Oligocene and Late Miocene-Pleistocene Elemental Records of Sedimentary Provenance, Basin Evolution, Chemical Weathering and Depositional Environment from the Northern South China Sea

Abstract

The elemental records of the sediments from two IODP cores, U1501C (Oligocene and Late Miocene-Pliocene) and U1499A (Pliocene to Pleistocene) in the Northern South China Sea have been studied here to understand the variability in the sedimentary provenance and depositional environment, which are impacted by the tectonic and East Asian monsoon evolution through time. The major oxides and REE abundances indicate the sources of sediment influx to be significantly from the South China, North and North eastern parts of SCS since ~ 33 Ma, and prominent contributions from Pearl River, Hainan Island and Taiwanese rivers since ~8.3 Ma. The depositional redox is corroborated by the Ce anomaly and trace element proxies such as U/Th, V/Cr, V/(V + Ni), and Ni/Co. The chemical weathering intensity, evidenced by the Chemical Index of Alteration and major elements (Ca/Ti, Na/Ti, Al/K, Al/Ti, AL/Na), and La/Sm ratios, was observed to be low. Early Oligocene witnessed the deposition of littoral sediments, caused by the initial rifting and spreading in SCS. During the late Miocene (~ 8.3 Ma), sedimentation was influenced by the prevailing arid climate and intensification of East Asian Winter monsoon (EAWM). Since Pliocene–Pleistocene (~ 5.3 Ma−0.01 Ma), the sediment deposition remained unaffected by tectonism, but was majorly influenced by the intensification of EAWM and the glacial-interglacial cycles.