Chapter PS

FORT UNION COAL IN THE POWDER RIVER BASIN,

WYOMING AND MONTANA: A SYNTHESIS

By R.M. Flores and L.R. Bader

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

Contents

Introduction...........................................................................................................................PS-1

History Of Coal Mining.....................................................................................................PS-4

Geological Setting................................................................................................................PS-8

Depositional Setting............................................................................................................PS-9

Coal Geology......................................................................................................................PS-14

Coal Resources and Coal Quality...................................................................................PS-18

Coal-Bed Methane Resource...........................................................................................PS-25

Conclusions.........................................................................................................................PS-28

References...........................................................................................................................PS-30

Figures

PS-1. Generalized geologic map showing the extent of the Powder River Basin in

Wyoming and Montana.

PS-2. Composite stratigraphic column showing subdivisions of Upper Cretaceous

rocks, Paleocene Fort Union Formation, and Eocene Wasatch Formation in

the Powder River Basin in Wyoming and Montana.

PS-3. Upper Fort Union conglomerate (more than 1,200 ft thick) exposed in the

Castle Rock area north of Buffalo. The conglomerate is a lateral facies to the

Tongue River Member.

PS-4. The erosional-based Fort Union conglomerate and coarse sandstone are

interbedded with variegated siltstone and mudstone, which were formed in

alluvial fan and interfan environments.
PS-iii

PS-5. Variegated and mottled siltstone and mudstone (lower part of picture) are

capped by partly oxidized, rooted carbonaceous mudstone (central part of

picture) representing a paleosol formed in the interfan environment.

PS-6. Pebble conglomerate of the Tongue River Member exposed north of

Kaycee; represents braided stream deposits.

PS-7. Floodplain mudstone, siltstone, and silty sandstone underlain by fluvial

channel sandstone beds (lower part of photo).

PS-8. Coarsening-upward mudstone, siltstone, and silty sandstone crevasse splay

deposits. These rocks are exposed along the Powder River in northeastern

Wyoming.

PS-9. Vertically stacked fluvial channel sandstone deposits interbedded with

floodplain and crevasse splay deposits. These deposits are below along the

“Sussex” coal zone, which is exposed north of Linch, Wyoming.

PS-10. Fluvial channel deposit consisting of multi-erosional, crossbedded

sandstone intercalated with basally erosional mudstone deposits that are

abandoned “clay plugs.” These deposits are below along the “Sussex” coal

zone, which is exposed north of Linch, Wyoming.

PS-11. Wyodak-Anderson coal, which is more than 100 ft thick, in the Eagle Butte

coal mine in the Gillette coalfield in Wyoming. Coal train is on horizon in

background.

PS-12. Diagrammatic cross section of a raised bog between two river estuaries in

Sumatra, Indonesia.

PS-13. Peat exposed along a drainage ditch cut near the margin of a raised bog in

central Kalimantan, Borneo, Indonesia.

PS-14. Wyodak-Anderson coal (Anderson-Dietz coal), showing a thin,

carbonaceous, coaly mudstone parting in the Spring Creek coal mine in

Montana.
PS-iv

PS-15. The split Wyodak-Anderson coal zone (upper bed is Anderson or Dietz 1

coal and the lower bed is Dietz 2 coal) in the Decker coal mine in Montana.

PS-16. The merged Wyodak-Anderson coal, which is more than 80 ft thick, in the

Spring Creek coal mine in Montana.

PS-17. Distribution of the number of coal beds in the Wyodak-Anderson coal zone

in the Powder River Basin.

PS-18. Biozones of the Wyodak-Anderson coal zone indicate early late Paleocene

(P5) to latest Paleocene (P6) from the center to the margins of the basin.

P5–P6 biozone is between these Paleocene ages.

PS-19. Clinker (orange-red) of the Anderson coal bed (upper clinker) and Canyon

coal bed (lower clinker) of the Wyodak-Anderson coal zone along the valley

wall of the Powder River in Wyoming. Here, the coal beds are susceptible

to burning, which progresses downdip (to the left of photo).

PS-20. A closer view of the clinker consisting of black, vesicular, cryptocrystalline

to glassy fused rock, range-red baked mudstone, siltstone, and sandstone,

and breccia composed of angular unfused to slightly fused rock fragments

(Coates, 1980).

PS-21. Clinker (orange-red on the left of the picture) of the Anderson or Dietz 1

coal bed (on the right of the picture) on the highwall of the Decker coal mine

in Montana. Burning has reduced the reserve of the Anderson coal bed.

PS-22. An outcrop (north of Linch, Wyoming) of the “Sussex” coal zone

consisting of a more than 20-ft- thick coal bed (upper part of picture) and

three underlying thin coal beds that are interbedded with silty sandstone,

siltstone, and mudstone representing floodplain deposits. The “Sussex”

coal zone is overlain by a fluvial channel sandstone.
PS-1

INTRODUCTION

Major coal resources of subbituminous rank exist in the Fort Union Formation

(Paleocene) in the Powder River Basin in Wyoming and Montana (fig. PS-1). Fort

Union strata make up the surface bedrock along the margins of the Powder River

Basin. These strata (fig. PS-2) are conformably underlain by the Lance Formation

(Upper Cretaceous) and conformably (in the basin center) and unconformably (at

the basin margins) overlain by the Wasatch Formation (Eocene). The coaly nature

of the Fort Union strata was first documented in mid-1850’s by Kemble Warren in

eastern Montana (Bryans, 1987). In 1859 and 1860 Ferdinand V. Hayden, a

member of Capt. W. F. Raynolds’ expedition exploring the Lower Yellowstone,

reported extensive lignite in an area between the Platte River and Pumpkin Buttes

(Bryans, 1987). In 1865, James A. Sawyer received a commission from the

Department of the Interior to survey the Montana gold fields. Traveling through the

Powder River country, he observed several sizeable coal deposits south of Gillette,

Wyoming (Gardner and Flores, 1989). Sawyer indicated that these coal deposits

were the best he had seen in the west, and an inexhaustible coal resource seemed to

be present, judging from the amount of outcrops he had observed (Bryans, 1987).

These coal deposits in the Powder River Basin remained undeveloped prior to 1877

because the coal was within tribal lands belonging to the Sioux, Cheyenne, and

Arapahoe (Gardner and Flores, 1989). Lands north of the North Platte River and

east of the Bighorn Mountains were designated as unceded Indian territory by the

Fort Laramie Treaty of 1868. However, reports of gold in the Black Hills in 1874

encouraged trespassers to the territory, and hostilities began between the U.S. Army

and the Sioux and Cheyenne that led to the Rosebud and Little Bighorn battles.

After the surrender of Crazy Horse in the spring of 1877, the Powder River Basin

was opened to development by settlers.
PS-2

Hayden (1861) first named the lignite beds between the Platte River and Pumpkin

Buttes as the Great Lignite Group, which was renamed the Fort Union Group by

Meek and Hayden (1862). The upper part of this group was dated by Newberry

(1868) as Tertiary, based on plant fossils. Later, the lower part of this group was

dated by Stanton and Knowlton (1897) as Cretaceous, based on dinosaur fossils,

and these workers identified this part as the Lance Formation. Brown (1907) named

the Hell Creek Formation in Montana, which is correlative to the Lance Formation

in Wyoming. However, Knowlton (1909) divided the Fort Union Group above the

Cretaceous Lance into the upper and lower Fort Union, with the lower part including

the Hell Creek Formation. The position of the Cretaceous-Paleocene boundary

between the Hell Creek Formation and the overlying Fort Union Group was

resolved by discovery of mammalian fossils and confirmed by plant fossils

(Simpson, 1937; Dorf, 1940, 1942; Brown, 1958, 1962). The paleobotanical

studies of Dorf (1940; 1942) resolved the position of the Cretaceous-Paleocene

(Lance-Fort Union) boundary in the Powder River Basin. The dated Fort Union

Group was divided into the Fort Union Formation in the lower part and the

Wasatch Formation in the upper part. Traditionally, the Fort Union is dated as

Paleocene and the Wasatch is dated as Eocene. The actual position of the PaleoceneEocene boundary between these formations remains controversial. The time

boundary and formation contact, often considered to be coincident, have been

recognized on the basis of: (1) the change in the lithology of mappable units (Taff,

1909; Wegemann, 1910, 1917, 1929; Davis 1912; Thom and Dobbin, 1924;

Dobbin and Barnett, 1928; Baker, 1929; Bass, 1932; Bryson, 1952; Olive, 1957;

Mapel, 1959; Bryson and Bass, 1973; Culbertson and Mapel, 1976); (2) erosion or

a regional unconformity (Glass, 1976; Kent 1986); (3) a change in the heavymineral suite (Denson and Chisholm, 1971; Denson and Horn, 1975; Denson and
PS-3

others, 1989a, 1989b); (4) mammalian fossils (Simpson, 1928; 1929; 1937); and

(5) plant microfossils (Tschudy, 1976; Pocknall, 1987). These differing criteria

placed the Fort Union-Wasatch formations contact and the Paleocene-Eocene

boundary at various positions within an interval of 175 to 725 ft between the top of

the Wyodak-Anderson coal zone and the base of the Felix coal bed (fig. PS-2). The

contact of the formations is generally placed above the Roland coal (see fig. PS-2).

The Fort Union Formation exists over 22,000 square miles in the Powder River

Basin in Wyoming and Montana. Over a large part of its extent in the central part of

the basin, it is overlain by the Wasatch Formation (fig. PS-1). Our study

investigates only the Fort Union Formation in the Powder River Basin in Wyoming

and Montana because coal (for example, Wyodak-Anderson and equivalent and

Rosebud coal zones) is mined from this formation and a large part of the coal

resource is strippable along the basin margin. More importantly, the Fort Union

coal contributed more than 340 million short tons or about 34 percent of the U.S.

total coal production in 1998 (Resource Data International, Inc., 1998). The coal

produced from 25 coal strip mines (see fig. PS-1) in the Wyodak-Anderson and

Rosebud coal zones supplies energy fuel to 144 power plants in 25 states of the

conterminous U.S. and also to Canada, France, and Spain (Resource Data

International, Inc., 1998). These coal zones are expected to produce an additional

150 million short tons by the year 2016 (Energy Information Administration,

1996). In addition, in this study the Knobloch coal zone is assessed as a potentially

minable deposit. The Fort Union coal deposits in the basin will be the focus of

development during the next several decades due to their clean and compliant

characteristics (low sulfur and ash contents).
PS-4

From the 1950’s through the 1980’s a number of subsurface data points became

available from petroleum exploration and exploration for uranium-enriched strata

(including coal beds) for the Fort Union Formation in the Powder River Basin. In

the 1970’s increased demand for low-sulfur Fort Union coal led to shallow drilling

by coal companies and by U.S. Geological Survey-Montana Bureau of Mines and

Geology cooperative drilling projects. These projects provided subsurface

stratigraphic information on the Fort Union Formation for coal assessments. In the

1980’s, drilling in association with coal leasing by the U.S. Bureau of Land

Management and various coal companies contributed additional stratigraphic

information. Log reports of these drilling activities are archived by the U.S.

Geological Survey and Wyoming State Geological Survey. These log reports were

converted into digital files by using spreadsheet software. A total of 6,909

proprietary and non-proprietary drill holes (coal, oil, and gas) was used for the

study. A database of these drill holes is stored and managed in the U.S. Geological

Survey’s National Coal Resources Data System in Reston, Virginia (e-mail:

mdcarter@usgs.gov).

HISTORY OF COAL MINING

Building of new railroads through northeastern Wyoming from 1886 to 1887

created growth in underground coal mining in the Powder River Basin. Mining of

Fort Union coal in the basin began in 1883 near Glenrock and Douglas, Wyoming.

The Inez mine near Douglas produced 12,986 tons of coal in 1888 (Gardner and

Flores, 1989). About the same year, the Deer Creek mine near Glenrock produced

13,000 tons of coal (Gardner and Flores, 1989). Converse County was producing a

total of 31,000 tons from these two mines by the end of 1888 (Trumbull, 1905). In

1904, Cole Creek Coal Company in Big Muddy, Wyoming, was mining multiple
PS-5

coal beds as much as 5.5 ft thick and annually produced 15,708 tons (Trumbull,

1905). The Glenrock Coal Company operating at Glenrock, Wyoming, a few miles

east of Big Muddy, produced as much as 60,440 tons in 1905 (Trumbull, 1905).

The total annual production in Converse County was about 80,000 tons (Trumbull,

1905).

In addition, in 1888 the Buffalo Fuel Company No. 1 mine opened near Buffalo,

Wyoming, and wagon mines opened near Sheridan (Gardner and Flores, 1989).

