Gondwana (IPAEng|ɡɒnˈdwɑːnə [OED] , originally Gondwanaland) was a southern
supercontinentthat existed about 500 to 200 Ma ago.Fact|date=September 2008 Gondwana included most of the landmasses in today's southern hemisphere, including Antarctica, South America, Africa, Madagascar, Australia-New Guinea, and New Zealand, as well as Arabiaand the Indian subcontinent, which are in the Northern Hemisphere. The name is derived from the Gondwana region of central northern India(from Sanskritgondavana "forest of Gond").
The adjective "Gondwanan" is in common use in
biogeographywhen 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; e.g., the Proteaceae, a family of plants that is known only from Chile, South Africa, and Australiaare considered to have a "Gondwanan distribution". This pattern is often considered to indicate an archaic, or relictlineage.
The assembly of Gondwana was a protracted process. Several orogenies led to its final amalgamation 550–500 million years ago in the
Cambrian. [ [http://gsa.confex.com/gsa/2004AM/finalprogram/abstract_78645.htm Linking Subduction Initiation, Accretionary Orogenesis And Supercontinent Assembly ] ] These include the Brasiliano Orogeny, the East African Orogeny, the Malagasy Orogeny, and the Kuunga Orogeny. The final stages of Gondwana assembly overlapped with the opening of the Iapetus Oceanbetween Laurentiaand western Gondwana. During this interval the Cambrian Explosionoccurred.
Gondwanaland was formed by these earlier continents and
microcontinents, and others, colliding in these orogenies:
Azania: much of central Madagascar, the Horn of Africaand parts of Yemenand Arabia. (Named by Collins and Pisarevsky (2005): "Azania" was a Greek name for the East African coast.)
* The Congo–
Tanzania– BangweuluBlock of central Africa.
* Neoproterozoic India: India, the
AntongilBlock in far eastern Madagascar, the Seychelles, and the Napier and Rayner Complexes in East Antarctica.
* The Australia/Mawson continent: Australia west of Adelaide and a large extension into
* Other blocks which helped to form
Argentinaand around, including a piece transferred from Laurentiawhen the west edge of Gondwana scraped against southeast Laurentia in the Ordovician[ [http://adsabs.harvard.edu/abs/2001AGUSM..GP32D03R The Assembly of Southern South America in the Late Proterozoic and Paleozoic: So ] ] [ [http://findarticles.com/p/articles/mi_qa3721/is_199801/ai_n8776512 Syntectonic magnetization of the mid-Palaeozoic Sierra Grande Formation: Further constraints on the tectonic evolution of Patagonia | Journal of the Geological Society | Find Articles at BNET.com ] ] .
One of the major sites of Gondwana amalgamation was the East African Orogen (Stern, 1994), where these two major orogenies are superimposed on each other:
The East African Orogeny (as later defined) at ~650–630 Ma ago 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– Tanzania– BangweuluBlock.
The later Malagasy orogeny at ~550–515 Ma ago affected Madagascar, eastern East Africa and southern India. In it Neoproterozoic India collided with the already combined Azania and Congo–Tanzania–Bangweulu Block.
At the same time, in the Kuunga Orogeny Neoproterozoic India collided with the Australia/Mawson continent.
Other large continental masses, including the cores of North America (
Canadian Shieldor Laurentia), Europe ( Baltica), and Siberiawere added over time to form the supercontinent Pangaeaby Permiantime. When Pangaea broke up (mostly during the Jurassic), two large masses, Gondwana and Laurasia, were formed.
When Pangaea broke up, the re-formed Gondwana continent was not precisely the same as before Pangaea formed; for example, most of
Floridaand southern Georgia and Alabamaare underlain by rocks that were originally part of Gondwana but that were left attached to North America when Pangaea broke apart.
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. India contains about 3% of the world's coal reserves and much of the mined coal is derived from the late PaleozoicGondwana sedimentary sequence. 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. But there is strong evidence of glaciation during Carboniferousto Permiantime, especially in South Africa.
