There has been a growing awareness of the importance of the weathered mantle in tropical landform evolution. In Gouveia geochemical characteristics and thickness of the weathered mantle have a close association with lithology, inherited landscape and erosional phases that has been taking place on a former erosion surface. This surface was elaborated on the granit-gnaiss from the crystalline basement and schist from the Supergroup Rio Paraúna. It has been reshaped, in a first phase, through the opening of the main drainage, accompanying broad geological features such as anticlinal axis and transforming fault systems, while the secondary drainage system had made its incision preferentially along basic and metabasic intrusions. Drainage incision has created lateral gradients that in some places presented headwater retreat. The retreat, characterising the second evolutionary phase of local relief has shaped amphitheatres and hollows that sometimes show the presence of "rampas de colúvio". This phase has been taking place at least since the upper Pleistocene (corresponding approximately to the Laschamps subchron) leaving humid-clays, with until 23% of organic matter, as correlative deposits. They were dated with C14 (ð13 C) and the results vary from 38,750 ± 5,100/3,100 Yrs. b.p. to 215 ± 150 Yrs. b.p. showing different periods of erosion/deposition cycles. X-ray analysis of clays shows the dominance of gibbsite and kaolinite in soils of the remaining older surface that still covers the tops of slopes. These soils present also high values of Al and Fe and very low Ca, Mg, P, K and N contents. The most recent phase is marked by gully incision. The reworking of the older surface has created conditions for a younger soil to develop with better edaphic conditions. Clays of 2:1 type are dominant in these soils that have also higher macronutrient content and were formed on the valley side, amphitheatres and hollows. The opening of lateral gradients has played an important role in increasing down-slope washing of clay and organic matter, propitiating accumulation on the lower slope, transforming these soils into better ones, capable of sustaining dense and rich vegetation cover, and intensive agricultural use.
*This research was financially supported by the Deutsche Forschungsgemeinschaft (DFG) and by FAPEMIG.