Testing models for the origin of the deepest carbon-isotope anomaly in Earth history? The Wonoka Formation of South Australia

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Testing models for the origin of the deepest carbon-isotope anomaly in Earth history -- The Wonoka Formation of South AustraliaAdam C. Maloof & Blair Schoene, Princeton UniversityEAR-1121034ABSTRACTOver the past two decades, carbon isotope chemostratigraphy has emerged as the most important correlation tool for the Precambrian. The dominant paradigm amongst chemostratigraphers is that delta13C in carbonate rocks (delta13Ccarb) reflects the delta13C of dissolved inorganic carbon (DIC) in contemporaneous sea water. If this assumption is true, then why do we observe negative delta13Ccarb excursions lasting millions of years that dip well below the canonical value for mantle carbon input to the ocean-atmosphere system (-6?)? Do these excursions in fact represent diagenetic alteration away from DIC-derived values? Even if diagenetic, are the excursions global in nature, making them still useful for correlation? To explore these questions, we propose work on the deepest delta13Ccarb excursion in Earth history -- the `Shuram' anomaly, recorded in Ediacaran carbonate sediments on at least seven paleo-continents during the early evolution of animals. We will combine detailed field mapping and sequence stratigraphy with isotope chemostratigraphy and U-Pb geochronology of ash beds to constrain the timing and duration of the Shuram anomaly. In particular, isotope conglomerate tests will constrain the relative timing of delta13Ccarb acquisition, canyon cutting, subaerial exposure, meteoric diagenesis, and burial diagenesis. Our investigation of the unprecedented isotopic variability during the Ediacaran will test whether delta13Ccarb is a record of the evolving global carbon cycle and may be used as a correlation tool -- vitally important for every Precambrian story (climatic, evolutionary, geochemical, tectonic) of global change.