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中国沙漠 ›› 2011, Vol. 31 ›› Issue (6): 1357-1364.

• 沙漠与沙漠化 • 上一篇    下一篇

巴丹吉林沙漠地表沉积物粒度特征及区域差异

钱广强, 董治宝, 罗万银, 张正偲, 肖生春, 赵爱国   

  1. 中国科学院寒区旱区环境与工程研究所 沙漠与沙漠化重点实验室, 甘肃 兰州 730000
  • 收稿日期:2010-10-20 修回日期:2011-05-04 出版日期:2011-11-20 发布日期:2011-11-20

Grain Size Characteristics and Spatial Variation of Surface Sediments in the Badain Jaran Desert

QIAN Guang-qiang, DONG Zhi-bao, LUO Wan-yin, ZHANG Zheng-cai, XIAO Sheng-chun, ZHAO Ai-guo   

  1. Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China
  • Received:2010-10-20 Revised:2011-05-04 Online:2011-11-20 Published:2011-11-20

摘要: 对巴丹吉林沙漠不同区域、不同类型沙丘、不同地貌部位的223个地表沉积物样品进行粒度分析表明,该沙漠的流动沙丘主要由细沙组成,其含量可达49.5%~66.1%;沙丘沙的平均粒径介于2.104~2.706 Φ之间,粗于塔克拉玛干沙漠和腾格里沙漠,与世界其他沙海中沙物质粒径相比处于中等粗细。粒径最细者为灌丛沙丘表面沙粒,最粗者为横向沙山迎风坡;分选度好至极好,均为正偏中等峰态。丘间地物质粗于沙丘沙,平均粒径为1.409 Φ,分选较好,正偏窄峰态。从频率曲线来看,沙丘沙为单峰,丘间地多为双峰或三峰。在典型横向沙山剖面上,自迎风坡坡脚至沙丘顶部平均粒径变细而分选性变好,最粗的沙粒出现在靠近迎风坡坡脚的丘间地,而最细和分选最好的沙粒出现在紧邻沙丘顶部的背风坡。尽管横向沙山与新月形沙丘和沙丘链的尺度不同,但二者同属横向沙丘系统,具有相似的沙丘动力机制,因而粒度参数之间关系的表现趋同。从区域上来看,在平行于主导风向的3条NW—SE向断面上,沙漠中北部高大沙山之间低矮“通道”上的沙粒平均粒径存在微弱的变细趋势,而高大沙山区则不存在明显的变化规律;在平行于雅布赖山的3条SW—NE向断面上,粒度参数沿断面方向无明显的变化规律,但断面越靠近雅布赖山平均粒径越粗。一般认为巴丹吉林沙漠是中国重要的沙尘源区之一,然而粒度分析结果表明,沙漠中北部几乎不含粉沙黏土(<0.0625 mm)组分,而东南部的横向沙山区含量则相对较高,这就需要进一步推断巴丹吉林沙漠具体的沙尘源区和沙尘释放过程。以上变化规律说明,除了物源和主导风向等宏观因素外,引起局地气流改变进而影响沙粒跃移过程的地形起伏、植被覆盖等微观因素也对沙粒分选过程起着重要的控制作用;宏观和微观因素共同作用,最终形成的粒度参数规律性在沙丘尺度上要好于区域尺度上。该粒度分析结果,对于分析巴丹吉林沙漠沙物质来源和形成演变过程、反演高大沙山形成机理、估算地表沙尘释放量等均具有重要参考意义。

关键词: 巴丹吉林沙漠, 沙丘, 沉积物, 粒度, 区域差异

Abstract: In the Badain Jaran Desert, 223 surface sediment samples from different dune types and geomorphological positions were collected and analyzed by means of sieving. The shifting dunes have a mean grain size between 2.104—2.706 Φ and are mainly composed of fine sands whose content may reach 49.5%—66.1%. It is coarser than sands in the Taklamakan Desert and the Tengger Desert in China, and has a moderate grain size on global scale. The sorting parameters show that the dune sands are well to very well sorted with a distribution of positively skewness and mesokurtic. The finest and the coarsest grains can be found on the surface of the shrub canopy dunes and the stoss base of transverse dunes, respectively. The sediments from inter-dunes have a mean grain size of 1.409 Φ, which are coarser and worse sorted than dune sands and with a positively skewness and leptokurtic distribution. Generally, the frequency curve is unimodal for dune sands while it is bimodal or multimodal for inter-dune sediments. On the surface of typical transverse mega-dunes, the grains become finer and better sorted from the windward slope bases to the dune crests, and the coarsest sands occur near the toe of the stoss while the finest and the best sorted sands are found at the crests and the nearest slip faces. The similarity of grain size parameters shows that the transverse mega-dune and barchan dune or barchanoid chains are both belong to the transverse dune system and endure some similar dynamic processes despite of the scale difference. From a regional perspective, in the NW—SE cross sections which are parallel to the dominant wind direction, the mean grain size has a slight fining trend downwind in the north central of desert where the dune heights are relative lower than the neighboring mega-dunes. However, the mean grain size has no distinct downwind change in the sections occupied by mega-dunes. In the SW—NE cross sections which are parallel to the Yabrai Mountain, although it's difficult to find the variation in grain size parameters along the sections, the sands become coarser with the section closer to the mountain. Generally, the Badain Jaran Desert is considered to be one of the important source region of dust, but there is nearly no silt and clay portions in the north central region according to the grain size analyses. Meanwhile there is relatively high contents of silt and clay at the southeast of the desert, the transverse mega-dune region. A further research is needed to determine the dust release region and processes in the Badain Jaran Desert. Results indicate that the microscopic factors which can affect the airflow structure and thereby the saltating processes, such as topography change and vegetation cover, would play an important role in the sorting process except the macroscopic factors (e.g. source region and dominant wind). The regularity of grain size parameters on a dune scale is better than on a regional scale which is resulted from the coactions of the macro and micro factors. The paper can provide some useful information for analyzing the material sources and formation processes of the mega-dunes and even also for estimating the amount of the release of dust in the Badain Jaran Desert.

Key words: Badain Jaran Desert, sand dune, sediment, grain size, spatial variation

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