Burial and Thermal History of the Paradox Basin,

Utah and Colorado, and Petroleum Potential of the

Middle Pennsylvanian Paradox Formation

By Vito F. Nuccio and Steven M. Condon

EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

A.C. Huffman, Jr., Project Coordinator

U.S. GEOLOGICAL SURVEY BULLETIN 2000–O

A multidisciplinary approach to research studies of

sedimentary rocks and their constituents and the 

evolution of sedimentary basins, both ancient and modern

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1996
For sale by U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and

does not imply endorsement by the U.S. Government

Library of Congress Cataloging-in-Publication Data

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

Nuccio, Vito F.

Burial and thermal history of the Paradox Basin, Utah and Colorado, and petroleum 

potential of the Middle Pennsylvanian Paradox Formation / by Vito F. Nuccio and Steven 

M. Condon.

p. cm. — (Evolution of sedimentary basins—Paradox Basin ; O)

(U.S. Geological Survey bulletin ; 2000)

Includes bibliographical references.

Supt. of Docs. no.: I19.3: 2000–O

1. Geology, Stratigraphic—Pennsylvanian. 2. Geology—Utah.

3. Geology—Colorado. 4. Petroleum—Geology—Utah.

5. Petroleum—Geology—Colorado. 6. Paradox Formation. I. Condon, Steven M.

II. Title. III. Series. IV. Series: Evolution of sedimentary basins—Paradox Basin ; 

ch. O.

QE75.B9 no. 2000-O

[QE673]

557.3 s—dc20

[553.2′8′09792] 96–5831

CIP
III

CONTENTS

Abstract........................................................................................................................... O1

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

Geographic and Structural Setting.................................................................................. 2

Stratigraphy .................................................................................................................... 5

Sub-Pennsylvanian Rocks ...................................................................................... 5

Pennsylvanian and Permian Rocks......................................................................... 8

Triassic and Jurassic Rocks .................................................................................... 10

Cretaceous and Tertiary Rocks............................................................................... 12

Methods .......................................................................................................................... 13

Kerogen Types and Related Hydrocarbons .................................................................... 18

Source Rock Potential of the Ismay–Desert Creek Interval and Cane Creek Cycle ...... 22

Thermal Maturity Trends................................................................................................ 23

Ismay–Desert Creek Interval .................................................................................. 24

Cane Creek Cycle ................................................................................................... 27

Burial, Thermal, and Petroleum-Generation Models ..................................................... 28

Monument Upwarp................................................................................................. 28

Confluence of the Green and Colorado Rivers....................................................... 30

Green River, Utah................................................................................................... 31

Moab, Utah ............................................................................................................. 33

Lisbon Valley Area, Utah....................................................................................... 34

Hermosa, Colorado................................................................................................. 35

Discussion and Summary ............................................................................................... 37

References Cited............................................................................................................. 39

PLATES

1. Map showing oil and gas wells producing from the Honaker Trail Formation through cycle 9 in the Pennsylvanian 

Paradox Formation with respect to thermal maturity at the Ismay–Desert Creek interval

2. Map showing oil and gas wells producing from cycle 10 in the Pennsylvanian Paradox Formation through the

Cambrian Lynch Dolomite with respect to thermal maturity at the Cane Creek cycle

FIGURES

1. Location map of the Paradox Basin....................................................................................................................... O3

2. Map showing structural elements of the Paradox Basin and adjacent areas ......................................................... 4

3. Correlation chart of the Paradox Basin and vicinity ............................................................................................. 6

4. Isopach map of sub-Pennsylvanian stratigraphic units in the Paradox Basin ....................................................... 7

5. Isopach map of Pennsylvanian and Permian stratigraphic units in the Paradox Basin ......................................... 8

6. Isopach map of Triassic and Jurassic stratigraphic units in the Paradox Basin..................................................... 10

7. Graph showing comparison of production index and vitrinite reflectance for samples from the

Ismay–Desert Creek interval and Cane Creek cycle ............................................................................................. 18

8. Modified van Krevelen diagram of the Ismay–Desert Creek interval ................................................................... 22

9. Modified van Krevelen diagram of the Cane Creek cycle..................................................................................... 23

10. Thermal maturity map of the Ismay–Desert Creek interval.................................................................................. 24

11. Thermal maturity map of the Cane Creek cycle.................................................................................................... 25
IV CONTENTS

12–17. Burial, thermal, and petroleum-generation model of:

12. Monument upwarp area................................................................................................................................. 26

13. Area near the confluence of the Green and Colorado Rivers........................................................................ 28

14. Green River, Utah, area................................................................................................................................. 30

15. Moab, Utah, area........................................................................................................................................... 32

16. Lisbon Valley, Utah, area .............................................................................................................................. 34

17. Hermosa, Colorado, area............................................................................................................................... 36

TABLES

1. Rock-Eval pyrolysis data for samples in the Paradox Basin..................................................................................O14

2. Vitrinite reflectance data for samples in the Paradox Basin................................................................................... 17

3. Data used to reconstruct the burial curves for six areas studied in the Paradox Basin .......................................... 19

4. Heat flow and timing of petroleum generation for the six areas studied ............................................................... 38
O1

BURIAL AND THERMAL HISTORY OF THE PARADOX BASIN, 

UTAH AND COLORADO, AND PETROLEUM POTENTIAL OF THE

MIDDLE PENNSYLVANIAN PARADOX FORMATION

By Vito F. Nuccio and Steven M. Condon

ABSTRACT

The Ismay–Desert Creek interval and Cane Creek cycle

of the Alkali Gulch interval of the Middle Pennsylvanian Paradox Formation in the Paradox Basin of Utah and Colorado

contain excellent organic-rich source rocks having total

organic carbon contents ranging from 0.5 to 11.0 percent. The

source rocks in both intervals contain types I, II, and III

organic matter and are potential source rocks for both oil and

gas. Organic matter in the Ismay–Desert Creek interval and

Cane Creek cycle of the Alkali Gulch interval (hereinafter

referred to in this report as the “Cane Creek cycle”) probably

is more terrestrial in origin in the eastern part of the basin and

is interpreted to have contributed to some of the gas produced

there.

Thermal maturity increases from southwest to northeast

for both the Ismay–Desert Creek interval and Cane Creek

cycle, following structural and burial trends throughout the

basin. In the northernmost part of the basin, the combination

of a relatively thick Tertiary sedimentary sequence and high

basinal heat flow has produced very high thermal maturities.

Although general thermal maturity trends are similar for both

the Ismay–Desert Creek interval and Cane Creek cycle,

actual maturity levels are higher for the Cane Creek due to the

additional thickness (as much as several thousand feet) of

Middle Pennsylvanian section.

Throughout most of the basin, the Ismay–Desert Creek

interval is mature and in the petroleum-generation window

(0.10 to 0.50 production index (PI)), and both oil and gas are

produced; in the south-central to southwestern part of the

basin, however, the interval is marginally mature (<0.10 PI)

for petroleum generation, and mainly oil is produced. In contrast, the more mature Cane Creek cycle contains no marginally immature areas—it is mature (>0.10 PI) in the central

part of the basin and is overmature (past the petroleum-generation window (>0.50 PI)) throughout most of the eastern

part of the basin. The Cane Creek cycle generally produces

oil and associated gas throughout the western and central

parts of the basin and thermogenic gas in the eastern part of

the basin.

Burial and thermal-history models were constructed for

six different areas of the Paradox Basin. In the Monument

upwarp area, the least mature part of the basin, the

Ismay–Desert Creek interval and Cane Creek cycle have thermal maturities of 0.10 and 0.20 PI and were buried to 13,400

ft and 14,300 ft, respectively. A constant heat flow through

time of 40 mWm–2 (milliwatts per square meter) is postulated

for this area. Significant petroleum generation began at 45

Ma for the Ismay–Desert Creek interval and at 69 Ma for the

Cane Creek cycle.

In the area around the confluence of the Green and Colorado Rivers, the Ismay–Desert Creek interval and Cane

Creek cycle have thermal maturities of 0.20 and 0.25 PI and

were buried to 13,000 ft and 14,200 ft, respectively. A constant heat flow through time of 42 mWm–2 is postulated for

this area. Significant petroleum generation began at 60 Ma

for the Ismay–Desert Creek interval and at 75 Ma for the

Cane Creek cycle.

In the area around the town of Green River, Utah, the

Ismay–Desert Creek interval and Cane Creek cycle have thermal maturities of 0.60 and greater and were buried to 14,000

ft and 15,400 ft, respectively. A constant heat flow through

time of 53 mWm–2 is proposed for this area. Significant

petroleum generation began at 82 Ma for the Ismay–Desert

Creek interval and at 85 Ma for the Cane Creek cycle.

Around Moab, Utah, in the deeper, eastern part of the

basin, the Ismay–Desert Creek interval and Cane Creek cycle

have thermal maturities of 0.30 and around 0.35 PI and were

buried to 18,250 ft and 22,000 ft, respectively. A constant

heat flow through time of 40 mWm–2 is postulated for this

area. Significant petroleum generation began at 79 Ma for the

Ismay–Desert Creek interval and at 90 Ma for the Cane Creek

cycle.

At Lisbon Valley, also in the structurally deeper part of

the basin, the Ismay–Desert Creek interval and Cane Creek

cycle have thermal maturities of 0.30 and greater than 0.60 PI

and were buried to 15,750 ft and 21,500 ft, respectively. A

constant heat flow through time of 44 mWm–2 is postulated

for this area. Significant petroleum generation began at 79

Ma for the Ismay–Desert Creek interval and at 100 Ma for the

Cane Creek cycle.
O2 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

The area around Hermosa, Colo., in the southeastern

part of the basin, has experienced a shallower burial history

than the other areas in the basin, yet it has one of the highest

thermal maturities. Here, the Ismay–Desert Creek interval

and Cane Creek cycle have vitrinite reflectance values of

1.58 and 1.63 percent and were buried to 13,700 ft and

15,500 ft, respectively. Due to Tertiary igneous activity in

this part of the basin, a variable heat flow is proposed: from

600 to 30 Ma, 45 mWm–2; from 30 to 25 Ma, 63 mWm–2;

and from 25 Ma to present, 50 mWm–2. Significant petroleum generation began at 72 Ma for the Ismay–Desert Creek

interval and at 76 Ma for the Cane Creek cycle.

INTRODUCTION

During Pennsylvanian time, the Paradox Basin of Utah

and Colorado was a rapidly subsiding northwest-trending

trough that was filled with sequences of organic-rich shale,

limestone, dolomite, anhydrite, halite, and siliciclastic

deposits. Although only a minor percentage of the stratigraphic section in the Paradox Basin comprises dark-colored,

organic-rich shale, the shales are of great importance due to

their petroleum-generation potential. The term “shale” is

somewhat misleading because these beds consist of more

than 30 percent carbonate, 20–30 percent fine-grained

quartz, and 40–50 percent clay and kerogen (Montgomery,

1992). Total organic carbon (TOC) values for these black

shales of from less than 0.5 percent to more than 11.0 percent

make them excellent petroleum source rocks. The black

shales were deposited during transgressive phases in basin

development and have produced in excess of 400 million barrels of oil and 1 trillion cubic feet (TCF) of gas (Baars and

Stevenson, 1982; Hite and others, 1984). Generally, petroleum accumulations are stratigraphic traps in (1) carbonate

rocks that are interbedded with the shales and (2) older (Mississippian) carbonates that are in fault contact with the

shales. Recently, fractured, organic-rich shales, such as in the

Cane Creek cycle of the Paradox Formation, have become an

attractive petroleum play in the basin.

In this study we address three critical, interrelated factors that have controlled the generation, distribution, and

accumulation of petroleum from the Paradox Formation in

the Paradox Basin: (1) structural and burial history of the

basin, (2) regional thermal-maturity trends, and (3) quality

and distribution of source rocks throughout the basin. The

burial history of stratigraphic units was determined by the

structural evolution of the basin, and thermal maturity trends

closely follow burial trends. Similarly, the petroleum-generation history of source rocks in the Paradox Formation is

directly related to both the burial and thermal regimes

throughout the basin.

The structural and burial history of the Paradox Basin is

illustrated using a series of isopach maps for Cambrian

through Jurassic rocks. Geohistory curves illustrate the burial

history for the entire stratigraphic section (Cambrian through

Tertiary) for six different locations in the basin. The variation

in the thermal history of the basin is illustrated using maturity

maps (constructed using production index (PI) and vitrinite

reflectance (Ro) values) on two stratigraphic and potential

source-rock intervals, the Ismay–Desert Creek interval and

the Cane Creek cycle of the Paradox Formation. The type,

quantity, and quality of organic matter in these two source

rocks are presented, and the petroleum potential is discussed.

Finally, using models that incorporate hydrocarbon-generation kinetics, we demonstrate that the timing of petroleum

generation, accumulation, and destruction within the Paradox Formation has been a function of the source rock and the

structural, burial, and thermal history of the basin.

Acknowledgments.—We thank Charles E. Barker and

Bonnie L. Crysdale for their help in collecting core and cutting samples and for data used for source-rock evaluation.

Ted Daws analyzed hundreds of samples for Rock-Eval

pyrolysis. Additional Rock-Eval pyrolysis data provided by

Michele Tuttle of the U.S. Geological Survey and Mark

Richardson of Exxon Production and Research were very

useful and greatly appreciated. We also acknowledge the

Utah Geological Survey for their interest in the project and

their assistance in identifying wells and providing samples

for us to collect. Critical review by Karen Franczyk and Ben

Law greatly added to the quality of the manuscript. Finally,

we thank Project Chief, Curt Huffman, and all people associated with the Evolution of Sedimentary Basins–Paradox

Basin Project for their helpful discussions and suggestions.

GEOGRAPHIC AND STRUCTURAL 

SETTING

The Paradox Basin (fig. 1) is an oval area in southeastern Utah and southwestern Colorado that is defined by the

maximum extent of salt in the Middle Pennsylvanian Paradox Formation (Hite and others, 1984). Using this definition,

the basin has a maximum northwest-southeast length of

about 190 mi, and a northeast-southwest width of about 95

mi. The basin was primarily a Pennsylvanian and Permian

feature that accumulated thick deposits of carbonate, halite,

and clastics in response to tectonic downwarping and simultaneous uplift along its northeastern border. The shape of the

basin was modified and obscured by later tectonic events,

primarily the Laramide orogeny. Today, the basin has been

dissected in places by uplift of the Colorado Plateau and

downcutting by the Colorado River and its tributaries.

The basin is bordered on the northeast by the

Uncompahgre Plateau, a broad anticline cored by Precambrian rocks (fig. 2). The east side of the basin is bounded by

the San Juan dome, an area that is covered, in part, by Tertiary volcanic rocks. In the Needle Mountains, a prominent

feature of the southern San Juan dome, Precambrian rocks
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O3

are widely exposed. The southeast end of the basin is defined

by the northeast-trending Hogback monocline that extends

southwestward from the Durango, Colo., area through northwestern New Mexico. The southern and southwestern border

of the Paradox Basin is ill-defined topographically and structurally; it extends northwestward from the Four Corners (the

junction of Utah, Colorado, New Mexico, and Arizona) to

the Henry Basin across the Monument upwarp. The northwest side is bounded by the San Rafael Swell, and the far

northern end of the basin merges with the southern side of

the Uinta Basin.

The structure and physical features of the Paradox

Basin within the area defined by the salt (figs. 1, 2) are also

very diverse. The northern part of the basin has been termed

the Paradox fold and fault belt (Kelley, 1958a). This area

consists of a series of roughly parallel, northwest-trending

faults, anticlines, and synclines. The northeastern part of this

area is more complexly folded, with piercement of some

anticlines by salt from the Paradox Formation. Dissolution

of salt along the crests of some anticlines in this region has

caused downfaulting and the development of grabens at the

crests. Rocks as old as Pennsylvanian are exposed in the

0 25 Mi

0 25 Km 

Utah

Arizona

Colorado

New Mexico

39 ̊30'

111 ̊00' 110 ̊30' 110 ̊00' 109 ̊30' 109 ̊00' 108 ̊30' 108 ̊00' 107 ̊30'

Green River

Grand

Junction

Gateway

Naturita

Ouray

Cortez

Blanding 

Moab

Mexican 

Hat

Kayenta

Bluff

Slick Rock

Monticello

San Juan River

Green River

Colorado

River

Colorado River

Durango

Rico

Farmington

Hanksville

Hite

Montrose

Navajo

Reservoir

Lake

Powell

Needle 

Mtns

Uncompahgre

Plateau

San

Rafael Swell

Maximum extent of salt

in Paradox Formation

B ook Cliffs

39 ̊00'

38 ̊30'

38 ̊00

37 ̊30'

37 ̊00'

36 ̊30'

Figure 1. Location map of the Paradox Basin. Large dots indicate areas where burial, thermal, and petroleum-generation histories

were reconstructed.
O4 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

cores of some of the anticlines, and remnants of Cretaceous

rocks are present in some synclines and in collapsed blocks

within the anticlines. The southwestern part of this basin subdivision is also folded and faulted but lacks the complex

piercement structures of the northeastern part.

South of the fold and fault belt are the Blanding Basin

and the Four Corners platform (fig. 2). The Blanding Basin

is a generally undeformed area in which Jurassic and Cretaceous rocks are at the surface. The Four Corners platform is

a structurally high bench that separates the Paradox and San

Juan Basins. The platform has mainly Cretaceous rocks at its

surface.

The southwestern part of the Paradox Basin is dominated by the Monument upwarp. This area consists of deep

canyons and high mesas that provide the setting for part of

Canyonlands National Park, Natural Bridges National Monument, and other recreation areas for which southeast Utah is

famous. The upwarp trends generally north and is a broad

anticline. It is bounded on the east by the steeply dipping

Comb Ridge monocline and merges to the west with the

Figure 2. Map showing structural elements of the Paradox Basin and adjacent areas. Modified from Kelley (1958a, 1958b).

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤ ➤

➤

➤

➤

➤

➤

➤

➤

➤

DEFIANCE 

PLATEAU

Carrizo

Mtns.

