Distribution, Lithotypes and Mineralogical Study of Newly Formed Thermogenic Travertines in Northern Euboea and Eastern Central Greece

Cent. Eur. J. Geosci. • 4(4) • 2012 • 545-560 DOI: 10.2478/s13533-012-0105-z

Central European Journal of Geosciences

Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece

Research Article

Christos Kanellopoulos∗

National University of Athens, Department of Geology and GeoEnvironment, Panepistimiopolis, 15784 Athens

Received 6 June 2012; accepted 20 September 2012

Abstract: In the northwestern part of Euboea Island and the neighbouring part of the mainland in eastern central Greece, many hot springs exist. We collected and analysed the newly formed material around the hot springs. The samples were studied at the lab with X-Ray Diffraction, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). In all cases the studied materials were thermogenic travertine presenting many different lithotypes. The studied travertine deposits consist mainly of aragonite and calcite, but in some cases, as the main mineral phase, an amorphous hydrous ferric oxyhydroxide, probably ferrihydrite (creating a laminated iron-rich travertine deposit), was identified. The lithotypes that were identified were of great variety (spicular, shrubs, etc). Some of them (pisoliths, rafts and foam rock types) are quite rare and one of them (framework type) is described for the first time. Morphological data and field observations suggest possible inorganic and organic controls on carbonate precipitation. Similar lithotypes have been recorded at Mammoth hot springs, Yellowstone National Park in USA and at Rapolano Terme, Italy. Keywords: hydrothermal system • lithotypes • Northern Euboea • Thermopylae • travertine deposits of hot springs © Versita sp. z o.o.

1. Introduction within a vadose or occasionally shallow phreatic environ- ment. Precipitation results primarily through the transfer (evasion or invasion) of carbon dioxide from or to a groundwater source leading to calcium carbonate super- Various researchers [1–6] have proposed many definitions saturation, with nucleation/crystal growth occurring upon for the term travertine. Perhaps the most comprehensive a submerged surface” and can take many forms. and clear definition was proposed by Pentecost [7], who defined travertine as “a chemically-precipitated continen- Travertine deposits exist in many places around the world. tal limestone formed around seepages, springs and along The most characteristic and studied travertine deposits streams and rivers, occasionally in lakes and consisting of are in Italy (Bagni San Filippo, Terme San Giovanni, calcite or aragonite, of low to moderate intercrystalline Tivoli, Guidonia Montecelio etc), USA (Yellowstone Na- porosity and often high mouldic or framework porosity tional Park), Turkey (Pamukkale), etc. [7–16] In Greece, there are hot springs in many areas. Magmatic ∗E-mail: [email protected] and volcanic processes and active fault systems favour the

545 Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece

Figure 1. Geological map showing the study area and the localities sampled.

rise of deep waters that are discharged at the surface as 2. Geological setting hot springs. From 1985-1988, the Institute of Geological and Mineral The investigated area includes the northwestern part of Exploration in Greece (IGME) performed the first system- Euboea island and the neighbouring part of the mainland, atic study on all known Greek hot springs and, along with in eastern central Greece (Fig. 1). The studied area be- that, they recorded systematically for the first time all the longs geologically to the western part of the Geotectonic thermogenic travertines [17–19]. Units of the internal zones of Greece, more specifically, At the northwestern part of Euboea Island (e.g. Edipsos the Pelagonian and Sub-Pelagonian zones [20, 21]. and Ilia) and in the neighbouring part of the mainland Eastern central Greece and, more specifically, the Sper- in eastern central Greece (e.g. Thermopylae), many hot chios graben, were Thermopylae placed, belong to the springs exist (Fig. 1). On the island of Euboea and more so-called “Sub-Pelagonian Geotectonic Unit”. The rock specifically, in the Edipsos and Ilia, around the hot springs basement consists mainly of carbonate rocks (limestones is depositing thermogenic travertine. In Thermopylae a and dolomites) of Middle Triassic-Middle Jurassic age. An similar process take place. The Edipsos and Thermopy- ophiolitic thrust sheet that is a relic of the Thetysian lae are probably the largest active travertine systems in oceanic crust is overthrusted onto the carbonates [22]. Greece. Since the Neogene, fluvio-deltaic sediments fill the Thermogenic travertine deposit near to the hot springs graben with intercalation of marls, clays, sandstones and where the hot water cools, degasses and rapidly precip- conglomerates [23]. itates calcium carbonate, creating different depositional In the northern Euboea Island, Paleozoic and Mesozoic facies-lithotypes with different crystal forms. sequences were folded together or imbricated as the re- The aim of this paper is to describe the various lithotypes sult of two main tectonic events (Alpine and Eo-Alpine). of newly formed travertine deposits in Northern Euboea These sequences belong to the “Pelagonian Geotectonic and Eastern central Greece. Among the studied systems Unit”. The latter is represented by nappes which over- are those of Edipsos and Thermopylae, which are proba- thrusted the units of the External Hellenides domain dur- bly the largest active travertine systems of Greece. A fur- ing Late Eocene-Oligocene times. The Pelagonian se- ther aim of this paper is to study their main mineralogical quence is made of continental crust elements (basement), phases and their variety of crystal morphologies. Through syn-rift deposits, carbonate platform sediments as well as morphological and mineralogical study, indications of pos- that of volcano-sedimentary sequences. The syn-rift de- sible organic controls on carbonate precipitation can be posits are composed of continental detrital sediments and identified, in addition to the inorganic ones. Late Permian shallow water carbonate incursions. The

