Marl

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File:Piece of marl.JPG
Marl
File:Scala dei Turchi panorama.jpg
Scala dei Turchi coastal marl formation, southern Sicily

Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae.

Marl makes up the lower part of the cliffs of Dover, and the Channel Tunnel follows these marl layers between France and the United Kingdom. Marl is also a common sediment in post-glacial lakes, such as the marl ponds of the northeastern United States and marl lakes of the Canadian Rockies.

Marl has been used as a soil conditioner and neutralizing agent for acid soil and in the manufacture of cement.

Description

File:Marl vs clay & lime EN.PNG
Scheme of the transitional lithotypes from mud (or mudstone) to lime (or limestone), illustrating the definition of marl (marlstone) as a mix of calcium carbonate and clay

Marl or marlstone is a carbonate-rich mud or mudstone which contains variable amounts of clays and silt. The term was originally loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay and calcium carbonate,Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. formed under freshwater conditions. These typically contain 35–65% clay and 65–35% carbonate.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. The term is today often used to describe indurated marine deposits and lacustrine (lake) sediments which are more accurately named 'marlstone'.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marlstone is an indurated (resists crumbling or powdering) rock of about the same composition as marl. This is more correctly described as an earthy or impure argillaceous limestone. It has a blocky subconchoidal fracture, and is less fissile than shale.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. The dominant carbonate mineral in most marls is calcite, but other carbonate minerals such as aragonite or dolomite may be present.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Glauconitic marl is marl containing pellets of glauconite, a clay mineral that gives the marl a green color.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. Glauconite is characteristic of sediments deposited in marine conditions.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Occurrences

File:Channel Tunnel geological profile 1.svg
Geological profile along the Channel Tunnel as constructed. For most of its length the tunnel bores through a chalk marl stratum (layer)

The lower stratigraphic units of the chalk cliffs of Dover consist of a sequence of glauconitic marls followed by rhythmically banded limestone and marl layers.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. Such alternating cycles of chalk and marl are common in Cretaceous beds of northwestern Europe.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. The Channel Tunnel follows these marl layers between France and the United Kingdom.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. Upper Cretaceous cyclic sequences in Germany and marl–opal-rich Tortonian-Messinian strata in the Sorbas Basin related to multiple sea drawdown have been correlated with Milankovitch orbital forcing.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marl as lacustrine sediment is common in post-glacial lake-bed sediments.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. Chara, a macroalga also known as stonewort, thrives in shallow lakes with high pH and alkalinity, where its stems and fruiting bodies become calcified. After the alga dies, the calcified stems and fruiting bodies break down into fine carbonate particles that mingle with silt and clay to produce marl.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. Marl ponds of the northeastern United States are often kettle ponds in areas of limestone bedrock that become poor in nutrients (oligotrophic) due to precipitation of essential phosphate. Normal pond life is unable to survive, and skeletons of freshwater molluscs such as Sphaerium and Planorbis accumulate as part of the bottom marl.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

In Hungary, Buda Marl is found that was formed in the Upper Eocene era. It lies between layers of rock and soil and may be defined it as both "weak rock and strong soil."Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marl is the dominant rock type in the Vaca Muerta Formation in Argentina.

Economic geology

Marl has been used as a soil conditioner and neutralizing agent for acid soilLua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. and in the manufacture of Portland cement.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. Because some marls have a very low permeability, they have been exploited for construction of the Channel Tunnel between England and France and are being investigated for the storage of nuclear waste.

Historical use in agriculture

Marl is one of the oldest soil amendments used in agriculture. In addition to increasing available calcium, marl is valuable for improving soil structure and decreasing soil acidityLua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. and thereby making other nutrients more available.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. It was used sporadically in Britain beginning in prehistoric timesLua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. and its use was mentioned by Pliny the Elder in the 1st century.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. Its more widespread use from the 16th century on contributed to the early modern agricultural revolution.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. However, the lack of a high-energy economy hindered its large-scale use until the Industrial Revolution.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marl was used extensively in Britain, particularly in Lancashire, during the 18th century. The marl was normally extracted close to its point of use, so that almost every field had a marl pit, but some marl was transported greater distances by railroad. However, marl was gradually replaced by lime and imported mineral fertilizers early in the 19th century.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. A similar historical pattern was seen in Scotland.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marl was one of a few soil amendments available in limited quantities in the southern United States, where soils were generally poor in nutrients, prior to about 1840.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. By the late 19th century, marl was being mined on an industrial scale in New JerseyLua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. and was increasingly being used on a more scientific basis, with marl being classified by gradeLua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. and the state geological survey publishing detailed chemical analyses.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Modern agricultural and aquacultural uses

Marl continues to be used for agriculture into the 21st century, though less frequently.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. The rate of application must be adjusted for the reduced content of calcium carbonate versus straight lime, expressed as the calcium carbonate equivalent. Because the carbonate in marl is predominantly calcium carbonate, magnesium deficiency may be seen in crops treated with marl if they are not also supplemented with magnesium.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marl has been used in Pamlico Sound to provide a suitable artificial substrate for oysters in a reef-like environment.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Portland cement

Marl has been used in the manufacture of Portland cement.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. It is abundant and yields better physical and mechanical properties than metakaolin as a supplementary cementitious materialLua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. and can be calcined at a considerably lower temperature.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Civil engineering

The Channel Tunnel was constructed in the West Melbury Marly Chalk, a geological formation containing marl beds. This formation was chosen because of its very low permeability, absence of chert, and lack of fissures found in overlying formations. The underlying Glauconitic Marl is easily recognizable in core samples and helped establish the right level for excavating the tunnel.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marl soil has poor engineering properties, particularly when alternately wetted and dried.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. The soils can be stabilized by adding pozzolan (volcanic ash) to the soil.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Nuclear waste storage

Some marl beds have a very low permeability and are under consideration for use in the storage of nuclear waste. One such proposed storage site is the Wellenberg in central Switzerland.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marl lakes

File:Siseebakwet Lake MN Marl deposition Eric Laska.jpg
Deposition from a Marl lake inside a sheltered paint can, taken from Siseebakwet Lake

Script error: No such module "Labelled list hatnote". A marl lake is a lake whose bottom sediments include large deposits of marl.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. They are most often found in areas of recent glaciationLua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. and are characterized by alkaline water, rich in dissolved calcium carbonate, from which carbonate minerals are deposited.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

Marl lakes have frequently been dredged or mined for marl, often used for manufacturing Portland cement.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. However, they are regarded as ecologically important,Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found. and are vulnerable to damage by silting, nutrient pollution, drainage, and invasive species. In Britain, only the marl lakes of the more remote parts of northern Scotland are likely to remain pristine into the near future.Lua error in package.lua at line 80: module 'Module:Footnotes/anchor_id_list' not found.

See also

References

Citations

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Bibliography

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Further reading

  • Schurrenberger, D., Russell, J. and Kerry Kelts. 2003. Classification of lacustrine sediments based on sedimentary components. Journal of Paleolimnology 29: 141–154.

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