Coastal Sedimentation Along a Segment of the 

Interior Seaway of North America, 

Upper Cretaceous Baxter Shale, and · 

Blair and Rock Springs Formations, 

Rock Springs Uplift, Southwest Wyoming 

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Coastal Sedimentation Along a Segment of the 

Interior Seaway of North America, 

Upper Cretaceous Baxter Shale, and 

Blair and Rock Springs Formations, 

Rock Springs Uplift, Southwest Wyoming 

By HENRY W. ROEHLER 

U.S. GEOLOGICAL SURVEY BULLETIN 2051 

Location and description of outcrops 

of paralic and marine delta, shelf, slope, 

and basin deposits 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1993 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting Director 

For sale by 

USGS Map Distribution 

Box 25286, Building 810 

Denver Federal Center 

Denver, CO 80225 

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. 

Library of Congress Cataloging-in-Publication Data 

Roehler, Henry W. 

Coastal sedimentation along a segment of the interior seaway of North America, Upper Cretaceous Baxter Shale, and Blair and Rock Springs formations, Rock Springs uplift, southwest Wyoming : location and description of outcrops of paralic and marine 

delta, shelf, slope, and basin deposits I by Henry W. Roehler. 

p. em. - (U.S. Geological Survey bulletin; 2051) 

Supt. of Docs. no.: I 19.3:2051 

1. Geology, Stratigraphic-Cretaceous. 2. Sedimentation and depositionWyoming. I. Title. II. Series. 

QE75.B9 no. 2051 

[QE688] 

557.3 s-dc20 92-42439 

[551. 7'7'09787] CIP 
CONTENTS 

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

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

Purpose and Methodology.......................................................................................... 1 

Geologic Setting ................... ............ ............................... .. ......................... .. . . ............ 1 

Sedimentology . . . .. . .. .......................................... ..... .. .. ..... . . . . . . . .. . . . . . . . .................. ... . . . . . . .. . . . . . . . .. 3 

Marine Basin Deposits................................................................................................ 3 

Submarine Fan Deposits............................................................................................. 7 

Marine Shelf Deposits................................................................................................ 10 

Longshore Bar ........ .... .. .. .. ... . .. . . . . .... .. .. .... .. .. .. .. . .. .. .. .. . . . . .. .... .. .. .. .. .. .. .. . .. .. . .. .. .. .. .. .. ... 11 

Submarine Channel and Overbank....................................................................... 11 

Prodelta Deposits ....................................................................................................... . 

Delta-Front Deposits ................................................................................................. .. 

Shoreline Sandstones .......................................................................................... .. 

Submarine Slumps ............................................................................................... . 

Heavy-Mineral Beach Placer .............................................................................. .. 

Flood-Tidal Delta and Tidal Inlet ........................................................................ . 

11 

13 

15 

16 

16 

19 

Delta-Plain Deposits................................................................................................... 20 

Distributary Stream Channel . .............. ....... .. ............ .. ........ ... .................. ............. 20 

Lower Delta Plain................................................................................................. 20 

Upper Delta Plain . . . . . .. . . . . . .. .. . . . . . . . .... .. ........... ... . . . . . . . .. . . . .. . . .... .. . . ... . . . . . . . .. . . . . .............. 25 

References Cited................................................................................................................... 25 

FIGURES 

1. Index map of study area......................................................................................................................................... 2 

2. Map of interior seaway of North America............................................................................................................. 4 

3. Restored regional cross section of Cretaceous rocks from northeast Utah to southeast Wyoming ...................... 5 

4. Block diagram illustrating types of paralic and marine deposits........................................................................... 5 

5. Map showing location of outcrops of Airport Sandstone Tongue of Baxter Shale in roadcut of Wyoming 

Highway 430 .... .. .. .. .. .. .. .. ...... .. .. .. . . . . . . . .. .. .. . .. .. .. .. . .. .. . . . . . .. .. . . . . . . . .. .. .. . . . .. .. .... .... .. . .. . .. .. .. .. .. .. .. .. .. .. . .. .. .. .. . . . . .. . .... .... .... .. .. . 6 

6. Photograph of outcrop of Airport Sandstone Tongue of Baxter Shale in roadcut of Wyoming Highway 430 .... 6 

7. Columnar section of measured section 7585 of Airport Sandstone Tongue of Baxter Shale ............................... 6 

8. Photograph of sharp basal contact of submarine fan in Blair Formation.............................................................. 7 

9. Photograph of sharp upper contact of submarine fan in Blair Formation............................................................. 7 

10. Map showing location of outcrops of submarine fan in Blair Formation on east flank of Rock Springs uplift... 8 

11. Pen sketches of submarine fan in Blair Formation along Interstate Highway 80, east of Rock Springs, Wyo .... 9 

12-14. Photographs of Blair Formation along Interstate Highway 80, showing: 

12. Convoluted bedding in channel deposit of submarine fan............................................................................ 10 

13. Anticlinal distortion in channel deposit of submarine fan ........................................................................... 10 

14. Synclinal distortion in channel deposit of submarine fan............................................................................. 10 

15. Photograph of fossil burrows, crawling trails, and feeding traces in submarine fan in Blair Formation.............. 10 

16. Photograph of marine reptile tracks(?) in submarine fan in Blair Formation....................................................... 11 

17. Map showing location of longshore bar, prodelta, and slumped delta-front deposits in Blair Formation............ 12 

18. Columnar section of measured section 7785 of longshore bar in Blair Formation on southeast flank of Rock 

Springs uplift......................................................................................................................................................... 13 

19. Photograph of sand wave in longshore bar in Blair Formation on southeast flank of Rock Springs uplift.......... 13 

20. Photograph of convoluted bedding on avalanche slope in longshore bar in Blair Formation on southeast 

flank of Rock Springs uplift.................................................................................................................................. 13 

III 
IV CONTENTS 

21. Map showing location of submarine channel and overbank deposits in Blair Formation on southeast flank of 

Rock Springs uplift............................................................................................................................................... 14 

22. Columnar section of measured section 9882 of submarine channel in Blair Formation on southeast flank of 

Rock Springs uplift............................................................................................................................................... 15 

23-26. Photographs of Blair Formation, on southeast flank of Rock Springs uplift, showing: 

23. Distant view of submarine channel sandstone.............................................................................................. 15 

24. Closeup view of submarine channel sandstone............................................................................................ 15 

25. Scoured base of submarine channel overbank deposit................................................................................. 16 

26. Coarsening-upward sandstone sequence in submarine channel overbank deposit....................................... 16 

27. Photograph of prodelta deposits in Blair Formation in roadcut of Wyoming Highway 430 ................................ 16 

28. Columnar section of measured section 7485 of prodelta deposits in Blair Formation in roadcut of Wyoming 

Highway 430.. ................... ............... ........... ................... .................. ............. .. .......................... .... ........................ 17 

29. Map showing location of delta-front sandstones and heavy-mineral beach placer in Rock Springs Formation on 

east flank of Rock Springs uplift........................................................................................................................... 17 

30. Photograph of delta-front sandstone and shale in Rock Springs Formation on tributary of Black Butte Creek .. 17 

31. Columnar section of measured section 3776 of delta-front sandstones in Rock Springs Formation on southeast 

flank of Rock Springs uplift.................................................................................................................................. 18 

32-34. Photographs of Rock Springs Formation, showing: 

32. Lower delta-front deposits on tributary of Black Butte Creek..................................................................... 18 

33. Middle delta-front sandstone on tributary of Black Butte Creek................................................................. 18 

34. Upper delta-front sandstone on tributary of Black Butte Creek................................................................... 19 

35. Columnar section of measured section 2580 of slumped lower delta-front sandstone in Blair Formation in 

Cutthroat Draw...................................................................................................................................................... 19 

36. Photograph of slumped beds in lower delta-front sandstone in Blair Formation in Cutthroat Draw.................... 20 

37. Photograph of heavy-mineral beach placer in Rock Springs Formation on tributary of Black Butte Creek........ 20 

38. Map showing location of flood-tidal delta and tidal inlet deposits in Rock Springs Formation near Thayer 

Junction, Wyo....................................................................................................................................................... 21 

39. Columnar section of measured section 7582 of flood-tidal delta sandstone in Rock Springs Formation near 

Thayer Junction, Wyo........................................................................................................................................... 22 

