Late glacial explosive activity on Mount Etna: Implications forproximal – distal tephra...

Journal of Volcanology and Geothermal Research 265 (2013) 9–26

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Late glacial explosive activity on Mount Etna: Implications forproximal–distal tephra correlations and the synchronisation ofMediterranean archives

P.G. Albert a,b,⁎, E.L. Tomlinson c, C.S. Lane b, S. Wulf d, V.C. Smith b, M. Coltelli e, J. Keller f, D. Lo Castro e,C.J. Manning a, W. Müller a, M.A. Menzies a

a Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UKb Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford OX1 3QY, UKc Department of Geology, Trinity College Dublin, College Green, Dublin 2, Irelandd GFZ German Research Centre for Geosciences, Section 5.2 – Climate Dynamics and Landscape Evolution, Telegrafenberg, 14473 Potsdam, Germanye Intituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, sezione Catania, Piazza Roma, 2 – 95123 Catania, Italyf Institute of Geosciences, Mineralogy – Geochemistry, Albert-Ludwigs-University Freiburg, Albertstrasse 23b, 79104 Freiburg, Germany

⁎ Corresponding author at: Department of Earth ScienceLondon, Egham Hill, Egham, Surrey TW20 0EX, UK. Tel.: +

E-mail address: [email protected] (P.G. Albert).

0377-0273/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.jvolgeores.2013.07.010

a b s t r a c t
a r t i c l e i n f o
Article history:Received 21 March 2013Accepted 13 July 2013Available online 1 August 2013

Keywords:Mount EtnaPlinianTephrochronologyGlass chemistryY-1 tephra

Plinian and Ignimbrite deposits represent explosive activity (ca. 17–19 cal ka)within the predominantly effusiveand mildly explosive (Strombolian) volcanic history of Mount Etna (Italy). Proximal glasses from the BiancavillaIgnimbrites and Unit D Plinian fall deposits are characterised. Fall deposits recorded at Acireale (D1b and D2b)and Giarre (D1a and D2a) are geochemically distinct confirming they relate to different eruptions. The AcirealePlinian fall (D1b and D2b) deposits compositionally overlap with the Biancavilla Ignimbrite deposits. These ex-plosive eruptions from Etna are considered responsible for widespread ash dispersals throughout the centralMediterranean region, producing the marker tephra layers (Y-1/Et-1) recorded in marine and lacustrine sedi-mentary archives. Stratigraphically these distal tephras occur at or close to the onset of the last deglaciation(Termination 1)within their respective palaeoenvironmental records, therefore making them potentially crucialtephrostratigraphic markers. This study investigates distal tephra deposits thought to be from Etna recorded inthe Ionian Sea (Y-1), Lago Grande di Monticchio (LGdM, Italy; tephras TM-11 and TM-12-1), Lago di Mezzano(Italy) and the Haua Fteah cave (Libya). The glass chemistry of Y-1 tephras recorded in the Ionian Sea and atHaua Fteah is consistent with the Biancavilla Ignimbrites (16,965–17,670 cal yrs BP) and the upper AcirealePlinian fall (D2b). The LGdM record indicates that explosive activity on Etna associated with Unit D spans a min-imum of 1540 ± 80 varve years. TM-12-1 (19,200–19,804 cal yrs BP) in LGdM appears to represent the oldestdistal counterpart of Etna Unit D explosive activity and is associated with the lower Acireale (D1b) Plinian erup-tion. The proximally undefined TM-11 (17,640–18,324 cal yrs BP) and distal correlatives are geochemically dis-tinct from the Ionian Sea Y-1 tephra. Such significant compositional differences seen between distal tephra layersare not observed within individual proximal units and are likely to indicate that the distal tephras relate to sep-arate eruptive phases. Until proximal relationships can be established, the TM-11 type Y-1 equivalents should betermed TM-11. Great care should be exercisedwhen using these distal ash layers to synchronise sedimentary re-cords during a crucial period of environmental change.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

The last glacial cyclewas characterised by abrupt-high amplitude cli-matic changes often occurring at centennial to millennial timescales(e.g., Dansgaard, 1985; Alley et al., 1993; Dansgaard et al., 1993;Rasmussen et al., 2006). High precision dating techniques are requiredto test the spatial and temporal relationship of rapid (centennial)

s, Royal Holloway University of44 7787 110909.

ghts reserved.

climatic events recorded in different environmental archives overwide geographical distances. Radiocarbon dating (14C) remains themost widely adopted geochronological tool for the last 50 ka BP, how-ever, the precision of 14C based agemodels is often insufficient to assessthe timing of climatic change between different archives. Furthermorecomparing marine and terrestrial archives is complicated by uncer-tainties associated with marine reservoir offsets.

In the central Mediterranean region the reoccurrence of explosivevolcanic activity has seen the successful application of volcanic ash/tephras as instantaneously deposited isochronous markers (e.g. Kelleret al., 1978; Paterne et al., 1986, 1988, 2008; Siani et al., 2004; Wulf

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1 All radiocarbon ages presented here (cal yrs BP) have been calibrated in OxCal 4.2(Bronk Ramsey, 2009) using the IntCal09 internationally accepted calibration curves(Reimer et al., 2009) as a 2 sigma age range. Year 0 is 1950 AD and published 14C agesare included in brackets.

10 P.G. Albert et al. / Journal of Volcanology and Geothermal Research 265 (2013) 9–26

et al., 2004, 2008; Lowe et al., 2007; Giaccio et al., 2008, 2009; Bourneet al., 2010; Sulpizio et al., 2010). Owing to the widespread distributionof tephras, they can be used to synchronise palaeoenvironmental ar-chives (tephrostratigraphy), thus enabling the assessment of geograph-ic leads and lags in climate variability (Lowe et al., 2007). Furthermore,where tephras can be precisely correlated to dated proximal depositsthey provide chronological markers (Lowe, 2011). Tephras successfullyused to synchronise palaeoenvironmental archives require a combina-tion of the following attributes; (1) diagnostic glass geochemistryand/ormineral assemblage; (2) good stratigraphic controls; (3) chrono-logical control (proximally or distally); and (4) widespread dispersalfrom the volcanic source (Lowe, 2011).

In this contributionwe assess the application of the Y-1/Et-1 tephrasas a tephrochronological tool within the Mediterranean region. Thesedistal tephras occur at or close to the onset of the last deglaciation/Termination 1 (e.g., Keller et al., 1978; Siani et al., 2004), a crucial periodof climatic change within their respective archives. Consequently, thesetephrasmay offer the potential to assess leads and lags in local environ-mental responses to abrupt climate changes within the Mediterraneanregion.

1.1. Tephrochronological background

Keller et al. (1978)first identified the Y-1 in the Ionian Sea sedimentsand owing to its Na-alkaline, Benmoreite affinity it was attributed toexplosive activity on Mount Etna. Paterne et al. (1988) recognisedNa-alkaline layers in the Southern Tyrrhenian Sea records and termedthem Et-1. These layers were more specifically ascribed to theBiancavilla Ignimbrites from Mount Etna, which form a succession of“block and ash” flow deposits that are exposed south-west of the sum-mit (Sparks et al., 1973; Kieffer, 1979; De Rita et al., 1991). Paterneet al. (1988) suggested a possible link between the Tyrrhenian Sea Et-1 layers and the Ionian Sea Y-1 marine tephra. Subsequently, distaltephras reported across the centralMediterraneanwith aNa-alkaline af-finity spanning northern hemisphere deglaciation were termed eitherY-1 or Et-1 (Vezzoli, 1991; Calanchi et al., 1998; Ramrath et al., 1999;Siani et al., 2004;Wulf et al., 2004, 2008).Within the annually laminated(varved) sediment record of Lago Grande di Monticchio (LGdM), Italy,Wulf et al. (2004) correlated the TM-11 tephra layer to the Y-1/Biancavilla Ignimbrite.Wulf et al. (2008) also described a second slightlyolder Na-alkaline tephra layer, TM-12-1, and this was labelled the ‘Ante-Biancavilla’ tephra. Consequently, from this distal record, at least twodistinct Late Glacial explosive eruptions of Mount Etna have been pro-posed. This led to a correlation with the two fallout deposits of Unit Drecognised in proximal sites east (Giarre) and southeast (Acireale) ofMount Etna, which are related to the Biancavilla Ignimbrites by Coltelliet al. (2000). All these proximal–distal correlations relied on proximalwhole rock major element data as no glass data sets were available toprecisely test the proposed proximal links. Discrepancies betweendistal–distal correlations of Y-1/Et-1 tephra were first reported byWulf et al. (2008).

In this contribution, we review the application of the Y-1 tephras asprecise tephrostratigraphic markers. We present grain specific multi-element proximal glass data and use this to: (1) define the diagnosticproximal glass geochemistry of Late glacial explosive volcanism atMount Etna (Unit D fall and the Biancavilla Ignimbrites); (2) assess cor-relations between theUnit D Plinian fall and the Biancavilla Ignimbrites;and (3) test proximal–distal tephra correlations. The resultant proxi-mal–proximal and proximal–distal links are used to revise and extendthe fall footprint of large explosive eruptions and to constrain theevent stratigraphy of this explosive activity at Mount Etna.

2. Geological setting

Mount Etna is a 3340 m high stratovolcano, which extends over anarea of 1250 km2 along the eastern coast of Sicily (Branca et al., 2011a)

(Fig. 1). Volcanic activity began at Etna ~ 500 ka (Gillot et al., 1994;Branca et al., 2011b; De Beni et al., 2011) and at ~200 ka the eruptedproducts began to display characteristic Na-alkaline compositions(Viccaro et al., 2010). The construction of a central-conduit stratovolcanostarted about 110 ka (De Beni et al., 2011). The volcanic history ofMountEtna is dominated by quasi-persistent mildly explosive activity at thesummit craters. This is interrupted by frequent effusive eruptions fromeither the summit or lateral vents that opened on theflanks of the volca-no. However, there is evidence for periodic, large, explosive eruptions inthe proximal tephrostratigraphic record since the first Plinian eruptionat 99 ka (De Beni et al., 2005). One of the most prominent tephraevent during recent times is related with the Unit D Plinian explosiveactivity recognised by Coltelli et al. (2000). 14C ages were determinedon charcoal samples underlying the Unit D deposits at Giarre (Coltelliet al., 2000) and these currently constrain the onset of Unit D activity toslightly younger than 18,533–18,818 cal yrs BP1 (15,420 ±60 14C yrs BP,Coltelli et al., 2000). A charcoal sample from an in situ tree stump at thebase of the Biancavilla Ignimbrite was dated at 14,180 ± 260 14C yrs BP(Kieffer, 1979), this same sample has been more recently re-dated at14,240 ± 90 14C yrs BP (Siani et al., 2001). The most recent, preciseage has been calibrated to produce an age of 16,965–17,670 cal yrs BPfor the proximal Biancavilla Ignimbrite (14,240 ± 90 14C yrs BP, Sianiet al., 2001). The ignimbrites are considered the final products of theEllittico caldera formation (Fig. 1) (Romano and Guest, 1979; De Ritaet al., 1991; Coltelli et al., 2000) and based on broad chronological agree-ment Coltelli et al. (2000) linked the unit D activity to these Ignimbritedeposits.

