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Abiotic pyrite formation produces a large Fe isotope fractionation

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<mark>Journal publication date</mark>24/06/2011
<mark>Journal</mark>Science
Issue number6037
Volume332
Number of pages4
Pages (from-to)1548-1551
Publication StatusPublished
<mark>Original language</mark>English

Abstract

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 δ 56Fe 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.