Goldman, D., Leslie, S. A., Nõlvak, J., Young, S. 2007.
The Black Knob Ridge section, southeastern Oklahoma, USA: The global stratotype-section and point (GSSP) for the base of Katian Stage of the Upper Ordovician series.Acta Palaeontologica Sinica46,
Suppl,144-154.
Nõlvak, J. 2003.
Distribution of Ordovician chitinozoans.Estonian Geological Sections Bulletin5,
23-25. Ruhnu (500) drill core, pp. 23-25.