Cenozoic stratigraphy, subsidence, and flexure of the West Taiwan basin of the South China Sea margin
Reporter: Yang-Chen Chen
Abstract
eismic and well data are used to determine the Cenozoic stratigraphic and tectonic development of the northern margin of the South China Sea . West Taiwan basins have evolved from a Palaeogene rift setting through a post-breakup setting into a latest Miocene-Recent foreland basin. Seismic data, together with the subsidence analysis of deep wells, show that during rifting (~58-37Ma), lithospheric extension occurred simultaneously in discrete rift belts. By ~37Ma, the focus of rifting shifted to the present-day continent-ocean boundary of southern Taiwan, which led to continental rupture and initial seafloor spreading of the South China Sea at ~30Ma. Intense rifting during the rift-drift transition (~37-30Ma) may have induced a transient, small- scale mantle convection beneath the rift. The coeval crustal uplift of the previously rifted margin, which led to erosion and development of the breakup unconformity, was most likely caused by the induced convection. Rapid subsidence of the inner margin is interpreted as thermally controlled subsidence, whereas rapid subsidence in the outer shelf of the outer margin was accompanied by fault activity during the interval ~30-21Ma. During the interval ~21-12.5Ma, the entire margin experienced broad thermal subsidence. Itwas not until ~12.5Ma that rifting resumed, being especially active in the Tainan Basin . Rifting ceased at ~6.5Ma due to the orogeny caused by the overthrusting of the Luzon volcanic arc.
The Taiwan orogeny created a foreland basin by loading and flexing the underlying rifted margin. Flexure modeling shows that surface loading is unable to explain the depth of the West Taiwan basin. Other, subsurface or buried loads are required. The depth of the base of the foreland sequence in the northern part of the West Taiwan basin can be explained well by an elastic plate model with an effective elastic thickness, T e , of 13km . In the southern part of the West Taiwan basin, however, the depth of the base of the foreland sequence dips too steeply to be explained by elastic plate models.
References
Lin, A.T., Watts , A.B., Hesselbo, S.P. 2003. Cenozoic stratigraphy and subsidence history of the South China Sea margin in the Taiwan region. Basin Research, 15(4), 453-478.
Lin, A.T., Watts , A.B. 2002. Origin of the West Taiwan Basin by orogenic loading and flexure of a rifted continental margin. Journal of Geophysical Research, 107(B9), 2185, doi: 10.1029/2001JB000669.