Impact of paleosalinity, dilution, redox, and paleoproductivity on organic matter enrichment in a saline lacustrine rift basin: A case study of paleogene organic-rich shale in dongpu depression, bohai bay basin, eastern China

Saline, lacustrine rift basins (SLRBs) can contain very productive shale oil plays, in which “sweet spots” are closely related to organic-rich shale intervals. However, organic matter enrichment in the shale intervals within SLRBs and the controlling factors have not been well-explored in past research. In this study, well Pu6-65 within the Dongpu Depression of the Bohai Bay Basin was systematically cored and analyzed for basic geochemistry, trace elements, clay mineral content, and original total organic carbon (TOC) to understand the relationships between TOC and paleosalinity, dilution, redox, and paleoproductivity. Results indicate that the Es3U and Es3L (upper and lower third member of the Paleogene Shahejie Formation) in the Dongpu Depression mainly developed in a brackish and weak anoxic to anoxic depositional environment, in which surface water featured relatively low paleoproductivity. In comparison, the dilution degree is stronger in the Es3L shale. Paleosalinity, dilution, redox, and paleoprodu...