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The Distribution and Formation of Permian-Triassic Red Beds
Red beds, associated with desert, evaporite and fluviatile environments, have a widespread distribution in the Permian-Triassic of the Northern Hemisphere. This contrasts with the Gondwanaland countries where the major red beds are of Triassic age and lack extensive evaporites. The Permian includes glacial and coal-bearing facies in the southern continents. These differences are in accord with the paleomagnetic evidence which shows that during the Permo-Carboniferous, the southern parts of Africa and South America lay at a latitude near to the South Pole. A general northward drift to lower latitudes occurred during the Permian and Triassic, until North America — Eurasia and considerable parts of Gondwanaland lay within 30° N and S of the equator, respectively. Such latitudes readily explain the environmental significance of the various red bed facies.
The occurrence of widespread continental red beds, often replacing marine sediments, and associated with late Paleozoic orogenies, supports the concept of large-scale continental emergence by Late Permian times, with concomitant withdrawal of shelf seas. This, and any fluctuations in salinity of sea water during the Permian evaporite maxima, was probably a contributory cause of the Late Permian biological revolution.
The origin of the red colour of the red beds is considered to be due to in situ diagenetic processes, similar to those demonstrated in late Tertiary to Recent red desert sediments in Mexico.
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