3. Sites and samples

3.1. Proximal

Ignimbrite deposits were sampled from the Biancavilla region on thelower SW flank of Mount Etna (Fig. 1). Four stratigraphic units are iden-tified each by a fine grained basal componentwhich becomes coarser upthrough the unit (Sparks et al., 1973; De Rita et al., 1991). The lower andupper flow deposits were sampled at Vallone di Licodia (37° 39′ 320″N,014° 54′ 870″E) and Contrada Monaci (37° 39′ 402″N, 014° 55′ 256″E)respectively. Theflowdeposits are poorly sorted comprising scoriaceouslapilli within an ashymatrix (Fig. 2). Samples comprised of dark (black),blocky, poorly vesiculated scoriaceous lapilli (Fig. 3). The phenocrystassemblage is heavy dominated by plagioclase and clinopyroxene.

Fall deposits were sampled from the lower eastern flank of MountEtna following the unit D stratigraphy of Coltelli et al. (2000). Pumicefall beds form two separate couplets outcropping in different areas ofthe south-eastern and eastern flank, Acireale (37° 35′ 847″N, 015° 07′616″E) and Giarre (37° 44′ 303″N, 015° 10′ 350″E) respectively (Fig. 1),and show no clear stratigraphic relationship between regions (Coltelliet al., 2000). Both couplets, D1b/D2b (Acireale) and D1a/D2a (Giarre),are separated by paleosols that comprise predominantly of volcaniclasticdeposits and represent temporal gaps between fall events (Fig. 2). Theindividual fall deposits comprise alternating, well sorted, clast supportedpumice lapilli beds that are interrupted by ash layers (Fig. 2). Giarre falldeposits are distinguished from the Acireale deposits based on the pres-ence of solely lighter more porphyritic pumices and the less consistentfall thicknesses (Coltelli et al., 2000). All Unit D pumices contain pheno-crysts of plagioclase and clinopyroxene, whilst olivine, magnetite andamphibole are found as microcrysts. The exception is amphibole whichwas not observed in the D2b glasses (Coltelli et al., 2000). The pumicesrecorded at both Acireale and Giarre are highly vesicular and very differ-ent from the scoriaceous blocky clasts sampled from the Biancavilla flow

Fig. 1.Map showing the location of Mount Etna within the central Mediterranean, also given are the locality of distal archives recording Etnean distal tephras. Inset shows the locality ofproximal samples taken from the lower slopes ofMount Etna relative to the Ellittico caldera at the summit. Etna = Mount Etna; CF = Campi Flegrei; IS = Ischia; SV = Somma-Vesuvius;Ae = Aeolian Islands; P = Pantelleria.

11P.G. Albert et al. / Journal of Volcanology and Geothermal Research 265 (2013) 9–26

deposits (Fig. 3). From the grain-size distribution, areal dispersal andlithofacies outlined in Coltelli et al. (2000) at least three of the fall unitsidentified on the eastern flank of Etna are confidently interpreted asPlinian falls (D2a, D1b, D2b). D2b is the thickness unit with distancefrom volcanic source (Coltelli et al., 2000).

3.2. Distal

METEOR core M25/4-11 was retrieved in 1993 with a piston corerfrom the Calabrian Rise (36°44′75″N; 17°43′05″E) in the Ionian Sea at3376 m water depth (Keller, 1994). Y-1 in the Ionian Sea core M25/4-11 is deposited at 75.5–76.5 cm depth and has an interpolated 14Cage of 14,290 ± 110 14C yrs BP (Kraml, 1997) which corresponds to17,002–17,790 cal yrs BP.

HF_T426 is a visible ~1 cm thick tephra layer identified within theexcavated post-LGM stratigraphy of Haua Fteah cave (HF), Libya(Douka et al., in press). HF is a karstic cave, with a large north-facingopening (~50 m wide by ~20 m tall), situated on the Mediterraneancoastline of Cyrenaica (Fig. 1). The cave is renowned for its long archae-ological record of human occupation and environmental change over atleast the last 100 kyr (McBurney, 1967).

Lago di Mezzano (LMZ) is a small maar lake west of Lake Bolsena inCentral Italy, ca 100 km north of Rome (42°37′N, 11°56′E, 452 m a.s.l;Fig. 1). Core sequence LMZ-B was taken in 1995with a modified Living-ston piston corer (Usinger corer) from central part of the lake basin.A 1 cm thick, greyish ash layer at a composite depth of 13 m has been

correlated to the Y-1 andhas beendated at 16,900 cal yrs BP by interpo-lation of the calibrated radiocarbon chronology (Ramrath et al., 1999).

Lago Grande di Monticchio (LGdM) is a crater lake in the MonteVulture Volcanic Massif in Basilicata, southern Italy (40°56′N, 16°35′E,656 m a.s.l.), located ca. 120 km east of Naples and approximately280 km southeast of Rome. The cores of interest were taken in 1990(composite profile LGM-B/D) at a 6 m water depth. Tephra TM-11 oc-curs at 9.57 m composite depth and is 0.5 mm thick. It is dated by thevarve supported sedimentation rate chronology at 16,440 ± 820varve years BP (Wulf et al., 2004, 2008). Tephra TM-12-1 was identifiedat 10.31 m composite depth and reveals a thickness of 1.4 mm. It isdated by the LGdM varve chronology at 17,980 ± 900 varve yrs BP(Wulf et al., 2008).

4. Methods

The clasts from both flow and fall deposits were cleaned, dried andmounted in Struers Epofix epoxy resin. Mounts were sectioned andpolished andscanning electronmicroscopywas conducted to determinesuitable glass locations for analysis avoiding phenocryst andmicrocrystphases. Distal tephras linked to this explosive activity on Etna (outlinedin Section 3.2), with the exception of those from LGdM, were also em-bedded in resin, sectioned and polished ready for geochemical analysis.Distal tephra layers from LGdMwere analysedwithin thin sections fromthe cored sediments.

Fig. 2. Sampled stratigraphy of the Biancavilla Ignimbrites and the unit D fall deposits recorded at Acireale and Giarre. Charcoal samples are marked and un-calibrated radiocarbon agedeterminations are presented.


4.1. Analytical

4.1.1. Electron microprobe analysis (EMPA)Major and minor element chemistry of individual juvenile clasts

(volcanic glass) was determined using a wavelength-dispersive JEOL8600 electron microprobe in the Research Laboratory for Archaeologyand the History of Art, University of Oxford. A beam accelerating voltageof 15 kV was used with a 6 nA current and a beam diameter of 10 μm.The instrument was calibrated with a suite of appropriate mineralstandards; peak count times were 30 s for most elements and 10 sfor Na. Secondary glass standards from the Max Plank institute(MPI-DING suite; Jochum et al., 2006) bracketing the possible chem-istries were also analysed alongside the unknown tephras. These in-cluded evolved felsic [ATHO-G (rhyolite)], through intermediate[StHs6/80-G (andesite)] to mafic [GOR128-G (Komatiite)] glasses.

All glass data was normalised to 100% for comparative purposes. Thisis of paramount importance for tephras inmarine and lacustrine cores, asglass shards may absorb water from their surroundings, which isreflected in low totals. Analytical totals b94% were discarded. Errorsare typically b±0.7% RSD for Si; ~±3% for most other major elements,except for the low abundance elements: Ti (~±7%), Mn (~±30%).

Error bars on plots represent reproducibility, calculated as a 2 x standarddeviation of replicate analysis ofMPI-DING StHs6/80-G. All standard datais presented in the supplementary material.

4.1.2. Laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)

Trace element analyses of both individual proximal and distal juve-nile tephra clasts were performed using an Agilent 7500es ICP-MScoupled to a Resonetics 193 nm ArF excimer laser-ablation in the De-partment of Earth Sciences, Royal Holloway, University of London. Ana-lytical procedures for tephras are reported in Tomlinson et al. (2010).Overall, 20, 25 and 34 μm spot sizes were used depending on the vesic-ularity and/or size of glass surfaces; distal tephras often required a small-er laser spot. The repetition ratewas 5 Hz and the count time 40 s on thesample and 40s on the gas blank to allow the subtraction of the back-ground signal. Blocks of eight sample/shards of glass and one MPI-DING reference glass were bracketed by NIST612 glass calibration stan-dard (GeoREM 11/2006). In addition MPI-DING reference glasses(Jochum et al., 2006) were used to monitor analytical accuracy.

The internal standard appliedwas 29Si (determined by grain-specificEPMA analysis). Three geochemically distinct reference glasses were

Fig. 3.Representative SEMand lightmicroscope images of both the proximal and distal glasses geochemically investigatedwithin this study; (a) Vallone di Licodia; (b-c) ContradaMonaci;(d) Acireale D1b; (e–f) Acireale D2b; (g) Giarre D1a; (h–i) Giarre D2a; (j–l) Y-1 Ionian Sea (M254/-11); (m–n) Lago di Mezzano tephra (o) HF_T426 Haua Fteah, Libya.



used to cover the possible geochemical spectrum often observed withinthe tephra deposits and for consistency these were the same secondarystandards used for EPMA analysis. LA-ICP-MS data reduction wasperformed in accordance with Tomlinson et al. (2010), using Microsoftexcel. Accuracies of LA-ICP-MS analyses of ATHO-G and StHs6/80-GMPI-DING glass were typically ≤ 5%. Relative standard errors (% RSE)for tephra samples are typically b3% RSE for V, Rb, Sr, Y, Zr, Nb, Ba, La,Ce, Pr, Th; b5% RSE for Nd, Eu, Dy, Er, Ta, U and b8% Sm, Yb and Lu. %RSE increases with smaller spot analyses. Standard data and full errorsfor individual sample analyses (standard deviations and standarderror) are given in the supplementary material. For consistency withEPMA error reporting, error bars on plots show 2 x the standard devia-tion of replicate analyses of MPI-DING StHs6/80-G.

4.2. Statistical approach

Herein statistical distance (D2; Perkins et al., 1995; Pearce et al., 2008)is used as an additional tool for assessing tephra correlations. Statisticaldistance measures the difference between sample pairs based on theirmean and standard deviations. Providing the data has a normal distri-bution, the D2

calculated value has a Chi-squared distribution betweencompositionally identical sample pairs. Where D2

calculated N the D2critical

then the null hypothesis (the same pairs are identical) can be rejected.A D2

calculated value less than the D2critical means that the sample pair can-

not be distinguished, however it does not indicate that they are identical.Compositionally identical samples can only be determined if D2 = 0.

Table 1Representativemajor,minor and trace element glass data from the Biancavilla Ignimbrite deposmaterial file.

Locality Biancavilla (V. Licodia) Biancavilla (C. Monaci) Acireale D1

Unit Unit 2 Unit 3 Fall-003 F

Sample 2A 5A 11C 3A 10B 14C 2A 3

Material Scoria Scoria Pumice

Major elementsSiO2 63.79 63.89 62.41 62.58 62.33 62.96 62.17TiO2 1.24 1.21 1.29 1.20 1.19 1.35 1.14Al2O3 17.24 17.02 17.07 16.93 16.85 17.15 17.27FeOt 4.91 4.61 5.00 5.11 5.07 4.35 4.70MnO 0.17 0.27 0.25 0.18 0.17 0.19 0.20MgO 1.75 1.43 1.62 1.68 1.68 1.68 1.49CaO 1.41 2.02 2.66 3.36 3.30 3.18 3.15Na2O 5.73 5.57 5.69 5.59 5.98 5.93 6.10K2O 3.76 3.97 4.01 3.36 3.42 3.23 3.78Analytical total 95.92 95.36 98.12 98.05 98.64 94.82 98.5K2O+Na2O 9.49 9.54 9.70 8.95 9.40 9.16 9.88

Trace elements ppmV 62.6 63.2 59.0 70.4 69.5 65.6 57.6Rb 82.3 95.1 70.2 87.6 84.6 74.5 88.9Sr 685 399 812 692 673 703 755Y 34.4 36.1 36.4 34.4 37.0 36.4 35.8Zr 433 419 415 413 425 424 435Nb 114 120 111 112 115 113 119Ba 1419 1349 1446 1299 1333 1360 1490 1La 121 124 120 120 124 124 128Ce 226 234 224 226 230 231 230Pr 22.6 22.8 23.2 22.8 23.6 23.4 23.3Nd 86.1 89 84.5 84.2 87.6 90.2 87.6Sm 13.6 14.4 13.6 14.6 14.4 15.6 12.2Eu 3.4 3.3 3.4 3.2 3.4 3.4 3.4Gd 8.9 10.3 9.8 10.6 10.6 10.0 9.9Dy 7.2 7.6 7.5 7.3 7.1 7.4 7.4Er 3.6 3.9 3.9 3.6 3.7 3.6 3.6Yb 3.1 3.4 3.3 3.2 3.6 3.6 3.1Lu 0.44 0.52 0.48 0.45 0.49 0.52 0.47Ta 5.4 5.3 5.4 5.0 5.4 5.3 5.0Th 21.6 22.1 22.1 21.3 22.4 21.9 23.8U 6.5 6.8 6.3 6.3 6.4 6.3 7.0

Whilst statistical distance is not always deemed statistically significantbetween sample pairs, lower D2 values relative to other sample pairsdo indicate greater compositional similarity and provide greater confi-dence in possible correlations (Pearce et al., 2008).

