1 Introduction
Tephrostratigraphy is a powerful tool that is widely applied to volcanology, Quaternary Science, palaeoceanography or archaeology. This is particularly true in the central Mediterranean region, which has borne witness to frequent and powerful volcanic explosive activity during both Holocene and Late Pleistocene (Coltelli et al., 2000; De Vivo et al., 2001; Di Vito et al., 2008; Keller et al., 1978; Mahood and Hildreth, 1986; Pappalardo et al., 1999; Paterne et al., 1988; Paterne et al., 1990; Poli et al., 1987; Santacroce, 1987; Santacroce et al., 2008; Siani et al., 2004; Sulpizio et al., 2003; Vezzoli, 1988; Wulf et al., 2004). Some of the tephra layers generated during these explosive eruptions have regional or extra-regional relevance (e.g. Y3, Y5, Y6, Y7, X5 and X6 tephra layers) (Giacco et al., 2008; Keller et al., 1978; Margari et al., 2007; Pyle et al., 2006; Sulpizio et al., 2003; Thunnell et al., 1978; Zanchetta et al., 2008), since they covered very wide areas, facilitating correlations between different geological archives. Many other tephra layers are less dispersed, but are frequently recognised in marine and lacustrine cores drilled in the central Mediterranean area (Calanchi et al., 1998; Lowe et al., 2007; Macdonald, 1974; Magny et al., 2006; Magny et al., 2007; Paterne et al., 1988; Paterne et al., 2008; Sulpizio et al., 2008; Wagner et al., 2008b; Wulf et al., 2004).
Owing to its position downwind of the Italian volcanoes, the Balkans were affected by tephra deposition during Holocene and Late Pleistocene (Sulpizio et al., 2010; Wagner et al., 2008b) (Fig. 1), but tephrostratigraphic studies are few. This article deals with the study of a long core (JO 2004; 9.88 m of length), collected on the Albanian side of Lake Ohrid, which records the last 130–140 ka of sedimentation (Lézine et al., 2010). Our aim is to provide a tephrostratigraphic reconstruction of the core JO 2004, and to provide the correlation of its tephra layers with marine, lacustrine or terrestrial deposits in the central Mediterranean. The correlation among the different archives provides an updated framework of the tephra dispersion in the central Mediterranean area, and, particularly, in the Balkans.
Location map of the study area. The Italian volcanoes active in the investigated time span and the location of cores used in this study are shown: CVZ: Campanian Volcanic Zone (Campi Flegrei, Somma-Vesuvius, Ischia and Procida volcanoes); PRG: Lake of Pergusa; LGM: Lago Grande di Monticchio. The insert in the upper right corner reports the location of the core JO 2004.
Carte de localisation du site d’étude. Les principaux volcans italiens actifs lors de la période étudiée et les sites des carottes utilisées dans cet article sont indiqués : CVZ : Campanian Volcanic Zone (Champs Phlégréens, Somma-Vesuvius, Ischia et Procida) ; PRG : lac de Pergusa ; LGM : Lago Grande di Monticchio. En haut à droite, la position du site de forage de la carotte JO 2004.
Few tephra studies have been carried out in the Balkans (Sulpizio et al., 2010; Wagner et al., 2008b), although their downwind position from the Italian volcanoes makes the area particularly subjected to distal ash deposition. On the other hand, the recognition of ash layers from Italian volcanoes in the Balkans contributes to shedding light into the complex and poorly understood dynamics of dispersal of ash particles during and after explosive eruptions.
2 Site description
The Ohrid Lake is one of the oldest lakes in Europe (Stankovic, 1960), and is located at the border between Albania and Macedonia (40°54′- 41°10′ N; 20°38′- 20°48′ E) (Fig. 1). The lake is at 705 m a.s.l., and has a surface of about 360 km2. Bathymetric measurements revealed that the lake has simple, tub-shaped basin morphology with a maximum water depth of 289 m (Stankovic, 1960). It is surrounded by two principals mountain chains: the Galiçica Mountains to the east (more than 1750 m a.s.l.), and the Mokra Mountains to the west (around 1500 m a.s.l.). The Lake Ohrid has a north-south orientation, and is located in a graben, which formed during the extension of the Albanian area during the Pleistocene (Aliaj et al., 2001; Wagner et al., 2008b). The Ohrid–Korca seismic zone comprises the Pliocene–Quaternary normal-fault-controlled Ohrid graben, and the Korca and Erseka half grabens, which are generally north trending (Aliaj, 2000; Aliaj et al., 2004). Active normal faulting with horst and graben structures is seen in the geomorphology and also determined from earthquake focal mechanisms (Aliaj et al., 2001; Goldsworthy et al., 2002).
Carbonate rocks of Triassic and Jurassic age crop out to the north and to the east, while ophiolitic rocks of Jurassic age crop out to the southwest. The southern end of the basin connects with a small graben filled by continental mudstones and sandstones of Pliocene age, overlain by fluvio-lacustrine sediments of Holocene age (Nicot and Chardon, 1983). Today, roughly half of its water is derived from a number of springs located in the southeast part of the lake, draining a karstic system fed by water from the nearby Lake Prespa (20 km to the southeast and 150 m higher than Lake Ohrid), and infiltration of rainwater (700 mm/yr on average) from the Galiçica mountain range. The remaining water comes from rivers (e.g. the Sateska River to the north) and from direct meteoric precipitation. The Black Drin River is the only surface outflow to the north part of the Lake Ohrid (Anovski et al., 1980; Lézine et al., 2010; Matzinger et al., 2006; Stankovic, 1960). Lakes with comparable volume and water depth, located in temperate and Mediterranean regions, are, in general, monomictic, with a mixing of the water column during winter (Wagner et al., 2008a). Complete overturn of the water column in Lake Ohrid occurs very irregularly, roughly every 7 years (Hadzisce, 1966; Stankovic and Hadzisce, 1953). Recent investigations have shown that in years without complete overturn the water column is mixed down to depths of 125–175 m during winter (Matzinger et al., 2006).
3 Materials and methods
Two series of piston cores (JO 2004-1 and JO 2004-1a) were drilled in the southwestern part of the Lake Orhid (Lézine et al., 2010) (40° 55,000′ N ; 20° 40,297′ E; WGS 84 reference ; Fig. 1), in a water depth of 100 m. The uppermost roughly 10 m of sediments were recovered using a cable-operated piston-core (63 mm in diameter and 3 m-long; Niederreiter Corer). In order to obtain a continuous sediment record, four sections were cored from a first drilling site (labelled JO 2004-1; Fig. 2), and three sections with a planed depth offset of 1.5 m from a second drilling site located at about 5 m of distance from the first (labelled JO 2004-1a; Fig. 2). The overlapping sections were correlated using marker layers clearly identified in both cores and the resulting composite profile checked for consistency using the magnetic susceptibility record (Fig. 2b).
Composite stratigraphy of the core JO 2004 (depth in cm): (a) lithostratigraphy (modified from Lézine et al., 2010) with tephra layers and calibrated 14C ages; (b) magnetic susceptibility curve; (c) relative glass shards abundance.
Stratigraphie recomposée de la carotte JO 2004 (profondeur en centimètre) : (a) lithostratigraphie (modifiée à partir de Lézine et al., 2010) avec les niveaux de tephra et les âges 14C calibrés ; (b) courbe de susceptibilité magnétique ; (c) abondance relative des esquilles de verres volcaniques.
