linking the north atlantic to central europe: a high-resolution holocene tephrochronological record...

JOURNAL OF QUATERNARY SCIENCE (2002) 17(1) 3–20Copyright 2002 John Wiley & Sons, Ltd.DOI: 10.1002/jqs.636

Linking the North Atlantic to central Europe: ahigh-resolution Holocene tephrochronologicalrecord from northern GermanyCHRISTEL VAN DEN BOGAARD* and HANS-ULRICH SCHMINCKE

GEOMAR, Forschungszentrum fur marine Geowissenschaften, Wischhofstr. 1-3, D-24148 Kiel, Germany

van den Bogaard, C. and Schmincke, H.-U. 2002. Linking the North Atlantic to central Europe: a high-resolution Holocene tephrochronological record from northernGermany. J. Quaternary Sci., Vol. 17 pp. 3–20. ISSN 0267-8179.

Received 5 December 2000; Revised 19 April 2001; Accepted 1 May 2001

ABSTRACT: A high-resolution Holocene tephrochronology for northern Germany has beenestablished based on systematic tephrostratigraphical analysis of three peat bogs. Microscopicvolcanic ash layers have been traced and characterised petrographically and by the chemicalcomposition of the glass shards. At least 37 ash horizons representing 16 different explosive volcaniceruptions have been identified and many can be correlated between the three sites, up to 100 kmapart. The tephra layers can be related to Icelandic volcanic sources and some correlated to theeruptions of Askja 1875, Hekla 3, Hekla Selsund, Hekla 4 and Hekla 5, as well as to unspecifiederuptions of Icelandic volcanic systems, e.g. Torfajokull. The source volcanoes for some tephralayers remain unidentified. Some tephra layers were known previously from the North Atlanticregion (e.g. Sluggan, Glen Garry), others have not been recorded previously in the literature (e.g.microlite tephra). This study provides the first comprehensive Holocene tephrostratigraphical recordfor northern Germany, complementing the North Atlantic tephrostratigraphical dating framework,effectively extending it into central Europe. The study shows that Icelandic ash layers are even morewidespread than hitherto thought. Copyright 2002 John Wiley & Sons, Ltd.

Journal of Quaternary Science

KEYWORDS: tephrochronology; Holocene; northern Germany; Iceland; Hekla.

Introduction

During large explosive volcanic eruptions, degassing silicatemelt is fragmented into glass particles, injected into theatmosphere, and carried up to stratospheric heights in buoyantash plumes. Prevailing winds transport volcanic ash cloudsacross oceans, glaciers and land, while ash (or tephra) particlesare deposited from the ash clouds through gravitational fallout.Owing to highly variable magma sources and evolutionaryprocesses (differentiation, magma mixing, etc.), silicate meltsoften acquire characteristic (sometimes unique) compositionsprior to eruption that are documented in the glass compositionsand can be used for ‘chemical fingerprinting’, i.e. theidentification of a specific eruptive event by major and traceelement analysis of the glass shards.

Depending on grain-size and density, typical atmosphericresidence and travel times of tephra particles during any

* Correspondence to: Dr C. van den Bogaard, GEOMAR, Forschungszentrum furmarine Geowissenschaften, Wischhofstr. 1-3, D-24148 Kiel, Germany.E-mail: [email protected]

Contract/grant sponsor: Bundesministerium fur Forschung und Technologie;Contract/grant number: 03SC-9-Kie.Contract/grant sponsor: Kultusministerium of Schleswig-Holstein.

eruption range from the order of minutes (coarse-grainednear-vent tephra deposits) to months at most (micrometre-size distal ash layers). The resulting ash blankets thus covervast areas, connect highly variable environments, and—ifpreserved in the geological record—represent compositionallydistinct stratigraphical markers that are isochronous on ageological time-scale. Because deposits near volcanic centresare frequently eroded or buried by younger eruption products,distal tephra layers also provide a more complete picture ofthe eruption record, magma evolution and mass balance inthe volcanic source areas.

The exact dating of marine, terrestrial and glacial strata andproxies is especially important in the Holocene, where thestudy of short-term climatic fluctuations and environmentalresponses require a resolution typical of tephrochronologicalmarkers (<1 yr), a precision unmatched by radiometricdating methods. In areas where millimetre- to centimetre-thick ash layers are deposited, tephrostratigraphy is thereforewell-established. Throughout the North Atlantic region, forexample, numerous ash layers, chiefly derived from Icelandiceruptions, have been detected in Late- and post-glacial strata,such as marine sediments (Mangerud et al., 1984; Bond et al.,1997; Eiriksson et al., 2000a,b), lake or peat bog depositsfrom the Faroe Islands (Mangerud et al., 1986; Hannon, 1999;Wastegard et al., 2001), the British Isles (Dugmore, 1989;

4 JOURNAL OF QUATERNARY SCIENCE

Bennet et al., 1992; Dugmore et al., 1992, 1995a; Pilcherand Hall, 1992, 1996; Pilcher et al., 1995, 1996; Lowe andTurney, 1997), and Sweden (Persson, 1971; Wastegard et al.,1998), and ice cores from Greenland glaciers (Gronvoldet al., 1995; Zielinski et al., 1995). The Holocene Icelandictephrostratigraphy and tephrochronology recently has beenreviewed in detail (Haflidason et al., 2000), and work iscontinuing in many areas.

In continental Europe, the end of the last glacial is well-constrained by the Laacher See Tephra (12 900 yr BP), aprominent, single ash layer that erupted from the East Eifel vol-canic field, which forms a widespread tephra marker horizonof the Late-glacial Allerød Interstadial throughout southern,central and northern Europe (Bogaard and Schmincke, 1984,1985; Bogaard, 1995). Volcanic centres active during theHolocene, however, such as in the Italian volcanic fields, inthe Aegean and in Iceland, are more than 2000 km away(Fig. 1). Holocene strata in northern Europe therefore lack vis-ible ash layers, and only two microscopic tephra occurrenceshave been detected during palaeoecological studies (Merktet al., 1993; Bogaard et al., 1994).

Here we present the results of a systematic tephrostrati-graphical study of Holocene deposits in northern Germany.Microscopic ash layers are detected and characterised petro-graphically and by the chemical composition of glass shards.The tephra layers are correlated between drill sites and withknown Holocene tephra markers, and traced to their erup-tive sources. The study connects the continental and Atlanticrecords of the Holocene and contributes to the tephrostrati-graphical dating framework of the North Atlantic region.

Sites, samples and analytical methods

In order to detect Holocene tephra layers in northernGermany, three large raised peat bogs were investigated. Peat

A t l a n t i c O c e a n

Brussels

London

Copenhagen

Berlin

Stockholm

Oslo

Dublin

Farφer

ParisBonnEVF

Reykjavik

Iceland

0° 10°10°20°

Arct ic c i rc le

60°

50°JAM

DOMGRAM

Figure 1 Locality map of bogs Jardelunder Moor (JAM),Dosenmoor (DOM) and Grambower Moor (GRAM) (EVF: East andWest Eifel volcanic fields)

from raised bogs is a highly favourable substratum for thedetection of minute volcanic particles because it consistsof up to >99% organic matter and only minor mineralcomponents, mainly from wind-blown dust. The peat bogsselected for this study (Jardelunder Moor, Dosenmoor andGrambower Moor) are located along a northwest–southeasttransect, extending from the Danish border through Schleswig-Holstein to Mecklenburg-Vorpommern (Fig. 1) and, frompalynological criteria (Dorfler, 1998), appear to represent theentire Holocene.

Bog sections were drilled with a piston-corer in sec-tions 100 cm long and 8 cm in diameter. Continuous peatcores are 415 cm (Jardelunde), 754 cm (Dosenmoor centre),617 cm (Dosenmoor margin) and 360 cm (Grambow) long.A total of four cores were analysed, three of which repre-sent the central facies of the bogs. In order to verify thelocal reproducibility and persistence of tephra horizons, anadditional core was studied from the marginal facies of theDosenmoor, which shows the highest peat accumulation rateamong the sections studied. None of the cores contained vis-ible ash layers. Moreover, volcanic ash horizons could notbe detected by non-destructive physical methods, includingmeasurements of magnetic susceptibility, detection of naturalgamma and alpha ray emissions. The saturation isothermalremanent magnetisation (SIRM) did not prove to be a success-ful method to detect microscopic tephra horizons (Bogaardet al., 1994). Entire cores were sampled in contiguous 4–6 cm(locally 1 cm) intervals. Two different methods were used (i) todetect ash horizons and (ii) to enrich volcanic glass shards formicroprobe analyses.

To detect traces of volcanic ash layers, organic compoundswere burned at 600 °C for 2–3 h. Samples were then washedin 10% HCl and sieved through 6 or 14 µm mesh. Clay-richsamples were sieved in an ultrasonic water bath. Volcanicglass shards were identified in grain mounts of the mineralresidue under a polarising microscope. This treatment alloweda rapid inspection of the entire cores in 4–6-cm segments, butthe glass shards recovered showed sintering of their surfacesand thus were clearly affected by the thermal treatment. Therapid burning procedure therefore was applied exclusively todetect volcanic glass shards, and material recovered by theburning procedure was not used for geochemical analyses ofthe tephra layers.

