Tephrostratigraphy and tephrochronology in the Philippi peat basin, Macedonia, Northern Hellas (Greece)

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Quaternary International 121 (2004) 53–65

*Correspondin

Patras, Rio-Patra

fax: +30-2610-9

E-mail addres

1040-6182/$ - see

doi:10.1016/j.qua

Tephrostratigraphy and tephrochronology in the Philippi peat basin,Macedonia, Northern Hellas (Greece)

Karen St. Seymoura,b,*, Kimon Christanisb, Antonis Bouzinosb, Stephanos Papazisimoub,George Papatheodoroub, Ernesto Moranc, Georges D!en"esc

a Department of Geography, Concordia University, Montreal, Canadab Department of Geology, University of Patras, Rio-Patras, Hellas GR-265 00, Greece

c Department of Chemistry, Concordia University, Montreal, Canada

Abstract

Three tephra layers have been identified in the upper 15 m of a 190-m section of peat beneath the Philippi fen. They provide

significant lithological and chronological markers throughout the fen and the Aegean region. The upper tephra (PhT1) consists of

shards of a transparent calcalkaline felsic glass and fragments of plagioclase, augite, hypersthene, and rare hornblende, magnetite,

apatite and quartz. Peat directly beneath PhT1 gave a radiocarbon approximate age of 13,000 yr. The middle tephra layer (PhT2),

which resembles PhT1 in chemistry and petrography but contains more crystals and lithic fragments, rests on peat dated ca 18,00014C yr BP. The lower tephra (PhT3) has colorless to brown glass shards with a trachytic chemistry and a mineral assemblage of

sanidine, sodic plagioclase, biotite, aegirine-augite, hornblende, titanite and apatite. Bracketing radiocarbon ages imply that PhT3

accumulated about B30,000 14C yr BP. The likely ages of PhT1 and PhT2, together with their mineralogical and chemical

characteristics, suggest that these tephras came from the volcanic field of Thera in the Hellenic arc. PhT2 particularly was derived

from a major, known explosive eruption ca 18,000 yr BP, the Cape Riva eruption, correlative to the Y-2 tephra layer. Evidence for

PhT3 suggests derivation from the Campanian Province of Italy, and correlation with the Campanian Ignimbrite and the Y-5 ash

beneath the Mediterranean Sea.

r 2004 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction

Layers of tephra in Quaternary sedimentary depositsprovide important key horizons that allow time correla-tion of sites across extensive areas. They providevolcanologists and archeologists with time synchronousmarker horizons elucidating the extent of ash dispersaland the impact of falling tephra on natural ecosystemsand civilizations.

Three tephra layers are found in the uppermost partsof the largest known peat deposit, that of Philippi inMacedonia, Northern Hellas (Greece) (Fig. 1). Finevolcanic ash may be transported several thousandkilometers before falling out, depending on the magni-tude of the eruption, the tephra size and weatherconditions. In mires, if the mixing ratio with epiclastic

g author. Department of Geology, University of

s, Hellas GR-265 00, Greece. Tel.:+30-2610-997613;

97560.

s: [email protected] (K.S. Seymour).

front matter r 2004 Elsevier Ltd and INQUA. All rights

int.2004.01.023

material permits, the ash fall deposits form distinct,isochronous layers that may be used as regionalchronostratigraphic markers. If the thickness of thetephra is limited, peat formation recovers and continues,otherwise the peat-forming plants die and peat forma-tion ends.

Tephra studies on peat deposits and coal basins havebeen extensive in northern Europe. Tephra layers arereported for example from coal deposits (Kaolinton-stein) (Diessel, 1992) and Holocene mires in Iceland(Einarsson, 1968), Scotland (Dugmore, 1989), Ireland(Pilcher and Hall, 1992), and have been traced tothe eruptions of Hekla in Iceland and the Eifel ventsin Germany (Fisher and Schmincke, 1984; Juvign!eet al., 1995). Such studies find extensive applicationsin archeology, palynology, and paleoclimatology(Federman and Carey, 1980).

The broad Middle and Eastern Mediterranean regionrepresents an area of intense Quaternary explosivevolcanism. Several volcanic centers of calcalkalineaffinity were active in the Aegean Volcanic Arc and

reserved.

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8

10

20

64

12

0

40 No

10 Eo 15o 20o 25o 30o

35o

HE

LLA

S

AEGEAN

IONIAN SEA

ADRIATICSEA

Kalodiki

PhilippiPhfR

P

R

Vl

Isc

E

AeI

Vs

Mi

ThK

YNs

SEA

200 km

T U R K E Y

A F R I C A

I TA

LY

TY

RR

HE

NIA

NSE

AMe

Fig. 1. Location of Philippi peatland, Heallas. Map has superimposed isopaches of the Y-5 ash layer derived from distribution of piston cores.

Isopachs are in centimeters (adapted from Cornell et al., 1983). Main Quaternary volcanoes: Th, Thera; Mi, Milos; Me, Methana; K, Kos; Y, Yali;

Ns, Nisyros; R, Roman; PhF-Vs-Isc-VI, Campanian Province Volcanoes (Phlegrean Fields, Vesuvius, Ischia, Vulture, respectively); AeI, Aeolian

Island; E, Etna; P, Pantelleria.

