Ronald K. Zimmerman
North central Gulf Coast Middle Mesozoic zones of crustal weakness caused by transform faulting associated with plate separation and rifting, became ideal areas for subsequent tectonic adjustments. Several lines of evidence - manifested in wrench faulting - point toward the existence of such adjustments occurring in the Upper Jurassic, Cretaceous, and Tertiary strata of this area.
Eight lines of evidence suggest that there are at least four zones of faulting in the region which have been affected by lateral (and vertical) movements and associated extension fracturing. Isopach maps, en echelon fault/fold patterns, location of time-specific igneous activity, offset basement features, anomalous saltwater incursions into freshwater aquifers, offset surface geomorphic features, surface lineaments, and regional hydrocarbon migration patterns all suggest dominant lateral motion along the affected zones in the subsurface and/or surface.
Two main results of the region's wrench faulting are evident in (1) the development of vertical pathways or conduits facilitating hydrocarbon migration from deep, thermally mature source rocks to shallower reservoirs located in non-mature source rock zones; and (2) the development of extension fractures that enhance reservoir porosity. Both results have created the potential for increasing hydrocarbon source volumes available for migration and reservoiring.
AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana