Landforms and surficial formations in the Ribeirão do Baú Basin, São Bento do Sapucaí, State of São Paulo, Brazil

Abstract

This paper presents the results of a morphological cartographic study carried out in the Ribeirão do Baú basin, São Bento do Sapucaí municipality, State of São Paulo - Brazil. This basin corresponds to a sector of the erosive escarpment of the Campos do Jordão plateau, which is a morphostructural compartment of the eastern part of the Mantiqueira Mountain Ridge. The legend design of the 1:50,000-scale morphological map of the Ribeirão do Baú basin, preliminarily prepared from 1:25,000-scale aerial photographs, took into account the principles established by RCP.77, CNRS, France, for detailed geomorphological cartography. Greater emphasis was given to the morphographic representation, having in mind the diversity and richness of landform features. The correlation between the morphological, slope, and hypsometric maps allowed the individualization of seven morphological compartments for the Ribeirão do Baú basin at the 1:50,000 scale. Among the morphological and morphometric characteristics of the basin, landforms clearly controlled by structural features are represented by ridges and slopes with triangular facets, and the rocky scarped divisors of the Baú-Bauzinho-Ana Chata complex. The convex interfluves are cut by encased valleys, with strangled areas (sills) and rocky outcrops and waterfalls. Erosive amphitheaters, with different sizes and at various levels, model the hillslopes and define zones in the headwaters with specific morphology (rough surfaces) connected to mass movements. Other particular features are the concavities that appear on the hillslopes and terraces, mapped as depressions and concavities with steps. In order to highlight the morphological characteristics of these zones and the hillslope features, a 1:10.000-scale morphological map was prepared from the interpretation of 1:8.000-scale aerial photographs, and complemented by soil investigation via auger surveying and trenching. The results showed that the rough surfaces correspond to deposits related to the erosion of amphitheaters, whereas the depressions and concavities with steps are related to geochemical erosion, which develops from fractures in the subjacent rock mass. The genesis of these morphological features is explained on the basis of models proposed in the literature for hillslope evolution in mountainous areas of Southeastern Brazil.