Abstract: K. TAMÁS and his wife G. FÖLDVÁRI, spent decades fossil hunting in the Balaton Highland region and in the process gathered a large collection of Triassic ammonoids; these are now housed in Kővágóörs (Veszprém county). The most beautiful examples from this collection warrant a publication devoted solely to themselves. On the other hand, some of the ammonoids, especially those from Szentkirályszabadja and Szentbékkálla, are also worth careful examination due to their considerable scientific (mainly palaeontological and stratigraphical) importance.
This paper presents short reports and illustrations of eleven ammonoid specimens, selected according to the above points of view. Besides the palaeontological data, the new collecting work and other field observations brought new stratigraphical results. The poor exposures in the Szentbékkálla vineyards, along with the earlier results of geological mapping and new ammonoid findings, provide evidence showing a continuous series of Anisian to Ladinian formations of basin facies. They represent the most westward lying occurrences of these formations in the Balaton Highland. The geological cross-section drawn between Farkas Hill and Kelemen Cliff reveals the south-eastward dipping series of the Megyehegy Formation, the Felsőörs Formation, the Vászoly Formation (Anisian), and both members (Nemesvámos and Keresztfatető Members) of the Buchenstein Formation (Ladinian). This complex of formations forms the NW limb of a local syncline which strikes parallel with the Litér overthrust, on the northern side of this major tectonic line. The newly collected ammonoids (Kellnerites cf. bosnensis, N. gen. aff. Kellnerites bagolinensis, Reitziites reitzi, R. cholnokyi, Latemarites latemarensis) complete ”missing parts” of the biostratigraphical units known previously in the Szentbékkálla locality and thus prove conclusively all four subzones (Felsoeoersensis, Liepoldti, Reitzi, Avisianum) of the Reitzi Zone. Several pieces of the Proarcestes sp. found in the scree of Nemesvámos Limestone (Buchenstein Formation) hint at the presence of the Ladinian Curionii Zone.
The previously described section of Szentkirályszabadja was completed upsection with two fossiliferous layers, revealed by new excavations and fossil collections. The newly exposed beds — like the deeper, major part of the section — represent an unusual (partly dolomitic, less siliceous) facies of the Vászoly Formation. The uppermost (No. –2) bed yielded a specimen of Ticinites cf. crassus, thus proving the Crassus Subzone of the Secedensis Zone, whereas the other specimen figured here (Nevadites sp.) underscores the presence of the Secedensis Zone in the Szentkirályszabadja section.
Keywords: Middle Triassic, ammonoidea, biostratigraphy, Balaton Highland
Abstract: On the basis of his studies in the 1940s, J. NOSZKY Jr. . published stratigraphical data on the Middle Jurassic of the Közös - kút Ravine of the Bakony Mountains. In several publications he reported the presence of Bathonian beds, based on the ammonites he found in the area. After a period in which his material was apparently “lost”, several decades later it was rediscovered in a repository of the Hungarian Geological and Geophysical Institute and thus became available for study. It turned out that all of the ammonites which NOSZKY’s found belong to Late Bajocian species, partly to forms which, in his time, were regarded as indicators of the Bathonian. The three most important species from the NOSZKY collection are: (Cadomites [C.] deslongchampsi, Vermisphinctes [S.] stomphus and Dimorphinites [D.] dimorphus) These are described briefly and figured in the present study. Although it is impossible to reconstruct the original position of these ammonites in the bed(s) exposed in NOSZKY’s (due to the lack of the original field notes), the indicated youngest stratigraphic record, i.e. the Parkinsonia parkinsoni Zone, represents an important contribution which is still relevant today. With this datum the heterochroneity of the calcareous/siliceous sedimentation change in the Bakony Mountains can be completed: namely, the former data on ?Late Toarcian – Early Aalenian (Úrkút), Early Bajocian (Bakonycsernye), and Late Batho ni an (Gyenespuszta) can now is supplemented with this Late Bajocian one. The corrected (Late Bajocian) age determination of the possibly youngest limestone bed(s) in the Közöskút Ravine confirms the former conclusion that the only hitherto known locality of Bathonian ammonite-bearing limestones in the Bakony Mountains is that in Gyenespuszta.
Keywords: Bajocian, Bathonian, Közöskút Ravine, Bakony Mts, ammonites, species descriptions
Abstract: In the Buda Hills the unevenly eroded surface of Triassic carbonate rocks is usually overlain by pyroclastite and tuffite layers; these represent the basal part of the Eocene succession. This interval is followed by conglomerate and subordinately sandstone beds which contain clasts of various lithology and size. The dolomite clasts are the most abundant, but in some places the amount of lava rock and tuff clasts are significant, and chert, sandstone and tuffite clasts also occur subordinately. The main aim of this study is to review earlier studies on the volcanic clast-bearing Eocene basal beds, as well as to consider the results of petrographic investigations into the clasts, with special regard to those of volcanic origin.
The lava rock and tuff clasts are strongly weathered. However, on the basis of textural observations, the determination of the original rock-type was usually possible. Based on microscopic investigations, the following types of volcanic rocks were distinguished: (i) andesite (originally with a probably porphyric, pilotaxitic texture, and with pseudomorphs after plagioclase and pyroxene); (ii) amafitic andesite (with an originally trachytic texture and pseudomorphs after oriented plagioclase, and subordinate pseudomorphs after mafic minerals); (iii) intermediate lava rock (with a porphyric and pilotaxitic texture, and with pseudomorphs after feldspar and mafic minerals); (iv) dacite–rhyolite tuff (with juvenile glass shards and pumice; crystals: pseudomorphs after plagioclase, and subordinate quartz, pseudomorphs after pyroxene and biotite); (v) rhyolite tuff (juvenile pumice and glass shard; crystals: pseudomorphs after feldspar, quartz, and pseudomorphs after a pyroxene, biotite, accessory; lithic fragments: andesite, acidic lava rock, siltstone/sandstone, siltstone and chert); (vi) acidic lava rock (consisting of coarse-grained, dark-coloured, spherulitic and fine-grained, light-coloured, alternating bands). The dolomite clasts have a fabric destructive texture (finely-, medium-, and coarsely crystalline).
