268 



BULLETIN 103, UjSTITED STATES NATIONAL MUSEUM. 



Stratigraphic distribution of coral reefs and reef corals in the southeastern United States 

 from Oligocene to Recent time, and their relation to changing sea level. 



Series. 



Geologic formations, members, 

 unconformities. 



Distribution of reef corals and 

 coral reefs. 



Change in 



relation of 



basement to 



sea level. 



Recent 



Pleistocene . 

 Pliocene 



Miocene . 



Oligocene. 

 Eocene... 



Erosion unconformit}'. 

 Key Largo limestone 



Erosion unconformity. 

 Caloosahatchee marl 



Erosion unconformity . 

 Choctawhatehee marl 



Erosion unconformity. 



I Shoal River marl , 

 Oak Grove sand , 

 Chipolamarl 



Chattahoochee formation-|][^PP^^ " 



Erosion imconformity. 

 Ocala limestone 



Coral reefs 



Coral reefs 



Reef corals 



No reefs, a few corals 



A few corals; slight development of h 

 reefs in central and northern 1 

 peninsular Florida. 



A few corals; one species of reef 1 

 facies. [J 



'Coral reefs (Tampa, Fla., etc.) 



Coral reefs (Bainbridge, Ga.) 



Submergence. 



Subsidence. 



Subsidence. 



Subsidence. 



Subsidence. 



Subsidence. 

 Subsidence. 



No coral reefs Subsidence. 



The table shows, besides the stratigraphic distribution of the reefs 

 and reef corals, that, with possibly one exception, each development 

 occurred during subsidence which followed subaerial erosion. 



To consider the basement of these fossil reefs: The geographic 

 extent and composition of the limestones of upper Eocene age, which 

 form the basement of the Floridian plateau, have been ascertained 

 with considerable exactness. The surface outcrop has been mapped 

 in Georgia and Florida, and well borings have revealed the presence 

 of limestone of this age and character under younger formations iu 

 west Florida, at Panama City, and in Peninsular Florida, at Tampa, 

 Key West, Key Vaca, and Palm Beach. The limestone is largely 

 composed of the remains of Foraminifera, including myriads of 

 Nummulites and orbitoidal Foraminifera, Bryozoa, and some moUusks 

 and echinoids, with which is an undetermined proportion of chemi- 

 cally precipitated calcium carbonate and some terrigenous material. 

 Corals are always rare and are usually absent. The organisms occur- 

 ring in the formation are characteristic of tropical, shoal water, 50 

 fathoms or less in depth. As the 100-fathom curve delimits the sub- 

 merged border of the Coastal Plain, it is evident that the Floridian 

 plateau was a part of the Coastal Plain and had essentially its present 

 outline back in upper Eocene time before the formation of the oldest 

 Chattahoochee reef, which was therefore superposed on a subsiding 

 platform not produced by corals. The paleogeographic development 

 of the Floridian plateau shows that each successive development of 

 Tertiary reefs was on an antecedent platform which was formed by 

 agencies other than those dependent on the presence of coral reefs. 

 In all instances the volume of coral as compared with material from 

 other sources is of minor and usually of negligible importance. 



