闽北近海柱状沉积物粒度特征及沉积速率研究

通过对闽北近海柱状沉积物的粒度频率曲线、粒度参数、粒度组成和沉积速率变化等特征分析,探讨闽北近海现代沉积环境条件变化.结果显示,闽北近海沉积物类型单一,以粘土质粉砂为主,粒级变化不大,粒度组成相对集中,粉砂级占绝对优势.频率曲线主要以主次双峰型为主,Zk1、Zk2柱样局部层位为主次三峰形态.Zk1、Zk2、Zk3柱样分别在78、69、87 cm处有不太明显的分段特征,上段平均粒径均略大于下段.研究表明潮流作用是该海域主沉积动力,沉积物主要以陆源物质为主,研究海域的水深整体略有变浅.研究区现代平均沉积速率为1.18～1.23 cm/a,里山湾和台山列岛附近海域沉积物平均沉积速率较快,分别为1.23、1.20 cm/a,大于七星列岛附近海域的沉积速率1.18 cm/a.海水动力条件是主要的控制因素,百年以来里山湾和台山列岛附近海域的水动力大小逐渐减弱,沉积物的沉积速率减小,台山列岛附近海域沉积速率减小幅度比较大;七星列岛附近海域水动力条件逐渐增强,沉积速率缓慢增加.

Research on grain-size characteristics and deposition rate of sediment cores in northern Fujian offshore area

Modern environment characteristics change of northern Fujian offshore deposition was discussed through characteristic analysis of frequency curve,grain-size parameters,grain-size composition and deposition rate change.The results showed only one deposit species in northern Fujian adjacent sea,mainly composed of clayey silt.The frequency curve is mainly of a primary-secondary bimodal except some horizons of core Zk1 and Zk2 are of primary-secondary trimodal frequency curves.The clay content of sediment cores is greater than the sand,with dominant silt accounts for more than 60%,showing that the grain-size composition is concentrated comparatively and the change of size grade is not great.The research showed tide is the main deposition force,and terrigenous sediment is the main deposition source.Average grain size of the sediment increases slightly from coast to inner land,indicating a gradually increasing impact of island origin sediment,however terrigenous sediment is still dominant.sediment cores Zk1,Zk2 and Zk3 have vague segment features at depth of 78 cm,69 cm and 87 cm respectively.Average grain size of the upper segment is slightly larger than the lower,and with a little greater frequency change,revealing that water has became a little shallower in the study area for 100 years on the whole.According to 210Pb dating,the modern average deposition rate was about 1.18~1.23 cm/a in the study area.The average deposition rates of Lishan Bay and the Taishan Islands surrounding waters in the recent 100 years（1.23 cm/a,1.20 cm/a） were greater than that of the Qixing Islands（1.18 cm/a） on the whole.The deposition rate increased gradually in the Qixing Islands surrounding waters,and decreased in the Lishan Bay and the Taishan Islands surrounding waters,with the latter showing a greater decreasing degree.Analysis of tide measurement data,indicated hydrodynamic condition change as the main control factor of the deposition rate change.In the recent 100 years,hydrodynamic conditions have been weakened gradually in the Lishan Bay and Taishan Islands waters,while intensified gradually in the Qixing Islands surrounding waters.