新疆博斯腾湖全新世沉积磁性矿物组成与沉积环境探讨  

Relationship between magnetic minerals and there sedimentary environment of Holocene sediments from Bosten Lake,Xinjiang

作　　者：谢海超[1] 魏海涛[1] 王强[1] 黄小忠[1] 彭卫[1] 陈发虎[1] 

机构地区：[1]兰州大学西部环境教育部重点实验室,兰州大学资源环境学院,甘肃兰州730000

出　　处：《干旱区地理》2017年第3期512-522,共11页Arid Land Geography

基　　金：国家自然基金重点项目(41130102);中央高校基本科研业务费专项资金(lzujbky-2013-121)联合资助

摘　　要：中国西北干旱区湖泊沉积物存在磁性矿物种类复杂和磁化率普遍偏低等问题,使得利用环境磁学手段重建古环境、古气候的方法受到了限制。选择新疆博斯腾湖BST12B钻孔顶部岩芯(深度0~2.5 m)不同沉积相的代表性样品,进行载磁性矿物富集,并将原样品和富集获得的样品分别做XRD(X荧光衍射)岩石矿物检测。结果显示,所有湖相样品中均有黄铁矿和磁铁矿检出,而没有磁黄铁矿和针铁矿检出,说明博斯腾湖全新世湖相沉积物的主要磁性矿物是磁铁矿,并含有少量黄铁矿;富集获得的样品中粘土矿物(如绿泥石等)含量明显增加,石英、长石和方解石含量降低,富集后的残留样品的磁化率大幅度降低,说明粘土矿物对干旱区湖泊沉积物的磁学贡献不容忽视。结合沉积物粒度、色度、硫元素含量以及沉积物磁性矿物的组合特征推断,黄铁矿可以作为湖泊高水位的指示矿物种类,因而具有重建湖泊古水位变化的潜力,并应用到博斯腾湖的全新世湖泊环境重建,发现博斯腾湖BST12B钻孔位置早全新世为接近氧化环境的浅湖相环境,而中晚全新世为深湖相沉积环境并存在一个浅水的湖滨相沉积环境。研究结果说明,利用载磁性矿物富集的方法对干旱区湖泊沉积物中所含磁性矿物进行富集后检测是开展干旱区湖泊环境磁学研究的可行手段,对研究湖泊环境变化具有重要意义。The long standing issues that low values of magnetic susceptibility as well as uncertainty of magnetic mineral types of lake sediments in arid area of northwest China are widely existed, making it limited in using the environmental magnetism methods to estimate the lake evolution as well as to reconstruct their regional paleoen- vironment and paleoclimate. Low values of magnetic susceptibility could enlarge the instrument error, while the uncertainty of magnetic mineral types of lake sediments may confuse researchers in studying the mechanism of enhanced magnetic susceptibility. To solve these problems, we extracted magnetic minerals with self-regulating magnetic mineral-extracting device from 5 samples chosen from different sedimentary units from the top 2.5 m of BSTI2B （42~00＇42.9＂N, 87~09＇53.8＂E） drilling core which was collected in the depth of 9.2 m in the central area of Bosten Lake in winter of 2012 and had the total length of 51.52 m. We tested mineral compositions of all the 5 samples both before and after extracting using XRD （X-Ray Diffraction） method, which had been proved to be very efficient in identifying minerals quantificationally. Results show that all the lacustrine samples contained Magnetite and Pyrite, neither Pyrrhotite nor Goethite were detected in all the samples, which meant that the major magnetic minerals in Holocene lacustrine sediments of Bosten Lake were magnetite and bits of pyrite. Moreover, in comparison with the residual parts, the extracted parts enriched clay minerals, such as Chlorite and Mica, which were widely distributed in lacustrine sedimentary environment and had relatively high magnetic suscepti- bility value. While the concentration of the major minerals in our tested samples, Quartz, Feldspar and Calcite de- creased dramatically. As a result, the values of magnetic susceptibility of these residual parts decreased synchro- nously, which indicated that the magnetism contribution of these clay minerals made to the lacustrine sediments in arid area should

关 键 词：干旱区 博斯腾湖 全新世 环境磁学 磁性矿物 

分 类 号：P512.2[天文地球—地质学] P534.632