K.S. Seymour et al. / Quaternary International 121 (2004) 53–6554

Anatolia (e.g. Robert et al., 1992; Temel et al., 1998;Aldanmaz et al., 2000) and alkaline volcanic centers inthe Roman and Campanian Provinces on the ItalianPeninsula, in Etna, Pantelleria and Aeolian Islands (e.g.Clift and Blusztajn, 1999; Gioncada et al., 2003) (Fig. 1).In the last two decades, numerous tephrochronologicalstudies in the Mediterranean region have focused on theidentification and distribution of tephras in cores fromdeep-sea sediments (Keller et al., 1978; Watkins et al.,1978; Thunnell et al., 1979; Keller, 1981; McCoy, 1981;Vinci, 1985; Narcisi and Vezzoli, 1999). By comparison,tephra dispersion on-land in this region is not wellknown (Narcisi and Vezzoli, 1999). On-land andlacustrine sediment studies are reported by Doumasand Papazoglou (1980), Vitaliano et al. (1981), Sullivan(1988), Kozlowski et al. (1989), Pyle (1990), Harkovskaet al. (1991), Kuzucuo&glu et al. (1998), and Eastwoodet al. (1999), as well as by St. Seymour and Christanis(1995) on the Kalodiki Tephra in northwestern Hellas(Greece).

This paper contributes to the knowledge, reportingnew geochemistry results for new discoveries of terres-trial-based tephra deposits, their implications of distalash distribution and new, hitherto possibly unknownLate Pleistocene eruptions in the Eastern Mediterraneanregion.

2. Geological setting

The 55-km2 Philippi peatland (fen) is located in thesouthern part of the 700-km2 Drama graben in eastern

Macedonia (Fig. 2). Formed since the Miocene bypost-alpine tectonic movements, the Drama basinis surrounded by igneous and metamorphic rocksof the Rhodope massif (Melidonis, 1981). In thePhilippi basin, peat has accumulated over the last700,000 yr (Wijmstra and Groenhart, 1983), until thearea was drained for agricultural use in 1931–1944.Lignite represents the deeper telmatic facies ofthis basin. The whole peat/lignite sequence reachesa maximum thickness of 190 m. As a result, thePhilippi peatland is the thickest known peatland inthe world and the largest fossil fuel resource inthe Balkans (Christanis, 1987). The upper 10–15 m ofthis sedimentary sequence consist mainly of peatintercalated with thin layers of limnotelmatic and limnicsediments, such as detrital muds, calcareous mudsand clays.

Three tephra layers were sampled across the wholefen area and are significant lithological and chronolo-gical markers (Fig. 3). The upper tephra (PhT1) isfound a few tens of centimeters above PhT2 and bothhave thicknesses up to 4 cm. The middle tephra (PhT2)occurs between depths 3.2 and 8.7 m and the lowertephra (PhT3) at depths between 5 and 15 m beneath thefen surface. The PhT3 is an unusually thick (B25 cm)bluish layer, which consists at the coring sites, of asuperior fine grained and an inferior relatively coarsergrained portion. PhT3 displays sand to silt variationexpressed as ‘‘normal graded bedding’’. Local >25 cmand up to 180 cm thicknesses of PhT3 tephra areattributed to slumping in the peat basin (Christanis,1983).

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Fig. 2. Geological map of Drama basin (K: borehole sites).

K.S. Seymour et al. / Quaternary International 121 (2004) 53–65 55

3. Methods and results

3.1. Radiocarbon dating

Cores were obtained in the peat with a hand-drivenEdelman auger. The PhT1 and PhT2 depositional ageswere determined by 14C dating of the underlying peatlayers. PhT3 was bracketed by 14C ages of the overlyingand underlying peat layers (Fig. 3, Table 1). The ageswere obtained by conventional 14C dating at theLaboratory of Archaeometry of the National Centerfor Scientific Research (NCSR) ‘‘Demokritos’’, Athens,using methods as described in Bard et al. (1993) andKromer and Becker (1993). For the calibration of the14C ages, the Radiocarbon Calibration Program Rev.4.4 of the Quaternary Isotope Laboratory of theUniversity of Washington was used (Stuiver andReimer, 1993).

3.2. Tephra sample preparation

The tephra samples were removed from the cores,wet-sieved and separated into sand and silt fractions.The sand fractions were treated with 10% H2O2 for theremoval of the organic material and then withCH3COOH (25%) to remove carbonates. They werethen cleaned with distilled water, placed in an ultrasonicbath and dried at 40�C for 24 h. The remaining dry-sandfraction consisted of glass shards, pumice shards, lithicfragments and phenocrysts. The tephra was embeddedin epoxy resin in custom-made fiberglass holders and

polished when dried for electron microprobe analysis.Phenocrysts were hand-picked for X-ray diffraction(XRD) and phenocrysts and lithic fragments forpetrography.