The magnetic susceptibility of core JO 2004 has not permitted the identification of any tephra layer, due to the high noise induced by the magnetic minerals from the drainage basin bedrocks (Wagner et al., 2008b). Tephra layer were identified by both visual inspection and continuously sampling the composite profile at 1 cm-interval, and washing and sieving each sample at 125, 63 and 40 μm using distilled water. The different grain-size fractions were dried in a laboratory heater at a temperature of 50 °C over 24 h. The three sediment fractions were carefully inspected under a stereomicroscope, looking for volcanic particles (i.e. glass shards, pumice, magmatic crystals, volcanic lithics). At least 400 particles were counted under the stereo-microscope to obtain the glass abundance.
In samples with volcanic glass in excess of 10%, glass shards and micropumice fragments were picked and sealed in resin beads. They were then polished to avoid compositional variations caused by surface alteration processes.
Major element compositions of the glass were obtained using an EDAX-DX micro-analyser (EDS analyses) mounted on a Philips SEM 515 at Dipartimento di Scienze della Terra (University of Pisa). Operating conditions were: 20 kV acceleration voltage, 100 s live counting, 10−9 Å beam current, beam diameter ≈500 μm, 2100 shots per second, with ZAF correction (Z: atomic number; A: absorption; and F: fluorescence). The ZAF correction procedure does not include natural or synthetic standards for reference, and requires the analyses normalization at a given value (which is chosen at 100%). Instrument calibration and performance are described in Marianelli and Sbrana (1998).
The composition of glass was classified using the Total Alkali vs. Silica diagram (TAS, Le Bas et al. (1986), Fig. 3a). Major element compositions allowed the discrimination among different volcanic sources and correlation to proximal deposits of known explosive eruptions (Santacroce et al., 2008; Wulf et al., 2004).
Chemical classification of the studied tephra layers and comparison with tephra from literature using the Total Alkali vs. Silica (TAS) diagram (Le Bas et al., 1986): (a) general classification using average glass analyses of the five identified tephra layers (1σ error bars are also reported); (b) analyses of JO-941 cryptotephra and KET 8222-563 and 555 cm tephra (Paterne et al., 2008); (c) analyses of JO-575 cryptotephra and KET 8222-350, 340 cm and DED 8708–1209 cm tephra (Paterne, 1985; Paterne et al., 2008); (d) analyses of JO-244 tephra layer. Compositions of TM-18 (Wulf et al., 2004) and ML-2 (Margari et al., 2007) tephra layers are reported for comparison; (e) analyses of JO-187 tephra layer. Compositions of TM-15 (Wulf et al., 2004) and MD90-917 920 cm (Zanchetta et al., 2008) tephra layers are reported for comparison; (f) analyses of JO-42 cryptotephra. Compositions of SK13 514 cm (Sadori and Narcisi, 2001), PRG06-03 390 cm (Sulpizio et al., 2010), Ohrid 310–315 cm (Wagner et al., 2008b), and Pergusa Type A and B (Sadori and Narcisi, 2001) tephra layers are reported for comparison.
Comparaison entre les compositions chimiques des niveaux de tephra identifiés et ceux issus de la littérature dans un diagramme Total Alcalin vs. Silice (TAS) (Le Bas et al., 1986) : (a) diagramme général des moyennes des analyses sur les verres des cinq niveaux de tephra (barre d’erreur 1σ) ; (b) analyses du crytotephra JO-941 comparées aux niveaux de tephra KET 8222-563 et 555 cm d’après Paterne et al. (2008) ; (c) analyses du crytotephra JO-575 comparées aux niveaux de tephra KET 8222-350, 340 cm et DED 8708–1209 cm d’après Paterne (1985) et Paterne et al. (2008) ; (d) analyses du niveau de tephra JO-244 comparées aux niveaux de tephra TM-18 d’après Wulf et al. (2004) et ML-2 d’après Margari et al. (2007) ; (e) analyses du niveau de tephra JO-187 comparées aux niveaux de tephra TM-15 d’après Wulf et al. (2004) et MD 90-917 d’après Zanchetta et al. (2008) ; (f) analyses du crytotephra JO-42 comparées aux niveaux de tephra de SK13 514 cm d’après Sadori et Narcisi (2001) et PRG06-03 390 cm d’après Sulpizio et al. (2010), Ohrid 310–315 cm d’après Wagner et al. (2008b) et Pergusa Type A et B d’après Sadori et Narcisi (2001).
Seven 14C datings were available from literature (Lézine et al., 2010) (Table 1; Fig. 2a). Raw radiocarbon measurements were converted into calibrated ages using the INTCAL04 method (Reimer et al., 2004) and the polynomial equation of Bard et al. (1998) for 14C ages older than 26 cal ka BP.
Tableau des âges AMS 14C de la carotte JO 2004 obtenus par UMS-ARTEMIS (Pelletron 3MV) CNRS-CEA Saclay, France (Lézine et al., 2010). Les âges ont été calibrés avec INT CAL04 (Reimer et al., 2004) pour les datations d’âge inférieur à 26 cal ka BP et avec le polynôme de Bard pour les datations d’âge supérieur à 26 cal ka (Bard et al., 1998).
| Laboratory number (Artemis-Saclay) | Sample | Mean composite depth (cm) | 14C age | Error | Age cal final | Error 1 s | Methods |
| SacA 8010 | JO2004-1A020 | 20.5 | 1285 | 30 | 1253 | 30 | intcal04 (Reimer et al., 2004) |
| SacA 8011 | JO2004-1A059 | 59.5 | 5840 | 35 | 6680 | 66 | intcal04 (Reimer et al., 2004) |
| 2653 | JO2004-1A074 | 74 | 6130 | 80 | 7048 | 156 | intcal04 (Reimer et al., 2004) |
| 2654 | JO2004-1A078 | 78.5 | 7800 | 80 | 8550 | 139 | intcal04 (Reimer et al., 2004) |
| SacA 8012 | JO2004-1A085 | 85.5 | 7850 | 40 | 8622 | 52 | intcal04 (Reimer et al., 2004) |
| SacA 8013 | JO2004-1A100 | 100.5 | 8275 | 40 | 9407 | 121 | intcal04 (Reimer et al., 2004) |
| 2655 | JO2004-1B113 | 307.6 | 39,100 | 1200 | 44,812 | 1055 | Bard et al. (1998) |
4 Results
Five tephra layers were recognised along the composite profile, and labelled JO-941 (938–942 cm), JO-575 (571–577 cm), JO-244 (235–252 cm), JO-187 (185.5–188.5 cm) and JO-42 (36.5–45.5 cm), respectively (Fig. 2a and b).
4.1 Cryptotephra JO-941 (938–942 cm)
The deepest tephra is dispersed in the sediment (cryptotephra), and glass shards were recognised in all the three sieving classes. The peak of abundance of glass particles is at 941 cm (60%; Fig. 2c), and comprises transparent, brown-honey, cuspated, thin glass shards (Fig. 4a). The groundmass is glassy, and EDS analyses show a homogeneous rhyolitic composition (Fig. 3a and b, Table 2). In the diagram Comendite-Pantellerite (FeO vs. Al2O3; (Macdonald, 1974)), all the analysed samples plot into the pantelleritic field.
Scanning Electron Microscope (SEM) pictures of volcanic particles from the five studied tephra layers and cryptotephra: (a) JO-941. Note the elongated glass shards with glassy groundmass; (b) JO-575. Note the coexistence of elongated glass shards and vesicular micropumices, both with glassy groundmass; (c) JO-244. Note the coexistence of elongated glass shards with thin septa and vesicular micropumices, both groundmass are glassy; (d) JO-187. Note the coexistence of convoluted glass shards and vesicular micropumice, both with glassy groundmass; (e) JO-42. Note the blocky shape of the tachylitic fragments, which contain few spherical vesicles. The groundmass comprises small crystals of plagioclase, clinopyroxene and olivine.
