Climate

Distribution of the ice shield during the late Carboniferous
Distribution of the ice shield during the late Carboniferous
Image Credit: Griem (2007) modified after L. Du Toit (1937)
Waick tillite, Brazil (Permian-Carboniferous glaciation)
Waick tillite, Brazil (Permian-Carboniferous glaciation)
Image Credit: D. Mertmann
Dwyka tillite, Karoo Basin South Africa (Permian-Carboniferous glaciation)
Dwyka tillite, Karoo Basin South Africa (Permian-Carboniferous glaciation)
Image Credit: D. Mertmann

Lithological indicators of climate, such as coal, evaporites, bauxite, and tillites, can be used to map the past position of the major climatic zones (Humid Tropics, Dry Subtropics, Warm and Cool Temperate, and Polar) that crossed the Gondwana supercontinent. The early proponents of continental drift (e.g., Wegener, 1912; du Toit, 1937) recognised this fact and inferred that apparent climate changes (e.g. Late Ordovician tillites in the Sahara Desert) were actually the result of Gondwana's movement across these climatic belts. It is now known that the changing width and location of these climatic zones reflects both: (1) Gondwana's latitudinal movement; and (2) changes in global climate from Icehouse to Greenhouse conditions.

Wegener showed how the otherwise mysterious distribution of Carboniferous glacial deposits in Africa, South America, Antarctica, India, Madagascar, Arabia and Australia would make sense if all these landmasses had been joined during the Paleozoic. Striated pavements created by glacier flow were used to infer the direction of ice flow away from centers of accumulation. In the case of the Carboniferous pavements, they appear to show, in many cases, ice moving onto continents from centers of accumulation in the sea. This pattern makes no sense given the present-day distribution of the the landmasses. Wegener, however, showed that when these landmasses are reassembled into their proposed predrift positions, these Paleozoic glacial deposits fit together like a puzzle, and show ice flowing in an outwardly radial pattern and are limited to a narrower latitudinal distribution, in the same manner as modern polar glaciers (www.geocities.com/earthhistory/plate.htm).