Messinian Mediterranean and Gibraltar - reconstructed landscape

The Zanclean flood or Zanclean deluge is theorized to have refilled the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

5.33 million years ago. This flooding ended the

Messinian salinity crisis In the Messinian salinity crisis (also referred to as the Messinian event, and in its latest stage as the Lago Mare event) the Mediterranean Sea went into a cycle of partial or nearly complete desiccation (drying-up) throughout the latter part of ...

and reconnected the Mediterranean Sea to the Atlantic Ocean, although it is possible that even before the flood there were partial connections to the Atlantic Ocean. The re-connection marks the beginning of the

Zanclean The Zanclean is the lowest stage or earliest age on the geologic time scale of the Pliocene. It spans the time between 5.332 ± 0.005 Ma (million years ago) and 3.6 ± 0.005 Ma. It is preceded by the Messinian Age of the Miocene Epoch, and f ...

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

which is the name given to the earliest age on the

geologic time scale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochro ...

of the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

refilled the dried-up basin through the modern-day

Strait of Gibraltar The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Europe from Africa. The two continents are separated by 7.7 nautical miles (14.2 kilometers, 8.9 miles) at its narrowest point. Fe ...

. Ninety percent of the Mediterranean Basin flooding occurred abruptly during a period estimated to have been between several months and two years, following low water discharges that could have lasted for several thousand years. Sea level rise in the basin may have reached rates at times greater than . Based on the erosion features preserved until modern times under the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Garcia-Castellanos ''et al.'' estimate that water rushed down a drop of more than with a maximum discharge of about , about 1,000 times that of the present-day Amazon River. Studies of the underground structures at the Strait of Gibraltar show that the flooding channel descended gradually toward the bottom of the basin rather than forming a steep waterfall.

Background

The geologic history of the

Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

is governed by

plate tectonics Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

involving the African Plate, the Arabian Plate and the Eurasian Plate which shrank the previously existing

Tethys Ocean The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasia ...

until its western part became the present-day Mediterranean. For reasons not clearly established, during the late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

the Mediterranean was severed from the

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

. It partly dried up when the Guadalhorce and Rifian corridors that had previously connected the Mediterranean to the Atlantic closed. This triggered the

Messinian Salinity Crisis In the Messinian salinity crisis (also referred to as the Messinian event, and in its latest stage as the Lago Mare event) the Mediterranean Sea went into a cycle of partial or nearly complete desiccation (drying-up) throughout the latter part of ...

with the formation of thick salt deposits on the former seafloor and erosion of the continental slopes. The

Nile The Nile (also known as the Nile River or River Nile) is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa. It has historically been considered the List of river sy ...

and

Rhône The Rhône ( , ; Occitan language, Occitan: ''Ròse''; Franco-Provençal, Arpitan: ''Rôno'') is a major river in France and Switzerland, rising in the Alps and flowing west and south through Lake Geneva and Southeastern France before dischargi ...

carved deep

canyon A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency t ...

s during this time. Water levels in the Mediterranean during this time dropped by kilometres. The exact magnitude of the drop, and whether it was symmetric between the

Western Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

and the

Eastern Mediterranean The Eastern Mediterranean is a loosely delimited region comprising the easternmost portion of the Mediterranean Sea, and well as the adjoining land—often defined as the countries around the Levantine Sea. It includes the southern half of Turkey ...

, is unclear; it is possible that interconnected seas remained on the floor of the Mediterranean. The presence of Atlantic fish in Messinian deposits and the volume of salt deposited during the Messinian Salinity Crisis implies that there was some remnant flow from the Atlantic into the Mediterranean even before the Zanclean flood. Already before the Zanclean flood, increased precipitation and runoff had lowered the salinity of the remnant sea, leading to the deposition of the so-called "Lago Mare" sediments, with some water putatively originating in the

Paratethys The Paratethys sea, Paratethys ocean, Paratethys realm or just Paratethys (meaning "beside Tethys"), was a large shallow inland sea that covered much of mainland Europe and parts of western Asia during the middle to late Cenozoic, from the lat ...

north of the Mediterranean.

