1 Origin and palaeo-environmental significance of the Berrazales carbonate spring 1 deposit, North of Gran Canaria Island, Spain 2 Jon Camuera a, Ana M. Alonso-Zarza a,b, Álvaro Rodríguez-Berriguete a,b, Alejandro 3 Rodríguez-González c 4 a Dpto. Petrología y Geoquímica, Facultad de Ciencias Geológicas. Universidad 5 Complutense de Madrid. José Antonio Novais 12, 28040 Madrid, Spain 6 b Instituto de Geociencas (CSIC, UCM), José Antonio Nováis 12, 28040 Madrid, Spain 7 c Dpto. Física GEOVOL, Campus de Tafira, Universidad de Las Palmas de Gran 8 Canaria, 35017 Las Palmas de Gran Canaria, Spain 9 * Corresponding Author’s telephone number and email: 913944915 / 10 jcamuera@gmail.com 11 12 ABSTRACT 13 The Berrazales carbonate spring deposit is a small outcrop constituted mainly by 14 cascade-like geometries. Four main facies have been identified: Fibrous dense 15 macrocrystalline formed by rapid degassing under high-flow conditions; Framestones 16 of coated plant molds formed in moderate energy flow favoured by the presence of 17 biogenic support; Micrite/Microsparite are primary precipitates in which crystalline 18 aggregates nucleated on organic filaments and/or EPS; Banded micrite-coarse 19 crystalline were the result of alternating physical-chemically and biologically induced 20 precipitation in areas of varying flow-velocities. Most facies underwent different 21 degrees of micritization processes. Micrite is distributed as thin lines penetrating the 22 crystals, as irregular patches or as micrite layers. In the first case organic filaments 23 penetrate crystals, suggesting that micritization is mainly biogenically driven. In the 24 latter cases micritization is caused mostly by partial dissolution. Microbe participation in 25 *Manuscript Click here to download Manuscript: Camuera Berrazales Manuscript Revised.doc Click here to view linked References 2 micrite formation increased micrite MgCO3 content in comparison with coarse 26 crystalline facies. 27 Isotopic analyses show positive δ13C values (+2.63 and +4.29‰ VPDB) and negative 28 δ18O (-5.65 and -4.48‰ VPDB) values. Positive δ13C values clearly indicate fluids of 29 thermal volcanogenic origin. 30 The Berrazales spring deposit studied here very probably is a small part of a larger 31 carbonate building that was largely eroded by fluvial incision. Calculations of spring 32 water temperature give a range from 20ºC to 35ºC, characteristic of a cold to warm 33 spring favouring precipitation of calcite and important biogenic activity (framestones). 34 Although the study deposit has textural characteristics of tufas, provide that the CO2 35 sourced from deep fluids, it should be consider as thermogene travertine, being one 36 more example of the difficulty of using those terms for ancient sedimentary deposits. 37 Carbonate springs deposits, very rare in the Canary Islands, are good archives of 38 recent volcanic activity, fluvial processes and vegetation regimes prevailing in the 39 islands in recent times. 40 Keywords: carbonate spring deposit; travertine facies; Canary Islands; microbes; stable 41 isotopes; volcanic setting. 42 43 1. Introduction 44 Calcareous spring deposits have been reported in various volcanic settings, such as in 45 the hot-spot of Yellowstone (Fouke, 2011), in the Bogoria and Turkana lakes of the 46 African Rift (Jones and Renaut, 1996; Renaut and Jones, 1997) and in arc-islands or 47 compressive systems as in Japan (Nishiwaka et al., 2012). Other calcareous spring 48 deposits are located along extensional fractures, such as the well-known Pamukkale-49 Karahayit travertines in Turkey (Hancock et al., 1999; Özkul, 2005), the Tivoli area 50 (Gandin and Capezzuoli, 2014) or the Euganean geothermal field (Pola et al., 2014) in 51 3 Italy. The large hydrocarbon reservoir of the South-Atlantic Pre-salt also contains facies 52 similar to carbonate spring deposits (Terra et al., 2010). In spite of increasing interest in 53 the study of these deposits there is not yet a consensus on how to interpret many of 54 their facies, nor on the role of biogenic versus abiogenic processes in their formation or 55 on their classification (Ford and Pedley, 1996; Pentecost, 2005; Gandin and 56 Capezzuoli, 2008; Gandin and Capezzuoli, 2014). Lack of consensus continues 57 regarding calcareous spring deposits and also fluvial carbonates with regard to the use 58 of terms travertine and tufa. Originally, travertine has been applied to compact rocks 59 used for building construction material, whereas tufa usually denotes a softer more 60 friable deposit (Viles and Pentecost, 2008). Even so, recently these terms have been 61 scientifically redefined by some authors as Capezzuoli et al., (2014). Thus, travertine is 62 defined for non-marine carbonates formed from hydrothermal-sourced waters, 63 associated with tectonically active areas (and high geothermal heat flux) and 64 characterized mainly by high depositional rates, low porosity, regular bedding and fine 65 laminations, and an inorganic crystalline fabric. In contrast, the tufa is generally 66 produced from meteoric water at ambient temperature and characterized by low 67 depositional rates, high porosity and high content of microphytes and macrophytes 68 (Capezzuoli et al., 2014, Table 1). Temperature of water feeding the spring is other 69 classification criteria, although in cases it is difficult to apply to ancient deposits. Two 70 main types of waters may feed springs: 1) organic CO2-rich and low temperature 71 waters (generally lower than 20ºC) coming from the soil and groundwater form 72 meteogene travertines, which have negative δ13C (-12 to -2‰ PDB) values; 2) δ13C 73 values of thermogene travertines, sourced from hot to warm waters (generally higher 74 than 30ºC) coming from the interaction between host rock and CO2 rich fluids at depth, 75 vary between -2 to +10‰ PDB (Kele et al., 2011; Capezzuoli et al,. 