A slope system in an intracontinental rift setting: the record from Western Gondwana in the Santos Basin, Brazil

This study investigates a rift-related lacustrine slope system characterized by authigenic high-magnesium phyllosilicates (e.g., kerolite-stevensite) and carbonates associated with volcaniclastic deposits. By integrating high-resolution 3D seismic data in the depth domain with multi-attribute blending (Dip, Azimuth, and Maximum Curvature), we reconstructed the structural framework, stratigraphic geometries, and 3D morphology of depositional elements. Lithological calibration was achieved through thin sections and cores, supporting the geomorphological characterization. Results reveal a complex slope system controlled by NE-SW normal faults, dipping ~ 30° SE over a 40 km strike, with maximum accumulated vertical throw of 2000 m. This system is segmented by NW-SE and W-E faults to the north and south, respectively. Stratigraphic analysis identifies proximal onlap and distal downlap along early syn-rift fault scarps (Piçarras Formation), followed by the onlap of the late syn-rift (Itapema Formation) and early post-rift (Barra Velha Formation), characterizing a bypass margin. In contrast, the late post-rift Barra Velha Formation marks the development of a platform basin on the hanging wall, featuring linearly aligned mounds transitioning downdip into a flat-topped platform. Its margin is defined by arcuate mounds and a slope characterized by gullies, slumps, fans, and aprons, signaling an evolution toward an accretionary margin. Despite the alkaline lacustrine setting, the post-rift slope system exhibits striking similarities to marine analogues, suggesting shared depositional processes and responses.