Paleoclimatic significance of mineral magnetic properties of loess sediments in northeastern Qinghai-Tibetan Plateau
Paleoclimatic significance of mineral magnetic properties of loess sediments in northeastern Qinghai-Tibetan Plateau
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DOI：
10.1360/02wd0567
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发表时间：
2003-10
影响因子：
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通讯作者：
Xiaoyong Wang;Huayu Lu;Zhen Li;C. Deng;H. Tan;Yougui Song
中科院分区：
文献类型：
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作者：
Xiaoyong Wang;Huayu Lu;Zhen Li;C. Deng;H. Tan;Yougui Song
青藏高原东北部的黄土沉积为该地区的气候和环境变化提供了极好的记录。对东川、腊拉口和盘子山三个剖面的黄土沉积物样品进行了多参数矿物磁学分析。所使用的方法包括磁化率、频率相关磁化率、温度相关磁化率、等温剩磁采集和磁滞回线。结果表明，磁铁矿是磁化率的主要贡献者。在黄土层和古土壤层中也存在磁铁矿和赤铁矿。古土壤中磁铁矿的含量较高，表明磁铁矿的形成发生在就地成土过程中，对磁化率的增强起着重要作用。与六盘山以东的中国黄土高原相似，所研究的黄土和古土壤中的磁性颗粒测量主要是伪单域(PSD)。然而，黄土中铁磁性矿物的平均粒度明显比古土壤(主要是PSD)粗(较大的PSD和多区域状)。黄土和古土壤的磁化率与超细磁铁矿/磁赤铁矿含量呈正相关，与就地成土强度呈正相关。因此，所研究的黄土-古土壤序列的磁化率增强可以解释为气候诱导的就地成壤作用。
Loess deposit in the northeastern Qinghai-Tibetan Plateau offers an excellent record of climate and environment changes in this region. We have conducted multiparameter mineral magnetic analyses of samples of loess deposits from the Dongchuan, Lalakou and Panzishan sections. The methods used include magnetic susceptibility, frequency-dependent susceptibility, temperature-dependent susceptibility, isothermal remanent magnetization acquisition, and magnetic hysteresis loops. The results reveal that magnetite is the dominant contributor to magnetic susceptibility. Maghemite and hematite is also present in the loess layers and paleosol horizons. The higher concentration of maghemite in paleosols suggests that the formation of maghemite occurred during in situ pedogenesis, which plays an important role in the enhancement of the magnetic susceptibility. Similar to that in the Chinese Loess Plateau lying to the east of the Liupan Mountains, magnetic granulometry in the studied loess and paleosols is predominantly pseudo-single-domain (PSD). However, the mean grain-size of the ferrimagnetic minerals in loess is evidently coarser (larger PSD and multidomain-like) than in paleosols (mainly PSD). The magnetic susceptibility of loess and paleosols is positively correlated with the content of ultrafine magnetite/maghemite grains, and hence with the intensity of in situ pedogenesis. Therefore, the enhanced magnetic susceptibility in the studied loess-paleosol sequences can be interpreted as being due to climatically induced in situ pedogenesis.