Glass shards for chemical analysis were enriched from aparallel peat sample, following an acid digestion procedure(Persson, 1971). The amount of mineral residues retrieved, aftersieving off the <6 µm fraction, was generally less than 0.1 ml.No attempt was made to further enrich the glass shards by, forexample, heavy liquid separation. Polished thin-sections wereprepared from the mineral residue. To ensure that the aciddigestion technique did not alter the chemical compositionof the shards, a set of glass shard samples in a size rangeanticipated to be present in the bogs (<125 µm fraction) wasmixed with peat and treated with the acid digestion procedure.Electron microprobe analysis of the treated and untreatedsample splits showed that no alteration had occurred in anyof the rhyolitic, dacitic and andesitic sample splits. For a moredetailed discussion of the effects of the enrichment procedureson glass shards see Bogaard (1997).

The chemical composition of glass shards—major elements,S, Cl and F—was analysed with a Cameca SX-50 electronmicroprobe at GEOMAR, Kiel. Analytical conditions were15 kV accelerating voltage, 6 nA beam current and 20 s of peakcounting time, 10 s on background. Analyses were performedwith a 5 × 7 µm electron beam.

Pumiceous clasts smaller than 40 µm, where only smalledges of glass were polished, required a reduction of the beam

Copyright 2002 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 17(1) 3–20 (2002)

HOLOCENE TEPHROCHRONOLOGY OF NORTHERN GERMANY 5

diameter to 3 µm, and a beam current as low as 2 nA was usedto exclude heating and degassing of the embedding material.The different analytical conditions were performed on Liparistandard (Hunt et al., 1998), showing a high precision andaccuracy of the results. Standards used for calibration werenatural glasses (KN18, Juan de Fuca Ridge and CFA 47: Na,Si, Al, Mg, K, Ca, Ti and Fe) and minerals (rhodonite, scapoliteUSNM R6600-1, Durango fluorapatite USNM 104021: F, P,Cl, S and Mn). Sodium was analysed first during all sessions;sodium loss was not observed. Internal standards (Lipariobsidian and KN18) were measured at the beginning and endof each analytical session, and every 20–40 measurements.Only analyses with totals better than 95% were accepted. Datain Table 1 show representative analyses of data normalised to100% on a volatile-free basis. Full details on data sets areavailable on request.

For correlation to individual source volcanoes and eruptions,the deposits of major plinian eruptions were sampled in near-vent type sections, and chemical characteristics of glass shardsin the ash fraction were determined.

To compare geochemical data measured in other laborato-ries, results of near-vent material analyzed in the GEOMAR

laboratory were compared with published analyses determinedon the same material in other laboratories. No significant dif-ferences were recognised between the Geomar, Belfast andEdinburgh microprobe results.

Results

Traces of volcanic ash were found at 37 different levels inthe four cores studied. Glass shards occur in distinct tephrahorizons separated from each other by glass-free peat sections.Estimates of the ash-layer thickness and vertical dispersal ofglass shards are limited by the sampling intervals (4–6 cm).Individual ash horizons in the different cores are assignedworking names and numbered from top to bottom (Dosenmoormargin Dom 0-11-M; Dosenmoor centre Dom 0-11-C;Jardelunde Jam1-7; Grambow Gram1-8; Fig. 2).

Glass particles are mainly colourless or light yellowish;brownish and greenish glass shards are rare. Particle mor-phologies include highly vesicular pumice, tubular pumice,

Jam-1

?

?

?

Jam-5

Jam-6Jam-7

Jam-8

Jam-4Jam-3Jam-2

Dom-0

Dom-10

Dom-11

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Dom-3

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Dom-6

Dom-7

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Dom-12

Gram-7Gram-8

Gram-6Gram-5

Gram-4

Gram-3

Gram-2

Gram-1

JardelunderMoor

GrambowerMoor

DosenmoorMargin Center

Inferredage

14C yrs BP

0

100

Depth [cm]

JAM-7

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(ca. 5800)

(ca. 7350)

(ca. 5600)

(ca. 3700)

(ca. 4500)

(ca. 4900)

(ca. 3200)

(ca. 3000)

(ca. 2700)

(ca. 2200)

(ca. 1550)

(ca. 1300)

(ca. 1000)

(ca. 700)

(ca. 300)

(< 150)

Figure 2 Stratigraphical sections of cores studied with detected tephra horizons. Tephra layers with glass shards that have been chemicallyfingerprinted are shown in black. Column at left provides a summary of correlated tephra layer found in bogs in northern Germany. The age of thetephra layers is deduced from the stratigraphical position in the cores and the 14C-dated organic sediments in the Dosenmoor core. The DOM-6tephra (microlite tephra) is shown by heavy black line for clarity



a

c

e

b

d

f

20 µm

Fsp-microlite

Figure 3 Photomicrographs of glass shards from selected tephra horizons. Images (a) and (b) show pumiceous glass shards, (c) and (d) bubble-wallshards, (e) shows a single crystal with glass rim from Dom-7 and (f) shows dense glass shard with fsp-microlite from the microlite tephra (DOM-6)

bubble wall shards and non-vesicular platy shards. Only oneigneous crystal (feldspar) with a glass rim was found (Fig. 3).Shards are up to 115 µm in diameter, the median being gen-erally less than 40 µm. Concentrations of glass shards rangefrom 1 to >30 cm−3 sample.

Glass shards were analysed from all horizons from whichenough material was recovered. Great care was taken toexpose glass surfaces in (repeatedly) polished thin-sections.Tephra horizons with insufficient glass shards to be anal-ysed by electron microprobe (EMP) analysis are quoted as‘composition not determined’ and discussed on the basisof shard morphologies and stratigraphical or chronologicalcontext only.

Glass shards are chiefly rhyolitic to rhyodacitic (SiO2 >

65%) and rarely andesitic (SiO2 < 62 wt%) in composition.The chemical composition of shard populations is eitherhomogeneous, bimodal or varies systematically betweentwo end-member compositions. The tephra layers resembleeach other compositionally, but can be distinguished from

each other, and correlated between cores, based on theircharacteristic major element composition, such as their SiO2

and K2O concentrations (Fig. 4) and their K2O–CaO–FeO(tot)ratios, glass particle morphologies, relative stratigraphicalposition and age. Correlation of compositionally identicaltephra horizons between cores reduces the total number oftephra layers detected to 16, each of which represents adistinct eruption event or tephra marker and is labelled witha capital letter abbreviation according to its first detection(DOM, GRAM, JAM). These tephra layers, from the youngestto the oldest are described below.

GRAM-1 (Gram-1)

The youngest tephra horizon, identified at 3–4 cm depth inthe Grambow bog only, consists of a few colourless andsingle greenish shards. The clasts are vesicular with anaverage diameter of 45 µm. The colourless glass shards are



2

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5

K2O

wt.

%

HKSA

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Dom-2Dom-3Dom-4Dom-5Dom-6Dom-7Dom-8Dom-9

DOM-2DOM-3DOM-4DOM-5DOM-6DOM-7DOM-8DOM-9

HORIZON TEPHRA

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K2O

wt.

%

HKSA

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JARDELUNDEHORIZON TEPHRAJam-1 Jam-2 Jam-3 Jam-4Jam-5 Jam-6 Jam-7

DOM-2DOM-5DOM-6DOM-7DOM-9JAM-6JAM-7

JAM-7bDOM-7a

+ Gram-1Gram-4Gram-5Gram-7Gram-8

GRAM-1DOM-5DOM-6JAM-6JAM-7

HORIZON TEPHRA

2

3

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5

70

K2O

wt.

%

SiO2 wt. %

MKSA

64 66 68 72 74 76 78

DOM-6a

DOM-6b

JAM-6

JAM-7aGRAM-1

DOM-5

GRAMBOW

HKSA

SHO

JAM-7b

6

7

8

DOSENMOOR

Figure 4 SiO2 –K2O variation diagrams of tephra layers fromnorthern Germany. The fields are defined by data from Dosenmoortephra horizons. All data are plotted volatile free. SHO, shoshonitic;HKSA, high K subalkaline; MKSA, medium K subalkaline; LKSA, lowK subalkaline. Field boundaries according to Rickwood (1989)

of subalkaline rhyolitic composition (SiO2 75.7 wt%, K2O2.8 wt%) (Fig. 4, Table 1). The composition of the greenishglass shards could not be determined. The composition of theshards resembles that of some of the older tephra layers inthe bogs (DOM-7, DOM-9 and GRAM-8, see below), but thestratigraphical position clearly indicates that the tephra eventis younger, with an age of less than 150 yr.

DOM-0 (Dom-0-C) and DOM-1 (Dom-1-M)

The uppermost tephra horizons identified in the two Dosen-moor cores (Dom-0-C, 16–28 cm; Dom-1-M, 37–49 cm)

consist of rare single glass shards, with a glass chemistrythat could not be determined. The horizon in the centre core(Dom-0-C) is approximately 300 yr BP, the horizon in the mar-gin core (Dom-1-M) is ca. 700 yr BP, possibly indicating twoseparate tephra events.

