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Refinements to the Depositional History of Lower Silurian Strata in the Northeastern United States by means of Conodont Biostratigraphy, d13C Chemostratigraphy, Sequence Stratigraphy, and Magnetic Susceptibility

Sullivan, Nicholas B
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378112630

Abstract Details

2013, MS, University of Cincinnati, Arts and Sciences: Geology.
Although Silurian of the eastern United States is characterized by abundant exposures and a rich history of study, high resolution stratigraphic correlation at a regional scale has been hindered by many factors. The following chapters offer additional data that bear on unresolved issues of stratigraphic correlation and depositional history for several of these problematic rock units. This is accomplished by integrating traditional methods such as physical stratigraphy and conodont biostratigraphy with newly developed methods such as d13C stratigraphy, bulk magnetic susceptibility analysis, and sequence stratigraphy. The first chapter outlines a revised correlation of lower Silurian strata along the Cincinnati Arch by means of d13C stratigraphy and sequence stratigraphy. A prominent unconformity and several lithologically and isotopically distinct stratigraphic units are traced with confidence along the Cincinnati Arch between Richmond, Kentucky and Dayton, Ohio. A positive d13C excursion recognized in this succession is identified as the Valgu Excursion. This signal is identified within the upper ferruginous division of the Waco Member at several localities, providing a chronostratigraphic anchor for this succession. The second chapter describes biostratigraphically significant conodonts, which were recovered from the Second Creek Phosphate Bed and Wolcott Furnace Hematite, which are thin stratigraphic units occupying a critical position in the Silurian of west-central New York State. The Wolcott Furnace is tentatively assigned to the Distomodus staurognathoides Biozone, allying it with the underlying Sodus Shale. The Second Creek Phosphate Bed is assigned to the Pterospathodus amorphognathoides angulatus Biozone, corroborating similar studies that were conducted further to the west and casting doubt on prior correlations of this unit with the Westmoreland Hematite, its presumed lateral equivalent to the east. An analysis of the sedimentological characteristics of the Second Creek Bed suggests that it was deposited in fairly deep and dysoxic environments during times of low sedimentation, wherein the sea floor was periodically scoured by deep waves, density currents, or gravity waves. This is reflected by the co-occurrence of rip-up clasts, suggesting erosion, with an abundance of pyritic internal molds of mollusks, suggesting the persistence of sulfidic conditions as the bed was deposited. The third and final chapter is an investigation of bulk magnetic susceptibility data collected from several ironstone bearing successions in New York and Kentucky. Previous studies generally assume an inverse relationship between rates of sea level rise and bulk magnetic susceptibility values recorded in marine sedimentary rock. However, the lower Silurian of eastern North America is generally characterized by an abundance of authigenic iron-bearing minerals which are especially concentrated at intervals thought to reflect deposition during rapid sea level rise. In oxic depositional environments, these minerals generally contain iron in its ferric state, which produces high magnetic susceptibility values. Thus, in these same successions, the relationship between magnetic susceptibility values and sedimentation rate is opposite of what would be expected according to traditional models. In deeper depositional environments, iron is also concentrated at sediment-starved intervals, though here, it is in its ferrous state, which does not result in a strong magnetic susceptibility signal. Thus, it is concluded that the redox conditions of the depositional environment can exert a powerful control over magnetic susceptibility values.
Carlton Brett, Ph.D. (Committee Chair)
Patrick I McLaughlin, Ph.D. (Committee Member)
David Meyer, Ph.D. (Committee Member)
Arnold Miller, Ph.D. (Committee Member)
110 p.
Geology
Silurian; Sequence Stratigraphy; Conodont; Ironstone; Magnetic Susceptibility; Carbon Chemostratigraphy

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Citations

  • Sullivan, N. B. (2013). Refinements to the Depositional History of Lower Silurian Strata in the Northeastern United States by means of Conodont Biostratigraphy, d13C Chemostratigraphy, Sequence Stratigraphy, and Magnetic Susceptibility [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378112630

    APA Style (7th edition)

  • Sullivan, Nicholas. Refinements to the Depositional History of Lower Silurian Strata in the Northeastern United States by means of Conodont Biostratigraphy, d13C Chemostratigraphy, Sequence Stratigraphy, and Magnetic Susceptibility. 2013. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378112630.

    MLA Style (8th edition)

  • Sullivan, Nicholas. "Refinements to the Depositional History of Lower Silurian Strata in the Northeastern United States by means of Conodont Biostratigraphy, d13C Chemostratigraphy, Sequence Stratigraphy, and Magnetic Susceptibility." Master's thesis, University of Cincinnati, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378112630

    Chicago Manual of Style (17th edition)

ucin1378112630
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© 2013, some rights reserved.Creative Commons License Refinements to the Depositional History of Lower Silurian Strata in the Northeastern United States by means of Conodont Biostratigraphy, d13C Chemostratigraphy, Sequence Stratigraphy, and Magnetic Susceptibility by Nicholas B Sullivan is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Cincinnati and OhioLINK.