A multi-faceted approach to determine the provenance of Eocene converging deltas, Dongying Depression, Bohai Bay Basin (E China)

Abstract

The middle interval of the 3rd member of the Shahejie Formation (Es3m) of the Dongying Depression accumulated as part of a system of converging deltas derived from multiple source regions. These complex deposits that are targets of oil/gas exploration and development in eastern China have yet to be studied at the level of detail necessary to elucidate their origin and sedimentary evolution. This paper relies upon a multi-faceted investigation of the Es3m depositional system that includes analysis of clastic compositions, heavy mineral assemblages and mineral ratios, and clay mineralogy to illuminate the provenance of Es3m deposits. Compositional data is obtained by analysis of logs and core material. Our results reveal that Es3m deposits were derived from source regions to northeast (Qingtuozi Uplift and Chenjiazhuang Uplift) and southeast (Weibei Uplift and Guangrao Uplift) of the Dongying Depression. Each source region shed sediment to the study area that accumulated in distributary channels, interdistributary swamps, natural levees, mouth bars, underwater distributary channels, sand sheets and underwater distributary interchannel regions. Moreover, lacustrine shore and semi-deep lacustrine deposits that include turbidites are recognized in the studied succession. The separate deltas appear to have converged approximately halfway through the depositional history of the Es3m Formation. Convergence continued in association with delta progradation, forming overlapping sand bodies that are targets of hydrocarbon exploration.