Sedimentology and Depositional History of the 

Upper Triassic Chinle Formation in the 

Uinta, Piceance, and Eagle Basins, 

Northwestern Colorado and Northeastern Utah

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Chapter W

Sedimentology and Depositional History of the 

Upper Triassic Chinle Formation in the 

Uinta, Piceance, and Eagle Basins, 

Northwestern Colorado and Northeastern Utah

By RUSSELL F. DUBIEL

A multidisciplinary approach to research studies of sedimentary 

rocks and their constituents and the evolution of sedimentary 

basins, both ancient and modern

U.S. GEOLOGICAL SURVEY BULLETIN 1787

EVOLUTION OF SEDIMENTARY BASINS UINTA AND PICEANCE BASINS
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

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purposes only and does not imply endorsement by the U.S. Government

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Library of Congress Cataloging-in-Publication Data

Dubiel, Russell F.

Sedimentology and depositional history of the Upper Triassic Chinle Formation 

in the Uinta, Piceance, and Eagle basins, northwestern Colorado and northeastern 

Utah / by RussellF. Dubiel.

p. cm. (Evolution of sedimentary basins Uinta and Piceance basins 

; ch. W) (U.S. Geological Survey bulletin ; 1787)

"A multidisciplinary approach to research studies of sedimentary rocks and their 

constituents and the evolution of sedimentary basins, both ancient and modern."

Supt. of Docs, no.: I 19.3:61787W

1. Geology, Stratigraphic Triassic. 2. Geology Colorado. 

3. Geology Utah. 4. Chinle Formation. I. Title. II. Series. III. Series: U.S. 

Geological Survey bulletin ; 1787. 

QE75.B9 no. 1787-W 

[QE679]

557.3 s dc20 91-23188 

[551.7'09788] CIP
CONTENTS

Abstract Wl 

Introduction Wl 

Previous work W2 

Geologic setting W4 

Stratigraphy W4 

Sedimentology W6

Lithofacies and depositional environments W6

Valley-fill and active channel-fill deposits W6

Lateral-accretion deposits W7

Floodplain deposits W10

Lacustrine-delta and crevasse-splay deposits W16

Lacustrine deposits W17

Eolian deposits W19

Depositional systems and paleogeography W19 

Paleoclimate W22 

Conclusions W22 

References cited W22

FIGURES

1, 2. Maps showing:

1. Schematic reconstruction of Late Triassic paleogeography on Colorado 

Plateau and adjacent regions W2

2. Study area in northwestern Colorado and northeastern Utah W3

3. Chart showing correlation of stratigraphic nomenclature of Upper Triassic 

strata W4

4. Measured stratigraphic sections of Upper Triassic Chinle Formation W8 

5-14. Photographs showing:

5. Fluvial valley-fill conglomerate and sandstone of Gartra Member W13

6. Purple-mottled sandstones of Temple Mountain Member W13

7. Lower part of red siltstone member of Chinle Formation near Derby 

Junction W14

8. Upper part of red siltstone member of Chinle Formation near Derby 

Junction W14

9. Intersecting sandstone-filled mudcracks in lower part of red siltstone 

member of Chinle Formation near Derby Junction W15

10. Pseudoanticlines in paleosols of middle part of red siltstone member of 

the Chinle Formation near Derby Junction W15

11. Root alteration haloes in red siltstone member of Chinle Formation near 

East Brush Creek, Eagle basin W16

12. Lacustrine-deltaic strata in Moss Back Member of Chinle Formation, San 

Rafael Swell W17

13. Lacustrine deposits in Chinle Formation W18

14. Eolian deposits at top of Chinle Formation, East Brush Creek, Eagle

basin W20

15. Map showing schematic reconstruction of Chinle depositional systems in Uinta, 

Piceance, and Eagle basins W21

Contents III
TABLE

1. Locations of measured sections of the Chinle Formation in the Uinta, Piceance, 

and Eagle basins, northwestern Colorado and northeastern Utah W12

IV Contents
EVOLUTION OF SEDIMENTARY BASINS UINTA AND PICEANCE BASINS

Sedimentology and Depositional History of the 

Upper Triassic Chinle Formation in the 

Uinta, Piceance, and Eagle Basins, 

Northwestern Colorado and Northeastern Utah

By Russell F. Dubiel

Abstract

Lithofacies analysis was used to examine depositional 

systems of the Upper Triassic Chinle Formation in the Uinta, 

Piceance, and Eagle basins in northwestern Colorado and 

northeastern Utah. Lithofacies analysis identified deposits of 

valley fills and active channel fills, point bars of moderate- to 

high-sinuosity fluvial systems, floodplains containing paleosols 

and rhizoliths, lakes and lacustrine deltas, and eolian sand 

sheets.

Lateral fades relations determined from field relations 

and stratigraphic cross sections depict the paleogeography at 

the time of Chinle deposition. The ancestral Uncompahgre and 

Front Range uplifts in Colorado supplied clastic detritus to the 

depositional basin. Fluvial systems flowed west and northwest 

from the bounding highlands and deposited sediment within 

paleovalleys and channels and on associated floodplains. 

Fluvial systems graded distally into lacustrine and lacustrinedeltaic systems in the southern and eastern Uinta and Piceance 

basins. In the Eagle basin, the close of Chinle time is marked by 

eolian sand-sheet deposition, reflecting the change from a 

tropical monsoonal climate earlier in the Late Triassic to drier 

conditions at the close of the Late Triassic.

INTRODUCTION

The Upper Triassic Chinle Formation is a sequence of 

continental rocks that was deposited in a back-arc cratonic 

basin (Dickinson, 1981). A magmatic-volcanic arc on the 

western and southwestern margin of the Triassic continent 

provided both volcanic ash and clastic detritus to the Chinle

Manuscript approved for publication, May 15, 1991.

depositional basin, which encompassed a large part of the 

Colorado Plateau and the regions adjacent to it. The Chinle 

depositional basin can be subdivided in this area into a 

major and a minor depocenter.

The major part of the Chinle depositional basin was 

centered near the Four Corners area of Colorado, Utah, 

Arizona, and New Mexico and was north of the Mogollon 

Highlands and south of the ancestral Rocky Mountains (fig. 

1) (Stewart and others, 1972; Blakey and Gubitosa, 1983; 

Dubiel, 1983, 1989a, b; Busbey-Spera, 1988). Detritus was 

shed northward and westward into this part of the Chinle 

basin from the Mogollon Highlands, which lay to the south, 

and southward and westward off the ancestral Rocky 

Mountains, which lay to the north. The ancestral Rocky 

Mountains consisted of the ancestral Uncompahgre 

Highlands and the ancestral Front Range and several minor 

ranges. Fluvial and lacustrine-deltaic depositional systems 

flowed north and west off of the Mogollon Highlands and 

south and west off of the ancestral Uncompahgre and Front 

Range highlands into the southern part of the Chinle 

depositional basin. A second smaller part of the Chinle 

depositional basin was coincident with the areas of the 

present-day Eagle basin in western Colorado and Uinta and 

Piceance basins in northwestern Colorado and northeastern 

Utah. The ancestral Uncompahgre Highlands and the 

ancestral Front Range also contributed clastic detritus 

northward and westward to this smaller part of the Chinle 

depositional basin.

Considerable effort has been focused on delineating 

stratigraphic and sedimentologic relations within the Chinle 

Formation of southeastern Utah, northern Arizona, and 

northern New Mexico (for example, Stewart and others, 

1972; Blakey and Gubitosa, 1983; Dubiel, 1987a, b, c,

Sedimentology of Chinle Formation, Colorado and Utah W1
120° 115° 110° 105°

40°

250 MILES

I ' ' I

0 300 KILOMETERS

Figure 1. Schematic reconstruction of Late Triassic paleogeography on the Colorado Plateau and adjacent regions. 

Arrows depict general transport directions of clastic 

sediment. Details of study area (shaded) are in figure 2.

1989a, b; Lucas and Hayden, 1989); however, few research 

efforts employing modern sedimentologic techniques have 

been applied to the Chinle in northwestern Colorado and 

northeastern Utah.

This study examined the sedimentology and 

deposhional history of the Chinle Formation in outcrops in 

the Uinta, Piceance, and Eagle basins of northwestern 

Colorado and northeastern Utah (fig. 2). Upper Triassic 

rocks are exposed in four widely separated areas within the 

broad region outlined for this study: (1) the Eagle basin and 

White River uplift in western Colorado, (2) the Uinta and 

Piceance basins in northwestern Colorado and northeastern 

Utah in the vicinity of Dinosaur National Monument and the 

Uinta Mountains, (3) the San Rafael Swell in east-central 

Utah, and (4) western Colorado and eastern Utah in the 

canyon country near Moab, Utah. This report presents the 

results of detailed sedimentologic examination of outcrops 

in the Uinta, Piceance, and Eagle basins and some 

preliminary data from the San Rafael Swell and near Moab.

Stratigraphy of the Chinle Formation and related 

Upper Triassic strata on the Colorado Plateau and 

correlations with Upper Triassic rocks northward into 

Wyoming are complicated by a combination of varied 

historical stratigraphic nomenclature, a lack of stratigraphic 

and biostratigraphic marker horizons within the continental 

strata, and the laterally persistent, but generally poorly 

exposed character of the Chinle. Exact stratigraphic 

relations between units are further complicated by rapid 

lateral facies changes typical of continental rocks. This

report does not establish new stratigraphic nomenclature but 

rather discusses the units in terms of genetic sedimentologic 

units and previously published stratigraphy.

