Chapter SW

A SUMMARY OF TERTIARY COAL RESOURCES OF

THE WIND RIVER BASIN, WYOMING

By R.M. Flores and C. W. Keighin

in U.S. Geological Survey Professional Paper 1625-A
SW-ii

Contents

Introduction.........................................................................................................................SW-1

Stratigraphy.........................................................................................................................SW-1

Description of Coal Zone.................................................................................................SW-2

Coal Quality........................................................................................................................SW-3

Original Resources............................................................................................................SW-3

Production History............................................................................................................SW-3

Coal-bed Methane..............................................................................................................SW-4

Conclusions.........................................................................................................................SW-5

References...........................................................................................................................SW-6

Figures

SW-1. Map showing locations of outcrops of the Fort Union Formation on the

periphery of the Wind River Basin, Wyoming.

SW-2. Generalized geologic map of the Wind River Basin.

SW-3. Generalized stratigraphic chart for the Paleocene Fort Union Formation.

SW-4. Cross section of the lower member of the Fort Union Formation and

associated thick coal beds.

SW-5. Total net-coal-thickness isopach map of the lower member of the Fort

Union Formation.
SW-iii

Figures—Continued

SW-6. Lithofacies and coal distribution in the Fort Union Formation along a south

to north line across the Wind River Basin.

SW-7. Total net-coal-thickness isopach map of the Shotgun Member, Fort Union

Formation, Wind River Basin.

SW-8. Lithofacies and coal distribution in the lower member and Shotgun Member

of the Fort Union Formation along a west to east cross section, Wind River

Basin.

SW-9. Summary of thermal maturity data to the base of the Paleocene Waltman

Shale Member of the Fort Union Formation, Wind River Basin.
SW-1

INTRODUCTION

Coal in the Wind River Basin of Wyoming is mainly found in the Paleocene Fort

Union Formation and subordinately in the Eocene Wind River Formation (figs.

SW-1 and SW-2). These deposits have low importance in the current National Coal

Resource Assessment because it is improbable they will be utilized in the next 20-30

years. This report is a brief summary of the geology, occurrence, quality,

production history, and coal-bed methane potential of Fort Union coal. Coal in the

Wind River Formation will not be assessed because it is generally less than 1 ft

thick (Thompson and White, 1952; Glass and Roberts, 1978; Thaden, 1978, 1979,

1980a-c; Gregory and others, 1991).

STRATIGRAPHY

Figure SW-3 illustrates the general stratigraphy of the Fort Union Formation (using

the terminology of Keefer, 1965) in the Wind River Basin. Isolated and widely

scattered outcrops of Fort Union coal are found along the margins of the basin

(Keefer, 1965; Glass and Roberts, 1978; Nuccio and Finn, 1994). The Fort Union

Formation outcrops (fig. SW-1) include minor amounts of coal; the coaly facies is

almost entirely in the subsurface (Johnson and others, 1994). Thompson and White

(1952) report four coal beds, ranging in thickness from 2 to 3 ft, in the subsurface in

the northwestern part of the basin. Outcrops of thin coal beds (a few inches to 2 ft

thick) are in the Jenkins Mountain, Shotgun Butte, Little Dome, Hudson, and Signor

Ridge areas (Flores and others, 1992; Flores and Keighin, 1993; Flores and others,

1993). Outcrops of thicker coal beds (as much as 15 ft thick) are in the Castle

Gardens and Coal Bank Hills areas (Flores and others, 1992; Flores, 1997). Coal
SW-2

beds are contained in the lower member and Shotgun Member of the Fort Union

Formation. (This terminology follows Keefer, 1965; “lower member” is an

informal term). A cross-section (A-A’) of the lower member and associated thick

coal beds (5-15 ft thick) in the Castle Gardens areas is shown in figure SW-4

(modified from Flores and others, 1992).

DESCRIPTION OF COAL ZONE

The Paleocene Fort Union Formation is considered a minor coal-bearing formation

in the Wind River basin; exposed coal is uncommon and thin, seldom reaching 3 ft

in thickness (Hogle and Jones, 1991). Woodruff and Winchester (1912) reported a

4.5-ft-thick Paleocene coal bed near Castle Gardens (fig. SW-5). However,

Johnson and Flores (1993), using geophysical logs, report that the Fort Union

Formation contains, in aggregate, more than 100 ft (net total) of coal in the western

part of the Wind River Basin. One coal bed in this coal zone is as much as 40 ft

thick. Recent work by Flores and others (1992), Flores and Keighin (1993), and

Flores (1997) shows coal beds 5-15 ft thick that are more than 2 mi in lateral extent.

