HR: 0800h
AN: PP41A-0575    [Abstracts]
TI: The effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies recorded in the Neoproterozoic Johnnie Formation, Death Valley, USA
AU: * Kaufman, A J
EM: kaufman@geol.umd.edu
AF: University of Maryland, Department of Geology, College Park, MD 20742-4211 United States
AU: Corsetti, F A
EM: fcorsett@usc.edu
AF: University of Southern California, Department of Earth Sciences, Los Angeles, CA 90089-0740
AB: Carbonates within the Rainstorm Member in the terminal Neoproterozoic Johnnie Formation of Death Valley, California record a remarkable negative $\delta$$^{13}$C anomaly to a nadir of near -11$\permil$, accompanied by a dramatic rise in trace sulfate abundance ($>$500 ppm) and drop in carbonate associated sulfate $\delta$$^{34}$S values from 26.6$\permil$ to 15.8$\permil$. The carbonates, including the laterally extensive Johnnie Oolite, were deposited during marine flooding atop a sequence boundary best observed in cratonward sections. A similarly dramatic carbon isotope anomaly is recorded in broadly equivalent successions that post-date known Marinoan glacial deposits and pre-date the Precambrian-Cambrian boundary in Oman, India, China, Australia, and Namibia. The cause of the carbon and sulfur isotopic excursions was likely associated with a rise in atmospheric O$_{2}$, which resulted in 1) the oxidation of exposed continental shelf sediments rich in fossil organic matter and sulfides, providing a source of $^{12}$C, $^{32}$S, and sulfate; and 2) the ventilation of the oceans. Large metazoan fossils (Ediacaran animals) first appear directly above this anomaly, suggesting that a critical threshold with respect to atmospheric O$_{2}$ had been crossed at this time. A negative $\delta$$^{13}$C excursion of similar magnitude occurs in overlying strata at the Precambrian-Cambrian boundary, which may reflect similar processes.
DE: 8130 Heat generation and transport
DE: 4870 Stable isotopes
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 1010 Chemical evolution
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting