History of gondwana

Gondwana is the name given to the southern continents that amalgamated before they joined, as a group, to the northern continents of Laurentia to form Pangaea. Most of Gondwana was assembled in the period between 600 million and 400 million years ago, when many Archean cratons were joined together by suturing during closure of several ocean basins that lay between them, forming a series of orogenic belts across Africa, India, South America, Madagascar, Antarctica, and Australia known as the Pan-African belts. The last of these oceans to close was the Mozambique Ocean, which lay between western Gondwana (eastern Africa and South America) on one side and eastern Gondwana (Madagascar, India, Australia, Antarctica) on the other side.

The fauna of Gondwana (southern fauna) were distinct from those in North America (northern fauna) until the Devonian, when they became similar. In the late Paleozoic Gondwana collided with North America during the Appalachian (also called the Alleghenian) Orogeny, forming Pangaea. In addition southern South America, western Antarctica, and New Zealand collided with southern Gondwana to form orogenic belts there and further increasing the size of Pangaea. Like the Taconic and Acadian orogens these orogenic belts also have clastic wedges associated with them, recording the history of uplift and erosion of these mountain ranges.

Gondwana shows a remarkably similar stratigraphy on all of the major southern continents, grading from Devonian tillite (glacial gravels), through Carboniferous and Permian coal, Triassic red beds (sandstone and conglomerate), and Jurassic through Cretaceous volcanic rocks. The Devonian glacial til-lites are remarkable rocks, found on all five southern continents. These were deposited unconformably on older rocks, and in many places the unconformity surface preserves scratches made by glaciers hundreds of millions of years ago. Boulders in the tillite also locally preserve glacial striations, plus isolated

Alex Du Toit's reconstruction of Gondwana showing areas affected by glaciation, striation directions, and other tectonic features

Gondwana History

pebbles called dropstones, dropped by glaciers into otherwise muddy sediments, showing beyond reasonable doubt that these rocks were deposited in a glacial environment. Most of these tillites are interbedded with nonmarine rocks that bear a distinctive fossil assemblage including a seed fern called Glossopteris that inhabited low swampy areas next to glaciated terrane. The Glossopteris flora is found across much of Gondwana, and was used by Du Toit and Wegener to support their reconstructions of the late Paleozoic supercontinent. The Gondwanan stratigraphy grades up into Carboniferous to Permian coals, and then Triassic red beds, and finally Jurassic-Cretaceous volcanic rocks consisting mostly of basalt flows. These basalts are related to the breakup of Gondwana and Pangaea, and spreading of the modern oceans.

The animals of Gondwana included a great variety of reptiles, amphibians, fish, and invertebrates, some with key correlations across present-day oceans. since these animals could not swim across such vast expanses of ocean, they provide additional supporting evidence that the continents were once joined together in a supercontinent mass. one of these animals, the Mesosauris, is a reptile that inhabited swampy areas and lived in present-day Brazil and southern Africa. other animals that show simi lar matches across the oceans include the dinosaurs and the reptiles Lystrosaurus and Cynognathus.

The climate of Pangaea was diverse. There are glacial deposits in some places and times (e.g., the Permian), indicating a cold climate, and in other places and times there were swamps (Glossopteris) forming coals, indicating warm and swampy climate conditions, and in still other places evaporates formed, indicating hot, dry conditions.

The breakup of Pangaea began after the supercontinent had been united for about 200 million years and is marked by the eruption of the voluminous Jurassic and Cretaceous volcanics across the continents. Laurasia saw its breakup in the Late Triassic, as indicated by the formation of many rift basins such as the Triassic rifts along the eastern seaboard of North America. The rifts were filled with coarse sandstones and conglomerates as well as volcanic rocks, and they are generally colored red by the iron oxides formed during the intense hot climate of these times. Many of the rift basins preserve dinosaur footprints and other interesting fossils. As waters from the ocean occasionally spilled into the rifts during short-lived sea-level rises, evaporates formed as these waters evaporated in the hot climate. Rifting continued until the Middle Jurassic, when North

America or Laurentia began drifting apart from Gondwana and the supercontinent began breaking up all over. Some models suggest that the reason Gondwana broke up, and saw so much magmatism during breakup, is that it came to rest over a mantle hot spot that heated the lithosphere and caused the volcanics to erupt.

In the latest Cretaceous (about 66 million years ago, at the Cretaceous-Tertiary boundary) North America began moving away from Europe, opening the North Atlantic Ocean. During the evolution of Pangaea a large ocean, the Tethys Ocean, separated parts of the Northern and Southern continents (which were connected elsewhere). During breakup of Pan-gaea and opening of the Atlantic Ocean, the Tethys began closing and is now largely closed except for remnants in the Mediterranean, Black, and Caspian Seas.

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  • Ricky Hinton
    What are history of Gondwanaland?
    10 months ago

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