Geomorphological analyses of the Teresópolis Plateau and Serra do Mar Cliff, state of Rio de Janeiro, Brazil with the help of summit level technique and ASTER GDEM, and its relation to the cenozoic tectonism

Abstract

This paper presents geomorphological analyses of the Teresópolis Plateau, the Serra do Mar Cliff, and the adjacent areas, State of Rio de Janeiro, Brazil, with the help of summit level technique using ASTER GDEM satellite topographic data, and its relation to the Cenozoic tectonism. According to the summit level map of the grid of 4 km, the studied area is divided into three geomorphologic domains, Rio de Janeiro Lowland (RJL), Serra do Mar Scarp (SMS), and Teresópolis Highland (TRH). The Rio de Janeiro Lowland, which corresponds to the Guanabara Graben area, is constituted by alluvial deposit planes and the areas of low hills that expose the metamorphic basement. Their limits are sharp and linear suggesting existence of small faults and grabens. The tops of the low hills are almost at the same altitude, constituting a summit level surface with approximate altitude of 100 m. The summit level maps of the grid of 4 km and 2 km show that the top of the Serra do Mar Scarp is of approximate altitude of 1300 m, and therefore, this normal fault has displacement of about 1200 m. The scarp strikes N75ºW and divided into the segments of 15 km to 30 km in length. At some localities on the halfway of the scarp, mega-landslide morphology is observed. The Teresópolis highland is tilted to N30ºW with mean dip of 0.9º. The drainage systems on the plateau shows three orientations, N60ºE, N10ºE e N75ºW. Along the Paraíba do Sul River, there is a morphologic depression of 20 km wide and 300 m deep, suggesting presence of a shallow graben. On the Teresópolis Highland, there are three alignments of morphologic protrusions oriented to N50ºE, with relative height up to 900 m. The height distribution diagrams for the summit level surfaces suggest that they should be remnant inselbergs before the fault movement of the Serra do Mar Scarp. The Cenozoic normal faults and the fracture systems of this area are often discordant with the basement structure. This phenomenon is explained by the model of the reactivation of the structures of the lithospheric mantle, and not of the continental crust.