The petrographical and volcanological investigation of the volcanogenic formation embedded in the bryozoan marl formation in the Mátyás Hill (Buda Hills, North Hungary)

Abstract

This study documents the basic volcanic-sedimentary and petrographical features of the volcanogenic layer (according to our genetic interpretation: volcanogenic sandstone) embedded in Upper Eocene bryozoan marl at Mátyás
Hill (Budapest). On the basis of the composition of the volcaniclastic layer (lithoclasts with a microholocrystalline, porphyric texture, pumice, quartz, carbonized feldspar, biotite, apatite, zircon, kaolinite) it is an altered product of silicarich volcanism. The composition, the well-sorted grain size, the unrounded and shard-like grains, the maximum grain size (2,5 mm) and the widespread distribution of the volcanoclastic layer suggest a strongly explosive eruption at least
several tens of kilometres far from the site of deposition. The provenance area of the pyroclastic material may have been an eruptive centre of the Eocene/Oligocene volcanic chain along the Periadriatic Lineament. The primer pyroclastic
material was slightly resedimented by gravity-driven mass flows before diagenesis, thus the examined formation must be considered as a volcaniclastic layer, more precisely volcanogenic sandstone.