The unclear understanding of the sedimentary environment and facies of the Baoshi Formation in the Pingbei Area of the Pinghu Slope Belt, Xihu Sag, East China Sea Basin, has restricted the evaluation of the Baoshi Formation reservoirs and source rocks in this area, and hindered the progress in oil and gas exploration. Based on the redefinition of the Baoshi Formation strata, a systematic study of the sedimentary environment and facies of the Baoshi Formation from nine wells in the study area was conducted by integrating paleontology, trace element analysis, core observation, grain size analysis, and logging facies analysis. The types of sedimentary facies in the Baoshi Formation were clarified. The results showed that the Baoshi Formation in the Pingbei Area had low contents of algae and palynomorphs, with hygrophilous fern spores being dominant. A small number of dinoflagellates, calcareous nannofossils, and foraminifera were present. These features indicated that during the deposition of the Baoshi Formation, the environment was a brackish marine-continental transitional setting under predominantly warm and humid climatic conditions. Comprehensive analysis of Sr, Ba, Ni, and V indicated that the Baoshi Formation was deposited under a weakly reducing, suboxic environment. Compared with the Tiantai Slope Belt, more freshwater terrestrial fossils were found in the Pingbei Area, suggesting a relatively restricted transitional sedimentary environment between land and sea. The sedimentary environment and facies varied across different structural zones in the study area. In the Kongqueting Structural Zone, the Baoshi Formation was mainly characterized by deltaic sedimentary facies, primarily consisting of underwater distributary channels, mouth bars, and interdistributary bay microfacies, with limited development of sheet sand bodies. In the Baoyunting and Wuyunting Structural Zones, the Baoshi Formation was deposited in an environment influenced by local seawater, where tidal flat facies and intertidal sand bodies were developed. The intertidal zone mainly contained tidal channels, sandflats, mixed flats, and mud flats as depositional microfacies. In the southern part of the western slope belt, the Tiantai Slope Belt developed thick mudstone layers, suggesting restricted marine deposition with a relatively limited spatial distribution.
Sedimentary environment and facies types of Eocene Baoshi Formation in Pingbei Area, Pinghu Slope Belt, Xihu Sag, East China Sea Basin
2026 03/11
