Stratigraphic unit of Miocene age in South Carolina, Georgia, and Florida
Hawthorn Group
Stratigraphic range: Miocene
Type
Group
Sub-units
(See text)
Overlies
Ocala Limestone
Thickness
> 330 feet
Location
Region
Southeastern United States
Country
United States
Type section
Named for
Hawthorne, Florida
Named by
L.C. Johnson, 1887
Location of the Hawthorn Group within Florida (in red).
The Hawthorn Group (also Hawthorne Group, previously called Hawthorn(e) Formation)[a] is a stratigraphic unit of Miocene age in South Carolina, Georgia, and Florida, in the United States. It is known for its phosphate rock resources, and for its rich assemblages of Neogene vertebrate fossils.
The Waldo Formation was described by L.C. Johnson of the United States Geological Survey in 1887. It was later included in the Hawthorne Beds, named for Hawthorne, Florida, where its phosphate-rich rock was quarried and processed for use as fertilizer. The Hawthrone Beds were later renamed the Hawthorne Formation. Late in the 20th century the Hawthorn Formation was redesignated as the Hawthorn Group consisting of several formations.[3]
The Hawthorn Group is the widest spread stratigraphic unit of Miocene age in the southeastern United States, making up almost the entire thickness of Miocene strata over the area in which it occurs. The Hawthorn group has complex bedding, primarily consisting of clay, silt and sand. Stratigraphy varies, but the group usually consist of three main zones, a lower calcareous zone, a middle clastic zone, and an upper mixed zone of clastic and carbonate rocks. Phosphate deposits are found throughout the Hawthorn group, but particularly in the lower zone, where beds of dolomite and dolomitic limestone are found. Hawthorn Group deposits are mined for phosphate in central Florida.[4]
The Hawthorn group was deposited on a continental shelf. It is predominantly siliciclastic, consisting primarily of fine-to medium-grained quartz sand. Clay is also a component, interstitially and in beds. Other common components of Hawthorn units include phosphate, palygorskite, sepiolite, chert, and dolomite or dolostone.[5]
^Scott 1988, p. 8.
^Weems & Edwards 2001, p. 10.
^"Geology of Florida Miocene to Holocene Chapter 5". University of Florida Geology Department. Archived from the original on March 16, 2012. Retrieved March 22, 2024.
^Miller, James A. (1986). Hydrogeologic Framework of the Florida Aquifer System in Florida and in Parts of Georgia, Alabama, and South Carolina (U.S. Geographical Survey Professional Paper 1403-B) (PDF) (Report). Washington, D.C.: U.S. Geological Survey. p. B37.
^Huddlestun 1993, p. 92.
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