Alum Bluff Formation
Encyclopedia
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.
to Neogene
Epoch
: Late Oligocene to Early Miocene
Faunal stage
: Chattian
through Hemphillian
~23.03—5.33 mya, calculates to a period of
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 outcrop
ping beneath a thin overburden
in the western panhandle from river valleys in Okloosa County
eastward to western Jackson County.
s, sand
s 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.
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.
Early Miocene
The Early Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages....
geologic formation
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...
in the central Florida Panhandle
Florida Panhandle
The Florida Panhandle, an informal, unofficial term for the northwestern part of Florida, is a strip of land roughly 200 miles long and 50 to 100 miles wide , lying between Alabama on the north and the west, Georgia also on the north, and the Gulf of Mexico to the south. Its eastern boundary is...
.
It was originally mapped by Brooks in 1982 and designated the Shoal River Formation.
Age
Period: PaleogenePaleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
to Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
Epoch
Epoch (geology)
An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...
: Late Oligocene to Early Miocene
Early Miocene
The Early Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages....
Faunal stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
: Chattian
Chattian
The Chattian is, in the geologic timescale, the youngest of two ages or upper of two stages of the Oligocene epoch/series. It spans the time between and . The Chattian is preceded by the Rupelian and is followed by the Aquitanian .-Stratigraphic definition:The Chattian was introduced by Austrian...
through Hemphillian
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 , typically set from 10,300,000 to 4,900,000 years BP, a period of . It is usually considered to overlap the Tortonian epoch of the Late...
~23.03—5.33 mya, calculates to a period of
Location
The Alum Bluff Group replaces the Hawthorn GroupHawthorn Group
The Hawthorn Group is a Late Oligocene to Pliocene grouping of several geologic formations and members in North Florida, United States.The Hawthorn Group was originally called the Waldo Formation in 1887 by L. C...
west of the Apalachicola River
Apalachicola River
The Apalachicola River is a river, approximately 112 mi long in the State of Florida. This river's large watershed, known as the ACF River Basin for short, drains an area of approximately into the Gulf of Mexico. The distance to its farthest headstream in northeast Georgia is approximately 500...
with occurrences in Bay
Bay County, Florida
Bay County is a county located in the U.S. state of Florida. The U.S. Census Bureau 2006 estimate for the county is 163,505 . Its county seat is Panama City, Florida. The county is best known for its white sand beaches and crystal blue water, where large pods of dolphins swim year-round...
, Calhoun
Calhoun County, Florida
Calhoun County is a county located in the U.S. state of Florida. As of 2000, the population was 13,017. The U.S. Census Bureau 2006 estimate for the county was 13,410 . Its county seat is Blountstown, Florida.- History :...
, Holmes
Holmes County, Florida
Holmes County is a county located in the U.S. state of Florida. As of 2000, the population was 18,564. The U.S. Census Bureau 2005 estimate for the county was 19,264 . Its county seat is Bonifay, Florida.-History:...
, Jackson
Jackson County, Florida
Jackson County is a county located in the U.S. state of Florida. The population as of the 2000 census was 46,755. As of 2005, the population was estimated to be 48,985 . Its county seat is Marianna, Florida.- History :...
, Liberty
Liberty County, Florida
Liberty County is a county located in the state of Florida. Its population was estimated in 2005 as 7,733. Its most populous incorporated area and county seat is Bristol....
, Okaloosa
Okaloosa County, Florida
Okaloosa County is a county located in the state of Florida. Located in northwest Florida, it extends from the Gulf of Mexico to the Alabama state line. As of the 2000 census, the population was 170,498. The U.S. Census Bureau 2005 estimate for the county is 182,172. The 2009 estimate for the...
, Walton
Walton County, Florida
Walton County is a county located in the state of Florida. As of 2000, the population was 40,601. The U.S. Census Bureau 2005 estimate for the county is 50,324. Its county seat is DeFuniak Springs, Florida. The county is home to the highest natural point in Florida: Britton Hill, at .- History...
, and Washington
Washington County, Florida
Washington County is a county located in the state of Florida. As of 2000, the population was 20,973. The U.S. Census Bureau 2005 estimate for the county was 22,299. Its county seat is Chipley, Florida...
counties. It is younger than the Torreya Formation
Torreya Formation
The Torreya Formation is a Miocene geologic formation with an outcrop in North Florida. It is within the Hawthorn Group.-Age:Period: NeogeneEpoch: Early Miocene...
to the east based on superpositioning.
The Alum Bluff Group has an outcrop
Outcrop
An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...
ping beneath a thin overburden
Overburden
Overburden is the material that lies above an area of economic or scientific interest in mining and archaeology; most commonly the rock, soil, and ecosystem that lies above a coal seam or ore body. It is also known as 'waste' or 'spoil'...
in the western panhandle from river valleys in Okloosa County
Okaloosa County, Florida
Okaloosa County is a county located in the state of Florida. Located in northwest Florida, it extends from the Gulf of Mexico to the Alabama state line. As of the 2000 census, the population was 170,498. The U.S. Census Bureau 2005 estimate for the county is 182,172. The 2009 estimate for the...
eastward to western Jackson County.
Lithography
The group is composed of clayClay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
s, sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
s and shell beds. These vary from fossil bearing sandy clays to sands, clays, and carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
beds absent of fossil content with glauconite
Glauconite
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
and phosphate mica
Mica
The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...
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
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
while carbonate lenses are quite hard. Permeability of the sediments are generally low and are part of the intermediate confining unit/aquifer system.
Members
The Alum Bluff Group are defined by the stratigraphic position and mollusks contained within. The group includes:- Chipola FormationChipola FormationThe Chipola Formation is a Late Oligocene to Early Miocene geologic formation in the Florida Panhandle and member of the Alum Bluff Group.-Age:Period: NeogeneEpoch: Early Miocene to Middle Miocene...
- Oak Grove Sand
- Shoal River Formation
- 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 both herbivorous and carnivorous in equal percentages.
- Filter feederFilter feederFilter feeders are 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 feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
s at ~7%
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)