Lower Cody Shale (Niobrara Equivalent) in the Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

110° 109° 110° 108° 109° 107° 108° 107° R15E R20E R25ER15E R20E R35ER25E EXPLANATIONR35E EXPLANATION

T T Tertiary volcanic rocks Tertiary volcanic rocks 5 NYE-BOWLER 5 NYE-BOWLER S S 0 20 40 MILES 0 20 40 MILES LINEAMENT LINEAMENT Cody Shale outcrop Cody Shale outcrop 110° 109° 108° 107° 0 20 40 KILOMETERS 0 Precambrian20 rocks 40 KILOMETERS Precambrian rocks R15E R20E R25E R35E 1,750 1,750 MOUNTAINSPRYOR MOUNTAINSPRYOR Bighorn Basin Province boundary Bighorn Basin Province boundary BEARTOOTH BEARTOOTH T EXPLANATION MOUNTAINS MOUNTAINS 5 NYE-BOWLER Eastern limit of lower memBer of Eastern limit of lower memBer of LowerS Cody Shale Mesaverde Formation (Niobrara Mesaverde Equivalent) Formation in the Bighorn Basin, 1,750 1,750 LINEAMENT Bighorn Basin Province Boundary T T 700 T Well location T Well location 9 9 9 9 Tertiary volcanic rocks MONTANA MONTANA 45° S 45° S R35E R40E S Thickness isopach,R35E in feet R40E S Thickness isopach, in feet 700 110°MOUNTAINSPRYOR 109° Cody Shale outcrop 108° 107° WYOMING R101W WYOMINGR95W R101W R95WBEARTOOTH BIGHORN Wyoming andBIGHORN <1,750 Montana—Thickness,<1,750 R25E Distribution,R35E and Source R15E R20E T T MOUNTAINS Precambrian rocks 57 57 T N N 8001,750 to 2,000 1,750 to 2,000 EXPLANATION T 5 NYE-BOWLER Well location T 9 9 MONTANA 2,000 to 2,250 S 2,000 to 2,250 Bighorn Basin Province Boundary 45° S 900 LINEAMENT0 R35E 20 40R40E MILES S T T Rock Potential 2,000 2,000 WYOMING T R101W2,250 to 2,500 R95W T 2,250 to 2,500 Tertiary volcanic rocks 55 55 55 700 55 BIGHORN 0 20 110° 40 KILOMETERS 109° 108° 107° N N T 57N 2,500 to 2,750 N 2,500 to 2,750 R90W R85W R90W R85W MOUNTAINSR15EPRYOR R20E Cody ShaleR25E outcrop R35E N 900 BEARTOOTH 550 2,750 to 3,000 2,750 to 3,000 MOUNTAINS 600 T Precambrian rocks EXPLANATION 800 650 5 NYE-BOWLER ABSAROKA ABSAROKA T 3,000 to 3,250 T 3,000 to 3,250 S Well location T T LINEAMENT Bighorn Basin Province Boundary 55 900 9 700 55 9 MOUNTAINS 3,250 to 3,500 MOUNTAINSMONTANA 3,250 to 3,500 40 MILES N 45° S N 0 R35E 20 R40E S R90W R85W 110° 109° Tertiary volcanic rocks 108° 107° 3,500 to 3,750 WYOMING R101W3,500 to 3,750 R95W 100 BIGHORN 20 40 KILOMETERS R20E R25E R35E T 0 MOUNTAINSR15EPRYOR Cody Shale outcrop 800 BEARTOOTH >3,750 57 >3,750

ABSAROKA T EXPLANATION N MOUNTAINS Precambrian rocks T 2,250 T 2,250 T T 5 NYE-BOWLER 50 50 100 50 900 50 S RANGE RANGE T T Bighorn Basin Province Boundary N N N N MOUNTAINS LINEAMENT Well location 9 9 T 1,100 T MONTANA S 0 R35E 20 40 MILESR40E S Tertiary volcanic rocks R104W R104W 55 45° 0.8 55 N WYOMING R101W R95W 2,750 2,750 N BIGHORN0.8 Frontier/Mowry/Muddy/Thermopolis R90W R85W MOUNTAINS40PRYOR KILOMETERS 750 T 100 BEARTOOTH 0 20 2,500 2,500 T T Formations outcrop 1,000 57 MOUNTAINS 50 N50 100 1.1 Precambrian rocks RANGE 1,000 N 800 N 1,100 ABSAROKA 44° 44° 850 T1.35 High-angle fault T 100 9 9 3,000 R104W 3,000 T MONTANA S 200 MOUNTAINS T ThrustR35E fault R40E S 3,750 3,750 55 45° R101W R95W 55 3,250 T 3,250 T N WYOMING BIGHORN Line of secton T T 2,750 2,750 Clark's N 3,500 45 3,500 45 T R90W R85W 45 45 1,200 Well sample point N N N N 57 44° T N Composite well sample point T Fork 1 1,200 100 . 0.8 R100W R100W 50 ABSAROKA 50 1.35 1 Outcrop sample point R105W R105W RANGE 950 R4W R4W 1,100 N 1,100 N sub-basin 1 1,100 1,000 400

300 Burial history location 1,200 200 . T R3E T R3E 1,100 1,000 100 T 1 T T T T T 55 MOUNTAINS 8 8 R104W 1.1 55 N 8 N 45 8 45 N 0 20 40 MILES N N N N 1,200 N R90W R85W R95W R95W 950 850 900 800 1 .1 0 20 40 KILOMETERS BIG TRAILS FAULT BIG TRAILS FAULT 1,000 R105W R100W 1,050 T 950 1.35 T R4W ABSAROKA 44° 50 200 OREGON 50 OWL OWL T R3E RANGE T T T T T 1,000 N N 40 T 40 T 408 40 CREEK CREEK N 8 950 MOUNTAINS

N 5 N MOUNTAINS 5 MOUNTAINSN N N R1W R1W R5E R5E R5W R5W R94W R94W 950 R1E R1E R85W R85W R90W N N R90W R95W R104W 700 T T BASIN 2.0

750 400

45 BIG TRAILS FAULT 45

N Emblem

R5W R1W R1E R5E R94WR5W R90WR1W R1E R85WR5E R94W R90W R85W 850 MOUNTAINS

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300 BIG TRAILS FAULT

BIG TRAILS FAULT N 8 300

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40 T CREEK T R3E .1

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45 45

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BIG TRAILS FAULT

3,750 3,750 MOUNTAINS

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3,000 3,000

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R105W

R100W 40

R105W 40 R100W

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TOWL R4W T

1,200

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BIG TRAILS FAULT

2,500 2,500

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OWL

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1,100

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MOUNTAINS MOUNTAINS

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1,000 N

BIG TRAILS FAULT

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900

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2,500 to 2,750 2,500 to 2,750

N N

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T T

MOUNTAINS N

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N 55 55 900 R104W

300

2,250 to 2,500 2,250 to 2,500

T T 2,000 2,000 8 T T

1,000 R3E

ABSAROKA T

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T T T

R104W Thickness isopach, in feet Thickness isopach, in feet

45° 45°

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R40E R40E S S S S

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800

MOUNTAINS

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1 9 9 9 9

Well location Well location

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50 900

50 °

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Mesaverde Formation Mesaverde Formation 57

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MOUNTAINS MOUNTAINS 0.6

Eastern limit of lower memBer of Eastern limit of lower memBer of 0 20 700 40 KILOMETERS

BIGHORN

BEARTOOTH BEARTOOTH

WYOMING

R95W R101W

750

PRYOR PRYOR

R90W R85W Bighorn Basin Province boundary Bighorn Basin Province boundary MOUNTAINS MOUNTAINS

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R40E 20 0 S N S 40 MILES MONTANA N

55 9

Precambrian rocks Precambrian rocks 55

R104W

0 0 20 20

40 KILOMETERS 40 KILOMETERS

Well location

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Cody Shale outcrop Cody Shale outcrop Dobie

S S

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Tertiary volcanic rocks Tertiary volcanic rocks BEARTOOTH

T T

FAULT T

PRYOR

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Emblem R15E R15E R20E R20E R25E R25E EXPLANATION EXPLANATION

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0 20 40 KILOMETERS

Tertiary volcanic rocks

BIGHORN

WYOMING

N R95W R101W 700 2.0 BASIN

109° 109° 110° 110° 107° 107° 108° 108°

LINEAMENT 55

45°

R35E Bighorn Basin Province Boundary R40E S

20 0

Scientific Investigations Report 2013–5138 40 MILES 200 MONTANA

MOUNTAINS

700 9

NYE-BOWLER 5

100

Well location T T

EXPLANATION T

650

OREGON

ABSAROKA 1.35

600 Precambrian rocks

R15E MOUNTAINS R20E R25E

R35E 100

550

BEARTOOTH 1

0 20

40 KILOMETERS

109° 110° 107° 108°

1 100

T PRYOR 0 20 40 KILOMETERS

MOUNTAINS Cody Shale outcrop

R90W R85W

BIGHORN

WYOMING R95W R101W

20 0

40 MILES

45°

. 55 Tertiary volcanic rocks 20 0

40 MILES R35E 1 55 R40E S S MONTANA

1 T 9

Burial history location LINEAMENT

sub-basin

Well location

Bighorn Basin Province Boundary

T T S

Outcrop sample point

1.35

NYE-BOWLER

5 .

100 0.8

1 Fork

Precambrian rocks EXPLANATION

T Composite well sample point MOUNTAINS N

BEARTOOTH 57

Well sample point

R15E Cody Shale outcrop R20E PRYOR R25E

R35E MOUNTAINS

Clark's

BIGHORN

100 WYOMING

Line of secton 109° 110° 107° 108° R95W R101W

U.S. Department of the Interior Tertiary volcanic rocks

45°

R35E R40E S Thrust fault

MONTANA S

LINEAMENT

Bighorn Basin Province Boundary

S High-angle fault

U.S. Geological Survey 1.35

NYE-BOWLER 5

EXPLANATION

Precambrian rocks

1 .

1 MOUNTAINS

Formations outcrop

BEARTOOTH

R15E

R20E R25E

R35E

PRYOR

MOUNTAINS Frontier/Mowry/Muddy/Thermopolis 0.8

109° 110° 107° 108°

0.8

Tertiary volcanic rocks

LINEAMENT

Bighorn Basin Province Boundary S

NYE-BOWLER 5

EXPLANATION T

R15E R20E R25E R35E

109° 110° 107° 108°

Lower Cody Shale (Niobrara Equivalent) in the Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

By Thomas M. Finn

Scientific Investigations Report 2013–5138

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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Suggested citation: Finn, T.M., 2014, Lower Cody Shale (Niobrara equivalent) in the Bighorn Basin, Wyoming and Montana—Thickness, distribution, and source rock potential: U.S. Geological Survey Scientific Investigations Report 2013–5138, 32 p., http://dx.doi.org/10.3133/sir20135138.

ISSN 2328-0328 (online) iii

Contents

Abstract...... 1 Introduction...... 1 Depositional Setting...... 4 Stratigraphy...... 9 Cody Shale...... 9 Methods...... 9 Results...... 16 Quantity of Organic Matter...... 16 Types of Organic Matter...... 16 Distribution of Organic Matter...... 18 Thermal Maturity...... 18 Conclusions...... 29 Acknowledgments...... 29 References...... 29

Figures 1. Map of Rocky Mountain region showing Laramide Basins...... 2 2. Index map of the Bighorn Basin...... 3 3. Map of Western Interior Seaway...... 5 4. Regional stratigraphic cross section of Cretaceous rocks in the Bighorn Basin...... 6 5. Paleogeographic reconstruction...... 7 6. Correlation diagram of Upper Cretaceous rocks...... 8 7. Isopach map of Cody Shale...... 10 8. Isopach map of lower member of Cody Shale...... 11 9. Type log...... 12 10. Electric log cross section of lower Cody Shale...... 13 11. Isopach map of basal Niobrara Formation equivalent...... 14 12. Isopach map of Carlile Shale equivalent...... 15 13. Index map showing sample localities...... 17

14. Tmax values versus depth plot...... 18 15. Total organic carbon plot...... 21

16. S2 and total organic carbon...... 22

17. HI versus OI and HI versus Tmax plots...... 23

18. S2/S3 plot...... 23 19. Basin-wide variation of total organic carbon content...... 24 20. Basin-wide variation of kerogen type...... 25 21. Thermal maturity map of lower member of Cody Shale...... 26 22. West-east structural cross section...... 27 23. Burial history curves...... 28

Table 1. Results of Rock-Eval and total organic carbon analysis...... 19

Lower Cody Shale (Niobrara Equivalent) in the Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

