Serpukhovian

The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from Ma to Ma. It is preceded by the Visean and is followed by the Bashkirian.
The Serpukhovian correlates with the lower part of the Namurian stage of European stratigraphy and the middle and upper parts of the Chesterian stage of North American stratigraphy.
Name and definition.
The Serpukhovian stage was proposed in 1890 by Russian stratigrapher Sergei Nikitin and was introduced in the official stratigraphy of European Russia in 1974. It was named after the city of Serpukhov, near Moscow. The ICS later used the upper Russian subdivisions of the Carboniferous in its international geologic time scale.
The base of the Serpukhovian is at the first appearance of the conodont "Lochriea crusiformis". As of December 2020, no lower GSSP had been assigned to the Serpukhovian stage yet. The top of the stage (the base of the Pennsylvanian subsystem and Bashkirian stage) is at the first appearance of the conodont "Declinognathodus nodiliferus" in the lower Bird Spring Formation, which overlies the Battleship Formation in Nevada. It is also slightly above the first appearance of the foram "Globivalvulina bulloides", genozone of the ammonoid genus "Homoceras" and the ammonoid biozone of "Isohomoceras subglobosum".
Subdivision.
The Serpukhovian stage includes four conodont biozones:
In Russian stratigraphy, the Serpukhovian is subdivided into three substages, from bottom to top: Tarusian, Steshevian, and Protvian, named after places near Serpukhov (Tarusa and Protva). In British stratigraphy, the Serpukhovian (lower Namurian) contains three substages. These are from bottom to top: Pendleian, Arnsbergian and Chokierian (only the lower Chokierian falls in the Serpukhovian, the top falls in the Bashkirian).