Oolite

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For the video game, see Oolite (video game).
Modern ooids from a beach on Joulter Cays, The Bahamas
Ooids on the surface of a limestone; Carmel Formation (Middle Jurassic) of southern Utah
Thin-section of calcitic ooids from an oolite within the Carmel Formation (Middle Jurassic) of southern Utah

Oolite or oölite (from

Ancient Greek ᾠόν (ōión) 'egg stone')[1] is a sedimentary rock formed from ooids, spherical grains composed of concentric layers.[2] Strictly, oolites consist of ooids of diameter 0.25–2 millimetres; rocks composed of ooids larger than 2 mm are called pisolites
. The term oolith can refer to oolite or individual ooids.

Composition

Ooids are most commonly composed of

Red Mountain near Birmingham, Alabama
, along with oolitic limestone.

They are usually formed in warm, supersaturated, shallow, highly agitated marine water intertidal environments, though some are formed in inland lakes. The mechanism of formation starts with a small fragment of sediment acting as a 'seed', such as a piece of a shell. Strong intertidal currents wash the 'seeds' around on the seabed, where they accumulate layers of chemically precipitated calcite from the supersaturated water. The oolites are commonly found in large

current bedding
structures that resemble sand dunes. The size of the oolites reflect the time that they were exposed to the water before they were covered with later sediment.

Oolites are often used in the home aquarium industry because their small grain size (0.2 to 1.22 mm) is ideal for shallow static beds and bottom covering of up to 1" in depth. Also known as "oolitic" sand, the sugar-sized round grains of this sand pass easily through the gills of gobies and other sand-sifting organisms. This unusually smooth sand promotes the growth of bacteria, which are important biofilters in home aquaria. Because of its extremely small grain size, oolitic sand has a lot of surface area, which promotes high bacterial growth.

Occurrence

Some exemplar oolitic

World Heritage City of Bath their distinctive appearance. Carboniferous Hunts Bay Oolite lies under much of south Wales
.

The

Miami Oolite.[4] This limestone was formed by deposition when shallow seas covered the area between periods of glaciation
. The material consolidated and eroded during later exposure above the ocean surface.

One of the world's largest freshwater lakebed oolites is the Shoofly Oolite,

ooids and depositing them on steeper benches near the shore in 2- to 40-foot thicknesses. When the lake drained (2 to 4 million years ago), the oolite was left behind, along with siltstone, volcanic tuffs and alluvium from adjacent mountain slopes. The other sediments eroded away, while the more resistant oolite weathered into hummocks, small arches and other natural "sculptures". The Shoofly Oolite lies on public land west of Bruneau, Idaho managed by the Bureau of Land Management
(BLM). The physical and chemical properties of the Shoofly Oolite are the setting for a suite of rare plants, which the BLM protects through land use management and on-site interpretation.

This type of limestone is also found in

Arlington, Virginia. Many of the buildings on the Indiana University campus in Bloomington are built with native oolitic limestone material, and the Soldiers' and Sailors' Monument in downtown Indianapolis
, Indiana, is built mainly of grey oolitic limestone.

Oolites also appear in the Conococheague limestone, of Cambrian age, in the Great Appalachian Valley in Pennsylvania, Maryland, West Virginia, and Virginia.

Rogenstein is a term describing a specific type of oolite in which the cementing matter is

argillaceous
.

See also

  • Geologic time scale – System that relates geologic strata to time
  • Pearl – Hard object produced within a living shelled mollusc – also formed from concentric layers of calcium carbonate
  • Oolitic aragonite sand – Sand composed of an egg-like form of aragonite

References

  1. ISBN 978-0-7112-5684-2
    .
  2. ^ "Oolite". Kansas Geological Survey. Retrieved October 8, 2021.
  3. ISBN 1-85471-044-3
    . Oolitic limestones … are among the most popular building stones and include Portland stone and Bath stone
  4. ^ "Miami Limestone". USGS. Retrieved May 7, 2019.
  5. ^ "Mud Flat Oolite". www.blm.gov. 2015-05-28. Archived from the original on 2016-03-06. Retrieved 2016-03-04.

External links

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