3.3. Particle morphology and chemistry

Glass and pumice shard morphology was studiedusing a JEOL JSM-820 scanning electron microscope(SEM) operating at an accelerating voltage of 5 kV atMerck Frosst (Plates 1–3). The samples were mountedon aluminum stubs and gold-coated using a sputtercoater (Edwards Auto 306, operating at 1.2 kV, 20 mAfor 5 min).

The chemistry of pumices and glass shards wasdetermined in the Electron Microprobe Center of Earthand Planetary Sciences Department of McGill Univer-sity using a JEOL 8900 fully automated microprobeequipped with an energy dispersive system (EDS) andSEM facilities. Operating conditions were 15 kV and10 nA beam current and 20-s counting times. Naturalglass standards were used and ZAF corrections wereapplied. A highly defocused beam (12 mm) was used toprevent devolatilization of alkalis from the glass.Analyses made within 2 years by two different analystsand under similar operating conditions gave nearlyidentical results indicating that analyses did not losealkalis during probe work. Because the shards wereusually pristine, we consider that the differences of theanalytical totals (from 100%) reported in Tables 2 and 4closely reflect H2O contents.

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Fig. 3. Simplified lithostratigraphy and radiocarbon ages of the Philippi cores (data in parenthesis from Christanis, 1983).

Table 1

Radiocarbon dates of the Philippi peat samples

Lab. No. Coring site Sample No.a Sampling position Radiocarbon age (yr BP) Calibrated age (2s 95.4%)

DEM-648 Ph-1 450–455 Below PhT2 17,3477234 19,537–17,869 BC

DEM-649 Ph-2 495–500 Below PhT1 10,152757 10,350–9407 BC


DEM-651 Ph-2 825–830 Above PhT3 28,1347716 NDb

DEM-652 Ph-2 860–865 Below PhT3 31,5777570 NDb


a Represents the sampling depth in centimeters beneath surface.b ND: not determined.


PhT1, PhT2, PhT3 are glass-rich tephras. Glassshards in the Philippi tephras are predominantly clearand cuspate, and a number of them appear derived fromtriple junctions of bubble walls. Pumice shards areelongated, with pipe vesicles and slightly fluidal forms.Shards were photographed at the SEM facility and

appeared usually pristine (Plates 1–3). Lithic fragmentsin both PhT1 and PhT2 appear blocky and equant withconchoidal fracturing and andesitic composition.

PhT1 and PhT2 are calcalkaline rhyolites. PhT3displays abundant clear shards (CS) and sparsebrown shards (BS) both of trachytic composition. The

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Plate 1. SEM images of glass shards and pumice fragments of the PhT1. Elongate, thin, pipe-shaped vesicles ((a) upper-center; (b) right-center;

(c) upper and right center; and (d) upper-left center) are common in eruptions that produce pyroclastic flows and falls. Pumice shards and cuspate,

Y-shaped glass shards or fragments thereof are present in all (a)–(d). Scale bar is 100mm.

Plate 2. SEM images of glass shards and pumice fragments of PhT2. Fluidal forms and pipe vesicles characterize this tephra adding a silky texture to

the pumice shards and indicating that they were still degassing and plastic while ejected. Ash shard morphology suggests a Plinian origin (a–d).

Broken bubble is filled with secondary minerals in the upper-left corner of (b). Scale bar is 100 mm.


brownish glass shards are higher in MgO, CaO and haveK2OcNa2O for similar SiO2 content than the CS,i.e. higher percentage of ferromagnesian constituents(Table 4). The trace element contents of two samplesfrom each of PhT1, PhT2 and PhT3 glass shard

populations were determined by ICP-MS at the Activa-tion Laboratories Ltd., Ancaster, Ontario, Canada. InFigs. 4a and b, the Zr contents and the Nb/Zr and La/Yb ratios of the Philippi tephras are compared withtephras of mainly similar SiO2 ranges from other Middle

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Plate 3. SEM images of glass shards and pumice fragments of PhT3. Cuspate, Y-shaped glass shards are abundant in PhT3 (c, d), indicative of a

Plinian than phreatomagmatic origin. Elongate pumice shards with pipe vesicles are characteristic in the PhT3 indicating an origin in a pyroclastic

flow (a–d). PhT3 shards are usually devoid of authigenic minerals. Scale bar is 100 mm.

Table 2

Microprobe analyses of glass shards of PhT1 and PhT2

Phillipi tuff PhT1a (n ¼ 17) Phillipi tuff PhT2b (n ¼ 39) Akrotiric G .olhisard

Min Max Mean Std. dev. Min Max Mean Std. dev. Mean Mean Std. dev.

