Tectonic subsidence characteristics on the northern continental Margin of the South China Sea since Late Miocene

The Late Miocene unconformity T3 at about 11.608 Ma is an important boundary at the post-rifting stage in the northern continental slope of the South China Sea, which separated the underlying thermal subsidence and overlying accelerated subsidence. Based on the tectono-sedimentary analysis, the strata of the accelerated subsidence stage could be classified into three structural layers, the Late Miocene, the Pliocene, and the Quaternary. In this study, the Airy equilibrium model and 1092 simulation locations were used to calculate the tectonic subsidence rate along with the back-stripping technology, which could reveal the characteristics of the burial history during an accelerated subsidence stage. On the whole, since the Late Miocene the tectonic subsidence have played the dominant role in the northern continental slope of the South China Sea, as much as 70%. The centers of the subsidence are located in the Central Depression Belt of the Qiongdongnan Basin, the deep-water areas in the Pearl River Mouth Basin, and the Southwest Taiwan Basin; especially in the Southwest Taiwan Basin, the significant tectonic subsidence rate of the Quaternary could be 190 m·Ma 1. The evolution of the subsidence rate displayed double segment character. From the Late Miocene to Pliocene, the tectonic subsidence rate decreased slightly and the average rate was 70 m·Ma 1; since the Quaternary, the rate had a rapid increase, to as much as 120 m Ma 1. The areas that had the intraday variation of the tectonic subsidence, such as the basin boundary, join belt between upheaval and depression, and the tectonic activity areas with fault and fold could provide the helpful geological setting for the accumulation of gas hydrate.