U.S. Department of the Interior

U.S. Geological Survey

Pamphlet to accompany

Scientific Investigations Map 3422

Stratigraphic Cross Sections of the Niobrara Interval of the 

Upper Cretaceous Cody Shale in the Bighorn Basin, 

Wyoming and Montana

Stratigraphic Cross Sections of the 

Niobrara Interval of the Upper Cretaceous 

Cody Shale in the Bighorn Basin, Wyoming 

and Montana

By Thomas M. Finn

Pamphlet to accompany

Scientific Investigations Map 3422

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Acting Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Finn, T.M., 2019, Stratigraphic cross sections of the Niobrara Interval of the Upper Cretaceous Cody Shale in the 

Bighorn Basin, Wyoming and Montana: U.S. Geological Survey Scientific Investigations Map 3422, pamphlet 19 p., 

1 sheet [cross section], https://doi.org/10.3133/sim3422.

ISSN 2329-132X (online)
iii

Contents

Introduction.....................................................................................................................................................1

Depositional Setting ......................................................................................................................................6

Stratigraphy ....................................................................................................................................................6

Cody Shale .............................................................................................................................................6

Niobrara Interval........................................................................................................................14

Sage Breaks Interval.................................................................................................................14

Acknowledgments.......................................................................................................................................17

References Cited..........................................................................................................................................17

Figures

1. Generalized map of the Rocky Mountain region showing the locations of

Laramide-age basins....................................................................................................................2

2. Index map of the Bighorn Basin showing major structural elements and principal

oil and gas fields ...........................................................................................................................3

3. Index map of the Bighorn Basin showing the cross section lines presented on the

map sheet.......................................................................................................................................4

4. Type log of Lower and lowermost Upper Cretaceous rocks in the southeastern part

of the Bighorn Basin.....................................................................................................................5

5. Map showing approximate extent of the Western Interior Seaway in North

America during late Coniacian (Scaphites depressus Zone)................................................7

6. Regional northwest-southeast stratigraphic cross section of Cretaceous rocks in

the Bighorn Basin .........................................................................................................................8

7. Schematic reconstruction of the Rocky Mountain region showing Niobrara

depositional trends during late Coniacian (Scaphites depressus Zone) time....................9

8. Correlation chart showing stratigraphic relations of mid-Cretaceous rocks in the

Bighorn Basin and correlation with equivalent rocks at various localities in the

Wind River, Powder River, northwestern Black Hills, and Denver Basins........................10

9. Isopach map of the Cody Shale................................................................................................11

10. Isopach map of the lower shaly member of the Cody Shale...............................................12

11. Isopach map of the upper part of the Cody Shale ................................................................13

12. Isopach map of the Niobrara interval in the lower part of the Cody Shale ......................15

13. Isopach map of the Sage Breaks equivalent interval in the lower part of the Cody

Shale .............................................................................................................................................16
iv

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above sea level.
Stratigraphic Cross Sections of the Niobrara Interval of 

the Upper Cretaceous Cody Shale in the Bighorn Basin, 

Wyoming and Montana

By Thomas M. Finn

Introduction

The Bighorn Basin is a large intermontane structural 

and sedimentary basin that formed in the Rocky Mountain 

foreland during the Laramide orogeny. It is about 180 miles 

(mi) long, 100 mi wide, and encompasses about 10,400 square 

miles (mi2) in north-central Wyoming and a small part of 

south-central Montana (fig. 1). The basin is bounded on the 

northeast by the Pryor uplift, on the east by the Bighorn uplift, 

and on the south by the Owl Creek uplift. The western and 

northwestern margins are formed by the Absaroka volcanics 

and Beartooth uplift, respectively. The northern boundary is 

formed by the Nye-Bowler lineament (figs. 1 and 2).

According to Hewett and Lupton (1917), oil was first 

discovered in the Bighorn Basin in 1884 at an oil seep near 

what is now the Bonanza oil field along the east margin of 

the basin (fig. 2). Several shallow wells were subsequently 

drilled in the area, but no hydrocarbons were found in commercial amounts (Hewitt and Lupton, 1917). It wasn’t until 

1906 that the first commercial hydrocarbon production in the 

Bighorn Basin was established from Cretaceous reservoirs 

at Garland field (fig. 2) (Biggs and Espach, 1960; Fox and 

Dolton, 1996). Since then, many important conventional oil 

and gas fields have been discovered that produce from reservoirs ranging in age from Cambrian through Tertiary; these 

fields primarily produce from anticlinal traps around the 

margins of the basin (Fox and Dolton, 1989, 1996; De Bruin, 

1993) (fig. 2). In addition, a potential unconventional (continuous) basin-centered gas accumulation may be present 

in low-permeability Cretaceous sandstones in the deeper 

parts of the basin (Ryder, 1987; Surdam and others, 1997; 

Johnson and Finn, 1998; Johnson and others, 1999; Finn 

and others, 2010). It has been suggested that various Upper 

Cretaceous marine shales, including the Cody Shale, are 

potential source rocks for many of these accumulations (see 

for example, Hagen and Surdam, 1984; Meissner and others, 

1984; Ryder, 1987; Fox and Dolton, 1989, 1996; Johnson 

and Keighin, 1998; Nuccio and Finn, 1998; Finn, 2014). 

