Everything about Gondwana totally explained
Gondwana (originally
Gondwanaland) was a southern
supercontinent that existed about 500 to 200
Ma ago. 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
Arabia and the
Indian subcontinent, which are in the
Northern Hemisphere. The name is derived from the
Gondwana region of central northern
India (from
Sanskrit gondavana "forest of
Gond").
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; for example, the
Proteaceae, a family of plants that's known only from
Chile,
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
orogenies led to its final amalgamation 550–500 million years ago in the
Cambrian. 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 Ocean between
Laurentia and western Gondwana. During this interval the
Cambrian Explosion occurred.
Gondwanaland was formed by these earlier continents and
microcontinents, and others, colliding in these orogenies:
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–
Bangweulu Block.
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.
Pangaea
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
Pangaea by
Permian time. 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 wasn't precisely the same as before Pangaea formed; 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.
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. 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, 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's strong evidence of glaciation during
Carboniferous to
Permian time, especially in South Africa.
Breakup
Mesozoic
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
Seychelles Islands, 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
Eocene epoch of the
Tertiary Period.
New Zealand probably separated from Antarctica between 130 and 85 million years ago.
Cenozoic
As the
age of mammals got underway, the continent of
Australia-New Guinea began 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 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. Cooler and drier climates developed on both continents because ocean currents enveloping Antarctica were no longer directed into the
subtropics, where they'd have flowed around northern Australia.
Another significant world climatic event was
South America separating from
West Antarctica some 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 Peninsula remained near southern South America acting as "
stepping stones" allowing continued biological interchange and stopped oceanic current circulation. But when
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's 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 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 .
The
Red Sea and
East African Rift are modern examples of the continuing dismemberment of Gondwana.
The continent of Gondwana was named by
Eduard Suess after an area of India called
Gondwana (meaning "Land of the
Gonds"), from which the Gondwana sedimentary sequences (Permian-Triassic) are also described.
Further Information
Get more info on 'Gondwana'.
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