Th dating of freshwater travertine from Middle Velino Valley (Central Italy): paleoclimatic and geological implications

Palaeogeography, Palaeoclimatology, Palaeoecology 184 (2002) 147^161 www.elsevier.com/locate/palaeo

U/Th dating of freshwater travertine from Middle Velino Valley (Central Italy): paleoclimatic and geological implications M. Soligo a , P. Tuccimei b; , R. Barberi c , M.C. Delitala b , E. Miccadei d , A. Taddeucci b a b

Dottorato di Ricerca in Geodinamica, Universita' ‘Roma Tre’, L.go S. Leonardo Murialdo 1, 00146 Rome, Italy Dipartimento di Scienze Geologiche, ‘Universita' Roma Tre’, L.go S. Leonardo Murialdo 1, 00146 Rome, Italy c Rilevatore CARG, Rome, Italy d Dipartimento di Scienze della Terra, Universita' degli Studi ‘G. d’Annunzio’ di Chieti, Via dei Vestini 31, 66013 Chieti Scalo (CH), Italy Received 18 May 2001; accepted 14 February 2002

Abstract Six travertine bodies outcropping along the Middle Velino Valley (Central Italy) have been studied and dated using the U/Th method in order to obtain new chronological constraints for the recent geological evolution of the area. The lithological and sedimentological characteristics of travertines have been described, showing that such deposits can be referred to waterfall, pool terraces and gentle slopes environment. Travertines have formed during warm periods and can be referred to marine oxygen isotope stages 5, 3 and 1. Travertine deposition seems to stop around 5 ka BP according to other European and Italian sites. Pollen stratigraphy and ostracod assemblages from the close sequence of Valle di Castiglione, characterized by the same climatic conditions of Velino Valley, have confirmed that periods of Velino Valley travertine deposition were effectively characterized by warm and wet climatic conditions. Seismic activity strongly active in the area since the Middle Pleistocene has deeply influenced the location and the discharge of springs which have deposited the travertines, influencing in turn the shape and size of travertine bodies. 6 2002 Elsevier Science B.V. All rights reserved. Keywords: U/Th dating; travertine; Velino Valley; Central Italy; warm periods; seismic activity

1. Introduction Recently travertine deposits have been considered as indicators of warm climatic phases in the

* Corresponding author. Tel.: +39-06-54888092/70; Fax: +39-06-54888201. E-mail address: [email protected] (P. Tuccimei).

continental environment (Pentecost, 1995; Frank et al., 2000; Horvatincic et al., 2000). Increased frequencies of travertine growth have been found in various European sites during interglacial periods (Pentecost, 1995; Maire, 1990), as already known about speleothems (Gascoyne et al., 1983; Maire, 1990). In order to verify such ¢ndings, travertines from the Middle Velino Valley (Central Italy) have been studied and dated using

0031-0182 / 02 / $ ^ see front matter 6 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 1 - 0 1 8 2 ( 0 2 ) 0 0 2 5 3 - 5

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the U/Th method. Holocene travertine deposits from other sites along the Central Apennines are already known (Calderoni et al., 1996), while the frequency of deposits from previous warm climatic periods is more scarcely documented in Italy. The travertines which have been taken into consideration formed as dams along the course of £uvial valley, taking origin from springs located along the NW^SE and E^W oriented border fault systems placed at the base of Reatini Mountains carbonate slopes and the Nuria-Velino Group. In some cases springs cannot be recognized close to travertine bodies and consequently

the dating of such deposits can help to obtain new chronological constraints for the formation of travertines and also improve the recent geomorphological and geological evolution of the area.

2. Geological setting and outcrops description Rieti basin is one of the largest intramountain depressions of Central Italy and, like other basins of Central Apennines, it is partially ¢lled with Upper Pliocene and Holocene continental sedimentary successions (Fig. 1).

Fig. 1. Simpli¢ed geological map of Central Apennines. (a) Continental successions (Pliocene^Holocene); (b) terrigenous marine successions (Pliocene^Holocene); (c) volcanic successions (Middle^Upper Pleistocene^Holocene); (d) marine terrigenous turbiditic successions (Upper Miocene); (e) undi¡erentiated carbonatic successions (Upper Trias^Middle Miocene); (f) thrust; (g) strike slip fault; (h) normal fault; (i) caldera rim; (l) study area. (TB) Tiber Basin; (NB) Norcia Basin; (LB) Leonessa Basin; (RB) Rieti Basin; (SVB) Salto Valley Basin; (AB) L’Aquila Basin; (ASB) Aterno-Subequano Basin; (FB) Fucino Basin; (SB) Sulmona Basin (after Bigi et al., 1990, simpli¢ed and redrawn).

