottled medium-gray and 

medium-light-gray, microcrystalline, slightly anhydritic; 

partly cherty; partly slightly pyritic and slightly glauconitic. Contains crinoids and fish fragments. White cryptocrystalline chert nodules, as much as 11 mm in diameter, 

at 5,803.0-5,803.5 ft (5,801.6-5,804.9)----------------- 3. 3

Dolomite, medium-light-gray to light-olive-gray, microcrystalline, slightly anhydritic, containing scattered 

conodonts and a few minute fish fragments. Wisps and 

laminae of medium-gray and brownish-black slightly 

hematitic, silty, and shaly coarsely microcrystalline dolomite in upper and lower parts and slight grayish-red and 

grayish-red-purple speckling and streaking in middle. 

Parting of light-greenish-gray silty shale at 5,805.4 

(5,804.9-5,805.9)____--_-_----------_-------------- 1.0

Dolomite, light-olive-gray, microcrystalline, sucrosic, slightly 

anhydritic, containing scattered fragmentary conodonts 

and fish teeth. A few scattered hematite and quartz silt 

grains in bottom 0.2 ft (5,805.9-5,806.9)__._____-_. 1. 0

Total described undifferentiated lower part of Madison

Limestone._____________________________________ 8.5

Gradational contact.
COTTOOSTWOOD CANYON MEMBER, MADISON LIMESlTONE B23

Subsurface reference section of the Cottonwood Canyon Member of the Madison

Limestone Continued 

Mississippian Continued

Madison Limestone Continued Thickness 

Cottonwood Canyon Member: (ft)

Dolomite, light-brownish-gray, mottled and streaked with 

pale-red, grayish-red-purple, dusky-red-purple, and grayish-red, coarsely microcrystalline, hematitic, slightly 

silty and slightly anhydritic; partly slightly crinoidal and 

medium fossil-f ragmen tal. Contains scattered fragmentary 

conodonts and fish teeth (5,806.9-5,809.2) __ _ ____ _____ 2. 3

Dolomite, silty, light-brownish-gray, mottled, streaked, 

and banded with pale-red, grayish-red, grayish-redpurple, and dusky-red, coarsely microcrystalline to 

microcrystalline, hematitic, slightly anhydritic. Contains 

scattered conodonts. Interbed, }i in. thick, of thinly 

laminated very silty dolomite at 5,810.5 (5,809.2-5,813.0) _ 3. 8

Dolomite, silty to very silty, mottled and irregularly banded 

light-brownish-gray, pale-red, grayish-red, and grayishred-purple, microcrystalline, laminated. Contains scattered 

conodonts, fish remains, and small black phosphatic 

nodules. Thin interbeds, laminae, and lenses of very 

dolomitic siltstone. Round nodules of white chert, in part 

fragmental, at 5,813.0-5,813.4 (5,813.0-5,815.0) ____ ._ 2. 0

Siltstone, very dolomitic, light-brownish-gray mottled and 

irregularly banded with pale-red, grayish-red, and grayishred-purple, hematitic; in part slightly glauconitic; laminated. Grades to coarsely microcrystalline to very finely 

crystalline very silty dolomite. Contains black phosphatic 

nodules, as much as 1 in. long, at 5,816.2-5,816.3. Bottom 

0.1 ft is thinly laminated friable dolomitic siltstone 

(5,815.0-5,816.8)-----------------_---_-------- 1. 8

Dolomite, very silty, grayish-red-purple and medium-light 

gray, microcrystalline, hematitic, containing unoxidized 

light-olive-gray slightly glauconitic mottles. Bottom 0.1 ft 

is laminated (5,816.8-5,817.2) ________ __ _ _ _________ . 4

Siltstone, very dolomitic, greenish-gray, slightly glauconitic

Siltstone, very dolomitic, light-brownish-gray and lightolive-gray mottled with pale-red and grayish-red-purple, 

hematitic, slightly glauconitic; quartzitic in bottom 0.2 ft. 

Gradational to very silty dolomite, with some dolomite 

replacing abundant quartz grains and sparse feldspar 

grains. Contains scattered glauconite grains, small black 

phosphatic nodules, fish teeth, fragmentary fish plates, 

vertical worm burrows, and conodonts, which are most 

abundant in bottom 0.5 ft (5,817.5-5,819.0) _ __ __ ___ 1. 5
B24 CONTRIBUTIONS TO GENEIKAL GEOLOGY

Subsurface reference section of the Cottonwood Canyon Member of the Madison

Limes tone Continued

Mississippian Continued.

Madison Limestone Continued ._.., Thickness

Cottonwood Canyon Member Continued CfO 

Sandstone, quartzitic, arkosic, dolomitic, yellowish-gray, 

medium- to coarse-grained, well-rounded. Quartz and feldspar grains partly replaced by dolomite. Contains interbeds and lenses of grayish-yellow-green highly glauconitic, 

grayish-red hematitic, and dark-gray carbonaceous dolomitic quartzose shale. Abundant large conodonts and fish 

bones, as long as }i in., in shale at top. Overlies a sharp, 

wavy surface (5,819.0-5,819.2)______________________ . 2

Total Cottonwood Canyon Member._______________ 12. 3

Unconformity. 

Devonian:

Birdbear Formation:

Dolomite conglomerate, regolithic, grayish-red mottled with palered, hematitic. Subordinate groundmass is grayish-red dolomitic 

quartzose shale. Predominant pebbles, which increase in abundance downward, are pale-red very finely crystalline rhombic 

sucrosic silty dolomite. Grades into underlying unit at horizon 

where pebbles become groundmass. Abundant cracks are filled 

with sand and silt grains that infiltrated from above unconformity. Pod, at least % in. long, at 5,819.7 is medium-grained 

sandstone, identical with that overlying unconformity (5,819.2- 

5,820.8)________________________________________________ 1. 6

Dolomite, silty, very finely crystalline, pale-red mottled with 

moderate-red, grading downward through grayish-orange-pink 

to pale-yellowish-brown. Irregular crevices, cracks, veinlets and 

seams filled by infiltrations of grayish-green dolomitic shale 

and light-olive-gray dolomitic siltstone containing inclusions of 

sandstone, fish remains, glauconite grains, and conodonts. 

Unit represents highly weathered zone that contributed to 

overlying regolith (5,820.8-5,821.6)________________________ .8

Dolomite, brecciated, pale-yellowish-brown, coarsely microcrystalline to very finely crystalline, sucrosic; massive; locally 

pseudobrecciated; partly mottled pale red and more locally 

grayish red by secondary hematite staining. Contains abundant 

fractures, sealed by anhydrite, that connect large vugs completely filled with white coarsely crystalline secondary anhydrite. Grayish-red halos in dolomite surround anhydrite-filled 

vugs. Infiltrations of greenish-gray shale, light-olive-gray 

siltstone, and quartz and glauconite grains are common in 

sealed fractures and on edges of anhydrite-filled vugs at 5,821.6- 

5,825.3 ft; below that only traces exist. Unit represents slightly 

weathered zone that grades into underlying unit (5,821.6- 

5,830.6)-------__________ _______.______-----_-_-------_ 9.0

Dolomite, pale-yellowish-brown, very finely crystalline to coarsely 

microcrystalline. Contains a few fractures, stylolites, and 

anhydrite-filled vugs (5,830.6-5,834.0)___._______-_-__-___ 3.4
'COTTONWOOD CANYON MEMBER, MADISON LIMESTONE B25

Subsurface reference section of the Cottonwood Canyon Member of the Madison

Limes tone Continued

Devonian Continued

Birdbear Formation Continued (ft)

Dolomite, yellowish-brown, dark-yellowish-brown, and brownishgray, microcrystalline, microsucrosic. Contains a few fractures, 

stylolites, and anhydrite-filled vugs (5,834.0-5,837.6)__----- 3. 6

Dolomite, silty to very silty, pale-brown and pale-, moderate-, and 

dark-reddish-brown, hematitic; thin bedded to laminated. 

Contains broken laminae of pale-red dolomitic siltstone and a 

few mottles of unoxidized grayish-yellow-green glauconitic 

silty dolomite (5,837.6-5, 838.2)..__._____._._.____.______ .6

Total Birdbear Formation..______________._-______ 19. 0

Conformable contact.

Duperow Formation:

Siltstone, dolomitic, greenish-gray, light-olive-gray, and yellowish-gray, glauconitic; in part laminated; in part stained pale 

red and dusky red by hematite. Contains thin interbeds and 

laminae of greenish-gray dolomitic quartzose shale and clay 

shale (5,838. 2-5,846. 5)._____._.___________._._._.__.______. 8. 3

DISTRIBUTION AND THICKNESS

The Cottonwood Canyon Member is largely continuous in an area of 

about 50,000 square miles in central, south-central, and southwestern 

Montana and in north-central, northwestern, and west-central Wyoming (fig. 1). It crops out in all the moutain ranges included within 

the limits shown in figures 1 and 2, except in the Crazy Mountains, 

Mont., where Paleozoic rocks are not exposed. It is also present in the 

subsurface of intervening and adjacent areas. The Cottonwood Canyon has been sampled and described at about 50 measured sections and 

recognized in sample and radioactivity logs of about a hundred wells. 

Thin isolated patches of the member or of related lag deposits at the 

base of the Lodgepole and Madison Limestones occur northwest, east, 

and southeast of the limits of the main body of the Cottonwood 

Canyon, but they are too small or too poorly delimited to be shown in 

figures 1 and 2.

Probable outliers of the shale and siltstone f acdes of the Cottonwood 

Canyon Member are recognized in the vicinity of the Big and Little 

Belt Mountains, Mont. (fig. 2). At Beaver Creek in the Big Belt 

Mountains, a black shale 20 inches thick, with a basal conodont-rich 

lag sandstone half an inch thick, underlies the Lodgepole Limestone 

and overlies unit 5 of the Sappington Member of the Three Forks 

Formation. At Bandbox Mountain and Grendah Mountain in the 

Little Belt Mountains, a y2 -inch-thick conodont-rich lag siltstone at the 

base of the Lodgepole overlies unit 2 of the Sappington. Similar de-
B26 CONTRIBUTION® TO GEKTEIRAL GEOL'OGY

posits are recognized at the base of the Lodgepole in the subsurface 

about 20 miles northwest of Lewistown, Mont. (fig. 1).

The eastern limit of the Cottonwood Canyon Member, which is also 

the limit of its dolomitic facies, is only approximately located in 

figure 1 because of a paucity of control wells in the Powder River 

Basin. Thin beds clearly related to the dolomitic facies are recognized 

beyond this approximate limit, however. At the Shell Oil 1 Clear 

Creek well, 38 miles east of Sheridan, Wyo. (fig. 1), the basal 7 feet 

of the Madison Limestone is silty dolomite that is lithologically 

similar to the Cottonwood Canyon Member (Sandberg, 1967). Likewise, at four wells, not shown in figure 1, in the southeast corner of 

the report area and just to the south, silty or sandy dolomite in the 

basal 3-15 feet of the Madison rests on Cambrian rocks. At Ragan 

Draw in the Hartville Uplift of east-central Wyoming, a conodontbearing sandstone 3 feet thick, described by Sandberg (1967), at the 

base of the lower part of the Guernsey Formation of Devonian and 

Mississippian age rests on Precambrian rocks and may be connected 

to both the Cottonwood Canyon Member and the equivalent Devonian 

and Mississippian Englewood Formation of the Black Hills (Sandberg, 1963).

The Cottonwood, Canyon Member ranges in thickness from 0 to 

about 80 feet in the report area, It probably is as much as 90-100 feet 

thick in the subsurface of the Green River Basin, just east of the 

Wyoming Range and south of the western part of the report area 

(fig. 1). At most measured sections it is less than 10 feet thick, but 

at four sections it is 10-20 feet thick and at eight 'sections it is more 

than 20 feet thick. The member is thicker than 20 feet in an elongate 

belt whose width ranges from 12 to 65 miles and averages 35 miles 

(fig. 1). The axis of this belt of thicker accumulation trends N. 15°~ 

20° E. from the west side of the Green River Basin, past the north end 

of the Wind River Range, to the south side of the eastward-trending 

Central Montana uplift near Roundup, Mont. (fig. 1). There, the 

axis bends sharply eastward and trends N. 75° E. to its eastern termination at Porcupine dome, on the east end of the uplift. Two centers 

of deposition lie within this belt: one is in the subsurface south of 

Roundup, where the member is about 70 feet thick; the other is in the 

western Washakie Range, Wyo., where the member is about 80 feet 

thick. Eastward and westward thinning from the narrow apparent 

basin of thicker accumulation to adjacent wide shelf areas of thinner 

accumulation takes place in such short distances, as shown in figure 4, 

that only a few critical isopachs within the transition zone could be 

shown in figure 1. The member is 55 feet thick at Clarks Fork Canyon, 

but it thins northeastward in 22 miles to a thickness of 12 feet at the
COTTQNWOOD CANYON MEMBER, MADISON LIME1STONE B27

subsurface reference section. It maintains a relatively constant thickness for 40 miles eastward from there to the type section, where it is 

13 feet thick. Abrupt thinning is further demonstrated by closely 

spaced measured sections in the Washakie Range (fig. 1), where the 

member thins eastward from about 80 to 4 feet in a distance of about 

20 miles.

LITHOLOGIC AND PHYSICAL CHARACTER

The Cottonwood Canyon Member in its dolomitic facies, as exemplified by the type and Shoshone Canyon sections (fig. 4, cols. 5, 6), 

is largely very finely crystalline to microcrystalline slightly calcitic 

silty dolomite that is platy to medium bedded, light colored, limonitic, 

glauconitic, and slightly hematitic. The fresh rock surfaces are most 

commonly yellowish gray, yellowish orange, grayish orange, light 

gray, medium light gray, light olive gray, light greenish gray, pale 

red, light brownish gray,, and pale yellowish brown. The silty dolomite 

generally weathers to yellowish-gray smooth surfaces, but where the 

silt content is high to moderate it weathers dark yellowish orange at 

the base and grades to yellowish orange and grayish orange at the top. 

The silty dolomite contains scattered to abundant very fine to very 

coarse rounded frosted quartz sand grains, fine to very fine glauconite 

grains, limonitic (probably originally sideritic) nodules, and phosphatic nodules and coprolites. Thin interbeds, lenses, and wisps of 

medium-dark-gray to black carbonaceous dolomitic quartzose shale 

are present at some localities. Conodonts, fish remains, and Zoophycus 

(Taonurus, Spirophyton) markings are common, and fucoids, crinoid columnals, and Syringopora sp. corals occur locally. The corals 

have been observed only where the silt content is relatively low.

In outcrop, the dolomitic facies generally forms the base of a cliff 

of Madison Limestone (fig. 5), or'slightly reentrant ledges just below. 

However, where the facies is very thin it may form, only a reentrant. 

