Carboniferous eruption covered central and western Bohemia with up to 1 m thick ash layer

The famous Bělka tuff is an areally extensive pyroclastic layer preserved in the central and western Carboniferous late- to post-orogenic basins of central and western Bohemia. This tuff represents a unique stratigraphic marker documented from tens of boreholes and numerous black coal mines within a large area between the southern edge of the Pilsen Basin in western Bohemia and the eastern part of the Kladno-Rakovník Basin over a distance of 100 km. However, its volcanic source has been as yet enigmatic. In a new study by Tomek et al., published in International Geology Review, a multidisciplinary approach using the LA-ICP-MS U/Pb zircon dating, analysis of thickness and grain size distribution, and volume calculation suggested that the source volcano was the Altenberg–Teplice Caldera located at the Czech–German border in NW Bohemian Massif. In detail, this volcano underwent a major caldera-forming ignimbrite eruption with an estimated volcanic explosivity index 7 (out of 8) at 314 Ma. From the northern caldera margin, pyroclastic density currents travelled south over a distance of ca. 40 km towards the area of Oparno valley (Porta Bohemica). From here, northeasterly winds distributed the volcanic ash cloud towards the southwest, where the ash was deposited in the sedimentary basins. As indicated by an isopach reconstruction, the Regensburg area (Germany), for instance, was covered by a 10 cm thick ash layer that originated from the Altenberg–Teplice Caldera nearly 220 km away. For additional information click here.