The lava rock and tuff clasts of the “Upper Eocene conglomerate” are derived from a calc-alkaline intermediate– acidic volcanism. In order to determine the potential source areas of the conglomerate further comparative studies are needed. However, preliminary studies carried out by the authors of this study suggest that the Triassic andesite (which penetrates the Budaörs–1 well is petrographically similar to the andesite clasts found in the “Upper Eocene basal conglomerate”. Consequently, it appears that the investigated Eocene clastic deposits were probably formed via the reworking of previously deposited sediments containing clasts of Triassic volcanites. The tectonically altered pyroclastite (foliated cataclastite) occurs at the basalmost part of the Eocene succession; in a few sections its origins are probably associated with a simultaneous Late Eocene pyroclastic fall.
Keywords: Buda Hills, Late Eocene conglomerate, andesite, tuff, dolomite, pyroclastite, petrography, deposition
Abstract: For this paper, the Eggenburgian Pétervására Sandstone — a shallow marine siliciclastic formation — was studied as a surface analogue for known reservoir rocks. Field observation in the area of Kishartyán, detailed petrography (including SEM, CL) and geochemical analysis (XRD, SEM-EDS, stable isotope analysis) were applied to find out more about the diagenetic processes, the burial history, the porosity evolution, and their relationship with the weathering forms. The composition of the fine to very coarse-grained sandstones varies between subarenite and litharenite. The most common detrital grains are mono- and polycrystalline quartz and sedimentary rock fragments (cherts, dolomites and metamorphic rock fragments). Ductile grains are represented by micas and altered volcanoclastic rock fragments. Based on the proportion of components, four lithofacies were distinguished: porous sandstone (LF1), matrix-rich sandstone (LF2), cement-rich sandstone (LF3), and matrix and cement rich sandstone (LF4). The eogenetic minerals are: glauconite, framboidal pyrite, flattened rhombohedral siderite crystals, K-feldspar overgrowth cement, kaolinite, and (supposedly) small amounts of calcite. The maximum burial temperature was likely reached at around 80 °C; this is indicated by the presence of quartz overgrowth cement, mixed layer illite/smectite, and replacive and cementing albite. These minerals were formed in the mesogenetic realm. During eogenesis and mesogenesis, the porosity of the sandstone progressively decreased due to compaction and the precipitation of authigenic minerals. Calcite is one of the latest diagenetic minerals and occurs both as a replacive phase and as cement. The distribution of calcite within the studied sandstone is heterogeneous. Calcite is present in elongated lenses where the sandstone has a very low porosity. Considering the geochemical data and the geological setting, the origin of the calcite can be explained by several genetic models. According to these models, the formation of the calcite may have taken place either in the mesogenetic realm from modified marine pore waters (buried together with the sediment), or from an exotic fluid channelled along fault zones. In the second scenario, there are two possibilities regarding the origin of the parent fluid: namely, (a) a formational fluid or (b) a deeply circulated, warmed-up meteoric fluid. The high porosity of the sandstone is the result of dissolution by meteoric water during uplift. Diagenetic evolution of the sandstone had a crucial role in the formation of the weathering morphology.
Keywords: sandstone, petrography, diagenesis, replacive and cement calcite, Miocene, Northern Hungary
Abstract: The morphostratigraphical subdivision of the Danube terrace system of the Visegrad Gorge was presented by PÉCSI (1959). However, in recent decades new studies have revealed some problems with this earlier model. The appearance of the gravel sediments in the high level terraces (V–VIII) is not continuous, and thus the morphostratigraphical position of the terrace level cannot be followed clearly. Consequently, for the correlation of the terrace levels a detailed analysis of the overlaying bed of the gravel horizon is necessary in order to reach more convencing conclusions. A litho stratigraphical description of the overlying sequences and the identification of the lithologically unique, or rare gravel components of the marker sediments, could provide more accurate information about the separation and correlation of the different terrace levels. During the investigation which is the subject of this paper, an interpretation of the geomorphological features of the area using field and digital elevation methods was carried out. Furthermore, the stratigraphic description of overlaying sediments and the fine-grained pebble examination (FPE) method were applied to get more information about the morphostratigraphical position of the high level terrace systems.
Keywords: Visegrad Gorge, Danube, Pebbles, Terraces, Miocene
Abstract: The Rózsadomb area is one of the Buda Thermal Karst’s discharge areas. It is important from both theoretical and practical point of view to understand the temporal changes of the physicochemical parametres of lukewarm waters and their relationships with temporal changes of precipitation. The Molnár János Cave – Boltív Spring – Malom Lake system and its theoretical recharge area were studied. Based on executed measurements and continuous data series, the effect of the precipitation were examined on the temperature, specific electric conductivity, pH, volume discharge and water level parametres of the Boltív Spring and on the karst water level of the theoretical recharge area.
The project was supported by the NK101356 OTKA research grant.
Keywords: Buda Thermal Karst, recharge, discharge, lukewarm springs, integrated precipitation