Depositional Environment 

of Upper Cretaceous 

Black Sandstones of the 

Western Interior

GEOLOGICAL SURVEY PROFESSIONAL PAPER 994-A
DEPOSITIONAL ENVIRONMENT OF

UPPER CRETACEOUS BLACK SANDSTONES

OF THE WESTERN INTERIOR
Black sandstone capping buttes 6 miles (9.6 km) north of Pendroy, Mont. All except two small buttes in the lower background are

capped by black sandstone that lies near top of Virgelle Sandstone.
Depositional Environment 

of Upper Cretaceous 

Black Sandstones of the 

Western Interior

By ROBERT S. HOUSTON and JOHN F. MURPHY

UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

GEOLOGICAL SURVEY PROFESSIONAL PAPER 994-A

Cretaceous black sandstone deposits of the 

Western Interior have strati graphic, structural, textural, 

and mineralogical characteristics helpful in reconstructing 

local and regional depositional environments

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1977
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Houston, Robert Stroud, 1923-

Depositional environment of Upper Cretaceous black sandstones of the Western Interior

(Upper Cretaceous black sandstones of the Western Interior) (Geological Survey Professional Paper 994-A) 

Bibliography: p. 28-29. *

1. Geology, Stratigraphic-Cretaceous. 2.,Sandstone--The West. 3. Placer deposits-The West. I. Murphy, John Francis, 

1922- II. Title. III. Series. IV. Series: United States Geological Survey Professional Paper 994-A.

QE685.H76 551.7T0978 77-608083

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

Washington, D.C. 20402

Stock Number 024-001-02974-0
CONTENTS

Page

Abstract .................................................................................................... Al

Introduction .............................................................................................. 2

Acknowledgments ............................................................................ 7

Factors controlling the development and preservation of

black sandstone .................................................................................... 7

Holocene black sand deposits ............................................................. 8

Cretaceous black sandstone deposits (the regressive

sequence) Marias River example ............................................... 11

Page

Significance of grain size .................................................................. A18

Shoreline trends .......................................................................... ......... 21

Some areas for future research ........................................................ 21

Possible wind directions during Late Cretaceous storms 23 

Width of Cretaceous beaches and tidal ranges ................... 26

Summary ................................................................................................... 27

References cited ....................................................................................... 28

ILLUSTRATIONS

Page

FRONTISPIECE. Photograph of fossil black sandstone capping buttes north of Pendroy, Mont.

FIGURE 1. Index map showing localities of Upper Cretaceous rock in the Rocky Mountains region .............................................. A2

2-5. Maps showing distribution of black sandstone deposits:

2. Montana ............................................................................................................................................................................................... 3

3. Wyoming ....................................................................................................................................................................^

4. Utah and Colorado ........................................................................................................................................................................... 5

5. Arizona and New Mexico ............................................................................................................................................................... 6

6. Diagram showing stratigraphic positions of black sandstone in Montana ............................................................................. 7

7. Chart showing percentages of Upper Cretaceous black sandstone of the Rocky Mountains region deposited

during time periods represented by Western Interior ammonite zones .............................................................................. 9

8. Idealized beach cross section showing major facies ....................................................................................................................... 10

9. Photograph of black sandstone deposit in the uppermost sandstone of the Rock Springs Formation, Wyo. ........... 12

10. Photograph of typical black sandstone, Utah ................................................................................................................................... 13

11. Diagram of typical vertical sequence of black sandstone, Marias River deposit, Montana ............................................. 13

12. Photograph of cross-lamination in middle part of black sandstone, Marias River deposit, Montana ......................... 14

13. Rose diagram showing directions of crossbedding dip in black sandstone typical of lower part of black sandstone 

at Marias River deposit, Montana ................................................................................................................................................. 14

14. Photograph showing laminated and burrowed black sandstone at the top of the Virgelle Sandstone, Mont. ......... 15

15. Photograph showing landward and seaward portions of black sandstone at the Marias River deposit, Montana 16

16. Photograph showing black sandstone at the top of the basal white sandstone of the Mesaverde Formation ........ 18

17. Diagram showing possible stages of development of black sandstone deposit .................................................................... 19

18. Histograms relating grain-size variation to light and heavy minerals in black sandstone deposits............................ 20

19. Map showing distribution of heavy minerals in deposit at Buffalo Creek, Wyo. ................................................................. 24

20. Map showing distribution of heavy minerals in deposit at Sanostee, N. Mex. ..................................................................... 25

21. Photograph of wedge-shaped body of black sandstone in the upper part of the Virgelle Sandstone ........................... 26

TABLE

Page

TABLE 1. Trends of Upper Cretaceous shorelines determined from black sandstone as compared with trends of shorelines

established by Gill and Cobban (1969) from regional stratigraphic and paleontologic study .............................. A22

UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

DEPOSITIONAL ENVIRONMENT OF UPPER CRETACEOUS 

BLACK SANDSTONES OF THE WESTERN INTERIOR

By ROBERT S. HOUSTON and JOHN F. MURPHY

ABSTRACT

Black sandstones of Late Cretaceous age that are fossil 

marine placer'deposits of heavy minerals have been known in the 

Rocky Mountains since 1914 when Stebinger reported occurrences 

in northwestern Montana. More than 100 of these deposits have 

been located in recent years in Alberta, Montana, Wyoming, Utah, 

Colorado, New Mexico, Arizona, and northeastern Mexico. These 

deposits are unquestionably of beach placer origin and have many 

characteristics in common with modern beach placers such as 

those on the southeast coast of Australia. Study of these deposits 

in Wyoming and throughout the Rocky Mountains region has 

provided basic information on Late Cretaceous shoreline trends, 

beach slopes, and sediment source areas. Recent investigations 

of better exposed deposits, especially in Montana, have added 

information and modified earlier concepts.

Black sandstone deposits are characteristically found in 

regressive sandstones; deposition during regression is evident 

from internal structure of individual deposits and from general 

stratigraphic relationships. Typical black sandstone is underlain 

by white nearshore marine sandstone and is overlain by nonmarine fine-grained sandstone, carbonaceous shale, and coal. 

Oyster-bearing beds, characteristic of lagoon and near-marine 

swamp deposits, are also fairly common in overlying deposits. In 

some localities the white nearshore marine sandstone can be 

divided into three structural units: a lower unit with horizontal 

laminations and low-angle medium- to large-scale trough and 

planar cross-lamination which contains nonabraded fossils and 

which is probably deposited in offshore areas seaward of the 

breaker zone; a middle unit with low- and high-angle mediumscale trough cross-lamination that may have formed on beachpoint bars in the breaker zone; and an upper unit containing the 

black sandstone marked by large-scale very low angle wedgeplanar cross-lamination thought to have developed in the forebeach.

The black sandstone deposit proper is characteristically a 

laminated black and white sandstone, averaging about 15 percent 

heavy minerals at the base, and a massive black sandstone 

composed of layers containing as much as 90 percent heavy 

minerals at the top. In some deposits the lower and upper parts of 

the black sandstone deposit characterized by seaward-dipping 

large-scale very low angle wedge-planar cross-lamination are 

separated from one another by crossbedded units with high-angle 

laminae that dip seaward and landward, with steeper dips, as 

much as 32°, landward. The lower black and white sandstone, 

lowermost part in particular, contains worm and possible Ophiomorpha burrows. The black sandstone deposit is itself considered 

to be a regressional deposit; the lower black and white sandstone

is considered to be a foreshore deposit, the high-angle crossbedded 

middle unit foreshore ridge deposits, and the upper heavy-mineralrich unit upper foreshore and backshore deposits. By analogy with 

modern deposits the black and white layers are thought to be 

deposited by traction processes operating in the swash zone which 

require constant deposition and reentrainment and which result 

in an association of light minerals too large to be hydraulic 

equivalents of associated heavy minerals. The thick black layers 

rich in heavy minerals deposited at the top of the beach are 

thought to be storm generated and deposited by combined gravityshear sorting. This gravity-shear sorting causes a sorting of large 

light grains to the top of a layer and small heavy grains to the 

bottom of a layer, and during storms the process is thought to be so 

effective as to remove most of the upper layer leaving behind a 

layer composed mostly of heavy minerals.

Black sandstone deposits are not uniformly distributed in the 

Upper Cretaceous rocks of the Rocky Mountains region. They are 

most abundant in Montana and northern Wyoming. Major episodes of black sandstone formation took place in the 80-82-m.y. 

and 71-72-m.y. time span in the northern areas. These episodes of 

black sandstone formation are thought to be related to igneous 

activity or to deformation associated with emplacement of the 

Idaho and Boulder batholiths, or both, in part because minerals of 

volcanic or igneous origin are more common in these northern 

area deposits and because the igneous activity could produce a 

larger supply of heavy minerals. The 80-82-m.y. period of black 

sandstone formation may relate to a part of the events associated 

with the Telegraph Creek-Eagle regression that Gill and Cobban 

believe was caused by tectonism and volcanism in western Montana.

The black sandstone is perhaps the most reliable shoreline 

marker known in rocks of Cretaceous age. If exposed in three 

dimensions and if the top of the deposit is uneroded, the thickest 

and most abruptly terminating part of the deposit is located 

landward, and the long axis of the deposit is the local shoreline 

trend. Although black sandstone deposits yield information on 

local shorelines only, the strike of shorelines deduced from black 

sandstone corresponds quite well with that determined by Gill and 

Cobban from regional stratigraphic studies.

The overall shape of a black sandstone deposit and the distribution of heavy minerals along strike may yield clues to storm 

wind directions during the Late Cretaceous. Tentative models 

developed in Gardner's study of Australian deposits suggest that 

black sand deposits should thicken toward headlands that face 

the direction of storm wind attack and that zircon tends to lag 

behind other minerals as clastic material is transported toward

Al
A2 UPPER CRETACEOUS BLACK SANDSTONES OP THE WESTERN INTERIOR

the headland. Evidence from black sandstone of Late Cretaceous 

age, though not conclusive, suggests that storm waves struck the 

Cretaceous coasts from the southeast.

The extraordinary width of individual black sand lenses perpendicular to strike, the very flat dip of laminae in deposits, and 

the very fine grain size suggest that Cretaceous beaches, especially in some Montana areas, may have been wide and flat. If 

subsidence and compaction were negligible, or if a given deposit is 

a product of progradation only, the thickness of a deposit may be 

an approximate measure of tidal range. In general, deposits are 

thicker in the northern Rocky Mountains, suggesting that tidal 

ranges may have been higher.

INTRODUCTION

Black sandstones of Late Cretaceous age that

are fossil marine placet deposits of heavy minerals 

have been known in the Rocky Mountains region 

since 1914 when Stebinger (1914) reported occurrences in the Horsethief and Virgelle Sandstones of 

northwestern Montana. Subsequently, similar deposits have been found sporadically, but exclusively, 

in regressive-type littoral sandstone along the entire 

belt of Upper Cretaceous rocks that crop out from 

Alberta southward through out the Rocky Mountains 

to Arizona and New Mexico and into northeastern 

Mexico (figs. 1-5). They occur in southwestern 

Alberta (Mellon, 1961) in the Belly River Formation; 

in Wyoming (Houston and Murphy, 1962) in the

722°

11 2° 110° 108° 106° 104

0 100 200 300 KILOMETERS

FIGURE 1. Index map showing distributions of Upper Cretaceous rock (black) in which black sandstone deposits are found in the Rocky Mountains region. Faults are heavy black lines. 

