Geology of Florida

"Florida plate" redirects here; not to be confused with Vehicle registration plates of Florida.

The Floridian peninsula is a porous plateau of karst limestone sitting atop bedrock known as the Florida Platform. The emergent portion of the platform was created during the Eocene to Oligocene as the Gulf Trough filled with silts, clays, and sands. Flora and fauna began appearing during the Miocene. No land animals were present in Florida prior to the Miocene.

The structure of the Florida platform, the foundation of which came from the African Plate over 200 million years ago.

Limestone over bedrock

The largest deposits of rock phosphate in the United States are found in Florida.^[1] Most of this is in Bone Valley in central and west-central Florida.^[2]

Extended systems of underwater caves, sinkholes and springs are found throughout the state and supply most of the water used by residents. This type of terrain (geomorphology) that develops over a carbonate platform or strata is called karst topography.

The limestone is topped with sandy soils deposited as ancient beaches over millions of years as global sea levels rose and fell. During the last glacial period, lower sea levels and a drier climate revealed a much wider peninsula, largely savanna.^[3] While there are sinkholes in much of the state, modern sinkholes most commonly form in the Tampa Bay area and Central Florida.^[4][5]

Early history of Florida

Calcite crystals in fossilized clamshell found in Fort Drum limestone deposit

During the early Mesozoic Era (251 – 66 mya) the supercontinent of Pangea began to rift and break apart.  As North America separated from Africa a small portion of the African Plate detached and was carried away with the North American Plate. This provided some of the foundation upon which Florida now rests.^[6]

The emergent portion of the platform was created during the Eocene to Oligocene as the Gulf Trough, which separated the mainland of what is now the southeastern United States from the Florida Platform, filled with silts, clays, and sands. Flora and fauna began appearing during the Miocene.^{[citation needed]}.

Geomorphology

Geomorphological units in Florida

Geomorphology is the study of the origins of landforms. Landforms in Florida include topographical elements such as ridges, valleys, plains, marine terraces, and karst landforms.^[7] All of Florida falls within the Coastal Plain of the Eastern United States, and has a maximum elevation above sea level of 104 metres (341 ft). Marine forces have dominated the shaping of landforms in Florida. Geologists began recognizing geomorphological regions in Florida in the late 19th century. In 1913, a report divided the central peninsula of Florida into four sections. A 1939 study divided Florida into more than 60 physiographic regions. A study in 1964 described Florida as having several physiographic regions; the Atlantic Coastal Lowlands, Intermediate Coastal Lowlands, Gulf Coastal Lowlands, Central Highlands, Northern Highlands, and Mariana Lowlands, with almost 100 secondary and tertiary sub-divisions.^[8] As of 2022, the Florida Geological Survey has designated 10 geomorphological districts and 71 geomorphological provinces in Florida. The districts share topography that has been produced by related processes. Provinces have shared features that have a common origin. Some of the districts and provinces in northern Florida are only partly in Florida, extending into Georgia or Alabama.^[9]

Ancient sea levels

Florida has a number of sand ridges that are believed to have formed as barrier islands, beach ridges or spits along ancient shore lines. The sand had been eroded from the southern Appalachian Mountains and the coastal plain at the foot of those mountains and eventually filled the Gulf Trough and then spread across the carbonate surface of the Florida Platform. Sea level fluctuations and ocean currents sculpted the sand into long ridges, the most prominent of which are Lake Wales Ridge, Trail Ridge (which extends into Georgia), Mount Dora Ridge, and Brooksville Ridge. Other ridges on peninsular Florida include the Atlantic Coastal Ridge, Bell Ridge, Bombing Range Ridge, Center Park Ridge, Crescent City Ridge, Green Ridge, Lake Henry Ridge, Lakeland Ridge, Orlando Ridge, Ten Mile Ridge, and Winter Haven Ridge.^[10] The Gordonville Ridge, Lake Henry Ridge, Lakeland Ridge, and Winter Haven Ridge are grouped with the Lake Wales Ridge in the Lake Wales Ridge Complex geomorphological province.^[11]

