Silurian K-bentonites of the Dnestr Basin, Podolia, Ukraine

The Dnestr Basin of Podolia, Ukraine, is an epicratonic basin consisting of neritic carbonate and calcareous mudstone facies including a nearly comple te Silurian sequence ranging from late Llandovery to late Pridoli in age. T he Silurian section has served as a standard for regional and interregional studies as a consequence of its well-documented macro- and microfaunal ass emblages. Approximately 24 mid- to Late Silurian K-bentonites are present i n this succession, and their lateral persistence has aided in establishing regional correlations. The K-bentonites range from 1 to 40 cm in thickness and occur in the Bagovitsa (late Wenlock), Malinovtsy (Ludlow) and Skala (P ridoli) Formations. Discrimination diagrams based on immobile trace element s together with rare earth element data suggest the K-bentonites had a volc anic origin in a collision margin setting related to subduction. Thickness and stratigraphic distribution considerations are consistent with a source area in the Rheic Ocean.