5. Results and interpretation

5.1. Glass chemistry of proximal deposits

Representative major, minor and trace element compositions ofproximal pumice and scoria glasses are given in Table 1. The full geo-chemical data sets are presented in the supplementary material. Glassesfrom juvenile clasts found in both fall and flow deposits have com-positions ranging from trachyandesite to trachyte (Fig. 4a) and arealso termed benmorite due to their Na-alkaline affinity (Na2O = 5.1–6.8 wt.% and K2O 2.8–4.4 wt.%). Overall major and minor element glasschemistries from the complete proximal suite of deposits show signifi-cant heterogeneity with 59.4–64.5 wt.% SiO2, 4.0–6.6 wt.% FeO (all Fepresented as FeO) and 1.4–5.5 wt.% CaO (Table 1).

All proximal glasses show similar levels of incompatible trace ele-ment enrichment reflected in their multi-element profiles and are upto more than 300 times more enriched than primitive mantle (Fig. 4b).Profiles are characterised by a trough atNb and Ta and a pronounced de-pletion in Ti (Fig. 4b). Glasses show light rare earth element (LREE) en-richment relative to the heavy rare earth elements (HREE) (La/Yb =31–45; Fig. 4b). Sr depletions are attributed to high level fractionation

its and theUnit D Plinian fall. Full geochemical data sets are available in the Supplementary

b Acireale D2b Giarre D1a Giarre D2a

all-004 Fall-005 Fall-008 Fall- 006 Fall-007

A 19D 5A 6B 20D 11C 2A 6B 3A

Pumice Pumice Pumice

61.87 62.89 62.29 62.23 62.70 59.97 60.99 61.33 61.451.31 1.15 1.25 1.29 1.30 0.88 0.82 0.82 0.84

17.03 17.21 16.89 16.95 16.79 17.91 17.86 16.97 17.905.16 4.26 5.25 5.02 4.95 5.77 5.15 6.00 5.620.12 0.18 0.20 0.19 0.20 0.19 0.15 0.24 0.121.84 1.42 1.65 1.58 1.71 1.89 1.42 1.56 1.253.49 3.28 3.34 3.43 3.40 4.54 3.90 3.86 3.325.84 6.31 5.71 6.00 5.68 6.07 6.56 5.77 6.133.34 3.29 3.42 3.30 3.28 2.79 3.13 3.45 3.37

98.67 97.84 97.88 98.72 97.47 98.19 97.98 97.78 95.329.18 9.6 9.13 9.30 8.96 8.86 9.69 9.22 9.50

70.8 63.0 62.6 62.5 71.6 58.3 48.5 60.1 43.084.0 84.5 75.1 79.2 82.2 82.5 82.3 85.3 94.4

751 759 797 737 754 860 675 788 43637.7 36.7 37.3 36.4 35.9 25.3 26.5 22.9 27.9

454 452 457 436 431 319 360 337 397115 121 112 112 111 102 108 99 117381 1565 1413 1431 1371 977 1003 969 1011127 131 123 122 119 98 103 98 108233 245 229 230 231 174 185 161 18924.4 24.6 22.5 23.3 23.2 17.4 18.9 15.9 18.792.3 87.6 91.4 80 81.2 60.8 64.9 56 64.914.3 14.1 14.3 14.5 16.3 10.3 9.9 8.4 11.23.7 3.5 3.6 3.6 3.7 2.5 2.3 2.4 2.4

10.9 10.0 9.1 10.0 12.2 6.4 6.6 6.4 9.88.3 7.9 7.7 6.9 7.4 5.4 5.5 4.6 5.43.9 3.9 3.7 4.2 3.9 2.6 2.7 2.3 3.03.6 3.9 3.9 3.8 3.0 2.6 2.8 2.2 bLOD0.51 0.56 0.50 0.57 0.55 0.36 0.41 0.38 bLOD5.6 6.0 4.9 5.5 5.2 4.4 4.9 5.0 5.6

22.8 24.1 20.6 22.2 21 19.7 21 18.9 21.77.0 6.6 6.7 6.8 6.4 6.0 6.1 5.9 6.1


associated with Ca rich phases like plagioclase and clinopyroxene.Glasses in the lower Biancavilla flow (V. Licodia) deposits are some ofthe most fractionated associated with low CaO concentrations (Fig. 5c)and a marked Sr anomalies (Sr/PrN = 0.34 ± 0.18 (2 s.d.); Fig. 4b).

Though the detailed analyses of the petrogenesis of the magmasfeeding Mount Etna is beyond the scope of this paper, it is worth notingthat these glasses produced during the explosive Unit D Plinian/Biancavilla Ignimbrites activities all show negative anomalies at Nb, Taand Ti which is characteristic of a subduction influence at source(Fig. 4b). The occurrence of uncharacteristically explosive volcanismwith Plinian columns on Mount Etna may reflect a switch from a solelyintra-plate mantle source (i.e., Cadoux et al., 2007; Viccaro andCristofolini, 2008) to one influenced by nearby lithospheric subduc-tion processes (i.e., Aeolian Islands). Such mechanisms, includingdetachment or roll back of the subducting Ionian slab to the northof Mount Etna have been previously proposed (Schiano et al., 2001;Tonarini et al., 2001; Schellart, 2010).

5.1.1. Biancavilla flow depositsThe flow units at Biancavilla have a trachyte glass composition

(Fig. 4a) and the lower member scoriaceous ignimbrite deposits atVallone Licodia (Flow unit 2) show some of the most fractionated glasscompositions with 62.4–64.5 wt.% SiO2 and 1.4–3.7 wt.% CaO. Theuppermember scoriaceous deposits at ContradaMonaci compositionallyoverlap with the least evolved lower member deposits at a major ele-ment level (62.3–63.4 wt.% SiO2, 3.0–3.6 wt.% CaO and 4.1–5.8 wt.%FeO; Fig. 5a–c). The blocky scoriaceous deposits within both flow unitsrecord increasing fractionation with decreasing FeO and CaO concen-trations (Fig. 5b–c), even though other major and minor elementconcentrations remain relatively consistent (Fig. 5a). Trace elementconcentrations within the Vallone Licodia glasses show limited varia-tion with 34–39 ppm Y; 415–455 ppm Zr; 111–120 ppm Nb; 1338–1446 ppm Ba, 224–238 ppm Ce and 22–24 ppm Th (Fig. 5c–d). Themost significant compositional variation in these glasses is in Sr concen-trations (399–812 ppm). Trace element concentrations within theupper member glasses (Contrada Monaci) are more homogeneouswith 35–37 ppm Y, 411–437 ppm Zr, 111–115 ppm Nb, 1307–1410 ppm Ba, 223–236 ppm Ce and 21–22 ppm. They do not showthe lower Sr (658–833 ppm) values and consequently overlap withthe least evolved lower Biancavilla flow deposits. High field strengthelement (HFSE) ratios to Th are consistent between the flow units(Table 2).

5.1.2. Unit D fall deposits

5.1.2.1. Acireale fall (lowerD1b and upper D2b). The varicoloured pumicesin the lower fall deposits of Acireale D1b show significant compositionalvariation defining an almost bi-modal population (Fig. 5a–c). Glass com-positions range from 61.3 to 62.9 wt.% SiO2, 4.3–5.4 wt.% FeO and 3.1–3.9 wt.% CaO. All D1b glasses are classified as trachytes (Fig. 4a). Thelighter coloured low-SiO2 pumices contrast with the darker, higherSiO2 pumices. The latter also display lower TiO2 (Fig. 5a), FeO (Fig. 5b),CaO (Fig. 5c), and MgO concentrations. The glasses in the D1b fallunit display some trace element variation with 34–39 ppm Y (Fig. 5e),410–455 ppm Zr, 113–122 ppm Nb, 1334–1565 ppm Ba (Fig. 5f), 215–245 ppm Ce (Fig. 5d) and 22–24 ppm Th (Fig. 5c–e). They show LREEenrichment relative to the HREE (La/Yb = 33–43; Fig. 4b). HFSE/Thratios are fairly constant within the D1b glasses (Table 2).

The varicoloured upper D2b fall deposits show similar compositionalvariation (61.8–63.3 wt.% SiO2, 4.2–5.4 wt.% FeO, 3.3–4.0 wt.% CaO;Fig. 5a–c) and all glasses are classified as trachytes (Fig. 4a). The highersilica glasses show lower FeO (Fig. 5b) andMgO, whilst the other majorandminor element concentrations remain constant (Fig. 5). D2b glassesshow some trace element variation with 33–40 ppm Y, 395–457 ppmZr, 106–120 ppm Nb, 1287–1495 ppm Ba, 211–237 ppm Ce and19–22 ppm Th (Fig. 5d–f). The glasses show LREE enrichment

relative to the HREE (La/Yb = 31–40; Fig. 4b). HFSE/Th ratios areconstant within the D2b glasses (Table 2).

5.1.2.2. Giarre fall (lower D1a and upper D2a). The lowermost fall depositD1a outcropping in the Giarre area comprises the least fractionatedglass compositions (59.4–61.7 wt.% SiO2, 4.7–6.6 wt.% FeO and 3.0–5.1 wt.% CaO; Fig. 5a) and glass compositions range from trachyandesiteto trachytes (Fig. 4a). Although these glasses show some scatter, proba-bly related to their high microcryst content, the data are considered tobe representative of the magma compositions related to this eruption.Only two successful trace element analyses were conducted on thesepumices again due to high microcryst concentrations in the glass, how-ever, both show similar levels of incompatible trace element enrich-ment (Fig. 5). Overall the D1a glasses show the lowest levels ofincompatible trace element enrichment (Fig. 4b). HFSE/Th ratios remainconstant within the D1a glasses (Table 2).

Glasses of the upper pumice fall unit D2a have a homogeneous com-position (60.6–61.5 wt.% SiO2, 4.6–6.1 wt.% FeO and 3.3–4.2 wt.% CaO;Fig. 5a–c). Alkali element concentrations range from 5.8–6.7 wt.%Na2O and 2.9–3.4 wt.% K2O, and these glasses classify as trachyandesiticto trachytic (Fig. 4a). D2a shows more variability in the trace elementconcentrations than the underlying D1a (Fig. 5d–f); with the exceptionof Sr, trace elements behave incompatibly with increasing fractionation.Glasses show LREE enrichment relative to the HREE (Fig. 4b). HFSE ele-ment ratios to Th remain fairly constant within these glasses (Table 2).

