Seasonal study of calcite-water oxygen isotope fractionation at recent freshwater tufa sites in Hungary

Recent fluvial tufa carbonates were investigated from the Szalajka Valley (Bukk Mts., Hungary) and Malom Valley (Balaton Uplands, Hungary) to (1) study the suitability of the published oxygen isotope-based palaeothermometers for tufa deposits, (2) find the most appropriate (closest to equilibrium) places downstream for temperature calculation. A good correlation was observed between 1000ln alpha and the temperature of the water from which the tufa precipitated close to the spring orifice in the Szalajka and Malom Valleys. Large differences between calculated and measured temperature values were seen in areas where the seasonal water temperature increased and decreased by several degrees during our studied period. The stable isotope composition of the measured Hungarian tufas represents intermediate values between the western and eastern parts of Europe, reflecting increasing continentality in climate from west to east.