Section III. CHARACTERISTICS OF SURFACE AND SHALLOW SUBBOTTOM 

 SEDIMENTS OF THE CONTINENTAL SHELF 



General 



The main source o£ information on sediments in the study area is the 

 collection of CERC ICONS cores. Additional descriptive data on surface 

 sediments is contained in reports by Hathaway (1966) and Moe (1963) , and 

 on hydrographic chart coverage of the study area. Size analysis data of 

 representative samples from the Florida ICONS cores are presented in 

 Appendix B; core descriptions are in Appendix C. 



Nearly all bottom and subbottom material recovered in cores from the 

 study area consisted of unconsolidated or semi-consolidated clastic sedi- 

 ments ranging in size from silt to fine gravel. Treatment of representa- 

 tive samples with dilute HCl showed that these sediments are generally 

 over 50 percent acid-soluble. Acid-soluble constituents, identified by 

 visual analysis, are biogenic, with a minor but locally important content 

 of oolitic material. Broken mollusk shell, barnacle plates and foramini- 

 fers dominate those biogenic constituents which are large^and complete 

 enough to be readily identified. The insoluble fraction of sediments from 

 the study area consists almost entirely of clear quartz sand ranging from 

 angular to well-rounded grains. 



Important biogenic constituents in the Fort Pierce sediments were 

 identified by examination of the >2 mm fraction of 46 representative sedi- 

 ment samples. Important contributing organisms are listed in Table II, 

 and some of the more common forms are shown in Figures 14 and 15. Identi- 

 fication of biogenic constituents was based largely on Abbott (1954 and 

 1968); Morris (1951); Perry and Schwengel (1955); and Ryland (1967); 

 nomenclature follows Abbott (1954). Dr. Joseph Rosewater and Mr. Walter 

 J. Byas of the Mollusk Division, Smithsonian Institution verified the 

 identification of a reference set of specimens. Most biogenic constitu- 

 ents in the finer ( >2mm) fraction appear to be broken or smaller particles 

 of the types of organisms identified. 



b. Fort Pierce Grid - Several sediment types can be recognized in the 

 Fort Pierce grid area. Based largely on color and gross composition, sedi- 

 ments in cores from the Fort Pierce grid are of five main types . In usual 

 stratigraphic sequence these are: 1) Type A - clean, poorly sorted, brown, 

 shelly sand; 2) Type B - gray, fairly well-sorted, calcareous sand; 

 3) Type C - silty gray sand and shelly gravel; 4) Type D - clean, light 

 gray, fine to medium- grained, well-sorted calcareous sand; 5) Type E - 

 white to light gray, generally poorly sorted, calcareous mud, sand, or 

 gravel - often lithified. 



The relative stratigraphic position of these types is uniform through- 

 out the study area. Such similarities point to a regional environmental 

 (Uniformity during time of deposition of sediments of a given category. 

 However, similar depositional conditions may have been recurrent or migra- 

 tory, leaving deposits of similar material but unrelated in age. Likely 



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