Geologica Romana 37 (2003-2004), 109-112
A NOTE ON THE TRAVERTINES OF SUIO, ROCCAMONFINA, WITH REFERENCE TO THEIR MICROBIAL COMMUNITIES AND GEOCHEMICAL ORIGINS
Allan Pentecost & Pietro Coletta
Department of Health and Life Sciences, King’s College London, Franklin Wilkins Building, 150 Stamford Street - London SE1
KEYWORDS: travertine, thermal, springs, Suio, algae, cyanobacteria.
INTRODUCTION
Deposits of calcium carbonate forming in springs and streams are termed travertine (Julia, 1983) and were exploited as a building material in Rome (lapis tiburti- nus of Vitruvius). Travertines are widespread in regions containing carbonate rocks and an abundant supply of water, and are well represented in Italy where at least 100 sites have been documented (Manfra et al., 1976;
Pentecost, 1995a). Deposition normally results from the equilibration of bicarbonate-rich groundwater with the atmosphere:
Ca2+2HCO3- CaCO3(travertine) + CO2+ H2O Aquatic plants colonise illuminated travertines and the unusual physico-chemical conditions result in a special- ist flora. Since plants also remove CO2during photosyn- thesis, they have often been implicated in travertine dep- osition (Ford & Pedley, 1992).
Most of the Italian sites are inactive but there is clear evidence of their association with Quaternary hot springs (Chafetz & Folk, 1984). Active sites are less common but appear throughout Italy, often in areas of recent tectonic activity (Pentecost, 1995b). An under- standing of modern travertine formation allows interpre- tation of older deposits and provides valuable insights into microbial mineralization in hot spring environments (Renaut & Jones, 2000).
Terme di Suio is situated on the Garigliano River, 20km SSE of Cassino and straddles Campania and Lazio. The site consists of 12 thermal springs aligned along two faults trending approximately NW and NE.
The faults separate a thick series of Mesozoic limestones and dolomites to the west from the leucite and alkali-tra- chyte lavas of Roccamonfina Volcano. Roccamonfina caldera is about 20 km in diameter, and was active 630- 53 ka (Caprano et al., 1992). The site was brought to our attention by Prof. R. Barbieri and the travertines do not appear to have been previously investigated, though the associated thermal waters are well known (D’Amore et
al., 1995, Duchi et al., 1995). Travertine is deposited at four springs as cascades or mounds and locally covered with colourful algae.
We aim here to provide a brief description of the Suio travertines, their geochemical origins and the associated photosynthetic microorganisms.
METHODS
Water samples were taken at four travertine-depositing spring vents in glass bottles and duplicate samples ana- lysed within 3hfor total CO2and pH. Alkalinity correc- tions for CO2were made for sulphide, borate and reac- tive-silicate. Major cations were determined on acid-pre- served samples using methods previously described (Pentecost, 1992). Stable carbon and oxygen isotope analyses were determined on SrCO3precipitated in situ from springwater using ammoniacal SrCl2. Free CO2 gas was also collected and adsorbed in a pure KOH solu- tion. Analyses were performed with a VG Optimer dual- inlet gas source mass spectrometer with external preci- sion ± 0.07‰ and are reported as VPDB. Algal samples and fresh travertines were preserved in CaCO3-saturated 1% glutaraldehyde and returned to the laboratory for examination.
RESULTS AND DISCUSSION Travertine setting and morphology
Water, gas and travertine sampling locations are shown in Fig.1. All sites were situated close to the Garigliano River and consisted of small mounds, slopes and cascade deposits. Travertine was deposited immedi- ately below thermal outfalls, all of which were artificial or modified for the provision of water for the Terme. The most extensive deposits occurred on the riverside below Terme Tomassi, consisting of a series of steep cascades 5m in total height. They were fed by intermittent efflu- ent at a temperature of ca. 30°C. The next largest is a travertine mound situated about 50 m west of Vasco degli Inferne. Water at 58°C issued from a well pipe at 9NN
ABSTRACT - The Suio travertines are deposited from CO2-rich thermal waters. Stable isotope analyses sug- gest the CO2is formed at depth, possibly as the result of contact metamorphism involving a carbonate rock. The travertines form small mounds and cascades and consist of poorly laminated equant calcite and calcite feather crystals. The photosynthetic microbial flora comprised 10 species of cyanobacteria and diatoms, mostly the cyanobacterium Phormidium laminosum. Several diatoms attain their known upper temperature limit on the travertine. A close relationship between travertine formation and algal growth was not observed at the sites.
about 1 l/sec and formed a travertine mound, 3 m high and 16 m wide, immediately below (Fig. 2). This loca- tion appeared to be nameless so we termed it CG Spring.
About 500m to the SE on the same side of the river is another piped source with water at 53°C forming traver- tine crusts in the water channel below. We named this site “AD spring”. A small quantity of travertine was also sampled from the sides of the hot water reservoirs at Terme Ciorra, 520 m south of Terme Tomassi. Travertine also occurred in the watercourse at Terme S. Egidio fur- ther north but we did not sample this site. At all sites the travertine was of high purity and consisted of calcite. At CG spring most of the calcite occurred as poorly lami- nated subhedral microspar (crystal diameter 20-30 µm) and irregular rhombohedra producing a massive, pow- dery fabric. Small vugs were surrounded by calcite scalenohedra. The mass included occasional vertically- arranged “feather crystals” 1.5 mm long (cfr. Fig. 5 in Guo & Riding, 1992). At Terme Tomassi the travertine forming along the side of a reservoir and consisted entirely of large feather crystals up to 5 mm long. The crystals were not closely associated with the overlying algal mats, which contained sparse irregular patches of
micrite.
