Diagenesis and Burial History of 

Nonmarine Upper Cretaceous Rocks in the 

Central Uinta Basin, Utah

U.S. GEOLOGICAL SURVEY BULLETIN 1787-D

Chapter D

Diagenesis and Burial History of 

Nonmarine Upper Cretaceous Rocks in the 

Central Uinta Basin, Utah

By JANET K. PITMAN, KAREN J. FRANCZYK, and 

DONALD E. ANDERS

A multidisciplinary approach to research studies of

sedimentary rocks and their constituents and

the evolution of sedimentary basins, both ancient and modern

U.S. GEOLOGICAL SURVEY BULLETIN 1787

EVOLUTION OF SEDIMENTARY BASINS-UINTA AND PICEANCE BASINS
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1988

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

(Revised for Ch. D)

Evolution of sedimentary basins Uinta and Piceance basins.

(U.S. Geological Survey bulletin ; 1787 A- )

Includes bibliographies.

Supt. of Docs, no.: I 19.3:1787-D

Contents: ch. A. Sedimentology and paleographic significance of six fluvial 

sandstone bodies in the Maroon Formation, Eagle Basin, northwest Colorado / 

by Samuel Y. Johnson, ch. B. Sedimentology of an eolian sandstone from the 

Middle Pennsylvanian Eagle Valley Evaporite, Eagle Basin, northwest Colorado / 

by Christopher J. Schenk. [etc.] ch. D. Diagenesis and burial history of 

nonmarine Upper Cretaceous rocks in the central Uinta basin, Utah / by Janet 

K. Pitman, Karen J. Franczyk, and Donald E. Anders.

1. Sedimentation and deposition. 2. Geology West (U.S.) I. Johnson, 

Samuel Y. II. Schenk, Christopher J. III. Nuccio, Vito F. IV. Series. 

QE75.B9 no. 1787A-C 557.3 s [551.3] 87-27737 

[QE571]

Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. 

Geological Survey.
CONTENTS

Abstract Dl 

Introduction Dl 

Geologic setting D2

Geologic nomenclature D3

Description of core D4 

Sedimentology D5 

Framework mineralogy D6

Quartz D8

Feldspar D8

Lithic fragments D9

Matrix D9

Cements D9

Clays DIG

Mechanical compaction DIG 

Diagenesis Dll

Silica cementation Dll

Carbonate and sulfate mineral development Dll 

Carbon and oxygen isotopes Dll 

Carbon isotopes D13 

Oxygen isotopes D14

Sulfate minerals D15

Authigenic clay mineral formation D15

Organic matter D16 

Reservoir potential D16 

Source rock evaluation D16 

Burial and thermal history D20 

References cited D23

FIGURES

1. Map showing location of Wilkin Ridge well, selected orogenic features 

and rock types, Uinta basin, Utah D2

2. Schematic cross section showing time-stratigraphic relations of

Cretaceous and Tertiary rocks along the southern margin of the Uinta 

basin D3 

3-5. Photographs showing:

3. Outcrop of Neslen Formation rocks similar to cored sequences in 

lower part of undifferentiated Tuscher and Farrer Formations in the 

Wilkin Ridge well D5

4. Gradational contact between Neslen and Farrer Formations D6

5. Typical sequence of overbank deposits preserved between extensive 

fluvial sandstones in the Tuscher and Farrer Formations D6

Contents III
6. Ternary diagram showing classification of sandstones in the

undifferentiated Tuscher and Farrer Formations in the Wilkin Ridge 

well D8 

7-10. Thin-section photomicrographs showing:

7. Replacement of relict iron-free calcite pore-filling cement by ironbearing calcite DIG

8. Late-stage poikilotopic anhydrite cement Dll

9. Barite replacing authigenic dolomite and detrital framework 

grains Dll

10. Replacement of secondary quartz overgrowths by authigenic 

anhydrite D13

11. Crossplot of carbon and oxygen isotope compositions for carbonate 

minerals in the undifferentiated Tuscher and Farrer Formations D15

12. Modified van Krevelen diagram showing hydrogen and oxygen indices 

for humic-rich source rocks in the undifferentiated Tuscher and Farrer 

Formations, Wilkin Ridge well D20

13. Modified time-temperature Lopatin diagram showing reconstructed burial 

and thermal history for Cretaceous and Tertiary rocks in the area of the 

Wilkin Ridge well Dll

TABLES

1. Mineralogic compositions of sandstones in the undifferentiated Tuscher and 

Farrer Formations, Wilkin Ridge well D7

2. Carbon and oxygen isotope analyses of selected samples of calcite and 

dolomite from sandstones in the undifferentiated Tuscher and Farrer 

Formations, Wilkin Ridge well D14

3. Reservoir properties of sandstones in the undifferentiated Tuscher and Farrer 

Formations, Wilkin Ridge well D17

4. Geochemical and Rock-Eval pyrolysis data for potential source rocks in the 

undifferentiated Tuscher and Farrer Formations, Wilkin Ridge well D19

5. Vitrinite reflectance and gas chromatography analyses of potential source 

rocks in the undifferentiated Tuscher and Farrer Formations, Wilkin Ridge 

well DIG

6. Parameters used to reconstruct the burial and tectonic history in the area of 

the Wilkin Ridge well Dll

IV Contents
EVOLUTION OF SEDIMENTARY BASINS-UINTA AND PICEANCE BASINS

Diagenesis and Burial History of 

Nonmarine Upper Cretaceous Rocks in the 

Central Uinta Basin, Utah

By Janet K. Pitman, Karen J. Franczyk, and Donald E. Anders

Abstract

Rocks of the Upper Cretaceous nonmarine undifferentiated Tuscher and Farrer Formations in the Uinta basin of 

northeast Utah yield thermogenic gas and some oil from 

carbonaceous shales and coal beds. These rocks, interbedded 

with fine-grained, lenticular, low-permeability sandstones, 

formed in a complex meandering and locally braided fluvial 

system in the Cretaceous Western Interior foreland basin.

Reservoir sandstones in the lowest cored sequence comprise quartz arenites and sublitharenites that are compositionally and diagenetically similar to rocks of the underlying Neslen 

Formation. Feldspathic sandstones in the upper cored sequence 

have a more complex diagenetic history than previously 

reported for either the Tuscher or Farrer Formations, a history 

that includes development of early quartz overgrowths and 

precipitation of iron chlorite rim cement, followed by dissolution of nonferroan and ferroan carbonate, crystallization of illite and chlorite in secondary pores, and finally localized 

formation of anhydrite and barite cement. Stable isotope studies 

indicate that isotopically heavy nonferroan carbonate formed 

early, at relatively shallow burial depths. Isotopically lighter ferroan carbonate, which reflects diagenetic modification at 

greater depths of burial and higher temperatures, is associated 

with bitumen and anhydrite. Porosity and permeability in rocks 

of the Tuscher and Farrer Formations typically are low. Porosity 

is reduced wherever deformed lithic grains, matrix, and 

authigenic clay are abundant and is enhanced wherever 

dissolution of carbonate and sulfate minerals and feldspar or 

chert grains has occurred.

Geochemical studies indicate that gas-prone source rocks 

in the Tuscher and Farrer Formations in the central Uinta basin 

are within the zone of catagenesis. A modified timetemperature Lopatin burial history model indicates that active 

hydrocarbon generation began about 30 Ma, when the rocks 

reached their maximum burial depth and temperature and 

following deposition of approximately 9,000 ft (2,743 m) of 

Tertiary sediments during basin subsidence. The similarity between past and present-day geothermal gradients (1.6 °F/100 

ft; 29 °C/km) in the Wilkin Ridge well suggests that heat flow 

through the central part of the basin has been relatively uniform 

from the Late Cretaceous to the present.

INTRODUCTION

The Upper Cretaceous, nonmarine, undifferentiated Tuscher and Farrer Formations in the Uinta basin 

of northeastern Utah locally contain thermogenic gas that 

was generated in place from carbonaceous shales and 

discrete coal beds. These gas-bearing rocks are complexly interbedded with lenticular, diagenetically modified, 

low-permeability sandstones. Successful exploration in 

these units has been difficult because of complex patterns 

of sandstone distribution, thickness, and geometry and 

variations in reservoir quality resulting from postdepositional mineral alteration. Moreover, source rock potential in the Tuscher and Farrer Formations throughout the 

basin is poorly understood because little is known about 

their hydrocarbon generation history.

Three cores of the undifferentiated Tuscher and 

Farrer Formations were taken in the Exxon No. 1 Wilkin 

Ridge well in the central Uinta basin (sec. 29, T. 10 S., 

R. 17 E.; fig. 1). Based on geophysical log responses, the 

Tuscher and Farrer Formations can be divided into a 

lower unit, represented by the cored interval from 11,185 

to 11,230 ft (3,409-3,423 m), and an upper unit, which 

includes cores from two intervals, 10,740 to 10,803 ft 

(3,274-3,293 m) and 10,273 to 10,295 ft (3,131-3,138 m). 

These cores represent the most deeply buried rocks of the 

Tuscher and Farrer Formations that are available for 

study and can be compared with less deeply buried, 

temporally equivalent units in other parts of the basin.

Distinct, commonly abrupt compositional changes 

in mineralogy from dominantly quartz to increasing 

amounts of feldspar have been observed between the 

Bluecastle Tongue of the Castlegate Sandstone and the 

overlying Tuscher and Farrer Formations in the southern, 

western, and central parts of the Uinta basin (Keighin and 

Fouch, 1981; Lawton, 1983; Pitman, Anders, and others, 

1986). Our studies of the Wilkin Ridge well indicate that 

rocks of the Tuscher and Farter Formations are mineralogically complex, in that they contain a quartzose

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D1
112

39° -

EXPLANATION

Tertiary volcanic and intrusive rocks

Tertiary sedimentary rocks

Precambrian sedimentary

rocks 

Precambrian metamorphic rocks 

Precambrian intrusive

rocks

Contact

Fault Hachured on

downthrown side 

Thrust fault Sawteeth

on upper plate 

Wilkin Ridge well 

Outcrop location

Figure 1. Location of Wilkin Ridge well and selected 

erogenic features and rock types, Uinta basin, northeast 

Utah.

mineral fades typical of the older Neslen Formation as 

well as a lithofeldspathic facies that is characteristic of 

these formations in other areas of the basin. Local variations in framework composition are accompanied by 

varied diagenetic patterns that reflect differing physiochemical conditions during burial. Time-temperature 

models indicate that intense hydrocarbon generation occurred in the central part of the Uinta basin during the 

early Oligocene, at which time potential source rocks in 

the Tuscher and Farrer Formations reached their maximum burial depth and paleotemperature. The results of 

our study should be useful in recognizing diverse mineral 

facies distributions within the Tuscher and Farrer Formations and in future exploration and evaluation of these 

complex hydrocarbon source and reservoir rocks.

Acknowledgments. We thank Exxon Oil Company for providing core material and production data for 

the Wilkin Ridge well. We are also grateful to T.D. 

Fouch, U.S. Geological Survey, who described the core 

and engaged in numerous stimulating discussions on

Uinta basin geology. Global Geochemistry Corporation 

determined carbon and oxygen isotope contents, and 

Mark Pawlewicz, U.S. Geological Survey, performed 

vitrinite reflectance analyses. W.B. Cashion and C.J. 

Schenk, U.S. Geological Survey, provided helpful comments to improve this manuscript. Our research was supported by the U.S. Geological Survey Evolution of 

Sedimentary Basins Program.

GEOLOGIC SETTING

Significant stratigraphic, nomenclature, facies, and 

thickness changes characterize Cretaceous rocks in the 

central Uinta basin. The area of the Wilkin Ridge well 

marks the transition from rapid tectonic subsidence near 

the Sevier thrust belt in the western part of the basin to 

a more technically stable area in the eastern part (fig. 

