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Abiotic Pyrite Formation Produces a Large Fe Isotope Fractionation

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    Rights statement: This is the author's version as submitted for publication following peer-review. The final version was published by the American Association for the Advancement of Science (2012).

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Original languageEnglish
Pages (from-to)1548-1551
Number of pages4
Issue number6037
Publication statusPublished - 24 Jun 2011


The iron isotope composition of sedimentary pyrite has been proposed as a potential proxy to trace microbial metabolism and the redox evolution of the oceans. We demonstrate that Fe isotope fractionation accompanies abiotic pyrite formation in the absence of Fe(II) redox change. Combined fractionation factors between Fe(II)(aq), mackinawite, and pyrite permit the generation of pyrite with Fe isotope signatures that nearly encapsulate the full range of sedimentary delta Fe-56(pyrite) recorded in Archean to modern sediments. We propose that Archean negative Fe isotope excursions reflect partial Fe(II)(aq) utilization during abiotic pyrite formation rather than microbial dissimilatory Fe(III) reduction. Late Proterozoic to modern sediments may reflect greater Fe(II)(aq) utilization and variations in source composition.

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