GEOMETRIA DO RELEVO E ESTRATIGRAFIA DO QUATERNÁRIO COMO BASE À TIPOLOGIA DE CABECEIRAS DE DRENAGEM EM ANFITEATRO - MÉDIO VALE DO RIO PARAÍBA DO SUL

Abstract

Research on slopes evolution in the Southeastern Brazilian Plateau has demostrated the existence of complex subsurface structures associated to apparently simple topographic features (rampas). It indicates the importance of systematizing stratigraphic studies associated to surface geometry. Considering the amphitheaterlike head-water as a fundamental unit of geomorphological evolution, an amphitheater typology extensive to drowned sub-basins is proposed, based on geometric.discontinuities verified at the articulation zone of the side slopes with the longitudinal axis of topographic concavities (hollows). Present knowledge on slope and drainage system dynamics has led to the identification of hollows as segments which are able to reproduce the amphitheater evolution in their subsurface structure. Two fundamental types have been defined. The first is related to the predominance of various episodes of colluviation, convergent to die main axis, defining the structure of rampa complexes in concave hollows (HQ. The second type is related to head-waters which in the recent geologic past have been subjected to intense process of accelerated linear erosion (paleogullies), which is represented in their longitudinal axis by alluvial-colluvial rampas. This is topographically characterized by a subhorizontal to horizontal plane hollow geometry (HCP). The typology proposed may represent an important subsidy in the definition of critical zones to present erosive processes by gullying, surface formations mapping and land-use planning.