Structural analysis of the perdido fold belt: timing, evolution, and structural style

The Perdido fold belt is the compressional toe of the complex system of detached structures in the western Gulf of Mexico. Located in the Alaminos Canyon protraction area in ultra deep-water, this extensive fold belt has the potential to accommodate large amounts of hydrocarbons. These folds detach upon Jurassic-age Louann salt, and are northeast-southwest trending and symmetrical to asymmetrical. The lower units in these folds are comprised of mostly carbonates and limy carbonate mud, whereas the upper portion consist of fine grained and muddy siliciclastics which are typical of turbidite and other typical deep water deposits. 2-D, prestacked, depth-migrated seismic data (TGS Phase 45) was interpreted in conjunction with Hess Corporation to determine the geometry and timing of the folds outboard of the allochthonous Sigsbee salt nappe. The interpretation of the seismic data consisted of evaluating the folds by mapping age-dated reflections and kink-band boundaries (fold axial surfaces), along with creating isochores and dip maps. Through the development of new geometric model building of excess areas, which identifies material being added to the cores of the anticlines, along with the extensive seismic interpretation, the Perdido fold belt is identified to have originated in the west as early as the early Paleocene, with some continual fold growth to near present day. The folds in the Perdido fold belt continue to form eastward into the basin, up to the basinward limit of the autochthonous Louann salt. Also, it has been determined that the geometries and structural styles of the folds are partially dependent on the type of sediment or rock type in place. The lower portions consisting of the carbonates give shallower dipping fold axial surfaces, whereas the upper portions (siliciclastics) provide more steeply dipping fold axial surfaces.