Acknowledgments. This paper has benefited from 

constructive reviews by Samuel Johnson and Robert B. 

O'Sullivan, U.S. Geological Survey. Gary Skipp, U.S. 

Geological Survey, provided invaluable assistance in the 

field. Steven C. Good, University of Colorado at Boulder, 

and J. Michael Parrish, Northern Illinois University, 

provided identifications of invertebrate and vertebrate 

fossils, respectively, and both collaborated on discussions 

and additional aspects of cooperative interdisciplinary 

research. The work on which this report is based was 

supported by the U.S. Geological Survey Evolution of 

Sedimentary Basins Program.

PREVIOUS WORK

The Chinle Formation has been the focus of many 

reports related to Triassic stratigraphy, Late Triassic 

paleontology, and economic uranium-vanadium deposits. 

Many of those reports discuss that part of the Chinle 

deposited in and around the Four Corners region of Utah, 

Colorado, New Mexico, and Arizona. An inclusive review 

of previous literature on the Chinle Formation and related 

Triassic rocks on the Colorado Plateau is in Stewart and 

others (1972). More recent reports, particularly those related 

to sedimentologic studies, are summarized in Dubiel 

(1987a, c, 1989a, b), Dubiel, Good, and Parrish (1989), and 

Dubiel and Skipp (1989).

In contrast to the many publications on the Chinle in 

the Four Corners region, relatively few publications deal 

with the Chinle Formation of northwestern Colorado and 

northeastern Utah. Despite being few in number, these 

publications describe the complex stratigraphy of Upper 

Triassic rocks and provide the basis for subsequent detailed 

studies both in the northern part of the Colorado Plateau and 

farther to the north in Wyoming. The Shinarump Member 

and Chinle Formation were recognized by most geologists 

working in the region (see, for example, Thomas and others, 

1945; Kinney, 1955). Thomas and Krueger (1946) first used 

the terms Stanaker Formation and Gartra Grit Member for 

the Upper Triassic rocks of the Uinta Mountains that they 

considered lithologically distinct from the Chinle. Keller 

(1952, 1953) suggested that the presence of analcime in the 

Chinle near Vernal, Utah, indicates that those rocks are 

correlative with the analcime-bearing Upper Triassic Popo 

Agie Formation in Wyoming. MacLachlan (1957) discussed 

Triassic stratigraphy in parts of Utah and Colorado. Poole 

and Stewart (1964) extended correlations of Upper Triassic 

strata on the Colorado Plateau northward into the Uinta 

Mountains. Sikich (1965) briefly discussed Upper Triassic 

stratigraphy in the eastern Uinta Mountains. High and 

Picard (1967), McCormick and Picard (1969), and High and 

others (1969) supported Keller's contention and extended

W2 Evolution of Sedimentary Basins Uinta and Piceance Basins
I Dinosaur 

I National 

I Monument

Figure 2. Map of the study area in northwestern Colorado and northeastern Utah showing geographic features, measured 

sections (numbered circles), and lines of cross sections referred to in text (see fig. 4). Outcrops of Chinie Formation shown in black. 

Modified from Stewart and others (1972) and Dubiel and Skipp (1989).

the Wyoming nomenclature to the Uinta Mountains area. 

Pipiringos (1968) described correlations and nomenclature 

of Triassic rocks in south-central Wyoming. Pipiringos and 

others (1969) discussed the stratigraphy of the Chinie 

Formation in north-central Colorado, just north of the Eagle 

basin. Pipiringos, in Segerstrom and Young (1972), 

described correlations of the Chinie and Popo Agie from 

north-central Colorado northward into Wyoming. Building 

on several earlier reports on Triassic stratigraphy, Stewart 

and others (1972) provided correlations and interpretations 

of depositional environments of the Chinie Formation and 

related Triassic strata throughout the Colorado Plateau and 

extended Chinie nomenclature into the Uinta Mountains in 

northeastern Utah and into northwestern Colorado.

Reports specifically describing the region of this 

report include several stratigraphic studies and only a few 

sedimentologic studies. Shropshire (1974) studied the 

stratigraphy and depositional environments of the Chinie 

and Jelm Formations in north-central Colorado. Red-bed

formations near Aspen, Colorado, including the Chinie, 

were briefly described by Freeman and Bryant (1977). 

Principal Triassic unconformities of the Western Interior of 

the United States are summarized in Pipiringos and 

O'Sullivan (1978), along with a discussion of Triassic 

correlations relevant to the present study. Lupe (1977,1979) 

interpreted depositional environments and measured 

stratigraphic sections of the Chinie in Utah from the San 

Rafael Swell to the Moab area. The sedimentology of the 

Upper Triassic Dolores Formation in southwestern 

Colorado, a correlative of the Chinie, was studied by 

Blodgett (1984, 1988). Lungfish burrows and possible 

freshwater crayfish burrows have been described from 

Chinie outcrops within the study area (Dubiel, Blodgett, and 

Bown, 1987, 1988, 1989; Hasiotis and Mitchell, 1989). 

Several reports discuss fossil fish (Schaeffer, 1967; Elliot, 

1983, 1987) and the sedimentology and paleoecology of 

Chinie outcrops (Dubiel, Good, and Parrish, 1989; Parrish 

and others, in press) near Bedrock in western Colorado.

Sedimentology of Chinie Formation, Colorado and Utah W3
Overlying 

units

Upper 

Triassic

Underlying 

units

Uinta Mountain area, northeastern Utah and

Thomas and 

Kreuger 

(1946)

Navajo 

Sandstone

Stanaker Formation / (not named)

Gartra 

Grit 

Member 

 \_^ ~- -^ ^_^^~^_^-~^~_^

Woodside 

Shale

Kinney 

(1955)

Navajo 

Sandstone

Chinie Formation

Upper 

member

Lower 

member

Shinarump 

Conglomerate

 - .^ ^^ -~~-~^

Monkopi 

Formation

Poole and 

Stewart 

(1964)

Glen Canyon 

Sandstone

( Chinie Formation

r- ^Rlj^

Upper J> Red 

member\ silt- 

<^> stone

^ Sand- \ 

Ocher\ stone\ 

silt-~-\ and \ 

stone\ conglom-\ 

membei\ erate J^ 

^member \^

Mottled 

member

Gartra 

Member

Moenkopi 

Formation

High and 

Picard 

(1967)

\ (Popo Agie\ Formation ~~ 

Navajo 

Sandstone

ymm

Upper 

carbonate 

unit

Ocher 

unit

Purple 

unit

Gartra 

Member

Moenkopi 

Formation

McCormick 

and Picard 

(1969)

\ )(Popo AgieFormation ~~ _

( /zi -^

ugget Sandstone 

avajo Sandstone)

mmm

Upper 

carbonate 

unit

Ocher 

unit

Purple 

unit

Gartra 

Member

** -^ \_^ ^ - ^\

Moenkopi 

Formation

Figure 3 (above and facing page). Diagram showing correlation of stratigraphic nomenclature of Upper Triassic 

strata in Colorado, Utah, and Wyoming.

Dubiel and Skipp (1989) reported on preliminary 

stratigraphic and sedimentologic studies of the Chinie 

Formation in the Eagle basin of western Colorado.

GEOLOGIC SETTING

The ancestral Rocky Mountains, which included the 

ancestral Uncompahgre and Front Range highlands, were 

uplifted in the Pennsylvanian and Early Permian (for 

example, Mallory, 1972; Kluth and Coney, 1981) and 

continued to provide clastic detritus to the Chinie 

depositional basin during the Late Triassic (fig. 1). Paleozoic and Early Mesozoic sedimentary strata deposited 

adjacent to the uplifts were eroded, reworked, and 

incorporated into the Chinie.

In the Eagle basin, the Chinie Formation unconformably overlies the Pennsylvanian and Permian Maroon 

Formation, including the Permian Schoolhouse Member 

(previously called the Schoolhouse Tongue of the Weber 

Sandstone; Johnson and others, 1990), or the Permian and 

Triassic State Bridge Formation (Stewart and others, 1972; 

Tweto and others, 1978; Johnson, 1987; Dubiel and Skipp, 

1989). On a regional scale, the unconformity is angular, in 

that the Chinie overlies progressively older strata in areas on 

or near the ancestral uplifts (Tweto and others, 1978). At 

Colorado National Monument, on the northeastern flank of

the present Uncompahgre uplift, the Chinie unconformably 

overlies Precambrian crystalline rocks.

In the area around Dinosaur National Monument, in 

the Uinta Mountains of northeastern Utah and northwestern 

Colorado, and in the San Rafael Swell and near Moab in 

eastern Utah, the Chinie Formation rests unconformably on 

the Lower and Middle (?) Triassic Moenkopi Formation 

(Stewart and others, 1972; Pipiringos and O'Sullivan, 

1978).

