Landscape and pedogenesis of an Oxisol-Inceptisol-Ultisol sequence in southeastern Brazil

The topographic sequence of Oxisols, Inceptisols, and Ultisols is frequently observed in tropical hilly surfaces in the southeastern region of Brazil. The purpose of this study was to relate pedogenesis to major geomorphic surfaces (MGS) in the Caetes watershed,located in Paty do Alferes, Rio de Janeiro State. The landscape is characterized by steep bedrock hills and cliffs of pre-Paleozoic gneiss, granite, and related metamorphic rocks rising above long, nearly Level, accordant ridge crests, convex hills, and narrow fluvial plains. Intense soil development, with deep weathering and kaolinite formation in the gneiss-granite rock, took place on the ridges and convex hills. Six pedons were examined using field investigation and laboratory soil characterization techniques. The degree of pedogenesis on the various geomorphic surfaces supports the landscape evolution theories of Penck and King. A Typic Hapludox, with the greatest degree of pedogenesis, formed on the stable summit position, MGS1. The upper part of the retreating slope, MGS2, bevels MGS1, and the material eroded from MGS2 moved downslope and formed a surface with lower gradient, MGS3. Dystrochrepts are on shoulder positions and shallow Hapludox are on backslope positions of the geomorphic surface MGS2, and Kandiudults formed on footslopes, MGS3. Eutrochrepts are on the youngest surface MGS4, a toeslope position.