Stratigraphic stacking patterns and their reflections on the holocene coastal barrier morphology of the middle coast of rio grande do sul, Brazil

Abstract

In this work, the Holocene barrier of the middle coast of Rio Grande do Sul (RS), located between Estreito and Bacupari, was investigated in detail. This stretch of the coast corresponds to the most expressive large-scale coastal projection of the RS coast. Important discoveries were made through subsurface geophysical (GPR) and surficial geomorphology data. In the southern portion of the projection, between Estreito and the northern sector of Lagoa do Peixe, the Holocene barrier exhibits a predominantly retrogradational evolutionary behavior (probably from 6 ka and the present), which was determined by a negative sediment budget in the long term. On the other hand, in the northern portion of the projection, between Balneário Mostardense and Bacupari, the barrier shows a reversal from retrogradational to progradational behavior. Such evolutionary change, expressed in a progradation ranging from 230 to 1800 m, is possibly attributed to a change in the sediment budget (negative to positive budget) that may have occurred only a few centuries ago, or even a few millennia. The reversal towards a progradational stacking pattern showed an increase in size (length of the progradational record) from the middle to the north of the coastal projection. It is possible to suggest that these evolutionary trends on a geological scale (102-103 years) will continue over the next decades. Information about the coastline evolutionary trends in the last centuries and millennia can be useful as subsidies for the coastal management of the middle coast of RS.