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95-596: The formation is dominantly dolomite with areas or layers of pure limestone . A shaley or glauconitic zone occurs in the lower portion and the base contains sand and conglomerate or breccia where the formation overlaps the Lamotte and lies directly on the granite of the mountain core. Early geologists offered a variety of names for what is now known as the Bonneterre Formation. In 1894, Missouri state geologist Arthur Winslow proposed St. Francois limestone as

190-429: A glacial armor . Ice can not only erode mountains but also protect them from erosion. Depending on glacier regime, even steep alpine lands can be preserved through time with the help of ice. Scientists have proved this theory by sampling eight summits of northwestern Svalbard using Be10 and Al26, showing that northwestern Svalbard transformed from a glacier-erosion state under relatively mild glacial maxima temperature, to

285-418: A French mineralogist and geologist whom it is named after. He recognized and described the distinct characteristics of dolomite in the late 18th century, differentiating it from limestone. Most dolomite was formed as a magnesium replacement of limestone or of lime mud before lithification . The geological process of conversion of calcite to dolomite is known as dolomitization and any intermediate product

380-426: A considerable depth. A gully is distinguished from a rill based on a critical cross-sectional area of at least one square foot, i.e. the size of a channel that can no longer be erased via normal tillage operations. Extreme gully erosion can progress to formation of badlands . These form under conditions of high relief on easily eroded bedrock in climates favorable to erosion. Conditions or disturbances that limit

475-434: A drop of dilute hydrochloric acid is dropped on it. This distinguishes dolomite from limestone, which is also soft but reacts vigorously with dilute hydrochloric acid. Dolomite usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Dolomite is usually granular in appearance, with a texture resembling grains of sugar . Under

570-408: A fall in sea level, can produce a distinctive landform called a raised beach . Chemical erosion is the loss of matter in a landscape in the form of solutes . Chemical erosion is usually calculated from the solutes found in streams. Anders Rapp pioneered the study of chemical erosion in his work about Kärkevagge published in 1960. Formation of sinkholes and other features of karst topography

665-479: A glacier-armor state occupied by cold-based, protective ice during much colder glacial maxima temperatures as the Quaternary ice age progressed. These processes, combined with erosion and transport by the water network beneath the glacier, leave behind glacial landforms such as moraines , drumlins , ground moraine (till), glaciokarst , kames, kame deltas, moulins, and glacial erratics in their wake, typically at

760-405: A high percentage of CaMg(CO 3 ) 2 in which natural caves or solution tubes have formed. Both calcium and magnesium go into solution when dolomite rock is dissolved. The speleothem precipitation sequence is: calcite , Mg-calcite, aragonite , huntite and hydromagnesite . Hence, the most common speleothem (secondary deposit) in caves within dolomite rock karst , is calcium carbonate in

855-544: A high-calcium limestone, such as manufacture of sodium carbonate . Dolomite is used for production of magnesium chemicals, such as Epsom salt , and is used as a magnesium supplement. It is also used in the manufacture of refractory materials . As with limestone caves , natural caves and solution tubes typically form in dolomite rock as a result of the dissolution by weak carbonic acid. Caves can also, less commonly, form through dissolution of rock by sulfuric acid . Calcium carbonate speleothems (secondary deposits) in

950-464: A homogeneous bedrock erosion pattern, curved channel cross-section beneath the ice is created. Though the glacier continues to incise vertically, the shape of the channel beneath the ice eventually remain constant, reaching a U-shaped parabolic steady-state shape as we now see in glaciated valleys . Scientists also provide a numerical estimate of the time required for the ultimate formation of a steady-shaped U-shaped valley —approximately 100,000 years. In

1045-423: A large river can remove enough sediments to produce a river anticline , as isostatic rebound raises rock beds unburdened by erosion of overlying beds. Shoreline erosion, which occurs on both exposed and sheltered coasts, primarily occurs through the action of currents and waves but sea level (tidal) change can also play a role. Hydraulic action takes place when the air in a joint is suddenly compressed by

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1140-487: A mountain mass similar to the Himalaya into an almost-flat peneplain if there are no significant sea-level changes . Erosion of mountains massifs can create a pattern of equally high summits called summit accordance . It has been argued that extension during post-orogenic collapse is a more effective mechanism of lowering the height of orogenic mountains than erosion. Examples of heavily eroded mountain ranges include

