Preliminary studies of freshwater tufa deposits in Mecsek mts., Hungary

The geochemical and stable isotope analyses of karst springs and their freshwater carbonate deposits provide an opportunity to reconstruct past climate changes. Nevertheless, there are still very few paleoclimate records obtained from freshwater carbonate deposits in Hungary. The present study focuses on five recently depositing freshwater tufa sites (Anyák Spring, Csurgó Spring, Pásztor Spring, Dagonyászó Spring and Kánya Spring) located in Mecsek Mts. (Southern Hungary) as possible sources for Holocene paleoclimate research. Carbonate samples were collected for stable isotope analyses in June and August 2011 and a monitoring programme was started in October 2011. The stable isotope analyses of the rock samples reflect the effect of continentality and suggest strong soil zone C02 contribution

What do we really know about early diagenesis of non-marine carbonates?

Non-marine carbonate rocks including cave, spring, stream, calcrete and lacustrine- palustrine sediments, are susceptible to early diagenetic processes. These can profoundly alter the carbonate fabric and affect paleoclimatic proxies. This review integrates recent insights into diagenesis of non-marine carbonates and in particular the variety of early diagenetic processes, and presents a conceptual framework to address them. With ability to study at smaller and smaller scales, down to nanometers, one can now observe diagenesis taking place the moment initial precipitates have formed, and continuing thereafter. Diagenesis may affect whole rocks, but it typically starts in nano- and micro-environments. The potential for diagenetic alteration depends on the reactivity of the initial precipitate, commonly being metastable phases like vaterite, Ca-oxalates, hydrous Mg‐carbonates and aragonite with regard to the ambient fluid. Furthermore, organic compounds commonly play a crucial role in hosting these early transformations. Processes like neomorphism (inversion and recrystallization), cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex, primary microtextures. If early diagenetic modifications are completed in a short time span compared to the (annual to millennial) time scale of interest, then recorded paleoenvironmental signals and trends could still acceptably reflect original, depositional conditions. However, even compact, non-marine carbonate deposits may behave locally and temporarily as open systems to crystal- fluid exchange and overprinting of one or more geochemical proxies is not unexpected. Looking to the future, relatively few studies have examined the behaviour of promising geochemical records, such as clumped isotope thermometry and (non- conventional) stable isotopes, in well-constrained diagenetic settings. Ongoing and future in-vitro and in-situ experimental approaches will help to investigate and detangle sequences of intermediate, diagenetic products, processes and controls, and to quantify rates of early diagenesis, bridging a gap between nanoscale, molecular lab studies and the fossil field rock record of non-marine carbonates

Calculation of temperature and δ18O of depositing water by measured δ18O of recent travertines deposited from the Budapest thermal karst water

Abstract 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

Dolomitization of Triassic microbial mat deposits (Hungary): Origin of microcrystalline dolomite

Dolomite most commonly forms via replacement of precursor carbonate minerals. For this reason, diagnosing primarily precipitated organogenic dolomite in microbial mat deposits from the rock record is not straightforward, even though the deposits exhibit microbial fabric. Single and multiple dolomite crusts exhibiting microbial fabric occur in a pervasively dolomitized Middle Triassic platform succession. Two sections were studied in the Transdanubian Range. In both sections, two fabric types occur in the upper part of the metre-scale cycles. One of that is microbial boundstone (fabric type 1)‒‒characterised by clusters of dolomite microcrystals which display diagnostic microbial features, such as calcimicrobes, clotted–spherular aggregates and globules. The other one is different in the two studied sections. In Section 1, it is micritic dolomite (fabric type 2) that is characterised by predominantly fine crystals and contains obscured microbial components. In Section 2, it is bioclastic dolomite (fabric type 3) that is rich in reworked dasycladalean alga fragments and consists of dolomite crystals of wide size-range from fine to coarse. The precipitation of the microcrystalline dolomite phase is interpreted as being facilitated by mats and biofilms favouring/tolerating an increasing frequency of subaerial conditions in the upper intertidal setting. Petrographic analyses revealed that organogenic calcite was also precipitated, especially in mat deposits rich in bioclasts. Synsedimentary dolomitization, resulting in fine crystals, was coupled with aragonite dissolution and it postdated the organogenic precipitation. It took place only in the peritidal caps of the shallowing-upward depositional units. Petrographic analyses provide circumstantial evidence constraining that microcrystalline dolomite did not form via mimetic replacement. Accordingly the microcrystalline dolomite, which shows microbial microfabrics in the studied samples, is interpreted as an organogenic primary precipitate. Both peritidal processes, dolomite precipitation and replacement, were likely controlled by the environmental factors in a semi-arid climate. Those components of the platform succession that were not dolomitized in the peritidal environment were replaced and cemented by medium and coarsely crystalline dolomite during further burial at elevated temperature, as shown by fluid inclusion homogenisation temperature (62 to 83 °C) and negative stable oxygen isotope values. Thus, the majority of the studied formation consists of fabric-destructive dolomite (fabric type 4)

Investigation of tillage elements of agricultural machinery

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U-series dating and isotope geochemical study of the Gellért Hill (Budapest) travertine

Abstract 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