Considerations Regarding Hillslope Evolution

Abstract

In this paper is discussed a new interpretation of the morphology of the tropical and subtropical areas of the oriental part of Brazil. The slope evolution is considered as being primarily the consequence of pleistocenic climatic changes. During epochs of humid climate (interglacial stages), the landscape was dissected. At this time the slope evolved through deep chemical decomposition and denudation achieved mainly by mass movement. During the semiarid epoch, correlated with the pleistocenic glaciations, the landscape was developed by mechanical morphogenesis, lateral degradation and parallel retreat of the slopes through pedimentation processes. The cyclicity of the climatic changes caused the cyclic appearance of degradational and aggradation al forms characteristic of each one of the climatic types. Uplift played a secondary role in the development of the cyclic forms. These features were originated simultaneously in the most variable elevations along the drainage system. They would be essentially the result of two factors: climatic changes and the recurrence of the local
base level at different elevations inside the drainage system this way is explained the origin of the pediplanes, pediments and their correlative deposits developed during semiarid climatic conditions. Forms and deposits of this type are conspicuous all over the landscape, being better preserved than the features developed during humid climatic conditions. The last ones are responsible for the succession of erosional levels and for the dissection of the landscape.