DOM-2 (Dom-2, Jam-1, Gram-2)

An approximately 1000-yr-old tephra layer occurs at all threesites studied (Dom-2-M, 67–71 cm; Jam-1, 28–32 cm; Gram-2, 26–32 cm; Fig. 2). Ash horizons at these sites comprisecolourless, pumiceous and highly vesicular glass shards, themedian diameter of the shards being 30 µm. Even shards<20 µm in diameter are highly vesicular with micrometre-thin bubble walls. These small pumiceous clasts are typicalfor the DOM-2 tephra layer, strongly contrasting with allother tephra layers studied. The chemical composition ofthe glass shards has been determined from Dom-2-M andJam-1. Shard populations of both layers are homogeneous,with subalkaline rhyolithic compositions. Only MgO contentsdiffer slightly, ranging from 0.1 to 0.4 wt% in Dom-2 comparedwith predominantly higher values in Jam-1 (0.3–0.5 wt%). TheDOM-2 glass shards can be distinguished from glasses of othertephra horizons by their characteristic SiO2 (74.4 wt% ± 0.5)and relatively high K2O contents (3.2 wt% ± 0.2) (Table 1).

DOM-3 (Dom-3, Gram-3)

Tephra DOM-3 is a minor ash horizon, which occurs inthe same stratigraphical position at Dosenmoor (Dom-3-M, 111–117 cm; Dom-3-C, 116–122/128–134 cm) and atGrambow bog (Gram-3, 56–68 cm). Glass shards analysedfrom Dosenmoor margin core are rhyolitic with high SiO2

content (76.8 wt%) and high K2O content (4.2 wt%) (Fig. 4).

DOM-4 (Dom-4)

Tephra DOM-4 comprises two minor ash horizons in bothDosenmoor cores, containing heterogeneous glass shard pop-ulations (Dom-4-C, 294–300 cm; Dom-4-M, 153–165 cm).Glass shards are characterised by high SiO2 contents(76.1 wt%) and high K2O (4.5 wt%), but also low K2O(2.6 wt%) contents and single shards with low SiO2 (63.2 wt%)and low K2O concentrations (1.8 wt%) (Fig. 4 and Table 1).


Tephra DOM-5 occurs at all sites studied, the Dosen-moor radiocarbon stratigraphy suggesting an age of ca.2200 yr BP (Dorfler, 1998) (Dom-5-C, 346–351 cm; Dom-5-M, 187–193 cm; Jam-2, 86–94 cm; Gram-4, 126–138 cm).The glass shards comprise mainly colourless vesicular andbubble wall shards. In Jam-2 and Gram-4, single brown glassshards occur, their medium grain size being 50 µm. At allsites, the tephra horizons consist of glass shards of subalka-line rhyolitic and rhyodacitic composition with the lowestK2O contents (2.0 ± 0.2 wt%) of all tephra layers identifiedso far in northern Germany. Colourless shards have variableSiO2 contents from 75.6 to 71.0 wt% (Fig. 4). This, and thevariation in MgO concentration from 0.2 to 0.8 wt% and ofFeO (3.5–5.4 wt%), indicate eruption of a chemically zoned



magma column. High CaO (2.4 ± 0.4 wt%) and TiO2 con-tents (0.6 ± 0.2 wt%) are also characteristic. Rare brownishglass shards could not be analysed.


Tephra DOM-6 is a very distinctive layer detected inall cores examined (Dom-6-C, 346–351 cm; Dom-6-M,279–285 cm; Jam-3, 102–110 cm; Gram-5, 150–162 cm;Fig. 2). It consists of colourless, highly vesicular, bubble-wall and non-vesicular angular glass shards. Their maximummeasured length is 100 µm, the median being <45 µm. About60% of the shards have characteristic feldspar microlitecrystals up to 20 µm long, occurring in all types of glassshards in Dom-6, Jam-3 and Gram-5 (Fig. 3). Electronmicroprobe analyses show a homogeneous rhyolitic glassshard population in Dom-6 and Jam-3, with SiO2 contentsof 76.6 ± 0.5 wt%, intermediate K2O (3.8 ± 0.2 wt%) and lowCaO contents (0.9 ± 0.1 wt%) (Fig. 4; Table 1), and with 70%of the Gram-5 glass shards yielding identical compositions(DOM-6a in Fig. 4). Subordinate glass shards with lowerSiO2 (71.5–75.1 wt%) and Na2O contents (0.9–2.1 wt%), andexceptionally high K2O values (up to 8.6 wt%) occur in thetephra at Grambow (DOM-6b), and are difficult to explain.Similar K-enriched glass compositions have been encounteredonly in glass shards enriched by the burning procedure (seeabove), possibly indicating that these Gram-5 glass shards werealtered during an ancient bog fire. However, neither sinteringof the glass shards, nor an enrichment of charcoal have beendetected at this level.

DOM-7 (Dom-7, Jam-4)

Tephra DOM-7 comprises ash horizons in both the Dosen-moor (Dom-7-C, 396–401 cm; Dom-7-M, 303–309 cm) andJardelunde sections (Jam-4, 114–122 cm) and contains themost abundant glass shards among the tephra layers detected.Glass shards are colourless, pumiceous to highly vesicularand bubble-wall shaped. Their median is about 50 µm, themaximum shard size being 90 µm. Few greenish and rarebrownish shards and one single feldspar crystal with a glassrim also occur (Fig. 3). The tephra layer is characterised bya bimodal glass shard suite, comprising rhyodacitic and rhy-olitic compositions, the latter being more abundant. The SiO2

contents are 73.0 ± 0.6 wt%, K2O is 2.5 ± 0.2 wt% and CaOcontents are 2.0 ± 0.2 wt%. Rhyodacitic shards have lowerSiO2, 67.7 ± 1.2 wt%, slightly lower K2O of 2.2 ± 0.1 wt%and higher CaO contents of 3.2 ± 0.2 wt% (Fig. 4, Table 1).

Tephra horizon Gram-6 in the Grambow section consists ofa few shards for which the chemical composition could not bedetermined. The peat sequence in this stratigraphical positionis condensed and the age of the horizon is poorly constrained.The Gram-6 horizon could be part of the DOM-7 tephra, butalso could belong to an older tephra layer.

DOM-8 (Dom-8)

Tephra DOM-8 occurs in the Dosenmoor section (Dom-8-C,428–434 cm; Dom-8-M, 363–369 cm) only, and is separatedfrom overlying tephra DOM-7 by a 27–54- cm glass-free peatsection (Fig. 2). Its glass shard population, analysed from themargin core, has a bimodal composition, the main glass shardpopulation having SiO2 contents of 73.7 ± 0.4 wt% and K2O

contents of 2.8 ± 0.1 wt% (Fig. 4). Major and minor elementcomposition of DOM-8 glass shards are indistinguishable fromthose of DOM-7, relative stratigraphic position and age beingthe only criteria to distinguish the two tephra layers.

DOM-9 (Dom-9, Jam-5)

This tephra layer (horizons Dom-9-C, 464–476 cm; Dom-9-M,417–423 cm; Jam-5, 186–194 cm) consists of colourless tubu-lar pumice, pumiceous and vesicular glass shards. The meanclast diameter is 45 µm, the largest clast of 100 µm occurringin the Jardelunde layer. The ash layer comprises a chemicallyhomogeneous glass shard population of subalkaline rhyoliticcomposition, with high SiO2 (76.0 ± 0.3 wt%) and mediumK2O contents (2.8 ± 0.1 wt%) (Fig. 4). The tephra layer con-tains a subordinate second population of glass shards lower inSiO2 concentrations (73.1 ± 0.9 wt%) and other elements onlyin the Jardelunder site. The chemical composition partly over-laps with that of the DOM-7 tephra layer. However, the glassshards can be distinguished from DOM-7 deposits by theirhigh SiO2 and low FeO and TiO2 concentrations (Figs. 4, 7).

DOM-10 (Dom-10), DOM-11 (Dom-11)

Two horizons with rare single glass shards occur inboth Dosenmoor cores (Dom-10-C, 539–545 cm; Dom-11-C, 587–593 cm; Dom-10-M, 541–547 cm; Dom-11-M,587–593 cm). The chemical composition is unknown. Theyare interpreted to represent separate events based on theirstratigraphical position and age.

