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

Sándor Kele a,⁎, Mehmet Özkul b, István Fórizs a, Ali Gökgöz b, Mehmet Oruç Baykara b,Mehmet Cihat Alçiçek b, Tibor Németh a

a Hungarian Academy of Sciences, Institute for Geochemical Research, Budaörsi út 45, H-1112 Budapest, Hungaryb Pamukkale University, Department of Geological Engineering, TR-20070 Denizli, Turkey

a b s t r a c ta r t i c l e i n f o

Article history:Received 21 December 2010Received in revised form 25 April 2011Accepted 26 April 2011Available online 1 May 2011

Editor: B. Jones

Keywords:PamukkaleTerraced-slope travertineStable isotopeTrace elementNon-equilibrium deposition

In this paper we present the first detailed geochemical study of the world-famous actively forming Pamukkaleand Karahayit travertines (Denizli Basin, SW-Turkey) and associated thermal waters. Sampling wasperformed along downstream sections through different depositional environments (vent, artificial channeland lake, terrace-pools and cascades of proximal slope, marshy environment of distal slope). δ13Ctravertine

values show significant increase (from +6.1‰ to +11.7‰ PDB) with increasing distance from the springorifice, whereas the δ18Otravertine values show only slight increase downstream (from −10.7‰ to −9.1‰PDB). Mainly the CO2 outgassing caused the positive downstream shift (~6‰) in the δ13Ctravertine values. Thehigh δ13C values of Pamukkale travertines located closest to the spring orifice (not affected by secondaryprocesses) suggest the contribution of CO2 liberated by thermometamorphic decarbonation besides magmaticsources. 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 waterisotope composition. Stable isotopic compositions of the Pamukkale thermal water springs show of meteoricorigin, and indicate a Local MeteoricWater Line of Denizli Basin to be between the Global MeteoricWater Line(Craig, 1961) and Western Anatolian Meteoric Water Line (Şimşek, 2003). Detailed evaluation of severalmajor and trace element contents measured in the water and in the precipitated travertine along thePamukkale MM section revealed which elements are precipitated in the carbonate or concentrated in thedetrital minerals.Former studies on the Hungarian Egerszalók travertine (Kele et al., 2008a, b, 2009) had shown that theisotopic equilibrium is rarely maintained under natural conditions during calcite precipitation in thetemperature range between 41 and 67 °C. In this paper, besides the detailed geochemical analyses alongdownstream sections, we present new evidences of non-equilibrium calcite-water fractionation in lowertemperature range (13.3 to 51.3 °C). Our measurements and calculations on natural hot water travertineprecipitations at Pamukkale and Egerszalók revealed that the δ18Otravertine is equal with the δ18OHCO3 at theorifice of the thermal springs, which means that practically there is no oxygen isotope fractionation betweenthese two phases. High rate of CO2 degassing with rapid precipitation of carbonate could be responsible forthis as it was theoretically supposed by O'Neil et al. (1969). Thus, for the determination of the depositiontemperature of a fossil travertine deposit we propose to use the water-bicarbonate oxygen isotopeequilibrium fractionation instead of the water-travertine fractionation, which can result 8–9 °C difference inthe calculated values. Our study is the first detailed empirical proof of O'Neil's hypothesis on a naturalcarbonate depositing system. The presented observations can be used to identify more precisely thedeposition temperature of fossil travertines during paleoclimate studies.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Nonmarine carbonates, including travertines, freshwater tufa, andspeleothems that form in lakes, rivers and caves are among the most

important continental climate-related deposits. Their deposition iscontrolled by a number of factors including CO2 degassing due toinorganic and organic (microbiology related) processes and evapora-tion. The term ‘travertine’ is generally used for carbonates depositedin hot water environments, while ‘freshwater tufa’ is a term for porousdeposits in cold water environments, containing higher plants andanimals (Janssen et al., 1999). Freshwater tufa and travertine depositshave been widely studied since the end of the 19th century (Weed,

Sedimentary Geology 238 (2011) 191–212

⁎ Corresponding author.E-mail address: keles@geochem.hu (S. Kele).

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1889), but their potential to provide high-resolution terrestrialpaleoclimate record has only become evident in the last few decades(e.g. Hennig et al., 1983; Pentecost, 1995; Ford and Pedley, 1996).Althoughmost of the previous studies (e.g. Andrews, 2006) investigatedfreshwater tufa deposits, thermogene travertines can also serve asimportant paleoclimatic archives (e.g. Pentecost, 2005; Jones andRenaut, 2010; Sun and Liu, 2010). The interpretation of the geochemicalsignatures of travertines, however, needs special attention because theCO2 may be derived from various sources, including decarbonation oflimestone, mantle degassing, hydrolysis and oxidation of reducedcarbon (Pentecost, 2005). In addition, isotope fractionation processesthat accompany travertine deposition may also overprint the originalclimate imprint. Thus, in order to obtain more reliable paleoclimatolo-gical and paleoenvironmental data from travertines, a better under-standing of theprocesses governing their precipitation and geochemicalcomposition – including stable isotopes – is needed.

The terraced travertine at Pamukkale (Cotton Castle) (Fig. 1),which is one of the best-known travertine sites of the world, is locatedin the Denizli Basin, about 17 km from the town of Denizli in SW-Turkey (Fig. 2). Moreover, the surrounding Denizli Basin is home fornumerous active (e.g. Pamukkale, Karahayit) and inactive (e.g. Akköy,Karakaya Hill) thermal travertines, especially along its northernmargin (Fig. 2). These travertines, which collectively cover an area ofmore than 100 km2, are up to 60 m thick. (Özkul et al., 2002). Many ofthese travertines have long been quarried for travertine that is widelyused in building industries.

Earlier studies of the Denizli travertines generally focused onPamukkale and on the hydrogeology, geothermal potential andchemistry of Pamukkale thermal waters (Gökalp, 1971; Şentürk et al.,1971; Koçak, 1976; Canik, 1978; Ekmekçi et al., 1995a,b; Gökgöz, 1995;Gökgöz and Filiz, 1998; Şimşek et al., 2000). Filiz (1984), who firstpublished stable isotopic data of Pamukkale Hot Springs, concluded thatthe CO2 content of the spring waters came from magmatic resources.Altunel and Hancock (1993a, b) classified the Pamukkale travertinesaccording to their morphology, while Altunel (1994) and Hancock andAltunel (1997) investigated the relationship between active fissuring,faulting and travertine deposition and presented some U/Th age datafrom the fissure ridge travertines. Çakır (1999) described the Balkayası,Yenice, Gölemezli and Pamukkale travertines and interpreted theirstructural attributes, paying particular attention to the fault zone. Özkulet al. (2002) described different lithofacies types from recent and oldtravertines in the Denizli Basin, determined their local depositionalenvironments, and presented some stable isotope data from variouslocations. In recent years, new geochemical and U-series dating studies

started around Pamukkale focussing on the co-seismic fissures alongmajor active faults (Uysal et al., 2007, 2009). The actively formingterraced-slope travertine of the Pamukkale Range-front, however,remained untouched as no systematic stable isotope and trace elementstudy have been done.

Former studies on the Hungarian Egerszalók travertine (Kele et al.,2008a,b, 2009) and on several famous hot spring travertineoccurrences, like at Mammoth Hot Springs, Yellowstone, U.S.A.(Friedman, 1970; Fouke et al., 2000) as well as at Bagni San Filippo,Italy (Gonfiantini et al., 1968) had shown that the isotopic equilibriumis rarely maintained under natural conditions during calcite precip-itation in the temperature range between 30 and 67 °C. The purpose ofthis paper is to study the behaviour of different chemical elementsand stable isotope fractionation processes during travertine deposi-tion to see how local circumstances and depositional environmentsinfluence carbonate composition. Besides, we present new evidencesof non-equilibrium calcite-water fractionation in the temperaturerange from 13.3 °C to 51.3 °C, which can be used in paleotemperaturecalculations in case of fossil travertines.

2. Geological setting

The Denizli Basin is a 70 km long and 50 km wide fault boundedNeogene–Quaternary depression located in the Western AnatolianExtensional Province, at the junction of the E–W-trending BüyükMenderes Graben and the NW–SE-trending Gediz Graben (Westaway,1993; Altunel and Karabacak, 2005; Alçiçek et al., 2007) (Fig. 2A). TheWestern Anatolian Extensional Province is one of the most seismicallyactive and rapidly extending regions (30–40 mm/year) in the world(Bozkurt, 2001). The regional tectonic movements affecting the areahave been ongoing since the Early Miocene (Alçiçek et al., 2007). Thebasement rocks of the basin consist of pre-Oligocene mica schists,quartzite, and marbles of the Menderes massif and the tectonicallyoverlain rocks of Mesozoic limestones of the Lycian nappes, whichtectonically overlie the massif (Okay, 1989; Alçiçek et al., 2007)(Fig. 2B). The pre-Neogene substratum of the basin, which crop out inthe horst areas along the northern and southern flanks, is overlain bythick sequences of Mio-Pliocene and Quaternary sediments that areformed of alluvial-fan, fluvial, and saline to freshwater lacustrinedeposits (Wesselingh et al., 2008).

TheDenizli depression,which formedas ahalf grabenduring the lateEarly Miocene, was controlled by the Babadağ fault to the south. By theEarly Quaternary, the Neogene Denizli half graben developed into a fullgraben due to activity associated with the Pamukkale fault to the north,which gave birth to hot springs that led to the formation of majortravertine precipitation in the basin (Alçiçek et al., 2007). Prominenttravertine deposits along northern and southern basin margins reflectthe newly established tectonic configuration in the basin. It is suggestedthat the travertine masses in the basin have formed where dip-slipnormal fault segments display step-over zones along the fault-strikes(e.g. Çakır, 1999). The thermal springs of the Pamukkale area emerge inthe Çürüksu graben,which belongs to thewidespreadMenderes grabensystem (Fig. 2B, C; Şimşek et al., 2000). As the main travertineoccurrences have been formed along the northerly fault strandsincluding Pamukkale, some minor travertine deposits (e.g. Karahayit,Pamukkale, Yenice, Gölemezli- Balkaya, Ballik)were also occurred alongthe southern margin of the basin (Özkul, 2005). Besides the travertinesprecipitated from thermal waters, calcareous tufas deposited from coolkarstic water also occur along themargins of the basin, especially in themarginal mountain areas (Güney, Sakizcilar, Honaz) (Horvatinčić et al.,2005; Özkul et al., 2010).

The initial time of travertine accumulation in the basin has notbeen determined yet because of the lack of reliable paleontologic orradiometric dating. At Pamukkale, the active travertine precipitationsite, the oldest age was calculated as at least 400 ky by using U–Thdating method (Altunel, 1996). Özkul et al. (2004a) performed

Fig. 1. Birds's eye view of the Pamukkale Range-front travertine indicating thedownstream section of the Jandarma- and Beltes-2 springs.

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thermoluminescence measurements to date the different horizons oftravertine masses and calculated an age interval of 330–510 ky for thetravertine deposition. Recently some vertebrate fossils including thefirst Homo erectus fossil of Turkey obtained from the quarried oldertravertine masses imply a Pleistocene age (Özkul et al., 2004b;Kappelman et al., 2008).

2.1. Hydrological setting

Themain reservoir rocks supplying water to the Pamukkale thermalsprings are the Paleozoic karstic marble and the Mesozoic limestone,which is recharged by infiltration of meteoric water through porousmarble and limestone rocks (Şimşek, 1990) (Fig. 2, Taner, 2001). The

Fig. 2. A) Simplified regional tectonic map of the eastern Mediterranean region (modified from Fig. 1 of Uysal et al., 2009). B) and C) Geological map and stratigraphy of the DenizliBasin-fill (based on Şimşek, 1984; Sun, 1990; Alçiçek, 2007; Alçiçek et al., 2007; Alçiçek, 2010).

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catchment area consistsmainly ofNeogene limestone(SazakFormation)and extends along the Yenice horst. According to Dilsiz (2006), based onδ18Omeasurements, the thermal springsof Pamukkale andKarahayit arerecharged frommeteoric waters at altitudes 600 and 750 m, respective-ly. On the other hand, according to the isotopic data presented by theInternational Research andApplication Center for KarstWater Resourcesthe elevation of the catchment area of the Pamukkale thermal waterswas interpreted as 1900 to 2300 m(unpublished report onConservationandDevelopment of Pamukkale Travertines, Interim Report I, HacettepeUniversity, Ankara 1993). These values are close to maximum elevationof ÇökelezMountain (1840 m) located north of thePamukkale basin andformed of Mesozoic limestone.

The Western Anatolian Province has high geothermal gradientsand heat flow associated with deep mantle melting and degassing(Güleç et al., 2002). The water percolates down into the aquifer and itis heated by the geothermal gradient. The heated thermal wateremerges then as thermal springs along thefissures and faults. Filiz et al.(1992) and Çağlar (1994) calculated the reservoir temperature ofPamukkale and Karahayit thermal springs (63–93 °C and 76–82 °C,respectively) using silica geothermometry.

There are five major thermal springs at Pamukkale above theterraced slope-travertine (360–366 m asl), namely the Özel İdare,İnciraltı, Beltes-1, Beltes-2, and Jandarma springs, which are locatedalong a major, NW–SE trending fault (Fig. 2). The Çukurbağ spring islocated at the foot of the terraced slope on the plain. The total annual

average discharge of the thermal springs varies between 365 and 385 L/s which are mostly stable throughout the year (Dilsiz, 2006).

3. Sampling and analytical methods

Field works at Pamukkale were carried out on 7 November 2007and 13 August 2008 at the Jandarma-spring section (Fig. 3), 7 May2009 at the Beltes-2 spring (Fig. 4) and Karahayit, Kırmızı Su thermalwell sections (Fig. 5). The sections were established along down-stream water flow paths in order to represent all existing facies at thetravertine localities mentioned above. Additional sampling wasperformed at the Çukurbağ-spring, at the foot of the Pamukkalerange front on 27 October 2007. In all cases, both recent and fossiltravertine samples were collected for mineralogical, petrographicaland geochemical analyses, including SEM observations, stable isotopemeasurements, and trace element analyses. The uppermost surface(2–3 cm in thickness) of the travertine was sampled in order to getfreshly precipitated carbonates and to avoid contamination with oldertravertine layers. Water samples were collected in 100 ml glassbottles for stable isotope analyses of δ18O, δD and δ13CDIC.

In situmeasurements of some physicochemical features of thermalwaters were completed at all sampling points. T, pH, Eh, and electricconductivity (EC) measurements were carried out using HACHsension 2 and HACH-LANGE HQ40D instruments. The free CO2 and

Fig. 3. Photo and cross-section of the Pamukkale Jandarma-spring downstream section. Sampling points, distances and elevations are also shown.

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Fig. 4. Photo and cross-section of the Pamukkale Beltes-2-spring downstream section. A) Outlet of the Beltes-2 spring; B) Closed concrete channel conducts the water from theBeltes-2 spring towards the terraced-slope; C) Opened channel above the major terraced slope environment of Pamukkale; D) Flow path of the water on the proximal slope of thePamukkale, Beltes-2 section. Altitudes of the sampling points and distances between them are presented in Table 2.

Fig. 5. A) Downstream section indicating the sampling points at Karahayit, Kırmızı Su; B) Red travertine mound at Karahayit; C) Green microbial mats around the outlet of Karahayit,Kırmızı Su thermal well.

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alkalinity analyses were performed in situ on the field by titrimetricmethods.

Petrographic observationswere conducted on polished thin sectionsusing optical microscopy. Microprobe work was carried out on someselected samples using a JEOL JSM-6490 LV scanning electronmicroscope (attached with energy dispersive analyzer, EDS) at TurkishPetroleum Corporation (TPAO) in Ankara. The mineral composition ofthe sampleswas determined by X-ray powder diffraction (XRD) using aPhilips PW 1710 diffractometer of the Institute for GeochemicalResearch (Budapest, Hungary) with CuKα radiation at 45 kV and35 mA. Semi-quantitative phase analysis was made on randomlyoriented samples. Amounts of calcite and aragonite were estimated bythe peak area of calcite 104 and aragonite 111 reflections on X-raydiffractograms. The relative error of the quantification is 5–10%.However, the results can be considered informative for the estimationof the calcite to aragonite ratio, as this being one of themain aims of thiswork.

Major constituents of thermal water samples were determined inthe Geochemistry Laboratory of the Geological Engineering Depart-ment at Pamukkale University. Ca2+, Mg2+, Na+, K+, Li+, NH4

+, SO42−,

Cl−, NO2−, NO3

−, F− and Br− concentrations of the water samples weredetermined using an ion chromatography instrument (Dionex).Major,trace and rare earth element measurements were carried out at AcmeAnalytical Laboratory (ACMELAB, Vancouver, Canada), using ICP-MStechnique. Total abundances of the major oxides and several minorelements are reported on a 0.1 g sample analysed by ICP-emissionspectrometry following a Lithium metaborate/tetrabortate fusion anddilute nitric digestion. Loss on ignition (LOI) is by weight differenceafter ignition at 1000 °C. The TOT/C (total carbon) and TOT/S (totalsulphur) were determined by Leco. The determination of traceelement and rare earth element composition was performed also byICP-MS technique, following a Lithiummetaborate/tetrabortate fusionand dilute nitric digestion. The concentration of boronwas determinedby Na2O2 fusion (ICP).

The stable isotope analyses were performed at the Institute forGeochemical Research, Hungarian Academy of Sciences, Budapest,Hungary. Carbon and oxygen isotope analyses of bulk carbonatesamples were carried out using both the conventional phosphoric acidmethod of McCrea (1950) and the continuous flow technique (Spötland Vennemann, 2003). δ18O analyses of waters were conductedusing the CO2–water equilibration method of Epstein and Mayeda(1953). Hydrogen isotope compositions were determined on watersamples using the H2O–Zn reaction method (Coleman et al., 1982;Kendall and Coplen, 1985; Demény, 1995) and Pt-assisted H2–H2Oequilibration (Coplen et al., 1991; Prosser and Scrimgeour, 1995). 2H/H, 13C/12C and 18O/16O ratios were determined in H2 and CO2 gasesusing Finnigan MAT delta S and Thermo delta plus XP massspectrometers. Isotopic compositions are expressed in the traditionalδ notation in parts per thousand (‰) relative to PDB (δ13C, δ18O) andSMOW (δ18O, δD). Reproducibilities are better than ±0.1‰ for δ13C

and δ18O values of carbonates, ±0.2‰ for the δ18O and ±2‰ for δDvalues of waters.

4. Results

4.1. Travertine subenvironment and facies description of the section atthe Jandarma-spring, Pamukkale

The Özel İdare, İnciraltı, Beltes-1, Beltes-2 and Jandarma springssupply the thermal water for travertine deposition at Pamukkale(Fig. 2). These springs are located above the terraced slope, 100–200 m away from the uppermost rim of the travertine. Although thesprings are widely spaced (the distance between them is maximum500 m), their physicochemical and chemical parameters are verysimilar (Table 1). The water from these springs is channelled to thespring terraces through a concrete and closed channel system thatdelays CO2 degassing and hence, carbonate deposition in the channels(Figs. 4B; 6A, B). Besides, the cooling of the water can also affect thecarbonate deposition, since the carbonate is more soluble in coolerwaters. The water flow path is controlled using the channel systemand each day, one part of the travertine is fed thermal water from oneof the springs, while the other parts of the area dry up during thatperiods. During our first sampling campaign, the water of theJandarma-spring was flowing down slope (see Fig. 4). Along thesection the following main depositional subenvironments weredistinguished: 1) the Jandarma-spring, 2) artificial ponds andchannels, 3) moundtop with terrace pools, 4) cascade, 5) proximalslope, and 6) distal slope (Fig. 6). Since the Beltes-2 section (Fig. 5) hassimilar morphology and distribution to the Jandarma section, thefacies description here is restricted to only the Jandarma section:

1) The Jandarma-springThe Jandarma spring is located 200 m away from the terrace edgeof the Pamukkale Jandarma section (Fig. 3) and the temperature ofthe water is 34.7 °C at the orifice (similarly to the other springs ofPamukkale) (Table 1). The water level of the Jandarma spring is0.5 m below the surface in a 30–40 cm deep manhole (Fig. 6A).Since the spring is closed from air, there is only a small CO2

degassing with slightly acidic water (Pk-1, pH=6.2) and nocarbonate precipitation occurs. The water of the spring isconducted then in a closed channel from the orifice 10 m further,to an artificial lake (Fig. 6A).

2) Artificial ponds and channelsThe first artificial pond (~60 m2) of the section is located 4 mdownstream of the spring's orifice. It is 1 m deep and at the outletof the pond (Pk-2 sampling point, Fig. 6B) the temperature of thewater is 33 °C and pH=6.4. Since the pH is still acidic, there is nocarbonate precipitation. From the first pond, the water flows alonga 200 m long closed tunnel into a second artificial pond, which islocated 15 m beyond the starting point of the slope (Fig. 6C). The

Table 1Physicochemical parameters and stable isotopic composition of thermal water samples collected from the major thermal springs of Pamukkale. The parameters were measureddirectly at the outlets of springs.

No Name of spring Date ofsampling

δ13CDIC δ18O δD Temp. pH Eh EC TDS Free CO2 Alkalinity

(‰ PDB) (‰ SMOW) (‰ SMOW) (°C) mV mS mg/L ppm

1 Özel Idare spring 2007.10.27. −1.0 −8.9 −58.5 34.7 6.1 4.3 2.35 1188 1200 9082008.08.13. – −8.9 −58.5 33.7 6 64.6 2.4 – 486 –

2 Inciralti spring 2007.10.27. – −8.8 −58 34.7 6.1 42.4 2.35 1188 – –

2008.08.13. – −8.8 −58 34.2 6.1 60.1 2.38 – 488 –

3 Beltes spring 2007.10.27. – −9.0 −58.7 34.7 6.1 41.1 2.34 1188 – –

2008.08.13. – −9.0 −58.7 34.4 6.1 62.8 2.36 – 502 –

4 Jandarma spring 2007.10.27. – −8.9 −58.7 34.7 6.1 44.1 2.32 1179 – –

2008.08.13. – −8.9 −58.7 32.9 6.2 52.8 2.37 – 400 –

5 Çukurbağ spring 2007.10.27. – −8.3 −58.9 56.1 6.9 4.3 3.01 – 960 11782009.07.14 – −7.6 −60.0

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second pond is 30 m long and 6–8 m wide in average. The Pk-3water sample was taken at the inlet point of this lake (T=34.1 °C,pH=6.4) and no carbonate precipitation is evident. From the pondan open channel runs to themargin of the slope, where an artificialdam causes strong degassing (Pk-4 sampling point, Fig. 6D); thus,the pH of thewater is close to neutral (6.9), andwater temperaturehas decreased (T=31.6 °C). At the dam, there is evidence ofcarbonate precipitation associated with a green microbial mat thatis similar to that described at Egerszalók (Kele et al., 2005, 2008a).Downstream of the dam, the slightly alkaline water flows onto thetravertine slope, where precipitation of white calcium carbonatestarts (Fig. 6E). Fig. 7A shows branching feather crystals in the Pk-4sample, while Fig. 7B presents alternating layers of pale spariticclumps, divided by dark micritic laminae from the same sample.

