Florida doesn't feel rock-forming quakes or volcanic activity because it's on a passive interior of the North American plate.
The state of Florida began to form from volcanic activity and the deposition of marine sediments among Africa's northwest about 530 million years ago. Florida sits mostly on limestone rock formations, which were created by billions of skeletons of marine invertebrates deposited onto the seafloor. Geologists have found diverse rock formations in Florida that were created by fossilized animals, the shifting of the Earth's tectonic plates and sea-floor spreading -- the process of lava creating new oceanic crust that forces plates apart.
Florida's Basic Rock Formations
Florida's rock formations are classified by three "basement rock" types: igneous, metamorphic and sedimentary. Igneous rocks, formed deep within the Earth's interior, are not exposed on Florida's surface but have been found thousands of feet below the surface in oil wells. Metamorphic rocks -- which were originally igneous or sedimentary rocks transformed by heat, pressure and chemically active fluids -- are also not exposed on Florida's surface but have also been found several thousand feet below the surface. Florida is mainly composed of sedimentary rocks, which were formed on Earth's surface by the accumulation and cementation of rocks, minerals, organisms and erosion. The most prominent sedimentary rock found throughout Florida is limestone. Prominent Floridian limestone rock is coquina, composed mostly of shells of marine organisms.
Types of Basic Rock Formations
Basement rocks have been found in north-central Florida by penetrating oil wells 3,500 feet below the surface. Basement rocks in south Florida and northern Florida are mostly basalts formed during the late Triassic and early Jurassic periods. In central Florida, the basement rocks are granite with small amounts of metamorphic rock formed during the Early Cambrian period around 550 million years ago. The northern Florida peninsula has sandstones, siltstones, and shales that date from the middle Paleozoic age. The fossils in the rocks -- brachiopods, mollusks and crinoids -- tell the age of the rock by matching the organisms with the time period in which they lived.
Rocks Throughout Florida
Carbonate platforms, which include limestone and dolostone, have been found throughout Florida. Rocks from the early Cenozoic era, which are sediments formed during the last 65 million years, form distinctive formations throughout Florida. Cenozoic rocks form high rock formations (platforms) and low formations (basins). The oldest sediments are on the crest of Ocala Platform, a major geologic feature in west-central Florida. Other large rock platforms, or "highs," are in the Chattahoochee Anticline, Sanford High and St. Johns Platform. The basins, or "lows," include the Okeechobee Basin and the Osceola Low.
Large Rock Formations
Eocene, Oligocene and Miocene limestones forming Florida's base influenced the development of Florida's Pleistocene landforms. Naturally acidic rain and groundwater flowed through the limestones, forming caverns in the rock. Some caverns collapsed and large valleys formed, such as Florida's western and central valleys. Dissolution and cementation of limestone by rainwater and acidic rain produced the craggy, jagged rock surface of the Everglades. The southern rim of Florida also has a fringe line of living and dead coral reefs, which form the Florida Keys.
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