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53-424: Greensand forms in anoxic marine environments that are rich in organic detritus and low in sedimentary input. Having accumulated in marine environments, greensands can be fossil -rich, such as in the late- Cretaceous deposits of New Jersey . Important exposures are known from both northern and western Europe , North America , southeastern Brazil and north Africa . Well known and important greensands are

106-508: A natural phenomenon , and have occurred throughout geological history. The Permian–Triassic extinction event , a mass extinction of species from the world's oceans, may have resulted from widespread anoxic conditions combined with ocean acidification driven by a massive release of carbon dioxide into Earth's atmosphere. Many lakes have a permanent or temporary anoxic layer created by respiration depleting oxygen at depth and thermal stratification preventing its resupply. Anoxic basins exist in

159-633: A byproduct of agricultural run-off and sewage discharge, can result in large but short-lived algae blooms. Upon a bloom's conclusion, the dead algae sink to the bottom and are broken down until all oxygen is expended. Such a case is the Gulf of Mexico where a seasonal dead zone occurs, which can be disturbed by weather patterns such as hurricanes and tropical convection. Sewage discharge, specifically that of nutrient concentrated "sludge", can be especially damaging to ecosystem diversity. Species sensitive to anoxic conditions are replaced by fewer hardier species, reducing

212-607: A line between Dunstable and Tatsfield and of uncertain extent to the east of London. Outcrops of the Upper Greensand occur in the southwest of England including the Blackdown Hills and East Devon Plateau and the Haldon Hills , remnants of a once much wider extent. The green color of greensand is due to variable amounts of the mineral glauconite , an iron potassium silicate with very low weathering resistance; as

265-728: A popular organic soil amendment. The porous properties of glauconite greensand allows for the absorption of water and minerals, making irrigation and nutrient delivery much more efficient (see soil conditioner ). Greensand can be used to absorb excess water in clay-rich soils and to prevent water loss in sandy soils. Anoxic sea water Anoxic waters are areas of sea water , fresh water , or groundwater that are depleted of dissolved oxygen . The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. Anoxic waters can be contrasted with hypoxic waters , which are low (but not lacking) in dissolved oxygen. This condition

318-529: A respiring organism is presented with little to no oxygen, chances of survival decrease. Therefore, eutrophication and anoxic conditions in water lead to a reduction in biodiversity. For example, the soft coral Xenia umbellata can resist some anoxic conditions for short periods. Still, after about three weeks, mean survival decreases to about 81%, and about 40% of surviving species experience size reductions, lessening in coloration, and compromised pinnate structures (Simancas-Giraldo et al., 2021). Another example of

371-404: A result, greensand tends to be weak and friable. It is a common ingredient as a source of potassium in organic gardening and farming fertilisers . Greensand glauconite is used as a water softener for its chemical-exchange properties. Greensand coated with manganese oxide (called manganese greensand) is used in well water treatment systems to remove dissolved (reduced) iron and manganese with

424-624: A series of geological strata laid down in the Cretaceous that have subsequently been lifted up, formed into a dome (i.e. anticline) and then deformed and faulted. The top-most and therefore youngest layer of the dome is Chalk , laid down in the Upper Cretaceous . Below it lie successively older strata of alternating clays and sandstones laid down in the Lower Cretaceous , namely Upper Greensand , Gault Clay , Lower Greensand , Weald Clay and

477-422: A susceptible organism is observed with The Sydney Cockle, Anadara trapezia . Enriched sediments have lethal and sublethal effects on this Cockle and, as stated in [Vadillo Gonzalez et al., 2021], "movement of cockles was reduced in enriched sediments compared to natural treatments." A study collecting over 850 published experiments "reporting oxygen thresholds and/or lethal times for a total of 206 species spanning

530-584: A system of transhumance whereby each autumn swine would be driven, sometimes over long distances, from the longer-settled areas on the periphery into the Wealden forest to feed on acorns of oak trees and beech mast. For these peoples the term Weald did not include the land cleared of forest and settled earlier, such as the fertile Vale of Holmesdale (which separates the North Downs from the Greensand Ridge), nor

