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

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 ~ 34–35 Ma (external/internal Ionian), and at ~ 41 Ma (middle Ionian). The top of the Ionian flysch at ~ 25 Ma constrains the emplacement of Gavrovo nappe, providing an average duration of at least 11–16 Myr for the flysch sedimentation. Gavrovo flysch deposition started at a mean age of ~ 34 Ma and lasted till ~ 29 Ma (emplacement of Pindos nappe), suggesting an average duration of approximately 5 Myr. Phenomena of synsedimentary tectonism have been reported at the external Ionian unit, indicating that pre-flysch extension of the basin lasted at least 4 Myr. The ~ 6–7 Myr 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.

► Onset of Ionian flysch sedimentation at ~34-35 Ma (external/internal Ionian) and at ~ 41 Ma (middle Ionian), top at ~ 25 Ma. Average duration of at least 11-16 Myrs for flysch sedimentation in the Ionian unit.
► Onset of Gavrovo flysch sedimentation at a mean age of ~ 34 Ma, top at ~ 29 Ma (emplacement of Pindos nappe). Average duration of ~ 5 Myrs for flysch sedimentation in the Gavrovo unit.
► ~ 6-7 Myrs difference of the onset of flysch sedimentation between the external/internal and middle parts of Ionian unit.
► Evidence for an axial symmetry of the Ionian foreland basin before the underthrusting of Mani unit under Pindos nappe.