1235-812: A name for thick limestone beds, including everything between what are now known as the Lamotte Sandstone and the St. Peter Sandstone . He described the lower part of that formation (now comprising the Bonneterre and the Elvins Group ) separately as the St. Joseph limestone. Charles Rollin Keyes 's Fredericktown limestone included everything between the Lamotte and the Potosi Dolomite when he first described it in 1896, but his later uses of

1330-566: A result, attempts to precipitate dolomite from seawater precipitate high-magnesium calcite instead. This substance, which has an excess of calcium over magnesium and lacks calcium-magnesium ordering, is sometimes called protodolomite . Raising the temperature makes it easier for magnesium to shed its hydration shell, and dolomite can be precipitated from seawater at temperatures in excess of 60 °C (140 °F). Protodolomite also rapidly converts to dolomite at temperatures of 250 °C (482 °F) or higher. The high temperatures necessary for

1425-432: A surface is eroded. Typically, physical erosion proceeds the fastest on steeply sloping surfaces, and rates may also be sensitive to some climatically controlled properties including amounts of water supplied (e.g., by rain), storminess, wind speed, wave fetch , or atmospheric temperature (especially for some ice-related processes). Feedbacks are also possible between rates of erosion and the amount of eroded material that

1520-453: A very high ratio of calcium to magnesium. Dolomite is used for many of the same purposes as limestone, including as construction aggregate ; in agriculture to neutralize soil acidity and supply calcium and magnesium; as a source of carbon dioxide ; as dimension stone ; as a filler in fertilizers and other products; as a flux in metallurgy ; and in glass manufacturing . It cannot substitute for limestone in chemical processes that require

1615-501: A wave closing the entrance of the joint. This then cracks it. Wave pounding is when the sheer energy of the wave hitting the cliff or rock breaks pieces off. Abrasion or corrasion is caused by waves launching sea load at the cliff. It is the most effective and rapid form of shoreline erosion (not to be confused with corrosion ). Corrosion is the dissolving of rock by carbonic acid in sea water. Limestone cliffs are particularly vulnerable to this kind of erosion. Attrition

1710-412: A weak bedrock (containing material more erodible than the surrounding rocks) erosion pattern, on the contrary, the amount of over deepening is limited because ice velocities and erosion rates are reduced. Glaciers can also cause pieces of bedrock to crack off in the process of plucking. In ice thrusting, the glacier freezes to its bed, then as it surges forward, it moves large sheets of frozen sediment at

1805-461: Is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite , CaMg(CO 3 ) 2 . It occurs widely, often in association with limestone and evaporites , though it is less abundant than limestone and rare in Cenozoic rock beds (beds less than about 66 million years in age). One of the first geologists to distinguish dolomite from limestone was Déodat Gratet de Dolomieu;

1900-537: Is already carried by, for example, a river or glacier. The transport of eroded materials from their original location is followed by deposition, which is arrival and emplacement of material at a new location. While erosion is a natural process, human activities have increased by 10–40 times the rate at which soil erosion is occurring globally. At agriculture sites in the Appalachian Mountains , intensive farming practices have caused erosion at up to 100 times

1995-490: Is also more prone to mudslides, landslides, and other forms of gravitational erosion processes. Tectonic processes control rates and distributions of erosion at the Earth's surface. If the tectonic action causes part of the Earth's surface (e.g., a mountain range) to be raised or lowered relative to surrounding areas, this must necessarily change the gradient of the land surface. Because erosion rates are almost always sensitive to

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2090-484: Is an example of extreme chemical erosion. Glaciers erode predominantly by three different processes: abrasion/scouring, plucking , and ice thrusting. In an abrasion process, debris in the basal ice scrapes along the bed, polishing and gouging the underlying rocks, similar to sandpaper on wood. Scientists have shown that, in addition to the role of temperature played in valley-deepening, other glaciological processes, such as erosion also control cross-valley variations. In

2185-467: Is characterized by its nearly ideal 1:1 stoichiometric ratio of magnesium to calcium. It is distinct from high-magnesium limestone in that the magnesium and calcium form ordered layers within the individual dolomite mineral grains, rather than being arranged at random, as they are in high-magnesium calcite grains. In natural dolomite, magnesium is typically between 44 and 50 percent of total magnesium plus calcium, indicating some substitution of calcium into

