Miocene tephra horizons in the Alpine–Carpathian Foredeep and an Intra-Alpine Basin: evidence for westward dispersal of Bükkalja Volcanic Field eruptions

Abstract Volcaniclastic layers interbedded in Miocene sedimentary successions of the Western Carpathian Foreland Basin (WCFB), North Alpine Foreland Basin (NAFB), and the Intra-Alpine Aflenz Basin represent distal fallout from large explosive eruptions. We present new zircon U–Pb ages, trace element and Hf-isotope data, and, where preserved, glass compositions to identify their sources. The results indicate derivation from successive Early to Mid-Miocene silicic eruptions of the Bükkalja Volcanic Field (BVF) in the Pannonian Basin, northern Hungary. Zircon laser ablation inductively coupled plasma–mass spectrometry ages cluster at 17 ± 0.3 Ma and 14.2 ± 0.2 Ma. Zircon Hf-isotope and trace-element compositions link the Early Miocene tephras to the 17.3 Ma Eger Ignimbrite (Hradiště) and the 16.8 Ma Bogács Ignimbrite (Ivančice-Réna, Straning). These provide the first geochemically confirmed north-western occurrence of the Eger eruption and the westernmost documented fallout from the Bogács eruption. Middle Miocene samples from the WCFB and Aflenz Basin yield slightly younger zircon ages (14.3–14.0 ± 0.2 Ma) than the 14.35 Ma Harsány Ignimbrite but display indistinguishable Hf-isotope and trace-element signatures, supporting correlation with this eruption. The new data expand the known dispersal of BVF tephras and provide firm evidence for westward ash transport. Revised zircon U–Pb ages reposition key tephra horizons within the Central Paratethys stratigraphy, shifting them to younger intervals and challenging earlier interpretations of Early Miocene marine transgressions in the WCFB and NAFB. Graphic Abstract