Submarine Slumps in 

Delta-Front Sandstones of the 

Upper Cretaceous 81(tir For[J'\~~i Qn 

Rock Springs Uplift, Wyoming · 

Submarine Slumps in 

Delta-Front Sandstones of the 

Upper Cretaceous Blair Formation, 

Rock Springs Uplift, Wyoming 

By H. W. ROEHLER 

Syndepositional slumps on 

the western shores of the 

interior Cretaceous sea 

U.S. GEOLOGICAL SURVEY BULLETIN 1699 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Any use of trade names is for descriptive purposes only and does not imply 

endorsement by the U.S. Geological Survey. 

Library of Congress Cataloging in Publication Data 

Roehler, Henry W. 

Submarine slumps in delta-front sandstones of the Upper Cretaceous Blair formation, Rock Springs uplift, Wyoming. 

(U.S. Geological Survey bulletin; 1699) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1699-B 

1. Sedimentary structures-Wyoming-Rock Springs Region. 2. Mass-wastingWyoming-Rock Springs Region. 3. Geology, Stratigraphic-Cretaceous. 4. Sandstone-Wyoming-Rock Springs Region. 5. Blair Formation (Wyo.) 6. GeologyWyoming-Rock Springs Region. I. Geological Survey (U.S.) II. Title. Ill. Series. 

QE75.B9 no. 1699 557.3 s 86-600344 
CONTENTS 

Abstract 1 

Introduction 1 

Location and accessibility of the study area 1 

Geologic setting 1 

Stratigraphy 4 

Nomenclature and previous investigations of the Blair Form~tion 4 

Regional correlations and paleogeography 4 

Measured sections and restored cr9~§ section of the study area 4 

Sedimentary structures and lithologies 7 

Sandstone petrology 9 

Conclusions 9 

References cited 9 

FIGURES 

1. Index map showing the location of the study area 2 

2. Geologic map of the study area showing the locations of measured 

sections 2 

3. Photograph of outcrops of the lower part of the Rock Springs Formation 

and upper part of the Blair Formation 2 

4. Regional stratigraphic cross section of the Blair and Rock Springs Formations in the Rock Springs uplift 3 

5. Regional paleogeographic map of the Blair Formation 4 

6. Measured sections and restored cross section of the slumped structures of 

the Blair Formation 5 

7. Measured section 2980 showing lithologies of the lower delta-front 

environment 6 

8. Photograph of the wave-rippled upper surface of bed 4 in measured section 

2980 7 

9. Photograph of fossil-crawling traces on wave-rippled upper surface of bed 4 

in measured section 2980 7 

10. Photograph of trace fossils on the wave-rippled upper surface of bed 4 in 

measured section 2980 7 

11. Photograph of convoluted sandstone in slumped bed 6 in measured section 

2980 7 

12. Photograph of in-phase climbing ripples near the base of bed 6 in measured 

section 2580 8 

13. Photograph of trace fossils including Ophiomorpha near the base of bed 6 

in measured section 2680 8 

14. Photograph of hummocky, parallel crossbeds in bed 9 in measured section 

2980 8 

15. Photograph of thin, parallel-bedded sandstone at the base of bed 11 in 

measured section 2980 8 

16. Photograph of very thin to thin, parallel-bedded sandstone at the top of bed 

11 in measured section 2980 9 

17. Photomicrographs of four sandstone thin sections from measured section 

2980 10 

18. Block diagrams illustrating the superposition and lateral seaward movement 

of slumped beds 11 

Contents Ill 

Submarine Slumps in Delta-Front Sandstones of the 

Upper Cretaceous Blair Formation, 

Rock Springs Uplift, Wyoming 

By H. W. Roehler 

Abstract 

Submarine slumps are present in sandstone beds in the 

upper part of the Blair Formation on the southeast flank of the 

Rock Springs uplift in southwest Wyoming. The slumped beds 

are part of a lower delta-front lithofacies that was present on 

the submarine margins of an arcuate delta on the western 

shores of the interior Cretaceous sea. The slumped beds are 

as much as 13ft thick, lenticular in cross section, convoluted, 

and intercalated with normally bedded sandstone and shale. 

