Large sulfur isotope fractionations associated with Neoarchean microbial sulfate reduction.
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.
Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA. zhelezka@umd.edu.
Iadviga
I
Zhelezinskaia
Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA.
Alan J
AJ
Kaufman
Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA.
James
J
Farquhar
Centre for Microscopy Characterization and Analysis, ARC Centre of Excellence for Core to Crust Fluid Systems, University of Western Australia, Crawley, WA 6009, Australia.
John
J
Cliff
D001419:Bacteria / Q000378:metabolism*; D002254:Carbonates / Q000737:chemistry; D005591:Chemical Fractionation; D007501:Iron / Q000737:chemistry; D010084:Oxidation-Reduction; D012623:Seawater / Q000737:chemistry* / Q000382:microbiology*; D013431:Sulfates / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D013440:Sulfides / Q000737:chemistry; D013460:Sulfur Isotopes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism
D002254:Carbonates; D013431:Sulfates; D013440:Sulfides; D013460:Sulfur Isotopes; C011342:pyrite; D007501:Iron