Event

The Zanclean flood occurred when the

opened. Tectonic subsidence of the Gibraltar region may have lowered the sill until it breached. The exact triggering event is not known with certainty;

faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

sea level rise The sea level has been rising from the end of the last ice age, which was around 20,000 years ago. Between 1901 and 2018, the average sea level rose by , with an increase of per year since the 1970s. This was faster than the sea level had e ...

are debatable. The most widely accepted hypothesis is that a stream flowing into the Mediterranean eroded through the Strait of Gibraltar until it captured the Atlantic Ocean and that the Strait did not exist before this erosion event. During the flood, a channel formed across the Strait of Gibraltar, which starts at the Camarinal Sill in the Strait of Gibraltar. The channel is eroded into the seafloor of the Alboran Sea, splits around the Vizconde de Eza high of the Alboran Sea and eventually connects with the Alboran Channel before splitting into several branches that end in the Algero-Balear basin. The channel has a U-like shape in its starting region, which is consistent with its formation during a giant flood. The formation of the channel mobilized about of rock, which was deposited in the Alboran Sea in the form of giant submarine bars. The sector of the Zanclean channel that passes through the Camarinal Sill may have a different origin, however. Whether the Zanclean flood occurred gradually or as a catastrophic event is controversial, but it was instantaneous by geological standards. The magnitude of a catastrophic flood has been simulated by modelling. One single-dimensional model assumes a catastrophic flood of more than 10–100

sverdrup In oceanography, the sverdrup (symbol: Sv) is a non- SI metric unit of volumetric flow rate, with equal to . It is equivalent to the SI derived unit cubic hectometer per second (symbol: hm3/s or hm3⋅s−1): is equal to . It is used almost ...

. Another estimate assumes that after the first breach of the sill, the flowing water eroded the threshold and formed the channel across the Strait of Gibraltar, increasing the flow of water which in turn increased the erosion until water levels rose enough in the Mediterranean to slow the flood. In such a scenario, a peak discharge of over occurred with water velocities of over ; such flow rates are about a thousand times larger than the discharge of the Amazon River and ten times as much as the Missoula floods. This flood would have descended a relatively gentle ramp into the Mediterranean basin, not as a giant

waterfall A waterfall is any point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf. Waterfalls can be formed in seve ...

. Later simulations using more explicit geography constrain the flow to about 100 sverdrup or . They further indicate the formation of large gyres in the Alboran Sea during the flooding and that the flood eroded the Camarinal Sill at a rate of . The exact size of the flood depends on the pre-flood water levels in the Mediterranean and higher water levels there would result in a much smaller flood. The flood affected only the

at first, because the Malta Escarpment (located at the present Straits of Sicily) formed a barrier separating its basin from the

basin that probably overflowed through the Noto Canyon across the Malta Escarpment; in addition a sill may have existed in the eastern Alboran Sea at this time. During the flooding across the Noto Canyon, vortices and reverse flows occurred, and large amounts of sediments were emplaced in the Ionian Sea. While it was at first assumed that the filling of the eastern Mediterranean would have taken thousands of years, later estimates of the size of the Strait of Gibraltar channel implied that it would have taken much less, potentially less than a year until reconnection. A large flood is not the only explanation for the reconnection of the Mediterranean with the Atlantic and concomitant environmental changes; more gradual reflooding of the Mediterranean including reflooding through other water sources is also possible, or a persistently open Strait of Gibraltar. The absence of a catastrophic flooding event is supported by geological evidence found along the southern margin of the Alboran Sea. On the other hand, deposits found around the Malta Escarpment imply that one intense flood led to the reconnection across the Straits of Sicily.

Timing

The timing of the Zanclean flood is uncertain, with one possibility being a flood around 5.33 million years ago; the end of the

Messinian The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the fir ...

and beginning of the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58 The main Zanclean flood may have been preceded by an earlier smaller flood event, and the presence of deep sea terraces has been used to infer that the refilling of the Mediterranean occurred in several pulses. Complete refilling of the Mediterranean may have taken about a decade.

Consequences

The Zanclean flood created the

; it is doubtful that tectonic or volcanic events could have created the strait since the main plate boundaries do not run through the strait and there is little seismic activity in its area. The current morphology of the strait is characterized by two aquatic sills: the Camarinal Sill, which is at its deepest point, and the deeper Espartel Sill farther west. The narrowest part of the strait is located east of either sill, and it is considerably deeper than the sills. It is possible that these sills were formed after the flood through gravity-induced movement of neighbouring terrain. The Zanclean flood caused a major change in the environment of the Mediterranean basin; the continental "Lago Mare" facies was replaced by

deep sea deposits. The flood may have affected global climate, considering that the much smaller flood triggered when

Lake Agassiz Lake Agassiz ( ) was a large proglacial lake that existed in central North America during the late Pleistocene, fed by meltwater from the retreating Laurentide Ice Sheet at the end of the last glacial period. At its peak, the lake's area wa ...

drained did result in a cold period. The hypothesized remote effects reached as far as the Loyalty Ridge next to

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

in the Southern Hemisphere. Rising sea levels made the deeply incised

Nile river The Nile (also known as the Nile River or River Nile) is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa. It has historically been considered the longest river i ...

become a ria as far inland as

Aswan Aswan (, also ; ) is a city in Southern Egypt, and is the capital of the Aswan Governorate. Aswan is a busy market and tourist centre located just north of the Aswan Dam on the east bank of the Nile at the first cataract. The modern city ha ...

