Structural Control on Distribution of 

Sedimentary Facies in the Pennsylvanian 

Minturn Formation of North-Central Colorado

U.S. GEOLOGICAL SURVEY BULLETIN 1 787-Y

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Chapter Y

Structural Control on Distribution of 

Sedimentary Facies in the Pennsylvanian 

Minturn Formation of North-Central Colorado

By KAREN J. HOUCK

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 1 787

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

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.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1991

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Houck, Karen J.

Structural control on distribution of sedimentary facies in the Pennsylvanian 

Minturn Formation of north-central Colorado/ by Karen J. Houck.

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

ch. Y) (U.S. Geological Survey bulletin ; 1 787-Y)

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

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

Includes bibliographical references.

Supt. of Docs, no.: I 19.3: 1787Y

1. Sedimentation and deposition Colorado Eagle County. 2. Geology, 

Stratigraphic Pennsylvanian. 3. Geology, Structural Colorado Eagle 

County. 4. Minturn Formation (Colo.) I. Title. II. Series. III. Series: U.S. 

Geological Survey bulletin ; 1787-Y. 

QE75.B9 no. 1787-Y 

[QE571]

557.3 s dc20 91-22419 

[552'.5'0978844] CIP
CONTENTS

Abstract Yl

Introduction Yl

Structural setting Y2

Procedures Y4

Paleocurrent trends and sedimentary facies patterns Y4

Structural influence on paleocurrent trends and facies patterns Yll 

Sediment distributions Y15

Structural influence on sediment distributions Y17 

Conclusions Y18 

References cited Y19 

Appendix Rose diagrams for depositional units of the Minturn Formation Y22

FIGURES

1. Generalized paleogeographic map of Colorado showing location of study area 

on eastern margin of the Central Colorado basin Y2

2. Chart showing stratigraphy of Pennsylvanian Minturn Formation Y3

3. Map showing outcrops of the study interval Y5 

4, 5. Maps showing paleocurrent directions and maximum clast sizes for:

4. Fluvial sequence in unit 3 Y6

5. Fluvial unit 4 Y7 

6, 7. Isopach maps showing thickness of:

6. Interval from base of laterally extensive limestone in unit 3 to top of 

unit 4 Y8

7. Turbidites and fluvial deposits in unit 5a Y9 

8, 9. Maps showing:

8. Paleocurrent directions and paleogeography during deposition of lower 

part of unit 5b Y10

9. Paleocurrent vectors compiled from measurement on fluvial deposits

from upper part of unit 5b Yll

10, 11. Maps showing paleocurrent directions and paleogeography during 

deposition of:

10. Lower part of unit 5c Y12

11. Unit 6 Y13 

12-14. Isopach maps showing thickness of:

12. Unit 6 Y14

13. UnitSb Y15

14. Units 5c and 6 Y16

15. Cross section showing units 3, 4, 5, and 6 of Minturn Formation Y18

16. Block diagram showing relationship between faults and sedimentary deposits 

during deposition of Minturn Formation Y19

Contents III

EVOLUTION OF SEDIMENTARY BASINS UINTA AND PICEANCE BASINS

Structural Control on Distribution of 

Sedimentary Facies in the Pennsylvanian 

Minturn Formation of North-Central Colorado

By Karen J. Houck1

Abstract

Field study of the middle part of the Pennsylvanian 

Minturn Formation in the McCoy-Bond area of north-central 

Colorado has yielded evidence for structural influences on 

sedimentation. The McCoy-Bond area was probably located 

near an en echelon offset in the fault zone bounding the 

eastern margin of the basin. Paleocurrent measurements show 

that sediment transport in nonmarine drainages and in marine 

deltas and turbidites was consistently to the south during 

several transgressive-regressive intervals. These trends may 

have been controlled by a topographic low that extended 

south from the offset zone to a termination in the southern part 

of the area. Mapping of sediment packages shows that 

drainages and sites of delta and turbidite accumulation were 

repeatedly established near the traces of two north-southoriented faults. The sediment packages also thicken and are 

more completely preserved closer to the fault traces. These 

trends suggest that these faults were active during middle 

Minturn deposition.

Individual fault blocks delineated by facies and thickness 

changes are similar in structural style to the Vail-McCoy 

trough, the Avon-Edwards high, and the Eagle sub-basin 

defined by other workers and illustrate the control of structure 

on sedimentation in the central Colorado basin.

INTRODUCTION

The purpose of this paper is to document paleocurrent 

trends and facies distributions in depositional sequences in 

the Pennsylvanian Minturn Formation near the villages of

Manuscript approved for publication May 21, 1991.

'Department of Geological Sciences, University of Colorado, 

Boulder, Colorado 80309-0250.

McCoy and Bond, Colorado. A secondary purpose is to 

provide a possible explanation that relates these trends and 

distributions to fault movements that occurred along the 

basin margin.

The Minturn Formation is a thick (as much as 1,921 

m, 6,300 ft) accumulation of clastic and minor carbonate 

sediments deposited along the eastern margin of the central 

Colorado basin during Middle Pennsylvanian (Atokan and 

Desmoinesian) time (Chronic and Stevens, 1958; DeVoto, 

1972; Tweto and Levering, 1977). The source of the arkosic 

clastic sediments probably was the Ancestral Front Range, 

which flanked the basin on its east side (Mallory, 1972; 

DeVoto, 1980) (fig. 1). Stevens (1958) showed that the 

Minturn Formation is approximately 610 m (2,000 ft) thick 

in the McCoy area. He divided the Minturn into 19 

stratigraphic units that are traceable throughout the McCoyBond area (Chronic and Stevens, 1958; Stevens, 1958). I 

have continued to use his numbering scheme in my work, 

which encompasses about 240 m (800 ft) of section from the 

base of Stevens' unit 3 to the top of his unit 6 (fig. 2).

Numerous relative sea-level changes during deposition of the Minturn Formation resulted in a series of 

transgressive-regressive sedimentary cycles (Houck and 

Lockley, 1986). These cycles average about 30 m (100 ft) in 

thickness and contain a variety of marine and nonmarine 

deposits. The cycles are traceable through two paleodrainages and the intervening divide and are thus presumed to be 

allocyclic in nature (Beerbower, 1964).

Two unexpected discoveries were made in the course 

of mapping lateral facies variations and taking paleocurrent 

measurements in these cycles. First, though the study area is 

on the eastern margin of the basin, Minturn fluvial systems 

repeatedly flowed to the south, rather than to the west. 