The slumps resulted from slope failure and mass-gravity movement of sand along oversteepened, descending slopes of a prograding submarine terrace. 

INTRODUCTION 

Syndepositional slumps are present in sandstone 

beds on the submarine margin of an arcuate delta that 

occupied a segment of the western shore of the interior 

Cretaceous sea. The slumps occur as distinct beds as much 

as 13 ft thick that are situated within a 60-ft-thick, ledgeforming, shaly-sandstone sequence in the upper part of 

the Blair Formation of early Campanian age. The shalysandstone sequence crops out in a north-south trend 

across parts of sec. 32, T. 18 N., R. 102 W., and sees. 

4, 5, 8, 9, 16, and 17, T. 17 N., R. 102 W., on the 

southeast flank of the Rock Springs uplift. Beds in the 

sequence are well exposed in the study area in sec. 9, T. 

17 N., R. 102 W. The distinguishing features of the 

slumped beds are lenticularity, undulating upper and 

lower surfaces, and internal convolutions. The slumped 

beds are intercalated with normally bedded sandstone and 

shale. 

The slumps in the Blair Formation are generally 

much smaller in scale than the mass-gravity flow deposits 

described by Coleman and Prior (1982) on the periphery 

of the Mississippi River delta. Similar submarine gravityslide and slump deposits are well known in the geological 

record (Reineck and Singh, 1973), but they apparently 

have not been reported in delta-front sandstones along 

the western shores of the interior Cretaceous sea in the 

western United States. 

Location and Accessibility of the Study Area 

The study area is 20 mi southeast of Rock Springs, 

Wyo. (fig. 1). It is accessible by an improved gravel road 

that branches eastward from Highway 430 18 mi southeast of Rock Springs (fig. 2). This gravel road parallels 

the north edge of Cutthroat Draw and is the primary access route to Brady Gas Field. Approximately 1. 7 mi east 

of Highway 430 on the gravel road to Brady Gas Field, 

an unimproved road branches northward, climbs a rocky 

slope, and continues northward along the crest of a low, 

cedar-covered ridge (fig. 2). The slumped beds are exposed along the lower west slopes of this ridge. The sandstone beds that form this ridge were mapped as marker 

bed UST in the Blair Formation on the Camel Rock 

quadrangle, GQ1521 (Roehler, 1979). 

Geologic Setting 

The upper part of the Blair Formation is exposed 

in the study area within a broad, deep, rectangularshaped, alluvium-filled valley formed by Cutthroat Draw 

(fig. 2). The valley is open to the west but is bounded 

by high ridges and plateaus to the north, east, and south. 

The Blair Formation crops out in the valley walls and 

along low hills and ridges that rise above the valley floor. 

The formation is covered locally by slump material, sandy 

soil, and sand dunes. The beds containing the slumps crop 

out at elevations between 6, 700 ft and 6,900 ft. Adjacent 

escarpments capped by the Chimney Rock Tongue of the 

Rock Springs Formation, also of Campanian age, rise to 

more than 7,500 ft (fig. 3). The area is hot and dry 

Introduction 
42° ...-----------.------------=-'f"' 

00' 

Figure 1. Index map showing the location of the study area 

on the southeast flank of the Rock Springs uplift in southwest 

Wyoming. Cretaceous rocks are shaded, the Blair Formation 

is stippled. 

during summer months, and vegetation consists mostly 

of clumps of sagebrush and thin desert grasses. Groves 

of cedar trees are present along sandstone ridges at higher 

elevations. 

The slumped beds dip 5 °-6 ° southeast on the 

southeast flank of the Rock Springs uplift. The overall 

structure is locally homoclinal, but it is interrupted in the 

northern part of the study area by ihree southwesttrending, high-angle, normal faults (fig. 2). The largest 

of these faults crosses the northwest corner of sec. 9, 

T . .17 N., R. 102 W., is down thrown to the northwest, 

ana has about 250 ft of displacement. Two minor faults, 

each having less than 25 ft of displacement, parallel the 

larger fault a few hundred feet to the sa\Itheast. The 

smaller faults offset the line of outcrops studied. The 

southwest trend of the faults in the study area is asso--

ciated with a larger pattern of Paleocene and older 

faulting that crosses the Rock Springs uplift (Love and 

Christiansen, 1985). 