These mine openings were followed by opening of the Dietz mine northwest of

Sheridan in 1890. The Dietz mine, which produced from 9- to 12-ft-thick coal beds,

expanded with the demand for coal, and by 1892 the mines in Sheridan County had

reached total production of 2,000 tons per year (Trumbull, 1905; Gardner and

Flores, 1989). These five mining districts produced the majority of coal in the

Powder River Basin in Wyoming before the turn of the century. Underground coal

mines in Sheridan County increased by 17 mines (for example, Dietz Nos. 4, 6, 8;

Old Monarch; Carney; Black Diamond, Acme, Kooi, Storm King, Minersville,

Hotchkiss Nos. 1 and 2; Schreibeis) from 1903 to 1925 (Dunrud and Osterwald,

1980). The total coal produced from these mines by September 30, 1904, was

429,153 tons (Trumbull, 1905). At the Carney mine, production was from coal

beds as much as 15 ft thick. At the Monarch mine, coal was produced from a 25- to

30-ft-thick bed, and as much as 200,000 tons was produced by 1905. In 1905,

Sheridan County was producing 550,000 tons annually (Trumbull, 1905). Seven

more mines were added from the mid-1920’s to the mid-1950’s. The increased

production in these mines was due to the onset of mechanization in underground

mines.
PS-6

While mechanization increased in underground mines in the early 1900’s, the U.S.

Geological Survey reported the first strip mining at the Peerless mine east of Gillette

in 1924 (Gardner and Flores, 1989). The overburden, which was 25 ft thick, was

stripped to expose a coal bed as much as 90 ft thick. A horse-drawn scraper known

as a fresno was used to peel back the overburden (Gardner and Flores, 1989). The

fresno was later replaced by full-revolving steam shovels, motorized graders, and

bulldozers to remove the surface cover. Thus, the Peerless mine was a harbinger of

more profitable mining methods in the Powder River Basin. The first large strip

mine in the Powder River Basin was opened near Gillette by the Wyodak Coal and

Manufacturing Company. This newly opened strip mine produced about 33,579

tons in 1925; the coal was extracted by 15 men, yielding about 2,239 tons of coal

per person per year. This mine was the only strip mine listed in the Wyoming state

coal mine inspector’s report in 1925. The Wyodak strip mine produced about 1,778

tons per man per year from 1925 to 1935.

In 1939 there were four strip mines in Wyoming and three were in the Powder

River Basin in Campbell, Sheridan, and Converse Counties (Gardner and Flores,

1989). These strip mines, with the exception of the Wyodak strip mine, were small

operations, which produced a total of 107,923 tons in 1939, as indicated in the

Wyoming state coal inspector’s report. In the 1940’s and 1950’s, mechanization

continued to increase in surface mines with improvements in mining equipment that

provided the opportunity for more efficient and profitable production. Strip mines,

such as the Big Horn mine northwest of Sheridan, eventually proved to be too

efficient for the competing underground mines, which were gradually put out of

business. Underground coal mining companies that were not put out of business

became part of stripping ventures, such as the Monarch and Storm King Coal

companies north of Sheridan. In 1955 the strip mines in Campbell County (for
PS-7

example, the Wyodak mine) produced a total of 349,566 short tons, in Sheridan

County (for example, the Big Horn mine) 437,222 short tons, and in Converse and

Johnson Counties (for example, the Dave Johnston mine) 9,433 short tons (Young

and others, 1957). These strip mines contained overburden that varied from 10 to

130 ft thick.

Coal production in the Powder River Basin from 1865 to 1949 was about 51 million

short tons according to Berryhill and others (1950). More than 45 million short tons

was produced from mines in the Sheridan coalfield, approximately 3 million short

tons in the Gillette coalfield, and about 1.5 million short tons in the Glenrock area.

These amounts represent about 15 percent of the total coal produced in Wyoming

during that 84-year period. The coal produced during this period was used mainly

for locomotive fuel on the Chicago, Burlington, and Quincy Railroad, and a

subordinate amount was used to fuel power plants, sugar factories, cement plants,

and for local heating (Mapel, 1958).

In the mid-1960’s the Powder River Basin coal industry expanded in response to the

demand for more electricity from newly built, coal-fired power plants (for example,

the Dave Johnston plant in Glenrock and the Wyodak plant in Gillette). Power

plants were built near the coal reserves in the Powder River Basin in Wyoming and

Montana where cheap coal could be obtained by strip mining. In addition, the

demand for clean coal to be used in these power plants, as mandated by the Air

Quality Act of 1967, which required emission reductions, was met by the compliant

coal of the Powder River Basin. During the early 1970’s, strip mines were opened

in Montana (for example, the Decker and Sarpy Creek mines) and Wyoming (for

example, the Bighorn and Belle Ayr mines). Additional mines were opened in the

Powder River Basin in the late 1970’s and 1980’s as public utility companies
PS-8

increased their consumption of Powder River Basin coal for generating electricity.

Initially, the utility companies gave the coal companies in the basin long-term

contracts (as long as 30 years), which helped to stabilize the coal industry.

Presently, the Gillette coalfield in the Wyoming part of the basin includes 19 mines

(Resource Data International, Inc., 1998). The Powder River Basin, in general, and

the Gillette coalfield, in particular, hold the distinction of being the number one coalproducing area in the United States.

GEOLOGICAL SETTING

The Powder River Basin is a structural and sedimentary basin located in the

northeastern part of Wyoming and southeastern part of Montana. It contains more

than 8,000 ft of Upper Cretaceous and Tertiary rocks along the axis in the western

part of the basin (Curry, 1971). The basin is asymmetrical with rocks dipping an

average of 20-25 degrees along the western margin of the basin and 2-5 degrees

along the eastern margin. The Miles City arch separates the northernmost Powder

River Basin in Montana from the Williston Basin in Montana and North Dakota

(fig. PS-1). Paleocene Laramide positive structures representing basement-block

uplifts (Curry, 1971; Perry and Flores, 1994) include the Bighorn uplift on the west,

the Casper arch-Laramie range-Hartville uplift on the south, and the Black Hills

uplift on the east (fig. PS-1). These ancestral uplifts reflect northeastward migration

of Laramide deformation because the uplift on the west (the Bighorn Mountains) is

older than that on the east (the Black Hills) (Perry and Flores, 1994).

Although the basin is structural in origin and was formed during the late Laramide

tectonic movements, accumulation of the Fort Union sediments was controlled

primarily by subsidence of the basin and accompanying depositional settings.
PS-9

Tectonic uplifts of surrounding areas influenced the nature of the Fort Union

sediments, which comprised mainly reworked Cretaceous fine- and coarse-grained

rocks (Whipkey and others, 1991) and subordinate Jurassic to Paleozoic rocks

(Obernyer, 1978). Tectonism may have played a significant control in accumulation

of thick Fort Union coal (Flores, 1983; Ayers and Kaiser, 1984; Kent, 1986).

The Fort Union Formation is more than 5,200 ft thick along the basin axis in the

western part of the Powder River Basin in Wyoming (Curry, 1971; Lewis and

Hotchkiss, 1981). The Fort Union Formation is divided, in ascending stratigraphic

order, into the Tullock, Lebo, and Tongue River Members (fig. PS-2; the Lebo

Member of Wyoming is known as the Lebo Shale Member in Montana). The

Tullock Member is as much as 740 ft thick, the Lebo Member is as much as 2,600

ft thick, and the Tongue River Member is as much as 1,860 ft thick. Subdivision of

Fort Union Formation is based on the color, dominant lithology, and thickness

variation of the rock units (Mapel, 1958; Tudor, 1975; Denson and others, 1989a,

1989b). For example, the Tullock and Tongue River Members include abundant

weathered, drab yellow and light-gray sandstone beds. The Tongue River Member

includes common light-gray to tan mudstone in contrast to the Lebo Member, which

contains abundant drab-gray mudstone. The coal beds of the Tullock Member are

thin to thick compared to the coal beds of the Tongue River Member, which are

mainly thick; the Lebo Member includes very thin and sparse coal beds and

carbonaceous mudstone.

DEPOSITIONAL SETTING

The lithological variations of the Fort Union Formation in the Powder River Basin

were controlled by tectonics and depositional environment (Brown, 1958; 1962;
PS-10

Mapel, 1958; Denson and Chisholm, 1971; Obernyer, 1978; Ayers and Kaiser,

1984; Flores, 1980, 1986; Kent, 1986; Culbertson, 1987). Brown (1958, p. 111)

reported that the “similarity of the lithology of the Fort Union Formation at

correlative stratigraphic levels over a large part of the terrain it occupies indicates that

relatively the same environmental and depositional conditions can be inferred as

having prevailed simultaneously at those levels.” Brown suggested that the Fort

Union sediments were deposited in floodplains, estuaries, sloughs, and swamps

sometimes considerably inland from the Cannonball sea, which was located east and

northeast of the Powder River Basin. He further reported that the presence of plant

fossils of palms and birches suggested warm temperate to temperate paleoclimate.

This paleoclimatic interpretation was modified by Wolfe and Upchurch (1986;

1987) and Nichols and others (1989) as warm tropical-subtropical paleoclimate,

based on characteristics of fossil leaves (for example, leaf size, leaf margins). These

workers suggested that the annual temperature was about 20°C (68°F) but reached

to as much as 23°C (73.4°F) and that annual precipitation was as much as 90.6 in.

(2,300 mm) during the late Paleocene. According to Brown (1958, p. 111), periods

of static basin deposition influenced accumulation of “materials that were to become

a coal seam,” and basin subsidence “changed stream flow and direction that caused

incipient coal to be buried by sand and silt.” These environmental and depositional

settings, unlike the modern alluvial valley of the lower Mississippi River (Fisk,

1944), were accompanied, according to Brown (1958, p. 111), by “orogenic

movements to the west of the basin from Late Cretaceous through Paleocene and

into Eocene.” Brown’s model of the environmental, depositional, and tectonic

settings of the Powder River Basin is an advanced interpretation that has withstood

the test of time.
PS-11

Modification of Brown’s model by succeeding workers included identification of

the types of stream or fluvial systems that drained the Powder River Basin and

flowed into the Cannonball sea in the Williston Basin (Flores, 1980, 1981, 1983,

1986; Flores and Ethridge, 1985; Ethridge and others, 1981; Flores and others,

1989; Warwick and others, 1997, 1998). Internal drainage of the basin was

interpreted by Ayers and Kaiser (1984) to include a lake in which the Lebo Member

was deposited. Perhaps the most controversial issue pertaining to the deposition of

the Fort Union sediments is the origin of the coal, particularly the accumulation of

very thick coal (that is, beds more than 200 ft thick). Kent (1986) proposed a

seesaw effect of tectonic subsidence and uplift in which coal accumulated in

swamps developed on paleoslopes affected by uplift; eastern uplift caused a

westward tilt of these paleoslopes and western uplift caused an eastward tilt. In

contrast, Ayers and Kaiser (1984) envisioned a rapidly subsiding basin infilled by

lacustrine deltas in which swamps formed thick peat. These workers assumed that

the presence of abundant mudstone in the central part of the basin, which bypassed

coarse sediments during deposition, represented lake deposits. However, Flores and

co-workers suggested that the mudstone was derived mainly from Cretaceous

marine shales exposed in surrounding uplifts and deposited in the basin by alluvial

fans and braided, meandering, and anastomosed streams. Intense uplift of

surrounding ancestral mountains (for example, Big Horn Mountains) is indicated by

deposition of conglomerates in alluvial fans (figs. PS-3, PS-4, and PS-5) and

braided streams (fig. PS-6).

The traditional interpretation of the origin of coal in the fluvial system, following

Brown’s model, is deposition in swamps formed on distal floodplains, abandoned

crevasse splays, and abandoned belts of rivers, as described by Flores (1980, 1981,

1983) and Flores and Hanley (1984). Examples of clastic deposits in floodplain,
PS-12

crevasse splay, and fluvial channel environments are shown in figures PS-7, PS-8,

PS-9, and PS-10. Very thick organic deposits (fig. PS-11) of these fluvial swamps

were interpreted by Flores (1980; 1981; 1986) and Flores and Ethridge (1985) as

ombrotrophic or rain-fed, raised bogs typically formed in wet, tropical-subtropical

climate as described by Wolfe and Upchurch (1986; 1987) and Nichols and others

(1989). Flores further suggested that the Fort Union raised bogs in the Powder

River Basin are exemplified by similar modern environmental, depositional, and

tectonic settings in the Kutai Basin drained by the Mahakam River in southeast

Kalimantan, Indonesia. These modern raised bogs are similar to those described by

Cecil and others (1993) and Neuzil and others (1993) in Borneo and Sumatra (figs.

