Geochemical characteristics and genesis of grapestone in Sinian Dengying Formation in south-eastern Sichuan basin
川东南地区灯影组葡萄石地球化学特征及成因分析

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.