川东南地区石牛栏组碳、氧、锶同位素特征及其地质意义

The C,O,Sr Isotope Composition of Shiniulan Formation in Southeast Area of Sichuan and Its Geologic Impolications

前人对川东南地区石牛栏组地层已进行了大量的研究工作,但有关同位素地球化学方面的研究尚未见报道。本区石牛栏组沉积成因碳酸盐岩的碳同位素值与前人的研究结果一致,而氧同位素值则有所偏低;白云岩δ13C值低,δ18O值高,反映受成岩环境的影响较明显;裂缝中方解石的碳、氧同位素组成分布于两个不同的区间,说明不同期次裂缝充填物形成时的流体性质发生了明显的变化;沉积成因碳酸盐岩具异常低的锶同位素值,与前人研究结果有明显的差异,推测是受贫87Sr同位素的成岩流体的影响;晚期裂缝充填物锶同位素比值较高,也表明它们受到了地表淡水的影响。

A lot of researches have been accomplished in the Shiniulan Formation of southeast area of sichuan, but few were about isotope geochemistry. Obtained data of carbon isotope of the Shiniulan formation is similar with those of the former researches in the Sichuan basin and around, while the oxygen isotope data is lower than those of others. Dolomite has low δ^13C value and high δ^18O value, reflecting the significant effects of its diagenesis environment; the δ^13C and δ^18O values of calcite in fractures distribute in two different spans indicates the different characteristics of filled liquids in two periods of fracturing; The ^87 Sr/^86 Sr ratio of sedimentary carbonate is very low and is obviously different from those of the former researches, and this may be caused by low ^87 Sr diagenetic fluids; calcite in the late fractures has relatively high value of ^87 Sr/^86 Sr reflects that calcite in the late fractures is affected by fresh water from the ground.