Fácies sedimentares e ambientes deposicionais associados aos sepósitos da Formação Barreiras no estado do Rio de Janeiro

Abstract

This paper characterizes the facies, sedimentary processes, and environments of the Barreiras Formation in the state of Rio de Janeiro between Maricá and Barra de Itabapoana. It also attempts to correlate the Barreiras deposits to well-defined Tertiary stratigraphic units in Rio de Janeiro, thereby contributing to the reconstruction of the Cenozoic sedimentary evolution of a continental area adjacent to important oceanic basins. Three gravelly facies, three sandy facies, and two muddy facies were recognized. The facies associations record high-energy traction deposits and suspension and debris-flow deposits, related to sandy to locally gravelly braided rivers, with varied occurrence of debris-flows. In Búzios, polymictic matrix-supported gravels interbedded with muddy sands occur adjacent to the Pai Vitório fault. These gravelly deposits were associated with syntectonic movements during the evolution of the Barra de São João Graben. Muddy-sandy sediments unconformably cap the Barreiras Formation. Their contact with the Barreiras Formation is generally marked by stone-lines of quartz and reworked Fe-oxide clasts. The deposits of the Barreiras Formation described here are faciologically similar to the Macacu and Resende formations (Eocene-Oligocene units). The main difference between them is the high-Fe oxidation in the Barreiras Formation deposits. Reliable geochronologic markers were not recognized in the Barreiras Formation, hence, its correlation with the Macacu and Resende formations can not be confirmed.