Uplift of the Bighorn Mountains, Wyoming 

and Montana A Sandstone 

Provenance Study

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Chapter D

Uplift of the Bighorn Mountains, Wyoming 

and Montana A Sandstone 

Provenance Study

By CE. WHIPKEY, V.V. CAVAROC, and R.M. FLORES

A multidisciplinary approach to research studies of sedimentary 

rocks and their constituents and the evolution of sedimentary 

basins, both ancient and modern

U.S. GEOLOGICAL SURVEY BULLETIN 1917

EVOLUTION OF SEDIMENTARY BASINS POWDER RIVER BASIN
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government.

UNITED STATES GOVERNMENT PRINTING OFFICF: 1991

For sale by the

Books and Open-File Reports Section

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Library of Congress Cataloging-in-Publication Data

Whipkey, C.E.

Uplift of the Bighorn Mountains, Wyoming and Montana a sandstone

provenance study / by C.E. Whipkey, V.V. Cavaroc, and R.M. Flores. 

p. cm. (Evolution of sedimentary basins Powder River Basin ; 

ch. D) (U.S. Geological Survey bulletin ; 1917-D)

Includes bibliographical references (p. ).

Supt. of Docs, no.: I 19.3:1917-D

1. Sandstone Wyoming Big Horn Mountains. 2. Sandstone Black Hills 

(S.D. and Wyo.) 3. Geology, Stratigraphic Paleocene. 4. Geology, 

Stratigraphic Eocene. 5. Geology Wyoming. 6. Geology Montana. I. Cavaroc, 

Victor V. II. Flores, Romeo M. III. Title. IV. Series. V. Series: U.S. 

Geological Survey bulletin ; 1917-D. 

QE75.B9 no. 1917-D 

[QE 471.15.525] 

557.3 s dc20

[552'.5] 90-14077

CIP
CONTENTS

Abstract Dl 

Introduction Dl

Lithologic types in the Black Hills and Bighorn Mountains D2 

Precambrian cores D2 

Sedimentary rocks of the Black Hills D3 

Sedimentary rocks of the Bighorn Mountains D3 

Provenance implications D4 

Study approach D4

Sample collection and preparation D4 

Methods of study D4 

Compositional data testing D5 

Sandstone mineralogy of the basin D5 

Classification D5 

Grain types D5

Quartz D5

Feldspar Dll

Granitic rock fragments Dll

Metamorphic rock fragments and mica Dll

Sedimentary rock fragments Dll

Glauconite Dll 

Cementation and diagenesis Dll

Vertical changes in petrographic facies of lower Tertiary sandstones D12 

Sample localities D12 

Petrographic facies D12 

Textures D13 

Mineralogy D13

Quartz D13

Carbonate rock fragments D13

Cherty fragments D14

Feldspar D14

Mica D15

Other rock fragments D15

Glauconite D15 

Discussion and interpretation D15

Lower petrographic facies D15

Middle petrographic facies D15

Upper petrographiic facies D16

Lateral variation within the Tongue River Member D16 

Sample localities D16 

Sandstone mineralogy groupings D16 

Textures D17 

Mineralogy D17

Quartz D17

Feldspar D17

Mica D18

Cherty fragments D18

Contents III
Carbonate rock fragments D18 

Other rock fragments D19 

Glauconite D19 

Discussion and interpretation D19

Summary and conclusions D19

References cited D19

FIGURES

1. Map showing Powder River Basin and surrounding area, Wyoming, Montana, 

and South Dakota D2

2. Chart showing lithology of lower Tertiary units, western Powder River

Basin D2 

3-4. Maps showing:

3. Generalized geology of the Powder River Basin and surrounding area D3

4. Sample areas used to determine vertical variation in mineralogy, western 

Powder River Basin D12

5. Ternary diagram showing the composition of sandstones along the western 

margin of the Powder River Basin D13

6. Graphical plot showing point-count data for sandstones from western margin of 

Powder River Basin D14

7. Map showing sample areas used to determine lateral variation in mineralogy of 

the Tongue River Member of the Fort Union Formation in the Powder River 

Basin D16

8. Ternary diagram showing the composition of sandstones from the Tongue River 

Member of the Fort Union Formation D17

9. Graphical plot showing point-count data for the Tongue River Member of the 

Fort Union Formation D18

TABLES

1. Stratigraphic and geographic locations of samples in study D5

2. Modal compositions of samples D6

3. Quartz extinction types and feldspar twin types expressed as percentage of total 

	framework grains D7

4. Rock-fragment types expressed as percentage of total framework grains D8

5. Grain counts of chert types D9

6. Quartz-grain apparent long axes and rounding D10

IV Contents
EVOLUTION OF SEDIMENTARY BASINS POWDER RIVER BASIN

Uplift of the EJighorn Mountains, Wyoming and 

Montana A Sandstone Provenance Study

ByC.E. Whipkey1 , V.V. Cavaroc1 , and R.M. Flores2

Abstract

Fluvial- and lacustrine-dominated clastic sedimentary 

rocks as thick as 1,800 m (6,000 ft) comprise the Paleocene 

Fort Union Formation and the Eocene Wasatch Formation of 

the western Powder River Basin in northeastern Wyoming and 

southeastern Montana. The systematic mineralogy of 45 

samples of channel-fill sandstone from this sequence reflects 

the uplift and erosion of the Bighorn Mountains. Samples were 

collected to study vertical changes in the mineralogy of lower 

Tertiary sandstones adjacent to the Bighorn Mountains, lateral 

variations in the composition of the upper Paleocene Tongue 

River Member of the Fort Union Formation along the eastern 

front of the mountains, and variations in the composition of 

equivalent upper Paleocene sandstones of the central and 

western parts of the basin.

Vertical changes in the mineralogy of a succession of 

Paleocene and Eocene sandstone units adjacent to the Bighorn 

Mountains most likely were produced by uplift and sequential 

erosion of the rocks that formerly overlaid the mountains. 

Uplift probably began in the middle Paleocene, during 

deposition of the Lebo Member of the Fort Union Formation, 

and continued into the Eocene. Differences in the mineralogy 

of the sandstone units along the western edge of the Powder 

River Basin that correspond to differences in the rock types 

now exposed along the crest of the Bighorn Mountains suggest 

that much of the erosional degradation of the Bighorn 

Mountains occurred during an early Tertiary tectonic episode. 

Lateral changes in the suite of unstable detrital grains within 

the Tongue River Member are compatible with facies and 

paleotransport studies that indicate a substantial eastward flux 

of detritus of early Tertiary age from the Bighorn Mountains 

into the central Powder River Basin.

Manuscript approved for publication June 26, 1990.

'Department of Marine, Earth, and Atmospheric Sciences, North 

Carolina State University, Raleigh, North Carolina 27695.

2U.S. Geological Survey, Box 25046, MS 972, Denver, 

Colorado 80225.

INTRODUCTION

The Powder River Basin covers about 56,000 km2 

(about 20,000 mi2) in northeastern Wyoming and an 

adjacent part of Montana (fig. 1) and contains Paleocene 

and Eocene terrigenous detrital sedimentary rocks as much 

as 1,800 m (6,000 ft) thick (fig. 2). Most of the detritus 

accumulated during and following rapid subsidence of the 

basin that started in the middle Paleocene (Curry, 1971; 

Flores and Ethridge, 1985; Ayers, 1986). The sedimentary 

fill of the basin is dominated by fluvial, floodplain, and 

lacustrine sediments deposited in association with a generally northward flowing paleodrainage system. Blackstone 

(1975) and Seeland (1985) believed that the difference in 

elevations of the Bighorn Mountains and the adjacent 

Powder River Basin in the Eocene is similar to the 

maximum present-day relief for that region (2,800 m or 

9,200 ft). This early Tertiary topography was buried beneath 

gently eastward sloping strata during the Oligocene and 

Miocene (Blackstone, 1975; Seeland, 1985). Erosion since 

that time has exposed the lower Tertiary strata, as well as 

the adjoining highlands of the Bighorn Mountains and 

Black Hills (King, 1977; Trimble, 1980; Swinehart and 

others, 1985).

The age of the beginning of uplift of the Bighorn 

Mountains has been debated. Along the western margin of 

the Powder River Basin, the Wasatch Formation of Eocene 

age (fig. 2) contains two thick conglomeratic members (in 

descending order, the Moncrief Member and Kingsbury 

Conglomerate Member). Cobbles and pebbles in the 

Wasatch are rich in feldspathic rock fragments derived from 

erosion of the Precambrian core of the Bighorn Mountains 

(Sharp, 1948; Hose, 1955; Mapel, 1959). The development 

of this uplift as a major source of sediment for the basin 

began, according to facies analysis studies, in either the late 

Paleocene (Flores and Ethridge, 1985) or the Eocene 

(Ayers, 1986). Merin and Lindholm (1986) and Ayers 

(1986) believed that most of the Paleocene detritus in the

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D1
107°

^VM .,,'

0 50 MILES

Figure 1. Powder River Basin and surrounding area, 

Wyoming, Montana, and South Dakota.

central part of the basin was derived from uplift of the Black 

Hills. This conclusion is based on the presence of lithic 

carbonate grains (0-11 percent) and some (0-2 percent) 

phyllitic rock fragments in uppermost sandstones in the 

Tongue River Member of the Fort Union Formation at a site 

east of the Powder River near the border of Wyoming and 

Montana.

Results of our study indicate that the Bighorn 

Mountains formed a significant highland during the late 

Paleocene (during deposition of the Tongue River Member) 

and likely began rising as early as the middle Paleocene 

(during deposition of the Lebo Member of the Fort Union). 

The results also demonstrate that the present-day pattern of 

outcrops in the Bighorn Mountains (fig. 3) was established 

during this early Tertiary episode of uplift and erosion.