PS-12 and PS-13). However, in order to accumulate very thick peat or coal

precursors, these raised bogs must be influenced by either local subsidence (for

example, peat autocompaction, sediment compaction) or basin subsidence.

Thickening of peat deposits, hence the resulting thickening of coal beds, may be

explained by stacking of peat deposits separated by organic or inorganic partings

(Moore, 1994). These partings (fig. PS-14) represent a demise of the swamp by

oxidation and degradation of organic matter yielding a deflated peat surface prone to

flooding events. Evidence of rapid flooding events over these peat surfaces were

discussed by Sholes and Cole (1981), Sholes and Daniel (1992), and Flores and

Moore (1994). The Fort Union peat swamps were mainly vegetated by conifers

related to the living bald cypress and also by ancestors of other living plant families,

including broad-leaved evergreens (Spindel, 1975; Rich, 1980; Satchell, 1985;

Pocknall and Flores, 1987; Wolfe and Upchurch, 1986, 1987; Nichols and others,

1989; Nichols, 1995).

The importance of tectonic control in the development of the Powder River Basin

and related coal deposits has been discussed by Curry (1971), Obernyer (1978),
PS-13

Jenkins (1986), Whipkey and others (1991), and Perry and Flores (1994). Curry

(1971) suggested that Laramide structural movements are evidenced in the Powder

River Basin during deposition of the Lebo Member, which thickens from 370 to

2,600 ft from east to west across the basin. He indicated that rapid subsidence

provided a space to accommodate Lebo sediments, particularly in the western part of

the basin. Also, he noted that when the Laramide movements were active in the

basin, only mudstones were derived from the uplifts. Flores and others (1994)

suggested that the fine-grained Lebo sediments were derived primarily from

Cretaceous marine shale. This interpretation is supported by the presence of

glauconite in the Lebo Member that was derived from marine rocks from the

Bighorn uplift (Whipkey and others, 1991). Faulting may be characterized in part

by normal faulting according to Obernyer (1978) and thrust faulting according to

Jenkins (1986) along the western basin margin. Obernyer proposed that the very

thick and linear (north-south orientation) Lake de Smet coal of the Wasatch

Formation (fig. PS-2) in the western part of the basin was formed on the subsiding

downthrown side of a fault. Effects of Laramide deformation of the Powder River

Basin and surrounding uplifts were discussed by Perry and Flores (1994). These

workers suggested that a northeastward younging and migrating Laramide

deformation front prompted evolution of the Powder River Basin from a foreland

basin into an intermontane basin in early to late Paleocene time. The basin was a

well-developed intermontane basin by the late Paleocene; it was surrounded by

uplifts on the west, south, and east. These surrounding uplifts may have contributed

to the orographically wet paleoclimate that promoted development of rain-fed, raised

bogs in the basin (Flores, 1998).
PS-14

COAL GEOLOGY

The coal geology of the Fort Union Formation in the Powder River Basin reflects

the tripartite subdivision of the formation, with the Tullock Member in the lower

part, the Lebo Member in the middle part, and the Tongue River Member in the

upper part (see fig. PS-2). This subdivision parallels differences in stratigraphy,

sedimentology or depositional settings, biostratigraphy, and coal geology, including

the thickness and areal distribution of coal and associated rocks in the members of

the Fort Union Formation.

The coal geology and stratigraphy of the Fort Union Formation differ in the vertical

and lateral patterns of coal beds and zones and associated clastic rocks. The vertical

stratigraphic pattern in the Tullock Member consists of abundant thick sandstone

interbedded with siltstone and mudstone and less abundant, thin (a few inches to

several feet) coal and carbonaceous beds. The Lebo Member consists of abundant

mudstone, subordinate siltstone and sandstone, and sparse coal and carbonaceous

mudstone. The Tongue River Member contains abundant sandstone, siltstone,

mudstone, and sparse limestone and carbonaceous shale. Coal beds are abundant

and range from thin (a few inches) to very thick (more than 200 ft).

Although the members of the Fort Union Formation were deposited in fluvial

environments, the depositional setting of the Tullock is different from that of the

Lebo and Tongue River Members. The Tullock Member was deposited primarily

by braided to meandering fluvial systems (Flores and others, 1994). The Lebo

Member was deposited in fine-grained fluvial systems, as proposed by Flores and

Ethridge (1985), although Ayers and Kaiser (1984) interpreted the deposition of the

Lebo sediments to have been in a lacustrine environment. The Tongue River
PS-15

Member was interpreted as fluvial deposits by Flores (1980; 1981; 1983; 1986),

Flores and Hanley (1984), Flores and Ethridge (1985), Warwick and Stanton (1986,

1988), but as deltaic deposits by Ayers and Kaiser (1984). The fluvial deposits

accumulated in meandering and anastomosed fluvial systems in the central part of

the basin and alluvial fans and braided streams in the basin margins. These fluvial

styles developed in response to accommodation space created by tectonic uplift,

basin subsidence, and base-level changes.

Biostratigraphy based on palynology (analysis of fossil spores and pollen) of the

Fort Union Formation in the northern Rocky Mountains and Great Plains region

was developed by Nichols and Ott (1978). Pocknall (1987) proposed zones for the

upper part of the Fort Union Formation in the central part of the Powder River

Basin; his zonation is mostly equivalent to part of that of Nichols (1994; 1996).

Using his zonation, Nichols subdivided the Fort Union Formation into six Zones,

P1-P6 (see fig. PS-2 and Chapter PB, the biostratigraphy section for the Powder

River Basin, in this CD-ROM). For the most part, the Tullock Member is within

Zones P1 and P2, the Lebo Member is within Zones P3 and P4, and the Tongue

River Member is within the Zones P4 through P6. Variations in occurrence of

certain groups of fossil pollen within the Wyodak-Anderson coal are depicted

graphically in Chapter PB, the biostratigraphy section of this CD-ROM, and some

of the biostratigraphically important species are illustrated. Detailed descriptions and

illustrations of the fossil spores and pollen of the Fort Union Formation in the

Powder River Basin can be found in Nichols and Brown (1992) and Pocknall and

Nichols (1996).

Our investigation focused on the coal geology and stratigraphy in the Tongue River

Member (fig. PS-2), which has been the subject of detailed studies by numerous
PS-16

workers in the U.S. Geological Survey. The publications of Dobbin (1929), Bass

(1932), Bryson (1952), Brown and others (1954), Olive (1957), Bryson and Bass

(1973), and Keefer and Schmidt (1973) focused on detailed areal mapping of coal

beds and description of coal-bearing stratigraphic sections in the Tongue River

Member. The publications of Mapel (1958; 1976), Culbertson and others (1979),

Law and others (1979), Kent and others (1980), Hardie and Van Gosen (1986),

Culbertson (1987), McLellan and Biewick (1988), McLellan and others (1990),

Hardie (1991), Pierce and others (1990), and Molnia and Pierce (1992) focused on

investigation of the coal stratigraphy or lateral and vertical variations of the coal

beds. Publications of Flores (1979), Flores and Canavello (1979), Weaver and

Flores (1985; 1987), Pierce and Johnson (1991), and Johnson and Pierce (1991)

concentrated on relating the variations of the rock types and their depositional

environments to the stratigraphic variations of the Tongue River Member.

There has been an evolution in the interpretation of the coal stratigraphy of the

Tongue River Member from coal existing as tabular, laterally continuous beds more

than 50 miles in extent (Mapel, 1958) to the existence of complex, laterally merging

and splitting beds and zones (Flores, 1979; Flores and Canavello 1979). Early

mapping suggests areal distribution of the coal as continuous mappable units. Later,

as more subsurface stratigraphic data and/or outcrop sections became available, coal

beds of the Tongue River Member were found to be more variable in lateral extent.

The work of Flores and his co-workers (Canavello, 1980; Lynn, 1980; Pait 1981;

Toth, 1982; Coss; 1985; Warwick, 1985; Moore, 1986; Whipkey, 1988) exhibited

that lateral continuity of the coal beds of the Tongue River Member of the Fort

Union Formation and the Wasatch Formation, which vary from a few hundred feet

to several miles in extent, was controlled by the depositional environments of related

rocks. For example, the splitting of coal beds caused by incursion of crevasse-splay
PS-17

sediments into the mires was demonstrated by Moore (1986) and Flores and Moore

(1994) in the Decker coalfield, Montana. The characteristic of the lateral continuity

of coal beds is revealed by the stratigraphic control points utilized for correlation.

Complex correlation is displayed by splitting (fig. PS-15) and merging (fig. PS-16)

of the Wyodak-Anderson, Rosebud, and Knobloch coal zones. The WyodakAnderson coal zone is distributed basinwide in Wyoming and Montana, and the

Rosebud-Robinson and Knobloch coal zones are distributed in the northern part of

the basin in Montana. The Wyodak-Anderson coal zone (Glass, 1980) is also

known as the Wyodak coal (Mapel, 1973) and Wyodak-Anderson coal, which is

coalesced Anderson, Canyon, and related coal beds (Denson and Keefer, 1974).

Splitting of the coal beds of the Wyodak-Anderson coal zone has generated 2 beds

(lower Wyodak bed comprising the merged Canyon and Werner coal, and upper

Wyodak bed comprising the merged Smith, Swartz, and Anderson coal; Mapel

1973; Kent and others, 1980), 3 beds (Anderson or Dietz 1, Dietz 2, and Dietz 3;

Sholes and Coles, 1981; Moore, 1986; Flores and Moore, 1994), 5 beds (lower and

upper Anderson and lower, middle, and upper Canyon beds; Molnia and Pierce,

1992), 6 beds (Smith, Swartz, Anderson, upper and lower Canyon, and Werner

beds; Kent and others, 1980), or as many as 11 beds (Sussex beds; Hardie and Van

Gosen, 1986). The local distribution of the split coal beds of the Wyodak-Anderson

coal zone is shown on figure PS-17. Split coal beds merge to form a single bed;

later splitting and remerging of this bed basinwide show overlapping, offsetting,

zigzagging, and shingling segments of the coal zone indicating older WyodakAnderson coal (for example, Big George coal) in the west-central part of the basin

than in the basin margins (for example, Smith, Anderson, Dietz, Canyon, School,

and Badger coal; see fig. PS-18). Splitting of the Knobloch coal zone created as

many as four beds that include the Knobloch, Calvert, Nance, and Flowers-Goodale
PS-18

(Culbertson 1987; Culbertson and Saperstone, 1987), which may be equivalent to

the Sawyer, Lay Creek, and King coal beds (Sholes and Daniel, 1992). Splitting of

the Rosebud-Robinson coal zone generated as many as 3 beds (Rosebud, McKay,

and Robinson). Various interpretations of coal splitting and merging led to

confused correlation of the different named coal beds of these coal zones. For

example, Sholes and Daniel (1992) correlated the Knobloch coal zone to the

Rosebud coal bed.

The sedimentology of the clastic rocks interbedded with the coal provides an

understanding of the depositional environments and the dynamic processes that

formed these rocks. These environments and accompanying processes controlled

the lateral and vertical variability of the coal beds. For example, the process of

autocyclicity or lateral shifting common in fluvial-channel and floodplain

aggradation caused associated swamps to shift with fluvial aggradation. Rapid

successions of avulsion or shift and abandonment of the fluvial depositional

systems along the width of the alluvial plain caused splitting and merging of the coal

beds and zones. In addition, the vast expanse of abandoned alluvial platforms on

which swamps developed promoted accumulation of laterally extensive coalforming peat deposits. This accounts for the variable distribution of coal deposits,

from local to widespread, in the Tongue River Member of the Fort Union

Formation.

COAL RESOURCES AND COAL QUALITY

Early estimates of the coal resources in the Powder River Basin were based mainly

on outcrop data from shallow coal beds in the Tongue River Member. The
PS-19

strippability (from less than 50 to as much as 129 ft of overburden) of the Tongue

River coal yielded coal resources estimated as strippable resources. An attempt to

estimate strippable resources of Tongue River Member coal in the Rosebud coalfield

in Rosebud and Custer Counties of Montana with 60 ft or less of overburden was

made by Pierce (1936). The Terret and Burley beds of the Tongue River Member

(see fig. PS-2), which vary from 5 to 8 ft thick with 50 to 60 ft of overburden, were

estimated to contain resources of as much as 817 million short tons. Kepferle

(1954) estimated strippable coal (with 120 ft of overburden) in central Rosebud

County at about 604 million short tons; this included nine strippable beds as much

as 20 ft thick (for example, Terret, Rosebud, Sawyer, Wall, Brewster-Arnold; see

fig. PS-2). In the adjoining areas of Custer and Powder River Counties, Brown and

others (1954) estimated strippable resources (with as much as 120 ft overburden) at

1,551 million short tons.

