The formation and evolution of the paleo-Pearl River and its influence on the source of the northern South China sea

Abstract

The paleo-Pearl River has been suggested as one of the major source terrains for the northern South China Sea, which headstreams in the hinterland of the Tibetan Plateau and flows through the South China Block, eventually discharges into the Pearl River Mouth Basin (PRMB) of the South China Sea (SCS). However, the drainage history of the paleo-Pearl River remains a matter of debate. Detrital zircon UPb ages, trace elements, Nd and Sr isotopes and clay minerals from the Eocene to Miocene sediments in the Pearl River Mouth Basin of the South China Sea have been used to investigate the sedimentary provenance and reconstruct the drainage history of the paleo-Pearl River. The Eu/Eu*, La/Sc, La/Co, Th/Sc and Th/Co ratios, the HfLa/Th and La/Sc-Co/Th diagrams, and the chondrite normalized REE patterns of the samples suggested that the Eocene to Miocene sediments were mainly derived from felsic source rock. The Lower Eocene sediments were mainly provided by the intrabasinal uplift regions. The Dong River and Bei River initiated since Upper Eocene supplied large amounts of felsic detritus from the Southern China Coast to Zhu Ⅰ Depression, and then transported sediments into the Zhu Ⅱ depression during the upper Early Oligocene. The Nd and Sr isotopes of the sediments suggested that the Liu River may not provide sediments for the PRMB, however, the Gui River may have made a very small contribution. The Nd and Sr isotopes of the sediments also suggested that the paleo-Pearl River began to extend westward to form Xi River and eventually the Hongshui River in the Late Oligocene. The trace element ratios of the samples also suggested that the Miocene sediments may have received more input from an intermediate rock area, indicating the main provenance switch from the coast of South China to a northern source during this time. This conclusion has been supported by the detrital zircon UPb ages, Nd and Sr isotopes and clay minerals data of the samples, which show that the provenance of the sediments supplied by the paleo-Pearl River had an abrupt shift in the Middle Miocene. The southeastern Tibetan Plateau rapid uplifted and experienced erosion in the Middle Miocene, leading to the progressive headward erosion of the Pearl River system into the continental interior.