Evolução da paisagem litorânea de Uruaú – CE, com base em dados estruturais e sondagens elétricas verticais

Abstract

The Barreiras Formation is a unit that extends along the Brazilian coast, from Rio de Janeiro to the state of Amapá, with an age attributed to the time interval that varies from the Miocene to the Pliocene-Pleistocene. For a long time this unit was considered as non-deformed, however, several researches have shown that it is deformed and that neotectonics has been the main responsible for the current geomorphological conformation of the brazilian northeast, presenting its reflexes in the sedimentation and evolution of the geological sequences , among them the Barreiras Formation. This research aims to find structural evidence, in mesoscale, of the influence of the deformation on the conformation of the Uruaú coastal landscape, east coast of the State of Ceará. The working method used is the analysis of geological, geomorphological and geophysical (eletrorresistivity) evidence that strongly suggest the effect of deformation on the landscape configuration through (1) mapping of the top of the crystalline basement, through the geoelectric behavior of the units; (2) integration of local geophysical results with regional data from geoelectric surveys and well profiles, in order to identify patterns of discontinuities; (3) determining the orientation of the surface brittle structures and analyzing their possible correlations; (4) and from performing the geometric and descriptive analysis from existing data related to the stress fields. The effect of the deformation in the study area is evidenced by the altitude variations in the crystalline basement, in the thickness variations of the units attributed to the Barreiras Formation deposits and by the reflections of the basement morphology in the conformation of the current landscape. These evidences suggest a depth variation of the crystalline substrate up to 60 meters that is associated to the tip of the block towards the ocean. This tilt may have promoted the generation of discontinuities that led to the lowering of the basement in the central sector of the area, here called Uruaú Block. The reflexes of the basement morphology in the conformation of the landscape can be observed (1) in the village of Uruaú, where the region is flat, lowered, contrasting with the higher adjacent areas and (2) in the dunes field, where the relief forms a depression, favoring the formation of interdunar lagoons and the dune field acts as a barrier to the Uruaú Lagoon. The morphology of these areas seems to have been configured by the Uruaú Block.