In the Powder River Basin in Wyoming, Berryhill and others (1950) estimated

original resources of the greater-than-3-ft-thick Roland and Smith coal beds (partly

equivalent to the Wyodak-Anderson coal zone) to include more than 45 billion short

tons. In the Powder River Basin in Montana, Combo and others (1949) estimated

original coal resources of coal beds more than 2.5 ft thick (for example, WyodakAnderson, Rosebud, and Knobloch coal zones; see fig. PS-2) in Bighorn and

Powder River Counties to be 86.9 billion short tons. Mapel (1958) revised the

original coal resources in the Lakota and Lance (Cretaceous), Fort Union

(Paleocene), and Wasatch (Eocene) Formations in the Powder River Basin in

Wyoming and Montana to be 200 billion short tons in coal beds more than 2.5 ft

thick. He estimated the original coal resources in the Fort Union in the Powder

River Basin in Wyoming to be about 82 billion short tons. Glass (1976) estimated

the coal resources in four formations in the Cretaceous, Paleocene, and Eocene
PS-20

rocks in the Powder River Basin in Wyoming to be 600-700 billion short tons.

Trent (1986) estimated resources of greater-than-5-ft-thick coal down to 3,000 ft

depth to be 775 billion short tons for non-leased Federally-owned coal in 243

quadrangles in the Powder River Basin.

Coal resource estimates for the past 25 years have focused on the important,

productive, and strippable Wyodak-Anderson coal zone. Some of the coal and

associated rocks of this zone were burned by spontaneous combustion resulting in a

red-orange rock called “clinker” (figs. PS-19 and PS-20); burning of coal beds has

reduced the coal resource of the coal zone along the outcrop (see fig. PS-21; Heffern

and others, 1993; Boyd and Ver Ploeg, 1997; Heffern and Coates, 1997). Mapping

by Denson and Keefer (1974) defined the Wyodak-Anderson coal zone as formed

from coalesced beds and equivalent to the Anderson and Canyon coal beds.

Mapping by Kent and Munson (1978) indicated the interval containing the Swartz

(upper) and Werner (lower) coal beds as coalescing with the Wyodak-Anderson

coal zone (see fig. PS-2). Glass (1976) correlated the Dietz 1, 2, and 3 (Anderson)

and Monarch (Canyon) beds in the Sheridan coalfield to the Wyodak-Anderson coal

zone of Denson and Keefer (1974). Coal beds (Anderson and Canyon) of the

Wyodak-Anderson coal zone in the eastern part of the Powder River Basin in

Wyoming range from 10 to 65 ft thick and coalesce into beds 70-125 ft thick

(Glass, 1976; Culbertson and others, 1979). Smith and others (1972) estimated the

strippable resource base of the Wyodak-Anderson coal zone south and north of

Gillette, Wyoming, to be about 19 billion short tons.

The equivalent Dietz coal beds (Anderson coal of the Wyodak-Anderson coal zone;

see fig. PS-2) in the Sheridan coalfield, which average 10-25 ft thick and coalesce

into beds as much as 75 ft thick, and the Monarch coal (Canyon coal of the
PS-21

Wyodak-Anderson coal zone; see fig. PS-2), which is as much as 60 ft thick, were

collectively estimated to contain a strippable resource base of more than 39 million

short tons (Glass, 1978). Smith and others (1972) estimated the strippable resource

base of the Monarch coal bed, which locally coalesces with the Dietz 3 coal bed, to

be 32 million short tons.

The Wyodak-Anderson coal zone in the Decker coalfield in the Powder River Basin

in Montana includes the Dietz 1, 2, and 3 coal beds (Dietz 1 is correlated with the

Anderson coal) and the Canyon coal bed (Matson and Blumer, 1973; Matson and

Pinchock, 1977). The Dietz coal beds (Dietz 2 and 3) and the Monarch or

equivalent to the Canyon coal bed occur in the Sheridan coalfield (Law and others,

1979). Matson and Blumer (1973) described the Dietz 1, Dietz 2, and Dietz 3 coal

beds (Anderson coal; see fig. PS-2) in the Powder River Basin in Montana as

varying from 4 to 18 ft thick and as coalescing to as much as 80 ft thick. According

to Matson and Blumer (1973) the Canyon coal bed in the basin in Montana ranges

from 4 to 25 ft thick; they estimated strippable coal resources (with less than 300 ft

of overburden) of the Dietz and Anderson coal beds to be greater than 8.6 billion

short tons. In addition, Matson and Blumer (1973) estimated the strippable coal

resources of the Canyon coal in the same area to be more than 1.7 billion short tons.

They described additional strippable coal beds in the Powder River Basin in

Montana to include the Knobloch coal, which is as much as 66 ft thick, and the

Rosebud coal, which averages 25 ft thick (fig. PS-2). Matson and Pinchock (1977)

estimated the strippable coal resources (with less than 300 ft of overburden) for the

Knobloch coal as more than 7.5 billion short tons and the Rosebud coal as more

than 1.5 billion short tons.
PS-22

In the central part of the Powder River Basin in Wyoming, the Wyodak-Anderson

coal zone coalesces from five coal beds of the Anderson and Canyon coal into a bed

as much as 202 ft thick known as “Big George” coal (Kent and others, 1980; Pierce

and others, 1982; Kent, 1986; Molnia and Pierce, 1992). This coal is a single bed

varying from 46 to 202 ft thick within a 950-square-mile area at a depth of 1,100 ft

below the surface (Pierce and others, 1982). The coal resource of this bed was

estimated by Pierce and others (1982) and Kent (1986) to be as much as 113 billion

short tons. This coal and laterally equivalent “Sussex” coal, which is as thick as 138

ft (a merged bed from as many as eleven beds; fig. PS-22), probably represent the

largest deposit (about 194 billion short tons) of the Wyodak-Anderson in a single

area (more than 1,000 square miles) in the Powder River Basin, but it is not

economically strippable. Basinwide, (see Chapter PN of this CD-ROM) the

resource of the Wyodak-Anderson coal zone is estimated to be as much as 550

billion short tons (Ellis and others, 1999). Volumes calculations of the WyodakAnderson coal zone, at a 90 percent confidence limit, range from 459 (lower limit)

to 642 billion short tons (upper limit) (Ellis and others, 1999; Schuenemeyer and

Power, in press).

The Fort Union coal in the Powder River Basin in Wyoming and Montana is mainly

subbituminous B, and coal in the northeastern part of the basin tends to be slightly

lower in rank, according to Fieldner and others (1931). These authors reported

sulfur content to be mostly between 0.4 and 1.0 percent and ash yield to be between

5 and 10 percent on a moisture-free basis. Berryhill and others (1950) demonstrated

the local variations in coal quality in the basin by reporting that the Sheridan coalfield

contains Fort Union coal (Dietz and Monarch coal beds) averaging 0.54 percent

sulfur, 4.3 percent ash, and 9,366 Btu/lb (subbituminous A and B) on an as-received

basis, whereas other Fort Union coal (Roland/Anderson coal beds) averages 0.5
PS-23

percent sulfur, 6.8 percent ash, and 7,868 Btu/lb (subbituminous C) on an asreceived basis. These analyses were performed for coal beds without partings.

Mapel (1958) reported that the calorific values of Fort Union coal (Dietz, Monarch,

and Rosebud coal beds) in the Powder River Basin in Montana range from 8,300 to

10,100 Btu/lb on a moist, mineral-matter-free basis.

Analyses of nine cores of the Anderson and Canyon coal beds (Wyodak-Anderson

coal zone) in Campbell County in the Powder River Basin, as reported by the U.S.

Geological Survey and Montana Bureau of Mines and Geology (1973) and the U.S.

Geological Survey (1974), yielded averages of 29.5 percent moisture, 30.1 percent

volatile matter, 33.9 percent fixed carbon, 6.5 percent ash, 0.52 percent sulfur, and a

calorific value of 7,979 Btu/lb for the Anderson coal. The same publications

reported averages of 29.6 percent moisture, 30.7 percent volatile matter, 34.6 percent

fixed carbon, 5.1 percent ash, 0.34 percent sulfur, and a calorific value of 8,286

Btu/lb for the Canyon coal in Campbell County.

Based on five analyses of mine samples in the Sheridan coalfield, Glass (1980)

reported 21.7-23.8 percent moisture, 33.6 percent volatile matter, 38.5 percent fixed

carbon, 5.6-6.6 percent ash, 0.74-1.02 percent sulfur, and a calorific value of 9,220-

9,387 Btu/lb (as-received basis) for the Dietz 2 coal bed. The Dietz 3 coal bed in the

same Sheridan mines contains 19.1 percent moisture, 34.8 percent volatile matter,

41.7 percent fixed carbon, 4.4 percent ash, 0.5 percent sulfur, and a calorific value of

9,710 Btu/lb (as-received basis). The Monarch or Canyon coal bed was reported by

Glass (1980) to contain averages of 21.5 percent moisture, 34.5 percent volatile

matter, 39.6 percent fixed carbon, 4.4 percent ash, 0.4 percent sulfur, and a calorific

value of 9,600 Btu/lb (as-received basis).
PS-24

In the Decker coalfield, north of the Sheridan coalfield in Montana, Matson and

Blumer (1973) reported 17.3-23.8 percent moisture, 29.4-34.9 percent volatile

matter, 26.6-42.8 percent fixed carbon, 2.9-34.8 percent ash, 0.2-0.6 percent sulfur,

and a calorific value of 8,609-9,850 Btu/lb (as-received basis) for the Anderson and

Dietz coal beds. These investigators reported 20.9-23.8 percent moisture, 26.3-32.5

percent volatile matter, 35.8-42.9 percent fixed carbon, 2.4-16.9 percent ash, 0.1-0.7

percent sulfur, and a calorific value of 8,081-9,691 Btu/lb (as-received basis) for the

Canyon coal in the Decker coalfield. They reported 23.7-36.4 percent moisture,

25.7-36.5 percent volatile matter, 28.1-40.4 percent fixed carbon, 2.9-10.6 percent

ash, 0.1-5.3 percent sulfur, and a calorific value of 7,458-9,314 Btu/lb (as-received

basis) for the Knobloch coal. These investigators reported 21.3-23.8 percent

moisture, 27.5-30.2 percent volatile matter, 34.7-41.2 percent fixed carbon, 7.7-12.5

percent ash, 0.5-7.2 percent sulfur, and a calorific value of 7,810-9,090 Btu/lb (asreceived basis) for the Rosebud coal.

The coal quality of the Wyodak-Anderson coal in the Powder River Basin in

Wyoming and Montana was studied by Ellis and others (1998), Flores and others

(1998), and Stricker and others (1998). Ellis and others (1998) and Flores and

others (1998) indicated a mean moisture of 28 percent, volatile matter of 30.1

percent, fixed carbon of 36 percent, ash yield of 6.4 percent, sulfur of 0.47 percent,

and calorific value of 8,220 Btu/lb. Stricker and others (1998) reported that the

Wyodak-Anderson coal contains lower concentrations of trace elements of

environmental concern (formerly known as hazardous air pollutants—antimony,

arsenic, beryllium, cadmium, chromium, cobalt, lead, manganese, mercury, nickel,

selenium, uranium) than other Fort Union coal. This was supported by a study of

trace elements in Fort Union coal in the Powder River Basin and elsewhere in the

Fort Union region by Hatch and Swanson (1977). Crowley and others (1993;
PS-25

1994) found that high concentrations of these trace elements are directly related to

high ash contents of the coal. Groundwater is also known to elevate concentrations

of trace elements, particularly sodium (Hildebrand, 1988). Flores and others (1994)

suggested that debris derived from uplifts adjoining the Powder River Basin also

contributed to the kind and concentrations of the trace elements. Additional

information on the coal quality and geochemistry of the Fort Union coal, particularly

the Wyodak-Anderson coal in the Powder River Basin in Wyoming and Montana,

are presented in Chapter PQ of this CD-ROM.

