currents rewash the sediment and carry off the finer fraction. In general, 

 sediment tends to become increasingly finer in an offshore direction. 



55. Because of the muddy character of many deltas, clean sand suitable 

 for beach fill is not of widespread occurrence and tends to be concentrated 

 near the shore where waves and currents winnow out fines. These sandy depos- 

 its are usually in the form of barrier islands and spits and associated shore - 

 face and offshore shoal deposits. Subsidence due to compaction of buried 

 sediments is a common occurrence in deltas and results in shoreline transgres- 

 sion, which may drown former shore and nearshore features. For this reason, 

 the shallower subtidal areas of the outer delta plain are the most likely to 

 contain suitable fill material for nearby beaches. 



56. In addition to existing deltas, it is probable that most streams 

 deposited deltaic sediments on the present continental shelf areas at times of 

 lower sea level stands and those of the late Wisconsin and Holocene transgres- 

 sion times may be preserved. Deltaic sediments have not been widely recog- 

 nized in shelf deposits; however, this may be due to the general lack of 

 detailed information on shelf sediments or to extensive reworking during the 

 Holocene transgression and by modern shelf processes. For example, Swift 

 (1973) identified a large mid-shelf shoal off Delaware Bay as a probable 

 ancient delta of the Delaware River built during a stillstand in the trans- 

 gression at -40 m that has a superimposed, cape-associated shoal retreat 

 massif. 



Relict Glacial Features 



57. During Pleistocene glaciations, the ice sheets advanced beyond the 

 present shorelines, leaving erosional and depositional features on the present 

 continental shelves. Subsequently, during interglacial periods, these fea- 

 tures were drowned by the sea level rise associated with deglaciation. Most 

 of the existing glacial features on the shelves probably originated during the 

 last major glaciation (late Wisconsin) and were inundated during the Holocene 

 transgression. Some types of glacial deposits contain material that is poten- 

 tially suitable for beach fill. The geomorphic features associated with gla- 

 cial deposits are helpful in locating suitable material, but because of the 

 great complexity of geomorphic forms associated with glacial deposits, are 

 less reliable indicators than for other types of deposits considered in this 



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