By Thomas M. Finn

Abstract and south-central Montana (fig. 1). The basin is bounded by major basement uplifts that include the Pryor Mountains on The lower shaly member of the Cody Shale in the Bighorn the northeast, the Beartooth Mountains on the northwest, the Basin, Wyoming and Montana is Coniacian to Santonian in Bighorn Mountains on the east, and the Owl Creek Mountains age and is equivalent to the upper part of the Carlile Shale on the south. The northern margin includes a zone of faulting and basal part of the Niobrara Formation in the Powder River and folding referred to as the Nye-Bowler lineament (Wilson, Basin to the east. The lower Cody ranges in thickness from 1936). The western margin is formed by volcanic rocks of the 700 to 1,200 feet and underlies much of the central part of the Absaroka Range (fig. 2). basin. It is composed of gray to black shale, calcareous shale, Hydrocarbon production from Cretaceous reservoirs bentonite, and minor amounts of siltstone and sandstone. was established in 1906 and 1907 with the discoveries of Sixty-six samples, collected from well cuttings, from the Garland and Greybull fields, respectively (Fox and Dolton, lower Cody Shale were analyzed using Rock-Eval and total 1996). Since then, cumulative production from Cretaceous organic carbon analysis to determine the source rock potential. and Tertiary reservoirs is about 94 million barrels of oil and Total organic carbon content averages 2.28 weight percent 830 billion cubic feet of gas (IHS Energy Group, 2007). for the Carlile equivalent interval and reaches a maximum In addition, a potential unconventional basin-centered gas of nearly 5 weight percent. The Niobrara equivalent interval accumulation may be present in Cretaceous reservoirs in the averages about 1.5 weight percent and reaches a maximum deeper parts of the basin (Ryder, 1987; Surdam and others, of over 3 weight percent, indicating that both intervals are 1997; Johnson and Finn, 1998; Johnson and others, 1999; good to excellent source rocks. S2 values from pyrolysis Finn and others, 2010). It has been suggested that various analysis also indicate that both intervals have a good to Cretaceous marine shales are the principal hydrocarbon source excellent source rock potential. Plots of hydrogen index versus rocks for these accumulations (Burtner and Warner, 1984; oxygen index, hydrogen index versus Tmax, and S2/S3 ratios Hagen and Surdam, 1984; Meissner and others, 1984; Fox and indicate that organic matter contains both Type II and Type III Dolton, 1989, 1996). kerogen capable of generating oil and gas. Maps showing the Recent advances and success in horizontal drilling and distribution of kerogen types and organic richness for the lower multistage fracture stimulation have led to an increase in shaly member of the Cody Shale show that it is more organic- exploration and completion of wells in Cretaceous marine rich and more oil-prone in the eastern and southeastern parts of shales in other Rocky Mountain basins that were traditionally the basin. Thermal maturity based on vitrinite reflectance (Ro) thought of only as source rocks (Sterling and others, 2009; ranges from 0.60–0.80 percent Ro around the margins of the Sonnenberg, 2011). Studies of the Mowry Shale by numerous basin, increasing to greater than 2.0 percent Ro in the deepest authors, including Schrayer and Zarella (1963, 1966, 1968), part of the basin, indicates that the lower Cody is mature to Nixon (1973), Burtner and Warner (1984), Davis (1986), overmature with respect to hydrocarbon generation. Miskell-Gerhardt (1989), and Finn (2010), have demonstrated its source rock potential in the Bighorn Basin. However, with the exception of a study of Cretaceous source rocks by Introduction Hagen and Surdam (1984), little or no geochemical data have been published about the source rock potential of the Upper The Bighorn Basin is a large intermontane basin that Cretaceous Cody Shale in the Bighorn Basin. The purpose formed in the Rocky Mountain foreland during the Laramide of this report is to present the results of Rock-Eval and total orogeny (Late Cretaceous through early Eocene). The basin organic carbon (TOC) analysis for samples collected from is nearly 180 miles (mi) long, 100 mi wide, and encompasses lower Cody Shale in the Bighorn Basin and characterize its about 10,400 square miles (mi2) in north-central Wyoming source rock potential. 2 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

112° 110° 108° 106° 104°

Bull Miles City arch 46° Crazy Reed Point Mountains syncline Basin Mountains N. DAK Bridger Basin uplift Bighorn S. DAK

Nye-Bowler Powder Beartoothlineament PRYOR uplift MOUNTAINS MONT uplift MONT Bighorn WYO IDAHO Black Hills uplift River Absaroka Basin 44° volcanic field Teton uplift Basin Owl Creek uplift Casper arch

Wind Wind River Basin S. DAK River Granite Mountains NEBR uplift uplift Shirley Hartville uplift Basin 42° IDAHO Rawlins

uplift UTAH Laramie WYO Greater Green Hanna Basin Sierra Madre Basin River Basin Cordilleran orogenic belt Medicine

uplift

Bow WYO NEBR Park

Uinta uplift uplift COLO Axial Denver Basin Range Basin uplift North and Middle 40° uplift Park Basins

Uinta White Front Basin Piceance River uplift Range

Sawatch

Basin uplift

Swell San Rafael uplift

Uncompahgre Gunnison South Park uplift uplift Basin

38º San Juan volcanic San Juan field Raton Basin uplift Rio UTAH COLO COLO

ARIZ N. MEX (Neogene) Grande N. MEX San Juan EXPLANATION Basin 36º

Thrust or reverse fault Zuni uplift rift

0 50 100 MILES

0 50 100 KILOMETERS Sangre de Cristo uplift

Nacimiento uplift

Figure 1. Map of the Rocky Mountain region extending from southern Montana to northern New Mexico showing locations of Laramide sedimentary and structural basins and intervening uplifts. Modified from Dickinson and others (1988). Introduction 3 BASIN BIGHORN PROVINCE WYOMING Index map of the EXPLANATION

Tertiary volcanic rocks Tertiary Type log Type Burial history location Gas field producing from reservoirs Cretaceous or Tertiary Oil field producing from reservoirs Cretaceous or Tertiary Cloverly Formation Precambrian rocks Bighorn Basin Province boundary Fault Anticline Syncline MONTANA Figure 2. and Bighorn Basin in Wyoming Montana showing locations of oil and Cretaceous and Tertiary gas fields, generalized structure, and physiographic features. Structure contours drawn on top of the Lower Cretaceous Cloverly Formation; contour interval, 5,000 feet. Modified from Finn and others (2010). T 9 S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS 20

30 MOUNTAINS R35E R35E

20 0 10 10 Hidden Dome BIGHORN R90W R90W

0 0 5,000 Worland Manderson

108 ° -5,000 Greybull log Type Five Mile

F R94W Creek Dobie

-5,000

Creek MOUNTAINS F trend F 1-11 Dobie R95W R5E -5,000 R95W Mile T 8 0 F N -10,000 Byron F Five CREEK PRYOR F 0 R3E Garland

MOUNTAINS Bench Emblem 0 OWL R25E F -5,000

axis Creek -15,000

M R1E Elk Basin

0 Basin F Little Grass T 5 F 0 N Little Basin

Buffalo 0 -5,000 F R100W

F R1W 0

Meeteetse 5,000 109 ° Dome Golden Basin F Oregon R101W M

Dry sub-basin Creek

Basin -10,000 Badger T 9 5,000 F S LINEAMENT Fork0 5,000 Clark's R20E

-5,000 R4W anticline T N T 8 N 57 Rattlesnake Mountain R5W R104W

NYE-BOWLER

F R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA R15E WYOMING T 5 S 110 ° T T N N 40 45 44 ° 45 ° 4 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

Depositional Setting deposits (fig. 4). The nonmarine deposits are represented by eastward-thinning wedges of marginal marine and nonmarine sandstone, siltstone, shale, carbonaceous shale, and coal. During much of Late Cretaceous time, the part of The marine deposits are represented by westward-thinning Wyoming and Montana that is now the Bighorn Basin was tongues of marine shale, siltstone, and marine sandstone. The located near the west edge of the Rocky Mountain foreland marine sediments were deposited during widespread marine basin, an elongate north-south structural depression that transgressions, creating highstand conditions that resulted in developed to the east of the tectonically active western deepening of the seaway, limiting clastic input, and forming Cordilleran highlands prior to the Laramide orogeny. anoxic bottom conditions favorable for the preservation of Throughout much of its history the foreland basin was flooded organic matter (Gries and others, 1992). These transgressions by a broad epicontinental sea, referred to as the Western also resulted in two episodes of carbonate deposition in the Interior Seaway (WIS), that developed in response to foreland WIS, the first being the Greenhorn Formation and the second basin subsidence and eustatic sea-level rise (Steidtmann, being the Niobrara Formation (Longman and others, 1998; 1993). At its maximum extent, the WIS extended for more Sonnenberg, 2011). The Niobrara interval is characterized than 3,000 mi from the Arctic Ocean to the Gulf of Mexico by deposition of chalks and marls composed of foraminifers (fig. 3) (Kauffman, 1977). Erosion of the western Cordilleran and coccolith debris that accumulated in the eastern part of highlands supplied sediment to the basin by eastward-flowing the seaway (Longman and others, 1998; Sonnenberg, 2011). streams; whereas, the eastern shore of the WIS was part of The chalks grade westward into more siliciclastic beds the stable craton that was topographically low and supplied that were derived from the eroding highlands to the west, little sediment (Molenaar and Rice, 1988). During much of that diluted the carbonate sediments (Longman and others, Late Cretaceous time, sediments accumulated in or adjacent 1998; Sonnenberg, 2011) (fig. 5). In the Bighorn Basin of to the WIS as the western shoreline repeatedly advanced and north-central Wyoming and southern Montana, the Niobrara retreated across the western part of the basin, resulting in equivalent rocks are represented by shales, calcareous shales, a complex pattern of intertonguing marine and nonmarine siltstones, and sandstones of the Cody Shale (fig. 6). Depositional Setting 5

ARCTIC OCEAN

GREENLAND ALASKA

CANADA

WESTERN Study W area E S

I N CORDILLERA T

O R UNITED STATES

Y PACIFIC OCEAN ATLANTIC OCEAN

MEXICO

GULF OF MEXICO

0 500 MILES

0 500 KILOMETERS

Figure 3. Map showing approximate extent of the Western Interior Seaway in North America during late Coniacian (Scaphites depressus Zone) time. Modified from Cobban and others (2005). 6 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

? ? Upper Cretaceous Upper Lower ? ? Jurassic Cretaceous SOUTHEAST Creek Cottonwood Cody Shale Lewis Shale Worland Coastal plain and floodplain sandstones, shales, and coals Floodplain and lacustrine sandstone, shale, and conglomerate Undifferentiated deposits Stratigraphic marker beds from well logs Unconformity Five Mile Frontier Formation Dobie Creek Muddy Sandstone Fritz Claggett Member of Cody Shale EXPLANATION Tidal sandstone, Tidal siltstone, and shale Marine shales Mesaverde Formation (middle part) Bench Emblem Lower member "chalk kick" Red Point Cloverly Formation Upper sandy member Meeteetse Formation (part) Interbedded sandstone and shale, marine Fluvial sandstone and conglomerate Marine and marginal marine sandstone and siltstone Fluvial and estuarine sandstone Peak Teapot Sandstone Member Teapot McCulloch N G A N Lower shaly member M I Mowry Shale SE (part) Y O O N T Mesaverde Formation M W Jurassic rocks undivided Thermopolis Shale NW Basin

Badger

Location of cross section Cody Shale BIGHORN BASIN PROVINCE WYOMING

Parkman Sandstone MONTANA of Eagle Sandstone 20 MILES Virgelle Sandstone Member Virgelle 15 10 5 Eagle Sandstone Judith River Formation (part) 0 Claggett Shale Frontier Formation Telegraph Creek Formation Telegraph 500 lineament Regional northwest-southeast stratigraphic cross section of Cretaceous (part) rocks in the Bighorn Basin, Wyoming and Montana. Modified from Finn others (2010). Regional northwest-southeast stratigraphic cross section of Cretaceous (part) rocks in the Bighorn Basin, Wyoming FEET 1,000 Nye-Bowler

? ? Upper Cretaceous Upper Lower ? ? Jurassic Cretaceous NORTHWEST Figure 4. Depositional Setting 7

116° 112° 108° 104° 100°

CANADA

48° MONTANA WESTERN NORTH DAKOTA

Cody Shale

Niobrara Formation

INTERIOR

SOUTH DAKOTA 44°

IDAHO Cody Shale WYOMING

Baxter NEBRASKA Shale

SEAWAY Niobrara 40° Formation

UTAH COLORADO KANSAS

Mancos Shale

EXPLANATION

36° Highlands Conglomerate

Coastal plain NEW MEXICO Coastal sandstones

Marine shale

Calcareous shale/marl ARIZONA Limestone Bighorn Basin Province Boundary 32° 0 100 200 MILES

0 100 200 KILOMETERS

Figure 5. Paleogeographic reconstruction of the Rocky Mountain region during late Coniacian (Scaphites depressus Zone) time showing major depositional trends. Bighorn Basin Province is outlined in red. Modified from McGookey (1972). 8 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential Red Bird Shale Silty Member Unnamed shale Mitten Member River Basin Gammon Member Belle Fourche Pool Creek Member Mowry Shale Sage Breaks Member Eastern Powder Turner Sandy Member Turner Sharon Springs Member

Niobrara Formation

Greenhorn Formation Muddy Sandstone Pierre Shale (part) Shale Pierre Carlile Shale Carlile Sussex and Unnamed Unnamed lower part upper part Member Member Shannon Ss. Beds (part) Belle Fourche

Emigrant Gap River Basin

Formation Niobrara Member Mesaverde Member Steele Wall Creek Member Wall Mowry Shale Sage Breaks Member Western Powder Western

Muddy Sandstone Cody Shale Cody Frontier Formation Frontier Claggett Mbr. member member Member (part) "chalk kick" (equivalent) Lower shaly Upper sandy Belle Fourche Formation Mesaverde Unnamed member Mowry Shale Lower member Bighorn Basin

Muddy Sandstone Cody Shale Cody Frontier Formation Frontier Eastern and southeastern member member Member (part) "chalk kick" (equivalent) Lower shaly Upper sandy Belle Fourche Formation Mesaverde Unnamed member Bighorn Basin Mowry Shale

Muddy Sandstone Cody Shale Cody Frontier Formation Frontier Western and southwestern Western Claggett Mbr. member member Member (part) "chalk kick" Lower shaly Upper sandy (equivalent) Belle Fourche Formation Mesaverde Lower member Unnamed member Mowry Shale

Muddy Sandstone Cody Shale Cody Northern Bighorn Basin Formation Frontier member member Member (part) "chalk kick" (equivalent) Lower shaly Upper sandy Belle Fourche Montana Formation Eagle Sandstone Unnamed member Judith River Claggett Shale Mowry Shale Virgelle Sandstone Mbr. Virgelle

