| System (period) | Series | Stage (age) | Lower boundary, Ma | |
|---|---|---|---|---|
| Triassic | Lower | Induan | 251.902±0.024 | |
| Permian | Lopingian | Changhsingian |  254.14±0.07
| |
| Wuchiapingian | 259.51±0.21
| |||
| Guadalupian | Capitanian | 264.28±0.16
| ||
| Wordian | 266.9±0.4
| |||
| Roadian | 273.01±0.14
| |||
| Cisuralian | Kungurian | 283.5±0.6 | ||
| Artinskian | 290.1±0.26
| |||
| Sakmarian | 293.52±0.17
| |||
| Asselian | 298.9±0.15
| |||
| Carb. | Pen. | Upper | Gzhelian | older |
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | ||||
The Asselian is the first of the four lower Permian series. It is especially well known in the Perm Region of Russia. Asselian deposits are shales and limestones interbedded with thin layers of sandstones and conglomerates. They were deposited on the eastern edge of the Russian Platform and the upper slope of the Uralian geosyncline in shallow marine environments.
It is well marked by the appearance of conodonts (especially Streptognathodus isolatus.) Well known fossil sites of this age also contain fusulinids, most notably Sphaeroschwagerina and Pseudoschwagerina alongside ammonites of the genus Properrinites.
It is preceded by the Gzhelian Stage of the Carboniferous Period and is overlain by the Sakmarian Stage.
- ↑ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.