Sedimentology of Quaternary Anastomosing River Systems in the Sanshui Basin, Guangdong, China

Key words: 
• anastomosing river deposit /
• Quaternary /
• Sanshui Basin /
• Pearl River delta

Abstract: Anastomosing river systems in the Sanshui Basin, northwestern part of the Pearl River deltaplain,were studied.They are multi-channel systems showing low gradients, low width /depth ratios and re-peated branching and rejoining.Channels, natural levees, interchannel lakes and wetlands are importantmorphological and sedimentary units.Well data revealed that the depositional records of the anastomos-ing river systems are mainly composed of fine grained sediments deposited in interchannel areas, coarsegrained channel deposits, on the other hand, are string-like and of limited lateral extent, and encased inthe overbank fine sediments.Trunk channels are more stable and often associated with deposits of thickchannel sand-bodies.Smaller channels are more easily abandoned bacause of crevasse and avulsion, thusthin sand-bodies are deposited in the fine-sediment-dominated deposits.Pet and silt rich in organic mate-rials are deposited in swamps and interchannel lakes.Tectonic subsidence and eustatic sea level haverisen since the Late Pleistocene, and the rapid vertical accretion in the floodplain hase been the maincause for the development of anastomosing river systems in the Pearl River deltaplain.