2280-409: Is distinguished from changes on the bed of the watercourse, which is referred to as scour . Erosion and changes in the form of river banks may be measured by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times. Thermal erosion is the result of melting and weakening permafrost due to moving water. It can occur both along rivers and at

2375-413: Is known as dolomitic limestone . The "dolomite problem" refers to the vast worldwide depositions of dolomite in the past geologic record in contrast to the limited amounts of dolomite formed in modern times. Recent research has revealed sulfate-reducing bacteria living in anoxic conditions precipitate dolomite which indicates that some past dolomite deposits may be due to microbial activity. Dolomite

2470-626: Is no consistent trend in its abundance with age, but most dolomite appears to have formed at high stands of sea level. Little dolomite is found in Cenozoic beds (beds less than 65 million years old), which has been a time of generally low sea levels. Times of high sea level also tend to be times of a greenhouse Earth , and it is possible that greenhouse conditions are the trigger for dolomite formation. Many dolomites show clear textural indications that they are secondary dolomites, formed by replacement of limestone. However, although much research has gone into understanding this process of dolomitization ,

2565-423: Is not seen to precipitate in the oceans. Likewise, geologists have not been successful at precipitating dolomite from seawater at normal temperatures and pressures in laboratory experiments. This is likely due to a very high activation energy for nucleating crystals of dolomite. The magnesium ion is a relatively small ion, and it acquires a tightly bound hydration shell when dissolved in water. In other words,

2660-405: Is of two primary varieties: deflation , where the wind picks up and carries away loose particles; and abrasion , where surfaces are worn down as they are struck by airborne particles carried by wind. Deflation is divided into three categories: (1) surface creep , where larger, heavier particles slide or roll along the ground; (2) saltation , where particles are lifted a short height into

2755-503: Is removed from an area by dissolution . Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres. Agents of erosion include rainfall ; bedrock wear in rivers ; coastal erosion by the sea and waves ; glacial plucking , abrasion , and scour; areal flooding; wind abrasion; groundwater processes; and mass movement processes in steep landscapes like landslides and debris flows . The rates at which such processes act control how fast

2850-419: Is resistant to erosion and can either contain bedded layers or be unbedded. It is less soluble than limestone in weakly acidic groundwater , but it can still develop solution features ( karst ) over time. Dolomite rock can act as an oil and natural gas reservoir. Dolomite takes its name from the 18th-century French mineralogist Déodat Gratet de Dolomieu (1750–1801), who was one of the first to describe

2945-416: Is secondary, formed by replacement of calcium by magnesium in limestone. The preservation of the original limestone texture can range from almost perfectly preserved to completely destroyed. Under a microscope, dolomite rhombs are sometimes seen to replace oolites or skeletal particles of the original limestone. There is sometimes selective replacement of fossils, with the fossil remaining mostly calcite and

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3040-404: Is sparse and soil is dry (and so is more erodible). Other climatic factors such as average temperature and temperature range may also affect erosion, via their effects on vegetation and soil properties. In general, given similar vegetation and ecosystems, areas with more precipitation (especially high-intensity rainfall), more wind, or more storms are expected to have more erosion. In some areas of

3135-538: Is stained by Alizarin Red S while dolomite grains are not. Dolomite rock consisting of well-formed grains with planar surfaces is described as planar or idiotopic dolomite, while dolomite consisting of poorly-formed grains with irregular surfaces is described as nonplanar or xenotopic dolomite. The latter likely forms by recrystallization of existing dolomite at elevated temperature (over 50 to 100 °C (122 to 212 °F)). The texture of dolomite often shows that it

3230-543: Is subject to high rates of evaporation. This results in precipitation of gypsum and aragonite , raising the magnesium to calcium ratio of the remaining brine. The brine is also dense, so it sinks into the pore space of any underlying limestone ( seepage refluxion ), flushing out the existing pore fluid and causing dolomitization. The Permian Basin of North America has been put forward as an example of an environment in which this process took place. A variant of this model has been proposed for sabkha environments in which brine