5.2. Relationships between proximal deposits

Proximal relationships are assessed in the following section usingthe glass geochemistry presented above. Diagnostic geochemical fea-tures are identified and proximal relationships are verified using statis-tical distance tests (Perkins et al., 1995).

5.2.1. Biancavilla flowsThere is significant overlap in glass compositions of the Vallone

Licodia (V. Licodia) lower member scoria and the upper member atContrada Monaci (C. Monaci) in the Biancavilla region (Figs. 4a, 5).The composition of the lower member scoriaceous deposits extend tothemost elevated SiO2 (N63 wt.%) and incompatible trace element con-centrations (i.e., Th, Nb, U), and the lowest CaO (Fig. 5c) and Sr concen-trations (Table 1). Broadly overlapping major, minor and trace elementglass chemistries for the lower and upper flowmembers mean they arestatistically indistinguishable based on their D2 values (D2 = 21.0 and2.3 for majors and traces, respectively; Table 3).

5.2.2. Acireale (D1b and D2b)The two temporally separate trachytic Acireale Plinian fall units, D1b

and D2b, share overlapping major, minor (D2 = 0.9) and trace (D2 =0.1) element glass chemistries. Overlap occurs between 62 and 63 wt.%SiO2 and at 22 ppm Th (Fig. 5). However, some subtle differences incompositional ranges can be observed: (1) D1b glasses present a lessevolved component that is not recognised in the D2b deposits (i.e. lowerSiO2; Fig. 5); (2) D2b glasses extend to more evolved compositions thanD1b glasses (i.e., higher SiO2, lower FeO andMgO; Fig. 5a–c); (3) despitean overlapping SiO2 wt.% the Acireale D1b glasses range to significantlyhigher Th than the D2b glasses (Fig. 5d–f). These subtle variationsaside, the significant geochemical major and trace element overlapmakes distally deciphering between these two temporally separatePlinian eruptions problematic based on glass chemistry alone (Fig. 5).

The two Plinian Acireale fall episodes geochemically overlap withthe Biancavilla Ignimbrite deposits both at a major and trace elementlevel (i.e., at 62–63 wt.% SiO2 and 22 ppm Th) (Fig. 5). Neither Plinianfall deposits present the most SiO2 rich glass compositions observed inthe lower flow deposits (V. Licodia) (Fig. 5a–c). Where SiO2 overlaps,subtle differences can be recognised between the lower D1b fall andthe Biancavilla flow deposits; the latter show greater TiO2 (Fig. 5a)

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D2b (Upper)

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Fig. 4. (a) TAS classification (Le Bas et al., 1986) diagrams showing the glass compositionsof proximal tephra deposits sampled from theUnit D Plinian fall and the Biancavilla Ignim-brites flow deposits. Error bar represents 2 × standard deviation of repeat analyses of theStHs60-8G standard glass. (b) Mantle normalised trace element profiles of representativeanalyses from the Unit D Plinian fall and the Biancavilla Ignimbrite flow deposits (Sun andMcDonough, 1989).


andMgO variability. In addition, at a trace element level the D1b glassesshow Th concentrations consistent with higher SiO2 glasses from thelower flow deposits (V. Licodia), despite having lower SiO2 (Fig. 5d)and higher CaO concentrations. Furthermore, the D1b glasses range tomore elevated Th (Fig. 5) and Nb concentrations than the upper flow(C. Monaci) deposits despite sharing consistent major element compo-sitions (Fig. 5). These subtle inconsistencies between major and traceelement data raise questionmarkswith regards to the precise geochem-ical affinity between glass compositions of the lower D1b pumices andthe scoriaceous Biancavilla Ignimbrite deposits as proposed by Coltelliet al. (2000).

In contrast, the upper Acireale D2b Plinian deposits have major andincompatible trace element concentrations that are more comparableto the Biancavilla ignimbrite deposits (Fig. 5). Consequently, statisticaldistance reveals lower D2 values when comparing D2b glasses to theBiancavilla flow glasses as opposed to the D1b glasses (Table 3). D2bglasses and the upper member (C. Monaci) glasses show particularlystrongmajor and trace element compositional agreement, where calcu-lated D2 values are 1.3 and 0.4, respectively (Table 3). General similari-ties in the glass data presented suggests a co-genetic link between themagmas feeding both the Acireale Plinian eruptions and the Biancavillaignimbrites, but their temporal relationships are not constrained as

proximal age determinations for the Acireale Plinian episodes are notavailable.

5.2.3. Giarre (D1a and D2a)The trachyandesite to trachyte glass compositions (Fig. 4a) of the

lower Giarre D1a fall can be easily distinguished from the Acireale falland Biancavilla ignimbrites on the basis of lower SiO2, K2O and TiO2

(Fig. 5a), and higher FeO and CaO concentrations (Fig. 5b–c). Theupper Giarre D2a Plinian fall shows trachyandesite to trachyte glass(Fig. 4a) compositions that partially overlap with the least evolvedAcireale D1b fall end-member (Fig. 5a–c). The Giarre D2a glasses dohowever show lower TiO2 concentrations consistent with the underly-ing D1a fall deposit. Low TiO2 concentrations were also observed inwhole rock analyses of the pumice samples from D1a and D2a,confirming this as a critical diagnostic feature of the Giarre eruptions(Fig. 5a; Table 2; Supplementary material). Statistical distance values,D2, confirm that the two Giarre fall deposits show greatest major andminor compositional affinity to one another, whilst demonstrating fargreater statistical distance from the Acireale fall and Biancavilla ignim-brite deposits (Table 3).

Whilst some trace element concentrations observed in the glasses ofboth Giarre fall units overlap with the Acireale/Biancavilla type glasses(i.e., Rb, Th and U), important diagnostic differences exist (Table 2).The Giarre glasses show noticeably lower REE enrichment relative tothe Acireale/Biancavilla type glasses (Fig. 4b). These lower concentra-tions are best observed in Ce (Fig. 5d) and Y (Fig. 5e) concentrations.Barium is also significantly lower in the Giarre glasses compared tothe Acireale/Biancavilla types (Fig. 5f; Table 2). Overall the Giarreglasses appear to reside on separate evolutionary trends from theAcireale/Biancavilla type glasses (Fig. 5e–f). The differences observedin some trace element concentrations are reflected in the D2 valueswhere the lower D1a Giarre fall pumices are statistically different tothe Acireale/Biancavilla type glasses (Table 2). Whilst D2 values do notconfirm a statistical difference between the trace element concentra-tions in D2a Giarre glasses and the Acireale/Biancavilla glasses, thesevalues are high (Table 3) reflecting the differences observed in thetrace element Harker diagrams (Fig. 5e–f). Geochemical data revealsthat deciphering the two Giarre eruptive episodes in a distal settingby glass composition will be challenging due to their overlappingmajor and trace element geochemistries. However, the limited thick-ness of D1a proximal deposits (Coltelli et al., 2000) indicates that thisunit is unlikely to represent Plinian activity and its dispersal distally isless likely than the thicker D2a. Geochemical variations between theAcireale and Giarre fall deposits support the stratigraphic and texturalinterpretations that these localities record separate explosive eruptions(Coltelli et al., 2000).

Glass geochemical data presented above indicates in part a relation-ship betweenmagmas feeding the Unit D Plinian fall reported by Coltelliet al. (2000) and the Biancavilla Ignimbrite deposits of De Rita et al.(1991). De Rita et al. (1991) identified four flow deposits and Coltelliet al. (2000) subsequently envisaged that the four fall deposits of unitD directly related to the individual Biancavilla ignimbrites. Suggestinga repeated cycle of activity that comprised: (1) an initial Plinian phase;(2) generation of a spatter rampart during waning eruptive intensity;and (3) block and ash flows, associatedwith the collapse of the hot spat-ter rampart, termed the Biancavilla ignimbrites.

However, a direct relationship between the four fall episodesrecognised in Unit D and the four flow deposits is problematic in lightof new glass geochemical data. Both the Giarre fall deposits (D1a andD2a) are less evolved and geochemically distinct from the Biancavillaflow deposits and the Acireale fall. In addition, the limited thicknessesof D1a fall indicate that this unit is unlikely to represent Plinian activity(Coltelli et al., 2000). Charred fragments at the base of the D1a and D2adeposits are dated between 18,533–18,818 cal yrs BP (15,420 ± 60 14Cyrs BP) and 18,019–18,560 cal yrs BP (15,050 ± 70 14C yrs BP), respec-tively (Coltelli et al., 2000). These ages are significantly older than the

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Fig. 5.Major, minor and trace element harker diagrams showing the proximal glass compositions of the Unit D Plinian falls and Biancavilla Ignimbrite deposits. Error bars represents 2 xstandard deviation of repeat analyses of the StHs60-8G standard glass.


age determination from a charred tree fragment at the base of theBiancavilla Ignimbrite, dated at between 16.965–17,670 cal yrs BP(14,240 ± 90 14C yrs BP, Siani et al., 2001). Differences in the glass geo-chemistry between the explosive fall deposits atGiarre andAcirealemaybe linked to temporal gaps between eruptions. Geochemical variationsmay reflect differences in residency time of the respective magmas insub-volcanic chambers or even replenishment with new magma. Thisis consistent with models for the current plumbing system beneathMount Etna where it is proposed that a complex high level magma sys-tem exists rather than a single magma chamber (Fertilo et al., 2008).

5.3. Distal tephras from eruptions of Mount Etna

In Fig. 1 the localities of distal tephras attributed to Late Glacial ex-plosive volcanism on Mount Etna are shown. Presented below are newmajor, minor and trace element data for the marine Y-1 tephra from

coreM25/4-11 in the Ionian Sea (Keller, 2006), the terrestrial Y-1 equiv-alent recorded in the sediments of Lago di Mezzano (LMZ) (Ramrathet al., 1999; Wulf et al., 2008) and a cave site in NE Libya, Haua Fteah(HF, Douka et al., in press). Additionally, new major element glass dataare presented for the two Etnean tephra layers TM-11 and TM-12-1(Wulf et al., 2004, 2008) recorded within the annually laminated sedi-ment record of Lago Grande di Monticchio (LGdM), Italy. Geochemicalglass data of distal samples (Table 4; Supplementary material) are com-pared to proximal glass data sets outlined above to define proximal cor-relations. New and existing data from the distal samples are integratedto help refine the proximal event stratigraphy and assess the applicationof the Y-1 as a tephrochronological marker.

5.3.1. Y-1 Ionian Sea (M25/4-11)Two glass shard morphologies are present in this tephra layer,

(1) blocky poorly vesiculated dark shards (Fig. 3j–l) and (2) light, highly

Table 2Diagnostic major, minor and trace element geochemical concentrations and ratios used to identify the proximal Biancavilla Ignimbrite, Acireale fall and Giarre fall deposits. Also includedare the same values for distal equivalents. Errors given are 2 standard deviations. Tra = Trachyte; TrA = Trachyandesite.