LITHOLOGIC TYPES IN THE BLACK 

HILLS AND BIGHORN MOUNTAINS

Precambrian Cores

The structures that define the Powder River Basin are 

made up of similar rock types. In particular, both the 

Bighorn Mountains and the Black Hills consist of Precambrian igneous and metamorphic rocks flanked by thick 

sequences of upturned Paleozoic and Mesozoic strata.

The Precambrian core of the Black Hills (fig. 3) crops 

out in an area of approximately 2,200 km2 (800 mi2). It 

consists of metasedimentary rocks and metagabbro and

TIME

Eocene

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Tongue River 

Member

(as thick as

2,000 ft)

Lebo

Member

(as thick as

900 m or

2,900 ft)

Tullock

Member

(as thick as

700 m or

2,300 ft)

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PETROGRAPHIC 

FACIES

Upper

Middle

Lower

EXPLANATION

0 A 

 

Pebble and boulder

Mudstone, siltstone,

-U~l~

1 1

1 1

i i

Coquinoid limestone

Channel sandstone

Coal

Figure 2. Lithology of lower Tertiary units, western Powder 

River Basin.

minor outcrops (less than 220 km2 or 80 mi2) of granitic 

rocks. The metamorphic rocks are sillimanite to biotite in 

grade (Redden, 1975). The metasedimentary rocks include 

conglomerate, quartzite, graywacke, arkose, iron-rich strata, 

and dolomitic marble. Metabasalt, amphibolite, phyllite, 

and schist have been reported (Redden, 1975). The youngest 

and most extensively exposed granite is composed chiefly 

of quartz, albite, microcline, and muscovite; the oldest 

granitic rocks are commonly gneissic.

Precambrian crystalline rocks of the Bighorn 

Mountains crop out over a much larger area (about 4,000 

km2 or 1,500 mi2). The southern half of the area includes 

Early Archean layered granitic gneiss, amphibolite, and 

felsic gneiss. These rocks are intercalated with metagraywacke, iron-bearing strata, quartzite, and other metasedimentary rocks. The northern half of the area consists of 

Middle Archean quartz diorite and quartz monzonite that 

have been intruded by amphibolite dikes (Love and Christiansen, 1985).

D2 Evolution of Sedimentary Basins Powder River Basin
105°

43

42

50 100 KILOMETERS

0 50 MILES

EXPLANATION

Upper Tertiary continental sedimentary rocks 

Eocene and Paleocene Wasatch Formation 

Paleocene Fort Union Formation

Mesozoic predominantly marine sandstone, siltstone, 

shale; minor limestone, dolomite, and evaporites

Paleozoic predominantly marine limestone; minor 

sandstone, siltstone, and shale

Precambrian schist and phyllite (Black Hills)

Precambrian quartz monzonite to diorite; minor metasedimentary rocks (Bighorn Mountains)

Precambrian granite and granite gneiss; minor metasedimentary rocks (Black Hills and Bighorn Mountains)

Basin axis

Figure 3. Generalized geology of the Powder River Basin and 

surrounding area. Modified from Love and Christiansen (1985) 

and Redden (1975).

Sedimentary Rocks of the Black Hills

The Paleozoic strata of the Black Hills are a mostly 

marine shelf sequence dominated by carbonate rocks but 

containing significant clastic beds. Cambrian and Ordovician strata consist of a few, relatively thin beds of 

sandstone, shale, and carbonate rocks. The Silurian and 

Devonian Periods for the most part are not represented in 

the Black Hills. A thick Mississippian sequence consists of

widespread limestone, dolomite, and argillaceous dolomite. 

The Pahasapa Limestone (equivalent in part to the Madison 

Limestone), for example, is as much as 183 m (600 ft) thick. 

The Upper Paleozoic sequence contains a larger p roportion 

of detrital sedimentary rocks. The Pennsylvanian and Lower 

Permian Minnelusa Formation, for example, consists of as 

much as 213 m (700 ft) of sandstone and dolomite and 

minor chert and shale. The remaining Permian strata consist 

of thinner units of carbonate rocks, silty shale, and shale that 

grade upward into red sandstone, siltstone, shale, and 

evaporite deposits of the mostly continental Upper Permian 

and Triassic Spearfish Formation.

Jurassic and Cretaceous formations of the Black Hills 

record the return of marine conditions to the region. They 

consist of detritus-dominated, shallow-marine strata and 

minor intervening continental rocks. A major clastic unit of 

Middle and Late Jurassic age in the Black Hills, the 

Sundance Formation, consists of locally glauconitic sandstone and shale. This unit thins southeastward from almost 

225 m (740 ft) thick in eastern Montana to a wedge edge in 

central South Dakota. It is overlain by as much as 107 m 

(350 ft) of nonmarine, predominantly clastic beds of the 

Morrison Formation. Lower Cretaceous strata in the area are 

dominated by marine and nonmarine sandstone and mudstone, including the Lakota Formation, as much as 168 m 

(550 ft) thick. The Upper Cretaceous Series contains large 

amounts of marine shale, typified by the Pierre Shale, as 

much as 915 m (3,000 ft) thick. This interval also includes 

the coarser grained, marginal-marine Fox Hills Sandstone 

and the nonmarine Hell Creek Formation (Lance Formation 

in Wyoming), which together are more than 350 m (1,000 

ft) thick.

Sedimentary Rocks of the 

Bighorn Mountains

Sedimentary strata of the Bighorn Mountains were 

deposited farther to the west of the stable craton than those 

of the Black Hills. Therefore, although they are similar in 

lithology, they tend to be both thicker and more marine. As 

in the Black Hills, the Paleozoic sequences are dominated 

by marine carbonate rocks, but they also contain extensive 

sandstone, siltstone, and shale. The Cambrian rocks consist 

of numerous fine-grained detrital beds, some arkosic 

sandstone and conglomerate, and a moderately thick limestone unit (50-65 m or 164-213 ft) near the top. The 

overlying Bighorn Dolomite (60-130 m or 197-426 ft) of 

Middle and Late Ordovician age contains thin sandstone 

and shale beds. As in the Black Hills, Silurian rocks are 

absent. Devonian strata are relatively thin and consist of 

carbonate rocks, sandstone, and shale.

The Upper Devonian and Mississippian Madison 

Limestone of the Bighorn Mountains is essentially the same 

as in the Black Hills. It is as much as 270 m (886 ft) thick

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D3
and marine in origin and contains extensive limestone, 

dolomitic limestone, and dolomite beds, some of which are 

oolitic. The thick, cliff-forming, Pennsylvanian sequence 

includes feldspathic quartz sandstone, limestone, and shale. 

A thin Permian sequence of limestone, red shale, red 

siltstone, and evaporites is present. The Triassic is dominated by the red sandstone and shale of the Chugwater 

Group (as much as 275 m or 902 ft thick).

Jurassic and Cretaceous strata of the Bighorn 

Mountains, similar to those of the Black Hills, are composed chiefly of poorly indurated sandstones and other 

siliciclastic beds of continental and marine origin. Minor 

amounts of carbonate rocks are locally present. Jurassic 

rocks (as much as 230 m or 755 ft thick) include limestone, 

shale, and siltstone that are locally glauconitic. The 

Cretaceous sequence consists mainly of marine shale that 

commonly contains sandy intervals. The thickest of the 

Cretaceous formations is the Cody Shale, 800-1,075 m 

(2,625-3,527 ft) of shale and minor sandstone. Other thick 

units are the shale and sandstone-dominated Mesaverde and 

Lance Formations.

Provenance Implications

Similarities between outcropping rocks of the Black 

Hills and Bighorn Mountains (fig. 3) suggest that early 

Tertiary uplift and erosion of either area would have yielded 

detritus comprising the same four, potentially distinguishable mineral assemblages.

1. The earliest uplift of either range would have 

been accompanied by erosion of the thick shales, sandstones, and siltstones of the Cretaceous formations. The 

mineralogically mature sandstones and siltstones would 

have yielded recycled, durable grains such as rounded 

monocrystalline quartz and chert, whereas erosion of the 

volumetrically more important marine shales would have 

introduced abundant clay-size detritus into the nearest 

basins.

2. Further uplift would have caused erosion of the 

Permian through Jurassic rocks. These strata would have 

yielded abundant recycled quartz and cherry grains from 

both continental and marine sandstones and siltstones. 

Rapid erosion of this relatively friable sequence, along with 

minimal transportation and quick burial, might have led to 

the preservation of generally unstable constituents such as 

glauconite. Minor amounts of carbonate fragments also 

could have survived transportation from the relatively 

unimportant outcrops of limestones and dolomites.

3. With exposure of the Paleozoic shelf sequence, 

large quantities of marine limestones, dolomites, and silicified carbonate rocks would have been truncated. During 

rapid uplift much of this material should have been 

mechanically eroded to form detritus dominated by recycled 

quartz grains but also exceptionally enriched in detrital 

carbonate fragments. These sediments would also have

contained chert grains and possibly sparse, recycled feldspar 

grains derived from the mature Paleozoic arkosic 

sandstones.

4. Only the Precambrian rocks of the two areas 

would provide significantly different erosional detritus. The 

core area of the Bighorn Mountains is composed mostly of 

diorite, monzonite, and gneiss. Erosion of these rocks would 

have yielded abundant quartz and feldspar and some 

relatively large mica booklets. Smaller quantities of slate, 

phyllite, and schist lithic fragments would have been eroded 

from the periphery of the core. The core of the Black Hills, 

on the other hand, is especially rich in metasedimentary 

rocks such as quartzite, slate, phyllite, and schist. The only 

rocks that could have yielded sand-sized grains of feldspar 

in any abundance are the areally small bodies of metaarkose and granite.

