Tethys Ocean

First phase of the Tethys Ocean's forming: the (first) Tethys Sea starts dividingPangaeainto two supercontinents,LaurasiaandGondwana.

TheTethys Ocean(/ˈtiːθɪs,ˈtɛ-/TEETH-iss,TETH-;Greek:ΤηθύςTēthús), also called theTethys Seaor theNeo-Tethys,was a prehistoric ocean during much of theMesozoic Eraand early-midCenozoic Era.It was the predecessor to the modernIndian Ocean,theMediterranean Sea,and the Eurasian inland marine basins (primarily represented today by theBlack SeaandCaspian Sea).

During the early Mesozoic, asPangaeabroke up, the Tethys Ocean was defined as the ocean located between the ancient continents ofGondwanaandLaurasia.After the opening of the Indian andAtlanticoceans during theCretaceousPeriod and the breakup of these continents over the same period, it came to be defined as the ocean bordered by the continents of Africa, Eurasia, India, and Australasia. During the early-mid Cenozoic, the Indian, African, Australian and Arabian plates moved north and collided with the Eurasian plate, which created new borders to the ocean, a land barrier to the flow of currents between the Indian and Mediterranean basins, and theorogeniesof theAlpide belt(including the Alps, Himalayas, Zagros, Caucasian and Ural Mountains). All of these geological events, in addition to a drop in sea level rise from Antarctic glaciation, brought an end to the Tethys as it previously existed, fragmenting it into the Indian Ocean, the Mediterranean Sea, and theParatethys.

It was preceded by thePaleo-Tethys Ocean,which lasted between theCambrianand theEarly Triassic,while the Neotethys formed during theLate Triassicand lasted in some form up to theOligocene–Mioceneboundary (about 24–21 million years ago) when it completely closed.A portion known as the Paratethys was isolated during the Oligocene (34 million years ago) and lasted up to thePliocene(about 5 million years ago), when it largely dried out.The modern inland seas of Europe and Western Asia, namely the Black Sea and Caspian Sea, are remnants of the Paratethys Sea.

Etymology

The sea was named afterTethys,who, in ancient Greek mythology, was a water goddess, a sister and consort ofOceanus,mother of theOceanidsea nymphs and of the world’s great rivers, lakes and fountains.

Terminology and subdivisions

The eastern part of the Tethys Ocean is sometimes referred to as Eastern Tethys. The western part of the Tethys Ocean is called Tethys Sea, Western Tethys Ocean, orParatethysor Alpine Tethys Ocean. TheBlack,Caspian,andAralseas are thought to be itscrustalremains, though the Black Sea may, in fact, be a remnant of the olderPaleo-Tethys Ocean. The Western Tethys was not simply a single open ocean. It covered many small plates,Cretaceousisland arcs,andmicrocontinents.Many smalloceanic basins(Valais Ocean,Piemont-Liguria Ocean,Meliata Ocean) were separated from each other by continentalterraneson theAlboran,Iberian,andApulianplates. The highsea levelin the Mesozoic flooded most of these continental domains, forming shallow seas.

During the early Cenozoic, the Tethys Ocean could be divided into three sections: the Mediterranean Tethys (the direct predecessor to the Mediterranean Sea), the Peri-Tethys (a vast inland sea that covered much of eastern Europe and central Asia, and the direct predecessor to the Paratethys Sea), and the Indian Tethys (the direct predecessor to the Indian Ocean).TheTurgai Straitextended out of the Peri-Tethys, connecting the Tethys with theArctic Ocean.

As theories have improved, scientists have extended the "Tethys" name to refer to three similar oceans that preceded it, separating the continental terranes: in Asia, thePaleo-Tethys(Devonian–Triassic),Meso-Tethys(lateEarly Permian–Late Cretaceous), andCeno-Tethys(Late-Triassic–Cenozoic) are recognized.None of the Tethys oceans should be confused with theRheic Ocean,which existed to the west of them in the Silurian Period.To the north of the Tethys, the then-land mass is calledAngaralandand to the south of it, it is calledGondwanaland.

Modern theory

From theEdiacaran(600Mya) into theDevonian(360Mya), theProto-Tethys Oceanexisted and was situated betweenBalticaandLaurentiato the north andGondwanato the south.

From theSilurian(440Mya) through theJurassicperiods, the Paleo-Tethys Ocean existed between theHunic terranesand Gondwana. Over a period of 400 million years, continentalterranesintermittently separated from Gondwana in the Southern Hemisphere to migrate northward to form Asia in the Northern Hemisphere.

