REE GEOCHEMICAL CHARACTERISTICS IN THE NORTHERN SOUTH CHINA SEA SINCE THE OLIGOCENE

The average abundance of REE in samples obtained from the Pearl River Mouth basin in the northern South China Sea (SCS) is 150.62×10^-6, close to the Loess record, reflecting a continental origin. Negative anomaly of Eu is obvious in these samples, with δEu values gradually decreasing from nearcoast to off-shore boreholes, which displays a stepwise diffusion of terrigenous matter from north to south. The REE geochemistry characteristics from the Pearl River Mouth basin show high consistency in their variation trends with those from ODP Site 1148. Stepwise tectonic movements occurring since the end of Oligocene caused major geochemical discontinuities mainly at 13.8 Ma, 16 Ma, 23.8 Ma, and 32 Ma, the most impressive of which at 23.8 Ma has changed the sediment supply in the northern SCS and enlarged differentiations of the sediment composition between various boreholes. Therefore, this 23.8 Ma event exerted a profound influence on the sedimentary environment and sedimentary fill characteristics in the northern SCS.