Murray, Mychal R.¹, Steven L. Dorobek² 
(1) ChevronTexaco, Houston, TX (2) Texas A&M University, College Station, TX

ABSTRACT: Regional Tectonics, Differential Subsidence, and Sediment Flux to the Southern South China Sea during Pliocene to Recent Time

Upper Miocene to Recent strata in the Nam Con Son, Malay, and West Natuna basins of the southern South China Sea (SCS) were examined using regional multi-channel seismic profiles and well control in order to document both long-term patterns of sediment supply to the region and long-wavelength patterns of differential subsidence. Basins of the southern SCS region initially formed during Paleogene rifting and then underwent inversion during Miocene time. Tectonic activity largely ceased by latest Miocene time. Since Pliocene time, the basins have undergone differential tectonic subsidence, which has affected regional sediment dispersal patterns and paleogeographic evolution. 
Long wavelength (>500 km) differential subsidence occurred across the southern SCS during Pliocene to Recent time. The Nam Con Son Basin (NCSB) subsided more than the Malay and West Natuna basins, which probably reflects both greater Paleogene stretching and less intense Miocene inversion in the NCSB. The more intensely inverted Malay and West Natuna basins were overfilled during Pliocene to Recent time, while the NCSB is still unfilled and continues to receive sediment that bypasses the Malay and West Natuna basins. 
Sediment flux to the southern SCS also has varied during Cenozoic time. Basement highs (e.g., Natuna Arch, Khorat Platform, Con Son High) were local sediment source areas to adjacent underfilled rift depocenters, especially during Paleogene eustatic lowstands. Major SE Asian rivers, such as the Mekong River, became progressively more important sediment suppliers to the southern SCS during Neogene time. The paleo-Mekong Delta began to prograde rapidly into the northern NCSB during late Miocene time and has continued to build southwestward since then. A second dispersal system supplied large volumes of sediment to the southern NCSB beginning in Pliocene time, after the Malay and West Natuna basins were effectively filled and sediments were able to bypass these basins.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.