Geochemical changes of the terrigenous sediments in the southern South China Sea and their paleoenvironmental implications during the last 31 ky

Abstract

Fifty-six subsamples of the 86GC core were collected from the southern South China Sea continental slope. Major and trace elements, including rare earth ele- ments (REEs), of detrital matters in these sediments were measured. The patterns of chondrite normalized REEs and the discrimination plots based on major and trace elements, respectively, indicate that the terrigenous sediments around this area had been supplied with one dominating prove- nience during the last 31 ky. The co-operation of sea level changes with the East Asian winter monsoon-related rain- fall and sea water circulations should be the main mecha- nism causing the geochemical characteristics variations. Higher ratios of Al/Ti and some other elements to Ti, except P/Ti and Mn/Ti, are present during the last glacial sea-level low stand and the winter monsoon periods owing to increased fluvial input of material with low Ti content from the Mekong River, followed by strengthened chemi- cal weathering intensity, causing higher Al2O3 and most other elements contents. The elemental patterns imply general warm and very humid climate in the tropical areas during the last glacial times; however, the climate since the last deglaciation was very changeable, especially during the Holocene. Even so, it can still be certain that the cli- mate during the early part (29-24 ky B.P.) of the last glacial maximum was much worse than during other stages. Additionally, it is very likely that the 8 k cold event and the Younger Dryas event have been impressed in the geochemical record of this core.