长江三峡地区黄土粒度特征及其成因分析$

Analysis on the characteristics and their origin of the grain-size of Wushan loess in the Three Gorges area,China

长江三峡地区的巫山黄土是中国黄土的重要组成部分,其来源具有重要的古气候环境意义.文章对三峡地区巫山黄土剖面先后进行野外考察、系统采样和光释光定年、粒度测试等工作,其中年代数据显示研究区黄土属于晚更新世黄土.巫山黄土的粒度组成特征与河流沉积物及同时期马兰黄土对比显示,巫山黄土与河流沉积物粒度组成明显不同,而与典型风尘黄土相似;粒度象显示巫山黄土与河流沉积物成因不同;频率累积曲线显示巫山黄土风积物特征.巫山黄土平均粒径与马兰黄土平均粒径从西北向东南逐步变细的空间分布不相符合,可能与气候及地形等因素有关.

Wushan loess in the Three Gorges area is an important part of China＇s loess and its source is of significance in paleoclimatic environment.Field investigation,systematic sampling,optically stimulated luminescence （OSL） dating and particle size testing have been done in this research.OSL data show that Wushan loess area belongs to Late Pleistocene.Compared to river sediments and Malan loess in the same period,the characteristics of the grain-size composition of Wushan loess are significantly different from river sediments,but similar to the typical eolian loess.The comparison of granularity image also indicates that Wushan loess is different from river sediments in origins.The cumulative frequency curves show the aeolian characteristics of Wushan loess.The spatial pattern of the average grain diameter of Wushan loess is not consistent with that of Malan loess becoming tapering gradually from northwest to southeast,probably due to climate and topography.