2 Submarine Slumps in the Blair Formation, Wyoming 

R 102 W 

4000 FEET 

17 

N 

Figure 2. Geologic map of the study area in sec. 9, T. 17 N., 

R. 102 W., showing the locations of measured sections. Kbl, 

Blair Formation; Krs, Rock Springs Formation; D, downthrown 

side of fault; U, upthrown side of fault. 

Figure 3. Outcrops near the northwest corner of sec. 9, T. 

17 N., R. 102 W. 1, Sandstone beds composing the Chimney 

Rock Tongue at the base of the Rock Springs Formation; 2, 

Shaly sandstone i,rtl the upper part of the Blair Formation that 

tb'ntains slump stru(:tures. The outcrops shown are about 500ft 

thick. View is northwest. 
A 

C/) 

~ 

u 

0 

a: 

c: 

-~ 

1-

Blair Formation 

0 

CDC:O 

.... > Ctl Ctl 

"lii ~ -~ E·21 

-~ 

~ 

u 

0 

a: 

> CD 

c: 

E 

:c 

u 

A' 

Black Butte Tongue 

Slumped 

sandstones 

Blair Formation 

·····~ 

["8 ........ ;::::;::::c··· ... :;-: ................... ~ 

EXPLANATION 

t:·~ "i; ~ Coastal-plain fluvial sandstone 

~ Delta-plain and coastal plain sandstone, siltstone, 

. .. .• shale, carbonaceous shale, and coal 

~:::\·(;J Delta-front and strand-plain sandstone 

D Prodelta, shelf, and slope sandstone, siltstone, and shale 

F---j Offshore marine shale 

.......,._... Unconformity 

5 MILES I 

Figure 4. Regional stratigraphic cross section showing the nomenclature and intertonguing relationships of the Blair and Rock 

Springs Formations in the Rock Springs uplift, Wyo. (Roehler, 1983). 

Introduction 3 
c,<v'?" 

f' 

~~ 

<8 

Area of slumped 

delta-front 

sandstone 

50 MILES 

Rawlins • 

Figure 5. Regional early Campanian paleogeographic map 

showing depositional environments and the location of 

slumped, delta-front sandstones in the upper part of the Blair 

Formation. 

STRATIGRAPHY 

Nomenclature and Previous Investigations of the 

Blair Formation 

The Blair Formation was named by Schultz (1920) 

for 1,000-1,200 ft of "sandstone and sandy shale which 

form the beds immediately below the Mesaverde." A 

geologic map published by Schultz (1920, pl. 1) shows 

that the outcrops of the formation are 1-7 mi wide and 

encircle the central basin of the Rock Springs uplift 

(fig. 1 ). The type area of the formation is on Blair Creek 

in sec. 4, T. 16 N., R. 103 W., 7 mi southwest of the study 

area. The Blair Formation conformably overlies the 

Baxter Shale of Coniacian-Campanian ages, but it intertongues with the overlying Rock Springs Formation. 

Rocks that compose the Blair Formation consist of 

prodelta shelf and slope sandstone, siltstone, and shale 

that were deposited during regressive stages of the interior 

Cretaceous sea (Hale, 1950). Parts of the western shorelines of the sea during these regressions trended northeast 

across the Rock Springs uplift area. As a result, the lower 

700 ft of the Rock Springs Formation-composed of 

delta-plain sandstone, siltstone, shale, carbonaceous shale 

and coal, and delta-front sandstone-intertongues with 

and grades laterally southeastward across the Rock 

Springs uplift into the upper part of the Blair Formation 

(fig. 4). The shaly-sandstone sequence that contains the 

slumped beds was deposited during one of these 

4 Submarine Slumps in the Blair Formation, Wyoming 

regressions. It is situated stratigraphically 320 ft below 

the base of the Chimney Rock Tongue of the Rock 

Springs Formation. 

