WOV

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GEOLOGICAL SURVEY BULLETIN 144

0)

B1

no.

Eocene Fluvial Drainage Patterns and 

Their Implications for Uranium and 

Hydrocarbon Exploration in the 

Wind River Basin, Wyoming

By DAVID A. SEELAND

GEOLOGICAL SURVEY BULLETIN 1446

A paleocurrent study that defines the 

Eocene paleogeography of the basin and 

the course of the paleo- Wind River

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1978
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Seeland, David A.

Eocene fluvial drainage patterns and their implications for uranium and

hydrocarbon exploration in the Wind River Basin, Wyoming. 

(Geological Survey Bulletin 1446) 

Bibliography: p. 20 

Supt. of Docs, no.: I 19.3:1446

1. Geology, Stratigraphic Eocene. 2. Geology Wyoming Wind River Basin. 

3. Uranium ores Wyoming Wind River Basin. 4. Petroleum Geology WyomingWind River Basin.

I. Title: Eocene fluvial drainage patterns and their implications for uranium and 

hydrocarbon exploration in the Wind River Basin, Wyoming.

II. Series: United States Geological Survey Bulletin 1446.

QE75.B9 no. 1446 [QE692] 557.3'08s [551.7*8] 77-608135

 For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 

Stock No. 024-001-03083-7
CONTENTS

Abstract ................................................................ 1

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

Geologic setting .......................................................... 3

Tertiary stratigraphy ................................................. 4

Fort Union Formation ............................................ 4

Indian Meadows Formation ....................................... 4

Wind River Formation ............................................ 5

Overlying Tertiary rocks .......................................... 5

Methods of study ......................................................... 6

Interpretation of paleocurrent results ...................................... 8

Summary and conclusions ................................................ 19

References cited ......................................................... 20

ILLUSTRATIONS

Page 

FIGURE 1. Map showing uranium-exploration target areas, eastern Wind

River Basin, Wyo. .......................................... 2

2. Map of Wyoming showing basins and ranges ................... 3

3. Vector-mean crossbedding map, Wind River and Fort Union Formations ................................................... 7

4. Moving-average crossbedding map, Wind River Formation ....... 11

5. Rose diagram of crossbedding-dip directions for the Wind River

Formation ................................................. 12

6. Histogram of crossbed-set thicknesses, Wind River Formation ... 13

7. Interpretative map of early Eocene stream pattern, Wind River

Basin ..................................................... 14

8. Rose diagrams showing crossbedding dip directions for the Fort

Union Formation .......................................... 16

9. Map of gas fields, Eocene paleo-Wind River location, and Waltman

Shale Member isopachs, northern Wind River Basin .......... 18

TABLE

Page

TABLE 1. Crossbedding statistical summary .............................. 9

in

EOCENE FLUVIAL DRAINAGE PATTERNS

AND THEIR IMPLICATIONS FOR URANIUM

AND HYDROCARBON EXPLORATION IN THE

WIND RIVER BASIN, WYOMING

By DAVID A. SEELAND

ABSTRACT

Paleocurrent maps of the fluvial lower Eocene Wind River Formation in the Wind 

River Basin of central Wyoming define promising uranium- and hydrocarbon-exploration target areas. The Wind River Formation is thought to have the greatest potential 

for uranium mineralization in areas where it includes arkosic channel sandstones 

derived from the granitic core of the Granite Mountains, as in the channel-sandstone 

bodies deposited in Eocene time by a 40-kilometer segment of the eastward-flowing 

paleo-Wind River that extended westward from near the town of Powder River on the 

east edge of the basin. Channel-sandstone bodies with a Granite Mountains source occur 

south of this segment of the paleo-Wind River and north of the Granite Mountains. The 

southwestern part of this area includes the Gas Hills uranium district, but the channelsandstone bodies between the Gas Hills district and the 40-kilometer segment of the 

paleo-Wind River may also be mineralized. This area includes the southeasternmost 

part of the Wind River Basin southeast of Powder River and contains northeasterly 

trending channel-sandstone bodies derived from the Granite Mountains.

Limited paleocurrent information from the margins of the Wind River Basin suggests 

that the paleo-Wind River in Paleocene time flowed eastward and had approximately 

the same location as the eastward-flowing paleo-Wind River of Eocene time.

The channel-sandstone bodies of the paleo-Wind Rivers are potential hydrocarbon 

reservoirs, particularly where they are underlain or overlain by the organic-rich shale 

and siltstone of the Waltman Shale Member of the Fort Union Formation.

If leaks of sulfur-containing gas have created a reducing environment in the Eocene 

paleo-Wind River channel-sandstone bodies, then I speculate that the areas of overlap 

of the channel-sandstone bodies and natural-gas fields in the underlying rocks may be 

particularly favorable areas in which to search for uranium deposits.

INTRODUCTION

The Tertiary basins of Wyoming contain 42 percent of the nation's 

$10 per pound U308 uranium ore (Patterson, 1970, p. 119). In the sedimentary models of the basins now being developed, the paleocurrent 

systems provide an integrating framework that systematizes the distribution, orientation, and composition of the sedimentary rocks that 

constitute the basin fill. Preliminary results define two promising exploration target areas in the eastern Wind River Basin (fig. 1).

