the Volusia-Brevard County line and merges with the modern analog, Mosquito Lagoon. 

 Crest elevations along the Atlantic Coastal Ridge are about 30 feet, which is interpreted by 

 White (1970) as evidence that the entire ridge system represents deposition during Pamlico 

 time (probably the Sangamon hiterglacial). 



White (1970) has noted that the eastern slope of the Atlantic Coastal Ridge is similar to 

 the modern offshore slope discussed later in this report. The relict offshore slope reaches a 

 nearly horizontal attitude at about 30 feet below tlie Pleistocene sea level and 

 approximately 1 mile offshore of the Pleistocene beach. The relict Atlantic Coastal Ridge is 

 wider and higher than older progradational beach ridges, a fact that White attributes to an 

 abundant terrigenous source of material and diminished shell contribution, hence little or no 

 loss of elevation through solution collapse. White's observation that prograding beaches, 

 which he states may develop under stable or regressing sea level, receive little nourishing 

 sand from sources to landward seems to be applicable only to this region and is not in 

 accord with studies by investigators from other areas. Curray (1965) has pointed out that 

 shoreline deposition and beach ridge construction are more common to regressions, whereas 

 erosion and only discontinuous deposition occur during transgressions. Tiiis is due in part to 

 lowering of stream base level and increased sediment discharge to the coast as sea level 

 recedes. During a rise in sea level, stream channels are flooded and sediments become 

 impounded in their lower reaches. 



In the study area no important sources of fluvial sediments exist south of the St. Johns 

 River. Therefore, prograding and regressing shorelines can be constructed only from 

 preexisting shelf sediments or organic production of materials. As evidence of this 

 assumption, reUct strand deposits lying at shallow depths and occasionally exposed along 

 the coast are more liighly enriched in shell material than are modern beaches. These shelly 

 deposits (coquinas) are believed to be the result of regressional deposition (Osmond, May, 

 and Tanner, 1970; Field, 1974) and are formed through diminished supply of terrigenous 

 quartz material and consequent relative increase in concentration of calcareous material. 



At least four, and in some locations as many as seven, terraces he along the Atlantic coast 

 of north Florida. They range in elevation from 10 to over 150 feet and are particularly well 

 developed in Volusia County. Morphology, age, and stratigraphy of tJie terrace surfaces have 

 been reviewed by Field and Duane (1974). In general, they are surfaces planed by higher 

 (than present) transgressing seas during Pleistocene and Pliocene eustatic events. The 

 terraces have been described by Flint (1940), Cooke (1945), Doering (1958), Altschulter ' 

 and Young (1960), and Alt and Brooks (1965), and found to correlate on a regional basis 

 with terraces in Georgia (Hoyt, Henry, and Weimer, 1968) and on the west coast of Florida 

 (Schnable and Goodell, 1968). 



The same eustatic events which have shaped the terrain of eastern Florida were 

 influential in modifying the submerged shelf area. Receding seas leave behind a veneer of 

 beach ridges and lagoons; advancing seas inundate those same areas and cut new terraces, 

 level off topographic features, and redistribute the sea floor materials. 



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