title: Fossilized iron bacteria reveal a pathway to the biological origin of banded iron formation.
abstract: Debates on the formation of banded iron formations in ancient ferruginous oceans are dominated by a dichotomy between abiotic and biotic iron cycling. This is fuelled by difficulties in unravelling the exact processes involved in their formation. Here we provide fossil environmental evidence for anoxygenic photoferrotrophic deposition of analogue banded iron rocks in shallow marine waters associated with an Early Quaternary hydrothermal vent field on Milos Island, Greece. Trace metal, major and rare earth elemental compositions suggest that the deposited rocks closely resemble banded iron formations of Precambrian origin. Well-preserved microbial fossils in combination with chemical data imply that band formation was linked to periodic massive encrustation of anoxygenic phototrophic biofilms by iron oxyhydroxide alternating with abiotic silica precipitation. The data implicate cyclic anoxygenic photoferrotrophy and their fossilization mechanisms in the construction of microskeletal fabrics that result in the formation of characteristic banded iron formation bands of varying silica and iron oxide ratios.
authors.affiliation: Swedish Museum of Natural History, Department of Palaeobiology, Stockholm, Sweden. ernest.chifru@nrm.se
authors.forename: Ernest
authors.identifier: 0000000326730565
authors.initials: E
authors.lastname: Chi Fru
authors.forename: Magnus
authors.initials: M
authors.lastname: Ivarsson
authors.forename: Stephanos P
authors.initials: SP
authors.lastname: Kilias
authors.forename: Stefan
authors.initials: S
authors.lastname: Bengtson
authors.forename: Veneta
authors.initials: V
authors.lastname: Belivanova
authors.forename: Federica
authors.initials: F
authors.lastname: Marone
authors.forename: Danielle
authors.initials: D
authors.lastname: Fortin
authors.forename: Curt
authors.initials: C
authors.lastname: Broman
authors.forename: Marco
authors.initials: M
authors.lastname: Stampanoni
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D005580:Fossils; D005843:Geography; D055593:Geological Phenomena; D006115:Greece; D007501:Iron / Q000378:metabolism*; D008954:Models, Biological; D010084:Oxidation-Reduction; D052817:Phototrophic Processes; D012822:Silicon Dioxide / Q000378:metabolism
chemical_list: D012822:Silicon Dioxide; D007501:Iron