2014). Mineralogy, 76 facies and microfacies of calcareous spring deposits are controlled by a set of 77 environmental parameters such as: water chemical composition and temperature, rate 78 CO2 degassing, saturation levels and calcite deposition rate, macro and microbial 79 4 activity or the presence of some inhibitors (Talbot, 1990; Jones and Renaut, 2010; Guo 80 and Chafetz, 2014; Sun et al., 2014). This makes spring deposits good palaeo-81 environmental archives (Andrews, 2006; Anzalone et al., 2007; Keppel et al., 2012; 82 Gradziński et al., 2013; Gradziński et al., 2014). 83 In the Canary Islands carbonate spring deposits are very scarce (Demény et al., 2010, 84 Alonso-Zarza et al., 2012; Rodríguez-Berriguete, 2012). In this paper we study the 85 Berrazales spring deposit, located in Gran Canaria Island. Our aims are to unravel: a) 86 the thermal-volcanic influence in the formation of carbonate spring deposits in volcanic 87 settings, b) the role of biogenic versus abiogenic processes and their interrelation 88 during and after crystalline growth and, c) water physicochemical conditions 89 (temperature, pH, chemistry, etc.) controlling the formation of the deposits. Our 90 conclusions can be an aid to the understanding of the processes and the main controls 91 involved in the formation of travertines in volcanic settings and their palaeo-92 environmental and palaeo-hydrological significance. 93 94 2. Geographical and geological setting 95 The Canary Islands (Spain) are located off the NW African coast, between 29º 25’ and 96 27º 37’ N and 18º 10’ and 13º 20’ W, developed over the Jurassic oceanic lithosphere 97 as a result of the eastward movement of the African plate over a mantle hotspot (Holik 98 et al., 1991; Carracedo et al., 1998; Carracedo et al., 2002). Similar to other intra-plate 99 volcanic islands, the Canarian archipelago displays the hotspot volcanic stages of 100 evolution: juvenile (shield), volcanic quiescence and rejuvenated stage. Gran Canaria, 101 actually in an advanced rejuvenated stage, is a nearly circular island located at the 102 centre of the Canarian archipelago. A dense radial network of deep ravines 103 (“barrancos”, the local toponomy) dissects the island, forming a rugged topography. 104 The sub-aerial development of Gran Canaria records a juvenile stage (ca. 14.5–8.0 105 Ma), a volcanic quiescent stage (ca. 8.0–5.5 Ma) and a rejuvenated stage (ca. 5.5 Ma 106 5 to present) including the Roque Nublo stratovolcano and the Post-Roque Nublo 107 volcanism (Pérez-Torrado et al., 1995; Carracedo et al., 2002; Guillou et al., 2004; 108 Aulinas et al., 2010). The most recent Post-Roque Nublo volcanism, Holocene in age, 109 created a monogenetic volcanic field with at least 24 vents. The eruptive style is mainly 110 strombolian with formation of small scoria cones and lava flows, mostly with aá 111 morphologies (Rodríguez-González et al., 2009; Rodríguez-González et al., 2012). The 112 Holocene vulcanism has a strong control on the development of the few carbonate 113 spring deposits have been studied in Gran Canaria. One of these deposit is Azuaje 114 travertine described by Rodríguez-Berriguete et al. (2012) located 9 km north-east of 115 the study area. 116 The carbonate deposits studied are located above the stratigraphic contact between 117 scoria cone and lava flow of the Berrazales eruption (Fig. 1A), in the upper part of 118 Barranco Los Ríos (Fig. 1B). The lava flow is classified as basanite (Rodríguez-119 González et al., 2009). Holocene lava flows were emplaced at the bottom of the 120 ravines, with little erosive incision and draining towards the coast (Rodríguez-González 121 et al., 2009; Rodríguez-González et al., 2012). This eruption is stratigraphically related 122 with Jabalobos (dated by 14C at 2,760 ± 60 BP) and Fagajesto (dated by 14C at 3,030 ± 123 90 BP) eruptions (Rodríguez-González et al., 2009; Aulinas et al., 2010). 124 125 3. Methods 126 Samples of the Berrazales outcrop were studied using conventional petrological, 127 mineralogical and geochemical analyses. Twenty six samples were chosen for 128 conventional optical petrographic study in thin sections. Fragile thin sections were 129 impregnated with epoxy resin. 130 Mineralogical semi-quantitative composition of all samples was determined by X-ray 131 powder diffraction (XRD) using a Philips PW-1710 with CuKα at 40 KV and 30 mA. 132 6 MgCO3 mole percent is measured from d-spacing of calcite crystal lattice, which was 133 determined by the variation of 2Ө value of the principal calcite peak of the X-ray 134 diffractograms (Goldsmith et al., 1961; Tucker, 1988; Scholle and Ulmer-Scholle, 2003; 135 Ries et al., 2008). 136 The texture and components studied in 12 gold-coated samples were determined using 137 a JEOL JSM 6400 scanning electron microscope on the Research Support Centre 138 (CAI) of Geological Techniques of UCM (Madrid, Spain), working at 20kV with a 139 resolution of 35Å. Secondary electron and backscattering detectors were used together 140 with an X-ray detector system to obtain semi-quantitative compositions. For the study it 141 was also necessary to use a FEI INSPECT (5350 NE Dawson Creek Drive Hillsboro, 142 Oregon 97124, USA) of the Museo Nacional de Ciencias Naturales (Madrid, Spain), 143 operating with high vacuum mode (0.08 to 0.60 torr) with conductive samples to be 144 studied with both the large field detector (LFD) and backscatter detector (BSED-145 detector electron backscatter). SEM resolution at high vacuum was 3.0 nm at 30 kV 146 (SE), 10 nm at 3 kV (SE), and 4.0 nm at 30 kV (BSE). The accelerating voltage was 147 20-30 kV, high vacuum 0.45 torr, working distance of 10 mm. 148 The δ13C and δ18O values from 21 selected powdered samples were analysed at the 149 Scientific and Technical Survey in Barcelona University (Spain). Samples were 150 obtained with a drill and reacted with 100% phosphoric acid at 70ºC for 3 minutes. CO2 151 was extracted using a Thermo Finnigan Carbonate Kiel Device III isotopic analyzer with 152 a Thermo Finnigan MAT-252 spectrometer, according to the McCrea (1950) method. 