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GYPSUM SPRING AND “LOWER SUNDA‘NCE"
FORMATIONS, EASTERN BIG HORN
MOUNTAINS, wvomme AND MONTANA

Thesis for “an Degree of M. S.
MICHEGAN STATE UNIVERSITY

Clifford M. Nelson
1963

EAST LANb.NG, MsgmcaAN

MICHIGAN STATE UNWERSI‘I’Y

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ABSTRACT

GYPSUM SPRING AND "LOWER SUNDANCE" FORMATIONS,
EASTERN BlG HORN MOUNTAINS,
WYOMING AND MONTANA

by
Clifford M. Nelson

As exposed in the eastern Big Horn Mountains, the Middle
Jurassic Gypsum Spring and Upper Jurassic "Lower Sundance"
Formations of north central and central wyoming are, respectively,
the equivalents of the Piper and Rierdon Formations of south central
Mbntana. The three regional members of the Piper and Gypsum Spring
Formations may be traced as distinct units from Montana as far south
as the town of Buffalo. A distinctive pelecypod limestone in the
middle member extends to the Little Tongue River area in Sheridan
County. Lithic and.faunal evidence indicates the members were
deposited under marginal or restricted marine conditions. The Gyp-
sum Spring Formation is believed to thin to a depositional feather-
edge south of Nayoworth against pre-Middle Jurassic rocks usually
termed "Popo Agie." As this sequence has not been definitely
identified, stratigraphic relations suggest it is a Middle Jurassic
facies equivalent.

The Rierdon and "Lower Sundance" Formations may be divided into

Clifford M. Nelson
three informal members. The formations are correlated on the occur-

rence of the Callovian oyster Gryphaea nebrascensis and unit contin-

 

uity. The upper oolitic limestone member is a significant strati-
graphic marker. The Canyon Springs Sandstone Member of the "Lower
Sundance" Formation may be traced from the subsurface of the south-
'western Black Hills region, west along the southern margin of the
Powder River Basin to exposures in the Casper area by means of
information from published outcrop and well sections. Use of the
term "Canyon Springs" north of the Casper area is questionable. A
neritic pelecypod fauna in the lower shale and.the extensive develop-
ment of oolites and associated features in the upper member indicate
that Callovian sediments were deposited in shallow to very shallow,
‘warm, normal marine waters, at times saturated with calcium carbonate.
The microfloral assemblage in the lower shale member suggests the
adjacent emergent areas were occupied by mesic lowland and.xeric up-
land floras. The distinctive fauna and sediments of the overlying
Swift and "Upper Sundance" Formations indicate the occurrence of a
major ecological-environmental change during the Late Callov1an and

Early Oxfordian.

GYPSUM SPRlNG-AND "LOWER SUNDANCE" FORMATIONS,
EASTERN BIG HORN MOUNTAINS,

WYOMING AN D MONTANA

by

Clifford M. Nelson

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SClEI~ICE
Department of Geology

1963

ACKNOWLEDGEMENTS

The writer is grateful to the thesis director, Dr. James H.
Fisher of the Department of Geology, Michigan State University, for
the original suggestion of the problem and advice and criticisms
during the investigation. He also expresses his appreciation to
Drs. Jane E. Smith and Harold B. Stonehouse, the other members of
the guidance committee.

Dr. Ralph‘w. Imlay of the U. 8. Geological Survey identified
the megafauna, allowed the use of a published section in the paper,
and commented on the application of nomenclature in the study area.
Bernard Shaffer, graduate student in the Department of Geology,
Michigan State university, identified the microfloral assemblage.

The Casper Division of Tenneco Oil Co. provided the writer
with outcrOp samples of the Canyon Springs Sandstone Member. Mc-
Dermott Oil Co. (Ash Creek) furnished collecting supplies. Dr.
Frederick W. Cropp, Director, University of Illinois Geology Field
Camp, allowed the writer to secure room and board at the camp in
Sheridan.

Owen E. Homeister critically reviewed the manuscript. Nessrs.
William R. Miller, James Olmstead, and.Norman E.'Wingard rendered
advice and assistance during portions of the laboratory phase of the

investigation.

-11-

TABLE OF CONTENTS

ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . ii
LIST OF TABLES . . . . . . . . . . . . . . . . iv
LIST OF FIGURES . . . . . . . . . . . . . . . . v
LIST OF PLATES . . . . . . . . . . . . . . . . vi

DITRODUCTION O O O O O O O O O O O O O O O O O 1

Purpose and Scope . . . . . . . . . . . . . 1
Previous Werk . . . . . . . . . . . . . . . 2
Location and Nature of Area . . . . . . . . . . 6
Field Procedure . . . . . . . . . . . . . . 7

STMTIQMI‘IY O 0 O O O O O O O O O O O O O O O 12

General Section . . . . . . . . . . . . . . l2
Chugwater Formation . . . . . . . . . . . . . l2
Piper-Gypsum Spring Interval . . . . . . . . . 1h
Rierdon-"Lower Sundance" Interval . . . . . . . . 25

(mm STRUCTURE . . . . . . . . . . . . . . . b7
SEDII-IE‘ITATION . . . . . . . . . . . . . . . .. 119

Laboratory Procedure . . . . . . . . . . . . E9

Provenance . . . . . . . . . . . . . . . . 50
GEOLOGIC HISTORY . . . . . . . . . . . . . . . 57
SUr~u~mRr AND CONCLUSIONS . . . . . . . . . . . . . 6h
SUGCESTIONS FOR FURTHER STUDY . . . . . . . . . . . 68
SELECTED RWERENCES . . . . . . . . . . . . . . 69

APPENDIX 0 o o o o o o o o o o o o o o o o o 81

Table

 

l.

2.

3.

LIST OF TABLES

 

Page
Thickness in feet of marine Jurassic formations,
eastern Big Horn Mountains, wyoming and Montana . . . . 17
Carbonate percentages . . . . . . . . . . . . . . . . . 52
Size analysis; middle sandstone member, Rierdon-
"Lower Sundance" interval 0 o o o o o o o o o o o o o 0 5h
Quartiles and coefficient of sorting; middle sandstone
member, Rierdon-"Lower Sundance" interval . . . . . . . 55
Heavy mineral analysis; middle sandstone member,
Rierdon-"Lower Sundance" interval . . . . . . . . . . . 56

-iv-

Figure
l.
2.
3.
h.
S. A.
B.
6. A.
B.
7. A.
B.
8. A.
B.
9. A.
B.
10. A.
B.
11.

Locationcfarea.000000000000co

History of marine Jurassic norenclature, eastern Big

Hornl"10mltains o o o o o o o o o 0

Correlation of marine Jurassic formations . .

Correlation of Canyon Springs? Sandstone Member, southern

meder R3378]? 138.3111 0 o o o o o o o

Triassic and marine Jurassic formations east of Red
GUlChcreek0.000000000000000

Gypsum Sprinngormation, "B" Member limestones north
OfColumbusCreek..............

Triassic and.marine Jurassic formations at Rapid Creek .

Triassic and marine Jurassic formations north of Little
Goose Creek . . . . . . . . . . . . . . . . . . . . . .

Triassic and marine Jurassic formations south of North

Fork, Crazy'Woman Creek . . . . .

Contact of Red Peak and Alcova Limestone Members south-
we S t Of Day Olly ort h . O Q O O O O O O O O O O 0

"Lower Sundance" Formation oolitic limestone member
soutl'n'IeS'b OfI‘IayOWOth. o o o o o o o o o o o o o o o o

Triassic, unnamed, and marine Jurassic formations at
Barnumoooooooooooooooooo.o

"Lower Sundance" Formation middle sandstone and oolitic

limestone members at'Willow Creek

Photomicrographs of "Lower Sundance" Formation oolitic
limestone member at South Fork, Little Poison Creek . .

Photomicrograph of “Lower Sundance" Formation oolitic
limestone member at South Fork, Little Poison Creek . .

Main Jurassic paleotectonic elements of the northern

Rocky Mountains and'Williston Basin

-v-

Page

10

ll

39

hi

hi

N2

h2

113

h3

h5

US

116

 

Plate

 

I.

Ii.

LIST OF PLATES

mplanatiOUOfPlatelooooo00000000000

Pelecypoda from the Gypsum Spring and "Lower
Sundance"FOI‘mationS.................

Correlation of Triassic and marine Jurassic

formations, eastern Big Horn Mountains, wyoming
andMontanaooooo00000000000000...

-vi-

30

Pocket

 

INTRODUCTION

Purpose and Scope

The marine Jurassic of the western Interior of the United States
has been extensively studied. This is particularly true of the
exposures in Myoming, Montana, and western South Dakota, through the
work of Cobban, Imlay, Love, J. A. Peterson, and others. Although
adjacent areas have been studied in some detail, the nature of
equivalent Jurassic rocks that crop out in the eastern Big Horn
Mountains is, by comparison, not as well known. Other than Imlay's
(1956) study of the marine Jurassic in the northern (Montana)
portion of the eastern Big Horn Mountains, no detailed surface in-
vestigations have been published. Previous work has included the
area herein discussed only as part of regional studies whose
correlations were based on sections too widely spaced for detailed
analysis of any Specific area. Jurassic rocks have also been dis-
cussed in independent studies of the general geology of specific
portions of the studied area.

The present study describes in detail the stratigraphic re—
lations of Upper Triassic and.marine Middle and Upper Jurassic
(exclusive of the Oxfordian) rocks exposed along the east flank
of the Big Horn Mountains in wyoming and Mentana. It is concerned
in particular with.the stratigraphy of the Piper-Gypsum Spring and

Rierdon-"Lower Sundance" intervals. The study attempts to show

-1-

 

 

-2-

their nature and correlation through information gained.from
measuring, sampling and.collecting fossils from eighteen surface
sections. Two published surface sections and the results of
sedimentary analyses of selected samples are also used in the in-
vestigation. Emphasis is placed on the correlation of marine
Jurassic formations in'wyoming and Montana. Underlying and over-
lying formations are considered only as they relate to contacts
with the studied intervals, form limits of the measured sections,
and represent distinct ecological-environmental changes in the area.
Details of the interval between definite Upper Triassic (Crow
Mountain Sandstone Member of the Chugwater Formation) and marine
Upper Jurassic ("Lower Sundance" Formation) rocks in the southern
part of the studied area are discussed. The massive sandstone unit
at the base of the "Lower Sundance" Formation in the Casper area

is compared to and correlated.with Canyon Springs Sandstone Member
occurrences in the southwestern Black Hills and along the southern
margin of the Powder River Basin. Areal and regional paleogeography
are discussed, based primarily on information available from pub-
lished studies and supplemented by the writer's field observations

and sedimentary analyses.

Previous‘WCrk
Previous marine Jurassic investigations are summarized in
Neeley (1937), Cobban (l9h5), Imlay (l9h7), Pipiringos (19h8),
wroble (1953), and J. A. Peterson (195ha, 1957a). Pipiringos and

wroble also include surveys of Upper Triassic and Lower Jurassic

-3-
studies in wyoming and adjacent areas. J. A. Peterson (1957a)
states that "published paleontologic information is summarized by
Imlay (19h8), Lalicker (1950), Loeblich and Tappan (1950a, b),
and.Peterson (l95ha)." He (Peterson) also includes a summary of
previous paleontological work on which current correlation is based.

Darton (l90h) applied the term "Sundance" to the marine
Jurassic exposures along the east flank of the Big Horn Mountains
in view of their similarity to the Sundance Formation of the Black
Hills. He proposed the Chugwater Formation for previously unnamed
Triassic "red bed" exposures in the area. Darton (1906, 1908)
published additional investigations on the general geology of the
Big Horn Mountains in which he expanded his work on the Triassic
and.marine Jurassic.

Although portions of eastern Myoming and Montana were included
in regional Jurassic studies in the northern Rocky Mountains after
1908 (Figure 2), no additional detailed work was available until
Imlay, and others, (l9h8) published two surface sections in the
northern part of the eastern Big Horn Mountains as a portion of a
regional study of the marine Jurassic of Mentana. Imlay used the
Ellis Group nomenclature (Sawtooth, Rierdon, and Swift Formations)
proposed by Cobban (19h5) in these sections. The term "Piper"
Formation was defined for Middle Jurassic rocks in eastern Montana
as a substitute for the term "Sawtooth", which was restricted to
equivalent exposures west of the Sweetgrass Arch in Montana.

Imlay recognized three regional members in the Piper Formation and

proposed that the type Gypsum Spring Formation of Love was equivalent

-5-
only to the basal red bed and gypsum member of the Middle Jurassic
sequences in Montana and north central Myoming.

Imlay (1952a, 1956) considers the "Gypsum Spring" Formation
of authors in the Big Horn Basin of‘Wyoming to be exactly equivalent
to the Piper Formation of south central Montana. Imlay recognized
the previously mentioned members in each formation. Love, and
others, (l9h5a), and Imlay used the terms "Lower" and "Upper Sun-
dance" Formation in'wyoming as provisional divisions of Darton's
Sundance Formation. This terminology has become accepted through
common usage. Imlay stated that they were equivalent to the Rier-
don and Swift Formations, respectively, of Montana. Imlay (1952b)
applied the Sundance Formation member nomenclature as generally
used in Black Hills (Imlay, 19h?) to exposures in the northern
part of the eastern Big Horn Mountains. However, later studies
(Imlay, l95h) revealed information which made it impractical to
continue its application in this area, and it has since been dis-
continued.

lmlay (195h, 1956) described in detail the marine Jurassic
stratigraphy of the Mentana portion of northern Big Horn MOuntains
in an investigation that also included equivalent exposures in the
adjacent Pryor Mountains and Big Horn Basin.

J. A. Peterson (l95ha) discussed the marine Upper Jurassic
formations of the eastern Big Horn Mountains as part of a study of
the marine Upper Jurassic of eastern‘wyoming. He applied the
formational nomenclature of the Ellis Group to the area, but pro-

posed that the term "Sundance" should be retained as a group name

-s.
for the Rierdon and Swift Formations in view of its historical
significance. On the basis of thickness and faunal evidence,
Peterson recognized paleogeographic features that were effective
in the area during the Middle and Upper Jurassic. His correlation
was based on five surface and two well sections. Peterson (1957a)
also included the area as a portion of a regional study of the marine
Jurassic of the northern Rocky Mountains and‘Williston Basin. He
proposed equivalency for the Jurassic formations along the eastern
flank of the Big Horn Mountains in a general correlation based on
the information from one well and four surface sections. The terms
Piper "A", "B", and "C" were applied to Imlay's members and.were
considered to be valid regional units. The Rierdon Formation was
divided into three members, also designated "A", "B", and "C". As
a result of this investigation and the previous work of lmlay, the
regional Jurassic paleogeography was more fully developed. An
excellent discussion of the paleoecology of the marine Jurassic of
the'Western Interior United States may be found in Imlay (1957a).

The Jurassic paleotectonic elements of the Powder River
Basin were discussed in detail by J. A. Peterson (1958). Al-
though he preferred the use of the Ellis Group terminology in the
area, he stated that the terms "Gypsum Spring-Piper", "'Lower
Sundance'-Rierdon", and "'Upper Sundance'-Swift" were interchange-
able.

Love (1958) correlated the basal Canyon Springs Sandstone
Member of the "Lower Sundance" Formation in the southern part of

the Powder River Basin. The writer's correlation of this member

-6-
(Figure h) from the southwestern Black Hills to Goose Egg Dome,
Section 20 of this paper, is based.mainly on Love's surface work
and.the subsurface correlations of Faulkner (1956) and M. L. Peter-
son (1956).

General subsurface correlations of Triassic and Jurassic
rocks in the western margin of the Powder River Basin have been
made by Olsen, and others, (19119), Faulkner (1956), and M. L.
Peterson (1956).

Several additional surface investigations have included the
Triassic and marine Jurassic formations as part of the general
geology of a Specific portion of the eastern Big Horn Mountains.
The more important contributors are: Thom (1935), Crow Indian
Reservation; Carlson (19h9), Red Fork, Powder River area; Oster-
wald (1950), Tongue River area; Richardson (1950), Mayoworth
region; Zakis (1950), Dayton area; Mapel (19%), Lake De Smet
area; Hose (1955), Crazy Woman Creek area; Ramzey (1955), Big
Goose Canyon area; Richards (1955), Big Horn Canyon-Hardin region;

and.woodward (1957), Deadman Butte area.

Location and Nature of Area
The outcrops studied in the present investigation are located
along the east flank of the Big Horn Mountains which trend in a
general northwest-southeast direction from southecentral Montana
to central'wyoming. Included are the counties of Sheridan, John-
son, and Natrona in Myoming, and Big Horn in Montana (Figure 1).

Detailed work was completed on samples from eighteen of the

-7-

twenty sections included in this study. The two additional sections,
numbered "1" and "20" in this paper, were measured and described
by Imlay (l95h) and'wroble (1953), reapectively. Distances between
the writer's sections range from 2.h to 16.7 miles and average 7.6
miles.

The Triassic-Jurassic exposures lie at elevations between
5000 and 5500 feet above sea level. lost of the area is readily
accessible by automobile and all of the measured sections are with-
in one mile of an access road. U. S. 87 passes across the area
in a north-south direction. Allaweather roads give access to an
improved gravel road net to the west of U. S. 87. Some of the out-

crop access routes, however, are unimproved dirt roads or trails.

Field.Procedure

Field work for this investigation was conducted in July and
August, 1962. The total interval was selected so that, where
possible, time equivalent units would.form the base and top of the
measured sections. Where present, the Alcova Limestone Member of
the Chugwater Formation forms the base of the sections. The
oolitic limestone member at the top of the "Lower Sundance"
Formation forms the upper limit of the measured sections. Eigh-
teen surface sections were measured, described, sampled.and.examined
for fossil content. Units were measured with a Brunton Pocket
Transit and a steel tape. Only lithic variations larger than one-
half foot were measured. Random samples from thick, apparently

homogeneous units were analyzed to determine vertical continuity.

 

 

 

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FIGURE I LOCATION OF AREA

-9-
Lateral continuity was traced as far as possible at each measured
section. Laboratory analyses of the samples were completed during
the academic year 1962-63. The field descriptions have been

modified and added to as a result of these analyses.

