New Palaeogeographic Reconstruction for the South Atlantic Aptian: Its Implication for Petroleum Exploration in Brazil

Mitsuru Arai
Research Center, PETROBRAS, Rio de Janeiro, Brazil

A new palaeogeographic model is proposed for the Aptian of the South Atlantic, based mainly on paleobiogeographic differentiation of dinoflagellate assemblages. This differentiation resulted from an emergent structural lineament, comprising the São Paulo Dorsal and Florianópolis High, which prevented free circulation and mixing of marine waters between the southernmost South Atlantic and the remainder of that ocean. This gave rise to two distinct environments on either side of the lineament-barrier, which persisted until the end-Albian. From Aptian to Albian all basins of the Brazilian Atlantic margin - except its southernmost part (Pelotas Basin) - were flooded by waters derived from the Central Atlantic (Tethys Ocean). North of the barrier, marine environments ranged from predominantly evaporitic (in basins of the Brazilian East margin) to paralic (in basins of the Brazilian Equatorial margin). During maximum flooding of the Aptian transgression, most of Brazil’s Atlantic margin basins were fed by Tethyan waters derived from the Central Atlantic, reaching as far south as the Santos Basin. The São Paulo Dorsal-Florianópolis High lineament prevented Tethyan waters from reaching the Pelotas Basin in the south, where open marine conditions are testified by fairly diverse dinoflagellate assemblages. The present model is contrary to the traditional one which has assumed that the South Atlantic invaded from south to north, accompanying the tectonic plate opening. These insights can promote the development of new exploration strategies for potential oil-plays in Aptian and stratigraphically contiguous sections (e.g., pre-salt, evaporitic and correlative strata, and early Albian carbonates).

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