Parkman Sandstone

Muddy Sandstone

Cody Shale Cody Telegraph Creek Formation Telegraph Formation Frontier I II III late form ) early form ) Fossil zone

Plesiacanthoceras wyomingense Acanthoceras granerosense Pseudaspidoceras flexuosum Dunveganoceras problematicum Didymoceras nebrascense Scaphites depressus Desmoscaphites erdmanni Acanthoceras bellense Clioscaphites choteauensis Desmoscaphites bassleri Baculites perplexus ( Baculites perplexus ( Prionocyclus wyomingensis Mammites nodosoides

Baculites sp. ( weak flank ribs ) Burroceras clydense Burroceras Scaphites hippocrepis Scaphites hippocrepis Clioscaphites saxitonianus Baculites gregoryensis Inoceramus erectus Scaphites hippocrepis Scaphites hippocrepis Baculites sp. ( smooth ) Baculites sp. ( smooth ) Neogastroplites maclerni Neogastroplites haasi Neogastroplites Scaphites hippocrepis Scaphites hippocrepis Vascoceras birchbyi Vascoceras Inoceramus deformis Baculites reduncus Prionocyclus percarinatus Neogastroplites muelleri Neogastroplites Clioscaphites vermiformis Colinoceras tarrantense Baculites obtusus Prionocyclus quadratus Prionocyclus macombi Inoceramus involutus Baculites asperiformis Scaphites whitfieldi Nigericeras scotti Baculites mclearni Baculites scotti Prionocyclus hyatti Collignoniceras woollgari Baculites gilberti

Middle Middle Upper Upper Middle Lower Upper Upper Lower Lower Mid

Middle U

Low (part) Low

Santonian Turonian Campanian (part) Campanian Coniacian Cenomanian Albian

Stage

(part)

UPPER CRETACEOUS (part) CRETACEOUS UPPER ? LK Series Correlation chart showing the stratigraphic nomenclature for Upper Cretaceous rocks in Bighorn Basin and relationship t o various localities Powder

CRETACEOUS (part) CRETACEOUS System 80 85 90 95 Ma 100 88.7 98.5 86.3 83.5 93.3 Figure 6. River Basin to the east. Radiometric ages and fossil zones are from Obradovich (1993) Merewether (1996). Powder Bas in columns modified Bighorn Basin columns compiled from Merewether (1996), Obradovich and others Keefer (1998), Kirschbaum (2009). LK, Lower Cretaceous. Methods 9

Stratigraphy the Frontier Formation is equivalent to the upper part of the Carlile Shale in the Powder River Basin to the east (figs. 6, 9, and 10). This interval, ranging in thickness from greater Cody Shale than 400 ft in the southeastern part of the basin to less than 100 ft in the northern part, reflects the back-stepping stacking The Cody Shale in the Bighorn Basin is in part pattern of the sandstones in the underlying Frontier Formation the equivalent to the Niobrara Formation in the Powder (figs. 10 and 12). River basin to the east (fig. 6). It consists of marine shale, The upper sandy member ranges in thickness from about interbedded with siltstone and sandstone, with the amount 2,700 ft in the southern part of the basin to around 1,000 ft in of sandstone increasing in the upper part (Keefer and others, the northern part of the basin. It consists of buff, or light- to 1998). The Cody was deposited during a major transgressive- medium-gray sandstones, and gray shales (Johnson and others, regressive cycle referred to as the “Niobrara Cyclothem” 1998). According to Johnson and others (1998), the sandstones by Kauffman (1977), and ranges in age from Coniacian are very fine to medium-grained, laterally persistent, and to middle Campanian (Keefer, 1972; Keefer and others, exhibit a variety of bedding features including horizontal 1998). The lower and upper contacts interfinger extensively laminae, ripple laminae, and hummocky crossbedding. with the underlying Frontier and overlying Mesaverde The Claggett Member of the Cody Shale (known as the Formations (fig. 4). The formation is about 1,750 ft thick in Claggett Shale in Montana) is a westward thinning tongue the northern part of the basin increasing to nearly 3,800 ft in of marine shale that is split from the upper part of the Cody the southeastern part (fig. 7). This southeastward thickening is Shale by the lower member of the Mesaverde Formation due to the eastward stratigraphic rise and intertonguing of the (Eagle Sandstone in Montana) (figs. 4 and 6). It is composed contact between the Cody Shale and the overlying Mesaverde predominantly of light- to medium-gray shale interbedded Formation, and the west to northwestward backstepping with thin siltstone and fine- to medium-grained sandstone nature of the Frontier/Cody contact (fig. 4). Three members (Johnson and others, 1998). The Claggett Member extends are recognized, in ascending order: (1) the unnamed lower across the eastern and central parts of the basin, and thickens shaly member (Keefer, 1972); (2) the unnamed upper sandy eastward from zero to nearly 500 ft thick at its eastern limit member (Keefer, 1972); and (3) the Claggett Member (Keefer where it merges with the upper part of the main body of the and others, 1998) (figs. 4 and 6). Cody Shale (fig. 4) (Finn and others, 2010). The unnamed lower shaly member reaches a maximum thickness of about 1,200 ft in the southern part of the basin and thins to the north to about 700 ft (fig. 8). It is composed of gray to black shale, calcareous shale, and bentonite, with Methods minor amounts of siltstone and sandstone that were deposited in an offshore marine environment. A persistent zone referred Sixty-six samples from 26 wells were collected from to as the “chalk kick” marker by Keefer (1972) is recognized well cuttings from the lower member of the Upper Cretaceous on resistivity logs in the lower part of the lower member Cody Shale stored at the U.S. Geological Survey Core (figs. 9 and 10). This zone, which can be traced in the Research Center in Lakewood, Colorado. The wells selected subsurface throughout most of the basin, separates calcareous are located near the outcrop belt along the margins of the beds above from noncalcareous beds below. Based on basin in order to obtain samples that were not subjected to correlations across the Powder River and Wind River Basins, the effects of deep burial and subsequent organic carbon loss the calcareous interval extending from the “chalk kick” to due to thermal maturation as described by Daly and Edman the base of the overlying upper sandy member is equivalent (1987) (figs. 13 and 14). Twenty samples are from the Carlile to the basal part of the Niobrara Formation in the Powder equivalent, and 46 from the lower Cody interval extending River Basin (Keefer, 1972; Merewether and others, 1977a, from the “chalk kick” marker to the base of the upper sandy b; Finn, 2007a). This interval thickens from about 500–700 member of the Cody (basal Niobrara equivalent of the Powder ft in the southeastern and northern parts of the basin to about River Basin). Sample intervals were determined by examining 1,000 ft in the southwestern part of the basin reflecting the cuttings under a binocular microscope and the darkest an increase in sediment supply eroded from the western chips were selected for analysis based on observations by Cordilleran highlands (fig. 11). In the subsurface, numerous Hosterman and Whitlow (1981), Charpentier and Schmoker marker beds or resistivity patterns can be identified in this (1982), Hunt (1996), and Landon and others (2001), who interval on electric logs (fig. 10). According to Asquith (1970) suggested that TOC content generally increases as color and Molenaar and Baird (1991), these distinct patterns are a goes from gray to black and therefore is a rough indicator response to variations in bentonite, sand, silt, and carbonate of organic richness. Obvious material from cavings and content, and can be considered time markers. In the basal contamination, such as wood chips, metal, and plastic, were Niobrara equivalent, the strata produce clinoform patterns removed. The cuttings were composited into samples from that dip to the east, downlapping onto the “chalk kick” marker thickness intervals that were generally 60 to 140 ft thick but (fig. 10). The interval extending downward from the “chalk ranged from 30 to 330 ft depending on how much material kick” marker to the top of the uppermost sandstone bed in was available for a proper analysis. 10 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential BASIN BIGHORN PROVINCE WYOMING EXPLANATION Isopach map of the

Well location Well Tertiary volcanic rocks Tertiary 1,750 to 2,000 2,500 to 2,750 3,250 to 3,500 Precambrian rocks <1,750 2,250 to 2,500 3,000 to 3,250 >3,750 Bighorn Basin Province boundary Cody Shale outcrop 2,000 to 2,250 2,750 to 3,000 3,500 to 3,750 Eastern limit of lower member Mesaverde Formation MONTANA Thickness, in feet Figure 7. Cody Shale excluding the lower member of the Mesaverde Formation and Claggett Member of the Cody Shale, Bighorn Basin; thickness interval 250 feet. From Finn and others (2010). T 9 S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS

20 MOUNTAINS 30 R35E R35E 20

10 3,750 10 R90W BIGHORN R90W

0 0 3,500

3,000 3,250 108 ° R94W 2,750

MOUNTAINS R95W R5E R95W T 8 N

2,500

PRYOR CREEK

MOUNTAINS R3E

OWL R25E 2,250 R1E 2,000 T 5 N

2,750 R100W R1W 109 °

1,750 R101W T 9 S LINEAMENT

1,750 R20E R4W T N T 8 N 57 R5W R104W

NYE-BOWLER R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA R15E WYOMING T 5 S 110 ° T T N N 40 45 44 ° 45 ° Stratigraphy 11 BASIN BIGHORN PROVINCE WYOMING Isopach map of the Isopach map of the EXPLANATION

Well location Well Tertiary volcanic rocks Tertiary 700 to 800 1,000 to 1,100 Precambrian rocks <700 900 to 1,000 >1,200 Bighorn Basin Province boundary Cody Shale outcrop 800 to 900 1,100 to 1,200 MONTANA Thickness, in feet Figure 8. lower member of the Cody Shale, Bighorn Basin. This map includes the interval from top of uppermost Frontier Formation sandstone to the base of upper sandy member of the Cody Shale; thickness interval 100 feet. T 9 S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W

R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS 20

30 MOUNTAINS R35E R35E 20

10 1,000

R90W 1,100 BIGHORN 1,200 R90W 0 0

1,200 1,100

108 ° 1,100

R94W 1,000 1,100

MOUNTAINS R95W R5E R95W T 8 N

PRYOR CREEK 800 MOUNTAINS 1,200 R3E 900 1,000 1,200

OWL R25E 1,100

900

1,100 700 R1E T 5 N

800 R100W R1W

109 °

900

800 700 900 R101W T 9 S

LINEAMENT R20E R4W T N T 8 N 700 57 R5W R104W

NYE-BOWLER R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA R15E WYOMING T 5 S 110 ° T T N N 40 45 44 ° 45 ° 12 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

Snyder Oil 1–26 Worland-Fee sec. 26, T. 47 N., R. 93 W. GR Res. EXPLANATION

Tidal sandstone, siltstone, and shale

7,000 Upper sandy Fluvial sandstone member and conglomerate (part) Marine and marginal marine sandstone and siltstone Fluvial and estuarine sandstone

Interbedded sandstone and shale, marine 7,500 Floodplain and lacustrine sandstone, shale, and conglomerate

Undifferentiated deposits Cody Shale (part)

equivalent Marine shales 8,000 Basal Niobrara Formation Lower shaly member "chalk kick marker" Upper Cretaceous (part) Carlile Shale equivalent 8,500

Frontier Formation

9,000 Clay Spur Bentonite Bed Upper siliceous part Mowry Shale

Lower part

Muddy Sandstone 9,500 Thermopolis Shale

"rusty beds" Lower

Greybull Ss. Mbr. Cretaceous Cloverly Formation Pryor Member 10,000 Morrison Formation Jurassic (part) (part)

Figure 9. Type log of Lower Cretaceous and lowermost Upper Cretaceous rocks in the southeastern part of the Bighorn Basin. Location shown in figure 2. GR, gamma ray; Res., resistivity. Stratigraphy 13 EAST R. 89 W. Govt. 1-5 4,500 5,000 4,000 3,500 Samedan Oil sec. 5, T. 45 N sec. 5, T. "chalk kick" R. 90 W. Pike Res. Federal 1-15 sec. 15, T. 45 N sec. 15, T. 6,000 4,500 5,500 5,000 R. 91 W. Coastal O & G sec. 25, T. 45 N sec. 25, T. 7,000 5,500 6,000 6,500 Old Quaker-Fed. 1-25 Old Quaker-Fed. R. 91 W. Altus 29-1 Altus Expl. sec. 29, T. 45 N sec. 29, T. 6,500 6,000 5,500 7,000 7,500 R. 92 W. Altus Expl. sec. 22, T. 45 N sec. 22, T. 6,500 7,000 6,000 5,500 Blackhawk 32-22 R. 92 W. Tenneco sec. 19, T. 45 N sec. 19, T. Neiber II Unit 1 6,500 7,000 5,500 6,000 R. 93 W. Anschutz sec. 13, T. 45 N sec. 13, T. USA 9383 13-13 6,000 6,500 5,500 7,000 R. 93 W. 6500 7,000 6,000 7,500 sec. 14, T. 45 N sec. 14, T. Gary-Williams Oil Finley Point 14-12 10 MILES 6500 R. 93 W. 7,000 7,500 8,000 Cabot Corp. sec. 7, T. 45 N sec. 7, T. (part) 10 KILOMETERS Neiber-Federal 1 Neiber-Federal 5 (part) Frontier Formation 5 Cody Shale EXPLANATION 0 0 Marine sandstone and siltstone Shale, and calcareous shale, with minor amounts of sandstone, and siltstone Interbedded sandstone, shale, sandy shale, and siltstone Marine shale R. 95 W. Continental Oil sec. 27, T. 45 N sec. 27, T. Boulder Gulch 1 7,000 6,500 7,500 8,000 R. 96 W. Husky Oil Nelson 23 3,000 1,000 2,500 sec. 2, T. 44 N sec. 2, T. 1,500 2,000 Formation equivalent equivalent Carlile Shale Basal Niobrara R. 97 W. State 1-16X Swenco Inc. sec. 16, T. 45 N sec. 16, T. 2,500 4,500 3,500 3,000 4,000 N G A N M I E Y O O N T M W R. 97 W. R. 97 W. 5,500 6,000 Midwest Oil 4,500 5,000 W sec. 29, T. 46 N sec. 29, T. Gywnn Ranch #1 (part) (part) Location of cross section BIGHORN BASIN PROVINCE member member Upper sandy Lower shaly Frontier Formation R. 99 W. sec. 15, T. 46 N sec. 15, T. Energy Reserve Little Grass Creek 1-15 1,500 1,000 2,000 2,500 3,000 West-east electric log cross section of the lower Cody Shale and associated strata. West-east

