Substantiation of the Barremian/Aptian boundary

This paper focuses on the Barremian/Aptian boundary in the Trans-Caspian area. Results of a stratigraphical study of the uppermost Barremian and the lower Aptian succession in the Trans-Caspian area are presented. The bed-by-bed description of three sections — Keldzhe, Tekedzhik and Utuludzha — is given as well as detailed lithologic columns. Five ammonite zones are known in the studied stratigraphic interval — the Turkmeniceras turkmenicum, Deshayesites tuarkyricus, D. weissi, D. deshayesi, and Dufrenoya furcata zones. These zones are correlated with those of Europe. The Barremian/ Aptian boundary in the Trans-Caspian area should be drawn at the base of the D. tuarkyricus Zone. It corresponds to the layers with the first occurrences of Deshayesites, Prodeshayesites and Paradeshayesites in Europe. It is proposed here to situate the boundary stratotype in the Utuludzha section, where the beds containing zonal representatives of the T. turkmenicum and D. tuarkyricus Zones are almost adjacent.