A STUDY OF PRIMARY SEDIMENTARY STRUCTURES AROUND THE MOAB ANTICLINE GRAND COUNTY, UTAH

by

Clayton Joseph Parr

A thesis submitted to the faculty of the University of Utah in partial fulfillment of the requirements for the degree of

Master of Science

Department of Geology

University of Utah

August 1965

UNIVERSITY OF UTAH LIBRARIES This Thesis for the Master of Science Degree

by

Clayton Joseph Parr

has been approved

June 1965

Chairman, Supervisor^ Committee

/ 1/ Reodfry Supervisory Committee

Reader, Supervisory Committee

Head, Major Department

iradu/te Sfchool /

ii

5736^9 ABSTRACT

This study was undertaken to describe the structural

development of the Moab salt anticline. Special emphasis was

placed on a study of primary sedimentary structures in order

to detect any influence the rising salt mass had on patterns

of sedimentation during various phases of its growth. The

study involved detailed plotting of current directions in the

Cutler Formation of Permian Age, the Moenkopi Formation of

Early and Middle Triassic Age, the Chinle Formation of Late

Triassic (?) Age, the Kayenta Formation of Late Triassic (?)

Age, and the Salt Wash Member of the Morrison Formation of

Late Jurassic Age.

The Cutler Formation has two distinct alternating

lithologies. Light-orange beds of fine-grained sandstones had a northern source; they are probably eastern extensions of

the Cedar Mesa Sandstone. These units interfinger eastward with purplish coarse arkosic beds deposited by high-energy

streams flowing off the ancestral Uncompahgre range. Streams

that deposited the arkosic beds flowed in a general northwest direction parallel to the structural trend toward a depression northwest of the main salt cell in Moab Valley.

The paleodrainage pattern of the Moenkopi Formation is definitely parallel to the local structural trend; however, since the mean direction of flow conforms to the published regional direction of flow, it cannot be determined definitely

iii whether or not the pattern was influenced by the salt structure.

Thinning and pinchouts indicate that there were separate salt cells at Moab Valley and Corral Canyon about ten miles to the northwest.

The number of current-direction indicators found in the

Chinle Formation was insufficient to plot a meaningful pattern.

Thickness variations indicate that a rim syncline developed west of Moab Valley and that slight uplift occurred just northwest of Moab Valley. The salt cell at Corral Canyon became a sharp piercement structure, and a large landslide block broke from the upturned older sediments on the flank and fell into accumulating Chinle sediments.

Paleodrainage patterns and other characteristics of the

Kayenta Formation indicate that salt movement had either ceased or was very localized during Kayenta time.

Northwest of Moab Valley the streams of the Salt Wash

Member of the Morrison Formation in general flowed unimpeded over the structure. Red siltstone particles included in an immature conglomerate along the Moab fault, together with an anomalous drainage pattern along the fault, are possible indications of activity along the fault during Salt Wash time.

The site of the Moab anticline was probably determined in Pennsulvanian time by faulting that took place during the initial stages of uplift of the ancestral Uncompahgre range either just previous to or during the initial stages of

iv deposition of the Paradox Member of the Hermosa Formation. A thick sequence of evaporites accumulated in a structural trough adjacent to the fault. The time of the first salt flowage is uncertain, but the most active period of movement was during the period from Cutler time through Chinle time. Salt movement had ceased or had become very minor by Kayenta time, and the structure was covered by the Jurassic sediments. The present anticlinal structure was formed along the ancient trend probably during a phase of the Laramide orogeny. Two stages of faulting later occurred. The first resulted in a large normal fault, the

Moab fault. The second resulted in collapse features around

Moab Valley.

v ACKNOWLEDGEMENTS

I wish to express my sincere appreciation to the following:

Dr. Wm. Lee Stokes for his supervision and guidance from inception to completion of the project; Drs. A. J. Eardl and R. A. Robison for their comments and suggestions on the manuscript; John Lawrence for suggestions and assistance in measuring sections; my wife for her patience and moral support; and Union Oil Company of California for generous financial assistance.

vi CONTENTS

ABSTRACT iii

ACKNOWLEDGEMENTS ... . vi

CONTENTS. vii'

ILLUSTRATIONS i*

INTRODUCTION 1 Purpose and Scope...... 1 Procedures 2 Location and Accessibility 4 Topography 4 Previous Work 5

REGIONAL GEOLOGIC HISTORY...... 7.

GENERAL GEOLOGY OF MOAB ANTICLINE...... 12

GENERALIZED SECTION OF EXPOSED SEDIMENTARY ROCKS. .... 16

PRIMARY SEDIMENTARY STRUCTURES...... 19 Ripple Marks 19 Rib-and-Furrow 20 Lineation 22 Festoons 24 Exhumed Channels 26 Convolute Lamination 26 Penecontemporaneous Structures '. . 27

FORMATION STUDIES '. 29 Cutler Formation ' 29 General description...... 29 Local character 30 Light-orange beds. . 31 Purple beds 33 Primary structures 34 Local trends 35 Moenkopi Formation 37 General description , . . 37 Local character 39 Primary structures 39 Local trends 42

vii Chinle Formation 44 General description 44 Local character 45 Primary structures * 48 Landslide block 51 Thickness variations 59 Regional Stream-direction pattern 61 Local trends 62 Kayenta Formation . 64 General description 64 Local character 65 Primary structures 66 Local trends. . . 68 Salt Wash Member of Morrison Formation 73 General description 73 Local character 74 Primary structures 76 Local trends 77

TECTONIC HISTORY. . 81

CONCLUSIONS 93

REFERENCES CITED. 96

viii ILLUSTRATIONS ure Page

Index map of salt anticline region 4a

Tectonic divisions of the Colorado Plateau. ... 7a

Photogeologic map of Moab anticline area. . . In Pocket

Photo mosaic of canyon walls on west flank of the Moab anticline 15a

Vertical air view of a 7%-degree quadrangle

at Moab3 Utah 15b

Rib-and-furrow structures in Chinle Formation. . . 22a

Current lineation in Kayenta Formation 22a

Diagram of festoon type of cross-lamination. . . . 24a

Festoon in Cutler Formation. 24a Transverse view of festoon in Cutler Formation. . .26a

Exhumed channel in Salt Wash Member of Morrison Formation 26a

Cross-stratification in Cutler Formation light- orange sandstone 32a

Transverse view of cross-stratification in Cutler Formation light-orange sandstone 32a

Plan of salt cores of anticlines showing hypothetical reconstruction of major surface drainage during Cutler (Permian) time ,36a

Paleodrainage pattern of Cutler Formation around

the Moab anticline. . „ 36a

Parallel ripple marks in Moenkopi Formation. . . . 40a

Cusp ripple marks in Moenkopi Formation 40a

Cusp ripple marks in recent sediments of Colorado River 40a Stream directions during deposition of Moenkopi Formation <,.... 42a

ix Figure Page

20 Paleodrainage pattern of Moenkopi Formation around the Moab anticline...... 43a

21 Photograph showing Chinle Formation thickening

from north toward Colorado River...... 45a

22 Profile showing subdivisions of Chinle Formation. . 45a

23 Location of landslide block...... 53a

24 Sketch of landslide block showing angular

relationship with enclosing beds...... 53a

25 View of landslide block...... 53b

26 View of landslide block showing upper contact with enclosing strata...... 53b 27 South contact of landslide block with enclosing Chinle strata...... 55a 28 North contact of landslide block with enclosing Chinle strata...... 55a

29 Diagrammatic cross section showing history of Chinle landslide block...... 57a

30 Penecontemporaneous deformation structure in the

Chinle Formation...... 57b

31 Salt intrusion in Fisher Valley3 Utah...... 57b

32 Stream directions during deposition of Chinle Formation a. Upper part of Chinle Formation...... 63a b. Lower part of Chinle Formation...... 63a 33 Paleodrainage pattern of Chinle formation around the Moab anticline...... 63b

34 Stream directions during deposition of Kayenta Formation...... 72a

35 Paleodrainage pattern of Kayenta Formation around the Moab anticline...... 72b

36 Map of resultant dip directions of cross-laminae in sandstones of the Salt Wash Member of the Morrison Formation...... 80a

x Figure Page

37 Paleodrainage pattern of Salt Wash Member of Morrison Formation around the Moab anticline- . 80b

38 Geologic cross section northwest part of Moab anticline...... 90a

39 Structure contour map of portion of west flank of Moab anticline...... 90b

xi INTRODUCTION

Purpose and Scope

This study was undertaken to describe the structural development of the salt anticline. Special emphasis was placed on a study of primary sedimentary structures in order to test two theses:

(1) Periodic movement of the salt structure along its

present trend from Late Paleozoic to the end of the

Jurassic would have resulted in topographic expression

that would have influenced the directions of streams

that traversed the area.

(2) A method of study utilizing detailed plotting of

paleocurrent directions in certain formations around

the anticline would reveal anomalous stream patterns

that resulted from such influences.

In order to test the criteria stated above, the method used was that developed by Stokes (1952, 1953) in his studies of primary sedimentary trend indicators in the uranium-bearing

Morrison Formation in the Thompsons area in east central Utah and in the Carrizo Mountain area in northern Arizona. This involved the detailed plotting of current directions over the entire outcrop of a stream-deposited unit within the limits of 2 an area of interest. Stokes showed that a composite plot of many

individual current directions reveals distinct patterns such as drainage confluences and shifts in direction. He also presumed that variations in the stream pattern caused by local structural-

topographic features could be determined by this method.

It was hoped that such variations could be detected around the Moab salt anticline and be related to contemporaneous salt deformation.

Influence on the depositional patterns of wind-deposited sediments would have been minor and difficult to detect, so the study was confined to the stream-deposited formations with exposures suitable for study. These were the Cutler Formation of Permian Age, the Moenkopi Formation of Early and Middle

Triassic Age, the Chinle Formation of Late(?) Triassic Age, the

Kayenta Formation of Late Triassic(?) Age, and the Salt Wash

Member of the Morrison Formation of Late Jurassic Age.

As an outgrowth of the main objectives, much information was obtained about specific primary sedimentary structures in the units studied.

Procedures

In order to get a plot of paleocurrent directions for each of the formations studied, it was necessary to follow each of the formations along most of its outcrop within the expected limits of influence by contemporaneous salt structures. 3

Aerial photographs of a scale of 1:24,000 were used with transparent overlays to record the observations. An azimuth compass was used to measure the current directions. The frequency of observa­ tions was determined by both the availability of structures and the scale of the photographs. Where there were many indicators, only as many notations could be made on the photograph as would be allowed by the space available. In this case, several readings at a particular station would be averaged. Where there were few structures, each reading would be noted on the photograph. Each measured current direction was noted by a small arrow on the overlay over the spot where the observation was made. The arrows were drawn in the approximate direction that was measured, and the actual compass reading was penciled in next to it. The data on the overlays was traced later, and the arrows were drawn according to their specific bearings. A composite map for each formation was then compiled from the tracings on a base map drawn at the same scale as the aerial photographs. These show the observed paleocurrent trends over the length of the anticline. Regional current-direction maps of each formation were used to compare the local with the regional stream patterns of each of the formations.

Other methods were used to provide additional information about the problem. Data from exploratory drill-holes for potash was used to compile a small structure-contour map of a portion of the area. This data and surface observations were combined for a geologic cross section. Thickening and thinning of beds and unconformities provided much information about the structural evolution of the salt anticline.

Location and Accessibility

The Moab anticline is a feature of easy accessibility in a region known for its wilderness areas. The anticline is located in southeastern Utah in Grand County, which borders with Colorado to the east (Figure 1). The area is accessible from the north and south by U.S. Highway 160, which traverses the entire length of the anticline. Moab, the county seat, is located over the main part of the structure and is a fine base of operations.

A spur of the Denver and Rio Grande Western Railroad has been extended from the main line at Crescent Junction for a distance of about 40 miles to the Texas Gulf Sulphur potash mine about 20 miles west of Moab. The spur follows Highway 160 until it reaches a point about four miles north of Moab where it leaves the valley through a tunnel.

Numerous jeep trails branch off from the highway and offer access to most of the outcrop. A paved road goes through Arches

National Monument, part of which is included in the area of study.

Topography

As is the case in most parts of the Colorado Plateau, the

Moab area is arid with rugged, rocky topography characterized by SCALE 5 deeply dissected canyons separated by broad benches. There are two main physiographic features, the Canyon of the Colorado River and

Moab Valley. The Colorado River cuts diagonally across Moab Valley from east to west; it enters and exits through steep canyons.

Moab Valley itself has steep canyon walls on both sides, but by far more prominent is the steep escarpment on the west side. The escarpment extends for about 30 miles with a maximum relief of about

1300 feet.

Previous Works

Most references to the salt structures of the Paradox Basin were of a reconnaissance nature before oil exploration caused more detailed studies to be made in the 1920's. The first work of any significance was by Prommel (1923). The nature of the salt structures and their structural histories were discussed by Prommel and Crum (1927), and the mechanics of the salt deformation were explained by Powers (1926) and Harrison (1927). The area was studied by the U.S. Geological Survey in the 1920's and maps were composed by Baker (1933), Dane (1935), and McKnight (1940). These three works gave detailed descriptions of the stratigraphy and structure of the area as well as accounts of the nature of origin of the salt structures. Later works dealing specifically with the problem of the mechanics of salt deformation and the structural evolution of the salt anticlines were published by Stokes (1948,

1956), Shoemaker (1954), Cater (1955), and Jones (1959). The 6 most complete description of the whole Paradox salt anticline region was given by Shoemaker and others (1958). In addition to these papers dealing specifically with the salt anticlines, there have been many publications written about the stratigraphy of the area. These are too numerous to mention at this point, but many of them will be referred to in the sections dealing with the individual formations studied. The uranium boom of the 1950's and a major oil discovery on the Lisbon anticline in 1959 initiated numerous intensive geologic studies both by private companies and the U.S. Geological Survey. Much of the results has been presented in various U.S. Geological Survey publications and in guidebook articles, particularly the Ninth Annual Field

Conference Guidebook of the Intermountain Association of Petroleum

Geologists, "Guidebook to the Geology of the Paradox Basin".

Important summary papers by U.S. Geological Survey workers are by Elston and others (1962) and Cater and Elston (1963). 7

REGIONAL GEOLOGIC HISTORY

The Moab anticline is in a tectonic subdivision of the

Colorado Plateau known as the Paradox basin fold and fault belt

(Figure 2). The boundaries of this division are the Uncompahgre

uplift and the Uinta basin on the northeast; the San Rafael swell

on the northwest; the Henry basin, Monument upwarp, and Blanding

basin on the southwest; and the Four Corners platform and San Juan

dome on the southeast (Kelley, 1955, p. 35).

The dominant features of the region are a series of anti­

clinal salt structures whose northwest trends roughly parallel the

trend of the adjacent Uncompahgre uplift. In general they consist

simply of long, nearly parallel, anticlines and synclines. Prominent

valleys have been eroded along the crests of the anticlines where

they have been pierced by the Paradox Member of the Hermosa Formation

and subsequently collapsed in long irregular grabens (Kelley, 1955,

p. 36).

Most of the Colorado Plateau was a stable shelf region during

the first half of the Paleozoic Era. The great Paleozoic Mesocor-

dilleran geosyncline lay to the west. Cambrian seas transgressed

the region from west to east in Middle Cambrian time, and the sub­ mergence continued through the Late Cambrian. Any sediments that might have been deposited during Ordovician and Silurian times were removed by pre-Late Devonian epeirogenic uplift. Encroaching EXPLANATION Jj I jfcvpMiao. I ufaH. . , .777..., u-nod,**Mooo^im directio orn oeteef dip limb of fold, WKMLline Sof onticlmedirectio, orchn o,f uplif plungt eup -

*Tr ^t' nlin directiot of tynclinen of ,plung bosm.o* r tog,

Mief-ong* fault, with down thrown side

Beundory of tectonic division

Uplift

Basin

W.OGOLLS

FIGURE 2 TECTONIC DIVISIONS OF THE COLORADO PLATEAU

After Kelley (1955) 8

seas from the west again submerged the area in Late Devonian time

and the marine conditions continued through the Mississippian.