Second, stream drainages, deltas, and turbidites were

Sedimentary Facies in Minturn Formation, North-Central Colorado Y1
109° 102°

NORTHERN FRONT RANGE UPLIFT FAULT

80 KILOMETERS 

50 MILES

TRANSVERSE FAULT 

CENTRAL COLORADO BASIN 

GORE FAULT

DENVER BASIN

UNCOMPAHGRE UPLIFT

PARADOX BASIN CRISTO UPLIFT

Figure 1. Generalized paleogeographic map of Colorado showing location of the study area on the eastern margin of the Central 

Colorado basin and approximate locations of the Core, transverse, and northern fault zones. Pattern delineates uplifted areas. 

Modified from DeVoto (1980) and DeVoto and others (1986).

repeatedly established in geographically restricted parts of 

the area and are thus "stacked" in vertical sections through 

the study interval. I interpret these paleocurrent trends and 

facies patterns to be the sedimentary response to fault 

movement and differential subsidence along the tectonically 

active margin of the central Colorado basin.

Acknowledgments. I thank the residents of Bond, 

McCoy, and Copper Spur for providing me with access to 

their property. Without their cooperation, this study would 

not have been possible. I also thank the Rocky Mountain 

Section of the Society for Sedimentary Geology (SEPM), 

the Colorado Mountain Club, Union Pacific Resources, and 

the Department of Geological Sciences at University of 

Colorado for financial support through three field seasons. 

An early version of the manuscript was reviewed by Bill 

Bilodeau and Ted Walker (University of Colorado). The 

version submitted for publication was reviewed by Sam 

Johnson and Chris Schenk (U.S. Geological Survey). Their 

comments resulted in a substantial improvement. I thank Al

Scott for drawing the block diagram (fig. 16) and Rick 

Allrnendinger for use of his Stereonet 3.6 program.

STRUCTURAL SETTING

During Pennsylvanian time, the central Colorado 

basin was an elongate, narrow, northwest-southeastoriented feature. The Pennsylvanian basin fill is as thick as 

3,050 m (10,000 ft) (Mallory, 1972; DeVoto, 1980). Fault 

zones are thought to have formed the eastern margin of the 

basin. These faults were active during Laramide (early 

Tertiary) deformation but are inferred to have had an earlier 

Pennsylvanian history as well (DeVoto, 1980; Tweto, 1980; 

DeVoto and others, 1986). The Gore fault zone, 19 km (12 

mi) east of the McCoy-Bond area, was active during 

Pennsylvanian time (Tweto, 1977; Tweto and Levering, 

1977). The Gore fault and related structures have undergone 

a large amount of dip-slip movement; DeVoto and

Y2 Evolution of Sedimentary Basins Uinta and Piceance Basins
Unit

3E

c 

o

o

LL 

C 

^"E

17/18

15/16

13/14

11/1;

9/10

7/8

5/6

3/4

Study 

interval

100-i 

METERa

0 -J-0

Unit

Fig. 14

Fig. 13

Fig. 6

100 

FEET

EXPLANATION

Limestone 

Shale

Interbedded sandstone 

and siltstone

Sandstone

Congiomerate 

Trough crossbedding

Planar crossbedding

Figure 2. Stratigraphy of the Pennsylvanian Minturn Formation in the study area near McCoy/ Colorado. The 

interval described in this report is enlarged at right. Stratigraphic positions of units depicted in figures 4-14 are 

shown along the right margin. Numbering system of units is from Chronic and Stevens (1958).

Sedimentary Facies in Minturn Formation, North-Central Colorado Y3
others (1986) estimated that 1,525-2,135 m (5,000-7,000 

ft) of offset occurred during the Desmoinesian alone. The 

amount of Pennsylvanian strike-slip movement on these 

faults (if any) is not known (Kluth, 1986). Faults within the 

Gore zone display a variety of orientations, but most are 

almost vertical and the zone as a whole is considered to be 

vertical (Tweto and Levering, 1977).

The bounding fault zones along the eastern margin of 

the basin presently have an en echelon configuration, and it 

is presumed that this was also the situation during the 

Pennsylvanian (DeVoto, 1980). The McCoy-Bond area is 

west of one of these areas of en echelon offset. The northern 

end of the Gore fault zone is truncated there by an 

east-west-oriented transverse fault that offsets the basin 

margin 16 km (10 mi) to the west. North of this transverse 

fault, an unnamed north-trending fault zone forms the basin 

margin (Tweto, 1976; Tweto and others, 1978) (fig. 1). The 

transverse fault and unnamed northern fault zone were 

inferred to be active during Pennsylvanian time by DeVoto 

and others (1986), but, because the Minturn Formation is 

not present in that area, Pennsylvanian movement on these 

faults cannot be conclusively demonstrated.

Despite a growing understanding of its structure, the 

mechanism by which the central Colorado basin formed is 

not well understood. Kluth (1986) has shown that formation 

of many of the Pennsylvanian sedimentary basins in the 

Western Interior of the United States coincides with the 

progressive suturing of South America to North America 

along the Ouachita-Marathon erogenic front. Studies of the 

modern collisional zone located between India and Asia 

(Molnar and Tapponier, 1975) show that structural 

deformation can take place as much as 3,000 km (1,860 mi) 

into the interior of a colliding continent. This deformation is 

expressed in a variety of structures formed by extensional, 

compressional, and strike-slip movements. The central 

Colorado basin could theoretically have formed under any 

one or a combination of these stress regimes.

PROCEDURES

The Minturn Formation in the McCoy-Bond area was 

deformed into a series of north-south-oriented folds, and 

outcrops of the study interval are in belts along the fold 

limbs. Exposures in the outcrop belts are continuous, and 

beds can be traced along the surface parallel with the fold 

axes (fig. 3).

Thirty-three detailed sections were measured using a 

Jacob's staff and Brunton compass. Ten sections span the 

entire study interval, from the base of unit 3 to the top of 

unit 6 (fig. 2); the others are partial sections. Wherever 

possible, beds were walked out between sections. Through 

areas where continuous exposure was not available, 

correlation was made by matching strata as well as possible 

on the basis of lithological, faunal, and directional features 

(Boggs, 1987). I am reasonably confident of the correlations

because the longest distance between outcrop belts in the 

entire study area is only 3.1 km (1.9 mi). The correlated 

sections served as a basis for subdividing the study section 

into intervals and for constructing lithofacies and paleogeographic maps of each interval.