40. Photograph of bidirectional crossbeds in tidal inlet associated with delta-front sandstone in Rock Springs 

Formation near Thayer Junction, Wyo.................................................................................................................. 22 

41. Photograph of flood-ramp sandstone in flood-tidal delta sandstone in Rock Springs Formation near Thayer 

Junction, Wyo ....................................................................................................................................................... 22 

42. Restored cross section of flood-tidal delta deposits in Rock Springs Formation near Thayer Junction, Wyo..... 23 

43. Photograph of landward-dipping fore set laminae in flood-tidal delta sandstone in Rock Springs Formation 

north of Interstate Highway 80 near Thayer Junction, Wyo................................................................................. 24 

44. Photograph of outcrops of tidal inlet sandstone in Rock Springs Formation near Thayer Junction, Wyo........... 24 

45. Map showing locations of distributary channel sandstone and lower upper delta-plain deposits in Rock Springs 

Formation 1Ih mi east of Rock Springs, Wyo ...................................................................................................... 24 

46. Photograph of distributary stream channel sandstone overlying delta-front sandstone in Rock Springs 

Formation 11h mi east of Rock Springs, Wyo ...................................................................................................... 25 

47. Columnar sections of measured sections 680 and 10482 of upper and lower parts of lower delta-plain deposits 

in Rock Springs Formation near Thayer Junction, Wyo. and near Superior, Wyo............................................... 26 

48. Map showing location of upper lower delta-plain deposits in Rock Springs Formation along Highway 371 

near Superior, Wyo ............................................................................................................................................... 27 

49. Photograph of outcrops of upper lower delta-plain deposits in Rock Springs Formation near Superior, Wyo.... 27 

50. Columnar sections of measured sections 3177 and 181 of upper delta-plain deposits in Rock Springs Formation 

in Rock Springs, Wyo........................................................................................................................................... 28 

51. Photograph of outcrops of lower upper delta-plain deposits in Rock Springs Formation in roadcut of 

Interstate Highway 80 1/2 mi east of Rock Springs, Wyo...................................................................................... 29 

52. Map showing location of upper delta-plain deposits in Rock Springs Formation in Rock Springs, Wyo............ 30 

53-55. Photographs of Rock Springs Formation, in Rock Springs, Wyo., showing: 

53. Upper upper delta-plain deposit along Killpecker Creek............................................................................. 31 

54. Outcrops of sandstone, carbonaceous shale, and coal in upper upper delta-plain deposits ......................... 31 
CONTENTS v 

55. Splay sandstone and shale in upper delta-plain deposits along Killpecker Creek........................................ 31 

56. Photograph of outcrops of point bars on meander loops of stream channels near top of Rock Springs Formation 

in Rock Springs, Wyo .................................. .. ......................... ............................ ........................... .. ..................... 31 

U.S. customary unit 

foot (ft) 

mile (mi) 

square mile (mi2) 

inch (in.) 

CONVERSION FACTORS 

Multiply by 

0.3048 

1.609 

2.59 

2.54 

To obtain metric unit 

meter (m) 

kilometer (km) 

square kilometers (km2) 

centimeters (em) 

COASTAL SEDIMENTATION ALONG A SEGMENT OF THE 

INTERIOR SEAWAY OF NORTH AMERICA, 

UPPER CRETACEOUS BAXTER SHALE, AND 

BLAIR AND ROCK SPRINGS FORMATIONS, 

ROCK SPRINGS UPLIFT, SOUTHWEST WYOMING 

By Henry W. Roehler 

ABSTRACT 

Outcrops of the Baxter Shale and the Blair and Rock 

Springs Formations in the Rock Springs uplift comprise 

rocks of paralic and marine delta, shelf, slope, and basin 

origins. When their depositional environments are synthesized, the rocks reveal the pattern of sedimentation along 

part of the west coast of the Late Cretaceous interior seaway of North America. The rocks investigated crop out 

in nine easily accessible geographic areas that are located 

in the report by detailed topographic maps. Columnar 

sections, photographs, and sketches illustrate and integrate the observations of the report, which contributes to 

studies of the sedimentology and to the understanding of 

the origin and location of mineral deposits in the Rock 

Springs uplift area. 

INTRODUCTION 

PURPOSE AND METHODOLOGY 

This study examines the sedimentary rocks deposited 

along a segment of the west coast of the interior seaway of 

North America in southwest Wyoming during the late Santonian and early Campanian subages of the Late Cretaceous 

Epoch. Sedimentologic data are presented in ascending 

paleoenvironmental sequence, beginning with descriptions 

of marine basin, slope, and shelf deposits in the Baxter 

Shale and Blair Formation and ending with descriptions of 

paralic delta-front and delta-plain deposits in the Rock 

Springs Formation. The study focuses on the geographic 

location of rocks deposited in selected depositional environments. It emphasizes the sedimentology of sandstone 

beds, but does not dwell on the origin of sedimentary structures, on paleogeography, or on paleontology. 

Rock outcrops were studied in nine geographic areas 

located between Tps. 16-21 N., and Rs. 101-105 W. in 

the central and southern parts of the Rock Springs uplift. 

The geographic interrelation of the nine study areas is 

shown in figure 1, which locates figures 5, 10, 17, 21, 29, 

38, 45, 48, and 52. When combined, the outcrop areas 

total about 75 mi2. They are mostly located along paved 

highways, but a few are located adjacent to improved 

gravel roads. All the outcrops are easily accessible by 

automobile. 

The sedimentologic data used in preparing this 

report were acquired by me during field investigations 

that began in 1952 and continued intermittently through 

1989. The data were derived primarily from hundreds of 

stratigraphic sections measured on the flanks of the uplift. 

Parts of nine of these sections are illustrated in the report 

by columnar sections. The stratigraphic sections were 

measured using a 5-ft Jacob staff with attached Abney 

level to compensate for the dip of strata; a pocket engineering tape measure was used to measure beds less than 

5 ft thick. Detailed lithologic descriptions of the stratigraphic sections are on file at the Wyoming Geological 

Survey, Laramie, Wyo. Sediment transport directions for 

some sandstone beds were recorded using a Brunton 

compass; several measurements appear in the report in a 

rose diagram. During these investigations, eighteen 71

h' 

geologic quadrangles were mapped along the southeast 

part of the Rock Springs uplift and a reconnaissance geologic map of the uplift was published at the scale of 1 in. 

= 2 mi (Roehler, 1977). 

GEOLOGIC SETTING 

The Rock Springs uplift area is a windy desert with 

cold winters and warm to hot summers. The general 
2 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

109° DO' 108° 45' 

41 ° 

45' ==~--+--:-:f:~.:::.- -~...,.k 

Tertiary rocks 

Undivided Eocene and 

Paleocene rocks 

Cretaceous rocks 

108° 30' 

Undivided Lance Formation, 

Fox Hills Sandstone, Lewis 

Shale, Almond Formation, 

and Ericson Formation 

Rock Springs Formation 

Blair Formation 

Baxter Shale 

Figure 1. Index map of the Rock Springs uplift showing formations studied (shaded). Outlines and figure numbers locate and designate 

detailed maps of outcrop areas studied. Base from U.S. Geological Survey 1:500,000 topographic map of Wyoming; contour interval500 ft. 
SEDIMENTOLOOY 3 

range of altitude is from 6,000 to 8,000 ft. Vegetation is 

sparse. Cedar trees are present on a few high-standing 

ridges, but most of the area is characterized by sage, 

greasewood, rabbit brush, cactus, lichens, and a variety of 

desert flowers. The major drainage is Bitter Creek, which 

flows perennially from east to west across the center of 

the uplift and whose valley the Union Pacific Railroad follows (fig. 1). Major intermittent tributaries of Bitter 

Creek include Salt Wells Creek and Little Bitter Creek. A 

number of villages and small towns are present in the 

uplift area, but the only sizable city is Rock Springs, 

whose population is about 25,000. The main industries 

are cattle and sheep ranching, oil and gas exploration and 

production, and coal mining. 

The structure of the Rock Springs uplift consists of a 

north-south-trending, doubly plunging, asymmetric anticline about 70 mi long and 40 mi wide located near the 

center of the greater Green River basin north of the common boundary of Wyoming, Utah, and Colorado (fig. 1 ). 

