珠江三角洲中部子平原形成演变机理研究——以大鳌平原为例

A PHYSICAL STUDY ON THE EVOLUTION OF THE SUB-DELTAIC PLAINS IN THE MID ZHUJIANG RIVER DELTA:A CASE STUDY OF DA′AO SUB-DELTA

海侵盛期以来珠江三角洲的形成演进受到原始地貌的控制，潮汐动力和河流作用被复杂的地貌单元分割和重塑。珠江三角洲中部平原依据其演进过程的空间位置和边界，相关的动力系统可以分成若干子平原，分别是番禺平原、顺德平原和大鳌平原。文章着重报道大鳌平原海侵盛期以来的形成演变机理的研究成果。基于收集的1700余个各类钻孔资料和本课题野外钻取的18个钻孔，进行了210个14^C测年和沉积物粒度等相关分析，应用本课题开发的PRD-LTMM长周期‘动力-沉积-形态’模型计算6000年以来的古珠江河口湾的流场、泥沙浓度场、冲淤厚度和岸线演变，以及对上述结果的地貌动力分析，揭示了大鳌子平原各主要沉积体的形成演变过程以及沉积动力机理。结果表明：1）大鳌子平原是外部海洋和河流等动力经过古磨刀门、古横门和五桂山所改造的复杂地貌动力环境下形成的；2）大鳌子平原可以依据其沉积动力结构进一步分成至少3个主要的动力沉积单元，分别是古磨刀门大鳌沙涨潮三角洲、五桂山北麓边沿沉积体和磨刀门-古横门汇潮点沉积体；3）3000-2500aB.P.的短暂高海面，导致古海湾纳潮量相应增大，出现大鳌沙第2次高沉积期。反映了局部小尺度动力结构与三角洲地形演进及海洋动力变化的密切互动关系。

The formation and evolution of the Zhujiang River delta since the end of the rapid Flandrian eustatic rise about 6000aB. P. have been strongly controlled by the geomorphology of the estuarine basin. Tides and river flows as major driving forces were redistributed and more or less separated by the convolute coastal line and hundreds of rocky islands in the paleo-estuarine bay. Based on their genetic evolution and related dynamic systems, we divide the mid Zhujiang River deltaic plain into three sub-deltaic plains （SDP） ： Panyu SDP, Shunde SDP, and Da＇ao SDP. The present paper mainly reports the research on the physical processes of the formation and evolution of Da＇ao SDP since the last transgression maximum. Based on more than 1700 sediment core records collected from literature, 18 bore holes taken in the field from which 210 sediment samples were 14^C dated and grain size and other sediment parameters were analyzed, and the application of the long-term morphodynamic model PRD-LTMM by which the current velocity, sediment concentration, deposition rate, and shoreline change of the paleo-estuarine bay were calculated for the last 6000 years in the time interval of 10a, this study reveals the following characteristics of the evolution of the major sedimentary bodies in the Da＇ao SDP and its associated dynamic processes： （1） The complicated morphodynamic environment controlling the evolution of Da＇ ao SPD was constructed by paleo-Modaomen, paleo-Hengmen, and Wugui Mt. by which the tides from open sea and river flows were strongly modified and redistributed. （2） Da＇ao SDP consists of three major sedimentary units according to the controlling dynamic structures. They are the paleo-Modaomen flood tidal delta, the fringing deposition along the north piedmont of the Wugui Mt., and the convergent/divergent flow deposition. （3） The second rapid deposition period of the Da＇ao flood delta was a response to the sea level rise during 3000 - 2500aB. P. that increased the tidal prism in the paleo-estuarine bay. It is an indication of the close interaction between local small scale dynamic structures and the evolution of the delta as well as the variation of marine forcing.