Cimmeria (continent)

Cimmeria was an ancient continent, or, rather, a string of microcontinents or terranes, that rifted from Gondwana in the Southern Hemisphere and was accreted to Eurasia in the Northern Hemisphere. It consisted of parts of what is today Turkey, Iran, Afghanistan, Tibet, Shan–Thai, and Malay Peninsula.[3] Cimmeria rifted from the Gondwanan shores of the Paleo-Tethys Ocean during the Carboniferous-earliest Permian and as the Neo-Tethys Ocean opened behind it, during the Permian, the Paleo-Tethys closed in front of it.[4] Cimmeria rifted off Gondwana from east to west, from Australia to the eastern Mediterranean.[5] It stretched across several latitudes and spanned a wide range of climatic zones.[6]

249 global
Cimmeria rifted off Gondwana's north-eastern shores around 250 Ma.[1]
230 Ma plate tectonic reconstruction
As Cimmeria migrated from Gondwana to Eurasia the Paleo-Tethys closed and the Neo-Tethys opened.[2]
100 global
After 150 million years Cimmeria collided with Eurasia and the Cimmerian orogeny closed the Paleo-Tethys. As the break-up of Gondwana began in the south, the opening of the Indian Ocean initiated the closure of the Neo-Tethys.[1]

History of the concept

First concepts

A "large, ancient Mediterranean Sea" was first proposed by Austrian palaeontologist Melchior Neumayr in 1883.[7] Studying the distribution of Jurassic faunas, he concluded that an equatorial ocean stretching from India to Central America must have separated a large continent in the northern hemisphere from one in the southern hemisphere. Austrian geologist Eduard Suess named this Mesozoic ocean the Tethys, a mythical ocean which separated a mythical continent – Gondwanaland, home of the tongue-shaped flora – from a boreal continent.[8] German geophysicist Alfred Wegener, in contrast, developed a concept of a single, global continent – the supercontinent Pangea – which, in his view, left no room for an equatorial ocean. A wedge-shaped, east-facing Tethys within Pangea was, nevertheless, proposed by Australian geologist Samuel Warren Carey in 1958.[9] This ocean was later identified as a succession of oceans separated by north-migrating terranes or continental blocks, one of which was Cimmeria.

Iranian microcontinent

In 1974, after extensive field work in the Middle East, Swiss geologist Jovan Stöcklin identified the northern foot of the Alborz Range in northern Iran as the suture which in the Paleozoic was the northern shore of Gondwana and the remains of the Paleo-Tethys Ocean. Stöcklin also noted that an early Mesozoic or late Paleozoic rift separated the Iranian Plate from the Arabian Plate, and that another southern suture must be the remains of the Neo-Tethys Ocean. The opening of this later ocean, Stöcklin realized, must have transformed Iran into a microcontinent. Those observations made Stöcklin the first to identify a small part of what would later be known as Cimmeria.[10]

Stöcklin also noted that his proposal resembled the old concept of the world in which there were two continents, Angaraland in the north and Gondwana in the south, separated by an elongated ocean, the Tethys. Iran belonged to neither continent but was part of the realm of Tethys.[10] Stöcklin's southern suture was later confirmed by observations of the evolution of microflora in Iran, which had a Gondwanan affinity during the Carboniferous but a Eurasian affinity during the Late Triassic – Iran had clearly drifted from Gondwana to Laurasia.[11]

Eurasian superterrane

Alpiner Gebirgsgürtel
The Alpide belt is a system of sutures stretching across Eurasia within which the Cimmerian blocks are now located.

