UNLV Theses, Dissertations, Professional Papers, and Capstones 5-2009 The Sheep Pass Formation, a record of late Cretaceous and paleogene extension within the Sevier hinterland, East-Central Nevada Peter Alexander Druschke University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Geology Commons Repository Citation Druschke, Peter Alexander, "The Sheep Pass Formation, a record of late Cretaceous and paleogene extension within the Sevier hinterland, East-Central Nevada" (2009). UNLV Theses, Dissertations, Professional Papers, and Capstones. 1188. http://dx.doi.org/10.34917/2598944 This Dissertation is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Dissertation in any way that is permitted by the copyright and related rights legislation that applies to your use. 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THE SHEEP PASS FORMATION, A RECORD OF LATE CRETACEOUS AND PALEOGENE EXTENSION WITHIN THE SEVIER HINTERLAND, EAST-CENTRAL NEVADA by Peter Alexander Druschke Bachelor of Science Sonoma State University 1999 Masters of Science University of Nevada, Las Vegas 2003 A dissertation submitted in partial fulfillment of the requirements for the Doctor of Philosophy Degree in Geoscience Department of Geoscience College of Sciences Graduate College University of Nevada, Las Vegas May 2009 UMI Number: 3384002 Copyright 2009 by Druschke, Peter Alexander INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. 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Box 1346 Ann Arbor, Ml 48106-1346 P\7^ Dissertation Approval m,^uu,.^^L, The Graduate College University of Nevada, Las Vegas March 2 ,20 09 The Dissertation prepared by Peter Alexander Druschke Entitled THE SHEEP PASS FORMATION, A RECORD OF LATE CRETACEOUS AND PALEOGENE EXTENSION WITHIN THE SEVIER HINTERLAND, EAST-CENTRAL NEVADA is approved in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree in Geoscience Examination Committee Chair Dean of the Graduate College Examination Committee Member Graduate College Faculty Representative 1017-52 11 ABSTRACT The Sheep Pass Formation, a record of Late Cretaceous and Paleogene extension within the Sevier hinterland, east-central Nevada by Peter Alexander Druschke Dr. Andrew Hanson, Examination Committee Chair Associate Professor of Geology University of Nevada, Las Vegas The Sevier hinterland of western North America is considered by many to be an ancient proxy for the modern Andean Puna-Altiplano or Tibetan Plateau. However, controversies exist as tectonic setting and overall paleogeography of the Sevier hinterland during the Late Cretaceous and Paleogene. The Sheep Pass Formation type section within the southern Egan Range of east-central Nevada comprises a > 1 km thick sedimentary succession spanning the latest Cretaceous to Eocene, and provides a rare opportunity to test prevailing tectonic and paleogeographic models for the Sevier hinterland. New 1:12,000 scale field mapping in the southern Egan Range indicates that up to three km of stratigraphic throw occurred along the Ninemile fault, a presently low-angle down-to-the- northwest normal fault, during deposition of the Sheep Pass Formation type section. Subsequent reactivation of the Ninemile fault produced an additional ~1 km of stratigraphic throw during deposition of the Garrett Ranch Group, which unconformably overlies the Sheep Pass Formation type section. New U-Pb and (U-Th)/He detrital zircon dating and U-Pb carbonate age analyses from the Sheep Pass Formation type section iii indicate that the Ninemile fault system was active in latest Cretaceous time, and documents for the first time the presence of surface-breaking, synconvergent normal faults within the Sevier hinterland. New U-Pb detrital zircon and 40Ar/39Ar age analyses from the overlying Garrett Ranch Group document reactivation of the Ninemile fault in the middle to late Eocene, indicating that two discrete episodes of extension affected the Sevier hinterland. Movement along the Ninemile fault was coeval with Late Cretaceous and early Paleogene mid-crustal extension within the Sevier hinterland, and suggests a possible link. Middle to late Eocene extension was coeval with extension in the