With recent advances and success in horizontal drilling and 

multistage fracture stimulation, there has been an increase 

in exploration and completion of wells in equivalent Upper 

Cretaceous marine shale source rocks in other Rocky Mountain Laramide basins (Matthews, 2011; Sonnenberg, 2011; 

Williams and Lyle, 2011; Durham, 2012a,b, 2013; Taylor and 

Sonnenberg, 2014; Hawkins, 2016).

The stratigraphic cross sections presented in this report 

were constructed as part of a U.S. Geological Survey (USGS) 

project to characterize and evaluate the undiscovered continuous (unconventional) oil and gas resources of the Niobrara 

interval of the Upper Cretaceous Cody Shale in the Bighorn 

Basin in north-central Wyoming and south-central Montana. 

The cross sections show the stratigraphic relationship and 

distribution of the Niobrara interval and associated rocks in 

the lower part of the Cody Shale.

Three cross sections were constructed using borehole geophysical logs from 45 wells drilled for oil and gas 

exploration and production (fig. 3, and map sheet). The cross 

sections include the stratigraphic interval extending from 

the uppermost part of the Frontier Formation to the middle 

part of the Cody Shale (map sheet). The datum is the base of 

the “chalk kick” marker bed, a distinctive resistivity peak or 

zone, in the lower part of the Cody Shale. This datum was 

selected because it is easily identified on most well logs and 

is present throughout the basin (fig. 4, and map sheet).

Gamma ray and (or) spontaneous potential (SP) logs 

were used in combination with resistivity logs to identify and 

correlate units. Gamma ray and SP logs are typically used to 

differentiate between sandstone and shale; however, in the 

Bighorn Basin, the SP response is subdued in some sandstone intervals showing little curve deflection. In areas with 

high drilling density, logs from wells located between control 

wells on the cross sections were used to aid in making correlations. Marine molluscan index fossils collected from 

nearby outcrop sections were projected into the subsurface 

to help determine the relative ages of the strata and also 

aid in correlation. The sources for the fossil data are from 

Cobban (1951), Cobban (1969), Gill and Burkholder (1979), 

Merewether and others (2010), and McKinney and Cobban 

(2018). For all cross sections on the map sheet, the horizontal scale is about 1 inch (in.) = 5.75 mi and the vertical scale 

is about 1 in.=500 ft.
2 Stratigraphic Cross Sections, Niobrara Interval, Upper Cretaceous Cody Shale Bighorn Basin, Wyom. and Mont.

Figure 1. Generalized map of the Rocky Mountain region showing the locations of Laramide-age 

basins.

42°

44°

46°

112° 110° 108° 106° 104° 102°

40°

38°

36°

Greater Green

River Basin

San Juan

Basin

Piceance

Basin

Uinta Basin

Paradox Basin

Bighorn Basin

Crazy

Mountains

Basin

Bull

Mountains

Basin

Raton

Basin

Las

Vegas

Basin

Rio

Grande

Rift

Powder River Basin

Denver Basin

Williston Basin

Sevier

thrust

belt

Sevier

thrust

belt

Snake River

Plain

Hanna

Basin

Laramie

Basin

Shirley

Basin

North and

Middle

Park

Basins

South

Park

Basin

Reed Point

syncline

Yellowstone-

 Absaroka

 volcanic

 field

San

 Juan

 volcanic

 field

Wind

 River

 Basin

UTAH ARIZONA NEW MEXICO

COLORADO

UTAH

IDAHO

MONTANA

WYOMING

OKLAHOMA

TEXAS

KANSAS

SOUTH DAKOTA

SOUTH DAKOTA

NORTH DAKOTA

NEBRASKA

NEBRASKA

COLORADO

WYOMING

Wind River uplift

uplift

uplift

Granite

Mountains

uplift

Owl Creek uplift

uplift

Bighorn

Casperarch

arch

Hartville uplift

Miles City

Washakie uplift

Uinta

Axial Basinuplift

uplift

Rawlins

uplift

Uncompahgre uplift

San Rafael

Swell

Zuni uplift

Sierra Madre

uplift Park Range uplift

Front

Range

White

 River

 uplift

Sangre

de

Cristo

Nacimiento uplift

Pryor

uplift

Black Hills uplift

Teton

uplift

Douglas Creek arch

Nye-Bowler

lineament Beartooth uplift

Apishapa arch

Laramieuplift

Las Animas arch

Base from U.S. Geological Survey, 1985, 1:5,000,000

Albers Equal Area Conic projection

EXPLANATION

Fold and thrust faulted

 terrane

Laramide sedimentary and

 structural basins

Undifferentiated deposits

Approximate eastern limit

 of Sevier thrust belt

Tertiary volcanics

Neogene rift deposits

0 50 100 KILOMETERS

0 50 100 MILES
Figure Bighostructoil ancontoof the Contosea le

S.L.

