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[J] MIAMI LIMESTONE 



Figure 22. Distribution of sur- 

 face exposed Pleis- 

 tocene formations 

 (adapted from Dubar 

 1974). 



Of the major formations laid 

 down during the Pleistocene, the 

 Miami Limestone is by far the most 

 prominent surface exposed formation 

 within the lower Everglades, Florida 

 Bay, and to some extent the Keys. 

 Miami Limestone, first named Miami 

 Oolite by Sanford (1909), refers to 

 the generally soft white limestone 

 that extends over much of the south- 

 ern tip of Florida and the terminal 

 Keys. To the northeast the forma- 

 tion gradually increases in sand 

 content until it merges, in the 

 vicinity of Palm Beach, with the 

 sandy Anastasia Formation also of 

 the Pleistocene Epoch (Cooke 1945). 

 In the lower Keys the formation 

 again gradually increases in sand 

 content, a fact which led Sanford 

 (1909) to name the formation the 

 "Key West Oolite" in the vicinity of 

 the Keys. However, more current re- 

 search on the origins and relation- 

 ships within the Miami Limestone 

 have led to general abandonment of 

 the term "Key West Oolite". 



Hoffmeister et al. (1967) de- 

 scribe the "Miami Limestone" as com- 

 posed of two distinguishable facies, 

 an upper oolitic facies and a lower 

 bryozoan facies. The upper oolite 

 facies began forming in the late 

 Pleistocene epoch when sea level 

 conditions favored the formation of 

 unstable oolite sand belts just back 

 from the outer edge of the Florida 

 platform. The constituent particles 

 of the oolitic facies are ooids, 

 pellets, and skeletal sand. Ooids 

 are concentrically laminated, spher- 

 ical to subspherical grains which 

 formed as a result of the unique 

 physical and chemical conditions 

 which occurred on shallow sand belts 

 along the southeast coast. The 



nuclei of ooids may be composed of 

 any type of rock fragment, such as 

 calcite, shell, or quartz sand. As 

 deep water from the Gulf Stream 

 rushed over the shallow bank, the 

 temperature and salinity of the 

 water increased, thus decreasing the 

 solubility of calcium carbonate. 

 The water became increasingly turbu- 

 lent and agitated, causing excess 

 carbon dioxide to be driven off, 

 further reducing the calcium carbon- 

 ate solubility. Together these 

 actions resulted in the precipita- 

 tion of calcium carbonate around 

 tiny rock fragments leading to the 

 formation of typical ooids (Hoff- 

 meister 1974). As would be expected 

 on a relict oolite sand belt, ooids 

 comprise the major rock type found 

 in the Atlantic Coastal Ridge. West 

 and northwest of the ridge (into the 

 Everglades and Taylor Slough headwa- 

 ters) ooids decrease to approximate- 

 ly 10% of the rock. The pelletal 

 component of the oolite refers to 

 grains which are ellipsoidal in 

 shape and carry no implication of 

 their origin, while the skeletal 

 sand component originates from the 

 remains of numerous shallow water 

 mollusks and bryozoans. 



52 



