天山北麓宁家河阶地上的黄土堆积及其磁学特征  

Loess deposit on the terrace of Ningjia River in the northern slope of the Tianshan Mountains and its magnetic characteristics

作　　者：吕镔[1,2] 刘秀铭[2,3] 陈秀玲[1] 

机构地区：[1]福建师范大学地理科学学院福建省湿润亚热带山地生态省部共建国家重点实验室培育基地,福州350007 [2]兰州大学西部环境教育部重点实验室,兰州730000 [3]Department of Environment and Geography Macquarie University

出　　处：《地球环境学报》2014年第2期111-119,共9页Journal of Earth Environment

基　　金：国家自然科学基金项目(41210002;40830105;41302149);福建省科技计划项目公益类项目(K3-296)

摘　　要：本文报道了新疆地区天山北麓宁家河阶地上的黄土堆积。研究剖面的两层黄土为河流砾石层所隔开,这在新疆地区较为少见。通过系统的岩石磁学和粒度测量,分析了该剖面两层黄土的磁学特征,并初步探讨磁化率变化机制。结果表明:黄土中的主要磁性矿物为磁铁矿和磁赤铁矿,并含有少量赤铁矿和针铁矿。亚铁磁性矿物主要以多畴(MD)、假单畴(PSD)颗粒为主,反映了这一地区极弱的成土作用。砾石层上下两层黄土磁学性质存在着差异,表现为上层黄土具有较高的磁性矿物含量、较粗的磁颗粒和相对含量较高的软磁性矿物。下层黄土受到后期河水的改造可能是导致这些差异的原因。磁化率与粒度呈现较好的正相关关系,与黄土高原的情况相反,说明干旱地区的黄土磁学性质主要受原生磁性矿物控制。搬运风力和源区变化是磁化率变化的主导因素。In this paper, we report a loess section which located on the terrace of Ningjia River in thenorthern slope of the Tianshan Mountains. The two loess layers are separated by gravel bed of the riverchannel. This is rare in Xinjiang region. Samples from the two loess layers were collected and carriedout rock magnetism and bulk sample grain size measurement. Base on the measurement, we analyze themagnetic characteristics of these tow loess layers and discuss the mechanism of magnetic susceptibilityvariation. The results show that magnetite and maghemite are the main magnetic minerals, and also,hematite and geothite are detected; the magnetic minerals domain is intermediate coarse pseudo-singledomain （PSD） and multidomain （MD）, indicating weak pedogenesis. The main differences of magneticcharacteristics between two loess layers above and below the gravel bed are that the top loess layer hadmore and coarser magnetic minerals, higher proportion of soft magnetic minerals. The water of rivermay be the reason of these differences. There is an excellent positive relationship between magneticsusceptibility and bulk sample grain size, which is opposite to Chinese Loess Plateau, suggesting that magnetic properties were mainly controlled by allochthonous magnetic minerals. Magnetic susceptibilitywas mainly controlled by wind velocity and loess sources change.

关 键 词：天山黄土 磁性矿物 磁化率 河流阶地 

分 类 号：P318.4[天文地球—固体地球物理学]