1). Figure 2 shows a schematic chronostratigraphic cross 

section of Cretaceous and lower Tertiary rocks from the 

Book Cliffs near Price, Utah, to the Colorado-Utah State 

line. The projected outcrop equivalent of the Upper 

Cretaceous section in the Wilkin Ridge well is between 

the Sunnyside and Green River locations (figs. 1,2), and, 

although analogies can be drawn between the outcrop and 

subsurface section, local differences probably exist in 

depositional events, subsidence rates, and effects of Late 

Cretaceous uplift and erosion. Comparison of depositional environments inferred from core and well logs of 

the Wilkin Ridge well to those ascertained from outcrop 

studies along the Book Cliffs helps delineate regional 

changes in facies patterns and burial history important 

in understanding and predicting distribution, abundance, 

and thermal evolution of hydrocarbon source and reservoir rocks.

Cretaceous rocks from the Wilkin Ridge well include (from oldest to youngest) 260 ft (79 m) of the uppermost, coal-bearing, nonmarine part of the Blackhawk 

Formation; 600 ft (183 m) of the nonmarine Castlegate 

Sandstone, which can be subdivided into three members; 

and about 2,000 ft (610 m) of the nonmarine, undifferentiated Tuscher and Farrer Formations, which can be 

divided into a lower and upper sequence. West of the 

Wilkin Ridge well, the nonmarine part of the Blackhawk 

Formation thickens and contains numerous thick coal 

beds and abundant carbonaceous, fine-grained clastic 

deposits. East of the Wilkin Ridge well, this coal-bearing 

interval thins markedly, and, east of the Green River, the 

sequence is very thin to absent.

Late Cretaceous movement of the Laramide San 

Rafael swell determined the thickness distribution of the 

nonmarine Cretaceous section in the southeastern part 

of the Uinta basin. Erosion of Upper Cretaceous rocks 

was most extensive along the Book Cliffs in the vicinity 

of Horse Canyon (sec. 9, T. 16 S., R. 14 E.), where only

D2 Evolution of Sedimentary Basins Uinta and Piceance Basins
AGE

(in Ma) AGE

1

Price

Canyon

I

Sunnyside 

I

Green River 

I

4

Sego

Canyon

I

Westwater

Canyon

I

San Arroyo

Canyon

I

45 

50 

55 

60 

65 

70 

75 

85

90 

95 

MIDDLE 

(part)

EARLY

GREEN RIVER 

' FORMATION ,

COLTON FORMATION

FLJ\GSTAFF MEMBER OF GREEN RIVER FM

LATE

EARLY

NORTH HORN 

FORMATION

MAESTRICHTIAN

BLUECASTLE

CASTLEGATE SANDSTONE

CAMPANIAN

WASATCH FORMATION

AND FARRER FORMATIONS

NESLEN FORMATION

SEGO SANDSTONE T 

BUCK TONGUE OF MANGOS SHALE

CONIACIAN

TURONIAN

TUNUNK MEMBER

CENOMANIAN DAKOTA SANDSTONE

ALBIAN 

(part)

CEDAR MOUNTAIN FORMATION

(part)

Figure 2. Schematic cross section showing time-stratigraphic relations of Cretaceous and Tertiary rocks along southern margin 

of Uinta basin. Outcrop localities are shown in figure 1; Wilkin Ridge well is near Green River location and is projected from 

subsurface to outcrop as shown by column. Shaded interval, cored sequence in well. Hachured area, unconformity. Modified 

from Fouch and others (1983).

330 ft (101 m) of Cretaceous rocks are preserved above 

the Bluecastle Tongue (Lawton, 1983). Along the Book 

Cliffs northwest of Horse Canyon, it is difficult to trace 

this interval and determine its thickness because of poor 

exposure and dense vegetation. At Range Creek, about 

20 miles east of Horse Canyon, 1,020 ft (311 m) of Upper Cretaceous rocks are preserved above the Bluecastle 

Tongue (Lawton, 1983), and, at Wilkin Ridge, about 37 

miles northeast of Horse Canyon, about 2,000 ft (610 m) 

of Upper Cretaceous rocks are preserved.

Late Cretaceous movement of the San Rafael swell 

(uplift) south of the Wilkin Ridge site caused appreciable 

local erosion of the upper, nonmarine part of the Cretaceous sequence. Thinning of the Upper Cretaceous section is most pronounced where the projected structural 

axis of the San Rafael uplift intersects outcrops of Upper Cretaceous rocks. The thin Upper Cretaceous section 

at Horse Canyon may result entirely from erosion or may

be related, at least in part, to nondeposition. Along the 

outcrop, the nonmarine Cretaceous section thickens progressively eastward, and, near the Colorado-Utah State 

line, about 2,600 (792 m) of Cretaceous rocks overlie the 

Castlegate Sandstone. In the eastern part of the Uinta 

basin at the Natural Buttes gas field, about 35 miles east 

of the Wilkin Ridge well and 45 miles northwest of the 

State-line outcrops, 2,050 ft (625 m) of Cretaceous rocks 

overlie the Castlegate. Just east of the Douglas Creek arch 

in the Piceance basin, the nonmarine Cretaceous section 

is about 1,500 ft (457 m) thicker than in the central part 

of the Uinta basin (R.C. Johnson, oral commun., 1986).

Geologic Nomenclature

Both a lack of subsurface information and the 

significant facies changes in the area around the Wilkin

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D3
Ridge well have caused confusion in picking unit boundaries and applying unit names. In this section, we outline 

the regional and local stratigraphy and nomenclature that 

are important in determining the selection of boundaries 

and nomenclature for Upper Cretaceous rocks of the 

Wilkin Ridge well.

Fouch and others (1983) and Lawton (1983) noted 

a threefold division of the Castlegate Sandstone in Price 

Canyon, northwest of Price, Utah: a basal unit of thickly bedded, laterally continuous sandstone that contains 

little interbedded fine-grained material; a middle unit of 

less laterally continuous sandstone interbedded with more 

abundant fine-grained material; and an upper unit of 

coarse-grained, thickly bedded, laterally continuous sandstone. The basal unit is equivalent to what is recognized 

as the Castlegate Sandstone along the eastern Book Cliffs, 

and the upper unit is equivalent to the Bluecastle Sandstone Tongue of the Castlegate Sandstone (Fouch and 

others, 1983), which can be traced eastward to Tuscher 

Canyon (fig. 2). The middle unit becomes less sandy and 

more organic rich eastward and is the landward equivalent of the Buck Tongue of the Mancos Shale and the 

Sego Sandstone west of their depositional pinchouts. 

Osterwald and others (1974) referred to this middle unit 

as the muddy member of the Price River Formation in 

the vicinity of Sunnyside and Horse Canyon; at Horse 

Canyon, Lawton (1983) referred to this same sequence 

as the Neslen Formation because it is depositionally 

similar and laterally equivalent to part of the Neslen Formation. Fisher and others (1960) did not extend the 

Neslen and Sego nomenclature west of the Green River, 

and, in the Wilkin Ridge area, this sequence is considered 

the middle unit of the Castlegate Sandstone. In the Wilkin 

Ridge well, the basal part of the Castlegate Sandstone 

is 265 ft (81 m) thick, the middle part 200 ft (61 m) thick, 

and the upper part, or Bluecastle Tongue, 135 ft (41 m) 

thick.

The undifferentiated Tuscher and Farrer Formations at Wilkin Ridge are equivalent to part of the Price 

River Formation to the west; the location of nomenclature change between these formations is arbitrary (fig. 

2). These rocks represent the final phase of alluvial infilling of the Western Interior Cretaceous basin, and 

abundant, thick coal beds and carbonaceous-clastic 

deposits are rare. The boundary between the Tuscher and 

Farrer Formations originally was chosen principally on 

differences in topographic expression and the relative 

abundance and geometry of sandstone beds (Fisher and 

others, 1960). Outcrop studies show, however, that, 

because of regional lithofacies changes and variable 

weathering characteristics, these criteria cannot be used 

to select a consistent contact between the two units on 

the outcrop and they cannot be applied in the subsurface. 

In this study, therefore, the Tuscher and Farrer Formations are undifferentiated. Gamma-ray and resistivity well

logs from the Wilkin Ridge well indicate a twofold division of the Tuscher-Farrer sequence: a lower, 452-footthick (138 m) interval composed of thin sandstone beds 

and abundant fine-grained deposits and an upper, 

1,535-foot-thick (468 m) interval composed mostly of 

thick sandstone beds. Log signatures for the lower interval resemble those for the upper part of the Neslen Formation east of the Green River.

Description of Core

The deepest core from the Wilkin Ridge well 

(11,185-11,230 ft, 3,409-3,431 m) penetrated the lower 

interval and consists of very fine to fine-grained sandstone, interbedded siltstone or sandstone and claystone, 

carbonaceous claystone, and thin (<0.5 ft, <0.15 m) coal 

beds. The sandstone units are 4-8 ft (1-2 m) thick, have 

sharp, slightly scoured bases, show no discernable upward 

change in grain size, and locally contain scattered clay 

rip-up clasts and coal clasts. Horizontal stratification is 

the dominant sedimentary structure, and low-angle crossstratification is less common. Locally, these structures 

have been obscured or obliterated by soft-sediment deformation. Disseminated carbonaceous material and root 

casts occur throughout the sandstone units. The organicrich interbedded siltstone or sandstone and claystone 

sequences are from less than 2 to as much as 8 ft thick 

(<l-2 m) and contain abundant root casts and possible 

burrows. Ripple stratification and wavy horizontal 

laminations are locally preserved, but most bedding has 

been obliterated by soft-sediment deformation. The carbonaceous claystone units are as thick as 5 ft (2 m) and 

are horizontally laminated where not penetrated by root 

casts. Thin coal beds (<0.5 ft (<0.15 m) thick) occur 

locally in the claystone units.

The core from the lower part of the upper unit 

(10,740-10,803 ft, 3,274-3,293 m) is composed almost 

entirely of fine- to medium-grained sandstone. Minor 

amounts of siltstone or claystone occur as rip-up clasts 

or as laminations in the sandstone. Individual sandstone 

units are 8-25 ft thick (2-8 m) and are defined by sharp, 

scoured basal contacts above which are abundant claystone rip-up clasts. Medium- to thin-bedded, mediumto low-angle cross-stratification and horizontal stratification are the dominant sedimentary structures in all sandstone units. Ripple stratification is common in the upper 

parts of units containing laminations of siltstone or 

claystone. Soft-sediment deformation is present locally 

but is not as abundant as in the deepest cored sequence.

A thin interval (10,273-10,295 ft, 3,131-3,138 m) 

containing a single sequence of sandstone that grades upward into carbonaceous claystone was cored in the upper part of the upper unit of the Tuscher and Farrer 

Formations. The sandstone is 8 ft (2 m) thick, has a sharp

D4 Evolution of Sedimentary Basins Uinta and Piceance Basins
basal contact, and fines upward from medium to fine 

grained at its base to very fine grained at its top. Mediumto thin-bedded, medium- to low-angle cross-stratification 

in the lower few feet of the sandstone is replaced upward 

by horizontal and ripple stratification. Root casts are also 

common in the upper part of the sandstone. Interbedded 

sandstone and claystone overlie the sandstone, and abundant root casts, ripple stratification, and laminations of 

coaly material characterize these interbeds. The amount 

of sandstone gradually decreases upward, and the claystone at the top of the sequence is very carbonaceous, 

contains coal fragments, and has horizontal laminations 

locally disrupted by root casts and deformation.

