Drilling and geophysical observations in the Cretaceous coastal basins of Brazil, both onshore and offshore, coupled with published information on the African margin, have led to a better understanding of the rifting mechanism of the south Atlantic and the way it controls the distribution of oil reserves. This information is crucial at a time when high exploration cots and unstable oil process make it imperative to select

End_Page 533------------------------------

the best targets for exploration.

A modified fit between the facing margins of the South Atlantic, based on the correlation of geologic features, shows oil provinces to alternate between the two continents, indicating a segmented rather than symmetrical partition of the underlying rift sequence. Basement highs on one margin correspond to base lows on the other, filled with a rift sequence acting variously as heat conductor, source rock, and reservoir.

The breakup of Africa and South America resulted from their differential rotation. Ductile deformation at the tip of the northward propagating rift increased sharply where transversel "tough" tectonic elements held up and eventually deflected the propagating rift. In such areas, as in the Campos and Reconcavo oil provinces, continued differential rotation of the separating continents, without corresponding rates of rift propagation, created anomalous stress concentrations resulting in horizontal rotation and translation of small crustal blocks. The higher oil reserves of these areas, compared to the low averages of the South Atlantic, and their pattern of oil field distribution reflect the tectonic movement of these crustal blocks.

End_of_Article - Last_Page 534------------