Abstract: Basins and Basin Evolution, Offshore Eastern Vietnam, 10° N Lat. to 16° N Lat.

Joel S. Watkins, Sugiarta Wirasantosa

The eastern margin of Vietnam between 10° N and 16° N includes all or part of 5 basins. From north to south, these are the South Hainan, Tam Ky, Quangda, East Mekong, and Northeast Conson basins. The South Hainan basin lies on the South China block north of the Red River fault extension, whereas the other basins lie on the Indochina block south of the Red River fault. The South Hainan basin appears to have formed during the Paleocene-Eocene rifting episode that formed the Pearl River Mouth and other basins of the northern South China Sea. This episode culminated in the N-S opening of the South China Sea during the Oligocene. The N-S trending Tam Ky and Quangda basins appear to have formed through a combination of N-S right-lateral strikeslip and NW-SE extension immediately p eceding the NW-SE Early-to-Middle Miocene phase of seafloor spreading of the western South China Sea. The Tam Ky basin was formed by predominately strikeslip movement with only modest E-W extension whereas the Quangda basin was formed predominantly by extension. The East Mekong and Northeast Conson basins trend NE-SW and appear to be early rift stage basins associated with the southwestward migration of the South China Sea spreading center prior to 15 Ma.

The Quangda and Tam Ky basins parallel older N-S fault and fracture trends onshore eastern Vietnam, whereas the East Mekong and Northeast Conson basins parallel older NE-SW fault and fracture trends onshore in southern Vietnam. This relationship suggests that these four basins developed along preexisting zones of lithospheric weakness in a common stress field. South Hainan basin fault trends require a different stress field.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994