COAL-BED METHANE RESOURCE

The presence of methane in Fort Union coal was reported by U.S. Geological

Survey investigators (Olive, 1957; Lowry and Cummings, 1966; Whitcomb and

others, 1966; Hobbs, 1978; Boreck and Weaver, 1984). A number of flowing

artesian wells at shallow depths (245 to 415 ft) contained substantial amounts of

methane as reported by Olive (1957), Lowry and Cummings (1966), and

Whitcomb and others (1966). Hobbs (1978) identified methane in 15 shallow drill

holes in the Recluse area of northeastern Campbell County and south of Gillette,

Wyoming. Drill holes for coal-bed methane were drilled to depths of no more than

500 ft and penetrated the Wyodak-Anderson zone in the Recluse area, which

includes the Anderson and Canyon coal beds. Methane has been encountered in the

coal beds as well as in overlying sandstone and interbedded sandstone and shale

beds. Gas flow rates varying from a trace in shale interbeds to more than 1,000,000

cubic ft/day in coal have been recorded. Hobbs (1978) suggested that there could be

potential methane production from the Anderson and Canyon coal beds and from

the fluvial channel sandstone between the coal beds and possibly below the Canyon

coal.
PS-26

Coal-bed methane exploration and development in the Powder River Basin has

rapidly accelerated in the past two to three years. Several hundred wells have been

drilled and recent operator forecasts projected more than 5,000 additional wells to be

drilled over the next few years. Development of shallow (less than 1,000 ft deep)

Fort Union coal-bed methane is confined to Campbell and Sheridan Counties,

Wyoming, and Big Horn County, Montana. The major lease area in Wyoming is in

43.39 to 45 degrees and 105.32 to 105.88 degrees (see fig. PS-1). Here the targeted

coal beds are mainly the Anderson and Canyon of the Wyodak-Anderson coal zone.

Perhaps the most promising methane play for the deep (more than 1,000 ft)

Wyodak-Anderson (or Big George and Sussex) coal bed and zone in the

southwestern part of the basin in Wyoming is in 43.50 to 44.63 degrees and 105.93

to 106.38 degrees (see fig. PS-1). The Wyodak-Anderson coal bed in this area is as

much as 202 ft thick and the Wyodak-Anderson coal zone is as much as 550 thick;

it contains as many as 11 coal beds that average 25 ft thick (Boreck and Weaver,

1984; Hardie and Van Gosen, 1986). The isopach map of the Wyodak-Anderson

coal zone (see Chapter PN of this CD-ROM) in this area exhibits a series of

discontinuous, ovoid (8- to 22-square-mile areas) coal bodies that have from 150 to

more than 200 ft of net coal thickness. These ovoid coal bodies, in turn, are

surrounded by an elongate (more than 1,000 square-mile area) coal body that has

from 100 to 150 ft of net coal thickness. These ovoid and elongate coal bodies are

generally oriented in a north-south direction and contain a coal resource of about 194

billion short tons. The coal beds and zone generally range from 1,000 to 2,000 ft

deep (see net coal thickness and overburden maps in Chapter PN of this CD-ROM).

The stratigraphic variation in this play (see Chapter PF of this CD-ROM) shows that

the northern part of the area includes merged beds of the Big George coal reaching
PS-27

as much as 202 ft thick; they split southward and merge with the Sussex coal, which

is as much as 138 ft thick. Where the coal beds are split, they are interbedded,

overlain, and underlain by fluvial channel sandstone (see stratigraphic cross sections

in Chapter PF of this CD-ROM). Where the coal beds are merged they are overlain

and underlain by similar rock types. The clastic rocks, particularly the sandstone,

potentially contain recoverable methane that has migrated from the coal.

Boreck and Weaver (1984) reported methane from a U.S. Geological Survey test

drill hole in the Wyodak-Anderson (or Big George coal bed) in the central part of

the basin in Johnson County, Wyoming (see fig. PS-1). Desorption data from

seven coal core samples from this test hole ranged from 56 to 74 standard cubic

ft/ton (scf/t). Methane recovered from these coal core samples indicated biogenic

origin. Core analysis (three samples) of the Wyodak-Anderson or Big George coal

bed at the Betop Incorporated Dead Horse Creek 8-32 well in Campbell County,

Wyoming (see fig. PS-1), indicated a gas content from 26 to 44 scf/t and an average

of 39 scf/t (summarized from a Core Laboratories report in BLM files).

Utilizing the minimum (26 scf/t) and maximum (74 scf/t) desorption data from the

U.S. Geological Survey drill hole and the Betop well and the coal resource estimate

(550 billion short tons) by Ellis and others (1999) (also see Chapter PN of this CDROM) provide an estimate of the methane resource for the Wyodak-Anderson coal

bed and zone basinwide. Other coal beds and zones above and below the AndersonWyodak coal bed and zone in the Fort Union Formation (for example, Wall, as

much as 25 ft thick; Pawnee, as much as 60 ft thick; Knobloch, as much as 70 ft

thick; Rosebud, as much as 20 ft thick; Broadus, as much as 30 ft thick; see fig. PS2) and in the Wasatch Formation (for example, Felix, as much as 40 ft thick and

Lake de Smet coal, as much as 250 ft thick; see fig. PS-2) are possible targets for
PS-28

coal-bed methane. The coal-bed methane play in the Powder River Basin was

reported by Rice and Finn (1995).

CONCLUSIONS

Fort Union coal, which represents a significant energy resource in the Powder River

Basin in Wyoming and Montana, has been mined and developed since 1886. The

most important use of this coal resource is energy fuel for mine-mouth power plants

and many other electric power generating plants outside the basin. Currently, openpit mines develop the Wyodak-Anderson and equivalent coal beds and the Rosebud

coal beds and zones. Production from these mines supports 144 electric power

plants in 26 states of the conterminous United States and three foreign countries.

The electric power plants are located in the western, midwestern, southern, and

southeastern parts of the United States. Coal production in 1998 from 25 mines in

the Powder River Basin attained more than 305 million short tons.

With the likelihood of this coal continuing to support electric power plants during

the next century, our assessment of the clean and compliant Fort Union coal in the

Powder River Basin focused on the Wyodak-Anderson, Rosebud, and Knobloch

coal beds and zones. The Wyodak-Anderson coal is as much as 202 ft thick,

mainly subbituminous, and contains resources of as much as 550 billion short tons

(in coal beds more than 2.5 ft thick, Ellis and others, 1999). The thick coal beds

were deposited mainly in raised swamps related to fluvial environments. The

extensive to limited areal distribution of these coal beds and zones reflects

accumulation in raised swamps on abandoned alluvial platforms as well as

depositional processes that affected the fluvial environments in late Paleocene time.
PS-29

The thickness, areal distribution, high quality, and trace-element chemistry of this

coal and associated coal-bed methane make it a clean and compliant energy resource.
PS-30

REFERENCES

Ayers, W.B., and Kaiser, W.R., 1984, Lacustrine-interdeltaic coal in the Fort Union

Formation (Paleocene), Powder River Basin, Wyoming and Montana,

U.S.A., in Rahmani, R.A. and Flores R.M., eds., Sedimentology of Coal and

Coal-bearing Sequences: International Association of Sedimentologists

Special Publication No. 7, p. 61-84.

Baker, A.A., 1929, The northward extension of the Sheridan coal field, Big Horn

and Rosebud Counties, Montana: U.S. Geological Survey Bulletin 806-B, p.

15-67.

Bass, N.W., 1932, The Ashland coal field, Rosebud, Powder River, and Custer

Counties, Montana: U.S. Geological Survey Bulletin 831, p. 19-105.

Berryhill, H.L., Jr., Brown, D.M., Brown, A., and Taylor D.A., 1950, Coal

resources of Wyoming: U.S. Geological Survey Circular 81, 78 p.

Boreck, D.L., and Weaver, J.N., 1984, Coalbed methane study of the Anderson coal

deposit, Johnson County, Wyoming—a preliminary report: U.S. Geological

Survey Open-File Report 84-831, 16 p.

Boyd, C.S., and Ver Ploeg, A.J., 1997, Geologic map of the Gillette 30’ x 60’

quadrangle, Campbell, Crook, and Weston Counties, northeastern Wyoming:

Wyoming State Geological Survey Map Series 49.

Brown, B., 1907, The Hell Creek beds of the Upper Cretaceous of Montana:

American Museum Natural Historical Bulletin, v. 23, p. 829-834.

Brown, A., Culbertson, W.C., Dunham, R.J., Kepferle, R.C., and May, P.R., 1954,

Strippable coal in Custer and Powder River Counties, Montana: U.S.

Geological Survey Bulletin 995-E, p. 151-199.
PS-31

Brown, R.W., 1958, Fort Union Formation in the Powder River Basin, Wyoming:

Wyoming Geological Association Guidebook, 13th Annual Field

Conference, p. 111-113.

_____1962, Paleocene flora of the Rocky Mountains and Great Plains: U.S.

Geological Survey Professional Paper 375, 119 p.

Bryans, W.S., 1987, A history of transcontinental railroads and coal mining on the

Northern Plains to 1920: University of Wyoming, Ph.D. thesis, 159 p.

Bryson, R.P., 1952, The Coalwood coal field, Powder River County, Montana:

U.S. Geological Survey Bulletin 973-B, p. 23-106.

Bryson, R.P., and Bass, N.W., 1973, Geology of the Moorhead coal field, Powder

River, Big Horn, and Rosebud Counties: U.S. Geological Survey Bulletin

1338, 116 p.

Bureau of Land Management, 1999, Wyodak coal-bed methane project draft

environmental impact statement, 263 p.

Canavello, D.A., 1980, Geology of some Paleocene coal bearing strata of the

Powder River Basin, Wyoming and Montana: North Carolina State

University, M.S. thesis, 63 p.

Cecil, C.B., Dulong, F.T., Cobb, J.C., and Supardi, 1993, Allogenic and autogenic

controls on sedimentation in the central Sumatra basin as an analogue for

Pennsylvanian coal-bearing strata in the Appalachian basin, in Cobb, J.C., and

Cecil, C.B., eds., Modern and Ancient Coal-Forming Environments:

Geological Society of America Special Paper 286, p. 3-22.

Coates, D.A., 1980, Formation of clinker by natural burning of coal beds in the

Powder River Basin, Wyoming, in Carter, L.M., ed., Proceedings of the

Fourth Symposium on the Geology of Rocky Mountain Coal—1980:

Colorado Geological Survey Resource Series 10, p. 37-40.
PS-32

Combo, J.X., Brown, D.M., Pulver, H.F., and Taylor, D.A., 1949, Coal resources

of Montana: U.S. Geological Survey Circular 53, 23 p.

Coss, J.M., 1985, Paleoenvironments of the upper Fort Union Formation at Pine

Ridge, western Powder River Basin, Wyoming: University of Colorado,

M.S. thesis, 84 p.

Crowley, S.S., Ruppert, L.F., Belkin, H.E., and Stanton, R.W., 1993, Factors

affecting the geochemistry of a thick, subbituminous coal bed in the Powder

River Basin: Volcanic, detrital, and peat-forming processes: Organic

Geochemistry, v. 20, p. 843-853.

Crowley, S.S., Ruppert, L.F., Stanton, R.W., and Belkin, H.E., 1994, Geochemical

studies of the Anderson-Dietz coal bed, Powder River Basin: Origin of

inorganic elements and environmental implications, 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. 173-184.

Culbertson, W.C., 1987, Diagrams showing proposed correlation and nomenclature

of Eocene and Paleocene coal beds underlying the Birney 30’ x 60’

quadrangle, Big Horn, Rosebud, and Powder River Counties: U.S.

Geological Survey Coal Investigations Map C-113.

Culbertson, W.C., and Mapel, W.J., 1976, Coal in the Wasatch Formation,

northwest part of the Powder River Basin near Sheridan, Sheridan County,

Wyoming: Wyoming Geological Association Guidebook 28th Annual Field

Conference, p. 193-201.

Culbertson, W.C., Kent, B.H., and Mapel, W.J., 1979, Preliminary diagrams

showing correlation of coal beds in the Fort Union and Wasatch Formations

across the northern Powder River Basin, northeastern Wyoming and

southeastern Montana: U.S. Geological Survey Open-File Report 79-1201.
PS-33

Culbertson, W.C., and Saperstone, H.I., 1987, Structure, coal thickness, and

overburden thickness of the Knobloch coal resource unit, Birney area, Big

Horn, Rosebud, and Powder River Counties, Montana: U.S. Geological

Survey Coal Investigations Map C-112, scale 1:100,000.

Curry, W.H., 1971, Laramide structural history of the Powder River Basin,

Wyoming: Wyoming Geological Association Guidebook, 23rd Annual Field

Conference, p. 49-60.

Davis, J.A., 1912, The Little Powder River coal field, Campbell County, Wyoming:

U.S. Geological Survey Bulletin 471, p. 423-440.

Denson, N.M., and Chisholm, W.A., 1971, Summary of mineralogic and lithologic

characteristics of Tertiary sedimentary rocks in the Middle Rocky Mountains

and the northern Great Plains, in Geological Survey Research 1971: U.S.

Geological Survey Professional Paper 750-C, p. C117-C126.

Denson, N.M., and Horn, G.H., 1975, Geologic and structural map of southern part

of the Powder River Basin, Converse, Niobrara, and Natrona Counties,

Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Map

I-877, scale 1:125,000.