5,000

SL

-5,000

-10,000

SL

-5,000

5,000

SL

5,000

SL

SL

5,000

-5,000

-10,000

-5,000

-5,000

SL

SL

SL

SL

SL

MONTANA

WYOMING

-5,000

Byron

Fritz

00 10 20 30 40 KILOMETERS

10 20 30 40 MILES

T

50

N

T

55

N

T9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T9

S

T5

S

R15E R20E R25E R30E R35E

R101W R95W

R90W R85W

R40E

R105W

T

40

N

T

45

N

T5

N

R5W R1W R1E R5E

T8

N

R4W

T8

N

R3E

110° 109° 108° 107°

45°

44°

Absaroka

volcanics

Beartooth

uplift

Creek

uplift

Owl

uplift

Bighorn 

Nye-Bowler

lineament

Pryor uplift

Manderson

Little Buffalo Basin

Grass Creek

Meeteetse

Oregon Basin

Hidden Dome

Worland

Greybull Greybull

West

FiveMile

DobieCreek

Dry Creek Golden

Dome

Badger Basin

Elk Basin

Frannie

Garland

Byron

Hamilton Dome

Heart

Mountain

Silver Tip

Cottonwood Creek

Neiber Dome

Murphy Dome

Black Mountain

Gebo

Fourteen Mile

Ralston

Pitchfork

Bonanza

Lamb

Torchlight

Fritz

Emblem

Bench

Seller Draw

Base from 1:2,000,0Lambert Standard Central mLatitude North Am

BIGHORN

BASIN

PROVINCE

WYOMING

MONTANA
Figure Bighocross the ma

A

A'

B

B'

C

C'

MONTANA

WYOMING

A

A

00 10 20 30 40 KILOMETERS

10 20 30 40 MILES

T

50

N

T

55

N

T9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T9

S

T5

S

R15E R20E R25E R30E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T5

N

R5W R1W R1E R5E

T8

N

R4W

T8

N

R3E

110° 109° 108° 107°

45°

44°

Absaroka

volcanics

Beartooth

uplift

Creek

uplift

Owl

uplift

Bighorn 

Nye-Bowler

lineament

Pryor uplift

Base from 1:2,000,0Lambert CStandard Central mLatitude oNorth Am

BIGHORN

BASIN

PROVINCE

WYOMING

MONTANA
Introduction 5

Figure 4. Type log of Lower and lowermost Upper Cretaceous rocks in the southeastern part of the 

Bighorn Basin. GR, gamma ray log; Res., resistivity log; Ss, sandstone; Mbr., member. Location shown in 

figure 2. 

4,500

5,000

5,500

6,000

6,500

7,000

7,500

GR Res.

API 4904320512

Pike Resources Federal 1–15

sec. 15, T. 45 N., R. 90 W.

Mowry

Shale

Upper

siliceous

part

Lower

part

Muddy Sandstone

Thermopolis Shale

Morrison Formation

(part)

“rusty beds”

Greybull Ss. Mbr. Cloverly

Formation

Frontier

Formation

Cody Shale (part)

Lower shaly member

Upper sandy

member

(part)

Niobrara interval

Sage

Breaks

interval

Jurassic

(part) Lower Cretaceous Upper Cretaceous (part)

“chalk kick

marker”

Clay Spur Bentonite Bed

EXPLANATION

Estuarine and fluvial sandstone

Floodplain and lacustrine sandstone,

 shale, and conglomerate

Tidal sandstone, siltstone,

 and shale

Marine and marginal marine sandstone

 and siltstone

Marine sandstone, shale, sandy shale,

 and siltstone

Marine shale

Marine shale, calcareous shale, sandy shale,

 silty shale, and marl

Laterally persistant zone within the Cody

 Shale showing higher gamma ray intensity

Siliceous marine shale

Undifferentiated deposits
6 Stratigraphic Cross Sections, Niobrara Interval, Upper Cretaceous Cody Shale Bighorn Basin, Wyom. and Mont.

