The Evolution of the Perdido Fold Belt, Northwestern Gulf of Mexico - Insights from Numerical Modeling

The Perdido Fold Belt (PFB) in the northwestern Gulf of Mexico is a large deep-water salt-tectonic structure. It is located above the seaward limit of the Jurassic Louann salt and lies within the compressional domain of a salt tectonic continental margin system. The PFB is well documented in several geophysical surveys and deep-water hydrocarbon discoveries associated with this structure have recently been made. The region consists of up to 8 symmetric, ~15 km wide and 60 km long folds in exceptionally thick (4.6 km) overburden sediments. Folding is estimated to have occurred synchronously within only ~6 Ma and the entire fold belt is tilted seawards. The conditions that led to the given geometry, timing and extent of the fold belt including the role of the landward located Sigsbee salt canopy are poorly understood. This work investigates the formation of the PFB using 2D finite-element models in which frictional-plastic sediments overly a viscous salt layer. The models comprise the sediments of a passive margin from shelf to deep water to account for the dynamical interaction of gravity gliding and spreading caused by shelf progradation. The model experiments also include flexural isostasy, loading by the overlying water column and sediment compaction. Effects of pore fluid pressures are included by parametric calculations of an effective internal angle of friction. An analytical stability analysis and numerical experiments reveal that gravity spreading alone can fold a 4.6 km thick layer of frictional-plastic sediments in a setting like the western Gulf of Mexico. To obtain failure along the margin, the overburden is required to have a strength of only moderately overpressured, wet sand. Sediment compaction, which increases density, increases the translational velocity of the unstable overburden and results in earlier and faster formation of the fold belt. It also enhances the evolution of buoyancy driven structures. Additional numerical model results show the role of an adjacent salt nappe on the evolution of the PFB and the inflation of the detachment layer. Furthermore, the influence of salt taper and basement steps on the timing and extent of the fold belt is shown which helps constrain the initial salt thickness.