冰后期最大海侵以来长江、钱塘江河口湾发育过程的沉积动力学研究

SEDIMENT DYNAMICS STUDY ON THE DEVELOPMENT PROCESSES OF THE PALEO-YANGTZE AND THE QIANTANGJIANG RIVER ESTUARIES SINCE THE POST-GLACIAL TRANSGRESSION MAXIMUM

利用二维潮流数学模型对冰后期最大海侵以来 5期古岸线与现在岸线条件下古长江河口湾、古钱塘江河口湾及其邻近海域的主要水动力 M2 潮流场进行了数值模拟 ;在此基础上 ,分别计算了进入不同时期潮流场的7种粒径泥沙的潮平均单宽悬移输沙率与推移输沙率及其相应的输沙率散度 ,据此得出不同粒径泥沙在当时潮流场中的悬移与推移输运趋势 ,划分了海底淤积区与冲刷区。计算结果表明 :在不同时期的潮流场作用下 ,长江入海泥沙除最大限度地沉积在古长江河口湾 (或古长江河口 )内及其附近海域外 ,部分向苏北沿海净输运 ;部分向钱塘江河口湾内净输运 ;部分南下向浙江—福建沿海的离岸区净输运 ,并使这些地区发生淤积。自冰后期最大海侵以来 ,古长江河口湾不断缩小 ,最终转变为长江三角洲。在该过程中 ,长江河口不断东进南偏最终达到现今长江口的位置 ,古钱塘江河口湾则不断向海扩展 ,同时不断被充填。钱塘江河口湾的发育和沉积与古长江河口湾的充填、长江三角洲的向海伸展密切相关。

The Yangtze River Delta,which is a typical tide controlled delta,was evolved from the huge paleo Yangtze River estuary,and the present Qiantangjiang River estuary is a famous funnel estuary with strong tide in the world.Therefore,the discussion on the sediment dynamic processes and evolutionary mechanism of the development of the Yangtze and the Qiantangjiang River esturies since the post glacial transgression maximum(PGTM)may promote the study on paleo environment evolution and land ocean interaction processes in this area.The M 2 tidal current fields,which have been the main hydrodynamics areas in the paleo Yangtze and Qiantangjiang River estuaries, and their adjacent area along five paleo coastlines and the present coastline since the PGTM,are simulated with a 2 D tide model.Based on the tidal current results,the sediment transport fields of 7 kinds of grain sizes are calculated,and the seabed erosion/accretion pattern is obtained in terms of the divergence of sediment transport rate during each period.The results show that most of the sediment from the Yangtze River is alwalys deposited as much as possible in the paleo Yangtze River estuary and its adjacent area below tidal current fields of different periods.One part of the rest is transported to the northern Jiangsu coast,one part to the Qiantangjiang River estuary,and the remaining moves southward and is transported to the offshore of the Zhejiang Fujian coasts.Thus,accretion has occurred in the northern Jiangsu coast,the Qiantangjiang River estuary and the offshore of the Zhejiang Fujian coasts.Since the PGTM,the paleo Yangtze River estuary has become smaller and smaller,and is finally transformed into the Yangtze River Delta.During this period,the Yangtze River mouth has gradually moved southeastward and finally to the present location;however,the paleo Qiantangjiang River estuary has gradually seaward stretched and been filled at the same time.The development and sedimentation of the Qiantangjiang River estuary is closely related to the filling of the paleo Yangtze River estuary and the seaward stretchability of the Yangtze River Delta.