3325-630: Is sucked up into the dolomitizing limestone by evaporation of capillary fluids, a process called evaporative pumping . Another model is the mixing-zone or Dorag model, in which meteoric water mixes with seawater already present in the pore space, increasing the chemical activity of magnesium relative to calcium and causing dolomitization. The formation of Pleistocene dolomite reefs in Jamaica has been attributed to this process. However, this model has been heavily criticized, with one 2004 review paper describing it bluntly as "a myth". A 2021 paper argued that

3420-514: Is the action of surface processes (such as water flow or wind ) that removes soil , rock , or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited . Erosion is distinct from weathering which involves no movement. Removal of rock or soil as clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material

3515-457: Is the main climatic factor governing soil erosion by water. The relationship is particularly strong if heavy rainfall occurs at times when, or in locations where, the soil's surface is not well protected by vegetation . This might be during periods when agricultural activities leave the soil bare, or in semi-arid regions where vegetation is naturally sparse. Wind erosion requires strong winds, particularly during times of drought when vegetation

3610-476: Is thermodynamically favorable, with a Gibbs free energy of about -2.2 kcal/mol. In theory, ordinary seawater contains sufficient dissolved magnesium to cause dolomitization. However, because of the very slow rate of diffusion of ions in solid mineral grains at ordinary temperatures, the process can occur only by simultaneous dissolution of calcite and crystallization of dolomite. This in turn requires that large volumes of magnesium-bearing fluids are flushed through

3705-400: Is where particles/sea load carried by the waves are worn down as they hit each other and the cliffs. This then makes the material easier to wash away. The material ends up as shingle and sand. Another significant source of erosion, particularly on carbonate coastlines, is boring, scraping and grinding of organisms, a process termed bioerosion . Sediment is transported along the coast in

3800-658: The Great Plains , it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years. Mass wasting or mass movement is the downward and outward movement of rock and sediments on a sloped surface, mainly due to the force of gravity . Mass wasting is an important part of the erosional process and is often the first stage in the breakdown and transport of weathered materials in mountainous areas. It moves material from higher elevations to lower elevations where other eroding agents such as streams and glaciers can then pick up

3895-651: The Proterozoic igneous core of the mountains. In the outcrop area the Bonneterre has an average thickness of 375 to 400 feet. It is present in the subsurface throughout Missouri and has a maximum recorded thickness of 1580 feet under Pemiscot County in the Missouri Bootheel . The dolomites and limestones of the Bonneterre Formation contain fossils of late Cambrian invertebrates. Algal stromatolites , echinoderms , and microfossils such as Girvanella are associated with fringing reef paleoecosystems surrounding

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3990-700: The Timanides of Northern Russia. Erosion of this orogen has produced sediments that are now found in the East European Platform , including the Cambrian Sablya Formation near Lake Ladoga . Studies of these sediments indicate that it is likely that the erosion of the orogen began in the Cambrian and then intensified in the Ordovician . If the erosion rate exceeds soil formation , erosion destroys

4085-416: The accumulation zone above the glacial equilibrium line altitude), which causes increased rates of erosion of the mountain, decreasing mass faster than isostatic rebound can add to the mountain. This provides a good example of a negative feedback loop . Ongoing research is showing that while glaciers tend to decrease mountain size, in some areas, glaciers can actually reduce the rate of erosion, acting as

4180-405: The impact of a falling raindrop creates a small crater in the soil , ejecting soil particles. The distance these soil particles travel can be as much as 0.6 m (2.0 ft) vertically and 1.5 m (4.9 ft) horizontally on level ground. If the soil is saturated , or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs. If

4275-455: The lower crust and mantle . Because tectonic processes are driven by gradients in the stress field developed in the crust, this unloading can in turn cause tectonic or isostatic uplift in the region. In some cases, it has been hypothesised that these twin feedbacks can act to localize and enhance zones of very rapid exhumation of deep crustal rocks beneath places on the Earth's surface with extremely high erosion rates, for example, beneath

4370-407: The surface runoff which may result from rainfall, produces four main types of soil erosion : splash erosion , sheet erosion , rill erosion , and gully erosion . Splash erosion is generally seen as the first and least severe stage in the soil erosion process, which is followed by sheet erosion, then rill erosion and finally gully erosion (the most severe of the four). In splash erosion ,

