Rapid reorganization of the Pearl River network driven by spreading of the South China Sea at around 32 Ma

Provenance analyses on sediments from depositional sinks have provided valuable information about the birth of the Pearl River, a key event in the landscape history of South China. However, uncertainty remains due to the difficulty in clearly identifying the source regions by geochemical or geochronological approaches, giving rise to disputes on the driving mechanisms underlying river network evolution. Here we combined pollen and grain-size analyses of terrigenous sediments from International Ocean Discovery Program site U1501 to further constrain the timing and pattern of the Pearl River network evolution during the late Eocene and Oligocene. The results reveal a sharp, synchronous transition at similar to 32 Ma in both proxies. The sudden occurrence of the rainforest coniferous pollen Dacrydium and increased abundances of the alpine coniferous pollen Abies/Picea indicate a new mountainous source region stretching across the tropical-subtropical ecotone after 31.5 Ma. The simultaneous input of a distinct coarse fraction of siliciclastic components implied that the terrigenous sediments were transported by a large, regional-scale river, in addition to the preceding small rivers draining local uplifts proximal to the site. The formation of a proto-Pearl River originating from the Cathaysian mountains and flowing through the rift basins of the continental margin is thus proposed. Moreover, when integrated with co-located calcareous nannofossil records indicative of a synchronous deepening process of the sea basin, our results link this early river network reorganization event to the spreading of the South China Sea rather than to the uplift of the Tibetan Plateau.