The age of the Blair Formation is early Campanian 

(rv77 Ma) based on fossils collected by Smith (1961) at 

U.S.G.S. Mesozoic locality 2214 in NE1/4 sec. 26, T. 16 

N., R. 103 W. These fossils include the ammonite 

Scaphites hippocrepis and several species of marine pelecypods, among them Inoceramus subcompressus. T~e 

fossil collection site is located near the top of the Blau 

Formation, 9 mi southwest of the study area (fig. 1). 

Regional Correlations and Paleogeography 

The 60-ft-thick, shaly-sandstone sequence that contains the slumped beds has been correlated for more than 

25 mi along the east flank of the Rock Springs uplift in 

measured sections (Roehler, 1983). Within the study area 

the sequence is a lower delta-front lithofacies composed 

of thin, parallel-bedded to subparallel-bedded (and convoluted) sandstone with some thin, interbedded shale. The 

sequence weathers to tan-brown, ledge-forming, steplike 

slopes. North of the study area in sec. 14, T. 19 N., 

R. 102 W., the lower delta-front lithofacies grades in a 

landward direction into a middle delta-front lithofacies 

consisting of 90 ft of large-scale, low-angle, troughcrossbedded sandstone that weathers to a tan-brown, 

massive cliff. Farther north, in sec. 21, T. 20 N., 

R. 102 W., adjacent to Interstate Highway 80, a similar 

middle delta-front lithofacies is present at the base of the 

sequence, but it is capped there by 16 ft of white, smallscale, trough-crossbedded and tabular-bedded sandstone 

that comprises surf and forebeach lithofacies. The geographic location of the surf and fore beach lithofacies suggests that the delta strandlines were formerly located in 

the vicinity of what is now Interstate Highway 80 near 

Thayer Junction (fig. 1). The interpreted paleogeography 

of the area is shown on figure 5. Water depths for the 

various lithofacies are unknown, but the author speculates that the lower delta-front sandstones in the study 

area were deposited below normal wave base at depths 

between 50 ft and 150 ft. 

Measured Sections and Restored Cross Section of 

the Study Area 

Fourteen stratigraphic sections were measured and 

described at the locations indicated on the geologic map 

(fig. 2). The measured sections (fig. 6) show that the 
North 

3380 

EXPLANATION 

Sandstone 

I Thin, parallel beds 

Cross bedded 

Wave rippled 

Convoluted 

Siltstone 

E¢."8 Thin bedded 

Shale 

~ Fissile 

§Silty 

[O~ET 

400 FEET 

I I 

South 

Figure 6. Measured stratigraphic sections (top) and restored cross section (bottom) showing the relationships of slump structures in the Blair Formation in the study area. Arrows identify the same bed in both illustrations. 

Stratigraphy 5 
Outcrop 

photograph 

(in text) 

F;g. 16 { 

Fig. 13 

Fig. 8 { 

* 

10 FEET 

Section 

2980 

Rock thin-section 

photomicrograph 

(in text) 

ig. 17A 

Bed 

no. 

11 

Sedimentary structure 

and lithology 

Thin, even, parallel-bedded, gray, 

very fine grained sandstone 

Fissile, gray shale and interbedded 

10 thin; parallel-bedded, gray, very 

fine grained sandstone 

9 

8 

7 

6 

5 

4 

3 

2 

Hummocky, crossbedded, gray, 

fine-grained sandstone 

Convoluted, gray, very fine 

grained sandstone 

Thin, parallel-bedded, gray, 

very fine grained sandstone 

Convoluted, gray, silty sandstone 

Fissile, gray, soft shale 

Rippled, gray, very fine grained sandstone 

Fissile, gray, soft shale 

Convoluted, gray, very fine grained 

sandstone 

Fissile, gray, soft shale 

* Denotes slumped beds 

Figure 7. Measured section 2980 showing lithologies of the lower delta-front environment in the 

Blair Formation. 

6 Submarine Slumps in the Blair Formation, Wyoming 
Figure 8. Wave-rippled upper surface of bed 4 in measured 

section 2980 (fig. 7). Pick handle is 17 in. long. 