3) Moundtop with terrace poolsTravertine precipitation starts on a smooth-sloping (2–5°)mound-top plateau, in some large (5–10 m) and 20–30 cm deep terrace-pools (Fig. 6E). The pools are separated from each other by 20–50 cm high terrace rims, but the difference in height between theneighbouring pools can exceed 1 m vertically. In this part of thesection, the water temperature varies between 26.6 and 30.1 °C(Table 2). On the bottom of the terrace- and microterrace-poolsand below cascades, pisolites, up to 1–2 cm in diameter, arecommon (Fig. 8A, B). Calcite-coated gas bubbles are frequentlyfound on the bottom of the pools and in some nearly stagnantponds calcite sheets and paper thin rafts cover the water surface.The best examples for calcite-coated gas bubbles and paper thinrafts can be found around the Çukurbağ spring (Fig. 8C, D). These

Fig. 6. Photographs of the major depositional subenvironments and facies occurring at Pamukkale, together with the sampling points. A) Outlet of the Jandarma-spring; B) Artificialchannel system and lake (C) located above the terraced slope part of the section. D) Wood pavement and a dam separates the channel from the travertine slope. E) View of wideterrace pools covering the top of the slope. F) Cascade on the top of the proximal slope. G) and H) Proximal and distal slopes with no terrace pools at the lower part of the slope.

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lithofacies are similar to those described from many other springsystems (e.g. Folk and Chafetz, 1983; Chafetz and Folk, 1984; Guoand Riding, 1998; Özkul et al., 2002; Kele et al., 2008a,b). The Pk-5and Pk-6 travertine samples were collected from the rims ofmoundtop terrace-pools (Fig. 6E), whereas the Pk-5/b travertinesample represents the pisolith lithofacies. Fig. 9A shows pisolitesin the range of 1–2 cm. Photomicrographs (Fig. 9B, C, D) revealradially growing sparry calcite crystals around the micritic–pelmicritic centre of pisoids from the Pk-5/b sample, while SEMimages (Fig. 9E, F) show rhombohedral calcite crystals from thesame sample, together with some filaments, which are presumablybacterial in origin.

4) CascadeThe active cascade, being 3 m high and 20–25 m long is an eye-catching morphological feature (Pk-7 sampling point, T=26.6 °C,pH=8.4, Fig. 6F). The upper part of the cascade containsoverhanging stalactites taller than 2 m (between samples Pk-7and Pk-8 in Fig. 6F), which are similar to those of described byJones et al. (2001) on some of the silica precipitating systems inNew Zealand. Below the cascade plants (fig trees) can grow, sincethere is an appropriate place for soil-accumulation (Fig. 8E). Thecascades are formed mainly of snow-white crystalline calcite crustand developedmainly upward on the terrace-rim. The water dropsfrom the upper part of the cascades into shallow (1–2 cm deep)

Fig. 7. Thin-section photomicrographs of travertines collected along the Pamukkale Jandarma-section showing the characteristic crystal types. A) Feather crystals of calcite showcrystallographic branching. B) Alternating layers of pale sparitic clumps, divided by dark micritic laminae (Pk-4 sample). C) Branching sparite crystals of the Pk-8 sample andenlarged view of a single crystal from the same sample showing side branches perpendicular to the main crystal orientation (D). E) Feather crystals from the Pk-11 sample, whichwas taken from a crystalline crust sample collected on the proximal slope. F) Layers of sparitic crystals are divided by dark micritic laminae (Pk-12 sample). Layered texture ofcrystalline crust samples collected at the end of the proximal slope (Pk-12, G) and at the distal slope (Pk-13, H).

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pools,wheredue to the agitationof thewater pisolites form(Fig. 8E).Fig. 7C shows a typical texture of the Pk-8 sample containingbranching sparite crystals, and a single crystal showing side branchesperpendicular to the main crystal orientation (Fig. 7D).

5) Proximal slopeThe proximal slope, which starts below the cascade, is 90 m longwith a slope that commonly exceeds 30° (Fig. 6F). Thus, waterflows rapidly in natural shallow channels or as a film on the surface

of travertine and terraces; terrace-pools do not form in theJandarma-section. Nevertheless, terrace-pools and connectedcascades are frequent morphological forms on the other parts ofPamukkale travertine slope (e.g. Fig. 4D). The Pk-8 sample wascollected with 3 m below the cascade (T=25 °C, pH=8.5)(Fig. 6F). Typical deposit of the proximal slope is the crystallinecrust travertine (samples Pk-9 to Pk-12, Fig. 7E, F, G). Thin sectionphotomicrographs of crystalline crust travertines from the Pk-11

Table 2Physicochemical parameters and stable oxygen and hydrogen isotope composition of thermal water samples and stable carbon and oxygen isotope compositions of travertinescollected along downstream sections at the Jandarma- and Beltes-2 springs of Pamukkale and at the Kırmızı Su section of Karahayit.

Name and dateof sampling

No. Facies δ13Ctravertine δ18Otravertine δ18Otravertine δ18Owater δDwater Temp. pH Eh EC TDS FreeCO2

Distance Height

(‰ PDB) (‰ PDB) (‰ SMOW) (‰SMOW)

(‰SMOW)

(°C) mV mScm−1

mg/L ppm m m

Jandarma spring,Pk-section(2007.11.07.)

1 Jandarma-spring – – – −8.9 −58.7 34.7 6.2 34.1 2.35 1184 – 0 0.02 Artificial dam – – – −8.8 −58.4 33.0 6.4 25.8 2.35 1183 – 15 0.03 Artificial channel – – – −8.8 −59.3 34.1 6.4 24.7 2.31 1174 – 215 −0.54 Artificial dam 11.3 −9.3 21.3 −8.8 −59.7 31.6 6.9 −4.7 2.31 1169 – 250 −0.65 Rim of a terrace pond 6.1 −10.7 19.9 −8.8 −58.0 30.1 7.4 −33.8 2.29 1161 – 260 −0.95/b Pisolith 6.6 – – – – – – – – – – 260 −0.96 Rim of a terrace pond 5.9 −10.2 20.4 −8.2 −54.5 28.7 7.8 −60.1 2.27 1151 – 285 −1.37 Rim of a terrace pond

above a cascade5.9 −10.6 20.0 −8.9 −58.4 26.6 8.4 −90.3 2.21 1114 – 292 −2.3

7/b Pisolith 6.4 – – – – – – – – – – 292 −2.38 Bottom of a cascade

with pisoliths5.8 −11.1 19.5 −8.8 −56.2 25.0 8.5 −98.0 2.19 1094 – 292 −5.3

9 Proximal slope 7.1 −10.3 20.3 −8.4 −56.5 21.5 8.8 −104.8 2.12 1055 – 305 −13.310 Proximal slope 8.2 −10.5 20.1 −8.8 −56.7 18.6 8.9 −121.3 2.05 1017 – 327 −21.011 Proximal slope 9.7 −9.7 20.9 −8.6 −54.9 15.1 8.1 −74.0 1.97 965 – 353.5 −41.012 Bottom of proximal

slope11.5 −9.0 21.6 −8.6 −57.8 15.3 8.2 −81.3 1.94 949 – 386 −60.0

13 Distal slope 11.7 −9.1 21.5 −8.5 −56.2 13.7 8.3 −82.9 1.89 920 – 419.5 −75.014 Distal slope – – – −8.6 −55.9 13.3 8.4 −88.1 1.88 916 – 442.5 −85.0

Jandarma spring,MM-section(2008.08.13.)

1 K9 Genderme (Pk-1) – – – −8.9 −58.7 32.9 6.2 52.8 2.37 – 400 0 0.02 Jandarma pool outlet

(Pk-2)– – – – – 33.1 6.3 49.5 2.36 – 406 15 0.0

4 Channel outlet(Pk-4)

– – – −8.8 −58.4 32.5 6.5 37.7 2.38 – 330 250 −0.6

1 The same place asPk-5

– – – −8.7 −62.7 30.8 6.7 26.1 2.36 – 274 264 −1.1

2 The same place asPk-6

– – – −8.2 −60.6 29.8 7.0 8.9 2.35 – 186 276 −1.5

3 The same place asPk-7

– – – −8.7 −60.8 26.8 7.5 −20.3 2.34 – 140 284 −2.0

4 The same place asPk-8

– – – −8.4 −58.4 23.6 7.7 −31.2 2.26 – 100 288 −6.4

5 Proximal slope – – – −8.7 −60.0 22.3 7.7 −28.4 2.18 – 76 307 −11.06 Proximal slope – – – −8.4 −58.0 16 7.7 −32.6 2.036 – 88 341.5 −24.47 Proximal slope – – – −8.0 −55.6 16.9 7.7 −33.7 2.017 – 76 356.5 −33.58 Proximal slope – – – −8.2 −57.0 14.5 7.7 −34.6 1.936 – 108 384.5 −45.49 Proximal slope – – – −7.7 −55.8 14.2 7.8 −34.5 1.916 – 80 417.5 −57.210 Distal slope – – – −7.7 −54.0 13.4 7.7 −37.7 1.886 – 74 446 −63.311 Distal slope – – – −7.7 −54.9 13.4 7.8 −35.4 1.832 – 48 457 −67.612 Distal slope – – – −7.8 −54.7 14.1 7.7 −32 1.844 – 54 478 −72.6

Pamukkale,Beltes-2(2009.05.07.)

1 Beltes-2 spring – – – −8.6 −61.6 33.40 6.1 57.00 2.36 – – 0 02a Small cascade at

the channel– – – −8.6 −59.8 32.60 6.8 17.70 2.36 – – 155 −3

2b Small cascade atthe channel

5.2 −11.2 19.3 −8.5 −59.8 33.20 6.8 20.70 2.36 – – 155 −3

3 At the bottom ofa 3 m high cascade

5.1 −11.1 19.5 −8.5 −60.2 32.40 7.3 −14.00 2.35 – – 160 −7.5

4 Smooth slopecrystalline crust

6.2 −10.8 19.8 −8.4 −59.2 31.00 7.6 −25.20 2.22 – – 181 −13.5

5 Smooth slopecrystalline crust

6.6 −10.1 20.5 −8.4 −59.7 29.50 7.5 −21.70 2.13 – – 191 −16.5

6 Distal slope directlyabove the road

– – – −7.9 −58.2 28.40 7.5 −20.00 2.03 – – 218.5 −24.5

Karahayit,Kirmizi su(2009.05.07.)

1 Orifice of the spring 5.1 −12.8 17.7 −7.8 −58.1 51.30 6.2 57.00 2.81 – – 0 02 “Proximal slope” 5.1 −12.5 18.1 −8.0 −56.8 39.70 7.3 −8.90 2.69 – – 11.5 −33 “Distal slope” 7.2 −8.9 21.8 −7.8 −55.3 30.90 7.6 −31.20 2.31 – – 26 7

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Fig. 9. A) Pisolith samples (Pk-5/b) taken from the bottom of a terrace pool at the Pamukkale Jandarma section. Photomicrographs are taken from the same sample and directly fromthe centre of a pisoid (B) using different enlargements. C) The centre of the pisoid consists of micritic aggregates (pelmicritic texture; dark areas), which is surrounded by branchingsparry calcite crystals (D). E) SEM images are taken from the Pk-5/b sample showing clumps of calcite sheets and rhombohedrons, with presumably bacterial filaments (F).

