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Abstract: Kinematic Evolution of Contractional Structures During Gravity Driven Deformation in Offshore Gabon (Seismic and Analogical Modelling Approach)

G. Guerin, S. Raillard, T. Mauduit, M. Gaillard, H. Lecanu

Raft tectonics and associated salt movements have dominated the evolution of the post Aptian sedimentary section along the West African passive margin. In this tectonic process, three main structural domains are classically recognized, from East to West (i.e. from shelf to basin):

- extensional domain, with pre-rafts structures;

- extensional-translational domain, with rafted structures separated by wide growth sequences along listric faults;

- downslope shortening domain.

Generally in West Africa, this last domain remains not well documented by seismic and wells due to great water-depth.

In the offshore Gabon, the contractional structures of this downslope shortening domain are important exploration targets because they are located close to the coastline. Consequently they are well covered by 2D and 3D seismic surveys and drilled by numerous exploration-production wells.

The case studies demonstrate that the contraction mainly affects previously existing extensional structures. It means that the contractional anticlines or reverse faults often correspond to reactivated listric faults or squeezed extensional diapirs.

Based on seismic data and applied analogical modelling (Sand-Silicone, performed by the CNRS, Geoscience, Rennes), we propose the following:

- the possible mechanisms explaining the late contraction.

- the relationships between the shapes of the shortening features and the previous extensional patterns.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France