THE STRUCTURAL FEATURES OF XISHA TROUGH BASIN

The Xisha Trough Basin, located on the continental slope of the northern South China Sea, is a Cenozoic deepwater basin. The sediment fill in the basin is about 1500~8000m in thickness, and becomes thinner from the center towards north and south. The sediments show a zonal distribution pattern in north-south direction. In seismic profiles, there is double-layer structure, of which the upper is formed with subsidence and the lower with rifting. The structures formed in the rifting stage were mainly of "Domino-style of half-graben", a series of half-graben controlled by major faults on one side (F1, F2, F3, F4, F5). The basin has experienced two stages of evolution:the first stage underwent rifting through Paleocene-Oligocene and filled with lacustrine deposits, the second stage underwent subsidence through Miocene-Quaternary and filled shallow or bathyal sediments.