Calcareous nannofossil dating of Ionian and Gavrovo flysch deposits in the External Hellenides Carbonate Platform (Greece): Overview and implications

Abstract

The available biostratigraphic data based on calcareous nannofossil analysis determine the mean ages for the onset of flysch sedimentation (base of transitional beds) of the Ionian unit at ~34–35Ma (external/internal Ionian), and at ~41Ma (middle Ionian). The top of the Ionian flysch at ~25Ma constrains the emplacement of Gavrovo nappe, providing an average duration of at least 11–16Myr for the flysch sedimentation. Gavrovo flysch deposition started at a mean age of ~34Ma and lasted till ~29Ma (emplacement of Pindos nappe), suggesting an average duration of approximately 5Myr. Phenomena of synsedimentary tectonism have been reported at the external Ionian unit, indicating that pre-flysch extension of the basin lasted at least 4Myr. The ~6–7Myr difference of the onset of flysch sedimentation between the external/internal and middle parts of Ionian unit implies evidence for an axial symmetry of the basin before the underthrusting of Mani unit under Pindos nappe.