汉江上游阶地黄土磁学特征研究
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P318

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国家自然科学基金项目(42071112,41371209,41971116,41771110)资助


Magnetic Characteristics of Terrace Loess in the Upper Hanjiang River
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the National Natural Science Foundation of China(Nos.42071112,41371209,41971116,41771110)

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    摘要:

    汉江上游地区位于北亚热带季风气候区边缘,对气候响应异常敏感。流域内发育不对称四级阶地,且阶地上覆盖有厚度不等的黄土堆积。以汉江上游三级阶地黄坪村(HPC)和高客站(GKZ)两个剖面作为研究对象,测量样品的磁化率和频率磁化率,并选取代表性样品进行热磁曲线、等温剩磁获得曲线和磁滞回线等的测定。结果表明,汉江上游黄土沉积物中的载磁矿物以磁铁矿和磁赤铁矿为主,同时含有一定量的赤铁矿和针铁矿,磁化率的增强以超顺磁和准单畴亚铁磁性矿物的贡献为主。GKZ剖面中低矫顽力亚铁磁性矿物含量低于HPC剖面,且黄土中含有更多的亚铁磁性矿物,HPC剖面中则黄土-古土壤中载磁矿物差别不大。汉江上游磁化率的降低与该区较高的有效降水量有关,季节性丰沛降水使土壤水分过饱和,在局部湿润的还原环境中,土壤中大量强磁性铁氧化物被溶解转化为能够在湿润环境中稳定存在的弱磁性矿物,磁性矿物的转化导致成壤强的汉江上游地区磁化率低于成壤弱的黄土高原地区。在成壤条件处于还原环境时,有效降水越高,还原程度也越高,强磁性铁氧化物被溶解的越多,磁化率就越低,这是GKZ剖面降水大于HPC剖面,但磁化率却更低的原因。

    Abstract:

    [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.

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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.

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  • 收稿日期:2020-06-04
  • 最后修改日期:2020-11-27
  • 录用日期:2021-03-10
  • 在线发布日期: 2021-03-11
  • 出版日期: 2022-02-11