- Email: [email protected]
Reply: Correlation of a widespread Pleistocene tephra marker from the Nisyros–Yali volcanic complex, Greece
Journal of Volcanology and Geothermal Research 181 (2009) 251–254
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Journal of Volcanology and Geothermal Research j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j vo l g e o r e s
Reply: Correlation of a widespread Pleistocene tephra marker from the Nisyros–Yali volcanic complex, Greece David M. Pyle a, Vasiliki Margari b,⁎ a b
Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK Earth and Biosphere Institute, School of Geography, University of Leeds, LS2 9JT, UK
a r t i c l e
i n f o
Article history: Received 6 November 2008 Accepted 7 November 2008 Available online 16 December 2008 Keywords: tephrostratigraphy Mediterranean Nisyros–Yali tephra marker Megali Limni Lesvos Greece
We thank Bichler et al. (2009-this volume) for their interest in our work, and for the opportunity to clarify our working hypotheses in terms of potential correlations of distal tephra deposits across the Eastern Mediterranean. In our original paper (Margari et al., 2007), we presented the results of a detailed down-core study of a sequence of lake deposits from Lesvos Island (Mytilene), Northeast Aegean, Greece. This core contains an important high-resolution pollen record of changing climate, has been independently dated by radiocarbon techniques, and spans the period ca. 22–62 ka (Margari et al., submitted for publication). Within the core, we found six macroscopic tephra layers. Potentially, therefore, this core sequence offers the exciting possibility to begin to link terrestrial and marine records of late Quaternary volcanism and climate in the Eastern Mediterranean. Of course, in order to get to this point, we first need to identify and correlate the tephra units to known eruptions, or identifiable source volcanoes. The process of developing hypotheses in terms of potential correlations between these distal ash units and known volcanic eruptions from the region is based on three lines of evidence: (1) stratigraphic and independent age constraints from the core: these place important constraints by limiting, on the basis of likely age, the units with which each tephra layer might correlate. (2) the major element compositions of the glass shards of each tephra layer: these are the primary data used, at present, for ⁎ Corresponding author. E-mail address: [email protected] (V. Margari). 0377-0273/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2008.11.033
establishing the plausibility of correlations between analysed and known tephra units. (3) trace elemental analysis of tephra layers: these data may permit refinement of correlations developed on the basis of glass shard composition. In our paper, we focussed on establishing the correlations between the tephra layers in the core (ML1–ML6), and deposits which had previously been identified and correlated within the Eastern Mediterranean, using the first two lines of evidence. We also presented some preliminary trace element data, and this is the part of the paper on which Bichler et al. (2009-this volume) have concentrated their remarks. We apologise at the outset for erroneously including an incorrect version of Table 4, in which we included rare-earth element concentrations normalised to chondrite, and with an interpolated estimate for Pm, which was the basis of the chondrite-normalised REE figure in the same paper. This was a ‘cut and paste’ error which we should have spotted, and we present a corrected version of the table below (Table 1). The substance of the comment by Bichler et al. (2009-this volume) is essentially that, had we compared our trace element data to the ‘database’ of Steinhauser et al. (2006), we might have come to a different set of conclusions regarding the correlations. As we show below, this is a point worthy of discussion since there are a number of unresolved questions relating to the temporal and stratigraphic relations between the eruptions of Yali and Nisyros volcanoes. We also show that interpretation of the trace element geochemistry is not as clear cut as Bichler et al. (2009-this volume) suggest.
