江苏圆陀角附近潮滩沉积岩芯粒度变化及其环境意义

江苏圆陀角位于长江北支岸线与江苏海岸线的交汇处,发育了粉砂淤泥质海岸典型潮滩地貌,潮滩岩芯沉积物粒度变化记录了潮滩环境变化的信息。2007年在圆陀角附近潮滩采集了192cm长的柱状岩芯,对沉积物的粒度组成进行了分析,分析结果显示,砂质粉砂是主要的沉积类型,岩芯分为三部分,从下部向上,粗颗粒沉积组分减少,反映了采样点附近潮滩环境由潮滩中部向上部转化的过程。根据岩芯沉积物¹³⁷Cs的1963年和1986年两个蓄积峰值时标推算,1963年以来的平均沉积速率为2.3cm/a,1986年以来的平均沉积速率为1.6cm/a,1963～1986年之间的平均沉积速率达到2.9cm/a。沉积速率变化表明20世纪60年代以来伴随潮滩淤积增高,圆陀角附近潮滩沉积物的沉积速率下降,大体与辐射沙洲南翼淤积型潮滩淤积速率一致,小于长江口外的泥沙沉积速率。泥沙来源主要是苏北沿岸流携带的部分泥沙在圆陀角附近沉积,伴随研究区围垦活动向海推进,在长江北支口门北侧形成了大片的泥质潮滩和水下沙嘴。

GRAIN SIZE AND ITS ENVIRONMENTAL SIGNIFICANCE OF THE CORE FROM THE TIDAL FLAT AT YUANTUOJIAO POINT,JIANGSU PROVINCE

The Yuantuojiao Point is the meeting point of the North branch of the Changjiang River and the south Yellow Sea.A typical tidal flat was developed along the coast at the Yuantuojiao Point.The sediments of a core from the tidal flat contain the information about the environmental changes.A core(YT Core)of 192cm was collected on April 19,2007.The sediments were sampled at the intervals of 2cm.Grain size analysis indicated that sandy silt was the main sedimentary type.The core was divided into three parts and from the bottom to the top the sediments become finer and finer,which refers to the environmental change of the sampling site from the middle part of tidal flat to the upper.Two peaks of 137Cs fallout radionuclide concentrations were presented at the depth of 102cm and 36cm,which refers to the year of 1963 and 1986,respectively.The average sedimentation rates were calculated as 2.3cm/a from the year of 1963 to present and 1.6cm/a from the year of 1986.The average sedimentation rate from the year of 1963 to 1986 was 2.9cm/a.The sedimentation rate has declined since the 1960's corresponding to the seaward reclamation at the Yuantuojiao Point.The average sedimentation rate at the Yuantuojiao Point was similar to that of the silt-muddy tidal flat in Southern Jiangsu coast,but lower than that of the estuary of the Changjiang River.The seaward reclamation in the past decades at the Yuantuojiao Point caused the high sedimentation area moving to the eastern part and formed the spit and large muddy tidal flat at the northern part of the north branch of the Changjiang River.The main sedimentation source at Yuangtuojiao Point was from the Jiangsu coastal tidal current from north to the south direction,which brought much fine sediments.