Paleogene Lowstand Systems Tract Sandstone Deposits of the Eastern Gulf Coastal Plain: Potential Reservoir Facies in the Offshore Northeastern Gulf of Mexico

Characterization of Paleogene stratigraphic sequences in the eastern Gulf Coastal Plain involving outcrop and well log studies resulted in the recognition of six Upper Paleocene (Selandian) and Eocene (Ypresian-Lutetian) third-order unconformity-bounded depositional sequences. These sequences include the Naheola Formation (Midway Group), the Nanafalia, Tuscahoma, and Hatchetigbee formations (Wilcox Group), and the Tallahatta Formation (Claiborne Group). The Paleogene depositional history of the eastern Gulf was dominated by fluvial-deltaic, marginal marine, and marine shelf sedimentation. The deposits of the systems tracts inherent to these Paleogene sequences consist of lowstand fluvial-deltaic, estuarine, tidal-influenced, and coastal barrier cross bedded sandstone of 40-100 ft (12-30 m) in thickness; transgressive nearshore marine shelf glauconitic sandstone and marlstone of 10-40 ft (3-12 m) in thickness; and highstand fluvial-deltaic, tidal-influenced, marginal marine, and marine shelf sandstone, siltstone, claystone, and lignite of 100-250 ft (30-76 m) in thickness. Stratigraphic architecture was formed primarily as a result of changes in base level. With a relative fall in sea level, the shelf was subaerially exposed and incisement through fluvial processes occurred. A subsequent relative rise in sea level and creation of accommodation resulted in filling the shelf incisements and incised valleys. During these times of erosion and deposition, Paleogene sandstone bypassed the shelf and accumulated in deeper-water settings as lowstand fan and wedge facies. These potentially quartz-rich sandstone facies are priority petroleum reservoir targets in the offshore northeastern Gulf of Mexico.