Asselian
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| Asselian | |
|---|---|
 | |
| Name | Asselian |
| Time start | 298.9 |
| Time end | 295.0 |
| Time unit | Age |
| Chronostrat unit | Stage |
| Period | Permian |
| Epoch | Cisuralian |
| Named by | Andrey Nikolaevich Stanosz |
| Named for | Assel River |
| Type section | Ufa Province |
Asselian The Asselian is a formal chronostratigraphic stage and geochronologic age at the base of the Cisuralian Epoch of the Permian Period. It marks the earliest interval of Permian time used in international stratigraphy, bounded below by strata that succeed the Gzhelian Stage of the Pennsylvanian and overlain by the Sakmarian Stage. The Asselian is important for correlating terrestrial and marine sequences across Eurasia, North America, and Gondwana and for anchoring biostratigraphic, magnetostratigraphic, and radiometric frameworks used by investigators from institutions such as the International Commission on Stratigraphy, Geological Society of America, and national geological surveys.
Definition and stratigraphic context
The Asselian was ratified as the lowermost stage of the Permian and is formally defined by a Global Boundary Stratotype Section and Point (GSSP) near the mouth of the Assel River in the southern Ural Mountains. The stage lies above the terminal Gzhelian and beneath the Sakmarian in the standard International Commission on Stratigraphy timescale promoted by organizations including the Subcommission on Permian Stratigraphy. Stratigraphic sections used to characterize the Asselian have been studied by teams from the Russian Academy of Sciences, the United States Geological Survey, and universities such as Moscow State University and the University of Cambridge. Correlation relies on conodont biostratigraphy, ammonoid occurrences, and shifts recorded in magnetostratigraphic logs by researchers from the British Geological Survey and the Geological Survey of Canada.
Age and geologic time
Numerical ages assigned to the Asselian currently place its start at approximately 298.9 million years ago and its end near 295.0 million years ago, based on radiometric calibrations reported in publications by the International Commission on Stratigraphy and synthesized in syntheses from the Geological Society of America. These ages derive from uranium-lead dating of intercalated volcanic ash beds in sections correlated to the GSSP and from integrated magnetostratigraphic and biostratigraphic studies by teams affiliated with institutions such as ETH Zurich and the Max Planck Institute for Chemistry. The Asselian occupies the base of the Cisuralian Epoch and therefore marks the transition into the Permian Period after the late Carboniferous Gzhelian.
Lithology and key type localities
Lithofacies within Asselian successions commonly include shallow marine carbonate rocks, siliciclastic sandstone, siltstone, and coal-bearing deltaic deposits preserved in basins of the Ural Mountains, Timan-Pechora Basin, and the Saratov Basin. The type section for the Asselian GSSP is located in the southern Urals near the Assel River where alternating limestones and shales host conodont faunas. Other key localities that have yielded diagnostic Asselian lithologies and faunas include sections in the Kazan region, the Donets Basin, the South China Block exposures studied by researchers from Nanjing University, and outcrops of the Permian Basin in western Texas and New Mexico examined by teams from the University of Texas at Austin.
Paleontology and fossil assemblages
Asselian strata preserve diverse marine and terrestrial fossil assemblages that serve as biostratigraphic markers. Conodont genera such as Streptognathodus and Neostreptognathodus are primary index fossils used to recognize the base of the Asselian in sections investigated by specialists from the Paleontological Society and universities including Uppsala University. Ammonoids, bivalves, and brachiopods occurring in Asselian limestones provide correlation tie-points with sections described by researchers from the Natural History Museum, London and the Smithsonian Institution. Terrestrial assemblages include early synapsid remains, pelycosaur-grade reptiles, and plant communities dominated by glossopterids and conifers documented by paleobotanists at Birkbeck, University of London and the Russian Paleontological Institute. Ichnofossils and vertebrate trackways in deltaic and fluvial Asselian deposits have been reported from sites investigated by teams from the University of Kansas and the Museo Argentino de Ciencias Naturales.
Correlation and regional equivalents
Regional equivalents and correlatives to the Asselian have been established across multiple paleocontinents. In the Russian Platform and Uralian basins, Asselian units correspond to lower Cisuralian successions. In western Europe, marine-to-terrestrial sequences correlated to the Asselian have been integrated with the regional stages used in the Permian Basin of North America by researchers at the Canadian Society of Petroleum Geologists and the American Association of Petroleum Geologists. Correlatives in South China and the Australian basins are established through conodont zonation and radiometric ties refined by collaborations among the Chinese Academy of Sciences, the Australian National University, and international stratigraphers.
Economic significance and research history
Asselian deposits host sources and reservoirs relevant to hydrocarbon exploration in basins such as the Timan-Pechora Basin and the Permian Basin, attracting applied research from industry groups including the International Association of Petroleum Geologists and service companies collaborating with national surveys. Coal-bearing Asselian strata have been mined in parts of the Donets Basin and studied by economic geologists at institutions such as the Moscow State Mining University. The research history of the Asselian began with 19th- and early 20th-century descriptions by Russian geologists and was formalized through 20th-century stratigraphic work culminating in a GSSP designation endorsed by the International Commission on Stratigraphy; ongoing work integrates high-precision geochronology, regional synthesis by teams at the University of California, Berkeley and Stanford University, and paleoenvironmental reconstructions by groups at the Max Planck Institute for Chemistry and the University of Oxford.
Category:Permian stages