546 C. Kanellopoulos

detrital formation is followed by dolomites of Middle Tri- 4. Location and Macroscopic de- assic age. The whole area is highly faulted due to ex- scription of travertine deposits tensional tectonics [24–26]. Vavassis’ study [27] has described a great number of linear tectonic features mostly NNE-SSW and NW-SE to E-W strike. In the studied area, newly formed thermogenic travertine deposits occur in three different areas: two in North- The volcanogenic islands of Lichades are located in the ern Euboea (Edipsos and Ilia) and one in Eastern Cen- center of the northern Euboea gulf [28]. They are made tral Greece (Thermopylae) (Fig. 1). In these areas the mainly of trachyandesite lava flows, dated at 0.5 Ma. The travertines are thermogenic, created by the local hot nearby Kamena Vourla outcrops (1.7 Ma) also comprise springs. In most cases along with the newly formed of lavas of trachyandesite composition. The total volume travertines, we also identified old travertine deposits. By of volcanic products is about 0.1 km3 [29]. The existence the term old travertines, we mean: all the travertines that of volcanic rocks is related to the tectonic processes of have been created in the past; and the precipitation pro- the area, because they are placed along one of the shear cess, which creates the specific form, has ended. zones [30]. This Plio-Pleistocene volcanic center is lo- In Thermopylae, extensive deposits of thermogenic traver- cated on the western continuation of the North Anatolian tine occur. Their color varies from white to grey. During Fault, in a back-arc position with respect to the active the field survey, we discovered newly formed travertine arc. Innocenti et al. [31], based on Sr–Nd–Pb isotopic deposits and some old ones, since the hot springs in the compositions, linked this volcanic center with the large area exist from historical times. Works for the construction volcanic belt that developed north of the Pelagonian– of a new National highway road as well as other support- Attic–Cycladic–Menderes massifs, encompassing a 35 Ma ing works were carried out in this area and many of these timespan which is widespread over a large area from NW works have destroyed the travertine lithotypes and mixed Greece–Macedonia to the Aegean–western Anatolia. the old and the new deposits (Fig. 2A). For these reasons it was not possible to identify, with certainty, which deposits are recent, with the only exception being that of 3. Materials and Methods the travertine deposits which are placed close to the hot- spring. Near the vent, newly formed thermogenic travertine deposits were identified which have a relatively high Over thirty samples were studied at the laboratories of the rate of deposition. Department of Geology and Geoenvironment, University of In the Edipsos area large deposits of thermogenic traver- Athens. tine occur, presenting great variety of morphological forms The samples were studied during the field survey and at and lithotypes. the lab with a stereoscope, for macroscopic structures. The most common active morphological forms in Edipsos are spring mounds, cascades and terraces. The spring The mineralogical composition was investigated mainly by mounds have fissure walls, which are usually between 10 X-Ray Diffraction. XRD analyses were carried out using to 50 mm height surrounding a spring or a drill orifice. a Siemens Model 5005 X-ray Diffractometer, Cu Ka radi- The cascades are indefinitely accretionary and occur on ◦ ation at 40 kV, 40 nA, 0.020 step size and 1.0 s step time. precipitous sites where deposition rates are high (Fig. 2B). The XRD patterns were evaluated using the EVA v.10.0 Also, many terraces exist. They are pools with small program of the Siemens DIFFRACplus and the D5005 depth and low flow velocity (Fig. 2C). They are probably software package. the most interesting morphological forms, because inside Scanning Electron Microscopy (SEM) and Energy Dis- them many lithotypes were observed (e.g. foam rock, rafts, persive Spectroscopy (EDS) analysis were carried out shrubs). using a Jeol JSM 5600 SEM instrument, equipped with Their color varies from white-yellow to red, with orange an Oxford ISIS 300 OXFORD, with the following operat- prevailing. During the field survey we discovered old and ing conditions: accelerating voltage 20 kV, beam current newly formed travertine deposits. The hot springs in Edip- 0.5 nA, time of measurement 50 sec and beam diameter 1 – sos exist from historical times and many ancient structures, 2 µm. The spectra were processed using the ZAF program such as Roman baths, prove it (Fig. 2D). The deposition (3 interaction). The microprobe analyses were conducted rate is high and in this area hot springs are self-settled in on polished sections of the samples after carbon coating. a short time with the depositing material and new springs SEM images of the structures were taken after gold coat- arising nearby. The high rate of deposition creates prob- ing of fragments from the sample. lems for the exploitation of hot springs for spa therapy,

547 Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece

61 to 63◦C and pH from 6.1 to 6.4. In the Thermopylae hot spring the temperature values are clearly lower than Euboea hot springs, ranging from 32.8 to 33.5◦C and the pH from 6 to 6.2.

5.2. Mineralogical study and chemical composition of main mineral phases

The main mineral phases identiﬁed by XRD analysis are presented in table 2. The two main mineral phases usually are aragonite and calcite, which in many cases coexist.

In the Edipsos samples the predominant phase is aragonite. Its crystals tend to create hexagonal prisms, which at many times appear as radial spheres (Fig. 3A), while calcite usually creates rhombohedral crystals. We also iden- tiﬁed the rare form of Gothic arch bars (Fig. 3A), which has been ﬁrst reported by Folk et al. [33] in the Italian hot spring deposits of Rapolano Serre and Bangi di Tivoli.

In the Ilia iron-rich travertine deposit, in addition to cal-

Figure 2. Morphologies of travertines. (A) Works in Thermopylae, cium carbonate mineral phases, an amorphous hydrous which have destroyed the travertine lithotypes, have also ferric oxyhydroxide phase was identified (Table 2). XRD mixed the old and the newly formed ones. (B) Cape forma- analysis was performed on this amorphous material and tion at Edipsos, composed only by travertine. It was cre- ◦ ated at the point where hot water from some hot springs the XRD pattern presents two broad peaks at about 35 falls to the sea. (C) Travertine terraces at Edipsos. (D) and 62◦ in 2θ (Fig. 4), which are typical signatures of Inside the site of Ancient Roman Baths at Edipsos. The baths have filled up with travertines. (E) Internal mate- amorphous ferrihydrite [34, 35]. The Ilia hot spring has rial of pipes at Edipsos. (F) A small travertine dome at significantly higher Fe concentrations (up to 11000 µg/L) Ilia, created at the point where the pipe from the borehole vents the hot water. It is a stromatolitic laminated Fe-rich compared to all other studied hot springs [32]. travertine. In Thermopylae samples, we only identified calcite as a main mineral phase. because in a short period of time it results in the clogging of pipes used for the transfer of the hot water (Fig. 2E). In some samples halite (NaCl) was also identified (Ta- Ilia is located 7 km east of Edipsos. The travertine de- ble 2). Usually the halite crystals were found at the rim posit in Ilia covers a small area (∼2 m2) and it is created of open pores or trapped inside the now-closed pores of at the point where the pipe from the borehole vents out the travertine (Fig. 3B). the hot water (Fig. 2F). At that position a reddish brown When studying the samples with a Scanning Electron Mi- dome has been created which consists of newly formed croscope (SEM) and through microprobe analysis, some Fe-rich travertine [32]. This travertine has Fe-rich parts, other mineral phases were identified, usually in the form which sometimes appear as metallic zone layers creating of very small crystals, which are trapped within the pores botryoid structures. of the travertine [32].

