Spatial variation in the recent geomorphological evolution of the turvo river basin, in the middle valley of the rio paraíba do sul: morphological and chronostratigraphic evidences/variação espacial na evolução geomorfológica recente da bacia do rio turvo

Morphological and chronostratigraphic evidence indicates that the region of the middle valley of the Paraiba do Sul River (MVRPS) went through two cycles of morphodynamic instability: the first between 10,000 and 8,000 years ago, and the second, which started about 250 years ago (cycle of coffee). This evolutionary dynamic was widely proven for the Bananal River basin, right slope of the MVRPS. Therefore, this study aimed to evaluate the repercussions of these two cycles in the Rio Turvo basin, left slope of the MVRPS. Surveys of fluvial deposits were made in several sub-basins, through mapping and thickness the volumetry of these deposits was obtained. 15 analyzes were performed by C14 dating in 9 stratigraphic profiles. Geochronological studies (AMS C14) on the river terraces of the Turvo and Pedras rivers show that they were formed in the same erosive-depositional cycle, between 8000-10000 years ago, identified for the Bananal River basin. However, erosion rates were higher in the Bananal River basin (Piracema River sub-basin) (38,500 m3/year), followed by the Pedras River sub-basin (2,240 m3/year) and other Turvo River sub-basins (320 m3/year). On the other hand, comparing the sedimentation rates of the coffee period, similar rates were observed between the basins of the Turvo and Bananal rivers (96,640 m3/year and 97,160 m3/year, respectively). The results point to a spatially non-uniform geomorphological evolution model, with the Rio Pedras sub-basin having a greater erosive-depositional magnitude, while in the rest of the Turvo river basin there is less sediment stock in the river valleys and the preservation of chemical denudation features. in the interfluves.