The dolomitic facies has been mapped, depending on its thickness 

and the local topography, with the Madison (Hose, 1955, p. 48-49) 

or with an unconf ormably underlying weakly resistant unit (Murphy 

and Richmond, 1965). In the subsurface this facies may be difficult to 

differentiate from overlying beds of the Madison except by close 

scrutiny of well cuttings. It is easily recognized in cores, however, 

and is generally expressed on radioactivity well logs by a moderate 

to slight deflection of the gamma-ray curve to the right.

The Cottonwood Canyon Member in its shale and siltstone facies, 

as characterized by the Clarks Fork Canyon reference section (fig. 4, 

col. 4; Sandberg, 1963), is dark-gray to black and greenish-gray 

carbonaceous dolomitic quartzose shale and mudstone interbedded
B28 CONTRIBUTIONS TO GENElRAL GEOLOGY

with medium-colored moderate yellowish brown, dark yellowish 

orange, and medium dark gray partly banded or mottled Avith light 

olive gray and yellowish gray limonitic glauconitic carbonaceous 

dolomitic siltstone, grading to very silty dolomite. A sample of carbonaceous shale from the Hunter Peak locality in the northern 

Absaroka Range, between Clarks Fork Canyon and Meridian Eidge 

(fig. 1), yielded 10.3 gallons of oil per ton on pyrolysis by the Ruska 

Still method (R. F. Gantnier, Avritten commun., 1959). The shale 

weathers dark to medium gray and light olive gray; the dolomitic 

siltstone weathers yellowish brown, dark yellowish orange, light 

brown, and yellowish gray. Botryoidal nodules or geodes !/£-! inch in 

diameter of white crystalline quartz with vugs and cracks partly filled 

with calcite, hematie, or pyrite are locally present in the shale (fig. 4, 

cols. 4, 5). The siltstone contains glauconite grains, limonitic (sideritic?) nodules, Zoophycus markings, and carbonaceous films and 

wisps. Scattered conodonts, fish remains, phosnhatic nodules and 

coprolites, 'and, less commonly, crinoid columnals occur in both the 

shale and siltstone. The shale also contains abundant marine palynomorphs including hystricosphaeres, Leiosphaeridia sp. cysts, Tasmanites, and Micrhystridium (R. H. Tschudy, written commun., 

1962), and linguloid brachiopods and, locally, fenestrate bryozoans 

and conularids.

In outcrop, the shale and siltstone facies commonly forms a reentrant, a slope, or moderately resistant ledges below a cliff or ledges 

of carbonate rocks of the Madison or Lodgepole Limestone. In areas 

of steep topography where the facies is thick, as in the Absaroka 

Range and southern Beartooth Mountains of Wyoming, however, it 

may form the base of a cliff of Madison Limestone. Recently, in 

neighboring quadrangles, the shale and siltstone facies has been 

mapped at the base of the Lodgepole Limestone (McMannis and Chadwick, 1964; Skipp and Peterson, 1965) or, alternatively, at the top 

of si poorly exposed underlying unit (Roberts, 1964). In the subsurface, this facies is readily identifiable in both well cores and cuttings 

and is expressed on radioactivity well logs by a moderate to very 

sharp deflection of the gamma-ray curve to the right.

The most diagnostic criterion for recognizing the Cottomvood Canyon Member in outcrop is the widespread occurrence of condensed or 

lag deposits formed by conglomeratic sandstone, quartzite, siltstone, 

or silty dolomite at the base of one or both tongues of the member 

regardless of their facies. Even though these deposits probably were 

not laid down originally as continuous sheets, preservation is so common that at least one such deposit has been recognized to be discontinuously present at every section examined by the authors. Moreover, a
COTTONWOOD CANYON MEMBER, MADISON LIMEISfTONE B29

%-inch-thick conodont-rich lag deposit commonly may be found at the 

base of the Lodgepole or Madison Limestone even where there is no 

vestige of the upper part of the Cottomvood Canyon Member, as at 

Bandbox Mountain and Grendah Mountain.

The lithologic character of the transgressive lag (or condensed) 

deposits of the Cottomvood Canyon Member is recognizably different 

from that of any other middle or loAver Paleozoic rocks in the report 

area. In gross features and in persistence, however, these deposits 

are very similar to other condensed deposits, as recognized by Goldman (1922), discussed by Twenhofel (1936), and recently described 

by McGugan (1965). The lag deposits of the Cotton wood Canyon 

range in thickness from a fraction of an inch to about 1 foot. They 

are characterized by abundant conodonts; fish plates, teeth, bones, 

and scales; glauconite grains; phosphatic coprolites, nodules, and 

pellets; large quartz sand grains and granules; and granules, pebbles, 

and cobbles derived from underlying rocks. Some of the conodonts 

are very large, especially at Baker Mountain, Mont. (fig. 1), where 

a specimen of re\vorked Palmatolepis measured more than 5y2 mm 

in length. The most common types of fish teeth are Helodus, Cladodus, 

and Orodus. Phosphatic nodules and coprolites as much as 1 inch in 

diameter are present at widely spaced localities such as North Crazy 

Woman Canyon, Baker Mountain, and Horse Creek, a locality 5 miles 

northAvest of Windy Gap (fig. 1). Many of the coprolites incorporate 

partly digested fish remains and conodonts. Fish bones as much as 4 

inches long are present at the base of the lag deposit at South Fork 

Rock Creek (fig. 4, col. 7). Broken plates of underlying rocks as much 

as 8 inches long and 1 inch thick are found in the lower part of the lag 

deposit at Bull Lake Canyon (fig. 1).

The total phosphate content of lag deposits of the Cottonwood 

Canyon Member may be moderately high as suggested by the following two examples. At Baker Mountain, Mont. (fig. 1), a lenticular 

quartzitic phosphatic sandstone, 0-4 inches thick, at the base of the 

shale and siltstone facies grades erratically to dark-gray sandy phosphorite composed largely of conodonts, phosphatic pebbles, and fish 

plates, bones, and teeth. Semiquantitative determination of this phosphorite by the Shapiro (1952) method indicates a phosphate content 

of 10-15 percent P2O5 . In the type section, the lag deposit (unit 2) 

at the base of the dolomitic facies contains 4-6 percent by weight 

phosphate largely in the form of conodonts. Although not as phosphatic as the deposit at Baker Mountain, the lag deposit at Cottonwood 

Canyon contains enough fluorapatite and collophane that the excess 

calcium from these calcium-phosphate sources exaggerates the apparent Ca :Mg molal ratio of the rock from 1.26 to 1.44, as determined

266-1,33 O &7 3
B30 CONTRIBUTIONS TO GENERAL GEOLOGY

by chemical analyses of powdered rock samples without and with the 

phosphatic material.

FACIES AND FACIES RELATIONS

The Cottonwood Canyon Member is divisible areally into two 

facies a western, shale and siltstone facies and an eastern, dolomitic 

facies (fig. 4). The shale and siltstone facies predominates in the apparent basin of maximum accumulation and occupies the entire shelf 

area of thin accumulation on the west. Its eastern limit is shown in 

figure 1. The dolomitic facies is largely within the more extensive 

shelf area on the east, but it extends slightly into the area of maximum 

accumulation (fig. 4, col. 4). Its eastern limit is approximately located 

in figure 1. The general lithologic and physical characteristics of rocks 

in both facies have already been discussed.

The extremes of the two facies, as illustrated by the most distant 

columns on the cross section (fig. 4, cols. 1, 7), appear to differ so 

greatly in lithologic character and resistance to weathering that their 

correlation might be difficult to prove without additional stratigraphic 

and paleontologic evidence. At some intervening sections, however, 

such complete lithologic gradations exist that the separation of the 

two facies as well as their differentiation from the Madison and Lodgepole Limestones is actually considered to be somewhat arbitrary. 

Furthermore, some depositional features, which are shared by both 

facies and by overlying undifferentiated beds in the lower part of the 

Lodgepole and Madison, help demonstrate the intertonguing and 

gradational relations between all these units.

The easternmost measured sections of the dolomitic facies of the 

Cottonwood Canyon Member are at South Fork Eock Creek (fig. 4, 

col. 7) and at North Crazy Woman Canyon in the eastern Bighorn 

Mountains, Wyo. (fig. 1). There, the member is largely light-greenish-gray, yellowish-gray, pinkish-gray, and very light gray silty to 

slightly silty dolomite that grades upward to similarly light-colored 

but nonsilty dolomite through a 5-foot-thick transition zone in the 

overlying part of the Madison Limestone. At these localities and at 

Shell Canyon (fig. 1), the member can be differentiated from overlying 

beds of the Madison by its visibly higher content of clastic material, 

hematite, and conodonts.

A little farther west at its type section, the Cottonwood Canyon 

Member grades upward almost imperceptibly into overlying beds of 

the Madison Limestone. This gradual transition begins directly above 

the basal lag deposit (unit 2 of the measured section) and continues 

upward through a 14-foot-thick zone (units 3-6) that includes the 

upper 12 feet of the member. The contact between the member and
COTTONWOOD CANYON MEMBER, MADISON LIMEiSTONK B31

the undifferentiated part of the Madison was selected at the base of 

unit 6 (fig. 5) only after careful consideration of the diagnostic 

characteristics of all the other beds within this transition zone. Unit 6 

contains scattered crinoid columnals, as does unit 5 at the top of the 

Cottonwood Canyon; but unlike unit 5 or any of the other underlying 

units, it weathers medium gray and more closely resembles carbonate 

rock in the undifferentiated part of the Madison at localities where 

the contact is sharp and unequivocal.

The gradational contact at the top of the Cottonwood Canyon Member at its type section could have been placed as much as 6 feet lower 

or 2 feet higher if only one of the several criteria that are useful in 

differentiating the member elsewhere had been employed. For example, 

if the characteristic color of \veathered surfaces were used, the top of 

the Cottonwood Canyon could have been placed at a conspicuous 

color break at the base of a bed 1 foot belo\v the top of unit 3 (fig. 5) 

and only 7 feet above the base of the member. Below this break the 

predominant weathering color is dark yellowish orange; above the 

break the weathering colors are largely yellowish gray, yellowish 

orange, and grayish orange. If the normally reliable silt content were 

used as the sole criterion, the contact could have been placed at the 

base of unit 4, or 8 feet above the base of the member. Unit 4 is a 

calcitic dolomite that contains about 10 percent silt and 90 percent 

carbonate, which is the average content of beds at the base of the 

undifferentiated part of the Madison elsewhere and is the same content as that of the massive beds of unit 8 here. Beds below unit 4 are 

silty calcitic dolomite that contains a maximum of 77 percent carbonate. However, the overlying unit (5) reverses the trend of an upward 

decrease in silt content within the member; it is silty calcitic dolomite 

containing 84 percent carbonate, which is intermediate between the 

content of units 3 and 4. If bedding thickness alone were used, then 

the contact could have been placed at the base of unit 7, or 2 feet 

above the present top of the member, because the beds above this 

horizon are medium bedded to massive whereas those below are thin 

to medium bedded (fig. 5). It is apparent, therefore, that the Cottonwood Canyon may grade into the undifferentiated lower part of the 

Madison through a thick transition zone and that all the physical and 

lithologic characteristics must be considered in selecting a contact at 

some localities.

Sections at Peak 9559 and at Baker Mountain (fig. 4, cols. 1, 2) are 

characteristic of the westernmost outcrops of the shale and siltstone 

facies in southwestern Montana (fig. 1). At Baker Mountain, the member consists mostly of dark-gray carbonaceous quartzose shale with the 

previously mentioned quartzitic sandstone and sandy phosphorite at
B32 CONTRIBUTIONS TO GENERAL GEOLOGY

the base. At Peak 9559 as well as throughout the Bridger and Gallatin 

Ranges and in the vicinity of Logan, Mont., the member is capped by 

a persistent bed of carbonaceous dolomitic siltstone, about 9 inches 

thick, that generally displays Zoophycus markings.

The shale and siltstone of these westernmost sections form a deep 

reentrant, and the lithologic change to overlying limestone in the lower 

part of the Lodgepole Limestone is so abrupt that the contact appears 

to be a disconformity. However, Avhen the overlying 5-10 feet of beds 

of the Lodgepole is analyzed, it is found to possess several constituents 

in common with the Cottonwood Canyon Member: crinoid columnals, 

highly abundant conodonts, abundant glauconite grains, and stringers 

and interbeds of carbonaceous shale. Interbeds of shale in the lower 

part of the Lodgepole locally may be thick. At Bandbox Mountain 

(fig. 1), a 6-foot-thick bed of dark-gray to black calcareous shale 

grading to shaly limestone (38-56 percent carbonate by chemical 

analysis) occurs 7 feet above the base. Moreover, the silt content of 

carbonate beds in the lower 10 feet of the Lodgepole is commonly high, 

and these beds may weather yellowish orange, as at Baker Mountain 

and at Picket Pin Ridge 12 miles southeast (fig. 1).

At sections between the eastern and western extremes of facies of 

the Cottonwood Canyon Member many other examples of gradation, 

interbedding, and continuity of lithologic features across contacts or 

facies boundaries exist. Only a few of these examples need be mentioned here for documentation. Carbonaceous shale of the Cottonwood 

Canyon Member is not only highly quartzose, as shown by its local 

gradations to carbonaceous dolomitic siltstone, but it is also highly 

dolomitic, as shown by its local gradations to carbonaceous shaly or 

silty dolomite. The carbonate content of this shale averages 20-40 percent in analyzed samples from widespread localities. At one locality, 

Picket Pin Ridge, the shale contains 50 percent carbonate. This high 

content closely resembles the content of shale interbeds such as the 

one previously mentioned at Bandbox Mountain in the undifferentiated part of the Lodgepole Limestone. It differs markedly, however, 

from the carbonate content of carbonaceous shale in the Devonian and 

Mississippian Bakken Formation, a partial equivalent of the Cottonwood Canyon in the Williston basin. Shale in the Bakken generally 

contains less than 10 percent carbonate. Carbonaceous siltstone of the 

shale and siltstone facies is also in part highly dolomitic and locally 

may grade to or contain interbeds of very silty dolomite. Conversely, 

silty dolomite of the dolomitic facies may locally grade to or contain 

interbeds of very dolomitic siltstone as well as wisps, laminae, and 

irregular patches that grade to dark-gray carbonaceous shale. 

Zoophycus markings, glauconite, and scattered crinoid columnals
COTTONWOOD CANYON MEMBER, MADISON LIMESTONE B33

occur in silty dolomite and dolomitic siltstone of both f acies. Perhaps 

the most conclusive proof of the close relation between the two f acies 

of the Cottonwood Canyon Member and the undifferentiated lower 

beds of the Madison and Lodgepole Limestones is the occurrence of 

lithologically and faunally identical lag deposits at the base of the 

member, regardless of its f acies, and at the base of the Lodgepole or 

Madison, where the member is too thin to be differentiated.

