C. GEOLOGY 



The bedrock of the Florida Keys is of a dual origin. The Keys from Big 

 Pine Key through Key Largo, are underlaid by Key Largo Limestone, an elevated 

 coral reef of Pleistocene age. According to Hofmeister and Multer (1964), 

 the Key Largo Limestone underlies Miami Beach to the north, comes to the 

 surface at Soldier Key and is submerged beneath the Miami Oolite from Big 

 Pine Key through Key West. The latter formation is an oolitic limestone 

 composed of many small spherites of calcium carbonate. The oolite covers 

 all of the Lower Keys and is thinnest over their southern borders, increasing 

 in thickness to the north (Hofmeister, 1974). 



The general consensus regarding the origin of the Florida Keys suggests 

 that about 95,000 years ago, during the last interglacial period (Sangamon), 

 the coral reefs which make up the Key Largo Limestone were a line of patch 

 reefs in the back reef area of a broad reef platform similar to the Florida 

 Reef Tract of today. Hofmeister and Multer (1968) hypothesize that marine 

 and subaerial erosion following the withdrawal of the sea during the Wisconsin 

 glacial period, possibly accompanied by a structural downward tilting or 

 faulting of the area, or both, resulted in the lowering of the platform to a 

 depth of about 23 meters at its seaward edge and progressively less further 

 inland. With the return of the sea, new reef growth began on the eroded 

 platform and continued to the present. 



D. FLORIDA REEF TRACT DISTINCTIVE CHARACTERISTICS 



As reported by Marszalek, et al (1977): 



"The outer bank reefs are typically elongate features 

 of variable vertical relief which occur at the 

 shallow shelf edge between the 5 meter and 10 meter 

 depth contours. Their long axes form a discontinuous 

 line of reefs oriented parallel to the shelf edge. 

 The northernmost reefs trend N/S and the reefs near 

 Key West E/W reflecting the change in orientation of 

 the arcuate shelf edge. Approximately 56 km of 

 linear bank reefs are located north of Tavernier 

 Creek (at the south end of Key Largo Key), 17 km 

 of reefs in the middle Keys and 23 km in the lower 

 Keys (west of Big Pine Key). A spur and groove system 

 is developed on the seaward face of most of the 

 bank reefs, with the spurs and grooves oriented 

 generally perpendicular to the shelf edge and to 

 the oncoming waves of the Florida Current. Spurs 

 and grooves are best developed on outer bank reefs 

 of the upper Keys and lower Keys; the spur and groove 

 pattern on reefs in the middle Keys is generally less 

 developed and exhibits a more random orientation." 



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