Characteristics and Geological Significance of Rare Earth Elements of the Second Member of Funing Formation in Gaoyou Sag,Subei Basin

The second member of the Funing Formation is the main source rock group and the focus of exploration in the Subei Basin. In recent years, the successful production of shale oil horizontal wells, such as HY1 in Gaoyou Sag, has shown great exploration potential for shale oil. However, current research on the sedimentation rate of the second member of the Funing Formation shale, whether the second member of the Funing Formation shale was influenced by diagenesis in later stages, the structural background, protolith properties, and provenance direction of the source area of the second member are relatively weak. This seriously constrains the further exploration of shale oil in the second member of the Funing Formation. In this study, the key shale of the second member of the Funing Formation, Gaoyou Sag, in the Subei Basin, was studied. The geochemical characteristics of rare earth elements were examined, and their significance in the diagenesis and sedimentary environment was discussed, along with the provenance characteristics of the second-member shale of the Funing Formation in the Subei Basin. The results show that the light rare earth elements are abundant, while the heavy rare earth elements are insufficient in the second member of the Funing Formation. The distribution curve is evident to the right; the negative Eu anomaly is evident, and the positive Ce anomaly is weak. The sedimentary environment of the second member of Funing Formation in Gaoyou Sag of the Subei Basin is a relatively stable anoxic reduction environment; the longitudinal REDOX conditions do not change significantly, and the sedimentation rate gradually decreases from bottom to top. Moreover, the tectonic background of the second member of the Funing Formation is an active continental margin related to a continental island arc. The parent rock is a mixture of sedimentary rocks and granite formed from felsic/basic materials in the continental crust. Its provenance mainly originates from the joint contribution of the Sulu orogenic belt in the northwest of the Subei Basin, the Dabie Mountain orogenic belt in the west, and the Zhangba Ridge uplift in the southwest.