Depositional Setting

During Late Jurassic and Cretaceous time, that part of 

Wyoming and Montana that is now the Bighorn Basin was 

located in the western part of the Western Interior Basin, 

an elongate north-south foreland basin, that developed to 

the east of the tectonically active Cordilleran highlands of 

western North America (fig. 5). From Albian to Maastrichtian 

time (latest Early Cretaceous to latest Cretaceous time), the 

foreland basin was periodically flooded by a broad epicontinental sea, referred to as the Western Interior Seaway (WIS), 

which developed in response to foreland basin subsidence and 

eustatic sea-level fluctuations (Steidtmann, 1993). At its maximum extent, the WIS extended for more than 3,000 mi from 

the Arctic Ocean to the Gulf of Mexico (fig. 5) (Kauffman, 

1977). Erosion of the Cordilleran highlands supplied sediment to the western part of the basin by eastward-flowing 

streams; whereas, the eastern part of the basin was adjacent 

to the topographically low and stable North American craton 

and received little sediment (Molenaar and Rice, 1988). The 

shoreline repeatedly advanced and retreated across the western 

part of the basin resulting in a complex pattern of intertonguing marine and nonmarine deposits (fig. 6). Marginal marine 

and nonmarine deposits are represented by eastward-thinning 

wedges of marginal marine and nonmarine sandstone, siltstone, shale, carbonaceous shale, and coal. The marine deposits are represented by westward-thinning tongues of marine 

shale, siltstone, and marine sandstone (fig. 6). The marine 

sediments were deposited during widespread transgressions 

creating highstand conditions as the seaway deepened, limiting clastic input, and at times forming anoxic bottom conditions favorable for the preservation of organic matter (Gries 

and others, 1992). In addition, these transgressions produced 

two widespread episodes of carbonate deposition in the WIS; 

the first resulted in the deposition of the Upper Cretaceous 

Greenhorn Formation, the second resulted in the deposition of 

the Upper Cretaceous Niobrara Formation and its equivalents 

(Longman and others, 1998; Sonnenberg, 2011). The Niobrara 

is characterized by deposition of chalks and marls composed 

of foraminifer and coccolith debris that accumulated in the 

sediment-starved eastern part of the seaway (Longman and 

others, 1998; Sonnenberg, 2011). The chalks grade westward 

into more siliciclastic beds that were derived from the eroding highlands to the west, diluting the carbonate content in 

the sediments (Longman and others, 1998; Sonnenberg, 2011) 

(fig. 7). In the Bighorn Basin, the Niobrara interval is represented by shales, calcareous shales, marls, siltstones, and sandstones in the lower shaly member of the Cody Shale (fig. 6).

Stratigraphy

A correlation diagram showing the stratigraphic nomenclature for the Cody Shale and associated rocks in the Bighorn 

Basin and correlative units at various localities in the Wind 

River, Powder River, and Denver Basins is shown on figure 8. 

The Wind River Basin nomenclature is modified from Keefer 

(1972) and Finn (2017), the western Powder River Basin 

nomenclature is modified from Merewether (1996), and the 

northwestern Black Hills and Pueblo, Colo. (Denver Basin) 

nomenclature is modified from Merewether and others (2011). 

The stratigraphic relationships and nomenclature for the 

Bighorn Basin are also illustrated on the regional stratigraphic 

cross section in figure 6.

Cody Shale

The Upper Cretaceous Cody Shale is composed of shales, 

calcareous shales, marls, bentonites, siltstones, and sandstones, with the amount of sandstone and siltstone increasing 

in the upper part (Keefer, 1972). The main body of the Cody 

Shale was deposited during a second-order transgressiveregressive cycle referred to as the “Niobrara Cyclothem” by 

Kauffman (1977), and ranges in age from latest Turonian to 

early Campanian. The early to middle Campanian age Claggett 

Member is the uppermost part of the Cody Shale, and was 

deposited during a subsequent transgressive-regressive cycle 

that Kauffman (1977) referred to as the “Claggett Cyclothem” 

(fig. 8). The lower and upper contacts of the Cody Shale are 

conformable and interfinger extensively with the underlying 

Frontier and overlying Mesaverde Formations (fig. 6).

The Cody Shale is about 1,750 feet (ft) thick in the 

northwestern part of the basin increasing to nearly 3,800 ft in 

the southeastern part (fig. 9). The eastward thickening is due to 

the eastward stratigraphic rise and intertonguing of the contact 

between the Cody Shale and the overlying Mesaverde Formation, and in part, to the west to northwest backstepping nature 

of the Frontier-Cody contact (fig. 6, map sheet). Three members 

are recognized, in ascending order: (1) the unnamed lower shaly 

member (Keefer, 1972), (2) the unnamed upper sandy member 

(Keefer, 1972), and (3) the Claggett Member or Claggett Shale 

in Montana (Keefer and others, 1998) (figs. 6 and 8).

The lower shaly member, extending from the top of the 

Frontier Formation to the base of the sandy member, reaches a 

maximum thickness greater than 1,200 ft in the southern part of 

the basin and thins northward to about 700 ft (fig. 10). It is composed of gray to black shale, calcareous shale, marl, and bentonite, with minor amounts of siltstone and sandstone that were 

deposited in an offshore marine environment. The lower shaly 

member ranges in age from latest Turonian to early Santonian.

