Sand and Gravel Resources on the Atlantic Continental Shelf: A New Look

Abstract

ABSTRACT Sand and gravel maps of the U.S. Atlantic Continental Shelf were recently compiled at a scale of 1:1,000,000 by the Minerals Management Service. The maps cover the North, Mid-, and South Atlantic, and South Florida areas. They show deposits of sand, gravel, silt, and clay as well as differences in mineral content, from carbonate-rich sediments in the South Florida area to quartz-rich sediments north of Cape Hatteras. Sand and gravel volumes were calculated for each of the map areas and include identified and undiscovered resource categories. The North Atlantic map area contains the greatest thicknesses of sand and gravel-most is concentrated on Georges Bank and Nantucket Shoals. Most of the deposits are of glacial origin and have an average thickness of 15 m. The North Atlantic contains about 1.6×1012m3 of sand and gravel. The area shown on the Mid-Atlantic map lies south of the maximum glacial advance and received large volumes of sand and gravel from meltwater streams. Sand covers most of the Mid-Atlantic Shelf with an average thickness of 6 m and an estimated volume of 4. 0×1011m3. Sand in the South Atlantic map area is richer in carbonate in the southward direction. The South Atlantic is estimated to have 3. 7×1011m3 of sand with an average thickness of 5 m. Sand in the South Florida offshore area is limited to the wider shelf areas from Cape Canaveral to Miami and around the Florida Keys. The sand is predominantly carbonate and averages 4 m in thickness. A volume of 6.3 × 10 10m3 of sand is estimated for this area. Total sand and gravel resources for the entire Atlantic Continnntal Shelf are estimated at 2.4×1012m3. The need for sand and gravel is expected to increase significantly in the next century as the United States rebuilds its infrastructure and onshore deposits are depleted. Offshore sand and gravel may have to be used to meet these needs. INTRODUCTION A series of sand and gravel maps were compiled from old and new data at a scale of 1: 1,000,000 for the U. S. Atlantic Continental Shelf 1. Unlike other sand and gravel maps, they focus on standardizing data from many sources including compilation at one scale and use of standard grain sizes and mineral content. The maps also emphasize the potential of the specific resource or deposit for commercial uses. Sand and gravel volumes were calculated from the maps and core hole data to estimate the quantities of potential aggregate available for specific geographic areas--for instance, near major metropolitan centers. The areas covered by the maps are shown in Figure 1. The Atlantic Continental Shelf is covered by a layer of unconsolidated rock and mineral particles of varying thickness ranging in size from silt to boulders. This layer has been subdivided into geologic units based on grain size and mineral content. Grain size classes are based on the Wentworth scale.