4465-499: The 21st century, a strong link has been drawn between the increase in storm frequency with an increase in sediment load in rivers and reservoirs, highlighting the impacts climate change can have on erosion. Vegetation acts as an interface between the atmosphere and the soil. It increases the permeability of the soil to rainwater, thus decreasing runoff. It shelters the soil from winds, which results in decreased wind erosion, as well as advantageous changes in microclimate. The roots of

4560-487: The Cambrian islands that are now the St. Francois Mountains . A variety of trilobite fossils have been reported from the Bonneterre, including Coosella , Holcacephalus , Meteoraspis , Tricrepicephalus , and Welleraspis . Several monoplacophorans have also been described from the Bonneterre; one, Hypseloconus bonneterrense is named for the formation. Dolomite (rock) Dolomite (also known as dolomite rock , dolostone or dolomitic rock )

4655-433: The air, and bounce and saltate across the surface of the soil; and (3) suspension , where very small and light particles are lifted into the air by the wind, and are often carried for long distances. Saltation is responsible for the majority (50–70%) of wind erosion, followed by suspension (30–40%), and then surface creep (5–25%). Wind erosion is much more severe in arid areas and during times of drought. For example, in

4750-463: The base along with the glacier. This method produced some of the many thousands of lake basins that dot the edge of the Canadian Shield . Differences in the height of mountain ranges are not only being the result tectonic forces, such as rock uplift, but also local climate variations. Scientists use global analysis of topography to show that glacial erosion controls the maximum height of mountains, as

4845-512: The coast. Rapid river channel migration observed in the Lena River of Siberia is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials. Much of this erosion occurs as the weakened banks fail in large slumps. Thermal erosion also affects the Arctic coast , where wave action and near-shore temperatures combine to undercut permafrost bluffs along

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4940-409: The coastline. Where there is a bend in the coastline, quite often a buildup of eroded material occurs forming a long narrow bank (a spit ). Armoured beaches and submerged offshore sandbanks may also protect parts of a coastline from erosion. Over the years, as the shoals gradually shift, the erosion may be redirected to attack different parts of the shore. Erosion of a coastal surface, followed by

5035-411: The direction of the prevailing current ( longshore drift ). When the upcurrent supply of sediment is less than the amount being carried away, erosion occurs. When the upcurrent amount of sediment is greater, sand or gravel banks will tend to form as a result of deposition . These banks may slowly migrate along the coast in the direction of the longshore drift, alternately protecting and exposing parts of

5130-405: The extremely steep terrain of Nanga Parbat in the western Himalayas . Such a place has been called a " tectonic aneurysm ". Human land development, in forms including agricultural and urban development, is considered a significant factor in erosion and sediment transport , which aggravate food insecurity . In Taiwan, increases in sediment load in the northern, central, and southern regions of

5225-575: The flood regions result from glacial Lake Missoula , which created the channeled scablands in the Columbia Basin region of eastern Washington . Wind erosion is a major geomorphological force, especially in arid and semi-arid regions. It is also a major source of land degradation, evaporation, desertification, harmful airborne dust, and crop damage—especially after being increased far above natural rates by human activities such as deforestation , urbanization , and agriculture . Wind erosion

5320-531: The formation of dolomite helps explain the rarity of Cenozoic dolomites, since Cenozoic seawater temperatures seldom exceeded 40 °C. It is possible that microorganisms are capable of precipitating primary dolomite. This was first demonstrated in samples collected at Lagoa Vermelha , Brazil in association with sulfate-reducing bacteria ( Desulfovibrio ), leading to the hypothesis that sulfate ion inhibits dolomite nucleation. Later laboratory experiments suggest bacteria can precipitate dolomite independently of

5415-479: The forms of stalactites , stalagmites , flowstone etc., can also form in caves within dolomite rock. “Dolomite is a common rock type, but a relatively uncommon mineral in speleothems”. Both the 'Union Internationale de Spéléologie' (UIS) and the American 'National Speleological Society' (NSS), extensively use in their publications, the terms "dolomite" or "dolomite rock" when referring to the natural bedrock containing

5510-404: The greater temperatures characterizing deeper burial, if a mechanism exists to flush magnesium-bearing fluids through the beds. Mineral dolomite has a 12% to 13% smaller volume than calcite per alkali cation. Thus dolomitization likely increases porosity and contributes to the sugary texture of dolomite. Dolomite is supersaturated in normal seawater by a factor of greater than ten, but dolomite

