Análise Batimétrica e Sedimentológica no Estudo Parcel do Carpinteiro, uma Peleolinha de Prais Pleistocênica na Anteprais atual do Rio Grande do Sul, Brasil

Abstract

The “Parcel do Carpinteiro” outcrop is a Pleistocene relict nearshore shoal located at the modern shoreface of Rio Grande do Sul, Brazil. The present work describes the results of the integration of high resolution bathymetry, 3.5 kHz ecosounding, side scan sonar, autonomous diving and sedimentological sampling in the study of this submarine feature. Characterized by the occurrence of coquina and sandstone facies, strongly cemented by calcium carbonate, the structure is densely colonized by fauna (corals, bryozoans, sponges and poliquetae) and flora (coralline algae). Similar sandstones in other parts of Brazil (Southeast and Northeast coast) date from the Holocene, and are composed by 70 to 80% of siliciclastic sands and 20 to 30% of carbonate cement. In the study area, as well as in the rest of the coast of Rio Grande do Sul, the sandstones are mainly Pleistocene and composed by 20 to 40% of siliciclastic sands and 60 to 80% of carbonate cement. The analysis of the sedimentary structures, textures and composition of the facies suggests a depositional environment of high energy, probably near the surf zone. Recrystallization of the coquinas indicates sub aerial exposition after the deposition. The presence of ridge-and-furrows structures along the outcrop suggests that the shoal was reworked by waves during sea level stabilization before its subsequent drowning. It was observed that the associated gravel banks do not present cementation or recrystallization indicating at least two distinct genetic processes, one during the Pleistocene and another during the last Post-Glacial Transgression.