Coosawhatchie Formation

Coosawhatchie Formation Stratigraphic range: Miocene
Type	Geological formation
Unit of	Hawthorn Group
Sub-units	Charlton Member
Lithology
Primary	Sand, clay, limestone, dolostone, phosphate clay
Location
Named for	Coosawhatchie River
Named by	Dall and Stanley-Brown (1894)
Region	North Florida
Country	United States

Location of Coosawhatchie Formation of Florida.

The Coosawhatchie Formation is a Miocene geologic formation with an outcrop in North Florida. It is within the Hawthorn Group.

Age

Period: Neogene
Epoch: Miocene ~23.03 to 5.33 mya, calculates to a period of 17.7 million years
Faunal stage: Arikareean through Hemphillian

Location

The Coosawhatchie Formation is located on the eastern flank of the Ocala Platform near southern Columbia County and southern Marion County, Florida. It extends south-southeast and is present in Alachua, Marion, Sumter, and Lake County. It is exposed or lies beneath a thin overburden.

Lithography

The Coosawhatchie Formation varies in color from a light gray to olive gray. It is poorly consolidated, variably clayey and phosphate containing sand which occasionally contain a dolomitic component but rarely is it dominated with dolostone or limestone.

Silicified nodules are often present in the sediments and may contain 20% or more phosphate. The permeability factor of the Coosawhatchie sediments is generally low, forming part of the intermediate confining aquifer system.

Members

Charlton Member outcrops in just one location, that being northern Nassau County, Florida near and along the St. Mary's River. Here it consists primarily of light gray to greenish gray, poorly to moderately consolidated, dolostone bearing to calcareous, silty, sandy, with few carbonate 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