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13Synsedimentary and early diagenetic oxygen levels are estimated by evaluating celadonite-14 smectite formation in marine Jurassic black shale-hosted manganese-carbonates. Celadonite 15 formed under suboxic-dysaerobic conditions, Al-rich Fe-smectite formed at suboxic-anaerobic 16 conditions, and nontronite formed at anoxic-anaerobic conditions during sedimentary burial. A 17 genetic pathway by direct precipitation from solution is proposed for the enormous mass of 18 celadonite, based on mineral and textural evidence. Lamination of the manganese ore is 19 independent of clay-mineral composition and was given by a series of mineralized microbial Fe-20 rich biomats. 21

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The Datangpo Formation manganese deposits (DFMnD) in South China formed during the interglacial stage between the Sturtian and Marinoan glaciations of the Cryogenian period. These black shale-hosted deposits are composed of massive Mncarbonates with microscopic laminae/laminations and cherty veins. To date, it has been thought that the DFMnD formed through inorganic processes, which were controlled by redox changes in the post-Sturtian Nanhua Rift Basin, South China. However, in this study, systematic petrographic, mineralogical, and geochemical analyses indicate a microbially mediated origin of the Mn ore deposits. Mineralized microbial woven micro-textures (observed at the μm scale) and microbial fossils are common in the laminated Mn-carbonate ores. We infer that microbial enzyme activity formed poorly crystallized Mn oxide/hydroxides and carbonaceous material, which 2 transformed to rhodochrosite, kutnohorite, ankerite/dolomite, framboidal pyrite, and apatite via diagenesis. Some micro-scale quartz and K-feldspar may be detrital but most appears to have formed during diagenesis or through hydrothermal activity. A micro-mineralogical profile determined by 2500 spectra via high-resolution in situ micro-Raman spectroscopy also revealed cyclic laminations of Ca-rhodochrosite as microbialite (ankerite/dolomite) and quartz, indicating a mineralized biomat system. Ca-rhodochrosite transformed to kutnohorite under elevated temperatures, as indicated by the maturation level of organic matter (determined via Raman spectroscopy). Alternating micro-laminae denote cyclic changes in microbial groups (Mn-and Fe-oxidizing microbes versus cyanobacteria) during the formation of the Mn ore deposits. Our proposed model for the microbially mediated metallogenesis of Mn-carbonate deposits begins with enzymatic multi-copper oxidase processes associated with autotrophic microbial activity under obligatory oxic conditions, which results in the precipitation of Mn bio-oxides. Following their burial in organic-rich sediments, the Mn(IV) oxides and hydroxides are reduced, producing soluble Mn(II) via processes mediated by heterotrophic microbes under suboxic conditions, which in turn form the Mn-carbonates. This microbial metallogenesis model for the Cryogenian DFMnD in South China is similar to that proposed for the Jurassic Úrkút Mn deposit in Hungary, indicating that a two-step microbially mediated process of Mn ore formation might be common throughout geological history.

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is really a grey shale with moderate to low TOC content that accumulated in a starved basin. The 33 organic matter content and anoxic characteristics resulted from rapid accumulation of microbial 34 organic matter from microbial booms, accompanied by a geothermally generated hydrothermal 35 circulation system, and a high rate of authigenic mineral formation (clay minerals and proto-ore 36 minerals). The inferred enzymatic Mn and Fe oxidation blocked carbonate formation by 37 decreasing the pH. The system remained suboxic via syngenetic mineral accumulation (Fe-rich 38 biomats), and became anoxic during diagenesis in conjunction with pyrite generation. The 39 separation of black shale beds and Mn-ore beds is not distinct through the section. Instead, a 40 distal hydrothermally induced clay-rich authigenic assemblage (marlstone) best describes the 41 black shale, in which Mn-oxide proto-ore beds (Mn-rich laminae) formed from the beginning of 42 black shale deposition, when the oxygen supply in the sedimentary basin was insufficient for 43 enzymatic Mn(II) oxidation. Mn-oxide proto-ore turned into Mn-carbonate ore via microbially 44 mediated processes during early diagenesis. The drivers for Mn-bearing organic matter-rich 45 marlstones were most probably a combination of regional and local processes, with generation of 46 a tectonic rift system that promoted geothermally generated hydrothermal fluids, which initiated 47 3 microbial blooms. Black shale mineralogy, geochemistry, and organic matter at Úrkút differ 48 from those of the epicontinental shelf black shales of the Tethyan ocean. 49 50

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