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The sedimentary facies and seafloor topography of the Mississippi-Alabama continental shelf are a product of late Pleis-tocene-Holocene regression and transgression. This region lies between the fine-grained facies associated with Holocene Mississippi River delta deposition and the carbonate facies on the western Florida shelf. Sediments in the shallow subsurface of the inner shelf were deposited by fluvial and coastal systems that developed on the shelf during Pleistocene sea-level fluctuations. Shoreface retreat associated with Holocene transgression allowed marine and coastal processes to modify these deposits, resulting in the present sediment distribution. Recent sedimentation on the inner shelf in this region has been minor and restricted primarily to a nearshore fine-grained facies.

The Southeast Banks area (SEBA), located on the Mississippi-Alabama continental shelf approximately 23 km south of Morgan Peninsula in water depths of 17 to 27 m, was selected for study based on the irregular seafloor topography and unusual bottom sediments present at Southeast Banks fishing ground, a site well known to local fisherman. Three sedimentary facies were identified in the Southeast Banks area: (1) a sand facies, (2) a shell gravel and sand facies, and (3) a mud, shell gravel and sand facies. Hardbottoms, which consist of shell debris as well as rubble and large fragments of carbonate-cemented sandstone and coquina, occur in association with the sedimentary facies at Southeast Banks.

The sea floor in the SEBA is characterized by a series of northwest-trending ridges and troughs. Lengths and widths of these ridges are highly variable. Additionally, variations in sediment textures are coincident with changes in seafloor topography. Ridge morphology, orientation, and sediment textures associated with the ridges indicate that these features developed as shoreface-connected ridges through marine reworking of older sediments and topographic features. In the present environment, ridge features and bottom sediments are disturbed primarily by periodic high-energy storm events.

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