Modified from Stose and Ljungstedt (1932).
106° 1

0 25 50 100 150 MILES

0 25 50 100 150 200 KILOMETERS

MONTANA

1.

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

1 n

DEPOSIT

Trunk Butte- ------

RiirH Hill. .........

STRATIGRAPHIC POSITION

--------- Do.

.......... Do.

--------- Do.

--------- Do.

--------- Do.

.--.----- rir>

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

DEPOSIT 

Sun RiverFreezeout LakeCounty Line- - - -

Bee DitchIron Hill-------

Bruno---------

Ringling-------

Iron CrossWall Rock BasinGreycliff-------

STRATIGRAPHIC P

------ Horsethie

...---- Virgelle S

------- Do.

------ Horsethie

------ Virgelle S

------ Do.

------ Do.

------ Slim Sam 

----- Virgelle S

------ Hell Cree

FIGURE 2. Distribution of Upper Cretaceous rocks (patterned) and black sandstone deposits (x), Montana. Faults are heavy b

Modified from Stose and Ljungstedt (1932).
A4 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

107 106

105°

45" , , 

41° U_

0 25 50 100 200 KILOMETERS

WYOMING

	DEPOSIT

21. Cowley-------------

22. Lovell--------------

23. Grass Creek----------

24. Mud Creek-----------

25. Buffalo Creek--------

26- Dry Cottonwood Creek27. Shotgun Bench-------

28. Coalbank Hills--------

29. Salt Creek-----------

30- Poison Spider Creek- - - 

31. Clarkson Hills--------

32. Seminoe- -----------.

33. Fiddlers-------------

34. Rock Springs- - ------

35. Cumberland Gap------

36- Sheep Mountain-------

STRATIGRAPHIC POSITION

Mesaverde Formation

Do.

Do.

Do.

Do.

Bacon Ridge Sandstone 

Mesaverde Group

Do.

Fox Hills Sandstone 

Lewis Shale 

Mesaverde Group 

Fox Hills Sandstone 

Lewis Shale

Rock Springs Formation 

Frontier Formation 

Mesaverde Group

37. Clay Basin (Utah-Wyoming)- - - - Rock Springs Formation

FIGURE 3. Distribution of Upper Cretaceous rocks (patterned) and black sandstone 

deposits (X), Wyoming. Faults are heavy black lines. Modified from Stose and 

Ljungstedt (1932).

Mesaverde (also of group rank which locally includes 

the Rock Springs and Frontier Formations), and in 

the Lewis Shale; in Colorado (Houston and Murphy, 

1962) in the Mesaverde Formation at Grand Mesa; in 

the San Juan Basin of New Mexico and Colorado 

(Chenoweth, 1956; Dow and Batty, 1961; Murphy,

1956) where the deposits are in sandstones of the 

Mesaverde Group including the Gallup, Point Lookout, and Pictured Cliffs Sandstones; in Utah (Dow 

and Batty, 1961) in the Straight Cliffs Formation 

and Ferron Sandstone Member of the Mancos Shale; 

in Arizona (Murphy, 1956) in the Toreva Formation;
42°

114°

112°

41 C

40°

39°

u

38°

37°

0 25 50 100 150 MILES

0 25 50 100 150 200 KILOMETERS 

UTAH-COLOR ADO

	DEPOSIT

38. Limon-----------

39. Lands End--------

40. Grand Mesa-------

41. Emery-----------

42. Henry Mountains- - -

43. Dave Canyon------

44. Long Shot--------

45. Sunday Canyon- - - -

46. Mancos River------

STRATIGRAPHIC POSITION 

POX Hills Sandstone 

Mesaverde Group

Do. 

Perron Sandstone Member of Mancos Shale

Do. 

Straight Cliffs Formation

DO.

Do. 

Point Lookout Sandstone

FIGURE 4. Distribution of Upper Cretaceous rocks (patterned) and black sandstone deposits (x), Utah and Colorado. Faults are heavy 

Modified from Stose and Ljungstedt (1932).
37°

114°

113°

 r 

36° V

35° rA

\

34

47.

48.

49. 

50-

51.

52.

53.

112°

 i 

111

110°

107

106°

R I

, PHOENIX

32°

-Winslow

O N

ALBUQUERQUE

25 50

ARIZONA-NEW MEXICO

DEPOSIT STRATIGRAPHIC POSITION

Shiprock- -------------- Point Lookout Sandstone

Stinking Lake- ----------- Mesaverde Group

Cimarron- -------------- Trinidad Sandstone

Sanostee- -------------- Gallup Sandstone

Toadlena- -------------- DO.

Oraibi Wash- ------------ Toreva Formation

Tah Chee Wash- ---------- DO.

0 25 50

DEPOSIT

100

100

I

150 

150 200 KILO

STRATIGRAPH

54. Dry Run Canyon- --------- DO.

55. Star Lake- -------------- Pictured Cliffs 

56- Standing Rock- ----------- Point Lookout 

57. Torreon Arroyo- ---------- Do.

58. Miquel Creek- ------------ DO.

59. Defiance- --------------- Gallup Sandsto

60. Herrera- ---------------- DO.

FIGURE 5. Distribution of Upper Cretaceous rocks (patterned) and black sandstone deposits (X), Arizona and New Mexico. Faults are heav

Modified from Stose and Ljungstedt (1932).
DEPOSITIONAL ENVIRONMENT A7

and in northeastern Mexico where the deposits are at 

the base of the Upper Cretaceous in Canon Del Tule 

(Baker, 1970, p. 218-219).

The most abundant heavy minerals in the black 

sandstone deposits are opaque iron-titanium oxides 

and zircon. Other minerals of lesser abundance are 

rutile, chromite, monazite, tourmaline, garnet, staurolite, amphibole, pyroxene, sphene, apatite, allanite, niobium-bearing opaque minerals, anatase, biotite, brookite, chlorite, epidote, kyanite, pyrite, 

spinel, and gold.

These deposits are unquestionably of beach 

placer origin and have many characteristics in 

common with modern beach placers such as those on 

the southeast coast of Australia (Gardner, 1955; 

Whitworth, 1959; Connah, 1961). Study of these 

deposits in Wyoming and throughout the Rocky 

Mountains region has provided basic information on 

Late Cretaceous shoreline trends, longshore current 

directions, beach slopes, and sediment source areas. 

Some of these features, relative to Wyoming deposits, 

have been described (Houston and Murphy, 1962), 

but investigations of better exposed deposits, especially in Montana, have added new information and 

modified earlier concepts.

ACKNOWLEDGMENTS

The late James R. Gill of the U.S. Geological 

Survey located a number of the black sandstone 

deposits studied and was most helpful in discussing 

regional stratigraphic problems. William A. Cobban 

of the U.S. Geological Survey supplied critical information on the age of deposits from throughout the 

Rocky Mountains area. Survey colleagues Ralph E. 

Hunter and Harry A. Tourtelot were responsible for 

major improvements in the manuscript but are not to 

be held responsible for its contents.

FACTORS CONTROLLING THE DEVELOPMENT 

AND PRESERVATION OF BLACK SANDSTONE

Black sandstone deposits are not uniformly 

distributed in Cretaceous beach deposits. They occur 

in regressive sandstone deposits (Houston and Murphy, 1962, p. 14) and are unknown in transgressive 

sandstone deposits (fig. 6). In the regressive sandstone beds of some areas, such as the Choteau area of 

northwestern Montana, black sandstone is very 

abundant, but in other areas of similar depositional 

environment, such as the Kaiparowits area of southwestern Utah, it is relatively uncommon.

A critical factor in black sand accumulation is 

the supply of clastic debris containing heavy minerals that is brought to the sea by rejuvenated

Nonmarine fluvial deposits

Black sandstone 

deposits

Volcanic rocks

Nonmarine fluvial end 

brackish-water deposits

FIGUKE 6. Diagram showing idealized stratigraphic position of 

major occurrences of black sandstone in Montana.

streams and rivers. For example, although black 

sand has been reported on most modern beaches, 

some of the major deposits are on beaches where the 

geomorphic history suggests that uplift in the source 

areas, and therefore increased detritus, has preceded 

the development of the deposits. Gillson (1959) noted 

that the major black sand deposits of Travancore 

and MK in India accumulated after uplift and erosion from a piedmont or upland undergoing lateritic 

weathering, and Gardner (1955, p. 17-33) emphasizes that geologic evidence suggests successive 

emergence and submergence of the land adjacent to 

Australian beaches during the Pleistocene and that 

an emergence of about 25 feet (6.2 m) in Holocene 

time took place during the development of major 

black sand deposits on the southeast coast of 

Australia.

The association of black sand deposits with 

regressive sandstone beds is in part related to the 

increase in detritus resulting from stream rejuvenation which was brought about by uplift and retreat 

of the sea. Evernden and Kistler (1970) have shown a 

remarkable correlation between Mesozoic plutonic 

episodes of California and Nevada and regression. 

They indicate five major episodes of batholithic 

emplacement and deformation during the Mesozoic 

and correlate each with a temporary regression of 

the epicontinental seas in the North American 

continent.

Temporally and genetically, the black sandstone deposited in Montana and Wyoming during 

periods of regression suggests relationship with the 

igneous activity and deformation associated with 

the emplacement of the Idaho batholith. Like the 

Mesozoic plutons of California and Nevada, the 

Idaho batholith is a composite intrusive with a long 

history of emplacement. Facies of the batholith have
A8 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

been dated as old as 217 m.y. (million years) and as 

young as 38 m.y. Although there is a clear overlap in 

age determinations between rocks of the Idaho batholith and rocks of the Mesozoic plutons of California 

and Nevada (Larsen and others, 1958), the dating is 

inadequate to relate the individual pulses of magma 

emplacement. If a relationship can be inferred, it is 

that a major magmatic episode in the emplacement 

of the Idaho batholith may have occurred during the 

Late Cretaceous in the period 90-79 m.y. ago 

(Evernden and Kistler, 1970, p. 24, fig. 10). Figure 7 

shows that this is the period during which more than 

50 percent of the known fossil black sandstone 

occurrences were deposited. Most of the deposits 

shown in figure 1 are in Wyoming and Montana, and 

their mineralogy indicates a significant contribution 

from igneous and (or) volcanic sources (Houston and 

Murphy, 1970, p. 246-248). In general, the deposition 

of black sandstone increases toward the end of the 

90-79-m.y. period.

