Coughs Creek Tongue 

A New Tongue of the

Eocene Green River Formation,

Piceance Creek Basin,

Colorado

GEOLOGICAL SURVEY BULLETIN 1 3 9 5 - (J

t/7

o, .'

Coughs Creek Tongue 

A New Tongue of the

Eocene Green River Formation,

Piceance Creek Basin,

Colorado

By ROBERT B. O'SULLIVAN

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1395-G

Definition and description of a conspicuous 

and useful stratigraphic marker that 

tongues into the lower part of the 

Uinta Formation

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1975
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

O'Sullivan, Robert Brett, 1923-

Coughs Creek Tongue a new tongue of the Eocene Green River Formation, Piceance

Creek basin, Colorado.

(Contributions to stratigraphy) (Geological Survey Bulletin 1395-G) 

Bibliography: p.

Supt.ofDocs.no.: I 19.3:1395-G

1. Geology, Stratigraphic Eocene. 2. Geology Colorado Piceance Creek watershed. 

I. Title. II. Series. III. Series: United States Geological Survey Bulletin 1395-G. 

QE75.B9 no. 1395-G [QE692.2] 557.3'08s [551.7'8] 75-619020

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

Washington, D. C. 20402 

Stock Number 024-001-02617-1
CONTENTS

Abstract................................................................. G1

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

Coughs Creek Tongue of Green River Formation ............................ 3

Definition and type section ........................................... 3

Thickness of tongue and associated rocks ............................... 4

Stratigraphic relationships ............................................ 5

References cited .......................................................... 7

ILLUSTRATIONS

Page

FIGURE 1. Index map of part of Piceance Creek basin ........................ G2

2. Section showing generalized stratigraphic relations of the Coughs Creek 

Tongue to other subdivisions of the Green River Formation and to 

the Uinta Formation ........................................... 6

CONTRIBUTIONS TO STRATIGRAPHY

COUGHS CREEK TONGUEA NEW TONGUE OF THE EOCENE

GREEN RIVER FORMATION,

PICEANCE CREEK BASIN,

COLORADO

By ROBERT B. O'SULLIVAN

ABSTRACT

The Coughs Creek Tongue is the name herein given to a sequence of light-gray 

marlstone, locally containing beds of sandstone and siltstone, in the upper part of the 

Green River Formation. The tongue forms a conspicuous stratigraphic marker over wide 

areas of east-central and southern Piceance Creek basin. At the type section, the Coughs 

Creek Tongue is 110 feet (33.5 m) thick and is underlain by about 200 feet (61 m) and 

overlain by about 600 feet (186 m) of dominantly clastic rocks assigned to the Uinta Formation. The tongue probably joined the main body of the Green River Formation in the 

southern part of the basin in an area where the Coughs Creek rocks are eroded.

INTRODUCTION

The youngest sedimentary rocks of Eocene age in the Piceance Creek 

basin in northwestern Colorado are assigned to the Uinta Formation 

(Cashion and Donnell, 1974). The Uinta Formation is as much as 1,250 

feet (381 m) thick and consists largely of brown sandstone and siltstone 

with thin beds of greenish-gray mudstone, shale, and light-gray 

marlstone. The Uinta forms the surface rocks over much of Piceance 

Creek basin.

The Green River Formation of Eocene age underlies and interfingers 

with the lower part of the Uinta Formation. The Parachute Creek 

Member, the uppermost unit in the main body of the Green River 

Formation, is at least 1,800 feet (548 m) thick and consists largely of 

marlstone. The member contains the richest and thickest oil-shale beds 

in the Green River Formation.

Numerous marlstone units in the upper part of the Green River 

Formation interfinger with the Uinta Formation. Four of these 

marlstone units have been formally named as tongues of the Green 

River Formation (Duncan and others, 1974). These are, in ascending

Gl
G2 CONTRIBUTIONS TO STRATIGRAPHY

15' 108°00'

10 KILOMETERS

FIGURE 1. Index map of part of Piceance Creek basin. Locality 5 marks position of type section of Coughs Creek Tongue. Cross section through localities 1 5 shown in figure 2.
COUGHS CREEK TONGUE, PICEANCE BASIN, COLORADO G3

stratigraphic order, the Yellow Creek, Dry Fork, Thirteenmile Creek, 

and Black Sulphur Tongues of the Green River Formation. These four 

tongues are present in a large part of the northern Piceance Creek basin. 

Southward they merge with the main body of the Green River 

Formation, and none of the four is present roughly south of the heavy 

line in figure 1 which marks the approximate southern limit of the 

Black Sulphur Tongue.

A stratigraphically higher marlstone unit occurs south of the limits of 

the tongues just described. It extends over wide areas of the east-central 

and southern parts of the Piceance Creek basin and forms a useful 

stratigraphic marker. This marlstone unit is discussed herein and 

designated the Coughs Creek Tongue of the Green River Formation. 