Images au microscope électronique à balayage (MEB) des tephra volcaniques des niveaux (a) JO-941 composé d’esquilles de verre fines et allongées dont la matrice est vitreuse ; (b) JO-575 composé d’esquilles de verre allongées ainsi que microponces vésiculées, dont chacune des matrices est vitreuse ; (c) JO-244 composé d’esquilles de verre allongées avec de fines parois et de microponces vésiculées, dont chacune des matrices est vitreuse ; (d) JO-187 composé d’esquille de verre et de microponces allongées et fibreuses, dont chacune des matrices est vitreuse ; (e) JO-42 composé de fragments de blocs et de tachylites finement vésiculées dont la matrice se compose de petits cristaux de plagioclase, de clinopyroxènes et d’olivine.
Compositions des éléments majeurs des cinq niveaux de tephra identifiés dans la carotte JO 2004.
| JO941 | SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | ClO | Total | Total Alkali |
| JO941-1 | 71.81 | 0.50 | 8.37 | 6.89 | 0.37 | 0.00 | 0.32 | 6.63 | 4.36 | 0.00 | 0.76 | 100.01 | 10.99 |
| JO941-2 | 72.30 | 0.44 | 8.55 | 6.79 | 0.25 | 0.11 | 0.19 | 6.35 | 4.43 | 0.00 | 0.61 | 100.02 | 10.78 |
| JO941-3 | 72.13 | 0.51 | 8.34 | 6.83 | 0.39 | 0.00 | 0.29 | 6.49 | 4.34 | 0.00 | 0.68 | 100.00 | 10.83 |
| JO941-4 | 72.52 | 0.32 | 8.63 | 6.69 | 0.24 | 0.80 | 0.34 | 5.93 | 4.59 | 0.00 | 0.66 | 100.72 | 10.52 |
| JO941-5 | 72.53 | 0.23 | 8.54 | 6.67 | 0.16 | 0.00 | 0.23 | 6.53 | 4.37 | 0.00 | 0.75 | 100.01 | 10.90 |
| JO941-6 | 71.93 | 0.45 | 8.49 | 6.97 | 0.49 | 0.12 | 0.31 | 6.30 | 4.25 | 0.00 | 0.69 | 100.00 | 10.55 |
| JO941-7 | 72.77 | 0.29 | 8.60 | 6.72 | 0.20 | 0.00 | 0.21 | 6.16 | 4.37 | 0.00 | 0.67 | 99.99 | 10.53 |
| JO941-8 | 72.30 | 0.35 | 8.62 | 6.83 | 0.23 | 0.08 | 0.22 | 6.41 | 4.29 | 0.00 | 0.67 | 100.00 | 10.70 |
| JO941-9 | 72.07 | 0.27 | 8.61 | 6.91 | 0.23 | 0.10 | 0.32 | 6.44 | 4.37 | 0.00 | 0.68 | 100.00 | 10.81 |
| JO941-10 | 72.24 | 0.32 | 8.53 | 6.85 | 0.38 | 0.00 | 0.32 | 6.18 | 4.42 | 0.00 | 0.76 | 100.00 | 10.60 |
| JO941-11 | 72.30 | 0.45 | 8.54 | 6.64 | 0.26 | 0.10 | 0.36 | 6.21 | 4.50 | 0.00 | 0.64 | 100.00 | 10.71 |
| JO941-12 | 72.61 | 0.17 | 8.68 | 6.63 | 0.18 | 0.00 | 0.34 | 6.33 | 4.32 | 0.00 | 0.74 | 100.00 | 10.65 |
| JO941-13 | 72.11 | 0.49 | 8.57 | 6.81 | 0.34 | 0.04 | 0.26 | 6.28 | 4.42 | 0.00 | 0.68 | 100.00 | 10.70 |
| Mean | 72.28 | 0.37 | 8.54 | 6.79 | 0.29 | 0.10 | 0.29 | 6.33 | 4.39 | 0.00 | 0.69 | – | 10.71 |
| Sd | 0.28 | 0.11 | 0.10 | 0.11 | 0.10 | 0.21 | 0.06 | 0.18 | 0.09 | 0.00 | 0.05 | – | – |
| JO575 | SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | ClO | Total | Total Alkali |
| JO575-1 | 60.59 | 0.53 | 18.42 | 3.24 | 0.39 | 0.27 | 1.78 | 7.29 | 6.66 | 0 | 0.82 | 99.99 | 13.95 |
| JO575-2 | 61.01 | 0.59 | 18.86 | 2.85 | 0.31 | 0.38 | 1.54 | 6.82 | 6.93 | 0 | 0.71 | 100 | 13.75 |
| JO575-3 | 60.9 | 0.44 | 18.46 | 3.13 | 0.2 | 0.31 | 1.84 | 7.08 | 6.76 | 0 | 0.87 | 99.99 | 13.84 |
| JO575-4 | 60.9 | 0.46 | 18.84 | 2.93 | 0.21 | 0.26 | 1.68 | 7.28 | 6.57 | 0 | 0.88 | 100.01 | 13.85 |
| JO575-5 | 60.71 | 0.5 | 18.63 | 3.08 | 0.4 | 0.47 | 1.63 | 6.85 | 6.94 | 0 | 0.78 | 99.99 | 13.79 |
| JO575-6 | 61.69 | 0.5 | 18.53 | 2.78 | 0.23 | 0.46 | 1.69 | 5.8 | 7.74 | 0 | 0.57 | 99.99 | 13.54 |
| JO575-7 | 61.48 | 0.36 | 18.74 | 2.8 | 0.13 | 0.36 | 1.84 | 5.62 | 8.11 | 0 | 0.57 | 100.01 | 13.73 |
| JO575-8 | 61.16 | 0.46 | 18.69 | 3 | 0.3 | 0.3 | 1.65 | 6.86 | 6.85 | 0 | 0.73 | 100 | 13.71 |
| JO575-9 | 60.69 | 0.61 | 18.54 | 3.21 | 0.4 | 0.39 | 1.59 | 7.2 | 6.56 | 0 | 0.81 | 100 | 13.76 |
| JO575-10 | 61.67 | 0.43 | 18.64 | 2.93 | 0.3 | 0.5 | 1.59 | 6.02 | 7.49 | 0 | 0.44 | 100.01 | 13.51 |
| JO575-11 | 61.68 | 0.64 | 18.79 | 2.82 | 0.42 | 0.35 | 1.5 | 6.33 | 6.81 | 0 | 0.65 | 99.99 | 13.14 |
| JO575-12 | 61.13 | 0.5 | 18.9 | 3.1 | 0.38 | 0.3 | 1.51 | 6.7 | 6.73 | 0 | 0.75 | 100 | 13.43 |
| JO575-13 | 61.83 | 0.52 | 18.69 | 2.95 | 0.27 | 0.43 | 1.56 | 5.56 | 7.54 | 0 | 0.64 | 99.99 | 13.1 |
| JO575-14 | 61.58 | 0.49 | 19.07 | 2.69 | 0.28 | 0.52 | 1.76 | 5.53 | 7.49 | 0 | 0.59 | 100 | 13.02 |
| JO575-15 | 61.11 | 0.37 | 18.85 | 3 | 0.24 | 0.43 | 1.59 | 6.73 | 6.87 | 0 | 0.8 | 99.99 | 13.6 |
| JO575-16 | 60.65 | 0.46 | 18.74 | 3.13 | 0.36 | 0.3 | 1.7 | 7.22 | 6.58 | 0 | 0.85 | 99.99 | 13.8 |