The combined thickness of the upper sandy member and 

the Claggett Member (Claggett Shale) ranges from greater 

than 2,700 ft in the southeastern part of the basin to around 

1,000 ft in the northern part (fig. 11). The upper sandy member 

consists of buff, or light- to medium-gray sandstones, and gray 

shales (Johnson and others, 1998). According to Johnson and 

others (1998), the sandstones are very fine to medium grained, 

laterally persistent, and exhibit a variety of bedding features 

including horizontal laminae, ripple laminae, and hummocky 

cross-bedding. The Claggett Member is composed of light- to 

medium-gray shale interbedded with thin siltstones and fineto medium-grained sandstones (Johnson and others 1998).
Stratigraphy 7

Figure 5. Map showing approximate extent of the Western Interior Seaway in North America during late Coniacian 

(Scaphites depressus Zone). Modified from Cobban and others (2005).

Study

area

ALASKA

GREENLAND

HIGHLANDS

CORDILLERAN

WESTERN

INTERIOR

SEAWAY

UNITED STATES

CANADA

ARCTIC OCEAN

ATLANTIC OCEAN PACIFIC OCEAN

GULF OF MEXICO

MEXICO

0

0 250 500 KILOMETERS

250 500 MILES
Figure 6. Regional northwest-southeast stratigraphic cross section of Cretaceous rocks in the Bighorn Basin. Modified from Finn (2010). Muddy Sandstone NORTHWEST

MONTANA

WYOMING

Nye-Bowler lineament Badger Basin McCulloch Peak Emblem Bench Red Point Fritz C

Dobie Creek Five Mile Worland

Mowry Shale

"chalk kick"

C

Meeteetse Formation (part) Lewis Shale

Teapot Sandstone Member

Claggett Member of Cody Shale

Frontier Formation

Frontier Formation

Jurassic rocks

undivided (part)

Thermopolis Shale

Cloverly Formation

Telegraph Creek Formation

Eagle Sandstone Virgelle Sandstone Member

Claggett Shale Parkman

Sandstone

Lower member

Lower shaly member

Upper sandy member

Mesaverde Formation (middle part) Mesaverde Formation

Judith River Formation (part)

Cody Shale

Niobrara interval

Sage Breaks interval

Upper Cretaceous

Lower

Cretaceous

Jurassic

? ?

? ?

Marker beds

Unconformity

EXPLANATION

Fluvial and estuarine sandstone

Fluvial sandstone and conglomerate

Marine and marginal marine sandstone and siltstone

Tidal sandstone, siltstone, and shale

Floodplain and lacustrine sandstone, shale, and conglomerate

Calcareous marine shale and marl

Marine shales

Siliceous marine shale

Nonmarine sandstone, siltstone, shale, carbonaceous shale, and coal deposited in poorly drained coastal environments

Undifferentiated deposits

Sandstone, siltstone, shale, carbonaceous shale, and coal deposited in coastal plain, alluvial plain, coastal swamp, and lagoonal environments 

Interbedded marine sandstone and shale

0 10 20 KILOMET

0

100

5

500

10 15 20 

200300 1,000

METERS FEET
Stratigraphy 9

Figure 7. Schematic reconstruction of the Rocky Mountain region showing Niobrara 

depositional trends during late Coniacian (Scaphites depressus Zone) time. Bighorn 

Basin outlined in red. Modified from McGookey and others (1972).

Base from Bureau of Land Management digital data, 2016

Lambert Conformal Conic projection

Standard parallels 33° and 45°, Central meridian −108°

Latitude of origin 39°

North American Datum of 1983 (NAD83)

112° 108° 104° 100°

36°

40°

44°

48°

Cody

Shale

Cody

Shale

Baxter

Shale

Mancos

Shale

Niobrara

Formation

Niobrara

Formation

INTERIOR

WESTERN

SEAWAY

NORTH DAKOTA

SOUTH DAKOTA

NEBRASKA

KANSAS

COLORADO

WYOMING

TEXAS

OKLAHOMA

NEW MEXICO

ARIZONA

UTAH

IDAHO

MONTANA

Highlands

Coastal plain

Coastal sandstones 

Marine shale

Calcareous marine

 shale/marl

Limestone/chalk

Bighorn Basin boundary

EXPLANATION

0 100 200 MILES

0 100 200 KILOMETERS
Figure 8. Correlation chart showing stratigraphic relations of mid-Cretaceous rocks in the Bighorn Basin and correlation with equivalent rocks at vaRiver, Powder River, northwestern Black Hills, and Denver Basins. The diagonal lines represent the Niobrara interval in the Bighorn Basin, as defined from Keefer (1972), Hicks and others (1995), Merewether (1996), Kirschbaum and others (2009), Merewether and others (2011), Finn (2014), and Finn (20periods of erosion or nondeposition. Radiometric ages and fossil zones are from Cobban and others (2006) and Merewether and McKinney (2015). Seafrom Kauffman and Caldwell (1993).

