Roundness in Holocene Sands of the Paraiba do Sul Coastal Plain, Rio de Janeiro, Brazil

Abstract

Sea level changes during the late Quaternary played an important role in the construction of the extensive Paraiba do Sul River mouth coastal plain in the State of Rio de Janeiro, Brazil. Large volumes of sand have been transferred from the adjacent inner shelf to the coastal plain, as a consequence of a continuous and gradual sea level drop during the past 5,000 years. At the same time, longshore currents, dominantly trending south-to-north, were important in the shaping of the asymmetric coastal plain on either sides of the Paraiba do Sul River mouth. Geological interpretation of the roundness of beach sands on both sides of the river mouth and in Holocene beach ridges from northern and southern terraces allows an evaluation of the roles played by sea level, river discharge fluctuations and longshore currents in the construction of the coastal plain.