153 δ13C and δ18O values, corrected using the NBS-19 standard and with an analytical 154 precision of ± 0.02‰ for δ13C and 0.03‰ for δ18O, are expressed in parts per thousand 155 (‰) referred to VPDB standard. 156 157 4. Results 158 7 4.1. Outcrop features of the Berrazales carbonate deposit 159 Berrazales carbonate deposit is a small outcrop approximately 6-7 m long, located 160 between volcanic cinder cones and Holocene lava materials. The outcrop has three 161 sectors: the eastern sector consists of cascade morphologies dipping to the east; the 162 western sector dips to the west; in the central sector the cascades are vertical. In the 163 eastern side the cascade geometries include large molds of tree trunks, one with a 164 diameter larger than 50 cm. 165 Individual carbonate cascade bodies, of a maximum height of 3 m and width of about 166 0.5-1.5 m, are composed of various vertical to oblique irregular centimeter-thick beds 167 (Fig. 2A, B). 168 169 4.2. Facies and microfacies: description and interpretation 170 171 4.2.1. Fibrous dense macrocrystalline facies 172 Description 173 Fibrous dense macrocrystalline facies, 1.5-2.0 cm thick bands of fibrous pale calcite 174 crystals, 1.0-1.5 cm long and length-width ratio >10:1 (Fig. 3A) have intercalations of 175 micritic and more porous laminae. Fibrous crystals nucleate and grow on sub-176 horizontal surfaces or on plant molds and have branching feather or dendrite 177 morphologies (Jones and Kahle, 1986; Jones and Kahle, 1993; Guo and Riding, 1992; 178 Jones et al., 2000; Kele et al., 2011). Sometimes feather or dendritic crystals appear 179 growing from a small filament (>300 μm long and around 12 μm thick) (Janssen et al., 180 1999; Gradziński, 2010) (Fig. 3B). Thin light-brown laminae (2-15 μm thick) are 181 included within the feather crystals. Also brownish-black darker laminae (10-15 μm 182 thick) separate dendritic crystalline bands (Fig. 3A). Above those laminae there are 183 8 small inclusions of triangular microsparite crystals inside large fibrous crystals (Freytet 184 and Verrecchia, 1999). Both light-brown and brownish-black sheets are curved and 185 acquire the upper surface morphology of dendrites. Terminations of fibrous crystals are 186 micritized (Fig. 3C, D) by microbes. Microbial filaments also penetrate coarse crystals 187 generating microborings (Fig. 3D, E) and parallel tubular porosity (Fig. 3F). 188 189 Interpretation 190 These crystalline facies appear to be the product of rapid precipitation from 191 supersatured water with respect to calcite due to rapid CO2 degassing under 192 disequilibrium conditions (Jones et al., 2005). In particular, calcite branching feathers or 193 dendrites have been described in areas of rapid growth (Jones and Kahle, 1986) due to 194 high-flow conditions (~2 m/s) (Okumura et al., 2012) favouring rapid CO2 loss. Thin 195 light-brown laminae alternating within feathers are the result of temporal variations in 196 precipitation, probably caused by rhythmic increases-decreases in diverse atomic 197 element content, such as Fe, probably reflecting recurrent annual growth cycles (Jones 198 et al., 2005; Jones and Renaut, 2008). Brownish-black laminae indicate stages of 199 interrupted crystal feather growth, due to variations in water geochemistry (presence of 200 undersaturated waters, low flow rates, microbial activity, etc.). Even so, the presence of 201 organic matter as the origin for brownish-black laminae cannot be ruled out, as 202 described by Freytet and Verrecchia (1999). Connected circular microborings are due 203 to the activity of microbes, such as cyanobacteria (Radtke and Golubic, 2011; Okumura 204 et al., 2012) or fungi (Calvet, 1982; Golubic et al., 2005) which penetrate, dissolve and 205 micritize calcite crystals. 206 207 4.2.2. Framestone facies 208 Description 209 9 Framestone is a porous macrocrystalline facies mostly composed of subparallel coated 210 plant molds 1-3 cm long and 0.5-8 mm in diameter (Fig. 4A). As in fibrous dense 211 macrocrystalline facies, small fibrous crystals (<3 mm long) are arranged perpendicular 212 to molds, forming fans (~3 mm) and including thin light-brown lamination (2-15 μm 213 thick) (Fig. 4B). The top surfaces of fans are covered by a dark-brown irregular micritic 214 mass (<0.2 mm thick). Micrite is also distributed between large fibrous crystals. Note 215 that plants molds have also well-defined parallel structure (Fig. 4C). 216 217 Interpretation 218 Vegetal molds provided nuclei for the precipitation of crystalline fans. Similar but larger 219 fans described on Pancura Pitu’s travertine (Centra Java, Indonesia) by Okumura et al. 220 (2012) were interpreted as having been precipitated under fast-flow conditions (~2 221 m/s). In our case flow velocities were probably lower than 2 m/s, as indicated by the 222 smaller size of fans and by the presence of plant molds, whose preservation would 223 have been inhibited under very high energy water (Okumura et al., 2012). Dark-brown 224 micritic masses are formed by the breakdown of coarse calcite crystals by abiogenic or 225 biogenic processes (Kobluk and Risk, 1977; Calvet, 1982; Jones and Kahle, 1995; 226 Martín-García et al., 2009). Even so, lack of biogenic features, such as filaments or 227 cyanobacterial microborings, suggest that dark micrite masses were formed by 228 abiogenic processes. 