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.
Marl has been used as a
soil conditioner and neutralizing agent for acid soil and in the manufacture of
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
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, formed under freshwater conditions. These typically contain 35–65% clay and 65–35% carbonate. The term is today often used to describe
indurated marine deposits and
sediments which more accurately should be named 'marlstone'.
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
argillaceouslimestone. It has a blocky
subconchoidal fracture, and is less
shale. The dominant carbonate mineral in most marls is
calcite, but other carbonate minerals such as
dolomite may be present.
Glauconitic marl is marl containing pellets of
glauconite, a clay mineral that gives the marl a green color. Glauconite is characteristic of sediments deposited in marine conditions.
Geological profile along the tunnel as constructed. For most of its length the tunnel bores through a
chalk marl stratum (layer)
Marl as lacustrine sediment is common in post-
glacial lake-bed sediments.Chara, a macroalga also known as stonewort, thrives in shallow lakes with high
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. 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
pond life is unable to survive, and skeletons of freshwater molluscs such as Sphaerium and Planorbis accumulate as part of the bottom marl.
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."
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 and thereby making other nutrients more available. It was used sporadically in Britain beginning in prehistoric times and its used was mentioned by
Pliny the Elder in the 1st century. Its more widespread use from the 16th century on contributed to the early modern agricultural revolution. However, the lack of a high-energy economy hindered its large-scale use until the
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. A similar historical pattern was seen in Scotland.
Marl was one a few soil amendments available in limited quantities the southern United States, where soils were generally poor in nutrients, prior to about 1840. By the late 19th century, marl was being mined on an industrial scale in
New Jersey and was increasingly being used on a more scientific basis, with marl being classified by grade and the state geological survey publishing detailed chemical analyses.
Modern agricultural and aquacultural uses
Marl continues to be used for agriculture into the 21st century, though less frequently. 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.
Marl has been used in
Pamlico Sound to provide a suitable artificial substrate for
oysters in a reef-like environment.
Marl has been used in the manufacture of Portland cement. It is abundant and yields better physical and mechanical properties than metakaolin as a supplementary cementitious material and can be
calcined at a considerably lower temperature.
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.
Marl soil has poor engineering properties, particularly when alternately wetted and dried. The soils can be stabilized by adding
volcanic ash) to the soil.
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.
Deposition from a Marl lake inside a sheltered paint can, taken from
A marl lake is a lake whose bottom sediments include large deposits of marl. They are most often found in areas of recent glaciation and are characterized by alkaline water, rich in dissolved calcium carbonate, from which carbonate minerals are deposited.
Marl lakes have frequently been dredged or mined for marl, often used for manufacturing
Portland cement. However, they are regarded as ecologically important, and are vulnerable to damage by
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.
Agricultural lime – soil additive containing calcium carbonate and other ingredientsPages displaying wikidata descriptions as a fallback
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