Budai Tamás, Csillag Gábor: A Bakony természettudományi kutatásának eredményei 22. - A Balaton-felvidék középső részének földtana (Zirc, 1998)

GEOLOGY OF THE CENTRAL PART OF THE BALATON HIGHLAND (TRANSDANUBIAN RANGE, HUNGARY)

GEOLOGY OF THE CENTRAL PART OF THE BALATON HIGHLAND (TRANSDANUBIAN RANGE, HUNGARY) Tamás Budai - Gábor Csillag Introduction Balaton Highland is one of the classic areas of Hungarian geology. A great number of famous Austrian and Hungarian geologists worked here in the previous (Hauer, Stäche, Paul, Hoffman, Böckh J. etc.) and present century (Lóczy sr., Laczkó, Lóczy jr., Teleki G., ErdélyiFazekas, Szabó I., Majoros etc.). The last geological mapping project of the Balaton Highland was carried out by the Hungarian Geological Institute during the eighties. Field work was made on 1:10 000 scale, providing the base for the final maps on 1:20 000 and 1:50 0000 scales. The detailed mapping produced a vast number of stratigraphie and tectonic results and paleogeographic and geohistoric reconstruction which were published in the last years. Central parts of the Balaton Highland were mapped by Tamás Budai and Gábor Csillag. Main results of their investigations were summarised in their PhD thesis and the present volume. Geological setting The Balaton Highland belongs to the Bakony Mountains which is located in the southwestern part of the Transdanubian Range (TR). The TR itself forms a NE-SW striking synclinorium. The Balaton Highland, being on the southern flank of the synclinorium is built up of the oldest rocks of the TR. Formations from Lower Ordovician to Upper Triassic in age crop out in this area, whereas younger Mesozoic and Paleogene rocks are missing. Showing NW dipping, the general strike of the Palaeozoic and Mesozoic formations on the Balaton Highland is SW-NE. The most important structural feature of the region is the Liter line of NE-SW strike, a transverse fault cutting through the Palaeozoic-Mesozoic sequences. Stratigraphy The oldest rocks of the Balaton Highland were formed in the Early Palaeozoic. They are siliciclastic marine sediments (clay, siltstone, sandstone) which are interbedded in certain levels with basic and acidic volcanites (e. g. Upper Ordovician porphyr). The SilurianDevonian series was effected by very low to low grade metamorphism and subsequent deformation during the Variscan orogeny. These rocks are known only in boreholes in the central part of the Balaton Highland. After the Variscan orogeny intense erosion took place during the Permian. Alluvial molasse was deposited under semiarid climatic conditions. The cyclic succession is made up by aliénation of red sandstone, siltstone and conglomerate beds. The Balatonfelvidék Sandstone Formation crops out in an anticline near Tótvázsony. In the southern part of the study area, it is explored only by boreholes.