Structure of the northern Brazilian continental margin
Results from two-ship seismic refraction profiles and supplementary data from several sonobuoys show that typical oceanic crust underlies both the landward and seaward sides of the North Brazilian Ridge. The Ceara Rise is also an oceanic structure, probably formed by local tectonic activity. Sediments of the upper Amazon Cone are more than 11 km thick, but they thin both landward and seaward. Owing to the great sedimentary thickness, refraction arrival times from oceanic basement could not be identified, but basement is assumed to extend under the cone.