5605-417: The growth of protective vegetation ( rhexistasy ) are a key element of badland formation. Valley or stream erosion occurs with continued water flow along a linear feature. The erosion is both downward , deepening the valley , and headward , extending the valley into the hillside, creating head cuts and steep banks. In the earliest stage of stream erosion, the erosive activity is dominantly vertical,

5700-411: The island can be tracked with the timeline of development for each region throughout the 20th century. The intentional removal of soil and rock by humans is a form of erosion that has been named lisasion . Mountain ranges take millions of years to erode to the degree they effectively cease to exist. Scholars Pitman and Golovchenko estimate that it takes probably more than 450 million years to erode

5795-409: The local slope (see above), this will change the rates of erosion in the uplifted area. Active tectonics also brings fresh, unweathered rock towards the surface, where it is exposed to the action of erosion. However, erosion can also affect tectonic processes. The removal by erosion of large amounts of rock from a particular region, and its deposition elsewhere, can result in a lightening of the load on

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5890-437: The magnesium ion is surrounded by a clump of water molecules that are strongly attracted to its positive charge. Calcium is a larger ion and this reduces the strength of binding of its hydration shell, so it is much easier for a calcium ion than a magnesium ion to shed its hydration shell and bind to a growing crystal. It is also more difficult to nucleate a seed crystal of ordered dolomite than disordered high-magnesium calcite. As

5985-461: The magnesium layers. A small amount of ferrous iron typically substitutes for magnesium, particularly in more ancient dolomites. Carbonate rock tends to be either almost all calcite or almost all dolomite, with intermediate compositions being quite uncommon. Dolomite outcrops are recognized in the field by their softness (mineral dolomite has a Mohs hardness of 4 or less, well below common silicate minerals) and because dolomite bubbles feebly when

6080-418: The material and move it to even lower elevations. Mass-wasting processes are always occurring continuously on all slopes; some mass-wasting processes act very slowly; others occur very suddenly, often with disastrous results. Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a landslide . However, landslides can be classified in a much more detailed way that reflects

6175-407: The material has begun to slide downhill. In some cases, the slump is caused by water beneath the slope weakening it. In many cases it is simply the result of poor engineering along highways where it is a regular occurrence. Surface creep is the slow movement of soil and rock debris by gravity which is usually not perceptible except through extended observation. However, the term can also describe

6270-451: The mechanism of dolomitization, the tendency of carbonate rock to be either almost all calcite or almost all dolomite suggests that, once the process is started, it completes rapidly. The process likely occurs at shallow depths of burial, under 100 meters (330 ft), where there is an inexhaustible supply of magnesium-rich seawater and the original limestone is more likely to be porous. On the other hand, dolomitization can proceed rapidly at

6365-438: The mechanisms responsible for the movement and the velocity at which the movement occurs. One of the visible topographical manifestations of a very slow form of such activity is a scree slope. Slumping happens on steep hillsides, occurring along distinct fracture zones, often within materials like clay that, once released, may move quite rapidly downhill. They will often show a spoon-shaped isostatic depression , in which

6460-571: The microscope, thin sections of dolomite usually show individual grains that are well-shaped rhombs , with considerable pore space. As a result, subsurface dolomite is generally more porous than subsurface limestone and makes up 80% of carbonate rock petroleum reservoirs . This texture contrasts with limestone, which is usually a mixture of grains, micrite (very fine-grained carbonate mud) and sparry cement. The optical properties of calcite and mineral dolomite are difficult to distinguish, but calcite almost never crystallizes as regular rhombs, and calcite

6555-427: The mineral. The term dolomite refers to both the calcium-magnesium carbonate mineral and to sedimentary rock formed predominantly of this mineral. The term dolostone was introduced in 1948 to avoid confusion between the two. However, the usage of the term dolostone is controversial, because the name dolomite was first applied to the rock during the late 18th century and thus has technical precedence. The use of