In the northern part of the study area, near the Uinta 

Mountains and Dinosaur National Monument, the Chinie 

Formation is unconformably overlain by an eolian unit that 

historically has been assigned to the Triassic (?) and 

Jurassic Nugget Sandstone (Pipiringos and O'Sullivan, 

1978), or the Lower Jurassic Navajo Sandstone, or the Glen 

Canyon Sandstone. Recent work suggests that the lower 

part of this eolian unit is correlative with the Lower Jurassic 

Wingate Sandstone of the Glen Canyon Group farther to the 

south in the San Rafael Swell and near Moab (Peterson, 

1988). Observations made during the present study indicate 

that the thin eolian unit immediately overlying the Chinie 

can be distinguished from an overlying eolian unit that is 

probably correlative with the Navajo Sandstone and the 

Nugget Sandstone. The results of the present study support 

Peterson's (1988) assignment of the lower thin eolian unit to 

the Wingate Sandstone. In the San Rafael Swell and near

W4 Evolution of Sedimentary Basins Uinta and Piceance Basins
western Colorado Western Colorado Southeastern 

Utah Wyoming

High and 

others 

(1969)

Stewart and 

others 

(1972)

Stewart and 

others 

(1972)

Shropshire 

(1974)

Stewart and 

others 

(1972)

High and 

Picard 

(1969)

Nugget 

Sandstone

A

Upper \ 

carbonate (,

Glen Canyon 

Sandstone

Ocher 

unit

SandPurple stone

unit and

conglom-

______erate_ 

unit

Gartra 

Member

Moenkopi 

Formation

Wingate 

Sandstone

SandMottled stone

member and

conglom- 

_______erate

nember

Moenkopi 

Formation

Red

siltstone 

member

State Bridge 

Formation

Entrada 

Sandstone

Upper 

unit

State Bridge 

Formation

Wingate 

Sandstone

Church

Rock

Member

Owl

Rock

Member

Petrified Forest 

Member__ 

Moss 

Back 

Member 

Monitor 

Butte Member

Nugget 

Sandstone

Upper

Carbonate

unit

Ocher 

unit

Purple 

unit

Moenkopi 

Formation

Crow Mountain 

Formation

Moab, the Chinle is unconformably overlain by the Lower 

Jurassic Wingate Sandstone. In part of western Colorado, 

the Chinle is unconformably overlain by the Middle Jurassic 

Entrada Sandstone.

STRATIGRAPHY

Stratigraphy of the Chinle Formation in the large area 

encompassed by the present study is complicated by the 

designation of different formal and informal nomenclature 

by several workers for exposures in widely separated 

regions (fig. 3). Stewart and others (1972) summarized the 

stratigraphic nomenclature of the Chinle on the Colorado 

Plateau, and those designations are followed in this report. 

In the San Rafael Swell and near Moab, the Chinle consists, 

in ascending order, of the Temple Mountain Member, 

mottled member, and Shinarump, Monitor Butte, Moss 

Back, Petrified Forest, Owl Rock, and Church Rock 

Members. For the area around Moab, Blakey and Gubitosa 

(1983) applied the name Kane Springs strata to lateral facies 

equivalents of the Petrified Forest and Owl Rock Members.

The issue is complicated, however, with the 

application by some workers of the name Popo Agie 

Formation, which is used in Wyoming, for Upper Triassic 

strata in the Uinta Mountains (High and Picard, 1967; High 

and others, 1969; McCormick and Picard, 1969). Despite 

the discrepancy over whether the rocks are assigned to the

Chinle Formation or the Popo Agie Formation, informally 

designated stratigraphic units and their lateral and vertical 

relations around the Uinta Mountains are common to each 

of the reports (fig. 3). The descriptive informal names of the 

subdivisions are virtually identical in each report. The 

Gartra Member is generally accepted in each report as the 

conglomeratic sandstone at the base of the Chinle or Popo 

Agie, although Kinney (1955) termed this unit the Shinarump Conglomerate. Overlying the Gartra is either a 

mottled member or a purple unit, clearly referring to the 

same stratigraphic unit. Shropshire (1974) provided the only 

significant deviation from this scheme, grouping the basal 

conglomerates and the mottled units directly above them 

into the lower unit and the remainder of the Chinle into an 

upper unit (fig. 3). As discussed in the sedimentology 

section later in this report, Shropshire's subdivisions have 

some validity because the present study interprets the 

mottled coloration to be the result of pedogenic or early 

diagenetic alteration that affected both the Gartra and the 

overlying siltstones and mudstones.

Above the Gartra Member, one or more fine-grained 

units of the Chinle Formation is recognizable as distinct 

lithostratigraphic units, and they have similar informal 

names (fig. 3). In northwestern Colorado, the red siltstone 

member constitutes the entire upper Chinle. In the eastern 

part of Dinosaur National Monument, the middle part of the 

Chinle contains a sandstone and conglomerate member that 

interfingers with the overlying red siltstone member and the

Sedimentology of Chinle Formation, Colorado and Utah W5
equivalent ocher siltstone member. The middle part of the 

Chinle is overlain and interfmgers with the upper member, 

also referred to as the upper carbonate unit. Each of these 

previously named units or members was recognized in the 

present study, and the general stratigraphic relations are 

supported by the sedimentology study.

The relationship between the Chinle Formation and 

the various overlying rocks that are referred to as the 

Nugget Sandstone, Navajo Sandstone, Glen Canyon 

Sandstone, or Wingate Sandstone has been described as 

interfmgered, unconformable, or an angular unconformity 

(fig. 3). The present study indicates that in the Uinta 

Mountains and in Dinosaur National Monument the Chinle 

Formation is unconformably overlain by eolian sandstones 

equivalent to the Lower Jurassic Wingate Sandstone, which 

unconformably overlies the Chinle in the San Rafael Swell 

and near Moab. Peterson (1988) assigned the eolian 

sandstone overlying the Chinle in the Uinta Mountains and 

around Dinosaur National Monument to the lower part of 

the Nugget Sandstone and stated that it is equivalent to the 

Wingate Sandstone farther to the south in Utah. 

Observations on grain size, lithology, and bedding made in 

the present study indicate that the eolian rocks unconformably overlying the Chinle in the Uinta Mountains can be 

subdivided into two distinct eolian units. The lower eolian 

unit is thin (10-30 ft, 3-10 m) and probably is equivalent to 

the Wingate Sandstone, whereas the upper eolian unit is 

much thicker and lighter in color and probably correlates 

with the Navajo Sandstone, supporting Peterson's (1988) 

conclusions. In western Colorado, the Chinle is unconformably overlain by eolian strata of the Middle Jurassic Entrada 

Sandstone. Despite the large-scale angular unconformity 

indicated by these regional relationships, on a local scale 

beds appear conformable, and there appears to be no angular 

unconformity between the Popo Agie and the overlying 

Nugget Sandstone as reported by High and others (1969) 

and Picard (1975). The contact shown in photographs of 

those reports most likely depicts a diastem within Chinle 

strata typical of a crevasse splay or lacustrine delta rather 

than an angular contact between the Chinle and the Nugget.

SEDIMENTOLOGY

In the study area, the Chinle Formation consists of as 

much as 1,000 ft (300 m) of predominantly dark-reddishbrown to moderate-reddish-orange, fine-grained sandstone, 

siltstone, and mudstone and lesser amounts of dark-gray to 

reddish-purple conglomeratic sandstone, limestone-pebble 

conglomerate, sandstone, and gray limestone. Stratigraphic 

sections of the Chinle Formation (fig. 4, table 1) were 

measured to record data on composition, color, grain size, 

bedding, physical sedimentary structures, and lithesome 

geometry. These data and additional observations on paleosols and biogenic sedimentary structures, including trace 

fossils and rhizoliths, were utilized to designate lithofacies

in the Chinle. Lithofacies then were grouped into lithofacies 

assemblages on the basis of rock type, lithosome geometry, 

sedimentary structures, fauna and flora, and repetition of the 

sequences. Each lithofacies assemblage represents a 

particular depositional environment (fig. 4).

This study utilized the concept of lithofacies analysis, 

rather than the traditional descriptive approach of lithostratigraphy, to decipher the depositional history of the 

Chinle in the Uinta, Piceance, and Eagle basins. Because of 

the lack of physical and biostratigraphic markers in the 

continental rocks of the Chinle, the lithofacies approach was 

deemed more suitable for correlating measured sections and 

for interpreting the succession of depositional environments 

and depositional history. Sections are not hung on a specific 

horizontal datum because no such datum exists within the 

Chinle to correlate definitively the laterally variable 

continental depositional facies. Because unconformities 

mark both the lower and upper contacts of the Chinle, those 

horizons also do not provide suitable datums for correlating 

Chinle strata. The method employed herein utilizes facies 

concepts and the application of Walther's Law, together 

with facies relations provided by sedimentologic studies of 

ancient and modern continental systems (for example, 

Reading, 1978; Miall, 1984), to make reasonable 

correlations of Chinle lithofacies assemblages (fig. 4). 

Where available, beds and units that can be identified from 

section to section were used as local stratigraphic markers. 

Because strata change facies in several areas, individual 

beds may not correlate precisely between sections; the 

lithofacies assemblages and transitions shown, however, 

provide the most reasonable and accurate correlations 

possible for depicting the Chinle depositional system.

Lithofacies and Depositional Environments

The lower part of the Chinle Formation fills local 

scours and large swales eroded into the underlying rocks. 