 

-IO-

 

 

 

 

 

 

 

 

 

 

  
    
   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

'Piper Fm. in south central Montana

zU=Upper redbed member, M: Middle limestone member,

L= Lower redbed and gypsum member

FIGURE 2 HISTORY OF MARINE JURASSIC NOMENCLATURE, EASTERN BIG HORN MOUNTAINS

 

 

 

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STRATIGRAPHY

General Section

The marine Middle and Upper Jurassic rocks that crOp out in
the eastern Big Horn Mountains are represented by the Piper,
Rierdon, and Swift Formations of the Ellis Group in Montana and
the Gypsum Spring, "Lower", and "Upper Sundance" Formations in
wyoming. The formations in these sequences in the two areas are
considered equivalent by Imlay (1952a, l9bh, 1956), J. A. Peterson
(l95ha, 1957a) and others. The nomenclature, therefore, may be
used interchangeably in south central Montana and north central
wyoming (Peterson, 1958). imlay'Qwritten communication, 1963)
suggests the most simple solution is to stop the usage at the
Iontana4wyoming boundary. The marine Jurassic rocks unconformably
overly the Triassic Chugwater Formation and are disconformably
overlain by the nonmarine Jurassic Morrison Formation. The marine
Jurassic exposures in adjacent areas have been dated mainly on the

basis Of their abundant ammonite fauna.

Chugwater Formation
The Triassic rocks in the eastern Big Horn Mountains comprise
the Red Peak, Alcova Limestone, and Crew MOuntain Sandstone Nembers
of the Chugwater Formation. Fisher and.Rhodes (1959) state that
"the Chugwater Formation ranges in thickness from hSO to 800 feet.
The Red Peak and.Crow Mountain Members can be distinguished where

the Alcova is present." The Alcova wedges out, apparently by

-12-

-13-
erosion, just south Of Rapid Creek (Section 10), near the town of
Big Horn, wyoming. The writer has identified the Crow Mountain
Sandstone Member north of the Alcova erosional edge. The Chugwater
Formation is unconformably overlain by rocks of the Piper-Gypsum
Spring interval.

The Red Peak Member consists of red shales and siltstones;
the lower one-half is mostly shale and forms strike valleys and
the upper part is mainly siltstone and forms a series of homoclinal
ridges and hogbacks with the uppermost portion of the member
normally a coarse-grained, thin-bedded.to massive, slabby and very
finely sandy siltstone. This member and.the overlying Crow Moun-
tain Member are considered marine sediments by some authors; others
believe them to be of terrestrial origin. No conclusive evidence
exists for either of these hypotheses. It has been dated as Lower
Triassic on the basis of position, correlation, and the occurrence
of reptile footprints in some exposures (Colbert, 1957).

The Alcova Member is a pink to light gray and purplish,
dolomitic, finely crystalline limestone. In some sections, it is
laminated, clayey and "sugary" in texture. Most exposures are
medium to thick-bedded and slabby. The Alcova ranges in thickness
from 3 to 6 feet throughout most of the study area, but is
erosionally terminated approximately 1.5 miles south of Rapid
Creek in Section 17, T. Sh N., R. 85 w. P. 1h. The writer has
traced the Alcova as far north as this location. it thickens
south Of'Willow Creek (Section 19) to 20 feet in the Casper area.

It has been dated as Upper Triassic by its marine reptile fauna.

-11.-

The Crow Mountain Sandstone Member is characteristically a red
to reddish-orange, massive, cross-bedded, silty, very fine-grained
sandstone. It forms distinctive massive, rounded cliffs. Locally
it may be a sandy, coarse-grained siltstone. It is present through-
out the eastern Big Horn Mountains and.where the Alcova Member is
present, ranges in thickness from h? to 72 feet. Where the Alcova
is absent by erosion, the Crow Mountain is recognized by its lithology,
position, and distinctive topographic expression. In the eastern
Big Horn Mountains, the Crow Mountain Member disconformably under-
lies rocks Of the Piper-Gypsum Spring interval. Regionally this
contact represents a.major erosional unconformity. Details Of the
contact are described in the discussion of the Piper-Gypsum Spring

interval.

Piper-Gypsum Spring Interval

General

The Gypsum Spring Formation was named by Love (1939) for
exposures on Red Creek approximately 18 miles southeast of Dubois,
Fremont County,'wyoming. It was originally defined by Love as the
uppermost member of the Chugwater Formation. Later, it was given
formational rank and placed in the Middle Jurassic on the basis of
its ammonite fauna (Love, and others, 19th).

Imlay (1952a) considers the type Gypsum Spring Formation in
the Wind River Basin to be equivalent only to the basal redbed and
gypsum member of the "Gypsum Spring" Formation which represents all

Middle Jurassic rocks in the Big Horn Basin. Beds equivalent to

-15-
the type Gypsum Spring in Montana are not mappable (Imlay, 1952a).
Imlay and others, (19h8) introduced the term "Piper" Formation for
Middle Jurassic rocks in eastern Montana equivalent (lmlay, 1952a,
1956: Peterson, 1957a) to the Gypsum Spring Formation of north
central and central wyoming. The Piper Formation was named for
exposures near the town of Piper in Fergus County, Montana. The
Sawtooth Formation is a western facies equivalent.

Three regional members have been recognized in the Piper-
Gypsum Spring interval on the basis of lithogenesis (Imlay, and
others,19h8). They include: a lower redbed and gypsum member, a
middle limestone member, and an upper redbed member. Peterson
(1957a) named these members Piper "A", "B", and "C", respectively.
This provisional member letter terminology has been adopted for
use in this study.

I Nordquist (1955) proposed a detailed subsurface nomenclature
for the pre-Rierdon Jurassic of northern Montana and northeastern
North Dakota. He divided the Piper Formation, from top to bottom,
into the Bowes, Firemoon Limestone and Tampico Shale Members.

He recommended the term "Nesson Formation" (Kline Limestone,
Picard, and Poe Members) be applied to the pre-Piper redbeds in
the area. J. A. Peterson (1957a) considers this terminology to be
locally valid, but states, however, that a regional application
"...restricts the Piper Formation to the upper part of what has
generally been called Piper." Peterson believes the "....Bowes'
Member is lithologically equivalent to the upper Piper redbed

member (Piper 'C'); the Firemoon, Tampico, and Kline Members are

-16-
equivalent to the Piper 'B'; and the Picard Shale and Poe Evaporite
Members are equivalent to the Piper 'A'." Imlay (written communica-
tion, 1963) does not regard as workable the application of Nordquist's

terminology to outcrops in Myoming and Mbntana.

Stratigraphy

 

The Piper-Gypsum Spring interval in the eastern Big Horn
Mountains ranges in thickness from 170 to 190 feet in the northern
part and thins southward over the Sheridan Arch and then thickens
again slightly in the Powder River Embayment. The interval is 62
feet thick at North Fork, Crazy Woman Creek. It thins to an
apparent depositional featheredge south of Mayoworth (J. A. Peterson,
1957a, 1958). The three members of the interval were traced by
the writer frcm.the Lodgegrass Creek area (Imlay, 1956) in Montana
along the east flank of the Big Horns as far south as North Sayles
Creek near the town of Buffalo,1&yoming. The members are not
definitely distinguishable south of this area. The writer ccnsiders
these units to be equivalent in the northern and central parts of
the eastern Big Horn MOuntains. Peterson (1957a) and Imlay (written
communication, 1963) state that these members are of sufficiently
wide distribution to be given formal names and type localities.
However, they suggest that nomenclature should not be applied until
more detailed correlations have been made with the type area of
the Piper Formation and adjacent areas in Montana and Myoming. In

view of the limited nature of this study, the writer did not attempt

TABLE 1. THICKNESS IN FEET OF NMRlNE JURASSIC FORMATIONS,
EASTERN BIG HORN MOUNTAINS, WYOMING AND MONTANA.

 

-17-

Rierdon or Gypsum
"Lower Sun- Spring or
dance" For- Piper
Section Location mation Formation
l Grapevine Creek, 6-63-313,
Big Horn Co., Montana 180.0 1b0.5
2 Little Big Horn River, 22-
95-33E, Big Horn 00., Mon-
tana 182.7 190.0
3 Red Gulch Creek, 23-58N-
89w, Sheridan Co., Myoming 180.5 170.0
h Columbus Creek, 18-57N-87w 78.0 186.0
6 Little Tongue River, 2h-56N-
87W' 12h.5 135.5
7 Wolf Creek, LI-SSII—Béw 50.0 161.0
8 Park Creek, 22-55N-86’I-I 33.0 99.8
9 Big Goose Creek, 35-55N-86W 28.0 117.0
10 Rapid Creek, 12-SIIN-86w h1.0 102.3
11 Little Goose Creek, 36-5hN-
85w, Sheridan Co., wyoming 1.7.0 13h.0
12 Rock Creek, 2h—52I-I-8hw,
Johnson Co., wyoming 1h.5 h6.0
13 North Sayles Creek, 6-51N-
83W' 29.0 138.0
1h North Fork, Crazy WOman
Creek, 26-h9N-83W’ h9.8 62.5
15 South Fork, Little Poison
Creek, l-hTN-83W 1h.0 79.0

-18.-

TABLE 1. (cont.)

16

17
18

19

20

South Fork, Crazy Woman Creek,

27-h6N-83W
Mayoworth, 5-th-83w

Barnum, 35-h3N-8hw, Johnson
Co., wyoming

Willow Creek, l5-hON-8EN,
Natrona Co., wyoming

Goose Egg Dome, 16-32N-8lw,
Natrona Co., wyoming

52.5
28.0

10.7

71.5

32.6

17.0

51.0

A*

* Absent, or unnamed interval is a Gypsum Spring Formation

facies equivalent.

-19-
to apply formal terminology to these units.
The Piper-Gypsum Spring interval lies unconformably on the
Crow Mountain Sandstone Member of the Chugwater Formation and is
lunconformably overlain by rocks of the Rierdcn-"Lower Sundance"
interval. A Middle Jurassic age has been well established by

Imlay (l9h5, 19h8), Love, and others, (19h5a) for this interval.

"A" Member In the eastern Big Horn Mountains, the lower member of

 

the Piper-Gypsum Spring interval consists of dark reddish-brown,
silty, calcareous shales. Most exposures are chunky to fissile
with green pods and some lenses and streaks of gypsum. In the
Pryor and western Big Horn Mountains, the member is characterized
by a basal, massive, white gypsum unit (Imlay, 1956). Massive
gypsum beds occur within the study area only at the Grapevine
Creek and South Fork, Little Poison Creek sections. Imlay (1956)
states that in the Pryor and northern Big Horn Mountains, the former
position of the massive gypsum "...is indicated only by 5-20 feet
of brecciated brownish red siltstone or limestone." The writer
noted a reddish-orange brecciated unit with a gray limestone
matrix, large angular cavities, and red shale casts, about half-
way up in the member in many of the northern sections in the
eastern Big Horn Mountains. Its occurrence may also be an indica-
tion of gypsum previously present at that position. The "A"
Member ranges in thickness from 55 to 98 feet and thins slightly
from north to south. It is not distinguishable as a unit south

of North Sayles Creek (Section 13).

-20-

"B" Member The middle member is composed of limestones and shales.
The limestones may be placed in two categories based on lithologic
character. One form is light to dark gray or grayish-green, shaly
to mediumébedded, dense, and lithographic. The other is white,
thin to medium-bedded, "chalky" to granular, and dolomitic. Clay-
sized particles and.minor amounts of chart form the major portion
of the insoluble residues of these limestones (Table 2). Most
of the limestone units weather tan and are expressed in the outcrop
as a series of relatively continuous ledges. The shale units are
dark red and shades of gray and green, calcareous, fissile and
silty in parts. The "B" Member varies in thickness from 32 to
57 feet and also thins slightly toward the south. Like the "A"
Member, it is not distinguishable south of North Sayles Creek.

Imlay (1956) recognized a distinctive lithologic unit of
"...pink to pale green shaly limestone whose surfaces are
characterized by green or greenish-yellow stains", containing

many small pelecypods (Tancredia and Isoqyprina spp.). This

 

unit occurs in the Gypsum Spring Formation in the eastern Big

Horn Basin and in the Piper Formation in south central Montana.

The writer traced the unit from the Lodgegrass Creek area in Montana
(Imlay, 1956) southward in the eastern Big Horn Mountains to the
Little Tongue River area in wyoming. The pelecypods from this

unit in the eastern Big Horn.Mountains were identified by Imlay

(written communication, 1963) as Isocypgina? sp. (Plate I, Figures
11’ 5).

 

-21-

"C" Member This member consists mostly of dark red and dark

 

reddish-brown shale. Some portions are calcareous and chunky

to fissile in texture. A white, dolomitic, cherty limestone is
present at the top of the member in some sections. The member
ranges in thickness from 1h to 81 feet in the eastern Big Horn
Mountains. This unit is also indistinguishable south of North

Sayles Creek.

Contacts

At all observed outcrops in the eastern Big Horn Mountains,
the rocks of the Piper-Gypsum Spring interval disconformably over-
lie the Chugwater Formation. There is a distinct lithologic change
across the contact from the reddish-orange, massive, cross-bedded
sandstone of the Crow Mountain Member, to the dark red shale of
the "A" Member of the Piper-Gypsum Spring interval. There is no
evidence that the disconformity is erosional. Regional studies
(Love, and others, 19h5b; Zieglar, 1956; Love, 1957; and McKee,
and others, 1959) however, have shown a major structural discor-
dance between the two intervals and this implies an erosional
disconformity in the eastern Big Horn Mountains. The Triassic
strata dip regionally to the south. The overlying Middle Jurassic
rests on increasingly younger rocks from Mississippian in northern
Montana to Lower Jurassic in central Wyoming (Schmitt, 1953; Mo-
Kee, and others, 1959).

The rocks of the Piper-Gypsum Spring interval are discon-

ffimrmably overlain by those of the Rierdon-"Lower Sundance" interval.

-22-
A sharp lithologic and faunal change occurs upward, from non-
fossiliferous, red shale or white, dolomitic limestone to
fossiliferous, green and grayish-green, fissile shale. Chert
nodules and tripolitic chert occur in the above limestone. Re-
gionally, however, the rocks of the two intervals are separated.by
an erosional unconformity (Faulkner, 1956; Imlay, 1956; McKee,
and others, 1956; and Alpha, 1958). Imlay, (1956) states that the
Gypsum.Spring Formation in the Big Horn Basin underlies an erosional
disconformity that truncates the formation "...unit by unit from

northwest to southeast."

Age and Paleontology

 

The Middle Jurassic age of the Piper-Gypsum Spring interval
has been well-established.in areas adjacent to the eastern Big
Horn MOuntains on the basis of its ammonite fauna (Imlay, 19h5,
19b7, l9h8; Love, and others, l9h5a).

Imlay, (1956) dated the Piper Formation in the Pryor Moun?
tains of western Big Horn County, Montana, on the occurrence of
the Bajocian ammonite Chondroceras (Defonticeras) sp. in the
middle member, and the middle member's extensive fauna. This fauna
is comprised chiefly of ammonites and pelecypods, which are also
found in exposures to the west associated with the ammonites
Teloceras and Chgndroceras sp. In the northern part of the eastern
Big Horn Mountains, the Piper Formation has not furnished diagnostic
fossils (Imlay, 1956). It is considered Middle Jurassic by Imlay

(1956), primarily on the basis of unit continuity. In particular,

-23-
Imlay traced the shaly, yellow-stained, pelecypod limeStone unit
in the middle member southeast from the Pryor Mountains to his
southern most section at Lodgegrass Creek near the Montana-
Wyoming boundary. The writer traced this unit, which contains

numerous specimens of Isocyprina? sp., southward from Lodgegrass

 

Creek to the Little Tongue River area in'wyoming. On the basis

of continuity and the correlation of the pelecypod limestone,

the writer considers the Piper-Gypsum Spring interval to be Middle
Jurassic in age. The writer was unable to collect diagnostic
fossils from the interval in the eastern Big Horn Mountains.

Mere definite dating will not be possible until ammonites or other
datable fossils are found. In addition to Isocyprina? sp. frOm
the "B" Member, the writer collected many specimens of a small
naticoid gastropod at North Sayles Creek, a shark's tooth, and a
few holostean fish scales at Red Gulch Creek. Selected samples
from.this interval and the underlying Chugwater Formation were
analyzed for spore and pollen content. The samples proved un-

productive.

Correlation and Facies Relations

The Piper Formation of south-central Montana and the Gypsum
Spring Formation of north central and central'wyoming are considered
equivalent (Imlay, 1956). The writer agrees with this interpretation
:for Middle Jurassic rocks exposed in the eastern Big Horn Mbuntains,
on the basis of the pelecypod unit correlation, continuity, and

similar lithology and.ccntact relations.

-28-

Rocks of the Piper-Gypsum Spring interval may be traced as
far south as Mayoworth. They are thought to thin to a depositional
featheredge between Mayoworth and Barnum. The members are also
considered to wedge out southward, with the lower member extending
the furthest south (J. A. Peterson, 1957a). Definite determination
of these relations is not possible with the available information
since the members are not distinguishable south of North Sayles
Creek.

At Barnum, the interval between definite Triassic (Crow
Mountain Sandstone Member) and Jurassic ("Lower Sundance" Formation)
rocks is composed of 1L1 feet of light to dark red, calcareous
siltstone, and subordinate dark red shale. This interval is 1h5
feet thick at'Willow Creek (Section 19) and is composed almost en-
tirely of light to dark red, calcareous siltstone. It thins toward
the south where it is 25 feet thick at Goose Egg Dome near Casper
and is represented primarily by reddish-orange and.rust-colored,
calcareous, cross-bedded sandstone, with subordinate amounts of
red shale and siltstone. To the writer's knowledge, no fossils
have been collected from this interval. As a consequence, age
determinations are difficult, and therefore, the interval has been
defined on the basis of lithology, position, and correlation from
adjacent areas. This interval, herein referred to as "unnamed",
has been termed "Popo Agie" (Faulkner, 19563'WOOdward, 19573
Eckelberg, 1958; Love, 1958; and McKee, and others, 1959) and
"Jelm" (Hares, and others, 19h6 and.Pipiringos, l9h8) in previous

investigations in the area. erble (1953) recognized both

-2§-
"Popo Agie" and "Jelm" exposures in the area south of Goose Egg
Dome.

If the rocks of the "unnamed" interval are Older than Middle
Jurassic, they may represent a facies equivalent of the Popo Agie
Member Of the Chugwater Formation. Fisher and Rhodes (1959),
however, state "...there appears to be no evidence for the re-
cognition of the Popo Agie Member in the area." Equally likely
are the possibilities that they may represent facies of the Jelm or
Nugget Formations to the south. The writer considers unlikely the
possibility that the interval represents either an upper portion
Of the Crow Mountain Sandstone Member or a lower part of the "Lower
Sundance" Formation. If these rocks are younger than Lower Jurassic,
current ideas of the Jurassic paleogeography of north central and
central wyoming suggest continuous deposition in the area during
the Middle Jurassic. The "unnamed" interval might then represent
an approximate facies equivalent of the Piper-Gypsum Spring rocks.
No conclusive evidence exists to support any of these hypotheses.
Additional field sutdy and attempts to collect diagnostic fossils
from this interval are required before a more definite determinar

tion of the age and relations of the unit in question can be made.
Rierdon-"Lower Sundance" Interval

General
The Sundance Formation was named by Darton (1899) for the
marine Jurassic rocks overlying the Triassic Spearfish Formation

and.underlying the Jurassic Morrison Formation, near the town of

-26-

Sundance, Crook County,'wyoming. Darton described.a type area, but
did not designate a type section. The formation was redefined by
lmlay (19b?) to represent only marine Upper Jurassic rocks. Imlay
divided the formation into five members from bottom to top: Canyon
Springs Sandstone, Stockade Beaver Shale, Hulett Sandstone, andLak
Member, all Callovian in age; and the Redwater Shale, Oxfordian.
Imlay designated a "standard of reference" from various localities,
as a representative type section does not exist in the area. Al-
though this terminology is very useful in the Black Hills region,

it has not been successfully applied elsewhere, as the units do

not retain their identity in the subsurface for any appreciable
distance away from the outcrops (J. A. Peterson, 1957a). Imlay
(1952b) applied the Black Hills member nomenclature to exposures

in the northern part of the eastern Big Horn Mountains (Red Gulch
Creek). Information from later studies (J. A. Peterson, 195ha;
lmlay, 1956) made its continued application in the area impractical,
and it has since been discontinued.

