Knowledge Resource Center for Ecological Environment in Arid Area
| 柴达木盆地线形沙丘发育环境与形成演化过程 | |
| 其他题名 | Development Environment, Formation and Evolution Processes for Linear Dunes in the Qaidam Basin |
| 李继彦 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 苏红波 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 线形沙丘是分布范围最广且形态类型多样的一种沙丘类型，不但在地球上的主要沙漠中均有分布，而且在火星和土卫六上也有分布。此外，该沙丘也是成因复杂且争议较多的一种沙丘类型，对其形成机制提出了多种假说。柴达木盆地中的线形沙丘不但在外部形态和分布格局上与火星和土卫六上的线形沙丘均比较相似，而且对其成因的侵蚀和堆积争论也十分激烈。基于上述研究背景，文章选择以柴达木盆地的线形沙丘为研究对象，对其发育环境及形成演化过程进行了研究。本研究基于多次野外详细的实地考察和对本区域内Google Earth高清影像的细致分析制定了研究方案。通过对研究沙丘区沉积物组成特征、长期的风况观测、沙丘形态与分布和沙丘地貌格局分析、内部沉积构造以及光释光测年等结果的分析，初步得出以下主要结论：（1）沙物质的粒级级配在沙丘表面不同部位呈现出一定的分异性，即沙丘底部主要为中沙、粗沙和极粗沙组成，而沙丘上部则主要由细沙组成。粒度参数同样表现出沿着采样横断面有规律的变化，具体而言，平均粒径自沙丘底部至顶部逐渐变细，分选逐渐变好，偏度趋于正偏，峰态趋于窄峰态。沙丘各部位沉积物的可溶盐含量的平均值相差并不大，这说明可溶盐可以通过毛管作用输移到沙丘的各个部位，通过固结沙物质在线形沙丘发育过程的始终均起着重要作用。（2）沙丘沙的矿物组成以石英、长石等轻矿物为主，轻矿物的平均含量高达88.16%，而重矿物的平均含量仅为10.19%。沙丘沙重矿物以不稳定重矿物组分占绝对优势，平均占重矿物总量的74.92%，与周边沙漠以稳定和极稳定重矿物为主的矿物组成模式有所不同。沙丘沙的元素组成表现为以SiO2—Al2O3—Na2O为主的构成模式，且其CIA值远低于周边沙漠和中国黄土的等风成沉积物。这些指标均表明柴达木盆地内沙物质的化学风化程度很低。（3）柴达木盆地的风能强度具有从西北部至东南部逐渐降低的趋势，而主导风向由西北部的西北风转变为南部和东南部的西风。察尔汗盐湖北岸的线形沙丘发育于宽单峰风况、风向变率为中等的中等风能环境中，与世界上其他区域无植被覆盖的活跃线形沙丘大都位于双峰风况环境有所不同。（4）依据分布区域下伏地形和沙丘类型与形态的差异，柴达木盆地沙丘分布区可以划分为花海子沙区、祁曼塔格山前沙区、察尔汗盐湖周边沙区和都兰沙区。其中线形沙丘仅在察尔汗盐湖周边的一些零星沙地中出现，这可能与该区域为察尔汗干盐滩的下伏地形有关。（5）依据地貌格局分析方法，察尔汗盐湖北岸线形沙丘区内的沙丘主要划分为三组，分别对应着三种不同的蚀积状态。第一组个体规模较小，为原较大线形沙丘的侵蚀残余；第二组为处于蚀积平衡的沙丘；而第三组主要为正处于快速垂直增高和纵向伸长的沙丘。这一划分方案通过野外考察得以验证。（6）柴达木盆地线形沙丘内部构造与Bagnold模型有所差异，而在一定程度上与Rubin和Hunter模型具有一定的相似性。区内线形沙丘形成于3.02±0.21–0.40±0.02 ka BP之间，且形成年代具有自上风向至下风向逐渐递减的规律，指示着区内线形沙丘是通过堆积作用沿着合成输沙方向逐渐伸长的。同时，在沙丘达到一定的高度之后，就会开始遭受风力吹蚀，导致沙丘的衰退和萎缩。因此，对于区内的线形沙丘单纯的侵蚀或者堆积理论均不能合理解释其发育和演化过程，而需要在不同的时空尺度上将两者合理结合。 |
| 英文摘要 | Linear dunes are the most widespread dune type and with multiple morphological diversity. They not only exist in the major deserts on Earth, but also distribute on Mars and Titan. Besides, the formation mechanism for linear dune is very complex and have been in heatedly arguing for hundred of years and researchers had proposed varied hypothese accounting for linear dunes’ formation. Against the above mentioned research background, this paper chose the linear dunes on the northern margin of Qarhan Salt Lake in the Qaidam Basin as the study object to investigate their development environment as well as their formation and evolution processes.The research project was carried out based on many times field observations and thoroughly analysis of the high resolution image of the study area provided by Google Earth. According the investigations to dune sediments’ composition, a long term wind regime observation, sand dunes’ distribution, morphology and the geomorphological pattern analysis, and dune internal structure as well as OSL dating results, we have drawn the following preliminary conclusions:(1) The bottom part of the linear dune are mainly composed of medium, coarse and very coarse sands, while the upper part of the dune are mainly composed of fine sands. Grain-size parameters show some regular variation along the the sampling transection, i.e. the mean grain-size of dune sands is gradually getting finer from dune base to the crest, the sorting is getting better, the skewness is tending to more positive and the kurtosis is tending to much narrower. The differences between the mean values of soluble salts for different position of the sampling transection is not too much, which means the soluble salts can be transported to every part of the dune by capillary action. Therefore, the cementation of dune sands by soluble salts had played an important role throughout the process of dune formation.