1.5 meters, particularly beneath shoals, but their relative abundance 

 decreases (Table 5) . However, there is a significant increase in abun- 

 dance of poorly sorted sands and muds (types III and IV) . These sediment 

 types account for over one-third of the samples, compared to only 14 per- 

 cent on the surface. Clean, fine sands show only a slight increase from 

 about 11 "to 14 percent. Atypical sediments account for only about 5 

 percent. The distribution of muds and very fine silty sands at -1.5 

 meters MSL is almost entirely restricted to flats or swales between 

 shoals, as for surface sediments. The clean, fine sands associated with 

 the shoreface-shoal complex in the southern part of the study area also 

 persist at shallow depths. 



Table 5. Percent abundance of major sediment 

 types on the sea floor and below. 



Depth (ft) 



Samp 



les 



(No.) 



I 



Type 

 II 



(pet] 

 III 



1 

 IV 



V 



Sea floor 





68 





74 



12 



7 



7 







-5 





63 





46 



14 



17 



18 



5 



-10 





54 





39 



11 



15 



31 



4 



-15 





33 





24 



18 



12 



46 







There are no abrupt changes in sediment distribution 3 meters below 

 the sea floor (Fig. 26). The trend of increasing muds and silty sands 

 concommitant with a decrease in abundance of clean, medium sands contin- 

 ues at this depth. Types III and IV account for about 45 percent of the 

 sediment, compared to 39 percent of clean, fine- and medium-size sand; 

 the location of type I is restricted primarily to the shoal areas. 



Only 33 of the cores penetrated deep enough into the shelf to plot 

 distribution of lithologies at 4.6 meters (15 feet) below the sea floor, 

 as shown in Figure 27. At this depth, 46 percent of the samples are gray 

 mud (type IV) and 12 percent are silty sand (type III). Clean, medium 

 to coarse sand has decreased in abundance to 24 percent, and clean, fine 

 sand is still confined to the central Assateague shoreface region. The 

 relative abundance of different sediment types at -3 meters and particu- 

 larly -4.6 meters is subject to some error due to the assumption that 

 cores penetrating to those depths sampled a representative population. 

 There is no precise way to test this assumption, but based on an examina- 

 tion of core locations with respect to topography, it appears that deep- 

 penetrating cores are representative and certain features or areas are 

 not selectively excluded. 



c. Radiometric Age Dates . Two cores (13 and 51) contained organic 

 material in sufficient quantity to obtain radiocarbon age dates. Both 

 cores are located close to shore in relatively shallow water, but have 

 significantly different C 11+ ages. Core 13 was collected in 9.1 meters 



62 