STUDY APPROACH

Sample Collection and Preparation

The three members of the Fort Union Formation and 

the Kingsbury Conglomerate Member and Moncrief 

Member of the Wasatch Formation were sampled along the 

western margin of the basin (fig. 3) to determine if 

differences in the petrography of the sandstone units can be 

used to accurately define the start of uplift of the Bighorn 

Mountains. The Tongue River Member of the Fort Union 

Formation was sampled at additional localities in the 

northern and central parts of the basin to determine if lateral 

changes in its mineralogy correspond to lateral changes in 

rocks that presently crop out along the axis of the Bighorn 

Mountains. All samples were obtained from fluvially 

dominated sandstones to minimize compositional variations 

related to changes in depositional environment (Davies and 

Ethridge, 1975). The stratigraphic and geographic positions 

of these samples are described in Whipkey (1988). Samples 

were restricted to the fine to medium sand range (1-3 phi) 

to minimize compositional variations related to differences 

in grain size (Mann and Cavaroc, 1973; Odom and others, 

1976).

Thin sections of selected samples (many of which 

required impregnation with epoxy) were prepared. A blue 

epoxy impregnation aided in evaluating grain diagenesis by 

accentuating pore geometry. Most thin sections were 

stained with sodium cobaltinitrite to aid in potassium 

feldspar identification.

Methods of Study

The 45 samples used in this study (table 1) were 

selected to obtain a representative distribution from the 

Tertiary stratigraphic interval exposed along the eastern

D4 Evolution of Sedimentary Basins Powder River Basin
Table 1. Stratigraphic and geographic locations of samples in study 

[Sample areas shown by number on figures 4 and 7]

Sample 

number

1

2-5

6-7

8-13

14-16

17-26

27-30

31-36

37-45

Rock unit

Tullock*

Lebo*

Lower part of Tongue River*

Lower part of Tongue River*

Upper part of Tongue River*

Upper part of Tongue River*

Wasatch Formation

Upper part of Tongue River*

Upper part of Tongue River*

Geographic location

Southwestern part of basin

Southwestern part of basin

Castle Rock area

TA Hills area

Castle Rock area

TA Hills area

Western margin of basin

Tongue River area

Powder River area

Sample area

1

2

4

3

4

3

4

5

6

*Member of the Fort Union Formation.

flank of the Bighorn Mountains, as well as to maximize 

geographic distribution within the Tongue River Member. 

Only four impregnated thin sections were made from 

sandstones of the Wasatch; their modal grain compositions 

are compatible with sections prepared from disaggregated 

sand grains of the Wasatch. All Tongue River outcrop and 

core sandstones collected from east of Gillette (fig. 3) were 

too fine grained to be included in this study.

Apparent long axes of 50 quartz grains were measured in each thin section (Connor and Perm, 1966) using 

Chayes' mechanical point-counting technique (Chayes, 

1956; Griffiths, 1967). Students' t testing (0.05 level) of 

data from a small sample of the thin sections confirm that 50 

counts are adequate to ensure precise results.

The thin sections were then point counted for modal 

composition by Chayes' technique using at least 100 grain 

counts. Matrix and cement types were also tallied. Iterative 

chi-square testing (0.05 level) indicates that there is no 

significant difference in modal grain composition (quartz, 

feldspar, mica, rock fragments, matrix and cement) between 

75 and 100 framework grain counts for the most mineral - 

ogically complex sandstone samples. Hence, two totals are 

used in the analyses of modal composition: (1) total grains 

counted (more than 100 per thin section), and (2) total 

counts of grains plus matrix and cement (as many as 252 

counts per thin section). These point-count data are 

presented in tables 2-6.

Compositional Data Testing

Chi-square testing of enumeration data was used to 

define broad mineralogical facies and petrographic trends 

that occur vertically in the Fort Union and Wasatch 

Formations along the western margin of the basin and 

laterally within the Tongue River Member. Data were 

converted to percentage for Students' t, analysis of variance 

(ANOVA), and Duncan's multiple range (DMR) tests that 

were used in comparisons of individual mineral constituents. Before testing, percentage compositional data 

were treated with the standard mathematical transformation,

X = arcsin squareroot percent,

that is applied to binomially distributed data (Griffiths, 

1967) or to data whose variances are likely to be 

proportional to their means (Ostle, 1963). Individual test 

formats and results are given in Whipkey (1988).

SANDSTONE MINERALOGY OF THE 

BASIN

Classification

The lower Tertiary sandstones (table 2) of the Powder 

River Basin tend to be consistently rich in quartz and 

contain variable amounts of detrital chert, feldspar, and rock 

fragments (including carbonate grains). Samples from the 

Tullock, Lebo, and lower part of the Tongue River commonly contain moderate amounts of chert (as much as 23 

percent) and are sublitharenites of the chert-arenite variety 

(Folk, 1980). Sandstones of the upper part of the Tongue 

River also contain moderate amounts of chert (as much as 

20 percent) and substantial amounts of carbonate rock 

fragments (as much as 23 percent). They plot near Folk's 

boundary between calclithite and chert-arenite. The four 

samples from the Wasatch Formation are rich in feldspar; 

individual samples contain as much as 40 percent feldspar. 

Due to low levels of carbonate (less than 1 percent) and 

cherty (4 percent) rock fragments, they plot in the subarkose 

to arkose range.

Grain Types

Quartz

Quartz is the dominant detrital grain in the sandstones, and monocrystalline quartz is the most common 

type. Extinction varies from almost straight to strongly 

undulatory (table 3). Common inclusions include rutile

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D5
Table 2. Modal compositions of samples

[Sample localities shown on figures 4 and 7 by sample area number (see table 1. Rk. frag., rock fragments)]

Sample

number

1

Percentage of framework grains

Quartz

75

Feldspar

9

Rk. frag.

16

Mica

0

Other

TULLOCK*

0

Percentage of total sample

Grains

95

Cement

0

Matrix

5

n

106

LEBO*

2

3

4

5

74

65

78

83

2

10

8

7

22

24

13

10

1

1

0

0

1

0

1

0

56

90

95

86

43

1

2

0

1

9

3

14

180

114

105

116

LOWER PART OF TONGUE RIVER*

6

7

8

9

10

11

12

13

75

92

79

90

75

85

78

80

5

3

0

1

3

0

2

3

17

4

18

7

18

13

19

15

2

1

3

2

1

1

0

2

1

0

0

0

3

1

1

1

77

68

85

94

77

76

94

67

0

0

0

0

1

1

0

0

23

32

15

6

22

23

6

33

130

147

120

110

142

143

106

176

UPPER PART OF TONGUE RIVER*

14

15

16

17

18

19

20

21

22

23

24

25

26

93

73

77

61

65

66

73

69

65

69

57

70

66

4

0

5

2

4

3

1

4

2

1

4

1

2

3

27

18

34

29

27

24

24

31

30

37

27

31

0

0

0

0

0

1

0

0

0

0

0

0

1

0

0

0

4

2

3

2

3

2

0

2

2

0

71

76

72

71

93

73

84

85

84

97

76

86

86

0

20

13

3

2

4

0

3

2

0

6

2

3

29

4

14

25

5

23

16

13

13

3

18

11

11

141

131

138

154

115

151

125

119

128

121

136

125

132

WASATCH FORMATION

27

28

29

30

56

70

77

50

21

20

13

40

16

4

7

1

5

4

1

7

2

2

2

2

53

51

54

57

44

44

45

41

3

5

1

2

195

198

185

175

UPPER PART OF TONGUE RIVER*

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

56

58

54

72

57

57

56

68

60

62

50

63

67

44

72

8

21

7

9

7

10

7

15

9

16

4

18

4

11

6

35

16

34

18

33

31

35

14

29

22

41

15

10

42

20

0

1

4

1

2

1

0

0

2

0

2

2

2

1

0

1

4

1

0

0

1

2

4

0

1

3

1

17

2

2

81

74

66

40

78

89

73

58

54

52

70

81

79

87

62

9

11

17

57

18

2

1

38

42

47

21

3

9

5

36

10

15

17

3

4

9

26

4

4

1

9

16

12

8

2

124

136

152

252

127

112

138

189

188

198

149

129

135

118

179

*Member of the Fort Union Formation.

D6 Evolution of Sedimentary Basins Powder River Basin
Table 3. Quartz extinction types and feldspar twin types expressed as percentage of total framework grains

[Sample localities shown on figures 4 and 7 by sample area number (see table 1). Str., straight to slightly undulose; Undl., strongly undulatory;

Poly., polycrystalline grains with three or less component crystals (<3), or more than three crystalline structures (>3) in the grain]

Sample

number

Quartz extinction

Str. Undl. Poly. <3 Poly. >3

Feldspar twinning

Untwinned Gridded Albite

TULLOCK*

1 42 27 5 2 9 1 0

LEBO*

2

3

4

5

59

5

49

57

13

62

23

21

3

0

2

4

0

0

4

1

2

9

8

6

0

0

0

1

0

1

0

0

LOWER PART OF TONGUE RIVER*

6

7

8

9

10

11

12

13

42

68

67

86

51

68

50

76

19

22

9

6

23

19

20

11

6

1

2

1

3

3

4

3

8

1

3

0

6

3

4

4

5

3

0

1

3

0

2

3

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

UPPER PART OF TONGUE RIVER*

14

15

16

17

18

19

20

21

22

23

24

25

26

73

52

56

52

58

53

73

44

55

63

46

61

58

18

19

18

13

10

14

23

14

9

9

12

14

2

2

2

1

0

3

4

3

0

5

1

2

2

0

0

1

1

1

3

0

1

4

3

1

1

3

0

5

2

4

2

1

4

2

0

3

1

1

1

0

0

0

0

0

0

0

0

1

1

0

1

0

0

0

0

0

1

0

0

0

0

0

0

0

WASATCH FORMATION

27

28

29

30

38

45

57

33

15

17

12

12

1

4

4

3

4

5

4

2

20

19

12

35

1

0

1

1

1

1

0

4

UPPER PART OF TONGUE RIVER*

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

26

36

23

37

36

25

48

55

39

45

36

46

58

34

62

14

18

15

21

8

14

4

12

16

13

7

15

6

3

9

5

4

2

6

0

6

1

4

4

2

2

0

2

3

8

11

0

14

9

13

12

4

4

2

3

8

5

6

5

2

8

18

6

8

6

10

4

9

4

14

4

14

3

9

5

0

1

1

1

1

0

1

5

2

0

0

0

1

0

0

0

2

0

0

0

0

2

2

3

2

0

5

0

3

2

*Member of the Fort Union Formation.