| JO575-17 | 60.73 | 0.35 | 18.92 | 3.02 | 0.34 | 0.35 | 1.73 | 7.08 | 6.6 | 0 | 0.88 | 100 | 13.68 |
| JO575-18 | 61.43 | 0.36 | 18.66 | 2.87 | 0.2 | 0.46 | 1.74 | 6 | 7.7 | 0 | 0.57 | 99.99 | 13.7 |
| JO575-19 | 62.04 | 0.38 | 18.96 | 2.86 | 0.24 | 0.42 | 1.61 | 5.87 | 6.89 | 0 | 0.73 | 100 | 12.76 |
| JO575-20 | 60.92 | 0.41 | 18.87 | 3.09 | 0.2 | 0.38 | 1.45 | 6.96 | 6.89 | 0 | 0.82 | 99.99 | 13.85 |
| Mean | 61.2 | 0.47 | 18.74 | 2.97 | 0.29 | 0.38 | 1.65 | 6.54 | 7.04 | 0 | 0.72 | – | 13.58 |
| Sd | 0.45 | 0.08 | 0.17 | 0.15 | 0.08 | 0.08 | 0.11 | 0.63 | 0.46 | 0 | 0.13 | – | – |
| JO244 | SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | ClO | Total | Total Alkali |
| JO244-1 | 60.87 | 0.46 | 19.19 | 2.97 | 0.2 | 0.38 | 1.59 | 6.62 | 7.08 | 0 | 0.65 | 100.01 | 13.7 |
| JO244-2 | 61.16 | 0.33 | 19.08 | 2.93 | 0.2 | 0.34 | 1.81 | 5.98 | 7.49 | 0 | 0.68 | 100 | 13.47 |
| JO244-3 | 60.68 | 0.42 | 19.04 | 2.94 | 0.21 | 0.38 | 1.88 | 6.25 | 7.51 | 0 | 0.68 | 99.99 | 13.76 |
| JO244-4 | 60.6 | 0.52 | 19.17 | 2.85 | 0.25 | 0.35 | 1.69 | 6.53 | 7.24 | 0 | 0.8 | 100 | 13.77 |
| JO244-5 | 60.57 | 0.51 | 19.11 | 2.9 | 0.31 | 0.51 | 1.68 | 6.58 | 7.17 | 0 | 0.65 | 99.99 | 13.75 |
| JO244-6 | 59.96 | 0.36 | 19.47 | 3.14 | 0.23 | 0.4 | 1.92 | 6.1 | 7.6 | 0 | 0.82 | 100 | 13.7 |
| JO244-7 | 61 | 0.38 | 19.1 | 2.86 | 0.18 | 0.28 | 1.78 | 6.48 | 7.22 | 0 | 0.71 | 99.99 | 13.7 |
| JO244-8 | 60.62 | 0.55 | 19.09 | 2.99 | 0.26 | 0.47 | 1.75 | 6.37 | 7.31 | 0 | 0.61 | 100.02 | 13.68 |
| JO244-9 | 60.34 | 0.37 | 19.84 | 2.97 | 0.2 | 0.4 | 1.73 | 6.21 | 7.28 | 0 | 0.66 | 100 | 13.49 |
| JO244-10 | 61.67 | 0.44 | 19.08 | 2.65 | 0.15 | 0.36 | 1.68 | 6.07 | 7.34 | 0 | 0.58 | 100.02 | 13.41 |
| JO244-11 | 58.97 | 0.45 | 19.68 | 3.48 | 0.07 | 0.8 | 2.6 | 5.08 | 8.46 | 0 | 0.41 | 100 | 13.54 |
| JO244-12 | 60.93 | 0.36 | 19 | 2.99 | 0.21 | 0.22 | 1.73 | 6.42 | 7.35 | 0 | 0.79 | 100 | 13.77 |
| JO244-13 | 60.86 | 0.45 | 19.08 | 2.87 | 0.21 | 0.32 | 1.7 | 6.37 | 7.39 | 0 | 0.75 | 100 | 13.76 |
| JO244-14 | 60.78 | 0.45 | 18.97 | 2.93 | 0.19 | 0.42 | 1.8 | 6.33 | 7.39 | 0 | 0.75 | 100.01 | 13.72 |
| JO244-15 | 61.31 | 0.26 | 19.25 | 2.92 | 0.19 | 0.34 | 1.8 | 5.65 | 7.57 | 0 | 0.71 | 100 | 13.22 |
| JO244-16 | 60.16 | 0.49 | 19.13 | 2.98 | 0.28 | 0.42 | 1.87 | 6.13 | 7.84 | 0 | 0.71 | 100.01 | 13.97 |
| JO244-18 | 60.76 | 0.29 | 18.94 | 2.96 | 0.28 | 0.37 | 1.83 | 6.39 | 7.49 | 0 | 0.7 | 100.01 | 13.88 |
| JO244-19 | 60.35 | 0.46 | 18.97 | 2.97 | 0.2 | 0.4 | 1.72 | 6.31 | 7.82 | 0 | 0.81 | 100.01 | 14.13 |
| Mean | 60.64 | 0.42 | 19.18 | 2.96 | 0.21 | 0.4 | 1.81 | 6.22 | 7.48 | 0 | 0.69 | – | 13.69 |
| Sd | 0.58 | 0.08 | 0.25 | 0.16 | 0.05 | 0.12 | 0.21 | 0.37 | 0.32 | 0 | 0.1 | – | – |
| JO244-17 | 60.26 | 0.38 | 18.8 | 3.33 | 0.07 | 0.96 | 2.66 | 3.34 | 9.92 | 0 | 0.3 | 100.02 | 13.26 |
| JO244-20 | 60.38 | 0.28 | 19.14 | 3.24 | 0 | 0.69 | 2.6 | 3.15 | 10.22 | 0 | 0.3 | 100 | 13.37 |
| Mean | 60.32 | 0.33 | 18.97 | 3.29 | 0.04 | 0.83 | 2.63 | 3.25 | 10.07 | 0 | 0.3 | – | 13.66 |
| Sd | 0.08 | 0.07 | 0.24 | 0.06 | 0.05 | 0.19 | 0.04 | 0.13 | 0.21 | 0 | 0 | – | – |
| JO188 | SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | ClO | Total | Total Alkali |
| JO188-1 | 61.22 | 0.42 | 18.77 | 3.18 | 0.11 | 0.67 | 2.26 | 3.62 | 9.39 | 0 | 0.36 | 100 | 13.01 |
| JO188-2 | 60.43 | 0.52 | 18.89 | 3.4 | 0.09 | 0.77 | 2.63 | 3.44 | 9.48 | 0 | 0.35 | 100 | 12.92 |
| JO188-3 | 60.11 | 0.49 | 18.71 | 3.74 | 0.12 | 0.93 | 2.87 | 3.13 | 9.59 | 0 | 0.31 | 100 | 12.72 |
| JO188-4 | 61.3 | 0.33 | 18.7 | 3.31 | 0.06 | 0.69 | 2.49 | 2.96 | 9.82 | 0 | 0.33 | 99.99 | 12.78 |
| JO188-5 | 60.25 | 0.5 | 18.85 | 3.27 | 0.28 | 0.64 | 2.03 | 4.32 | 9.35 | 0 | 0.51 | 100 | 13.67 |
| JO188-6 | 61.88 | 0.31 | 18.53 | 2.9 | 0.12 | 0.47 | 2.22 | 3.83 | 9.26 | 0 | 0.49 | 100.01 | 13.09 |
| JO188-7 | 59.89 | 0.53 | 18.75 | 3.64 | 0.1 | 0.87 | 2.63 | 2.95 | 10.3 | 0 | 0.35 | 100.01 | 13.25 |
| JO188-8 | 61.4 | 0.35 | 18.68 | 3.07 | 0.17 | 0.42 | 2.16 | 4.38 | 8.79 | 0 | 0.59 | 100.01 | 13.17 |
| JO188-9 | 61.47 | 0.32 | 18.7 | 3.09 | 0 | 0.72 | 2.32 | 3.53 | 9.42 | 0 | 0.44 | 100.01 | 12.95 |
| JO188-10 | 61.94 | 0.26 | 18.81 | 2.98 | 0.06 | 0.64 | 2.19 | 3.77 | 8.9 | 0 | 0.44 | 99.99 | 12.67 |
| Mean | 60.99 | 0.4 | 18.74 | 3.26 | 0.11 | 0.68 | 2.38 | 3.59 | 9.43 | 0 | 0.42 | – | 13.02 |
