VISUALIZATION AND 3D CHARACTERIZATION OF THE FORMATION HISTORY OF A MISSISSIPPI RIVER-SCALE DEEPWATER CHANNEL-LEVEE SYSTEM ON THE BASIN PLAIN, GULF OF MEXICO

Using modern 3D seismic surveys and state-of-the-art visualization software to visualize the formational history of a 300+ mile long relict channel-levee system that lies nearly two miles below sea level in the Eastern Gulf of Mexico. This system once rivaled the scale of the modern subaerial Mississippi River. The meandering system was first imaged using side-scan sonar in 1987 by the United States Geological Survey’s GLORIA EEZ-Scan 85 Scientific Staff project, and briefly described by Twichell et al. in 1991. The U.S. Bureau of Ocean Energy Management (BOEM) used 3D seismic survey time slices to visualize the channel system that originates out of an ancestral canyon to the northeast of Mississippi Canyon and is confined by the stacked Mississippi fan complex to the southwest, salt domes to the north, and the Florida Escarpment to the east. Due to this constraining architecture, the system developed a nearly perfect linear geometry along the floor of the basin and remains observable on the seabed for approximately 175 miles. An additional 150 miles is fully buried beneath younger Pleistocene turbidite deposits and Holocene slope facies. Regional mapping of this system has established it as part of the “Blue Unit,” a well-known shallow mapping unit in the Mississippi Canyon leasing protraction. Beneath the 30 to 200 ft thick hemipelagic veneer, the relict system’s defining characteristics include: 1) a 100 ft deep by 2000 ft wide meandering channel axis, as measured from levee crest-to-crest, 2) a system width of 25 mi, as measured from levee toe-to-toe, with maximum sediment thickness approaching 1000 ft, 3) steep levee walls prone to point failure with resulting overbank deposits, and 4) long-lived, stable channel slip faces within the meander plain. The architecture, sequence stratigraphy, scale, and temporal aspect of this Gulf of Mexico meandering system are effectively identical to the Late Pleistocene Upper Levee Complex of the Amazon fan. Both the Amazon and The Gulf Channel complexes have mass transport complexes at their base, upon which sit thin, high amplitude acoustic events interpreted to be levee-less channels, which then became the base for a traditional channel-levee package, and finally concluded with a thick veneer of ongoing hemipelagic drape.