Development Environment And Process Of Aeolian Landforms In The Chaerhan Salt Lake Area Of ??the Qaidam Basin

The Qaidam Basin is one of typical Aeolian Geomorphology regions in China.It is an ideal place to carry out the comparative study of planetary Aeolian geomorphology.Given serious natural conditions,the researching of the Qaidam Basin was limited and hadn't enough evidences to support the formation and evolution of Aeolian Landforms.It is necessary to have a survey,observation and collection of natural geographical environment data so that a scientific basis will be provided for further understanding of desertification process in alpine region,and a support will be provided for improvement research results of regional Aeolian geomorphology.Based on two in-depth investigation of Qaidam Basin Desert,the first-hand data were gathered from sedimentary of different Geomorphology and near-surface wind flow.According to the analysis of characterize both the Aeolian Geomorphology sedimentary and near-surface wind flow in the Qaidam Basin,the developing environment of Aeolian Geomorphology were concluded.As the research methods,the WV-1 panchromatic remote sensing image,Google Earth HD video and 1:50000 regional contour maps were used to measure the macro pattern and geomorphology parameters of Aeolian geomorphology,discuss the formation process of typical sand dunes and its factors and conclude the mechanism of dunes symbiotic appearance pattern formation.In this paper,some results were drawn as follows:1.Formation environment of Aeolian geomorphology in the Qaidam Basin.(1)In the research area,mean value of grain size is 0.79??5.11?.Fine sand is dominant in the sand composition.The mean value of standard deviation is 0.69.The mean value of skewness is 0.11.The mean value of kurtosis is 1.25.the sedimentary environment of study area is very complex,including Aeolian environment,lacustrine environment and fluvial environment;however,Aeolian environment is important.Light mineral dominate in sedimentary mineral content is mainly composed of the Quartz and Feldspar and some unstable components such as Halite exist also in the sediments.Halite content of linear sand dunes is 13.25%and 2%in crescent dunes.Hornblende and biotite unstable minerals accounted for a higher proportion of heavy minerals.By the ATi ratio(average 68.82),GZi ratio(average 80.91)and ZTR ratio(average 2.15)in the heavy mineral,the deposition environment of Qaidam Basin was indicated that heavy minerals in sediments of maturity is not high and the provenance is near.Soluble salt content in surface sediments ranged from 0.483%to 19.601%,with a mean value of 42.935%.Na+ in cation is dominated by the average content is 6.286%;the Cl-in anion is main by the average content of 10.894%;Soluble salt type is different from marginal basin to the center of the basin.The main type is Sulfate on the alluvial fan and is Chlorine near the center of the basin or salt lake salt.Soluble salt content in the linear dunes sediments is higher than that of barchans dune.The surface wind field in the Qaidam Basin is influenced by the flow around the North Branch of the westerly jet in the planetary wind system so the direction of sand-driving wind is mainly WNW.Seasonal variations of wind speed and wind direction in the near surface were controlled by the plateau monsoon and the low pressure of the Qaidam basin.The annual average wind speed is 3.7m·s-1 in this area,with the peak value in spring and the minimum value in the winter.Although the direction of the sand driving wind is mainly NW and WNW in the area,the combinations between the first wind direction and the second wind direction were significantly different.Linear dunes appeared in a 45 degree angle between the two groups in the wind.The wind energy environment was intermediate in the Qaidam Basin.The wind direction on variability RDP/DP belongs to intermediate or low ration and blunt unimodal or obtuse bimodal wind regimes.2.Aeolian landform types and spatial distribution in the Qaidam Basin.(1)The area of sand landforms is 3.95×104km2 in the Qaidam Basin,including wind-erosion landform area of 2.64 X 104km2,which is one of the largest wind erosion landform areas in our country,and wind-accumulation landform area of 1.31×104km2.Aeolian landform in the Qaidam Basin has the characteristics of general dispersion and local concentration in spatial patterns.According to the location and underlying landform,the Aeolian geomorphology in the Qaidam Basin is divided into four distribution areas.(2)The trend of linear dunes keeps from 289° to 298°.For it has the height of 10?20m,width of 30?40 m,the ratio of width to height of sand dunes is about four times as tall.The length of linear dune shave is 1?2 km and the distance between the adjacent sand dunes is 100?200 m.The shape of linear dunes changes the long and straight linear model into short and high "Y" model from southeast to northwest.(3)Crescent dune windward slope is 3?5 times of the leeward slope length in the study area.The height of dune is about 10?20 m.The width of horns width is 80?140 m.the width is 3?5 times of the height.Crescent dunes are mainly distributed on the edge of desert area where the supply of sand is relative short.The windward slope of crescent dune chain is about 139.4 m,with the leeward slope of about 22.4 m.The distance of the top between the adjacent sand dunes is 84.3?170.4 m.The strikes of linear sand dunes keep from 196° to 258°.The maturity of crescent dune sand dunes chain is low in the edge of desert,but it is high in the heart.3.Development process of sand landforms in the Qaidam Basin.(1)The terrain features of high mountains and deep basin controls the scale and speed of the terrigenous detrital material moving from the edge to center,which caused the geomorphic types of different external agent and their spatial heterogeneity.The fluvial terraces and alluvial fan of the modern drainage pattern,which is poor in north and rich in southern,provides ample source of sand and the site for the wind erosion and accumulation,which is the main driving factors of landscape formation and evolution about the Aeolian landform.The fluvial plain and salt scrap material which were created during the process of salt lake degradation change the shape and pattern of the sand landscape.The desert basement of the Qaidam Basin formed at the end of the last glacial stage of late Pleistocene in quaternary period,the forming time of mass basement may be around 12.5 ka p.The evolution mode of the Qaidam Basin is the fluctuant development pattern,where formed the "west wind-monsoon type" desert.(2)The Linear sand dunes in the study area are divided into linear model,Y type and dysfunction of three types.The linear sand dunes develop on fluvial plain which lays in the downwind direction of the wind that has the large-scale vertical scroll vortex existence;The development of "Y" type dune may be more related to the silt clay and soluble salt which have high percentage in the sand substance;The barrier types of sand dune develop mainly in the leeward side of streamlined yardman body and vegetation body.Because the crescent dunes and sand dune chain in the study area were influenced by the nature of the underlying surface and fine-grained lacustrine sediment and the accumulation of soluble salt on the surface that's ratio increases in the Aeolian sand,the form of sand dunes appeared the reverse succession from complex to the simple form.(3)The character of a single stable wind conditions is the basic factor of the formation and development of the symbiotic landscape pattern about sand dunes.The underlying surface characters,such as a flat and open dry salt flats,is the key factor of the formation about the symbiotic landscape pattern.That sediment contains a certain percentage of the soluble salt and silt clay is the important factor of dune symbiotic geomorphic landscape development.