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Tectonic and Sequence Stratigraphic Implications of the Morrison Formation-Buckhorn Conglomerate Transition, Cedar Mountain, East-Central Utah

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Tectonic and Sequence Stratigraphic Implications of the Morrison Formation-Buckhorn Conglomerate Transition, Cedar Mountain, East-Central Utah TECTONIC AND SEQUENCE STRATIGRAPHIC IMPLICATIONS OF THE MORRISON FORMATION-BUCKHORN CONGLOMERATE TRANSITION, CEDAR MOUNTAIN, EAST-CENTRAL UTAH A thesis presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Master of Science Xavier Roca November 2003 This thesis entitled TECTONIC AND SEQUENCE STRATIGRAPHIC IMPLICATIONS OF THE MORRISON FORMATION-BUCKHORN CONGLOMERATE TRANSITION, CEDAR MOUNTAIN, EAST-CENTRAL UTAH BY XAVIER ROCA has been approved for the Department of Geological Sciences and the College of Arts and Sciences Gregory Nadon Assistant Professor of Geological Sciences Leslie Flemming Dean, College of Arts and Sciences ROCA, XAVIER M.S. November 2003. Geological Sciences Tectonic and Sequence Stratigraphic Implications of the Morrison Formation-Buckhorn Conglomerate Transition, Cedar Mountain, East-central Utah (222 pp.) Director of Thesis: Gregory Nadon Abstract The contact between the Morrison Formation and the Buckhorn Conglomerate has been interpreted as a low order unconformity bridging the Jurassic and Cretaceous Periods in the northwestern Colorado Plateau. However, sedimentologic and stratigraphic data gathered at Cedar Mountain, the Buckhorn type section in east-central Utah, provide new evidence of the conformable transition of the two stratigraphic units. This evidence consists of gutter casts, mud injection, and dinosaur tracks at the base of the Buckhorn as well as interfingering of the Buckhorn with Morrison mudstones. The Buckhorn braided river deposit is interpreted to be the result of the exhumation, reworking, and eastern propagation of older synorogenic coarse materials of a late Jurassic flexural foredeep located in western Utah. This interpretation, when combined with accommodation rates inferred from Late Jurassic fluvial styles, defines a Morrison depositional sequence. Evidence of the Jurassic onset of Buckhorn deposition precludes its chronostratigraphic correlation with similar Lower Cretaceous conglomeratic deposits found throughout the North American Western Interior. Approved: Gregory Nadon Assistant Professor of Geological Sciences To Carol Acknowledgements I would like to thank Greg Nadon for the help offered during the preparation of this thesis, John Bird for the assistance received during the field work, and Mike Leschin for access to the Cleveland Lloyd Dinosaur Quarry. I also would like to express my gratitude towards the faculty of the Department of Geological Sciences for offering me the opportunity to continue my studies in geology. Finally, I would like to thank my people back home, for making me feel that I never left. Table of Contents Page Abstract ................................................................................................................... 3 Dedication ................................................................................................................ 4 Acknowledgements .................................................................................................. 5 List of Tables ............................................................................................................ 8 List of Figures ........................................................................................................... 9 Chapter 1: Introduction ........................................................................................... 13 1.1 Introduction .......................................................................................... 13 1.2 Regional Tectonic Context .................................................................... 13 1.3 Stratigraphic Overview ......................................................................... 18 1.4 This Study ............................................................................................ 22 1.5 Study Area ........................................................................................... 23 Chapter 2: Previous Work ....................................................................................... 30 2.1 Introduction .......................................................................................... 30 2.2 Regional Stratrigraphy ........................................................................... 30 2.3 Chronostratigraphy ............................................................................... 47 2.4 Jurassic – Cretaceous Compression ...................................................... 49 2.5 Lower Cretaceous Conglomerate Tectonic Models ............................... 57 Chapter 3: Methodology ......................................................................................... 67 3.1 Introduction .......................................................................................... 67 3.2 Stratigraphic Data ................................................................................. 67 3.3 Sedimentologic Data ............................................................................. 67 3.4 Petrographic Data. ................................................................................ 69 Chapter 4: Facies Analysis ...................................................................................... 71 4.1 Introduction .......................................................................................... 71 4.2 General Stratigraphy. ............................................................................ 71 4.3 Mudstone and Siltstone Facies .............................................................. 81 4.4 Sandstone Facies .................................................................................. 88 4.5 Conglomerate Facies .......................................................................... 104 4.6 Carbonate Facies ............................................................................... 114 4.7 Depositional Environments .................................................................. 116 6 Chapter 5: Stratigraphic Model ............................................................................. 121 5.1 Introduction ........................................................................................ 121 5.2 Stratigraphic Contacts ......................................................................... 121 5.3 Source Area ....................................................................................... 124 5.4 Timing of deposition ............................................................................ 128 5.5 Stratigraphic Model ............................................................................ 130 Chapter 6: Depositional Model ............................................................................. 134 6.1 Introduction ........................................................................................ 134 6.2 Eustasy ............................................................................................... 134 6.3 Climate ............................................................................................... 136 6.4 Tectonics ............................................................................................ 137 6.5 Depositional Model ............................................................................ 145 Chapter 7: Conclusions ......................................................................................... 151 References ........................................................................................................... 153 Appendix A: Stratigraphic Sections ....................................................................... 165 Appendix B: Basin Member and Buckhorn Conglomerate Sandstone Point Counts.. 196 Appendix C: Buckhorn Conglomerate Pebble Lithologies ...................................... 197 Appendix D: Brushy Basin Member and Buckhorn Conglomerate Paleoflow Data .. 198 7 List of Tables Page 4.1 Lithologies of the Brushy Basin Member and Buckhorn Conglomerate of the study area ................................................................................................ 74 8 List of Figures Page 1.1 Map of the North American Western Interior Basin during the Jurassic Period .................................................................................. 14 1.2 Paleogeographic maps of United States Western Interior from the Middle Jurassic to the Early Cretaceous .............................................. 15 1.3 Schematic block diagram of the Mesozoic subduction zone and related tectonic settings of the United States Western Interior ...................... 16 1.4 Map Showing Tectonic features of the Western United States ............................ 17 1.5 Paleoflow directions of the Lower Cretaceous conglomerate in the Western Interior Basin ............................................................................ 19 1.6 Chronostratigraphic diagram of the Jurassic-Cretaceous transition in western North America ................................................................................ 20 1.7Location map of the Study area .......................................................................... 24 1.8 Buckhorn type section ..................................................................................... 25 1.9 Morrison and Cedar Mountain Formations exposures in central Utah ................ 26 1.10 Stratigraphic section of the Study area ............................................................ 27 1.11 Geologic map of the Study area .....................................................................
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