g. Seismic Refraction Data. Seismic refraction studies on the East Coast Shelf off 

 Georgia and north Florida (WoUard, Bonini, and Meyer, 1957; Hersey, et al., 1959; Antoine 

 and Henry, 1965: Sheridan, et al., 1966) reveal three velocity layers within the 0- to 

 500-foot niaxiniuni depth range of CERC reflection records. Only a few shelf data points 

 are available from these studies but they are m fair agreement on velocity-depth 

 relationships (Table 2). 



Table 2. Tentative correlation of seismic refraction layers and reflection units. 



Reflection unit 



Refraction layers 





Hersey, etal.( 1959) 



Antoine and Henry (1965) 



Sheridan, etal.< 1966) 



Recent 

 A 



Layer with characteristic velocity near that of seawater 



Miocene 

 B, C, and D 



A 



1 



V2 



Eocene 

 E 



C 



2 



V3 



The uppermost layer in these refraction studies is thin and discontinuous 0- to 90-feet 

 thick, and has a characteristic velocity near that of seawater. Below this layer is a second 

 layer characterized by variable thickness and sound velocities ranging from 5,169 to 6,300 

 feet per second. This second layer is called Layer A by Hersey, et al. (1959), Layer 1 by 

 Antoine and Henry (1965), and V2 by Sheridan, et al. (1966). The base of the second layer 

 and top of the third layer range from about —200 to —900 feet MSL; the few data points 

 indicate that the base is shallowest inshore and dips generally eastward. Antoine and Henry 

 (1965) believe that the contact between the second and third layer is the top of the 

 Oligocene or Eocene section. 



The third layer within range of the CERC subbottom records is characterized by a 

 velocity range of 7,218 to 9,514 feet per second. This is Layer C of Hersey, et al. (1959); 

 Layer 2 of Antoine and Henry (1965); and V3 of Sheridan, et al. (1966), (Table 2). The top 

 of the third layer is probably within range of CERC reflection records only under the 

 innermost part of the shelf. 



From the sparse data available it seems probable tliat the uppermost velocity layer 

 determined from these refraction studies corresponds to reflection unit A of this study. The 

 second velocity layer may correspond to the reflection units B, C, and D. The contact 

 between velocity layers two and three would thus correspond to the green reflector of this 

 study. 



h. JOIDES-1 Reconnaissance Lines. Two seismic reflection lines were run from the 

 Fernandina and Jacksonville grids across the shelf to the site on the central shelf where 



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