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Table 1 Trace (A) and rare earth (B) elements of the samples analysed in this study NLP
Kos
MNLP
NUPb
Yali a
Yali b
RY5a
RY5b
MY5
MY5b
ML2 av
st
ML3 av
st
ML4 av
st
A. Trace Elements Li 36.3 Be 2.20 P 386 Sc 14.0 Ti 2421 V 33.7 Mn 518 Co 4.53 Cu 6.45 Zn 42.3 Ga 17.9 Rb 97.9 Sr 243 Y 18.9 Zr 121 Nb 17.5 Cd 0.04 Cs 3.45 Ba 784 Hf 3.14 Ta 1.38 Tl 0.50 Pb 15.2 Th 13.5 U 3.66
NUPa
23.9 2.23 473 4.78 2409 28.8 666 4.21 9.05 52.1 16.3 54.9 212 16.0 179 17.0 0.07 2.56 729 4.18 1.29 0.47 12.5 7.80 2.89
43.6 2.60 391 5.32 2625 34.0 616 8.34 34.5 44.4 16.0 107 230 18.7 161 20.4 0.05 4.12 600 3.93 1.66 0.54 15.9 14.6 3.93
48.3 1.52 392 9.51 2475 66.5 956 24.0 36.7 60.4 11.4 68.9 453 19.6 60.5 10.4 0.05 3.61 291 1.77 0.82 0.43 11.2 7.20 2.01
29.1 1.71 751 7.93 4025 88.0 1025 9.76 5.85 65.4 17.0 69.8 317 16.8 87.3 16.5 0.05 2.39 674 2.28 1.14 0.34 9.91 8.57 2.27
33.7 2.25 324 4.45 2270 24.5 569 2.46 3.83 37.3 15.6 107 182 19.1 162 19.4 0.05 3.63 651 3.97 1.59 0.56 12.7 12.7 3.73
36.9 2.33 332 4.33 2297 24.1 597 2.15 2.82 37.1 16.5 112 188 18.6 169 20.1 0.06 3.65 662 4.06 1.65 0.60 12.9 13.2 3.98
66.6 15.4 534 4.92 3416 50.7 1498 5.78 14.5 112 22.5 294 276 46.8 437 80.9 0.13 21.0 700 8.93 3.98 1.40 47.1 35.8 10.5
66.7 16.2 551 4.91 3335 48.2 1632 5.91 15.7 116 22.5 296 262 46.9 450 84.1 0.14 21.6 687 9.21 4.06 1.43 48.3 36.1 10.6
92.3 14.0 659 5.04 3996 58.7 1151 27.1 110 100 18.1 211 220 37.1 425 88.6 0.13 15.9 197 10.4 5.57 0.88 49.6 45.5 7.90
78.2 13.3 572 8.14 3769 59.5 1311 24.1 66.7 104 18.9 235 215 38.2 407 81.3 0.11 17.1 192 9.44 5.12 0.91 50.1 42.6 8.71
58.4 16.0 368 3.25 2855 28.8 1368 3.17 52.6 130 21.6 312 117 46.4 542 96.4 0.16 25.1 175 11.1 5.07 1.98 51.2 39.0 12.5
12.4 1.76 21.4 0.20 111 0.93 80.2 0.12 4.24 9.67 1.26 5.56 6.88 1.53 16.8 3.46 0.02 1.82 5.75 0.40 0.22 0.09 1.52 1.82 0.54
42.9 2.08 150 3.57 1571 9.48 284 1.74 26.6 36.3 14.0 119 105 17.6 144 18.3 0.06 4.41 817 3.86 1.57 0.59 16.4 13.4 3.96
8.58 0.21 14.4 0.24 30 0.14 7.2 0.14 6.94 5.27 0.51 4.65 1.79 2.16 6.38 0.88 0.006 0.35 41.8 0.21 0.09 0.02 0.22 2.5 0.18
43.9 2.08 146 3.69 1601 9.58 287 1.97 25.2 37.6 13.9 120 105 19.0 143 18.0 0.053 4.34 810 3.84 1.55 0.58 16.6 14.9 4.00
7.45 0.22 7.49 0.22 114 0.94 25.3 0.44 6.44 1.26 0.97 5.34 7.80 1.04 10.3 1.35 0.005 0.43 49.7 0.27 0.10 0.04 0.94 0.81 0.28
B. REE La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
24.1 50.2 5.01 16.8 2.85 0.55 2.51 0.43 2.59 0.56 1.72 0.28 1.99 0.35
30.3 55.9 5.88 19.9 3.41 0.68 2.97 0.47 2.83 0.59 1.81 0.29 1.99 0.33
19.8 40.2 4.74 17.6 3.46 0.74 3.36 0.53 3.18 0.65 1.89 0.29 1.89 0.29
29.0 54.1 5.62 19.3 3.18 0.73 2.86 0.44 2.67 0.55 1.64 0.26 1.77 0.29
29.6 53.8 5.62 18.8 3.24 0.63 2.94 0.47 2.93 0.62 1.89 0.30 2.10 0.36
29.9 55.1 5.64 18.7 3.18 0.61 2.85 0.46 2.82 0.60 1.85 0.3 2.10 0.36
82.1 166 18.1 62.3 10.8 1.64 9.16 1.36 7.71 1.49 4.31 0.65 4.18 0.60
83.9 169 18.4 63.3 11.2 1.66 9.08 1.40 7.86 1.49 4.35 0.66 4.23 0.61
65.4 155 15.1 51.9 9.25 1.41 7.83 1.18 6.53 1.23 3.55 0.53 3.46 0.47
69.9 155 15.7 53.8 9.57 1.44 7.86 1.20 6.65 1.26 3.63 0.54 3.53 0.50
93.7 190 20.5 68.5 11.7 1.50 9.51 1.46 8.16 1.55 4.49 0.68 4.38 0.62
1.52 3.23 0.47 0.95 0.20 0.03 0.39 0.05 0.26 0.06 0.17 0.03 0.16 0.018
31.3 60.5 5.85 18.6 3.06 0.37 2.76 0.46 2.82 0.61 1.90 0.31 2.16 0.37
4.25 1.66 0.40 1.15 0.14 0.03 0.12 0.02 0.058 0.009 0.03 0.003 0.02 0.01
33.5 61.3 6.05 19.3 3.15 0.39 2.80 0.46 2.88 0.62 1.93 0.32 2.21 0.37
1.58 3.08 0.26 0.85 0.16 0.03 0.16 0.03 0.17 0.03 0.11 0.02 0.12 0.02
31.2 57.1 5.76 18.9 3.10 0.58 2.78 0.45 2.78 0.59 1.82 0.30 2.06 0.35
Concentrations in ppm measured by solution ICP-MS in the University of Cambridge. NUP a: Nisyros Island Upper Pumice a. NLP: Nisyros Island Lower Pumice. Kos: Marine Core Kos Plateau Tuff. MNLP: Marine Core Nisyros Lower Pumice. NUP b: Nisyros Island Upper Pumice b. Yali a: East Yali Island. Yali b: Pigada Yali Island. RY5 a: Russia (Rudkino) Y5a. RY5 b: Russia (Rudkino) Y5b. MY5 a: Marine Y5 a. MY5b: Marine Y5b. ML2av: ML2 Tephra Layer Average (based on repeat dissolution and analysis of samples in two different analytical sessions) ML3av: ML3 Tephra Layer Average. ML4av: ML4 Tephra Layer Average. st: Standard Deviation.