SAN JUAN

BASIN

UNCOMPAHGRE PLATEAU

SAN RAFAEL

SWELL

PARADOX

FOLD

FAULT

BELT

AND

UINTA BASIN

TYENDE

SADDLE

BLACK

MESA

BASIN

KAIBITO

SADDLE

PIUTE

FOLDS

Navajo

Mtn

BLANDING WHITE CANYON SlLOPE

BASIN

Henry Mtns.

HENRY

BASIN

CIRCLE CLIFFS

UPLIFF

Abajo

Mtns

➤

La Sal

 Mtns

0 25 Mi

0 25 Km 

Utah

Arizona

Colorado

New Mexico

111 ̊00' 110 ̊30' 110 ̊00' 109 ̊30' 109 ̊00' 108 ̊30' 108 ̊00' 107 ̊30'

Durango

Farmington

Hanksville

Hite

Montrose

Navajo

Reservoir

Lake

Powell

FOUR CORNERS

PLATFORM

Sleeping Ute

Mountain MONUMENT UPWARP

HOGBACK

MONOCLINE

RED ROCK

BENCH

➤ ➤

➤ ➤➤ ➤

➤ ➤

➤ ➤

➤ ➤ ➤ ➤

➤ ➤

➤ ➤

➤ ➤

➤ ➤

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➤ ➤

➤ ➤

➤ ➤

➤ ➤

➤ ➤

➤ ➤

➤ ➤

➤ ➤

➤ ➤

➤ ➤ COM B

RIDGE MONOCL NI E

San 

Miguel

Mtns

La Plata

Mtns

Green 

River

Grand

Junction

Gateway

Naturita

Ouray

Cortez

Blanding 

Moab

Bluff

Slick 

Rock

Monticello

San Juan River

Green River

Colorado

River

Mexican 

Hat

Kayenta

Colorado River

Rico

SAN JUAN DOME

Rico

Mtns

Needle 

Mtns

OILETO

SAG

39 ̊30'

39 ̊00'

38 ̊30'

38 ̊00'

37 ̊30'

37 ̊00'

36 ̊30'

LISBON VALLEY

ANTICLINE
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O5

Henry Basin across the White Canyon slope. A northeast-trending anticline along the Colorado River extends

beyond the Monument upwarp into the fold and fault belt.

Permian and some Pennsylvanian rocks are widely exposed

on the upwarp and along the river.

Also adding to the picturesque qualities of the Paradox

Basin are the intrusive rocks of the La Sal, Abajo, and Sleeping Ute Mountains within the basin and intrusive centers

such as the Henry, Carrizo, La Plata, Rico, and San Miguel

Mountains in surrounding areas. These intrusions are Late

Cretaceous to Tertiary in age and deformed the enclosing

sedimentary rocks into broad domes.

STRATIGRAPHY

Sedimentary rocks of the Paradox Basin overlie an

Early Proterozoic basement of metamorphic gneiss and

schist that is locally intruded by granite. An Early and Middle Proterozoic sedimentary unit, the Uncompahgre Formation, is present in the southeastern part of the basin (Tweto,

1987). A possibly Middle to Late Proterozoic sequence of

metasedimentary rocks is present in the western and southern parts of the basin.

Cambrian through Jurassic strata unconformably overlie the basement rocks in much of the basin. Remnants of

Cretaceous rocks are also present, especially in the southeastern part of the basin, but, except for the igneous intrusive

centers, Tertiary rocks have been completely eroded away.

Data are complete enough to construct isopach maps for

Cambrian through Jurassic units, which have been combined

into three groups: sub-Pennsylvanian, Pennsylvanian and

Permian, and Triassic and Jurassic.

SUB-PENNSYLVANIAN ROCKS

In pre-Pennsylvanian time, Utah was divided roughly in

half by the Wasatch hinge line, a feature still prominent

today. This line extends through the southern tip of Nevada

north-northeasterly to the southeastern corner of Wyoming

and beyond. Cambrian through Devonian sedimentation

west of this line was in a deep miogeocline that encompassed

western Utah, eastern Nevada, and adjacent areas. Sedimentation east of the Wasatch line was on a stable shelf in mainly

shallow marine conditions (Poole and others, 1992). The

structural setting changed in the latest Devonian and Mississippian when the Antler orogeny uplifted a north-trending

highland in Nevada and adjacent areas, resulting in terriginous clastic influx into adjacent basins (Poole and Sandberg,

1991). The Paradox Basin was far east of the orogenic belt

and remained a shallow-marine shelf during the Late Devonian and Mississippian. Many of the sub-Pennsylvanian

units have correlatives in central Colorado and northwestern

New Mexico, indicating that the shelf conditions extended

some distance eastward from the Paradox Basin.

Sub-Pennsylvanian rocks consist of the Lower and

Middle Cambrian Tintic Quartzite, Upper Cambrian Ignacio

Quartzite, Middle Cambrian Ophir Formation (or Shale),

Middle Cambrian Maxfield Limestone, Middle(?) and

Upper Cambrian Lynch Dolomite, Upper Devonian Aneth

and Elbert Formations and Ouray Limestone, and the Mississippian Leadville Limestone. Correlative units, whose

names originated in the Grand Canyon area, are the Lower

Cambrian Tapeats Sandstone, Middle Cambrian Bright

Angel Shale and Muav Limestone, and Mississippian Redwall Limestone (fig. 3). An isopach of sub-Pennsylvanian

units shows those units thickening uniformly westward

except for an area near the Four Corners (fig. 4). This interval ranges in thickness from about 300 ft to about 2,600 ft.

The thicknesses of individual formations are shown in

figure 3.

The Tapeats, Ignacio, and Tintic each consist of a basal

conglomerate overlain by silica-cemented sandstone and

minor shale beds. The conglomerates were deposited by

streams that filled in depressions on the Precambrian erosion

surface. The middle and upper parts of each unit were deposited in a shallow-marine environment by a sea that transgressed from the miogeocline to the west. The Ophir and

Bright Angel Shales are mixtures of sandstone, limestone,

and shale. They represent deeper water sedimentation during

the continuation of the Cambrian marine transgression. The

Maxfield and Muav Limestones and Lynch Dolomite are

carbonates deposited on the relatively stable cratonic shelf

on the margin of the continent (Lochman-Balk, 1972).

Rocks of Ordovician, Silurian, and Early and Middle

Devonian age are not recognized in the Paradox Basin. It is

possible that thin accumulations of at least part of this

sequence were deposited in the basin, but post-Cambrian

erosion may have removed all traces of them.

Upper Devonian rocks were also deposited in shallow-marine conditions on the cratonic shelf (Baars, 1972;

Poole and others, 1992). The Aneth Formation consists of

black shale and dolostone deposited in euxinic conditions.

The Aneth is recognized only in a relatively small area in the

southern part of the basin. It may have been more widespread, but a sea-level drop and accompanying erosion prior

to deposition of the overlying Elbert Formation would have

removed the Aneth from most of the basin.

Low to moderately elevated uplands in central Colorado shed clastic debris into the basin that was reworked

into the McCracken Sandstone Member of the Elbert Formation. The McCracken is recognized in most of the basin.

The upper member of the Elbert is a dolostone and shale

unit that includes intervals of sandstone in its lower part. In

some exposures in Colorado, the Elbert contains salt hoppers, indicating evaporitic, subaerial conditions. Devonian

fish remains have been found in the upper member as well

as in the McCracken Sandstone Member and the Aneth

Formation. The upper member is recognized in all parts of

the basin.
O6 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

Figure 3. Correlation chart for rocks of the Paradox Basin and vicinity. Modified from Molenaar (1987).



























































(SOUTHWEST AND WEST)

SAN RAFAEL SWELL

AND HENRY MOUNTAINS

NORTHERN PARADOX BASIN

AND BOOK CLIFFS

(NORTHEAST AND EAST)

UNCOMPAHGRE

PLATEAU

TERTIARY

CRETACEOUS JURASSIC TRIASSIC PERMIAN PENNSYLVANIAN MISS. DEV. CAMBRIAN

PRECAMBRIAN

SILURIAN

ORDOVICIAN

UPPER

MIDDLE

LOWER

LOWER

MIDDLE

UPPER

KINDERHOOKIAN

OSAGEAN

MERAMECIAN

CHESTERIAN

MORROWAN

ATOKAN

DESMOINESIAN

MISSOURIAN

VIRGILIAN

WOLFCAMPIAN

OCHOAN

GUADALUPIAN

LEONARDIAN

LOWER

MIDDLE

UPPER

LOWER

MIDDLE

UPPER

LOWER

UPPER

WASATCH FORMATION 1800'

FARRER FORMATION 1000'

(ERODED) "MESAVERDE" GROUP NESLEN FORMATION 600'

SEGO SANDSTONE 50-200'

BUCK TONGUE 0-200'

CASTLEGATE SANDSTONE 0-300'

BLACKHAWK

EQUIVALENT

JUANA LOPEZ MEMBER ("FERRON MARKER")

MANCOS SHALE

4000'

GREENHORN LIMESTONE MEMBER

➤

➤ ➤

?

?

?

?

?

UNNAMED BEDS

MESAVERDE FORMATION 300'

MASUK

MBR 700'

(TYPE AREA)

EMERY SS 300'

BLUE GATE SHALE MEMBER 1500'

FERRON SS 0-400'

TUNUNK SHALE MEMBER 600'

➤ ➤

DAKOTA SANDSTONE 50-200'

CEDAR MTN FORMATION 100-250'

MORRISON FORMATION

600-800'

BRUSHY BASIN MEMBER

BURRO CANYON FORMATION

SALT WASH MEMBER

SLICK ROCK MEMBER

?

TIDWELL MEMBER

GRANITIC AND HIGH-RANK METAMORPHIC ROCKS

TINTIC QTZITE - TAPEATS SS 100-300'

OPHIR SH - BRIGHT ANGEL SH 0-400'

MAXFIELD LS - MUAV LS 0-500'

LYNCH DOL 0-600' ? IGNACIO QTZITE

REDWALL LIMESTONE 500-800' LEADVILLE LIMESTONE 0-500'

QURAY LIMESTONE 100'

ELBERT FORMATION 250' UPPER MBR

MC CRACKEN SS MBR











ANETH FORMATION (SO. PARADOX)

0-200'



HERMOSA FORMATION

OR GROUP

0-2000'

?

➤ ➤

PINKERTON TRAIL FM 0-300'

MOLAS FM 0-100'

ISMAY

DESERT CR

AKAH

BARKER CR

CANE CR CYCLE OF

THE ALKALI GULCH INTERVAL

PRODUCTION INTERVALS

PARADOX FORMATION

(SALT)

0-15,000' (Incl. salt flowage)

CUTLER FORMATION

OR GROUP

0-8000'

HONAKER TRAIL FORMATION

0-3000' HERMOSA GROUP

2000-14,000'

LOWER CUTLER 0-1500'

CEDAR RIM SS 0-700'

ORGAN ROCK FORMATION 0-400'

WHITE RIM SS 0-500'

MOENKOPI FORMATION 0-800'

PARIOTT MBR

SEWEMUP MBR

ALI BABA MBR

TENDERFOOT MBR

MOODY CANYON MBR

TORREY MBR

SINBAD LS MBR

BLACK DRAGON MBR

HOSKINNINI MBR

SO PARADOX

SHINARUMP CGL

MONITOR BUTTE MBR

MOSS BACK MBR

PETRIFIED FOREST MBR

OWL ROCK MBR

CHURCH ROCK MBR

GROUP 

GLEN CANYON 

CHINLE FORMATION 300-600'

DEWEY BRIDGE MEMBER

ENTRADA SANDSTONE

MOAB TONGUE WANAKAH FM

ENTRADA SANDSTONE 100-500'

CURTIS EQUIV.

CARMEL FORMATION 100-300'

SAN RAFAEL GROUP

CURTIS FORMATION 0-200'

SUMMERVILLE FORMATION

M.Y.

66

138

205

240

290

330

360

410

435

500

570

WINGATE SS 300'

BUCKHORN CGL

 NAVAJO SANDSTONE 0-450'

KAYENTA FORMATION 100-250'

?
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O7

The uppermost Devonian unit in the basin is the Ouray

Limestone. The Ouray is a carbonate unit deposited in a

warm, shallow-water marine environment. It contains beds

of dolostone and intervals of green shale in some areas. The

Ouray is thin but extensive and is present in all parts of the

basin.

Sea-level fall after deposition of the Ouray ended the

Devonian Period. There is some evidence of exposure of the

Ouray surface to subaerial erosion (Armstrong and Mamet,

1977), but there was not enough erosion to remove the Ouray

in most places. Renewed transgression of the sea from the

west initiated deposition of the Mississippian Leadville and

Redwall Limestones. These units formed during a series of

transgressive and regressive events that were affected by the

Antler orogeny. Irregularities on the sea floor, possibly

caused in part by tectonics, led to development of a wide

variety of depositional subenvironments and a corresponding diversity of fauna.

A final sea-level fall in the Late Mississippian exposed

the carbonates of the Leadville and Redwall to a subaerial

environment. A regolith developed on this surface, as well as

solution cavities and karst topography in some areas. This

Figure 4. Isopach map of sub-Pennsylvanian stratigraphic units in the Paradox Basin. Contour interval 200 ft.

800

1000

1200

1400

1600

1800

2000

2200 2400

2600

1200

400

600

400

600

2000

1800

1600

1400

1200

1000

800

0 25 Mi

0 25 Km 

Utah

Arizona

Colorado

New Mexico

39 ̊30'

39 ̊00'

38 ̊30'

38 ̊00'

37 ̊30'

37 ̊00'

111 ̊00' 110 ̊0' 110 ̊00' 109 ̊30' 109 ̊00' 108 ̊30' 108 ̊00' 107 ̊30'

Green River

Grand

Junction

Gateway

Naturita

Ouray

Cortez

Blanding 

Moab

Mexican 

Hat

Kayenta

Bluff

Slick Rock

Monticello

San Juan River

Green River

Colorado

River

Colorado River

Durango

Rico

Farmington

Hanksville

Hite

Montrose

Navajo

Reservoir

Lake

Powell

Needle 

Mtns

Uncompahgre

Plateau

San

Rafael Swell

Maximum extent of salt

in Paradox Formation

B ook Cliffs

36 ̊30'
O8 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

residual deposit is considered to be a part of the overlying

Lower and Middle Pennsylvanian Molas Formation.

PENNSYLVANIAN AND PERMIAN ROCKS

The collision of the Laurentia and Gondwana supercontinents in the Pennsylvanian and Permian (Scotese and

McKerrow, 1990) had a profound effect on the area of the

Paradox Basin. During this time, the Uncompahgre Plateau

experienced rapid and large-scale uplift, and the adjacent

northeastern side of the Paradox Basin subsided. All Cambrian through Mississippian rocks were stripped from the

plateau, as was an unknown thickness of Precambrian rock.

Sediments of great thickness (as much as 12,000 ft) accumulated in the trough just to the southwest of the

Uncompahgre Plateau during the Pennsylvanian and Permian (fig. 5). Subsidence was less southwest of a line

extending from the San Rafael Swell through the confluence of the Green and Colorado Rivers to about the Cortez,

Colo., area. In this area, as much as about 4,000 ft of sediment accumulated during the Pennsylvanian and Permian,

Figure 5. Isopach map of Pennsylvanian and Permian stratigraphic units in the Paradox Basin. Contour interval 1,000 ft.

3000

4000

8000

9000

10000

11000

12000

2000

7000

3000

4000

4000

5000

6000

4000

2000

3000

0 25 Mi

0 25 Km 

Utah

Arizona

Colorado

New Mexico

39 ̊30'

39 ̊00'

38 ̊30'

38 ̊00'

37 ̊30'

37 ̊00'

36 ̊30'

111 ̊00' 110 ̊30' 110 ̊00' 109 ̊30' 109 ̊00' 108 ̊30' 108 ̊00' 107 ̊30'

Green River

Grand

Junction

Gateway

Naturita

Ouray

Cortez

Blanding 

Moab

Mexican 

Hat

Kayenta

Bluff

Slick Rock

Monticello

San Juan River

Green River

Colorado

River

Colorado River

Durango

Rico

Farmington

Hanksville

Hite

Montrose

Navajo

Reservoir

Lake

Powell

Needle 

Mtns

Uncompahgre

Plateau

San

Rafael Swell

Maximum extent of salt

in Paradox Formation

B ook Cliffs
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O9

although this is only about one-third as much as accumulated in the deepest part of the basin.

Deposits within the oldest Pennsylvanian formation,

the Molas Formation, are transitional from nonmarine to

marine. The lower part of the Molas may have begun forming in Mississippian time as a residual deposit on the

exposed carbonate surface of the Leadville and Redwall

Limestones. The middle part of the Molas was deposited and

reworked by streams. The upper part has, in addition to fluvial strata, marine limestone beds deposited by the transgressing Middle Pennsylvanian sea.

The Middle and Upper Pennsylvanian Hermosa Group

makes up most of the Pennsylvanian rocks in the basin. The

Hermosa includes, from oldest to youngest, the Middle

Pennsylvanian Pinkerton Trail and Paradox and the Middle

and Upper Pennsylvanian Honaker Trail Formations (Wengerd and Matheny, 1958). The Pinkerton Trail consists of

interbedded marine limestone and dark shale. It was deposited in shallow-marine conditions of normal salinity.

The Paradox Formation is a very diverse unit composed of dolostone, black shale, anhydrite, halite, and other

salts. Halite is the most abundant constituent of the Paradox,

occurring in beds tens of feet thick. Black dolomitic shale is

also an important rock type because it is the source of some

of the oil and gas recovered in the Paradox Basin. Many of

the samples used for this study are from the black shales of

the Paradox. The Paradox was deposited in a series of

cycles (Hite and Buckner, 1981) that represent repeated desiccation and marine flooding of the basin. In the southwestern part of the basin, the Paradox grades into shelf

carbonates, including algal-mound buildups that act as

petroleum reservoirs. In the easternmost part of the basin,

the Paradox cannot be differentiated, and the undivided

Hermosa contains abundant clastic material that was shed

from the Uncompahgre Plateau; this clastic material is interbedded with carbonate (Franczyk, 1992).