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D7
Table 4. Rock-fragment types expressed as percentage of total framework grains 

[Sample localities shown on figures 4 and 7 by sample area number (see table 1)]

Sample

number

Granitie

rock fragments

Metamorphic Sedimentary rock fragments

rock fragments Silt/shale Carbonate Chert

Glauconite

present?

TULLOCK*

1 2 1 1 0 12 No

LEBO*

2

3

4

5

0

0

0

0

1

0

0

0

1

2

0

2

0

0

0

0

20

23

13

8

Yes

Yes

No

Yes

LOWER PART OF TONGUE RIVER*

6

7

8

9

10

11

12

13

0

0

0

0

0

0

0

0

2

0

0

0

2

0

0

1

2

0

0

0

1

0

0

4

0

0

0

0

0

0

0

0

13

4

18

7

17

14

19

13

Yes

No

No

No

No

Yes

Yes

Yes

UPPER PART OF TONGUE RIVER*

14

15

16

17

18

19

20

21

22

23

24

25

26

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1

0

7

0

0

0

1

0

0

0

0

0

0

1

0

0

6

5

2

0

0

2

18

15

17

16

16

18

14

23

15

13

22

21

0

9

3

20

15

12

7

3

4

15

23

6

14

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

WASATCH FORMATION

27

28

29

30

0

2

0

1

0

0

0

0

2

2

1

0

0

0

2

0

12

2

3

0

No

No

Yes

Yes

UPPER PART OF TONGUE RIVER*

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

3

0

1

1

2

0

1

2

0

0

0

0

0

0

1

4

1

3

5

7

6

0

0

0

1

0

4

2

0

0

3

0

7

2

5

6

7

1

3

4

6

2

3

12

2

9

8

12

0

5

8

7

4

4

5

26

0

1

14

6

16

7

11

10

14

11

20

8

22

12

11

10

5

17

13

No

No

Yes

No

Yes

No

Yes

No

No

No

Yes

Yes

No

No

No

*Member of the Fort Union Formation.

D8 Evolution of Sedimentary Basins Powder River Basin
Table 5. Grain counts of chert types (inclusions)

[Sample localities shown on figures 4 and 7 by sample area number (see table 1)]

Sample

number

Normal

(incl. free)

Carbonate

inclusions

Quartz

blebs Chalcedony Cloudy Clay

Aligned

mica

Detrital

grains Total

TULLOCK*

1 3 0 4 0 0 2 0 3 12

LEBO*

2

3

4

5

6

6

3

4

0

1

0

0

9

5

5

1

3

2

2

1

0

4

0

0

0

0

0

1

1

5

0

1

1

0

3

0

20

23

13

8

LOWER PART OF TONGUE RIVER*

6

7

8

9

10

11

12

13

4

2

5

4

8

2

5

6

2

0

0

0

0

1

0

0

2

1

3

3

7

2

5

1

0

1

0

0

0

0

0

0

2

0

0

0

0

6

0

0

3

0

5

0

2

3

0

3

0

0

5

0

0

0

0

3

0

0

0

0

0

0

0

0

13

4

18

7

17

14

10

13

UPPER PART OF TONGUE RIVER*

14

15

16

17

18

19

20

21

22

23

24

25

26

0

3

2

2

7

5

5

3

1

6

1

0

2

0

0

0

1

0

0

1

0

0

1

1

1

1

0

1

0

6

5

3

1

0

2

4

2

3

3

0

1

0

0

1

0

0

0

0

2

0

1

1

0

0

0

0

1

1

0

0

1

0

0

1

4

0

0

0

3

0

0

0

0

0

0

2

0

0

0

0

0

8

1

3

0

0

4

0

0

0

3

0

0

0

0

0

0

0

0

1

2

0

0

0

0

5

2

20

15

12

7

3

9

15

6

6

14

WASATCH FORMATION

27

28

29

30

3

1

2

0

0

0

0

0

4

0

0

0

0

0

0

0

4

0

1

0

1

0

0

0

0

0

0

0

0

1

0

0

12

2

3

0

UPPER PART OF TONGUE RIVER*

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

2

4

3

2

1

5

4

4

10

3

3

4

2

6

2

1

0

0

0

0

0

1

0

1

1

0

0

0

0

3

1

0

2

0

3

2

2

1

6

3

2

4

2

6

4

0

0

0

0

0

0

1

0

2

0

0

0

0

0

0

11

2

5

0

4

3

8

1

0

3

0

0

0

2

1

0

0

1

6

2

0

1

2

3

1

3

1

1

2

3

1

0

0

1

4

0

0

0

0

0

1

1

0

1

0

0

1

0

1

0

0

3

0

0

1

2

0

0

0

0

16

7

11

10

14

11

20

8

22

12

11

10

5

17

13

*Member of the Fort Union Formation.

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D9
Table 6. Quartz-grain apparent long axes (phi scale) and rounding (Powers' scale)

[Sample localities shown on figures 4 and 7 by sample area number (see table 1). n, is number of quartz grains measured]

Sample

number n

Quartz apparent

Mean ($.

long axes

) Sorting n

Quartz rounding

Power's

TULLOCK*

1 50 1.93 0.45 50 3.5

LEBO*

2

3

4

5

50

50

50

50

2.57

2.40

2.26

2.43

0.44

0.55

0.60

0.49

50

50

50

50

3.7

3.7

3.9

3.6

LOWER PART OF TONGUE RIVER*

6

7

8

9

10

11

12

13

50

50

50

50

50

50

50

50

2.31

2.84

2.99

2.91

3.16

2.86

2.30

2.42

0.60

0.58

0.45

0.43

0.49

0.60

0.61

0.61

50

50

50

50

50

50

50

50

3.4

3.8

3.5

3.4

3.3

3.3

3.5

3.4

UPPER PART OF TONGUE RIVER*

14

15

16

17

18

19

20

21

22

23

24

25

26

50

50

50

50

50

50

50

50

50

50

50

50

50

2.72

2.29

2.32

3.09

2.02

2.79

1.55

3.16

3.06

1.08

2.33

2.35

2.38

0.55

0.68

0.66

0.41

0.73

0.62

0.42

0.60

0.54

0.46

0.74

0.78

0.71

50

50

50

50

50

50

50

50

50

50

50

50

50

3.9

4.5

4.2

3.1

3.4

3.3

3.9

3.3

3.4

4.1

3.9

3.7

3.5

WASATCH FORMATION

27

28

29

30

50

50

50

50

2.26

2.57

1.64

1.87

0.62

0.62

0.74

0.56

50

50

50

50

3.7

3.1

3.8

3.4

UPPER PART OF TONGUE RIVER*

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

50

50

50

50

50

50

50

50

50

50

50

50

50

50

50

2.44

2.71

2.30

2.69

2.31

2.27

2.33

1.94

2.03

2.17

2.57

2.08

2.82

2.64

2.30

0.39

0.40

0.40

0.46

0.51

0.50

0.44

0.49

0.73

0.52

0.57

0.37

0.68

0.51

0.48

50

50

50

50

50

50

50

50

50

50

50

50

50

50

50

2.8

2.7

2.8

2.7

2.6

2.8

2.7

2.8

2.7

2.9

2.9

2.7

3.1

3.0

2.8

*Member of the Fort Union Formation.

needles, mica flakes, tourmaline, zircon, and various minor 

opaque minerals. Less common are inclusions of vermicular 

chlorite.

Semicomposite grains (Folk, 1980) are not common. 

Other varieties of polycrystalline quartz were divided into

two categories: those containing three or fewer crystals (that 

is, not in optical alignment) and those containing more than 

three crystals. Included in the latter group is schistose 

"stretched" polycrystalline quartz, which commonly 

contains aligned mica crystals and (or) crenulate subgrain

D10 Evolution of Sedimentary Basins Powder River Basin
boundaries. Polycrystalline quartz composed of three or 

fewer crystals is probably derived from granitic or highrank metamorphic source terranes (Basu and others, 1975).

Feldspar

Untwinned feldspar, generally orthoclase, is the most 

common type of feldspar (table 3). Albite and carlsbadalbite feldspar twins were identified simply as plagioclase. 

Gridiron (tartan) twinned feldspars were assumed to be 

microcline. Perthitic grains are relatively rare. Alteration 

due to sericitization and replacement by calcium carbonate 

is common, especially in samples of the upper part of the 

Tongue River and the Wasatch. If identifiable, a partially 

replaced grain was counted as the original grain. A few 

feldspar overgrowths were observed.

Granitic Rock Fragments

Granitic rock fragments (GRF's) (table 4) were 

distinguished by the presence of relatively large interlocked 

crystals of quartz and feldspar, with or without mafic 

minerals or mica. These are the products of either granitic or 

gneissic source terranes. Few were noted, probably in part 

because of the fine grain size of the sandstones.

Metamorphic Rock Fragments and Mica

Common phyllosilicate minerals include muscovite 

and biotite booklets, which are present in almost all 

samples, and chlorite, which is much less common. Schistose and phyllitic metamorphic rock fragments (MRF's) 

(table 4) were identified by the parallel orientation and 

relatively large size of their constituent mica crystals. Slate 

fragments are very fine grained and difficult to distinguish 

from intraformational shale grains (relict "clay balls"). 

These were therefore combined into a single category 

(low-grade MRF's) unless other evidence, such as included 

detrital quartz silt, was observed.