6650-492: The mixing zone serves as domain of intense microbial activity which promotes dolomitization. A third model postulates that normal seawater is the dolomitizing fluid, and the necessary large volumes are flushed through the dolomitizing limestone through tidal pumping. Dolomite formation at Sugarloaf Key , Florida, may be an example of this process. A similar process might occur during rises in sea level, as large volumes of water move through limestone platform rock. Regardless of

6745-484: The morphologic impact of glaciations on active orogens, by both influencing their height, and by altering the patterns of erosion during subsequent glacial periods via a link between rock uplift and valley cross-sectional shape. At extremely high flows, kolks , or vortices are formed by large volumes of rapidly rushing water. Kolks cause extreme local erosion, plucking bedrock and creating pothole-type geographical features called rock-cut basins . Examples can be seen in

6840-404: The most erosion occurs during times of flood when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone that erodes: suspended abrasive particles, pebbles , and boulders can also act erosively as they traverse a surface, in a process known as traction . Bank erosion is the wearing away of the banks of a stream or river. This

6935-413: The most stable polymorph form of calcite. Speleothem types known to have a dolomite constituent include: coatings, crusts, moonmilk , flowstone , coralloids, powder, spar and rafts. Although there are reports of dolomite speleothems known to exist in a number of caves around the world, they are usually in relatively small quantities and form in very fine-grained deposits. Erosion Erosion

7030-553: The name were in a more restricted sense equivalent to the modern Bonneterre. In 1901, Frank Lewis Nason was the first to apply the name Bonneterre (originally spelled Bonne Terre) to these rocks, identifying a type section near the city of Bonne Terre, Missouri . The Bonneterre is conformably overlain by the Davis Formation . The Bonneterre Formation lies conformably on the Lamotte Sandstone and in places lies directly on

7125-531: The natural rate of erosion in the region. Excessive (or accelerated) erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes ) ecological collapse , both because of loss of the nutrient-rich upper soil layers . In some cases, this leads to desertification . Off-site effects include sedimentation of waterways and eutrophication of water bodies , as well as sediment-related damage to roads and houses. Water and wind erosion are

7220-434: The nutrient-rich upper soil layers . In some cases, the eventual result is desertification . Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses. Water and wind erosion are the two primary causes of land degradation ; combined, they are responsible for about 84% of the global extent of degraded land , making excessive erosion one of

7315-411: The order of a few centimetres (about an inch) or less and along-channel slopes may be quite steep. This means that rills exhibit hydraulic physics very different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when runoff water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to

7410-556: The plants bind the soil together, and interweave with other roots, forming a more solid mass that is less susceptible to both water and wind erosion. The removal of vegetation increases the rate of surface erosion. The topography of the land determines the velocity at which surface runoff will flow, which in turn determines the erosivity of the runoff. Longer, steeper slopes (especially those without adequate vegetative cover) are more susceptible to very high rates of erosion during heavy rains than shorter, less steep slopes. Steeper terrain

7505-427: The pore space in the dolomitizing limestone. Several processes have been proposed for dolomitization. The hypersaline model (also known as the evaporative reflux model ) is based on the observation that dolomite is very commonly found in association with limestone and evaporites , with the limestone often interbedded with the dolomite. According to this model, dolomitization takes place in a closed basin where seawater

7600-401: The process remains poorly understood. There are also fine-grained dolomites showing no textural indications that they formed by replacement, and it is uncertain whether they formed by replacement of limestone that left no textural traces or are true primary dolomites. This dolomite problem was first recognized over two centuries ago but is still not fully resolved. The dolomitization reaction

7695-456: The question of whether this can lead to precipitation of dolomite. Dolomitization can sometimes be reversed, and a dolomite bed converted back to limestone. This is indicated by a texture of pseudomorphs of mineral dolomite that have been replaced with calcite. Dedolomitized limestone is typically associated with gypsum or oxidized pyrite , and dedolomitization is thought to occur at very shallow depths through infiltration of surface water with

7790-413: The relief between mountain peaks and the snow line are generally confined to altitudes less than 1500 m. The erosion caused by glaciers worldwide erodes mountains so effectively that the term glacial buzzsaw has become widely used, which describes the limiting effect of glaciers on the height of mountain ranges. As mountains grow higher, they generally allow for more glacial activity (especially in

