BUILDING AN INTERNATIONAL PERMIAN SYSTEM AND ITS CORRELATION IN THE USA

Murschison named the Permian System in 1841 for rocks that formed a great arc on the western side of the Urals, characterized at the base by an evaporitic succession, now known as the Kungurian. Subsequent Russian workers extended the base of the Permian stratigraphically downward established on the recognition of faunas with post-Carboniferous affinities. The base is now recognized as the base of the Asselian, defined by the first appearance of the conodont Streptognathodus isolatus at the Aidaralash section in the southern Urals; nearly coincident with the base of fusulinid and ammonoid zones. The Subcommission on Permian Stratigraphy recognized that marine successions for the Permian are best represented for its lower part in the Urals, in its middle part in West Texas, and its upper part in China and Iran, leading to a natural three-part subdivision. Most of the proposed faunal (conodont) definers for the Lower and Middle Permian stages are present in the West Texas succession. Only the Kungurian is difficult to place because its proposed definer, Neostreptognathodus pnevi, is rare in the West Texas succession; but, it occurs commonly with West Texas forms in northeastern Nevada which allows confident correlation. Upper Permian faunas are very rare in North America. The bases of the Asselian, Sakmarian, and Artinskian are found in 1) Texas: within the uppermost part of the Grey Limestone Member, the Neal Ranch Formation, the Lenox Hills Formation; 2) Kansas: the base of the Bennett Shale, within the Eiss Limestone, and near the base of the Florence Limestone and 3) Nevada: within the Riepe Spring Limestone, the Rib Hill Formation, and the Pequop Formation, respectively. The Kungurian is found within the lower part of the Skinner Ranch Formation in Texas, is not represented by good marine faunas in Kansas and within the Pequop Formation in Nevada. The Roadian, Wordian and Capitanian are defined within the Cutoff Formation, the Getaway Limestone, and Pinery Limestone in the Guadalupe Mountains. The bases of the Roadian and Wordian are found within the lower and upper parts, respectively, of the Meade Peak Phosphatic Shale in southeastern Idaho.