The marine Permian faunas of the world are subdivided into eight stages and nineteen substages: the Asselian Stage, with the Surenan, Uskalikian, and Kurmaian Substages; the Sak- marian Stage, with the Tastubian, Sterlitamakian, and Aktastinian Substages; the Baigendzinian Stage, with the Sarginian and Krasnoufimian Substages; the Kungurian Stage, with the Filippovian and Irenian Substages (the latter including the Nevolin, Elkin, and Ufimian horizons); the Kazanian Stage, with the Kalinovian and Sosnovian Substages; the Punjabian Stage, with the Kalabaghian and Chhidruan Substages; the Djulfian Stage, with the Urushtenian and Baisalian Substages, and the Dorashamian Stage with the Vedian and Ogbinan Substages and perhaps the Griesbachian Substage or a modification thereof. This offers the most extensive and refined scheme of correlation available for the Permian System, in which brachiopod correlations agree well with those proposed for the less abundant Permian ammonoids, and paleotropical Fusulinacea.
Short-lived normal events during the predominantly reversed paleomagnetic late Paleozoic interval offer prospects of a few well-defined horizons within the Permian, but are poorly dated and additional short-lived events may yet be recognized. Radiometric values, although showing considerable scatter, suggest that the length of the period should be extended from earlier estimates, and that it commenced about 300 m.y. B.P., and ended, as generally recognized, about 230 m.y. B.P. Perhaps the best support for these dates is provided by solar chronology, which postulates that the energy budget from the sun varied in rhythmic fashion, leading to major refrigerations every 30 million years or so.