| Sd | 0.75 | 0.1 | 0.1 | 0.27 | 0.07 | 0.16 | 0.26 | 0.5 | 0.43 | 0 | 0.09 | – | – |
| JO42 | SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | ClO | Total | Total Alkali |
| JO42-1 | 52.98 | 1.79 | 17.85 | 8.38 | 0.25 | 3.27 | 6.79 | 5.3 | 2.68 | 0.38 | 0.33 | 100 | 7.98 |
| JO42-2 | 54.6 | 1.63 | 18.1 | 7.39 | 0.22 | 2.39 | 6.14 | 5.65 | 3.03 | 0.51 | 0.31 | 99.97 | 8.68 |
| JO42-3 | 53.79 | 1.67 | 17.76 | 8.52 | 0 | 2.72 | 5.9 | 5.57 | 3.23 | 0.51 | 0.32 | 99.99 | 8.8 |
| JO42-4 | 54.69 | 1.86 | 18 | 7.45 | 0.28 | 2.03 | 5.45 | 5.72 | 3.67 | 0.54 | 0.3 | 99.99 | 9.39 |
| JO42-5 | 53.96 | 1.7 | 17.41 | 7.92 | 0.14 | 2.99 | 6.05 | 5.94 | 3.15 | 0.44 | 0.31 | 100.01 | 9.09 |
| JO42-7 | 52.51 | 2.23 | 16.55 | 9.77 | 0.25 | 2.84 | 5.86 | 5.18 | 3.94 | 0.54 | 0.33 | 100 | 9.12 |
| JO42-8 | 53.88 | 1.83 | 17.81 | 8.41 | 0.09 | 2.57 | 5.24 | 5.97 | 3.56 | 0.38 | 0.26 | 100 | 9.53 |
| JO42-9 | 61.35 | 0.53 | 18.75 | 3.06 | 0.24 | 0.54 | 2.18 | 3.96 | 8.9 | 0 | 0.49 | 100 | 12.86 |
| JO42-11 | 54.2 | 1.84 | 17.05 | 8.13 | 0.24 | 2.98 | 6.23 | 5.23 | 3.32 | 0.51 | 0.27 | 100 | 8.55 |
| JO42-12 | 56.22 | 1.5 | 19.13 | 5.45 | 0.09 | 1.12 | 5.24 | 6.53 | 3.93 | 0.44 | 0.34 | 99.99 | 10.46 |
| JO42-13 | 54.61 | 1.86 | 17.53 | 7.68 | 0.18 | 2.38 | 5.28 | 5.67 | 3.89 | 0.57 | 0.35 | 100 | 9.56 |
| Mean | 54.8 | 1.68 | 17.81 | 7.47 | 0.18 | 2.35 | 5.49 | 5.52 | 3.94 | 0.44 | 0.33 | – | 9.46 |
| Sd | 2.38 | 0.42 | 0.72 | 1.8 | 0.09 | 0.83 | 1.2 | 0.65 | 1.7 | 0.16 | 0.06 | – | – |
4.2 Cryptotephra JO-575 (571–577 cm)
This cryptotephra mainly comprises white to light-brown, elongated and cuspated glass shards and rare, white micropumice fragments (Fig. 4b). The peak abundance of glass shards is between 574 and 575 cm (95%; Fig. 2c). The groundmass is glassy (Fig. 4b), and the composition shows a small variability within the trachy-phonolitic field (Fig. 3a and c; Table 2).
4.3 Tephra layer JO-244 (235–252 cm)
This tephra layer is composed of two distinct parts with different colours. The first one (between 244 and 244.5 cm) is yellowish gray (5Y 7/2; (GSA, 1991)), while the second one (between 247 and 248 cm) is moderate olive brown (5Y 4/4; (GSA, 1991)). The tephra comprises white, vesicular micropumices and elongated glass shards with thin septa. Most of the glass shards are transparent, with few dark-brown in colour (Fig. 4c). The abundance of glass shards and micropumice has its maximum (100%) between 244 and 244.5 cm (Fig. 2c). The groundmass is glassy (Fig. 4c), and the glass composition is trachy-phonolitic (Fig. 3a and d; Table 2).
4.4 Tephra layer JO-187 (185.5–188.5 cm)
This tephra layer is yellowish gray in colour (5Y 4/1; (GSA, 1991)), and comprises transparent, tubular, elongated micropumice fragments and transparent, brownish glass shards (Fig. 4d). The maximum abundance (99%) is at 187 cm (Fig. 2c). The groundmass is glassy (Fig. 4d), and the glass composition is homogeneous and trachytic (Fig. 3a and e; Table 2).
4.5 Cryptotephra JO-42 (36.5–45.5 cm)
This cryptotephra has a peak abundance of glass particles (80%) at 42 cm of depth (Fig. 2c), and comprises dark-brown, blocky, tachylitic fragments with few spherical vesicles (Fig. 4e). The groundmass comprises small crystals of plagioclase, clinopyroxene and minor olivine (Fig. 4e). The glass composition ranges between mugearites and benmoreites (Fig. 3a and f).
5 Discussion
5.1 Correlation of tephra layers
The K- to Na-alkaline affinity of glass compositions of the five tephra layers recognised in the core JO 2004 indicate that all of them were from explosive eruptions of Italian volcanoes, since during Late Quaternary the products of the Aegean arc were characterised by calc-alkaline affinity (Keller et al., 1978; Paterne et al., 2008; Thunnell et al., 1978). Two of them (JO-941 and JO-42) present peculiar glass compositions that indicate a source from Pantelleria Island and from Mount Etna, respectively. The other three tephras display trachytic to phonolitic composition, and can be correlated to the explosive activity of Campanian volcanoes. In the following, the precise correlation of each tephra layer with a specific eruption of these volcanoes will be discussed in detail. For comparison, the average compositions of the correlated tephra layers are reported in Table 3.
