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AN ABSTRACT OF THE THESIS OF Daniel Glenn Carpenter for the degree ofMaster of Science in the Department of Geology presented onjj February 1989 Title: GEOLOGY OF THE NORTH MUDDY MOUNTAINS.CLARK COUNTY, NEVADA AND REGIONAL STRUCTURAL SYNTHESIS: FOLD-THRUST AND BASIN-RANGE STRUCTURE IN SOUTHERN NEVADA.SOUTHWEST UTAH, AND NORTHWEST ARIZONA Signature redacted for privacy. Abstract approved: "T/ Dr. R. S. Yeats The North Muddy Mountains are locatedin southern Nevada, about 65 km northeast of Las Vegasand near the eastern boundary of the Basin and Rangeprovince. The north-south-trending range block is bounded on theeast and west, respectively, by east- and west-dipping,high-angle normal faults. Sevier age contractional and Cenozoic age extensional structures are present in the range. The Summit thrust and Willow Tankthrust crop out, respectively, on the southwest and northeastsides of the North Muddy Mountains. A newly mapped thrustsegment connects the Summit and Willow Tank thrusts. It juxtaposed Jurassic on Cretaceous age rocks.The most recent displacement on the thrust is bracketed between95.8+1-3.5 Ma (age of youngest deformed rocks) and 93.1+/- 3.4 Ma (age of oldest overlying undefornied beds). These numbers indicate an Albian to Turonian(?) age rangefor the thrust. The Summit-Willow Tank thrust sheet waslater folded by a northwest-southeast-trending, southwest inclined foldtrain by displacement on the Arrowhead fault, aMiocefle and possibly younger(?) extensional structure. The oldest (Albian) synorogenicdeposits in the area contain exotic clasts of formations that werenot involved in local thrusting; the debris was transportedeastward from older thrust sheets. Younger (Cenoinanian) synorogenicbeds are composed of Mesozoic age clastsat the base of the section, grading to early paleozoic age clasts nearthe top (reverse clast stratigraphy). This succession represents progressively deeper erosion of thrust sheetsduring thrusting. The younger synorogenic beds do notcontain exotic clasts from older, more westerly, thrustsheets. This observation suggests that local thrustsheets formed highlands that shut of f the westerly source provenance. Rotation of horst and graben blocks onCenozoic normal and oblique-slip faults caused dismemberingof older Sevier- age fold-thrust structures, andin some cases refolded them into new orientations. Seismic reflection sections show wedge-shaped sedimentary beds, indicating that range- bounding normal faults formed half-grabens. The normal faults appear to be listric impling that thenet slip on these faults is a measure of the regionalhorizontal extension. GEOLOGY OF THE NORTH MUDDYMOUNTAINS CLARK COUNTY, NEVADA AND REGIONAL STRUCTURAL SYNTHESIS: FOLD-THRUST AND BASIN-RANGE STRUCTURE IN SOUTHERN NEVADA, SOUTHWESTUTAH AND NORTHWEST ARIZONA by Daniel G. Carpenter A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed February 24, 1989 Commencement June 1989 APPROVED: Signature redacted for privacy. Professor of GeO g , reof)r /7 Signature redacted forprivacy. Ch- rflof trie 've1 Signature redacted for privacy. Dean of Grad e School( Date thesis is presented , 1989 ACKNOWLEDGEMENTS Drs. Robert S. Yeats; Robert J. Lillie;J. G. Johnson; Keith F. Oles; and Richard G. Couch (OSU); SpenCe3. Reber, Chevron; Dr. Ulrich A. Franz, and AlWitherspoon, Mobil; provided guidance and are greatly appreciated. R. S. Yeats, S. J. Reber, U. A. Franz, the 1988 ChevronStructure School (30 geoscientists), A. Brandon, (Ph.D.student, University of Washington), and 3. Carpenter (Mobil)visited the area. P. Gans, Stanford Univ.; D. Reif,CimarrOn Resources; S. Snelson, Shell Oil; K. Ketner, USGS; C.Thormari, USGS; C. Kiuth and p. Verral, Chevron; G. Lister,Univ. of Melbourne; and E. Miller; Stanford provided furtherinsight into my work. W. Dickinson, Univ. of Arizona; and R.Allinendinger, Cornell Univ., are appreciated forenlightening discussions at the 1988 AAPG convention where I gave a paper. My parents, Ken and Mary, providedsteadfast encouragement, as they have done for all myendeavors. My sister, Ann Carpenter-Jansen, Freightliner Corp., contributed her professional expertise inediting. P. Caldwell, B. McCollum, T. McKinflOfl, and C.Hammerberg of Chevron provided logistical help. Mobil and Chevron provided financialgifts, reproduction facilities, and some vehicularsupport during the years I have worked for them. R. L. Clawson, Seisdata Services Inc., approved the release of 261 km ofseismic data for my project and that of 3. Carpenter. I greatly appreciate the understanding and good wishes from my supervisor, R. Hiseler, Chief Geologist, R. Charles, and Geological Manager, A. Koch of Mobil Oil Corp. They helped to make the transition to professional life mucheasier. Copyright 1989 by Daniel G. Carpenter, all rights reserved. Unauthorized duplication is a violation of applicable laws. TABLE OF CONTENTS CHAPTER 1 STRUCTURAL GEOLOGY OF THE NORTH MUDDY MOUNTAINS, CLARK COUNTY, NEVADA ABSTRACT 1 INTRODUCTION 2 PREVIOUS INVESTIGATIONS 3 GEOLOGIC SETTING 6 STRATIGRAPHY 8 PALEOZOIC ERA 10 Cambrian System 10 Bonanza King Formation 10 Dunderberg Shale 11 Nopah Formation 11 Ordovician System 11 Pogonip Group 11 Devonian System 12 Muddy Peak Limestone 12 Mississippian System 12 Monte Cristo Limestone 12 Miss issippian/Pennsylvanian/Permiafl Systems 13 Bird Spring Formation 13 Permian System 13 Red Beds 13 Toroweap Limestone 14 Kaibab Limestone 14 MESOZOIC ERA 14 Triassic System 15 Moenkopi Formation 15 Chinle Formation 15 Jurassic System 16 Moenave Formation 16 Kayenta Formation 16 Aztec Sandstone 16 Cretaceous System 17 Willow Tank Formation 17 Baseline Sandstone 17 SYNOROGENIC STRATIGRAPHIC RECORD 19 Early Synorogenic Rocks 23 Late Synorogenic Rocks 24 CENOZOIC ERA 25 Tertiary System 26 Horse Spring Formation 26 Muddy Creek Formation 26 Quaternary System 27 Undifferentiated Sediments 27 STRUCTURAL GEOLOGY 29 SEVIER OROGENIC BELT OF SOUTHERN NEVADA 29 North Buff ington Back Thrust 30 Weiser syncline 36 Muddy Mountain Thrust 36 Thrust Relations 38 Weiser Back Thrust 42 Snow Drift Back Thrust 43 Anderson Syncline 43 Summit-Willow Tank Thrust 44 Upper Plate Stratigraphy 50 Subcrop Map 50 Structure Contour Map 53 Tectonic Map 54 Structure Sections 54 Structural Evolution 60 DEPO-TECTONIC MODEL FOR THRUST GENERATED DEPOSITS 