To set the discussion in context, we summarise below the key findings from Margari et al. (2007). Of the six tephra layers we found within the core, three can be firmly correlated to well known, widelydispersed tephra deposits from the region (c.f. Keller et al., 1978; Narcisi and Vezzoli, 1999; Pyle et al., 2006) based on their major elemental composition and age: (1) a rhyodacite tephra layer (ML1) corresponds to the ca. 22 ka Cape Riva eruption of Santorini, and the correlative Y2 ash layer. (2) a trachytic tephra layer (ML2) corresponds to the ca. 39.3 ka Campanian Ignimbrite eruption of the Campi Flegrei, southern Italy, and the correlative Y5 ash layer. (3) a compositionally bimodal tephra layer (ML5) corresponds to the highly distinctive products of the ca. 50–55 ka eruption of the Green Tuff of Pantelleria, and its correlative Y6 ash layer. The three remaining layers (ML3, ML4 and ML6) are vitric ash layers, predominantly of rhyolitic glass, which are compositionally very similar. We suggested that each of these most likely originated from the Eastern
islands of the Hellenic Arc: the Nisyros–Yali complex. In the remainder of this note, we focus our discussions on the layers ML3 and ML4. 1. Stratigraphic and age relationships of ML3 and ML4 Tephra ML3 and ML4 lie stratigraphically between the very well dated Y5 deposit (39.3 ka) and Y6, which is independently dated to ca. 50–55 ka. They are separated in the core by ~1.3 m of sediment, corresponding to ca. 800 years in this part of the core. Our analysis showed that these two layers are essentially of identical composition, and therefore probably represent the products of two closely spaced eruptions from a single volcano. Our estimate of the age of emplacement of these deposits is ca. 46 +/− 6 ka. Independently, Aksu et al. (2008) recently presented the results of a detailed analysis of a suite of marine cores from the north Aegean and the Sea of Marmara. They identified a widespread tephra horizon which is rhyolitic in composition, stratigraphically older than Y5, and has an approximate age of 42–44 ka. Aksu et al. (2008) presented major and trace elemental data on this ash layer (which they called tephra layer δ, or Tephra Group 8) and, on the basis of the compositional similarity,
D.M. Pyle, V. Margari / Journal of Volcanology and Geothermal Research 181 (2009) 251–254
proposed that their layer δ correlates with the ML3/ML4 ash layers. Together, these two papers confirm that there is a widely-distributed volcanic ash sequence which can be traced across the North Aegean. The next question is whether a correlation can be made with the potential source volcano? From the major element analysis of glass shards by electron microprobe it is clear that the “ML3/ML4/δ” sequence originated from a major explosive volcanic eruption from the Nisyros–Yali complex. However, the complexity of the stratigraphy of Nisyros and Yali, and the poor age constraints on their late Quaternary eruptive histories, means that, despite much effort, there is still no coherent linked stratigraphy for these two islands — nor is there a very clear understanding of the precise relationships between the two closelylinked volcanic centres (see discussion in Margari et al., 2007; Aksu et al., 2008). It is entirely possible, for example, that eruptions at the two centres have tapped different parts of the same magma system (e.g. St Seymour 1996; Zouzias and St Seymour, 2008). One consequence of this close magmatic linkage between the two islands is that the compositions of the volcanic products may overlap. Bichler et al. (2009-this volume) suggest that, had we used the available trace element data, we might have come to a different conclusion in terms of our proposed correlation. In fact, it is not obvious that this is the case. Bichler and colleagues have carried out a sustained series of analyses of Aegean pumices (bulk rock) and glasses over the past few years. On the basis of this, they have proposed that a chemical plot of Eu/Ta vs. Th/Hf is an efficient way to separate tephra from different Aegean volcanoes. The potential difficulty with using these elemental ratios as source discriminants is that both ratios are very sensitive to the effects of fractional crystallisation. Crystallisation of plagioclase feldspar, for example, will lead to a rapid decrease in the ratio Eu/Ta; while late-stage crystallisation of zircon will increase the ratio Th/Hf. It is likely, therefore, that a suite of glasses sampled from the same chemically-stratified and compositionallyevolved magma system will show a compositional range in both parameters, and will be different from the compositions of bulk pumices. The trace element ratios Eu/Ta and Th/Hf are not likely to be unique indicators of a particular magmatic source region. We illustrate this point in Fig. 1, where we plot published trace elemental data from samples from Nisyros and Yali on the Eu/Ta–Th/Hf diagram. In Fig. 1A, we plot both whole rock (bulk pumice and lavas), bulk tephra, and glass data: notice that, as expected, there is a very wide range in both elemental ratios. In Fig. 1B, we concentrate on the data from tephra, pumice and glass. Three features are particularly relevant: (1) on the basis of the analyses of pumice from the exposed portions of Yali, the Yali 2 eruption of Keller (1980; also called Yali-C by Bond, 1976) is compositionally distinct from the other products of Yali (predominantly, the major submarine eruption known as Yali 1 or Yali D; Bond, 1976; Keller, 1980; Allen and McPhie, 2000). Since Yali tephra are very crystal-poor (b2%), both glass and bulk pumice compositions are essentially identical. Yali-2 (or Yali-C) has been correlated with tephra across a number of marine cores, but its age remains poorly constrained (ca. 30–35 ka; see Federman and Carey, 1980; Hardiman, 1999; Narcisi and Vezzoli, 1999; Aksu et al., 2008). (2) in contrast to the Yali datasets, the trace element ratios Eu/Ta and Th/Hf are not able to clearly distinguish whole rock (bulk pumice) compositions of the two major Nisyros eruptions (Upper and Lower Pumice) at least, based on the data published by Peltz et al. (1999). Note that Sterba et al. (2006) imply that Upper Pumice and Lower Pumice eruptions can be distinguished, but they present no data and make no comparison with their earlier work. In addition, and as a consequence of the crystal-rich nature of the Niysros pumice, the compositions of Nisyros glasses (published by Saminger et al., 2000, but not referred to in Steinhauser et al., 2006) are compositionally distinct from the bulk pumice — in exactly the direction that
253
Fig. 1. Comparison of Eu/Ta–Th/Hf elemental ratios in the magmatic products of Nisyros and Yali. A: Whole rock and glass data show that both Eu/Ta and Th/Hf ratios are highly variable during magma evolution. Mafic to intermediate rocks have high Eu/Ta and low Th/Hf. Fractional crystallization and removal of plagioclase feldspar and zircon will yield evolved magmas with low Eu/Ta and high Th/Hf. B: comparison of Niyros and Yali pumice and glass data with the North Aegean tephra layers (ML3, ML4, δ) described by Margari et al. (2007) and Aksu et al. (2008): the closest match for these samples is with Nisyros glass. Data sources: Nisyros and Yali whole rock (‘WR) — (Francalanci et al., 1995; Buettner et al., 2005). Bulk Nisyros Lower Pumice (LP) and Upper Pumice (UP) — (Peltz et al., 1999). Nisyros glass — (Saminger et al., 2000). Bulk Yali pumice — (Peltz et al., 1999). Bulk Yali 2 pumice and Yali 2 tephra — (Peltz et al., 1999; Margari et al., 2007; Aksu et al., 2008). ML3, ML4 — Margari et al., 2007; Tephra Group 8 (or layer δ) — (Aksu et al., 2008).