Recognition of the Coughs Creek Tongue aids interpretation of local 

geologic structures, serves to divide the thick sequence of rocks assigned 

to the Uinta Formation, and aids in determining the character and 

thickness of overburden above the oil-shale zones of the Parachute 

Creek Member.

COUGHS CREEK TONGUE OF GREEN RIVER FORMATION

DEFINITION AND TYPE SECTION

A light-gray marlstone sequence is here named the Coughs Creek 

Tongue of the Green River Formation. The name is taken from Coughs 

Creek, a small tributary to Cow Creek, which, in turn, is a tributary to 

Piceance Creek (fig. 1). The type section, which is readily accessible by 

road, is located in Rio Blanco County about 1% miles (3 km) south of 

the junction of the dirt road along Cow Creek and the paved county 

road along Piceance Creek. The type section was measured on the west 

side of Cow Creek in the SWMSE 1/* sec. 12, T. 4 S., R. 95 W. The base 

of the section is about 160 feet (48 m) above the level of Cow Creek.

Throughout the area, the Coughs Creek Tongue is clearly 

distinguishable by its gray-weathering marlstone which contrasts with 

the brown-weathering sandstone and siltstone of the Uinta Formation.

Type section of the Coughs Creek Tongue of Green River Formation

[SWMSEW sec. 12, T. 4S., R. 95 W., Rio Blanco County, Colo.]

Uinta Formation (part): ( J^^m 

Sandstone, tan, very fine grained, silty, abundant m

carbonaceous trash........................................ Not measured

Coughs Creek Tongue of Green River Formation:

Marlstone, medium-gray; weathers very light gray;

variably silty; in thin beds about Vi in. (12 mm)

thick; contains a lenticular bed of very fine

grained grayish-orange very calcareous sandstone

as much as 1.5 ft (46 cm) thick that is 6.7 ft (2.0 m)

above base; unit weathers to very small chips; base is

sharp.................................................... 23.3 7.1
G4 CONTRIBUTIONS TO STRATIGRAPHY

Type section of the Coughs Creek Tongue of Green River Formation Continued 

Coughs Creek Tongue of Green River Formation Continued Thickness 

Siltstone, sandstone, and marlstone in irregular and (M ( m )

lenticular beds 2-10 ft (0.6-3.0 m) thick. Siltstone

is tan and grades to tan very fine grained

sandstone; gray marlstone, variably silty, weathers

to very light gray. Unit tends to form a

cliff; basal contact is sharp but is mostly

obscured................................................. 55.2 16.8

Marlstone, gray; weathers very light gray and

light tan, particularly in lower part; laminated to

thin beds generally less than Vz in. (12 mm)

thick; at base of unit a % in. (1 cm)-thick white

tuff; weathers tan; very fine grained; flat and

even upper and lower contacts; a 0.1 ft (3 cm)-

thick bed of grayish-black oil shale weathers

bluish gray and contains 15 20 gallons

of oil per ton at 14.5 ft (4.4 m) above base;

unit as a whole weathers to plates as much

as 2 ft (0.6 m) across ..................................... 30.0 9.1

Siltstone, tan; weathers tan; in beds 0.1 ft (3 cm)

thick; grades upward into light-gray marlstone

in beds 1A in. (6 mm) thick; unit forms a

transitional zone with underlying rocks ..................... 2.3 .1

Total thickness Coughs Creek Tongue .................... 110.8 33.7

Uinta Formation (part):

Siltstone, grades to very fine grained sandstone; light tan;

weathers tan and brown; abundant carbonaceous trash;

upper part slabby; tends to form a cliff .................... Not measured

In addition, the tongue is exposed in many places in steep slopes that 

are set back on a bench developed at the top of the part of the Uinta 

Formation that underlies the Coughs Creek Tongue.

THICKNESS OF TONGUE AND ASSOCIATED ROCKS

The Coughs Creek Tongue ranges in thickness from 50 to 130 feet (15 

to 40 m) along Piceance Creek in the area between Cow Creek and Story 

Gulch. The tongue is thickest where a middle sandstone or siltstone, as 

much as 55 feet (17 m) thick, separates upper and lower beds of 

marlstone. The middle sandstone is apparently confined to the eastcentral part of the Piceance Creek basin.

In Story Gulch the Coughs Creek Tongue is 50-85 feet (15-26 m) 

thick, and the middle sandstone is absent. Variations in thickness of 

the tongue in Story Gulch are due to channeling prior to or during 

deposition of the overlying sandstone beds of the Uinta Formation. 