Paleocurrent measurements were made on a variety of 

features including logs, tool marks, current-ripple marks, 

trough crossbeds, planar-tabular crossbeds, and Gilbert 

delta foresets. At every outcrop selected for measurement, 

readings were taken on as many features as were available, 

to a maximum of 25 for crossbeds and 50 for linear features. 

Data were rotated to paleohorizontal, either by hand on a 

stereonet or by using a computer.

PALEOCURRENT TRENDS AND 

SEDIMENTARY FACIES PATTERNS

The McCoy-Bond area is close to the eastern margin 

of the basin, so one might expect the major Pennsylvanian 

drainages in the area to have flowed westward, away from 

the scarp of the Gore fault zone. Paleocurrent data from 

numerous horizons situated within the 240-m (800 ft) study 

interval show, however, that the Minturn drainages were 

consistently oriented north-south through several episodes 

of marine transgression and regression. To illustrate this 

point, reconstructions of five nonrnarine and three marine 

intervals are displayed in figures 4-13. Their positions in 

the study section are shown in figure 2.

Braided fluvial deposits in unit 3. This interval is 

exposed as an erosionally resistant band below a laterally 

extensive marine limestone. Conglomerate bodies about 

5-8 m (15-25 ft) thick are encased in purple siltstone. The 

conglomerates are granular and pebbly and have a matrix of 

coarse-grained sand. The most common sedimentary 

structures are medium-scale trough crossbedding, planar 

bedding, and medium-scale planar-tabular crossbedding. 

These conglomerate bodies are interpreted as braided fluvial 

deposits. Paleocurrent data from foresets in the trough and 

planar-tabular crossbedding indicate that flow in these 

braided channels was predominantly to the southeast, south, 

and southwest. Row directions are dispersed radially 

around a north-south-oriented axis situated between Rock 

Creek and the Bond fault (fig. 4). Maximum clast sizes at 

the various locations range from about 15 cm (6 in.), 

presumably near major channels, to about 1 cm (!/2 in.), 

presumably away from major channels.

Braided fluvial deposits in unit 4. In the eastern part 

of the study area (fig. 5) this unit is distinctive because it is 

unusually coarse; in the western part of the study area the 

unit is difficult to identify. The conglomerates are lensoid 

bodies of granules and pebbles in a matrix of coarse-grained 

sand. The conglomerate bodies have pronounced erosional 

relief on their lower surfaces and contain common rip-up 

clasts of sandstone, siltstone, and limestone. Massive

Y4 Evolution of Sedimentary Basins Uinta and Piceance Basins
39°57'30"

106° 40'

39*52" 30"

ANTELOPE 

CREEK 

FAULT

COLORADO

Figure 3. Outcrops of the study interval. Screen pattern indicates outcrops of units 3 and 4; diagonal pattern indicates outcrops 

of units 5 and 6. Locations of the Bond and Antelope Creek faults and line of cross section A-A' (fig. 15) are also shown.

conglomerate is along the channel bases. The conglomerate 

bodies are encased in purple siltstone. Trough and planartabular crossbedding and planar bedding are the most 

common structures. Current measurements taken on the 

trough and planar-tabular crossbedding again show a radial 

distribution with flow to the east, southeast, and west (fig. 

5). Like the fluvial interval in unit 3, the axis of the system 

probably is oriented north-south and situated between Rock 

Creek and the Bond fault. The largest clast sizes, as much as 

30 cm (12 in.) in diameter, are found north and west of 

Bond (fig. 5) in an area interpreted as a major channel 

system in the Minturn drainage network. Smaller channels 

are interpreted to have been present at other locations in the 

study area.

Erosional surface on top of unit 4. The thickness of 

unit 4 is irregular in the study area. An isopach map of the 

interval from the base of a laterally extensive marine 

limestone in unit 3 to the top of unit 4 (fig. 6) shows an 

incised channel system that has about 40 m (130 ft) of relief.

The axis of this channel system also trends roughly north 

and lies slightly west of Copper Spur (fig. 6). South of Eagle 

County Road 31, between Copper Spur and McCoy, two 

channels are present: one continues south through Bond, 

and the other trends to the southwest. This pattern of two 

channels, oriented southward and southwestward, continues 

to manifest itself in both the marine and nonmarine deposits 

of the next two transgressive-regressive cycles (figs. 7, 8). 

Turbidity current deposits in unit 5a. These deposits 

are confined to the eastern part of the study area. They 

consist of thinly interbedded, tan, medium-grained 

sandstone and dark-gray siltstone. Both the sandstone and 

siltstone beds are laminated on a millimeter scale. The bases 

of the sandstone beds contain abundant tool marks and rare 

flute marks. The tops commonly show primary current 

lineation, current ripples, and small pieces of plant debris. 

Paleocurrent directions based on orientations of tool marks 

and ripple marks show two trends, following the courses of 

the valleys incised into the underlying conglomerate. The

Sedimentary Facies in Minturn Formation, North-Central Colorado Y5
106°4730" 

39*5730"

106*40'

39 52'30"

COLORADO

EXPLANATION

V Paleocurrent vector mean

! ! ! Ruvial deposits

Maximum clast size 

(in centimeters)

 0-2

 3-10

 11-20

 21-30

Figure 4. Paleocurrent directions and maximum clast sizes for a fluvial sequence in unit 3. Stratigraphic position of the sequence 

is shown in figure 2. Rose diagrams for paleocurrent vectors are given in the appendix.

deposits north and west of Bond are oriented generally to 

the south, whereas those west of Copper Spur are oriented 

to the southwest (fig. 7). South of Bond, this part of the 

section is made up mostly of siltstone.

Thickness variations in the turbidity current deposits 

are also instructive. Because the overlying fluvial deposits 

in unit 5a channel into the turbidites at some locations, an 

isopach map was made of the fluvial deposits and the 

turbidites together. The resulting contour map (fig. 7) shows 

a sediment package that fits into the valleys incised on the

top of unit 4. This relationship suggests that the turbidity 

currents moved down the incised valleys after the valleys 

were drowned by a marine transgression. The turbidites and 

overlying fluvial deposits then filled the valleys.

Fluviodeltaic deposits in unit 5b. This interval 

contains three Gilbert-type deltas (Gilbert, 1885) (fig. 8). 