The black shales of the Paradox have been used as

marker beds to correlate depositional cycles throughout the

basin. The cycles have been grouped into larger zones, “substages” (Baars and others, 1967) (fig. 3), or “production

intervals” (Hite and others, 1984) (fig. 3). For this study,

maturity maps were prepared for the Ismay and Desert Creek

production intervals and for the Cane Creek cycle, which is

in the upper part of the Alkali Gulch production interval of

the Paradox Formation (fig. 3).

The Honaker Trail Formation is composed of cyclically

deposited limestone, sandstone, and shale. It represents a

return to normal marine conditions in contrast to the evaporitic marine conditions of the Paradox Formation. In addition,

the Honaker Trail contains significant eolian and fluvial

strata, especially on the northeastern side of the basin.

Continued uplift of the Uncompahgre Plateau in Late

Pennsylvanian and Early Permian time eventually unroofed

the Precambrian basement rocks. The Cutler Formation is

mostly a product of this unroofing process and consists of

arkose, sandstone, and relatively minor amounts of mudstone. The Cutler was deposited in a series of alluvial fans

that were transporting material southwestward (Campbell,

1980). The Cutler is commonly viewed as a Lower Permian

unit; however, it cannot be dated precisely because the fluvial strata composing it are nonfossiliferous. Intertonguing

relations of fluvial strata of the Cutler with underlying carbonates of the Hermosa Group suggest that the Cutler is in

part Pennsylvanian (Wengerd and Matheny, 1958).

In the northwestern and southwestern parts of the Paradox Basin, the Cutler is raised to group status and includes

the Elephant Canyon Formation or the Halgaito Formation,

the Cedar Mesa Sandstone, the Organ Rock Formation, and

the White Rim Sandstone or the De Chelly Sandstone

(Baars, 1962). The southwestward transition of arkosic redbeds of the undifferentiated Cutler into lighter colored sands

of the Cedar Mesa is evident at about the confluence of the

Green and Colorado Rivers (fig. 1).

The Elephant Canyon Formation is recognized in the

northwestern part of the basin. It is a mixed marine and nonmarine unit containing limestone beds interbedded with

marine sandstone as well as with fluvial and eolian strata.

The Elephant Canyon grades southward into the Halgaito

Formation, a redbed unit exposed along the San Juan River

in southeastern Utah. The Halgaito consists of sabkha sandstone as well as minor fluvial sandstone and mudstone.

The Cedar Mesa Sandstone is composed of thick sandstone beds separated by thin silty sandstone and limestone

beds. It is mainly an eolian dune deposit but includes interdune and thin playa facies. In the vicinity of the Comb Ridge

monocline in the southern part of the basin, the Cedar Mesa

grades eastward into an evaporite facies of interbedded sandstone, shale, and gypsum.

The Organ Rock Formation is another redbed unit,

composed mostly of sandstone and siltstone. Much of the

unit was deposited in sabkha environments; however, in

places, it contains significant amounts of eolian strata. The

Organ Rock thins and pinches out westward on the San

Rafael Swell.

The uppermost units of the Cutler Group are the correlative White Rim Sandstone and De Chelly Sandstone. The

White Rim is in the northwestern part of the basin and

pinches out southward and eastward at about the Colorado

River. The De Chelly Sandstone is present in large areas in

northeastern Arizona and northwestern New Mexico but

only extends a short distance northward into the area of the

Paradox Basin. It pinches out before merging with the White

Rim. Both the White Rim and De Chelly are eolian deposits

composed almost entirely of sandstone.

The youngest Permian unit in the basin is the marine

Kaibab Limestone (Lower Permian). The western side of the

basin is at the eastern depositional edge of the Kaibab. Erosion in latest Permian and earliest Triassic time left only

remnants of the Kaibab on the San Rafael Swell and in
O10 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

scattered subsurface areas along the western side of the

basin. It is a marine deposit.

TRIASSIC AND JURASSIC ROCKS

In the Triassic and Jurassic, sedimentation in the area of

the Paradox Basin was influenced to a great degree by development of magmatic arcs to the south and west of the current

basin (Dickinson, 1989). Development of the arcs had the

effect of periodically uplifting source areas and providing

sediment to the Western Interior, including the area of the

Paradox Basin. Triassic and Jurassic sedimentary units contain large volumes of ash derived from volcanic activity in

the arcs. Times of less tectonic activity, especially in the

Middle Jurassic, led to deposition of marine, sabkha, and

eolian deposits.

Western and southwestern source areas are indicated by

the thickness patterns displayed by Triassic and Jurassic

units (fig. 6). In general, the combined units thin uniformly

from west-southwest to the east-northeast in the study area.

An exception is in the northern part of the basin (fig. 6). This

thick area is probably due to the influence of salt tectonics.

Figure 6. Isopach map of Triassic and Jurassic stratigraphic units in the Paradox Basin. Contour interval 200 ft.

4800

4600

4400

4200

4000

3800

3600

3400

3200

3000

2800

2600

2400

2200

2000

1800

1600

1400

1200

4000

3800

3800

3600

3600

3400

3200

3000

2800

2600

2400

2400

1200

0 25 Mi

0 25 Km 

Utah

Arizona

Colorado

New Mexico

38 ̊30'

38 ̊00'

37 ̊30'

37 ̊00'

36 ̊30'

111 ̊00' 110 ̊30' 110 ̊00' 109 ̊30' 109 ̊00' 108 ̊30' 108 ̊00' 107 ̊30'

Green River

Grand

Junction

Gateway

Naturita

Ouray

Cortez

Blanding 

Moab

Mexican 

Hat

Kayenta

Bluff

Slick Rock

Monticello

San Juan River

Green River

Colorado

River

Colorado River

Durango

Rico

Farmington

Hanksville

Hite

Montrose

Navajo

Reservoir

Lake

Powell

Needle 

Mtns

Uncompahgre

Plateau

San

Rafael Swell

Maximum extent of salt

in Paradox Formation

B ook Cliffs

39 ̊30'

39 ̊00'
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O11

Deposition of Permian, Triassic, and Jurassic sediment onto

thick sequences of salt in the Middle Pennsylvanian Paradox

Formation led to the diapiric rise of the salt in several

anticlines in the fold and fault belt (fig. 2). When the salt

moved up into the anticlines, it moved out of the synclines,

forming sediment traps. Individual Triassic and Jurassic

units have been shown to thin on the flanks of anticlines and

to thicken in the synclines (Cater, 1970).

The basal Triassic unit in the basin is the Moenkopi

Formation of Early and Middle(?) Triassic age. The Moenkopi has been divided into several members with different

names in various parts of the basin (fig. 3). In the western

part of the basin, lower beds of the Moenkopi are fluvial

strata shed eastward from a highland west of the Paradox

Basin area (Huntoon, 1992; Huntoon and others, 1994).

Younger members of the Moenkopi are a combination of

sabkha, mudflat, and fluvial deposits, and one marine limestone unit, the Sinbad Limestone Member (fig. 3). A combination of erosion in the Middle Triassic and, possibly,

nondeposition led to absence of the Moenkopi in parts of

southeastern Utah and most of southwestern Colorado

(Stewart and others, 1972a).

Uplift south of the study area in Late Triassic time led

to development of a northwestward-flowing fluvial system

in the lower part of the Upper Triassic Chinle Formation

(Dubiel, 1989). Other components of the Chinle fluvial system had sources in the Uncompahgre Plateau. The Chinle

has also been divided into several members in various parts

of the basin (Stewart and others, 1972b) (fig. 3). In southwestern Colorado, a correlative unit is known as the

Dolores Formation. The Chinle and Dolores are mostly

redbed units that were deposited in fluvial, lacustrine,

sabkha, and eolian environments.

Previously, the contact between Triassic and Jurassic

strata was thought to be gradational and to lie within the Glen

Canyon Group (Harshbarger and others, 1957). Pipiringos

and O’Sullivan (1978) have, however, interpreted the contact at the top of the Chinle to be an unconformity and the

Triassic-Jurassic boundary to lie at that unconformity.

The oldest Jurassic unit is the Lower Jurassic Glen Canyon Group, which is composed of the Wingate Sandstone,

Kayenta Formation, and Navajo Sandstone. The Wingate

and Navajo are massive eolian units, and the Kayenta is fluvial. Contacts between formations of the group are gradational; an unconformity is at the top of the Navajo Sandstone.

The Navajo was removed by pre-Middle Jurassic erosion in

the northeastern part of the study area. The Navajo contains

local limestone beds that are as thick as 10 ft. These limestones were deposited in interdune playas and are associated

with fossil trees, dinosaur footprints, and invertebrate

remains.

Unconformably overlying the Glen Canyon Group is

the Middle Jurassic San Rafael Group, named for exposures

on the San Rafael Swell (Gilluly and Reeside, 1928). The

San Rafael Group consists of the Page Sandstone, Carmel

Formation, Entrada Sandstone, Curtis Formation, and the

Summerville Formation (west) or Wanakah Formation

(east). These formations were deposited in and on the

margins of an inland sea that transgressed from the north

during at least two transgressive-regressive cycles.

The Page Sandstone is an eolian deposit that had previously been included with the Navajo Sandstone but that was

distinguished by Peterson and Pipiringos (1979). It is conformably overlain by the Carmel Formation, a marine limestone, sandstone, and shale. The Carmel is overlain, in part,

by the Entrada Sandstone, but near the Green River, Wright

and others (1962) interpreted the Carmel to change facies

eastward to a sabkha deposit, which they included as the

lowest member of the Entrada Sandstone. In the San Rafael

Swell, the Entrada is a silty sandstone, probably deposited in

or near shallow water. Eastward, the Entrada changes to an

eolian deposit; near Moab, an upper eolian member, the

Moab Tongue, is recognized.

There was apparently a fall in sea level after deposition

of part of the Entrada, followed by another cycle of transgression during which the marine Curtis Formation was

deposited. The fall in sea level is inferred from the presence

of an unconformity between the Entrada and Curtis (Pipiringos and O’Sullivan, 1978). The Curtis consists of fossiliferous limestone, sandstone, and shale that unconformably

overlies the main body of the Entrada. The Curtis changes

facies eastward and pinches out between the Green and Colorado Rivers beneath the Moab Tongue of the Entrada. In the

western part of the basin, the Summerville Formation, a

sabkha deposit, conformably overlies the Curtis.

In the eastern part of the basin, the Wanakah Formation overlies and, in part, grades laterally into the Entrada

Sandstone. In Colorado, the Wanakah includes a limestone

and gypsum unit, the Pony Express Limestone Member, at

the base. The upper part of the Wanakah consists of sandstone and shale redbeds that have been interpreted to partly

grade into the Entrada Sandstone (O’Sullivan, 1980).

Upper beds of the Wanakah are correlative with beds of the

Summerville Formation.

The Upper Jurassic Morrison Formation is the youngest Jurassic unit in the basin. In many places there is an

unconformity separating the Morrison from underlying

Middle Jurassic strata. The Morrison was deposited in a

variety of depositional environments, ranging from eolian

to fluvial and lacustrine. In the southern part of the basin,

the lowest member of the Morrison is the Bluff Sandstone

Member. This member was deposited in an eolian erg and is

partly equivalent to the Junction Creek Sandstone of southwestern Colorado (Condon, 1992). Much of the Morrison is

composed of fluvial sandstone and mudstone that have

sources to the west and southwest of the basin (Peterson

and Turner-Peterson, 1987). An upper member, the Brushy

Basin Member, was deposited in a combination of lacustrine and marginal lacustrine environments (Turner and

Fishman, 1991).
O12 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

The contact between the Morrison Formation and overlying strata has been the subject of much discussion. In the

northwestern part of the basin, the overlying unit is the

Lower Cretaceous Cedar Mountain Formation, whereas in

the southeast, a correlative unit is the Lower Cretaceous

Burro Canyon Formation. The contact between these units

and the Morrison was interpreted to be a disconformity

(Young, 1960); however, Tschudy and others (1984) indicated that the Cedar Mountain and Burro Canyon may be a

continuation of deposition of the Morrison Formation.

Recent studies by Aubrey (1992) also suggest interfingering

between the Morrison and overlying units.

CRETACEOUS AND TERTIARY ROCKS

Late Tertiary to Holocene erosion removed Cretaceous

and Tertiary rocks throughout most of the Paradox Basin. In

order to reconstruct the burial history of the region, we

assume that similar thickness and lithology trends of Cretaceous and Tertiary strata from areas around the periphery of

the basin (such as the Henry Basin, Book Cliffs, and the

Mesa Verde National Park area) can be extrapolated across

the Paradox Basin.

The Cedar Mountain and Burro Canyon Formations of

Early Cretaceous age overlie the Morrison Formation. The

Cedar Mountain is recognized in areas west of the Colorado

River and the Burro Canyon in areas to the east (Molenaar,

1981). Many of the mesas in the eastern and southern parts of

the basin are capped by the Burro Canyon. The Cedar Mountain and Burro Canyon Formations, comprising conglomeratic sandstone beds and mudstone, are mostly fluvial and

flood plain in origin. The Cedar Mountain was derived from

areas to the west, whereas the Burro Canyon was derived

from areas to the south and southwest of the Paradox Basin

(Molenaar, 1981). The thickness of the Cedar Mountain and

Burro Canyon ranges from 50 to 200 ft.

The Upper Cretaceous Dakota Sandstone unconformably overlies the Cedar Mountain and Burro Canyon Formations. The Dakota is a coastal-plain unit deposited in front of

the advancing Mancos sea (Molenaar, 1981). It comprises, in

ascending order, conglomeratic channel sandstone,

dark-gray carbonaceous shale, coal, and, in places, a marine

sandstone. Regionally, the Dakota is about 200 ft thick.

Conformably overlying the Dakota is the Upper Cretaceous Mancos Shale. The Mancos was deposited in the

Western Interior Cretaceous seaway and is primarily composed of uniform, dark-gray mudstone, shale, and siltstone.

The Mancos ranges in thickness from about 3,500 ft in the

Book Cliffs area to about 2,000 ft in southwestern Colorado

(Molenaar, 1981).

The Upper Cretaceous Mesaverde Group is partially

preserved in only a few areas in the Paradox Basin; however,

it is fully preserved in the Book Cliffs area in the northern

part of the basin and in the Mesa Verde National Park area

southeast of Cortez, Colo. (Molenaar, 1981). The Mesaverde

gradationally overlies the Mancos Shale and consists of marginal-marine sandstones, coastal- or delta-plain paludal carbonaceous shale and coal with channel sandstones, and

alluvial or upper delta plain noncarbonaceous shales and

channel sandstones (Molenaar, 1981).

In the Mesa Verde area, the group is divided into three

formations: in ascending order, the Point Lookout Sandstone, the Menefee Formation, and the Cliff House Sandstone. The total thickness of the Mesaverde in this area is

about 900 ft; it thins to the northeast and thickens to the

southwest. In the Book Cliffs area, the Mesaverde Group is

divided into, in ascending order, the Castlegate Sandstone,

Sego Sandstone, and Neslen, Farrer, and Tuscher Formations (Fisher and others, 1960; Molenaar, 1981) (fig. 3). The

combined thickness of the Mesaverde Group and the intertonguing Buck Tongue of the Mancos Shale in this area is

about 2,300 ft.

The dominant event of latest Cretaceous and Tertiary

time was the development of uplifts and adjacent basins associated with the Laramide orogeny. Major structural features

in the Paradox Basin region are the Uncompahgre Plateau,

San Rafael Swell, Monument upwarp, San Juan dome, and

Uinta Basin (fig. 2). Records of Tertiary sedimentation in the

Paradox Basin are absent due to late Tertiary uplift and erosion; however, it is very likely that Paleocene, Eocene, and

possibly even Oligocene, Miocene, and Pliocene rocks were

once present in the northernmost part of the basin (Robinson,

1972; McDonald, 1972).

The North Horn Formation is Maastrichtian to late Paleocene in age (Spieker, 1949; Robinson, 1972; Fouch, 1976;

Fouch and others, 1983) and comprises a series of interbedded sandstone, conglomerate, shale, and limestone. The

thickness of the North Horn is highly variable throughout

central and eastern Utah, ranging from 500 ft to more than

3,800 ft. The North Horn is thought to have once been

present as far south as lat 39°N. and covered much of the

northern part of the Paradox Basin (Robinson, 1972).

Eocene rocks once present in the northern Paradox

Basin probably include the Wasatch, Green River, and

Uinta Formations (Robinson, 1972). The Wasatch Formation is composed of silty, micaceous, and calcareous shale

that grades into mudstone and fine- to medium-grained

sandstone. The Green River Formation comprises

organic-rich, laminated shale; sandstone; siltstone; silty

shale; and oolitic, algal, and ostracodal limestone. The

lithology of the Uinta Formation is extremely variable,

including boulder conglomerate, sandstone, siltstone, and

limestone. These combined Eocene strata extended southward to around lat 38°30′N., likely covering the northern

part of the Paradox Basin (Robinson, 1972). Eocene rocks

in the northern Paradox Basin area could have been as thick

as 1,000–2,000 ft (McDonald, 1972).

Volcanic activity during Oligocene through Pliocene

time undoubtedly contributed to the rock column in the
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O13

Paradox Basin. Igneous intrusions in the area include the La

Sal, Henry, Abajo, and San Juan Mountains. Ash and flows

likely covered much of southwestern Colorado and southeastern Utah and may have been as thick as 1,000 ft.

METHODS

The isopach maps prepared for this report were constructed from a database of about 200 well logs from oil and

gas test wells in the Paradox Basin. The geophysical logs

were checked against sample logs prepared by the American Stratigraphic Company (AMSTRAT), and correlations

were made from one log to another. Thickness files were

then generated and were gridded and contoured using a program called Interactive Surface Modeling (ISM), a product

of Dynamic Graphics, Inc. The area shown on the contour

maps was divided into a grid of 300 rows and 300 columns,

equivalent to a grid size in the x direction (longitude) of

about 0.75 mi and in the y direction (latitude) of about 0.9

mi. Each grid node was calculated by considering the eight

closest control points.

