长江三峡库区不同坡段坡地土壤风化特征

Weathering Characteristics of Soil on Different Slope Sections in Three Gorges Reservoir Area Based on XRD

通过野外采样和实验室XRD分析,建立了基于XRD分析图谱的风化指标,研究了三峡库区不同坡段坡地的风化程度。三峡库区草堂河流域不同坡段坡地风化特征有一定的共性,如土壤中的主要特征矿物种类相同,主要有高岭石、云母和蛭石;所有样品中高岭石峰值均不高,甚至个别样品图谱上几乎没有高岭石峰的出现;3种主要的特征粘土矿物中以蛭石峰值最高;表层和底层的粘土矿物总量差异也不大。但是不同坡段土壤的风化程度仍存在一定差异。从顶部的分水岭山脊段到山坡上部直形坡崩塌段、山坡下部直形坡搬运段以及最下部的山坡坡麓洪冲积堆积段这4个坡段,4项风化指标均呈增加的趋势,说明从坡上到坡下土壤的风化程度逐渐加大。

Three Gorges Reservoir Area is an important one in China due to its ecological and environmental conditions. Slope land is defined as that the land locates from top to bottom of slope,so it is a major kind of geomorphology classifications in this area. It accounts above 70 percentages in whole area. Division of four sections in Three Gorges Reservoir Area used in this paper is originally put forward by Zheng Du. From top to bottom,the whole slope can be divided into four sections such as top section of divide ridge,above section of line slope with collapse,below section of line slope with transportation,and bottom section of foothill with alluviation and pluviation. The research of weathering characteristics of soil on slope land is a very important issue in modern geomorphology and many fields of applied geography. Based on field sampling in Caotanghe River Basin and the X-ray diffraction testing of all samples,the paper analyses their XRD charts,and then builds four indexes to assess the weathering intensity of soil on different slope sections. The four indexes are peak value of kaolinite,total mass of clay minerals,ratio between quartz and feldspar,and percentage of vermiculite turned from mica. The results are as following. In general,there are some similar characteristics in the weathering intensity of soil on slope fields in Caotanghe River basin. They have same classifications of diagnostic clay minerals such as kaolinite,mica and vermiculite. The peak values of kaolinite in all samples are very low; evenly one or two samples have no peak value. The peak value of vermiculite in every sample is highest among three diagnostic clay minerals. There is not much difference in gross clay mineral between surface layer and bottom layer. But there are general differences of weathering intensity among different slope sections. From top to bottom,four weathering indexes of the four sections have an obvious tendency to increase. So the total intensity of weathering from top section to bottom section shows a tendency to increase. And from above results,it is right that the mass transportation on slope land is always from top to bottom.