Sedimentary Rock Fragments

A wide variety of chert and siliceous grains forms a 

major category of sedimentary rock fragments (SRF's). The 

grains were grouped into eight basic types, based partly on 

the presence and nature of mineral inclusions (table 5): 

(1) clean, inclusion-free chert; (2) chert containing calcium 

carbonate fragments, which probably are remnants of the 

replacement of limestone or dolomite; (3) chert containing 

small "blebs" of megaquartz that probably is recrystallized 

chert because of its clarity, irregular shape, and gradational 

boundaries with the surrounding microcrystalline quartz;

(4) grains composed partly or totally of chalcedony;

(5) siliceous rock fragments ("cloudy chert") that contain 

dispersed, very fine grained clay or mud; chert containing

significant coarse clay or fine-grained mica in (6) random or 

preferred (7) orientation; and (8) chert containing detrital 

grains (silt-size quartz or mica).

Detrital calcium carbonate grains are a major SRF 

type (table 4). Both micritic and sparry calcite are common. 

The latter was commonly recognized by its aggregate nature 

or rhombic habit.

Some shale fragments were distinguished from slate 

by the inclusion of silt-size detrital quartz. Siltstone, 

although fine grained, commonly was distinguished from 

metaquartzite by the presence of intergranular clayey matrix 

material within the rock fragment. These SRF's are also 

designated on table 4.

Glauconite

Detrital glauconite is a common trace constituent 

(table 4) and was identified by its pelletlike shape, aggregate 

nature, and green absorption color, which masks birefringence. Some glauconite is surrounded by a reddish rim of 

oxidized iron that has been leached from the grain. 

Although generally found as a discrete grain, in a very few 

samples several glauconite pellets were within single detrital calcite grains.

Glauconite is thought to form only in marine environments (Folk, 1980). Although not a durable mineral, it is 

reported to survive limited sedimentary transport and has 

thus been found in nonmarine sedimentary rocks (Galliher, 

1935; Pettijohn and others, 1972; Selley, 1978). Survival 

during prolonged transportation is not likely, however, 

because of its unstable nature, and its presence in a 

freshwater deposit is a reliable indicator of short, rapid 

transport and quick burial.

Cementation and Diagenesis

Calcium carbonate in the form of calcite is the most 

common cementing agent. It makes up more than 40 percent 

by volume of each of the Wasatch samples but generally 

less than 6 percent of the Paleocene rocks along the western 

margin of the basin (samples 1-30, table 2). Calcite cement 

probably formed as a result of recrystallization of detrital 

calcium carbonate grains or as a result of their dissolution 

and subsequent calcite precipitation. Evidence to support 

these possibilities includes the large size of many cementfilled pores, which indicates that their volume was once 

occupied by grains. Partly recrystallized (or dissolved) 

detrital carbonate was found embedded within the cement of 

some samples.

Partial replacement of feldspar and, to a much lesser 

extent, quartz by calcite cement is fairly common, 

especially in the Wasatch samples, which are very rich in 

both feldspar grains and carbonate cement. In some 

samples, ghosts of twinned former plagioclase grains 

indicate that replacement was almost complete.

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D11
Some samples contain small amounts of silica or 

feldspar as overgrowths, and authigenic clay was noted in 

very few samples; however, these materials are very minor 

cementing agents. No evidence of fine-clay matrix grading 

to larger clay or mica crystals was found.

VERTICAL CHANGES IN 

PETROGRAPHIC FACIES OF 

LOWER TERTIARY SANDSTONES

Sample Localities

Samples from the Paleocene Fort Union and the 

Eocene Wasatch Formations were collected at outcrops 

along the western margin of the basin (fig. 4) in an attempt 

to document the time of Tertiary uplift of the Bighorn 

Mountains. Sample localities were selected as close as 

possible to the uplift in order to minimize the possibility 

of contamination of the samples with detritus from other 

sources and to ensure the least possible modification of 

the mineralogy of the samples due to the effects of paleotransport.

107

43° 

42'

50 MILES

Figure 4. Sample areas used to determine vertical variation in 

mineralogy in the western Powder River Basin. Areas 1 and 2 

are referred to in text as southwestern basin, area 3 as TA Hills 

area, and area 4 as Castle Rock area. Sample numbers for areas 

given in table 1.

The Tullock Member of the Fort Union Formation is 

the lowermost Tertiary unit of the Powder River Basin, and 

some studies suggest that the basin did not exist during 

deposition of this unit (see, for example, Curry, 1971). 

Because paleocurrent directions in the Tullock are controversial (see, for examples, Flores and Ethridge, 1985; 

Ayers, 1986), only one crossbedded channel sandstone 

(area 1, fig. 4) was collected from this interval as a check for 

consistency with the younger sandstones.

Samples of the Lebo Member (middle Paleocene) 

were collected from four localities in areas 1 and 2 (fig. 4). 

The Lebo is a mudstone-dominated lacustrine unit along the 

western margin of the basin but contains some coarse to 

pebbly, crossbedded, channelized sandstone.

Unlike the Tullock and Lebo, the upper Paleocene 

Tongue River Member is rather extensively exposed. 

Samples of the lower part of the Tongue River were 

collected at several localities in the southwestern part of the 

basin (areas 1 and 2, fig. 4), as well as from pebbly channel 

sandstones of the TA Hills (area 3). An upper, conglomeratic facies of the member (Weaver and Flores, 1985) 

also was sampled (area 4, fig. 4).

Samples from sandy parts of the Kingsbury Conglomerate Member and the Moncrief Member of the Eocene 

Wasatch Formation were also collected along the western 

margin of the basin near Castle Rock (area 4, fig. 4). 

Pebbles and cobbles in the Kingsbury, a distal fan deposit, 

are composed predominantly of chert and carbonate but also 

contain rare granitic fragments (Hose, 1955). The Moncrief, 

a proximal fan deposit, contains mainly coarse sandstone 

and granitic and gneissic cobbles and boulders.

- Petrographic Facies

Three stratigraphically sequential petrographic facies 

are apparent on the ternary diagram of figure 5. The diagram 

contains the poles Q (quartz and chert), F (feldspar and 

granitic rock fragments), and L (lithic fragments, including 

carbonate grains). Quartz (including polycrystalline quartz) 

and chert were placed at the same pole (Q) because of their 

stability during transport and because of their possible 

significance concerning source terrane. Feldspar and 

granitic rock fragments (GRF's) were placed at a second 

pole (F) because of their utility as possible indicators of 

intrusive igneous or higher grade metamorphic source 

terranes. Very few GRF's are actually present, so their 

inclusion at the F pole has a negligible effect on the ternary 

plots. Unstable lithic fragments (L) include metamorphic 

rock fragments (MRF's) and sedimentary rock fragments 

(SRF's). Although detrital carbonate grains are commonly 

excluded from ternary plots because of their instability and 

the possible ambiguity as to their source, they were included

D12 Evolution of Sedimentary Basins Powder River Basin
Figure 5. Ternary diagram showing the composition of 

sandstones along the western margin of the Powder River 

Basin. Petrographic facies (described in text): solid circle 

indicates upper facies; open square indicates middle facies; 

open circle indicates lower facies. Q indicates quartz plus 

chert; F indicates feldspar plus granitic rock fragments; L 

indicates lithic fragments.

as lithic fragments because (1) they are very common in 

some samples, and (2) limestone and dolomite beds 

comprise much of the Paleozoic sequence in nearby 

potential source areas.

One petrographic facies forms a cluster very near the 

quartz (Q) pole. It includes the Tullock and Lebo Members 

and the lower part of the Tongue River Member. Samples 

from the upper part of the Tongue River form a middle 

facies, which, as a whole, plots more toward the lithic 

fragments (L) pole. Samples of the Wasatch Formation 

comprise a third facies marked by abundant feldspar and 

relatively low rock-fragment content. Chi-square testing 

(0.05 level) confirms that significant mineralogical 

differences exist between the three facies, primarily due to 

the higher amounts of feldspar in the upper facies and 

carbonate fragments in the middle facies.

Textures

The samples were selected in the field to be relatively 

uniform in grain size (table 6). Most samples were in the 

fine sand range (2-3 phi), although a few are in the medium 

sand range (1-2 phi). Based on 50 measurements per thin 

section of quartz apparent long axes, mean values for the 

three petrographic facies are lower, 2.56 phi (s=0.35 phi); 

middle, 2.40 phi (s=0.60 phi); and upper, 2.08 phi (s=0.41). 

No major differences were observed in quartz grain 

roundness between the three petrographic facies. Average 

numerical values (Power's scale, in Folk, 1980) based on 50

observations per thin section are lower, 3.5; middle, 3.7; and 

upper, 3.5. Thus, most grains are in Power's subrounded 

range. The sandstones contain substantial amounts of matrix 

material (as much as 33 percent) and thus are texturally 

immature. This type of textural inversion (Folk, 1980) can 

be caused by relatively short transport of recycled 

sedimentary strata.

Mineralogy

Plots of percentage composition of individual mineral 

constituents (fig. 6) expand and illuminate trends shown in 

the ternary diagram. The lower (quartzose) facies is 

represented by samples 1-13. Note in particular the lack of 

carbonate grains. The increase in rock fragments in the 

middle facies (samples 14-26) is due mainly to an abrupt 

and large increase in detrital carbonate grains (calcite and 

dolomite). The upper facies (samples 27-30) is marked by 

a substantial increase in feldspar and mica. Cherty fragments and, to a much greater extent, carbonate fragments 

decrease in this facies. Carbonate cement is very prominent 

in the upper facies.

Quartz

Total quartz in the lower petrographic facies is almost 

80 percent (s=7.2 percent) of framework grains but only 

69.5 percent (s=8.8 percent) in the middle facies. Total 

quartz (63 percent, s=12.4 percent) is also low in the upper 

(Wasatch Formation) facies. ANOVA-DMR tests (0.05 

level) of transformed data indicate that total quartz 

decreases significantly between the lower and upper facies. 

Polycrystalline quartz (including metamorphic quartz) 

accounts for 6.4 and 4.4 percent of total quartz in the lower 

and middle facies, respectively, and 10.3 percent in the 

upper facies (significant in ANOVA-DMR tests, 0.05 

level).

