Gondwana

The southern supercontinent Gondwana (originally Gondwanaland) included most of the landmasses which make up today's continents of the southern hemisphere, including Antarctica, South America, Africa, Madagascar, Australia-New Guinea and New Zealand, as well as Arabia and India, which are in the Northern Hemisphere. The assembly of Gondwana was a protracted process. Several distinct orogenic events led to its final amalgamation during the 550-500 Ma interval (Cambrian time). These include the Brasiliano, East African and Kuungan Orogens. The final stages of Gondwana assembly overlapped with the opening of the Iapetus Ocean between Laurentia and western Gondwana. It was also during this same interval of time that the Cambrian Explosion occurred. Other large continental masses, including the cores of North America (Canadian Shield or Laurentia), Europe (Baltica), and Siberia were added over time to form the supercontinent Pangea by Permian time. With the breakup of Pangea (mostly during Jurassic time), two large masses, Gondwana and Laurasia were formed.

During the late Paleozoic, Gondwana extended from a point at or near the south pole to near the equator. Across much of the supercontinent, 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 Paleozoic Gondwana sedimentary sequence. During the Mesozoic, average global temperatures were considerably warmer than they are today. Gondwana was then host to a huge variety of flora and fauna for many millions of years. Nonetheless, strong evidence of glaciation during Carboniferous to Permian time exists, especially in South Africa.

The supercontinent began to break up in the mid- to late Jurassic (about 167 million years ago) when East Gondwana, comprising Antarctica-Madagascar-India-Australia, began to separate from Africa during the Middle Jurassic. South America began to drift slowly westward from Africa as the South Atlantic Ocean opened, beginning about 130 million years ago (Early Cretaceous) and resulting in open marine conditions by 110 million years ago. East Gondwana itself began to be dismembered as India began to move northward, in the Early Cretaceous (about 120 million years ago).

India was further broken into the Madagascar block and a narrow remnant microcontinent presently occupied by the Seychelles Islands; elements of this breakup are nearly coincident with the Cretaceous-Tertiary extinction event that wiped out about 50% of all species on the planet, most notably the dinosaurs, 65 million years ago. The India-Madagascar-Seychelles separations appear to coincide with the eruption of the Deccan basalts, perhaps an expression of the initiation of the Reunion hot spot. Australia began to separate from Antarctica perhaps as long ago as 80 million years (Late Cretaceous), but sea-floor spreading between them became most active about 40 million years ago during the Eocene epoch of the Tertiary Period. New Zealand probably separated from Antarctica between 130 and 85 million years ago.

When Pangaea broke up, the re-formed Gondwana continent was not precisely the same as the one that contributed to Pangaea's formation by amalgamation; for example, most of Florida and southern Georgia and Alabama are underlain by rocks that were originally part of Gondwana but that were left attached to North America when Pangaea broke apart.

As the age of mammals got underway, the continent of Australia-New Guinea began to gradually 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 a considerable time.

About 45 million years ago, the Indian subcontinent collided with Asia, forcing the crust to buckle and forming the Himalayas. At about the same time, the southern-most portion of Australia (modern Tasmania) finally separated from what is now Antarctica, allowing ocean currents to flow between the two continents for the first time. This in turn produced cooler and drier climates on the two landmasses.

Another significant world climatic event was the final separation of South America from West Antarctica sometime during the Oligocene, perhaps 30 million years ago. With the opening of Drake Passage, 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 which locks up much of the world's fresh water as ice. Sea temperatures dropped by almost 10 degrees, and the global climate became much colder. Note that the main continental masses of South America and East Antarctica were not connected directly, but the many microplates of the Antarctic Peninsula remained near southern South America - perhaps near enough to permit biological interchange and to provide the barrier to oceanic circulation mentioned above.

About 15 million years ago, New Guinea began to collide with southern Asia, once again pushing up high mountains, and more recently still, South America became joined to North America via the Isthmus of Panama. This had the effect of cutting off circulation of warm water, creating the Arctic.

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

The continent was named by Eduard Suess after Gondwana, literally "Land of (wana) the Gonds". The Gondwana sedimentary sequences (Permian-Triassic) are also described from the India section.

External links and References

Animation showing the dispersal of Gondwanaland
Another animation
Graphical subjects dealing with Tectonics and Paleontology, here: http://www.scotese.com/earth.htm
DeWit, M., and others, 1999, Gondwana Reconstruction and Dispersion: American Assoc. of Petroleum Geologists, Search and Discovery ^*
International Polar year ^*
König, M., Jokat, W., 2006, The Mesozoic breakup of the Weddell Sea: Journal of geophysical research ^*
Turner, Brian, Tectono-stratigraphic modelling of the Upper Karoo foreland basin: orogenic unloading versus thermally-induced Gondwana rifting ^*
Scheffler, K., and others, 2003, Global changes during Carboniferous–Permian glaciation of Gondwana: Linking polar and equatorial climate evolution by geochemical proxies ^*

Historical continents

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See also

External links and References