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Quaternary Science Reviews 67 (2013) 190e206

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Isotopic (SreNd) and major element fingerprinting of distal tephras: anapplication to the Middle-Late Pleistocene markers from the Colli Albanivolcano, central Italy

Biagio Giaccio a,*, Ilenia Arienzo b, Gianluca Sottili a, Francesca Castorina a,c, Mario Gaeta a,c,Sebastien Nomade d, Paolo Galli a,e, Paolo Messina a

a Istituto di Geologia Ambientale e Geoingegneria, CNR, via Salaria km 29.300, 00015 Monterotondo, Rome, Italyb Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Napoli, Osservatorio Vesuviano, via Diocleziano 328, 80124 Naples, ItalycDipartimento di Scienze della Terra, Università di Roma “La Sapienza”, Rome, Italyd Laboratoire des Sciences du Climat et de l’Environnement, IPSL, Laboratoire CEA/CNRS/UVSQ, Bât. 12, Avenue de la terrasse, 91198 Gif-Sur-Yvette, FranceeDipartimento della Protezione Civile, via Vitorchiano 4, 00189 Rome, Italy

a r t i c l e i n f o

Article history:Received 11 December 2012Received in revised form24 January 2013Accepted 25 January 2013Available online

Keywords:Ultra-potassic tephra markersRoman Comagmatic ProvinceMajor elements glass compositionsIsotopic 87Sr/86Sr and 143Nd/144Ndfingerprinting40Ar/39Ar dating

* Corresponding author. Tel. þ39 (0)690672747.E-mail address: biagio.giaccio@cnr.it (B. Giaccio).

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a b s t r a c t

We describe the diagnostic lithological and chemical features of distal tephras from major Middle-Late Pleistocene (560e36 ka) explosive eruptions of the Colli Albani volcanic district, central Italy.In particular, we explore the time-dependent variability of the Sr and Nd isotope compositions asa tool for recognising and pinpointing individual Colli Albani tephra in distal settings. The distaltephras investigated are in lacustrine and fluvial sediments of central Apennine intermountain basinslocated 70 kme100 km east of Colli Albani. The recognition of the Colli Albani tephras is essentiallybased on the K-foiditic composition of their glass, which, within the Italian volcanological framework,is a distinctive character of the Colli Albani pyroclasts. In detail, these tephras are attributed to thefollowing eruptive units: Tufo Pisolitico di Trigoria (561 � 2 ka); Tufo del PalatinoeTufo di BagniAlbule (530 � 2/527 � 2 ka), Tufo di Bagni AlbuleePozzolane Rosse air-fall sequence (517 � 1to 500 � 3 ka), Pozzolane Rosse (457 � 4 ka), Villa Senni (365 � 4 ka), and Albano 5e7 (41 � 7 to36 � 1 ka). These correlations are supported by 40Ar/39Ar dating of the distal tephras correlated to thePozzolane Rosse (457.4 � 1.7 ka), Villa Senni (365 � 2 ka) and Albano 5e7 (41 � 9 ka) and by 87Sr/86Srmeasured on clinopyroxene crystals and fresh glassy scoria from distal Colli Albani tephras that rangefrom w0.711 to w0.709. These ratios are similar to those that characterise the individual proximalcorrelative units, and show the same decreasing trend over time. In contrast, the 143Nd/144Nd ratiosfor proximal and distal bulk samples and clinopyroxene increase from w0.51212 to w0.51215 fromthe oldest to the youngest tephra deposit. In summary, the study of Sr and Nd isotope compositionsthat is here applied on products from the Colli Albani volcanic district is a powerful, complementarytool to the more traditional tephrostratigraphic methods (e.g., componentry and electron microprobeanalysis) for fingerprinting of distal tephras over a large region of the central Mediterranean, and overa large time interval, such as from 560 ka to 36 ka.

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1. Introduction

Pyroclastic particles generated during explosive volcanic eventsare dispersed and deposited over wide areas, where they can act asrelevant stratigraphic markers for Quaternary studies. Indeed, therecognitionof dated tephramarkersprovides a useful tool for refiningthe chronology of Quaternary sedimentary successions, and more

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importantly, for synchronising paleo-environmental records acrosslarge regions. These aspects are crucial for a number of scientific is-sues (e.g., Lowe et al., 2008; for a detailed outline, see; Lowe, 2011).Moreover, tephrostratigraphy is relevant even under a volcanologicalperspective, and it allows a better reconstruction of key eruptionparameters (e.g., Costa et al., 2012) and an assessment of both thevolcanic hazard related to large explosive events, and the eruptivehistory on a regional scale (Paterne et al., 2008; Wulf et al., 2012).

The recurrent and long-lasting explosive activity from theperi-Tyrrhenian Quaternary volcanic centres makes the central

Fig. 1. Reference map of the successions investigated. The highlighted area in panela matches that of panel b, where the locations of the sampling tephras are shown.Inset: sampling area within Italy. PSC: PaganicaeSan DemetrioeCastelnuovo; CC:Carapelle Calvisio; CF: Campo Felice.

B. Giaccio et al. / Quaternary Science Reviews 67 (2013) 190e206 191

Mediterranean region a potentially suitable area for the applicationof the tephrostratigraphic method, as has been shown in anincreasing number of tephra studies (e.g., Siani et al., 2004; Turneyet al., 2004, 2008; Wulf et al., 2004, 2008, 2012; Munno andPetrosino, 2007; Blockley et al., 2008; Giaccio et al., 2008; Paterneet al., 2008; Zanchetta et al., 2008; Bourne et al., 2010; Smithet al., 2011; Zanchetta et al., 2011; Lowe et al., 2012; Tamburrinoet al., 2012; Tomlinson et al., 2012; Giaccio et al., 2012a). However,to date, tephrostratigraphic studies have mainly focused on therelatively short interval of the Upper Pleistocene to the Holocene,with few studies for the longer, and tephrostratigraphically poten-tially relevant, Middle Pleistocene period (e.g., Karner et al., 1999;Munnoet al., 2001). Indeed, in spite of the relatively robust 40Ar/39Argeochronological framework (e.g., Marra et al., 2004, 2011; Sottiliet al., 2010), the correlation of distal tephra records to proximalvolcanic successions is currently a difficult task, as only a fewmajorand trace element content analyses are available, determined byperforming electron microprobe analysis (EMPA) and laser ablationon glass from the major Middle Pleistocene eruptions of the peri-Tyrrhenian Quaternary volcanic centres. Furthermore, hitherto,tephrostratigraphic studies have been essentially based on thecompositions of the major, and sometimes trace, elements, whileonly a few cases have proposed the application of the strontium (Sr)and neodymium (Nd) isotope compositions for recognition of thevolcanic sources of distal tephras (e.g. Roulleau et al., 2009).

Among the Middle Pleistocene volcanic centres, the ColliAlbani volcanic district, central Italy, is particular relevant fortephrostratigraphic purposes. Indeed, when compared to the py-roclastics from other Middle Pleistocene volcanic districts, thosefrom Colli Albani eruptions are characterised by lithological andchemical diagnostic features that allow their relatively straight-forward and unambiguous recognition and correlation (e.g., Galliet al., 2010; Freda et al., 2011; Giraudi et al., 2011). In the presentstudy, we describe the lithological and geochemical features ofa series of tephras that occur in distal settings of central Italy, ascorrelated to major and well-dated explosive eruptions from ColliAlbani volcano. The aim is to provide a comprehensive dataset ofdiagnostic criteria for recognising these Colli Albani tephras indistal settings. Several of these tephras have already beendescribed in previous studies (e.g., Galli et al., 2010; Freda et al.,2011), although they were not systematically depicted in a per-spective of tephrostratigraphic applications. Specifically, startingfrom a detailed study of the individual distal tephras from majorMiddle-Late Pleistocene explosive eruptions of the Colli Albanivolcanic district, we explore the use of 87Sr/86Sr and 143Nd/144Ndisotope compositions as tools for tephrostratigraphy.

2. Geological and volcanological setting of the proximal anddistal products from the Colli Albani explosive activity

2.1. The Colli Albani volcanic district

The Colli Albani volcanic district belongs to the QuaternaryRoman Comagmatic Region (e.g., Washington, 1906) (Fig. 1). Itseruptive history can be roughly subdivided into three main phasesthat were characterised by volumetrically and dynamically differ-ent eruptive events (e.g., De Rita et al., 1988, 1995; Karner et al.,2001; Giordano et al., 2006; Marra et al., 2003, 2009) (Fig. 2).