Another major period of black sandstone deposition in Montana occurred between 72 m.y. and 71 

m.y. ago (fig. 7). These deposits also contain abundant minerals derived from the intrusive and extrusive rocks associated with the Boulder batholith of 

Montana. Volcanism associated with the emplacement of the Boulder batholith began 85 m.y. ago, 

reached maximum intensity about 78 m.y. ago, and 

ceased about 72 m.y. ago; plutonism began 78 m.y. 

ago, peaked about 76 m.y. ago, and ceased about 68 

m.y. ago (Robinson and others, 1968, p. 551-576).

If the frequency of occurrence of black sandstone reflects in some degree igneous activity and 

deformation associated with the emplacement of 

either the Idaho or the Boulder batholith, or both, the 

deposits are more likely to mirror local events such as 

those suggested by Gill and Cobban (1973, p. 20-33) 

than regional events such as those suggested by 

Evernden and Kistler (1970). The major episodes of 

black sandstone formation are in the 80-82-m.y. and 

71-72-m.y. time span, much briefer episodes than the 

dating of either batholith indicates (in fact, if 

Gilluly's plots of the number of ages of salic plutons 

and volcanics in the North American cordillera 

(Gilluly, 1973, p. 505) are representative of the regional events, the 80-82-m.y. episode is a regional 

low in the number of ages reported in the period 45- 

105 m.y.). The 80-82-m.y. period of black sandstone 

formation, largely representing deposits in Montana 

and northern Wyoming, may relate to a part of the 

events associated with the Telegraph Creek-Eagle 

regression that Gill and Cobban (1973, p. 20) believe 

was caused by tectonism and volcanism in western 

Montana. The 71-72-m.y. period of black sandstone

deposition, largely in Montana, corresponds, in part, 

to the Fox Hills regression (initial phase) which Gill 

and Cobban (1973, p. 28) could not relate to either 

volcanism or tectonism but which they suggested 

possibly was caused by uplift related to late stages of 

emplacement of the Boulder batholith.

The absence of black sand deposits in transgressive littoral sandstone is due to the fact that 

transgressive littoral sandstone bodies are not preserved or were not formed because rates of transgression were more rapid than rates of regression.

It is also quite possible that the black sand 

concentrating process is more effective, all other 

factors being equal, if more time is available to work 

on a given volume of sand before that volume is 

covered by newly supplied sediment (Ralph E. 

Hunter, written commun., 1973). This possibility 

might suggest that some of the major black sandstone concentrations are evidence of temporary stillstands during regression. Perhaps factors that 

influence outcrop of black sandstone-bearing rocks 

play as important a role in determining their present 

known distribution and apparent abundance as any 

of the preceding considerations, but we consider 

volcanism the key factor that directly or indirectly 

causes major black sandstone concentrations in any 

given area.

HOLOCENE BLACK SAND DEPOSITS

Connah (1961, p. 3-5) classified Australian black 

sand deposits of Holocene age into four types 

according to origin: (1) storm-wave deposits at top of 

beach, (2) wind-sorted deposits in dunes, (3) tidalcurrent interaction deposits, and (4) high-grade dune 

deposits of unknown origin. The fossil black sandstone deposits of Late Cretaceous age most closely 

resemble storm-wave deposits at the top or landward 

edge of the beach. According to Gardner (1955, p. 38) 

the storm-wave deposits on the southeast coast of 

Australia are formed by the surf on the upper or 

landward part of a beach during stormy weather. 

These deposits are dark layers of heavy minerals 30- 

50 feet (9.2-15.2 m) wide that may extend along the 

beach for the greater part of its length. In cross 

section, they appear wedge shaped, tapering gradually seaward toward the foreshore and dipping 

seaward at a low angle. In southeast Australia the 

thickest of these deposits occur in beaches that 

terminate northward in a headland or other natural 

barrier. Such deposits may be 5 feet (1.5 m) thick near 

the headland and taper gradually to the south. 

Connah (1961, p. 3-5) stated that storm-wave deposits show all degrees of concentration from single 

to repeated pencil streaks to layers of pure black sand
DEPOSITIONAL ENVIRONMENT A9

Stages and substages

Maestrichtian

Campanian

Santonian

Coniacian

Turonian

Cenomanian

lower

upper

lower

upper

middle

lower

upper

middle

lower

upper

middle

lower

K/Ar or other 

dates

Estimated 

dates

Millions of years 

before present

70 

75±2

83±3

87 + 3

68 

69 

70 

71 

72 

73 

74 

75 

76 

77 

78 

79 

80 

81 

82 

83

84 

85 

86

Western Interior ammonite sequence

Discoscaphites nebrascensis 

Hoploscaphites nicolleti 

Sphenodiscus (Coahuilites) 

Baculites clinolobatus 

Baculites grandis 

Baculites baculus

Baculites eliasi 

Baculites jenseni 

Baculites reesidei 

Baculites cuneatus 

Baculites compressus 

Didymoceras cheyennense 

Exiteloceras jenneyi 

Didymoceras stevensoni 

Didymoceras nebrascense 

Baculites scotti 

Baculites gregoryensis 

Baculites perplexus (late form) 

Baculites gilberti 

Baculites perplexus (early form) 

Baculites sp- (smooth) 

Baculites asperiformis 

Baculites mclearni

Baculites obtusiis 

Baculites sp. (weak flank ribs) 

Baculites sp. (smooth) 

Haresiceras natronense 

Haresiceras placentiforme 

Haresiceras montanaense

Desmoscaphites bassleri 

Desmoscaphites erdmanni

Clioscaphites choteaitensis 

Clioscaphites vermiformis

Clioscaphites saxitonianus

Scaphites depressus

Scaphites preventricosus 

Barroisiceras

Scaphites corvensis 

Scaphites nigricollensis 

Prionocyclus wyomingensis 

Scaphites ferronensis 

Scaphites warreni

Prionocyclus hyatti 

Collignoniceras woollgari

Inoceramus labiatus 

Sciponoceras gracile

Dunveganoceras albertense 

Dunveganoceras pondi 

Plesiacan thoceras wyomingense 

Acanthoceras amphibolum 

Calycoceras gilberti

^ ^

f ^>

L^

 -> i ^^^ c^"

 >

r

5 10 

PERCENT OF KNOWN BLACK SANDSTONE DEPOSITS

FIGURE 7. Percentages of known Upper Cretaceous black sandstone deposits of the Rocky Mountains region deposited 

during time periods represented by Western Interior ammonite zones.
A10 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

as much as 8 feet (2.4 m) thick. Two or more layers 

may be deposited successively and overlapping en 

echelon. By inference Connah (1961, p. 12-13) suggested that where deposits overlap each other the 

combined thickness of both low-grade (3 percent 

heavy minerals) and high-grade (as much as 80 

percent heavy minerals) layers may exceed 20 feet 

(6.2 m).

According to Foxworth, Priddy, Johnson, and 

Moore (1962, p. 35-41), who studied modern black 

sand deposits on beaches of the Mississippi Gulf 

Coast, heavy minerals are deposited primarily by 

wind-generated waves that result from squalls or 

storms at sea. The heavy minerals may be deposited 

on different parts of the beach depending on the 

wave height and tide. Waves generated by winds of 

low intensity are capable of depositing layers of 

heavy minerals on the foreshore. (See fig. 8 for beach 

terminology used in this report.) The heavy and light 

minerals are carried to the foreshore, and the retreating low-energy wave returns most of the light minerals, leaving the heavy minerals marooned on the 

upper foreshore in thin laminae that outline the 

relatively steep slope in this area of the foreshore. 

Moderate-intensity waves carry the heavy minerals 

to and over the berm crest. The heavy minerals are 

frequently draped over the berm crest and in cross 

section outline a depositional anticline with dips on 

one side toward the forebeach and on the other 

toward the backshore. Erosion and redeposition on 

these berms (especially on the foreshore side) may 

result in truncation of one set of black sand beds and 

redeposition of another set at a slightly different dip. 

The black sand is interlayed with white quartz-rich 

layers and shows distinct laminations. Highintensity waves, generated at high tide or during 

major storms, carry sediment over the berm crest to 

the backbeach and return light minerals seaward 

back over the berm crest. Gulf Coast backbeach 

deposits are rich in heavy minerals and are apparOFFSHORE

Oscillatory waves

Dune

BACKSHORE

 ^ 7 

Backbeach Bern 

or berm

FORESHORE INSHORE

A A

Swash, backwash 

Upper7^ ?

Collision

> 

Bores, Ic 

currents, 

return 

rip cu

__- jT^-~-^_" "^ 

ngshore 

seaward 

flow, 

rrents

Wavecollapse 

breaker

-^N -""-

5

Swamp or 

lagoon

foreshore Runnel, i Lowe ~~ ~~

1 Ridge- and- runnel system may be replaced by low-tide terrace foreshore 

or by planar slope. At low tide, swash uprush and backwash occur 

on seaward edge of foreshore.

2 Step is present at lower edge of foreshore on low-energy sand 

beaches and on most pebbly beaches.

Path of water movement'

Facies Characteristics

Swamp or lagoon

Dune 

Backbeach

Berm crest 

Upper foreshore

Ridge and runnel 

Lower foreshore

Trough 

Bar

Offshore

Burrowed lagoonal silt and clay; rich in organic material; disrupted laminations; small-scale low-angle

trough and planar cross-lamination; ripple marks; oyster and coquinoid lime deposits 

Very fine sand 1 ; trough cross-laminations; vertical root traces; laminated to structureless 

Fine sand; low-angle landward, seaward, or horizontal, dipping wedge-planar cross-lamination;

channels common; nonfossiliferous

Fine sand; convex laminae; low- to moderate- to high-angle planar cross-lamination; nonfossiliferous 

Fine sand; low-angle seaward-dipping wedge-planar cross-lamination; rare micro-cross-lamination;

burrows present but not abundant 

Fine sand; locally coarser and bimodal on ridge; high-angle cross-lamination; trough cross-lamination;

burrows uncommon 

Fine sand; low-angle wedge-planar cross-lamination dipping seaward; burrows common. Coarse sand

at lower edge of foreshore

Fine sand, high-angle trough and planar cross-lamination; shell fragments 

Locally coarser sand; high-angle cross-lamination in some examples. Sand in trough may be coarser

than on bar 

Very fine sand; thin bedded; undulatory wave ripples; plants and animals in growth position;

structureless where bioturbated

Grain size may vary in all facies because it is, in part, dependent 

on material supplied.

FIGURE 8. Major facies of idealized beach cross section (modified from Ingle, 1966).
DEPOSITIONAL ENVIRONMENT All

ently of the same type formed on Australian beaches. 

Probably during intense storms, when deposits are 

formed on the backbeach, preexisting beach ridge 

and perhaps forebeach deposits are partly destroyed 

and redeposited on the backbeach to add to the 

greater heavy mineral concentrations in this area. In 

the Mississippi Gulf Coastal areas, autumn and 

winter storm waters may carry heavy minerals 

inland beyond the backbeach and distribute them 

among sand dunes.

The preservation of the heavy minerals on various parts of the beach depends on the deposition of 

protective layers of light minerals soon after formation of the heavy layer. The heavy minerals laid 

down on the foreshore, especially in the seaward 

foreshore area, are more subject to erosion than those 

deposited on the backbeach, which are most likely to 

be preserved.

