Editing Marl (section)

==Economic geology==
Marl has been used as a [[soil conditioner]] and neutralizing agent for acid soil{{sfn|Parker|2005}}{{sfn|Warncke|2015}} and in the manufacture of [[Portland cement]].{{sfn|Jackson|1997|loc="marl lake"}} Because some marls have a very low [[Permeability (earth sciences)|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 acidity{{sfn|Mathew|1993}} and thereby making other nutrients more available.{{sfn|Winiwarter|Blum|2008}} It was used sporadically in Britain beginning in prehistoric times{{sfn|Dodgshon|1978}} and its use was mentioned by [[Pliny the Elder]] in the 1st century.{{sfn|Frossard|Bünemann|Jansa|Oberson|2009}} Its more widespread use from the 16th century on contributed to the early modern agricultural revolution.{{sfn|Dodgshon|1978}}  However, the lack of a high-energy economy hindered its large-scale use until the [[Industrial Revolution]].{{sfn|Winiwarter|Blum|2008}}

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.{{sfn|Shannon|2020}} A similar historical pattern was seen in Scotland.{{sfn|Dodgshon|1978}}

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.{{sfn|Sheridan|1979}} By the late 19th century, marl was being mined on an industrial scale in [[New Jersey]]{{sfnp|Geological Survey of New Jersey|1880|p=184}} and was increasingly being used on a more scientific basis, with marl being classified by grade{{sfnp|Woll|1896|p=295}}{{sfnp|New Jersey State Centennial Board|1877|p=203}} and the state geological survey publishing detailed chemical analyses.{{sfnp|Geological Survey of New Jersey|1887}}

===Modern agricultural and aquacultural uses===
Marl continues to be used for agriculture into the 21st century, though less frequently.{{sfn|Morse|Smith|2011}} 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.{{sfn|Warncke|2015}}

Marl has been used in [[Pamlico Sound]] to provide a suitable artificial substrate for [[oyster]]s in a reef-like environment.{{sfn|Morse|Smith|2011}}

===Portland cement===
Marl has been used in the manufacture of Portland cement.{{sfn|Jackson|1997|loc="marl lake"}} It is abundant and yields better physical and mechanical properties than metakaolin as a supplementary cementitious material{{sfn|Rakhimov|Rakhimova|Gaifullin|Morozov|2017}} and can be [[calcined]] at a considerably lower temperature.{{sfn|Soltani|Tarighat|Varmazyari|2018}}{{sfn|Rakhimova|Rakhimov|Morozov|Gaifullin|2018}}

===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.{{sfn|Rankin|Williams|2012}}

Marl soil has poor engineering properties, particularly when alternately wetted and dried.{{sfn|Miščević|2020}} The soils can be stabilized by adding [[pozzolan]] ([[volcanic ash]]) to the soil.{{sfn|Bahadori|Hasheminezhad|Taghizadeh|2019}}

===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.{{sfn|Pearson |Scholtis|2021}}