earlier discussions. Both major sediment types, white foraminiferal sands and brown sand 

 with dolomite silt, comprise at least 50 percent cjuartz and contain few heavy minerals. The 

 quartz grains are rounded to well rounded and show microscopic solution features on grain 

 surfaces, hke grains from the shelf surface. 



In many parts of the study area post-Tertiary quartz sands are thin. Contacts between 

 the Tertiary sediments and overlying quartz sand are megascopicaUy botiv sharp and 

 transitional. Microscopic analysis of transitional intervals in cores shows gradual gradients in 

 grain characteristics. 



Subsurface Tertiary deposits (Types L and M) display continuity with overlying sands. 

 Grain surfaces of dolomite rhombs are sliarp and well defined below contacts and become 

 increasing degraded up through the transitions. Gradual and increasing surface degradation is 

 traceable in some cores for several feet. This transition exists between type L and type M 

 sediments, and between type M and surface quartz sands where type L is absent. Where 

 type L deposits are present at shallow depth, the contact with overlying quartz is sharp with 

 a fine-grained "soil profile" often lying in between. The base of quartz sands usually contains 

 small white calcareous fragments. The fragments are highly altered and recrystaUized from 

 diagenetic effects and cannot be identified by faunal type. Based on color, degree of 

 degradation and alteration, these shell fragments are believed derived from the lower unit. 



(3) Shoreface Sands. The entire shoreface in the survey area is mantled by slightly 

 silty fine quartz sand (Type F) which, except for its finer texture, is similar to type A sand. 

 Origin of the fine sand, like that of the coarser shelf facies, is difficult to determine. 

 However, the sand may be derived in part from direct fluvial-Uttoral transport, and in part 

 from substrate erosion and reworking. 



Most cores from the shoreface are uniform in sediment type, but one core encountered 

 Tertiary sediments a few feet down. Thicknesses of the fine quartz sand over Tertiary strata 

 cannot be accurately determined, since few cores penetrated beneath it; the bulk of 

 shoreface cores does not exceed 8 feet in length. The composite information collected in 

 this survey suggests that the shoreface, or at least the upper 10 feet, is an aggrading deposit 

 possibly superimposed in places on a preexisting geomorphic surface. 



From St. Augustine northward, and especially north of Jacksonville, the shoreface in 

 most places is a poorly defined irregular slope having a base at about 50 feet below MLW. As 

 a topographic feature in this area the shoreface is difficult to distinguish and is similar in this 

 respect to tiie Georgia shoreface. This is due in part to the mass of remnant inlet-shoals that 

 have been stranded and redistributed as the coastal sector retreated during the last rise in sea 

 level. 



Shallow subsurface structure of the shoreface is variable and can be characterized in two 

 ways. Some areas are underlain by horizontal acoustic reflectors which may indicate either 

 constructional or erosional origin; others by bottom parallel reflectors indicate construction 

 upon a preexisting surface. 



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