Morphodynamic limits of shoreface and inner shelf at the northern coast of Rio Grande do Sul, Brazil

Abstract

Detailed geology, bathymetry and sonographic data have been obtained over 80 km of the northern shoreline section of Rio Grande do Sul, the southernmost state of Brazil. This data was collected up until 50 m water depth, to determine the outer limits of the shoreface-inner shelf sediment exchange and evolution. Integrated data of 278 bottom samples, taken from the inner shelf, including 27 cores and 11 transverse shoreface bathymetric profiles, depth of up to 15 m, were analyzed. Geoprocessing data patterns show a regular bottom with gentle slopes, identifying three distinct morpho-sedimentaty sections: North, Central and South. The North and South sections reveal a heterogeneous pattern in the morphology and sedimentary distribution, contrasting with the South section, which has a more gradual sedimentary distribution fining out seaward. Correlations among textural statistic parameters, maps and sonographic records revealed variations, classifying 8 main facies. Bathymetric extended profiles, from the shoreface to the depth of 40 m, characterized the morphological shoreface-inner shelf dynamic boundaries (toe) at 18mon the Northern section, from 16mto 25mat the Central and South sections The shoreface shows marine dynamics over the geological control. Core facies and fauna show a morpho-structural and geological inheritance, responding to a coastline translation displacement. This process was responsible for the local variations of palimpsest and relict sediments, affecting ancient topography control of the coastline translation and past still steady sea levels, of the barrier variability, during the last HoloceneTransgression.