The few ICONS samples available from the shoal area also suggest 

 existing processes are actively reworking the surficial layers of shoals 

 and that local erosion and redeposition probably occur. For example, 

 the sediment in core 62, obtained 22.2 kilometers (12 nautical miles) 

 offshore on the shallow crest of a shoal in the Cape Fear complex, 

 contains the highly polished mollusk fragments and clean, well-sorted 

 sand typical of high-energy beach sediments, which suggests vigorous 

 periodic reworking of the shoal crest sediments. 



Little is known of the substructure of the shoreface in the study 

 area. It may be either a relict or essentially a modem feature. In 

 its simplest form, the shoreface slope comprises the ramplike seaward 

 face of a barrier spit or island which is composed entirely of sand, and 

 which formed initially during the late phases of the transgression. In 

 many places, however, barriers seem to have a more complex structure. 

 For example, barrier sands may comprise a relatively thin surficial 

 veneer covering a slope carved into lagoonal, washover, and possibly 

 relict sediments which are progressively exposed on the shoreface as a 

 result of erosional retreat of the coastline. In addition, some barriers 

 are underlain by preexisting topographic features which form a core to 

 the modem beach and shoreface superstructure (Tanner, 1960; Pierce and 

 Colquhoun, 1970). In such cases, the shoreface is essentially an ancient 

 feature although the veneer of modern sand may modify the slope charac- 

 teristics toward closer equilibrium with the prevailing wave and current 

 regimens . 



There is evidence that an ancient relict substructure may exist 

 beneath the shoreface near New River Inlet where outcrops of Oligocene 

 carbonate rock occurring inshore (Lawrence, 1975; Crowson and Riggs, 

 1976) are apparently contiguous with carbonate rocks of the same age 

 found at about -12.2 meters (-40 feet) MLW in ICONS cores 98, 99, and 

 100 near the toe of the shoreface. This evidence indicates the rock 

 surface probably underlies the entire shoreface slope. 



Secondary topographic features on the relatively level inner shelf 

 surface are sparse and of low relief. Some features may be erosional 

 remnants of Pleistocene sediment accretions which survived late Wisconsin 

 subaerial exposure of the shelf and subsequent transgression. Other highs 

 have developed by differential erosion around resistant rock outcrops. 

 A notable example of this topography occurs off New River Inlet where 

 Crowson and Riggs (1976) report scarps up to 5 meters (16 feet) high sur- 

 mounted in places by worm reefs. These features are formed by outcrop- 

 ping Tertiary carbonate rocks. Another example was reported by Mixon 

 and Pilkey (1976) who found knobs and ledges of Pleistocene coquina 

 on the shelf floor south of Cape Lookout shoals. Elsewhere in the study 

 area rocky ledges and knobs occur in the areas underlain by the Pliocene 

 calcarenites and where scattered patches of shell coquina of probable 

 Pleistocene age crop out on the shelf floor. Most of the inner shelf 

 secondary topography, however, was probably molded by marine processes 

 operating in the shallow waters near the leading edge of the transgress- 

 ing Holocene sea, or by present shelf and nearshore processes subsequent 



65 



