MOHRIAK, WEBSTER U., Petroleo Brasileiro S.A.-DEPEX, Rio de Janeiro, Brasil

ABSTRACT: Contrasts and Similarities in the Geologic Evolution of the Campos and Santos Basins, Offshore Brazil: The Cabo Frio Frontier Region

The Cabo Frio region, offshore Rio de Janeiro, is located between two of the most prolific Brazilian oil provinces, the Campos and Santos basins. Several outstanding geological features have been identified using a multi-disciplinary approach integrating seismic, gravity, petrographic and borehole data from both basins.

Early Cretaceous rift-phase volcanics are present in the Cabo Frio region, underlying lacustrine sediments of Neocomian age. A quiescent period follows a regional unconformity that predates the deposition of the Aptian evaporites. The Albian is characterized by deposition of calcarenites and calcilutites in Campos, while in the Santos Basin, south of Rio de Janeiro City, a carbonate ramp was highly influenced by clastic input and early salt mobilization towards deep waters, where the Albian sequence, if present, corresponds to a thin condensed section. In the middle to Late Cretaceous, this area was the site of a phenomenal clastic input sourced by coastal mountains, resulting in the accumulation of several quilometers of transitional to shallow marine sediments. A regional magmatic e isode is characterized by basalt flows between the Campos and Santos basins, and shows a marked preference for the latter basin. The flows are intercalated with volcaniclastic (autoclastic) sediments that have been dated as Capanian to Santonian. Particularly in the southern part of Campos, seismic and borehole information characterize and Early Tertiary episode of magmatism with volcaniclastic mounds. In the Late Cretaceous, salt mobilization was extremely active in the Santos region, and the structural style of antithetic faulting contrasts markedly with the salt tectonics structural style normally observed in the Campos Basin. Sedimentary depocenters also migrate towards the northern region of the Cabo Frio interbasinal province during the Tertiary. Deepwater turbidites are the main e ploratory target in this frontier region.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.