Florida's Geologic History

Florida's geologic history begins deep beneath its surface where ancient rocks indicate that Florida was once a part of northwest Africa. As ancient supercontinents split apart, collided, and rifted again, a fragment of Africa remained attached to North America. This fragment formed the base for the carbonate buildup which includes the Florida and Bahamas Platforms.

Download a Quicktime animation of Florida's tectonic history

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Florida experienced cycles of sediment deposition and erosion in response to sea-level changes throughout the Cenozoic Era (the last 65 million years). Florida's Cenozoic-aged sediments include two major groups: the Paleogene and Neogene-Quaternary. During the Paleogene, carbonate sediments formed due to biological activity and are mostly made up of whole or broken fossils including foraminifera, bryozoa, molluscs, corals and other forms of marine life. Very little siliciclastic sediment (quartz sands, silts, and clays) was able to reach Florida because the "Gulf Trough" separated the Florida Platform from the siliciclastic source area of the Appalachian Mountains.

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Download a Quicktime animation of Florida's ancient geography through geologic time

Note: The graphic to the right explains the colors in the animation. The numbers in this legend refer to meters above or below sea level.

In the late Paleogene, the Appalachians were uplifted, erosional rates increased, and siliciclastic sediments filled the Gulf Trough. Siliciclastic sediments then encroached upon the carbonate depositing environments. Thus, the sediments deposited during the Neogene were primarily quartz sands, silts and clays with varying amounts of limestone, dolomite and shell. In southern Florida carbonate sediments still predominated because most of the siliciclastic sediments, moving south with the coastal currents, were funneled offshore. The area of the modern-day Everglades was a shallow marine bank where calcareous sediments and bryozoan reefs accumulated. These sediments compacted and eventually formed the limestone that floors the Everglades today.

Colonies of coral formed reefs in the shallow sea along the southern rim of the Florida platform. As sea levels fluctuated, the corals maintained footholds along the edge of the plateau; their reefs grew upward when sea level rose and retreated to lower depths when sea levels fell, accumulating 75 to 100 feet of limestone. The last drop in sea level exposed the ancient reefs which are the present Florida Keys. Living coral reefs continue to grow in the shallow waters seaward of the Keys.