Formation of fossiliferous concretions in the Cretaceous Santana Formation - Assessing the role of microbial processes

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Exceptional fossil preservation (incl. soft-tissue phosphatization) within organic-rich black shales is often associated with the formation of a protective carbonate shell surrounding the fossil specimen. Whereas the mechanisms controlling soft-tissue mineralization during the earliest stage of fossilization are considerably well understood, only limited information is currently available on the complex biogeochemical processes which lead to the precipitation of the concretionary carbonate body around the fossils. The proposed pilot study will focus on the organic and inorganic geochemistry of carbonate concretions derived from black shale deposits of the Early Cretaceous Santana Formation (Araripe Basin, NE Brazil). This konservat-type fossil lagerstätte is world famous for its fossiliferous concretions hosting an exceptionally preserved fish and reptile fauna. The principle aim of this study is twofold including (1) identification of the type and source of organic matter trapped within the Santana concretions and (2) assessment of the different microbial or microbially-mediated processes associated with successive concretion growth during early burial. The achievement of these goals is expected from the combination of organic molecular geochemistry (incl. compound-specific δ13C analytics) with high-resolution inorganic geochemistry and sedimentary petrography.