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94-655: Sediment samples from below the deep seafloor of the Mediterranean Sea, which include evaporite minerals, soils , and fossil plants, show that the precursor of the Strait of Gibraltar closed about 5.96 million years ago, sealing the Mediterranean off from the Atlantic. This resulted in a period of partial desiccation of the Mediterranean Sea, the first of several such periods during the late Miocene. After

188-525: A general circulation model can indicate physically consistent responses to the desiccation. There is no consensus as to whether the Mediterranean Sea dried out completely; it seems likeliest that at least three or four large brine lakes on the abyssal plains remained at all times. The extent of desiccation is very hard to judge, owing to the reflective seismic nature of the salt beds, and the difficulty in drilling cores, making it difficult to map their thickness. Atmospheric forces can be studied to arrive at

282-565: A desiccation of the sea. The main evidence for the evaporative drawdown of the Mediterranean comes from the remains of many (now submerged) canyons that were cut into the sides of the dry Mediterranean basin by rivers flowing down to the abyssal plain . For example, the Nile cut its bed down to 200 metres (660 feet) below sea level at Aswan (where Ivan S. Chumakov found marine Pliocene Foraminifera in 1967), and 2,500 m (8,200 ft) below sea level just north of Cairo . In many places in

376-661: A few percent of evaporite minerals, the remainder being composed of the more typical detrital clastic rocks and carbonates . Examples of evaporite formations include occurrences of evaporite sulfur in Eastern Europe and West Asia. For a formation to be recognised as evaporitic it may simply require recognition of halite pseudomorphs , sequences composed of some proportion of evaporite minerals, and recognition of mud crack textures or other textures . Evaporites are important economically because of their mineralogy, their physical properties in-situ, and their behaviour within

470-554: A flood-prone property to qualify for government-subsidized insurance, a local community must adopt an ordinance that protects the floodway and requires that new residential structures built in Special Flood Hazard Areas be elevated to at least the level of the 100-year flood. Commercial structures can be elevated or floodproofed to or above this level. In some areas without detailed study information, structures may be required to be elevated to at least two feet above

564-445: A floodplain. The quantity of sediments in a floodplain greatly exceeds the river load of sediments. Thus, floodplains are an important storage site for sediments during their transport from where they are generated to their ultimate depositional environment. When the rate at which the river is cutting downwards becomes great enough that overbank flows become infrequent, the river is said to have abandoned its floodplain. Portions of

658-620: A large waterfall higher than today's Angel Falls at 979 m (3,212 ft), and far more powerful than either the Iguazu Falls or the Niagara Falls , but recent studies of the underground structures at the Gibraltar Strait show that the flooding channel descended in a rather gradual way to the dry Mediterranean. An enormous deposit of unsorted debris washed in by a massive catastrophic flood-wash has been found in

752-437: A picture into past Earth climates. Some particular deposits even show important tectonic and climatic changes. These deposits also may contain important minerals that help in today's economy. Thick non-marine deposits that accumulate tend to form where evaporation rates will exceed the inflow rate, and where there is sufficient soluble supplies. The inflow also has to occur in a closed basin, or one with restricted outflow, so that

846-483: A role in forcing the periodic filling and emptying of the basins, and that tectonic factors must have played a part in controlling the height of the sills restricting flow between the Atlantic and Mediterranean. The magnitude and extent of these effects, however, is widely open to interpretation. In any case, the causes of the closing and isolation of the Mediterranean Sea from the Atlantic Ocean must be found in

940-591: A speculation on the climate. As winds blew across the "Mediterranean Sink ", they would heat or cool adiabatically with altitude. In the empty Mediterranean Basin, the summertime temperatures would probably have been extremely high. As a first approximation, using the dry adiabatic lapse rate of around 10 °C (18 °F) per kilometer, the maximum possible temperature of an area 4 km (2.5 mi) below sea level would be about 40 °C (72 °F) warmer than it would be at sea level. Under this extreme assumption, maxima would be near 80 °C (176 °F) at

1034-448: A synchronous deposition (image c) of the first evaporites in all the basins before the major phase of erosion; and the other that favours a diachronous deposition (image a) of the evaporites through more than one phases of desiccation which would first have affected the marginal basins and later the central basins. Another school suggests that desiccation was synchronous, but occurred mainly in shallower basins. This model would suggest that

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1128-460: A wind-blown cross-bedded deposit of deep-sea foraminiferal ooze that had dried into dust and been blown about on the hot dry abyssal plain by sandstorms , mixed with quartz sand blown in from nearby continents, and ended up in a brine lake interbedded between two layers of halite . These layers alternated with layers containing marine fossils, indicating a succession of drying and flooding periods. The massive presence of salt does not require

