title: A Rare Glimpse of Paleoarchean Life: Geobiology of an Exceptionally Preserved Microbial Mat Facies from the 3.4 Ga Strelley Pool Formation, Western Australia.
abstract: Paleoarchean rocks from the Pilbara Craton of Western Australia provide a variety of clues to the existence of early life on Earth, such as stromatolites, putative microfossils and geochemical signatures of microbial activity. However, some of these features have also been explained by non-biological processes. Further lines of evidence are therefore required to convincingly argue for the presence of microbial life. Here we describe a new type of microbial mat facies from the 3.4 Ga Strelley Pool Formation, which directly overlies well known stromatolitic carbonates from the same formation. This microbial mat facies consists of laminated, very fine-grained black cherts with discontinuous white quartz layers and lenses, and contains small domical stromatolites and wind-blown crescentic ripples. Light- and cathodoluminescence microscopy, Raman spectroscopy, and time of flight-secondary ion mass spectrometry (ToF-SIMS) reveal a spatial association of carbonates, organic material, and highly abundant framboidal pyrite within the black cherts. Nano secondary ion mass spectrometry (NanoSIMS) confirmed the presence of distinct spheroidal carbonate bodies up to several tens of μm that are surrounded by organic material and pyrite. These aggregates are interpreted as biogenic. Comparison with Phanerozoic analogues indicates that the facies represents microbial mats formed in a shallow marine environment. Carbonate precipitation and silicification by hydrothermal fluids occurred during sedimentation and earliest diagenesis. The deciphered environment, as well as the δ13C signature of bulk organic matter (-35.3‰), are in accord with the presence of photoautotrophs. At the same time, highly abundant framboidal pyrite exhibits a sulfur isotopic signature (δ34S = +3.05‰; Δ33S = 0.268‰; and Δ36S = -0.282‰) that is consistent with microbial sulfate reduction. Taken together, our results strongly support a microbial mat origin of the black chert facies, thus providing another line of evidence for life in the 3.4 Ga Strelley Pool Formation.
authors.affiliation: Department of Geobiology, Geoscience Centre, Georg-August-University Göttingen, Goldschmidtstr. 3, 37077, Göttingen, Germany.|'Origin of Life' Group, Göttingen Academy of Sciences and Humanities, Theaterstraße 7, 37073, Göttingen, Germany.
authors.forename: Jan-Peter
authors.initials: JP
authors.lastname: Duda
authors.affiliation: Australian Centre for Astrobiology and School of Biological, Earth and Environmental Sciences, University of New South Wales, Kensington, NSW 2052, Australia.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Van Kranendonk
authors.affiliation: Department of Geobiology, Geoscience Centre, Georg-August-University Göttingen, Goldschmidtstr. 3, 37077, Göttingen, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Thiel
authors.affiliation: Department of Experimental Limnology, Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB), Alte Fischerhütte 2, 16775, Stechlin, Germany.
authors.forename: Danny
authors.initials: D
authors.lastname: Ionescu
authors.affiliation: Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstraße 24, 48149, Münster, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Strauss
authors.affiliation: Department of Geobiology, Geoscience Centre, Georg-August-University Göttingen, Goldschmidtstr. 3, 37077, Göttingen, Germany.
authors.forename: Nadine
authors.initials: N
authors.lastname: Schäfer
authors.affiliation: Department of Geobiology, Geoscience Centre, Georg-August-University Göttingen, Goldschmidtstr. 3, 37077, Göttingen, Germany.|'Origin of Life' Group, Göttingen Academy of Sciences and Humanities, Theaterstraße 7, 37073, Göttingen, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Reitner
mesh_terms: D002254:Carbonates / Q000032:analysis*; D005580:Fossils; D019015:Geologic Sediments / Q000737:chemistry*; D010163:Paleontology; D013460:Sulfur Isotopes / Q000032:analysis*; D014904:Western Australia
chemical_list: D002254:Carbonates; D013460:Sulfur Isotopes