Microbially-induced carbonate precipitation and alteration in organic-rich marine sediments

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In the present world, microbially-induced carbonate precipitation is well documented for non-normal marine depositional systems such as hypersaline microbial mats and stromatolites; but information is still scarce on how microbes facilitate carbonate crystallization in organic-rich sediments that are covering vast areas of coastal shelves and continental margins. From the viewpoint of carbonate archive research, this aspect is significant, because fossil carbonate oozes are widely used as proxy carriers in many studies dealing with the reconstruction of the palaeo-environment. It is expected that heterotrophic carbonatogenesis is ubiquitous since the Precambrian and probably always played an important role in the formation of carbonate deposits. The first aim of the project is to provide in-depth analyses of carbonate precipitation in organic-rich sediments mediated by anaerobic heterotrophic microorganisms. More specific objectives include characterization of environmental prerequisites for carbonate precipitation, role of extracellular polymeric substances for crystal nucleation, and alteration of isotopic signatures and element ratios during crystallization. The second aim is the investigation of microbially-induced alteration (“microbial weathering”) of biogenic carbonates in early diagenetic sediment/porewater environments. While the concept of microbial alteration of carbonates (boring and etching of carbonate hardparts) is generally accepted, the mechanisms of the processes involved and the traces that are evident for microbial involvement yet need to be identified. With the investigation of microbial processes in the upper sediment column that are capable of altering carbonates (i.e., weakening of carbonate skeletons and providing pathways for diagenetic fluids), or inducing secondary carbonate precipitation, the analysis of early diagenetic processes in biogenic carbonate deposits from the microbiological perspective is intended.