North of Piceance Creek and in the area east of Oldland Gulch, the 

tongue gradually changes northward to gray siltstone, and, about 2 

miles (3 km) north of Piceance Creek, the gray siltstone of the Coughs 

Creek Tongue is indistinguishable from the siltstones of the Uinta 

Formation.
COUGHS CREEK TONGUE, PICEANCE BASIN, COLORADO G5

An unnamed sandstone tongue of the Uinta Formation between the 

base of the Coughs Creek Tongue and the top of the Parachute Creek 

Member varies considerably in thickness. Along Story Gulch this 

tongue is about 400 feet (122 m) thick. In the lower reaches of Cow 

Creek, the tongue varies locally in thickness because of great 

irregularities in the upper contact of the Parachute Creek Member. On 

the east side of Cow Creek in the SEttNEMSEM sec. 12, T. 4 S., R. 95 

W., the tongue of the Uinta Formation below the Coughs Creek Tongue 

is 130 feet (40 m) thick. Less than one-half mile (0.8 km) to the north in 

the NV&SEV4NEV4 sec. 12, the sandstone tongue of the Uinta 

Formation is more than 240 feet (73 m) thick inasmuch as its base is not 

exposed at creek level. In several nearby drill holes, the basal tongue of 

the Uinta Formation appears to average about 200 feet (61 m) in 

thickness in the Cow Creek area. Farther south, along East Middle Fork 

of Parachute Creek, the tongue of the Uinta Formation is 85 feet (26 m) 

thick, and, near Mount Callahan in the southern part of Piceance Creek 

basin, it is about 60 feet (18 m) thick. The Coughs Creek Tongue is 

eroded from the area where it probably merged with the main body of 

the Green River Formation, somewhere east of Mount Callahan in the 

vicinity of the Colorado River.

STRATIGRAPHIC RELATIONSHIPS

The stratigraphic relation of the Coughs Creek Tongue to the Uinta 

Formation, to other tongues, and to the Parachute Creek Member of the 

Green River Formation is shown in figure 2. The diagram is generalized, 

and lithologic detail is omitted. Detailed stratigraphic changes and 

thicknesses of units between sections are not precisely recorded. 

Obviously, however, there are very large differences from north to south 

in thicknesses of stratigraphic units. Much of this variation is due to 

pronounced changes in the thickness of the dominantly clastic rocks of 

the Uinta Formation.

All the named marlstone units are arbitrarily assigned as tongues of 

the Green River Formation, although they are stratigraphically and 

lithologically related to the Parachute Creek Member of the Green 

River Formation. It did not seem appropriate either to raise the 

stratigraphic rank of the Green River Formation and all its subdivisions 

or to classify the thick and varied units as beds within the Parachute 

Creek Member, inasmuch as one of the units, the Thirteenmile Creek 

Tongue, consists of as much as 200 feet (61 m) of marlstone, sandstone, 

siltstone, ostracodal beds, limestone, and thin beds of rich oil shale.

The columnar section shown at Cow Creek (loc. 5, fig. 2) is a 

composite that includes the type section of the Coughs Creek and 

several measurements of overlying and underlying rocks along Cow 

Creek and Piceance Creek. The interval from the base of the Coughs 

Creek Tongue to the top of the Mahogany ledge is about 600 feet
PARACHUTE CREEK M

FIGURE 2. Generalized stratigraphic relations of the Coughs Creek Tongue to other subdiv

mation. In part from Duncan, Hail, O'Sullivan, and Pipiringos (1974, fig. 4). Green R

is top of Mahogany ledge, a rich oil-shale sequence in the upper part of the Parach
COUGHS CREEK TONGUE, PICEANCE BASIN, COLORADO G7

(183 m) thick near the Coughs Creek type section. Southward, at the 

U.S. Bureau of Mines corehole D (fig. 1) in sec. 11, T. 5 S., R. 95 W., on 

the north side of East Middle Fork of Parachute Creek, the same 

interval is about 575 feet (175 m). The interval thickens westward from 

Cow Creek and is about 1,050 feet (320 m) at the Equity Oil Co. 1 

Evans-Government drill hole in sec. 29, T. 3 S., R. 95 W., on Story 

Gulch.

The Coughs Creek Tongue is overlain by very fine grained sandstone 

and siltstone several hundred feet thick assigned to the Uinta 

Formation. Judged from a composite of three sections measured along 

the West Branch of Cow Creek, about 1 2 miles (1.6 3.2 km) south of 

the type section, the Uinta Formation overlying the Coughs Creek 

Tongue is 610 feet (186 m) thick.

REFERENCES CITED

Cashion, W. B., and Donnell, J. R., 1974, Revision of nomenclature of the upper part of

the Green River Formation, Piceance Creek basin, Colorado, - and eastern Uinta

Basin, Utah: U.S. Geol. Survey Bull. 1394-G, 9 p. 

Duncan, D. C., Hail, W. J., Jr., O'Sullivan, R. B., and Pipiringos, G. N., 1974, Four newly

named tongues of Eocene Green River Formation, northern Piceance Creek basin,

Colorado: U.S. Geol. Survey Bull. 1394-F, 13 p.

U.S. GOVERNMENT PRINTING OFFICE: 1975-677-309/38