title: Abiotic pyrite formation produces a large Fe isotope fractionation.
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(56)Fe(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.
authors.affiliation: School of Geosciences, University of Edinburgh, Grant Institute, Edinburgh, UK. R.Guilbaud@sms.ed.ac.uk
authors.forename: Romain
authors.initials: R
authors.lastname: Guilbaud
authors.forename: Ian B
authors.initials: IB
authors.lastname: Butler
authors.forename: Rob M
authors.initials: RM
authors.lastname: Ellam
mesh_terms: D001419:Bacteria / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D007503:Iron Isotopes / Q000737:chemistry*; D010084:Oxidation-Reduction; D013440:Sulfides / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D007503:Iron Isotopes; D013440:Sulfides; C011342:pyrite; D007501:Iron; C022597:ferrous sulfide