Abstract: Kinematic Analysis of a Growth Fault System in the Niger Delta from Restoration in Map View

Delphine Rouby, Peter Cobbold

In order to study the kinematics of a growth fault system (involving a major fault, its antithetic and a faulted roll-over) located within the Niger Delta (offshore Nigeria), we have restored in map view six stratigraphic horizons. We computed, for each horizon, the horizontal displacements due to normal faulting in order to determine the associated displacement, rotations and strain fields. The extension computed for each horizon increases with depth, as expected for a continuous extension history. From the fields of finite displacement, block rotation and strain, we infer that the horizontal extension mainly perpendicular to fault traces is associated with a bulk sinistral shear accommodated by counterclockwise rotation of blocks and dextral displacement on faults. The overall strain thus differs from a plane strain. Balancing of cross sections alone in this area would have led to some errors. We improved the method in order to compute incremental displacement fields between times of deposition of successive horizons. During the first stages of development of the growth fault system, displacement occurs only on the major faults. During later stages, larger horizontal displacements are accommodated by numerous small faults probably responsible for the roll over collapse.

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