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Its evolution began in the Upper Pliocene, following the distensive tectonic activity that, in this period, involved the Central Apennines (Cavinato and Parotto, 1990; Cavinato, 1993; Cavinato et al., 1989, 1994). In the ¢rst period, from the Upper Pliocene to the Lower Pleistocene, the evolution of the basin was guided by tectonic activity along a NNW^ SSE boundary fault system. In that period a thick continental sequence of alluvial fan, £uvial and lacustrine sediments was deposited, with a 450 m outcropping thickness (Bosi and Messina, 1992; Barberi and Cavinato, 1993; Cavinato, 1993). At the beginning of the Middle Pleistocene, a renewal of tectonic activity caused the collapse of the Northern portion of the basin, along E^W and NW^SE faults, forming the area of the present Rieti Plain. These faults cut o¡ the continental successions, lowering them towards the N and W with a maximum observable throw of 200^ 300 m (Fig. 2). A consequence of this tectonic activity was the heavy headward erosion of rivers that lead to the incision of the Velino, Turano, Salto Rivers and Ariana Stream valleys, cutting the Plio^Pleistocene successions and the carbonate bedrock (Cavinato, 1993). In that period, talus, alluvial fan, £uvial, lacustrine deposits and travertine bodies were deposited along the Velino Valley, giving rise to a complex sedimentary succession consisting of several depositional and erosional terraces located at different heights above the present £oodplain (Brunamonte et al., 1993; Carrara et al., 1995; Calderini et al., 1998; Michetti et al., 1995). Travertine deposits outcropping in this area created several bodies along the right bank of the Velino Valley. Several travertine deposits have been collected in four sites, located E of the city of Rieti. From W to E these localities are: Casa Colarieti (site 4); Villa Roselli (sites 1, 2 and 3); Cittaducale (site 5); Cotilia Power Plant (site 6). A brief description of the lithological characteristics and the sedimentation environments of travertines follows. In the area of Casa Colarieti travertines outcrop over an area of about 0.3 km2

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forming a terrace bounded, toward S and E, by a scarp 5^10 m above the £oodplain of the Velino River (Fig. 3a). These deposits are formed by smooth slope and terrace slope facies, built up by wedge-shaped travertine bodies (Fig. 3a), irregularly strati¢ed downward (to the S and the E) with lenses of interbedded calcareous phytoclastic sands. Waterfall facies, mostly made up of plant incrustations, are also present (Ferreri, 1985; D’Argenio and Ferreri, 1992; Brancaccio et al., 1992; Brunamonte et al., 1993; Carrara et al., 1995; Violante et al., 1996; Guo and Riding, 1999). In the sampling site there are also outcrops of lithoid travertines, where incrustations around plants can be recognized. The travertines are capped by lenses of soil covered, with an erosional contact, by £uvial conglomerates (Fig. 3b). The Villa Roselli travertines outcrop over an area of about 1 km2 , with a vertical outcropping thickness of about 50 m. In this site travertines are characterized by the presence of two sub-horizontal surfaces located at about 450 and 410 m above sea level (masl), about 50 and 10 m, respectively, above the £oodplain (Fig. 3a). The travertines are made up of calcareous phytoclastic sand beds, horizontal or slightly dipping towards the valley (to the S), with small interbedded phytohermal lenses of plant incrustations referable to palustrine and lacustrine environments, or massive phytohermal travertine of plant incrustations in waterfall facies. There are also levels of immature soil interbedded with the sandy facies at di¡erent stratigraphic levels (Fig. 3b). The Cittaducale travertines constitute a tabular body, with an area of about 0.5 km2 , and a thickness of about 5^10 m. These deposits form a wide terrace at a height of about 480 masl, about 75^ 80 m above the £oodplain (Fig. 3a). They are built up with well strati¢ed and laminated bodies, showing a wedge-shaped geometry and a slight but constant dip of strata toward the valley (to the S), referable to smooth slope facies. The travertines overlay alluvial fan conglomerates trough an unconformity, underlined by the presence of lenses of reddish soil containing volcanic materials. Moving toward the valley to the S there are phytoclastic sands and plant incrustations (Fig. 3b).

