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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χ,χ_(fd),SIRM和χ_(ARM);χ和χ_(fd)呈正相关关系(r~2=0.87),黄土层的χ_(ARM)/SIRM与χ_(ARM)/χ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,~(87)Sr/~(86)Sr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。
Sediment deposition in the subtropical regions of China includes different types of sediments such as homogeneous laterite, yellow-brown soil, reticulate laterite and Xia Shu. In this paper, three sections of JL, PJ and XG-3 in Jiangxi Province were selected and various magnetic parameters were measured. The results show that: 1) The yellow-brown soil and reticulate red clay superimposed on the profile to form an accretionary red clay profile. The differences in magnetic mineral content, types and magnetic domains between the two resulted in different magnetic susceptibility. Yellow brown soil high magnetic susceptibility, high content of magnetic minerals, magnetic particles to small ferrimagnetic minerals magnetite and maghemite based. According to semi-quantitative estimation, the content of SP particles in yellow-brown soil is mostly between 50% and 75%, and the content of SP particles in ancient soil samples is mostly more than 75%. The reticulate red clay has low magnetic susceptibility, low content of magnetic minerals, and the diameter of magnetic particles is thicker than that of yellow-brown soil. The mineral type is mainly composed of incomplete antiferromagnetic hematite. (2) The Xiashu loess has higher χ, χ fd, SIRM and χ ARM; χ and χ fd have a positive correlation (r 2 = 0.87), χ ARM / SIRM and χ_ (ARM) / χ is much lower than that of paleosol, reflecting that coarser PSD / MD particles exist in addition to finer particle size components. Fine-grained ferrous magnetic minerals have a great contribution to the magnetic susceptibility. 3) According to the magnetic parameters and other physical and chemical indexes, it is speculated that the formation environment of yellow-brown soil and Xiashuhuang loess is similar to the current subtropical environment, but the ratio of silt-clay to yellow soil shows the chemical weathering is lower than that of Xiashu loess Strong, showing a certain latitude effect. 4) The reticulate lateritic magnetites widely distributed in the subtropical regions are similar in magnetic characteristics, with similar grain-size composition and geochemical indicators, indicating that the zonation differences of the natural elements in the region during the formation period are not obvious today. On the other hand, the higher HIRM in the ettringite, coercivity and Curie temperature indicate that it contains more hematite and the magnetic mineral particles are thicker than the yellow-brown soil on it and the total iron content is slightly higher than that of yellow Brown soil, the ratio of ~ (87) Sr / ~ (86) Sr is also higher than that of yellow brown soil, all of which corroborate that the red soil and yellow brown soil may not have the same material source.