TONGUES

The Cottonwood Canyon Member comprises two tongues a lower 

tongue and an upper tongue whose conodont faunas and stratigraphic relations are recognizably different, as shown diagrammatically in figure 3. The lower tongue, which contains very late to possibly 

latest Devonian conodont faunas, is less extensive than the upper 

tongue and is present at the base of the Madison Limestone only in 

Wyoming. The upper tongue, which contains Early Mississippian 

conodont faunas, is widely distributed at the base of the Lodgepole 

Limestone in Montana and at or near the base of the Madison Limestone in Wyoming. The limit of the upper tongue generally coincides 

with the limit of the member (fig. 1). Both tongues occur together and 

in stratigraphic succession at some localities in northern Wyoming, 

where they are separated by a disconf ormity indicated both by cutand-fill and by the absence from adjacent beds of conodont faunas 

that are represented elsewhere. At some localities in west-central 

Wyoming (fig. 3), however, the tongues are separated by undifferentiated beds of the Madison Limestone. At other nearby localities, where 

the lower tongue is poorly developed or not preserved, the member is 

represented only by its upper tongue, which lies 16-20 feet above a 

marked unconformity at the base of the Madison.

The lower tongue of the Cottonwood Canyon Member has been 

recognized at Shoshone and Cottonwood Canyons (fig. 4, cols. 5, 6), 

where it directly underlies the upper tongue, at Dinwoody Canyon 

(fig. 1), where it directly underlies beds of Devonian age in the undifferentiated part of the Madison Limestone, and at Bull Lake Canyon (fig. 1), where the directly overlying upper tongue is very thin. 

The lower 16 feet of the Madison Limestone at North Crazy Woman 

Canyon (fig. 1) is tentatively considered to represent the lower tongue 

of the member. The lower tongue may be present, although poorly 

developed, at the base of the Madison at Windy Gap. The lower 

tongue probably is also present at Clarks Fork Canyon (fig. 4, col. 4) 

and other measured sections that lie within the area of maximum 

accumulation. The precise contact between the two tongues in this
B34 CONTRIBUTIONS TO GENEIRAL GEOLOGY

area has not been clearly defined, however, because deposition of the 

member was more nearly continuous.

At Cottonwood Canyon (fig. 4, col. 6), the loAver tongue is 10 feet 

thick and comprises units 2^ of the type section. Each of these units, 

including the basal lag deposit (unit 2), yields an identical very late 

Devonian (upper toV] conodont fauna. The highest collection of this 

fauna comes from 1 foot below a wavy cut-and-fill surface, interpreted as a disconformity, at the top of unit 4. The upper tongue is 

represented by the next higher unit (5), which is 3 feet thick. Although unit 5 does not appear to have a basal lag deposit at the locality where the type section was measured, it is more silty than unit 

4 and contains crinoid columnals, which do not occur in unit 4. These 

differences from unit 4 suggest changed depositional conditions. 

Furthermore, a Lower Carboniferous (upper cnl) conodont fauna is 

present throughout unit 5. At least one conodont zone that has been 

recognized in the member in the report area (fig. 3) and as many as 

three conodont zones that are reported elsewhere (Collinson and 

others, 1962, chart 6) are apparently missing between conodont collections from either side of the disconformity between units 4 and 5 and 

only 1 foot apart stratigraphically.

At Shoshone Canyon (fig. 4, col. 5), the lower tongue is 15 feet thick 

and the upper tongue is 8 feet thick. Each tongue yields a different 

conodont fauna and has a basal lag deposit. The lag deposit of the 

lower tongue contains a very late Devonian (upper toV) conodont 

fauna, whereas the lag deposit and upper part of the upper tongue both 

contain a Lower Carboniferous (upper cul) conodont fauna.

At Dinwoody Canyon on the east side of the Wind River Range 

(fig. 1), the lower tongue is 6 feet thick and contains a very late 

Devonian (upper toV) conodont fauna. It is overlain by undifferentiated Madison Limestone that in its lower 16 feet also contains a very 

late Devonian (upper to~V) conodont fauna, as determined from five 

conodont collections at stratigraphic intervals of 2^ feet. Directly 

above these Devonian beds, pronounced related changes in lithologic 

character and bedding thickness suggest a disconformity or hiatus at 

a horizon where the upper tongue would be expected to occur on the 

basis of correlation with the nearby Windy Gap section (fig. 1). The 

physical break at this horizon apparently coincides with a faunal 

change. Lower Carboniferous (cul-lla) conodonts were collected 

from a bed 5 feet higher in the Madison.

At Bull Lake Canyon (fig. 1), the southernmost outcrop at which 

it has been differentiated from the Madison Limestone in the Wind 

River Range, the Cottonwood Canyon Member is greatly condensed. 

Although only 1.2 feet thick, the member apparently comprises both
COITTONWOOD CANYON MEMBER, MADISON LIMEOTONE1 B35

tongues in a section measured on the north wall of the canyon. The 

lower tongue is 0.8 foot thick and the upper tongue is 0.4 foot thick. 

Each tongue has a very thin basal sandy shale and a different conodont 

fauna. The lower tongue contains a very late Devonian (upper toV) 

fauna. The upper tongue, which is bed 2 of Klapper (1958) on the 

south side of the canyon, contains an Early Mississippian (Kinderhook) conodont fauna identified by J. W. Huddle (written commun., 

1964). Although this fauna is not large nor well preserved, it includes 

fragments of siphonodellids, which indicate an age younger than 

earliest Mississippian (fig. 3).

At North Crazy Woman Canyon, a 16-foot-thick unit consisting 

predominantly of light-colored hematitic slightly silty dolomite but 

containing interbeds of very sandy dolomite and silty shale in its basal 

3 feet is tentatively assigned to the lower tongue. This unit underlies 

the upper tongue of the Cottonwood Canyon Member, which is 6 feet 

thick at this locality. The clastic content of the upper part of the 16- 

foot unit is so low, however, that only the basal 3 feet alternatively 

might be considered the lower tongue. By this interpretation, the 

upper 13 feet would be considered a tongue of undifferentiated Madison Limestone intervening between tongues of the Cottonwood Canyon 

Member. The alternative interpretation is regarded as less likely, however, because of the uncommonly high hematite content of the upper 

13 feet. Regardless of whether all or part of the 16-foot unit represents 

the lower tongue, the assignment of the entire unit to the Madison is 

unequivocal. The unit contains a conodont fauna that lacks species 

diagnostic for a zonal assignment but includes a new genus, provisionally designated as 1/Scaphignathus veil/era by Glenister and Klapper 

(1966, pi. 94, fig. 3), that occurs in the uppermost Devonian (toV-YL) 

of Western Australia. Previously the unit was included incorrectly 

in the Jefferson Formation of early Late Devonian age (Sandberg, 

1961, pi. 6).

At all other localities where the presence or probable presence of the 

lower tongue is not mentioned here, the member comprises only the 

upper tongue, which generally but not everywhere lies at the base of 

the Madison or Lodgepole Limestone. Several localities where the 

member consists only of the upper tongue and yields a diagnostic conodont fauna are shown in figure 4 (cols. 1-3, 7). Also, only the upper 

tongue is present at the reference well. Other well-exposed sections, 

where the member is constituted by its upper tongue and where diagnostic conodont faunas may be collected, are readily accessible on roads 

through the Bighorn Mountains. These sections include: Little Tongue 

Canyon, along U.S. Highway 14, 19 miles west of Sheridan; Tensleep 

Canyon, north of U.S. Highway 16 and 25 miles southeast of North
B36 CONTRIBUTIONS TO GENEIRAL GEOLOGY

Crazy Woman Canyon; and Shell Canyon, north of U.S. Highway 

U (fig. 1).

One of the most significant measured sections of the Cottonwood 

Canyon Member and of the undifferentiated lower part of the Madison 

Limestone is at Windy Gap in the Washakie Range, Wyo. (fig. 1). 

There, the lower tongue is poorly developed and is tentatively considered to be represented by a %-foot-thick bed of silty dolomite without a lag deposit at the base of the Madison. This bed contains a very 

late Devonian (upper toV) conodont fauna. The next two higher beds 

of dolomite in the Madison, which aggregate 15% feet in thickness and 

contain Syringopora sp. and other corals, are probably of about the 

same age. Their lithologic character and thickness closely match those 

of the Devonian part of the Madison at Dinwoody Canyon, 21 miles 

to the south in the Wind River Range. The well-developed upper 

tongue of the Cottonwood Canyon Member, which lies 16 feet above 

the base of the Madison, is about 3 feet thick and yields two different 

conodont faunas. An earliest Mississippian conodont fauna, assigned 

to the Siphonodella sulcata (lower cul) Zone, is present in three thin 

beds of pinkish-gray silty dolomite within the basal 1 foot of the upper 

tongue. This is the only fauna of this age that was found in the present 

study. The second conodont fauna, which indicates an Early Mississippian (upper cul) age, is from a 1-foot-thick bed in the middle of 

the tongue. A fauna of this same age also was found in undifferentiated 

beds of the Madison, 1 foot above the top of the upper tongue. The 

stratigraphic and age relations of the upper tongue at Windy Gap 

provide further proof of intertonguing between the Cottonwood Canyon Member and the undifferentiated lower part of the Madison 

Limestone.

AGE

The age of the Cottonwood Canyon Member, based on conodont 

determinations, ranges from very late Devonian to Early Mississippian 

in Wyoming, but it is entirely Early Mississippian in Montana. The 

presence of the lower tongue in Wyoming accounts for the slightly 

older age of the member there. In terms of ammonoid Stufen, the 

member ranges from the upper part of the Ctymenia-Stufe. of the 

Upper Devonian to the lower part of the Pericycfais-Stufe of the 

Lower Carboniferous (fig. 3). To state the age using the symbols that 

are conventionally employed to express ages based on conodont determinations, the Cottonwood Canyon ranges in age from upper toV to 

lower cuFLa.

The lower tongue of the Cottonwood Canyon Member generally 

yields a very late Devonian (upper toV) conodont fauna. At North 

Crazy Woman Canyon and other nearby localities in the central Big-
'COTTGNWOOD iCANYON MEMBER, MADISON LIMEiSfTONIE1 B37

horn Mountains (fig. 1), however, it yields an impoverished conodont 

fauna dominated by ^ScaphignatJius velifera that may suggest an age 

as young as latest Devonian (toVI). The more widespread upper 

tongue yields three successive Early Mississippian conodont faunas 

lower cul, upper cuL^ and lower cuTIa. The upper cuT and lower cuULa 

faunas are widespread, but the lower cul fauna was found only at 

Windy Gap, Wyo. The scarcity of the latest Devonian (&>VI) and 

earliest Mississippian (lower cuT) faunas in the member and in the 

undifferentiated lower part of the Madison Limestone might be attributed to inadequate sampling or to unsuccessful differentiation of 

slightly older and younger faunas. These explanations seem unlikely, 

however, because of the large number of samples that were processed 

from stratigraphic intervals of only a few inches at several localities 

and because of the many phylogenetic sequences of conodonts that were 

recognized. A more likely explanation of the scarcity of toVI and 

lower cul faunas is provided by regional paleotectonic events, which 

will be interpreted later.

CORRELATION

The Cotton wood Canyon Member of the Madison Limestone is equivalent to the Devonian and Mississippian Englewood Formation, which 

crops out below the Pahasapa Limestone, a partial equivalent of the 

Madison, in the Black Hills of northeastern Wyoming and western 

South Dakota. The lithologic character, stratigraphic relations, thickness, and age of the Englewood and Cottonwood Canyon are very 

similar, as discussed by Sandberg (1963). The equivalence of their 

conodont faunas was discussed by Klapper (1966).

The Englewood Formation occupies a narrow elongate area 70-270 

miles wide and 450 miles long that trends about N. 42° E. from the 

southeastern Powder River Basin, Wyo., through the Black Hills to 

the eastern Williston basin in northeastern North Dakota. Its thickness ranges from 18 to 54 feet at outcrops in the Black Hills and 

reaches a maximum of about 90 feet at a depositional center in the 

subsurface of north-central South Dakota.

The Englewood Formation and Cottonwood Canyon Member are 

now separate rock bodies although their limits locally are only about 

30 miles apart in the subsurface of the Powder River Basin. Their 

original depositional areas may have coalesced briefly in Early Mississippian time, but vestiges of any very thin connecting shelf deposits 

are difficult to locate because of sparse subsurface control. A hypothesized connection between the two rock bodies may be documented by 

further study of outcrops in the Hartville Uplift, southeast of the 

Powder River Basin in east-central Wyoming. There, at Ragan Draw, 

a conodont-bearing sandstone that is lithologically similar to both
B38 CONTRIBUTIONS TO GENEiRAL GEOLOGY

units has been found at the base of the Guernsey Formation of Devonian and Mississippian age.

The Cottonwood Canyon Member was deposited penecontemporaneously with a complex of related thin carbonaceous Devonian and 

Mississippian strata that extends arcuately from the Wllliston basin 

in North Dakota through southern Manitoba, southern Saskatchewan, 

and northern Montana northwestward into Alberta and then southward into southwestern Montana. This complex comprises three partly 

connected units that had discrete depositional centers: the Bakken 

Formation in the Williston basin, the Exshaw Formation in Alberta, 

and the Sappington Member of the Three Forks Formation in southwestern Montana. The Bakken Formation comprises upper and lower 

transgressive black shales separated by a medial siltstone. Because of 

later erosion, the upper black shale of the Bakken now extends only 

as far west as north-central Montana, but the medial siltstone and 

lower black shale continue into Alberta, where they form the Exshaw 

Formation. The black shale of the Exshaw, which commonly has a 

very thin lag sandstone at its base, extends southward into Montana 

and connects with the basal black shale of the Sappington in southwestern Montana. The upper siltstone of the Exshaw is separated 

from the equivalent units (2-5) of the Sappington, however, by a 

40-mile-wide area of erosional thinning in northwestern Montana. 

Thus, despite later erosion, the lower black shale remains continuous 

between all three units of this depositional complex, and the overlying 

siltstone is only narrowly separated.

The age equivalence of the complex of Devonian and Mississippian 

strata on the north to the Cottonwood Canyon Member has not been 

firmly established on the basis of conodonts, but it can be indirectly 

approximated from known stratigraphic relations and from widely 

scattered conodont evidence.

The lower black shale of the complex, at least where it forms the 

base of the outcropping Sappington Member of the Three Forks 

Formation, is dated from conodonts as very late Devonian (lower 

foV), which is older than the lower tongue of the Cottonwood Canyon 

Member (fig. 3). As this lower shale is transgressive and the direction 

of transgression is unknown, its age beneath the Sappington does not 

precisely establish its age beneath the Exshaw or Bakken Formation, 

where it may be either slightly older or slightly younger. The Bakken 

and Exshaw occur largely in the subsurface in North Dakota and 

northern Montana, where their conodont faunas are not well known. 

In eastern Alberta, however, conodont evidence suggests that the lower 

black shale is approximately the same age very late Devonian at 

the base of the Bakken as it is at the base of the Sappington. A sup-
CQTTONWOOD CANYON MEMBER, MADISON LIMESTONE B39

posed Kinderhook conodont fauna was described by Cooper (Cooper 

and Sloss, 1943) from a subsurface unit informally called "Exshaw" 

in the Steveville oil field of eastern Alberta. This subsurface unit is 

now regarded as the lower black shale of the Bakken, according to 

Penner (1958). The conodont fauna figured by Cooper and Sloss 

(1943) was reevaluated in the light of more recent evidence of conodont zonation (Klapper, 1966, p. 10) ; it contained no species diagnostic of a Kinderhook age but did contain two species indicative of very 

late Devonian (toV-VT) age.