A total net coal thickness isopach map of the lower member of the Fort Union

Formation, modified from Johnson and others (1994) to include coal-bed thickness

measurements from outcrops by Flores and others (1992), Flores and Keighin

(1993), Flores and others (1993), and Flores (1997), is shown in figure SW-5.

Lithofacies and coal-bed distribution in the Fort Union Formation along a south to

north cross section (B-B’) are shown in figure SW-6. The ovoid areal distribution

of the lower member coal beds across the east-central part of the Wind River Basin

was influenced by interchannel swamps related to east-northeast-flowing fluvial

systems. A total (net) coal thickness isopach map of the Shotgun Member is shown
SW-3

in figure SW-7; lithofacies and coal-bed distribution are illustrated in cross section

C-C’ (fig. SW-8). The elongate areal distribution of the Shotgun Member coal beds

across the west-central part of the basin was controlled by shoreline transgression

accompanied by coastal regression of Waltman Lake.

COAL QUALITY

Tertiary coal in the Wind River Basin is generally considered to be subbituminous,

but no analyses are available to verify its rank or coal quality (Glass and Roberts,

1978; Glass, 1981). Thermal maturity levels (Ro = 0.36-0.55%) of surface samples

of Fort Union coal on the periphery of the basin are consistent with subbituminous

rank (fig. SW-9; Nuccio and Finn, 1994). Thermal maturity levels of Fort Union

coal may reach levels consistent with high volatile A bituminous rank (Ro as much

as 0.99%) in deeper parts of the basin (Nuccio and Finn, 1994; Nuccio and others,

1996; Rice, 1993).

ORIGINAL RESOURCES

Because of limited, no resource calculations have been made of potential coal

resources in the Fort Union Formation in the Wind River Basin.

PRODUCTION HISTORY

Coal mining in the Wind River Basin apparently started in approximately 1870, but

Tertiary coal appears to have mined only from the Arminto field (T. 34 N., R. 90
SW-4

W., sec. 4) in about 1900. There is apparently no record of the amount of coal

produced, but the quantity was probably very limited and for local use only.

COAL-BED METHANE

Tertiary coal of the Wind River Basin at depths less than 1,000 ft is normally of low

rank and exhibits none of the maturation characteristics needed for significant

methane generation (Rieke and Kirr, 1984). Coal-bed gases found in the structurally

shallow areas of the basin (for example, within the Wind River Indian Reservation)

are mixtures of biogenic and thermogenic gases. These coal beds are immature and

were never buried deeply enough to have generated significant quantities of

thermogenic gas. The thermogenic component may have migrated into the coal

from a deeper, more thermally mature source sometime after the coal was buried in

Paleocene time (Johnson and Rice, 1993).

Nuccio and Finn (1994) reported thermal maturity levels of the Fort Union

Formation vary from very immature (0.29% Ro) in outcrops (Nuccio and others,

1993) in the southern part of the basin, to mature (0.99% Ro) for the lower

unnamed member in the deeper part of the basin. The higher level of thermal

maturity is sufficient to generate thermogenic gas. Less-thermally mature coal (Ro

< 0.6%) in shallow parts of the basin may serve as a source of biogenic gas. A

summary of thermal maturity data available to the base of the Paleocene Waltman

Shale Member of the Fort Union Formation shows the potential for thermogenic

gas generation in the northern and central part of the Wind River Basin and biogenic

gas in the southern and eastern part (fig. SW-8). Jones and de Bruin (1990),

however, consider Tertiary Fort Union coal in the Wind River Basin to be too

deeply buried to be a target for coal-bed methane production.
SW-5

CONCLUSIONS

Fort Union coal is not economically minable today because the thick deposits are

found only in the deep parts of the Wind River Basin, and they are not high enough

in quality (based on normal Tertiary coal quality) to warrant development of large

underground mines. However, thermogenic and biogenic gases from the Fort

Union coal in the deep and shallow parts of the basin may serve as potential coalbed methane resources. Much of the infrastructure for coal-bed methane

transportation, such as gas pipelines, is in place in the basin. Rail systems for coal

transportation from areas where the thickest coal accumulations exist is not

available.
SW-6

REFERENCES

Flores, R.M., 1997, Tectono-stratigraphic framework of the Fort Union in the Wind

River Basin: A window to the northern Rockies paleogeography: Wyoming

Geological Association Proceedings 1997 Field Conference, 3 p.