Locality Biancavilla Acireale Giarre Ionian Sea Haua Fteah LMZ LGdM

Sample V. Licodia C. Monaci D1b D2b D1a D2a Y-1 (M25/4-11) HF_T426 Y-1 TM-12-1 TM-11

Deposit Flow Flow Fall Fall Fall Fall Fall Fall Fall Fall Fall

Classification Tr Tr Tr Tr TrA-Tr Tra Tra Tra TrA-Tr Tr TrA-Tr

TiO2 wt.% N1 wt.% N1 wt.% N1 wt.% N1 wt.% b1 wt.% b1 wt.% N1 wt.% N1 wt.% N1 wt.% N1 wt.% N1 wt.%

V (ppm) 62 ± 8 67 ± 5 64 ± 11 64 ± 8 48–58 43–60 66 ± 4 67 ± 9 92 ± 19 – –

Ba (ppm) 1395 ± 96 1359 ± 69 1412 ± 122 1394 ± 138 990 ± 37 990 ± 59 1336 ± 80 1357 ± 51 1300 ± 74 – –

Sr (ppm) 612 ± 305 740 ± 126 740 ± 93 750 ± 97 767 ± 262 612 ± 497 696 ± 142 760 ± 114 906 ± 102Nb/Th 5.1 ± 0.4 5.2 ± 0.2 5.2 ± 0.3 5.3 ± 0.4 5.2 ± 0.1 5.3 ± 0.2 5.2 ± 0.3 5.2 ± 0.2 5.1 ± 0.6 – –

Zr/Th 19.3 ± 1.2 19.2 ± 0.6 19.1 ± 1.2 20.5 ± 1.8 16.7 ± 1.4 18.1 ± 0.6 18.6 ± 1.2 19.5 ± 0.7 18.4 ± 1.4 – –

Ta/Th 0.24 ± 0.01 0.24 ± 0.01 0.24 ± 0.02 0.24 ± 0.02 0.23 ± 0.01 0.26 ± 0.1 0.24 ± 0.02 0.24 ± 0.01 0.23 ± 0.02 – –

Y/Th 1.62 ± 0.04 1.64 ± 0.06 1.61 ± 0.14 1.72 ± 0.1 1.28 ± 0.03 1.25 ± 0.1 1.61 ± 0.06 1.66 ± 0.08 1.73 ± 0.2 – –

La/Th 5.5 ± 0.2 5.6 ± 0.2 5.5 ± 0.3 5.7 ± 0.3 5.0 ± 0.1 5.1 ± 0.3 5.4 ± 0.4 5.5 ± 0.2 5.8 ± 0.6 – –

Ce/Th 10.3 ± 0.5 10.4 ± 0.4 10.0 ± 0.5 10.7 ± 0.6 8.8 ± 0.01 8.6 ± 0.2 10 ± 0.7 10.2 ± 0.4 10.7 ± 1.2 – –

Nb/Zr 0.27 ± 0.02 0.27 ± 0.01 0.27 ± 0.02 0.26 ± 0.01 0.31 ± 0.03 0.29 0.28 ± 0.01 0.27 ± 0.01 0.28 ± 0.2 – –


vesicular tubular shards (Fig. 3k). Shards are typically 200–300 μmin size (major-axis). Glass compositions observed in this Y-1 IonianSea tephra layer span a narrow range with 62.5–63.8 wt.% SiO2, 4.4–5.2 wt.% FeO and 2.9–4.1 wt.% CaO. Glasses also have more Na2O (5.5–6.0 wt.%) than K2O (2.5–3.6 wt.%) and are classified as trachytes(Fig. 6a). They show significant trace element variability including384–438 ppm Zr, 109–123 ppm Nb, 1274–1396 ppm Ba (Fig. 7f),557–837 ppm Sr and 21.4–25.8 ppm Th (Fig. 7c–f) and LREE areenriched relative to the HREE (La/Yb = 36 ± 2; Fig. 6b). HFSE contentsrelative to Th and other diagnostic incompatible trace element ratiosremain relatively constant (Table 2).

5.3.2. Y-1 Lago di Mezzano (LMZ)Glass shards are largely dark, blocky and poorly vesiculated and less

than 100 μm in size (long axis) (Fig. 3m–n). Glasses from this tephralayer are relatively heterogeneous with 59.1–61.8 wt.% SiO2, 4.5–6.5 wt.% FeO and 3.3–5.1 wt.% CaO. Glasses show elevated Na2O (5.5–6.4 wt.%) with respect to K2O (2.5–3.4 wt.%) and range fromtrachyandesite to trachyte in composition (Fig. 6a). They are enrichedin LREE relative to the HREE (La/Yb = 37 ± 5; Fig. 6b). Trace elementconcentrations observed in the glasses show some significant variability(i.e., 357–402 ppm Zr, 1247–1335 ppm Ba, whilst other incompatibletrace element concentrations are homogeneous (i.e., 36 ± 1 ppm Y).Strontium appears to remain fairly constantwith increasing fractionation(906 ± 51 ppm Sr). HFSE/Th ratios and other diagnostic incompatibletrace elements ratios remain constant (Table 2).

5.3.3. Haua Fteah tephra (Libya) (HF_T426)Microscopic investigations reveal two dominant glass shard compo-

nents within a visible tephra layer (~1 cm thick; HF_426) identifiedwithin the stratigraphy of Haua Fteah (HF) cave, Northern Libya:(1) clear/light brown highly vesicular/elongate shards and; (2) darkbrown/black, blocky poorly vesicular angular shards (Fig. 3o). Theshards in this tephra layer record some compositional variability with,61.1–62.9 wt.% SiO2, 4.2–5.7 wt.% FeO and 3.0–4.17 wt.% CaO (Fig. 7).Glasses show Na2O (5.6–6.6 wt.%) N K2O (2.4–3.7 wt.%) and are alltrachytes (Fig. 6a). Glasses display LREE enrichment relative to theHREE (La/Yb =35 ± 1; Fig. 6b). Trace element concentrations general-ly show only limited variation (i.e., 76 ± 2 ppm Rb, 37 ± 1 ppm Y(Fig. 7e), 22.0 ± 0.6 ppm Th), whilst there is some variability in otherselements (i.e., 670–890 ppm Sr and 1276–1403 ppmBa) (Fig. 7f). HFSEratios to Th and other diagnostic incompatible trace element ratiosremain constant (Table 2).

5.3.4. Lago Grande di Monticchio (LGdM)New analyses of TM-11 and TM-12-1 LGdM tephra layers are

presented on glasses within the thin sections of the varved sediments.

These analyses were more challenging than separately mounted glassshards. Given the difficulties of analysis the dataset is limited and re-stricted to major and minor elements (EPMA).

TM-11 glasses are dark brown, blocky and poorly vesiculated andshow a homogeneous composition with 60.2 ± 0.8 wt.% SiO2, 5.4 ±0.3 wt.% FeO and 4.0 ± 0.4 wt.% CaO (Fig. 7a–c). Glasses display concen-trations of Na2O (5.9 ± 0.2 wt.%) N K2O (3.2 ± 0.2 wt.%) and rangefrom trachyandesites to trachytes (Fig. 6a). TM-12-1 glasses are moreheterogeneous in major and minor element composition than TM-11with 60.5–62.3 wt.% SiO2, 5.1–6.1 wt.% FeO and 3.3–4.2 wt.% CaO(Fig. 7a–c). Glasses show concentrations of Na2O (5.6–6.2 wt.%) N K2O(2.7–3.9 wt.%) and range from trachyandesite to trachyte (Fig. 6a).

5.4. Proximal–distal glass correlations

The integration of published data and newdistal glass data presentedabove demonstrates significant geochemical variability in the composi-tions of tephras termed the Y-1/Et-1 (Figs. 6a; 7a–c). The glass com-position of distally investigated tephras range from trachyandesite totrachyte which is consistent with the proximal variability observed(Fig. 6a; a–c). In the following section we assess geochemicallyproximal–distal correlations.

5.4.1. Correlations with the Acireale fall/Biancavilla flow depositsGiven the proximal geochemical overlap between the glasses of the

Acireale fall (D1b/D2b) and the Biancavilla Ignimbrite deposits we firstconsider distal tephraswhich showbroadly consistent glass geochemis-tries (Figs. 4; 5). Distal tephras showing themore evolved trachytic glasscompositions include the Ionian Sea Y-1 (M25/4-11), the Haua Fteahash (HF_T426) and TM-12-1 at LGdM. All three distal tephras showmore elevated SiO2, K2O and TiO2 than the Giarre fall deposits(Figs. 6a; 7a). Trace element concentrations observed within the IonianSea Y-1 (M25/4-11) and HF_T426 glasses are different from the Giarreeruptive episodes, with significantly higher LREE, Y, HREE and Ba con-centrations, suggesting they do not correlate (Figs. 6b; 7e–f).

5.4.1.1. Y-1 (Ionian Sea). Y-1 in the Ionian Sea core M25/4-11comprisesof glasses that are consistent with the most evolved proximal glasses,(i.e., SiO2-rich) in particular the scoriaceous Biancavilla ignimbrite de-posits (Fig. 7a–c). At ca. 63 wt.% SiO2 the Y-1 (M25/4-11) glasses showmore variable TiO2, MgO and FeO concentrations than the two Acirealefall glasses. These Y-1 glasses range to more elevated concentrationsthat are exclusive to the Biancavilla ignimbrite deposits (Fig. 7a–c). Y-1(M25/4-11) shards geochemically show very limited major elementoverlap with the lower Plinian fall at Acireale (D1b). These observationsare reflected by statistical distance, D2, values (Table 3).

Table 3(a) Statistical distance (D2) matrix, it compares glass sample pairs both proximally and distally. Samples names in bold are based on glass data presented in this investigation and theremaining are based on published data. In blue D2 values based on major and minor elements (excludes MnO), whilst, in grey are the D2 values are based on trace elements concentra-tions (Rb, Sr, Y, Ba, Nb, Zr, La, Ce, Th, U). (b) The p (confidence limits) values for statistical distancewhere f (degrees of freedom) is either 8 or 10. D2

critical, is defined from the Chi squaredtables depending on the degrees of freedom (f), where f = number of elements used. Thus, where f = 10 (elements), at a 95% confidence limit, the D2

calculated would need to exceed theD2

critical value of 18.307 for the sample pair to be significantly different.


Trace element concentrations in the Y-1 (M25/4-11) glasses alsooverlap with those seen in the Biancavilla flow deposits and bothAcireale Plinian fall deposits (Fig. 7d–f). Y-1 glasses extend to thehighest levels of incompatible trace element enrichment (i.e. Th, Nb;Fig. 7d) which is consistent with the lower Biancavilla flow member(V. Licodia) and the lower Acireale Plinian fall (D1b) (Fig. 7d–f). How-ever, a correlation with the latter can be ruled out owing to discrepan-cies in the major element glass chemistries (Fig. 7a–c). Consequently,Y-1 (M25/4-11) in part comprises glass from the lower Biancavilla ig-nimbrite member (V. Licodia). This is supported by Sr concentrationsin the Y-1 (M25/4-11) glasseswhich extend to lower concentrations ob-served in the lower V. Licodia glasses (Table 2). The remaining shardsappear to correspond to both the trace element concentrations in theupper ignimbrite member (C. Monaci) and the upper D2b AcirealePlinian Fall (Fig. 7d–f), which is reflected in both major and trace ele-ment derived D2 values (Table 3). This geochemical data suggests thatthe Y-1 (M25/4-11) layer is dominated by input from a co-ignimbriteash associated with the Biancavilla Ignimbrites (i.e., V. Licodia andC.Monaci deposits),whilst glass data also suggest the presence of glassesassociated with the upper Acireale Plinian fall (D2b; Fig. 7d–e). Thisis very much consistent with physical parameters of the distal ashlayer which comprises both dark blocky shards typical of the flow de-posits and lighter vesicular shards characteristic of the Plinian pumices(Fig. 3).

