Major and trace element characterization of tephra layers offshore Pantelleria Island: insights into...

Major and trace element characterization of tephralayers offshore Pantelleria Island: insights into the last200 ka of volcanic activity and contribution to theMediterranean tephrochronology

STELLA TAMBURRINO,1* DONATELLA D. INSINGA,1 MARIO SPROVIERI,2 PAOLA PETROSINO3 and MASSIMO TIEPOLO4

1Istituto per l’Ambiente Marino Costiero (IAMC)–CNR, Calata Porta di Massa, Porto di Napoli, 80133 Napoli, Italy2Istituto per l’Ambiente Marino Costiero (IAMC)–CNR, Campobello di Mazara, Italy3Dipartimento di Scienze della Terra - Universita degli Studi ‘‘Federico II’’ di Napoli, Napoli, Italy4Istituto Geoscienze e Georisorse (IGG)-CNR, Pavia, Italy

Received 3 November 2010; Revised 21 February 2011; Accepted 27 February 2011

ABSTRACT: A detailed tephrochronological study was carried out on the deep-sea core collected from Site 963A inthe Sicily Channel during ODP Leg 160. The chronology of the succession is provided by an age–depth model basedon isotope stratigraphy and quantitative eco-biostratigraphy. Major, trace and rare earth element content was obtainedon single glass grains through electron probe micro-analysis and laser ablation–inductively coupled plasma massspectrometry techniques from six well-preserved tephra layers, characterized by a discrete thickness found along thesuccession. These deposits were correlated with the volcanic activity of Pantelleria and dated at 42.5, 127.5, 128.1,129.1, 188.7 and 197.7 ka. This detailed chemical characterization of the studied deposits aims to provide a valuablereference database for scientists working on both proximal and distal products erupted at Pantelleria island during theLate Pleistocene. This study, moreover, offers the opportunity to better identify Pantelleria-related marker tephraswithin the tephrochronological framework of the central and eastern Mediterranean area. Copyright # 2012 JohnWiley & Sons, Ltd.

KEYWORDS: major and trace elements; Pantelleria; Site 963A; tephrochronology.

Introduction

Geochemical characterization of individual tephra layers hasbeen widely used in stratigraphic correlation studies andrequires the composition of individual deposits to be accuratelydetermined. Grain-discrete methods are the most appropriateto characterize distal tephras which are often affected byreworking and difficult to analyse by bulk methods. Electronprobe micro-analysis (EPMA) is commonly applied to deter-mine the major element content of the tephra layers because itenables detection of small-scale variation in the chemistry ofthe glass fraction (Westgate et al., 1994). This type of approachhas been effective in research carried out in the Mediterraneanregion over recent decades, thus improving previous resultsobtained through bulk-rock analysis. A tephrochronologicalframework for the last 200 ka has been built from terrestrial,shallow- and deep-sea successions (e.g. Keller et al., 1978;Thunnel et al., 1979; Vinci, 1985; Paterne et al., 1986, 1988,2008; Vezzoli, 1991; Calanchi et al., 1996, 1998; Narcisi,1996; Siani et al., 2004; Wulf et al., 2004, 2008; Munno andPetrosino, 2007; Insinga et al., 2008; Wagner et al., 2008;Giaccio et al., 2009; Sulpizio et al., 2009; de Alteriis et al.,2010). However, despite the large amount of chemical data,attribution of a given tephra layer to a single event is not alwaysstraightforward because several factors may hamper a goodmatch, such as: (1) absence of known proximal counterpartsbecause of erosion or burial by younger products; (2)incomplete or inaccurate chrono-stratigraphic reconstructionof the volcanic activity on land; (3) the frequent occurrence ofheterogeneous juvenile fragments at the field scale (bothlaterally and stratigraphically) and even within a single glassshard within the same eruption (e.g. Ukstins Peate et al., 2008);and (4) bias in analytical techniques applied to characterize

proximal and distal deposits (usually, bulk analyses for theformer and single grains for the latter). All these factorsrepresent relevant issues to confront when dealing withtephrochronological studies. To solve these problems, attentionhas recently been dedicated to laser ablation–inductivelycoupled plasmamass spectrometry (LA-ICP-MS) for the analysisof trace elements on single shards, which can provide moreinformation and may allow more confident sourcing of tephralayers (e.g. Beget and Keskinen, 2003; Clift and Blusztajn,1999; Pearce et al., 1997, 2002, 2004; Schiavi et al., 2006). Theavailability of a database comprising more than 40 elements fora single shard allows us, for example, (1) to detect magmaticevolution of the sources and (2) to recognize chemicallydifferent populations of shards within one deposit whichsometimes may not be easily distinguishable from the electronprobe data alone. This approach to the tephrochronologicalstudy of sedimentary successions is of great potential if weconsider that in the central Mediterranean area magmaticsources exhibit a very large compositional range of eruptedrocks (e.g. Lustrino et al., 2011).This paper presents major- and trace- (including rare earth)

element analysis of six tephra layers found in the marinesuccessions of Site 963A (ODP Leg 160) cored 100km east ofPantelleria. These deposits were correlated to the volcanicactivity of the island during the late Pleistocene. Despite adetailed stratigraphic description of the proximal depositsrelated to the main volcanic cycles (Civetta et al., 1998, andreferences therein), their geochemistry and chronology arelacking detail (Cornette et al., 1983; Civetta et al., 1984, 1988,1998; Orsi et al., 1991; Avanzinelli et al., 2004; Rotolo et al.,2007; White et al., 2009) thus often making proximal–distalcorrelations problematic. The downwind position of the corewith respect to the source area and the recovery of thick andwell-preserved tephra layers interbedded within an age-constrained marine succession offered a favourable opportunityto produce a high-quality analytical reference database from

JOURNAL OF QUATERNARY SCIENCE (2012) 27(2) 129–140 ISSN 0267-8179. DOI: 10.1002/jqs.1504

Copyright � 2012 John Wiley & Sons, Ltd.

