【摘要】 风蚀坑是高寒地区草原沙漠化的起点,气流对坑内沙物质的侵蚀、搬运和堆积为沙漠化进程提供了重要的物源。以共和盆地龙羊峡水库上游黄河阶地高寒草原上不同发育阶段的风蚀坑为研究对象,通过分析表层沉积物的粒度组成特征,比较风蚀坑表层沉积物粒度组成随坑体形态和地貌部位的变化趋势,探讨风蚀坑内沉积物的粒度分异在其形成演化过程中的动力学意义。结果表明:风蚀坑表面沉积物来源主要是古风沙沉积物。尽管研究区风蚀坑空间尺度相差很大,但因为动力学过程的相似性,沉积物粒度变化依然在宏观尺度上表现出了一致性。随着风蚀坑面积扩大,在积沙区迎风坡的中下部以及坑底部位粗沙、极粗沙成分显著增多。与此同时,沉积物分选性变差,表层沉积物分布模式由单峰态渐趋向多峰,粒度参数变幅明显增大。受盆地内盛行风以及坡向影响,风蚀坑两侧侵蚀壁受侵蚀程度差异明显,东北壁受到了更强的风力掏蚀且分选性更好。沉积物粒度分析作为风沙地貌学的基础性工作,也为高寒草原风蚀坑的发育演变、空气动力学过程等后续研究提供了基础参数。更多还原

【Abstract】 Blowout is the driving factor of sandy desertification in alpine meadow region.The sediment within deflation basin which is eroded,transported,and deposited by airflow provides a dominant source material for desertification.This study focuses on the different blowouts under different developmental stages which formed in alpine meadow region on the terrace of Yellow River upper reaches of Longyangxia Dam in Gonghe basin,and its aim is to investigate the variation of grain-size associated with topography,morphology and its dynamical significance by comparing the particle size distribution of surface sands.The result indicates that surface sediment of blowout mainly provenances from paleo-sediments.Although the sampling blowouts show considerable differences in sizes and shapes,grain-size characteristics remain constant in macroscale because of the similar al process operative within the blowout.With the increase of the blowout area,significant increasing rate of coarse and very coarse sand is found on the middle-lower windward slope and deflation basin.In addition,the surface sediments tend to be less well sorted and varied to multimodal distribution;the variation scale of the grain size parameter also became wider with the increase of the blowout size.The effect of the slope aspect and the prevailing wind from northwest leads to the preferential erosion and better sorting on northeast wall compared to opposing wall.The grain size analysis of blowout surface sediments as the base research of aeolian geomorphology provides the primary datum for the following study to clarify the development and dynamical evolution process of blowouts in alpine meadow regions.更多还原