The early ‘Tuscolano-Artemisio’ (w561e351 ka; Karner et al.,2001; Marra et al., 2009), or ‘Vulcano Laziale’ (Giordano et al.,2006), phase was the most explosive and voluminous, as testifiedby at least seven (Marra et al., 2009) or eight (Giordano et al., 2006)large pyroclastic flow-forming eruptions, emplacing deposits withvolumes up to tens of km3 (Freda et al., 1997), and minor effusiveactivity (Fig. 2). This phase endedwith caldera collapse, followed by

intra-caldera and peri-caldera effusive activity, and subordinateexplosive activity from peri-calderic scoria cones, and maar vol-canoes. A second phase of activity (the ‘Faete’ phase, at w308e250 ka; Marra et al., 2003) started with peripheral effusive erup-tions and sub-contemporaneous hydromagmatic activity of sometuff rings on the northern slopes of the caldera, and it ultimately ledto the formation of a central edifice (Mt. Faete) and several minorintra-calderic scoria cones. The third ‘Late Hydromagmatic’ phase(w200e36 ka; Marra et al., 2003) was dominated by hydro-magmatic eruptions from a few monogenic and multiple maars(e.g., Freda et al., 2006; Giaccio et al., 2007, 2009a; De Benedettiet al., 2008; Sottili et al., 2009) and a scoria cone (Gaeta et al.,2011), clustered to the south-west of the Mt. Faete edifice.

From the tephrostratigraphic perspective, the Tuscolano-Artemisio or Vulcano Laziale phase, characterised by large explo-sive eruptions, is indeed the most relevant as it includes the fol-lowing main pyroclastic units (Marra et al., 2009): Tufo Pisolitico diTrigoria (w561 ka); Tufo del PalatinoeTufo di Bagni Albule (w530e527 ka); Pozzolane Rosse (w457 ka); Pozzolane Nere (w407 ka);and Villa Senni (w365 ka). Minor scoria-fall events occurred in-between these, as recorded by the Tufo Pisolitico di TrigoriaeTufo

Fig. 2. Simplified stratigraphy and 40Ar/39Ar chronology of the main eruptive units from the explosive activity of the Colli Albani volcanic district (from Marra et al., 2011, andreferences therein).

B. Giaccio et al. / Quaternary Science Reviews 67 (2013) 190e206192

del Palatino scoria-fall deposits (555 � 1 ka; Marra et al., 2011), theTufo di Bagni AlbuleePozzolane Rosse scoria-fall units (517 � 1 to500 � 3 ka; Marra et al., 2009); the Pozzolane Rosse-PozzolaneNere scoria fall (Corcolle fall, Giordano et al., 2006; 442 � 3 ka,Marra et al., 2011) and the Pozzolane NereeVilla Senni scoria-fall(Centogocce fall succession, Giordano et al., 2006; 404 � 5 ka,Marra et al., 2011) (Fig. 2).

In addition to the main eruptions of the Tuscolano-Artemisiophase and for the purpose of this study, we also considered therelatively low-magnitude events from the most recent explosiveactivity of the Late Hydromagmatic phase, which took place atAlbano maar between w70 ka and w36 ka (Freda et al., 2006;Giaccio et al., 2009a). In particular, the Albano maar stratigraphicsuccession consists of seven eruptive units (Albano 1e7; Fredaet al., 2006; Giaccio et al., 2007, 2009a; De Benedetti et al., 2008;Sottili et al., 2009). Among these, four sub-Plinian events (Albano 1,3, 5, 7) generated widespread fall-out deposits that have also beenrecognised in distal areas of the central (Giaccio et al., 2007; Giraudiet al., 2011) and southern (Wulf et al., 2012) Apennines. Fora detailed description of the most widespread Albano units 1, 3, 5and 7 see Giaccio et al. (2007).

Overall, juvenile clasts in the pyroclastic products from theTuscolano-Artemisio phase and the Albano maar are aphyric toporphyritic, leucite-bearing, generally poorly to moderately vesic-ular dark scoria, with variable amounts of clinopyroxene, raresanidine and no plagioclase crystals (Trigila et al., 1995; Gaeta,1998). Usually, the Colli Albani pyroclastics also include abundantgranular lithic clasts that are made up of millimetre-sized, clino-pyroxene and leucite (hereafter called italites), which represent thelow-pressure crystallisation of potassic magmas (Freda et al., 1997).Typically, the composition of the Colli Albani juvenile clasts is K-foiditic and it is characterised by a high content of iron (FeO up to12 wt%), calcium (CaO up to 16 wt%), sulphur (SO3 up to 1 wt%) andradiogenic isotopes. These juvenile clasts also show relatively high87Sr/86Sr ratios, which range from 0.709 to 0.711. In particular, theclinopyroxene phenocrysts are characterised by a significant time-dependent 87Sr/86Sr variability (Gaeta et al., 2006). This isotoperatio decreases in parallel with the age of the pyroclastic units,possibly reflecting the progressive depletion of the metasomatisedmantle source of the magmas (Gaeta et al., 2011). Along with thetextural features and the K-foiditic composition, this isotopic vari-ability is a peculiarity within the framework of Italian Quaternary

B. Giaccio et al. / Quaternary Science Reviews 67 (2013) 190e206 193

volcanism and can be regarded as diagnostic and exclusive char-acters of the Colli Albani pyroclastics (Peccerillo, 2005; Lustrinoet al., 2011, and references therein).

2.2. The Colli Albani distal tephras

The Neogene northeast-verging thrust system of the centraland southern Apennine chain hosts a number of tectonic inter-mountain basins that developed during the Plio-Quaternaryextensional phase, and that are filled by thick fluvial and lacus-trine successions (e.g., Galadini et al., 2003). These basins arelocated in a distance range of some tens to a few hundred kilo-metres east of the peri-Tyrrhenian Quaternary volcanic districts(Fig. 1a); i.e., in a favourable position with respect to the pre-vailing eastward direction of the stratospheric winds, and hencefor tephra dispersion. As a result, the tephra layers from theactivity of these volcanoes are a common feature of the basininfillings (e.g., Karner et al., 1999; Munno et al., 2001; Giaccioet al., 2012a). In particular, recent investigations in the inter-mountain basins of PaganicaeSan DemetrioeCastelnuovo, Car-apelle Calvisio, Fucino, Sulmona and Campo Felice (Fig. 1b) haveallowed the recognition of several cm- to dm-thick and relativelycoarse tephra layers that have been attributed to eruptions fromthe Colli Albani explosive activity (e.g., Narcisi, 1994; Giaccioet al., 2007; Galli et al., 2010; Freda et al., 2011; Giraudi et al.,2011; Giaccio et al., 2012b).

Up to now, the identification and correlation of these tephraswith Colli Albani volcanic activity was essentially based on: (i) thepeculiar K-foiditic compositions of the glass from these tephras(Table 1; Fig. 3); (ii) the lithological features; (iii) the 40Ar/39Ar or14C chronological constraints; and (iv) the dispersal areas. Indeed,among the Italian Plio-Quaternary volcanoes, foiditic pyroclasticrock types occur only at Mt. Vulture volcano in southern Italy (e.g.,Peccerillo, 2005) (Fig. 1a) and at the Colli Albani volcanic district incentral Italy. However, the Mt. Vulture pyroclastics are Na-foiditesand are derived from substantially lower magnitude eruptionsthan those from the Colli Albani volcanic district. In addition, withrespect to Colli Albani, the Vulture volcano is located at more than200 km southeast of the basins of central Italy and in the oppositedirection to the prevailing eastwards ash dispersion, to justify therelatively coarse graining and the geographical distribution of thecentral Italy foiditic tephra layers (Fig. 1). Therefore, the origin ofthe K-foiditic layers has been restricted to the Colli Albani volcanicdistrict.