7885-828: The rolling of dislodged soil particles 0.5 to 1.0 mm (0.02 to 0.04 in) in diameter by wind along the soil surface. On the continental slope , erosion of the ocean floor to create channels and submarine canyons can result from the rapid downslope flow of sediment gravity flows , bodies of sediment-laden water that move rapidly downslope as turbidity currents . Where erosion by turbidity currents creates oversteepened slopes it can also trigger underwater landslides and debris flows . Turbidity currents can erode channels and canyons into substrates ranging from recently deposited unconsolidated sediments to hard crystalline bedrock. Almost all continental slopes and deep ocean basins display such channels and canyons resulting from sediment gravity flows and submarine canyons act as conduits for

7980-515: The runoff has sufficient flow energy , it will transport loosened soil particles ( sediment ) down the slope. Sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of

8075-532: The shoreline and cause them to fail. Annual erosion rates along a 100-kilometre (62-mile) segment of the Beaufort Sea shoreline averaged 5.6 metres (18 feet) per year from 1955 to 2002. Most river erosion happens nearer to the mouth of a river. On a river bend, the longest least sharp side has slower moving water. Here deposits build up. On the narrowest sharpest side of the bend, there is faster moving water so this side tends to erode away mostly. Rapid erosion by

8170-593: The soil. Lower rates of erosion can prevent the formation of soil features that take time to develop. Inceptisols develop on eroded landscapes that, if stable, would have supported the formation of more developed Alfisols . While erosion of soils is a natural process, human activities have increased by 10-40 times the rate at which erosion occurs globally. Excessive (or accelerated) erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes ) ecological collapse , both because of loss of

8265-400: The sulfate concentration. With time other pathways of interaction between microbial activity and dolomite formation have been added to the discord regarding their role in modulation and generation of polysaccharides , manganese and zinc within the porewater. Meanwhile, a contrary view held by other researchers is that microorganisms precipitate only high-magnesium calcite but leave open

8360-422: The surrounding matrix composed of dolomite grains. Sometimes dolomite rhombs are seen cut across the fossil outline. However, some dolomite shows no textural indications that it was formed by replacement of limestone. Dolomite is widespread in its occurrences, though not as common as limestone. It is typically found in association with limestone or evaporite beds and is often interbedded with limestone. There

8455-526: The term dolostone was not recommended by the Glossary of Geology published by the American Geological Institute . In old USGS publications, dolomite was referred to as magnesian limestone , a term now reserved for magnesium -deficient dolomites or magnesium-rich limestones. Dolomite rock is defined as sedimentary carbonate rock composed of more than 50% mineral dolomite . Dolomite

8550-433: The terminus or during glacier retreat . The best-developed glacial valley morphology appears to be restricted to landscapes with low rock uplift rates (less than or equal to 2mm per year) and high relief, leading to long-turnover times. Where rock uplift rates exceed 2mm per year, glacial valley morphology has generally been significantly modified in postglacial time. Interplay of glacial erosion and tectonic forcing governs

8645-409: The transfer of sediment from the continents and shallow marine environments to the deep sea. Turbidites , which are the sedimentary deposits resulting from turbidity currents, comprise some of the thickest and largest sedimentary sequences on Earth, indicating that the associated erosional processes must also have played a prominent role in Earth's history. The amount and intensity of precipitation

8740-563: The two primary causes of land degradation ; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant environmental problems worldwide. Intensive agriculture , deforestation , roads , anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion. However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall , and

8835-427: The valleys have a typical V-shaped cross-section and the stream gradient is relatively steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain. The stream gradient becomes nearly flat, and lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far

8930-550: The world (e.g. western Europe ), runoff and erosion result from relatively low intensities of stratiform rainfall falling onto the previously saturated soil. In such situations, rainfall amount rather than intensity is the main factor determining the severity of soil erosion by water. According to the climate change projections, erosivity will increase significantly in Europe and soil erosion may increase by 13–22.5% by 2050 In Taiwan , where typhoon frequency increased significantly in

9025-491: The world (e.g. the mid-western US ), rainfall intensity is the primary determinant of erosivity (for a definition of erosivity check, ) with higher intensity rainfall generally resulting in more soil erosion by water. The size and velocity of rain drops is also an important factor. Larger and higher-velocity rain drops have greater kinetic energy , and thus their impact will displace soil particles by larger distances than smaller, slower-moving rain drops. In other regions of

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