毛乌素沙地东南部边缘不同地质成因类型土地沙漠化粒度特征及其地质意义

首次对毛乌素沙地东南部边缘沙漠—黄土地带的土地沙漠化进行系统的地质学分类，提出了沙地内部就地起沙型沙漠化、河流谷地就地起沙型沙漠化、风化残积就地起沙型沙漠化和风沙侵入型沙漠化等四种土地沙漠化类型。通过深入分析不同地质成因类型土地沙漠化的粒度特征，探讨了不同地质作用对土地沙漠化的贡献及其对土地沙漠化防治方面的重要意义。研究表明，研究区的土地沙漠化以就地起沙型为主，河流的水力搬运是沙漠化物质搬运的主要途径，风力作用则是对河流湖泊沉积物的进一步分选和再沉积。最后，提出了不同类型的土地沙漠化防治对策建议。

Grain Size Distribution Characteristics of Different Geo-genetic Types of Sandy Desertification and Their Geological Significance in Southeast Mo Us Desert

Sandy desertification in southeast Mo Us desert and its neighboring regions, according to their material origins〖KG*2〗and physiographic〖KG*2〗characteristics, can be classified into four types, sandy land in situ type, flow valley in situ type, weathered residual in situ type and finally the wind drifted type. The sands of sandy desertification of sandy land in situ type come from both palaeo aeolian〖KG*2〗sand and those of paleo or modern fluvial or lacustrine facies. Sands of this type of desertification have the characteristics such as coarse grain, of which mid grain size are between 200－300μｍ or even bigger than 1mm, lower standard〖KG*2〗deviation, and narrow and positive leaning distribution〖KG*2〗patterns. Researches on grain size parameters show that their formation environment is likely fluvial.  Sandy desertification of valley in situ type distributes mainly in river valleys and their neighbored regions, such as flood beds, terraces and nearby districts. Sands of this type may have varieties of sources, such as modern and paleo fluvial or flooded sediments Quaternary Epoch. Sands of this type have the characteristics of broad range mid grain size (40-445μｍ), middle degree of sorting, narrow and positive leaning distribution patterns. These features suggest that the sands of river valley type desertification are mixtures of different geologic processes, mainly fluvial and aeolian. Weathered residual in situ type desertification are formed by the erosion and separation by wind and fluvial forces of any sediments occurred in the region. During this process, fine grains become less and less, coarse grains remained. This type of sandy desertification mainly occurred in the north part of loess plateau. Their sands may come from paleo aeolian sands, sandy loess, paleosols as well as paleo fluvial terrace sediments. Re active paleo aeolian sands have the characteristics of both homogeneous in limited areas and features of different layers. Palaeo aeolian sands have two grain grades in the studied area, of which average grain size are between 23-60μm and 152－202μm respectively. They also have narrow, positive leaning distribution curves.  Wind drifted sandy desertification have the characteristics such as coarse grained sands (140－310μm), low clay contents ( <5% ), and very narrow and positive leaning distribution curves. This suggests that they are the products of modern wind blown sands. For the purpose of combating sandy desertification of different genetic type, it is important that different protect and renovate measurements should be used. It is strongly suggested that using the methods of seeding grasses and manpower projects to fix the drifting sands during combating sandy land in situ desertification. As for the river valley in situ desertification, the methods of reducing soil erosion, protecting terraces and flood beds should be firstly used. To deal with the weathered residual desertification, methods of reducing water and wind erosion protecting fine grain materialsfrom losses can be used, such as reducing herding, vegetation and plantation. Finally, for combating wind drifted sandy desertification, manpower projects can be used to reduce wind harm and organic measurements to increase the percentage of coverage.