JAM-6 (Jam-6, Gram-7)

Tephra JAM-6 was identified in Jardelunde and Grambow bogs(Jam-6, 234–238 cm; Gram-7, 221–227 cm) and possibly inthe Dosenmoor (Dom-11-M) where only few glass shardsoccur. Glass shards in JAM-6 and Gram-7 are colourlessand vesicular, with a medium grain size of ca. 50 µm. Theglass shard populations of both samples are compositionallyhomogeneous, with a distinct potassic subalkaline rhyoliticcomposition. Tephra JAM-6 glass shards have SiO2 contentsof 71.9 ± 0.5 wt% and can be distinguished from other tephralayers in northern Germany by their characteristically highK2O (4.6 ± 0.1 wt%), Na2O (5.4 ± 0.3 wt%) and low CaOcontents (<1 wt%). In both bogs, tephra layer JAM-6 isimmediately underlain by another tephra (JAM-7), in theGrambow bog separated by a glass-free peat interval only6 cm thick. Tephra layer JAM-6 can be distinguished easilyfrom JAM-7, however, by its significantly higher K2O contents,among other elements.

JAM-7 (Jam-7, Gram-8)

In Jardelunde and Grambow bogs, ash horizons Jam-7(238–242 cm) and Gram-8 (233–239 cm) consist of colourlessvesicular glass shards, with a medium diameter of ca. 50 µm.The glass shard population of tephra JAM-7 is bimodalwith 75% of the glass shards in the main population. Thecomposition of the glass shards is identical to the compositionof tephra DOM-9, with high SiO2 contents of 76.7 ± 0.4 wt%in the main population and the same characteristically



Table 1 Chemical composition of single glass shards of Holocene tephra layers in northern Germany. The electron microprobe (EMP) analysisdata given are representative data determined by EMP analysis, volatile-free normalised for ease of comparison and original totals. FeO as total FeO

Tephra SiO2 TiO2 Al2O3 FeO∗ MnO MgO CaO Na2O K 2O P2O5 � (volatile SO2 F Cl Totalfree)

GRAM-1Gram-1 75.75 0.11 13.24 1.93 0.20 0.03 1.32 4.61 2.80 0.00 95.01 0.06 0.00 0.11 95.17Gram-1 75.77 0.21 13.30 1.82 0.07 0.01 1.39 4.65 2.78 0.00 94.69 0.00 0.00 0.08 94.78

DOM-2Jam-1 74.90 0.36 14.34 1.09 0.00 0.30 1.62 4.05 3.34 0.00 96.41 0.00 0.01 0.37 96.78Jam-1 74.87 0.40 14.25 1.31 0.06 0.37 1.77 3.92 3.06 0.00 96.37 0.09 0.00 0.39 96.84Jam-1 74.44 0.00 14.58 1.74 0.00 0.40 1.88 4.07 2.90 0.00 96.14 0.00 0.00 0.34 96.48Jam-1 74.42 0.18 14.64 1.41 0.11 0.37 1.92 4.19 2.76 0.00 96.46 0.00 0.00 0.43 96.89Jam-1 74.31 0.11 14.36 1.56 0.17 0.39 1.93 3.82 3.34 0.00 97.15 0.10 0.00 0.30 97.55Jam-1 74.23 0.00 14.28 1.46 0.05 0.50 2.08 4.09 3.30 0.00 97.54 0.02 0.00 0.29 97.85Jam-1 74.17 0.18 14.39 1.28 0.05 0.38 2.18 4.10 3.28 0.00 96.14 0.00 0.00 0.35 96.49Jam-1 74.09 0.00 14.67 1.62 0.00 0.43 2.03 4.01 3.09 0.06 97.60 0.19 0.00 0.36 98.15Dom-2 75.26 0.22 14.41 1.10 0.02 0.11 1.65 3.90 3.32 0.00 96.59 0.00 0.05 0.39 97.03Dom-2 75.15 0.22 14.13 1.27 0.08 0.14 1.90 3.97 3.15 0.00 96.56 0.00 0.03 0.36 96.94Dom-2 74.43 0.14 14.57 1.37 0.12 0.17 2.04 3.99 3.16 0.00 96.37 0.00 0.00 0.26 96.63Dom-2 74.37 0.18 14.68 1.52 0.12 0.17 1.83 4.08 3.06 0.00 97.69 0.03 0.05 0.45 98.22Dom-2 74.16 0.36 14.83 1.50 0.09 0.22 1.75 3.92 3.16 0.00 96.35 0.00 0.00 0.24 96.59Dom-2 74.12 0.14 14.65 1.53 0.05 0.22 1.85 4.06 3.38 0.00 96.66 0.19 0.00 0.38 97.23Dom-2 74.10 0.25 14.66 1.52 0.02 0.22 1.89 4.03 3.30 0.00 96.37 0.03 0.00 0.48 96.88Dom-2 74.08 0.57 14.62 1.44 0.17 0.07 1.99 3.88 3.15 0.04 97.91 0.00 0.00 0.43 98.34Dom-2 73.86 0.54 14.75 1.41 0.08 0.21 2.11 3.80 3.24 0.00 96.67 0.00 0.00 0.37 97.04Dom-2 73.76 0.17 14.51 1.58 0.06 0.42 2.01 4.17 3.32 0.00 97.07 0.07 0.00 0.37 97.51

DOM-3Dom-3 77.11 0.00 13.18 0.78 0.26 0.02 0.84 3.57 4.25 0.00 93.25 0.03 0.00 0.14 93.43Dom-3 76.84 0.00 13.13 1.22 0.08 0.13 0.74 3.81 4.05 0.00 94.37 0.00 0.00 0.11 94.48Dom-3 76.62 0.00 13.54 0.84 0.00 0.06 0.89 3.73 4.32 0.00 93.69 0.00 0.03 0.16 93.88

DOM-4Dom-4-C 77.34 0.11 12.79 0.86 0.17 0.00 0.56 3.60 4.57 0.00 95.89 0.12 0.00 0.12 96.13Dom-4-M 76.13 0.33 13.10 1.00 0.02 0.08 0.79 4.03 4.53 0.00 95.42 0.00 0.06 0.21 95.69Dom-4-C 76.75 0.07 13.15 0.76 0.09 0.00 0.67 3.99 4.52 0.00 95.00 0.00 0.16 0.17 95.32Dom-4-C 75.94 0.11 13.99 1.04 0.09 0.00 0.83 3.71 4.29 0.00 95.09 0.00 0.00 0.14 95.23Dom-4-M 76.64 0.00 13.38 1.55 0.11 0.02 1.40 4.17 2.73 0.00 95.28 0.19 0.00 0.02 95.49Dom-4-M 76.18 0.28 12.90 2.25 0.17 0.06 1.48 4.07 2.61 0.00 97.67 0.00 0.08 0.11 97.86Dom-4-M 73.91 0.96 12.60 3.36 0.28 0.78 2.70 3.09 2.33 0.00 97.19 0.24 0.00 0.08 97.51Dom-4-M 63.95 1.06 15.49 7.43 0.34 1.15 4.63 4.16 1.71 0.08 96.57 0.02 0.00 0.11 96.70Dom-4-M 62.53 1.49 15.19 7.72 0.38 1.27 4.91 4.66 1.86 0.00 96.37 0.10 0.00 0.04 96.51

DOM-5Jam-2 75.55 0.53 12.44 3.52 0.08 0.39 2.19 3.28 1.97 0.05 97.61 0.00 0.00 0.04 97.65Jam-2 74.52 0.95 12.64 3.60 0.00 0.43 2.29 3.34 2.23 0.00 98.49 0.09 0.00 0.03 98.61Jam-2 74.36 0.40 12.70 3.84 0.17 0.42 2.36 3.72 2.03 0.00 98.83 0.03 0.00 0.02 98.88Jam-2 74.23 0.82 12.71 3.81 0.23 0.46 2.36 3.38 2.00 0.00 97.47 0.00 0.00 0.06 97.53Jam-2 74.17 0.48 12.95 3.57 0.11 0.42 2.38 3.90 2.01 0.00 98.24 0.00 0.00 0.06 98.30Jam-2 74.15 0.60 12.54 4.10 0.11 0.38 2.24 3.80 2.07 0.00 97.94 0.00 0.00 0.05 98.00Jam-2 74.15 0.59 12.63 3.82 0.12 0.41 2.47 3.88 1.94 0.00 98.91 0.10 0.00 0.03 99.04Jam-2 74.07 0.81 12.90 3.86 0.21 0.36 2.19 3.53 2.06 0.00 98.02 0.00 0.00 0.06 98.08Jam-2 73.77 0.54 12.78 3.95 0.11 0.48 2.53 3.81 2.04 0.00 98.84 0.00 0.00 0.04 98.88Jam-2 73.20 0.25 13.08 4.31 0.08 0.55 2.86 3.71 1.96 0.00 97.19 0.00 0.00 0.01 97.21Jam-2 71.84 0.99 13.08 4.71 0.05 0.66 2.77 3.95 1.95 0.00 97.14 0.02 0.00 0.09 97.24Jam-2 71.03 1.04 12.98 4.85 0.05 0.63 3.39 4.17 1.87 0.00 96.10 0.17 0.00 0.09 96.36Dom-5-M 74.48 0.92 12.90 3.89 0.11 0.17 2.31 3.31 1.92 0.00 98.29 0.00 0.00 0.00 98.29Dom-5-M 74.44 0.63 12.72 3.69 0.18 0.16 2.36 3.46 2.35 0.01 98.59 0.00 0.00 0.05 98.64Dom-5-M 74.18 0.42 13.14 4.10 0.14 0.20 2.32 3.44 2.08 0.00 98.76 0.00 0.00 0.04 98.79Dom-5-C 75.24 0.18 12.81 3.55 0.11 0.18 2.41 3.41 2.12 0.00 97.88 0.00 0.00 0.04 97.92Dom-5-C 74.65 0.49 12.50 3.83 0.15 0.17 2.59 3.39 2.21 0.00 97.96 0.15 0.00 0.03 98.14Dom-5-C 74.13 0.69 13.10 3.65 0.35 0.45 2.44 3.17 1.91 0.12 99.46 0.02 0.15 0.03 99.66Dom-5-C 74.00 0.41 13.13 4.17 0.11 0.41 2.37 3.21 2.06 0.14 99.81 0.01 0.12 0.04 99.99Dom-5-C 72.71 0.77 13.67 4.30 0.00 0.30 2.91 3.57 1.75 0.02 98.69 0.10 0.00 0.05 98.84Gram-4 75.37 0.43 12.96 3.71 0.08 0.40 2.27 2.77 2.02 0.00 97.51 0.00 0.00 0.05 97.56Gram-4 75.19 0.29 12.77 3.71 0.07 0.41 2.53 2.92 2.11 0.00 97.45 0.01 0.00 0.03 97.49

