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大量研究证实成壤磁铁矿和磁赤铁矿是黄土-红粘土磁化率变化主要原因,但是对这些磁性矿物起源于无机沉淀还是生物作用尚需深入研究。为此,本文选择黄土高原200余米厚的西峰黄土-红粘土序列为主要研究对象,采用化学分析和透射电镜手段,对其中有机质含量和磁性矿物成因进行研究,结果表明:S_5以来的沉积层有机质含量相对较高,集中在0.25%～0.50%之间,有机质含量变化与黄土和古土壤层磁化率变化基本一致,即有机质高值对应磁化率高值,有机质与磁化率值成正相关;S_5以下至午城黄土底部不仅有机质含量降低而且变化幅度减小;红粘土沉积层中,虽然不能完全遵循磁化率高值对应有机质高值,但基本符合峰-峰和谷-谷对应规律。有机质和磁化率的相关性以及透射电镜研究表明,生物成因磁性矿物是风尘序列磁化率变化的主要原因,有机质含量高低反映风尘序列成壤过程中生物地球化学强度变化,生物将磁化率和古气候密切联系起来。黄土和红粘土磁化率古气候意义相似,但是由于黄土和红粘土形成于不同气候背景下,不能仅仅利用二者磁化率大小对比反演古气候,利用表土磁化率重建古气候要考虑气候载体形成的气候背景差异。
A large number of studies have confirmed that pyrite and maghemite are the main reasons for the change of magnetic susceptibility of loess-red clay. However, further study on whether these magnetic minerals originate from inorganic precipitation or biological activity is needed. Therefore, in this paper, the Xifeng loess-red clay sequence of 200 m thick in the Loess Plateau was selected as the main research object. The chemical composition and the transmission electron microscope were used to study the organic matter content and magnetic minerals. The results show that the depositional layer The content of organic matter is relatively high, concentrated in the range of 0.25% ~ 0.50%. The change of organic matter content is basically the same as that of the loess and palaeosol. The high value of organic matter corresponds to the high value of magnetic susceptibility and the organic matter has a positive correlation with the susceptibility. The following loess bottom at Loess Plateau not only decreases the organic matter content but also decreases the variation range. In the red clay sediments, although it can not completely follow the high value of organic matter with high magnetic susceptibility, it basically accords with the corresponding law of peak-peak and valley-valley. The correlation between organic matter and magnetic susceptibility and transmission electron microscopy showed that the biogenic magnetic minerals are the main reason for the change of magnetic susceptibility of the dust-dust sequence. The organic matter content reflects the change of biogeochemical intensity during the dust-forming sequence. The magnetic susceptibility and palaeoclimate Closely linked. The paleomagnetic characteristics of loess and red clay have similar meanings. However, because loess and red clay formed in different climate backgrounds, the paleo-climate can not be compared with the magnetic susceptibility of the two, and the formation of paleoclimate should be considered when using the magnetic susceptibility of the topsoil. The difference in climate background.