Dips in Cretaceous, Paleocene, and Eocene rocks exposed 

on the flanks of the uplift range from 3 o to 35° on the 

west flank and from 3° to go on the east flank. The center 

of the uplift is composed of deeply eroded, soft shale, 

which is surrounded by numerous resistant sandstone 

ridges separated by shale valleys. The uplift is a Laramide structure that was uplifted at least twice during the 

Late Cretaceous and at least three times during the Paleocene and Eocene (Roehler and others, 1977). The uplift 

was extensively faulted during the Paleocene, eroded to a 

peneplain during the Oligocene and Miocene, and the site 

of intensive volcanic activity during the Pliocene and 

Pleistocene. 

SEDIMENTOLOGY 

The sedimentary rocks of paralic and marine origins 

investigated in this report were deposited in subtropical to 

warm temperate climates that prevailed along the west 

coast of the interior seaway during the Late Cretaceous 

(Kauffman, 1977). The interior seaway at that time 

extended in a north-south direction across central North 

America from southern Alaska and Canada southward to 

the Gulf of Mexico (Gill and Cobban, 1966). The rocks 

investigated were deposited when the seaway was nearly 

1,000 mi wide east of the study area (fig. 2). The basin of 

the seaway was asymmetric, with the area of maximum 

subsidence and thickest sediment accumulation located 

along its western margins (King, 1959). 

Upper Cretaceous rocks exposed in the Rock 

Springs uplift, in ascending sequence, are the Baxter 

Shale of marine origin, the Mesaverde Group (consisting 

of the Blair and Rock Springs Formations, Ericson Sandstone, and Almond Formation) of shallow marine and 

continental origins, the Lewis Shale of marine origin, 

and the Fox Hills Sandstone and Lance Formation of 

shallow marine and continental origins. The stratigraphic 

positions and intertonguing relationships of these and 

other formations of Late Cretaceous age are illustrated in 

a restored regional west-east cross section across the 

study area (fig. 3). 

The formations studied are of Santonian and Campanian Ages. These ages have been determined by the Late 

Santonian ammonite index fossil Desmoscaphites bassleri 

collected at the top of the Airport Sandstone Tongue of 

the Baxter Shale by Hale (1950) and the early Campanian 

ammonite index fossil Scaphites hippocrepis collected at 

several stratigraphic levels in the Blair Formation by 

Smith (1961). Regional correlations of stratigraphic units 

containing these and other Late Cretaceous index fossils 

were discussed by Roehler (1990). 

The environmental relationships and types of paralic 

and marine deposits discussed in this report are illustrated 

by a block diagram in figure 4. Figure 4 is a crosssectional view of the onshore, nearshore, and offshore 

parts of an arcuate delta, a type that is generally wave 

dominated. These features are characteristic of all the delta 

systems present in Upper Cretaceous rocks in the Rock 

Springs uplift area. The following discussion identifies, 

locates, and describes deposits that correspond to the features illustrated in figure 4. 

MARINE BASIN DEPOSITS 

The Airport Sandstone Tongue in the Baxter Shale is 

a marine basin deposit. It takes its name from the Rock 

Springs airport in sec. 30, T. 19 N., R. 103 W., where it 

forms a broad, flat bench on which the runways are 

located. The upper exposed part of the sandstone locally 

stands more than 75 ft high; along its north edge, it arcs in 

an east-west direction across the axis of the Rock Springs 

uplift. This arcing is visible across the southeastern part of 

T. 19 N., R. 104 W., 1-2 mi south of and parallel to Interstate Highway 80. The Airport Sandstone Tongue is generally 400-550 ft thick and consists of a "sandy" interval 

of thin interbedded and interlaminated sandstone, siltstone, 

and shale situated about 1 ,300 ft below the top and 2,500 

ft above the base of the Baxter Shale. The lithology of the 

tongue coarsens upward, and thin beds of very fine 

grained, limy sandstone are abundant near the top. 

The Airport Sandstone Tongue is well exposed in a 

roadcut of Wyoming Highway 430, 10 mi southeast of 

Rock Springs, Wyo., in SW'/4NE'/4 sec. 28, T. 18 N., R. 

103 W. (fig 5). At this locality, it trends north-northeast, 

dips about 3° SE., and weathers to an extensive roundtopped ridge (fig. 6). The lithology of the upper 40 ft of 

the unit was examined on the east side of the highway 

roadcut and is illustrated in measured section 7585, figure 

7. As indicated in figure 7, the beds are extensively 
4 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

500 

(') 

::0 

~ 

J> 

(') 

rn 

0 

c ........_ (/) 

-------

1000 MILES 

D 

---

Figure 2. Map of interior seaway of North America during Campanian Age of Cretaceous Period. Modified from Gill and 

Cobban ( 1966). 
A 0 

>. 

3: 

~ 

~ ()) 

E 

E 

()) 

~ 

SEDIMENTOLOGY 

0 

>. 

3: 

en01 

c: 

·c 

0. 

CJ) 

STUDY AREA 

~Ss r. 

Baxter Sh. 

FEET 

[" DL-.1.__.___._~ 

0 

>. 

3: 

L!" 

()) 

> 

0: 

----~ Ss.Mbr. 

~~Mbr. 

~G+- -._.~:_~O'Brien Spr; 

~-Tnft-~ngSs.Mbr ~Ss·Mbr. . 

Steele Sh. 

5 

A' 

Figure 3. Restored regional cross section of Cretaceous rocks from northeast Utah to southeast Wyoming. Shaded fonnations are 

continental in origin; unshaded formations are marine in origin. From Roehlcr (1990). 

Lower delta-plain distributary channel 

Coal swamp 

Delta-front distributary channel Shelf channel overbank 

I 

Shelf 

channel 

Longshore I t:iar I 

INTERIOR 

Basin sand, 

Slopi too ,ut or m"' 

CRETACEOUS 

Figure 4. Types of paralic and matine deposits in the Baxter Shale and Blair and Rock Springs Formations in the Rock Springs uplift. 
6 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

R 103W 

T 

18 

N 

Figure 5. Location of marine basin deposits (measured section 

7585, fig. 7) in Airport Sandstone Tongue in the Baxter Shale, in 

roadcut of Wyoming Highway 430. Base from U.S. Geological 

Survey 1:24,000 Baxter, Wyo.; contour interval 20ft. 

Figure 6. Outcrop of Airport Sandstone Tongue in the Baxter 

Shale in roadcut of Wyoming Highway 430 in SWI/4NEI/4 sec. 28, 

T. 18 N., R. 103 W. Outcrop location shown in figure 5. 

current rippled. Deposition probably took place under 

more than 300 ft of water, and a possible explanation for 

the presence of the current ripples is the activity of turbidity currents. 

7585 

EXPLANATION 

Current-rippled 

sandstone 

Current-rippled 

siltstone 

Current-rippled 

shale 

FEET 

Figure 7. Measured section 7585 of Airport Sandstone 

Tongue in the Baxter Shale in roadcut of Wyoming Highway 

430, 11 mi southeast of Rock Springs, Wyo. Section location 

shown in figure 5. 
SEDIMENTOLOGY 7 

SUBMARINE FAN DEPOSITS 

The basal part of the Blair Formation exposes parts 

of 12 submarine fans. These fans compose what is commonly called the "basal Blair sandstones." The fans were 

deposited on submarine slopes (or coastal rises) that were 

located between the shelf and basin of the interior seaway 

(fig. 4 ). The fans are lenticular in cross section, as much 

as 100 ft thick, and 3-10 mi wide. They occasionally 

overlap each other, but have never been observed to coalesce. That some of the fans have upper and lower 

benches indicates the presence of superposed fan lobes. 

Most of the fans fine upward from sharply defined bases 

(fig. 8), but a few coarsen upward to sharply defined tops 

(fig. 9). 

Good exposures of one of these fans are present in a 

roadcut on the north side of Interstate Highway 80 in 

SE1/4NW1/4 sec. 32, T. 20 N., R. 102 W., 16 mi east of 

Rock Springs, Wyo. (location shown in fig. 10). Parts of 

the same fan are exposed 1-1Ih mi south of this roadcut 

in sees. 5 and 6, T. 19 N., R. 102 W. The highway 

roadcut exposures (figs. 11-14) are situated 2,000 ft west 

of an overpass on Interstate Highway 80 at the exit of 

Wyoming Highway 371 to Superior, Wyo. 

