The drainage reorganization during the Cenozoic in the Middle Vale of Paraíba do Sul: the influence of tectonic and neotectonic controls on drainage captures

The river system plays a very important role in denudation processes and, consequently, in relief evolution in non-glacial landscapes. Several theoretical and empirical studies have contributed to a better understanding of how rivers change after modifications in their boundary conditions, such as tectonics or climate. The region of the Middle Valley of Paraíba do Sul (MVPS) has important records of recent drainage captures, which show a state of transition of the landscape and, consequently, a reorganization of the drainage networks. This region is in the Southeast of Brazil, topographically characterized as an area with escarpment of passive continental margin, where, close to the coast, the Serras do Mar and Serra da Mantiqueira stand out. The relief of the PSMV area and its respective drainage network had its evolution conditioned to the tectonic and climatic events that occurred during the Cenozoic. The oldest tectonic event is described as a NW-SE (E1) stretch, of Paleogenic age, followed by an E-W sinistral transcurrence (TS) event in the Neogene and a dextral transcurrence (DT) event, which occurred in the Pleistocene-Holocene. Finally, the extension event (E2) in the Holocene was associated with generalized reactivations of NE-SW structures, locally related to the generation of grabens, such as the Rio Bananal graben.Although of great importance in studies involving relief evolution, there are still few works that use river profiles and fluvial gradient indices such as χ and ksn to analyze the role of river captures in the reorganization of drainage networks and their relationship with neotectonics. Thus, the present study aims to investigate the causes of the reorganization of the drainage network in the MVPS region and its relationship with the evolution of the relief and its respective neotectonic activity. The E1 event was responsible for the consolidation of the hemi-graben configuration of the sedimentary basins in the MVPS. The normalized steepness index calculated for the main rivers demonstrates that this configuration possibly established a greater erosive power for the basins that drained the active fault, represented by the basins of the northern sector of the study area. During the Neogene, the TS event occurred, responsible for the inflections of the main channels to N-NW. These inflections are marked by knickpoints and sudden changes of χ and ksn in the fluvial profiles of the main channels. The paleotension analysis showed that structures associated with the TD event may be related to the filling and clogging of valleys with alluvium-colluvium ramps. The E2 event generated a system of normal transcurrent faults associated with a NW-SE Holocene extensional regime, responsible for captures oriented preferentially to SE and secondarily to NW. In the field, the relationship between TD and E2 was observed: the first related to NW-SE triangular facets and filling by valleys with alluvial-colluvium ramps and then, the fluvial capture promoted by E2. The Chi-z fluvial profiles and longitudinal profiles corroborate this model, indicating migration of the dividers compatible with the main capture directions observed.