3. Analytical methods

3.1. Major and minor elements

The determination of the major and minor elements in thetephra glass (one layer from site 2 of the Sulmona basin lacustrinesuccession, Fig. 1; see details in Table 1) were carried out at theIstituto di Geologia Ambientale e Geoingegneria of the Italian Na-tional Research Council (IGAG-CNR) (Rome, Italy) using a CamecaSX50 electron microprobe that was equipped with a five-wavelength dispersive spectrometer. The operating conditionswere as follows: accelerating voltage, 15 kV; beam current, 15 nA;beam diameter,10 mme15 mm; and counting time, 20 s per element.The following standards were used: wollastonite (Si and Ca),corundum (Al), diopside (Mg), andradite (Fe), rutile (Ti),orthoclase (K), jadeite (Na), phlogopite (F), potassium chloride(Cl), baritina (S), and metals (Mn). The Ti content was correctedfor the overlap of the Ti and Ka peaks. To evaluate the accuracy ofthe analyses, three international secondary standards (Kakanuiaugite, Iceladic Bir-1, and rhyolite RLS132 glasses, from the United

States Geological Survey) were analysed prior to the measure-ments. The mean analytical precision was <1% for SiO2, 1% forAl2O3, 5% for K2O, CaO, MgO and FeO, and 6%e9% for the otherelements.

3.2. Strontium and neodymium

The Sr andNd isotope compositionswere determined by thermalionisation mass spectrometry at the Istituto Nazionale di Geofisica eVulcanologia, Osservatorio Vesuviano (Naples, Italy), using a Thermo-Finnigan Triton TI multicollector mass spectrometer (details on thetype and number of the analysed tephras are provided in Tables 1and 2). After a wet sieving of the tephras, the largest fresh glassshards (0.1 g) were handpicked. They were then rinsed with de-ionised water in an ultrasonic bath, and dissolved in a mixture ofhigh purity HNO3 and HF in closed Savillex Teflon beakers on a hot-plate. The samples were then dried, taken up in concentrated HNO3,anddriedonce again.After this step, theyweredissolved in6NHCl inclosed Savillex Teflon beakers on a hotplate, and then dried down.Then they were taken up in 2.5 N HCl and loaded onto quartz col-umns, to extract the Sr and Nd by conventional ion-exchange chro-matographic techniques. Before their dissolution,w0.02 g pyroxenecrystalswere cleaned in dilute HF for 5min in an ultrasonic bath. Theacid solutionwas then removedwith a pipette, and the crystals wererinsed with de-ionised water in an ultrasonic bath. The mineralswere then dried, weighed out, and dissolved following the sameprocedure described for the glass shards, in closed Savillex Teflonvials. The Sr and Nd fractions were re-dissolved in dilute HNO3 andloaded with tantalum chloride solution and phosphoric acid onoutgassed Re filaments, for the thermal ionisation mass spectro-metric analysis. The 87Sr/86Sr and 143Nd/144Nd isotope ratios meas-ured were normalised for within-run isotopic fractionation to86Sr/88Sr ¼ 0.1194 and 146Nd/144Nd ¼ 0.7219, respectively. The Srblank was of the order of 0.1 ng during the period of chemistryprocessing. The mean measured value of 87Sr/86Sr for the SRM 987standard was 0.710215 � 0.000017 (2s, N ¼ 58) and that of143Nd/144Nd for the La Jolla standard was 0.511843 � 0.000015 (2s,N ¼ 26) during the period of the measurements; the externalreproducibility of 2s was calculated according to Goldstein et al.(2003).

Additional determinations of the Sr isotopic compositions ofbulk tephras were carried out at the IGAG-CNR. Conventional ion-exchange methods were used for Sr separation. These isotopicanalyses were carried out using a FINNIGAN MAT 262RPQ multi-collector mass spectrometer in static mode. The Sr was run on Redouble filaments. The internal (within-run) precision of each singleanalytical result is given as the two-standard error of the mean(2se). Repeated analyses of standards gave means and errorsexpressed as 2s as follows: NBS 987 87Sr/86Sr ¼ 0.710263 � 7(n¼ 22); 86Sr/88Sr normalised to 0.1194. The total procedural blankswere below 2 ng Sr.

All of the Sr andNd isotope ratios reported inTables 2 and 3werenormalised to 87Sr/86Sr ¼ 0.71025 and 143Nd/144Nd ¼ 0.51185,respectively (Thirlwall, 1991).

3.3. 40Ar/39Ar dating

The 40Ar/39Ar dating was performed on pristine leucite crystals,400 mme500 mm in size, from a layer of the Sulmona basinlacustrine succession (site 2; Fig. 1). These were hand-picked un-der a binocular microscope and slightly leached for 5min in a 5% HFsolution. A total of 20 single crystals were finally hand-picked afterleaching and separately loaded into a single pit in an aluminiumdisk. This sample was irradiated for 105 min (Irr 50) in the b1 tubeof the OSIRIS reactor (CEA Saclay, France). After irradiation, the

Table 1Meanmajor element compositions of the scoria fragments and/or glass shards from themajor explosive units of the Colli Albani that occurred in both distal and proximal areas(see Fig. 1 for site locations). The full analytical data for the individual glass measurements are given in Supplementary Table S2.

Unit Tufo Pisolitico di Trigoria Tufo di Bagni Albule Tufo di Bagni Albulee Pozzolane Rosse scoria fall

Setting Carapelle(site 1)a

ColliAlbania

Acerno(site 14)h

Sulmona(site 2)b

Oricola(site13)e

ColliAlbanic

Sulmona(site 2)d

ColliAlbanic

Population a a a a a a a a

N� analyses 11 s.d. 6 s.d. 27 s.d. 7 s.d. 7 s.d. 46 s.d. 5 s.d.

SiO2 43.77 0.36 43.17 0.18 43.91 44.73 1.18 45.62 0.70 45.74 0.85 44.33 1.08 41.68 0.66TiO2 1.10 0.02 1.19 0.02 1.28 0.82 0.10 n.d. 0.00 0.76 0.12 1.17 0.11 1.39 0.21Al2O3 16.89 0.33 16.37 0.24 16.73 19.48 0.71 19.03 0.33 19.16 0.15 16.09 0.72 11.31 0.30FeO 10.08 0.29 10.47 0.28 10.04 8.17 0.79 8.36 0.52 7.80 0.21 11.15 0.98 12.53 0.83MnO 0.31 0.02 0.31 0.04 0.26 0.36 0.05 0.32 0.04 0.30 0.04 0.27 0.05 0.29 0.03MgO 3.32 0.09 3.32 0.23 3.29 1.45 0.14 1.54 0.13 1.40 0.06 3.73 0.37 6.19 0.51CaO 12.30 0.39 12.97 0.08 12.35 10.90 1.18 11.53 0.73 10.20 0.50 12.32 1.13 16.62 0.86Na2O 5.00 0.12 5.35 0.19 6.04 5.59 0.65 4.95 0.30 5.49 0.29 3.41 0.39 3.56 0.28K2O 6.66 0.17 6.34 0.09 6.1 8.31 0.91 8.42 0.79 8.93 0.31 6.75 1.12 5.26 0.37P2O5 0.57 0.09 0.52 0.07 n.d. 0.18 0.03 0.23 0.04 0.21 0.04 0.77 0.11 1.18 0.14F 0.51 0.07 0.69 0.10 n.d. 0.85 0.21 0.13 0.05 0.86 0.15 0.43 0.12 0.75 0.12Cl 0.17 0.03 0.18 0.02 n.d. 0.18 0.03 0.13 0.02 n.d. 0.12 0.02 n.d.SO3 0.63 0.23 0.69 0.05 n.d. 0.75 0.27 0.80 0.11 0.85 0.10 0.55 0.15 0.19 0.03Original 96.83 0.81 96.09 0.34 96.73 1.34 95.56 1.07 98.02 0.76 95.98 1.34 98.69 1.49K2O/Na2O 1.33 0.02 1.19 0.22 1.01 1.53 0.41 1.70 0.18 1.63 0.13 2.03 0,51 1.48 0.14

Unit Pozzolane Rosse

Setting Paganica (site 5)a Sulmona (site 2a)aed Raiano (site 3)a Sul. (site 2)b Colli Albani

Population a b a b a b a (basal fall)d

N� analyses 9 s.d. 8 s.d. 20 s.d. 7 s.d. 7 s.d. 15 s.d. 23 s.d. 10 s.d.