1222-491: Is a chart that shows minerals that form the marine evaporite rocks. They are usually the most common minerals that appear in this kind of deposit. Evaporite minerals start to precipitate when their concentration in water reaches such a level that they can no longer exist as solutes . The minerals precipitate out of solution in the reverse order of their solubilities, such that the order of precipitation from sea water is: The abundance of rocks formed by seawater precipitation

1316-546: Is a problem in freshwater systems. Much of the phosphorus in freshwater systems comes from municipal wastewater treatment plants and agricultural runoff. Stream connectivity controls whether phosphorus cycling is mediated by floodplain sediments or by external processes. Under conditions of stream connectivity, phosphorus is better able to be cycled, and sediments and nutrients are more readily retained. Water in freshwater streams ends up in either short-term storage in plants or algae or long-term in sediments. Wet/dry cycling within

1410-406: Is advantageous for the rapid colonization of large areas of the floodplain. This allows them to take advantage of shifting floodplain geometry. For example, floodplain trees are fast-growing and tolerant of root disturbance. Opportunists (such as birds) are attracted to the rich food supply provided by the flood pulse. Floodplain ecosystems have distinct biozones. In Europe, as one moves away from

1504-401: Is an area of land adjacent to a river . Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high discharge . The soils usually consist of clays, silts , sands, and gravels deposited during floods. Because of regular flooding, floodplains frequently have high soil-fertility since nutrients are deposited with

1598-498: Is any area subject to inundation by a 100-year flood. A problem is that any alteration of the watershed upstream of the point in question can potentially affect the ability of the watershed to handle water, and thus potentially affects the levels of the periodic floods. A large shopping center and parking lot, for example, may raise the levels of 5-year, 100-year, and other floods, but the maps are rarely adjusted and are frequently rendered obsolete by subsequent development. In order for

1692-541: Is considerably saltier than the North Atlantic , owing to its near isolation by the Strait of Gibraltar and its high rate of evaporation . If the Strait of Gibraltar closes again (which is likely to happen in the near future in geological time ), the Mediterranean would mostly evaporate in about a thousand years, after which continued northward movement of Africa may obliterate the Mediterranean altogether . Only

1786-460: Is described as vertical accretion , since the deposits build upwards. In undisturbed river systems, overbank flow is frequent, typically occurring every one to two years, regardless of climate or topography. Sedimentation rates for a three-day flood of the Meuse and Rhine Rivers in 1993 found average sedimentation rates in the floodplain of between 0.57 and 1.0 kg/m . Higher rates were found on

1880-466: Is in the same order as the precipitation given above. Thus, limestone (dolomite are more common than gypsum , which is more common than halite, which is more common than potassium and magnesium salts. Evaporites can also be easily recrystallized in laboratories in order to investigate the conditions and characteristics of their formation. Recent evidence from satellite observations and laboratory experiments suggest evaporites are likely present on

1974-565: Is largely a result of flood control, hydroelectric development (such as reservoirs), and conversion of floodplains to agriculture use. Transportation and waste disposal also have detrimental effects. The result is the fragmentation of these ecosystems, resulting in loss of populations and diversity and endangering the remaining fragments of the ecosystem. Flood control creates a sharper boundary between water and land than in undisturbed floodplains, reducing physical diversity. Floodplain forests protect waterways from erosion and pollution and reduce

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2068-402: Is most common in sections of rivers where the river bed is accumulating sediments ( aggrading ). Repeated flooding eventually builds up an alluvial ridge, whose natural levees and abandoned meander loops may stand well above most of the floodplain. The alluvial ridge is topped by a channel belt formed by successive generations of channel migration and meander cutoff. At much longer intervals,

2162-483: Is relied upon to compare the dates of sediments. The typical case study compares the gypsum evaporites in the main Mediterranean basin with those of the Sorbas basin , a smaller basin on the flanks of the Mediterranean Sea that is now exposed in southern Spain . The relationship between these two basins is assumed to represent the relationships of the wider region. Recent work has relied on cyclostratigraphy to correlate

2256-768: The Gibraltar Arc , the Calabrian Arc , and the Aegean Arc . The kinematics and dynamics of this plate boundary and of the Gibraltar Arc during the late Miocene are closely related to the causes of the Messinian salinity crisis. Tectonic movements may have closed and re-opened passages, as the region where the connection with the Atlantic Ocean was situated is permeated by strike-slip faults and rotating blocks of continental crust. As faulting accommodated

