A study of a 477.5 km² 3D seismic survey offshore Cabinda, West Africa examined the relationship between the structures in the Pre- and Post-Salt sequences.

The Pre-Salt interpretation at the Mayombe interval shows a predominantly extensional fault network controlled by a major southwest dipping listric extensional fault with subsidiary synthetic faults accommodating the deformation in the hangingwall. These extensional structures are compartmentalized by anastomosing strike-slip shear zones.

The Post-Salt structure pre-Vermelha (pre-Cenomanian) is interpreted as a linked network of extensional listric faults and steeper transfer faults orthogonal to the extensional structures. The hangingwall deformation displays well developed roll-over anticlines adjacent to extensional faults and less well developed syncline anticline pairs adjacent to transfer faults.

The Pre-Salt and Post-Salt extensional structures terminate at the Base Salt horizon implying that there was no basement extension succeeding salt deposition. However, vertical to steeply dipping anastomosing shear zones are observed that carry through the basement succession up into the Tertiary sequence. Two hypotheses can explain these features. Firstly that the strike-slip shear zones are short lived recent events. However, evidence suggests that the strike-slip features are long-lived and this implies that there has been little actual transport of the post-salt during extension and that the structures observed in the Post-Salt are probably the result of salt withdrawal and halokinesis.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah