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- Author or Editor: Attila Demény x
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Partial and pervasive dolomitization of foreslope and toe-of-slope deposits of an early Carnian carbonate platform was investigated to understand the process and mechanism of dolomitization. Based on petrographic observations and C and O isotope data, the dolomitization took place in a near-surface to shallow burial setting; seawater of slightly elevated salinity was likely the dolomitizing fluid. The circulation system was maintained by reflux of evaporated sea water and geothermal heating of cold seawater derived from the surrounding deeper basin. The dolomitization was mostly controlled by the permeability of the platform-derived calcareous sediments.
The intraformational paleosol and calcareous muddy cavity fills interbedded in the travertine of the Vár-hegy (Castle Hill) in Budapest were analyzed for carbon and oxygen isotope compositions and compared with the isotope compositions of the host travertine. Microscopic investigations of these layers indicate mechanical reworking of the travertine and mixing with the allothigenic siliciclastic material. Micromorphological features, e.g. needle-fiber calcite, carbonate hypocoatings around pores, ferruginous precipitations and clay infillings in the paleosol and cavity fills indicate that in situ pedogenic processes were active in both layers. The presence of ferrihydrite in the A horizon of the paleosol also supports pedogenic alteration. The stable carbon and oxygen isotope compositions of bulk carbonate of paleosol and cavity fills (d13C= -0.6 to 2.1‰ and d 18O= -16.7 to -12.9‰) are very close to the compositions of the host travertine (d 13C=1.1 to 2.1‰ and d 18O = -17.7 to -13.7‰,) and differ from the probable isotope composition of pedogenic carbonate (d 13C values around -11‰). These results indicate that the studied paleosol and cavity fills have only minor pedogenic component (authigenic carbonate content up to 20%); thus the paleosol represents a weakly developed soil, mostly composed of travertine clasts and allothigenic siliciclastic material.
The ophiolitic rocks of the easternmost Penninic unit, the Kõszeg-Rechnitz series, were analyzed for their H, C and O stable isotope compositions. Serpentinite, gabbro, blueschist, talc deposits, ophicarbonates, as well as calcite and inclusion fluids from quartz segregation veins were analyzed in order to determine the effects of different metamorphic events on the stable isotope compositions.
The oxygen isotope compositions have a wide range depending on rock type and locality. Gabbro and serpentinite of Bienenhütte (Bernstein Window) have preserved mantle-like δ 18O values (5.9 to 6.3‰; all values are in ‰ relative to V-SMOW), whereas the serpentinite of Glashütten and Rumpersdorf (Kõszeg-Rechnitz Window) and the silicate minerals of the ophicarbonate rocks show a strong 18O-enrichment (up to 16.2‰). The 18O-enrichment may have been induced by low-temperature serpentinization or interaction with 18O-rich fluids that had been in equilibrium with sedimentary rocks. Contrary to the O isotope compositions, the H isotope compositions seem to be homogeneous in the entire series, with D values of −63 ± 7‰. Only some serpentinite rocks were depleted in D (down to −106‰), usually regarded as a result of interaction with meteoric water infiltrating during late-stage metamorphism. The meteoric water infiltration was rather limited, as even samples taken directly from slickensides within serpentinite bodies preserved isotopic compositions close to those of the bulk series. H and O isotope compositions of fluids mobilized in the metasedimentary rocks of the Penninic unit during the main metamorphic stage were determined by analyzing inclusion fluids and calcites in quartz-carbonate veins. The isotope compositions indicate interaction between these fluids and the ophiolite series, although relative deuterium enrichment has been preserved in the ophiolitic rocks.
The strong D-enrichment characteristic for oceanic crust that has experienced high-temperature interaction with seawater was not detected. However, the H isotope compositions obtained for the Kõszeg-Rechnitz series indicate that subduction of the Penninic oceanic crust and the associated devolatilization may have been potentially responsible for mantle metasomatism, resulting in H isotope compositions of about −40‰, similar to the range determined from mantle-derived amphibole megacrysts (Demény et al. 2005). To conclude, the present dataset is discussed in the light of earlier studies on the formation of the Sopron leucophyllite.
Linear correlation between the temperature and measured δ18Owater of Budapest thermal karst water system presents an opportunity to estimate both the temperature and δ18O of the depositing water if only the δ18Otravertine is known.
