Marl Vs Clay
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Marl is an earthy material rich in
carbonate minerals Carbonate minerals are those minerals containing the carbonate ion, . Carbonate divisions Anhydrous carbonates *Calcite group: trigonal **Calcite CaCO3 **Gaspéite (Ni,Mg,Fe2+)CO3 **Magnesite MgCO3 **Otavite CdCO3 **Rhodochrosite MnCO3 **Sider ...
,
clays Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
, and
silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...
. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of
algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
. Marl makes up the lower part of the
cliffs of Dover The White Cliffs of Dover are the region of English coastline facing the Strait of Dover and France. The cliff face, which reaches a height of , owes its striking appearance to its composition of chalk accented by streaks of black flint, depos ...
, and the
Channel Tunnel The Channel Tunnel (), sometimes referred to by the Portmanteau, portmanteau Chunnel, is a undersea railway tunnel, opened in 1994, that connects Folkestone (Kent, England) with Coquelles (Pas-de-Calais, France) beneath the English Channel at ...
follows these marl layers between France and the United Kingdom. Marl is also a common sediment in post-
glacial lake A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land and then melts, filling the depression created by the glacier. Formation Near the end of the last glacial period, roughly 10,0 ...
s, such as the marl ponds of the northeastern United States. Marl has been used as a
soil conditioner A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics. In general usage, the term "soil conditioner" is often ...
and neutralizing agent for acid soil and in the manufacture of
cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...
.


Description

Marl or marlstone is a
carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...
-rich mud or
mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...
which contains variable amounts of
clays Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
and
silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...
. 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 Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
, formed under freshwater conditions. These typically contain 35–65% clay and 65–35% carbonate. The term is today often used to describe
indurated In materials science, friability ( ), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under stress or contact, especially by rubbing. The opposite of friable is indurate. Substances tha ...
marine deposits and
lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...
(lake)
sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
s which are more accurately 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
argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay mineral ...
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
. It has a blocky subconchoidal fracture, and is less
fissile In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal Nuclear chain reaction#Fission chain reaction, chain reaction can only be achieved with fissil ...
than
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...
. The dominant carbonate mineral in most marls is
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
, but other carbonate minerals such as
aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...
or dolomite may be present. ''Glauconitic marl'' is marl containing pellets of
glauconite Glauconite is an iron potassium phyllosilicate ( mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Greek ...
, a clay mineral that gives the marl a green color. Glauconite is characteristic of sediments deposited in marine conditions.


Occurrences

The lower
stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...
units of the
chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...
cliffs of Dover The White Cliffs of Dover are the region of English coastline facing the Strait of Dover and France. The cliff face, which reaches a height of , owes its striking appearance to its composition of chalk accented by streaks of black flint, depos ...
consist of a sequence of
glauconitic Glauconite is an iron potassium phyllosilicate (mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Greek () m ...
marls followed by rhythmically banded limestone and marl layers. Such alternating cycles of chalk and marl are common in
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
beds of northwestern Europe. The
Channel Tunnel The Channel Tunnel (), sometimes referred to by the Portmanteau, portmanteau Chunnel, is a undersea railway tunnel, opened in 1994, that connects Folkestone (Kent, England) with Coquelles (Pas-de-Calais, France) beneath the English Channel at ...
follows these marl layers between France and the United Kingdom. Upper
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
cyclic sequences in
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
and marl–
opal Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...
-rich
Tortonian The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Tort ...
-
Messinian The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the fir ...
strata in the Sorbas Basin related to multiple sea drawdown have been correlated with Milankovitch orbital forcing. Marl as lacustrine sediment is common in post-
glacial lake A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land and then melts, filling the depression created by the glacier. Formation Near the end of the last glacial period, roughly 10,0 ...
-bed sediments. '' Chara'', a macroalga also known as stonewort, thrives in shallow lakes with high pH and
alkalinity Alkalinity (from ) is the capacity of water to resist Freshwater acidification, acidification. It should not be confused with base (chemistry), basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer s ...
, 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 pond A kettle (also known as a kettle hole, kettlehole, or pothole) is a depression or hole in an outwash plain formed by retreating glaciers or draining floodwaters. The kettles are formed as a result of blocks of dead ice left behind by retreating g ...
s in areas of limestone bedrock that become poor in nutrients (
oligotrophic An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates o ...
) due to precipitation of essential
phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
. Normal
pond life Pond life is an umbrella term for all life forms found in ponds. Although there is considerable overlap with the species lists for small lakes and even slow-flowing rivers, pond life includes some species not found elsewhere, and as a biome it r ...
is unable to survive, and skeletons of freshwater molluscs such as ''
Sphaerium ''Sphaerium'' is a genus of very small freshwater clams, aquatic bivalve molluscs in the family Sphaeriidae, known as the fingernail clams. The small clams in this genus are unusual in that many of them, such as ''Sphaerium corneum'', can climb ...
'' and ''
Planorbis ''Planorbis'' is a genus of air-breathing freshwater snails, aquatic animal, aquatic pulmonate gastropod molluscs in the family (biology), family Planorbidae, the sheep, ram's horn snails, or planorbids. All species in this genus have sinistral o ...
'' accumulate as part of the bottom marl. In Hungary, Buda Marl is found that was formed in the
Upper Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', 'Dawn') an ...
era. It lies between layers of rock and soil and may be defined it as both "weak rock and strong soil." Marl is the dominant rock type in the Vaca Muerta Formation in Argentina.


