Restoration and Evolution of the Paleogene (E1f2) Shale Sedimentary Environment in the Subei Basin, China

Restoring the sedimentary environment of paleolakes is of great significance to the formation of laminated calcareous shale deposited in paleolakes and the prediction of shale oil reservoir distribution. This article focuses on the second section shale of the Paleogene in the Funing Formation in the Gaoyou Sag, Subei Basin, China, and uses X-ray fluorescence diffraction technology and core lithology analysis methods to obtain the content datum of major and trace elements such as Sr, Cu, Ba, Ga, V, and Ni in shale at different depths. Based on the empirical values of Sr/Cu, Sr/Ba, V/(V + Ni), and total organic carbon, paleoenvironmental evolution of the continental shale was determined and studied, including the changes in paleoclimate temperature, paleosalinity, paleowater depth, and strong or weak redox intensity. The research results indicate that the sedimentary environment of the paleolake in the Paleogene Funing Formation, second section, in the Gaoyou Sag is mainly characterized by a dry and hot climate; the salinity of paleolake water is that of stable brackish water, and the entire sedimentary period of the Funing Formation, second section, is dominated by a reduction environment, which is conducive to the preservation of sedimentary organic matter. The frequent changes in the depth of sedimentary water and the alternating dry and hot climate are the main reasons for the development of laminated calcareous shale in the second section of the Paleogene Funing Formation of the Gaoyou Sag and have also contributed to the abundant commercial resources of laminated calcareous shale oil in the second section of the Funing Formation.