南流江河口水下三角洲表层沉积物端元分析及其沉积动力环境意义

沉积物粒度分布特征可揭示沉积动力环境。基于广西南流江河口水下三角洲的粒度分析数据,采用Folk分类法进行分类,应用端元分析对其粒度数据进行分解,探讨了南流江河口水下三角洲的物源和现代沉积动力环境。结果表明,研究区表层沉积物可划分为9类,其中含砾沉积物5类,不含砾沉积物4类,沉积物类型与河口环境动力特征相吻合。端元分析结果显示,研究区有5个不同类型的端元,分别代表着5种类型的沉积物动力环境:端元1反映了风浪和潮流对表层沉积物的动力作用;端元2指示了外海涌浪对表层沉积物的作用过程;端元3代表了南流江冲淡水引起的表层沉积物的输运;端元4代表了大陆架残留沉积物;端元5为干扰端元,可能是由于工程建设等人类活动所引起的。利用端元分析探讨复杂环境(如小型山溪性河口)下的沉积动力环境时,一方面需要综合考虑研究区域的物源与环境动力特征;另一方面可以结合参数拟合、粒径趋势分析等研究手段。

End-Member Analysis for Surficial Sediment of Nanliujiang River Subaqueous Delta and Associated Sediment Dynamic Environmental Significance

The sediment grain size distribution can be used to reveal sediment dynamic environments. Based on the grain size analysis of the surficial sediment collected from the Nanliujiang River subaqueous delta, Guangxi province, we identified the sediment sources and discussed associated sediment dynamic environments of the study area using end-member analysis and Folk classification. The analyzed results indicate that the surficial sediment can be divided into 9 types, including 5 types of sediment with gravel and 4 types of sediment with no gravel. The spatial distribution of the surficial sediment type is coincidental with environmental dynamic characteristics near the estuarine environment. According to end-member analysis, there are 5 distinguishable end-members (EM1-5), which represent 5 types of sediment dynamic environments. EM1 reflects the dynamic effects of wind waves and tidal currents on surficial sediments; EM2 indicates the dynamic process of surges on surficial sediments; EM3 reveals the effects of diluted Nanliujiang River water on surficial sediment transport processes; EM4 represents the relict sediment in the inner continental shelf; and EM5 is an end member disturbed by some noise, which may be induced by anthropogenic activities, such as coastal engineering construction. Based on our study results, if we try to use end-member analysis to study the sediment dynamic environment in an area with complex environments (e.g. small mountainous river estuary-shelf systems), we need to note two aspects: (1) we should take into consideration sediment sources and environmental dynamic characteristics in the study area; and (2) we can also combine other methods for mutual corroboration, such as parametric curve-fitting, and grain size trend analysis (GSTA).