The Alum Bluff Group is a

geologic group Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...

in the states of Georgia,

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

, and

Alabama (We dare defend our rights) , anthem = "Alabama (state song), Alabama" , image_map = Alabama in United States.svg , seat = Montgomery, Alabama, Montgomery , LargestCity = Huntsville, Alabama, Huntsville , LargestCounty = Baldwin County, Al ...

. It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

dating back to the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

period.

Age

Period:

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

Epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

: Late Oligocene to Early Miocene
Faunal stage:

Chattian The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...

through

Hemphillian The Hemphillian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP. It is usually considered ...

~23.03–5.33

mya Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...

, calculates to a period of

Location

The Alum Bluff Group replaces the Hawthorn Group west of the

Apalachicola River The Apalachicola River is a river, approximately 160 mi (180 km) long in the state of Florida. The river's large watershed, known as the ACF River Basin, drains an area of approximately into the Gulf of Mexico. The distance to its fa ...

with occurrences in

Bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a Gulf (geography), gulf, sea, sound (geography), sound, or bight (geogra ...

Calhoun John C. Calhoun (1782–1850) was the 7th vice president of the United States. Calhoun can also refer to: Surname * Calhoun (surname) Inhabited places in the United States *Calhoun, Georgia *Calhoun, Illinois *Calhoun, Kansas *Calhoun, Kentucky ...

, Holmes, Jackson,

Liberty Liberty is the ability to do as one pleases, or a right or immunity enjoyed by prescription or by grant (i.e. privilege). It is a synonym for the word freedom. In modern politics, liberty is understood as the state of being free within society fr ...

, Okaloosa, Walton, and

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered on ...

counties. It is younger than the

Torreya Formation The Torreya Formation is a Miocene geologic formation with an outcrop in North Florida. It is within the Hawthorn Group. Age Period: Neogene Epoch: Early Miocene Faunal stage: Aquitanian through early Messinian ~19–15.3 mya, calculates to a ...

to the east based on superpositioning. The Alum Bluff Group outcrops beneath a thin

overburden In mining, overburden (also called waste or spoil) is the material that lies above an area that lends itself to economical exploitation, such as the rock, soil, and ecosystem that lies above a coal seam or ore body. Overburden is distinct from tai ...

in the western panhandle from river valleys in Okloosa County eastward to western Jackson County.

Lithology

The group is composed of

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

s and shell beds. These vary from fossil bearing sandy clays to sands, clays, and

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

beds absent of fossil content with glauconite and phosphate

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

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 Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifi ...

while carbonate lenses are quite hard. Permeability of the sediments are generally low and are part of the intermediate confining unit/aquifer system.

Subdivision

The Alum Bluff Group are defined by the stratigraphic position and

mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

contained within. The group includes: *

Chipola Formation The Chipola Formation is a Late Oligocene to Early Miocene geologic formation in the Florida Panhandle and member of the Alum Bluff Group. Age Period: Neogene Epoch: Early Miocene to Middle Miocene Faunal stage: Aqitanian ~18.9 to 18.3 mya, ...

* Oak Grove Sand *

Shoal River Formation The Shoal River Formation is a geologic formation in Florida. The sandstones and marls of the formation preserve fossils dating back to the Serravallian epoch of the Middle Miocene of the Neogene period.Pineda Salgado et al., 2016

* Choctawhatchee Formation * Jackson Bluff Formation 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.

Fossils

Mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

both herbivorous and carnivorous in equal percentages.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
/ref> *

Filter feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

s at ~7%

References

* {{cite web, title= Fossilworks: Gateway to the Paleobiology Database, author= ((Various Contributors to the Paleobiology Database)), url= http://www.fossilworks.org/cgi-bin/bridge.pl?action=home, access-date= 17 December 2021 *Finch, J., Geological essay on the Tertiary formation in America: American Journal of Science, v. 7, p. 31–43, 1823.

Age

Location

Lithology

Subdivision

Fossils

See also

References

Further reading