The Gzhelian is the youngest stage of the Carboniferous. It follows the Kasimovian and precedes the Asselian stage of Permian. The top of the Gzhelian stage/ base of the Permian system is at the first appearance of the conodont Streptognathodus isolatus within the St. wabaunsensis chronomorphocline. The GSSP for the top of the Gzhelian stage is located at 27m above the base of bed 19 at Aidalarash creek, in Kazakhstan.

However, at this moment, a GSSP for the base of Gzhelian stage is yet lacking. The FAD of conodont Streptognathodus simulator has been recently accepted as the best global marker for this boundary by the SCCS task group.