SiO2 70.67 71.51 71.09 0.22 70.86 72.17 71.78 0.26 72.10 73.54 0.58

TiO2 0.41 0.59 0.47 0.039 0.39 0.57 0.45 0.04 0.46 0.29 0.05

Al2O3 14.16 15.00 14.69 0.22 14.09 14.54 14.34 0.09 13.90 14.01 0.23

FeO� 3.22 3.57 3.32 0.073 3.06 3.87 3.17 0.13 2.83 2.04 0.15

MgO 0.42 0.54 0.44 0.026 0.36 0.45 0.41 0.017 0.41 0.23 0.12

CaO 1.71 1.89 1.77 0.05 1.57 1.86 1.68 0.055 1.56 1.41 0.07

Na2O 4.48 5.41 5.02 0.26 4.86 5.56 5.11 0.15 4.43 4.84 0.61

K2O 2.66 2.85 2.78 0.05 2.54 2.87 2.70 0.064 3.14 3.24 0.14

MnO 0.06 0.16 0.11 0.023 0.07 0.14 0.11 0.017 N/A 0.07 0.03

Note: n; number of analyses; min, minimum content; max, maximum content; std. dev., standard deviation; N/A, not analyzed; FeO�, iron expressed

as total iron.a Age B13,000 yr BP, PhT1.b Age B18,000 yr BP, PhT2.c From Federman and Carey (1980).d From Eastwood et al. (1999).


and Eastern Mediterranean sources. It is apparent fromFigs. 4a and b that PhT1–PhT2 and PhT3 tephras groupwith juvenile Theran and Campanian Ignimbrite (CI)glass compositions, respectively. For this reason, inTable 3 the trace element contents of PhT1 and PhT2are compared with Theran tephras from Eastwood et al.(1999) and PhT3 is compared with CI glass traceelement compositions from Civetta et al. (1997). Basedon this deduction, further statistical treatment of themajor element compositions of the Philippi tephras isperformed taking into consideration only data from

Theran and Campanian events (see ‘‘Statistical treat-ment of glass chemistry data’’).

3.4. Mineralogical analysis

XRD characterization of minerals in the Philippitephras was done at the Department of PharmaceuticalResearch and Development, Merck-Frosst Canada Inc.,using a Scintag 2000 diffractometer with a solid-statesemiconductor detector and employing the Ka radiationof copper (a ¼ 1:54178 (A). Operating conditions were

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Table 3

Trace element and REE analyses for separated glass shards from the tephra layers PhT1 and PhT2 deposited at Philippi compared with data of Minoan tephra from G .olhisar, southwest Turkey

(Eastwood et al., 1999)

Sample G .olhisar 1 G .olhisar 2 G .olhisar 3 G .olhisar 4 Thera Knossos PhT1 EEM-1-

UT

PhT1 PH-

3-UT

PhT2 EEM-7-

MT

PhT2 PH-

1-LT

PhT2 PH-

1-LT

PhT2 PH-

1-LT

Caprigilia

OF592b4

Caprigilia

OF592a

Caprigilia

OF59Fa

Method ICP-MS

sol

ICP-MS sol ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP ICP ICP

N 5� 5� 5� 5� 5� 7 5� 5� 5� 5� 5� 5�

Be 1.38 1.85 1.83 1.87 1.57(0.09) 2 2 2 2 13 11

Sc 8.59 6.22 6.63 6.23 15.5 14 13.7 14.8 3.9 4.8 4 4 3

V 65.04 34.88 31.68 25.80 49 33 31 42 35 36 42 35 18

Cr 17.09 2.90 2.90 1.78 10.05 (4.12) 14.7 12.3 12.9 14.7 8.2 13.8

Co 4.86 2.37 2.76 2.46 3.94 (0.41) 9.7 7.5 7.5 7.6 5.8 5

Ni 8.84 2.54 1.77 16.65 5.93 (2.43) 5 3 3 4 2 5

Cu 9.51 8.97 16.76 9.42 15.38 (1.97) 34 23 16 39 18 33

Zn 55.37 44.20 53.07 55.97 59.41 (3.05) 134 245 204 205 120 103

Rb 86.93 97.51 97.48 92.32 94.8 (2.88) 88 92 106 92 332 290 353 362 392

Sr 107.70 66.66 73.38 69.30 136.40 (62.47) 102.90 (6.18) 113 109 103 112 165 166 193 152 56

Y 36.23 36.37 35.90 36.37 35.10(0.95) 42 42 46 42 44 37 48 51 58

Zr 242.0 279.8 266.9 276.50 267.00 (9.75) 258.40 (10.84) 255 271 280 269 586 559 458 522 586

Nb 11.76 9.32 12.8 11.82 12.60 (1.67) 8.33(0.75) 9 12 10 11 83 91 89 86 91

Cs 2.33 2.58 2.49 2.48 2.36 (0.30) 2.71 (0.11) 3.2 3.4 3.9 4 27.7 25.3

Ba 518.70 523.0 506.0 514.30 480.60 (44.27) 488.9 (12.92) 418 465 469 442 447 506 210 198 54

Hf 6.55 7.91 7.39 7.64 7.13 (0.54) 6.73 (0.44) 8.3 8.4 8.6 8.6 14.2 14.3

Pb 34.15 19.15 17.96 18.79 13.80 (2.17) 18.56(3.85) 31 29 23 16 50 61

La 28.40 29.1 29.20 30.3 25.20 (2.63) 26.30 (1.08) 30.06 31.90 33.40 29.70 137.00 116.00 105 116 131.00

