埃及Faiyum盆地沉积物中粒度和磁化率对风沙活动的指示意义

摘要

埃及Faiyum盆地是尼罗河下游的泛滥平原,沉积物主要来自尼罗河和撒哈拉沙漠.本文通过对钻孔FYAM(孔深4.6m)沉积物的粒度、磁化率的分析,并结合石英形态、石膏和碳酸盐含量分析,旨在寻找Faiyum盆地沉积物中代表风沙活动的粒度、磁化率特征.研究结果显示,钻孔沉积物中共发现7种粒度频率曲线类型,主要为细粒组(6-20μm)和粗粒组(80-100μm)两个峰值组合而成的单峰或双峰曲线.除去人类活动影响的高磁化率层以及高碳酸盐含量导致的低磁化率层外.其余层位沉积物的磁化率随着曲线类型的不同呈现规律性变化,当80-100μm峰为主峰时.磁化率明显偏低,风成石英颗粒含量升高,代表着风沙活动强烈,当6-20μm的峰为主峰时,磁化率相对较高,风成石英颗粒含量减少,意味着风沙活动减弱,以尼罗河物质输入为主.%The Faiyum Depression, a flood plain of the Nile downstream, receives sediments from the Nile and the Sahara Desert.By means of grain size and magnetic susceptibility analysis of sediments from core FYAM ( 4.6m deep), combined with surficial characteristic of quartz grains, occurrence of gypsum and carbonate contents, the paper is aiming to reveal some indicators for eolian activity in the Faiyum sediments. The results suggest that there are totally seven patterns of sediment grain-size distribution, including unimodal and biomodal patterns composed of a fine-grain peak (6 -20μm) and a coarse-grain peak (80 - 100μm). These patterns have a close relation to magnetic susceptibility except for the sediments of two layers with high or low magnetic susceptibility cansed probably by human activity and carbonate content. When the coarse-grain peak appears as a major pattern, the sediments are characterized by low magnetic susceptibilities, implying eolian quartz content increased, and strong sandstorms. When the finegrain peak is dominated, the sediments were consistent with high magnetic susceptibility and less eolian quartz grains, probably revealing increasing sediment supply from the Nile.