During Pennsylvanian time, and continuing into Permian

time, the northwesterly trending positives of the ancestral

Rockies became clearly and strongly developed (Kelley, 1955, p. 76).

The ancestral Uncompahgre uplift was one of the major features of

the disturbance and it played a major role in the development of

the fold and fault belt. At about the same time, the Paradox basin developed west of the mountains, and a thick evaporite

sequence was deposited to form the Paradox Member of the Hermosa

Formation. At the end of Paradox time the marine waters became

less restricted and the Upper or Honaker Trail Member of the

Hermosa was deposited along the eastern margin of the sea.

Beginning in Late Pennsylvanian time and continuing into

Permian time, the progressive action in the Uncompahgre uplift projected its energy into the Paradox basin to produce the salt anticlines and early piercements (Kelley, 1955, p. 80). Of great significance is the parallelism of the structural trends of the fold and fault belt with the trend of the ancestral Uncompahgre.

Flowage of the salt then was continuous throughout the Triassic and Jurassic and possibly even locally into the Cretaceous (Stokes,

1948, p. 26, and Shoemaker and others, 1958, p. 38).

The major uplift of the ancestral Uncompahgre probably began near the close of the Pennsylvanian and extended well into Permian time (Elston and Shoemaker, 1960, p. 54). Immediately to the west,

the conglomeratic, arkosic Cutler Formation was shed as a fanglo-

merate from the uplift.

After a long period of non-deposition, a broad floodplain

developed in Triassic time west of the still emergent Uncompahgre

and spread toward a shallow sea. Probably most of the constituents

of the resulting Moenkopi Formation were derived from the ancestral

Uncompahgre (Elston and Shoemaker, 1960, p. 54).

The end of deposition of the Moenkopi essentially marks

the close of a period of great structural displacement along the

Uncompahgre front. Uplift of the ancestral Uncompahgre nearly

ceased by Late Triassic time; the Chinle and Wingate Formations of

Late Triassic age thin gradually across the Uncompahgre front and

overlap the ancestral highland tens of miles to the northeast

(Kelley, 1955).

The great Mesocordilleran geanticline began to develop during

or near Middle Triassic time. The eastern margin of this important

element evidently coincided with the present Wasatch line through

northern and central Utah (Stokes, 1958, p. 26). This effectively

Sealed off the plateau from any marine invasions from the west and mostly continental sediments then accumulated until Cretaceous times.

The Glen Canyon Group and the San Rafael Group were deposited during

this period. Large thicknesses of eolian sand accumulated at various times and formed the Wingate and Navajo Sandstones and parts

of other units. 10

Stokes (1958, p. 29) notes the occurrence of a distinct change in sedimentation late in the Jurassic when significant tectonic changes in highlands to the south, southwest, and west, resulted in the integration of relatively large sediment laden river systems that spread out to form the various lower members of the Morrison Formation over the Colorado Plateau.

During the Cretaceous the Mesozoic Rocky Mountain geosyncline was the dominant feature. The Cretaceous was a period of widespread marine sedimentation in the Colorado Plateau, but there were extensive periods of non-marine deposition during the first half of the period and again near its close (Stokes, 1958, p. 30).

At the end of the Cretaceous and continuing well into

Tertiary time, the Laramide orogeny took place and produced the major anticlines and sync lines of the region and probably rejuvenated the Uncompahgre Plateau along essentially the same lines as the ancestral element produced in the Late Paleozoic

(Stokes, 1948, p. 40). This dates the major structural features seen today in the Colorado Plateau as Laramide including the present salt anticlines. Shoemaker and others (1958, p. 39) describe the broad anticlines over the salt cores as being post-Early Montanan

(post-Mesaverde). They also explain that these folds are greater in width than the pre-existing salt structures, and, though localized by them, do not reflect the older salt cores in every detail. The structures maintain their northwest trend established earlier by forces associated with the uplift of the ancestral Uncompahgre. Sedimentation during the Tertiary consisted primarily of

sediments being shed from Laramide uplifts into adjacent basins.

In Middle Tertiary time, the entire Colorado Plateau was uplifted

as a block between 6,000 and 8,000 feet and the lacoliths, such

as the La Sal Mountains, were emplaced (Eardley, 1962, p. 424).

Erosion and collapse of the salt anticlines have produced the

spectacular cliffs, canyons, and other features seen today.

O 12

GENERAL GEOLOGY OF MOAB ANTICLINE

The anticlinal axis of the Moab anticline extends for about

15 miles with a trend of about N.45°W. From the Colorado River

bridge northwest of Moab, the anticline extends southeast down

Moab Valley for about seven miles, where the structure flattens

and then becomes synclinal. Shoemaker and others (1958, p. 45)

extend the structural trend southeast for another 25 miles through

interpretation of a continuous line of structures on the surface.

The axis extends northwest of the bridge for about eight miles before dying out.

For descriptive purposes, the Moab anticline can be divided

into two parts with the Colorado River defining an arbitrary line

of separation. Figure 3 (in pocket) is provided as a geologic reference map. The crest of the portion extending southeast has been eroded to form a broad valley with steep canyon walls on both sides made up of sandstones of the Glen Canyon Group. The valley from the river to the town of Moab is fairly flat-bottomed and has been eroded to an elevation only slightly exceeding the base level of the river. Marginal fault zones on both sides

of the valley consist principally of normal faults with a maximum displacement of about 300 feet (Baker, 1933, p. 64). Gypsiferous beds of the Paradox Member of the Hermosa Formation are exposed along the margins of the valley. 13

About half a mile northwest of the Colorado River, the

valley closes. A minor drainage then follows the trend of the

anticline, but the axis is no longer topographically defined

by erosion of the crest. Surface expression of the structure

finally disappears just north of where it crosses Seven Mile

Canyon.

Along this northwest part of the anticline, the major

structural feature is a large-scale normal fault known as the

Moab fault. It becomes clearly evident just north of the

entrance to Arches National Monument. From there it extends

northwest generally parallel to the anticlinal axis, but southwest

of it a short distance, for about 10 miles before dying out.

The fault extends about four miles past the point where the

anticlinal axis disappears.

Maximum displacement along the fault is about 2,600 feet

(McKnight, 1940, p. 117) and the northeast block is downthrown.

Along most of the length of the fault, the Morrison Formation

of Late Jurassic Age has been faulted into contact with the

Cutler Formation of Permian Age. West of the fault there is a steep escarpment topped by vertical cliffs of Wingate Sandstone capped by resistant lower beds of the Kayenta Formation. This escarpment begins at Corral Canyon and extends for about 30 miles

southeast along the entire length of the anticline. Where it first appears, the cliff is about 320 feet high; it reaches a maximum height of about 1,300 feet just west of the entrance to

Arches National Monument where a stratigraphic interval from

Pennsylvanian Hermosa to Triassic(?) Kayenta is exposed. This is the most prominent topographic feature in the area, and it conveniently follows almost the entire length of the anticline.

East of the fault the terrain is comparatively flat over gently dipping Jurassic strata.

The fault line is easily observed along its entire length.

Since it is southwest of the anticlinal crest, the beds on the downthrown block are dipping gently to the west at the fault contact, but at a point about two miles northwest of the entrance to Arches National Monument, the Salt Wash has a 50-degree dip toward the fault. The dip is then sharply reversed along the fault by tight drag folding.

The Cutler, Moenkopi, Chinle, and Wingate Formations are well exposed along much of the length of the escarpment. The lower Kayenta forms a continuation of the Wingate cliff and the soft upper Kayenta weathers back and forms the greater part of the plateau above the cliffs (McKnight, 1940, p. 78).

Thickness variations in the Cutler, Moenkopi and Chinle

Formations are very important in any interpretation of the geologic history of the structure. The Cutler Formation is about 1,200 feet thick by the highway just below Little Canyon.

At the Texas Gulf railroad tunnel portal less than four miles 15 away, it has thinned to a feather edge. The Moenkopi is about

450 feet thick just south of Little Canyon; it thins to a feather edge in about four miles at a point about one mile south of where the Cutler pinches out. With the Cutler and Moenkopi absent, the

Chinle then rests unconformably on the Hermosa Formation (Figure 4).

The Moenkopi also pinches out near the north end of the structure at Corral Canyon (Finch, 1954, p. 3). The thickness of the Cutler at that point is uncertain.

Pronounced jointing is evident around the anticline. The joints stand out particularly in the Navajo Sandstone east and west of Moab (Figure 5). Shoemaker and others (1958, p. 43 and

45) define a major structural salt cell underlying Moab Valley proper at the epicenter of a pronounced system of arcuate joints on the southwest limb. Figure 4. Photo mosaic of canyon walls on west flank of the Moab anticline. Jn-Navajo Sandstone; Ik k-Kayenta Formation; !R w-Wlngate Sandstone; % c-Chinle Formation! % m-Moenkopl Formation; Pc-Cutler Formation; Ph-Hermosa Formation.

GENERALIZED SECTION OF EXPOSED SEDIMENTARY ROCKS

Modified after Stokes (1948) including descriptions by McKnight (1940) and Williams (1964)

Group or System Series Formation Lithologic characters, thickness, etc.

River and terrace gravel, dune sand, - pediment cover, landslice debris, etc. UNCONFORMITY Littoral, esstuarine and brackish water Mesaverde sediments. Gray and yellow sandstone C Group with interbedded gray shale. Removed by erosion from Moab area. Exposed Upper R in book cliffs about 30 miles north.

E Slate gray marine shale with a few lenses of yellow gray sandstone and Mancos T light gray marl. Soft and easily Shale eroded, forms badlands and graded A slopes. Fossils of Late Cretaceous Creta­ are abundant, especially near the ceous C base. Estimated total thickness 3,000 feet. E 1 Yellow $and stone, yellow and gray 0 Dakota conglomeratic sandstone, gray shales, and thin impure coal. Conglomerates U Sandstone contain pebbles of chert and quartzite. Forms cliffs and dip slopes. Contains s plant remains of Late Cretaceous age. 0-60 feet. TTNP.ONFnRMTTV Extremely variegated terrestrial Lower sediments including varicolored Burro shale, chert, limestone, conglomerate, Canyon 1 and sandstone. Lower conglomeratic Formation member usually forms cliff and dip Creta­ slope. Contact with Morrison obscure ceous where basal conglomerate is absent. Fossils suggest but do not prove early Cretaceous age. Thickness varies from 5 to 260 feet.

• 17

Group or System Series Formation Lithologic characters, thickness, etc. UNCONFORMITY Upper Brushy Basin Shale Member: Morrison Varicolored bentonitic mudstone with Formation minor lenses of sandstone, conglomerate Jurassic limestone, and quartzite. Forms slopes and badlands. Silicified wood and dinosaur bones common. 300 feet. Salt Wash Member: Gray medium to coarse grained sandstone R and gray pebble conglomerate inter- bedded with red to gray sandy mudstone. Usually forms rough, ledgy slope. A fluvial deposit. Locally gypsiferous at base. 250-350 feet.

Summer- Thin-bedded red or chocolate-brown ville sandy mudstone, fine-grained sandstone and shale. Contains abundant gray- Forma­ white to red chert occuring in tion spherical or elongate masses. Usually forms a well-defined gentle slope above the Entrada Sandstone. 25-65 feet.

Moab Tongue: A single massive cross- bedded grayish-white to pink bed of Entrada sandstone. Usually forms a perpen­ Sand­ dicular cliff separated from the rest stone of the Entrada by a definite bedding plane. 90-100 feet.

Main Entrada: Orange-buff or reddish massive cross-bedded or horizontal- bedded sandstone weathering into sheer or rounded cliffs. 260-300 feet.

Pink to red to reddish-brown muddy Carmel sandstone with, locally, considerable Sand­ gray to reddish sandy mudstone. stone Bedding irregular and contorted. Commonly forms a bench between the massive Entrada and Navajo Sandstones. 150-300 feet.

\ 18 Group or System Series formation Lithologic characters, thickness, etc. JURASSIC Light-buff, massive, highly cross-bedded, Navaj o aeolian sandstone. Contains a few thin ? Jur,assi:? i 1 Sand­ beds of limestone. Forms rounded cliffs a stone and hummocky benches. 150-300 feet. T R 1 Irregularly bedded, fluvial, micaceous I Upper Kayenta sandstone and sandy shale. Red, gray, A Q a Forma­ and lavender. Much lineation. Forms q Triassic i tion characteristic bench between Wingate LJ / and Navajo Sandstones. Lower portions TX D usually cap Wingate cliffs. 160-200 feet. C [1 Reddish-buff, massive sandstone in Wingate thick horizontal beds with much fine r cross-bedding within them. With lower 0 part of overlying Kayenta, usually u forms rim of canyon walls. 200 feet. P ! Terrestrial sedimentary rocks, including Chinle red, reddish-brown, and orange-red Formation' siltstone interbedded with lenses of red sandstone and shale, limestone- pebble and shale-pellet conglomerate, with lenses of grit and quartz-pebble conglomerate near base. 0-600+ feet. UNCONFORMITY " "" Middle(? ) Evenly-bedded, ripple-marked, chocolate and Moenkopi reddish-brown, shale and mudstone with Lower Formation numerous thin ledges of flaggy fine­ Triassic grained red-brown and gray sandstone. 0-450 feet. UNCONFORMITY p E Medium- to rather thick-bedded conglom­ R Cutler eratic sandstones and arkoses, which M Formation in detail may be either massive, I horizontally bedded, or cross-bedded. A Prevailing color is brown to red-brown N or purplish brown. 0-1,200 feet. P Upper or Honaker Trail Member: E Massive to thin-bedded, gray and bluish- N gray fossiliferous, marine limestone; N gray, greenish-gray, and green shale and

C O white, gray and greenish sandstone. Top Y Hermosa part only is exposed. Upper part called L Formation "Rico" Formation by many. 1550 feet. V Paradox Member-Crops out only in much A deformed and structurally complex areas N in the form of gypsum masses. Shown by I well logs to consist of common salt, A gypsum, anhydrite, various potash and N magnesium salts, black shale and limestone. Drill thickness of 7,000 feet. 19

PRIMARY SEDIMENTARY STRUCTURES

Ripple Marks

Ripple marks are perhaps the best known of the primary sedimentary structures because of their abundance in both recent and ancient sediments and their ease of recognition. A multitude of papers have been written about them, but good summaries are available by Bucher (1919), Twenhofel (1943), and Shrock (1948).

An excellent bibliography on ripple marks and other primary sedimentary structures is given by Potter and Pettijohn (1963).

Ripple mark is defined by Shrock (1948, p. 93) as the undulating surface sculpture produced in noncoherent granular materials by the wind, by currents of water, and by agitation of water in wave action. The usual sculpture consists of nearly parallel sinuous low ridges separated by shallow troughs.

As implied by the definition,, there are two basic types, current, ripple mark and wave or oscillation ripple mark. Stokes

(1953, p. 16) describes the distinctions as follows:

"As the names imply wave ripples are produced by the oscillation of water in wave action while current ripple- mark is the result of the passage of a current of air or water over a loose aggregation of granular particles. Current ripples form in moving water and migrate down­ stream due to erosion of particles on the upstream slopes and their accretion on the downstream slopes. In wave ripples the crests and troughs are usually symmetrical in cross-section while current ripples display asymmet­ rical profiles with a short steep downstream slope and a long gentle upstream slope."

