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Abstract

Many Neoproterozoic successions contain viable hydrocarbon source rocks, even though they were deposited before most extant life forms evolved. Eukaryotic microalgae, bacteria, chlorophyte micoalgae, marine pelagophyte algae and dinoflagellates may have contributed organic matter. Major global-scale glaciations, which are commonly attributed to a ‘snowball’ or ‘slushball’ Earth scenario, or deposited under a ‘zipper rift’ scenario, are believed to have played an important role in the deposition of hydrocarbon source rocks during the mid- Neoproterozoic (Cryogenian). Phases of Cryogenian deglaciation may have culminated in the deposition of high total organic carbon shales and ‘cap carbonates’ in restricted anoxic basins, which may have been carved by ice sheets themselves or, alternatively, formed as restricted extensional half graben as Rodinia began to fragment. One example of these organically enriched deglacial sediments comprises shales and dolostones deposited following the Sturtian glaciation in the Centralian Superbasin of Australia, an amalgam of basins that extends almost continent-wide across Australia. Data from the Marmot MMDD-1 drill core on the Stuart Shelf in the southern part of the Centralian Superbasin, together with previously published data on organic enrichment in the Amadeus Basin in the central part of the Centralian Superbasin, suggest that the deposition of organically enriched shales was widespread during the Sturtian deglaciation.

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