Bashkirian Stage
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Bashkirian Stage, first of four internationally defined stages of the Pennsylvanian Subsystem of the Carboniferous System, encompassing all rocks deposited during the Bashkirian Age (323.2 million to 315.2 million years ago). The name is derived from Gornaya Bashkiriya in the southern Ural Mountains of Russia.
The base of the Bashkirian Stage is defined to correspond to the internationally accepted Mississippian-Pennsylvanian boundary, drawn at the appearance of the conodont (a primitive chordate with tooth-shaped fossil remains) Declinognathodus noduliferus. The International Commission on Stratigraphy (ISC) has located the Global Standard Section and Point (GSSP) for the base of Bashkirian Stage, and thus the Pennsylvanian Subsystem, at Arrow Canyon near Las Vegas in the southwestern United States. The stage can be recognized and subdivided readily by calcareous foraminiferans (pseudopod-using unicellular organisms protected by a test or shell), ammonoid cephalopods, conodonts, and palynomorphs (microfossils composed of tiny remnants of plant and animal structures) on a worldwide basis.
A definition for the top of the Bashkirian Stage is currently being evaluated. It appears to be coincident with the appearance of the conodonts Idiognathoides postsulcatus and Declinognathus donetzianus and advanced forms of Neognathodus nataliae. The Bashkirian Stage overlies the Serpukhovian Stage of the Mississippian Subsystem and is itself overlain by the Moscovian Stage of the Pennsylvanian Subsystem.