The geological history of the Mediterranean Sea

Written by astrid on 16. March 2009. Posted in Geology, Sea, Nature, Naxos.

In the Palaeozoic era

The first precursor to the Mediterranean Sea was the Palaeozoic ocean known as Palaeotethys. This existed as a huge bay at the end of the first (and longest) of the three geological eras documented by fossils, the Palaeozoic (540 to 250 million years ago). During the last epochs of the Palaeozoic, the Carboniferous (345 to 295 million years ago) and the Permian (295 to 250 million years ago), all the continents were clustered together (Pangaea) and arranged themselves in a C-shape around the gigantic sea bay of the Palaeotethys.

North of the Palaeotethys, which was open to the east, lay Euramerica, which only extended as far as Central Asia, and to the south lay the large southern continent of Gondwana, consisting of South America, Africa, India, Australia and Antarctica. To the west, the Paleotethys extended as far as south-eastern Europe during the Permian period.

Euramerica and Gondwana collided during the Variscan orogeny in the late Palaeozoic, forming the mountains in eastern North America, Morocco and Central Europe due to the collision of Africa with North America and Europe (the southern European regions still belonged to Africa and were only later separated from it). In addition, the Urals were formed by the further convergence of the already connected continents of Europe and Asia, and the mountainous regions in Asia north of the Himalayas were formed by the accretion of smaller continental fragments from the southeast. Southern China and other areas of Southeast Asia migrated northwards as isolated islands south of Asia, to collide later with the continent.

In the Mesozoic Era

After the Permian began the Mesozoic Era (Triassic, Jurassic, Cretaceous; 250 to 65 million years ago). During the Mesozoic, Pangaea broke apart. The Paleo-Tethys closed (see below) and its successor, the Neo-Tethys, was formed. The western part of this ocean was later replaced by another ocean arm, the Mediterranean Sea.

In the Triassic

Since the Permian, the northern edge of Gondwana had been split off by the opening of a new ocean arm, the Neotethys, forming an elongated piece of continent or island system: the Cimmerian (sub)continent. This drifted northwards with a counterclockwise rotation and collided with Eurasia from west to east during the Mesozoic era. This resulted in the formation of parts of the Balkan region, Crimea, Asia Minor, Iran, Tibet and Indochina. During the collision, the Paleotethys north of Cimmeria was closed, while the Neotethys opened up to the south.

In Europe, the collision of the Cimmerian continent took place during the first Mesozoic epoch, the Triassic (250 to 203 million years ago). As the Paleo-Tethys closed to the north of Cimmeria, the Neotethys was forming to the south, continually widening and extending further west until Europe was almost completely separated from Africa.

On the northern edge of Africa, several more rift valleys formed from east to west, running parallel to the Neotethys, each splitting off small continent pieces. These terranes also migrated northwards over time, eventually colliding one after the other with the southern edge of Europe. Initially these terranes were flat platforms which, like large parts of south-eastern and central Europe, were covered by the sea during most of the Mesozoic era, resulting in the deposition of thick layers of sediments.

In the Jurassic

In the next epoch, the Jurassic (203 to 135 million years ago), Pangaea began to break apart. A rift valley formed between North America and north-western Africa, in which the first section of the Atlantic Ocean was formed. At the same time, Antarctica, Australia and India separated from Africa in one piece which later broke up into separate parts. Africa continued to move away from Europe, and the ocean between them, the Neotethys, expanded.

In the area of today’s Alps, the Penninic Ocean was formed as an eastward extension of the Atlantic Ocean which connected it to the Tethys. Here, too, hundreds of meters of sediment were deposited. Southeast of the Penninic Ocean lay the Adriatic Plate, which was still part of the flooded shelf area of Africa. This plate now moved eastwards together with Africa through the opening of the Penninic Ocean and the Atlantic. These movements pushed the small terranes, that had split off northeast of Africa, to the north, and the first two of them collided with southeastern Europe during the Jurassic. This resulted in the formation of the northern parts of the Greek mainland and the Aegean region as the first phases of the Alpine orogeny.

During the collisions, the ocean arms of the Neotethys located to the north of the terranes were closed. Their sediment layers were largely sheared off during the subduction of the ocean floor beneath the European Plate and folded or pushed on top of each other forming mountain ranges. At the transition to the next period, the Cretaceous, another terrane was added to south-eastern Europe. (The last terrane collided with Europe in the Eocene.) To the south of the terranes and continent fragments moving towards Europe, a new large ocean arm gradually opened up: the Mediterranean Sea.

In the Cretaceous

In the next epoch, the Cretaceous (135 to 65 million years ago), the Atlantic Ocean expanded and North America separated from Europe. The Iberian Plate split off from Europe. South America separated from Africa, with the latter beginning to rotate counterclockwise.

Since the Middle Cretaceous, Africa started to drift back towards Europe. This led to further orogenic processes in southern Europe, resulting in the first orogenetic movements in the Alpine region. The Neotethys was already largely closed in the European region and replaced by the Mediterranean Sea. As in the Jurassic, sea levels were very high due to the absence of ice caps at the poles and the relatively large extent of the land masses (with only few young fold mountain chains), so that large parts of Europe, North America and North Africa were flooded by the sea. Through these flooded continental areas the Atlantic was connected to the Tethys south of Asia. In the Tethys area, India split off from Madagascar, with which it had previously separated from Australia, and began to migrate rapidly northwards.

In the Cenozoic Era (Tertiary and Quaternary)

After the Cretaceous, the Cenozoic Era began (Tertiary and Quaternary, or: Palaeocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene; from 65 million years ago to the present day). During the Cenozoic, Africa continued to move closer to Europe, and the ocean in between, the Mediterranean, became increasingly narrower. The Adriatic Plate was pushed further north by Africa and collided with Europe, causing the Alps to fold (recent phases of the Alpine orogeny; starting in the Palaeocene, 65 million years ago, and culminating in the Miocene, about 20 million years ago). During the Eocene, the last terrane collided with the southern edge of Europe in the area of Greece, forming Crete and the other southernmost Aegean islands. Iberia reattached itself to Europe and the Pyrenees were folded. India collided with Asia from the Eocene onwards, leading to the formation of the Himalayas; to the south, the Indian Ocean opened, which, like the Mediterranean, is a successor ocean to the Tethys.

Africa and Europe now moved so close together that they were separated in the west only by a very narrow strait at Gibraltar. This sea connection to the Atlantic was later temporarily interrupted. In the east, Arabia started to collide with Asia in the Oligocene (30 million years ago); this area had previously been part of the submerged shelf at the north-eastern edge of Africa. The collision cut off the Mediterranean Sea from the Tethys (now the Indian Ocean). Europe and America separated completely in the Tertiary. In the Pliocene, land bridges formed between North and South America and between North America and East Asia.

Around 5.9 million years ago (in the Miocene), the connection between the Mediterranean Sea and the Atlantic Ocean at Gibraltar closed, and the Mediterranean Sea dried up (in several cycles) in desert-like climate conditions, forming endless salt lakes and deserts with thick salt deposits. Extremely high temperatures must have prevailed in the depression, which was over 3 kilometers deep, but numerous animal species migrated along the rivers into the area from Africa and the Levant. About 600,000 years later, the connection to the Atlantic suddenly reopened, and within a few years, the Mediterranean Sea filled up through a gigantic waterfall that carried about 1,000 times as much water as Niagara Falls does today. In the process, small populations of the immigrant species (elephants, hippopotamuses, antelopes, numerous rodents, etc.) became isolated on islands and survived there in some cases until the Holocene.

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