5.4.1.2. Haua Fteah tephra (Libya) (HF_T426). The visible ash layerHF_T426 recorded in Libya at Haua Fteah shows major element

compositions that correspond precisely to the two temporally separatePlinian fall episodes recorded at Acireale (Fig. 7a–c; Table 3). Further-more, glasses overlap with the lower SiO2 components of both theBiancavilla flow members (V. Licodia and C. Monaci). Trace elementconcentrations reveal particularly good agreement with the upperflow member (C. Monaci) and the upper Plinian D2b fall episoderecorded at Acireale (Fig. 7d–f). D1b Plinian fall glasses extend to higherTh than those observed in theHF_T426 ash (Fig. 7d). Statistical distance,D2, reveals that the upper Plinian D2b provides the most reliable proxi-mal equivalent (Table 3). However, owing to the geochemical overlap ofboth proximal Acireale Plinian episodes it becomes difficult to attributethis ash layer to one fall episode over the other. The trace element con-centrations verify a co-ignimbrite component given their geochemicalconsistency with the C. Monaci flow deposits (Fig. 7d–f; Table 3).Again, this would corroborate the physical shard parameters observedmicroscopically, where both light and dark glasses are identified(Fig. 3). The identification of a Plinian component within HF_T426 atHaua Fteah (HF) is consistent with SE dispersal axis of both the AcirealePlinian episodes (Coltelli et al., 2000). This visible tephra layer extendsthe confirmed distribution of tephra erupted during this period of ex-plosive volcanism on Mount Etna to over 800 km from source (Fig. 8).Interestingly, the greater geochemical affinity of HF_T426 to the D2bAcireale Plinian fall is consistent with a wider proximal distribution ofthis unit relative to the older D1b (Coltelli et al., 2000). Given the thick-ness of the ash deposits recorded in northern Libya it is unlikely torepresent the geographical limit of this particular dispersal (Fig. 8).The Haua Fteah ash deposit shows both the physical and chemical


characteristics the Biancavilla Ignimbrite/Plinian Acireale glasses con-sistent with the Ionian Sea Y-1 (M25/4-11) and leads us to redefineHF_T426 as the correlative of the marine Y-1 tephra in the Ionian Sea.

5.4.1.3. TM-12-1 (LGdM). TM-12-1 (LGdM) trachyte glass analyses showless chemical variability than those presented in Wulf et al. (2008),where both trachytic and rhyolitic end-members are observed. Neitherdatasets are extensive owing to the difficulty of analysing such finegrained and microcryst rich material. This distal tephra, previouslytermed ‘Ante Biancavilla’, correlateswith both Plinian deposits recordedat Acireale (Fig. 7a–c). TM-12-1 glasses show comparable D2 valueswhen compared to both D1b (D2 = 1.7) and D2b (D2 = 1.9). Whilstglass data verify an Etnean source associatedwith Acireale unit D explo-sive activity, geochemistry alone is insufficient to decipher the preciseproximal counterpart.

5.4.1.4. Other Y-1 distal occurrences. Published tephra glass data obtainedfrom the literature and compared to newly presented data herein maynot be precisely comparable owing to the use of different analyticalsetups. However, the following distal tephras appear to correspond tothe Acireale fall/Biancavilla flow compositions and include the IonianSea Y-1 from core M25/4-13 (Keller, 2006; Wulf et al., 2008), Y-1/Et-1in the southern Adriatic core MD90917 (Siani et al., 2004) and Et-1tephras from the Tyrrhenian Sea cores KET80-03 and KET80-11(Paterne et al., 1988). The Y-1 in core M25/4-13 is far more composi-tionally homogeneous than the Y-1 in core M25/4-11 (Figs. 6a; 7a–c),just 100 km further south in the Ionian Sea (Fig. 1). The major elementdata suggests the deposits is mostly associated with the least evolvedend-member of the flow deposits (Fig. 7a–c). Instead, this tephra

Table 4Representativemajor, minor and trace element glass data from the distal tephra investigated inTM-12-1 from LGdM. Full geochemical data sets are available in the Supplementary material fi

Y-1 (M25/4-11) HF_T426 Haua Fteah

Shard I.D 14B 16B 27C 64 63 60

Major elements (wt.%)SiO2 63.20 63.10 62.80 61.60 62.69 62.80TiO2 1.40 1.30 1.30 1.20 1.11 1.30Al2O3 16.80 17.00 17.00 16.60 16.92 16.70FeOt 4.70 4.90 4.80 5.50 4.76 4.90MnO 0.20 0.10 0.20 0.20 0.21 0.00MgO 1.70 1.60 1.70 1.70 1.59 1.70CaO 3.10 3.40 3.50 3.80 3.28 3.30Na2O 5.60 5.60 5.50 6.00 6.12 5.90K2O 3.20 3.10 3.30 3.30 3.31 3.30Analytical Total 99.50 99.10 98.90 98.10 96.91 97.50K2O + Na2O 8.80 8.70 8.80 9.30 9.43 9.20

Trace elements ppmV 66.8 65.4 67.2 72.3 60.7 72.5Rb 80.7 77.9 77.8 79.9 79.4 77.9Sr 711 716 725 670 739 754Y 36.4 36.1 36.2 36.5 36.1 38.3Zr 427 413 419 439 440 439Nb 119 115 109 114 115 118Ba 1362 1351 1375 1350 1375 1379La 125 122 122 122 121 125Ce 229 224 225 233 226 233Pr 23.7 23.0 23.2 23.0 22.6 24.4Nd 82.0 81.0 88.0 85.0 81.1 85.0Sm 14.1 16.6 13.9 14.2 14.2 14.5Eu 3.3 3.4 3.4 3.9 3.7 3.8Gd 10.1 11.2 11.6 11.4 9.5 10.1Dy 8.0 7.4 7.4 7.7 7.3 7.6Er 4.0 3.8 3.9 3.7 3.7 3.9Yb 3.7 3.4 3.0 3.5 3.6 3.4Lu 0.52 0.48 0.58 bLOD bLOD bLODTa 5.3 5.3 5.1 5.1 5.5 5.5Th 23.2 21.8 21.4 22.3 22.8 22.6U 6.5 6.6 6.4 6.8 7.0 6.4

show best geochemical agreementwith the Acireale Plinian falls. Statis-tical distance, D2, values would indicate that the upper Acireale Plinianepisode (D2b) provides the best geochemical match (Table 3). Adetailed cryptotephra investigation of the Ionian Sea core M25/4-12,further north, did not identify the Y-1 tephra (Albert, 2012; Fig. 1).Y-1/Et-1 reported from the southern Adriatic Sea core MD909-17 bySiani et al. (2004) shows some significant geochemical scatter whichsignificantly affects the D2 values when comparing this tephra to ourdatasets. However, the glasses of this distal tephra correlate best tothe SiO2-rich lower Biancavilla flow member (V. Licodia; Fig. 7a–c).This observation is also supported by the statistical distance values(Table 3). Geochemical data does not support the presence of a Pliniancomponent, suggesting a purely co-ignimbritic record of ash dispersalat this locality (Fig. 7a–c). Of all the distal tephras the Y-1 in the IonianSea core M25/4-11 presents the best geochemically correlative for theAdriatic tephra, this is supported by their shared proximal links to thelower Biancavilla flow deposits (V. Licodia; Fig. 7a–c; Table 3). Y-1/Et-1 in the southern Adriatic is dated to between 17,465 and 18,071 cal yrsBP (14650 ± 90 14C yrs BP, Siani et al., 2004). A distal–distal tephracorrelation enables the more precise distal age estimate to be importedto the Ionian Sea Y-1 (M25/4-11). The southern Adriatic tephra wasdated at the precise stratigraphic depth (Siani et al., 2004), whereas,the age of 14, 290 ± N100 yrs BP (including a marine reservoircorrection of 400 years) in the Ionian Sea core was determined by14C interpolation (Kraml, 1997). An single glass data average of theEt-1 tephras presented by Paterne et al. (1988) falls within the com-positional field of the lower Acireale Plinian fall deposits (Fig. 7a–c).However, without site specific and grain-specific glass data it re-mains difficult to assess precise proximal or distal links.

cluding Y-1 Ionian Sea (M25/4-11), previously interpreted Y-1 at LMZ and both TM-11 andle.

Y-1 Lago di Mezzano TM-11 (LGdM) TM-12-1 (LGdM)

14B 25C 4A

59.50 59.60 61.00 59.70 60.00 60.92 62.301.40 1.50 1.20 1.40 1.40 1.58 1.40

17.60 17.70 17.90 17.20 17.70 16.63 16.705.80 5.80 5.00 5.70 5.50 5.94 5.100.20 0.10 0.10 0.20 0.20 0.21 0.202.20 2.30 1.80 1.90 2.10 1.73 1.504.40 4.60 3.70 4.50 4.30 4.17 3.305.90 5.60 6.20 6.00 5.90 6.15 6.102.90 2.80 3.10 3.30 3.00 2.68 3.50

96.80 98.10 97.60 95.60 96.90 96.75 96.708.80 8.40 9.30 9.30 8.90 8.83 9.60

87.2 107.4 81.168.0 63.0 70.0 – – – –

888 1016 881 – – – –

35.0 36.0 36.0 – – – –

357 363 396 – – – –

104 103 108 – – – –

1247 1254 1331 – – – –

116 121 118 – – – –

216 224 220 – – – –

21.0 23.0 21.4 – – – –

74.0 84.0 79.0 – – – –

13.9 14.9 14.0 – – – –

3.3 3.8 3.9 – – – –

7.7 9.6 9.4 – – – –

6.7 8.0 8.0 – – – –

3.6 3.5 3.7 – – – –

2.4 3.4 3.8 – – – –

0.42 0.46 0.49 – – – –

4.5 5.0 5.0 – – – –

18.3 21.0 21.2 – – – –

5.8 5.5 6.3 – – – –

Biancavilla Ignimbrites(SW of summit)



C. Monaci (Upper)

V. Licodia (Lower)

D2b

D1b

D2a

D1a

Y-1(M25/4-11)

Y-1(M25/4-13)

HF (HF_T426)

TM-12-1 (LGdM)TM-11 (LGdM) Y-1(MD90917)

Et-1 (Tyrrh. S) Pal 94-66

Distal

LMZ Y-1BAN

This Study Published

6

8

10

12

58 60 62 64 60

1

10

100

1000

Rb Ba Th U Nb Ta La Ce Pb Pr Sr Nd Zr Sm Eu Ti Gd Dy Y Er Yb Lu

Contrada Monaci (Upper flow)

Vallone Licodia (Lower flow)

D2b Fall

D1b Fall

D2a Fall

D1a Fall

(a)

(b)

Trachyte

Trachy-andesite

Dacite

K2O

+ N

a 2O (

wt.%

)

SiO2(wt.%)

Rep

rese

ntat

ive

Sam

ple/

Prim

itive

Man

tle

1

2

3

4

5

Y-1(M25/4-11)

HF (HF_T426)

LMZ

Fig. 6. (a) TAS classification (Le Bas et al., 1986) diagrams showing the glass compositionsof distal Etnean tephras from the central Mediterranean region compared to the composi-tional fields of investigated proximal deposits. (1) Paterne et al. (1988); (2) Calanchi et al.(1998); (3) Vezzoli (1991); (4) Siani et al. (2004); (5) Keller (2006); Wulf et al. (2008).Error bar represents 2 x standard deviation of repeat analyses of the StHs60-8G stan-dard glass. (b) Mantle normalised trace element diagrams showing average shardanalyses of distal Y-1 Ionian Sea (M25/4-11; Red), Y-1 LMZ (blue) and HF_T426(Haua Fteah, Green) compared to proximal profiles (Sun and McDonough, 1989).


