Lacustrine microbial dolomite of the Middle Permian Lucaogou Formation in rümqi，Xinjiang
Lei Chuan1，2 Li Hong1 Yang Rui1 Cheng Jun3
1 State Key Laboratory of Continental Dynamics，Department of Geology，Northwest University，Xi′an 710069，Shaanxi;2 Lanzhou Center for Oil and Gas Resources, Institute of Geology and Geophysics,Chinese Academy of Sciences，Lanzhou 730000,Gansu;3 Shaanxi Institute of Geological Survey，Xianyang 712000，Shaanxi
The dark-gray，middle to thin-bedded dolostone，limestone，siltstone，and gray or black shale and mudstone，deposited in shallow to open lake settings, are mainly developed in the Middle Permian Lucaogou Formation in southern Hongyanchi section of rümqi in Xinjiang. Dolostone which is rich in organic matter is mainly composed of dolomite and ankerite with small amount of calcite and Mg-calcite.The dolomite ranges from 3 to 10μm in crystal sizes and shows homogeneously dark-red luminescence.Micromorphologies of the dolomite vary from microspherules(5～8μm in diameter)，clusters(about 2μm long)，to anhedral dolomite under the SEM.Microspherules have microlaminae structure called “growth coating” which consists of numerous nanoscale particles in the 60000 times enlarged SEM photomicrographs.Anhedral dolomite which is mainly composed of massive particles(about 0.25μm)in 40000 times enlarged SEM photomicrographs shows the features of microbial mineralization.The above morphologies of dolomite are highly similar to the typical modern microbial dolomite in experiment-culture and natural environments.The δ13CPDB value of dolomite ranges from 1.8‰ to 13.8‰，and δ18OPDB value ranges from-12.1‰ to-4.1‰.The higher δ13CPDB value may be the result of isotope fractionation led by methane-producing bacteria.The characteristics of micromorphologies and stable isotope indicate that the precipitation of the Middle Permian dolomite had close relation to activities of anaerobic organisms.
Lei Chuan,Li Hong,Yang Rui et al. Lacustrine microbial dolomite of the Middle Permian Lucaogou Formation in rümqi，Xinjiang[J]. JOPC, 2012, 14(6): 767-776.
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