Neotectonics and Petroleum Accumulation in Offshore Chinese Basins

The Tertiary offshore Chinese basins have been undergoing the most rapid post-rift thermal subsidence since the end of the Miocene (about 5.2 Ma). The thermal subsidence is accompanied by tectonic re-activation. Tectonic movements, i.e. the neotectonics as defined in this paper, modify and control the ultimate petroleum accumulation and distribution in these offshore petroleum-bearing basins. The concept, distinguishing characteristics, genetic mechanism of the neotectonics as well as their controlling role on petroleum accumulation are presented and discussed in this paper. The main manifestations of the neotectonics in the offshore Chinese basins include the formation of unconformities on the end of the Miocene and the Pliocene within the sequences, the shift of sedimentation centers, the strong late-stage fault activities and the active natural earthquakes. The intensity, development mechanism of the neotectonics, and their controls on petroleum accumulation and distribution are quite different in different basins. Some case studies from the Bozhong depression in the Bohai Bay basin, the Yinggehai basin in the South China Sea, and the Xihu depression in the East China Sea basin indicate that the neotectonics plays an important role on late petroleum accumulation in the offshore Chinese basins.