## 4 Results
### Tufa Facies
#### Origin of Tufa Deposits  
Freshwater carbonates such as tufa can be useful tools for environmental conditions, assuming isotopic equilibrium during calcite precipitation. However, equilibrium between water and precipitated calcite is often disturbed due to different factors. The changes in water temperature are the most responsible for the variations in \(\delta^{18}\)O. Increasing water temperature is related to decreasing \(\delta^{18}\)O values [3]. Thus, we can assume that differences in \(\delta^{18}\)O can be related to seasonal changes. Generally, oxygen isotopic composition suggests that tufa precipitated from cold, freshwaters enriched in calcium bicarbonate. Carbon isotope composition suggests that CO\({}_{2}\) is dominantly of an atmospheric origin, with various amounts of soil (organic) CO\({}_{2}\). Sample Five displays a very high carbon isotope value (\(-6.50\%\)). The carbon isotopes of carbonate rocks seem to be more complex than oxygen isotopes, which may have resulted from the many potential agents (e.g., abiotic and photosynthetic), degassing of CO\({}_{2}\), deposition of calcite, and CO\({}_{2}\) exchange with the atmosphere [46]. A higher \(\delta^{13}\)C value in this sample can point to the input of heavier carbon isotope from dissolved limestones. In general, no attention is paid to stable isotope analyses in tufas in Serbia. Nevertheless, tufa deposits have been studied worldwide as their isotopic composition can point to environmental conditions. A number of studies dealt with tufa deposits from an environmental point of view in the Mediterranean region [17; 22; 26; 39; 42; 47; 48; 49; 50; 51; 52], Central Europe [21; 38; 53], and Great Britain [54; 55; 56]. Stable isotope data of the studied sites were compared with some well-known tufa deposits in Europe at Figure 6.  
It is evident that most of the tufa deposits have \(\delta^{18}\)O values between \(-9.5\%\) and \(-6\%\). The highest \(\delta^{18}\)O values are recorded in France [42], as well as in Great Britain [54]. It is interesting that stable oxygen values from SRB and GRB are generally lower than in mentioned studies. The most similar \(\delta^{18}\)O signatures to SRB and GRB have tufa deposits from Turkey [50], Poland [38], and a part of tufa from Dinaric Karst [17; 22], but they are, still, generally higher than tufa from SRB and GRB. The situation with the \(\delta^{13}\)C isotope data is even more complicated, i.e., more variations in different studies are noted. Most of the tufa deposits have \(\delta^{13}\)C values between \(-10\%\) and \(-6\%\). Tufa samples from Serbia display more similarity with other deposits in \(\delta^{13}\)C values than in \(\delta^{18}\)O values. However, \(\delta^{13}\)C values in this study are generally lower than in other sites in Europe. In many studies, \(\delta^{13}\)C values in some samples are very high, usually near 0, or even positive [39; 47; 49; 50]. Only data from France [42], and a part of data from Great Britain [54] have lower \(\delta^{13}\)C (minimum \(-12.1\%\)) than the samples from SRB and GRB. Compared to stable isotope analyses of tufa in Dinaric Karst [17,20,22,26], tufa from SRB and GRB have similar \(\delta^{13}\)C values and lower \(\delta^{18}\)O values to other tufa accumulations in the region. The comparison between the stable isotope compositions from GRB and SRB to other tufa sites in Dinaric Karst is given in Figure 7. Mean \(\delta^{13}\)C values for SRB and GRB are \(-9.01\)%, whereas the mean value is \(-9.60\)% in the Zrmanja River Canyon, Kraka River, and Krupa River [17,22,26]. In the Plitrice lakes, mean \(\delta^{13}\)C values are around \(-8.1\)% [17]. On the other side, \(\delta^{18}\)O values are a bit lower for SRB and GRB than in other tufa sites in the region. Mean \(\delta^{18}\)O values for SRB and GRB is \(-9.81\)%, whereas it is \(-7.02\)% in the Zrmanja River Canyon [22], \(-8.08\)% in the Kraka River [26], and \(-7.8\)% in the Krupa River [17].