1
44°

110° 109° 108° 107°

URANIUM-EXPLORATION 

TARGET AREAS

43°

No granite / Grartite;. 

outcrops /' 'oytfcrops' .'

PRE-EOCENE ROCKS ''' "' '" '"

\ \ PRE-AN

__ Y-Beaver N^3RANITE MOUNTAINS EOCENE

( "" Divide \

. \ ^ ^ 0 10 20 30 40 50 KILOMETERS

- -- PRE-AND POST- ROCKS

o

O SO >

z >

Q

O

HHZ O

_L I I

FIGURE 1. Uranium-exploration target areas in eastern Wind River Basin, Wyo.
GEOLOGIC SETTING 3

Recent comprehensive work on the Wind River Basin has been by 

Reefer (1965; 1970). Zeller (1957), Soister (1968), and Armstrong 

(1970) have studied the Gas Hills uranium mining district in the 

southern Wind River Basin; Harshman (1968; 1972) has studied the 

nearby Shirley Basin district; and Stephens (1964) has studied the 

Crooks Gap district on the northern margin of the Great Divide Basin. 

The locations of these three uranium mining districts are shown in 

figure 2.

105°

41°iJ

MEDICINE BOW MTS 

ARATOGA VALLEY

100 200 KILOMETERS

FIGURE 2. Wyoming basins and ranges (modified from Love, 1961). Uranium mining districts: Crooks Gap (CG), Gas Hills (GH), and Shirley Basin (SB).

GEOLOGIC SETTING

The western topographic margin of the Wind River Basin is the 

Wind River Range. Its northern margin is formed by the Washakie 

and Absaroka Ranges and the Owl Creek and southern Bighorn 

Mountains. Topographically its southern margin is formed by the 

Beaver Divide, an erosional escarpment in rocks of Eocene, Oligocene,
4 EOCENE FLUVIAL DRAINAGE PATTERNS, WYOMING

and Miocene age. The eastern margin is topographically undefined 

and merges into the high plains surface of the Powder River Basin. 

The Wind River Basin is well defined structurally. Paleozoic rocks 

dip 12° to 15° NE. into the basin along the Wind River Range. Dips 

along the Washakie Range and the Owl Creek and Bighorn Mountains 

are into the basin in most places, but are much less regular, varying 

from flat to overturned. Structurally the east margin of the basin is 

well defined by the Casper arch, an anticline whose west limb is steep 

to overturned. The south Owl Creek Mountains thrust fault, with as 

much as 6 km (kilometers) of stratigraphic displacement, extends the 

length of the west side of the Casper arch. The southern structural 

margin of the basin is formed by the Granite Mountains, a unique collapsed Laramide uplift. Paleozoic and Mesozoic rocks dip 10° to 15° off 

the north flank of the mountains and are broken by east-west normal 

faults. Post-Wind River Tertiary rocks conceal most of the granitic 

core of the Granite Mountains, with the exception of a series of granite knobs. Generally flat-lying strata of the Wind River Formation 

floor the central part of the Wind River Basin and are the host rocks 

for the uranium in the Gas Hills district. The structural relief between 

the mountains and the basin, on the upper surface of the Precambrian, exceeds 9 km on the north side of the basin close to the Owl 

Creek Mountains (Reefer, 1970, p. Dl).

TERTIARY STRATIGRAPHY

FORT UNION FORMATION

The lower part of the Paleocene Fort Union Formation was 

deposited by streams carrying clastic debris from the highlands that 

had begun to define the Wind River Basin into the subsiding trough 

area along the north edge of the basin. The upper part of the Fort 

Union consists of shale, siltstone, claystone, and sandstone (the Waltman Shale Member) deposited in a large lake which had at least a 

limited connection with an Open sea to the east (Keefer, 1961, p. 1323). 

Along the north edge of the basin the Fort Union is as thick as 2,500 m 

(meters); on the west and south sides it ranges from 50 to 350 m in 

thickness (Keefer, 1965, p. A22).

INDIAN MEADOWS FORMATION

The Indian Meadows Formation, named by Love (1939, p. 58- 59), 

is of earliest Eocene age and crops out on the northern margin of the 

Wind River Basin. It is impossible to distinguish it from the overlying 

Wind River Formation in drill-hole data. The Indian Meadows is commonly banded in shades of red, gray, and tan. Coarse conglomerates 

originated as stream-channel and alluvial-fan deposits. Clays and silts
GEOLOGIC SETTING 5

were deposited as overbank deposits on flood plains. Masses of 

Paleozoic rock, as much as 400 m long, are found within the formation 

and may be landslide deposits or may be remnants of thrust sheets 

formed during uplift of the Owl Creek Mountains and Washakie 

Range (Reefer, 1965, p. A42). The Indian Meadows is absent along the 

southwest side of the basin and may be a thousand or more meters 

thick in the subsurface along the north side of the basin.

WIND RIVER FORMATION

The Wind River Formation of early Eocene age is exposed over 

much of the central area of the basin. The Wind River Formation was 

deposited during the period following uplift of the Wind River and 

Washakie Ranges and the Owl Creek Mountains in earliest Eocene 

and is composed of debris eroded from these areas that was deposited 

in alluvial fans near the mountains, and in stream channels, flood 

plains, lakes, and swamps farther out in the basin.

