塔里木盆地塔中地区晚寒武世—奥陶世碳酸盐岩碳、氧同位素特征

Carbon and oxygen isotope features of Late Cambrian-Ordovician in central Tarim Basin

为了探讨塔里木盆地塔中地区寒武系—奥陶系碳酸盐岩碳同位素变化的原因,对取自塔中地区中3、中4、中12和中13等井的49块碳酸盐岩样品进行了分析,结果显示δ13C值的变化曲线与同时期该区海平面的升降变化一致,说明寒武-奥陶系海相碳酸盐岩的碳同位素变化可能与海平面变化有密切联系。在晚寒武世—早奥陶世晚期为一海退期,有机质产率及有机碳埋藏速率的下降导致碳酸盐岩δ13C值的降低;而在早奥陶世晚期—中奥陶世为一海侵期,有机质产率及有机碳埋藏速率的增加导致了碳酸盐岩1δ3C值的增高;晚寒武世—早奥陶世海水中的硫酸盐含量高,硫酸盐细菌的还原作用使有机质氧化,从而导致碳酸盐岩δ13C值降低。

In order to discuss variation causes of Late Cambrian-Ordovician carbonate rock isotope in central Tarim Basin, 49 carbonate rock samples obtained from Well Ta 3, 4, 12 and 13 are analyzed. The results show that, variation curve of δ^13C value is same with up and down variation of sea level, hence indicating that its variation is correlated with sea level variation. Late Cambrian-Early Ordovician is in the period of regression, production ratio of organic matter and buried ration of organic matter declined will result in declining of carbonate rock δ^13C value, while early Ordovician-middle Ordovician is incursion period, the increasing of them results in the increasing of carbonate rock δ^13C value. In addition, sea water contains sulphate with high content in Late Cambrian-Ordovician period. Sulphate bacterium deoxygen- ation can lead organic matter to oxidate, thereby resulting in declining of carbonate rock δ^13C value.