CRETACEOUS (part)

UPPER CRETACEOUS (part)

Lower Lower Lower

Upper

Upper Upper Upper Middle Middle Middle

System

Series

Stage

Substage

Campanian (part) Santonian

Lower

MiddleMiddle

Upper

Coniacian Turonian Cenomanian (part)

Western Interior

ammonite zones

Western Interior

inoceramid zones

Western Wind

River Basin

Northern Bighorn

Basin,

Wyoming

Northern Bighorn

Basin,

Montana

Western and

southwestern

Bighorn Basin

Eastern and

southeastern

Bighorn Basin

Eastern and

southeastern

Wind River Basin

Western Powder

River Basin

Northwestern

Black Hills

Southern and

central Wind

River Basin

Age

(Ma)

75.19 ± 0.28

80.58 ± 0.55

81.86 ± 0.3684.43 ± 0.34

86.3 ± 0.5

87.14 ± 0.39

88.55 ± 0.59

89.8 ± 0.3

90.21 ± 0.5490.51 ± 0.4593.48 ± 0.58

93.68 ± 0.5093.99 ± 0.7294.71 ± 0.49

94.96 ± 0.50

95.73 ± 0.61

93.32 ± 0.38

93.82 ± 0.30

83.6 ± 0.2

75.56 ± 0.11

75.84 ± 0.26

Upper sandy

member

Upper sandy

member

Upper sandy

member

Upper sandy

member

Upper sandy

member

Lower member Lower member

Claggett

Member

Claggett

Member Claggett Shale

Upper sandy

member

Upper

sandy

member

Mesaverde

Formation

(part)

Mesaverde

Formation

(part)

Mesaverde

Formation

(part)

Niobrara

Member Niobrara

interval Niobrara

interval Niobrara interval Niobrara interval Niobrara interval Niobrara interval Niobrara Formation

Steele Member

(undivided)

Mesaverde

Formation

(part)

Mesaverde

Formation

(part)

Mesaverde

Formation

(part)

Mesaverde

Formation

(part)

Cody Shale

Cody Shale

Cody Shale

Cody Shale

Cody Shale

Frontier Formation (part)

Frontier Formation (part)

Frontier Formation (part)

Frontier Formation (part)

Frontier Formation (part)

Frontier Formation (part)

Frontier Formation (part)

Frontier Formation (part)

Cody Shale

Cody Shale

Cody Shale

Lower shaly member

Lower shaly member

Lower shaly

member

Lower shaly member

Lower shaly member

Lower shaly member

Lower shaly member

Alkali Butte

member

Basal sandstone member

Fales Sandstone

Member

Conant Creek

tongue

Sage Breaks

Member

Sage Breaks

interval

Sage Breaks

interval

Sage Breaks

Sage Breaks

interval

Sage Breaks

interval

Sage Breaks

interval

Sage Breaks

interval

?

?

Belle Fourche

Shale

Belle Fourche (part) Member

(part)

Belle Fourche

equivalent

(part)

Belle Fourche

equivalent

(part)

Belle Fourche

equivalent

(part)

Belle Fourche

Member

(part)

Belle Fourche

Member

(part)

Belle Fourche

Member

(part)

Pierre Shale

(part)

Pierre Shale

(part)

Carlile Shale

(part) 

Greenhorn

Formation

Wall Creek

Member

Emigrant Gap

Member

Emigrant Gap

Member Emigrant Gap Member Emigrant Gap Member

Carlile Shale

(part)

Wall Creek

Member

Wall Creek

Member

Wall Creek

Member

"chalk kick" "chalk kick" “chalk kick” "chalk kick" "chalk kick" "chalk kick" "chalk kick"

Eagle Sandstone

Telegraph Creek Fm.

Judith River

Formation

(part)

Parkman Sandstone

Unnamed

member

Unnamed

 member

Unnamed

member

Unnamed

member

Unnamed

member

Niobrara

interval

Wallace Creek Tongue

Baculites sp. (weak flank ribs)

Baculites sp. (smooth)

Baculites sp. (smooth)

