Ildikó GYOLLAI^1,2, Márta POLGÁRI^3*, Krisztián FINTOR⁴, Friedrich POPP⁵, Dieter MADER¹, Elemér PÁL-MOLNÁR^4,6, Szabolcs NAGY^2,4 & Christian KOEBERL^1,7
1Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
²Cosmic Materials Research Group, Geobiomineralization and Astrobiological Research Group, Eötvös Loránd University of Budapest, 1117 Budapest, Pázmány P. Street 1/A, Hungary
³Research Center for Astronomy and Geosciences, Geobiomineralization and Astrobiological Research Group, Institute for Geology and Geochemistry, Hungarian Academy of Sciences, 1112 Budapest, Budaörsi Street 45, Hungary, e-mail: rodokrozit@gmail.com, *corresponding author
⁴ Department of Mineralogy, Geochemistry and Petrology, University of Szeged, 6722 Szeged, Egyetem Str. 2, Hungary
⁵Department of Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
⁶MTA-ELTE Volcanology Research Group, H-1117 Budapest, Pázmány P. Street 1/C, Hungary
⁷Natural History Museum, Burgring 7, A-1010 Vienna, Austria

MICROBIALLY MEDIATED DEPOSITION OF POSTGLACIAL TRANSITION LAYERS FROM THE NEOPROTEROZOIC OTAVI GROUP, NAMIBIA: EVIDENCE OF RAPID DEGLACIATION AFTER THE STURTIAN CRYOGENIC PERIOD

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Iron-rich postglacial transition layers from early Cryogenian “Snowball Earth” sedimentary environments of the Otavi Group (Namibia) were studied by microtextural high-resolution mineralogical and geochemical methods. Series of Fe-rich biomats (goethite, hematite) were identified, and signs of diverse microbial, filamentous Fe-oxidizing, and cyanobacterial activity were documented for the first time. The matrix mineralogy consists of quartz and dolomite, diverse organic matter, muscovite, apatite, and pyrite. On the basis of mineralized bacterial layering of the Fe-rich biomats, the postglacial transition layers are interpreted to have formed within a few hundred years under suboxic, neutrophilic, shallow, fresh- to brackish-water conditions during an initial rapid deglaciation process from a Neoproterozoic “Snowball Earth” environment. Thus we suggest that the overlying Rasthof cap carbonates, influenced by tectonic subsidence of the region, may also have been deposited within a very short period, comprising the entire deglaciation process.