J. A. Peterson (l95ha) proposed that the "lower" and "upper"

provisional divisions of Imlay's Sundance Formation be formalized

as separate fermations for exposures in north central and central
'Wyoming approximately equivalent to the Rierdon and Swift formations,
respectively, of Montana. The Rierdon Formation was named by Cobban
(l9h5) for marine Callovian rocks at Rierdon Gulch, Teton County,
Ifiontana. It has since been applied to equivalent rocks throughout
IUordana (Imlay, and others, 19h8) and in some studies (J. A. Peter-

scxa, 195ha, 1957a) to portions of north central and central‘wyoming.

-27-

The Rierdon and "Lower Sundance" Formations are considered to be
equivalent units (lmlay, 19h7, 19h8, 1956; J. A. Peterson, 1957a,
1958).

J. A. Peterson (l95ha) described three informal divisions
of the Rierdon-"Lower Sundance" interval in the eastern Big Horn
Mountains. They include: "...abasal gray to greenish-gray...silty
shale;...an overlying light gray to buff massive sandstone,...and
an upper thin, oolitic,...slightly sandy...1imestone." The writer
traced these units south from imlay's (1956) Grapevine Creek section
in Montana along the eastern flank of the Big Horn Mountains.
Although the lateral and vertical relations of the shale and sand-
stone units vary to the south over the Sheridan Arch, the oolitic
limestone occurs in the same position and almost the same character
and thickness. it appears to be an time equivalent unit in each
of the measured sections. For convenience in this study, the
above informal divisions of the Rierdon-"Lower Sundance" interval
are discussed as the "lower shale member", the "middle sandstone

member", and the "upper oolitic limestone member".

Stratigrgphy

The Rierdon-"Lower Sundance" interval in the eastern Big
Horn Mountains ranges in thickness from 1b to 180 feet. Exposures
reach a maximum in the northern part of the area, thin rapidly to
xthe south over the Sheridan Arch, and thicken again in the Powder
iRiver Embayment. The rocks of the interval are provisionally

divided into three members; a lower shale, a middle sandstone, and

-28-
an oolitic limestone. These members may be traced along the east
flank of the Big Horn Mountains from south central Montana to
central'wyoming.

The Rierdon-"Lower Sundance" interval lies unconformably on
rocks of the Piper-Gypsum Spring interval and is unconformably
overlain by the Swift and "Upper Sundance" Formations. The
Callovian age of the Rierdon-"Lower Sundance" interval in Montana
andeyoming has been established primarily on the basis of its
ammonite and pelecypod fauna (Imlay, 19h7, l9h8, 1952a, 1956; Imlay,

and others, 191.8; Love, and others, 19h5a).

Lower shale member In the eastern Big Horn Mountains, the lower
member of the Rierdon-"Lower Sundance" interval consists of grayish-
green and green, thin-bedded to fissile, calcareous shale. Some

of the shales are silty or slightly sandy. The member is expressed
topographically as a relatively steep slope and is usually represented
as a covered interval, or is at best poorly exposed. In the northern
part of the study area, the member is characterized.hy numerous
specimens of the oyster, Gryphaea nebrgscensis Meek and.Hayden (Plate
I, Figures 1-3). The writer did not Observe any Specimens of this
pelecypod south of‘WOlf Creek in Sheridan County,‘Wyoming. At
‘Willow Creek, the lower shale is soft, platy and'wamy. Bernard
Shaffer (oral communication, 1963) identified specimens of gymnos-
‘permous (conifer?) bisaccate pollen, fern - like spores, other plant

rmicrofossils, and a dinoflagellate from a sample of the member at

'this location (unit 19-17).

Figs. 1 - 3
b - 5
Reference:

EXP L 331' AT I ON

Gryghaea nehrascensis Meek and Hayden from the Rierdon

 

and "Lower Sundance" Formations, eastern Big Horn
Mountains, Myoming and Montana. 1, dorsal; 2, lateral;
3, ventral; x 1.3.

Isoczprina? sp. from "B" Member, Piper and Gypsum

 

Spr ng Formations, eastern Big Horn Mountains, wyoming
and Montana. h, right and left valves, x 6.6; 5,
left valve, x 5.7.

Imlay (19h7; written communication, 1963).

-29-

PLATE I

 

-31-

The lower shale member ranges in thickness from 12 to 160
feet for most of the sections in the study area, but it 15
locally absent in three of the southern sections. it is thickest
in the northern part of the eastern Big Horn Mountains (108—160
feet). The member thins rapidly south of the Little Tongue River
area over the Sheridan Arch and into the Powder River Embayment
where it varies from 12 to hh feet in thickness. Additional field
work would be required to determine the nature and stratigraphic

relations of the member south of'Willow Creek.

Middle sandstone member The middle member is composed of tan to
yellowish-tan, medium-bedded to massive, very fine-grained,'well-
sorted, calcareous, quartzose sandstone. The majority of the ex-
posures are hard, slightly friable, and coarsely silty. Some of
the sandstone units are micaceous. Current ripple marks were Ob-
served at two Of the measured sections. The middle member usually
forms a series of ledges or a small cliff. Locally it is a poorly
exposed, very finely sandy, coarse-grained siltstone. All of the
sandstone units are well-sorted (mean 30- 1.25) and quartzose,
however some quartz grains and rounded rock and mineral fragments
as large as 1 mm. occur in the extreme southern sections.
Leucoxene, garnet, tourmaline, and hornblende comprise
the major portion of the heavy mineral suites. Pyrrhotite,
hematite, sillimanite, Sphene, magnetite, and ilmenite are pre-
sent in minor amounts. Rare occurrences of staurolite, apatite,

and corundum were observed. Quartz forms more than 95% of the

-32-
1ight mineral fraction. The remainder of the light suite is
primarily feldspar with rare glauconite.

The middle sandstone member ranges from 2 to 29 feet in
thickness in the eastern Big Horn Mbuntains. The member becomes
slightly thinner over the Sheridan Arch.

The writer collected a small number of pentagonal crinoid
columnals (Isocrinus? Sp.), pelecypod molds, cytherid? ostracodes,

coprolites and worm? casts, and a pecten-like clam (Ctenostreon? Sp.)

 

from the member at various localities in the eastern Big Horn

Mountains.

Upper oolitic limestone member The upper member of the Rierdon-

 

"Lower Sundance" interval is a prominent marker unit in the eastern
Big Horn Mountains. The member consists of an olive-gray to olive,
medium to thick-bedded, oolitic, slightly sandy limestone.

Locally the oolitic limestone is crystalline and cross-bedded. In
most exposures, it contains many pelecypod? shell fragments and some
pentagonal crinoid columnals (Isocrinus? sp.). The member forms
resistant ledges or caps ridges and cliffs. The thicknesses of

this unit range from 0.5 to 9 feet along the east flank of the

Big Horns. However, it is usually 1 to 2 feet thick in most
sections. It thickens slightly south of the Sheridan Arch area.

The writer has traced the unit southward from exposures in the
Lodgegrass Creek area in Montana to the Willow Creek area in Natrona
County,'wyoming, and considers it to be a time equivalent unit in

each of the measured sections. The limestone unit at a similar

-33-
position in the Goose Egg Dome section may possibly be an equiva-
lent unit.

In addition to the continuity and relatively uniform
thickness of the upper member, it is also characterized by its
oolitic nature. Most of the oolites are medium green and oval in
shape. Some, however, are spherical or elongate to flattened
ellipsoids. They range in size from 0.25 to 2 mm., but average
about 0.5 to 1 mm. The oolites exhibit radial and concentric
growth patterns, or both, in two or three "rings" about the nuclei
(Figures 98, 10A and B). The occurrence suggests more than one
growth stage. Nuclei consist of quartz grains, shell fragments and
colorless calcite. The matrix is composed of colorless calcite
with scattered quartz grains.

Love (l95h) and Guilinger and Theobald (1957) describe
occurrences of the uranium mineral metatyuyamunite in portions of
the oolitic limestone member in the Mayoworth area. These deposits
were not of economic importance as of 1957. The mineral replaces
calcite in oolites and in the matrix and is also found as a coating

along joints and.fracture planes. Its occurrence suggests a secon-

dary origin.

Contacts

The upper oolitic limestone member of the Rierdon-"Lower
Sundance" interval disconformably underlies the rocks of the Swift-
"Upper Sundance" interval in the eastern Big Horn Mountains. At

the outcrops, the contact is represented by a distinct change from

~3h-
an oolitic, sandy limestone to a grayish-green, glauconitic shale,
or locally, a glauconitic, massive sandstone. No physical evidence
of truncation was observed in the area. Regionally, however, the
contact is considered a major unconformity. J. A. Peterson (1957a)
states that the upper units of the Rierdon Formation in Montana
are truncated by post-Rierdon erosion northward toward the Belt
Island trend. He (Peterson) also considers the widespread sandy,
oolitic limestone at the top of the Rierdon-"Lower Sundance"
interval evidence for a submarine disconformity in the area.
Alpha (1958) considers the erosional interval as occupying most
of the Upper Callovian. '

The contact is also considered an erosional disconformity

by Imlay (1956) on the basis of regional stratigraphic and faunal
relations. He states that a distinct faunal change occurs between
the two intervals. In the Pryor Mountains and adjacent areas of
Montana and‘wyoming, rocks of the Swift and "Upper Sundance"
Formations have been dated as Oxfordian on the occurrence of

Cardioceras and Quenstedtoceras sp. The Rierdon-"Lower Sundance"

 

 

interval is characterized by Articoceras, Gowericeras and Kepplerites

 

sp. Characteristic of the fauna of the lower portion of the Rierdon-

"Lower Sundance" interval, are the large numbers of Gayphaea

 

nebrascensig. This peledypod decreases in abundance upwards in the
interval. The fauna of the Swift-"Upper Sundance" interval is

dominated by belemnites, in particular, Pachyteuthis "densus".

 

Belemnites have not been found in the lower shale of the Rierdon-

"Lower Sundance" interval and they are rare or absent in its upper

_35-

portion. SpeCimens of E. nebrascensis have not been collected from

 

the Swift-"Upper Sundance" interval. This suggests that during
the Middle and Upper Callovian, the Montanaewyoming area under-
went a slow major environmental-ecological change which is re-
flected in the Oxfordian sediments and fauna.

The writer agrees with Imlay's interpretation of the nature
of this contact for exposures in the eastern Big Horn Mountains.

Large numbers of 9. nebrascensis were collected from the lower

 

shale member of the Rierdon-"Lower Sundance" interval in the
northern part of the area. Specimens were not found above this
unit in the section, although some of the shell fragments in the
oolitic limestone member may represent occurrences of the pelecypod.
There is a complete absence of belemnites in the Rierdon-"Lower

Sundance" interval. Specimens of Pachyteuthis sp., however, are

 

common in the overlying Swift and "Upper Sundance" Formations.
The character of the sharp lithologic change, eSpecially that of
little or no glauconite to heavily glauconitic sediments, also

supports the conclusion that the contact is disconformable.

Age and Paleontology

The Callovian age of the Rierdon-"Lower Sundance" interval
has been previously established (Imlay, l9h7, 19h8, 1952a; Love,
and others, 19h5a). Imlay (1956) has dated the Rierdon Formation
in the Pryor MOuntains on the occurrence of the Lower Callovian

ammonites Kepplerites typchonis Ravn and Cadoceras mulleri Imlay

 

at the base of the formation, the abundance of Egyphaea nebrascensis

 

-36-
in the lower part of the formation in the Pryor and.horthern Big
Horn MOuntains, and the stratigraphic relations with more fossili-
ferous units in central Montana. The writer considers the Rierdon-
"Lower Sundance" interval to be Callovian in the eastern Big Horn
Mountains on the occurrence of 9. nebrascensis in the northern
sections as far south as'Wolf Creek, and the position and correla-
tion of units, in particular, the continuity of the upper oolitic
limestone member from Montana southward to Natrona County,'wyoming.

Imlay (1952a) described five Lower Callovian faunal zones
in the Rierdon Formation of Montana which are characterized from
bottom to top by the following ammonites:

(l) Articoceras codyense

(2) Gowericeras costidensum

 

(3) Gowericeras subitum

(h) Kepplerites tychonig (with Cadoceras sp.)

 

(5) Kepplerites mclearni (with Gulielmiceras sp.)

 

 

The occurrence of two distinct ostracode biofacies in the Rierdon-
"Lower Sundance" interval is described by J. A. Peterson (l95ha).
The Rierdon fauna in the Pryor Mountains contain large numbers of
pelecypods, some ammonites, gastropods, brachiopods, and bryozoans,
and a few fragmental echinoids and crinoids (Imlay, 1956).

The writer collected numerous Specimens of E" nebrascensis
from the lower shale member in the northern part of the eastern
Big Horns. The spores and pollen identified from this unit at
Willow Creek were common but poorly preserved. Definite de-

scriptions were not possible, however, it appears that the specimens

-37-
have affinities for the groups previously discussed. Selected
samples of the other members were digested and examined for micro-
floral content, however, no specimens were Observed. Pelecypod
molds, pentagonal crinoid columnals, and a few dytherid? ostracode
fragments, coprolites and worm? casts were collected from the
middle sandstone member at various localities. Specimens of the

pecten-like Ctenostreon? sp. were observed.at Red Gulch Creek.

 

Pentagonal crinoid columnals were also collected from the upper
member in addition to pelecypod? shell fragments. The crinoid
columnals collected from the sandstone and limestone members are

generally referred to as Pentacrinus sp. 0n the basis of generic

 

revisions (Springer, 1909, and others) and the similarity of these

fbrms to specimens of Isocrinus wyomingensis described by Koch

 

(1962) from the North Fork, Crazy WOman Creek area, the writer
has identified the columnals as Isocrinus? sp. No occurrences of
belemnites in the rocks of the Rierdon-"Lower Sundance" interval
were observed in the area. The writer did not observe ammonites

in the Callovian exposures in the eastern Big Horn Mbuntains.

Correlation and Facies Relations

 

The Rierdon Formation of south central Montana and the "Lower
Sundance" Formation of'wyoming are considered equivalent units
(Imlay, 19h7, 1952a, 1956; Downs, 19h8; Love, and others, 19h5a;
and J. A. Peterson, 1957a). J. A. Peterson (l95ha) proposed
equivalency for the marine Callovian units along the east flank

of the Big Horn Mountains. The writer concurs with this general

-38-

correlation, but also proposes equivalency for the members of the
Rierdon-"Lower Sundance" interval in the eastern Big Horn Mountains
north of Wolf Creek on the basis of faunal and stratigraphic rela-
tions. South of this area, equivalency is based on position and
member continuity, especially that of the upper oolitic limestone
member. Additional information is required to determine strati-
graphic relations south of'Willow Creek.

wroble (1953) and Love (1958) consider the light tan, massive,
cross-bedded, very fine-grained, calcareous sandstone at the base
of the "Lower Sundance" Formation in the'west Uasper Mountain
area (Section 20, 21) to be equivalent to the Canyon Springs
Sandstone Member of the "Lower Sundance" Formation of the Black
Hills. Love (1958) described it as the Canyon Springs? Sandstone
Member on the basis of outcrop and subsurface correlation in the
southern Powder River Basin. The writer has correlated this unit
(Figure h) from the subsurface of the southwest Black Hills along
the south margin of the Powder River Basin to the'west Casper
Mountain area, and agrees with Love's provisional identification
of the member. This correlation is based primarily on Love's
outcrop studies, the subsurface correlations of Faulkner (1956)
and.M. L. Peterson (1956), and the writer's interpretation of de-
finite Canyon Springs lithology in three wells in the southwestern
Black Hills near Edgemont, South Dakota.

Additional work is required on the sandstone units in the
"Lower Sundance" Formation between'Willow Creek and Goose Egg Dome

'before the Canyon Springs? Sandstone Member nomenclature can be

-39-

z_w<m mmZm 5030a zmuIHDOm

 

£32m.)- mzoemozqm a. moz-mdm 2923 3 2923330 e 33-..-
ZOIHPHCA¢va= Pcutl, “ n-_ “no... 3008’ I ’ 8‘38 D
31373 .34». To... :3 a: -u 38: 32.3: J... .. .- 3233 0
3.3.: £3232. -.oz 23.525.- 45.24 - a 3:: 26.- I .- 3: 0
2-2-6. ..P>oo .o .62 zap-.3) 2.23.- -_ .32. 52-33:- I .- 33225. .3
.2 ua¢ua as so:

PIOIUOOU

--
moE-am .0:

 

 

 

 

<m<mmo_z

_U on

mmmw>zoo

 

 

————_———_

ml

.keo

(zomhdz

 

 

-ho-
extended north of the Casper area. Certain problems are involved,
however, in applying the Black Hills member nomenclature in the
western Powder River Basin, that have been previously discussed.
J. A. Peterson (l95ha) states that although a basal sandstone occurs
in the "Lower Sundance" Formation in many parts of the Powder River
Basin, definite correlation of this unit with the Canyon Springs
Sandstone of the Black Hills is difficult due to the indistinct
character of the upper contact in the subsurface and that in many
outcrops, "...the unit is only one of several thin sandstone units
interbedded with shale near the base of the formation..." In
view of this and.with the small amount of information available
concerning the area between'Willow Creek and Goose Egg Dome, the
writer has not attempted to extend the term "Canyon Springs" north

of the Casper area.

 

 

 

A. Triassic and marine Jurassic formations east of Red Gulch Creek

"R o 63

 

 

B. mpsum Spring Formation "B" Member limestones north of Columbus Creek

-hl-

FIGURE 6

 

 

 

 

A. Triassic and marine Jurassic formations at Rapid Creek

APR 3 53

 

 

 

B. Triassic and.marine Jurassic formations north of Little Goose Creek

-h2-

FIGURE 7

 

 

 

A. Triassic and marine Jurassic formations south of North Fork,
Crazy Woman Creek

 

 

 

 

B. Contact of Red Peak and Alcova Limestone Members southwest of Mayoworth

-h3-

FlGURE 8

APR - 55

 

 

 

A. "Lower Sundance" Formation oolitic limestone member southwest
of Mayoworth

APR 0 63

 

 

 

.B. Triassic, unnamed, and.marine Jurassic formations at Barnum

-hh-

FIGURE 9

APR .' 53

 

A. "Lower Sundance" Formation middle sandstone and upper oolitic
limestone members at Willow Creek

 

 

 

B. Photomicrograph of "Lower Sundance" Formation oolitic limestone
member at South Fork, Little Poison Creek, thO, plain light

-hS-

Eva Q 53

 

 

 

APR . s3 "

 

 

 

B.

tion oolitic
' ' re a ha of "Lower Sundance" Forma . .
:Flgmme lgme°iggzégimbe§ra§ South Fork, Little POison Creek, thO, plain light

-b,6-

GENERAL STRUCTURE

The Big Horn Mountains are considered by Demorest (l9hl),
Eardley (1951), and others, to be an arcuate, asymmetrical,
anticlinal range, convex eastward. Bucher, and others, (l93h)
divided the range into three parts or blocks, based on varying
degrees of asymmetry and delineated by large thrust faults, the
largest of which is the Tensleep-Horn Fault Zone, which separates
the central and southern blocks. The northern and southern blocks
have steep western sides and relatively gentle eastern slopes.

The central block, which is steeper on its eastern side, has been
locally overturned. Numerous small faults occur in the sedimentary
margins of the range. They occur primarily in the center block.

Although the Triassic and marine Jurassic rocks have been
folded to varying degrees and in some places faulted, they have
not otherwise been greatly deformed. The dips on the outcrops
reflect the structural divisions of the range. The dips at the
ends of the northern and southern blocks are very gentle (0o - 100
NE), however, they increase to 20° - 30° toward the center block.
The units in these areas form homoclinal ridges or cuestas and
strike valleys. Dips in the center section are steep to very
steep (boo - 75°). Individual units, in particular the Alcova
ILimestone Member of the Chugwater Formation and the upper oolitic
limestone member of the Rierdon and "Lower Sundance" Formations,

-h7-

-hg-
form or cap hogbacks in parts of the central block.

In some parts of the eastern Big Horn Mountains the Triassic
and.marine Jurassic rocks are covered by Tertiary conglomerate
terraces. In most of the area, however, the exposures are very
cmtinuous. This is especially true of the extreme northern and
southern parts, where the rocks may be traced for miles in almost

continuous exposures.

S m) DENT AT ION
Laboratory Procedure

The samples to be analyzed were disaggregated.by hand or
crushed between boards. Fifty grams of each sample were weighed,
placed in a l:h solution of HCl, and boiled until the reaction
ceased. Additional solution was added as necessary to completely
‘dissolve the carbonate fraction. Samples were then washed, filtered,
dried, and.weighed. water or acid-soluble materials other than the
carbonates are considered to occur only in negligible quantities.
The insoluble residues were examined.with a binocular microscope.
Carbonate percentages were calculated (Table 2).

Samples of Rierdon-"Lower Sundance" sandstones were also
analyzed for size distribution and heavy mineral content. The
insoluble fractions were sifted (10 minutes in Ro-Tap) through
U. S. standard sieves with openings of 1651, 1000, 500, 250, 125,
and 62 microns. A pan was used to retain the fraction smaller than
62 microns. Amounts retained in each fraction were weighed and
weight percentage values calculated (Table 3). Phi scale intervals
were used in expressing the fractions. Cumulative curves were
plotted, the quartile values derived and coefficient of sorting
was calculated for each sample (Table h). Heavy minerals of the

+h phi fraction were separated in bromoform (sp. gr. = 2.87), and

u-hg-

-50..
their weight percentages calculated (Table 5). They were then
mounted in piperine (n = 1.68) and identified.with a petrographic
microscope. A composite sample of light minerals was also pre-
pared and examined.

A thin section was made of a sample of the Rierdon-"Lower
Sundance" oolitic limestone member from the South Fork, Little
Poison Creek area. Oolite and matrix details were examined.with
a petrographic microscope and photomicrographs prepared (Figures

98, 10A and B).

Provenance

The heavy minerals suggest an ultimate source for the
Rierdon-"Lower Sundance" middle sandstone member could have been
an igneous and metamorphic rock complex. wroble (1953) discussed
a Canyon Springs Sandstone Member suite in the Casper area some-
what similar to that of the writer's; however, he did not mention
the occurrence of metamorphic minerals. Love, in Reeside, and
others, (1957), states that the Canyon Springs Member "...resembles
both the Nugget and the Crow Mountain Sandstones and.may well have
been derived from them."

In the eastern Big Horn Mountains, the units of the middle
sandstone member are slightly coarser to the south. Rounded rock
and mineral grains as large as one millimeter in diameter occur
in the extreme southern part of the area. This may be indicative
of a southerly source. Imlay (1957a) and J. A.Peterson (l95ba)

suggest a southerly source for the Rierdon-"Lower Sundance"

-51-
sediments, based on the increased sand content in those directions.
In view of the general lack of evidence and the limited lateral
nature of the study, the writer has not speculated on the location

and type of source for the middle member sandstones.

TABLE 2. CARBOI‘IATE PERCENTAGES

A. Piper-~Gypsum Spring Interval: "B" and "C" Member Limestones.

 

 

 

 

Unit 5 Unit g Unit Z.
2-2h 76.5 (s)* 5- 6 85.7 10-12 8h.6 (0)
'22 8905 "' S 9hob “10 93.8
-21 76.6 - 8 90.3
-20 80.3 6-16 90.2 (c) - 7 8h.1
-18 85.2 -1h 77.2 - S 72.0
-16 79.9 -12 8b.? - 3 9h.3
-15 88.8 -10 87.8 - 2 92.8
-13 87.6 - 8 88.0
-11- 80.8 - 7 88.2 11-13 91.2 (TC)
-10 56.2 (CP) - 6 86.5 -11- 9h.7
- 8 930,4 " S 8909 "’ 9 9ho9
- 6 8905 - 7 Bile?
- h 8708 7.111» 91101 "' S 9605
-13 86.2
3-16 81.5 (TC) —11 81.1 12-10 92.h (0)
-12 79.7 - 9 8h.8 - 6 78.?
-11 77.2 - 7 89.5 - h 87.8
-10 81.2 - 5 91.9
- 6 92.6 - n 93.9 (C) 13-17 96.3
- 5 81.0 —13. 81.5
- u 66.8 8-11 90.0 (0) -11 88.u
- 8 9h.8 (C) - 9 90.h
h-17 82.6 (c) - 7 92.1 - 7 85.2
-15 83014 "' 6 92oh " 5 960,4
-13 85.3 - h 92.2 - h 87.2
—10 89.1
" 9 8901 9’10 7900 1’4" 5 93.1
- 7 9h.6 - 7 78.1 - h 91.1
- 5 90.3 - S 86.9
- h 95.2 15- S 7h.2
5" 8 9503 " 3 8905

* Insoluble residue in addition to particles smaller than 1/16
mm. in diameter:

(C) Chert

(CP) Clay pods

(S) Very fine-grained sand
(TC) Tripolitic Chert

-52-

TABLE 2. (Cont.)

-53-

B. Rierdon-"Lower Sundance" Interval: Middle Sandstone Member.

 

 

Isa

hh.0

35.6
25.7

h9.2

11.8
21.7

32.3
16.7
38.2
h3.S

 

Unit ‘3
1h- 8 27.8
15" 6 I450].
16- 8 80.1

"' 7 2209
17- 9 29.h
18-17 6l.h
19-20 61.5

-19 25.8
21" 2 2109

"" 1 705

C. Rierdon-"Lower Sundance" interval: Oolitic Limestone Member.

 

~—

 

Unit ‘E
2-28 9007
11-15 90.6

17-10' 90.3

TABLE 3.

Unit

 

2-26

3-20
-19

8-21

18-17

19-20
-19

21- 2
- l

*Tr:

k3

Trace;

SIZE ANALYSIS; 101301.73 SANDSTONB I~E~lBER,
RIERDQ-I—J'LGER SUNDMICE"

INTERVAL.

Weight Percent (Phi Scale)

 

:1—

< 0.005%

+2—

Tr%

0.02

0.78

0.01

0.91
1.06

3.23..
0.08

0.89
0.03

0.08

0.67
0.15

0.06
0.11
0.08
0.38
0.21
2.19

2.22
Tr

Tr
2.80

0.53
3.09

25.55
3.81

:1:
75.73

83.18
57.88

19.80

79.92
78.16

69.52
75.75
37.88
83.80
83.70
88.38

70.83
82.60

27.98
76.83

65.62
87.58

65.86
80.82

+S-+11

28.23

15.97
82.88

80.56

19.81
21.69

30.82
28.18
62.88
15.82
16.10
13.85

27.35
57.80

72.06
17.27

33.88
9.36

7.68

TABLE 8.

Unit

 

2—26

3-20
-19

8-21

5-18
-13

6-18
7-16
12-12
13-19
18- 8
15- 6
16- 8

- 7
17- 9
18-17

19-20
-19

21- 2
- 1

Arithmetic Mean

*Trask:

well-sorted sediment
1938, p. 232.)

QUARTIIES AND COHFICIENT 0F SORLL‘ING;
MIDDLE SAA'DSTOI'JE f-ECI-IBER, PIERDON-J'LCI'JER SUI‘JDANCE" INTERVAL

‘93
.078

.085
.069

.0142

.080
.078

.076
.078
.058
.082
.082
.080

.076
.056

.086
.088

.073
.088

.097
.088

.078

(Krumbein

g;
.062

.071
.088

.035

.062
.081
.068
.068
.070

.060
o 0’42

.036
.067

.055
.070

.075
.069

.059

.éofi
1.20

1.13
1.39

1.23

1.20
1.20

1.30
1.28
1.27
1.21
1.21
1.16

1.28
1.37

1.35
1.25

1.31
1.13

1.31
1.20

1.28

and Pettijohn,

TABLE 5. HEAVY MINERAL ANALYSIS; MlDDLE SANDSTONE
1121-1838, RIERDON-J'LCWER 5811012103" DJ‘I'ERVAL

Unit Heagy Minerals'weight % Light Ninerals'Weight %

 

 

2-26 0.03 99.9?
3-20 0.03 99.97
-19 0.08 99.96
8-21 0.06 99.98
5-18 0.08 99.92
-13 0.03 99.97
6-18 0.08 99.92
7-16 0.12 99.88
12-12 0.09 99.91
13-19 0.18 99.82
18- 8 0.02 99.98
15- 6 0.12 99.88
16- 8 0.12 99.88
- 7 0.02 99.98
17- 9 0.08 99.96
18-17 0.13 99.87
19-20 0.10 99.90
-19 0.08 99.96
21- 2 0.11 99.89
- 1 0.08 99.96
Arithmetic Mean 0.07 99.92

-55-

GEOLOGIC HISTORY

Several excellent studies of the depositional environment
and paleoecology of the marine Jurassic sediments of the Western
Interior United States have been made by Imlay (1952b, 1957a),

J. A. Peterson (1957a), and McKee, and others (1956). The follow-
ing discussion is based primarily on the results of these investi-
gations. In addition, supplemental information derived from the
writer's field observations and the results of the sedimentary
analyses, is used in the interpretation of Jurassic depositional
history in the eastern Big Horn Mountains.

The western interior of North America underwent four major
marine transgressions during the Jurassic. Each successive incur-
sion spread somewhat farther south and east. The first of these
transgressions occurred in the Lower Jurassic. The seas apparently
did not extend beyond the southern British Columbia-Alberta area,
as marine Lower Jurassic sediments have not been recognized in the
United States. The seas spread farther south in the Middle Jurassic
and deposited the Gypsum Spring, Piper, Sawtooth, and (lower) Twin
Creek Formations and their equivalents in the'Western Interior of
the United States. The Rierdon, "Lower Sundance", and (upper)

Twin Creek Formations were laid down during the Callovian invasion.

The-last and.most extensive transgression occurred in the Oxfordian,

-57-

-55-
when the Swift, "Upper Sundance", and Curtis--Summervi11e Forma-
tions and equivalent units were deposited.

Marine Jurassic sedimentation in the'Western Interior
United States was controlled by the position of two prominent
negative features; the Alberta and.Twin Creek Troughs (Figure 11).
The'Williston Basin was a major subsiding "low" on the shelf area
east of the main seaways. The Hardin Trough and Powder River
Embayment were minor negative-trending features on the Montana-
Wyoming Shelf. Although the positive-trending Belt Island and
Sheridan Arch were rarely, if at all, emergent, they significantly
influenced sediment distribution on the shelf by forming barriers
to current movement which resulted in the modification of water
temperature and salinity.

In the early part of the Middle Jurassic, the seas spread
from the northern Alberta Trough southward to the Twin Creek Trough
and southeastward across the Montana4wyoming Shelf. These seas
deposited three major marginal or restricted marine units. Each
successive transgression is considered to have covered less area.
This interpretation seems questionable, at least for exposures
in the eastern Big Horn Mountains, in view of the indistinct
character of the members south of North Sayles Creek. The thick—
ness, facies distribution, and faunal relations of these units
were directly related to the effectiveness of Belt Island and
the Sheridan Arch trends as circulation barriers. During the Early

and Late Middle Jurassic, these features effectively cut off major

-59-

 

 

 

 

 

 

FIGURE II MAIN PALEOTECTONIC ELEMENTS IN THE
NORTHERN ROCKY MOUNTAINS AND WILUSTON BASIN
JURASSIC

UODIFIIO AFTER PETERSON (IOGTAI

-60..

current circulation from the Alberta Trough, producing extensive
lagoonal conditions on the shelf, which yielded a wide-spread
sequence of gypsum, redbeds, dolomite and dolomitic limestone
("A" and "C" Members). Imlay (1957a) states that "the large areal
extent of the gypsum at the same stratigraphic position suggests
that it was formed nearly simultaneously in a single body of water
rather than numerous lagoons, that the depth of water was exceed-
ingly shallow and uniform throughout a large area, and that the
climate was so arid that few streams entered the area." Apparently
the degree of restriction was less during the deposition of the
upper member since it contains only minor amounts of gypsum compared
to the massive beds which occur at the base of the lower member.
The barriers were much less effective during the Middle Middle Jurassic
as evidenced by the normal marine (limestone, dolomitic limestone and
shale) sediments of the "B" Member. The prolific fauna, mainly
uppermost neritic pelecypods, is suggestive of continued shallow
water. J. A. Peterson (1957a) suggests a low-lying Paleozoic
carbonate terrane located to the west of the primary troughs as a
source for these sediments. A partial sea withdrawal near the end
of the Late Middle Jurassic created local disconformities on the
wyoming-Montana Shelf.

The Belt Island and Sheridan Arch positive trends also ex-
erted a major influence on the distribution and character of the
Lower Callovian normal marine sediments. Peterson (1958a) considers

the Sheridan Arch to have separated the distinct lithologies and

5‘

-61-
ostracode biofacies of the Hardin Trough and the Powder River
Embayment. The waters over the shelf were again shallow as evidenced
by the numerous uppermost neritic pelecypods, in particular

Ggyphaea Egbrascensis, and the associated fauna of the lower shale

 

member. Bernard Shaffer (oral communication, 1963) suggests the
spore and pollen assemblage identified in this unit represents

at least two habitats in the emergent areas adjacent to the Montana-
Wyoming Shelf. These include: lowland mesic sites which may have
supported a flora comprised of ferns and.fern allies; and, a

xeric upland.flora where the gymnOSpermous elements were possibly
conifers.

According to Peterson (1958a) the basal sandstone, usually
the result of a transgressive sea, is absent over much of the shelf
area due to the lack of a suitable source in the underlying units.
It occurs only in the southern part of the area where the Canyon
Springs Sandstone Member overlies the Nugget Sandstone, which may
be a partial source. The amount of sand increases upwards, how-
ever, in the Rierdon-"Lower Sundance" sediments, indicating increased
effectiveness of the Sheridan Arch during the Callovian. Peterson
considers that marine deposition "...was influenced by numerous
shifting minor irregularities in the sea bottom, as shown by local
variations in thickness...and by the association of lenticular
sand bodies commonly interbedded.with green to gray shales."
Southerly and easterly sources have been suggested.for the units

of the middle sandstone member.

-62-

Late in the Middle Callov1an, the Belt Island area in central
Montana was uplifted.and the seas partially withdrew from the
shelf. Where present, the waters were very shallow, as is evidenced
by the widespread deposition of the upper oolitic limestone member
of the Rierdon-"Lower Sundance" interval in areas near the submarine
swells. Peterson (1958a) considers this sandy limestone to be a
regressive clastic unit, deposited in very shallow water "...along
an offshore barrier." The extensive development of oolites and
associated features in this unit is also indicative of very shallow
water conditions and also warm waters, supersaturated.with calcium
carbonate (Imlay, 1957a; Lochman, 1957; and Pettijohn, 1957).

The relatively rapid Oxfordian transgression was the last
and most widespread of the Jurassic invasions. Somewhat deeper
waters existed over the shelf at this time. Peterson (1957a)
considers the submarine barriers to have been relatively ineffective
on the basis of faunal and lithic continuity, the abundance of
a coolerawater fauna, and the general rarity of limestones in the
Swift-"Upper Sundance" sediments.

Peterson (1957a) considers the Oxfordian sea to have been
occupied by water, cooler than those of previous Jurassic in-
cursions on the basis of the following evidence: a coolerawater
fauna, dominated by belemnites, is present in the Oxfordian sedi-
ments and not in earlier deposits; an accompanying marked decline
(or complete absence) in the occurrence of oysters, previously

extremely abundant; and, a rarity or absence of limestone units

-63-

in most of the Oxfordian sediments. The great abundance of belem-
nites indicates a significant ecological change in the Oxfordian.
In addition to a temperature indication, Imlay (1957a) considers
their large numbers suggestive of increased amounts of organic
material, as does the occurrence of driftwood in western equiva-
lents and the large quantity of glauconite in the sediments.
Since glauconite is considered to have been formed in a reducing
environment, its occurrence may also indicate increased amounts of
organic matter. In view of the evidence for increased organic
material in the Oxfordian, Imlay suggests that the abundant
belemnite population is also related to increased food supply.

During the latter part of the Upper Jurassic the seas with-
drew slowly from the western Interior United States, and the non-
marine Jurassic Morrison Formation was deposited on the Oxfordian

sediments.

