Abstract: Tectonic-Stratigraphic Evolution of Offshore Potiguar Basin, Brazil

Cremonini, Oscar A., Goulart, José P. M., Soares, Ubiraci M. - Petrobras/E&P

The Potiguar Basin, the northeastern-most Brazilian rift basin, had a complex tectonic evolution as a consequence of rift propagation between the Equatorial and Eastern margins of the South Atlantic. Rifting was originated during the late Berriasian as a result of a WNW-ESE extension, which lasted until early Barremian. The rift stage resulted in ENE-WSW normal faults and WNW-ESE transfer faults, which led to the sedimentation of fluvial, lacustrine and deltaic continental sediments. Presently, this rift is partially covered by the Atlantic Ocean. A second rift phase (late Barremian to early Aptian) can only be recognized in the offshore portion of the basin, overprinting the previous rift phase and expanding rift deformation westward, being controlled by a roughly E-W extension. During this second rift stage, deltaic, lacustrine and alluvial-fan continental sediments were deposited.

The post rift stage initiated in the Aptian, and can be divided in two second order megasequences - a transgressive one, from Aptian to early Campanian, and a regressive megasequence, from late Campanian to Recent. The first marine incursion occurred in the late Aptian and the maximum transgression took place in the Turonian. The stratal patterns in the transgressive sequences shows low-angles dips and shingled to sigmoidal clinoforms, characteristic of a ramp margin basin. On the other hand, the stratal patterns in the regressive sequences shows relatively abrupt shelf breaks and oblique clinoform patterns. The unconformities associated with third order sequences boundaries were responsible for the formation of important canyons in the offshore Potiguar Basin. Among the most important, one can mention the Pescada Canyon (Lower Albian), Ubarana Canyon (Late Albian), Agulha Canyon (Coniacian/Santonian) and Fortim Canyon (Late Campanian). During the deposition of the regressive megasequence an important volcanic activity (Late Eocene/Early Oligocene) took place, when olivine-basalts flowed into subaqueous environment.

In the late Campanian the Potiguar Basin was subjected to further tectonic activity, when dextral transcurrent faults were generated, causing transtensional and transpressional features aligned through a roughly WNW-ESE direction. Associated with this tectonism occurs a very important unconformity in the offshore portion of the basin. Even thought this major unconformity (late Campanian) can be related to eustatic sea level changes, a thermal uplift caused by a transient spreading center might also give a tectonic explanation for such voluminous erosion.

During the Cenozoic (probably from Oligocene to Recent) the Potiguar Basin underwent new tectonic activity, when a roughly E-W compression originated a series of NNE-SSW long-wavelength folds and reactivated previous rift and post rift faults.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil