Abstract: Compressive Anticlines of the Mid-outer Slope, Central Niger Delta

Connors, Christopher D.; Daniel B. Denson; Gunvor Kristiansen and David M. Angstadt - Texaco

It is well accepted that tectonics in the central Niger delta are dominated by translation of gravity-driven extensional fault blocks from the shelf out to the mid-outer slope and basin floor forming compressive anticlines. We present interpretations of these so-called "toe thrusts" from 2-D and recently acquired 3-D seismic data that show that the contractional response to this loading results in two end-member folding mechanisms. Most of the anticlines have long back limbs that lie above well imaged thrust ramps. These fault-related folds form as displacement along the basal detachment in the Akata Fm. is transferred up the thrust ramps. A poorly developed upper detachment is present in places resulting in the development of short front limbs to the anticlines, but most thrusting has broken through this detachment and ramped to the paleo-seafloor. Other folds appear to be due to viscous thickening within the Akata Fm. These folds have no clearly imaged thrusts, are generally symmetric and display subtle crestal normal faulting. The geometry of syntectonic sedimentation is manifest differently in the two end-member folding cases. Progressively shallower dips to growth strata of folds associated with viscous thickening suggest progressive limb rotation to these structures. In contrast, the fault-related folds have growth strata with consistent dip, separated by angular unconformities, and are consistent with kink-band migration under conditions where uplift rate has exceeded sedimentation rate during fold growth. A significant number of the anticlines in the central Niger delta appear to have formed by a combination of both folding mechanisms.

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