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.)

NEOTECTONIC INFLUENCE ON RIVER CAPTURE SYSTEMS IN THE PARAÍBA DO SUL RIVER MIDDLE VALLEY (SOUTHEASTERN BRAZIL)

Mello, C.L; Metelo, C.M.S.; Rodrigues, L.F. and Carmo, I.O.

Universidade Federal do Rio de Janeiro, RJ, Brasil, limeira@igeo.ufrj.br


This work aims to analyze the influence of neotectonic mechanisms on the development of distinctive river capture patterns in the Paraíba do Sul river middle valley. This area is inserted in the Continental Rift of Southeastern Brazil (CRSB), that corresponds to a block-faulted morphology originated by a NW-SE extensional tectonic regime during Eocene/Oligocene times. The resulting morphology is characterized by mountainous escarpments alternate to Cenozoic sedimentary basins. The area is dominantly constituted of Precambrian crystalline rocks (biotite gneisses and migmatites) with a well-marked NE-SW orientation related to metamorphic foliation, ductile shear zones and transcurrent faults. The regional landscape evolution is more influenced by Cenozoic tectonic events than lithologic variations. By detailed analysis of the regional drainage network, three river capture systems could be distinguished. Allostratigraphic analysis of the Cenozoic deposits and structural analysis of the joints and faults affecting them support the interpretations about neotectonic controls and its chronologic ordenation. An older river capture system is marked by abrupt inflections of the major fluvial courses mainly to NW direction. The most impressive example of this system is the Barreiro de Baixo river inflection. The supposed paleovalley preserves a thick succession of Tertiary sediments. This capture system is tentatively related to a NW-SE extensional stress caused by a Neogene (Pliocene?) sinistral E-W transcurrence. Another capture system is characterized by SW and NE orientations and affects a large number of low-hierachy drainages and the traces of main fluvial courses. It seems to be controlled by NW-SE structures and leaves Pleistocene deposits at the divide position. The structural control and morpho-allostratigraphic relationships led to relate this capture system to a Pleistocene/Holocene E-W dextral transcurrence. It is better distinguished on the northern border of Resende basin. A more recent capture system is characterized by orientations mainly to SE and less prominent to NW and by the ocurrence of Holocene alluvial deposits at divide positions. The divide of Barreiro de Baixo and Piracema rivers is the best example of this system, that is caused by NE-SW normal faulting related to an Holocene NW-SE extensional event.


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