229 230 4.2.3. Micrite-coarse banded crystalline facies 231 Description 232 Micrite-coarse banded crystalline facies consist of palisade calcite crystals (up to 1 mm 233 long) sub-perpendicular to substrate. Crystals include very thin (2-10 μm) reddish-234 translucent microlaminae and dark-micritic laminae (Fig. 4D). Redish-translucent 235 10 microlaminae are laterally very uniform and regular whereas dark-micritic ones are 236 more irregular. V-shaped morphologies of both laminae are governed by the 237 morphology of crystal edges. Sometimes the laminae penetrate crystal edges. Dark 238 micritic laminae are amalgamated and contain very small filaments (<0.1 mm long) in 239 contact with the external surface. 240 241 Interpretation 242 The lack of any biogenic features in the palisadic crystals suggests that purely 243 physicochemical processes mainly governed crystal formation (Riding, 2008). The thin 244 reddish translucent microlaminae are similar to those described in the afore-mentioned 245 fibrous dense macrocrystalline facies, indicating cyclic changes in chemical, physical 246 and/or environmental conditions (Valero-Garcés et al., 2001) or even diurnal cycles of 247 microbial activities (Okumura et al., 2013a; Okumura et al., 2013b). Dark micritic 248 laminae within the palisade crystals are probably formed when calcite crystals come 249 into contact with undersaturated fluids with respect to CaCO3 (Jones and Kahle, 1995) 250 as also described in coarse crystalline speleothems (Martín-García et al., 2009), or due 251 to the presence of very small concentrations of organic matter (Pedley, 1992; 252 Gradziński, 2010). Small filaments on external surfaces suggest that biological 253 micritization of those dark-micritic laminae cannot be ruled out. 254 255 4.2.4. Micrite/Microsparitic facies 256 Description 257 Micrite (<4 μm) / Microsparitic (4-100 μm) facies are either homogeneous or banded. 258 Homogeneous microfacies are composed of micrite/microsparitic masses which 259 include crystalline aggregates of pale calcite crystals, arranged on thin organic 260 filaments (~700 μm long and <10 μm thick). Transversally, these aggregates have 261 11 spherulitic morphologies (Fig. 5A). Banded microfacies consist of an alternation of: a) 262 Microsparitic bands containing crystalline fans (~500 μm) (Fig. 5B); b) Dendrolitic fabric 263 (Perri et al., 2012) composed of filamentous cyanobacteria (500-800 μm long) arranged 264 vertically and calcified by sparite crystals (around 100-200 μm long) (Fig. 5C, D) with a 265 length-width ratio of 3:1; c) Dark micritic layers around 0.2 mm thick; d) Irregular porous 266 sheets (>0.5 mm thick) with semi-circular pores (0.5 mm to 1.5 cm across), making the 267 rock significantly porous. Some pores are filled by light-translucent bladed sparitic 268 crystals (around 100 μm long and 25 μm thick) arranged as gravitational, meniscus and 269 also as isopachous cements. These facies also contain not-mineralized exopolymeric 270 substances (EPS) (Fig. 5E, F) from microbial activity. 271 272 Interpretation 273 Lack of dissolution features of crystalline aggregates and absence of any primary fabric 274 substitution suggest that micrite/microsparite is a primary precipitate. Crystalline 275 aggregates probably nucleated on organic filaments which provided a site for calcium 276 carbonate nucleation (Pentecost, 2005). Several studies have linked the formation of 277 similar spherulites with microbial activity, which generated a favourable 278 microenvironment for Ca2+ and Mg2+ concentration and calcium carbonate precipitation 279 (Castanier et al., 1989; Buczynski and Chafetz, 1991). Similar processes led to both 280 the formation of crystalline fans, as the result of initial calcite nucleation on biogenic 281 structures within the micrite, and subsequent growth by purely physicochemical 282 processes (CO2 degassing, evaporation…) (Jones and Renaut, 2010). However, 283 organic nuclei are not always preserved (Guo and Riding, 1992), because bacteria and 284 cyanobacteria may be completely destroyed within hours by crystal growth (Krumbein 285 et al., 1977). 286 Dark micritic layers probably represent the precipitation of micrite on extracellular 287 polymeric substances (EPS) (Chacón et al., 2006) in association with cyanobacteria 288 12 and biological processes (Perri et al., 2012). EPS can be partially decomposed by 289 aerobic heterotrophic bacteria, inducing CaCO3 precipitation (Dupraz et al., 2004; 290 Gautret et al., 2004; Decho et al., 2005). The result is the calcification of the EPS 291 biofilm by micritic crystals (Turner and Jones, 2005; Okumura et al., 2013b). 292 Irregular porous sheets may result from dissolution of micrite precipitated on EPS or 293 from organic matter degradation (Perri et al., 2012). Gravitational and meniscus 294 cements consist of bladed crystals, suggesting that samples were subject to both 295 vadose and phreatic post-depositional processes. 296 297 4.3. Diagenetic features 298 The main diagenetic processes that influence the final aspect of Berrazales travertine 299 are micritization, dissolution and cementation. 300 Micritization consists of partial or total substitution of coarse calcite crystals by a mass 301 of micritic/microsparitic calcite crystals (2-15 μm). There are two types of micritization. 302 The first type affected some specific bands and the topmost fibrous feather crystals of 303 fibrous dense macrocristalline facies. Bands less than 1 cm thick are composed of 304 irregular micrite patches alternating with non-micritized fibrous calcite crystals (Fig. 6A). 305 Besides, tops of fibrous feather and dendrite crystals are also perforated by a biogenic 306 network (Fig. 6B) composed of thin microbial filaments (Fig. 6C), suggesting a biogenic 307 origin for micritization (Radtke and Golubic, 2011; Okumura et al., 2012). Microespar is 308 considered an intermediate product between coarse calcite and micrite. 