【作者】 白旸；

【导师】 王乃昂；

【作者基本信息】 兰州大学 ， 地球系统科学， 2011， 博士

【摘要】 随着亚洲内陆干旱化、水资源与生态恢复、沙尘暴源区等研究的不断深入,风沙地貌的形成机理研究已成为国内外十分关切的问题。巴丹吉林沙漠东南部的高大沙山是一种独特的风沙地貌,是罕见而珍贵的世界性地质遗产,为世界上规模最宏大的沙山地貌。自20世纪30年代以来,吸引了众多国内外学者对其进行研究。从区域整体的角度来看,巴丹吉林沙漠东南部的高大沙山的形成与局部地形起伏对气流的阻滞作用有关,即横亘于巴丹吉林沙漠东南缘的雅布赖山与南缘的北大山成为西北风与西风运行的障碍,受主风场西北风的携带,沙物质由沙漠西北缘的弱水冲积扇进入沙漠东南部,在阻滞作用下,沙物质沉积下来,逐渐形成复合型的高大沙山,表现为风积作用为主；在沙漠中北部和西北部地区,没有大型的风场运行障碍,且较沙漠南部和东南部地区干燥,贴地层水分较少,地表植被相对较少,贴地面风速大,沙物质不容易附着,沙尘很容易被扬起进入大气,因此较少发生次级沙丘叠置的情况,沙丘形态单一,相对高差较小,其地貌特征反映了风积作用与风蚀作用的共同影响。复合型高大沙山地貌特征表现为整体的横向沙丘相、迎风坡次生简单横向沙丘及顶部星状沙丘相相结合的复合形态,解释高大沙山的成因需逐一解释其复合形态中的各个地貌单元,巴丹吉林沙漠北部、中部的星状沙丘、横向沙丘等与沙漠东南部的高大沙山具有相同的沙源,虽各自所受局域风况有所差别,但从整体区域的角度来分析,处于同样的区域风况下,即同处季风边缘区域,受西风带,高原季风,东南季风三个大气环流系统的共同控制。因此,从巴丹吉林沙漠区域整体的角度研究从简单沙丘到复合型高大沙山的形成机理具有合理性、可行性和必要性。在当今地学界,对于巴丹吉林沙漠高大沙山的形成机理的研究手段主要依赖于沙山表层资料,方法与视角相对单一,研究区域仅限于巴丹吉林沙漠东南部地区,在高大沙山形成演化的解释上存在较大争议,对于其复合形态中的各个地貌单元未曾逐一深入研究；对于高大沙山内部结构所掌握的数据资料较少。因此,本研究采用遥感、野外资料采集、粒度组成实验、风沙地貌分形计算、沙波纹与沙丘形态参数关系建模、探地雷达勘察、沙丘层理电磁波正反演建模、光释光测年等技术、方法、手段,对巴丹吉林沙漠整个区域的风积地貌特征、形态参数规律、粒度分布规律、沙丘沙山内部结构、下伏地形等方面进行了系统的研究,以巴丹吉林沙漠区域整体的角度,由古到今的时间序列,由外到内的思路,揭示了高大沙山的内部结构与形成过程,得到以下主要结论：1.高大沙山的规则排列揭示了风力对高大沙山形成具有重要影响。本研究基于实测数据,修正了高大沙山高度、间距关系的经验公式,得出H=0.08Sp1.01(其中H表示沙山的高度,Sp表示沙山的间距)。2.高大沙山的粒度组成揭示了高大沙山迎风坡的下部以侵蚀作用为主,沙山中上部以风力的堆积为主,背风坡下部以重力的堆积为主的沙粒沉积方式。3.从平面的角度来看,沙波纹的分维数为1.798,沙山分维数为1.179。从垂向的角度来看,沙波纹的分维数为1.072,沙山的分维数为D=1.307。证明分维数可以描述沙波、沙丘形态的延展性和复杂性。验证了分形地貌学描述风沙地貌的有效性。4.国内前人的沙漠探地雷达工作中均缺乏背风坡的剖面资料,本研究的野外考察选用了瑞典MALA公司RTA超强地面耦合天线,经过设计改造,在国内首次获得了高大沙山迎风坡至背风坡的连续剖面,国际上虽有完整的沙丘探地雷达剖面,但都仅限于几米至几十米高度的沙丘。因此,本研究中的天线选取使得探地雷达剖面具有良好的高差程度、连续性以及完整性。5.建立了雷达波在不同含水量沙层中的正反演模型,可用于探地雷达反演模型的迭代拟合,探地雷达图像揭示了古沙丘的存在以及水位层的存在。6.通过古沙丘的产状与光释光年代学证据,复原了特征时期的古风向,在巴丹吉林沙漠西北部钙质胶结出露的年龄为89.61±2.45ka BP,而沙漠东南部钙质胶结出露的年龄为113.89±5.51ka BP,结合统计古沙丘产状,得出末次间间冰期以前巴丹吉林地区以西风为主导风向,西北风次之,而末次间间冰期以来则以西北风为主导风行,西风次之。7.前人缺乏在巴丹吉林沙漠腹地同一测区获取连续的年代序列,在本研究结果中,获取了位于巴丹吉林沙漠南部一个连续的湖相沉积与风成沙交错分布的年代剖面,其下部光释光年代结果为101.35±17.12ka BP,139.48±19.63ka BP,说明了在MIS 5e阶段和MIS 3阶段,巴丹吉林沙漠东南部存在高湖面或大湖期。8.综合分析解释了高大沙山内部结构与形成过程,即在雅布赖山与北大山对风沙流的阻滞作用下,使得沙物质沉积下来,在风力作用下,形成规则排列的沙丘,巴丹吉林沙漠湿润的环境使得古沙丘胶结保存下来,沙物质不断加积其上,层层叠置形成复合型的高大沙山。更多还原

【Abstract】 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.更多还原