Mechanism of the magnetic susceptibility enhancements of the Chinese loess
Mechanism of the magnetic susceptibility enhancements of the Chinese loess
复制标题
DOI：
10.1029/2004jb003249
复制
发表时间：
2004-12
影响因子：
--
通讯作者：
Qingsong Liu;M. Jackson;Subir K. Banerjee;B. Maher;C. Deng;Yongxin Pan;R. Zhu
中科院分区：
文献类型：
--
作者：
Qingsong Liu;M. Jackson;Subir K. Banerjee;B. Maher;C. Deng;Yongxin Pan;R. Zhu
中国黄土/古土壤序列被认为是编码过去 2.5 Myr 连续古气候变化的优秀大陆档案。然而，中国古土壤的磁增强（特别是低场质量比磁化率，χ）的机制仍未完全解决。本研究通过磁提取技术量化了风成磁性颗粒和成土磁性颗粒对中国黄土/古土壤整体磁性的贡献。通过磁滞回线、磁化率的频率和低温依赖性以及参数间比，全面研究了覆盖黄土和古土壤的五个特征样品的磁性分离物（可提取）和相应残留物（不可提取）的磁性。结果表明：（1）成土作用中等程度（χ (10–12) × 10−7 m3 kg−1），与成土相关的细粒伪单域（PSD，~100 nm至几微米）颗粒的贡献变得显着；（2）成土颗粒具有狭窄的粒度分布，集中在SP/SD阈值以上；（3）滞回剩磁（ARM）主要由SD颗粒携带。此外，我们提出只有不可提取的 χ 分数、饱和磁化强度（M s）和剩磁化强度（M rs）与成土程度有很强的关系。这种对磁增强的新解释有助于我们检索中国黄土/古土壤序列记录的更准确和定量的古气候信号。
Chinese loess/paleosol sequences have been regarded as excellent continental archives for encoding continuous paleoclimatic variations over the past 2.5 Myr. However, the mechanism for magnetic enhancements (especially the low-field mass-specific magnetic susceptibility, χ) of Chinese paleosols is still not completely resolved. This study quantifies contributions of aeolian and pedogenic magnetic particles to the bulk magnetic properties of the Chinese loess/paleosols by using a magnetic extraction technique. Magnetic properties of magnetic separates (extractable) and the corresponding residues (nonextractable) for five characteristic samples covering both loesses and paleosols were comprehensively investigated by hysteresis loops, frequency and low-temperature dependence of magnetic susceptibility, and interparametric ratios. Results show that (1) with moderate degrees of pedogenesis (χ (10–12) × 10−7 m3 kg−1, contributions of pedogenically related fine-grained pseudosingle-domain (PSD, ∼100 nm to several microns) particles become significant; (2) pedogenic particles have a narrow grain size distribution concentrated above the SP/SD threshold; and (3) anhysteretic remanent magnetization (ARM) is carried dominantly by SD grains. Moreover, we propose that only the nonextractable fraction of χ, saturation magnetization (M s) and remanent magnetization (M rs) show a strong relationship with the degree of pedogenesis. This new interpretation of magnetic enhancements helps us to retrieve more accurate and quantitative paleoclimatic signals recorded by the Chinese loess/paleosol sequences.