Arquitetura deposicional e datação absoluta das cristas de praia pleistocênicas no complexo deltaico do Paraíba do Sul (RJ)

Abstract

Beach ridges are depositional features associated with prograding coasts, where each ridge represents an ancient shoreline. These features store records of coastal evolution during the Quaternary, especially when investigated with geochronological and morphostratigraphical methods. The Rio Paraíba do Sul delta complex has two extensive plains of of Holocene and Pleistocene beach ridges, the latter of which still insufficiently known. Therefore, the aim of this work is to characterize the sedimentary architecture of the Pleistocene ridges using GPR profiles, vibracores and absolute ages obtained by OSL and AMS. A radar facies was identified comprising a sequence of regressive or prograded barriers, with a depositional thickness of around oito meters. Beach ridges showed absolute ages of marine oxygen-isotope substage 5a (~85.000 ka), although some samples require analysis of more aliquots using the SAR protocol. The integration of GPR and OSL methods allowed identification of depositional units of the dated samples as well as the boundary between aeolian and foreshore radar facies, regarded as an indicator of mean sea level. This research resulted in the discussions about the genesis and evolution of beach ridges and the potentialities and limitations in association methods for investigation of Quaternary coastal plains.