SEDIMENTOLOGY

Environments during Tuscher-Farrer deposition 

can be inferred from the cores, geophysical logs, and outcrop equivalents. The lower part of the Tuscher-Farrer 

sequence (from the base of the formation to a depth of 

11,090 ft, 3,380 m) was deposited on extensive floodplains 

crossed by shallow, meandering rivers. The abundance 

of organic-rich, extensively rooted beds in the lowest unit 

indicates deposition on floodplains containing levees, 

both well- and poorly drained swamps, crevasse splays, 

and freshwater lakes. Sandstone units having sharp scour 

bases are of channel origin, but both their thinness and 

the abundance of low-flow-regime sedimentary structures 

suggest deposition in shallow crevasse channels that 

formed adjacent to larger channels. Outcrop sequences 

from the Neslen Formation are similar to those observed 

in core of the lower units (fig. 3). Relatively thin, locally 

stacked channel-sandstone units that exhibit welldeveloped large-scale lateral-accretion cross-stratification 

are surrounded by carbonaceous, fine-grained, slopeforming units. A lower-alluvial-plain environment, 

characterized by relatively shallow meandering streams 

flowing through extensive vegetated floodplains, has been 

inferred for the upper part of part of the Neslen Formation in the Tuscher and Sego Canyon areas (K.J. 

Franczyk, unpub. data, 1985) and probably existed in the 

Wilkin Ridge area during deposition of the lower part 

of the undifferentiated Tuscher and Farrer Formations. 

Mineralogic compositions of sandstones in the lowest 

cored unit are similar to those of sandstones in the Neslen 

Formation and are discussed later.

Both geophysical logs and petrographic studies of 

core from the upper part of the Tuscher and Farrer Formations indicate that stacked sandstone sequences, some 

as thick as 80 ft (24 m), predominate; shaly material is 

significantly less common than in the lower unit but is 

locally present. The transition from the lower to the upper part of the Tuscher and Farrer Formations is gradational and is represented in outcrop by the transition from

Figure 3. Outcrop of Neslen Formation exposed on north side 

of Cottonwood Canyon, Grand County, Utah; view is looking 

north. These rocks are similar to cored sequences in lower part 

of the undifferentiated Tuscher and Farrer Formations in Wilkin 

Ridge well. The transition between the Neslen (Kn) and Farrer 

(Kf) Formations is gradational. The more resistant units in the 

dominantly slope forming Neslen Formation show lateralaccretion crossbedding and were deposited by meandering 

channels. The dark zones at the base or top of channel deposits 

are thin coal beds.

the Neslen to Farrer Formations (fig. 4). This transition 

indicates an increase in the clastic supply transported by 

deeper meandering rivers (Pitman, Anders, and others, 

1986) whose extensive migrations across the alluvial plain 

prevented accumulations of thick overbank deposits. 

Although sandstone predominates in the upper unit, 

geophysical logs indicate that intervals as thick as 160 ft 

(49 m) are composed dominantly of fine-grained shaly 

material and only minor sandstone. These fine-grained 

overbank deposits (fig. 5) formed when major rivers 

avulsed and abandoned an area or when changes in rates 

of sediment supply or subsidence caused a decrease in 

channel migration. Organic-rich floodplain deposits, 

potential hydrocarbon source rocks, occur locally in the 

upper unit of the Tuscher and Farrer Formations at 

Wilkin Ridge, but, because they vary greatly in thickness 

and lateral extent, it is difficult to predict their location 

on a regional scale.

The increase in abundance of sandstone from the 

lower to upper part of the undifferentiated Tuscher and 

Farrer Formations in the Wilkin Ridge core is accompanied by a change in sandstone mineralogy similar to 

that observed in outcrop between the Bluecastle Tongue 

of the Castlegate Sandstone and the Farrer Formation 

or between the Neslen and the Farrer Formations east of 

the Bluecastle pinchout. Lawton (1983) and Dickinson 

and others (1986) interpreted the western and northwestern thrust belt to be the Bluecastle and Neslen source area. 

In their interpretation, this source area shifted at the 

beginning of Farrer deposition to the southern thrust belt

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D5
Figure 4. Cradational contact between Neslen (Kn) and Farrer (Kf) Formations, as exposed on north side of Cottonwood 

Canyon, Grand County, Utah; view is looking north. The lower 

part of Tuscher Formation (Kt) is just visible on skyline. Fluvial 

sandstones in Farrer and Tuscher Formations are laterally extensive and locally stacked.

and areas outside of the thrust belt. Our study suggests 

that, in the Wilkin Ridge area, the western and northwestern thrust belt continued to supply sediment during 

early stages of Farrer deposition.

FRAMEWORK MINERALOGY

Sandstones representative of the lower and upper 

units of the undif ferentiated Tuscher and Farrer Formations in the Wilkin Ridge well were studied petrographically to determine detrital and authigenic mineral 

compositions (table 1) and their effects on reservoir quality. In the lower unit, fine-grained, moderately well sorted 

sandstones are composed mostly of quartz grains, varying proportions of sedimentary lithic fragments, and 

matrix; they are devoid of feldspar. This distinctive 

mineral suite has previously been reported only for the 

Neslen Formation (Keighin and Fouch, 1981; Lawton, 

1983; Pitman and others, 1987). In the upper unit, fineto medium-grained, moderately to well-sorted sandstones 

are composed of monocrystalline quartz, feldspar, and 

lithic fragments, mostly of sedimentary and volcanic 

origin, a mineral assemblage characteristic of the Tuscher 

and Farrer Formations in other parts of the basin 

(Keighin and Fouch, 1981; Lawton, 1983; Pitman, 

Anders, and others, 1986). Most of the mineral constituents except feldspar in the Tuscher and Farrer were derived from sedimentary and igneous source terranes in 

the Sevier orogenic belt in western Utah; some feldspar 

and volcanic lithic fragments most likely originated in 

rocks previously exposed in provinces southwest of the 

thrust belt (Fouch and others, 1983; Dickinson and 

others, 1986; Pitman, Anders, and others, 1986).

Figure 5. Typical sequence of overbank deposits preserved 

between extensive fluvial sandstones in the Tuscher and Farrer 

Formations in outcrops on north side of Cottonwood Canyon, 

Grand County, Utah. Siltstones and mudstones generally are 

greenish gray and contain little organic material; coal beds 

are rare, but fragments of coaly material are locally present. 

Thick sandstone in photograph is part of a crevasse channel 

deposit. Backpack (lower part of photograph) gives scale.

A ternary diagram showing the relative proportions 

of quartz, feldspar, and lithic fragments delineates 

mineralogic variations within and between the lower and 

upper sandstone units (fig. 6). According to the classification scheme of Folk (1974), sandstones in the lower unit 

are quartzarenites and sublitharenites; these lithologies, 

which show only minor diagenetic alterations, are typical 

of the Neslen Formation and have not been previously 

reported for the Tuscher and Farrer Formations. Sandstones in the upper unit are characterized by two mineral 

populations. In the upper part of the upper unit, sandstones contain significantly altered and dissolved feldspar 

grains and lithic fragments, indicating the rocks have 

undergone intense diagenetic modification; these sandstones are now sublitharenites. In contrast, the lower part 

of the upper unit contains sandstones that have undergone only moderate diagenetic alteration; these rocks are

D6 Evolution of Sedimentary Basins Uinta and Piceance Basins
Table 1. Mineralogic compositions of sandstones in the undifferentiated Tuscher and Farrer Formations, Wilkin Ridge well 

[Petrographic properties in percent; Tr, trace amount. Thin sections were impregnated with blue epoxy and then stained with potassium ferrocyanide and alizarin red to identify carbonate minerals and with potassium cobaltinitrate to distinguish between potassium and sodium feldspars. 

Three hundred points were counted per thin section]

Depth

(meters)

Depth

(feet) Quartz

Potassium

feldspar

Plagioclase Matrix

Rock

fragments Chert Dolomite Calcite

Visible

pore

space Anhydrite Other

Upper unit

3,134.0

3,134.3

3,134.7

3,134.9

3,135.4

3,136.0

3,136.4

3,137.3

3,137.6

3,138.1

3,138.7

3,139.0

3,139.4

3,140.1

3,140.8

3,273.6

3,274.2

3,275.1

3,275.8

3,276.5

3,277.0

3,278.2

3,278.8

3,279.6

3,280.7

3,281.3

3,281.9

3,282.8

3,283.5

3,284.0

3,284.8

3,285.2

3,286.2

3,286.9

3,287.3

3,288.4

3,288.9

3,289.2

3,289.9

3,290.3

3,290.7

3,291.2

3,292.9

10,282.0

10,283.0

10,284.5

10,285.0

10,286.7

10,288.6

10,290.0

10,293.0

10,294.0

10,295.5

10,297.5

10,298.7

10,299.8

10,302.0

10,304.5

10,740.3

10,742.0

10,745.1

10,747.4

10,749.5

10,751.2

10,755.3

10,757.3

10,759.7

10,763.5

10,765.4

10,767.3

10,770.2

10,772.7

10,774.2

10,776.8

10,778.3

10,781.4

10,783.7

10,785.2

10,788.7

10,790.2

10,791.3

10,793.5

10,795.0

10,796.3

10,797.8

10,800.6

50

58

78

73

72

69

69

80

79

69

75

78

74

52

41

53

42

50

49

46

44

33

50

37

46

45

29

44

52

47

52

48

40

46

50

49

48

50

46

51

47

45

41

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1

0

0

0

0

3

0

0

0

0

1

3

0

0

0

0

0

0

0

0

0

0

0

0

2

0

0

0

0

Tr

Tr

1

1

2

1

2

2

2

2

1

5

3

9

4

8

8

8

7

20

16

14

12

15

11

8

7

9

9

7

8

8

5

10

15

10

9

10

9

9

9

46

37

0

0

0

7

0

1

0

0

0

0

0

0

20

1

17

0

0

0

3

10

2

3

2

3

18

2

2

3

1

3

7

2

2

2

1

2

2

1

1

5

7

2

0

8

6

7

6

7

4

3

11

5

3

10

22

20

14

13

16

14

11

13

14

11

16

11

11

9

17

16

17

14

16

17

19

14

15

13

12

4

16

14

14

13

0

2

3

5

7

2

8

5

3

5

8

7

4

4

9

4

3

5

4

3

5

7

9

7

9

9

4

6

6

7

5

7

4

4

3

9

5

10

11

6

9

7

7

0

0

1

0

0

10

4

3

2

1

0

1

3

1

5

6

12

4

8

12

9

3

2

3

4

6

6

7

6

6

4

5

6

5

11

3

4

2

2

2

6

6

6

0

0

1

0

2

2

3

0

0

0

0

Tr

0

Tr

0

2

0

2

3

6

14

0

1

1

2

3

1

0

3

3

2

2

1

1

1

0

1

2

3

3

2

3

5

0

0

8

14

9

1

6

4

8

10

5

7

7

13

0

6

0

13

11

11

1

4

8

15

10

6

2

8

5

5

8

5

7

10

10

10

10

8

10

8

4

6

6

0

0

0

0

0

0

2

2

1

0

4

2

Tr

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

3

3

1

1

1

2

0

0

2

1

1

0

1

1

2

4

8

2

2

3

4

8

2

4

4

3

18

7

3

4

4

6

9

4

4

3

2

4

3

4

7

4

6

Lower unit

3,411.3

3,411.9

3,412.9

3,415.1

3,417.0

3,418.6

3,421.1

11,192.0

11,194.0

11,197.3

11,204.5

11,211.0

11,215.7

11,224.3

45

56

69

77

70

65

89

0

0

0

0

0

0

0

0

0

0

0

0

0

0

52

40

15

13

17

12

7

Tr

1

2

3

3

2

Tr

3

2

1

1

2

2

1

0

1

5

3

8

13

1

0

0

Tr

0

0

3

Tr

0

0

Tr

0

0

Tr

Tr

0

0

0

0

0

0

0

0

1

7

3

1

4

1

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D7
QUARTZ

Quartzarenite

95%

FELDSPAR ROCK FRAGMENTS

EXPLANATION 

Tuscher-Farrer Formations

 Upper part of upper unit

 Lower part of upper unit 

O Lower unit

Figure 6. Classification of sandstones in the undifferentiated Tuscher and Farrer Formations in the Wilkin Ridge well. Modified 

from Folk (1974).

predominantly feldspathic litharenites. Both lithologies 

in the upper unit are similar to those of the Tuscher and 

Farrer Formations in outcrop along the Book Cliffs in 

the southern part of the Uinta basin and in the subsurface east of the Green River.

unit, quartz is less abundant and constitutes 29 to 80 percent. Quartz grains in both units typically are subangular 

to moderately rounded and range from very fine to 

medium in size. Most are monocrystalline, have slight undulatory extinction, and contain minute vacuoles.

