Timing and mode of initial marine flooding in the southern Pannonian Basin: New U-Pb age constraints from the Prnjavor and Tuzla basin

The Pannonian Basin in Central and Southeastern Europe is a huge landlocked basin delineated by Alpine-Carpathian-Dinarides chain. This extensional backarc basin originating by tectonic rifting at about 18 Ma; was successively flooded by the Central Paratethys Sea. The Slovenian Corridor along the Alpine-Dinarides junction enabled its communication with the Mediterranean Sea. Marine flooding along the southern margin of the Pannonian Basin – between the Styrian Basin in Austria and Velika Morava Basin in Serbia - is still poorly understood. While the conflicting biostratigraphic interpretations contribute to ongoing discussions on the timing and mode of this major environmental turnover; independent radiometric data are still rare. The present study contributes three new U-Pb zircon ages which are the very first such data on the Miocene marine transgression in northern Bosnia and Herzegovina. Datings from primary volcaniclastic deposits prove the middle Badenian age for marine transgression uniformly; with a 0.5 Ma eastwards-younging trend of its onset; dated at 14.6 Ma in Prnjavor Basin and at 14.1 Ma in the Tuzla Basin. This trend stays in line with the literature data suggesting a steady eastwards propagation of extension along the Pannonian Basin southern margin. Towards a better understanding of the interplay between tectonic and glacioeustatic forcing of the regional marine progression; a review of published stratigraphic data has been conducted; depicted correspondingly in four paleogeographic maps of ~1-Myr resolution. Building on these data; we bracket the initial gradual flooding interval to the late Burdigalian–early Serravallian (17 to 13.5 Ma) time interval; respectively; attaining up to 3.5 Myr overall duration in a step-wise manner. We infer fault growth and linkage as mechanisms controlling the hydrological pathways and thereby the direction of the transgression. This implies a transgression direction oblique to the main regional extensional direction. In some cases; local stress changes may lead to formation of sea pathways/gates opposite to the direction of extension. Although the tectonic phases were the main drivers in the creation of accommodation space; along the NE Dinarides; glacioeustasy driven by the global climate suspended the landward propagation of the coastline during sea-level low-stands at long obliquity nodes.