SUMMARY AND CONCLUSIONS

The Piper and Rierdon Formations of south central.Montana
are, respectively, the equivalents of the Gypsum Spring and
"Lower Sundance" Formations of north central and central
Myoming, in exposures in the eastern Big Horn Mountains. The
writer bases this correlation on stratigraphic position,
correlation of lithic and faunal marker units, and the occur-
rence of a limited diagnostic fauna.

In the eastern Big Horn Mountains, the three regional
members of the Middle Jurassic Piper-Gypsum Spring interval,
herein referred to as "A", "B", and "C", were traced as distinct
units from Montana as far south as North Sayles Creek near the
town of Buffalo. In view of their indistinct character south of
this locality, the Opinion that each successively younger unit
covered less area is questionable, at least in the study area.

A distinctive pelecypod limestone unit in the "B" lember extends
southward to the Little Tongue River area. Lithic and faunal
evidence is considered by Imlay (1957a) and Peterson (1957a)

to indicate deposition of the Middle Jurassic units in restricted
("A" and "C" Members) and marginal("B" Member) marine environments,
established by the shelf submarine barriers.

The Gypsum Spring Formation is thought to thin to a deposi-

tional featheredge south of Mayoworth. This opinion is based on

~68-

-65-
the belief that rocks in an equivalent stratigraphic position
in the Barnum area are older than Middle Jurassic. This sequence,
herein referred to as "unnamed”, has not been definitely identi-
fied, however, it has been referred to in previous studies as a
facies equivalent of the Popo Agie Member of the Chugwater Forma-
tion, the Jelm Formation, and the Nugget Formation. The thickness
of the Gypsum Spring Formation at Mayoworth, its general continuity
north of the area, and current concepts of Jurassic paleogeography
suggest to the writer that the "unnamed " interval is a facies
equivalent of the Gypsum Spring Formation. No conclusive evidence
is available for either of these hypotheses.

The upper and lower contacts of the Piper-Gypsum Spring
interval are locally disconformable, but are interpreted regionally
as erosional unconformities. The Middle Jurassic age of the in-
terval has been previously established. In the eastern Big Horn
Mountains, the interval is dated on the basis of stratigraphic
relations with more fossiliferous units in Montana, as diagnostic
fossils were not found in the area.

The Rierdon and "Lower Sundance" Formations were divided
into three informal members. Correlation of these Callovian
formations in the eastern Big Horn Mountains is based on the

occurrence of Gryphaea nebrascensis in the lower shale member as

 

far south as'wolf Creek and unit continuity, in particular, that
of the oolitic limestone member. The Canyon Springs? Sandstone

{ember of the "Lower Sundance" Formation in the Casper area,

--66-

previously identified by'wroble (1953) and Love (1958), was
traced eastward by the writer, using published sections, along the
south margin of the Powder River Basin to definite occurrences
in the southwestern Black Hills. Lack of information and nomen-
clatural problems prevent the extension of the term north of the
CaSper area. The results of the writer's sedimentary analyses
suggest a southerly source for the units of the middle sandstone
member.

The Rierdon-"Lower Sundance" interval is disconformably
overlain by Oxfordian rocks in the eastern Big Horn Mountains;
regionally, this contact is also an erosional unconformity. The

interval is dated as Callovian on the occurrence of G. nebrascensis

 

and stratigraphic relations with more fossiliferous units in
Montana. The occurrence of an uppermost neritic pelecypod fauna,
and oolites and associated features, indicate the sea covering
the Montana4Wyoming Shelf during the Callovian was shallow (upper
neritic) to very shallow (littoral), warm, and at times saturated
with calcium carbonate. The Spore and pollen assemblage in the
lower shale member suggests the adjacent emergent areas contained
both mesic lowland and xeric upland floras. Variations in the
thickness of the Rierdon-"Lower Sundance" interval; the development
of a sandy, oolitic limestone at the top of the interval; and

the complete absence of oysters south of the Little Tongue River

area indicates the effectiveness of the Sheridan Ardh as a submarine

-67-
barrier during the Callovian.

The occurrence of large amounts of glauconite and a cooler-
water fauna dominated by belemnites in the Swift and "Upper Sundance"
Formations, indicates a major ecological-environmental change dur-
ing the Late Callovian and Early Oxfordian. The writer did not

study the Oxfordian sediments in detail.

SUGGESTIONS FOR FUTURE WORK

Additional field work is required in the area south of
Mayoworth to determine the stratigraphic relations of the Piper-
Gypsum Spring and "unnamed" intervals. In particular, the area
between Mayoworth and Barnum should be studied. Additional sections
between'Willow Creek and the Casper area are also required. The
study should be extended eastward by means of well information.
Additional lithic and faunal correlations of the Piper and Gypsum
Spring Formations are required in Montana and'wyoming before
formal nomenclature and type localities may be assigned to the
members of this interval.

A more accurate determination of provenance and depositional
environment of the Callovian sandstones may be gained by an in-
creased vertical and lateral sampling at the outcrops, and de-
tailed petrologic analyses.

More detailed paleontological study is required. Further
attempts should be made to collect diagnostic fossils from the
marine Jurassic exposures in the eastern Big Horn Mountains.

A microfaunal analysis of all units might prove valuable in
correlation. In view of the spore and pollen assemblage found
in the Rierdon—"Lower Sundance" lower shale, units should be
resampled palynologically and analyzed for microfloral content,
with assemblages to be used as environmental indicators and in

correlation.

-58_

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-69-

Q
F— a Q
A I
.
Q
Q ‘
O
D c .
9 a
O
a - Q - C

 

 

 

 

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-73-

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Yellowstone-Big Horn Research Assoc., Guiiebook, p. 176-177.

, and others, 1935, Geology of Big Horn County and the Crow
Indian Reservation, Montana: U. S. Geol. Survey Bull. 856, 200 p.

Towse, D. F., 195k, Jurassic System in'Williston Basin: Amer.
Assoc. Petrol. Geol. Bull., Vol. 38, p. hSh-hoa.

Trask, P. D., ed., 1955, Recent marine sediments: reprinted
by the Sec. Econ. Paleon. and.Min. Spec. Publ. b, Tulsa,
Oklahoma, 736 p.

‘Walton, P. T., 19h6, Ellis, Amsden and Big Snowy Group, Judith
Basin, Montana: Amer. Assoc. Petrol. Geol. Bull., Vol.
30, p. 129h-l305.

Weitz, J. L. and Love, J. D., 1952, Geologic map of southern
Big Horn Basin, Myoming: ‘Myoming Geol. Assoc., Seventh
Ann. Field Conf., insert.

and Harbison, S. A., 195h, Geologic map of Natrona County,
'Myoming: wyoming Geol. Assoc., Ninth Ann. Field Conf., insert.

-50-

'Nilmarth, M. G., 1938, Lexicon of geologic names of the United
States: U. S. Geol. Survey Bull. 896, 2396 p.

'Wilson, Druid, and other; 1957, Geologic names of North America
introduced in 1936-1955: U. S. Geol. Survey Bull. 1056, 622 p.

Neodward, T. G., 1957, Geology of Deadman Butte area, Natrona
County, Myoming: Amer. Assoc. Petrol. Geol. Bull., Vol.
’41, p0 212'262 o

wroble, J. L., 1953, Stratigraphy and sedimentation of the POpo
Agie, Nugget and Sundance Formations in centra1.Myoming:
unpubl. MA thesis, Univ.'wyoming.

Zakis, W} N., 1950, Geology of the east flank of the Big Horn
Mountains near Dayton, Sheridan County,‘Nyoming: unpubl.
MA thesis, Univ. Wyoming.

Zieglar, D. L., 1956, Pre-Piper, post-Minnekahta red beds in the
Williston Basin: North Dakota and Saskatchewan Geol. Soc.,
Williston Basin Symposium, First International, p. 170-178.

APPENDIX

Section Descriptions

-81..

SECTlON l: GRAPEVlNE CREEK

Marine Jurassic formations near Grapevine Creek 1% miles north-

west of the Big Horn River in center of Section 6, T. 6 S.,

R. 31

B., Big Horn County, Montana. Description taken from lmlay (195h).'

Piper Formation member nomenclature added by the writer.
Unit Description
SWIFT FORItlTI ON
RIERDON FCRMATI ON
27. Limestone, medium brownish-gray, oolitic, slightLy
sandy, mediums to thin-bedded, some cross-bedding,

formstopofcliff................o

26. Sandstone, light yellowish—gray, weathers brownish-
gray, massive, cores-bedded . . . . . . . . . . . ..

25. Claystone, medium.gray, soft, fissile, contains
abundant Gryphaea nebrascensis Meek and Hayden . . .

 

2h. Covered. Probably gray Claystone. Gryphaea shells
common on weathered surfaces . . . . . . . . . . . .

Approximate thickness of Rierdon Formation
PIPER FORMATlON
23. Claystone, brownish-red, soft . . . . . . . . . . .
(Approximate thickness of "C" Member 22.0)
22. Limestone, light yellowish-gray, surface marked by
yellowish-gray chert pebbles, massive, contains

many shell fragments . . . . . . . . . . . . . . .

21. Claystone, moderate brownish-red, soft, poorly
eXposed O I l O O O O O O O 0 0 O O O O O O O O O O

20. Limestone, pinkish to medium gray, upper surface
covered with brownish-gray blocky chert, medium to
thin-bedded, mostly granular, some beds contain
many tiny cavities, ledge-forming . . . . . . . . .

19. Claystone, pale red, calcareous, grading upward into
shaly limestone . . . . . . . . . . . . . . . . . .

-82..

Thickness
(Feet)

8.0

13.0

122.0

 

22.0

3.0

5.0

14.0

h.0

~83—

18. Limestone, pink at base but mostly light gray, thin-
bedded to shaly, surfaces covered with greenish-
yellow stains and many small pelecypods (Tancredia
and Isoqyprina) . . . . . . . . . . . . . . . . . . . h.5

 

17. Claystone, pale red, soft . . . . . . . . . . . . . . 2.0
16. Limestone, nearly white, dolomitic . . . . . . . . . 2.5
15. Claystone, pale red to light green, soft . . . . . . 2.5
lb. Limestone, nearly white, dense, dolomitic . . . . . . 1.0
13. Claystone, moderate brownish-red, soft . . . . . . . 6.0
12. Limestone,medium to light gray, medium to thin-bedded,
mostly dense, some beds contain many tiny cavities,
cliff-forming . . . . . . . . . . . . . . . . . . . 7.0
11. Claystone, medium red, soft . . . . . . . . . . . . . 0.5
10. Limestone, medium gray, thinly laminated . . . . . . 1.0
9. Claystone, medium brownish-red to gray, soft . . . . 2.0
8. Limestone,mediumgray............... 1.0
7. Limestone, nearly white, dolomitic . . . . . . . . . 2.0
6. Claystone, brownish-red, soft . . . . . . . . . . . . 2.5
5. Limestone, nearly white, dolomitic . . . . . . . . . 1.0
h. Claystone, red to gray, soft . . . . . . . . . . . . h.5
3. Limestone, medium gray, granular . . . . . . . . . . 0.5

(Total Thickness of "B" Member 56.5)

2. Claystone, dark brownish-red, silty, soft, many
thin beds and nodules of gypsum . . . . . . . . . . . 27.0

1. Gypsum,white,massive ............... 32:2
(Total thickness of "A" Member 62.0)
Total thickness of Piper Formation 1h0.5
CHUGWATER FORHKTLON (not measured)

Total thickness of measured section 321.5

SECTION 2: LITTLE BIG HORN RIVER

Marine Jurassic formations on Fuller's Ranch, 2.h miles(by road)

northwest of the Little Big Horn River in Section 22, T. 9 S., R.
33 B., Big Horn County, Montana.

Unit

SWIFT

Description

FORMATION (nOt measured)

RIERDON FORMATION

28.

27.

26.

25.

PIPER
2h.

23.

22.

21.

Limestone, light olive-gray, weathers tannish~brown
oolitic, many oolites, medium-bedded, slightly
sandy, pelecypod fragments, forms top of cliff,

pentagonal crinOid COlUImals, o o o o o o o o o o o

Sandstone, grayish-tan, oolitic, massive to thick-
bedded, hard, very calcareous, upper portions a

sandy limestone, cliff-forming, fossil fragments . .

Sandstone, light gray, yellowish-tan shades, very
fine-grained, well-sorted, hard, calcareous, a

few pelecypod molds, coprolites and.worm casts . . .

Shale, light grayish-green, reddish shades at base
and top, sandy in upper one-quarter, medium-hard
contains abundant Gryphaea nebrascensis Meek and
Hayden,p00rlyexp058d 00000000000000

 

Total thickness of Rierdon Formation
FORMATlON

Limestone, medium gray, medium-bedded, blocky,
crystalline, clayey, slightly sandy, forms a ledge .

Shale, dark reddish-brown, thin calcareous lenses
1 to 2 inches thick, dark green pods, many

gryphaeas as float, poorly eXposed . . . . . . .1.

(Total thickness of "C" Member 81.5)

Limestone, white to light gray, yellowish-brown
Stains, medim'bedded, dOlomitiC o o o o o o o o o

Limestone, variegated, mostly grayish-green and
light red, very thin bedded to shaly, clayey . . .

-8h-

Thickness

(Feet)

1.5’

2207

6.0

 

182.7

5.5

76.0

6.0

h.o

20.

19.

18.

17.

16.

15.

1h.
13.

12.

10.

9.

8.

7.

-85—

Limestone, medium gray, yellowish-green stains,
thin—bedded, lithographic, many small pelecypods
(Isocypring? sp.), ledge-forming . . . . . . . .

 

Shale, grayish-red, hard, nodular, calcareous,

S ilty O O O C O O O C O O O O O O O O O O O O O O

Limestone, white to light gray, weathers light

yellowish-tan, medium-bedded, dolomitic . . . . -

Shale, dark red, green pods, calcareous, poorly
exposed.....................

Limestone, medium gray, base variegated, medium
to thin-bedded, blocky, some clay pods . . . . . .

Limestone, medium gray, weathers yellowish-tan,
medium-bedded, thin-bedded near top, ledge-forming

Shale, dark reddish-brown, hard, chunky . . . . .

Limestone, white to light gray, medium-bedded,
Chalky',d010n1itic 0.00.00.00.00...

Shale, dark reddish-brown, grading upwards to

dark red, grayish-green pods, hard, silty, 9 inch
bed of thin-bedded light gray limestone, 1.5 feet
from base, shale poorly exposed . . . . . . . . .

Limestone, light grayish-green, medium-bedded,
Clayey, ledge-fmming o o o o o o o o o o o o o o

limestone, variegated, mostly gray and light red,
very thin-bedded, dark brown stains, clay pods . .

Shale, variegated, mostly reddish-brown, non-
calcareOUS...................

Limestone, white to light gray, weathers light
yellowish-tan, medium-bedded, blocky, dolomitic,
some calcite crystals, forms a ledge . . . . . . .

Shale, medium gray, hard, light gray pods, cal-

careous, lowest occurrence of G. nebrascensis float

 

Limestone, light gray, thin-bedded, ledge-forming .

Shale, medium grayish-green, hard, fissile, very

calcareous . . . . . . . . . . . . . . . . . . . .

6.0

8.0

1.5

2.0

3.0

2.0

1.7

1.0

5.5
1.6
1.0

2.0

2.0

1.0

1.7

1.0

3.

1.

-86-

Limestone, dark gray, medium-bedded, blocky,
ledge-forming0.0000000000000000

(Total thickness of "B" Member 53.6)
Shale, variegated, mostly red, calcareous . . . .
Shale, dark reddish-brown, dark green pods, chunky

Shale, dark red, dark green pods, scattered gypsum
partiCleSoooooooooooooooooooo

(Total thickness of "A" Member 55.0)

Total thickness of Piper Formation

CHUGWATER Fem-mm (not measured)

Crow Mountain? Sandstone Member

Sandstone, light red, weathers medium red with tan
shades, uppermost 3 feet weathers light gray with
small cavities, fine-grained, massive, forms promi-
nent rounded cliff

Red Peak Member

Total thickness of measured section

2.5

1.0

20.0

3h.0

190.0

372.7

SECTION 3: RED GULCH CREEK

Marine Jurassic formations one-half mile east of Red Gulch
Creek 1.9 miles by road south of Fuller's Ranch.in Section 23,

T. 58 N., R. 89'W., Sheridan County, Myoming.

Unit Description Thickness

"UPPER SUNDANCE" FORMATION (not measured)
"LOWER sm-mmms' FOREI’ATION

22. Limestone, light olive gray, weathers tannish-
brown, medium-bedded, oolitic, slightly sandy,
crystalline in parts, fossil fragments, forms
top Of Cliff o o o o o o o o o o o o o o o o c

21. Shale, medium gray, sort 0 o o o o o o o o o o

20. Sandstone, yellowish—tan, grades upwards to
whitish-tan, massive, blocky in lower one-third,
cross-bedded, ripple marks at top, calcareous,
very fine grained, well-sorted, few Ctenostreon?
Sp., Cliff-former o o o o o o o o o o o o o o o

 

19. Sandstone, white to light grayish-tan, massive
soft, calcareous, silty, very fine-grained,
forms base of cliff of unit 20 . . . . . . . .

18. Shale, light tannish-gray, sandy, no fossils,
poorly exposed o o o o o o o o o o o o o o o o

17. Shale, light grayish-green, weathers light olive
where exposed, fissile in parts, many 9.
nebrascensis, poorly exposed . . . . . . . . .

 

Total thickness of "Lower Sundance" Formation
GYPSUM SPRING-FORMATION
l6. Limestone, white to light gray, weathers light
tan, thin-bedded, tripolitic chert, clayey, dolo-
mitic, forms an indefinite ledge . . . . . . .

15. Shale, medium gray, laminated, hard . . . . . .

1h. Claystone, nearly white, calcareous, soft . . .

-87-

(Feet)

1.0
h.o
12.0

10.0

37.5

116.0

 

180.5

6.7
2.5

7.5

13.

12.

11.

10.

9.

3.

2.

-88..

Shale, dark red, green pods, calcareous, soft,
small irregular white streaks . . . . . . . . .

(Total thickness of "C" Member 2h.7)

Limestone, very light gray, weathers light tan,
medium-bedded, clayey, ledge-former . . . . . .

Limestone, variegated, mostly light red and gray,
very thin-bedded to shaly, clayey . . . . . . .

Limestone, light grayish-green, thin-bedded,
yellowish-green stains, numerous lsocyprina? sp.,
Clayey, forms 19dge o o o o o o o o o o o o o o

 

Shale, dark reddish-brown, green pods, cal-
Careous o o o o o o o o o o o o o o o o o o o o

Limestone, light gray, very thin-bedded, clayey.

Shale, variegated, mostly grayish-green, fissile,
holostean fish scales . . . . . . . . . . . . .

