Caracterização e gênese de solos desenvolvidos de cobertura quaternária sobre embasamento cristalino, na Baixada Litorânea do Estado do Rio de Janeiro

Morphological, physical, chemical, mineralogical and micromorphological characterizations were carried out in soil samples of four soil profiles, which were developed from a Quaternary colluvial cover over the regolith of the pre-Cambrian crystalline basement. Characterizations were undertaken in order to provide a better understanding of the formation and classification of these soils. Two soils showed an abrupt boundary with a stone line between the cover and the basement. In addition to routine laboratory analyses, the zero point of charge of the soil samples was determined. Soils were typically kaolinitic, with ki ration of 1.7 and Al:Fe ration greater than 6.0, moderate to strongly acid, allic (100. Al/(Ca + Mg + K + Na + Al) 50%) and dystrophic, with clay activity after discount oforganic carbon contribution less than 65 mmol c kg -1 . They are variable in depth and well drained. Their textural classes were medium clayey and clayey to very clayey. The higher clay content in the subsurface horizon seems to be due to in situ formation of clay, by post-depositional weathering, including some contribution of clay illuviation processes and selective surface erosion. Biological activity is probably mainly responsible for the relative homogeneity of the parent material and soil structure formation. According to the Brazilian Classification System, medium texture/clayey profiles are considered as soils with textural B Horizon (approximately equivalent to the USDA Soil Taxonomy). Despite the fact that the clayey to very clayey profiles show clay illuviation, this resulted in a low textural gradient. Soils were classified as intermediate due to the lack of an alternative in soil classification criteria currently in use.