Ce 56.10 55.50 55.80 57.7 51.30 (4.74) 55.90 (1.42) 70.00 69.00 72.00 70.00 264.00 221.00 198 219 239.00

Nd 24.80 26.00 25.40 26.4 23.30 (0.30) 23.20 (0.98) 33.00 33.00 33.00 30.00 92.00 75.00 70 76 86.00

Sm 5.71 5.77 5.49 5.86 5.05 (0.06) 5.060 (0.15) 7.57 7.33 7.33 7.41 15.20 13.50 13 15 16.00

Eu 1.25 0.99 1.01 1.13 0.95 (0.05) 1.02 (0.03) 1.58 1.57 1.50 1.50 2.050 1.89 2.1 2.3 2.00

Tb 0.83 1.06 1.06 1.06 0.94 (0.06) 1.02 (0.06) 1.10 1.10 1.10 1.10 1.30 1.20

Yb 4.92 5.14 5.17 5.25 4.31 (0.20) 4.48 (0.21) 5.30 5.79 5.59 5.53 4.53 4.30 4.2 4.5 5.02

Lu 0.79 0.79 0.84 0.84 0.79 (0.03) 1.01 1.05 1.06 1.03 0.80 0.81 0.7 0.7 0.90

Th 15.59 17.58 6.75 17.49 16.04 (1.18) 16.00 (1.18) 21.00 18.60 18.70 19.80 54.90 54.70

U 4.84 5.56 5.26 5.49 4.75 (0.73) 4.64 (0.47) 9.00 6.30 6.30 7.20 14.90 14.90

Ta 1.04 0.86 1.67 1.52 1.10 1.10 1.10 1.00 5.60 5.60

Note: Minoan pumice from Thera (Vitaliano et al., 1990) and Knossos, Crete (Warren and Puchelt, 1990). Trace element and REE data for separated glass shards from tephra layer PhT3 compared

with Campanian Ignimbrite glass and pumice (Civetta et al., 1997). Concentrations in ppm. N=number of averaged analyses. One standard deviation given in parentheses (�=average of five

acquisitions from one sample digestion).

K.S

.S

eym

ou

ret

al.

/Q

ua

ternary

Intern

atio

na

l1

21

(2

00

4)

53

–6

559

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40 50 60 70 80

SiO2 (wt %)

0

200

400

600

Zr (

pp

m)

CAMPANIANIGNIMBRITE &PhT3

DODECANESE PROVINCE

THERA, PhT1, PhT2

AEOLIAN & ANATOLIAN CENTERS

AEGEAN ARCMILOSNISYROSYALI

(a)

0 10 20 30 40

La / Yb

0

0.05

0.1

0.15

0.2

0.25

Nb

/ Zr

CAMPANIANIGNIMBRITE &PhT3

DODECANESE PROVINCE

ANATOLIAN CENTERS

AEOLIAN ARC

AEGEAN ARCMILOSNISYROSYALI

THERAPhT1PhT2

(b)

Fig. 4. Plot of two Q-mode factor aces: (a) PhT1 and PhT2 tephras

and Minoan and Cape Riva pumices display continuity of composi-

tions. Extensive compositional overlap is displayed between PhT3, CI

Tephra dn Kalodiki tephra chemical compositions. (b) In the lower

tephra PhT3 two distinct groups are distinguished: the group of CS

and the group of BS.


step-scanning mode at a speed of 2y ¼ 0:3� per minutewith a step size of 0.02�. Background subtraction andpeak search was performed using the SIETRONICS,SIE 112 software and phase identification by the FEINMARQUAT mPDSM software and the JCPDS databasewith the 55984 phases contained in the JCPDS powderfile compared to the experimental diffraction pattern.

Where crystals make up less than 15 vol% of the ash,they were identified solely by optical methods (Table 5).

PhT1 and PhT2 mineral assemblages are identical;however, the PhT2 is 20% richer in lithic fragments ofandesitic composition and has a higher content ofphenocrysts than PhT1. The main mineral phasesidentified in these tephras by XRD are plagioclase andaugite (Table 5). Hypersthene, hornblende, apatite,magnetite and rare quartz were present in very smallmodal concentrations and were identified by opticalmethods (Table 5 and in Christanis, 1983). PhT3consists of a mineral assemblage of sanidine, sodicplagioclase, biotite, aegirine-augite, hornblende, titaniteand apatite identified by XRD (Table 5) and opticalmethods (Christanis, 1983).

3.5. Statistical treatment of glass chemistry data

Radiocarbon dating (Table 1), ash geochemistry(Tables 2–4, Figs. 4a and b) and mineralogy (Table 5)all suggest that the provenance of tephra PhT3 is thePhlegrean Fields, whereas tephras PhT1 and PhT2 wereprobably derived from Thera. In order to evaluate thedata rigorously, we have performed a statistical treat-ment of our major element data with major element datafrom explosive events of similar ages from PhlegreanFields and Thera (Tables 2 and 4, St. Seymour andChristanis, 1995; Druitt et al., 1999).

