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)

- The Tagyon Formation is made up by alternation of white or light grey, bedded limestones and of yellow, algal laminated limestones with bird's eye structures and mud cracks. In the borehole Dörgicse Drt.l. (Fig. 3) thick-bedded dasycladacean and thin-bedded calcite-spotted limestones alternate rhythmically, forming Lofer cycles with intertidal B and subtidal C members. Outcrops of the Middle Anisian platform carbonates are known in a large area from Balázs-tető (Szentantalfa) to Ágasmagas (Örvényes), and in a smaller area between Barnag and Tótvázsony (Fig. 30,1). In the Late Anisian, contemporaneously with the initiation of an alkaline acid volcanism, the relatively deep Buchenstein basin began to develop in the Balaton region (Fig. 30, II). The pelagic basin persisted more or less uniformly up to the Late Ladinian. Deposition of pelagic basinal limestones continued also at the beginning of the Carnian after secession of the volcanic input (Füred Fm.). - The Buchenstein Formation is made up predominantly by bedded, nodular, often cherty limestones, and volcanoclastics (Fig. 3.). The lowermost tuffs with bioclastic limestones and dolomites (Fig. 6.) were separated from the Buchenstein Formation in the recent lithostratigraphic subdivision (Fig. 4.). In the area of the „Tagyon platform" laminated siliceous limestones with Daonella and Posidonia lumachelle occurs in the upper part of the sequence (Fig. 7.). The maximum thickness of the formation is not more than 50 metres above the Anisian platforms, whereas it can reach 80 metres in the basin areas. - The Füred Limestone develops gradually from the Buchenstein Formation with decrease of volcanoclastics. It consists of grey nodular limestones with marl intercalations in the upper part (Fig. 9). It reaches its maximum thickness (60 metres) in the deepest part of the Ladinian basin in the surroundings of Balatonfüred. At the beginning of the next cycle, in the Early Carnian (Julian) the intrashelf basins began to fill up by siliciclastics (Veszprém Fm.), while the large carbonate platforms (Budaörs and Sédvölgy platforms) maintained and prograded in the highstand periods (Fig. 30, IV). By the latest Carnian (Tuvalian) as a result of upfilling of the basins (Sándorhegy Fm.) and platform progradations an extremely levelled topography developed giving rise to the formation of a widely extended platform (Main Dolomite Fm.). - The Veszprém Formation is made up by a lower (about 120 m thick) and an upper (about 300 m thick) marl member. In the middle part of the basin they are separated by nodular pelagic limestones which transit into proximal debris-flow deposits toward the platforms. - The Budaörs and Sédvölgy Dolomite consist mainly of bedded or thick bedded dolomites. Cyclic alternation of subtidal lagoon facies and peritidal algal mat facies is generally characteristic. The Budaörs platform was formed in the Middle Ladinian. Its first prograding period may have been near to the Ladinian/Carnian boundary in the Balaton Highland. The Sédvölgy platform was developed probably from the older Budaörs platform, anyhow its thickness and lateral extension is much greater in the Balaton Highland. Progradation of the platform took place in two distinct stages: in the Middle Julian and around the Julian/Tuvalian boundary. - The lower part of Sándorhegy Formation consists of bituminous laminites of restricted lagoon facies. It is partly coeval with the youngest prograding edge of the Sédvölgy platform. Marls with large oncoids, nodular limestones with Megalodontids, brachiopod-echinoderm coquinas are characteristic for its upper member. The maximum thickness of the formation is 170 m. - Lofer cyclic platform carbonates of the Main Dolomite cover both the former basins and platforms. Paleokarst phenomena at the base of the formation indicate subaerial expo-