Avon Park Formation

Avon Park Formation
Stratigraphic range: Eocene
Avon Park Formation; Stratigraphic range: Eocene
	Packstone from a dredge pile by the Cross Florida Barge Canal
Type	Geological formation
Sub-units	None
Underlies	Ocala Limestone (in part)
Lithology
Primary	Grainstone, packstone, wackestone
Other	Mudstone
Location
Region	Central Florida
Country	United States
Extent	Citrus and Levy County
Type section
Named for	Avon Park, Florida
Named by	Applin & Applin 1944

Last updated July 04, 2019

The Avon Park Formation is a Middle Eocene geologic formation and is the oldest exposed sediments in Florida, United States.

Florida is the southernmost contiguous state in the United States. The state is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Atlantic Ocean, and to the south by the Straits of Florida. Florida is the 22nd-most extensive, the 3rd-most populous, and the 8th-most densely populated of the U.S. states. Jacksonville is the most populous municipality in the state and the largest city by area in the contiguous United States. The Miami metropolitan area is Florida's most populous urban area. Tallahassee is the state's capital.

The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the most populous city is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.

Age

Period : Paleogene
Epoch : Middle Eocene~55.8 to 33.9 mya, calculates to a period of 21.9 million years
Faunal stage : Clarkforkian through early Chadronian

The Paleogene is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago (Mya) to the beginning of the Neogene Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon. The Paleogene is most notable for being the time during which mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period. The United States Geological Survey uses the abbreviation PE for the Paleogene, but the more commonly used abbreviation is PG with the PE being used for Paleocene.

In geochronology, an epoch is a subdivision of the geologic timescale that is longer than an age but shorter than a period. The current epoch is the Holocene Epoch of the Quaternary Period. Rock layers deposited during an epoch are called a series. Series are subdivisions of the stratigraphic column that, like epochs, are subdivisions of the geologic timescale. Like other geochronological divisions, epochs are normally separated by significant changes in the rock layers to which they correspond.

The Eocene Epoch, lasting from 56 to 33.9 million years ago, is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by a brief period in which the concentration of the carbon isotope ¹³C in the atmosphere was exceptionally low in comparison with the more common isotope ¹²C. The end is set at a major extinction event called the Grande Coupure or the Eocene–Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay. As with other geologic periods, the strata that define the start and end of the epoch are well identified, though their exact dates are slightly uncertain.

Location

The Avon Park formation is located on the crest of the Ocala Platform in Citrus County with three distinct outcroppings. Levy County has one outcropping near the county line with Citrus County.

The Ocala Platform or Ocala Uplift is a geologic feature, a structural high, and a northwest-trending uplift paralleling the Peninsular Arch along the west coast.

Citrus County is a county located in the U.S. state of Florida. As of the 2010 census, the population was 141,236. Its county seat is Inverness, and its largest community is Homosassa Springs.

Levy County is a county located in the U.S. state of Florida. As of the 2010 census, the population was 40,801. Its county seat is Bronson.

Composition

The Avon Park Formation consists of cream to light-brown or tan, poorly hardened to very hard, grainstone, packstone and wackestone, with rare mudstone. Fossils found throughout but not densely. These limestones are interbedded with vuggy dolomites which are soft to very hard and tan to brown, very fine to medium crystalline structure.

Under the Dunham classification system of limestones, a grainstone is defined as a grain-supported carbonate rock that contains less than 1% mud-grade material. This definition has recently been clarified as a carbonate-dominated rock that does not contain any carbonate mud and where less than 10% of the components are larger than 2 mm. The spaces between grains may be empty (pores) or filled by cement.

Packstone class of limestone in the Dunham classification system

Under the Dunham classification system of limestones, a packstone is defined as a grain-supported carbonate rock that contains 1% or more mud-grade fraction. This definition has been clarified by Lokier and Al Junaibi (2016) as a carbonate-dominated lithology containing carbonate mud in a fabric supported by a sand grade grain-size fraction and where less than 10% of the volume consists of grains >2 mm'.

Under the Dunham classification system of limestones, a wackestone is defined as a mud-supported carbonate rock that contains greater than 10% grains. Most recently, this definition has been clarified as a carbonate-dominated rock in which the carbonate mud component supports a fabric comprising 10% or more very fine-sand grade or larger grains but where less than 10% of the rock is formed of grains larger than sand grade .

The Avon Park Formation, as with many formations, is part of the Floridan Aquifer system. Parts of the Avon Park Formation comprise important, subregional confining units within that system.

Fossils

The fossils are in molds and casts and include:

Mollusks
Foraminifers
Echinoids
Algae
Carbonized plants

Algae is an informal term for a large, diverse group of photosynthetic eukaryotic organisms that are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular microalgae, such as Chlorella and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata, xylem, and phloem, which are found in land plants. The largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example, Spirogyra and stoneworts.

Carbonization is the conversion of organic matters like plants and dead animal remains into carbon through destructive distillation.

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References

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