Cenozoic plate reconstruction of Southeast Asia and sequence stratigraphy and tectonics of the Tainan Basin, offshore southwestern Taiwan

Analysis of available data were used to produce a detailed Cenozoic plate reconstruction of the Southeast Asia region. A 3-D computer graphics system was used to manipulate the data, and to test published models of the Cenozoic tectonic evolution of Southeast Asia to determine their consistency with the known geology and the recorded geophysical data. Previous models required modification to produce a new, unique model that is most consistent with the available data. At least two and possibly three stages of extension can be recognized in the South China Sea region. The earliest one, active from the Late Cretaceous to Eocene, involved NW-SE extension. The second one, active from Late Eocene to Early Miocene involved north-south extension. The third stage of extension, which was probably NW-SE, can be dated as post-Oligocene. The first extensional event produced the NE-SW trending proto-South China Sea and a series of sedimentary basins along the South China margin. Following the southeastward extrusion of Indochina, the proto-South China Sea has been mostly consumed at the Palawan Trough. Renewed north-south extension in the South China continental margin started the present-day South China Sea spreading in the Oligocene. The southeastward extrusion of Indochina, blocked by the Sundaland, resulted in the NW-SE opening of the South China Sea Basin in the Early Miocene. Collision of the North Palawan microcontinental block with the West Philippines block stopped the opening of the South China Sea at the end of Early Miocene. In the Pliocene, subduction along the northern Manila Trench placed the North Luzon Arc on a collision path with the East Asia continental margin at Taiwan.; The Tainan Basin is located at the eastern end of the South China continental shelf about 10 km offshore from southwestern Taiwan. About 5000 km of industrial seismic reflection profiles and data from the 17 exploration wells in the Tainan Basin have been made available for this study. The sediment fill in the Tainan Basin is a reflection of the regional geological history. Five major seismic sequences can be recognized that directly related to the opening of the South China Sea. From Early Oligocene to Early Miocene, the Tainan Basin generally deepened to the south with active normal faulting. During the change in spreading direction from N-S to NW-SE in the South China Sea at late Early Miocene, the Tainan Basin experienced a major inversion of the depocenter. The North Luzon Arc began to collide with the South China continental margin along the eastern margin of Taiwan during the Pliocene time. Since then the Tainan Basin has been transformed from a passive margin setting into a foreland setting.