Origin of the hydrothermal karstic phenomena in the Buda-Hills (Hungary), 1984, Kovacs Judit, Müller Pal

Brittle tectonics and major dextral strike-slip zone in the Buda karst (Budapest, Hungary), 1999, Benkovics L, Obert D, Bergerat F, Mansy Jl, Dubois M,

Three large (kilometric-scale) caves were studied in the Buda hills and the main directions of cave corridors, fault planes and mineralized veins were measured. Different stages of mineralizations are recognised: calcite scaleno-hedrons, baryte, silica, gypsum. New investigations of fluid inclusions in the baryte suggest a crystallization temperature of 50 degrees C and a freshwater fluid source. Microtectonic analysis allows the reconstruction of the successive tectonic events: (1) a NE-SW extensional phase at the Late Eocene-Early Oligocene limit (phase I), (2) a strike-slip phase with NW-SE compression and NE-SW extension during the Late Oligocene-Early Miocene (phase II), (3) a NW-SE transtensional phase (phase III) and finally (4) a NE-SW extensional phase of Quaternary age (phase IV). The major phase is the strike-slip one, characterized by an important dextral strike-slip zone: the Ferenc-hegy zone. (C) Elsevier, Paris

Paleokarst features and other climatic relics in Hungarian caves, 1999, Bolnertaká, Cs Katalin

Relics of climatic changes during the modern phase of karstic development have been preserved in the morphology, sediments and speleothems of several caves in Hungary; and there are examples of real paleokarst features exposed by modern caves as well. The unique sandstone morphology of Cserszegtomaj Well Cave (Keszthely Mts., Transdanubian Mountain Range), developed along the contact of Triassic dolomite and Pannonian sandstone, displays the relief of a karst surface formed probably under the subtropical conditions of the Early Miocene. The uppermost parts of Beremend Crystal Cave (Villány Mts., South Transdanubia) exposes also from below the clastic fill of an ancient karst shaft that, according to its rich vertebrate remains, dates back at least to the Lower Pleistocene. With their Late Eocene marine sediment fill, the small paleokarst cavities exposed in the Eocene bedrock of Mátyás-hegy and Pál-völgy Caves (Buda Hills) are interpreted as salt-fresh water mixing zone cavities formed during a short immersion of a tropical reef.

Hydrothermal speleogenesis in the Hungarian karst, 2000, Dublyansky Y. V.

Hydrothermal karst caves in Hungary were formed in a variety of speleogenetic settings. The oldest small solutional cavities (vugs) were formed in the deep-seated low-gradient zone at temperatures in excess of 90 oC. The temperatures decreased with time, as inferred from fluid inclusion studies of cave calcite. The caves were formed by normal carbonate corrosion. Large two-dimensional mazes of the Buda Hills were formed in the shallow low-temperature (but still hydrothermal) setting. The leading speleogenetic processes were normal carbonate corrosion (including mixing/cooling corrosion) and sulfuric acid corrosion. Temperatures at this stage were lower: ca. 50 oC and less. Above the thermal water table, in the subaerial zone, some specific and powerful speleogenetic processes occurred; condensation corrosion (by CO2-bearing waters) and replacement corrosion involving sulfuric acid reactions. Three-dimensional bush-like caves composed of connected spherical niches were formed as the result of this subaerial karstification.

U-series dating and isotope geochemical study of the Gellért Hill (Budapest) travertine, 2009, Kele S. , Scheuer G. , Demény A. , Shen Ch. C. , Chiang H. W.

