During the early Mesozoic, asPangaea broke up, the designation “Tethys Ocean” refers to the ocean located between the ancient continents ofGondwana andLaurasia. After the opening of the Indian andAtlantic oceans during theCretaceous Period and the breakup of these continents over the same period, it refers to 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 theorogenies of theAlpide belt (including theAlps,Himalayas,Zagros, andCaucasus Mountains). All of these geological events, in addition to a drop in sea level from Antarctic glaciation, brought an end to the Tethys as it previously existed, fragmenting it into the Indian Ocean, the Mediterranean Sea, and theParatethys.[1][2]
It was preceded by thePaleo-Tethys Ocean, which lasted between theCambrian and theEarly Triassic, while the Neotethys formed during theLate Triassic and lasted in some form up to theOligocene–Miocene boundary (about 24–21 million years ago) when it completely closed.[1][3] A portion known as theParatethys was isolated during the Oligocene (34 million years ago) and lasted up to thePliocene (about 5 million years ago), when it largely dried out.[4] The modern inland seas of Europe and Western Asia, namely the Black Sea and Caspian Sea, are remnants of the Paratethys Sea.[1]
The sea is named afterTethys, who, in ancient Greek mythology, is a water goddess, a sister and consort ofOceanus, mother of theOceanid sea nymphs and of the world's great rivers, lakes and fountains.
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).[6] TheTurgai Strait extended out of the Peri-Tethys, connecting the Tethys with theArctic Ocean.[7]
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.[8] None of the Tethys oceans should be confused with theRheic Ocean, which existed to the west of them in the Silurian Period.[9] To the north of the Tethys, the then-land mass is calledAngaraland and to the south of it, it is calledGondwanaland.[10]
From theSilurian (440Mya) through theJurassic periods, the Paleo-Tethys Ocean existed between theHunic terranes and Gondwana. Over a period of 400 million years, continentalterranes intermittently separated from Gondwana in the Southern Hemisphere to migrate northward to form Asia in the Northern Hemisphere.[8]
Plate tectonic reconstruction of the Tethys realm at 249 Mya
About 250 Mya,[11] 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.[citation needed]
During theJurassic period 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 theMediterranean and 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 aboutlatitude 30°N and theEquator. Thus,ocean currents at the time around theEarly Cretaceous ran very differently from the way they do today.[citation needed]
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. During the Late Cretaceous the Tethys sea was home to many different animals, includingmarine reptiles,bony fish,cartilaginous fish andcephalopods. Theislands that were located in the northern parts of the Tethys sea (Europe) createdbiodiverseecosystems that had animals that went throughinsular dwarfism andinsular gigantism. The insular dwarfism process happened mostly to thedinosaurs that lived on the islands, like thesauropods and thehadrosaurs.Telmatosaurus is a good representation of the insular dwarfism process. While the insular dwarfism process happened to the dinosaurs, thepterosaurs that lived on the islands went through the process known as insular gigantism.Hatzegopteryx was a hugeazhdarchid pterosaur that lived on the islands of the Tethys sea. This giant pterosaur would have filled itsecological niche as anapex predator. During theMaastrichtian, the Tethys sea had many different large mosasaurs that lived in the same geographical area and would have competed with each other. Europe had large mosasaurs likePrognathodon giganteus, Prognathodon saturator, Prognathodon sectorius,Mosasaurus hoffmannii and Mosasaurus lemonnieri.North Africa would have also had large mosasaurs like Prognathodon giganteus, Prognathodon currii,Thalassotitan atrox,Hainosaurus boubker and Mosasaurus beaugei. The competition between many different apex predators is something we don't only see in the Tethys sea, but also in theWestern Interior Seaway.[citation needed]
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.[2] The complete closure of the Tethys led to a global reorganization of currents, and is what is thought to have allowed forupwelling in theArabian Sea and led to the establishment of the modernSouth Asian Monsoon. It also caused major modifications to the functioning of theAMOC andACC.[2]
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, andElburz mountains during theAlpine orogeny. During the lateMiocene, the Paratethys gradually disappeared, and became an isolated inland sea.[12] Separation from the wider Tethys during the early Miocene initially led to a boost inprimary productivity for the Paratethys, but this gave way to a total ecosystem collapse during the late Miocene as a result of rapid dissolution ofcarbonate.[3]
In Chapter 13 of his 1845 book,[13]Roderick Murchison described a distinctive formation extending from theBlack Sea to theAral Sea in which the creatures differed from those of the purely marine period that preceded them. TheMiocene deposits ofCrimea and Taman (south of theSea of Azov) are identical with formations surrounding the presentCaspian Sea, in which theunivalves of 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.
... and leads at once to the conviction, that during long periods antecedent, as will be hereafter explained, to the historic æra, a vast region of Europe and Asia was covered by a Mediterranean Sea of brackish water, of which the present Caspian is the diminished type. ... To render the distinction between these accumulations and all others clear and unambiguous, we have adopted the term Aralo-Caspian, first applied in a geographical sense, by our great precursor Humboldt, to this region of the globe. ... 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 theTurkomans andKirghis, and was bounded only by the mountains of theHindoo Kusk andChinese Tartary. ... there can be no sort of 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!
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 river to 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 basin and onto theSwabian Jura with thickness of up to 250 m (820 ft); these were deposited in theParatethys when the Alpine front was still 100 km (62 mi) farther south.[14][15]
In 1893, the Austrian geologistEduard Suess proposed the hypothesis that an ancient and extinctinland sea had once existed between Laurasia and the continents which formedGondwana II. 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.[17] He proposed the concept ofTethys in his four-volume workDas Antlitz der Erde (The Face of the Earth).[18]
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 twosupercontinents which lasted from the late Palaeozoic until continental fragments derived from Gondwana obliterated it.
From 1920s to the 1960s, "fixist" geologists, however, regarded Tethys as a composite trough, which evolved through a series oforogenic cycles. They used the terms 'Paleotethys', 'Mesotethys', and 'Neotethys' for theCaledonian,Variscan, and Alpine orogenies, respectively. In the 1970s and 1980s, 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.[19]
In the 1960s, the theory ofplate tectonics became 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 crust cansubduct undercontinental crust.[citation needed]
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).[citation needed]
^Steininger, F.F.; Wessely, G. (2000). "From the Tethyan Ocean to the Paratethys Sea: Oligocene to Neogene stratigraphy, paleogeography and paleobiogeography of the circum-Mediterranean region and the Oligocene to Neogene Basin evolution in Austria".Mitteilungen der Österreichischen Geologischen Gesellschaft.92:95–116.
^Steininger, F. F.; Wessely, G. (2000). "From the Tethyan Ocean to the Paratethys Sea: Oligocene to Neogene stratigraphy, paleogeography and paleobiogeography of the circum-Mediterranean region and the Oligocene to Neogene Basin evolution in Austria".Mitteilungen der Österreichischen Geologischen Gesellschaft.92:95–116.
^Suess 1893, p. 183: "This ocean we designate by the name 'Tethys' after the sister and consort of Oceanus. The latest successor of the Tethyan Sea is the present Mediterranean."
^Suess 1901, Gondwana-Land und Tethys, p. 25:"Dasselbe wurde von Neumayr das 'centrale Mittelmeer' genannt und wird hier mit dem Namen Tethys bezeichnet werden. Das heutige europäische Mittelmeer ist ein Rest der Tethys." ("It was named by Neumayr the 'central Mediterranean [literally: Middle] Sea' and here it will be designated by the name 'Tethys'. The current European Mediterranean Sea is a remnant of the Tethys.")
