Kozan, and Swift (1974) . The reports all show that ridges are not 

 controlled or formed by subsurface strata but rather rest disconformably 

 on an essentially flat base, a convincing argument for a depositional 

 origin. 



It has been argued that these shoals are the remnants of Pleistocene 

 barrier islands that had been stranded by a drop in sea level and then 

 resubmerged during the Holocene transgression (Sanders, 1962; Kraft, 1971) 

 Duane, et al . (1972) and Field (1976) believe the linear ridges are not 

 pre-Holocene in age. They suggest that regardless of where formed origin- 

 ally (subaerial, estuarine, or open marine environment), shoals would 

 retain evidence of having been subaerial ly exposed and then resubmerged. 

 The shallow structure of the ridges would show a core of Pleistocene 

 sediments, and subsurface sediments would consist of modern marine sands 

 overlying iron-stained relict sands. Seismic reflection and vibratory 

 core data presented in this study indicate the shoals are essentially 

 planoconvex in cross section and that the flat-lying reflector beneath 

 the shoals is the contact between modern shoal sands and Holocene lagoonal 

 deposits. A generalized cross section of the northern Delmarva inner 

 shelf depicting these relationships is shown in Figure 34. Constructed 

 from seismic and core data, the diagram illustrates general shallow- 

 stratigraphic relationships as interpreted from many actual cross sections 

 For illustration purposes, uncommon or discontinuous lithologies (units C 

 and D in Fig. 33) are excluded. Of significance in the figure are the 

 surface sands resting disconformably on a relatively flat mud deposit that 

 is interpreted as Holocene in age, thus ruling out a pre-Holocene age for 

 the shoals. Kraft (1971) suggested that because offshore ridges are 

 alined with onshore Pleistocene beach ridges that intersect the present 

 coastline at a small acute angle, they are genetically related. Several 

 areas in this hypothesis that are disputable, as discussed by Field (1976) 

 become clear when shoal characteristics of both shoals and dunes are 

 examined. Equally important is the consideration of the difficulty in 

 finding an example (ancient or modern) of an unconsolidated sand body, 

 regardless of how or where formed, surviving the passage of a transgress- 

 ing surf zone. This last constraint is a strong one and one that has 

 argued for various theories of barrier island origin other than overstep- 

 ping; it is also one to contend with in considering a Holocene barrier 

 island origin of shoals. 



Direct and indirect evidence accumulated in this study strongly 

 suggests that linear shoals have evolved, and are evolving, in the sub- 

 marine environment of the shoreface and Inner Continental Shelf. That 

 they are related in some respect to the adjacent barrier island is clear 

 from their distribution: the northern limit of the linear-shoal field 

 coincides with the merging of the barrier spit to the headland coast; the 

 southern limit is marked by the termination of the long barrier spit at 

 southern Assateague Island. This relationship is probably genetic but it 

 in no way substantiates a barrier origin of shoals. More likely and 

 supportable is the concept of linear shoals forming and being maintained 

 on the seaward side of the retreating barrier island. 



79 



