中文摘要：

江苏圆陀角位于长江口北支与江苏海岸交汇处，海岸沉积动力环境复杂，潮滩沉积物粒度变化记录了潮滩环境变化的信息。根据2007年4月采集的表层样和钻孔岩芯粒度分析，圆陀角附近YYb断面表层沉积物粒度在互花米草滩前缘较粗，大堤前岸滩最粗，光滩和互花米草滩粒度较细。YY孔岩芯沉积物粒度组成以砂质粉砂为主，粒度变化自下向上呈先由粗变细再变粗的特点，表层样和钻孔岩芯粒度变化反映了潮滩沉积物对风暴潮、潮汐海洋动力、大米草和互花米草种植以及大规模围垦的综合响应。^137Cs测年结果推算出YY孔岩芯1954年以来、1963年以来、1975年以来和1986年以来的平均沉积速率分别为2．38em／a，2．23cm／a，2．44cm／a和1．24cm／a。岩芯沉积物的沉积速率总体随潮滩淤积增高而下降，1975—1986年间沉积速率的快速增加，主要与圆陀角附近互花米草的快速淤积有关。

英文摘要：

The Yuantuojiao Point is the intersecting point of the north branch of the Changjiang River with the South Yellow Sea coastal line. A typical salt marsh environment （tidal flat ）occurs near the Yuantuojiao Point. The specific geographic location and the complexity of regional morphological dynamics determined the sensitive responses of the Yuantuojiao Point tidal flat to environmental changes. The grain sizes of the tidal flat sediments recorded the information about environmental changes. We collected samples of the tidal flat surficial sediments and core YY and analyzed their grain-sizes. The grain size analyzing results indicate that sandy silt is the main sediment. As a whole, the surficial sediments in front of the of the Spartina alternflora tidal flat and in the levee reclaimed by Hengda Group are coarser,but finer in the exposed beach and in the Spartina alternflora tidal flat. The core is divided into three parts： A（0 -116cm）,B（116 -194cm）,and C（194 - 218cm）from the upper to the lower. The sediments become finer and finer from C to B, corresponding to the environmental change of the middle part of tidal flat to the upper part, but the sediments become coarser and coarser from B to A, corresponding to the seaward reclamation near Yuantuojiao Point. These grain size changes of the surficial sediments and the core were synthetic responses to storm surge ,tide process, Spartina angilica, Spartina alternflora ,and sea reclamation. The first non-zero accumulation peak and maximum accumulation peak of ^137Cs fallout radionuclide concentrations present at the depths of 126cm and 98cm of borehole YY, corresponding to the years of 1954 and 1963, respectively. Two larger accumulation peaks at the depths of 78cm and 26cm of borehole YY correspond to the years of 1975 and 1986,respectively. From the ^137Cs dating analysis of the core samples,the average sedimentation rate were calculated to be 2. 38cm/a from 1954 to 2007, and 2.23cm/a from 1963 to 2007, and 2. 44cm/a from 1975 to 2007, and 1.24cm/a