The deltas are composed of tan, granular, coarse-grained 

sandstone and are encased in gray siltstone. They are 

characterized by large-scale planar-tangential foresets 

inclined at about 20°-25° and are lobate in plan view. North

Y6 Evolution of Sedimentary Basins Uinta and Piceance Basins
10604730" 

39*5730' 106M01

39* 52'30"

EXPLANATION

V Paleocurrent vector mean

i;"; Ruvial deposits

Maxim urn clast size 

(in centimeters)

 0-2

 3-10

 11-20 

21-30

Figure 5. Paleocurrent directions and maximum clast sizes for fluvial unit 4. Stratigraphic position of the unit is shown in figure 

2. Rose diagrams for paleocurrent vectors are given in the appendix.

of the Gilbert delta, outcrops are 1.5-5-m (5-15 ft)-thick 

bodies of tan, trough crossbedded, granular and coarsegrained sandstone containing common wood fragments. 

These sandstone bodies are also encased in gray siltstone. 

They are interpreted as fluvial deposits of the drainage 

systems that fed the deltas.

Paleocurrent measurements were made on the Gilbert 

delta foresets. Two deltas, both prograding to the south, are 

exposed above the south-flowing channel incised in unit 4.

Another delta, prograding to the southwest, is exposed 

above the southwest-flowing channel. The orientation of 

these three deltas shows a continued trend of drainage from 

north to south, along channels established after deposition 

of unit 4.

Fluvial deposits in unit 5b. This interval caps the 

aforementioned fluviodeltaic interval in unit 5b. It is 

composed of thick (6-12 m, 20-40 ft), laterally extensive 

deposits of pebbly and sandy granular conglomerate

Sedimentary Facies in Minturn Formation, North-Central Colorado Y7
39°57 30"

106*40'

39*52' 30"

Figure 6. Isopach map showing the thickness of the interval from the base of a laterally extensive limestone in unit 3 to the top 

of unit 4. Stratigraphic position of the interval is shown in figure 2. Contour interval 6 m. Solid circles indicate locations of 

measured sections.

separated by siltstone deposits 3-6 m (10-20 ft) thick. 

Although cobbles as large as 25 cm (10 in.) in diameter 

were found at one location in the southeastern part of the 

study area, the maximum clast size is 15 cm (6 in.) at most 

locations. Trough crossbedding, planar bedding, and planartabular crossbedding are the most common structures. 

Paleocurrents were measured on the trough- and planartabular crossbeds. Measurements show flow to the 

southwest, south, and southeast (fig. 9). This flow is 

dispersed about the same axis as in the underlying deltaic 

and turbidite intervals.

Deltaic deposits in unit 5c. Gilbert-type deltas are 

also present in unit 5c, but, unlike the preceding marine 

interval, the main sites of delta progradation are in the 

western part of the study area. In other respects, the deltas 

are similar to those of unit 5b, consisting of granular, 

coarse-grained sandstone in large-scale (average height 6 m,

21 ft) foresets inclined at about 20°-25°. Paleocurrent 

measurements show that progradation was generally toward 

the south and east. Strata in this interval that crop out in the 

area near Bond and Copper Spur contain only siltstone and 

thin sandstone beds (fig. 10). These sandstone and siltstone 

beds are inferred to be marine because they contain marine 

trace fossils at one location.

Braided fluvial deposits in unit 6. Unit 6 is an 

unusually thick, widespread interval containing very coarse 

grained fluvial deposits in the western part of the study area, 

finer grained fluvial deposits in the central part, and Gilbert 

delta deposits in the southeastern part (fig. 11). The fluvial 

conglomerates occur as solid bands in the outcrop rather 

than as isolated channels in siltstone. Presumably, 

amalgamation of multiple channels (Alien, 1978; 

Leeder, 1978) produced this sheetlike appearance. The

Y8 Evolution of Sedimentary Basins Uinta and Piceance Basins
106e47'301'

39°57'30'

106° 40'

39* 52'30"

Figure 7. Isopach map showing thickness of turbidites and fluvial deposits in unit 5a. Paleocurrent vectors (solid arrows) compiled 

from measurements on current ripples and tool marks are also displayed. Rose diagrams for vectors are shown in appendix. 

Stratigraphic position of the unit is shown in figure 2. Contour interval 6 m. Solid circles indicate locations of measured sections.

conglomerates consist mostly of pebbles and cobbles in a 

coarse sandy and granular matrix. Trough crossbedding and 

planar bedding are the most common stratification types. In 

the western part of the study area, massive bedding and 

planar-tabular crossbedding are also common.

The deltas are lobate in plan view and contain 

large-scale (average thickness 13 m, 42 ft) planar-tangential 

foresets inclined at 20°-30°. The deltas are composed of 

granular, coarse-grained sandstone and are encased in 

siltstone. Paleocurrents were measured on both the fluvial 

and deltaic deposits using trough and planar-tabular crossbedding in the fluvial deposits and the large-scale, planartangential crossbedding of the delta foresets. The results 

show that fluvial currents were distributed radially around a 

north-south axis running through the western part of the 

area. The deltas also prograded to the south over the 

location those in the underlying marine interval in unit 5b 

(fig. 8). The trend of decreasing clast sizes from west to east

(fig. 11) and the transition from a nonmarine to a marine 

environment also provide evidence that the main trunk 

stream lay in the western part of the area.

An isopach map of unit 6 (fig. 12) shows that the 

greatest accumulation of sediment (49 + m, 160 + ft) was in 

the western part of the study area, with thinning to the east. 

This trend is reversed west of Bond and Copper Spur, where 

a linear pattern of thicker sediment accumulation occurs. 

These patterns are consistent with progradation of a 

sediment wedge from the north, rather than from the east.

Studies of overlying units. Studies of other units of 

the Minturh and Maroon Formations, overlying those 

discussed here, also provide evidence that the regional slope 

of the area was from north to south. T.R. Walker (University 

of Colorado) and J.C. Harms (Harms and Brady, Inc.) 

(written commun., 1985) showed that deltas in the western 

part of the McCoy-Bond area prograded to the southeast

Sedimentary Facies in Minturn Formation, North-Central Colorado Y9
106°4730"

39*5730" 106MO'

39D 5Z30M

ANTELOPE 

CREEK 

FAULT

ID

COLORADO

Maximum clast sizes 

(in centimeters)

 0-2

 3-10

 11-20

 21 -30

Explanation 

V Paleocurrent vector mean

Distributary channel

Gilbert delta

Shaley interfluvial/interdeltaic area

Figure 8. Paleocurrent directions and paleogeography during deposition of the lower part of unit 5b. Stratigraphic position of the 

unit is shown in figure 2. Rose diagrams for paleocurrent vectors are shown in appendix.

during deposition of unit 7 and to the south during 

deposition of unit 9. Stevens (1958), in reporting on 

distribution of marine limestone in the area, noted that 

marine limestones in units 13, 15, and 17 thin and decrease 

in fossil content to the north and east.

