巴丹吉林沙漠高大沙山沉积物粒度特征及其与植被、地貌关系

沙丘形成演变是风-沉积物-其他地理因子相互反馈作用的一个动态系统过程,粒度可以揭示其中包含的部分环境信息并被广泛应用于风沙地貌研究。本文分析了巴丹吉林沙漠伊和吉格德湖高大沙山区沉积物粒度特征及其与植被、地貌形态的关系。结果表明:迎风坡中上部及中部剖面各层沉积物主粒径均一,分别为中沙、细沙;迎风坡中下部及底部剖面细沙、中沙及粗沙等不同主粒径层交替,粒配复杂,其成因与粗沙粒保护作用、风向季节变化及地质时期气候变迁等因素有关;背风坡表层沉积物以细沙为主,趋向底部粗沙、中沙及极细砂增多,说明不同粒径对风及重力作用的响应存在差异;粒度参数散点图可以区分不同部位样品,趋向迎风坡底部剖面,沙粒分选性变差,正偏、负偏及近对称沙层交替,说明风力分选作用在不同部位差异明显及存在其他外力作用;沙层粒配影响植被多样性,迎风坡中上部中沙含量高,背风坡表层中部偏上极细沙及大于2.65 Φ细沙含量突然增加,是植被影响粒配的反映;迎风坡沉积环境的差异,说明随地质时期气候变迁,沙山形成可能经历了两个重要阶段,一是早期风力和水动力交替影响、具有风成与非风成环境交替特征的基底形成时期,二是以风力作用为主的现代沙山形成时期。

Grain Size Characteristic of Mega-dunes in the Badain Jaran Sand Sea and Its Correlation with Vegetation and Landform

The formation and evolution of dune is a dynamic systematic process with the interaction of wind, sediments, and other geographical factors, through grain size analysis we could know part of the environmental information contained in this process, so it is widely used in aeolian research. This article analyzed the grain size characteristic of mega-dunes in the Badain Jaran Sand Sea and its correlation with vegetation and landform, the results showed that the main gain size of sediments had homogeneity in different layer of the upper-middle and middle sections of windward slope and were respectively composed of middle sand and fine sand; But in the lower-middle and bottom sections, the grain size distribution had complexity, different layer alternated with different main grain size including fine sand and middle sand and coarse sand, the reasons for that may include the protective action of coarse sand and the seasonal change of wind direction and the climate change in geological periods; The surface sediments were mainly composed of fine sand in the leeward slope, but toward bottom the content of coarse sand and middle sand and very fine sand increased, this indicated the discrepancy of different particle size on the response of the wind and gravity; The scatter diagram of grain size parameters could distinguish the samples very well in different parts of mega-dunes, toward the bottom sections of windward slope, the sorting of sand particles became worse, and the sand layer alternated with positive or negative or near symmetrical skewness, these demonstrated that there existed discrepancy of wind action in different parts and some other exogene processes. The grain size distribution had an impact on vegetation diversity, and vegetation aslo affected it, for example, the high content of middle sand in the upper-middle section of windward slope and the sudden increase content of very fine sand and fine sand greater than 2.65 Φ in the middle part with a little higher of leeward slope; The different depositional environment in the windward slope indicated that with the climate change in geological periods the mega-dunes may undergo at least two important formation stages, the first period was the basement formation with the alternate layer of aeolian or nor-aeoline depositional environment under the influence of wind and hydraulic action, the second period was the formation of modern mega-dunes mainly based on the wind action.