潜江凹陷潜江组盐湖地层演化与层序发育特征

Evolution and Development of Sequence Stratigraphy Saline Qianjiang Formation in Qianjiang Depression

结合盐湖层序地层分析 ,在系统测试了潜江凹陷潜江组碳、氧同位素后 ,对其演化规律与层序地层的关系进行了探讨 ,研究结果表明 :潜江组内δ13 C和δ18O值的变化范围分别是 -7.3 7‰～ 2 .3 5‰和 -6.42‰～ 0 .2 3‰ (PDB)。在低位体系域的初期和高位体系域的末期 ,由于湖水范围较小 ,这时如果降雨量小于蒸发量就会有盐岩的沉积 ,所以其碳、氧同位素的值偏大 ;而在水进体系域时期 ,由于湖平面上升 ,湖水的注入量大于蒸发量 ,所以这一时期没有盐岩的沉积 ,碳、氧同位素的值也偏低。然而在对潜江组的潜四段进行研究时 ,却发现碳、氧同位素的分布不具上述规律。在潜四段盐岩不仅分布于低位体系域的初期和高位体系域的末期 ,而且在水进体系域中也可见盐岩。

Combined with the analysis of the sequence stratigraphy of saline lake, the stable isotope δ 13 C, δ 18 O values of Qianjiang Formation in Qianjiang Depression are systematically measured. The relations of their evolution to the sequence stratigraphy are then discussed. The research results indicate that the δ 13 C values and δ 18 O values range from -0.737%～0.235% and -0.642%～0.023% (PDB) respectively. At the initial stage of the lowstand system and the late stage of highstand system the area of the lake was small. Meanwhile, if the evaporation excessed the rainfall, the salt would be deposited. Therefore the δ 13 C and δ 18 O values are higher. During the transgressive systems tracts, because the lake-level ascended and there was more water flowing into the lake, none salt were deposited, resulting in lower δ 13 C and δ 18 O values. Nevertheless the values of δ 13 C and δ 18 O of the 4th member of Qianjiang Formation donot comply with about rules. The salt was deposited not only at the initial stage of the lowstand systems tracts and the late stage of the highstand systems tracts, but also in the transgressive systems tracts. Another salt model is thus considered.