The fan exposed in the Interstate Highway 80 roadcut 

consists of three fining-upward lithologic sequences. (1) 

The entire fan fines upwards from a sharp base; (2) internal parts of the fan are composed of fining-upward units 

3.0-4.5 ft thick that comprise multiple beds of alternating 

sandstone and shale; and (3) the individual sandstone and 

shale beds form couplets 4-8 in. thick that are composed 

of very fine grained, silty sandstone at the base and silty 

shale or shale at the top. Interbedded in these sequences 

Figure 8. Sharp basal contact (arrow) and fining-upward sandstone in submarine fan in basal Blair Formation on north slopes of 

Black Butte Creek in NE1/4SE1/4 sec. 6, T. 19 N., R. 102 W. Outcrop location shown in figure 10. Scale indicated by person standing in lower part of view. 

Figure 9. Sharp upper contact (arrow) and coarsening-upward 

sandstone in submarine fan in basal Blair Formation in NWI/4 sec. 

23, T. 17 N., R. 103 W. Bench-forming outcrop is about 40ft thick. 

are a few channel deposits composed mostly of sandstone. 

The overall fining-upward relationships of these lithologic 

units suggest that the fan was retrogradational. 

The beds exposed in the highway roadcut are current 

rippled and contain numerous trace fossils. The trace fossils consist of variously oriented burrows, crawling trails, 

and feeding traces (fig. 15), and possible marine reptile 

tracks (fig. 16). Flute casts, oriented in east-southeast 

directions, are present on the lower surfaces of some sandstone beds. The sedimentary structures and fossil data 

suggest that the fan was deposited under as much as 250ft 

of water. 

The channel deposits in the roadcut section have 

erosional bases and contain deformed and convoluted 

beds. Slumping was apparently initiated within the channels by the seaward flow of soft sediments to where the 

channels filled and overflowed and the channel sediments 

spread outward onto gently seaward sloping adjacent 

parts of the fan. 

The fan in the roadcut section is similar to turbidite 

facies described by Mutti and Lucchi (1978). The turbidite 

facies described by these authors contains isolated channel 

sandstones interbedded in sandstone and shale couplets in 

the middle and outer parts of fans. The section primarily 

consists of sandstone and shale couplets at the outer margins of the fans. The coarse material (sandstone) was 

deposited by traction and the fine material (shale) settled 

out of suspension. The fans in the Blair Formation are 

composed of very finely textured sediments and bear little 

resemblance to the "Bouma sequence" (Bouma, 1962). 

I have reached a number of conclusions concerning 

the submarine fans in the basal Blair Formation. Among 

them are: (1) The source of the sandstone was probably 

distant beaches located northwest of the Rock Springs 

uplift; (2) as most of the fans fine upwards, they were 
8 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

R 102W 

i 

I 

... 

T 

. 20 

N 

T 

19 

N 

Figure 10. Location of submarine fan outcrops in basal Blair Formation, east flank of Rock Springs uplift. Base from U.S. Geological 

Survey 1:24,000 Thayer Junction, Wyo.; contour interval 20 ft. 
West 

A 

B 

c 

D 

Fig.l2 

I 

Fig.l3 

I 

B 

c 

['"' 

0 25 FEET East L...._ ,___.___.___j E 

Figure 11. Pen sketches illustrate a cross-sectional view of part of the peripheral submarine fan in basal Blair Formation in roadcut of Interstate Highway 80, 16 mi east of Rock 

Springs, Wyo. Sedimentary structures and fossils are described and illustrated in figures 12-14. Fan location shown in figure 10. 

C/) 

tTl 

0 

3: 

tTl 

r 

~ 

8 

-< 

\0 
10 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

Figure 12. Convoluted bedding (arrow) in channel sandstone in 

submarine fan in basal Blair Formation in roadcut on north side of 

Interstate Highway 80, 16 mi east of Rock Springs, Wyo. Outcrop 

location shown in figures 10 and 11. 

Figure 13. Anticlinal distortion in channel deposits in submarine 

fan in basal Blair fonnation in roadcut on north side of Interstate 

Highway 80, 16 mi east of Rock Springs, Wyo. Outcrop location 

shown in figures 10 and 11 . 

probably deposited as a result of either tectonic disturbances or repetitious climate changes, which occurred suddenly and then moderated; and (3) the geographic 

distribution of the fans suggests that they are not part of a 

single river system, unless they are associated with distributary streams of a very large delta. 

MARINE SHELF DEPOSITS 

Two types of linear, shelf sandstone deposits have 

been identified in marine shale in the middle part of the 

Blair Formation in Tps. 16-17 N., Rs. 102-103 W., on the 

Figure 14. Syncline in defonned bedding in channel of submarine fan in basal Blair Formation in roadcut on north side of Interstate Highway 80, 16 mi east of Rock Springs, Wyo. Outcrop 

location shown in figures 10 and 11. 

Figure 15. Trace fossils at base of submarine fan in basal Blair 

Fonnation in NEI/4SEI/4 sec. 6, T. 19 N .. R. 102 W. Outcrop location shown in figure 10. 
SEDIMENTOLOGY 11 

Figure 16. Trace fossils including possible reptile tracks (arrow) 

at base of submarine fan in basal Blair Formation in NEI/4 SEI/4 sec. 

6, T. 19 N., R. 102 W. The animal that made the tracks appears to 

have had three toes and webbed feet. Outcrop location shown in 

figure 10. 

southeast flank of the Rock Springs uplift. The first type 

comprises a longshore bar that paralleled the northeast 

trend of the Blair Formation shorelines. The second type 

consists of submarine channel and overbank deposits that 

are perpendicular to the trend of the Blair Formation 

shorelines. 

LONGSHORE BAR 

The longshore bar identified in the Blair Formation 

crops out as isolated knobs along the tops of ridges 

located in sees. 7 and 18, T. 17 N., R. 102 W. The bar is 

particularly well exposed in SEI/4NWI/4 sec. 18, T. 17 N., 

R. 102 W., where eroded remnants cap a low ridge (fig. 

17). The bar there is composed mostly of sandstone (section 7785, fig. 18), which exhibits southeast-dipping, planar crossbeds in the direction of prevailing longshore 

currents (fig. 19). Some of the foreset laminae in these 

beds dip as much as 20°, which, in places, resulted in avalanche slope failure and bed convolutions (fig. 20). 

SUBMARINE CHANNEL AND OVERBANK 

A submarine channel sandstone is exposed in a thick 

section of marine shale in the middle part of the Blair Formation in SWI/4SWI/4SEI/4 sec. 36, T. 17 N., R. 103 W. 

(fig. 21). The channel trends about S. 18° E., is lenticular 

and about 400 ft wide in cross section, and has a maximum recorded thickness of about 18 ft (section 9882, fig. 

22). The channel is a coarsening-upward sequence. The 

lower 8 ft is transitional with underlying marine shale and 

consists of thin, parallel beds of gray siltstone and interbedded gray, sandy shale. The upper 10 ft is composed of 

tan, very fine grained to fine-grained sandstone in lowangle, canoe-shaped trough crossbeds that are 12-15 ft 

wide and as much as 75 ft long (figs. 23, 24). 

A few limy layers in the channel sandstone, composed of mostly lag material, contain small, flat, rounded, 

gray clay pebbles and abundant marine fossils. Fossil mollusks include Nucula sp., Inoceramus balticus, and 

unidentified small gastropods. Ammonite fossils were 

identified as Baculites sp., Scaphites hippocrepis, and 

Glyptoxoceras rubeyi (USGS Mesozoic locality D11913). 

Trace fossils are present in thin beds of shale near the 

base of the channel, and small black shark teeth were collected from adjacent ant hills. Similar but smaller shelf 

channels are present in outcrops a few hundred feet north 

and south of this channel. 

Marine channel and overbank deposits are exposed in 

SEI/4 sec. 2, T. 16 N., R. 103 W. (fig. 21). The contact of 

one of these overbank deposits with underlying marine 

shale is a sharply defined scoured surface (fig. 25). Above 

this sharply defined basal contact, the overbank deposit 

consists of current-rippled, parallel to subparallel beds of 

dark-gray, silty shale, and interlaminated gray siltstone. 