Johnson (1987), in studying fluvial sediments of the 

lower part of the Maroon Formation (overlying the Minturn), showed that a fluvial channel complex cropping out 

1.6 km (1 mi) northwest of McCoy is oriented northeastsouthwest and has a paleocurrent bearing of 228° (S. 48° 

W.). His estimate of the paleodischarge rate of the river 

associated with this channel is 417-1,250 m3/sec, 

comparable to that of the modern South Platte River and 

"surprisingly large."

Y10 Evolution of Sedimentary Basins Uinta and Piceance Basins
106e4730 

39*5730

106°40'

0 1 KILOMETER I '-i i

0 1 MILE ID

COLORADO

Explanation

Maximum clast sizes 

(in centimeters)

 0-2

 3-10

 11-20

 21-30

V Paleocurrent vector mean

Figure 9. Paleocurrent vectors compiled from measurements made on fluvial deposits from the upper part of unit 5b. 

Stratigraphic position of the unit is shown in figure 2. Rose diagrams for paleocurrent vectors are shown in appendix.

Structural Influence on Paleocurrent 

Trends and Facies Patterns

The study area is near an en echelon offset in the fault 

zones thought to have bounded the eastern margin of the 

central Colorado basin. These areas of lateral offset between 

faults are known as transfer zones (Dahlstrom, 1969). They

are recognized in both extensional (Crossley, 1984; Gibbs, 

1984; Leeder and Gawthorpe, 1987; Leeder and others, 

1988) and compressional (Dahlstrom, 1969, 1970) settings. 

They are described by Dahlstrom (1969) as "a kind of lap 

joint wherein the fault whose displacement is diminishing is 

replaced by an echelon fault whose displacement is 

increasing."

Sedimentary Facies in Minturn Formation, North-Central Colorado Y11
106°4730"

39°5730"

106°40'

39'5Z30"

ANTELOPE 

CREEK 

FAULT

COLORADO

Maximum clast sizes 

(in centimeters)

 0-2

 3-10

 11-20

 21-30

Explanation 

Paleocurrent vector mean

Distributary channel 

Beach

Gilbert delta lobe

Marine sandstone

I-I-I-! Marine shale

Figure 10. Paleocurrent directions and paleogeography during deposition of the lower part of unit 5c. Stratigraphic position of 

the unit is shown in figure 2. Rose diagrams for paleocurrent vectors are shown in appendix.

Transfer zones have important effects on the 

sedimentology of the basin fill. Fault-offset zones in the 

Malawi Rift Valley of Central Africa have large drainages 

developed on them that yield the greatest quantities of 

sediments to the rift basin (Crossley, 1984). The sediments 

accumulated at the bases of the transfer zones as "extensive 

sheets of coarse alluvium." The transfer zones may be 

underlain by transverse faults (Leeder and others, 1988).

Leeder and Gawthorpe (1987) also noted that large 

drainages tend to be developed along fault-offset zones in 

extensional settings. These drainages may extend far back 

into the hinterland, as a consequence of structural weakness 

in the offset zone.

The basin-margin faults of the Central Colorado basin 

in the McCoy-Bond area (that is, the Gore fault, unnamed 

northern fault, and unnamed transverse fault) were almost

Y12 Evolution of Sedimentary Basins Uinta and Piceance Basins
39°5730

106°40'

39* 52'30"

ANTELOPE 

GRiEEK 

FAULT

Maximum clast sizes 

(in centimeters)

 0-2

 3-10

 11-20

 21-30

Explanation 

Paleocurrent vector mean

Fluvial deposits 

Distributary channel deposits

Gilbert delta deposits 

Shaley interfluvial deposits

Figure 11. Paleocurrent directions and paleogeography during deposition of unit 6. Stratigraphic position of the unit is shown 

in figure 2. Rose diagrams for paleocurrents are shown in appendix.

certainly active during Pennsylvanian time. Thus, the Minturn Formation in this area was probably deposited at the 

base of a transfer zone. The presence of a transfer zone to 

the north of the study area would provide a zone of 

structural weakness and a topographic gradient necessary 

for development of south-flowing drainages. The 

surprisingly large size of the stream drainage noted by 

Johnson (1987) near McCoy may have been the result of an

extensive drainage network developed to the north, along 

the dying trace of the Gore fault.

The concentration of deltas south of a line extending 

through McCoy and Copper Spur (figs. 8, 10, and 11) may 

also be a consequence of the transfer zone. The variety of 

marine and nonmarine deposits in each depositional cycle 

attests to fluctuations in relative sea-level position, yet only 

one Gilbert delta of the eighteen known from the area has

Sedimentary Facies in Minturn Formation, North-Central Colorado Y13
106°4730"

39°5730"

106°40'

39* 52'30"

ANTELOPE 

CREEK 

FAULT

Explanation

Maximum clast sizes 

(in centimeters)

 0-2

 3-10 

11-20 

21-30

Paleocurrent vector mean

Figure 12. Isopach map showing the thickness of unit 6. Paleocurrent vectors from fluvial and deltaic deposits are shown for 

reference. Stratigraphic position of the unit is shown in figure 2. Contour interval 6 m.

been identified in outcrops at any horizon in the Minturn 

Formation north of the line through McCoy and Copper 

Spur. If the shoreline gradient were steep in this area, a large 

rise in sea level would be required to advance the shoreline 

any appreciable distance northward. Marine shorelines may 

have been repeatedly established in the area because the 

steep topographic gradient to the north did not permit

further northward transgression. Southward-flowing 

drainages would have dropped their loads to form deltas 

repeatedly in approximately the same location.

A third consequence noted by Leeder and Gawthorpe 

(1987) is the presence of unusually large depocenters at the 

bases of transfer zones. The McCoy-Bond area, with its 

concentration of deltas and coarse fluvial deposits, may

Y14 Evolution of Sedimentary Basins Uinta and Piceance Basins
106*4730"

39°5730"

106° 40'

COLORADO

Figure 13.

6 m. Solid

Isopach map showing the thickness of unit 5b. Stratigraphic position of the unit is shown in figure 2. Contour interval 

circles indicate locations of measured sections.

represent one of these large depocenters. Wood and 

Ethridge (1988) and Ethridge and Wescott (1984) suggested 

that braided fluvial and Gilbert delta deposits make 

excellent hydrocarbon reservoirs. Transfer zones such as 

that described for the McCoy-Bond area may thus be likely 

locations for multiple stacked reservoirs of unusually large 

size.

