--> A Basin-Scale Perspective on the Oxfordian Norphlet Sandstone, Eastern USA

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A Basin-Scale Perspective on the Oxfordian Norphlet Sandstone, Eastern USA

Abstract

Recent hydrocarbon discoveries have extended the play fairway for the Jurassic Norphlet Sandstone from its traditional onshore deep gas domain into the present-day deep-water of the eastern Gulf of Mexico. This has necessitated a complete reevaluation of the Oxfordian paleogeography of eastern North America and the factors controlling eolian erg development and cessation across the basin. Reconstruction of the Norphlet erg system was challenging from several perspectives. First, the Gulf Basin configuration needed to be restored to original position prior to sea floor spreading and the 30-degree counterclockwise rotation of Yucatan that occurred after Norphlet and Smackover deposition. Second, post-Oxfordian rafting of the Norphlet was corrected for by restoring structural gaps mapped from modern 2D and 3D seismic data. Rafting estimates range from 56 to 2 km with a mean displacement of 28 km. The resulting paleogeography depicts a large eolian erg (58,000 square km) concentrated on the eastern side of the basin in the low paleolatitudes where many modern erg systems are formed. Convergence of northerly and northeastly winds transporting sand from exposed Appalachian and Suwannee terranes allowed concentration of potential reservoir in several areas including Mobile Bay, Destin Dome, and the Appomattox corridor near present-day Desoto Canyon. Eolian dune deposits have been reported in other areas, including in Mexico's Ek-Balam field area and interior Mexico but these are small coastal systems in contrast to the major sand sea (erg) in the Eastern Gulf. Recent drilling results, both success and failure, can be viewed from this new basin-scale perspective. Deflection of dominant winds around the Middle Ground Arch may have led to a sand deficit in the downwind migrating edge of the erg. Incorrect estimates of rafting direction and magnitude may contribute to well placement outside the favored erg center paleoenvironment.