These beds coarsen upward into parallel to subparallel 

beds, as much as 0.2 ft thick, consisting of gray, very fine 

grained to fine-grained sandstone (fig. 26). The channel 

deposit shown in figures 25 and 26 is part of an isolated 

outcrop, which makes the overall size and geometry of the 

deposit impossible to determine. One overbank deposit in 

the area, however, is more than 7 ft thick and at least 300 

ft wide. 

PRODELTA DEPOSITS 

Prodelta deposits are exposed in a roadcut and in outcrops above the roadcut along the east side of Wyoming 

Highway 430 in NW1/4NE1/4 sec. 29, T. 17 N., R. 102 W., 

19 mi southeast of Rock Springs, Wyo. (figs. 17, 27). The 

prodelta deposits consist of more than 120 ft of mostly 
12 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

R 102W 

T 

17 

N 

Figure 17. Location of measured sections 7485 (prodelta deposits), 7785 (longshore bar), and 2580 (slumped delta-front deposits) in the 

Blair Formation, and figures 18, 19, 20, 27, 28, 35, and 36. Base from U.S. Geological Survey 1:24,000Camel Rock, Wyo.; contour interval 

20ft. 
SEDIMENTOLOOY 13 

7785 

EXPLANATION 

Tabular crossbedded 

sandstone 

Subparallel-bedded 

sandstone 

Convoluted sandstone 

5 ~ Marine shale 

Figure 18. Measured section 7785 of longshore bar in Blair Formation on southeast flank of Rock Springs uplift. Section location 

shown in figure 17. 

Figure 19. Large sand wave with southeast-dipping foreset laminae in longshore bar in Blair Formation on southeast flank of Rock 

Springs uplift. Outcrop location shown in figure 17. Pick handle is 

1.5 ft long. 

Figure 20. Convoluted bedding (arrow) on avalanche slope of 

sand wave in longshore bar in Blair Formation on southeast flank 

of Rock Springs uplift. Outcrop location shown in figure 17. 

dark gray, silty shale that is interbedded with numerous 

very thin beds of gray, sandy siltstone and some gray, 

very fine grained sandstone (section 7485, fig. 28). The 

siltstone and sandstone occur in parallel, partly wave rippled beds and laminae containing abundant Ophiomorpha, 

Skolithus, and worm borings and trails. The prodelta 

deposits thicken and coarsen upward in the outcrops to 

where they merge imperceptibly with still thicker beds of 

sandstone and shale that cap the slopes on the east side of 

Highway 430. The cap rocks are part of a lower deltaplain sequence in the overlying Chimney Rock Tongue of 

the Rock Springs Formation (fig. 3). 

DELTA-FRONT DEPOSITS 

Outcrops of delta-front deposits are ubiquitous in the 

basal part of the Rock Springs Formation on the east and 
14 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS. SOUTHWEST WYOMING 

T 

17 

N 

T 

16 

N 

Figure 21. Location of submarine channel and overbank deposits in measured section 9882 and in figures 23-26, Blair Formation on 

southeast flank of Rock Springs uplift. Base from U.S. Geological Survey 1:24.000 Camel Rock. Wyo.; contour interval 20 ft. 
SEDIMENTOLOGY 15 

9882 

EXPLANATION 

• . . 

. 

. 

Trough-crossbedded 

sandstone 

Parallel-bedded 

sandstone 

~- ~ Marine shale 

FEET 

Figure 22. Measured section 9882 of submarine channel sandstone in Blair Formation on southeast flank of Rock Springs uplift. 

Section location shown in figure 21. 

Figure 23. View to north of trough-crossbedded submarine 

channel sandstone (arrow) in Blair Formation on southeast flank of 

Rock Springs uplift. Jacob staff near center of photograph is 5 ft 

long. Outcrop location shown in figure 21. 

Figure 24. Closeup view of submarine channel sandstone in Blair 

Formation shown in figure 23. Pick handle is 1.5 ft long. Outcrop 

location shown in figure 21 . 

west flanks of the Rock Springs uplift. They are conspicuous along Interstate Highway 80 a few miles west of 

Point of Rocks, Wyo., and a few miles east of Rock 

Springs, Wyo., where they crop out as stacked beds of tan 

and light-gray sandstone that generally weather to cliffs. 

SHORELINE SANDSTONES 

Seven delta-front shoreline sandstones are superposed 

in outcrops that dip about 5° E. along an east-west-trending ridge near the center of sec. 24, T. 19 N., R. 102 W., 

on the east flank of the Rock Springs uplift. One of these 

delta-front sandstones, well exposed near the east end of 

the ridge in NEI/4NEI/4SEI/4 sec. 24 (fig. 29), displays the 
16 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

Figure 25. Scoured, sharp basal contact (arrow) of submarine 

channel overbank siltstone and very fine grained sandstone overlying marine shale in Blair Formation on southeast flank of Rock 

Springs uplift. Pick handle is 1.5 ft long. Outcrop location in 

figure 21. 

Figure 26. Coarsening-upward, current-rippled, very fine 

grained sandstone in submarine channel overbank deposit in Blair 

Formation on southeast flank of Rock Springs uplift. Pocket knife 

is 3.3 in. long. Outcrop location shown in figure 21. 

three characteristic lithofacies of delta-front deposits in the 

uplift area (figs. 30, 31). The three lithofacies are (1) the 

lower delta front consisting of tan, very fine grained to 

fine-grained sandstone and some interbedded gray, silty 

shale, deposited distances offshore (fig. 32); (2) the middle delta front consisting of massive or thick, subparallel 

beds of tan, fine-grained sandstone, deposited in shallow, 

nearshore water (fig. 33); and (3) the upper delta front 

consisting of variously bedded, light-gray, fine- to 

medium-grained sandstone deposited inshore and onshore 

(fig. 34 ). The upper delta-front sandstone can be further 

subdivided into small-scale trough crossbeds that comprise 

a surf zone at the base (fig. 34, No. 1 ), thin, parallel, tabular beds that comprise a forebeach zone in the middle (fig. 

Figure 27. Prodelta deposits in upper part of Blair Formation in 

roadcut of Wyoming Highway 430, 20 mi southeast of Rock 

Springs, Wyo. Outcrop location shown in figure 17. 

34, No. 2), and deeply weathered, faintly crossbedded 

remnants of eolian dunes at the top (fig. 34, No. 3). 

SUBMARINE SLUMPS 

Submarine slumps are present in lower delta-front 

sandstones in measured section 2580 in the Blair Formation in Cutthroat Draw in sec. 9, T. 17 N., R. 102 W. on 

the southeast flank of the Rock Springs uplift (figs. 17, 

35). The slumped beds are as much as 13 ft thick and 

partly convoluted (fig. 36), and they are interbedded with 

shale and uncontorted parallel-bedded and hummockycrossbedded sandstone. The slumped beds are believed to 

be the product of submarine slope failure and the mass 

movement of unconsolidated sand toward the periphery of 

an arcuate delta (Roehler, 1988). The sand bodies were 

not confined to channels, but flowed downslope (marineward) in sheetlike masses. The mechanics of the slumping 

are analogous to those of snow avalanches. 

HEAVY-MINERAL BEACH PLACER 

A heavy-mineral beach sandstone placer deposit is 

present in SI/2NI/2NWI/4SWI/4 sec. 19, T. 19 N., R. 101 

W., 1,000 ft east of the previously described delta-front 

sandstone deposit in section 3776 (fig. 29). The placer 

deposit is located along the top of an upper delta-front 

sandstone that overlies section 3776 (fig. 37). The placer 

deposit, in turn, is overlain by a thick section of interbedded sandstone, shale, and carbonaceous shale of lagoon 

origin. The mineralized zone is nearly 2,000 ft wide, about 

3 ft thick, and trends northeast parallel to the strike of the 

delta-front shoreline. An erosional remnant of the placer is 
SEDIMENTOLOOY 17 

7485 

EXPLANATION 

• ~ 

~ 

~ 

~ 

Parallel-bedded 

sandstone 

Parallel-bedded 

siltstone 

Marine shale 

FEET 

[ 

Figure 28. Measured section 7485 of prodelta deposits in Blair 

Formation in roadcut of Wyoming Highway 430. 19 mi southeast 

of Rock Springs, Wyo. Section location shown in figure 17. 

