World Library  
Flag as Inappropriate
Email this Article

Oolite

Article Id: WHEBN0000621379
Reproduction Date:

Title: Oolite  
Author: World Heritage Encyclopedia
Language: English
Subject: Cotswolds, Soldiers' and Sailors' Monument (Indianapolis), Venus of Willendorf, Bath stone, Nunney Castle
Collection: Limestone, Petrology, Sedimentary Rocks
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Oolite

Modern ooids from a beach on Joulter's Cay, 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 (egg stone) is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Ancient Greek word ᾠόν for egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm; rocks composed of ooids larger than 2 mm are called pisolites. The term oolith can refer to oolite or individual ooids.

Contents

  • Composition 1
  • Occurrence 2
  • See also 3
  • References 4

Composition

Ooids are most commonly composed of calcium carbonate (calcite or aragonite), but can be composed of phosphate, chert, dolomite or iron minerals, including hematite. Dolomitic and chert ooids are most likely the result of the replacement of the original texture in limestone. Oolitic hematite occurs at 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', e.g. 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 oolite reflects the time they have had 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. Importantly, 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 limestone, a common term for an oolite, was formed in England during the Jurassic period, and forms the Cotswold Hills, the Isle of Portland with its famous Portland Stone,[1] and part of the North Yorkshire Moors. A particular type, Bath Stone, gives the buildings of the World Heritage City of Bath their distinctive appearance.

The islands of the Lower Keys in the Florida Keys, as well as some barrier islands east of Miami bordering Biscayne Bay, are mainly oolitic limestone, which 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, a section of the Glenns Ferry Formation on southwestern Idaho's Snake River Plain. 10 million years ago, the Plain formed the bed of Lake Idaho. Wave action in the lake washed sediments back and forth in the shallows on the southwestern shore, forming ooids and depositing them on steeper benches near the shore in 2- to 40-feet 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 intriguing 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 Indiana in the United States. The town of Oolitic, Indiana, was founded for the trade of limestone and bears its name. Quarries in Oolitic, Bedford, and Bloomington contributed the materials for such iconic U.S. landmarks as the Empire State Building in New York and the Pentagon 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

References

  1. ^ Atkinson, Richard; Atkinson, Frances (1992) [1979]. Rocks & Minerals. The Observer's Book of. London: Bloomsbury. pp. 161–162.  
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from Hawaii eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.