Gondwana began to break up in the mid-Jurassic (about 167 million years ago), when 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 million years ago during the Early
Cretaceous, and resulting in open marine conditions by 110 million years ago. East Gondwana itself began to be dismembered about 120 million years ago as India began to move northward.
The Madagascar block, and a narrow remnant microcontinent presently occupied by the
SeychellesIslands, were broken off India; elements of this breakup nearly coincide with the Cretaceous-Tertiary extinction event. The India–Madagascar–Seychelles separations appear to coincide with the eruption of the Deccan basalts, whose eruption site may survive as the Réunion hotspot.
Australia began to separate from Antarctica perhaps 80 million years ago (Late Cretaceous), but sea-floor spreading between them became most active about 40 million years ago during the
Eoceneepoch of the TertiaryPeriod. New Zealandprobably separated from Antarctica between 130 and 85 million years ago.
As the age of mammals got underway, the continent of
Australia-New Guineabegan gradually to separate and move north (55 million years ago), rotating about its axis to begin with, and thus retaining some connection with the remainder of Gondwana for about 10 million years.
About 45 million years ago, the
Indian Platecollided 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. Cooler and drier climates developed on both continents because ocean currents enveloping Antarctica were no longer directed into the subtropics, where they would have flowed around northern Australia.
Another significant world climatic event was
South Americaseparating from West Antarcticasome time during the Oligocene, perhaps 30 million years ago. Immediately before this, South America and East Antarctica were not connected directly, but the many microplates of the Antarctic Peninsularemained near southern South America acting as " stepping stones" allowing continued biological interchange and stopped oceanic current circulation. But when Drake Passageopened, there was now no barrier to force the cold waters of the Southern Oceannorth, 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 million years ago, 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 shadoweffect 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 ArcticFact|date=October 2007.
Red Seaand East African Riftare modern examples of the continuing dismemberment of Gondwana.
The continent of Gondwana was named by
Eduard Suessafter an area of India called Gondwana (meaning "Land of the Gonds"), from which the Gondwana sedimentary sequences (Permian-Triassic) are also described.
Alexander du Toit
Polar dinosaurs in Australia
* Geology of the Australasian ecozone
* Cattermole, Peter John. "Building Planet Earth: Five Billion Years of Earth History." Cambridge, Cambridge University Press, 2000.
* Collins A.S. and Pisarevsky, S.A. 2005 Amalgamating Eastern Gondwana: The evolution of the circum-Indian orogens. Earth Science Reviews, 71, 229–270.
* Cowen, Richard. "History of Life." London, Blackwell Publishing, 2000.
*Lowrie, William. "Fundamentals of Geophysics." Cambridge, Cambridge University Press, 1997.
*Meert, J.G., 2003, A synopsis of events related to the assembly of eastern Gondwana, Tectonphysics, 362, 1-40.
* Stern, R.J. 1994 Arc Assembly and continental collision in the Neoproterozoic East African orogeny—implications for the consolidation of Gondwana. Annual Reviews of Earth and Planetary Sciences, 22, 319–351.
* Meert, J.G., 2003, A synopsis of events related to the assembly of eastern Gondwana, Tectonphysics, 362, 1-40.
* Scheffler, K., and others, 2003, Global changes during Carboniferous–Permian glaciation of Gondwana: Linking polar and equatorial climate evolution by geochemical proxies
* [http://earth.leeds.ac.uk/~greg/Gond.html Animation showing the dispersal of Gondwanaland]
* [http://kartoweb.itc.nl/gondwana/index.asp Another animation]
* [http://www.scotese.com/earth.htm Graphical subjects dealing with Tectonics and Paleontology]
* [http://www.searchanddiscovery.com/documents/97019/index.htm Gondwana Reconstruction and Dispersion]
* [http://www.ipy.org/development/eoi/details.php?id=156 Study of the Separation between Antarctica and South America]
* [http://www.awi-bremerhaven.de/Publications/Kni2005c_abstract.html König, M., Jokat, W., 2006, The Mesozoic breakup of the Weddell Sea: Journal of geophysical research]
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