Shallow and Deep Structural Provinces of the Northern Gulf of Mexico
Mark G. Rowan1 and Kerry Inman2
1 Rowan Consulting, Inc, Boulder, CO
2 Exploration Consultant, Houston, TX
Structural styles observed on the GulfSpan regional 2-D, pre-stack depth-migrated seismic array are used to delineate structural provinces for both the shallow (allochthonous) level and the deep (supra-Louann) level. At the shallow level, linked systems of proximal extension and distal contraction characterize regionally extensive canopies, whereas vertical subsidence of minibasins dominates in areas of isolated or discontinuous canopies with common primary basins. The ultimate controls on the size and lateral continuity of canopies are the original thickness of the deep salt layer and the extrusion history of the allochthonous salt.
At the deep level, proximal extension occurs mostly onshore, and distal contraction is accommodated in the deepwater foldbelts (including significant subsalt portions) and in a frontal, Mesozoic nappe. In between, a broad zone of translation has some areas of vertical diapiric feeders and associated turtle structures, but is mostly dominated by inclined feeders and monoclinal minibasins. These may have been triggered by extension or contraction, but their geometries are mostly a result of salt withdrawal and passive diapirism. During basinward translation of the margin, however, these structures may get minor reactivation in extension, contraction, or strike-slip, and there are local occurrences of more concentrated contractional folds or late extensional structures.