The contact is generally sharp and irregular, but it is 

difficult to pick in places where conglomeratic units of the 

Chinle overlie compositionally similarly conglomeratic 

strata of the Maroon or State Bridge Formations. The upper 

part of the Chinle is characterized by a variety of lithofacies 

that includes several lithologies and associated biogenic and 

physical sedimentary structures. The following lithofacies 

assemblages were designated to describe the different 

depositional environments of the Chinle in the study area 

(fig. 4).

Valley-Fill and Active Channel-Fill Deposits

The basal part of the Chinle Formation consists of as 

much as 60 ft (18 m) of gray to yellow and darkW6 Evolution of Sedimentary Basins Uinta and Piceance Basins
reddish-brown or dark-reddish-purple conglomerate, conglomeratic sandstone, and sandstone containing pebbles of 

quartz, granite, and gneiss as large as 4.5 in. (11 cm) in 

diameter (fig. 5). Freeman (1971) reported 388 ft (117 m) of 

a unit he termed the "coarse unit of Toner Creek" of the 

State Bridge Formation. In the same area near Toner Creek, 

S.Y. Johnson (U.S. Geological Survey, written commun., 

1989) measured about 170 ft (52 m) of conglomerate that he 

believed correlates with Freeman's unit but that should be 

assigned to the Chinle. It was not possible to corroborate 

this observation at Toner Creek during the present study. 

Conglomeratic units are medium to thick bedded and 

exhibit medium- to large-scale trough and planar crossbeds, 

or they are massive. Sandstone strata are coarse to fine 

grained, are thin to medium bedded, and contain planar and 

trough crossbeds, climbing-ripple laminations or horizontal 

laminations. In general, both the grain size and the scale of 

the sedimentary structures decrease upward within this unit.

Conglomeratic units at the base of the Chinle are 

generally assigned to the Gartra Member in northwestern 

Colorado and northeastern Utah and to the Temple 

Mountain and Shinarump Members in the San Rafael Swell. 

At Derby Junction (figs. 3, 4), the Gartra contains blocks of 

eolian sandstone from the underlying State Bridge 

Formation that are as large as 1.5 ft (0.5 m), indicating 

lithification of the underlying strata prior to erosion and 

redeposition within the Chinle. At East Brush Creek (figs. 3, 

4), the Gartra contains clasts of silicified wood that are as 

long as 2 ft (0.6 m). Plots of the maximum pebble size in the 

Gartra Member (Shropshire, 1974), coupled with data on 

pebble sizes in basal units of the Chinle from the present 

study, indicate a general decrease in maximum size of 

siliciclastic pebbles toward the northwest and away from the 

area of the ancestral Uncompahgre and Front Range uplifts. 

The size distribution and composition of the clasts indicate 

a highland source for the clasts. Paleocurrent indicators in 

the Gartra (Stewart and others, 1972; Shropshire, 1974) 

suggest that deposition was generally away from the 

bounding uplifts and toward the northwest into the Uinta, 

Piceance, and Eagle basins.

The grain size, sedimentary structures, and overall 

geometry of coarse-grained deposits in the Gartra, Temple 

Mountain, and Shinarump Members resemble those 

described for modern and ancient fluvial sequences (for 

example, Alien, 1965a, b; Harms and others, 1975). The 

massive conglomeratic and planar crossbedded sandstones 

represent fluvial bedload deposition. The large variations in 

thickness observed on outcrops and between measured 

sections, and the erosional contact with significant relief cut 

into underlying units, indicate that the basal conglomerates 

are valley fills. The grain size and sedimentary structures 

suggest that deposition was by fluvial systems on in-channel 

bars (Rust, 1978). The upward transition to finer grained

sandstone containing trough crossbedding and horizontal 

and climbing-ripple laminations reflects fluvial bedload 

deposition by migrating dunes, ripples, and plane beds 

(Jackson, 1976).

The upper part of the Gartra Member, the lower part 

of the overlying red siltstone member, and the Temple 

Mountain Member of the Chinle Formation (fig. 3) are 

locally mottled purple and white (fig. 6). In western 

Colorado, these mottled strata were termed the mottled 

member by Stewart and others (1972), but Shropshire 

(1974) included the mottled rocks along with the Gartra in 

his lower unit of the Chinle. The present study recognizes a 

gradational contact between the Gartra Member and the 

mottled strata and a gradational contact between the mottled 

strata and the overlying red units of the Chinle. In places, 

each unit intertongues with the others. There is a gradual 

change in grain size and sedimentary structures upward 

through the units that reflects a transition of depositional 

environments. In the San Rafael Swell, mottled strata of the 

Temple Mountain Member generally underlie the Shinarump Member, but, locally in the San Rafael Swell, 

mottled strata are present stratigraphically higher in the 

Chinle.

The mottled coloration of these units is thought to 

reflect alteration and translocation of iron-bearing minerals 

in the rocks, similar to the purple mottled unit of the 

Monitor Butte Member of the Chinle Formation in 

southeastern Utah (Dubiel, 1987a, b, c). Many of the 

mottled units contain ubiquitous, large-diameter, cylindrical 

trace fossils interpreted as lungfish burrows (fig. 6) (Dubiel, 

Blodgett, and Bown, 1987, 1988, 1989) and as freshwater 

crayfish burrows (Hasiotis and Mitchell, 1989). The mottles 

probably represent relocation of iron due to fluctuating 

water tables penecontemporaneous with deposition; thus, 

the strata represent a gleyed paleosol. Both the mottles and 

the long trace fossils reflect fluctuating water tables. A 

similar interpretation is proposed for the development of the 

mottled coloration in the Gartra Member and the Temple 

Mountain Member and associated rocks in this study.

Lateral-Accretion Deposits

The largest part of the upper part of the Chinle 

Formation overlying the conglomerates and sandstones of 

the Gartra, the Shinarump, and the Temple Mountain 

Members consists almost entirely of dark-reddish-brown to 

reddish-orange, very fine to fine grained, thin- to thickbedded sandstone, siltstone, and mudstone. The finegrained units are assigned to the red siltstone member in the 

Eagle basin, to the red siltstone member and the upper 

member or unit in the Uinta Mountains and near Dinosaur 

National Monument, and to the Moss Back and the Church 

Rock Members in the San Rafael Swell and near Moab 

(figs. 2, 3).

Sedimentology of Chinle Formation, Colorado and Utah W7
11

Buford

7

Snowmass 

Creek

Figure 4 (above and following pages). Measured stratigraphic sections of the Upper Triassic Chinle Formation. Lines 

of section shown on figure 2. Sections show lithofacies, depositional environments, and stratigraphic units. A, Cross 

section of Chinle Formation in the Eagle basin. B, Cross section across the Uinta Mountains to the San Rafael Swell.

The red strata can be assigned to two distinct lithofacies, referred to as lateral-accretion deposits and 

floodplain deposits (discussed in the next section). The 

lateral-accretion deposits are characterized by large-scale 

cross-stratification, whereas the floodplain deposits are 

dominantly massive to horizontally bedded. The lateralaccretion deposits contain sets of large-scale, epsilon crossstratification (ECS) (Alien, 1963, 1965a, b) (fig. 7). Within 

the sets, the lithology grades upward from gray to reddishgray, limestone- and siltstone-pebble conglomerate and 

quartzose sandstone at the base, through reddish-brown, 

interbedded sandstone, siltstone, and mudstone, to 

dominantly reddish-brown siltstone and mudstone at the 

top. Individual strata within the ECS are thin to thick

W8 Evolution of Sedimentary Basins Uinta and Piceance Basins
EXPLANATION

O o O 

o o O

©<£>

V

Limestone 

Conglomerate 

Sandstone 

Siltstone 

Mudstone 

Carbonate nodules 

Purple-white mottles 

Crossbedding

ffff

Ripples

Oscillation 

Climbing 

Mudcrack fillings

Meniscate burrows 

Burrows 

Rhizoliths 

Bioturbation 

Covered interval

DEPOSITIONAL 

ENVIRONMENT

p Paleosol

pb Point bar

a Active channel fill

f Floodplain

e Eolian sand sheet 

I Lake

c Channel lag 

d Delta

FEET METERS

lOO ir-30

 20

50-

Sedimentology of Chinie Formation, Colorado and Utah W9
23

Temple 

Mountain

B

bedded and dip as much as 10°-15°. Internally, the beds of 

the ECS contain small-scale trough and ripple crossstratification with trough axes oriented oblique or 

perpendicular to the dip of the ECS. ECS sets are as thick as 

12 ft (3.7 m), and locally sets are superposed. Generally, the 

ECS units can be traced laterally into horizontally bedded 

strata described in the following section as overbank floodplain deposits.

The large-scale epsilon cross-stratification is 

interpreted as lateral-accretion stratification (LAS) (Alien, 

1965b), because the trend of the small-scale sedimentary 

structures within the units indicates that flow was across the 

dip of the ECS. The interbedded sandstone, siltstone, and 

mudstone of the LAS are interpreted as point bars that 

resulted from helical channel flow in moderately to highly 

sinuous fluvial systems, and the finer grained deposits at the 

top of the sequences represent deposition by waning 

currents in abandoned channels and oxbow lakes (MoodyStuart, 1966; Jackson, 1976). The predominantly fine grain 

size of the strata and the carbonate clasts indicate a mixedto suspended-sediment load in the fluvial system. The 

limestone-pebble conglomerate at the base of the LAS 

represents the basal channel lags of the fluvial system. The 

carbonate clasts are intraformational, derived from calcic 

paleosols developed on floodplain deposits described in the 

following section. The carbonate pebbles also represent the

largest clasts available to the streams and suggest a lack of 

siliciclastic pebbles in the source area of the streams or a 

lack of shear velocity to transport them.

