Hawthorn Group

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Hawthorn Group
Stratigraphic range: Miocene
TypeGroup
Sub-units(See text)
OverliesOcala Limestone
Thickness> 330 feet
Location
RegionSoutheastern United States
Country United States
Type section
Named forHawthorne, Florida
Named byL.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]

Age[edit]

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 19.4 million years[6]
North American land mammal age: Late Arikareean through early Blancan[7]

Location[edit]

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.[8] The Hawthorn overlies Ocala Limestone[9]

Units[edit]

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.[22]

Paleofauna[edit]

Reptiles

Birds

Mammals

See also[edit]

Notes[edit]

  1. ^ The name has been spelled both with and without the final "e" since 1913. The Florida Geological Survey uses the spelling "Hawthorn", and the U.S. Geological Survey defers on the spelling of a unit name to the usage of the geological survey of the state in which the stratotype is located.[1][2]

References[edit]

  1. ^ Scott 1988, p. 8.
  2. ^ Weems & Edwards 2001, p. 10.
  3. ^ "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.
  4. ^ 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.
  5. ^ Huddlestun 1993, p. 92.
  6. ^ Scott 1988, pp. xii, 49, 100.
  7. ^ Scott 1988, p. 122.
  8. ^ USGS Florida Geology
  9. ^ Faulkner, Glen L. (1973). Geohydrology of the Cross-Florida Barge Canal Area With Special Reference to the Ocala Vicinity, Water Resources Investigation Report I-73 (Report). Tallahassee: U. S. Geological Survey.
  10. ^ Scott 1988, p. 56.
  11. ^ Scott 1988, pp. 65, 68, 70, 73.
  12. ^ Scott 1988, pp. 73.
  13. ^ Abbott, William H.; Andrews, George W. (1979). "Middle Miocene diatoms in the Hawthorn Formation Within the Ridgeland Trough, South Carolina and Georgia". Micropaleontology. 25 (3): 225, 228. doi:10.2307/1485301. JSTOR 1485301.
  14. ^ Scott 1988, pp. 41–43.
  15. ^ Scott 1988, p. 46.
  16. ^ Scott 1988, p. 34.
  17. ^ Scott 1988, pp. 33–34.
  18. ^ Scott 1988, pp. 79, 81, 86.
  19. ^ Scott 1988, pp. 18, 21, 24.
  20. ^ Scott 1988, pp. 50–54.
  21. ^ Scott 1988, pp. 91, 100–102.
  22. ^ Scott 1988, p. 54.

Sources[edit]

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