Fig. 8. Pisolites at the bottom of a terrace pool (A) and microterrace pools (B) Recently forming coated bubbles (C) and paper thin rafts (D) cover the water surface around theÇukurbağ spring. E) Pisolites are frequent deposits below the cascades of the proximal slope. F) Encrusted leaf of Nerium oleander on the distal slope.

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(Fig. 7E) and Pk-12 (Fig. 7F, G) samples revealed layers of spariticcrystals divided dark micritic laminae. On the proximal slopeplants, bushes occur and below the plants the travertine hasreddish-black colour due to the contamination with organicmatter (Fig. 6G). On the lower part of the proximal slope nearlyvertical (2–4 m high) walls alternate with relatively flat surfacesformed of travertines (Fig. 6H). In summary, on the proximal slopethe water cools down from 25 °C to 15.3 °C, while the pH isincreasing continuously until 8.2 and intensive travertine precip-itation is characteristic.

6) Distal slopeThe distal slope is 440 m away from the spring vent and developsgradually from the proximal slope with a slope of about 15–20°(Fig. 6G). Microterrace-pools, -rims, micro-waterfalls (1–2 cm insize) and cascades characterise this part of the system. Due to thelow water temperature (13.3–15.3 °C) on the distal slope andshallow water depths (1–5 cm) plants (especially Nerium oleanderand high grass, reeds) are growing (Fig. 6H). Leafs of oleandersencrusted by carbonate are characteristic of the distal slope(Fig. 8F) and in the marsh-pool area, where growing plantsbecomemore frequent. The water from the distal slope flows awayto a marsh-pool area producing negligible carbonate precipitationand partly disappears in a 1 m deep sinkhole located at the end ofthe section. From the distal-slope the Pk-13 and 14 samples werecollected, representing crystalline crust travertine. Fig. 7H showsthe layered texture of crystalline crust samples collected from thedistal slope (Pk-13 sample) and the feather crystals of calcite aresimilar to those of the Pk-4 and Pk-11 samples, which werecollected upward in the section (Fig. 7A, B, E).

4.2. Water geochemistry

4.2.1. Physicochemical parametersThe in situ measured parameters are listed in Tables 1 and 2.

Sections at Jandarma, Beltes-2 and Karahayit Kırmızı Su well waterwere investigated in detail in order to establish the downstreamvariations in the measured parameters: temperature, Eh, EC and freeCO2 content decrease, while pH increases downstream (Table 2). Theparameters of the major thermal springs of Pamukkale (Özel İdare,İnciraltı, Beltes, Jandarma) were determined in the vent (Tables 1, 2):their temperatures range from 32.9 to 34.7 °C, pH is 6.1, EC varies from2.3 to 2.4 mS cm−1, Eh is between 41 and 44 mV and their free CO2

content is ranging between 400 and 486 ppm (Table 1). The Çukurbağspring, located at the foot of the terraced slope travertines ofPamukkale differs from the other springs in the measured parameters(Table 1): T=56.1 °C, pH=6.9, EC=3.01 mS cm−1, Eh=4.3 mV,free CO2 content is 960 ppm.

There is a strong correlation between the Eh and pH (Fig. 10A,R2=0.99) and Eh and free CO2 (Fig. 10B, R2=0.97) values. At thedownstream sections the travertine deposition starts when Eh valueof the water moves below zero and pH≥6.8. Based on the thickness ofthe travertine, the deposition rate of travertine seems the highest onthe proximal slope, at the rims of terraces and cascades. Totaldissolved solids (TDS) have been determined only at the Jandarma Pk-section and the data range between 1179 and 1188 mg/L at the outletof the major springs (Table 1) and decrease gradually downstream(Table 2). The Pamukkale Jandarma MM-section has similar physico-chemical values as the Jandarma Pk-section (Table 2), thus it will benot discussed in detail in the text. The longest is the Pamukkale

Fig. 10. A) Correlation between Eh and pH of water samples collected along the downstream sections of Pamukkale and Karahayit. B) Bivariation plot of Eh values and free CO2

content of water samples collected along the Pamukkale JandarmaMM-section. C) Bivariation plot of EC values and Ca concentration of water samples collected along the PamukkaleJandarma MM-section. D) Downstream decrease of free CO2 content of the thermal water along the Jandarma, MM-section.

201S. Kele et al. / Sedimentary Geology 238 (2011) 191–212

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Jandarma section (~450 m), while the Beltes-2 section is only 218.5 min length. The shortest (26 m), Karahayit Kırmızı Su section showsalso significant change in the measured parameters downstream.

4.2.2. Major and trace element compositionsThe waters of the major springs of Pamukkale are of Ca–Mg–HCO3–

SO4 type; the Çukurbağ spring and Karahayit waters are of Ca–Mg–SO4–

HCO3 type. The Na+, K+, Mg2+, NH4+ and Cl−, NO3

−, and F− are presentin low concentrations (Table 3) in the waters, while other ions arerepresented in minor (ppb) quantities. Only the B shows higherconcentrations (Table 3). The Çukurbağ spring shows higher cation(Ca2+, Na+, K+, Mg2+, NH4

+ HCO3−, SO4

2−) and anion (Cl−, F−)concentrations than thosemeasured at the other major thermal springsof Pamukkale. The Al, B, Ba, Br, Cs, Fe, Li, Mn and Rb concentrations alsoexceed the values measured at the major springs (Table 3).

The Karahayit Belediyesi and KH-2 wells have been characterisedby high concentrations of the three major ions (Ca2+, HCO3

−, SO42−),

while the concentrations of Na+, K+, Mg2+, NH4+, Cl− and F− are

similar to those measured at the Çukurbağ spring (Table 3). TheKarahayit thermalwaters show significantly higher Fe, B, Br, Cs, Li, andMn concentrations than those of measured at Pamukkale springs(Table 3). The high Fe-concentration of Karahayit thermal water is inagreement with the deposition of reddish-brownish travertine atKarahayit.

Downstream changes of major and trace element concentrationsof thermal waters can be followed at the Jandarma MM-section(Table 4). Some elements show constant (Cs+, Fe3+ Li+) or nearlyconstant (K+, Cl−, SO4

2−, NO3−, Al3+, B, Rb) concentrations down-

stream, whereas others display large variations. The Na+, Mg2+ andNH4

+ ions showed slight downstream increase, while the Ca2+, HCO3−,

Ba2+, Mn2+, Cu2+ and Sr2+ decreased significantly from the springoutlet to the distal parts of the section (Table 4).

4.2.3. Stable isotopic compositionThe δ18O and δD values of the major springs (Özel İdare, İnciraltı,

Beltes-1, Jandarma-springs) ranged from −9.0 to −8.8‰ and from−58.9 to −58.0‰ (SMOW), respectively. The measurement of thestable isotope compositions of thermal waters collected duringdifferent seasons (7 November 2007 and 13 August 2008) resultedin the same values (Table 1). The Çukurbağ spring (sampled at 27October 2007 and 14 July 2009) has similar values (δ18O=−8.3 and−7.6‰, and δD=−58.9‰ and −60.0‰) to those measured at themajor springs of Pamukkale.

The downstream change of δ18O and δD values of Pamukkalethermal waters were measured at two different times (7 November2007: Pk-section; 13 August 2008: MM-section) at the Jandarmaspring section, and once (7 May 2009) at the Beltes-2 and theKarahayit Kırmızı Su sections (Table 2). At the Jandarma springsection in both cases the δ18O values varied between −8.9 and−8.6‰ (Pk-section) and −8.9 and −7.8‰ (MM-section), while theδD values ranged between −58.7 and −55.9‰ (Pk-section) and−58.7 and −54.7‰ (MM-section). The δ18O values of the Beltes-2section varied between−8.6 and−7.9‰, while the δD values rangedbetween −61.6 and −58.2‰. At Karahayit the δ18O values showedslight variation between −7.8 and −8.0‰, while the δD valuesincreased downstream (from −58.1 to −55.3‰).

4.3. Travertine mineralogy and geochemistry

4.3.1. Mineralogical compositionThe XRD analyses showed that the Pamukkale travertines are

composed of almost pure calcite (N95–100%) along both the Jandarma-and Beltes-2 sections,whereas aragonite (b1%) anddetrital componentswere detected only in traces (Table 5). Thefirst samples (Pk-1 and Pk-3)were collected at the spring's orifice and from the artificial whiteningchannel, where no “real” travertine deposition occurs due to the acidic Ta

ble3

Elem

entalc

ompo

sition

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ayitthermal

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theou

tletsof

thesp

ring

s(d

ateof

sampling:

3March

2009

).

Elev

ation

Na

KCa

Mg

NH4

HCO

3Cl

SO4

NO3

FAl

As

BBa

BrCs

CuFe

LiMn

RbSi

Sr

m(asf)

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppb

ppb

ppb

ppb

ppb

ppb

ppb

ppb

ppb

ppb

ppb

ppb

ppb

Pamuk

kale,

K1(B

eltes)

spring

360

38.5

5.2

446.4

86.1

0.23

945

9.6

659.9

1.69

1.48

46b5

1043

2478

132.8

2614

123

2322

,293

6371

Pamuk

kale,

Inciraltis

pring

366

42.4

5.5

449.9

93.6

0.07

940

9.6

676.9

1.49

1.47

41b5

1011

2581

133.3

4113

523

2523

,687

6492

Pamuk

kale,

Öze

lIda

resp

ring

360

425.7

451.6

88.4

0.10

945

10.0

682.3

2.13

1.76

43b5

940

2890

123.2

131

130

2825

22,786

6092

Pamuk

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K9Jand

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ring

360

41.3

5.6

461.7

88.6

0.10

955

10.0

681.8

1.31

1.42

42b5

941

2384

122.8

3512

921

2321

,650

6069

Pamuk

kale,

Cuku

rbag

spring

290

127.5

25.5

527

114

0.88

1235

26.5

980

n.d

2.78

84b5

2724

6116

737

3.6

780

323

5110

020

,544

7619

Karah

ayit,

Belediye

siwell

338

116.6

23.0

456

116

0.45

867

26.9

1096

n.d

2.68

41b5

1845

4721

125

4.4

331

323

3386

28,738

9096

Karah

ayit,

KH-2

well

338

115.2

23.5

537

117

0.51

1085

22.2

1078

n.d

2.94

736

1948

6016

733

3.6

2706

324

6811

023

,345

10,701

202 S. Kele et al. / Sedimentary Geology 238 (2011) 191–212

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pH of thewater, and these samples contain only 0–7% calcite besides thedetrital components. Themineralogical composition of thepisolites (Pk-5/b, Pk-7/b and Pk-8 samples) is similar to the other (e.g. crystallinecrust) travertines. In one case, at the Pk-10 sample both the outer(white) and inner (brownish) parts were studied and the XRD analysesrevealed only slight differences: while the outer part composed of 100%calcite, the inner part contained some detrital quartz and mica. Themineralogical composition of the three samples collected from theKarahayit section was pure calcite, except one, which had 5% aragonitecontent.

