Abstract

We interpret the Perdido fold belt to be composed of detachment folds flanked by megascopic-scale kink bands. The two previous principal fold models for the Perdido fold belt incorporated components of large-scale faulting: an imbricate fault-bend fold model and a high-angle, reverse-faulted detachment fold model. We interpret the Perdido fold belt to be fold dominated. The belt consists of detachment folds overlying a ductile decollement layer. The detachment fold crests are bounded by kink bands, which are narrow zones of angularly folded strata. The low-reflectivity, low–signal-to-noise zones seen in seismic profiles across the Perdido fold belt are poorly imaged sections of the folds that result from steeply dipping bedding in the kink bands. The substantial width of these low-reflectivity zones, their subparallel edges in cross section, and their orientation at a high angle to layering, as well as their organized spacing and conjugate geometry, support a kink-band interpretation. Propagating reverse faults are unlikely in the folds because of the absence of backlimbs overlying the locations of hypothetical faults. Improved seismic imaging efforts have illuminated steeply dipping bedding that is not cut by faulting in many of the low-reflectivity zones in the Perdido fold belt.

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