3D Seismic Geomorphology and Seismic Stratigraphy of Late Quaternary Shelf and Shelf -Margin Depositional Systems, Northern Gulf of Mexico,

Optimal exploitation of deltaic reservoirs needs detailed facies and architectural element analysis as a base for a comprehensive geological model. To date, very few studies have evaluated regional shelf-margin deltaic systems using 3D seismic data and 3D seismic geomorphologic and seismic stratigraphic analysis. High-resolution 3D seismic data, covering an area of 8,000 km2 offshore Louisiana at the modern shelf edge of the central northern Gulf of Mexico, was used to reconstruct the distribution and evolution of the paleo-Mississippi shelf-margin deltaic system during the last full cycle of fall and rise in sea level, which spans the last 125,000 years. Three-dimensional seismic geomorphological analysis was complemented with computed seismic attributes, including coherence, curvature, spectral components, sweetness, and amplitude gradient, with the objective of identifying shelf-margin geological features not typically observed in seismic profiles. The results show that salt tectonism in the Gulf of Mexico controlled the morphology of the shelf and the slope, forcing the paleo-Mississippi deltaic system to split, and concentrate its progradation and deposition in four separate along-strike salt withdrawal minibasins. Each minibasin shows different deltaic constructional patterns. Progradation and aggradation patterns vary from minibasin to minibasin due to the response of the sediment supplied by the paleo-Mississippi delta, variations on sea level, the morphology of the seafloor, the arrival angle when the delta reaches the upper slope minibasin, and the shape of the minibasin. The 3D reconstruction of the system shows lateral variation of the deltaic processes from wave- to fluvial-dominated; wave-dominated deltaic strandplains were identified in the western minibasins and fluvial distributary channels were recognized in the eastern minibasins. This research highlights the importance of lowstand wave-dominated deltaic strandplains as important elements for the transport of sediment from the shelf to the slope in a salt-controlled setting like the Gulf of Mexico. The fluvial dominated shelf-margin delta is also related to direct transfer of sediment from the shelf to the slope.