Abstract: Tectonics of Cenozoic Sedimentary Basins in Southeast Asia

Claude Rangin

In southeast Asia, marginal basins, floored with oceanic crust, and shelf basins, developed on the continental basement of Sundaland, were created during two main extensional events in the Cenozoic. First, an Eocene-early Oligocene northeast-southwest-directed

extensional event prevailed, controlling spreading in the Celebes Sea, rifting in the South China Sea, and shelf basin development, the latter mainly in Borneo and the Java Sea. A late Oligocene-early Miocene north-south-directed extension period was responsible for spreading in the South China Sea and the development of large shelf basins in Malaysia, western Indonesia, and Vietnam. This major change within the regional tectonic extension field in southeast Asia is also marked by a widespread middle Oligocene unconformity. We suggest it is directly linked to changes of trench-pull forces along the Eurasian plate boundary at 30 Ma, the time for incipient docking of the Philippine Sea plate along the eastern margin of Eurasia. We conclude that during the Eocene-early Oligocene, opening of both the Celebes Sea and the coeval shelf basins took place with mismatch basins forced along northwest-southeast strike-slip shear zones as a result of Indochina extrusion and trench pull along the free boundary into the east. To the contrary, after docking of the Philippine Sea plate, trench-pull forces were only present along the Sunda trench, and the South China Sea as well as the shelf basins of western Sundaland were induced by north-south extension.