The chemical composition of calcium carbonate minerals 5. Results varies from area to area. The calcium carbonate mineral phases from Thermopylae in addition to Ca, C, and O, 5.1. Temperature and pH of the local hot contain Mg and/or S (Table 3). The calcium carbonate springs mineral phases from Edipsos in addition to Ca, C, and O, contain S and/or Si and/or Na and/or Cl and/or Fe The temperature and pH values at the vents vary from (Table 3). Finally, the calcium carbonate mineral phases area to area (Table 1). More speciﬁcally, in Edipsos the from Ilia, in addition to Ca, C, and O, contain Fe and/or temperature of hot springs ranges from 50.8 to 82◦C and As and/or Si and/or S and/or Sr and/or Na and/or Cl pH from 5.6 to 7.5. Ilia hot spring temperature ranges from (Table 3).

548 C. Kanellopoulos

Table 1. List of hot-springs with their temperature and pH values.

Code Geographical Area T (◦C) pH Sampling Type of coordinates Date sampling site AD-1-D-WM N38 51.264 Edipsos 80.5 6.43 16/11/2004 Drill E23 02.930 AD-20-WM N38 51.264 Edipsos 82 7.4 17/6/2005 Drill (AD-1-D-WM)* E23 02.930 AD-2-WM N38 51.264 Edipsos 75 5.85 16/11/2004 Drill E23 02.930 AD-21-WM N38 51.264 Edipsos 74 7.15 17/6/2005 Drill (AD-2-WM)* E23 02.930 AD-3-WM N38 51.264 Edipsos 60.7 5.65 16/11/2004 Drill E23 02.930 AD-4-WM N38 51.313 Edipsos 65.4 6.86 19/11/2004 Spring E23 03.220 AD-5-WM N38 51.296 Edipsos 69.9 6.3 19/11/2004 Drill E23 03.179 AD-6-WM N38 51.182 Edipsos 50.8 7.54 19/11/2004 Spring E23 02.876 AD-15-WM N38 51.400 Edipsos 55.6 7.35 20/11/2004 Drill E23 02.945 AD-100-W N38 51.265 Edipsos 70.5 6.52 16/6/2008 Drill E23 02.929 AD-101-W N38 51.264 Edipsos 61 6.34 16/6/2008 Drill E23 02.930 AD-102-W N38 51.264 Edipsos 74 6.4 16/6/2008 Drill E23 02.930 AD-103-W N38 51.264 Edipsos 73.3 6.4 16/6/2008 Drill E23 02.930 AD-104-W N38 51.264 Edipsos 70 6.15 16/6/2008 Drill E23 02.930 AD-105-W N38 51.313 Edipsos 58 7.13 16/6/2008 Drill E23 03.219 AD-9-WM N38 51.118 Ilia 63.4 6.25 20/11/2004 Drill (HL-1-WM)* E23 07.749 HL-1-D-WM N38 51.118 Ilia 60.9 6.07 14/3/2005 Drill (AD-9-WM)* E23 07.749 HL-11-W N38 51.152 Ilia 63 6.45 16/6/2008 Drill (AD-9-WM)* E23 07.740 KB-5-WM N38 47.560 Thermopylae 33.5 5.97 27/10/2004 Spring E22 31.561 THE-1-D-WM N38 47.560 Thermopylae 32.8 6.24 12/4/2005 Spring (KB-5-WM)* E22 31.561 * = Into the parenthesis are the code of the sampling site, if it was measured again in a diﬀerent time

5.3. Lithotypes of newly formed travertines (e.g. rafts, foam rock, shrubs, lamination). A new lithotype, named framework, was identiﬁed.

In the studied areas, seven main newly formed travertine The main lithotypes are: lithotypes were identiﬁed. Some of them are quite com- i) Crystalline crusts (Fig.5)[9, 37] typically are layers mon (e.g. crystalline crust), while some others are rare, of travertines (up to some cm) that overlap either older

549 Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece

Table 2. Summary results from the mineralogical study conducted by X-ray Diﬀraction.

Area Code Lithotypes (color) Aragonite Calcite Gypsum Halite Ferrihydrite Edipsos AD-4-R cement between pisoliths (grey) *** *** ** ** AD-4-R pisoliths (white) *** * ** AD-EOT-R-2 foam (orange) *** AD-EOT-R-3 lamination (orange) *** * EOT-1 crystaline crust (bright white) *** AD-EOT-R-4 spicular (white) ** *** AD-EOT-R-4 spicular (black) ** *** * AD-5-R rafts ** *** AD-13-R rafts *** ** ** MAST-1 spicular *** ** ** * MAST-2 spicular (white) *** MAST-3 spicular (brown) *** MAST-5 crystalline crust (grey) *** MAST-6 compact mass (light orange) *** ** MAST-7 terraces (white) *** MAST-8 terraces (dark orange) ** *** ** MAST-9 boytroial lamination (bright white) ** *** * MAST-10 crystalline crust with lamination *** * MAST-11 rafts *** ** * MAST-11A rafts ** *** Ilia HL-SYM-MET (enriched)F lamination (brown) *** ** HL-SYM-METAL-RF lamination (brown) *** *** HL-1-RF lamination (brown) *** ** MAST-13F lamination (brown) *** ** * MAST–14F lamination (brown) ** *** MAST-14AF lamination (brown) *** * Thermopylae THE1B lamination *** * THE2B lamination *** THE2B lamination *** THE-1-R high porosity, lamination *** THE-2-R framework *** F = the identiﬁcation of ferrihydrite was achieved only to one enriched sample. This mineral phase is also present in all samples from Ilia (veriﬁed by SEM study and micro-probe analysis) as main mineral phase.