583-625: Is depleted in a basin, bacteria first turn to the second-best electron acceptor, which in sea water, is nitrate . Denitrification occurs, and the nitrate will be consumed rather rapidly. After reducing some other minor elements, the bacteria will turn to reducing sulfate . This results in the byproduct of hydrogen sulfide (H 2 S), a chemical toxic to most biota and responsible for the characteristic "rotten egg" smell and dark black sediment color: These sulfides will mostly be oxidized to either sulfates (~90%) in more oxygen-rich water or precipitated and converted into pyrite (~10%), according to

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636-451: Is generally found in areas that have restricted water exchange. In most cases, oxygen is prevented from reaching the deeper levels by a physical barrier, as well as by a pronounced density stratification, in which, for instance, heavier hypersaline waters rest at the bottom of a basin. Anoxic conditions will occur if the rate of oxidation of organic matter by bacteria is greater than the supply of dissolved oxygen . Anoxic waters are

689-585: Is made between the Upper Greensand and Lower Greensand. The term greensand was originally applied by William Smith to glauconitic sandstones in the west of England and subsequently used for the similar deposits of the Weald , before it was appreciated that the latter are actually two distinct formations separated by the Gault Clay . The Upper Greensand was also once known as either the "Malm" or "Malm Rock Of Western Sussex". Both Upper and Lower Greensand outcrops appear in

742-735: Is oxygen free. Anoxia is further influenced by biochemical oxygen demand (BOD), which is the amount of oxygen used by marine organisms in the process of breaking down organic matter. BOD is influenced by the type of organisms present, the pH of the water, temperature, and the type of organic matter present in the area. BOD is directly related to the amount of dissolved oxygen available, especially in smaller bodies of water such as rivers and streams. As BOD increases, available oxygen decreases. This causes stress on larger organisms. BOD comes from natural and anthropogenic sources, including: dead organisms, manure, wastewater, and urban runoff. Eutrophication , an influx of nutrients (phosphate/nitrate), often

795-609: Is quite varied, ranging from fertile to fairly sterile. On the fertile soils chestnut and stands of hazel and oak are common, while Scots pine and birch colonise the poorer soils. These Greensand Ridges are popular long distance walking routes, for instance the Greensand Way in Kent. The Lower Greensand (known as the Woburn Sand north of the London Basin ) is of Aptian age. In

848-502: Is separated by a mixed deep and shallow, fertile depression from the North Downs referred to as the ' Vale of Holmesdale ', formed on Gault Clay, and a narrow band of Upper Greensand that outcrops at the foot of the chalk scarp (ridge). In some places the clay vale is very narrow: for example at Oxted the gap between summits of the Greensand Ridge and the North Downs is less than 2 kilometres (1.2 mi). The Greensand Ridge, capped by

901-814: The Baltic Sea , the Black Sea , the Cariaco Trench , various fjord valleys, and elsewhere. Eutrophication has likely increased the extent of anoxic zones in areas including the Baltic Sea, the Gulf of Mexico , and Hood Canal in Washington State. Anoxic conditions result from a combination of environmental conditions including density stratification , inputs of organic material or other reducing agents , and physical barriers to water circulation. In fjords, shallow sills at

954-623: The Chalk Group which underlies the basin; the Gault lies directly on eroded Jurassic or Devonian rocks under much of the area. The Upper Greensand is of Albian age. It represents a sandy lithofacies deposited in areas of stronger currents than the Gault Clay . Like the Lower Greensand it is not present beneath the whole of the London Basin, apparently passing laterally into Gault clay east of

1007-646: The Chartlands , where it reaches another high point at Toys Hill , Kent (235 metres (771 ft)). Here there are views to the south of the Weald from a terrace donated in 1898 by Octavia Hill , one of the founders of the National Trust . The ridge continues eastwards past Sevenoaks, until south-west of Maidstone it is broken by the valley of the River Medway . The ridge then continues as far as Pluckley , Kent. From there

1060-628: The East Sussex coast, wrapping around the High Weald and Low Weald. It reaches its highest elevation, 294 metres (965 ft), at Leith Hill in Surrey—;the second highest point in south-east England , while another hill in its range, Blackdown , is the highest point in Sussex at 280 metres (919 ft). The eastern end of the ridge forms the northern boundary of Romney Marsh . About 51 per cent of

1113-531: The Greensand Way . Extending for 108 miles, it starts in the west at Haslemere and ends in the east at Ham Street, Kent, on the edge of Romney Marsh. The route passes through or close to Godalming, Cranleigh , Dorking , Reigate, South Nutfield, Oxted, Westerham , Sevenoaks , Maidstone and Ashford . The south-west part of the Greensand ridge and hills is in the South Downs National Park . Much of

