长江三峡库区中坝遗址地层洪水沉积粒度特征及其沉积环境

通过对三峡库区中坝遗址1981年洪水沉积和疑似古洪水沉积的粒度对比分析，发现它们的平均粒径、分选系数、偏度、峰度和众值粒径都在同一值域范围内；频率分布曲线相似，呈单峰态；概率累积曲线都呈明显的三段式。从而推断出中坝遗址的文化间隙层为古洪水沉积。在考古断代和AMS14C测年基础上，对洪水沉积环境研究发现，中坝遗址洪水沉积大多发生在我国的暖期，但周朝和宋代的洪水沉积发生在我国冷期，这与我国气候小循环和当地独特的地貌特征有关。清代以后，沉积物平均粒径明显变大，表明当地植被已经退化；沉积物平均粒径和峰度变化幅度大，说明人类活动使当地生态系统变得脆弱，气候多变。

Grain Size Characteristics of Flood Sedimentary Environment in Zhongba Site, the Three Gorges Reservoir, Changjiang River

The grain size analysis of sediments from 1981 flood and possible paleoflood in Zhongba Site, the Three Gorges reservoir, Changejiang river shows that their average diameters, sorting coefficients, skew coefficients and kurtosis coefficients are all in the same style, and they bear similar frequency curve of grain size with one crest and simi- lar probability cumulative curve with an obvious pattern of three segments. So it is reasonable to infer that the culture interruption layers are paleoflood deposits. The study on the sedimentary environment based on the AMS14C dating and the age judged by cultural relics reveals that most paleoflood sediments occurred during the warm and wet period, but the paleofloods of the Zhou Dynasty and the middle Song Dynasty occurred during the cold period, possibly, due to the climate hypocirculation of our country and the particular topography of the place. After the Qing Danasty, the average diameters of grain size became much bigger, which suggests the local environment was degradation. The wider range of diameters of grain size and kurtosis coefficients after the Qing Dynasty, especially in modern age indicates that human activities have made the local ecosystem fragile and the climate volatile.