This study used 3D seismic data to extract detailed depositional information for Prospect B. The analysis included assessment of the build-up’s external morphology and internal seismic facies, measuring the dip and dip direction of inclined reflectors, making horizon slices, mapping internal surfaces onto which seismic attributes were extracted (RMS amplitude, spectral decomposition), and creating thickness maps to show build-up evolution through time. These data were then evaluated against known and published observations made on volcanic and carbonate systems (continental and marine). Architectural elements like vents, igneous flows and complex clinoform geometries suggest that a large portion of the build-up is likely volcanic in origin. Though it has carbonate-like features, no definitive carbonate geometries were identified. Thus, Prospect B is more likely to be dominated by igneous materials such as hyaloclastites. Contrary to existing interpretations, Prospect B and its equivalents probably represent a late, waning phase of regional volcanism, and are an important bathymetric record of the South Atlantic’s formation.