Source rock characterization of 107 shale samples from

the Ismay–Desert Creek interval and Cane Creek cycle was

performed using Rock-Eval pyrolysis analysis. Rock-Eval

pyrolysis is used to evaluate rapidly the petroleum-generation potential of rocks, and it provides information on the

quantity, type, and thermal maturity of the organic matter in

a rock. Pyrolysis is the heating of organic matter in the

absence of oxygen to yield organic compounds. Complete

details of the Rock-Eval pyrolysis technique and associated

problems are given in Espitalie and others (1977) and Peters

(1986). Most of the Ismay–Desert Creek and Cane Creek

samples used in this study were taken from a larger set of

samples from several stratigraphic units (Cretaceous through

Mississippian) throughout the Paradox Basin (Barker, Nuccio, and others, in press). Barker, Szmajter, and others (in

press) statistically analyzed this same larger data set and

interpreted the petroleum potential for various source rocks.

The Rock-Eval pyrolysis technique yields several measurements that determine the thermal maturity and hydrocarbon generation potential of source rocks (table 1). Total

organic carbon content (TOC) is a useful parameter for evaluating the quantity of organic matter in a potential source

rock. Total organic carbon was determined using the

Rock-Eval II instrument and is the sum of the carbon in the

pyrolyzate plus the carbon from the residual oxidized

organic matter. In general (depending on the type of organic

matter and lithology), and for this study, fine-grained rocks

having a total organic carbon content of greater than 0.50

percent are considered a potential hydrocarbon source rock.

Interpretation of the total organic carbon content and source

rock potential of the Paradox Formation samples is presented

in a later section.

Other Rock-Eval measurements include the S1 peak,

which is the amount of hydrocarbons that are thermally

distilled from the rock; the S2 peak, the amount of hydrocarbons generated by pyrolytic degradation of the kerogen; and

the S3 peak, the amount of carbon dioxide (in milligrams)

generated during heating to 390°C.

Rock-Eval pyrolysis also measures Tmax, the temperature at which the S2 peak occurs; that is, the temperature of

maximum hydrocarbon yield. Tmax can be used as a thermal

maturity indicator because the temperature for maximum

hydrocarbon yield increases as kerogen matures. Hydrocarbons begin to be generated between Tmax values of 435°C

and 440°C, and thermal cracking to gas and condensate

occurs at about 460°C (Tissot and Welte, 1984).

The hydrogen index (HI) is defined as the S2 yield

(remaining hydrogen-generating capability of the organic

matter) normalized by the total organic carbon content

(TOC); in other words, the fraction of the total organic carbon

that is generated as hydrocarbons. The hydrogen index is also

useful in describing the type of organic matter present in the

source rock, as will be discussed in a later section on source

rock potential. The oxygen index (OI) is the quantity of carbon dioxide from the S3 peak normalized by the total organic

carbon content and, if plotted against the HI, yields information about the type of organic matter in the source rock.

The production index (PI), or transformation ratio, is

defined as the ratio S1/(S1 + S2), or the ratio of volatile

hydrocarbon yield to total hydrocarbon yield. The production index can be used to evaluate thermal maturity because,

if there is no migration of hydrocarbons, it increases with

heating. In general, the beginning of generation is at a production index of about 0.08–0.10, and thermal cracking of

oil to gas and condensate occurs at about production indices

of 0.40–0.50.

In addition to Tmax and PI values, vitrinite reflectance

(Ro) was also used to define levels of thermal maturity for

some of the shale samples (table 2). Vitrinite, a maceral

derived from woody plant material, is common in coal and

organic-rich shale. Vitrinite reflectance is a measure of the

proportion of light reflected from a polished vitrinite grain.

It is related to the degree of metamorphism of the vitrinite

grain and can be related to other thermal maturity indicators. Thirty-five samples of shale from the Paradox Formation were analyzed for vitrinite reflectance (table 2). The

samples were prepared by crushing, mounting in epoxy on

a microscope slide, planing off when hardened, and polishing. The mean random vitrinite reflectance (from randomly

oriented indigenous vitrinite grains) was determined using

plane-polarized incident white light and a 546-nm monochromatic filter, in immersion oil, on a reflected light

microscope with a nonrotating stage (Bostick, 1979;

Bustin, 1986).

Vitrinite reflectance values have been correlated with

oil and gas generation for potential source rocks (Dow, 1977;

Waples, 1985). For example, Waples (1985) stated that,

depending on the type of kerogen, oil generation begins over

a range of Ro values—onset of oil generation ranges from
O14 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

Table 1. Rock-Eval pyrolysis data, Paradox Formation, Paradox Basin, Utah and Colorado.

[Location given as section-township-range. Tmax is temperature at which maximum yield of hydrocarbons occurs during pyrolysis; S1 is integral of first

peak (existing hydrocarbons volatized at 250°C for 5 minutes); S2 is integral of second peak (hydrocarbons produced by pyrolysis of solid organic matter

between 250° and 550°C); S3 is integral of third peak (CO2 produced by pyrolysis of kerogen between 250° and 390°C); PI, production index

(S1/S1+S2); TOC, total organic carbon; HI, hydrogen index (S2/TOC); OI, oxygen index (S3/TOC)]

Well Location Depth Production Tmax S1 S2 S3 PI TOC HI OI

name (ft) interval or zone (°C) (mg/g) (mg/g) (mg/g) (wt.%)

Gulf Oil Co. 8-31S-22E 4,385 Ismay-Des. Ck. 440 0.16 1.85 0.70 0.08 0.62 298 112

No. 1 Hart Point Unit 4,515 Ismay-Des. Ck. 438 1.44 11.58 0.93 0.11 2.34 494 39

4,635 Ismay-Des. Ck. 439 0.69 6.16 0.74 0.10 1.39 443 53

7,090 Cane Creek 443 0.22 1.11 0.56 0.17 0.60 185 93

Superior Oil 20-25S-17E 4,310 Ismay-Des. Ck. 438 0.24 0.66 0.18 0.27 0.49 135 37

Bow Knot 5,670 Cane Creek 437 7.65 29.69 1.07 0.20 8.21 362 13

43-20 5,780 Cane Creek 438 2.27 7.86 0.83 0.22 2.75 286 30

5,830 Cane Creek 436 9.46 40.57 1.13 0.19 10.99 369 10

5,850 Cane Creek 437 6.62 28.33 0.91 0.19 7.71 367 12

Skelly Oil 26-31S-23E 4,810 Ismay-Des. Ck. 435 0.33 2.03 0.50 0.14 0.76 267 65

No. 1 Church Rock 4,870 Ismay-Des. Ck. 435 0.23 0.92 0.50 0.20 0.58 158 86

4,930 Ismay-Des. Ck. 44 0 0.80 3.27 0.66 0.20 1.51 216 43

5,000 Ismay-Des. Ck. 436 0.11 0.38 0.45 0.23 1.71 22 26

5,030 Ismay-Des. Ck. 437 0.35 1.19 0.52 0.23 1.47 80 35

5,060 Ismay-Des. Ck. 436 0.70 2.42 0.97 0.22 1.23 196 78

5,090 Ismay-Des. Ck. 436 0.75 3.28 0.72 0.19 1.30 252 55

6,420 Cane Creek 439 10.91 27.40 1.31 0.28 11.06 247 11

7,940 Cane Creek 436 5.25 13.05 1.48 0.29 4.98 262 29

Superior Oil 14-21S-15E 6,940 Ismay-Des. Ck. 440 0.73 0.40 0.42 0.65 1.07 37 39

No. 14-25 7,000 Ismay-Des. Ck. 444 0.85 0.56 0.25 0.60 1.03 54 24

Grand Fault 7,010 Ismay-Des. Ck. 439 2.05 2.42 0.63 0.46 2.71 89 23

7,170 Ismay-Des. Ck. 441 0.91 0.41 0.54 0.69 0.94 44 57

8,960 Cane Creek 462 1.06 0.53 0.45 0.67 1.34 40 34

9,020 Cane Creek 460 2.19 1.27 0.55 0.63 2.87 44 19

Conoco No. 1 36-27S-13E 5,160 Ismay-Des. Ck. 437 0.29 0.84 0.22 0.26 0.52 162 42

Hanksville 5,360 Ismay-Des. Ck. 430 0.43 0.75 0.64 0.36 0.50 150 128

Standard Oil 32-25S-15E 4,630 Ismay-Des. Ck. 444 0.43 0.82 0.37 0.34 0.80 103 46

No. 1 Moonshine 4,768 Ismay-Des. Ck. 440 2.18 14.21 0.39 0.13 3.37 422 12

4,858 Ismay-Des. Ck. 432 0.99 7.45 0.52 0.12 2.14 348 24

Pan Am Oil 15-23S-17E 5,100 Ismay-Des. Ck. 440 0.23 0.50 1.16 0.32 0.59 84 196

No. 1 Salt Wash 5,660 Ismay-Des. Ck. 442 1.58 2.19 0.66 0.42 2.26 97 29

5,790 Ismay-Des. Ck. 443 0.65 0.65 0.57 0.50 1.02 64 56

5,990 Ismay-Des. Ck. 438 0.84 1.61 2.39 0.34 2.38 67 100

8,100 Cane Creek 440 4.83 7.94 0.99 0.38 7.41 107 13

8,150 Cane Creek 443 2.70 4.17 0.77 0.39 4.06 103 19

General 5-24S-15E 4,945 Ismay-Des. Ck. 452 0.04 0.19 0.25 0.17 0.57 33 44

Petroleum 5,130 Ismay-Des. Ck. 425 0.05 0.09 0.15 0.36 0.48 19 31

No. 45-5-G 5,225 Ismay-Des. Ck. 447 0.79 1.45 0.25 0.35 1.26 115 20

5,298 Ismay-Des. Ck. 444 0.57 1.95 0.63 0.23 1.50 130 42
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O15

Table 1. Rock-Eval pyrolysis data, Paradox Formation, Paradox Basin, Utah and Colorado—Continued.

Well Location Depth Production Tmax S1 S2 S3 PI TOC HI OI

name (ft) interval or zone (°C) (mg/g) (mg/g) (mg/g) (wt.%)

Carbonit 16-39S-21E 5,659 Ismay-Des. Ck. 455 0.67 3.92 0.42 0.15 1.86 210 22

Exploration 5,702 Ismay-Des. Ck. 45 2 0.69 9.13 0.67 0.07 3.27 279 20

No. 1-16 State 5,704 Ismay-Des. Ck. 444 0.55 4.25 0.64 0.11 1.29 329 49

5,708 Ismay-Des. Ck. 446 1.17 8.68 0.89 0.16 2.63 330 33

5,712 Ismay-Des. Ck. 445 1.72 8.97 0.76 0.16 2.38 376 31

McCulloch Oil 4-38N-18W 5,920 Ismay-Des. Ck. 390 0.50 0.73 0.76 0.41 1.12 60 62

Norton Federal 5,925 Ismay-Des. Ck. 368 0.57 0.72 0.77 0.45 1.30 55 59

No. 1-4 5,920 Ismay-Des. Ck. 36 9 0.51 0.58 0.76 0.47 1.30 44 58

5,930 Ismay-Des. Ck. 371 0.62 0.66 0.68 0.48 1.47 44 46

6,042 Ismay-Des. Ck. 484 1.49 7.03 0.60 0.17 10.98 64 5

6,058 Ismay-Des. Ck. 400 0.16 0.16 0.61 0.50 0.80 20 76

6,062 Ismay-Des. Ck. 45 0 0.35 0.52 0.78 0.41 2.71 19 28

6,066 Ismay-Des. Ck. 454 0.31 0.42 0.49 0.43 2.20 19 22

6,068 Ismay-Des. Ck. 458 0.50 0.61 0.42 0.45 3.07 19 13

Department of 21-30S-21E 2,758 Ismay-Des. Ck. 450 1.18 12.46 0.83 0.09 2.85 437 29

Energy 2,879 Ismay-Des. Ck. 450 1.17 18.11 0.92 0.06 4.15 436 22

Gibson Dome No. 1 2,951 Ismay-Des. Ck. 435 0.53 2.35 0.62 0.18 1.03 228 60

3,109 Ismay-Des. Ck. 431 2.91 6.90 0.63 0.29 1.46 472 43

5,239 Cane Creek 438 4.15 15.27 1.04 0.21 3.96 386 26

Equity Oil 33-21S-21E 11,570 Ismay-Des. Ck. 428 0.44 0.78 4.95 0.36 1.65 47 300

No. 1 Unit 12,500 Ismay-Des. Ck. 335 0.15 0.11 1.38 0.58 0.63 17 219

Belco 1-Floy 11-23S-17E 5,100 Ismay-Des. Ck. 429 0.22 0.78 1.10 0.22 0.56 139 196

Salt Wash 6,000 Ismay-Des. Ck. 415 0.28 0.19 1.12 0.61 0.66 28 169

Texaco 17-23S-17E 5,380 Ismay-Des. Ck. 426 0.46 0.77 1.18 0.38 0.71 108 166

No. 1 Govt. 5,710 Ismay-Des. Ck. 447 1.68 1.79 4.26 0.49 3.0 59 142

Smoot 6,230 Ismay-Des. Ck. 442 1.46 1.57 2.92 0.48 2.28 68 128

8,230 Cane Creek 445 1.86 3.47 4.52 0.35 4.71 73 95

Tidewater 11-26S-19E 4,602 Ismay-Des. Ck. 429 1.88 12.11 3.02 0.13 4.43 273 68

74-11 Big Flat 4,646 Ismay-Des. Ck. 440 0.12 1.11 1.54 0.10 0.64 173 240

Delhi-Taylor Oil 25-26S-20E 1,847 Ismay-Des. Ck. 439 0.33 2.37 1.35 0.12 1.11 213 121

Cane Creek No. 1 1,881 Ismay-Des. Ck. 443 1.31 11.38 1.82 0.10 3.76 302 48

2,146 Ismay-Des. Ck. 438 1.11 6.41 3.66 0.15 3.56 180 102

2,153 Ismay-Des. Ck. 441 1.50 8.08 3.51 0.16 3.93 205 89

2,159 Ismay-Des. Ck. 440 1.12 6.65 3.35 0.14 3.38 196 99

Delhi-Taylor Oil 15-27S-20E 2,542 Ismay-Des. Ck. 445 6.73 25.66 1.65 0.21 5.97 429 27

Shafer No. 1 2,881 Ismay-Des. Ck. 412 3.5 20.72 1.6 0.14 4.71 439 33

E.B. Larue 15-27S-22E 7,350 Ismay-Des. Ck. 462 0.34 1.02 1.21 0.25 2.32 43 52

Govt. Moab 7,860 Ismay-Des. Ck. 462 0.50 1.71 1.11 0.23 2.80 61 39

Gulf Oil 1 Lockhart 22-28S-20E 2,455 Ismay-Des. Ck. 435 0.19 1.37 0.97 0.12 0.87 183 111

Pure Oil 19-29S-24E 4,200 Ismay-Des. Ck. 439 0.44 1.79 1.31 0.20 0.86 208 152
O16 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

about 0.45 percent Ro to 0.50 percent Ro for high-sulfur kerogen, to 0.60 percent Ro for marine kerogen, to 0.65 percent

Ro for terrestrial kerogen. The end of oil generation also

occurs over a range of vitrinite reflectance values, but 1.35

percent Ro is commonly accepted as the value at which oil

begins to break down into shorter chain hydrocarbons. Dow

(1977) stated that oil generation by liptinitic-rich source

rocks occurs between 0.50 and 1.35 percent Ro. Wet gas is

Table 1. Rock-Eval pyrolysis data, Paradox Formation, Paradox Basin, Utah and Colorado—Continued.

 Well Location Depth Production Tmax S1 S2 S3 PI TOC HI OI

name (ft) interval or zone (°C) (mg/g) (mg/g) (mg/g) (wt.%)

Pure Oil No. 1 10-30S-24E 4100 Ismay-Des. Ck. 439 0.34 1.88 1.64 0.15 1.22 154 134

NW Lisbon

Tennessee Gas 4-31S-12E 4,190 Ismay-Des. Ck. 432 0.31 0.77 1.19 0.29 0.94 81 126

A-2 USA Poison Springs 4,889 Ismay-Des. Ck. 316 0.16 0.32 0.86 0.33 0.33 96 260

Texas Co. No. 2 18-32S-19E 1,610 Ismay-Des. Ck. 430 0.53 3.31 1.22 0.14 1.10 300 110

Cataract Canyon 1,726 Ismay-Des. Ck. 436 0.78 4.12 1.56 0.16 1.29 319 120

Lear Oil 27-11 Jones 27-35S-26E 6,417 Ismay-Des. Ck. 370 0.16 0.73 0.58 0.18 0.81 90 71

Transco 1-32 32-35S-26E 6,435 Ismay-Des. Ck. 464 0.95 2.42 1.30 0.28 3.84 63 33

Pan Am Co. 20-37S-24E 5,803 Ismay-Des. Ck. 448 0.63 1.75 0.98 0.26 1.42 123 69

No. 1 6,120 Ismay-Des. Ck. 446 0.49 5.12 1.58 0.09 2.60 196 60

Dead Man Canyon 7,630 Cane Creek 430 1.31 2.07 1.43 0.39 4.11 50 34

Sinclair Oil 7-38S-18E 2,416 Ismay-Des. Ck. 440 0.10 0.39 0.98 0.21 0.35 111 280

No. 1 Fed. Fehr 2,610 Ismay-Des. Ck. 439 0.21 1.25 1.04 0.14 0.75 166 138

Great Western 22-38S-20E 2,550 Ismay-Des. Ck. 430 0.15 0.41 0.95 0.27 0.62 66 153

No.1 Fish Creek

Total Pet. 1-15 15-38S-25E 5,633 Ismay-Des. Ck. 416 0.73 1.59 0.67 0.31 1.91 83 35

Cliffhouse

Mcor Oil and Gas 19-38S-26E 5,721 Ismay-Des. Ck. 455 2.02 4.73 2.32 0.30 3.46 136 67

McCulloch 20-38S-26E 5,518 Ismay-Des. Ck. 448 0.18 0.33 0.74 0.36 0.41 80 180

2 Fed.-20 5,669 Ismay-Des. Ck. 45 1 2.21 6.76 2.56 0.25 3.99 169 64

Shell Oil No. 1 32-39S-23E 5,640 Ismay-Des. Ck. 432 0.10 0.48 0.89 0.17 0.30 160 296

Bluff Unit 5,958 Ismay-Des. Ck. 444 0.73 4.92 2.10 0.13 2.55 192 82

Carter Oil 12-114 8-41S-25E 5,625 Ismay-Des. Ck. 441 0.47 2.12 1.8 0.18 1.24 170 145

Ohio Oil 10-43S-21E 4,915 Ismay-Des. Ck. 441 1.01 3.07 2.11 0.07 4.09 319 51

No. 1 Navajo

Celsius 20-18W-37N 5,911 Ismay-Des. Ck. 465 1.48 2.85 1.97 0.34 4.44 64 44

1-5 Unit

Davis Oil No. 1 22-39N-20W 6288 Ismay-Des. Ck. 390 0.47 1.63 0.71 0.32 2.02 81 35

State line Fee
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O17

generated from mixed lacustrine-marine-terrestrial organic

matter and from the thermal cracking of oil between Ro

values of 0.80 and 2.0 percent. Thermogenic methane is generated from humic organic matter and from the breakdown

of wet gas between Ro values of about 1.0 percent and 3.0

percent. Biogenic gas can be generated at levels of maturity

as low as those for peat (0.20 percent Ro).

For this study, Tmax, PI, and Ro were used in conjunction to define the thermal maturity of the Paradox Formation

source rocks. This approach was taken because no single

maturity indicator was consistent for all samples. Several

factors can influence the results of each of the three maturity

indicators used; for a complete explanation and discussion,

see Peters (1986) and Nuccio and Barker (1989). Tmax values vary quite a bit , even for closely spaced samples within

a single well (table 1). Production indices are fairly consistent within a single well and throughout the basin. Vitrinite

reflectance values correlate well with production indices and

serve to corroborate them (fig. 7). The following table illustrates the correlation between Tmax, production index (PI),

and vitrinite reflectance (Ro) and the levels of thermal maturity and petroleum generation used in this study:

Table 2. Vitrinite reflectance data, Paradox Basin, Utah and Colorado.

[Location given as section-township-range. U. Hon. Trail, Upper Honaker Trail; Des. Ck., Desert Creek]

Well name or Location Depth Production Vitrinite reflectance

sample no. (feet) interval or zone (Ro, in percent)

PH91KF59 35-37N-9W Outcrop ..............Ismay.................................1.58

PH91KF6 24-37N-9W Outcrop ..............Cane Creek........................1.62

PH91KF10 24-37N-9W Outcrop ..............Cane Creek........................1.52

KF90PB1 18-30S-25E Outcrop ..............U. Hon. Trail.....................0.97

91PCH1HT ?-41S-18E Outcrop ..............Ismay-Des. Ck. .................0.49

Gibson Dome 21-30S-21E 2,888 ................Ismay-Des. Ck. .................0.73

No. 1 2,890 ................Ismay-Des. Ck. .................0.52

2,895 ................Ismay-Des. Ck. .................0.70

5,256 ................Cane Creek........................1.09

Elk Ridge 30-37S-19E 2,812 ................Ismay-Des. Ck. .................0.43

No. 1 2,988 ................Ismay-Des. Ck. .................0.67

General 5-24S-15E 5,443 ................Ismay-Des. Ck. .................1.04

Petroleum 6,180 ................Cane Creek........................1.24

No. 45-5-G 6,681 ................Cane Creek........................1.49

Pan Am 15-23S-17E 5,910 ................Ismay-Des. Ck. .................1.28

No. 1 Salt Wash 5,660 ................Ismay-Des. Ck. .................1.15

7,620 ................Cane Creek........................1.49

8,100 ................Cane Creek........................1.85

Standard Oil 32-25S-15E 4,630 ................Ismay-Des. Ck. .................0.88

No. 1 Moonshine 4,768 ................Ismay-Des. Ck. .................0.92

4,858 ................Ismay-Des. Ck. .................0.93

Superior Oil 20-25S-17E 3,400 ................Ismay-Des. Ck. .................0.59

Bow Knot 4,630 ................Ismay-Des. Ck. .................0.92

43-20 5,580 ................Cane Creek........................1.08

5,670 ................Cane Creek........................1.07

5,830 ................Cane Creek........................1.03

Conoco No. 1 So. 36-27S-13E 4,860 ................Ismay-Des. Ck. .................0.85

Hanksville 5,160 ................Ismay-Des. Ck. .................0.90

Superior Oil 14-21S-15E 8,840 ................Cane Creek........................1.72

14-25 Grand 9,080 ................Cane Creek........................1.82

Fault 9,250 ................Cane Creek........................1.72

Skelly Oil No. 1 26-31S-23E 5,000 ................Ismay-Des. Ck. .................0.72

Church Rock 7,940 ................Cane Creek........................0.73

Gulf Oil No. 1 8-31S-22E 4,510 ................Ismay-Des. Ck. .................0.69

Hart Point Unit 7,180 ................Cane Creek........................0.63
O18 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

Burial curves (sometimes called geohistory curves)

were constructed for six distinctively different areas using a

variety of information. Cambrian through Jurassic stratigraphy was reconstructed using the drill-hole database discussed previously, and Cretaceous and Tertiary stratigraphy

was reconstructed by extrapolation from nearby areas where

these rocks crop out. Numerical ages for the major periods

were adapted from Harland and others (1990). Due to the

uncertainties associated with determining amounts of erosion, unconformities between formations were treated as

hiatuses with no erosion. Table 3 lists the thicknesses and

ages used to reconstruct the burial histories of the six areas.

Present-day heat-flow values for the Paradox Basin

range from 43 to 105 mWm–2 (Bodell and Chapman, 1982;

Sass and others, 1983). Heat-flow values are lower in the

interior of the Colorado Plateau and are higher around the

periphery. The Paradox Basin is mostly within the interior of

the Colorado Plateau, and it is likely that heat flow in the

basin has been stable throughout its history (Hite and others,

1984). It is possible that the Paradox Basin may be at maximum heat-flow today (Bodell and Chapman, 1982; R.J. Hite,

oral commun., 1993). The measured thermal maturity data

(Tmax, PI, and Ro) discussed previously were used to calibrate the thermal history models. Assuming that our burial

curves are representative of the six different areas, the heat

flow was adjusted either upward or downward until the modeled thermal maturity trends matched the measured data.

Once the modeled thermal maturity data were brought

into agreement with the measured thermal maturity, hydrocarbon-generation kinetic models were constructed to determine the petroleum-generation history of the Paradox

Formation throughout the basin. The computer program BasinMod (Platte River Associates, 1992) was used for the thermal and kinetic modeling. Kinetic modeling is useful in

estimating the time at which the Paradox Formation was in

the oil window. It is the best method for predicting petroleum-generation history because it is based on the kinetic

reactions of organic matter during burial and thermal maturation rather than on just temperature. In the model, all reactions are treated as first-order reactions; that is, the rate is

proportional to the amount of reactant. The Arrhenius equation is used to describe the temperature dependence of the

rate constant. The result of the modeling relates the amounts

of oil and gas to time and temperature for a particular kerogen or mix of kerogens. For a complete explanation of kinetic

modeling, see discussions in Tissot and Espitalie (1975),

Ungerer (1983), Yukler and Kokesh (1984), Sweeney and

others (1987), and Tissot and others (1987).

KEROGEN TYPES AND RELATED 

HYDROCARBONS

Three general types of kerogen have the potential, under

optimum conditions, to generate hydrocarbons: type I, alginite (sapropelic or lipid-rich); type II, exinite (phytoplankton, zooplankton, and other microorganisms); and type III,

vitrinite and huminite (terrestrial plant debris). There is no

absolute point at which hydrocarbon generation starts, and it

probably begins over a range of maturity values (and temperatures) depending on the specific type of organic matter. Several models have been developed that relate the generation of

hydrocarbons to types of kerogen and thermal maturity (Tissot and others, 1974; Dow, 1977; Waples, 1980, 1985). It

Figure 7. Production index (PI) versus vitrinite reflectance (Ro)

for samples from the Ismay–Desert Creek interval and Cane Creek

cycle of the Paradox Formation. Correlation is a best-fit line.

0.4

PRODUCTION INDEX

0.5 1.0 1.5 2.0

0.1

0.2

0.3

0.5

.0.6

0.7

VITRINITE REFLECTANCE (Ro), IN PERCENT

Tmax (°C) PI Ro (percent)

Immature for oil.........<435 .............. <0.08........... <0.60

Mature for oil..........435–460 ........0.80–0.50 .... 0.60–1.35

Overmature for oil-

 dry gas zone ............>460 .............. >0.50............>1.35
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O19

Table 3. Data used to construct burial curves for six areas studied in the Paradox Basin, 

Utah and Colorado.

[ss, sandstone; sh, shale; carb, carbonate; lime, limestone; mud, mudstone; silt, siltstone; evap, evaporite; Penn,

Pennsylvanian; L., Lower; M., Middle; U., Upper]

System/series, Age range Thickness Generalized lithology

unit, or event (Ma) (feet) (meters)

Monument upwarp area

Uplift and erosion........... 25–0......... –10,550......... –3,216

Tertiary .......................... 66–25............ 1,000.............. 305.............75% ss, 25% sh

Unconformity ................ 74–66................... 0.................. 0

Cretaceous ..................... 97–74............ 5,800........... 1,768.............25% ss, 75% sh

Unconformity ............... 146–97.................. 0.................. 0

U. and M. Jurassic....... 174–146.......... 1,400.............. 427.............60% ss, 40% mud

Unconformity .............. 178–174................. 0.................. 0

L. Jurassic.................... 205–178............. 900.............. 275.............60% ss, 40% mud

Unconformity .............. 208–205................. 0.................. 0

U. Triassic ................... 220–208............. 900.............. 275.............50% ss, 50% sh

Unconformity .............. 225–220................. 0.................. 0

L. Triassic.................... 235–225............. 300................ 92.............50% ss, 50% sh

Unconformity .............. 255–235................. 0.................. 0

Permian........................ 290–255.......... 1,750.............. 533.............70% ss, 30% silt

Pennsylvanian.............. 327–290.......... 2,285.............. 696

Honaker Trail Fm... 300–290............. 900.............. 275.............15% sh, 85% carb

Ismay-Desert Ck..... 303–300............. 360...............110.............15% sh, 85% carb 

Middle Penn ........... 307–303............. 700.............. 213.............15% sh, 80% carb, 5% evap

Lower Penn ............ 327–307............. 325.............. 100.............20% sh, 80% carb

Unconformity .............. 345–327................. 0.................. 0

Mississippian............... 358–345............. 450.............. 137.............100% limestone

Unconformity .............. 363–358................. 0.................. 0

Devonian ..................... 409–363............. 650.............. 198.............25% ss, 15% sh, 60% carb

Unconformity .............. 510–409................. 0.................. 0

Cambrian ..................... 570–510............. 500.............. 152.............50% ss, 40% sh, 10% carb

Confluence of the Green and Colorado Rivers

Uplift and erosion........... 25–0......... –10,350......... –3,155

Tertiary .......................... 66–25............ 1,000.............. 305.............75% ss, 25% sh

Unconformity ................ 74–66................... 0.................. 0

Cretaceous ..................... 97–74............ 5,800........... 1,768.............25% ss, 75% sh

Unconformity ............... 146–97.................. 0.................. 0

U. and M. Jurassic....... 174–146.......... 1,150.............. 350.............60% ss, 40% mud

Unconformity .............. 178–174................. 0.................. 0

L. Jurassic.................... 205–178.......... 1,150.............. 350.............60% ss, 40% mud

Unconformity .............. 208–205................. 0.................. 0

U. Triassic ................... 220–208............. 500.............. 152.............50% ss, 50% sh

Unconformity .............. 225–220................. 0.................. 0

L. Triassic.................... 235–225............. 450.............. 137.............50% ss, 50% sh

Unconformity .............. 255–235................. 0.................. 0

Permian........................ 290–255.......... 1,500.............. 457.............65% ss, 20% silt, 15% carb

Pennsylvanian.............. 327–290.......... 3,625........... 1,105

Honaker Trail ......... 300–290.......... 1,100.............. 335.............15% sh, 85% carb

Ismay-Desert Ck..... 303–300............. 400.............. 122.............15% sh, 75% carb, 10% evap

Middle Penn ........... 307–303.......... 1,700.............. 518.............20% sh, 10% carb, 70% evap

Lower Penn ............ 327–307............. 425.............. 130.............20% sh, 30% carb, 50% evap

Unconformity .............. 345–327................. 0.................. 0

Mississippian............... 358–345............. 500.............. 152.............100% limestone

Unconformity .............. 363–358................. 0.................. 0

Devonian ..................... 409–363............. 375...............114.............25% ss, 15% sh, 60% carb

Unconformity .............. 510–409................. 0.................. 0

Cambrian ..................... 570–510.......... 1,050.............. 320.............50% ss, 40% sh, 10% carb
O20 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

Table 3. Data used to construct burial curves for six areas studied in the Paradox Basin, 

Utah and Colorado—Continued.

System/series, Age range Thickness Generalized lithology

unit, or event (Ma) (feet) (meters)

Green River, Utah

Uplift and erosion........... 37–0........... –8,050......... –2,454

Tertiary .......................... 66–37............ 2,000.............. 610.............25% ss, 75% sh

Unconformity ................ 74–66................... 0.................. 0

Cretaceous ..................... 97–74............ 6,000........... 1,829.............25% ss, 75% sh

Unconformity ............... 146–97.................. 0.................. 0

U. and M. Jurassic....... 174–146.......... 1,450.............. 442.............55% ss, 45% mud

Unconformity .............. 178–174................. 0.................. 0

L. Jurassic.................... 205–178.......... 1,000.............. 305.............55% ss, 45% mud

Unconformity .............. 208–205................. 0.................. 0

U. Triassic ................... 220–208............. 400.............. 122.............50% ss, 50% sh

Unconformity .............. 225–220................. 0.................. 0

L. Triassic.................... 235–225............. 800.............. 244.............50% ss, 50% sh

Unconformity .............. 255–235................. 0.................. 0

Permian........................ 290–255.......... 1,250.............. 381.............65% ss, 20% silt, 15% carb

Pennsylvanian.............. 327–290.......... 2,460.............. 750

Honaker Trail ......... 300–290............. 750.............. 230.............15% sh, 85% carb

Ismay-Desert Ck..... 303–300............. 360...............110.............15% sh, 45% carb, 40% evap

Middle Penn ........... 307–303.......... 1,000.............. 305.............20% sh, 10% carb, 70% evap

Lower Penn ............ 327–307............. 350.............. 107.............20% sh, 30% carb, 50% evap

Unconformity .............. 345–327................. 0.................. 0

Mississippian............... 358–345............. 650.............. 198.............100% limestone

Unconformity .............. 363–358................. 0.................. 0

Devonian ..................... 409–363............. 350.............. 107.............15% sh, 85% carb

Unconformity .............. 510–409................. 0.................. 0

Cambrian ..................... 570–510.......... 1,250.............. 381.............10% ss, 45% sh, 45% carb

Moab, Utah

Uplift and erosion........... 37–0......... –11,575......... –3,528

Tertiary .......................... 66–37............ 2,000.............. 610.............25% ss, 75% sh

Unconformity ................ 74–66................... 0.................. 0

Cretaceous ..................... 97–74............ 5,900........... 1,798.............25% ss, 75% sh

Unconformity ............... 146–97.................. 0.................. 0

U. and M. Jurassic....... 174–146.......... 1,125.............. 343.............55% ss, 45% mud

Unconformity .............. 178–174................. 0.................. 0

L. Jurassic.................... 205–178.......... 1,250.............. 381.............55% ss, 45% mud

Unconformity .............. 208–205................. 0.................. 0

U. Triassic ................... 220–208............. 400.............. 122.............50% ss, 50% sh

Unconformity .............. 225–220................. 0.................. 0

L. Triassic.................... 235–225............. 400.............. 122.............50% ss, 50% sh

Unconformity .............. 255–235................. 0.................. 0

Permian........................ 290–255.......... 4,500........... 1,372.............80% ss, 20% sh

Pennsylvanian.............. 327–290.......... 6,310........... 1,923

Honaker Trail ......... 300–290.......... 1,950.............. 595.............20% ss, 15% sh, 65% carb

Ismay-Desert Ck..... 303–300............. 860.............. 262.............20% sh, 20% carb, 60% evap

Middle Penn ........... 307–303.......... 2,400.............. 732.............15% sh, 10% carb, 75% evap

Lower Penn ............ 327–307.......... 1,100.............. 335.............20% sh, 20% carb, 60% evap

Unconformity .............. 345–327................. 0.................. 0

Mississippian............... 358–345............. 400.............. 122.............100% limestone

Unconformity .............. 363–358................. 0.................. 0

Devonian ..................... 409–363............. 325.............. 100.............10% ss, 10% sh, 80% carb

Unconformity .............. 510–409................. 0.................. 0.............15% sh, 85% carb

Cambrian ..................... 570–510............. 900.............. 275.............35% ss, 30% sh, 35% carb
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O21

Table 3. Data used to construct burial curves for six areas studied in the Paradox Basin, 

Utah and Colorado—Continued.

System/series, Age range Thickness Generalized lithology

unit, or event (Ma) (feet) (meters)

Lisbon Valley, Utah, area

Uplift and erosion........... 25–0......... –13,350......... –4,069

Tertiary .......................... 66–25............ 1,000.............. 305.............50% ss, 50% sh

Unconformity ................ 74–66................... 0.................. 0

Cretaceous ..................... 97–74............ 6,000........... 1,829.............25% ss, 75% sh

Unconformity ............... 146–97.................. 0.................. 0

U. and M. Jurassic....... 174–146.......... 1,050.............. 320.............65% ss, 35% mud

Unconformity .............. 178–174................. 0.................. 0

L. Jurassic.................... 205–178.......... 1,000.............. 305.............65% ss, 35% mud

Unconformity .............. 208–205................. 0.................. 0

U. Triassic ................... 220–208............. 550.............. 168.............50% ss, 50% sh

Unconformity .............. 225–220................. 0.................. 0

L. Triassic.................... 235–225................. 0.................. 0.............50% ss, 50% sh

Unconformity .............. 255–235................. 0.................. 0

Permian........................ 290–255.......... 3,750........... 1,143.............80% ss, 20% sh

Pennsylvanian.............. 327–290.......... 8,200........... 2,500

Honaker Trail ......... 300–290.......... 1,900.............. 580.............10% ss, 15% sh, 75% carb

Ismay-Desert Ck..... 303–300............. 500.............. 152.............20% sh, 20% carb, 60% evap

Middle Penn ........... 307–303.......... 4,900........... 1,494.............15% sh, 5% carb, 80% evap

Lower Penn ............ 327–307............. 900.............. 275.............20% sh, 20% carb, 60% evap

Unconformity .............. 345–327................. 0.................. 0

Mississippian............... 358–345............. 400.............. 122.............100% limestone

Unconformity .............. 363–358................. 0.................. 0

Devonian ..................... 409–363............. 300................ 91.............10% ss, 10% sh, 80% carb

Unconformity .............. 510–409................. 0.................. 0

Cambrian ..................... 570–510............. 550.............. 168.............50% ss, 25% sh, 25% carb

Hermosa, Colo.

