Section IV. INTERPRETATION 



1. Sediment Distribution and Origin 



a. Fort Pierce Grid Area 



(1) Bedding Sequence and Extent - The usual vertical sequence 

 of cored sediment layers in Fort Pierce grid from the lowest is, E, D, 

 C, B, and A. The stratum containing Type E material is believed to be 

 continuous throughout; other sediment types recognized are not everywhere 

 present and it appears from seismic and core data that none extend far 

 seaward of the inner shelf (Figure 21). Type E material is found in 23 

 of the 62 cores from the grid area, and in these it persists to the bottom 

 of the core. In the remaining 39 cores - particularly those of the inner 

 shelf shoals - overburden thickness prevents core penetration to Type E 

 level. Cores and geophysical profiles from the outer shelf and descrip- 

 tive data from the study by Moe (1963) indicate that extensive exposures 

 of Type E material may occur in that zone. A large area of exposure or 

 near exposure on the inner shelf is centered about 5 miles east of Fort 

 Pierce Inlet (Figure 21) . Elsewhere on the inner shelf, local exposures 

 may occur in swales between shoal areas. 



Type D sediment occurs in 17 cores from the grid area. Where re- 

 covered. Type D sediments are either the bottom layer in the core or 

 overlie Type E material. The close resemblance of sediments in many 

 samples of Type D with underlying E material, suggests that it may be 

 derived partly from reworking of this underlying stratum. 



Type C sediment is second only to Type A in frequency of occurrence 

 in the Fort Pierce grid cores. It is probably nearly continuous through- 

 out the inner shelf area. Only Types A and B, and occasional miscellan- 

 eous unclassified sediments, overlie the C layer. Surface exposures of 

 the material are uncommon. 



Type A sediment is the characteristic surface sediment of the inner 

 shelf area. Nearly all inner-shelf cores contain A sediment as the sur- 

 face layer. Usually Type A sediment overlies Types B or C, but it is 

 also found in direct contact with Types D and E. 



Thickness of the sediment layers revealed by Fort Pierce cores is 

 variable. Type A sediments vary from a foot to at least 12 feet in depth 

 and possibly reach more than 30 feet 'in places. The thickness of the 

 Type A layer is generally related to shelf topography, being thick under 

 shoals and thin in the flats and swales. Sediment Types B, C, and D are 

 relatively thin bedded - average sections are about 5 feet or less. The 

 E layer has not been completely penetrated by cores, thus there is no 

 direct evidence of thickness. Available data indicate a thickness of 

 over 10 feet. 



Most of the sediments which were not classifiable consisted of 

 silty, cohesive, fine sands and probable mixtures of sediment types 



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