The Tethys Ocean (Greek: Τηθύς) was an ocean that existed between the continents of Gondwana and Laurasia during much of the Mesozoic era, before the opening of the Indian and Atlantic oceans during the Cretaceous period. It is also referred to as the Tethys Sea or Neotethys.
About 250 million years ago,〔(Palaeos Mesozoic: Triassic: Middle Triassic )〕 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 (Laurasia). The Tethys Ocean formed between Cimmeria and Gondwana, directly over where the Paleo-Tethys used to be.
During the Jurassic Period (150 Ma), 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 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 that today is the part of the Atlantic Ocean that is between the Mediterranean and 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 that time—around the Early Cretaceous—ran very differently from the way they do today.
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. Also, throughout the Cenozoic, 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.
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 such as Eduard Suess and other geologists 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 also 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. Marine, marsh-dwelling, and estuarian fossils from these shelves are of considerable paleontological interest. The Solnhofen limestone in Bavaria, originally a coastal lagoon mud of the Tethys Ocean, yielded the famous ''Archaeopteryx'' fossil.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』