长江口水下三角洲泥质区近期沉积物粒度变化特征及其影响因素

RECENT VARIATION IN SEDIMENT GRAIN SIZE IN THE MUD AREA OF CHANGJIANG SUBAQUEOUS DELTA AND ITS INFLUENCE FACTORS

河口水下三角洲是河流和海洋环境共同作用的产物,沉积地层中蕴藏了许多环境变化信息。在长江口水下三角洲泥质区采集了柱样SC09,首先利用放射性同位素210Pb确定了沉积柱样的平均沉积速率,其次对沉积柱样以0.2cm间隔进行高分辨率取样,获得了沉积物粒度参数,然后提取了沉积物粒度敏感组分,并对其进行了经验模态分解(EMD)分析。结果表明,沉积物粒度敏感组分具有明显的周期性和趋势性变化特征,与长江入海泥沙的变化特征、近海风暴潮等极端天气事件的发生周期有较好的对应关系。沉积物细颗粒敏感组分的变化特征可能主要受控于长江入海泥沙的变化;而沉积物粗颗粒敏感组分的变化,既体现了风暴潮等极端天气事件对该区域的影响,同时,也可能与历史上长江入海主泓位置的变化有关。

The subaqueous delta is a sink on the terrigenous clastic continental shelf.It contains tremendous information on environmental changes influenced by both the sediment supply and marine environmental dynamics.The core of SC09 was collected from the mud area of the subaqueous delta of the Changjiang River.Samples were taken for every 0.2cm of interval.Sediment grain sizes were measured by Mastersizer 2000 laser particle analyzer.Moreover,sediment grain-size sensitive populations were retrieved for analysis using the Empirical Mode Decomposition（EMD）.The results show that the sensitive populations of grain-size are distinctly characterized by periodicity and a definite trend.The characteristics of fine grained sensitive populations were mainly relative to the changes in sediment supply from the Changjiang River,and the periodic changes and the trend of the coarse sensitive population reflect either the influence of extreme events,such as storm,or changes in the main course of Changjiang River.