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佳县红粘土磁学性质

ISSN号：1001-7410
期刊名称：第四纪研究
时间：2013
页码：415-423
分类：P318.41[天文地球—固体地球物理学;天文地球—地球物理学] P534.61[天文地球—古生物学与地层学;天文地球—地质学]
作者机构：[1]兰州大学西部环境教育部重点实验室,西部环境与气候变化研究院,兰州730000, [2]福建师范大学地理科学学院,福州350007, [3]Department of Environment and Geography,Macquarie University,Sydney NSW 2109,Australia, [4]浙江师范大学地理与环境科学学院,金华321004
相关基金：国家自然科学基金项目（批准号：41072124,40830105和40721061）资助
相关项目：甘肃新生代风积与湖积过渡地带地层特征及其变化研究

关键词：红粘土, 磁学性质, 异常变化, 原因, red clay, magnetic properties, abnormal variation, the reason

中文摘要：

黄土／古土壤序列和红粘土均已被证明是风积成因，然而红粘土研究的程度远低于黄土／古土壤序列，比如强发育红粘土获得比较低磁化率值的原因并没有得到清楚解释，红粘土磁化率代用指标问题和红粘土搬运路径等问题还存在较大的争议，红粘土记录古气候意义研究也相对薄弱，因此加强对红粘土的研究，有助于对古气候的理解。佳县位于黄土高原与毛乌素沙漠交接地区，季风区与非季风区过渡地带。对佳县厚60m的红粘土样品进行系统磁学参数测量分析发现，佳县红粘土以软磁性矿物（磁铁矿、磁赤铁矿）为主，同时含有一定量硬磁性矿物（赤铁矿、针铁矿，主要是赤铁矿）；强发育古土壤层含有较多软磁性矿物，弱发育古土壤层含有较多硬磁性矿物；磁颗粒粒径基本在0．21zm以下，x〉64×10^（-8）m^3／kg时，磁颗粒粒径小于0．1μm。剖面底部磁学参数变化存在异常，原因可能是：赤铁矿含量增加，超顺磁（SP）亚铁磁性颗粒含量急剧减少，单畴（SD）颗粒相对含量增加。该异常原因解释符合前人提出的成壤路径：水铁矿→SP磁赤铁矿→SD磁赤铁矿→SD赤铁矿。

英文摘要：

Both Chinese loess-paleosol sequences and red clay are aeolian deposits. However, red clay has not been studied as intensive as loess. The question why the strongly developed red clay shows low magnetic susceptibility remains unclear. There are some controversies on whether magnetic susceptibility of red clay can be used as a proxy to trace the variation of summer paleomonsoon and what the pathway of aeolian dust transportation for red clay is. In addition, the paleoclimatic significance of red clay needs to be further explored. Therefore, more research on red clay is urgently needed. Jiaxian is located in the northern edge of the Chinese Loess Plateau, close to the Mu Us desert, in the transitional zone of monsoon and non-monsoon areas, where the present annual precipitation is about 400mm. The Jiaxian red clay （38 ~15＇50＂N, 110~06＇14.9＂E ; 1171 _＋8m a. s. 1. ） is located at Fangta Town, which is about 30km eastwards to Yulin downtown and is about 50km northwest to Jiaxian County. In order to obtain high-resolution paleoclimatic record, 1800 powder samples were collected in the 60m thick red clay,with 3 samples collected every 10cm; 90 powder samples were collected every 5cm in the overlying Wucheng loess. In total, 1890 samples were collected in the 64.5m thick section. The samples from Jiaxian section were provided by Ding Zhongli and Yang Shiling. In order to better analyze the data, combining with field observations,we divided the selected samples into 5 types according to pedogenetic intensity, loess （ 48.3m ）, the weakly developed horizons （ Bw, 47.27m ）, the developed horizons （ W-Bt, 17.27m）, the strongly developed horizons （ S-Bt, 26. 37m ） and abnormally strongly developed horizons （ abn. S-Bt, 64.5 m）. Systematic magnetic analyses show that ferrimagnetic minerals （ magnetite and maghemite） dominate the Jiaxian red clay. Antiferromagnetic minerals （ hematite and goethite, mainly hematite） are also present. The strongly developed paleosols have relative

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