TTNrT.AS.STFTF.r) 



SECURITY CLASSIFICATION OF THIS PAGE(Wh«n Dmtm Bnfnd) 



The major structural trend in tlie study area shallow subbottom is a broad coastal plain high 

 consisting of truncated strata judged to be of Eocene and Miocene ages. Overlying strata not 

 affected by the high are late Miocene to Holocene in age and are characterized by a predominant 

 eastward dip, common occurrence of internal bedding features, and filled erosional channels. The 

 Pleistocene and Holocene sediments disconformably overlie late Tertiary sediments which crop out 

 in many places north of St. Augustine, Florida. The dominant Uthology of both surficial and 

 shallow subsurface strata is quartz sand. Detrital accessory silicate minerals, carbonates, and 

 phosphorite comprise the remaining 5 to 10 percent of the sediments. Surface exposures and 

 near-surface occurrences of Tertiary unconsolidated quartzose sands are recognized by diagnostic 

 microfauna or dolomite silt matrix. 



Quaternary sediments are unusually thin and discontinuous. The paucity of recognizable 

 Pleistocene fluvial deposits in tliis region and the thin nature of the Holocene sand blanket suggests 

 tliat shelf sands were derived in part from transgressive erosion and that Georgia streams supplied 

 little material to the inner shelf. 



Sand suitable for beach restoration and maintenance on the adjacent north Florida coast occurs 

 abundantly in places on the irmer shelf. Ten potential borrow sites and an additional 21 possible 

 sites have been deUneated, each comprising a sand reserve ranging in volume from 5 to 178 mQUon 

 cubic yards, all within 13 nautical miles of the coast. Underlying quartzose Tertiary deposits 

 contain an estimated 100 billion cubic yards of sand. 



Filled erosional channels in shallow subbottom strata, especially north of Jacksonville, and the 

 occasional occurrence of sinkholes, complicate generalization of foundation conditions. Clays and 

 cohesive sandy silts occur throughout the area in various stratigraphic associations. The character 

 and strength properties of these fine-grained deposits are variable; however, soft watery clays, 

 usually interbedded with fine sand, are most common in the area from Jacksonville to Georgia. 



UNCLASSIFIED 



SECURITY CLASSIFICATION OF THIS PAGE(TWien Data Enterad) 



