Levelling surfaces as a result of geomorphic processes acting in the past has been a very usual geomorphic interpretation for landscape of some areas. There were identified five standard types of laterites located at the east border of the São Francisco Craton. They were grouped in accordance with their morphological characteristics that show a correlation with their probable genesis and with some geologic and geomorphic aspects related to their development. The sampled areas are representative of an extensive planation surface occurring in the Serra do Cabral and Įgua Fria. Sometimes these laterites are associated with the presence of massive deposits of well rounded pebbles of fluvial origin, possibly Cretaceous, occurring between 800 and 950m height, well above the base level of nowadays drainage. In this research the evolution of lateritic profiles was analysed based on pedogeochemical aspects that could be associated with the profile genesis. Emphasis was placed on the degree of weathering and on the chemical characteristics of the material, in order to establish possible chronologies for the elaboration of the levelling surfaces. Analysis of some of the lateritic profile constituents (Fe2O3, Al2O3, SiO2, TiO2 and P2O5), show certain homogeneity in the values of all chemical elements, except TiO2 that occurs with values varying from 3,00 to 4,00 in 3 of the 10 studied profiles. These different values suggest the existence of a relationship between the high values found for TiO2 with the type of rock underlying the profiles. This has been also detected by others researchers, indicating genetic association between laterite types and local geological diversity. In studies of several laterites over the world high ratios of TiO2, which is found in basic rocks, were observed. This lithology coincides with those presenting high values of TiO2 occurring in the study area. The alteration degree of the ten profiles, on the basis of their chemical characteristics, allowed to identify the following chronological sequences: a younger surface, with Ki index values ranging from 2,07 to 2,12; an older one, with Ki index around 1,59; and a third surface with very low Ki index values (0,64) indicating the existence of a larger amount of free aluminium (gibbsite), contrasting with the amount of kaolinita which is dominant in the other profiles.
*This research was financially supported by FAPEMIG.