Tvpe A deposits adjacent to Mosquito Lagoon and south arc more calcareous tlian tliose 

 to the north and represent a transition to tlie medium to coarse, quartzose-calcareous 

 deposits of Cape Canaveral. These deposits are designated the Cape Canaveral fades in 

 Figure 28 and described by Field and Duane (1974) as a modern sand sheet derived from 

 reworking of Pleistocene substrata. 



b. TJiickness and Spatial Distribution of Lithologic Units. 



(1) Georgia Border to Jacksonville Beach. South from the Georgia border to 

 Jacksonville the shallow shelf is characterized by three distinct litholigies: (a) fine to 

 medium quartz sand (Type A); (b) poorly sorted very fine to fine quartz sand (Type F); and 

 (c) an assemblage of dolomite silt and quartz sand (Type M) overlain in places by quartzose 

 foraminiferal sands (Type L). 



As discussed previously, type F sands characteristically mantle the shoreface and 

 innermost ramp areas along the entire survey area and are mostly restricted to that zone. 

 The shoreface is topographically indistinct in the Jacksonville to Georgia area but roughly 

 extends 4 to 5 nautical miles offshore. Most cores from this region are relatively short 

 (6 feet) but provide evidence tliat these deposits extend in most places to sediment depths 

 of 4 feet and are not simply a thin veneer overlying the outcropping shoreface deposits. 

 Some of the seismic reflection and core data suggests that in some locales there may be an 

 older sedimentary framework underlying the shoreline. Similar fine-grained silty sands occur 

 seaward of the shoreface in a few isolated locations on the shelf surface or at shallow 

 sediment depths but are not continuous with or genetically related to the modern shoreface 

 deposits. 



Most of the shelf region between Georgia and Jacksonville is covered by type A fine to 

 coarse quartz sand. Deposits are normally 1- to 3-feet thick but in a few places are thicker 

 than 6 feet. Off Fernandina and Jacksonville type A quartz sand is thicker and more 

 uniform in lateral extent. This pattern appears to be related to tlie presence of St. Johns and 

 St. Marys Rivers, although it may be only an apparent pattern due to the lack of detailed 

 surveying between the two areas. However, near St. Johns River the surface sand sheet is less 

 than 8 feet thick. 



A marked characteristic of sediment distribution in the region is the widespread 

 occurrence at or near the surface of late Tertiary dolomite silts (Type M) and foraminiferal 

 sands (Type L). These sediments are usually present several feet below the sea floor in cores 

 from tlie Fernandina and Jacksonville grids and the reconnaissance line connecting the two 

 grid areas. Joint occurrence of these two Tertiary -age deposits is fairly common. Cores 

 containing only the white planktonic foraminiferal sand (Type L) appear not to have 

 penetrated deep enough to reacli the underlying dolomite silt (Type M). In the Jacksonville 

 grid several cores containing only t) pe M, the stratigraphically lower unit, appear to have an 

 erosional surface separating them from the higher type A sands, indicating that the 

 associated type L may have been removed through erosion. 



60 