309 The second type of micritization consists of thin micritic laminae (2-15 μm) separating 310 large crystal formations, mainly in micrite-coarse banded crystalline facies and in 311 fibrous dense macrocrystalline facies. Lack of biogenic features in framestone facies 312 and the fact that micrite does not penetrate in large crystals suggests that micrite 313 formation is due to inorganic physicochemical changes, probably caused by 314 13 undersatured water inflow or variations in environmental conditions (Jones and Kahle, 315 1995; Martín-García et al., 2009). 316 Dissolution processes also play an important role in micritic/microsparitic samples, 317 forming irregular and non-continuous, fenestral-like porosities. Dissolution may be due 318 to undersatured calcite water input (Martín-García et al., 2009) and/or due to the 319 degradation of microbial organic matter. 320 Cements occur in micrite/microsparitic facies either as bladed calcite crystals (80-150 321 μm long) covering the whole surface of the pore or as meniscus and gravitational 322 cements, indicating that cementation occurred in both vadose and phreatic 323 environments. 324 325 4.4. Mineralogy and isotope geochemistry 326 Samples are mainly (proportions higher than 95%) composed of Low Magnesium 327 Calcite (LMC) along with minor traces of phyllosilicates (< 5%). Content of MgCO3 in 328 most samples varies between 2% and 5%, except in sample BER-17 which has two 329 calcite peaks corresponding to two calcite phases with 4% and 11% in moles of MgCO3 330 (Table 1). In general, higher Mg contents (4-11% in moles of MgCO3) are in 331 micrite/microsparitic facies. Macrocrystalline facies (fibrous dense macrocrystalline 332 facies and framestone facies) contain between 0% and 3% in moles of MgCO3 333 whereas micrite-coarse banded crystalline facies lack magnesium (Table 1). 334 Isotopic values obtained from different facies show only slight variations in δ13C and in 335 δ18O, probably due to the small size of the outcrop and absence of fractionation 336 between water and mineral phase (HCO3 -). All samples have positive (+2.63 and 337 +4.29‰ VPDB) δ13C and negative (-5.65 and -4.48‰ VPDB) δ18O values (Fig. 7A, B), 338 with a correlation coefficient of 0.59. The lightest values of δ18O correspond to the 339 macrocrystalline samples while heaviest ones are found in micritic facies, which are 340 14 also enriched in Mg. Some micritized bands in macrocrystalline facies show an 341 increase in δ18O relative to non-micritized ones. Changes between different facies in 342 δ13C show smaller variations. 343 344 5. Discussion 345 5.1. Facies types, biogenic versus abiogenic processes and palaeo-environmental 346 setting 347 The small Berrazales deposit, one of the few carbonate deposits found in Gran Canaria 348 Island, outcrops in Los Rios Valley, formed after the last volcanic event around 2,700 – 349 3,100 years ago, surely in relation with volcanic eruptions occurred in Jabalobos and 350 Fagajesto (Fig. 1A). Its exceptional situation on a recent lava flow deposit, along with 351 its cascade morphology, strongly suggests formation from spring waters, similar to 352 nearby Azuaje travertine (Rodríguez-Berriguete et al., 2012). 353 Facies indicate different conditions for calcite precipitation. Fibrous dense 354 macrocrystalline facies precipitated during rapid CO2 degassing (Jones et al., 2005), 355 favouring the rapid growth of fibrous branching feather or dendrite crystals (Jones and 356 Kahle, 1986; Okumura et al., 2012). Vegetal molds, stems and microbial filaments act 357 as support and nuclei for calcite precipitation. In framestone facies, the absence of 358 reworking and preservation of molds in live position suggest that water-flow velocity 359 was not higher than <2 m/s (Okumura et al., 2012), allowing growth and later 360 calcification of vegetal molds. In contrast, primary micrite precipitated in a calm water 361 environment highly saturated in CaCO3 (Jones and Kahle, 1995). 362 It is difficult in these deposits to distinguish the role of biogenic from abiogenic 363 processes in the formation of the various facies. In most cases both processes acted 364 together. For example, the formation of fibrous feather crystals faithfully reflects the 365 interaction of biogenic and abiogenic processes and denote changing of crystallization 366 15 rates of calcite. In a first stage, microbial filaments (Fig. 8A) act as templates for small 367 calcite crystal (up to 100 μm long) nucleation (Fig. 3B; Fig. 5A, C, D; Fig. 8B). Organic 368 filaments provided a favourable site for calcite nucleation (Pentecost, 2005; Gradziński, 369 2010) and a good microenvironment for Ca2+ and Mg2+ concentration (Castanier et al., 370 1989; Buczynski and Chafetz, 1991), although the slow crystal growth allows filaments 371 not to be completely entombed. In contrast, during a second stage, crystallization rate 372 is too fast for microbial community and physicochemical precipitation prevails. Thus, 373 the rapid growth of calcite, principally due to the rapid abiogenic CO2 degassing, 374 enables the development of large branching feathers or dendrites (Fig, 3A; Fig. 8C). In 375 a final stage, large fibrous crystals are infected by microbes (fungi or cyanobacteria) 376 (Fig. 3E and Fig. 6C), which penetrate them causing partial micritization (Fig. 3C, D; 377 Fig. 6A, B; Fig. 8D) (Radtke and Golubic, 2011; Okumura et al., 2012). These microbial 378 colonization indicate a diminishing growth rate of crystals or their completely cessation. 379 On the contrary, framestone facies underwent abiogenic micritization by dissolution 380 caused by undersatured water inflow (Fig. 4B) (Jones and Kahle, 1995; Martín-García 381 et al., 2009). 382 A more clearly biogenic influence is seen in the formation of micrite/microsparite with 383 higher MgCO3 due to the replacement of exopolymeric substances (EPS) by high 384 magnesium calcite (HMC) (Dupraz et al., 2004; Dupraz and Visscher, 2005). The 385 degradation of EPS by heterotrophic bacteria (Decho et al, 2005) liberates Ca+2, Mg+2 386 and HCO3- which were bound to EPS, increasing cation concentration in solution and 387 allowing micritic Mg-calcite precipitation (Dupraz et al., 2004, Okumura et al., 2013a). 