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Microbially Induced Carbonate Precipitation in a Middle Triassic Microbial Mat Deposit from Southwestern China:New Implications for the Formational Process of micrite

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Journal of Earth Science 2021年第3期32卷 633-645页

作者： Mao Luo Jitao Chen Wenkun Qie Jinyuan Huang Qiyue Zhang Changyong Zhou Wen Wen State Key Laboratory of Palaeobiology and Stratigraphy Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and PalaeoenvironmentChinese Academy of SciencesNanjing 210008China University of Chinese Academy of Sciences Beijing 100049China Institute of Geological Survey China University of GeosciencesWuhan 430074China Chengdu Center of China Geological Survey Chengdu 610081China

Lime mud(i.e.,micrite)is a major component of carbonate *** mechanisms(biotic versus abiotic)have been proposed for the formation of lime mud in Earth’s ***,the detailed role that microbes play in the nucleation and subsequent precipitation of micrites remains to be *** we undertook a detailed geobiological characterization of laminated lime mudstone from the Middle Triassic Guanling Formation in Yunnan Province,southwestern *** features,together with previous geobiological investigations,suggest that the laminated lime mudstones represent the former presence of microbial *** lime mudstones consist mainly of calcite,dolomite and quartz,with clay minerals and pyrites as subordinate *** particular,micro-analysis shows copious nano-globules(65–878 nm)and capsule-shaped nano-rods in *** low-Mg calcite nano-globule aggregates are closely associated with mucilaginous biofilms resembling extracellular polymeric substances(EPS).Nano-sized globules coalesce to form semi-euhedral micrite *** suggest that a decaying hydrolytic destruction of the EPS by microbial communities within microbial mat leads to the precipitation of the nano-globules by enhancing alkalinity in local *** an intermediate,these nano-globules further aggregate to form micrite crystals possibly through a dissolution-reprecipitation process.

关键词： nano-globule EPS micrite microbial mat Middle Triassic Luoping Biota

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Heterogeneous Mg isotopic composition of the early Carboniferous limestone: implications for carbonate as a seawater archive

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Acta Geochimica 2018年第1期37卷 1-18页

作者： Haoran Ma Yihe Xu Kangjun Huang Yuanlin Sun Shan Ke Yang Peng Xianguo Lang Zhen Yan Bing Shen Key Laboratory of Orogenic Belts and Crustal Evolution MOE School of Earth and Space Sciences Peking University State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences

Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from *** isotopes are significantly(up to 5%)fractionated during carbonate precipitation by preferential incorporation of ^(24)Mg,while hydrothermal reactions are associated with negligible Mg isotope fractionation by preferential sequestration of^( 26)***,the marine Mg cycle could be reflected by seawater Mg isotopic composition(δ^(26)Mg_(sw)),which might be recorded in marine ***,carbonates are both texturally and compositionally heterogeneous,and it is unclear which carbonate component is the most reliable for reconstructing δ^(26)Mg_(sw).In this study,we measured Mg isotopic compositions of limestone samples collected from the early Carboniferous Huangjin Formation in South *** on petrographic studies,four carbonate components were recognized:micrite,marine cement,brachiopod shell,and *** four components had distinct δ^(26)Mg:(1)micrite samples ranged from -2.86% to -2.97%;(2)pure marine cements varied from -3.40% to -3.54%,while impure cement samples containing small amount of Rugosa coral skeletons showed a wider range(-3.27% to-3.75%);(3)values for the mixture component were-3.17% and -3.49%;and (4)brachiopod shells ranged from -2.20% to -3.07%,with the thickened hinge area enriched in ^( 24)*** to having multiple carbonate sources,neither the micrite nor the mixture component could be used to reconstruct δ^(26)Mg_(sw).In addition,the marine cement was homogenous in Mg isotopes,but lacking the fractionation by inorganic carbonate precipitation that is prerequisite for the accurate determination of δ^(26)Mg_(sw).Furthermore,brachiopod shells had heterogeneous C and Mg isotopes,suggesting a significant vital effect during ***,the heterogeneous δ^(26)Mg of the Huangjin limestone makes it difficult to reconstruct δ^(26)Mg_(sw)using bulk carbonate/calcareous ***,δ^(26)Mg_(sw)was only slightly affected by

关键词： Seawater Mg isotopic composition Limestone Fossil micrite Cement

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Calcified Biofilms from Cambrian Oolitic Limestones in China

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Acta Geologica Sinica(English Edition) 2015年第1期89卷 70-76页

作者： LIU Wei ZHANG Xingliang State Key Laboratory of Continental Dynamics and Department of Geology Northwest University

Calcified biofiims are preserved as thin micritic coatings in the Cambrian oolitic limestone of two sections in North and South China. Standard petrographic examination revealed that the biofilms were developed during the early diagenetic stage immediately after the freshly deposited ooids, proceeding in the continuous sequence of depositional processes. The biofilm outlines are highly irregular, with steep sides, tower-like structures and overhanging projections; the internal fabric of the biofilms is composed of roughly laminated micrite aggregates with channel-like structures. Biofilms exhibit a strong fluorescent reaction. Detailed SEM examination suggests that the biofilms are biotically dominated by cyanobacteria. Our study demonstrates that microbial colonies, such as biofilms, can develop on ooid cortices and influence the formation and microstructures of those ooids.

关键词： geobiology ooids micrite cyanobacteria Cambrian Hubei and Shaanxi provinces

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