Limestone, medium gray, medium—bedded, some
laminae, black Specks, small cavities, ledge-

fomer O O O O O O O O O O O O O O O O I O O O O

Limestone, white, weathers light tan, massive,
Clayey, Slightly dOlomitiC o o o o o o o o o o o

Limestone, light gray, thin-bedded to platy,
a few thin brown streaks, clayey, forms ledge .

(Total thickness of "B" Member b6.8)
Shale, light grayish-green, hard, chunky . . . .
Shale, maroon to dark reddish-brown, dark gray-
ish-green pods, massive to chunky, calcareous,
hard poorly BXPOSed o o o o o o o o o o o o o o
Shale, dark red, soft, becoming harder and more
chunky in upper one-half, basal portion medium
red, silty, poorly exposed . . . . . . . . . . .

(Total thickness of "A" Member 98.5)

Total thickness of Gypsum Spring Formation

8.0

6.0

14.0

h.3

114.0
0.5

6.5

5.0

2.5

h.0

8.0

35.0

U1
U1
0

U1

17C.0

-89..
CHUGWATER FORMATION (not measured)
Crow Mountain? Sandstone Member
Siltstone, medium red, very massive, coarse-
grained, some cross-bedding, Slightly sandy,
forms prominent rounded cliff

Red Peak Member

Total thickness of measured section

350.5

SECTION h: COLUMBUS CREEK

Marine Jurassic formations on Billingsley's Ranch about
one-third mile northeast of Columbus Creek in Section 18, T. 57

N., R. 87 N}, Sheridan County, Myoming.
Unit Description
"UPPER SUNDANCE" Fommi'lor (not measured)
"IOWER.SUNDANCE" FORMATION
22. limestone, light olive gray, weathers light
olive, medium to thick-bedded, blocky, oolitic,

many oolites, slightly sandy, fossil fragments,
formStOPOflowridge0000000000000

21. Siltstone, light tan, coarse-grained, well-sorted,

sandy, soft, friable, calcareous, poorly exposed

20. Limestone, dark gray, thin—bedded, slabby, litho-
graphic, dense o o o o o o o o o o o o o o o o o

19. Shale, yellowish-tan, soft, sandy in layers and
streaks, poorly exposed . . . . . . . . . . . . .

18. Shale, medium green, tan and gray shades, some
local thin—bedding, calcareous, poorly exposed,
some gryphaeas, mostly as float . . . . . . . . .

Total thickness of "Lower Sundance" Formation

Offset approximately one—quarter mile southwest
along strike

GYPSUM SPRING FORMATION

17. limestme, light gray, medium-bedded, crystalline,

white and pink laminae, clayey, small yellowish
chert nodules, forms top of ridge . . . . . . . .

l6. Shale, dark red, hard, chunky, light gray streaks
in lower one-half, light grayish-green in upper-
mOSt 2.5 feet 0 o o o o o o o o o o o o o o o 0

(Total thickness of "C" Member 38.0)

Offset approximately 200 yards northeast along
strike

-90-

Thickness
(Feet)

1.5

5.0

1.5

6.0

5.0

33.0

15.

13.

12.

ll.

10.

3.

2.

-91-

Limestone, light grayish-green, thin-bedded to platy,
dense, clayey, some yellowish-brown stains, upper
one-halfformsledge................

Shale, medium grayish-green, fissile, soft . . . . .
Limestone, light grayish-green, weathers light tan,

thin-bedded, yellowish—tan stains, manr Jsogyprina?
Sp.,ledge-f0rmer.................

 

Shale, dark red, hard, chunky, few green pods . . ...

Shale, medium.tan to light chocolate, light gray
streaks, soft, calcareous, clayey . . .‘. . . . . ..

limestone, dark gray, weathers tan, medium-bedded,
dense,1edge-f0rmer.................

Shale, light green, hard, calcareous . . . . . . . .

Limestone, dark gray, weathers light gray, medium-
bedded, lithographic, forms ledge . . . . . . . . . .

Limestone, white, weathers yellowish-tan, medium-
bedded, dense, chalky, dolomitic, forms ledge . . . .

Shale, light gray, soft, calcareous . . . . . . . . .
Limestone, nearly white, weathers tan, granular,
dolomitic, small cavities in basal portion, calcite
crys-tlalsOQOOOOOOOOOOOOOOOOOOOO
(Total thickness of "B" Member 55.5)
Shale, light gray, soft, dark green laminae and

streaks, some white streaks, some hard, chunky
layers,b1ackspecks................

Shale, dark red to maroon, light green pods, hard,
Chunky,softerneart0p...............

Breccr; light to medium red, orange shades, light
gray limestone matrix, large angular cavities, dark
red shale casts, forms rounded irregular ledge . . .

Shale, dark reddish-brown, hard, chunky, green pods,
yellmiSh-tanShadeS0000000000000...

(Total thickness of "A" Member 92.5)

Total thickness of Gypsum Spring Formation

h.5
h.5

5.5
805

13.5

h.0
h.5

3.0

2.5
2.0

3.0

no.0

-92-
CHUGWATER FORMATION (not measured)
Crow Mountain? Sandstone Member
Sandstone, light red, massive, very fine-grained,
some cross-bedding, calcareous, slabby in uppermost
10 feet, forms rounded cliff
Red Peak Member

Total thickness of measured section

26h.0

ECTION 5: AI-ISDEN Cli'fEK

Marine Jurassic formations one-half mile south of Amsden
Creek in Section 35, T. 57 N., R. 87 N., Sheridan County, Myoming.

Unit Description Thickness
(Feet)
"UPPER SUNDAI‘ICE" FOFJ-IATION (not measured)

" LG'IER SUNDAN C E" FORT-Bill ON

15. Limestone, pale yellowish-brown, weathers tannish-
brown, medium-bedded, micro-oolitic, slightly sandy,
fossil fragments, forms top of ridge . . . . . . . 0.5

lb. Sandstone, light yellowish-tan, massive, very fine
grained, well-sorted, hard, scattered tripolitic
Chert partiCleS . Q A o o a o g o o O O 0 O O O O 0 16.5

13. Sandstone, nearly white, weathers very light tan,
very fine-grained, well—sorted, calcareous, fri-
able, maSSive o o o o o o o o o o o o o o o o o o 2300

12. Shale, medium grayish-green, calcareous, gryphaea
float, poorly exposed o o o o o o o o o o o o o o o 2200

11. Covered. Probably green shale. Gryphaea float
in upper one-half o o o o o o o o o o o o o o o o o 9900

Approximate thickness of "Lower Sundance" Formation 161.0
GYPSUM SPRLN Cr FOPE’UJ'ION

10. Limestone, nearly white, medium.to thick-bedded,
dolomitic, soft, brown specks, forms ledge . . . . h.5

9. Shale, light red, variegated near top, hard,
chunky, poorly exposed . . . . . . . . . . . . . . h2.0

(Total thickness of "c" Member no.5)

8. Limestone, white to light gray, thin-bedded in lower
one-half, upper one-half medium-bedded, blocky, 1am-
inated, dense, some yellow stains,very few lsocyprina?
sp., forms ledge . . . . . . . . . . . . . . . . . 5.0

 

7. Shale, light to medium red, hard, chunky, poorly
exposed O O O O O O O O O O O O I O C O O O O O O 20.0

-93-

3.

2.

1.

-9h-

Limestone, light to medium gray, weathers greenish-
tan, medium-bedded, small cavities, ledge-former . .

Limestone, white, weathers light tan, thin-bedded,
dolomitic, chalky, calcite crystals in small cav-
ities, some interbeds of white Claystone, forms
irregularledge...................

(Total thickness of "B" Member 37.0)

Shale, variegated, purple, light green, light red,
calcareous, thin white Claystone bed at top . . . .

Breccia, medium red, white to light gray limy
shale matrix, small cavities, dark red shale casts,
hard, angular . . . . . . . . . . . . . . . . . . .

Shale, medium.red, tan and light gray shades,
C31C8I€0U5,hard,Chunk:YOooooooooooooo

Shale, dark red to dark reddish-brown, dark gray-
iSh‘gI'Cen pOdS, hard, Chunlfy o o o o o o o o o o o 0

(Total thickness of "A" Member 55.0)

Total thickness of Gypsum Spring Formation

CHUCE-IATER Fem-mum (not measured)

Crow Mountain? Sandstone Member

Siltstone, light red, coarse-grained, sanVV, massive,

5.5

6.5

5.5

1.0

26.5

22.0

138.5

calcareous, upper 6 feet thin-bedded, forms rounded cliff

Red Peak Member

Total thickness of measured section

299.5

SECTION 6: LITTLE TONGUE R VER

Marine Jurassic formations on Horseshoe Ranch, approximately
one-third mile northvrst of the Little Tongue River and the ranch
buildings in Section 2h, T. so N., R. 87 w., Sheridan County,
Myoming.

Unit Description Thickness
(Feet)
"UPPER SUNDAMCB" FORMATION (not measured)

" EKER SUNDAIICE" FO’RJVLTT'IOI‘I

l9. Limestone, light yellowish-gray, weathers olive
drab, thin to medium-bedded, blocky, oolitic,
slightly sandy, crystalline, fossil fragments,
forms top of ridge . . . . . . . . . . . . . . . 2.0

18. Sandstone, yellowish—tan, some white streaks, very
fine-grained, well-sorted, calcareous, moderately
soft, friable, coarsely silty, some glauconite,
poorlyeXpOSed................. ll-LOO

17. Covered. Probably gray shale . . . . . . . . . . 108.5

 

Approximate thickness of "Lower Sundance" Formation 12h.5
GYPSUM SPRING FORMATION

l6. Limestone, light gray, medium-bedded, blocky, hard,
crystalline, cherty, white laminae, forms top of

ridge.......-.............. 305
15. Shale, light gray, some red shades, calcareous . 20.7
(Total thickness of "C" Member 2h.2)

lb. Limestone, light to medium grayish-green, weathers
tannish-gray, thin-bedded, dense, clayey, some
glauconite, chert in basal 1 foot, yellow stains,
shark? tooth, numerous lsogyprina sp., ledge-

former ebooooooooooooqoooooo 3.

 

\f1

13. Shale, medium to dark red, uppermost 1 foot gray-
ish-green, hard, some green pods . . . . . . . . 19.6

12. Limestone, medium grayish-green, weathers greenish-

tan, lower one-half thin-bedded, medium-bedded in
upper one-half, blocky, lithographic, forms ledge 3.5

-95-

ll.

10.

5.

h.
3.

2.

l.

Shale, dark red, some tan and gray shades, hard,
chunky, calcareous . . . . .

Limestone, light grayish-green, medium-bedded,
lithographic, formsledge

Shale, light grayish-green to chocolate, fissile,
calcareous, poorly exposed

Limestone, dark gray, weathers grayish-tan, medium-
bedded, blocky, dense, forms ledge . . . . . . . .
Limestone, white to very light gray, weathers light
yellowish-tan, medium-bedded, dense, dolomitic,

chalky, forms irregular ledge . . . . . . . . . . .

Limestone, nearly white, weathers light tan, thin-
bedded, slabby, dolomitic, calcite crystals,
granular, forms ledge

Limestone, dark grayish-green, weathers light gray,
medium-bedded, lithographic, forms ledge

113.3)

(Total thickness of "B" Member
Shale, medium gray and purple, soft, calcareous . .

Shale, dark red, hard, chunky . . . . . . . . . .
Breccia, medium red, weathers light reddish-orange,
white to light gray limy matrix, large angular
cavities with some dark red shale casts, forms
rounded irregular ledge

Shale, medium to dark reddish-brown, calcareous,
few thin partings and interbeds of white gypsum,
basal portion silty . . . . . . . . . . . . . . . .
(Total thickness of "A" Member 68.0)

Total thickness of Gypsum Spring Formation

onus-miss FORMATION (not measured)

Crow Mountain? Sandstone Member

Siltstone, light to medium red, massive, coarse-
grained, forms rounded cliff

Red Peak Member

Total thickness of measured section

207

1.5

h.5

2.0

1.0

3.0

26.0

135.5

260.0

SL‘SCTIOI‘I 7: WOLF CREEK

Marine Jurassic formations on Eaton's Ranch approximately
one—half mile south of'Wolf Creek near the west boundary of Sec-
tion h, T. 55 N., R. 86'W., Sheridan County'wyoming.

Unit Description Thickness
(Feet)
"UPPER summer FOPJ-Lki‘lOI‘l (not measured)

"LOC‘JIP. SUNDAIICE" FORMATION

l7. Limestone, medium grayish-green, medium-bedded,
blocky, oolitic, slightly sandy, crystalline,
fossil fragments, forms top of ridge . . . . . . 1.3

16. Sandstone, yellowish-tan, orange shades, very
fine-grained, well—sorted, very soft, friable,
white streaks, calcareous, poorly exposed, upper-
most 6 inches very thin-bedded, "papery" sandy,
grayish-tan limestone . . . . . . . . . . . . . h.5

15. Shale, light grayish-green, soft, calcareous,
gryphaea float, mostly in upper one-half, poorly
exposed to covered . . . . . . . . . . . . . . . hh.0
Approximate thickness of "Lower Sundance" Formation h9.8
GYPSUM RlNG FORT-LATI ON
1h. Limestone, white, weathers light tannish-gray,
medium-bedded, blocky, granular, dolomitic,
ledge-former 00000000000000000 7.0
13. Limestone, very light gray, medium-bedded, hard,
lithographic, conchoidal fracture, yellow stains,

formSledge000000000000000000 100

12. Shale, light red to lavender, hard, chunky, gray
in uppermost 2.5 feet, poorly exposed . . . . . 29.0

(Total thickness of "C" Member 37.0)

11. Limestone, medium grayish-green, weathers light gray-
ish-tan, very thin-bedded, fissile, clayey . . . 3.0

-97-

10.

9.

3.

2.

l.

-98-

Shale, medium to dark red, some light gray streacs,
thin-bedded to fissile, calcareous, poorly exposed . 5.5

Limestone, medium-gray, thin-bedded, dense, clayey . 3.0

Shale, medium red, lower one-half soft, calcareous,
upper one-half hard, chunky, darker red upwards,
light gray in uppermost h feet, poorly exposed . . . 28.0

Limestone, medium gray, weathers tannish-brown,
medium-bedded, lithographic, forms ledge . . . . . . 1.0

Shale, dark red, hard, chunky, calcareous . . . . . 3.0

Limestone, dark grayish-green, weathers yellowish-

tan, mediumrbedded, lithographic, some small cavities,
uppermost 10 inches nearly white, dolomitic, thin-

bedded, limestone, weathers yellowish-tan, black

specks, forms ledge . . . . . . . . . . . . . . . . h.5

Limestone, nearly white, weathers yellowish-tan,
thin-bedded, dense, dolomitic, cherty, chalky,
forms irregular ledge . . . . . . . . . . . . . . . 9.0

(Total thickness of "B" Member 57.0)
Shale. maroon to dark red, hard, finely chunky,
grayiSh-Lgreen pods, few white streaks, uppermost
6 feet medium green, poorly exposed . . . . . . . . 25.0
Breccia, light red, light gray crystalline limestone
matrix, large angular cavities with some medium red
shale casts, forms rounded irregular ledge . . . . . 8.0
Shale, dark reddish-brown, some green pods, white
streaks and very thin interbeds of gypsum, hard,
slightly silty, poorly exposed . . . . . . . . . . . 3h.0

(Total thickness of "A" Member 67.0)

Total thickness of Gypsum Spring Formation 161.0

cam-man Pom-mum (not measured)

Crow Mountain? Sandstone Member

Siltstone, medium red, massive, coarse-grained,
sandy, forms rounded cliff

Red Peak Member

Total thickness of measured section 210.8

SECT I OH 8: PAPJL CREEK

Marine Jurassic formations on Beckton Stock Farm approximate-
ly one-quarter mile northwest of Park Creek in Section 22, T. 55
N., R. 86 N., Sheridan County, Myoming.

Unit Description Thickness
(Feet)
"UPPER SUNDANCE" Fozum'riON (not measured)
"LONE-ZR SUNDAIJCL" FOPJ-lA‘i‘IOZJ
l3. Limestone, light greenish-gray, weathers tannish-
gray, medium-bedded. crystalline, slightly sandy,
few oolites, unfossiliferous, forms top of ridge . . 1.0

12. Covered. Probably grayish-green shale. 32.0

 

Approximate thickness of "Lower Sundance" Formation 33.0
GYPSUi-l SPRLN G FORE-111111016
ll. Limestone, dark gray, weathers light gray, medium-
bedded, faint dark laminae, lithographic, cherty,
upper one-third nearly white, thin-bedded, dolo-
mitic limestone, forms ledge . . . . . . . . . . . . 9.5
10. Shale, dark red, hard, chunky, poorly exposed . . . h.5
(Total thickness of "C" Member lh.0)
9. Limestone, light gray, lithographic, forms ledge . . h.5
8. Limestone, dark gray, weathers tannish-gray,
medium-bedded, lithographic, bloclqr, cherty,

formSledge.0000000000000000000 105

7. Limestone, nearly white, weathers light tan, thin-
bedded, slabby, granular, dolomitic, black specks . 0.5

6. Limestone, very light gray, thin-bedded, dense,
dolomitic, chalky, clayey . . . . . . . . . . . . . 1.0

S. Shale, dark red, grading to light gray and green
at top, very thin-bedded, calcareous . . . . . . . . 2.8

-100-

h. Limestone, nearly white, weathers yellowish-tan,
medium-bedded, granular, dolomitic, black specks,
calcite crystals, ledge-farmer . . . . . . . . . . 3.5

(Total thickness of "S" Nember 13.8)

3. Shale, dark red, hard, chunlqy, grayish-green pods,
gray streaks and layers, variegated in uppermost
1 foot, dark gray, purple, and chocolate, scattered
gypsmnpartiCles0.000000000000000 2905

2. BreCCia, light red, orange shades, white to light
gray crystalline limy matrix, small to large angular
cavities with light reddish-orange shale casts,
forms rounded indefinite ledge . . . . . . . . . . 9.5

1. Shale, medium to dark reddish-brown, very soft,

white streaks, calcareous, poorly exposed . . . . . 33.0
(Total thickness of "A" Member 72.0)
Total thickness of Gypsum Spring Formation 99.8

CHUQ‘JATFR FORMATlON (not measured)
Crow Mountain? Sandstone Member
Siltstone, light red, coarse-grained, sandy, slabby
Red Peak Member

Total thickness of measured section 132.8

SECTION 9: BlG GOOSE CREEK

Marine Jurassic formations on Colket's (T Bar T) Ranch
approximately one-quarter mile south of Big Goose Creek and the
ranch buildings in Section 35, T. 55 N., R. 86'w., Sheridan County,

'wyoming.
Unit Description Thickness
(Feet)
"UPPER smmmlczs" FormeiON (not measured)
" LOWER SUI‘JDANCL" FGPJLXTlON
13. Limestone, pinkish-gray, weathers light tan,
medium-bedded, oolitic, most oolites same color
as matrix, slightly dolomitic and clayey,
calcite crystals, fossil fragments, forms top
Oflowridge000000000000000000 100
12. Shale, dark grayish-green, hard, finely chunky . 27.0
Total thickness of "Lower Sundance" Formation 28.0
GIPSUM SPRING-FORMATION
ll. Shale, dark red, hard, calcareous . . . . . . . . 1h.0
(Total thickness of "C" Member 1h.0)
10. Limestone, very light to light gray,'weathers light
tan, thin-bedded, dense, clayey, dolomitic,'with red
shale interbeds, 0.5 to 1 feet thick, hard, chunky,
some purple and.chocolate shades . . . . . . . . 18.5
9. Shale, medium red, very thin-bedded, hard, slightly
Silty’calcareous 000000000000000 700
8. Shale, chocolate, red shades, very soft, very cal-
Carecus, poorly eXposed 0 0 0 0 0 0 0 0 0 0 0 0 0 12.0
7. Limestone, light gray, weathers tan, medium-bedded,
yellow stains, hard, clayey, forms ledge . . . . 3.0
6. Shale, dark red, hard, chunky, calcareous, gray
Streak5000000000000000000000 20S

~101-

5.

