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Bearworks Cyclostratigraphic Trends of Δ13c in Upper Cambrian Strata BearWorks MSU Graduate Theses Spring 2017 Cyclostratigraphic Trends of δ13C in Upper Cambrian Strata, Great Basin, Usa: Implications for Astronomical Forcing Wesley Donald Weichert Missouri State University As with any intellectual project, the content and views expressed in this thesis may be considered objectionable by some readers. However, this student-scholar’s work has been judged to have academic value by the student’s thesis committee members trained in the discipline. The content and views expressed in this thesis are those of the student-scholar and are not endorsed by Missouri State University, its Graduate College, or its employees. Follow this and additional works at: https://bearworks.missouristate.edu/theses Part of the Geochemistry Commons, and the Sedimentology Commons Recommended Citation Weichert, Wesley Donald, "Cyclostratigraphic Trends of δ13C in Upper Cambrian Strata, Great Basin, Usa: Implications for Astronomical Forcing" (2017). MSU Graduate Theses. 3143. https://bearworks.missouristate.edu/theses/3143 This article or document was made available through BearWorks, the institutional repository of Missouri State University. The work contained in it may be protected by copyright and require permission of the copyright holder for reuse or redistribution. For more information, please contact [email protected]. CYCLOSTRATIGRAPHIC TRENDS OF δ13C IN UPPER CAMBRIAN STRATA, GREAT BASIN, USA: IMPLICATIONS FOR ASTRONOMICAL FORCING A Masters Thesis Presented to The Graduate College of Missouri State University TEMPLATE In Partial Fulfillment Of the Requirements for the Degree Masters of Science, Geospatial Sciences in Geography and Geology By Wesley Donald Weichert May 2017 Copyright 2017 by Wesley Donald Weichert ii CYCLOSTRATIGRAPHIC TRENDS OF δ13C IN UPPER CAMBRIAN STRATA, GREAT BASIN, USA: IMPLICATIONS FOR ASTRONOMICAL FORCING Geography, Geology, and Planning Missouri State University, May 2017 Master of Science Wesley Donald Weichert ABSTRACT Composite geochemical studies of carbonate isotope values (δ13C) by other investigators have established that the Cambrian period is punctuated by a series of significant, globally correlated, positive and negative δ13C excursions. However, it remains unclear if low-amplitude secular variations in δ13C values exist superimposed on, or between large- scale perturbations in the Cambrian carbon cycle, especially in cyclic successions. Rocks of Steptoean-Sunwaptan (Paibian-Jiangshanian) stage, exposed in the Great Basin of Utah and Nevada, are excellent candidates for testing the hypothesis that sedimentary cycles record minor variations in Earth’s orbit (Milankovitch cycles) through application of high-resolution chemostratigraphic analysis. High-resolution δ13C data was collected from intervals in two correlative sections in Utah and Nevada. In addition, gamma-ray profiles were measured from a total of eight sections across the Great Basin, providing a sequence stratigraphic framework. Here, secular variations in δ13C values up to +/- 1.33 ‰ and +/- 0.70 ‰ exist between correlative 5th order cycles in Utah and Nevada respectively. Carbonate cycles can be correlated laterally 115 km based on key marker beds in the dominantly subtidal succession. REDFIT time-series analyses of δ13C reveals peak frequencies that compare favorably with the precession, obliquity, and eccentricity bands estimated from long-term sedimentation rates. A 1:1, 2:1 and 5:1 bundling of cycles additionally suggests astronomical controls on sedimentation. This investigation of Late Cambrian cyclic carbonates provides evidence of putative Milankovitch-style cyclicity recorded in mid-to outer-shelf carbonate deposits of Laurentia. KEYWORDS: Cambrian, sequence stratigraphy, carbon isotopes, time-series analysis, Milankovitch cycles. This abstract is approved as to form and content _______________________________ Kevin Ray Evans Chairperson, Advisory Committee Missouri State University iii CYCLOSTRATIGRAPHIC TRENDS OF δ13C IN UPPER CAMBRIAN STRATA, GREAT BASIN, USA: IMPLICATIONS FOR ASTRONOMICAL FORCING By Wesley Donald Weichert A Masters Thesis Submitted to the Graduate College Of Missouri State University In Partial Fulfillment of the Requirements For the Degree of Masters of Science, Geospatial Science in Geography and Geology May 2017 Approved: _______________________________________ Kevin Ray Evans, PhD _______________________________________ Gary Michelfelder, PhD _______________________________________ Melida Gutierrez, PhD _______________________________________ Julie Masterson, PhD: Dean, Graduate College iv ACKNOWLEDGEMENTS Foremost, I would like to give special thanks to Dr. Kevin Evans for introducing me to the Cambrian stratigraphy of the Great