Plinthite and petroplinthite are commonly present features in soils developed on sandstone of the Bauru Group, Adamantina Formation, in the northern and western region of São Paulo State. The objective of this study was to evaluate chemical properties as well as pedogenic processes that led to the formation of these materials and the soil profile. Two soils at the foot of a representative mountainside of the local landscape with plinthic, petroplinthic and mottling features were selected within areas of the Experimental Station Pindorama of the Agronomic Institute Campinas (IAC), in the North of São Paulo State. Based on pedological routine analyses, selective dissolution, and X-ray fluorescence, the predominantly oxidic origin of the glaebules was diagnosed. These gleabules are not associated with organic compounds, contain low amounts of manganese, and higher levels of poor crystalline iron in the plinthites than in the petroplinthites. Main pedogenic processes that affected chemical characteristics of the saprolitic horizons in the studied profiles are: segregation and precipitation of high amounts of iron; mechanisms of eluviation-iluviation of clay and iron compounds, the ferrolysis; degradation of the petroplinthic horizons releasing iron to originate underlying plinthite.
plinthite; petroplinthite; selective dissolution; X-ray fluorescence
