Hydrogeology

Limestone

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Limestone pavement, The Burren, Ireland. @ C.Michael Hogan

 

Limestone  is a sedimentary rock whose chief mineral component is calcite (calcium carbonate: CaCO3). Limestone can be formed by precipitation of calcite dissolved in water or by depostion of marine organisms and entrainment of secondary minerals. Approximately 80 to 90% of limestone composition are skeletal fragments of marine organisms such as coral or foraminifera. 

Some other carbonate grains comprising limestones are soil types such as ooids, peloids, intraclasts, and extraclasts; moreover, certain limestones do not consist of grains at all, but rather and are formed completely by the chemical precipitation of calcite or aragonite, the latter also known as travertine.

Due to the ease of dissolution and precipitation processes of calcium carbonate, limestone occurrences are linked to fascinating topographic phenomena of cave, karst and limestone pavements, the latter often called alvar.

Precipitation and solution

Calcite exhibits an atypical solubility feature termed retrograde solubility, meaning it becomes less water soluble at higher temperatures. Thus precipitation is favored in warm ocean conditions, especially in waters deficient in dissolved carbon dioxide. The study of marine carbonate chemistry is quite important since the oceans are the world's largest carbon sink, with an approximate present carbon storage of 38,000 petagrams. Furthermore, as the world's oceans absorb more carbon dioxide, a steady marine acidification has been occurring over the last 250 years. 

Conversely, limestones can be dissolved by surface or groundwater when conditions of pH, temperature and ionic concentration are favorable, by reaction with dissolved carbon dioxide; the inverse process of natural precipitation can be produced by groundwater as in the case of stalactite or stalagmite formation. When conditions are conducive for precipitation, calcite can also form mineral coatings that cement the existing rock grains together or fill fractures. The most rapidly growing stalactites may progress as much as three millimetres per annum,[1] in conditions of reasonably brisk subsurface water feed, and where warm groundwater is rich in calcium bicarbonate and deficient in dissolved carbon dioxide.

The ease of solution of limestone by water contact in the presence of weak acidity leads to widespread formation of caves and karst landscapes.[2] Landscapes above limestone bedrock have a proclivity to manifest a paucity of surface waters, since streams and lakes readily drain downward through the porous and easily dissolved limestone formation. During this downward flow, water and organic acids from the soil enlarge the crevices created in a geologic time scale, as the calcium carbonate is slowly dissolved and transported away via groundwater subsurface flow.

Marine skeletons and trace minerals

Most of the seabed limestone formation has arisen by benthic deposition of aragonite or calcite shells and skeletons from marine organisms. In addition, this limestone often contains variable amounts of silica in the form of chert, flint, jasper or siliceous skeletal fragments from sponge spicules, diatoms and radiolarians. Furthermore, quantities of silt, clay and river carried terrestrial detritus may be entrained in the limestone. Coral reef formation is a specialised type of limestone formation where generations of reef building organisms who live atop the coral structure deposit further materials to form exotic shapes. At depths greater than 3000 meters, water pressure and temperature causes the dissolution of calcite to increase non-linearly so that limestone typically does not form in waters at such depths. The role of limestone in coral reefs has been recognized by scientists for a considerable time.[3]

Landscape occurrence

caption Limestone tsingy formation at Indian Ocean, Madagascar. @ C.Michael Hogan

Limestone strata can be found in virtually every world region, except for the deeper ocean realms. Because of the unique soil mineral and pH characteristics, limestone formations are often associated with high levels of species endemism. These outcomes as well as dramatic karst landscapes are seen in such diverse regions as the Burren in western Ireland; the island of Oland, Sweden; the northwest coast of Madagascar along the Indian Ocean;[4] and Mayan regions of Mexico and Central America.

Limestone is water soluble, especially in low pH solution, leading to a wide spectrum of erosional landforms.  These include limestone pavement (or alvar), sink holes (or  cenotes, bluffs, caverns and gorges).  Such erosion landscapes are often termed karst.  Limestone is generally less resistant to weathering than igneous rock, although more resistant than sandstone, mudstone and other sedimentary formations. Thus limestone topography is often a prominent residual feature to weathering in locales with other sedimentary rocks and clays.

Bands of limestone emerge from the Earth's surface in often spectacular rocky outcrops and islands. Examples include the {C}Burren in western Ireland; the Nullarbor region of Australia{C}; the Verdon Gorge  France; bluffs and caves in the Anjajavy Forest of Madagascar; covering most of the Swedish island of Oland, the Niagara Escarpment in North America, various parts of the {C}Colorado Plateau in Utah; many cenotes and caverns in the Yucatan Peninsula of Mexico and northern Belize; Ha Long Bay National Park in Vietnam; and the Lijiang River valley of China;[5] the Florida Keys, small islands off {C}Florida's south coast consist chiefly of oolitic limestone (Lower Keys) and the carbonate skeletons of coral reefs (Upper Keys), which thrived in the area during interglacial periods of the Ice ages when sea levels were higher. Unique habitats are found on alvars, extremely level expanses of limestone with thin soil mantles.  The largest such expanse in Europe is the Stora Alvaret on the island of Öland, Sweden. Another area with limited occurrence flora due to the underlying limestone is the Burren of west-central Ireland, where major expanses of limestone pavement result in unique plant associations. In western Europe, such as at Mt Saint Peter in Belgium and Netherlands, major quarry-able occurrences of limestone extend more than 100 kilometers.

