Seabed characterization of the Trindade island shelf, Brazil.

This paper presents the first mapping of bedform morphological features on the Trindade Island shelf, with the goal of identifying and defining them. By using a side scan sonar, collecting seabed samples, and taking submarine photographs, five different morphological types were identified on this shelf: an erosive type: (i) characterized by the dispersion of rocks and rock blocks; and four depositional types: (ii) one formed by calcareous algal reefs, (iii) one composed by rhodoliths, (iv) one formed by medium sands with large symmetrical wave ripples, (v) and the last one formed by fine sands with asymmetrical wave ripples. The main result is a morphological map of the Trindade Island shelf, which shows the occurrence of these five seabed units. To further understand the sedimentological factors that affect the island shelf, we also examined the sediments that were collected for this study. Our results show that the amount of carbonate-formed grains on the collected sand sediments is higher than the amount of grains formed by the volcanoclastic ones, generated by the disaggregation of the main building on Trindade Island. The sediments formed by bioclastic grains are more frequently found in the coarser fractions than in the finer fractions when compared to lithic ones. • First seabed characterization on the Trindade Island shelf. • Boulders and rock outcrops occur at shallow depths, near the shoreline. • Rhodoliths and algal reefs are the main shelf seabed types. • Bioclasts are the main component that forms sandy deposits. [ABSTRACT FROM AUTHOR]