travertine deposits or other materials, usually found in Edipsos and Ilia. They reflect rapid precipitation from fast flowing waters, creating botryoid shapes. Crystalline crusts are generally layered and dense. They can be sev- eral to tens of centimeters in thickness. Old and dry crystalline crusts are compact and hard, but when they are forming and are underwater they can be easily crushed. Their color can be white (Fig. 5A, 5B), grey (Fig. 5C, 5D), Figure 3. SEM photomicrographs. (A) Typical forms of radial or reddish, depending on the chemistry of hot water and, spheres of aragonite, coexisting with Gothic arch bars calcite. (B) Crystals of halite developed at the rims of the more specifically, depending on the iron concentration. In pores in Edipsos travertine. The hydrothermal fluid, which our cases they are composed mostly of aragonite crystals. passes through the pores of the travertine in this area, is rich in Na and Cl (up to 11150 mg/L Na, 21100 mg/L Cl) [32]. ii) Rafts (or calcite ice) (Fig. 6) were found only in Edip- sos terracettes. They are thin, semi-transparent, brittle

550 C. Kanellopoulos

Table 3. Representative microanalysis of aragonite and calcite (CaCO3, in compound %).

Thermopylae Edipsos Sample THE-1-R THE-12-R AD-4-R AD-10-R2 EOT-16-R AD-3-R1 EOT-13 AD-11-R1 Lithotype Laminated Pisoliths Laminated Laminated and spicular Laminated Shrubs Laminated Analysis X75 X130 X134 X61 X62 X91 X99 X6 X7 C49 X72 C44

SiO2 ------0.49 - 0.34 FeO ------1.30 1.24 1.17 - 0.35 MgO 2.04 1.39 1.29 ------CaO 46.62 47.87 47.73 46.44 43.61 47.18 46.65 35.71 44.87 48.30 48.97 48.17

Na2O ------0.31 0.73

SO3 0.90 1.07 - 0.92 0.32 1.17 0.40 0.77 0.80 1.12 - 3.70

As2O3 ------SrO ------Cl - - - 0.34 0.39 - 0.18 0.44 0.16 ---

Total 49.56 50.33 49.02 47.70 44.33 48.35 47.23 38.22 47.07 51.09 49.2800 53.2900

Atoms 2 2 2 2 2 2 2 2 2 2 2 2

Si ------0.0096 - 0.0064 Fe ------0.0680 0.0525 0.0458 - 0.0130 Mg 0.1133 0.0553 0.0528 ------Ca 1.8616 1.9020 1.9472 1.9470 1.9678 1.9515 1.9755 1.8685 1.9068 1.8909 1.9874 1.8081 Na ------0.0252 0.0546 S 0.0084 0.0142 - 0.0129 0.0049 0.0162 0.0056 0.0135 0.0113 0.0147 - 0.0462 As ------Sr ------Cl - - - 0.0143 0.0176 - 0.0076 0.0230 0.0068 - - -

Figure 4. XRD pattern from iron-rich material. The background (gray thick line) shows two characteristic broad peaks at around 35◦ and 62◦ in 2θ, which are typical signatures of amorphous ferrihydrite [34–36] and the sharp peaks cor- respond mostly to aragonite (black arrows). Figure 5. Crystalline crust (botryoid) travertines from Edipsos. (A) White colored botryoid shape travertine. (B) Section of a white botryoid form, in which the variety of diﬀerent materials overlapped, can be seen. (C) Grey colored botryoid crystalline layers of calcium carbonate, which precipitate travertine. (D) Cut surface of a grey botryoid shape sam- at the water surface usually inside terraces or hot water ple, showing the older travertine layers overlapped. bodies with low ﬂow velocity. Rafts have been described to be calcitic (central Italy, [33]), aragonitic (Colorado,

551 Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece

Table 4. (Continued, in compound %).

Ilia Sample HL-M-1 HL-M-2 HL-M-3 HL-1-R HL-M-2 Lithotype Laminated Analysis C8 A22 A24 B43 D37 A3

SiO2 1.95 3.66 - 0.26 0.34 2.27 FeO 7.20 13.17 - 0.36 1.24 7.17 MgO ------CaO 44.90 39.75 49.87 49.69 48.24 45.92