Travertine is quite a common formation in the area of Budapest (Hungary) indicating strong hydrothermal activity during the Pliocene and Quaternary. It covers former terraces of the Danube River and older geomorphologic horizons; thus, it is an important archive to date fluvial terraces and tectonic movements. Despite numerous investigations performed on these deposits, only few radiometric data are available so far and the absence of the exact timing information hindered paleoclimatic interpretation. The area of Gellért Hill consists mainly of Upper Triassic dolomite, but Quaternary travertine can also be found. In this study a detailed petrographic and stable isotope geochemical study of four travertine sites (1. Ifjúsági Park; 2. Számadó u. (Street); 3. Kelenhegyi u. (Street); 4. Somlói u. (Street)) of the Gellért Hill area is presented, along with analyses on the recent carbonate deposits of Gellért Hill and Sárosfürdõ. The travertine of Ifjúsági Park and Számadó u. are spring cone deposits, while the travertine of the Kelenhegyi u. represents a shallow-water depositional environment. based on the paleontological studies of Jánossy (in Scheuer and Schweitzer, 1988) the Gellért Hill travertine was thought to have been formed during the Lower Pleistocene; however, no radiometric age dating had been performed on these deposits prior our study. Our U/Th analyses yielded ages of 250±44 ky for the Ifjúsági Park travertine (220 m asl) and 180±49 ky for the Számadó u. travertine (195 m asl). These new U/Th ages are in contradiction with the previously assumed Lower Pleistocene age, implying gradual relative decrease in the paleokarst water-level and proving that the elevation of the individual travertine deposits not necessarily show their relative age. The uplift rates of Gellért Hill calculated from the U/Th age data and elevation of travertine occurrences range between 0.47 and 0.52 mm/yr, which is significantly higher than the uplift rates calculated for the Rózsadomb area (0.20 0.25 mm/yr; Kele et al., submitted). The difference in the incision rates between the individual sub-areas suggests that selective uplift was characteristic for the Buda Hills during the Middle Pleistocene; thus, up-scaling reconstruction of paleokarst waterlevel for the whole area from a given locality is not possible. Oxygen isotope analyses of recent carbonate deposits of Gellért Hill, Sárosfürdõ and Rudas Spa revealed that these calcites precipitated under non-equilibrium conditions, and the measured calcitewater oxygen isotope fractionation show the same positive shift relative to "equilibrium values" as was observed in the case of the recently-forming Egerszalók travertine (Kele et al. 2008). Assuming that the water of the paleo-springs of Gellért Hill derived from precipitation infiltrated during interstadial periods of the Pleistocene and considering non-equilibrium deposition (i.e. using the empirical calcite-water oxygen isotope fractionation of Kele et al. 2008), their calculated paleotemperature could range between 22 (±4) °C and 49 (±6) °C. based on the 18Otravertine differences the Ifjúsági Park and the Számadó u. spring cone type travertine was deposited from the highest temperature water, while from the lowest temperature water the travertine of Kelenhegyi u. was formed.

Contributions of geophysical techniques to the exploration of the Molnár János Cave (Budapest, Hungary), 2010, Surá, Nyi Gergely, Dombrá, Di Endre, Leé, LŐ, Ssy Szabolcs

Located in the centre of the Pannonian, one of the hottest basins in Europe with high average heat flow values, Hungary has long been famous for hot water springs and frequent cave occurrences. The Molnár János Cave, an active thermokarstic cave, belonging to the Buda Hills karst system, lies beneath a highly populated district of Budapest. Its large passages are almost completely filled by lukewarm water. Only the upper part of its largest known chamber rises above the water level, which offers an excellent site to examine recent cave generation processes. However, hitherto, no dry subsurface gateway existed towards this chamber; it was only accessible underwater. In this paper, we present the results of various geophysical investigations including GPR, magnetic and seismic methods, carried out in a close cooperation between geophysicists and speleologists. The aim of the measurements was to determine the precise position of the hall relative to a nearby drift. Based upon the successful seismic survey and first break analysis, a precise and efficient boring could be designed to realise the connection. Finally, a passage between the two cavities has been established and, thus, the chamber of the cave is now accessible to the whole scientific community.

Imprints of hydrocarbon-bearing basinal fluids on a karst system: mineralogical and fluid inclusion studies from the Buda Hills, Hungary, 2011, Poros Zsofia, Mindszenty Andrea, Molnar Ferenc, Pironon Jacques, Gyori Orsolya, Ronchi Paola, Szekeres Zoltan

Calcite veins and related sulphate–sulphide mineralisation are common in the Buda Hills. Also, abundant hypogenic caves are found along fractures filled with these minerals pointing to the fact that young cave-forming fluids migrated along the same fractures as the older mineralising fluids did. The studied vein-filling paragenesis consists of calcite, barite, fluorite and sulphides. The strike of fractures is consistent—NNW–SSE—concluding a latest Early Miocene maximum age for the formation of fracture-filling minerals. Calcite crystals contain coeval primary, hydrocarbon-bearing- and aqueous inclusions indicating that also hydrocarbons have migrated together with the mineralising fluids. Hydrocarbon inclusions are described here for the first time from the Buda Hills. Mixed inclusions, i.e., petroleum with ‘water-tail’, were also detected, indicating that transcrystalline water migration took place. The coexistence of aqueous and petroleum inclusions permitted to establish the entrapment temperature (80°C) and pressure (85 bar) of the fluid and thus also the thickness of sediments, having been eroded since latest Early Miocene times, was calculated (800 m). Low salinity of the fluids (<1.7 NaCl eq. wt%) implies that hydrocarbon-bearing fluids were diluted by regional karst water. FT-IR investigations revealed that CO2 and CH4 are associated with hydrocarbons. Groundwater also contains small amounts of HC and related gases on the basin side even today. Based on the location of the paleo- and recent hydrocarbon indications, identical migration pathways were reconstructed for both systems. Hydrocarbon-bearing fluids are supposed to have migrated north-westward from the basin east to the Buda Hills from the Miocene on.

Fluid migration and porosity evolution in the Buda Hills, Hungary – selected examples from Triassic and Paleogene carbonate rocks/Dissertation submitted to the Ph.D. program for Geology and Geophysics at the Ph.D. School of Earth Sciences, Eötvös Lorï, 2011, Poros, Zsófia

Porosity evolution of carbonates in the Buda Hills was the subject of this research. The aim was to provide an analogue for carbonate reservoirs that underwent multiphase diagenesis. Two major porosity types were recognized: 1) micro-porosity of powdered Triassic dolomites 2) cavernous and fracture porosity represented by the famous hypogenic cave system, hosted by Triassic and Paleogene carbonates. Powderization of dolomite is a general phenomenon in the Buda Hills, where its areal extent is exceptionally large compared to similar occurrences elsewhere in the world. Geochemistry and mineralogy of the dolomite remained constant throughout the disintegration. Powderization is absent at places where the Triassic dolomites are partially calcitized as a result of karst related dedolomitization. Since powderization was controlled by surface related processes and no geochemical changes were associated with it, disintegration of dolomite is interpreted as the result of sub-recent physical weathering, supposedly related to frost action.

Hypogenic caves are found along older calcite-barite-fluorite-sulphide veins, pointing to the fact that young cave-forming fluids migrated along the same fractures as the older mineralizing fluids did. Predominantly NNW–SSE strike of fractures concludes a latest Early Miocene maximum age for the fracture-filling minerals. Vein-calcite contains coeval primary, HC-bearing- and aqueous inclusions indicating that also HCs have migrated together with the mineralizing fluids. The coexistence of aqueous and HC inclusions permitted to establish the entrapment temperature (80°C) and pressure (85 bar) of the fluid and thus also the thickness of sediments, having been eroded since latest Early Miocene times, was calculated (800 m). Low salinity of the fluids (<1.7 NaCl eq. wt%) implies that HC-bearing fluids were diluted by regional karst water. Fluid inclusion studies also revealed that aggressive gases (e.g. CO2, H2S) were associated with HCs and that these gases may have played a role in dissolution of the carbonates. Based on the location of the paleo- and recent HC indications, identical migration pathways were reconstructed for both systems. It was proved that HC-bearing fluids have migrated northwestward from the basin east to the Buda Hills from the Miocene on. Due to the uplift related intensification of groundwater circulation, the proportion of hydrothermal fluids has diminished in favour of cold meteoric fluids. Establishment of the actual porosity of the Buda Karst initiated in Miocene times and earlier diagenetic history of the carbonates affected only the powderization of dolomite, and it had no direct effect on the localization of hypogenic caves.