| 摘要: |
| 喀拉库里地处帕米尔高原东部，整个湖区被中纬度西风带贯穿，湖水主要由冰川融水和夏季降水补给，对气候变化响应敏感，是重建西风气候和冰川环境演变的理想区域，然而对于喀拉库里沉积物的组成和来源还知之甚少。本文以喀拉库里表层沉积物为研究对象，获得了其组成及空间分布特征，进而探讨了其物源及输入方式。根据沉积物粒度、矿物组成及湖水等深线分布，表层沉积物可分为三种类型：第Ⅰ类以细砂粒为主，以高石英和低粘土为特征，分布在近湖岸；第Ⅲ类以分选良好的细粉砂为主，主要分布在深湖区；第Ⅱ类粗、细颗粒混杂，分选性差，位于Ⅰ、Ⅲ类沉积物过渡区域。喀拉库里沉积物的SiO2含量同粒径呈正相关关系，粒径越大、含量越高；Al2O3、Fe2O3和K2O则相反。结合河流泥沙和慕士塔格冰芯中粉尘颗粒的粒度分布及区域气候特征，初步认为深湖区分选良好的细粉砂可能主要来自西风携带的高空粉尘，而近岸细砂是岩石就地物理风化的产物。这些认识对于钻点的选取及沉积序列气候、环境信息的提取具有重要价值。 |
| 关键词: 喀拉库里 表层沉积物 粒度 矿物学 元素 控制因素 |
| DOI：10.7515/JEE201604006 |
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| 基金项目:国家自然科学基金项目（41403111，41225015） |
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| Spatial distribution of surface lake sediment compositions in Kala Kul Lake and its implications for provenances |
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YIN Duo, JIN Zhangdong, ZHANG Fei, ZHANG Xiaolong, WANG Xiaqing, PENG Yumei1,2,3
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of
Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
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| Abstract: |
| Background, aim, and scope Kala Kul Lake (38°25.32' — 38°27.57'N, 75°02.27' — 75°04.17'E, 3661 m above sea level) is located in the eastern part of the Pamir Plateau and is a hydrologically-open freshwater lake mainly fed by meltwater from the Mustagh Ata ices and rainfall in summer. The climate of the lake catchment is dominated by northern hemisphere mid-latitude westerly jet carrying rain and dust in summer. Owing to little human activity, lake sediment in Kala Kul Lake has been considered to be ideal for reconstructing regional climate and environment evolution, and even for glacial advance and retreat. However, until now little is known about the compositions, spatial distribution and sources of the lake sediments, as well as their relationship with the glacier variations and the westerly climate. The objectives of this study are (1) to obtain the mineralogical and geochemical compositions of the surface lake sediments and (2) to address the spatial distribution and sources of the sediments in Kala Kul Lake. Materials and methods Thirty samples of surface sediments (topmost 2 cm) were collected in June and July 2014 across Kala Kul Lake with the water depths ranging from 0.5 m to 18.5 m. Meanwhile, one river sediment and five wind-driven sand samples were collected surrounding the catchment. After pretreated by adding H2O2 and HCl to remove organic matter, carbonates, and iron oxides, grain size distribution was measured by a Malvern 2000 laser diffraction instrument with 100 bins ranging from 0.02 μm to 2000 μm. X-ray diffraction and fluorescence spectrometer were used for analyzing mineralogical and elemental compositions. Results Being combining the grain size parameters with water depth, surface lake sediment samples were classified into three types. The type Ⅰ sediments are distributed in the near lake shore and are characterize by fine sand with double peaks, high contents of quartz and low clays, Fe2O3, and K2O. The type Ⅲ sediments are dominated by fine and clayey silt that are well sorted and are mainly distributed in the deep water area. The contents of SiO2, CaO, and Sr in the type Ⅲ sediments are the lowest in all types of sediments, with constant contents of Al2O3, Fe2O3, and K2O with the standard deviations less than 1.0. At the narrow area between the typesⅠand Ⅲ, there are the type Ⅱ sediments that are mixed with poorly-sorted coarse and fine particles. Discussion Since Kala Kul Lake belongs to a typical moraine lake, lakebed topography, sediment sources, grain sorting and focusing play dominant roles in the difference of detrital mineralogy and elements in the three types of surface sediments in the lake. The lake has a relatively complex topography of the lakebed, such that water depth affects mineral compositions and spatial distribution of major elements of the surface lake sediments. Comparison of the grain-size distributions of the three types of surface sediments with those of eolian dust from Mustagh Ata ice cap, five wind-driven sand and one river sediment samples indicate that the typesⅠand Ⅱ sediments might mainly stem from local fine sand detrital transported by wind and rivers, whereas the type Ⅲ sediments (2 — 8 µm in size) may be dominated by eolian dust carried by the westerly jet during the summer from western and central Asia, as same as those trapped in the Mustagh Ata ices. Conclusions In Kala Kul Lake, the well-sorted fine and clayey silt dominated in the deep water area might stem from eolian dust by the westerly jet during the summer, whereas the fine sand and silt near lake shore are from local detrital transported by wind and rivers into the lake. High contents of albite and biotite but low clays in the fine detrital mineral are mainly the products of physical eroded rocks after sorted by strong wind, indicating weak weathering within the catchment. Recommendations and perspectives The fine and clayey silt in deep lake therefore is potential for reconstructing the history of dust input and westerly jet in central Asia. |
| Key words: Kul Lake surface lake sediment grain size mineralogy elements sediment sources |
