克里雅河沿线沙丘沉积物石英砂表面特征分析

对沙漠内部典型河流沿线沙丘石英颗粒表面微形态特征的系统研究尚少。沿塔里木盆地南缘克里雅河下游丹丹乌里克、喀拉墩、圆沙古城、北方墓地及其北部塔里木河一带的沙丘顶部采到5件表沙样品。扫描电镜观察172颗经能谱挑选的石英颗粒表面微形态，筛析法测定5件样品的粒度。结果表明:1）丹丹乌里克样品以极细沙为主，其余均以细沙为主，各样品几乎不含黏土；2）样品磨圆度特征以次棱和次圆状为主，圆状很少，未见棱状特征，次棱状与次圆状特征之间消长关系显著，沙漠南北边缘样品的次棱状特征出现频率较腹地高；3）颗粒中V形坑频率呈现出沙漠边缘较高腹地低的特征，而沙漠边缘的化学作用结构特征低于腹地。石英砂表面特征结构以机械作用为主，同时伴生化学环境作用特征，可认为克里雅河下游沙物质包括了河流、冰川与戈壁成因及风输送而来的颗粒；颗粒表面特征总体新鲜，沙丘应较年轻。纵穿塔克拉玛干沙漠沉积物样品的表面微形态观察与粒度测定，为该地区沉积环境分析与沙丘砂溯源研究增添了新数据。

Surface Features of Quartz Sand Grains in Dune Sediments,Keriya River Basin

Few previous systematic studies have focused on the effects of a river on desert sand supply， by analyzing the micromorphology of quartz-grain surfaces. Five surface bulk samples were collected from dune ridges from south to north along the Keriya River at the southern margin of the Tarim Basin， in Dandan Oilik， Karadun， Yuansha Site， Beifang cemetery and an area near the Tarim River. The particle sizes of the five samples were determined by dry sieving， and 172 quartz grains were selected using energy dispersive spectroscopy （EDS）. The surface micromorphology of each sample was observed by scanning electron microscope （SEM）. The results show: （1） The Dandan Oilik sample was dominated by very fine grain sizes， and the other four samples were all predominantly fine sand； almost no sample contained clay. （2） The grain samples were mainly sub-rounded and sub-angular with a few round grains， and no angular particles were found. The relationship between the sub-angular and sub-rounded features is remarkable: the frequency of sub-angular quartz grains from the northern and southern edges of the desert was higher than in the samples from the desert hinterland. （3） Grains with V-shaped pits occurred more frequently at the edge of desert than in the hinterland， and the structure formed by chemical weathering also appeared more frequently at the desert edge than in the desert hinterland. The surface structure of the quartz sand particles in the Keriya River Basin was dominated by mechanical features， apparently due to their particular environment （e.g.， glacial， fluid flow， salt weathering， eolian）. Significantly， most of these different characteristics were observed to be multiply overlain on individual grains. It appears that the source of eolian sand in the lower reaches of the Keriya River is a complex blend of grains directly originating from glaciers， rivers and the Gobi desert， and grains transported both by river and wind. Importantly， the surface features of the dune samples are freshly formed， suggesting relatively recent dune sand accumulation. The surface micromorphology observations and grain size determinations of sediment samples from the Taklimakan desert provide new data for the analysis of the sedimentary environment and the study of the provenance of dune sand in this area.