Abstract: Origin and Early Development of the Gulf of Mexico Basin Based on 15-Second Record Seismic in the Louisiana Shelf and Upper Slope

David J. Hall

A 4×4 mile grid of new 15-second record seismic data covering the entire Louisiana shelf and upper slope reveals new insights into the deep structure of the Gulf of Mexico Basin. Noteworthy is the absence of evidence for major horst and graben basement faulting predicted in some models for the early Gulf under the shelf. Instead, the basement appears generally smooth, with a reasonably conformable early section 1 to 1.5 seconds thick immediately overlying it. This suggests either that the basement was formed as lower plate continental crust (in a simple shear detachment fault scenario, below the brittle-ductile crustal transition) or as oceanic crust similar to that observed under autochthonous salt in the Perdido fold belt. If the latter is correct, the edge of ocea ic crust needed to reconstruct the sea-floor spreading history may nearly coincide with the current northern limit of the sub-salt hydrocarbon play, possibly because the play location depends on 3-4 km thick salt originally deposited in the area under the southern shelf. The southern limit of thick LouAnn salt is related to depositional factors (evaporation, oceanic circulation, etc.) rather than to underlying crustal type. An unresolved question is the nature of the section overlying the smooth basement event. Both deepwater Lower Cretaceous (chalks, marls ?) and Eagle Mills deepwater equivalents (shales) are plausible interpretations.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas