巴丹吉林沙漠东南部沙山与湖泊形成研究

【作者】 邵天杰；

【导师】 赵景波； 董治宝；

【作者基本信息】 陕西师范大学 ， 区域环境学， 2012， 博士

【摘要】 巴丹吉林沙漠除具有世界上高差最大的沙山外,还拥有沙山与湖泊呈交替排列分布的特殊景观,所以巴丹吉林沙漠地貌一直都是沙漠地理学者高度关注的对象。该区沙山与湖泊密切相关,把两者联系在一起进行研究有助于深刻认识它们的形成和内在关系。沙山风沙物质组成、地貌分带、湖水及地下水化学特性、沙层水分含量和水分运移等对沙山和湖泊的形成具有重要的作用,但因自然环境条件恶劣、深入沙漠腹地困难等原因,对巴丹吉林沙漠的物质组成、地貌分带、沙山发育模式、沙层水分与沙山形成及湖泊形成的关系等研究总体较少。过去对巴丹吉林沙漠地貌的研究,大多集中在较大尺度范围的沙丘地貌与沙漠地表物质组成的分布特征方面,目前还没有见到单个沙山的物质组成与地貌分带相结合的系统、定量研究成果的发表,也没有见到将深部沙层含水量与沙山形成及湖泊形成相联系的研究成果发表。本文研究了该区沙山与湖泊形成的主要环节,为最终解决沙山与湖泊的形成提供了依据。巴丹吉林沙漠区沙山、湖泊地貌与沙层水分的研究,对揭示沙山与湖泊形成机制及动力变化、沙层水分对湖水的补给和对沙山形成的作用有重要科学意义,对维护当地生态环境平衡、保护生物多样性、控制沙漠化和科学开发利用沙漠水资源等具有重要实际意义。为了查明巴丹吉林沙漠东南部沙山与湖泊的形成、沙漠湖水的补给来源,揭示极端干旱的荒漠沙山区沙层水分对沙山形成的作用,选择巴丹吉林沙漠东南部沙山与湖泊密集分布的中心地区,通过野外观测、粒度分析、元素测定、水化学分析、扫描电镜鉴定与能谱分析等方法,获得了沙山迎风坡地貌分带、沙山不同部位沉积物的粒度组成和各粒级含量的变化、沙山不同部位沉积物中常量元素和微量元素的含量、沙漠湖泊及地下水化学成分、沙层水分含量、沙层中次生盐类晶体形态和化学成分等数据。根据野外观察资料和实验分析数据,研究了巴丹吉林沙漠东南部沙山迎风坡的地貌分带特征、沙山不同部位沉积物的粒度组成和含量变化与沙山形成风动力条件之间的关系、沙山常量元素和微量元素的含量变化对地貌分带的指示作用、水化学成分空间变化规律对湖泊及地下水补给来源的指示作用、高含量薄膜水与次生石膏对沙山水分运移及对湖水和地下水补给的重要指示作用,获得了以下主要结论：(1)根据沙山迎风坡次级地貌类型的分布和变化的观测数据,将沙山迎风坡地貌从下向上划分为四个地貌带。第l地貌带是风蚀粗化的低平沙地洼地带,第2地貌带是中下部的稀疏简单的新月形沙丘或沙丘链带,第3带是密集叠置的新月形沙丘和沙丘链带,第4带是陡峭的沙山主峰带。(2)提出了全球高差最大沙山形成的模式,即组成该区沙山的风沙物质不是一次搬运到达沙山中上部的,而是经过了多次的风力搬运阶段才达到沙山上部。首先是沙山下部的中细沙物质由风力搬运达到沙山的中部,并形成沙山中部新月形沙丘和新月形沙丘链。然后沙山中部新月形沙丘和新月形沙丘链在风力作用下不断向沙山上部移动,相对靠下部的新月形沙丘为靠上部的新月形沙丘提供风沙物质,经多次搬运,最后达到沙山上部并形成沙山主峰。