are echinoid spines, sponge spicules, alcyonarian sclerites, worm tubes, 

 ostracod carapaces, and many smaller foraminifers. Of the nonskeletal 

 material the dominant constituents are rod-shaped and elliptical pellets 

 (possibly fecal), semiconsolidated calcarenite, oolites and agluttenated 

 worm tubes. Locally such materials are volumetrically important and the 

 calcarenites are especially evident in cores from the Miami grid which 

 have presumably penetrated to bedrock. Constituents of the calcarenite 

 fragments making up the rock at the base of several cores are similar to 

 the finer carbonate skeletal sands occurring in the superposed unlithified 

 strata. In general, these fragments are white or cream colored, many 

 containing large, well-rounded quartz grains, and fragments of mollusk 

 shell, foraminifers, spicules, and pellets. 



In z:ost of the Section A sediments (Figure 13) , the wide range of 

 sizes, poor sorting, and the character and condition of the constituent 

 particles suggest that these, sediments were formed more or less in situ 

 with relatively little transportation involved. Indeed, numerous seismic 

 profiles (Appendix A) show an asymmetrical accumulation of sediment filling 

 the troughs shoreward of the second and third reefs. The surface slope of 

 this accumulation is shoreward and is judged to be evidence supporting the 

 idea of local source of sediment; the local source is the crest and seaward 

 edge of the reef: debris from the reef is carried over the reef crest to 

 be deposited in the shoreward trough. Much of the quartz present in the 

 samples might possibly be eroded from exposures of quartzitic calcarenite 

 (Anastasia Formation) cropping out on the nearshore bottom and especially 

 in the vicinity of the inner flat where such rock appears in several cores 

 and where wave erosion would be most effective. The quartz might also be 

 windblov.Ti or represent material carried in the littoral stream from the 

 north, albeit markedly diluted by the addition of large quantities of 

 carbonate in the southern waters. 



In Section B (north of 26°20' N) , most of the material recovered in 

 cores is a clean, homogeneous, fine to medium-grained sand (Figure 14). 

 It is a calcareous quartz sand (55 to 65 percent quartz) comprised of sub- 

 angular and subrounded clear quartz grains mixed with subrounded to rounded 

 gray, black and bro'.^Ti calcareous particles (Figure 10). Minor amounts of 

 presumably "fresh" skeletal material occur in most of the cores. Chiefly 

 these consist of fragile mollusk fragments and foraminiferal tests. The 

 quantity of such fragments is small, and there is little evidence that 

 such organisms presently contribute substantial amounts of sediment to the 

 shelf in Section B. Difference in sediments throughout Section B is not 

 large; however, sediments of the southern part of Section B (cores 26, 24, 

 23, and 22) are generally someuhat coarser and higher in carbonate content 

 than the sediments to the north (cores 21, 20, 31, 30, 29 and 28). In 

 essence, sediments of the southern half of Section B seem to represent a 

 transition from the extremes of the sediment in Sections A and B. In all 

 Section 3 cores, sediment comprising the surface (0-2 cm) sample is finer 

 than the material belo\v-; the same is not true of Section A sediments. 



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