From a geometric analysis of the fault pattern in the Reconcavo basin, Brazil, supported by a reinterpretation of the early opening history of the South Atlantic Ocean, it is inferred that the basin formed as a result of Valanginian (Early Cretaceous) motion on a major N40°E-striking left-lateral transform fault located offshore between Salvador and Recife. This left-lateral motion was due to the location of the Valanginian pole of South American-African plate rotation within northern Brazil, at 2.5°S, 45.0°W, rather than farther north as interpreted previously.

Left-lateral movement along the inferred transform created three fault sets: (1) a predominant set striking N30°E ± 20° (1^sgr); and two lesser developed sets striking (2) N13°W ± 6° and (3) N37°W ± 12° (1^sgr). Sets (1) and (3) are interpreted, respectively, as Riedel and conjugate Riedel shears (with an extensional component) to the N40°E-trending left-lateral transform fault. Set (2) formed as an extensional fault system. Intersections of these three sets subdivide the basin into triangular and diamond-shaped blocks.

The Reconcavo basin continues northward in northeastern Brazil into the Tucano and Jatoba basins. These basins collectively form a north-south-trending, mega half-graben within continental crust.

Geohistory curves for Early Cretaceous units in the Reconcavo basin indicate that the syn-tectonic Valanginian shales of the lacustrine Candeias Formation began to generate hydrocarbons during the earliest subsequent deposition of the Ilhas Formation (?Hauterivian). Because diamond-shaped structural traps had formed earlier during the Valanginian, hydrocarbons generated in the Candeias Formation are believed to have then migrated into the Sergi Formation (?Upper Jurassic) reservoir units in structurally juxtaposed fault blocks. During Barremian to Aptian time, deposition of fluvial, lacustrine, and alluvial sediments of the Ilhas and Sao Sebastiao Formations occurred.

Rejuvenation as normal faults of earlier formed strike-slip and normal faults occurred in the latest Aptian (106 Ma) when the pole of South American-African plate rotations jumped to 41.3°N, 43.8°W. This pole jump caused extension along the previously formed transform margin between Salvador and Recife and the abandonment of rifting in the Reconcavo basin.

Rejuvenated faults tapped earlier filled Sergi Formation reservoirs, which then leaked earlier reservoired hydrocarbons up these fault planes into higher reservoirs in the Ilhas and Sao Sebastiao Formations. This structural history thus explains the frequency distribution and orientation of faults in the basin, Sergi Formation production from corners of diamond-shaped fault blocks, and production from stratigraphically and structurally higher reservoirs (Ilhas and Sao Sebastiao Formations) in rollover folds and stratigraphic traps charged by second-phase faulting.