The Arcadia Formation and its sub-unit, the Tampa Member, are Late Oligocene 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...

s in North Florida

North Florida

North Florida refers to the northernmost part of the U.S. state of Florida, including some counties that border the state of Georgia. It also borders the Big Bend with Madison County and Taylor County to the east and the Central Florida region to its south....

, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. It is part of the Hawthorn Group

Hawthorn 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...

.

Age

Period: Paleogene

Paleogene

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...

: Early Late Oligocene through Pliocene

Pliocene

The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...

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 early Blancan

Blancan

The Blancan 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 4,750,000 to 1,808,000 years BP, a period of .. It is usually considered to start in the early-mid Pliocene epoch and end...

 ~28.4 to ~2.588 mya, calculates to a period of

Location

The Arcadia Formation and Tampa Member is located southwestern flank of the Ocala Platform

Ocala Platform

The Ocala Platform or Ocala Uplift is a geologic formation, a structural high, and a northwest-trending uplift paralleling the Peninsular Arch along the west coast.-Age:Period: NeogeneEpoch: Early Late Oligocene through Pliocene...

 from Pasco County

Pasco County, Florida

Pasco County is a county located in the U.S. state of Florida. As of 2000, the population was 344,765. The July 1, 2007 census estimate according to the U.S. Census Bureau for the county is 462,715. Its county seat is Dade City, Florida which is in the northeast part of the county - somewhat...

 and southward in to Hillsborough

Hillsborough County, Florida

As of the census of 2000, there were 998,948 people, 391,357 households, and 255,164 families residing in the county. The population density was 951 people per square mile . There were 425,962 housing units at an average density of 405 per square mile...

 and Sarasota County, Florida

Sarasota County, Florida

Sarasota County is a county located in the U.S. state of Florida. The U.S. Census Bureau 2008 estimate for the county was 372,057. Its county seat is Sarasota, Florida....

. The Tampa Member and the lower part of the Arcadia Formation form the upper part of the Floridan Aquifer

Floridan Aquifer

The Floridan Aquifer is a portion of the principal artesian aquifer that extends into Florida and is composed of carbonate rock and located beneath the coastal regions of the Southeastern United States and is one of the world's most productive aquifers. It is under all of Florida as well as ...

 system in parts of southern Florida.

Composition

The Arcadia Formation is composed of limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

s and dolostone

Dolostone

Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is...

s which are yellowish gray to light olive gray to light brown in color. The texture is micro to finely crystalline with varying sandy, clayey limestones and dolostones containing phosphate

Phosphate

A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

. The clays are yellowish gray to light olive gray in color. They are moderately hard as well as sandy, silty, phosphatic and dolomitic. Silicified carbonates and opal

Opal

Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...

ized claystone

Claystone

Claystone is a geological term used to describe a clastic sedimentary rock that is composed primarily of clay-sized particles ....

 have also been found.

Tampa Member

The Tampa Member consists predominantly of limestone with subordinate dolostone, sand and clay very similar to that of the subsurface limestone part of the Arcadia Formation. There is considerably less phosphate. The color is white to yellowish gray. It is fossil bearing and variably sandy and clayey mudstone

Mudstone

Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...

, wackestone

Wackestone

Wackestone is a matrix-supported carbonate rock that contains over 10% allochems in a carbonate mud matrix. This is part of the Dunham classification of carbonate rocks. In the other widely used classification due to Folk, an equivalent description would be, for example, an oopelmicrite, where the...

, and packstone with little to no phosphate grains. Sand and clay beds are like those in the undifferentiated sediments of the Arcadia Formation.

Paleofauna

The Arcadia Formation proper contains molds and casts in dolostone containing mollusks. The Tampa Member contains mollusks and coral

Coral

Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

s in molds and casts with silicified pseudomorph

Pseudomorph

In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form , resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another...

s and shell material.