(unpaginated).

Flores, R.M, Clark, A.C., and Keighin, C.W., 1993, Architecture of Fort Union

paleovalley conglomerates related to aquifer potential in the western Wind

River Basin, in Keefer, W.R., Metzger, W.J., and Godwin, L.H., eds., Oil

and Gas and other Resources of the Wind River Basin Wyoming: Wyoming

Geological Association Special Symposium 1993, p. 143-162.

Flores, R.M., and Keighin, C.W., 1993, Reservoir anisotropy and facies

stratigraphic framework in the Paleocene Front Union Formation, western

Wind River Basin, Wyoming, in Keefer, W.R., Metzger, W.J., and Godwin,

L.H., eds., Oil and Gas and other Resources of the Wind River Basin

Wyoming: Wyoming Geological Association Special Symposium 1993, p.

121-141.

Flores, R.M., Keighin, C.W., and Nichols, D.J., 1992, Sedimentology,

conglomerate petrology, and palynostratigraphy of the Fort Union Formation

(Paleocene), Castle Gardens, Wind River basin, Wyoming, in K.A. Sundell

and T.C. Anderson eds., Road Log Volume for Rediscover the Rockies:

Casper, Wyo., Wyoming Geological Association, p. 21-27.

Glass, G.B., 1981, Coal deposits of Wyoming: Thirty-Second Annual Field

Conference—1981, Wyoming Geological Association, p. 181-236.

Glass, G.B., and Roberts, J.T., 1978, Update on the Wind River coal basin:

Wyoming Geological Association 30th Annual Field Conference, Casper,

Wyo., p. 363-377.
SW-7

Green, G., and Drouillard, P.M., 1994, Wyoming digital geologic map: U.S.

Geological Survey Open-File Report 94-0425, scale 1:250,000.

Gregory, R.W., Jones, R.W., and Glass, G.B., 1991, Results of coal drilling

projects in the Wind River coal field, Wyoming: Laramie, Wyo., Geological

Survey of Wyoming, Report of Investigation 46, 47 p.

Hogle, D.G., and Jones, R.W., 1991, Subsurface geology of Upper Cretaceous and

Lower Tertiary coal-bearing rocks, Wind River basin, Wyoming: The

Mountain Geologist, v. 28, no. 2-3, p. 13-35.

Johnson, R.C., and Flores, R.M., 1993, Stratigraphy, areal distribution, and

paleodepositional environments of Fort Union Formation coal beds, Wind

River Reservation, Wyoming, implications for coal-bed methane

development, in Keefer, W.E., Metzger, W.J., and Godwin, L.H., eds., Oil

and Gas and other Resources of the Wind River basin, Wyoming: Wyoming

Geological Association Special Symposium 1993, Casper, Wyo., p. 281-294.

Johnson, R.C., Flores, R.M., Szmajter, R., and Finn, T.M., 1994, A preliminary

study of coal-forming environments during deposition of the Paleocene Fort

Union Formation, Wind River basin, Wyoming, in Flores, R.M., Mehring,

K.T., Jones, R.W., and Beck, T.L., eds., Organics and the Rockies Field

Guide: Wyoming State Geological Survey Circular 33, p. 69-81.

Johnson, R.C., and Rice, D.D., 1993, Variations in composition and origins of

gases from coal bed and conventional reservoirs, Wind River Basin,

Wyoming, in Keefer, W.E., Metzger, W.J., and Godwin, L.H., eds., Oil and

Gas and other Resources of the Wind River basin, Wyoming: Wyoming

Geological Association Special Symposium 1993, Casper, Wyo., p. 319-335.

Jones, R.W., and DeBruin, R.H., 1990, Coalbed methane in Wyoming: Wyoming

State Geological Survey Public Information Circular 30, 15 p.
SW-8

Keefer, W.R., 1965, Stratigraphy and geologic history of the Uppermost

Cretaceous, Paleocene, and Lower Eocene rocks in the Wind River

basin, Wyoming: U.S. Geological Survey Professional Paper 495-

A, p. 1-77.

Nuccio, V.F., and Finn, T.M., 1994, Structural and thermal history of the Paleocene

Fort Union Formation, central and eastern Wind River Basin, with emphasis

on petroleum potential of the Waltman Shale Member, in Flores, R.M.,

Mehring, K.T., Jones, R.W., and Beck, T.L., eds., Organics and the Rockies

Field Guide: Wyoming State Geological Survey Public Information Circular

No. 33, p. 53-68.

