Relationship between magnetic properties and weathering in red soil profiles developed on weakly magnetic parent rock in the tropical and subtropical region of Yunnan, China

Abstract

Abstract Magnetic studies of loess-paleosol sequences have shown that the magnetic properties of loess and its parent material is sensitive to weathering degree. However, the relationship between magnetic properties and weathering processes in red soils of southern China remains unclear due to the diversity of parent rocks and the influence of climate. This study focused on red soils developed on weakly magnetic sandstone, in tropical and subtropical regions of Yunnan, China. The principal element content, magnetic susceptibility, temperature-dependent susceptibility curve(ꭓ-T curves), hysteresis loop and Isothermal Remanent Magnetization (IRM) of the samples were determined, the weathering characteristics and magnetic properties of profile samples were analyzed, and their relationship was examined, as well as the impact of climate change on fine-grained ferrimagnetic minerals and magnetic properties. The results revealed that red soils developed on weakly magnetic sandstone exhibited significant correlations between three magnetic indices, low-frequency magnetic susceptibility (χlf), frequency-dependent susceptibility (χfd),(χpost−pre + χd)/χpara, and the silica-sesquioxide ratio (SAF), indicating that these indices can be used to assess soil weathering. Additionally, this study proposed a new index based on the 1 < Log10Bh < 1.5 mT component obtained from decomposition of the IRM curve, which can also be used to assess soil weathering. The enhancement of magnetic properties in red soils along a single profile was found to be related to the increase in the content of fine-grained ferrimagnetic com-ponents controlled by weathering. Comparing the two climatic regions, it was found that in Yunnan, China, as the climate changes from subtropical humid to tropical humid, the weathering of the red soil profiles becomes stronger, and the fine-grained ferrimagnetic components increase, indirectly enhancing the magnetic properties of red soils.