b. General. Based on partly subjective selection criteria, six reflection units and five 

 primary reflectors under tlie inner shelf between tlie Georgia border and Cape Canaveral 

 have been defined. The typical disposition of reflection units and reflectors in various parts 

 of the study area is shown by a series of schematic shore-normal profiles (Figs. 11,12, and 

 13) and by a scliematic sliore-parallel profile (Fig. 14). Location of the profiles is shown in 

 Figure 11; selected reduced seismic reflection profiles are shown in Appendix A. 



All but one of the identified reflection units and all five primary reflectors are present in 

 the Jacksonville-Fernandina area as depicted on profiles A and B, Figure 12. Shore-normal 

 profiles to tlie south and the shore-parallel profile (Fig. 14) show progressive southward 

 changes in the section. These clianges are primarily the result of a southward rise of the two 

 lower units, D and E, to a triuicated crest near Daytona Beach. Between Jacksonville and 

 Flagler Beach, units B and C pinch out against the flank of this high and are supplanted by 

 underlying units. Unit D is truncated over the crest of the high and only units A and E 

 appear to be present in that area. 



Dip in primary and secondary reflectors within study limits is almost everywhere 

 eastward. In the two lowermost units, D and E, predominant nortii or south dip occurs in 

 places. Westward dip is very rare and occurs only locally in secondary reflector patterns. 



Broad shallow undulatory flexures, probably of structural origin, are common 

 throughout the area (Fig. 9). Many of the flexures affect the entire vertical section wliile 

 others are confined to one or more of the lower units indicating intermittent structural 

 deformation may have occurred over a long period of time. Pronounced folding is evident in 

 a few places by truncated synchnal features (Fig. 10). 



No convincing evidence of faulting was observed on the records but there are numerous 

 small displacements in reflectors which could be attributed to faulting among other causes. 



Reflection patterns indicate the common presence of filled channels or inlets (Fig. 10) 

 incised into the upper two units, A and B. Neitlier the filled channels or the structural 

 features appear to have topographic expression on the shelf floor. 



c. Reflection Units. 



(1) Unit A. Unit A includes all sediments lying above the red reflector (Figs. 15, 16, 

 and 17). The unit, usually less than 20 feet thick, is missing in places. Internal reflectors in 

 unit A generally dip gently eastward and are often discontinuous and variable in intensity. 

 Locally there are complex bedding patterns reflected from channel or inlet fill. 



(2) Unit B. Unit B is 70 feet thick near the Georgia border and tliins progressively 

 southward to near Flagler Beach where it pinches out. A distinctive feature of unit B is an 

 inshore zone about 5 nautical miles wide with uniform eastward-dipping internal reflectors 

 suggesting a progradational bedding sequence. Seaward of this zone the internal reflectors 

 become nearly horizontal and mutually parallel. 



Tlie upper part of unit B is incised by many cliannel-hke features which generally 

 originate in tlie overlying unit A. The largest of these ciiannels trends soutlieast from the 

 present St. Johns River Entrance and is presumed to be a rehct Pleistocene channel of the 

 St. Johns River. 



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