The formation of soils with argillic horizons was investigated to identify the pedological processes involved in the formation of lamellae and the abrupt textural gradient as well as their implication on the soil physical, chemical and mineralogical attributes. This study was carried out on a sandstone-derived soil toposequence, with profile (P1) occupying the higher part of the landscape (summit), profile (P2) on the backslope, and profile (P3) on the footslope. Soil chemical, mineralogical, micromorphological and particle size distribution analyses were performed. The profiles presented an A-E-Bt horizon sequence, being classified as Hapludults. The soils were acid, with clay mineralogy dominated by kaolinite. The analyzed materials evidenced uniformity in relation to particle size distribution, average diameter, roundness and sand fraction zircon/turmaline relation, as well as uniform morphological aspects, showing the autochthonous origin of these soils. The pedogenetic processes responsible for the abrupt textural gradient are clay degradation under oxi-reduction conditions and lessivage. The first process is evidenced by micro-domains at the E/Bt contact, where gleization colors can be seen, indicating temporary water saturation conditions. In this case, the formation of the albic horizon is due to the destruction of the top of the Bt horizon. The lamellae would be an inheritance of the Bt horizon in the albic horizon. The presence of illuvial clayskins, associated to argillans observed in the micromorphological studies, suggested a contribuion of the lessivage process to textural gradient formation.
argillic horizon; ferrolysis; illuviation; micromorphology; mineralogy; pedology