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1166-589: The Hastings Beds . Differential fluvial erosion has virtually flattened the dome into a series of hills and vales. On the surface the strata of which the dome is composed crop out in a series of concentric circles, shaped like a horseshoe, with the more resistant chalk and sandstones forming hills and ridges (such as the North and South Downs, the Greensand Ridge, and the High Weald), and the weaker clays forming vales (such as

1219-613: The Low Weald ) between them. The very resistant rocks of the Lower Greensand, in particular the Hythe Beds, have produced prominent escarpments that form an arc around the northern edge of the Low Weald, running parallel to and just south of the chalk escarpment of the North Downs . This stretch of the Greensand has become the most closely identified with the term "Greensand Ridge", and it includes

1272-792: The Serra da Saudade Formation, Bambuí Group, of Neoproterozoic / Ediacaran age. The outcrops occur in the Serra da Saudade ridge, in Alto Paranaíba region, Minas Gerais . It is a silt-clay sedimentary rock, laminated, bluish-green, composed of glauconite (40–80%), potassium feldspar (10–15%), quartz (10–60%), muscovite (5%) and minor quantities of biotite (2%), goethite (<1%), titanium and manganese oxides (<1%), barium phosphate and rare-earth elements phosphates (<1%). Enriched levels of potash have K 2 O grades between 8% and 12%, thickness up to 50 m (160 ft) and are associated to

1325-516: The Bargate and Sandgate Layers, was much quarried for the cloth industry. The seam, which lies about 20 to 30 feet below the surface between Nutfield and Bletchingley, was considered the best in the country and for several centuries large quantities were excavated. Resources are now running low and little is now extracted. Principal settlements lying on the southern part of the Greensand in Sussex, adjacent to

1378-714: The Greensand Ridge in Surrey is one limb of the Surrey Hills Area of Outstanding Natural Beauty while a section of the Greensand hills in western Kent, from Limpsfield Chart near Westerham through Sevenoaks to Plaxtol , forms part of the Kent Downs Area of Outstanding Natural Beauty , where it is known as the Sevenoaks Greensand Ridge . Hills on the Greensand Ridge at least 200 metres high and with 30 metres or more of topographical prominence are here listed, along

1431-406: The Greensand is quite varied, ranging from fertile to fairly sterile. On the fertile soils we see chestnut and stands of hazel and oak , while Scots Pine and Birch colonise the poorer soils. Broadly speaking, the Greensand Ridge runs along the northern edge of the Weald in a west-east arc from Surrey into Kent, just south of and parallel to the chalk escarpment of the North Downs. The ridge

1484-500: The Hythe Beds, have yielded a distinctive yellow stone seen in many local buildings. Ironstone, from layers embedded in the Sandgate Beds, is often seen in chips ( gallets ) pressed into the mortar between such stones. To the east, especially around Maidstone, Kent, the Hythe Beds yield a blue-grey sandstone with a high lime content. Known as ragstone, this is seen in many local buildings. Fuller's earth , which lies interbedded between

1537-455: The South Downs, include Storrington (at the eastern end of the ridge) and Midhurst . Petersfield marks the western end, where the ridge turns north east. Settlements on the main part of the ridge, running from Surrey into Kent include Haslemere , Godalming , Reigate and Redhill , Oxted and Sevenoaks . Much of the ridge in Surrey and Kent is followed by a long-distance walking route,

1590-608: The Upper and Lower Greensands of England and occur within Eocene and Cretaceous sedimentary strata underlying the coastal plains of New Jersey and Delaware . Although greensand has been found throughout Phanerozoic and Late Precambrian sedimentary deposits, it appears to be most common in Eocene, Cambrian , and Cretaceous sedimentary deposits. In Brazil , greensand refers to a fertilizer produced from glauconitic siltstone units belonging to

1643-455: The Weald and the "Wealden Anticline" that embraces all the land bounded by the chalk escarpments of the North and South Downs, including the Greensand hills. The Folkestone Beds consist of seams of pebbles and sand. It is from here that the stone known as chert is found, familiar in the High Chart hills around Limpsfield , Surrey. In Surrey the Sandgate Beds and Bargate Beds, which lie on top of