CRETACEOUS BLACK SANDSTONE DEPOSITS

(THE REGRESSIVE SEQUENCE) MARIAS

RIVER EXAMPLE

A typical Upper Cretaceous black sandstone 

deposit crops out along the Marias River in Montana 

northeast of Pendroy in sec. 4, T. 28 N., R. 5 W. (fig. 2, 

No. 8). Where exposed, the deposit is 0.8 mile (1.3 km) 

long and 0.1 mile (0.16 km) wide. It lies near the top of 

the Virgelle Sandstone. The long dimension of the 

deposit trends N. 50° W., which is in agreement with 

the generalized Late Cretaceous shoreline trends 

shown by Gill and Cobban (1969). The deposit is 

about 18 feet (5.5 m) thick in the center and thins 

northwestward to about 9 feet (2.8 m) where it is 

concealed by younger sediments; it thins similarly to 

the southeast. The deposit is wedge shaped in cross 

section it is thickest on the southwest (shoreward) 

and thins northeastward to a featheredge (fig. 9 

shows similar thinning in deposit at Red Creek, 

Wyo., fig. 3, No. 37).

The Marias River deposit overlies a coarser 

grained white massive sandstone that is not well 

exposed in this area. As in most black sandstone 

deposits the percentage of heavy minerals increases 

from the base to the top (fig. 10). The lowermost zone 

of the Marias River deposit, zone A (fig. 11) is generally an iron-stained brown sandstone with a few thin 

laminae of heavy minerals. This zone, which ranges 

in thickness from 2 to 5 feet (0.6-1.5 m), is generally 

structureless at the base and indistinctly bedded 

near the top. Sporadic casts and molds of burrows 

are present. Some are small tubular casts that may 

be worm burrows.

Overlying zone A is a laminated sandstone with

more abundant thin apparently horizontal laminae 

of heavy minerals zone B (fig. 11). About 20-50 

percent of zone B consists of heavy mineral laminae, 

some of which show a dip of 4°-5° NE., or seaward. 

Only one current ripple mark was well enough 

exposed to determine its orientation strike N. 30° 

E. and steep limb facing northwest, which suggests 

northwest transport. Some layers of heavy minerals 

are deformed, some of them being almost convolute. 

Locally the laminae have been faulted, probably 

penecontemporaneously with deposition inasmuch 

as the layers are overlain and underlain by undeformed beds. The faults are miniature thrust faults, 

and most show apparent displacement to the northwest. This zone averages 3 feet (0.9 m) in thickness 

and is overlain by a similar laminated zone (zone C, 

fig. 11) with thicker and more abundant laminae of 

heavy minerals.

Crossbeds outlined by laminae of heavy minerals are common in zone C. The crossbedded units 

vary in thickness, but most are about 6 inches (15 cm) 

thick (fig. 12). Most of the crossbedding dips (8°-32°) 

either northeast or southwest and strikes roughly 

parallel to the long dimension (shoreline direction) of 

the deposit (fig. 13). Thick layers (2-8 in. or 5-20 cm) 

composed almost entirely of heavy minerals occur 

sporadically in the zone but with greater frequency 

near the top. Burrows are present, some as large as 2 

inches (5 cm) in diameter. The larger burrows, which 

were probably made by animals "swimming" 

through the sediment, are as much as 6 inches (15 

cm) in length and are U-shaped in cross section with 

a series of concentric concave layers from bottom to 

top of the burrow (fig. 14). Other, usually smaller, 

burrows resemble Ophiomorpha (Toots, 1961), a term 

used for a burrow probably constructed by a decapod 

crustacean like Callianassa major, whose burrows 

from beaches along the Georgia coast were described 

by Weimer and Hoyt (1964). Zone C is 5-6 feet (1.5-1.8 

m) in thickness.

Overlying zone C is zone D, the uppermost part 

of the black sandstone deposit and the part richest in 

heavy minerals. Zone D (fig. 11), which is 4-6 feet 

(1.2-1.8 m) thick, is characterized by thick massive 

layers containing 80-90 percent heavy minerals. The 

layers range in thickness from a few inches to nearly 

1 foot (5-30 cm). They are not continuous and may 

overlap each other or be separated by laminated 

black sandstone, crossbedded sandstone, or even 

white almost structureless sandstone barren of 

heavy minerals. Commonly the higher grade and 

thickest layers are at the top of zone D. In many 

deposits this upper zone is overlain by 2-3 feet (60-90 

cm) of massive white sandstone which in turn is
A12 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

^-E;*^'*^w ^J!jfr" v2L."1t!ra~'."1 ^es^sv 

FIGURE 9. Black sandstone deposit in the uppermost sandstone of the Rock Springs Formation at Red Creek. Note distinct thinning of 

the deposit to the east or right (seaward) and abrupt termination to the west or left. Photograph shows a cross section of the deposit 

taken nearly at right angle to the shoreline. NEl/4 sec. 22, T. 12N., R. 105 W., Sweetwater County, Wyo.; view looking north.

overlapped from the seaward side of the deposit by 

another rich heavy mineral zone, perhaps part of 

another cycle, with characteristics like those of zone 

D. Burrows are rare in zone D.

Some individual high-grade heavy mineral 

layers in zone D can be traced in cuts perpendicular 

to the shoreline nearly to the exposed seaward edge 

of the deposit where they intertongue with white 

sand (fig. 15). The layer may be 2-6 inches (15 cm) 

thick at the landward edge, and an individual layer 

between marker laminae gradually thins in a seaward direction until it is less than one-sixteenth inch 

thick. Beds above and below an individual heavy 

mineral layer appear to parallel the layer when 

examined in outcrop, but when viewed at a distance, 

some truncation surfaces dip more steeply than 

underlying beds, whereas others are flatter than 

underlying beds. Again when viewed at a distance 

the entire sequence appears to be stacked seaward, 

and, overall, beds show a decrease in dip in the 

seaward direction.

The vertical sequence within deposits A-D can
DEPOSITIONAL ENVIRONMENT A13

Uppermost foreshore 

or backbeach

Uppermost foreshore 

or backbeach

Upper foreshore or 

uppermost lower 

foreshore

FIGURE 10. Black sandstone at the top of the John Henry 

Member of the Straight Cliffs Formation south of Escalante, 

Utah. The base of the unit is a white burrowed sandstone 

which is overlain by laminated black and white sandstone 

capped by thick massive beds very rich in heavy minerals.

be seen, by the lateral tracing of beds, to follow 

Walther's Law (Walther, 1893) and clearly reflects 

the regressive environment during which it was 

deposited. In any given locality the layers represent, 

successively from base to top, deposits typical of the 

foreshore to .backbeach and possibly including dune 

remnants.

Basal white sandstone

The basal white sandstone that underlies the 

black sandstone (fig. 16) is massive without distinctive or well-developed structures. Samples of this 

unit taken a few feet below the black sandstone are 

coarser grained than the black sandstone. This fact, 

plus its lack of sedimentary structures, might be used 

to support the concept that the bulk of the white 

sandstone was deposited in the inshore or portions of 

the offshore nearest the beach. Ingle (1966, p. 181) 

has pointed out that inshore deposits (collision and 

wave collapse areas) are generally coarser grained 

than beach sand and that, inasmuch as bedding is

EXPLANATION

J C2> Burrows 

O

Contorted laminations of organic and 

inorganic origin

Crossbedding

Ripple marks

Beds containing over 60 percent heavy minerals

Laminae of heavy minerals in sandstone

Beds containing less than 4 percent heavy minerals

FIGURE 11. Typical vertical sequence of black sandstone, Marias 

River deposit, Montana.

more likely to be disrupted by the action of organisms in the inshore and offshore areas (Hunter and 

others, 1972), well-developed structure may not be 

typical of sandstone that was deposited in this 

environment.

The basal white sandstone is not without structure in all areas, however. High-angle trough crosslamination can be recognized in some deposits (fig. 4,
A14 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

A Jf9KiUh^«ft«i» JMK^^KtfrfMT ^n

FIGURE 12. Cross-lamination in middle part of black sandstone of Marias River deposit. Landward-dipping cross laminae are 

curved so that steepest dip is in the central section of the laminae, suggesting bed has undergone little or no truncation. Ruler 

is 7 in. (18 cm) long.

No. 44), and in others the white sandstone has faint 

thin laminations with very low dip. Burrows (Ophiomorpha(?)) are unusually abundant in some white 

sandstone (fig. 4, No. 43), and, in still another area, a 

channel about 2 feet (0.6 m) deep and 10 feet (3 m) 

wide has been filled with very complex small- and 

medium-scale cross-laminated sandstone (fig. 2, No. 

8). These various organic and inorganic structures 

could have formed on the lowermost foreshore or 

inshore. Thin laminae with low dip and burrowed 

sandstone could be fossil analogs of structures described by Hoyt and Weimer (1963, p. 530) on the 

lower foreshore of modern beaches at Sapelo Island, 

Ga. The trough cross-lamination may represent 

small and large cut-and-fill structures (trough) described in the inshore (surf zone) portion of beaches 

of Padre Island, Tex. (Jacka, 1970, p.^ 192-193).

Further indication as to the environment of 

deposition of the white sandstone was given by 

Petersen (1969, p. 133), who described a threefold 

vertical sequence of structures in the John Henry 

Member of the Straight Cliffs Formation of Utah, 

where black sandstone occurs in the upper part of 

barrier sandstone bodies. The lower unit of this 

sequence is a grayish-orange sandstone with horizontal laminations and low-angle medium- to largescale trough and planar cross-lamination, and it 

commonly contains nonabraded fossils. The middle 

unit is a grayish-orange to light-gray sandstone with

FIGURE 13. Rose diagram showing direction of crossbedding dip 

in black sandstone at Marias River deposit, Montana. Data 

plotted in 10° azimuth classes; radial scale in percent of total 

number of measurements. Dashed line at N. 50° W. is strike of 

shoreline in this area; seaward side is to the northeast.
DEPOSITIONAL ENVIRONMENT A15

FIGURE 14. Laminated black sandstone typical of lower part of 

black sandstone at the top of the Virgelle Sandstone on the 

north side of the Dry Fork Marias River, sec. 4, T. 28 N., R. 5 W., 

Pondera County, Mont. Note local disruption of bedding by 

burrows.

low- and high-angle medium-scale trough crosslamination. The upper unit contains the black sandstone and is very light gray to white with very low 

angle medium- to large-scale wedge-planar crossstratification, and it lacks fossils.

The presence of nonabraded fossils in the lower 

be'dding unit is considered evidence that this part of 

the vertical sequence formed in offshore areas seaward of the breaker zone where lower flow-regime 

conditions prevailed (Peterson, 1969, p. 139). The 

high-angle medium-scale trough cross-lamination of 

the middle unit may have formed on break-point bars 

modified by longshore currents in the breaker zone, 

and laminae may reflect the form of longshore bars 

and troughs. The large-scale very low angle wedgeplanar cross-lamination of the upper unit was interpreted by Peterson (1969, p. 137) as evidence that this 

sandstone developed on the forebeach.