In the 1980s Turkish geologist Celâl Şengör finally extended Stöcklin's Iranian microcontinent further west to Turkey and further east to Tibet and the Far East.[12] Şengör also reused the name introduced by Suess in 1901, the "Kimmerisches Gebirge" – the "Crimean" or "Cimmerian Mountains".[11][13][14]

In the mountain range that now stretches from the Alps to Indonesia Şengör identified, using a simplified scheme, two distinct but superimposed orogenic systems containing a large number of anastomosing sutures: the older Cimmerides and the younger Alpides together forming what Şengör called the Tethysides super-orogenic system. These two orogenic systems are thus associated with two major periods of ocean closure: the earlier, northern, and much larger Cimmerides, and the later, southern, and smaller Alpides. Cimmeria was the long continental "archipelago" that separated the two oceans before the Paleo-Tethys closed.[14]

This realm of Tethys thus covers most of Eurasia and a large time span (from north to south):[14]

  • Laurasia, Permian to Cretaceous
  • Palaeo-Tethys, Early Carboniferous to Middle Jurassic
  • Cimmeria, Triassic to Middle Jurassic
  • Neo-Tethys, Permian or Triassic to Eocene, locally still extant
  • Gondwana, Ordovician to Jurassic

This simple scheme, however, partly obscures the complex nature of the Tethyan cycles and terms such as "Eocimmerian" and "Neocimmerian" is often used for Late Triassic and Late Jurassic events respectively.[15] Furthermore, a distinction is often made between two more recent Tethyan domains: the Alpine Tethys and the Neo-Tethys. The Alpine Tethys, the western domain in this scheme, separated south-western Europe from north-western Africa and was connected to the Central Atlantic. It is now completely closed and its suture encompasses the Maghrebids (stretching from Gibraltar to Sicily) as well as the Apennines and the Alps. The Neo-Tethys, the eastern domain, opened between Arabia and the Cimmerian terranes. The East Mediterranean Basin and the Gulf of Oman are considered relics of the Neo-Tethys which is thus still closing. These two domains were connected east of Sicily until the end of the Jurassic.[16]

Tectonic history

In the Late Paleozoic, when the Cimmerian blocks were still located on the northern margin of Gondwana, they were far away from any active margins and orogenic belts, but they had been affected by thermal subsidence since the Siluran opening of Paleo-Tethys. Carboniferous to Permian ophiolites along suture zones in Tibet and north-eastern Iran indicate that the active margin of Paleo-Tethys was located here.[17] It was slab-pull forces in the Paleo-Tethys that detached Cimmeria from Gondwana and opened the Neo-Tethys. The mid-ocean ridge in the Paleo-Tethys subducted under Eurasia, as evidenced by Permian MORB (mid-ocean ridge basalt) in Iran. Slab roll-back in the Paleo-Tethys opened a series of back-arc basins along the Eurasian margin and resulted in the collapse of the Variscan cordillera. As the Paleo-Tethys subducted under the Eurasian southern margin, back-arc oceans formed from Austria to China. Some of these back-arcs closed during the Cimmerian orogeny (e.g. the Karakaya-Küre sequence of back-arc oceans in Turkey), others remained open (e.g. the Meliata-Maliac-Pindos back-arc oceans in the eastern Mediterranean) leading to the formation of younger back-arc oceans.[5]

Turkey

Anatolian Plate
Geological map of Turkey

Turkey is an assemblage of continental blocks that during the Permian were part of the northern margin of Gondwana. During the Permian-Triassic, as the Paleo-Tethys subducted under this margin (in what is today northern Turkey) a marginal sea opened and quickly got filled with sediments (today the basement of the Sakarya Composite Terrane in the Pontides). During the Late Triassic the Neo-Tethys began opening behind Cimmeria when the Eastern Mediterranean and its two eastern branches opened into the Bitlis-Zagros ocean (the southern branch of the Neo-Tethys).[18]

During Early Jurassic Cimmeria began to disintegrate behind the Paleo-Tethyan volcanic arc. This opened the northern branch in the Neo-Tethys — the Intra-Pontide, Izmh-Ankara, and the Inner Tauride oceans. The closure of the Paleo-Tethys in the Middle Jurassic reduced the Cimmerian archipelago in Anatolia. South of the Cimmerian blocks there were now two branches of the Neo-Tethys, a northern, larger and more complex, and a southern, more reduced; the Anatolide-Tauride continent separated them, the small Sakarya continent was located within the northern branch. The Apulian continent was connected to the Anatolide-Tauride continent.[18]

