Resolving sedimentary sulphur cycling during the Shunga Event (early Paleoproterozoic) with sulphur isotopes

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One of the key events during early Paleoproterozoic time is the deposition of unprecedented amounts of organic matter during the ca. 2000 Ma old Shunga Event. Autochthonous sedimentary organic matter, migrated pyrobitumen und petrified subaquatic oil spills characterize a thick sedimentary succession in the Onega Basin on the Fennoscandian Shield, NW Russia. Petrographic and geochemical evidence clearly indicates that the organic matter is being remineralized microbially via a diverse suite of aerobic and anaerobic pathways. Sulphur isotopic evidence suggests that microbial sulphur cycling, and most prominently bacterial sulphate reduction appears to be of prime importance but that it occurred under highly variable conditions. Resulting sedimentary sulphides display a wide textural spectrum, underlining temporal and spatial variability in the diagenetic realm. A qualitative and quantitative understanding of the Shunga event requires a firm assessment of its depositional and diagenetic history in order to unravel its importance for the evolution of the ocean-atmosphere system during the Archean-Proterozoic transition.