The age of the top of the complex can also be indirectly dated by 

correlating from outcrops to the subsurface. The top of the Sappington, although not precisely dated, must be the same age as or slightly 

older than the overlying Cottonwood Canyon where they occur together in stratigraphic succession. The age of the top of the Sappington, however, does not definitely establish the upper age limit of the 

Exshaw Formation nor of the Bakken Formation. These formations 

are thicker and contain beds stratigraphically higher than the upper 

part of the Sappington. Consequently, their upper age limit may be 

roughly the same as youngest part of the Cottonwood Canyon, which is 

Early Mississippian (Kinderhook), equivalent to the Lower Carboniferous (lower cu ILx) of Europe. An age no younger than lower cuTLa. 

for the Bakken is supported by collections of conodonts diagnostic of 

that age from basal beds of the Lodgepole Limestone, which directly 

overlies the upper shale of the Bakken in the Little Rocky Mountains of 

north-central Montana. Although this is the only area in which the 

Bakken is known to crop out on the margins of the Williston basin, 

the outcrops lie close to the limit of the farthest southward transgression by the upper shale of the Bakken in north-central Montana. 

Hence, the Bakken probably is as young there as anywhere in the 

subsurface.

In summary, although the northern complex has not been conclusively dated on the basis of conodonts, its age can be inferred to range 

approximately from very late Devonian (lower toV) to Early 

Mississippian (lower

MADISON LIMESTONE (LOWER PART)

GENERAL FEATURES

The lower 10-25 feet of the undifferentiated part of the Madison 

Limestone in all of Wyoming except the extreme western part, where 

the Lodgepole Limestone is recognized, consists largely of lightcolored microcrystalline to very finely crystalline microsucrosic to 

sucrosic slightly crinoidal dolomite. The most commonly observed 

colors of freshly broken rock surfaces are yellowish gray, light olive
B4tO OO'NTRIBTJTIONS TO GOBNEIRAL GEOLOGY

gray, and light gray. Less common colors, in decreasing order of 

abundance, are pale yellowish brown, medium light gray, grayish 

orange pink, very light gray, yellowish orange, medium gray, light 

brownish gray, yellowish orange, grayish orange, and pale yellow. 

The dolomite commonly is slightly calcitic and less commonly is 

calcitic, but the calcite content approaches that of dolomitic limestone. The dolomite may be characterized as slightly silty to nonsilty; 

analyses of more than 25 samples from about 15 widespread localities 

show that the silt content ranges from 3 to 17 percent and averages 

about 10 percent. Glauconite grains are rare, but scattered very fine 

to coarse quartz sand grains locally are present in the basal few 

inches. Crinoid columnals are not as large nor as abundant as those 

in the Lodgepole Limestone farther north and west, but they do occur 

at most sections. Even in samples in which crinoid columnals or their 

molds are not discernible megascopically or microscopically, differentially dolomitized columnals can be etched from the dolomite by 

partial solution in acetic acid.

The thickness of the beds in the lower 10-25 feet of the Madison 

is generally 4 feet or greater, but it may be as little as 1-2 feet, particularly in the basal 10 feet. Although the lower part of the Madison 

generally forms part of a high cliff or thick resistant ledges, the basal 

10 feet characteristically forms a reentrant in the cliff face or thinner 

less resistant ledges than those above.

Two diagnostic features of the basal beds of the undifferentiated 

lower part of the Madison in outcrop are the high vuggy porosity and 

the common occurrence of Syringopora sp. corals, which are not present in underlying Devonian formations. The vuggy porosity results 

from the presence of abundant leached fossil molds, which were 

formed during dolomitization of the original limestone. Many of the 

fossil molds are of crinoid columnals. Large colonies of Syringopora 

sp. occur in the basal 10 feet, generally where the silt content is low 

and particularly in the Bighorn and Owl Creek Mountains and Wind 

River Eange.

Large well-preserved conodont faunas generally are more difficult 

to obtain from the basal part of the undifferentiated Madison Limestone in Wyoming than from the corresponding part of the Lodgepole 

Limestone in Montana and western Wyoming. The scarcity of conodonts in the Madison is believed to be due to a facies change that 

affected their rate of accumulation and to the widespread dolomitization in central and eastern Wyoming. The crinoid content was noted 

to be much lower in rocks of the Madison in the area east of the belt 

of maximum thickness of the Cottonwood Canyon Member than in 

rocks of the Lodgepole in the area on the west. A correspondingly
OOTTONWOOD CANTON MEMBEiR, MADISON LIMESlTONE B41

abrupt eastward change in the content of glauconite and chert was 

also noted. The environment of deposition of the basal Madison is 

therefore believed to differ from that of the basal Lodgepole, and 

it probably was less favorable for the concentration of conodonts. 

Furthermore, many of the larger conodonts obtained from dolomite 

of the Madison are badly broken. This may result partly from their 

breakage prior to deposition and partly from their fragmentation 

during dolomitization.

In the Pry or and northern Bighorn Mountains of south-central 

Montana (fig. 2), the basal 25 feet of the undifferentiated lower part 

of the Madison Group is dolomite that is lithologically identical with 

the dolomite at the base of the Madison in most of Wyoming. This 

area of Montana also lies east of the belt of maximum accumulation 

of the Cottoiiwood Canyon Member. Beds directly above the basal 25 

feet in the Pryor Mountains are very cherty dolomite and dolomitic 

limestone. Their chert content is similar to that of the basal Lodgepole 

Limestone farther west in Montana.

AGE

The age of the basal part of the Madison Limestone in Wyoming 

ranges from very late Devonian (upper toV) to Early Mississippian 

(Kinderhook), equivalent to the Gattendorfia- or Pericyclus-Stafe 

(cul-lla.) of the Lower Carboniferous of Europe. Collections of 

conodonts suitable for approximate age determinations were found 

in the undifferentiated lower part at many localities, but only several 

collections were sufficiently large and well preserved to be assigned 

to one of the established conodont zones. Five collections of conodonts 

diagnostic of a very late Devonian (upper toV) age were made at 

Dinwoody Canyon, and collections diagnostic of the Lower Carboniferous (upper cul) wTere made directly above the Cottonwood Canyon 

Member at Clarks Fork Canyon (fig. 4, col. 4) and at Windy Gap. 

Collections indicative of an Early Mississippian (Kinderhook) age 

but containing species that range from upper cul to lower cuYLa. were 

made at Bull Lake, Little Tongue, and Cottonwood Canyons. At 

most other localities, age assignments of the undifferentiated part of 

the Madison were based on the presence of broken siphonodellids, 

indicative of a Mississippian (Kinderhook) age, and were supported 

by well-dated conodont faunas from the underlying or interbedded 

Cottonwood Canyon Member.
B42 OQNTBIBUTIONiSl TO GENERAL GEOLOGY

LODGEPOLE LIMESTONE (LOWER PART)

GENERAL FEATURES

The basal 10 feet of the undifferentiated lower part of the Lodgepole Limestone at Peak 9559 in the Bridger Kange, at the type section 

of the Madison Group near Logan, Mont., and in most other areas 

farther west and north in Montana has a nearly uniform lithologic 

character. It consists of medium-gray to medium-dark-gray bioclastic 

limestone that is microcrystalline to cryptocrystalline and medium 

to very coarsely fossil fragmental and contains abundant glauconite. 

It is composed largely to almost entirely of crinoid columnals and 

fragments. The columnals range from y8 to i/2 mcn i*1 diameter. In 

and near the Little Belt Mountains, this limestone may contain lenses 

or very thin to thick interbeds of black calcareous shale grading to 

very shaly limestone. At the mouth of Swimming Woman Canyon, 

on the south side of the Big Snowy Mountains (located but not named 

in fig. 1), well-exposed porous bioherms composed almost entirely 

of dolomitized algae and crinoid fragments interrupt the normal 

stratigraphic sequence and extend upward through surrounding thin 

beds for at least 150 feet above the base of the Lodgepole. A bioherm 

was also observed at Bandbox Mountain in the Little Belt Mountains, 

but its base was about 125 feet above the base of the Lodgepole.

South and east of the Bridger Range, the basal 10-25 feet of the 

Lodgepole Limestone in the Gallatin Range and Beartooth Mountains, 

Mont., and the Teton Range, Wyo., differs slightly in lithologic character from areas farther north and west. It generally consists of 

medium-gray, medium-light-gray, light-olive-gray, and yellowishgray slightly argillaceous crinoidal limestone that is microcrystalline 

to finely crystalline, medium to coarsely fossil fragmental, and commonly dolomitic to slightly dolomitic. This limestone is slightly less 

glauconitic and crinoidal than that in areas farther north and west, 

but crinoidal debris commonly constitutes 25-50 percent and rarely 

as much as 75 percent of the rock. Chert is generally present and 

locally very abundant. Large chert nodules or stringers as much as 

3 inches thick and 10 feet long may constitute as much as 20 percent 

of the rock. This very cherty zone is at the base of the undifferentiated 

part of the Lodgepole in some areas, but elsewhere the basal 2-12 feet 

may be relatively chert free. The zone appears to rise stratigraphically 

toward the southeast.

A lower crinoidal unit of the Lodgepole Limestone in western Wyoming and southwestern Montana was also recognized by Sando and 

Dutro (1960), who reported that it contained a Zone A megafauna.

The thickness of bedding in the lower 10-25 feet of the undifferentiated part of the Lodgepole Limestone ranges from 4 inches to 4 feet
'COTTONWOOD CANYON MEMBE.R, MADISON LIMESTONE B43

but is most commonly about 2 feet. This basal part of the Lodgepole 

is commonly more resistant than the overlying part and forms a low 

cliff or moderately resistant ledge.

The most diagnostic features of the basal carbonate beds of the 

Lodgepole in outcrop are their moderate to high glauconite content, 

high to very high crinoid content, and moderate to high content of 

white, bluish-white, light-olive-gray, olive-gray, or medium-darkgray spicular chert. These features also serve to identify the basal 

10-15 feet of the Lodgepole in the subsurface throughout eastern Montana and North Dakota. The high glauconite content is observable in 

both well cuttings and cores. Moreover, the uniformly high total carbonate content of the crinoidal limestone is represented on radioactivity well logs by a deflection of the gamma-ray curve to the left. 

This deflection is most striking on logs from wells where overlying 

beds of the Lodgepole are largely thin-bedded argillaceous limestone 

grading to calcareous shale.

Conodonts are characteristically abundant and well preserved in the 

lower 10 feet of the undifferentiated part of the Lodgepole Limestone 

and particularly in the basal few inches of the more calcareous facies 

in the northern and western areas of Montana. Conodonts in these 

beds, unlike those at some places in the Cottonwood Canyon Member, 

are generally not recognizable on either fresh or weathered surfaces.

AGE

The basal part of the undifferentiated lower part (or locally of the 

Paine Shale Member) of the Lodgepole Limestone is Early Mississippian (Kinderhook), equivalent to a part of the Pericyclus-Stnfe 

(lower cuTLa) of the Lower Carboniferous of Europe. It is also a 

time equivalent of the upper part of the Hannibal Shale and lower 

part of the Chouteau Limestone of the Upper Mississippi Valley 

(Collinson and others, 1962). Conodont faunas indicative of this age 

are present at every sampled section of the Lodgepole in northcentral, central, west-central, southwestern, and south-central Montana. The localities include: (1) Little Chief Canyon in the Little 

Rocky Mountains, where the Lodgepole Limestone was named, north 

of the report area, (2) Bandbox Mountain, (3) Crystal Lake Road 

on the north side of the Big Snowy Mountains (located but not named 

in fig. 1), (4) Peak 9559, (5) Mystic Lake in the north-central Gallatin Range (located but not named in fig. 1), (6) Castle Rock in the 

west-central Beartooth Mountains (located but not named in fig. 1), 

(7) Baker Mountain, and (8) Meridian Ridge. The basal carbonate 

beds of the Lodgepole also contain a lower cuTLa conodont fauna at 

the type section of the Madison Group at Logan and at six other
B44 OONTEIBimONSi TO GENERAL GEOLOGY

nearby localities which lie within an 11-mile radius of Three Forks, 

Mont. These localities, which are located but not named in figure 1, are 

Nixon Gulch, Kekap Station, Mud Spring Gulch, Milligan Canyon, 

Dry Hollow, and Ingleside Quarry. Lower culla conodonts are also 

present in the basal carbonate beds of the Lodgepole at Teton Canyon, 

Wyo. (fig.l).

CONODONT ZONES

The conodont zonation of the Three Forks Formation, the Cottonwood Canyon Member (dark shale unit), and the basal strata of the 

Madison and Lodgepole Limestones was previously discussed by 

Klapper (1966, p. 11-12 and fig. 2). Additional comments on this 

zonation are made here to incorporate findings based on more recent 

conodont collections that are listed elsewhere in this report. A conodont zone that previously was treated informally by Klapper (1966) 

is here named the Siphonodella sandbergi-Siphonodella duplicata 

Zone. The first finding of the Siphonodella sulcata Zone of Collinson, 

Scott, and Eexroad (1962) in the Northern Kocky Mountains region 

is recorded from Windy Gap in west-central Wyoming (fig. 1). The 

conodont zones that are presently recognized in the Upper Devonian 

and Lower Mississippian of Wyoming and Montana are shown in 

figure 3.

UPPER DEVONIAN ZONES

SCAPHIGXATHTJS VEJ.IFERA ZONE (UPPER toIIIa-LOWER tOlV)

A conodont fauna found in the top 2 feet of the Trident Member of 

the Three Forks Formation at Peak 9559 is assigned to the Scaphignathus velifera Zone (Ziegler, 1962). The S. velifera represented in 

this fauna resembles the form with a low free blade that was illustrated 

by Ziegler (1962, pi. 11, fig. 19) from the Upper S. velifera Zone 

(upper fc>III/J-lower toTV] at Ball-Berg, Ehenish Schiefergebirge, 

Germany. Polygnatlius comnwnis has a questionably lowest occurrence in the Upper /S. velifera Zone but is definitely found as low as 

the directly overlying Lower P. styriaca Zone according to Ziegler 

(1962, p. 88). P. perplexa occurs in higher toIII and in toIV strata 

(Helms, 1961, p. 693). P. irregularis (Thomas) [not Cooper] is found 

in highest toTV strata (Helms, 1961, p. 686). Thus the fauna at Peak 

9559 suggests a correlation with the Upper S. velifera Zone, although 

the occurrence of Pseudopolygnathus granulosa Ziegler would be 

necessary to establish this more precise correlation.