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Fig. 2. Geological sketch of Middle Velino Valley. Continental successions: (a) Holocene deposits; (b) travertine deposits (Middle Pleistocene^Holocene); (c) alluvial, lacustrine and slope deposits (Middle^Upper Pleistocene); (d) ultrama¢c lava £ow (Middle Pleistocene); (e) alluvial fan and £uvial deposits (Upper Pliocene^Lower Pleistocene). Marine successions: (f) turbiditic successions (Upper Miocene); (g) successions of Umbro^Sabina transition domain (Lias^Miocene); (h) successions of Latium^Abruzzi Carbonate platform domain (Lias^Miocene); (i) thrust; (l) normal fault; (m) study area.

The Cotilia Power Plant travertines outcrop mostly along a scarp of 5^10 m (about 15 m above the £oodplain), at the top of which there is a low inclined surface dipping toward the valley

to the S almost completely covered with eluvio^ colluvial deposits (red soils) (Fig. 3a). The facies are represented by plant incrustations, mostly present along the scarp that borders the outcrop

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Fig. 3. (a) Geological sketch of study area. Continental successions: (a) Holocene deposits; (b) travertine deposits (Middle Pleistocene^Holocene); (c) alluvial, lacustrine and slope deposits (Middle^Upper Pleistocene); (d) alluvial fan and £uvial deposits (Upper Pliocene^Lower Pleistocene). Marine successions: (e) successions of Umbro^Sabina transition domain (Lias^Miocene); (f) thrust; (g) normal fault. (b) Stratigraphic log of sampled sites: (a) phytohermal travertine; (b) phytoclastic travertine; (c) phytoclastic calcareous sands; (d) well strati¢ed and laminated travertine; (e) alluvial fan conglomerate; (f) paleosoil levels; (g) volcanic material; (h) sampled levels.

(Fig. 3b). In the inner part of the travertine the exposures are more isolated and made up of calcareous sands with phytohermal lenses.

3. Sampling and analytical methods Four sub-samples from each outcrop were sampled at the same stratigraphic level, with the exception of Cotilia Power Plant travertine, whose outcrop was so heavily covered by vegetation that

it was not possible to collect several coeval subsamples. Travertines were cut with a diamond saw in order to remove the altered parts and were then crushed and ultrasonically washed in deionized water. Fragments were also checked with a stereoscopic microscope to discard any recrystallized portions. About 20 g of sample was dissolved in suprapure 1 N nitric acid and ¢ltered to separate the leachates from the insoluble residue (about 2^ 3%). Few milliliters of hydrogen peroxide was added to the leachate and heated at 100‡C in or-

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Fig. 4. a, b, c, d and e report data of sub-samples from Villa Roselli (site 1), Villa Roselli (site 2), Villa Roselli (site 3), Casa Colarieti (site 4) and Cittaducale (site 5), respectively. Each ¢gure consist of two diagrams: (230 Th/232 Th) vs (234 U/232 Th) and (234 U/ 232 Th) vs (238 U/232 Th) whose slopes give respectively the (230 Th/234 U) and (234 U/238 U) activity ratios in the carbonate fractions.

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Fig. 4 (Continued).

der to destroy organic matter. Isotopic complexes of uranium and thorium were extracted according to the procedure described in Edwards et al. (1986) and alpha-counted using high resolution ion implanted Ortec silicon surface barrier detectors. The ages of travertines were calculated using the method described in Schwarcz and Latham (1989), the so-called L/L procedure, which uses the measurements of (230 Th/232 Th), (234 U/232 Th) and (238 U/232 Th) activity ratios on several coeval sub-samples in order to obtain the value of (230 Th/234 U) and (234 U/238 U) activity ratios in the pure carbonate fraction. Such values are respectively calculated from the slopes of the regression lines in the (230 Th/232 Th) vs (234 U/232 Th) and (234 U/232 Th) vs (238 U/232 Th) isochron plots reported in Fig. 4a^e. Calculations have been car-

ried out using ISOPLOT, a plotting and regression program for radiogenic-isotope data (Ludwig, 1994).