SiO2 42.16 1.54 45.11 0.58 42.15 0.38 45.14 0.44 42.36 0.34 44.30 0.61 41.92 0.64 42.83 0.18TiO2 1.22 0.12 0.96 0.07 1.23 0.10 1.01 0.14 1.34 0.09 0.93 0.09 1.19 0.05 1.41 0.12Al2O3 14.40 1.99 16.52 0.17 14.22 0.25 16.15 0.55 12.47 0.10 15.44 0.37 14.23 0.20 12.65 0.11FeO 11.67 1.09 9.87 0.38 12.16 0.42 9.96 0.98 11.61 0.23 10.16 0.42 12.50 0.36 11.60 0.10MnO 0.32 0.07 0.24 0.04 0.30 0.05 0.24 0.05 0.27 0.07 0.28 0.04 0.32 0.03 0.22 0.04MgO 5.23 1.53 4.23 0.16 5.23 0.19 3.54 1.28 6.78 0.14 4.52 0.19 5.20 0.19 6.51 0.11CaO 14.65 1.94 11.28 0.30 14.45 0.33 11.44 1.50 15.88 0.16 12.67 0.49 14.20 0.38 16.30 0.30Na2O 3.97 1.30 3.48 0.39 3.96 0.20 3.51 0.64 3.43 0.29 3.58 0.32 4.00 0.32 2.96 0.06K2O 5.56 0.96 7.49 0.96 5.23 0.31 8.18 1.07 4.82 0.16 7.32 0.35 5.43 0.29 4.42 0.11P2O5 0.83 0.24 0.81 0.05 1.07 0.07 0.84 0.13 1.05 0.07 0.81 0.05 1.02 0.08 1.10 0.07F 0.53 0.15 0.35 0.12 0.48 0.10 0.37 0.14 0.50 0.13 0.41 0.09 0.49 0.08 0.48 0.15Cl 0.16 0.06 0.11 0.02 0.16 0.01 0.11 0.01 0.11 0.01 0.14 0.02 0.16 0.02 n.d.SO3 0.25 0.16 0.30 0.07 0.11 0.04 0.22 0.06 0.03 0.02 0.29 0.08 0.16 0.05 0.03 0.03Original 96.48 0.83 97.26 1.36 98.33 0.36 98.31 2.12 97.82 0.29 97.77 0.81 97.72 1.43 97.96 0.90K2O/Na2O 1.51 0.41 2.20 0.49 1.32 0.10 2.43 0.64 1.41 0.10 2.06 0.20 1.36 0.15 1.49 0.04

Unit Pozzolane Nere Tufo di Villa Senni Albano 5e7

Setting Colli Albanic Paganica (site 7)a Colli Albanic Campo Felice (site 9)f Colli Albani (A7)g

Population a Lc-free Lc-free Lc-bearing a (Mid area) (Near vent)

N� analyses 11 s.d. 17 s.d. 19 s.d. 18 s.d. 21 s.d. 28 s.d. 23 s.d.

SiO2 45.79 0.35 47.75 0.33 47.86 0.23 45.83 0.27 44.89 1.65 46.09 1.28 48.94 1.50TiO2 0.85 0.08 0.73 0.05 0.71 0.03 0.93 0.05 0.85 0.15 0.86 0.11 0.62 0.14Al2O3 18.36 0.12 19.60 0.19 19.89 0.18 18.57 0.21 19.81 1.40 19.37 0.83 20.97 1.09FeO 8.35 0.33 6.73 0.26 6.88 0.23 8.96 0.30 7.95 1.02 8.44 0.78 6.03 1.28MnO 0.31 0.07 0.23 0.05 0.23 0.04 0.29 0.05 0.29 0.06 0.32 0.06 0.26 0.05MgO 2.14 0.08 1.58 0.08 1.55 0.04 1.99 0.05 1.73 0.80 1.32 0.42 1.27 0.64CaO 10.11 0.34 8.33 0.51 7.92 0.19 10.35 0.17 11.79 1.98 11.41 1.09 8.11 1.47Na2O 7.41 0.34 4.84 0.23 5.07 0.21 5.83 0.16 5.10 1.41 5.59 0.94 6.54 1.24K2O 6.33 0.37 9.99 0.58 9.67 0.24 7.00 0.29 7.33 1.83 6.29 1.34 7.01 1.65P2O5 0.34 0.06 0.22 0.03 0.22 0.03 0.25 0.05 0.26 0.14 0.30 0.16 0.25 0.14F 0.85 0.10 0.54 0.11 0.51 0.14 0.68 0.15 0.75 0.17 n.d. 0.63 0.29Cl n.d. 0.19 0.03 0.18 0.01 0.25 0.02 0.23 0.08 n.d. n.d.SO3 0.32 0.05 0.70 0.11 0.53 0.09 0.50 0.12 1.30 0.95 0.99 0.48 0.41 0.07Original 99.24 96.05 0.42 98.77 0.42 98.31 0.51 97.38 1.13 95.95 1.18 95.69 2.04K2O/Na2O 0.85 2.07 0.20 1.91 0.12 1.20 0.07 1.66 0.99 1.20 0.53 1.14 0.44

Data are means (in bold) � standard deviation (s.d., in italics).a Galli et al. (2010).b Present study.c Marra et al. (2009).d Freda et al. (2011).e Stoppa et al. (2005).f Giraudi et al. (2011).g Giaccio et al. (2007).h Munno et al. (2001; SEM-EDS).

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Fig. 3. Total alkali versus silica classification diagrams (Le Bas et al., 1986) for the proximal and the equivalent distal Colli Albani tephras (see Table 1 for references, Fig. 1 for sitelocations, and Fig. 5 for stratigraphic positions of the tephra from site 2).

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crystals were transferred one by one into a copper sample holderand then loaded into a differential vacuum Cleartran� window. Atotal of 15 crystals were individually fused atw12% full laser power.The Ar isotopes were analysed using a VG5400 mass spectrometerequipped with a single ion counter (Balzers� SEV 217 SEN), fol-lowing procedures outlined in Nomade et al. (2010). Each Ar iso-tope measurement consisted of 20 cycles of peak switching of theargon isotopes. The neutron fluence (J) was monitored by co-irradiation of Alder Creek sanidine (ACs) standard (Nomade et al.,

2005) placed in the same pit as the leucite. The J value was deter-mined from analyses of three single ACs crystals. The correspond-ing J value (see online Supplementary Table S1) was calculatedusing an age of 1.193 Ma (Nomade et al., 2005) and the total decayconstant of Steiger and Jäger (1977).

Recent revisions of decay (Renne et al., 2011) and monitor con-stants suggest values of w0.64% (Kuiper et al., 2008, 1.201 Ma forACs) and1.0% (Renne et al., 2011; 1.2056Ma forACs),which areolderthan is used hereafter. However, there has been no formal

Table 2Strontium isotope analyses of the clinopyroxene, glass and/or bulk samples from both the distal and proximal Colli Albani pyroclastic units (see Fig. 1 for site locations).

Unit Stratigraphic-geographic setting

Distal Proximal

Site 87Sr/86Sr (�2s � 10�6) 40Ar/39Arage (ka)

87Sr/86Sr (�2s � 10�6) 40Ar/39Arage (ka)