Uplift and erosion........... 25–0......... –12,550......... –3,825

Tertiary .......................... 66–25............ 2,500.............. 762.............60% ss, 40% sh

Unconformity ................ 74–66................... 0.................. 0

Cretaceous ..................... 97–74............ 6,250........... 1,905.............25% ss, 75% sh

Unconformity ............... 146–97.................. 0.................. 0

U. and M. Jurassic....... 174–146............. 900.............. 274.............65% ss, 35% mud

Unconformity .............. 178–174................. 0.................. 0

L. Jurassic.................... 205–178................. 0.................. 0.............65% ss, 35% mud

Unconformity .............. 208–205................. 0.................. 0

U. Triassic ................... 220–208............. 600.............. 183.............50% ss, 50% sh

Unconformity .............. 225–220................. 0.................. 0

L. Triassic.................... 235–225................. 0.................. 0.............50% ss, 50% sh

Unconformity .............. 255–235................. 0.................. 0

Permian........................ 290–255.......... 2,500.............. 762.............90% ss, 10% mud

Pennsylvanian.............. 327–290.......... 2,770.............. 844

Honaker Trail ......... 300–290............. 730.............. 223.............70% ss, 25% silt, 5% lime

Ismay-Desert Ck..... 303–300............. 300................ 91.............34% ss, 33% silt, 33% lime

Middle Penn ........... 307–303.......... 1,320.............. 402.............60% ss, 20% silt, 20% carb

Lower Penn ............ 327–307............. 420.............. 128.............50% ss, 10% sh, 40% lime

Unconformity .............. 345–327................. 0.................. 0

Mississippian............... 358–345............. 150................ 46.............100% limestone

Unconformity .............. 363–358................. 0.................. 0

Devonian ..................... 409–363............. 175................ 53.............25% ss, 20% sh, 55% carb

Unconformity .............. 510–409................. 0.................. 0

Cambrian ..................... 570–510............... 50................ 15.............100% ss
O22 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

should be noted that there is another type of kerogen, type IV,

which is composed of inert organic matter (oxidized and biologically altered organic matter, charcoal, and recycled

organic matter); it has low hydrogen content and virtually no

hydrocarbon-generation potential.

Type I kerogen is hydrogen rich, is primarily in

marine and lacustrine rocks, and generates mainly oil during catagenesis. The vitrinite reflectance value for the onset

of oil generation from type I organic matter varies depending on the model. Dow (1977) used 0.50 percent Ro as the

onset of oil generation for type I kerogen, whereas Anders

and Gerrild (1984) and Tissot and Welte (1984) used 0.70

percent Ro.

Type II kerogen is mainly in marine rocks but can be

present in lacustrine rocks, and it generates oil and gas during

catagenesis. Waples (1985) stated that oil generation from

type II kerogen begins over a range of Ro values of about

0.45–0.50 percent for high-sulfur kerogen to 0.60 percent for

“typical” type II kerogen.

Huminite and vitrinite, or type III kerogen, is oxygen

rich and hydrogen poor; is mainly in terrestrial, marginal-lacustrine, or marginal-marine rocks; and generates

mostly gas (methane) during catagenesis. For type III kerogen, vitrinite reflectance is the best and most widely used

measure of thermal maturity. Two important reflectance

thresholds are used to define regions of gas generation from

type III kerogen: these are 0.75 percent and 1.10 percent. An

Ro of about 0.75 percent represents the maturity required for

the onset of significant gas generation (Juntgen and Karweil,

1966; Juntgen and Klein, 1975). Gas accumulations in rocks

having an Ro of less than 0.75 percent contain either early

biogenic gas or gas migrated from more mature source rocks.

An Ro of 1.10 percent represents the level of maximum gas

expulsion from type III kerogen (Meissner, 1984). The upper

limit of maturity for gas preservation is unknown but could

be as high as 3.5 percent Ro (Dow, 1977) or 4.0 percent Ro

(Waples, 1980).

SOURCE ROCK POTENTIAL OF THE 

ISMAY–DESERT CREEK INTERVAL 

AND CANE CREEK CYCLE

As mentioned previously, total organic carbon (TOC)

content is a useful parameter for evaluating the amount of

organic material and the petroleum-generation potential of a

source rock. For this study, we assumed that if shale within

the Ismay–Desert Creek interval and the Cane Creek cycle

has TOC values ≥0.50 percent, it is a good source rock. Table

1 shows that only 6 (all in the Ismay–Desert Creek interval)

of the 107 samples had total organic carbon contents of less

than 0.50 percent. The most striking and important feature of

these shales is the high total organic carbon content—as high

as 11.0 percent. These high values are somewhat biased and

probably do not represent the intervals as a whole; when collecting samples, dark-gray to black shale was generally chosen. These values do demonstrate, however, that there are

very organically rich zones in both the Ismay–Desert Creek

interval and the Cane Creek cycle and that both have excellent petroleum-generation potential.

Another parameter used to evaluate the hydrocarbon-generating capacity of a source rock is the genetic potential or S1 + S2. Tissot and Welte (1984) established a genetic

potential classification, as follows:

Using this classification, 62 percent of all samples have

(S1 + S2) >2.0 mg/g and are considered to be moderate to

excellent source rocks (table 1).

As mentioned in the previous section, organic matter

type determines the quality and kind of hydrocarbons generated. The most widely used parameter for defining the type

of organic matter contained in a source rock is the modified

Figure 8. Modified van Krevelen diagram for samples from the

Ismay–Desert Creek interval. Type I kerogen generates mainly oil;

type II kerogen generates oil and gas; and type III kerogen generates

mainly gas.

1000

HYDROGEN INDEX

0

0 50 100 150

400

800

600

200

OXYGEN INDEX

III

II

I

(S1 + S2) (mg/g) Source rock characterization

<2.0 Poor source rock or non-source rock.

2.0–6.0 Moderate source rock.

>6.0 Good to excellent source rock.
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O23

van Krevelen diagram (van Krevelen, 1961; Tissot and

Welte, 1984). This diagram plots hydrogen index versus

oxygen index as determined from Rock-Eval analysis and

illustrates the type of organic matter and its relative position

on the maturation evolutionary path. Figures 8 and 9 are

modified van Krevelen diagrams for the Ismay–Desert

Creek interval and the Cane Creek cycle, respectively.

The modified van Krevelen diagram of the

Ismay–Desert Creek interval (fig. 8) shows mainly types II

and III organic matter, sources for both oil and gas. We

believe that the organic matter is of both marine and terrestrial origin, with a transition zone between the two (types II

and III). The transition zone may consist of either (1) a mixture of types II and III kerogen, (2) an area having type II kerogen and a relatively low hydrogen index, or (3) an area

having type III kerogen and a relatively higher hydrogen

index. A few samples plot near the type I line and are likely

to be good source rocks for oil. Samples nearer the eastern

part of the basin may be more terrestrial in origin and are

likely to be good source rocks for mainly gas. For example,

Ismay–Desert Creek samples from the Norton Federal 1-4

well in sec. 4, T. 38 N., R. 18 W. (table 1) plot near the type

III line. Similarly, a carbonaceous shale from the Ismay

interval (PH91KF59), collected from outcrop near Hermosa,

Colo., on the easternmost edge of the basin, comprised

organic matter having a terrestrial affinity.

The wide distribution of samples on the diagrams not

only is due to differences in organic matter type and source

but also to the degree of thermal maturation. In general, plotted samples migrate toward the origin of the diagram (HI=0,

OI=0) with increasing thermal maturity. Caution should be

taken when interpreting the origin and source of organic

matter in samples that have a high level of thermal maturation. For example, a rock that originally had an HI=400 and

an OI=75 (type II kerogen of marine origin) will decrease in

hydrogen and oxygen indices with increasing thermal maturation (migrate toward the origin of the diagram ) and will

ultimately plot as a type III kerogen. The wide range of plotted samples in figure 8 is indicative of variations in kerogen

type as well as differences in the thermal history of the basin.

The modified van Krevelen diagram of the Cane Creek

cycle (fig. 9) illustrates that this unit contains types I, II, and

III kerogen, sources for both oil and gas. Samples from the

Cane Creek cycle are more mature than those from the

Ismay–Desert Creek interval and generally have lower

hydrogen indices. This is not to say that, before maturation,

the Cane Creek was not as good a source rock as the

Ismay–Desert Creek, but, because the Cane Creek is mature

everywhere in the basin, several of the samples probably plot

closer to the origin of the diagram.

As with the Ismay–Desert Creek interval, organic matter in the lower part of the Paradox Formation near the eastern side of the basin has a more terrestrial origin. For

example, humic coals (samples PH91KF6 and PH91KF10)

were collected just below the Cane Creek cycle on the

extreme eastern side of the basin near Hermosa, Colo. Some

Cane Creek cycle samples in the central part of the basin also

plot near the type III line. For example, a Cane Creek sample

from the Texaco No. 1 Gov’t. Smoot well in sec. 17, T. 23

S., R. 17 E. plots on the type III line. Caution should be

taken, however, in interpreting kerogen type because the

maturity of this sample is fairly high in that it has a PI of 0.35

and a Tmax of 445°C.

THERMAL MATURITY TRENDS

Thermal maturity maps for the Paradox Basin illustrating the highly variable maturation trends for two horizons,

the Ismay–Desert Creek interval in the upper part of the Paradox Formation and the Cane Creek cycle of the Alkali

Gulch interval near the bottom of the Paradox Formation,

were constructed using production indices (PI) from

Rock-Eval pyrolysis and some vitrinite reflectance data. Production index was chosen because it is more consistent in the

Paradox Formation than either Tmax or vitrinite reflectance

and represents, fairly well, the maturity within the intervals

for a given well, as well as for the entire basin. Data points

Figure 9. Modified van Krevelen diagram for samples from the

Cane Creek cycle. Type I kerogen generates mainly oil; type II kerogen generates oil and gas; and type III kerogen generates mainly

gas.

1000

HYDROGEN INDEX

0

0 50 100 150

400

800

600

200

OXYGEN INDEX

III

II

I
O24 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

on the maps of the Ismay–Desert Creek interval (fig.10) and

the Cane Creek cycle (fig. 11) are listed and correspond to

table 1. Vitrinite reflectance data (table 2) supplement the

large production index data set and serve as a check (analytical comparison) on the thermal maturity. In almost every

case, vitrinite reflectance corroborates the thermal maturity

derived from production index data.

ISMAY–DESERT CREEK INTERVAL

The thermal maturity map of the Ismay–Desert Creek

interval (fig. 10) shows a general trend of increasing maturity

from southwest to northeast. This trend corresponds with the

thickening of Pennsylvanian and Permian units (fig. 5). In

Pennsylvanian and Permian time, the eastern part of the basin

Figure 10. Thermal maturity map of the Paradox Basin at the Ismay–Desert Creek interval. Contours are production indices, interval = 0.10. Large dots are locations of the six areas where burial, thermal, and petroleum-generation histories were reconstructed;

small dots are production-index control points.

0 25 Mi

0 25 Km 

Utah

Arizona

Colorado

New Mexico

39 ̊30'

39 ̊00'

38 ̊30'

38 ̊00'

37 ̊30'

37 ̊00'

36 ̊30'

111 ̊00' 110 ̊30' 110 ̊00' 109 ̊30' 109 ̊00' 108 ̊30' 108 ̊00' 107 ̊30'

Green River

Grand

Junction

Gateway

Naturita

Ouray

Cortez

Blanding 

Moab

Mexican 

Hat

Kayenta

Bluff

Slick Rock

Monticello

San Juan River

Green River

Colorado

River

Colorado River

Durango

Rico

Farmington

Hanksville

Hite

Montrose

Navajo

Reservoir

Lake

Powell

Needle 

Mtns.

Uncompahgre

Plateau

San

Rafael Swell

Maximum extent of salt

in Paradox Formation

B ook Cliffs

0.30

0.40

0.50

0.60

0.10

0.10

0.10

0.20

0.20

0.30

0.40 0.50

0.60
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O25

subsided rapidly, and a thick sedimentary sequence accumulated. As a direct result of the greater depth of burial in the

eastern part of the basin, the thermal maturity is greater

there. In the northernmost part of the basin, the thermal

maturity of the Ismay–Desert Creek is also very high. In this

area, the high thermal maturity is most likely the result of

greater depth of burial during Tertiary time when a thick sedimentary package was deposited there.

Areas of high thermal maturity may be present

throughout the basin but are not represented by the generalized production index contours. High heat flow associated

with Tertiary igneous events such as the La Sal, Henry,

Abajo, and San Juan Mountains affected immediately adjacent areas; however, these heat sources were fairly localized

and are not noticeable at a basinwide scale or within the resolution of the contours. An area of high thermal maturity

Figure 11. Thermal maturity map of the Paradox Basin at the Cane Creek cycle. Contours are production indices, interval = 0.10.

Large dots are locations of the six areas where burial, thermal, and petroleum-generation histories were reconstructed; small dots are

production-index control points.

0 25 Mi

0 25 Km 

Utah

Arizona

Colorado

New Mexico

39 ̊30'

39 ̊00'

38 ̊30'

38 ̊00'

37 ̊30'

37 ̊00'

36 ̊30'

111 ̊00' 110 ̊30' 110 ̊00' 109 ̊30' 109 ̊00' 108 ̊30' 108 ̊00' 107 ̊30'

Green River

Grand

Junction

Gateway

Naturita

Ouray

Cortez

Blanding 

Moab

Mexican Hat

Kayenta

Bluff

Slick Rock

Monticello

San Juan River

Green River

Colorado

River

Colorado River

Durango

Rico

Farmington

Hanksville

Hite

Montrose

Navajo

Reservoir

Lake

Powell

Needle 

Mtns.

Uncompahgre

Plateau

San

Rafael Swell

Maximum extent of salt

in Paradox Formation

B ook Cliffs

0.30

0.40

0.50

0.60

0 3. 0

0.60

0.50

0.40

0.20
O26 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

(Ro = 1.58 percent) is in the southeastern part of the study

area near Hermosa, Colo. (table 2). This part of the basin has

been penetrated by several Tertiary intrusive stocks, dikes,

and sills and experienced a higher heat flow in the Tertiary

than the rest of the basin.

Localized low-maturity areas, such as salt anticlines,

also likely are present, especially within the area of high

maturity in the northeastern part of the basin. These salt anticlines are thought to have been actively growing since Late

Pennsylvanian time—in these positive-relief areas, deposition of Pennsylvanian and Permian sediments, as well as

younger Mesozoic sediments, may have been significantly

less than in the adjacent synclines. Differences in the burial

histories between the anticlines and synclines are significant

but localized and are not obvious when compared to the

regional thermal maturity trends represented by basin-scale

maps. A much smaller scale study is needed to detail the

maturity differences for the salt anticline areas.

The thermal maturity map of the Ismay–Desert Creek

interval (fig. 10) reveals three areas of PI ≤0.10 that represent the most immature parts of the basin. As previously

discussed, a production index of 0.08 is the minimum

threshold for significant oil generation, and a few such low

values are present in the immature areas; however, based on

the fact that oil is produced in these “immature” areas,

good-quality source rocks in the areas with PI ≤0.10 may

have the sufficient thermal maturity to have generated at

least some petroleum.

Production indices between 0.08 and 0.50 represent

thermal maturity levels sufficient for significant petroleum

generation. Figure 10 illustrates that the Ismay–Desert Creek

interval is within these levels of thermal maturity in most of

the basin. Except for the overmature northern and easternmost parts of the basin, source rocks in the Ismay–Desert

Creek interval in most of the basin could be considered to

have the potential for generation, accumulation, and possible

migration of petroleum.

In the areas where production indices exceed 0.50, one

would expect maturities to be too high for the preservation of

oil. Unless there was a later, postmaturation migration of oil

from a less mature part of the basin, reservoirs in the PI >0.50

areas should not contain oil. In these areas of high maturity,

Figure 12. Burial, thermal, and petroleum-generation model of the area near the Monument upwarp (see figs. 1 and 2). A, Cambrian

through present. B, Expanded time scale illustrating 100 Ma to present.

600 500 400 300 200 100 0

16,000

14,000

12,000

10,000

8000

6000

4000

2000

0

DEPTH, IN FEET 

pe e O S D M h P T J K

PA

E

TIME (Ma)

Permian

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

 100 ̊F

150 ̊F

200 ̊F

250 ̊F

A

O

M
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O27

it is very likely, however, that thermogenic gas generated

from kerogen in the rocks, as well as gas and condensate

generated from the cracking of oil, may be present. The distribution of petroleum and its relationship to thermal maturity will be discussed in a later section.

CANE CREEK CYCLE

Thermal maturity trends at the Cane Creek cycle (fig.

11) generally follow the structural configuration of the basin

and are similar to maturity trends of the Ismay–Desert Creek

interval. The maturity of the Cane Creek generally increases

from southwest to northeast, and the Cane Creek is the least

mature in the west-central part of the basin. The overall level

of maturity, however, is higher at the Cane Creek cycle than

at the Ismay–Desert Creek interval and is directly related to

the thickness of the Pennsylvanian strata overlying the Cane

Creek that did not influence the Ismay–Desert Creek interval. Another significant difference between the Cane Creek

cycle and the Ismay–Desert Creek interval is that the production index contours are much closer together at the Cane

Creek horizon. This also can be explained by the additional

thickness of sedimentary rocks overlying the Cane Creek

cycle in the rapidly subsiding deeper part of the basin. As a

consequence of the greater depth of burial for the Cane

Creek cycle, much more of the basin is overmature (>0.50

PI) at this interval (compare figs. 10 and 11). For an explorationist, the target area for oil is significantly smaller at the

Cane Creek cycle than at the Ismay–Desert Creek interval.

As with the thermal maturity of the Ismay–Desert

Creek interval, thermal maturity in the northernmost part of

the basin is very high. This high maturity is a result of thick

sedimentation and deep burial during Tertiary time in that

part of the basin.

The least mature area at the Cane Creek cycle is in the

west-central part of the basin and is represented by the

0.20-PI contour. This production index is much higher than

that of the least mature areas at the Ismay–Desert Creek

interval, and there are no immature areas at the Cane Creek

cycle. The area in which potential source rocks would be

mature for oil generation ranges from the 0.20-PI contour to

the 0.50-PI contour, and as mentioned earlier, is a much

smaller area than at the Ismay–Desert Creek interval. In the

areas ≥0.50 PI, the potential for condensate, gas from

100 90 80 70 60 50 40 30 20 10 0

TIME (Ma)

Early generation

Mof hydrocarbons

M10% to 25%

Main phase, generation

Mof hydrocarbons

M25% to 65% 

Permian

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

EXPLANATION

16,000

14,000

12,000

10,000

8000

6000

4000

2000

0

DEPTH, IN FEET 

K PA E PO

250 ̊F

200 ̊F

150 ̊F

100 ̊F

O M

B
O28 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

thermally cracked oil, and thermogenic gas from kerogen in

the rock is good.

An area of high thermal maturity, near Hermosa, Colo.,

similar to that described previously for the Ismay–Desert

Creek interval, is evidenced in the Cane Creek cycle by two

samples having vitrinite reflectance values of 1.62 and 1.52

percent (table 2). As previously discussed, this part of the

basin contains several igneous intrusions and experienced a

higher heat flow during Tertiary time. It is hard to determine

the pre-Tertiary thermal and petroleum-generation history of

Paradox Formation source rocks within this area of high

maturity because the Tertiary heating has masked all previous events. It is likely that oil once generated in the area has

been destroyed; however, the high maturity should not discount the potential for gas generation and accumulation in

this area.

BURIAL, THERMAL, AND 

PETROLEUM-GENERATION MODELS

The following models illustrate the burial and thermal

histories for six areas in the Paradox Basin (shown by large

dots on figs. 1, 10, and 11) for the time period of Cambrian

through present. Most of the discussion focuses on petroleum

generation from the Ismay–Desert Creek interval and the

Cane Creek cycle of the Paradox Formation. Two burial,

thermal, and petroleum-generation curves are shown for each

model: one illustrating Cambrian through present and a second illustrating the last 100 or 200 m.y. The detail curve is

necessary to identify important petroleum-generation events,

as well as the time period of rapid uplift and erosion between

37 or 25 Ma to present.

MONUMENT UPWARP

The area encompassing the Monument upwarp (figs. 1,

2) is in the least deeply buried, least mature part of the Paradox Basin. The burial history for Cambrian through present

is illustrated by figure 12A. During late Paleozoic time, this

area was in the stable to slowly subsiding western shelf

region of the basin and is characterized by a relatively thin

Pennsylvanian and Permian stratigraphic section (fig. 5,

table 3). During Triassic and Jurassic time, only a relatively

moderate to thin stratigraphic section was deposited (fig. 6,

Figure 13. Burial, thermal, and petroleum-generation model of the area near the confluence of the Green and Colorado Rivers (see

figs. 1 and 2). A, Cambrian through present. B, Expanded time scale illustrating 100 Ma to present.

0

2000

4000

6000

8000

10,000

12,000

14,000

16,000

18,000

500 400 300 200 100 0

250 ̊F

200 ̊F

150 ̊F

100 ̊F

DEPTH, IN FEET

600

TIME (Ma)

Permian

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

pe e O SD M h P J K PA T E

A

O M
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O29

table 3), indicating a time of structural and sedimentological

quiescence. An estimated 5,800 ft of Cretaceous rocks were

once present in the area of the Monument upwarp (Molenaar,

1981; R.S. Zech, written commun., 1994) representing thick,

rapid deposition in the Cretaceous interior seaway. Because

of igneous activity that occurred in the southern part of the

Paradox Basin from about 32 to 25 Ma, we estimate that

1,000 ft of Tertiary volcaniclastics were deposited in the

area. Beginning at approximately 25 Ma and continuing until

present time, uplift and subsequent erosion have removed

Tertiary, Cretaceous, Jurassic, Triassic, and uppermost Permian strata from the Monument upwarp area (fig. 12).

PI values for the Ismay–Desert Creek interval and Cane

Creek cycle are 0.10 and about 0.20, respectively, in the

Monument upwarp area (figs. 10, 11). In this area, the

Ismay–Desert Creek interval was buried to a maximum

depth of about 13,400 ft at 25 Ma, and the Cane Creek cycle

was buried to a maximum depth of about 14,300 ft (fig. 12).

Maximum maturity was achieved at about 25 Ma. A constant

heat flow of 40 mWm–2 for the entire burial and thermal history is required to match the measured maturity values for

the area. It is possible that an elevated heat flow associated

with igneous activity during the Tertiary occurred; however,

the thermal effects from intrusive bodies are generally localized, and there are no intrusive bodies in the immediate area.

An increased heat flow in the Monument upwarp area during

the Tertiary results in thermal maturity values that are too

high for this area. The isotherms calculated using the above

heat-flow value illustrate temperature variations with depth

and through time (fig. 12).

The petroleum-generation model for the Monument

upwarp area (fig. 12B) indicates that early oil generation

from the Ismay–Desert Creek interval began at about 74 Ma.

Significant oil generation, enough for accumulation and

migration (PI=0.10), began later, at about 45 Ma, and likely

lasted until the time of uplift, erosion, and subsequent cooling at 25 Ma. Oil generation from the Cane Creek cycle

began earlier than for the Ismay–Desert Creek interval due to

greater depth of burial associated with deposition of Middle

Pennsylvanian strata. Early oil generation from the Cane

Creek began at about 77 Ma, and significant oil generation

began at about 69 Ma (fig. 12B). As with the Ismay–Desert

Creek interval, oil generation from the Cane Creek lasted

until 25 Ma.

Permain

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

18,000

16,000

14,000

12,000

10,000

8000

6000

4000

2000

0

DEPTH, IN FEET

TIME (Ma)

Early generation

Mof hydrocarbons

M10% to 25%

EXPLANATION

Main phase, generation

Mof hydrocarbons

M25% to 65%

Late generation

Mof hydrocarbons

M65% to 90%

100 90 80 70 60 50 40 30 20 10 0

K PA E PO

250 ̊F

200 ̊F

150 ̊F

100 ̊F

B

O M
O30 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

CONFLUENCE OF THE GREEN AND

COLORADO RIVERS

The area around the confluence of the Green and Colorado Rivers (figs. 1, 2) has experienced a similar burial history as the Monument upwarp (compare figs. 12A and 13A);

however, in the confluence area, the maturity of the

Ismay–Desert Creek interval and the Cane Creek cycle is

slightly higher (figs. 10, 11). The Pennsylvanian section

(especially the Middle Pennsylvanian) in the confluence area

is thicker than that in the Monument area, and the Permian

sections are similar. Triassic and Jurassic rocks are thinner in

the confluence area (fig. 6, table 3), and thicknesses of Cretaceous and Tertiary strata are the same as used for the Monument upwarp area (5,800 ft and 1,000 ft, respectively).

Beginning at approximately 25 Ma and continuing until the

present, erosion has removed Tertiary, Mesozoic, and uppermost Permian rocks from the confluence area.

Production-index values for the Ismay–Desert Creek

interval are near 0.20, and, for the Cane Creek cycle, they are

about 0.25—higher than indices for the Monument upwarp

area (figs. 10, 11). In the confluence area, at maximum burial

at 25 Ma, the Ismay–Desert Creek interval was buried to

about 13,000 ft and the Cane Creek cycle to about 14,200 ft.

Although overall depth of burial is similar to that for the

Monument upwarp area, the Middle Pennsylvanian and

Honaker Trail sections are sufficiently thicker in the confluence area to have an effect on the maturity of the

Ismay–Desert Creek interval and the Cane Creek cycle at

maximum burial.

A constant heat flow of 42 mWm–2 for the entire burial

and thermal history is required to match the measured maturity values for the area. Similar to the Monument upwarp

area, it is possible that an elevated heat flow associated with

igneous activity during the Tertiary occurred; however, there

are no intrusions in the immediate area. Raising the heat flow

would result in an excessively high maturity for this area.

The isotherms calculated using the heat-flow value of 42

mWm–2 illustrate temperature variations with depth and

through time (fig. 13).

The combination of (1) a thicker Pennsylvanian section

for the confluence area than in the areas to the southwest in

Figure 14. Burial, thermal, and petroleum-generation model of the area near Green River, Utah (see figs. 1 and 2). A, Cambrian through

present. B, Expanded time scale illustrating 100 Ma to present.

600 500 400 300 200 100 0

18,000

16,000

14,000

12,000

10,000

8000

6000

4000

2000

0

TIME (Ma)

DEPTH, IN FEET

Upper and Middle

Jurassic

Lower Jurassic

Upper Triassic

Lower Triassic

Permian

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

E PA pe e O S D M h P T J K

100 ̊F

150 ̊F

200 ̊F

250 ̊F

300 ̊F

350 ̊F

O M

A
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O31

conjunction with (2) a slightly higher heat flow has resulted

in an earlier timing for oil generation from the Ismay–Desert

Creek interval and the Cane Creek cycle. The petroleum-generation model for the area around the confluence of

the Green and Colorado Rivers (fig. 13B) indicates that early

oil generation from the Ismay–Desert Creek interval began

at about 75 Ma. Significant oil generation, enough for accumulation and migration (PI=0.10), began at about 60 Ma and

likely lasted until the time of uplift at 25 Ma. Oil generation

from the Cane Creek cycle began before oil generation from

the Ismay–Desert Creek interval due to greater depth of

burial associated with deposition of Middle Pennsylvanian

strata. Early oil generation from the Cane Creek began at

about 80 Ma and significant oil generation at about 75 Ma

(fig. 13B). The petroleum-generation model indicates that

temperatures and maturities were sufficiently high (PI >0.20,

equivalent to about 0.80–0.90 percent Ro) for some gas generation from kerogen in the Cane Creek cycle beginning at

57 Ma. As with the Ismay–Desert Creek interval, oil and gas

generation from the Cane Creek lasted until uplift, erosion,

and subsequent cooling after 25 Ma.

GREEN RIVER, UTAH

The area around the town of Green River, Utah, is one

of the most thermally mature areas in the Paradox Basin

(figs. 10, 11). Three factors play integral roles in determining

this high level of thermal maturity: (1) a relatively thick Tertiary section (eroded), (2) less erosion than other parts of the

basin, and (3) a high heat flow. The petroleum-generation

history for this area shows that source rocks in the Paradox

Formation were in the oil window for only a short duration

before overmaturity and destruction.

During late Paleozoic time, the area around Green

River, Utah, was in the western part of the Paradox Basin on

a fairly stable shelf or platform, and a relatively thin Pennsylvanian and Permian section was deposited (fig. 5, table

3). The Triassic and Jurassic section is relatively thin in this

area; however, it thickens dramatically to the southeast (fig.

6). A thick Cretaceous section of 6,000 ft is estimated to

have covered this area, similar to those thicknesses preserved at the Book Cliffs immediately to the north. As discussed previously, Paleocene and Eocene strata are also

thought to have once been present in this area. We assume

Middle and Upper

Jurassic

Lower Jurassic

Upper Triassic

Lower Triassic

Permian

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

TIME (Ma)

K PA E PO

0

2000

4000

6000

8000

10,000

12,000

14,000

16,000

18,000

100 90 80 70 60 50 40 30 20 10 0

DEPTH, IN FEET

350 ̊F

300 ̊F

250 ̊F

200 ̊F

150 ̊F

100 ̊F

Early generation

Mof hydrocarbons

M10% to 25%

Main phase, generation

Mof hydrocarbons

M25% to 65%

Late generation

Mof hydrocarbons

M65% to 90%

EXPLANATION

B

O M
O32 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

that 2,000 ft of Tertiary rocks (North Horn and Green River

Formation equivalents) were deposited in this area; however, this may be a conservative estimate. In the area around

Green River, Utah, uppermost Jurassic strata are present on

the surface. We estimate that about 8,000 ft of erosion

occurred here, much less than in most of the Paradox Basin.

Therefore, source rocks in the Green River, Utah, area were

subjected to a greater burial depth and temperature for a

longer period of time.

In the Green River, Utah, area, production indices for

the Ismay–Desert Creek interval are about 0.60, and production indices for the Cane Creek cycle are greater than 0.60.

During maximum burial at about 37 Ma, the Ismay–Desert

Creek interval was buried to a depth of about 14,000 ft and

the Cane Creek was buried to about 15,400 ft (fig. 14).

Because there are no intrusive rocks in the area, a constant

heat flow of 53 mWm–2 was used to match the measured

maturity values. Except for the Hermosa, Colo., area, which

was influenced by Tertiary igneous activity, the Green River,

Utah, area has the highest heat flow of the areas discussed in

this report. The isotherms in figure 14 illustrate the high temperatures with depth and time for this area.

Petroleum generation in the Ismay–Desert Creek interval and Cane Creek cycle is illustrated by figure 14B. Oil

generation in the Ismay–Desert Creek interval began at about

85 Ma, and significant oil generation occurred at about 82

Ma. Due to the high temperatures, oil began to be thermally

cracked to gas at about 78 Ma, and the upper limit for petroleum preservation occurred at about 74 Ma. Thus, the

Ismay–Desert Creek was only in the petroleum-generation

window for about 11 m.y. The onset of oil generation in the

Cane Creek cycle began at about 89 Ma, and significant oil

generation occurred at about 85 Ma. Again, due to the high

temperatures, oil began to crack to gas at about 81 Ma, and

the upper limit for petroleum preservation occurred at about

77 Ma. The Cane Creek cycle was only in the petroleum-generation window for about 12 m.y. Comparison of this petroleum-generation history to that of the Monument upwarp

(fig. 12B) and the confluence area (fig. 13B), in both of

which the Ismay–Desert Creek interval and Cane Creek

cycle were in the petroleum-generation window for more

Figure 15. Burial, thermal, and petroleum-generation model of the area near Moab, Utah (see figs. 1 and 2). A, Cambrian through

present. B, Expanded time scale illustrating 200 Ma to present.

Permian

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

600 500 400 300 200 100 0

25,000

20,000

15,000

10,000

5000

0

pe e O S D MP h T J K PA E

DEPTH, IN FEET

100 ̊F

150 ̊F

200 ̊F

250 ̊F

300 ̊F

TIME (Ma)

O M

A
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O33

than 65 m.y., shows the importance of temporal relationships

between hydrocarbon generation, migration and entrapment,

and structural trap development.

MOAB, UTAH

The area around the town of Moab, Utah, is in the structurally deeper part of the Paradox Basin. In late Paleozoic

time, this part of the basin was rapidly subsiding, and thick

sequences of Pennsylvanian and Permian strata were deposited (fig. 5, table 3). During Triassic and Jurassic time, only

a moderate 3,175 ft of strata were deposited in this part of the

basin; however, to the north, thousands of feet more sediment was deposited (fig. 6). We estimate that 5,900 ft of Cretaceous rocks and 2,000 ft of Paleocene and Eocene rocks

were once present in this part of the basin. Beginning at

about 37 Ma and continuing until the present, uplift and erosion have removed approximately 11,575 ft of rocks from

the area, leaving Permian rocks at the surface (fig. 15). It

should be noted that thicknesses of Pennsylvanian and Permian strata, as well as amounts of erosion and rocks present

at the surface, change very rapidly in this area. Consequently, depending on the exact location, the geologic history may be quite different.

In the Moab area, production indices for the

Ismay–Desert Creek interval are slightly less than 0.30; for

the Cane Creek cycle, production indices are about 0.35.

During maximum burial at about 37 Ma, the Ismay–Desert

Creek interval was buried to about 18,250 ft and the Cane

Creek cycle to 22,000 ft. A constant heat flow of 40

mWm–2 for the entire burial and thermal history is required

to match the measured maturity values for the area. Elevated heat flow in the Tertiary in conjunction with igneous

activity is inappropriate for this area because the nearest

intrusive bodies are 15 mi to the east. In addition, an

increase in heat flow would result in an excessively high

thermal maturity in this area.

The petroleum-generation history illustrated in figure

15B indicates that early oil generation from the

Ismay–Desert Creek interval began at about 82 Ma. Significant oil generation began at 79 Ma, and primary gas generation from kerogen, as well as gas generation from

DEPTH, IN FEET

TIME (Ma)

EXPLANATION

Late generation

Mof hydrocarbons

M65% to 90%

Early generation

Mof hydrocarbons

M10% to 25

Main phase, generation

Mof hydrocarbons 

M25% to 90%

200 180 160 140 120 100 80 60 40 20 0

25,000

20,000

15,000

10,000

5000

0

PO

J K PA E

Permian

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

300 ̊F

250 ̊F

200 ̊F

150 ̊F

100 ̊F

B

O M
O34 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

thermally cracked oil, began at 74 Ma. The upper limit for

petroleum preservation within Ismay–Desert Creek interval

occurred between 50 (lower part) and 40 (upper part) Ma.

Early oil generation from the Cane Creek cycle began at

about 120 Ma—much earlier than for the previously mentioned areas because of the much thicker Middle Pennsylvanian section in the Moab area. Significant oil generation

from the Cane Creek began at 90 Ma, and primary gas generation from kerogen, as well as gas generation from thermally cracked oil, began at about 80 Ma. The upper limit

for petroleum preservation within the Cane Creek occurred

at approximately 75 Ma.

