Geotectonic context and morphogenesis of the watershed between the Paraná and Amazon basins in Mato Grosso, Brasil

Abstract

The watershed between the Cuiaba and Paraguai river basins (Parana River hydrogra phical basin) and the Arinos and Teles Pires rivers (Amazon hydrographical basin), is characterized by a large area (aproximately 400km by 40km) of residual relief, remaining from erosive phases of the pre-Cretaceous and the Cenozoic. The relief resulted initially from an orogenic activity that occurred during the Upper Precambrian, starting from a geosynclinal basin and from the generation of the orogenetical belts of the Brazilian Cycle. From this process resulted the extensive Paraguai-Araguaia geosyncline. The residual mountains sustained by sandstone and secondarily by limestone are part of this great geosyncline. The foldings associated to elapsed and inverted faults followed by several erosive phases are responsible for the relief of the best preserved folded structures in Brasil. In this kind of modelling one can specially observe: asymmetric ridges on the borders of internally eroded anticlinals; raised synclinals or, still, abrupt slopes on the sides oflevel led top anticlinals, parallel to synclinal valleys; closed anticlinal depressions; superimposed valleys, water and wind-gaps, flat-topped interfluves at various altimetric levels and also large sorrounding depressions. The genesis of these reliefs can be found not only in the former tectonics that produced the orogenic belt but also in the Cenozoic tectonics that brought them back to salience, with the epeirogenic lifting of the Southamerican Platform and the erosive processes that followed mainly in the Upper Cenozoic