Permian

Permian The Permian System was named by Sir Roderick Murchison in 1841 after the Russian province of Perm. He had been invited by the Tsar to report upon the geology of European Russia and had noted the great outcrop of red rocks lying close to the western Ural Mountains. These rocks follow on the Carboniferous and strata of this age were already known in Germany and Britain as part of the New Red Sandstone. In Perm the formations include fossiliferous red limestones, evaporites, and continental red beds. Murchison's account was based upon beds which are nowadays regarded as only the upper two-thirds of the Permian System. The lower part of the Lower Permian contains marine limestones thought in the nineteenth century to be Carboniferous. Today the System is divided into a Lower Series with four stages, and an Upper Series with two stages. By 1853 the Permian had been recognized over a wide area between the Mississippi and the Colorado rivers in the USA. Other regions in which marine rocks of Permian age were soon to be found include the Himalayas and the high Arctic from Canada to Siberia.

The Permian Period lasted from 290 Ma to 250 Ma. From the Late Carboniferous into the Triassic the Earth was experiencing a long phase of reverse magnetic polarity, which is conspicuous in magnetostratigraphic records.

Permian palaeogeography is that of the single supercontinent Pangaea, extending from the equatorial latitudes to the South Pole (Fig. 1). Pangaea resulted from the gathering together by plate collisions of the major continental masses throughout Carboniferous and Permian times. One of the later events in this process was the juxtaposition of Angaraland (Siberia) with eastern Laurussia to produce the Ural Mountains. Sea level sank to an all-time Phanerozoic low, probably in response to the widespread glaciation of much of southern Gondwanaland. The fixation of carbon dioxide in the coals of the Carboniferous and Permian had been the first step in initiating the global change from ‘glasshouse’ (hot humid) to ‘ice-house’ (cold arid) conditions. The cold exercised an enormous effect directly in the multiple glaciations of the Southern Hemisphere. This precipitated several waves of extinction, seeing the demise of almost all corals, fusuline foraminifera, brachiopods, bryozoans, and ammonoids. By the end of the period some 90 per cent of all invertebrates had perished.

On land, the mammal-like reptiles first appeared in the early Permian, but by the end of the period most of them, too, were extinct. Permian marine biostratigraphy is based on the fusulinid foraminifera, brachiopods, and goniatitic ammonoids. In South Africa terrestrial deposits contain great numbers of reptiles, which provide a form of biostratigraphy.

D. L. Dineley

Bibliography

Erwin, D. H. (1993) The Great Palaeozoic Crisis: life and deathin the Permian. Columbia University Press, New York.
Ramsbottom, W. H. C. (1978) Permian. In McKerrow, W. S. (ed.) The ecology of fossils, pp. 184–93. Duckworth, London.
Stanley, S. M. (1987) Extinction. Scientific American Library, New York.
Sweet, W. C., and Yang Zunyi , et al. (1992) Permo-Triassic events in the Eastern Tethys. Stratigraphy, classification and relations with the Western Tethys. Cambridge University Press.