4. Results The isotopic data and the ages are reported in Table 1 and plotted in Fig. 4a^e. U concentrations of leachates ranged from 209 to 430 ppb (Table 1) and (234 U/238 U) activity ratios deducted for the carbonatic fraction of the travertines (see (234 U/232 Th) vs (238 U/232 Th) diagrams) ranged from 1.02 to 1.42 (Table 1). This latter value was found only for Casa Colarieti samples, whereas in all the others it ranged between 1.02 and 1.13. (230 Th/232 Th) activity ratios of the majority of

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Table 1 Isotope data and ages of Middle Velino Valley travertine from sites 1, 2, 3, 4, 5 and 6 Sample

Subsample

U

(230 Th/232 Th) (234 U/232 Th) (238 U/232 Th) (234 U/238 U)carb: (230 Th/234 U)carb: Age

(ppb) Villa Roselli site 1

1.1 1.2 1.3 Villa Roselli site 2 2.1 2.2 2.3 Villa Roselli site 3 3.1 3.2 3.3 3.4 Casa Colarieti site 4 4.1 4.2 4.3 Cittaducale site 5 5.1 5.2 5.3 5.4 Cotilia Power Plant 6.1 site 6

216 M 14 247 M 7 250 M 8 339 M 17 290 M 10 320 M 10 289 M 7 242 M 8 209 M 6 320 M 9 282 M 11 386 M 16 352 M 12 368 M 11 430 M 13 420 M 12 279 M 7 356 M 11

(yr) 0.88 M 0.04 0.96 M 0.05 1.61 M 0.11 1.21 M 0.06 1.22 M 0.07 1.02 M 0.04 1.25 M 0.06 1.03 M 0.05 1.15 M 0.09 1.69 M 0.11 7.50 M 0.41 11.26 M 0.98 16.34 M 1.74 19.8 M 1.7 32 M 3 7.84 M 0.44 10.34 M 0.92 22.1 M 2.2

4.15 M 0.12 8.6 M 0.24 15.11 M 0.37 6.84 M 0.17 7.66 M 0.24 4.92 M 0.13 7.68 M 0.25 7.82 M 0.28 11.25 M 0.31 20.79 M 0.62 15.81 M 0.41 23.83 M 0.59 37.83 M 1.01 26.49 M 0.57 52.02 M 1.3 11.53 M 0.28 15.9 M 0.41 ^

sub-samples are close to 1 (Table 1), justifying the use of a correction method for most of them. It is worth noting that in case of travertines from Casa Colarieti (site 4) and Cittaducale (site 5), the ages obtained from the isochrons agree within the limits of error with those that can be calculated from the purest sub-samples (those with the lowest proportion of detritic component and thus with the highest (230 Th/232 Th) activity ratios, respectively sub-samples 4.3 and 5.2 (Table 2)). Data points reported in Fig. 4a^e de¢ne good regression lines with MSWD (mean squared weighted deviates) values always lower than 1, demonstrating a low scattering of data. Travertine from Cotilia Power Plant deserves special attention. Although it has not been possible to gather

3.70 M 0.09 8.51 M 0.22 14.14 M 0.32 7.03 M 0.21 7.28 M 0.22 4.90 M 0.13 7.44 M 0.23 7.67 M 0.27 11.10 M 0.30 19.99 M 0.59 12.45 M 0.39 18.26 M 0.41 27.82 M 0.97 25.39 M 0.6 50.92 M 1.1 10.92 M 0.26 15.53 M 0.39 ^

1.05 M 0.06

0.07 M 0.02

7 900 M 2 300

1.04 M 0.16

0.08 M 0.03

9 100 M 3 500

1.04 M 0.02

0.05 M 0.01

5 300 M 1 100

1.42 M 0.03

0.42 M 0.02

57 500 M 5 300

1.02 M 0.02

0.65 M 0.06

113 600 M 18 000

1.13 M 0.03

0.59 M 0.02

94 800 M 5 000

several coeval sub-samples from the outcrop, a meaningful age has been directly calculated from the only collected sample, because it turned out to have a high (230 Th/232 Th) activity ratio (equal to 22) and consequently negligible detrital 230 Th (Table 1).

