he southwestern region of Rio Grande do Sul (RS) is characterized by large portions of sandy soils that have high environmental vulnerability, due to their low fertility and high susceptibility to erosion. Some of these soils have increased clay, suggesting allochtonous pedogenesis. In this case, the aims of this study were to determine evidence of allochtonous pedogenesis on sandstones Botucatu Formation in the southwestern region of the RS. A profile of Argissolo Vermelho and other of Neossolos Quartzarênico were analyzed, both formed on quartz sandstones of the Botucatu formation. Through morphological, physical, chemical and mineralogical analysis was possible to verify the process of allochthonous pedogenesis by higher clay content in the B horizon of the Argissolo profile and confirmed by the absence of clay forming minerals in the rock and in the presence of ilmenite in the pedogenetic horizons and its absence in the rock matrix. The environmental conditions suggest that the ilmenite originates from alteration of the surrounding volcanic rocks.
