广东三水盆地第四纪网状河沉积特征

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

珠江三角洲西北部的三水盆地范围内发育典型的网状河体系。它们具有重复分叉合并、坡降低以及河道深且窄的特点，并且发育天然堤、河间湖泊和洼地等地貌单元。钻井资料显示，网状河的沉积记录以泛滥平原地区沉积的悬浮负载的细粒沉积物为主，由砂砾和砂组成的河道沉积物分布比较局限，呈较窄的带状，被包裹在细粒的泛滥平原积物之中。主干河道表现出较高侧向稳定性垂向继承性，形成了较厚的砂体。较小的分叉河道则容易发生决口改道，沉积了较薄的砂体。河间湖泊沉积主要为含植物碎片的灰黑色粉砂质淤泥，沼泽中植物遗体的堆积形成了泥炭层。晚更新世以来的构造沉降。

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 repeated branching and rejoining. Channels, natural levees, interchannel lakes and wetlands are important morphological and sedimentary units. Well data revealed that the depositional records of the anastomosing river systems are mainly composed of fine grained sediments deposited in interchannel areas, coarse grained channel deposits, on the other hand, are string like and of limited lateral extent, and encased in the overbank fine sediments. Trunk channels are more stable and often associated with deposits of thick channel sand bodies. Smaller channels are more easily abandoned bacause of crevasse and avulsion,thus thin sand bodies are deposited in the fine sediment dominated deposits. Pet and silt rich in organic materials are deposited in swamps and interchannel lakes. Tectonic subsidence and eustatic sea level have risen since the Late Pleistocene, and the rapid vertical accretion in the floodplain hase been the main cause for the development of anastomosing river systems in the Pearl River deltaplain.