Cataceramus subcompressus

Cataceramus balticus

′′Inoceramus′′ tenuilineatus

′′Inoceramus′′ azerbaydjanensis

Baculites scotti

Baculites reduncus

Baculites gregoryensis

Baculites perplexus

Baculites asperiformis

Baculites maclearni

Baculites obtusus

Didymoceras nebrascense

Scaphites hippocrepis III

Volviceramus

involutus

Volviceramus

koeneni

Magadiceramus crenelatus Magadiceramus subquadratus

Cladoceramus undulatoplicatus

Cordiceramus bueltensis

Sphenoceramus lundbreckensis

Cremnoceramus waltersdorfensis

Cremnoceramus waltersdorfensis hannoverensis

Cremnoceramus

deformis deformis

Cremnoceramus deformis erectus

Cremnoceramus

crassus crassus

Cremnoceramus crassus inconstans

"Inoceramus" gibbosus

Scaphites leei III

Scaphites depressus

Scaphites ventricosus

Scaphites preventricosus

Scaphites mariasensis

Scaphites hippocrepis II

Scaphites hippocrepis I

Desmoscaphites bassleri

Desmoscaphites erdmanni

Clioscaphites choteauensis

Clioscaphites vermiformis

Clioscaphites saxitonianus

Mytiloides scupini

Mytiloides incertus

Mytiloides hercynicus

Mytiloides mytiloides

Mytiloides kossmati

Inoceramus

perplexus

Inoceramus dimidius

Inoceramus howelli

Inoceramus n. sp.

Inoceramus aff. dimidius

Inoceramus

dakotensis

Scaphites nigricollensis

Scaphites whitfieldi

Scaphites warreni

Prionocyclus germari

Prionocyclus ferronensis

Prionocyclus macombi

Prionocyclus hyatti

Collignoniceras praecox

Collignoniceras woolgari

Mammites nodosoides

Vascoceras birchbyi

Pseudaspidoceras flexuosum

Colinoceras tarrantense

Plesiacanthoceras wyomingense

Acanthoceras amphibolum

Acanthoceras bellense

Acanthoceras muldoonense

Acanthoceras granerosense

Dunveganoceras conditum

Dunveganoceras albertense

Dunveganoceras problematicum

Dunveganoceras pondi

Mytiloides puebloensis

Mytiloides hattini

Inoceramus pictus

Inoceramus ginterensis

Inoceramus prefragilis

Inoceramus rutherfordi

Inoceramus arvanus

Inoceramus macconnelli

Watinoceras devonense

Nigericeras scotti

Neocardioceras juddii

Burroceras clydense

Euomphaloceras septemseriatum

Vascoceras diartianum
FigurCody the inuppeundeto thFormloweFormin WSandin M250 f

MONTANA

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3,500

3,500

3,000

2,500

3,750

3,250

3,250

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2,250

2,250

2,000

2,250

2,500

2,750

1,750

3,250

00 10 20 30 40 KILOMETERS

10 20 30 40 MILES

T

50

N

T

55

N

T9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T9

S

T5

S

R15E R20E R25E R30E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T5

N

R5W R1W R1E R5E

T8

N

R4W

T8

N

R3E

110° 109° 108° 107°

45°

44°

Absaroka

volcanics

Beartooth

uplift

Creek

uplift

Owl

uplift

Bighorn 

Nye-Bowler

lineament

Pryor uplift

Base fr1:2,000LambeStandaCentraLatitudNorth A

BIGHORN

BASIN

PROVINCE

WYOMING

MONTANA
Figurthe loCody the iuppeundeto thmemModThic

MONTANA

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1,000

1,000

1,000

900

700

700

800

800

900

900

1,200

1,100

1,200

1,100

1,100

1,00

00 10 20 30 40 KILOMETERS

10 20 30 40 MILES

T

50

N

T

55

N

T9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T9

S

T5

S

R15E R20E R25E R30E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T5

N

R5W R1W R1E R5E

T8

N

R4W

T8

N

R3E

110° 109° 108° 107°

45°

44°

Absaroka

volcanics

Beartooth

uplift

Creek

uplift

Owl

uplift

Bighorn 

Nye-Bowler

lineament

Pryor uplift

Base fr1:2,000LambeStandaCentraLatitudNorth A

BIGHORN

BASIN

PROVINCE

WYOMING

MONTANA
MONTANA

WYOMING

1,500

1,500

2,000

2,500

1,750

2,250

2,750

1,250

1,250

1,000

1,500

1,500

1,500

1,250

1,25

00 10 20 30 40 KILOMETERS

10 20 30 40 MILES

T

50

N

T

55

N

T9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T9

S

T5

S

R15E R20E R25E R30E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T5

N

R5W R1W R1E R5E

T8

N

R4W

T8

N

R3E

110° 109° 108° 107°

45°

44°

Absaroka

volcanics

Beartooth

uplift

Creek

uplift

Owl

uplift

Bighorn 

Nye-Bowler

lineament

Pryor uplift

Base fr1:2,000LambeStandaCentraLatitudNorth A

BIGHORN

BASIN

PROVINCE

WYOMING

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FiguruppeThis from sandMesaincluthe MClaggShale Sandin Mo250 f
14 Stratigraphic Cross Sections, Niobrara Interval, Upper Cretaceous Cody Shale Bighorn Basin, Wyom. and Mont.

