The microbial dolomite model has been used to interpret the origin of sedimentary dolomite.In this model,the formation of low-temperature protodolomite,an important precursor to sedimentary dolomite,can be facilitated...The microbial dolomite model has been used to interpret the origin of sedimentary dolomite.In this model,the formation of low-temperature protodolomite,an important precursor to sedimentary dolomite,can be facilitated either by actively metabolizing cells of anaerobic microbes and aerobic halophilic archaea or by their inactive biomass.Aerobic halophilic bacteria are widely distributed in(proto-)dolomite-depositing evaporitic environments and their biomass might serve as a template for the crystallization of protodolomite.To test this hypothesis,carbonation experiments were conducted using dead biomass of an aerobic halophilic bacterium(Exiguobacterium sp.strain JBHLT-3).Our results show that dead biomass of JBHLT-3 can accelerate Mg2+uptake in carbonate mineral precipitates.In addition,the amount of Mg incorporated into Ca-Mg carbonates is proportional to the concentration of biomass.High Mg-calcite is produced with 0.25 or 0.5 g/L biomass,whereas protodolomite forms with 1 g/L biomass.This is confirmed by the main Raman peak of Ca-Mg carbonates,which shifts towards higher wavenumbers with increased Mg substitution.Microbial cells and their imprints are preserved on the surface of high Mg-calcite and protodolomite.Hence,this study furthers our understanding of the dolomitization within buried and dead microbial mats,which provides useful insights into the origin of ancient dolomite.展开更多
To find out the origin of dolomite, the precipitation of primary dolomite, and the formation of pores in dolomite, petrologic and geochemical characteristics of typical samples from Sichuan and Tarim Basin were analyz...To find out the origin of dolomite, the precipitation of primary dolomite, and the formation of pores in dolomite, petrologic and geochemical characteristics of typical samples from Sichuan and Tarim Basin were analyzed based on the previous understandings, and three aspects of results were achieved.(1) A classification of dolomite origins based on petrologic features, forming environment, and time sequence was proposed, which shows clear boundaries of diagenetic and characteristic realms and evolved clues between different types of dolomite.(2) Petrographic and geochemical identification marks for different types of dolomite were presented, revealing that the orderly geochemical variation of different types of dolomite is the response to the change of forming environment of dolomite during continuous time sequence.(3) The contribution of dolomitization to the formation of porosity was re-evaluated, revealing that the porosity in dolomite was mostly attributed to the primary pores and supergene dissolution and burial dissolution, and early dolomitization was conducive to the preservation of primary pores. These understandings are of great theoretical significance for identifying the origins and types of dolomite, and can guide the prediction of dolomite reservoirs.展开更多
基金jointly supported by the National Natural Science Foundation of China(Nos.42272046,42072336 and 41772362)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB26000000)+1 种基金the 111 Project of China(No.BP0820004)the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)(No.CUGCJ1703)。
文摘The microbial dolomite model has been used to interpret the origin of sedimentary dolomite.In this model,the formation of low-temperature protodolomite,an important precursor to sedimentary dolomite,can be facilitated either by actively metabolizing cells of anaerobic microbes and aerobic halophilic archaea or by their inactive biomass.Aerobic halophilic bacteria are widely distributed in(proto-)dolomite-depositing evaporitic environments and their biomass might serve as a template for the crystallization of protodolomite.To test this hypothesis,carbonation experiments were conducted using dead biomass of an aerobic halophilic bacterium(Exiguobacterium sp.strain JBHLT-3).Our results show that dead biomass of JBHLT-3 can accelerate Mg2+uptake in carbonate mineral precipitates.In addition,the amount of Mg incorporated into Ca-Mg carbonates is proportional to the concentration of biomass.High Mg-calcite is produced with 0.25 or 0.5 g/L biomass,whereas protodolomite forms with 1 g/L biomass.This is confirmed by the main Raman peak of Ca-Mg carbonates,which shifts towards higher wavenumbers with increased Mg substitution.Microbial cells and their imprints are preserved on the surface of high Mg-calcite and protodolomite.Hence,this study furthers our understanding of the dolomitization within buried and dead microbial mats,which provides useful insights into the origin of ancient dolomite.
基金Supported by the China National Science and Technology Major Project(2016ZX05004-002)
文摘To find out the origin of dolomite, the precipitation of primary dolomite, and the formation of pores in dolomite, petrologic and geochemical characteristics of typical samples from Sichuan and Tarim Basin were analyzed based on the previous understandings, and three aspects of results were achieved.(1) A classification of dolomite origins based on petrologic features, forming environment, and time sequence was proposed, which shows clear boundaries of diagenetic and characteristic realms and evolved clues between different types of dolomite.(2) Petrographic and geochemical identification marks for different types of dolomite were presented, revealing that the orderly geochemical variation of different types of dolomite is the response to the change of forming environment of dolomite during continuous time sequence.(3) The contribution of dolomitization to the formation of porosity was re-evaluated, revealing that the porosity in dolomite was mostly attributed to the primary pores and supergene dissolution and burial dissolution, and early dolomitization was conducive to the preservation of primary pores. These understandings are of great theoretical significance for identifying the origins and types of dolomite, and can guide the prediction of dolomite reservoirs.