3.

2.

l.

-102-

Limestone, light gray, weathered tannish—gray, thin-
bedded, lithographic, hard, forms ledge . . . . . . . 2.0

Limestone, medium.gray, thin to mediumrbedded,
dense, light gray streaks . . . . . . . . . . . . . 2.0

Limestone, white, weathers light tan, thin-bedded,
dolomitic, calcite crystals, granular, forms
irregUIarIEdge 00.0000000000000000100

(Total thickness of "B" Member h8.0)

Shale, dark red, hard, chunky, many small green pods-
uppermost 2 feet variegated, mostly gray, calcareous. 10.0

Shale, light red, grading upwards to medium red,
few green pods, calcareous, some white streaks,
Siltyatbase00000000000000000000500

(Total thickness of "A" Member 55.0)

Total thickness of Gypsum Spring Formation 117.0

CHUCE'IATER FORMM‘ION (not measured)

Crow Mountain? Sandstone Member

Siltstone, medium red, coarse-grained, sandy, some

massive, rounded outcrops, but mostly slabby in

upper one-half, lower one-half a vertical cliff

Red Peak Member

Total thickness of measured section lh5.0

SECTION 10: RAPlD CREEK

Marine Jurassic formations on Sage's (Triangle T) Ranch
approximately one-third.mi1e northwest of Rapid Creek in Section
12, T. 5h N., R. 86 N., Sheridan County, wyoming.

Unit Description Thickness
(Feet)
"UPPER surnames qumion (not measured)
HOMER SUNDMICE" FORL'IATION
15. Limestone, medium yellowish-green, weathers dark
green, medium-bedded, blocky, oolitic, sandy,
crystalline, fossil fragments, forms top of ridge . 1.5
lb. Limestone, dark yellowish-brown, tan shades, weathers
dark green, massive to medium-bedded, blocky, sandy,
crystalline, few oolites, some portions a limy
SaIlClS'bone O O O I 0 0 O 0 0 O O O O 0 0 0 0 o 0 0 O 1000

l3. Shale, light grayish-green, hard, calcareous,
poorly exposed 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2905

Total thickness of "Lower Sundance" Formation h1.0
GYPSUM SPRING-FORMATlON

l2. Limestone, dark gray, weathers tan, very thin-bedded,
platy, clayey, cherty, forms ledge . . . . . . . . 5.0

11. Shale, pink, light gray shades, hard, very calcareous,
some portions fiSSile 0 0 0 0 0 0 0 0 0 0 0 0 0 0 300

(Total thickness of "C" Member 8.0)

10. Limestone, dark grayish-green, mediumpbedded, hard,
lithographic, blocky, ledge-former . . . . . . . . 2.0

9. Shale, medium red grading to variegated at top,
lavender, gray, green, hard, Chunky 0 0 0 0 0 0 0 0 1805

8. Limestone, dark grayish-green, mediumAbedded,
slabby, forms ledge . . . . . . . . . . . . . . . . 2.0

7. Limestone, medium gray, weathers dark tan, medium-
bedded, lithographic, ledge-former . . . . . . . . 1.3

-103-

h.

3.

2.

1.

-10h-
Shale, dark red, hard, calcareous . . . . . . . . . 2.0

Limestone, light gray, weathers tan, thin-bedded,
Clearebr00000000000000 00000000 100

Shale, dark reddish-brown, hard, chunky, con-
choidal fracture, calcareous . . . . . . . . . . . 3.0

Limestone, medium grayish-green, weathers tan, thin-
bedded, dolomitic white streaks . . . . . . . . . . 1.0

Limestone, light grayish-green, medium-bedded, hard,
lithographic, conchoidal fracture . . . . . . . . . 1.5

(Total thickness of "B" Member 32.3)
Shale, dark reddish-brown, very few green pods, hard,
chunky in parts, some portions fissile, basal por-
tion Silty O O O O O O O O O O O O O O O O O O O O 62.0

(Total thickness of "A" Member 62.0)

Total thickness of Gypsum Spring Formation 102.3

CHUCMATER FORE-M1011 (not measured)

Crow Mountain? Sandstone Member

Siltstone, light to medium red, massive, some
portions slabby, coarse-grained, sandy, forms
prominent rounded to vertical cliff

Red Peak Member

Total thickness of measured section 1h3.3

SECTION 11: LITTLE GOOSE CREEK

Triassic and.marine Jurassic formations on Smith's (Crossed
U Bar) Ranch approximately one-half mile west of Little Goose Creek
in Section 36, T. 5h N., R. 85 N., Sheridan County, wyoming.

Unit Description Thickness
(Feet)
"UPPFR same-zest Fear TIOM (not measured)
"LCWS SIE-EDAI‘ICE" FORI-ZATIOI-I
15. Limestone, medium grayish-green, medium to thick-
bedded, slabby, oolitic, numerous oolites, slightly
sandy, crystalline, fossil fragments, forms top of
hogbaCk 0 0 0 0,0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 900
1h. Covered. Probably green shale . . . . . . . . . . 232$;
Approximate thickness of "Lower Sundance" Formation h7.0
GYPSUI‘f SPRIN G FORMATlON
13. Limestone, nearly white, weathers light gray, medium-
bedded, dolomitic, calcite crystals, chalky, tripo-
litie chert, forms ledge . . . . . . . . . . . . . 1.5
12. Covered. Probably red shale . . . . . . . . . . . .' 6.5
11. Limestone, white, weathers tannish—gray, massive,
granular, soft, "friable", dolomitic, porous,
blaCkSpeCkS00000000000000000000 300
10. Covered. Probably dark red shale . . . . . . . . . 3h.S
(Approximate thickness of "C" Member h5.5)
9. Limestone, dark greenish-gray, weathers light gray,
medium-bedded, hard, lithographic, some conchoidal

fracture, black Specks, upper one-half forms ledge . h.5

8. Shale, dark reddish-brown, very soft, calcareous,
poorly exposed 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1605

7. Limestone, light gray, weathers dark tan, thin—bedded,
small caVitieS, Clayey 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 h0S

6. Shale, dark red, soft, calcareous . . . . . . . . . 2.0

-105-

—106-
5. Limestone, medium.to dark gray, weathers tannish-
gray, medium-bedded, very blocky, hard, litho-
gI'aphiC,f0mSledgeoo00.00.000.000 (400

(Total thickness of "B" Kember 31.5)

h. Shale, light greenish-gray, some red shades,
30ft, White Streaks, calcareous o o o o o o o o o 13.0

3. Shale, medium to dark red, hard, chunky, a few small

green pods, calcareous, silty in basal 6 feet . . hh.0
(Total thickness of "A" Member 57.0)
Total thickness of Gypsum Spring Formation l3h.0

CHUG'IATER FOPJ‘JLATION (measured in part)
Crow Mountain Sandstone Member
2. Sandstone, light reddish—orange, weathers light red,
massive, very fine-grained, silty, soft, friable,
porous, forms small, rounded cliff . . . . . . . 19.0
Alcova Limestone Member
1. Limestone, white to pink, weathers light tan, medium-
bedded, slabby, finely crystalline, "sugary," some

gray laminae, slightly dolomitic, ledge-former . 6.0

Total thickness of measured portion of Chugwater
Formation 25.0

Red Peak Kember (not measured)

Sandstone, red, thin-bedded, slabby, very fine-
grained, silty, locally light gray, massive

Total thickness of measured section 206.0

SECTION 12: ROCK CP??K

Triassic and marine Jurassic formations on HF Bar Ranch
approximately one mile by road northwest of the ranch buildings
and 100 feet north of Rock Creek in Section 2h, T. 52 N., R. an
H., Johnson County, Wyoming.

Unit Description Thickness
(Feet)

"UPPER JNDANCE" FORMATlON (not measured)
" LOWER summon" FORMAT ION

13. Limestone, pale grayish-olive, weathers greenish-tan,
medium-bedded, oolitic, slightly sandy, crystalline,
light gray calcite veinlets, fossil fragments, forms
ledge and in places top of low ridge . . . . . . . . 1.0

12. Siltstone, light yellowish-tan, coarse-grained, well-
sorted, sandy, very fine—grained, moderately soft,
friable, calcareous, white streaks, some yellowish-
brown shale partings, poorly exposed . . . . . . . 2.0

ll. Shale, dark green, thin-bedded to slightly chunky,
hard, calcareous, silty, poorly exposed . . . . . . 11.5

 

Total thickness of "Lower Sundance" Formation 1h.
GYPSUM SPRlNG FORMATION
10. Limestone, white, weathers light tan, lower one-
half massive, dense, chalky, cherty, very dolomitic,
medium-bedded in upper one-half, granular,
dolomitic, black specks, forms ledge . . . . . . . . b.5

9. Shale, medium greenish-gray, pink shades, hard,
poorlye};posedooooooooooooooooooo1200

8. Shale, medium to dark red, hard, some portions
Chuniq,calcareousooooooeoo00.00.001100

(Total thickness of "C" Member 27.5)

7. Limestone, nearly white, weathers light tan, thin-
bedded, dolomitic, light gray laminae, very clayey . 3.5

-107...

-108-

6. Limestone, dark gray, very thin-bedded to shaly,
platy, dense, clayey o o o o o o o o o o o o o o o 305

5. Shale, medium grayish-green to chocolate, fissile,
calcareous, poorly exposed . . . . . . . . . . . . 3.0

h. Limestone, light grayish-green, weathers light tan-
nish-gray, lower one-half medium-bedded, dense,
lithographic, upper one-half thin-bedded, fissile,

formsledge................... 2.0
(Total thickness of "B" Member 12.0)
3. Shale, dark reddish-brown, hard, chunky, some dark

green pods, some portions calcareous . . . . . . . _6_._5_
(Total thickness of "A" Member 6.5)

Total thickness of vasum Spring Formation h6.0

CHUGJATER FORMATICN (measured in part)
Crow Mountain Sandstone Member

2. Sandstone, light tannish-red, orange shades,
weathers light red to yellowish-tan, massive,
some cross-bedding, very fine-grained, silty,
moderately soft, case hardened, forms rounded
Cliff e o o o o o o o o o o o o o o o o e o o o o 72.0

Alc ova Limestone Member

1. Limestone, pink, some portions white to buff,
medium-bedded, finely crystalline, sugary, light
gray laminae, dolomitic, slabby, forms ledge
and in places a prominent small hogback . . . . . 7.5

Total thickness of measured portion of
Chugwater Formation 79.5

Red Peak Manber (not measured)

Sandstone, light to medium red, very fine-grained,
massive to thin-bedded in uppermost portion, silty

Total thickness of measured section 1140.0

 

ECTION 13: NORTH SAYLES CREEK

Triassic and marine Jurassic formations on Tarbert's (U-M)
Ranch approximately 100 yards north of Robert Taylor's Ranch
buildings in Section 6, T. 51 N., R. 83 W., Johnson County,
Vlyomingo

Unit Description Thickness
(Feet) -
"UPPER SUNDANCE" FORMATION (not measured)

" IDWER SUNDANCE' FORMAT ION

20. Limestone, light grayish-olive, weathers tannish-
g'ay, medium-bedded, blocky, oolitic, many oolites,
slightly sandy, few fossil fragments, forms top of
ridge........................1.0

19. Sandstone, light yellowish-tan, massive, very fine-
grained, well-sorted, moderately hard, friable, cal-

careous, micaceous, few green shale partings, basal
3 feet white, soft, poorly exposed . . . . . . . . 9.0

18. Shale, light grayish-green, soft, calcareous,
portions silty, poorly exposed . . . . . . . . . . 19.0

Total thickness of "Lower Sundance" Formation 29.0
GYPSUM SPRING FORMATION

17. Limestone, white, weathers light tan, medium-bedded,
dense, dolomitic, chalky, forms ledge . . . . . . . 6.0

16. Shale, medium grayish-green, grades darker upwards,
hard, chunky, calcareous, some tan laminae . . . . 6.5

15. Shale, dark red, hard, chunky, calcareous . . . . . 11.5
11].. Shale, medium red, 50ft, calcareous o o o o o o o o 15.0
(Total thickness of “C" Member 39.0)

13. Limestone, variegated, mostly light grayish-green,
and light red, very thin-bedded, platy, hard, clayey 2.0

12. Shale, light gray, fissile, calcareous . . . . . . h.5

-109...

 

-110-

11. Limestone, light gray, weathers tan, thin-bedded,
lithographic, hard, yellow stains, forms ledge . .

10. Shale, light greenish-gray, fissile . . . . . . .
9. Limestone, light gray, thin-bedded . . . . . . . .

8. Shale, light greenish-gray, medium red at base,
hard, Chmw O O O O O O O O O O O O O O O O O O O

7. Limestone, nearly'white, weathers tan, thin-bedded,
dolomitic, chalky, poorly exposed . . . . . . . .

6. Shale, light red, hard, calcareous . . . . . . . .

5. Limestone, light gray, weathers dark tan, medium—
bedded, blocky, finely crystalline to granular, few
small cavities, numerous small natiCOld gastropods,
formsledge...................

h. Limestone, light gray,'weathers tan, thin-bedded,
hard,lith0graphiC................

(Total thickness of "B" Member 33.5)

3. Shale, medium red, very thin-bedded, platy, fissile
in parts, hard, calcareous, some light green pods.

(Total thickness of "A" Member 65.5)
Total thickness of Gypsum Spring Formation
CHUCMATER FommTlON (measured in part)
. Crow Mountain Sandstone Member?
2. Covered......................
Alcova Limestone Member
1. Limestone, pink, nearly white in sane portions,
medium-bedded, slabby, finely crystalline, forms
tOp of small hogback . . . . . . . . . . . . . . .

Approximate thickness of measured portion of
Chugwater Formation

Red Peak Member (not measured)

Sandstone, light red, massive, rounded, silty,
variegated in uppermost portion

Total thickness of measured section

1.2

3.3

1.0

5.0

1.5

10.0

3.0

2.0

 

138.0

71.0

2th.?

SECTION 1h: NORTH FORK, CRAZY WOMAN CREEK

Triassic and marine Jurassic formations on Klondike Ranch
approximately 2.8 miles by road.west of the ranch buildings and
one-half mile south of the road, in Section 26, T. h9 N., R.

83 W.,

Unit
"UPPER
"LOWER

9.

7.

GYPSUM
5.

3.

Johnson County, wyoming.

Description Thickness
(Feet)
SUTJDANCE" FORMATION (not measured)

SUNDAI‘ICE" FORMATlON

Limestone, light olive gray, weathers medium olive,

medium to thickebedded, slabby, oolitic, many oolites,
slightly sandy, forms top of small vertical

Cliff o o o o o o o o e o o o o o o o o o o o o o o 2.0

Sandstone, light tan, white shades, massive, cross-
bedded, hard, very fine-grained,'well-sorted, cal-
careous, basal portion yellowish-tan, soft, friable,
ripple marks in float, peleqypod molds, forms

small vertical Cliff e o e a o o o o o o o o o o o 12.8

Shale, medium grayish-green, mostly hard, portions
chunky, soft light tan lenses, sandy in uppermost
5 feet, pOOrIY EXPOSBd o o o o o o o o e o o o o o 23.0

Shale, yellowish-tan, very silty, light tan silt-
stone lenses, basal 2 feet light grayish-green,
very thin-bedded, poorly exposed . . . . . . . . . 12.0

Total thickness of "Lower Sundance" Formation h9.8
SPRINGZFORMATlON

Limestone, nearly white, weathers very light tan,
medium-bedded, slabby, dolomitic . . . . . . . . . 1.0

Limestone, medium greenish-gray, weathers tannish-
green, medium to thick-bedded, blocky, hard,
lithographic a o o o o o o o . o o o o o o o o o o 2.5

Shale, dark tannishybrown, very soft, crumbly,

calcareous, upper one-third light grayish-green,
hard, poorly exposed o o o o o o o o o o o o o o o 905

-111-

-ll2-

2. Shale, dark red to dark reddish-brown, hard,
chunky, calcareous, few dark green pods, basal
portion silty, thin white gypsiferous lenses

hear tOp, poorly exposed o o o o o o o o o o o o h9os
Total thickness of Gypsum Spring Formation 62.5

CHUGWATER FORMATION (measured in part)

Crow Mountain Sandstone Member

1. Sandstone, light to medium reddish-orange, very
massive, cross-bedded, very fine-grained, soft,
friable, silty, white streaks, forms prominent
Slightly rounded vertical Cliff o o o o o o o o 51.0

Alcova Limestone Member (locally absent)

Red Peak Member (not measured)
Siltstone, medium red, thin-bedded, sandy

Total thickness of measured section 163.3

 

15: SOUTH FORK, LITTLE POISQI CREEK

nd marine Jurassic formations on Young's Ranch
0 yards south of the ranch buildings in the north-
of Section 1, T. h? N., R. 83 N., Johnson

Description Thickness
(Feet)
FORMATION (not measured)

FORMATICN

, olive gray, weathers dark olive, medium

bedded, oolitic, numerous oolites, slabby,

sandy, some portions crystalline, fossil

, forms top Of hogback o o o o o o e o o 1‘00

, light tan, light gray shades, thin-bedded,
ome parts cross-bedded, very fine-grained,
ed, hard, calcareous, dark tan laminae,

t grayish-tan shale lenses in uppermost 2.5

ms ledge . C . O O O O . O C . -. . C O . 10.0
ckness of "Lower Sundance" Formation 114.0
{UNION

, light gray, thin-bedded, hard, dense,
hoidal fracture, clayey, with thin inter-
early white, dolomitic, chalky limestone 3.0

rk red, hard, mostly chunky, light gray-
lenses in uppermost 10 feet, most
poorlyexposed............. 14605

lite, weathers nearly white to bluish-gray

some red wash, massive to granular, soft,

ities; with thick dark red to dark reddish-

Le interbeds, hard, chunky, with thin

as lenses. The interbeds are lens-like
laterally; thicknesses range from 2 to

r both lithologies, and average 3.5 feet . 29.5

:kness of Gypsum Spring Formation 79.0

-113-

 

 

-11h-
CHUGWATER FORMAflON (measured in part)
Crow Mountain Sandstone Member?