Clast lithology in the conglomerates of the Wind River and the underlying Indian Meadows and Fort Union reflects areal variations of 

the rock types exposed in the mountain ranges bordering the basin. 

Clast lithology also strongly reflects progressive unroofing of the bordering mountain ranges. The lower part of the Indian Meadows and 

the Fort Union contain conglomerate derived from Mesozoic rocks. 

Conglomerate in the upper part of the Indian Meadows is coarser than 

conglomerate in the Fort Union and consists of fragments of Paleozoic 

rocks. The Wind River conglomerates contain abundant Precambrian 

rock fragments that record exposure of the igneous and metamorphic 

cores of the ranges bordering the basin.

Alternating red and grayish-green banded siltstones and claystones 

and light-brown sandstones make up most of the Wind River Formation. The thickness of the Wind River ranges from a few meters at the 

basin margin to several thousand meters in the trough in the northern 

part of the area.

OVERLYING TERTIARY ROCKS

Rocks overlying the Wind River Formation are present in depositional contact only in the northwest, south, and southeast parts of the 

basin. The most characteristic difference between the Wind River and 

the overlying rocks is that the younger rocks contain substantially 

more volcanic debris. The middle Eocene Ay cross Formation has been 

described by Love (1939), and the overlying middle and upper Eocene 

Tepee Trail Formation of the northwest part of the basin has been 

described by Keefer (1957). The Aycross consists of tuffaceous 

claystone, shale, sandstone, and conglomerate with hornblende- and 

biotite-rich volcanic rocks in the upper part of the formation. The
6 EOCENE FLUVIAL DRAINAGE PATTERNS, WYOMING

Tepee Trail consists of greenish andesitic conglomerates, sandstone, 

shale, and tuff. The overlying Eocene Wiggins Formation is composed 

of volcanic conglomerate and breccia, both interbedded with tuffs.

On the southeastern and southern margins of the Wind River Basin 

the Wind River Formation is conformably overlain by the Wagon Bed 

Formation of middle and late Eocene age. The Wagon Bed is made up 

of a series of laterally persistent beds of sandstone, siltstone, and 

mudstone, which contain volcanic debris and bentonitic clay, and 

which range from 40 to 200 m in thickness (Van Houten, 1964, p. 36).

The Oligocene White River Formation along the Beaver Divide on 

the south side of the basin is a calcareous tuffaceous mudstone and a 

fine-grained muddy sandstone, although sandstone and conglomerate 

are also present (Van Houten, 1964, p. 56-57). The White River has a 

maximum exposed thickness of 200 m along the Beaver Divide (Van 

Houten, 1964, p. 55). To the east, in the Shirley Basin, the White River 

is divided into a lower fine-grained siltstone member and an upper 

member, which is about one-third of the unit, of conglomerate, 

sandstone, and siltstone (Harshman, 1972, p. 26).

METHODS OF STUDY

The orientations of 815, mostly trough, crossbeds were determined 

at 72 localities in the Eocene Wind-River Formation1 in the Wind 

River Basin. A total of 19 crossbedding orientations were determined 

at 2 localities in the Paleocene Fort Union Formation. Courdin and 

Hubert (1969, p. 29) measured 203 Fort Union crossbeds at 5 localities 

in the Wind River Basin. The locations of these field stations are 

shown in figure 3.

True, not apparent, crossbed dips and dip directions (azimuths) 

were determined with a compass-and-level crossbed-measuring 

device. The thickness of crossbed sets was usually measured for each 

set whose orientation was determined. The number of crossbed sets 

measured at each locality was determined either by availability or by a 

rough plot of dip azimuths made after 10 Crossbeds had been 

measured. If the azimuths were strongly grouped, no further measurements were made; if they were strongly dispersed, about 10 additional 

randomly selected measurements were made, if possible. Sedimentation-unit samples of conglomerate, sandstone, and siltstone-shale 

were also collected at each outcrop.

1 Some of the crossbed localities in the western part of the basin were in strata mapped by Keefer (1970, pi. 1) as 

"lower Eocene rocks undivided," and therefore a few localities may have actually been in the Indian Meadows Formation, which underlies the Wind River Formation.
44°

110° 109* 108° 107°

43'

EXPLANATION

VECTOR MEAN CROSSBEDDING DIP DIRECTIONS 

AND STATION NUMBERS

WIND RIVER FORMATION

This study

FORT UNION FORMATION 

104. This study

o Grant, 1954 -» Courdin and Hubert, 1969 

Length of arrow proportional to vector strength

'v PRE- AND POST-^ 

\ EOCENE ROCKS,/' ._J______^ -^ 0 10 20 30 40 50 KILOMETERS

I I I I I I

O O OGa

FIGURE 3. Vector-mean crossbedding map, Wind River and Fort Union Formations, Wind River Basin, Wyo.
8 EOCENE FLUVIAL DRAINAGE PATTERNS, WYOMING

A computer program written by E. S. Robinson of Virginia 

Polytechnic Institute and State University and George Van Trump of 

the U.S. Geological Survey was used to correct for post-depositional 

tectonic tilt and to provide vector means, standard deviation of vector 

means, mean vector of dip, standard deviation of dip, and percentages 

of corrected crossbed azimuths in 30° segments (used to construct rose 

diagrams).