Plate tectonic reconstruction of the Tethys realm at 249Mya

Triassic Period

About 250 Mya,during theTriassic,a new ocean began forming in the southern end of the Paleo-Tethys Ocean. A rift formed along the northern continental shelf of SouthernPangaea(Gondwana). Over the next 60 million years, that piece of shelf, known asCimmeria,traveled north, pushing the floor of the Paleo-Tethys Ocean under the eastern end of northernPangaea(early / proto-Laurasia). The Neo-Tethys Ocean formed between Cimmeria and Gondwana, directly over where the Paleo-Tethys formerly rested.

Jurassic Period

During theJurassicperiod about 150 Mya, Cimmeria finally collided with Laurasia and stalled, so the ocean floor behind itbuckled under,forming theTethys Trench.Water levels rose, and the western Tethys shallowly covered significant portions of Europe, forming the first Tethys Sea. Around the same time, Laurasia and Gondwana begandrifting apart,opening an extension of the Tethys Sea between them which today is the part of the Atlantic Ocean between theMediterraneanand theCaribbean.As North and South America were still attached to the rest of Laurasia and Gondwana, respectively, the Tethys Ocean in its widest extension was part of a continuous oceanic belt running around the Earth between aboutlatitude30°N and theEquator.Thus,ocean currentsat the time around theEarly Cretaceousran very differently from the way they do today.

Late Cretaceous

Plate tectonic reconstruction of the Tethys realm at 100 Mya

Between the Jurassic and theLate Cretaceous,which started about 100 Mya, Gondwana began breaking up, pushing Africa and India north across the Tethys and opening up the Indian Ocean.

Cenozoic

Vast regions of Europe and west-central Asia were still covered by a contiguous Tethys at the start of theEocene(top image), but by the Oligocene, most of this had dried out (bottom image), and the Tethys was almost entirely divided into the Indian Ocean, Mediterranean and Paratethys.

Throughout theCenozoic(66 million to the dawn of the Neogene, 23 Mya), the connections between the Atlantic and Indian Oceans across the Tethys were eventually closed off in what is now the Middle East during theMiocene,as a consequence of the northern migration of Africa/Arabia and global sea levels falling due to the concurrent formation of theAntarctic Ice Sheet.This decoupling occurred in two steps, first around 20 Mya and another around 14 Mya.The complete closure of the Tethys led to a global reorganization of currents, and is what is thought to have allowed forupwellingin theArabian Seaand led to the establishment of the modernSouth Asian Monsoon.It also caused major modifications to the functioning of theAMOCandACC.

During theOligocene(33.9 to 23 Mya), large parts of central and eastern Europe were covered by a northern branch of the Tethys Ocean, called theParatethys.The Paratethys was separated from the Tethys with the formation of the Alps,Carpathians,Dinarides,Taurus,andElburzmountains during theAlpine orogeny.During the lateMiocene,the Paratethys gradually disappeared, and became an isolated inland sea.Separation from the wider Tethys during the early Miocene initially led to a boost inprimary productivityfor the Paratethys, but this gave way to a total ecosystem collapse during the late Miocene as a result of rapid dissolution ofcarbonate.

Historical theory

In Chapter 13 of his 1845 book,Roderick Murchisondescribed a distinctive formation extending from theBlack Seato theAral Seain which the creatures differed from those of the purely marine period that preceded them. TheMiocenedeposits ofCrimeaand Taman (south of theSea of Azov) are identical with formations surrounding the presentCaspian Sea,in which theunivalvesof freshwater origin are associated with forms of Cardiacae and Mytili that are common to partially saline or brackish waters. This distinctive fauna has been found throughout all the enormously developed Tertiary formations of the southern and south-eastern steppes.

... there can be no doubt that all the masses of water now separated from each other, from the Aral to the Black Sea inclusive, were formerly united in this vast pre-historical Mediterranean; which (even if we restrict its limits to the boundaries we already know, and do not extend them eastward, amid low regions untrodden by geologists) must have exceeded in size the present Mediterranean!... Judging from the recital of travellers and from specimens of the rock, we have no doubt that it extended to Khivah and the Aral Sea; beyond which the low level of the adjacent eastern deserts would lead us to infer, that it spread over wide tracts in Asia now inhabited by theTurkomansandKyrgyz people,and was bounded only by the mountains of theHindu KushandChinese Tartary... and leads at once to the conviction, that during long periods, a vast region of Europe and Asia was covered by aMediterranean Seaof brackish water, of which the present Caspian is the diminished type... we have adopted the term Aralo-Caspian, first applied to this region of the globe by Humboldt, for this formation.

On the accompanying map, Murchison shows the Aralo-Caspian Formation extending from close to the Danube delta across Crimea, up the east side of theVolga riverto Samara, then south of the Urals to beyond the Aral Sea. Brackish and upper freshwater components (OSM) of the Miocene are now known to extend through theNorth Alpine foreland basinand onto theSwabian Jurawith thickness of up to 250 m (820 ft); these were deposited in theParatethyswhen the Alpine front was still 100km farther south.