Ripple marks can form in any environment where a fluid is in motion over noncoherent granular material. This includes many environments and many types of sediments. Most current ripple marks are formed at right angles to the current direction, so

they can be used to determine the paleocurrent direction. Two

types are found in the Moab area. The most common one is

characterized by even, parallel ridges and troughs, averaging

about one inch from crest to crest. The other is the linguoid

or cusp type described by Shrock (1948, p. 102) as a modified normal ripple mark with unit forms characterized by tongueiike

outline (See Figures 17 and 18).

Ripple marks are very common in the Moenkopi Formation and are present in the Chinle Formation. No ripple marks were observed in the Cutler or Kayenta Formations and very few in the

Salt Wash Member of the Morrison Formation.

Rib-and-Furrow

The term "rib-and-furrow" was proposed by Stokes (1953,p. for a primary sedimentary feature observed in the Salt Wash Sand stone consisting of parallel ridges separated by shallow trough similar to ripple marks which form parallel with the direction o current movement and not at right angles like ordinary ripple marks (Figure 6).

"The grooves and separating ridges are never sharply marked or smooth but are broken and irregular chiefly from the fact that the whole structure is made up of scale-like imbricating chips of rock which by peeling and erosion usually produce an uneven surface. The separating ridge between the grooves is usually rather sharp but cannot be said to be continuous or well-defined Average width from crest to crest is about 2% inches. 21

The groove is never sharp, being usually gently rounded. Surfaces marked by ribbing have been observed to be many square yards in area and are inferred to be even larger. Individual marks may extend for at least as much as 20 feet but the exact maximum dimensions are unknown. Especially notable is the straightness of the feature, there being no evidence of curving or anastomozing as is sometimes seen in ripple mark."

Stokes (1953, p.19) goes on to describe rib-and-furrow as being formed from ripple marks by an increase in the velocity of the overlying water.

Another description of this type of structure is given by

Hamblin (1961) from his observations in upper Keweenawan sediments of northern Michigan. Detailed study by Hamblin revealed that except for its extremely small size, the structure is identical to the trough or festoon bedding described by Knight (1929), and he therefore referred to it as "micro-cross-lamination" that is probably formed by migrating cusp-ripples whose crests are decapitated before being buried by the next ripple upstream.

Hamblin (1961, p. 399) believes that the structures are formed in a shallow water environment that was repeatedly subjected to subaerial erosion such as would exist on a flood plain or tidal flat.

In the Moab area rib-and-furrow markings were found in the

Salt Wash, the Chinle, and the Moenkopi. Occurrences were generally sparse with only a few being observed in the Moenkopi and Salt Wash and slightly more in the Chinle. 22

Lineation

Stokes (1947s p. 52) proposed the term "primary current

lineation" for linear structures that consist essentially of a

streamlining or streaming effect of sand particles in relatively

low and poorly defined windrow-like ridges parallel with the current direction (Figure 7).

Current lineation limits the depositing current to two possible opposing directions. The correct direction must be ascertained by reference to other evidence, usually current, bedding (Stokes, 1947, p. 54).

Lineation may be thought, of as a drag effect of shallow water over loose sand. The only observations of lineation markings forming at present have been in stream beds and along beaches where they form just as water ceases to flow over an area. These conditions would result from the backwash of waves as the water rushes seaward (Stokes, 1953, p. 23) or from receding water in streams. However, these examples are not very common and are not felt to represent the conditions causing the formation of the lineation in ancient sediments.

In the Moab area, lineation is abundant in the Kayenta

Formation and is by far the most prevalent type of structure in the unit. Lineation is the second most common structure in the Salt Wash, comprising about 30 to 40 percent of the observations. It is present to a lesser degree in the Chinle and Moenkopi Formations and was not observed in the Cutler.

I Figure 6. Rib-and-furrow structures in Chinle Formation. Also called "micro-eross-laminatlons.* Pencil points in direction of current.

Figure 7. Current lineation in Kayenta Formation. Pencil points in direction of current. 23

Although lineation markings are extremely abundant in the Kayenta Formation it is strange that no ripple marks were observed in that unit. It is difficult to envision widespread fluvial conditions such as were responsible for the deposition of the Kayenta sandstones without having the forming of associated ripple marks as are very common along modern streams.

This situation is also true for the Salt Wash both in the Moab area and in the Carrizo Mountains of northern Arizona (Stokes,

1953, p. 17) where very few ripple marks were observed. This could be due possibly to a combination of effects of current velocity and grain size. The average grain size in both the

Kayenta and the Salt Wash is larger than that of the Moenkopi.

Assuming that both the Kayenta and the Salt Wash represent broad plains over which threaded many meandering streams, the average sand grain size would be determined in part by the distance from the source areas and in part by the range of current velocities of the streams. Fairly slow moving streams with a large bed load might not achieve a high enough current velocity to form ripples in the manner described by Weller

(1960, p. 155):

"Bed-load transportation is of three types that succeed each other as current velocity increases. At low velo­ cities individual particles roll or slide along a relatively even bottom. Larger particles of sand and silt size are moved somewhat more easily than smaller ones because they offer larger surfaces to the pressure of flowing water. At higher velocities, ripples form and the movement of individual particles becomes rhythmic, alternating between active and resting places." 24

Possibly, uniform conditions of grain size and current velocities were such in the Kayenta and Salt Wash that the

first stage of bed load transportation persisted throughout most of the period of deposition leaving lineation but no ripple marks. The shales in the Salt Wash represent periodic

flooding, where the streams broke out through their natural

levees. The sudden lowering of current velocity and the resulting bodies of standing water would allow the finer particles normally held in suspension to settle out. The general lack of currents in these bodies of water would explain the lack of ripple marks in these units also.

So far as is known, lineation of the type observed in

these ancient sediments has not been described in recent

sediments. Most of the lineation seen forming today is slightly wavy. There are numerous confluences of tiny drainages even though the whole effect gives the impression of linearity.

Festoons

Knight (1930) described a particular type of cross- stratification resulting from (1) the erosion of plunging troughs having the shape of a quadrant of an elongate ellipsoid,

(2) the filling of the troughs by sets of thin laminae conforming in general to the trough floors, and (3) the partial destruction of the filling laminae by subsequent erosion, producing younger troughs (Figures 8, 9, and 10). These features will be referred to simply as festoons in this report. McKee (1953) classified festoons as a form of trough cross-stratification. Figure 8. Diagram of festoon type of cross-lamination showing pattern on longitudinal, transverse and horizontal rock faces. Arrow shows direction of current. Modified after Knight (1929).

Figure 9. Plan view of festoon in Cutler Formation. Knife points in direction of current. Knight (1929, p. 59) describes the troughs as varying in size, the smallest being five to ten feet wide, 25 to 50 feet long and one to three feet deep. The largest were 500 to 1,000 feet wide, several times as long, and at least 100 feet deep.

The angle of plunge of the axis of each trough decreases rapidly away from the closed end of the trough and the axis becomes a horizontal line which is cut off by a younger erosion trough.

The troughs have the general shape of long, shallow, scoop-like depressions. The troughs observed by Knight were usually not found isolated one from another; many superposed troughs would form an entire unit. The festoons were ascribed to moving sea water, particularly strong currents.

Stokes (1953, p. 23-29) amplified the understanding and application of festoons from his observations of the features in the Salt Wash Sandstone. He pointed out that the formation of festoon cross-stratification must represent a fundamental type of action that is possible in flowing currents of water which may be very large as in the ocean or very small as in a river. Stewart (1961, p. 128) suggests that some trough cross-strata may have formed by the downstream migration of arcuate bars that are similar to barchan dunes in shape.

Of more importance to this study, Stokes also explains the use of festoons in determining current directions:

"Experience shows that measurements along the longitudinal profile are difficult because of the necessity of distin­ guishing apparent and true dip when the structure is not exposed along the exact long dimension. Exposures on 26

the transverse vertical profile are meaningless for indicating direction for they show confused and opposing inclinations. The plan view presents the most easily measured aspect. Compass directions of the estimated mid-line of a trough are easy to observe and are accurate enough for the problem of current direction."

These criteria for measurement were used in the Moab area, where festoons are very common in several formations. The

objective at all times was to find plan-view exposures in order

to measure current directions. Although exposures along the

longitudinal profile are often abundant and give a good idea

of the general current direction, tftiey are very difficult to

use for plotting many indicators over a large area. This

contrasts with the usual method of current-direction plotting

by determining the resultant dip directions of cross strata.

In the Moab area festoons were the most frequently used

direction indicators in the Salt Wash and the Cutler. They are

found less frequently in the Kayenta and Chinle Formations.

Exhumed Channels

In the Salt Wash Member of the Morrison Formation it is

not unusual to find actual meandering pleochannels that have

been uncovered by erosion of the enclosing softer shale beds

(Figure 11). These are readily apparent on aerial photographs

and can be traced.

Convolute Lamination

Convolute lamination is a structure characterized by marked crumpling or intricate folding of the laminations within Figure 10. Transverse view of festoon in Cutler Formation. Pick handle points in current direction. 27 a well-defined, undeformed sedimentation unit (Potter and

Pettijohn, 1963, p. 152). They are distortions that appear to have resulted from a slow, small-scale "oozing" of bedded sediments before lithification occurred. This type of structure is common in the Moab area in the Cutler Formation.

There have been many explanations for the mode of origin of convolutions and probably there are several ways by which the sliding could be caused. Potter and Pettijohn (1963, p. 154) summarize by saying that seemingly localized slight differential forces acting on a very weak hydroplastic deposit during its process of accumulation are needed to explain the structure.

Concerning the directional significance of convolutions,

Potter and Pettijohn (1963, p. 153-154) say the following:

"The directional significance of the orientation, if any, of the axis of the convolutions is uncertain. In some cases, they show a definite trend perpendicular to the depositing current and display down-current overturning (Kuenen, 1953b; Kuenen and Sanders, 1956, p. 661). Kuhn-Velten (1955, p. 18) measured, on bedding surfaces, the normals to the fold axes of a structure, termed "Gleitfaltchen" that appears to be convolute bedding. The measurements when plotted on a map, disclosed a consistent pattern thought to be related to regional anticlinal fold axes and to indicate movement down the flanks of rising structures."

Penecontemporaneous Structures

These are defined as structures that form in sediments shortly after they are deposited. Common examples are folds, faults, contorted layers, and brecciated beds. 28

Shrock (1948, p. 259) states that structural features ascribed to penecontemporaneous deformation show by their internal structure and peripheral relations that they could have been formed only by dislocation of loose, incoherent sands and silts, by flowing and folding of hydroplastic sediments, or by fragmentation of partly consolidated sediments.

Such structures are described in the section on the

Chinle Formation. 29

FORMATION STUDIES

Cutler Formation

General description

The Cutler Formation was named by Cross (1905) for Permian

redbeds along Cutler Creek near Ouray, Colorado. The name is used

for the red shales, siltstones, sandstones, coarse arkoses, and

arkosic conglomerates that overlie the marine Pennsylvanian near

the ancient Uncompahgre uplift. To the west and southwest the

unit changes character and has been divided into different members,

the basic nomenclature for which was proposed by Baker and Reeside

(1929). The Cutler has recently been treated as a group by

Wengerd and Matheny (1958).

The Cutler exposed in the area of study falls into the

category labeled by Baars (1962, p. 164) as "Cutler Group

undifferentiated". The phrase is applied to that part of the unit

near the Uncompahgre source area which cannot be differentiated.

It can therefore be called the Cutler Formation in this area.

Baars describes the formation as typically being fine to coarse,

poorly sorted sandstones that are generally arkosic and conglomeratic.

The predominant color is reddish-brown. The Cutler reaches a

maximum thickness of about 8,000 feet near the Uncompahgre, and it

generally thins to the west. It thins markedly over all the salt

structures, and reaches a zero thickness over the Moab anticline.

Westward the unit grades into the Cedar Mesa Sandstone, the Organ

Rock Shale, and the White Rim Sandstone. The earliest Cutler 30

sedimentation in the greater Moab area is Lower Permian (Baars,

1962, p. 268).

Local character

The Cutler Formation crops out for about eight miles along

the cliff northwest of Moab. Its thickness ranges drastically

from 1,200 feet near the head of Little Canyon to zero at the

Texas Gulf railroad tunnel four miles southeast. It can easily

be distinguished from the overlying dark reddish-brown Moenkopi

shales by its distinctive bright coloring of various shades of

reddish-brown. Where exposed, the contact with the underlying

Hermosa is conformable. There is a barely discernible angular

discordance with the overlying Moenkopi, which implies that the

rapid thinning is mostly intraformational.

McKnight (1940, p. 38) describes the sequence near Moab

as medium- to rather thick-bedded conglomeratic sandstones and

arkoses, which in detail may be either massive, horizontally

bedded, or cross-bedded. The prevailing color of the sandstones

is brown to red brown or purplish brown. The unit weathers

commonly into fluted cliffs.

Some confusion has resulted in attempting to define the base

of the Cutler in the Moab area. The underlying Rico Formation

supposedly represented a transitional facies between the purely marine Hermosa and the terrestrial Cutler. However, the

distinctions were vague and in the Moab area, it has been customary

to lump the Rico with the Cutler. The lower contact with the 31

Hermosa, however, was uncertain and arbitrary, usually being placed at the last occurrence of pure marine limestones.

Baars (1962, p. 158) has discussed the whole Rico problem in detail. His reference to the Moab area would seem to clear up the problem:

"Uppermost Hermosa sediments are also exposed in the vicinity of Moab, Utah along the Colorado River and along the fault zone north of Moab. Here Cutler redbeds equivalent to the Wolfcamp carbonates on the west overlie limestones containing Virgil fusilinids. Henbest (1948) found Des Moinesian fusilinids in uppermost Hermosa beds near Moab, but Virgilian fusilinids were collected along the Colorado River west of Moab and at Arches National Monument about 5 miles north of Moab. Here, as at most exposures, the Hermosa-Cutler contact is abrupt."

Baars goes on to recommend that the term "Rico Formation" or "Rico facies" be abandoned and that beds previously assigned to the unit be considered as part of the Hermosa Formation.

The Cutler near Moab is composed of two distinct alternating lithologies. They can be distinguished in the outcrop by their general color difference; one has a distinct light-orange appearance and the other a more purplish hue. The thicknesses of the units vary, but generally they are in the magnitude of ten to twenty feet.

The two are described separately below.

Light-orange beds. These units are predominantly thick to very thick bedded, poorly sorted, silty sandstones. The primary constituent is quartz with small amounts of dark minerals, mainly biotite. Larger particles are subangular to subround and smaller particles are angular to subangular. There is indistinct horizontal bedding at places, but the units are primarily cross-stratified. 32

Because of the steep cliff exposures, the true nature of the cross-stratification is difficult to determine except at a few places where the overlying units have been stripped back.

The cross-bedding resembles typical eolian cross-bedding such as is common in the Navajo Sandstone in this area(Figures 12 and 13).

The general direction of dips of the cross-beds is to the south and southeast in direct contrast to the general direction of sediment transport of the purplish beds. This indicates a different source area and mode of transport for these sediments.

These light-orange beds are probably eastward extensions of the Cedar Mesa Sandstone. Baars (1961, p. 183; 1962, p. 177) gives detailed descriptions of the Cedar Mesa. It is generally described as a white or light-gray through, light-tan, light-brown and pale reddish-brown sandstone composed of fine- to medium- sized subangular sandstone composed of fine- to medium- sized subangular quartz grains, many of which are frosted. Horizontal bedding is common, but the unit is extensively cross-laminated.