The mean direction of the crossbedding at a given locality was 

calculated by the vector summation method first used by Reiche 

(1938). Arithmetic means of circular data are not useable because 

they vary depending on the choice of origin. In a vector summation 

each crossbed azimuth is assigned a unit length, and these vectors are 

added "tail to head." The resultant is the vector mean, and the length 

of this resultant divided by the number of crossbed measurements 

times 100 is the vector strength. If all crossbeds at a field station have 

the same orientation, the vector strength is 100 percent; if the 

crossbeds have a completely random orientation, the vector strength 

will approach zero.

Locality vector means were plotted on a vector-mean map, the 

length of the arrow being proportional to the vector strength (fig. 3). 

The numerical results of this study are summarized in table 1. The 

vector-mean map was smoothed to produce the moving average map 

(fig. 4) using the following technique: a 10-km grid was placed over the 

vector-mean paleocurrent map, and at each intersection on the grid 

the vector-mean direction was graphically obtained for the field stations in the four squares surrounding the intersection; the mean direction thus derived was represented by an arrow at the grid intersection.

Because each grid square adjoins four intersections, each locality 

vector-mean current direction is used four times. Therefore, a single 

divergent current direction in a marginal area of the map, where sampling density is low, could result in as many as four moving averages 

that repeat the one direction. This effect is particularly misleading 

because vectors near the map edge are visually prominent. In order to 

minimize this effect, a minimum of three current directions were used 

in formulating each moving average; that is, the mean current directions from the three crossbed localities closest to each intersection 

were always used in the vector summation, regardless of whether one, 

two, or all three were in squares adjacent to the intersection.

INTERPRETATION OF PALEOCURRENT RESULTS

The fluvial-channel sandstones of the Wind River Formation in the 

Wind River Basin can be seen to cap linear ridges, as at station 128
INTERPRETATION OF PALEOCURRENT RESULTS 9 

TABLE 1. Crossbedding statistical summary

[All stations are in the Eocene Wind River Formation (or in the "lower Eocene rocks undivided" of Keefer, 1970)

unless otherwise noted]

Station No.

(fig. 3)

53 ...............

55 ...............

56 ...............

57 ...............

58 ..............

59 ...............

60 ...............

61 ...............

62 ...............

65 ...............

66 ...............

67 ................

68 ...............

69 ...............

70 ...............

71 ................

73 ................

74 ...............

75 ...............

76 ...............

77 ...............

78 ................

79 ................

80 ................

81' ..............

82 ................

83 ................

84 ................

85.................

86 ...............

87 ................

88 ................

89 ................

90.................

92 ...............

93 ................

98 .................

100 ...............

101 ...............

103 ...............

104a ...............

105 ...............

106 ...............

107 ...............

108" ...............

109 ...............

110 ...............

Ill ................

112 ................

113 ...............

114 ................

115 ................

116 ................

119 ................

120 ................

122 ................

123 ................

124 ................

125 ................

126 ................

127 ................

128 ................

130 ................

131 ................

132 ................

Vectormean azimuth

(degrees)

75.8

43.4

132.7

77.6

102.6

280.2

69.8

151.8

92.6

60.7

17.8

356.6

59.5

31.3

110.4

77.4

143.8

135.2

143.7

135.9

154.6

175.1

42.4

26.7

36.6

120.5

86.5

98.5

114.6

105.8

148.5

113.4

29.5

94.1

157.1

120.6

45.1

333.5

66.8

90.4

109.2

122.4

71.0

120.1

107.1

100.0

183.9

205.1

64.7

48.5

69.1

15.3

83.0

330.0

64.0

30.1

83.8

289.3

86.5

134.6

62.5

129.8

70.0

43.7

22.1

Azimuth

vector weight

(percent)

59

43

45

36

62

67

86

61

56

40

40

66

69

10

72

72

82

41

48

66

52

28

70

79

94

37

44

59

50

69

70

54

59

50

85

66

88

58

27

75

58

79

54

77

22

74

83

77

80

71

54

55

83

89

35

71

44

93

75

71

35

84

46

52

27

Mean crossbed dip

(degrees)

28.3

24.3

19.2

22.0

22.5

19.2

19.2

22.6

28.6

19.4

18.5

19.6

21.3

23.4

27.4

22.7

19.7

20.1

25.7

16.0

21.8

16.5

21.5

22.0

54.2

18.9

19.2

15.8

20.1

15.9

20.9

21.5

19.9

19.9

24.4

19.9

21.3

19.2

27.6

26.0

18.9

23.6

26.2

24.6

32.6

25.5

24.0

20.9

21.0

21.3

22.6

18.0

21.9

22.5

18.4

17.2

20.3

22.2

1S.2

24.6

19.3

23.7

19.4

19.4

22.3

Number of

crossbeds

measured

11

17

8

17

15

12

5

11

5

20

14

13

14

16

10

12

12

11

18

11

4

8

12

10

9

14

15

13

6

11

9

11

17

15

11

14

12

14

19

6

8

5

4

9

11

14

6

8

11

11

18

4

11

6

20

12

12

6

12

15

20

14

11

10

17
10 EOCENE FLUVIAL DRAINAGE PATTERNS, WYOMING 

TABLE 1. Crossbedding statistical summary Continued.