A fauna that is similar to the one at Peak 9559 in that it also contains both Scaphign&thus velifera and Polygnathus semicostata was 

reported from the Upper Famennian (7^m2a) of Belgium in beds 62 

and 63 of the Gres de Montfort section by Bouckaert and Ziegler 

(1965, p. 16 and chart 8).
COTTONWOOD CANYON MEMBE.R, MADISON LIMESTONE' B45 

UPPER POLYGNATETUS STYRIACA ZONK (LOWER toV)

The fauna from the basal lag deposit (sample BB-15) of the Sappington Member of the Three Forks Formation at Bandbox Mountain 

is assigned to the Upper Polygnathus styriaca Zone. It includes three 

significant taxa: Pdlmatolepis rugosa postera, Spathognathodus jugosus, and Pseudopolygnathus marburgensis. The highest occurrence of 

P. rugosa postera and the lowest occurrence of S. jugosus are diagnostic of this zone, according to Ziegler (1962, table 2). The overlap in 

ranges of these two taxa occurs in four samples from the Upper 

P. styriaca Zone at the Honnetal roadcut, near the Honnetal railroad 

cut, in the Ehenish Schiefergebirge (Ziegler, 1962, table 5). In addition, P. marburgensis is restricted to the same zone at Ziegler's Honnetal locality.

The finding of a large well-preserved fauna at Bandbox Mountain 

confirms the previously reported finding of the Upper Polygnathus 

styriaca Zone in the basal part of the Sappington Member at Frazier 

Lake, just north of Peak 9559 in the Bridger Eange (Klapper, 1966, 

p. 7). Unlike the Bandbox Mountain fauna, the Frazier Lake fauna 

was obtained from a hydrofluoric acid residue, and the conodonts 

were not well preserved because of chemical change caused by the acid.

LOWER SPATHOGNATHODUS COSTATUS ZONE (UPPER toV)

Faunas referable to this zone were described from the lower tongue 

of the Cottonwood Canyon Member at Cottonwood, Dinwoody, and 

Bull Lake Canyons, from the basal 4 feet of the Madison Limestone 

at Dinwoody Canyon, and from the middle part of the Englewood 

Formation in the Black Hills by Klapper (1966). Listed elsewhere in 

this report are the more relevant of these faunas, as well as previously 

unlisted faunas from the Lower Spathognathodus costatus Zone. The 

previously unlisted faunas are from the lower tongue of the Cottonwood Canyon Member at Shoshone Canyon, and from 12-16 feet 

above the base of the Madison Limestone at Dinwoody Canyon. This 

zone is also present but represented only by a sparse fauna in the undifferentiated part of the Madison Limestone between the two tongues 

of the Cottonwood Canyon Member at Windy Gap.

A fauna from the 16-foot-thick unit tentatively assigned to the 

lower tongue of the Cottonwood Canyon Member at North Crazy 

Woman Canyon is dominated by a new genus, which was provisionally 

designated as IScaphignathus velifera by Glenister and Klapper 

(1966, p. 834, and pi. 94, fig. 3). The new genus is present in the uppermost Devonian (toV-VI) beds of the Fairfield Formation in Western 

Australia (Glenister and Klapper, p. 838, sample GSWA 3240). It 

does not occur with other diagnostic taxa in the Wyoming fauna, how-
B46 CXWTRIBUTIONS TO GfENEIRAL GEOLOGY

ever. In the absence of other evidence, it is suggested that the beds 

containing IScaphignathus velifera at North Crazy Woman Canyon 

may be uppermost Devonian and thus somewhat younger than the 

Lower Spathognathodus costatus Zone.

LOWER MISSISSIPPIAN ZONES

The Gattendorfia-Stufe (cul) of the Lower Carboniferous in Germany was divided into three conodont zones by Voges (1959, 1960). 

These zones in ascending order are the Gnathodus kockeli-Pseudopofygnathus dentilineata Zone, the Siphonodella-Pseudopolygnathas 

triangula inaegucHis Zone, and the Siphonodella-Pseudopolygnathus 

triangula triangula Zone. Voges based this zonation on samples of the 

Hangenberg Limestone mainly at the Honnetal railroad cut, Sauerland, Rhenish Schiefergebirge, but also at three other sections of the 

Hangenberg in the Sauerland. The Honnetal railroad cut is the formal 

reference section for the Devonian-Carboniferous boundary, as decided by the Second Carboniferous Congress at Heerlen, Netherlands, 

in 1935. (See Voges, 1960, figs. 1, 2, for locations of these sections.)

The concept of Siphonodella duplicata as used by Voges (1959) is 

much broader than that later employed by Collinson, Scott, and Rexroad (1962) and by Klapper (1966). Because Voges included both S. 

duplicata s.s. and S. cooperi in S. duplicata, the correlation of his 

zones with North American cul faunas, in which S. duplicata s.s. is 

differentiated, is difficult. Sampling of cul strata at the Honnetal 

railroad cut by Klapper in 1963, however, clarifies some aspects of this 

problem, as summarized below.

The Gnathodus JcocTceli-Pseudopolygnathus dentilineata Zone, the 

lowest of Voges' three conodont zones, includes his Honnetal samples 

1-4 (Voges, 1959, p. 270 and fig. 1). Our sample X-41, which represents the combined interval of Voges' samples 3 and 4, contains 

Siphonodella sulcata. This finding extends the range of Siphonodella 

downward into the G. kockeli-P. dentilineata Zone.

The overlying Siphonodella-Pseudopolygnathus triangula inaequalis Zone includes Honnetal samples 5-9 of Voges (1959, p. 270 and 

fig. 1). Our samples X-42 and X-43 are equivalent to Voges' samples 

5 and 6, respectively, and mark the lowest occurrence of S. duplicata 

s.s. S. sandbergi occurs in our sample X-45, which is equivalent to 

Voges' Honnetal sample 9.

In Wyoming only two cul conodont zones the Siphonodella sulcata 

Zone and the Siphonodella sandbergi-Siphonodella duplicata Zone 

are recognized. An exact correlation between these two zones and 

Voges' three conodont zones in Germany cannot be made at present, 

but a tentative correlation is suggested. The S. sulcata Zone, which is
COTTOJSTWOOD CANTON MEMBER, MADISON LIME,S|TONE' B47

here designated as lower cul, probably is correlative with the higher 

part of the Gnathodus Jcockeli-Pseudopolygnathus dentilineata Zone 

of Voges. The S. sandbergi-S. duplicata Zone, which is here arbitrarily 

designated as upper cul, seems to be correlative with both the 

Siphonodella-P. triangula inaegualis and the Siphonodella-P. 

triangula triangula Zones of Voges. Consequently, the designations 

lower cul and upper <?wl, as used herein, do not refer to formal subdivisions of cul but merely indicate relative positions within cul.

SIPHONODEtLLA SULCATA ZONE (LOWER OUl)

The faunas in three samples (WG-20, WG-1, and WG-22) from 

the basal 1 foot of the upper tongue of the Cotton wood Canyon Member at Windy Gap, Wyo., apparently correlate with the Siphonodella 

sulcata Zone of Collinson, Scott, and Eexroad (1962, p. 20). The finding of S. sulcata in strata equivalent to Voges' samples 3 and 4 at the 

Honnetal railroad cut suggests that the Windy Gap faunas, although 

they lack Gnathodus kockeli, also correlate with the G. JcockeUPseudopolygnathus dentilineata Zone of Voges (1960).

SIPHONODELLA SANDBERGI-SIPHONODELLA OUPLICATA ZONE

(UPPER OUl)

The "Montana and Wyoming cul" zone of Klapper (1966, p. 11-12 

and fig. 2) is here formally named the Siphonodella sandbergiSiphonodella duplicata Zone to avoid confusion with the older cul 

Siphonodella sulcata Zone now recognized at Windy Gap. Faunas 

referable to the S. sandbergi-S. duplicata Zone were reported from 

six localities by Klapper (1966, table 1). Five of these occurrences are 

in the upper tongue of the Cottonwood Canyon Member; the sixth is 

in the basal 1 inch of the undifferentiated Madison Limestone at 

Clarks Fork Canyon. Previously unreported occurrences of the zone 

are in the upper tongue of the Cottonwood Canyon Member at Clarks 

Fork, Shoshone, Warm Spring, Shell, and North Crazy Woman Canyons and at Horse Creek and Windy Gap. The zone also occurs in the 

undifferentiated lower part of the Madison Limestone directly above 

the upper tongue of the Cottonwood Canyon at Windy Gap.

In faunas at two localities in Wyoming Warm Spring Canyon and 

Horse Creek the siphonodellids are predominantly Siphonodella 

duplicata. The fauna from sample HC-7F at Horse Creek resembles 

faunas obtained from strata equivalent to Honnetal samples 5 and 6 

of Voges (1959, p. 270 and fig. 1), in which the dominant siphonodellid 

is also S. duplicata. This suggests a correlation of the HC-7F fauna 

with a position low in Voges' Siphonodella-Pseudopolygnathus triangula inaegualis Zone, although the zonal name-bearing Pseudopol/ygnathus has not yet been found in the Wyoming faunas.
B48 CONTEIBUTIONiS/ TO GENEIRAL GEOLOGY

In faunas at most of the other upper cui localities in Montana and 

Wyoming, Siphonodella duplicata a*nd S. sandbergi occur together 

with S. cooperi, /S. quadruplicata, 8. obsoleta, and rare S. sexplicata. 

These faunas appear to correlate with a position high in the Siphonodella-P. triangula, inaequalis Zone (Voges, 1959, Honnetal sample 

9) or low in the SipJionodella-P. triangula triangula Zone for reasons 

Klapper stated previously (1966, p. 12).

Future work may permit the Siphonodella sandbergi-S. duplicata 

Zone to be separated into an older part in which only S. duplicata and 

rare S. sulcata are present and a younger part in which both zonal 

name-bearers are present. Faunas that are representative of the two 

prospective parts of this zone are listed elsewhere in the report. Significantly, at one locality Horse Creek, Wyo. both the older and 

younger faunas are present in succession within the upper tongue of 

the Cottonwood Canyon Member.

LOWER SIPHONODELLA CRENULATA ZONE (LOWER culla)

The fauna of the Lower Siphonodella crenulata Zone was described 

from basal beds of the undifferentiated part of the Lodgepole Limestone at 10 localities by Klapper (1966). Previously unreported occurrences of this zone are in the basal beds of the Lodgepole at Bandbox 

Mountain, Little Chief Canyon, Mystic Lake, Castle Eock, Mud Spring 

Gulch, and Meridian Ridge. The zone also is recognized in the upper 

tongue of the Cottonwood Canyon Member at Meridian Ridge. The 

fauna from this latter occurrence seems to extend the range of Pseudopolygnathus dentilineata upward from the top of cui into the 

Lower S. crenulata Zone. The base of the Lower S. crenulata Zone is 

recognized primarily by the lowest occurrence of the zonal name-bearer but also by the lowest occurrence of P. marginata and the abundant 

occurrence of P. triangula triangula. Only one specimen of the latter 

taxon has been found below cuiia. in upper cui strata at Baker Mountain (Klapper, 1966, table 1, loc. 9).

REPRESENTATIVE CONODONT COLLECTIONS

The conodont collections listed below present the diagnostic faunas 

that were found at all the localities shown in the cross section (fig. 4) 

and at the more significant localities mentioned in the stratigraphic 

discussion. Representative conodont collections are given for each 

geologic unit that bears a single conodont zone and for each conodont 

zone within geologic units that bear two or more zones. The number 

of specimens identified is shown in parentheses. Conodonts that are 

believed to be reworked from lower strata are indicated by an asterisk 

preceding the generic name.
COTTONWOOD CANYON MEMBER, MADISON LIMESTONE B49 

TRIDENT MEMBER OF THREE FORES FORMATION

The following fauna was obtained from a 2-foot-thick bed of limestone at the top of the Trident Member of the Three Forks Formation 

at Peak 9559, south of Hardscrabble Peak in the Bridger Eange. The 

locality is at an elevation of about 9,280 feet in the SE^4 SE*4 SE^ 

sec. 21, T. 2 N., R. 6 E., Gallatin County, Mont., in the Sedan 15-minute 

quadrangle. The fauna is assigned to the Scaphignathus velifera Zone, 

which indicates a Late Devonian (Upper Famennian, upper folllalower toTV) age.

/Scaphignathus velifera Helms (3)

Polygnathus irregularis (Thomas) [not Cooper] (1)

P. perplexa Thomas (2)

P. semicostata Branson and Mehl (7)

P. communis Branson and Mehl (8)

Pelekysgnathus communis Thomas (2)

Apatognathus varians Branson and Mehl (early form) (3)

A nearly identical fauna containing abundant well-preserved specimens of Scaphignathus velifera is present in limestone at the top of 

the Trident Member at Sheep Mountain in the Centennial Range, 

Mont. This locality is just north of the Idaho State line at the west 

edge of the report area (fig. 1). It is at an elevation of about 7,800 feet 

near the center of the west edge of sec. 28, T.°14 S., R. 1 W., Beaverhead County, Mont., in the Upper Red Rock Lake 15-minute 

quadrangle.

A fauna that has several species in common with the fauna at Peak 

9559 was found in a 2-inch-thick bed of limonitic bioclastic limestone, 

which is interbedded with greenish-gray shale, in the top 5 feet of 

the Trident Member 2 miles north of Mud Spring Gulch. This locality 

at an elevation of about 4,630 feet, is in the center NE^SWi/4 sec1, T. 2 N., R. 1 E., Broadwater County, Mont, in the Three Forks 

15-minute quadrangle. The fauna, which is listed below, lacks the zonal 

name-bearer and therefore cannot be referred to the Scaphignathus 

velifera Zone with certainty.

Polygnathus irregularis (Thomas) [not Cooper] (1)

P. semicostata Branson and Mehl (31)

Pelekysgnathus communis Thomas (4)

Apatognathus varians Branson and Mehl (early form.) (23)

Spathognathodus stabilis (Branson and Mehl) (5)

SAPPINGTON MEMBER OF THREE FORKS FORMATION

The conodont fauna listed below was obtained from sample BB-15 

at a section of the Three Forks Formation and lower part of the
B50 CONTRIBUTION'S TO GENEiRAL GEOLOGY

Lodgepole Limestone measured on the west face of Bandbox Mountain 

in the Little Belt Mountains. The locality is about 250 feet vertically 

below the 7,952-foot summit of the mountain in the NE^NW1/^ sec. 

20, T. 14 N., R. 10 E., Judith Basin County, Mont., on the White 

Sulphur Springs 1: 250,000 Army Map Service sheet NL 12-5. Sample 

BB-15 represents the basal limonitic conglomeratic lag sandstone, 

0-2 inches thick, of the Sappington Member. Conodonts are abundant 

on the weathered surfaces of the rock and are readily visible under a 

X 10 hand lens. The fauna is assigned to the Upper Polygnathus 

styriaca Zone, which is indicative of a very late Devonian (lower toV) 

age.

