Editing Everglades (section)

===Limestone and aquifers===
Fluctuating sea levels compressed numerous layers of [[calcium carbonate]], sand, and shells. The resulting permeable [[limestone]] formations that developed between 25&nbsp;million and 70&nbsp;million years ago created the [[Floridan aquifer]], which serves as the main source of fresh water for the northern portion of Florida. However, this aquifer lies beneath thousands of feet of impermeable sedimentary rock from Lake Okeechobee to the southern tip of the peninsula.<ref>Lodge, pp.&nbsp;6–7.</ref>[[File:Everglades by Sentinel-2 (Original 10m Res).jpg|thumb|A satellite image of the Everglades, taken in March 2019|alt=]][[File:Everglades Geology.png|thumb|Limestone formations in South Florida. Source: [[U.S. Geological Survey]]]]

Five geologic formations form the surface of the southern portion of Florida: the [[Tamiami Formation]], [[Caloosahatchee Formation]], [[Anastasia Formation]], [[Miami Limestone]], and the [[Fort Thompson Formation]]. The Tamiami Formation is a compression of highly permeable light-colored fossiliferous sands and pockets of [[quartz]], {{convert|150|ft|m}} thick. It is named for the [[Tamiami Trail]] that follows the upper bedrock of the Big Cypress Swamp, and underlies the southern portion of the Everglades. Between the Tamiami Formation and Lake Okeechobee is the Caloosahatchee Formation, named for the river over it. Much less permeable, this formation is highly calcitic and is composed of sandy shell marl, clay, and sand. Water underneath the Caloosahatchee Formation is typically very mineralized. Both the Tamiami and Caloosahatchee Formations developed during the [[Pliocene Epoch]].<ref>{{cite web| publisher = Florida Department of Environmental Protection| title= Florida Geological Survey: Tamiami Formation| date= January 24, 2006| url = http://www.dep.state.fl.us/geology/geologictopics/rocks/tamiami_fm.htm| access-date = 2008-04-29}}</ref><ref>UF & USDA (1948), p. 26–30.</ref>

Surrounding the southern part of Lake Okeechobee is the Fort Thompson Formation, made of dense, hard limestone, shells, and sand. Rain water is less likely to erode the limestone to form ''solution holes''—smaller versions of sinkholes that do not intersect with the water table. In this formation the beds are generally impermeable.<ref name="uf30-33">UF & USDA (1948), p. 30–33.</ref> Underneath the metropolitan areas of [[Palm Beach County, Florida|Palm Beach County]] is the Anastasia Formation, composed of shelly limestone, [[coquina]], and sand representing a former mangrove or salt marsh. The Anastasia Formation is much more permeable and filled with pocks and solution holes.<ref name="uf30-33"/> The Fort Thompson and Anastasia Formations, and Miami Limestone and (x), were formed during the [[Sangamonian]] interglacial period.<ref name="Lodge, p. 10">Lodge, p.&nbsp;10</ref>