Na2O - - - 0.47 - -

SO3 - 0.82 - - 3.05 0.72

As2O3 0.62 0.53 - - 0.78 0.53 SrO - - 1.03 0.98 - - Cl 0.09 - - - - - Figure 6. (A) Travertine terraces from Edipsos, with rafts on the water surface. Green growths near and inside the terrace Total 54.76 57.94 50.90 51.76 53.65 56.61 are cyanobacteria and/or algae. (B) – (E) SEM photomicrographs of rafts. (B) Cross-section of a raft, with the two layers: the subaqueous with aragonite spherulites and Atoms 2 2 2 2 2 2 trapped calcite crystals and the overwater layer with fan- shaped radiating aragonite needles. (C) Close-up of the Si 0.0355 0.0631 - 0.0050 0.0064 0.0401 transition between the two layers. (D) Cross section of aggregated spherulites showing the hollow centers. The Fe 0.2631 0.4548 - 0.0139 0.0460 0.2532 thin layer occurs at the base of the needle crust and the Mg ------external radical crust of needle crystals. (E) Development of the NaCl layer (overwater) over the spherulites. Ca 1.6398 1.3723 1.9596 1.9200 1.7986 1.6225 Na - - - 0.0365 - - S - 0.0095 - - 0.0379 0.0085 As 0.0151 0.0122 - - 0.0194 0.0124 the spherulites (Fig. 9E). Usually the rafts are a few mm Sr - - 0.0404 0.0379 - - thick and they end up breaking and settling to the bot- Cl 0.0033 - - - - - tom of the pool due to gravity, when their weight becomes larger than the force of buoyancy. Rafts, also termed “hot- water ice” [12] or “calcitic ice” [13] were first described in U.S.A., [38]), or bimineralic (Rapolano Terme Italy, [9]). hot springs by Weed [39]. Similar lithotypes were found The rafts from Edipsos are mainly aragonitic in composi- in Mammoth, Yellowstone, U.S.A. [12, 13], Colorado, U.S.A. tion having also calcite and halite (Table 2). They have a (aragonitic rafts) [38] and Rapolano Terme Italy [9]. generally flat and smooth surface above water and a rough iii) Foam type travertines have been deposited at the bot- underwater surface. They are composed of a three-layer tom of terraces (Fig. 7, 8). Rapidly precipitated calcium structure (Fig. 6B). The upper layer is composed of radiat- carbonate crystals settled at the surface of underwater gas ing aragonite needles. These aragonite crystals have fan- bubbles and encrusted them, creating hollow spherical ac- shaped radiating arrays (Fig. 6B, 6C). Under this layer, cumulations. In some cases these structures are described which is over the water-surface, exists a massive layer as calcitic [12, 40–42], aragonitic [43], or bimineralic [44]. composed mainly of aragonite spherulites (Fig. 6B, 6C). The carbonate-encrusted bubbles from Edipsos are arag- Spherulites are usually hollow with diameters of 50 µm. onitic in composition (Table 2). In our cases they usu- They typically have internal diameters of 5 µm and consist ally are creating hollow cylindrical capsules, produced by of an external radical crust of needle crystals (Fig. 6D). chains of amalgamated vertically elongated bubbles with A thin layer of tiny subspherical grains occurs between diameters up to 0.3 mm and lengths up to 2 mm. Surface the needle rim and the hollow nucleus. Guo and Rid- tension facilitates chain formation by creating sufficient ing [37] describe similar spherulite structures in Rapolano time for incipient calcification [9]. This implies stagnant Terme, suggesting that in the hollow centers originally or- conditions in standing water bodies, which exist at ter- ganic bodies might have existed. Between the aggregate races. The carbonate encrustation on the bubbles ranges of spherulites, crystals of calcite are trapped. The third from 600 µm to 1.75 mm in thickness (Fig. 8A). The bub- layer, which is under the water surface, is composed of bles have a rough exterior and generally a smooth interior halite. It is a thin layer, 5 µm thick, which develops over wall. They are composed of a two-layer structure (Fig. 8C,

552 C. Kanellopoulos

Figure 7. Travertine terraces from Edipsos. (A) Overview image of Figure 8. Foam types from Edipsos. (A) Foam travertine from terracettes. (B) Sample from travertine microterracettes. Edipsos developed at the bottom of terraces. Some gas (C) Section of sample from terracettes, at which can be bubbles can be seen before they were coated. Green seen as layers of shrubs separated by laminae of silt-sized growths are cyanobacteria and/or algae. (B) Section of micritic aggregates. (D) Coexistence of shrubs and foam a foam travertine sample, showing gas bubble cham- lithotypes, in a sample of travertine terracettes. bers, which are hollow cylindrical capsules, produced by chains of amalgamated vertically elongate bubbles between shrub forms. Figures (C) and (D) are SEM photomicrographs of carbonate-encrusted bubbles. (C) Part of a 8D). The inner layer is composed of stellate clusters of carbonate-encrusted wall, showing a typical rough exterior and smooth interior. The outer layer is composed of radi- flat-thin aragonite crystals, which are oriented with their ating aragonite needles. These aragonite crystals have a flat plane tangential to the inside wall of the carbonate- fan-shaped radiating array, oriented with their long axes perpendicular to the plane of the stellate clusters, i.e. ra- encrusted bubbles. With continued growth, the stellate dially away from the interior wall. (D) Development of the crystals grew laterally and coalesced into a smooth curved fine, essentially planar stellate clusters of flat-thin aragonite crystals, comprising the innermost layer. The stel- sheet, which comprises the interior wall of the carbonate- late clusters of aragonite needles are oriented with their encrusted bubbles. The outer layer is composed of radiat- flat plane tangential to the inside wall of the carbonate- ing aragonite needles. These aragonite crystals have fan- encrusted bubbles. With continued growth, the stellate crystals grew laterally and coalesced into a smooth curved shaped radiating arrays orientated with their long axes sheet, which comprises the interior wall of the carbonate- perpendicular to the plane of the stellate clusters, i.e. encrusted bubbles. radially away from the interior wall. Similar lithotypes were described in Rapolano travertines by Chafetz and Folk [42]. Although we did not analyse the gas present layers are separated by laminae composed by micritic within the bubbles, Chafetz et al. [38] and Guo & Riding [9] sized material and in many cases can be distinguished suggested that they were initially composed of oxygen through eye observation. In some cases, the shrubs have which was generated as a product of photosynthesis; in an irregular morphology showing no specific crystallo- cases like at Edipsos, the gas bubbles around which the graphic influence in their morphology. These samples precipitate formed are on sunlit microbial mats (Fig. 8A). were collected from terraces, which have been observed iv) Shrubs (Fig. 9, 7) are very common in the samples from to grow cyanobacteria and/or algae, so it is possible for Euboea. Travertine shrubs are short, stubby, dense crys- them to be bacterial shrubs. talline masses of calcium carbonate that expand upward v) Lamination (Fig. 10, 7) is a very common lithotype by irregular branching [42]. In our cases they are created in our samples. The development of this type may be usually at the bottom of terraces (Fig. 7). Genetically due to inorganic processes, where the release of CO2 shrub-like types present considerably different morpholo- caused supersaturation of the solution and precipitation gies. Chafetz and Guidry [45] separated them to those of CaCO3 [43, 46], to biogenic processes [42], or to multi- whose outline is typical of the common garden-variety ple abiotic and biotic factors combined. In our cases the woody shrub or bush (bacterial shrubs, [42]), to those that laminas can be composed of either aragonite (Edipsos) or have regular geometric patterns (crystal shrubs) and to calcite (Thermopylae), or can alternate between calcium crystalline calcite fans (ray-crystal crusts, [33]). Usually carbonate minerals and other mineral phase (e.g. iron-rich in Edipsos, the shrubs have regular geometric patterns travertines, Ilia). Usually the laminas can be distinguished (crystal shrubs) and create layers (Fig. 7). These shrubs through eye observation and consist of yellow-grey and