388 389 5.2 Discussion of stable isotope data 390 The δ13C and δ18O values in continental carbonate deposits are mainly controlled by 391 the isotopic composition of water, temperature of formation, pH of the solution, calcite 392 deposition rate, saturation degree, diagenesis, microbial activity, evaporation, CO2 393 16 outgassing and fractionation between water and mineral phase (Talbot, 1990; Valero-394 Garcés et al., 2001; Dietzel et al., 2009; Guo and Chafetz, 2014; Sun et al., 2014). 395 Positive δ13C values indicate “deep-source” fluids in relation with volcanic activity or 396 decarbonation (Pentecost, 2005). Considering the volcanic area of the study, δ13C 397 positive values of Berrazales may suggest that this continental deposit was precipitated 398 from thermal waters which were saturated with heavy CO2 from bedrock (Özkul et al., 399 2014), influenced by significant contribution of volcanic-hydrothermal CO2. Carbonate 400 spring deposits precipitated from heavy hydrothermal CO2 waters, have typical values 401 ranging between -2 and +10‰ PDB (Pentecost, 1995; Pentecost, 2005; Viles and 402 Pentecost, 2008). The Berrazales deposit is in this range, with similar δ13C values to 403 the Azuaje travertine described by Rodríguez-Berriguete et al. (2012) and to other 404 travertines of the world (Fig. 9). These deposits can be classified as thermogene 405 deposits following Pentecost (2005) classification. δ13C values in hot-water travertine 406 deposits are mainly controlled by physical (CO2 degassing or water temperature) and 407 microbial processes (Kele et al., 2008; García-del-Cura et al., 2014). On the other 408 hand, changes in δ18O values can also reflect the effect of evaporation, temperature of 409 water and, at the time of precipitation, degassing of CO2 and/or groundwater inflow 410 (Chafetz and Lawrence, 1994; Valero-Garcés et al., 2001; Kele et al., 2008). In 411 Berrazales deposit changes in evaporation, water temperature or degassing were 412 probably not significant because the small size of the deposit did not allow water to re-413 equilibrate. CO2 removal and subsequent variations in δ13C values in Berrazales 414 travertine could occur due to biological processes, such as respiration or microbial 415 photosynthesis (García-del-Cura et al., 2014). Microbes consumed preferably the 416 lighter carbon isotope, enriching water and the precipitated calcite in the heaviest 417 isotope, as shown by heavy δ13C values and high Mg content on micrite/microsparite, 418 precipitated under the influence of EPS. 419 A temperature of 23ºC of the water of the abandoned spa, placed 570 m downflow of 420 the Berrazales deposit (Garralda-Iribarren, 1952) and the δ18O values of the crystalline 421 17 crust (sample BER-11) were used to obtain the possible original δ18O signal of the 422 water precipitating this crust. A value of -3.33‰ V-SMOW was obtained for equilibrium 423 precipitation using Kim and O’Neil (1997) equation, whereas the value for 424 disequilibrium conditions, obtained through Halas and Wolacewicz, (1982) equation, 425 according to Kele et al. (2011), was 5.5‰ V-SMOW. These values, which are in the 426 range of the reported from Gran Canaria Island, -2 to -6‰, (Gonfiantini et al, 1976; 427 Gasparini et al., 1990), were used to calculate the probable temperature of precipitation 428 of the other facies of the deposit (Table 2A, B). 429 Temperatures obtained under equilibrium conditions and δ18Ow = -5.5‰ (9.4 to 14.8ºC) 430 are very low compared to reported groundwater temperatures for Gran Canaria Island 431 of 14-35ºC (Gonfiantini et al., 1976; Custodio et al., 1987; Gasparini et al., 1990). The 432 later are similar to temperature calculations under disequilibrium (19.7-35.4ºC) and fit 433 well with the measured value of 23ºC (Garralda-Iribarren, 1952). Cooling trends in 434 surface needed to pass from, at least, 23ºC (at spring) to 9ºC (downflow) are also 435 highly improbable at this altitude on Gran Canaria Island, suggesting that if calcite 436 precipitated from waters with δ18Ow = -5.5‰ (or slightly higher values) at about 23ºC, it 437 occurred under disequilibrium conditions (Table 2B). The relatively narrow values of 438 temperatures obtained for the different facies indicate that the probable vent (crystalline 439 crust) and cascade deposits (the other facies) were very near as shown by the small 440 size of the Berrazales outcrop. However, these calculations may be not that precise as 441 desirable, as for example there may be 18O isotope shift effects and temperature could 442 have changed along the life of the spring. 443 δ13C value from the same sample has been used to obtain the original signal of δ13CCO2 444 (Table 3). The values obtained using Mook et al. (1974) HCO3 - - CO2(g) equilibrium 445 equation (used here for disequilibrium precipitation) are similar to those of fluids 446 derived from tectono-metamorphic processes (Hoefs, 1997; Minissale, 2004). 447 However, they are in the range of those reported in literature as volcanic originated 448 fluids from Canary Islands, which are usually higher than -4‰ (Albert et al., 1986; 449 18 Custodio et al., 1987; Gasparini et al., 1990). The calculated values using Bottinga 450 (1968) and Panichi and Tongiorgi (1976) equations (Table 3) fit well with the typical 451 range of volcanic CO2, -5 to -7‰ PDB (Hoefs, 1997), which are slightly lighter than 452 those of the volcanic CO2. Therefore, only deep source for CO2 can be invoked here 453 through isotopic calculations, and no precisions between tectono-metamorphic derived 454 or volcanic derived CO2 can be assessed. However, giving the overall setting, the CO2 455 was probably of volcanic origin. 