(continued overleaf )



Table 1 (Continued)


Gram-4 74.93 0.65 12.74 3.85 0.14 0.41 2.45 2.77 2.06 0.00 99.19 0.03 0.00 0.04 99.26Gram-4 74.90 0.59 12.98 3.67 0.07 0.40 2.49 2.82 2.08 0.00 98.15 0.04 0.00 0.00 98.19Gram-4 74.87 0.65 12.95 3.84 0.05 0.45 2.42 2.69 2.09 0.00 97.94 0.04 0.00 0.04 98.02Gram-4 74.17 0.47 12.96 3.64 0.08 0.42 2.40 3.89 1.97 0.00 97.81 0.04 0.00 0.05 97.90Gram-4 73.97 0.73 12.71 3.64 0.17 0.42 2.34 3.99 2.03 0.00 98.48 0.08 0.00 0.06 98.61Gram-4 73.76 0.65 13.17 4.26 0.12 0.49 2.68 2.93 1.94 0.00 97.60 0.08 0.00 0.04 97.72Gram-4 72.81 0.52 13.44 4.72 0.12 0.62 2.95 2.88 1.95 0.00 98.42 0.08 0.00 0.00 98.50Gram-4 72.67 0.67 13.01 4.20 0.18 0.69 2.76 3.92 1.90 0.00 97.99 0.00 0.00 0.07 98.06Gram-4 72.37 0.76 13.12 4.93 0.17 0.69 3.24 2.82 1.88 0.02 98.60 0.02 0.00 0.04 98.66Gram-4 71.49 0.71 13.29 5.43 0.03 0.83 3.40 3.00 1.76 0.05 97.57 0.00 0.00 0.06 97.62

DOM-6Jam-3 76.95 0.23 12.80 1.27 0.00 0.01 0.97 3.96 3.82 0.00 94.98 0.11 0.21 0.11 95.40Jam-3 76.80 0.00 12.88 1.50 0.10 0.08 0.82 4.11 3.71 0.00 94.63 0.05 0.00 0.04 94.72Jam-3 76.70 0.11 12.86 1.81 0.13 0.06 0.70 3.99 3.64 0.00 94.75 0.00 0.04 0.10 94.89Jam-3 76.68 0.30 12.38 1.69 0.26 0.03 0.79 3.94 3.93 0.00 94.61 0.04 0.00 0.10 94.75Jam-3 76.57 0.00 13.02 1.60 0.15 0.10 1.04 3.97 3.56 0.00 94.78 0.07 0.09 0.15 95.08Jam-3 76.31 0.34 12.91 1.75 0.16 0.10 0.93 4.15 3.35 0.00 94.84 0.00 0.00 0.13 94.96Dom-6-M 77.83 0.15 12.25 1.53 0.22 0.06 0.75 3.46 3.76 0.00 94.79 0.00 0.00 0.14 94.93Dom-6-M 77.31 0.00 12.71 1.48 0.00 0.04 0.80 3.91 3.76 0.00 95.18 0.02 0.00 0.12 95.32Dom-6-C 77.29 0.26 12.84 1.75 0.05 0.07 0.89 3.11 3.71 0.03 95.53 0.00 0.11 0.09 95.73Dom-6-C 76.44 0.18 13.21 1.81 0.13 0.07 0.88 3.36 3.82 0.10 96.24 0.00 0.09 0.23 96.56Dom-6-C 76.23 0.22 13.20 1.76 0.12 0.09 1.07 3.46 3.84 0.02 96.12 0.20 0.22 0.08 96.61Dom-6-C 76.20 0.18 13.03 1.77 0.18 0.04 0.83 3.65 4.00 0.10 95.96 0.09 0.08 0.18 96.31Dom-6-C 76.18 0.37 13.10 2.07 0.00 0.09 0.81 3.60 3.77 0.02 95.89 0.00 0.11 0.14 96.15Gram-5-a 75.26 0.05 13.33 1.83 0.07 0.00 1.39 3.76 4.31 0.00 95.54 0.00 0.00 0.10 95.63Gram-5-a 75.64 0.24 12.96 1.89 0.09 0.13 0.99 4.43 3.63 0.00 95.35 0.00 0.07 0.20 95.62Gram-5-a 75.99 0.16 12.86 1.92 0.06 0.07 0.91 4.26 3.76 0.00 95.86 0.00 0.00 0.13 95.99Gram-5-a 76.24 0.16 12.80 1.86 0.08 0.06 0.88 4.16 3.77 0.00 95.56 0.01 0.00 0.14 95.71Gram-5-a 76.70 0.31 12.96 1.83 0.10 0.14 0.91 3.19 3.87 0.00 95.01 0.00 0.00 0.12 95.12Gram-5-a 76.81 0.21 12.95 1.62 0.10 0.07 0.93 3.55 3.76 0.00 95.50 0.03 0.00 0.14 95.67Gram-5-a 77.05 0.26 12.47 1.40 0.02 0.02 0.69 4.16 3.93 0.00 95.13 0.00 0.00 0.18 95.31Gram-5-b 71.85 0.21 13.92 2.81 0.13 0.12 2.09 1.98 6.89 0.00 95.44 0.01 0.00 0.10 95.44Gram-5-b 75.14 0.25 12.71 1.92 0.06 0.03 1.16 1.71 7.02 0.00 96.78 0.00 0.00 0.12 96.78Gram-5-b 71.49 0.13 13.58 3.21 0.08 0.15 2.12 2.10 7.13 0.00 95.93 0.04 0.00 0.14 95.93Gram-5-b 74.13 0.07 12.95 2.11 0.19 0.03 1.30 1.57 7.65 0.00 96.38 0.00 0.00 0.08 96.45Gram-5-b 74.24 0.18 12.90 1.70 0.13 0.00 1.35 0.90 8.60 0.00 95.01 0.09 0.00 0.02 95.01