one would expect for a differentiating rhyolite magma body: glasses have lower Eu/Ta and higher Th/Hf ratios than the bulk pumice samples. (3) The ML3/ML4/δ tephras from the northern Aegean are compositionally distinct from both Yali and Yali-2. These tephras are, like most distal volcanic ash deposits, predominantly made up of glass shards. Direct comparison of the composition of these tephra to those of glass separates is, therefore, valid, and Bichler et al. (2009-this volume) are mistaken when they assert otherwise. On the basis of the published major and trace element data, we re-affirm our suggestion that the closest match to the ML3/ML4/δ tephra is the glass from the Nisyros Upper and Lower Pumice units. Our working hypothesis, therefore, is that the ML3/ML4/δ layers most likely correspond to the major caldera-forming eruption of
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Nisyros, the Lower Pumice unit. Whether the two layers ML3 and ML4 record both the Upper Pumice (ML3) and Lower Pumice (ML4) eruptions remains to be resolved, although based on a range of evidence (including X-rays, high-resolution grain-size analysis of the tephra layers and pollen analysis) it is clear that the ML3 and ML4 stata correspond to separate events. This proposal is consistent with the regional stratigraphy around Nisyros and Yali: Yali 1 was a major submarine eruption; deposits from this eruption have not been found on Nisyros, or elsewhere. We propose that Yali 1 pre-dates the formation of the Nisyros caldera, and the Nisyros Lower and Upper Pumice eruptions. Uplift and emergence of the island of Yali prior to the eruption of Yali 2 would have been accompanied by significant erosion, removing the deposits of the intervening Nisyros eruptions, which are known to pre-date Yali 2, based on the caldera-wall stratigraphy (Limburg and Varekamp, 1991; Hardiman, 1999). This hypothesis will be testable by the analysis of trace elemental compositions of individual glass shards from distal tephra (by, for example, laser ablation ICP-MS or ion microprobe techniques), with parallel analytical work on glasses from proximal pumice samples. 2. Concluding remarks Analysis of compositional data from distal tephra dated to ca. 46 +/ − 6 ka which have been recognised in terrestrial and marine contexts across the north Aegean (Margari et al., 2007; Aksu et al., 2008), shows a close match to the compositions of glass from the Nisyros Lower and Upper Pumice deposits. On this basis, we propose that major calderaforming eruption of Nisyros (the Lower Pumice) dates to ca. 46 +/ − 6 ka, and that this eruption was indeed accompanied by the emplacement of a widespread distal ash-fall deposit. References Aksu, A.E., Jenner, G., Hiscott, R.N., Isler, E.B., 2008. Occurrence, stratigraphy and geochemistry of Late Quaternary tephra layers in the Aegean Sea and the Marmara Sea. Marine Geology 252, 174–192. Allen, S.R., McPhie, J., 2000. Water-settling and resedimentation of submarine rhyolitic pumice at Yali, eastern Aegean, Greece. Journal of Volcanology and Geothermal Research 85, 285–307. Bichler, M., Pearce, N., Steinhauser, G., Sterba, J.H., 2009. More than just a convoluted table? A comment on Margari et al. (2007). Journal of Volcanology and Geothermal Research 181, 247–250 (this volume).
Bond, A., 1976. Multiple sources of pumice in the Aegean. Nature 259, 194–195. Buettner, A., Kleinhanns, I.C., Rufer, D., Hunziker, J.C., Villa, I.M., 2005. Magma generation at the easternmost section of the Hellenic arc: Hf, Nd, Pb and Sr isotope geochemistry of Nisyros and Yali volcanoes (Greece). Lithos 83, 29–46. Federman, A.N., Carey, S.N., 1980. Electron Microprobe correlation of tephra layers from Eastern Mediterranean abyssal sediments and the Island of Santorini. Quaternary Research 13, 160–171. Francalanci, L., Varekamp, J.C., Vougioukalakis, G., Defant, M.J., Innocenti, F., Manetti, P., 1995. Crystal retention, fractionation and crustal assimilation in a convecting magma chamber, Nisyros Volcano, Greece. Bulletin of Volcanology 56, 601–620. Hardiman, J.C., 1999. Deep sea tephra from Nisyros Island, Eastern Aegean Sea, Greece. In: Firth, C.R., McGuire, W.J. (Eds.), Volcanoes in the Quaternary. Geological Society of London Special Publications, vol. 161, pp. 69–88. Keller, J., 1980. Prehistoric pumice tephra on Aegean Islands. In: Doumas, C. (Ed.), Thera and the Aegean World II. Thera and the Aegean World, London, pp. 49–56. Keller, J., Ryan, W.B.F., Ninkovich, D., Altherr, R., 1978. Explosive volcanic activity in the Mediterranean over the past 200,000 yr as recorded in deep-sea sediments. Bulletin, Geological Society of America 89, 591–604. Limburg, E.M., Varekamp, C., 1991. Young Pumice deposits on Nisyros, Greece. Bulletin of Volcanology 54, 68–77. Margari, V., Pyle, D.M., Bryant, C., Gibbard, P.L., 2007. Mediterranean tephra stratigraphy revisited: Results from a long terrestrial sequence on Lesvos Island, Greece. Journal of Volcanology and Geothermal Research 163, 34–54. Margari, V., Gibbard, P.L., Bryant, C.L., Tzedakis, P.C., submitted for publication. Character of vegetational and environmental changes in southern Europe during the last glacial period; evidence from Lesvos Island, Greece. Quaternary Science Reviews. Narcisi, B., Vezzoli, L., 1999. Quaternary stratigraphy of distal tephra layers in the Mediterranean — an overview. Global and Planetary Change 21, 31–50. Peltz, C., Schmid, P., Bichler, M., 1999. INAA of Aegaean pumices for the classification of archaeological findings. Journal of Radioanalytical and Nuclear Chemistry 242, 361–377. Pyle, D.M., Ricketts, G.D., Margari, V., van Andel, T.H., Sinitsyn, A.A., Praslov, N.D., Lisitsyn, S., 2006. Wide dispersal and deposition of distal tephra during the Pleistocene 'Campanian Ignimbrite/Y5' eruption, Italy. Quaternary Science Reviews 25, 2713–2728. Saminger, S., Peltz, C., Bichler, M., 2000. South Aegean volcanic glass: Seperation and analysis by INAA and EPMA. Journal of Radioanalytical and Nuclear Chemistry 245, 375–383. St Seymour, K., 1996. Geochemistry of the Yali volcano rhyolites and their relationship to the volcanic products of Nisyros, Aegean Volcanic Arc. Neues Jahrbuch fur Mineralogie Monatshefte H2, 52–72. Steinhauser, G., Sterba, J.H., Bichler, M., Huber, H., 2006. Neutron activation analysis of Mediterranean volcanic rocks — an analytical database for archaeological stratigraphy. Applied Geochemistry 21, 1362–1375. Sterba, J.H., Steinhauser, G., Bichler, M., 2006. Application of NAA to develop a chemostratigraphy of volcanic deposits on Nisyros and Telos, Greece. Czechoslovak Journal of Physics 56, D283–D289. Zouzias, D., St Seymour, K., 2008. Consanguineous geochemistry of the Kos Plateau and Tilos D and E Pumices, Aegean Volcanic Arc, Hellas. Neues Jahrbuch fur Mineralogie. Abhandlungen 184, 231–241.