Sevier foreland of central Utah, and foundering of the Farallon slab. Evidence that extension significantly predated volcanism within the Sevier hinterland invalidates the theory that Paleogene volcanism drove coeval extension. Recognition of synconvergent extensional basins within the Sevier hinterland strengthens comparisons to the modern Puna- Altiplano and Tibetan plateau, where similar processes have been documented. IV TABLE OF CONTENTS ABSTRACT iii LIST OF FIGURES viii ACKNOWLEDGEMENTS ix CHAPTER 1 DISSERTATION OVERVIEW 1 CHAPTER 2 SYNCONVERGENT SURFACE-BREAKING NORMAL FAULTS OF LATE CRETACEOUS AGE WITHIN THE SEVIER HINTERLAND, EAST-CENTRAL NEVADA 6 Abstract 6 Introduction .7 Previous Work: The Sheep Pass Formation 9 Revised Age Control: U-Pb and (U-Th)/He Detrital Zircon Dating 10 Revised Age Control: U-Pb Microbial Carbonate Dating 11 New Structural Interpretations: TheNinemile Fault 12 New Structural Interpretations: Intra-basinal Faulting and Influence on Stratigraphy 13 Discussion and Conclusions 14 Figure Captions : 16 CHAPTER 3 PALEOGEOGRAPHIC ISOLATION OF THE CRETACEOUS TO EOCENE SEVIER HINTERLAND, EAST-CENTRAL NEVADA: INSIGHTS FROM U-Pb AND (U-Th)/He DETRITAL ZIRCON AGES OF HINTERLAND STRATA 20 Abstract : 20 Introduction 21 Geologic Background: Pre-Mesozoic Framework 25 Geologic Background: Mesozoic to Cenozoic Tectonic Framework 26 Cretaceous-Eocene Hinterland Stratigraphy: Newark Canyon Formation 30 Cretaceous-Eocene Hinterland Stratigraphy: Sheep Pass Formation 31 Cretaceous-Eocene Hinterland Stratigraphy: Eocene Volcanism and "Tuffaceous" Sheep Pass Formation 34 Methods: U-Pb Zircon Geochronology 37 Methods: (U-Th)/He Zircon Thermochronology 39 U-Pb Detrital Zircon Geochronology Results: Scotty Wash Sandstone 40 U-Pb Detrital Zircon Geochronology Results: Newark Canyon Formation 41 U-Pb Detrital Zircon Geochronology Results: Sheep Pass Formation Type v Section 42 U-Pb Detrital Zircon Geochronology Results: Stinking Spring Conglomerate 44 U-Pb Detrital Zircon Geochronology Results: "Tuffaceous" Sheep Pass Formation 44 (U-Th)/He Detrital Zircon Thermochronology Results 48 Discussion: Zircon Provenance 48 Discussion: Tectonic and Paleogeographic Interpretations 57 Conclusions 62 Figure Captions 65 CHAPTER 4 STRUCTURAL, STRATIGRAPHIC, AND GEOCHRONOLOGICAL EVIDENCE FOR EXTENSION PREDATING PALEOGENE VOLCANISM IN THE SEVIER HINTERLAND OF EAST-CENTRAL NEVADA 81 Abstract 81 Introduction 82 Regional Tectonic Framework 86 Background: The Sheep Pass Formation 89 40Ar/39Ar Geochronology Methods 93 40Ar/39Ar Geochronology Results: The Egan Range 94 Ar/3 Ar Geochronology Results: The Schell Creek Range 97 Paleocurrent Analysis Methods and Results 99 Late Cretaceous to Paleogene Structure and Stratigraphy of the Egan and Schell Creek Ranges: The Blue Spring Fault System 100 Late Cretaceous to Paleogene Structure and Stratigraphy of the Egan and Schell Creek Ranges: The Tectonic Significance of the Basal Garrett Ranch Group in the Southern Egan Range 102 Late Cretaceous to Paleogene Structure and Stratigraphy of the Egan and Schell Creek Ranges: The Shingle Pass Fault 104 Late Cretaceous to Paleogene Structure and Stratigraphy of the Egan and Schell Creek Ranges: The Schell Creek Range 105 Late Cretaceous to Paleogene Structure and Stratigraphy of the Egan and Schell Creek Ranges: Seismites in the Sevier Hinterland? 107 Discussion: Paleogene Extension in the Sevier Hinterland of East-Central Nevada 110 Discussion: Implications for Paleogeography of the Sevier Hinterland 114 Conclusions 118 Figure Captions 121 APPENDIX I U-Pb DETRITAL ZIRCON ANALYSES on cd rom APPENDIX II (U-Th)/He DETRITAL ZIRCON ANALYSES on cd rom APPENDIX III U-Pb CARBONATE ANALYSES on cd rom APPENDIX IV 40Ar/39Ar ANALYSES on cd rom VI APPENDIX V PALEOCURRENT DATA on cd rom REFERENCES CITED 138 VITA 162 vn LIST OF FIGURES CHAPTER 2 Figure 1: Geologic maps of Sevier hinterland and Egan Range 13 Figure 2: Detrital zircon and U-Pb carbonate age plots 13 Figure 3: Detailed geologic maps of Sheep Pass andNinemile Canyons 14 CHAPTER 3 Figure 1: Geologic map of the western U.S. Cordillera 65 Figure 2: Geologic map of Nevada 66 Figure 3: Stratigraphic