* Correspondence: S. Tamburrino, as above.E-mail: [email protected]

EPMAand LA-ICP-MS analyses on single glass grains. The resultspresented represent a valid contribution to studies dealing withPantelleria volcanic activity and with the areal dispersion of itsexplosive products in the central Mediterranean area.

Volcanism at Pantelleria and correlateddistal tephra layers

Pantelleria Island (�83 km2) is located about 100 km south-west of Sicily and 70 km off the Tunisian coast, on the axis of theSicily Channel Rift Zone (Fig. 1). The volcanic edifice is atypical stratovolcano, emerging for about half of its height at836m above sea level and about 2200m above the sea floor.The subaerial deposits mostly consist of pantellerites, iron-richperalkaline- and silica-oversaturated volcanic rocks that aretypical of continental rifts and oceanic islands. Pantelleria rocksare characterized by a bimodal suite represented by minormafic lavas that include mildly alkaline basalts (ranging incomposition from �46 to 49wt% SiO2) and felsic lavas andtuffs that include metaluminous trachytes, peralkaline trachytesand pantellerites (ranging in composition from �62 to 72wt%SiO2) (Esperanca and Crisci, 1995; Civetta et al., 1998;Avanzinelli et al., 2004). The volcanic history of the island ischaracterized by large explosive eruptions alternating withperiods dominated by less energetic events. The oldestdeposits, represented by a few voluminous lava flows, wereerupted in a time span ranging from 324 to 239 ka (Wright,1980; Mahood and Hildreth, 1986). Since then, several cyclesof explosive activity occurred and some of their products weredescribed and dated (Mahood and Hildreth, 1986). A majorexplosive eruption, the so-called Green Tuff (GT) event,occurred at ca. 45–50 ka. The GT eruption producedignimbritic deposits up to 20m thick, overlying thin fall andsurge beds (Orsi and Sheridan, 1984). Tephra layers related toPantelleria volcanism were recovered in both marine andlacustrine successions of the central and eastern Mediterraneanarea (Table 1). Among these deposits, the most widespread

marker horizon was correlated with the GT event. Following afew pioneering investigations on the central Mediterranean(Muerdter, 1984; Morche, 1988) during the last decade, severalstudies have been carried out on distal tephras related to pre-GTactivity and a number of layers from different archives werecharacterized in terms of major element content (Wulf et al.,2004; Margari et al., 2007; Paterne et al., 1988, 2008; Vogelet al., 2009).

Dataset and methods

Hole 963A (37802.1480N, 13810.6860E; 470,5m below sealevel; total length of the core 197.5m below seafloor) wasdrilled in the Sicily Channel on a short ridge between theAdventure Bank to the north-west and the Gela basin to thesouth-east (Fig. 1). The sedimentary succession was describedin detail in the preliminary report of Leg 160 by Emeis et al.(1996). It mainly consists of brown to grey calcareousnannofossil clay with a carbonate content ranging from 20to 45% by weight and organic carbon values from 0.1 to 1.5%.No significant lithological changes were observed along thewhole succession and, consequently, it is considered as a singlelithostratigraphic unit. The dataset of this study includes sixprimary tephra layers found along the succession (Fig. 2). Thenomenclature adopted to label these deposits refers to thestratigraphic position of the layers in the succession (ODP1being the youngest and ODP6 the oldest). Tephras ODP1 toODP3 were sampled at their top and bottom whereas tephrasODP5 and ODP6 are represented by one sample due to theirreduced thickness. Multiple samples were picked fromcryptotephra ODP4 which is not visible by naked eye(according to Turney et al., 2004) and recognized throughmicropalaeontological analysis.

Chronology of the core

The age–depth model of the studied interval of Hole 963A core(Fig. 3) was reported recently for the same record by Incarbona

Figure 1. Sketch map showing the location of the investigated ODP Leg 160 Site 963A core (white cylinder) and the Pantelleria Island in the centralMediterranean area. It also includes the position of reference sedimentary successions cited in the text (white cylinders): RC9-191 (Keller et al., 1978),TR171-17, TR171-19 and Ly II-3 (Muerdter, 1984), KET8004 (Paterne et al., 1988), LGM (Wulf et al., 2004), KET8222 and DED 8708 (Paterne et al.,2008), ML01 (Margari et al., 2007), Co1202 (Vogel et al., 2009), and JO 2004 (Caron et al., 2010).