Station No. 

(fig. 31

134 ..............

136 ............:.

140 ..............

143 ..............

144 145 :.............

146 ..............

147 ..............

Vectormean azimuth 

(degrees)

354.9

58.8

64.4

345.0

91.2

71.4

34.1

2.8

22.2

Azimuth 

vector weight 

(percent)

43

72

57

95

85

58

78

67

82

Mean cross - 

bed dip

(degrees)

15.8

14.7

19.9

29 o

21.4

99 1

18.8

23.0

Number of 

crossbeds 

measured

11

3

7

2

9

12

18

10

7

Pebble imbrication. 

2 In Paleocene Fort Union Formation.

(fig. 3) 11 km northeast of Ocean Lake, or extend from ridge to ridge 

in dissected topography, as at station 73 located 2.4 km south of 

Lysite. However, channel trends are generally difficult to ascertain 

visually, particularly in areas of poor outcrop. The average transport 

direction and thus the average channel azimuth in the Wind River 

Formation is N. 80° E. This direction was obtained by a vector summation of all 815 crossbed measurements. The corresponding overall vector strength is 36 percent. The degree of dispersion of transport directions can also be visually estimated from the crossbedding-dip-directions rose diagram for the Wind River Formation (fig. 5). The mean 

crossbed dip in the Wind River Basin is 22.1°. The mean exposed 

thickness of 632 crossbed sets was 43.1 cm; the range was 5-224 cm. 

Set thickness is presented in a histogram in figure 6.

The moving-average map (fig. 4) has been used to prepare the interpretative map of the Wind River Basin early Eocene stream pattern 

(fig. 7). The course of the paleoriver is obvious on both the movingaverage map (fig. 4) and the interpretative map (fig. 7). The paleoWind River flowed east-southeast across the northern part of the 

basin, left the basin near the present town of Powder River, and 

flowed eastward across the Casper arch into the Powder River Basin. 

Northeasterly trending tributary streams carried coarse-grained 

arkosic sand, which formed the host sandstones in the Gas Hills 

uranium district. Eocene arkosic sandstones of the Shirley Basin 

uranium district were deposited by streams flowing eastward from the 

east end of the Granite Mountains. The Crooks Gap uranium district 

is on the south side of the Granite Mountains where deposits are in 

arkosic sandstones and conglomerates derived from the granitic core 

of the Granite Mountains and deposited by southerly flowing streams 

(Groth, 1970, p. 10).
INTERPRETATION OF PALEOCURRENT RESULTS 11

I

c a

T»

I 

§

3

I
12 EOCENE FLUVIAL DRAINAGE PATTERNS, WYOMING

270° -

180

FIGURES. Crossbedding-dip-directions rose diagram for 815 crossbed measurements in the Wind River Formation, Wind River Basin, Wyo.

The source of uranium in the ore-bearing solutions has been the 

subject of much discussion. Love (1970, p. C129) lists the following primary sources which have been proposed for the uranium deposits in 

the Granite Mountains area: (1) Precambrian granite of the Granite 

Mountains, (2) arkosic sandstones derived from the Precambrian 

granite of the Granite Mountains, (3) Precambrian vein deposits of 

hydrothermal origin (Guilinger, 1963), (4) Tertiary uraniferous tuff 

(Love, 1954; Pipiringos, 1961), and (5) hydrothermal solutions 

(Melbye, 1957; Gabelman and Krusiewski, 1964).

Harshman (1970, p. 227) favors a multiple source for the deposits: 

Precambrian granite in the cores of the flanking ranges, and Tertiary 

tuffaceous rocks that once were more widespread in the eastern twothirds of Wyoming. Love (1970, p. C132) favors Tertiary tuffaceous 

rocks as the source of the uranium in the Gas Hills and Crooks Gap 

districts. Soister (1968, p. A48) believes that the arkose itself is the
INTERPRETATION OF PALEOCURRENT RESULTS 13

140

120

c/j 

01

CO

100

CO 

CO 

CO

O

or

O 

LL 

O 

CC

D 

Z

80

60

40

20

51 102 153 204 254

THICKNESS OF CROSSBED SETS.IN CENTIMETERS

FIGURE 6. Histogram of thickness of crossbed sets, Wind River Formation, Wind

River Basin, Wyo.

most likely source. Because the altered sandstone contains slightly 

more uranium and 10 to 20 times more selenium than the unaltered 

sandstone, Harshman concludes that the altered arkose is not the 

source of the uranium.
14 EOCENE FLUVIAL DRAINAGE PATTERNS, WYOMING
INTERPRETATION OF PALEOCURRENT RESULTS 15

But whatever the source of the uranium-bearing solutions, permeable clastic units and particularly paleochannel sandstones are 

favorable environments for uranium-ore formation (Harshman, 1961; 

Davis, 1970, p. 24; Armstrong, 1970, p. 35; Groth, 1970, p. 11; Grant, 

1954; Hayashi, 1970, p. 233; Zeller, 1957, p. 158). Therefore, if a Granite Mountains sediment source and the existence of fluvial-channel 

sandstones are important parameters in the localization of uranium 

deposits in the Wind River Basin, then paleocurrent maps define two 

favorable target areas as shown in figure 1.