The geologic formations that have the most influence on the Everglades are the Miami Limestone and the Fort Thompson Formation. The Miami Limestone has two [[facies]]. The Miami Oolite facies, which underlies the [[Atlantic Coastal Ridge]] from southern Palm Beach County to southern Miami-Dade County, is made up of [[ooids]]: tiny formations of egg-shaped concentric shells and calcium carbonate, formed around a single grain of sand or shell fragment. The other facies, which underlies the eastern lower Everglades (in Miami-Dade County and part of Monroe County) consists of fossilized [[bryozoan]] organisms.<ref>{{Cite web|url=http://www.geosciences.fau.edu/events/virtual-field-trips/miami-limestone/index.php|title=Virtual Field Trip of Selected Exposures of the Miami Limestone|publisher=Research Labs : Florida Atlantic University – Department of Geosciences|website=www.geosciences.fau.edu|access-date=May 15, 2019}}</ref> The unique structure was some of the first material used in housing in early 20th-century South Florida. The composition of this sedimentary formation affects the hydrology, plant life, and wildlife above it: the rock is especially porous and stores water during the dry season in the Everglades, and its chemical composition determines the vegetation prevalent in the region. The Miami Oolite facies also acts to impede flow of water from the Everglades to the ocean between [[Fort Lauderdale, Florida|Fort Lauderdale]] and Coot Bay (near [[Cape Sable]]).<ref>{{cite journal| last = Ginsburg| first = Robert| title = Surface Rock in the Lower Everglades| journal = Everglades Natural History| publisher = Everglades Natural History Association| volume = 1| issue = 1| pages = 21–24|date=March 1953| url = http://everglades.fiu.edu/fiu/enhj/enh1105.html| access-date = 2008-03-17| archive-url = https://web.archive.org/web/20050503130449/http://everglades.fiu.edu/fiu/enhj/enh1105.html| archive-date = 2005-05-03}}</ref>

The metropolitan areas of [[Miami, Florida|Miami]], Fort Lauderdale, and [[West Palm Beach, Florida|West Palm Beach]] are located on a rise in elevation along the eastern coast of Florida, called the [[Miami Rock Ridge]], a relict oolite shoal deposited on top of the Anastasia Formation.<ref>{{Cite report |last=White |first=William A. |year=1970 |title=The Geomorphology of the Florida Peninsula (Geological Bulletin 51) |url=https://ufdc.ufl.edu/UF00000149/00001/images |publisher=Florida Bureau of Geology |pages=58–59}}</ref> Along the western border of the Big Cypress Swamp is the Immokolee Ridge (or Immokolee Rise), a slight rise of compressed sand that divides the runoff between the Caloosahatchee River and The Big Cypress.<ref>{{cite web| last = U.S. Geological Survey| title = Environmental Setting – The Natural System: Watersheds and Coastal Waters (Big Cypress Watershed)| work = Circular 1134: The South Florida Environment – A Region Under Stress| publisher = U.S. Department of the Interior| year = 2004| url = http://sofia.usgs.gov/publications/circular/1134/esns/bcw.html| access-date = 2008-03-17| archive-date = May 15, 2009| archive-url = https://web.archive.org/web/20090515061002/http://sofia.usgs.gov/publications/circular/1134/esns/bcw.html| url-status = dead}}</ref> This slight rise in elevation on both sides of the Everglades creates a basin, and forces water that overflows Lake Okeechobee to creep toward the southwest.<ref>{{cite web| last = Duke University Wetland Center| title = Historic Everglades Basin Topography| work = Everglades Field Trip| publisher = Duke University| url = http://www.env.duke.edu/wetland/geology.htm| access-date = 2008-03-15}}</ref>
Under both the Miami Limestone formation and the Fort Thompson limestone lies the [[Biscayne Aquifer]], a surface aquifer that serves as the [[Miami metropolitan area]]'s fresh water source. Rainfall and stored water in the Everglades replenish the Biscayne Aquifer directly.<ref name="Lodge, p. 10"/>

With the rise of sea levels that occurred during the [[Pleistocene]] approximately 17,000&nbsp;years ago, the runoff of water from Lake Okeechobee slowed and created the vast marshland that is now known as the Everglades. Slower runoff also created an accumulation of almost {{convert|18|ft|m}} of [[peat]] in the area. The presence of such peat deposits, dated to about 5,000&nbsp;years ago, is evidence that widespread flooding had occurred by then.<ref>{{cite web| last = U.S. Geological Survey| title = Environmental Setting – The Natural System: Geology| work = Circular 1134: The South Florida Environment – A Region Under Stress| publisher = U.S. Department of the Interior| year = 2004| url = http://sflwww.er.usgs.gov/publications/circular/1134/esns/geo.html| access-date = 2008-03-15}}{{Dead link|date=April 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>