Palmatolepis rugosa rugosa Branson and Mehl (11)

P. rugosa postera Ziegler (24)

P. rugosa subsp. undet. (15)

P. perlobata perlobata Ulrich and Bassler (1)

P. gracilis gracilis Branson and Mehl (3)

Icriodus sp. undet. (1)

jSpathognathodus jtugosus (Branson and Mehl) (6)

8. praelongus Cooper (9)

S.stdbilis (Branson and Mehl) (5)

Polylophodonta sp. undet. (2)

PolygnatJms perplexa Thomas (5)

P. triangularis Branson and Mehl (8)

P. semicostata Branson and Mehl (4)

P. granulosa Branson and Mehl sensu Thomas (14)

Pseudopolygnathivs marburgensis Bischoff and Ziegler (1)

LOWER TONGUE OF COTTONWOOD CANYON MEMBER

Representative conodont collections from the lower tongue of the 

Cottonwood Canyon Member at three localities in Wyoming are listed 

in table 1. All three faunas are assigned to the lower SpathognathodMS 

costatus Zone, which is indicative of a very late Devonian (upper toV) 

age. The fauna at Shoshone Canyon was collected from a 2-inch-thick 

lag sandstone at the base of the member (fig. 4, col. 5). The locality 

is at an elevation of about 5,800 feet on a prominent ridge on 

the north side of the canyon at the south end of Rattlesnake Mountain. It is in the W%SE%NW% sec. 5, T. 52 N., R. 102 W., Park 

County, Wyo., in the Cody 15-minute quadrangle. The fauna at 

Cottonwood Canyon was collected from unit 3 of the type section 

of the member (fig. 5). It is the middle of three conodont collections 

dated toV (fig. 4, col. 6). The fauna listed for Din woody Canyon is 

from a combined sample that represents the upper 3 feet of the tongue 

except for the top 2 inches, which was sampled separately and was
COTTONWOOD CANTON MEMBEE, MADISON LIMESTONE1 B51

listed by Klapper (1966, table 1). The locality is at an elevation of 

about 6,870 feet just south of the trail on the north side of Dinwoody 

Canyon in the center NW%NW% sec. 12, T. 4 N., E. 6 W., Fremont 

County, Wyo., in the Hays Park 7%-minute quadrangle.

TABLE 1. Representative conodont collections from the Lower Spathognathodus 

costatus Zone (upper toF) in the lower tongue of the Cottonwood Canyon Member 

in Wyoming

[Shows number of identified specimens of indigenous (unreworked) conodonts]

Conodonts

Spathognathodus aculeatus. __ __ _ __ ____

S. stabilis---- _ ____ _ __ _________ ____

S. praelongus ____ ______ __ _________ __

S.jugosus.. __ _ ___ _________ ________

Palmatolepis gracilis qracilis _________ _____

1 criodus costatus.. _____ _______ _______

/. constrictus... __________ _____ _____ _

Polygnathus communis.. ______ ____ ______

P. delicatula ______ __ _ __ ___________

P. obliguicostata _ _ __ __ __ _______ __

Apatognathus varians. __ _____ __ _ _

Shoshone 

Canyon 

(fig. 4, col. 5)

22

2

9

1

9

4

11

2

7

9

Locality

Cottonwood 

Canyon 

(fig. 4, col. 6)

15

21

9

1

6

3

18

31

112

16

Dinwoody 

Canyon

10

9

5

11

1

11

20

27

1

UPPER TONGUE OF COTTONWOOD CANYON MEMBER

The upper tongue of the Cottonwood Canyon Member contains 

faunas assigned to three conodont zones the Siphonodella sulcata 

Zone (lower cul), the S. sandbergi-S. duplicata Zone (upper cui), 

and the Lower S. orenulata Zone (lower culla) all of which are indicative of an Early Mississippian (Kuiderhook) age. The oldest 

conodont faunas, those of the S. sulcata Zone, were found in three 

samples but at only one locality, near Windy Gap in the Washakie 

Range, Wyo. The collecting locality is at an elevation of about 8,200 

feet on the north end of Black Mountain about 0.9 mile south of 

Windy Gap in the E%SW%SE}4 sec. 36, T. 43 N., R. 106 W., Fremont County, Wyo., in the Indian Point 7^-minute quadrangle. The 

fauna, listed below, occurs in sample WG-1 from a 1-inch-thick bed 

in the middle of the basal 1 foot of the upper tongue of the member 

16 feet above the base of the Madison Limestone.

Siphonodella sulcata (Huddle) (23) 

Pseudopolygnathus dentilineata Branson (25) 

GnatJwdus n. sp. (13) 

Polygnathus inomata Branson (5)
B52 OOOSTTRIBUTION'SI TO GENEtEAL GEOLOGY

Polygnathus communis Branson and Mehl (218)

Spathognathodus aculeatus (Branson and Mehl) (61)

$. stabilis (Branson and Mehl) (24)

n. gen., n. sp. Rhodes, Austin, and Druce (1967, pi. 2, figs. 8-11)

The second sample (WG-20), which is from 2-6 inches below sample WG-1, contains virtually the same fauna including Siphonodella 

sulcata and Gnathodus n. sp., but it also has another species of 

Gnathodus comparable to Gnathodus n. sp. B of Collinson, Scott, and 

Rexroad (1962, chart 3). The third sample (WG-22), from 5-6 inches 

above sample WG-1, contains S. sulcata and the same Gnathodus n. 

sp. as sample WG-1.

The next to the oldest conodont faunas found in the upper tongue 

are assigned to the SipJionodella sandbergi-S. duplicata Zone. At 

Horse Creek and Warm Spring Canyon the basal lag deposit of this 

tongue contains conodont faunas that definitely are younger than 

faunas of the S. sulcata Zone at Windy Gap but probably are slightly 

older than the faunas assigned to the S. sandbergi^S. duplicata Zone 

at other localities.

The following fauna, which is considered to represent an older 

part of the SipJionodella sandbergi-S. duplicata Zone, was obtained 

from sample HC-7F of a y2 -foot-thick highly glauconitic and phosphatic lag deposit at the base of the tongue at Horse Creek in the 

Washakie Range. The locality, which is only 5 miles northwest of 

the Windy Gap locality, is at an elevation of 7,660 feet in an abandoned quarry just, south of the Horse Creek road in the SW^SE^ 

SW*4 sec. 19, T. 43 N., R, 106 W., Fremont County, Wyo., in the 

Ramshorn Peak 71/£-minute quadrangle.

SipJionodella duplicata (Branson and Mehl) (25)

S. sulcata (Huddle) (1)

S. cooperi Hass (1)

S. obsoleta Hass (1)

Pseudopolygnathus dentilineata Branson (10)

P. prima Branson and Mehl (1)

Polygnathus communis Branson and Mehl (14)

P. inomata Branson (7)

P. symmetrica Branson (1)

P. longipostica Branson and Mehl (3)

Spathognathodus aculeatus (Branson and Mehl) (14)

Elictognathus lacerata (Branson and Mehl) (2)

From a cut of the same sample (HC-7F) from Horse Creek, J. W. 

Huddle (written commun., 1964) obtained and identified approximately the same fauna and also one specimen of Gnathodus sp.
COTTOJSTWOOD CANTON MEMBER, MADISON LIMEISfTONE' B53

The following poorly preserved fauna, which is tentatively considered to represent an older part of the Siphonodella sandbergi^S. 

duplicata Zone, was obtained from sample WS-1F of a 2-inch-thick 

lag deposit at the base of the tongue at Warm Spring Canyon in the 

Wind River Range. The locality, which is about 11 miles southwest 

of the Horse Creek locality, is just above creek level at an elevation 

of about 7,350 feet in the Sy2SW^SW% sec. 31, T. 42 K, R. 107 W., 

Fremont County, Wyo., on the west edge of the Dubois 7%-minute 

quadrangle.

Siphonodella duplicata (Branson and Mehl) (1)

SipJionodella sp. undet. (9)

Pseudopolygnathus dentilineata Branson (1)

Polygnathus communis Branson and Mehl (1)

P. symmetrica Branson (1)

P. longipostica Branson and Mehl (1)

Spathognathodus aculeatus (Branson and Mehl) (3)

From a cut of the same sample (WS-1F) from Warm Spring Canyon, J. W. Huddle (written commun., 1964) obtained and identified 

the following fragmentary conodonts, which he stated do not appear 

to be waterworn like the bulk of the specimens:

Siphonodella s$. (4)

Pseudopolygnathus primal Branson and Mehl (2) 

Polygnathus communis Branson and Mehl (5) 

Polygnathusinornata'l Branson (8)

The upper tongue of the Cottonwood Canyon Member at most other 

localities yielded conodont faunas that are assigned to the Siphonodella 

sandbergi^S. duplicata Zone and are considered to represent the upper 

part of this zone. These faunas are very similar, as shown in table 2, 

which lists the major faunal constituents from one locality in Montana 

and five localities in Wyoming. The fauna at Baker Mountain was 

collected from the previously mentioned basal lag sandstone (fig. 4, 

col. 2) at an elevation of about 5,680 feet on the east end of Baker 

Mountain about 500 feet above the Boulder River road in the N% 

SW14NW1/4 sec. 35, T. 3 S., R. 12 E., Sweetgrass County, Mont., in 

the McLeod Basin 7%-minute quadrangle. The fauna listed for Shoshone Canyon, Wyo., was collected from the base of the upper tongue 

(fig. 4, col. 5) at an outcrop just above river level on the north bank of 

the Shoshone River about half a mile east of the location described for 

the fauna from the lower tongue at Shoshone Canyon. This upper 

tongue fauna also is present but is not as abundant at the location described for the lower tongue fauna. The fauna from the upper tongue
B54 CKJNTRIBUTIONiSI TO GSENEiKAL GEOLOGY

at Cottonwood Canyon, Wyo., was collected from unit 5 of the type 

section of the member (fig. 4, col. 6; fig. 5). The fauna at South Fork 

Rock Creek was collected from the basal lag deposit of the upper 

tongue (fig. 4, col. 7) about 300 feet above the creek on its north side. 

The locality is in the NW^SW^ sec. 25, T. 52 N., R. 84 W., Johnson 

County, Wyo., on the Sheridan 1:250,000 Army Map Service sheet 

NL 13-10. The fauna listed for North Crazy Woman Canyon was collected from the basal lag deposit of the upper tongue about 30 feet 

above a dirt road on the north side of the canyon. The locality is in the 

NE%NW^SEi4 sec. 28, T. 49 N., R. 83 W., Johnson County, Wyo., 

as located on a geologic map of the Crazy Woman Creek area (Hose, 

1955, pi. 6). The fauna from the upper part of the S. sandbergi-S. 

duplicata Zone at Windy Gap, Wyo., was obtained from sample WG-2, 

which was collected from the middle of the upper tongue and 0.3 to 

0.7 foot above the highest bed containing the S. sulcata Zone at the 

same location.

TABLE 2. Representative conodont collections from the upper part of the Siphonodella sandbergi-Siphonodella duplicata Zone (upper cu/) in the upper tongue 

of the Cottonwood Canyon Member in Montana and Wyoming

[Shows number of identified specimens of indigenous (unreworked) conodonts that occur at more than one

locality]

Conodonts

Siphonodella sandbergi __

S. duplicata...- ____

S. obsoleta--- _ _ _ _

S. quadruplicata

Pseudopolygnathus

Polygnathus communis- _ . 

P. symmetrica __._ ___

P. inornata. ____

P. longipostica--. ______

Spathognathodus stabilis..

S. aculeatus _ _ ^ __

Eliriognathus bialata. ___

E. lacerata...

Baker 

Mountain 

(fig. 4, 

col. 2)

6

5

17

8

7

^4.

9 

1

17

2

2

4

2

Shoshone 

Canyon 

(fig. 4, 

col. 5)

6

12

6

32

18 

1

9

1

3

Cottonwood 

Canyon 

(fig. 4, 

col. 6)

4

1

3

1

1

6 

3

3

3

1

1

3

South Fork 

Rock 

Creek 

(fig. 4, 

col. 7)

9

9

8

14

7

7 

4

71

6

4

2

1

North 

Crazy 

Woman 

Canyon

1

2

1

5

1 

5

24

4

1

2

2

Windy 

Gap

10

6

26

9

36

29

10

77

19

2

31

1

3

1

The following fauna, which also is assigned to the upper part of the 

Siphonodella sandbergi-S. duplicata Zone, was found within the upper 

tongue and 2.1-2.3 feet above the basal lag deposit (sample HC-7F) 

that contains the lower part of this zone at Horse Creek, Wyo.

/Siphonodella sandbergi JOapper (10) 

S. cooperiUsiSS (5)
CGTTONWOOD CANTON MEMBEE, MADISON LIMESfTONE1 B55

/S. obsoletaH&ss (1)

Polygnathus communis Branson and Mehl (4)

P. inornata Branson (3)

P. longipostica Branson and Mehl (10)

Elictognathus bialata (Branson and Mehl) (3)

Dinodus leptus Cooper (2)

The following fauna, which is similar to those listed in table 2 

and, hence, is also assigned to the upper part of the /Siphonodella sandberg-/S. duplicata Zone, was identified by J. W. Huddle (written 

commun., 1965). It was obtained from sample SH-3 of the upper 

tongue at a section measured by Sandberg (1967) at Shell Canyon 

(fig. 1), on the west side of the Bighorn Mountains. The locality 

(USGS 22243-PC) is at an elevation of about 4,760 feet on the north 

side of the canyon, on the opposite side of Shell Creek from U.S. 

Highway 14, in the SE^SE^SW^ sec. 9 (unsurveyed), T. 53 K, R. 

90 W., Big Horn County, Wyo., in the Black Mountain 7%-minute 

quadrangle.

/Siphonodella sandbergi Klapper (31)

S. cooperi Hass (56)

S. obsoletaHass (9)

S. quadruplicata Branson and Mehl (1)

PseudopolygnatJius prima Branson (7)

Polygnathus communis Branson and Mehl (10)

P. symmetrica Branson (20)

P. inornata Branson (170)

*P. aff. P. scobiniformis Branson (15)

*Spathognathodus costatus Branson (11)

*S. spp. (many fragments) 

Elictognathus bialata (Branson and Mehl) (2) 

E. lacerata (Branson and Mehl) (2) 

Dinodus fragosus Branson (4)

At some localities in Montana, the upper tongue of the Cottonwood 

Canyon Member contains well-preserved conodont faunas that arc 

younger than any found in the tongue in Wyoming and as young as 

any found in the basal carbonate beds of the Lodgepole Limestone. 

These faunas are asigned to the Lower /Siphonodella crenulata Zone 

(lower cwlla), which indicates an Early Mississippian (Kinderhook) 

age.

The fauna in the following list was collected 5-9 inches above the 

base of the upper tongue at Meridian Ridge. It is the lower of two 

collections from the tongue dated as culla (fig. 4, col. 3). The other 

collection, from 5.2-5.5 feet above the base of the tongue, does not 

contain as many conodont specimens but is similar in composition.
B56 OONTRIBUnONSl TO GENEiRAL GEiOL'OGY

The locality is at an elevation of about 9,000 feet on the south side of 

the ridge that extends westward from Meridian Peak and forms the 

narrow divide between Pebble and Soda Butte Creeks about 1 mile 

northwest of the Northeast Entrance in Yellowstone National Park, 

in the Ny2SW% sec. 29, T. 9 S., R. 14 E. (unsurveyed), in the Cutoff 

Mountain 15-minute quadrangle, Mont.

