Reconstructing the paleogeography and basement structure of the Eastern Gulf of Mexico before and during deposition of the Upper Jurassic Norphlet, Smackover, and Haynesville Formations is important because these formations have hydrocarbon potential and determining the distribution may help us predict the location of these hydrocarbons. Strictly regulated lease sales and drilling moratoria have minimized exploration, leaving the Triassic and Jurassic kinematic evolution and distribution of the Eastern Gulf of Mexico Upper Jurassic sedimentary rocks poorly understood. Previous studies suggest that basement topographic highs are horsts and lows are grabens formed during NW-SE directed Triassic extension. This research uses 2-D seismic reflection data to analyze the southern boundary of a basement high, the Middle Ground Arch/Southern Platform, to determine if there is a fault present. The seismic data show an ENE-WSW (055, 45°NW) trending normal fault; however, the downthrown block is on the NW side.Offset stratigraphic units show that the fault was active until Middle Jurassic time. If the Middle Ground Arch/Southern Platform or Tampa Embayment was structurally controlled by a horst and graben system, the fault should be down to the SE to form the Tampa Embayment low and up to the NW to form the Middle Ground Arch/Southern Platform. This normal fault with throw down to the NW and up to the SE suggests that the formation of the Middle Ground Arch/Southern Platform and the Tampa Embayment is not structurally controlled by Triassic extension as a horst and graben system.