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1696-570: The Weald the Lower Greensand consists of four deposits which are partly diachronous : the Atherfield Clay 5–15 m (15–50 ft) thick, the Folkestone Beds 20–80 m (60–250 ft) thick; the Hythe beds 20–110 m (60–350 ft) thick and the Sandgate Beds 2–37 m (5–120 ft) thick. Although it appears both north and south of the London Basin it is not present everywhere beneath

1749-526: The Wealden Greensand is protected as the South Downs National Park , Kent Downs Area of Outstanding Natural Beauty and Surrey Hills Area of Outstanding Natural Beauty . The Greensand Ridge, formed of Lower Greensand , much of which is sandstone and where hardest is locally termed Bargate stone , is a remnant of the Weald dome, part of the great Weald-Artois Anticline that runs from south-east England into northern France. The Weald dome consists of

1802-507: The addition of an oxidant, usually potassium permanganate, under controlled pH conditions. It is also used as a type of rock for stone walls in areas where greensand is common. In Roman times in Britain, coarse grits derived from the lower greensand were used to line the inner surface of mortars (grinding bowls) produced in Oxfordshire pottery kilns. Recently, glauconitic greensand has become

1855-419: The amount of dissolved oxygen it can hold. Following Henry's law , as water becomes warmer, oxygen becomes less soluble in it. This property leads to daily anoxic cycles on small geographic scales and seasonal cycles of anoxia on larger scales. Thus, bodies of water are more vulnerable to anoxic conditions during the warmest period of the day and during summer months. This problem can be further exacerbated in

1908-411: The entrance may prevent circulation, while at continental boundaries, circulation may be especially low while organic material input from production at upper levels is exceptionally high. In wastewater treatment , the absence of oxygen alone is indicated anoxic while the term anaerobic is used to indicate the absence of any common electron acceptor such as nitrate , sulfate or oxygen. When oxygen

1961-443: The following chemical equations: Some chemolithotrophs can also facilitate the oxidation of hydrogen sulfide into elemental sulfur , according to the following chemical equation: Anoxia is quite common in muddy ocean bottoms where there are both high amounts of organic matter and low levels of inflow of oxygenated water through the sediment. Below a few centimeters from the surface the interstitial water (water between sediment)

2014-465: The full taxonomic range of benthic metazoans." Individual species will have different adaptive responses to anoxic conditions based on their biological makeup and the condition of their habitat. While some can pump oxygen from higher water levels down into the sediment, other adaptations include specific hemoglobins for low-oxygen environments, slow movement to reduce the rate of metabolism, and symbiotic relationships with anaerobic bacteria. In all cases,

2067-410: The further east one goes. The Lower Greensand is a predominantly arenaceous sandstone consisting of sediment that accumulated apparently in a shallow sea in the later part of the Lower Cretaceous . It also contains important subsidiary elements of silty and argillaceous material. Chert, ironstone and calcareous deposits occur in small amounts. When fresh the rocks have a greenish colouration owing to

2120-609: The glauconitic levels, dark green in color. Glauconite is authigenic and highly mature. The high concentration of this mineral is related to a depositional environment with a low sedimentation rate. The glauconitic siltstone has resulted from a high level flooding event in the Bambuí Basin. The sedimentary provenance is from supracrustal feldsic elements on a continental margin environment with an acidic magmatic arc (foreland basin). In Great Britain , greensand usually refers to specific rock strata of Early Cretaceous age. A distinction

2173-541: The highest point in Sussex. South of here the Vale of Fernhurst has been eroded down into the Low Weald by what is now a small stream following a line of a gentle west-east trending upfold. This stream, the River Lod , runs parallel to the larger River Rother which flows about 10 km further south in the lee of the chalk escarpment of the South Downs. Valley slope processes in the Vale of Fernhurst have resulted in escarpments to

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2226-506: The land levels until it drops to the old sea-cliff line above Romney Marsh. In the area around Haslemere local anticlinal features are superimposed on the main axis of the Wealden anticline, causing the outcrop of resistant Hythe Beds to widen from 2 kilometres (1.2 mi) to more than 12 kilometres (7.5 mi) and to produce an escarpment that is particularly marked between Haslemere and Midhurst, where Blackdown rises to 280 metres (920 ft),

