塞尔维亚北部末次间冰期古土壤的磁性增强机理：以Ruma和Titel黄土剖面为例

Mechanism of magnetic enhancement of the last interglacial paleosols in northern Serbia: example from the Ruma and Titel loess profiles

关键词:  东欧黄土  磁化率  环境磁学  古环境变化

Key words:  Eastern European loess  magnetic susceptibility  environmental magnetism  paleoenvironmental change

摘要:

塞尔维亚北部的Vojvodina地区是东欧黄土的重要分布区，对该地区著名的Ruma和Titel剖面的末次间冰期古土壤及其下覆黄土层进行多种环境磁学参数的分析对比。结果显示：两个剖面末次间冰期古土壤的磁学性质基本一致，可以代表Vojvodina地区末次间冰期古土壤地层磁性变化的整体情况，其所含磁性矿物的种类与中国黄土相似，有亚铁磁性的磁铁矿和磁赤铁矿，以及反铁磁性的赤铁矿和针铁矿。成壤过程中形成的细粒亚铁磁性矿物是Vojvodina地区末次间冰期古土壤磁性增强的主要原因。相对于中国黄土高原，Vojvodina地区末次间冰期古土壤的成壤环境可能更为湿润，但其磁性增强的幅度却小得多，对该差异的进一步研究可能有助于深入理解黄土磁性变化的成壤模式机理。

Abstract:

Background, aim, and scope The Vojvodina region in northern Serbia is among the most important archives of aeolian deposits in Eastern Europe, and the parameter of magnetic susceptibility perhaps is the most widely used proxy in reflecting the paleoclimate change. However, the mechanism of magnetic variations of the paleosols in this region is poorly understood. In this study, we investigated magnetic properties of two last interglacial paleosols and the underlying loess layers separately from the typical Ruma and Titel loess profiles in Vojvodina to determine the mechanism of magnetic enhancement and the associated paleoenvironmental information. Materials and methods Eight samples from each paleosol V-S1 and the underlying loess layer V-L2 were collected from the Ruma and Titel loess profiles for study. For all 16 samples, we measured or calculated low-frequency and high-frequency magnetic susceptibility, frequency-dependent susceptibility, percentage frequency-dependent susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, saturation isothermal remanent magnetization, remanent coercivity, hard isothermal remanent magnetization, hysteresis loops, and thermomagnetic curves. Results Magnetic properties of the V-S1 paleosols were consistent between the Ruma and Titel loess profiles, hence possibly characterizing the magnetic behavior of the last interglacial paleosols throughout Vojvodina. Both paleosols contained the same ferrimagnetic minerals, magnetite and maghemite, and antiferromagnetic minerals, hematite and goethite. The fine-grained superparamagnetic and single-domain magnetic particle abundances increased markedly from V-L2 to V-S1. Discussion Based mainly on the recognitions from Chinese loess deposits, we discussed the relationships among the magnetic parameters and pedogenic environment, and the results showed the increase of ultrafine ferrimagnetic superparamagnetic particles in paleosols was the main reason leading to the enhancement of magnetic susceptibility. More single-domain particles generated during pedogenesis were included in Serbian loess than Chinese loess, but the underlying reason is still unclear. Meanwhile, we pay more attention to the differences of the thermomagnetic characteristics of the studied samples to realize the difference in paleoenvironment. The lower concentration of magnetic minerals, especially maghemite was another reason caused the lower magnetic susceptibility in Serbian loess than Chinese loess. Conclusions The increase of fine-grained ferromagnetic minerals in the last interglacial paleosols in the Vojvodina region was the dominant cause for their magnetic enhancement, and the variations of maghemite was an important reason for the enhancement of magnetism in Serbian loess. Recommendations and perspectives The results of this study can provide basic understanding for the proxy of magnetic susceptibility in Eastern European loess, especially for the inconsistencies with Chinese Loess Plateau. It seems that the pedogenic environment of paleosols V-S1 in the Vojvodina region was more humid relative to the Chinese Loess Plateau, but the amplitudes of magnetic enhancements in which were significantly lower than Chinese counterparts, further research on this difference would be beneficial for a better understanding of the paleoclimate change.