R 102W 

T 

19 ·h~·c~· =....,----~"'-·-• ...... 1 N 

R 101 W 

Figure 29. Location of delta-front deposits and heavy-mineral 

beach placer in measured section 3776 and in figures 31-34 and 37, 

Rock Springs Formation on tributary of Black Butte Creek on east 

flank of Rock Springs uplift. Base from U.S. Geological Survey 

I :24.000 Point of Rocks SE, Wyo.: contour interval 20ft. 

Figure 30. Outcrops of 1, lower. 2. middle, and 3, upper deltafront sandstone and shale in Rock Springs Formation on tributary 

of Black Butte Creek on east flank of Rock Springs uplift. Outcrops 

arc 185 ft thick. 
18 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

3776 

Upper delta front 

(dunes, forebeach, surf) 

EXPLANATION 

Sandstone; variously 

bedded 

~:]Shale 

t: ~ j Carbonaceous shale 

~Coal 

Middle delta front 

FEET 

25 

Lower delta front 

Figure 31. Measured section 3776 of delta-front sandstones in 

Rock Springs Formation on tributary of Black Butte Creek on east 

flank of Rock Springs uplift. Section shown in figure 29. 

Figure 32. Parallel-bedded lower delta-front sandstone and shale 

in Rock Springs Formation on tributary of Black Butte Creek. illustrated in measured section, figure 31. 

Figure 33. Subparallel-bedded, middle delta-front sandstone in 

Rock Springs Formation on tributary of Black Butte Creek, illustrated in measured section, figure 31. Note that some foreset laminae dip to the left in a southeast (seaward) direction. 

separated from the main part of the deposit on the 

upthrown side of a west-northwest-trending, high-angle 

normal fault. The erosional remnant surrounds the common comer of sees. 24 and 25, T. 19 N., R. 102 W. and 

sees. 19 and 30, T. 19 N., R. 101 W. (fig. 29). Examination of a channel sandstone that is the stratigraphic equivalent of the placer, in outcrops 500 ft northeast of the 

placer, indicates that the placer formed at the mouth of a 

small distributary stream that flowed southeast from an 

adjacent delta plain. Ophiomorpha, Arenicolites, and other 

trace fossils are abundant in the placer deposit, and Corhula undifera and Thalassinoides were identified in nearby 

outcrops. 

The heavy-mineral placer deposit weathers dark red 

brown and contains radioactive zircon. Because of this 

radioactivity, the deposit was claimed by uranium 
SEDIMENTOLOOY 19 

Figure 34. Upper delta-front sandstone in Rock Springs Formation on tributary of Black Butte Creek, illustrated in measured section, figure 31. 1, Small-scale, trough-crossbedded surf sandstone; 

2, parallel, tabular-bedded forebeach sandstone; 3, deeply weathered dune(?) sandstone. 

prospectors in the 1950's, who dug several exploratory 

pits and trenches along the outcrops. The grain-size distribution of the deposit is about 15 percent coarse, 30 percent medium, 20 percent fine, 20 percent very fine, and 15 

percent silt and clay (Roehler, unpub. data, 1978). Magnetic heavy-mineral fractions consisting of ilmenite and 

magnetite compose 50-55 percent. The nonmagnetic 

heavy-mineral fraction is composed of more than 95 percent zircon, with the remaining fractions composed of 

mostly garnet and rutile. The composition is similar to six 

other beach placer deposits described by Roehler (1989) in 

Upper Cretaceous rocks in the Rock Springs uplift area. 

The placer deposit has proven to be uneconomic as a 

source for uranium, but it remains a possible source for 

titanium. The titanium is present in the ilmenite, which is 

composed 52-68 percent of titanium dioxide. 

FLOOD-TIDAL DELTA AND TIDAL INLET 

The lower part of the Rock Springs Formation 

exposes several delta-front sandstones along Interstate 

Highway 80 in sees. 21, 22, 27, and 28, T. 20 N., R. 102 

W., on the east flank of the Rock Springs uplift. These 

sandstones weather to tan benches. Some are stacked one 

upon the other and many have white sandstone cap rocks. 

At the top of one of these delta-front sandstones, where it 

crosses Interstate Highway 80 near Thayer Junction in the 

south-center of sec. 22, T. 20 N., R. 102 W. (fig. 38), is a 

tidal-inlet sandstone. The tidal-inlet deposits (section 

7582, fig. 39) comprise 12 ft of tan-gray fine- to mediumgrained sandstone in thick, planar crossbeds having bidirectional (northwest- and southeast-dipping) foreset 

2580 

EXPLANATION 

• . 

. 

. 

. 

. 

~ 

~ 

II . 

. 

. . 

iii 

Parallel-bedded 

sandstone 

Hummocky 

cross bedded 

sandstone 

Convoluted 

sandstone 

Marine shale 

Figure 35. Measured section 2580 of slumped lower delta-front 

sandstone in Blair Formation in Cutthroat Draw on southeast flank 

of Rock Springs uplift. Section location shown in figure 17. 

laminae (fig. 40). The bidirectional bedding is the result of 

the landward flow of flood tides and the seaward flow of 

ebb tides near a flood ramp at the head of the flood-tidal 
20 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

Figure 36. Submarine slump of lower delta-front sandstone in 

Blair Formation in Cutthroat Draw on southeast flank of Rock 

Springs uplift. Convoluted interval is 7.5 ft thick. Outcrop location 

shown in figure 17. 

Figure 37. Heavy-mineral beach placer (arrow) in delta-front 

sandstone in Rock Springs Formation on tributary of Black Butte 

Creek, southeast flank of Rock Springs uplift. The placer deposit 

has a maximum thickness of about 3 ft. Outcrop location shown in 

figure 29. 

delta (fig. 41). The flood-tidal delta was aligned southeast 

and opened in a landward direction into a large, brackish, 

open-water lagoon located to the northwest. The sandstone 

that makes up the flood-tidal delta thins in outcrops for 

about 4,000 ft in a northwest direction from where it 

crosses Interstate Highway 80. It wedges out in gray, 

slightly carbonaceous shale of lagoon origin in the eastcenter of NEI/4NWI/4SEI/4 sec. 21, T. 20 N., R. 102 W., 

near measured section 10482 (figs. 38, 42). The flood-tidal 

delta sandstone consists of parallel to subparallel beds 

with mostly landward dipping foreset laminae across the 

middle and distal parts of the delta (fig. 43). 

Eroded remnants of the seaward part of the tidal-inlet 

sandstone associated with the flood-tidal delta are present 

in measured section 7682 in WI/2SEI/4NEI/4 sec. 27, T. 20 

N., R. 102 W., on the south slopes of Bitter Creek, 3,000 

ft south-southeast of where the flood-tidal delta sandstone 

crosses Interstate Highway 80 (fig. 38). The upper part of 

the inlet there is composed of 12 ft of light-gray, fine- to 

medium-grained sandstone in parallel beds with bidirectional (landward- and seaward-dipping) foreset laminae. 

These beds are underlain by 14 ft of tan, fine- to mediumgrained, partly shaly sandstone beds that occur in lenses 

up to 4 ft thick made up of broad, low-angle trough crossbeds having scoured bases (fig. 44 ). 

DELTA-PLAIN DEPOSITS 

Delta-plain deposits are divided into lower delta plain 

and upper delta plain, based on their paleogeographic 

location and lithology. The lower delta plain consisted of 

the seaward parts of deltas, where large, open-water bays 

were present. The lower delta plain is composed mostly 

of thick beds of bay-fill shale and thin interbedded splay 

sandstone, carbonaceous shale, and coal (fig. 4). The 

upper delta plain consisted of the landward parts of deltas, 

where large swamps and coal bogs were present. The 

upper delta plain is composed of thick interbedded carbonaceous shale, coal, splay sandstone, stream-channel sandstone, and thin interbedded bay-fill shale (fig. 4). The 

dividing line between the lower delta plain and the upper 

delta plain in modern deltas is generally placed at the 

uppermost limit of salt water (tidal) influence. The dividing line is easily recognized in modern deltas by distinct 

changes of freshwater to saltwater vegetation, but it is 

generally vague in rock outcrops of ancient deltas. 

