Distribuição sedimentar e geomorfologia da plataforma interna adjacente ao estuário do Rio Açu, Macau-RN

Abstract

The tropical semi-arid estuarine systems have a scarce sediment supply, but contribute to the deposition and development of sedimentary reserves at its mouths. Thus, the coastline and estuary undergo the depositional and erosional processes influenced by sediment supply and hydrodynamic. The estuarine zones have a high population density and are a region very vulnerable. The region of study develops socioeconomic activity focused on tourism, fishing, shrimp farming, oil industry, etc. This work aims to understand the submarine geomorphology, associated sediment distribution, and hydrodynamic performance as well, located on the inner shelf adjacent to Açú, a tropical semi-arid estuary on the Brazilian NE. The databank consisted of single-beam bathymetry, side-scan sonar records, surface sediment samples and satellite images. In the inner continental shelf were identified 8 textured patterns associated with 8 sedimentary facies, and 1 textural pattern as submerged rocky outcrops. In the shelf, the coverings of the siliciclastic and bioclastic facies are deposited in different places, influenced by the morphologies, estuarine performance and hydrodynamic. Thus, the siliciclastic facies (composed of mud and sand) are deposited in the regions in from of the Açú River mouth, and on the other hand, the bioclastic facies are located in the eastern portions of the area, but also associated with siliciclastic facies. The morphological diversity developed in the shelf is correlated with the sea level rise and fall, where the main features identified are sand ridges, incised valley, sand and mud banks, superimposed by lower order morphologies, such as, wavy relief with the presence of subaqueous 2D dunes and ripples. The tidal currents and wave trend direction are consistent with the subaqueous 2D dunes and ripples, respectively. In addition, the diversity of the ripples orientations in the Açú River mouth indicates a higher complexity of the currents and waves in this region.