Formal definition and description of lithostratigraphic units related to the Miocene silicic pyroclastic rocks outcropping in Northern Hungary: A revision

Abstract

Repeated explosive eruptions of large volume silicic magmas during the earlyto mid-Miocene resulted in pyroclastic deposits covering at least 50,000 km2 in the Pannonian Basin. They form extended marker horizons and therefore these pyroclastic formations have a great stratigraphic importance. Lithostratigraphic characterization and classification of these rocks go back for more than a century and have been used widely in geological mapping among other things. In this paper, we outline the former stratigraphical schemes developed for silicic pyroclastic products in Northern Hungary; however, using the new geochronological, volcanological, petrological, and geochemical results, we propose a revision of the lithostratigraphic units, including the unit names as well. Four main units are distinguished, named, and described following the International Stratigraphic Guide. Stratotypes of the revised units were also redefined based on accessibility and representativeness. The four newly-defined lithostratigraphic units are the following: (1) The Tihamér Rhyolite Lapilli Tuff Formation (formerly Gyulakeszi Fm.), 18.2–17.1 Ma (Ottnangian–Karpatian); (2) The Bogács Dacite Lapilli Tuff Formation (formerly classified into the Tar Fm.), 16.8–16.2 Ma (Karpatian); (3) The Tar Dacite Lapilli Tuff Formation, 15.1–14.8 Ma (Badenian) and (4) The Harsány Rhyolite Lapilli Tuff Formation, 14.7–14.4 Ma (Badenian) – four formerly existing formations merged in the latter. Three of these units have corresponding distal volcanic products recognized around Hungary and beyond the Pannonian Basin as well. A correlation of the scattered volcanic products can be made based on lithological characteristics, as well as the chemical composition of glass shards, juvenile clasts, and zircon.