Gondwana

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Biography

In paleogeography , Gondwana (),
originally Gondwanaland, was the southernmost of two supercontinent s (the other being Laurasia ) that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180& nbsp;million years ago& nbsp;(Mya). Gondwana is believed to have suture (geology)|suture d between ca. 570 and 510& nbsp;Mya, thus joining East Gondwana to West Gondwana. It separated from Laurasia 200-180& nbsp;Mya (the mid Mesozoic era (geology)|era ) during the breakup of Pangaea, drifting further south after the split.

Gondwana included most of the landmasses in today's Southern Hemisphere , including Antarctica , South America , Africa , Madagascar and the Australia (continent)|Australian continent , as well as the Arabian Peninsula and the Indian subcontinent , which have now moved entirely into the Northern Hemisphere .

The continent of Gondwana was named by Austrian scientist, Eduard Suess , after the Gondwana (India)|Gondwana region of central northern India (from Sanskrit gondavana "forest of the Gondi people|Gonds "), from which the Gondwana sedimentary sequences ( Permian - Triassic ) are also described.

The adjective Gondwanan is in common use in biogeography when referring to patterns of distribution of living organisms, typically when the organisms are restricted to two or more of the now-discontinuous regions that were once part of Gondwana, including the Antarctic flora . For example, the Proteaceae , a family of plants known only from southern South America, South Africa and Australia, are considered to have a "Gondwanan distribution". This pattern is often considered to indicate an archaic, or relict , lineage.

Formation

The assembly of Gondwana was a protracted process. Several Orogeny|orogenies led to its final amalgamation 550–500& nbsp;Mya at the end of the Ediacaran , and into the Cambrian . These include the Brasiliano Orogeny , the East African Orogeny , the Malagasy Orogeny , and the Kuunga Orogeny . The final stages of Gondwanan assembly overlapped with the opening of the Iapetus Ocean between Laurentia and western Gondwana. During this interval the Cambrian explosion occurred.

Gondwana was formed from the following earlier continent s and microcontinents , among others, colliding in the following orogenies:

Azania : much of central Madagascar , the Horn of Africa and parts of Yemen and Arabia. (Named by Collins and Pisarevsky (2005): "Azania" was a Greek name for the East African coast.)

The Congo Basin|Congo – Tanzania – Bangweulu Block of central Africa.

Neoproterozoic India: India, the Antongil Block in far eastern Madagascar, the Seychelles , and the Napier and Rayner Complexes in East Antarctica .

The Australia/ Mawson Sea|Mawson continent: Australia west of Adelaide and a large extension into East Antarctica .

Other blocks which helped to form Argentina and some surrounding regions, including a piece transferred from Laurentia when the west edge of Gondwana scraped against southeast Laurentia in the Ordovician . This is the Famatinian block (named after Famatina in northwest Argentina) and it formerly continued the line of the Appalachians southwards. http://sp.lyellcollection.org/content/142/1/219.abstract Laurentia-Gondwana collision: the origin of the Famatinian-Appalachian Orogenic Belt (a review)

One of the major sites of Gondwanan amalgamation was the East African Orogeny (Stern, 1994), where these two major orogenies are superimposed on each other. The East African Orogeny at ~650–630& nbsp;Mya affected a large part of Arabia, north-eastern Africa, East Africa and Madagascar . Collins and Windley (2002) propose that in this orogeny Azania collided with the Congo craton|Congo – Tanzania craton|Tanzania –Bangweulu Block.

The later Malagasy orogeny at ~550–515& nbsp;Mya affected Madagascar, eastern East Africa and southern India. In it Neoproterozoic India collided with the already combined Azania and Congo–Tanzania–Bangweulu Block, suturing along the Mozambique Belt .

At the same time, in the Kuunga Orogeny Neoproterozoic India collided with the Australia/Mawson continent.

Pangaea

Other large continental masses, including the core craton s of North America (the Canadian Shield or Laurentia), Europe ( Baltica ), and Siberia were added over time to form the supercontinent Pangaea by Permian time. When Pangea broke up (mostly during the Jurassic ), two large masses, Gondwana and Laurasia, were formed. The re-formed Gondwanan continent was not precisely the same as that which existed before Pangaea formed; for example, most of Florida and southern Georgia (U.S. state)|Georgia and Alabama are underlain by rocks that were originally part of Gondwana but that were left attached to North America when Pangea broke apart.