Copyright � 2012 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 27(2) 129–140 (2012)

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et al. (2009) back to �430 ka and is based on correlation ofbenthic and planktonic foraminifera d 18O curves to theSPECMAP stack curve (Imbrie et al., 1984; Martinson et al.,1987). The studied interval comprises Marine Isotopic Stage(MIS) 3 down to the upper part of MIS 7 (a time interval rangingfrom � 20 to 200 ka).A strategy of ‘orbital tuning’ was used to develop the

chronology of the record by directly correlating the d18O curvesand the summer insolation at high northern latitudes.Recent high-precision U/Th coral dating of sea-level changesreported by Thompson and Goldstein (2006) provided keyinformation on the reliability of the SPECMAP chronology.Specifically, the authors evidenced an average 1.3-kadifference (as 2s error estimates and propagated from theanalytical uncertainties) between radiometrically determinedand orbitally tuned ages of the SPECMAP chronology, thusdemonstrating that the uncertainty of �5 ka in the SPECMAPchronology reported by Martinson et al. (1987) is over-estimated. This strongly supports the accuracy of the SPECMAPchronology, suggesting that the astronomical theory of climatechange provides a robust basis for orbital tuning strategies.Only at MIS 7/6 (the well-known Termination II, TII) did theauthors report a larger 10-ka mismatch between their U/Thdating and the SPECMAP chronology. However, the wide rangeof age estimates reported for TII with different methodologicalapproaches (Winograd et al., 1992; Henderson and Slowey,2000; Gallup et al., 2002) seems to reflect previously

unsuspected suborbital climate variability that needs furtherand more detailed investigation. However, although thecalibration of the TII interval may be debated, this does notchange the conclusion that the SPECMAP timescale isextremely accurate.

Chemical analysis

Tephra samples were observed under a binocular microscopefor lithological description and juvenile materials were hand-picked for chemical analyses (Fig. 4, Table 2). For each sample5–20 glass shards were mounted on epoxy resin in 2.5-cm-diameter� 1.0-cm-thick slides and suitably polished. Themajor element content of the selected materials was deter-mined at the Istituto di Geologia Ambientale e Geoingegneria(CNR, Rome, Italy) with EMPA. Analyses were carried outusing a Cameca SX50 electron microprobe, equipped withfive wavelength-dispersive spectrometers. Measuring con-ditions consisted of a 15-kV accelerating voltage, a 15-nAbeam current, a 10–15-mm beam size, and 20 s countingfor peaks and 10 s for backgrounds. All the results ofchemical analyses were recalculated to 100% on an an-hydrous basis and individual analyses with total oxide sumslower than 93wt% were excluded (Supporting information,Table S1).The trace element content of a number of single glass shards

of the ODP tephra layers was determined by LA-ICP-MS at the

Table 1. Tephra layers related to Pantelleria volcanic activity for the last 200 ka recovered in the deep-sea and lacustrine records from the central-eastern Mediterranean area.

Tephras andcryptotephrasfrom distalarchives

Chemical composition(analytical methods) Site (core) Age (ka) Dating methods Reference�

Y6y Pantellerite (XRF) Ionian Sea (RC9-191) 45 Sapropel stratigraphy 1ML-5y From pantelletire to

trachy-comendite(EPMA-WDS, ICP-MS)

Greece, Lake Megali Limni(ML01)

53.6� 5.69 Interpolation between AMS14C dating and arborealpollen stratigraphy (AP)

2

OT0702-7y Pantellerite (EDS) Albania–Macedonia, NorthLake Ohrid (Co1202)

/ / 3

P-10 Pantellerite (EDS) Tyrrhenian Sea (KET 8004) 77.1 Oxygen-isotope stratigraphy 4? (pre-Petrazzaevent)

/ Stromboli volcano 79� 4 / 5

TM22 From rhyolite toNa-trachydacite (WDS)

Italy, Lago Grande diMonticchio

(composite LGM-B/D/E/J)

85.32 Interpolation among AMS14C dating, 40Ar/39Ar dating

and varve stratigraphy

6

/ / Estern Mediterranean basin(LyII-3, TR171-17, TR171-19)

107�5 Sapropel stratigraphy andbiostratigraphy

7

OT0702-10 From pantellerite totrachy-comendite (EDS)

Albania, North Lake Ohrid(Co1202)

/ / 3

JO-941 Pantellerite (EDS) Albania, South Lake Ohrid (JO2004)

/ / 8

P-11 From pantellerite totrachy-comendite (EDS)

Ionian Sea (KET 8222) 130.6 Oxygen-isotope stratigraphy 9

P-12 Pantellerite (EDS) Ionian Sea (KET 8222) 163.6 Oxygen-isotope stratigraphy 9V0 / / 170� 21 40Ar/39Ar 10, 11P-13 Pantellerite (EDS) Ionian Sea (KET 8222) 192.5 Oxygen-isotope stratigraphy 9P-14 Trachy-comendite,

tephriphonolite (EDS)Ionian Sea (KET 8222) 192.5 Oxygen-isotope stratigraphy 9

P-15 Trachy-comendite (EDS) Tyrrhenian Sea (DED 8708) 197.4 Oxygen-isotope stratigraphy 9P-16 From pantellerite to

trachy-comendite (EDS)Tyrrhenian Sea (DED 8708) 198.4 Oxygen-isotope stratigraphy 9

�1, Keller et al. (1978); 2,Margari et al. (2007); 3, Vogel et al. (2009); 4, Paterne et al. (1988); 5,Morche (1988); 6,Wulf et al. (2004); 7,Muerdter (1984);8, Caron et al. (2010); 9, Paterne et al. (2008); 10, Scheld (1995); 11, Kraml (1997). y Proximal deposits: Green Tuff, 48.5�3.35/50.8�3.6 ka (K/Ar,Cornette et al., 1983); 45�4/50� 4 ka (K/Ar, Mahood and Hildreth, 1986).