5.4.2. Correlations with Giarre fall deposits

5.4.2.1. TM-11(LGdM) and Y-1 (LMZ). The remaining distal terrestrialtephras characterised in this study, TM-11 (LGdM) and Y-1 (LMZ) showan indistinguishable trachyandesite glass composition (D2 = 0. 3). Thebest proximal match for these distal deposits, based on major elementdata, is the lowerGiarre fall (D1a). This is supported by statistical distancevalues shown in Table 3. However, the distal tephras show significantlyhigher TiO2 concentrations than the Giarre pumices which thereforeraise question marks over this correlation (Table 2; Fig. 7a).

Trace element data from the Y-1 LMZ glasses reinforces the prob-lems with a proximal link to the Giarre pumice fall. The LMZ glassesshow greater REE enrichment (Fig. 5b) and more elevated Y (Fig. 7e)and Ba (Fig. 7f) relative to the Giarre pumices. At a trace element levelthe Y-1 LMZ glasses are statistically different to the Giarre D1a pumices(D2 = 21.0). Whilst the Y-1 LMZ glasses are generally less enrichedthan the Acireale Plinian/Biancavilla flow glasses (i.e., Nb and Th;Fig. 7d), their compositions are more akin to these trace elementconcentrations than those of the Giarre fall deposits (Fig. 7e–f).

The Na-alkaline trachyandesite glass composition undoubtedly con-firms that the TM-11 and Y-1 LMZ are from Etna and trace element datafrom the latter supports a genetic link to the evolved magmas feeding

the explosive activity of Unit D. However, neither can be firmly linkedto a known proximal unit on Etna (Fig. 7a).

Other published tephra layers displaying this kind of Etnean trachy-andesitic composition include the Y-1 recorded in central AdriaticSea core PAL94-66 (Calanchi et al., 1998) and the Y-1 recorded in theBannock Basin core BAN-84 (Vezzoli, 1991) north-east and south-eastof Etna, respectively (Figs. 7a–c; 8). Particularly strong geochemicalagreement, supported by D2 values (Table 3), is seen between theTM-11, Y-1 LMZ and Y-1 central Adriatic tephras. This reinforces astrong distal–distal marine–lacustrine correlation in this particular re-gion of the Mediterranean, crucial to the assessment of continental–marine responses to climate forcing (Fig. 8). The geochemical link be-tween these northerly dispersed tephras and the Y-1 in the BannockBasin offers additional complexity to this dispersal (Fig. 8). This wouldinfer amorewidespread dispersal of this proximally undefined eruptiveepisode which is not yet identified in any other southern archives(Fig. 8). Future cryptotephra investigationsmight help resolve the pres-ence of this eruptive phase and its application as a stratigraphic markerin these southern archives.

Crucially, none of the published distal tephras or those investigatedin this contribution have shown shards matching the diagnosticTi-poor (b1 wt.%) glass chemistry of the Giarre fall pumices (Fig. 7a).

5.5. Towards an integrated proximal–distal event stratigraphy

In this section, we attempt to integrate geochemical proximal–distalcorrelations, distal–distal correlations and chronological information toestablish an event stratigraphy for Late Glacial explosive activity onMount Etna.

The Lago Grande di Monticchio (LGdM) record provides an essentialarchive when attempting to resolve explosive event stratigraphy onMount Etna owing to the existence of two confirmed Etnean ash layerswithin the varve chronology (Wulf et al., 2004, 2008). The absolutevarve ages recorded at LGdM for TM-11 (16,440 ± 820 calendaryrs BP) and TM-12-1 (17, 980 ± 900 calendar yrs BP) are likely to beunderestimates given a systematic deviation of ca. 8% (ca. 1500 calendaryears) from calibrated radiometric ages of other tephras in this sectionof the record (Wulf et al., 2012). However, in this instance the benefitsof the independent chronology are revealed when we count the varveyears between TM-11 and TM-12-1. In this way we can calculate thatMount Etna's explosive activity spanned a minimum of 1540 ± 80varve years (Fig. 9). Furthermore, an important stratigraphic marker be-tween the two Etnean layers is particularly useful in refining the eventstratigraphy and chronology (Fig. 9). Tephra TM-12 (17,560 ± 880varve yrs BP) is correlated to the Greenish/Verdoline sub-Plinian erup-tion of Somma-Vesuvius (Wulf et al., 2004, 2008, 2012). Proximally,charcoal underlying this tephra has been dated to 18,820–19,384 cal yrsBP (15,870 ± 90 14C yrs BP, Siani et al., 2001), and this age is verifieddistally in the marine setting (18,828–19,410 cal yrs BP; 15,970 ± 13014C yrs BP, Siani et al., 2004) (Fig. 9). The calibrated proximal radiocar-bon age for the Greenish/TM-12 (which avoids marine carbon reservoiruncertainties) can be imported into the LGdM stratigraphy, meaningthat it is possible to count the number of varve years above and belowthis fixed chronological point to precisely determine the age of TM-11and TM-12-1 (Fig. 9). The calibrated 14C age range of the Greenish teph-ra/TM-12, coupled with the varve counting uncertainty, is propagatedgiving a maximum and minimum age ranges for the two respectiveEtnean tephras recorded at LGdM (Fig. 9).

TM-11 is 1120 ± 60 varve years younger than TM-12/Greenish pre-senting an interpolated age of between 17,640–18,324 cal yrs BP. Con-sequently, the TM-11 age bracket overlaps the proximal BiancavillaIgnimbrite age (Fig. 9; Siani et al., 2001), the distal 14C age of the Y-1/Et-1 from the southern Adriatic (Siani et al., 2004) and the interpolated14C radiocarbon age of the Y-1 in its Ionian Sea (Kraml, 1997) (Fig. 9).TM-12-1 is 400 ± 20 varve years older than TM-12/Greenish, withan interpolated age of between 19,200–19,805 cal yrs BP (Fig. 9).

Fig. 7.Major, minor and trace element harker diagrams showing the distal tephras glass compositions in comparisonwith the compositional fields of the Unit D Plinian fall and BiancavillaIgnimbrites deposits.(1) Paterne et al. (1988); (2) Calanchi et al. (1998); (3) Vezzoli (1991); (4) Siani et al. (2004); (5) Keller (2006); Wulf et al. (2008). Error bars represents 2 x standarddeviation of repeat analyses of the StHs60-8G standard glass.


Geochemically this tephra can be attributed to either of the AcirealePlinian fall episodes. The age of TM-12-1 clearly predates the basalage of the Biancavilla Ignimbrite (Fig. 9) and confirmed distal correla-tives (i.e., Ionian Sea Y-1, southern Adriatic Y-1; Fig. 9). AdditionallyTM-12-1 ages predate the proximal age determinations of the two falldeposits reported at Giarre (Fig. 9; Coltelli et al., 2000), suggesting theTM-12-1 represents the earliest unit D explosive activity distally dis-persed fromMount Etna.

Combined geochemical and physical (morphology, colour) charac-teristics of distal tephras from the Ionian Sea Y-1 layers (M25/4-11and M25/4-13) and Haua Fteah ash (HF_T426) indicate the presenceof both Biancavilla ignimbrite (co-ignimbrite) and Acireale fall (Plinian)components. Consequently, it is possible to infer a temporal overlap of

these two eruptive phases at the resolution of the respective distal ar-chives. The basal ages of the Biancavilla Ignimbrites and confirmed dis-tal equivalents are significantly younger than the age of the markertephra TM-12/Greenish (Fig. 9). The evidence of shards indicative ofAcireale Plinian fall combinedwith co-ignimbrite ashwithin some distallayers thus verifies that oneof the Acireale Plinianphasesmust be youn-ger than the TM-12/Greenish tephra and more consistent in age withthe Biancavilla Ignimbrites (Fig. 9). TM-12-1 at LGdM also overlapsthe Acireale Plinian fall type glass geochemistry and considering theproximal stratigraphic superposition at Acireale, it might seem sensiblethat the lower D1b relates to the older TM-12-1 and the upper D2b iscontemporaneous with the Biancavilla Ignimbrites (Fig. 9). This is sup-ported by evidence of a temporal gap between the two recorded Plinian

Fig. 8. A map of the Mediterranean demonstrating the complex dispersal patterns of tephras erupted from Mount Etna spanning the last glacial–interglacial transition. Important is theextension of the Biancavilla Ignimbrite/Acireale D2b deposits into North Africa and perhaps beyond. Also critical is the uncertainty associated with the precise origin of the southernTyrrhenian Sea Et-1 tephras.


fall deposits at Acireale (Fig. 2). Given that all Unit D fall deposits displayeither an eastern or southeastern dispersal, it is not entirely clear howTM-12-1 is recorded to the north at LGdM. A previous explanation isthat the northern dispersals of ash from Mount Etna may relate to thesedimentation of finer pyroclasts from the higher-atmospheric circula-tion (Coltelli et al., 2000; Wulf et al., 2008).

The absence of the Giarre type glass chemistries from the distal re-cordsmight indicate a less widespread dispersal for these two explosiveepisodes on Mount Etna. Indeed the dispersal of the lower D1a fall ispoorly constrained owing to its limited thickness and the upper D2ahas a smaller distribution when contrasted to the Acireale Plinian fallepisodes (Coltelli et al., 2000). Chronologically, the lower D1a fall pre-dates the Biancavilla ignimbrite proximal age and the distal Y-1 age de-terminations (Fig. 9). The calibrated age of the D2a Giarre fall predatesthe proximal age of the Biancavilla Ignimbrites; whilst showing anover-lap with the distal marine ages of the Biancavilla Ignimbrites (i.e., Y-1southern Adriatic). It seemsmost likely that the Giarre D2a eruption oc-curred prior to the eruption of the Biancavilla Ignimbrites (Fig. 9). Giventhe distal chronological constraints placed on the two Acireale Plinianfall episodes, it seems plausible that the two Giarre explosive fall epi-sodes may record geochemically distinct eruptions occurring betweenthe two Plinian eruptions recorded at Acireale.

Integrating proximal–distal correlations and associated chronologi-cal constraints we can begin to construct an event stratigraphy for theinvestigated units (Table 5). This begins to help unravel the order of

explosive activity on Mount Etna, whilst suggesting that the explosivevolcanism associated with Unit D may have extended over 2000 years(Table 5). The potential of Mount Etna to switch to, and more impor-tantly sustain, a period of explosive volcanism has important implica-tions for potential hazards associated with the volcano.

5.6. The problem of the ‘Y-1’ tephra marker horizon

When constructing an event stratigraphy for this period of explosivevolcanism on Mount Etna (Table 5) it becomes apparent that some sig-nificant complexities still exist regarding the application of the Y-1/Et-1tephra as a tephrostratigraphic tool and these are discussed below.

Significant geochemical variability exists between the distal tephrastermed ‘Y-1’ (Figs. 6a, 7a–c). Y-1 in its type locality, the Ionian Sea, is con-firmed as being a distal equivalent of the Biancavilla Ignimbrites and theupper Acireale Plinian fall (D2b). In contrast, the TM-11 LGdM tephraand the geochemically similar tephras correlated to Y-1 recorded atLago diMezzano (Y1-LMZ), in the Central Adriatic andBannockBasin ar-chives differ significantly from the herein defined Ionian Sea Y-1 glasschemistry. Furthermore, TM-11 type distal tephras are currentlywithouta precise proximal glass counterpart onMount Etna (Fig. 7a–c). This con-tradicts published proximal correlations that were based on whole rockdata (Vezzoli, 1991; Calanchi et al., 1998; Ramrath et al., 1999; Wulfet al., 2004) (Fig. 7a–c). Given that the TM-11 type Y-1 glass geochemis-try is predominantly identified to thenorth of Etna (Fig. 8), itmaybe that

Fig. 9. Integrated proximal–distal calibrated chronostratigraphy for explosive volcanism spanning the last glacial–interglacial transition onMount Etna (Termination 1). The calibrated 14Cage range of the Greenish tephra/TM-12, coupled with the varve counting uncertainty, is propagated giving a maximum and minimum age range for the two respective Etnean tephrasat LGdM of 17,640–18,324 cal yrs BP for TM-11 and 19,200–19,805 cal yrs BP for TM-12-1. Integrated proximal–distal chronological information indicates that Late Glacial explosivevolcanism on Mount Etna extended for over 2 ka. The proximal Biancavilla Ignimbrite age post-dates the Giarre eruptions. The LGdM tephra TM-11 also post-dates the lower Giarreeruptive unit (D1a), but chronologically overlaps with both the Biancavilla Ignimbrite age and that of the upper Giarre eruptive unit (D2a). LGdM TM-12-1 appears to predate the Giarreexplosive activity on Mount Etna.


proximal investigations are yet to identify comparable explosive de-posits to the north of the volcano. In addition, further proximal investiga-tions are required to gain access to the very basal flow deposits in theBiancavilla region in order to establish whether these deposits offer acorrelative for the TM-11 type tephras.