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Journal of Volcanology and Geothermal Research j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j vo l g e o r e s
Reply: Correlation of a widespread Pleistocene tephra marker from the Nisyros–Yali volcanic complex, Greece David M. Pyle a, Vasiliki Margari b,⁎ a b
Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK Earth and Biosphere Institute, School of Geography, University of Leeds, LS2 9JT, UK
a r t i c l e
i n f o
Article history: Received 6 November 2008 Accepted 7 November 2008 Available online 16 December 2008 Keywords: tephrostratigraphy Mediterranean Nisyros–Yali tephra marker Megali Limni Lesvos Greece
We thank Bichler et al. (2009-this volume) for their interest in our work, and for the opportunity to clarify our working hypotheses in terms of potential correlations of distal tephra deposits across the Eastern Mediterranean. In our original paper (Margari et al., 2007), we presented the results of a detailed down-core study of a sequence of lake deposits from Lesvos Island (Mytilene), Northeast Aegean, Greece. This core contains an important high-resolution pollen record of changing climate, has been independently dated by radiocarbon techniques, and spans the period ca. 22–62 ka (Margari et al., submitted for publication). Within the core, we found six macroscopic tephra layers. Potentially, therefore, this core sequence offers the exciting possibility to begin to link terrestrial and marine records of late Quaternary volcanism and climate in the Eastern Mediterranean. Of course, in order to get to this point, we first need to identify and correlate the tephra units to known eruptions, or identifiable source volcanoes. The process of developing hypotheses in terms of potential correlations between these distal ash units and known volcanic eruptions from the region is based on three lines of evidence: (1) stratigraphic and independent age constraints from the core: these place important constraints by limiting, on the basis of likely age, the units with which each tephra layer might correlate. (2) the major element compositions of the glass shards of each tephra layer: these are the primary data used, at present, for ⁎ Corresponding author. E-mail address: [email protected] (V. Margari). 0377-0273/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2008.11.033
establishing the plausibility of correlations between analysed and known tephra units. (3) trace elemental analysis of tephra layers: these data may permit refinement of correlations developed on the basis of glass shard composition. In our paper, we focussed on establishing the correlations between the tephra layers in the core (ML1–ML6), and deposits which had previously been identified and correlated within the Eastern Mediterranean, using the first two lines of evidence. We also presented some preliminary trace element data, and this is the part of the paper on which Bichler et al. (2009-this volume) have concentrated their remarks. We apologise at the outset for erroneously including an incorrect version of Table 4, in which we included rare-earth element concentrations normalised to chondrite, and with an interpolated estimate for Pm, which was the basis of the chondrite-normalised REE figure in the same paper. This was a ‘cut and paste’ error which we should have spotted, and we present a corrected version of the table below (Table 1). The substance of the comment by Bichler et al. (2009-this volume) is essentially that, had we compared our trace element data to the ‘database’ of Steinhauser et al. (2006), we might have come to a different set of conclusions regarding the correlations. As we show below, this is a point worthy of discussion since there are a number of unresolved questions relating to the temporal and stratigraphic relations between the eruptions of Yali and Nisyros volcanoes. We also show that interpretation of the trace element geochemistry is not as clear cut as Bichler et al. (2009-this volume) suggest.
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Table 1 Trace (A) and rare earth (B) elements of the samples analysed in this study NLP
