| Earth System Processes 2 (811 August 2005) | |
| Paper No. 8-4 | |
| Presentation Time: 2:30 PM-2:50 PM | ||
CARBON AND SULFUR ISOTOPIC EVIDENCE FOR THE TERMINAL NEOPROTEROZOIC DEEP OCEAN OXYGENATION, HUQF SUPERGROUP, SULTANATE OF OMAN | ||
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FIKE, David A., Earth, Atmospheric, & Planetary Sciences, MIT, 77 Massachusetts Ave., 54-812, Cambridge, MA 02139, dfike@mit.edu, GROTZINGER, John P., Earth, Atmospheric, & Planetary Sciences, MIT, 77 Massachusetts Ave., 54-816, Cambridge, MA 02139, PRATT, Lisa M., Geological Sciences, Indiana Univ, 1001 East 10th Street, Bloomington, IN 47405, ROTHMAN, Daniel H., Earth, Atmospheric, and Planetary Sciences, MIT, 77 Massachusetts Ave., 54-626, Cambridge, MA 02139, and SUMMONS, Roger E., Earth, Atmospheric and Planetary Sciences, MIT, E34-546, 42-44 Carleton Street, Cambridge, MA 02139 High resolution carbon and sulfur chemostratigraphy of the Huqf Supergroup [~635 540 Ma] indicate the progressive oxygenation of the ocean during the terminal Neoproterozoic (~580 542 Ma). Detailed analysis of carbonate d13C reveals multiple positive and negative excursions including a globally-extensive negative excursion of >13 recorded within the Shuram Formation. This Shuram excursion extends through >500m of stratigraphic section in Oman. Sulfate d34S remained relatively invariant throughout deposition of the Shuram, indicating that the oxidation of depleted carbon responsible for the Shuram d13C excursion was not accompanied by significant oxidation of sulfide. Analysis of coupled organic carbon and carbonate d13C reveals non-steady state carbon cycling in which organic d13C is buffered from changes in coexisting carbonate d13C. In this case, the Shuram excursion may be explained by the oxidation of a vast reservoir of dissolved organic carbon in the deep ocean. Following the Shuram excursion, paired organic and carbonate d13C indicate that the carbon cycle evolved to a quasi-steady-state. At the time of this transition, sulfate d34S increased dramatically from ~23 to a maximum of ~42 at the Precambrian/Cambrian boundary. Pyrite d34S suggests the increase in sulfate d34S results from an increase in the fractionation between sulfate and sulfide, possibly coupled with increased pyrite burial. The earliest Cambrian strata in Oman record a decrease in sulfate d34S to ~39. This decline, which follows the Precambrian/Cambrian boundary, reflects a progressive increase in the concentration of seawater sulfate as oceanic oxygen levels increased. Together these data indicate a stepwise reorganization of the global carbon and sulfur biogeochemical cycles in the terminal Neoproterozoic and the ventilation of the deep ocean. | ||
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Earth System Processes 2 (811 August 2005)
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| Session No. T5 Late Neoproterozoic Biospheric, Climate, and Evolutionary Events Westin Hotel: Bonavista 1:30 PM-4:30 PM, Monday, August 8, 2005 | ||
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