The decrease in total quartz above the lower petrographic facies reflects the increase in carbonate rock 

fragments in the middle and upper facies and feldspar in the 

upper facies. The moderate increase in polycrystalline 

quartz in the upper facies may be attributed either to shorter 

transport distances (these Wasatch Formation samples are 

from alluvial fans) or to deeper erosion levels in the igneousmetamorphic core of the Bighorn Mountains.

Carbonate Rock Fragments

The detrital carbonate content of the lower quartz-rich 

petrographic facies is almost zero. The upward decrease in 

quartz in the middle facies (upper part of the Tongue River 

Member) is accompanied by an increase in detrital 

carbonate (calcite and (or) dolomite) to more than 15 

percent (s=2.9 percent) of framework grains. Detrital

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D13
Rock unit Sample 

number

Percentage of framework grains

Quartz Feldspar Mica Carbonate 

40 100 0 40 0 10 0 40

Chert Glauconite 

0 40 present?

Other constituents

Matrix Cement 

0 50 0 60

Wasatch 

Formation

30

29

28

27

Tongue

River

Member

26

25

24

23

22

21

20

19

18

17

16

15

14

Lebo 

Member

Tullock 

Member

13

12

11

10

9

8

7

6

5

4

3

2

1

I

Figure 6. Point-count data for sandstones from the western margin of the Powder River Basin. Clastic grains are given as 

percentages of total framework grains; matrix and cement are given as percentages of the total volume of the sample. The presence 

of detrital glauconite (always less than 1 percent) is indicated. Point-count values are given in tables 2-6.

carbonate content then drops to a very low level (less than 

1 percent) in the upper facies. ANOVA-DMR tests (0.05 

level) confirm that detrital carbonate is significantly more 

abundant in the middle facies than in either the lower or 

upper facies.

The most likely source of the large quantities of 

carbonate fragments in the middle facies is the extensive 

Paleozoic limestone and dolomite beds of the Bighorn 

Mountains. The drastic decrease in detrital carbonate in the 

upper facies may be related to the greatly increased abundance of calcite cement.

Cherty Fragments

Chert makes up about 13.5 percent of framework 

grains in the lower petrographic facies, 9.5 percent in the 

middle facies, and only about 4 percent in the upper facies. 

ANOVA-DMR tests detect significant differences (0.05 

level) only between the lower and upper facies. Cherty 

fragments are very diverse in these facies (table 5). Normal 

microcrystalline chert is most common, but chalcedony and 

grains containing various inclusions are also present. Too 

few chert grains were tabulated in point counts for statistical 

tests between the different varieties. Subjectively, the data 

do suggest that samples of the Tullock and Lebo contain 

slightly more chalcedony than those of the overlying

Tongue River and Wasatch. Chert grains of the middle 

facies more commonly have carbonate inclusions than those 

of the other facies.

Feldspar

Untwinned feldspar (generally orthoclase, 91 percent 

of total feldspar) is most common, but smaller amounts of 

grid-twinned (microcline, 5 percent) and albite-twinned 

(plagioclase, 4 percent) feldspar also are present. A few 

perthitic grains were noted. No systematic vertical changes 

in feldspar types were observed.

Feldspar is a very minor component in the Paleocene 

sandstones, only about 3 percent of framework grains in the 

lower and middle facies; however, it makes up more than 23 

percent of grains in the upper facies (significant on 

ANOVA-DMR, 0.05 level). In rocks of the upper facies, 

feldspar has been diagenetically replaced by calcite cement, 

and thus these percentages may be lower than the original 

feldspar content.

The increase in feldspar in the upper facies is 

probably associated with erosion of the Precambrian core of 

the uplift. This inference is supported by the previously 

noted concurrent increase in polycrystalline quartz. The 

relatively low quantities of feldspar in the lower and middle 

facies may have been derived from recycled Paleozoic and 

Mesozoic arkosic sandstones.

D14 Evolution of Sedimentary Basins Powder River Basin
Mica

Muscovite, as well-developed booklets, is the most 

common mica; biotite and chlorite are less common. Mica 

content is less than 1 percent in the lower and middle facies 

(a few samples contain as much as 3 percent) and only 4 

percent in the upper facies. The increase in well-developed 

mica booklets in the upper facies (significant on ANOVADMR tests, 0.05 level) agrees with the preceding evidence 

for Eocene exposure of the Precambrian granitic and 

gneissic core of the Bighorn Mountains.

Other Rock Fragments

Rock fragments other than chert and carbonate are not 

abundant in these rocks. Rocks of the upper facies contain 

a few (1-2 percent) granitic fragments, and one sample of 

the Tullock contains 2 percent granitic fragments.

Sedimentary rock fragments, as well as high-grade 

(schistose) and low-grade (phyllitic and slate) metamorphic 

rock fragments, are present in small amounts (generally less 

than 2 percent) throughout the interval. These amounts are 

well within the range of phyllite rock fragments reported by 

Merin and Lindholm (1986) from the basin center.

Glauconite

Glauconite is present in all samples of the Tongue 

River and Wasatch, although always in volumes of less than 

1 percent of the grains. It most probably was derived from 

the nearby, friable, glauconite-bearing Mesozoic strata of 

the eastern Bighorn Mountains. Although difficult to 

characterize quantitatively because of the small amounts, 

glauconite probably is much more common in the middle 

petrographic facies than in either of the others.

Discussion and Interpretation

The three vertically sequential sandstone petrographic 

facies along the western margin of the Powder River Basin 

are characteristic of progressive uplift and erosion of a 

basement-cored structure; however, they are mineralogically very similar. The same basic grain types are present in 

all facies, and differences are in relative proportion rather 

than kind. This compositional similarity strongly suggests 

that the Fort Union and Wasatch sedimentary rocks have, at 

least in part, a common provenance. Because the conglomerates of the Wasatch Formation (Kingsbury Conglomerate Member and Moncrief Member) are well 

established as alluvial fan deposits shed from the eastern 

front of the Bighorn Mountains (Sharp, 1948; Mapel, 1959), 

the similarity argues that the provenance of the Tongue 

River also is the Bighorn Mountains (Whipkey and others, 

1987). Such a conclusion is bolstered by the proximity of 

Tongue River outcrops to the uplift margin, by sedimentary

structures indicating eastward paleotransport in the TA Hills 

(Weaver and Flores, 1985), by the ubiquitous presence of 

nondurable glauconite grains, and by the pebbly to conglomeratic character of many sandstones of the upper part 

of the Fort Union Formation.

Lower Petrographic Facies

The lowest petrographic episode consists of accumulation of large amounts of rounded, monocrystalline, probably recycled quartz in sandstones of both the Lebo and the 

lower part of the Tongue River Members of the Fort Union 

Formation. This mineralogy is consistent with the sample 

from the Tullock Member of the Fort Union. The channel 

sandstones contain subordinate chert grains, and many 

contain trace amounts of detrital glauconite, a mineral that 

is unstable during freshwater transport. This characteristic 

mineralogy strongly indicates proximity to a source of 

friable clastic sedimentary strata, some of which contain 

appreciable amounts of glauconite. Local chert-pebble conglomeratic lenses in channelized sandstones of both the 

Lebo and the lower part of the Tongue River indicate that 

fairly competent, high-gradient drainage systems existed 

adjacent to the present Bighorn Mountains in both middle 

and late Paleocene time.

These observations all point to the start of uplift and 

erosion of the Bighorn Mountains by at least middle 

Paleocene time. The body of friable Mesozoic strata that 

formerly overlaid the mountains is the probable source of 

much of the sediment associated with sandstones of the 

lower petrographic facies. Sandy Cretaceous strata (Lance 

Formation) may have been stripped to provide sands to the 

Tullock depositional sites, whereas thick, younger Cretaceous shales provided a local source for the voluminous 

lacustrine mudstones of the Lebo Member. Younger quartzdominated channel sandstones of the lower part of the 

Tongue River Member reflect erosion of the more sandstone 

dominated lower Mesozoic rocks in the mountains. The 

abundant cherty pebbles in the conglomeratic channels of 

the Tongue River, as well as the large amounts of chert in 

the sand fraction of those rocks, are difficult to explain at 

this time. Erosion of one of the locally chert rich areas of the 

Lower Cretaceous Cleverly Formation is a one explanation. 

Another is deep tributary dissection along the front of the 

uplift that may locally have exposed more deeply buried 

cherty rocks of the Paleozoic marine sequence. Such deeply 

entrenched tributaries characterize the present-day eastern 

slope of the Bighorn Mountains.

Middle Petrographic Facies

A marked increase in carbonate rock fragments 

(calcite and dolomite) is the distinctive feature of the middle 

petrographic facies (upper part of the Tongue River

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D15
Member). Quartz, although less common, retains the 

rounded, monocrystalline character of the lower facies. 

Chert continues to be a relatively constant subordinate grain 

type. Fragments of carbonate in some chert grains suggest 

that the chert represents replacement of limestone or 

dolomite in the source rock area. Glauconite is also a 

ubiquitous trace mineral that, at times, is present within 

carbonate grains.

Paleocurrent measurements of channel sandstones in 

the TA Hills (area 3, fig. 4) indicate an eastward-flowing 

drainage network (Weaver and Flores, 1985). The coarseness of these sandstones suggests that the stream gradient 

was relatively high. The high stream gradient and the 

relatively high detrital carbonate content indicate that by the 

time of deposition of the upper part of the Tongue River 

continued uplift of the Bighorn Mountains had exposed the 

carbonate-rich Paleozoic sequence to extensive erosion. 

Concurrent erosion of previously exposed clastic-rich 

Mesozoic strata continued to supply quartz, glauconite, and 

finer grained detritus into these fluvial systems.

Upper Petrographic Facies

Feldspar is a major framework grain type in the 

sandstones of the upper petrographic facies (Wasatch 

Formation), and mica booklets are a common minor 

component. Detrital carbonate and chert grains, which are 

abundnant in the middle facies, are relatively unimportant. 

