-295 to -325 feet MLW, may correlate with a Holocene stillstand some 

 15,000 years B.P. Tliis date corresponds to the maximum regression of 

 Milliman and Emery (196S) . 



North of 26°20' N (Section B) to the limits of the study area 

 (26°48' K3 , a blanket of sediment that almost exhibits sonic-isotropism 

 covers all but the outermost of the three prominent "reef" lines present 

 further south. The old reef surface is locally a prominent reflector; 

 the bedrock structure consists typically of a series x)f step-like terraces 

 with the actual topographic reef features forming the riser to each of 

 the next lower steps . 



(4) Subbottom Sediment Characteristics and Distribution . 

 Information concerning the character of subbottom sediments in the study 

 area is based upon analyses of samples from 31 cores obtained during the 

 field phase of the Florida Sand Inventory Program. These 3-inch (inside 

 diameter) cores range from 1.5 to 11 feet long. Twenty-seven were taken 

 in water depths of -35 to -48 feet MLW, thus are significantly represent- 

 ative of a linited shelf zone. Unpublished Corps of Engineers studies, 

 chart notations, and the Broward County, Florida, "Bathymetric and Sand 

 Inventory Survey" (Ocean Science Engineering, Inc., 1967) were used to 

 supplement and extend core data. Granulometric statistics are contained 

 in Appendix B; visual descriptions of core samples are contained in 



Appendix C. 



The two distinct shelf sediment facies, distinguished in the surface 

 sediments in the study area, persist in general aspects in depth. In 

 Section A, sediments are more poorly sorted than in Section B to the 

 north and are, on the whole, far less uniform in depth and in lateral 

 extent. There is, moreover, a great dissimilarity in the composition of 

 these sedir.ents (compare Figures 8 and 10) . The unconsolidated Holocene 

 sediments in Section A are carbonate skeletal sands and gravels composed 

 largely of the hard parts of the biota living in the warm shallow waters 

 covering the shelf. About one-third of the skeletal fragments are intact 

 or sufficiently complete to be readily recognized. The remaining two- 

 thirds of the particles are probably derived from the same organisms 

 constituting the identifiable fraction. Examples of the more prevalent 

 skeletal constituents are shown in Figure 9. In comparison to the sands 

 of Section B, quartz is rare in Section A sediments and generally repre- 

 sents less than 10 percent by weight of the total sample. Although of 

 little significance in terms of volume, the quartz present in Section A 

 is of interest in that many of the particles are considerably larger and 

 better rounded than those in the northern section; numerous particles 

 are frosted. 



The largest contributors to the skeletal material of Section A sedi- 

 ments are r.arine algae with characteristic leaf-like or triform shapes 

 (Halimeda) 3 and mollusks. Foraminifers, especially large benthonic mili- 

 olids such as ? enevoyZis and Arahias^ bryzoa, and corals are significant 

 contributors. See Figure 9 a-e. Frequently encountered in minor amounts 



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