The St. Marks Formation is a

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

in the eastern

Florida Panhandle The Florida panhandle (also known as West Florida and Northwest Florida) is the northwestern part of the U.S. state of Florida. It is a Salient (geography), salient roughly long, bordered by Alabama on the west and north, Georgia (U.S. state ...

Age

Period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...

Epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

~23.03 to 5.33 mya, calculates to a period of

Faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by conven ...

Arikareean The Arikareean North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 30,600,000 to 20,800,000 years BP, a period of . It is usuall ...

through

Hemphillian The Hemphillian North American Stage on the geologic timescale is a North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP. It is usually considered t ...

Location

The St. Marks Formation is exposed in Wakulla, southern

Leon Leon, Léon (French) or León (Spanish) may refer to: Places Europe * León, Spain, capital city of the Province of León * Province of León, Spain * Kingdom of León, an independent state in the Iberian Peninsula from 910 to 1230 and again fro ...

and southern

Jefferson County, Florida Jefferson County is a county located in the Big Bend region in the northern part of the U.S. state of Florida. As of the 2020 census, the population was 14,510. Its county seat is Monticello. Jefferson County is part of the Tallahassee, F ...

on the northwestern flank of the Ocala Platform and along with

Suwannee Limestone The Suwannee Limestone is an Early Oligocene geologic formation of exposed limestones in North Florida, United States. Description Suwannee Limestone is found in the peninsula carbonate outcroppings on the northwestern, northeastern and southw ...

and

Ocala Limestone The Ocala Limestone is a late Eocene geologic formation of exposed limestones near Ocala, Marion County, Florida. Age Period: Paleogene Epoch: Late Eocene Faunal stage: Late Clarkforkian through early Orellan Absolute Age: ~55.8 to ~33.9 mya, ...

makes up the upper part of the

Floridan Aquifer The Floridan aquifer system, composed of the Upper and Lower Floridan aquifers, is a sequence of Paleogene carbonate rock which spans an area of about in the southeastern United States. It underlies the entire state of Florida and parts of Alaba ...

in the eastern panhandle.USGS Florida Geology, Open File Report 80
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Composition

The St. Marks Formation consists of a white to yellowish gray, poorly to moderately hard, sandy, fossil bearing rock in molds and casts within

packstone Under the Dunham classification (Dunham, 1962Dunham, R.J. (1962) Classification of carbonate rocks according to depositional texture. In: Classification of Carbonate Rocks (Ed. W.E. Ham), Am. Assoc. Pet. Geol. Mem., 1, 108–121.) system of limesto ...

wackestone Under the Dunham classification (Dunham, 1962Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In: W.E. Ham (Ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir. Amer ...

Fossils

The fossils are in molds and casts and include: *

Mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...

References

{{reflist
Florida Carbonate "Formations" and Conflicting Interpretations of Injection Well Regulations
*Finch, J., Geological essay on the Tertiary formation in America: American Journal of Science, v. 7, p. 31-43, 1823. Neogene Florida Miocene United States Miocene Series of North America Geologic formations of Florida Paleontology in Florida