科尔沁沙地大型沙波纹的初步研究

Preliminary study of the large-scale ripples in the Korqin Sandy Land

通过实地考察、观测和采样,利用Google Earth遥感影像和激光粒度分析仪,研究了科尔沁沙地大型沙波纹(large-scale ripples, LSR)的空间分布、单体和群体的基本形态和粒度特征,探讨了LSR粗颗粒的来源、它同普通沙波纹和普通风成沙在颗粒组成、形态特征和内部沉积结构方面的区别。结果表明:(1)科尔沁沙地的LSR主要分布于翁牛特旗中部和北部地区。(2)LSR空间单元的空间形态具有片状、斑块状和条带状3种类型,分别发育于宽阔的丘间地、沙丘中上部、槽形低地3类地形部位。(3)LSR平均长度为6.32 m,总体走向为东北—西南,平均波长为1.68 m,空间分异较为明显;单体LSR的前后坡不对称。(4)LSR的颗粒为中砂-粗砂粒级,其中粗颗粒主要来自旧河道的河流冲积层、下伏Q3河湖相地层、剥蚀残山的风化壳和山麓洪积物。(5)LSR同普通沙波纹在外观、物质组成、几何形态和内部沉积结构方面有明显差异。该项研究将有助于促进风沙地貌学的理论发展和实践。

Although large-scale ripples(LSRs) are widely distributed in various desert regions of the globe, there are few studies on LSR in China. Through field investigations and observation, remote sensing imagery analysis by Google Earth, and a laser particle size analyzer, spatial distribution patterns and fundamental morphometric and grain size features of both individual and collective forms of LSRs in the Korqin Sandy Land of China are explored. Furthermore, coarse grain sources, differences in granulometric distribution, morphometric features,interior sedimentary structures between LSRs and common ripples, and differences between sands from LSR and common wind ripple are discussed in this study. The results are as follows:(1) LSRs are primarily concentrated on the central and northern parts of Ongniud Bannar, the western extreme of Korqin Sandy Land, and close to or surrounding nearby rocky mountains;they are also primarily distributed in the southern zone of the middle Xilamulun River, on the eastern banks of the Xiangshui River, in the area of the Songshu Mountain, and on the fluvial plain of the lower Chaganmulun River.(2) In line with the dimension, shape, and location of LSRs, plot-,patch-, and stripe-shaped LSR spatial units can be recognized, which are mainly generated on such geomorphic positions as broad interdune, central and upper stoss of a dune, and trough-like lowland, respectively.(3) The average length of LSR is 6.32 m, with an obvious spatial difference;the average strike is NE-SW, significantly perpendicular to the local predominant wind direction and with an insignificant spatial difference;the average spacing is 1.68 m,with a spatial difference;individual LSR has a dissymmetric cross-section.(4) The grains of LSR are comparatively coarser, belonging to the class of middle-coarse sand, which are, however, thinner than those in northwestern China,West Asia, and North Africa;coarse grains are mainly derived from fluvial sediments on ancient river channels,underlying fluvial-lacustrine sediments of late Quaternary, and weathering crusts and alluvial deposits on foothills of nearby denuded mountains.(5) There are considerable differences in appearance, grain composition, geometric morphology, and internal sedimentary structure between LSRs and common sand ripples, which are the smallscale perpendicular bedforms among aeolian depositional landforms and can superimpose on the surfaces of various dunes. The research will, to some extent, advance the principle theories of aeolian geomorphology and effective sand-control practice.