South China Sea - Geology

Geology

The sea lies above a drowned continental shelf; during recent ice ages global sea level was hundreds of metres lower, and Borneo was part of the Asian mainland.

The South China Sea opened after around 45 million years ago when the Dangerous Grounds (Reed Tablemount) were rifted away from southern China. Extension culminated in seafloor spreading around 30 million years ago, a process that propagated to the SW resulting in the V-shaped basin we see today. Extension ceased around 17 million years ago. Arguments have continued about the role of tectonic extrusion in forming the basin. Paul Tapponnier and colleagues have argued that as India collides with Asia it pushes Indochina to the SE. The relative shear between Indochina and China caused the South China Sea to open. This view is disputed by geologists who do not consider Indochina to have moved far relative to mainland Asia. Recent marine geophysical studies by Peter Clift has shown that the Red River Fault was active and causing basin formation at least by 37 million years ago in the NW South China Sea, consistent with extrusion playing a part in the formation of the sea. Since opening the South China Sea has been the repository of large sediment volumes delivered by the Mekong River, Red River and Pearl River. Several of these deltas are rich in oil and gas deposits.