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