The sudden decrease in carbonate grains may be explained 

in part by dissolution and subsequent recrystallization to 

form the abundant carbonate cement in the Wasatch 

Formation. Rounded, monocrystalline quartz is the major 

quartz type, but polycrystalline varieties are proportionally 

more abundant than in the other two facies. As in the other 

facies, detrital glauconite is a distinctive trace mineral.

This change in mineralogy, particularly the increases 

in amounts of feldspar and mica, strongly suggests renewed 

uplift and widespread exposure of the intrusive igneous and 

high-grade metamorphic core of the Bighorn Mountains 

during deposition of the Wasatch Formation. This renewed 

uplift may reflect major thrusting reported by Grow and 

others (1988) along the mountain front northwest of Buffalo 

(fig. 1) that juxtaposed Precambrian igneous gneiss atop the 

Fort Union Formation.

LATERAL VARIATION WITHIN THE 

TONGUE RIVER MEMBER

Sample Localities

Rocks now exposed along the crest of the Bighorn 

Mountains in Wyoming (fig. 3) are Paleozoic carbonate 

rocks in the south and Precambrian crystalline rocks in the

north. Samples were collected from outcrops of the Tongue 

River Member within three general areas along the Bighorn 

Mountains (areas 3, 4, and 5 of fig. 7) in order to determine 

if a corresponding mineralogical change could be detected. 

These samples were restricted to the upper, detritalcarbonate-enriched-sandstone part of the Tongue River in 

the TA Hills (area 3) and the Castle Rock vicinity (area 4). 

Channel-fill sandstones of the Tongue River (area 5), 

showing north to northeast paleotransport directions (Toth, 

1982), were sampled from both the middle and upper parts 

of the Tongue River Member. Preliminary paleobotanical 

correlations suggest that the base of the carbonate-bearing 

sandstones is correlative between areas 3 and 4 but is older 

northward, toward area 5.

Additional sandstone samples were collected from the 

valley of the Powder River (area 6, fig. 7) to determine 

whether the mineralogy of Tongue River channel fills in the 

center of the basin is compatible with eastward transport 

from the Bighorn uplift. Here, paleotransport of channel 

sandstones ranges from northeast to southeast (Canavello, 

1980; Lynn, 1980).

Sandstone Mineralogy Groupings

Sandstone samples from the TA Hills and Castle 

Rock areas (areas 3 and 4), which were obtained from the

107° 105°

50 MILES

Figure 7. Sample areas used to determine lateral variation in 

mineralogy of the Tongue River Member of the Fort Union 

Formation in the Powder River Basin. Sample numbers for 

areas are given in table 1.

D16 Evolution of Sedimentary Basins Powder River Basin
Figure 8. Ternary diagram showing the composition of 

sandstones from the Tongue River Member of the Fort Union 

Formation in the Powder River Basin. Areas: open circle 

indicates west-central areas; solid circle indicates Powder 

River valley of the northern areas; solid square indicates 

Tongue River valley of the northern areas. Q indicates quartz 

plus chert; F indicates feldspar plus granitic rock fragments; L 

indicates lithic fragments.

carbonate-enriched middle petrographic facies (upper part 

of Tongue River Member) described earlier, plot very near 

to the Q-L line on the ternary diagram (fig. 8). The 

remaining samples, from the Tongue River and Powder 

River valleys (areas 5 and 6), form a statistically distinct 

(chi-square, 0.05 level) dispersed group of sandstones. 

Although these samples contain carbonate grains, they are 

also markedly enriched in feldspar grains.

No difference can be detected using either figure 8 or 

chi-square tests between the modal mineralogy of sandstones of the Tongue River and Powder River valleys or 

between that of the TA Hills and Castle Rock areas. Data 

from these areas are therefore pooled into "northern areas" 

and "west-central areas," respectively, in much of the 

following discussion.

Textures

Mean grain size (table 6) is uniformly in the fine sand 

range (2-3 phi). Mean grain size for samples from the 

Tongue River and Powder River drainages (northern areas) 

is 2.45 phi (s=0.20 phi) and 2.32 phi (s=0.30 phi), 

respectively; whereas, that for samples from the TA Hills 

and Castle Rock areas (west-central areas) are 2.53 phi 

(s=0.6 phi) and 2.50 phi (s=0.26 phi).

Rounding of grains is markedly different in the 

west-central areas and the northern areas. Quartz grains 

from the northern areas are subangular (average rho=2.8

and 2.7 for the Tongue River and Powder River drainages, 

respectively, on Power's scale), whereas those from the 

west-central areas are more commonly subrounded (average 

rho=3.5 and 4.0 for the TA Hills and Castle Rock areas, 

respectively).

Mineralogy

General trends noted on the ternary diagram are 

shown in more detail in the plot of major mineral 

constituents (fig. 9). Sandstones from the Powder River and 

Tongue River drainages (samples 31^-5) of the northern 

areas are considerably enriched in feldspar and moderately 

rich in mica booklets and rock fragments (other than chert 

and carbonate). On the other hand, sandstones from the TA 

Hills (samples 17-26) and Castle Rock (samples 14-16) of 

the west-central areas contain more carbonate rock 

fragments and quartz.

Quartz

The mean quartz content of carbonate-bearing facies 

of the west-central areas is 69.5 percent (s=8.8 percent); 

polycrystalline quartz accounts for 5.6 percent of this total 

(table 4). The quartz content in the northern areas is 

significantly less (t-test, 0.05 level), 59.7 percent (s=7.8 

percent) of framework grains. Polycrystalline quartz, 

however, is distinctly more abundant (ANOVA-DMR, 0.05 

level) in the northern areas, where it is 16.3 percent (s=8.6 

percent) of the total quartz. The proportion of polycrystalline quartz within the northern areas decreases significantly 

eastward (ANOVA-DMR, 0.05 level) between the Tongue 

River (23.4 percent of quartz; s=9.1 percent) and the 

Powder River drainages (11.6 percent of total quartz; s=4.1 

percent).

The lower total quartz content in the northern areas 

reflects the higher proportion of feldspar, mica, and micaceous rock fragments. The concurrent proportional increase 

in the percentage of polycrystalline quartz indicates that 

much of the detritus was derived from first-cycle erosion of 

nearby granitic or high-grade metamorphic terranes. The 

basinward decrease in polycrystalline quartz content 

(Powder River valley) suggests longer transport distances, 

consistent with reported eastward paleocurrent indicators.

Feldspar

Untwinned varieties of feldspar (generally orthoclase) 

make up 80 percent of the total feldspar. Grid-twinned 

(microcline; 8.5 percent) and albite-twinned (plagioclase; 

11.6 percent) feldspar and perthite are less common 

(table 4). Feldspar grains in rocks of the Tongue River 

Member of the northern areas have been replaced by 

carbonate cement, as discussed earlier in the discussion of

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D17
Sample location Sample 

number

Percentage of framework grains

Quartz Feldspar Mica Carbonate 

40 100 0 40 0 10 0 40

Chert

Glauconite 

present?

40

Other constituents

Matrix Cement 

0 50 0 60

Powder River 

Valley

45

44

43

42

41

40

39

38

37

Tongue River 

Valley

36

35

34

33

32

Castle Rock 

area

16

15

JL4_

TA Hills area

26

25

24

23

22

21

20

19

18

17

Figure 9. Point-count data for the Tongue River Member of the Fort Union Formation, Powder River Basin. Clastic grains are 

expressed as percentages of total framework grains; matrix and cement are represented as percentages of the total volume of the 

sample. The presence of glauconite (always less than 1 percent) is indicated. Point-count values are given in tables 2-6.

samples of the upper petrographic facies. Partly consumed 

grains are common, and some of the grains may be totally 

replaced. Therefore, the content of feldspar actually 

determined for the northern areas probably represents a 

minimum value.

Feldspar content increases markedly northward. Feldspar makes up about 2 percent of framework grains in 

sandstones of the west-central areas, detectably (t-test, 0.05 

level) less than an average of 10.1 percent in the northern 

areas (an individual thin section contains as much as 21 

percent). No basinward differences could be detected (t-test, 

0.05 level) between the two areas of the northern areas.

Feldspar distribution in the upper sandstones of the 

Tongue River probably is closely related to rock types now 

exposed in the Bighorn Mountains. Granitic and high-grade 

metamorphic rocks crop out in the northern part of the uplift 

in Wyoming (fig. 3), whereas Paleozoic rocks cap the 

southern part. The TA Hills sample area is approximately 

east of the present-day surface contact of these two rock 

types. One fault block lying to the west of the Castle Rock 

sample area does expose Precambrian basement, but much 

of the movement along its underlying fault(s) postdates the 

early Tertiary.

Mica

Mica booklets are a minor component of Tongue 

River Member rocks. They make up less than 1 percent of

the framework grains in the west-central areas and slightly 

more than 1 percent in the northern areas. The most 

common types of mica are muscovite, biotite, and chlorite. 

The small amounts of mica are compatible with the lack of 

major outcrops of schistose rocks in the northern Bighorn 

Mountains.

Cherty Fragments

No major variations in total chert content were noted 

between the sampled areas, although the amount of chert 

varies considerably from sample to sample (table 5). Mean 

content of cherty rock fragments is 10.1 percent (s=7.1 

percent) in the west-central areas and 12.5 percent (s=4.7 

percent) in the northern areas.

Carbonate Rock Fragments

Carbonate clasts are significantly (t-test, 0.05 level) 

less common (less than 7 percent) in the northern areas than 

in the west-central areas, perhaps in part because of dissolution of carbonate grains to form the carbonate cement 

common (fig. 9) in sandstones of the northern areas. In great 

part, however, the lesser amounts of carbonate grains 

probably reflect the smaller outcrop areas of carbonate rock 

types in the northern area of the uplift during uncovering of 

the Precambrian crystalline rocks. A more rapid rate of 

erosion in the northern Bighorn Mountains may also

D18 Evolution of Sedimentary Basins Powder River Basin
explain the presence of carbonate fragments stratigraphically lower in the north than along the west-central basin 

margin.

quartz. Similarly, the apparent paucity of sandstones as 

coarse as fine to medium grained east of Gillette can be 

explained by such a paleogeographic model.

