Tectonostratigraphic Evolution of the South China Sea

Abstract

The present configuration of the South China Sea (SCS) is the result of a complex succession of tectonic processes involving rifting, subduction and collision phases. Magnetic anomaly data suggest that the opening of the SCS occurred from North to South in several phases between 32 Ma and 15.5 Ma. A major collisional episode along the NW Borneo margin took place around the Mid-Miocene and is recorded onshore and offshore by a succession of major unconformities. We have used seismic reflection and well data along the Vietnamese margin of the SCS (Phu Khanh and Nam Con Son basins) as well as published data along the southern and eastern margins of the SCS to design a new tectonostratigraphic model of the region. Five seismic stratigraphic megasequences and bounding unconformities have been identified on the Vietnamese side of the SCS and interpreted in terms of depositional environments. Each of these seismic stratigraphic intervals records a tectonic phase related to the opening of the SCS and is not related to collisional events recorded along the NW Borneo margin. This tectonostratigraphic model involves a sag phase that postdates the main rifting phase and predates the propagating break-up of the SCS. It explains several critical observations similar to those intensely debated in Atlantic-type passive margins: 1/ the presence of a thick shallow marine sequence (M2) overlying thinned continental crust, 2/ the diachronous nature of the break-up unconformity, 3/ the rare occurrence of high-angle faults and well-defined tilted blocks in seismic sections and 4/ mantle exhumation observed in the Phu Khanh Basin. Finally, this tectonostratigraphic model opens new perspectives for the hydrocarbon exploration of the SCS. Each of the tectonic phases is characterised by a dominant play type and underpins play-based exploration.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015