Denson, N.M., and Keefer, W.R., 1974, Map of the Wyodak-Anderson coal bed in

the Gillette area, Campbell County, Wyoming: U.S. Geological Survey

Miscellaneous Investigations Series Map I-848-D.

Denson, N.M., Macke, D.L., and Schumann. R.R., 1989a, Geologic map and

distribution of heavy minerals in Tertiary rocks of the Gillette 30’ x 60’

quadrangle, Campbell, Crook, and Weston Counties, Wyoming: U.S.

Geological Survey Miscellaneous Investigations Series Map I-2023, scale

1:125,000.

_____1989b, Geologic map and distribution of heavy minerals in Tertiary rocks of

the Gillette 30’ x 60’ quadrangle, Campbell, Crook, and Weston Counties,
PS-34

Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Map

I-2025, scale 1:125,000.

Dobbin, C.E., 1929, The Forsyth coal field, Rosebud, Treasure, and Big Horn

Counties, Montana: U.S. Geological Survey Bulletin 812, p. 1-55.

Dobbin, C. E., and Barnett, V. H., 1928, The Gillette coal field, northeastern

Wyoming: U.S. Geological Survey Bulletin 796, p. 1-50.

Dorf, E., 1940, Relationship between floras of type Lance and Fort Union

Formations: Geological Society of America Bulletin, v. 51, p. 213-236.

_____1942, Upper Cretaceous floras of the Rocky Mountain region; II, Flora of the

Lance Formation at its type locality, Niobrara County, Wyoming: Carnegie

Institution of Washington Publication 580, p. 79-159.

Dunrud, C.R., and Osterwald, F.W., 1980, Effects of coal mine subsidence in the

Sheridan, Wyoming, area: U.S. Geological Survey Professional Paper 1164,

49 p.

Ellis, M.S., Gunther, G.L., Flores, R.M., Ochs, A.M., Stricker, G.D., Roberts,

S.B., Taber, T.T., Bader, L.R., and Schuenemeyer, J.H., 1999, Preliminary

report on coal resources of the Wyodak-Anderson coal zone, Powder River

Basin, Wyoming and Montana: U.S. Geological Survey Open-File Report

98-789A, 49 p.

Ellis, M.S., Stricker, G.D., Flores, R.M., and Bader, L.R., 1998, Sulfur and ash in

Paleocene Wyodak-Anderson coal in the Powder River Basin, Wyoming and

Montana: a fuel source beyond 2000: 23rd International Technical

Conference on Coal Utilization and Fuel System Proceedings, p. 849-858.

Energy Information Administration, 1996, Annual Energy Outlook 1996, reference

coal forecast. National Energy Modelling System run: AEO96B,

D101995C.
PS-35

Ethridge, F.G., Jackson, T.J., and Youngberg, A.D., 1981, Floodbasin sequence of

a fine-grained meander belt subsystem: the coal-bearing lower Wasatch and

upper Fort Union Formations, southern Powder River Basin, Wyoming, in

Ethridge, F.G., and Flores, R.M., eds., Nonmarine Depositional

Environments: Models for Exploration: Society of Economic

Paleontologists and Mineralogists, Special Publication 3l, p. 191-209.

Fieldner, A.C., Cooper, H.M., and Osgood, F.D., 1931, Analyses of Wyoming

coals: U.S. Bureau of Mines Technical Paper 484, 154 p.

Fisk, H.N., 1944, Geological investigation of the alluvial valley of the lower

Mississippi River: Mississippi River Commission, Vicksburg, 78 p.

Flores, R.M., 1979, Restored stratigraphic cross sections and coal correlations in the

Tongue River member of the Fort Union Formation, Powder River area,

Montana: U.S. Geological Survey, Miscellaneous Field Studies Map MF1127.

_____1980, Fluvial coal setting of the Tongue River Member of the Fort Union

Formation in the Powder River-Clear Creek area, Wyoming, in Glass, G.B.,

eds., Guidebook to the Coal Geology of the Powder River Basin, Wyoming:

Geological Survey of Wyoming, Public Information Circular No. 14, p. 71-

95.

_____1981, Coal deposition in fluvial paleoenvironments of the Paleocene Tongue

River Member of the Fort Union Formation, Powder River area, Powder

River Basin, Wyoming and Montana, in Ethridge, F.G., and Flores, R.M.,

eds., Nonmarine Depositional Environments: Models for Exploration:

Society of Economic Paleontologists and Mineralogists, Special Publication

31, p. 169-l90.

_____1983, Basin facies analysis of coal-rich Tertiary fluvial deposits, northern

Powder River Basin, Montana and Wyoming, in Collinson, J.D. and Lewin,
PS-36

J., eds., Modern and Ancient Fluvial Systems: International Association of

Sedimentologists Special Publication No. 6, p. 501-515.

_____1986, Styles of coal deposition in Tertiary alluvial deposits, Powder River

Basin, Montana and Wyoming, in Lyons, P.C., and Rice, C.L., eds.,

Paleoenvironmental and Tectonic Controls in Coal-forming Basins of the

United States: Geological Society of America, Special Paper 210, p. 79-104.

_____1998, Chronostratigraphic distribution and depositional sequences of

producing Paleocene Fort Union coals in the northern Great Plains:

Geological Society of America, Abstract with Programs, Toronto, Canada.

Flores, R.M., Bader, L.R., Cavaroc, V.V., Ellis, M.S., Gunther, G.L., Johnson,

R.C., Keighin, C.W., Likarish, D., Nichols, D.J., Ochs, A.M., Roberts, S.B.,

Stricker, G.D., Takahashi, K.I., Taber, T.Y., Warwick, P.D., Goven, G.,

Murphy, E.C., and Wilde, E., 1998, Compilation of data on strippable coals

in the northern Rocky Mountains and Great Plains region: a CD-ROM

presentation, in Sakkestad, B.A., ed., Proceedings of the 23rd International

Technical Conference on Coal Utilization and Fuel Systems, p. 839-848.

Flores, R.M., and Canavello, D.A., 1979, Restored stratigraphic cross sections and

coal correlations in the Tongue River member of the Fort Union Formation,

Powder River Basin, Wyoming: U.S. Geological Survey Miscellaneous

Field Studies Map MF-1126.

Flores, R.M., and Ethridge, F.G., l985, Evolution of intermontane fluvial systems

of Tertiary Powder River Basin, Montana and Wyoming, in Flores, R.M. and

Kaplan, S.S., eds., Cenozoic Paleogeography of the West-Central United

States: Society of Economic Paleontologists and Mineralogists, Rocky

Mountain Section, Symposium 3, p. l07-l26.

Flores, R.M., and Hanley, J.H., l984, Anastomosed and associated coal-bearing

fluvial deposits: Upper Tongue River Member, Paleocene Fort Union
PS-37

Formation, northern Powder River Basin, in Rahmani, R., and Flores, R.M.,

eds., Sedimentology of Coal and Coal-bearing Sequences, Association of

Sedimentologists Special Publication No. 7, p. 85-l03.

Flores, R.M., and Moore, T.A., 1994, Mechanisms of splitting of the AndersonDietz coal bed in the Decker area, Montana: a synthesis, 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. 153-161.

Flores, R.M., Roberts, S.B., and Perry, W.J., Jr., 1994, Paleocene paleogeography

of the Wind River, Bighorn, and Powder River Basins, 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, Public Information

Circular No. 33, p. 1-16.

Flores, R.M., Warwick, P.D., and Moore, T.A., 1989, Depositional aspects and a

guide to Paleocene coal-bearing sequences, Powder River Basin: 28th

International Geological Congress, Field Trip Guidebook T132, p. 1-10.

Gardner, A.D., and Flores, V.R., 1989, Forgotten Frontier, A History of Wyoming

Coal Mining: Westview Press, Boulder, Colorado, 243 p.

Glass, G.B., 1976, Update on the Powder River coal basin: Wyoming Geological

Association Guidebook, 28th Annual Field Conference, p. 209-220.

_____1978, Wyoming coal fields, 1978: Geological Survey of Wyoming Public

Information Circular No. 9, 91 p.

_____1980, Coal resources of the Powder River Basin coal basin, in Glass, G.B.,

ed., Guidebook to the Coal Geology of the Powder River Coal Basin,

Wyoming: Wyoming Geological Survey Public Information Circular No.

14, p. 97-131.
PS-38

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

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

Hardie, J.K., 1991, Coal stratigraphy of the southwestern Powder River Basin,

Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Map

I-1959-C.

Hardie, J.K., and Van Gosen, B.S., 1986, Fence diagram showing coal bed

correlations within upper Fort Union Formation in and adjacent to the eastern

part of the Kaycee 30’ x 60’ quadrangle, Johnson and Campbell Counties,

Wyoming: U.S. Geological Survey Coal Investigations Map C-107.

Hatch, J.R., and Swanson, V.E., 1977, Trace elements in Rocky Mountain coals, in

Murray, D.K., ed., Geology of Rocky Mountain coal, Proceedings of the

1976 Symposium: Colorado Geological Survey, Resource Series 1, p. 143-

163.

Hayden, F.V., 1861, Sketch of the geology of the country about the headwaters of

the Missouri and Yellowstone rivers: American Journal of Science, v. 31, p.

229-245.

Heffern, E.L., and Coates, D.A., 1997, Clinker—its occurrence, uses, and effects on

coal mining in the Powder River Basin: Wyoming State Geological Survey

Public Information Circular 38, p. 151-165.

Heffern, E.L., Coates, D.A., Whiteman, J., and Ellis, M.S., 1993, Geologic map

showing distribution of clinker in the Tertiary Fort Union and Wasatch

Formations, northern Powder River Basin, Montana: U.S. Geological

Survey Coal Investigations Map C-142.

Hildebrand, R.T., 1988, Sodium and associated elements in the Anderson-Dietz coal

zone from the Decker area, Big Horn County, Montana: Colorado School of

Mines Professional Contributions 12, p. 217-219.
PS-39

Hobbs, R.G., 1978, Methane occurrences, hazards, and potential resources, Recluse

geologic analysis area, northern Campbell County, Wyoming: U.S.

Geological Survey Open-File Report 78-401, 18 p.

Jenkins, C.D., Jr., 1986, A preliminary tectonic analysis of the northeastern margin

of the Bighorn uplift, Buffalo-Dayton, Wyoming: South Dakota School of

Mines and Technology, M.S. thesis, 121 p.

Johnson, E.A., and Pierce, F.W., 1991, Stratigraphic cross section showing upper

Paleocene coal-bearing rocks of the Tongue River Member of the Fort Union

Formation in the Coal Bank Draw and Dugout Creek North quadrangles,

Campbell and Weston Counties, southeastern Powder River Basin,

Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Map

I-2013.

Keefer, W.R., and Schmidt, P.W., 1973, Energy resources map of the Powder

River Basin, Wyoming and Montana: U.S. Geological Survey Miscellaneous

Investigations Series Map I-847-A, scale 1:500,000.

Kent, B.H., 1986, Evolution of thick coal deposits in the Powder River Basin,

northeastern Wyoming, in Lyons, P.C. and Rice, C.L., Paleoenvironmental

and Tectonic Controls in Coal-Forming Basins in the United States:

Geological Society of America Special Paper 210, p. 105-121.

Kent, B.H., Berlage, L.J., and Boucher, E.M., 1980, Stratigraphic framework of

coal beds underlying the western part of the Recluse 1° x 2° quadrangle,

Campbell County, Wyoming: U.S. Geological Survey Coal Investigations

Map C-81-C.

Kent, B.H., and Munson, B.E., 1978, Isopach maps of the Canyon and associated

coal beds, western half of the Recluse 1° x 2° quadrangle, Campbell County,

Wyoming: U.S. Geological Survey Coal Investigations Map C-81-B.
PS-40

Kepferle, R.C., 1954, Selected deposits of strippable coal in central Rosebud

County, Montana: U.S. Geological Survey Bulletin 995-I, p. 333-381.

Knowlton, F.H., 1909, The stratigraphic relations and paleontology of “Hell Creek

Beds”, “Ceratop Beds” and equivalents, and their reference to the Fort Union

Formation: Washington Academy of Science Proceedings, v. 11, p. 179-

328.

Law, B.E., Barnum, B.E., and Wollenzien, T.P., 1979, Coal bed correlations in the

Tongue River Member of the Fort Union Formation, Monarch, Wyoming,

and Decker, Montana, areas: U.S. Geological Survey Miscellaneous

Investigations Series Map I-1128.

Lewis, B.D., and Hotchkiss, W.R., 1981, Thickness, percent sand, and

configuration of shallow hydrologic units in the Powder River Basin,

Montana and Wyoming: U.S. Geological Survey Miscellaneous

Investigations Series Map I-1317.