Point-bar deposits in the Chinle Formation are 

common in the red siltstone member of the Eagle basin (fig. 

4A) and also have been reported from the Chinle Formation 

near Bedrock, Colorado. (Dubiel, Good, and Parrish, 1989), 

and the equivalent Dolores Formation on the western flank 

of the Uncompahgre Plateau (Blodgett, 1984, 1988, 1990). 

Low-gradient, moderate- to high-sinuosity fluvial systems 

developed on both sides of the ancestral Uncompahgre 

uplift subsequent to filling of paleovalleys by coarsegrained fluvial deposits of the Gartra Member. These 

meandering fluvial systems dominated Chinle deposition in 

the Eagle basin as proximal depositional systems that 

supplied sediment to depositional settings to the northwest. 

The point-bar deposits are virtually nonexistent in outcrops 

examined in the Uinta Mountains and near Dinosaur 

National Monument and are rare in the San Rafael Swell 

sections measured for this study (fig. 45).

Floodplain Deposits

A large part of the upper Chinle Formation is 

composed of dark-reddish-brown to reddish-orange, 

massive to horizontally stratified, thin- to thick-bedded

W10 Evolution of Sedimentary Basins Uinta and Piceance Basins
ooo

ov

Limestone

Conglomerate

Sandstone

Siltstone

Mudstone

Carbonate nodules

(A=analcime) 

Purple-white mottles

Crossbedding

Ripples

EXPLANATION

Oscillation 1 

Climbing J 

Mudcrack fillings

Meniscate burrows 

Burrows 

Rhizoliths 

Bioturbation 

Covered interval

DEPOSITIONAL 

ENVIRONMENT

p Paieosol

pb Point bar

a Active channel fill

f Floodplain

e Eolian sand sheet

I Lake

Im Lake margin

c Channel lag

d Delta

mudstone, siltstone, and fine-grained sandstone (fig. 8). 

Locally, the flat-lying strata can be traced laterally into the 

lateral-accretion deposits described in the preceding section 

of this report. Individual beds are laterally extensive, but 

substantial cover between measured sections precludes 

tracing individual beds more than a few hundred yards. 

Locally, the beds are directly adjacent to lateral-accretion 

deposits, forming cutbanks eroded during lateral migration 

of the sinuous fluvial system. The strata form the cut bank 

of the outside bend of the meandering stream deposits. At 

these localities, the strata contain abundant, superposed and 

intersecting sand-filled desiccation cracks (fig. 9). The 

abundance and intersecting nature of the cracks indicate 

many episodes of channel-overbank flooding and 

subsequent desiccation. Internally, the beds are very 

uniform in grain size and exhibit few physical sedimentary 

structures, but they do display abundant evidence of pedogenic modification and biogenic structures that provide 

critical information for interpreting their genesis.

The horizontally stratified strata contain indurated, 

isolated or coalesced carbonate nodules and several types of 

rhizoliths, or plant-root trace fossils, and invertebrate trace 

fossils. Carbonate nodules are present as single, isolated 

carbonate glaebules as large as 2 in. (5 cm), as coalesced 

nodules, or as laterally extensive coalesced nodular beds. 

The arrangement of the carbonate from isolated nodules to 

coalesced nodular beds corresponds to carbonate 

accumulations designated as Stage I to Stage IV by Gile and 

others (1966). Nodule formation penecontemporaneous 

with sedimentation and nodule induration prior to transport 

are indicated by the abundance of similar carbonate nodules 

as clasts elsewhere in fluvial deposits in the Chinle.

Several attributes of the carbonate nodules suggest 

that their early development in the Chinle was the result of 

pedogenic accumulation of carbonate. Virtually all of the 

nodules in a single bed are similar in size and distribution; 

however, beds of similar lithology and grain size 

immediately below or above may contain nodules of either

Sedimentology of Chinle Formation, Colorado and Utah W11
Table 1 . Locations of measured sections of the Chinle 

Formation in the Uinta, Piceance, and Eagle basins, 

northwestern Colorado and northeastern Utah 

[Location of section shown by number on figures 2 and 4]

Measured section number and name

Location 

(sec., township, range)

1. State Bridge

2. Edwards West

3. East Alkalai Creek

4. Derby Junction

5. East Brush Creek

6. Basalt

7. South Canyon Creek

8. Snowmass Creek

9. East Rifle Creek

10. Main Elk Creek

11. Buford

12. Irish Canyon

13. Deerlodge Park

14. Skull Creek

15. Cliff Creek

16. Vernal

17. naming Gorge

18. Maeser

19. Lake Fork

20. Hanna

21. BuckhornWash

22. 1-70

23. Temple Mountain

24,2 S., 83 W. 

35, 4 S., 83 W. 

21, 2 S., 84 W. 

31, 2 S., 85 W. 

7, 6 S., 83 W. 

5, 8 S., 86 W. 

2,6 S., 90 W. 

26,8 S., 86 W. 

34,4 S., 92 W. 

15, 5 S., 91 W. 

19, IS., 92 W. 

30,10 N., 100 W. 

21,6 N., 99 W. 

31, 4 N., 100 W. 

21, 5 N., 24 E. 

5,2N.,22E. 

8,2N., 109 W. 

18,2N.,21E. 

34,2N.,5W. 

3,1 S., 8 W.

11. 20 S., 11 E.

12. 22 S., 13 E. 

35, 24 S., 11 E.

24. Colorado National Monument-North 32,1 N., 2 W.

lesser or greater size and abundance, but again with similar 

size and distribution within that bed. The implication is that 

the process responsible for nodule formation was selectively 

operating to different degrees on individual beds of similar 

lithology and texture.

Other specific attributes of the carbonate 

accumulations closely resemble pedogenic accumulation of 

carbonate in certain types of modern soils and published 

examples of ancient paleosols (Wright, 1982). The 

carbonate in some Chinle beds is present as closely packed, 

vertically oriented, prismatic columns as much as 1 in. (2.5 

cm) in diameter and 6-8 in. (15-20 cm) long. Other beds 

contain accumulations of nodules oriented along concaveupward, intersecting fractures localized near the tops of 

beds (fig. 10). These features closely resemble pseudoanticlines described by Alien (1974) for the Old Red Sandstone 

and also closely resemble gilgai or moundlike microrelief 

produced by carbonate accumulation and repeated wetting 

and drying of clay-rich soils, or vertisols, in modern tropical 

settings (Young, 1976). Similar vertic paleosols containing 

carbonate nodules have been described for the Upper 

Triassic Dolores Formation in southwestern Colorado 

(Blodgett, 1984, 1988, 1990).

The lateral relation of these horizontally stratified 

beds to fluvial point-bar deposits, the early formation and 

induration of carbonate nodules in the beds, and the 

association of these nodules with alteration haloes 

interpreted below as plant-root trace fossils indicate that this 

lithofacies represents floodplain deposits lateral to Chinle 

meandering fluvial systems. The floodplain deposits were 

pedogenically modified and represent calcic and vertic 

paleosols, expressed as isolated carbonate nodules, 

pseudoanticlines, and abundant intersecting and superposed 

desiccation cracks. The induration of the carbonate nodules 

within the soil profiles and the superposed desiccation 

cracks both suggest extensive and repeated drying of the 

floodplains.

The floodplain lithofacies contains several types of 

ichnofossils, including rhizoliths or plant-root trace fossils 

(Klappa, 1980), invertebrate trace fossils, and largediameter (4 in., 10 cm) trace fossils attributed to either 

lungfish or freshwater crayfish. There are three types of 

rhizoliths in the floodplain facies (Dubiel, 1988). The first 

type, root alteration haloes, are dark-reddish-purple, 

vertical, cylindrical alteration mottles that formed around 

plant roots that grew in Chinle time. Locally the root 

alteration haloes taper and bifurcate downward and grade 

into finer rootlet traces (fig. 11). The second type of 

rhizolith, called rhizotubules, consists of alteration haloes 

surrounded by localized carbonate nodules that are stacked 

parallel to the vertical axis of the halo. The less cemented 

interiors of the haloes weather out, leaving the moldic 

interior. Rhizocretions, the third type of rhizolith, are 

formed by stacked carbonate nodules that coalesce and 

completely encase the root alteration halo. The increased 

carbonate cementation in the rhizocretions indicates that 

more time was available in distal floodplain settings to 

accumulate more carbonate cement in the paleosols (Bown 

and Kraus, 1987). The interpretation of rhizoliths supports 

the contention that these strata represent pedogenically 

modified floodplain deposits lateral to Chinle fluvial 

systems.

Several types of trace fossils are present in the 

floodplain lithofacies. Large-diameter (4 in., 10 cm) trace 

fossils, interpreted as lungfish burrows or the trace of 

freshwater decapod crustaceans (Dubiel, Blodgett, and 

Bown, 1987, 1988, 1989; Hasiotis and Mitchell, 1989; 

Hasiotis and Dubiel, in press), are locally very abundant. 