, some upstream from the modern coast. The Zanclean flood resulted in the final isolation of numerous Mediterranean islands such as

Crete Crete ( ; , Modern Greek, Modern: , Ancient Greek, Ancient: ) is the largest and most populous of the Greek islands, the List of islands by area, 88th largest island in the world and the List of islands in the Mediterranean#By area, fifth la ...

, resulting in

speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

of animals found there. On the other hand, the formation of the Strait of Gibraltar prevented land animals from crossing over between Africa and Europe. Further the reconnection allowed sea animals such as

cetacean Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

s and their ancestors and

pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant taxon, extant families Odobenidae (whose onl ...

s to colonize the Mediterranean from the Atlantic. Evidence of the flooding has been obtained on Zanclean-age sediments, both in

borehole A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petr ...

s and in sediments that were subsequently uplifted and raised above sea level. A sharp erosional surface separates the pre-Zanclean flood surface from the younger deposits, which are always marine in origin. The waters flooding into the

probably overspilled into the

Ionian Sea The Ionian Sea (, ; or , ; , ) is an elongated bay of the Mediterranean Sea. It is connected to the Adriatic Sea to the north, and is bounded by Southern Italy, including Basilicata, Calabria, Sicily, and the Salento peninsula to the west, ...

through

Sicily Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...

and the Noto submarine canyon off

Avola Avola (; /, becoming / if preceded by vowel; ) is a city and in the province of Syracuse, Sicily (southern Italy). History The foundation of the city in an area previously inhabited by the Sicani and invaded by the Sicels in the 13th-12th ...

; the spillover flood had a magnitude comparable to the flood in the Strait of Gibraltar. The rates at which the Mediterranean filled during the flood were more than enough to trigger substantial induced seismicity. Resulting large

landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...

s would have sufficed to create large

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

s with wave heights reaching , evidence of which has been found in the Algeciras Basin. The infilling of the basin created tectonic stresses, which would have influenced the development of the

Apennine Mountains The Apennines or Apennine Mountains ( ; or Ἀπέννινον ὄρος; or – a singular with plural meaning; )Latin ''Apenninus'' (Greek or ) has the form of an adjective, which would be segmented ''Apenn-inus'', often used with nouns s ...

Similar megafloods

Similar floods have occurred elsewhere on Earth throughout history; examples include the Bonneville flood in North America, during which Lake Bonneville overflowed through Red Rock Pass into the Snake River Basin, and the Black Sea deluge hypothesis that postulates a flood from the Mediterranean into the

Black Sea The Black Sea is a marginal sea, marginal Mediterranean sea (oceanography), mediterranean sea lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bound ...

through the

Bosporus The Bosporus or Bosphorus Strait ( ; , colloquially ) is a natural strait and an internationally significant waterway located in Istanbul, Turkey. The Bosporus connects the Black Sea to the Sea of Marmara and forms one of the continental bo ...

Research history

In his book '' Historia Naturalis'',

Pliny the Elder Gaius Plinius Secundus (AD 23/24 79), known in English as Pliny the Elder ( ), was a Roman Empire, Roman author, Natural history, naturalist, and naval and army commander of the early Roman Empire, and a friend of the Roman emperor, emperor Vesp ...

mentions a legend that

Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...

dug the Strait of Gibraltar between the Mediterranean and the Atlantic Ocean, connecting the two. The actual Zanclean flood theory however only arose during the 1970s, when it became clear that salt deposits and a widespread

erosion surface In geology and geomorphology, an erosion surface is a surface of rock (geology), rock or regolith that was formed by erosion and not by construction (e.g. lava flows, sediment deposition) nor fault (geology), fault displacement. Erosional surfaces ...

in the Mediterranean had been emplaced during a prolonged sea level lowstand, and that the subsequent reflooding took place in only a few millennia or less.

Notes

References

Inline citations

Sources

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External links

* * {{DEFAULTSORT:Zanclean Flood History of the Mediterranean Mediterranean Sea Megafloods Messinian Miocene Africa Miocene Europe Pliocene Africa Pliocene Europe Zanclean