Doctor of Philosophy (PhD)
First Committee Member
Second Committee Member
Third Committee Member
Fourth Committee Member
Fifth Committee Member
The Devonian-Carboniferous (D-C) transition was a critical interval in earth history, witnessing profound environmental changes associated with plant and animal evolution and extinction. Two first-order mass extinctions occurred leading up to the D-C boundary: the Kellwasser Event at the Frasnian-Famennian (F-F) boundary (~371 Ma) and the D-C boundary Hangenberg Event (~359 Ma). Both events were associated with significant sea level changes and major carbon cycle perturbations, evidenced by widespread deposition of black shale and positive carbon isotope (δ13C) excursions, all of which have been used to correlate these events across the globe. Because preservation of black shale requires anoxic conditions, ocean anoxia is a leading hypothesis for the cause of the extinctions. However, the relationship between the extinctions, climate and sea-level changes, and anoxia remains unproven. To better understand the relationship between paleoenvironmental changes and the extinctions, ẟ13C chemostratigraphy is integrated with lithostratigraphy and available biostratigraphic data to reconstruct the stratigraphic framework of Late Devonian-Early Mississippian strata in the southern Great Basin and South China. Paleoredox change is examined within reconstructed framework using cerium anomaly [Ce/Ce* = CeN/(PrN2/NdN)] and the redox sensitive trace elements (RSTEs) U and V. In the Great Basin, the Kellwasser and Hangenberg ẟ13C excursions are documented in multiple sections. High Ce/Ce* values (0.8–1.2) and low U/Th and V/Al ratios of Famennian carbonates suggest protracted anoxic depositional environments in the Great Basin during the Famennian. Three sections in South China covering proximal and distal carbonate platform and platform top depositional settings were examined to better understand synchroneity of the anoxic event within different depositional environments during the extinction. Ce/Ce*, U/Th, and V/Al data from these sections indicate significant spatial heterogeneity of redox change during the D-C transition. High Ce/Ce* values (0.8–1.1) of the proximal platform and platform top sections indicate protracted reducing conditions for up to 4-million-years, while Ce/Ce* values from the distal platform record oxic conditions with only a brief anoxic event at the beginning of the Hangenberg ẟ13C excursion. This redox heterogeneity requires the development of locally restricted environments in the proximal and isolated platform sections, which is supported by U/Th and V/Al variations. When compared to existing ‘local’ and ‘global’ redox proxy data in the same area, our results suggest diachroneity of anoxic events during the extinction. In both the Great Basin and South China, Ce/Ce*, U/Th, and V/Al indicate spatial heterogeneity of anoxic environments during both extinctions and emphasize the necessity evaluating the diachronous development of anoxic and extinction events within a broad environmental context of each sedimentary basin.
cerium anomaly; chemostratigraphy; mass extinction; ocean anoxia; stratigraphy
Geochemistry | Geology | Sedimentology
University of Nevada, Las Vegas
Warren, Audrey M., "Paleoenvironmental Changes Across the Devonian-Carboniferous Transition" (2022). UNLV Theses, Dissertations, Professional Papers, and Capstones. 4626.
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