These Neo-Tethyan branches reached their maximum width during the Early Cretaceous, after which subduction under Eurasia gradually consumed them. During the Middle-Late Cretaceous this subduction opened a back-arc basin, the Western Black Sea Basin, which stretched west into the Balkans north of the Rhodope-Pontide island arc there.[19] In the Cretaceous, this basin pushed the Istanbul terrane (near today's Istanbul) southward in front of it, from the Odessa Shelf in the north-western Black Sea. In the Eocene, the terrane finally collided with Cimmeria thereby ending the extension in the western Black Sea. Contemporaneously, the East Black Sea Basin opened when the East Black Sea Block was rotated counter-clockwise towards Caucasus.[20]

In the late Cretaceous northwards intra-oceanic subduction within the Neotethys gave way to the obduction of ophiolitic nappes over the Arabian platform from Turkey to Oman region. North of this subduction zone, remnants of the Neotethys ocean started to subduct northwards and led to the collision of Tauride Block with the Arabian plate during post-Oligocene times. North of these systems, the Tauride block collided with the southern margin of Eurasia by the end of the Cretaceous. Convergence continued until the end of Oligocene. The Arabian-Eurasian collision in eastern Turkey during the Late Eocene closed the two basins.[18]

During the Paleogene Neo-Tethyan oceanic crust attached to the African Plate subducted along the Crete and Cyprus trenches. The Anatolide-Tauride continent collided with the Pontide and Kırşehir blocks in the Late Paleocene-Early Eocene. This closed the Ankara-Erzincan branches of the northern Neo-Tethys. During this closure, slab roll-back and break-off in the Eocene resulted in inversion in the Pontides and widespread magmatism in northern Turkey. Extension and upwelling followed, resulting in melting of lithospheric material beneath the Pontides.[21]

In southern Turkey the northward subduction of the Neo-tethys along the Bitlis-Zagros subduction zone resulted in magmatism in the Maden-Helete arc (south-eastern Turkey) during the Late Cretaceous-Eocene and back-arc magmatism in the Taurides. The Bitlis-Zagros subduction zone finally closed in the Miocene and throughout the Oligocene-Neogene and Quaternary volcanism became increasingly localised. In the Late Oligocene, slab roll-back in the Hellenic Trench resulted in extension in the Aegean and western Turkey.[21]

Iran

The subduction of western Neo-Tethys under Eurasia resulted in extensive magmatism in what is now northern Iran. In the Early Jurassic this magmatism had produced a slab pull force which contributed to the break-up of Pangea and the initial opening of the Atlantic. During the Late Jurassic-Early Cretaceous the subduction of the Neo-Tethys mid-ocean ridge contributed to the break-up of Gondwana, including the detachment of the Argo-Burma terrane from Australia.[5] The Central-East Iranian Microcontinent (CEIM) sutured with Eurasia in the Late Triassic during the regional "Eocimmerian" orogenic event in northern Iran, but Iran is made of several continental blocks and the area must have seen a number of ocean closures in the Late Paleozoic and Early Mesozoic.[22]

Caucasus

The Greater and Lesser Caucasus has a complicated geological history involving the accretion of a series of terranes and microcontinents from the Late Precambrian to the Jurassic within the Tethyan framework. These include the Greater Caucasian, Black Sea-Central Transcaucasian, Baiburt-Sevanian, and Iran-Afghanistan terranes and island arcs.[23] In the Caucasus region remnants of the Paleo-Tethys suture can be found in the Dzirula Massif which outcrops Early Jurassic sequences in central Georgia. It consists of Early Cambrian oceanic rocks and the possible remnants of a magmatic arc; their geometry suggests that suturing was followed by strike-slip faulting. Ophiolites also outcrop in the Khrami Massif in southern Georgia and another possible segment of the suture is present in the Svanetia region. The suture is older east of the Caucasus (northern Iran–Turkmenistan) but younger both west of the Caucasus and further east in Afghanistan and the northern Pamirs.[24]