A total of 166 major element analyses of glass shardsby electron microprobe from the Philippi tephras wasstatistically treated in order to delineate the provenanceof these tephras by observing their statistical grouping.Factor analysis, a multivariate statistical method, wasapplied to the glass shard major element concentrations.Factor analysis is actually a generic term that describes anumber of mathematical methods designed to analyzeinter-relationships within a set of variables (R-mode) orobjects (Q-mode) (Davis, 1986; Reyment and Joreskog,1993).

The method fails to identify distinct groups betweenPhT2 and PhT1 data sets (Fig. 5a), suggesting that thePhT2 and PhT1 glass shards are not separated on thebasis of chemical composition. Q-mode factor analysisshows that the three Philippi tephras can be separatedinto two clusters (Fig. 5a): one cluster comprises thePhT3 and the second the PhT2 and PhT1. That is, PhT1and PhT2 display continuity of compositions, thevariance of which when assessed by R-factor analysiscan be attributed mainly (B44% of the total variance)to amphibole/pyroxene fractionation. There is alsocontinuity of compositions between PhT1, PhT2 andCape Riva and Minoan pumices on land.

Q-mode analysis of the PhT3 data set has alsoconfirmed the existence of two meaningful groups ofglass shards within the PhT3 data set: the clear (CS) andthe brown (BS) glass shards (Fig. 5b). Similarly, Q-modeanalysis indicates that the PhT3, the CI pumice and the

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Table 4

Microprobe analyses of glass shards of PhT3

Philippi tuff PhT3a

Clear shards (n ¼ 104) Brown shards (n ¼ 6) Campanian Ignimbrite

Min Max Mean Std. dev. Min Max Mean Std. Dev. A B C D

SiO2 59.62 62.83 60.68 0.74 59.84 61.74 60.59 0.67 61.40 61.21 60.16 62.30

TiO2 0.37 0.48 0.42 0.023 0.36 0.40 0.38 0.014 0.42 0.42 0.38 0.46

Al2O3 17.88 20.25 19.14 0.45 18.22 18.88 18.61 0.23 18.67 18.65 19.98 18.98

FeO 2.75 3.21 3.08 0.082 3.24 3.77 3.59 0.18 3.35 3.52 3.03 3.25

MgO 0.30 0.41 0.34 0.019 0.65 0.83 0.77 0.063 0.47 0.36 0.09 0.35

CaO 1.58 1.94 1.75 0.067 2.35 2.74 2.64 0.15 2.03 1.60 3.43 1.62

Na2O 5.98 7.60 6.99 0.37 3.12 4.07 3.73 0.37 5.49 5.18 4.12 5.51

K2O 5.40 7.39 6.61 0.35 8.89 9.63 9.23 0.26 7.28 7.66 8.92 7.03

MnO 0.12 0.26 0.22 0.021 0.09 0.13 0.11 0.013 N/A N/A N/A N/A

Note: n; number of analyses; min, minimum content; max, maximum content; std. dev., standard deviation; N/A, not analyzed. Values A, B from

Civetta et al. (1997), C from Paterne et al. (1988) and D from St. Seymour and Christanis (1995).a Age between 31,78571200 and 28,4007430 yr BP.


Kalodiki glass shards are not clearly separated on thebasis of chemical composition (Fig. 5a).

4. Discussion and conclusions

4.1. Type of eruption

Volcanic ash essentially forms in two ways: either bymagmatic eruptions due to exsolution and expansion ofvolatiles and the consequent disintegration of magma asit approaches the Earth’s surface or by phreatomag-matic eruption when magma mixes with ground orsurface water (sea, glacial, lacustrine).

The shape of the glass fragments produced dependson the physical properties of the melt and the rate ofheat energy released (Wohletz, 1983). Viscosity plays animportant role in defining vesicle morphology, vesicledensity, and mode of fragmentation and consequently indefining the shape of glassy ash particles. Shardmorphology from eruptions of high- and relativelyhigh-viscosity magmas depends entirely on vesicle shapebefore disintegration. Elongate, thin, pipe-shaped vesi-cles (Plates 1–3) are common in colorless glasses duringeruptions that produce pyroclastic flows and falls(Heiken, 1972, 1974; Heiken and Wohletz, 1985). Thefluidal forms of the Philippi shards in PhT1, PhT2 andPhT3 indicate that they were still degassing and plasticwhile ejected (Plates 1–3). Ash shard morphologysuggests Plinian rather than phreatomagmatic origin(Heiken, 1972, 1974; Heiken and Wohletz, 1985).

4.2. Philippi PhT1 and PhT2: Theran explosive events

The interval 17,000–6000 yr BP was a peak period ofvolcanic events for Northern Hemisphere volcanoes,perhaps because of ice-sheet recession and relatedcrustal stress (Zielinski et al., 1996). However, the

tephra of the large Laacher See eruption, Germany, ca12,920 yr ago, has an alkaline character (Bogaard andSchmincke, 1985) and the Icelandic Vedde tephra, whichwas deposited ca 10,000 yr ago, has rhyolitic calcalkalinecomposition (Birks et al., 1996), but displays distinctlylower Ti and Mg contents than the PhT1 and PhT2.

