粗粒叠层石研究进展OA

Coarse-grained stromatolites are a unique type of microbialite that emerged relatively late in geological history;however,only limited sedimentary records of coarse-grained stromatolites have been found to date.In this review,we utilize these scarce sedimentary records to unravel the intrinsic and extrinsic factors governing their formation.This endeavor holds immense significance in comprehending the intricate interplay between microorganisms and their environment,as well as elucidating the driving mechanisms behind the evolution of stromatolite microfabrics throughout geological epochs.Based on the research findings of coarse-grained stromatolites in Shark Bay,Western Australia and the Bahamas,this study provides a comprehensive review of the macromorphology,microstratification,and sedimentary environment of classic coarse-grained stromatolites throughout geological history.Furthermore,a comparative analysis was conducted to examine and compare the different background factors,such as paleoclimate,sea levels,and paleo-ocean physicochemical conditions,which influenced their formation.Microbial mats rich in eukaryotes,such as diatoms and green algae,exhibit a significantly greater capacity for trapping and binding coarse particles compared to simpler cyanobacteria-dominated microbial mats.The abrupt emergence of coarse-grained stromatolites may be linked to the evolutionary development of larger eukaryotic organisms.Most commonly,these structures form in shallow or marginal marine environments under the influence of tides,waves,or storms where turbulent water facilitates continuous particle supply onto the surface of microbial mats.High ion concentration and diversity in seawater within this intermittent high-energy environment contribute to improved adhesion properties of extracellular polymers and enhanced particle binding ability for microbial mats.Meanwhile,calcium carbonate saturation in such settings is insufficient to promote calcification of microbial mats,but it can support subsequent lithification processes involved in forming coarse-grained stromatolites.Additionally,relatively higher sea temperatures,gradual fluctuations in sea levels,suitable atmospheric CO2 content,elevated seawater calcium carbonate saturation levels,and lower metazoan biodiversity all favor favorable conditions for the development of coarse-grained stromatolites.Although the conditions necessary for the formation of marine coarse-grained stromatolites have been increasingly clarified,there remain certain limitations and uncertainties in the genetic interpretation of these special microbialites.Further research is required to investigate the sources of coarse particles,the development scale of coarse-grained stromatolites,and the formation mechanisms of continental coarse-grained stromatolites,which could provide a better understanding of the influence of both intrinsic and extrinsic factors on their formation.