库姆塔格沙漠灌丛沙堆物源之粒度分析

Comparative Grain Size Analysis of Nebkhas and Sand Materials Source in the Kumtagh Desert

摘要: 灌丛沙堆主要发育在干旱、半干旱地区水分和植物生长条件相对较好的富含沙物质的区域，对其研究有助于理解沙物质来源和堆积过程。本文对库姆塔格沙漠西北缘典型灌丛沙堆及其周围沙源样点的表层沉积物进行了粒度对比分析，结果表明：库姆塔格沙漠灌丛沙堆沉积物以极细沙为主(含量47.52%)，较周围对照样点沉积物颗粒要细；灌丛沙堆沉积物的粒度参数分选性中等，偏度为负偏，峰态为中等峰态；灌丛沙堆与其周围丘间地沙物质和雅丹体中埋藏古风成砂的粒度频率曲线在粒级>1Φ范围内的粒度分布趋势表现出明显的一致性；概率累积曲线反映出灌丛沙堆沉积物以跳跃组分和悬浮组分为主，即以跃移搬运和悬移搬运为主要运移方式；通过灰色关联度对灌丛沙堆的沙源做了定量分析，反映出灌丛沙堆的物源除其周围的丘间地供给外，其上风向崩塌雅丹体中出露的埋藏古风成砂通过风力运移被灌丛阻拦沉降，也是灌丛沙堆的沙源之一。

Abstract: Nebkhas are developed in sand sediments of arid regions or semi-arid regions with good moisture conditions and plant growth conditions. Studies on the nebkhas helped to understand the provenance and deposition of the sand sediments. The grain size of the sediment samples from nebkhas and other correlative points in the northwestern parts of the Kumtagh Desert in the west of China were analyzed. The main composition of nebkhas is very fine sand and its ratio of 47.52 percent, finer than other sample points. The grain size composition of the nebkhas is similar to that of the interdune lowlands in the west and the southeast. The sediments of nebkhas have a sorting coefficient of medium characteristic, and negative skew distribution, and the kurtosis has a typical medium characteristic. The grain size parameter of the nebkhas is similar to that of the paleo-dune deposit of yardang. The grain size distribution trends of the nebkhas, the interdune lowlands and the paleo-dune deposit of yardang over 1Φ are highly correlated. From the probability cumulative curves, the results showed that the sediments of the nebkhas are mainly composed of the saltation and suspension components. Their transport ways are saltation and suspension. The quantitative analyses of grey relevancy of the nebkhas and the sand materials source showed that sediments of the interdune lowlands and shifting sand dune and paleo-dune deposit of yardang are correlated with nebkhas. The paleo-dune deposit of yardang correlates the most closely with nebkhas (γ = 0.73). Analyses indicated that besides the neighboring interdune lowlands, the paleo-dune deposit of yardang also helps to form the nebkhas, and the dune deposits of collapsing yardang are from the upwind edge of nebkhas. The surface deposits are carried by the wind, and then they settled when they met the nebkhas. In the process, nebkhas formed gradually. In conclusion, nebkhas are formed with the help of the interdune lowlands in the west and the southeast under the wind deflation, and the paleo-dune deposit of yardang may be one of the sand material sources of the nebkhas.