Quartz

Detrital quartz is a dominant framework grain and 

comprises an average of 67 percent of the whole rock in 

the lower cored unit in the Wilkin Ridge well. In the upper

Feldspar

Feldspar is absent in sandstones in the lower unit 

of the Tuscher and Farrer Formations, but plagioclase 

constitutes from trace amounts to 21 percent and

D8 Evolution of Sedimentary Basins Uinta and Piceance Basins
potassium feldspar a few percent in the upper unit. Most 

plagioclase grains are individual, untwinned, subangular 

to subrounded, and fresh to extensively altered. Altered 

plagioclase grains show evidence of replacement by 

sericite, carbonate, barite or anhydrite, and the effects 

of partial to complete dissolution. Potassium feldspar 

grains are both twinned and untwinned and similar in size 

and shape to plagioclase. Most grains are orthoclase, 

although a few grains of microcline were recognized by 

their grid twinning. Because both sodium and potassium 

feldspars are susceptible to leaching, potassium feldspar 

typically has undergone more extensive dissolution such 

that only a skeleton of the original grain is preserved. 

Rare grains of feldspar within volcanic rock fragments 

also appear to have undergone some dissolution.

Lithic Fragments

Lithic fragments of diverse origin are abundant in 

the undifferentiated Tuscher and Farrer Formations, constituting from a trace to 3 percent of the grains in the 

lower unit and from 2 to 22 percent of the grains in the 

upper unit. The most abundant grains are of sedimentary origin and include polycrystalline carbonate, 

argillaceous shale, and mudstone and siltstone. Many 

have been extensively altered to sericite and are mechanically unstable; as a result, they have been deformed between framework grains to form a pseudomatrix or have 

been partly to completely dissolved. Chert forms a significant proportion (2-11 percent) of the lithic fragments in 

the upper unit. Much of the chert is unaltered and composed of interlocking microcrystalline quartz crystals that 

range from cryptocrystalline (<0.05 mm) to polycrystalline (<0.1 mm). It is commonly difficult to differentiate 

between polycrystalline quartz and coarse-crystalline chert 

because of the gradation in grain size. Some chert grains 

are medium to very dark brown as a result of inclusions 

of carbonaceous material, and some grains are cut by 

veins of quartz. A few chert grains are micaceous or contain small dolomite rhombs that grew after sediment 

deposition. In some sandstones, chert grains contain fossil 

crinoid fragments that have been locally dissolved. These 

fossiliferous grains perhaps are fragments of silicified 

limestone reworked from Paleozoic carbonate rocks. In 

the upper unit, other lithic fragments include plutonic igneous fragments containing feldspar and quartz, 

polycrystalline quartz grains having straight to undulose 

extinction and curved to sutured boundaries between individual crystals, and numerous altered volcanic grains 

composed of feldspar and chlorite.

Matrix

Varying amounts of detrital matrix are present in 

Tuscher and Farrer sandstones, and, although detrital

matrix locally constitutes as much as 52 percent by 

volume, overall it is a minor constituent. Pseudomatrix 

resulting from mechanical deformation of unstable lithic 

fragments is common, particularly in the lower unit, 

because of the presence of argillaceous grains. In sandstones containing abundant pseudornatrix and detrital 

matrix, porosity and permeability have been s^gnificantly reduced.

Cements

Secondary quartz, developed as syntaxial overgrowths on detrital grains, locally is a widespread mineral 

cement in sandstones in the lower and upper units of the 

Tuscher and Farrer Formations. It is most abundant in 

rocks containing only small amounts of matrix and compressible framework grains. In areas where quartz overgrowths are well developed, they typically are difficult 

to distinguish from the detrital grains, and, as a result, 

their relative abundance is uncertain. Partly abraded grain 

overgrowths in optical continuity with framework quartz 

grains in the upper unit suggest some grains and overgrowths may have been recycled from older terrane. Most 

quartz overgrowths are recognized by their euhedral, 

rhombohedral, and prismatic crystal faces. In sandstones 

in which discrete grain overgrowths have coalesced to 

form a cement, the effects of pressure solution may be 

seen. In the upper unit, quartz overgrowths have clearly 

developed in sandstones in which the exposed grain surfaces were not coated with early authigenic chlorite or 

the amounts of detrital matrix and mechanically unstable 

lithic grains were minimal. In the lower part of the upper unit, overgrowths commonly contain dissolution 

voids created by the removal of replacement anhydrite 

and possibly barite or have been etched as a result of the 

dissolution of precursor carbonate cement.

A mineralogically complex assemblage of iron-rich 

and iron-poor carbonate cements was observed in sandstones in the upper unit of the undifferentiated Tuscher 

and Farrer Formations; most sandstones in the lower unit 

contain only minor amounts of carbonate. In the upper 

unit, authigenic ferroan calcite is locally abundant and 

constitutes from trace amounts to 14 percent; dolomite 

is less abundant and constitutes from 1 to 12 percent. 

Because it is difficult to differentiate between grains of 

detrital dolomite and authigenic anhedral replacement 

dolomite, their relative abundances are only approximate.

In sandstones in the upper unit, two generations of 

calcite can be distinguished based on mode of occurrence 

and texture. Rare iron-free calcite occurs as relicts surrounded by optically continuous ferroan calcite (fig. 7). 

Most calcite now in the sandstones is enriched in iron and 

forms a poikilotopic spar cement that embays grain 

margins and cleavage traces or replaces framework grains

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D9
Figure 7. Replacement of relict iron-free calcite pore-filling cement (C; red stain) by ironbearing calcite (fc; blue stain). Note that secondary quartz overgrowths (og) predate development of authigenic calcite. Q, quartz.

such as feldspar. The relative distribution of ferroan 

calcite varies: wherever it is abundant, framework-grain 

alteration and compaction usually have been minimal. 

In many sandstones, ferroan calcite is preserved only 

locally in pores lined with authigenic iron chlorite, as 

relicts in secondary voids, and as a grain replacement. 

In sandstones having well-developed inter- and intragranular porosity, dissolution features that closely resemble the texture of undissolved carbonate and calcite 

remnants that occupy pores both are evidence that calcite 

was a preexisting cement.

In the upper part of the upper unit, the sulfate 

minerals anhydrite and barite are present locally from 

trace amounts to 4 percent. The presence of these minerals 

positively correlates with the occurrence of small amounts 

of bitumen, although neither anhydrite nor barite was 

observed in direct contact with kerogen. The mode of occurrence of anhydrite and barite ranges from small scattered patches to large poikilotopic crystals that replace 

and surround framework grains and early silica and carbonate cement (figs. 8-10). In some sandstones, either one 

or both of these minerals have been partly to completely 

dissolved. Irregular clay-filled voids that cut across detrital 

quartz grains and overgrowths are features closely resembling the texture of anhydrite where it is still preserved.

Clays

The principal clay-mineral assemblage in the

undifferentiated Tuscher and Farrer Formations is composed of illite, chlorite, and mixed-layer illite-smectite. 

Thin, isopachous rims of authigenic chlorite and porefill cement are preserved locally in some sandstones in 

the upper unit. X-ray diffraction analysis indicates that 

all chlorite is well crystallized and iron rich.

Individual chlorite rims typically are composed of 

pseudohexagonal platelets that are oriented perpendicular 

to grain surfaces forming a cement. Quartz overgrowths 

are rare in sandstones displaying widespread rim cement. 

In areas where chlorite is abundant, it lines pores and 

coats framework grains except where the grains are in 

contact with each other. Pores lined with chlorite often 

contain carbonate relicts or are filled by a late generation of chlorite. If voids are open, the rim cement may 

be crushed or contorted due to mechanical compaction.

Authigenic illite and illite-smectite are abundant 

clay-mineral constituents throughout the undifferentiated 

Tuscher and Farrer Formations. They commonly are attached to authigenic chlorite grain surfaces, display a 

fibrous habit in pores, or are distributed as thin coats on 

detrital grains. Illite and illite-smectite are particularly 

widespread in secondary pores that contain evidence for 

preexisting carbonate and sulfate cement.

MECHANICAL COMPACTION

The effects of mechanical compaction are evident 

in all of the cored sandstones from the Wilkin Ridge well

D10 Evolution of Sedimentary Basins Uinta and Piceance Basins
Figure 8. Late-stage poikilotopic anhydrite cement (a).

and generally are more pronounced as burial depth increases. A few sandstones containing framework grains 

floating in carbonate cement and an early generation of 

iron chlorite display only slight to moderate compaction 

effects, principally grain rotation.

DIAGENESIS

Based on our petrographic studies, the diagenetic 

history of Upper Cretaceous sandstones in the undifferentiated Tuscher and Farrer Formations in the central Uinta 

basin appears to be more complex than that of rocks of 

similar age and origin that have been less deeply buried 

in the eastern part of the Uinta basin (Keighin and Fouch, 

1981; Pitman, Goldhaber, and Fouch, 1986; Pitman and 

others, 1987). Sandstone paragenesis in the lower unit includes: (1) mechanical compaction of framework grains, 

(2) quartz overgrowths developed locally on framework 

quartz grains, (3) authigenic carbonate preserved as a pore 

fill and as a replacement mineral, and (4) authigenic illite and chlorite occluding secondary pores. These 

diagenetic features also are characteristic of the underlying Neslen Formation.

Sandstones in the upper unit, particularly those that 

contain bitumen, have undergone a more complex diagenetic history that includes: (1) mechanical compaction 

of detrital grains, (2) development of secondary quartz 

overgrowths, (3) formation of iron chlorite rim cement, 

(4) precipitation and subsequent dissolution of nonferroan and ferroan carbonate, (5) formation of authigenic 

illite and chlorite in secondary pores, (6) crystallization

and dissolution of anhydrite and barite, and (7) maturation and generation of hydrocarbons. The chemically 

diverse mineral assemblage that characterizes the upper 

unit suggests diagenesis occurred under the influence of 

depositional fluids whose compositions evolved during 

burial. Most of the constituents necessary for crystallization of the authigenic minerals probably either were derived from the redistribution of ions within the sandstones 

or were transported locally from interbedded shales.

Silica Cementation

Secondary quartz was the earliest cement to form 

in most sandstones. In the upper unit, textural relations 

between discrete quartz overgrowths and other mineral 

cements indicate secondary quartz predated formation of 

all mineral cements except iron chlorite. Pressure solution 

was evidently important in the development of secondary quartz in both units. Well-developed concavo-convex 

grain contacts and sparse sutured contacts suggest silica 

may have precipitated from migrating pore water, as well 

as from oversaturated fluids resulting from local pressure 

solution. At shallow burial depths, the transformation of 

smectite to illite may have provided an additional source 

of silica. Later in the burial history, silica also may have 

been derived from dissolution of feldspar.