Figure 9. Fossil-crawling traces on wave-rippled upper surface of bed 4 in measured section 2980 (figs. 7, 8). Scale is in 

centimeters. 

slumped beds are lenticular in cross section and occur intermittently along outcrops. The slumped beds are recurrent and rise stratigraphically from north to south across 

the study area in the direction of the paleoslope. The 

restored cross section on figure 6 depicts the sea floor 

and bottom sediments as they may have appeared following the period of slumping that is identified by arrows. 

Figure 10. Trace fossils on wave-rippled upper surface of bed 

4 in measured section 2980 (figs. 7, 8). Arrow points to probable feeding trace. Scale is in centimeters. 

Figure 11. Convoluted sandstone in slumped bed 6 in measured section 2980. Black and white scale is in inches and 

centimeters. 

SEDIMENTARY STRUCTURES AND LITHOLOGIES 

Measured section 2980 (fig. 7) is typical of the 

stratigraphic sections in the study area and illustrates 

primary sedimentary structures and lithologies. The 

geographic location of the section is shown on figure 2 

and the stratigraphic relationships are shown on figure 6. 

Sedimentary Structures and Lithologies 7 
Figure 12. In-phase climbing ripples near the base of bed 6 

in measured section 2580 (figs. 6, 7). Jackknife used for scale 

is 3 1/2 in. long. 

Figure 13. Trace fossils including Ophiomorpha near the base 

of bed 6 in measured section 2680 (figs. 6, 7). 

Beds 2 and 4 near the base of measured section 2980 

(fig. 7) are very fine grained, poorly sorted, angular 

sandstones that are interbedded with fissile gray shale. 

The sandstones are thin bedded and wave rippled. Bed 

2 is convoluted in the upper part. The upper wave-rippled 

surface of bed 4 (fig. 8) has numerous small, fossilcrawling and feeding traces that include Helminthoida 

(figs. 9, 10). Bed no. 6 (fig. 7) is composed of sandy 

siltstone and has undulating upper and lower contacts 

with adjacent beds. It is entirely convoluted (fig. 11). The 

basal 3 ft of bed 6 has in-phase climbing ripples in section 2580 (fig. 12) and small, variously oriented trace 

fossils, including Ophiomorpha, in section 2680 (fig. 13). 

8 Submarine Slumps in the Blair Formation, Wyoming 

Figure 14. Hummocky, parallel crossbeds in bed 9 in measured section 2980 (fig. 7). 

Figure 15. Thin, parallel-bedded sandstone at the base of bed 

11 in measured section 2980 (fig. 7). Pick handle is 17 in. long. 

Bed 7 is very fine grained sandstone that exhibits thin, 

parallel bedding. It is visible above the convoluted beds 

on figure 11. Bed 8 (fig. 7)"is very fine grained sandstone 

with convolutions similar to bed 6. Bed 9 (fig. 7) is very 

fine grained, poorly sorted, angular sandstone with hummocky, parallel crossbedding (fig. 14). The hummocky 

crossbedding probably resulted from storm-generated 

waves that reworked bottom sediments. Bed 10 (fig. 7) 

consists of gray shale and interbedded very thin to thin, 

parallel-bedded, very fine grained sandstone. Bed 11 

(fig. 7) is poorly sorted, angular, very fine grained sandstone in even, parallel beds that thin upwards (figs. 15, 

16). 
Figure 16. Very thin to thin, parallel-bedded sandstone at the 

top of bed 11 in measured section 2980 (fig. 7). Scale is in centimeters and inches. 

SANDSTONE PETROLOGY 

Four sandstone samples were collected for petrographic analysis at randomly selected stratigraphic 

intervals in section 2980, as indicated on figure 7. Photomicrographs of thin sections of the sandstone samples are 

shown on figure 17. The sandstones are light gray 

(unweathered) and tan brown (weathered) quartzose and 

range from sandy silt to fine grained. The grains are 

angular and poorly sorted, and cementing materials consist of clay and hematite. The sandstones are composed 

of 65-85 percent quartz grains, 10-25 percent rock 

fragments, and 5-8 percent miscellaneous mineral grains 

and cement. They contain about 2 percent heavy-mineral 

grains, mostly tourmaline, zircon, and garnet. The 

coarsest sandstones are present in the hummocky beds, 

where fine sand grains are mixed with interstitial silt and 

mud. The -convoluted beds are composed of silty sand. 