Resultant dip directions of cross-strata of the Cedar Mesa are shown to be south and southwest by Stewart and others (1957, p.347).

The Cedar Mesa interfingers eastward with arkosic red sandstones of the Cutler within a northwest-trending belt that is projected to pass by Moab about 15 to 20 miles to the west. Baars deduces that the environment was probably a marginal marine to beach environment With offshore marine current-deposited beds, beach deposits, and back-beach eolian deposits. Figure 13. Transverse view of cross-stratification in Cutler Formation light-orange sandstone. 33

The light-orange beds of the Moab anticline area probably represent an eastward extension of the zone of interfingering of the Cedar Mesa with the Cutler. The cross-bedding resembles eolian cross-bedding, so the beds may represent back-beach eolian deposits. Some geologists consider much of the Cedar Mesa to be purely eolian (e.g. Stokes, 1961, p. 155), so these beds may just be extensions of the wind-blown sand into the area receiving arkosic debris being shed off the ancestral Uncompahgre uplift.

McKee (195 7) says that the dip of beach foreshore cross- strata is usually less than 12 degrees while the dip of dune cross-strata is mostly 30 degrees or more. The dips of the cross-strata in the light-orange beds is around 20 degrees so this factor is not diagnostic. Shepard and Young (1961, p. 196) say that dune sands are more round, have larger silt content, and the silt has a higher content of heavy minerals. According to these criteria, the orange beds resemble dune sands.

Purple beds. These beds are the typical coarse arkoses shed by streams from the ancestral Uncompahgre range. The rocks are generally coarse, ranging from coarse sandstone to conglomerates containing pebbles about, one to two inches long. In. the coarser sands and conglomerates there is much biotite, muscovite, quartz, gneiss, crystalline feldspar, and other material representing rapid erosion of a youthful mountain terrain. The sands are typically soft and friable, and they weather easily. Nearly all the sandstones are cross-laminated. The breaks are accentuated by dark areas of 34 biotite along the bedding planes. Festoons are very common and are the only current indicators present. The beds are often contorted on a small scale into wavy convolute laminations. The overall color of grayish purple may be the result of a large amount of biotite in the rocks (L. Schmit, Columbia University, personal communication).

Primary structures

As has been mentioned, the light-orange beds are character­ ized by possible eolian cross-bedding. Since these beds were not stream-deposited and hence not directly germaine to the problem, they were not. studied in detail.

Festoons are very common in the purple beds. The festoons are fairly small, usually from five to twenty feet, long and three to eight feet wide. They are formed usually in coarse sand. The coarseness of the material and the complete absence of ripple marks and lineation indicates deposition by high-energy streams.

Although individual units are extensively cross-bedded, readings were comparatively few for the Cutler as a whole. Along

Highway 160 from the entrance to Arches National Monument north for about three miles, the lower part of the Cutler has been eroded into a series of small cuestas. Good measurements of current direction can be made along the dip slopes of the cuestas where good plan-view exposures of the festoons are available.

Except for this particular area where conditions are favorable, it is very difficult to get. accurate current-direction readings. 35

Most of the good Cutler outcrop is along the cliff where access is

difficult. The soft, friable nature of the rock causes the

exposures to be weathered into smooth rounded surfaces. The cross-

laminations are clearly evident, but it is difficult to calculate

anything except a very general direction of sediment transport.

The difficulties are compounded by zones of convolute lamination

where little can be ascertained from the contorted beds.

Local trends

Figure 15 shows the plotted current indicators for the

Cutler Formation. As mentioned above, much of the exposed Cutler was not suitable for study and only 85 readings were taken, all

of festoons. The indicators shown are from measurements in the

lower part of the unit along a three-mile stretch of favorable

exposures along highway 160. There is a definite parallelism

of the general current trend to the trend of the anticline. The

parallelism is quite consistent around point (1) and generally

remains that way until the area around point (2). In that

vicinity there is a strong swing to the west away from the anticline

Another strong trend to the west appears around point (3), but there

was still some drainage parallel to the structure.

There is no way to compare drainage on both sides of the

anticline. However, it would appear that there was a definite

deviation from the regional trend around the Moab anticline.

The channels probably followed a fringe trough or sink on the

northwest side of the structure. Around points (2) and (3) 36 it appears as though the streams veered away along their normal trend. Shoemaker and others (1958, p. 55) suggest that a major salt cell existed during Cutler time that extended northwest from

Moab to about the entrance to Arches National Monument (Figure 14).

They postulated a possible major drainage to have passed just north of the cell in a southwesterly direction. The plotted current indicators in Figure 15 suggest that the influence, of the salt cell extended farther to the north at least to point (2).

The swinging of the current trends and the great thickness of the

Cutler in that area might be evidence of a major drainage across the anticline.

The comments on page 27 concerning convolute laminations suggest a very interesting possibility for the origin of the contorted bedding in the Cutler. To repeat briefly the statement,

"Measurements of convolute bedding axes, when plotted on a map, disclosed a consistent pattern thought to be related to regional anticlinal fold axes and to indicate movement down the flanks of rising structures." Since the Cutler Formation was being deposited very rapidly around a rising salt, structure, similar conditions to those mentioned would have existed, and it is a possibility that the convolute laminations resulted from movement down the flanks of the rising anticline. 20 MILES

SALT CORE OF ANTICLINE BLANK- CORE DOES NOT PENETRATE BEYOND ORIGINAL STRATI GRAPHIC POSITION. LIGHT STIPPLE- CORE PENETRATES MOST OF THE BEDS OF THE CUTLER FORMATION; STRATI- GRAPHIC RELATIONS OF MESOZOIC FORMATIONS VARY. HEAVY STIPPLE- SALT CORE PENETRATES BEDS OF THE CUTLER; SOME MESOZOIC FORMATIONS THIN ACROSS CREST.

POSSIBLE LINE OF MAJOR SURFACE DRAINAGE IN CUTLER TIME. E QNAR Fig. J4 - PL AN OF SALT CORES OF ANTICLINES SHOWING HYPOTHETICAL RECONSTRUCTION OF MAJOR SURFACE DRAINAGE DURING CUTLER (p«rmion) TIME. After Shoemaker and others (1958) 37

Moenkopi Formation

General description

The Moenkopi Formation of Triassic Age is generally described as a series of deposits that form a wedge thinning eastward from a maximum of about 2,000 feet in western Utah and southern Nevada to the vanishing point along an irregular margin in western Colorado, northeastern Arizona^ and western New Mexico.

It is partly marine and partly continental in the thick western sections and entirely continental in the east (McKee, 1954, p.l).

Shoemaker and Newman (1959, p. 1837) describe the Moenkopi over the salt anticline region:

"The Moenkopi formation underlies a large part of the salt anticline region. It is exposed principally along the walls of several large valleys excavated in the crests of the salt anticlines and in deep canyons carved by the Dolores and Colorado rivers, the major streams draining the region. Toward the Uncompahgre Plateau, the Moenkopi thins to a feather-edge and is absent over the Plateau, where younger beds of Triassic age rest directly on Precambrian crystalline rocks. Over most of the salt anticline region beds of the Moenkopi lie unconformably on the Cutler Formation of Permian age but locally, over the salt anticlines, the moenkopi rests with sedimentary contact directly on upthrust beds of the Paradox member of the Hermosa formation of Pennsylvanian age. The Moenkopi is everywhere overlain by the Chinle formation of Triassic age. Like the basal contact, the upper contact is an unconformity, and locally over the salt anticlines, the Moenkopi is either cut out entirely by angular unconformity at the base of the Chinle or is absent because of non- deposition along the crests of the salt intrusions."

The Moenkopi has been subdivided into four members in the salt anticline region by Shoemaker and Newman (1959, p. 1838). 38

They are, in descending order:

(1) Pariott Member- an upper unit composed of inter- stratified sandstone and siltstone.

(2) Sewemup Member- a unit composed dominantly of fissile siltstone with minor beds of conglomeratic sandstone and gypsum.

(3) All Baba Member- a unit of interstratified arkosic conglomeratic sandstone and fissile siltstone.

(4) Tenderfoot Member- a basal unit composed dominantly of muddy or silty poorly sorted sandstone.

The Moenkopi is dominantly reddish-brown and has three primary lithologic types: (1) cross-stratified and cusp ripple- marked sandstone and coarse siltstone; (2) parallel ripple-marked siltstone characterized by platy or slabby splitting; and

(3) horizontally stratified siltstone (Stewart and others, 1958, p. 130). Because of contrasts in hardness between individual beds, and a general lack of resistance to erosion, the Moenkopi characteristically weathers into gentle steplike slopes that surround small mesas or extend outward from escarpment bases

(McKee, 1954, p. 3).

The conditions of deposition of the Moenkopi vary from purely continental on the east to dominantly marine on the west. The source area for the sediments in the salt anticline region was the ancestral Uncompahgre uplift (Dane, 1935, p. 45).

Along this eastern margin of the Moenkopi basin, mudflat deposits consisting of red shaly siltstones, many of them ripple-marked, are interspersed between units of stream deposited sandstone

(McKee, 1954, p. 78). The consensus seems to be that the 39 environment of deposition was variable between gently seaward sloping flood plains and wide, muddy tidal falts.

Local character

The Moenkopi Formation in the Moab anticline area can be identified easily as the dark reddish-brown slope-forming unit between the bright reds of the underlying Cutler and the more grayish browns of the overlying Chinle. Minor ledges of flaggy siltstones break the general slope along the outcrop. The unit is exposed only on the upthrown block of the Moab fault where it outcrops along the fault cliff. Its thickness is about 450 feet at the cliff across from the entrance to Arches National Monument.

From there it thins to the south and pinches out about half a mile north of where the Colorado River leaves Moab Valley. It also thins to the north and pinches out at Corral Canyon.

The Moenkopi is composed mainly of dark reddish-brown shaly siltstone with some thin beds of muddy sandstone. The more resistant beds form small ledges. Ripple marks are common throughout the section, and there is some cross-lamination.

The members defined by Shoemaker and Newman were not differentiated for this study.

t

Primary structures

Ripple marks are abundant in the Moenkopi nearly everywhere it is exposed (McKee, 1954), and around the Moab anticline they were the basis for the current-direction study. 40

Both of the basic types described by McKee were observed, and they conform to his description (McKee, 1954, p. 57):

"Of the two basic types of asymmetrical ripple marks, the more common one is characterized by even, parallel ridges and troughs, averaging about 1 inch from crest to crest. It is largely confined to the surfaces of thin, shaly siltstones believed to have been developed on extensive mud flats, either tidal or flood plain. The second principal variety is much larger and more irregular, normally appearing as a series of cusps or crescentic mounds and hollows. It occurs mostly among thick-bedded siltstones and sandstones that apparently formed under the stronger and more diverging current action of active stream channels. No ripple marks are present, so far as known, among the brittle mudstones, doubtless because they developed through settling of mud particles in quiet water."

By far the most prevalent of these in the Moab area, is the type characterized by even, parallel ridges and troughs

(Figure 16). This indicates that much of the environment of deposition was the mud-flat variety. Although they are current ripple marks, the asymmetry is not pronounced, and the actual direction of sediment transport is often difficult, to determine.

It is fairly certain that, this kind of ripple mark was formed by moving shallow water, but whether it was along flood plains or tidal flats is uncertain. The uniformity of dimensions and the small size of the ripple marks would seem to favor the tidal-flat concept where there would be a low energy environment with uniform conditions over a wide area.

The cusp ripple marks are probably the linguoid variety described by Schrock (1948, p. 102).* Figure 17 is an illustration of the type found in the Moenkopi and Figure 18 shows similar Figure 18. Cusp ripple marks in recent sediments of Colorado River. 41 structures found in recent sediments along the Colorado River.

Very few of these were found in the. area of study. Those observed were associated with thick-bedded siltstones and therefore conform to McKee3s description of active stream- channel deposits.

The structureless3 brittle mudstones described by McKee are also quite common. These represent quiet, water deposition, so they could have been formed in quiet pools on a tidal flat or in bodies of standing water on a flood plain. In addition to ripple marks, a few rib-and-furrow structures were observed.

There is occasional cross-lamination, but no festoons were seen.

The Moenkopi, therefore, was formed under varying conditions of deposition, the overall result, being a random mixture of tidal flat, flood plain, and channel deposits. This factor alone complicates a study of current trends, because the random inter­ mingling of structures, formed under different conditions, would result in haphazard patterns. This problem could be overcome if the different units were so distinct that they could be studied separately, but. such is not the case.

Like the Chinle and Cutler Formations, the Moenkopi outcrop extends along the steep fault cliff west of the main

Moab fault. It. weathers into a steep slope with numerous small ledges. Good ripple-mark exposures are found mostly where individual ledges have been swept clean of debris. Where the cliff is steep, good exposures for current measurement are not 42

abundant. Where prominent ledges are formed, they are often

covered by loose debris from above. The best conditions for

study are those where the gradient is not steep and steplike benches have formed. Unfortunately this situation is rare. As mentioned previously, the direction of asymmetry of the ripple marks is often difficult to determine, so it is necessary to

look continually for cross-lamination in order to verify the readings being taken.

On the steep slopes, only the resistant ledge-forming beds could be measured, and most of these occur around the middle of the unit. Over much of the area, 50 feet from the

top of the Moenkopi, there is a five- to ten-foot bed of massive siltstone, and above this most of the rock is the structureless variety.

Local trends

Figure 20 shows the plotted current indicators for the

Moenkopi Formation. The number of individual readings is actually very small compared to what would be expected from a heavily ripple-marked unit averaging about 250 feet in thickness. The situation causing this has been explained above.

The mean direction for 105 readings is 310 degrees, roughly northwest. There is again an obvious parallelism to the structural trend. Figure 19 shows that the general current trend is roughly in harmony with the plotted northwest regional trend. The preferred SALT LAKE CITY \\FI

)/ 0,.KNVBR UTAH J I ( .-fssa COLORADO

X, 1 ! SANTA FE KlnK"tnff i Gallup""^ NFAV ARIZONA N* <, V MEXICO

}PHOENIX MOGOLLON A. Ali Rnba member ^ B. I*MiK!*-fortninK' sandstone C Ix>wcr muHBivp BRndntonp 0. Unrliffrrpntiatfd RAnrintone E. HoiUrook mnmbor F. Utidifforentiated conglomerate

Figure 19 . Stream directions during deposition of Moenkopi Formation. (Modified after Poole, 1961)

EXPLANATION

Hirfc• Approximat. ™ e limit of depositio- „ n• '""isonaoloopatnh lin lineo Generalizer i:'d J directio J- T~n of rstrea . m How Barb, on *ule of non deposttimi or ero*um ^hei where inferred, [nterval 500/eel

O L. 20O MILES 43 direction along the anticline is northwest with occasional swings to the west and southwest. In Little Canyon a well-developed southwest trend veers away from the dominant northwest flowage pattern.

Since the plotted regional trend for the Moenkopi is in the same general direction as the trend along the Moab anticline, it is uncertain whether the salt mass influenced sedimentation.

However, if all the salt structures were emergent during the time of deposition of the Moenkopi, as they well might have been, the structural grain may have been so pronounced topographically that the tidal currents and the streams were forced to move in a general northwest-southeast direction. Also, if Poole made his measurements along the salt structures, the northwest trend he determined might be due to the influence of ancient salt masses on Moenkopi sedimentation adjacent to the structure and would not be of true regional significance.