DOM-7Jam-4 73.92 0.25 14.44 2.74 0.20 0.12 1.99 4.16 2.18 0.00 97.78 0.21 0.00 0.09 98.07Jam-4 73.00 0.07 14.32 3.32 0.08 0.16 2.15 4.33 2.57 0.00 97.47 0.02 0.00 0.10 97.59Jam-4 73.69 0.36 14.34 2.76 0.00 0.10 1.93 4.03 2.79 0.00 97.33 0.00 0.00 0.00 97.33Jam-4 72.07 0.39 14.33 3.78 0.08 0.21 2.71 4.18 2.26 0.00 96.41 0.00 0.00 0.09 96.50Jam-4 73.78 0.32 14.00 2.95 0.09 0.06 2.00 4.31 2.49 0.00 96.36 0.00 0.00 0.11 96.47Dom-7-C 73.04 0.28 14.60 2.95 0.08 0.09 2.04 4.38 2.49 0.06 97.78 0.00 0.11 0.07 97.96Dom-7-C 73.51 0.12 14.53 2.99 0.03 0.12 2.06 4.16 2.43 0.05 97.18 0.00 0.23 0.12 97.53Dom-7-M 72.34 0.10 14.57 3.02 0.10 0.15 2.11 5.08 2.53 0.00 98.21 0.00 0.21 0.08 98.50Dom-7-M 72.85 0.26 14.29 2.72 0.09 0.11 2.18 4.92 2.59 0.00 97.76 0.08 0.15 0.08 98.06Dom-7-M 72.74 0.17 14.52 2.98 0.07 0.11 2.14 4.70 2.57 0.00 97.69 0.02 0.26 0.11 98.08Dom-7-M 72.98 0.23 14.45 2.74 0.09 0.11 2.18 4.47 2.74 0.00 97.46 0.01 0.08 0.11 97.66Dom-7-M 72.39 0.23 14.61 2.83 0.09 0.11 2.01 5.18 2.55 0.00 97.31 0.01 0.17 0.11 97.60Jam-4 71.96 0.36 14.88 3.82 0.00 0.15 2.38 4.13 2.31 0.00 95.44 0.14 0.00 0.04 95.62Jam-4 69.79 0.40 15.08 4.86 0.08 0.29 3.11 4.20 2.20 0.00 95.66 0.00 0.00 0.12 95.78Jam-4 69.48 0.25 15.51 5.07 0.12 0.34 2.99 3.93 2.30 0.00 95.74 0.10 0.00 0.09 95.93Jam-4 68.78 0.04 15.65 5.32 0.23 0.31 3.26 4.14 2.27 0.01 96.05 0.00 0.00 0.01 96.07Jam-4 68.65 0.39 15.03 5.66 0.29 0.28 3.39 4.16 2.15 0.00 95.94 0.00 0.00 0.11 96.05Dom-7-C 69.72 0.35 15.32 4.77 0.09 0.27 3.10 4.26 2.08 0.04 97.65 0.04 0.21 0.11 98.01Dom-7-C 69.44 0.37 15.37 4.86 0.14 0.25 2.90 4.33 2.26 0.07 97.92 0.04 0.19 0.09 98.24Dom-7-C 69.35 0.38 15.11 4.67 0.13 0.36 3.16 4.56 2.17 0.09 98.93 0.18 0.05 99.17Dom-7-C 69.29 0.41 15.11 4.54 0.22 0.34 3.33 4.52 2.13 0.10 98.96 0.16 0.02 99.14Dom-7-M 68.65 0.54 14.86 5.01 0.18 0.34 3.52 4.65 2.24 0.00 97.67 0.05 0.17 0.07 97.95Dom-7-M 68.42 0.47 15.47 5.23 0.13 0.34 2.98 4.82 2.14 0.00 98.51 0.05 0.22 0.08 98.85Dom-7-M 68.36 0.63 15.04 5.02 0.23 0.34 3.37 4.87 2.13 0.00 97.99 0.04 0.18 0.09 98.29



Table 1 (Continued)


DOM-8Dom-8 74.29 0.00 13.99 2.47 0.11 0.00 2.12 4.33 2.64 0.05 95.47 0.09 0.00 0.00 95.56Dom-8 74.09 0.25 13.91 2.92 0.20 0.03 1.77 4.53 2.29 0.00 95.34 0.00 0.00 0.01 95.35Dom-8 73.84 0.00 14.54 2.81 0.20 0.04 1.85 4.30 2.41 0.00 95.72 0.03 0.00 0.02 95.77Dom-8 73.79 0.07 14.51 3.08 0.11 0.03 1.87 4.08 2.47 0.00 98.00 0.00 0.00 0.14 98.13Dom-8 73.76 0.29 14.15 2.84 0.02 0.01 2.09 4.48 2.36 0.00 96.71 0.05 0.00 0.09 96.86Dom-8 73.71 0.14 14.17 2.88 0.00 0.07 2.11 4.26 2.65 0.00 97.12 0.00 0.00 0.08 97.20Dom-8 73.68 0.00 14.03 2.97 0.25 0.01 1.92 4.57 2.58 0.00 96.66 0.00 0.00 0.00 96.66Dom-8 73.55 0.00 14.54 2.79 0.16 0.04 1.99 4.43 2.49 0.00 96.46 0.16 0.00 0.09 96.70Dom-8 73.35 0.51 14.11 3.23 0.14 0.01 1.95 4.34 2.36 0.00 95.39 0.10 0.00 0.14 95.63Dom-8 73.12 0.00 14.37 2.86 0.29 0.05 2.21 4.47 2.63 0.00 97.31 0.00 0.00 0.12 97.44Dom-8 73.09 0.49 14.56 2.97 0.26 0.09 1.95 4.18 2.43 0.00 98.73 0.03 0.00 0.12 98.88Dom-8 73.02 0.36 14.47 3.08 0.00 0.00 2.08 4.33 2.66 0.00 96.65 0.00 0.00 0.09 96.73Dom-8 72.78 0.14 14.64 3.38 0.09 0.07 2.22 4.27 2.41 0.00 98.07 0.02 0.00 0.06 98.14Dom-8 69.98 0.00 15.36 4.78 0.00 0.11 3.13 4.25 2.36 0.01 96.83 0.00 0.00 0.08 96.91Dom-8 69.64 0.14 14.91 5.01 0.25 0.09 3.38 4.45 2.05 0.07 96.10 0.14 0.00 0.15 96.39Dom-8 69.19 0.35 15.41 5.16 0.43 0.10 3.05 4.42 1.90 0.00 97.94 0.03 0.00 0.12 98.09Dom-8 68.88 0.18 15.17 5.33 0.15 0.11 3.40 4.60 2.18 0.00 96.19 0.05 0.00 0.08 96.32Dom-8 68.85 0.33 14.79 5.67 0.03 0.12 3.32 4.40 2.49 0.00 95.51 0.07 0.00 0.17 95.75Dom-8 67.78 0.57 15.32 5.89 0.09 0.13 3.72 4.35 2.14 0.00 97.25 0.26 0.00 0.13 97.64

DOM-9Jam-5 76.44 0.00 12.89 1.98 0.20 0.02 1.30 4.15 3.01 0.00 95.32 0.00 0.21 0.01 95.54Jam-5 76.34 0.07 13.11 1.91 0.17 0.05 1.45 4.19 2.71 0.00 95.07 0.05 0.00 0.14 95.26Jam-5 76.23 0.00 13.50 1.75 0.18 0.02 1.43 4.21 2.68 0.00 95.21 0.00 0.00 0.11 95.31Jam-5 76.18 0.15 13.08 1.83 0.27 0.02 1.45 4.26 2.77 0.00 95.52 0.05 0.19 0.07 95.83Jam-5 76.02 0.19 13.32 1.85 0.13 0.00 1.49 4.40 2.60 0.00 95.41 0.00 0.00 0.13 95.53Jam-5 75.92 0.00 13.69 1.60 0.28 0.06 1.26 4.18 3.00 0.00 94.90 0.15 0.00 0.06 95.10Jam-5 75.44 0.30 13.54 1.75 0.11 0.04 1.49 4.57 2.75 0.00 96.53 0.11 0.14 0.07 96.84Dom-9 M 75.97 0.07 13.12 2.04 0.05 0.00 1.42 4.55 2.79 0.00 96.31 0.10 0.10 0.00 96.52Dom-9 M 75.89 0.18 13.28 2.05 0.03 0.00 1.43 4.43 2.72 0.00 95.98 0.00 0.13 0.08 96.18Dom-9 M 75.83 0.15 13.26 1.97 0.06 0.00 1.40 4.47 2.85 0.00 95.73 0.03 0.00 0.10 95.87Dom-9 C 76.21 0.26 13.68 2.24 0.00 0.05 1.50 3.45 2.58 0.01 95.42 0.00 0.21 0.06 95.69Dom-9 C 76.09 0.25 13.34 2.13 0.00 0.00 1.35 3.84 2.99 0.00 97.70 0.00 0.13 0.13 97.96Dom-9 C 75.92 0.51 13.52 2.04 0.12 0.00 1.24 3.88 2.70 0.08 96.77 0.00 0.28 0.15 97.20Dom-9 C 75.81 0.33 13.47 2.21 0.18 0.00 1.43 3.88 2.70 0.00 97.20 0.02 0.34 0.00 97.55Dom-9 C 75.75 0.33 13.80 2.17 0.13 0.00 1.44 3.70 2.60 0.08 96.14 0.00 0.25 0.02 96.41Jam-5 73.16 0.30 13.91 3.03 0.16 0.08 2.22 4.51 2.64 0.00 96.25 0.09 0.04 0.07 96.44Jam-5 73.45 0.00 14.45 2.80 0.06 0.04 1.91 4.70 2.59 0.00 95.44 0.20 0.00 0.06 95.69