SEDIMENT DISTRIBUTIONS

Another unexpected result of the present study is the 

discovery that Minturn fluvial drainages in the McCoyBond study area were repeatedly established at the same 

locations. Because braided rivers have excessive sediment 

loads and shallow channels with unstable banks, avulsion 

occurs frequently (Miall, 1977), and broad braidplains may 

develop in the lower reaches of the rivers (McPherson and

others, 1987). Braided fluvial sediments in the study 

interval are not distributed randomly over the study area; 

rather, the coarsest sediments are repeatedly restricted to the 

same geographic locations through several transgressiveregressive cycles. The intervening marine units also show a 

concentration of sand bodies, including Gilbert deltas and 

turbidites, at the same locations as the coarse fluvial 

deposits. Paleocurrents measured on the Gilbert deltas, 

turbidites, and fluvial deposits show a radial distribution 

about these sites of coarsest sediment accumulation. Two 

sequences can be used to illustrate these points.

Units 4, 5a, and 5b. These units all show sediment 

dispersion about a north-south axis just west of Bond and 

Copper Spur (figs. 5-8). This axis coincides with the trace 

of a north-south-oriented basement fault (the Bond fault of 

Schmidt, 1961), along which an unnamed drainage 

presently flows. Pennsylvanian drainages also flowed along 

this axis; the isopach map (fig. 6) shows a large valley

Sedimentary Facies in Minturn Formation, North-Central Colorado Y15
incised into unit 4 along the trace of the present-day Bond 

fault. It is not known whether a fault also underlies the 

drainage extending southwest from Copper Spur. Paleocurrent measurements made on tool marks and current 

ripples in the overlying turbidites show that turbidity 

currents also flowed down the incised channels (fig. 7).

This same area continued to be a site of coarse 

sediment accumulation during deposition of successive 

intervals. The overlying marine part of unit 5b, for example, 

contains three Gilbert deltas located over the sites of the two 

channels incised into unit 4 (fig. 8). Their paleocurrent 

directions coincide with those measured on the turbidites 

(fig. 7). Similarly, the braided fluvial deposits overlying 

these deltas (fig. 9) show the same dispersal patterns. An 

isopach map (fig. 13) of the marine and nonmarine deposits 

in unit 5b shows that, again, the thickest deposits are at the 

same locations as in unit 5a.

Units 5c, 6, and 7. Following deposition of unit 5b, 

the axis of sediment dispersion shifted to the western part of 

the study area. The new axis is coincident with the trace of

another north-south-oriented basement fault (herein referred 

to as the Antelope Creek fault) and a modern drainage, 

Antelope Creek (fig. 3).

After a marine transgression, Gilbert deltas prograded 

south and southeast from the axis along the trace of 

Antelope Creek fault. Five delta lobes were discovered in 

the western part of the study area (fig. 10), whereas in the 

eastern part only siltstone and thin sandstone beds were 

noted (fig. 10).

Overlying these deltas are coarse fluvial deposits of 

unit 6. This unit shows paleocurrents radiating outward 

from the trace of the present-day Antelope Creek fault (fig. 

11). The area east of the Bond fault contains mostly 

sandstone and siltstone, and Gilbert deltas formed in the 

southeastern part of the study area.

An isopach map of units 5c and 6 (fig. 14) shows that 

the thickest accumulations of sediments are in the western 

part of the study area, though the area near the trace of the 

Bond fault also received more sediment than the 

immediately surrounding area. The area around McCoy, by

106°4730"

39°5730'

106° 40'

3&5230"

Figure 14. Isopach map showing the combined thickness of units 5c and 6. Stratigraphic position of the unit is shown 

figure 2. Contour interval 6 m. Solid circles indicate locations of measured sections.

Y16 Evolution of Sedimentary Basins Uinta and Piceance Basins
contrast, contains thinner accumulations of units 5c and 6 

and no accumulation of units 5a and 5b.

Unit 7 is a marine unit containing Gilbert deltas that 

were studied by T.R. Walker and J.C. Harms (written 

commun., 1985). At locations about 0.8 km (1/2 mi) east of 

Antelope Creek fault and 0.8 km (J/2 mi) north of the 

Colorado River, these workers discovered three lobes of a 

delta prograding to the east and southeast. This delta may 

also have been fed from paleodrainages following the trace 

of the Antelope Creek fault.

Structural Influence on 

Sediment Distributions

The repeated coincidence of stream drainages (and 

hence sites of delta progradation and turbidite deposition) 

and the traces of the Bond and Antelope Creek faults 

strongly suggests that these faults were active during 

deposition of the Minturn Formation. They exerted control 

on local sedimentation patterns by restricting drainages to 

specific paths and by increasing subsidence at specific 

locations.

DeVoto and others (1986, fig. 1) also inferred that the 

Bond and Antelope Creek faults were active in 

Pennsylvanian time, although they make no specific 

reference to them. Contemporaneous movement on the 

Bond and Antelope Creek faults during deposition of the 

Minturn Formation cannot, however, be directly confirmed. 

Modern valley incision and deposition do not permit direct 

observation of the faults where they pass through the study 

interval. These faults are two of several in the area that are 

present along the axes of folds associated with the Laramide 

orogeny. They are oriented parallel with the Gore fault 

zone, but their exact attitudes are not known. The Bond fault 

is exposed in a railroad cut southwest of Copper Spur (fig. 

3); at this location the fault is essentially vertical. The Gore 

fault was also described as vertical by Tweto and Lovering 

(1977).

Thickness changes within the study interval provide 

indirect evidence for movement on the Bond and Antelope 

Creek faults during deposition of the Minturn Formation. A 

northwest-southeast cross section through these two faults 

(fig. 15) shows that the interval from the base of unit 3 to the 

top of unit 5b thickens substantially from 134 m (440 ft) 

near Antelope Creek fault to 207 m (680 ft) near the Bond 

fault and that units 5 a and 5b are preserved only in the 

vicinity of the Bond fault. The interval containing units 5c 

and 6 shows the reverse relationship and thickens from 55 m 

(180 ft) near the Bond fault to 85 m (280 ft) near Antelope 

Creek fault. These thickness changes may have been the 

result of differential tilting and subsidence; the area east of 

the Bond fault subsided most rapidly during deposition of 

units 3 through 5b, and the area west of the Antelope Creek 

fault subsided most rapidly during deposition of units 5c

and 6. The area between the two faults contains the thinnest 

sections and thus subsided most slowly.

