| Desert geomorphological evolution and environmental changes are serious problems which attract almost domestic and overseas desert geographers attention,along with development of researches on the inland arid,water source,ecological resume and sand-dust storm origin. Mechanism of the desert geomorphological evolution is still unknown and being studied. A special sand geomorphology existed in Southeast Badain Jaran Desert is essential made from Mega-dunes,which are the largest sand geomorphology in the world and kept as valuable geological heritage in the nature. More and more scientists pay attention to studying the special geomorphology since 1930s. This work studies the structure and formation of mega-dunes.From the overall aspect of the region,the forming of mega-dunes in the south part of Badain Jaran Desert is related with the regional terrain that has blocked the air current,the Yabulai mountain which lays in the southeast of the Badain Jaran Desert and the Dabei mountain in the south have been the block for the motion of northwest wind and west wind. The northwest wind as a main filed,which contains a lot of sand,and because of the block the sand has been deposited,the sand go into the southeast area through the northwest access,based on the block sand has become a comprehensive mega-dunes. In the mid-north and the northwest area,there's no big block for the wind filed,and it's drier than the south and the southeast area,which cause fewer water in the surface of the ground and fewer plants,thus the wind blows fast on the surface of the ground,it's hard for sand depositing,sand are blowing into the air,so there's fewer secondary dunes overlaying. The dunes here are shaped simple and of low height-gap,which reflects the co-influence of wind-deposit and wind-rust. The terrain of compound mega-dunes has presented as an overall landscape transverse dunes,and the compound of simple secondary transverse dunes in the windward slopes and star dunes on top. It's necessary to explain every individual element of the mega-dunes for reasoning the forming of the mega-dunes. The star dunes and the transverse dunes of the north and middle have the same sand origins to the mega-dunes in the south of Badan Jaran Desert. Though the wind is different of the regions,for the overall aspect they are all at the edge of the monsoon,and controlled by westerlies,tableland monsoon and southeast monsoon. Therefore, it's quite reasonable necessary and operational for the research from the overall aspect of forming of simple duns and mega-dunes. 1. The regular order of mega-dunes display that the wind have strong influence on it, and it took off the probability that the underlying terrain control the mega-dunes. In this paper, based on the data from experiments,we modified the height of mega-dunes,and the distance of experimental equations.then get the height is equal to 0.08Sp1.01. (Sp is the distance between dunes).2. Granularity of mega-dunes reveals that lower windward slope of mega-dunes is mainly effected by erosion, and higher slope is mainly effected by the accumulation of wind-based,and lower leeward is effected by the accumulation of sands gravity.3. The fractal dimension of star sand hills is 1.041, the fractal dimension of complex star sand hills is 1.117,the fractal dimension of complex star sand hills chain body is 1.158,which improved that using fractal geomorphology to discraibe aeolian geomorphology is valid4. For lacking of information about the profile of the leeward slope in previous domestic study,we used RTA super ground-based coupling antennas of MALA Company in Sweden,and we obtained the constant profile of both windward slope and leeward slope for the first time in China by improving design. Although integrated dune-detected radar profile can be obtained internationally,the height of the dunes are limited from a few meters to tens of meters. Hence, the selection of antenna in this research made the profile of ground detect radar has a fine degree of elevation, continuity and integrity.5. The establish of forward and inverse model of radar wave in different hydrous sand layers can be used in the iterative fitting of GPR inversion model,and the images of GPR depicted the existence of both ancient dunes and water layer.6. The paleo wind directions were reconstructed by the sand dune occurrence. In NW Badain Jaran Desert, the calcareous cementation were dated at 89.61±2.45ka BP by the OSL,at the same time,113.89±5.51ka BP by the OSL in SE Badain Jaran Desert. The ancient dunes showed that the west wind prevail in Last interglacial Glacial, while during the Last Glacial the NW winds dominate.7. In previous research, during the interior areas in Badain Jaran Desert, there are no continuous data results in the profile. In this paper, the dating results were achieved from a profile which is continuous and rhythmic by the lake sediments and aeolian sediments deposited. The profile is 4 m depth, and the lowest in the profile were dated at 101.35±17.12ka BP, 139.48±19.63ka BP by optically stimulated luminescence (OSL) results. The dating results showed there were humid in South Badain Jaran Desert during MIS 5e and MIS 3.8. Inner structure and forming process in large sand hill were interpreted by the holistic, from outside to inside and from old to young analysis. The results showed that wind-blown sand was blocked by the Yabulai and Beida Mountains, then the sand were deposited and formed the sand dunes which were regularly arranged. The paleo-sand dune cementation were preserved by the humid environments,at the same time,the sands deposited on them continually,finally,the large sand hill were formed. Meanwhile, whether the water layer in the sand hill can support the attitude of the sand hill or not,further researches are needed.
|
PDF Full Text Request