Sequence and Chemostratigraphic Study Across the Basal Eureka Quartzite Unconformity in the Great Basin, Nevada
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UNLV Theses, Dissertations, Professional Papers, and Capstones 2009 Sequence and chemostratigraphic study across the basal Eureka Quartzite unconformity in the Great Basin, Nevada: Implications for the origin of the Late Ordovician carbon isotope excursion Apostolos Paul Kosmidis University of Nevada Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Geochemistry Commons, and the Geology Commons Repository Citation Kosmidis, Apostolos Paul, "Sequence and chemostratigraphic study across the basal Eureka Quartzite unconformity in the Great Basin, Nevada: Implications for the origin of the Late Ordovician carbon isotope excursion" (2009). UNLV Theses, Dissertations, Professional Papers, and Capstones. 60. http://dx.doi.org/10.34870/1375741 This Thesis 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). 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SEQUENCE AND CHEMOSTRATIGRAPHIC STUDY ACROSS THE BASAL EUREKA QUARTZITE UNCONFORMITY IN THE GREAT BASIN, NEVADA: IMPLICATIONS FOR THE ORIGIN OF THE LATE ORDOVICIAN CARBON ISOTOPE EXCURSION by Apostolos Paul Kosmidis University of Nevada, Las Vegas Bachelor of Science Temple University 2005 A thesis submitted in partial fulfillment of the requirements for the Master of Science in Geoscience Department of Geoscience College of Science Graduate College University of Nevada, Las Vegas August 2009 TABLE OF CONTENTS ABSTRACT.......................................................................................................................iii LIST OF FIGURES ............................................................................................................ v ACKNOWLEDGMENTS ................................................................................................. vi CHAPTER 1 INTRODUCTION .................................................................................... 1 CHAPTER 2 GEOLOGIC BACKGROUND................................................................. 7 Tectonic Setting ............................................................................................................ 7 Ordovician Paleogeography of Laurentia ..................................................................... 9 Ordovician Biostratigraphy of the Great Basin ............................................................ 9 Sequence Stratigraphic Concepts and Controls .......................................................... 14 CHAPTER 3 METHODOLOGY ................................................................................. 19 Sequence Stratigraphy and Chemostratigraphy.......................................................... 19 CHAPTER 4 DATA AND RESULTS ......................................................................... 22 Stratigraphic Analysis................................................................................................. 22 Chemostratigraphic Data ............................................................................................ 29 CHAPTER 5 DISCUSSION......................................................................................... 33 CHAPTER 6 SUMMARY............................................................................................ 40 APPENDICES .................................................................................................................. 71 Isotopic results ............................................................................................................ 71 Location of measured sections.................................................................................... 75 Facies reconstruction and sedimentary structure key ................................................. 81 BIBLIOGRAPHY............................................................................................................. 82 VITA................................................................................................................................. 94 ABSTRACT Sequence and chemostratigraphic study across the basal Eureka Quartzite unconformity in the Great Basin, Nevada: implications for the origin of the Late Ordovician carbon isotope excursion by Apostolos Paul Kosmidis Dr. Ganqing Jiang, Examination Committee Chair Assistant Professor of Geoscience University of Nevada, Las Vegas The positive carbon isotope (δ13C) excursion from the late Middle Ordovician Copenhagen Formation that underlies the Eureka Quartzite in central Nevada has been hypothesized to record a global cooling event ~10 Myr prior to the well-recognized Late Ordovician Hirnantian glaciation (~443 Ma). However, direct evidence for pre- Hirnantian continental glaciation remains scarce, raising uncertainties in the relationship between the inferred eustatic sea-level fall and the origin of the positive δ13C excursion. Additionally, previous stratigraphic studies from southern Nevada and California suggest relative sea-level fall in excess of ~ 150 meters, which exceeds estimates for younger glacial periods (e.g., Hirnantian: ~45-60 m, Late Paleozoic: ~ 60-75 m, and Last Glacial Maximum: ~125 m of sea-level fall) despite the paucity of glaciogenic deposits at this time. An integrated sequence and chemostratigraphic study across the basal Eureka Quartzite unconformity and underlying carbonate strata (Antelope Valley Limestone) indicates that the Copenhagen Formation in central Nevada was most likely deposited in a fault-controlled sedimentary basin. The absence of a comparable positive δ13C iii excursion in sections away from the Monitor and Copenhagen valleys suggests that the δ13C excursion reported from the Copenhagen Formation in central Nevada was likely a localized signal formed through carbon cycling (e.g., high biologic production and eutrophication) in a restricted, geographically limited formation that was deposited during the period of exposure and karstification of the paleo-shelf in southern Great Basin locations. iv LIST OF FIGURES Figure 1 Isotopic excursions and stratigraphy of Late Ordovician strata................... 42 Figure 2 Hypothetical Model 1 .................................................................................. 43 Figure 3 Hypothetical Model 2 .................................................................................. 44 Figure 4 Paleogeographic reconstruction of Middle Ordovician ............................... 45 Figure 5 Correlation of North American and British Stages and Series .................... 46 Figure 6 Girvanella-algae of the Great Basin ............................................................ 47 Figure 7 Parasequence set stacking patterns .............................................................. 48 Figure 8 Systems tract architecture ............................................................................ 49 Figure 9 Site location map of studied sections in Nevada ......................................... 50 Figure 10 Paleoenvironmental reconstruction of sequences ........................................ 51 Figure 11 Lithostratigraphic correlation of facies........................................................ 52 Figure 12 Lithofacies comprising Facies Association 1 .............................................. 53 Figure 13 Field photographs of Facies Association 1 .................................................. 54 Figure 14 Interpretation of Facies Association 1 ......................................................... 55 Figure 15 Interpretation of Facies Association 2 ......................................................... 56 Figure 16 Thin-section photographs of Facies Association 3 ...................................... 57 Figure 17 Interpretation of Facies Association 3 ......................................................... 58 Figure 18 Field and thin-section photographs of Facies Association 4 ....................... 59 Figure 19 Bioclastic packstone and wackestone lithofacies ........................................ 60 Figure 20 Intraclast conglomerate lithofacies .............................................................. 61 Figure 21 Thin-section photographs of Copenhagen Formation lithofacies................ 62 Figure 22 Lithofacies comprising Facies Association 4 .............................................. 63 Figure 23 Carbon isotope chemostratigraphy .............................................................. 64 Figure 24 Oxygen isotope chemostratigraphy.............................................................. 65 Figure 25 Sequence stratigraphic and chemostratigraphic results ............................... 66 Figure 26 Erosional relief at sequence boundary ......................................................... 67 v ACKNOWLEDGMENTS The greatest debt of gratitude is owed to my advisor Dr. Ganqing Jiang for all the support and his belief that I could finish this project my way. Thanks also to Drs. Andrew Hanson and Wanda Taylor for their insightful questions that made sense