Stable and clumped isotope characterization of travertine spring mounds from Santovka and Dudince (Southern Slovakia)

Carbon, oxygen and clumped isotope (Δ₄₇) values were measured from recently inactive travertine mounds located in Santovka and Dudince (Slovakia) to provide information about the origin of carbon, precipitation conditions, and paleotemperature. δ¹⁸O and δ¹³C analyses of carbonates were performed at the Institute for Geological and Geochemical Research (IGGR), Research Centre for Astronomy and Earth Sciences (Budapest, Hungary) and the clumped isotope analysis were performed at the Isotope Climatology and Environmental Research Center (ICER) of the Institute for Nuclear Research (Debrecen, Hungary). δ¹³C values show a range between +5.3‰ and +9.7‰ (V-PDB) and δ¹⁸O values (V-PDB) range between –11.2‰ and −7.5‰. These data are in accordance with the typical isotopic signature of thermogene travertines. Positive δ¹³C values also suggest that the thermal waters were charged with isotopically heavy CO₂ of deep origin, possibly produced through metamorphic reactions, as decarbonation of carbonate rocks. Calculated δ¹³C_CO2 values of −4.2% to −0.9‰, more positive than values of CO₂ coming from the pure igneous source possibly, support this suggestion. Mineral and thermal waters in Slovakia are mainly observed in the Inner Carpathians depressions and lowland, making the most plausible carbon sources as being the Triassic limestones and dolomites, where the aquifers were formed. Clumped isotope composition (Δ₄₇) of the inactive Santovka Mound and two inactive mounds from Dudince were measured. D_{47(CDES 25)} values range from 0.646 ± 0.012‰ and 0.717 ± 0.010‰, corresponding to temperature estimates (T(Δ₄₇)) that range from 17°C to 43°C using the calibration of Petersen et al. (2019) and 12°C to 33°C, using Kele et al. (2015) calibration. Calculated paleotemperatures of the paleosprings are slightly higher than the present equivalents measured directly in thermal water wells from Santovka and Dudince (14.5 °C to 26.9°C). δ¹⁸O (V-PDB) of the travertine precipitating fluid was calculated using the T(Δ₄₇) data, giving values on the range of –11.1‰ and −5.8‰, while the δ¹⁸O_water values measured from thermal water well on Santovka and Dudince vary from –11.3‰ to 10.1‰ The observed difference in the δ¹⁸O_water values could be interpreted as the influence of the present-day precipitation (–10.4‰ to –8.7‰) on the waters on this region.