The Potential of Tufa as a Tool for Paleoenvironmental Research—A Study of Tufa from the Zrmanja River Canyon, Croatia

Abstract

Tufa is a fresh-water surface calcium carbonate deposit precipitated at or near ambient temperature, and commonly contains the remains of macro- and microphytes. Many Holocene tufas are found along the Zrmanja River, Dalmatian karst, Croatia. In this work we present radiocarbon dating results of older tufa that was found for the first time at the Zrmanja River near the Village of Sanaderi. Tufa outcrops were observed at different levels, between the river bed and up to 26 m above its present level. Radiocarbon dating of the carbonate fraction revealed ages from modern, at the river bed, up to 40 kBP ~20 m above its present level. These ages fit well with the hypothesis that the Zrmanja River had a previous surface connection with the Krka River, and changed its flow direction toward the Novigrad Sea approximately 40 kBP (Marine Isotope Stage 3). Radiocarbon AMS dating of tufa organic residue yielded a maximum conventional age of 17 kBP for the highest outcrop position indicating probable penetration of younger organic material to hollow tufa structures, as confirmed by radiocarbon analyses of humin extracted from the samples. Stable carbon isotope composition (δ13C) of the carbonate fraction of (−10.4 ± 0.6)‰ and (−9.7 ± 0.8)‰ for the Holocene and the older samples, respectively, indicate the autochthonous origin of the carbonate. The δ13C values of (−30.5 ± 0.3)‰ and (−29.6 ± 0.6)‰ for organic residue, having ages <500 BP and >5000 BP, respectively, suggest a unique carbon source for photosynthesis, mainly atmospheric CO2, with an indication of the Suess effect in δ13C during last centuries. The oxygen isotopic composition (δ18O) agrees well with deposition of tufa samples in two stages, the Holocene (−8.02 ± 0.72‰) and “old” (mainly MIS 3 and the beginning of MIS 2) (−6.89 ± 0.34‰), suggesting a ~4 °C lower temperature in MIS 3 compared to the current one.

Facies and Origin of Tufa Deposits from the Gostilje River Basin and the Sopotnica River Basin (SW Serbia)

“…On the other side, δ 18 O values are a bit lower for SRB and GRB than in other tufa sites in the region. Mean δ 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 Krka River [26], and −7.8‰ in the Krupa River [17]. The most similar to this study are the δ 18 O values for the Plitvice lakes-with a mean value of −9.7‰ [17].…”

“…Only data from France [42], and a part of data from Great Britain [54] have lower δ 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 δ 13 C values and lower δ 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.…”

“…The comparison between the stable isotope compositions from GRB and SRB to other tufa sites in Dinaric Karst is given in Figure 7. Mean δ 13 C values for SRB and GRB are −9.01‰, whereas the mean value is −9.60‰ in the Zrmanja River Canyon, Krka River, and Krupa River [17,22,26]. In the Plitvice lakes, mean δ 13 C values are around −8.1‰ [17].…”

“…It is interesting that stable oxygen values from SRB and GRB are generally lower than in mentioned studies. The most similar δ 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.…”

“…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.…”