北极新奥尔松冰川沉积物的地球化学特征研究

发布时间：2018-09-18 19:06

【摘要】：高纬度冰川沉积物是全球冰川成因粉尘释放的重要来源,粉尘的释放影响着全球的气候、大气气溶胶、海洋化学元素和生产力。过去对粉尘的源区(如沙漠和黄土)的研究主要集中在中、低纬度地区,对来自高纬度的冰川成因的粉尘研究较少。本文以北极新奥尔松地区冰川沉积物为研究对象,通过野外调查、实验分析和数据处理等综合方法,对冰碛物和冰水沉积物的粒径、磁化率、主微量元素、同位素组合、碳酸盐矿物、粘土矿物和铁氧化物矿物组合等特征进行详细分析,探究现代新奥尔松高纬度冰川作用下冰川沉积物的产出特征以及剥蚀作用和化学风化对冰川沉积物的地球化学特征的影响。主要获得了以下的认识:(1)新奥尔松冰碛物平均粒径介于9.5～194.4μm,平均值为69.6μm,以粉砂级和砂级为主,粘粒较少。粒度频率分布大部分呈双峰或多峰特征,典型的细颗粒组分峰值在10～30μm,粗颗粒组分峰值在100～200μm。新奥尔松冰川压碎和磨碎的颗粒界限是1mm,大于一般认为的0.5mm,说明该地区冰川作用可能相对较弱。冰碛物沉积之后受剥蚀作用影响会造成细组分损失。冰水沉积物平均粒径为23.7μm,粒度分布呈单峰特征,峰值在20～30μm,代表着冰碛物中的细组分部分。(2)冰碛物和冰水沉积物磁化率平均值分别为9.7×10-8m3Kg-1和8.5×10-8m3Kg-1,于当地基岩相当,且于铁元素含量正相关。不同沉积物区位和年龄的冰川沉积物磁化率无显著差异,说明该地区很弱的成壤作用。对A冰川冰碛物的研究发现出露时间长的冰碛物的磁化率值与粒度组成有关,粒度越小,磁化率越高。本文认为冰川沉积物的磁化率由母岩决定还受剥蚀作用制约。(3)冰碛物化学风化指数(CIA)值主要介于55～70,CIA值能从整体上反映LIA冰碛物和冰沼土的化学风化差异。就LIA冰碛物而言,CIA值变化受剥蚀作用影响,并不指示风化强度。冰碛物平均化学组成与黄土和上部大陆地壳非常接近,且CIA值集中分布在UCC至黄土的平均化学组成风化趋势线上,说明黄土粉尘可能起源于由一系列的冰川和高山作用的剥蚀。(4)冰碛物在冰缘环境易发生碳酸盐矿物的淋溶作用,非以富含碳酸盐矿物的岩石为母质的冰碛物中,粒径小于2μm的碳酸盐矿物基本被完全淋溶。苔原植被演替导致的生物化学风化作用可能是碳酸盐淋溶的主要动力。(5)冰水沉积物与冰碛物地球化学特征无显著差异,冰水沉积物除顶部碳酸盐矿物被淋失外,其余整个剖面均含小于2μm的碳酸盐矿物,说明剖面沉积物有相当一部分直接来自冰川压磨岩屑,可能未接受苔原表生作用影响。冰川沉积物的粘土矿物为碎屑沉积,以伊利石(平均含量为63%)、高岭石(平均含量为19%)、绿泥石(平均含量为17%)为主;粘粒中高的87Sr/86Sr比值可能是当前新奥尔松乃至斯尔瓦巴群岛冰川粉尘释放的重要指纹特征。冰川沉积物的铁氧化物矿物并非成壤控制,其特征由其母岩决定,针铁矿和赤铁矿的平均含量分别为 0.34%和 0.2%。(6)本文中冰水沉积物的地球化学特征的变化主要反映物源波动,并不指示区域化学风化强度。总体而言,冰缘环境下冰川末端输出的岩屑其地球化学特征由其母岩决定,受环境、气候变化影响很小;碳酸盐矿物淋失是冰川沉积物在冰缘环境风化的主要体现。
[Abstract]:High latitude glacial sediments are an important source of global glacial-derived dust emissions, which affect global climate, atmospheric aerosols, marine chemical elements and productivity. In this paper, the glacial sediments in the New Orson area of the Arctic are taken as the research object. The grain size, magnetic susceptibility, major and trace elements, isotope composition, carbonate minerals, clay minerals and iron oxide mineral assemblages of till and glacial water sediments are analyzed in detail through field investigation, experimental analysis and data processing. The characteristics of glacial sediments and the effects of denudation and chemical weathering on the geochemical characteristics of glacial sediments under the action of modern high latitude glaciers in New Orleans are studied. The grain size distribution is mostly bimodal or multi-modal. The typical peak value of fine-grained components is 10-30 micron and that of coarse-grained components is 100-200 micron. The average grain size of the glacial water sediments is 23.7 micron, and the grain size distribution shows a single peak, with a peak value of 20-30 micron, representing the fine fraction of the till. (2) The average magnetic susceptibility of the till and glacial water sediments are 9.7 *10-8 m3 Kg-1 and 8.5 *10-8 m3 Kg-1, respectively, which are equivalent to the local bedrock and the content of iron element. The magnetic susceptibility of glacial sediments at different locations and ages is not significantly different, indicating that the area is weak in the formation of soil. The study of glacial tills at A shows that the magnetic susceptibility of glacial sediments with long exposure time is related to grain size composition. The smaller the grain size, the higher the magnetic susceptibility. (3) The chemical weathering index (CIA) of tills is mainly between 55 and 70, which can reflect the difference of chemical weathering between LIA tills and glacial marsh soils as a whole. The CIA values are very close to each other and are concentrated on the weathering trend line of the average chemical composition from UCC to the loess, indicating that the Loess dust may originate from erosion by a series of glaciers and mountains. (4) The tills are prone to leaching of carbonate minerals in periglacial environments, while the tills are not derived from carbonate-rich rocks. The biochemical weathering caused by vegetation succession in tundra may be the main driving force for carbonate leaching. (5) There is no significant difference in geochemical characteristics between glacial water sediments and tills. Except that carbonate minerals are leached from the top of glacial water sediments, the whole section contains less than 2 microns. Carbonate minerals indicate that a considerable portion of the sediments in the profile come directly from glacial grinding debris and may not be affected by tundra epigenesis. Clay minerals in the glacial sediments are clastic deposits, dominated by illite (63%), kaolinite (19%) and chlorite (17%) with a high 87Sr/86Sr ratio in clay grains. The average content of goethite and hematite is 0.34% and 0.2% respectively. (6) The geochemical characteristics of glacial water sediments in this paper are the main changes. Generally speaking, the geochemical characteristics of the debris exported from the end of the glacier in periglacial environment are determined by its parent rocks, and the influence of environment and climate change is very small. The leaching of carbonate minerals is the main manifestation of the weathering of the glacial sediments in periglacial environment.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P343.6

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