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风成沉积物中不同粒径石英颗粒表面微结构特征的研究
赵雪
学位类型硕士
导师穆桂金
2016
学位授予单位中国科学院大学
学位授予地点北京
学位专业自然地理学
关键词风成沉积物 不同粒级 石英颗粒 表面结构
摘要石英颗粒表面微结构特征被用于判断沉积物的来源、搬运过程和早期的成岩历史。风成石英颗粒表面微结构的特征还没有统一标准,因粒级对表面微结构的发育情况具有重要影响,故本文以典型的风成沉积物为例,包括地表风成粗砂、沙漠砂、黄土、降尘等,由细到粗逐级对其进行表面结构分析,试图全面揭示风成石英颗粒表面微结构的特征。共统计了5-1000m内的817颗风成石英颗粒,统计表面结构的类型,测量其数量和大小,计算表面结构的面积,并作记录,随后按搬运方式,将颗粒分为5级,依次是长距离悬浮搬运为主的石英颗粒(5-20m)、短距离悬浮搬运为主的石英颗粒(20-70m)、远距离跃移搬运为主的石英颗粒(70-100m)、近距离跃移搬运为主的石英颗粒(100-500m)、滚动搬运为主的石英颗粒(500-1000m)。逐级对比后发现不同粒级的风成石英颗粒的表面结构特征不同,总结如下: (1)风成石英颗粒表面发育典型的贝壳状断口、蝶形坑、新月形坑、V形坑、不规则坑、V形沟等结构,其中以70-500μm的风成石英颗粒表面发育的结构类型最丰富,多为大而深的结构,500-1000μm的颗粒表面结构的数量最多,以不规则坑为主,伴随新月形坑和贝壳状断口,多为浅而小的结构,5-70μm的颗粒表面结构类型单一、数量少,并存在继承性大结构; (2)随粒径增大,风成石英颗粒的形状从矛形、水滴形逐渐转变纺锤形、椭圆形,到最后成为标准的圆形,磨圆度越来越好,麻面、风蚀结构均随粒径增大更加显著,表面结构的完整性随粒径增大而变好。5-70μm的风成石英颗粒的表面发育不规则坑-V形坑组合,7-500μm的风成石英颗粒表面结构的特征组合为不规则坑-蝶形坑-V形坑-新月形坑,500-1000μm的风成石英颗粒表面形成了不规则坑-新月形坑-贝壳状断口的结构组合。表面结构的分布面积随粒径发生变化,70-500μm的颗粒表面结构的分布面积最大,其次是500-1000μm的颗粒,最小的是5-70μm的颗粒; (3)各类表面结构之间的相对大小基本稳定,贝壳状断口是比新月形坑大的弧形结构,最小的撞击坑是V形坑,蝶形坑、不规则坑是较大的撞击坑,片状剥落和V形沟始终是大表面结构。 (4)不同粒级的风成石英颗粒经不同的搬运方式后形成不同的表面结构特征,撞击频率、颗粒大小、搬运速度共同影响表面结构的发育。高撞击频率、大粒径才能形成并承载更多的表面结构,大动能、多样化的撞击方式则是形成多种类且大尺寸的表面结构的必要条件。分析沉积环境时须根据沉积物的粒度大小选取相应粒级的石英颗粒表面结构特征进行对比研究,做出判断。
其他摘要The characteristics of surface textures of quartz grains are widely used in identification of material source of sediments, transportation process and early diagenesis history. There is still not a unified standard about the characteristics of surface textures of eolian quartz grains now. But as we know grain size has a great influence on surface textures of quartz grains, therefore, we choose some typical eolian sediments, including eolian coarse sand, desert sand, loess, dust full and so on, to analyze the surface textures of quartz grains in them from fine to coarse, which aims to establish a sequence of surface textures of eolian quartz grains cover different sized grains. Finally, 817 eolian quartz grains ranged from 5m to 1000m have been tested, including the type, quantity, size and area of surface textures, and then grade these 817 quartz grains into five groups by transportation forms: 5-20μm, which mainly transported by long-distance suspension, 20-70μm, which mainly transported by close-distance suspension, 70-100μm, which mainly transported by long-distance saltation, 100-500μm, which mainly transported by close-distance saltation, 500-1000μm, which mainly transported by rolling, analyzing each grade one by one. The findings imply that different sized eolian quartz grains have different surface textures feature: (1) There are typical surface textures on eolian quartz grains including conchoidal fractures, rounded pits, crescent pits, V-shaped pits, irregular pits, V-shaped ditches. Beyond that, the type of surface textures on 70-500μm grains is the most diversified, and these textures are always large and deep. The quantity of surface textures on 500-1000μm grains is the most, and the irregular pits are the main type. Grains of 5-70μm with some inherited textures have the least amount of surface textures and the types is lack too. (2) As the size of quartz grains increased, the shape of quartz grains changes from sharp-angled lance shape to spindle and ellipse shape, to standard ground shape finally. At the same time, roundness of grains is getting better, pitted surface and eolian erosion trace are getting clearer. Meanwhile, the integrity of surface textures is getting higher too. Grains of 5-70μm only form the combination of irregular pits-V shaped pits. There are different kinds of textures on the surface of grains of 70-500μm, which makes grains feature with irregular pits-rounded pits-V shaped pits-crescent pits. The types of surface textures on 500-1000μm grains are consisted of irregular pits-crescent pits-conchoidal fractures. The distribution area of surface textures is changed among grades, such as 70-500μm grains own the maximum distribution area of surface textures, 500-1000μm grains have the moderate distribution area of surface textures, and 5-70μm grains have the minimum distribution area of surface textures. (3) The sizes of surface textures of different types have a settled pattern that the conchoidal fracture is always larger than crescent pit, V-shaped pit is the smallest impact crater and rounded pit, irregular pit are relatively larger impact craters, exfoliation and V-shaped ditch are always large textures. (4) Different sized eolian quartz grains transported by different forms develop absolutely unlike characteristics of surface textures. Three main factors composed of impacting frequency, grain size and velocity of movement effect the growing condition of surface textures on eolian grains. A large quantity of surface textures could be formed by high impacting frequency and supported by coarse grains. Meanwhile, high velocity collision would lead to grow out diversified and large sized textures. In the detection of sedimental environment by surface textures of quartz grains, choosing relevant fraction of surface textures characteristic by grain size is crucial and efficient in identifying.
学科领域自然地理学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14696
专题研究系统_荒漠环境研究室
作者单位中科院新疆生态与地理研究所
推荐引用方式
GB/T 7714
赵雪. 风成沉积物中不同粒径石英颗粒表面微结构特征的研究[D]. 北京. 中国科学院大学,2016.
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