High resolution variability of clay mineral assemblages in the northern South China Sea during the Mid-Pleistocene Transition and its paleoceanographic significance

Distribution of clay minerals in modern oceans has been widely used to reconstruct paleoclimates. Their distribution is controlled primarily by the rock type and climate in their source regions and by the transport agents and directions. Temporal changes of clay mineral contents in marine sediment cores could therefore provide useful information on both paleoclimates on adjacent lands and past oceanic circulation patterns. The clay-mineral composition of the Mid-Pleistocene Transition sediments (1000~780 ka) at the Ocean Drilling program (ODP) Site 1144 on the northern slope of South China Sea (SCS) consists mainly of smectite (20~60%) and illite (23~45%), with associated chlorite (10~25%) and kaolinite (4~12%). Hydrodynamic and mineralogical studies indicate that illite and chlorite sources were mainly Taiwan and Pearl River, that smectite originated predominantly from the Luzon volcanic arc, and that kaolinite was primarily derived from the Pearl River. Clay mineral assemblages indicate strong glacial-interglacial cyclicity, with high illite, chlorite, and kaolinite contents during glacials and high smectite content during interglacials. The ratio of smectite/(illite+ chlorite+ kaolinite) was adopted as a proxy for the sea level change. Wavelet analysis and filtering of the proxy for the sea level change reveals the filtering signal of 20 kyr precession cycles experienced a decrease after 900 ka. It may suggest that the influence of tropical ocean for the northern SCS has weakened after MPT. Clay mineral results show that the sea level change has undergone a great variation after MPT, and it caused the transportation mechanism of terrigenous particles changing greatly. There are more terrigenous input during glacial periods on the northern slope of SCS as the extent of sea level change increased which result in the strengthening of shelf reworking on northern slope of SCS.