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
Region North Florida
Country  United States
Type section
Named for Coosawhatchie River
Named by Dall and Stanley-Brown (1894)
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