No abstract

Bondoró Volcanic Complex (shortly Bondoró) is one of the most complex eruption centre of Bakony-Balaton Highland Volcanic Field, which made up from basaltic pyroclastics sequences, a capping confined lava field (∼4 km 2 ) and an additional scoria cone. Here we document and describe the main evolutional phases of the Bondoró on the basis of facies analysis, drill core descriptions and geomorphic studies and provide a general model for this complex monogenetic volcano. Based on the distinguished 13 individual volcanic facies, we infer that the eruption history of Bondoró contained several stages including initial phreatomagmatic eruptions, Strombolian-type scoria cones forming as well as effusive phases. The existing and newly obtained K-Ar radiometric data have confirmed that the entire formation of the Bondoró volcano finished at about 2.3 Ma ago, and the time of its onset cannot be older than 3.8 Ma. Still K-Ar ages on neighbouring formations (e.g. Kab-hegy, Agár-tető) do not exclude a long-lasting eruptive period with multiple eruptions and potential rejuvenation of volcanic activity in the same place indicating stable melt production beneath this location. The prolonged volcanic activity and the complex volcanic facies architecture of Bondoró suggest that this volcano is a polycyclic volcano, composed of at least two monogenetic volcanoes formed more or less in the same place, each erupted through distinct, but short lived eruption episodes. The total estimated eruption volume, the volcanic facies characteristics and geomorphology also suggests that Bondoró is rather a small-volume polycyclic basaltic volcano than a polygenetic one and can be interpreted as a nested monogenetic volcanic complex with multiple eruption episodes. It seems that Bondoró is rather a "rule" than an "exception" in regard of its polycyclic nature not only among the volcanoes of the Bakony-Balaton Highland Volcanic Field but also in the Neogene basaltic volcanoes of the Pannonian Basin.

Recent nautiloid and ammonoid finds from the Middle Triassic Zuhánya Limestone Formation in the Mecsek Mountains (south Hungary) proved that the formation encompasses the whole Pelsonian and the lower Illyrian substages of the Anisian Stage. On the basis of 11 identified ammonoid species, the Balatonicus and Trinodosus zones have a complete record. The stratigraphical position of the Zuhánya Limestone on the whole corresponds to the Felsőörs Limestone in the Balaton Highland. The palaeobiogeographical evaluation of the cephalopod fauna showed that the elements of the nautilid fauna point mostly to Germanic and partly to Sephardic affinity. On the other hand, the ammonoid fauna has no Germanic elements; most of the species are Alpine in character, while the species Procladiscites brancoi indicates Dinaridic connection, or at least an occasional appearance of pelagic organisms. These results endorse the previous palaeogeographical assumption and suggest that during the Middle Triassic the Mecsek succession was situated along the European shelf, between the Vindelician-Bohemian Land and the open Tethyan Ocean.

Remains of Triassic vertebrates discovered in the Villány Hills (SW Hungary) are described here. After the well-documented Late Cretaceous Iharkút locality, this material represents the second systematically collected assemblage of Mesozoic vertebrates from Hungary. Fossils were collected from both the classical abandoned road-cut at Templom Hill (Templom-hegy) and a newly discovered site at a construction zone located 200 meters west of the road-cut. Macrofossils of the construction site are mainly isolated bones and teeth of nothosaurs from the Templomhegy Dolomite, including a fragmentary mandible referred to as Nothosaurus sp. and placodont teeth tentatively assigned here to cf. Cyamodus sp. Affinities of these fossils suggest a Middle Triassic (Ladinian) age of these shallow marine deposits.New palynological data prove for the first time a Late Triassic (Carnian) age of the lower part of the Mészhegy Sandstone Formation. Vertebrate remains discovered in this formation clearly represent a typical Late Triassic shallow-marine fauna including both chondrichthyan (Lissodus, Palaeobates, Hybodus) and osteichthyan (cf. Saurichthys, ?Sphaerodus sp.) fish fossils. The presence of reworked nothosaur and placodont tooth fragments as well as of possible archosauriform teeth, suggest an increase of terrestrial influence and the erosion of underlying Triassic deposits during the Late Triassic.A belemnite rostrum collected from the lowermost beds of the Somssichhegy Limestone Formation proves that this Lower Jurassic (Pliensbachian) layer was deposited in a marine environment. Most of the vertebrate remains (nothosaurs, placodonts, hybodont shark teeth, perhaps Palaeobates, Lissodus) recovered from these beds are also reworked Triassic elements strongly supporting an erosive, nearshore depositional environment.

The Upper Permian Boda Claystone Formation (BCF) in SW Hungary has been previously been identified as a saline lake deposit. A country-wide screening found this 800-1000 m thick succession the most suitable for the disposal of high-level radioactive waste in Hungary, and research into this formation has consequently been intensified since. The investigations included a detailed study of the sedimentological characteristics. Data obtained by mapping of the 25 km 2 outcrop area of the formation and from more than 40 boreholes were processed. The sedimentary structures were investigated on outcrop to microscopic scales, and cycles in the succession were interpreted. The main lithofacies, sedimentary structures and ichnofossils are presented. They indicate that the major part of the succession was deposited in a playa mudflat and is not of lacustrine origin in a strict sense. The lake sediments are represented by laminated and ripple-marked/flaser-type cross-laminated claystones and siltstones and by massive dolomites; trace fossils include crawling traces and burrows. Partial or complete drying out of the lake commonly occurred after the formation of carbonate mud by evaporation. Periodic fluvial influx is recorded by cross-bedded sandstones and unsorted gravelly sandstones of up to pebble-sized angular grains. Fenestral and stromatolitic structures reflect the repeated appearance of playa mudflat conditions. The silty claystones, which compose the major part of the succession, lost their primary structures due to pedogenic processes and indicate prolonged subaerial intervals with soil formation and only ephemeral inundations. The presence of pedogenic carbonate concretions supports the interpretation of an arid climate and a relatively shallow groundwater table. Drying-out events shown by desiccation cracks and authigenic breccias can be traced all over the succession. The various facies form small-scale sedimentary cycles showing a shallowing-upward trend and the growing influence of aridity and subaerial exposure.