major significance to shallow subshelf stratigraphy. Exposures of these strata at the shelf 

 surface have not been reported previously nor has their proximity to the surface been 

 suspected. This is due in part to the lack of seismic profiling in inner shelf waters and the 

 preponderance of surface-type grab samplers used by investigators for reasons of efficiency 

 and economics. The occurrence of Tertiary-age sedimentary units marked approximately by 

 a widespread, mappable, acoustic reflector and containing white, quartzose-foraminiferal 

 sands and brown quartz-sand dolomite silt, has several marked imphcations toward 

 interpretation of Holocene coastal retreat and sediment sources. 



Both sedimentary units are judged to represent primary deposition, and therefore have 

 not resulted from major reworking and secondary transport. Evidence for this is severalfold 

 as discussed below. 



Tlie lower unit (Type M) contains an abundance of well rounded, very fine to fine 

 phosphorite grains and rounded medium quartz grains. The sediments are distinctly bimodal 

 with quartz, phosphorite and occasionally, foraminifera comprising the sand fraction, and 

 dolomite or finely particulate organic matter and unidentifiable degraded carbonate grains 

 comprising the silt fraction. 



Dolomite silt grains are wholly intact and lack any evidence of an abrasional history. 

 Degraded grain surfaces occur only in isolated cores, and in those instances there is a noted 

 increase in grain surface irregularity towards the surface, which is interpreted to be the 

 result of in situ weathering processes. Studies of sediments obtained from JODIES hole J-1 

 seaward of the study area showed a generic relationship between dolomite silt clusters and 

 overlying calcareous deposits. A gradual transition between the two sediments exists, with 

 decreases in calcareous fauna accompanied bj^ an increase in similar-sized authigenic 

 dolomite clusters (Schlee and Gerard, 1965). Furthermore, in a study of dolomite sediments 

 offshore of Charlotte Harbor on tlie gulf coast of Florida, Huang and Goodell (1967) 

 concluded that abraded grain surface characteristics indicated the sediments had been 

 derived from an inland source. In contrast, dolomite grains in the present survey area have 

 clean unaltered rhombohedral surfaces and occur in silt-size friable clusters that suggest a 

 complete absence of transport. 



Overlying the dolomite silty sands are type L deposits composed of quartz, phosphorite, 

 and calcium carbonate grains. The calcareous fraction is principally composed of 

 foraminifera and small, largely unidentifiable carbonate fragments. Foraminifera in one 

 representative sample and ostracods in several samples were determined to be Pliocene in age 

 by Dr. Josepli Hazel and Miss Ruth Todd of the U.S. Geological Survey (letter reports to 

 CERC dated 3 and 15 December 1970). Several ages and environments are judged to be 

 represented by type L sediments. Hazel's analysis showing that both early and late Pliocene 

 types were present, and tliat certain species suggested deeper water than otiiers. 



Presence of many planktonic foraminifera in sediments would indicate water deeper tlian 

 that of the survey area. Similar fauna are presently accumulating in outer shelf and shelf 

 edge (200 to 300 feet below sea level) sediments along the southeastern U.S. continental 

 margin where sediment influx is very low (MiUiman, PUkey, and Ross, 1972). 



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