"chalk kick" R. 99 W. USA C-1 Pan American sec. 17, T. 47 N sec. 17, T. 500 WEST 1,500 2,000 1,000 Figure 10. 14 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential BASIN BIGHORN PROVINCE WYOMING Isopach map of Isopach map of EXPLANATION

Well location Well Tertiary volcanic rocks Tertiary 550 to 650 750 to 800 950 to 1,000 Precambrian rocks <550 700 to 750 850 to 900 900 to 950 >1,050 Bighorn Basin Province boundary Cody Shale outcrop 650 to 700 800 to 850 1,000 to 1,050 MONTANA Thickness, in feet Figure 11. the basal Niobrara Formation equivalent interval of the lower Cody Shale in the Bighorn Basin. This interval extends from the “chalk kick” marker to the base of the upper sandy member; thickness interval 50 feet. T 9 S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS 20

30 MOUNTAINS R35E

R35E 20 700 10 10 R90W BIGHORN 750 R90W 0 0 108 °

800 850 R94W

850 MOUNTAINS R95W R5E R95W T 8 900 950 1,000 N

PRYOR CREEK 950 MOUNTAINS 750 R3E

OWL R25E 800 1,000 950

950 1,000 950 850 R1E T 5 N R100W 1,050 R1W

550 600 109 ° 650

700 R101W T 9 S

LINEAMENT R20E R4W T N T 8 N 57 R5W R104W

NYE-BOWLER R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA R15E WYOMING T 5 S 110 ° T T N N 40 45 44 ° 45 ° Stratigraphy 15 BASIN BIGHORN PROVINCE WYOMING Isopach map of the EXPLANATION

Well location Well >400 Tertiary volcanic rocks Tertiary 100 to 200 Precambrian rocks <100 300 to 400 Bighorn Basin Province boundary Cody Shale outcrop 200 to 300 MONTANA Thickness, in feet Figure 12. Carlile Shale equivalent interval of the lower Cody Shale in Bighorn Basin. This map includes the interval from uppermost Frontier Formation sandstone to the “chalk kick” marker in lower part of the Cody Shale; thickness interval 100 feet. T 9 S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS

20 MOUNTAINS 30 R35E R35E 20

10 300 10 R90W BIGHORN R90W 0 0

400 300

108 ° 200

400 R94W

300 MOUNTAINS R95W R5E

R95W 200 T 8 100 N PRYOR CREEK

MOUNTAINS R3E

200

OWL R25E 200 R1E T 5 N R100W 100 R1W

100 100 109 °

R101W

100 100 T 9 S

LINEAMENT R20E R4W

T N T 8 N 57 100 R5W R104W

NYE-BOWLER R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA R15E WYOMING T 5 S 110 ° T T N N 40 45 44 ° 45 ° 16 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

The whole-rock samples were ground to a fine powder S2 measurements for the lower Cody Shale are presented and splits were sent with an internal U.S. Geological Survey in table 1 and on figure 16. The 20 samples from the Carlile laboratory standard to an outside geochemical laboratory for equivalent show a range of S2 values from 0.9 to 22; all but analysis. Total organic carbon content was determined using 6 have an S2 greater than 2.5, indicating that it is a fair to the Leco combustion method described by Jarvie (1991), excellent source rock. Around 30 of the samples from the and the pyrolysis analysis was done using a Rock-Eval 2 Niobrara equivalent part of the lower Cody Shale have S2 pyroanalyzer. (See Espitalie and others, 1977; Tissot and values of less than 2.5 and therefore are considered poor Welte, 1978; Peters, 1986; Hunt, 1996, for detailed discussions source rocks. The remaining samples from the Niobrara of the pyrolysis method.) The results are presented in table 1. equivalent have S2 values in the fair to very good range.

Types of Organic Matter Results According to Jacobson (1991) and Peters and Cassa (1994), there are four types of kerogen in sedimentary rocks: Quantity of Organic Matter Type I, composed of oil-prone, hydrogen-rich organic matter generally found in lacustrine and some marine sediments; According to Jarvie (1991), the quantity of organic matter Type II, also composed of oil-prone, hydrogen-rich organic in a formation measured as weight percent total organic carbon matter mainly found in marine sediments; Type III, composed (TOC) is an indicator of the organic richness and generative of terrestrial organic matter derived mainly from woody plant potential. Rocks with less than 0.5 weight percent TOC have material that is low in hydrogen content and generates mainly poor generative potential; rocks with 0.5 to 1 weight percent gas; and Type IV, composed of dead or inert carbon that has TOC have fair generative potential; rocks with 1–2 weight little or no generating capacity. Even though oil is the main percent TOC have good generative potential; rocks with product of Type II kerogen, it actually produces more gas than 2–4 weight percent TOC are considered to have very good Type III kerogen (Hunt, 1996). Using the results of pyrolysis generative potential; and rocks with greater than 4 weight analysis, the type of kerogen present in a source rock can be percent TOC are considered to have excellent generative determined from plots showing hydrogen index (HI) versus potential (Peters and Cassa, 1994). Table 1 and figure 15 show oxygen index (OI) which are defined as (S2/TOC) ×100 and the results of TOC analyses of the lower Cody Shale in the (S3/TOC) ×100, respectively (Espitalie and others, 1977; Bighorn Basin. Tissot and Welte, 1978; Hunt, 1996). According to Hunt The results of TOC analyses of the 20 samples collected (1996), the type of hydrocarbons (oil or gas) generated from from the Carlile equivalent of the lower Cody Shale show a source rock depends on the hydrogen content of the organic values ranging from about 1.0 to nearly 5 percent, with matter. an average of 2.28 percent indicating a good to excellent The HI and OI results from pyrolysis analysis of the generative potential (fig. 15). The 46 samples collected from samples collected for the lower Cody Shale are shown on the basal Niobrara equivalent part of the lower Cody Shale table 1 and plotted in figure 17A. The plots for the samples have TOC values that range from about 0.5 to 3.36 percent, from the Carlile equivalent and basal Niobrara equivalent with an average of 1.46 percent. However, most samples strata from the lower Cody Shale show that most of the from this interval have TOC contents greater than 1 percent, kerogen is Type II and mixed Type II and Type III, indicating indicating a good to very good generative potential. that both intervals in the lower Cody have the potential to Peters and Cassa (1994) and Dembicki (2009) point generate both oil and gas. Similar results are shown on a plot out that TOC is not always a good indicator of source rock of HI versus Tmax (fig. 17B). potential because measurements may include inert carbon S2/S3 ratios are also an indicator of the type of that has little or no generating potential, and that the S2 hydrocarbons generated from a source rock. According to measurement derived from pyrolysis analysis is a better Peters (1986), Peters and Cassa, (1994), and Hunt (1996), indicator of generative potential of source rocks. The value the ratio S2/S3 is proportional to the amount of hydrogen in

S2, expressed as milligrams of hydrocarbons per gram of a source rock and is an indicator of the potential to generate rock, represents the fraction of original kerogen in a source oil and gas. According to Peters (1986), rocks with an S2/S3 rock capable of generating hydrocarbons that have not yet ratio less than 3 produce gas, those with ratios between 3 and been converted to oil or gas or both (Tissot and Welte, 1978). 5 produce both oil and gas, and those with ratios greater than

According to Peters and Cassa (1994), rocks with S2 values 5 produce mainly oil. Peters and Cassa (1994) went on to less than 2.5 have poor generative potential; rocks with S2 state that rocks with S2/S3 values less than 1 are not likely to values between 2.5 and 5 have fair generative potential; rocks produce any oil or gas. with S2 values ranging from 5 to 10 have good generative The S2/S3 values for samples collected from the lower potential; rocks with S2 values from 10 to 20 are considered to Cody Shale are shown on table 1 and plotted in figure 18. have very good generative potential; and rocks with S2 values Three samples from the Carlile equivalent have S2/S3 values greater than 20 have excellent generative potential. between 1 and 3, indicating that it is gas prone. The remaining Results 17 BASIN BIGHORN PROVINCE Index map of the WYOMING

EXPLANATION Sample location Tertiary volcanic rocks Tertiary Precambrian rocks Bighorn Basin Province boundary Cody Shale outcrop MONTANA 21 Figure 13. Bighorn Basin showing sample localities. T 9 S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W

R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS 20

30 MOUNTAINS 4 R35E R35E 11 20 1 10 2 10 R90W R90W 13 BIGHORN 5 0 0 3 6 15 19 7 18 108 ° 17 8 21 R94W 9

MOUNTAINS R95W R5E R95W 10 T 8 N 24

PRYOR CREEK

MOUNTAINS R3E 12

OWL R25E 25 26 14 R1E T 5 N 22 20 R100W R1W 109 ° 16 R101W 23 T 9 S

LINEAMENT R20E R4W T N T 8 N 57 R5W R104W

NYE-BOWLER R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA WYOMING R15E T 5 S 110 ° T T N N 40 45 44 ° 45 ° 18 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

Oil window weight percent and reaches a maximum of nearly 5 weight percent. The TOC content decreases to the west where it is

Immature Early Peak Late 0 generally less than 2 weight percent (fig. 19). Regional studies of the Niobrara and equivalent rocks in the WIS by Longman and others (1998) and Landon and others (2001) documented

500 a similar trend of decreasing TOC content from east to west. Finn (2007b) also noted a similar trend for equivalent rocks in the Wind River Basin to the south. Longman and others (1998) and Landon and others (2001) believed that sediments with 1,000 the higher TOC contents accumulated in the sediment-starved central and eastern parts of the seaway and that the westward decrease in TOC content was due to clastic dilution. 1,500 Figure 20 shows the variation in kerogen types for the lower member of the Cody Shale in the Bighorn Basin. The more oil-prone source rocks occur in the eastern and 2,000 southeastern part of the basin. Here, HI values are generally greater than 200 and maximum values are up to over 500, Depth, in feet the predominant kerogen being Type II derived from marine

2,500 sources. In the western part of the basin, HI values decrease to less than 200, and the organic matter is predominantly Type III gas-prone kerogen. Meissner and others (1984) and Landon and others (2001) observed these same geographic variations 3,000 for equivalent rocks from regional studies and concluded that the Type III organic material was derived mainly from terrestrial sources to the west. 3,500

Thermal Maturity 4,000 400 405 410 415 420 425 430 435 440 445 450 455 460

Tmax (ºC) A map showing the levels of thermal maturation based

on vitrinite reflectance (Ro) measurements for the Bighorn Basin is presented in figure 21. The map is fromFinn Figure 14. Tmax values versus depth. Plot shows that samples are immature with respect to oil generation. and Pawlewicz (2014) and was constructed using Ro data Parameters describing stages of thermal maturity are from published by Nuccio and Finn (1998), Finn and Pawlewicz Peters and Cassa (1994). (2007), Roberts and others (2008), and Pawlewicz and Finn (2012). The isoreflectance contours are drawn on top of the lower Cody Shale, which ranges from 700 to 1,200 ft

thick across the basin (fig. 8); so the oR values presented here (fig. 21) are considered to represent minimum levels of 17 samples from the Carlile equivalent strata have S /S values 2 3 thermal maturation for the interval. The R values generally ranging from 3 to nearly 15, indicating this interval is capable o range from less than 0.60–0.80 percent around the basin of generating both oil and gas (fig. 18). Ten samples from margins, increasing to greater than 2.0 percent in the deeper the basal Niobrara equivalent part of the Cody Shale have part of the basin, a pattern that generally reflects the basin an S /S value of less than 1 and are not likely to generate 2 3 structure (fig. 2). Figure 22 is a generalized west-east any hydrocarbons. Twenty-one samples fall between 1 and 3 structural cross section extending across the central part and are gas prone. The remaining samples have S /S values 2 3 of the basin showing the relationship between present-day ranging from 3 to about 9, indicating kerogen types capable of structure and thermal maturity. In general, the isoreflectance generating both oil and gas. lines are subhorizontal and cut across structures indicating that the thermal maturation trends developed after structural Distribution of Organic Matter development of the basin (Bustin and others, 1985). Two burial history curves (using PetroMod 1D Express) Basin-wide variations of the type and amount of organic were used to determine the depth of burial, and the timing of matter present in the lower Cody Shale are shown in figures petroleum generation of the lower Cody Shale (figs. 23A–B). 19 and 20. Figure 19 shows that the richest source rocks based The Forest Oil 1 Emblem Bench, located near the basin axis, on TOC content occur in the eastern and southeastern part of in sec. 2, T. 51 N., R. 98 W., represents an area of the basin the basin. Here the TOC content is generally greater than 2 that underwent maximum burial (fig. 2). The Exxcel Energy Thermal Maturity 19 70 73 47 47 53 57 82 76 61 77 58 64 47 64 45 48 49 53 42 41 35 79 71 51 49 58 42 42 45 OI 144 68 60 72 82 76 44 44 60 40 29 88 HI 114 117 165 407 161 226 348 156 263 198 133 200 448 200 100 130 105 133 250 , milligrams of 2 TOC 1.40 1.18 1.61 2.69 1.18 0.48 1.52 1.12 1.54 2.78 1.81 2.86 2.16 1.64 0.98 1.41 2.61 2.17 1.08 1.03 1.30 1.28 1.03 1.05 1.00 1.66 0.81 0.91 0.96 1.52 3 /S 2 S 1.63 0.93 3.50 8.60 2.19 0.41 2.80 0.88 2.90 5.69 2.00 4.50 3.10 2.83 1.27 4.41 9.43 4.08 1.44 2.40 3.19 3.00 0.56 0.61 1.18 2.72 0.68 0.68 2.10 5.51 PI 0.21 0.34 0.13 0.06 0.13 0.31 0.14 0.10 0.09 0.04 0.10 0.05 0.04 0.11 0.21 0.10 0.04 0.05 0.10 0.14 0.10 0.12 0.16 0.20 0.14 0.05 0.35 0.26 0.16 0.07 3 S 0.98 0.86 0.76 1.27 0.63 0.69 0.87 0.92 1.20 1.70 1.40 1.67 1.39 0.77 0.63 0.64 1.24 1.06 0.57 0.43 0.53 0.45 0.81 0.75 0.51 0.81 0.47 0.38 0.40 0.69