4.3.2. Major and trace element compositionsMajor and trace elements measured in the travertine samples are

generally fixed in the carbonate phase, but can be also fixed in detritalminerals. Elemental composition of eight travertine samples collectedalong the Pamukkale Jandarma spring Pk-section has been deter-mined (Table 6). The Pk-9 sample is extremely rich in SiO2, Al2O3,Fe2O3, Na2O, P2O5, K2O, Ba, Cs, Nb, Rb, Zr, Mo, Cu, Pb, Zn, Ni, As, Au, B

and rare earth elements (Table 6), while the Pk-9 sample contains lessCa, Sr, than the other samples and its LOI (loss on ignition) and TOT/Cvalues are also lower than the average values of the samples. Theseresults coincide with the mineralogical analyses, which pointed outthat the Pk-9 sample contains high amount of detrital materials. ThePk-4 and Pk-8 samples contain also some detrital material andenrichment of SiO2, Na2O, K2O, Mo, Cu, Pb, Ni, As and Au is observablein the Pk-4 sample.

In the travertines, Ca and Mg have the highest concentration andthey are in inverse proportion. The Sr content ranges between 1971and 3028 ppm and shows slight increase downstream. The lowest Caand Sr concentrations were observed in the pisolitic Pk-5b, Pk-7bsamples, while other elements represent higher concentration in thepisolite samples than in the other samples (Table 6). The Baconcentration shows a slight decrease, while the TOT/C values arenearly constant through the downstream section. The Rb, Zr, U, Y, andLa show no systematic change downstream, probably due to thepresence of detrital materials. Phosphorous occurs at the lower part of

Table 4Elemental composition of Pamukkale thermal water collected downstream at the Jandarma-spring (MM-section; date of sampling: 13 August 2008).

Na K Ca Mg NH4 HCO3 Cl SO4 NO3 F Al As B Ba Br Cs Cu Fe Li Mn Rb Si Sr

ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppb ppb ppb ppb ppb ppb ppb ppb ppb ppb ppb ppb ppb

K9 Jandarma 41.3 5.6 461.7 88.6 0.10 955 10.0 681.8 1.31 1.42 42 b5 941 23 84 12 2.8 35 129 21 23 21,650 6069Jandarma pool outlet 42.5 5.5 463.1 93.1 0.00 935 11.2 684 n.a. 1.68 42 b5 969 23 84 12 2.9 47 131 21 24 22,056 6310channel outlet 42.5 5.7 462.4 91.1 0.02 940 11.0 676.2 n.a. 1.57 37 b5 972 25 83 12 2.8 44 127 21 23 22,760 6325M1 43.2 5.8 465.8 93.9 0.21 910 12.0 685.9 1.53 1.81 42 b5 1060 24 81 12 2.9 34 130 21 24 22,700 6302M2 42.5 5.7 461.6 94.3 0.08 930 11.8 688.3 1.56 1.79 41 b5 1034 26 79 14 3.2 26 139 20 24 22,629 6299M3 42.6 5.8 396.9 94.4 0.06 770 10.1 679.8 n.a. 1.43 35 b5 1020 23 78 12 3 25 137 16 23 20,910 5150M4 42.7 5.7 339.9 91.2 0.06 685 10.2 682.4 n.a. 1.37 34 b5 941 19 76 11 2.9 28 141 15 20 19,860 4491M5 42.6 5.6 338 91 0.08 655 10.3 680.7 1.86 1.36 45 b5 1060 20 76 12 2.7 40 148 15 20 20,381 4405M6 43.3 5.8 325.8 95.3 0.22 600 10.2 684.8 1.25 1.28 37 b5 1016 18 76 12 2.3 25 136 15 22 21,188 4835M7 42.9 5.7 317.8 95.4 0.11 560 10.3 684 1.09 1.27 42 b5 1035 18 77 12 2.3 38 137 15 21 21,063 4265M8 43.2 5.7 310.6 96.1 0.22 560 10.2 690.9 n.a. 1.24 43 b5 1068 18 79 12 2.3 24 144 15 22 20,978 4039M9 42.7 5.7 298.6 94.7 0.19 560 10.5 678.6 n.a. 2.05 45 b5 1047 18 78 13 2.3 47 143 15 21 20,816 4104M10 44.4 6.0 303.5 97.7 0.25 540 10.6 704.4 n.a. 1.22 42 b5 1050 17 79 12 2.3 24 127 14 20 21,124 4066M11 43.5 5.9 263.3 93 0.12 505 10.5 689.5 n.a. 1.25 38 b5 1012 21 77 12 2.3 36 144 15 22 20,917 4210M12 43 5.6 290.9 95.4 0.11 505 10.7 682.4 3.40 1.18 41 b5 1056 18 83 15 2.3 23 143 14 26 23,583 4784

Table 5Mineralogical composition of the travertines collected at Pamukkale and Karahayit (date of sampling: 7 November 2007 and 7May 2009 at Pamukkale, and 7May 2007 at Karahayit).

Name of sections Samples Calcite Aragonite Quartz Mica Chlorite K-feldspar Plagioclase

Pamukkale-Jandarma (Pk) 1a

2a

3a

4 99 15 1005/b 1006 99 17 99 17/b 1008 99 19 95 3 1 b1 b1 b110 10010b 98 1 111 10012 10013 99 114

Pamukkale, Beltes-2 1a

2a 1002b 1003 1004 1005 100

Karahayit, Kirmisi su 1 1002 1003 95 5

a No travertine observed.

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the section, whereas the Pb concentration decreases downstream(Table 6).

4.3.3. Downstream change of stable isotope composition of travertinesThe δ13C and δ18O values of travertines are strongly correlated

(R2=0.85, Fig. 11) and increase along the Jandarma section exceptPk-4 sample (formed on the artificial dam above the travertine slope)having significantly high δ13C and δ18O values (Table 2). The first

travertine is the Pk-5 sample located at the highest point of thetravertine slope showing low δ13C (6.1‰ PDB) and δ18O (−10.7‰PDB) values, whereas the last Pk-13 travertine sample, located at theend of the downstream section has the highest δ13C (11.7‰) and δ18O(−9.1‰) values. The shift in the δ13C values (+5.6‰) is significantlyhigher than the downstream change in the δ18O values (+1.6‰)(Table 2). At the Beltes-2 section (Fig. 5) the δ13C and δ18O valuesincreased downstream from 5.2 to 6.6‰ and from−11.2 to−10.1‰,

Table 6Elemental composition of Pamukkale travertines collected downstream at the Jandarma-spring section (date of sampling: 7 November 2007).

Analyte SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O TiO2 P2O5 Ni LOI Ba Be Co Cs Ga Hf

Unit % % % % % % % % % ppm % ppm ppm ppm ppm ppm ppm

Det. limit 0.01 0.01 0.04 0.01 0.01 0.01 0.01 0.01 0.01 20 −5.1 1 1 0.2 0.1 0.5 0.1

PK-4 0.72 0.03 0.08 0.54 56.14 0.15 0.02 0 0 0 42 19 0 0 0.3 0 0PK-5B 0.65 0.09 0.04 0.68 55.22 0.08 0.02 0 0 162 42.9 22 1 1.3 0.8 0 0PK-7B 0.41 0.07 0 0.74 55.53 0.06 0.01 0 0 20 43 21 2 0 0.7 0 0PK-8 0.11 0 0 0.54 56.36 0.04 0 0 0.01 0 42.7 19 2 0 0.1 0 0PK-9 10.24 1.56 0.3 0.64 48.89 0.50 0.45 0.03 0.03 25 37.1 69 0 0.9 1.4 1.3 0.7PK-10 0.99 0.15 0 0.51 56.11 0.08 0.05 0 0.01 43 41.8 22 0 0 0.3 0 0PK-12 0.48 0.07 0 0.64 55.47 0.05 0.02 0 0.03 0 42.9 18 0 0 0.7 0 0PK-13 0.24 0.03 0.12 0.62 55.81 0.04 0 0 0.02 0 42.8 15 0 0 0.4 0 0

Analyte Nb Rb Sr Th U Zr Y La Ce Pr Nd Sm Eu Gd Tb Dy

Unit ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

Det. Limit 0.1 0.1 0.5 0.2 0.1 0.1 0.1 0.1 0.1 0.02 0.3 0.05 0.02 0.05 0.01 0.05

PK-4 0.5 0.4 2991 0 0.7 2.2 0.1 0.2 0.3 0.04 0 0 0 0 0 0PK-5B 0.6 1.1 1971 0 0.9 3.1 0.8 0.6 0.7 0.11 0 0.1 0.02 0.09 0.02 0.13PK-7B 0.4 0.9 1973 0 0.8 2 0.6 0.3 0.6 0.07 0 0 0 0.06 0 0.07PK-8 0.4 0.3 2219 0 0.7 2.4 0.8 0.2 0 0.03 0 0 0 0 0.01 0.07PK-9 1.1 13.5 1920 1.2 0.9 23.2 4.3 2.7 5.6 0.66 2.6 0.58 0.08 0.49 0.11 0.75PK-10 0.4 1.5 2346 0 0.7 2.4 0.6 0.5 0.8 0.1 0 0 0 0.1 0.02 0.09PK-12 0.4 0.8 3028 0 0.9 3.6 0.3 0.2 0.6 0.06 0 0 0 0 0.01 0PK-13 0 0.5 2715 0 0.6 1.1 0 0 0.3 0.04 0 0 0 0 0 0

Analyte Ho Er Tm Yb Lu TOT/C TOT/S Mo Cu Pb Zn Ni As Au Hg B

Unit ppm ppm ppm ppm ppm % % ppm ppm ppm ppm ppm ppm ppb ppm ppm

Det. Limit 0.02 0.03 0.01 0.05 0.01 0.02 0.02 0.1 0.1 0.1 1 0.1 0.5 0.5 0.01 3

PK-4 0 0 0 0 0 11.9 0.84 0.1 1.8 1.1 6 7.9 0.7 1.5 0 0PK-5B 0 0 0 0.06 0 11.75 0.66 0 0.8 1.4 15 7.6 1.2 1.2 0.02 6PK-7B 0 0.04 0 0 0 12.64 0.66 0 0.5 0.8 10 7.5 0 0 0.01 0PK-8 0.02 0 0 0 0 11.9 0.82 0 0.4 0.5 16 6.3 0 0 0.02 0PK-9 0.15 0.48 0.08 0.49 0.07 10.56 0.67 0.1 10.5 1.8 16 10 1.8 1.2 0.01 43PK-10 0 0 0 0 0 11.91 0.81 0 1.3 0.4 3 4.6 0 0 0.02 7PK-12 0 0 0 0 0 12.11 0.6 0 0.5 0.7 2 8 0 0 0 4PK-13 0 0 0 0 0 12.15 0.79 0 0.2 0.3 0 5 0 0 0.01 0

Fig. 11. Oxygen and carbon isotopic compositions of travertine samples collected from the downstream sections of Pamukkale and Karahayit (data included in Table 2). (date ofsampling: 7 November 2007 and 7 May 2009 at Pamukkale, and 7 May 2007 at Karahayit).

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respectively. At the Kırmızı Su section (Fig. 5, Table 6) the δ13C andδ18O values increased from 5.1 to 7.2‰ and from −12.8 to −8.9‰,respectively.

5. Discussion

5.1. Downstream trends in physicochemical, chemical parameters andstable isotope composition of thermal waters and travertines

Many former studies dealt with the downstream change ofgeochemical components of travertine depositing thermal waters (e.g.Chafetz and Lawrence, 1994; Fouke et al., 2000; Kele et al., 2008a). Ourstudy interprets the downstream change in the characteristics oftravertines and related thermal waters at Pamukkale. Due to secondaryeffects (CO2 degassing, evaporation, temperature change) downstreamflow of thermal water within each section causes similar changes in themeasured parameters. Themorphology of the sections influences theseeffects and governs the downstream increase or decrease of geochem-ical parameters and elemental concentrations.