Kos
MNLP
NUPb
Yali a
Yali b
RY5a
RY5b
MY5
MY5b
ML2 av
st
ML3 av
st
ML4 av
st
A. Trace Elements Li 36.3 Be 2.20 P 386 Sc 14.0 Ti 2421 V 33.7 Mn 518 Co 4.53 Cu 6.45 Zn 42.3 Ga 17.9 Rb 97.9 Sr 243 Y 18.9 Zr 121 Nb 17.5 Cd 0.04 Cs 3.45 Ba 784 Hf 3.14 Ta 1.38 Tl 0.50 Pb 15.2 Th 13.5 U 3.66
NUPa
23.9 2.23 473 4.78 2409 28.8 666 4.21 9.05 52.1 16.3 54.9 212 16.0 179 17.0 0.07 2.56 729 4.18 1.29 0.47 12.5 7.80 2.89
43.6 2.60 391 5.32 2625 34.0 616 8.34 34.5 44.4 16.0 107 230 18.7 161 20.4 0.05 4.12 600 3.93 1.66 0.54 15.9 14.6 3.93
48.3 1.52 392 9.51 2475 66.5 956 24.0 36.7 60.4 11.4 68.9 453 19.6 60.5 10.4 0.05 3.61 291 1.77 0.82 0.43 11.2 7.20 2.01
29.1 1.71 751 7.93 4025 88.0 1025 9.76 5.85 65.4 17.0 69.8 317 16.8 87.3 16.5 0.05 2.39 674 2.28 1.14 0.34 9.91 8.57 2.27
33.7 2.25 324 4.45 2270 24.5 569 2.46 3.83 37.3 15.6 107 182 19.1 162 19.4 0.05 3.63 651 3.97 1.59 0.56 12.7 12.7 3.73
36.9 2.33 332 4.33 2297 24.1 597 2.15 2.82 37.1 16.5 112 188 18.6 169 20.1 0.06 3.65 662 4.06 1.65 0.60 12.9 13.2 3.98
66.6 15.4 534 4.92 3416 50.7 1498 5.78 14.5 112 22.5 294 276 46.8 437 80.9 0.13 21.0 700 8.93 3.98 1.40 47.1 35.8 10.5
66.7 16.2 551 4.91 3335 48.2 1632 5.91 15.7 116 22.5 296 262 46.9 450 84.1 0.14 21.6 687 9.21 4.06 1.43 48.3 36.1 10.6
92.3 14.0 659 5.04 3996 58.7 1151 27.1 110 100 18.1 211 220 37.1 425 88.6 0.13 15.9 197 10.4 5.57 0.88 49.6 45.5 7.90
78.2 13.3 572 8.14 3769 59.5 1311 24.1 66.7 104 18.9 235 215 38.2 407 81.3 0.11 17.1 192 9.44 5.12 0.91 50.1 42.6 8.71
58.4 16.0 368 3.25 2855 28.8 1368 3.17 52.6 130 21.6 312 117 46.4 542 96.4 0.16 25.1 175 11.1 5.07 1.98 51.2 39.0 12.5
12.4 1.76 21.4 0.20 111 0.93 80.2 0.12 4.24 9.67 1.26 5.56 6.88 1.53 16.8 3.46 0.02 1.82 5.75 0.40 0.22 0.09 1.52 1.82 0.54
42.9 2.08 150 3.57 1571 9.48 284 1.74 26.6 36.3 14.0 119 105 17.6 144 18.3 0.06 4.41 817 3.86 1.57 0.59 16.4 13.4 3.96
8.58 0.21 14.4 0.24 30 0.14 7.2 0.14 6.94 5.27 0.51 4.65 1.79 2.16 6.38 0.88 0.006 0.35 41.8 0.21 0.09 0.02 0.22 2.5 0.18
43.9 2.08 146 3.69 1601 9.58 287 1.97 25.2 37.6 13.9 120 105 19.0 143 18.0 0.053 4.34 810 3.84 1.55 0.58 16.6 14.9 4.00
7.45 0.22 7.49 0.22 114 0.94 25.3 0.44 6.44 1.26 0.97 5.34 7.80 1.04 10.3 1.35 0.005 0.43 49.7 0.27 0.10 0.04 0.94 0.81 0.28
B. REE La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
24.1 50.2 5.01 16.8 2.85 0.55 2.51 0.43 2.59 0.56 1.72 0.28 1.99 0.35
30.3 55.9 5.88 19.9 3.41 0.68 2.97 0.47 2.83 0.59 1.81 0.29 1.99 0.33
19.8 40.2 4.74 17.6 3.46 0.74 3.36 0.53 3.18 0.65 1.89 0.29 1.89 0.29
29.0 54.1 5.62 19.3 3.18 0.73 2.86 0.44 2.67 0.55 1.64 0.26 1.77 0.29
29.6 53.8 5.62 18.8 3.24 0.63 2.94 0.47 2.93 0.62 1.89 0.30 2.10 0.36
29.9 55.1 5.64 18.7 3.18 0.61 2.85 0.46 2.82 0.60 1.85 0.3 2.10 0.36
82.1 166 18.1 62.3 10.8 1.64 9.16 1.36 7.71 1.49 4.31 0.65 4.18 0.60
83.9 169 18.4 63.3 11.2 1.66 9.08 1.40 7.86 1.49 4.35 0.66 4.23 0.61
65.4 155 15.1 51.9 9.25 1.41 7.83 1.18 6.53 1.23 3.55 0.53 3.46 0.47
69.9 155 15.7 53.8 9.57 1.44 7.86 1.20 6.65 1.26 3.63 0.54 3.53 0.50
93.7 190 20.5 68.5 11.7 1.50 9.51 1.46 8.16 1.55 4.49 0.68 4.38 0.62
1.52 3.23 0.47 0.95 0.20 0.03 0.39 0.05 0.26 0.06 0.17 0.03 0.16 0.018
31.3 60.5 5.85 18.6 3.06 0.37 2.76 0.46 2.82 0.61 1.90 0.31 2.16 0.37
4.25 1.66 0.40 1.15 0.14 0.03 0.12 0.02 0.058 0.009 0.03 0.003 0.02 0.01
33.5 61.3 6.05 19.3 3.15 0.39 2.80 0.46 2.88 0.62 1.93 0.32 2.21 0.37
1.58 3.08 0.26 0.85 0.16 0.03 0.16 0.03 0.17 0.03 0.11 0.02 0.12 0.02
31.2 57.1 5.76 18.9 3.10 0.58 2.78 0.45 2.78 0.59 1.82 0.30 2.06 0.35
Concentrations in ppm measured by solution ICP-MS in the University of Cambridge. NUP a: Nisyros Island Upper Pumice a. NLP: Nisyros Island Lower Pumice. Kos: Marine Core Kos Plateau Tuff. MNLP: Marine Core Nisyros Lower Pumice. NUP b: Nisyros Island Upper Pumice b. Yali a: East Yali Island. Yali b: Pigada Yali Island. RY5 a: Russia (Rudkino) Y5a. RY5 b: Russia (Rudkino) Y5b. MY5 a: Marine Y5 a. MY5b: Marine Y5b. ML2av: ML2 Tephra Layer Average (based on repeat dissolution and analysis of samples in two different analytical sessions) ML3av: ML3 Tephra Layer Average. ML4av: ML4 Tephra Layer Average. st: Standard Deviation.
