干旱区生态环境知识资源中心(Arid): 西昆仑山黄土的岩石磁学特征及其磁化率增强机制

Arid

	西昆仑山黄土的岩石磁学特征及其磁化率增强机制
其他题名	ROCK-MAGNETIC CHARACTERISTICS AND THE ENHANCING MECHANISM OF MAGNETIC SUSCEPTIBILITY FOR WEST KUNLUN MOUNTAINS LOESS
	昝金波 1; 杨胜利 2; 方小敏 2; 李香钰 2; 王九一 2; 张涛 1
来源期刊	第四纪研究
ISSN	1001-7410
出版年	2010
卷号	30 期号:1 页码:46-53
中文摘要	成壤过程中形成的细颗粒的软磁性矿物被认为是导致古土壤磁化率增加的主要原因.但近来的研究表明,在一些地区,尤其是靠近沙漠边缘的黄土-古土壤序列,源区对黄土磁化率的影响要远大于成壤作用.因此,有必要对不同地区、不同环境条件下的典型黄土堆积进行详细的岩石磁学研究.日前,我们在西昆仑山北侧钻取了一根长达671m的岩芯,这为研究极端干旱区黄土的岩石磁学性质提供了难得的契机.本文对第一期黄土钻探得到的207m岩芯进行了详细的岩石磁学研究,结果表明:昆仑山黄土的主要载磁矿物为磁铁矿和磁赤铁矿,同时还含有少量的针铁矿、赤铁矿;该地区磁化率的变化主要受源区粗颗粒的软磁性矿物含量的影响,成壤作用形成的细颗粒磁性矿物对磁化率的贡献极小;磁化率、粒度在0.5Ma左右急剧升高和变粗,主要与气候干旱化加剧有关.
英文摘要	Variations in magnetic susceptibility(MS) of Chinese loess-paleosol layers show a high correlation with marine oxygen isotope records,and have been widely used as a proxy of East Asian summer wind intensity over the past two decades.At present,increasing concentration of SP (superparamagnetic particles) and SD (single-domain) grains during the pedogenesis is considered as the main reason for enhancement of magnetic susceptibility (MS) of paleosol.Recently,however,many researches have shown the influence of coarse lithogenic magnetic minerals to be also very important,especially in the loess-paleosol sequence adjacent to the desert edge.Loess in the Kunlun Mountains is so far the thickest loess found in the extreme arid region of China’s inland,recording continuously histories of the desert and dust-carrying winds and circulation.Lately,we obtained a 671m long loess core through drilling on the northern slope of the West Kunlun Mountains (36°12’N,81°20’E;elevation 3300m),which provides a good opportunity to study the mechanisms of MS enhancement in the arid Asian heartland for us.In this study,we investigated its 207m long loess core by integrating both rock-magnetic and grain size proxies.The study results suggest that the low coercivity minerals,i.e.,magnetite and maghemite are dominated in the loess.The hard magnetic minerals including goethite and hematite were also found but made a minor contribution to the signal of susceptibility.The characteristics of typical hysteresis loops probably imply the presence of paramagnetic component to a certain extent.In addition,the results also show that MS and grain size both increase sharply at depth 111m with an age of ca.0.5Ma,and meanwhile,magnetic grain size became much coarser(from PSD to MD-like) and magnetic minerals change toward a higher concentration of soft magnetic components (i.e.magnetite and maghemite).All these suggest a drying event might occur at that time.The event made a larger number of lithogenic materials relatively rich in coarse-grained(MD-like grains)ferrimagnetic minerals magnetite and maghemite to be carried and deposited on the north slope of the Kunlun Mountains more easily,which resulted in the enhancement of susceptibility after depth 111m sharply.These results improved our understanding of the enhancing mechanism of susceptibility at different sites with different paleoenvironmental conditions:in comparison with the uhrafine pedogenic minerals,coarse lithogenic magnetic minerals can also play an important role in enhancement of MS at some time.
中文关键词	昆仑山黄土 ; 磁化率 ; 干旱化
英文关键词	Kunlun Mountains Loess magnetic susceptibility aridification
语种	中文
国家	中国
收录类别	CSCD
WOS类目	GEOSCIENCES MULTIDISCIPLINARY
WOS研究方向	Geology
CSCD记录号	CSCD:3820717
来源机构	兰州大学
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/224874
作者单位	1.兰州大学, 资源环境学院西部环境教育部重点实验室, 兰州, 甘肃 730000, 中国; 2.中国科学院青藏高原研究所盆地资源与环境研究中心, 北京 100085, 中国
推荐引用方式 GB/T 7714	昝金波,杨胜利,方小敏,等. 西昆仑山黄土的岩石磁学特征及其磁化率增强机制[J]. 兰州大学,2010,30(1):46-53.
APA	昝金波,杨胜利,方小敏,李香钰,王九一,&张涛.(2010).西昆仑山黄土的岩石磁学特征及其磁化率增强机制.第四纪研究,30(1),46-53.
MLA	昝金波,et al."西昆仑山黄土的岩石磁学特征及其磁化率增强机制".第四纪研究 30.1(2010):46-53.