Smaller diameter trace fossils commonly are present with 

the larger traces and locally with the rhizoliths. The small 

ichnofossils are sinuous and cylindrical, about V* in. 

(0.6 cm) in diameter. The traces do not branch but do 

interpenetrate. Internally, very fine, concave backfills are 

accentuated by alternating hematite-rich and hematite-poor 

meniscae. These backfilled trace fossils are interpreted as 

endichnial burrows belonging to the ichnogenus Muensteria 

sp., on the basis of meniscate backfill without apparent wall 

structure. Assignment to that ichnogenus solely on those

W12 Evolution of Sedimentary Basins Uinta and Piceance Basins
Figure 5. Fluvial valley-fill conglomerate and sandstone of the Gartra Member at base of the 

Chinle Formation near Basalt, Colorado. Ledge-forming Gartra Member unconformably 

overlies eolian dune deposits within the Sloan Peak Member of the State Bridge Formation. 

Geologist with 5-ft (1.5 m) staff on ledge.

Figure 6. Purple-mottled sandstones of the Temple Mountain Member at the base of the 

Chinle Formation, Buckhorn Wash in the northern San Rafael Swell. Dark areas are purple and 

light areas are white. Note the distinctive tubular trace fossils (arrows) within the mottles.

Sedimentology of Chinle Formation, Colorado and Utah W13
Figure 7. Lower part ot the red siltstone member of the Chinle Formation near Derby 

Junction, Eagle basin, Colorado. Lateral-accretion stratification dipping to the right was 

deposited as point bars in high-sinuosity fluvial systems. Geologist at right center for scale.

Figure 8. Upper part of the red siltstone member of the Chinle Formation near Derby 

Junction, Colorado. Horizontally stratified, fine-grained sandstone and siltstone were 

deposited on fluvial floodplains. At this location, the floodplain deposits display extensive 

pedogenic modification. Thick white cliff at top is the Entrada Sandstone, which unconformably overlies the Chinle at this location. Geologist (circled) at lower left for scale.

W14 Evolution of Sedimentary Basins Uinta and Piceance Basins
Figure 9. Intersecting sandstone-filled mudcracks in the lower part of the red siltstone 

member of the Chinle Formation near Derby Junction, Eagle basin, Colorado. Abundant 

mudcracks are in cut bank of high-sinuosity fluvial strata and indicate repeated wetting and 

drying of the sediments during episodic flood events. Scale at upper left is marked in 

centimeters (left) and inches (right).

Figure 10. Pseudoanticlines in paleosols of the middle part of the red siltstone member of the 

Chinle Formation near Derby Junction, Eagle basin, Colorado. Paleosols are formed on 

floodplain deposits. Pseudoanticlines, also called gilgai microrelief, are formed in surface soil 

horizons as the result of horizontal compressive stresses caused by expansion of clays and 

growth of carbonate nodules caused by repeated wetting and drying cycles. Scale at lower 

right is marked in centimeters (left) and inches (right).

Sedimentology of Chinle Formation, Colorado and Utah W15
Figure 11. Root alteration haloes, or rhizoliths, in the red 

siltstone member of the Chinle Formation near East Brush 

Creek, Eagle basin, Colorado. The rhizoliths exhibit a 

downward branching and tapering morphology. Scale marked 

in centimeters (left) and inches (right).

criteria, however, was recently questioned by 

D'Allessandro and Bromley (1987). These small traces 

were probably formed as the fodinichnia of sedimentingesting invertebrates and indicate a quiet-water 

depositional setting and a low sedimentation rate. The 

burrows are present in the floodplain lithofacies, but 

extensive bioturbation has destroyed any physical 

sedimentary structures and interpretations of these strata are 

difficult. Although present within the floodplain lithofacies, 

these bioturbated units were probably deposited in small 

ponds on the floodplains.

Vertebrate remains are conspicuously absent from red 

strata of the Chinle Formation. The section at Derby 

Junction did produce two vertebrate fossils from rocks of 

the floodplain lithofacies. A vertebral centrum of Hesperosuchus (J.M. Parrish, written commun., 1988), a 3-ft-long 

crocodylomorph, was recovered from the upper part of the 

Chinle. The similarity between this crocodylomorph and 

modern crocodiles supports the interpretation of fluvial and

floodplain systems in which aquatic habitats were abundant. 

One additional unidentified vertebrate fossil was observed 

in a limestone bed that was probably deposited in a small 

pond within the floodplain facies.

The floodplain strata, paleosols, and rhizoliths are 

intimately associated with the meandering stream deposits 

and have a similar distribution in the study area (fig. 4). The 

floodplain deposits and the associated paleosols and rhizoliths are very abundant in the red siltstone member of the 

Eagle basin and are rare to absent in the Uinta Mountains, 

near Dinosaur National Monument, and in the San Rafael 

Swell. Similar features are present in the Chinle on the 

western flank of the Uncompahgre uplift near Bedrock 

(Dubiel, Good, and Parrish, 1989) and in the Dolores 

Formation (Blodgett, 1984, 1988, 1990). The paleosols and 

the rhizoliths are restricted to proximal settings of the 

Chinle depositional system in which subaerial floodplains 

formed lateral to fluvial systems and for which the 

sedimentation rate was low enough so as not to inhibit the 

development of soil horizons.

Lacustrine-Delta and Crevasse-Splay Deposits

Reddish-brown to brown and gray sandstone and 

minor conglomerate that form thin, laterally restricted to 

persistent beds are common within many of the Chinle 

sections and locally makes up a significant part of the 

Chinle at other sections. These lithofacies are found in the 

sandstone and conglomerate member in the eastern part of 

Dinosaur National Monument and in the Moss Back and 

Church Rock Members of the San Rafael Swell (fig. 4). The 

conglomerate is thin bedded and contains siliciclastic and 

carbonate nodules that are generally less than 1 in. (2.5 cm) 

in diameter. The sandstone is thin to medium bedded and is 

characterized by abundant small- to medium-scale trough 

crossbedding, very abundant climbing-ripple laminations, 

abundant horizontal laminations, and minor symmetrical 

oscillation ripples. Both units exhibit abundant cut-and-fill 

features and locally superposed, small- to medium-sized 

lenticular scours (fig. 12).

The units range in size from small lenticular bodies 

that can be traced over tens of yards to units that make up 

large parts of the section. Each can be traced laterally into 

fine-grained strata of either the floodplain or lacustrine 

lithofacies. Sedimentary structures indicative of channelized flow are present, as are features indicative of rapid 

sedimentation, standing water, and wave reworking. The 

lateral facies relationships indicate an environment of 

deposition lateral to both fluvial systems and lacustrine and 

floodplain settings. The strata are interpreted to be laterally 

extensive lacustrine deltas and smaller crevasse-splay 

deposits. High and others (1969) also interpreted the 

sandstone and conglomerate unit in eastern Dinosaur 

National Monument as a lacustrine delta. Many of the strata 

in the Moss Back and Church Rock Members in the San 

Rafael Swell previously have been interpreted as fluvial

W16 Evolution of Sedimentary Basins Uinta and Piceance Basins
f - * jt'WX.-r&r

Figure 12. Lacustrine-deltaic strata in the Moss Back Member of the Chinle Formation, 

Temple Mountain, San Rafael Swell, Utah. The deltaic deposits contain abundant cut-and-fill 

structures (dashed), small-scale crossbedding, and abundant silicified logs.

deposits (Stewart and others, 1972; Lupe, 1977, 1979). 

Although many of these units represent deposition by 

channelized flow, other attributes of the rocks, particularly 

the fining-upward sequences into abundant climbing and 

oscillation ripples, interbedded burrowed and bioturbated 

mudstone, and lateral facies changes into fine-grained 

rocks, all indicate a lacustrine-deltaic interpretation for the 

upper part of the sandstone and conglomerate sequence. 

These coarse-grained units probably represent fluvial 

deposition at the base and a facies change both upward and 

distally into proximal and distal deltaic lithofacies.

Lacustrine Deposits

Many thin-bedded to laminated, horizontally 

stratified and aerially extensive fine-grained units are 

exposed in the upper part of the Chinle Formation 

throughout the study area. These deposits include the red 

siltstone member, the ocher siltstone member, the upper 

member, and, in the San Rafael Swell, parts of the Church 

Rock Member. The units range in color from reddishbrown, to reddish-orange, reddish-purple, yellow, 

yellowish-brown, and light-brown, to tan. The beds consist 

of very fine grained sandstone, siltstone, abundant mudstone, and rare gray to pink limestone. The strata exhibit 

very thin laminations and abundant climbing-ripple crossstratification or symmetrical-ripple laminations (fig. 13).

Sedimentary structures are absent in many of the units, but 

the strata do contain trace fossils or exhibit a bioturbated 

fabric.

The fine grain size of the clastic strata, local 

carbonate beds, tabular and laterally extensive thin beds, 

abundant bioturbation, and a distinct lack of rhizoliths 

suggest a lacustrine origin for this lithofacies. The finegrained strata were deposited from suspension in a quietwater environment. Symmetrical oscillation ripples and 

abundant unidirectional climbing ripples indicate shallowwater, marginal-lacustrine settings and deposition by waves 

and bottom currents, respectively.

