Lower Miocene (upper Burdigalian, Karpatian) volcanic ash-fall at the south-eastern margin of the Bohemian Massif in Austria – New evidence from ⁴⁰Ar/³⁹Ar-dating, palaeomagnetic, geochemical and mineralogical investigations

An Early Miocene acidic tuff that accumulated in a small tectonic graben at the south-eastern margin of the Bohemian Massif in north-eastern Austria was dated by means of ⁴⁰Ar/³⁹Ar dating. Feldspar crystals from the tuff have an inverse isochron age of 17.23 ± 0.18 Ma, which is interpreted to reflect its crystallisation age. The tuff shows a reversed palaeomagnetic polarity and can be correlated with chron C5Cr of the late Burdigalian (early Karpatian) and with the lowstand systems tract (LST) of the Bur 4 global 3^rd order sea level cycle. The tephra originates from acid (rhyodacitic to dacitic) calc-alkaline arc volcanism. Our study demonstrates that the investigated volcaniclastics are significantly different from other Burdigalian (Eggenburgian, Ottnangian) and Langhian (early Badenian) tephra from the area with regard to their volcanic zircon and Rare Earth element (REE) composition. The volcanic source of the Straning tuffs might be traced back to the western Inner Carpathian volcanic arc. The tuffs are most likely genetically related to the Middle Rhyolite Tuff (late Burdigalian, Karpatian) of northern Hungary and southern Slovakia.