University of Nanjing, China

The Song Hong-Yinggehai (SH-Y) and Qiongdongnan (Qi) basins together form one of the largest Cenozoic sedimentary basins in SE Asia. Here we present new records based on the analysis of seismic data, which we compare to geochemical data derived from cores from Ocean Drilling Program (ODP) Site 1148 in order to derive proxies for continental weathering and thus constrain summer monsoon intensity. The SH-Y Basin started opening during the Late Paleocene-Eocene. Two inversion phases are recognized to have occurred at c. 34 Ma and c. 15 Ma. The Qi Basin developed on the northern, rifted margin of South China Sea, within which a large canyon developed in a NE-SW direction. Geochemical and mineralogical data show that chemical weathering has gradually decreased in SE Asia after c. 25 Ma, whereas physical erosion became stronger, especially after c. 12 Ma. Summer monsoon intensification drove periods of faster erosion after 3-4 Ma and from 10-15 Ma, although the initial pulse of eroded sediment at 29.5-21 Ma was probably triggered by tectonic uplift because this precedes monsoon intensification at c. 22 Ma. Clay mineralogy indicates more physical erosion together with high sedimentation rates after c. 12 Ma suggesting a period of strong summer monsoon in the Mid-Miocene.