CHARACTERIZATION OF TEPHRA LAYERS OFFSHORE PANTELLERIA ISLAND 131

Istituto di Geoscienze e Georisorse – U.O.S. Pavia (CNR, Pavia,Italy) laboratory (Table 2). The adopted instrument combines anLA microprobe based on an Nd:YAG laser source (Brilliant,Quantel) operating at 266 nm (for details see Tiepolo et al.,2003), and a quadrupole ICP-MS (Drc-e, Perkin Elmer). Thirty-four masses from 7Li to 238U were acquired in peak hoppingmode using laser spots 15/50mm in diameter. The data qualityfor glass samples can be compromised by the small diameterand thickness of the areas available for analysis. For this reason,selection of the spot size to use during ablation was adjustedaccording to the dimension of each sample and where thethickness of the glass was too reduced no data were acquired.Analyses of small samples, in fact, required a reduction in thesize of ablation crater from 50 to 15mm (consequently reducingthe volume of ablated material) with an associated controlledincrease in the lower limit of detection (LLD) but withoutchanging sensitivity (Tiepolo et al., 2003). Accuracy wasassessed on the USGS BCR-2 reference glass (analysed as anunknown together with tephra samples in each analytical run)and was better than 20% at the sub p.p.m. level. Data reductionwas carried out with the software package GLITTER (van

Achterbergh et al., 2001) and using NIST SRM 610 and 29Si asexternal and internal standards, respectively. The correlation oftephras with age-dated volcanic events was mainly based onthe comparison with published whole rock data from exposeddeposits.

Results

The studied tephras are generally represented by fine- tomedium-grained ash. The medium-sized grains are mostlyangular to subrounded and consist of pumices, sporadicscoriae, obsidians and crystals of feldspar, while the finerfractions are dominated by glass shards. All the tephra layers aremarked by peaks in magnetic susceptibility (Emeis et al., 1996).Layer ODP4 is a reversely graded cryptotephra mainly formedby well-preserved vesicular pumices and glass shards anddispersed along 24 cm of sediment. Glass shards may display athick bubble wall (tephra ODP1), a thin wall (tephra ODP3)and elongated morphologies. Loose crystals of feldspar andclinopyroxene are the main phases in most of the layers,

Figure 2. Stratigraphic position and photographs of the studied tephras along the ODP Site 963A marine record.



whereas dark dense scoriae and obsidian fragments occur asminor constituents (Table 2).According to the total alkali/silica diagram (Le Bas et al.,

1986), theODP samples fall in the field of trachyte and rhyolite,while only the samples at the top part of tephra ODP2 show a

benmoreitic composition (Fig. 5). The rhyolitic glasses and partof the trachytic glasses are characterized by an Agpaitic Index(AI) of>1 [AI¼molar ratio of (Na2OþK2O)/Al2O3], and hencethey may be classified as pantellerites and comenditic trachytesrespectively in the Al2O3/FeOtot grid (MacDonald, 1974;Fig. 5). Based on this major element composition, along withthe location of the core site, we correlate the ODP tephra layerswith the Pantelleria activity although chemical features of thetop part of ODP2 pose several questions.

ODP1–ODP3–ODP4 tephra layer

The tephra layers ODP1, ODP3 and ODP4 show a consistentbimodal composition: samples fall in the trachyte (comenditictrachyte for several points) and pantellerite fields (Fig. 5). In tephraODP1 andODP3, the pantelleritic composition generally prevailsat the bottom of the deposits whereas the trachytic (main) andcomenditic trachyte composition characterizes the top part(Fig. 5). In the case of cryptotephra ODP4, these populationsare mixed along the whole thickness of the layer, althoughtrachytic and peralkaline trachytic glasses are predominant.The compositional trend from trachyte and comenditic

trachyte to pantellerite, which is typically continuous in thePantelleria felsic suite (Civetta et al., 1984), here displays asilica gap of ca. 6%. The SiO2 content ranges from ca. 63 to ca.66wt% (trachyte and comenditic trachyte) and from ca. 73 toca. 75wt% (pantellerites) (Fig. 5). This is accompanied by adiscrete decrease of Al2O3, CaO and MgO, a slight decrease ofNa2O, while TiO2 and FeOtot of ODP1 show an opposite trendcompared with ODP3. The K2O content shows no substantialvariation. These variations are well correlated with theperalkalinity of the rocks, as the AI increases with increasingsilica content in agreement with data on Pantelleria felsicproximal deposits (Ferla and Meli, 2006). Overall, in terms oftrace element content, the ODP1, ODP3 andODP4 tephras arecharacterized by a regular and strong enrichment in lanthaniderare earth elements (LREE), Rb, Zr, Nb, Y and Th (particularly intephra ODP3) whereas Ba, Sr and Ti decrease from trachyte topantellerite (see Fig. 6). The main features of the chondrite-normalized patterns as differentiation increases from comen-ditic trachyte to pantellerite are: (1) an increase of the totalconcentration of REE; (2) a slight increase of LREE relative toheavy REE (HREE) enrichment ([La/Lu]N ranging from 5.6 to

Figure 3. Age versus depth plot for the ODP succession (Incarbonaet al., 2009; modified). Calibrated radiocarbon ages (squares), corre-lation with the SPECMAP curve (circles) and the tephra layers identifiedalong the ODP Site 963A are shown.

Figure 4. Selected photographs of glassshards and micro-pumices of the ODP1 andODP3 tephras. (a) Bubble-wall junction shardsand pumice with tubular vesicles from ODP1(top part); (b) pumices with tubular vesiclesfrom ODP1 (bottom part); (c) micropumiceswith tubular and spherical vesicles and thin-walled junction shards from ODP3 (top part);and (d) pumices with tubular vesicles andbubble-wall junction shard from ODP3 (bot-tom part). This figure is available in colouronline at wileyonlinelibrary.com.