Lowry, M.E., and Cummings, T.R., 1966, Ground water resources of Sheridan

County, Wyoming: U.S. Geological Survey Water Supply Paper 1807, p.

46-48.

Lynn, L.R., 1980, Stratigraphic framework of some Tertiary coal-bearing alluvial

strata, Powder River Basin, Wyoming and Montana: North Carolina State

University, M.S. thesis, 94 p.

Mapel, W.J., 1958, Coal in the Powder River Basin: Wyoming Geological

Association Guidebook, 13th Annual Field Conference, p. 218-224.

_____1959, Geology and coal resources of the Buffalo-Lake de Smet area, Johnson

and Sheridan Counties, Wyoming: U.S. Geological Survey Bulletin 1078,

148 p.
PS-41

_____1973, Preliminary geologic map of the Rawhide School quadrangle,

Campbell County, Wyoming: U.S. Geological Survey Open-File Report 73-

177, scale 1:24,000.

_____1976, Geologic map and coal sections of the Birney quadrangle, Rosebud,

Montana: U.S. Geological Survey Miscellaneous Field Studies Map MF813.

Matson, R.E., and Blumer, J.W., 1973, Quality and reserves of strippable coal,

selected deposits, southeastern Montana: Montana Bureau of Mines and

Geology Bulletin 91, 135 p.

Matson, R.E., and Pinchock, J.M., 1977, Geology of the Tongue River Member,

Fort Union Formation of eastern Montana, in Murray, D.K., ed., Geology of

Rocky Mountain Coal, A Symposium 1976: Colorado Geological Survey

Resource Series 1, p. 91-114.

McLellan, M.W., and Biewick, L.H., 1988, Stratigraphic framework of the

Paleocene coal beds in the Broadus 30’ x 60’ quadrangle, Powder River

Basin, Montana—Wyoming: U.S. Geological Survey Coal Investigations

Map C-119-A.

McLellan, M.W., Biewick, L.H., Molnia, C.L., and Pierce, F.W., 1990, Coal

stratigraphy of northern and central Powder River Basin, Montana and

Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Map

I-1959-A.

Meek, F.B., and Hayden, F.V., 1862, Descriptions of the new lower Silurian

(Primordial), Jurassic, Cretaceous, and Tertiary fossils, collected in Nebraska

and adjoining states with some remarks on the rocks from which they were

obtained: Philadelphia Academy of Natural Science Proceedings, 1861, v.

13, p. 415-435.
PS-42

Molnia, C.L., and Pierce, F.W., 1992, Cross sections showing coal stratigraphy of

the central Powder River Basin, Wyoming and Montana: U.S. Geological

Survey Miscellaneous Investigations Series Map I-1959-D.

Moore, T.A., 1986, Characteristics of coal bed splitting in the Anderson-Dietz coal

seam (Paleocene), Powder River Basin, Montana: University of Kentucky,

M.S. thesis, 108 p.

_____1994, Organic compositional clues to a stacked mire sequence in the

Anderson-Dietz 1 coal bed (Paleocene) Montana, 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. 163-172.

Neuzil, S.G., Supardi, Cecil, C.B., Kane, J. S., and Soedjono, K., 1993, Inorganic

geochemistry of domed peat in Indonesia and its implication for the origin of

mineral matter in coal, in Cobb, J.C., and Cecil, C.B., eds., Modern and

Ancient coal-forming environments: Geological Society of America Special

Publication, Special Paper 286, p. 23-44.

Newberry, J.S., 1868, Note on the later extinct floras of North America, with

descriptions of some new species of fossil plants from the Cretaceous and

Tertiary strata: Lyceum Natural History New York Annals, v. 9, p. 1-76.

Nichols, D.J., 1994, Palynostratigraphic correlation of Paleocene rocks in the Wind

River, Bighorn, and Powder River Basins, 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, Public Information Circular

No. 33, p. 17-29.

_____1995, The role of palynology in paleoecological analyses of Tertiary coals:

International Journal of Coal Geology, v. 28, p. 139-159.
PS-43

_____1996, Palynological zonation of the Paleocene of the Rocky Mountain

intermontane basins: Geological Society of America, 1996 Annual Meeting,

Abstracts with Programs, v. 28, no. 7, p. 372.

Nichols, D.J., and Brown, J.L., 1992, Palynostratigraphy of the Tullock Member

(lower Paleocene) of the Fort Union Formation in the Powder River Basin,

Montana and Wyoming: U.S. Geological Survey Bulletin 1917-F, 35 p., 10

pls.

Nichols, D.J., and Ott, H.L., 1978, Biostratigraphy and evolution of the MomipitesCaryapollenites lineage in the early Tertiary in the Wind River Basin,

Wyoming: Palynology, v. 2, p. 93-112.

Nichols, D.J., Wolfe, J.A., and Pocknall, D.T., 1989, Latest Cretaceous and early

Tertiary history of vegetation in the Powder River Basin, Montana and

Wyoming: 28th International Geological Congress, Field Trip Guidebook

T132, p. T132:28- T132:33.

Obernyer, S., 1978, Basin-margin depositional environments of the Wasatch

Formation in the Buffalo-Lake de Smet area, Johnson County, Wyoming, in

Hodgson, H.E., ed., Proceedings of the Second Symposium on the Geology

of Rocky Mountain Coal—1977: Colorado Geological Survey Resource

Series 4, p. 49-65.

Olive, W.W., 1957, The Spotted Horse coal field, Sheridan and Campbell Counties,

Wyoming: U.S. Geological Survey Bulletin 1050, 83 p.

Pait, E.D., 1981, The stratigraphy and facies relationships of some coal-bearing

alluvial plain strata, Powder River Basin, Montana and Wyoming: North

Carolina State University, M.S. thesis, 66 p.

Perry, W.J., Jr., and Flores, R.M., 1994, Sequential Laramide deformation and deep

gas-prone basins of the Rocky Mountain region, in Dyman, T.S., Rice, D.D.,
PS-44

and Wescott, W.A., eds., Geologic Controls of Deep Natural Gas Resources

in the U.S.: U.S. Geological Survey Bulletin 2146-E, p. 49-59.

Pierce, F.W., Johnson, E.A., Molnia, C.L., and Sigleo, W.R., 1990, Coal

stratigraphy of the southeastern Powder River Basin, Wyoming: U.S.

Geological Survey Miscellaneous Investigations Map I-1959-B.

Pierce, F.W., and Johnson, E.A., 1991, Stratigraphic cross section showing upper

Paleocene coal-bearing rocks of the Tongue River Member of the Fort Union

Formation in the Piney Canyon NE and Piney Canyon NW quadrangles,

Campbell and Weston Counties, southeastern Powder River Basin,

Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Map

I-2011.

Pierce, F.W., Kent, B.H., and Grundy, W.D., 1982, Geostatistical analysis of a 113-

billion-ton coal deposit, central part of the Powder River Basin, northwestern

Wyoming, in Gurgel, K.D., ed., Proceedings Fifth Symposium on the

Geology of Rocky Mountain Coal 1982: Utah Geological and Mineral

Survey Bulletin 118, p. 262-273.

Pierce, W.G., 1936, The Rosebud coal field, Rosebud and Custer Counties,

Montana: U.S. Geological Bulletin 847, p. 43-120.

Pocknall, D.T., 1987, Palynomorph biozones for the Fort Union and Wasatch

Formations (upper Paleocene-lower Eocene), Powder River Basin, Wyoming

and Montana, U.S.A.: Palynology, v. 11, p. 23-35.

Pocknall, D.T., and Flores, R.M., 1987, Coal palynology and sedimentology in the

Tongue River member, Fort Union Formation, Powder River Basin,

Wyoming: Palaois, v. 2, p. 133-145.

Pocknall, D.T., and Nichols, D.J., 1996, Palynology of coal zones of the Tongue

River Member (upper Paleocene) of the Fort Union Formation, Powder River
PS-45

Basin, Montana and Wyoming: American Association of Stratigraphic

Palynologists Contributions Series 32, 58 p., 7 pls.

Raines, G.L., and Johnson, B.R., 1996, Digital representation of the Montana State

geology map: a contribution to the Interior Columbia River: U.S. Geological

Survey Open-File Report 95-691.

Resource Data International, Inc., 1998, COALdat: Coal database, 1320 Pearl St.,

Suite 300, Boulder, Colorado 80302.

Rice, D.D., and Finn, T.M., 1995, Coalbed gas plays, Powder River Basin Province

(033) in Gautier, D.L., Dolton, G.L., Takahashi, K.I., and Varnes, K.L. eds.,

1995 National assessment of the United States oil and gas

resources—Results, methodology, and supporting data: U.S. Geological

Survey Digital Data Series 30, one CD-ROM.

Rich, F.J., 1980, Brief survey of chemical and petrographic characteristics of

Powder River Basin coals, in Glass, G.B., ed., Guidebook to the Coal

Geology of the Powder River Coal Basin, Wyoming: Wyoming Geological

Survey Public Information Circular No. 14, p.

Satchell, L.S., 1985, Climate and depositional environment of Glyptostrobus forest

swamp that formed thick low coals in the Paleocene Powder River Basin:

2nd Annual Meeting Program Abstracts, The Society of Organic Petrology,

p. 11.

Schuenemeyer, J.H., and Power, H.C., in press, Uncertainty estimation for regional

resource assessment—an application to coal: Mathematical Geology.

Sholes, M.A., and Cole, G.A., 1981, Depositional history and correlation problems

of the Anderson-Dietz coal zone, southeastern Montana: The Mountain

Geologist, v. 18, p. 35-45.

Sholes, M.A., and Daniel, J.A., 1992, The Knobloch coal bed, Powder River and

Rosebud Counties, Montana: correlation and petrography, in Sholes, M.A.,
PS-46

ed., Coal Geology of Montana: Montana Bureau of Mines and Geology,

Special Publication 102, p. 105-135.

Simpson, G.G., 1928, A new mammalian fauna from the Fort Union of southern

Montana: American Museum Novitates, no. 297, 15 p.

_____1929, Third contribution to the Fort Union fauna at Bear Creek, Montana:

American Museum Novitates, no. 345, 12 p.

_____1937, The Fort Union of the Crazy Mountain field, Montana, and its

mammalian faunas: U.S. National Museum Bulletin 169, 287 p.

Smith, J.B., Ayler, M.F., Knox, C.C., and Pollard, B.C., 1972, Strippable coal

resources of Wyoming: U.S. Bureau of Mines Information Circular IC

8538, 51 p.

Spindel, S., 1975, Palynological determination of the Paleocene-Eocene boundary

between the Tongue River Member and Wasatch Formation, southeastern

Montana: Northwest Geology, v. 4, p. 38-45.

Stanton, T.W., and Knowlton, F.H., 1897, Stratigraphy and paleontology of the

Laramie and related formations in Wyoming: Geological Society of America

Bulletin, v. 8, p. 127-156.

Stricker, G.D., Ellis, M.S., Flores, R.M., and Bader, L.R., 1998, Elements of

environmental concern in the 1990 Clean Air Act Amendments: A

prospective of Fort Union coals in northern Rocky Mountains and Great

Plains region, in Sakkestad, B.A., ed., The Proceedings of the 23rd

International Technical Conference on Coal Utilization and Fuel Systems, p.

967-976.

Taff, J.A., 1909, The Sheridan coal field: U.S. Geological Survey Bulletin 341, p.

123-150.
PS-47

Thom, W.T., and Dobbin, C.E., 1924, Stratigraphy of Cretaceous-Eocene transition

beds in eastern Montana and the Dakotas: Geological Society of America

Bulletin, v. 35, p. 481-505.

Toth, J.C., 1982, Facies of Paleocene alluvial plains, Powder River Basin, Montana:

North Carolina State University, M.S. thesis, 69 p.

Trent, V.A., 1986, Estimated resources of non-leased federal coal, Powder River

Basin, Montana and Wyoming: U.S. Geological Survey Miscellaneous Field

Studies Map MF-1887.

Trumbull, L.W., 1905, Coal resources of Wyoming: University of Wyoming,

School of Mines Bulletin No. 7, 98 p.

Tschudy, R.H., 1976, Pollen changes near the Fort Union-Wasatch boundary,

Powder River Basin: Wyoming Geological Association Guidebook 28th

Annual Field Conference, p. 73-81.

Tudor, M.S., 1975, Geologic exploration and development of coal in the Sarpy

Creek area, Big Horn County, Montana: Montana Geological Society

Guidebook, Annual Field Conference, p. 159-164.

U.S. Geological Survey, 1974, Preliminary report of coal drill-hole data and

chemical analyses of coal beds: U.S. Geological Survey Open-File Report,

241 p.