2350-852: The Grand Canyon ) around the Mediterranean. Later stages (5.50–5.33 Ma) are marked by cyclic evaporite deposition into a large "lake-sea" basin ("Lago Mare" event). About 5.33 million years ago, at the start of the Zanclean age (at the start of the Pliocene epoch), the barrier at the Strait of Gibraltar broke one last time, re-flooding the Mediterranean basin in the Zanclean flood ; favouring slope destabilization. The basin has not desiccated since. The amount of Messinian salts has been estimated as around 4 × 10 kg (but this estimate may be reduced by 50 to 75% when more information becomes available) and more than 1 million cubic kilometres, 50 times

2444-722: The Great Salt Lake in Utah and the Dead Sea , which lies between Jordan and Israel. Evaporite depositional environments that meet the above conditions include: The most significant known evaporite depositions happened during the Messinian salinity crisis in the basin of the Mediterranean . Evaporite formations need not be composed entirely of halite salt. In fact, most evaporite formations do not contain more than

2538-557: The Yellow River in China – see list of deadliest floods . The worst of these, and the worst natural disaster (excluding famine and epidemics), was the 1931 China floods , estimated to have killed millions. This had been preceded by the 1887 Yellow River flood , which killed around one million people and is the second-worst natural disaster in history. The extent of floodplain inundation depends partly on flood magnitude, defined by

2632-747: The return period . In the United States, the Federal Emergency Management Agency (FEMA) manages the National Flood Insurance Program (NFIP). The NFIP offers insurance to properties located within a flood-prone area, as defined by the Flood Insurance Rate Map (FIRM), which depicts various flood risks for a community. The FIRM typically focuses on the delineation of the 100-year flood inundation area, also known within

2726-612: The 19th century, the Swiss geologist and paleontologist Karl Mayer-Eymar (1826–1907) studied fossils embedded between gypsum -bearing, brackish , and freshwater sediment layers, and identified them as having been deposited just before the end of the Miocene Epoch. In 1867, he named the period the Messinian after the city of Messina in Sicily , Italy. Since then, several other salt-rich and gypsum-rich evaporite layers throughout

2820-457: The Hole 124 core, Kenneth J. Hsu found that: The oldest sediment of each cycle was either deposited in a deep sea or in a great brackish lake. The fine sediments deposited on a quiet or deep bottom had perfectly even lamination. As the basin was drying up and the water depth decreased, lamination became more irregular on account of increasing wave agitation. Stromatolite was formed then, when

2914-527: The Mediterranean Sea, for the first time and then repeatedly, partially desiccated. The basin was finally isolated from the Atlantic Ocean for a longer period, between 5.59 and 5.33 million years ago, resulting in a large or smaller (depending on the scientific model applied) lowering of the Mediterranean sea level. During the initial, very dry stages (5.6–5.5 Ma), there was extensive erosion, creating several huge canyon systems (some similar in scale to

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3008-468: The Mediterranean basin would warm by up to 15 °C (27 °F) in summer and 4 °C (7.2 °F) in winter, while for a depressed water surface, temperatures would warm by only about 4 °C (7.2 °F) in summer and 5 °C (9.0 °F) in winter. In addition, the model results indicated global stationary wave response to the introduction of the topographic depression causes patterns of warming and cooling by up to 4 °C (7.2 °F) around

3102-407: The Mediterranean region have been dated to the same period. Seismic surveying of the Mediterranean basin in 1961 revealed a geological feature some 100–200 m (330–660 ft) below the seafloor. This feature, dubbed the M reflector , closely followed the contours of the present seafloor, suggesting that it was laid down evenly and consistently at some point in the past. The origin of this layer

3196-481: The Mediterranean region. Each refilling was presumably caused by a seawater inlet opening, either tectonically , or by a river flowing eastwards below sea level into the "Mediterranean Sink" cutting its valley head back west until it let the sea in, similarly to a river capture . The last refilling was at the Miocene / Pliocene boundary, when the Strait of Gibraltar broke wide open permanently. Upon closely examining

3290-437: The Mediterranean seawater. Assuming that this major drawdown corresponds to the major Messinian drawdown, they concluded that the Mediterranean bathymetry significantly decreased before the precipitation of central basins evaporites. Regarding these works, a deep water formation seems unlikely. The assumption that central basin evaporites partly deposited under a high bathymetry and before the major phase of erosion should imply

