Facies Characteristics and Sedimentary Evolution Model of the 7thMember of Dameigou Formation in Yuqia Area, North Qaidam Basin

In recent years, shale oil in China's continental basins has become a hot spot and difficulty in oil and gas exploration and development. Taking the seventh member of the Middle Jurassic Dameigou Formation in the Yuka area on the northern margin of the Qaidam Basin as the research object, the author studied the formation of the seventh member of the Dameigou Formation through core, ordinary thin-section observation, organic geochemistry, and X-ray diffraction experiments. The lithofacies characteristics and sedimentary evolution model provide a theoretical basis for the development and distribution of high-quality source rocks. The research results show that there are 6 types of lithofacies developed in this section, which can be divided into 3 depositional stages vertically. Stage A is a delta front and shallow lake environment in a warm and humid climate, where organic-poor massive clay and siliceous mudstone facies are developed, and strong terrigenous input leads to oxygen-enriched water bodies, which makes the shale oil and gas potential in this stage poor, and the average TOC is 0.79%; stage B is a semi-deep lake-deep lake environment under tectonic subsidence, where organic-rich massive clayey mudstone facies develops, and the reduction environment of deep lake provides good preservation conditions for organic matter, making shale oil and gas potential high in this stage. The average TOC is 4.16%; Stage C is a semi-deep lake-deep lake environment controlled by arid climate and tectonic subsidence, where organic-rich lamellar calcareous, clay-rich calcareous, and clayey mudstone facies develop, and the lamellar salinization stratification provides Good organic matter preservation conditions are provided, and adaptive algal blooms provide high productivity, making the shale oil and gas potential the highest at this stage, with an average TOC of 5.03%.