The western end of a 40-km segment of favorable channelsandstone bodies of the paleo-Wind River was determined by projecting the westernmost extent of the granites of the Granite Mountains 

(fig. 1) northeast parallel to the stream directions represented on the 

moving-average paleocurrent map (fig. 4). The channel-sandstone 

bodies2 of this 40-km-long segment of the Eocene Wind River Formation define one uranium-exploration target area (I in fig. 1). The second target area (II in fig. 1) includes channel-sandstone bodies with a 

Granite Mountains source found in the area south of this segment and 

north of the Granite Mountains. The southwestern part of this area 

includes the Gas Hills uranium district, but channel-sandstone bodies 

between the Gas Hills district and the 40-km segment of the paleoWind River may be mineralized. This area extends into the 

southeasternmost part of the Wind River Basin and contains northeasterly trending channel-sandstone bodies derived from the Granite 

Mountains.

Note that the position of the paleo-Wind River cannot be located 

more closely than.the grid spacing of the moving-average map (10 

km). More closely spaced moving-average grid lines would require 

more closely spaced field stations, which in some areas of the basin 

would be difficult to obtain because of the scarcity of outcrops. 

Furthermore, the position of the paleo-Wind River is based on 

stratigraphically uncontrolled crossbed measurements. If the 

stratigraphic position of the crossbed measurements were random, 

then the location of the paleo-Wind River would be the mean position 

during that portion of early Eocene time represented by the remaining 

beds of an originally thicker Wind River Formation. The stability of 

the current pattern and of the position of the paleo-Wind River is estimated to be fairly high, based on the similarity of Eocene and 

Paleocene current rose diagrams (fig. 5, 8).

The likelihood of uranium mineralization depends in part on the1 

source of the uranium-bearing ground water and the relative volume 

of the channel-sandstone bodies. The channel sandstones of the paleo1 "Channel sandstone" includes point-bar, channel-lag, channel-bar, and channel-fill deposits.
16 EOCENE FLUVIAL DRAINAGE PATTERNS, WYOMING

NORTH

0°

270° -

180°

FIGURE 8. Crossbedding-dip-directions rose diagrams for the Fort 

Union Formation. A, 19 crossbed orientations, this study. B, 208 

crossbed orientations from Courdin and Hubert (1969, fig. 1).
INTERPRETATION OF PALEOCURRENT RESULTS 17

Wind River (target area I, fig. 1) and the ground-water flow through 

them are only partially derived from the Granite mountains. So, in 

spite of the fact that the channel-sandstone bodies of the paleo-Wind 

River should be the largest of any in the two areas, dilution of the 

Granite Mountain sediment and ground water by sediment and 

ground water derived elsewhere should decrease the potential of this 

area. But if uraniferous tuffs are the source of the uranium, then the 

area with the largest channel-sandstone bodies, the area defined by 

channel-sandstone bodies of the paleo-Wind River, should be most 

favorable. It is necessary though, as Love (1970, p. C132) points out, 

that a hydraulic connection exist between the host rock and the source 

rock, and it is not known if such a connection existed in this area 

because the overlying tuffaceous rocks have been eroded away. The 

second area (target area II, fig. 1) should have smaller channelsandstone bodies, but the arkose in these, and the ground water that 

has flowed through them, should have come exclusively from the 

Granite Mountains.

Channel-sandstone bodies should be larger and accumulations of 

plant debris more likely in the deposits of the lower velocity downstream parts of the tributaries to the paleo-Wind River. These factors 

suggest that the northern part of the second area may be more favorable than the southern part (excepting, of course, the Gas Hills mining 

district).

Sulfur in the gas or in associated oil of the Waltman gas field (fig. 9) 

could have reacted with iron in the Tertiary sediments to form pyrite 

and to create a reducing environment that would precipitate uranium, 

as suggested by Love (1970, p. C132). This gas field seems to lie directly 

on the course of the paleo-Wind River near the east margin of the 

basin, where the amount of arkose and ground-water flow from a 

Granite Mountains source would be maximized, and where the channel-sandstone bodies should reach their greatest size. This area, 

therefore, seems to be an especially favorable target.