DISTRIBUTARY STREAM CHANNEL 

A distributary stream channel sandstone rests upon a 

delta-front sandstone in outcrops of the Rock Springs Formation in NW1/4 sec. 29, T. 19 N., R. 104 W., about 1,000 

ft north of Interstate Highway 80, li/2 mi east of Rock 

Springs, Wyo. (figs. 45, 46). The channel sandstone is 

about 26 ft thick and lenticular in cross section, and it has 

a scoured base. It is composed of mostly gray, very fine 

grained to fine-grained sandstone in large-scale trough 

cross beds. 

LOWER DELTA PLAIN 

The lower part of a lower delta-plain deposit is 

exposed in the Rock Springs Formation in measured section 10482 located in NWI/4SWI/4 sec. 22, T. 20 N., R. 

102 W., overlying the previously described flood-tidal 
SEDIMENTOLOGY 

R 102W 

21 

T 

20 

N 

Figure 38. Location of flood-tidal delta and tidal inlet deposits in Rock Springs Formation in measured sections 7582 and 7682 and in 

figures 39-41 and 43-44. Base from U.S. Geological Survey 1:24,000 Thayer Junction, Wyo.; contour interval 20ft. 
22 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

7582 

EXPLANATION 

II 

B 

m . 

. 

. - . - . 

~--

~ 

-

-

--

~ 

Flood tidal-delta 

sandstone 

Forebeach sandstone 

Splay sandstone and 

shale 

Bay-fill shale 

Reed swamp carbonaceous shale 

Forest swamp coal 

F---l Hematite concretions 

Bidirectionality of 

foreset laminae 

FEET 

10 

Figure 39. Measured section 7582 of flood-tidal delta sandstone 

in Rock Springs Formation near Thayer Junction, Wyo., on east 

flank of Rock Springs uplift. Section location shown in figure 38. 

delta near Thayer Junction, Wyo. (fig. 38). Measured 

section 10482 is composed mostly of gray shale of bay-fill 

origin, and thin interbedded sandstone and siltstone of 

splay origin, carbonaceous shale of reed swamp origin, 

Figure 40. Bidirectional crossbeds in tidal inlet associated with 

delta-front sandstone in Rock Springs Formation near Thayer Junction, Wyo. Crossbeds are shown in measured section 7582, figure 

39. Outcrop location shown in figure 38. 

Figure 41. Crossbedded flood-ramp sandstone in flood-tidal delta in Rock Springs Formation on north side of Interstate Highway 

80 near Thayer Junction, Wyo. The sandstone is underlain by the 

No. 15 coal bed. Outcrop location shown in figure 38. 

and coal of forest swamp origin (figs. 42, 47). Thin beds 

of dolomite and hematite concretions are also present at 

several stratigraphic levels. Sandstone beds of distributary 

stream channel origin are widely spaced in the lower part 

of the lower delta plain, but in this section they are 

missing. 

The sediments deposited across the lower delta plain 

undergo subtle changes from its lower (seaward) part to its 

upper (landward) part, as shown by a comparison of measured sections 10482 and 680 (fig. 47). Measured section 

680 illustrates the type of rocks deposited in the upper part 

of a lower delta plain in the Rock Springs Formation. 

