Neoproterozoic sulfur isotopes, the evolution of microbial sulfur species, and the burial efficiency of sulfide as sedimentary pyrite
- 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
- 2Pennsylvania State Astrobiology Research Center, Pennsylvania State University, University Park, Pennsylvania 16802, USA
- 3Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
Abstract
Significant variability in δ34Spyrite values in Neoproterozoic sedimentary rocks has been attributed to the evolution of nonphotosynthetic sulfide-oxidizing bacteria and the advent of sulfur disproportionation reactions in response to Earth's evolving redox chemistry. We analyzed trace sulfate in carbonates from South Australia and Namibia and reconstructed the sulfur isotope evolution of seawater sulfate. Comparison of our δ34Ssulfate record with published δ34Spyrite data from the same or equivalent successions indicates that δ34Ssulfate − δ34Spyrite (Δ34S) rose gradually through the second half of the Neoproterozoic and fluctuated coincident with episodes of glaciation, but did not exceed 46‰ before ca. 580 Ma. Large variability in δ34Spyrite in the Neoproterozoic can be explained as a consequence of low sulfate concentrations and rapidly fluctuating δ34Ssulfate in seawater rather than the onset of sulfur disproportionation reactions mediated by nonphotosynthetic sulfide-oxidizing bacteria.
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- Received 14 June 2004.
- Accepted 22 September 2004.
- Revision received 21 September 2004.
- Geological Society of America
