The Ordovician Billingen/Volkhov boundary interval (Arenig) at Lava River, northwestern Russia

A detailed study of the conodont distribution within the condensed carbonate beds around the boundary of Billingen and Volkhov Stages (Lower Ordovician, Arenig) in northwestern Russia confirms the presence of a continuous succession of conodont biozones recognized in contempora­neous sequences in Scandinavia. The Baltoniodus triangularis and Microzarkodina sp. A zones are reported for the first time from East Baltica, where carbonates of this interval underwent extensive bioturbation and are characterized by a number of closely spaced and distinctive glauconi­tic hardground surfaces. It has been revealed that the distribution of conodont elements around the hardground surfaces is strongly affected by bioturbation.