黄土高原南缘S5-1古土壤中胶膜的特征及其环境意义
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华中农业大学

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S151

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国家自然科学基金项目(面上项目,重点项目,重大项目)


Characteristics of cutan in the S5-1 paleosol on the southern Chinese Loess Plateau and its environmental significance
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    摘要:

    以中国黄土高原南缘武功地区S5-1古土壤为研究对象,对比分析其胶膜与基质土壤的矿物学与地球化学特征,明确古土壤结构体表面深色胶膜的类型及其环境意义。拉曼光谱中400-800 cm-1的宽峰可能是多种铁和锰(氢)氧化物的混合光谱。锰和游离铁(Fed)的相对富集证实结构体表面的深色胶膜为铁锰胶膜,这说明在S5-1古土壤发育期间经历了周期性的氧化还原。S5-1古土壤中的淀积粘化过程导致其容重大、总孔隙度低,降低土层透水性,易发生季节性淹水,为铁锰胶膜的形成提供有利环境条件。然而,因S5-1古土壤中铁和锰的分离与积累时间短,其Mn/Fe比值较低,未达到亚热带地区典型铁锰胶膜中的水平。Fed/Fet比值反映的胶膜与基质土壤之间化学风化的差异未体现在矿物组成上,二者的原生矿物与粘土矿物组成基本一致。S5-1古土壤中铁锰胶膜的存在进一步证实了发育期间中国黄土高原南缘盛行亚热带气候。

    Abstract:

    To provide more insight in the characteristics of the cutan in the S5 and its environmental significance, the mineralogy and geochemical composition of the cutan and matrix soil in the S5-1pedon at the Wugong section on the southern Chinese Loess Plateau (CLP) was investigated. The broad band between 400-800 cm-1 in the Raman spectrum of the dark cutan was attributed to the groups of Fe and Mn hydroxide/oxide. Enrichment of Mn and free iron (Fed) in the cutan verified the presence of Fe-Mn cutan in the S5-1 pedon which signified a periodic reduction under waterlogged conditions during the pedogenesis of S5-1 pedon on the southern CLP. The low permeability of S5-1 pedon as a result of lessivage of clay fraction characterized by high bulk density and low total porosity made the development of a seasonal perched water table possible. It provided favorable environmental conditions for the formation of Fe-Mn cutan. However, the low Mn/Fe ratio in the cutan suggested that the separation and accumulation of iron and manganese in the S5-1 pedon was not up to the level of typical Fe-Mn cutan from subtropical regions. Silicate minerals in the Fe-Mn cutan was was almost identical to the matrix soil. The difference of chemical weathering between the cutan and the matrix soil reflected by the Fed/Fet ratio was not epitomized by the mineralogical composition. While the S5-1 developed a subtropical climate prevailed on the southern CLP was further corroborated by the occurrence of Fe-Mn cutan.

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  • 收稿日期:2020-07-12
  • 最后修改日期:2020-08-31
  • 录用日期:2020-09-04
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