61 LARANIDE OROGENY 63 STRIKE SLIP FAULTS 64 Arrowhead Fault 64 CRUSTAL EXTENSION 69 SUMMARY AND CONCLUSIONS 70 CHAPTER 2 REGIONAL STRUCTURAL SYNTHESIS: FOLD-THRUST AND BASIN-RANGE STRUCTURE IN SOUTHERN NEVADA, SOUTHWEST UTAH, AND NORTHWEST ARIZONA 73 ABSTRACT 73 INTRODUCTION 76 REGIONAL TECTONIC SETTING 79 BASAL CENOZOIC UNCONFORMITY AND CENOZOIC STRATIGRAPHY 80 SUBSURFACE INFORMATION 82 WELL DATA 82 GRAVITY DATA 83 SEISMIC REFLECTION DATA 84 STRUCTURAL INTERPRETATION 86 SEISMIC INTERPRETATION 86 VIRGIN VALLEY BASIN 87 CENOZOIC SEISMIC SEQUENCE BOUNDARY 91 MEADOW VALLEY BASIN 93 COYOTE SPRING BASIN 96 TULE DESERT BASIN 96 CENOZOIC DOMING AND UPLIFT OF THE MORMON MOUNTAINS 98 GRAVITY SLIDE BLOCKS 100 LOW-ANGLE NORMAL FAULT MODEL FOR CRUSTAL EXTENSION 102 RECONSTRUCTION 103 THRUST TRENDS 108 TULE SPRINGS THRUST SHEET 111 CORDILLERAN HINGE STRATIGRAPHIC TRENDS 113 CASTLE CLIFF GRAVITY SLIDE SYSTEM 114 DISCUSSION AND CONCLUSIONS 119 CHAPTER 3 NEW K-AR AGES FROM ThE BASELINE SANDSTONE (CENOMANIAN): NORTh MUDDY MOUNTAINS, CLARK COUNTY, NEVADA 12). ABSTRACT 121 INTRODUCTION 122 POTASSIUM ARGON DATING 122 CONCLUSIONS 125 ACKNOWLEDGEMENTS 126 SAMPLE DESCRIPTIONS 127 CHAPTER 4 BIBLIOGRAPHY 128 APPENDICES 141 APPENDIX 1: TABLES 141 APPENDIX 2: PLATE CAPTIONS 144 LIST OF FIGURES Figure Paqe 1) Index mapof western North America showing Nevada and Clarkand Lincoln Counties 4 Index mapof Clark and Lincoln Counties showing basin andrange physiography 5 Cretaceous units in the North Muddy Mountains 21 Generalized Stratigraphic Column of the Cretaceous beds in the North Muddy and Muddy Mountains area, Nevada 22 Sketch section showing the Tertiary-CretaCeouS unconformity at Overton Ridge 28 Index map of the North Muddy Mountains showing klippen and windows of the Muddy Mountain thrust sheet in the context of a new interpretation of the major thrust sheets 31 Index map of the North Muddy Mountains showing the Muddy Mountain and North Buff ington-Suinmit-WillOW Tank thrust interpretation of Bohannon 32 Sketch section showing truncation of the Aztec Sandstone by the North Buff ington back thrust 33 Sketch section showing imbricate back thrusts in the North Buff ington thrust sheet 34 Index map of the North Muddy Mountains showing the Glendale and Muddy Mountain thrust interpretation of Longwell Sketch section showing the Connecting thrust segment of the Summit-Willow Tank thrust 49 Sketch section showing the Summit-Willow Tank thrust at an exhumed culmination in the thrust surface.... 52 LIST OF TABLES Table Page, 3.1) Sample Descriptions of Cretaceous synorogenic rocks showing Potassium-Argon age determina- tions 127 LIST OF APPENDIX TABLES Table Page 2.1) Velocity Analysis SP #1069, Line 4-4A 141 2.2) Basin configurations 142 2.3) Stratigraphy of the Meadow Valley Mountains and the Mormon Mountains 143 LIST OF PLATES (filed in map tube) Plate CHAPTER 1 1.1) Major tectonic elements of Southern Nevada, Southwest Utah, and Northwest Arizona. 1.2) Generalized Stratigraphic Column, Mormon and Muddy Mountains area, Clark and Lincoln Counties, Nevada. l.3A) Geologic map, scale 1:12,000, of the central portion of the North Muddy Mountains, Clark County, Nevada.