Fluctuations in sea level during the Quaternary glaciation resulted in sea water periodically inundating parts of Florida. Geologists have identified several raised beaches, also known as marine terraces, in Florida at various elevations above the current sea level. These features were believed to have been created by wave action when the sea level was relatively steady for a prolonged period. Eight marine terrace levels have been identified at various locations in Florida, although not all in the same study, including:^[12]

• The Hazelhurst terrace or delta shoreline, formerly called the Brandywine terrace, is a reported relic shoreline found in Forida's panhandle and, less extensively, eastward to Jefferson and Madison counties. Deposits attributed to the terrace or delta are found at elevations of 65.5 to 97 metres (215 to 318 ft), and may have been formed in the late Miocene or early Pliocene epochs.
• The Coharie terrace is found at elevations of 215 to 220 feet (66 to 67 m), and may have formed during the Pre-Illinoian stage of the Quarternary glaciation.
• The Sunderland or Okeefenokee terrace is found at elevations of 150 to 170 feet (46 to 52 m), and may have formed during the Pre-Illinoian stage of the Quarternary glaciation.
• The Wicomico terrace is found at elevations of 90 to 105 feet (27 to 32 m), and may have formed during the Sangamonian stage of the Quarternary glaciation.
• The Penholloway terrace is found at elevations of 70 to 80 feet (21 to 24 m), and may have formed during the Sangamonian stage of the Quarternary glaciation.
• The Talbot terrace is found at elevations of 40 to 45 feet (12 to 14 m), and may have formed during the Sangamonian stage of the Quarternary glaciation.
• The Pamlico terrace is found at elevations of 25 to 35 feet (7.6 to 10.7 m), and may have formed during the interglacial period between the Early and Late Wisconsin glaciations.^[13][14]
• The Silver Bluff terrace is found at elevations of 8 to 10 feet (2.4 to 3.0 m), and may have formed during the Holocene epoch.

While it was formerly thought that sea levels had risen as high as 70 metres (230 ft) above the current sea level during the Pleistocene, and that the above reported terraces had been produced during periods in which the sea level had remained at the corresponding elevation for an extended period of time, it is now believed that the sea level never rose more than 20 metres (66 ft) above the current level during the Pleistocene, and that not all of the terraces are from the Pleistocene. The terraces are no longer considered valid stratigraphic units, and the sediments forming them are often described as "undifferentiated sands".^[15]

Earthquakes

Florida is tied with North Dakota as having the fewest earthquakes of any US state.^[16] Because Florida is not located near any tectonic plate boundaries, earthquakes are very rare, but not completely unknown. In January 1879, a shock occurred near St. Augustine. There were reports of heavy shaking that knocked plaster from walls and articles from shelves. Similar effects were noted at Daytona Beach 50 miles (80 km) south. The tremor was felt as far south as Tampa and as far north as Savannah, Georgia. In January 1880, Cuba was the center of two strong earthquakes that sent severe shock waves through the city of Key West, Florida.^[17] Another earthquake centered outside Florida was the 1886 Charleston earthquake. The shock was felt throughout northern Florida, ringing church bells at St. Augustine and severely jolting other towns along that section of Florida's east coast. Jacksonville residents felt many of the strong aftershocks that occurred in September, October, and November 1886.^[18] A magnitude 6.0 earthquake in 2006 centered about 260 miles (420 km) southwest of Tampa and west of Fort Myers in the Gulf of Mexico sent shock waves through southwest and central Florida. The earthquake was too small to trigger a tsunami, and no damage was reported. Minor shaking was felt in Southwest Florida. Some taller buildings in the city of Cape Coral reported swaying.^[19] On January 28, 2020, a 7.7 magnitude earthquake between Cuba and Jamaica was felt in Florida, causing many office and residential buildings in Miami to be evacuated. In Orlando, the Spectrum Stadium at University of Central Florida shook from the earthquake.^[20]