Table 5A integrated proximal event stratigraphy for the explosive volcanism on Mount Etnathat spans the last glacial–interglacial transition. Age references: (1) Radiocarbon agesfrom the base of the proximal Biancavilla Ignimbrite following (Kieffer, 1979; Siani et al.,2001). (2) interpolated age of the distal TM-11 tephra in LGdM (Wulf et al., 2004; thisstudy); (3) Radiocarbon ages from the base of the proximal Giarre unit D fall units (Coltelliet al., 2000); (4) interpolated age of distal the TM-12-1 tephra in LGdM (Wulf et al., 2008;this study). Compositional classifications follow Le Bas et al. (1986).

Age (cal yrs BP) Proximal deposit /Eruptive event

Classification Distal occurrence

16,965–17,670 (1) D2b Acirealeand BiancavillaIgnimbrites

Tr Y-1 Ionian Sea (M25/4-11;M25/4-13)Y-1 southern Adriatic SeaY-1 Haua Fteah_T426 Libya

17,640–18,324 (2) Undefined Eruptivephase

TrA to Tr TM-11Y-11 Lago di MezzanoY-1 Central Adriatic

18,019–18,560 (3) D2a Giarre TrA to Tr Not recorded18,533–18,818 (3) D1a Giarre TrA to Tr Not recorded19,200–19,804 (4) D1b Acireale Tr TM-12-1

HF_T426 Libya?(Composite layer)

Tephrostratigraphy and the synchronisation of distal archives relyupon the assumption that a tephra represents a single volcanic event.The compositional variation of all the distally labelled ‘Y-1’ tephras isfar beyond the range of any single characterised proximal unit (Fig. 6a;7a–c), therefore it seems difficult to accept that all the ‘Y-1’ tephras re-ported can relate to a synchronous explosive event. Consequently, theassessment of potential climatic leads or lags between different archivesusing the ‘Y-1’ tephra must be considered carefully. For instance using‘Y-1’ tephras to link central Adriatic and Ionian Sea records may resultin incorrect deductions regarding the timing of climatic fluctuations.

The absence of proximal correlatives for the TM-11 LGdM type ‘Y-1’distal tephrasmake it difficult to assess their temporal relationship withthe Ionian Sea Y-1 tephra and the proximal event stratigraphy on Etna(Table 5). Y-1 recorded in the sediments of the Ionian Sea (M25/4-11),the southern Adriatic (Siani et al., 2004) and at Haua Fteah (Doukaet al., in press) all precisely link to Biancavilla Ignimbrite glass compo-nents, therefore importing the calibrated proximal age estimate fromthe base of the Biancavilla flow is currently the most reliable age forthis marker tephra. Charcoal produced by the hot flows records theprecise time when the organic material stopped living; furthermore,the proximal of age of 16,965–17,670 cal yrs BP (Siani et al., 2001) isunaffected by marine reservoir uncertainties. Indeed adopting purelyterrestrial 14C chronological constraints for identified distal tephrasindicates that TM-11 (17,640–18,324 cal yrs BP) might predate theBiancavilla Ignimbrites (Fig. 9). This would suggest that the BiancavillaIgnimbrites and upper Acireale fall (D2b) represent the final phase ofUnit D explosive activity on Mount Etna. However, this interpretation


must be taken with a degree of caution as the dated, marine reservoircorrected, distal age of the Biancavilla Ignimbrite are older and stronglyoverlaps with the TM-11 interpolated age (Fig. 9; Siani et al., 2004).

The overlapping distal ages for the Ionian Sea type Y-1 tephrasand TM-11 type tephras, emphasises the demands placed upontephrochronology to offer a higher precision means to correlateddistal archives. The independent chronological constraints imposedon the respective proximal and distal tephras are insufficient to en-abling us to conclusively determine whether the Ionian Sea Y-1 andTM-11 are indeed temporally separate events and if so in whichorder they occur (Table 5). Et-1 tephras presented marine coresfrom the southern Tyrrhenian Sea recording Et-1 tephras (Paterneet al., 1988), show variable stratigraphic positions relative to the C-3Campanian tephra. This potentially indicates that different cores recordseparate ash dispersals from Mount Etna. Indeed, testing the preciseproximal and distal links of these stratigraphically variable Et-1 tephrasmay offer the best opportunity to determine the stratigraphic order ofpotentially separate ash dispersals.

Given the regional tephrostratigraphic importance of the LagoGrande di Monticchio (LGdM) archive, until a precise proximal equiva-lent of the TM-11 type Etnean tephras (i.e., Y-1 in Lago di Mezzano, thecentral Adriatic, and the Bannock basin) or evidence of a precise tempo-ral link to the Ionian Sea Y-1 is identified, then these tephras should becorrelated to ‘TM-11’ not the Y-1 owing to their significant geochemicaldifferences. The term Y-1 should be reserved for those distal tephrasthat correlate to the Y-1 in the Ionian Sea and that share the same prox-imal links on Mount Etna (i.e., Biancavilla Ignimbrites and AcirealeD2b fall). A complex series of ash dispersal lobes emanating from explo-sive volcanism on Etna are linked to Unit D and span Termination 1(Fig. 8). Consequently, extreme caution must be exercised when corre-lating these Etnean tephras between distal archives given the generationof overlapping and repeat magma compositions that span a significantperiod of time. The potential for numerous ash dispersals from MountEtna spanning the combined age range of the Ionian Sea/S. Adriatic Y-1tephra layers and TM-11 is unsurprising in light of proximal observa-tions. This includes evidence for four Biancavilla flow units (De Ritaet al., 1991), each capable of producing widely dispersed co-ignimbriticash (i.e., 800 km to Libya), coupledwith evidence of at least one contem-poraneous and distally dispersed Plinian episode (Acireale D2b), alsoidentified south-east of Etna at Haua Fteah.

Finally, this study necessitates a revision of the proposed eruptivecycles occurring on Mount Etna. Currently, Coltelli et al. (2000)envisage a repeated succession of activity comprising of an earlyPlinian/sub-Plinian episode, which subsides leading to the formationof a spatter rampart, subsequent over steepening triggering collapsethat produces the Biancavilla Ignimbrites. However, a direct causallink between the four individual Plinian/sub-Plinian fall episodesrecorded (D1b, D2b, D1a and D2a) on the lower slopes of the volcanoand the four Biancavilla flow deposits has been shown to be prob-lematic owing to the following factors; (1) at least two of the UnitD fall episodes (D1b and D1a) appear to pre-date the BiancavillaIgnimbrites and their distal equivalents (Fig. 9); (2) both Giarre fall(D1a and D2a) episodes are significantly less evolved and geochem-ically distinct from the Ignimbrite glasses that they would precede inthe envisaged eruptive sequence (Fig. 4a; a–c); and (3) currentlyonly one Plinian episode (D2b) can be confirmed as contemporane-ous to the generation of the Biancavilla Ignimbrites (Table 5). Insummary, combined varve and calibrated radiocarbon chronologiessuggest that Plinian explosive activity involving chemically similarmagmas spanned ca. 2 ka (Fig. 9).

6. Conclusions

1. Detailed glass major, minor (EPMA) and trace (LA-ICP-MS) elementcharacterisation of proximal and distal tephra explosively eruptedon Mount Etna close to the onset of the last glacial–interglacial

transition (Termination 1) are presented herein. This glass data pro-vides an essential reference data set for proximal–distal and distal–distal tephra correlations.

2. All glasses show highly fractionated Na-alkaline trachyandesite totrachyte compositions and have Nb, Ta and Ti depletions potentiallysuggesting a switch to a subduction influence at source during thisperiod of explosive volcanism.

3. Proximal Unit D fall glass chemistries confirm that the Giarre andAcireale fall deposits record separate Plinian eruptions.

4. Glass analyses reveal considerable geochemical overlap betweenthe temporally separate Acireale (D1b Lower and D2b Upper) andGiarre (D1a and D2a) fall deposits respectively. Both Acireale Plinianepisodes geochemically overlap with the Biancavilla Ignimbrites,suggesting a co-genetic link between the magmas feeding theseeruptive phases. Statistical analysis reveals closest geochemicalagreement between the D2b upper and the Biancavilla Ignimbrites.

5. Distal tephra glass chemistries and chronological constraints indicatea complex series of dispersals fromMount Etna spanning ca. 2 ka andthe last glacial–interglacial transition (Termination 1) (Fig. 8).

6. Distally reported ‘Y-1’ tephras are geochemically diverse, the compo-sitional differences observed between some Y-1 tephra deposits farexceed those observed in the individual proximal deposits investi-gated. Proximal–distal correlations reveal that the Ionian Sea Y-1(M25/4-11; M25/4-13) and the Haua Fteah tephra (HF_T426)are comprised of a Biancavilla Ignimbrite (Co-ignimbrite) and theupper Acireale D2b (Plinian) glass components. Importantly thissupports a temporal link between the two eruptive phases and a cal-ibrated 14C age of 16,965–17,670 cal yrs BP can be imported to thesedistal sites. The identification of this eruptive episode at Haua Fteah(Douka et al., in press) extends the known dispersal of ash from ex-plosive activity on Mount Etna to over 800 km.

7. Distal chronological constraints placed on the proximally undefinedgeochemical equivalents of Lago Grande diMonticchio TM-11 tephra(17,640–18,324 cal yrs BP), overlap in time with proximal anddistal Y-1/Biancavilla Ignimbrite ages. Therefore establishing thetephrostratigraphic ordering of these eruptive events remainschallenging.

8. Geochemical and chronological variability in the many tephra layersfrom across the central Mediterranean region that have been corre-lated to the Y-1 show that the Y-1 must not be used as a singlecontemporaneous tephrostratigraphic marker for synchronisingarchives.

9. The nameY-1 should be applied solely to distal tephras that unequiv-ocally correspond to the Y-1 in its type locality, of the Ionian Sea,or the same proximal deposits at volcanic source. Those distaltephras matching the less evolved TM-11 should be correlated to‘TM-11’ rather thanY-1,whilst a proximal counterpart is not defined.

Acknowledgments

Research was conducted as part of a PhD funded by the ReidScholarship, Royal Holloway University of London. With support fromthe Central Research Council, University of London and the NERCRESET consortium (project number NE/E015905/1). This paper formsthe RHOXTOR contribution 031.Wewould like to thank the anonymousreviewer for their constructive feedback which greatly improved themanuscript. We would like to thank Neil Holloway (Royal Holloway,University of London) for preparing samples in epoxy resin stubsready for geochemical analysis.

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.jvolgeores.2013.07.010.




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