川东南地区灯影组葡萄石地球化学特征及成因分析

长期以来,人们对灯影组葡萄石的成因存在较大的争议。本文对灯影组葡萄石及基岩的地球化学特征进行了详细的对比分析,讨论了灯影组葡萄石的形成环境。灯影组葡萄石与基岩相比,具有较明显的Ce负异常和相对低的稀土总含量,说明了葡萄石并非是和基岩同时沉积而成;葡萄石中Na、K元素含量低而Mn、 Fe含量较高,具有很低的Sr/Ba比值,同时具有碳、氧同位素明显偏负和⁸⁷Sr/⁸⁶Sr值偏高的特点,表明葡萄石是在淡水的作用下形成的。证实了灯影组在沉积过程中有过一次短暂暴露过程,这次沉积间断使灯影组暴露地表接受淡水淋滤,形成了小规模的岩溶现象,为葡萄石的形成创造了条件。这次短暂暴露过程对人们更好地理解葡萄石的成因及灯影组中部储层的形成有重要的意义。

Geochemical characteristics and genesis of grapestone in Sinian Dengying Formation in south-eastern Sichuan basin

For a long time, there is a dispute about the genesis of the grapestone in Dengying Formation. The geochemical characteristics of grapestone and basement rock are analyzed and compared in detail and the genetic environments of the grapestone are discussed in this article. Compared with basement rock, there are relatively obvious Ce negative anomaly and relatively low total content of rare-earth elements in the grapestone, which indicates that the grapestone and basement rock were not deposited simultaneously. There are low content of Na , K, high content of Mn, Fe, low content of Sr/Ba ratio, high content of ⁸⁷Sr/⁸⁷Sr ratio and both carbon and oxygen isotope negative anomaly, which illustrates that the grapestone was formed under fresh water. It can be corroborated that there was a brief exposure during the deposition of Dengying Formation which made Dengying Formation expose to earth's face, leached by meteoric water and emerge small-scale karst to create the conditions for the genesis of the grapestone. The brief exposure has very important significance for a better understanding of the genesis of the grapestone and the development of the reservoirs in the middle of Denying Formation.