Earth:Peace River Formation (Florida)

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Short description: Geological formation in Florida
Peace River Formation
Stratigraphic range: Late Oligocene-Early Miocene
Phosphatic Gravel Peace River Formation.jpg
Phosphatic gravel exposed on the bank of the Peace River near Zolfo Springs
TypeGeological formation
Unit ofHawthorn Group
Sub-unitsBone Valley Member
Thickness600 feet
Lithology
PrimarySand, clay, carbonates
Otherdolomite with phosphate, chert
Location
RegionCentral Florida
Country United States
Type section
Named forPeace River, Florida
Location of the Peace River Formation in Florida.
Fossil (Gavialosuchus americanus) from the Peace River Formation, Florida

The Peace River Formation is a Late Oligocene to Early Miocene geologic formation in the west-central Florida peninsula.

Age

Period: Neogene
Epoch: Miocene to Pliocene
Faunal stage: Arikareean through Hemphillian, ~23.03–4.9 mya, calculates to a period of ~18.13 million years

Location

The Peace River Formation appears as an outcropping or is beneath a thin overburden from Hillsborough County to Charlotte County on the southern part of the Ocala Platform. extending into the Okeechobee Basin. It is widespread in Florida and part of the intermediate confining aquifer system.

Lithology

The formation is composed of sands, clays and carbonates which are interbedded. The sands are light gray to olive gray and poorly consolidated. They are clay-like with some dolomite with a very fine to medium grained phosphate component. Carbonates are usually light gray to yellowish dolomite found in outcroppings. The dolomites are soft to hard with variably sandy, clay-like, phosphate components with opaline chert often found. The phosphate content is high enough to warrant mining.[1][2]

Three sequences of sediment deposition were defined in 1998. Five lithofacies were identified in 2000 (upper part of the formation).[3]

  • Diatomaceous mudstone
  • Terrigenous mudstone
  • Clay-rich quartz sand
  • Quartz sand
  • Pelecypod-rich quartz sand or sandstone

Fossils

  • Mollusks occur as reworked casts, molds, and limited original shell material.
  • Vertebrate fossils
  • Shark's teeth
  • Silicified corals and wood

Members

The Bone Valley Member is a subunit of the Peace River Formation (originally the Bone Valley Formation) and occurs in a limited area on the southern part of the Ocala Platform in Hillsborough, Polk County, and Hardee County. (Webb & Crissinger). It is consistently clastic with sand-sized grains and larger grains of phosphate in a mixture of quartz sand, silt and clay. The consolidation is poor and colors range from white, light brown and yellowish gray to olive gray and blue green.[4]

See also

  • Polk County, Florida paleontological sites

References

  • Finch, J., Geological essay on the Tertiary formation in America: American Journal of Science, v. 7, p. 31–43, 1823.

Further reading

  • Berkenkotter, Richard D, Application of statistical analysis in evaluating bedded deposits of variable thickness—Florida phosphate data (United States. Bureau of Mines. Report of investigations, U.S. Dept. of the Interior, Bureau of Mines (1964)