Master of Science (MS)
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Large negative carbon isotope (δ13C) excursions have been documented from late Neoproterozoic-Paleozoic successions. These δ13C excursions have been widely used for regional and global stratigraphic correlation, particularly in strata with limited paleontological and radiometric age controls. Recent studies, however, argued that some negative δ13C excursions from stratigraphic record may have been resulted from meteoric/burial diagenesis, which commonly shifts both carbon and oxygen isotopes toward lower values. Testing the diagenetic origin of δ13C excursions in stratigraphic successions without independent stratigraphic framework has been difficult because it evolves into circular arguments about stratigraphic completeness vs. diagenetic imprints. To address this issue, carbon and oxygen isotope analyses was conducted on the biostratigraphically controlled Middle Ordovician Antelope Valley Limestone Formation in the Arrow Canyon Range, Nevada, USA to document (1) the C-O isotope patterns of meter-scale cycles leading up to a well-known karstic unconformity and (2) isotope variability among carbonate lithologies and facies. The data are then compared with coeval isotope records regionally and globally to identify the maximum and minimum degree of isotope variations associated with meteoric/burial diageneses below a karstic unconformity. The results may have implications for interpreting the origin of some negative δ13C excursions, particularly those in the late Neoproterozoic.
Carbon; Isotope; Karst; Limestone; Oncoid; Ordovician
Geochemistry | Geology | Sedimentology
Williams, Patricia Suzanne, "Carbon Isotope Variations Associated with a Middle Ordovician Karstic Unconformity" (2015). UNLV Theses, Dissertations, Professional Papers, and Capstones. 2447.