46 • Marine Minerals: Exploring Our New Ocean Frontier 



Figure 2-3.— Sand and Gravel Deposits Along the Atlantic, Gulf, and Pacific Coasts 



Gorda 

 Ridge 



Central 

 California l ^^ 

 Seamounts 



Southern 

 California 

 Borderland 



Guaymas 

 Basin 



East Pacific Rise 



Explanation 



Sand and gravel 



Known Likely 



occurrence occurrence 



Blake Plateau 



© 



1000 Miles > <?-?'~"'"«-»i C?(T) 



Significant sand and gravel deposits lie on the continental shelf near urban coastal areas. As local onshore supplies of con- 

 struction aggregate become exhausted, offshore deposits become more attractive. Sand is also needed for beach replenish- 

 ment and erosion control. 



SOURCES: Office of Tecfinology Assessment, 1987; S. Jeffress Williams, "Sand and Gravel— An Enormous Offsfiore Resource Wilfiin ttie U.S. Exclusive Economic 

 Zone," manuscript prepared for U.S. Geological Survey Bulletin on commodity geology researcfi, edited by Jofin DeYoung, Jr. 



mined the general characteristics and distribution 

 of the sand and gravel resources on the shelf. 



The northern part of the Atlantic shelf as far 

 south as Long Island was covered by glaciers dur- 

 ing the Pleistocene Ice Age. At least four major epi- 

 sodes of glaciation occurred. Glacial deposition and 

 erosion have directly affected the location of sand 

 and gravel deposits in this region. Glacial till and 

 glaciofluvial outwash sand and gravel deposits cover 

 much of the shelf ranging in thickness from over 

 300 feet to places where bedrock is exposed at the 

 surface. The subsequent raising of sea level has al- 

 lowed marine processes to rework and redistribute 



sediment on the shelf. Major concentrations of 

 gravel in this region are located on hummocks and 

 ridges in the vicinity of Jeffrey's Bank in the Gulf 

 of Maine and off Massachusetts on Stellwagen Bank 

 and in western Massachusetts Bay. 



Concentrations of sand are found off Portland, 

 Maine, in the northwestern Gulf of Maine and in 

 Cape Cod Bay northward along the coast through 

 western Massachusetts Bay to Cape Ann (figure 2- 

 3). Large accumulations of sand also occur along 

 the south coast of Long Isljmd and in scattered areas 

 of Long Island Sound. Large sand ridges on Georges 

 Bank and Nantucket Shoals are also an impressive 