Comparaison des moyennes et des écarts-types des compositions des niveaux de tephra identifiés aux analyses issues de la littérature : KET 8222 340 cm, 350 cm, 555 cm, 563 cm, 765 cm, DED 8708 1209 cm d’après Paterne (1985) et Paterne et al. (2008) ; ML-2 d’après Margari et al. (2007) ; TM-15 et TM-18 d’après Wulf et al. (2004) ; MD90-917 920 cm d’après Zanchetta et al. (2008) ; tephra Ohrid 310-315 cm d’après Wagner et al. (2008b) ; Pergusa type A et B d’après Sadori and Narcisi (2001) et PRG06-03 390 cm et SK13 514 cm d’après Sulpizio et al. (2010).
| SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | SO3 | ClO | F | Total Alkali | ||
| KET 8222 563 cm | Mean | 73.09 | 0.39 | 8.88 | 7.05 | – | 0.09 | 0.27 | 5.81 | 4.42 | – | – | – | – | 10.23 |
| n = 13 | sd | 0.36 | 0.08 | 0.13 | 0.12 | – | 0.06 | 0.11 | 0.37 | 0.16 | – | – | – | – | – |
| KET 8222 555 cm | Mean | 72.95 | 0.31 | 8.89 | 7.23 | – | 0.05 | 0.20 | 5.90 | 4.48 | – | – | – | – | 10.38 |
| n = 13 | sd | 0.47 | 0.05 | 0.05 | 0.33 | – | 0.03 | 0.04 | 0.36 | 0.10 | – | – | – | – | – |
| KET 8222 765 cm | Mean | 72.97 | 0.50 | 9.02 | 7.34 | – | 0.10 | 0.20 | 5.44 | 4.42 | – | – | – | – | 9.86 |
| sd | 0.49 | 0.06 | 0.16 | 0.28 | – | 0.07 | 0.02 | 0.30 | 0.06 | – | – | – | – | – | |
| SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | SO3 | ClO | F | Total Alkali | ||
| KET8222 350 cm | Mean | 61.47 | 0.52 | 19.20 | 3.20 | – | 0.40 | 1.66 | 6.27 | 7.30 | – | – | – | – | 13.56 |
| n = 11 | sd | 0.06 | 0.04 | 0.10 | 0.22 | – | 0.06 | 0.10 | 0.53 | 0.77 | – | – | – | – | |
| KET8222 340 cm | Mean | 61.98 | 0.47 | 19.18 | 3.06 | – | 0.42 | 1.70 | 6.08 | 7.11 | – | – | – | – | 13.19 |
| n = 14 | sd | 0.27 | 0.10 | 0.13 | 0.15 | – | 0.09 | 0.10 | 0.68 | 0.46 | – | – | – | – | |
| DED 8708 1209 cm | Mean | 61.81 | 0.48 | 18.18 | 3.04 | 0.33 | 0.31 | 1.71 | 5.72 | 7.29 | 0.02 | 0.11 | 0.97 | – | 13.02 |
| n = 19 | sd | 0.68 | 0.10 | 0.31 | 0.23 | 0.12 | 0.07 | 0.32 | 0.91 | 0.86 | 0.04 | 0.08 | 0.28 | – | – |
| SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | SO3 | ClO | F | Total Alkali | ||
| TM-18 | Mean | 61.69 | 0.42 | 19.11 | 2.93 | 0.24 | 0.35 | 1.73 | 5.66 | 6.83 | 0.05 | – | 0.78 | 0.19 | 12.49 |
| n = 43 | sd | 0.46 | 0.02 | 0.21 | 0.09 | 0.02 | 0.02 | 0.07 | 0.71 | 0.29 | 0.03 | – | 0.05 | 0.17 | – |
| ML-2 | Mean | 61.01 | 0.48 | 18.18 | 3.02 | 0.21 | 0.44 | 2.12 | 5.64 | 8.05 | 0.07 | – | 0.71 | – | 13.7 |
| n = 105 | sd | 0.42 | 0.04 | 0.19 | 0.21 | 0.06 | 0.15 | 0.32 | 1.21 | 1.02 | 0.04 | – | 0.20 | – | – |
| SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | – | ClO | F | Total Alkali | ||
| TM-15 | Mean | 62.22 | 0.38 | 18.36 | 3.27 | 0.13 | 0.61 | 2.19 | 3.85 | 8.36 | 0.12 | – | 0.52 | 0 | 12.21 |
| n = 20 | sd | 0.78 | 0.03 | 0.21 | 0.29 | 0.04 | 0.15 | 0.22 | 0.44 | 0.55 | 0.06 | – | 0.11 | 0 | – |
| MD90-917 920 cm | Mean | 61.41 | 0.36 | 18.72 | 3.17 | 0.08 | 0.70 | 2.44 | 3.52 | 9.14 | – | – | 0.44 | – | 12.66 |
| n = 20 | sd | 0.86 | 0.12 | 0.17 | 0.38 | 0.08 | 0.21 | 0.33 | 0.40 | 0.40 | – | – | 0.09 | – | – |
| SiO2 | TiO2 | Al2O3 | FeOtot | MnO | MgO | CaO | Na2O | K2O | P2O5 | SO3 | ClO | F | Total Alkali | ||
| SK13 514 cm | Mean | 56.81 | 1.21 | 20.52 | 4.86 | 0.09 | 1.38 | 5.27 | 6.22 | 3.10 | 0.24 | – | 0.30 | – | 9.32 |
| n = 14 | sd | 1.78 | 0.44 | 2.39 | 2.49 | 0.09 | 1.27 | 1.83 | 1.04 | 1.26 | 0.22 | – | 0.11 | – | – |
| Tephra Ohrid 310–315 cm | Mean | 54.25 | 1.76 | 17.48 | 8.15 | 0.00 | 2.85 | 6.02 | 5.40 | 3.29 | 0.48 | – | 0.31 | – | 8.69 |
| n = 15 | sd | 0.73 | 0.22 | 0.51 | 0.53 | 0.00 | 0.33 | 0.50 | 0.41 | 0.34 | 0.10 | – | 0.06 | – | – |
| PRG06-03 390 cm | Mean | 52.82 | 2.04 | 16.86 | 9.43 | 0.23 | 3.21 | 6.13 | 4.99 | 3.58 | 0.47 | – | 0.24 | – | 8.57 |
| n = 11 | sd | 0.82 | 0.17 | 0.47 | 0.90 | 0.10 | 0.42 | 1.03 | 0.37 | 0.67 | 0.07 | – | 0.06 | – | – |
| Type A Pergusa | Mean | 55.61 | 1.58 | 16.97 | 7.25 | 0.15 | 3.98 | 5.62 | 6.02 | 2.37 | – | – | 0.46 | – | 8.39 |
| n = 14 | sd | 2.28 | 0.20 | 0.78 | 1.35 | 0.09 | 0.57 | 0.95 | 1.13 | 0.34 | – | – | 0.09 | – | – |
| Type B Pergusa | Mean | 54.91 | 1.61 | 17.65 | 6.83 | 0.15 | 3.90 | 5.65 | 5.79 | 3.06 | – | – | 0.45 | – | 8.86 |
| n = 11 | sd | 0.91 | 0.23 | 0.49 | 1.16 | 0.09 | 0.47 | 1.04 | 0.88 | 0.25 | – | – | 0.43 | – | – |
5.1.1 Cryptotephra JO-941
The pantelleritic glass composition of cryptotephra JO-941 (Table 2) indicates it was generated from Pantelleria Island. The Island of Pantelleria produced several large explosive eruptions with pantelleritic composition (Mahood and Hildreth, 1986). Among them, the most dispersed are the Green Tuff (45–50 ka), the Ignimbrite Q (113.9 ± 3.6 ka), the Ignimbrite P (133.1 ± 3.3 ka), the Welded tuff S (162–164 ka) and the Welded tuff M (174.8 ± 2.8 ka; (Mahood and Hildreth, 1986)). Two other 40Ar/39Ar datings are available for the Ignimbrite P (126.8 ± 1.5 ka; (La Felice et al., 2009)) and for the Welded tuff S (174.5 ± 1.5 ka; (La Felice et al., 2009)). Pantelleritic tephra layers have been found in the Ionian Sea core KET 8222 (Paterne et al., 2008) (Table 3) and named P11 (estimated age at about 131 ka, 555 cm depth) and P12 (estimated age at about 164 ka, 765 cm depth), which have similar ages as Ignimbrite P and Welded tuff S. The composition of P11 and P12 is quite similar, and the two tephra layers are hardly distinguishable on the basis of major elements.
