of interbedded dark-gray silty clays, brown coarse silts, and light-gray 

 fine sands, all of which vary in thickness from 3 to 15 centimeters [0.1 

 to 0.5 foot). Beneath this unit lies a brown, very coarse to coarse, 

 quartz sand containing highly weathered-altered shell fragments; the 

 unit terminated abruptly at 4.2 meters (13.7 feet). The underlying and 

 lowest unit in the core is a gray, fine quartz sand with molluskan shell 

 fragments evenly distributed throughout. In simplest form, the entire 

 sequence represented by this core demonstrates two high-energy deposi- 

 tional environments separated by a low-energy environment. It differs 

 from core 33, which showed the same sequence, by the presence of marine 

 organisms in all sand units. The color (brown) and altered state of 

 carbonates in the coarse sand unit at 3.9 to 4.2 meters suggest the sand 

 was previously exposed under subaerial conditions and thus predates the 

 last transgression. Overlying fine-grained sediments are probably mar- 

 ginal marine (estuarine, lagoonal) and the upper sands are modern shelf 

 and possibly relict barrier island deposits. 



e. Changes in Sediment Character . The large number of vibratory 

 cores collected on and near the shoals provides a strong basis for inter- 

 preting the internal and underlying sediments. Cores obtained along shoal 

 crests recovered only sand in most instances, indicating thicknesses in 

 excess of 6.1 meters (see Fig. 25); those obtained from the edges often 

 penetrated the first subsurface horizon (acoustic horizon A 2 ) that 

 appears beneath each shoal. The shoal sands almost exclusively type I 

 gray-brown, well-sorted, medium quartz sands. Underlying sediments are 

 variable, but the most common are type IV gray muds and type III poorly 

 sorted fine sands. This association, particularly that of the medium, 

 clean sands overlying muds, produces the strong acoustic contrast gener- 

 ating an identifiable reflector. 



Figure 31 shows lithostratigraphic cross sections along the long 

 axes of two shoals, Ocean City shoal and Isle of Wight shoal. The cross 

 sections were constructed solely in the basis of lithology and are dis- 

 cussed in more detail by Field (1976) . Ocean City shoal is a shoreface 

 shoal-complex extending northeast from the vicinity of Ocean City Inlet; 

 the shoal comprises several individual arms or ridges. The shoal appears 

 to be perched upon a layer of sandy, clayey silt, overlying silty sand 

 that rises toward the southwest. The age of subsurface deposits on the 

 onshore profile indicates that the base of the shoal is not simply a 

 remnant Holocene lagoonal facies after it had been transgressed and 

 reexposed, but rather a former (mid-Wisconsin) lagoonal or estuarine 

 deposit that has been covered by modern barrier-shoreface facies. A 

 marked hiatus exists between the surface sand body and these underlying 

 relict deposits. 



A cross section of an isolated or offshore shoal is shown in Figure 

 31, profile B-B'. Five cores were collected along the long axis of Isle 

 of Wight shoal. Cores 4, 5, and 15 contained gray-grown, fine- to medium- 

 sized quartz sand throughout their entire length. Cores 19 and 20, how- 

 ever, penetrated into fine-grained deposits underlying the shoal. These 

 two cores provide some significant information about the formation of this 



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