(3)在呼和吉林湖东沙山等沙山斜坡上首次发现了对大气降水通过入渗进入沙山深处和水循环有重要指示作用的次生石膏的存在,并发现次生石膏与沙层中缓慢渗出的重力水相伴出现,指示大气降水通过沙层入渗已经到达了沙山的深部,并在沙山斜坡出露于地表,表明大气降水能够通过入渗补给湖水和地下水。水分进入沙层增加了沙层湿度和沙粒间的粘结,对沙山的形成起到了促进作用。(4)根据4m深度钻孔剖面含水量测定,首次确定了巴丹吉林沙漠地表之下1～2m深度的沙层中存在高含量薄膜水,表明大气降水在经过蒸发、植物蒸腾之后,仍有一些剩余的水分通过沙层向下运移,至少可成为湖水和地下水的补给来源,这与沙山区植被的带状分布、沙山次生石膏的形成和斜坡水分的渗出指示的湖水和地下水补给来源一致。同时充分证明该区沙层水分具有正常循环和沙层水分具有正平衡的特点。该区沙层水分的正平衡对沙山形成也起到了重要作用。(5)巴丹吉林沙漠沙山风沙物质具有双层结构,表层10cm粒度较10cm之下明显粗,表层风沙物质的粗化指示沙山仍然存在一定的活动性。不同部位沉积物粒度组成存在明显的差异性,从沙山坡脚到坡顶粒度组成呈现由粗变细的趋势,这是它们的形成过程和受到的动力作用存在差异造成的。迎风坡坡脚粒度成分较粗,这是在风力侵蚀作用下细小砂粒被风力搬运带走、剩下了较粗粒的成分决定的。迎风坡中上部粒度成分较细是由中上部坡度和高度较大,对风力搬运产生阻碍作用,导致风力搬运能力降低并产生沉积的结果。(6)巴丹吉林沙漠沙山表层中Si元素含量从迎风坡下部到顶部呈逐渐减少的趋势,这是稳定性强含Si的石英矿物在粗颗粒中的含量较高的结果。Al、K、Nb、 Rb、Ni等元素的含量从迎风坡下部到顶部呈增加趋势,这是这些元素含量在细颗粒沉积物中含量较高造成的。Si、Al、K、Nb、Rb、Ni等元素的含量变化对沙山地貌分带具有重要的指示作用。(7)巴丹吉林沙漠湖泊水化学特征空间差异明显,由南到北沙漠湖泊的化学类型逐渐由指示盐度较低的Na-(Mg)-(Ca)-Cl-(SO4)-(HCO3)型微咸湖泊过渡为指示盐度较高的Na-(K)-Cl-(SO4)型盐水湖泊。沙漠南部湖泊靠近山地接受来自山区降水入渗的补给要多于北部湖泊,这是南部湖泊中的离子浓度低于北部湖泊的原因。南部湖泊水面高度普遍高于北部湖泊,北部湖泊在接受南部湖泊水分补给的同时会带入南部湖泊中的可溶盐离子,导致北部湖水的盐度变大。在一般情况下,离子浓度低的方向代表补给水的来源方向,离子浓度高的方向代表水流前进和汇聚方向,因此该区的湖水由南向北流动。(8)沙漠湖泊水化学特征和湖面水位分布高度的调查资料表明,湖泊主要来自当地降水补给及沙漠东南缘雅布赖山和南缘的黑山头地区的降水入渗迁移补给。此外,巴丹吉林沙漠湖泊及大气降水离子聚类特征也指示巴丹吉林沙漠东南部的湖水与大气降水具有同源性。巴丹吉林沙漠东南部湖水位高于其南部河西走廊的地下水位,表明该区众多沙漠湖泊的湖水不可能来自南部的祁连山区。更多还原