5. Discussion 5.1. Paleoclimatic implications Travertine deposition is correlated with warm and wet climatic conditions (Goudie et al., 1993; Sturchio et al., 1994; Pentecost, 1995; Frank et al., 2000; Horvatincic et al., 2000; Rihs et al.,

Table 2 Isotope data and ages of sub-samples 4.3 and 5.2, characterized by the highest (230 Th/232 Th) activity ratio Sample

Sub-sample

(230 Th/232 Th)

(234 U/238 U)

(230 Th/234 U)

Age (yr)

Casa Colarieti site 4 Cittaducale site 5

4.3 5.2

16.34 M 1.74 32 M 3

1.36 M 0.05 1.02 M 0.02

0.43 M 0.02 0.61 M 0.02

59 400 M 3 600 102 000 M 5 500

The ages obtained on these sub-samples agree within the limits of errors with the ages deduced from the corresponding isochron plots of Fig. 4d,e.

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2000). Freshwater travertines from the Middle Velino Valley seem to have the same climatic signi¢cance because the obtained ages fall within the warm periods evidenced in the marine paleoclimatic N18 O record (Martinson et al., 1987) as shown in Fig. 5 and also in the oxygen and carbon isotope records from a core drilled in the Mediterranean Sea (Pierre et al., 1999). Travertine from Cittaducale can be attributed within the limit of error to isotopic stages 5e or 5c, travertine from Cotilia Power Plant can be referred to isotopic stage 5c, samples from Casa Colarieti deposited during stage 3 and the travertines from Villa Roselli can be attributed to stage 1. Recently, Dramis et al. (1999) proposed a model to explain the mechanism of travertine deposition, pointing out the role played by the strong temperature di¡erence between the bedrock and the atmosphere at the beginning of warming phases. In this situation water percolates through the newly formed soils where the biological activity is intense acquiring higher CaCO3 dissolution capacity. In addition, the bedrock is still cold because of its low thermal conductivity and consequently the solubility of CO2 in circulating water is increased. When it emerges in a warm environment a rapid degassing occurs causing the deposition of travertines. Travertines investigated in

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the present paper cannot unequivocally be considered as deposited at the beginning of the warming phases because the errors associated to the ages are too large compared to the resolution of the oxygen isotopic record. According to Dramis et al. (1999), travertine formation may continue for a long time (up to thousands of years) until the temperature di¡erence between bedrock and the atmosphere becomes negligible. This model seems to ¢t with the decline of travertine deposition observed after the V^IV millennium BP for many travertines in Central Italy: Esino, Potenza and Chienti Valleys (Calderoni et al., 1996), and in other European sites : Southern France (Vaudour, 1994), Belgium (Gullentop and Mullenders, 1972) and Central Spain (Pentecost, 1995). The younger age (5300 M 1100 yr) found for travertines from Villa Roselli con¢rms the above mentioned data. It must be mentioned that the decline of travertine formation after 5000 yr BP has also been explained by the e¡ects of human impact on slopes for agricultural or pastoral use (Gullentop and Mullenders, 1972; Goudie, 1981). In particular, widespread forest clearing might have reduced the production of CO2 in soil and consequently the content of CaCO3 in percolating water. To corroborate what is found for Middle Veli-

Fig. 5. U/Th ages (black polygons) of travertines from Middle Velino Valley compared with the SPECMAP marine paleoclimatic N18 O record (after Martinson et al., 1987). The growth period of freshwater travertine coincides with marine N18 O stages 5, 3, 1.

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no Valley travertine, it is important to compare our record with others from South Europe. In Southern Germany (Stuttgart area) Frank et al. (2000) report the occurrence of travertine deposits referable to stage 5c, as Cittaducale and Cotilia Power Plant outcrops (this work). Travertines from Croatia, Krka River area, can also be referred to stage 5 (Horvatincic et al., 2000). The same authors also report other data relative to travertines from Plitvice Lakes area where two deposits have been dated at stage 5a and another at stage 5c. Pentecost (1995) and Hennig et al. (1983) report the presence of several Eemian and Holocene travertine deposits in di¡erent sites of France. Other Holocene deposits occur in Spain and in Bulgaria (Pentecost, 1995). These bodies are coeval with Villa Roselli travertines (this work). In conclusion, the formation of freshwater travertines provides information on the warm periods recorded in the continental environment. Such periods correspond to the analogous phases evidenced in the oxygen marine records and predicted by the insolation cycles (Lourens et al., 1996). Good correspondence can also be found with the warm periods in the paleoclimatic curve of Capotondi and Vigliotti (1999) obtained from a planktonic foraminifer assemblage in Late Quaternary sediments from the Western Mediterranean. 5.2. Comparison with other paleoclimatic proxies from Valle di Castiglione (Latium region) Pollen stratigraphy and ostracods assemblage studies performed in sites located in the vicinity of Velino Valley support the ¢ndings that the periods in which travertine deposition occurred were characterized by warm and wet climatic conditions. The most interesting sites are: Castiglione Valley, Lago Lungo, Ripa Sottile and others in the Latium region. The results from these studies will be compared with information coming from Middle Velino Valley travertines. Castiglione Valley is an ancient crater lake, arti¢cially dried out, belonging to the Alban Hills volcanic complex, about 20 km east of Rome, located in a climatic area comparable to the Ve-

