Applications of ground-penetrating radar to investigate the Quaternary evolution of the south part of the Paraiba do Sul river delta (Rio de Janeiro, Brazil)

Abstract

Rocha, T.B.; Fernandez, G.B. and Peixoto, M.N.O.The coastline of the Rio de Janeiro is dominated by coastal sandy barriers which the main aspects of Quaternary evolution is determined by sea level oscillations in the Pleistocene and the Holocene. Such barriers have been studied in terms of geomorphological mapping, sediment transport and detailed morphology, mainly in the Holocene barrier. This work pretend by using geophysical techniques, describe the characteristics in subsurface of the coastal plain in part of Paraiba do Sul River Delta, one of worldwide example of wave dominated deltas. To achieve the objectives we use different frequencies with the antennas with 80, 200 and 400 MHz, with the equipment made by Geophysical Survey System Inc. The results showed that the GPR lines obtained in the Pleistocene Beach ridges describe a observation of sequences of reflectors of foredunes in the top, and beach and upper and lower shoreface in the base of the line, a typical sequence of regressive coastal barrier, formed under conditions of sea level falling. On the other hand the morphology of the Holocene barrier is characterized by transgressive barrier and lagoon spit, even of the regressive pattern of the sea level in the last 5.500 years B.P. In this case the radar facies showed a well preserved sedimentary structures by the continuous overwhash process and lagoon spits, along barrier lagoon system. We conclude that the radar facies showed important indicators about the genesis of these features and the relative sea level.