天山冰川与塔克拉玛干风沙沉积的颗粒特征和分异过程分析

Analysis of Particle Characteristics and Differentiation Processes of Glacial Sediment in Tianshan and Eolian Sediment in the Taklimakan Desert

通过对比天山阿拉沟冰碛及冰水扇和塔中沙丘砂的颗粒特征,探讨其搬运与堆积分异过程。研究表明:冰川沉积粉砂颗粒占相对优势,砂颗粒次之,黏土颗粒最少,且石英砂表面出现较多的多棱角、棱脊磨损、大贝壳断口、撞击深坑等反映冰川底部强烈挤压研磨动力的特征。冰水沉积颗粒特征与冰川沉积相似,粉砂仍是优势组分,石英砂表面显微特征显示轻微的流水改造。风沙沉积中砂颗粒占绝对优势,石英砂表面出现较多次圆–圆边缘、碟形坑、不规则小麻坑等风力作用特征,且有少量大贝壳状断口、裂纹、棱脊磨损等冰川作用痕迹,以及V形坑等流水作用痕迹。推测冰碛物为塔克拉玛干沙漠重要物源之一,冰碛物中的粉砂为塔里木盆地边缘黄土的主要提供者。

To study the transportation, deposition and differentiation of till and outwash in Allah valley area of Tianshan and dune sand in Tazhong area, the characteristics of particles in the two areas were comparatively analyzed. Results show that in the glacial sediments： the content of the silt grain was the largest, followed by sand grain, and clay grain was the least, besides there were lots of more-angulars, worn ridges, large conchoidal fractures, impact pits on the surface of quartz sands, which indicated the strong crushing and grinding force at the bottom of the glacier. The particle characteristics of outwash sediments were similar to that of glacial sediments＇, and silt grain was still the dominant component, but the features of quartz sand surface showed that it was slightly reformed by water. In the eolian sediments, sand grain was the main component, and the surface of those grains had lots of subround-round edges, dished pits and irregular small pockmarked pits which were caused by wind action. In addition, there were some large conchoidal fractures, cracks and worn ridges that reflected glaciation and a few V-shaped pits that indicated fluviation. It could be concluded that till is the dominant source of the sand in the Taklimakan Desert, and the silt of till is the main supply for the loess in the edge of Tarim Basin.