The distribution of facies in the study area further 

supports this interpretation. Other workers have noted that 

structural lows tend to be sites of river channels, deltas, 

estuaries, and turbidites, whereas structural highs are interchannel and interdeltaic areas, shoals, and reefs (Alien, 

1978; Bridge and Leeder, 1979; Weimer, 1986). These 

distributions are also evident in the Minturn Formation. 

Note, for example, the repeated occurrence of major fluvial 

channels, deltas, and turbidites near the Bond fault in units 

5a, 5b, and 6 (figs. 6-9, 11, 12) and near Antelope Creek 

fault in units 5c and 6 (figs. 10-12). T.R. Walker and J.C. 

Harms (written commun., 1985) showed additional deltas 

near Antelope Creek fault in units 7 and 9. Also note that 

during deposition of units 3 through 5b the coarsest deposits 

were repeatedly concentrated near the Bond fault (figs. 4, 5, 

and 9). During deposition of units 5c and 6, coarse deposits 

were concentrated near the Antelope Creek fault (figs. 10,

11).

By contrast, it is noteworthy that deltas and turbidites 

are lacking in the outcrops around McCoy. The McCoy area 

received finer fluvial sediments during deposition of the 

nonmarine intervals. It was an interdeltaic area during 

deposition of most of the marginal-marine intervals and was 

the site of small carbonate buildups during deposition of 

marine intervals in units 3 and 5c.

If the Minturn Formation in the study interval were 

petroliferous (which it is not), structural control on facies 

distributions would cause the areas near the faults to be 

much better exploration targets than interfault areas. Near 

the faults a drill hole would likely encounter multiple 

stacked delta and channel deposits, whereas in an interdeltaic area a drill hole would probably encounter smaller 

fluvial channels and more shaley and carbonate facies.

An additional consequence of the structural control 

on facies distributions is that a vertical section measured at 

any location in the study area will not necessarily predict 

lateral relations accurately. An important qualification on 

Walther's Law is that facies belts must be able to migrate 

freely in order for all facies to be represented in a vertical 

section; however, structural control of drainage paths 

precludes free lateral migration of facies belts. Thus, any 

paleoenvironmental reconstruction based on a vertical 

section may omit laterally adjacent facies that are volumetrically significant.

The Bond and Antelope Creek faults can be related to 

other structural features along the eastern margin of the 

basin. They are the southernmost strands of the northern 

fault zone that forms the continuation of the eastern margin 

of the basin north of the transfer zone at McCoy (fig. 16). In 

the McCoy-Bond area, the thickest sections through the 

study interval are on the east side of the Bond fault. Workers 

in the Minturn and Avon areas, about 40 km (24 mi) to the 

southeast, also noted thickening of the Minturn Formation 

as they traced sections eastward toward the Gore fault zone

Sedimentary Facies in Minturn Formation, North-Central Colorado Y17
NW 

UNIT

5C/6

10 SE

Subsurface 

data

Fluvial channel conglomerate 

Foreshore sandstone 

Gilbert delta sandstone

Turbidite (sandstone and 

shale)

0

h

o

Marine limestone

Marine and nonmarine shale

1 KILOMETER

1 MILE

Figure 15. Northwest-southeast cross section showing units 3, 4, 5, and 6 of the Minturn Formation. Datum is base of unit 7. 

Heavy lines represent unit boundaries. Subsurface data are from Stevens (1958). Line of section shown in figure 3. Locations of 

measured sections (numbered) shown in appendix map.

(Boggs, 1966; Tillman, 1971; Walker, 1972; Schenk, 1989). 

This area of unusual thickness in the Minturn Formation 

was named the Vail-McCoy trough by Walker (1972).

By contrast, the area between the Bond and Antelope 

Creek faults received consistently thinner sediment 

accumulations during deposition of units 3 through 6. 

Schenk (1989) showed an area of thinner sediments to the 

south in the area around Edwards and Avon that he 

attributed to block faulting and differential subsidence 

associated with a structural high which he refers to as the 

Avon-Edwards high. He also showed an area of thicker

sediment accumulation in the area around Eagle, about 40 

km to the southwest, that he termed the Eagle sub-basin. 

Additional evidence for block-faulting within the central 

Colorado basin has been presented by Waechter and 

Johnson (1986) and Johnson and others (1990).

CONCLUSIONS

Study of the middle part of the Pennsylvanian Minturn Formation along the eastern margin of the Eagle basin

Y18 Evolution of Sedimentary Basins Uinta and Piceance Basins
TRANSVERSE 

FAULT ZONE

NORTHERN FAULT 

ZONE

ANCESTRAL 

FRONT RANGE

Precambrian 

basement rocks

X'

Fluvial channels

^ GORE FAULT 

ZONE

BOND FAULT

^

Gilbert delta lobes

Turbidites

Pro-delta mud

ANTELOPE 

CREEK FAULT

Figure 16. Block diagram showing the relationship between faults and sedimentary deposits in the study area during deposition 

of the Minturn Formation. Placement of faults is after Tweto (1976) and Tweto and others (1978). Teeth are on downthrown blocks, 

and heavy arrows show direction of relative movement during Pennsylvanian time. Top of block is approximately 32 by 40 km 

(20 by 25 mi).

has resulted in the following interpretations in regard to the 

relationship between structure and sedimentation in the 

area.

An en echelon offset in the bounding faults along the 

basin margin was a significant structural influence on 

sedimentation. Presence of a transfer zone may have caused 

the repeated southward orientation of stream drainages in 

the area and the concentration of shoreline sediments at the 

base of the zone in the southern part of the study area.

The southernmost strands of the basin margin fault to 

the north extended into the McCoy-Bond area and were 

active during deposition of the middle part of the Minturn 

Formation. The block east of the Bond fault subsided most 

rapidly during deposition of units 3 through 5b, and the 

block west of Antelope Creek fault subsided most rapidly 

during deposition of units 5c through 9. This subsidence 

caused the locations of major drainages, deltas, and turbidites to be restricted to the subsiding blocks, whereas the 

intervening upthrown block was the site of interdeltaic 

deposits and small carbonate buildups. This differential 

subsidence caused thicker and more complete sections to be

preserved east of the Bond fault and west of the Antelope 

Creek fault and thinner, less complete sections to be 

preserved on the intervening block.