Our observations on several Hungarian groundwaters and travertines deposited recently from them resulted that δ18O data of travertines originating from cold karst water and thermal water of porous aquifer are close to the “experimental“ curve presented by Friedman and O'Neil (1977). Conversely, the calculated fractionation factors of thermal karst waters significantly deviate from the experimental curve following an “empirical-curve“ (R2 = 0.99) as: 1000*lnα = (2.76*106)/T2 − 1.31.
The empirical equations calculated by this “empirical-curve“ as Twater = (25 − δ18Otrav)/0.22 and δ18Owater = 0.186*δ18Otrav − 14.22 are usable only for the Budapest thermal karst regime and only for recent travertines. Extrapolation of these equations to the past and use them to estimate the deposition temperature of paleo-travertines needs detailed information of the paleoclimate and age of travertine.
In this paper we present sedimentological and geochemical data for a section of fluvial deposits from SE Hungary covering the period of 25 to 5 ky BP. Major and trace element geochemistry of bulk sediments as well as stable C and O isotope compositions of the carbonate content indicate significant changes in depositional facies and/or sediment provenance. Correlations of mineralogical and geochemical compositions were used to determine the stable isotope compositions of authigenic calcite component. Additionally, C and O isotope compositions of Unio crassus shell fragments were analysed that show a good agreement with climate change. Major climate change events within the studied time period were detected both in the shells and the authigenic calcite's compositions.
In the area of the town of Tata (Hungary) there are several Quaternary travertine outcrops, of which the Porhanyó Quarry is the best-exposed one. The travertine of the Porhanyó Quarry can be vertically divided into six units. Algal and other phytoclastic and phytohermal grainstone, boundstone and floatstone are the dominant microfacies. On the walls of the quarry carbonate vents and cones were detected; these forms are indicators of former spring activity at the bottom of a shallow lake. The lake, fed by thermal springs, was formed in a siliciclastic floodplain. The upwelling thermal water brought quartz and other detrital grains from the underlying Pannonian siliciclastic sediments to the surface, concentrating them in the vents. The three main phases of lacustrine evolution were interrupted first by a drying and flooding event, followed by a fluvial-eolian event and finally by eolian sedimentation. The oxygen isotope compositions of the vents differ from the values of vertical sections and slope samples, whereas the carbon isotope compositions show less variation. The different facies migrated during the evolution of the Tata Travertine Complex due to changes in morphology and flow direction. The integrated model of lake evolution suggests an upward cooling climatic trend, beginning with a humid Mediterranean climate in the early phase and closing with a cold, dry continental one in the late phase. The Tata Travertine Complex shows a marked d13C difference from the travertine occurrences of the Buda Mts. that is attributed to local effects. The ascending solutions at Tata may have infiltrated through organic-rich bedrocks and could have carried dissolved C enriched in 12C.
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 Sárosfürdő. 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, Sárosfürdő 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 δ18Otravertine 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.
In this study we report the first hydrogen isotope composition analyses on carbonado diamond along with cathodoluminescence and scanning electron microscopic imaging, electron microprobe analyses, and stable (H and C) and radiogenic (Sr) isotope measurements. The hydrogen of bulk carbonado (consisting diamond and pore-filling minerals) yielded ∼ −4‰, consistent with usual crustal or mantle-derived fluids. The diamond-related hydrogen component is about 70 ± 30 ppm and shows a D-depletion down to −200‰. Determined H isotope values — together with C isotope compositions — overlap the ranges for mantle-derived hydrocarbons. Textural characteristics and Sr isotope ratios of pore-filling florencite indicate that the carbonado was formed in a fluid-rich environment, underwent a significant high-temperature influence and finally suffered thorough alteration. Based on these observations, a terrestrial formation during interaction of mantle rocks/melts or subducted crustal materials and reduced C-H fluids seems to be more plausible than an extraterrestrial origin.
Stable carbon and oxygen isotope compositions of living Unio shells and oxygen isotope compositions of water samples were determined in order to demonstrate how the shells' compositions can reflect environmental conditions. With this information in hand, fossil shell fragments from a sedimentary section at Tiszapüspöki covering the period of about 3.5 to 10 ky BP were analyzed for their stable isotope as well as trace element compositions. Beside the determination of sedimentary facies effects on the geochemical compositions, the combined evaluation of isotopic and trace element records allowed us to detect past environmental changes at a millennial scale. The data indicate that the period of 6 to 8 ky BP was characterized by humid summers that — on the basis of comparison with an Alpine speleothem record — was associated with a generally warmer climate and increased winter precipitation in the Alps.