The paleo-Wind River shown in figure 9 intersects or passes near 

several other gas fields located by Lane, Root, and Glass (1972). These 

fields are Frenchie Draw, Reservoir Creek, Pony Creek, Dinty Moore 

Reservoir, Shoshoni, Poison Creek, Muddy Ridge, and Pavillion. These 

fields, with the exception of Frenchie Draw, lie west of the area in 

which arkose and ground water derived from the Granite Mountains 

area occurs (or occurred), but the paleo-Wind River channelsandstone bodies in the vicinity of these fields could be mineralized if 

other arkoses or uraniferous tuffs were the source of the mineralizing 

solutions. These fields produce gas mostly from the Paleocene Fort 

Union Formation, but the Muddy Ridge and Lost Cabin fields produce 

partly from the lower Eocene Wind River Formation, and the Lysite
44 C

43'

110 C 109° 108° 

'creek'* Oil and 9as 

Glass, 1

 300 Isopach 

Fort Un

1965, f

-* *- Thrust fau

10 

I 

FIGURE 9. Gas fields in northern Wind River Basin, Eocene paleo-Wind River location, a

of Fort Union Formation.
SUMMARY 19

field produces chiefly from the lower Eocene (Keefer, 1969, p. 1859). 

All these fields lie within 10 km of the approximate location of the 

paleo-Wind River. Since the location of the paleo-Wind River channel 

is approximate, gas leaks from these fields could also create a reducing environment in nearby channel-sandstone bodies of the paleoWind River.

It is possible that the fluvial channel sandstones of the paleo-Wind 

Rivers are potential natural gas or petroleum reservoir rocks. Comparison of crossbed-dip-direction rose diagrams of Courdin and Hubert 

(1969) and those obtained during this study from the lower fluvial 

part of the Paleocene Fort Union Formation (fig. 8) with the Wind 

River Formation rose diagram (fig. 5) suggests a similarity in current 

pattern, as do the vector-mean current directions (fig. 3). The overall 

vector means of N. 73° E. for the Fort Union (Courdin and Hubert, 

1969, p. 29) and N. 80° E.for the Wind River Formation are very close. 

These facts may indicate the paleo-Wind River channel system occupied approximately the same position in Paleocene time as in 

Eocene time. Thus, the Eocene and Paleocene paleo-Wind River channel sandstones are potential hydrocarbon reservoirs and worthy exploration targets, particularly where the channel sandstones are underlain or overlain by the organic-rich shale and siltstone of the Waltman Shale Member of the Fort Union Formation. An isopach map of 

the Waltman Shale Member (from Keefer, 1965, fig. 14) is shown in 

figure 9 with the approximate position of the Eocene paleo-Wind River 

(which is also the inferred position of the Paleocene paleo-Wind 

River). This map, therefore, shows where the paleo-Wind River channel sandstones have maximum oil and gas potential. Keefer (1969, p. 

1859) does state, however, that the amount of hydrocarbons found in 

sandstones adjacent to the Waltman Shale Member has been smaller 

than expected.

SUMMARY AND CONCLUSIONS

The source of the uranium-bearing solutions that formed the ore 

deposits near the Granite Mountains is not known but the uranium 

may have been leached from post-Wind River tuffaceous rocks of 

Oligocene and Miocene age, from granitic rocks of Precambrian age in 

the core of the Granite Mountains, or from arkosic sandstones of early 

Eocene age derived from the Granite Mountains. A Granite Mountains 

source for the host rock and the presence of fluvial-channel sandstone 

bodies of the Wind River Formation are apparently important factors 

in the localization of the Gas Hills, Shirley Basin, and Crooks Gap 

uranium deposits. Based on these two factors, paleocurrent maps
20 EOCENE FLUVIAL DRAINAGE PATTERNS, WYOMING

derived from a study of fluvial crossbedding of the Wind River Formation in the Wind River Basin of central Wyoming were used to identify two areas having a maximum probability of uranium mineralization (fig. 1). An additional factor favoring uranium precipitation is the 

possibility that gas containing reductants leaked into the sandstone 

from adjacent gas fields, such as the Waltman field, which underlies 

the paleo-Wind River channel-sandstone bodies. The movingaverage paleocurrent map of the Wind River Formation clearly shows 

the source areas for the lower Eocene rocks of the basin and locates 

the area in which channel-sandstone bodies of the paleo-Wind River 

are most likely to be found. The location of the paleo-Wind River in 

Paleocene time is quite probably similar to that of the river in Eocene 

time, based on limited paleocurrent data from the margin of the basin. 

Oil and gas accumulations in the channel sandstones of the Eocene 

and Paleocene paleo-Wind Rivers are more likely where they overlie 

or underlie the organic-rich Waltman Shale Member in the central 

and northeastern Wind River Basin.

REFERENCES CITED

Armstrong, F. C., 1970, Geologic factors controlling uranium resources in the Gas Hills 

district, Wyoming, in Wyoming Geol. Assoc. Guidebook 22d Field Conf., Wyoming 

sandstones, 1970: p. 31 44.

Courdin, J. L., and Hubert, J. F., 1969, Sedimentology and mineralogical differentiation 

of sandstones in the Fort Union Formation (Paleocene), Wind River Basin, Wyoming, in Wyoming Geol. Assoc. Guidebook 21st Field Conf., Tertiary rocks of Wyoming, 1969: p. 29-37.

Davis, J. F., 1970, Uranium deposits of the Powder River Basin, Wyoming, in Wyoming 

Geol. Assoc. Guidebook 22d Field Conf., Wyoming sandstones, 1970: p. 21-29.

Gabelman, J. W., and Krusiewski, S. V., 1964, Zonal distribution of uranium deposits in 

Wyoming, U.S.A.: Internat. Geol. Cong., 22d, New Delhi 1964, Proc., pt. 5, p. 