cpx Glass Bulk cpx Bulk

Tufo Fosso Colleraso 0.711204 � 9b 608 � 2c

0.711169 � 10b

Tufo Pisolitico diTrigoria

1 0.711003 � 6a 0.710905 � 6a

0.711008 � 6a 561 � 5c

0.711038 � 10b

0.711310 � 10b

Tufo del Palatino/Bagni Albule

2 0.710587 � 5a >457.4 � 1.7a

13 0.710917h w531i

0.710862 � 9b 530 � 2c/527 � 2c

Tufo di Bagni AlbuleePozzolane Rossescoria fall

2 0.710555 � 8a >457.4 � 1.7a 517 � 1c/500 � 3c

Pozzolane Rosse 2a 0.710727 � 6a 457.4 � 1.7a

4 0.710624 � 5a

3 0.710699 � 7a 0.710534 � 6a

6 0.710659 � 6a

5 0.710640 � 6a 0.710441 � 6a

0.710623 � 9b 457 � 4c

0.710616 � 9a

Pozzolane Nere 0.710486 � 9b 407 � 2c

0.710512 � 9b

Tufo di Villa Senni 7 0.710436 � 6a 0.710437 � 6a 365 � 2g

0.710459 � 9b 365 � 4c

0.710421 � 10b

0.710475 � 10b

0.710476 � 7b

0.710494 � 10b

0.710347 � 6a

0.710484a

Mt. Faete succession 0.71031 � 20e 308 � 2/250 � 1c0.710304 � 9a

0.710382 � 9a

Ariccia 0.710078 � 10b 201 � 1c

0.710126 � 9a

Albano 1 0.709385 � 9b 69.4 � 0.6d

0.70950 � 20e 72.0 � 3.0f

Albano 3 0.708477 � 9b 68.6 � 1.1d

0.70963 � 20e 73.0 � 3.0f

Albano 5 0.709644 � 9b

0.709590 � 9b

0.70959 � 20e 41.0 � 7.0f

0.70963 � 20e

0.70955 � 20e

0.70967 � 20e

Albano 6 0.709512 � 9j 36.1 � 0.3d

Albano 7 9 0.709598 � 6a 41 � 9k

10 0.709551 � 7a

0.709548 � 10b 35.9 � 0.6d

37.0 � 3.0f

33.0 � 4.0f0.709513 � 10b

0.70958 � 20e

0.70957 � 20e

0.70953 � 20e

0.70953 � 20e

0.70945 � 20e

0.70953 � 20e

Mt. due Torri scoriacone

0.709645 � 6j 40.1 � 7.1j

a This study.b Gaeta et al. (2006).c Marra et al. (2011).d Freda et al. (2006).e Giaccio et al. (2007).f Giaccio et al. (2009a).g Giaccio et al. (2012b; recalculated).h Barbieri et al. (2002).i Bosi et al. (1991).j Gaeta et al. (2011).k Giraudi et al. (2011).

Table 3Neodimium isotope analyses of the clinopyroxene, glass and/or bulk samples from both the distal and proximal Colli Albani pyroclastic units (see Fig. 1 for site locations).

Unit Geological-geographic setting

Distal Proximal

Site 143Nd/144Nd (�2s � 10�6) 40Ar/39Arage (ka)

143Nd/144Nd (�2s � 10�6) 40Ar/39Arage (ka)

Cpx Glass Bulk cpx Bulk

Tufo Pisoliticodi Trigoria

1 0.512124 � 7a 0.512129 � 7a 561 � 5b

Pozzolane Rosse 2a 0.512114 � 6a 457.4 � 1.7a 0.512106 � 8a 456 � 3b

4 0.512116 � 6a

6 0.512111 � 6a

5 0.512105 � 8a

Tufo di Villa Senni 7 0.512119 � 5a 365 � 2e 0.512120 � 8aei 365 � 4b

Ariccia 0.512120 � 8a 201 � 1b

Albano 6 0.512153 � 9g 36.1 � 0.3c

Albano 5e7 9 0.512147 � 6a 41 � 9f 35.9 � 0.6c

37.0 � 3.0d

33.0 � 4.0d

Mt. due Torri scoriacone

0.512146 � 6g 40.1 � 7.1g

a This study.b Marra et al. (2011).c Freda et al. (2006).d Giaccio et al. (2009a).e Giaccio et al. (2012b, recalculated).f Giraudi et al. (2011).g Gaeta et al. (2011).i Glass.

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acceptance of either of these two calibrations, or of the 40K totaldecay constant proposed by Renne et al. (2011). As a consequence,here, we remain with the conventional values for all of the agesreported hereafter, to be able to compare our ages to others thathave beenpublished over the past 10 years. Furthermore, even if the40Ar/36Ar atmospheric ratio was also recently suggested to be w1%higher (Lee et al., 2006; Valkiers et al., 2010), here, we used the ratiogiven by Steiger and Jäger (1977). This has negligible impact on theage calculation, as we used the same value for both the mass dis-crimination and the air calibration (see Renne et al., 2009). Proce-dural blanks weremeasured every three to four crystals, dependingon the sample beam size previously measured. For a typical 9-minstatic blank, typical backgrounds were w2.0e2.2 � 10�17 mol and5.0 to 6.0 � 10�19 mol for 40Ar and 36Ar, respectively. The precisionand accuracy of the mass discrimination correction was monitoredby daily measurements of the air argon (see full experimentaldescription in Nomade et al., 2010). Nucleogenic production ratiosused to correct for reactor produced Ar isotopes from K and Ca arethe same as those used in Nomade et al. (2011).

4. Results and discussion: stratigraphic, chemical, 87Sr/86Sr,143Nd/144Nd and 40Ar/39Ar data

4.1. General background

The previously recognised distal tephras from the Colli Albaniexplosive activity included: the Tufo Pisolitico di Trigoria(561 � 2 ka; Palladino et al., 2001), the Tufo del PalatinoeTufodi Bagni Albule (530 � 2/527 � 2 ka; Marra et al., 2009),the Tufo di Bagni AlbuleePozzolane Rosse air-fall sequence(517 � 1e500 � 3 ka; Marra et al., 2009), the Pozzolane Rosse(457 � 4 ka; Freda et al., 2011), the Villa Senni eruptive sequence(365 � 4 ka; Marra et al., 2009) and Albano unit 5e7 (41 � 7/36 � 1 ka; Freda et al., 2006; Giaccio et al., 2009a) (Table 1; Fig. 3).In the following sections, we provide a general overview of thestratigraphic settings and of the chemical compositions of thetephras, mostly previously determined by EMPA (Table 1; full

analytical data for individual glass shards are given in the onlineSupplementary Table S2), and present the new 87Sr/86Sr,143Nd/144Nd and 40Ar/39Ar determinations of both previouslydescribed and newly recognised layers. We also discuss and pro-pose a reassessment of the attribution of some of the K-foiditictephras not previously correlated to Colli Albani activity.

4.2. Tufo Pisolitico di Trigoria (561 � 2 ka)

This tephra has been recognised in some outcrops in theCarapelle Calvisio intermountain depression (Fig. 1b, CC basin).Here, the Tufo Pisolitico di Trigoria tephra is inter-bedded inlacustrine deposits, or when it occurs in marginal settings of thebasin, it rests on a reddish paleosol (Fig. 4). The w5 cm-thick pri-mary Tufo Pisolitico di Trigoria layer is commonly covered byreworked ash of variable thickness up to severalmetres (Fig. 4). Dueto the relevant thickness of the reworked ash, it was interpreted inthe past as a product from a local volcanic centre (Bosi and Locardi,1991).

The primary layer shows the typical features of a fallout deposit(i.e., uniform thickness and internal stratigraphy, planar-bedding,good sorting), and is made up of a basal level of poorly vesicularfine lapilli, grading upwards into an ash level that contains mm-sized accretionary lapilli (Fig. 4). This peculiar lithological featurehas also been described in proximal settings of the Colli Albani (e.g.,Palladino et al., 2001). Dark grey, sub-aphyric juvenile clasts areassociated with loose crystals of leucite, granular italite and sub-mm-sized lithic lava clasts. The juvenile glass is homogeneous,foiditic in composition (SiO2 w43.5wt%, MgO w3.3wt%) witha relatively low alkali ratio (K2O/Na2O w1.3) (Table 1).

The 87Sr/86Sr analyses were performed on both clinopyroxeneand juvenile scoria clasts and yielded values of w0.711003 and0.710905, respectively. The highest isotopic ratio (clinopyroxene)was close to the Sr isotope composition measured for clinopyrox-ene crystals from the proximal Tufo Pisolitico di Trigoria pyroclasts(Table 2). Although the Sr isotope composition measured in scoriaclasts appears lower than those determined for both the distal and

Fig. 4. Lithological features of the distal Tufo Pisolitico di Trigoria (TPT) that outcrops in the Carapelle Calvisio (CC) intermountain basin (Fig. 1b, site 1).

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proximal clinopyroxene fractions, the Nd isotope composition ofthe scoria clasts (143Nd/144Nd ¼ 0.512124 � 7) is similar, within themargins of error, to those of the clinopyroxenes from the proximalTufo Pisolitico di Trigoria deposit (0.512129 � 7; Table 3).