The glass composition of sample JO-941 matches well that of both tephra layers P11 and P12 (Tables 2 and 3, Fig. 3b). Indeed, the tephra layer P11 has been recognised over a wide area of the Ionian Sea while the dispersal of P12 is more limited (Paterne et al., 2008). Nevertheless, stratigraphic and paleoclimatic considerations support the correlation of the JO-941 cm tephra with P11 marine tephra layer, and then with Ignimbrite P deposits on Pantelleria Island. This is because both carbonate and pollen curves carried out on JO 2004 core sediments (Lézine et al., 2010) unequivocally indicate that these tephra were emplaced close to the inception of the Last Interglacial. The onset of the Last Interglacial may have been recorded at different times in different archives (Tzedakis et al., 2003), but, in any case, the age of 164 ka (which corresponds to P12 tephra layer) is too old of some 10,000 years with respect to that commonly accepted for the inception of Last Interglacial at Mediterranean latitudes (e.g. 126.8 and 120.3 ka; (Tzedakis et al., 2003)).
The recognition of tephra layer P11 is the first in the Balkans, and significantly enlarges its dispersal well beyond the Ionian Sea (Fig. 5a).
Reconstructed dispersal areas of the five tephra layers recognised in core JO 2004 and using previously published data. (a) P11 tephra layer. The dashed line indicates the previous inferred dispersal area. KET 8222, data from Paterne et al. (2008); (b) X6 tephra layer. The dashed line indicates the previous inferred dispersal area. KET 8222 and DED 8708 data from Paterne et al. (2008); (c) Y5 tephra layer. Dispersal area from (Giacco et al., 2008; Pyle et al., 2006); (d) Y3 tephra layer. C6 and C145 data from Munno and Petrosino (2004), V10-68, RC9-190, 22M60 data from Keller et al. (1978), KET 8004 and KET 8011 data from Paterne et al. (2008) and Zanchetta et al. (2008), LZ 1120 data from Wagner et al. (2008b) and MD90-917 data from Paterne et al. (1986) and Zanchetta et al. (2008); (e) FL dispersal area is from Sulpizio et al. (2010). Blue dots indicate the location of the JO 2004 core. Stars indicate the volcanic sources.
Reconstruction des zones de dispersion des cinq éruptions identifiées dans la carotte JO 2004 : (a) les tephra de P11 ont été identifiés dans la carotte KET 8222 (Paterne et al., 2008) ; (b) les tephra de X6 ont été identifiés dans les carottes KET 8222 et DED 8708 (Paterne et al., 2008) ; (c) la carte de dispersion des cendres de Y5 est modifiée à partir de Giacco et al. (2008) ; Pyle et al. (2006) ; (d) les tephra de Y3 ont été identifiés dans les carottes C6 et C145 (Munno et Petrosino, 2004), V10-68, RC9-190, 22M60 (Keller et al., 1978), KET 8004 et KET 8011 (Paterne et al., 2008 ; Zanchetta et al., 2008), LZ 1120 (Wagner et al., 2008b) et MD90-917 (Paterne et al., 1986 ; Zanchetta et al., 2008) ; (e) la carte de dispersion des cendres de Etna FL est modifiée à partir de Sulpizio et al. (2010). Les points bleus indiquent la localisation de la carotte JO 2004. Les étoiles indiquent les sources volcaniques et les précédentes surfaces de dispersion sont limitées par un trait jaune et noir.
5.1.2 Cryptotephra JO-575
This low alkali ratio (LAR) trachytic tephra layer occurs between the calibrated 14C age of 44,812 ± 1055 cal yr BP (Lézine et al., 2010) (Table 1) and the P11 tephra layer.
Composition of the tephra layer JO-575 shows a good match with marine tephra C-31 (KET 8222 and DED 8708 deep-sea cores, Fig. 3c and Table 3), which has an interpolated age of 107 ka (Paterne et al., 2008). Paterne had related the C-31 tephra with the LAR-trachyte X6 from the 22M-60 core (Keller et al., 1978). This supports the correlation of JO-575 sample to the X6 tephra layer. The age of X6 tephra layer at 107 ka is also supported by extrapolation of the X5 tephra layer age (105 ± 2 ka; 40Ar/39Ar technique) (Kraml, 1997) based on sedimentation rate extrapolation. The source of the X6 eruption has been located in the Campanian volcanic zone (Keller et al., 1978). The X6 tephra layer was for the first time described in Ionian Sea cores (Keller et al., 1978), and successively in a Tyrrhenian Sea core (Paterne et al., 2008) and in the Lago Grande di Monticchio succession (Wulf et al., 2007). This is the first recognition of X6 tephra layer in the Balkans, and it considerably enlarges its dispersal area to the east (Fig. 5b).
5.1.3 Tephra layer JO-244
This tephra layer is 11 cm thick (Fig. 2) and comprises both glass shards and micropumice fragments. When plotted on TAS diagram, the glass composition has a narrow variability within the trachytic and phonolitic fields (Fig. 3d). However, the tephra layer shows a variable alkali ratio passing from the base to the top. In particular, the basal part shows the coexistence of glasses with two different alkali ratios (Table 2), whereas the upper part has a very homogeneous LAR-trachytic glass composition (Table 2).
The glass composition indicates the Campanian area as the source for this tephra that, on the basis of the peculiar variability in alkali ratio and the deposit thickness, can be confidently correlated to the Campanian Ignimbrite eruption from Campi Flegrei. The geochemical comparison of major elements shown in Table 3 is applied with the ML-2 layer (Margari et al., 2007) and the TM-18 layer (Wulf et al., 2004) among the many analyses available. The Campanian Ignimbrite eruption was dated at 39,280 ± 110 years (40Ar/39Ar technique; (De Vivo et al., 2001)), and corresponds to the Y5 tephra layer, widely dispersed in the central and eastern Mediterranean and in mainland Europe (Giacco et al., 2008; Keller et al., 1978; Margari et al., 2007; Narcisi and Vezzoli, 1999; Paterne et al., 1986; Paterne et al., 1988; Pyle et al., 2006; Sulpizio et al., 2003; Vezzoli, 1991; Wagner et al., 2008b; Wulf et al., 2004). The recognition in Albanian side of Lake Ohrid succession confirms the previous finding of Wagner et al. (2008b) from the Macedonian side of the lake (Fig. 5c).
5.1.4 Tephra layer JO-187
The JO-187 tephra is chronogically constrained between the Campanian Ignimbrite (≈39 ka) and the 14C age of 9,407 ± 121 cal yr BP obtained at 100 cm depth (Table 1; Fig. 2a). The homogeneous trachytic composition (Table 2, Fig. 3e) of this tephra layer suggests it originated from the Campanian volcanic zone, and shows a good match with the composition of SMP1-e eruption from Campi Flegrei (Di Vito et al., 2008). The SMP1-e eruption corresponds to the Y3 tephra layer (Table 3; Di Vito et al., 2008; Sulpizio et al., 2003; Zanchetta et al., 2008), which is widely dispersed in the central Mediterranean area (Keller et al., 1978; Munno and Petrosino, 2006; Narcisi and Vezzoli, 1999; Sulpizio et al., 2003; Wulf et al., 2004; Zanchetta et al., 2008) with an estimated age between 30 and 31 cal ka BP (Zanchetta et al., 2008). The recognition in Albanian side of Lake Ohrid succession confirms the previous finding of Wagner et al. (2008b) from the Macedonian side of the lake (Fig. 5d).