The fault-bounded blocks in the study area are similar 

in structural style to the Vail-McCoy trough of Walker 

(1972) and Schenk (1989) and the Avon-Edwards high and 

Eagle sub-basin of Schenk (1989).

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Y20 Evolution of Sedimentary Basins Uinta and Piceance Basins
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D.S., ed., New interpretations of northwest Colorado 

geology: Rocky Mountain Association of Geologists, 

p. 51-64.

Walker, T.R., 1972, Bioherms in the Minturn Formation (DesMoinesian age), Vail-Minturn area, Eagle County, 

Colorado: Colorado School of Mines Quarterly, v. 67, no. 4, 

p. 249-278.

Weimer, R.J., 1986, Relationship of unconformities, tectonics, and 

sea level changes in the Cretaceous of the Western Interior, 

United States, in Peterson, J.A., ed., Paleotectonics and 

sedimentation in the Rocky Mountain region: American 

Association of Petroleum Geologists Memoir 41, 

p. 397-422.

Wood, M.L., and Ethridge, F.G., 1988, Sedimentology and 

architecture of Gilbert- and mouth bar-type deltas, Paradox 

Basin, Colorado, in Nemec, W., and Steel, R.J., Fan 

deltas Sedimentology and tectonic settings: Glasgow, 

Blackie and Son, p. 250-263.

Sedimentary Facies in Minturn Formation, North-Central Colorado Y21
APPENDIX ROSE DIAGRAMS FOR DEPOSITIONAL UNITS OF THE MINTURN 

FORMATION

Data for each paleocurrent arrow on the maps (text figs. 4-12) are shown as rose diagrams. The diagrams are grouped 

by units, and the unit numbers are given at the top of each set of diagrams (see also text fig. 2). Location numbers are given 

for each diagram; see the map that immediately follows for locations of measured sections (shown as solid circles on map). 

The number of measurements is given in the lower left below each diagram, and the percentage value of the outer perimeter 

(in relation to the entire data set) is given in the lower right. The trend and plunge of the mean paleocurrent vector for each 

data set is shown as a small black square.

106°4730"

39 P5730"

39° 52'30"

106°40'

COLORADO

86/14 

 87/17

Bond

87/18

Y22 Evolution of Sedimentary Basins Uinta and Piceance Basins
Fluvial Deposits, Upper Part of Unit 3a

84/1 

Troughs

84/26 

Troughs

N = 38 Circle » 30% Circle = 50%

84/42 

Troughs

84/50 

Troughs

N = 13 Circle » 30% N-14 Circle - 20%

86/1 

Troughs

86/8a 

Troughs

N = 13 Circle - 50% N-18 Circle = 30%

Sedimentary Facies in Minturn Formation, North-Central Colorado Y23
Fluvial Deposits, Upper Part of Unit 3a

87/13 

Troughs

87/15 

Troughs

Circle = 30% Circle « 50%

87/16a 

Troughs

87/17 

Troughs

Circle - 30% Circle 30%

Y24 Evolution of Sedimentary Basins Uinta and Piceance Basins
Fluvial Deposits, Unit 4

84/1 

Troughs

84/26 

Troughs

N = 30 Circle = 40% N = 26 Circle = 30%

84/33 

Troughs

84/50 

Troughs

N = 14 Circle 30% N-14 Circle = 30%

86/1 

Trough and planar crossbeds

86/3 

Troughs

Circle = 30% Circle = 50%

Sedimentary Facies in Minturn Formation, North-Central Colorado Y25
Fluvial Deposits, Unit 4

87/15 

Troughs

87/17 

Troughs

N = 22 Circle = 30% N = 22 Circle = 20%

Y26 Evolution of Sedimentary Basins Uinta and Piceance Basins
Turbidites, Lower Part of Unit 5a

84/26 

Current ripples

84/26 

Tool marks

N=35 Circle . 50% Circle = 50%

84/33 

Tool marks 86/1 

Current ripples

NX: 41 Circle - 50% Circle = 50%

86/1 

Tool marks

Equal Area

87/13 

Tool marks

Equal Area

Circle - 50% Circle = 50%

Sedimentary Facies in Minturn Formation, North-Central Colorado Y27
Turbidites, Lower Part of Unit 5a

87/14 

Tool marks

N=54 Circle = 50%

87/15 

Tool marks

Circle - 50%

87/17 

Tool marks

Circle = 50%

Y28 Evolution of Sedimentary Basins Uinta and Piceance Basins
Delta Deposits, Lower Part of Unit 5b

87/13 

Large planar foresets

87/14 

Large planar foresets

N=27 Circle = 50% N = 20 Circle = 50%

87/15 

Large planar foresets

87/17 

Large planar foresets

N = 32 Circle = 30% NX: 15 Circle = 50%

87/17 

Troughs

N = 15 Circle = 50%

Sedimentary Facies in Minturn Formation, North-Central Colorado Y29
Fluvial Deposits, Upper Part of Unit 5b

84/33 

Troughs

87/14 

Troughs

N = 23 Circle = 50% N = 59 Circle = 50%

87/15 

Troughs

87/17 

Troughs

Circle = 50% N = 54 Circle = 20%

Y30 Evolution of Sedimentary Basins Uinta and Piceance Basins
Delta Deposits, Lower Part of Unit 5c

87/5 

Large planar foresets

87/6 

Large planar foresets

Circle - 50%

87/16 

Large planar foresets

87/19 

Troughs

N = 24 Circle = 50% N = 23 Circle = 50%

Sedimentary Facies in Minturn Formation, North-Central Colorado Y31
Fluvial Deposits, Unit 6

84/3-4 

Planar crossbeds

N = 41 Circle = 30%

86/1 

Planar crossbeds

N = 18

84/33 

Troughs

Circle - 20%

86/8 

Troughs

Circle = 50% Circle = 30%

86/11 

Planar crossbeds

87/2+5 

Planar crossbeds

Circle - 60% Circle = 30%

Y32 Evolution of Sedimentary Basins Uinta and Piceance Basins
Fluvial Deposits, Unit 6

87/6+7 

Troughs

Circle = 50%

87/9 

Trough and planar crossbeds

Circle = 50%

87/11 

Troughs

87/8 

Trough and planar crossbeds

N

Circle = 30%

87/10 

Trough and planar crossbeds

N = 14 Circle = 50%

87/19 

Planar crossbeds

N = 32 Circle = 50% N = 21 Circle - 50%

Sedimentary Facies in Minturn Formation, North-Central Colorado Y33

*U.S. GOVERNMENT PRINTING OFFICE: 1991-573-049/46009



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