Calcareous nannofossil biostratigraphy of the External Dinarides flysch (Vrčić-Staravasa Pag Island, Croatia): A key to an Eocene tectono-stratigraphic and paleoenvironmental interpretation

It is largely accepted that in the Dinaric shallow foredeep basin, the onset of Cenozoic synorogenic sedimentation is diachronous along strike and shows orogen-parallel southward younging, creating a large uncertainty in the age of the Dalmatian flysch. Calcareous nannofossil biostratigraphy was studied to investigate a turbiditic succession exposed in Pag Island (Croatia) with the main purpose of constraining its age, which is still a matter of debate. The age assignment for the turbiditic deposition bears important implications for better understanding of the geodynamic and paleoenvironmental evolution of the External Dinarides. We logged a well-exposed sedimentary section in the south-western limb of the Pag anticline and performed calcareous nannofossil quantitative analyses revealing a high species diversity and abundant assemblage. The age diagnostic species indicate CNE14-CNE15 biozones, suggesting that flysch deposition occurred in the Lutetian–Bartonian. This age can be further restricted to the CNE14 (42.37–40.51 Ma) by means of the lowest occurrence of Reticulofenestra reticulata and the highest occurrence of Sphenolithus furcatolithoides. Vertical facies variation and paleoecological indications suggest an increase in paleobathymetric depth during deposition. Our data support a post-Lutetian age of folding and thrusting for the Pag Island region and suggest a relatively short time span during the middle-late Eocene period for the main contractional stage in this sector of the External Dinarides. This result has important implications for the evolution of the Dinaride foreland basin system in Cenozoic times.