U.S. Geological Survey and Montana Bureau of Mines and Geology, 1973,

Preliminary report of coal drill-hole data and chemical analyses of coal beds:

U.S. Geological Survey Open-File Report, 51 p.

Warwick, P.D., 1985, Depositional environments and petrology of the Felix coal

interval, Powder River Basin, Wyoming: University of Kentucky, Ph.D.

thesis, 333 p.

Warwick, P.D., Flores, R.M., Nichols, D.J., Murphy, E.C., and Obradovich, J.D.,

1997, Fort Union chronostratigraphic and depositional sequences, Williston
PS-48

Basin, North and South Dakota, and Montana: Geological Society of

America, Abstract with Programs, v. 29, no. 6, p. 204.

Warwick, P.D., Flores, R.M., Nichols, D.J., Murphy, E.C., and Ochs, A.M., 1998,

Lower Fort Union chronostratigraphic depositional sequences, Williston

Basin, North Dakota, South Dakota, and Montana: Geological Society of

America, Abstracts with Programs, v. 30, no. 7, p. 174.

Warwick, P.D., and Stanton, R.W., 1986, Depositional controls on the geometry of

the Wyodak-Anderson coalbed, northeastern Wyoming, in Carter, L.M.H.,

ed., The Second Annual McKelvey Forum on Mineral and Energy

Resources: U.S. Geological Survey Circular 974, p. 71-72.

_____1988, Depositional models for two Tertiary coal-bearing sequences in the

Powder River Basin, USA: Journal of the Geological Society of London, v.

145, p. 613-620.

Weaver, J.N., and Flores, R.M., l985, Stratigraphic framework of the upper Fort

Union Formation at the TA Hills, western Powder River Basin, Wyoming:

U.S. Geological Survey Miscellaneous Field Studies Map, MF l779.

_____l987, Sedimentologic and stratigraphic framework of the upper part of the

Paleocene Fort Union Formation, western Powder River Basin, Wyoming:

U.S. Geological Survey Miscellaneous Field Studies Map MF-l929.

Wegemann, C.H., 1910, Notes on the coals of the Custer National Forest, Montana:

U.S. Geological Survey Bulletin 381-A, p. 108-114.

_____1917, Wasatch fossils in so-called Fort Union beds of the Powder River

Basin, Wyoming, and their bearing on the stratigraphy of the region: U.S.

Geological Survey Professional Paper 108, p. 57-60.

_____1929, The Pumpkin Buttes coal field, Wyoming: U.S. Geological Survey

Bulletin 806, p. 1-14.
PS-49

Whitcomb, H.A., Cummings, T.R., and McCullough, R.A., 1966, Ground-water

resources and geology of northern and central Johnson County, Wyoming:

U.S. Geological Survey Water Supply Paper 1806, p. 70-72.

Whipkey, C.E., 1988, Provenance of lower Tertiary sandstones of the Powder River

Basin, Wyoming: North Carolina State University, M.S. thesis, 145 p.

Whipkey, C.E., Cavaroc, V.V., and Flores, R.M., 1991, Uplift of the Bighorn

Mountains, Wyoming and Montana—A sandstone provenance study: U.S

Geological Survey Bulletin 1917, 20 p.

Wolfe, J.A., and Upchurch, G.R., 1986, Vegetation, climatic and floral changes at

the Cretaceous-Tertiary boundary: Nature, v. 324, p. 148-152.

_____1987, Maestrichtian-Paleocene vegetation and climate of the Powder River

Basin, Wyoming and Montana: Geological Society of America, Abstracts

with Programs, v. 19, p. 896.

Young, W.H., Anderson, R.L., and Hall, E.M., 1957, Coal—bituminous and

lignite: U.S. Bureau of Mines Minerals Yearbook, (1955 preprint).
106° 108° 104°

46°

45°

44°

43°

Miles City Arch

USGS

Drill Hole

Betop

Well

Spring

Creek

Mine

Williston

Basin

Powder River

Basin

0 20 Miles

Montana

North

Dakota

South

Dakota

Sheridan Wyoming

Johnson Campbell

Converse

Big Horn

Methane Prospect Areas

 Surface mines

Tertiary Wasatch Formation

Tertiary Tongue River Member

of the Fort Union Formation

Tertiary Lebo Shale Member

of the Fort Union Formation

Tertiary Tullock Member

of the Fort Union Formation

Undifferentiated

Fort Union Formation

Twr 

Twr 

Tfl

Tfl Tfl

Tfl

Tft

Tft

Tft

Tftr

Tftr

Tfu

Tfu

Tw

Tw

Tw

Quaternary alluvium

Tertiary White River Formation

Qal

Qal

Deep Wyodak-Anderson coal bed and zone

(Bureau of Land Management, 1999)

Shallow Fort Union coal

(Bureau of Land Management, 1999)

Yello w st one R i ver

Tongue

River

River

Powder

Bighorn

Mountains

Casper Arch

Laramie Mountains Hartville

Uplift

Black Hills

Glenrock

Sheridan

Buffalo

Kaycee

Lynch

Gillette

Figure PS-1. Generalized geologic map showing the extent of the

Powder River Basin in Wyoming and Montana (adapted from Raines and

Johnson, 1996; Green and Drouillard, 1994). Also shown are county

boundaries, geological structures, mines, and cities. Coal-bed methane

may be targeted for exploration in the eastern (shallow) and southwestern

(deep) parts of the basin (Bureau of Land Management, 1999).
Conglomerate

Sandstone

Palynostratigraphic

zonation

Sandstone, siltstone,

mudstone, and limestone

Coal and carbonaceous

shale

P1

P3

P4

P5

P6

P2

0 0

1000

feet

300

meters

P1-P6

Moncrief

Member

Eocene

Wasatch

Formation

Paleocene

Fort Union Formation

Tongue

Ri

ver

Member

Lebo Shale

Member

Tullock

Member

Kingsbury

Member

Upper Conglomerate

Cretaceous Lance

Formation

Wyodak-Anderson

coal zone

Lake de Smet coal

Felix coal

Roland coal

Knobloch

coal zone

Sawyer coal

Wall coal

Pawnee coal

Terret coal

Broadus coal

Rosebud coal zone

Brewster-Arnold coal

Burley coal

Smith (Swartz) coal

Anderson (Dietz 1, 2, & 3) coal

Canyon (Monarch) coal

Werner coal

Knobloch coal

Calvert coal

Nance coal

Flowers-Goodale coal

Sawyer coal

Lay Creek coal

King coal

}

}

} }

- OR -

Figure PS-2. Composite stratigraphic column showing subdivisions of Upper Cretaceous rocks, Paleocene Fort

Union Formation, and Eocene Wasatch Formation in the Powder River Basin, Wyoming and Montana. Major

coal beds and zones are identified in the Fort Union and Wasatch Formations. Biostratigraphic zones(P1–P6) of

the Fort Union Formation are also shown. The Wyodak-Anderson coal zone is synonymous to the Big George

and Sussex coal in the central part of the Powder River Basin.
Figure PS-3. Upper Fort Union conglomerate (more than 1,200 ft thick) exposed in the Castle Rock area north of Buffalo. The 

conglomerate is lateral facies to the Tongue River Member. Photograph by R.M. Flores. 
Figure PS-4. The erosional-based Fort Union conglomerate and coarse sandstone are interbedded with variegated siltstone and 

mudstone, which were formed in alluvial fan and interfan environments. Photograph by R.M. Flores.
Figure PS-5. Variegated and mottled siltstone and mudstone (lower part of picture) are capped by partly oxidized, rooted 

carbonaceous mudstone (central part of picture) representing a paleosol formed in the interfan environment. 

Photograph by R.M. Flores. 
Figure PS-6. Pebble conglomerate of the Tongue River Member exposed north of Kaycee; represents braided stream deposits. 

Photograph by R.M. Flores.
Figure PS-7. Floodplain mudstone, siltstone, and silty sandstone underlain by fluvial channel sandstone beds (lower part 

of photo). The floodplain deposits have undergone pedogenesis that transformed the deposits into a stack of palesols. 

Each palesol consists of carbonaceous mudstone deposits with roots in the upper part and ironstone deposits in the lower 

part. These deposits underlie the “Sussex” coal zone and exposed north of Linch, Wyoming. Photograph by R.M. Flores.
Figure PS-8. Coarsening-upward mudstone, siltstone, and silty sandstone crevasse splay deposits. These rocks are 

exposed along the Powder River in northeastern Wyoming. Photograph by R.M. Flores
Figure PS-9. Vertically stacked fluvial channel sandstone deposits interbedded with floodplain and crevasse splay 

deposits. These deposits are below the “Sussex” coal zone, which is exposed north of Linch, Wyoming.

Photograph by R.M. Flores.
PS-10. Fluvial channel deposit consisting of multi-erosional, crossbedded sandstone intercalated with basally erosional 

mudstone deposits that are abandoned "clay plugs." These deposits are below along the "Sussex" coal zone, which is 

exposed north of Linch, Wyoming.
Figure PS-11. Wyodak–Anderson coal, which is more than 100 ft thick, in the Eagle Butte coal mine in the Gillette coalfield in

Wyoming. Coal train is on horizon in background. Photograph by R.M. Flores.
SIAK TO KAMPAR

0

0 20 40 Kilometers

20 Meters

10

SIAK RIVER/

ESTUARY

LAKE

PEAT DOME

KAMPAR RIVER/

ESTUARY

B B'

Figure PS-12. Diagrammatic cross section of a raised bog between two river estuaries in Sumatra, Indonesia.

The thickest peat measured here is 13 meters (modified from Neuzil and others, 1993).

Rock Sandstone Peat
Figure PS-13. Peat exposed along a drainage ditch cut near the margin of a raised bog in central

Kalimantan, Borneo. Photograph by C. Blaine Cecil.
Figure PS-14. Wyodak–Anderson coal (Anderson–Dietz coal), showing a thin carbonaceous shale, coaly mudstone 

parting in the Spring Creek coal mine in Montana. Photograph by R.M. Flores.
Figure PS-15. The split Wyodak–Anderson coal zone (upper bed is Anderson or Dietz 1 coal and the lower bed is Dietz 2 

coal) in the Decker coal mine in Montana. The coal beds are split by tabular crevasse splay sandstone interbedded with 

mudstone and siltstone. Photograph by R.M. Flores.
Figure PS-16. The merged Wyodak–Anderson coal, which is more than 80 ft thick, in the Spring Creek coal mine in 

Montana. Photograph by R.M. Flores.
MONTANA

WYOMING

107°

46°

44°

105°

Powder River

Basin

10 0 10 20 Miles

1 Bed

2 Beds

3 Beds

>4 Beds

Number of coal beds

in the

Wyodak-Anderson coal zone

fluvial

clastic rocks

fluvial

clastic rocks

Figure PS-17. Distribution of the number of coal beds in the

Wyodak-Anderson coal zone in the Powder River Basin.
MONTANA

WYOMING

107°

46°

44°

105°

Powder River

Basin

10 0 10 20 Miles

P6

P5-P6

P5-P6

P5

P5-P6

P6

P5-P6

Gillette

Sheridan

Decker mines

Dave Johnston mine

Figure PS-18. Biozones of the Wyodak-Anderson coal zone indicate early late Paleocene

(P5) to latest Paleocene (P6) from the center to the margins of the basin. P5–P6 biozone

is between these Paleocene ages (see Chapter PB, Biostratigraphy by Nichols, in this CD-ROM).
Figure PS-19. Clinker (orange-red) of the Anderson coal bed (upper clinker) and Canyon coal bed (lower clinker) of the 

Wyodak–Anderson coal zone along the valley wall of the Powder River in Wyoming. Here, the coal beds are susceptible to burning,

which progresses downdip (to the left of photo). Photograph by R.M. Flores.
Figure PS-20. A closer view of the clinker consisting of black, vesicular, cryptocrystalline to glassy fused rock, orange-red baked 

mudstone, siltstone, and sandstone, and breccia composed of angular unfused to slightly fused rock fragments (Coates, 1980).
Figure PS-21. Clinker (orange-red at the left of the picture) of the Anderson or Dietz 1 coal bed (at the right of the picture ) on the 

Decker coal mine in Montana. Burning has reduced the reserve of the Anderson coal bed. Photograph by R.M. Flores.
Figure PS-22. An outcrop (north of Linch, Wyoming) of the “Sussex” coal zone consisting of a more than 20-ft- thick coal bed 

(upper part of picture) and there underlying thin coal beds that are interbedded with silty sandstone, siltstone, and mudstone 

representing floodplain deposits. The “Sussex” coal zone is underlain by a fluvial channel sandstone. Photograph by R.M. Flores.