This same general sequence has been recognized 

by Jacka (1965, p. 88-89; 1970, p. 214-216) in other 

areas in his Fox Hills Sandstone, Rock Springs 

Formation, Almond Formation, and Lazeart Sandstone of Wyoming and in bis Tocito Sandstone and

Sanostee Members of the Gallup Sandstone, Point 

Lookout Sandstone, Cliff House Sandstone, and 

Pictured Cliffs Sandstone of New Mexico.

Black sandstone

Figure 11 shows the subdivision of a typical 

black sandstone and suggests the environments of 

deposition. Zone A was deposited on the lower 

foreshore, where laminae of heavy minerals are thin 

and rarely formed or preserved. The low seaward dip 

of laminae, scarcity of heavy mineral laminae, and 

presence of worm and possible Ophiomorpha burrows all suggest the lower foreshore environment. 

Zone B may represent the upper foreshore or upper 

part of the lower foreshore. This interpretation depends on the interpretation of the crossbedded units 

with high-angle laminae in zone C. Some crossbeds 

dip seaward and others landward, which suggests 

structures like those on berm crests described by 

Foxworth, Priddy, Johnson, and Moore (1962, p. 32) 

or structures on foreshore ridges located beneath the 

upper and lower foreshore described by Hoyt (1962) 

and Hoyt and Weimer (1963). If these are crossbedded units on the berm crest, then units below 

them are upper foreshore and units above them are 

backshore deposits, but if the crossbeds were formed 

on the foreshore ridge, then the units below them 

would be lower foreshore and units above them upper 

foreshore.

Figure 13 shows that more beds dip landward 

than seaward in the crossbedded unit at Marias 

River. The landward-dipping crossbeds dip as much 

as 32°. Ridge and runnel systems that develop on flat 

beaches (Hoyt, 1962) may be modern analogs of 

these crossbedded structures. Hoyt noted that these 

ridges commonly originate on the lower foreshore, 

are 50-150 feet (15.2-46 m) wide, and may extend 

along a beach for as much as 1 mile (1.6 km). The 

landward slope of the ridge is steep, as much as 30°, 

whereas the seaward slope is l°-2° (Hoyt, 1962, p. 

311). The landward-dipping laminae in the Sapelo 

Island, Ga., deposits studied by Hoyt are well defined 

by laminae of black heavy minerals that alternate 

with layers of quartz. The stratification planes are 

curved, with the steepest dips in the central section, 

and are virtually identical to similar structures in 

fossil black sandstone (fig. 12). The landwarddipping crossbedded units in fossil black sandstone 

deposits are therefore interpreted as being part of 

fossil foreshore ridges.

In figure 7, a ridge and runnel system is shown 

separating the lower and upper foreshore of a typical 

beach, and this is also shown as a collision zone 

(Ingle, 1966, p. 181), an area where backwash encounters incoming waves. This zone has most recently been described as the "inner rough zone" by
A16 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

Clifton, Hunter, and Phillips (1971, p. 656), who have 

studied structures of steep high-energy beaches of 

the Oregon coast. They found that off steep beaches 

this inner rough facies consists of a series of steepsided symmetrical ripples of coarse sand and gravel 

but that on more gently sloping beaches sets of 

troughs or depressions develop, 3-6 feet (1-2 m) 

across and 4-20 inches (10-50 cm) deep, that are 

parallel to the beach and are separated by broad flat 

"ridges." According to Clifton, Hunter, and Phillips 

(1971), the seaward-facing side of these troughs is 

generally steeper than the landward side, and these 

structures migrate seaward, which is in direct contrast to the similar structures at Sapelo Island, 

described by Hoyt, that migrate landward.

Fossil ridges in the fossil black sandstones seem 

to be of a type that develops on flat low-energy 

beaches, such as the Sapelo Island example, rather 

than on steep high-energy beaches, such as the 

Oregon coast example. If these beach ridges are 

developed some place on the foreshore, as suggested 

by Hoyt (1962), the thick beds rich in heavy minerals 

probably were deposited on the upper foreshore of the 

Cretaceous beaches, and the laminated beds below 

the crossbedded unit on the lower foreshore. This 

hypothesis undoubtedly is an oversimplification for 

several reasons. Ridge and runnel systems may 

develop on different parts of flat beaches, and a 

given beach may have a series of these structures 

that parallel one another on the lower foreshore and

FIGURE 15. Landward (A) and seaward (B) portion of a black sandstone at the Marias River deposit. The pencil shown in both 

photographs is at the base of the same bed that can be traced 200 feet (60 m) in a direction perpendicular to the shoreline. A, The 

landward portion. The bed above the pencil is a layer of sandstone 3 inches (8 cm) thick composed almost entirely of heavy 

minerals. The sandstone in the upper half of A is composed of layers containing 80-90 percent heavy minerals, whereas that in 

the lower half is laminated and more like the beds in B. B, Very thin locally burrowed laminae of heavy minerals typical of the 

seaward edge of the deposit. Very low angle wedge-planar cross-laminations are shown in the top right. Below the pencil, the 

laminae are less well developed and burrowed; at the base truncated landward-facing cross-laminae having dark silty layers in 

the troughs are exposed. The sandstone at the base of B is coarser grained than that at the top.
DEPOSITIONAL ENVIRONMENT A17

even on the upper foreshore near the berm. King 

(1959, p. 341-347) stated that the ridges develop at 

the upper limit of the swash zone and that their 

position is related to the tides. At low tide a ridge may 

develop on the upper part of the lower foreshore, and 

at high tide on the upper foreshore nearer the berm, 

but ridges on the upper foreshore are generally 

poorly developed. All ridges will be marked by 

steeper landward-facing crossbedding in fossil black 

sandstone so that their value in separating upper 

and lower foreshore can be questioned.

A characteristic of the black sandstone at 

Marias River as well as in other areas in the Rocky 

Mountains is that the thick heavy-mineral-rich 

layers at the top of the deposits truncate lower beds 

and characteristically dip in a seaward direction (fig. 

11, zone D). Aside from the crossbedded unit in zone 

C, landward-dipping beds and landward-dipping 

wedge-planar structure cut by numerous troughs and 

channels (McKee, 1957, p. 1712) that are characteristic of the surface of the berm or backshore are not 

present. In areas subject to severe storms the berm

would have been destroyed, and probably any upper 

beach ridges would be removed as well. It seems 

probable that the high-angle crossbedded units of 

zone C were deposited on foreshore ridges and that 

the thich beds rich in heavy minerals that lie above 

these units were deposited on the upper foreshore. 

Probably, on most Cretaceous beaches where black 

sandstone occurs, the upper foreshore extended landward to the dunes. In any event the vertical sequence 

observed in most black sandstone deposits must 

represent successively higher or landward portions 

of the beach, and the layers rich in heavy minerals 

found near the top of virtually all deposits must be 

deposited on the upper part of the beach. In a 

regressive sequence these rich layers represent the 

uppermost true beach deposits of a given regressive 

sandstone.

An interesting aspect of most black sa'ndstone 

deposits is the absence of positively recognizable 

dune deposits overlying the uppermost black sandstone layers. Fine-grained structureless sandstone 

that may have formed in dunes overlies some black

FIGURE 15. Continued.
A18 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

FIGURE 16. Black sandstone at the top of basal white sandstone of the Mesaverde Formation on the north rim of the Grass Creek 

anticline in Hot Springs County, Wyo. The rocks exposed here are typical of the regressive sequence a basal white massive 

sandstone about 150 feet (46 m) thick, overlainjay 10-15 feet (3-4.6 m) of black sandstone, which is overlain by nonmarine shale 

and carbonaceous shale containing lignite and coal beds. Photograph taken looking south.

sandstone and is interbedded with thick heavymineral-rich layers at the top of some deposits (fig. 

11), but structures characteristic of modern dunes are 

not present. Perhaps the dunes, being topographically high and thus more prone to erosion, were 

readily removed and replaced by lagoonal or coastal 

swamp deposits during regression. It is also possible 

that sedimentary structures in dunes were destroyed 

by weathering processes, plant roots, animals, and 

movement of vadose water as has been shown to be 

the case on Galveston Island, Tex., by Bernard, 

LeBlanc, and Major (1962, p. 200).

None of the immediately (?) overlying beds are 

exposed in the Marias River deposit, but in many 

deposits the overlying beds are fine-grained sandstone, carbonaceous shale, and coal. Oyster-bearing 

beds, typical of lagoon and near-marine swamp 

deposits, are also fairly common.

Figure 17 shows possible stages in the development of the thick wedges of black sandstones on a

relatively flat Cretaceous beach and suggests how 

the various facies may overlap to develop the typical 

regressive sequence previously described.

SIGNIFICANCE OF GRAIN SIZE

Fossil black sandstones of Late Cretaceous age 

are very fine grained; modal diameters are related to 

the proportion of light and heavy minerals in a 

sample. Samples with a predominance of light minerals have modal diameters that range from 0.15 to 

0.21 mm, and samples with a predominance of heavy 

minerals have modal diameters close to 0.10 mm. 

Because of the response of heavy minerals to 

hydraulic factors that influence deposition, heavy 

minerals are smaller than associated light mineral 

grains within a black sandstone deposit.

Upward fining from water level to the top of a 

beach is the general rule in beaches (Miller and 

Zeigler, 1958) and is especially true of beaches with 

abundant heavy minerals for reasons cited above.
Berm crest

Berm crest

id black sand layer

Berm crest 

D

Berm crest 

Berm crest

m-generated black sand layer

E

FIGURE 17. Possible stages of development of black sandstone deposit. A, Simplified flat Cretaceous beach showing internal structure o

and ridge-and-runnel system. B, Black sand layer, flattening of overall beach gradient, and partial destruction of ridge, all genera

C, New ridge developed in attempt to steepen beach gradient. D, Shifting of beach facies during regression. E, Storm-generated blac

formed after regression. 
A20 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

Thus the forebeach environment, and black sandstone in particular, is an exception to the general 

trend of upward increase in grain size in a regressive 

marine sequence (Sabins, 1965).

In many of the black sandstone deposits the 

principal heavy mineral is magnetite and the principal light mineral is quartz. The modal diameter of 

the heavy minerals is 0.10 mm, whereas the modal 

diameter of associated light minerals varies depending on the percentage of heavy minerals of the 

sample. Light minerals in samples with alternating 

laminae of black and white sand that average more 

than 50 percent light minerals have modal diameters 

of 0.21 mm. Light minerals in samples composed 

largely (more than 60 percent) of heavy minerals 

have modal diameters that average 0.15 mm (fig. 18; 

also Houston and Murphy, 1962, fig. 4, pi. 3; Mellon, 

1961, table 1). Grains transported in suspension and 

deposited as current velocity decreases should have 

the same settling velocity (Rubey, 1933) or be 

hydraulic equivalents (Rittenhouse, 1943). Light and 

heavy minerals in fossil black sandstone approximate this ideal in that the heavier mineral grains are 

smaller than light mineral grains, but they are not 

exact hydraulic equivalents. Ideally, a single lamina 

(depositional unit of Apfel, 1938) should be used to 

test for hydraulic equivalency so that grains deWentworth scale

Mm

Medium sand 

1/4 0250 

Fine sand 

1/8 0.125 

Very fine sand 

1/16 0.0625

sm

Tyler sieve

Mesh 

No.

