Calpionellid, nannofossil and calcareous dinocyst bioevents and integrated biochronology of the Tithonian to Valanginian in the Western Balkanides, Bulgaria

This joint study on calpionellids, calcareous nannofossils and calcareous dinocysts of the Tithonian, Berriasian and Valanginian sediments in the Western Balkanides allowed detailed documentation of the stratigraphic ranges and selection of reliable diagnostic bioevents, within the parallel microfossil successions. The individual zonations based on calpionellids, nannofossils and dinocysts are made more precise, refined and directly correlated to each other. The calpionellid zones and subzones recorded in Bulgaria are widely accepted for the Mediterranean. The proposed nannofossil zonation is considered as a regional one for the Western Balkanides. Ten dinocyst zones are recognized three of them being introduced here: Stomiosphaera wanneri, Colomisphaera conferta and Carpistomiosphaera valanginiana. A number of intrinsic coinciding bioevents between two or all the three planktonic microfossil groups are documented and interpreted related to certain stage acid substage boundaries. This approach of direct correlation of three fossil groups enhances the argumentation and resolution of the zonation. It may represent a basis for a reference biochronology of the Tithonian to Valanginian, applicable to various lithologies in the Tethyan Realm.