Tethys Ocean

First phase of the Tethys Ocean's forming: the (first) Tethys Sea starts dividing Pangaea into two supercontinents, Laurasia and Gondwana.

The Tethys Ocean (Ancient Greek: Τηθύς), Tethys Sea or Neotethys was an ocean during much of the Mesozoic era located between the ancient continents of Gondwana and Laurasia, before the opening of the Indian and Atlantic oceans during the Cretaceous period.

Etymology

The name stems from the mythological Greek Sea Goddess Tethys, sister and consort of Oceanus, mother of the great rivers, lakes and fountains of the world and of the Oceanid sea nymphs.

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 or Paratethys or Alpine Tethys Ocean. The Black, Caspian and Aral Seas are thought to be its crustal remains, though the Black Sea may in fact be a remnant of the older Paleo-Tethys Ocean.^[1] The Western Tethys was not simply a single open ocean. It covered many small plates, Cretaceous island arcs and microcontinents. Many small Oceanic basins (Valais Ocean, Piemont-Liguria Ocean, Meliata Ocean) were separated from each other by continental terranes on the Alboran, Iberian, and Apulian plates. The high sea level in the Mesozoic era flooded most of these continental domains, forming shallow seas. As theories have improved, scientists have extended the "Tethys" name to refer to 3 similar oceans that preceded it, separating the continental terranes: in Asia, the Paleo-Tethys (Devonian–Triassic), Meso-Tethys (late Early Permian–Late Cretaceous) and Ceno-Tethy (Late-Triassic–Cenozoic) are recognized.^[2] Neither Tethys oceans should be confused with the Rheic Ocean, which existed to the west of them in the Silurian period.^[3] To the north of the Tethys, the then land mass was called Angaraland and to the south of it, it was called Gondwanaland.

Modern theory

From the Ediacaran (600 Ma) into the Devonian (360 Ma), the Proto-Tethys Ocean existed and was situated between Baltica and Laurentia to the north and Gondwana to the south.

From the Silurian (440 Ma) through the Jurassic periods, the Paleo-Tethys Ocean existed between the Hunic terranes and Gondwana. Over a period of 400 million years, continental terranes intermittently separated from Gondwana in the Southern Hemisphere to migrate northward to form Asia in the Northern Hemisphere.^[2]

Triassic period

Plate tectonic reconstruction of the Tethys realm at 249 Ma.

About 250 million years ago,^[4] during the Triassic, a new ocean began forming in the southern end of the Paleo-Tethys Ocean. A rift formed along the northern continental shelf of Southern Pangaea (Gondwana). Over the next 60 million years, that piece of shelf, known as Cimmeria, traveled north, pushing the floor of the Paleo-Tethys Ocean under the eastern end of Northern Pangaea (i.e.Laurasia). The Tethys Ocean formed between Cimmeria and Gondwana, directly over where the Paleo-Tethys used to be.

Jurassic period

During the Jurassic Period about 150Ma, Cimmeria finally collided with Laurasia and stalled, so the ocean floor behind it buckled under, forming the Tethyan 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 began drifting apart, opening an extension of the Tethys Sea between them which today is the part of the Atlantic Ocean between the Mediterranean and the Caribbean. 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 about latitude 30° N and the Equator. Thus, ocean currents at the time around the Early Cretaceous ran very differently from the way they do today.

Late Cretaceous

Plate tectonic reconstruction of the Tethys realm at 100 Ma

Between the Jurassic and the Late Cretaceous, which started about 100 Ma, Gondwana began breaking up, pushing Africa and India north across the Tethys and opening up the Indian Ocean. As these land masses crowded in on the Tethys ocean from all sides, to as recently as the Late Miocene 15 Ma, the ocean continued to shrink, becoming the Tethys Seaway or second Tethys Sea. Throughout the Cenozoic (66 million to the dawn of the Neogene, 23 million years), global sea levels fell hundreds of meters, and eventually the connections between the Atlantic and the Tethys closed off in what is now the Middle East.

Oligocene

During the Oligocene (33.9 million to 23 million before annum), large parts of central and eastern Europe were covered by a northern branch of the Tethys Ocean, called the Paratethys. The Paratethys was separated from the Tethys with the formation of the Alps, Carpathians, Dinarides, Taurus and Elburz mountains during the Alpine orogeny. During the late Miocene the Paratethys gradually disappeared, and became an isolated inland sea.

Today

Today, India, Pakistan, Indonesia, and the Indian Ocean cover the area once occupied by the Tethys Ocean, and Turkey, Iraq, and Tibet sit on Cimmeria. What was once the western arm of the Tethys Sea was the ancestor of the present-day Mediterranean Sea. Other remnants are the Black, Caspian, and Aral Seas via a former inland branch known as the Paratethys. Most of the floor of the Tethys Ocean disappeared under Cimmeria and Laurasia.

Geologists including Eduard Suess have found fossils of ocean creatures in rocks in the Himalayas, indicating that those rocks were once underwater, before the Indian continental shelf began pushing upward as it collided with Cimmeria.

Similar geologic evidence can be seen in the Alpine orogeny of Europe, where the movement of the African plate raised the Alps. Greece and the Levant also retain many units of limestone and other sedimentary rocks deposited by various stands of the Tethys Ocean.

Paleontologists find the Tethys Ocean particularly important, because much of the world's sea shelves were found around its margins for such an extensive length of time with Marine, marsh-dwelling, and estuarian fossils from these shelves. The Solnhofen limestone in Bavaria, originally a coastal lagoon mud of the Tethys Ocean, yielded the famous Archaeopteryx fossil.

Historical theory

Geologist Eduard Suess in 1869

In 1885, the Austrian palaeontologist Melchior Neumayr deduced the existence of the Tethys Ocean from Mesozoic marine sediments and their distribution, calling his concept 'Zentrales Mittelmeer' and described it as a Jurassic seaway, which extended from the Caribbean to the Himalayas.^[5]

In 1893, the Austrian geologist Eduard Suess proposed the theory that an ancient and extinct inland sea had once existed between Laurasia and the continents which formed Gondwana 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.^[6] He proposed the concept of Tethys in his four-volume work Das Antlitz der Erde (The Face of the Earth).^[7]

In the following decades during the 20th century "mobilist" geologists like Uhlig (1911), Diener(1925), and Daque (1926) regarded Tethys as a large trough between two supercontinents which lasted from the late Palaeozoic until continental fragments derived from Gondwana obliterated it. After WW2, 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 of orogenic cycles. They used the terms 'Paleotethys', 'Mesotethys', and 'Neotethys' for the Caledonian, 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.^[8]

In the 1960s, the theory of plate tectonics became established, and it became clear Suess's "sea" had in fact been an ocean. Plate tectonics provided an explanation for the mechanism by which the former ocean disappeared: oceanic crust can subduct under continental crust. Tethys was considered an oceanic plate by Smith (1971), Dewey, Pitman, Ryan and Bonnin (1973), Laubscher and Bernoulli (1973), Bijou-Duval, Dercourt and Pichon (1977),

See also

• Hațeg Island
• Paleo-Tethys Ocean
• Pannonian Sea
• Paratethys
• Piemont-Liguria Ocean
• Proto-Tethys Ocean
• Tethyan Trench
• Ruhpolding Formation

References

Notes

Sources

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