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

Abstract

<p>Carbon, oxygen and clumped isotope (Δ<sub>47</sub>) 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. δ<sup>18</sup>O and δ<sup>13</sup>C 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). <em>δ</em><sup>13</sup>C values show a range between +5.3‰ and +9.7‰ (V-PDB) and <em>δ</em><sup>18</sup>O values (V-PDB) range between –11.2‰ and −7.5‰. These data are in accordance with the typical isotopic signature of thermogene travertines. Positive δ<sup>13</sup>C values also suggest that the thermal waters were charged with isotopically heavy CO<sub>2</sub> of deep origin, possibly produced through metamorphic reactions, as decarbonation of carbonate rocks. Calculated δ<sup>13</sup>C<sub>CO2 </sub>values of −4.2% to −0.9‰, more positive than values of CO<sub>2</sub> 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 (Δ<sub>47</sub>) of the inactive Santovka Mound and two inactive mounds from Dudince were measured. D<sub>47(CDES 25) </sub>values range from 0.646 ± 0.012‰ and 0.717 ± 0.010‰, corresponding to temperature estimates (T(Δ<sub>47</sub>)) that range from 17°C to 43°C using the calibration of Petersen <em>et al. </em>(2019) and 12°C to 33°C, using Kele <em>et al</em>. (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). δ<sup>18</sup>O (V-PDB) of the travertine precipitating fluid was calculated using the T(Δ<sub>47</sub>) data, giving values on the range of –11.1‰ and −5.8‰, while the δ<sup>18</sup>O<sub>water</sub> values measured from thermal water well on Santovka and Dudince vary from –11.3‰ to 10.1‰ The observed difference in the δ<sup>18</sup>O<sub>water</sub> values could be interpreted as the influence of the present-day precipitation (–10.4‰ to –8.7‰) on the waters on this region.</p>