The Coosawhatchie Formation is a

Miocene The Miocene ( ) is the first 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 means "less recent" ...

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 ...

with an

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...

North Florida North Florida is a Regions of the United States#Florida, region of the U.S. state of Florida comprising the northernmost part of the state. Along with South Florida and Central Florida, it is one of Florida's three most common "directional" regi ...

. It is within the Hawthorn Group.

Age

Period:

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, 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 Mya. ...

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 by ...

~23.03 to 5.33 mya, calculates to a period of {{Mya, 23.03-5.33, million years

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 convent ...

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 usual ...

through

Hemphillian The Hemphillian 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 10,300,000 to 4,900,000 years BP. It is usually considered ...

Location

The Coosawhatchie Formation is located on the eastern flank of the

Ocala Platform 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 of Florida. Age Period: Neogene Epoch: Early Late Oligocene through Pliocene Fau ...

near southern Columbia County and southern

Marion County, Florida Marion County is located in the northern portion of the U.S. state of Florida. As of the 2020 census, the population was 375,908. Its county seat is Ocala. Marion County comprises the Ocala, FL Metropolitan Statistical Area. it includes par ...

. It extends south-southeast and is present in Alachua, Marion,

Sumter Sumter may refer to: People Given name * Sumter S. Arnim (1904–1990), American dentist * Sumter de Leon Lowry Jr. (1893–1985), United States Army general Surname * Rowendy Sumter (born 1988), Curaçaoan footballer * Shavonda E. Sumter ( ...

, and Lake County. It is exposed or lies beneath a thin

overburden In mining, overburden (also called waste or spoil) is the material that lies above an area that lends itself to economical exploitation, such as the rock, soil, and ecosystem that lies above a coal seam or ore body. Overburden is distinct from t ...

Lithography

The Coosawhatchie Formation varies in color from a light gray to olive gray. It is poorly consolidated, variably clayey and

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

containing sand which occasionally contain a

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dol ...

component but rarely is it dominated with dolomite or

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

. Silicified nodules are often present in the sediments and may contain 20% or more

. The permeability factor of the Coosawhatchie sediments is generally low, forming part of the intermediate confining

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteri ...

system.

Members

Charlton Member outcrops in just one location, that being northern

Nassau County, Florida Nassau County is the northeasternmost county of the U.S. state of Florida. According to the 2020 United States Census, the county's population was 90,352. The county seat and the largest incorporated city is Fernandina Beach. Nassau County ...

near and along the St. Mary's River. Here it consists primarily of light gray to greenish gray, poorly to moderately consolidated, dolomite bearing to

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an a ...

, silty, sandy, with few

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonat ...

beds.

Fossils

Few to no fossils and mostly contained in the Charlton Member.

References

*Scott, T. M., The lithostratigraphy of the Hawthorn Group (Miocene) of Florida: Florida Geological Survey Bulletin 59, 148 p. 1988. *Veatch, O., and Stevenson, L. W., 1911, Geology of the coastal plain of Georgia: Georgia Geologic Survey Bulletin 26, 466 p. *USGS: Florida Geology
/small> Neogene Florida Miocene United States Miocene Series of North America Geologic formations of Florida