The Hawthorn Group (also Hawthorne Group, previously called Hawthorn(e) Formation) 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 .
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.
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 rock 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.
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.
Age
Period:
Neogene
Epoch: Earliest
Miocene (Aquitanian) to early Miocene (
Burdigalian) in the eastern Florida panhandle, to middle Miocene (
Serravallian) in northern Florida, Georgia, and South Carolina, and to earliest
Pliocene (
Zanclean) in southern Florida, ~23 to ~3.6 mya a period of
North American land mammal age: Late
Arikareean through early
Blancan
Location
The Hawthorn Group includes several geologic formations found in southeastern South Carolina, the coastal plain of Georgia, and much of the Florida Peninsula.The Hawthorn Group extends from southeastern South Carolina through the coastal plain of Georgia and the Florida Peninsula to south Florida.
In Florida, the Hawthorn Group encompasses in part the counties of Gilchrist, Levy, Dixie, Citrus, Sumter, Alachua and Marion County. The Hawthorn is also present below undifferentiated sediments (TQu) as well as the Tamiami Formation from Polk County south through Highlands, Glades, Hendry, Dade, Collier, and Monroe County at depths ranging from mean sea level near Polk to below 600 meters in Monroe Co.
Units
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The Arcadia Formation is the lower carbonate layer of the Hawthorn Group in southern Florida.
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The Tampa Member is the lowest level of the Arcadia Formation in the Tampa Bay area. It is distinguished from other parts of the Arcadia Formation by the low percentage of phosphate present.
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The Nocatee Member is the lowest part of the Arcadia Formation in southwestern Florida. It is primarily siliciclastic, while the rest of the Arcadia Formation is primarily Carbonate rock.
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The Coosawhatchie Formation is the top member of the Hawthorn Group in southeastern South Carolina and northeastern Georgia.
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The Charlton Member is the upper part of the Coosawatchie Formation in southern Georgia and northern Florida.
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The Marks Head Formation is the middle member of the Hawthorn Group in southeastern Georgia and northern Florida.
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The Parachucla Formation forms the lower part of the Hawthorn Group in southern Georgia. It grades into the Penney Farms Formation to the south.
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The Peace River Formation was proposed by Scott to include the Bone Valley Formation, the Murdock Station and Bayshore Clay members and other siliciclastic beds of the Tamiami Formation. The Peace River Formation overlies the Arcadia Formation.
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The Penney Farms Formation is the lower part of the Hawthorn Group in northern and central Florida.
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The Statenville Formation is the top of the Hawthorn Group along the Alapaha River near Statenville, Georgia, extending into Columbia and Hamilton counties in Florida.
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The Torreya Formation is in the eastern part of the Florida Panhandle and adjacent southwestern Georgia. It includes the Dogtown and Sopchoppy members.
The Alachua Formation may have resulted from the weathering of Hawthorn Group sediments, intermixed with Pliocene deposits. Scott does not consider it to be part of the Hawthorn Group.
Paleofauna
Reptiles
Birds
Mammals
Fish
See also
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List of fossiliferous stratigraphic units in South Carolina
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Paleontology in South Carolina
Notes
Sources