15.9); (3) LREE strongly fractionated in pantellerites ([La/Sm]Nup to 4) and HREE presenting almost flat patterns ([Gd/Yb]Nbetween 1 and 1.6); and (4) development of a progressivelydeepening trough of Eu due to the feldspar fractionation, withEu/Eu� ranging from 1.2 in trachytes and comenditic trachytesto 0.3 in pantellerites (Fig. 6 and supporting Fig. S2).

ODP2 tephra layer

The top part of tephra ODP2 shows a trachytic (main) andbenmoreitic composition whereas the bottom part is charac-terized by trachytes (two points in the comenditic trachytefield). Although the correlation with Pantelleria activity is

Table 2. Lithology, main stratigraphic features, total number of glass shards mounted on the slides and total number of points analysed in the ODPtephras.

Analysed points

Core section,tephra layer(and tephrathickness)

Depth belowsea floor (mbsf)

ConstituentsNo. of

glass shardsEPMA-WDS,

beam 10-15 (mm) (n)

LA_ICP-MS

Volcanic Other (n) Spot (mm)

ODP1 (4 cm)Top 20.84 Abundant white pumices with tubular and

spherical vesicles, brown bubble-wall andthick-walled glass shards; rare dense darkscoria; common crystals of kf, few crystalsof cpx; rare lithics

13 8 1 10

Bottom 20.86 Abundant white pumices with tubular andspherical vesicles; few brown bubble-wallglass shards and dense dark scoria;abundant crystals of kf, few crystalsof cpx

18 6 8 10–25

ODP2 (4 cm)Top 47.52 Few bubble-wall juction shards,

pumices and obsidians; abundantcrystals of kf, common crystals of cpx;common lithics

Common CF 9 9 8 25–35

Bottom 47.54 Few brown-honey thin-walled glassshards; rare dark scoria; abundantcrystals of kf, common crystals of cpx;common lithics

Common CF 9 9 5 10–25

ODP3 (18 cm)Top 47.58 Abundant thin-wall glass shards; few dark

scoria; abundant crystals of kf; few lithicsFew CF 10 10 9 25–50

Bottom 47.72 Abundant white pumices with tubularvesicles; few bubble-wall glass shardsand dark scoria; common crystals of kf;common lithics

Few CF 14 8 5 10–25

ODP4 (24 cm)47.76 Abundant pumices with spherical vesicles

and brown-honey bubble-wall glass shards;rare dark scoria and few obsidians;common crystals of kf; rare lithics

Rare CF 11 7

47.86 Abundant light pumices with sphericalvesicles and brown-honey bubble-wallglass shards; rare dark scoria and fewobsidians; common crystals of kf, rarecrystals of cpx

Common CF 7 7

47.9 Abundant brown-honey bubble-wall glassshards; few white pumices and dark scoria;common crystals of kf, rare crystals of cpx

Common CF 10 7

47.92 Abundant brown-honey bubble-wall glassshards; few white pumices and dark scoria;common crystals of kf, rare crystals of cpx

Common CF 12 7

47.98 Few brown-honey bubble-wall glass shardsand dark scoria; rare white pumices;common crystals of kf, rare crystals of cpx

Common CF 9 9

ODP5 (2 cm)63.84 Abundant light pumices with spherical

vesicles; few crystals of kf, rare crystalsof cpx

9 5 5 10–25

ODP6 (2 cm)66.56 Abundant grey vesicular glass shards; few

crystals of kf, rare crystals of cpx10 8 8 25–50

CF, calcareous foraminifera; cpx, clinopyroxene; Kf, potassium feldspar.



quite clear for the bottom part of the deposit (Fig. 5), the majorelement variation diagrams for the top part, in some cases,do not show a definitive match with the volcanic rocksexposed at Pantelleria. The top of the tephra is characterizedby a less acid deposit compared with the intermediateproducts of Pantelleria, with greater TiO2, Al2O3, MgO andCaO contents while FeOtot ranges between 4.13 and5.51wt% (Fig. 5). The trace element content of the topand bottom part of tephra ODP2 normalized to primordialmantle and REE content normalized to chondritic valuesshow scattered patterns but similar to the other trachytic

layers (Fig. 6). Generally, they show a minor degree ofdifferentiation and less deep Ba and Eu troughs except fortwo analysed samples, which are analogous to felsic tephralayers (Fig. 6).

ODP5 tephra layer

The samples representative of tephra ODP5 have a homo-geneous pantelleritic composition (Fig. 5). The silica content,ranging from 69.8 to 70.2wt%, falls in the compositional rangeof the Pantelleria felsic products. TiO2, CaO and MgO show

Figure 5. (a) Total alkali/silica (TAS) diagram (Le Bas et al., 1986) showing the chemical compositional range of Pantelleria proximal products (fields);(b) chemical classification of the studied ODP tephras according to the TAS diagram; (c) classification of the ODP tephras according to theFeOtot–Al2O3 diagram (after Macdonald, 1974).

Figure 6. (a) Normalized primi-tive mantle (after Sun and McDo-nough, 1989) and (b) normalizedchondrite (after Boynton, 1984)diagrams. The compositionalrange of Pantelleria proximaldeposits is shown for comparison.Data from Avanzinelli et al.(2004), Civetta et al. (1984[XRF, INAA], 1998 [ICP-MS])and Esperanca and Crisci (1995[ICP-MS]).



a discrete decrease, while other major elements have nosubstantial variation. The total concentration of trace elementsof ODP5 results is slightly lower than for ODP1 andODP3. REEcontents normalized to chondritic values give enrichmentpatterns ([La/Lu]N¼ 6.5–12.2), with almost flat patterns forHREE ([Gd/Yb]N¼ 0.7–1.6) and troughs of Eu (Eu/Eu�¼ 0.45).Primitive mantle-normalized diagrams show decreasing pat-terns from Rb to Lu, Sr and Ti troughs, to a lesser extent Ba,K and Sm, and small positive peaks of Ta and Zr (Fig. 6).

