Chernykh, V. V.; Chuvashov, B. I.; Davydov, V. I.; Schimtz, M.; Snyder, W. S. Usolka section (southern Urals, Russia): a potential candidate for GSSP to define the base of the Gzhelian Stage in the global chronostratigraphic scale . geologija 2006, 49 (2), 205-217. https://doi.org/10.5474/geologija.2006.015.