Lamelas (Bandas Onduladas) em argissolo vermelho-amarelo como indicadores da evolução do relevo: o caso das colinas médias do platô de Bauru (SP)

Abstract

The big structural geomorphic surface situated in the west of the State of São Paulo, Brazil, and named Paulista OccidentalPlateau is supported by fine sandstones dated from Cretaceous of Paraná Sedimentary Basin and developed under Post-Cretaceous tropical denudation environments, compound residual and dissected plateaux. One of them, representing one of the mostly lowered and dissected surface, named Bauru Plateau, situated on its center-southern sector is constituted by big smoothed interfluves with length slopes related to the typical Red Ferralsol (Oxisol in USA and Latosol in Brazil) in center part and medium dissected interfluves to the boarders, with convex-concave-convex slopes related to soil succession interpreted as lateral pedological transformation system, constituted by Red and Red Yellow Ferralsol on the tops, Red Yellow Ferralsol with elevated textural gradient (Ultisol in USA and Argisol in Brazil) dominant in middle slopes, and Gleisol on the foothills and alluvial plain. This Red Yellow Ferralsol with eluvial horizon (E) frequently presenting numerous suspended and undulated fine yellowish sandy clayed lamellae, or red, thick, clayed and connected to the subjacent hydromorphic B argilic horizon (Btg) by a little peduncle projected in semi-arc to the foothill, is related to controversies about its origin. One representative soil profile from a typical toposequence was selected in order to illustrate the lamellae genesis and its relationships with the hydromorphic B horizon and the hillslope evolution. Macromophological and micromorphological study and physical - hydrological measures (texture, porosity and saturated hydraulic conductivity) over collected soil samples on length pit, was done. The results emphasizes the formation of lamellae and Btg horizon by e-illuvial mechanisms related to the hydromorphic action in the E-Btg transition and elluviation in E horizons associated to a suspended water level; a transitory soil features in pedological development of medium slope by consequence of internal lateral loss of clay and residual accumulation of sandy in superficial horizon conducting to a topographic deepening and potentialized by superficial concentrated water flows in favors to dissection. The origin of these processes is attributed to successive hydraulic adjustments of the interfluves inducted by depression of the base level under humid post-cretaceous climate. The lamella features representing the notables preserved features of the soil geomorphology development witch is functional until present.