Abstract:  Based on the analysis of major and trace elements in source rock samples of the Paleogene Shahejie Formation in the Dongpu sag, the paleoredox conditions, paleoproductivity level and limitations of paleo-water body during the formation of high-quality source rock of the Shahejie Formation in the Dongpu sag were studied, and the development model of high-quality source rock of Shahejie Formation was discussed. The results show that the development of high-quality source rocks in the third member of Shahejie Formation in the north of Dongpu sag belongs to the model of“stratified sedimentation of deep-water narrow basin water body”. The water body is mainly brackish-super-brackish water, which has strong limitations and deep salinity stratification, which results in stable anoxic conditions of bottom water and is conducive to the preservation of organic matter. According to the analysis of major and trace elements and the reduction of paleoproductivity, the surface layer of Sha 3 member is rich in oxygen, and a large amount of organic matter is developed. After biological death, organic matter 1flocculates, adsorbs on the surface of ferromanganese oxide at the redox interface, and settles to the bottom, and the bottom water is anoxic to reductive, which is suitable for preserving organic properties. The development of high-quality source rocks in the third member of Shahejie Formation in the south of Dongpu sag belongs to the model of“shallow wide basin and basin anoxic deposition”. The lake water body is fresh water, and its limitation is very weak. It belongs to open water area. Because surface rivers and floods bring a lot of nutrients, surface water body has high paleoproductivity, lacking of oxygen-deficient preservation conditions, and consumes more organic matter in biochemical stage. However, weak reducing water body can also be developed locally, thus forming high-quality hydrocarbon source rocks.

Key words: Dongpu sag, Paleogene, source rocks, redox, paleoproductivity, preservation conditions, development model