浑善达克沙地沉积物粒度特征及其指示意义

Grain size characteristics of sediments in the Hunshandake Sandy Land and its implications

沙漠/沙地中沉积物的粒度是物源及各种地表过程长期作用的结果。研究沉积物粒度特征对认识沙漠/沙地形成演变和防沙治沙具有重要意义。本文对浑善达克沙地不同类型沉积物进行了详细采样,对其进行粒度和端元分析。结果表明,浑善达克沙地风成沙受风力分选作用影响,平均粒径和分选系数沿盛行风向存在显著变化趋势。偏度和峰度的空间格局较为复杂,可能与局地物源、沉积环境和植被覆盖等因素有关。端元分析结果显示,风成沙含有6个端元(EM),其中EM1与沙地西部湖相沉积露头有关;EM2来自松散的河湖相沉积物,在风力作用下呈现显著空间变化;EM3是风成沙的主要物质来源,与河流携带的碎屑物质有关;EM4可能来源于周围山体的冲洪积物;EM5和EM6粒度最粗,与间冰期河湖相沉积物中的粗粒组分相似。浑善达克沙地沉积物粒度特征表明,风成沙主要来自沙地附近不同时期的河湖相沉积物,远源贡献较少。沙地西部是风成沙的主要源区,在风力作用下较细组分的风成沙向沙地中东部运移,而沙地南缘和东缘河流也为其邻近区域贡献了沙源。本文研究说明,通过高密度采样并结合端元分析,沉积物粒度可解决地表过程复杂的沙漠地区风沙物源识别问题。

The grain size of sediments in sand seas is influenced by both sand provenance and various surface processes.This study collected 224 sedimentary samples from the Hunshandake Sandy Land including aeolian sand,fluvial and lacustrine sediments.Grain size measurement and end member analysis found that the mean grain size and sorting of aeolian sand generally decreased across the Hunshandake Sandy Land downwind in the SE direction.The spatial variations of skewness and kurtosis are more complex,indicating that the grain size parameters of aeolian sand are affected by the local provenance,depositional environment,and vegetation coverage.The end member analysis shows that the aeolian sand contains six end members(EM).EM1 is related to lacustrine outcrops in the western sandy land,while EM2 is likely to originate from loose fluvial and lacustrine sediments,controlled by both wind and topography.Fluvial deposits contribute to the widely distributed EM3,which is the dominant aeolian sand fraction found across the region.EM4 is predominantly found in the outer regions of the sand sea and closely associated with alluvial/fluvial deposits.EM5 and EM6 have the coarsest grain size and may originate from lacustrine/fluvial sediments that accumulated during past interglacials.Our findings suggest that the dune sand in Hunshandake mainly comes from the lacustrine/fluvial deposits around the sand sea,while the sand belt is unlikely to be a major source of dune sand.Aeolian sand with different sources is mixed in the western Hunshandake with fine fractions moved by the prevailing wind to the central and eastern parts of the sand sea.Rivers originating from the southern and eastern mountains also contribute aeolian sand to the adjacent areas.This study highlights the importance of extensive sampling combined with end member modeling for discriminating aeolian sand sources in desert areas.