Siphonodellacrenulata (Cooper) (11)

8. cooperi Hass (55)

S. obsoletaH&ss (23)

S. quadruplicata (Branson and Mehl) (44)

Pseudopolygnathus marginata (Branson and Mehl) (19)

P. dentilineata Branson (2)

Polygnathus communis Branson and Mehl (18)

P. symmetrica Branson (5)

P. inornata Branson (30)

P. longipostica Branson and Mehl (9)

*P. semicostata Branson and Mehl (1) 

Spathognathodus stabUis (Branson and Mehl) (71) 

S.aculeatus (Branson and Mehl) (1) 

S. crassidentatus (Branson and Mehl) (1) 

Elictognathuslacerata (Branson and Mehl) (48)

*Palmatolepis rugosa subsp. undet. (6)

At Bandbox Mountain a y2 -inch-thick lag deposit, which may be 

related to the upper tongue of the Cottonwood Canyon Member, at the 

base of the Lodgepole Limestone yielded the following fauna, which 

also is assigned to the Lower Siphonodella crenulata Zone (lower 

cwlla). The location of this collection is identical with that previously 

given for the collection from the Sappington Member of the Three 

Forks Formation at Bandbox Mountain.

Siphonodella crenulata (Cooper) (2)

S. cooperi Hass (2)

8. obsoletaHass (1)

Pseudopolygnathus prima Branson and Mehl (1)

Polygnathus inornata Branson (1)

P. longipostica Branson and Mehl (1)

The following sparse poorly preserved fauna, which could not 

definitely be assigned to either the Siphonodella sandbergi-S. duplicata 

or Lower S. crenulata Zone, was collected from the upper tongue of the 

Oottonwood Canyon Member at Peak 9559, Mont., near the location 

described for the collection from the Trident Member of the Three 

Forks Formation there. In the absence of species that are diagnostic 

of only one of these zones, the fauna is dated as cul-Tla. (fig. 4, col. 1).
CJOTTONWOOD ANYON MEMBE.B, MADISON LIMESTONE B57

Siphonodella obsoleta Hass (1)

8. sp. undet. (5)

Polygnathus sp. undet. (1)

/Spathognathodus sp. widet,. (1)

Elictognathus lacerata (Branson and Mehl) (1)

MADISON LIMESTONE

The lower 10-25 feet of carbonate rocks in the undifferentiated part 

of the Madison Limestone (or Group) in areas of Wyoming where the 

Lodgepole Limestone is not recognized yielded conodont faunas assignable to two and possibly three conodont zones. Faunas assignable 

to the Lower Spathognathodus costatus Zone (upper toV) were found 

at Dinwoody Canyon and Windy Gap. Faunas assignable to the 

/Siphonodella sandbergi-8. duplicata Zone (upper cul) were found at 

Clarks Fork Canyon and Windy Gap. Faunas assignable to either the 

S. sandbergi-S. duplicata or the Lower 8. crenulata Zone (upper cullower culla) were found at Bull Lake, Cottonwood, and Little 

Tongue Canyons.

The oldest of these conodont faunas, that of the Lower SpatJiognathodus costatus Zone, which is indicative of a very late Devonian (upper 

foV) age, is best displayed by five collections from the lower 16 feet 

of the Madison Limestone at Dinwoody Canyon. The location of these 

collections is identical with that given for the collection from the lower 

tongue of the Cottonwood Canyon Member at Dinwoody Canyon. As 

the intermediate three collections contain the same conodont species, 

only the representative faunas from the lowest and highest collections 

are listed.

The following very late Devonian (upper to"V) fauna was obtained 

from the basal 4 feet of the undifferentiated lower part of the Madison 

Limestone, which overlies the Cottonwood Canyon Member, at Dinwoody Canyon.

Icriodus costatus (Thomas) (2) 

Polygnathus delicatula Ulrich and Bassler (5) 

P. obliquicostataZi&gler (18) 

P. com/munis Branson and Mehl (14) 

Spathognathodus praelongus Cooper (1) 

8. stabilis (Branson and Mehl) (3) 

Apatognathus varians Branson and Mehl (15)

The very late Devonian (upper toV) fauna in the following list was 

obtained from sample DW-13 collected by the senior author and J. F. 

Murphy 12-16 feet above the base of the undifferentiated lower part of 

the Madison Limestone at Dinwoody Canyon.
B58 CONTRIBUTIONS TO GENEiEAL GEOLOGY

Icriodus costatus (Thomas) (3)

Polygnathus delicatula Ulrich and Bossier (4)

P. obliguicostataZtiegl&r (4)

P. communis Branson and Mehl (3)

SpathognatJiodus aculeatus (Branson and Mehl) (1)

8. stabilis (Branson and Mehl) (1)

ApatognatJius varians Branson and Mehl (3)

As the Madison Limestone has long been regarded as entirely Mississippian in Wyoming, cuts of all five samples from Dinwoody Canyon 

were submitted to J. W. Huddle, whose identifications and age determinations closely match those of the authors. Only Huddle's f aunal 

list from the highest sample (DW-13) is presented here, because its 

determination as Late Devonian precludes a Mississippian age for the 

four lower samples.

The following fauna was obtained and identified by J. W. Huddle 

(written commun., 1965) from sample DW-13 of the Madison Limestone at Dinwoody Canyon (USGS loc. 7574-SD).

Icriodus costatus (Thomas) (4)

Pabnatolepis sp. (fragment)

Polygnathus obUquicostataZisgl&r (5, small)

P. sp. (3)

Spathognathodus costatus Branson (3)

8. aculeatus (Branson and Mehl) (2)

In reference to this fauna, Huddle wrote:

The presence of Icriodus and P. obliquicostata indicates a Late Devonian age 

for this collection. 8. costatus and S. aculeatus occur in Upper Devonian and 

Lower Mississippian rocks. If the Devonian forms are reworked (they do not 

look reworked but they could be), the fauna could be as young as Kinderhook 

and equivalent to faunas of the Hannibal or Chouteau Formation of the 

Mississippi Valley. I prefer a Late Devonian age (upper toy, Lower Spathognathodus costatus Zone) for this collection.

The following conodont fauna, which is assigned to the SipJionodella 

sandbergi-S. duplicata Zone, was obtained from a sample of the 

basal 1 inch of the undifferentiated part of the Madison Limestone 

that directly overlies the Cottonwood Canyon Member at the Clarks 

Fork Canyon, Wyo., reference section (fig. 4, col. 4).

SipJionodella sandbergi Klapper (4)

S. cooperiHass (3)

Pseudopotygnathus dentilineata Branson (1)

Polygnathus comrwmis Branson and Mehl (1)

P. inornata Branson (5)

P. longipostica Branson and Mehl (1)
OQTTONWOOD CANTON MEMBER, MADISON LIME.STONE' B59

The conodont fauna in the following list was obtained 19-22 feet 

above the base of the undifferentiated Madison Limestone and directly 

above the upper tongue of the Cottonwood Canyon Member at Windy 

Gap, Wyo. It is assigned to the Siphonodella sandbergi-S. duplicata 

Zone, although it may represent a very high part of that zone and 

possibly even the boundary with the overlying Lower S. crenulata 

Zone. Most of the conodonts listed are characteristic of the 8. sandbergi-S. duplicata Zone. However, SpathognatJiodus abnormis has 

not been found below the Lower Siphonodella crenulata Zone elsewhere in the report area. The fauna was collected at the same location 

as that given for the faunas from the S. sulcata Zone at Windy Gap.

Siphonodella sandbergi Klapper (3)

S. cooperi Hass (1)

S. quadruplicata (Branson and Mehl) (2)

Polygnathus comnwnis Branson and Mehl (8)

P. inornata Branson (4)

P. longipostica Branson and Mehl (4)

SpathognatJiodus abnormis (Branson and Mehl) (1)

S. crassidentatus (Branson and Mehl) (1)

Blictognathus bialata (Branson and Mehl) (1)

E. lacerata (Branson and Mehl) (2)

Dinodus leptus Cooper (1)

The following fauna was collected from the undifferentiated lower 

part of the Madison Limestone, 6 inches above the top of the Cottonwood Canyon Member, at Bull Lake Canyon. It may represent either 

the Siphonodella sandbergi-S. duplicata or Lower S. crenulata Zone. 

In the absence of conodonts that occur exclusively in either zone, the 

fauna is assigned a Kinderhook (upper mi-lower culla) age. The 

collection was made from an outcrop at an elevation of 5,900 feet just 

north of a trail at the base of the north wall of the canyon in the 

center SW^SE^ sec. 3, T. 2 N., R. 4 W., Fremont County, Wyo., 

as located on the geologic map of the Bull Lake West quadrangle 

(Murphy and Richmond, 1965).

Siphonodella sp. (1)

Polygnathus inornata Branson (2)

P. sp. (8)

Spathognathodus crassidentatus (Branson and Mehl) (2)

S.stabilis (Branson and Mehl) (1)

The following fauna was collected from unit 7 in the undifferentiated lower part of the Madison Limestone 5.1-5.6 feet above the 

top of the Cottonwood Canyon Member at its type section. This fauna 

also is assigned a Kinderhook (upper cwl-lower cutta) age.
B60 CONTRIBUTIONS TO GENEiRAL GEOLOGY

Siphonodella obsoletaTLas& (16)

/S. quadruplicata (Branson and Mehl) (2)

Polygnathus communis Branson and Mehl (3)

P. inomata Branson (7)

P. longipostica Branson and Mehl (1)

P. symmetrical Branson (3)

Spathognathodus crassidentatus (Branson and Mehl) (2)

S. stabilis (Branson and Mehl) (1)

Elictognathus lacerata (Branson and Mehl) (1)

The following conodont fauna from Little Tongue Canyon (USGS 

loc. 22163-PC) was identified by J. W. Huddle (written commun. to 

W. J. Sando, April 19, 1966) from a sample of the undifferentiated 

lower part of the Madison Limestone, 5.6-6.6 feet above the top of the 

Cottoiiwood Canyon Member, collected by W. J. Sando. The authors 

consider this fauna to be comparable with that from the Madison at 

Cottonwood Canyon, 36 miles to the west, and to likewise represent 

a Kinderhook (upper ewl-lower cuTIa) age. The locality is in a roadcut on the north side of U.S. Highway 14 in sec. 27, T. 56 N., E. 87 W., 

Sheridan County, Wyo.

Siphonodella cooperi Hass (13)

S. obsoleta Hass (4)

Pseudopolygnatfius sp. (4)

Polygnathus communis Branson and Mehl (2)

P. inor-nata Branson (10)

P. sp. (3)

Spathognathodus stabilis (Branson and Mehl) (6)

S. sp. (2)

LODGEPOLE LIMESTONE

The basal 10 feet of bioclastic crinoidal limestone in the undifferentiated lower part of the Lodgepole Limestone in Montana and western Wyoming yielded conodont faunas assignable to only one zone, 

the Lower Siphonodella crenulata Zone. These faunas are indicative 

of an Early Mississippian (Kinderhook) age, equivalent to a part of 

the Pericyelus-Stufe (lower cuTIa) of the Lower Carboniferous of 

Europe. Faunas assigned to this zone at nine localities in Montana 

and at one locality in Wyoming were listed by Klapper (1966, table 1). 

Table 3 lists representive faunas from the Lower S. crenulata Zone at 

the three localities in Montana that are shown on the cross section 

(fig. 4, cols. 1-3) and at the recently discovered Bandbox Mountain, 

Mont., locality. The collection at Peak 9559 is from the basal 1 foot 

of the undifferentiated Lodgepole, which directly overlies the Cottonwood Canyon Member, near the location of the collection from the
OOTTONWOOD CANTON MEMBER, MADISON LIMESTONE B61

Trident Member of the Three Forks Formation there. The collection 

at Baker Mountain is from the basal 3 feet of the undifferentiated 

Lodgepole at the same location as the collection from the Cottonwood 

Canyon Member there. The collection at Meridian Ridge is from 

2.1-2.6 feet above the base of the undifferentiated Lodgepole at the 

same location as the collection from the Cottonwood Canyon Member 

there. The collection at Bandbox Mountain is from 2.0-2.3 feet above 

the i/^-inch-thick basal lag deposit of the Lodgepole or Cottonwood 

Canyon at the same location as the collection from the Sappington 

Member of the Three Forks there.

TABLE 3. Representative conodont collections from the Lower Siphonodella 

crenulata Zone (lower culla) in the basal part of the undifferentiated Lodgepole 

Limestone in Montana

Conodonts

Siphonodella crenulata.. _ - -_ ___ _

S. abnormis... . __________________

Locality

Peak 9559 

(fig. 4, 

col. 1)

35 

29 

9 

12 

10 

11 

7 

7 

6 

6 

4

5

4 

1 

1

Baker 

Mountain 

(fig. 4, 

col. 2)

7 

2

2 

2

1 

2

1

1

1

Meridian 

Ridge 

(fig. 4, 

col. 3)

4 

27 

5 

2 

1

10 

19 

2 

4 

1

1 

1 

10

Bandbox 

Mountain

4 

10 

42 

9

10 

17 

5

6 

5

5 

5

PALEOTECTONIC INTERPRETATIONS

Deposition of the Cottonwood Canyon Member of the Madison (or 

Lodgepole) Limestone was closely related to and controlled by widespread paleotectonic events that occurred during Late Devonian and 

Early Mississippian time throughout western North America. The 

interpretations presented for the Cottonwood Canyon may be applicable to related lithologically similar clastic rocks that were deposited 

penecontemporaneously in shelf areas of western Canada and the 

central United States.

In the region encompassing the southern or United States part of 

the Williston basin and Northern Rocky Mountains, the earlier move-
B62 CONTRIBUTION® TO GENERAL GEOLOGY

ments are interpreted as epeirogenic and the later movements as mildly 

orogenic. The epeirogenic movements were manifested at first by retarded subsidence of parts of shallow intracratonic basins in early 

Late Devonian (Frasnian) time, then by a gradual regression of the 

seas, followed by a short cessation of deposition on the cratonic shelf 

in late Late Devonion time. A brief but moderately widespread transgression by the Madison sea occurred locally as the orogenic movements were beginning. These later movements were manifested 

regionally by sporadic locally intense uplifts that occurred around the 

margins of the Williston basin. They began in very late Devonian 

(toV) time and culminated in earliest Mississippian time (Sandberg, 

1960, 1961, 1964). As the orogenic movements lessened, a second and 

more widespread transgression by the Madison sea began. Both the 

epeirogenic and orogenic movements in the region of the southern 

Williston basin and Northern Rocky Mountains probably are related 

to and partly contemporaneous with the more intense movements of 

the Antler orogeny 5 in regions on the west and southwest in Idaho 

and Nevada.