The sedimentary pattern of the Moenkopi, like that of the

Cutler, appears to have been influenced by the ancient upwelling of the salt mass. The lack of precision data detracts from the strength of these conclusions, but this seems to be the best explanation for the definite uniformity of current direction parallel to the trend of the salt structure. Sheet flows of the tidal flat or flood plain types would account for the directional uniformity with the direction being determined by a contemporaneous salt structure. 44

Chinle Formation

General description

The widespread Chinle Formation was deposited over the

entire Colorado Plateau. It is essentially a series of contin­

ental redbeds and variegated beds characterized, throughout most

of the Plateau, by peculiar intraformational lime-mud conglomerates,

by conspicuous logs and petrified wood, and by the fragmental remains

of a reptilian fauna that only locally is well enough preserved for

identification (McKnight, 1940, p. 66). Recently the Chinle has

been the object of very extensive study with regard to uranium.

The U.S. Geological Survey has conducted studies of the strati­

graphy over the Colorado Plateau and much of these studies has

been summarized under the senior authorship of J. H. Stewart.

The Chinle has been subdivided into seven members over the

Colorado Plateau region. They are listed and described by

Stewart (1957) and by Stewart and others (1959, p. 500):

"In southeastern Utah and in the Monument Valley of Arizona, the Chinle is divided into seven members, which are, in ascending order, the Temple Mountain, Shinarump, Monitor Butte, Moss Back, Petrified Forest, Owl Rock, and Church Rock members. The Temple Mountain member is a thin unit composed largely of siltstone and is restricted to the San Rafael Swell. The Shinarump and Moss Back members are widespread sandstone and conglomerate units. The Monitor Butte and the Petrified Forest members are mostly bentonitic claystone and clayey mudstone. The Monitor Butte member contains some lenses of sandstone. The Owl Rock and Church Rock members are largely reddish siltstone. Minor amounts of limestone are present in the Owl Rock member." 45

In the salt anticline region the Chinle consists dominantly of reddish-brown siltstone and sandstone. In most of the region a thin discontinuous coarse sandstone and conglomeratic sandstone layer is present at the base of the formation (Stewart and Wilson,

1960, p. 103).

Local character

The Chinle is exposed along the cliff of the west flank of the Moab anticline from Moab northwest no Corral Canyon, a distance of about 12 miles. It is also present northeast of

Moab between Mill Creek Canyon and Moab Bridge across the

Colorado River, but it is nowhere more than a few feet thick

(Baker, 1933, p. 40). Lithologic and erosional characteristics enable the Chinle to be described in terms of three different units (Figure 22). NcKnight (1940, p. 68) recognized the three units over much of the area between the Green and Colorado Rivers.

The lower division is composed of interbedded sandstone, siltstone, and conglomerate; it usually appears as a debris covered slope with an overall color of light greenish-gray. The lower 10 to

20 feet of the lower division is the thin coarse sandstone and conglomeratic sandstone described above by Stewart and Wilson.

The layer is varicolored with splotches of manganese and limonite stain. Much carbonaceous plant debris is present. Copper oxides, malachite and azurite, and lesser amounts of the sulfide chalcocite are very common along this lower interval. The copper minerals are finely disseminated through the coarse sandstones and have Figure 21. Photograph showing Chinle Formation thickening from north toward Colorado River. 46 replaced wood in many places. This interval is also the host rock for the uranium mineralization in the area, and it has been exposed by bulldozers along much of the outcrop as part of the exploration activity.

Still in the lower division but above the coarse sandstone and conglomeratic sandstone member is a slope-forming sequence of siltstone and fine-grained sandstone. The sandstones are generally pale-red and some places they form small ledges.

Limestone-pellet conglomerates occur in small lenses randomly throughout this interval.

The second division is a prominant cliff-forming sandstone locally known as the Black Rim. The unit is composed of fine and very fine grained sandstone interbedded with siltstone and conglomerate. On a fresh surface the sandstone is light reddish gray or light greenish gray, but the weathered surface is dark gray

The third and uppermost division is another slope-forming unit of sandstone and siltstone. The sandstone is pale red and is horizontally laminated. The overall color of the unit when viewed from a distance is brownish red.

Although the three divisions are readily apparent along the

Chinle outcrop, closer observation reveals that the units cannot be distinctly separated. The cliff-forming unit ranges in thicknes markedly from place to place depending on the steepness of the slope and the nature of erosion. This variation occurs where the top part of the lower unit forms a continuous vertical cliff with 47 the middle unit. Any contact; drawn between the two is completely arbitrary. As a rule., the contact between the middle and upper units is much more distinct, being placed where the cliff abruptly becomes a slope of reddish-brown sandstone and siltstone.

A thin and discontinuous bed of white coarse-grained sandstone crops out: at the base of the Chinle around Little Canyon.

Earlier writers called this unit the Shinarump Formation, but

Stewart and Wilson (I960, p. 103) state that it may be correlated with the Moss Back Member but more likely includes stratigraphically higher sandstone units as well as strata physically continuous with the Moss Back Member. Local custom has been to refer to any coarse-grained sandstone or grit at the base of the Chinle as

Shinarump, and the practice will undoubtedly continue in spite of

Stewart's efforts at clarification.

Stewart and Wilson (I960, p. 103) also discusses the corre­ lation of the remainder of the Chinle section along the Moab anticline:

"On the Moab Valley anticline, approximately the lower 100 feet of the Chinle formation, or the lower third, contains abundant greenish-gray strata, some of which is probably bentonitic, intermixed with reddish-brown siltstone. The greenish-gray bentonitic units are probably, in part, the northeasternmost remnants of the Petrified Forest member, which to the southwest in southeastern Utah contains most of the bentonitic strata in the Chinle formation. In Moab Valley the red siltstone units in the lower third of the formation probably represent westward-extending tongues of the red beds of the upper part of the formation."

Stewart and others (1957, p. 459) assign the remainder of the

Chinle in the Moab area to the Church Rock Member. 48

The Moss Back Member was deposited in a fairly quiescent time in the Chinle basin of deposition and on an alluvial plain with little relief, so that the streams could migrate freely

(Stewart and others, 1959, p. 522). The Petrified Forest Member was probably deposited in an alluvial-plain environment including stream and flood plain deposits. The Church Rock Member was deposited in a series of interconnected lakes on a broad alluvial plain (Stewart and others, 1958, p. 135). The sandstone units indicate local stream-channel deposits. The Black Ledge or middle unit of the Moab area is part of a northwest trending sandy belt interpreted by Stewart and Wilson (1960, p. 105) as an elongate "deltaic" mass built out into shallow lakes. The source of sediments for the Church Rock Member was probably the ancestral Uncompahgre highland of western Colorado.

Primary structures

With respect to the availability of primary sedimentary structures, the Chinle is the least productive of the formations studied for this report. The main reason for this is that the

Chinle nearly everywhere crops out as a debris-covered steep ledgy slope beneath the vertical Wingate cliff, and therefore it provides a two-dimensional view only. A detailed plot of current directions requires good exposures, preferably of the type where the beds can be observed from plan view. Such exposures were available locally in Little Canyon and Seven Mile

Canyon, but as a rule, a great deal of energy was expended scaling 49 the steep alope for a meager number of readings. Where the exposures are good, many primary structures are seen in the Chinle and even on the steep slopes, ripple markings and lineation can be seen on talus blocks broken from the sandstone ledges. But conditions are such that reliable direction indicators are difficu to find in numbers necessary for detailed study of current trends.

Another problem arises from the fact that each of the three divisions as well as the basal grit may have been deposited in different environments of deposition. The regional correlations by Stewart referenced previously also indicate that this is so.

Therefore, to get a complete picture of depositional trends for the entire Chinle sequence, it would be necessary to plot current trends for no fewer than the three main divisions. Such an attempt was made, but it proved to be unfeasible.

Primary structures are especially difficult to find in the lower division. The coarse sandstone and conglomeratic sandstone at the base is well cross-bedded at places; it appears to be the tabular planar type. There is also some lineation in the lower division that, is useful where it can be measured in association with dipping cross-strata for direction determination.

The middle ledge-forming division yields the most primary structures where exposures are good. Good festoons are commonly found where the top surface of the ledge has been exposed. The beds as a group contain many structures, but these are usually concealed where the unit crops out as a vertical cliff. Talus 50 blocks from the sandstones show much lineation. Where the unit is a vertical cliff, it is mainly massive with lenses of conglomerate. Indistinct cross-stratification is present but not in abundance.

The top division is laminated reddish-brown sandstone and siltstone and has the most varied types of structures. Near the top there are good current ripple marks. Rib-and-furrow markings and more rarely lineation markings are also present in this unit.

Just beneath the Wingate in Little Canyon, the upper division has many tabular-planar cross-strata. These give a good idea of general direction but are difficult to use for a precise direction when the exposure is two dimensional.

Penecontemporaneous deformation structures are common in the Chinle Formation along the Moab anticline (Figure 30). Beds of different stratigraphic intervals have been bent, contorted, and broken to form unusual bedding relationships. The deformation usually appears where the thinner bedded sandstones and siltstones of the beds above and below the middle ridge sandstone are contorted between horizontal beds above and below. The features show different degrees of distortion from place to place. The contorted beds are vertical at some places and only gently unconformable at others with all degrees of variation in between. The structures are discontinuous, there being badly contorted beds at one locality and the same beds in a normal bedding sequence a hundred feet away. 51

The origin of these features is uncertain, but it is possible that the beds were deposited on an initial slope where occasionally the angle became sufficiently steep to cause local sliding and slumping. Upward movement of the salt mass could have been responsible for this effect. As a possible alternative to purely gravity-triggered slumping, actual earth tremors may have initiated the movement.

Landslide block. An unusual and significant feature occurs in the Chinle Formation along the cliff just south of the "Shinarump" uranium mines in the Seven Mile Canyon area about 11 miles northwest of Moab. An actual landslide block of older sedimentary rock was found by Stokes in the middle sandstone unit of the Chinle

(Figure 23).

The enclosing rock is dark-gray weathered, hard, massive light greenish-gray sandstone with beds three to six feet in thickness, separated by beds of reddish-brown shaly sandstone and siltstone one to two feet in thickness. The attitude of these beds is in conformance with the remainder of the section striking S.30°W. and dipping about 5 degrees NW.

The enclosed block is composed of thick-bedded siltstone with an overall color of pale reddish-brown to moderate reddish- brown. The block is about 100 feet long and 25 feet high at its maximum exposure, and the beds within it strike about S.22°W. and dip 42 degrees NW. 52

The following characteristics of the block indicate the nature of its origin:

1. Complete angular discordance on all sides with enclosing strata.

2. Different color, lithology., and weathering character­ istics from enclosing rock.

3. Abrupt termination of bedding of enclosing strata on both sides of the block.

4. Irregular upper contact with enclosing rock.

5. No evidence of lower extension or "root" to underlying beds.

Figure 24 is a sketch showing the angular relationship between the block and the enclosing strata. Figures 25 and 26 also illustrate the relationship. The contact on both sides of the block and along the top is quite distinct. The bottom contact is covered, but Figure 25 indicates that the block also abuts directly against underlying strata.

The color, lithology3 and weathering characteristics are distinctly different from the enclosing rock. The overall color of the block when viewed from a distance is much brighter than the surrounding dark brownish-gray Chinle sandstone ledge. Most of the rock composing the block is siltstone. The beds are generally

thick, up to 10 feet of massive siltstone2 but there are gradations into shaly zones and also thin shaly intervals between the main beds. The weathering surfaces of the massive structureless siltstone beds have been shaped into irregular rounded surfaces sometimes referred to as "biscuit" weathering. As a rule, the 53 massive beds are fairly hard and the shaly beds relatively soft.

The dominant color of the massive siltstones is moderate reddish- brown. The lithology is fairly constant with the exception of a three-foot bed of very hard light greenish-gray siltstone that weathers into a vertical face. The whole unit is mottled with randomly occurring light greenish-gray splotches. figure 23. Location of landslide block. Ikw-Wingate: Rc-Chinle; R m-Moenkopl; Pc-Cutler.

Figure 24. Sketch of landslide block showing angul, relationship with enclosing beds. Figure 25. View of landslide block. 54

Following is a measured section going from the south contact to the north contact:

Contact with Chinle enclosing rocks at south end. Middle unit of Chinle abutting against block is composed of massive sandstone beds three to six feet in thickness separated by beds of shaly reddish-brown siltstone one to two feet in thickness. The sandstone is light greenish-gray and weathers pale brown with desert varnish. The beds strike S.30°W. and dip 5 degrees NW. Contact is abrupt. Chinle beds are slightly upturned against the block.

Block lithology Thickness (feet)

Siltstone, moderate reddish-brown; shattered zone 5

Siltstone, moderate to dark reddish-brown, hard, calcareous; weathers into irregular rounded surfaces; grades laterally into more shaly bedding; color changes irregularly; shaly zone is mostly grayish red; irregularly mottled into brownish-gray splotches.... 8

Covered zone. Probably same material as above 13

Same as 8-foot siltstone above 4

Siltstone, pale to moderate reddish-brown, mottled light brownish-gray, calcareous, massive; weathers into irregular rounded surfaces 20

Siltstone, light greenish-gray, very hard,, calcareous, quartzose, clean; single massive bed; weathers into vertical face; well defined bottom contact but gradational into moderate reddish-brown siltstone at top and laterally 3

Fault

Repeat of part of 20-foot siltstone..... 8

Repeat of 3-foot light greenish-gray siltstone 3

Siltstone, pale to moderate reddish-brown, slightly sandy, slightly calcareous, hard, massive; contains clay pellets, mottled 14

Total 78

Abrupt contact with enclosing Chinle sandstones. 55

The contacts with the enclosing rock are exposed on both sides of the block. Figure 27 is the south contact, and it shows the beds of the enclosing rock abutting directly against the block and being slightly upturned. The upturning was probably caused by settling of the sediments deposited around the block with a result­ ing drag effect on those beds resting directly against it. The north contact is shown in Figure 28. Several shaly beds and a massive siltstone bed are abruptly terminated against one of the hard massive sandstone beds of the middle unit of the Chinle.

As shown by the sketch (Figure 24), the contact along the top of the block is irregular. This indicates that sediments engulfed a mass already lithified. If the phenomenon had resulted from distortion of unconsolidated sediments, the top should have been planed off by ensuing actions of the agents of erosion.

The lower contact of the block is concealed by talus debris, but close examination has not revealed any extension or

"root" to underlying beds as would be necessary if the feature was the result of penecontemporaneous deformation. Figure 25 also indicates that the block abuts directly against underlying strata in normal position.

Penecontemporaneous deformation is very common in the

Chinle Formation along the flanks of the Moab anticline, and at first glance it is tempting to classify the structure described herein as such. However, a comparison of the features observed in association with zones of penecontemporaneous Figure 27. South contact of landslide block with enc Chinle strata.

figure 2ti. North contact of landslide block with enclosing Chinle strata. 56 deformation to those of the landslide block indicates a different origin for the latter. The main evidences for the distinction are the nature of the contacts with the enclosing strata, the lack of an extension or "root", and the unique lithology of the landslide block. These features have already been described.

Figure 30 is an example of penecontemporaneous deformation in the Chinle. The upturned beds can be projected back to an interval that is part of the normal stratigraphic sequence. Also, the top of the upwarped strata has been planed off.

The conditions necessary for such an event to have occurred could have very easily existed along the flanks of the Moab anticline. Studies have shown that there was movement and upwelling of the salt along the Moab anticline during the time of deposition of the Chinle. Along the cliff where the landslide block is exposed, the Moenkopi Formation thins rapidly and pinches out about half a mile to the north. The Chinle Formation also thins slightly toward the north. It is 370 feet thick at Little

Canyon to the south, and about. 300 feet thick where the block is exposed. Joesting and Case (1962, p. 1888) interpret a gravity anomaly several miles northwest near Tenmile Wash as being related to a buried salt anticline, which is probably a northwestward extension of the Moab salt anticline. The influence of the buried salt anticline could have extended sufficiently far southeastward to have affected this locality.