Since the EC value of thermogene waters varies normally in the 1–10 mS cm−1 range (Pentecost, 2005), based on its EC values (2.3–2.4 mS cm−1) the Pamukkale waters are of thermogene origin. At theJandarma MM-section the positive correlations between the EC values,Ca, free CO2, TDS concentrations andpHvalues andgradual downstreamdecrease of dissolved Ca2+ and HCO3

− (and Ca/Mg ratio) (Table 2 and 4,Fig. 10) are the consequence of the continuous CO2 outgassing andtravertine deposition. With the progressive removal of 12CO2, thehighest δ13Ctravertine values (11–12‰ PDB) were measured at thefarthest point (442.5 m) from the Jandarma spring orifice. The onlyexception is thePk-4 samplewith δ13C ashigh as11.3‰ (PDB) (Table 2),which formed on an artificial concrete dam above the travertine slope,where bacterial mats were observed and these organisms can locallyremove isotopically light CO2 (Guo and Riding, 1994). At the shortBeltes-2 and Karahayit, Kırmızı Su sections the downstream increase ofδ13Ctravertine values wasmuch smaller (from 5.2 to 6.6‰ and from 5.1 to

7.2‰, respectively) than at the long Jandarma-spring section. Thus, thelengthof the section (i.e. durationof CO2outgassing)– togetherwith themorphology – seems an important controlling parameter of theδ13Ctravertine values.

In all the investigated sections at Pamukkale the slight downstreamincrease in the δD and δ18Owater values (Table 2) is attributed to theeffect of evaporation (e.g. Fouke et al., 2000) and decrease in watertemperature. The length of the section and the rate of evaporationdetermine thedegree of downstream increase,whichwas the highest incase of the longest Jandarma-spring MM-section (Table 2) sampled inAugust. Consequently, also the δ18Otravertine values increase along thesections studied (Table 2). Although the Karahayit, Kırmızı Su section isthe shortest among the investigated sections (Table 2), its δ18Otravertine

values show the highest increase (4.1‰) compared to the much longersections where the increase in δ18Otravertine values is smaller than 1.5‰.One of the possible reasons could be that the Kırmızı Su section showsthe highest cooling rate (30.4 °C) in the shortest distance (26 m), whereisotopic equilibrium is nevertheless not attained, but the effect ofoxygen isotope exchange between DIC and water is significant. Thepreferential loss of 16O from the water due to evaporation can alsoincrease indirectly the δ18Otravertine values. The gradual downstreamincrease of the concentration of some elements (e.g. Na+, K+, Cl−, andMg2+) in the travertine along theMM section (2.2%, 2.6%, 5.2% and 1.9%increase, respectively) indicates the effect of evaporation. Although theMg content increases downstream, it cannot be regarded as aconservative constituent, because it is easily incorporated into thecrystal lattice of calcite. Thismay explainwhy the increase inMgcontentis the lowest (1.9). The conservative chlorine shows the greatest (5.2%)downstream increment indicating that about 5% of water evaporatedalong the MM section.

No close relationship can be observed between the depositionalenvironments and geochemical composition of travertines. Thepresence of phosphorous in the samples collected at the lower partof the Jandarma Pk-section is connected to the plants and organicmatter (Table 6). The downstream decrease of Sr, F, Mn and Ba

Fig. 12. Downstream variation in the concentration of Sr, F, Mn, Ba in water samples collected along the Pamukkale Jandarma MM-section.

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concentrations correlates with the distance from the spring orifice(Fig. 12), and the highest concentration decrease of these elements inthe water coincides with the places of the highest CO2 outgassing. Thewater flows slowly from the Jandarma spring orifice 250 m on theplateau (Fig. 6A, B, C) and at the border of the plateau and the slope(Fig. 6E, F) intensive turbulent flow causes CO2 degassing anddissolution of oxygen from the air leading to significant decrease ofEh values (Table 2) and as a consequence significant decrease in theconcentration of the elements mentioned above.

5.2. Mineralogy

Travertines are composed of almost pure CaCO3, which can occur ascalcite or aragonite depending on numerous controlling factors astemperature (Folk, 1994; Fouke et al., 2000), chemical composition(Mg/Ca ratio) of thermal water (Leitmeier, 1915; Folk, 1994), saturationrate (Buczynski and Chafetz, 1991), presence of Sr2+ and SO4

2− (Malesaniand Vanucci, 1975), pCO2 and rate of CO2 degassing (Kele et al., 2008a).The “calcite–aragonite question” was discussed in detail by Renaut andJones (1997), Pentecost (2005) and Kele et al. (2008a). Friedman (1970)pointed out that aragonite usually occurs around thermal springs, wherethe temperature ranges from 30 °C to 60 °C, whereas Folk (1994) andFouke et al. (2000) noted that aragonite would precipitate, if the watertemperature is above 40 °C, and calcite would form, if the water is rich inCa and cooler than 30 °C. Calcite can, however, precipitate directly fromwaters with temperatures N90 °C in Kenya (Jones and Renaut, 1995) andin New Zealand (Jones and Renaut, 1996).

The Mg/Ca ratio of thermal water (which is increasing along thedownstream sections) has an effect on the formation of aragonite(Leitmeier, 1915; Folk, 1994) and according to Fischbeck and Müller(1971) the aragonite precipitation becomes significantwhen theMg/Caratio is ~2.9. During the study of the Hungarian Egerszalók travertineKele et al. (2008a) found that aragonite-bearing samples have higher Srabundance than aragonite-free ones, while Ishigami and Suzuki (1977)observed the samebehaviour in Japanese travertines. The reason for thisis that aragonite hosts more Sr relative to calcite (Gaetani and Cohen,2006). This kind of Sr-preference cannot be observed at Pamukkale,because of the low (1–5%) aragonite concentration of travertines. At theJandarma-section the measured Mg/Ca ratio ranges from 0.3 to 0.5,while the water temperature is below 40 °C, thus, these observationsconfirm the above statements.

5.3. Origin of CO2 in the Denizli Basin

The stable isotopic composition of travertines depends on manyparameters (e.g. tectonism, origin of CO2, type of bedrock and karsticreservoir, local climate) which can differ by areas. In order to find theorigin of CO2 contributed during travertine deposition, the isotopeanalysesmust be supported by exhaustive geological knowledge of thearea, involving sedimentological and tectonic studies. The stableisotope analyses of fossil and active travertines (especially their δ13Cvalues) can indicate thermal, magmatic and metamorphic processes.Although the condition of travertine deposition (including CO2 escape,microbiological activity, and temperature) affects the δ13Ctravertinevalue, the two major controlling factors are: 1) the δ13C value of theprimary carbonate (i.e. the parent rock of the travertine) dissolved inthe parent water of travertine; 2) δ13C value of various CO2 sources(soil, atmospheric and deep-seated CO2) dissolved in the parent waterof the travertine. Many former studies dealt already with the origin ofCO2 in different geological locations (e.g. in Italy Turi, 1986; Minissale,2004; Anzalone et al., 2007). The importance of the origin of CO2 isshown by the fact that many authors used it as a basis for hisgeochemical classification of travertines (Pentecost and Viles, 1994;Kele et al., 2003; Pentecost, 2005; Kele et al., 2008a).

In the Denizli Basin both thermogene travertines (e.g. Pamukkale)andmeteogenecalcareous tufa (e.g. Güney) occur (e.g. Filiz, 1984;Özkulet al., 2002; Horvatinčić et al., 2005; Özkul et al., 2009). Based on He andC isotope analyses Güleç et al. (2002, 2005) pointed out that the highCO2 pressure in the spring waters of Pamukkale derives mainly frommantle source, whereas Filiz (1984) concluded that the CO2 content ofthe Pamukkale Hot Springs derives from magmatic sources. Uysal et al.(2007) observed significantly positive δ13C values (4.7 to 5.8‰) at thePamukkale geothermal field on some fissure ridge vein travertines andsuggested a thermogenic origin for the CO2. According to Uysal et al.(2009) in the case of fissure ridge travertines the possible cause for thepositive δ13C values can be the non-equilibrium fractionation duringquick degassing of the dissolved CO2 gas (rich in 12C) during seismicstrain cycles. However, our measurements showed (Fig. 13) that therecently forming terraced-slope travertine of Pamukkale has alsosignificantly positive δ13C values, thus, it is not necessary to assumenon-equilibrium fractionation during the formation of fissure ridgetravertine and consequently, δ13Ctravertine can be used to determine theorigin of CO2.

Fig. 13. Stable carbon and oxygen isotope compositions of various bedrock samples from the Denizli Basin. See Table 7 for rock types.

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One frequently appliedmethod for the determinationof the origin ofCO2 is the formula (δ13CCO2=1.2 δ13Ctravertine−10.5) published byPanichi and Tongiorgi (1976) (e.g. Kele et al., 2003; Minissale, 2004;Sierralta et al., 2010). Using themeasured δ13Ctravertine this formula givesthe δ13C of theCO2 released fromthewater during travertinedeposition.However this calculated δ13CCO2 is not necessarily representative of δ13Cof the original CO2 mixed to the water in depth. At Pamukkale theδ13Ctravertine values obtained along the Jandarma, Beltes-2 and KarahayitKırmızı Su downstream sections range from 5.2‰ to 11.7‰ (Table 2).Fig. 13 shows the stable carbon and oxygen isotope compositions ofPamukkale and Karahayit travertines and related bedrock samples.Previous studies (Turi, 1986; Kele et al., 2008a) pointed out that only thesamples located closest to the spring's orifice (i.e. free from secondaryeffects) can be used to determine the origin of CO2 at travertinelocalities. Using the empirical equation of Panichi and Tongiorgi (1976)the δ13C of “original CO2” of the Pamukkale travertines is −3.2‰. TheCO2 coming from magmatic sources has generally very low δ13C values(from−7‰ to−5‰; Hoefs, 1997). Measuring the 3He/4He Güleç et al.(2002) revealed the presence of mantle derived gas in the area of theDenizli Basin. However, the δ13C values calculated from the measuredtravertine values aremore positive (−3.2‰) than the δ13C value of CO2

coming frompure igneous source, obviously due to the additional heavycarbon.

Another way of assessment of δ13CCO2 is if we suppose 1:1 ratio ofbedrock carbonate dissolved into the water and the amount of CO2

mixed to the water. The δ13Cbedrock is around 1.8‰ (Table 7), whereasthe measurement of δ13CDIC resulted −1‰ for one of the Pamukkalesprings (Özel Idare) (Table 1). From these numbers the calculatedδ13CCO2 is −3.9‰, which is very close to that calculated by theformula of Panichi and Tongiorgi (1976). Carbon dissolved from theprimary (marine) carbonate rock reservoir could also positivelyinfluence the final stable carbon isotope composition of travertine.Since the δ13C values of bedrock carbonates are lower than 4‰ (andgenerally between 1 and 2.5‰) the positive character of δ13C values ofthe Pamukkale and Karahayit travertines could derive from isotopi-cally heavy CO2 sources. According to Shieh and Taylor (1969) heavyCO2 can be produced through methamorphic reactions (i.e. decar-bonation of carbonate rocks) and the high δ13C values of travertinesaround Pamukkale could be partly attributed to the contribution ofheavy CO2 (rich in 13C isotope) liberated during thermometamorphicdecarbonation of carbonate basement rocks (Triassic–Jurassic marble,Miocene terrestrial limestone). This model is in good agreement withstatements of Özler (2000) and Şimşek et al. (2000) who suggestedthat thermometamorphic decomposition of Mesozoic limestones andPaleozoic marbles produced CO2 with high δ13C values. To conclude,the CO2 dissolved into the water seems to be a mixture of magmaticand thermometamorphic origin based on stable carbon isotope data.

