Misplaced Pages

#336663

40-529: The Kendlbach Formation consists of clay-rich marls and other sediments deposited during and immediately after the Triassic-Jurassic extinction event at the end of the Rhaetian stage. It has two subunits: the thick Tiefengraben Member, which is deprived of limestone , and the succeeding Breitenberg Member, a thinner sequence which shows the return of limestone. Like the underlying Kössen Formation, sediments of

80-414: A hard, fissile, metamorphic rock known as slate . With continued increase in metamorphic grade the sequence is phyllite , then schist and finally gneiss . Shale is the most common source rock for hydrocarbons ( natural gas and petroleum ). The lack of coarse sediments in most shale beds reflects the absence of strong currents in the waters of the depositional basin. These might have oxygenated

120-521: 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

160-482: 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 . 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

200-673: Is calcite , but other carbonate minerals such as aragonite or 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. 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. Such alternating cycles of chalk and marl are common in Cretaceous beds of northwestern Europe. The Channel Tunnel follows these marl layers between France and

240-1201: Is accompanied by telogenesis , the third and final stage of diagenesis. As erosion reduces the depth of burial, renewed exposure to meteoric water produces additional changes to the shale, such as dissolution of some of the cement to produce secondary porosity . Pyrite may be oxidized to produce gypsum . Black shales are dark, as a result of being especially rich in unoxidized carbon . Common in some Paleozoic and Mesozoic strata , black shales were deposited in anoxic , reducing environments, such as in stagnant water columns. Some black shales contain abundant heavy metals such as molybdenum , uranium , vanadium , and zinc . The enriched values are of controversial origin, having been alternatively attributed to input from hydrothermal fluids during or after sedimentation or to slow accumulation from sea water over long periods of sedimentation. Fossils , animal tracks or burrows and even raindrop impressions are sometimes preserved on shale bedding surfaces. Shales may also contain concretions consisting of pyrite, apatite , or various carbonate minerals. Shales that are subject to heat and pressure of metamorphism alter into

280-485: 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

320-420: Is characterized by its tendency to split into thin layers ( laminae ) less than one centimeter in thickness. This property is called fissility . Shale is the most common sedimentary rock. The term shale is sometimes applied more broadly, as essentially a synonym for mudrock , rather than in the narrower sense of clay-rich fissile mudrock. Shale typically exhibits varying degrees of fissility. Because of

360-638: Is composed of about 58% clay minerals, 28% quartz, 6% feldspar , 5% carbonate minerals, and 2% iron oxides . Most of the quartz is detrital (part of the original sediments that formed the shale) rather than authigenic (crystallized within the shale after deposition). Shales and other mudrocks contain roughly 95 percent of the organic matter in all sedimentary rocks. However, this amounts to less than one percent by mass in an average shale. Black shales, which form in anoxic conditions, contain reduced free carbon along with ferrous iron (Fe ) and sulfur (S ). Amorphous iron sulfide , along with carbon, produce

400-430: Is evidence that shale acts as a semipermeable medium, allowing water to pass through while retaining dissolved salts. The fine particles that compose shale can remain suspended in water long after the larger particles of sand have been deposited. As a result, shales are typically deposited in very slow moving water and are often found in lakes and lagoonal deposits, in river deltas , on floodplains and offshore below

440-455: Is more likely to form nonfissile mudstone than shale. On the other hand, black shales often have very pronounced fissility ( paper shales ) due to binding of hydrocarbon molecules to the faces of the clay particles, which weakens the binding between particles. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as

SECTION 10

#1732852075337

480-452: Is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution . Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. It is during compaction that shale develops its fissility, likely through mechanical compaction of

520-461: Is today often used to describe indurated marine deposits and lacustrine (lake) 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 argillaceous limestone . It has a blocky subconchoidal fracture, and is less fissile than shale . The dominant carbonate mineral in most marls

560-399: The U.S. Gulf Coast . As sediments continue to accumulate, the older, more deeply buried sediments begin to undergo diagenesis . This mostly consists of compaction and lithification of the clay and silt particles. Early stages of diagenesis, described as eogenesis , take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in

600-599: The wave base . Thick deposits of shale are found near ancient continental margins and foreland basins . Some of the most widespread shale formations were deposited by epicontinental seas . Black shales are common in Cretaceous strata on the margins of the Atlantic Ocean , where they were deposited in fault -bounded silled basins associated with the opening of the Atlantic during the breakup of Pangaea . These basins were anoxic, in part because of restricted circulation in

640-464: 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

680-482: 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

720-713: The Kendlbach Formation were deposited within the Eiberg Basin, a seaway which developed along the northwest tip of the Neotethys Ocean in the region now occupied by the Northern Calcareous Alps . The boundary between the Kössen and Kendlbach formations is marked by a sharp transition from limestone to dark shales and marls. The boundary also shows a strong negative δ C organic carbon isotope excursion as well as

760-624: The Schattwald Beds occur the first fossils of Jurassic ammonites such as Psiloceras spelae , indicating the formal beginning of the Jurassic period. This article about a specific stratigraphic formation in Austria is a stub . You can help Misplaced Pages by expanding it . This article related to the Jurassic period is a stub . You can help Misplaced Pages by expanding it . Marl Marl

800-585: The United Kingdom. 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. 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 pH and alkalinity , where its stems and fruiting bodies become calcified. After

840-478: 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 phosphate . Normal pond life is unable to survive, and skeletons of freshwater molluscs such as Sphaerium and Planorbis accumulate as part of

SECTION 20

#1732852075337

880-421: The black coloration. Because amorphous iron sulfide gradually converts to pyrite , which is not an important pigment, young shales may be quite dark from their iron sulfide content, in spite of a modest carbon content (less than 1%), while a black color in an ancient shale indicates a high carbon content. Most shales are marine in origin, and the groundwater in shale formations is often highly saline . There