ODP6 tephra layer

Chemical analyses carried out on glass shards of tephra ODP6show a uniform trachytic composition with peralkaline features(trachy-comenditic) (Fig. 5). Similar patterns reported for thetrachytic populations of the preceding ODP tephras (inparticular of the top samples of ODP3) can be made for thisdeposit. The REE pattern shows a strong fractionation of LREEcompared with HREE ([La/Lu]N¼ 8.8–11.1) and light negativepeaks of Eu (Eu/Eu�¼ 0.4–0.9) (Fig. 6). In terms of trace elementcontent, the same consideration made for ODP3 can beadvanced for ODP6, which is characterised by a higher totalconcentration of incompatible elements, variable Ba contentand few scattered data (Fig. 6 and supporting Fig. S2).

Discussion

Pantelleria Island is known to have been highly active duringthe Late Pleistocene, as suggested by tephrostratigraphicanalysis of continental and marine successions (Keller et al.,1978; Mahood and Hildreth, 1986; Narcisi and Vezzoli, 1999;Wulf et al., 2004; Margari et al., 2007; Paterne et al., 1988,2008; Vogel et al., 2009). However, the lack of completedata from exposed deposits and the different techniquesadopted to analyse proximal and distal samples often hamperstheir correlation when we deal with chemically zonedexplosive eruptions. The chemical characterization of theODP tephras is discussed below in terms of major and traceelement content, along with their extrapolated ages, first torelate each layer with a single unit on land (where known) andthen to correlate them with other Pantelleria-sourced markertephras found at more distal areas (Table 3a and b). The latterhave been, as yet, characterized chemically on the basis of justtheir major element content (supporting Table S2).

Bulk rock vs. single grain analysis: analyticalproblems with comparing proximal and distaldeposits

Bulk rock analysis is most commonly employed (ICP-MS,INAA, X-ray fluorescence, etc.) to chemically characterizevolcanic deposits in proximal areas. The resulting compositionis affected by several factors, including the different juvenilematerials analysed and the presence of varying amounts ofmicro-phenocryst phases (typically feldspar but also quartz,zircon, apatite andmicas) that can cause considerable variationin the major and trace element content of the same depositfrom different localities (Pearce et al., 2004). Moreover, bulktechniques are unable to distinguish between separatepopulations of shards within the same sample and to producethe information that single-shard EMPA and LA-ICP-MS canoffer. The grain-discrete method is, to date, the most accuratein characterizing distal deposits that are generally made up offine-grained materials. In this context, potential problemswithin single-grain analytical techniques should also bepointed out: energy-dispersive spectroscopy (EDS) andwavelength-dispersive spectroscopy (WDS), for example,may produce some differences in the analytical results dueto the different degree of resolution. Indeed, the resolution of anEDS detector can be affected by the overlap of adjacent peaks,many of which can be handled through deconvolution of thesignals but others remain more difficult to manage especiallywhen the glass contains only a small amount of one of theoverlapping elements; the two methods can suffer sodium losswhose control often depends on the skills of the operators.

Table 3a. Distal equivalents and potential source eruption of theODP1 tephra.

This study Marine tephraLayer ODP1Age (ka)� 42.5

Keller et al. (1978) Marine tephraLayer Y6Age (ka)y 45

Margari et al. (2007) Lacustrine tephraLayer ML-5Age (ka)z 53.6� 5.7

Cornette et al. (1983) Continental tephra (Caldera)Layer Green Tuff (Monastero)Age (ka)x 47�3.2 to 50.8�3.6

Mahood and Hildreth (1986) Continental tephra (Caldera)Layer Green Tuff (Cinque Denti)Age (ka)x 44.5�3.1 to 49.5�4.5

Age (ka) from: �oxygen-isotope stratigraphy and eco-biostratigraphy;yoxygen-isotope stratigraphy; zpollen stratigraphy; and x the 40K/40Armethod.

Table 3b. Marine equivalents and potential source volcanic unit of ODP2, ODP3, ODP4, ODP5 and ODP6 tephra layers.

This study, marine tephraLayer ODP2 ODP3 ODP4 ODP5 ODP6Age (ka)� 127.5 128.1 129.1 188.7 197.7

Paterne et al. (2008), marine tephraLayer P11 P-13 P-15Age (ka)y 130.6 192.5 197.4

Mahood and Hildreth (1986), Continental Unit (Caldera)Layer Unit P (Pre-La Vecchia) Unit I (Pre-La Vecchia)Age (ka)z 132.3�5.7 to 133.5� 6.2 189� 6

La Felice et al. (2009)Age (ka)x 126.8� 1.5 – –

Age (ka) from: �oxygen-isotope stratigraphy and eco-biostratigraphy; yoxygen-isotope stratigraphy; z the 40K/40Ar method; and x the 40K/39Ar method.



Moreover, the major element composition of glasses may notalways provide decisive fingerprints for correlation, becausebimodal or multimodal glass composition could be overlookedby bulk analyses.Given these considerations, the correlation of tephra

ODP with their proximal and distal counterparts inevitablyencountered a number of problems mainly due to: (1) thecomplete absence of single-grain data for the exposed productsof Pantelleria; and (ii) the comparison between our WDS dataand literature EDS data (Paterne et al., 2008) for the distal-equivalent products. In particular, the former represents afundamental issue if we consider that ODP single glasses mayshow a composition still unreported from bulk analyses ofPantelleria rocks (e.g. the top part of tephra ODP2; see below).