2 +S 1 2.03 1.21 3.06 1.59 0.41 2.84 0.9 3.82 3.12 7.92 4.43 2.45 1.01 3.13 4.57 0.91 1.19 1.88 1.53 0.53 0.57 0.7 2.32 0.5 0.35 1 4.1 S 11.6 10.08 12.19 2 S 1.60 0.80 2.66 1.38 0.28 2.44 0.81 3.48 9.67 2.82 7.51 4.27 2.18 0.80 2.82 4.33 0.82 1.03 1.69 1.35 0.45 0.46 0.60 2.20 0.32 0.26 0.84 3.80 11.69 10.95 1 , milligrams of hydrocarbons per gram of rock; S , milligrams of hydrocarbons S 1 0.43 0.41 0.4 0.65 0.21 0.13 0.4 0.09 0.34 0.41 0.30 0.41 0.16 0.27 0.21 0.31 0.5 0.24 0.09 0.16 0.19 0.18 0.08 0.11 0.1 0.12 0.18 0.09 0.16 0.3 max 429 431 433 419 422 420 428 432 426 421 424 421 425 431 425 429 414 424 430 426 429 429 430 428 426 423 452 427 429 429 T Formation Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. 770 990 640 Bottom 1,100 1,360 1,480 1,410 1,670 2,090 1,240 1,360 1,030 1,100 3,510 1,000 1,220 1,310 1,390 1,140 1,380 1,560 1,850 1,510 1,690 1,810 1,900 1,460 2,090 2,290 2,390 )]; TOC, total organic carbon in weight percent; HI, hydrogen index; OI, oxygen index] carbon in weight percent; HI, hydrogen total organic TOC, )]; 2 +S 1 510 770 800 500 940 900 Top 1,140 1,390 1,240 1,510 1,910 1,000 1,290 1,050 3,350 1,020 1,250 1,320 1,000 1,140 1,410 1,620 1,420 1,600 1,720 1,810 1,370 1,880 2,090 2,290 /(S 1 - 7 7 7 7 16 16 16 14 14 14 35 35 35 28 31 31 31 31 27 27 27 27 21 21 21 21 28 28 28 28 tion Sec 89W 89W 89W 89W 90W 90W 90W 91W 91W 91W 88W 88W 88W 91W 91W 91W 91W 91W 92W 92W 92W 92W 93W 93W 93W 93W 94W 94W 94W 94W Range - ship 43N 43N 43N 43N 43N 43N 43N 43N 43N 43N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N 44N Town API, American Petroleum Institute; top and bottom depths are in feet; S API, Well 1 Govt. 1 Govt. 1 Govt. Kiralay 1 Kiralay 1 Kiralay 1 Kiralay 1 USA 1–B USA 1–B USA 1–B USA per gram of rock; PI, production index [S 2 State 11–16 State 11–16 State 11–16 1 Bruce Unit 1 Bruce Unit 1 Bruce Unit 1 Bruce Unit Federal 14–27 Federal 14–27 Federal 14–27 Federal 14–27 1 Govt–Wilson 1 Govt. Gardner 1 Govt. Gardner 1 Govt. Gardner 1 Govt. Gardner Federal–Mercer 1 Federal–Mercer 1 Federal–Mercer 1 Federal–Mercer 1 , milligrams of CO NCRA NCRA NCRA NCRA 3 Operator Sohio Pet. Sohio Pet. Sohio Pet. Sohio Pet. Sohio Pet. Cosden Pet. Cosden Pet. Cosden Pet. Texas Pacific Texas Pacific Texas Pacific Texas Continental Oil Continental Oil Continental Oil Continental Oil Shannon O& G Shannon O& G Shannon O& G Shannon O& G Arrowhead Expl. Arrowhead Expl. Arrowhead Expl. Arrowhead Expl. Arrowhead Expl. Arrowhead Expl. Arrowhead Expl. API Rock-Eval and total organic carbon data for the Bighorn Basin, Wyoming and Montana.—Continued Rock-Eval and total organic carbon data for the Bighorn Basin, Wyoming

49043050320000 49043050320000 49043050320000 49043050320000 49043050290000 49043050290000 49043050290000 49017053320000 49017053320000 49017053320000 49043050480000 49043050480000 49043050480000 49043050690000 49043050390000 49043050390000 49043050390000 49043050390000 49043050680000 49043050680000 49043050680000 49043050680000 49017201820000 49017201820000 49017201820000 49017201820000 49017054630000 49017054630000 49017054630000 49017054630000 1 1 1 1 2 2 2 3 3 3 4 4 4 5 6 6 6 6 7 7 7 7 8 8 8 8 9 9 9 9 no. Map Table 1. Table [Map number in column 1 refers to well locations shown on figure 13. hydrocarbons per gram of rock; S 20 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential 97 58 58 50 37 30 35 59 46 37 54 58 46 58 58 83 32 50 46 42 61 67 64 51 76 OI 101 46 98 81 98 HI 110 118 243 131 242 543 166 171 422 415 167 247 354 123 294 253 323 319 189 140 242 194 , milligrams of 2 TOC 1.07 1.60 1.37 2.03 4.02 1.23 1.49 3.36 4.87 1.45 1.01 2.67 3.62 1.42 1.17 1.18 2.17 1.81 2.20 4.33 0.82 1.59 1.33 1.70 2.06 1.49 3 /S 2 S 0.50 4.17 2.25 4.86 5.50 4.90 7.20 9.10 4.50 1.80 4.30 7.70 2.10 1.40 1.30 9.30 5.10 7.00 7.60 1.00 3.10 2.10 1.80 4.80 2.50 14.66 PI 0.33 0.04 0.08 0.05 0.02 0.06 0.11 0.03 0.03 0.06 0.09 0.04 0.02 0.10 0.11 0.18 0.05 0.07 0.04 0.04 0.16 0.07 0.08 0.09 0.05 0.07 3 S 1.04 0.93 0.80 1.01 1.49 0.37 0.52 1.97 2.22 0.54 0.54 1.55 1.66 0.83 0.68 0.97 0.69 0.9 1.02 1.83 0.83 0.97 0.89 1.09 1.04 1.14

2 +S 1 0.74 4.05 1.96 5.15 2.18 2.85 2.58 1.09 6.87 1.95 1.06 1.57 6.75 4.95 7.43 0.96 3.20 2.01 2.22 5.22 3.13 S 22.37 14.61 20.75 13.18 14.40 2 S 0.49 3.88 1.80 4.91 2.04 2.55 2.43 0.99 6.59 1.75 0.94 1.29 6.39 4.59 7.10 0.81 2.99 1.86 2.01 4.98 2.90 21.84 14.17 20.21 12.89 13.83 1 , milligrams of hydrocarbons per gram of rock; S , milligrams of hydrocarbons S 1 0.25 0.17 0.16 0.24 0.53 0.14 0.30 0.44 0.54 0.15 0.10 0.28 0.29 0.20 0.12 0.28 0.36 0.36 0.33 0.57 0.15 0.21 0.15 0.21 0.24 0.23 max 411 417 424 428 425 422 426 427 410 409 429 428 423 416 427 426 421 420 424 421 429 427 427 423 424 427 T Formation Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. 750 Bottom 1,110 1,510 2,490 2,870 2,990 3,050 2,000 2,120 2,390 2,480 2,150 2,220 2,310 2,370 1,700 1,790 1,400 1,490 1,000 1,600 1,750 1,990 2,050 1,760 1,840 )]; TOC, total organic carbon in weight percent; HI, hydrogen index; OI, oxygen index] carbon in weight percent; HI, hydrogen total organic TOC, )]; 2 +S 1 630 920 Top 1,400 2,190 2,690 2,900 2,990 1,900 2,040 2,320 2,420 2,080 2,170 2,210 2,320 1,600 1,700 1,300 1,400 1,500 1,610 1,910 2,000 1,700 1,760 1,020 /(S 1 - 1 1 1 1 9 9 9 9 6 6 6 11 35 35 18 18 17 17 14 24 15 15 15 16 16 20 tion Sec 96W 89W 89W 89W 89W 98W 98W 90W 90W 99W 99W 91W 91W 92W 92W 92W 92W 92W 93W 93W 101W 101W 100W 100W 100W 100W Range - ship 44N 45N 45N 45N 45N 46N 46N 47N 47N 47N 47N 48N 48N 48N 48N 50N 50N 50N 50N 50N 50N 50N 50N 51N 51N 52N Town API, American Petroleum Institute; top and bottom depths are in feet; S API, Well 3 Ltd. 3 Ltd. Unit 6 Unit 6 Unit 2 Unit 2 Unit 2 1 Govt. 1 Govt. USA C–1 USA C–1 USA per gram of rock; PI, production index [S 2 1 Henderson 1 Henderson Federal LK 1 1 Govt.–Social 1 Govt.–Social 1 Govt.–Social LA Sheep 35–1 LA Sheep 35–1 LA Govt.-Lockhart 1 Govt.-Lockhart 1 1–14 Chambers–Fed. W. Bud Kimball 31–1 W. Bud Kimball 31–1 W. Bud Kimball 31–1 W. Bud Kimball 31–1 W. , milligrams of CO 3 Operator MKM Expl. MKM Expl. MKM Expl. Chorney Oil Chorney Oil Chorney Oil Chorney Oil Viking Expl. Viking Expl. Viking Empire State Aztec O & G Signal O & G Signal O & G Occidental Pet. Occidental Pet. Occidental Pet. Grayrock Corp. Western Empire Western Ajax Oil & Dev. Ajax Oil & Dev. Pan American Pet. Pan American Pet. Pan American Pet. Pan American Pet. Ashmun & Hilliard Ashmun & Hilliard API Rock-Eval and total organic carbon data for the Bighorn Basin, Wyoming and Montana.—Continued Rock-Eval and total organic carbon data for the Bighorn Basin, Wyoming

49017058750000 49043204100000 49043204100000 49043204100000 49043204100000 49017059910000 49017059910000 49043052730000 49043052730000 49017600010000 49017600010000 49043054950000 49043054950000 49029052680000 49029052680000 49003052790000 49003052790000 49003052790000 49003204060000 49003052550000 49029053390000 49029053390000 49029053390000 49003204970000 49003204970000 49029068330000 11 11 11 10 12 12 13 13 14 14 15 15 16 16 17 17 17 18 19 20 20 20 21 21 22 no. Map Table 1. Table [Map number in column 1 refers to well locations shown on figure 13. hydrocarbons per gram of rock; S Thermal Maturity 21 64 95 82 71 57 86 60 90 66 47 OI 66 78 58 HI 113 228 177 134 208 157 295 , milligrams of 2 TOC 1.90 1.34 1.44 1.39 1.12 1.14 1.54 1.19 1.24 2.53 3 /S 2 S 3.60 0.70 1.40 2.50 1.40 1.60 4.50 0.60 2.40 6.20 PI 0.07 0.23 0.12 0.05 0.06 0.13 0.08 0.19 0.10 0.05 3 S 1.21 1.27 1.18 0.99 0.64 0.98 0.92 1.07 0.82 1.2

2 +S 1 4.65 1.16 1.86 2.60 0.92 1.74 3.48 0.85 2.18 7.86 S 2 Plot showing distribution of total organic S 4.33 0.89 1.63 2.46 0.87 1.52 3.21 0.69 1.95 7.45

1 , milligrams of hydrocarbons per gram of rock; S , milligrams of hydrocarbons S 1 0.32 0.27 0.23 0.14 0.05 0.22 0.27 0.16 0.23 0.41 Figure 15. carbon content for samples from the lower shaly member of Parameters the Cody Shale in Bighorn Basin, Wyoming. describing source rock generative potential are from Peters and Cassa (1994).

max

428 424 431 426 430 432 430 422 427 422 T Good Very good Very Poor Excellent Fair Formation Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Carlile equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Niobrara equiv. Bottom 1,180 1,800 1,920 2,700 2,780 2,840 2,940 1,630 1,990 2,080 )]; TOC, total organic carbon in weight percent; HI, hydrogen index; OI, oxygen index] carbon in weight percent; HI, hydrogen total organic TOC, )]; 2 +S 1 Top 1,120 1,650 1,800 2,600 2,720 2,750 2,850 1,560 1,930 2,050 /(S 1 - 1 1 20 19 19 27 27 27 27 27 tion Sec 95W 95W 98W 98W 98W 98W 98W 100W 103W 103W Range Niobrara equivalent - ship 52N 54N 54N 55N 55N 56N 56N 57N 57N 57N Town API, American Petroleum Institute; top and bottom depths are in feet; S API, Well Unit 7 Unit 7 Unit 7 per gram of rock; PI, production index [S Unit 73–27 Unit 73–27 2 Federal LK 1 1–1 Pat O’Hara 1–1 Pat O’Hara Jolly Unit 42–19 Jolly Unit 42–19 , milligrams of CO 3 Operator Husky Oil Husky Oil Krueger Oil Krueger Oil Aztec O & G Huckabay Ltd Huckabay Ltd Mule Creek Oil Mule Creek Oil Mule Creek Oil Carlile equivalent API Rock-Eval and total organic carbon data for the Bighorn Basin, Wyoming and Montana.—Continued Rock-Eval and total organic carbon data for the Bighorn Basin, Wyoming

