Lithology, geochemistry and nannofossil content of a concretionary phosphate-bearing bed from the Upper Cretaceous of the South Moesian Peri-Platform Subsidence, NE Bulgaria

This study investigates an Upper Cretaceous concretionary phosphate-bearing bed (CPBB) from the Dobrindol Formation near Povelyanovo (Devnya), NE Bulgaria. The CPBB is defined as a phosphate-bearing bed due both to its matrix-supported fabric and low P2O5 content. Petrographic, mineralogical and geochemical analyses reveal structural differences between the host sediments and individual concretions, variable authigenic mineralisations within the concretions and generally low trace element contents. Calcareous nannofloras from the host sediments indicate a middle–late Coniacian age (nannofossil zone UC10), while poorly preserved assemblages within individual concretions may suggest older age of phosphatic concretion formation.