5.4. Controls on the stable hydrogen and oxygen isotopic compositions ofPamukkale thermal waters

Precipitation in the Eastern Mediterranean region is characterisedby a deuterium-excess (d-excess) value higher than that of the Global

Meteoric Water Line (δD=8 δ18O+10‰; Craig, 1961). Gat andCarmi (1970) reported δD=8 δ18O+22‰ as the Eastern Mediterra-nean Meteoric Water Line (EMMWL), while Şimşek (2003) used theequation δD=8 δ18O+16‰ as Western Anatolian Meteoric WaterLine. In the latter equation the d-excess (16‰) is greater than 10‰(GMWL), but smaller than 22‰ (EMMWL) indicating that the portionof precipitation originating from the evaporation of the Mediterra-nean Sea is smaller in Anatolia than in the Eastern MediterraneanRegion. Greater d-excess than that observed globally are due tointense evaporation of seawater in conditions of relative humidity lessthan global average (Gat and Carmi, 1970), which is characteristic forthe Mediterranean Sea.

The stable isotopic compositions of the lukewarm Pamukkalesprings (Beltes, İnciraltı, Özel İdare and Jandarma) are the samewithin the analytical uncertainty, and are situated between the GlobalMeteoric Water Line (GMWL) and the Local Meteoric Water Line(LMWL) (Fig. 14). Since the infiltrated water usually keeps theisotopic characteristics of the local precipitation, we can infer that theMediterranean component of the precipitation in the Denizli Basin islower than that of the Western Anatolia (LWML).

The high temperature Çukurbağ spring is situated below theGMWL (Fig. 14). Its δD value is the same as those of the otherPamukkale springs, while its δ18O value is more positive by 0.6‰.Since all the Pamukkale springs should be on the samemeteoric waterline, the Çukurbağ spring water may be affected by oxygen isotopeexchange with the host rock, because water-rock oxygen isotopeexchange shifts the δ18Owater to positive direction. The oxygen isotopeexchange betweenwater and rock supposedly takes place around andabove 200 °C, while the temperature of the Çukurbağ spring isdefinitely lower (55 °C). The most reasonable explanation is that hotwater (≥200 °C shifted δ18O value) ascends along the tectonic linesandmixes to the shallow cool water resulting 55 °Cwarmwater at theÇukurbağ spring. The existence of this kind of water in theneighbouring Kizildere area has been documented by Şimşek (2003).

The δD–δ18O data of the two sections (Pk and MM) starting fromthe Jandarma spring show the effect of evaporation (Fig. 15). Themainfactor which determines the slope of evaporation line is the relativehumidity. The observed difference between the slopes (4.9 and 5.8) ofevaporation lines may derive from difference in weather conditions(temperature, relative air humidity and wind velocity) duringsampling campaigns in November and August. High dispersion ofthe data within each section can be explained by the differences in thedepositional environments downstream (e.g. pools and falls) causingdifferences in the rate of evaporation (i.e. in the preferential loss oflight isotopes).

5.5. Non-equilibrium isotope fractionation at lowandmedium temperature,travertine depositing thermal springs

Calcite oxygen isotope paleothermometry generally uses the well-known equation of Friedman and O'Neil (1977) assuming equilibriumisotope fractionation during carbonate precipitation. However, as theincreasing number of papers have shown (e.g. Gonfiantini et al., 1968;

Table 7Stable carbon and oxygen isotope compositions of various bedrock samples from the Denizli Basin for comparison with travertines.

Site name Sample name Type Rock type δ13C (‰ PDB) δ18O (‰ PDB) δ18O (‰ SMOW)

Belevi BL-1 Bedrock Limestone −2.3 28.5Belevi BL-2 Bedrock Dolomitic (?) limestone 0.9 −4.1 26.7Gölemezli GL-1a Bedrock Crystalline marble 2.9 −3.2 27.6Gölemezli GL-1b Bedrock Crystalline marble 0.7 −3.6 27.2Gölemezli GL-1c Bedrock Calc-schist 2.1 −7.0 23.7Karateke KRT-1 Bedrock Limestone 1.5 −10.1 20.5Pınarbaşı PN-1 bedrock Mesozoic limestone 3.8 −12.3 18.2Gökpınar GPN-4 Bedrock Dolomitic (?) limestone 0.9 −6.7 24.1Güney Şelalesi GŞ-1 Bedrock Crystalline marble 1.9 −3.6 27.2

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Friedman, 1970; Fouke et al., 2000; Lojen et al., 2004, 2009; Coplen,2007; Kele et al., 2008a,b, 2009), isotopic equilibrium is rarelymaintained under natural conditions during calcite precipitation. Intravertine depositing environments the situation is even more complexisotopically than in other cases, due to kinetic isotope effectsaccompanying with elevated CO2 outgassing and high precipitationrates. Thus, the study of calcite-water oxygen isotopic fractionationduring travertinedeposition is crucial for paleotemperature calculations.

Kele et al. (2008a,b) showed that the Hungarian Egerszalóktravertine deposited under non-equilibrium conditions in the41.2 °C to 67 °C temperature range. Coplen (2007) studied the DevilsHole calcite and observed that the oxygen isotopic fractionationbetween calcite and water was higher than the theoretical valuecalculated using the equation of O'Neil et al. (1969). Therefore Coplen(2007) proposed a new equilibrium fractionation factor, whichnevertheless has not been accepted as an equilibrium value byChacko and Deines (2008). Dietzel et al. (2009) experimentallystudied in laboratory the stable oxygen isotopic fractionation duringinorganic calcite precipitation at various pH, precipitation rates andtemperatures using the CO2 diffusion technique and their resultssupported Coplen's results.

In this paper we present oxygen isotope data from actively formingtravertines and from their parent waters along downstream sectionsto study the physical–chemical processes governing the calcite-wateroxygen isotope fractionation during travertine deposition in the13.3 °C to 51.3 °C temperature range. In all downstream sectionsinvestigated so far, deviation from the equilibrium calcite-waterfractionationwas observed to be the highest around the vents and thisdeviation decreases with increasing distance from the spring orifice(Fig. 16), thus, the Δ(calcite-water) values converge to the equilibriumcurve. At the Pamukkale Jandarma spring section the Δ(calcite-water)

values (measured apparent in Table 8, Fig. 16) intersect theequilibrium curve, showing Δ(calcite-water) values lower than atequilibrium conditions. However, at the Pamukkale Beltes-2 spring

and Karahayit Kırmızı Su well sections the Δ(calcite-water) values of allsamples collected downstream are located above the equilibriumcurve.

At Egerszalók (Hungary) (temperature is between 41.2 °C and67 °C) the data obtained for the travertine precipitated at the vent(67 °C) plot slightly higher than the equilibrium curve by 1.3±0.1 onthe 1000 lnα axis (Fig. 16; Kele et al., 2008a). At Pamukkale twodownstream sections were investigated: the Jandarma-spring Pksection (34.7 °C to 13.3 °C; length 442.5 m), the Beltes-2 springsection (33.4 °C to 28.4 °C; 218.5 m), and one section at Karahayit(Kırmızı Su well, 51.3 °C to 30.9 °C; 26 m). At the Beltes-2 section,where the cooling is the smallest, all the measured Δ(calcite-water)

values are located above the theoretical equilibrium curve, on thenon-equilibrium curve defined by Kele et al. (2008a) (Fig. 16).However, not only the length but also the morphology of the sectionscan affect the degree of water cooling, andmixingwith locally warmerwater flowing on the slope can cause local increase in watertemperature downstream. The Pamukkale Jandarma and Beltes-2sections represent terraced-slope environment, but contain also along artificial channel system (Figs. 4 and 6). Differently, the Karahayit(Kırmızı Su) section is represented only by terrace-pools with nearlystagnant water (Fig. 5), where evaporation and cooling is increased.

It is also important to know the mineralogical compositions of theinvestigated travertines. According to Zhou and Zheng (2003), andTarutani et al. (1969) the aragonite-water oxygen isotope fraction-ations differ from calcite-water fractionations in the 40 °C to 70 °Ctemperature interval. At Pamukkale in both the Jandarma and Beltes-2sections the travertines composed of almost pure calcite (Table 5),while at the Karahayit Kırmızı Su well farthest from the spring only 5%aragonite was determined (Table 5). Thus, the aragonite-wateroxygen isotope fractionations do not play a role during the depositionof the investigated travertines.

At the outlets of the Pamukkale springs the dissolved inorganiccarbon in the thermal water at the measured pH=6.1 is in the form of

Fig. 14. Stable isotopic composition of the Pamukkale springs. GMWL = Global Meteoric Water Line (Craig, 1961), LMWL = Local Meteoric Water Line.

Fig. 15. Stable isotopic composition of the water samples collected along the Pamukkale Pk- and MM-sections.

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CO2(aq) and HCO3−, and practically no CO3

2−. CaCO3 solid phase can beformed only from the CO3

2− ion, when the solution is oversaturated.Gaseous CO2 quickly escapes from the discharging thermal waterresulting in pH increase near the surface of thewater. As a consequenceHCO3

− dissociates into CO32−+H+ and the solution becomes over-

saturated and CaCO3 precipitates. These processes are so fast thatoxygen isotopic equilibrium between the newly formed CO3

2− ion andH2O cannot be attained. The CO2 escapes and CaCO3 precipitation takesplace in a very narrow surface layer of the water. We suppose thatduring the above described quick saturation and precipitation processesthe δ18OCaCO3 should be very close to that of the parent HCO3

− fromwhich the carbonate deposited. To check this hypothesis using theformula 1000 lnα(HCO3

− -H2O)=2,920,000/T2−2.66 (Halas andWolacewicz, 1982) we calculated the relevant HCO3

−–H2O oxygenisotope fractionations for Jandarma, Beltes-2 and Kırmızı Su springs(Turkey), and for Egerszalók (Hungary), and compared them with themeasured δ18OCaCO3−δ18Owater values (tabulated under the “MeasuredapparentΔ(cc-w)” heading, Table 8). Since no isotopic re-equilibrium isattained betweenHCO3

− andH2O along the section,we suppose that theinitial δ18Owater value at the orifice should be taken into account forcalculating the fractionation between thewater and calcite precipitated.Along the downstream sections an increase in δ13C and δ18O values ofCaCO3 can be observed (Table 8) indicating that secondary processesaffect the isotope fractionation between DIC and CaCO3. Since we wantto characterise the nature of isotope fractionation between water andCaCO3 avoiding the effect of secondary processes along the section, weused initial δ18Owater value (at the orifice) and δ18OCaCO3 belonging tothat part of the section where the δ13Ctravertine can be regarded asconstant value (σ=0.1‰; e.g. Table 8, Pk-section, No. 5 to 8 samples).The fractionation values calculated this way are tabulated under theheading “Measured modelled Δ(cc-w)” in Table 8. The calculated(Halas and Wolacewicz, 1982) oxygen isotope fractionations be-tween the HCO3

− and water are tabulated under the “CalculatedΔ(HCO3-w)” heading. Jandarma spring water flows from the orificeto a pool (Fig. 6), where it stays enough time to reach oxygen isotopicequilibrium between water and bicarbonate, therefore we used thetemperature of this pool (PK-4, 31.6 °C) for calculating the Δ(HCO3-w)

[=δ18OHCO3−δ18Owater(initial)] fractionation. The measured modelledδ18OCaCO3−δ18Owater is between 28.3 and 29.2 (with a mean of 28.75)for the Jandarma PK-5 to PK-8 samples, which is very close to thecalculated δ18OHCO3−δ18Owater(initial) value of 28.8. The CaCO3 formed atPK-4 is not a representative product of the above described process (forexplanation see Section 5.1), therefore we have not taken it intoconsideration. For the calculation of the “measured modelled Δ(cc-w)”we used−8.9±0.1‰, which is the characteristic δ18Owater value of thePamukkale springs (Table 1). At the Beltes-2 section the calculatedΔ(HCO3-w) value is 28.4, while the “measured modelled Δ(cc-w)” is28.3, thus, they are practically the same within the analyticaluncertainty. At Kırmızı Su (Karahayit) the “measured modelled Δ(cc-w)” is a little bit higher (mean 25.8) than the calculated Δ(HCO3-w)(25.1),while at Egerszalók (Hungary) (Kele et al., 2008a) the “measuredmodelled Δ(cc-w)” value is the same as the calculated Δ(HCO3-w)(22.7). For comparison, theoretical equilibrium Δ(cc-w) values werecalculated using the formulas of Friedman and O'Neil (1977) and Kimand O'Neil (1997) (Table 8). In all cases these calculated equilibriumvalues are lower than the measured ones indicating non-equilibriumprecipitation at the observed sites.