Volcanoes flanking the Middle and Eastern Mediter-ranean basin do not qualify as the provenance for thePhT1 and PhT2: Italian tephras are distinctly alkaline(Phlegrean Fields, Vesuvius, Etna, Pantelleria) and thetiming of the switch-over in the chemical character fromcalcalkaline to alkaline for the Aeolian volcanoes (Ellamet al., 1988) does not relate with the time of PhT1 andPhT2 deposition. Aeolian volcanic products plot also indifferent fields in Zr-SiO2 and Nb/Zr-La/Yb space thanthe upper and middle Philippi tephras (Figs. 4a and b).As for the Anatolian volcanic province to the east, threecalcalkaline rhyolitic ashes are reported by McCoy(1981) to have been deposited between 8000 and10,000 yr (in Narcisi and Vezzoli, 1999). However, theextent of deposition of these tephras and of mostAnatolian tephras is rather restricted, due to thetectonic-sedimentological framework of volcanism inAnatolia (Narcisi and Vezzoli, 1999). Moreover, traceelement contents of Anatolian tephras are different thanthose reported here (Figs. 4a and b).

In the Quaternary Hellenic Arc, Milos erupted at380,000–80,000 yr mainly in phreatomagmatic fashion(Fytikas et al., 1984) and the Plinian eruptions ofNisyros and Yali occurred ca 31,000 yr BP (Hardiman,1996; Narcisi and Vezzoli, 1999). Milos, Nisyros andYali glasses define their own field in Zr-SiO2 and Nb/Zr-La/Yb space (Figs. 4a and b) whilst the PhT1 and PhT2tephras plot outside this field and the fields defined byAeolian, Anatolian and Dodecanese tephras and plot inthe compositional field of the Theran glasses. Therefore,the major element chemistry (Table 2, Fig. 5a), traceelement compositions (Table 3, Figs. 4a and b) and

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mineralogy (Table 5) of PhT1 and PhT2 are similar andall lines of evidence suggest that these tephras originatefrom the volcano of Thera. The radiocarbon ages thatwe have obtained for the peat layer underlying the PhT2are 17,000–18,000 yr BP (Table 1). Therefore, weconclude that the PhT2 at Philippi is equivalent to theY-2 tephra from the Mediterranean Basin, which onland can be correlated to the 18,000 yr Akrotiriignimbrite eruption on Thera of Federman and Carey(1980) (Table 2), i.e. the Cape Riva eruption of Druitt(1985) and Druitt et al. (1989, 1999).

A single 14C age determination for the peat underlyingPhT1 in this study gave an age of deposition of ca10,000 yr BP (Table 1). However, several 14C agedeterminations by Christanis (1983) for similar material

ARTICLE IN PRESSK.S. Seymour et al. / Quaternary International 121 (2004) 53–65 63

from Philippi fen yielded an average age of ca 13,900 yrBP. Therefore, we consider the age of deposition ofPhT1 to be ca 13,000 yr. As discussed above, the PhT1chemical and mineralogical data and the statisticalgrouping of PhT2 and PhT1 major element data inone set (Fig. 5a) strongly suggest that PhT1 also camefrom Thera. Pichler and Friedrich (1976) reported a 14Cage of 12,9507760 yr BP from carbonized wood at thelower parts of the Bo paleosol at Thera (also in Fig. 1aof Cita and Aloisi, 2000). Comparing this age data ofland occurrences with our 14C ages and PhT1 chemistryand mineralogy, we conclude that the PhT1 tephra caneither be related with a ca 13,000 yr as yet stillundetected explosive event of Thera or alternatively,carbon dates from PhT1 gave us erratic valuescontaminated with older carbon. However, CNRS‘‘Demokritos’’ ascertained the removal of ‘‘dead’’carbon. We conclude then, that both the PhT1 andPhT2 are derived from Thera volcano. Tephra PhT2 iscorrelated with a major, distinct and known explosiveevent that occurred on Thera ca 18,000 yr ago, i.e. theCape Riva eruption and PhT1 probably with a stillunknown Theran event.