5.1.5 Cryptotephra JO-42
This cryptotephra is stratigraphically younger than the 14C age of 6,680 ± 66 cal yr BP (Table 1), and the mugearitic-benmoreitic composition easily indicates the Mount Etna as the source. The shallow position within the core and the glass composition indicates a correlation with the FL eruption from Mount Etna, dated at 3,370 ± 70 cal yr BP (Coltelli et al., 2000; Wagner et al., 2008b). The recognition in Lake Ohrid succession confirms the previous finding in the same lake (Macedonian side) (Wagner et al., 2008b) and in the Lake Shkodra successions (Albania) (Fig. 5e; (Sulpizio et al., 2010)).
5.2 Significance of tephra layer recognition in Lake Ohrid
The recognition of tephra layers in the Lake Ohrid has relevance for both volcanology and Quaternary Sciences.
From a volcanological point of view, the five tephra layers recognised in the sediments testify for episodes of ash deposition in very distal areas with respect to the Italian volcanoes (Fig. 5), irrespective if they are from large (P11, X6, Y5 and Y3 tephra layers) or intermediate (FL tephra layer) explosive eruptions.
Three out of five tephra layers were already recognised in Lake Ohrid sediments (Y5, Y3, and FL), but from a core located in the Macedonian side of the lake (Wagner et al., 2008b). Their recognition in core JO 2004, confirms their deposition was not sporadic but probably they affected all the lake area and its drainage basin. Two of them (P11 and X6) were recognised for the first time in the Balkan area, significantly enlarging to the northeast their dispersal that was previously limited to Ionian and Tyrrhenian seas (Keller et al., 1978; Paterne et al., 2008) or Lago Grande di Monticchio (Wulf et al., 2007).
The distance between the studied site and the inferred source areas is 550 km for the Campanian volcanic area, 620 km for Mount Etna and 900 km for Pantelleria Island (Fig. 5). Bearing in mind that they represent minimum values, the area affected by ash deposition can be assessed at ca. 207,000 km2 for P11, ca. 471,000 km2 for X6, at ca. 550,000 km2 for the Y3 tephra layers. The dispersal area of the Y5 was previously assessed between 1.5–3 × 106 km2 (Pyle et al., 2006).
The paucity of accurate studies on distal ash deposits mainly relies in their poor preservation and in their dispersal behaviour. The accumulation of volcanic ash in distal zones often represents a hazard, since most of the attention and mitigation procedures are usually devoted to proximal areas. Deposition of ash in distal sites can cause damage to infrastructures, disturbance to communications, water pollution and breathing problems. Therefore the recognition and the collection of very distal samples can improve hazard mitigation plans and procedures over very large area far from the volcanic sources.
From a Quaternary Science point of view, Lake Ohrid represents an exceptional natural archive. A previous work (Wagner et al., 2008b) studied a core (Lz1120) from the Macedonian side of the lake, but analysed and discussed only the last 40 ka of sedimentation record of Lake Ohrid with a similar core length than the JO 2004. This apparent difference in sedimentation rate relies in both the presence of sedimentary hiatus in core JO 2004 (Fig. 6; (Belmecheri et al., 2009; Lézine et al., 2010)) and the different locations of the two cores, with the Lz1120 closer to the major karstic springs than the JO 2004 (Belmecheri et al., 2009).
Sedimentation curves for core JO 2004 calculated using the available calibrated 14C (cross) and the correlated ages of tephra layers (diamonds). The grey-shaded area indicates the inferred sedimentary hiatus. P11 = JO-941, X6 = JO-575, Y5 = JO-245, Y3 = JO-187, Etna FL = JO-42. Numbers in italic underlined indicate the calculated sedimentation rate (mm.yr−1) for each segment of the curve.
Courbe de sédimentation de la carotte JO 2004 calculée à partir des âges 14C calibrés (croix) et des datations corrélées aux niveaux de tephra (losanges). La zone grisée indique le hiatus sédimentaire. P11 = JO-941, X6 = JO-575, Y5 = JO-245, Y3 = JO-187, Etna FL = JO-42. Les chiffres soulignés en italiques représentent le taux de sédimentation (mm.an−1) pour chaque section de la courbe.
The core JO 2004 offers the opportunity to study about 130 ky of the sedimentary record, which encompasses the last interglacial. In this scenario, the presence of two important regional markers like the P11 and X6 tephra layers allow the physical correlation of the deep part of the cores JO 2004 to other important archives of the central Mediterranean area.
The available 14C datings (Table 1) and the tephra layers allow the drawing of a sedimentation curve (Fig. 6). The sedimentation curve was built using the seven 14C datings and the tephrochronology, and shows three main rates of sedimentation. The first one between 0 and 100 cm is about 0.10 mm.yr−1, the second one, between 100 and 575 cm is around 0.05 mm.yr−1 and the third one between 575 and 988 cm is about 0.15 mm.yr−1 (Fig. 6).
These variable sedimentation rates reflect different paleo-environmental information. Below the X6 tephra layer, there is the transition between the last-glacial and the last-interglacial phases (Eemian, transition from marine isotopic stage 5 and 6, around 125 ka BP; (Lézine et al., 2010)), which was characterised by a high sedimentation rate (0.15 mm.yr−1; Fig. 6). Between 100 and 575 cm depth, there is a glacial period record with a low sedimentation rate (0.05 mm.yr−1) and low sediment dynamic. It is important to note that this sedimentation rate is probably underestimated, since it does not take into account the occurrence of the inferred sedimentary hiatus between 90 and 103 ka (Fig. 6; (Belmecheri et al., 2009)). The upper 100 cm of core sediments (younger than 10 cal ky BP) correspond to the current interglacial period, which is characterised by a higher sedimentation rate (0.10 mm.yr−1; Fig. 6).
6 Conclusions
The study of the JO 2004 cores yields some important results for the tephostratigraphy and tephrochronology of the Balkans. Five tephra layers were recognised and described, and two of them were for the first time discovered in the area. The tephra layer P11 is the oldest in the whole recognised succession and testifies for ash deposition at more than 900 km from its source on Pantelleria Island. Similarly, the recognition of tephra layer X6 enlarges to the east its dispersal, since it was previously described only in Ionian and Tyrrhenian Sea cores and in the Lago Grande di Monticchio. The other three tephra layers (FL, Y3 and Y5) were already recognised in Lake Ohrid succession, and the new findings testify for their extensive deposition in the area.
The recognition of the two deeper tephra layers (X6 and P11) is especially important, since they allow the establishment of a chronology for the part of the core older than 40 ka BP, and its physical link to other archives of the central Mediterranean area.
In perspective, this work will allow one to obtain a better estimation of the distal tephra dispersion from Italian volcanoes. These results must be integrated in the mitigation and rescue plans that concern the population of the central Mediterranean area.
Acknowledgements
We acknowledge the French (INSU-CNRS) research program ECLIPSE, the French School of Athens (Greece) and the Archaeological museum of Korça (Albania) for financial support and authorizations. We thank Anne-Marie Lézine, Uli von Grafenstein and Nils Andersen for providing samples for the piston core JO 2004 and for the useful discussions. Alain Mazaud is thanked for the magnetic susceptibility. BC was partially supported by Vinci program of Université Franco-Italienne and SETCI from region of Île-de-France. Franco Colarieti (DST Pisa) is gratefully acknowledged for the preparation of samples and assistance during EDS analyses. Amandine Bordon, Soumaya Belmecheri and Sonia La Felice are thanked for helpful discussions. An anonymous reviewer provided helpful suggestions for improving the manuscript.