NanoSIMS Analysis of Sulfur Isotopes in Sulfides from ca. 2.7 Ga BIFs and Cherts as Tracers of Microbial Activity

Details NanoSIMS Analysis of Sulfur Isotopes in Sulfides from ca. 2.7 Ga BIFs and Cherts as Tracers of Microbial Activity NanoSIMS Analysis of Sulfur Isotopes in Sulfides from ca. 2.7 Ga BIFs and Cherts as Tracers of Microbial Activity

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53d..05p&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P53D-05

Biology

0315 Biosphere/Atmosphere Interactions (0426, 1610), 0406 Astrobiology And Extraterrestrial Materials, 0424 Biosignatures And Proxies, 0454 Isotopic Composition And Chemistry (1041, 4870), 0488 Sulfur Cycling

Scientific paper

Archean hydrothermal environments often host various types of sedimentary rocks that include banded iron formations (BIFs) and cherts. Modern microbial communities that inhabit these ecosystems are diverse and tend to play a strong role in sulfur cycling. The sulfur isotopic composition of sulfide minerals in ancient BIFs and cherts from volcano-sedimentary environments thus potentially preserves a record of microbial sulfur metabolism. In addition, sulfur isotopic compositions may contain information on the redox state of the atmosphere if the sulfur cycled in it and was eventually transferred to marine sediments before its crystallization into sulfide. We used the nanoSIMS 50L to measure in situ the isotopic composition of sulfides from ca. 2.7 Ga BIFs and cherts from the Abitibi terrain in Quebec and Ontario and from the Bababudan/Sandur area in Karnataka, India. Using a beamsize of 15 X 15 microns, the 2-sigma reproducibility on standards was ± 1.0 and ± 0.3 permil for δ34S and Δ33S values, respectively, and we obtained mass dependent fractionation slopes of 0.5167 and 0.5172. Important instrumental mass fractionation effects were observed for analyses intentionally targeting areas with topographic defects, poor polish, and re-analysis of old craters. So far, our survey of 2.7 Ga Abitibi and Bababudan/Sandur BIF and chert sulfides has revealed a range of about 15 permil in δ34S (between +6 and -9 permil) and mostly positive Δ33S values up to +2.9 permil. These data are consistent with a generally anoxic Neoarchean atmosphere and possibly with some microbial sulfur processing in the original environment.

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