Grain size parameters and their distribution on feather-like dune of Kumtag Desert
Grain size parameters and their distribution on feather-like dune of Kumtag Desert
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发表时间：
2008
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通讯作者：
E. You-hao
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作者：
E. You-hao
羽毛状沙丘是一种形态独特的沙丘，主要分布在库姆塔格沙漠北部，由“羽毛”和“羽状”两部分组成，形似羽毛。“羽管”是由单个新月形沙丘组成的纵向沙脊，轮廓清晰，并已合并（前者沙丘迎风坡的基座与后者东南侧合并）和延长。“羽状”是由脊间起伏的沙地组成，起伏沙地的峰谷几乎垂直于沙脊，由此形成“羽毛状沙丘”，从航片和卫片上都可以看到。关于羽毛状沙丘物质沉积过程和粒度变化的系统观测和取样研究，目前还未见报道。本文通过对“羽毛状沙丘”物质沉积过程和粒度变化的系统观测和取样研究，通过对库姆塔格沙漠羽毛状沙丘表层沉积物的取样分析，初步探讨了沙丘的粒度分布特征，在不同地点采集了108个面积约20 cm×20 cm、深度0-5 cm的羽毛状沙丘砂样，结果表明，新月形沙脊砂的粒度分布范围为1.57 ~ 3.14φ，平均为2.42φ（0.187毫米）;粒径为0.125- 0.25mm的细砂占优势，平均占60.8%从两坡脚到新月形沙脊尖，砂质逐渐变细，西北坡的砂质比东南坡的砂质细，从东南坡的砂质比西北坡的砂质细，从西北坡的砂质比东南坡的砂质细，从东南坡的砂质比西北坡的砂质细，从东南坡的砂质比西北坡的砂质细，从西北坡的砂质比东南坡的砂质细，从东南坡的砂质比东南坡的砂质细，从西北坡的砂质比东南坡的砂质细，从东南坡的砂质比东南坡的砂质细，从西北坡的砂质比东南坡的砂质细，从东南坡的砂质比东南坡的砂质细，从西北坡的砂质比东南坡的砂质细，从东南坡的砂质比东南坡的砂质细。沙丘迎风坡向沙丘顶和新月形沙丘迎风坡向沿着沙脊方向的变化，表明沙脊正在发育，大部分沙脊沙分选较好，标准差范围为1.09 ~ 0.33，平均值为0.65，偏度范围为-0.31 ~0.35，平均值为0.08，峰度分布范围为0.70 ~ 1.57，平均值为1.08，表明大部分粒度频率曲线属于中等峰度，脊间砂以宽峰度为主，比新月形沙脊上的沙粒粗，分选性差，沙粒的平均粒径与标准差呈明显的负相关，羽状沙丘的累积概率尺度-频率曲线以4段模式为主，羽状沙丘的累积概率尺度-频率曲线以4段模式为主新月形沙脊为单峰型，占96.7%;而“羽毛笔”的曲线（脊间洼地），双峰型，占54.2%（沙脊与脊间洼地的交替）在一定程度上会影响粒度的分布，本文的研究结果将为进一步研究羽毛状沙丘的形成和发展机制提供参考。
Feather-like dune is a kind of dune with unique shape,mainly distributed at the north of Kumtag desert.The dune,looking like a feather,is composed of two parts as "quill" and "plume"."Quill" are the longitudinal sand ridges formed by individual barchan dunes with clear profile which have coalesced(the plinth of the windward slop of the former dune is coalesced with the southeast flank of the latter one) and elongated."Plume" is composed of the inter-ridge undulate sand land.The peaks and valleys of the wavy land are almost perpendicular to the sand ridge,from which,the "feather-like dune" is formed.It can be viewed from the aerial and satellite photos.There is no report concerning systematic observation and sampling research on the substance deposition process and the variation of grain size in the feather-like dunes.This paper,based on sampling analysis of the sediments on the surface of feather-like dune,preliminarily discussed the distribution characteristics of grain size on the dune.One hundred and eight sand samples were taken from feather-like dunes in Kumtag Desert.The samples were collected from different sites with areas of approximately 20 cm×20 cm and to a depth of 0-5 cm,and analyzed with the sieving method.The results show that the grain size of barchan sand ridge sands ranges from 1.57φ to 3.14φ with a mean value of 2.42φ(0.187 mm);the fine sands with diameter of 0.125-0.25 mm are the dominant one,averagely making up 60.8% in each sample.The sands become gradually finer from the feet of both slopes to the tip of the barchan sand ridge.The sand on northwestern slope is finer than that on southeastern slope.The sands also become gradually finer from the upwind slope to the dune tip and to the downwind slope of barchan dune along the direction of sand ridge,which indicates that the ridge is growing up.Most of the ridge sands are better sorted.The standard deviation ranges from 1.09 to 0.33,with the mean value of 0.65.The skewness ranges from-0.31 to 0.35,with average of 0.08,it belongs to symmetric distribution.The range of kurtosis is from 0.70 to 1.57 with mean value of 1.08,which means most of the grain size frequencies curves belong to medium-kurtosis.The inter-ridge sands,dominated by wide kurtosis,are coarser and more badly sorted than sands on barchan sand ridges.There is an apparent negative relationship between the mean diameter of sand and the standard deviation,between the skewness and the kurtosis.In terms of cumulative probability size-frequency curves of feather-like dune,the 4-section-mode is the dominate one.The cumulative probability size-frequency curve of "plume"(barchan sand ridge),with single peak,occupies 96.7% in all samples;while the curve of "quill"(inter-ridge depressions),with double peaks,make up 54.2% in all samples.The complete and partial landforms(the alternated sand ridges and inter-ridge depression) will impact,to some extent,the distribution of grain size.Subsequently,the findings of the paper will offer references for the further research on the mechanism of formation and development of feather-like dunes.