JAM-6Jam-6 72.00 0.13 14.66 2.01 0.03 0.13 0.77 5.50 4.79 0.00 97.20 0.04 0.29 0.19 97.70Jam-6 71.97 0.07 14.57 2.17 0.10 0.18 0.81 5.50 4.64 0.00 98.90 0.00 0.24 0.19 99.33Jam-6 71.95 0.36 14.48 2.17 0.10 0.18 0.73 5.38 4.64 0.00 97.02 0.01 0.16 0.23 97.42Jam-6 71.89 0.25 14.61 2.14 0.00 0.20 0.67 5.60 4.66 0.00 97.27 0.03 0.26 0.22 97.78Jam-6 71.78 0.23 14.29 2.18 0.16 0.16 0.73 5.68 4.78 0.00 97.48 0.00 0.29 0.25 98.01Jam-6 71.71 0.19 14.60 2.31 0.06 0.22 0.84 5.63 4.44 0.00 97.08 0.02 0.31 0.17 97.58Jam-6 71.63 0.26 14.66 2.28 0.07 0.20 0.77 5.62 4.51 0.00 98.03 0.01 0.27 0.18 98.49Jam-6 71.61 0.32 14.81 2.14 0.09 0.19 0.79 5.53 4.53 0.00 97.18 0.04 0.34 0.25 97.80Jam-6 71.27 0.36 14.65 2.14 0.06 0.25 0.94 5.79 4.54 0.00 97.60 0.00 0.30 0.24 98.14Jam-6 70.97 0.32 15.09 2.13 0.05 0.25 0.97 5.69 4.55 0.00 97.18 0.05 0.25 0.23 97.71Jam-6 70.91 0.29 14.88 2.54 0.00 0.26 0.99 5.65 4.48 0.00 97.11 0.06 0.18 0.27 97.62Gram-7 72.78 0.35 14.13 2.21 0.06 0.12 0.66 5.08 4.62 0.00 95.04 0.08 0.00 0.27 95.39Gram-7 72.68 0.10 14.19 2.25 0.11 0.14 0.64 5.12 4.78 0.00 95.06 0.00 0.00 0.18 95.24Gram-7 72.67 0.13 14.15 2.16 0.03 0.17 0.76 5.27 4.67 0.00 96.98 0.00 0.00 0.23 97.20Gram-7 72.66 0.10 14.17 2.25 0.12 0.15 0.68 5.32 4.55 0.00 96.91 0.00 0.00 0.18 97.08Gram-7 72.20 0.06 14.27 2.34 0.09 0.20 0.93 5.27 4.64 0.00 96.46 0.00 0.06 0.28 96.79Gram-7 72.14 0.11 14.41 2.36 0.00 0.25 0.93 5.39 4.41 0.00 95.86 0.00 0.08 0.19 96.12Gram-7 71.93 0.22 14.47 2.62 0.07 0.23 0.83 5.15 4.47 0.00 95.16 0.00 0.00 0.27 95.43Gram-7 71.72 0.43 14.69 2.52 0.00 0.24 1.07 4.83 4.49 0.00 97.02 0.20 0.05 0.20 97.47Gram-7 71.65 0.26 14.45 2.53 0.05 0.21 0.96 5.35 4.55 0.00 98.54 0.05 0.02 0.25 98.85Gram-7 71.56 0.44 14.77 2.32 0.00 0.30 0.98 5.15 4.49 0.00 95.02 0.00 0.29 0.27 95.57

(continued overleaf )



Table 1 (Continued)


JAM-7Gram-8 76.92 0.18 12.96 1.85 0.05 0.06 1.32 3.86 2.80 0.00 94.53 0.09 0.00 0.16 94.77Jam-7 76.34 0.08 13.16 1.76 0.18 0.04 1.43 4.17 2.85 0.00 94.12 0.03 0.24 0.10 94.48Jam-7 76.75 0.23 12.77 1.64 0.12 0.02 1.27 4.27 2.93 0.00 94.20 0.00 0.14 0.07 94.41Jam-7 76.44 0.06 13.18 1.67 0.15 0.03 1.30 4.32 2.86 0.00 94.48 0.00 0.24 0.10 94.82Jam-7 76.66 0.15 13.07 1.56 0.18 0.02 1.29 4.28 2.79 0.00 94.86 0.03 0.17 0.05 95.11Jam-7 76.55 0.22 12.99 1.63 0.02 0.03 1.31 4.29 2.95 0.00 95.24 0.01 0.21 0.07 95.52Jam-7 75.93 0.09 13.65 1.31 0.07 0.01 1.58 4.69 2.68 0.00 95.37 0.01 0.28 0.07 95.72Jam-7 70.49 0.52 14.74 4.79 0.41 0.24 2.80 3.76 2.24 0.00 96.52 0.06 0.01 0.03 96.62Jam-7 70.49 0.69 14.45 4.54 0.23 0.27 3.13 3.75 2.45 0.00 96.53 0.06 0.15 0.06 96.81Jam-7 70.87 0.29 14.44 4.40 0.15 0.22 2.98 4.26 2.38 0.00 96.71 0.00 0.25 0.07 97.03Jam-7 70.32 0.38 14.36 4.76 0.33 0.30 2.90 4.31 2.34 0.00 96.83 0.00 0.25 0.04 97.12Jam-7 70.01 0.39 14.35 4.86 0.27 0.26 2.93 4.55 2.38 0.00 97.23 0.07 0.25 0.07 97.61Gram-8 70.61 0.42 14.12 5.16 0.12 0.25 2.95 4.24 2.12 0.00 97.35 0.03 0.00 0.14 97.52Gram-8 71.07 0.46 14.27 4.56 0.09 0.27 2.78 4.28 2.21 0.00 97.77 0.00 0.00 0.06 97.83Gram-8 70.61 0.23 14.23 4.69 0.04 0.27 2.81 4.23 2.89 0.00 98.00 0.00 0.00 0.07 98.08

low FeO (1.6 ± 0.2 wt%) and TiO2 contents (0.2 ± 0.1 wt%)(Fig. 5).

JAM-8 (Jam-8)

The oldest tephra horizon in the Holocene sequence occursin Jardelunde bog (Jam-8 at 270–274 cm); the chemicalcomposition of the glass shards is unknown.

Discussion

Holocene volcanoes that could represent potential sourcesof the ash layers in northern Germany are located at about2100 km distance in the North Atlantic region (Iceland, JanMayen), 400 to 2200 km in central and southern Europe(Eifel, Massif Central, Campanian and Aeolian Islands, Etna,Aegean Arc), about 3300 km in the eastern North Atlantic(Azores, Canary Islands), and beyond. However, the chemicalcomposition of the glass shards and age range of the ashlayers indicate that the northern Germany ash horizons arederived exclusively from Icelandic sources (Fig. 5). Here,highly differentiated magmas have been erupted frequentlyduring the Holocene, magmas with rhyolitic composition andlow alkali contents being derived from central volcanoes inthe rift systems (Hekla, Askja and Krafla, among others) andrhyolitic magmas with high alkali concentrations being knownfrom off-rift volcanoes (e.g. Eyjafallajokull, Snaefellsjokull;Imsland, 1978; Jakobsson, 1979; Oskarsson et al., 1985).Other Holocene volcanic centres in Europe, such as JanMayen, the Eifel, the French Massif Central, the Italian volcanicfields and the Aegean arc, the Canaries and Azores can besafely excluded because of their significantly different magmacompositions (Figs 5 and 8). Rhyolitic tephra deposits fromeven more distant Holocene volcanic sources in the NorthernHemisphere (e.g. Aleutians, Kamchatka and Cascades) would,in part, be difficult to distinguish compositionally, but wouldrequire transport distances in excess of 7000 km, and arethus considered unlikely sources of the ash layers in northernGermany.

Based on their distinct chemical composition, we correlateindividual tephra layers in northern Germany to single eruptive

events in Iceland and tephra marker horizons in the NorthAtlantic region. Approximate radiocarbon ages of the tephralayers are based on the correlation to well-dated tephra markers(in brackets [. . .]), or inferred from 14C-dated organic sedimentsof the cored peat (in parentheses (. . .)) (Bogaard et al., 1994;Dorfler, 1998).

GRAM-1 (<150 yr BP) [Askja AD 1875]

In this time interval, two ash clouds derived from Icelandicvolcanoes have been reported over northern Europe: the ashcloud of the Askja 1875 and the ash of the Hekla 1947 eruption(Mohn, 1878; Salmi, 1948; Thorarinsson, 1954). Whereasthe Hekla magma is of dacitic and andesitic composition(Thorarinsson, 1967; Thorarinsson and Sigvaldason, 1972),and thus cannot be the source of the young ash event in theGrambow bog, the magma erupted during the Askja 1875event, a mixture of basaltic and subalkaline rhyolitic magma(Sigurdson and Sparks, 1978; Sigvaldason, 1979; Sparks et al.,1981; MacDonald et al., 1987) could be the source for GRAM-1 tephra. The GRAM-1 glass shards chemically resemble therhyolitic glass shards of Askja 1875, except for the lowerFeO contents of Gram-1 glass shards. The greenish glassshards could represent the basaltic fraction of the zonedAskja eruption. Strengthening the correlation are Askja tephraoccurrences in Scandinavia (i.e. Persson, 1971; Oldfield et al.,1997) and is the documented path of the Askja 1875 ash cloud,which moved eastward from Iceland towards Scandinavia andthen turned south over Sweden (Mohn, 1878; Thorarinsson,1954). Extrapolating the path of the ash cloud based on theAskja 1875 tephra isochron map (Mohn, 1878) shows that asouthward moving cloud could have passed Grambow bog,but may have missed the more westerly sites Dosenmoorand Grambow. An unambiguous correlation needs furtherchemical analyses, however.