lino Valley. A sediment core was drilled down to a depth of about 88 m and was the subject of a multidisciplinary study concerning the lithostratigraphy (Narcisi et al., 1992), geochronology and geochemistry (Alessio et al., 1986), fauna (Gliozzi and Mazzini, 1998) and fossil pollen (Follieri et al., 1989). The 14 C chronology, the annual lamination counting, the comparison between pollen diagrams and oxygen isotope curves and the synchronization with the precessional motion of the earth (Magri, 1989) indicate that the sequence is about 250 000 yr old. Pollen stratigraphy (Follieri et al., 1989) shows various vegetational phases distinguishable on the basis of the AP^NAP (arboreal pollen and nonarboreal pollen) diagram and by the total concentration diagram. Warm and wet periods are characterized by high percentages of arboreal pollen with respect to non-arboreal and by high total pollen concentration. In the time interval 130 ka BP to Present the following phases have been recognized: Eemian (129^115 ka), St Germain I (100^95 ka), St Germain II (88^81 ka), ‘pleni-glacial interstadials’ (64^39 ka) and Holocene (from 13.5 ka). Eemian is dominated by evergreen Mediterranean vegetation as Zelkova, Olea, Quercus, Ilex and Carpinus. The deposition of Cittaducale travertine (about 115 ka) can be attributed to this period. In St Germain I Fagus and Quercus are the main components of the forest. Carpinus and Ulmus are well represented. Cotilia Power Plant travertine (about 95 ka) can be ascribed to this period. No travertine deposition comparable to St Germain II occurred in Middle Velino Valley. Pleni-glacial interstadials cannot be considered a true forest phase, but deciduous and evergreen oaks and Fagus are present testifying the occurrence of short forest expansion. In this period the deposition of Casa Colarieti travertine (about 57 ka) occurred. Holocene is characterized by deciduous oaks, Corylus and Alnus. Around 5000 yr ago the wettest climatic condition of the Holocene occurred, accompanied by the rise of Fagus. About 3000 yr ago a decrease in humidity is evidenced (Alessio et

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al., 1986). Villa Roselli travertines belong to the Holocene. Ostracods assemblage studies performed on sediment cores from Valle di Castiglione (Gliozzi and Mazzini, 1998) have provided results comparable with the pollen stratigraphy. Before the Eemian the variations in the Ostracod associations do not show a signi¢cant relationship with climatic changes, while in the Eemian^Holocene interval (period of Middle Velino Valley travertine deposition) such correlation is evident. Di¡erent intervals have been recognized. Those connected with the age of Middle Velino Valley deposition will be discussed. An interval from 140 to 90 ka, corresponding with the Eemian^St Germain I interval (oxygen isotope stage 5e^5c), is characterized by an ostracod association suggesting a decrease in salinity of the waters probably due to abundant precipitation. In the interval from 60 to 26 ka (stage 3) some levels rich in low-salinity species have been studied, even if their occurrence could be ascribed to changes in water chemistry due to volcano-tectonic events. A last interval (from 17 ka) is characterized by a progressive decrease of aridity conditions leading to a more freshwater environment. Further studies on pollen stratigraphy (Follieri et al., 1995), ostracod assemblages (Calderoni et al., 1994; Ricci Lucchi et al., 2000) and lithostratigraphy (Narcisi et al., 1992) performed in Lago Lungo and Ripa Sottille sites, located in the Middle Velino Valley area, con¢rm the climatic information coming from the Valle di Castiglione sequence, according to which periods of travertine deposition were warm and wet. 5.3. Geological and geomorphological implications Datings carried out in the present work have shown that the deposition of travertine has been active in di¡erent episodes from the beginning of the Upper Pleistocene (Cittaducale ^ site 5) to the Mid-Holocene (Villa Roselli ^ sites 1, 2 and 3). The geological and geomorphological evidences allow us to hypothesize that the occurrence of travertine dams along the Velino River since the Middle Pleistocene would have obstructed the valley causing the deposition of lacustrine deposits