553 Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece

Figure 10. Laminated travertine. (A) Calcitic laminated travertine with an abundance of fenestral-type porosity common Figure 9. Different types of shrub-like forms from Edipsos samples. throughout the area of Thermopylae. (B), (C), (D), (E) (A) Sample with shrub-like forms, developed over the Different types of aragonitic laminated travertine from black laminae. (B) Sample with layers of crystal shrub-like Edipsos. forms separated by laminae composed of micritic sized material. (C) – (F) SEM photomicrographs presenting shrub-like forms. in some cases, the laminas can be distinguished through eye observation (Fig. 11D). These parts consist of ex- white colored layers or black and white colored layers or tensively flattened rhombohedral crystals of calcite and orange-brown colored layers, which can reach a maximum hexagonal prismatic crystals of aragonite (Fig. 11E). of 1 mm thickness. Their magnified view shows fine scale vii) Pisoliths (Fig. 12). Nearby to a recently self-bunged laminae of a few tens of micrometers (Fig. 10D, 10E, 10F). hot-water drill in Edipsos, a calcitic deposit with pisoliths was found. This specific deposit is brittle with white color vi) Spicular types (Fig. 11) develop near hot springs, usu- pisoliths. The pisoliths are loosely connected with each ally at the edge of the pathway of hot water. Spicular other and can be easily separated by hand. Their usual lithotypes are, in most cases, siliceous [46, 47]. The most size is approximately 5 mm. In some pisoliths, there are, characteristic examples of this type were found in Edip- as a nucleus, small fragments of other travertines. In some sos and Ilia, where the iron concentration of the water other pisoliths, no foreign nucleus was found. They are is higher than at the other hot springs (Edipsos up to composed of well-developed radiating aragonite needles 1200 µg/L, Ilia up to 11000 µg/L, [32]). At the edge of the (Fig. 12B) and some crystals of halite. Between the arag- pathway of hot water the travertine part, which is usually onite needles sometimes crystals of calcite are trapped. beneath the surface of the hot water, is iron-rich and de- The cement between the pisoliths consists mainly of cal- velops spicular lithotypes having a red-brown color. The cite less aragonite, gypsum and halite. part of the travertine, which is above the hot water, is Ca- viii) Framework (Fig. 13) is a new type of newly formed rich and presents spicular and (or) botryoid shapes, having travertine deposit identified in Thermopylae and only to a white-yellow color (Fig. 11). The spiculars range from one site, in a channel used by hot water near the hot 0.2 cm to 0.5 cm in thickness and up to 1 cm in length. Af- spring. Framework lithotype consists of randomly posi- ter detailed study by XRD and SEM it was found that the tioned and interrelated cylindrical bars. These travertine Ca-rich parts consist of shrubs and, in addition to calcite bars give the image of a hollow stockwork. They look like and aragonite, they sometimes have crystals of halite and grey “corrals” and they are hard to break. Their usual size gypsum. Fe-rich parts present lamination lithotypes and, is approximately 0.7 cm in diameter and up to 5 cm length.

554 C. Kanellopoulos

Figure 13. Framework type travertines from Thermopylae. (A) Framework type travertine with high porosity from Ther- mopylae. (B) Cores of the cylindrical bars are pine needles. (C), (D) are SEM photomicrographs. (E) Cross- section at a cylindrical bar, the hollow center is where the pine needle stands. (D) The ﬁrst zone created around the pine needle presents forms similar to those of created by bacteria calciﬁcation process.

Figure 11. Lithotypes created at rims, in the pathway of hot water near the spring in Edipsos. (A) Overview of the hot times when two bars are too close, they tended to unite. spring and the pathway of hot water. (B) The edge of the pathway with the two phases of travertine. (C) Spicular In these cases the diameter of the new bar is subsequently sample from the edge of the pathway. (D) Section of the bigger. sample from the edge of the pathway of hot water showing clearly two phases. The reddish color phase created under the surface of the hot water is iron-rich, while the 5.4. Characteristics of active Fe-rich traver- white color area created above the surface of hot water is Ca-rich. (E) SEM photomicrographs of spicular struc- tine deposit ture (iron-rich part). As it was mentioned before, in Ilia, a newly formed iron- rich travertine deposit [32] covers a small area (Fig. 2A). It is laminated and creates botryoid structures. Both the iron-rich (reddish brown, metallic color) and carbonate- rich parts (light-colored) show a layered appearance and the thickness of the layers reaches a maximum of 1 mm (Fig. 14A- 14C). A magnified view of the iron-rich parts shows fine scale laminae of an iron mineral that alternates with aragonite-rich laminae at intervals of a few tens of micrometers (up to 100 µm). Figure 12. Pisolithic deposit from Edipsos. (A) Sample from pisolithic deposit. (B) SEM photomicrograph from the Through Scanning Electron Microscope (SEM) and micro- surface of one pisolith. It is composed of well-developed probe analysis, we proved that the altered laminas con- radiating aragonite needles. tain different mineral phases. The Ca-rich regions (light- colored layers) typically have Ca 32-35%, Fe 1-6%, Si 0.5- 1%, As 0-1% (Table 3), while the Fe-rich regions (reddish All of them contain, as a nucleus, pine needles from pine brown or metallic colored layers) show a large reduction trees standing near the deposition area, indicating high in Ca and a corresponding increase of Fe, followed by Si deposition rate. Around each nucleus, zones of calcite de- and As, with a smaller increase of their concentrations. velop (Fig. 13C). The first zone created around the pine Specifically, the Fe-rich regions typically have Ca 2-3%, needle presents structures similar to those created by a Fe 38-39%, Si 5-7%, and As 2-4% (Table 5). Figure 15 il- bacterial calcification process (Fig. 13D). Many times, a lustrates the concentrations of each element in areas that nucleus used more than one pine needle or some other present this phenomenon.