The fine texture and poor sorting in these beds probably 

reflects random mixing of bottom sediments during 

slumping. 

CONCLUSIONS 

Syndepositional slumps in the Blair Formation are 

the products of submarine slope failure and mass movement of ,Sand toward the periphery of an arcuate delta. 

The slump scarps were probably linear but did not form 

blocks and steps. The shear planes had high angles of 

seaward dip adjacent to the scarps but were otherwise 

nearly horizontal. All of the slumped sandstone beds are 

underlain by shale, which suggests that the semifluid 

muds from which the shale formed comprised soft, incompetent substrates for overlying, more-competent 

sands. The slumped sands were not confined to channels, 

but flowed downslope as sheetlike masses. The mechanics 

of slumping were probably similar to those of snow 

avalanches-where material suddenly detached at a scarp 

splits, separates, and moves rapidly downslope in an accelerating wave. The energy of the movement is dissipated 

at the base of the slope by loss of acceleration and increase in drag. Mechanisms that triggered the slumps are 

unknown, but they may have involved rapid sediment influx, severe storms, or earthquakes. 

The superposition and lateral offset of the slump 

structures in a north-to-south direction across the study 

area are interpreted by the author as caused by oversteepened slopes that developed along a migrating submarine terrace. The terrace prograded, but its steep, 

descending-seaward slopes were periodically destroyed by 

slumping. The recurrent pattern of terrace sedimentation 

followed by slumping is depicted by block diagrams on 

figure 18. 

REFERENCES CITED 

Coleman, J. M., and Prior, D. B., 1982, Deltaic Environments, 

in Sandstone Depositional Environments: American Association of Petroleum Geologists Memoir 31, p. 167-174. 

Hale, L.A., 1950, Stratigraphy of the Upper Cretaceous Montana Group in the Rock Springs uplift, Sweetwater County, Wyoming, in Wyoming Geological Association 

Guidebook, 5th Annual Field Conference, Southwest 

Wyoming, p. 50-56, fig. 1. 

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

Wyoming: U.S. Geological Survey, Denver, Colo., 3 

sheets. 

Reineck, H. E., and Singh, I. B., 1973, Depositional sedimentary environments: SpringerVerlag, New York, p. 387-388. 

Roehler, H. W., 1979, Geologic map of the Camel Rock 

Quadrangle, Sweetwater County, Wyoming: U.S. Geological Survey Geologic Quadrangle Map GQ-1521. 

___ 1983, Stratigraphy of Upper Cretaceous and lower Tertiary outcrops in the Rock Springs uplift, Wyoming: U.S. 

Geological Survey Miscellaneous Investigations Series Map 

1-1500. 

Schultz, A. R., 1920, Oil possibilities in and around Baxter 

Basin, in the Rock Springs uplift, Sweetwater County, 

Wyoming: U.S. Geological Survey Bulletin 702, p. 32, pl. 1. 

Smith, J. H., 1961, A summary of stratigraphy and paleontology, Upper Colorado and Montanan Groups, southcentral Wyoming, northeastern Utah, and northwestern 

Colorado, in Wyoming Geological Association Guidebook, 

16th Annual Field Conference, Symposium on Late Cretaceous rocks, Wyoming and adjacent areas, p. 107-108. 

References Cited 9 
Figure 17. Photomicrographs of sandstone thin sections. Samples from measured section 2980: A, bed 4; 8, bed 6; C, bed 

13; 0, bed 16. The stratigraphic positions of the beds are shown on figure 7. 

10 Submarine Slumps in the Blair Formation, Wyoming 
~ Paleoslope 

A 

B 

c 

D 

E 

Figure 18. Block diagrams illustrating the superposition and lateral seaward movement 

of successive slumps along the descending slopes of lower delta-front terraces in the Blair 

Formation. A, early deposition prior to slumping, followed by periods of deposition and 

slumping, 8, C, 0, and f. 

Submarine Slumps in the Blair Formation, Wyoming 11 

->I U.S. GOVERNMENT PRINTING OFFICE: 1988-573-047/66,101 REGION NO.8