These facts, together with the presence of the landslide block, indicate that there was a salt intrusion along this part 57

of the Moab anticline during the deposition of the Chinle,

Shoemaker and others (1958, p. 43) describe the nature of the

intrusions along the Paradox salt anticlines as being separate

cells. This particular structure has been covered by the

sediments of younger formations and has also been downfaulted

along the Moab fault, so there is no surface expression, but it

is believed that a cell such as that described by Shoemaker once was present. It could have been an extension of the structure

described by Joesting and Case or it could have been a separate

small circular intrusion similar to those mentioned by Shoemaker

and others (1958, p. 43) along the Sinbad Valley-Fisher Valley

trend. The uplift associated with the salt movement was probably

more broad during Moenkopi deposition, thus explaining the Moenkopi

pinchout on the west flank. A more restricted piercement occurred

during Chinle deposition producing a sharp upturning of beds

adjacent to the salt core. Shoemaker and others (1958, p. 52)

say that the greatest vertical movement of salt in the cells might be expected to occur in the smallest cells. The exact

attitude of the beds flanking this intrusion can only be speculated,

but all degrees of sudden upwarping are possible. Figure 31 shows

an intrusion in Fisher Valley, Utah.

A possible explanation for the landslide block is shown

in Figure 29. The upwarped older sedimentary rocks on the flanks

of the intrusion were topographically higher than the plain of

sedimentation of the Chinle Formation. A large block of the older A. Block slides down flank of salt intrusion into accumulating Chinle sediments.

Kmv Km Jtrv-Kd

B. Block is covered by Chinle sediments. Intrusion is eroded to near base level; covered by Glen Canyon Group, San Rafael Group,, Morrison, Dakota, Mancos, and I'esa Verde.

C. Faulting occurs in Early Tertiary. Erosion has excavated present topography. Landslide block is exposed on escarpment.

Figure 29. Diagrammatic cross section showing history of Chinle landslide block. Figure 30. Penecontemporaneous deformation structure in the Chinle Formation.

Figure 31. Salt intrusion in Fisher Valley, Utah. 58 rock broke off and tumbled or slid down the steep flank of the intrusion onto freshly deposited Chinle sediments below. The actual triggering mechanism could have been similar to whatever caused the nearby zones of penecontemporaneous deformation. It could have been gravity alone or a combination of gravity and an earth tremor that actually broke the block loose. Subsequent accumulating Chinle sediments later covered the block completely and it became part of the middle sandstone unit.

A similar occurrence has been described by Shoemaker

(1956, p. 1801). He describes a series of small anticlines confined to the Moenkopi Formation that radiate from the intrusive salt mass of Fisher Valley, Utah, and concludes that the anticlines originated by lateral sliding of the Moenkopi Formation over hills on the pre-Moenkopi surface. The sliding would have been initiated by movement of the salt intrusion during and after the deposition of the Moenkopi.

A situation where the mechanics may have been similar is described in the Gunnison Plateau, Utah (Burma and Hardy, 1953, p. 552). There a large block of Morrison rests unconformably on younger rocks of the Price River Formation of Cretaceous Age.

Horizontal beds of the North Horn Formation then rest with sharp angular discordance on the Morrison and the Price River. This situation has been explained by thrust faulting associated with major orogenic activity, but it is possible that a large block of the Morrison broke off the flank of a sharp upwarp, slid down over the Price River sediments, and then was enveloped by sediments of the North Horn. 59

The parent rock of the landslide block is uncertain.

Comparison of hand specimens has failed to reveal any definite relationship to any of the older formations of the area, but the rock most closely resembles elastics in the uppermost Hermosa or "Rico" exposed on the flanks of the Moab anticline about seven miles to the southeast. If the Cutler Formation has thinned at the landslide block locality in like manner to the Moenkopi, such an origin is very possible.

Thickness variations. Very pronounced variations in thickness occur in the Chinle Formation along the Moab anticline. The unit is almost 600 feet thick about half a mile northwest of where the Colorado River leaves Moab Valley. Three miles northwest along the cliff above the entrance to Arches National

Monument it has thinned to 170 feet. In Little Canyon, two and one half miles farther northwest, it has thickened to 370 feet.

At Corral Canyon, five miles farther northwest, the Chinle again thins and is about 300 feet thick at its last exposure. On the east side of Moab Valley, at the mouth of Mill Creek Canyon, the Chinle is absent, and between Mill Creek Canyon and Moab

Bridge across the Colorado River it is nowhere more than a few feet thick (Baker, 1933, p. 40). Baker also comments that the thickness of the Chinle is fairly uniform over this area, averaging about 450 feet except, for local irregularities.

An unusual situation exists in that the Chinle is thickest where the Colorado River leaves Moab Valley, while at this same 60

locality, both the Cutler and Moenkopi are absent. Within three

miles to the northwest, the Chinle has thinned to only 170 feet,

and at the same place the Moenkopi reaches its greatest local

thickness of 450 feet. The Moenkopi then thins steadily to the

northwest until it pinches out at Corral Canyon. The Chinle at

first thickens to 370 feet at Little Canyon and then thins gently

to 300 feet at Corral Canyon. The Cutler Formation is approxi­

mately 1,200 feet thick at Little Canyon, only four miles

northwest of where it pinches out. The thickness of the Cutler

is unkonwn at Corral Canyon.

Variations in thickness of the Chinle are probably due to

vertical salt movement during the time of deposition. Shoemaker

(1955) observed that the Chinle is about 700 feet thick on the

northeast flank of the Sinbad Valley anticline and two miles to

the southwest the formation wedges out over the crest of the Sinbad

Valley salt intrusion. Four miles northeast of Sinbad Valley

along the Dolores River, it thins to 300 feet. Stewart and Wilson

(1960, p. 101) refer to this data and postulate that the thick

section on the northeast flank of Sinbad Valley anticline was

deposited in a basin formed by withdrawal of salt, peripheral to

the salt intrusion. The thick Chinle section northwest of Moab

probably accumulated under similar conditions (Figure 21).

The salt structure at Moab Valley must, have been broader during the deposition of the Cutler and Moenkopi Formations and during the intervals of time separating Cutler from Moenkopi and Moenkopi from Chinle deposition. The area along the cliffs east of Moab was positive throughout the time interval from

Cutler to Wingate times, except that the topography was close to base level during the deposition of the Chinle.

The area in the vicinity of the entrance to Arches National

Monument was a minor depression during deposition of the Moenkopi and Cutler. However, the pattern shifted during Chinle time and salt movement caused thinning of the Chinle sediments on the flank of the ensuing structure. The exposed Chinle is a mile away from the present anticlinal axis, so there is no way of knowing how intense the deformation was. It: is possible that there was a local piercement, or the strata may have just been bowed up slightly.

Regional stream-direction pattern

A regional study of stream directions in the Chinle has been made by Poole (1961). Figures 32A and 32B are maps by

Poole summarizing his observations of the upper and lower parts of the formation. Figure 32A is the most important with respect to the Moab area, because, it shows the observed stream directions in the Church Rock Member. Specifically, the arrow labeled AB appears to be located in the vicinity of Moab and it shows an average westerly direction for the paleocurrents.

Concerning the origin, Poole (1961, p. 141) states:

"Cross-strata dip directions in sandstone units of the upper part of the Chinle indicate that the sediment was derived from positive areas adjacent to the depositional basin. The red siltstone and sandstone in the upper part of the Chinle were probably derived largely from older sedimentary rocks exposed on and adjacent to the Uncom- pahgre and Front Range highlands." 62

Local trends

Figure 33 shows the plotted current trends for the Chinle

Formation. As previously mentioned, the Chinle is not very

suitable for this type of study. The exposures are poor as a rule,

and there were probably different conditions in existence during

deposition of the different units. This assumption is borne out

by the lack of any pattern or consistency to the plotted readings.

The only areas where there are suitable exposures are in Little

Canyon and along a spur southeast of the mouth of Seven Mile

Canyon.

Around point A, there is one group of fairly consistent

readings heading about 350 degrees. All these readings are

from the lower unit of the Chinle. Another group around point B

average out to about 270 degrees. These are from the middle unit.

In Little Canyon there is a wide diversity of trends with very little consistency appearing. The group clustered

around the downstream end of the canyon (point C) are from the

top and middle units. Their general direction is southwest.

At point D there is a shift in direction to north northwest, and

there are a few readings to the northeast.

Grouped data for the Chinle shows that there is a bimodal

distribution with one concentration toward the west and southwest

and another northeast. The mean direction for the whole unit is

286 degrees. This conforms in general to Poole's regional pattern,

but the fact remains that there is little consistency to the local pattern. The paucity of structures and the difficulty in separating the particular units for study prevented any firm conclusions from being reached by this method. No relationship to the salt anticline can be inferred from the data that was gathered. _SALT LAKE CITY \\ Q."* i DENVER UTAH ' Grand ,yci. - '-~9'i't-

^ i U l\ *«* X' L. 7/.-yLv^>^) T~

-SANTA FE

ARIZONA NEW MEXICO i A. Black led(te (local usa(tc) of Church, Rock membfr I B Undifferentiated Bandstone and ailt-i i stone of Church Rock member i C Hite bed (local usage) of Church Rock i member \ | D Middle part of Dolores formation I

ZOO MILES A* Upper part of Chinle Formation

SALT ""LAKE rTrYJ; A ° —A 1 DENVER UTAH I I V O . v jJunjuta.- * COLORADO

I COG'/ yV.Mnv'Spo >\ SANTA "! I "... -,0OO \ , Ji f, 0 1 I Flagataff \ CM ' H1 / J \ G CG/ c I H / ^ \ d(/ -ARIZONA COH ^ NEW MEXICO E. Ba.sal sandstone and conglomerate of Dolores formation , F. Lower part of Dolor ea formation G. Undifferentiated sandstone and silt- S PHOENIX '*•-.. atone in lower part of the Chinle J ^'G^/formation v |**»0H.Sonsela sandstone bed of Petrified <* Raaal sandstone and conglomerate of | Forest meml-'r Chinle formation (Ciartra icrit of' I. Agua Zarca sandstone member Thomas and Kruetrer, 1946) _ j Basal sandstone of Chinie formation : < Back member I K. Poleo sandstone lentil >- arump member > t. Santa Rosa sandstone of Dockum » •- ifferentiated sandstone of Petri- group fled Koresl member M. Middle Randstone of Chinle formation B. Lower part of Chinle Formation

Figure 32. Stream directions during deposition of Chinle Formation (Modified after Poole, 1961)

' " EXPLANATION v-"*~_J ' ' ' oo •-"> " ; Approximate limit of depositiol0n Isopach line Generalized direction of stream flow Barba on tide of non deposition or erosion bashed where inferred. Interval 500 feet , , . 64

Kayenta Formation

General description

The Kayenta Formation was named by Baker, Dane, and Reeside

(1936, p. 5) for beds in northern Arizona and southeastern Utah

that had previously been designated Todilto Formation. The type

locality is near Kayenta, Arizona. The Kayenta is defined mostly

on the basis of its stratigraphic position between the thick,

massive underlying Wingate Sandstone and the overlying Navajo

Sandstone. The lower part commonly is hard and forms a cap on

the Wingate cliff, and the upper part is softer and usually weather

back to form a broad bench between the Wingate and Navajo. The

formation is composed chiefly of irregularly bedded sandstones with subordinate lenses of shale or mudstone and local thin beds

of impure limestone and beds of mud-pellet conglomerate.

The Kayenta becomes progressively thicker and more silty

to the south and southwest (Harshberger and others, 1957, p. 17)

(Wilson, 1958). To the east and northeast it becomes almost

entirely sandstone. The maximum thickness is 320 feet with an

average of about 200 feet. Rapid thinning occurs along the

Utah-Colorado boundary, and the unit reaches an ill-defined

north-south pinchout line in southwestern Colorado (Stewart,

1956, p. 95). Near the pinchout. Baker and others (1936, p. 44)

note an increase in grain size and mica content.

The Kayenta is a continental unit deposited largely by

streams as indicated by the fossil evidence, the comparative coarseness of the grain, the lenticularity of the beds, cross-

bedding, and channeling between beds (Baker and others, 1936,

p. 50). There is no strong evidence of a specific source area

for the sediments, but much of the material was probably shed

from the much worn down ancestral Uncompahgre in western Colorad

(Stewart, 1956, p. 95). Poole and Williams (1956) give the

general current direction of Kayenta streams as southwest.

Local character ^ 1

In the Moab area the Kayenta Formation has the same

distinctive character that identifies it wherever it appears.

It forms a series of benches and ledges between the vertical

Wingate cliff and the familiar rounded erosion surface of the

Navajo sandstone. The lower beds are hard and they form a

resistant cap over the Wingate cliff. The softer upper beds

weather back into broad, craggy benches. The unit is not very

shaly but rather is irregularly bedded with many lenticular

sandstones.

North of the Colorado River and west of the Moab fault

the Kayenta caps the steep canyon walls and then provides the

surface for a wide dissected plain extending many miles to the

west. Along the canyon walls, where the Colorado River enters

Moab Valley and where it leaves, the whole formation is exposed

and forms a craggy slope between the Wingate and Navajo cliffs. 66

An informative general description is taken from Dane

(1935, p. 76):

"The formation consists predominantly of sandstone, ranging in color from white to fairly dark-brown, with intermediate shades of buff and tan and with many beds distinctly lavender-gray. The sandstones are composed chiefly of quartz, but contain also considerable biotite and chlorite. The average grain, size is coarser than that of the underlying Wingate, and in many of the beds the diameter of the grains averages 0.01 inch. The grains are mostly rounded or subrounded, but rounding is less perfect and uniform than in the Wingate. The sandstone is in discontinuous beds and lenses, rarely more than 1,000 feet long and typically 20 feet or less thick. Within these beds, cross-bedding of both angular and tangential types is prevalent. Much of the sandstone is thin-bedded, platy, or shaly, and there are numerous thin beds of soft red earthy sandstone, red shale, and greenish-gray shale. A minor but significant proportion of the formation consists of irregular beds of conglo­ merate with pebbles and chunks of shale, sandstone, and limestone."

Primary structures

Of all the units studied, the Kayenta provided the greatest abundance of current-direction indicators. By far the most common structure is lineation, which made up about 80 percent of the readings. The remainder were from festoons. No ripple marks of rib-and-furrow structures were seen.

Much of the formation is made up of thin platy sandstone beds whose bedding surfaces are abundantly lineated (Figure 7).

At some places these weather back into small steplike ledges, giving a multitude of horizons from which to take a reading.

In contrast, where the Kayenta weathers into long dip slopes, a particular resistant bed might cover the surface for an 67

area of several hundred yards square. Each thin bed has its own

general lineation orientation and is only one of a great number.

Although lineation is very abundant, festoons are not uncommon, and they provide very important information because

of their unidirectional nature. One weakness of lineation markings is that they provide only a line of bearing and not

a specific current direction. Therefore, in consonance with

lineation measurements it is best to have occasional cross- bedding to refer to to ensure that readings being taken are in

the direction of dip of the cross-laminae and not 180 degrees off

The festoons are the typical fluvial type similar to those

of the Cutler and Chinle. They occur in lenticular beds that are

often associated with intraformational channeling. Overturned

festoons are infrequently observed. Distribution of festoons is generally random throughout the formation, but occurrence is most common in about the middle portion.

The primary sedimentary structures and the overall

lithology of the Kayenta suggest deposition by slow-moving, debris-laden streams. No conglomerates were observed except mud-pellet and sand-pellet types, and these imply reworking of previously deposited material. The abundant lineation markings

also indicate slow-moving streams with a large bed load as described on page 23. The festoons probably resulted from periodic increases in the water velocity. 68

If the source area was the ancestral Uncompahgre uplift,

the fine sandstones suggest that the provenance area was

tectonically stable and that the previous ancestral Rockies were much subdued. The relative uniformity of size of the

particles would be the result of sorting by the slow-moving

streams that flowed off the uplands into the adjacent interior

basin.