Tephra correlation with proximal counterpart

Tephra ODP1

The chemical composition of the ODP1 tephra layer along withthe age of 42.5 ka suggests a correlation of the studied depositwith the GT event (Civetta et al., 1984; Avanzinelli et al., 2004;White et al., 2009) (Table 3a). However, the continuous trendfrom trachytes and comenditic trachytes to pantellerites whichcharacterizes the GT deposits onland is not observed in themarine tephra where a silica gap (from ca. 73 to 63wt%)characterizes the transition from the bottom part, pantelleriticin composition, to the trachytic topmost part (Fig. 7). Whenplotting data in binary diagrams with Zr used as differentiationindex, the ODP1 tephra displays a lower chemical variabilitythan its terrestrial counterparts (Fig. 8). Primitive mantle-normalized and chondrite-normalized REE patterns show verycomparable features between the studied tephra and the GTproximal deposits. According to K–Ar dating, the age attributedto this event ranges from 44.5� 3.1 to 50.8� 3.6 ka (Cornetteet al., 1983; Civetta et al., 1988).

ODP2, ODP3 and ODP4 tephra layers

Tephras ODP2, ODP3 and ODP4 are chemically classified astrachytes and pantellerites. They were dated here to 127.5,128.1 and 129.1 ka, respectively. Single-glass analysis of thetop part of tephra ODP2 shows a major element content that isanomalous if we compare it with bulk-rock analysis of theexposed Pantelleria deposits (less silicic trachytes trendingtoward the benmoreitic field) (Fig. 7). Ferla and Meli (2006)studied the presence of intermediate rocks (mugearites,benmoreites and mafic lavas falling in the so-called ‘‘DalyGap’’), but which occur exclusively in the form of enclaves intrachytes and pantellerites inside the ‘‘Cinque Denti’’ calderaas a result of the intrusion of a fresh batch of magma into morefelsic host-rocks. Despite chemical features of the top part oftephra ODP2 resembling those of Etna products, the traceelement composition confirms a Pantellerian provenance(Fig. 7). This correlation can be supported by the sedimentarycharacteristics of the tephra (e.g. homogeneous grain sizeat both the bottom and top) and its well-preserved naturealong the core. Moreover, the effusive and strombolianeruptive style of Etna activity before 150 ka (Chester et al.,1987) and the absence of coeval dispersed tephra layersrelated to Etna activity (Paterne et al., 2008) make thiscorrelation unlikely.Based on their ages, the studied tephras can be linked to the

‘‘pre-La Vecchia caldera’’ activity (Mahood and Hildreth,1986) (Table 3b). In particular, during this phase the welded tuff‘‘Unit P’’ was erupted at 126.8� 1.5 ka (40Ar/39Ar age, La Feliceet al., 2009). Unit P is a densely welded rheomorphic tuff(Mahood and Hildreth, 1986) that probably represents the

major pyroclastic deposits preceding the ‘‘La Vecchia’’ calderacollapse, which occurred at ca. 114 ka. No chemical data,however, are available onland for these deposits so that thecorrelation of tephra ODP2, ODP3 or ODP4 with Unit P ismerely based on chronological constraints. The occurrence inthe marine record of three tephra layers that are close in timeand related to that period might suggest that previouslyunknown explosive events occurred on land or that Unit Pprobably resulted from different events.The robust chronological correlation of tephra ODP3 (128.1ka)

with Unit P (126. 8� 1.5ka) of La Felice et al. (2009) definitivelyattributed to the Late Pleistocene Pantelleria explosive activityconfirms the reliability of the SPECMAP age model also for thispart of the Pleistocene and offers new constraints to validatedating of the near Termination II interval.

ODP5 and ODP6 tephra layers

Tephra layers ODP5 and ODP6 are dated at 188.7 and197.7 ka, respectively. Tephra ODP5 is composed of homo-geneous pantellerites whereas tephra ODP6 comprises glasseswith a trachytic and trachy-comenditic composition. The lackof chemical data for the ancient volcanic activity of Pantelleria

Figure 7. TAS diagram (Le Bas et al., 1986) showing the chemicalcomposition of the studied ODP tephras compared with that of somenear-vent deposits and distal tephras found in the central and easternMediterranean region (see text). Dashed field shows the compositionalrange of Etnean distal tephras (Keller et al., 1978; Paterne et al., 1988;Calanchi et al., 1996, 1998; Siani et al., 2004; Wulf et al., 2004).



does not provide a precise correlation of these ODP tephraswith specific eruptions or units. Following the stratigraphicframework proposed by Mahood and Hildreth (1986), it is,however, possible to hypothesize a correlation with thevolcanic activity of the ‘‘Pre-La Vecchia’’ caldera (older than163 ka), represented by Unit S, Unit M and Unit I (Table 3b). Inparticular, tephra ODP5 could be the marine counterpart ofUnit I dated at 189� 6 ka (K/Ar dating, Mahood and Hildreth,1986), while tephra ODP6 testifies to an as yet undocumentedolder activity.