3384-510: The Mediterranean, fossilized cracks have been found where muddy sediment had dried and cracked in the sunlight and drought. In the Western Mediterranean series, the presence of pelagic oozes interbedded within the evaporites suggests that the area was repeatedly flooded and desiccated over 700,000 years. Based on palaeomagnetic datings of Messinian deposits that have since been brought above sea level by tectonic activity,

3478-514: The Messinian, the Red Sea was connected at Suez to the Mediterranean, but was not connected with the Indian Ocean , and dried out along with the Mediterranean. When the Strait of Gibraltar was ultimately breached, the Atlantic Ocean would have poured a vast volume of water through what would have presumably been a relatively narrow channel. This refill has been envisaged as resulting in

3572-549: The Miocene. The Messinian salinity crisis resulted in major extinctions of marine fish and other marine fauna native to the basin. The present day biodiversity gradient of the Mediterranean, where diversity decreases eastward, developed after the crisis. The land mammal faunas of the Mediterranean also suffered diversity losses. Due to the fusion of the Iberian Peninsula and North Africa, a faunal interchange between

3666-560: The NFIP as the Special Flood Hazard Area. Where a detailed study of a waterway has been done, the 100-year floodplain will also include the floodway, the critical portion of the floodplain which includes the stream channel and any adjacent areas that must be kept free of encroachments that might block flood flows or restrict storage of flood waters. Another commonly encountered term is the Special Flood Hazard Area, which

3760-594: The Northern Hemisphere. Today the evaporation from the Mediterranean Sea supplies moisture that falls in frontal storms, but without such moisture, the Mediterranean climate that we associate with Italy, Greece , and the Levant would be limited to the Iberian Peninsula and the western Maghreb . Climates throughout the central and eastern basin of the Mediterranean and surrounding regions to

3854-467: The Sorbas Basin being filled with evaporites at 5.5 million years ago (Ma), compared to the main basin at 5.96 Ma.). Recent works have highlighted a pre-evaporite phase corresponding to a prominent erosional crisis (also named " Messinian erosional crisis "; the termination of the "Mes-1" unconformity bound depositional sequence of van Dijk, 1992) responding to a major drawdown of

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3948-400: The abandoned floodplain may be preserved as fluvial terraces . Floodplains support diverse and productive ecosystems . They are characterized by considerable variability in space and time, which in turn produces some of the most species-rich of ecosystems. From the ecological perspective, the most distinctive aspect of floodplains is the flood pulse associated with annual floods, and so

4042-511: The advantages provided by the richness of the alluvial soil of the floodplain are severely offset by frequent floods brought on by cyclones and annual monsoon rains. These extreme weather events cause severe economic disruption and loss of human life in the densely-populated region. Floodplain soil composition is unique and varies widely based on microtopography. Floodplain forests have high topographic heterogeneity which creates variation in localized hydrologic conditions. Soil moisture within

4136-549: The amount of salt normally in the Mediterranean waters. This suggests either a succession of desiccations or a long period of hypersalinity during which incoming water from the Atlantic Ocean was evaporated with the level of the Mediterranean brine being similar to that of the Atlantic. The nature of the strata points strongly to several cycles of the Mediterranean Sea completely drying and being refilled (Gargani and Rigollet, 2007), with drying periods correlating to periods of cooler global temperatures ; which were therefore drier in

4230-623: The area where the Strait of Gibraltar is now, the location of one of the tectonic boundaries between the African Plate and the European Plate and its southern fragments such as the Iberian Plate . This boundary zone is characterised by an arc-shaped tectonic feature, the Gibraltar Arc , which includes southern Spain and northern Africa . In the present day area of the Mediterranean Sea, are three of these arc-shaped belts:

4324-408: The basin receiving more freshwater from rivers , progressively filling and diluting the hypersaline lakes into larger pockets of brackish water (much like today's Caspian Sea ). The Messinian salinity crisis ended with the Strait of Gibraltar finally reopening 5.33 Ma, when the Atlantic rapidly filled up the Mediterranean basin in what is known as the Zanclean flood . Even today, the Mediterranean

4418-506: The basins now observed as "deep" were actually also deep during the Messinian Episode and gave different names to the end-member scenarios described above. Distinguishing between these hypotheses requires the calibration of gypsum deposits. Gypsum is the first salt (calcium sulphate) to be deposited from a desiccating basin. Magnetostratigraphy offers a broad constraint on timing, but no fine detail. Therefore, cyclostratigraphy