Nuccio, V.F., Finn, T.M., and Johnson, R.C., 1996, Thermal maturity data used for

the assessment of gas resources in the Wind River Basin, Wyoming: U.S.

Geological Survey Open File Report 96-064, 57 p.

Nuccio, V.F., Finn, T.M., and Pawlewicz, M.J., 1993, Surface vitrinite reflectance

study of the Wind River basin, central Wyoming, in Keefer, W.R., Metzger,

W.J., and Godwin, L.H., eds., Oil and Gas and Other Resources of the Wind

River Basin Wyoming: Wyoming Geological Association Special

Symposium 1993, Casper, Wyo., p. 307-317.

Rice, D.D., 1993, Composition and origins of coal-bed gas, in Law, B.E., and Rice,

D.D., eds., Hydrocarbons from Coal: American Association of Petroleum

Geologists Studies in Geology no. 38, p. 159-184.

Rieke, H.H., and Kirr, J.H., 1984, Geologic overview, coal, and coal-bed methane

resources of the Wind River basin, Wyoming, in Rightmire, C.T., Eddy,

G.E., and Kirr, J.N., eds., Coalbed methane resources of the United States:

American Association of Petroleum Geologists Studies in Geology Series no.

17, p. 295-334.
SW-9

Thaden, R.E., 1978, Geologic map of the Bonneville quadrangle, Fremont County,

Wyoming: U.S. Geological Survey Geologic Quadrangle Map GQ-1439,

scale 1:24,000.

_____1979, Geologic map of the Lysite quadrangle, showing chronolithofacies and

coal beds in the Wind River Formation, Fremont County, Wyoming: U.S.

Geological Survey Geologic Quadrangle Map GQ-1511, scale 1:24,000.

_____1980a, Geologic map of the Birdseye Pass quadrangle, showing

chronolithofacies and coal beds in the Wind River Formation, Fremont and

Hot Springs Counties, Wyoming: U.S. Geological Survey Geologic

Quadrangle Map GQ-1537, scale 1:24,000.

_____1980b, Geologic map of the Gates Butte quadrangle, showing

chronolithofacies and coal beds in the Wind River Formation, Fremont

County, Wyoming: U.S. Geological Survey Geologic Quadrangle Map GQ1538, scale 1:24,000.

_____1980c, Geologic map of the Picard Ranch quadrangle, showing

chronolithofacies and coal beds in the Wind River Formation, Fremont

County, Wyoming: U.S. Geological Survey Geologic Quadrangle Map GQ1539, scale 1:24,000.

Thompson, R.M., and White, V.L., 1952, The coal deposits of the Alkali Butte, the

Big Sand Draw, and the Beaver Creek fields, Fremont County, Wyoming:

U.S. Geological Survey Circular 152, 24 p.

Woodruff, E.G., and Winchester, D.E., 1912, Coal fields of the Wind River region,

Fremont and Natrona Counties, Wyoming: U.S. Geological Survey Bulletin

471, p. 516-564.
0 20 Miles

0 20 Kilometers

108° 107°

43° Riverton

Hudson

Waltman

WIND RIVER

 BASIN

Jenkins

Mtn. 

hotgun Butte

Little Dome

Signor

Ridge

Casper

Arch

Owl Cr Big Horn

Ridge

eek Mts.

43°

Castle

Gardens

Coal Bank

Hills

Fort Union outcrops

Granite Mts.

Wind River Mts.

Mts.

WIND RIVER

RESERVATION

Figure SW-1. Map showing locations of outcrops of the Fort Union Formation 

on the periphery of the Wind River Basin, Wyoming. Approximate location of 

very limited mining of Fort Union coal from the Arminto field around the year 

1900 is marked by . Section A-A' is shown in figure SW-4. *

A

*

A'

Wyoming

Wind River Basin
108°30' 108°00' 107 107°00' °30' 106°30'

Geology of the Wind River Basin

Alluvium

Fort Union Formation

Indian Meadows Formation

Wagon Bed Formation

Wind River Formation

Holocene and Quaternary

Eocene

Paleocene

Wyoming

Wind River Basin

25 0 25 Miles

Figure SW-2. Generalized geologic map of the Wind River Basin showing distribution of

Tertiary rocks. Adapted from Green and Drouillard, (1994).
Figure SW-3. Generalized stratigraphic chart for the Paleocene Fort Union 

Formation, Wind River Basin. The term "lower member" is informal. Fort Union Formation

Paleocene

lower Member

Waltman

Shale

Sh

Member otgun

Member
50 feet

0

Fluvial channel sandstone;

lenticular; conglomeratic

Crevasse splay sandstone;

lenticular; tabular

Floodplain

Siltstone and Mudstone

Coal and Carbonaceous

shale

Line of measured

section

Figure SW-4. Cross section of the lower member of 

the Fort Union Formation and associated thick coal 

beds (5-15 ft thick) in the Castle Gardens area. 

