中文摘要：

中国亚热带地区的风尘沉积包括均质红土、黄棕色土、网纹红土和下蜀土等不同类型沉积层。本文选择江西九江（JL）、浙江浦江（PJ）和江苏新港（XG-3）3个剖面,进行了多种磁学参数测量。研究结果表明：1）黄棕色土与网纹红土在剖面上叠加组成加积型红土剖面构型,两者的磁性矿物含量、类型和磁畴的差异,导致磁化率的不同。黄棕色土磁化率高,磁性矿物含量高,磁性颗粒以细小的亚铁磁性矿物磁铁矿和磁赤铁矿为主。根据半定量估算,黄棕色土样品中SP颗粒含量大多介于50%-75% 之间,其中的古土壤样品SP颗粒含量多数大于75%。网纹红土磁化率低,磁性矿物含量低,磁性颗粒粒径较黄棕色土粗,矿物类型以不完整反铁磁性矿物赤铁矿为主。2）下蜀黄土具有较高的X,Xfd,SIRM和XARM; X和Xfd呈正相关关系（r2=0.87）,黄土层的XARM/SIRM与XARM/X远低于古土壤,反映除较细的粒度组分外,还有较粗的 PSD/MD 颗粒存在。细颗粒亚铁磁性矿物对磁化率贡献较大。3）据磁学参数辅以其他理化指标推测,黄棕色土与下蜀黄土形成环境与现在亚热带环境类似,但黄棕色土以较低的粉砂与粘土比值反映其化学风化作用较下蜀黄土强,显示了一定的纬度效应。4）广泛分布于亚热带地区的网纹红土磁学特征类同,粒度组成和地球化学指标也相似,反映形成时期区域内的自然要素的地带性分异不及今日明显。另一方面,网纹红土中较高的HIRM、矫顽力和居里温度指示其含有较多的赤铁矿,而且磁性矿物颗粒较其上的黄棕色土粗,全铁含量略高于黄棕色土,87Sr/86Sr 比值也较黄棕色土高,所有这些都佐证网纹红土与黄棕色土可能具有不完全相同的物质来源。

英文摘要：

The Quaternary red earth and Xiasu loess that derived from aeolian dusts is widespread in the present subtropical area of China.Like the loess-paleosol sequences in the north of China,the red earth and Xiasu loess provides detailed records of Quaternary environmental and climatic change.Variations in the magnetic susceptibility of Chinese loess have been used to indicate pedogenetic intensity and the past climate change across the Chinese Loess Plateau.According to pedogenetic enhancement model,the magnetic enhancement of paleosols in the Chinese Loess Plateau is mostly attributed to the formation of pedogenetic superparamagnetic particles（SP）,which resulted from strengthened East Asia summer monsoon activity.However,the relationship between climate and magnetic properties of eolian deposits is uncertain in the south of China.In this study,we have investigated two red earth sections（JL and PJ）at Lushan（29°42＇2.04＂N,116°01＇42.1＂E） and Pujiang（29°27＇06＂N,119°56＇14.9＂E）,and a section（XG-3）of the Xiasu loess（32°08＇45.5＂N,118°50＇51.6＂E） at Xingang,China.All the sections are situated in a modern subtropical climate region with a thickness of 2.75m（PJ section）,18.5m（JL section）and 9.0m（XG-3 section）respectively.Three stratigraphic units are included in these sequences：Xiashu Loess,vermiculated red earth and yellow brown earth.Magnetic low field susceptibility（X）was measured with a Bartington MS2 meter at frequencies of 470 Hz（Xlf） and 4700 Hz（Xhf）.Two parameters of frequency-dependent magnetic susceptibility Xfd（Xlf-Xhf） and Xfd% （（Xlf-Xhf）/Xlf×100% ）were calculated from these measurements.Anhysteresis remnant magnetization（ARM）,isothermal remnant magnetization（IRM）and saturation isothermal remnant magnetization（SIRM）were also measured.High-temperature magnetic susceptibility measurements were made using a KLY -3 Kappabridge.The results suggest：（1）JL and PJ red earth profile are made of two different units,yell