| As the material basis of aeolian geomorphology, sand source is significant in the process of dunes formation. The analysis of sand source can also provide theoretical basis for to river management and the control of riverine dunes. The analysis on characteristic of grain size and heavy mineral is important tools of aeolian geomorphic research and play significant role in the research of sand source and the process of dunes evolution. Through the field research, samples of riverine dunes on the right bank of Xiangshui River in the west of the Horqin Sandy land are collected. On the foundation of the studies on dunes shape, grain size and heavy mineral, combining with observations in the middle reaches of Xiangshui River, the results were obtained as follows:(1)Due to abundant sand source, dunes adjacent to the valley consist of coarse sand, while those away from valley fine sand dune to limiting sand source. The windward slopes of dunes adjacent to the valley are usually covered by some sand ridges composed of coarse sand, however small sand ripples on ensuring dunes is composed of fine sand. That’s because sand source of dunes adjacent to the valley include a lot of coarse sand and dunes away from the valley gain most medium sand and fine sand. The windward slope of dunes adjacent to the valley form some accumulation areas of fine sand with different size.(2)The research region are mainly medium sand(45.95%) and fine sand(34.73%), good sorting(0.70Φ), a near symmetrical distribution(-0.03) and a narrow kurtosis(1.13). Due to the influence of particle size of sand source, the mean grain size of dunes adjacent to the valley decrease from stoss toe to the summit, while the mean grain size of dunes away from valley increase from stoss toe to the slope top, and the mean grain size of dunes nearby valley include both cases mentioned in dunes adjacent to the valley and dunes away from valley. Regarding to dunes of research region, the sorting becomes better from the toes of windward slope to the dune tops.(3)According to the analysis of sedimentary environment, 137 samples is the deposited environment of the lacustrine, and the following is deltaic, Aeolian and diluvial. The main deposited of environment about samples of research area is Aeolian, suggesting that stream action carried debris and deposited. These deposits become sand source of dunes under wind-water erosion.(4)Hematite and limonite, epidote and garnet content is the most. Mineral species are mainly silicate minerals, and the content of relatively stable mineral is the most in the aspect of resisting weathering. The result about metamorphic rock and intermediate-acidic magmatic rocks is found by the analysis of GZi index and ATi index.(5)The value of ZTR and stable coefficient of heavy minerals increase from dune c1 to dune c3, suggesting the sand source of the first three dunes is influenced by stratum sand of valley slope. The grain size about dune adjacent to valley is coarse and dune nearby valley fine, suggesting that dune adjacent to valley gain mainly coarse sand from brae of valley and dune nearby valley gain mainly fine sand. The value of ZTR and stable coefficient of heavy minerals have not a prominent order from dune c4 to dune c7, suggesting the sand source of dunes away from valley derive from interdunes.(6)The grain of sand on the north side of research area is more coarse than the middle and south side of windy desert region. This is because the river migration in north, and coarse sand of the deep stratum are extracted from different part of physiognomy. The dune sand adjacent to valley is coarser than dune sand away from valley. The difference of grain size between dune adjacent to valley and dunes away from valley is because them have different sand source. |
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