To conclude, we have observed at three sites (Pamukkale-Jandarma, Pamukkale-Beltes and Egerszalók) that the δ18Otravertine isthe same as the δ18O of HCO3

− dissolved in the water. O'Neil et al.(1969) after speculative considerations stated “On extremely rapidprecipitation the solid is expected to have the same 18O/16O ratio asthe bicarbonate ion in solution”. Our observations on natural hotspring travertines verify O'Neil's hypothesis. The application of twoapproaches:1. water-bicarbonate oxygen isotope equilibrium frac-tionation (Halas and Wolacewicz, 1982); 2. water-travertine equilib-rium fractionation of (Friedman and O'Neil, 1977) may result 8–9 °Cdifference in paleotemperature calculations, which is rather signifi-cant. Based on our observations in the 33 to 66 °C temperature range(Table 8) we recommend the use of water-bicarbonate oxygenisotope equilibrium fractionation factor for paleotemperature calcu-lations in case of travertines precipitated around spring orifice.However, to strengthen our results, more analyses at other activethermal springs are needed.

103lnα(CaCO3-water)

20

20

10

30

40

50

60

70

80

22 24 26 28 30 32

x

x

xx

x

x

xx

Egerszalók travertine 2006 October (Kele 2008)et al.

Egerszalók travertine 2004 August (Kele 2008)et al.

Pamukkale, Jandarma-spring section (Turkey, this study)

Calcite-water equilibrium curve

Aragonite-water equilibrium curve(Zhou & Zheng, 2003, 2006)

Equilibrium curve for biogenic aragonite(Grossman and Ku, 1986)Non-equilibrium empirical” travertine curve”(Kele 2008 and this study)et al.

X

Main Spring (Mammoth Hot Springs, Yellowstone, USA), Friedman (1970).

New Highland Terrace ( ellowstone,USA),Mammoth Hot Springs, Y Friedman (1970).

Bagni San Filippo(Italy), Gonfiantini et al.(1968).

Bagnaccio ( ),Italy Gonfiantini et al.(1968).

Angel Terrace (Mammoth Hot Springs, Yellowstone, USA), Fouke et al. (2000).

Narrow Gauge (Mammoth Hot Springs, Yellowstone, USA) (Chafetz and Lawrence 1994)

Le Zitelle (Viterbo, )(Chafetz and Lawrence 1994).Italy

Durango (Colorado)(Chafetz and Lawrence 1994).

Pagosa Springs (Colorado)(Chafetz and Lawrence 1994).

Bridgeport (California)(Chafetz and Lawrence 1994).

Devils Hole (Nevada, U.S.A), Coplen (2007)

Pamukkale, Beltes-2-spring section (Turkey, this study)

Karahayit, Kirmisi Su section (Turkey, this study)

Data of present study

Data from literature

LEGENDT

(oC

)

Fig. 16. Fractionation of oxygen isotopes between calcite and water vs. the measured temperature (based on Fig. 46 of Pentecost, 2005 and Fig. 17 of Kele et al., 2008a) in theinvestigated temperature range (grey background). Besides the samples collected along the downstream sections of Pamukkale and Karahayit, other hot spring travertineoccurrences around the world are shown together with the calculated equilibrium curve and the travertine curve presented in Kele et al. (2008a). Data of Gonfiantini et al.(1968),Friedman (1970), Turi (1986), Chafetz and Lawrence (1994), Fouke et al. (2000) and Coplen (2007) were used for comparison. Calcite-water equilibrium curve is shown based onthe equation of Friedman and O'Neil (1977). Data from Grossman and Ku (1986) and Zhou and Zheng (2006).

209S. Kele et al. / Sedimentary Geology 238 (2011) 191–212

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6. Conclusions

At two recent Turkish travertine sites (Pamukkale and Karahayit)different depositional subenvironments and facies (vent, artificialchannel and lake, terrace-pools and cascades of proximal slope,marshy environment of distal slope) have been distinguished. Alongthree sections δ13Ctravertine values show significant downstreamincrease (~6‰) due to continuous CO2 degassing. The downstreamincreases of δ18Otravertine values are rather moderate and resultant ofthe superimposed isotope effects caused by carbonate precipitation,evaporation and temperature decrease. Evaporation was estimated tobe 2–5% based on the gradual downstream increase of theconcentration of some conservative elements (Na+, K+, Cl−). Stableisotopic compositions of the Pamukkale thermal water springs showof meteoric origin, and indicate a Local Meteoric Water Line of DenizliBasin to be between the Global MeteoricWater Line (Craig, 1961) andWestern Anatolian Meteoric Water Line (Şimşek, 2003).

The high δ13C values of Pamukkale travertines suggest thecontribution of CO2 liberated by thermometamorphic processesbesides magmatic sources.

Based on our measurements on the paired thermal-water andtravertine samples of Pamukkale and Karahayit we proved that non-equilibrium calcite-water fractionation controls the δ18O values of thetravertines deposited in the 13.3 °C to 51.3 °C temperature range.

According to our measurements and calculations, the δ18Otravertine

equals the δ18OHCO3 in water at the orifices of the thermal springswithin the analytical uncertainty, which means that practically there

is no oxygen isotope fractionation between the solid (i.e. travertine)and dissolved (HCO3

−) carbonate phases at the beginning of travertinedeposition. The absence of isotope fractionation could be a conse-quence of extremely rapid carbonate precipitation caused by very fastCO2 degassing, as it was theoretically supposed by O'Neil et al. (1969).Our study is the first detailed empirical proof of O'Neil's hypothesis ona natural carbonate depositing system.

Our new observations in the 33 to 66 °C temperature range arecrucial in paleoenvironmental, in particular paleoclimatologicalstudies as they can be used 1) for a better understanding of thegeochemistry of fossil travertines and 2) to more precisely estimatethe temperature of deposition of travertines in very fast CO2-degassing settings, by using the water-bicarbonate oxygen isotopeequilibrium fractionation (Halas and Wolacewicz, 1982 instead of thewater-travertine equilibrium fractionation of Friedman andO'Neil,1977). The application of two approaches in case of travertinesprecipitated around spring orifice may result 8–9 °C difference inpaleotemperature calculations.

Acknowledgements

The authors express their gratitude to Professor Brian Jones for hiscomments and linguistic corrections. Special thanks goes to OrhanParlak who allowed us to make field observations and sampling atPamukkale. This study was performed in the frame of a Turkish–Hungarian joint project supported by The Scientific and TechnicalResearch Council of Turkey (TÜBITAK, Project Number: 106 Y 207)

Table 8Calculations of the apparent and modelled Δ(calcite-water) fractionations using the water temperature and δ18O water data measured at the downstream sections of Pamukkale,Karahayit (Türkey) and Egerszalók (Hungary, Kele et al., 2008a) and using the equations of Friedman and O'Neil (1977) and Kim and O'Neil (1997). The Δ(HCO3

−–water)fractionations were calculated using the equation of Halas and Wolacewicz (1982).

Name No. Temp. Temp. δ18Owater δ13Ctravertine δ18Otravertine Measuredapparent

Measuredmodelled

Friedman andO'Neil (1977)

Kim andO'Neil (1997)

Calculateda

(°C) (Kelvin) (‰ SMOW) (‰ PDB) (‰ SMOW) Δ(cc-w) Δ(cc-w) Δ(cc-w) Δ(cc-w) Δ(HCO3-w)

Pamukkale, Jandarma spring,Pk-section

1 34.7 307.7 −8.9 – – – 26.5 26.22 33.0 306.0 −8.8 – – – 26.8 26.53 34.1 307.1 −8.8 – – – 26.6 26.34 31.6 304.6 −8.8 11.3 21.3 30.1 27.1 26.8 28.85 30.1 303.1 −8.8 6.1 19.9 28.7 28.7 27.4 27.16 28.7 301.7 −8.2 5.9 20.4 28.6 29.2 27.7 27.37 26.6 299.6 −8.9 5.9 20 28.9 28.8 28.1 27.88 25.0 298.0 −8.8 5.8 19.5 28.3 28.3 28.4 28.19 21.5 294.5 −8.4 7.1 20.3 28.7 29.2 28.810 18.6 291.6 −8.8 8.2 20.1 28.9 29.8 29.411 15.1 288.1 −8.6 9.7 20.9 29.5 30.6 30.212 15.3 288.3 −8.6 11.5 21.6 30.2 30.6 30.113 13.7 286.7 −8.5 11.7 21.5 30.0 30.9 30.514 13.3 286.3 −8.6 – – – – –

Pamukkale, Beltes-2-section 1 33.4 306.4 −8.6 – – – – –

2a 32.6 305.6 −8.6 – – – – –

2b 33.2 306.2 −8.5 5.2 19.3 27.8 28.2 26.8 26.5 28.43 32.4 305.4 −8.5 5.1 19.5 28.0 28.4 26.9 26.64 31.0 304.0 −8.4 6.2 19.8 28.2 27.2 26.95 29.5 302.5 −8.4 6.6 20.5 28.9 27.5 27.26 28.4 301.4 −7.9 – – – – –

Karahayit, Kirmizi su-section 1 51.3 324.3 −7.8 5.1 17.7 25.5 25.6 23.5 23.2 25.12 39.7 312.7 −8.0 5.1 18.1 26.0 26.0 25.5 25.23 30.9 303.9 −7.8 7.2 21.8 29.6 27.2 26.9

Egerszalók, De-42., 1. section,February 2004 (Kee et al., 2008)

1 66.1 339.1 −11.1 – – – – –

2 65.2 338.2 −11.2 2.3 11.5 22.7 22.7 21.4 20.9 22.73 64.9 337.9 −11.1 2.3 11.5 22.6 22.7 21.5 20.94 64.7 337.7 −11.1 2.5 11.6 22.7 22.8 21.5 21.05 64 337.0 −11 2.5 11.5 22.5 22.7 21.6 21.16 63.6 336.6 −11 2.8 11.9 22.9 21.6 21.17 59.9 332.9 −10.9 3 12.0 22.9 22.2 21.78 54.1 327.1 −10.8 3.7 12.5 23.3 23.1 22.79 51.3 324.3 −10.8 3.6 12.5 23.3 23.5 23.210 48.5 321.5 −10.6 3.5 12.3 22.9 24.0 23.711 42.6 315.6 −10.6 4 12.8 23.4 25.0 24.7

a (Based on Halas and Wolacewicz, 1982).

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and the National Office for Research and Technology (NTKH, Hungary,project number: TR-10/2006). We are also grateful to the anonymousreviewers for their useful suggestions.

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