555 Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece

Figure 14. Travertines from Ilia. (A) Iron-rich travertine with botryoid form. (B) Cross section at iron-rich botryoid travertine. At the base of the sample lamination also can be seen. (C) Lamination type with iron-rich zones inside.

Studying these areas, it was proven that the Ca-rich regions in most of the cases consisted of aragonite crystals while the Fe-rich regions consisted of an amorphous hy- Figure 15. Picture (A) is a back-scattered electron image (BSEI) of drous ferric oxyhydroxide mineral phase, probably ferrihy- Fe-rich laminated travertine from Ilia. Pictures (B)-(D) are false color BSEI results of mapping, displaying the drite (5Fe2O39H2O). The amorphous hydrous ferric oxyhy- distribution of Fe (red), Ca (green) and Si (blue). Picture droxide mineral phase occurs as spherical particles up to (E) is an advanced false color BSEI result of the combi- 6 µm in diameter (Fig. 16A) and the aragonite as radiating nation of the pictures (B)-(D). aggregation of long and broad needles (Fig. 16B). Some- times, inside the laminas, shrubs-like forms can be observed (Fig. 17). Takashima and Kano [48] and Takashima et al. [36] found laminated iron-rich travertine with ferrihydrite, at hot springs deposits in the Shionoha region of Southwest Japan. They prove that, responsible for the precipitation of the ferrihydrite, are species of genus Siderooxidans.

Figure 16. SEM photomicrograph of Fe-rich travertines from Ilia. (A) The amorphous hydrous ferric oxyhydroxide mineral 6. Discussion phase, which occurs as spherical particles. (B) Detail image of the transition from the iron-rich laminae (amorphous hydrous ferric oxyhydroxide mineral phase) to the For this study, newly formed travertines, which were found Ca-rich laminae (fan-shaped radiating arrays are crys- to precipitate around hot springs in Northern Euboea tals of aragonite). (Edipsos and Ilia) and Eastern Central Greece (Thermopy- lae) were collected and analysed. In that material, a large variety of lithotypes and rare mineral forms of aragonite to create hexagonal prisms, which many times appear as and calcite were identiﬁed. Edipsos and Thermopylae are radial spheres (Fig. 5A) or fan-shaped radiating needles probably the biggest active travertine-forming systems in (Fig. 9B, 9C), while calcite usually creates rhombohedral Greece, while Ilia is a smaller one. Also some of the data crystals. The rare form of Gothic arch bars was also iden- recorded during this study suggest possible organic con- tiﬁed (Fig. 5A). trols on carbonate precipitation in the studied hot springs. From the mineralogical study it was found that the pre- The studied travertine deposits are composed of two cal- dominant phase of the travertines in Euboea was arag- cium carbonate polymorphs (i.e. aragonite and calcite), onite, while in Thermopylae it was calcite. The ex- which, in some cases, coexist (Table 2). Aragonite tends act conditions that favor aragonite precipitation at one

556 C. Kanellopoulos

Table 5. Representative microanalysis of amorphous hydrous ferric oxyhydroxide, possible ferrihydrite (5Fe2O39H2O, in element %).

Area Edipsos Ilia Sample EOT-16-R HL-1-C HL-1-R HL-M-2 HL-M-3 Lithotype Laminated and spicular Laminated Analysis M28 M32 Z42 Z43 D36 A21 B38 C29 C33 Si - 4.71 9.03 7.56 7.82 6.37 6.88 5.64 4.67 Fe 43.86 41.44 33.00 37.30 38.24 38.34 40.30 34.86 39.49 Ca 1.03 2.98 3.14 2.28 1.25 3.12 1.89 2.55 1.60 As - - - 0.95 2.08 2.92 2.14 3.64 5.19 Cl - 0.27 - 0.27 - - - - -

Total 44.89 49.4 45.17 48.36 49.39 50.75 51.21 46.69 50.95

Atoms 2 2 2 2 2 2 2 2 2

Si - 0.1691 0.2920 0.2348 0.2376 0.1915 0.2043 0.1848 0.1429 Fe 1.9502 1.4965 1.2833 1.3935 1.3972 1.3861 1.4395 1.3739 1.4539 Ca 0.0498 0.1500 0.1328 0.0926 0.0497 0.1227 0.0734 0.1093 0.0641 As - - - 0.0243 0.0520 0.0722 0.0523 0.0982 0.1307 Cl - 0.0154 - 0.0078 - - - - -

