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Science. 2014 Nov 7;346(6210):742-4. doi: 10.1126/science.1256211.

Large sulfur isotope fractionations associated with Neoarchean microbial sulfate reduction.

Author information

1
Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA. zhelezka@umd.edu.
2
Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA.
3
Centre for Microscopy Characterization and Analysis, ARC Centre of Excellence for Core to Crust Fluid Systems, University of Western Australia, Crawley, WA 6009, Australia.

Abstract

The minor extent of sulfur isotope fractionation preserved in many Neoarchean sedimentary successions suggests that sulfate-reducing microorganisms played an insignificant role in ancient marine environments, despite evidence that these organisms evolved much earlier. We present bulk, microdrilled, and ion probe sulfur isotope data from carbonate-associated pyrite in the ~2.5-billion-year-old Batatal Formation of Brazil, revealing large mass-dependent fractionations (approaching 50 per mil) associated with microbial sulfate reduction, as well as consistently negative Δ(33)S values (~ -2 per mil) indicative of atmospheric photochemical reactions. Persistent (33)S depletion through ~60 meters of shallow marine carbonate implies long-term stability of seawater sulfate abundance and isotope composition. In contrast, a negative Δ(33)S excursion in lower Batatal strata indicates a response time of ~40,000 to 150,000 years, suggesting Neoarchean sulfate concentrations between ~1 and 10 μM.

PMID:
25378623
DOI:
10.1126/science.1256211
[Indexed for MEDLINE]
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