4.3. Philippi PhT3: a Phlegrean fields event

Two radiocarbon ages obtained from the peat layersoverlying and underlying the PhT3 tephra at Philippipeat basin have yielded values of ca 28,000 and31,000 yr, respectively (Table 1). The likely ages,geochemistry (Tables 3 and 4, Figs. 4a, b and 5a),mineralogical composition (Table 5) and morphology ofglass shards (Plate 3) of PhT3 are highly suggestive of aprovenance located in the Campanian Volcanic Pro-vince of Italy, an area known for its intense pyroclasticactivity (Fig. 1). The PhT3 tephra has a trachyticcomposition and on Zr-SiO2 and Nb/Zr-La/Yb dia-grams (Figs. 4a and b) falls in the same field with CI apyroclastic flow deposit of saturated potassic trachytecomposition, erupted ca 30,000 yr ago (see also below)in the Phlegrean Fields area (Barberi et al., 1978). Thestatistical treatment of the Philippi samples (Fig. 5a)indicates that the PhT3 is indistinguishable from the CIand the Kalodiki tephra geochemical compositions.St. Seymour and Christanis (1995) have argued thatthe Kalodiki tephra, from a small peat basin in Epirus(Fig. 1) is identical to the CI Tephra of the PhlegreanFields. The co-existence of both varieties of shards(Table 4, Fig. 5b) in the PhT3 tephra, alludes to thepresence of a zoned subvolcanic magma chamber as theone from which the CI was erupted (Civetta et al., 1997).The PhT3 is equivalent then to the Y-5 tephra in seacores and to the deep-sea C-13 tephra layer (Vinci, 1985;Ton-That et al., 2001). 40Ar/39Ar ages presented byDeino et al. (1992, 1994) date the CI at 37,1007400 yr,by De Vivo et al. (2001) at 39,3937119, 39,375765 and

39,170770 yr and by Ton-That et al. (2001) an earlyphase of the CI is dated at B41,000 yr. The radiocarbonages of 28,000 yr above and 31,500 yr below the PhT3are possibly not in serious conflict with the 40Ar/39Arages, since they are uncalibrated and qualitatively onecan admit a calibration need of plus/minus severalthousand years in this age range. Therefore, we concludethat the PhT3 is equivalent to the CI Tephra of thePhlegrean Fields.

4.4. Tephra dispersal

In the light of the findings of Sparks and Huang(1980) the deposition of the CI Tephra covered an areain excess of 1.4� 106 km2 at distances up to 1500 kmaway from the source (Fig. 1). It displays sizebimodality, which migrates from a coarse to a finemode with derivation of the fine mode from the co-ignimbrite clouds (Sparks and Huang, 1980). Thepresence of two size grades in PhT3 firstly presentsone more argument in favor of the common origin of theCI and the PhT3 tephra and secondly suggests that theCI Tephra was transported even further than Philippi.Indeed, a tephra correlative to the CI and the Y-5tephras has been reported from the Temnata cave innorthern Bulgaria (Kozlowski et al., 1989), approxi-mately 1500 km away from its source The expectedthicknesses of the PhT3 tephra by extrapolation of theisopachs of Fig. 1 should be between 6 and 8 cm. Locallyobserved PhT3 excessive thicknesses are thus attributedto slumping in the Philippi basin (Christanis, 1983).

The Cape Riva fall deposits CR-A and CR-B arethought to be the on-land equivalent of the widespreadmarine Y-2 tephra (Druitt et al., 1999), which gives aninterpolated oxygen isotope stratigraphy age ca18,000 yr. Distribution of the Y-2 tephra layer suggestsinitially an easterly dispersal direction for the Cape Rivaeruption plume (Druitt et al., 1999). However, correla-tion of the PhT2 tephra with the Cape Riva eruptionproducts on land (this work) supports the findings ofWulf et al. (2002) reporting the presence of Y-2 tephra inthe Sea of Marmara and obviates the significance of thereconstruction of the Cape Riva fall deposits dispersionaxis toward the northeast.

The B3300 yr ‘‘Minoan’’ or Z-2 tephra of Thera hasbeen reported on-land from Kos (Keller, 1981), Rhodes(Doumas and Papazoglou, 1980), Crete (Warren andPuchelt, 1990) and from the Nile delta (Stanley andSheng, 1986). It is also known from numerous studies ofcores of deep-sea sediments in the Eastern Mediterra-nean Sea (summarized in Eastwood et al., 1999). Fromearly deep-sea sediment core work, a south-easterlydispersal axis was initially suggested by Ninkovich andHeezen (1965). Recent discoveries from terrestrialrecords implied an easterly dispersal (Sullivan, 1988,1990; Pyle, 1990), but the presence of Minoan tephra in

ARTICLE IN PRESSK.S. Seymour et al. / Quaternary International 121 (2004) 53–6564

sediments of the Black Sea (Guichard et al., 1993)suggests a dispersal axis for the Minoan tephra fallouttoward a northeasterly direction. Previous research onthe Cape Riva and Minoan eruptions of Santorinisuggests that tephra from Hellenic Arc volcanic centershad the potential to reach locations as far away asPhilippi. Tephra unit PhT1 is most likely the product ofa hitherto unknown Theran eruption and futureresearch should focus on ascertaining a completeinventory of the tephra deposits on Santorini.

Acknowledgements

Kimon Christanis thanks Dr. Y. Maniatis, Dr. G.Fakorellis, K. Gogidou and M. Korozi, at the NationalCenter for Scientific Research (NCSR) ‘‘Demokritos’’,Athens, for radiocarbon dating. Maria Geraga, MariaKoulis and Costas Vamvoukakis are thanked for theirtechnical help. Ernesto Moran thanks Merck FrosstCompany for the use of XRD and SEM equipment. Theauthors also thank the anonymous reviewers for theircomments.

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Documents

Tephrostratigraphy and tephrochronology in the Philippi peat basin, Macedonia, Northern Hellas (Greece)