Abstract
Rio Grande Rise is a large aseismic ridge in the southwest Atlantic Ocean. Though the nature of its basement only can be inferred from geophysical evidence, shallow-water sediments recovered from various locations along its flanks show that it was a large towering 2 km above sea level during Santonian-Campanian times (75 to 85 m.y. ago) and that it slowly submerged since that time. Lithic fragments of basaltic material present with shallow-water sediments suggest that this island has a volcanic base of Santonian/pre-Santonian age. From the locations of shallow-water sediment components, subsidence rates of former shorelines were reconstructed. Application of the sedimentation rates from DSDP drill sites allowed estimation of the subsidence of the volcanic basemen and backtracking of the paleodepth of deposition of the pelagic-sediment facies recovered from the flanks of the rise. These facies can be correlated to similar sediments on the adjacent Brazilian continental margin (Sao Paulo Plateau) and on the southwest African continental margin.
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