New Structural Concepts for the Deep Miocene, Southern Louisiana Shelf

Robert O. Brooks, David J. Hall

Until recently, structuring of the bathyal Miocene shales and scattered turbidite sands of the southern Louisiana shelf and slope was thought to duplicate that of the overlying Plio-Pleistocene deltaic sands and shales. These younger syndepositional structures are dominated by large extensional growth faults, salt and shale flowage, and shifting depocenters to accommodate a massive, rapid influx of sediments. Over the past 50 years, it is within these sediments that most of the hydrocarbons have been found.

Recently, however, due to improved 2-D and 3-D seismic resolution, new deep well control and industry exploration in sub-horizontal salt, it has become evident that the Miocene is much more complex than previously believed. In contrast to the overlying section, local extensional features and compressional folding, major unconformities, large untested structural closures, and erratic but at times thick turbidite sands have been observed. The folding and faulting were apparently caused by a combination of rapid loading, reactivated salt movement, and down-slope creep. These factors led to a complex system of folds, isolated high blocks, and both normal and reverse faults distinctively different from the overlying Plio-Pleistocene. The surface (or surfaces) separating the disharmonic str ctural regimes often merges with the base of horizontal salt bodies.

We suggest the surface (or surfaces) separating the disharmonic structural regimes is in large part a salt weld formed as a residual structure after withdrawal of salt from earlier tabular salt bodies.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995