洞庭盆地红土地层中网纹的成因探讨

Genesis of Reticulate Clay in the Laterite of the Dongting Basin

在野外考察的基础上 ,运用化学全量分析、X射线衍射分析、红外光谱分析和扫描电镜微形貌分析等实验方法和手段 ,对洞庭盆地第四系红土地层中网纹的元素地球化学、矿物组合特征和微形貌特征进行了系统研究 ,对洞庭盆地红土地层中 2种主要的网纹类型———蠕虫状网纹和根状网纹的成因进行了探讨。认为 :土壤孔隙空间的形成和化学元素的迁移是网纹产生的 2个必要条件。蠕虫状网纹孔隙空间的产生是由于地层静压力和地下水位季节性变化造成的 ,而根状网纹的孔隙空间则是植物根系腐烂分解后提供的。地下水和地表水强烈的淋溶作用使土壤中硅、铝、铁、锰等元素的迁移能力增强 ,土壤胶体粒子之间的化学反应 ,使得这些孔隙空间在后期逐渐被次生黏土矿物和石英所充填 ,最终 ,在洞庭盆地第四系红土地层中形成大量的蠕虫状和根状白色网纹。

The authors studied the characteristics of element geochemistry, mineral assemblage and microtexture of the white reticulate clay in the Quaternary laterite of the Dongting Basin with some experimental analysis methods, such as chemical analysis, X-ray diffraction analysis, IR and SEM analysis. The genesis of the vermiculate reticulate clay and the rhizomatic reticulate clay in the Quaternary laterite of the Dongting Basin are discussed. The formation of crannies or holes in the soil and the transference of soil elements are absolutely necessary conditions to form the white reticulate clay in laterite. The formation of crannies of the vermiculate reticulate clay results from the stratigraphical pressure and the seasonal fluctuating of the groundwater level. The formation of holes of the rhizomatic reticulate clay results from the decomposition of the botanic roots. The intense eluviation and weathering of soil with groundwater and run-off result in the enhancing of capacity of transference of some elements, such as Si, Al, Fe, Mn. The chemical reactions of the colloid particles in the soil water make those crannies or holes filled by some epigenetic clay minerals and quartz. Then a great deal of white reticulate clay comes into being in the Quaternary laterite of the Dongting Basin.