Carbonate and Sulfate Mineral Development

At least two episodes of calcite crystallization occurred in the Tuscher and Farrer Formations at different

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D11
Figure 9. Barite (b) replacing authigenic dolomite (d) and detrital framework grains of quartz 

(Q) and chert (ch).

times and at different depths during burial. Nonferroan 

calcite, the earlier carbonate, most likely precipitated 

from near-surface waters during early diagenesis at 

shallow burial depths before clay-mineral transformations 

and release of iron. At greater burial depths during a later 

stage of diagenesis, ferroan calcite, now the most abundant carbonate cement, formed from iron-bearing fluids. 

Ferroan dolomite also formed late in the burial history, 

probably from the same diagenetic fluids that precipitated 

ferroan calcite. In sandstones exhibiting extensive cementation by ferroan calcite, the relatively minor chemical 

alteration and mechanical compaction of framework constituents suggest the ferroan calcite probably was 

deposited relatively early in the burial history, before 

significant compaction occurred. The ferroan calcite may 

have absorbed a considerable amount of overburden 

pressure during burial and thus prevented further 

mechanical compaction in the sandstones. The relative 

abundance of carbonate and the sparsity of point contacts between individual detrital grains indicate that 

porosities and permeabilities were high when the sandstones were initially cemented; these initial high porosities 

and permeabilities are further evidence that a large fraction of the carbonate, as calcite, formed during an early 

stage of diagenesis.

Cementation by ferroan calcite is incomplete in 

many sandstones; relict calcite in intergranular pores suggests that, in selected intervals, a period of dissolution 

occurred. Replacement calcite that formed along cleavage

traces in individual feldspar grains also is commonly 

leached. Many partly to completely dissolved feldspar 

grains may have originally been more calcic than adjacent grains that show virtually no effects of leaching or 

surface etching. The dissolution of ferroan and nonferroan calcite was an important diagenetic event in the 

reservoir development of the upper unit because it 

resulted in a substantial increase in overall porosity and 

permeability of the sandstones. Dissolution of carbonate 

cement and framework grains probably occurred at 

moderate rather than shallow burial depths because most 

feldspar relicts are delicate structures showing little 

evidence of the mechanical compaction that would result 

from surface or near-surface leaching. Clay-mineral and 

organic reactions in shales during diagenesis may have 

produced sufficient water, organic acids, and complexing agents to dissolve chemically unstable framework 

grains and authigenic cements in nearby sandstones 

(Siebert, 1984).

Carbon and Oxygen Isotopes

Carbon and oxygen isotope compositions were 

determined for selected ferroan calcite and dolomite 

samples in order to establish the chemical conditions that 

governed carbonate cementation (table 2). The range in 

compositions is similar to those reported by Pitman, 

Goldhaber, and Fouch (1986) and Pitman and others

D12 Evolution of Sedimentary Basins Uinta and Piceance Basins
Figure 10. Replacement of secondary quartz overgrowths (og) by authigenic anhydrite (a).

(1987) for temporally equivalent rocks farther east in the 

basin. In the lower unit, 613C ranges from -0.99 to -3.25 

per mil and 6 18O ranges from -9.83 to 13.36 per mil. 

Calcite in sandstones from the lower part of the upper 

unit displays isotope compositions similar to those for 

calcite from sandstones from the lower unit, from -1.06 

to -2.12 per mil 613C and from -10.28 to -14.70 per mil 

6 18O. Sandstones from the upper part of the upper unit 

contain calcite that is distinctly lighter than the underlying rocks; 613C varies from -3.95 to -7.75 per mil, and 

6 18O from -12.21 to -14.04 per mil.

Isotope compositions for dolomite closely approximate those for calcite. In the lower unit, 613C ranges 

from +0.24 to -3.53 per mil and 6 18O from -9.83 to

-13.36 per mil. In the lower part of the upper unit, 

dolomite displays isotopically heavier compositions var>- 

ing from -0.01 to -0.66 per mil 613C and from -5.41 to

-7.36 per mil 5 18O. Most dolomite in the upper part of 

the upper unit is isotopically light compared to the underlying rocks, and ranges from -1.16 to -5.32 per mil 613C 

and from -6.88 to -11.99 per mil 6 18O.

A crossplot of 613C and 6 18O compositions for the 

Tuscher and Farrer Formations is shown in figure 11. 

Calcite compositions that lie along the upper linear trend 

represent early carbonate that has remained virtually 

unaltered since deposition, whereas compositions that 

either cluster along the dashed line or in the extreme left 

corner of the diagram represent calcite that has undergone 

diagenetic modification during burial.

Isotope compositions of dolomite also form a

distinct linear trend (fig. 11). The isotopically heaviest 

compositions represent dolomite of detrital origin, 

whereas the lighter compositions (along the dashed part 

of the line) represent dolomite affected by diagenetic 

alteration. The linear trends along which most samples 

plot suggest that authigenic carbonate formed dominantly 

under the influence of meteoric waters.

Carbon Isotopes

The variation in 613C reflects the contribution of 

carbon from different sources. Isotopically heavy carbon 

(about -1.0 per mil) probably was derived from dissolved marine carbonate species, inasmuch as the 613C compositions are within the range commonly reported for 

normal marine carbonate sediments (Gross, 1964). 

Isotopically lighter carbon compositions in the upper part 

of the upper unit and locally in the lower unit characterize 

sandstones having somewhat high initial porosity and 

permeability. Hence, these sandstones probably were 

locally affected by a higher degree of water-rock interaction. It is also possible that the fluids contained a small 

amount of organic carbon.

The 613C compositions for dolomite in the lower 

unit and in the lower part of the upper unit are very 

similar to those associated with marine dolomite (Weber, 

1964). Petrographic observations indicate that most of 

the dolomite is detrital and only a small fraction is 

authigenic. This isotopically heavy carbon most likely was

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D13
Table 2. Carbon and oxygen isotope analyses for selected samples of calcite and dolomite 

from sandstones in the undifferentiated Tuscher and Farrer Formations, Wilkin Ridge well 

[Asterisk (*), sample having unusually light isotope composition; leaders ( ), not determined. Parentheses enclose results of duplicate analyses]

Depth 

(meters)

Depth 

(feet)

Calcite

613CD 5180n

Dolomite

6 13Cn 5 180C

*3,030.8

*3,139.4 

3,140.8 

3,273.6 

3,277.0

10,298.7

10,299.8

10,304.5

10,740.3

10,751.2

-7.75

-1.22

-2.06

Upper unit

*3, 136.0

*3,136.4

*3,137.3

*3,137.6

*3,138.7

10,288.6

10,290.0

10,293.0

10,294.0

10,297.5

-3.95

-6.66

___

-12.39

-14.04

-1.16

-3.22(-3.42)

-3.22

-2.71

-5.32

-7.12

-9.75(-9.96)

-10.43

-9.39

-10.17

-12.21

-10.54

-14.00

Lower unit

-3.28

-4.33

-1.32

-0.31

-0.66

-10.55

-11.99

-6.88

-6.28

-7.36

3,279.6

3,282.7

3,286.2

3,287.3

3,289.2

3,292.0

10,759.7

10,770.2

10,781.4

10,785.2

10,791.3

10,800.6

-1.61

-1.53

-1.06

-1.74

-2.12

-12.80

-12.00

-10.28

-12.77

-14.70

-0.27

-0.01(-0.05)

-0.17

-0.19

-0.48

-0.36

-6.78

-5.41(-5.46)

-6.36

-5.91

-6.78

-7.01

3,410.4

3,412.9

*3,413.3

3,417.1

*3,418.6

*3,418.8

3,419.0

3,420.3

3,421.8

11,189.0

11,197.3

11,198.4

11,211.0

11,215.7

11,216.5

11,217.3

11,221.5

11,226.5

-1.58

-2.66

-3.15

-3.25(-3.33)

-1.35(-1.19)

-1.42

-0.99

-10.66

-11.26

-12.46

-13.36(-13.13)

-10.34 (-9.99)

-9.83

-10.37

-0.73

-2.23

-3.53

-1.71

-2.61

-2.95

-0.60

+ 0.24

-1.06

-6.56

-9.09

-11.40

-8.54

-10.66

-11.71

-7.01

-4.33

-7.85

derived locally from dissolved marine carbonate grains 

that originated within individual sandstone beds or interbedded shales. The significantly lighter carbon compositions of dolomite in the upper part of the upper unit 

reflect precipitation from pore waters containing a component of light carbon possibly of organic origin and 

similar in composition to the fluids that precipitated 

calcite.

Oxygen Isotopes

Variations in oxygen isotope compositions of calcite 

(-9.83 to -14.70 per mil) may reflect either changes in 

temperature with increasing burial depth or the influence 

of meteoric water circulating through the sandstones. 

Some of trie isotopically light oxygen may be the result

of carbonate precipitation at high temperatures while the 

rocks were close to maximum burial depth; however, 

6 18O compositions of the cements do not consistently 

decrease with increasing burial depth, as would be 

expected if they formed at higher temperatures under conditions of deeper burial. Moreover, textural characteristics suggest that much of the calcite formed at relatively 

shallow burial depths. The differences in the depleted oxygen isotope compositions between the different units 

therefore most likely represent changes in the isotopic 

composition of meteoric waters during carbonate 

precipitation and, hence, record the isotopic evolution 

of these fluids through time.

The oxygen isotope compositions for dolomite are 

significantly lighter in the upper part of the upper unit 

than in the underlying sequences. This isotopically light 

oxygen probably was generated during diagenesis,

D14 Evolution of Sedimentary Basins Uinta and Piceance Basins
-1

-2

a ^ § 3

DC:

LU 

Cu

o

-4

-5

-6

-7

D

-15 -14 -13 -12 -11 -10 -9 -8 -7

518O, PER MIL

-6 -5 -4

Upper unit

EXPLANATION 

Tuscher-Farrer Formations

 Calcite

A Anomalous calcite

 Dolomite/ankerite

3 Anomalous dolomite/ankerite

Lower unit 

O Calcite

A Anomalous calcite

D Dolomite/calcite

0 Anomalous dolomite/ankerite

Figure 11 . Carbon and oxygen isotope compositions for carbonate minerals in the undifferentiated Tuscher and 

Farrer Formations.

possibly from pore fluids having isotope compositions 

similar to the fluids that deposited calcite. Isotopically 

light calcite and dolomite may thus have formed during 

closely spaced diagenetic events.

Sulfate Minerals

Textural relations between anhydrite, barite, and 

iron carbonate in the upper part of the upper unit in the 

undifferentiated Tuscher and Farrer Formations indicate 

that sulfate minerals formed relatively late in the burial 

history, following the generation of carbonate. The

apparent association between sulfate mineral phases and 

bitumen suggests that sulfate-enriched pore waters 

associated with the maturation of organic matter may 

have played a role in the formation of anhydrite and 

barite. The chemical conditions governing the local 

dissolution of these minerals are uncertain.

Authigenic Clay Mineral Formation

The complex authigenic clay mineral assemblage 

that characterizes Tuscher and Farrer sandstones in 

the Wilkin Ridge well reflects the evolution of fluid

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D15
chemistries during burial. Iron chlorite was the earliest 

authigenic mineral to form in the feldspathic sandstones 

after initial grain compaction. The absence of features 

indicative of widespread compaction in sandstones containing abundant chlorite is attributed to early formation 

of isopachous rim cement, as well as to development of 

carbonate that prevented further grain compaction. The 

rare occurrence of chlorite at grain contacts suggests that 

chlorite was not present as surface coatings on grains 

before the grains were reworked from the source area to 

the present site of deposition. Quartz overgrowths typically are poorly developed in sandstones that display 

widespread chlorite rim cement. Pittman and Lumsden 

(1968) have suggested that the growth of secondary quartz 

is limited in sandstones in which authigenic chlorite is 

abundant because nucleation sites for its growth commonly are not available. Chlorite cementation may have 

predated framework grain dissolution, as suggested by 

isopachous chlorite that commonly surrounds primary 

and secondary pores. The absence of numerous broken 

or crushed rims around the secondary pores implies that 

leaching of the host grain occurred after significant 

burial. Authigenic iron chlorite in the Tuscher and Farrer Formations may have been derived from volcanic 

grains, from the alteration of ferromagnesian minerals 

in preexisting lithic grains, from detrital clays of similar 

mineral composition, or from constituents in adjacent 

shale beds.