In the Uinta Mountains, a distinctive yellow to 

yellowish-brown unit in the upper Chinle has been referred 

to as the ocher unit (High and others, 1969) or the ocher 

siltstone member (Stewart and other, 1972). The unit is 

predominantly mudstone and siltstone and contains very 

thin sandstone beds. It is characterized by the presence of 

analcime nodules and spherules that are probably the result 

of volcanic ash fall into the waters of a saline-alkaline lake 

(Keller, 1952, 1953; High and others, 1969). The analcimerich strata in the Uinta Mountains have been correlated with 

a similar yellowish-brown, analcime-bearing unit within the 

Upper Triassic Popo Agie Formation in central Wyoming; 

in fact, the analcime is the basis for the contention that the 

Upper Triassic rocks in the eastern Uinta Mountains should 

be included in the Popo Agie (High and others, 1969). X-ray

Sedimentology of Chinle Formation, Colorado and Utah W17
Figure 13. Lacustrine deposits in the Chinle Formation. Scale marked in centimeters (left) 

and inches (right). A, Abundant ripple cross-stratification in the red siltstone member of the 

Chinle Formation at Skull Creek south of Dinosaur National Monument. B, Interbedded 

mudstone and fine-grained sandstone containing oscillation ripples and fine, horizontal 

laminations, near Hanna, Utah, south of the Uinta Mountains.

diffraction and petrographic thin-section analyses of several 

samples collected during the present study from the 

yellowish-brown unit in the Uinta Mountains confirm the 

presence of analcime in nodules and spherules, and it is

W18 Evolution of Sedimentary Basins Uinta and Piceance Basins

likely that these strata reflect deposition of clastic sediment 

and air-fall volcanic ash into a saline-alkaline lake as 

suggested by Keller (1952). The fact that this unit interfingers with other lacustrine units of the Chinle in the region
that lack analcime indicates that the saline-alkaline lacustrine conditions were not persistent throughout the region 

nor did they exist for the duration of Chinle deposition. The 

analcime-bearing unit extends from the Popo Agie 

Formation in Wyoming to outcrops of the Chinle Formation 

in the Uinta Mountains, but it is absent in equivalent 

outcrops of the Chinle farther to the south in Utah. The 

lacustrine system proposed to have existed in southern 

Wyoming by High and others (1969) probably expanded 

south at times into the area of the Uinta Mountains and 

deposited the ocher unit in both regions.

Freshwater lacustrine systems existed during 

deposition of the Monitor Butte and Owl Rock Members of 

the Chinle Formation in the Four Corners region (Dubiel, 

1987a, b, 1989a). The presence of a saline-alkaline lake 

farther north in Wyoming during deposition of the Popo 

Agie Formation suggests that more arid climatic conditions 

existed in this northern area. This relationship is consistent 

with paleogeographic and paleoclimatic reconstructions for 

the depositional basin and is discussed in a subsequent 

section.

Eolian Deposits

A distinct lithofacies consisting of eolian deposits is 

restricted to the upper part of the Chinle Formation in the 

central part of the Eagle basin (fig. 44). The eolian deposits 

consist of reddish-orange to light-orange-brown, thin- to 

thick-bedded, horizontally laminated to low-angle crossstratified, very fine to fine grained sandstone and lightred-brown siltstone (fig. 14). The thin, parallel and wavy 

laminations are locally highlighted by very thin clay drapes 

that are mudcracked on a very small scale and contain small, 

meniscate-backfilled trace fossils. The eolian lithofacies 

does not contain the abundant rhizoliths characteristic of the 

floodplain deposits but is instead characterized by abundant, 

small trace fossils and a bioturbated texture.

The horizontal laminations in fine to very fine grained 

sandstone, the thin clay drapes, and the thick, laterally 

extensive tabular bedding suggest an origin as eolian sand 

sheets and minor eolian dunes (Kocurek and Nielson, 1986). 

Similar eolian sand sheets have been described from the 

Dolores Formation in southwestern Colorado (Blodgett, 

1984, 1988, 1990). Eolian and sand-sheet facies are present 

only in the three thickest sections of the Chinle measured 

for this study. This possibly implies that a part of this 

lithofacies and an unknown part of the upper Chinle was 

removed by erosion prior to deposition of the overlying 

strata elsewhere. The stratigraphically upward change from 

subaerial and subaqueous depositional facies in the lower 

Chinle to predominantly eolian deposits at the end of Chinle 

time indicates a significant drying of the overall climate at 

the close of the Late Triassic.

A second possible correlation exists for the lightorange eolian beds at the top of the section. These eolian

beds beneath the Entrada Sandstone in the Eagle basin may 

correlate to the Wingate Sandstone farther to the west and 

thus may represent erosional remnants of the Wingate 

preserved beneath the Triassic-Jurassic unconformity in this 

small area of the Eagle basin. An unconformity was not 

recognized in the sections between the floodplain facies 

below and the eolian facies above; however, such a contact 

might be difficult to recognize in a flatbedded sequence 

composed of similar eolian facies.

DEPOSITIONAL SYSTEMS AND 

PALEOGEOGRAPHY

The reddish-brown conglomerate, sandstone, siltstone, and mudstone of the Chinle Formation in western 

Colorado within the Eagle basin were deposited in a 

succession of fluvial channel, floodplain, lacustrine-deltaic, 

lacustrine, and eolian environments. Coarse-grained 

sediment was deposited within paleovalleys eroded into 

underlying rocks by fluvial systems that generally flowed 

northwest. Deposits at the base of the Chinle are coarse 

grained, they exhibit more numerous cut-and-fill features, 

and they lack lateral-accretion bedding compared to 

overlying deposits. The basal conglomerates represent fluvial deposition in low-sinuosity fluvial and valley-fill 

systems. As the paleovalleys filled with sediment, gradients 

on the streams were lowered, and Chinle sedimentation was 

mainly by fluvial deposition within moderate- to highsinuosity channel systems. Overbank flooding by the 

streams deposited fine-grained floodplain strata. Floodplain 

units are characterized by petrocalcic and vertic paleosols 

that contain rhizoliths and abundant trace fossils. In places, 

small ponds formed on the floodplains.

The direction of transport of clastic material for the 

Chinle depositional systems in northwestern Colorado was 

north and northwest from the ancestral Uncompahgre uplift, 

which formed the bounding highland on the southwestern 

part of the basin, and south and west from the ancestral 

Front Range uplift, which was the source area on the eastern 

margin of the basin (fig. 15). Paleostream directions 

determined from plots of maximum pebble size and trend of 

crossbed axes in fluvial rocks indicate that paleoflow was to 

the northwest in the Eagle basin (Stewart and others, 1972; 

Shropshire, 1974).

Stratigraphic panels of measured sections (fig. 4A) 

depict a thinning of the Chinle Formation along the margins 

of the Eagle basin near the flanks of the uplifts. The thinning 

probably results both from erosion of the upper part of the 

Chinle prior to deposition of the overlying rocks and from 

increased subsidence and preservation along the northwesttrending axis of the Eagle basin. Increased subsidence in the 

central Eagle basin near East Brush Creek is supported by 

the fact that the thickest preserved section of the Chinle is 

present at this location. The thickest section of the Chinle in 

this area is coincident with a thicker section of the

Sedimentology of Chinle Formation, Colorado and Utah W19
Figure 14. Eolian deposits at the top of the Chinle Formation, East Brush Creek, Eagle basin, 

Colorado. A, Eolian sand sheet strata ("Re) at the top of the Chinle Formation (arrows) 

unconformably overlain by the Lower Jurassic Entrada Sandstone (Je). About 200 ft (60 m) of 

eolian strata exposed. B, Eolian sand sheet showing horizontal laminations and thin clay 

drapes.

Pennsylvanian and Permian State Bridge Formation (S.Y. 

Johnson, oral commun., 1988). The greater subsidence in 

this area inferred from the increased thickness of the Chinle 

and the State Bridge may reflect increased tectonic

W20 Evolution of Sedimentary Basins Uinta and Piceance Basins

subsidence, or it may be related to subsidence as a result of 

movement of salt in the underlying Pennsylvanian Eagle 

Valley Evaporite (RJ. Kite, U.S. Geological Survey, oral 

commun., 1989).
111

EXPLANATION

Fluvial systems

Figure 15. Schematic reconstruction of Chinie depositional systems in the Uinta, Piceance, and Eagle basins. Diagram shows 

paleogeography and location and trend of major fluvial, deltaic and lacustrine systems. Outcrops of Chinie Formation shown in 

black. Compare to figure 2 for locations of measured sections.

Stratigraphic panels of the Chinie Formation across 

the Uinta Mountains into northeastern Utah and 

northwestern Colorado near Dinosaur National Monument 

(fig. 45) depict the sequence of depositional environments 

in this region. Conglomerates and sandstones at the base of 

the Chinie represent the initial development of fluvial 

systems. These fluvial strata contain mostly carbonate 

intraclasts and very few siliciclastic pebbles, a composition 

indicating an intrabasinal source for the pebbles. It is likely 

that the ancestral Rocky Mountains were reduced in 

elevation or even covered by Chinie deposits at this time. 