Local trends

Figure 35 shows the plotted current-direction readings

for the Kayenta Formation. Because of different situations

at separated localities, seven rosette diagrams labeled A-F have been constructed, and each will be discussed separately.

The diagrams are divided into 30-degree sectors. The radius

of each sector is determined by the number of measurements with directions within the limits of the sector. In this manner

the overall pattern can be examined as well as the separate

trends. Six of the diagrams are for individual areas and the

larger seventh one comprises all the readings.

Diagram A. This area is especially significant because it is

the only place where observations could be made on the east side

of the anticline and then compared to those on the opposite side.

Also, because of the steepness of the outcrop, the entire

formation could be covered. This is a disadvantage in a sense,

because a great many arrows have to be crowded into a small

space. However, the main advantage is that by being able to 69 study different horizons at the same spot, it reduces the likelihood of being misled by a deceiving trend from a particular horizon. The overall pattern has a wide range of directions, which, when grouped, indicate no definite relationship to the salt structure.

The cluster of arrows around Courthouse Wash represents readings taken from the entire Kayenta sequence. The streams seem to have meandered along in accordance with the general regional trend (Figure 34). The readings along both sides of the

Colorado River are from the middle and upper parts of the Kayenta.

One strong trend developed parallel to the anticlinal axis but other trends still head right toward it.

The rosette represents 177 readings. Most of the readings fall into the large interval from 180 degrees to 300 degrees with nearly equal amounts in each of the 30-degree sectors. The mean direction is in the 240- to 270-degree sector, indicating a westerly trend overall.

Diagram B. The exposure here is along the cliff-face, but benches weathered into the Kayenta allow for easy access. Once again the readings were taken from the whole formation. There does not appear to be any relationship to the salt structure.

In fact, the drainage pattern indicates that at this point the streams flowed right across the area where the valley is now.

Gypsum beds from the Paradox Member are exposed within a few hundred yards, so this spot is not far from the area of most active salt movement. 70

The rosette is generally similar to that on the other side of the valley. It represents 51 readings and shows a mean direction of west.

Diagram C. This is an area of difficult, access. The Kayenta caps the vertical Wingate cliff and then weathers back into a series of benches on a gentle dip slope. The edge of the cliff here and to the north marks the beginning of a wide expanse of

Kayenta outcrop extending for many miles to the west. It was decided to restrict the study in this area to the area just along the top of the cliffs and back about a quarter of a mile.

The outcrop is already quite a distance from the anticlinal axis, so it is doubtful if any influence of sedimentation by the salt mass would have extended much farther to the west. Also, a normal thickness of the underlying Wingate Sandstone is present. Area

C and area D are separated by a canyon shown by the blank strip between the two distinct groups of arrows.

The arrangement of the arrows in section C can be thought of as an inverted "V" with the apex pointing north. Readings near the apex are from dip slopes in the Kayenta just above the Wingate contact. Hence, the consistency of certain trends.

One goes progressively higher up the section along the leg extending toward the southeast until the Navajo contact is reached. Again, the overall pattern shows no discernible relationship to the salt structure.

The rosette represents 93 readings with a wide variation of directional trends. Most, of the readings fall into the 180 to 270 degree sector with the most common direction being from

180 to 210 degrees. 71

Diagram D. This area is quite similar to area C except that most of the readings are confined to the lower part of the section capping the Wingate cliffs. Many of the readings are along the same horizon, as is shown by the consistency of the directions along the cliff edge. There appear to have been two predominant current directions here, one heading about 250 degrees and another cutting across it at about 220 degrees. The rosette illustrates this and also indicates that the bulk of the readings were in a westerly direction. The diagram represents 70 readings.

Diagram E. The situation here is similar to that of C and D.

Because of the distance from the main structural axis, a smaller sample was taken than normally would be needed. Although a more northerly trend is indicated, the overall array resembles those of C and D. The diagram represents 42 readings.

Diagram F. Once again the readings are confined to the lower part of the Kayenta. The primary current direction is transverse to the structural trend, so again no relationship is evident.

The rosette shows that the dominant direction was southwest.

Entire Kayenta. The rosette near the north arrow shows the overall pattern for the observed current directions in the Kayenta Formation.

It shows that the streams generally flowed to the west and south­ west across the present Moab Valley. The diagram for the entire

Kayenta closely resembles diagram A where the entire section was studied. In summary, the paleocurrent directions in the Kayenta

Formation do not indicate that sedimentation was influenced by the salt mass. Small salt intrusions may have existed, but not of sufficient size to affect the overall pattern. i ' A Undifferentiated sandstone and silt-1 i stone of Kayenta formation I 1

Figure 3*. Stream directions during deposition of Kayenta Formation. (Modified after Poole, 1961)

EXPLANATION 100° " — Approximate limit of deposition Isopach line Generalized direr! ion of stream flow Barns on tide of non deposition or erosion Dashed where inferred. Interval 500 feet

o _zooJ WILES L. 73

Salt Wash Member of Morrison Formation

General description

In the Moab area the Morrison Formation is divided into

two members, the upper or Brushy Basin Shale Member and the lower

or Salt Wash Member. This study was confined to the Salt Wash.

The Salt Wash Member (Lupton, 1914, p. 127) is a fluvial

unit present through eastern Utah and parts of western Colorado,

northeastern Arizona, and northwestern New Mexico. Because of

the uranium in the Salt Wash, more has been written about the

regional nature of it than any other of the units studied.

Detailed regional stratigraphy and lithofacies studies were

done by Craig and others (1951) and Mullens and Freeman (1954).

Craig and others (1951, p. 5) describe the unit as a large

alluvial plain or "fan" formed by an aggrading system of braided

streams diverging to the north and east from an apex in south- central Arizona. The Salt Wash has been divided into four facies, grading from predominantly coarse-textured sediments at the apex

of the "fan" to fine-textured sediments at the outer margin.

The Salt Wash in the Moab area is part of the sandstone and mudstone facies. 74

The Salt Wash consists mainly of lenticular cross-laminated sandstone and conglomeratic sandstone interstratified with clay- stone, siltstone, and structureless to horizontally laminated sandstone (Mullens and Freeman, 1954, p. 8). Mullens and

Freeman (1954, p. 11) separate the rocks into stream deposits and flood-plain deposits. Generally, the coarser-grained, cross-laminated sandstones are the stream deposits and the finer, structureless or horizontally laminated claystones and siltstones, are the flood-plain deposits.

Concerning the paleogeographic setting, the following is said by Mullens and Freeman (1954, p. 27):

"Salt Wash deposition was initiated by uplift southwest of the present junction of the Colorado and San Juan Rivers. This uplift created a source area for Salt Wash sediments and a source of water to carry the sediments. An apex of a distributary stream system, fed by water and clastic sediments from the source area, developed near the present junction of the rivers. Then, from the apex of the system sediments were spread north, east, and southeast on the plain of deposition by distributary streams. Once established, the general pattern of the drainage system persisted throughout the time of deposition of the Salt Wash Member. Continued aggradation by the distributary streams resulted in deposition of the fan-shaped wedge of sediments now called the Salt Wash member of the Morrison formation."

Local character

In the Moab area the Salt Wash is exposed over a wide area east of Seven Mile Canyon, and also it extends southeast along the Moab fault almost to the entrance to Arches National

Monument. Unfortunately, the unit, has been removed by erosion around Moab Valley itself, the area of most active salt movement. 75

In appearance it conforms to the regional character described above. It is composed of lenticular cross-bedded sandstones and conglomeratic sandstones interstratified with structureless claystones and mudstones. In the Thompson's area just to the north, the thickness of the Brushy Basin Shale is 306 feet and the Salt Wash 238 Feet (Stokes, 1952, p. 12).

The sandstones are more resistant and form ledges and benches around drainages cut. into the softer mudstones and siltstones. Along the steeper cliffs, rapid weathering of the softer beds beneath the sandstone ridges has caused the breaking off of large sandstone blocks. Where the unit has been thoroughly dissected by numerous drainages, individual flat-topped mesas form, each capped by a sandstone bed.

The cross-bedded sandstones represent stream deposits and the shales, flood-plain deposits. Because of this, individual sandstone beds are not continuous over very large areas. Some can be traced for half a mile or so, but the general situation is one of transitions from sands to shales and back.

The sandstone beds are composed generally of light-gray sandstone ranging from fine- to coarse-grained often containing stringers of pebble-sized conglomerate. Silicified wood and dinosaur-bone fragments are commonly found. Although more resistant than the shales, the weathering surface is generally crumbly and mealy. The sandstone units are nearly always cross- stratified although a few are massive. Cross-stratification is both the trough type and the planar type. 7 6

The shale beds are light brown and lavender. They can rarely be examined thoroughly because they are usually covered by alluvium or talus from the sandstones.

Primary structures

Of the units studied, the Salt Wash is the most suitable for a study of primary sedimentary structures. The method used in this report is patterned after the original works of

Stokes (1952, 1953), who made detailed plots of sedimentary current indicators of the Salt Wash in the Thompsons area north of the Moab area and in the Carrizo Mountains area of Arizona and New Mexico. The method was very effective there and subsequently was applied in the Blanding area (Stokes, 1954) with equally satisfactory results. The abundance of primary structures and the favorable nature of the outcrop make it possible to make a comprehensive plot in the Moab area also.

Very thorough descriptions of the primary sedimentary structures found in the Salt Wash are given by Stokes in the above-mentioned references. The Salt Wash in the Moab area seems to be almost identical to what has been described in these other areas.

The festoon is the most prevalent current indicator in the unit. The Salt Wash weathers into benches, especially along the rims of drainages, and where the surface is clear of debris, good plan-view exposures of festoons are available.

The festoons are the common stream-channel type, about five 7 7 to eight feet wide and 15 to 20 feet long. Some are clearly exposed and others can be measured only by their lines of intersection with adjacent structures. The general direction of particular series of festoons seems to lie parallel to the cliffs. This phenomenon is also mentioned by Stokes (1954, p. 20). Another feature observed was hollowed out scoops or depressions on weathered surfaces that appear to be weathered- out festoons.

The second most abundant current indicator in the Salt

Wash is lineation. Lineated surfaces are distinctively flat and are commonly dark with desert varnish. The lineated beds are not so platy as those in the Kayenta. Few rib-and-furrow markings and very few ripple marks were observed in the Salt

Wash.

A feature peculiar to the Salt Wash is the exhumed channel (Figure 11). These are sinuous sandstone bodies, actual paleochanneIs, that have been exposed by erosion of the surround­ ing shaly beds. They are very distinct on aerial photographs and can simply be traced off. Several can be seen as curving arrows on Figure 37. The channel shown in Figure 11 is about

300 yards long and ten yards wide.

Local trends

Figure 37 shows the plotted current-direction readings for the Salt Wash. As was done with the Kayenta, several rosettes have been constructed to aid in the interpretation. 78

Diagrams labeled A, B, and C are each representative of areas covered by a single aerial photograph. The diagram labeled D represents all the readings from the Salt Wash.

Overall, the drainage pattern of the Salt Wash conforms to the regional pattern. An unusual opportunity for comparison is afforded by Stoke's pi ot in the Blanding area (1954, p. 23) and in the Thompsons area (1952, p. 2). By placing Figure 37 directly over Stokes's plots, a striking similarity can be seen in general and variation of stream flow in the areas.

The pattern around diagram A is probably most representative of the overall Salt Wash pattern. The bedding is nearly horizontal in this area and the exposures are very good along the major drainages. Most of the readings were taken far enough away from the zone of deformation that they should be indicative of conditions of undisturbed sedimentation. The rosette diagram shows that the primary directional trend of the Salt Wash is to the east and northeast. The individual patterns indicate that there were two predominate trends, one heading generally northeast and the other to the east and southeast. The longer snake-like arrows are traces of exhumed channels.

The pattern around diagram B is generally similar except that the main direction is northeast. There is, however, a representative number of readings occurring in the 150-to 180- degree sector and the 300- to 330-degree sector. This factor has more significance when the readings near the fault are 79

examined. The trends around the numerals 1 and 2 appear to be

anomalous to the general trend. They are in alignment with

the structural trend.

Around diagram C, there is more evidence of disparity

from the normal. This is especially true around the numeral 3 where the trend is generally parallel to the fault. The anomalous

nature of these readings is also illustrated by the excessive

size of the 300- to 330-degree sector. A trend in the exact

opposite direction occurs at number 4.

The trend at number 4 is accompanied by a significant

lithology. The rock at that particular locality is an immature

conglomerate with pebbles up to two inches in length. The

conglomerate is different from the usual Salt Wash material

because it has a reddish tinge as well as large pebbles.

Also, some of the pebbles are reddish-brown siltstones. These would not normally be expected in the Salt Wash in which most

of the pebbles are predominantly light-gray chert. Siltstone

in the gravels of the Salt Wash streams could not be expected

to be transported any great distance without being broken

down. Therefore, the siltstone can be presumed to be of local

origin, and it was probably eroded from a nearby exposure of

older redbeds.

The evidence indicates that there may have been minor

movement along the Moab fault during the latter phases of

Salt Wash deposition. The undisturbed nature of the underlying 80

Entrada Sandstone along the fault casts doubt upon the possibility

of a salt intrusion as does the overall pattern of the current

directions in the Salt Wash, which indicates no interruption of

flow of any magnitude. The anomalous flow patterns parallel to

the fault and the presence of an immature conglomerate with

siltstone pebbles indicate that tectonic activity of some kind was taking place, and the relationship of these phenomena to

the fault suggest that, the fault may have been active at the

time of deposition, even though on a very minor scale.

Evidence of any possible movement over Moab Valley

itself has been removed by erosion. WYOMING

Explanation

Direction of arrow is resultant dip direction of cross- laminae. Length of arrow is proportional to consis­ tency factor. Tail of arrow marks location of cross- lamination study...

Figure 3s_. Map of resultant dip directions of cross- laminae in sandstones of the Salt Wash Member of the Morrison Formation. (After Craig and others, 1951) 8(1

TECTONIC HISTORY

In order to discuss the geologic history of the Moab anticline, it is necessary first to review the extensive literature pertaining to the salt anticline region as a whole.

The salt anticlines are all very similar in their gross features, and the geologic history of each is likewise similar. Observa­ tions at one salt anticline do not necessarily apply to the others, but when information about all the structures is assimilated, it provides much aid in understanding any one of them.

After the pioneering works of Baker (1933), Dane (1935), and McKnight (1940), the first important work of a regional nature was by Stokes (1948) in which he proposed continuous salt movement from Late Paleozoic throughout the Triassic and

Jurassic and possibly even locally into the Cretaceous. The

U.S. Geological Survey began an intensive investigation of the region early in the 1950's and many important papers have resulted. Cater (1955) gives a resume of the geologic history of the region up to recent times. Shoemaker and others (1958) describe each of the major salt anticlines, and they also discuss the history of growth and the mechanics of growth of the structures.

Jones (1959), an oil company geologist, discusses the origin of the salt anticlines by differential loading. Other important papers by U.S. Geological workers are by Elston and Shoemaker

(i960), Elston and Landis (1960), and Elston and others (1962).

These papers concentrate mostly on the Late Paleozoic and Early 82

Mesozoic history of the region with special emphasis on the Paradox

Valley and Gypsum Valley anticlines. The works of these writers

are summarized by Elston and others (1962) and Cater and Elston

(1963). Geophysical studies have been made by the U.S. Geological

Survey under the direction of H. R. Joesting (1956; 1960; 1962).

