微生物与沉积岩的协同演化

Coevolution of Microorganisms and Sedimentary Rocks

[意义]生物圈是地球区别于其他星球的一大关键,微生物因时空分布广、代谢功能多样、繁殖快、丰度高而对地球宜居性产生重要影响,探索微生物与沉积岩的协同演化关系对了解宜居地球的形成过程与途径具有重要意义。[进展]太古宙虽然以火成岩为主,少量的沉积岩也以物理作用为主,但铁代谢微生物广泛参与了条带状硅铁建造的形成。元古宙的沉积岩发生了革命性变化,其丰度远比火成岩多,而且微生物作用明显加强。元古宙出现了大量丰富多彩的钙质微生物岩和微生物成因沉积构造,白云岩出现峰值,微生物形成的碳酸盐台地形态也多变。在元古宙末期,泥岩丰度的增加与陆地低等生物繁盛而导致黏土矿物工厂的生产机制升级有关。在元古宙与显生宙的过渡时期,出现了从硅质、磷质到钙质的转换,这与原核微生物向真核微生物再向多细胞动物的演化以及海洋环境的pH和Eh等条件变化有关。到了显生宙,多细胞动物大发展,而微生物群落受到压制,白云岩丰度开始降低。在真核微生物方面,古生代绿藻类的优势被中—新生代的红枝藻系所代替,使得碳酸钙沉积从浅水向深水扩展。特别是,在显生宙一些重大突变期,碳酸盐工厂出现从骨架灰岩到钙质微生物岩的多次大转换,并且出现一些错时相和微生物成因沉积构造,这些都与宏体生物出现危机后微生物生态系统的短暂发展有关。泥岩丰度在志留纪以后猛增,这与高等植物登陆导致黏土矿物工厂的又一次变革以及植物—微生物相互作用导致有机质絮凝作用的加强有关。[结论与展望]地质时期的条带状硅铁建造、灰岩、白云岩、磷块岩、硅质岩等沉积岩都与微生物作用密切相关,甚至一部分泥岩的形成也可能与微生物作用有关。微生物参与了许多沉积岩的形成,导致微生物在地质时期与沉积岩具有协同演化的关系。未来可以利用地质大数据定量化研究各类沉积岩在地质时期的分布和丰度及其与不同微生物之间的关系,由此进一步探索地球深部与表层的联动。

[Significance]Earth differs from other planets because of the presence of the biosphere.Microorganisms in the biosphere have played,and are playing,important roles in shaping Earth habitability owing to their wide spa-tiotemporal occurrence,diverse metabolism functions,rapid multiplication,and great abundance.To explore the co-evolution of microorganisms and sedimentary rocks is of great significance in understanding the processes and dynam-ics of the formation of Earth habitability.[Progress]The Archean is dominated by magmatic rocks,and its sedimen-tary rocks are primarily related to physical processes.However,banded iron formation is related to the contribution of photoferrotrophic bacteria.Significant changes occurred in the Proterozoic when sedimentary rocks overtook magmatic rocks in abundance and diverse biogenic rocks(calcimicrobialites and dolomites)greatly increased in abundance.Microbially-induced sedimentary structures were also diverse and occurred in great abundance.Mudstone began to in-crease in abundance at the end of the Proterozoic owing to the development of microorganisms on land,which generat-ed a new clay factory.The transition interval across the Neoproterozoic and Cambrian boundary witnessed the shift from siliceous to phosphatic and finally to calcareous rocks,coincident with the evolution from prokaryotes to eukary-otic microorganisms and finally to metazoans,showing their causal relationship.In the Phanerozoic,dolomite exhibit-ed a sharp decrease in abundance due to the metazoan expansion and its suppression on microorganisms.Green algae dominance in the Paleozoic shifted to the dominance of red algae in the Mesozoic and Cenozoic,favoring the expan-sion of calcium carbonate from shallow to deep water.In particular,carbonate factory showed the shift from skeleton limestones to calcimicrobialites for at least five times,in association with the occurrence of anachronistic facies as well as microbially-induced sedimentary structures;these are due to the transient expansion of microbial communi-ties immediately after the biotic crisis.Mudstones increased in abundance immediately after the development of terres-trial ecosystems due to the innovation of a clay factory on land and the enhanced precipitation of clay minerals caused by organic-induced flocculation.[Conclusions and Prospects]Microbial involvement of sedimentation resulted in the biogenic formation of sedimentary rocks including banded iron formations,limestones,dolomites,phosphorites,siliceous rocks,and certain mudstones,which in turn have caused the coevolution of microbes and sedimentary rocks throughout Earth history.Current research has summarized such a co-evolution framework on the geological times-cales.Future studies will quantitatively define the abundance of various sedimentary rocks over geological time based on reanalysis of the geological database,and quantitatively analyze microbial sedimentary rocks to better understand the coupled deep Earth-surface processes.