Location shown in figure SW-1. Modifed from Flores 

and others, (1992).

A
80

50

20

10

30

30

40

90

0 10

10

20

20

10

0?

30

0?

Granite Mts.

0 20 Miles

0 20 Kilometers

108° 107°

43° Riverton

Hudson

Waltman

Jenkins

Mtn.

Shotgun Butte

Signor

Ridge

Castle

Gardens

Casper Arch

Owl Cr Big Horn

Ridge

eek Mts.

43°

Coal Bank

Hills

Fort Union outcrops

Isopach contour showing total net coal

thickness in feet. Dashed where inferred.

Merriam

Anticline

Little Dome

Wind River Mts.

B

B'

WIND RIVER

RESERVATION

Figure SW-5. Total net-coal-thickness isopach map of the lower member of the Fort 

Union Formation (modified from Johnson and others, 1994) that includes coal-bed 

thickness measurements from outcrops (Flores and others, 1992, 1993; Flores and 

Keighin, 1993; Flores, 1997). Lithofacies and coal-bed distribution along a south to 

north cross section are illustrated in figure SW-6.

10

10

a Mts.

Wyoming

Wind River Basin
0

1000

2000 Feet Coaly, mudstone-dominated

fluvial facies

Undifferentiated coaly, sandy,

and mud-dominated fluvial

facies

Lacustrine delta facies

Lacustrine facies

Fort Union Formation

Paleocene

Waltman

Shale

lower member

Shotgun

Member

Mud-dominated facies Coal beds

Figure SW-6. Lithofacies and coal distribution in the Fort Union Formation 

along a south to north line (see fig. SW-5) across the Wind River Basin. 

uth

37 Miles

North

B'
10

20

30

40

30

20

40

10

0

0

0

10080

60

50

40

20

10

30

10

30

60

20

50

10

108° 107°

43° Riverton

Hudson

Waltman

WIND RIVER

 BASIN

Jenkins

Mtn. 

hotgun Butte

Little Dome

Casper Arch

Owl Cr Big Horn

Ridge

eek Mts.

43°

Maximum extent

of Waltman Lake Wind River Mts.

C'

10

C

Figure SW-7. Total net-coal thickness of the Shotgun Member, Fort Union 

Formation, Wind River Basin. Lithofacies and coal-bed distribution are 

shown in figure SW-8.

0 20 Miles

0 20 Kilometers

a Mts.

10

Signor

Ridge

Castle

Gardens Hills

Granite Mts.

WIND RIVER

RESERVATION

Coal Bank

Wyoming

Wind River Basin

Fort Union outcrops

Isopach contour showing total net coal

thickness in feet. Dashed where inferred.
0

1000 Feet

Shotgun Member

Waltman

Shale

Member

West East

Coaly, mudstone-dominated

fluvial facies

Undifferentiated coaly, sandy,

and mud-dominated fluvial

facies

Lacustrine delta facies

Lacustrine facies

Coal beds

C C'

Lo

wer Member

e SW-8. Lithofacies and coal distribution in the lower member and Shotgun 

ber of the Fort Union Formation along a west to east cross section, Wind River 

. Location shown on figure SW-7.

92 Miles
0 20 Miles

0 20 Kilometers

108° 107°

43°

Hudson

Waltman

WIND RIVER

 BASIN

Jenkins

un Butte Mtn.

e Dome

Signor

Ridge

CasperArch

Owl Cr Big Horn

Ridge

eek Mts.

43°

Castle

Gardens

Coal Bank

Hills

Granite Mts.

Wind River Mts.

WIND RIVER 

RESERVATION

1.10

0.6

0.6

0.73 0.73

gure SW-9. Summary of thermal maturity data to the base of the 

aleocene Waltman Shale Member of the Fort Union Formation, Wind 

iver Basin. Modified from Nuccio and others, (1996).

Fort Union outcrops

Thermal maturity expressed as 

.6

vitrinite reflectance levels (Ro)

Riverton

ka Mts.

Wyoming

Wind River Basin