Discrete illite was one of the last mineral phases to 

precipitate in the Tuscher and Farrer sandstones. The 

presence of illite in secondary pores suggests that the illite formed when the rocks were near their maximum 

burial depth, either after or coincident with dissolution 

of ferroan calcite and anhydrite. The occurrence of illite 

also may be related to the transformation of smectite to 

illite. Most of the silica and aluminum necessary for illite crystallization probably was derived from nearby 

shales and transported into the more porous and permeable sandstone beds.

Organic Matter

Small amounts of bitumen are present locally in the 

lower unit and in the upper part of the upper unit of the 

Tuscher and Farrer Formations. In some sandstones, the 

bitumen is along stylolites in areas where some dissolution of framework grains may have occurred. In other 

sandstones, the bitumen forms patches in clay-filled 

dissolution pores. Both the replacement of feldspar grains 

by iron carbonate and its subsequent enclosure by 

bitumen and the absence of bitumen inclusions in 

authigenic mineral cements suggest that most of this 

organic material formed relatively late in the burial 

history, after precipitation and subsequent dissolution of 

the authigenic minerals.

RESERVOIR POTENTIAL

Reservoir property data for cored sandstones in the 

Wilkin Ridge well are presented in table 3. Measured 

porosity in the potential reservoir rocks is variable, ranging from 1.0 to 8.0 percent. Permeability is typically low, 

less than 0.1 millidarcy (mD), except in the upper part 

of the upper unit where it varies from 0.8 to 1.6 mD. 

Sandstone porosity and permeability generally decrease 

with increasing burial depth because of variations in 

mineral composition and grain size; higher porosity and 

permeability in the upper part of the upper unit probably 

correspond to the presence of bitumen. Coarser grained, 

better sorted sandstones commonly have higher porosity 

and permeability than do finer grained, more poorly 

sorted sandstones.

Porosity in the Tuscher and Farrer Formations is 

lowest in sandstones containing abundant detrital- and 

pseudo-matrix, ductile framework grains, widespread 

secondary quartz cement, and early-formed carbonate. 

It is enhanced in sandstones in which carbonate cement 

and chemically unstable grains such as feldspar and chert 

have been dissolved. Porosity in sandstones exhibiting 

early iron chlorite rim cement commonly is well developed; the early development of chlorite may have 

prevented further grain compaction and preserved initial 

pore volume for infilling by later mineral cements.

Low permeability is a characteristic of Upper 

Cretaceous nonmarine sandstones and can be attributed 

to the presence of detrital- and pseudo-matrix and 

mechanically unstable lithic fragments and to the development of authigenic clay minerals in secondary pores. 

Sandstones having these characteristics typically have a 

complex pore network and a high, irreducible water 

saturation resulting from the large surface areas of individual clay particles. As a consequence of reduced 

movement of fluids through the pore system, effective 

permeability is low.

SOURCE ROCK EVALUATION

Selected samples of carbonaceous mudstone (shale) 

and coal from the Tuscher and Farrer Formations in the 

Wilkin Ridge well were evaluated geochemically by RockEval pyrolysis and by vitrinite reflectance to determine 

their source rock characteristics and level of thermal 

maturity (tables 4, 5).

Tissot and Welte (1978) have indicated that clastic 

rocks having good source potential contain greater than 

1 percent total organic carbon; the organic content of all 

samples from the undifferentiated Tuscher and Farrer 

Formations is greater than 1.0 percent.

Hydrocarbon and oxygen indices (table 4) are 

shown in a modified van Krevelen diagram (fig. 12). 

Mclver (1967) and others have shown that the elemental

D16 Evolution of Sedimentary Basins Uinta and Piceance Basins
Table 3. Reservoir properties of sandstones in the undifferentiated Tuscher and Farrer Formations, Wilkin Ridge well 

[Data provided by Exxon Oil Corporation (written commun., 1984)]

Depth 

(meters)

Depth 

(feet)

Permeability 

(millidarcys)

Porosity 

(percent)

Residual saturation 

Oil Water 

(percent pore space)

Upper unit

3,134.0-134.3

3,135.8-136.1

3,136.1-136.4

3,136.4-136.7

3,136.7-136.8

3,136.8-137.3

3,137.3-137.6

3,137.6-137.9

3,137.9-138.2

3,138.2-138.5

3,138.5-138.8

3,138.8-139.1

3,139.1-139.4

3,139.4-140.1

3,140.1-140.4

3,274.9

3,275.1

3,275.7

3,275.8

3,276.1

3,276.5

3,276.7

3,277.0

3,278.0

3,278.2

3,278.6

3,278.8

3,279.1

3,279.6

3,279.7

3,280.0

3,280.5

3,280.7

3,280.9

3,281.3

3,281.5

3,281.9

3,282.2

3,282.5

3,282.8

3,283.1

3,283.5

3,283.7

3,284.0

3,284.3

10,282-83

10,288-89

10,289-90

10,290-91

10,291-92

10,292-93

10,293-94

10,294-95

10,295-96

10,296-97

10,297-98

10,298-99

10,299-00

10,301-02

10,302-03

10,744.4

10,745.1

10,746.9

10,747.4

10,748.3

10,749.5

10,750.4

10,751.2

10,754.4

10,755.3

10,756.5

10,757.3

10,758.1

10,759.7

10,760.2

10,761.2

10,762.8

10,763.5

10,764.1

10,765.4

10,766.2

10,767.3

10,768.4

10,769.2

10,770.2

10,771.4

10,772.7

10,773.4

10,774.2

10,775.4

0.09

.10

.92

.14

.14

.11

.12

.13

.23

1.60

1.30

.65

1.30

.11

.08

.07

.06

.06

.06

.05

.05

.01

.03

.07

.06

.28

.14

.11

.08

.07

.07

.06

.05

.04

.05

.04

.03

.04

.04

.02

.04

.05

.03

.05

.05

2.7

2.4

5.5

5.5

5.5

6.9

5.7

5.1

6.3

6.2

6.8

6.7

4.8

5.9

5.5

6.9

6.8

6.3

6.5

5.7

5.0

1.4

2.3

6.5

4.0

5.1

7.0

7.0

7.3

6.8

6.4

6.4

5.9

6.1

7.9

7.2

5.5

6.2

6.2

5.5

5.9

6.7

4.5

6.4

7.1

9.2

9.3

9.7

11.4

8.5

10.7

8.2

10.9

9.2

9.5

11.6

8.9

10.3

3.6

4.2

2.0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

55.3

64.9

31.2

35.7

20.5

18.3

13.1

21.8

23.8

21.8

23.2

20.4

23.6

61.5

54.2

72.1

40.0

44.4

44.1

40.4

51.5

40.3

47.4

44.4

63.4

63.8

48.6

35.4

50.2

36.3

65.1

37.2

55.7

51.1

47.8

59.2

54.8

55.9

63.4

69.8

45.8

56.2

38.5

34.6

53.1

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D17
Table 3. Reservoir properties of sandstones, Wilkin Ridge well Continued

Residual saturation

Depth

(meters)

Depth

(feet)

Permeability

(millidarcys)

Porosity

(percent)

Oil

(percent

Water

pore space)

Upper unit Continued

3,284.8

3,285.0

3,285.2

3,285.5

3,285.9

3,286.2

3,286.4

3,286.9

3,287.2

3,287.3

3,287.7

3,287.9

3,288.4

3,288.6

3,288.9

3,289.2

3,289.7

3,289.8

3,290.1

3,290.4

3,290.7

3,291.2

3,291.4

3,291.7

3,292.0

10,776.8

10,777.5

10,778.3

10,779.3

10,780.4

10,781.4

10,782.1

10,783.7

10,784.7

10,785.2

10,786.4

10,787.1

10,788.7

10,789.4

10,790.2

10,791.3

10,792.8

10,793.4

10,794.3

10,795.4

10,796.3

10,797.8

10,798.4

10,799.4

10,800.6

.07

.05

.05

.05

.08

.03

.10

.05

.06

.04

.05

.08

.15

.05

.06

.07

.07

.07

.09

.06

.04

.03

.04

.03

.03

7.1

6.8

6.6

6.5

6.9

4.9

6.8

7.0

7.1

6.3

6.2

7.7

8.0

7.1

7.3

6.9

6.6

7.3

6.9

6.7

3.3

5.7

6.1

5.5

4.7

0

0

0

0

0

0

0

1.2

0

0

0

0

0

0

0

0

1.4

0

1.3

0

0

0

1.9

0

0

51.3

32.9

47.5

42.3

42.6

53.0

50.2

39.0

59.6

45.0

49.5

66.5

34.7

47.8

41.1

38.0

35.7

41.3

40.6

47.2

51.2

58.7

53.5

62.0

59.6

Lower unit

3,413.0

3,413.3

3,418.0

3,418.2

3,418.6

3,418.7

3,419.0

3,420.6

3,421.0

3,421.3

11,197.5

11,198.4

11,213.8

11,214.6

11,215.7

11,216.3

11,217.3

11,222.4

11,223.7

11,224.7

0.02

.07

.01

.02

.01

.01

.01

.02

.02

.02

4.9

4.8

2.0

1.6

1.5

1.0

1.0

1.5

2.7

2.4

27.6

15.9

5.7

9.2

0

10.1

0

0

4.6

7.7

31.5

13.6

68.6

55.2

57.4

60.6

76.3

58.0

64.0

77.4

compositions of organic matter are directly related to 

these index values and plot along well-defined curves that 

merge at high levels of thermal maturity. The consistently 

low hydrogen and oxygen indices (<70 mg/g of rock and 

<6 mg/g of rock) that characterize the Tuscher and Farrer Formations signify that potential source rocks contain type III (humic rich) kerogen that has attained a high 

level of thermal maturity. The level of thermal alteration

estimated from the production indices (as high as 0.40) 

and from pyrolysis temperatures (Tmax >452 °C) suggests that the interbedded organic-rich mudstone and 

shales have reached the main stage of gas generation. 