Sibumasu

The easternmost part of Cimmeria, the Sibumasu terrane, remained attached to north-western Australia until 295–290 Ma when it began to drift northward, as supported by paleomagnetic and biogeographic data. The Qiangtang terrane was located west of Sibumasu and contiguous with it. Lower Permian layers in Sibumasu contain glacial-marine diamictites and Gondwanan faunas and floras which then developed independently before Sibumasu docked with Cathaysia. Sibumasu's rapid northern journey is especially evident in the development of brachiopods and fusulinids.[25]

The Baoshan terrane in western Yunnan, China, forms the northern part of Sibumasu. It is separated from the Burma Block by the Gaoligong Suture Zone to the west, and from the South China and Indochina continents in the east by the Chongshan Suture Zone and Changning-Menglian Belt. Like other parts of eastern Cimmeria, it was highly deformed by the intra-continental strike-slip faulting that followed the India-Asia collision.[26]

Paleomagnetic data indicate South China and Indochina moved from near Equator to 20°N from the Early Permian to Late Triassic. Baoshan, in contrast, moved from 42°S in the Early Permian to 15°N in the Late Triassic. These blocks and terranes occupied similar paleo-latitudes during Late Triassic to Jurassic which indicates that they probably collided in the Late Triassic. This is also supported by geological evidence: 200–230 Ma granite in Lincang, near the Changning-Menglian suture, indicate a continent-continent collision occurred there in the Late Triassic; pelagic sediments in the Changning-Menglian-Inthanon ophiolite belt (between Sibumasu and Indochina) ranges in age from Middle Devonian to Middle Triassic, while, in the Inthanon suture, in contrast, Middle to Late Triassic rocks are non-pelagic with radiolaran cherts and turbidic clastics indicating the two blocks had at least approached each other by that time; volcanic sequences from the Lancangjiang igneous zone indicate a post-collisional setting had developed before the eruptions there around 210 Ma; and, the Sibumasu fauna developed from a non-marine peri-Gondwanan assemblage in the early Permian, to an endemic Sibumasu fauna in the Middle Permian, and to an Equatorial-Cathaysian in the Late Permian.[27]

During the Early and Middle Palaeozoic Cimmeria was located at an Andean-style active margin. Glacial deposits and paleomagnetic data indicate that Qiangtang and Shan Thai-Malaya were still located far south adjacent to Gondwana during the Carboniferous. The equatorial fauna and flora of China indicate that it was separated from Gondwana during the Carboniferous.[3]

Lhasa

The Lhasa terrane has been interpreted as part of Cimmeria and, if this is the case, must have rifted from Gondwana together with Sibumasu and Qiantang. The timing of Lhasa's northward drift is still controversial, however, and paleomagnetic data is extremely scarce. Sedimentological and stratigraphical evidence, for example, suggest that it separated from Gondwana in the Late Triassic when Qiantang was already being accreted to Eurasia.[28] This proposed Late Triassic rifting of Lhasa has also been documented along the north-western shelf of Australia where the Western Burma and Woyla terranes eventually separated from Gondwana in the Late Jurassic.[29]

Today the Bangong suture separates the Lhasa terrane from the Qiangtang terrane.

Economic importance

The present remains of Cimmeria, as a result of the massive uplifting of its continental crust, are unusually rich in a number of rare chalcophile elements. Apart from the Altiplano in Bolivia, almost all the world's deposits of antimony as stibnite are found in Cimmeria, with the major mines being in Turkey, Yunnan and Thailand. The major deposits of tin are also found in Malaysia and Thailand, whilst Turkey also has major deposits of chromite ore.

