The Great Ice Age actually consists of four shorter and smaller ice ages with periods of warming in between. During the warmer interglacial stages, large areas of ice melted, returning large amounts of fresh meltwater to the sea. The last interglacial stage occurred about , years ago. At its peak, sea level in south Florida rose about feet above present levels.
Over time, sea-level fluctuations resulted in constantly changing conditions during which periods of sediment deposition alternated with periods of erosion. The variable layering of rocks and sediments that tells the story of Florida's sedimentary history is the result of these variations in sea level.
Composed of limestone or carbonate sand and mud, the Florida Keys subprovince consists of long, narrow islands that stretch in an arc from the northernmost keys of Biscayne National Park to the southwesternmost keys of remote Dry Tortugas National Park. The islands that make up the northern, upper keys are the exposed remnants of coral reefs that fossilized and were exposed as sea level declined.
North of Elliott Key in Biscayne National Park lie several small transitional keys that are composed of sand built up around areas of exposed ancient coral reefs. Yet further north in the Miami metropolitan area, Key Biscayne is composed of sand, as are the barrier islands that protect much of the entire east coast of Florida. To the south, the middle keys, along with much of Florida Bay, consist of oolitic limestone that is similar to the bedrock that makes up the previously discussed Atlantic Coastal Ridge.
The shallow waters of Florida Bay are separated into many smaller basins by shallow banks and small islands. As far south and west as the Dry Tortugas, the lower keys consist of carbonate sands and muds that consist of the remains of small marine plants and animals.
Drastic fluctuations in sea level resulting from the Ice Age further shaped the Florida Keys into the landscape we see today. When sea level was above current levels, several parallel reefs formed along the edge of the submerged coastline, depositing the Key Largo Limestone. Later sea-level fluctuations caused some of the Miami Limestone to dissolve and then redeposit as a denser cap rock overlying the Key Largo and Miami limestones.
Rounding out the physiographic subprovinces that make up south Florida are the Miocene 5 to 23 million years ago and Pliocene 3 to 5 million years ago sedimentary rocks and sediments that underlie the Southwestern Flatwoods subprovince, which lies to the northwest of the Everglades subprovince and west of the Okeechobee Basin subprovince. Landforms in this subprovince include flatwoods, cypress swamps, rocklands, and marl plains.
Also present in the northwestern corner of Everglades National Park, the wedge-shaped Tamiami Formation crops out at land surface in the lower reaches of Big Cypress National Preserve and appears as far north as Fort Lauderdale on the east coast of Florida.
Following deposition of the sediments of the Tamiami Formation in a warm, shallow sea, rising sea levels eroded and dissolved the uppermost layers, and a subsequent decline in sea levels resulted in deposition of the Miami Limestone on top of the Tamiami Formation. The highly permeable calcareous sandstones and sandy limestones that make up the Tamiami Formation are layered with impermeable clay-rich layers that cannot transport large amounts of groundwater.
Commonly found fossils in the Tamiami Formation include barnacles, mollusks, corals, echinoids, foraminifera marine amoeboid protists , and calcareous nanoplankton.
Explore This Park. Everglades National Park Florida. Info Alerts Maps Calendar Reserve. Alerts In Effect Dismiss. Dismiss View all alerts. The Shark Valley Observation Tower offers visitors a comprehensive degree view of Everglades landscapes. NPS photo The landscapes we see today in Everglades National Park, and in all of south Florida, are the direct result of geologic events of the past and ongoing environmental processes.
Everglades humor. NPS photo As in most areas of south Florida, subtle changes in elevation result in dramatic changes in vegetation communities. Map of geologic subprovinces in south Florida. Satellite image of central and south Florida acquired during the late s. The large blue circular area is Lake Okeechobee and the red area south of the lake is agricultural. Everglades National Park is to the south. Frequent thunderstorms during the summer rainy season ensure a seasonal supply of freshwater to the Everglades.
Precipitation becomes increasingly acidic as it infiltrates organic plant matter before seeping into the ground. NPS photo Karst is a term used for the characteristic terrain produced by the chemical erosion of carbonate rocks such as limestone and dolomite.
National Park Service biologists assessing the status of solution holes in the karstic Rocky Glades area of Everglades National Park during the winter dry season. NPS photo The extensive carbonate rocks of Florida are inherently porous and have been exposed to weathering processes since the last significant interglacial period led to widespread flooding about , years ago.
The boardwalk trail to Pahayokee Overlook offers visitors distant, sweeping, expansive views of marl prairie while simultaneously providing a chance to examine the marl soil directly underfoot, all without getting your feet wet. NPS photo Two kinds of soil, marl and peat, occur in the Everglades.
The darkness of sawgrass peat results from the ash left behind from frequent, hot fires that burn during the winter dry season. NPS photo Peat soil is a product of long-hydroperiod long-term flooding wetlands and typically occurs in areas of deeper bedrock.
Perfect conditions in Snake Bight for the formation and accumulation of mangrove peat. NPS photo Marl and peat soils are like opposites that cannot coexist. Big Cypress National Preserve. Pine rocklands, also called pinelands, commonly occur along the relatively higher elevations of sandy limestone that form the Atlantic Coastal Ridge.
The West Lake trail immerses visitors in a forest of white mangrove, black mangrove, red mangrove, and buttonwood trees. Inflow of fresh water into Florida Bay occurs through sheet flow across the southern Everglades. However, during the rainy season, freshwater enters Florida Bay from rainfall, surface runoff, and groundwater. This results in a salinity gradient across the bay, increasing in salinity from north to south.
Portions of the bay often become hypersaline, with salinities reaching over 35 parts per thousand ppt. Dominant habitats in the Florida Bay include seagrass meadows , mangrove islands , and hard bottom areas. Turtle grass Thalassia testudinum and manatee grass Syringodium filiforme are abundant, providing nursery areas for commercially important species of shrimp, lobster, and crabs.
Florida Bay is a large approximately 2,square-kilometer , shallow lagoon bounded to the north by the Florida peninsula and to the south and east by the Florida Keys see map below. Though connected to the Gulf of Mexico to the west, a series of shallow banks, typically covered with and stabilized by seagrass communities, limits the exchange of water between the gulf and the bay.
These banks separate the bay into basins, each with its own physical characteristics. These basins provide unique habitat for many plants, invertebrates, fishes, birds, mammals, and reptiles, including several threatened or endangered species such as the Florida manatee Trichechus manatus latirostris and species of special concern such as the roseate spoonbill Platalea ajaja.
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