Correlations of ODP tephra layers with distaltephras in Mediterranean records

ODP1

Tephra ODP1 can be considered the most proximal facies inthe marine setting of the well-known marker layer Y6 (Kelleret al., 1978), which has been reported from widely dispersedvery distal areas (see Table 1). It was recognized in the IonianSea (Y6 tephra; Keller et al., 1978; Narcisi and Vezzoli, 1999)and in lacustrine records fromGreece (Margari et al., 2007) andAlbania (Vogel et al., 2009), suggesting a wide distributiontowards the north eastern sector of the volcano (see Fig. 1).Tephra Y6 was correlated with the basal part of the GTformation (member a; Orsi and Sheridan, 1984), which isrelated to the plinian phase of the eruption. From a chemicalpoint of view, however, the trachytic portion of tephra ODP1shows a lower degree of differentiation than the more distaldeposits (Fig. 7 and supporting Table S2). No conclusions canbe made concerning the trace element content due to the lackof these data for the distal marine and lacustrine layers.Regarding the ages attributed to the distal tephras on the basis ofthe age–depth plots adopted, Keller et al. (1978) and Margari etal. (2007) give different resulots (ca. 45 and 54 ka, respectively).However, they are within the error range of the ages obtainedby Cornette et al. (1983) and Mahood and Hildreth (1986) forproximal deposits, as well as the age adopted in this study(42.5 ka), which suggests a tendency to the youngest age(Table 3a and supporting Table S2).

ODP3

Evidence of volcanic activity preceding the GT eruption is alsogiven by distal archives. Vogel et al. (2009) and Caron et al.(2010) have described trachy-comenditic to pantelleriticdeposits in lacustrine records from Lake Ohrid (OT0702-10and JO-941, respectively; see Fig. 1) and correlated them withtephra P11 found in the Ionian Sea by Paterne et al. (2008). Thislatter deposit, dated at ca. 130.6 ka, was related to the pre-GTPantelleria volcanic activity and, in particular, to Unit P.According to the major element-based compositional match

between tephra ODP3 and P11, along with the stratigraphicalfeatures of the former (e.g. a well-preserved horizon with adiscrete thickness) that might suggest a high-intensity eventemplacing pyroclastic products over large areas, we proposetephra ODP3 as a more proximal facies of tephra P11 (Table 3band supporting Table S2). There is, however, lower alkalicontent of tephra ODP3 compared with that of tephra P11. Thedifferent methodologies used (WDS and EDS, respectively),along with the only chemical average available for tephra P11,can be invoked to explain this difference.

ODP5 and ODP6

Distal tephra layers correlated with the volcanic period around200 ka have been recovered in the Ionian and Tyrrhenian Seas(Paterne et al., 2008) (see Table 1). According to the availablechronological constraints, ODP5 can be correlated withtephras P13 and P14, both dated at ca. 192 ka (Paterneet al., 2008) (Table 3b and supporting Table S2). Based onmajor element content analysis, however, we favour tephraP13, pantelleritic in composition, and exclude tephra P14because it is characterized by a bimodal population: trachytesand tephriphonolites (Fig. 7 and supporting Table S2). Finally,the oldest tephra, ODP6, shows a chemical signature verysimilar to tephra P15 recovered along the DED 87-08 core(Tyrrhenian Sea) and dated at ca.198 ka (Paterne et al., 2008)(Table 3b and supporting Table S2).

Conclusions

This paper presents a high-quality chemical database whichincludes the major and trace element content (including rareearths) of single glass shards from six tephra layers sampledalong ODP site 963 A and correlated with Pantelleria volcanicactivity. The results, along with the availability of an age-constrained marine succession, contribute to the stratigraphicreconstruction of the main eruptive events that occurred on theisland between ca. 42 and ca. 198 ka. Moreover, the dataprovide a first step towards a new and accurate chemicalcharacterization of Pantelleria deposits which are widespreadin the central Mediterranean area but are often lacking adefinitive correlation with proximal counterparts.

Updating of chemical datasets from terrestrial depositsthrough single-grain methods is needed to establish a definitiveland–sea correlation and to implement the tephrochronologicalframework for the central Mediterranean area.

Supporting information

Additional supporting information can be found in the onlineversion of this article:

Figure 8. Selected trace elementcontents forthe analysed tephraODP1 vs SiO2 (wt%). Dataof GT proximal products (Civetta et al., 1984;Avanzinelli et al., 2004;White et al., 2009) arealso reported for comparison.



Table S1. Major elements, and trace and rare earth elementsof all investigated tephra layers.Table S2. Representative compositions, recalculated to

100% water free, of ODP tephras and their proximal anddistal counterpart in terrestrial, marine and lacustrine settings.Fig. S1. Binary diagrams of major elements and Agpaitic

Index vs. SiO2 for tephras ODP1, ODP3 and ODP4.Fig. S2. Binary diagrams of selected trace elements vs. Zr

content for ODP tephra samples.Please note: As a service to our authors and readers, this

journal provides supporting information supplied by theauthors. Such materials are peer-reviewed, and may be re-organized for online delivery, but are not copy-edited or typesetby Wiley-Blackwell. Technical support issues arising fromsupporting information (other than missing files) should beaddressed to the authors.

Acknowledgements. We thank Lucia Civetta for her comments on themanuscript; Marcello Serracino and Michele Lustrino for their skilledassistance during microprobe analyses; and Patricia Sclafani andSietske Batenburg for proofreading of the English text. Comments fromSabine Wulf and Giovanni Zanchetta greatly improved the quality ofthe manuscript.

Abbreviations. AI, Agpaitic Index; EDS, energy-dispersive spec-troscopy; EPMA, electron probe micro-analysis; GT, Green Tuff; HREE,heavy rare earth elements; LA-ICP-MS, laser ablation–inductivelycoupled plasma mass spectrometry; LLD, lower limit of detection;LREE, lanthanide rare earth elements; MIS, Marine Isotope Stage;WDS, wavelength-dispersive spectroscopy.

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