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Study of the Spatial Variations in Eolian Stratigraphic Architecture in the Norphlet Formation, Southwestern Alabama

Abstract

The Norphlet Formation is an Upper Jurassic unit (Oxfordian) present in the subsurface of the southeastern United States. The formation extends across the states of Louisiana, Mississippi, Alabama, and western Florida, and into the waters of the Gulf of Mexico (Honda and McBride, 1981; Mitchell-Tapping, 1982; Mancini et al., 1985). The Norphlet overlies Louann salt and is typically overlain by the Smackover Formation.

This succession has been interpreted as deposited under arid conditions by a fluvial-eolian depositional system (Mancini et al., 1985; Marzano et al., 1988). The Norphlet comprises oil and gas reservoirs in several locations in onshore and offshore Alabama, Mississippi and Florida. In addition, recent discoveries of offshore Norphlet oil plays (Rydberg, Appomattox, and Vicksburg prospects by Shell and Nexen) have awoken the interest of obtaining a better understanding of the architectural elements' spatial distribution and the main depositional processes that controlled the evolution of this ancient dune field, as well as its extent into offshore regions.

Based on the premise that the distribution of eolian geomorphological dune elements exhibit a fairly predictable arrangement from an upwind source area (Ewing and Kocurek, 2010), the architectural components of eolian stratigraphy should also be relatively predictable in the subsurface. In modern dune fields, dunes grow in size and crestline spacing and decrease in the number of dune-dune interactions (a prominent source of internal bounding surfaces) away from a source area. Is this pattern apparent in the eolian rock record? Recognizing the spatial configuration of eolian stratification types provides a means to identity source areas, characterize reservoir geometries and heterogeneities and reconstruct ancient paleoenvironments.

The goal of the project is to infer the stratigraphic configuration of a limited area of the Norphlet fluvio-eolian system, based on the preserved eolian and fluvial facies and their vertical and lateral variations from three Norphlet cores at increasing distance from inferred upland source areas.