Fluvial systems were succeeded by a large lacustrine 

system. Aspects of the lacustrine facies, such as the 

presence of analcime, indicate not only that the lake was at 

times saline and alkaline, but also that it was, at least in part, 

contiguous with a large lake system interpreted to have 

existed in the Upper Triassic Popo Agie Formation farther 

to the north in Wyoming. The presence of limestone in the 

sections in the eastern part of Dinosaur National Monument 

attests to the lack of clastic and volcanic detritus in some

lacustrine settings. Lacustrine deltas, which provided clastic 

material to the lake, existed in the eastern Uinta Mountains. 

The deltas were fed in part by fluvial systems that flowed 

northwest out of the Eagle basin and northwest off of the 

northwestern flank of the ancestral Uncompahgre uplift.

Preliminary studies in the San Rafael Swell, Colorado 

National Monument, (fig. 45) and near Bedrock, Colorado 

(Dubiel, Good, and Parrish, 1989), provide insight about the 

relationship between Chinie environments there to those in 

the Uinta, Piceance, and Eagle basins. The Moss Back and 

Church Rock Members in the sections measured in the San 

Rafael Swell represent fluvial and deltaic deposition that 

flowed northwest into a large lake. Lacustrine strata at the 

top of the Chinie in the San Rafael Swell probably correlate 

with similar strata at the top of the Chinie in the Uinta 

Mountains, although the distances between the outcrops are 

very large. The lacustrine deposits may also be correlative, 

but, as suggested by McCormick and Picard (1969), 

additional unrecognized facies changes may be present 

beneath the Uinta basin.

Sedimentology of Chinie Formation, Colorado and Utah W21
PALEOCLIMATE

Several aspects of the sedimentology of the Chinle 

Formation can be used to infer the paleoclimate during 

Chinle deposition. Paleomagnetic reconstructions place this 

part of the Colorado Plateau at about 5°-15° N. paleolatitude, clearly within the tropics, during the Late Triassic 

(Van der Voo and others, 1976; Bazard and Butler, in 

press). Temperatures probably were warm to hot the entire 

year. The fluvial, floodplain, and lacustrine deposits 

indicate that water was abundant in the Chinle depositional 

system, at least until eolian deposition in the final stages of 

Chinle time. In a tropical setting, the accumulation of 

pedogenic calcic horizons, in particular the presence of 

single, indurated carbonate nodules in clay-rich soils, is 

characteristic of seasonal precipitation. Additionally, the 

presence of vertic paleosol features such as abundant 

desiccation cracks and pseudoanticlines representing gilgai 

micro-relief indicates that moisture input to the floodplains, 

either by flooding of the fluvial systems or by precipitation, 

was seasonal (Mohr and others, 1972; Young, 1976). Thus 

the region of Chinle deposition in the Uinta, Piceance, and 

Eagle basins probably had a tropical monsoonal climate. A 

tropical monsoonal climate has been suggested for that part 

of the Chinle depositional basin around the Four Corners 

region (Dubiel, 1987a, c, 1989a; Parrish and others, 1989; 

Dubiel and others, 1991) and is thought to result from the 

unique configuration of the supercontinent Pangea during 

the Late Triassic and the location of the Colorado Plateau 

near the western edge of that continent (Dubiel, 1989b; 

Parrish and others, 1989; Dubiel and others, 1991). The 

advent of eolian deposition in the final stages of Chinle 

deposition both in this region and in the Four Corners area 

(Dubiel, 1989a, b) supports the concept that climate became 

significantly drier at the close of the Late Triassic. The 

change to a drier climate was probably the result of the 

northward migration of Pangea, moving the Colorado 

Plateau northward out of latitudes affected by monsoonal 

circulation and into the drier mid-latitudes (Parrish and 

others, 1989; Dubiel and others, 1991). In contrast to the 

lacustrine systems of the Chinle of the Four Corners region, 

the development of a saline-alkaline lake within the Popo 

Agie Formation is probably due to the position of the Popo 

Agie depositional basin farther north in Pangea and in drier 

latitudes not under the direct influence of the monsoonal 

circulation.

CONCLUSIONS

The Chinle Formation represents a sequence of 

continental lithofacies deposited in a complex fluvialdeltaic-lacustrine-eolian system. Individual depositional 

environments reflect the interaction of tectonic, paleogeographic, and climatic controls. Analysis of depositional

systems in widely separated areas can be used to reconstruct 

the paleogeography of the Chinle basin throughout the 

Colorado Plateau and beyond its present margins.

Lithofacies analysis reveals several distinct 

continental depositional environments within the Chinle 

Formation of the Uinta, Piceance, and Eagle basins. In 

settings adjacent to the ancestral Uncompahgre and Front 

Range uplifts, the Chinle is characterized by basal valley-fill 

gravels overlain by meandering fluvial and associated 

floodplain sequences replete with paleosols and small 

ponds. These facies are present on all flanks of the ancestral 

Uncompahgre uplift. The fluvial facies grade westward and 

northwestward toward the Uinta and Piceance basins into 

lacustrine-deltaic and lacustrine deposits. The close of 

Chinle deposition in the Eagle basin, where the greater 

thickness of Chinle Formation is preserved, is dominated by 

eolian sand-sheet strata. Tropical monsoonal circulation 

affecting the western coast of Pangea provided abundant but 

seasonal moisture to the Chinle depositional basin until the 

end of the Late Triassic. The close of Chinle deposition is 

marked by eolian strata that indicate a change to 

significantly drier conditions as Pangea migrated northward 

in the latest Triassic and earliest Jurassic and moved the 

Colorado Plateau northward into drier latitudes.

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Triassic and Jurassic rocks in south-central Wyoming: U.S. 

Geological Survey Professional Paper 594-D, 26 p.

Pipiringos, G.N., Hail, W.J., Jr., and Izett, G.A., 1969, The Chinle 

(Upper Triassic) and Sundance (Upper Jurassic) Formations 

in north-central Colorado: U.S. Geological Survey Bulletin 

1274-N, p. N1-N35.

Pipiringos, G.N., and O'Sullivan, R.B., 1978, Principal 

unconformities in Triassic and Jurassic rocks of the Western 

Interior United States A preliminary survey: U.S. 

Geological Survey Professional Paper 1035-A, 29 p.

Poole, F.G., and Stewart, J.H., 1964, Chinle Formation and Glen 

Canyon Sandstone in northeastern Utah and northwestern 

Colorado: U.S. Geological Survey Professional Paper 

501-D, p. D30-D39.

Reading, H.G., ed., 1978, Sedimentary environments and facies: 

New York, Elsevier, 569 p.

Rust, E.G., 1978, Depositional model for braided alluvium, in 

Miall, A.D., ed., Fluvial Sedimentology: Canadian Society 

of Petroleum Geologists Memoir 5, p. 605-625.

Schaeffer, Bobb, 1967, Late Triassic fishes from the western 

United States: Bulletin of the American Museum of Natural 

History, v. 135, p. 285-342.

Segerstrom, Kenneth, and Young, E.J., 1972, General geology of 

the Harms Peak and Farwell Mountain Quadrangles, Routt 

County, Colorado with a discussion of Upper Triassic and 

pre-Morrison Jurassic rocks, by G.N. Pipiringos: U.S. 

Geological Survey Bulletin 1349, 63 p.

Shropshire, K.L., 1974, The Chinle and Jelm Formations (Triassic) 

of north-central Colorado: Boulder, University of Colorado, 

Ph.D. thesis, 229 p.

W24 Evolution of Sedimentary Basins Uinta and Piceance Basins
Sikich, S.W., 1965, Upper Triassic stratigraphy in the eastern 

Uinta Mountains: The Mountain Geologist, v. 2, 

p. 167-172.

Stewart, J.H., Poole, F.G., and Wilson, R.F., 1972, Stratigraphy 

and origin of the Upper Triassic Chinle Formation and 

related strata in the Colorado Plateau region: U.S. 

Geological Survey Professional Paper 690, 336 p.

Thomas, C.R., McCann, F.T., and Raman, N.D., 1945, Mesozoic 

and Paleozoic stratigraphy in northwestern Colorado and 

northeastern Utah: U.S. Geological Survey Oil and Gas 

Investigations (Preliminary) Chart 16, scale 1 in. = 12 miles.

Thomas, H.D., and Krueger, M.L., 1946, Late Paleozoic and early 

Mesozoic stratigraphy of Uinta Mountains, Utah: American

Association of Petroleum Geologists Bulletin, v. 30, 

p. 1255-1293.

Tweto, Ogden, Moench, R.H., and Reed, J.J. Jr., 1978, Geologic 

map of the Leadville I°x2° Quadrangle, northeastern 

Colorado: U.S. Geological Survey Miscellaneous 

Investigations Series Map 1-999, scale 1:250,000.

Van der Voo, R., Mauk, F.J., and French, R.B., 1976, PermianTriassic continental configurations and the origin of the 

Gulf of Mexico: Geology, v. 4, p. 177-180.

Wright, V.P., 1982, Calcrete paleosols from the lower Carboniferous Llanelly Formation, South Wales: Sedimentary 

Geology, v. 24, p. 671-675.

Young, Anthony, 1976, Tropical soils and soil survey: Cambridge, 

England, Cambridge University Press, 468 p.

*U.S. GOVERNMENT PRINTING OFFICE: 1992-673-049/46026 Sedimentology of Chinle Formation, Colorado and Utah W25



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engineers. Included are reports on the results of resource studies and of 

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