Types

Numerous very specific types of limestone are recognized on every world continent other than Antarctica. These types often have specific regional names and possess distinct color, hardness and other morphological distinctions. The following is a representative set of world occurrence types:

Egypt: Tura Limestone, used for facing stones of the Great Pyramid; Mokattam Limestone, used for Great Pyramid core and head of the Great Sphinx

Morocco: Turonian limestone scarps in southern Morocco

Israel: Meleke limestone is a white, coarsely crystalline, thickly bedded formation thought to be used in the tomb of Jesus;[6] found in the Judean Hills and West Bank

Canada: Eramosa lagerstätte is a Silurian formation, dating to 425 million years ago, notable for fossils of organisms whose soft tissue is preserved in phosphate[7]

Croatia: Istrian stone, whitish stone used widely in Dalmatia, likely a chief component of the Diocletian Palace, the largest extant Roman palace

France: Caen stone is a light creamy-yellow Jurassic limestone quarried in northwestern France near the city of Caen

Germany: Solnhofen limestone is a Jurassic formation preserving a rare assemblage of fossilized organisms

Australia: Wallabi limestone is the dense calcrete limestone platform underlying the Wallabi Group of the Houtman Abrolhos, an archipelago off of Western Australia

New Zealand: Oamaru stone is a hard, compact limestone, quarried at northern Otago, South Island

England: Bath Stone is a honey colored Oolitic limestone; Lincolnshire limestone occurs in the Inferior Oolite Series of the Middle Jurassic strata of eastern England; Portland stone is from the Jurassic period quarried on the Isle of Portland, Dorset: used in many major public buildings such as Buckingham Palace

USA: Kaibab limestone is a geologic formation occurring in much of the southwest including northern Arizona, southern Utah, east central Nevada and southeast California; Bear Gulch Limestone in Montana is a fossiliferous lagerstätte laid down in the Mississippian

History and uses

Prehistoric uses of limestone included lime mortar, pulverized limestone for agricultural uses and burnt lime, also for crop fertilization. In Turkey, lime mortar dating to 15,000 to 7,000 years before present has been recovered in terrazzo floors.[8] Lime mortar was also used for portions of the Great Wall of China.

Since ancient times limestone has been an important material for building and industrial purposes. Very early civilizations employed limestone blocks in many of the grandest edifices of the ancient world, including the Great Pyramids, many of the greatest Roman cities including Volubilis, HIstria and Rome itself; most of the Mayan cities; the Parthenon and other monuments of early Greece; Knossos and other late Neolithic centers in Crete; many Persian monuments such as the tomb of Cyrus the Great. The great structures and outdoor sculptures from antiquity and the Middle Ages are at risk of decay due to the impact of acid rain.

Other uses include:[9]

  • Calcium supplement for animal feeds
  • Crushed for use as construction aggregate as a roadway base
  • Use of geological formations of limestone for reservoirs construction
  • In flue gas desulfurization for sulfur dioxide scrubbing
  • Some forms of glass manufacture
  • Additive to paper, plastics, paint, tiles, and other materials as both white pigment and a cheap filler.
  • Toothpaste
  • Suppression of methane explosions in underground coal mines
  • Food supplement as a source of calcium
  • Certain pharmaceuticals
  • Remineralizing and increasing the alkalinity of purified water to prevent pipe corrosion and to return essential nutrients
  • Certain cosmetics

References

  1. ^ Stephen P. Kramer and Kenrick L. Day. 1995. Caves. Carolrhoda Books  ISBN 9780876144473
  2. ^ Elery Hamilton-Smith and Brian Finlayson. 2003. Beneath the surface: a natural history of Australian caves. UNSW Press. 182 pages
  3. ^ Thomas Wayland Vaughan. 1919. Corals and the formation of coral reefs. United States Government Printing Office. 125 pages
  4. ^ Nick Garbutt, C. Michael Hogan, Hilton Hastings, Wendy Pollecutt and Tahiana Andriaharimalala. 2006. Anjajavy, the village and the forest, Lumina Technologies.
  5. ^ Piotr Migo?. 2010. Geomorphological Landscapes of the World. Springer. 375 pages
  6. ^ James H. Charlesworth. 2006. Jesus and archaeology. William B.Eerdmans Publishing. 740 pages
  7. ^ P.H.Von Bitter, M.A.Purnell, D.K.Tetreault and C.A.Stott. 2007. Eramosa Lagerstätte—Exceptionally preserved soft-bodied biotas with shallow-marine shelly and bioturbating organisms (Silurian, Ontario, Canada). Geology 35: 879
  8. ^ U.S.Society for Mining, Metallurgy, and Exploration. 2006. Industrial minerals & rocks: commodities, markets, and uses, SME. 1548 pages
  9. ^ R.S.Boynton et al. 1983. Lime, Industrial Minerals and Rocks, 5th ed. vol. 2. S.J.Lefond ed. AIME, New York

 

Glossary

Citation

Hogan, C. (2012). Limestone. Retrieved from http://www.eoearth.org/view/article/51cbee577896bb431f697268

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