(2) The mineral composition of dune sands predominates by quartz and feldspar and the average content of light minerals for dune sands can attain as high as 88.16%, while the heavy minerals merely 10.19%. The average content of unstable heavy minerals attains 74.92% of the total heavy mineral content, which is different from the surrounding deserts predominated by stable and very stable heavy minerals. The chemical elements of dune sands predominate by SiO2, Al2O3 and Na2O, and the CIA value is much smaller than the surrounding deserts and Chinese loess. All these indices indicate that the dune sands in the Qaidam Basin are of lower weathering degree.(3) The wind strength in the northwestern part of the basin is much stronger than the southeastern part, and the dominant wind direction is gradually changing from northwesterly in the northwestern part to westerly in the southern and southeastern part. The linear dunes in the northern margin of Qarhan Salt Lake are developed in an intermediate-energy wind environment, with a wind regime of wide unidirectional and intermediate wind directional variability. This is different from the other active linear dune without vegetation cover, which are developed in bidirectional wind regimes.(4) According to the difference of the substrates and dunes’ type and morphology, the dune distribution area of Qaidam Basin can be divided into Huahaizi dune-fields, Qiman Tagh piedmont dune-fields, Qarhan Salt Lake dune-fields and Dulan dune-fields. And the linear dunes only occurred in the scattering dune-fields around the Qarhan Salt Lake, which may be owing to that they are developed on the dry playa surface of Qarhan Salt Lake.(5) The linear dunes on the northern margin of Qarhan Salt Lake can be classified into three groups, which are corresponding to their different erosion-deposition status, according to the geomorphological pattern analysis. The first group are the erosion remnants of the former larger dunes and they are much smaller in size; the second group are in their balance status of erosion versus deposition; the last group are in their fast vertical accretion and longitudinal elongation stage. This classification scheme had been verified by the field observation.(6) The internal structure of linear dunes in the Qaidam Basin is different from the Bagnold model and similar with the Rubin and Hunter model in some degree. The study dunes have ages between 3.02±0.21 and 0.40±0.02 ka BP, and these ages show a decreasing tendency from the upwind end to the downwind end throughout the dune-field, which indicates that the dunes are elongated by deposition along the resultant drift direction. And the dunes began to experienced aeolian erosion when they attain a certain height, which lead to the dunes shrink their size and gradually degradation. Therefore, the single depositional or wind-rift theory cannot accounting for the formation and evolution processes of linear dunes in the Qaidam Basin, and need to combine both theories in different spatial-temporal scales. |
| 中文关键词 | 线形沙丘 ; 纵向沙丘 ; 风沙地貌 ; 柴达木盆地 ; 察尔汗盐湖 |
| 英文关键词 | linear dune longitudinal dune aeolian geomorphology Qaidam Basin Qarhan Salt Lake |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287709 |
| 推荐引用方式 GB/T 7714 | 李继彦. 柴达木盆地线形沙丘发育环境与形成演化过程[D]. 中国科学院大学,2016. |
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