known that the accumulation of tre- 

 mendous amounts of fragments of a 

 thin branched Porites accounts for 

 much of it. 



"The stratigraphic relation 

 between the Key Largo Limestone and 

 Miami Oolite can be seen at a con- 

 tact at the southeastern point of 

 Big Pine Key. Here the Miami Oolite 

 gently overlaps the old coral reef 

 in a southern direction. The con- 

 tact appears to be of a transitional 

 character. No other surface contact 

 has been seen in the lower Keys. 

 However it is known that the oolite 

 cover of these Keys is relatively 

 thin, particularly along their 

 southern borders. For example at 

 Boca Chica and Stock Island it has 

 a thickness of only 3 to 6 feet. 

 The oolite cover appears to thicken 

 gradually to the north; at the 

 center of Key West is reaches 20 

 feet." 



Multer (1977), with more recent 

 coring data, reports an expanded 

 range of the Key Largo Limestone to 

 occupy an area up to or exceeding a 

 20 km (12. 4 ft) width (extending 

 both seaward and into the Florida 

 Bay) and extending at least 376 km 

 (235 miles) in a continuous band 

 from North Miami Beach to the Dry 

 Tortugas (Multer and Hoffmeister 

 1968). The interface of the Key 

 Largo Limestone with the Miami Lime- 

 stone Formation on the southeast 

 Atlantic Coastal Ridge is illustra- 

 ted in Figure 23. The Key Largo 

 Limestone intermingles with the 

 bryozoan facies of the Miami Lime- 

 stone Formation, tapering off in a 

 westerly and northerly direction. 

 The maximum elevation for the forma- 

 tion is +5.5 m (18 ft) on Windley 

 Key in the upper Florida Keys (Dubar 

 1974). The core borings, besides 

 establishing the formation range, 

 led Multer and Hoffmeister (1968) to 

 divide it petrologically into three 

 major facies: 



"( 7 ) an outer reef facies (2 to 

 4 miles seaward of the present Keys) 

 containing 4 common rock types, in- 

 cluding encrustate Acropora palmata 

 boundstone, (2) a back-reef facies 

 (2 miles seaward and approximately 

 I mile lagoonward of the Keys) con- 

 taining 6 common rock types, and (3) 

 a lagoonal facies in the approximate 

 site of modern Florida Bay contain- 

 ing five common rock types. 



"Vertical persistence of major 

 facies and similarity of each with 

 overlying Holocene sediments indi- 

 cate a general continuity of envi- 

 ronments for at least the last 

 100,000 years." 



4.4 HOLOCENE SEDIMENTS 



Holocene sediments in the lower 

 Everglades and Taylor Slough are the 

 result of a seasonal abundance of 

 rainfall and a warm subtropical cli- 

 mate which have, over the last 5,000 

 years, stimulated both luxuriant 

 plant growth and case hardening of 

 periodically exposed limestone rock. 

 The case hardening has, in time, 

 made surface penetration of the 

 Everglades trough caprock difficult, 

 thus promoting retention of water 

 and the growth of wetland vegeta- 

 tion. Together these conditions 

 lead to an ideal setting for the 

 production of alternating layers of 

 organic peat and calcitic mud in 

 recent sediments. Holocene sedi- 

 ments in the Keys reflect a much 

 more pervasive marine influence. 



4.41 THE EVERGLADES AND 

 SOUTHWEST COAST 



Gleason et al. (1974) consider 

 all Holocene sediments and soils of 

 the south Florida mainland to be of 

 the Lake Flirt Formation. Sellards 

 (1919) first named this formation 

 the Lake Flirt Marl based on geo- 

 logic cross sections exposed in old 

 Lake Flirt to the west of Lake 



56 



