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

在目前的世界上，微生物诱导的碳酸盐沉淀对于非正常海洋沉积系统，如高盐度微生物席和叠层石，有很好的记录；但关于微生物如何促进覆盖沿海陆架和大陆边缘大片地区的富含有机物质的沉积物中的碳酸盐结晶的信息仍然很少。从碳酸盐档案研究的角度来看，这一方面具有重要意义，因为在许多涉及古环境重建的研究中，化石碳酸盐软泥被广泛用作代理载体。异养碳酸盐化作用自前寒武纪以来普遍存在，并可能在碳酸盐岩矿床的形成中一直起着重要作用。该项目的第一个目标是对厌氧异养微生物介导的富有机沉积物中的碳酸盐沉淀进行深入分析。更具体的目标包括描述碳酸盐沉淀的环境先决条件、胞外聚合物对结晶成核的作用以及结晶过程中同位素特征和元素比率的变化。第二个目标是研究早期成岩沉积/孔隙水环境中微生物诱导的生物碳酸盐蚀变(“微生物风化”)。虽然碳酸盐的微生物蚀变(碳酸盐硬质部分的钻孔和蚀刻)的概念被普遍接受，但所涉及的过程的机制和微生物参与的明显痕迹仍需确定。通过研究上部沉积柱中能够改变碳酸盐(即碳酸盐骨架的弱化并为成岩流体提供通道)或诱导次生碳酸盐沉淀的微生物过程，从微生物学的角度分析生物成因碳酸盐矿床的早期成岩过程。

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.