49029068330000 49029207130000 49029207130000 49003206060000 49003206060000 49029059030000 49029059030000 49029060310000 49029060310000 49029060310000 0

6.0 2.0 3.0 5.0 4.0 1.0 22 23 23 24 24 25 25 26 26 26 no. carbon organic total percent, Weight Map Table 1. Table [Map number in column 1 refers to well locations shown on figure 13. hydrocarbons per gram of rock; S 22 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

100.0 EXPLANATION Niobrara equivalent Carlile equivalent Excellent Very good

10.0 Good Fair (mg HC/g rock) 2 S

1.0 Poor

Poor Fair Good Very good Excellent 0.1 0.1 1.0 10.0 Total organic carbon, in weight percent

Figure 16. Plot of S2 versus total organic carbon for samples from the lower part of the Cody Shale in the Bighorn Basin. Parameters describing source rock generative potential are from Peters and Cassa (1994); mg HC/g rock, milligrams of hydrocarbons per gram of rock. Thermal Maturity 23

A B 1,000 EXPLANATION 1,000 EXPLANATION Niobrara equivalent Niobrara equivalent Type I Carlile equivalent Carlile equivalent 900 900

Type I 800 800

700 700 Type II

600 600

500 500 Hydrogen index Hydrogen index 400 400 Type II 300 300

200 200

Type III 100 100 Type III Type IV 0 0 0 50 100 150 200 390 400 410 420 430 440 450 460 470 480 490

Oxygen index Tmax (ºC)

Figure 17. Plots showing: (A) hydrogen index versus oxygen index, and (B) hydrogen index versus Tmax (°C) for samples from the lower part of the Cody Shale, Bighorn Basin. The plots indicate that the kerogen in the lower Cody Shale in the Bighorn Basin is a mix of Type II and Type III capable of generating both oil and gas. Maturation lines and kerogen types

(dashed lines) for HI/OI diagram from Hunt (1996), maturation lines and kerogen types (dashed lines) for HI/ Tmax diagram from P.G. Lillis, written commun. (2007).

EXPLANATION Niobrara equivalent Carlile equivalent

None Gas Oil and gas Oil 0 5 10 15

S2 /S3

Figure 18. S2/S3 ratios for the lower part of the Cody Shale, Bighorn Basin. Parameters describing types of hydrocarbons generated are from Peters (1986), and Peters and Cassa (1994). S2, milligrams of hydrocarbons per gram of rock; S3, milligrams of CO2 per gram of rock. 24 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential BASIN BIGHORN PROVINCE WYOMING 0.5 percent 4.0 percent Map of Bighorn < 0.5 to 1.0 percent 1.0 to 2.0 percent 2.0 to 4.0 percent > EXPLANATION

Tertiary volcanic rocks Tertiary Precambrian rocks Bighorn Basin Province boundary Cody Shale MONTANA Total organic carbon, in weight percent Total Figure 19. Basin showing distribution of total organic carbon content for the lower member of Cody Shale. T 9 S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W

R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS 20

30 MOUNTAINS R35E R35E 20 10 10 R90W

BIGHORN R90W 0 0 108 ° R94W

MOUNTAINS R95W R5E R95W T 8 N

PRYOR >2.0% TOC CREEK

MOUNTAINS R3E

OWL R25E <2.0% TOC R1E T 5 N R100W R1W 109 ° R101W T 9 S

LINEAMENT R20E R4W T N T 8 N 57 R5W R104W

NYE-BOWLER R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA R15E WYOMING T 5 S 110 ° T T N N 40 45 44 ° 45 ° Thermal Maturity 25 BASIN BIGHORN PROVINCE Map of Bighorn WYOMING 50 300 EXPLANATION

< 50 to 200 200 to 300 > Hydrogen index Tertiary volcanic rocks Tertiary Precambrian rocks Bighorn Basin Province boundary Cody Shale MONTANA Figure 20. Basin showing distribution of kerogen types based on the hydrogen index for the lower member of the Cody Shale. T 9 T 9 S S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W

R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS 20

30 MOUNTAINS R35E R35E 20 10 10 R90W

BIGHORN R90W 0 0 Oil-prone 108 ° R94W

MOUNTAINS R95W R5E R95W T 8 N Oil and

PRYOR CREEK gas-prone

MOUNTAINS R3E

OWL R25E R1E T 5 N Gas-prone R100W R1W 109 ° R101W Gas-prone T 9 S

LINEAMENT R20E R4W T N T 8 N 57 R5W R104W

NYE-BOWLER R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA R15E WYOMING T 5 S 110 ° T T N N 40 45 44 ° 45 ° 26 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential ) o BASIN BIGHORN PROVINCE Map of the Bighorn WYOMING EXPLANATION

Tertiary volcanic rocks Tertiary Burial history location Frontier/Mowry/Muddy/ Thermopolis Formations outcrop Bighorn Basin Province boundary High-angle fault Thrust fault Line of section sample point Well Composite well sample point Outcrop sample point >2.00 0.80 to 1.10 Precambrian rocks 1.35 to 2.00 <0.60 0.60 to 0.80 1.10 to 1.35 Vitrinite reflectance (R Vitrinite MONTANA Figure 21. Basin showing levels of thermal maturity based on vitrinite reflectance for the top of lower shaly member of the Cody Shale. From Finn and Pawlewicz (2014) T 9 S T T T T N N N N 45 50 40 55 R40E 40 MILES 107 ° R85W R85W

30 BIG TRAILS FAULT TRAILS BIG 40 KILOMETERS

20 MOUNTAINS 30 R35E R35E 20 10 10 0.6 R90W BIGHORN R90W 0 0

108 ° 0.8 Dobie Creek R94W

MOUNTAINS

0.6

0.8 R95W R5E R95W

T 8

1 N .

PRYOR 1

CREEK MOUNTAINS R3E 1.35

OWL R25E 1 Bench . Emblem 0.8 1 2.0

FAULT R1E BASIN T 5 OREGON N 1.1 R100W R1W

109 ° 0.6 1.1 sub-basin 1.1 R101W Fork .1 0.8 1 1.35 1.35 LINEAMENT Clark's T 9 S R20E R4W T N T 8 N 57 R5W

R104W NYE-BOWLER 0.8 R105W T T N N 50 55

BEARTOOTH MOUNTAINS RANGE ABSAROKA MONTANA R15E WYOMING T 5 S 110 ° T T N N 40 45 44 ° 45 ° Thermal Maturity 27 – 20,000 – 5,000 – 15,000 – 10,000 – 25,000 FEET 5,000

SEA LEVEL >

> N G A N M I EAST

Kf Y O O N T

J – > > E M W Rio thrust fault

Lamb > >> > W Kc Stone (2004) Modified from Greybull monocline Location of cross section BIGHORN BASIN PROVINCE Kf 33-20 Rio Unit Kmr 1 Adams 1 Otto Jurassic to Triassic sedimentary Jurassic to Triassic rocks — Undivided Precambrian crystalline rocks Paleozoic sedimentary rocks — Undivided Lower Cretaceous — Cloverly Formation (projected) J – Kcv J – Kmv Tw Kc Tfu Kl Kml Kcv

10 MILES

Drilling well for hydrocarbon exploration Plugged and abandoned well Plugged and abandoned well, gas show >> Shaly member Sandy member 10 KILOMETERS Five Mile trend Michaels Ranch 20-1 5 Kmt EXPLANATION 5 Upper Cretaceous — Mesaverde Formation Upper and Lower Cretaceous — Frontier Formation and Mowry Shale Lower Cretaceous — Muddy Sandstone and Thermopolis Shale Upper Cretaceous — Cody Shale K f Kc 0 0 K mr Kmv Kmt Oil well Fault —Dashed where inferred Isoreflectance line, in percent 1 Emblem Bench

1.1

0.6 0.60

0.8 >

2.0

1.35 J – Upper Cretaceous — Meeteetse Formation and Lewis Shale Paleocene — Fort Union Formation Upper Cretaceous — Lance Formation Lower Eocene — Willwood Formation

1.5 Kl Tfu Tw Kml

> ? Loch Katrine Unit 1 > thrust fault Modified from Oregon Basin Blackstone (1986) Oregon Basin Kf Kc J – Kmv Kmr West-east structure cross section showing the relationship between thermal maturity, based on vitrinite reflectance, and present-day structure. Arrows structure cross section showing the relationship between thermal maturity, West-east WEST

FEET 5,000 –5,000 – 20,000 – 25,000 – 15,000 – 10,000 Figure 22. exaggeration = 4x. indicate relative movement along faults. Modified in part from Blackstone (1986), Stone (2004), and Finn others (2010). Vertical SEA LEVEL 28 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

Age (Ma) 120 100 80 60 40 20 0 MESOZOIC (PART) CENOZOIC

CRETACEOUS PALEOGENE NEOGENE & QUATERNARY 0 Willwood Formation Fort Union Formation 5,000 Lance Formation Meeteetse Formation Mesaverde Formation Sandy member Cody Shaly Shale member 10,000 Frontier Formation EXPLANATION Mowry Shale % R range (calculated) Muddy/Thermopolis O Formation 0.50 to 0.60

15,000 0.60 to 0.80 Burial depth, in feet 0.80 to 1.10

1.10 to 1.35 20,000

A 25,000

Age (Ma) 120 100 80 60 40 20 0 MESOZOIC (PART) CENOZOIC

CRETACEOUS PALEOGENE NEOGENE & QUATERNARY 0 Willwood Formation

5,000

Fort Union Formation

10,000 EXPLANATION % R range (calculated) O Lance Formation Meeteetse Formation 0.50 to 0.60 Mesaverde Formation Sandy member 15,000 0.60 to 0.80 Cody Burial depth, in feet Shale 0.80 to 1.10 Shaly member Frontier Formation 1.10 to 1.35 Mowry Shale Muddy/Thermopolis 20,000 1.35 to 2.00 Formation Cloverly Formation Jurassic Rocks (part) B 25,000

Figure 23. Burial history curves for the: (A) Exxcel Energy 1–11 Dobie Creek Unit and (B) the Forest Oil 1 Emblem Bench. Location of

wells is shown on figures 2 and 21. Modified from Roberts and others (2008). Ma, millions of years; %, percent; Ro, vitrinite reflectance. References 29

1-11 Dobie Creek Unit, located along the Five Mile trend in Beartooth uplift and adjacent basins: Yellowstone Bighorn the eastern part of the basin, in sec. 11, T. 49 N., R. 94 W., Research Association–Montana Geological Society, 50th represents a part of the basin that underwent shallower burial Anniversary Guidebook, p. 125–135. (fig. 2). In the eastern shallow part of the basin, modeling results for the Dobie Creek well show that hydrocarbon Burtner, R.L., and Warner, M.A., 1984, Hydrocarbon generation in lower Cretaceous Mowry and Skull Creek Shales generation from the lower Cody Shale began (Ro of 0.6 percent) about 53 Ma at a burial depth of about 10,400 ft (fig. of the northern Rocky Mountain area, in Woodward, Jane, 23A). In the deeper part of the basin, modeling results for the Meissner, F.F, and Clayton, J.L., eds., Hydrocarbon source Emblem Bench well indicate that generation began about 59 rocks of the greater Rocky Mountain region: Rocky Moun- Ma at a burial depth of about 12,400 ft (fig. 23B). Based on the tain Association of Geologists Guidebook, p. 449–467.

Ro levels and burial history modeling, the source rocks in the Bustin, R.M., Cameron, A.R., Grieve, D.A., and Kalkreuth, lower part of the Cody Shale in most of the Bighorn Basin are W.D., 1983, Coal petrology—Its principles, methods, and in the early to late stages of thermal maturity with respect to oil applications: Geological Association of Canada, Short generation (0.6–1.35 percent Ro), except in the deepest parts, Course Notes, v. 3, 230 p. where it is post-mature (>1.35 percent Ro) with respect to oil generation (Peters and Cassa, 1994). Charpentier, R.R., and Schmoker, J.W., 1982, Volume of organic-rich Devonian shale in the Appalachian Basin; relat- ing “black” to organic-matter content: American Association Conclusions of Petroleum Geologists Bulletin, v. 66, no. 3, p. 375–378. Cobban, W.A., Dyman, T.S., and Porter, K.W., 2005, Paleon- Results of TOC and Rock-Eval analyses of the lower tology and stratigraphy of upper Coniacian–middle Santo- Cody Shale in the Bighorn Basin indicate that it contains nian ammonite zones and application to erosion surfaces potential petroleum source rocks. Total organic carbon content and marine transgressive strata in Montana and Alberta: for the Carlile equivalent strata is up to nearly 5.0 weight Cretaceous Research, v. 26, p. 429–449. percent, and averages around 2.28 weight percent, while the basal Niobrara equivalent strata is up to over 3.0 weight Daly, A.R., and Edman, J.D., 1987, Loss of organic carbon from percent and averages around 1.5 weight percent, indicating source rocks during thermal maturation: American Associa- that both intervals are potential source rocks. Both intervals tion of Petroleum Geologists Bulletin, v. 71, no. 5, p. 546. contain organic matter primarily composed of Type II and Davis, H.R., 1986, Amount and type of organic matter in the Type III kerogen capable of generating both oil and gas, with Cretaceous Mowry Shale of Wyoming: U.S. Geological the most organic-rich and oil-prone rocks found in the eastern Survey Open-File Report 86–412, 17 p. and southeastern parts of the basin. Maturity levels based on vitrinite reflectance and burial history reconstructions indicate Dembicki, Harry, Jr., 2009, Three common source rock evalu- that the lower Cody Shale is in the early to late stages of oil ation errors made by geologists during prospect or play generation throughout most of the basin, except in the deeper appraisals: American Association of Petroleum Geologists parts where it is post-mature. Bulletin, v. 93, no. 3, p. 341–356. Dickinson, W.R., Klute, M.A., Hayes, M.J., Janecke, S.U., Lundin, E.R., McKittrick, M.A., and Olivares, M.D., 1988, Acknowledgments Paleogeographic and paleotectonic setting of Laramide sedimentary basins in the central Rocky Mountain region: The manuscript benefited from reviews by Paul Lillis, Geological Society of America Bulletin, v. 100, no. 7, Sarah Hawkins, Tom Judkins, and Dave Ferderer, and their p. 1023–1039. suggestions and comments are greatly appreciated. Espitalie, Jean, Madec, J.M., Tissot, B., Mennig, J.J., and Leplat, P., 1977, Source rock characterization method for petroleum exploration, in Offshore Technology Conference, References Houston, Tex., May 2–4, 1977, Proceedings: Offshore Tech- nology Conference, v. 3, no. 9, p. 439–444. Asquith, D.O., 1970, Depositional topography and major marine environments, Late Cretaceous, Wyoming: Ameri- Finn, T.M., 2007a, Subsurface stratigraphic cross sections of can Association of Petroleum Geologists Bulletin, v. 54, no. Cretaceous and Lower Tertiary rocks in the Wind River 7, p. 1184–1224. Basin, central Wyoming, in USGS Wind River Basin Prov- ince Assessment Team, comps., Petroleum systems and geo- Blackstone, D.L., Jr., 1986, Structural geology—Northwest logic assessment of oil and gas resources in the Wind River flank of Bighorn basin—Park County, Wyoming and Car- Basin province, Wyoming: U.S. Geological Survey Digital bon County, Montana, in Garrison, P.B., ed., Geology of the Data Series DDS–69–J, chap. 9, 28 p., CD–ROM. 30 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

