长江北支口门圆陀角附近潮滩沉积物元素地球化学特征及其环境指示意义

圆陀角地处长江北支与江苏海岸的交汇处,发育了典型的粉砂淤泥质潮滩,潮滩沉积物元素可记录海岸环境变化的信息。在圆陀角附近潮滩采集了长度为218 cm的YY孔岩芯,常量与微量元素分析结果显示,岩芯沉积物平均粒径与大多数元素之间相关性好,“粒控效应”特征明显。除Ca、Na、Ti、P、Sr外,岩芯大部分元素含量自下向上呈现由低变高再变低的趋势,并在岩芯132 cm深度出现最大值。根据圆陀角附近海岸沙嘴长江北支变迁的证据,苏北岸外海域是长江北支的重要泥沙来源;粒度和粘土校正后的元素含量呈自下而上由低变高的趋势。邻近区域沉积物元素富集系数分析显示,在1956年前后,圆陀角附近潮滩沉积物发生了较大的变化,1956年以前的主要来源于长江,1956年以后演变为主要来源于南黄海辐射沙洲南翼。

Geochemical characteristics of the sediment elements at tidal flat and its environmental implications at Yuantuojiao Point,estuary of the north branch of the Changjiang River

Yuantuojiao Point is located at the intersecting site of the north branch of the Changjiang River and Jiangsu coast. In the study area the typical silt-mud tidal flat has been the main morphological type. The geochemical elements of the tidal flat sediments are the proxies indicating the coastal environmental changes. In this study, a 218 cm drilling core was collected on the tidal flat at the Yuantuojiao Point. The grain size, 7 macroelements (Al, Fe, K,Mg, Ca, Na, Ti) and12 microelements (Mn, Ni, Sr, V, Zn, P, Ba, Be, Cr, Co, Cu, Li) of the YY core were measured. The chronology of this core was established by the method of ¹³⁷Cs dating. The results indicate that the contents of most macroelements and microelements had higher values in the lower part of the core, but in the upper part the values of the contents were lower.The maximum value of most macroelements and microelements existed at a depth of 132 cm of the YY core (except Ca, Na, Ti, P and Sr), which should be studied in the future. The mean grain size of the YY core had a good relationship with most elements contents, indicating a distinct feature of "grain size control effect". The grain size and the contents of elements corrected by clay from the YY core had greater difference before and after 1956. The evidences of the longshore current direction, coast spit extension direction, hydrodynamic change of north branch of the Changjiang River indicated the Jiangsu offshore region was the sediment source of the north branch of the Changjiang River. We made an analysis of the elements enrichment coefficients of the sediments of the YY core before and after 1956 at the Yuantuojiao Point and the adjacent areas. It is indicated that the main sediments of the tidal flat at the Yuantuojiao Point derived mainly from the Changjiang River before 1956, but they were mainly from the southern part of the submarine radial sand ridges of South Yellow Sea after 1956.