ABSTRACT

As part of an ongoing assessment of the occurrence and economic potential of sand resources in the Alabama Exclusive Economic Zone, a geological investigation was conducted in a 50-square-mile area of the Gulf of Mexico continental shelf south of Dauphin Island to prospect for sand deposits that could be used to nourish eroding beaches. Subsurface geologic data were provided by analysis of 28 vibracores and four hydrocarbon industry platform foundation borings. Sea-bottom grab samples collected at each vibracore location were used to describe sea-floor sediment texture. Evaluation of the geologic framework of the prospect area indicates that sediments there consist of Holocene ebb-tidal delta, shelf sand sheet, and shelf sand ridge deposits overlying an erosional unconformity of late Pleistocene-early Holocene age.

A shelf sand ridge containing up to 11 feet of graded shelly sand can provide a suitable quantity and quality of sand for beach nourishment projects. The vibracores and borings were used to model sediment texture, lithofacies patterns, aerial extent and volume of sand, three-dimensional distribution of sediment type, and compatibility for beach nourishment. These data indicate that the portion of the ridge with the highest potential for recoverable sand resources is confined to federal waters some 5 to 7 miles off the southeast coast of Dauphin Island in water depths of 40 to 55 feet. The upper surface of the prospective portion of the ridge is exposed on about 5 square miles of sea floor. The ridge shows a marked lithologic contrast with the enclosing muddy sediments, thickens toward the southwest, and has a main axis trending northeast-southwest, nearly perpendicular to shelf bathymetry.