Alum Bluff Formation

Alum Bluff Group
Stratigraphic range: Late Oligocene-Early Miocene
Type Geological formation
Sub-units Chipola Formation, Oak Grove Sand, Shoal River Formation, Choctawhatchee Formation, Jackson Bluff Formation
Lithology
Primary Dolostone, phosphate, clay, sand
Location
Region Florida Panhandle
Country  United States
Type section
Named for Alum Bluff on the Chipola River
Named by Dall & Stanley-Brown, 1894
Location of the Alum Bluff Formation of the Florida Panhandle.

The Alum Bluff Formation is a Late Oligocene to Early Miocene geologic formation in the central Florida Panhandle. It was originally mapped by Brooks in 1982 and designated the Shoal River Formation.

Age

Period: Paleogene to Neogene
Epoch: Late Oligocene to Early Miocene
Faunal stage: Chattian through Hemphillian ~23.03—5.33 mya, calculates to a period of 17.7 million years

Location

The Alum Bluff Group replaces the Hawthorn Group west of the Apalachicola River with occurrences in Bay, Calhoun, Holmes, Jackson, Liberty, Okaloosa, Walton, and Washington counties. It is younger than the Torreya Formation to the east based on superpositioning.

The Alum Bluff Group has an outcropping beneath a thin overburden in the western panhandle from river valleys in Okloosa County eastward to western Jackson County.

Lithography

The group is composed of clays, sands and shell beds. These vary from fossil bearing sandy clays to sands, clays, and carbonate beds absent of fossil content with glauconite and phosphate mica which is common. The coloration is from cream to olive gray with mottled reddish brown in the weathered sections. The sands are soft and very fine to coarse with sporadic gravel while carbonate lenses are quite hard. Permeability of the sediments are generally low and are part of the intermediate confining unit/aquifer system.[1][2]

Members

The Alum Bluff Group are defined by the stratigraphic position and mollusks contained within. The group includes:

The Alum Bluff Group has a residuum on Miocene sediments and undifferentiated sediment of the Miocene. This consists of reddish brown, variably sandy clay with inclusions of variably fossiliferous, silicified limestone. The residuum includes Lower to Upper Miocene and younger weathered sediments.[3]

Fossils

References

  1. ↑ United States Geological Survey: Lithostratigraphic Units
  2. ↑ Matson, George Charles, The phosphate deposits of Florida, Bulletin - United States Geological Survey, 1915
  3. ↑ United States Geological Survey: Alum Bluff Group
  4. ↑ Kline, H., Herbert, G., Harries, P., Oches, E., CHES, E., and Portell, R., Trophic Structure OF Shell Beds from the Early Miocene Chipola Formations of Florida

Further reading

This article is issued from Wikipedia - version of the 9/27/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.