661-672.

Grant, S. C., 1954, Channel deposits of the Wind River Formation in Fremont County, 

Wyoming, as a guide to uranium ore: Laramie, Wyo., Wyoming Univ. unpub. M.S. 

thesis, 70 p.

Groth, F. A., 1970, New sandstone uranium deposit in the Battle Spring Formation, 

Lost Soldier-Green Mountain area, Sweetwater County, Wyoming, in Wyoming 

Geol. Assoc. Guidebook 22d Field Conf., Wyoming sandstones, 1970: p. 9-12.

Guilinger, R. R., 1963, Source of uranium in the Gas Hills area, Wyoming: Econ. 

Geology, v. 58, no. 2, p. 285-286.

Harshman, E. N., 1961, Paleotopographic control of a uranium mineral belt, Shirley 

Basin, Wyoming, in Short papers in the geologic and hydrologic sciences: U.S. Geol. 

Survey Prof. Paper 424-C, p. C4-C6.

___ 1968, Geologic map of the Shirley basin area, Albany, Carbon, Converse, and 

Natrona Counties, Wyoming: U.S. Geol. Survey Misc. Geol. Inv. Map 1 539.
REFERENCES CITED 21

^1970, Uranium ore rolls in the United States, in Uranium exploration geology: 

Vienna; Austria, Internat. Atomic Energy Agency, p. 219 230. 

.1972, Geology and uranium deposits, Shirley Basin area, Wyoming: U.S. Geol.

Survey Prof. Paper 745, 82 p. 

Hayashi, S., 1970, Uranium occurrences in small sedimentary basins in Japan, in

Uranium exploration geology: Vienna, Austria, Internat. Atomic Energy Agency, p.

233-242. 

Keefer, W. R., 1957, Geology of the Du Noir area, Fremont County, Wyoming: U.S. Geol.

Survey Prof. Paper 294-E, p. 155-221. 

___1961, Waltman Shale and Shotgun members of Fort Union Formation

(Paleocene) in Wind River Basin, Wyoming: Am. Assoc. Petroleum Geologists Bull.,

v. 45, no. 8, p. 1310-1323. 

___ 1965, Stratigraphy and geologic history of the uppermost Cretaceous, Paleocene,

and lower Eocene rocks in the Wind River Basin, Wyoming: U.S. Geol. Survey Prof.

Paper 495 A, 77 p. 

___1969, Geology of petroleum in Wind River Basin, central Wyoming: Am. Assoc.

Petroleum Geologists Bull., v. 53, no. 9, p. 1839-1865. 

.1970, Structural geology of the Wind River Basin, Wyoming: U.S. Geol. Survey

Prof. Paper 495-D, p. D1-D35.

Lane, D. W., Root, F. K., and Glass, G. B., 1972, Energy resources map of Wyoming: 

Laramie, Wyoming Geol. Survey.

Love, J. D., 1939, Geology along the southern margin of the Absaroka Range, Wyoming; 

Geol. Soc. America Spec. Paper 20, 134 p.

___1954, Preliminary report on uranium in the Gas Hills area, Fremont and 

Natrona Counties, Wyoming: U.S. Geol. Survey Circ. 352, lip.

 1961, Definition of Green River, Great Divide, and Washakie basins, southwestern Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 45, no. 10, p. 

1749-1755. 

. 1970, Cenozoic geology of the Granite Mountains area, central Wyoming: U.S.

Geol. Survey Prof. Paper 495-C, 154 p. 

Melbye, C. E., 1957, Structural control of Crooks Gap U3O8 gives clues for Wyoming

prospectors: Mining World, v. 19, no'. 12, p. 54-57, 108-109. 

Patterson, J. A., 1970, Character of the United States uranium resources, in Uranium

exploration geology: Vienna, Austria, Internat. Atomic Energy Agency, p.

117-128. 

Pipiringos, G. N., 1961, Uranium-bearing coal in the central part of the Great Divide

Basin: U.S. Geol. Survey Bull. 1099-A, 104 p. [1962]. 

Reiche, Parry, 1938, An analysis of cross-lamination the Coconino sandstone: Jour.

Geology, v. 46, no. 7, p. 905-932. 

Soister, P. E., 1968, Stratigraphy of the Wind River Formation in south-central Wind

River Basin, Wyoming: U.S. Geol. Survey Prof. Paper 594 A, p. A1-A50. 

Stephens, J. G., 1964, Geology and uranium deposits at Crooks Gap, Fremont County,

Wyoming: U.S. Geol. Survey Bull. 1147-F, p. F1-F82. 

Van Houten, F. B., 1964, Tertiary geology of the Beaver Rim area, Fremont and

Natrona Counties, Wyoming: U.S. Geol. Survey Bull. 1164, 99 p. [1965]. 

Zeller, H. D., 1957, The Gas Hills uranium district and some probable controls for ore

deposition, in Wyoming Geol. Assoc. Guidebook 12th Ann. Field Conf., Southwest

Wind River Basin, 1957: p. 156 160.

*U.S. Government Printing Office: 1978-777-102/27