60 

80 

115 

170 

250

325

Mm

0 246-

0 088- 

0 061 -

0 043- A

I I I

1

': ' :'''. ' ; "':'. ': 

^i B

i

-

i

^

c

\ 1 t

i 10 15 20 0

PERCENT

10 15 20 0

PERCENT

; 10 15 20

PERCENT

10 15 20 25 300 5 10 15 0 5 10 15

PERCENT PERCENT PERCENT

FIGURE 18. Histograms relating grain-size variation to light (no 

pattern) and heavy (black) mineral fractions in black sandstone deposits. Line pattern represents ferromagnetic 

fraction (ferric iron and carbonate matrix removed by 10 percent HC1). A, Rollins(?) Sandstone Member of Mesaverde 

Formation, Grand Mesa, Colo. B, Straight Cliffs Formation, 

Escalante, Utah. C, Point Lookout Sandstone (of Shiprock 

deposit), Salt Creek Wash, N. Mex. D, Gallup Sandstone, 

Sanostee, N. Mex. E, Gallup Sandstone, Toadlena, N. Mex. 

F, Toreva Formation, Tah Chee Wash, Ariz.

posited together may be compared. The higher grade 

(60-90 percent heavy minerals) samples are from 

single layers rich in heavy minerals, and they should 

be ideal depositional units; for example, if the 

dominant heavy and light minerals, magnetite (sp. 

gr. 5.18) and quartz (sp. gr. 2.67), are used to test for 

hydraulic equivalency, and assuming the grains to 

be spherical, a magnetite grain of 0.10 mm diameter 

should be associated with a quartz grain 0.16 mm in 

diameter. The observed modal size of the light 

minerals is 0.15 mm and therefore is slightly smaller 

than it should be. Quartz in black sandstone (fig. 

18.F, C) has a modal diameter of 0.21 compared to the 

0.10 of the associated heavy minerals, somewhat 

larger than would be expected if deposition was 

controlled by settling velocities.

Clifton (1969) has demonstrated that heavy 

minerals are deposited in the swash zone of Oregon 

beaches as a type of reverse graded depositional unit. 

The base of a unit is a fine-grained layer rich in 

heavy minerals, and this grades upward into a 

coarser grained light-colored layer with a high proportion of light minerals. Constant erosion and redeposition in the swash zone causes this layering to 

vary, in that part or all of some layers are removed so 

that individual depositional units may not be complete, but the process results in the development of 

alternating light and dark laminae very much like 

that in the lower parts of black sandstone deposits. 

Clifton suggested that the reverse graded bedding is 

formed by sorting action that takes place as sediment is transported by traction. He stated (Clifton, 

1969, p. 557) "segregation between coarse and fine 

grains, and between light and heavy grains occurred 

very quickly within a moving layer of sand following 

the maximum erosion during backwash." This 

general type of sorting in dense layers of sand has 

been discussed from a theoretical viewpoint by 

Bagnold (1954, p. 62), who stated that when grains of 

mixed sizes are sheared together the larger grains 

should drift toward the zone of least shear (top of the 

layer). It is also reasonable to assume (Clifton, 1969, 

p. 557) that grains of higher density will work their 

way to the bottom of a layer even if all grains are of 

equal size. This general process of combined gravityshear sorting has been observed not only by Clifton 

but by many others including Inman (1949) and 

Krumbein (1944).

Hand (1967) has demonstrated by use of settling 

tube techniques that heavy minerals are too small to 

be the hydraulic equivalents of light grains on New 

Jersey beaches. He noted that once a grain is 

entrained, the distance it will travel should be controlled by settling velocities and that under these 

circumstances grains that are deposited in a given 

area should be hydraulic equivalents, but he stressed
DEPOSITIONAL ENVIRONMENT A21

the point that an additional and perhaps more 

important control on whether a grain will remain in 

a particular place is the ability of the existing current 

to remove it the process of reentrainment. He noted 

that if two grains have the same settling velocity but 

different densities, the denser grain will be smaller, 

and that since a small particle among larger ones is 

physically removed and shielded from high velocity 

flow, its movement will be blocked by the larger 

grains. He further stated (Hand, 1967, p. 516)

It follows that in a mixture of quartz (S.G. 2.65) and garnet (S.G. 

4.0), all of whose grains had the same settling velocity, the quartz 

should be less likely to remain as part of the permanent deposit 

than the garnet. To make the garnet equivalent to the quartz in a 

true sense, it would be necessary to decrease the settling velocity 

(grain size) slightly. With only a slight change, the geometric 

disadvantage of the garnet will not be greatly increased, but the 

ratio of fluid drag to grain mass will be substantially increased. 

When the probability of entrainment for garnet just equals that 

for associated quartz, the grains should be truly equivalent.

Hand's concept therefore emphasizes the role of 

reentrainment in controlling grain size of associated 

minerals of different specific gravity and would seem 

to apply best to areas on a beach where there is 

constant erosion and redeposition of grains the 

swash zone. The overall tendency with time might be 

an association of heavy minerals that are too small 

or light minerals that are too large to be hydraulic 

equivalents in the sense of having equal settling 

velocities.

The preceding discussion suggests that there 

may have been two processes at work on the 

Cretaceous beaches: one that resulted in the deposition of alternating black and white sand on the forebeach (swash zone) where light minerals are too 

large to be hydraulic equivalents of associated heavy 

minerals and one that resulted in the deposition of 

black layers composed of at least 60 percent heavy 

minerals, and often more than 80 percent heavy 

minerals, on the landward edge of the beach where 

associated heavy and light minerals are nearly 

hydraulic equivalents. Deposition of the black and 

white sand on the forebeach may be the result of the 

traction processes described by Clifton (1969) and 

Hand (1967), but deposition of the black layers on the 

landward edge of the beach may be the result of a 

different process.

The thick black layers rich in heavy minerals 

found at the top of the black sandstone deposit are 

thought to be storm generated. High-energy storm 

waves are capable of destroying and flattening parts 

of the forebeach, and they probably carry in suspension grains that were previously deposited on the 

forebeach plus other clastic particles picked up seaward of the forebeach. When this material is carried 

to the top of the beach, the wave energy decreases

and grains must begin to settle from suspension as 

the wave moves along the beach. As the wave moves 

along the beach and eventually returns seaward, 

traction processes may take over and the mechanism of combined gravity-shear sorting as discussed by Clifton (1969) may be carried almost to 

completion with the removal of most of the upper 

coarser grained light-colored layer, leaving only the 

black fine-grained layer rich in heavy minerals. The 

process of combined gravity-shear sorting would be 

carried to completion because of the higher energy of 

the storm wave as it moves along the beach and 

eventually seaward.

Light and heavy minerals in the lower layer of a 

storm-generated deposit of this type would not be 

affected by the reentrainment process of Hand and 

would therefore be closer to hydraulic equivalents.

SHORELINE TRENDS

The black sandstone is perhaps the most reliable 

shoreline marker known in rocks of Cretaceous age. 

If exposed in three dimensions and if the top of the 

deposit is uneroded, the thickest and most abruptly 

terminating part of the deposit is located landward 

(fig. 9). The deposit thins and feathers out seaward or 

may be made up of an en echelon series of black sand 

lenses that are repeated slightly higher in the 

section seaward. The long axis of the deposit is the. 

local shoreline trend. However, if the deposit is made 

up of lenses that are en echelon in a horizontal plane 

as well as in cross section, the long axis of the deposit 

may diverge from the shoreline direction, and the 

observer should thus make certain that he considers 

a single black sand lens when a shoreline direction 

is determined.

Table 1 compares shoreline trends deduced from 

black sandstone deposits with those determined by 

Gill and Cobban (1969) from regional stratigraphic 

studies. Although the comparison cannot be made at 

exactly the same instant of Late Cretaceous time, 

there is reasonably close agreement. Significant 

departures between the two methods occur only 

where there are known major age differences between the black sandstone and the stratigraphic unit 

used by Gill and Cobban.

SOME AREAS FOR FUTURE RESEARCH

In the course of this study, which was primarily 

to consider the economic potential of fossil black 

sandstone, a number of concepts were considered 

that we believe will be useful in determining more 

about the Late Cretaceous environment. The results 

of studying these concepts were not conclusive partly 

because detailed information on modern black 

sandstone deposits is not available and partly 

because of less than adequate study of fossil
A22 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

TABLE 1. Trends of Upper Cretaceous shorelines determined from black sandstone as compared with trends of shorelines established 

by Gill and Cobban (1969) from regional stratigraphic and paleontologic study

Stages and 

substages

C

<& vS 

,n 

 r Lower

Age from Western Interior 

ammonite sequence

Sphenodiscus 

(Coahuilites)

Baculites clinolobatus

Location of black sandstone 

deposits

Colorado 

(northwest of Limon)

Stratigraphic unit

Fox Hills 

Sandstone

Shoreline trend from 

black sandstone

North-northwest 

(approx.)

Shoreline trend of closest age 

from Gill and Cobban (1969)

Northwest (approx.) 

(Baculites clinolobatus)

Baculites grandis Wyoming Fox Hills N. 10° W.(?) 

(southeast of Midwest) Sandstone

North (approx.) 

(Baculites clinolobatus)

Baculites baculus

Baculites jenseni

Montana 

(north of Browning)

Montana 

(west of Browning 

Kiowa Junction area)

Horsethief 

Sandstone

Horsethief 

Sandstone

N. 25°-30° W. N. 25° W. 

(Baculites reesidei)

N. 40° W. N. 25° W. 

(Baculites reesidei)

Baculites reesidei

Baculites cuneatus

Baculites compressus

Northern Montana 

(near Augusta)

New Mexico (Star Lake 

Trading Post)

Horsethief 

Sandstone

Fruitland 

Formation

N. 65° W. N. 30° W. 

(Baculites reesidei)

N. 60° W. N. 55° W. 

(Baculites reesidei)

Didymoceras cheyennense

Exiteloceras jenneyi

Upper Didymoceras stevensoni Wyoming 

(west of Laramie)

Mesaverde Group North-northwest 

(approx.)

North 

(Baculites scotti)

Didymoceras nebrascense

Baculites scotti

Baculites gregoryensis

Baculites perplexus 

(late form)

Wyoming Parkman Sand- North 

(southwest of Casper) stone Member 

of Mesaverde 

Formation

North 

(Baculites scotti)

mnian

a«B 

O

Baculites gilberti

Baculites perplexus 

(early form)

Baculites sp. (smooth)

Baculites asperiformis

Baculites mclearni

Baculites obtusus

Wyoming 

(south of Tensleep)

Wyoming 

(south of Hiland)

Wyoming (northern 

Bighorn Basin)

Mesaverde N. 15° E. 

