微生物成因鲕粒研究进展

鲕粒岩在古气候、古环境，以及古海洋领域有着独特的研究价值，然而学术界对于鲕粒成因目前仍没有统一认识。近年来，随着鲕粒形成过程中微生物诱导矿化证据的不断丰富，广为接受的“无机成因”观点正不断受到挑战。本论文从历史和当前视角，回顾了从“藻类参与”到“细菌参与”，以及现在“有机矿化过程”在微生物成因鲕粒研究方面的历程，对鲕粒形成的地球生物学过程进行了系统阐述，并着重介绍了鲕粒形成的各类生物—化学模型。但是这些模型能否解决所有鲕粒的成因问题，还有待进一步工作的检验。考虑到现阶段关于鲕粒成因的认识仍然存在非常大的争议，研究某些特定类型鲕粒的形成机制可为探究鲕粒成因之谜提供一个突破口，而具有条带状纹层结构的Kalkowsky型鲕粒则最有可能存在微生物参与。这是由于Kalkowsky型鲕粒一般以贫有机质和富有机质纹层的交替出现为特征，这与Robert Burne所述的“规则纹层状叠层石”或Robert Riding所述的“混合结构叠层石”特征非常相近，可能意味着它们具有相似的成因。富含有机质的纹层状（或带状）鲕粒虽然在现代巴哈马碳酸盐沉积环境中很少见，但在其他地区和地史记录中较为常见，通过对这种与叠层石特征非常相似的鲕粒进行研究可为了解这类鲕粒纹层形成的有机矿化过程提供了一个新的视角。

Recent Advances in Ooid Microbial Origin:A review

The study of ooids has a long history， and there is not yet a consensus as to their origin. The “inorganic process” that has been accepted by most sedimentologists has recently been challenged by the accumulating evidence of microbially-mediated mineralization within modern and ancient ooids. For microbial mechanisms involved in the genesis of ooids， photosynthetic microorganisms （e.g.， cyanobacteria） use light energy to produce organic carbon and to create alkaline microenvironments during metabolism that induce ambient carbonate nucleation. The organic matter that they produce may feed heterotrophic microorganisms， and some of these heterotrophs （e.g.， sulfate-reducing bacteria） are capable of increasing neighboring alkalinity and facilitating carbonate precipitation during their metabolic activities. It is possible that physicochemical conditions rearrange pre-precipitated nanograins produced by biologically-induced and -influenced mineralization processes， and promote the genesis of modern ooids with delicate tangential fabrics （Diaz’s model）. In addition， some types of ancient ooids （e.g.， alternating dark- and light-colored laminar ooids， and cerebroid ooids） with natural organic matter-rich laminae， closely resemble so-called “regularly laminational stromatolites” or “hybrid stromatolites”， implying their similar origins. The microbial accretion mechanism of such ooids resembles the growth model of laminar stromatolites，i.e.， combined biologically-induced （mainly photosynthetic microorganisms and sulfate-reducing bacteria） and biologically-influenced （providing templates for carbonate nucleation） mineralization. Organic matter-rich， laminar （or banded） fabric ooids are rare in modern marine settings but not uncommon in ancient records. Further work focusing on this kind of ooids may provide a new perspective to understand the organomineralization process in the genesis of ooids.