Formation environment and organic matter enrichment mechanism of high-quality source rocks in the Buqu Formation in the Shenglihe area,northern Qiangtang basin
The Qiangtang basin is the Mesozoic marine sedimentary basin with the lowest degree of oil and gas exploration in the new land area,and its main source rocks have not been clearly understood.In this paper,the organic geochemistry and element geochemistry of the source rocks of the Middle Jurassic Buqu Formation in Shenglhe area have been systematically studied,and the formation environment and organic matter enrichment mechanism of the source rocks of the Buqu Formation have been discussed.This provides a theoretical basis for predicting the distribution of high-quality source rocks in the Middle Jurassic Buqu Formation in the North Qiangtang depression.The source rocks of the Buqu Formation in Shenglihe area have high abundance of type Ⅱ of organic matter in mature stage.During the Buqu period,the climate was arid and hot,and the primary productivity level of the study area was relatively high,which was a weakly confined basin with shallow water,high salinity and oxygen-poor depositional environment.During the Buqu period,large-scale transgression occurred in the Qiangtang basin,and the study area was adjacent to the central uplift.A large number of nutrients such as phosphorus and iron from terrigenous input and hydrothermal activities were carried into the ocean,resulting in higher primary productivity,which was the main controlling factor for the enrichment of organic matter in high-quality source rocks of the Buqu Formation in the North Qiangtang depression.The study area is located in the minimum oxygen-containing zone of the North Qiangtang depression,which is conducive to the anoxic death and burial of a large number of planktons.Through the analysis of organic matter enrichment mechanism,the coastal shelf slope zone of the North Qiangtang depression may be a favorable area for the distribution of high-quality source rocks in the Middle Jurassic Buqu Formation.
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