Section 680 was measured in a roadcut of Wyoming 
10482 7582 

I I 

:::.:__;___~--:;-- --:-:-- .....,. -::....,.~Splay,-: · ~ · 7--.:;:_-c:c- - Bay and marsh deposits 

~~~~~~ ---::-~~?7 ·.· ·. ~splay:--_;-=-"-c--==--::..~ -'~~;:3-~--:-:-c-c.::._~ · 

......:-/s_pfay~ _ _ 

-~=:.~:-__~~·. ~-=-~~/~~~~~;- ·· ~_:__.,..-,-~-:-,-~~~ 

_ --...;:_Splay -~.:.:-~:.:.:~- · _ .. ...,., cc_""""' .:c._- Bay and marsh deposit 

~ -~--:::_ ....._....._--_-~play- ~----==---- =---:_ ---:::..~~ ~--'-~--'- --=-- -::So lav-'-~~ --. ~ . ~ ... ~ --~...:...:.... -:---

15 coal bed 

ENVIRONMENTS AND LITHOFACIES 

Bay and marsh (Lower delta plain) 

D Open water sha!e and salt marsh carbonaceous shale 

ISE"]j Splay siltstone and sandstone 

• Forest swamp coal 

EXPLANATION 

Tidal inlet 

;~:.f'i~ Tidal inlet sandstone (seaward part) 

• Tidal inlet sandstone (landward part) 

Tidal delta 

• Flood-tidal delta sandstone 

Shoreface (Delta-front sandstone) 

~ 

f~JJ 

CJ 

E) 

Forebeoch sandstone l 

Upper della front 

Surf sandstone 

Middle delta -front sandstone 

Lower della front 

7682 

25 FEET 

Nearshore marine (Prodelta) 

F-:= d Prodelta shale and siltstone 

Contact 

Unconformity 

0 

Figure 42. Restored cross section of flood-tidal delta deposits in Rock Springs Formation near Thayer Junction, Wyo. Locations of measured sections 10482 (fig. 47) and 

7582 (figs. 39, 40) and of figure 44 are shown in figure 38. 

C/) 

tTl 

CJ 

~ tTl 

l' 

~ 

8 

-< 

N 

Vol 
24 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

Figure 43. Flood-tidal delta sandstone in Rock Springs Formation near Thayer Junction, Wyo. Note very low angle left- (landward-) dipping foreset laminae. Jacob staff in lower right is 5 ft 

long. Outcrop location shown in figure 38. 

R 105W 

Figure 44. Sandstone beds near mouth of tidal inlet near measured section 7682 in Rock Springs Formation near Thayer Junction, Wyo. Scale (arrow) near center of photograph is in inches. 

Outcrop location shown in figure 38. 

R 104 W 

T 

19 

N 

Figure 45. Location of distributary stream channel and lower upper delta-plain deposits in Rock Springs Formation in measured section 

3177 (1 1

h mi east of Rock Springs) and in figures 46 and 52. Base from U.S. Geological Survey 1:24,000 Rock Springs, Wyo.; contour 

interval 20 ft. 
REFERENCES CITED 25 

Figure 46. Distributary stream channel sandstone (arrow) overlying delta-front sandstones in Rock Springs Formation north of 

Interstate Highway 80, 11/z mi east of Rock Springs, Wyo. Channel 

sandstone is about 26 ft thick. Outcrop location shown in figure 45. 

Highway 371, 2 mi south of Superior, Wyo., near the center of N£1/4 sec. 6, T. 20 N., R. 102 W. (figs. 48, 49). 

From comparison of measured sections 10482 and 680, it 

is obvious that the upper part of the lower delta plain contains thicker and more numerous beds of sandstone and 

siltstone of splay origin, carbonaceous shale of reed 

swamp origin, and coal of forest swamp origin than does 

the lower part of the lower delta plain. 

UPPER DELTA PLAIN 

A segment of the lower part of an upper delta-plain 

deposit in the Rock Springs Formation is illustrated in 

measured section 3177 (fig. 50). Measured section 3177 

is located north of Interstate Highway 80, }1/z mi east of 

Rock Springs, Wyo. (fig. 45). A section similar to measured section 3177 is exposed in a roadcut along the north 

side of Interstate Highway 80, 1 mi to the west of the 

measured section, in NW1/4SE1/4 sec. 30, T. 19 N., R. 104 

W. (fig. 51). The lower part of the upper delta-plain 

deposit consists of interbedded dark-gray to dark-brown 

carbonaceous shale of reed swamp origin, coal of forest 

swamp origin, gray, partly current rippled sandstone and 

siltstone of splay origin, gray shale of bay-fill origin, and 

tan, fine-grained, trough-crossbedded sandstone of distributary stream channel origin. The beds are generally less 

than 5 ft thick and rarely exceed 10 ft in thickness. Beds 

of coal, stream channel sandstone, and splay sandstone 

and siltstone are thicker and more numerous, and beds of 

bay-fill shale are thinner and less numerous than in the 

previously discussed lower delta-plain deposits. (Compare 

figures 47 and 50.) 

The upper part of an upper delta plain is exposed in 

measured section 181 located on the west slopes of Killpeeker Creek near its confluence with Bitter Creek, in the 

city of Rock Springs, in Wt/zSWt/4 sec. 26, T. 19 N., R. 

105 W. (fig. 52). The upper delta plain in measured section 181 is composed of thick beds of sandstone of stream 

channel and splay origins, thick interbedded carbonaceous 

shale of reed swamp origin, and coal of forest swamp origin (figs. 53, 54). Beds of shale of bay-fill origin are 

sparse and thin. The splay sandstones are composed of 

mostly thin subparallel beds of current-rippled silty sandstone and interbedded gray silty shale (fig. 55). A few thin 

beds of tuff (tonstein) are present in and overlying the 

Rock Springs coal bed No. 5 (fig. 50). 

Beds of stream sandstone in the delta-plain sequence 

in the Rock Springs Formation were mostly deposited in 

channels having straight or nearly straight stream courses. 

These sandstone beds are linear but generally lenticular 

and symmetrical in cross section. They are thick in relation to their width, exhibit large-scale trough crossbedding, and have convex, scoured lower surfaces. Near the 

top of the upper delta-plain deposits in the Rock Springs 

Formation, immediately underlying the Ericson Sandstone 

of alluvial plain origin, the stream channel courses become 

sinuous and large meander loops are exposed in cliffforming outcrops along Dewar Drive in the western part 

of the city of Rock Springs in NWt/4SEt/4SEt/4 sec. 34, T. 

19 N., R. 105 W. (figs. 52, 56). The meander loops are 

lenticular in cross section but are wide in relation to their 

thickness. The meander loops are wedge shaped and have 

convex upper surfaces; well-developed point bars are visible in long, low-angle accretionary beds that are present at 

the outer margins of the channels (fig. 56). 

REFERENCES CITED 

Bouma, A.H., 1962, Sedimentology of some flysch deposits-A 

graphic approach to facies interpretation: Amsterdam, Elsevier, 168 p. 

Gill, J.R., and Cobban, W.A., 1966, The Red Bird section of the 

Upper Cretaceous Pierre Shale in Wyoming: U.S. Geological 

Survey Professional Paper 393-A, 73 p. 

Hale, L.A., 1950, Stratigraphy of the Upper Cretaceous Montana 

Group in the Rock Springs uplift. Sweetwater County, Wyoming, in Harrison, J.S., ed., Wyoming Geological Association, 

5th Annual Field Conference of Southwest Wyoming: Casper, 

Wyo., p. 49-58. 

Kauffman, E.G., 1977, Geological and biological overview; western interior Cretaceous basin: The Mountain Geologist, v. 14, 

nos. 3 and 4, p. 75-100. 

King, P.B., 1959, The evolution of North America: Princeton, N.J., 

Princeton University Press, 190 p. 

Mutti. E., and Lucchi, F.R., 1978, Turbidites of the northern Apennines; Introduction to facies analysis: International Geology 

Review, v. 20, no. 2, p. 125-166. 

Roehler, H.W., 1977, Geologic map of the Rock Springs uplift and 

adjacent areas, Sweetwater County, Wyoming: U.S. Geological Survey Open-File Report 77-242, scale 1:125,000. 
26 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

680 

. 

. . 

§ 

10482 

EXPLANATION 

Splay sandstone and siltstone 

Bay-fill shale 

8 

~ 

B 

Reed swamp carbonaceous shale 

Forest swamp coal 

Hematite concretions 

~ Dolomite concretions 

Figure 47. Measured sections 680 and 10482 of upper and lower parts of lower delta-plain deposits in Rock Springs Fonnation near 

Thayer Junction, Wyo. and Superior, Wyo. Section locations are shown in figures 48 and 38. 

---1988, Submarine slumps in delta-front sandstones of the 

Upper Cretaceous Blair Fonnation, Rock Springs uplift, Wyoming: U.S. Geological Survey Bulletin 1699, 11 p. 

---1989, Origin and distribution of six heavy-mineral placer 

deposits in coastal-marine sandstones in the Upper Cretaceous 

McCourt Sandstone Tongue of the Rock Springs Fonnation, 

southwest Wyoming: U.S. Geological Survey Bulletin 1867, 

34 p. 

---1990, Stratigraphy of the Mesaverde Group in the central 

and eastern greater Green River basin, Wyoming, Colorado, 

and Utah: U.S. Geological Survey Professional Paper 1508, 

52 p. 

Roehler, H.W., Swanson, V.E., and Sanchez, J.D., 1977, Summary report of the geology, mineral resources, engineering 

geology, and landscape geochemistry of the SweetwaterKemmerer area, Wyoming. Part A, Geology and mineral resources: U.S. Geological Survey Open-File Report 77-360, 

80 p. 

Smith, J.H., 1961, A summary of stratigraphy and paleontology, 

Upper Colorado and Montanan Groups, south-central Wyoming, northeastern Utah, and northwestern Colorado, in 

Wiloth, G.J., ed., Wyoming Geological Association, 16th Annual Field Conference; Symposium on Late Cretaceous rocks: 

Casper, Wyo., p. 101-112. 
REFERENCES CITED 27 

R 102W 

Figure 48. Location of upper lower delta-plain deposits in Rock 

Springs Fonnation in measured section 680 along Highway 371 

near Superior, Wyo. Base from U.S. Geological Survey 1:24,000 

Thayer Junction, Wyo.; contour interval 20ft. 

--- --...: ~ ... -- --...... -

Figure 49. Upper lower delta-plain deposits in Rock Springs 

Fonnation in roadcut of Wyoming Highway 371, 2 mi south of 

Superior, Wyo. Outcrop location shown in figure 48. Person in upper middle gives scale. 
28 

181 

BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

EXPLANATION 

r~~~~:t1:!:~ Stream channel sandstone 

~ Splay sandstone and siltstone; 

partly current rippled 

[§; 1:3 Bay-fill shale 

~ ~ Reed swamp carbonaceous shale 

I!! Forest swamp coal 

~ Tuff (tonstein) 

3177 

Figure 50. Measured sections 3177 and 181 of lower and upper parts, respectively, of upper delta-plain deposits in Rock Springs Formation on west flank of Rock Springs uplift, in Rock Springs, Wyo. Section locations shown in figures 45 and 52. 
REFERENCES CITED 

Figure 51. Lower upper delta-plain deposits in Rock Springs Formation along north side of 

Interstate Highway 80, Ih mi east of Rock Springs, Wyo. Outcrop location shown in figure 45. 

29 
30 BAXTER SHALE AND BLAIR AND ROCK SPRINGS FORMATIONS, SOUTHWEST WYOMING 

R 105W 

T 

19 

N 

Figure 52. Location of upper delta-plain deposits in Rock Springs Formation in measured section 181 and in figures 53-56, in Rock 

Springs, Wyo. Base from U.S. Geological Survey 1:24,000 Rock Springs, Wyo.; contour interval 20ft. 
REFERENCES CITED 31 

Figure 53. View to northwest of upper upper delta-plain deposits 

in Rock Springs Formation along Killpecker Creek in Rock 

Springs, Wyo. Coal (arrow) is Rock Springs No.5 bed. Scale indicated by person standing in upper right. Outcrop location shown in 

figure 52. 

Figure 54. View to west of faulted upper upper delta-plain sandstone, carbonaceous shale, and coal deposits in Rock Springs Formation in Rock Springs, Wyo. Man gives scale. Outcrop location 

shown in figure 52. 

"I'! U.S. GOVERNMENT PRINTING OFFICE: 1993-573-038/86005 

Figure 55. Upper upper delta-plain current-rippled sandstone and 

silty shale of splay origin in Rock Springs Formation along Killpeeker Creek in Rock Springs, Wyo. Outcrop location shown in figure 52. Pencil (arrow) gives scale. 

Figure 56. View to northwest of sandstone point bars (arrows) 

on meander loops of stream channels in the upper upper delta-plain 

deposits in Rock Springs Formation in Rock Springs, Wyo. Outcrop location shown in figure 52. 

Manuscript approved for publication November 13, 1992 

Published in the Central Region, Denver, Colorado 

Photocomposition by Shelly A. Fields 

Graphics by H.W. Roehler and Roger Highland 

Edited by Lorna Carter 



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