The Volgian Praechetaites exoticus Zone: Geochronological range, stratigraphic position and interregional correlation (a Response to the Paper by S.V. Meledina et al. 'On the Position of the Praechetaites exoticus Zone in the Volgian Stage')

摘要

The Praechetaites exoticus Zone is characterized; its definition, geographical range and correlation in the Panboreal Superrealm are discussed. New evidence supports the Middle Volgian age of the Exoticus Zone. It is shown that the presence of the characteristic ammonoid assemblage allows the recognition of this zone in the sections of North Siberia and Spitzbergen. The suggested key characters defining the zone include the appearance of the ammonites from the P. exoticus group at the lower boundary and Craspedites ex gr. okensis at the upper boundary. The stratigraphic distribution of boreal genera of ammonites at the Middle-Upper Volgian boundary is discussed.