To set the discussion in context, we summarise below the key findings from Margari et al. (2007). Of the six tephra layers we found within the core, three can be firmly correlated to well known, widelydispersed tephra deposits from the region (c.f. Keller et al., 1978; Narcisi and Vezzoli, 1999; Pyle et al., 2006) based on their major elemental composition and age: (1) a rhyodacite tephra layer (ML1) corresponds to the ca. 22 ka Cape Riva eruption of Santorini, and the correlative Y2 ash layer. (2) a trachytic tephra layer (ML2) corresponds to the ca. 39.3 ka Campanian Ignimbrite eruption of the Campi Flegrei, southern Italy, and the correlative Y5 ash layer. (3) a compositionally bimodal tephra layer (ML5) corresponds to the highly distinctive products of the ca. 50–55 ka eruption of the Green Tuff of Pantelleria, and its correlative Y6 ash layer. The three remaining layers (ML3, ML4 and ML6) are vitric ash layers, predominantly of rhyolitic glass, which are compositionally very similar. We suggested that each of these most likely originated from the Eastern
islands of the Hellenic Arc: the Nisyros–Yali complex. In the remainder of this note, we focus our discussions on the layers ML3 and ML4. 1. Stratigraphic and age relationships of ML3 and ML4 Tephra ML3 and ML4 lie stratigraphically between the very well dated Y5 deposit (39.3 ka) and Y6, which is independently dated to ca. 50–55 ka. They are separated in the core by ~1.3 m of sediment, corresponding to ca. 800 years in this part of the core. Our analysis showed that these two layers are essentially of identical composition, and therefore probably represent the products of two closely spaced eruptions from a single volcano. Our estimate of the age of emplacement of these deposits is ca. 46 +/− 6 ka. Independently, Aksu et al. (2008) recently presented the results of a detailed analysis of a suite of marine cores from the north Aegean and the Sea of Marmara. They identified a widespread tephra horizon which is rhyolitic in composition, stratigraphically older than Y5, and has an approximate age of 42–44 ka. Aksu et al. (2008) presented major and trace elemental data on this ash layer (which they called tephra layer δ, or Tephra Group 8) and, on the basis of the compositional similarity,
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proposed that their layer δ correlates with the ML3/ML4 ash layers. Together, these two papers confirm that there is a widely-distributed volcanic ash sequence which can be traced across the North Aegean. The next question is whether a correlation can be made with the potential source volcano? From the major element analysis of glass shards by electron microprobe it is clear that the “ML3/ML4/δ” sequence originated from a major explosive volcanic eruption from the Nisyros–Yali complex. However, the complexity of the stratigraphy of Nisyros and Yali, and the poor age constraints on their late Quaternary eruptive histories, means that, despite much effort, there is still no coherent linked stratigraphy for these two islands — nor is there a very clear understanding of the precise relationships between the two closelylinked volcanic centres (see discussion in Margari et al., 2007; Aksu et al., 2008). It is entirely possible, for example, that eruptions at the two centres have tapped different parts of the same magma system (e.g. St Seymour 1996; Zouzias and St Seymour, 2008). One consequence of this close magmatic linkage between the two islands is that the compositions of the volcanic products may overlap. Bichler et al. (2009-this volume) suggest that, had we used the available trace element data, we might have come to a different conclusion in terms of our proposed correlation. In fact, it is not obvious that this is the case. Bichler and colleagues have carried out a sustained series of analyses of Aegean pumices (bulk rock) and glasses over the past few years. On the basis of this, they have proposed that a chemical plot of Eu/Ta vs. Th/Hf is an efficient way to separate tephra from different Aegean volcanoes. The potential difficulty with using these elemental ratios as source discriminants is that both ratios are very sensitive to the effects of fractional crystallisation. Crystallisation of plagioclase feldspar, for example, will lead to a rapid decrease in the ratio Eu/Ta; while late-stage crystallisation of zircon will increase the ratio Th/Hf. It is likely, therefore, that a suite of glasses sampled from the same chemically-stratified and compositionallyevolved magma system will show a compositional range in both parameters, and will be different from the compositions of bulk pumices. The trace element ratios Eu/Ta and Th/Hf are not likely to be unique indicators of a particular magmatic source region. We illustrate this point in Fig. 1, where we plot published trace elemental data from samples from Nisyros and Yali on the Eu/Ta–Th/Hf diagram. In Fig. 1A, we plot both whole rock (bulk pumice and lavas), bulk tephra, and glass data: notice that, as expected, there is a very wide range in both elemental ratios. In Fig. 1B, we concentrate on the data from tephra, pumice and glass. Three features are particularly relevant: (1) on the basis of the analyses of pumice from the exposed portions of Yali, the Yali 2 eruption of Keller (1980; also called Yali-C by Bond, 1976) is compositionally distinct from the other products of Yali (predominantly, the major submarine eruption known as Yali 1 or Yali D; Bond, 1976; Keller, 1980; Allen and McPhie, 2000). Since Yali tephra are very crystal-poor (b2%), both glass and bulk pumice compositions are essentially identical. Yali-2 (or Yali-C) has been correlated with tephra across a number of marine cores, but its age remains poorly constrained (ca. 30–35 ka; see Federman and Carey, 1980; Hardiman, 1999; Narcisi and Vezzoli, 1999; Aksu et al., 2008). (2) in contrast to the Yali datasets, the trace element ratios Eu/Ta and Th/Hf are not able to clearly distinguish whole rock (bulk pumice) compositions of the two major Nisyros eruptions (Upper and Lower Pumice) at least, based on the data published by Peltz et al. (1999). Note that Sterba et al. (2006) imply that Upper Pumice and Lower Pumice eruptions can be distinguished, but they present no data and make no comparison with their earlier work. In addition, and as a consequence of the crystal-rich nature of the Niysros pumice, the compositions of Nisyros glasses (published by Saminger et al., 2000, but not referred to in Steinhauser et al., 2006) are compositionally distinct from the bulk pumice — in exactly the direction that
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Fig. 1. Comparison of Eu/Ta–Th/Hf elemental ratios in the magmatic products of Nisyros and Yali. A: Whole rock and glass data show that both Eu/Ta and Th/Hf ratios are highly variable during magma evolution. Mafic to intermediate rocks have high Eu/Ta and low Th/Hf. Fractional crystallization and removal of plagioclase feldspar and zircon will yield evolved magmas with low Eu/Ta and high Th/Hf. B: comparison of Niyros and Yali pumice and glass data with the North Aegean tephra layers (ML3, ML4, δ) described by Margari et al. (2007) and Aksu et al. (2008): the closest match for these samples is with Nisyros glass. Data sources: Nisyros and Yali whole rock (‘WR) — (Francalanci et al., 1995; Buettner et al., 2005). Bulk Nisyros Lower Pumice (LP) and Upper Pumice (UP) — (Peltz et al., 1999). Nisyros glass — (Saminger et al., 2000). Bulk Yali pumice — (Peltz et al., 1999). Bulk Yali 2 pumice and Yali 2 tephra — (Peltz et al., 1999; Margari et al., 2007; Aksu et al., 2008). ML3, ML4 — Margari et al., 2007; Tephra Group 8 (or layer δ) — (Aksu et al., 2008).
