Misplaced Pages

#41958

14-609: The Asselian Stage was introduced into scientific literature in 1954, when the Russian stratigrapher V.E. Ruzhenchev split it off from the Artinskian . At the time, the Artinskian still encompassed most of the lower Permian – its current definitions are more restricted. The Asselian is named after the Assel River in the southern Ural Mountains of Kazakhstan and Bashkortostan . The base of

28-604: A much younger age of 280.3 Ma for the Sakmarian -Artinskian boundary. The top of the Artinskian (and the base of the Kungurian ) is defined as the place in the stratigraphic record where fossils of conodonts Neostreptognathodus pnevi and Neostreptognathodus exculptus first appear. The proposed GSSP candidate — the Mechetlino section (Southern Urals). Around 287 million years ago occurred an interval of pronounced warming known as

42-674: Is named after the goniatite grits of Artinsk which was introduced by Roderick Murchison , Édouard de Verneuil and count Alexander von Keyserling in their The Geology of Russia in Europe and the Ural Mountains (1845). The grits of Artinsk, in turn, get its name from the Artinsky District with center in the Russian smalltown of Arti (formerly Artinsk zavod ), situated in the middle Urals , about 170 km southwest of Yekaterinburg . The stage

56-626: Is some debate over the exact sequence of species; one option, according to Henderson (2018), lists the following biozones , from youngest to oldest: In North America, the regional equivalent of the Asselian is the Nealian stage. The Nealian (lower Wolfcampian ) is named after the Neal Ranch Formation in the Glass Mountains of west Texas. In South China , the Asselian is equivalent to at least

70-751: The Ordovician Period is marked by the first appearance of the conodont Iapetognathus fluctivagus in the geologic record. This occurs in bed 23 of the rock formation known as the Green Point section, located in western Newfoundland , as well as in geologically correlated strata in many parts of the world. However, diachronous FADs can be problematic for correlating chronostratigraphic units, particularly over longer distances. Use of other data, such as radiometric data , may be ultimately necessary in order to establish more reliable correlations of chronostratigraphic units. This paleontology article

84-584: The geologic timescale , the Artinskian is an age or stage of the Permian . It is a subdivision of the Cisuralian Epoch or Series . The Artinskian likely lasted between 290.1 and 283.5 million years ago (Ma) according to the most recent revision of the International Commission on Stratigraphy (ICS) in 2022. It was preceded by the Sakmarian and followed by the Kungurian . The Artinskian

98-497: The AWE is evidenced by a positive δ O excursion observed in brachiopod fossils , with arid and semi-arid conditions expanding across much of Pangaea as glaciers receded to refugia in the polar regions of Gondwana . First appearance datum First appearance datum (FAD) is a term used by geologists and paleontologists to designate the first appearance of a species in the geologic record. FADs are determined by identifying

112-654: The Artinskian Warming Event (AWE). This period of global warming accelerated the deglaciation that had been occurring since the Sakmarian following the end of the most intense glacial phase of the Late Palaeozoic Ice Age . In addition, it is also associated with significant global drying , which had gradually been occurring since the Carboniferous-Permian boundary. Major aridification during

126-780: The Asselian Stage is equivalent to the base of the Cisuralian Series and the Permian System . It is defined as the point in the stratigraphic record where fossils of the conodont Streptognathodus isolatus first appear. The global reference profile for the base (the GSSP or golden spike ) is located in the valley of the Aidaralash River , near Aqtöbe in the Ural Mountains of Kazakhstan . Other reference species which approximate

140-634: The Dal'ny Tulkas roadcut in the Southern Urals , near the town of Krasnousolsky — was eventually ratified in February 2022. U-Pb radiometric dating found that the base of the Artinskian was approximately 290.1 million years old (Ma), based on the position of the rock layer at the Dal'ny Tulkas roadcut containing the FAD of S . whitei relative to three precisely dated ash beds surrounding it. Earlier radiometric reported

154-407: The base of the Asselian include Streptognathodus invaginatus and Str. nodulinearis (conodonts) and Sphaeroschwagerina vulgaris and Sph. fusiformis ( fusilinids ). The top of the Asselian stage (the base of the Sakmarian stage) is at the first appearance of conodont species Mesogondolella monstra . Asselian biostratigraphy is mostly defined by the evolution of Streptognathodus . There

SECTION 10

#1732845445042

168-472: The geologically oldest fossil discovered, to date, of a particular species. A related term is last appearance datum (LAD), the last appearance of a species in the geologic record. FADs are frequently used to designate segments in the geologic time scale . A given FAD can be used to define a Global Boundary Stratotype Section and Point (GSSP). For example, the beginning of the Tremadocian Stage of

182-685: The lower part of the regional Zisongian stage of the Chuanshanian Series. Both the Nealian and Zisongian are defined by fusilinid assemblages, so their precise correlation to the conodont-based global timescale is uncertain. The Asselian occupies a portion of major terrestrial sediment units in Europe, namely the Autunian series of France and the lower Rotliegend of Germany. 50°14′45″N 57°53′29″E  /  50.2458°N 57.8914°E  / 50.2458; 57.8914 Artinskian In

196-551: Was introduced into scientific literature by Alexander Karpinsky in 1874. The base of the Artinskian Stage is defined as the first appearance datum (FAD) of the conodont species Sweetognathus whitei and Mesogondolella bisselli . In order to constrain this age, the ICS subcommission on Permian stratigraphy informally proposed a candidate GSSP in 2002, later followed by a formal proposal in 2013. The proposed GSSP location —

#41958