920-594: 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 the dominant rock type in the Vaca Muerta Formation in Argentina. Marl has been used as a soil conditioner and neutralizing agent for acid soil and in the manufacture of Portland cement . Because some marls have

960-506: The clumps of clay particles produced by flocculation vary in size from a few tens of microns to over 700 microns in diameter. The floccules start out water-rich, but much of the water is expelled from the floccules as the clay minerals bind more tightly together over time (a process called syneresis ). Clay pelletization by organisms that filter feed is important where flocculation is inhibited. Filter feeders produce an estimated 12 metric tons of clay pellets per square kilometer per year along

1000-408: The color of the rock. Red, brown and green colors are indicative of ferric oxide ( hematite – reds), iron hydroxide ( goethite – browns and limonite – yellow), or micaceous minerals ( chlorite , biotite and illite – greens). The color shifts from reddish to greenish as iron in the oxidized ( ferric ) state is converted to iron in the reduced ( ferrous ) state. Black shale results from

1040-427: The extinction of many species of palynomorphs and marine invertebrates . The interval experiences an influx of freshwater palynomorphs , namely Classopollis pollen (from drought-tolerant Cheirolepidiaceae conifers ) followed by spores and Cymatiosphaera (a type of prasinophyte algae ). Some outcrops show a layer of reddish sediment, the Schattwald Beds, which follows the initial boundary interval. Above

1080-447: The marl lakes of the more remote parts of northern Scotland are likely to remain pristine into the near future. Shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g., kaolin , Al 2 Si 2 O 5 ( OH ) 4 ) and tiny fragments ( silt -sized particles) of other minerals, especially quartz and calcite . Shale

1120-577: 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 cement . 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 , formed under freshwater conditions. These typically contain 35–65% clay and 65–35% carbonate. The term

1160-592: The mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. The clay minerals may be altered as well. For example, smectite is altered to illite at temperatures of about 55 to 200 °C (130 to 390 °F), releasing water in the process. Other alteration reactions include the alteration of smectite to chlorite and of kaolinite to illite at temperatures between 120 and 150 °C (250 and 300 °F). Because of these reactions, illite composes 80% of Precambrian shales, versus about 25% of young shales. Unroofing of buried shale

1200-433: The narrow Atlantic, and in part because the very warm Cretaceous seas lacked the circulation of cold bottom water that oxygenates the deep oceans today. Most clay must be deposited as aggregates and floccules, since the settling rate of individual clay particles is extremely slow. Flocculation is very rapid once the clay encounters highly saline sea water. Whereas individual clay particles are less than 4 microns in size,

1240-415: The original open framework of clay particles. The particles become strongly oriented into parallel layers that give the shale its distinctive fabric. Fissility likely develops early in the compaction process, at relatively shallow depth, since fissility does not seem to vary with depth in thick formations. Kaolinite flakes have less tendency to align in parallel layers than other clays, so kaolinite-rich clay

Kendlbach Formation - Misplaced Pages Continue

1280-631: The parallel orientation of clay mineral flakes in shale, it breaks into thin layers, often splintery and usually parallel to the otherwise indistinguishable bedding planes . Non-fissile rocks of similar composition and particle size (less than 0.0625 mm) are described as mudstones (1/3 to 2/3 silt particles) or claystones (less than 1/3 silt). Rocks with similar particle sizes but with less clay (greater than 2/3 silt) and therefore grittier are siltstones . Shales are typically gray in color and are composed of clay minerals and quartz grains. The addition of variable amounts of minor constituents alters

1320-817: The presence of greater than one percent carbonaceous material and indicates a reducing environment. Pale blue to blue-green shales typically are rich in carbonate minerals . Clays are the major constituent of shales and other mudrocks. The clay minerals represented are largely kaolinite , montmorillonite and illite. Clay minerals of Late Tertiary mudstones are expandable smectites , whereas in older rocks (especially in mid-to early Paleozoic shales) illites predominate. The transformation of smectite to illite produces silica , sodium , calcium , magnesium , iron and water. These released elements form authigenic quartz , chert , calcite , dolomite , ankerite , hematite and albite , all trace to minor (except quartz) minerals found in shales and other mudrocks. A typical shale

1360-444: The richest source rocks may contain as much as 40% organic matter. The organic matter in shale is converted over time from the original proteins, polysaccharides , lipids , and other organic molecules to kerogen , which at the higher temperatures found at greater depths of burial is further converted to graphite and petroleum. Before the mid-19th century, the terms slate , shale and schist were not sharply distinguished. In

1400-433: The sediments, with only slight compaction. Pyrite may be formed in anoxic mud at this stage of diagenesis. Deeper burial is accompanied by mesogenesis , during which most of the compaction and lithification takes place. As the sediments come under increasing pressure from overlying sediments, sediment grains move into more compact arrangements, ductile grains (such as clay mineral grains) are deformed, and pore space

1440-798: The soil. 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. 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 silting , nutrient pollution , drainage , and invasive species . In Britain, only

1480-453: 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. Marl continues to be used for agriculture into

1520-414: The waters and destroyed organic matter before it could accumulate. The absence of carbonate rock in shale beds reflects the absence of organisms that might have secreted carbonate skeletons, also likely due to an anoxic environment. As a result, about 95% of organic matter in sedimentary rocks is found in shales and other mudrocks. Individual shale beds typically have an organic matter content of about 1%, but

1560-419: 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 pozzolan ( volcanic ash ) to

1600-638: Was used sporadically in Britain beginning in prehistoric times and its use 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 Industrial Revolution . Marl was used extensively in Britain, particularly in Lancashire , during

#336663