2279-435: The later medieval colonisation of the Wealden portion of these parishes, called today Sevenoaks Weald, Sundridge Weald and Boughton Malherbe Weald. A practice of treating the Greensand Ridge regularly as part of the Weald arose in geology when natural scientists, starting in the late 18th century, began to include it in their analysis of the geological history of the Wealden dome. Geology still confuses by using interchangeably

2332-426: The more lightly wooded and open hills found on the sandstones of the Greensand Ridge, which also seem to have been settled earlier. Local people regarded the hills of the Greensand Ridge as overlooking the Weald, rather than forming a part of it, and hence a distinction came to be made between the settlements on the Greensand Ridge, such as Sevenoaks, Sundridge Upland and Boughton Malherbe Upland, and those formed during

2385-401: The north and south that are steep enough to have collapsed by land slipping. Further east, the Lower Greensand has not produced any pronounced topographical features. In many places along the escarpment of the Greensand Ridge erosion by wind and rain, landslips on the steep scarp face, and solifluction in glacial times have further combined to create steep-side coombes, and low hillocks below

2438-424: The overall variability of the affected area. Gradual environmental changes through eutrophication or global warming can cause major oxic-anoxic regime shifts. Based on model studies this can occur abruptly, with a transition between an oxic state dominated by cyanobacteria , and an anoxic state with sulfate-reducing bacteria and phototrophic sulfur bacteria . The temperature of a body of water directly affects

2491-495: The presence of glauconite , but on exposure to the atmosphere this is rapidly oxidised to limonite, giving rise to a yellow or reddish brown staining. The Lower Greensand is composed of alternating mudstones (sandy, with clay particles such as smectite ) and sandstones, up to a maximum thickness of about 400 metres (1,300 ft), and is composed of a number of distinct formations, namely the Folkestone Beds, Sandgate Beds, Bargate Beds, Hythe Beds and Atherfield Clay. The soil of

2544-516: The prevalence of excess nutrients results in low levels of biological activity and a lower level of species diversity if the area is not ordinarily anoxic. Greensand Ridge The Greensand Ridge , also known as the Wealden Greensand , is an extensive, prominent, often wooded, mixed greensand / sandstone escarpment in south-east England. Forming part of the Weald , a former dense forest in Sussex, Surrey and Kent, it runs to and from

2597-461: The resistant sands and sandstones of the Hythe Beds, reinforced by bands of chert , rises steeply as a series of high, wooded escarpments between Gibbet Hill, Hindhead (272 metres (892 ft)), north of Haslemere, and the ridge's highest point, Leith Hill (294 metres (965 ft)). It then flattens for several miles, before re-emerging east of Nutfield to run eastwards as a high wooded ridge into an area between Oxted and Sevenoaks known locally as

2650-845: The scarp slopes surrounding the London Basin and the Weald. Prominent seams are to be found in the Vale of White Horse , in Bedfordshire , in Kent , Surrey , the South Downs National Park , elsewhere in Hampshire , the Isle of Wight , and the Jurassic Coast in Dorset . Some minor seams are found further west in Devon in the Blackdown and Haldon hills. The soil of the greensand

2703-618: The scarp. The Greensand Ridge is sometimes associated with the Weald ; the ridge forms the high border of area of the Weald. The Jutes and Saxons who settled in south-east England in the centuries following the collapse of the Roman empire applied the term Weald (a Germanic term for woodland) to the very large, heavily wooded forest that they found lying inland of the coastal lands and river valleys that they initially settled. This forest, difficult to penetrate and settle, and difficult to exploit agriculturally, in due course became an essential part of

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2756-454: The second highest point in south-east England, Leith Hill in Surrey. West of the Weald the Lower Greensand has produced a more extensive area of hills and valleys, including the highest point in Sussex, Blackdown . On the south side of the Weald the Lower Greensand also forms another arc of rather less pronounced hills parallel to and just north of the South Downs , which become less prominent

2809-682: The vicinity of industrial discharge where warm water used to cool machinery is less able to hold oxygen than the basin to which it is released. Daily cycles are also influenced by the activity of photosynthetic organisms. The lack of photosynthesis during nighttime hours in the absence of light can result in anoxic conditions intensifying throughout the night with a maximum shortly after sunrise. Individual species’ reactions to eutrophication can vary widely. For example, some organisms, such as primary producers, can adapt quickly and even thrive under anoxic conditions. However, most organisms are highly susceptible to slight changes in aquatic oxygen levels. When

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