4512-567: The beginning of the crisis in the central Mediterranean Basin. The geometric physical link between the evaporitic series identified in marginal basins accessible for field studies, such as the Tabernas Desert and Sorbas Basin , and the evaporitic series of the central basins has never been made. Using the concept of deposition in both shallow and deep basins during the Messinian (i.e. assuming that both Basin types existed during this period), two major groupings are evident: one that favours

4606-467: The channel shifts varies greatly, with reported rates ranging from too slow to measure to as much as 2,400 feet (730 m) per year for the Kosi River of India. Overbank flow takes place when the river is flooded with more water than can be accommodated by the river channel. Flow over the banks of the river deposits a thin veneer of sediments that is coarsest and thickest close to the channel. This

4700-620: The climate of what is now the Balkans and other areas north of the Mediterranean basin. The Pannonian Sea was a source of water north of the Mediterranean basin until the middle Pleistocene before becoming the Hungarian plain. Debate exists whether the waters of the Wallachian-Pontic basin (and the possibly connected Pannonian Sea) would have had access (thus bringing water) to at least the eastern Mediterranean basin at times during

4794-554: The connection between the Mediterranean and the Atlantic. One particularly major glacioeustatic fluctuation, a sea level drop of about 30 metres (98 ft), occurred around 5.26 Ma, around the Miocene-Pliocene boundary. The climate of the abyssal plain during the drought is unknown. There is no situation on Earth directly comparable to the dry Mediterranean, and thus it is not possible to know its climate by direct observation of comparable geographic settings. Simulation using

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4888-415: The fine muds brought in by the next deluge. Research since then has suggested that the desiccation-flooding cycle may have repeated several times during the last 630,000 years of the Miocene epoch. This could explain the large amount of salt deposited. Recent studies, however, show that the repeated desiccation and flooding is unlikely from a geodynamic point of view. Some major questions remain concerning

4982-422: The flood waters. This can encourage farming ; some important agricultural regions, such as the Nile and Mississippi river basins , heavily exploit floodplains. Agricultural and urban regions have developed near or on floodplains to take advantage of the rich soil and freshwater. However, the risk of inundation has led to increasing efforts to control flooding . Most floodplains are formed by deposition on

5076-448: The floodplain ecosystem is defined as the part of the river valley that is regularly flooded and dried. Floods bring in detrital material rich in nutrients and release nutrients from dry soil as it is flooded. The decomposition of terrestrial plants submerged by the floodwaters adds to the nutrient supply. The flooded littoral zone of the river (the zone closest to the river bank) provides an ideal environment for many aquatic species, so

5170-462: The floodplain has a big impact on phosphorus availability because it alters water level, redox state, pH, and physical properties of minerals. Dry soils that were previously inundated have reduced availability of phosphorus and increased affinity for obtaining phosphorus. Human floodplain alterations also impact the phosphorus cycle. Particulate phosphorus and soluble reactive phosphorus (SRP) can contribute to algal blooms and toxicity in waterways when

5264-599: The floodplain. Other smaller-scale mitigation efforts include acquiring and demolishing flood-prone buildings or flood-proofing them. In some floodplains, such as the Inner Niger Delta of Mali , annual flooding events are a natural part of the local ecology and rural economy , allowing for the raising of crops through recessional agriculture . However, in Bangladesh , which occupies the Ganges Delta ,

5358-465: The impact of floodwaters. The disturbance by humans of temperate floodplain ecosystems frustrates attempts to understand their natural behavior. Tropical rivers are less impacted by humans and provide models for temperate floodplain ecosystems, which are thought to share many of their ecological attributes. Excluding famines and epidemics , some of the worst natural disasters in history (measured by fatalities) have been river floods, particularly in

5452-440: The inflow of Atlantic water maintains the present Mediterranean level. When that was shut off sometime between 6.5 to 6 MYBP, net evaporative loss set in at the rate of around 3,300 cubic kilometers yearly. At that rate, the 3.7 million cubic kilometres of water in the basin would dry up in scarcely more than a thousand years, leaving an extensive layer of salt some tens of meters thick and raising global sea level about 12 meters. In

5546-448: The inside of river meanders and by overbank flow. Wherever the river meanders, the flowing water erodes the river bank on the outside of the meander. At the same time, sediments are simultaneously deposited in a bar on the inside of the meander. This is described as lateral accretion since the deposition builds the point bar laterally into the river channel. Erosion on the outside of the meander usually closely balances deposition on

5640-417: The inside so that the channel shifts in the direction of the meander without changing significantly in width. The point bar is built up to a level very close to that of the river banks. Significant net erosion of sediments occurs only when the meander cuts into higher ground. The overall effect is that, as the river meanders, it creates a level flood plain composed mostly of point bar deposits. The rate at which