Basin. Without Kevin’s expertise and experience, I would have never had the opportunity to study the geology of the American West. Additionally, Kevin inspired me to pursue my academic goals and aspirations with confidence, a trait that will never leave me. I want to extend a special thanks to Brett Kenning, whom joined Kevin and I in the field and facilitated sample collection and measurements of gamma-ray profiles. I am especially appreciative for the help of Damon Basset for teaching the fundamentals of carbon isotope geochemistry, sample preparation, and analysis. In addition, I would like to thank Ken MacLeod and Shannon Haynes at the stable isotope laboratory at the University of Missouri for allowing me access to their facility. This thesis was made possible through the financial support from the American Association of Petroleum Geologists grants-in-aid of graduate research, the Geologic Society of America grants-in-aid of graduate research, and the Missouri State University Graduate College for funding this thesis research. Without this support, this project would not be possible. Finally, I want to dedicate this thesis to all my family and friends whom were always there to support me. Especially my wife, Morgan, who always believed in me and my abilities. v TABLE OF CONTENTS Introduction ..........................................................................................................................1 Background: a review of previous work and concepts ........................................................6 Geology of the Great American Carbonate Bank ....................................................6 The Biomere Concept ..............................................................................................8 Carbon Isotope Geochemistry................................................................................11 Sea-level History of the Pterocephaliid Biomere...................................................14 Past Studies of Meter-scale Cycles ........................................................................15 Cyclostratigraphy and Milankovitch Cycles ..........................................................16 Methods..............................................................................................................................22 Stratigraphic Sections and Sampling .....................................................................22 Gamma-ray Profiles ...............................................................................................25 Isotope Sample Preparation and Analysis ..............................................................26 Carbonate Carbon (δ13C) and Oxygen (δ18O) Isotope Analysis ............................26 Sequence Stratigraphy ...........................................................................................27 Time Series Analysis .............................................................................................30 Estimated Sedimentation Rates..............................................................................36 Results ...............................................................................................................................37 Stratigraphy of Measured Sections ........................................................................37 Fish Springs Section – Fish Springs – Juab Co. UT ..............................................38 Candland Canyon Section – Central House Range – Millard Co. UT ...................40 Steamboat Mountain Section – Southern House Range – Millard Co. UT ...........46 Lawson Cove Section – Wah Wah Mountains – Millard Co. UT .........................48 Spring Gulch Section – Northern Schell Creek Range – White Pine Co. NV .......53 North Egan Range Section – North Egan Range – White Pine Co. NV ................58 McGill Section – Duck Creek Range – White Pine Co. NV .................................60 Shingle Pass Section – South Egan Range – Lincoln Co. NV...............................62 Gamma-ray Profiles and Time Series Analysis .....................................................64 Results of δ13C and 18O Isotopic Values and Time Series Analysis ....................71 Estimated Accumulation Rates in the Great Basin ................................................78 Discussion ..........................................................................................................................82 Sequence Stratigraphy and Platform Evolution .....................................................82 Stratigraphic Trends of Gamma-Ray Values .........................................................90 Stratigraphic Trends of 13C Values at Spring Gulch, NV ....................................93 Stratigraphic trends of 13C values at Candland Canyon, UT ...............................99
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