Also, based on major element compositions, the Tufo Pisoliticodi Trigoria units possibly correlates with the A19 layer that occurs atthe base of the Acerno lacustrine succession in southern Italy(Fig. 1a, site 14; Table 1) (Munno et al., 2001). The A19 layer wasattributed to an eruption from the Mt. Vulture volcano (Munnoet al., 2001) e possibly because of the unavailability of EMPA ma-jor element glass composition for the Colli Albani tephras e but itsK-foiditic composition is really close to that of the Tufo Pisolitico diTrigoria (Table 1). In the light of the attribution of the layer A19 tothe Tufo Pisolitico di Trigoria here proposed, the Acerno pollenrecord, which was correlated to marine isotope stage (MIS) 10e8(w350e250 ka; Munno et al., 2001), should bew200 ka older thanpreviously thought and thus be dated back to the MIS 14e12 in-terval (w560e460 ka).

4.3. Tufo del PalatinoeTufo di Bagni Albule (530 � 2 ka e

527 � 2 ka)

The Tufo del PalatinoeTufo di Bagni Albule distal tephra occursin a lacustrine sequence of the Sulmona basin that outcrops nearthe village of Popoli (Fig. 2). On the basis of U-series geo-chronological data, this tephra was previously attributed to a con-siderably younger eruption from Somma-Vesuvius volcano (inGiaccio et al., 2009b, tephra SUL1-6). However, recent strati-graphic investigations, paleomagnetic analyses, and 40Ar/39Ar agedeterminations (Scardia et al., 2012) have indicated that the U-se-ries dating in Giaccio et al. (2009b) were aberrantly young, and thatthe unit that contains this tephra should be dated to the middlepart of the Middle Pleistocene.

In this distal setting, the Tufo del PalatinoeTufo di Bagni Albuletephra is a w50 cm-thick layer of partially reworked ash. This ismade up of green, porphyritic and finely grained poorly vesiculated,sub-mm scoria, and it lies on top of a paleosol that separates twolacustrine units (in Giaccio et al., 2009b, SUL2, SUL1) (Fig. 5). The

glass composition is a relatively evolved foidite, quite similar to thatof the Villa Senni eruptive units (SiO2 w45 wt%, MgO w1.5 wt%,K2O/Na2O w1.6) (Table 1). Due to the very low content of clino-pyroxene crystals, 87Sr/86Sr analyses were measured on the bulksample, which yielded 0.710587 � 5. This is substantially lowerthan the Sr isotope ratio measured in the clinopyroxene from theproximal equivalent (0.710862 � 9, Table 2).

A thick and relatively coarse tephra layer with a foiditic glasscomposition and an 40Ar/39Ar age (541 � 9 ka) comparable to thatof Tufo del PalatinoeTufo di Bagni Albule was recognised in thedepocentral area of the Fucino basin (Fig. 1b, site 12), at a depth ofw100 m from the top of the lacustrine sequence (Narcisi, 1995).Similarly to other relatively thick tephra layers found in the intra-Apennine basins, it was previously attributed to a local volcaniccentre (Follieri et al., 1991). However, later Narcisi (1995) reinter-preted it as a distal tephra from the peri-Tyrrhenian volcanic dis-tricts, and now we propose to restrict its correlation to the Tufo delPalatinoeTufo di Bagni Albule.

An additional pyroclastic unit matching the chemical composi-tion (Table 1), the 40Ar/39Ar age (w531 ka; Bosi et al., 1991) and theSr isotopic ratio (0.710917; Table 2) of the Tufo di Bagni Albule is theso-called Oricola tuff. This pyroclastic unit outcrops in the Carsolibasin, at less than 40 km northeast from the Colli Albani caldera rim(Fig.1), andwas related to the activity of a local volcanic centre (e.g.,Stoppa et al., 2005; D’Orefice et al., 2006). However, in the light ofsignificant chronological, isotopic and major element compositionaffinities between the two pyroclastic units, and by considering therelatively short distance of the Carsoli basin from the Colli Albanivolcano, we propose that the Oricola tuff could represent a mid-distal occurrence of the Tufo di Bagni Albule, and thus its volca-nological significance accordingly reassessed.

4.4. The Tufo di Bagni AlbuleePozzolane Rosse scoria-fallsuccession (517e500 ka)

The Tufo di Bagni AlbuleePozzolane Rosse scoria fall occurs inthe same Sulmona lacustrine succession that contains the Tufo delPalatinoeTufo di Bagni Albule tephra, fromwhich it is separated by

Fig. 5. Composite section of the lacustrine succession of the Sulmona basin thatcontains the distal counterparts of the Tufo del PalatinoeTufo Bagni Albule (TPeTBA),Tufo di Bagni AlbuleePozzolane Rosse (TBAePR) scoria-fall successions and the Poz-zolane Rosse (PR) eruptive unit (Fig. 1b, site 2).

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w3.5 m-thick lacustrine silts (Fig. 5). It consists of a w1 cm-thickgreyegreenish ash layer that contains sub-mm brown, blocky,leucite-bearing scoria and lighter coloured and moderately vesic-ular microscoria, which are foiditic in composition (Fig. 3). EMPA ofthe glasses relative to the proximal Tufo di Bagni AlbuleePozzolaneRosse scoria-fall succession is available only for the most recentunit of this cluster of eruptive scoria fall-out (Marra et al., 2009),which appears to be different from this distal layer (Table 1).

In spite of this, the correlation of this tephra to a unitbelonging the Tufo di Bagni AlbuleePozzolane Rosse scoria-fall succession is supported by robust field evidence, because,similarly to its proximal counterpart, it is stratigraphically sand-wiched between the Tufo di Bagni Albule and the Pozzolane Rossedistal tephras (see section below; Fig. 5). A 87Sr/86Sr measure-ments performed on a bulk sample yielded w0.710555 � 8(Table 2).

4.5. The Pozzolane Rosse eruptive unit (457 � 4 ka)

The distal equivalent of the Pozzolane Rosse unit is the mostwidespread distal tephra from the Colli Albani volcanic district, as ithas been recognised in a number of localities from the PaganicaeSan DemetrioeCastelnuovo and Sulmona basins (Galli et al., 2010;Giaccio et al., 2012b), both of which are located along the currentcourse of the Aterno River (Fig. 1b).

In the PaganicaeSan DemetrioeCastelnuovo basin area (Fig. 1b),the Pozzolane Rosse tephra is a widespread marker within fluvialsedimentary units of the Raiale and Aterno rivers and in someslope derived deposits (Giaccio et al., 2012b). In the Sulmona basinarea, it has been recognised in the same lacustrine sequence thatcontains the distal tephras of the Tufo del PalatinoeTufo di BagniAlbule and the Tufo di Bagni AlbuleePozzolane Rosse scoria-fallsuccessions, which outcrop in the basin depocentre area, aroundPopoli (Fig. 1b, site 2). It also occurs in the fluvial deposits of theSulmona basin, in outcrops near the village of Raiano at the north-western margin of the basin (Fig. 1b, site 3, Fig. 6), which belong tothe same fluvial unit of the PaganicaeSan DemetrioeCastelnuovobasin, and which can be almost continuously traced along theAterno River valley between the two tectonic depressions (Fig. 1b).In this particular context of the Raiano area the Pozzolane Rossetephra was related to a local intra-Apennine volcanic centre(D’Orefice et al., 2006).

Typically, two distinct layers can be distinguished (Fig. 6): (i)a lower, 5 mm-thick layer of very fine ash made up of browneblack, leucite-bearing micro-scoria and loose crystals of leuciteand clinopyroxene; and (ii) an upper, upward fining, 5 cm-thicklayer of well-sorted, purpleeblack coarse ash to fine lapilli,enclosing black, moderately porphyritic scoria and lava, italites,and thermally metamorphosed sedimentary lithic fragments. Theinternal subdivision of the Pozzolane Rosse unit is justified bymajor differences in the textural characters of the scoria clasts(generally darker, more dense and glassy in the lower layer), thehigher amount of lithic fragments in the upper layer, and theabrupt grain-size increase at the base of the upper subunit(Fig. 6). Diffuse star-like leucite microcrystals provide anotherdiagnostic microtextural feature characterising the micro-scoriain the lower sub-layer of this tephra. On the other hand, thescoria from the upper subunit may include peculiar, variablydecarbonatated, limestone lithic clasts. Based on microtexturalfeatures, the lower sub-layer can be considered as the distalequivalent of the Pozzolane Rosse basal fall-out, while the uppersub-layer can be related to the phoenix cloud that was associatedwith the main pyroclastic-flow-forming phase of the PozzolaneRosse eruption.

