Heinsalu, H., Kaljo, D., Kurvits, T. & Viira, V. 2003.
The stratotype of the Orasoja Member (Tremadocian, Northeast Estonia): lithology, mineralogy, and biostratigraphy.Proceedings of the Estonian Academy of Sciences. Geology52,
3,135-154.
Viira, V., Sergeyeva, L. & Popov, L. 1987.
Earliest representatives of the genus Cordylodus (Conodonta) from Cambro-Ordovician boundary beds of North Estonia and Leningrad Region.Proceedings of the Academy of Sciences of the Estonian SSR. Geology36,
4,145-153.
Viira, V. 1970.
Conodonts of the Varangu Member (Estonian Upper Tremadoc).Proceedings of the Academy of Sciences of the Estonian SSR. Chemistry and Geology19,
3,224-233.