Mineralogies and Stable Isotopic Compositions of Methane-derived Carbonates from the Northeastern South China Sea
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摘要: 取自南海北部的3块自生碳酸盐岩主要为圆环状、结核状和结壳状。X射线衍射分析显示,这3件碳酸盐岩主要由黏土矿物、陆源碎屑(石英、长石)和碳酸盐矿物(高镁方解石和铁白云石)组成;碳氧同位素分析表明,结核状和结壳状碳酸盐岩具有极负的δ13C (分别为-32.83‰和-38.01‰PDB)和正的δ18O (分别为+2.19‰和+2.96‰PDB),不同于正常沉积的海相碳酸盐岩,甲烷厌氧氧化过程控制了这些碳酸盐岩的形成。碳酸盐岩为甲烷成因,记录了南海东北部海底富含甲烷的冷泉活动历史。Abstract: Three authigenic carbonates are retrieved from the seafloor of northeastern South China Sea, showing the morphologies of doughnut, concretion and crust. X-ray results show that carbonates mainly consist of clay minerals, terrigenous constituents (quartz, feldspar), high-Mg calcite, and ankerite. Except the doughnut, the concretion and the crust are characterized by very light δ13C values (-32.83‰PDB and -38.01‰PDB, respectively) and positive values of δ18O (2.19‰PDB and 2.96‰PDB, respectively) in comparison with ‘normal carbonates’. These isotopic compositions of the carbonates suggest that methane participated in the formation of carbonates, due to its anaerobic oxidation. The methane-derived carbonates are the recorders of methane-associated seeping, which is active on the seafloor of northeastern South China Sea in the past.
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Key words:
- carbonates /
- isotopic compositions /
- methane /
- South China Sea
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