CENOZOIC SUBSIDENCE HISTORY OF THE QIONGDONGNAN AND YINGGEHAI BASINS, NORTHERN SOUTH CHINA SEA: IMPLICATIONS FOR THE BASIN DYNAMICS

Qiongdongnan and Yinggehai Basins are important basins in northern continental margin of the South China Sea. The Cenozoic subsidence history of these two basins recorded their subsidence and filling processes, which is significant to understand the evolution of the basins, as well as the northern continental margin of the South China Sea. We studied the basins subsidence characteristics through 1-D, 2-D, and holistic subsidence first. Next, we contrasted basins subsidence characteristics with the evolution of some spectacular geological processes occurred in the South China Sea and its adjacent areas. The results indicate that the holistic subsidence of the Qiongdongnan Basin can be separated into three episodes: the first one was the Eocene with the mean total subsidence rate of 20 m/Ma; the second one was from the Oligocene to the Middle Miocene with the mean total subsidence rate of 205 m/Ma; and the last episode was from the Late Miocene to the Quaternary with the mean total subsidence rate of 177 m/Ma. The holistic basin subsidence process, from the Late Oligocene to the Quaternary, can also be divided into three episodes in the Yingggehai Basin: the first one was composed of the Late Oligocene and the Early Miocene with the mean total subsidence of 381 m/Ma; the second episode was from the Middle Miocene to the Late Miocene with the mean total subsidence rate of 266 m/Ma; and the third episode included the Pliocene and the Quaternary with the mean total subsidence rate of 311 m/Ma. Moreover, the subsidence variation between these two basins is obvious. The dynamic difference between the two basins is the main controlling factor for the subsidence variation between the two basins. In the Qiongdongnan Basin, the subsidence characteristics was mainly controlled by the mantle material flow under the South China Block in the Eocene, and the spreading of the South China Sea from the Oligocene to the Miocene. In the Yinggehai Basin, the subsidence characteristics was chiefly controlled by the coupling between the uplift of the Tibetan Plateau and the strike-slip of the Red River Fault before the Early Miocene, but only the effect of the strike-slip of the Red River Fault from the Middle Miocene to the Late Miocene. Since the Pliocene, the subsidence characteristics of both basins was principally controlled by the dextral strike-slip of the Red River Fault. The major faults contributed to the temporal-spatial variation of the subsidence in the same basin.