Interações geomorfológicas entre bacias de cabeceira e vales fluviais principais: abordagem multiescalar na Bacia do Ribeirão Mata Porcos, Quadrilátero Ferrífero-MG

Abstract

The Geomorphology, as interdisciplinary and multi-scale knowledge body, demonstrates that these approaches are possible and even desirable in Science. Thus, I present this work which has the general aim of testing the possibility of multi-scalar and interdisciplinary analysis for the landform evolution phenomena having as verification locus the Ribeirão Mata Porcos watershed. Located in the mid-southeastern region of the Moeda Syncline, this watershed is inserted in western flank of the Quadrilátero Ferrífero, Minas Gerais state, Brazil. The specific aims are (i) understanding the events responsible for the morphogenesis of main valleys, headwaters, and Ribeirão Mata Porcos watershed as a whole; (ii) characterizing the pedological coverage of headwaters; and (iii) characterizing the fluvial depositional levels in the rivers of higher hierarquical order. Consequently, morphometric analysis, field and laboratory procedures were performed. At the watershed scale a more aggressive denudation, the occurrence of knickpoints as well as tectonic tilting affecting the drainage reorganization were found. At the headwaters scale, were found pedological coverage with distinct evolution patterns. These patterns demonstrated the action of a geochemical weathering front which has been propagated from downstream to upstream, possibly related to both fluvial incision and chemical downwearing at the lower hillslopes segments. At the main valleys scale, six depositional records were found. Two of them are holocenic floodplains. Another one, which has characteristics of a cut-in-bedrock terrace, was built in the Lower Pleistocene. Two originally-fluvial deposits were elaborated between the Middle and Lower Pleistocene. The latters, initially cut-in-bedrock terraces were disturbed by hillslope processes. The multiscalar approach of all these data demonstrates the existence of a transient geomorphological state defined by the quaternary river capture of Rio das Velhas and by the searching of a new equilibrium profile in the Ribeirão Mata Porcos watershed, its tributaries and its headwaters. Finally, I conclude that if the investigation had been carried out in only one of those elements, the connections would not have been found. So, the performed approach was essential for a better understanding of quaternary geomorphological changes in the Ribeirão Mata Porcos watershed.