IAG 1999 Regional Conference on Geomorphology
Gloria Hotel of Rio de Janerio, Brasil, July 17-22, 1999
Abstracts - Sandra Baptista da Cunha and Antonio Jose Teixeira Guerra (Eds.)

LANDFORM MOSAIC RESULTING FROM THE CRETACEOUS AND CENOZOIC TECTONIC EVOLUTION OF SOUTHEASTERN BRAZIL

Motta, M.1, Eirado, L.2, Tupinambá, M.2 and Almeida, J.2

1Universidade Federal do Rio de Janeiro, RJ, Brasil
1Universidade Estadual do Rio de Janeiro, RJ, Brasil


The NE trending structural framework of the crystalline rocks that occur between the Coastal Plain, the Mar and Mantiqueira mountain ranges and the Paraíba do Sul river valley is inherited from the Neoproterozoic to Ordovician Western Gondwana assembly, during the Brasiliano Orogeny. At Cretaceous, huge NW trending hog-back morphology had modified the landform. It represents the continuation to the continent of structural highs that separate marginal basins of the same age at the South Atlantic passive margin. The Cabo Frio High separates Santos and Campos marginal basins since late Cretaceous and can be identified in the continent by drainage basin organization in the Paraíba do Sul valley. Hydrologic convergence areas had evolved at the base of steep scarps near Tres Rios, Volta Redonda-Resende, Taubaté regions, respective to Cabo Frio, Rio de Janeiro and Queluz highs. Similar features occur at the Coastal Plain, associated with the Guanabara and Sepetiba bays. The Tertiary tectonics rearranged the drainage network, increasing the topographic gradient and the erosional-depositional activities. Sedimentary deposits have filled the resulting basins (Taubaté, Resende, Volta Redonda and Guanabara). The Barra Mansa transfer zone displaced the rifting axis to SE, close to the coast, in a way that no sediment deposits have formed at Tres Rios area, probably due to a less effective Tertiary tectonics. The Paraiba do Sul Delta is a late Cenozoic feature, which indicates that the present drainage basin is a consequence of a capture along a Neoproterozoic vertical shear zone during Neogene times. Therefore, at Southeastern Brazil we can observe relict Cretaceous and reworked Cenozoic land surfaces. In this way, the Paraíba do Sul valley landscape may be considered as a mosaic of landforms with different slope evolution along the geological time.


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