456 457 6. Conclusions 458 The Berrazales carbonate building is characterized mainly by cascade morphologies, 459 with different types of facies, such as (1) Fibrous dense macrocrystalline facies, (2) 460 Framestone facies, (3) Micrite/microsparitic facies and (4) Micrite-coarse banded 461 crystalline facies. Fibrous feather or dendrite crystals grew from the interaction 462 between biogenic and abiogenic processes, starting from crystalline nucleation on 463 microbial filaments to the last phase of rapid physicochemical crystal growth (CO2 464 degassing) under rapid water flow and disequilibrium conditions. In Framestone facies, 465 presence of parallel plant molds suggests that water energy could not be very high (<2 466 m/s), preserving plants apparently in live positions. On the contrary, primary micrite 467 precipitated during lower flow and calmer waters probably in relation with EPS. Finally, 468 the thin banded facies indicate chemical, physical or environmental changes during 469 carbonate precipitation. Micritization processes are also under both biogenic (crystal 470 perforations by microbial filaments) and abiogenic (undersatured water inflow, changes 471 in environmental conditions) processes. 472 Calcite is the principal mineral making up the travertine, generally with low Mg 473 contents, except micritic samples formed from microbial activities and EPS formation. 474 19 Positive δ13C values (+2.63 and +4.29‰ VPDB) found in thermogene travertines 475 indicate formation from “deep source” fluids, in this volcanic area probably related with 476 thermal waters and volcanic activity. Whereas, negative δ18O values (-5.65 and -4.48‰ 477 VPDB) reflect a meteoric water signal. Thus, temperatures calculated (20-35ºC), heavy 478 δ13C values and the situation of the Berrazales deposit indicate that the CO2 was very 479 probably of thermal origin and sourced from or below the Earth`s crust. 480 As are other thermogene spring deposits in Gran Canaria, Berrazales carbonate 481 deposit is an excellent example of the interplay between volcanic and sedimentary 482 processes, due to its location on previous volcanic materials deposited 2,700 – 3,100 483 years ago. The described deposit is a particular case study of a carbonate spring which 484 from the textural point of view can be classified as tufa (meteogene travertine) but from 485 the geochemical point of view ( 13C) as travertine (thermogene travertine). 486 The study of the Berrazales deposit has provided valuable information about thermal 487 water temperature, volcanic CO2 contribution to thermal water springs, the role of 488 abiogenic versus biogenic processes in its formation and the presence of fresh water 489 streams in the island. At present very few examples of carbonate springs have been 490 described in the Canary Islands as their preservation in erosive regimes of volcanic 491 settings is exceptional. 492 493 7. Acknowledgements 494 We acknowledge A. Meléndez, M.C. Cabrera and J.F. Pérez-Torrado for his assistance 495 during the field work. 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Blackwell Publishing Ltd., 769 Oxford, pp. 173-199. 770 771 30 772 Figure captions 773 774 Fig. 1. (A) Location of the Berrazales area, in the north-west of Gran Canaria Island. 775 (B) Situation of the Berrazales Carbonate Deposit (BCD) between volcanic materials in 776 the Barranco Los Ríos. 777 778 Fig. 2. (A) Photograph of the main part of Berrazales deposit. (B) Sketch from 779 Photograph A, showing the dominance of cascade facies and location of the samples. 780 Two molds of trunks can be observed (red arrows). The carbonate deposits overlie the 781 volcanic lava. 782 783 Fig. 3. Photographs of Fibrous dense macrocrystalline facies. (A) Fibrous feather or 784 dendrite crystals separated by dark micritic laminae. (B) Microbial filaments (arrows) 785 encased within feather dendrite crystals. (C) Tops of crystalline feathers are micritized 786 (arrows). (D) Detailed view of the red rectangle of C, showing microbial filaments 787 penetrating large crystals and generating circular microborings (arrow). (E) SEM image 788 of circular microbial filament microborings. (F) SEM image showing parallel porosity 789 created by penetration of a network of microbial filaments. 790 791 Fig. 4. (A) Framestone facies composed of parallel plant molds coated with calcite. (B) 792 Plant mold surrounded by coarse calcite crystals. (C) SEM image showing parallel 793 structure of plants molds. (D) Micrite-coarse crystalline banded facies with reddish-794 translucent (1) and dark-micritic (2) laminae. Arrows show V-shaped morphologies, 795 located between the edges of palisade crystals. 796 31 797 Fig.5. Photographs of Micrite/microsparitic facies. (A) Crystalline microsparitic 798 aggregates growing from organic filaments within a micritic mass. (B) Microsparitic 799 band composed of crystalline fans in a porous micritic mass. (C) Dendrolitic fabric 800 composed of calcified cyanobacterial filaments. (D) SEM image of a calcified filament 801 in transverse view. Arrow indicates the central hole left by dissolved filament. (E) 802 Exopolymeric substances (EPS) (arrows) intercalated within calcite crystals and 803 cyanobacterial filaments (f). (F) Detail of EPS (arrows). 804 805 Fig. 6. (A) Calcite crystals penetrated by a network of microbes. (B) Fibrous feather 806 calcite crystals intercalated with altered micritic masses. (C) Detail of calcite crystals 807 penetrated and altered by thin microbial filaments (arrows). 808 809 Fig. 7. Stable carbon and oxygen isotope composition of Berrazales carbonate deposit 810 samples according to: (A) facies and (B) Mg content. 811 812 Fig. 8. Growth phases of fibrous branching feather or dendrite morphologies. (A) 813 Microbial filament. (B) Sparite nucleating on biogenic support. (C) Abiogenic growth of 814 fibrous calcite crystals. (D) Perforation and micritization of fibrous calcite by microbes 815 (cyanobacteria or fungi). 