2. Covered. Small outcrop with typical Crow Mountain
lithology and color approximately 100 yards north
on the north bank of creek . . . . . . . . . . . . 66.0

Alcova Limestone Member

1. Limestone, pink to nearly white, weathers light tan,
medium-bedded, slabby in upper one-half, very finely
crystalline, hard, dense, dolomitic, few black Specks,
forms top of upper Red Peak Member hogback . . . . 3.0

*

Approximate thickness of measured portion of
Chugwater Formation 69.0

Red Peak Member (not measured)

Siltstone, medium red, tan shades, massive,
slabby at top, sandy

Total thickness of measured section 162.0

SECTION 16: SOUTH FORK, CRAZY WOI-LAN CREEK

Triassic and marine Jurassic formations on Ramsbottom's
Ranch approximately one-half mile by road northwest of the ranch
buildings and 200 yards south of the road in Section 27, T. 146
N., R. 83 W., Johnson County, Wyoming.

Unit Description Thickness
(Feet)
" UPPER SUNDANCE" FORMATION (not measured)

" LUJER SUNDANCE" FGlI'IATlON

9. Limestone, medium yellowish-green, weathers dark
tannish-green, medium-bedded, oolitic, slightly
sandy, crystalline, tan streaks, forms top of
10W hill 0 o o o o o o o o o o o o o o o o o o o o 300

8. Sandstone, medium tan, yellow shades, massive to
thick-bedded, some cross-bedding, very fine-gained,
well-sorted, hard, calcareous, silty, forms ledge. 6.0

7. Siltstone, light tan, coarse-gained, well-sorted,
very finely sandy, soft, friable, calcareous,

micaceous, poorly exposed . . . . . . . . . . . . 3.5
6. Shale, medium to dark gayish-geen, soft, silty,

calcareous, poorly exposed . . . . . . . . . . . . 140.0

Total thickness of"Lower Sundance" Formation 52.5

GYPSUM SPRING F ORI-lAT .LON
5. Shale, dark red, hard, chunky, calcareous . . . . 3.0
h. Breccia, light tannish-red, light gay limestone

matrix, finely crystalline, hard, small cavities,
angular dark reddish-brown silty shale inclusions,

few Small angular caVitieS o o o o o o o e o o o o 200
3. Shale, dark reddish-brown, thin-bedded some por-

tions fissile, hard, silty . . . . . . . . . . . . 12u0

Total thickness of Gypsum Spring Formation 17.0

-115...

 

-116-
CHUGWATER FORMATION (measured in part)

Crow Mountain Sandstone Member

2. Sandstone, light reddish-orange, massive, some
cross-bedding, very fine-grained, brown laminae,
silty, forms low-angle rounded "cliff" . . . . .

Alcova Limestone Member

1. Limestone, light grayish-pink to buff, weathers
light gay, medimn-bedded, blocky, dense, hard,
finely crystalline, dolomitic, forms top of
upper Red Peak Member ridge . . . . . . . . . .

Total thickness of measured portion of
Chugwater Formation

Red Peak Member (not measured)

Siltstone, light red, yellowish-tan shades,
massive to slabby, sandy

Total thickness of measured section

1:75

122.0

 

SECTION 17: MAYOWORTH

id marine Jurassic formations on Gordon's Ranch
3 miles by road west of Mayoworth and 300 yards
1 in Section 5, T. hh N., R. 83 W}, Johnson County,

Description Thickness
(Feet)
FORMATION (not measured)

F GREAT lON

, light olive gray, weathers tannish-

ick-bedded, blocky, oolitic, numerous

slightly sandy, finely crystalline,

Of ridge 0 o o o o o o o e o o o o o e o 300

, light yellowish-tan, coarse-grained,
ad, very finely sandy, soft, friable,
3, uppermost 1 foot light green, shaly . 7.0

, very light tan, light green shades,
led, shft,.friable, calcareous,
pms O O O O O O O O O O O O O O O O O O 2.5

, light to medium tan, weathers white in

7 feet, fine-grained, very soft, friable,

3n streaks, shaly, few small hard, light

Le incluSiOnS o o o o e o o o o o o o o o 1300

, nearly white to pinkish-gray, yellow-
1ades, medium to fine-grained, white
:alcareous, few small cavities, some

rystals . . . . . . . . . . . . . . . . . _g;§
:kness of "Lower Sundance" Formation 28.0
HEAT ION

rk red, moderately soft, calcareous . . . 6.0

lite, weathers light tan, massive; thin
lenses, medium gray, medium-bedded,

) feet thick, finely crystalline, with
laminae occur locally; forms indefinite

O O O O I O O O O O O O O O O O O O O O 10$

-117-

 

-118...

3. Shale, dark red to dark reddish-brown, mostly hard,
some portions softer, silty, calcareous, basal part
silty, thin light gay limy streaks . . . . . . . . 11.3.5

Total thickness of Gypsum Spring Formation 51.0
CHUGrIATER FORItiTION (measured in part)
Crow Mountain Sandstone Member
2. Sandstone, light reddish-orange, massive, cross-
bedded, very fine-gained, moderately hard, friable,
silty, lower and uppermost portions poorly exposed,
middle two-thirds forms rounded, low-angle "cliff". 68.0
Alcova Limestone Member
1. limestone, pink to buff, weathers light gray to
tan, thick-bedded, slabby, very finely crystalline,

clayey in parts ,tan laminae, forms prominent
ledgeOOOOOOOOOOO0.0.0.0.0... (4.5

Total thickness of measured portion of
Chugwater Formation 72 .5

Red Peak Member (not measured)

Siltstone, light to medium red, massive,

slightly sandy

Total thickness of measured section 151.5

 

 

 

SmTION 18: BARMUM

Triassic and marine Jurassic formations on Graves Ranch

approximately one-half mile east of Barnum on wyoming Secondary

1000 and 300 yards north of the road in Section 35, T. h3 N.,

R. 8h'W., Johnson County,‘Wyoming.

Unit

Description Thickness
(Feet)

"UPPER SUNDANCE" FORMATION (not measured)

" LOWER SUNDANCE" FORT-IATION

18.

17.

Limestone, light olive, weathers olive tan, medium-

bedded, slabby, oolitic, many oolites, thin parallel
non—oolitic, light tan laminae, slightly sandy, forms

tOpOfridgeoooooooeeo000000.000

Sandstone, light tan, weathers medium to dark tan,
massive to medium-bedded, cross-bedded, very fine-
grained, some rounded rock and mineral particles

to 1 mm. in diameter, well-sorted, green oolites

in thin bands in upper one-half, hard, very cal-
careous, basal portion yellowish-tan, softer,

upper 7.5 feet forms prominent ledge . . . . . . . .

Total thickness of "Lower Sundance" Formation

UNNAMED INTERVAL

13.

12.

Siltstone, light red, massive, fine-grained, hard .

Siltstone, dark red, coarse-grained, soft, friable,
calcareous, clayey, some gayish-geen nodules,
poorlyexposed...................

Siltstone, very light tan, weathers medium tan,
maSSive,b10C1q,hard0.000.000.0000.

Shale, dark red, very thin-bedded to finely chunky,
hard, few green pods, some light gray lenses,silty .

Siltstone, light red, some orange shades, massive,
medium-bedded, slabby in basal 15 feet, middle 7
feet thin-bedded, thick-bedded, blocky in upper h
feet, mediumpgrained, soft, friable, micaceous,

some tan streaks, forms a series of ledges . . . . .

-119-

0.7

10.0

10.7

8.0

16.0

h.o

11.5

26.0

-120-

rk red, basal h feet tan, fissile in 1
rd, green pods, some parts very silty . . 11.5

, very light red, medium to thickebedded,
edium-grained, moderately soft, basal 1

Ly white,thin-bedded, calcareous, lower

rms prominent ledge . . . . . . . . . . . 13.0

rk red to dark reddish-brown, hard, silty 7.5

, medium tan, light gray irregular streaks
itrations, fine-grained, very calcareous 1.0

rk red, dark green shades, slightly
hard, Silty O 0 O O O O O O O O O O 0 O 105

, lower one-half light red, upper one-half
yish-tan, medium-bedded, some cross-bedding,
ned, calcareous, some medium red laminae,

Se 0 o o o o o e o o o e o o o o o e o o 905

rk red, some portions dark green, fissile,

by. O O O O O O O O O O O O O I O O O O O 1‘00

, mostly light red, portions light tannish-
3 to medium-bedded, slabby, medium to
dined, calcareous o o o o o o o e o o o 505

, light to medium.red, thin to medium-
oarse-grained, very finely sandy, few
r streaks, very few dark green "pods" . 22.0

ckness of Unnamed lnterval 1hl.O
LON (measured in part)
Sandstone Member

, light reddish-orange, massive, cross-

2ry fine-grained, moderately soft, friable,

in light gray streaks, forms very prominent

Li—ff O O O O O O O O O O O O O O O O O O 62 O S

10 Member

, light pinkish-gray to buff, some purplish-
:S, thin to medium-bedded, slabby, very finely
1e, variegated color rings and patterns on

; surfaces, tan laminae, forms prominent

O O O 0 O O O O O O O O O O O O O O O 0 £5-

 

 

-121-

:kness of measured portion of
Formation - 69.0

' (not measured)

. light red, massive to thick bedded,
Le

c
i measured section 220.7

 

SECTION 19: WILLOW CREEK

Triassic and marine Jurassic formations on Hollman's
Ranch approximately one-third mile by road west of the ranch build-
ings and 100 yards north of the road in Section 15, T. to N.,
R. 83 N., Natrona County, Wyoming. Measured portion of the
Chugwater Formation in offsets to the west in Section 16.

Unit Description Thickness
(Feet)
"UPPER SUNDANCE" FORMATION (not measured)

" IOWER SUNDANCE" FORMATION

21. Limestone, moderate yellowish-geen, weathers dark
tannish-geen, thick-bedded, slabby, oolitic, medium
to finely crystalline, sandy, many fossil fragments
including pentagonal crinoid columnals (Isocrinus?
sp.),formstopOfridge............. 505

20. Sandstone, medium yellowish-tan,massive to medium-
bedded, some cross-bedding, very fine-gained, well-
sorted, coarsely silty, moderately hard, very cal-
careous, pentagonal crinoid columnals (Isocrinus?
sp.), few cytherid? ostracodes, forms prominent .
ledge...................... 5.0

19. Sandstone, very light tan, some portions nearly
white, lower 1/3 covered, middle 1/3 massive,
rounded, upper 1/3 thin to medium-bedded, slabby,
very fine-gained, well-sorted, hard, calcareous,
few pelecypod molds, upper 1/3 forms ledge . . . . 22.5

18. Covered. 00000000000000.0000. 1500

17. Shale, dark green, yellbwish-tan shades, thin-
bedded, platy, moderately soft, waxy in parts,
calcareous, gsm‘iospermous bisaccate pollen,
fern-like Spores, other plant microfossils, and
a dinoflagellate, most portions poorly exposed . . 23.5

Total thickness of "Lower Sundance" Formation 71.5
UNNAI-IED INTERVAL
16. Siltstone, very light tan, light gay shades, thin
bedded, flaggy in parts, medium to fine-gained,

hard, calcareous, lower 2 feet and upper 14 feet
covered, middle 2 feet forms ledge . . . . . . . . 8.0

~122-

 

~123-

dark red, fine-gained, hard, chunky,
haly, poorly exposed . . . . . . l. . . . 14.5

light tannish-gray, weathers dark tan,
d, slabby, medium-grained, hard, cal-
.ight red bands, forms ledge . . . . . . . 6.5

dark reddish-brow, hard, calcareous,
m green pods, clayey and softer in
half, poorly exposed o o o o o o o e o o 1007

very light gay, weathers tan, thin-
,abby, hard, thin laminae, forms ledge . . 10.7

dark red, moderately hard, chunky,

O O O O O O O O O O O O O O O O O O O O 707

very light gray, weathers light tan,
dium-bedded, medium-grained, moderately
.ble 0 O O O O O O O O O O O O O O O O O O 1105

light reddish-orange, weathers light
ve, coarse-gained, very finely sandy,
’ soft, friable, forms rounded ledge . . . 6.5

light to medium red, tan shades, basal
y light gay, massive to thick-bedded,
.ined, hard, calcareous, forms ledge . . . 9.3

k red, light green in parts, hard,
hunky, very Silty o o o o o o o o o o o o 707

light red, massive, blocky in parts,
.ed, calcareous, hard, forms rounded "cliff" 21.3

dark red, weathers light.red, thin-
.ightly fissile to chunky, fine-grained,
.t gray streaks, thin shaly lenses and

some purplish shades, forms series of

O O C O 0 O O O O O O O O O O I O O C O 19.?

very light gay, light tan shades,
an, thick-bedded, slabby, fine to
ined, hard, calcareous, basal 2 feet

,9 o o o o o o o o a o o o o o o o o o e 1007

medium red, tan shades, medium-bedded,
:derately hard, friable, calcareous,
.CS or small ledges o e o o o o o o o e o 17.5

 

-12h-
Total thickness of unnamed interval ' 1145.3

Offset approximately one mile by road west;
0.14 miles along dip

CHUGJATER FORMATION (measured in part)
Crow Mountain Sandstone Member

2. Sandstone, light red to light reddish-orange,
tan shades, massive, cross-bedded, very fine-
gained, moderately soft, friable, silty, some
light tan laminae, forms irregularly rounded
Cliff e o o e o o o o o o o o o o e o o o o e 0 S705

Offset approximately 3/l4 mile by road west;
l/h mile along dip

Alcova Limestone Member

1. Limestone, lower one-half light pinkish-grayr to
buff, thick-bedded, blocky, thin gray and tan
laminae, upper one-half purple and dark gray,
medium to thin-bedded, slabby; entire unit is
very finely crystalline, hard, forms prominent
ledge o o e o e o o o o o o o e o o o o o o o o 5.0

Total thickness of measured portion of
Chugwater Formation 62. 5

Red Peak Member (not measured)

Siltstone, light red, massive, rounded, slabby in
parts, sandy, calcareous

Total thickness of measured section 279.3

 

SECTION 20: GOOSE EGG DUE

Triassic and marine Jurassic formations on the northeast
flank of Bessemer Mountain approximately 10 miles southwest of
CaSper, 1.2 miles northwest of Wyoming 220 in Section 16, T.
32 N. , R. 8114., Natrona County, Wyoming. The description is
taken from Wroble (1953) , and the interpretation and nomencla-
ture modified by the writer to fit that used in this paper.

Unit Description Thickness
(Feet)
' "IOWEIR SWDANCE" FCRI-IATION (measured in part)
Stockade Beaver Shale Member (not measured)-
Canyon Springs Sandstone Manber
1h. Limestone, gray, thin-bedded, finely crystalline,
crinkled, irregular contact with underlying
sandStone o o o e o o e o o o o o o o o e o o o e 108
13. Sandstone, gayish-white, massive to medium-bedded,
cross-bedded, fine-gained, frosted gains, fairly
well-sorted, fairly hard, friable, slightly
calcareous o o o o e o o e e o o o e o o o o o o o _ 30.8
Total thickness of Canyon Springs Sandstone Member 32.6
UNNAJ-ED DJTERVAL

12. Shale, red/green, fissile, calcareous . . . . . . 2.8

11. Sandstone, mottled gay, fine-gained, very well-
sorted, hard, calcareous, brownish-red stains . . 1.1

10. Shale, red/geen, fissile, numerous clay pellet
inclusions averaging about l/h inch in diameter,
calcareous o o o o o e o o o o o o e o o o o e o o hol

9. Sandstone, tannish-rust, massive to medium-bedded,
cross-bedded, fine-gained, soft, friable, cal-
careous o o e e e o o o o o e o o o o o o o o o e 803

8. Siltstone, red to maroon, soft, friable, calcareous 1.0
7. Sandstone, rust to reddish-orange, fine-grained,

calcareous, with fissile, maroon shale interbeds . 8.0

-125-

 

-126...

Total thickness of unnamed interval 25.3

CHUCMATER FORMATION (measured in part)

Crow Mountain Sandstone Member

6.

5.

he

3.
2.

Sandstone, rust to reddish-orange, medium-bedded,
cross-bedded, fine-grained, frosted, sub-angular 9.14

grains.......................

Sandstone, tan, massive to medium-bedded, cross-
bedded, fine-gained, fairly well-sorted, friable,
calcareous, limonitic bands near top . . . . . . . . lh.0

Sandstone,similartounit6..... . . .. . .. 5.7
covered-OOOOOOOOOOOOO0000000001500
Sandstone, rust to reddish-orange, massive to medium-
bedded, very fine-gained, frosted, sub-rounded

gains, fairly well-sorted, friable, silty, calcareous,
lenticular00.000000000000000...80,4

Total thickness of Crow Mountain Sandstone Member 52.5

Alcova Limestone Member

1.

Limestone, purplish-gay, finely crystalline,
purple bands, crinkled laminations . . . . . . . . . 20.1

Total thickness of measured portion of
Chugwater Formation 72.6

Red Peak Member (not measured)

Siltstone, medium red, sandy

Total thickness of measured section 130.5

 

SECTION 21: WEST COAL I'IOUI-I'I‘Alli

Canyon Springs? Sandstone Member of the "Lower Sundance"
Formation at the west end of Coal MOuntain in the Red Buttes area
along Wyoming 220 approximately 2 miles by road south of Goose
Egg in the center of Section 22, T. 32 N., R. 81‘W., Natrona
County,'wyoming. The section is 1.5 miles southeast of section
20 and the writer considers it equivalent to unit 20-13. Sampled
by Tenneco Oil Company, Casper Division.

Unit Description Thickness
(Feet)

" LOVER SIHJDMICE' FORMATLON
Canyon Springs? Sandstone Member

2. Sandstone, light tan, yellow shades, weathers medium
tan, massive, cross-bedded, very fine-grained, very
few quartz grains to 1/2 mm. in diameter, well-sorted,
moderately hard, calcareous, sample location near
top of unit.

1. Sandstone, very light tan, massive, cross-bedded, very
fine-grained, some rounded rock and mineral particles
to 1 mm. in diameter,'well-sorted, very soft, friable,
pelecypod? mold, sample location 10 feet from base of
member, forms massive, rounded cliff with unit 2

Approximate thickness of Canyon Springs?
Sandstone Member 20.0

—127-

 

 

 

 

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