ABSTRACT

Located in the northwestern part of the Gulf of Mexico the Perdido fold belt is defined by a series of large-scale fold structures that extend southwest into Mexican waters and northeast beneath the well-defined Sigsbee salt escarpment. Within US waters, the visible fold belt consists of a series of northeast to southwest trending, sub-parallel, concentric, box folds cut on one or both of their flanks by high-angle reverse faults.

Structural mapping and cross section restoration have produced a model for the geological evolution of the Perdido fold belt that is consistent with sequence stratigraphic analysis of the seismic data. The main phase of compressional deformation in the Perdido fold belt occurred during the Oligo-Miocene by gravity sliding on a detachment at the top of the Jurassic Louann salt sequence. The overall geometry of the fold belt indicates that autochthonous salt thicknesses are highly variable, possibly related to basement structural highs and lows. Middle to Upper Miocene strata onlap the folded sequences, with later Pliocene to present-day uplift possibly a result of either active diapirism of the salt-fired cores of the highest-relief structures, or contractional reactivation of the folds with differential stress field orientation. Gravity slides off the crests of the anticlines are common within the younger folded sequences, resulting in a complex fault geometry in the higher parts of the folds.

With more than 7000m of strata involved in the fold belt structures, the presence of both reservoir and source horizons within the section is predicted. As yet, the petroleum potential of the Perdido fold belt has still to be tested. On the basis of correlations with deep Gulf of Mexico sequences, folded strata include late Jurassic through Oligocene rocks. Anticipated possible reservoir horizons include possible Upper Jurassic and Lower Cretaceous carbonates, Upper Cretaceous chalks and lower Tertiary turbidite sandstones. Within a deep water setting, there are significant risks regarding reservoir quality. Adequate seal over the faulted crests of the anticlinal structure is also a recognized problem. However, the Perdido fold belt remains an untested possible future petroleum province in US waters.