Genetic potential, a qualitative estimate of hydrocarbon resource potential, ranges from 0.74 to 2.61 mg/g; 

values greater than 2 mg/g suggest good liquid hydrocarbon potential. Source beds in the Tuscher and Farrer are

D18 Evolution of Sedimentary Basins Uinta and Piceance Basins
Table 4. Geochemical and Rock-Eval pyrolysis data for potential source rocks in the undifferentiated Tuscher and Farrer Formations, Wilkin Ridge well 

[Asterisk (*), sample from upper unit]

Depth 

(meters)

*3, 134.0

*3, 143.1

3,409.5

3,410.4

3,414.1

3,416.5

3,420.3

Depth

(meters)

*3, 134.0

*3, 143.1

3,409.5

3,410.4

3,414.1

3,416.5

3,420.3

Depth 

(feet)

10,282.0

10,312.0

11,186.0

11,189.0

11,201.0

11,209.0

11,221.5

Depth

(feet)

10,282.0

10,312.0

11,186.0

11,189.0

11,201.0

11,209.0

11,221.5

Total 

organic 

carbon 

TOC 

(percent)

1.35

1.76

2.02

1.10

2.35

2.34

1.43

Free

hydrocarbon

5,

(mg/g)

0.20

.55

.65

.67

.99

1.00

.39

Extractable 

organic 

matter 

£OM 

(ppm)

238

569

386

484

760

831

360

Pyrolyzable

hydrocarbon

S2

(mg/g)

0.55

1.01

1.03

.37

1.54

1.65

.59

Saturated 

hydrocarbons 

SATS 

(ppm)

53

186

171

309

413

507

105

Organic

C02

53

(mg/g)

0.18

.17

.16

.51

.15

.15

.19

Aromatic 

hydrocarbons 

AROMS 

(ppm)

101

261

123

94

188

195

153

Genetic

potential

S, + S2

(mg/g)

0.74

1.56

1.68

1.04

2.54

2.61

.98

SATS/ 

AROMS

0.52

.71

1.33

3.29

2.20

2.60

.69

Production

index

5^1(5^+ 5 2)

0.27

.35

.39

.64

.39

.37

.39

Asphaltines 

and polar 

organic 

compounds 

(ppm)

84

122

92

81

159

129

102

Hydrogen

index

S2/TOC

(mg/g of rock)

40

57

51

34

66

70

42

Extractable 

hydrocarbons 

SATS+ AROMS 

(ppm)

154

447

294

403

601

702

258

Oxygen

index

S3/TOC

(mg/g of rock)

13

9

8

46

6

6

13

Extractable 

hydrocarbons 

HC/fOC 

(mg/g of rock)

11

25

15

37

26

30

18

Maximum

temperature

Tmax

<"Q

461

452

468

476

474

463

470

DEFINITIONS

Genetic potential (S + S)

Quantity of organic matter existing as free or adsorbed hydrocarbons

Quantity of hydrocarbons and hydrocarbonlike compounds released from the sample at pyrolytic temperatures (250-550 °C)

Quantity of CO2 released at pyrolytic temperatures (>250-390 ^C)

Sum of original genetic potential and residual genetic potential. A minimum value for oil source rocks is considered to be 2 mg/g

Production index (Sj/(Sj + S2)) Transformation ratio or index of maturation. With respect to hydrocarbon generation, the transition from immature to mature occurs 

at about 0.1

Hydrogen index (S2/TOC) Quantity of hydrocarbons (measured as S2) in the sample relative to organic carbon content 

Oxygen index (S^/TOC) Quantity of CO2 (measured as S3) in the sample relative to organic carbon content

Tmax Temperature at maximum hydrocarbon generation during pyrolysis (S2) and an indicator of prior thermal history. The transition 

from immature to mature occurs at about 440 °C

composed predominantly of nonmarine, terrestrially 

derived organic matter that contains condensed polyaromatic and oxygen-rich structures, and, as a result, 

most hydrocarbons generated in these units will be gas. 

Hydrocarbons in the lower unit (11,186 and 11,209 ft; 

3,049.5-3,416.5 m) display a shift to higher saturate to 

aromatic ratios (SATS/AROMS>\\ table 4) and pristane 

to phytane ratios (>4, table 5). This suggests either a 

possible source change or staining by migrated hydrocarbons. The higher ratios, as well as the relatively constant 

hydrogen indices for both the upper and lower units and 

the high production index for the sample at 11,189 ft

(3,410.4 m), collectively suggest the rocks have been 

stained to differing degrees by migrated hydrocarbons. 

Vitrinite reflectance values (R0) for coaly samples 

from the Wilkin Ridge well vary widely: R0 values for 

the lower unit at depths of about 11,000 ft (3,353 m) range 

from 0.88 to 1.32 percent, whereas R0 values for the upper unit at burial depths of about 10,000 ft (3,048 m) 

range from 0.73 to 0.75 percent (table 5). These reflectance values are significantly higher than those reported 

by Pitman, Anders, and others (1986) and Pitman and 

others (1987) for the Neslen, Tuscher, and Farrer Formations at shallower burial depths in the eastern part of

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D19
Table 5. Vitrinite reflectance and gas chromatography 

analyses of potential source rocks in the undifferentiated 

Tuscher and Farrer Formations, Wilkin Ridge well 

[Asterisk (*), weathered sample; N.S., no sample]

Depth

(meters)

3,134.0

3,143.1

*3,407.7

3,409.5

3,410.4

*3,414.1

3,416.5

3,420.2

3,422.6

Depth

(feet)

10,282.0

10,312.0

11,180.0

11,186.0

11,189.0

11,201.0

11,209.0

11,221.5

11,229.0

Vitrinite

reflectance

(R0, in pet.)

0.73

.75

1.22

.97

1.32

.93

.95

.95

.88

Pristane/

phytane

ratio

2.1

2.9

N.S.

4.2

4.4

4.5

4.4

2.9

N.S.

nC17

pristane

ratio

3.6

3.4

N.S.

1.8

1.7

1.3

2.1

2.1

N.S.

the basin. The reliability of these values is uncertain 

because of their extreme variability. The unusually high 

values may reflect either a component of altered vitrinite 

or possibly vitrinite reworked from older rock because 

there is no direct evidence to support either a late-stage 

heating event or migration of high-temperature fluids in 

the area of the well. Some values also may be lower than 

their true reflectance because of suppression effects 

resulting from abnormally high formation pressures 

(C.W. Spencer, oral commun., 1986). Despite variations 

in individual reflectance values, it is evident that the thermal maturity of these Cretaceous source rocks increases 

with depth of burial. In the more deeply buried Tuscher 

and Farrer rocks, gas-prone source rocks are well within 

the catagenesis zone of hydrocarbon generation, and these 

rocks probably have produced significant amounts of 

thermal gas.

BURIAL AND THERMAL HISTORY

The hydrocarbon generation history of the undifferentiated Tuscher and Farrer Formations was evaluated 

by using Lopatin-style burial reconstruction, a method 

in which both time and temperature are taken into account to model sediment-burial and thermal history 

through geologic time. The depositional and tectonic 

history of Cretaceous rocks in the vicinity of the Wilkin 

Ridge well is shown by the Lopatin reconstruction of 

burial depth and temperature as a function of time for 

the Tuscher and Farrer Formations (fig. 13). The data 

used to construct the model (table 6) are from Larson 

and others (1975), Fouch and others (1983), and Hansen 

(1984). The burial history model assumes a uniform

Isx tcV) o

750

600

450

i 300

x o

UJ a;

O HI

Z 0-

Z

LLJ

§ 150 

oc

Q

II

EXPLANATION 

Tuscher-Farrer Formations

o Upper unit 

 Lower unit

OIL PRONE

GAS PRONE

III

50 100 150 200

OXYGEN INDEX, IN MILLIGRAMS CO, 

PER GRAM ORGANIC CARBON

Figure 12. Modified van Krevelen diagram showing hydrogen 

and oxygen indices for humic-rich source rocks in the undifferentiated Tuscher and Farrer Formations, Wilkin Ridge well. 

Roman numerals indicate kerogen types I, II, and III.

sedimentation rate and a constant geothermal gradient 

with depth. The present-day geothermal gradient in the 

vicinity of the Wilkin Ridge well is estimated to be the 

same as the gradient in the Natural Buttes area, that is, 

1.6 °F/100 ft (29 °C/km) (Chapman and others, 1984). 

This gradient is similar to gradients calculated from drillstem test results for wells near the Wilkin Ridge well (D.E. 

Anders, unpub. data, 1986) and is within the range 

reported for sedimentary basins in the Rocky Mountain 

region. The paleogeothermal gradient in the model is considered to be the same as the present-day gradient; any 

differences probably amount to no more than a few 

degrees.

Waples (1980) demonstrated that the timetemperature index (TTf), the length of time sediment has 

been exposed to a specific paleotemperature interval, can 

be used as a maturation indicator in a Lopatin model 

because it correlates well with other commonly used 

parameters such as vitrinite reflectance. In our study, 

vitrinite reflectance, as inferred from TTI for the top of 

the Neslen, was systematically compared with measured 

reflectance values for the same unit in order to constrain 

the timing and magnitude of tectonic and associated 

erosional events and the variations in the geothermal 

gradient through time. Based on TTI, the best-fit timetemperature model (fig. 13) indicates that sedimentary

D20 Evolution of Sedimentary Basins Uinta and Piceance Basins
100

AGE, IN MILLIONS OF YEARS 

60 40

Undifferentiated Duchesne River, 

Uinta, and Green River Formations

Undifferentiated Colton, Flagstaff,

and North Horn Formations

TTI 20

Geothermal gradient 29 °C/km 

(1.6 °F/100ft)________

Undifferentiated Tuscher 

and Farrer Formations

0.70% RQ(C) 

0.74% RQ(C)

XO.74% Ro(m)

0.97% RO(C) 

X1.03% Ro(m) 

1.06% R0 (c)

Late Cretaceous Paleocene Eocene Oligocene Miocene Pliocene/Pleistocene

Figure 13. Modified time-temperature Lopatin diagram showing reconstructed burial and thermal history for Cretaceous and 

Tertiary rocks in the area of the Wilkin Ridge well. Isotherms reflect past and present geothermal gradients; wavy line represents 

Cretaceous-Tertiary boundary. Hachured area, zone of active hydrocarbon generation (Ro X).07 percent; C, calculated R0 value; 

m, measured Rn value.

burial through tectonic subsidence controlled the maturation of organic matter in Cretaceous rocks in the central 

part of the Uinta basin. Moreover, fluctuations in the 

geothermal gradient do not appear to be an important 

influence governing the maturation of hydrocarbons.

Regional studies in the Uinta basin indicate that 

relatively continuous sedimentation in marine and continental depositional environments during the Cretaceous 

was followed by a complex depositional history during 

the Cenozoic. A change in deformation style from Sevier 

thrusting to Laramide basement-controlled deformation, 

beginning in the Late Cretaceous and continuing through 

the Paleogene (Fouch and others, 1983; Lawton, 1983), 

was accompanied by rapid sedimentation throughout the 

basin as it tectonically subsided. By the middle Oligocene, 

the Tuscher and Farrer Formations had attained their 

maximum burial depth following deposition of more than 

9,000 feet (2,743 m) of Tertiary sediments. Between the 

early Oligocene and the present, the depositional and tectonic history is uncertain because rocks that span this time 

period are not preserved in the basin. From the late

Miocene (about 10 Ma) to the present, regional uplift and 

erosion associated with the development of the Colorado 

Plateau were widespread through the Rocky Mountain 

region (Larson and others, 1975; Hansen, 1984). During 

the early Oligocene, post-Laramide uplift and erosion 

associated with the development of the Gilbert Peak erosion surface may have extended southward into the central part of the Uinta basin (W.R. Hansen, oral commun., 

1986). If this was the case, erosion during this period 

probably was minor in comparison with erosion during 

plateau uplift and did not affect the hydrocarbon generation history.

Based on a present-day temperature gradient of 

1.6 °F/100 ft (29 °C/km), the Lopatin model (fig. 13) 

indicates that about 1,000 feet (305 m) of Tertiary strata 

may have been eroded from the area of the Wilkin Ridge 

well from the late Miocene to the present. In the Indian 

Canyon area, about 30 miles northwest of the well, a 

minimum of 2,000 ft (610 m) of upper Eocene lacustrine 

deposits lies stratigraphically above the present erosion 

surface in the Wilkin Ridge area (Ray and others, 1956);

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah D21
Table 6. Parameters used to reconstruct the burial and tectonic history in the area of the 

Wilkin Ridge well

[N.A., not applicable; query (?), date uncertain. Data from Larson and others (1975), Fouch and others 

(1983), and Hansen (1984)]

Depositional or tectonic event

Formation

Time boundaries 

(Ma) (depth, in ft)

Cumulative

Thickness thickness 

(feet) (feet)

Colorado Plateau uplift and erosion ... 0 

Depositional hiatus .................. 10

Undifferentiated Duchesne River, 

Uinta, and Green River 

Formations .................

