The Permian period lasted from 290 to 248 million years ago and was the last period of the Paleozoic Era. The distinction between the Paleozoic and the Mesozoic is made at the end of the Permian in recognition of the largest mass extinction recorded in the history of life on Earth. It affected many groups of organisms in many different environments, but it affected marine communities the most by far, causing the extinction of most of the marine invertebrates of the time. Some groups survived the Permian mass extinction in greatly diminished numbers, but they never again reached the ecological dominance they once had, clearing the way for another group of sea life. On land, a relatively smaller extinction of diapsids and synapsids cleared the way for other forms to dominate, and led to what has been called the Age of Dinosaurs. Also, the great forests of fern-like plants shifted to gymnosperms, plants with their offspring enclosed within seeds. Modern conifers, the most familiar gymnosperms of today, first appear in the fossil record of the Permian. In all, the Permian was the last of the time for some organisms and a pivotal point for others, and life on Earth was never the same again.
The global geography of the Permian included massive areas of land and water. By the beginning of the Permian, the motion of the Earth's crustal plates had brought much of the total land together, fused in a supercontinent known as Pangea. Many of the continents of today in somewhat intact form met in Pangea (only Asia was broken up at the time), which stretched from the northern to the southern pole. Most of the rest of the surface area of the Earth was occupied by a corresponding single ocean, known as Panthalassa, with a smaller sea to the east of Pangea known as Tethys.
Models indicate that the interior regions of this vast continent were probably dry, with great seasonal fluctuations, because of the lack of the moderating effect of nearby bodies of water, and that only portions received rainfall throughout the year. The ocean itself still has vast unexplored reaches. There are indications that the climate of the Earth shifted at this time, and that glaciation decreased, as the interiors of continents became drier.
Stratigraphy of the Permian
A standard global correlation of the Permian period has been undertaken only in recent years (Jin et al. 1994), since there are difficulties in correlation, especially within relatively newer strata. Until recently, there was little consensus on the order of strata in the Upper Permian. Since the upper strata of various locations lack numbers of fossils, correlation via index fossils must involve different fossils that are in some cases native only to the local regions where they were found, and older work had to use assumptions that have changed in more recent years (Menning. 1995; Jin et al. 1994). Even though knowledge of the Permian has increased, study of stratigraphic correlation still yields relatively new conclusions (Jin et al. 1994).
Older classifications relied on the Ural stratigraphy. An example of a recent effort to formulate a worldwide stratigraphy of the Permian period by Jin, et al. (1994) has four series: the Uralian, the Chihsian, the Guadalupian, and the Lopingian. These epochs include two or three stages each (ten in all). The names are derived from local areas -- the Uralian is named for the Urals, the Chihsian and the Lopingian are named for Chinese localities, and the Guadalupian is named for the Guadalupe Mountains of New Mexico, USA.
Examples of localities noted for their Permian strata are found over several continents (Jin et al., 1994, Ross and Ross, 1995)
- Urals: This area, for which the Permian is named (Perm is a region in the Urals), includes the traditional standard series: the Asselian (290-282 mya), Sakmarian (282-269 mya), and Artinskian (269-260 mya); the Kungurian (260-256 mya), Kazanian (256-252 mya), and Tatarian (252-248 mya). The standard series work well until the late Permian, when the paucity of fossils makes correlations more difficult.
- Southwestern North America: Permian stratigraphy in North America has its standard in the Glass Mountains, Texas, where the strata are classified into the Wolfcampian (which includes the Nealian and the Lenoxian) (~295-280 mya), the Leonardian (Hessian and Cathedralian) (~280-270 mya), the Guadalupian (Roadian, Wordian, and Capitanian) (~270-258 mya), and the Ochoan (~258-250s mya), named for localities in the area. The Glass Mountains are part of a larger region of Permian strata called the Permian Basin, and other areas of North America also contain Permian strata.
- China: China contains the Mapingian or the Chuanshanian (which includes the Zisongian and the Longlinian), and which corresponds to the Wolfcampian, the Chihsian (Luodianian and Xiangboan), which corresponds to the Leonardian, theMaokouan (Kuhfengian and Lengwuan), which corresponds to the Guadalupian, and the Wuchiapingian and the Changhsingian, which correspond to the Ochoan in the North American series.
There are similar sites in Europe, the Middle East, Japan, and Australia.
Permian shale, sandstone, siltstone, limestone, sands, marls, and dolostones were deposited by sea-level fluctuations. The fluctuation cycles can be seen in the layers of rock (Ross and Ross, 1995). Only a relative few sites lend themselves to direct radioactive dating, so the age of intermediate strata is often estimated (Menning, 1995). Radiometric dating may be used for certain sites, but other sites are not of sufficient quality to permit accurate dating, and other layers are dated in between layers where datable sites are located.
Permian fossils that have been used as index fossils include brachiopods, ammonoids, fusilinids, conodonts, and other marine invertebrates (Menning, 1995), and some genera occur within such specific time frames that strata are named for them and permit stratigraphic identification through the presence or absence of specified fossils.
- Jin et al. 1994. An operational scheme of Permian chronostratigraphy. Paleoworld (4).
- Jones, T.S. (1953). Stratigraphy of the Permian Basin of West Texas. West Texas Geological Society.
- Menning, M. 1995. A numerical time scale for the Permian and Triassic periods: an integrative time analysis. In Scholle, Peter A., Tadeusz M. Peryt, and Dana S. Ulmer-Scholle (eds.), The Permian of Northern Pangea, Springer-Verlag.
- Ross, C.A., and Ross, J.R.P (1995). Permian Sequence Stratigraphy. In Scholle, Peter A., Tadeusz M. Peryt, and Dana S. Ulmer-Scholle (eds.), The Permian of Northern Pangea, Springer-Verlag.
- Geologic Time pages updated to reflect Geological Society of America (GSA), 1999. Geologic Timescale, compiled by A.R. Palmer and J. Geissman
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This article is based on text originally authored by Chavé Alexander, Henry Chang, Carl Tsai and Peggy Wu.