Abstract
A zone of offshore diapiric structures is present with a region of known continental-shelf salt and associated evaporites on the margin of eastern Brazil. The zone extends along the Brazilian margin for approximately 18° of latitude. At its southern end, off Santos, the diapir zone is approximately 350 mi wide where it forms the Sao Paulo plateau. At the northern extreme, the zone has been mapped solely on the basis of the presence of known continental-shelf salt. Except for the northern extreme part, seismic-reflection and refraction data have been used to map the offshore limits. Although it is debatable whether salt produced all of the diapirs, the offshore limit is referred to as the “salt edge.” The Brazilian zone is compared with, and matched against, a West African diapir zone. The latter zone extends for approximately 12° of latitude along the West African margin from Gabon to Angola, and probably also is related to the salt in the coastal basins. If the two zones are matched, they form a model of the early South Atlantic. The model indicates that the West African Walvis Ridge was part of a barrier to open-sea conditions as the Atlantic opened from the south. A prominent basement escarpment at the southern edge of the Brazilian Sao Paulo plateau abutted, or was adjacent to, the Walvis Ridge to complete the barrier.