Gondwana

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The major continents Laurasia and Gondwana in the Triassic , about 200 million years ago
Video on the formation of New Zealand initially shows Pangea , Tethys Sea , Gondwana and Laurasia

Gondwana , also Gondwanaland or more rarely Gondwania , is the name of the major continent that existed in the southern hemisphere during most of the known history of the earth . From the late Carboniferous to the Jurassic , Gondwana formed the southern part of the supercontinent Pangea over a period of about 150 million years , with an area of ​​about 73 million km² during the Permian .

At least twice, Gondwana formed a supercontinent together with the northern continental floes of Laurasia :

The late Archaic supercontinent Kenorland two and a half billion years ago is not considered to be stratigraphically secure.

history

With the help of the paleobiogeographical distribution areas of Cynognathus , Mesosaurus , Glossopteris and Lystrosaurus marked here in color , the arrangement of today's separate continents into Gondwana can be reconstructed.
Cratons in West Gondwana

Gondwana comprised the continents or cratons of South America , Africa , Antarctica , Australia , Arabia , Madagascar , New Guinea , Zealandia and India , which were then united in one land mass .

The great continent was formed in the early Earth period ( Precambrian ) by the collision of East and West Gondwana - fragments of Rodinia - in the course of the Pan-African orogeny 600 million years ago. After it was grouped around the South Pole for a long time, it merged in the late Carboniferous (approx. 310 million years ago) in the course of its drift to the north with the then North American-Scandinavian continent Laurussia and the craton of Asia to form the supercontinent Pangea . The connection between Gondwana and North America lasted until about 180 million years ago ( Jura ). After that, Gondwana existed again as an independent major continent, which however began to break up around 150 million years ago (towards the end of the Jura), initially between Africa and Madagascar, and most recently between Australia and the Antarctic.

After the breakup of Gondwana - as a fragment of Pangea - about 100 million years ago, Africa collided with Europe in the course of the continental drift , which bulged the Alps , while the collision of India with Asia in the Paleogene created the Himalayas . This recent process is called Alpidic orogenesis .

Eastern Gondwana: Orogens and Kuunga Orogens

Climate, geography and vegetation

In the course of the Phanerozoic Gondwana was twice covered by glaciers and ice sheets, the first time during the Andes-Sahara Ice Age (also called the Brain-like Ice Age or Silur-Ordovician Ice Age). This began around 460 million years ago in the Upper Ordovician , reached its climax at the last Ordovician stage of the Hirnantium and ended in the Lower Silurian 430 million years ago. On the basis of glacial deposits, the drift and the direction of movement of the major continent over the southern polar regions could be reconstructed in chronological order. The core area of ​​the glaciation was concentrated on the Arabian plate 450 to 440 million years ago and then on today's Sahara, then migrated westwards towards South America (Brazil and the lower Amazon region) and 430 million years ago did not cover the region of the then in a weaker form existing Andean chain .

During the Permocarbon glaciation (also known as the Karoo Ice Age ), Gondwana again became the center of large-scale glaciation. This affected what is now southern Africa and large parts of South America between 359 and 318 million years ago. In a second glacial phase in the Pennsylvania 318 to 299 million years ago, the ice sheets shifted to the cratons of India and Australia, before southern Africa glaciated again during the Dwyka Glacial (until 280 million years ago). The Permocarbone Ice Age was the second longest ice age in the history of the earth. It comprised a large part of the Carboniferous and ended during the Permian about 265 million years ago. The position of Gondwana in the Antarctic , which has changed little over many millions of years, was a major climatic factor for the formation of the two Paleozoic glacial periods, since ice formations on the mainland are generally more stable and voluminous than over the open sea and are caused by the process of ice albedo Further reinforce feedback .

In the Upper Carboniferous ( Kasimovian stage ) a rapid reduction of the rainforests near the equator occurred 305 million years ago (English Carboniferous Rainforest Collapse ). The tropical forests were decimated to a few islands of vegetation within a geologically very short period of time, and many wetlands and marshlands also disappeared. During the transition from the Carboniferous to the Permian , new forest biotopes were created, which were adapted to a cooler and dry climate with seasonal temperature fluctuations. An example of this change is the cold-resistant and deciduous Glossopteris flora in the southern part of Gondwana, which there developed into a species-poor but widespread type of plant.

Large continents and supercontinents are characterized by a pronounced continental climate with an annual temperature amplitude of up to 50 ° C, extensive arid and desert areas in the interior, and a low level of biodiversity in the fauna area . After the major continents Laurussia and Gondwana merged in the Upper Carboniferous to form the supercontinent Pangea and thus to form a huge continental barrier, the water and heat exchange of the equatorial ocean currents was interrupted. Instead, Antarctic cold water flowed increasingly north along the coast of Gondwana.

Surname

In 1861, the Austrian geologist Eduard Suess suggested the name Gondwana for the primary continent . The name comes from the Gondwana region in central India (from Sanskrit gondavana "land of the Gonds ", after the Indian people ).

The adjective gondwana is used in biogeography to describe distribution patterns of living organisms that occur only in two or more of the now spatially separated regions that were once part of Gondwana, including the restricted Antarctic flora . For example, the silver tree family (Proteaceae) is only known in southern South America, South Africa and Australia; it is therefore "gondwana-distributed".

Individual evidence

  1. ↑ Spencer G. Lucas, Joerg W. Schneider, Giussepe Cassinis: Non-marine Permian biostratigraphy and biochronology: an introduction. In: Spencer G. Lucas, Giuseppe Cassinis, Joerg W. Schneider (Eds.): Non-Marine Permian Biostratigraphy and Biochronology (= Special Publications . Volume 265). The Geological Society of London , London 2006, print ISBN 978-1-86239-206-9 pp. 1–14, accessed on January 19, 2017 (PDF; 4.2 MB, English).
  2. ↑ Isabel P. Montañez, Neil J. Tabor, Deb Niemeier, William A. DiMichele, Tracy D. Frank, Christopher R. Fielding, John L. Isbell, Lauren P. Birgenheier, Michael C. Rygel: CO 2 -Forced Climate and Vegetation Instability During Late Paleozoic Deglaciation . (PDF) In: Science . 315, No. 5808, January 2007, pp. 87-91. doi : 10.1126 / science.1134207 .
  3. ↑ Borja Cascales-Miñana, Christopher J. Cleal: The plant fossil record reflects just two great extinction events . In: Terra Nova . 26, No. 3, 2013, pp. 195-200. doi : 10.1111 / ter.12086 .
  4. ^ William A. DiMichele, Neil J. Tabor, Dan S. Chaney, W. John Nelson: From wetlands to wet spots: Environmental tracking and the fate of Carboniferous elements in Early Permian tropical floras . (PDF) In: GSA (Geological Society of America) . Special Paper 399, 2006, pp. 223-248. doi : 10.1130 / 2006.2399 (11) .
  5. ^ Neil J. Tabor: Wastelands of tropical Pangea: High heat in the Permian . In: Geology . tape 41 , no. 5 , 2013, p. 623–624 , doi : 10.1130 / focus052013.1 .

Web links

Commons : Laurasia and Gondwana  - Collection of Images