Relict Nearshore Shoals of Rio Grande do Sul, Southern Brazil: Origin and Effects on Nearby Modern Beaches

Abstract

aiH^HHB^HBHI^^^HaHHBHBaHaBHBH BUCHMANN, F. S. C. and TOMAZELLI, L. J., 2003. Relict nearshore shoals of Rio Grande do Sul, southern Brazil: origin and effects on nearby modern beaches. Journal of Coastal Research, SI 35 (Proceedings of the Brazilian Symposium on Sandy Beaches: Morphodynamics, Ecology, Uses, Hazards and Management), 3 1 8-322. Itajai, SC Brazil, ISSN 0749-0208. The nearshore morphology of the barrier, wave-dominated, microtidal coast of Rio Grande do Sul is marked by the presence of several distinct shoals whose origin is not directly related to modern depositional processes. These shoals are relict features formed by beach and shallow marine deposits of Late Pleistocene age that, due to their consolidation, have partly resisted wave erosion during the Post-glacial Transgression. Today, during storms, the waves attack these Pleistocene deposits and transfer part of the eroded sediments to the adjacent beaches. These sediments include bioclastic and siliciclastic components (fossils of several kinds plus medium and coarse quartz sands) that strongly modify the composition and texture of the adjacent modern beach sands. ADDITIONAL INDEX WORDS: Beach sedimentation, shoreface morphology, coastal erosion, coastal evolution.