precipitate, regardless of the fluid composition and calcite would form if the water is rich in Ca and cooler than 40◦C. Fouke et al. [14] also showed that if the water temperature is above 44◦C, aragonite forms. The Sr content in Thermopylae hydrothermal fluid reaches 11900 µg/L and in travertines formed in Thermopy- lae, this reaches 2160 mg/kg [32], with the predominant phase as calcite. The Sr content in Euboea is notice- Figure 17. Back-scattered electron images (BSEI) of Fe-rich laminated travertines from Ilia. Black and white BSEI show- ably higher. In Edipsos, the Sr in hydrothermal fluid ing areas with lamination, at which different laminae reaches 17400 µg/L and in travertines formed in Edip- (zones) have different average atomic weights. Light areas have a higher average atomic weight (Fe-rich) than sos, it reaches 3960 mg/kg. In Ilia, the hydrothermal the dark areas (Ca-rich). At picture (B) shrubs can be fluid reaches 29900 µg/L and, in travertines formed in observed. Ilia, it reaches 4260 mg/kg [32]. In these two areas, which have higher Sr content, the predominant phase is aragonite. Similar cases have been presented by other studies. time and calcite at another are unclear. Previous stud- Ishigami and Suzuki [50] point out a strong positive corre- ies [7, 14, 25] show that the main factors controlling the lation between Sr content and the proportion of aragonite precipitation of calcite and aragonite can be: tempera- in Japanese travertines. Malesani and Vannucchi [51] sug- ture [8, 14, 25, 44, 49], the Sr content [50, 51], (Mg/Ca) gest that a high level of Sr in hydrothermal fluid favors ratio [25, 52], pCO [38], rate of CO degassing [43] and 2 2 the deposition of aragonite. precipitation rate [53, 54]. In our case the temperature in Thermopylae hot springs (predominant phase calcite) The travertine deposits developed in hot springs with a ranges from 33 to 40◦C, while the temperature in Eu- high concentration of iron (e.g. Ilia), containing the amor- boea hot springs (predominant phase aragonite) ranges phous hydrous ferric oxyhydroxide mineral phase, proba- from 43 to 82◦C (Table 1). The formation of aragonite bly ferrihydrite (5Fe2O39H2O, Fig. 6, Tables 2, 5), which, from high-temperature waters is not surprising given that along with aragonite, are the main mineral phases. This amorphous hydrous ferric oxyhydroxide mineral phase aragonite is the CaCO3 polymorph that commonly forms around springs, where the temperature ranges from 40◦C usually occurs as spherical particles (Fig. 16A). to 60◦C (8, 14, 25, 43, 44, 49, 55). Folk [55] observed that The chemical composition of calcium carbonate mineral if the water temperature is above 40◦C, aragonite would phases varies from area to area, depending on the chem-

557 Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece

ical composition of the hydrothermal fluid. Probably the 1. Around the hot springs of Euboea, which have tem- most characteristic example of this is the newly formed peratures of 43 to 82◦C and high Sr content (Edip- iron-rich thermogenic travertine in Ilia. This travertine sos hot springs up to 17400 µg/L, and Ilia hot deposit is created by the precipitation of the local hot spring, 29900 µg/L), the predominant phase of the spring water which has high concentration of elements travertines is aragonite. In the hot spring of Ther- such as Fe up to 11000 µg/L, As up to 84 µg/L, Si up to mopylae, which has a lower temperature of 33 to 69200 µg/L, Sr up to 29900 µg/L, Na up to 7300 mg/L 40◦C and lower Sr content (11900 µg/L), the pre- and Cl up to 12700 mg/L [32]. Therefore, respectively, the dominant phase of the travertines is calcite. calcium carbonate mineral phases from Ilia, in addition to Ca, C, and O contain Fe and/or As and/or Si and/or S 2. The travertine deposits developed in hot springs and/or Sr and/or Na and/or Cl (Table 3). with high concentration of iron (e.g. Ilia), containing as their main mineral phase an amorphous hydrous In the studied travertines, except for the calcium carbon- ferric oxyhydroxide mineral, probably ferrihydrite ate minerals identified, other mineral phases were found (5Fe O 9H O), along with aragonite. to be present, usually in the form of very small crystals, 2 3 2 which are trapped within the pores of the travertine de- 3. The chemical composition of calcium carbonate posits [32]. The most characteristic example, in Edipsos, mineral phases varies from area to area, depend- is the existence of halite crystals (Table 2) at the rim of ing on the chemical compassion of the hydrothermal open pores or trapped inside the now closed pores of the fluids. travertine. The formation of halite can be explained on the basis of the chemical composition of the hydrothermal 4. Except for the calcium carbonate minerals other fluids, which are rich in Na (Edipsos 8400-11150 mg/L) mineral phases were identified to be present, usu- and Cl (Edipsos 13300-21100 mg/L) [32]. ally in the form of very small crystals, which are The lithotypes that were found were of great variety, espe- trapped within the pores of the travertine deposits. cially in Edipsos. More specifically, in the studied areas, eight main newly formed travertine lithotypes were iden- 5. In the areas that were studied, eight main newly tified. Some of them are common (i.e. crystalline crust), formed travertine lithotypes were identified (crys- while some others are rare ones (i.e. rafts, foam types, talline crusts, rafts, foam types, shrubs, lamination, shrubs, lamination), and a new lithotype was identified spicular types, pisoliths, framework). which is named framework. So many lithotypes have been recorded to coexist usually in large travertine systems, 6. A new lithotype in Thermopylae was identified, e.g. Mammoth hot springs, Yellowstone National Park in which is named framework. It consists of cylindrical USA, Rapolano Terme, Italy. bars randomly positioned. All of them contain, as a nucleus, pine needles from the pine trees, which The framework lithotype identified in Thermopylae con- stand near the deposition area, indicative of the sists of cylindrical bars randomly positioned and interre- high deposition rate. lated. All of them contain, as a nucleus, pine needles from the pine trees, which stand near the deposition area, in- 7. Some of the lithotypes and crystal forms (lami- dicative of the high deposition rate. Around each nucleus, nation, shrubs etc), along with field observations zones of calcite develop (Fig. 13C). (e.g. cyanobacteria and/or algae growths at the Signs of biological processes were detected both directly bottom of the terraces) suggest possible inorganic (during the sampling growths of cyanobacteria and/or al- and organic controls on carbonate precipitation in gae in the travertines, which were observed many times) the studied systems. and indirectly (lithotypes and crystal forms), suggesting possible inorganic and organic controls on carbonate precipitation in the studied systems. References

[1] Mitchell R.S., Dictionary of Rocks, New York (Van 7. Conclusions Nostrand), 1985 [2] Whitten D.A., Brooks J.V.R., The Penguin Dictionary The study of the newly formed thermogenic travertine de- of Geology, London (Penguin), 1972 posits in Northern Euboea (Edipsos and Ilia) and in East- [3] Riding R., Classiﬁcation of microbial carbonates. In: ern Central Greece (Thermopylae) has led to the following R. Riding (Ed.), Calcareous Algae and Stromatolites, conclusions: Berlin (Springer-Verlag), 1991, 21–51

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