Freddy Corredor¹, John H. Shaw¹, Frank D. Bilotti²

(1) Harvard University, Cambridge, MA
(2) Texaco, Bellaire, TX

ABSTRACT: Modeling of Complex Imbricate Thrust Systems Using Growth Strata in the Deep-Water Niger Delta

Imbricate thrust structures are common in deep-water environments of passive margins worldwide, including the "Outer Fold Belt" of the Niger Delta. These structures are the product of contraction due to gravity-driven extension on the shelf. The Niger Delta offers a unique opportunity to study imbricate thrust systems, as these structures are extremely well imaged at deep levels in seismic reflection profiles and because they preserve growth strata that record fold kinematics.

Using growth strata, fold shapes, and fault plane reflections, we model the geometry and kinematics of these imbricate structures using fault-related fold theories. The timing and sequence of thrusting, and the kinematics of structural growth, in this imbricate system, influence hydrocarbon maturation and charge. These structures develop pronounced seafloor expressions and time transgressive angular unconformities and disconformities as they formed in an environment with low rates of deposition. Individual fault-related folds within the imbricate sequences are characterized by long planar backlimbs with increasingly shallower dips to growth strata, suggesting a component of progressive limb rotation. Forelimbs are short compared to backlimbs, but growth strata show more consistent dips that suggest a component of folding by kink-band migration. Combined mechanisms of kind-band migration and kind-band rotation are thus invoked to model the kinematics of these imbricate sequences. The sequence of imbrication is also resolved using patterns of growth strata, and we present examples of both break-forward and break-backward thrusting.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado