| 内蒙古嘎顺诺尔湖泊沉积物磁化率与粒度的古环境意义 |
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| 引用本文： | 王君兰,李晖,邓伟,郭小燕,李双,张家武.内蒙古嘎顺诺尔湖泊沉积物磁化率与粒度的古环境意义[J].中国沙漠,2012,32(3):661-668. |
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| 作者姓名： | 王君兰 李晖 邓伟 郭小燕 李双 张家武 |
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| 作者单位： | 1. 兰州大学西部环境教育部重点实验室／西部环境与气候变化研究院,甘肃兰州,730000
2. 甘肃省地质调查院,甘肃兰州,730000 |
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| 基金项目： | 国家重点基础研究发展计划项目(2009CB421306);国家自然科学基金项目(40871093;40721101)资助 |
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| 摘 要： | 湖泊沉积物磁化率和粒度已被广泛地应用于古环境和古气候研究，但在不同地区两者的关系不同，一般与磁性矿物来源、种类和赋存粒级有关。查明磁性矿物来源和赋存状态是利用粒度和磁化率恢复古环境的重要基础。通过测定干旱区嘎顺诺尔GXN剖面湖泊沉积物的磁化率与粒度及两者的相关关系，结合代表性样品的岩石磁学特征，揭示此类地区湖泊沉积物磁性矿物来源和赋存状态，探讨它们在干旱区湖泊沉积物中所反映的环境变化信息。结果显示，剖面下部（200~105 cm）和上部（36~0 cm）沉积物磁化率与粗砂含量呈正相关，中部（105~36 cm）与粉砂含量呈正相关，表明磁性矿物主要富集于粗颗粒和较粗颗粒组分中。剖面下部和中部沉积物以顺磁性矿物为主，含少量亚铁磁性矿物（如磁铁矿+磁赤铁矿）,含少量顺磁性矿物；剖面上部沉积物以亚铁磁性矿物为主（如磁赤铁矿+磁铁矿），含少量顺磁性矿物。根据嘎顺诺尔晚全新世湖泊沉积物剖面的岩性、磁化率和粒度组合特征，可将其划分为河漫滩相沉积（200~105 cm）、浅湖相沉积（105~36 cm）和滨浅湖相沉积（36~0 cm）3个阶段。该湖粒度组分中<4 μm和4~64 μm颗粒主要反映了湖泊水动力的变化，受碎屑物来源和水动力条件的控制；而河漫滩相中>64 μm粗颗粒组分的峰值是风力作用的结果。河漫滩相及滨浅湖相的磁化率高值则指示了湖面较低，水动力较强，有较多的磁性矿物随粗颗粒入湖；浅湖相的磁化率低值则指示该时期湖面较高，水动力较弱，磁性矿物随入湖粗颗粒含量的减少而降低。
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| 关 键 词： | 嘎顺诺尔 磁化率 粒度 古环境意义 |
| 收稿时间： | 2011-10-23; |
Paleoenvironmental Significance of Magnetic Susceptibility and Grain Size of Lake Sediments from Gaxun Nur,Inner Mongolia,China |
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| WANG Jun-lan,LI Hui,DENG Wei,GUO Xiao-yan,LI Shuang,ZHANG Jia-wu.Paleoenvironmental Significance of Magnetic Susceptibility and Grain Size of Lake Sediments from Gaxun Nur,Inner Mongolia,China[J].Journal of Desert Research,2012,32(3):661-668. |
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| Authors: | WANG Jun-lan LI Hui DENG Wei GUO Xiao-yan LI Shuang ZHANG Jia-wu |
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| Institution: | 1(1.MOE Key Laboratory of Western China’s Environmental Systems/Research School of Arid Environment & Climate Change,Lanzhou University,Lanzhou 730000,China;2.Gansu Institute of Geological Survey,Lanzhou 730000,China) |
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| Abstract: | Grain size and magnetic susceptibility information of lake sediments have been widely used in palaeoenvironment and paleoclimate research.However,the relationship between these two parameters is different due to different types,sources,and particle sizes of magnetic minerals in different regions.In order to identify the environmental change information and the magnetic mineral sources and their occurrence states in lake sediments from arid regions in northwest China,we analyzed the magnetic susceptibility and grain size of the lake sediments along a section in Gaxun Nur,Inner Mongolia,in combination with rock magnetic information.Results show that the magnetic susceptibility of the bottom and the top of the section is positively correlated to the content of coarse sand;the magnetic susceptibility in the middle part of the section is positively correlated to the content of fine sand.The main magnetic minerals down the middle part of the section are ferrimagnetic minerals with small amount of paramagnetic materials(maghemite+magnetite).The main magnetic minerals in the upper part of the section are paramagnetic materials with some ferrimagnetic minerals(magnetite+maghemite).Three stages of environmental change could be identified from the section of Gaxun Nur: the flood plain(200~105 cm),shallow lake(105~36 cm) and near-shore environment(36~0 cm).Fractions of <4 μm and 4~64 μm mainly reflect the changes of water dynamics,which is determined by the detritus compositions and hydrodynamic conditions.The >64 μm coarse sand components in the flood plain period may have been transported by wind.Coarser grain size and higher magnetic susceptibility in the flood plain and the near-shore periods indicate decreased lake level with increased hydrodynamics and more magnetic mineral flow into the lake with sand components.Finer grain size and lower magnetic susceptibility during the shallow lake period suggest relatively higher lake level with lowered hydrodynamics and less magnetic mineral flow into the lake with coarser components. |
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| Keywords: | Gaxun Nur magnetic susceptibility grain size paleoenvironmental significance |
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