Ch. 2— Resource Assessments and Expectations * 47 



Figure 2-4.— Plan and Section Views of Shoals 

 Off Ocean City, Maryland 



Several drowned barrier beach shoals off the Delmarva 

 Peninsula are potential sources of sand and possibly heavy 

 mineral placers. 



SOURCE: S. Jeffress Williams, U.S. Geological Survey. 



potential resource of medium to coarse sand. These 

 ridges range in height from 40 to 65 feet and in 

 width from 1 to 2 miles, with lengths up to 12 miles. 

 The ridge tops are often at water depths of less than 

 30 feet, and a single ridge could contain on the or- 

 der of 650 million cubic yards of sand. 



South of Long Island through the mid-Atlantic 

 region, the shelf area was not directly affected by 

 glacial scouring and deposition, but the indirect ef- 

 fects are extensive. During the low stands of sea 

 level, the shelf became an extension of the coastal 

 plain through which the major rivers cut valleys 

 and transported sediment. The alternating periods 

 of glacial advance and marine transgression re- 

 worked the sediments on the shelf, yet a number 

 of inherited features remain, including filled chan- 

 nels, relict beach ridges, and inner shelf shoals. Fea- 

 tures such as these are particularly common off New 

 Jersey and the Delmarva Peninsula and are poten- 



tial sources of sand and possibly gravel (figure 2- 

 4). Seismic profiles and cores indicate that the 

 majority of these shoals consist of medium to coarse 

 sand similar to onshore beaches. Geologic evidence 

 suggests that most of the shoals probably formed 

 in the nearshore zone by coastal hydraulic proc- 

 esses reworking existing sand bodies, such as relict 

 deltas and ebb-tide shoals.® Some of the shoals may 

 also represent old barrier islands and spits that were 

 drowned and left offshore by the current marine 

 transgression. Typical shoals in this region are on 

 the order of 30 to 40 feet high, are hundreds offset 

 wide, and extend for tens of miles. South of Long 

 Island, gravel is much less common and found only 

 where ancestral river channels and deltas are ex- 

 posed on the surface and reworked by moving 

 processes. 



The southern Atlantic shelf from North Caro- 

 lina to the tip of Florida was even further removed 

 from the effects of glaciation and also from large 

 volumes of fluvial sediment. The shelf is more thinly 

 covered with surficial sand, and outcrops of bed- 

 rock are common. Furthermore, unlike the mid- 

 dle Atlantic region, the southern shelf is not cut by 

 river channels and submarine canyons. Sand re- 

 sources in this region are described as discontinuous 

 sheets or sandy shoals with the carbonate content 

 (consisting of shell and coral fragments, limestone 

 grains, and oolites) increasing to the south. 



Although there is more information on the At- 

 lantic EEZ than on other portions of the U.S. FEZ, 

 estimates of sand and gravel resources on the At- 

 lantic continental shelf are limited by a paucity of 

 data. Resource estimates have been made using 

 assumptions of uniform distribution and average 

 thickness of sediment but these are rough approx- 

 imations at best since the assumptions are known 

 to be overly simplistic. A number of specific areas 

 have been cored and studied in sufficient detail by 

 the U.S. Army Corps of Engineers to make local 

 resource estimates.'' Resource assessments of spe- 

 cific sand deposits on the Atlantic shelf in water 



•^S.J. Williams, "Sand and Gravel Deposits Within the U.S. Ex- 

 clusive Economic Zone: Resource Assessment and Uses," Proceed- 

 ings of the 18th Annual Offshore Technology Conference, Houston, 

 TX, May 5-8, 1986, pp. 377-386. 



'D.B. Duane and W.L. Stubblefield, "Sand and Gravel Resources, 

 U.S. Continental Shelf," Geology of North America: Atlantic Re- 

 gion, U.S. , Ch. XI-C, Geological Society of America, Decade of North 

 American Geology (in press). 



