Thermal subsidence and sedimentary processes in the South China Sea Basin

We coupled analysis of regional reflection seismic data with core data from International Ocean Discovery Program (IODP) Expedition 349 and found differences in both depositional features and calculated subsidence between the East and Southwest Subbasins. We calculated the original (decompacted) thicknesses of sediment for different time slices. The depositional features of the basin show that the sedimentation is controlled by both climate and tectonics. Decoupling of sedimentation rates and fluxes is often observed between the continental margin and deep basin. An abrupt increase in sedimentation rates since the Pliocene suggests that glacial-interglacial climate variability impacted erosion rates. The sedimentation rate peaked during the Pliocene in the Southwest Subbasin, but peaked during the Quaternary in the East Subbasin, showing strong influence of surrounding tectonic events, such as the buildup of Taiwan Orogen, on erosion rates. We examine thermal subsidence of the two subbasins by fitting the isostatically balanced basement depths from the seismic profiles with the half space cooling model. The estimated thermal diffusivity of the lithosphere in the Southwest Subbasin is much higher than in the East Subbasin. These contrasting observations suggest that lithospheric rock compositions may contribute to different tectonic subsidence curves between the East and the Southwest Subbasins.