Three-Dimensional Modeling of Two Low Taper Wedges Using Critical Taper Wedge Mechanics

Chris A. Guzofski¹, John H. Shaw¹, Freddy Corredor¹, and Frank Bilotti^2
1 Harvard University, Cambridge, MA
² Unocal Corporation, Sugar Land, TX

We present a new implementation of critical taper wedge mechanics to model the three-dimensional geometry of two unique fold and thrust belts. These include the compressive toe of the Niger Delta and the Southern Caribbean accretionary prism of Colombia. In the Niger Delta, compressive deformation is driven by the gravitational collapse of shelf sediments, while in the Southern Caribbean accretionary prism deformation results from the collision of the Caribbean and South American plates. While the driving mechanisms are quite different, both fold and thrust belts have a regional detachment that dips in toward the continent, while imbricate thrust faulting builds a bathymetric slope that dips away from the shelf, defining an internally deforming wedge. These features are consistent with a critical taper wedge model, where an influx of sediments into the system causes the wedge to internally deform by Coulomb failure in order to maintain a constant taper angle. These two wedges are striking in their similarities, most notably their low taper angle which is likely indicative that they both have a weak basal detachment.

We use these observations to create a three-dimensional model of the Niger delta and the Southern Caribbean accretionary prism using critical taper wedge mechanics. Regional 2-D seismic reflection profiles, detailed bathymetric data, and three-dimensional maps of the main detachment are used to define the regional geometry of the wedges. We investigate if topographic variations in the regional detachment directly influence the bathymetric slope of the wedges and what mechanical parameters control the low taper angle.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005