Section II. GEOMORPHOLOGY AND SHALLOW SUBBOTTOM STRUCTURE 

 OF THE CONTINENTAL SHELF 



1. Continental Shelf Geomorphology 



a. General - The Shelf between Palm Beach and Cape Kennedy covers 

 about 2,500 square miles. From about Gomez {;27°05'N) northward, the shelf 

 plain is divided into inner and outer zones by a subtle slope break gener- 

 ally falling between the 70- and 80-foot depth contour. The first major 

 break in slope on the Continental Shelf occurs at the top of the Florida- 

 Hatteras Slope (Uchupi , 1968). The break of the Florida-Hatteras Slope 

 in the study area trends almost due north-south, while the alignment of 

 the shoreline trends about 20 degrees west of north. This divergence 

 between shoreline and slope break accounts for the great increase of 

 shelf width northward from Palm Beach to Cocoa Beach. 



In general, the shelf off the study area is typical of a submerged 

 coastal plain with gentle seaward inclination and subdued topographic 

 relief. Based on slope characteristics, differences in sediments, and 

 minor relief features, the shelf can be divided into three linear zones; 

 a profile is schematically illustrated in Figure 4. A narrow shoreface 

 zone extends from the low water line to about ,-40 feet MLW. Next is an 

 inner- shelf plain lying between -40 and -75 feet MLW which is succeeded 

 seaward by a more steeply sloping irregular outer shelf that is transi- 

 tional from the "flat" inner shelf to the top of the Florida-Hatteras 

 Slope lying at -80 to -230 feet MLW. Linear features on the inner shelf 

 often parallel the shoreline alignment while outer shelf features tend 

 to follow the shelf break. 



b. Shoreface - Between North Palm Beach (26°48'N) and Cape Kennedy 

 (28°27'N), the shoreface zone is a relatively narrow terrace-like feature 

 extending from mean low water to depths of -30 to -40 feet (Figure 4). 

 Most of this 1,000- to 1,500-yard wide zone dips seaward on a slope of 

 about 1 on 80. Many shoals lie in the segment between Hobe Sound and 

 Vero Beach; some extend into the shoreface area and are possibly an 

 integral part of the shoreface. (In the absence of more detailed data 

 concerning this zone and for reasons of clarity, the shoreface as out- 

 lined on Figure 5 excludes these shoal projections.) 



Coquina outcrops occur alojigshore from place to place throughout 

 the study area. Moe (1963) describes a "reef" in this area lying about 

 -35 feet MLW but covered in many places by overlying sediment. Borings 

 in the Intracoastal Waterway have also revealed consolidated coquina 

 layers - in some places at depths of less than -20 feet MLW. This sug- 

 gests that the core of the shoreface maybe partly composed of consolidated 

 or semi-consolidated coquina rock of the Anastasia Formation. The few 

 ICONS cores obtained in the zone indicate that consolidated rock does not 

 occur within 5 to 10 feet of the water-sediment interface (approximately 

 -30 feet MLW) . 



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