Climate

During the late Paleozoic , Gondwana extended from a point at or near the south pole to near the equator. Across much of Gondwana, the climate was mild. During the Mesozoic , the world was on average considerably warmer than today. Gondwana was then host to a huge variety of flora and fauna for many millions of years. The laurel forest of Australia, New Caledonia and New Zealand have a number of other related species of the laurissilva de Valdivia, through the connection of the Antarctic flora as gymnosperms and deciduous angiosperm Nothofagus. Corynocarpus laevigatus is called the bay of New Zealand, Laurelia novae-zelandiae belongs to the same genus Laurelia . The sempervirens tree niaouli , it grows in Australia, New Caledonia and New Zealand. New Caledonia and New Zealand ecoregion are separated by continental drift from Australia 85 million years ago. The islands still retain Flora|plants and animal s that originated in Gondwana and spread to the southern hemisphere continents later.
But there is strong evidence of glaciation during Carboniferous to Permian time, especially in South Africa.

Breakup

Mesozoic

Gondwana began to break up in the Jurassic|early-Jurassic (about 184& nbsp;Mya) accompanied by massive eruptions of basalt lava, as East Gondwana, comprising Antarctica, Madagascar, India and Australia, began to separate from Africa. South America began to drift slowly westward from Africa as the South Atlantic Ocean opened, beginning about 130& nbsp;Mya during the Early Cretaceous|Early Cretaceous , and resulting in open marine conditions by 110& nbsp;Mya. East Gondwana then began to separate about 120& nbsp;Mya when India began to move northward.

The Madagascar block, and a narrow remnant microcontinent presently occupied by the Seychelles Islands, were broken off India; elements of this breakup nearly coincide with the Cretaceous–Paleogene extinction event . The India–Madagascar–Seychelles separations appear to coincide with the eruption of the Deccan Traps|Deccan basalts , whose eruption site may survive as the Réunion hotspot .

Australia began to separate from Antarctica perhaps 80& nbsp;Mya (Late Cretaceous), but sea-floor spreading between them became most active about 40& nbsp;Mya during the Eocene epoch of the Paleogene Period.

New Zealand probably separated from Antarctica between 130 and 85& nbsp;Mya.

Cenozoic

As the Cenozoic|age of mammals went underway, the continent of Australia-New Guinea began gradually to separate and move north (55& nbsp;Mya), rotating about its axis to begin with, and thus retaining some connection with the remainder of Gondwana for about 10 million years.

About 45& nbsp;Mya, the Indian Plate collided with Asia, buckling the crust and forming the Himalayas . At about the same time, the southernmost part of Australia (modern Tasmania ) finally separated from Antarctica, letting ocean currents flow between the two continents for the first time. Antarctica became cooler and Australia became drier because ocean currents circling Antarctica were no longer directed around northern Australia into the subtropic s.

The separation of South America from West Antarctica some time during the Oligocene , perhaps 30& nbsp;Mya also caused climate change s. Immediately before this, South America and East Antarctica were not connected directly, but the many microplates of the Antarctic Peninsula remained near southern South America acting as " Stepping Stones (islands)|stepping stones " allowing continued biological interchange and stopped oceanic current circulation. But when the Drake Passage opened, there was now no barrier to force the cold waters of the Southern Ocean north, to be exchanged with warmer tropical water. Instead, a cold circumpolar current developed and Antarctica became what it is today: a frigid continent that locks up much of the world's fresh water as ice. Sea temperatures dropped by almost 10°C, and the global climate became much colder.

By about 15& nbsp;Mya, the collision between New Guinea (on the leading edge of the Australian Plate) and the southwestern part of the Pacific Plate pushed up the New Guinea highlands, causing a rain shadow effect which drastically changed weather patterns in Australia, drying it out.

Later, South America was connected to North America via the Isthmus of Panama , cutting off a circulation of warm water and thereby creating the Arctic , as well as allowing the Great American Interchange|Great American Faunal Interchange .

The Red Sea and East African Rift are modern examples of the continuing dismemberment of Gondwana.

Notes

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