The lithological correlation between the distal and proximalPozzolane Rosse deposits is strongly supported by the chemicalcomposition of the lower layer of the distal Pozzolane Rossetephra, which is characterised by the same, peculiar, ratherhomogeneous, K-foiditic composition of the glass from the basalfall-out deposits of the proximal Pozzolane Rosse, with verylow SiO2 (w42 wt%) and high MgO contents (w6.5 wt%) anda K2O/Na2O of w1.5 (Freda et al., 2011, Table 1). On the otherhand, the composition of the coarser, upper layer is typically

Fig. 6. Stratigraphic section and lithological features of the distal tephras of the Pozzolane Rosse (PR) and Villa Senni (VS) eruptive units that are interbedded in the fluvial depositsthat outcrop near the village of Raiano, at the easternmost margin of the Sulmona basin (Fig. 1, site 3), and in the PaganicaeSan DemetrioeCastelnuovo basin (PSC, Fig. 1, sites 4, 5, 7).At sites 4 and 5, the Pozzolane Rosse tephra occurs jointly with a whitish ash layer, which is trachytic in composition, and which correlates to the eruption of Tufo Rosso a ScorieNere (TRSN; w449 ka) from the Sabatini volcanic field (Galli et al., 2010).

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heterogeneous, as it ranges from a poorly evolved K-foiditiccomposition, similar to those of the basal fall-out, to a moreevolved composition (SiO2 w45 wt%, MgO w4 wt% and K2O/Na2Ow2.0) (Table 1 and Fig. 3).

A sample of the Pozzolane Rosse tephra from Sulmona lacus-trine sediments (Fig. 1b, site 2) was also dated by the 40Ar/39Armethod. A total of 15 leucite crystals were analysed (Fig. 7), andthe full analytical details for the individual crystals are given in

Fig. 7. Age-probability density spectra with individual leucite ages and inverse isochrons for the distal tephra of the Pozzolane Rosse (PR) eruptive unit that occurs in the Sulmonabasin (Fig. 1, site 2; Fig. 4). The atmospheric 40Ar/36Ar initial intercept is identical to the atmospheric one, which suggests no excess argon component. The data reduction andisochron regressions were calculated using ArArCalc (Koppers, 2002). The weighted mean ages and corresponding uncertainties were calculated using IsoPlot 3.0 (Ludwig, 2001).The 40Ar/39Ar ages obtained for the Pozzolane Rosse (PR) distal tephra is quoted at the 1s level throughout the text (Renne et al., 2009).

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Supplementary Table S1. The ageeprobability density spectra forthis sample is simple, and is dominated by juvenile crystals (Fig. 7).The weighted mean age of 457 � 1 ka (�5 ka, external uncertainty,MSWD ¼ 0.6, P ¼ 0.8) was obtained using all of the crystals ana-lysed. This weighted mean age is consistent with the isochron one(w458 � 5 ka), and it has an atmospheric 40Ar/36Ar initial inter-cept (Fig. 7). This 40Ar/39Ar dating provide a robust chronologicalconstraint which confirms the attribution of this distal tephra tothe Pozzolane Rosse eruptive unit, as in the proximal volcanicsetting it was dated to the same age of 457 � 4 ka (Karner et al.,2001).

Eight 87Sr/86Sr isotope measurements were performed onclinopyroxene and scoria clasts from five different samples of thePozzolane Rosse distal tephra, and one sample from the proximalunit. Three of these samples were collected in different strati-graphic settings of the PaganicaeSan DemetrioeCastelnuovobasin (Fig. 1b, sites 4, 5, 6), and two in the lacustrine (Fig. 1b,site 2a) and fluvial (Fig. 1b, site 3) deposits of the Sulmona basin.The six measurements performed on clinopyroxene, five of whichwere from distal samples, yielded 87Sr/86Sr from 0.710616 to0.710727, close to the values reported in Gaeta et al. (2006), whilethe scoria clasts yielded lower Sr isotope compositions (Table 2).On the contrary, the Nd isotope compositions determined on thefour distal samples studied, both as clinopyroxene and scoriaclasts, and on the clinopyroxene from the proximal deposit, aresimilar, within the margin of error (143Nd/144Nd w0.51211;Table 3).

4.6. The Villa Senni eruptive sequence (365 � 5 ka)

To date, the distal occurrence of the Villa Senni eruptive unithas been recognised in a single locality of the PaganicaeSanDemetrioeCastelnuovo basin (Fig. 1b, site 7), within the above-mentioned sandy fluvial succession that also contains the Poz-zolane Rosse tephra as well (Galli et al., 2010; Giaccio et al.,2012b). It consists of a w2 to 5 cm-thick, discontinuous, coarse,greenish ash layer (Fig. 6) that is made up of both dense leucite-bearing and blackish, vesicular leucite-free scoria, leucite, looseclinopyroxene crystals, and italite lithic clasts. The distal VillaSenni tephra was dated by the 40Ar/39Ar method at 367 � 2 ka(Giaccio et al., 2012b), an age that is statistically indistinguishablefrom that of the proximal Villa Senni eruptive unit, dated at365 � 5 ka (Karner et al., 2001). Furthermore, by normalising to

the same standard used in Karner et al. (2001) (c.a. FCs at28.02 Ma), the 40Ar/39Ar age by Giaccio et al. (2012b) would be365 � 2 ka; i.e., exactly the same as for the proximal Villa Sennieruptive units.

The foiditic glass in aphyric scoria of the distal tephra of the VillaSenni eruptive units is homogeneous in composition and amongthemost evolved of the Colli Albani tephras, as it is characterised bythe highest SiO2 (w48 wt%) and by low MgO (w1.5 wt%) contents,with a high alkali ratio (K2O/Na2O w2.0) (Table 1). Two 87Sr/86Srisotope measurements performed on clinopyroxene and glassyscoria clasts from the distal Villa Senni tephra yielded comparableresults of 0.710436� 6 and 0.710437� 6 (Table 2). These values arewithin the relatively wide range of 87Sr/86Sr obtained for clino-pyroxene and bulk rock of the proximal Villa Senni units (87Sr/86Srfrom 0.710347 to 0.710494) (Table 2). The 143Nd/144Nd of theinvestigated distal Villa Senni tephra is even closer the value weobtained for the proximal products, as they are both w0.51212(Table 3).

4.7. The Albano 5e7 unit (41 � 7e36 � 1 ka)

The Albano 5e7 cluster distal tephra is widely dispersed in thecentral Apennine basins of Fucino, Sulmona, Tirino and CampoFelice (Giaccio et al., 2007; Giraudi et al., 2011). Due to similarlithological and compositional features of the distal Albano 5 toAlbano 7 units, here we refer to a cluster of tephras rather than ofindividual units. Commonly, this cluster consists of one to threesuperimposed cm- to dm-thick, crystal-rich, dark tephra layers thatare inter-bedded in the lacustrineefluvialealluvial deposits of theLast Glacial Period. They are made up of sub- to mm-sized, poorlyvesicular, greyeblack scoria, with abundant leucite and clinopyr-oxene, and up to cm-sized phlogopite crystals. The currentlyavailable geochronological data for this cluster of layers comprisea radiocarbon measurement performed on a terrestrial gasteropod,which yielded an age of 36.6 � 0.2 cal ka (sample from Sulmonabasin, Fig.1b, site 10; Giaccio et al., 2007), and an 40Ar/39Ar dating at41�9 ka (Giraudi et al., 2011) (Fig. 1b, site 9), both within the rangeof the ages of the proximal deposits (41 �7e36 � 1 ka; Freda et al.,2006; Giaccio et al., 2009a).

The Albano 5e7 tephras are relatively evolved foidites (SiO2 46e44 wt%, MgO <2 wt%) featured by a relatively low alkali ratio (K2O/Na2O 1.3e1.0) (Table 1). Two 87Sr/86Sr measurements that wereperformed on clinopyroxene crystals from the tephra in Sulmona

Fig. 8. Variability of the concentration of some selected major elements in the glassfrom both distal (circles) and proximal (crosses) tephras of the Colli Albani, showingthe compositional differences/analogies between each eruptive unit. TPT, Tufo Pisoli-tico di Trigoria; TP-TBA, Tufo del Palatino-Tufo di Bagni Albule; PR, Pozzolane Rosse;PN, Pozzolane Nere; VS, Villa Senni; A, Albano.

