O papel das capturas fluviais na morfodinâmica das bordas interplanálticas do sudeste do Brasil

Abstract

In southeastern Brazil, specifi cally in Minas Gerais, there are stepped plateaus drained by different river basins, which are often divided by morphological steps resultant of the difference in the erosive potential between the interfl uves, as a long-term response to Cenozoic distensive tectonics. In addition, fl uvial captures enforces the captured drainage network to a new equilibrium profi le, changing the morphology of the involved channels (captor, captured, decapitated and direct tributaries). This paper presents the role of the great river captures (named São Vicente, Carandaí and Vilas-Boas) in the morphodynamics of three interplateau-escarpments between the four major river basins in southeastern Brazil: Paraná River, São Francisco River, Doce River e Paraíba do Sul River. The carthographic analysis (geologic, geomorphologic and topographic maps) and the following fi eldworks - when the involved channels, valleys and surrounding slopes have been described - showed that the studied river captures have different characteristics: 1) at the Vilas-Boas capture, the escarpment crest remains in the original location (pre-capture), and the landscape changes are restricted to the valleys surrounding the capture, by the fl uvial incision of 2,5m up to 1km upstream of the capture point; 2) at the Carandaí capture, the escarpment crest retreated around 1,5 km from the capture point, lowered by 100m, and the landscape changes reach around 3km upstream of the capture point; and 3) at the São Vicente capture, the escarpment crest retreated around 3,5 km from the capture point, lowered by 250m (reaching the lowlands) and he landscape changes reach around 8 km upstream of the capture point. These results revealed the river captures hole in the morpho-dynamics of the escarpment between stepped plateaus: the escarpments retreat with greater rates when there are fl uvial captures, which are dissected and recessed, contributing to the change o