5734-457: The levees (4 kg/m or more) and on low-lying areas (1.6 kg/m ). Sedimentation from the overbank flow is concentrated on natural levees, crevasse splays , and in wetlands and shallow lakes of flood basins. Natural levees are ridges along river banks that form from rapid deposition from the overbank flow. Most of the suspended sand is deposited on the levees, leaving the silt and clay sediments to be deposited as floodplain mud further from

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5828-431: The lowest points of the dry abyssal plain , permitting no permanent life but extremophiles . Further, the altitude 3–5 km (2–3 mi) below sea level would result in 1.45 to 1.71 atm (1102 to 1300 mmHg) air pressure , further increasing heat stress. However, these simple estimates are likely far too extreme. Murphy et al.'s 2009 general circulation model experiments showed that for completely desiccated conditions,

5922-617: The makeup towards ash (49%) with maple increasing to 14% and oak decreasing to 25%. Semiarid floodplains have a much lower species diversity. Species are adapted to alternating drought and flood. Extreme drying can destroy the ability of the floodplain ecosystem to shift to a healthy wet phase when flooded. Floodplain forests constituted 1% of the landscape of Europe in the 1800s. Much of this has been cleared by human activity, though floodplain forests have been impacted less than other kinds of forests. This makes them important refugia for biodiversity. Human destruction of floodplain ecosystems

6016-461: The marine environments. Common minerals that are found in these deposits include blödite , borax , epsomite , gaylussite , glauberite , mirabilite , thenardite and trona . Non-marine deposits may also contain halite, gypsum, and anhydrite, and may in some cases even be dominated by these minerals, although they did not come from ocean deposits. This, however, does not make non-marine deposits any less important; these deposits often help to paint

6110-762: The nitrogen-to-phosphorus ratios are altered farther upstream. In areas where the phosphorus load is primarily particulate phosphorus, like the Mississippi River, the most effective ways of removing phosphorus upstream are sedimentation, soil accretion, and burial. In basins where SRP is the primary form of phosphorus, biological uptake in floodplain forests is the best way of removing nutrients. Phosphorus can transform between SRP and particulate phosphorus depending on ambient conditions or processes like decomposition, biological uptake, redoximorphic release, and sedimentation and accretion. In either phosphorus form, floodplain forests are beneficial as phosphorus sinks, and

6204-575: The north and east would have been drier even above modern sea level. The eastern Alps , the Balkans , and the Hungarian plain would also be much drier than they are today, even if the westerlies prevailed as they do now. However, the Paratethys ocean provided water to the area north of the Mediterranean basin. The Wallachian-Pontic and Hungarian basins were underwater during the Miocene, modifying

6298-406: The observation of a major detritic event above evaporites in the basin. Such a depositional geometry has not been observed on data. This theory corresponds to one of the end-member scenarios discussed by van Dijk et al. Several possible causes of the series of Messinian crises have been considered. While there is disagreement on all fronts, the most general consensus seems to agree that climate had

6392-591: The original water depth remains. At this point, minor carbonates begin to form. The next phase in the sequence comes when the experiment is left with about 20% of its original level. At this point, the mineral gypsum begins to form, which is then followed by halite at 10%, excluding carbonate minerals that tend not to be evaporites. The most common marine evaporites are calcite , gypsum and anhydrite , halite, sylvite , carnallite , langbeinite , polyhalite , and kainite . Kieserite (MgSO 4 ) may also be included, which often will make up less than four percent of

6486-535: The other arc shaped features in the Mediterranean: Of these, only the first model, invoking rollback, seems to explain the rotations observed. However, it is difficult to fit it with the pressure and temperature histories of some metamorphic rocks . This has led to some interesting combinations of the models which at first hand looked bizarre, in attempts to approach the true state of affairs. Changes in climate must almost certainly be invoked to explain

6580-458: The overall content. However, there are approximately 80 different minerals that have been reported found in evaporite deposits, though only about a dozen are common enough to be considered important rock formers. Non-marine evaporites are usually composed of minerals that are not common in marine environments because in general the water from which non-marine evaporite precipitates has proportions of chemical elements different from those found in

6674-552: The periodic nature of the events. They occur during cool periods of Milankovic cycles , when less solar energy reached the northern hemisphere. This led to less evaporation of the North Atlantic, hence less rainfall over the Mediterranean. This would have starved the basin of water supply from rivers and allowed its desiccation. Glacioeustatic sea level falls with an amplitude of around 10 metres (33 ft) that began approximately 6.14 Ma were likely responsible for modulating

