南海北部冷泉碳酸盐岩和石化微生物细菌及地质意义

Seep Carbonate and Preserved Bacteria Fossils in the Northern of the South China Sea and their Geological Implications

通过对2002年广州海洋地质调查局在南海北部海域拖网采集的碳酸盐岩样品进行岩石、矿物、微量元素和同位素特征的研究,证实在南海水合物远景区发育有冷泉碳酸盐岩。冷泉碳酸盐岩形态类似于烟囱,主要由方解石、伊利石、石英、黄铁矿和一种未知的矿物组成。保存了很可能是石化的甲烷氧化和硫酸盐还原细菌。碳酸盐岩矿物的δ13CPDB为-51.24‰--51.757‰。碳酸盐岩矿物的页岩标准化稀土元素配分模式具无Ce和Eu异常、微弱的轻稀土亏损和中稀土富集特征,表明形成于还原的缺氧环境,显示了冷泉碳酸盐岩的特征,指示在南海北部水合物远景分布区内冷泉活动的近海底可能发育有水合物。

The carbonate samples described in this paper were collected by Guangzhou Marine Geological Survey in April 2002 from the northern continental slope of the South China Sea using the tow-net samples. Petrology and geochemistry show the chimney-like carbonate is seep carbonate. The chimney-like carbonate possibly preserves MOA/SRB fossils, and consists of calcite, illite, quartz, pyrite, and an unknown mineral. The very light carbon isotopic compositions （-51.24‰～-51. 757‰） of the chimney-like carbonates suggest that their carbon was derived from methane microbial oxidization. The shale-normalized REE patterns of the chimney-like carbonates with characteristics of no of negative Ce and Eu anomalies, slightly LREE depletion and MREE enrichment are significantly different to those of the normal marine algal carbonate. This suggests that the chimney-like carbonates were formed in anaerobic condition. Above characteristics suggest that gas venting has occurred recently on the seafloor in the northeastern continental slopes of the South China Sea.