Neoproterozoic variations in the C-isotopic composition of seawater: stratigraphic and biogeochemical implications.

摘要: The recent proliferation of stratigraphic studies delta 13C variation in carbonates and organic C later Neoproterozoic basal Cambrian successions (approximately 850-530 Ma) indicates a strong oscillating trend the C-isotopic composition surface seawater. Alone, this does not adequately characterize discrete intervals time. However, integrated with vectorial signals provided by fossils Sr-isotopic variations, isotope chemostratigraphy facilitates interbasinal correlation successions. Results these are evaluated terms four intervals: (1) Precambrian/Cambrian boundary, (2) post-Varanger terminal Proterozoic, (3) late Cryogenian, (4) early Cryogenian. Where biostratigraphic or radiometric data constrain age sedimentary sequences, secular variations Sr isotopes can provide level resolution exceeding that alone. Isotopic place constraints on chemical evolution seawater, linking it to major tectonic paleoclimatic events. They also biogeochemical framework for understanding initial radiation macroscopic metazoans, which is associated stratigraphically, perhaps causally, global increase burial concomitant rise atmospheric O2.