Niobrara Interval

The Niobrara interval of the Cody Shale in the Bighorn 

Basin is represented by gray to black shale, calcareous shale, 

marl, and bentonite, with minor amounts of siltstone and 

sandstone. In many samples, the more calcareous zones are 

often characterized by varying amounts of coccolith-rich 

fecal pellets that appear as distinctive “white specks” similar to those described by Hattin (1975). A persistent zone or 

high-resistivity peak identified on resistivity logs in the lower 

40–350 ft of the lower shaly member (fig. 4, map sheet), 

referred to as the “chalk kick” marker by Keefer (1972) and 

Keefer and others (1998), represents the base of the Niobrara 

interval and top of the Sage Breaks interval of the Cody 

Shale in the Bighorn Basin based on correlations projected 

from the Wind River Basin by Finn (2017). The “chalk kick” 

marker can be traced in the subsurface throughout most of the 

basin, and based on sample descriptions from well cuttings, 

separates noncalcareous shales in the lowermost part of the 

shaly member from overlying calcareous strata (fig. 4; map 

sheet). The top of the Niobrara interval is placed at the base 

of the overlying sandy member. The Niobrara interval thickens from about 500–700 ft in the northern and southeastern 

parts of the basin to about 1,100 ft in the southwestern part of 

the basin (fig. 12).

Fossil data reported by Cobban (1951, 1969), Gill and 

Burkholder (1979), Merewether and others (2010), and 

McKinney and Cobban (2018) indicate that the Niobrara interval extending from the “chalk kick” marker to the base of the 

upper sandy member is middle Coniacian to early Santonian in 

age (fig. 8).

Sage Breaks Interval

Finn (2014) referred to the interval of the shaly member 

of the Cody Shale below the “chalk kick” marker and above 

the top of the Frontier Formation as the Carlile Shale. Here, it 

is referred to as the Sage Breaks interval to be consistent with 

the terminology of Finn (2017) for the Wind River Basin, and 

Merewether (1996), who referred to the interval as the Sage 

Breaks Member of the Cody Shale in the western part of the 

Powder River Basin (fig. 8). This interval, ranging in thickness from nearly 350 ft in the eastern and southeastern parts 

of the basin to less than 50 ft in the central and northern parts, 

reflects the backstepping stacking pattern of the sandstones 

in the underlying Frontier Formation (figs. 6, 13; map sheet). 

Ammonite and inoceramid fossils collected from the underlying Frontier Formation and within the Sage Breaks interval 

indicate that it is latest Turonian to middle(?) Coniacian in age 

(fig. 8).
FigurNiobpart inclubase to thof thFinn 50 fe

MONTANA

WYOMING

700

900

800

800

700

750

750

850

600

650

550

900

1,000

950

1,000

1,100

1,050

850

800

00 10 20 30 40 KILOMETERS

10 20 30 40 MILES

T

50

N

T

55

N

T9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T9

S

T5

S

R15E R20E R25E R30E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T5

N

R5W R1W R1E R5E

T8

N

R4W

T8

N

R3E

110° 109° 108° 107°

45°

44°

Absaroka

volcanics

Beartooth

uplift

Creek

uplift

Owl

uplift

Bighorn 

Nye-Bowler

lineament

Pryor uplift

Base fr1:2,000LambeStandaCentraLatitudNorth A

BIGHORN

BASIN

PROVINCE

WYOMING

MONTANA
FiguSage in thShalinter“chathe uundeModThic

MONTANA

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300

200

200

200

200

100

100

300

100

100

100

200

200

100

00 10 20 30 40 KILOMETERS

10 20 30 40 MILES

T

50

N

T

55

N

T9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T9

S

T5

S

R15E R20E R25E R30E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T5

N

R5W R1W R1E R5E

T8

N

R4W

T8

N

R3E

110° 109° 108° 107°

45°

44°

Absaroka

volcanics

Beartooth

uplift

Creek

uplift

Owl

uplift

Bighorn 

Nye-Bowler

lineament

Pryor uplift

Base fr1:2,000LambeStandaCentraLatitudNorth A

BIGHORN

BASIN

PROVINCE

WYOMING

MONTANA
References Cited 17

Acknowledgments

The manuscript and sheet benefited from reviews by 

Ron Johnson, Jon Haacke, Ofori Pearson, Janet Slate, and 

Dave Ferderer of the U.S. Geological Survey (USGS); their 

suggestions and comments are greatly appreciated. Important 

data about fossil collections and locations were provided 

by K.C. McKinney, curator of the USGS fossil collection in 

Denver, Colo.

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Outcrops, fossils, geophysical logs, and tectonic interpretations of the Upper Cretaceous Frontier Formation and 

contiguous strata in the Bighorn Basin, Wyoming and 

Montana: U.S. Geological Survey Scientific Investigations 

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Finn—Stratigraphic Cross Sections, Niobrara Interval, Upper Cretaceous Cody Shale, Bighorn Basin, Wyom. and Mont.—Scientific Investigations Map 3422

ISSN 2329-132X (online)

https://doi.org/10.3133/sim3422