喀斯特地区风化与成土过程特征:黄壤和石灰土剖面Sr同位素地球化学研究

The weathering and soil formation process in karstic area,southwest China:A study on Strontium isotope geochemistry of yellow and limestone soil profiles

西南喀斯特山地土壤(主要有黄壤和石灰土)的母质来源和形成过程至今存在较多争议。本研究选择黔中地区喀斯特典型的黄壤和石灰土土壤剖面作为研究对象,以Sr同位素为主要研究手段探讨了喀斯特地区风化成土过程特征,不同土壤母质来源及不同类型土壤的相互成因关系。研究发现:石灰土与砂岩黄壤具有明显不同的Zr/Nb和Th/Nb比值;石灰土较砂岩黄壤具有高的Rb/Sr和^(87)Sr/^(86)Sr比值;石灰土和砂岩黄壤的Rb/Sr与^(87)Sr/^(86)Sr相关关系不同。这些事实说明这两种类型土壤的成土母质来源不同,黔中高原广泛分布的红色风化壳来源物质可能与这两种土壤的成土母质有一定关系。另外,土壤剖面Sr同位素比值,Rb/Sr含量比值变化说明,喀斯特山地土壤主要通过风化-搬运-堆积-再风化过程形成。

The parent materials and formation processes of the soils distributing in the karst area（ mainly yellow soil and limestone soil） of southwest China are still in dispute. The typical limestone and yellow soil profiles in the central Guizhou province are studied , using the strontium isotope as a main tool to discuss the soil weathering and formation process, origin of parent materials and relationship between the formation processes of different soils. The Th/Nb and Zr/Nb ratios of the limestone soil profiles differ from the yellow soil profiles. The limestone soil profiles show higher Rb/Sr and 87Sr/SrSr ratios compared with the yellow soil profiles studied. The two kinds of soil profiles have different Rb/Sr versus 87Sr/86Sr relationship. All the geochemical characteristics indicate a different origin of parent material, and that the parent materials of the red residua are likely derived from the same parent materials with one or two of the kinds of soils studied. The variations of strontium isotope and Rb/Sr content ratios suggest that the soils of the karst area are formed first by the weathering-transporting-depositing processes and then the in situ weathering.