Exploring the Fossils of Florida USA

The U.S State of Florida is among the richest states for both terrestrial and marine fossils spanning several geological periods. Though surprisingly Florida does not have an official state fossil or dinosaur. Agatized Coral found in Tampa Bay and in the Econfina, Withlacoochee and Suwannee River beds was instead designated in 1979 as the State Stone that dates back to the formation of the The Floridian Peninsula a porous geological plateau of karst limestone sitting atop of the much older bedrock known as the Florida Platform.

Tropical Coral Reef System - Image by Ayanadak123

The Agatized coral of the western coast of central and south Florida is also known as petrified coral or fossilised coral and occurs when silica, mineral and trace element rich groundwater over millions of years replaces the calcium carbonate of the original coral with colourful agate known as chalcedony through a process known as permineralisation.

Agatized coral from the Hawthorn Group (Oligocene-Miocene) of Florida - Image by Wilson44691

Agate is a microcrystalline-quartz mineraloid that has a lustrous multi-colour banding of white, grey, red, green, and blue as a result from long-term accumulations of siliceous groundwater deposits. A similar process is also associated with the petrified fossil forests of Arizona at the Petrified Forest National Park.

Petrified fossil wood of Arizona at the Petrified Forest National Park - Image by NPS

A Brief History of Florida

The first Floridians settled approximately 12,000 years ago near to the end of the last Ice Age by Native American Paleoindian hunters from the Timucua and Calusa tribes who had migrated south to the peninsula of Florida. This was a time when the time the sea level was much lower than today, the Florida peninsula was as much as three times the size and home to the now extinct megafauna that lived in the region.

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In 1565, St. Augustine was settled by the Spanish and it was not until 1821 that Florida was acquired from Spain as a U.S. Territory. In 1845 Florida became the 27th US State and William D. Moseley was elected the new state's first governor, and David Levy Yulee, one of Florida's leading proponents for statehood, became a U.S. Senator.

To date over a dozen Native American tribes had resided on the Florida peninsula and today now only two federally recognised tribes remain in South Florida, the Seminole Tribe of Florida and the Miccosukee Tribe of Indians of Florida.

Florida’s Geodiversity

The U.S State of Florida lies within the Southern Zone of the coastal lowlands of the Coastal Plain physiographic province of the eastern United States. Florida is located upon a geological platform known as the Florida Platform that today is mostly submerged. The Florida platform is separated from the neighbouring states southern Georgia and Alabama by a 200-metre isobath.

Over millions of years the changes in global sea levels has seen the Florida Platform almost entirely submerged during interglacial periods and exposed during glacial periods. It is the impact of sea level change that has greatly influence the geodiversity and fossil record for Florida.

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The origin of the Florida platform dates back to when supercontinent of Pangea began to break apart into Laurasia in the northern hemisphere and Gondwana in the southern hemisphere. Florida was located between the tectonic plates of the Americas and Africa and as rifting began to pull Pangea apart the underlying Suwannee Basin Block and Florida-Bahama Block that form part of the Florida platform was dragged along by Laurasia and therefore its basement rock composition is very similar to that found in West Africa.

As the building blocks for the Florida platform were forming the climate was very warm and the sea level was very high. During the Late Cretaceous the Florida platform was separated from mainland North America by the Suwannee Seafloor Channel leading to the build-up and formation of marine calcium carbonate sediments from corals, plankton, algae and other marine invertebrates.

Coral reefs and shoal sediments built around the margins of the then submerged Florida Platform and created evaporative lagoons where evaporites and carbonate rocks formed in the warm shallow seas. These extensive carbonate reef systems and shoals located along the continental shelf edges and on the shallower inner shelf of the Florida Platform were created by rudist reef builders. A similar system was created rudist bivalve assemblages of the Late Cretaceous Jamaica’s Guinea Corn Formation.

The reefs restricted water circulation allowing for the formation of salts and other evaporite across the Florida platform creating two rock formations known as the Avon Park Formation and the Ocala Limestone.

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The Ocala Limestone Formation formed during the Eocene the second of the three epochs of the Paleogene Period dated between 33.9 - 56.0 million years ago. Its fossil record includes sea turtles, sea snakes, primitive dugongs (manatee-like creatures), toothed archaeocete whales, fish, sharks, and rays.

The limestone of Florida is responsible not only for the states extensive karst scenery of caves, sinkholes, and complex underground drainage systems. The porosity and permeability of limestone is the source of the Floridan Aquifer that underlies the entirety of Florida and parts of Alabama, Georgia, Mississippi, and South Carolina.

Dames Cave Withlacoochee State Forest part of Florida's extensive karst scenery - Image by Autumn Kuney

During the Pleistocene, the first of two epochs of the Quaternary Period dating back 11,000 years to 2.58 million years, the climate and environment of Florida was of a grassland savanna that supported a diverse megafauna including mastodons, giant armadillo, camels, bison and horses. It was these animals that were hunted until their extinction by the Native American’s who settled on the peninsula over 12,000 years ago.

During the Pleistocene large parts of the Earth were covered in ice sheets and glaciers, including significant portions of North America. Florida was never covered by glaciers and the impacts of the ice age was primarily related to changes in sea levels and climate.

The warming climate and the retreat of the glaciers had profound effects on the geography of Florida as well as other regions. One notable formation was the Everglades a 1.5-million-acre subtropical wetland of South Florida between 5,000 - 7,000 years.

Described by the author Marjory Stoneman Douglas in her 1947 book, “The Everglades: River of Grass”, the Everglades is a vast, shallow, slow-flowing ecosystem characterised by a mosaic of wetlands, marshes, prairies, and mangroves, teeming with a biodiversity of flora and fauna.

American Alligator, Alligator mississipiensis of the Florida Everglades - Image by tswinner

Much of Florida’s soil, landscape and topography is from marine sediments created or deposited during periods when sea levels were high. Such a soil is the official state soil known as the Myakka soil the most extensive soil in the state found on the flatwoods of low-lying dry pine timber land occupying most of the Florida peninsula. These sandy marine deposits were laid down in former high tidal areas, flood plains, depressional areas and barrier islands.