The subsurface component of the Wilcox Group (Paleocene-Eocene) within Louisiana exhibits two well-defined trends of oil and gas production. One trend is located in the 'shallow' subsurface (900 to 1800 m: 2953 to 5905 ft) which is in the area that has been the subject of the majority of previous Wilcox studies. The second production trend is located downdip from the shallow trend and is coincident with the approximate location of early Cretaceous and early Tertiary shelf-margins. The section of the Wilcox which corresponds with the location of this downdip trend is an example of an early Tertiary shelf-margin.

Up to seven stratigraphic sequences can be recognized in the Wilcox shelf-margin trend. These sequences are bounded by regionally extensive shale horizons. The vertical succession of sequences reflects an apparent balance between basin subsidence and deposition throughout the period of Wilcox deposition. Basinward migration of the shelf-margin during Wilcox deposition therefore was relatively minor.

The Wilcox shelf-margin exhibits three regions of structural stability. Two of the regions are located in western and eastern central Louisiana and exhibit relatively stable shelf-margins as manifested by the minimal occurrence of syndepositional-faulting (growth-faulting). Between these two stable regions, the shelf-margin is structurally unstable due to the preponderance of large-scale growth-faults. The stable shelf-margin regions occur where Wilcox sediments did not prograde significantly beyond the previous maximum advance (Tuscaloosa shelf-margin).

A thick ubiquitous shale interval (the Big Shale) which was believed by previous workers to represent the occurrence of a major marine transgression midway through Wilcox deposition is not readily apparent on regional well-log cross-sections. However, localized thickening of this interval is apparent within the Wilcox shelf-margin. The discordant relationship with underlying strata and a channelized form suggests that a period of extensive downcutting occurred during the middle Wilcox. The channel is almost 24 km (15 mi) wide and up to 300 m (984 ft) thick and is interpreted to have formed close to the shelf-margin by fluvial downcutting during a sea-level low-stand. New, deep (4,600-6,000 m : 15,000 - 20,000 ft) hydrocarbon exploration targets potentially exist in the low-stand system tracts associated with the formation of this channel.

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