Finn, T.M., 2007b, Source rock potential of Upper Cretaceous Hosterman, J.W., and Whitlow, S.I., 1981, Munsell color value marine shales in the Wind River Basin, Wyoming, in USGS as related to organic carbon in Devonian shale of the Appa- Wind River Basin Province Assessment Team, comps., lachian Basin: American Association of Petroleum Geolo- Petroleum systems and geologic assessment of oil and gas gists Bulletin, v. 65, no. 2, p. 333–335. resources in the Wind River Basin province, Wyoming: U.S. Geological Survey Digital Data Series DDS–69–J, chap. 8, Hunt, J.M., 1996, Petroleum geochemistry and geology 24 p., CD–ROM. (2d ed.): New York, W.H. Freeman, 743 p. Finn, T.M., 2010, New source rock data for the Thermopolis IHS Energy Group, 2007, [includes data current as of Decem- and Mowry Shales in the Wyoming part of the Bighorn ber, 2007], PI/Dwights PLUS U.S. Well Data: Englewood, Basin, in USGS Bighorn Basin Province Assessment Team, Colo., IHS Energy Group database, available from IHS comps., Petroleum systems and geologic assessment of Energy Group, 15 Inverness Way East, D205, Englewood, oil and gas in the Bighorn Basin Province, Wyoming and CO 80112. Montana: U.S. Geological Survey Digital Data Series Jacobson, S.R., 1991, Petroleum source rocks and organic DDS–69–V, chap. 4, 15 p., CD–ROM. facies, in Merrill, R.K., ed., TR—Source and migration Finn, T.M., and Pawlewicz, M.J., 2007, New vitrinite reflec- processes and evaluation techniques: American Association tance data for the Bighorn Basin, north-central Wyoming of Petroleum Geologists Treatise of Petroleum Geology, and south-central Montana: U.S. Geological Survey Open- Handbook of Petroleum Geology, p. 1–11. File Report 2007–1246, 9 p. Jarvie, D.M., 1991, Total organic carbon (TOC) analysis, in Finn, T.M., and Pawlewicz, M.J., 2014, Maps showing thermal Merrill, R.K., ed., TR—Source and migration processes and maturity of Upper Cretaceous marine shales in the Bighorn evaluation techniques: American Association of Petroleum Basin, Wyoming and Montana: U.S. Geological Survey Geologists Treatise of Petroleum Geology, Handbook of Scientific Investigations Map 3285, pamphlet, 3 sheets, Petroleum Geology, p. 113–118. scale 1:500,000. Johnson, R.C., Crovelli, R.A., Lowell, B.G., and Finn, T.M., Finn, T.M., Kirschbaum, M.A., Roberts, S.B., Condon, S.M., 1999, An assessment of in-place gas resources in the Roberts, L.N.R., and Johnson, R.C., 2010, Cretaceous- low-permeability basin-centered gas accumulation of the Tertiary Composite Total Petroleum System (503402), Big- Bighorn Basin, Wyoming and Montana: U.S. Geological horn Basin, Wyoming and Montana, in USGS Bighorn Basin Survey Open-File Report 99–315–A, 123 p. Province Assessment Team, comps., Petroleum systems and geologic assessment of oil and gas in the Bighorn Basin Johnson, R.C., and Finn, T.M., 1998, Is there a basin- province, Wyoming and Montana: U.S. Geological Survey centered gas accumulation in Upper Cretaceous rocks in Digital Data Series DDS–69–V, chap. 3, 146 p., CD–ROM. the Bighorn Basin?, in Keefer, W.R., and Goolsby, J.E., eds., Cretaceous and Lower Tertiary rocks of the Bighorn Fox, J.E., and Dolton, G.L., 1989, Petroleum geology of the Basin, Wyoming and Montana: Wyoming Geological Wind River and Bighorn Basins, Wyoming and Montana: Association, 49th Annual Field Conference Guidebook, U.S. Geological Survey Open-File Report 87–450P, 41p. p. 257–273. Fox, J.E., and Dolton, G.L., 1996, Petroleum geology of the Johnson, R.C., Keefer, W.R., Keighin, C.W., and Finn, Bighorn Basin, north-central Wyoming and south-central T.M., 1998, Detailed outcrop studies of the upper part Montana, in Bowen, C.E., Kirkwood, S.C., and Miller, of the Upper Cretaceous Cody Shale and the Upper T.S., eds., Resources of the Bighorn Basin: Wyoming Cretaceous Mesaverde, Meeteetse, and Lance Forma- Geological Association, 47th Annual Field Conference tions, Bighorn Basin Wyoming, in Keefer, W.R., and Guidebook, p. 19–39. Goolsby, J.E., eds., Cretaceous and Lower Tertiary rocks of the Bighorn Basin, Wyoming and Montana: Wyoming Gries, R.R., Dolson, J.C., and Raynolds, R.G.H., 1992, Structural Geological Association, 49th Annual Field Conference and stratigraphic evolution and hydrocarbon distribution, Rocky Guidebook, p. 59–78. Mountain Foreland, in Macqueen, R.W., and Leckie, D.A., eds., Foreland basins and fold belts: American Association of Kauffman, E.G., 1977, Geological and biological overview— Petroleum Geologists Memoir 55, p. 395–425. Western Interior Cretaceous basin, in Kauffman, E.G., ed., Cretaceous facies, faunas, and paleoenvironments across Hagen, E.S., and Surdam, R.C., 1984, Maturation history and the Western Interior Basin: The Mountain Geologist, v. 14, thermal evolution of Cretaceous source rocks of the Bighorn nos. 3 and 4, p. 75–99. Basin, Wyoming and Montana, in Woodward, Jane, Meiss- ner, F.F., and Clayton, J.L., eds., Hydrocarbon source rocks Keefer, W.R., 1972, Frontier, Cody, and Mesaverde Formations of the greater Rocky Mountain region: Rocky Mountain in the Wind River and southern Bighorn Basins, Wyoming: Association of Geologists Guidebook, p. 321–338. U.S. Geological Survey Professional Paper 495–E, 23 p. References 31

Keefer, W.R., Finn, T.M., Johnson, R.C., Keighin, C.W., 1998, Molenaar, C.M., and Rice, D.D., 1988, Cretaceous rocks of Regional stratigraphy and correlation of Cretaceous and the Western Interior Basin, in Sloss, L.L., ed., Sedimentary Paleocene rocks, Bighorn Basin, Wyoming and Montana, cover—North American craton, U.S.: Geological Soci- in Keefer, W.R., and Goolsby, J.E., eds., Cretaceous and ety of America, The Geology of North America, v. D–2, Lower Tertiary rocks of the Bighorn Basin, Wyoming and p. 77–82. Montana: Wyoming Geological Association, 49th Annual Field Conference Guidebook, p. 1–30. Nixon, R.P., 1973, Oil source beds in Cretaceous Mowry Shale of northwestern interior United States: American Kirschbaum, M.A., Merewether, E.A., and Condon, S.M., Association of Petroleum Geologists Bulletin, v. 57, no. 1, 2009, Stratigraphy and age of the Frontier Formation and p. 136–161. associated rocks, central and southern Bighorn Basin, Wyo- ming—Surface to subsurface correlation: The Mountain Nuccio, V.F., and Finn, T.M., 1998, Thermal maturity and Geologist, v. 46, no. 4, p. 125–147. petroleum generation history of Cretaceous and Tertiary source rocks, Bighorn Basin, Wyoming and Montana, Landon, S.M., Longman, M.W., and Luneau, B.A., 2001, Hydro- in Keefer, W.R., and Goolsby, J.E., eds., Cretaceous and carbon source rock potential of the Upper Cretaceous Niobrara Lower Tertiary rocks of the Bighorn Basin, Wyoming and Formation, Western Interior Seaway of the Rocky Mountain Montana: Wyoming Geological Association, 49th Annual region: The Mountain Geologist, v. 38, no. 1, p. 1–18. Field Conference Guidebook, p. 211–231. Longman, M.W., Luneau, B.A., and Landon, S.M., 1998, Obradovich, J.D., 1993, A Cretaceous time scale, in Caldwell, Nature and distribution of Niobrara lithologies in the Cre- W.G.E., and Kauffman, E.G., eds., Evolution of the Western taceous Western Interior Seaway of the Rocky Mountain Interior Basin: Geological Association of Canada Special Region: The Mountain Geologist, v. 35, no. 4, p. 137–170. Paper 39, p. 379–396. McGookey, D.P., and others, 1972, Cretaceous system, in Obradovich, J.D., Cobban, W.A., Merewether, E.A., and Geologic atlas of the Rocky Mountains: Rocky Mountain Weimer, R.J., 1996, A time framework for the late Albian Association of Geologists, p. 190–228. and early Cenomanian strata of northern Wyoming and Meissner, F.F., Woodward, Jane, and Clayton, J.L., 1984, Montana: Geological Society of America Abstracts with Stratigraphic relationships and distribution of source rocks Programs, 1996 Annual Meeting, Denver, Colo., v. 28, in the greater Rocky Mountain region, in Woodward, Jane, no. 7, p. A–66. Meissner, F.F., and Clayton, J.L., eds., Hydrocarbon source Pawlewicz, M.J., and Finn, T.M., 2012, Vitrinite reflectance rocks of the greater Rocky Mountain region: Rocky Moun- data for Cretaceous marine shales and coals in the Bighorn tain Association of Geologists Guidebook, p. 1–34. Basin, north-central Wyoming and south-central Montana: Merewether, E.A., 1996, Stratigraphy and tectonic implica- U.S. Geological Survey Open-File Report 2012–1254, 11 p. tions of Upper Cretaceous rocks in the Powder River Basin, northeastern Wyoming and southeastern Montana: U.S. Peters, K.E., 1986, Guidelines for evaluating petroleum source Geological Survey Bulletin 1917–T, 92 p. rock using programmed pyrolysis: American Association of Petroleum Geologists Bulletin, v. 70, no. 3, p. 318–329. Merewether, E.A., Cobban, W.A., Matson, R.M., and Magathan, W.J., 1977a, Stratigraphic diagrams with electric Peters, K.E., and Cassa, M.R., 1994, Applied source rock logs of Upper Cretaceous rocks, Powder River Basin, geochemistry, in Magoon, L.B., and Dow, W.G., eds., Campbell, and Weston counties, Wyoming: U.S. Geological The petroleum system—From source to trap: American Survey Oil and Gas Investigations Map OC–74. Association of Petroleum Geologists Memoir 60, p. 93–120. Merewether, E.A., Cobban, W.A., Matson, R.M., and Roberts, L.N.R., Finn, T.M., and Lewan, M.D., 2008, Burial Magathan, W.J., 1977b, Stratigraphic diagrams with electric history, thermal maturity, and oil and gas generation his- logs of Upper Cretaceous rocks, Powder River Basin, tory of source rocks in the Bighorn Basin, Wyoming and Natrona, Converse, and Niobrara counties, Wyoming: U.S. Montana: U.S. Geological Survey Scientific Investigations Geological Survey Oil and Gas Investigations Map OC–75. Report 2008–5037, 27 p. Miskell-Gerhardt, K.J., 1989, Productivity, preservation, and Ryder, R.T., 1987, Oil, gas, and coal resources of the cyclic sedimentation within the Mowry Shale depositional McCullough Peaks Wilderness study area, Bighorn Basin, sequence, Western Interior Seaway: Houston, Tex., Rice Wyoming: U.S. Geological Survey Open-File Report University, Ph.D. dissertation, 432 p. 87–646, 59 p. Molenaar, C.M., and Baird, J.K., 1991, Stratigraphic cross sections Schrayer, G.J., and Zarrella, W.M., 1963, Organic geochemis- of Upper Cretaceous rocks in the northern San Juan Basin, try of shale—I Distribution of organic matter in the siliceous Southern Ute Indian Reservation, southwestern Colorado: U.S. Mowry Shale of Wyoming: Geochimica et Cosmochimica Geological Survey Professional Paper 1505–C, 12 p. Acta, v. 27, no. 10, p. 1033–1046. 32 Lower Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, and Source Rock Potential

Schrayer, G.J., and Zarrella, W.M., 1966, Organic geochem- [abs.], in Rocky Mountain Association of Geologists and istry of shale—II Distribution of extractable organic matter Petroleum Technology Transfer Council Fall Symposium, in the siliceous Mowry Shale of Wyoming: Geochimica et Denver, Colo., September 14, 1999, Proceedings: Rocky Cosmochimica Acta, v. 30, no. 4, p. 415–434. Mountain Association of Geologists and Petroleum Tech- nology Transfer Council, 1 p. Schrayer, G.J., and Zarrella, W.M., 1968, Organic carbon in Mowry Formation and its relation to the occurrence of petro- Stone, D.S., 2004, Rio thrusting, multi-stage migration, and leum in Lower Cretaceous reservoir rocks, in Wulf, G.R., formation of vertically segregated Paleozoic oil pools at ed., Black Hills area South Dakota, Montana, Wyoming: Torchlight field on the Greybull platform (eastern Bighorn Wyoming Geological Association, 20th Field Conference Basin)—Implications for exploration: The Mountain Geolo- Guidebook, p. 35–39. gist, v. 41, no. 3, p. 119–138. Sonnenberg, S.A., 2011, The Niobrara Petroleum System—A Surdam, R.C., Jiao, Z.S., and Heasler, H.P., 1997, Anoma- major tight resource play in the Rocky Mountain Region, lously pressured gas compartments in Cretaceous rocks of in Estes-Jackson, J.E., and Anderson, D.S., eds., Revisiting the Laramide basins of Wyoming—A new class of hydro- and revitalizing the Niobrara in the central Rockies: Rocky carbon accumulation, in Surdam, R.C., ed., Seals, traps, and Mountain Association of Geologists, p. 13–32. the petroleum system: American Association of Petroleum Geologists Memoir 67, p. 199–222. Steidtmann, J.R., 1993, The Cretaceous foreland basin and its sedimentary record, in Snoke, A.W., Steidtmann, J.R., and Tissot, B.P., and Welte, D.H., 1978, Petroleum formation and Roberts, S.M., eds., Geology of Wyoming, v. 2: Geological occurrence: New York, Springer-Verlag, 538 p. Survey of Wyoming Memoir No. 5, p. 250–271. Wilson, C.W., Jr., 1936, Geology of the Nye-Bowler linea- Sterling, Rob, Silverman, M., and Stewart, G., 2009, The ment, Stillwater and Carbon Counties, Montana: American Mowry Shale, review of potential in the Bighorn Basin, Association of Petroleum Geologists Bulletin, v. 20, no. 9, Unconventional reservoirs—Oil and gas shales and CBM p. 1161–1188.

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For more information concerning this publication, contact: Center Director, USGS Central Energy Resources Science Center Box 25046, Mail Stop 939 Denver, CO 80225 (303) 236-1647

Or visit the Central Energy Resources Science Center Web site at: http://energy.usgs.gov/ 110° 109° 108° 107° R15E R20E R25E R35E EXPLANATION

T Tertiary volcanic rocks 5 NYE-BOWLER S 0 20 40 MILES LINEAMENT Cody Shale outcrop 110° 109° 108° 107° 0 20 40 KILOMETERS Precambrian rocks R15E R20E R25E R35E Finn 1,750 MOUNTAINSPRYOR Bighorn Basin Province boundary T BEARTOOTH EXPLANATION 5 NYE-BOWLER MOUNTAINS Eastern limit of lower memBer of S —Cody Shale, Bighorn Basin, Wyoming and Montana—Thickness, Distribution, Source Rock Potential— Mesaverde Formation LINEAMENT 1,750 Bighorn Basin Province Boundary 700 T T Well location 9 Tertiary volcanic rocks 9 MONTANA 45° S R35E R40E S Thickness isopach, in feet 110° 109° 108° 700 MOUNTAINSPRYOR 107° Cody Shale outcrop BEARTOOTH WYOMING R101W R95W R15E R20E R25E R35E BIGHORN <1,750 MOUNTAINS T Precambrian rocks 57 T 800 EXPLANATION N 1,750 to 2,000 5 NYE-BOWLER T Well location T 9 9 S MONTANA Bighorn Basin Province Boundary 2,000 to 2,250 LINEAMENT 45° S 900 0 R35E 20 40R40E MILES S T WYOMING R101W Tertiary volcanic rocks R95W 2,000 T 2,250 to 2,500 110° 109° 108° 107° 700 55 BIGHORN 0 20 40 KILOMETERS 55 T N 57 N 2,500 to 2,750 R15E R20E R25E R35E MOUNTAINSPRYOR Cody Shale outcrop R90W R85W BEARTOOTH 550 N 900 2,750 to 3,000 T MOUNTAINS 600 EXPLANATION Precambrian rocks 5 NYE-BOWLER 650 800 ABSAROKA S T T Well location T 3,000 to 3,250 LINEAMENT Bighorn Basin Province Boundary T 9 700 55 900 9 55 MONTANA 40 MILES MOUNTAINS 3,250 to 3,500 45° S N 0 R35E 20 R40E S N 110° 109° 108° 107° Tertiary volcanic rocks R90W R85W 100 WYOMING R101W R95W 3,500 to 3,750 R20E R25E R35E BIGHORN 20 40 KILOMETERS R15E MOUNTAINSPRYOR T Cody Shale outcrop 0 BEARTOOTH 800 57 >3,750

T EXPLANATION ABSAROKA MOUNTAINS N Precambrian rocks 5 NYE-BOWLER T 2,250 T 100 50 S 900 50 T Bighorn Basin Province Boundary T RANGE LINEAMENT Well location N MOUNTAINS N 9 9 T 1,100 T MONTANA S Tertiary volcanic rocks 0 R35E 20 40 MILESR40E S 0.8 45° 55 R104W55 WYOMING R101W R95W N 0.8 Frontier/Mowry/Muddy/Thermopolis BIGHORN N 2,750 MOUNTAINSPRYOR 40 KILOMETERS R90W R85W BEARTOOTH T 100 0 20 750 Formations outcrop T 2,500 T MOUNTAINS 57 1,000 1.1 N 100 Precambrian rocks 50 50 RANGE 1,000 800 N N ABSAROKA 1,100 T1.35 High-angle fault T 850 44° 9 100 9 MONTANA S T R104W 3,000 ThrustR35E fault 200 R40E S T MOUNTAINS 45° 55 3,750 R101W R95W 55 WYOMING N BIGHORN Line of secton 3,250 T Clark's N T 2,750 T R90W R85W 3,500 45 Well sample point 45 1,200 57 N N N Composite well sample point T 44° Fork 1 T . 0.8 100 1,200 1.35 1 ABSAROKA Outcrop sample point 50 50 R100W RANGE 950 R105W N 1,100 N R4W 1,100 sub-basin 1 400 1,000 1,100

Burial history location 300 . 200 1,200 T 1 100 T T 1,100 1,000 R3E 55 T MOUNTAINS T T 1.1 55 R104W 8 N 0 20 40 MILES 45 N 8 45 N N R90W R85W N 1,200 N 950 850 R95W 1 900 800 .1 0 20 40 KILOMETERS 1,000 BIG TRAILS FAULT T 1,050 R105W R100W 1.35 950 T ABSAROKA R4W OREGON 50 44° 200 50 RANGE T R3E OWL N 1,000 N T T T 8 40 T 40 MOUNTAINS 950 N 8 CREEK

N N 5 MOUNTAINS N R1W R5E R5W 950 R94W R1E R85W R104W 700 R95W N R90W BASIN 2.0 T T 400 750

45 45 BIG TRAILS FAULT

Emblem N

850 R5W R1W R1E R5E R94W R90W R85W

N N MOUNTAINS

N 5

0.6 Bench N

T FAULT 0.8 200 T CREEK 40OWL T

T 40

50 50 T

RANGE R100W T R105W T 40 T 44° 40 OWL N N R4W CREEK

Dobie N 5 MOUNTAINS N R1W R5E R5W R94W R1E R85W T R3E R90W Creek T N R104W 8

300

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T N

T N R5W R1W R1E R5E R94W R90W R85WR95W

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1 N T 5 N

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MOUNTAINS N

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T N R90W

N N

T 45

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0.8 3,250 N N R3E

N R5W R1W R1E R5E R94W T R90W R85W

BIG TRAILS FAULT

3,750 MOUNTAINS

0.6 N R4W

3,000

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R105W

R100W 40

R105W R100W 40

° OWL 44

R4W T OWL T

1,200

T N R3E N

40 T T CREEK 40

8 45

N 8 5 MOUNTAINS N 45

BIG TRAILS FAULT

2,500

T R1W R5E R5W R94W R1E R85W N R90W

N N T

1,100

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1,200

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1,100

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R5W R1W R1E BIG TRAILS FAULT R5E R94W R90W R85W R104W 8

MOUNTAINS

1,200 T

44°

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T T

T RANGE 1,200 OWL

R105W 50

40 T 40 R100W

CREEK 2,250

N 5 MOUNTAINS N T

>3,750

N BIG TRAILS FAULT

N N 850

R1W R5E R5W R94W

R1E R85W R90W

R104W

R95W

750

3,500 to 3,750

N T

R5W R1W R1E R5E R94W N R90W R85W

700

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1,100

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3,250 to 3,500

N 950

5 N

1,000

RANGE

R3E

CREEK

T 40 1,000

1,000

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3,000 to 3,250

T 44° T R105W

R100W OWL ABSAROKA

950

1,050 2,750 to 3,000

1,000 N

BIG TRAILS FAULT

800

900

R90W R85W 45 1,100 850

45 950

2,500 to 2,750

R95W

T T

MOUNTAINS N

300 55

N 55 900 R104W

300

2,250 to 2,500

T 2,000 8 T

1,000 R3E

T ABSAROKA

N 2,000 to 2,250

800

950 R4W

RANGE

44°

R105W Scientific Investigations Report 2013–5138 R100W

T 1,750 to 2,000 200

0.6

R90W R85W

N N

N 0.8

<1,750

900

55 45

BIGHORN

WYOMING

R95W R101W 400

T T T

R104W Thickness isopach, in feet

45°

R35E

R40E S S

MONTANA

800

MOUNTAINS

1 .

1 9 9

Well location

N T T

RANGE 850 200

50 900

50 °

44 ABSAROKA 1,750

Mesaverde Formation 57

800

MOUNTAINS 0.6

Eastern limit of lower memBer of 0 20 700 40 KILOMETERS

BIGHORN

BEARTOOTH

WYOMING

R95W R101W

750

PRYOR

R90W R85W Bighorn Basin Province boundary MOUNTAINS

45°

R35E 1,750 900

R40E 20 0 S N S 40 MILES MONTANA N

55 9

Precambrian rocks 55

R104W

0 20

40 KILOMETERS

Well location

T T T MOUNTAINS Creek

800

100

200 300

400

LINEAMENT

Cody Shale outcrop Dobie

N N

Precambrian rocks 20 0 40 MILES

MOUNTAINS

RANGE

ABSAROKA 5 50

NYE-BOWLER

100

Tertiary volcanic rocks BEARTOOTH

FAULT T

PRYOR

0.8 Cody Shale outcrop MOUNTAINS 700 Bench

0.6 57

Emblem R15E R20E R25E EXPLANATION

R35E

R90W R85W

0 20 40 KILOMETERS

Tertiary volcanic rocks

BIGHORN

WYOMING

N R95W R101W 700 2.0 BASIN

109° 110° 107° 108°

LINEAMENT 55

45°

R35E Bighorn Basin Province Boundary R40E S

20 0 40 MILES

200 MONTANA

MOUNTAINS

700 9

NYE-BOWLER 5

100

Well location T T

EXPLANATION T

650

OREGON

ABSAROKA 1.35

600 Precambrian rocks

R15E MOUNTAINS R20E R25E

R35E 100

550

BEARTOOTH 1

0 20

40 KILOMETERS

109° 110° 107° 108°

1 100

T PRYOR 0 20 40 KILOMETERS

MOUNTAINS Cody Shale outcrop

R90W R85W

BIGHORN

WYOMING R95W R101W

20 0

40 MILES

45°

. 55 Tertiary volcanic rocks 20 0

40 MILES R35E 1 55 R40E S S MONTANA

1 T 9

Burial history location LINEAMENT

sub-basin

Well location

Bighorn Basin Province Boundary

T T S

Outcrop sample point

1.35

NYE-BOWLER

5 .

100 0.8

1 Fork

Precambrian rocks EXPLANATION

T Composite well sample point MOUNTAINS N

BEARTOOTH 57

Well sample point

R15E Cody Shale outcrop R20E PRYOR R25E

R35E MOUNTAINS

Clark's

BIGHORN

100

WYOMING Line of secton 109° 110° 107° 108° R95W R101W

Tertiary volcanic rocks

45°

R35E R40E S

Thrust fault

MONTANA

S ISSN 2328-0328 (online)

LINEAMENT

Bighorn Basin Province Boundary

High-angle fault

T http://dx.doi.org/10.3133/sir20131538 1.35

NYE-BOWLER 5

EXPLANATION

Precambrian rocks

1 .

1 MOUNTAINS

Formations outcrop

BEARTOOTH

R15E

R20E R25E

R35E

PRYOR

MOUNTAINS Frontier/Mowry/Muddy/Thermopolis 0.8

109° 110° 107° 108°

0.8

Tertiary volcanic rocks

LINEAMENT

Bighorn Basin Province Boundary S

NYE-BOWLER 5

EXPLANATION T

R15E R20E R25E R35E

109° 110° 107° 108°