Formation

Mesaverde Northwest 

Formation

Mesaverde N. 45° W. 

Formation

North 

(Baculites scotti)

North 

(Baculites scotti)

N. 45° W. 

(Baculites mclearni)

Baculites sp. 

(weak flank ribs)

Wyoming (southeast 

of Rock Springs)

Lower

Rock Springs Northeast 

Formation of 

Mesaverde 

Group

Northeast 

(Baculites mclearni)

Baculites sp. (smooth) 

Haresiceras natronense

New Mexico Menefee 

(northeast of Shiprock) Formation

Wyoming (southeast 

of Bighorn Basin)

Mesaverde 

Formation

N. 70° W. 

N. 15° W.

N. 70° W. 

(Baculites sp. [smooth]^

N. 15° W. 

(Baculites sp. [smooth p

deposits; however, these results are discussed below 

to suggest areas where future research may be

helpful in the study of fossil black sandstone and 

modern analogs. Interpretations are tentative, and it
DEPOSITIONAL ENVIRONMENT A23

TABLE 1. Trends of Upper Cretaceous shorelines determined from black snadstone as compared with trends of shorelines established 

by Gill and Cobban (1969) from regional stratigraphic and paleontologic study (Continued)

Stages and Age from Western Interior Location of black sandstone Shoreline trend from Shoreline trend of closest age 

substages ammonite sequence deposits Stratigraphic unit black sandstone from Gill and Cobban (1969)

Wyoming (northwest 

Wind River Basin)

Mesaverde North 

Formation

New Mexico Point Lookout N. 60°-70° W. 

Hnrozir* * pln^tifnrmo (northeast of Shiprock) Sandstone

New Mexico (Standing 

Rock Trading Post)

New Mexico 

Lower (west of Cabezon)

(Con-> Montana 

(east of Valier)

Point Lookout N. 54° W. 

Sandstone

Point Lookout N. 50° W. 

Sandstone

Virgelle N. 55° W. 

Sandstone

Montana Virgelle N. 55° W. 

Haresiceras montanaense (northeast of Pendroy) Sandstone

Montana 

(near Choteau)

Desmoscaphites bassleri Utah 

Tinner (south of Escalante)

 g Desmoscaphites erdmanni

"S MiHdlp Clioscaphites choteauensis

Virgelle N. 45° W. 

Sandstone

Straight Cliffs N. 15° W. 

Formation

Clioscaphites vermiformis Utah (southeastern Straight Cliffs N. 35° W. 

Kaiparowits Plateau) Formation

North 

(Baculites sp. [smooth]^

N. 60°-70° W. 

(Baculites sp. [smooth] )

N. 50° W. 

(Baculites sp. [smooth]^

N. 50° W. 

(Baculites sp. [smooth]^

N. 50° W. 

(Baculites sp. [smooth] )

N. 50° W. 

(Baculites sp. [smooth] )

N. 50° W. 

(Baculites sp. [smooth] )

N. 20° W. 

(Desmoscaphites)

N. 40° W. 

(Desmoscaphites)

Lower Clioscaphites saxitonianus

Upper Scaphites depressus

Middb Scaphites ventricosus

c Arizona 

 3 (north of Pinon)

«S 

 g Sra.phit.pR prpiipntri.rn.tus

O Lower Arizona 

(Tah Chee Wash)

Barroisciceras New Mexico (west 

of Laguna Pueblo)

Toreva Forma- Northwest 

tion of Mesaverde Group

Toreva Forma- Northwest 

tion of Mesaverde Group

Gallup N. 30° E.(?) 

Sandstone

N. 55° W. 

(Desmoscaphites)

N. 55° W. 

(Desmoscaphites)

N. 65° W. 

(Desmoscaphites)

Scaphites corvensis

New Mexico

Sraphit** niarirnll*n*i* (Sanostee)

Gallup N. 25° W. 

Sandstone

New Mexico Gallup N. 25° W. 

fl (southwest of Gallup) Sandstone

«S

'3 JT Prionocyclus Arizona (north of 

8 wyomingensis Black Mountain 

£ Trading Post)

Utah 

(southeast of Emory)

Srn.ph.itpR ferrnnenRis

Utah (south 

of Mount Killers)

will be clear to the reader that comparisons with 

modern analogs are inconclusive and that similarities and differences may cancel each other in our 

present state of knowledge.

Toreva Forma- Northwest 

tion of Mesaverde Group

Ferron Sandstone N. 40° W. 

Member of 

Mancos Shale

Ferron Sandstone N. 27° W. 

Member of 

Mancos Shale

N. 60° W. 

(Desmoscaphites)

N. 60° W. 

(Desmoscaphites)

N. 55° W. 

(Desmoscaphites)

North 

(Desmoscaphites)

North 

(Desmoscaphites)

% POSSIBLE WIND DIRECTIONS DURING ^

LATE CRETACEOUS STORMS

In an earlier study (Houston and Murphy, 1962, 

p. 72-74) it was suggested that the form and shape of
A24 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

black sandstone deposits and their heavy mineral 

distribution might give clues as to prevailing stormwind directions. This suggestion was based on the 

work of Gardner (1955), who reported a relationship 

between shape of black sand deposits and mineral 

distribution in black sand deposits in Australia and 

the direction that storm waves strike the Australian 

beaches. Gardner (1955, p. 38) stated that the width 

(plan view) of a seam of heavy minerals is 30-50 feet 

(9.2-15.2 m) and that the thickest deposits (cross 

section) occur on beaches that terminate northward 

at a headland or other natural barrier. This type of 

deposit may be 5 feet (1.5 m) thick near the headland 

and thins gradually toward the south. Gardner did 

not state whether the entire beach interval thickens 

northward or just the heavy mineral deposits. 

Gardner (1955, p. 53-61) also stated that heavy 

minerals in Australia deposits are dis tributed 

according to their relative rates of transport, all 

other factors being equal. He ranked zircon slowest, 

ilmenite as intermediate, and rutile as having the 

most rapid rate of transport. He demonstrated that 

in deposits that terminate in a headland or creek 

mouth there is a small but steady decrease in zircon 

and increase in rutile from south to north. The 

Australian deposits studied by Gardner are on northtrending beaches located on the southeast coast. 

Storm waves strike this coast from the southeast, 

and Gardner believed that both the increase in 

thickness toward headlands at the northern termination of a deposit and the mineral distribution result 

from northern transport of sediment during storms. 

Information on both shape and mineral distribution in Upper Cretaceous black sandstone is 

limited to two deposits, one in Wyoming and one in 

New Mexico. The best exposed deposit in Wyoming is 

at Buffalo Creek (sees. 34 and 35, T. 45 N., R. 89 W., 

and sees. 2 and 11, T. 44 N., R. 89 W.; fig. 19; fig. 3, No. 

25) in the southeast Bighorn Basin. This deposit is 

thin at its southern end and gradually increases in 

thickness (cross section) to the north, which suggests 

northern transport using the Australian analog. At 

Buffalo Creek zircon decreases in abundance to the 

north (table beneath fig. 19), again suggesting 

northern transport using the Australian analog. At 

Buffalo Creek, however, the northern decrease in 

abundance of zircon is with respect to magnetite 

rather than ilmenite and rutile as is the case with the 

Australian analog. If the ratio of rutile to zircon is 

considered, a first approximation might be to assume that the lighter mineral rutile is being trans. 

ported farther, but if the ratio of zircon to magnetite 

is considered, the reverse would have to be true or we 

must state that transport is southerly in the WyoD5

EXPLANATION

Black sandstone Contact 

dashed where approximately located

Sample locality

 Unimproved dirt road

1000 2000 FEET

0100 300 500 METERS

Dll

Deadline .;^ >L....yxv

R.89W.

Sample locality

Ratio of zircon to 

total opaque minerals

Ratio of euhedral 

to well-rounded zircon

North D-5 

D-4 

D-6 

D-3 

D-8 

D-9 

D-10

South D-ll

0.014

.025

.017

.056

.020

.120

.097

.096

0.11 

.09 

.36

.72 

.23 

.55 

.45 

.30

FIGURE 19. Planetable map of Buffalo Creek black sandstone 

deposit, Washakie County, Wyo.

ming deposit according to mineral distribution 

evidence and northerly according to deposit shape. 

We believe that size is a more important factor in the 

transport of a mineral than specific gravity, as 

reviewed in the discussion on significance of grain
DEPOSITIONAL ENVIRONMENT A25

size. Zircon is significantly smaller than magnetite 

in the Upper Cretaceous black sandstone (Houston 

and Murphy, 1962, p. 35, fig. 8; Mellon, 1961, p. 95). 

Therefore, if processes of combined gravity-shear 

sorting are operative on beaches during storms, 

larger magnetite may be selectively winnowed from 

smaller zircon despite the higher specific gravity of 

magnetite.

A well-exposed deposit in New Mexico near the 

Sanostee Trading Post (fig. 5, No. 50; fig. 20; lat 

36°27'-36°28', long 108°53'45"-108°54'45") is thicker 

in the southeast, suggesting southerly transport; 

the deposit is probably a series of overlapping 

lenses (Bingler, 1963), and it is questionable how far 

each lens extends in the shoreline direction. A series 

of localities distributed along the length of the 

Sanostee deposit (shoreline) were sampled vertically 

at 2-foot (0.6-m) intervals. These samples were

108° 55' 108° 50'

36" 

27' 

45"

36° 

25'

SC-1

1 MILE

J

Black sandstone Contact 

approximately located

X Sample locality

 Light-duty road

- Unimproved dirt road

Sample locality

North SC-1

SC-S

SC-2

SC-3

South SC-4

Ratio of zircon to

total opaque minerals

0.39

.27

.55

.67

.71

Ratio of euhedral

to well-rounded zircon

0.07

.12

.21

.23

.43

FIGURE 20. Sketch map of black sandstone deposit, Sanostee, 

San Juan County, N. Mex.

averaged, and heavy mineral grain counts were 

made (table beneath fig. 20). Zircon is more 

abundant in the south, and a euhedral variety of 

zircon is more abundant than a well-rounded variety 

in the south. At Sanostee the distribution of zircon is 

compared with that of ilmenite, and from size, shape, 

and specific gravity the distribution suggests 

northerly transport. However, inasmuch as the 

Sanostee samples may not come from the same lens, 

the significance of the mineral distribution is 

questionable.

