Sedimentary source area and paleoenvironmental reconstruction since late Miocene in the southern South China Sea

The South China Sea (SCS) is the largest marginal sea of the Western Pacific and is located in the low-latitude of the world. The Site 1143 of the Ocean Drilling Program (ODP) Leg 184 in the southern South China Sea provides continuous sedimentary records from late Miocene to Holocene. To better understand the evolution of climate, paleo-productivity and the source of sediments during the 6.0-0.8 Ma period in the southern South China Sea, 36 sediment core samples (45.77-251.36 mcd) were collected and analyzed for major and trace elements. The results show that the provenance area of sediments is in a high intensity of chemical weathering at 6.0-5.2 Ma, and the terrestrial materials input increases due to the combined effect of the Vietnam tectonic uplift and the enhancement of the East Asian summer monsoon, while the precipitation driven by the strengthened East Asian summer monsoon also results in a high paleo-productivity. From 5.2 to 1.7 Ma, the climate in the provenance of sediment has cooled, resulting in a weakening of the marine biological activities and lower marine paleo-productivity. The decrease of Rb/Sr and MgO/CaO and an extremely high Al flux at 3.5-2.5 Ma suggests an erosional response to both the uplift of the Tibetan Plateau and the strengthening of the East Asian summer monsoon. At 6.0-5.2 Ma, the lower content of Mo and the ratios of Ni/Co and Mo/TOC indicate that sediments were deposited in an oxidizing restricted marine environment. During 1.4-1.0 Ma, the lower V/(V + Ni) ratio and the increase of the content of Mo and Mo/TOC reflect a suboxic environment and the gradually increased water cycle in the basin. The tectonic environment of the provenance area might be continental island arc, and granite is a major type of the source rock. The potential provenance area of sediments at Site 1143 might be similar to that of the Mekong River.