In general, the anticlines closest to the Uncompahgre front are the most complex. The Moab anticline is farther away and is less intensely deformed. The outermost structures, the

Lisbon Valley-Dolores anticline and the Cane Creek anticline are comparatively simple.

The oldest rocks exposed along the Moab anticline are from the Paradox Member of the Hermosa Formation, so pre-Paradox history has to be compiled from sketchy subsurface information together with general knowledge of the structural evolution of the region as a whole. Prior to 1959, the nature of the pre-

Paradox was mostly speculative. Stokes (1948) and Cater (1955) speculated that the salt anticlines were associated with deep- seated faulting that was genetically related to the trend of the ancestral Uncompahgre Range. Shoemaker and others (1958) attributed the origin of the anticlines to decollement folding resulting from compressional forces related to the Uncompahgre uplift without control by deep-seated structures. Jones (1959), in presenting his argument for an origin by differential loading, said that there was probably no correlation between surface and subsurface structure. 83

However, in 1959, a new phase of interpretation commenced with the discovery of an oil-bearing faulted anticline in the pre-Paradox beds beneath the southwest flank of the Lisbon Valley anticline. The subsurface anticline has no surface expression and is about two miles southwest of the axis of the surface anticline at Lisbon Valley. The structure is described in detail by Parker (1961) and Kunkel and Schick (1963). Since the discovery, evidence of associated subsurface structures has been found or implied for several of the major salt structures.

Elston and others (1962, p. 1873) summarize as follows:

"Deeply buried structural relief is present on pre-salt Paleozoic rocks near several of the salt anticlines. The relief, which at places is measurable in thousands of feet, locally is abrupt, suggesting that faults displace the pre-salt rocks. The structural relief on the pre-salt rocks is more than 3,000 feet near Moab Valley anticline, more than 2,500 feet near the Lisbon Valley and Gypsum Valley anticlines, and more than 5,000 feet near the Paradox Valley anticline. Large structural relief in pre-salt rocks appears to underlie much of the south flank of the Paradox Valley anticline; this interpretation is based on the existence of a larger gravity gradient along the south flank of the anticline than along the north flank (Joesting and Byerly, 1958, p. 2). An inferred structural boundary in pre-salt rocks along the south flank of the Paradox Valley anticline has been shown by Joesting and Case (1960, Figure 114.2)."

The abnormal thickness of salt under the salt anticlines is explained by Hite (1960, p. 88) as being the result partially of original sedimentary thickening in depositional troughs adjacent to pre-salt highs.

This background information is used to predict the nature of the subsurface structure beneath the present Moab anticline. In accordance with the history of the whole region, and in view of the evidence applying specifically to the Moab anticline, it is believed that there was faulting either just previous to or during the deposition of the Paradox Member. The faulting was along the trend of the present surface structure but probably beneath the present southwest flank (Figure 38). The exact date of movement is uncertain, but it was probably related to the first forces that worked to delineate the ancestral Uncompahgre front. The first stratigraphic evidence of the existence of the upland is found in the middle salt-bearing unit of the

Paradox Member (Elston and Shoemaker, 1960, p. 51), but the new structural interpretation has indicated that the structures in and bordering the area that was to become the deep trough of the

Paradox basin were defined during the interval that includes

Late Mississippian and Early and Middle Pennsylvanian time

(Elston and others, 1962, p. 1874). It is possible that the pre-Paradox terrain was subject to erosion especially along the structurally high areas (Elston and others, 1962, p. 1874).

A trough probably formed beneath the present Moab anticline either just previous to or during the early stages of deposition of the Paradox. As beds of the Paradox were deposited, the trough first filled and then continued to downfold making room for succeeding beds (Hite, 1960, p. 88). A long narrow belt of thickened Paradox sediments resulted. Deepening of parts of the trough early in salt time apparently resulted in the folding of lower salt beds near abrupt structural relief in 85 pre-salt rocks; these folds were masked by younger salt beds

(Elston and others, 1962, p. 1874).

The first salt movement in the basin probably began during

the time interval between the deposition of the Paradox Member

and the Honaker Trail Member of the Hermosa Formation. The record of earliest growth of the salt cores is found in central

Paradox Valley where a discontinuous breccia-rubble unit composed

of detritus derived from the Paradox Member lies with apparent marked unconformity between the Paradox Member and the upper member of the Hermosa Formation (Elston and others, 1962, p. 1876).

Exposures along the Moab anticline are not available to reconstruct the detailed history of salt movement through the

interval of time from cessation of Paradox sedimentation through

the desposition of the Honaker Trail Member and the "Rico"

Formation. At. other localities the salt structures grew gradually, and in part spasmodically, as is recorded by local unconformities beneath and within the upper member of the

Hermosa Formation, and beneath the Rico Formation of the Paradox

and Gypsum Valley salt anticlines (Elston and others, 1962, p. 1876). It is possible that some movement took place along the

Moab Valley proper segment of the Moab anticline during this

period, but deformation was less intense. Figure 39 indicates

that no disturbance was felt in the northwestern segment of the

structure.

Where exposed, the Cutler-Hermosa contact is conformable, but in the zone of maximum deformation west of Moab, the relation­

ship is unknown. (This contact has been referred to by others as 86

the Cutler-Rico contact.) Parker (1961, p. 103) feels that the

Cutler-Rico thickness, plus the flowed nature of the Paradox

salt into anticlines, plus the salt depositional environment make it necessary to have the most substantial period of salt

flowage at approximately the end of Rico time before Cutler

time began. There is no evidence of this along the Moab anticline.

Shoemaker and others (1958, p. 48) believe that although

the Cutler Formation is partly cut out at the base of younger

beds, it also thins internally adjacent to the salt core and

in many places pinchout against the core is due chiefly to

internal thinning. The Cutler thins along strike along the

cliffs northwest of Moab from about 1,200 feet at Little Canyon

to zero thickness four miles southwest with very minor angular

discordance with the overlying Moenkopi Formation. McKnight

(1940, p. 51) reports a maximum of four degrees, but the dis­

cordance is generally barely discernible. The paleocurrent pattern of the lower Cutler beds described earlier indicates

that Cutler streams on the southwest flank of the anticline

flowed in a general northwest direction parallel to the

structural trend toward a depression northwest of a main salt

cell in Moab Valley. Thinning and pinchout of the Cutler

indicate that the rising salt kept pace with the rapid deposition

of the Cutler. Deposition of the finer sands being carried in

from the north probably took place at a much slower rate than

deposition of the coarse arkoses and conglomerates being washed 87

in from the prominant upland to the east. Accumulation of large

thicknesses of Cutler sediments around the salt provided additional differential loading forces that intensified the salt movement.

During the long interval before the commencement of

Moenkopi time the salt continued to slowly rise, causing gentle

folding of the adjacent Cutler beds. Slight erosion of the upper

Cutler took place northwest of the main salt cell. Uplift was more pronounced along Moab Valley where Hermosa beds were folded and cut off by erosion (Figure 4). Another cell was probably active just north of Seven Mile Canyon.

The Moenkopi Formation was deposited unconformably over the Cutler and Hermosa Formations. During deposition of the

Moenkopi, the salt continued slowly to rise causing some thinning of the sediments along the main salt cells. The local structure probably influenced the direction of transport of sediments as is indicated by a definite parallelism of paleocurrent directions to the structural trend. A depression continued to exist between Moab Valley and the cell north of Seven Mile Canyon where as much as 450 feet of Moenkopi accumulated.

Previous to the deposition of the Chinle Formation, uplift continued, especially at Moab Valley, where the Moenkopi has been truncated by erosion.

The pattern of salt movement changed during Chinle time.

The former positive area west of Moab, where the Colorado River now leaves the valley became a rim sync line where up to 600 feet 88 of sediments accumulated. The thin or absent Chinle Formation on the east side of the valley indicates that salt movement was still taking place, but perhaps the structure was more compact, possibly because of release of pressure by piercement to the surface. Just south of Little Canyon, thinning of the Chinle along the cliff shows that the former depression of Cutler and

Moenkopi times was broadly bowed upward, probably without pierce­ ment. Just north of Seven Mile Canyon, the beds were sharply upturned against a salt core, and a large landslide block fell into the accumulating Chinle sediments.

East of Moab Valley the thin Chinle was probably upturned and slightly eroded before the Wingate Sandstone began to accumulate.

The Wingate lies unconformably over a thin section of Chinle which in turn rests on apparent Hermosa limestones. An apparent normal thickness of Wingate exists on the cliff face west of the valley, but the unit seems to be thinned east of Moab from the Colorado

River southeastward along the cliff face. Perhaps the windblown sands accumulated normally west of the structure and then lapped over, leaving a thinner section on the east side. North of Moab there is no evidence of salt movement during Wingate times, but the unit is not exposed other than on the cliff face on the southeast flank.

The fairly uniform thickness of the Kayenta Formation, its conformable relationship with beds above and below, and its paleocurrent trends indicate that salt movement had either 89

ceased or was very localized during Kayenta time. The plotted

current trends, in particular, show that Kayenta streams flowed

undisturbed over the site of the present anticlinal structure.

The Navajo Formation and the Glen Canyon Group probably

were deposited in normal fashion over the anticline. The Glen

Canyon Group is not present along the flanks of Moab Valley

itself, so its history is unknown there, but the sequence appears

to be normal where it is exposed over the anticlinal axis at

Arches National Monument.

The plotted paleocurrent trend of the Salt Wash Member

of the Morrison Formation indicates that the Salt Wash streams

as a whole flowed undisturbed across the site of the anticline

northwest of the entrance to Arches National Monument. The Salt

Wash beds are not present adjacent to Moab Valley itself. Cater

(1955, p. 129) says that the Morrison Formation buried all the

salt intrusions for the first time, although thickness variations

developed over some of the anticlines as some movement of the

underlying salt continued. Red siltstone particles included

in an immature Salt Wash conglomerate along the Moab fault,

together with an anomalous paleodrainage pattern along the fault,

are possible indications of activity along the Moab fault as early as Salt Wash time.

After deposition of the Burro Canyon and Dakota Formations

the great Cretaceous sea inundated the area and the thick Mancos

and Mesaverde Formations accumulated. 90

The post-Mesaverde history is largely speculative, especially concerning the period of folding that created the present anticlinal structures. Cater's ideas are as follows

(1955, p. 129):

"Early in the Tertiary, probably during the Eocene, the region was compressed into a series of broad folds guided and localized by the pre-existing salt intrusions. Although salt flowage was renewed, it seems unlikely that any considerable amount of new salt was forced into the intrusions; flowage probably consisted largely of redistribution of salt already present. By the end of this period of deformation, these folds had attained approximately their present structural form, except for modifications imposed by later collapse of the anticlines overlying the salt intrusions."

Cater (1955, p. 129) says that collapse of the axial parts of the salt anticlines occurred in two stages widely separated in time, the first closely following the Early Tertiary period of folding and the second after epeirogenic uplift of the entire

Colorado Plateau in the Middle and Late Tertiary. The second phase is still continuing.

Most of the movement along the Moab fault probably occurred during the first phase of collapse. Cater (1955, p.129) suspects that the faulting took place during relaxation of the compressional stresses responsible for folding. The Moab fault extends along a single trace for 11 miles northwest of the entrance to Arches National Monument. Maximum displacement is about 2,600 feet. Figure 38 shows that the fault is not a simple collapse feature over the crest of the anticline, because displacement of the downthrown block is broad rather than 'OOO .k=-T I—I_I—I T Scale

Drill-/?o/& /nfor-m&tion courtesy TCAJJ GaJf ^>u/phu.r Corp- localized. These factors indicate that the fault resulted from

a regional adjustment as indicated by Cater. Since this is the

case, it is likely that the Moab fault extends through the salt

to the pre-salt and basement rocks. It is probably associated

at depth with the inherent zone of weakness established during

the initial stages of the uplift of the ancestral Uncompahgre

uplift. This zone determined the location of the anticline

initially.

The second period of collapse began in Middle and Late

Tertiary time after regional uplift of the Colorado Plateau

rejuvenated the streams and increased ground water circulation.

The Colorado River began to cut down to the Moab anticline, and

eventually it breached the crest and exposed the underlying salt

to rapid solution and removal (Cater, 1955, p. 129). As the

salt was removed, renewed collapse began. Cater believes that

salt movement occurred from parts of the anticlines still

overlain by thick layers of sediments to parts where the over­

lying sediments had been moved. With support removed, collapse

of the overlying sediments took place around Moab Valley itself.

The walls of the east side were faulted into long narrow slivers

parallel to the length of the valley. The Kayenta Formation

locally dips valleyward due to slumping. Another fault zone

parallels the valley on the west side. This gives a graben

effect. Where the valley walls curve around just north of the

Colorado River, rocks of the Glen Canyon Group have been badly shattered by collapse. Numerous minor faults and joints extend northward for a short distance from the chaos. Downsagging of the southern part of the structure occurred forming the Spanish

Valley Sync line. Erosion along the salt structure has continued to the present to produce the features seen today. 93

CONCLUSIONS

Conclusions with respect to the structural development of the Moab anticline have been presented in the preceding section.

The following discussion is an evaluation of the method of study of paleocurrent trends.

To reiterate briefly, the method of study involved the detailed plotting of current-direction observations from the five units studied all along their exposures around the anticline with the intent of detecting any influence a rising salt mass may have had on the patterns of sedimentation. This method was developed by Stokes (1952; 1953) for his studies of the Salt Wash Member of the Morrison Formation.

The primary difficulty in applying the method to the

Moab anticline was that I was unable to compare the drainage patterns of the key formations on both sides of the structure.

One can visualize ancient streams deviating from their normal pattern as they sought to get past a topographic obstruction created by a rising salt mass. If it were possible to plot the drainage patterns on both sides, the paths of the ancient streams could be traced to the suspected area of influence and then examined for any revealing divergences. A comparison with the pattern on the lee side would permit reconstruction of a complete picture. The Cutler, Moenkopi, and Chinle Formations are not present on the east side of Moab Valley, and to the 94 4 northwest they are faulted below the surface on the downthrown east side of the Moab fault. Since the stream-deposited fractions of these sediments were brought in mostly from the east, their absence on the critical upstream side of the structure makes it much more difficult to reconstruct the local paleogeography.

Also, the exposures of these three units are not too good for this method of study except at certain favorable localities.

Current-direction indicators were especially difficult to find in the Chinle along the steep canyon walls in spite of the fact that the formation contains many such primary structures.

The Kayenta Formation comes closest to the ideal situation, because it is well exposed on both sides of Moab Valley.. Plots of the many available direction indicators made it possible to arrive at the firm conclusion that the Kayenta streams flowed virtually unimpeded over the area where Moab Valley now is.

As was the case in the areas studied by Stokes, the Salt

Wash is an excellent unit for the study of paleocurrent trends and patterns. Even though it is exposed only on the east side of the Moab fault, the pattern as a whole is diagnostic of uninterrupted flowage with the exception of minor divergences along the fault. However, the Salt Wash has been eroded away from the critical Moab Valley area, so its history there remains unknown.

All this boils down to the conclusion that, providing the key beds crop out on both sides of a structure, and providing the exposures are suitable for observation and plotting of the primary structures, firm conclusions can be reached concerning whether or not a rising salt mass had influenced sedimentation.

Of course in geology, the ideal situation is a rare exception, so a realistic appraisal takes this into account. All things considered, I feel that this method can be a very useful tool to be used in conjunction with all the other approaches to a problem of this nature. In some areas, conditions may be such that the method cannot be employed at all; however, at other places a study of primary sedimentary current structures could add much information to the overall knowledge of the history of development of a geologic structure. 96 REFERENCES CITED

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