Other deposits in the Rocky Mountains region 

have some characteristics that may be helpful in 

determining storm transport directions. For example, a well-exposed deposit in Montana near 

Castle Rock, in sec. 22, T. 28 N., R. 5 W., is thinner in 

the southeast and thicker at the northwestern end, 

suggesting northern transport. A vertically dipping 

Montana deposit east of Ringling, in sec. 17, T. 7 N., 

R. 9 E., is well exposed along the strike probably 

parallel to the ancient shoreline. It consists of a 

series of overlapping lenses of black sandstone that 

rise stratigraphically to the southeast. This configuration suggests that as the beach regressed seaward (northeast) it also migrated to the southeast 

and thus that there is a general southeast transport 

of material. Each individual black sandstone bed in 

this deposit thickens to the northwest (fig. 21). If the 

lenses of black sand rise in section as the sea 

regresses, the fact that the lenses rise in section to the 

southeast in the deposit near Ringling suggests that 

the direction of beach migration and sediment 

transport is to the southeast. The thickening of 

individual layers of black sandstone and overall 

thickening of deposits to the northwest suggests 

northwest transport of sand during storms. Perhaps 

the primary direction of longshore current movement was southeast, but during storms transport 

was in the opposite direction.

Other deposits appear thicker in the center and 

thinner at each end. Undoubtedly, the various configurations are related to the position of a deposit on 

the coast and its location with respect to headlands. 

Deposits on long stretches of beach at some distance 

from headlands or river mouths or other barriers 

might be expected to thin at each end.

Sediment source areas

The formation of a black sand deposit is 

controlled in good part by the availability of a major 

supply of heavy minerals. On some modern beaches, 

black sands are in greater abundance near deltas 

and distributaries (Higazy and Naguib, 1958; 

Mahadevan, 1958). Some of the large concentrations
A26 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

FIGURE 21. Wedge-shaped body of black sandstone that pinches 

out to the southeast and thickens to the northwest (behind 

viewer) in the upper part of the Virgelle Sandstone. White 

objects in the background of both photographs are sample 

bags approximately 9 by 5 inches (23 by 13 cm) in size. NE14, 

sec. 17, T. 7 N., R. 8 E., east of Ringling, Mont., view toward 

southeast. Beds strike N. 30° W. and dip 80°-90° E.

are on shorelines located on the lee side of deltas with 

respect to the direction of longshore current 

movement (Mahadevan, 1958).

In southwestern Wyoming, about 34 miles south 

of Kemmerer, sees. 18,19, and 30, T. 18 N., R. 116 W., 

and Wl/2 sec. 25, T. 18 N., R. 117 W. (fig. 3, No. 35), a 

number of black sandstone deposits are in the lower 

sandstone units of the Frontier Formation (120 and 

355 ft above the base of the formation) that are 

probably late Belle Fourche or early Greenhorn in 

age. The deposits lie south of a postulated major distributary (McGookey and others, 1972, p. 209) that 

may have developed in the area between early Belle 

Fourche and middle Greenhorn time. This same 

deltaic system is believed (McGookey and others, 

1972) to have been present in late Coniacian time, 

and, from micropaleontologic evidence, Kent (1968) 

has postulated a southward drift of longshore 

currents.

Possible relationships of other black sandstone

deposits to deltas or distributaries are conjectural, 

but the deposits may be useful in locating 

distributaries or may eventually correlate with 

distributaries as detailed paleogeographic data 

become available.

WIDTH OF CRETACEOUS BEACHES AND TIDAL RANGES

Certain features of black sandstone deposits 

may indicate the widths and tidal ranges of 

Cretaceous beaches. These features include width of 

individual black sand lenses, grain size, dip of long 

traceable beds, and structure in the deposits.

Obviously, the width of an individual black 

sandstone deposit cannot be used as a measure of the 

width of the beach at any time. For example, the 

deposit at Choteau, Mont. (fig. 2, No. 9, T. 25 N., Rs. 5 

and 6 W.) is VA miles (2 km) wide, but it represents at 

least three distinct shifts of the shoreline in a 

seaward direction. At the Marias River deposit in 

Montana, however, it is possible to trace individual 

heavy-mineral-rich layers that cut obliquely across 

the deposit from its top in the landward direction to 

its base in a seaward direction. The minimum width 

of one of these layers has been found to be 200 feet (60 

m). This is about four to six times the width of similar 

black sand layers in Australia (Gardner, 1955). The 

total width of Australian beaches varies, and there is 

little information on the width of a beach from the 

dune edge to mean low water in Australian deposits; 

however, Gardner (1955, p. 15) stated that a typical 

beach is 100-200 feet (30-60 m) wide, depending on 

the weather and tide. A direct comparison based on 

comparable width of black sandstone would suggest 

! that the Cretaceous beach at the present site of the 

! Marias River deposit was 800-1,000 feet (240-300 m) 

I wide. Although other factors, such as storm 

i intensity, are known to affect the width of a black 

1 sand lens, the ancient beach of the Marias River area 

undoubtedly fell within the flat beach classification 

of Bascom (1964, p. 194).

Additional support for the flat beach concept is 

the 4° dip of long traceable beds on the upper 

foreshore at Marias River; the dip decreases seaward 

and seems to flatten to less than 1°. Grain size may 

also be a clue to the slope of a beach for, as Bascom 

(1964, p. 199-201) has shown, where other factors are 

equal, flat beaches have fine sand and steep beaches 

coarse sand. The very fine grain size of sandstone of 

the Late Cretaceous beaches thus suggests a flat 

beach.

In inland seas, such as the Gulf of Mexico and 

the Mediterranean, the amplitude of tides is small 

except perhaps in narrow straits or estuaries. Small 

tidal amplitudes may have characterized much of
DEPOSITIONAL ENVIRONMENT A27

the Cretaceous seaway. Hayes (1971) classified 

depositional coasts that have strong downwarp 

and rapid sedimentation (Hayes, 1964) into hypotidal [tidal range 0-5 ft (0-1.5 m)], mesotidal [tidal 

ranges 5-10 ft (1.5-3 m)], and hypertidal [tidal ranges 

greater than 10 ft (3 m)]. Hayes noted that, as a rule, 

coasts with small tidal ranges are dominated by 

wave enrgy and that they are characterized by welldeveloped deltas of the arcuate and cuspate types 

at the mouths of major rivers. Between major rivers, 

long barrier islands are present with beaches 

marked by a series of breakpoint bars parallel to 

the beach. Hayes cited the Gulf Coast of the 

United States, the southern Baltic coast, and 

coasts of southern Australia and the Mediterranean as having beaches of this type.

The Late Cretaceous beaches, especially those of 

New Mexico and Utah, seem to fit the hypotidal 

category very well; Peterson's (1969, p. 193) 

reconstruction of the paleogeography during the 

time of deposition of the John Henry Member of the 

Straight Cliffs Formation of southwestern Utah is 

an almost perfect analogy of a hypotidal coast.

The landward-facing foreshore ridges that are 

well substantiated in Montana have been considered 

by King (1959, p. 338) to be typical of very flat 

beaches with high tidal ranges. According to King, 

the development of a ridge-and-runnel system 

depends on several factors:

1. The beach should be very flat and have a high 

tidal range.

2. The ridge-and-runnel system is developed on 

flat beaches where waves striking the 

beach have a short fetch because there is an 

attempt to steepen the beach gradient to 

adjust to shorter waves. Flat beaches exposed to the open ocean may not develop 

ridge-and-runnel systems because the long 

fetch of the waves may adjust more readily 

to the flatter beach.

3. Ideally a large supply of sand-sized material 

also enhances the development of beach 

ridges, as the sand is needed to build up the 

gradient in response to the short fetch 

waves.

King's criteria seem opposed to those used to 

support the classification of the southern Cretaceous 

beaches as hypotidal, but Davis, Fox, Hayes, and 

Boothroyd (1972) cited evidence that suggests that 

ridge-and-runnel systems may develop on beaches 

with low tidal ranges. They compared beaches on 

Lake Michigan where tidal ranges are small with 

beaches of the northern Massachusetts coast where 

tidal ranges are large, and they showed that both

types of beaches may have well developed ridge-andrunnel systems. Davis, Fox, Hayes, and Boothroyd 

(1972, p. 416) showed that ridge-and-runnel systems 

develop after storms when erosion of the beach and 

adjacent dune areas supplies a source of sediment for 

ridge development. Therefore the presence of a 

foreshore ridge does not seem definitive of tidal 

range.

If subsidence during progradation was negligible and postdepositional compaction is negligible, 

the thickness of a black sandstone deposit may be 

used to approximate tidal range. The thickness may 

be representative of the height of a beach from the 

lower foreshore to the base of the dune, if the 

environmental interpretations are correct. The 

thickness, therefore, may be an indicator of tidal 

range plus height of swash. The 18-foot (5.5-m) 

thickness of the Marias River deposit suggests a 

substantial tidal range or that the beach was subject 

occasionally to very large waves. We do not suggest 

that the thickness of individual black sandstone 

deposits is a direct measure of tidal range because 

we are not certain that subsidence was negligible, 

compaction was negligible, or that a given deposit is 

a product of progradation only, but if the same 

general processes operate to form the various 

deposits, thicker deposits may be indicative of higher 

tidal ranges. In general, thicker deposits are in 

northern Wyoming and Montana, although thickness varies greatly even in a local area.

Summarizing, the hypotidal classification seems 

appropriate for the overall characteristics of the 

Utah, New Mexico, and perhaps the southern 

Wyoming beaches as they have been described, but 

evidence from the black sandstone deposits suggests 

that tidal ranges may have been higher in northern 

Wyoming and Montana.

SUMMARY

Fossil black sandstones may aid in reconstructing the characteristics of beaches of the Late 

Cretaceous seaway of the Rocky Mountains region. 

Although the character of the deposits varies 

considerably from one locality to another, most of 

the interpretations have been formulated through 

study of the better exposed deposits in Montana and 

Wyoming, and these deposits are different from 

those in Utah, New Mexico, and Arizona. Certain 

characteristics of Upper Cretaceous black sandstones seem common to all or most deposits and are 

reasonably well documented:

1. The deposits occur only in regressive sandstone where a large supply of heavy-mineral 

rich detritus was available.
A28 UPPER CRETACEOUS BLACK SANDSTONES OF THE WESTERN INTERIOR

2. The black sandstone deposit is itself a smallscale example of a regressive unit. Each 

deposit typically has a laminated sandstone at the base overlain by thick beds rich 

in heavy minerals. The laminated black 

sandstone was deposited on the lower part 

of the beach, and the heavy-mineral-rich 

layers on the upper part. Each deposit is 

typically overlain by carbonaceous shale, 

coal, or oyster beds deposited in lagoons or 

swamps during regression.

3. The upper heavy-mineral-rich layers are 

probably formed during major storms. 

Berm crests and structures typical of the 

backshore are largely destroyed during the 

storms, and so most laminae dip seaward.

4. Evidence of original dune deposits is lacking; 

presumably the dunes were destroyed during regression by lateral planation or by 

action of plants and ground water.

5. Processes of reentrainment and gravity-shear 

sorting may have played major roles in the 

deposition of laminated black sandstone. 

The heavy-mineral-rich layers probably 

resulted chiefly from gravity-shear sorting.

6. Well-exposed black sandstone deposits are 

useful in determining local shoreline directions.

7. The very fine grain size and low dip of 

laminae of most black sandstone suggests 

deposition on flat beaches.

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