• 责任者：Wang Yanzai (State Key Laboratory of Earth Surface Processes and Resource Ecology ; Beijing Normal University ; Beijing 100875 ; China)
• 刊名：Quaternary Sciences
• 出版年：2013
• 卷期：33(2)
• 关键词：沉积物 ; sediments ; 粒度分布 ; size distribution
• 页码：p.376-387
• 图表：illus., 6 tables, 42 refs.
• 分类号：1400
• issnNo：ISSN1001-7410
• isbnNo：CN11-2708/P

Particle size and sorting characteristics of surface sediment are primarily dependent on antecedent wind  condition. Particle size analysis is an essential approach for classifying sedimentary dynamics. Particle size fraction  has been used to be as a proxy indicator of winter monsoon strength in Quaternary in the studies of Chinese loess  sections. But correspondingly artificial particle size fraction （for example, the diameter of the particle 〈 5txm is  classified as clay; 5.0 - 62.5μm as silt sand; 62.5 - 125.0μ m as very fine sand; 125 - 2501μm as fine sand; 250 -500μm as medium sand; 〉500μm as coarse sand）was often used to qualify the effect of wind speed on the  surface sediment in previous studies. Whether the artificial method is reasonable is still debatable. In this study, we  aimed to establish a proxy indicator to quantify the wind speed effect on surface sediment particle size distribution  based on the correlation between the magnitude of wind speed and fraction of dominant particle size.  The field work has been undertaken in a longitude dune field in the central of Taklimakan Desert,located in the site of K352 along the Desert Highway, near the small town of Tazhong. The longitude dune covers about 2.7km between the latitude of 38 °54＇28.75＂N and 38 °55 ＇58.06＂N and longitude 83 °32＇13.87＂E and 83 °32 ＇25.41 ＂E. The sand protection system along the highway was correspondingly constructed to keep the sand off the highway in windy days, which includes shrub barriers and artificial barriers. The artificial barriers have lost its protective role, but meantime shrub barriers still work. The width of the shrub barriers perpendicular to the highway is about 78m,while 48m for the upwind side and 30m for the downwind side. The appearance of the shrub barriers not only modified the overlaying surface along the Desert Highway, but also influenced the near-surface wind fields and thus minimized the movement of sand flow. This facility also provided us a case study of how surface wind speed might affect the sediment particle size distribution. To achieve this goal, we firstly collected 92 samples in the depth of 0 -5cm below the ground surface from five cross-sections located on the longitude dune, among which 15 samples was collected from the bottom of the windward slope, 18 samples from the central of the windward slope,20 samples from the top of the longitude dune, 15 samples from the central of the leeward slope and 24 samples from the bottom of the leeward slope. We also got the data of wind speed at each sand sample site by using measuring instruments in the field. And then we used EOF （ empirical orthogonal function） method to quantify the spatial variation of the particle size fraction ,finally analyzed the correlation between wind speed and the dominant particle size fraction, by which we want to build up a proxy indicator or sensitive grain size fraction of wind speed based on the surface sediment samples data. Our main results are as follows： （ 1 ） Surface sediment particle size has a single peak distribution character within shrub barriers, which inherits the original distribution patterns of dune sediment. Particle size corresponding to single peak has a difference value at different topography positions of longitude dune. The coarse sand concentrated in the central of windward slope, which related to the erosion and accumulation distribution of large terrain. （2）The correlation between the second eigenvector and wind speed along the cross- section is quite nice. The spatial distribution of the second eigenvector can be used as a sensitive proxy of wind speed. （3）Two grain-size distribution patterns are observed that of the finer grain-size fraction （≤ Xμm, 125.6 μm ≥ X ≥ 109.4 μm） and that of a coarser grain-size fraction （≥μm, 125.6 μm ≥ X ≥109.4 μm） , which wgre defined as sensitive size fraction corresponding to wind speed variation. The determination of the sensitive size fraction has a great significance for the evaluation of protective effect of shrub barriers. （4）The difference of sensitive size fraction between outside and inside area of shrub barrier is almost greater than 10% ,which maximums at the bottom of the windward slope of longitude dune, and minimums at the bottom of the leeward slope of longitude dune.