local relief. In addition, minor irregularities of a few feet relief are common. While these 

 small irregularities are clearly visible on the seismic reflection profiles, they are too small 

 and discontinuous to be delineated with existing bathymetric data. 



From profile C northward to the Georgia border the shelf floor continually widens and 

 reaches about 59 nautical miles off Fernandina. The surface topography remains similar to 

 that at profile C but, in addition, several broad shallow southeast -trending depressions 

 appear crossing the mid and outer shelf floor (60-, 80-, and 100-foot-depth contours in 

 Fig. 6). The ahnement and configuration of these lows suggest a stream drainage pattern 

 while many of the flat-topped highs are so situated as to suggest they are relict interfluves. 



Near St. Augustine (Fig. 6, profile B) the edge is narrow and convex, taking on the 

 sharply rounded profile of the classic shelf "break" which it maintains to the Georgia 

 border. The shelf floor-edge junction remains between —140 and —160 feet MLW 

 throughout the segment north of profile C; this characteristic depth range persists as far 

 north as Cape Hatteras. The break between the camber and Florida-Hatteras Slope seems to 

 be at about -180 feet but available bathymetric data for this zone are poor. 



The steep narrow shoreface is very consistent from profile C north to near St. Augustine 

 where it is interrupted by a broad shoal area (ebb tidal delta) around St. Augustine Inlet. 

 From St. Augustine to Jacksonville Beach there is again a well developed shoreface slope 

 with the toe at about —45 feet MLW. North of Jacksonville a distinct shoreface does not 

 exist and tlie broad inshore part of the ramp is comparatively shallow with locally complex 

 topography. 

 2. Shallow Subbottom Structure and Bedding. 



a. Background. Seismic reflection records from this ICONS study show reflectors to 

 depths of 500 feet below MLW. As a working assumption, reflections are considered 

 representative of some geologically significant interface. 



Reflectors wliich persist over a large area are called primary reflectors, and presumably 

 dehneate extensive stratigraphic breaks (Figs. 9 and 10). Between primary reflectors there 

 are usually numerous localized reflectors, called secondary reflectors. Most secondary 

 reflectors appear to be associated with internal bedding surfaces, local erosional 

 discontinuities such as stream channels, or relatively small sediment bodies (Figs. 9 and 10). 



The term reflection unit is used to designate layers distinguished by their position 

 between two specific primary reflectors or by persistent internal reflector characteristics and 

 patterns (Figs. 9 and 10). 



Primary reflectors are most often located between two reflection units; however, strong 

 and persistent reflectors may occur internal to a unit. The blue reflector of this study is an 

 example. 



In tliis study reflection units are identified by a serial letter and primary reflectors are 

 identified by a color name. Two of the primary reflectors, red and green, have previously 

 been identified and discussed (Meisburger and Duane, 1969, 1971; Meisburger and Field, 

 1972; Field and Duane, 1974). 



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