Other Rock Fragments

Rock fragments other than carbonate and chert are 

more abundant in the northern areas (more than 8 percent) 

than in the west-central areas (about 2 percent). These 

consist primarily of high-grade (schistose) and low-grade 

(phyllitic and slaty) metamorphic rock fragments and some 

shale fragments and a few granitic rock fragments. Similar 

to the variation in carbonate content, this difference in 

abundance probably mirrors the exposed rocks of the 

adjacent uplift.

Within the northern areas, rock fragment content 

detectably decreases eastward (t-test, 0.05 level) from the 

Tongue River valley (about 10 percent) to the Powder River 

valley (about 5 percent). Similar to the equivalent eastward 

decrease in polycrystalline quartz, this decrease may be 

caused by progressive destruction with increased transport 

distance (Davies and Ethridge, 1975).

Glauconite

Glauconite is present in trace amounts in all of the 

samples from the west-central areas but in only 6 of 15 

samples from the northern areas. This difference can be 

explained by the proximity of the basin-margin sandstones 

to probable Mesozoic-age source rocks.

Discussion and Interpretation

Changes in sandstone mineralogy within the 

carbonate-bearing facies of the Tongue River Member of 

the west-central areas closely parallel differences in potential source rocks now exposed along the crest of the Bighorn 

Mountains. In the south, only the Bighorn Mountains 

Phanerozoic cover rocks were eroded and transported into 

the west-central areas. In the north, the greater amounts of 

feldspar, metamorphic rock fragments, and polycrystalline 

quartz suggest that detritus from exposed intrusive and 

high-grade metamorphic rocks was being deposited in the 

northern part of the basin.

Westward-flowing paleotransport for the Tongue 

River Member (for example, Ayers, 1986) is unlikely to 

have introduced basement-derived feldspathic detritus into 

the northern part of the basin because there are few outcrops 

of coarsely crystalline intrusive or metamorphic potential 

source rocks in the Black Hills. The reported generally 

northeastward paleotransport directions (Canavello, 1980; 

Lynn, 1980; Toth, 1982) for the interval are consistent with 

the easterly decline in mechanically less durable grain types 

such as metamorphic rock fragments and polycrystalline

SUMMARY AND CONCLUSIONS

Early Tertiary deposition within the Powder River 

Basin in Wyoming was strongly dependent upon an episode 

of tectonic uplift of the Bighorn Mountains that extended 

from at least middle Paleocene into Eocene time. Grain 

types derived from the erosion of this uplift indicate that the 

northerly change from exposed Paleozoic strata to Precambrian core along the present-day crest of the Bighorn 

Mountains developed during this early Tertiary tectonic 

episode.

Subsidence along the western margin of the basin was 

in progress by the middle Paleocene and led to the formation of the extensive Lebo lake. Mud-dominated sediments 

of the lake probably reflect early transfer of large volumes 

of uplifted Cretaceous shale from the mountains into the 

western flank of the basin. Pebbly sand channel fills in 

lacustrine mudstones of the Lebo Member along the western 

margin of the basin attest to substantial local relief 

associated with deeply entrenched drainage tributaries.

By late Paleocene time, the subsidence rate for the 

basin was more closely matched by the rate of detrital 

influx, and sandy fluvial systems of the Tongue River 

Member prograded eastward into the central part of the 

basin. Paleozoic marine sequences exposed in the southern 

mountains provided carbonate-rich sands to the fluvial 

systems of the upper part of the Tongue River along the 

west-central basin margin. Uplift and erosion probably was 

greater in the northern Bighorn Mountains. Stratigraphically 

equivalent channels in the adjacent northern basin area 

transported feldspar grains, coarse mica, metamorphic rock 

fragments, and complex quartz types in sands derived from 

the Precambrian core of the uplift.

Renewed uplift of the Bighorn Mountains during the 

Eocene (Grow and others, 1988) led to deposition of the 

conglomerates of the Kingsbury Conglomerate Member and 

Moncrief Member of the Wasatch Formation along the 

eastern flank of the mountains (Seeland, 1985). Feldspathic 

sandstones of the Wasatch Formation, deposited by a 

network of eastward-flowing fluvial systems, characterize 

Eocene rocks across most of the western half of the Powder 

River Basin.

REFERENCES CITED

Ayers, W.B., 1986, Lacustrine and fluvial-deltaic depositional 

systems, Fort Union Formation (Paleocene), Powder River 

Basin, Wyoming and Montana: American Association of 

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Basu, A., Young, S.W., Suttner, L.J., James, W.C., and Mack, 

G.H., 1975, Re-evaluation of the use of undulatory

Sandstone Provenance, Bighorn Mountains, Wyoming and Montana D19
extinction and polycrystallinity in detrital quartz for 

provenance interpretation: Journal of Sedimentary Petrology, v. 45, no. 4, p. 873-882.

Blackstone, D.L., Jr., 1975, Late Cretaceous and Cenozoic history 

of Laramie Basin region, southeast Wyoming, in Curtis, 

Bruce, ed., Cenozoic history of the southern Rocky 

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p. 249-279.

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

strata of the Powder River Basin, Wyoming and Montana: 

Raleigh, North Carolina State University, M.S. thesis, 63 p.

Chayes, P., 1956, Petrographic modal analysis: New York, John 

Wiley, 113 p.

Connor, C.W., and Perm, J.C., 1966, Precision of linear and areal 

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

River Basin, Wyoming: Wyoming Geological Association 

Guidebook, 23rd Annual Field Conference, p. 49-60.

Davies, D.K., and Ethridge, F.G., 1975, Sandstone composition 

and depositional environment: American Association of 

Petroleum Geologists Bulletin, v. 59, no. 2, p. 239-264.

Flores, R.M. and Ethridge, F.B., 1985, Evolution of Tertiary 

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: Rocky Mountain Section, Society of 

Economic Mineralogists and Paleontology, p. 107-126.

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Hemphill, 184 p.

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Association of Petroleum Geologists Bulletin, v. 19, no. 12, 

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Griffiths, J.C., 1967, Scientific method in analysis of sediments: 

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S.L., 1988, Laramide thrusting of the Bighorn Mountains 

near Buffalo, Wyoming: Geological Society of America 

Abstracts with Programs, v. 20, no. 7, p. A355-A356.

Hose, R.K., 1955, Geology of the Crazy Woman Creek area, 

Johnson County, Wyoming: U.S. Geological Survey 

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King, P.B., 1977, The evolution of North America: Princeton, N.J., 

Princeton University Press, 197 p.

Love, J.D., and Christiansen, A.C., 1985, Geologic map of 

Wyoming: U.S. Geological Survey, scale 1:500,000.

Lynn, L.R., 1980, Stratigraphic framework of some Tertiary 

coal-bearing alluvial strata, Powder River Basin, Wyoming 

and Montana: Raleigh, North Carolina State University, 

M.S. thesis, 94 p.

Mann, W.R., and Cavaroc, V.V., 1973, Composition of sand 

released from three source areas under humid, low relief 

weathering in the North Carolina Piedmont: Journal of 

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Mapel, W.J., 1959, Geology and coal resources of the BuffaloLake De Smet area, Johnson and Sheridan Counties, 

Wyoming: U.S. Geological Survey Bulletin 1078, 148 p.

Merin, I.S., and Lindholm, R.C., 1986, Evidence that the 

crystalline cores of uplifts adjacent to the Powder River 

Basin were breached during Paleocene time: The Mountain 

Geologist, v. 23, p. 128-131.

Odom, I.E., Doe, T.W., and Dott, R.H. Jr., 1976, Nature of 

feldspar-grain relations in some quartz-rich sandstones: 

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Ostle, Bernard, 1963, Statistics in research (2nd ed.): Ames, Iowa 

State University Press, 585 p.

Pettijohn, F.J., Potter, P.E., and Siever, R., 1972, Sand and 

sandstone: New York, Springer-Verlag, 600 p.

Redden, J.A., 1975, Precambrian geology of the Black Hills, in 

Mineral and water resources of South Dakota: U.S. 

Government Printing Office, p. 21-29.

Seeland, D., 1985, Oligocene paleogeography of the northern 

Great Plains and adjacent mountains, in Flores, R.M., and 

Kaplan, S.S., eds., Cenozoic paleogeography of the westcentral United States: Rocky Mountain Section, Society of 

Economic Paleontologists and Mineralogists, p. 187-206.

Selley, R.C., 1978, Ancient sedimentary environments (2nd ed.): 

Ithaca, N.Y., Cornell University Press, 278 p.

Sharp, R.F., 1948, Early Tertiary fanglomerate, Bighorn 

Mountains, Wyoming: The Journal of Geology, v. 56, no. 1, 

p. 1-15.

Swinehart, J.B., Souders, V.L., DeGraw, H.M., and Diffendal, 

R.F., Jr., 1985, Cenozoic paleogeography of western 

Nebraska, in Flores, R.M., and Kaplan, S.S., eds., Cenozoic 

paleogeography of the west-central United States: Rocky 

Mountain Section, Society of Economic Paleontologists and 

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Toth, J.C., 1982, Facies of Paleocene alluvial plains, Powder River 

Basin, Montana: Raleigh, North Carolina State University, 

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contrasted with that of the Southern Rocky Mountains A 

synthesis: The Mountain Geologist, v. 17, no. 3, p. 59-69.

Weaver, J.N., and Flores, R.M., 1985, Stratigraphic framework of 

the Upper Fort Union Formation, TA Hills, western Powder 

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the Powder River Basin, Wyoming: Raleigh, North Carolina 

State University, M.S. thesis, 145 p.

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no. 2, p. 136.

D20 Evolution of Sedimentary Basins Powder River Basin *U.S. GOVERNMENT PRINTING OFFICE: 1991-573-049/26034
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