Isotopic Evolution of Proterozoic Sediments and Seawater

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Recent investigation point to the latest Proterozoic (0.5-0.9 Ga) as being a time of vast evolutionary change. Well-preserved sedimentary successions in Namibia, Spitsbergen, South Africa and China have been studied in detail as they contain important economic deposits and remnants of the first metazoan faunas. In addition, strong carbon- and strontium-isotopic variations are found in these sequences and may be useful for the correlation of coeval strata world-wide. We propose to continue research on the isotopic variations in C, Sr and Nd in well-characterized and well- preserved stratigraphic samples from the Nama, Polarisbreen and Kango groups as well as the Doushantuo and Dengying formations to better characterize the rate of isotopic change during the latter part of the Proterozoic Eon. Given a better knowledge of the rate of isotopic changes in latest Proterozoic seawater our goals are to: 1) trace the major mass fluxes in the exogenic geochemical cycle and understand the relationship between the evolution of the sedimentary reservoir, the oceans and the atmosphere during the Late Proterozoic, 2) determine rates of erosion, organic carbon burial and hydrothermal alteration and their relation to global tectonics, 3) investigate the relationship of strong isotopic variations to known events of glaciations, phosphorite and banded iron-formation deposition, and 4) strengthen the tie between chemo- stratigraphic and bio-stratigraphic correlations between these Late Proterozoic successions. During the Proterozoic, seawater Nd and Sr budgets appear to have changed from dominantly hydrothermal inputs (as in the Archean) to dominantly continental (river) inputs. Modeling of the data obtained from this research will be used to constrain the changes in rates of hydrothermal circulation, continental erosion rates, burial rates of organic carbon and variations in the mean age of continental erosion products through the late Proterozoic. Implications for the evolution of O2 and CO2 in the Earth's atmosphere will also be considered. We have demonstrated with our previous work that high resolution Sr and C isotopic curves may be obtained for late Proterozoic sedimentary successions and are confident that this research will lead to major breakthroughs in our understanding of Late Proterozoic evolution.