the National Natural Science Foundation of China（Nos.42071112,41371209,41971116,41771110）
[Objective] The upper section of the Hanjiang River flows along the edge of the northern subtropical monsoon climate zone and the catchment is extremely sensitive to climate change. A special landform of asymmetric four-level terraces has been developed in the catchment, and the terraces are covered with loess deposits varying in thickness. In this study, two profiles, located in HPC (Huangpingcun) and GKZ (Gaokezhan) on the third-order terrace in the upper reaches of the Hanjiang River were selected as the research objects.[Method] Soil samples were collected from the two profiles for determination of magnetic susceptibility and frequency susceptibility, and furthermore, some representative samples were tested for measurement of thermomagnetic curves, IRM acquisition curves, and hysteresis loops.[Result] Results suggest that the main magnetic minerals in the paleosol and loess of the terrace are magnetite and maghemite, and a certain amount of hematite and goethite. Superparamagnetic and pseudo-single domain ferrimagnetic minerals are the major contributors of enhanced susceptibility. Profile GKZ is lower than Profile HPC in content of low-coercivity ferromagnetic minerals, and contains more ferromagnetic minerals in loess. But in Profile HPC section, little difference in content of magnetic minerals was found between loess and paleosol.[Conclusion] The lower magnetic susceptibility in the upper reaches of the Hanjiang River is related to the high effective precipitation in this area. Seasonal abundant precipitation makes soil moisture supersaturated in the area. In the locally humid reducing environment, a large volume of strongly ferromagnetic iron oxides in the soil are dissolved and transformed into weakly magnetic minerals that persist stably in humid environments. The transformation of magnetic minerals leads to lower magnetic susceptibility in the upper reaches of Hanjiang River strong in soil formation than in the Loess Plateau weak in soil formation. When the soil forming condition remains to be a reducing environment, the higher the effective precipitation and the reduction degree, the more the strongly magnetic iron oxide dissolved and the lower the magnetic susceptibility, which is the reason why GKZ is higher in precipitation larger than HPC section, but lower in magnetic susceptibility.
闫雪娇,周亚利,黄春长,庞奖励,刘丽方,羊俊敏,孙晓巍,张岳敏.汉江上游阶地黄土磁学特征研究[J].土壤学报,2022,59(2):405-419. DOI:10.11766/trxb202006040276 YAN Xuejiao, ZHOU Yali, HUANG Chunchang, PANG Jiangli, LIU Lifang, YANG Junmin, SUN Xiaowei, ZHANG Yuemin. Magnetic Characteristics of Terrace Loess in the Upper Hanjiang River[J]. Acta Pedologica Sinica,2022,59(2):405-419.复制