ABSTRACT

The formation of residual limestone clays, though controlled by the same factors that act upon non-carbonate rocks, takes place at a rate that is many times slower. This results chiefly from two factors: 1) the limited amount of insoluble residues available as "source materials" for the residual clays, following solution of the limestones; and 2) the strong dependency of profile thickness on the geomorphic stage of erosion present in the area. Unlike basalts, granites, shales, etc., thick residual soils are found in karst terranes only where sufficient relief has developed to permit extensive accumulation of the weathered debris in depressions formed either by solution or by uplift and deformation of the region.

Chemical and mineralogical analyses carried out on residual clays forming on limestones disclosed that the clays undergo development and transformations that are, in part, dependent on the climatic zone in which they form. Tropical clays, ultimately, will consist almost wholly of iron oxides and kaolinite, whereas, in temperate regions, varying amounts of illite may be present and persist meta-stably along with the kaolinite and iron oxides. Multiple discriminant analysis was successfully used to identify other basic differences between temperate and tropical residual limestone clays. Trace element analyses for a number of metals indicated high concentration levels in the clays, when compared with the original limestones, but, with the exception of manganese, no trends towards further concentration with geomorphic stage were noted.