VPW: Extension of the Temporal Scale of Newly Resolved Middle Cambrian Sr Isotope Stratigraphy

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Seawater 87Sr/86Sr variations during the Early Paleozoic are poorly documented relative to the resolution of the Late Paleozoic through Cenozoic portions of the Phanerozoic seawater Sr isotope curve. The Cambrian portion of the Phanerozoic seawater Sr isotope curve is especially characterized by a significant degree of scatter and a large uncertainty envelope. Moreover, the newly emerging data base of secular seawater 87Sr/86Sr variations for pre-Middle Cambrian time underscores a conspicuous gap in the Middle to Late Cambrian seawater Sr isotope record. Consequently, the potential of Sr isotopes for enhanced chronostratigraphic resolution of Middle to Upper Cambrian stratigraphic successions, is extremely limited for providing insight into the Middle to Late Cambrian ocean- atmosphere-biosphere system, and for potentially constraining rates of biogeochemical cycling during this time interval. The two main objectives of this study focus on critically addressing these limitations; the results of this research should minimize or potentially overcome these limitations. The first objective is to complete a detailed Sr isotopic analysis of a second section of Bonanza King carbonates from the southern Great Basin in order to test the robustness of the newly resolved Sr isotope stratigraphy. The second objective is extend the integrated study to lower Middle Cambrian carbonates of the Papoose Lake Member of the Bonanza King Formation and the upper Carrara Formation, southern Great Basin. The results of this research, when integrated with our new resolved Sr isotope curve and recently published Early Cambrian seawater 87Sr/86Sr values, will provide a Cambrian seawater Sr isotope curve of resolution comparable to many portions of the Late Paleozoic and Mesozoic Sr isotope curve. In turn, this will afford enhanced chronostratigraphic resolution of Cambrian stratigraphic successions, a refined understanding of the Cambrian ocean-atmosphere-biosphere system, and potent ial for constraining rates of biogeochemical cycling during this time interval. Lastly, the 87Sr/86Sr database which will ultimately result from this integrated study will inevitably contribute insight into and potentially resolve many controversial 'Cambrian' issues. Interactive activities consist of four facets: 1) teaching one graduate-upper division undergraduate level seminar in cycle stratigraphy, 2) actively participating in other carbonate sedimentology, stratigraphy and digenesis seminars, 3) actively involving undergraduate and graduate students in this research project, and 4) leading department field trips to the Cretaceous of Texas and northeastern Mexico.