Subaqueous dunes of Northern Shelf of Rio Grande do Norte (Brazil)

The Northern Shelf of Rio Grande do Norte (NSRN), between the cities of Areia Branca and Sao Bento do Norte, is characterized by its carbonatic-siliciclastic sedimentary coverage; mixed energy, dominated by waves and tides; and presence of geomorphological seabed features. These features include subaqueous dunes oblique to coastline, recovering a great part of inner shelf. Many researches have been produced in regional scale in this shelf. However, the seabed dynamic and sedimentary patterns are not known accurately. In this way, this work aim to map the inner shelf of NSRN in detail. For this, it was used the interferometric sonar system EdgeTech 4600. It was acquired 11 km
²
of bathymetric and sonographic data that allowed: geomorphologic classification of the dunes; semi-automatic classification of backscatter patterns; observation of sediments dynamic. Small dunes were observed between 5.5 m–8.0 m depth, presenting 1.5 m of maximum height. Large dunes are located between 4.3 m–10.3 m depth, presenting maximum height of 4 m. It was possible to recognize 5 backscatter patterns (P1 to P5). P1 and P2 showed high intensity, though the first is smooth and homogeneous and the second is rough and heterogeneous. The other patterns revealed medium intensity varying from rough (P3) to smooth (P4 and P5). The proportional increase of the dunes height to the depth is probably related to a rising of accommodation space and/or a more acting erosive process near the coast, where the currents are stronger It was also possible to notice the both dunes migration parallel to coastline and to NW offshore.