See also

  • Alpide belt
  • Cathaysia – A microcontinent or group of terranes that rifted off Gondwana during the Late Paleozoic
  • Cimmerian Orogeny
  • Panjal Traps
  • Permian–Triassic extinction event – Most severe extinction event of Earth's chronology, occurring approx 252 million years ago, ending the Paleozoic era (and the Permian period) and beginning the Mesozoic era (and the Triassic period)
  • South China – An ancient continent that contained today's South and Southeast China, Indochina, and parts of Southeast Asia

References

Notes

  1. ^ a b Reconstruction from Dèzes 1999, p. 16
  2. ^ Reconstruction from Stampfli & Borel 2002, p. 27
  3. ^ a b Scotese & McKerrow 1990, pp. 4, 5, 17
  4. ^ Golonka 2007, p. 182
  5. ^ a b c Stampfli & Borel 2002, pp. 24, 28
  6. ^ Metcalfe 2002, p. 556
  7. ^ Neumayr 1883
  8. ^ Suess 1893; Suess 1901
  9. ^ Hsü & Bernoulli 1978, Paleotethys, pp. 943–944 and references therein including Carey 1958
  10. ^ a b Stöcklin 1974, Introduction, p. 873
  11. ^ a b Stampfli 2000, Some definitions, pp. 1–2
  12. ^ Şengör 1984, Şengör 1987
  13. ^ Suess 1901, p. 22
  14. ^ a b c Şengör et al. 1988, pp. 119–120, 123
  15. ^ See for example Frizon de Lamotte et al. 2011, The Zagros Domain and Its Arabian Foreland, p. 4
  16. ^ Frizon de Lamotte et al. 2011, Introduction, pp. 1, 4
  17. ^ Stampfli et al. 2001, Initial Conditions, pp. 57–58
  18. ^ a b c Şengör & Yilmaz 1981, Abstract
  19. ^ Hippolyte, J.-C.; Müller, C.; Kaymakci, N.; Sangu, E. (2010). "Dating of the Black Sea Basin: new nannoplankton ages from its inverted margin in the Central Pontides (Turkey)". Geological Society, London, Special Publications. 340 (1): 113–136. doi:10.1144/SP340.7.
  20. ^ Okay, Şengör & Görür 1994, Abstract; Fig. 3, p. 269
  21. ^ a b Richards 2015, Turkey, pp. 329–330
  22. ^ Buchs et al. 2013, Introduction, pp. 267–268
  23. ^ Gamkrelidze & Shengelia 2007, Introduction, p. 57
  24. ^ Şengör et al. 1988, pp. 139–140
  25. ^ Metcalfe 2002, p. 556; Position of the Sibumasu Terrane, pp. 562–563; Position of the Qiangtang Terrane, p. 563
  26. ^ Zhao et al. 2015, Geological setting and sampling, p. 3
  27. ^ Zhao et al. 2015, The closure of the East Paleotethys Ocean, pp. 10–11, 13
  28. ^ Metcalfe 2002, Position of the Lhasa Terrane, p. 563
  29. ^ Metcalfe 1996, Late Triassic to Late Jurassic rifting, pp. 104–105

Sources

Cathaysia

Cathaysia was a microcontinent or a group of terranes that rifted off Gondwana during the Late Paleozoic.

Cimmeria

Cimmeria may refer to:

Cimmeria, an ancient name of Crimea, a peninsula in the northern part of the Black Sea

The Bosporan Kingdom, a polity of antiquity located on Crimea, also referred to as the Kingdom of the Cimmerian Bosporus, or more simply, Cimmeria

Cimmerians, an ancient people who lived in the North Caucasus in the 8th and 7th century BC, usually associated with the ancient Cimmeria or Crimea

Cimmeria (continent), an ancient microcontinent separating the ancient Paleo-Tethys and Neo-Tethys oceans

Cimmeria (Conan), a fictional country created by Robert E. Howard for his Conan the Barbarian stories

Cimmeria (poem), a poem by Robert E. Howard

Cimmeria, a fictional country in If on a winter's night a traveler by Italo Calvino