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basin (i.e., the same that were dated by 14C atw36 ka; Giaccio et al.,2007; Fig. 1b, site 10) and from the Campo Felice basin (41 � 9 ka;Giraudi et al., 2011, Fig. 1, site 9) yielded 0.709551 � 7 and0.709598 � 6, respectively. Previous 87Sr/86Sr analyses on a distalsample from Fucino basin (Fig. 1b, site 11) (Giaccio et al., 2007)again yielded a comparable value of 0.70969. Similar isotope ratiosthat are less enriched in radiogenic Sr were measuredon clinopyroxene from the proximal Albano maar units(87Sr/86Sr ¼ 0.709512 � 9) (Gaeta et al., 2006; Giaccio et al., 2007)(Table 2) and on the sub-coeval bulk rock from the Monte due Torriscoria cone (87Sr/86Sr ¼ 0.709645 � 6) (Gaeta et al., 2011). The Ndisotope ratios measured on clinopyroxene and bulk rock from boththe distal and proximal Albano units are similar, within the marginof error (143Nd/144Nd w0.51215) and are, so far, the highest ratiosmeasured on the Colli Albani eruption products.

4.8. General diagnostic features of the Colli Albani tephras andapplicability of the isotope method

The above reported data, reviewed from literature and/orpresented in the present study, provide a broad dataset of diag-nostic lithological, geochemical and isotopic features of thetephras from the main eruptive units of the Colli Albani volcanicdistrict. The relatively uncommon foiditic composition of the glassfrom the Colli Albani tephras, makes their recognition and dis-tinguishing from other tephras in distal settings of PeninsularItaly rather straightforward. Furthermore, when considering andcomparing in detail, element per element, the compositionalspectrum of their foiditic glass, each tephra can be reasonablyindividually distinguished from others (Figs. 3 and 8), even ifsome units may appear rather similar in terms of major elementcompositions (e.g. Tufo di Bagni Albule and Albano 5e7; Fig. 8). Inthese more controversial cases, the lithological features and,above all, the Sr and Nd isotope compositions may be decisive foran accurate recognition of the individual Colli Albani tephras.Indeed, the Sr and Nd isotope compositions of the pristine cli-nopyroxene crystals and/or fresh glassy scoria from distal ColliAlbani tephras are strictly comparable to those of the proximalequivalent units (Fig. 9), and thus isotope analyses can be suc-cessfully applied for tephrostratigraphic purposes. In conjunctionwith 40Ar/39Ar geochronological and major element composi-tional data, 87Sr/86Sr and 143Nd/144Nd isotope ratios also revealthat some pyroclastic units occurring in the central Apennineintermountain basins, which were previously attributed to localvolcanisms (e.g. Carapelle Calvisio, site 1; Raiano, site 3; Fucino,site 12; Carsoli site 13; Fig. 1), actually represent mid-distal oc-currences of the largest Colli Albani explosive units. On thisground, the Sr and Nd isotope studies may be relevant also fordealing with this specific volcanological issue.

On the other hand, contrary to what obtained for theclinopyroxene crystals and/or fresh glassy scoria, the 87Sr/86Srcompositions of the bulk samples from the distal Colli Albanitephras are systematically slightly lower than those measuredon pristine tephra components, selected from both distal andproximal equivalent units (Fig. 9). This possibly results by me-chanical mixing among the bulk and lithic clasts that are char-acterised by lower 87Sr/86Sr values (i.e. carbonate), and/or by anisotopic shift due to preferential mineral and/or glass fractionweathering, and/or by isotopically heterogeneous samples, tes-tifying the occurrence of open-system processes in magmachamber/s (e.g. Arienzo et al., 2009). In contrast, due to theincompatible nature of Nd and as it is less fluid-mobile withrespect to Sr, the Nd isotope compositions of the bulk samplesare similar to those of the clinopyroxene from both the proximaland the distal deposits. Therefore, in order to obtain reliable

Fig. 9. The 87Sr/86Sr and 143Nd/144Nd versus age plot for the Colli Albani proximal units and their correlative distal tephras. The 40Ar/39Ar ages of the dated distal tephras, theestimated volcanic explosive index (VEI) of the Colli Albani eruptions and the general features of the late Quaternary climatic changes from Antarctic ice (Jouzel et al., 2007) are alsoshown. TPT, Tufo Pisolitico di Trigoria (w561 ka); TPeTBA, Tufo del PalatinoeTufo di Bagni Albule (w530 ka); PR, Pozzolane Rosse (w457 ka); PN, Pozzolane Nere (w407 ka); VS,Villa Senni (w365 ka).

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tephra correlations, a combined measurement of both Sr, the Ndisotopes is recommended.

5. Summary and concluding remarks

A recent study pointed out a significant variability of the87Sr/86Sr ratios over the whole eruptive history of the Colli Albani

volcanic district (Gaeta et al., 2006). The 87Sr/86Sr isotope ratiosmeasured on clinopyroxene crystals from Colli Albani pyroclasticand lava rocks have regularly decreased with the age of theeruptive units, ranging from w0.711, for the earliest units dated atw608 ka, to w0.709 for the most recent pyroclastic depositsdated at w36 ka (Gaeta et al., 2006; Giaccio et al., 2007; Boariet al., 2009).

B. Giaccio et al. / Quaternary Science Reviews 67 (2013) 190e206204

To explore the applicability and reliability for tephrostrati-graphic purposes of this peculiar time-dependent variation of the87Sr/86Sr ratios, and to test the use of 143Nd/144Nd ratios as well, weperformed 87Sr/86Sr and 143Nd/144Nd analyses on samples fromsome proximal Colli Albani units and from several distal tephras.Thesewere previously attributed to dated eruptive units of the ColliAlbani volcanic district and represent almost all of its explosivehistory. A synopsis of the 87Sr/86Sr and 143Nd/144Nd data is shown inFig. 9, where the new Sr and Nd isotopic compositions from boththe proximal and distal Colli Albani tephras are plotted against theage, together with data from the literature.

Our results indicate that the 87Sr/86Sr isotope ratios measuredon pristine clinopyroxene crystals and/or fresh glassy scoria fromdistal Colli Albani tephras are substantially indistinguishablefrom those of the proximal correlative units, which follow thesame time-dependent trend (Fig. 9). This does not apply to the Srcompositions determined on bulk samples from relativelyweathered ash layers, as they gave lower values (Fig. 9). In con-trast, irrespectively of the analysed material and its degree ofweathering, 143Nd/144Nd isotope ratios yielded more consistentresults which are inversely correlated to Sr isotopes, increasingfrom w0.51212 to w0.51215, from the oldest to the youngesttephra deposit. Therefore, in conjunction with the standardtephrostratigraphic analytical methods (e.g., componentry, EMPAand laser ablation), Sr and Nd isotope compositions can providea reliable integrative tool for the fingerprinting of individualeruptive units in distal settings. Here, the reliability of thismethod has been successfully tested on Colli Albani eruptiveproducts, for which new 40Ar/39Ar dating of the Pozzolane Rossedistal tephra and previous age determinations of distal occur-rences of the Villa Senni and Albano 5e7 units have confirmedthe early attribution based on the major and minor elementcompositions of the glass.

In conclusion, the wide dispersal area of the products frommoderate to high magnitude explosive eruptions of the Colli Albanivolcanic district, their peculiar lithology, K-foidic glass compositionand 87Sr/86Sr and 143Nd/144Nd ratio time-dependent variability, aswell as the reliable geochronology, make the Colli Albani tephrasamong the most diagnostic markers in the central Mediterraneantephrostratigraphic framework. In this regard, by providing largeand reliable geochemical datasets, the present study has provideduseful constraints for the recognition of the Colli Albani tephramarkers in such distal settings, as well as for the reassessment ofprevious miscorrelations and/or volcanological misinterpretationsand for extending a consisting central Mediterranean tephros-tratigraphy back to 560 ka.

Acknowledgements

We are grateful to Carlo Giraudi for providing us with a sample ofthe tephra correlated to Albano 5e7 from the Campo Felice succes-sion. Constructive and valuables comments and suggestions by Gio-vanni Zanchetta and an anonymous reviewer greatly improved anearly version of the paper.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.quascirev.2013.01.028.

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