GeologistEduard Suessin 1869

In 1885, the Austrian palaeontologistMelchior Neumayrdeduced the existence of the Tethys Ocean from Mesozoic marine sediments and their distribution, calling his conceptZentrales Mittelmeerand described it as a Jurassic seaway, which extended from the Caribbean to the Himalayas.

In 1893, the Austrian geologistEduard Suessproposed the hypothesis that an ancient and extinctinland seahad once existed between Laurasia and the continents which formedGondwanaII. He named it the Tethys Sea after the Greek sea goddess Tethys. He provided evidence for his theory using fossil records from the Alps and Africa.He proposed the concept ofTethysin his four-volume workDas Antlitz der Erde(The Face of the Earth).

In the following decades during the 20th century, "mobilist"geologists such as Uhlig (1911), Diener (1925), and Daque (1926) regarded Tethys as a large trough between twosupercontinentswhich lasted from the late Palaeozoic until continental fragments derived from Gondwana obliterated it.

AfterWorld War II,Tethys was described as a triangular ocean with a wide eastern end.

From 1920s to the 1960s, "fixist" geologists, however, regarded Tethys as a composite trough, which evolved through a series oforogeniccycles. They used the terms 'Paleotethys', 'Mesotethys', and 'Neotethys' for theCaledonian,Variscan,and Alpine orogenies, respectively. In the 1970s and '80s, these terms and 'Proto-Tethys', were used in different senses by various authors, but the concept of a single ocean wedging into Pangea from the east, roughly where Suess first proposed it, remained.

In the 1960s, the theory ofplate tectonicsbecame established, and Suess's "sea" could clearly be seen to have been an ocean. Plate tectonics provided an explanation for the mechanism by which the former ocean disappeared:oceanic crustcansubductundercontinental crust.

Tethys was considered an oceanic plate by Smith (1971); Dewey, Pitman, Ryan and Bonnin (1973); Laubscher and Bernoulli (1973); and Bijou-Duval, Dercourt and Pichon (1977).

See also

• Hațeg Island– Prehistoric island
• List of ancient oceans– List of Earth's former oceans
• Paleo-Tethys Ocean– Ocean on the margin of Gondwana between the Middle Cambrian and Late Triassic
• Pannonian Sea– Shallow ancient sea where the Pannonian Basin in Central Europe is today
• Paratethys– Prehistoric shallow inland sea in Eurasia
• Piemont-Liguria Ocean– Former piece of oceanic crust that is seen as part of the Tethys Ocean
• Ruhpolding Formation
• Tethyan Trench– Ancient oceanic trench

References

Sources

• Bialik, Or M.; Frank, Martin; Betzler, Christian; Zammit, Ray; Waldmann, Nicolas D. (2019)."Two-step closure of the Miocene Indian Ocean Gateway to the Mediterranean".Scientific Reports.9(8842): 8842.Bibcode:2019NatSR...9.8842B.doi:10.1038/s41598-019-45308-7.PMC6586870.PMID31222018.
• Kollmann, H. A. (1992)."Tethys—the Evolution of an Idea".In Kollmann, H. A.; Zapfe, H. (eds.).New Aspects on Tethyan Cretaceous Fossil Assemblages.Springer-Verlag reprint ed. 1992. pp. 9–14.ISBN978-0387865553.OCLC27717529.Retrieved6 October2015.
• Metcalfe, I. (1999)."The ancient Tethys oceans of Asia: How many? How old? How deep? How wide?".UNEAC Asia Papers.1:1–9.Retrieved6 October2015.
• Metcalfe, I. (2013)."Gondwana dispersion and Asian accretion: tectonic and palaeogeographic evolution of eastern Tethys".Journal of Asian Earth Sciences.66:1–33.Bibcode:2013JAESc..66....1M.doi:10.1016/j.jseaes.2012.12.020.Retrieved6 October2015.
• Stampfli, G. M.; Borel, G. D. (2002)."A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrons".Earth and Planetary Science Letters.196(1): 17–33.Bibcode:2002E&PSL.196...17S.doi:10.1016/S0012-821X(01)00588-X.
• Suess, E. (1893)."Are ocean depths permanent?".Natural Science: A Monthly Review of Scientific Progress.Vol. 2. London. pp. 180–187.Retrieved6 October2015.{{cite book}}:CS1 maint: location missing publisher (link)
• Suess, E. (1901).Der Antlitz der Erde(in German). Vol. 3. Wien F. Tempsky.Retrieved6 October2015.
• Van der Voo, Rob (1993).Paleomagnetism of the Atlantic, Tethys and Iapetus Oceans.Cambridge University Press.ISBN978-0-521-61209-8.

External links

• Media related toTethys Oceanat Wikimedia Commons