Gas and Water Geochemistry
The thermal waters were highly mineralised and con- tained large quantities of dissolved CO2(Table 1). All springs contained traces of oxygen (resazurin positive) possibly from surface water contamination, along with H2S (ca 0.2 mmol/L). The chemical composition of these waters is similar to other thermal Italian springs such as the Viterbo group and Rapolano Terme near Siena which deposit much travertine (Guo & Riding, 1992). Previous measurements of CO2at Tomassi and Ciorra (D’Amore et al., 1995) gave values similar to those reported here, but their Ca values were higher than ours.
Stable isotope composition demonstrated enrichment of the travertine with 13C (δ13C 7.68-7.96 ‰). Similar enrichments are known from other Italian travertines such as those of Tivoli (Manfra et al., 1976). The CO2
gas emissions at Aqua Salamone and the Bridge site (Fig. 1) were also slightly enriched (δ13C + 0.59 ‰ and +0.96 ‰ respectively). Equilibrium fractionation of this gas with precipitated calcite should give a δ13C of ca.
+ 8 ‰ for the travertine, close to the observed values.
Carbonate rocks subjected to contact metamorphism undergo decarbonation leading to 13C enrichment of the resulting CO2 (Turi, 1986) and this has been used to explain the occurrence of 13C-enriched travertines throughout Italy. The same process may explain the Suio travertines although the δ13C of the source carbonate is unknown. If the CO2emissions at Aqua Salamone and Bridge result directly from decarbonation, the parent limestones must be slightly depleted in 13C over marine limestones, unless further water-rock interactions have occurred en route to the surface. Oxygen isotope compo- PENTECOST et al.
110 Geologica Romana 37 (2003-2004), 109-112
Fig.1 - Map of sampling sites and thermal springs/gas emissions (cir- cles) at Suio.
Fig. 2 - Detailed plan of the travertine mound at CG Spring, Suio, showing setting and distribution of the cyanobacterium Phormidium laminosum in relation to water temperature.
sitions of the travertine (Table 1) are more difficult to interpret due to probable water-CO2 exchange but the values are typical of other Italian travertines originating from thermal springs (Fritz, 1965; Manfra et al., 1976).
While Roccamonfina volcano does not appear to provide a magmatic contribution to the thermal springs at Suio (Duchi et al., 1995), deep faults exist along the course of the Garigliano River and most likely provide an easy passage to the surface for gases forming at depth.
Associated microorganisms
A limit flora occurred on the travertines (Table 2). The flora was dominated by a narrow (0.4-1.0 µm diameter) filamentous cyanobacterium Phormidium laminosum which occurred as highly coloured (deep green to orange) strata at the travertine surface. It formed blue- green strands in the hot flowing water at temperatures of 43-53°C but only became abundant when water temper- ature fell below 48°C. On cooler areas of the CG spring mound, where algae were kept moist by capillarity, the orange form became conspicuous (Fig. 2). This may be due to production of carotenoid UV-protective pigments in areas where growth is retarded by reduced water availability. P. laminosum is a well known hot-spring
cyanobacterium which is abundant on the Viterbo travertines (Pentecost, 1995c). The coccoid cyanobac- terium Synechocystis minuscula was abundant at Terme Tomassi. This organism has not been previously record- ed from travertine. Few diatoms occurred, the most abundant being Achnanthes minutissima and Nitzschia frustulum. The latter has been noted at the thermal springs of Carlsbad, Czech Republic (Sprenger, 1930) and at Yellowstone, Wyoming (Stockner, 1967). The occurrence of diatoms at 48°C is notable as few species have been previously found at this temperature, which is high for diatoms (Stockner, 1967). Overall, the flora was limited in extent with 10 species recorded, possibly the result of dissolved sulphide inhibiting the growth of other algae. In some travertines, a close association has been found with certain algae and the deposition of cal- cite (Viles & Goudie, 1990) but this was not observed at Suio, so the participation of algae in depositing the Suio travertines is unlikely to be significant.
ACKNOWLEDGEMENTS - We are grateful to the owners of Terme Ciorra and Terme Tomassi for permission to sample.
Thanks also to Dr. B. Spiro for undertaking the stable isotope analyses.
Genus/phylum species nomenclature CG spring 35°C
CG spring 44°C
CG spring 48°C
Terme Tomassi 30°C Cyanobacteria
Calothrix parietina Thuret X
Chroococcus helveticus Naeg. X X
Phormidium incrustatum (Naeg.) Gom. X
Phormidium laminosum Gom. XX XX XX XX
Schizothrix cf pulvinata (Kuetz.) Gom. X X
Synechocystis minuscula Woronich. XX
Diatoms*
Achnanthes minutissima Kuetz. 19 34 35 87
Navicula cf. pupula Kuetz. 11 2 3 8
Nitzschia frustulum (Kuetz.) Grunow 67 64 52 4
Nitzschia sp. 4
X scarce ; XX frequent
* Percent relative abundance based on 500 counts except CG where based on 100
Determinand AD spring CG spring Terme Ciorra Terme Tomassi
temperature °C 52.90 57.80 63.00 55.00
pH 6.41 6.48 6.78 6.55
TDIC* mmol/L 38.20 41.80 32.80 40.30
Ca mmol/L 4.13 6.66 4.29 5.16
Mg mmol/L 3.50 2.40 3.10 3.40
TDIC δ13C ‰ 7.68 7.96
TDIC δ18O ‰ -12.03 -11.37
*Total dissolved inorganic carbon
A NOTE ON THE TRAVERTINES OF SUIO, ... Geologica Romana 37 (2003-2004), 109-112 111
Tab.1 - Suio thermal spring chemistry.
Tab. 2 - Suio travertine: photosynthetic microorganisms.
PENTECOST et al.
112 Geologica Romana 37 (2003-2004), 109-112
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Accettato per la stampa: Marzo 2003