6768-430: The regional compression caused by Africa's convergence with Eurasia , the geography of the region may have altered enough to open and close seaways. However, the precise tectonic activity behind the motion can be interpreted in a number of ways. Any model must explain a variety of features of the area: There are three contending geodynamic models that may fit the data, models which have been discussed in an equal way for

6862-414: The remaining water is enriched in salts, and they precipitate when the water becomes supersaturated. Marine evaporites tend to have thicker deposits and are usually the focus of more extensive research. When scientists evaporate ocean water in a laboratory, the minerals are deposited in a defined order that was first demonstrated by Usiglio in 1884. The first phase of precipitation begins when about 50% of

6956-504: The right amount of sediment everywhere before the gypsum was deposited. The proponents claim that the gypsum was deposited directly above the correlated marl layers, and slumped into them, giving the appearance of an unconformable contact. However, their opponents seize upon this apparent inconformity, and claim that the Sorbas Basin was exposed—therefore eroding—while the Mediterranean sea was depositing evaporites. This would result in

7050-580: The river may abandon the channel belt and build a new one at another position on the floodplain. This process is called avulsion and occurs at intervals of 10–1000 years. Historical avulsions leading to catastrophic flooding include the 1855 Yellow River flood and the 2008 Kosi River flood . Floodplains can form around rivers of any kind or size. Even relatively straight stretches of river are capable of producing floodplains. Mid-channel bars in braided rivers migrate downstream through processes resembling those in point bars of meandering rivers and can build up

7144-511: The river, the successive plant communities are bank vegetation (usually annuals); sedge and reeds; willow shrubs; willow-poplar forest; oak-ash forest; and broadleaf forest. Human disturbance creates wet meadows that replace much of the original ecosystem. The biozones reflect a soil moisture and oxygen gradient that in turn corresponds to a flooding frequency gradient. The primeval floodplain forests of Europe were dominated by oak (60%) elm (20%) and hornbeam (13%), but human disturbance has shifted

7238-418: The river. Levees are typically built up enough to be relatively well-drained compared with nearby wetlands, and levees in non-arid climates are often heavily vegetated. Crevasses are formed by breakout events from the main river channel. The river bank fails, and floodwaters scour a channel. Sediments from the crevasse spread out as delta -shaped deposits with numerous distributary channels. Crevasse formation

7332-488: The salinity crisis started at the same time over all the Mediterranean basin, at 5.96 ± 0.02 million years ago. This episode comprises the second part of what is called the "Messinian" age of the Miocene epoch. This age was characterised by several stages of tectonic activity and sea level fluctuations, as well as erosional and depositional events, all more or less interrelated (van Dijk et al., 1998). The Mediterranean-Atlantic strait closed tight time and time again, and

7426-568: The same time, the salt was cored during Leg 13 of the Deep Sea Drilling Program conducted from the Glomar Challenger under the supervision of co-chief scientists William B.F. Ryan and Kenneth J. Hsu . These deposits were dated and interpreted for the first time as deep-basin products of the Messinian salinity crisis. The first drilling of the Messinian salt at the deeper parts of the Mediterranean Sea came in

7520-419: The sea level of the whole Mediterranean basin fell at once, but only shallower basins dried out enough to deposit salt beds. See image b. As highlighted in the work of van Dijk (1992) and van Dijk et al. (1998) the history of desiccation and erosion was complexly interacting with tectonic uplift and subsidence events, and erosional episodes. They also questioned again like some previous authors had done, whether

7614-697: The seabed southeast of the south corner of Sicily . This is suspected to have been deposited by the Zanclean flood. Evaporite An evaporite ( / ɪ ˈ v æ p ə ˌ r aɪ t / ) is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution . There are two types of evaporite deposits: marine, which can also be described as ocean deposits, and non-marine, which are found in standing bodies of water such as lakes. Evaporites are considered sedimentary rocks and are formed by chemical sediments . Although all water bodies on

7708-489: The sediment has time to pool and form in a lake or other standing body of water. Primary examples of this are called "saline lake deposits". Saline lakes includes things such as perennial lakes, which are lakes that are there year-round, playa lakes, which are lakes that appear only during certain seasons, or any other terms that are used to define places that hold standing bodies of water intermittently or year-round. Examples of modern non-marine depositional environments include

