Stratotype of Theporkuni Stage With Comments on the Röa Member (Uppermost Ordovician, Estonia)

A revised interpretation of the subdivisions within the unit stratotype section of the topmost Ordovician Porkuni Stage is presented together with an improved description of the section.The boundary beds with the underlying Pirgu Stage in the stratotype section are described for the first time.The "Encrinitenlager", a crinoidal limestone (dolomite) bed, established by Schmidt (1858, Arch.Naturk.Liv-, Ehst-und Kurl., Ser.I) in the base of his "Borkholmsche Schicht" (Porkuni Stage of current use) is considered to be identical with the Roa Member comprising the lower part of the Arina Formation.The correlation of the Arina Formation (including the stratotype of the Porkuni Stage) with the Kuldiga and Saldus formations in South Estonia and Latvia, based on the distribution of chitinozoans and carbon isotope data, shows that the Arina Formation represents only the lower part of the Porkuni Stage, which in full is correlated with the Hirnantian Stage elsewhere.