Redai dili (Nov 2023)
Soil Magnetic Characteristics of Weakly Magnetic Sandstones in Tropical and Subtropical Yunnan and Their Environmental Significance
Abstract
As an important surface ecosystem of the earth, the soil records abundant geological and environmental information. During the formation and development of soil, the magnetic minerals it contains will also change. Therefore, soil magnetism is related to the climatic environment information of the soil formation period and can be used to reconstruct the paleoenvironment. Currently, the research on soil magnetism in temperate semi-arid areas and its corresponding climatic and environmental indicators is relatively mature; however, the climatic and environmental indicators of soil magnetism in tropical and subtropical areas remain controversial and need further research. In this study, magnetic and diffuse reflectance spectroscopy were used to analyze the weathering crust of sandstone in different climatic zones in Yunnan. The results show that: (1) the three selected ferrimagnetic minerals in weathering crust profiles are magnetite and maghemite; the antiferromagnetic minerals are goethite and hematite. The main magnetic-bearing minerals in the soil of EF, PF, and F samples are magnetite and maghemite. The soil of PF and F samples contains relatively more antiferromagnetic minerals, goethite, and hematite, and the mean χfd% values in the three sections are 16.01%, 14.58%, and 10.06%, respectively. These results indicate that the three profiles all contain a large number of SP particles, and the ferrimagnetic mineral content in EF samples is much higher than that in PF and F samples. (2) From the perspective of the soil developed on the parent material of sandstone, no obvious correlation between the magnetic susceptibility changes of the three profiles and temperature and precipitation was observed. The magnetic susceptibility applicable to the temperate loess area is difficult to use as a climate proxy index in this region. Temperature and precipitation are not the main factors affecting the changes in magnetic susceptibility of soil, and various factors affect these changes. A large-scale and multi-section comparative study is necessary to evaluate the relationship between soil magnetic characteristics and the environment in tropical and subtropical areas. (3) The levels of Hm and Gt are affected by the difference in magnetic minerals in the parent rock, and characterizing the change in temperature or precipitation is difficult. The ratios Hm/Gt and Hm/ (Hm+Gt) have a good correspondence with temperature and have application potential in indicating temperature.
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