Deciphering magnetoclimatological patterns of late Early to early Middle Pleistocene loess–paleosol sequences in the western Chinese Loess Plateau
Deciphering magnetoclimatological patterns of late Early to early Middle Pleistocene loess–paleosol sequences in the western Chinese Loess Plateau
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DOI：
10.1016/j.gloplacha.2015.04.003
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发表时间：
2015-07
影响因子：
3.9
通讯作者：
Xishen Wang;Zhenyu Yang;Yun Chen;Jianyong Hu;L. Tang;Mei Sheng;R. Løvlie
中科院分区：
文献类型：
--
作者：
Xishen Wang;Zhenyu Yang;Yun Chen;Jianyong Hu;L. Tang;Mei Sheng;R. Løvlie
对九州台黄土剖面和草滩黄土剖面早更新世晚期至中更新世早期黄土-古土壤序列进行了详细的环境磁学研究，并结合地球化学、粒度和红度分析，探讨了磁学参数作为黄土高原古气候指标的可靠性。结果表明，早、中更新世黄土-古土壤序列的磁性增强不仅是由于成土作用中超细磁性颗粒的新形成，L 8和L9）更多地归因于与沙漠边缘的推进和/或与当地沉积物输入的显着变化相关的粗粒度磁性矿物的显着输入。由于所研究的磁气候信号明显地受成壤作用和风势的共同控制，磁化率（χ）和饱和等温磁化强度（SIRM）的测量结果对成壤作用的超细磁性颗粒和风成作用的粗粒假单畴/多畴磁性颗粒都有响应，不能提供明确的解释磁响应东亚夏季风强度。而对磁性微粒响应显著的非滞后剩磁（ARM）和频率相关磁化率（χfd%）则能较好地反映成壤磁性微粒浓度的变化，可作为成壤强度的可靠指标。磁性晶粒尺寸相关的代理，例如，ARM/χ和ARM/Ms（Ms，饱和磁化强度）、地球化学指标（例如，化学蚀变指数、Zr/Rb和Al/Si比值）和整体粒度记录都表现出一致的变化，是解决东亚季风变率的更直接的代理。因此，将矿物磁性、地球化学和粒度等多参数分析相结合，对于识别、划分和对比黄土层序，准确地揭示弱风化黄土中的古气候信息是十分有用的。由于经典的降水驱动的成壤模型磁化率增强是不完全适用于早更新世中期黄土在半干旱的西部CLP开发，相当谨慎，也应保证单独使用磁化率测量在定量重建古降水。
A detailed environmental magnetic investigation in conjunction with geochemical, bulk grain size and redness analyses of late Early to early Middle Pleistocene loess–paleosol sequences at the Jiuzhoutai and Caotan loess sections has been carried out, aimed to explore the reliability of magnetic parameters as paleoclimatic proxies in the western Chinese Loess Plateau (CLP). The results show that magnetic enhancement of early- to mid-Pleistocene loess–paleosol sequences at both sites is not solely due to the neoformation of ultrafine magnetic particles through pedogenesis, but in the case of several loess layers (e.g., L8 and L9) is more attributed to the significant input of coarse-grained magnetic minerals associated with the advance of desert margin and/or with significant changes in local sediment input. Since the magnetoclimatological signals studied here are obviously controlled by both pedogenesis and wind vigor, measurements of magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM), both of which are responsive to both ultrafine pedogenic magnetic particles and eolian coarse-grained pseudo-single domain/multi-domain magnetic particles, could not provide unambiguous interpretation of the magnetic response to the East Asian summer monsoon intensity. In contrast, anhysteretic remanent magnetization (ARM) and the percentage of frequency-dependent magnetic susceptibility (χfd%), which are notably responsive to ultrafine magnetic particles, can aptly trace changes in the concentration of pedogenic magnetic particles and can therefore be used as reliable proxies of pedogenic intensity. The magnetic grain size dependent proxies, e.g., ARM/χ and ARM/Ms(Ms, saturation magnetization), geochemical indices (e.g., chemical index of alteration, Zr/Rb and Al/Si ratios), and bulk grain size records all exhibit concordant variations and are more straightforward proxies for addressing the East Asian monsoon variability. Therefore the combination of multi-parameter mineral magnetic, geochemical and grain size analyses is very useful for distinguishing, delimiting and correlating loess sequences, and for accurately deciphering their paleoclimatic signals embedded in the weakly weathered loess. As the classical precipitation-driven pedogenic model for magnetic susceptibility enhancement is not entirely applicable to the early- to mid-Pleistocene loess developed in the semi-arid western CLP, considerable caution should also be warranted in using magnetic susceptibility measurements alone in the quantitative reconstruction of paleoprecipitation.