LISBON VALLEY AREA, UTAH

The Lisbon Valley area (Lisbon Valley is a northwest-trending valley, which is located approximately 22 mi

north-northwest of Monticello, Utah) is similar to the Moab,

Utah, area in that it is in the structurally deeper part of the

Paradox Basin (fig. 5). During the Pennsylvanian and Permian, 11,950 ft of strata was deposited around Lisbon Valley

(fig. 5, table 3). Especially important to the thermal and

petroleum-generation history of the Cane Creek cycle are the

4,900 ft of Middle Pennsylvanian rocks. Triassic rocks are

thin in the Lisbon Valley area, and a modest 2,050 ft of Jurassic rocks are present (fig. 6). We estimate that 6,000 ft of Cretaceous rocks (Molenaar, 1981; R.S. Zech, written commun.,

1994) and 1,000 ft of Tertiary rocks were once present in the

Lisbon Valley area. Paleocene North Horn Formation and

Eocene Green River Formation equivalents probably did not

extend this far south; however, some Tertiary strata composed of volcaniclastic and ash beds were likely deposited

here. Beginning at about 25 Ma and continuing until the

present, uplift and erosion have stripped approximately

13,350 ft of strata from the area, exposing Upper Pennsylvanian rocks at the surface (fig. 16). The Lisbon Valley area has

experienced the greatest amount of erosion of the six areas

studied in this report and is among those areas with the most

erosion in the entire Paradox Basin.

The production index for the Ismay–Desert Creek interval in Lisbon Valley is 0.30, and, for the Cane Creek cycle,

it is greater than 0.60 (figs. 10, 11). The large difference in

Figure 16. Burial, thermal, and petroleum-generation model of the Lisbon Valley, Utah, area (see fig. 2 for location of Lisbon Valley anticline). A, Cambrian through present. B, Expanded time scale illustrating 200 Ma to present.

600 500 400 300 200 100 0

25,000

20,000

15,000

10,000

5000

0

TIME (Ma)

DEPTH, IN FEET

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

100 ̊F

150 ̊F

200 ̊F

250 ̊F

300 ̊F

pe e O S D M h P T J KE PA

Honaker Trail

O M

A
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O35

production index, and the reason why the Cane Creek is so

much more mature than the Ismay–Desert Creek, is the thick

Middle Pennsylvanian section (4,900 ft) that overlies the

Cane Creek cycle. At 25 Ma, in Lisbon Valley, the

Ismay–Desert Creek interval reached a maximum burial

depth of 15,750 ft (fig. 16), whereas the Cane Creek was buried to a maximum depth of approximately 21,500 ft (fig. 16).

A constant heat flow of 44 mWm–2 for the entire burial and

thermal history is required to match the calculated maturity

with the measured maturity for Lisbon Valley. As for most

areas of the basin, raising the heat flow in the Tertiary for

Lisbon Valley results in excessively high levels of thermal

maturity. The fact that the Tertiary La Sal Mountain intrusive rocks are only 10 mi north of Lisbon Valley demonstrates the extremely localized effect of heating from these

igneous bodies.

Due to the thicker Pennsylvanian and Permian section

and the slightly higher heat flow in Lisbon Valley, oil generation from the Ismay–Desert Creek interval and Cane Creek

cycle began earlier here than in the Moab area. To the east

and northeast of Lisbon Valley, the Pennsylvanian and Permian section thickens rapidly, and one would expect petroleum generation to begin earlier and the upper limit for

petroleum preservation to occur earlier. The petroleum-generation history illustrated in figure 16B shows that early oil

generation from the Ismay–Desert Creek began at around 82

Ma, similar to the Moab area. Significant oil generation

began at 79 Ma, and gas generation from kerogen as well as

gas generation from cracked oil began at 74 Ma, again similar to the Moab area. The upper limit for petroleum preservation within Ismay–Desert Creek occurred between 42 (lower

part) and 32 (upper part) Ma. Early oil generation from the

Cane Creek cycle began at around 156 Ma—much earlier

than for the previously mentioned areas, again because of the

thicker Middle Pennsylvanian section. Significant oil generation from the Cane Creek began at 100 Ma, and gas generation from kerogen as well as gas generation from cracked

oil began at about 84 Ma. The upper limit for petroleum preservation within the Cane Creek occurred at approximately 78

Ma (fig. 16B).

HERMOSA, COLORADO

Of the six areas studied for this report, the Hermosa,

Colo., area (located approximately 10 mi north of Durango,

Colo.) is unique in that it has undergone the least amount of

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

Cambrian

Ismay-Desert Creek

Honaker Trail

TIME (Ma)

Main phase, generation

Mof hydrocarbons

M25% to 65%

EXPLANATION

Early generation

Mof hydrocarbons

M10% to 25%

Late generation

Mof hydrocarbons

M65% to 90%

200 180 160 140 120 100 80 60 40 20 0

25,000

DEPTH, IN FEET

20,000

15,000

10,000

5000

0

J K PA E PO

300 ̊F

250 ̊F

200 ̊F

150 ̊F

100 ̊F

B

O M
O36 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

Cambrian through Jurassic burial in the Paradox Basin, yet it

is one of the most thermally mature. Figures 4 and 6 and table

3 illustrate the relatively thin sub-Pennsylvanian, Triassic,

and Jurassic units in the Hermosa area. Figure 5 shows Pennsylvanian and Permian thickness trends in the southeastern

part of the basin near Hermosa, Colo. Thicknesses of Pennsylvanian strata were also obtained from measured sections

near Hermosa Mountain, approximately 10 mi north of

Durango, Colo. (Franczyk, 1992, and K.J. Franczyk, oral

commun., 1994). By extrapolating from nearby outcrops, we

estimate that 6,250 ft of Cretaceous rocks and 2,500 ft of Tertiary rocks (including some volcanics) were once present in

the Hermosa area. This represents the thickest Cretaceous

and Tertiary section of the six study areas. Beginning at

about 25 Ma and continuing until the present time, uplift and

erosion have removed approximately 12,550 ft of Permian

through Tertiary rocks from the Hermosa area, exposing lowermost Permian rocks at the surface (fig. 17).

In the Hermosa, Colo., area, vitrinite reflectance values

of 1.58 percent for the Ismay–Desert Creek interval and 1.62

and 1.52 percent for the Cane Creek cycle indicate that this

is one of the most mature areas in the Paradox Basin. At

about 25 Ma, the Ismay–Desert Creek interval was buried to

a maximum depth of 13,700 ft and the Cane Creek cycle was

buried to about 15,500 ft. Depth of burial in conjunction with

present-day heat-flow values cannot account for the high

level of thermal maturity measured in this area. Several igneous bodies have intruded this part of the basin, and, although

they are not exposed at Hermosa, intrusions may underlie the

area. In order to match the modeled maturity with the measured vitrinite reflectance data, we must assume a variable

heat flow: 600–30 Ma, 45 mWm–2; 30–25 Ma, 63 mWm–2;

and 25–0 Ma, 50 mWm–2. Heat flow in the Tertiary was sufficiently high to mask the previous thermal maturity

achieved during normal burial and heat flow. Isotherm lines

shown in figure 17 illustrate the increase in temperature associated with high heat flow from 30 to 25 Ma.

The petroleum-generation history for the Ismay–Desert

Creek interval and Cane Creek cycle in the Hermosa area is

shown in figure 17B. Petroleum generation, accumulation,

and possible migration predated the increase in heat flow in

Tertiary time; however, the high temperatures between 30

and 25 Ma would have thermally destroyed any liquid hydrocarbons still present in the area. Early oil generation from the

Figure 17. Burial, thermal, and petroleum-generation model of the area near Hermosa, Colo. (this area is represented by the large dot

immediately north of Durango, Colo., on fig. 1). A, Cambrian through present. B, Expanded time scale illustrating 200 Ma to present.

600 500 400 300 200 100 0

16000

14000

12000

10000

8000

6000

4000

2000

0 Permian

Honaker Trail

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Ismay-Desert Creek

Devonian

E PA R C O S D M h P T J K

TIME (Ma)

DEPTH, IN FEET

150 ̊F

250 ̊F

300 ̊F

350 ̊F 

A

O M

200 ̊F

100 ̊F
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O37

Ismay–Desert Creek began at about 74 Ma, and significant

oil generation began at about 72 Ma. Gas generation from

kerogen itself, as well as gas generation from cracked oil,

began at 34 Ma, but, because of the increase in heat flow in

Tertiary time, temperatures quickly exceeded the preservation limit and most petroleum was destroyed at 33 Ma (fig.

17B). It should be noted that the preservation limit for dry

gas has been postulated to occur at higher temperatures and

thermal maturities (Ro as high as 4.0 percent; Waples, 1980)

than those in the Hermosa area. Thus, it is possible that gas

may still be present in this part of the basin. Early oil generation from the Cane Creek cycle began at about 78 Ma, and

significant oil generation began at about 76 Ma. Gas generation from kerogen itself, as well as gas generation from

cracked oil, began at about 66 Ma, and the upper limit for

petroleum preservation within Cane Creek occurred at

approximately 34 Ma. Generation, accumulation, migration,

and even the upper limits for preservation of petroleum from

the Cane Creek cycle occurred prior to, and were not affected

by, the high heat flow in the Tertiary at 30 Ma (fig. 17B).

Similar to the Ismay–Desert Creek interval, however, Cane

Creek gas is still likely preserved in reservoirs in the Hermosa area.

DISCUSSION AND SUMMARY

The petroleum potential of the Ismay–Desert Creek

interval and Cane Creek cycle of the Middle Pennsylvanian

Paradox Formation of the Paradox Basin is directly related to

source rock quality and thermal maturity. Thermal maturity,

in turn, is directly related to the structural, burial, and

heat-flow history. Samples from the Ismay–Desert Creek

and Cane Creek indicate that these strata contain good to

excellent source rocks (table 1). The majority of samples

from both horizons have total organic carbon values of 0.50

percent or more, and some values are as high as 11.0 percent.

The Ismay–Desert Creek interval contains some type I

organic matter, but mainly contains types II and III organic

matter, which are sources for both oil and gas. The Cane

Creek cycle contains types I, II, and III organic matter, which

are sources for oil and gas. For both intervals, samples near

Permian

Honaker Trail

Ismay-Desert Creek

Middle Pennsylvanian

Lower Pennsylvanian

Mississippian

Devonian

200 180 160 140 120 100 80 60 40 20 0

16,000

14,000

12,000

10,000

8000

6000

4000

2000

0

DEPTH, IN FEET

TIME (Ma)

Early generation

Mof hydrocarbons

M10% to 25%

Main phase, generation

Mof hydrocarbons

M25% to 65%

Late generation

Mof hydrocarbons

M65% to 90%

EXPLANATION

PO Ps

J K PA E

100 ̊F

150 ̊F

200 ̊F

300 ̊F

250 ̊F

350 ̊F

B

O M
O38 EVOLUTION OF SEDIMENTARY BASINS—PARADOX BASIN

the eastern part of the basin have a more terrestrial origin and

are likely to be good source rocks for mainly gas.

Thermal maturity for both the Ismay–Desert Creek

interval and Cane Creek cycle follows structural and burial

trends throughout the basin and increases in a general southwest-to-northeast direction (figs. 10, 11). In Pennsylvanian

and Permian time, the eastern part of the basin subsided rapidly, and a thick accumulation of sediments was deposited

(fig. 5). As a direct result of greater depth of burial in the

eastern part of the basin, thermal maturity increases eastward

(figs. 10, 11). In the northernmost part of the basin, near

Green River, Utah, the combination of a relatively thicker

Tertiary sedimentary sequence and a relatively higher basinal heat flow has resulted in a very high thermal maturity.

Although general thermal maturity trends are similar for both

the Ismay–Desert Creek interval and the Cane Creek cycle,

actual maturity levels are higher for the Cane Creek due to

the additional thickness of the Middle Pennsylvanian section.

Another significant difference between the two horizons is

that, in the south-central to southwestern part of the basin, the

Ismay–Desert Creek interval is marginally mature (<0.10 PI)

for petroleum generation, but, throughout most of the basin,

it is mature and in the petroleum-generation window (0.10 to

0.50 PI). The more mature Cane Creek cycle, however, contains no marginally immature areas; it is mature (>0.10 PI) in

the central part of the basin and is overmature and past the

petroleum-generation window (>0.50 PI) throughout most of

the eastern part of the basin (compare figs. 10, 11).

Estimating paleo heat flow is speculative; however,

because the Paradox Basin is in the stable interior of the Colorado Plateau, it is likely that heat flow in the basin has not

changed dramatically through time. It is also probable that a

large part of the Paradox Basin is at maximum heat flow

today. Heat-flow values range from about 40 mWm–2 in the

interior of the basin to as high as 105 mWm–2 on the southeastern periphery of the basin. During the Tertiary, heat flow

near intrusions was undoubtedly high; however, the effect on

the thermal maturity was extremely localized. Heat-flow values required to match the measured thermal maturity values

are consistent with present heat-flow values (table 4). A constant heat flow through time allows a good match for five of

the six areas studied: Monument upwarp, 40 mWm–2; confluence area, 42 mWm–2; Green River, Utah, 53 mWm–2;

Moab, Utah, 40 mWm–2; and Lisbon Valley, 44 mWm–2.

The sixth area, Hermosa, Colo., has a high thermal maturity

that cannot be accounted for by burial alone and is surrounded by Tertiary igneous bodies. A variable heat flow of

45 mWm–2 from 600 to 30 Ma, 63 mWm–2 from 30 to 25

Ma, and 50 mWm–2 from 25 to 0 Ma is required (table 4).

The relationship between structural, burial, and

heat-flow trends in the basin has resulted in differences in the

petroleum-generation history for the Ismay–Desert Creek

interval and the Cane Creek cycle. For example, in the Monument upwarp area, in the most immature, least deeply buried part of the basin, significant oil generation for the

Ismay–Desert Creek interval and the Cane Creek cycle began

at about 45 Ma and 69 Ma, respectively. Oil generation likely

lasted until uplift, erosion, and subsequent cooling began at

about 25 Ma. Thermal maturities sufficiently high for gas

generation were probably never achieved in the Monument

upwarp area. In contrast, in Lisbon Valley, in the more thermally mature, deeply buried part of the basin, significant oil

generation for the Ismay–Desert Creek interval and Cane

Creek cycle began at about 79 Ma and 100 Ma, respectively,

and extreme temperatures and thermal maturities caused

these horizons to pass through the oil window at 74 Ma and

84 Ma, respectively. For the Ismay–Desert Creek interval,

gas generation from kerogen, as well as the cracking of oil,

began at 74 Ma, and the upper limit for gas preservation

occurred at 32 Ma. For the Cane Creek cycle, gas generation

from kerogen, as well as the cracking of oil, began at 84 Ma,

and the upper limit for gas preservation occurred at 78 Ma.

Timing of petroleum generation and destruction has

important implications for the migration and accumulation

Table 4. Heat-flow values used for the burial and thermal models, and timing of petroleum generation from the 

Ismay–Desert Creek interval and Cane Creek cycle for the six areas studied in the Paradox Basin Utah and Colorado.

[The six areas studied are shown by large dots on figs. 1, 10, and 11. Key used for ages of timing of petroleum generation: early oil generation, significant

oil generation, gas generation (from either kerogen or thermal cracking of oil), and upper limit for petroleum preservation]

Monument Confluence Green River, Moab, Lisbon Valley, Hermosa,

upwarp area area Utah Utah Utah, area Colo.

Heat flow

40 mWm-2 42 mWm–2 53 mWm–2 40 mWm–2 44 mWm–2 45 mWm–2 600–30 Ma

constant constant constant constant constant 63 mWm-2 30–25 Ma

50 mWm–2 25–0 Ma

Timing of petroleum generation (Ma)

Ismay–Desert 74, 45, 25 75, 60, 25 85, 82, 78, 74 82, 79,74, 40 82, 79, 74, 32 74, 72, 34, 33

Creek interval

Cane Creek 77, 69, 25 80, 75, 57, 25 89, 85, 81, 77 120, 90, 80, 75 156, 100, 84, 78 78, 76, 66, 34

cycle
BURIAL, THERMAL HISTORY; PETROLEUM POTENTIAL, PARADOX FM., UTAH AND COLORADO O39

of oil and gas. Petroleum generated prior to structural

movement may never accumulate in structural traps or

stratigraphic accumulations and may be lost to the atmosphere through faults and fractures formed during movement. Alternatively, petroleum generated during or after

structural movement can accumulate in structural and

stratigraphic traps.

The distribution of petroleum in the Paradox Basin is

likely related to the type of organic matter in the source

rock and to the burial and thermal history (plates 1, 2).

Plate 1 shows oil and gas wells producing from the

Honaker Trail Formation down through cycle 9 in the Paradox Formation. Also shown are the thermal-maturity production-index contours of the Ismay–Desert Creek interval,

which should represent the thermal maturity of the upper

part of the Paradox Formation. In general, oil, and associated oil and gas, are in areas where the thermal maturity is

in the generation window (PI<0.30–0.40). In the eastern,

more mature part of the Paradox Basin where production

indices are greater than 0.40 (in the range for cracking of

oil to gas), mainly gas is produced. The relationship

between thermal maturity and type of hydrocarbon produced is strong; however, all of the gas in the eastern part

of the basin may not be cracked oil; a contribution of gas

from gas-prone, type III kerogen is probable as well.

Plate 2 shows wells producing from cycle 10 of the Paradox Formation through the Cambrian Lynch Dolomite, as

well as production-index contours for the Cane Creek cycle.

The contours should be representative of these deeper horizons. Although there are fewer producing wells at these

depths in the Paradox Basin, the relationships described for

the younger strata still generally hold true. In the northern

part of the basin, where production indices are 0.20–0.40, oil

only—and oil and gas—are generally produced. In Lisbon

Valley, where maturities are greater (in the gas generation

range), mainly oil and gas and associated gas are produced.

In the southeastern part of the basin where maturities are

high, mainly gas only is produced. As previously discussed,

gas-prone kerogen has likely contributed to some of the gas

in this part of the basin.

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Published in the Central Region, Denver, Colorado

Manuscript approved for publication November 21, 1995

Edited by Richard W. Scott, Jr. and Judith Stoeser

Graphics prepared by William E. Sowers; use made

of author-drafted material

Photocomposition by Joan G. Nadeau