7802-490: The site of deposition fell within an intertidal zone. The intertidal flat was eventually exposed by the final desiccation, at which time anhydrite was precipitated by saline ground water underlying sabkhas . Suddenly seawater would spill over the Strait of Gibraltar , or there would be an unusual influx of brackish water from the eastern European lake. The Balearic abyssal plain would then again be under water. The chicken-wire anhydrite would thus be abruptly buried under

7896-408: The spawning season for fish often coincides with the onset of flooding. Fish must grow quickly during the flood to survive the subsequent drop in water level. As the floodwaters recede, the littoral experiences blooms of microorganisms, while the banks of the river dry out and terrestrial plants germinate to stabilize the bank. The biota of floodplains has high annual growth and mortality rates, which

7990-420: The strait closed for the last time around 5.6 Ma, the region's generally dry climate at the time dried the Mediterranean basin out nearly completely within a thousand years. This massive desiccation left a deep dry basin, reaching 3 to 5 km (1.9 to 3.1 mi) deep below normal sea level, with a few hypersaline pockets similar to today's Dead Sea . Then, around 5.5 Ma, wetter climatic conditions resulted in

8084-674: The subsurface. Evaporite minerals, especially nitrate minerals, are economically important in Peru and Chile. Nitrate minerals are often mined for use in the production on fertilizer and explosives . Thick halite deposits are expected to become an important location for the disposal of nuclear waste because of their geologic stability, predictable engineering and physical behaviour, and imperviousness to groundwater. Halite formations are famous for their ability to form diapirs , which produce ideal locations for trapping petroleum deposits. Halite deposits are often mined for use as salt . This

8178-407: The summer of 1970, when geologists aboard the Glomar Challenger brought up drill cores containing arroyo gravels and red and green floodplain silts; and gypsum , anhydrite , rock salt , and various other evaporite minerals that often form from drying of brine or seawater, including in a few places potash , left where the last bitter, mineral-rich waters dried up. One drill core contained

8272-399: The surface and in aquifers contain dissolved salts, the water must evaporate into the atmosphere for the minerals to precipitate. For this to happen, the water body must enter a restricted environment where water input into this environment remains below the net rate of evaporation. This is usually an arid environment with a small basin fed by a limited input of water. When evaporation occurs,

8366-479: The surface of Titan , Saturn's largest moon. Instead of water oceans, Titan hosts lakes and seas of liquid hydrocarbons (mainly methane) with many soluble hydrocarbons, such as acetylene , that can evaporate out of solution. Evaporite deposits cover large regions of Titan's surface, mainly along the coastlines of lakes or in isolated basins ( Lacunae ) that are equivalent to salt pans on Earth. Floodplain A floodplain or flood plain or bottomlands

8460-459: The surrounding grade. Many State and local governments have, in addition, adopted floodplain construction regulations which are more restrictive than those mandated by the NFIP. The US government also sponsors flood hazard mitigation efforts to reduce flood impacts. California 's Hazard Mitigation Program is one funding source for mitigation projects. A number of whole towns such as English, Indiana , have been completely relocated to remove them from

8554-523: The two regions occurred. The crisis also allowed the dispersal of terrestrial animals to remote landmasses such as the Balearic Islands , where several animal species, such as the goat-antelope Myotragus , would continue to be isolated until the Holocene , over 5 million years later. The notion of a completely waterless Mediterranean Sea has some corollaries. There is an opinion that during

8648-476: The underlying marl beds, which appear to have given way to gypsum at exactly the same time in both basins. The proponents of this hypothesis claim that cyclic variations in bed compositions are astronomically tuned, and the beds' magnitude can be calibrated to show they were contemporaneous—a strong argument. In order to refute it, it is necessary to propose an alternative mechanism for generating these cyclic bands, or for erosion to have coincidentally removed just

8742-672: The upper 30 cm of the soil profile also varies widely based on microtopography which affects oxygen availability. Floodplain soil stays aerated for long stretches of time in between flooding events, but during flooding, saturated soil can become oxygen-depleted if it stands stagnant for long enough. More soil oxygen is available at higher elevations farther from the river. Floodplain forests generally experience alternating periods of aerobic and anaerobic soil microbe activity which affects fine root development and desiccation. Floodplains have high buffering capacity for phosphorus to prevent nutrient loss to river outputs. Phosphorus nutrient loading

8836-565: Was largely interpreted as related to salt deposition. However, different interpretations were proposed for the age of salt and its deposition. Earlier suggestions from Denizot in 1952 and Ruggieri in 1967 proposed that this layer was of Late Miocene age, and the same Ruggieri coined the term Messinian Salinity Crisis . New and high-quality seismic data on the M-reflector were acquired in the Mediterranean Basin in 1970. At

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