Grain-size Features Of Quaternary Sediments In Three Gorges Reservoir Of Yangzi River In Wushan Area

Grain-size analysis is a matrual method in the research of Quaternary environmental research,it is the material for the identification of sediment sources, transport media and power, sedimentary environments and their changes are of great significance. Grain-size is one of the most important feature of sediments in the paleo-environment analysis and treconstruction. Because of different sediment transport medium and the intensity of the different composition of the particles are different, so grain-size analysis can be studied through the formation of sediment environment and its dynamic handling characteristicsIn this paper, Wangtianping profile,is located on the left bank of Yangzi river,is selected as research site as deserving of unique grain-size distribution of Quaternary sediments.,based on the investigation in the field selected a typical profile of Quaternary sediments and with roughly the same latitude in this area of the two central Suining, Sichuan region red weathering crust sections, through the grain size characteristics of these samples were analyzed to explore a variety of grain size parameters in the profile changes in the characteristics and distribution. Thesis come to look at a few conclusions:(1)According to field site observation, to look on the soil texture is more uniform floor section can be divided into two layers, namely, the upper section of the brown layer and the lower brown layer, lower moisture content than the upper level, and this with the South more clay profile is similar.(2) From the profile in terms of grain-size characteristics of sand(>63μm) content is extremely low, with an average of 0.7%; silt (4～63μm) content in the highest, with an average 68.64 percent, for public Counting Unit;clay (<4μm) content followed a mean of 30.66% for the second mode grain group; eolian basic grains group with higher levels of 10～50μm, with an average of 52.07%, suggesting the soil-forming parent materials have a certain style into a feature.(3)From the grain-size distribution curve and the parameters point of view, the upper section (brown-yellow soil) showed single-peak distribution pattern, and drag a small tail, and aeolian loess is similar to post-deposition may direct experience the role of wind into soil; profile lower (red-brown soil) and kurtosis more complex, in a single peak as the main drag and refined against the backdrop of the end as well as the coarse tail, reflecting the diversity of its sedimentary dynamics, and the southern red soil is similar to.The average particle size as well as the median grain size parameters such as the relatively small size, average values are 12.5μm and 7.75μm, the upper section (brown-yellow soil) were 13.89μm and 10.19μm, lower (red-brown soil) were 9.96μm and 6.75μm, the value of the upper particle size is closer to the wind into the loess, the lower part closer to the South red clay, may reflect the first pass through weathering and go through a sequence of eolian deposition.(4) A comprehensive look on Wangtianping profile,the grain-size composition, distribution curves, parameters and magnetic susceptibility and other indicators, and with the northern and southern red clay loess contrast, because it is both similar, so we can not simply to be the causes attributed to "wind-stacking," or "wind turned into earth" but more likely to experience these two processes, reflecting the diversity of the South Quaternary environmental and complexity. Wang Ping-day trends in the vertical profile of particle size, may reflect the late Quaternary climate in the South have changed the trend of dry and cold, but its environmental significance to be in the dating and other environmental indicators on the basis of comparative study for further exploration.