Desenvolvimento de drenagem e compartimentação morfotectônica em ambientes de escarpas de falhas: o exemplo do rio Santana e adjacências, borda ocidental do graben da Guanabara – RJ

Abstract

The landscape and geology of the basin of the river Santana and vicinity, in the northwestern of Rio de Janeiro state, reveal the influence of faults and fractures in morphogenesis and morphotectonics compartmentalization of the region. From the geological point of view, this region is located in a segment of the pre-Cambrian suture zone of Ribeira track between the Eastern and West territories, the Central Tectonics CTB-Contact of NE direction. Its reactivation in Mesozoic-Cenozoic periods was of great importance to the geological and geomorphological evolution of the area, as well as other structures, faults and joints of directions NE and NW, preferably NS and EW. The flaws in pre-Cambrian rocks have normal, normal/oblique and transcurrent movements and reveal striated plans, sometimes with overlapping of slickensided surface, indicating reactivations, breccia/gouge and cataclase zones, playing fundamental role in controlling the upping and dowing landscape shooting up or down and / landslides process. Similarly, families of joints of preferential directions between NW and NE were relevant, especially in watercourse dynamics. The influence of tectonics in the drainage network can be highlighted by: longitudinal profiles that emphasize suspended and staged valleys with a strong vertical incision, particularly over segments of faults or joints; strong changes in directions of the channels; types of patterns; morphology of drainage headboards; dissection of the cliffs, where valleys delimit triangular facets in different dimensions, showing neotectonics reactivations and recursive erosions. Changes in the erosive and depositional behavior are also emphasized in the suspended alveolar plains, in deposits of talus and falling blocks and, preferably, on catches of drainage that showed coincide with faults and joints. The morphotectonics compartmentalization, which meets preferably directions NE and NW, shows large scale variation of topography, from 10 to more than 1000 m in elevation, and can reach to 1500 m. Were defined compartments and subcompartments of NE direction in embedded, scarps and summit surfaces. Four blocks associated with the failures of normal direction NW (failures of Paracambi-Japeri, Paulo de Frontain, Arcadia and Miguel Pereira) divide this relief and promote disruptions with staggering toward SW. Directional movements show displacements of relief compartments, such as the embedded surface C-Ie where the Saco River is installed in the region of Miguel Pereira. This is a drainage surface with direction of flow for NE, contrary to the others, whose valley is a suspended landscape and the Javari lake is a suggestive area of paleocourse.