b. Yellow Horizon. The yellow horizon lies at a subsea depth of about 60 feet MLW near 

 the shore and dips seaward at a varying slope to about —125 feet MLW at the eastern edge 

 of the survey area. The contour map of the yellow horizon (Fig. 8) shows most of the 

 surface is of low relief and low inclination. Seaward of the 100-foot deptli contour the 

 surface dips more steeply and regularly, with an average slope of 1 on 500. 



Slope change and small undulations and minor irregularities landward of the 100-foot 

 depth contour further distinguish the character of the yellow horizon from the deeper part. 

 These irregularities in the smooth surface indicate probable effects of subaerial exposure 

 during periods of lower sea level. There is no apparent relationship between the yellow 

 horizon configuration and the present sea-floor configuration. 



An analogous surface, also termed the yellow horizon, has been mapped by Meisburger 

 and Duane (1971), from Fort Pierce to Cape Canaveral. The surface has a near north-south 

 strike and lies from —60 to —140 feet MLW in the Fort Pierce Inner Continental Shelf 

 region. Although the surface is more regular at Fort Pierce than at Cape Canaveral it also 

 exhibits a marked increase in slope at about —100 feet MLW. Between Cape Canaveral and 

 Fort Pierce the reconnaissance geophysical survey lines foUow the north-northwest 

 orientation of the coastline; and thus the survey is up dip of both the Fort Pierce and Cape 

 Canaveral areas and the yellow horizon rises accordingly. The surfaces are judged correlative 

 in both study areas and of the same stratigraphic horizon. 



No subbottom samples known definitely to be of the yeUow horizon have been obtained 

 in either survey. A recrystaUized shell Mercenaria campechiensis filled with a lime matrix 

 was found in the bottom of core 179 near Fort Pierce; penetration stopped just above the 

 acoustic reflector. The shell, if derived from the yellow horizon, further suggests that the 

 yellow surface underwent extensive subaerial exposure. 



c. Blue Horizon. The blue horizon Ues 10 to 30 feet above the yellow horizon and is 

 similar to the yellow in slope, dip direction and general continuity. Stratigraphic position 

 and structural character of the blue reflector are shown in Figure 6. Near shore the blue Ues 

 at about —40 feet MLW and drops off to —100 feet MLW at the outer edge of the study area. 

 Most of the grid surface has an undulatory configuration marked by minor irregularities, 

 similar to the yellow horizon. The blue surface also changes in slope and increases in 

 regularity on the seaward side of the grid, where near —70 feet MLW, the slope increases to 

 1 on 700. (See Figure 9.) 



Steeply inclined internal bedding is occasionally present below the blue horizon and 

 above the yellow horizon. The bedding dips seaward and is more commonly associated with 

 the outer part of the survey grid. The steep dip angle and monocUnal nature of these units 

 surest they represent progradational units. 



Configuration of the blue horizon, as shown in Figure 9, slightly resembles the modern 

 shelf surface. The pattern of the 60-foot depth contour may indicate the outline of a relict 

 analog to the present BuU, Chester and Southeast Shoals. Comparison of Figures 4 and 9 

 show a possible similarity in size, shape, and orientation between features of the blue 

 horizon and those on the present sea floor. 



Detailed examination of the surfaces, however, show that similarities are only superficial; 

 the blue is flat-lying or nearly flat-lying beneath the shoals. (See Figure 6.) Thickness of 

 sediment overlying the blue horizon, indicates that increased sediment thicknesses as shown 



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