Chemical Weathering Intensity and Element Migration Features of the Xiashu Loess Profile in Zhenjiang
Chemical Weathering Intensity and Element Migration Features of the Xiashu Loess Profile in Zhenjiang
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发表时间：
2007
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通讯作者：
Yang Dayuan
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作者：
Yang Dayuan
本文研究了镇江下蜀黄土剖面的化学风化强度和元素迁移特征。通过与其他风沙沉积的比较，通过对黄土高原第四纪黄土-古土壤和晚第三纪红粘土剖面，以及安徽宣城风沙红土剖面的分析，得出以下结论：①下蜀黄土剖面经历了中度的化学风化作用，其化学风化作用强于洛川黄土和古土壤，远弱于宣城风沙红土，与西峰晚第三纪红粘土相似。研究区风沙沉积化学风化的差异主要是由气候条件的差异引起的，气候条件的差异通过年平均气温和年降水量对地球化学环境产生重要影响。年降水量对化学风化过程的影响更为重要。(2)化学风化过程中Si、K、Na、Ca、Mg、Mn、P等主要元素发生迁移浸出，Fe、Ti等元素略有富集。根据迁移能力，主要元素排列顺序为：P Na Ca Mg K Fe2+ Si Mn Al Ti Fe3+。主元素迁移特征表明，下蜀黄土完成了以Ca、Na浸出为特征的初级化学风化过程，几乎达到了以k浸出为特征的次级化学风化过程。除Sr、Ga元素外，Th、Ba、Cu、Zn、Co、Ni、Cr、V等微量元素在化学风化过程中富集。这种富集可能是生物地球化学过程和化学风化过程中粘土矿物和有机物对微量元素的吸附作用共同作用的结果。(3)下蜀黄土剖面的元素迁移差异表明，中更新世早中期（0.24 Ma以前）的气候是温暖湿润的，但具有干湿交替的特征。在中更新世末期，它变得干燥和凉爽，导致最弱的风化和元素迁移。晚更新世早期，古气候再次变暖变湿，形成了较强的成土作用，下蜀黄土剖面形成了古土壤S1。从整体上看，中更新世开始，该地区的古气候总体上变干变凉。
The chemical weathering intensity and element migration features of the Xiashu loess profile in Zhenjiang are studied in this paper.Based on the comparison with other aeolian-dust deposits,i.e.Quaternary loess-palesol and late-tertiary red-clay profiles in the Loess Plateau,and aeolian dust red earth in Xuancheng of Anhui province,we draw the following conclusions:(1)The Xiashu loess profile underwent moderate chemical weathering,which was stronger than that of the loess and palesol in Luochuan,much weaker than that of the aeolian dust red earth in Xuancheng,and similar to that of late-tertiary red-clay in Xifeng.The chemical weathering differences among the studied aeolian-dust deposits were mainly induced by the distinction of the climate condition,which imposed important influence on the geochemical environment through the mean annual temperature and annual precipitation.It seems that the annual precipitation has more important influence on the chemical weathering process.(2)The major elements such as Si,K,Na,Ca,Mg,Mn and P were migrated and leached,while the elements Fe and Ti were slightly enriched during the chemical weathering process.According to the migration ability,the major elements are ranked in the following order:P Na Ca Mg K Fe2+ Si Mn Al Ti Fe3+.The migration features of the major elements reveal that the Xiashu loess finished the primary process of chemical weathering characterized by leaching of Ca and Na,and almost reached the secondary process characterized by leaching of K.Except the elements Sr and Ga,other trace elements such as Th,Ba,Cu,Zn,Co,Ni,Cr and V were enriched during the chemical weathering process.And this enrichment might be caused by both the biogeochemical process and the adsorption of trace elements by clay mineral and organic materials during the chemical weathering.(3)The difference of element migration down the Xiashu loess profile reveals that the climate was warm and wet at the early-middle stage of the Middle Pleistocene(before 0.24 Ma),however,bearing the feature of an alternate dry and wet fluctuation.At the end of the Middle Pleistocene,it became dry and cool,which resulted in the weakest weathering and element migration.At the early stage of the Late Pleistocene,the paleoclimate became warm and wet again,which led to rather strong pedogenesis and the formation of the paleosol S1 in the Xiashu loess profile.As a whole,the paleoclimate generally became drier and cooler in this region from the beginning of the Middle Pleistocene.