ANDESITE WEATHERING AND SOIL FORMATION IN A MODERATELY HUMID CLIMATE: A CASE STUDY FROM THE WESTERN CARPATHIANS (SOUTHERN POLAND)

The main aim of this study was to describe andesite weathering and soil formation in a moderately humid climate based on the physical, chemical, and micromorphologic properties of soil profiles from the Western Carpathians in southern Poland. Andesite weathering and soil formation in a moderately humid climate are reflected by significant depletion of SiO2, Al2O3, CaO, and Na2O from soils in relation to unweathered andesite bedrock. The chemical index of alteration and weathering (CIA and CIW) and plagioclase index of alteration (PIA) as well as weathering index of Parker (WIP) all indicate that soil material obtained from all the studied profiles (except the Jarmuta profile, which is enriched in carbonate by meteoric water during the Holocene) is clearly more weathered in comparison with andesitic bedrock. However, these chemical indexes do not show clear differences in weathering degree of soil material between different soil horizons, which is most likely related to excessively thin soil profiles and/or the occurrence of lithologic discontinuities in some of them. Micromorphologic observations indicate that in the process of weathering many fragments of andesite undergo cracking and iron in the phenocrysts of hornblende and augite undergoes oxidation. The crystals of hornblende exhibit very often irregular linear alteration along lines of cleavage. Additionally, many fragments of andesite and coarser mineral grains are characterized by the presence of weathering rims, which are composed mainly of iron hydroxides, clay minerals together with iron hydroxides, and sometimes also organic matter.