816 817 Fig. 9. Stable isotope composition of some travertines and tufas from the world 818 including the data from this study. 819 820 32 Table 1. Berrazales carbonate deposit samples: type of facies; mineralogy; principal 821 calcite peak with the respective content of MgCO3; and stable isotope composition. 822 823 Table 2. Calculations of: δ18Ocalcite (‰, VSMOW); δ18Owater (‰, VSMOW); ΔHCO3–H2O; 824 and Temperature under disequilibrium and equilibrium conditions. (A) Calculated with 825 δ18Owater = -3.33‰ VSMOW. (B) Calculated with δ18Owater = -5.50‰ VSMOW. 826 827 Table 3. Calculation of the original δ13CCO2 from calculated temperatures of the 828 crystalline crust (BER-11) (see temperature in disequilibrium from Table 2A, B). 829 δ13CCO2 is calculated with equations of Mook et al. (1974), Panichi and Tongiorgi 830 (1976), and Bottinga (1968). 831 Fi gu re C lic k he re to d ow nl oa d hi gh re so lu tio n im ag e Fi gu re C lic k he re to d ow nl oa d hi gh re so lu tio n im ag e Figure Click here to download high resolution image Fi gu re C lic k he re to d ow nl oa d hi gh re so lu tio n im ag e Figure Click here to download high resolution image Figure Click here to download high resolution image Fi gu re C lic k he re to d ow nl oa d hi gh re so lu tio n im ag e Fi gu re C lic k he re to d ow nl oa d hi gh re so lu tio n im ag e Fi gu re C lic k he re to d ow nl oa d hi gh re so lu tio n im ag e % C al ci te % P hy llo si lic at es B ER -1 Fr am es to ne 10 0 * 29 .1 6 0 3. 67 -5 .2 5 B ER -2 M ic rit e- m ic ro es pa rit ic 10 0 * 29 .5 8 5 3. 15 -4 .8 0 B ER -3 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 6 2 2. 83 -5 .5 3 B ER -3 .1 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 8 2 2. 63 -5 .2 1 B ER -4 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 8 2 2. 69 -5 .5 7 B ER -5 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 6 2 3. 00 -5 .6 5 B ER -6 Fr am es to ne 10 0 * 29 .4 6 2 3. 24 -5 .2 3 B ER -7 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 8 2 3. 07 -5 .4 7 B ER -8 M ic rit e- m ic ro es pa rit ic 90 10 29 .5 4 4 3. 82 -4 .4 8 B ER -9 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 8 2 3. 30 -5 .1 1 B ER -1 0 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 4 2 3. 12 -5 .4 2 B ER -1 1 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 5 2 2. 79 -5 .2 1 B ER -1 1. 1 Fi br ou s de ns e m ac ro cr ys ta lli ne 10 0 * 29 .4 5 2 2. 84 -5 .2 4 B ER -1 2 M ic rit e- m ic ro es pa rit ic 90 10 29 .5 3 4. 29 -4 .8 6 B ER -1 3 Fr am es to ne 10 0 * 29 .5 3 3. 96 -5 .2 0 B ER -1 4 Fr am es to ne 10 0 * 29 .4 8 2 3. 75 -5 .1 8 B ER -1 5 M ic rit e- m ic ro es pa rit ic 10 0 * 29 .5 7 5 4. 15 -4 .6 6 B ER -1 7 M ic rit e- m ic ro es pa rit ic 10 0 * 29 .5 4 - 2 9. 77 4 - 1 1 3. 76 -4 .5 5 B ER -1 8 Fr am es to ne 10 0 * 29 .4 6 2 2. 85 -5 .2 4 B ER -1 8. 1 M ic rit e- m ic ro es pa rit ic 10 0 * 29 .5 4 4 3. 03 -4 .8 7 B ER -1 9 M ic rit e- m ic ro es pa rit ic 10 0 * 29 .5 8 5 3. 44 -4 .5 2 B ER -2 0 M ic rit e- co ar se b an de d cr ys ta lli ne 10 0 * 29 .3 1 0 3. 90 -4 .4 8 A st er is ks (* ) i nd ic at e th at th e pr op or tio n of p hy llo si lic at es is b el ow 5 % δ18 O ca lc ite (‰ , V PD B ) Sa m pl e Ty pe o f F ac ie s M in er al og y (S em i-q ua nt ita tiv e) Pr in ci pa l c al ci te pe ak (º 2Ө ) % M ol es M gC O 3 δ13 C ca lc ite (‰ , V PD B ) Ta bl e C lic k he re to d ow nl oa d Ta bl e: T ab le 1 .x ls Sa m pl e δ18 O ca lc ite (‰ ,V SM O W ) Δ H C O 3– H 2O T di se q. (ºC ) (1 ) T eq .(º C ) (2 ) δ18 O ca lc ite (‰ ,V SM O W ) Δ H C O 3– H 2O T di se q. (ºC ) (1 ) T eq .(º C ) (2 ) B ER -1 25 .1 3 28 .4 6 33 .3 23 .2 25 .1 3 30 .6 3 23 .2 13 .0 B ER -2 25 .5 9 28 .9 2 31 .1 20 .9 25 .5 9 31 .0 9 21 .1 10 .9 B ER -3 24 .8 4 28 .1 7 34 .8 24 .6 24 .8 4 30 .3 4 24 .5 14 .3 B ER -3 .1 25 .1 7 28 .5 0 33 .1 23 .0 25 .1 7 30 .6 7 23 .0 12 .8 B ER -4 24 .8 0 28 .1 3 34 .9 24 .8 24 .8 0 30 .3 0 24 .6 14 .5 B ER -5 24 .7 2 28 .0 5 35 .4 25 .2 24 .7 2 30 .2 2 25 .0 14 .8 B ER -6 25 .1 5 28 .4 8 33 .2 23 .1 25 .1 5 30 .6 5 23 .1 12 .9 B ER -7 24 .9 0 28 .2 3 34 .5 24 .3 24 .9 0 30 .4 0 24 .2 14 .0 B ER -8 25 .9 2 29 .2 5 29 .5 19 .4 25 .9 2 31 .4 2 19 .7 9. 4 B ER -9 25 .2 7 28 .6 0 32 .6 22 .5 25 .2 7 30 .7 7 22 .5 12 .3 B ER -1 0 24 .9 6 28 .2 9 34 .2 24 .0 24 .9 6 30 .4 6 23 .9 13 .8 B ER -1 1 25 .1 7 28 .5 0 33 .1 23 .0 25 .1 7 30 .6 7 23 .0 12 .8 B ER -1 1. 1 25 .1 4 28 .4 7 33 .3 23 .1 25 .1 4 30 .6 4 23 .1 12 .9 B ER -1 2 25 .5 3 28 .8 6 31 .4 21 .2 25 .5 3 31 .0 3 21 .4 11 .2 B ER -1 3 25 .1 9 28 .5 2 33 .0 22 .9 25 .1 9 30 .6 9 22 .9 12 .7 B ER -1 4 25 .2 0 28 .5 3 33 .0 22 .8 25 .2 0 30 .7 0 22 .8 12 .6 B ER -1 5 25 .7 4 29 .0 7 30 .4 20 .2 25 .7 4 31 .2 4 20 .5 10 .2 B ER -1 7 25 .8 5 29 .1 8 29 .8 19 .7 25 .8 5 31 .3 5 20 .0 9. 7 B ER -1 8 25 .1 4 28 .4 7 33 .3 23 .1 25 .1 4 30 .6 4 23 .1 12 .9 B ER -1 8. 1 25 .5 3 28 .8 6 31 .4 21 .2 25 .5 3 31 .0 3 21 .4 11 .2 B ER -1 9 25 .8 8 29 .2 1 29 .7 19 .6 25 .8 8 31 .3 8 19 .9 9. 6 B ER -2 0 25 .9 2 29 .2 5 29 .5 19 .3 25 .9 2 31 .4 2 19 .7 9. 4 (1 ) 1 03 ln α (H C O 3- – H 2O ) e q. ≈ 1 03 ln α (C aC O 3 – H 2O ) d is eq . = 2 .9 2 x 10 6 /T 2 – 2 .6 6 (H al as a nd W ol ac ew ic z, 1 98 2) (2 ) 1 03 ln α (C aC O 3 – H 2O ) = 1 8. 03 x 1 03 /T – 3 2. 42 (K im a nd O 'N ei l, 19 97 ) Ta bl e 2A Ta bl e 2B Ta bl e C lic k he re to d ow nl oa d Ta bl e: T ab le 2 A , B .x ls A ut ho r Eq ua tio n Te m pe ra tu re (º C ) δ13 C C O 2 (‰ , V PD B ) 33 -4 .3 1 23 -5 .3 8 33 -6 .5 8 23 -7 .9 5 B ot tin ga (1 96 8) 10 3 ln α c = -2 .4 91 2 + (7 .6 63 x 1 03 / T ) – (2 .9 88 0 x 10 6 / T 2 ) M oo k et a l. (1 97 4) 10 3 ln α (H C O 3- – C O 2( g) ) = 9 .5 52 x (1 03 /T ) - 2 4. 1 Pa ni ch i a nd T on gi or gi (1 97 6) δ13 C co 2( g) = 1 .2 x δ 13 C c - 1 0. 5 in de pe nd en t -7 .1 5 Ta bl e C lic k he re to d ow nl oa d Ta bl e: T ab le 3 .x ls