Economic geology

Marl has been used as a
soil conditioner A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics. In general usage, the term "soil conditioner" is often ...
and neutralizing agent for acid soil and in the manufacture of
Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...
. Because some marls have a very low permeability, they have been exploited for construction of the
Channel Tunnel The Channel Tunnel (), sometimes referred to by the Portmanteau, portmanteau Chunnel, is a undersea railway tunnel, opened in 1994, that connects Folkestone (Kent, England) with Coquelles (Pas-de-Calais, France) beneath the English Channel at ...
between England and France and are being investigated for the storage of
nuclear waste Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear ...
.


Historical use in agriculture

Marl is one of the oldest
soil amendments A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics. In general usage, the term "soil conditioner" is often ...
used in agriculture. In addition to increasing available calcium, marl is valuable for improving
soil structure In geotechnical engineering, soil structure describes the arrangement of the solid parts of the soil and of the Pore space in soil, pore space located between them. It is determined by how individual soil granules clump, bind together, and Soil a ...
and decreasing soil acidity and thereby making other nutrients more available. It was used sporadically in Britain beginning in prehistoric times and its use was mentioned by
Pliny the Elder Gaius Plinius Secundus (AD 23/24 79), known in English as Pliny the Elder ( ), was a Roman Empire, Roman author, Natural history, naturalist, and naval and army commander of the early Roman Empire, and a friend of the Roman emperor, emperor Vesp ...
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
Industrial Revolution The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...
. Marl was used extensively in Britain, particularly in
Lancashire Lancashire ( , ; abbreviated ''Lancs'') is a ceremonial county in North West England. It is bordered by Cumbria to the north, North Yorkshire and West Yorkshire to the east, Greater Manchester and Merseyside to the south, and the Irish Sea to ...
, 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 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. By the late 19th century, marl was being mined on an industrial scale in
New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...
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 Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
deficiency may be seen in crops treated with marl if they are not also supplemented with magnesium. Marl has been used in
Pamlico Sound Pamlico Sound ( ) is a large estuarine lagoon in North Carolina. The largest lagoon along the North American East Coast, it extends long and wide. It is part of a large, interconnected network of similar lagoons that includes Albemarle Sou ...
to provide a suitable artificial substrate for
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but no ...
s in a reef-like environment.


Portland cement

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 Calcination is thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), generally fo ...
at a considerably lower temperature.


Civil engineering

The Channel Tunnel was constructed in the West Melbury Marly Chalk, a
geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...
containing marl beds. This formation was chosen because of its very low permeability, absence of
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...
, 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
pozzolan Pozzolans are a broad class of siliceous and aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide (Ca(OH)2 ...
(
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...
) 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 Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear ...
. One such proposed storage site is the Wellenberg in central Switzerland.


Marl lakes

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 Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...
. However, they are regarded as ecologically important, and are vulnerable to damage by
silting Siltation is water pollution caused by particulate Terrestrial ecoregion, terrestrial Clastic rock, clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the i ...
,
nutrient pollution Nutrient pollution is a form of water pollution caused by too many Nutrient, nutrients entering the water. It is a primary cause of eutrophication of surface waters (lakes, rivers and Coast, coastal waters), in which excess nutrients, usually ni ...
,
drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess water. The internal drainage of most agricultural soils can prevent severe waterlogging (anaerobic conditions that harm root gro ...
, and
invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...
. In Britain, only the marl lakes of the more remote parts of northern Scotland are likely to remain pristine into the near future.


See also

* *


References


Citations


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.


External links


Chalk of Kent by C. S. Harris

Palaeoenvironmental Interpretation of the Early Postglacial Sedimentary Record of a Marl Lake
{{Authority control Limestone Sedimentary rocks