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upstream (Carrara et al., 1993; Brunamonte et al., 1993). The formation of the Velino Valley travertines is connected to the presence of ambient temperature springs. They currently occur at the base of the Terminillo Mount carbonate slopes at heights ranging from 400 to 450 masl, and have variable water discharges (from a few liters/s to 500 l/s). Velino Valley travertines cannot be correlated to a simple model of regional uplift and progressive incision of the £uvial valley because the oldest travertines are not always the highest above the £oodplain (Fig. 6). In addition, travertines of di¡erent ages as those from site 3 and 4 (5300 M 1300 and 57 500 M 5300 ka BP, respectively) are located at approximately the same elevation above the present £oodplain (Fig. 6). Another apparently unclear situation is that of the oldest travertines from sites 5 and 6, located respectively at 75^80 and 5^10 m above the £oodplain (Fig. 6), but characterized by ages overlapping within the error limits. To better understand such a situation it is important to note that the deposits dated in this work are located along the NW^SE and E^W oriented border fault systems placed at the base of the Reatini Mountains and Nuria-Velino Group carbonate slopes, where they are associated with thick areas of cataclastic rocks. During the Middle and Upper Pleistocene, tectonic activity along such fault planes could have modi¢ed the geometries of the underground karst circuit producing new permeability barriers and in£uencing the location of springs producing travertine bodies and consequently their elevation over the £oodplain. This is also con¢rmed by the present landscape, characterized by several karst springs located at di¡erent elevations and with di¡erent water discharges, showing a karst circuit not in equilibrium with the present base level. In addition, it must be considered that the area is still a¡ected by a strong seismic activity. Villa Roselli travertines (site 1, 2 and 3) dated to Holocene deserve special attention. The chronological resolution obtained by the U-series dating does not permit to distinguish the di¡erent outcrops because the ages overlap within the error limits. It is possible to hypothesize that the

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Fig. 6. Geomorphological sections across Middle Velino Valley. See Fig. 3a for location of pro¢les. Circled numbers correspond to site numbers as in Fig. 3a.

sampled travertines belong to the same body covering an older deposit ascribed to Middle Pleistocene, the latter representing an old threshold which obstructed the Velino River (Fig. 6).

6. Conclusions Travertine deposits from the Middle Velino Valley have formed during warm periods ranging

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in age from 113 ka (Cittaducale, site 5) to about 5 ka (Villa Roselli, site 3). They can be referred to warm marine oxygen isotope stages 5, 3 and 1. This suggests that travertines could be considered as climatic proxies in continental environments, in the same way as oxygen marine records from planktonic foraminifer assemblages. Pollen stratigraphy and ostracod assemblages from the close sequence of Valle di Castiglione, characterized by the same climatic conditions of Velino Valley, have con¢rmed that periods of travertine deposition were e¡ectively characterized by a warm and wet climate. This seems to be the case also for stage 3, where few evidences of a short forest expansion have been recorded. Travertine deposition seems to interrupt around 5 ka BP in agreement with other European and Italian sites. Such phenomena can be explained by invoking climatic causes or human impact on the environment. In addition to the in£uence of climate on travertine deposition, the recent tectonic activity affecting the Velino Valley area must also be considered. The location, the shape and the size of travertine bodies have been in£uenced by the tectonic activity interesting the area since the Middle Pleistocene producing new permeability barriers and in£uencing the location of karst springs. In conclusion, in the frame of such complex geological evolution, it is not possible to simply correlate the elevation of £uvial terraces to the age of associated travertines and make reference to a simple model of £uvial incision due to regional uplift. On the basis of the obtained data it is necessary to further consider the respective in£uence of paleoclimates and tectonic activity a¡ecting the area. This opens new perspectives regarding the interpretation of these travertine bodies in the frame of the general evolution of the studied area.

Acknowledgements This work has been carried out in the frame of the ‘Progetto CARG’, Italian Geological Cartography Project, scale 1:50 000, Foglio 357 Cittaducale. Delegate Functionary: Prof. Maurizio

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Parotto; Scienti¢c Coordinator : Prof. Domenico Cosentino; Field Survey Director : Dott. Enrico Miccadei; Plio^Quaternary deposits from Rieti Sud and Cittaducale ¢eld surveyor: Dott. Roberto Barberi.

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