【Abstract】 The landform of Badain Jaran Desert is always a focus to geographers, because it not only has the world’s largest height difference of megadune, but also has a desert and lakes were arranged alternately distribution of special landscape.The megadune and lake are closely related. It helps to deeply understand their formation and internal relationship to research them by putting together. Many factors play an important role in the formations of megadune and lake, such as the material composition, megadunes, physiognomy zonations, chemical characters of lake water and groundwater, moisture content and migration of sand layer. However, due to the natural environment condition and the difficulty of entering in desert hinterland etc., study on the problems of material composition, physiognomy zonations, development mode of megadunes, the relations between the moisture content of sand layer and the formation of megadune was less. Previously, study on the landform of Badain Jaran Desert mainly concentrated on the larger scale and wide range of dune geomorphology and characteristics of surface material composition and distribution. At present, any result of single megadune about the systematic and quantitative, the material composition and physiognomy zonations hasn’t yet published. Also did not see the published result on the relations between moisture contant of sand layer and formations of megadune and lake. The paper analysed the main-formation process of the formations of megadune and lake, and provides important grounds for settlement the formations of megadune and lake.The study on the landform of megadune and water, moisture content of sand layer has great science meaning for revealing formation mechanism and dynamic variation of megadune and lake, and also has practical significance for maintaining local ecological balance, protecting biodiversity, controlling desertification and scientifically utilizing desert water resources.In order to find out the formation of megadune, supply source of lake and the moisture effect of sand layer on the formation of megadune, densely distributed central area of megadune and lake in the southeastern Badain Jaran Desert was chosen as study area. Methods of field observation, particle size analysis, determination of chemical element, water chemical analysis, Environmental scanning electron microscopy (ESEM) and energy spectrum analysis were used to obtain the data of physiognomy zonations at the windward slope, sediment size composition, major element and trace element contents at the different parts of megadune, chemical constituents of lake water and groundwater, moisture content of sand layer, the crystal habit and chemical constituents of secondary salts. According to these data, the landform zoning characteristics of megadune windward slope, the relationship between sediment size composition and wind dynamic conditions at different parts of megadune, indicative function of content variation of major elements and trace elements on landform, space variation regular pattern of water chemical composition and its indication role on the supply source of lake and groundwater, high content of film moisture and secondary gypsum s indicating effect on the water migration and supply sources of lake water and groundwater were researched. Some results were drawn as follows:(1) According to the observational data of secondary physiognomy, the windward slope of megadune was divided into four geomorphological zones from the bottom up. The first was low-lying sandy depression zones which was undergoing wind erosion and coarsening. The second was sparse simple barchans or barchanoid chains zoning at the down of the middle part of megadune. The third was dense barchans and barchanoid chains zoning at the up of the middle part of megadune. The fourth was steep main peak zoning of megadune.(2) The paper proposed the formation patterns of megadunes. That aeolian sand material was not carried to the middle and upper part of megadune one time, but carried to the upper part of megadune by numerousness wind-force transport. Firstly, medium sand and fine sand in the lower of megadune was carried to the middle part, and shaped barchan and barchanoid chains. After repeatedly transport, finally the peak of megadune was shaped.(3) The research first discovered the secondary gypsum which has important indication function to water cycle and atmospheric precipitation seeping into megadune internal in the slopes of Huhejilin-E megadune etc. The emerging of secondary gypsum and gravity water in sand layer, imply that the precipitation has infiltrated into the deep position and exposed to the surface. These indicates that atmospheric precipitation can supply the lake water and groundwater via sand layer. Moisture entrance sand layer increase the humidity of sand layer and bond between sand particles, which was beneficial to the formation of megadunes.(4) According to the data of moisture content in the depth of4m, it is first determined that there were high content of film moisture at1-2m depth of sand layer in Badain Jaran Desert, which shows that precipitation after evaporation and transpiration there were still some residual water downward migration, and at least can become one of the supply sources of lake water and groundwater. These identify the supply source of lake water and groundwater indicated by the vegetation zonal distribution, secondary gypsum and water exudation at the slope of megadune. Meanwhile, fully proves that the sand layer moisture in the region has normal cycle and positive balance characteristics. The positive balance of moisture in the sand layer played an important role in the formation of megadunes.(5) The aeolian sand material has a double-layer structure in Badain Jaran Desert. The particle size of surface is coarser than the below10cm, indicated that the aeolian sand material was undergoing wind erosion and coarsening, and directed megadunes still exist certain activity. The particle composition of sediment has obvious difference at different parts. From the bottom to top of megadune, particle composition present taper off trend, this was caused by the differences of their formation process and the dynamic effect. The coarse particle size composition at the bottom of windward slope was determined by that the fine sand was carried away by the wind erosion and only coarse component was left. The fine particle size composition in the upper part of the windward slope was the result that the slope and height was large, which hindered the wind moving up, lead to wind transport ability decrease and generate deposition.(6) In the windward slope surface of megadune, the content of Si from bottom to top decreased gradually, which was the result of the strong stability of quartz mineral and its high purity in coarse particles. The content of Al、K、Nb、Rb、Ni increased from bottom to top, this was caused by the high content of these elements in fine sediments. The content variations of Si、Al、K、Nb、Rb、Ni play an important role in indicating the landform zoning of megadune.(7) In the Badain Jaran Desert, the chemical characteristics and spatial difference of lake water were very evident. From south to north, the chemical type of lake water gradually transit from Na-(Mg)-(Ca)-Cl-(SO4)-(HCO3) type to Na-(K)-Cl-(SO4) type. The southern lakes close to the Yabulai Mountains, receive the supply of precipitation infiltration of the Yabulai Mountains more than northern lakes, which was the reason that the ions concentration of southern lakes were lower than the northern lakes. The lake surface altitude of southern lakes were generally higher than the northern lakes, so the ions of soluble salt move with the lake water from southeast to northwest, and accumulate in the north lakes, leading to a higher salinity in the northern lakes. In general, the directions of low ion concentrations represent the source direction of recharge water, and the directions of high ion concentrations mean the advance and convergence direction of flow.(8) The data of chemistry characteristics of lake water and lake surface altitude indicates that the main supply source come from local precipitation and precipitation infiltration migration of the Yabulai Mountains and Heishantou Mountains. In addition, the hierarchical cluster analysis of lake water and precipitation also indicate the lake water of southeastern and precipitation has homology. In the southeastern lakes of Badain Jaran Desert, the elevations of lake surface were higher than the groundwater level in the Hexi Corridor, which indicates that the formation of desert lakes was not necessarily associated with the water supplies from the Qilian Mountains.更多还原