Late Middle Devonian seas were restricted to a northward-trending 

Cordilleran miogeosyncline on the far west and to an embayment that 

extended southeastward from the miogeosyncline in Alberta to the 

intracratonic Williston basin in North Dakota; following this restriction, early Late Devonian seas transgressed the intervening cratonic 

shelf that included most of the report area. A western sea, in which 

the Maywood Formation was cyclically deposited, transgressed eastward with minor fluctuations from the Cordilleran miogeosyncline. 

At the same time an eastern sea, in which the Souris River Formation 

was cyclically deposited, transgressed westward and southwestward 

from the Williston basin.

After the eastern and western seas had coalesced in north-central 

and central Montana, an early Late Devonian sea, in which the Jefferson Formation (or Group) was cyclically deposited, transgressed 

southward and southeastward with major fluctuations and covered 

most of the Wyoming part of the report area. Anomalously thin deposition caused by retarded subsidence marked the onset of epeirogenic 

movements related to the Antler orogeny in areas such as the ancestral 

Cedar Creek anticline and an ancestral anticline near the present 

Poplar dome in eastern Montana and the ancestral Nesson anticline 

in North Dakota (Sandberg, 1964). The maximum transgression of 

the early late Devonian sea occurred near the close of deposition of

5 The term "Antler orogeny" is here applied in a broad sense to all associated orogenic 

movements that took place during Late Devonian and Early Mississippian time, although 

in a stricter sense it might be used only for those that occurred on the east margin of the 

eugeosyncline.
OOTTONWOOD CANYON MEMBER, MADISON LIMESTONE B63

the Jefferson. The thicker lower and middle parts of the Birdbear 

Member (or Formation) represent an episode of stillstand of a widespread clear well-aerated sea.

Between early and late Late Devonian time, epeirogenic movements 

initiated a withdrawal of the sea that is indicated by restricted marine 

deposits. Anhydrite is interbedded with dolomite in the upper part of 

the Birdbear Member (or Formation), and a moderately thick 

evaporitic sequence makes up the overlying Logan Gulch Member of 

the Three Forks Formation. This regression was ended in the middle 

of late Late Devonian time by a transgression during which limestone 

and shale of the Trident Member of the Three Forks Formation were 

deposited. The oldest conodont fauna (Famennian, £0111-1V) recovered during the present investigation comes from the highest beds 

of the Trident, directly below a disconformity at the base of the Sappington Member.

Following deposition of the Trident Member, many local uplifts 

began sporadically around the margins of the Williston basin and in 

northwestern, central, and southwestern Montana and west-central 

Wyoming. In southwestern Montana, an erosion surface of low relief 

formed on the Trident (Sandberg, 1965, p. 15). Elsewhere in Montana and Wyoming, the Trident was deeply eroded or completely 

truncated.

As erosion diminished, the Sappington Member was deposited disconformably on the Trident Member in southwestern Montana. Although the Sappington is largely regressive, its deposition began with a 

brief marine transgression represented by its basal black shale, which 

contains very thin interbeds of lag sandstone. Conodonts from this 

lag sandstone positively date the lower part of the Sappington as 

very late Devonian (lower toV) Like the lower part of the Sappington, the lower parts of the Exshaw Formation in northwestern Montana and of the Bakken Formation in northeastern Montana and 

North Dakota were deposited penecontemporaneously in shallow 

basins interspersed among the areas of uplift during episodes of lessened orogenic activity.

While the Sappington Member was being deposited in an isolated 

regressive sea in southwestern Montana, the first moderately widespread advance by a Madison sea began in western Wyoming. Conodont faunas recovered from lag deposits at the base of the lower 

tongue of the Cottonwood Canyon Member date the start of this 

transgression as very late Devonian (upper toV), and recently discovered conodont faunas, on which work is still in progress, suggest 

that the transgression continued into the latest Devonian (toVI).
B64 CONTRIBUTIONS TO GENEiRAL GEOLOGY

At least three embayments probably extended eastward from the 

Cordilleran miogeosyncline into Wyoming during the first transgression of the Madison sea. Evidence for their exact delineation was 

largely destroyed, however, by ensuing erosion and by reworking 

during a second transgression. Two of the embayments are roughly 

located in figure 1 as eastward-projecting lobes of the 5- and 10-foot 

isopachs of the Cottonwood Canyon Member in the Bighorn Mountains. Remnants of deposits in the northernmost embayment are shown 

in cross section (fig. 4). The other embayment probably extended 

eastward in west-central Wyoming through the area between Bull 

Lake Canyon and Windy Gap. This embayment is not indicated by 

the isopachs in figure 1 because only its basal clastic deposits are assigned to the Cottonwood Canyon. The upper deposits within this 

southern embayment were slightly silty to nonsilty carbonate rocks 

assigned to the undifferentiated lower part of the Madison Limestone, 

which yields a very late Devonian (upper toV) conodont fauna at 

Dinwoody Canyon and Windy Gap. Possibly latest Devonian (toVI) 

conodont faunas from beds in the lower part of the Madison in the 

Bighorn Mountains and Wind Eiver Range are currently being 

investigated.

The more intense of the moderate movements associated with the 

Antler orogeny in the southern Williston basin and Northern Rocky 

Mountains occurred in a rather brief episode of earliest Mississippian 

time, following deposition of the lower tongue of the Cottonwood 

Canyon Member. Significantly, conodont faunas assignable to the 

earliest Mississippian Sipkonodella sulcata (lower cul) Zone, when 

these movements were maximal, have been recognized in the report 

area only at Windy Gap. Elsewhere in Wyoming a hiatus representing earliest Mississippian (lower cul) as well as possibly part of latest 

Devonian (toVI) time is present in the lower part of the Madison 

Limestone or between the lower and upper tongues of the Cottonwood 

Canyon Member, as at its type section.

During the earliest Mississippian erogenic episode, the ancestral 

Central Montana uplift, an area 215 miles long from east to west and 

75 miles wide, was elevated. Accompanying erosion removed as much 

as 300 feet of Upper Devonian rocks and locally, near the center of the 

uplift., truncated Devonian and Ordovician rocks and cut into Cambrian rocks. The area where pre-Devonian rocks directly underlie the 

upper tongue of the Cottonwood Canyon Member is shown in figure 

2. In eastern Montana, east of the report area, the 125-mile-long northwest-plunging ancestral Cedar Creek anticline was uplifted, and its 

steep west flank was reversed faulted (Sandberg, 1961). Accompanying erosion stripped as much as 750 feet of Devonian and Silurian
(XHTONWOOD CANiYON MEMBEH, MADISON LIMESfTONE B65

rocks from domes along the crest of this ancestral anticline. Minor uplifts related to these major uplifts probably took place sporadically 

throughout the region and within the report area. They are not as well 

defined because accompanying erosion only locally truncated exposed 

rock units.

While these movements were taking place, clastic sediments that 

formed the Sappington Member of the Three Forks Formation continued to be deposited in an isolated regressive sea in southwestern 

Montana. Silty sediments that formed the upper part of the Exshaw 

Formation and the medial part of the Bakken Formation were also 

laid down at about the same time in other regressive seas.

As erosion related to the orogenic episode diminished, the second 

major advance of the Madison sea began. This eastward transgression 

apparently occurred along the entire length of the Cordilleran miogeosyncline west of the report area and was not initially confined to 

embayments as was the first transgression. The basal lag deposits of 

the upper tongue of the Cottonwood Canyon Member were laid down 

on an irregular land surface, composed in the report area of earliest 

Mississippian to Late Cambrian rocks (fig. 2). The resulting unconformity is part of a major interregional unconformity that is widespread in the Western United States and Western Canada. Where 

the transgressive Madison sea engulfed the residual Sappington sea 

in southwestern Montana, however, no subaerial erosion occurred. 

There, the stratigraphic break at the base of the Cottonwood Canyon 

is inconspicuous, although generally marked by a very thin conodontbearing lag sandstone that rests on unit 5 of the Sappington Member. 

In parts of Wyoming where the lower tongue of the Cottonwood 

Canyon previously had been deposited, a disconformity resulting from 

the short episode of erosion separates the two tongues.

That the second transgression of the Madison sea took place briefly 

in Early Mississippian time is proved by the lack of zonally significant 

diachronism in the basal deposits. The upper tongue of the Cottonwood Canyon Member and the lower undifferentiated part of the 

Lodgepole Limestone almost everywhere yield conodont faunas assigned to the upper part of the Siphonodella sandbergi-S. duplicata 

(upper cul) and Lower S. crewdata, (lower culla) Zones, which together represent a short time span. Only in the Washakie Range and 

northern Wind River Range, Wyo., is there faunal evidence that the 

second transgression began, possibly as an embayment, slightly earlier 

in the Mississippian.

The geographic distribution and facies relations between the virtually synchronous bioclastic crinoidal limestone in the lower, midifferentiated part (or locally in the Paine Shale Member) of the
B66 CONTRIBUTIONS TO GENERAL GEOLOGY

Lodgepole Limestone and the shale and siltstone facies and the dolomitic facies of the upper tongue of the Cottonwood Canyon Member 

have a definite pattern that can be explained paleotectonically. Their 

succession laterally from east to west and vertically both regionally and 

at some measured sections is dolomitic facies, shale and siltstone facies, 

and bioclastic limestone facies. The dolomitic facies occupies a northtrending belt east of the shale and siltstone facies (fig. 1). On the 

west it grades and intertongues upward into the shale and siltstone 

facies. The shale and siltstone facies, which is in turn overlain by 

the bioclastic limestone facies of the Lodgepole, occupies a medial 

belt. Farther west, along the west side of the report area, the shale 

and siltstone facies apparently thins to extinction and only the bioclastic limestone facies, which contains interbeds and laminae of black 

carbonaceous shale, is present. All three facies are believed to be transgressive deposits of an eastward-advancing Madison sea, although the 

shale and siltstone facies suggests an approach to stillstand.

The dolomitic facies contains abundant rounded glauconite grains, 

well-rounded quartz sand grains, and fish bones, plates, and teeth. 

Many of the fish bones are small broken fragments that were evidently rounded by abrasion. These constituents and the rarity of 

marine invertebrate fossils, such as corals and brachiopods, suggest 

that this facies was deposited in shallow turbulent water. Consequently, and particularly in view of its eastern paleogeographic position, the dolomitic facies is interpreted to represent littoral and marginal marine deposition.

The carbonaceous dolomitic siltstone of the shale and siltstone 

facies, like the dolomitic facies to which it is gradational, contains 

glauconite grains and scattered conodont and fish remains. The siltstone, however, contains marine palynomorphs and carbonized plant 

fragments, which are uncommon in the dolomitic facies. The carbonaceous shale contains more marine palynomorphs and macerated 

plant remains but fewer conodonts and fish remains than the siltstone. Both the shale and siltstone contain nodules of limonite, probably pseudomorphous after siderite, and nodules of quartz and hematite. Limonite is more common than glauconite in the shale and siltstone facies. Open-marine invertebrate fossils are generally scarce, 

but linguloid brachiopods are present. Crinoid columnals are abundant in the siltstone, particularly farther west, and bryozoans and 

conularids have been found locally in the shale. The environment of 

deposition of the shale and siltstone facies was less aerated and agitated than that of the dolomitic facies, but the depth of the water 

probably was as shallow. The sediments and their contents indicate 

reducing conditions that suggest a slight restriction of the sea and,
OOTTONWOOD CANTON MEMBER, MAMSON LXMESfTONE? B67

hence, a lessening rate of transgression. The shale and siltstone f acies 

is interpreted to be a lagoonal or mud-flat deposit in which many of 

the plant and animal remains were partly destroyed by burrowing 

organisms, as indicated by abundant worm trails and burrows at some 

localities.

The crinoidal debris in siltstone of the shale and siltstone facies 

probably originated elsewhere, as there is no probable source in the 

environment of deposition. It probably did not come from the east 

where the sandy and silty dolomitic facies was being deposited, because crinoid fragments are relatively scarce in that facies. Hence, 

if probably came from the west.

Unconsolidated deposits related to the bioclastic limestone facies, 

which generally forms the basal 2-15 feet of the Lodgepole Limestone, may have served as the barrier that partly restricted the waters 

in which the shale and siltstone facies was laid down. These deposits 

may also have provided a source for some of the crinoidal debris 

found in siltstone of that facies. Such a barrier could have been in 

the form of discontinuous banks of crinoidal debris parallel to the 

shoreline and not much higher than 10-15 feet above the sea bottom. 

Some of these banks, in fact, may have been much higher. Biostromes 

as much as 150 feet high are recognized in the Lodgepole along the 

western limit of the shale and siltstone facies of the Cottonwood 

Canyon Member in the Big Snowy Mountains, Mont. (fig. 1). More 

detailed study in southwestern Montana and western Wyoming may 

reveal the presence of similarly high biostromes in the Lodgepole 

farther south along this same limit.

The bioclastic limestone facies contains abundant glauconite and 

open-marine invertebrate fossils and was laid down as a transgressive 

deposit in shallow well-aerated water. As the Madison sea transgressed farther eastward, the bioclastic limestone facies was deposited 

over the shale and siltstone facies. Although the bioclastic limestone 

facies has not been recognized above the dolomitic facies of the Cottonwood Canyon in central Wyoming, it is present above the Bakken 

Formation in the southern Williston basin of northeastern Montana 

and North Dakota.

As the Madison sea eventually covered the entire report area as well 

as the entire region of the Northern Rocky Mountains and southern 

Williston basin, deposition of thick beds of carbonate became widespread. The resulting Madison Group, which is as much as 2,800 

feet thick in the central Williston basin, completely buried the latest 

Devonian to earliest Mississippian ancestral structural features and 

now dwarfs the thin but paleotectonically important transgressive deposits at its base.
B68 CONTRIBUTION® TO GENERAL GEiOLOGY 

REFERENCES CITED

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Field Gonf., Aug. 1959: p. 41-49.

Andrichuk, J. M., 1955, Mississippian Madison group stratigraphy and sedimentation in Wyoming and southern Montana: Am. Assoc. Petroleum Geologists 

Bull., v. 39, no. 11, p. 2170-2210.

Balme, B. E., and Hassell, C. W., 1962, Upper Devonian spores" from the Canning 

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Benson, A. L., 1966, Devonian stratigraphy of western Wyoming and adjacent 

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Blackstone, D. L., Jr., and McGrew, P. O., 1954, New occurrence of Devonian 

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Bouckaert, J., and Ziegler, W., 1965, Conodont stratigraphy of the Famennian 

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Geol. Survey Circ. 328, 32 p., 6 charts.

Cooper, C. L., and Sloss, L. L., 1943, Conodont fauna and distribution of a Lower 

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17, no. 2, p. 168-176.

Ethington, R. L., Furnish, W. M., and Wingert, J. R., 1961, Upper Devonian 

conodonts from Bighorn Mountains, Wyoming: Jour. Paleontology, v. 35, 

no. 4, p. 759-768.

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