Andean-Saharan glaciation

The Andean-Saharan glaciation occurred during the Paleozoic from 450 Ma to 420 Ma, during the late Ordovician and the Silurian period. For the Ordovician/Saharan part, see the more extensive article on the Late Ordovician glaciation.

According to Eyles and Young, "A major glacial episode at c. 440 Ma, is recorded in Late Ordovician strata (predominantly Ashgillian) in West Africa (Tamadjert Formation of the Sahara), in Morocco (Tindouf Basin) and in west-central Saudi Arabia, all areas at polar latitudes at the time. From the Late Ordovician to the Early Silurian the centre of glaciation moved from northern Africa to southwestern South America."[1]

During this period glaciation is known from Arabia, Sahara, West Africa, the south Amazon, and the Andes. The center of glaciation migrated from Sahara in the Ordovician (450–440 Ma) to South America in the Silurian (440–420 Ma). The maximum extent of glaciation developed in Africa and eastern Brazil.[2]

A minor ice age, the Andean-Saharan was preceded by the Cryogenian ice ages (720–630 Ma, the Sturtian and Marinoan glaciations), often referred to as Snowball Earth, and followed by the Karoo Ice Age (350–260 Ma).[3]

Causes

Although solar output was about 4.5% weaker during the Late Ordovician, a difference that would trigger a glaciation today, carbon dioxide levels were about 18 times higher. However during this time, the Atlantic oceanic crust was subducting under the North American continent, resulting in the Appalachian orogeny (325–260 Ma) which caused carbon dioxide levels to fall via silicate weathering. This, combined with the configuration of the continents & the Earth's orbit, may have triggered the Andean-Saharan ice age.

See also

References

  1. ↑ Eyles, Nicholas; Young, Grant (1994). Deynoux, M.; Miller, J.M.G.; Domack, E.W.; Eyles, N.; Fairchild, I.J.; Young, G.M., eds. Geodynamic controls on glaciation in Earth history, in Earth's Glacial Record. Cambridge: Cambridge University Press. pp. 10–18. ISBN 0521548039.
  2. ↑ Aber, James S. (2008). "ES 331/767 Lab III". Emporia State University. Retrieved 7 November 2015.
  3. ↑ Högele, M. A. (2011), Metastability of the Chafee-Infante equation with small heavy-tailed Lévy Noise (PDF), Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, retrieved 7 November 2015
  4. ↑ https://www.newscientist.com/article/dn18949-the-history-of-ice-on-earth/
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