Does calcium carbonate influence clay mineral transformation in soils developed from slope deposits in Southern Poland?

Purpose Literature reported that soils characterized by heterogeneity would reveal the different direction of clay minerals transformation. Hence, in this study, four soils developed on menilite shales slope deposits were investigated to test if the clay minerals transformations in soils with varied calcium carbonate distribution would show multidirectional paths of clay mineral weathering, or if transformation of secondary phases in such stratified materials would reveal only one trajectory. Methods The separated clay fractions were analysed using X-ray diffractometry and Fourier-transform infrared spectroscopy. Geochemical analyses were performed using ICP-ES and ICP-MS after sample fusion with lithium borate and an alloy dissolution with nitric acid. Results Calcium carbonate did not influence the composition and transformation of clay minerals. Despite the fact that soils were characterized by different content and distribution of calcium carbonate within the solum and additionally indicated various morphological features, the mineralogical composition of clay fraction was very uniform. Among the secondary phases, chlorite, illite, vermiculite, kaolinite and mixed phases illite-smectite and vermiculite-chlorite were detected in all horizons. Conclusions The uniform composition of the clay minerals in the studied soils suggested that mass movement, which controlled the formation of slope covers, was probably of a similar character and intensity across the whole of the slope. Furthermore, it seems that the pedogenesis in all soils proceeded on the same scale of advancement. This was indicated by a similar degree of weathering of soil material and lack of depth-dependent weathering in the profiles, confirmed by values of weathering indices (CIA and ICV) as well as by micromorphologically visible, highly weathered coarse fragments. Moreover, weak intensity of the illuviation process within the homogeneous substrate could have resulted in the very uniform composition of clay minerals in the studied soils.

Automated summary

The study found that despite different calcium carbonate distributions and morphological features, the clay mineral composition in soils developed on menilite shales slope deposits was very uniform, with secondary phases such as chlorite, illite, vermiculite, kaolinite, and mixed phases present in all horizons. This suggests a similar mass movement controlling the slope covers formation and a consistent scale of pedogenesis advancement across all soils. The weak intensity of illuviation process within the homogeneous substrate may have contributed to the uniform composition of clay minerals in the soils.