Colton, Flagstaff, and North Horn 

Formations ...................

Cretaceous-Tertiary boundary 

erosion ..................

32

47

58

0- 5,090

N.A.

0- 5,090

5,090- 9,555

9,555

Undifferentiated Tuscher and 

Farrer Formations. 

Upper part ..................... 72 9,555-11,090

Lower part ..................... 74? 11,090-11,542

Bluecastle Tongue of the 

Castlegate Sandstone .............. 75 11,542-12,140

-800 

0

5,890

4,465

-1,500

2,735

452

598

11,242

12,042

12,042

6,152

1,687

3,187

452

N.A.

an equally thick lacustrine and alluvial sequence should 

have been deposited contemporaneously in the Wilkin 

Ridge area. If a geothermal gradient of 1.4 °F/100 ft 

(27 °C/km) is used in the Lopatin model instead of 

1.6 °F/100 ft (29 °C/km), then 2,000 ft (610 m) of erosion is compatible with measured vitrinite values. There 

is no evidence to suggest that the paleogeothermal gradient was lower than the present gradient, thus it is possible that the few measured vitrinite values we could obtain 

for this study do not accurately reflect the thermal 

history. Additional vitrinite data throughout the entire 

section would resolve this uncertainty and support more 

confident estimates of the paleogeothermal gradient.

It is evident from the burial history model that 

potential source rocks in the Tuscher and Farrer Formations in the area of Wilkin Ridge were immature until 

they reached maximum burial depths during the early 

Oligocene, at which time they attained their present thermal maturity. Although the duration of maximum burial 

for these Cretaceous rocks was brief, about 20 million 

years, hydrocarbon generation was most active during this 

period. If significant hydrocarbon generation is assumed 

to begin at a vitrinite reflectance of about 0.7 percent (777 

20; Waples, 1980), then active hydrocarbon generation 

in potential source beds in the Tuscher and Farrer

Formations occurred between approximately 10 and 30 

Ma when the rocks were close to maximum burial (about 

10,500-12,000 ft, 3,200-3,658 m). Based on the Lopatin 

time-temperature model, paleotemperatures during maximum burial of the Tuscher and Farrer Formations are 

estimated to have been as high as 248 °F (120 °C); 

however, the time-independent relationship of Barker and 

Pawlewicz (1986) indicates that maximum paleotemperatures for the Tuscher and Farrer exceeded 300 °F 

(150 °C). These temperatures seem unlikely, inasmuch 

as they require a much higher paleogeothermal gradient 

and one inconsistent with the reconstructed burial history 

of the central part of the basin. The rate of hydrocarbon 

generation in the Tuscher and Farrer Formations may 

have declined from 10 Ma to the present because of the 

removal of overburden during Colorado Plateau uplift. 

TTI calculations indicate that a vitrinite reflectance level 

of about 0.70 percent (7T/20) projects to a present-day 

burial depth of about 9,000 ft (2,743 m), a depth that 

closely approximates the depth of the Cretaceous-Tertiary 

boundary. Thus, the Tuscher and Farrer rocks as well 

as older rocks are still undergoing hydrocarbon generation assuming they contain sufficient quantities of organic 

matter.

Spencer (1987) and Law (1984) have suggested that

D22 Evolution of Sedimentary Basins Uinta and Piceance Basins
generation of hydrocarbons in low-permeability reservoir 

rocks in the Rocky Mountain region contributed to the 

development of high formation pressures. Indirect 

pressure data for the Wilkin Ridge well (bottom-hole 

temperatures and mud weights) indicate that the lower 

cored sequence in the undifferentiated Tuscher and Farrer Formations currently is overpressured. Such an overpressured system may have created some of the local 

occurrences of closed hairline fractures in sandstones and 

shale beds in both the lower and upper units; similar fractures have been reported in rocks of similar age and origin 

from other parts of the basin (Pitman, Anders, and 

others, 1986; Pitman and others, 1987). It is also plausible that abnormally high pressures existed in younger 

rocks when they were at maximum burial and undergoing active hydrocarbon generation. As a result of uplift 

and erosion during the late Tertiary, these higher 

pressures may have dissipated to form the lower pressure 

regime that now characterizes the basin.

REFERENCES CITED

Barker, C.E., and Pawlewicz, M.J., 1986, The correlation of 

vitrinite reflectance with maximum temperature in humic 

organic matter, in Buntebarth, Gunter, and Stegena, L., 

eds., Lecture notes in earth sciences, v. 5; paleogeothermics: New York, Springer-Verlag, p. 79-93.

Chapman, D.S., Keho, T.H., Bauer, M.S., and Picard, M.D., 

1984, Heat flow in the Uinta Basin determined from bottom hole temperature (BHT) data: Geophysics, v. 49, 

p. 453-466.

Dickinson, W.R., Lawton, T.F., and Inman, K.F., 1986, Sandstone detrital modes, central Utah foreland region; 

stratigraphic record of Cretaceous-Paleogene tectonic 

evolution: Journal of Sedimentary Petrology, v. 56, 

p. 276-293.

Fisher, D.J., Erdmann, C.E., and Reeside, J.B., Jr., 1960, 

Cretaceous and Tertiary formations of the Book Cliffs, 

Carbon, Emery, and Grand Counties, Utah, and Garfield 

and Mesa Counties, Colorado: U.S. Geological Survey Professional Paper 332, 80 p.

Folk, R.L., 1974, Petrology of sedimentary rocks: Austin, 

Texas, Hemphill's, 182 p.

Fouch, T.D., Lawton, T.F., Nichols, D.J., Cashion, W.B., and 

Cobban, W.A., 1983, Patterns and timing of synorogenic 

sedimentation in Upper Cretaceous rocks of central and 

northeast Utah, in Reynolds, M.W., and Dolly, E.D., eds., 

Mesozoic paleogeography of the west-central United States: 

Society of Economic Paleontologists and Mineralogists, 

Rocky Mountain Section, Rocky Mountain Paleogeography Symposium, 2nd, Denver, 1983, p. 305-336.

Gross, M.G., 1964, Variations in the O18/O16 and C13 /C12 

ratios of diagenetically altered limestones in the Bermuda 

Islands: Journal of Geology, v. 72, no. 2, p. 170-194.

Hansen, W.R., 1984, Post-Laramide tectonic history of the 

eastern Uinta Mountains, Utah, Colorado, and Wyoming: 

The Mountain Geologist, v. 21, no. 1, p. 5-29.

Keighin, C.W., and Fouch, T.D., 1981, Depositional environments and diagenesis of some nonmarine Upper 

Cretaceous reservoir rocks, Uinta basin, Utah, in Ethridge, 

F.G., and Flores, R.M., eds., Recent and ancient nonmarine depositional environments; models for exploration: 

Society of Economic Paleontologists and Mineralogists 

Special Publication 31, p. 109-125.

Larson, E.E., Osima, M., and Bradley, W.C., 1975, Late 

Cenozoic basic volcanism in northwestern Colorado and 

its implications concerning tectonism and the origin of the 

Colorado River system, in Curtis, B.F., ed., Cenozoic 

history of the southern Rocky Mountains: Geological 

Society of America Memoir 144, p. 155-178.

Law, B.E., 1984, Relationships of source-rock, thermal maturity, and overpressuring to gas generation and occurrence 

in low-permeability Upper Cretaceous and lower Tertiary 

rocks, greater Green River basin, Wyoming, Colorado and 

Utah, in Woodward, Jane, Meissner, F.F., and Clayton, 

J.L., eds., Symposium on hydrocarbon source rocks of the 

greater Rocky Mountain region: Rocky Mountain Association of Geologists Symposium, Denver, 1984, p. 469-490.

Lawton, T.F., 1983, Late Cretaceous fluvial systems and the 

age of foreland uplifts in central Utah, in Lowell, J.D 

and Gries, Robbie, eds., Rocky Mountain foreland basins 

and uplifts: Rocky Mountain Association of Geologists 

Field Conference, Steamboat Springs, Colorado, 1983, 

p. 181-199.

Mclver, R.D., 1967, Composition of kerogen-clue to its role 

in the origin of petroleum, in Origin of oil, geology, and 

geophysics: World Petroleum Congress, 7th, Mexico, 1967, 

Proceedings, v. 2: London, Elsevier, p. 25-36.

Osterwald, F.W., Maberry, J.O., and Dunrud, C.R., 1974, 

Bedrock, surficial and economic geology of the Sunnyside 

coal mining district, Carbon and Emery Counties, Utah: 

U.S. Geological Survey Professional Paper 1166, 68 p.

Pitman, J.K., Anders, D.E., Fouch, T.D., and Nichols, D.J., 

1986, Hydrocarbon potential of nonmarine Upper 

Cretaceous and lower Tertiary rocks, eastern Uinta basin, 

Utah, in Spencer, C.W., and Mast, R.F., eds., Geology 

of tight gas reservoirs: American Association of Petroleum 

Geologists Studies in Geology 24, p. 235-252.

Pitman, J.K., Franczyk, K.J., and Anders, D.E., 1987, Marine 

and nonmarine gas-bearing rocks in the Upper Cretaceous 

Blackhawk and Neslen Formations, eastern Uinta basin, 

Utah; sedimentology, diagenesis, and source-rock potential: American Association of Petroleum Geologists 

Bulletin, v. 71, no. 1, p. 76-94.

Pitman, J.K., Goldhaber, M.B., and Fouch, T.D., 1986, 

Mineralogy and stable isotope geochemistry of carbonate 

and sulfate minerals in diagenetically altered Tertiary and 

Cretaceous sandstones, Uinta basin, Utah, in Mumpton, 

F.A., ed., Studies in diagenesis: U.S. Geological Survey 

Bulletin 1578, p. 207-218.

Pittman, E.D., and Lumsden, D.N., 1968, Relationship between 

chlorite coatings on quartz grains and porosity, Spiro Sand, 

Oklahoma: Journal of Sedimentary Petrology, v. 38, 

p. 668-670.

Price, L.C., 1983, Geologic time as a parameter in organic 

metamorphism and vitrinite reflectance as an absolute 

paleogeothermometer: Journal of Petroleum Geology, v. 

6, p. 5-38.

Nonmarine Upper Cretaceous Rocks, Central Uinta Basin, Utah O23
Ray, R.G., Kent, B.H., and Dane, C.H., 1956, Stratigraphy 

and photogeology of the southwestern part of Uinta basin, 

Duchesne and Uintah Counties, Utah: U.S. Geological 

Survey Oil and Gas Investigations Map OM-171, 2 sheets, 

scale 1:63,360.

Siebert, R. M., 1984, A theory of framework grain dissolution 

in sandstones, in McDonald, D.A., and Surdam, R.C., 

eds., Clastic diagenesis: American Association of 

Petroleum Geologists Memoir 37, p. 163-175.

Spencer, C.W., 1987, Hydrocarbon generation as a mechanism 

for overpressuring in the Rocky Mountain region: 

American Association of Petroleum Geologists Bulletin, 

v. 71, no. 4, p. 368-388.

Tissot, B.P., and Welte, D.H., 1978, Petroleum formation and 

occurrence; a new approach to oil and gas exploration: New 

York, Springer-Verlag, 538 p.

Waples, D.W., 1980, Time and temperature in petroleum formation; application of Lopatin's method to petroleum exploration: American Association of Petroleum Geologists 

Bulletin, v. 64, no. 6, p. 916-926.

Weber, J.N., 1964, Trace element composition of dolostones 

and dolomites and its bearing on the dolomite problem: 

Geochimica et Cosmochimica Acta, v. 28, no. 11, 

p. 1817-1868.

D24 Evolution of Sedimentary Basins Uinta and Piceance Basins

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