The blue layer, well defined by mapping of upper reflector surface (blue horizon) and 

 recovery of sediments comprising the layer (Type E), is a lagoon-barrier -inner shelf 

 sedimentary complex deposited during initial stage of the late Wisconsin regression and later 

 exposed subaerially until inundated by the Holocene Transgress. Evidence for its relative age 

 development (Fig. 23) is that peats which stratigraphically overlie the blue horizon at Fort 

 Pierce, Cape Canaveral and Jacksonville, are mid-Holocene in age (7,000 to 10,000 B.P.) and 

 subbottom samples from the blue layer (Type E material) show subaerial exposure. Thus 

 deposition occurred at least before the late Wisconsin low sea level. Deposition during 

 regression is postulated from abundance of acoustically defined and steeply inclined seaward 

 dipping internal stratification in the blue layer and correlation of the blue horizon with a 

 subsurface strand line deposit of Donax variabilis (Core 144) having a radiocarbon age of 

 23,500 B.P. (Field, 1974.) Interpretation of environment of deposition is from abundance 

 of lagoonal and infertidal biota (Chione cancellata, Mulinia lateralis, Mercenaria 

 campechiensis, and Donax variables) and the presence of oolitic grains, generally accepted as 

 indicators of shallow, agitated water masses. Elevation of the mid-Wisconsin sea level high is 

 not firmly established (Curray, 1969), but substantial evidence shows that the sea covered 

 the shelf to the approximate position of modern coastal regions. (Guilcher, 1969), (Hoyt, 

 Henry, and Weimer, 1968.) The age and materials of onshore Cape Canaveral relict barriers 

 (Osmond, May, and Tanner, 1970), agree with those of a similar deposit offshore. (Field, 

 1974.) Exposure of the blue layer following the late Wisconsin regression probably resulted 

 in differential weathering and formation of a soil profile. Preceding the last sea level rise, it 

 is judged the surface of the blue layer exhibited the general characteristics of a low-lying 

 limestone plain described by Legrand and Stringfield (1971), and similar in appearance to 

 the present coastal province of Florida between Cape Canaveral and Fort Pierce. 



Overlying the blue horizon are reUct and modern Holocene lagoon and nearshore 

 deposits. Preservation of a peat deposit (Core 100) of probable freshwater origin suggests 

 the following sequence of events— subsequent to the last lowering of sea level as the ocean 

 transgressed the inner shelf about 5,000 to 8,000 B.P., the exposed, weathered surface of 

 the blue layer was inundated, eroded, and later mantled by coastal deposits. The poorly 

 sorted character of Type C sediments, and the abundance and unabraded, fractured 

 appearance of lagoonal mollusks indicates a quiet, protected environment. Mantling most of 

 the study area is a well-sorted, medium-to-coarse quartzose-calcareous sand (Type A) which 

 is presently being reworked and redistributed. These surficial sediments have been generated 

 in part by biogenic activity and southerly littoral transport of eroded coastal materials; 

 most, however, have been derived by bottom erosion of the underlying Pleistocene deposits. 

 Most erosion of the older weathered surface occurred as the sea transgressed the area, but 

 both physical and biological erosion are still active in some areas. At a few locations in the 

 grid area the Pleistocene surface (blue layer) crops out; seaward, numerous ledges, outcrops, 

 and rock surfaces have been delineated by Moe (1963). Derivation of surficial sands from 

 the Pleistocene substrate is evidenced by similarities in composition between the two layers. 

 Specifically, the modern sands contain ooids, clasts of intergranular carbonate cement, few 

 heavy minerals, similar fauna, and well rounded quartz grains characteristic of the 

 underlying semilithified sediments. Thus Type A sands, actively resorted at present, display 

 attributes of a previous depositional environment and are interpreted as palimpset 

 sediments, defined by Swift, Stanley and Curray, (1971). 



53 



