Tethys Ocean
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The Tethys Ocean is a former (Mesozoic era) ocean that existed between the continents of Gondwana and Laurasia before the opening of the Indian Ocean.
Terminology and Subdivisions
Like every science, geology is a continuously evolving system of theories, and the terms used to describe various pre-historic formations have fluctuated as more accurate theories have emerged. For example, many internet sources use "Tethys Ocean" to refer to the "Tethys Sea" and vice versa. Some even (erroneously) appear to refer to the growing Atlantic Ocean during the Jurassic as the Tethys Sea.The western end of the Tethys Ocean is called Tethys Sea, Western Tethys Ocean or Alpine Tethys Ocean. It is the geological ancestor of the modern Black, Caspian and Aral Seas, which are assumed to be crustal remains of it. This "Western Tethys" was not a one-part open ocean. It contained many small plates, Cretaceous island arcs and microcontinents. Small oceanic basins (Valais Ocean, Piemont-Liguria Ocean) were separated from each other by continental terranes on the Alboran plate, the Iberian plate and Apulian plate. Most of these more continental domains were (because of the high sealevel in the Mesozoic age) in fact flooded by shallow seas.
The eastern part of the Tethys Ocean is likewise sometimes referred to as Eastern Tethys.
In the same way the Indian Ocean has today replaced the Tethys Ocean, older oceans existed before the Tethys. Confusingly, some are called Tethys as well:
- the Paleo-Tethys Ocean existed from the Silurian till the Jurassic, between the Hunic terranes and Gondwana (later the Cimmerian terranes).
- the Proto-Tethys Ocean existed from the Ediacaran till the Devonian, and was situated between Baltica and Laurentia to the north and Gondwana to the south. It should not be confused with the (later) Rheic Ocean.
Historical Theory
In 1893, using fossil records from the Alps and Africa, Eduard Suess proposed the theory that a shallow inland sea had once existed between Laurasia and Gondwana. He named it the 'Tethys Sea' after the Greek sea goddess Tethys. The theory of plate tectonics later disproved or overrode many parts of Suess's theory, even determining the existence of an earlier body of water called the Tethys Ocean. However, Suess's overall concept was still relatively accurate and remarkably imaginative for its day, so he generally is credited with the discovery of both the Tethys Sea and the Tethys Ocean.Modern Theory
About 250 Million years ago, during the late Permian Era, 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 (Laurasia). The Tethys Ocean formed between Cimmeria and Gondwana, directly over where the Paleo-Tethys used to be.During the Jurassic Period (150 Mya), Cimmeria finally collided with Laurasia. There it stalled, the ocean floor behind it buckling under, forming the Tethyan Trench. Water levels rose and the western Tethys came to shallowly cover significant portions of Europe. Around the same time, Laurasia and Gondwana began drifting apart, leaving the Atlantic Ocean between them. Between the Jurassic and the Cretaceous (100 Ma), even Gondwana began breaking up, pushing Africa and India north, across the Tethys. As these land masses pushed in on it from all sides, up until as recently as the Late Miocene (15 Ma), the Tethys ocean contiued to shrink, becoming the Tethys Seaway or 'Tethys Sea'.
Today, India, Indonesia and the Indian Ocean cover the area once occupied by the Tethys Ocean. Turkey, Iraq, and Tibet sit on the small continent once known as Cimmeria. What was once the Tethys Sea has become the Black, Caspian and Aral Seas. Most of the floor of the Tethys Ocean disappeared under Cimmeria and Laurasia. We only know the Tethys existed because geologists like Suess found fossils of ocean creatures in rocks in the Himalayas. So, we know those rocks were underwater, before the Indian continental shelf began pushing upward as it smashed into Cimmeria. We can see similar geologic evidence in the Alpine orogeny of Europe, where the movement of the African plate raised the Alps.
Paleontologists also find the Tethys Ocean particularly important because much of the world's sea shelves were found around its margins for such an extensive period of time. Marine, marsh-dwelling, and estuarian fossils from these shelves are of considerable paleontological interest.
External link
- [Palaeos Earth]: The Tethys Sea
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