one would expect for a differentiating rhyolite magma body: glasses have lower Eu/Ta and higher Th/Hf ratios than the bulk pumice samples. (3) The ML3/ML4/δ tephras from the northern Aegean are compositionally distinct from both Yali and Yali-2. These tephras are, like most distal volcanic ash deposits, predominantly made up of glass shards. Direct comparison of the composition of these tephra to those of glass separates is, therefore, valid, and Bichler et al. (2009-this volume) are mistaken when they assert otherwise. On the basis of the published major and trace element data, we re-affirm our suggestion that the closest match to the ML3/ML4/δ tephra is the glass from the Nisyros Upper and Lower Pumice units. Our working hypothesis, therefore, is that the ML3/ML4/δ layers most likely correspond to the major caldera-forming eruption of
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Nisyros, the Lower Pumice unit. Whether the two layers ML3 and ML4 record both the Upper Pumice (ML3) and Lower Pumice (ML4) eruptions remains to be resolved, although based on a range of evidence (including X-rays, high-resolution grain-size analysis of the tephra layers and pollen analysis) it is clear that the ML3 and ML4 stata correspond to separate events. This proposal is consistent with the regional stratigraphy around Nisyros and Yali: Yali 1 was a major submarine eruption; deposits from this eruption have not been found on Nisyros, or elsewhere. We propose that Yali 1 pre-dates the formation of the Nisyros caldera, and the Nisyros Lower and Upper Pumice eruptions. Uplift and emergence of the island of Yali prior to the eruption of Yali 2 would have been accompanied by significant erosion, removing the deposits of the intervening Nisyros eruptions, which are known to pre-date Yali 2, based on the caldera-wall stratigraphy (Limburg and Varekamp, 1991; Hardiman, 1999). This hypothesis will be testable by the analysis of trace elemental compositions of individual glass shards from distal tephra (by, for example, laser ablation ICP-MS or ion microprobe techniques), with parallel analytical work on glasses from proximal pumice samples. 2. Concluding remarks Analysis of compositional data from distal tephra dated to ca. 46 +/ − 6 ka which have been recognised in terrestrial and marine contexts across the north Aegean (Margari et al., 2007; Aksu et al., 2008), shows a close match to the compositions of glass from the Nisyros Lower and Upper Pumice deposits. On this basis, we propose that major calderaforming eruption of Nisyros (the Lower Pumice) dates to ca. 46 +/ − 6 ka, and that this eruption was indeed accompanied by the emplacement of a widespread distal ash-fall deposit. References Aksu, A.E., Jenner, G., Hiscott, R.N., Isler, E.B., 2008. Occurrence, stratigraphy and geochemistry of Late Quaternary tephra layers in the Aegean Sea and the Marmara Sea. Marine Geology 252, 174–192. Allen, S.R., McPhie, J., 2000. Water-settling and resedimentation of submarine rhyolitic pumice at Yali, eastern Aegean, Greece. Journal of Volcanology and Geothermal Research 85, 285–307. Bichler, M., Pearce, N., Steinhauser, G., Sterba, J.H., 2009. More than just a convoluted table? A comment on Margari et al. (2007). Journal of Volcanology and Geothermal Research 181, 247–250 (this volume).
Bond, A., 1976. Multiple sources of pumice in the Aegean. Nature 259, 194–195. Buettner, A., Kleinhanns, I.C., Rufer, D., Hunziker, J.C., Villa, I.M., 2005. Magma generation at the easternmost section of the Hellenic arc: Hf, Nd, Pb and Sr isotope geochemistry of Nisyros and Yali volcanoes (Greece). Lithos 83, 29–46. Federman, A.N., Carey, S.N., 1980. Electron Microprobe correlation of tephra layers from Eastern Mediterranean abyssal sediments and the Island of Santorini. Quaternary Research 13, 160–171. Francalanci, L., Varekamp, J.C., Vougioukalakis, G., Defant, M.J., Innocenti, F., Manetti, P., 1995. Crystal retention, fractionation and crustal assimilation in a convecting magma chamber, Nisyros Volcano, Greece. Bulletin of Volcanology 56, 601–620. Hardiman, J.C., 1999. Deep sea tephra from Nisyros Island, Eastern Aegean Sea, Greece. In: Firth, C.R., McGuire, W.J. (Eds.), Volcanoes in the Quaternary. Geological Society of London Special Publications, vol. 161, pp. 69–88. Keller, J., 1980. Prehistoric pumice tephra on Aegean Islands. In: Doumas, C. (Ed.), Thera and the Aegean World II. Thera and the Aegean World, London, pp. 49–56. Keller, J., Ryan, W.B.F., Ninkovich, D., Altherr, R., 1978. Explosive volcanic activity in the Mediterranean over the past 200,000 yr as recorded in deep-sea sediments. Bulletin, Geological Society of America 89, 591–604. Limburg, E.M., Varekamp, C., 1991. Young Pumice deposits on Nisyros, Greece. Bulletin of Volcanology 54, 68–77. Margari, V., Pyle, D.M., Bryant, C., Gibbard, P.L., 2007. Mediterranean tephra stratigraphy revisited: Results from a long terrestrial sequence on Lesvos Island, Greece. Journal of Volcanology and Geothermal Research 163, 34–54. Margari, V., Gibbard, P.L., Bryant, C.L., Tzedakis, P.C., submitted for publication. Character of vegetational and environmental changes in southern Europe during the last glacial period; evidence from Lesvos Island, Greece. Quaternary Science Reviews. Narcisi, B., Vezzoli, L., 1999. Quaternary stratigraphy of distal tephra layers in the Mediterranean — an overview. Global and Planetary Change 21, 31–50. Peltz, C., Schmid, P., Bichler, M., 1999. INAA of Aegaean pumices for the classification of archaeological findings. Journal of Radioanalytical and Nuclear Chemistry 242, 361–377. Pyle, D.M., Ricketts, G.D., Margari, V., van Andel, T.H., Sinitsyn, A.A., Praslov, N.D., Lisitsyn, S., 2006. Wide dispersal and deposition of distal tephra during the Pleistocene 'Campanian Ignimbrite/Y5' eruption, Italy. Quaternary Science Reviews 25, 2713–2728. Saminger, S., Peltz, C., Bichler, M., 2000. South Aegean volcanic glass: Seperation and analysis by INAA and EPMA. Journal of Radioanalytical and Nuclear Chemistry 245, 375–383. St Seymour, K., 1996. Geochemistry of the Yali volcano rhyolites and their relationship to the volcanic products of Nisyros, Aegean Volcanic Arc. Neues Jahrbuch fur Mineralogie Monatshefte H2, 52–72. Steinhauser, G., Sterba, J.H., Bichler, M., Huber, H., 2006. Neutron activation analysis of Mediterranean volcanic rocks — an analytical database for archaeological stratigraphy. Applied Geochemistry 21, 1362–1375. Sterba, J.H., Steinhauser, G., Bichler, M., 2006. Application of NAA to develop a chemostratigraphy of volcanic deposits on Nisyros and Telos, Greece. Czechoslovak Journal of Physics 56, D283–D289. Zouzias, D., St Seymour, K., 2008. Consanguineous geochemistry of the Kos Plateau and Tilos D and E Pumices, Aegean Volcanic Arc, Hellas. Neues Jahrbuch fur Mineralogie. Abhandlungen 184, 231–241.