Cimmeria (Stargate), a fictional planet in the Stargate setting

Terra Cimmeria, a region on Mars

Cimmerian Orogeny

The Cimmerian Orogeny was an orogeny that created mountain ranges that now lie in Central Asia. The orogeny is believed to have begun 200–150 million years ago (much of the Jurassic Period), when the Cimmerian plate collided with the southern coast of Kazakhstania and North and South China, closing the ancient Paleo-Tethys Ocean between them. The plate consisted of what are now known as Turkey, Iran, Tibet and western Southeast Asia. Much of the plate's northern boundary formed mountain ranges that were as high as the present-day Himalayas. The orogeny continued well into the Cretaceous and Early Cenozoic.

Evolution of insects

The most recent understanding of the evolution of insects is based on studies of the following branches of science: molecular biology, insect morphology, paleontology, insect taxonomy, evolution, embryology, bioinformatics and scientific computing. It is estimated that the class of insects originated on Earth about 480 million years ago, in the Ordovician, at about the same time terrestrial plants appeared. Insects evolved from a group of crustaceans. The first insects were land bound, but about 400 million years ago in the Devonian period one lineage of insects evolved flight, the first animals to do so. The oldest insect fossil has been proposed to be Rhyniognatha hirsti, estimated to be 400 million years old, but the insect identity of the fossil has been contested. Global climate conditions changed several times during the history of Earth, and along with it the diversity of insects. The Pterygotes (winged insects) underwent a major radiation in the Carboniferous (356 to 299 million years ago) while the Endopterygota (insects that go through different life stages with metamorphosis) underwent another major radiation in the Permian (299 to 252 million years ago).

Most extant orders of insects developed during the Permian period. Many of the early groups became extinct during the mass extinction at the Permo-Triassic boundary, the largest extinction event in the history of the Earth, around 252 million years ago. The survivors of this event evolved in the Triassic (252 to 201 million years ago) to what are essentially the modern insect orders that persist to this day. Most modern insect families appeared in the Jurassic (201 to 145 million years ago).

In an important example of co-evolution, a number of highly successful insect groups — especially the Hymenoptera (wasps, bees and ants) and Lepidoptera (butterflies) as well as many types of Diptera (flies) and Coleoptera (beetles) — evolved in conjunction with flowering plants during the Cretaceous (145 to 66 million years ago).Many modern insect genera developed during the Cenozoic that began about 66 million years ago; insects from this period onwards frequently became preserved in amber, often in perfect condition. Such specimens are easily compared with modern species, and most of them are members of extant genera.

Geological history of Earth

The geological history of Earth follows the major events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.

Earth was initially molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as a result of the impact of a planetoid with the Earth. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans.

As the surface continually reshaped itself over hundreds of millions of years, continents formed and broke apart. They migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago, the earliest-known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia, 600 to 540 million years ago, then finally Pangaea, which broke apart 200 million years ago.

The present pattern of ice ages began about 40 million years ago, then intensified at the end of the Pliocene. The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40,000–100,000 years. The last glacial period of the current ice age ended about 10,000 years ago.

Outline of plate tectonics

This is a list of articles related to plate tectonics and tectonic plates.

Permian

The Permian ( PUR-mee-ən) is a geologic period and system which spans 47 million years from the end of the Carboniferous period 298.9 million years ago (Mya), to the beginning of the Triassic period 251.902 Mya. It is the last period of the Paleozoic era; the following Triassic period belongs to the Mesozoic era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia.The Permian witnessed the diversification of the early amniotes into the ancestral groups of the mammals, turtles, lepidosaurs, and archosaurs. The world at the time was dominated by two continents known as Pangaea and Siberia, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, which could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors.

The Permian (along with the Paleozoic) ended with the Permian–Triassic extinction event, the largest mass extinction in Earth's history, in which nearly 96% of marine species and 70% of terrestrial species died out. It would take well into the Triassic for life to recover from this catastrophe. Recovery from the Permian–Triassic extinction event was protracted; on land, ecosystems took 30 million years to recover.

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