Quaternary evolution of the landscape of the Parana Basaltic Plateau, South America

KRÖHLING, DANIELA

Nagoya

Congreso; XIX INQUA Int. Congress; 2015

International Union for Quaternary Research (INQUA)

New geomorphological data of the Parana Basaltic Plateau (S Brazil and NE Argentina) are presented. The plateau is a stepped system separated by escarpments and with incised fluvial valleys, mainly belonging to the Upper Paraná and Uruguay basins. The region is under subtropical humid conditions hence some of the landscape development processes can be linked to tropical geomorphology. Main late Cretaceous-Cenozoic regional erosion surfaces were identified and mapped from morphometric analyses. These planation surfaces are mainly related to fluvial erosion and slope retreat process. Field data indicate that pediplanation, and also geomorphic processes like fluvial, surface wash and mass movement were important. The main recognized discrete erosion surfaces in the plateau can be correlated to the three known principal uplift episodes (late Cretaceous, Paleogene and Neogene) post-breakup of the Gondwana. The last uplift phase, linked to the Andean compressive context, is restricted to the Plio-Pleistocene. The Uruguay river bedrock, with its upper basin entirely developed on the basaltic plateau, played a key role in erosional landscape evolution. Extensive high-level, low-relief planation surfaces were identified there. The fluvial collector has headwaters at the Serral Geral erosive scarp and presents a pattern of incised meanders. Erosional features of the bedrock channel are highly preserved because of the great flow turbulence and their fluctuations; base level history also has influenced. A persistent characteristic of the river is a narrow, deeply incised channel (ca. 10-100 m) into the bedrock river channel, detected along ca. 1,000 km. It is almost continuous and permanently submerged, except in a segment where the river crosses an elevated tectonic block producing the emergence of the canyon and forming a scenic system of longitudinal waterfalls. High-precision bathymetric sonar data of the inner canyon and other landforms are discussed in order to contribute to the reconstruction of the landscape evolution.