Stable isotope geochemical study of Pamukkale travertines: New evidences of low-temperature non-equilibrium calcite-water fractionation

In this paper we present the first detailed geochemical study of the world-famous actively forming Pamukkale and Karahayit travertines (Denizli Basin, SW-Turkey) and associated thermal waters. Sampling was performed along downstream sections through different depositional environments (vent, artificial channel and lake, terrace-pools and cascades of proximal slope, marshy environment of distal slope). delta C-13(travertine) values show significant increase (from +6.1 parts per thousand to +11.7 parts per thousand PDB) with increasing distance from the spring orifice, whereas the delta O-18(travertine) values show only slight increase downstream (from -10.7 parts per thousand to -9.1 parts per thousand PDB). Mainly the CO2 outgassing caused the positive downstream shift (similar to 6 parts per thousand) in the delta C-13(travertine) values. The high delta C-13 values of Pamukkale travertines located closest to the spring orifice (not affected by secondary processes) suggest the contribution of CO2 liberated by thermometamorphic decarbonation besides magmatic sources. Based on the gradual downstream increase of the concentration of the conservative Na+, K+, Cl-, evaporation was estimated to be 2-5%, which coincides with the moderate effect of evaporation on the water isotope composition. Stable isotopic compositions of the Pamukkale thermal water springs show of meteoric origin, and indicate a Local Meteoric Water Line of Denizli Basin to be between the Global Meteoric Water Line (Craig, 1961) and Western Anatolian Meteoric Water Line (Simsek, 2003). Detailed evaluation of several major and trace element contents measured in the water and in the precipitated travertine along the Pamukkale MM section revealed which elements are precipitated in the carbonate or concentrated in the detrital minerals.