DOM-2 (ca.1000 yr BP) [Sluggan Tephra, AD860 ± 20]

The glass composition indicates an Icelandic origin, whererhyolitic magmas with high potassium contents are known



from the older (>6000 ka) eruptions in the Krafla systemand from the AD 1724 Viti Eruption (Thoroddsen, 1907–15;Saemundsson, 1991). However, at the time of the DOM-2deposition no rhyolitic eruption is known to have occurred inthe Krafla system. A silicic tephra layer called ‘landnam lag’ or‘Settlement layer VII’ is reported from the Vatnaoldur eruptionca. AD 900 in the Torfajokull system (Thorarinsson, 1944;Larsen, 1984; Haflidason et al., 1992; AD 871 ± 2: Gronvoldet al., 1995; Larsen et al., 1999). Moreover, a small volumeof dacitic ash was erupted during the Eldgja eruption of AD

936 in an explosive event (Larsen, 1993). Distal tephra layersrepresenting both events, the Eldgja eruption AD 938 and theLandnam event AD 871 ± 2, are recorded in the Greenland ice-cores (Gronvold et al., 1995; Zielinski et al., 1995; Zielinskiet al., 1997). However, neither the Landnam tephra nor theEldgja tephra can be correlated with tephra DOM-2, based onthe chemical composition of the glass shards (Fig. 6).

Tephra horizons dated to AD 1000 are reported fromSwedish bogs (Person, 1971). The ash has not been chemicallycharacterised; a correlation with the Hekla AD 1104 ash fallwas assumed, however (Person, 1971). An Icelandic tephralayer of similar age is detected in Irish bogs (Sluggan Tephra).It consists of a distinct rhyolitic glass population with low SiO2

and medium K2O contents (Sluggan B). At Sluggan bog thistephra contains a second glass shard population with higherSiO2 and K2O contents (Sluggan A) (Pilcher et al., 1995; Pilcherand Hall, in press).

The composition of the DOM-2 glass shards agrees well thecomposition of the Sluggan B population only. The age of theSluggan tephra has been determined, calibration by wigglematch dating showed deposition at AD 776–887 (Pilcher et al.,1996). Age and glass shard compositions indicate that tephraDOM-2 was deposited from the same eruption event as tephraSluggan B. Showing a wide dispersal, this tephra layer is amajor marker horizon in the North Atlantic region. The lackof Sluggan A components in DOM-2 tephra may reflect thesmaller magnitude, more limited dispersal and/or differingash cloud transport during the Sluggan B eruption and/or thegreater distance of the northern Germany bogs from Iceland.

DOM-3 (ca. 1300 yr BP) and DOM-4 (ca. 1550 yrBP)

These two minor ash layers occur in the Dosenmoor coresonly. Their composition is typically Icelandic, but no eruptionfrom this time interval with this magma composition has beendescribed in the literature. Amount of shards and descriptivecriteria do not make these tephra layers tephra isochrons. Theiroccurrence indicates as yet unknown volcanic eruptions onIceland.

DOM-5 (ca. 2200 yr BP) [Glen Garry Tephra,ca. 2100 yr BP]

The tephra DOM-5 is an unambiguous marker horizon inall three bog sections studied. The composition of the tephrapoints towards Iceland, but a Holocene volcanic system thaterupted rhyolitic magma with potassium contents <2 wt% isso far unknown to our knowledge.

A tephra layer with an age of ca. 2100 yr BP has beendescribed in peat from Scotland and northern England(Dugmore et al., 1995b; Pilcher and Hall, 1996). This so-called‘Glen Garry tephra’ has glass shards that are predominantly

Laacher See Tephra

French MassifCentral

55 60 65 70 75

4

6

8

10

12

14

DACITEANDESITE RHYOLITE

Iceland

SiO2 wt.%

Na 2

O +

K2O

wt.%

Hekla

DOM-4

DOM-7

DOM-5

DOM-2

DOM-9JAM-7

JAM-6

DOM-6

Italy

JanMayen

(a)

SiO2 (wt.%)

3

5

K2O

(w

t.%)

SHO

HKSA

MKSA

64 68 72 76

JAM-6

JAM-7

DOM-5

DOM-2DOM-6

(c)

SiO2 wt.%

Na 2

O +

K2O

wt.%

(II)Askja

Kerlingarfjö

ll

Torfaj

ökull

Snaefellsjöku

ll

Öra

efajökull

Hekla6

8

10

55 6050 65 70 75

JAM-6

DOM-5

DOM-2

DOM-7(I)

(II)

DOM-9

JAM-7

DOM-6

(b)

Tephra/EventGlen Garry (a) Sluggan A+B (b) Torfajökull (d)

T-92Kebister (a)Hoy/Scotland (a)Lairg B/Scotland (a)

Microlite (c)Lairg B/Irland (b)Lairg A (b)

Eyjafjallajökull

Figure 5 Comparison of composition of northern German tephralayers with that of Late Quaternary to Holocene volcanic eruptions innorthern Europe. (a) Late-glacial to Holocene magma compositionsfrom Iceland (Jacobcson, 1979), Jan Mayen (Imsland, 1984), FrenchMassif Central (modified from Juvigne, 1993), Italian volcanic fields(Paterne et al., 1988; Orsi et al., 1992; Narzisi, 1996) and fromLaacher See (Bogaard, 1983). Hekla fields comprise the glass shardcomposition of major known Plinian eruptions of Hekla (H1, H3, H4,H5; Bogaard, 1997). (b) Hatched fields show the composition ofsilicic to intermediate rocks in the alkaline off-rift zone (I) and thesubalkaline rift zone (II) (modified from Imsland, 1978). (c) SiO2 –K2Odiagram showing the composition of tephra layers in Scotland (a:Dugmore et al., 1995a), Ireland (b: Pilcher et al., 1996; c: Pilcher andHall, in press) and tephra layers from Iceland (d: O’Nions andGronvold, in Oskarson et al., 1982). The fields representcompositions of northern Germany tephra layers as in Fig. 4



40

60

80

20

60 804020

K2O

FeOCaO

80

60

40

20

= Landnam ash, Vö 870AD (1)= Eldgja 938 AD (2)= Hekla 1104 AD= Hekla 1158 AD (3)= Öraefajokull 1362 AD= Hekla 1510 AD (4)= Viti 1724 AD (5)= Eyjafallajökull 1821 AD (4)= Askja 1875 AD= Hekla 1947AD (6)

ABCDEFGHIJ

DOM-2Sluggan-ASluggan-B

A

B C

D

E

F

G

H

I

J

DOM-2

Figure 6 Composition of rhyolitic and dacitic historic (≥AD 900) tephra layers on Iceland compared with northern Germany tephra DOM-2 andthe Irish Sluggan tephra. Data for Sluggan tephra from Pilcher et al. (1995). (1: Gronvold et al., 1995; 2: Zielinski et al., 1995; 3: Annertz et al.,1985; 4: Larsen et al., 1999; 5: Jonasson, 1994; 6: Sigmarsson et al., 1992.)

silicic, with a subordinate intermediate population, the SiO2

contents ranging from 75 to 62 wt%. The compositional rangeof DOM-5 tephra is similar to Glen Garry tephra (Fig. 5), withdacitic clasts probably being present in low quantities (fewbrownish shards).

DOM-6 (ca. 2700 yr BP) [Microlite Tephra,730–664 cal. BC]

The microlite tephra layer has been AMS 14C dated to730–664 cal. BC (Bogaard et al., submitted). Explosive erup-tions of this age are known on Iceland from the Hekla (H-X,H-Y and H-Z) and Katla volcanoes. However, Hekla H-X, H-Yand H-Z erupted dacitic magmas (Larsen and Vilmundardottir,1992) and tephra from the Katla System (i.e. UN 2660 ± 50 yrBP) has lower SiO2 (ca. 65%), higher FeO (ca. 6%) and lowerTiO2 (ca. 1.4%) contents (Zielinski et al., 1995, Larsen et al.,2001). A volcanic event that erupted magmas with the com-position of the microlite tephra is unknown on Iceland. Inthe North Atlantic region a tephra layer with this age andchemical composition has been detected recently at Irish sites(Pilcher and Hall, in press). This tephra consists of glass shardswith a wider range of geochemical compositions (Fig. 5c), butits glass shards contain microlite crystals such as describedhere from DOM-6. The distinct chemical composition and thepetrological features make the ‘microlite tephra’ a valuableEuropean marker horizon.

DOM-7 (ca. 3000 yr BP) [Hekla 3 tephra,2879 ± 34 yr BP]

Tephra DOM-7 is the most prominent tephra layer in theJardelunder and Dosenmoor bog. The range in chemical

composition of the glass shards either could result from differ-ent eruptions occurring within a short time interval or reflectan eruption from a compositionally zoned magma column.A strongly chemically zoned magma was erupted during theHekla 3 event on Iceland. During the initial Plinian phase ofthis compositionally zoned eruption, magma of rhyolitic com-position was discharged in high eruption columns, followed bydacitic to andesitic magma compositions (and lower eruptioncolumns) during a terminal stage (Fig. 5; Larsen and Thorarins-son, 1977; Annertz et al., 1985). The DOM-7 tephra is, basedon its chemical composition and age, interpreted to representpart of the Hekla 3 eruption. The DOM-7 tephra consists ofglass shards of the highly differentiated Plinian eruptive phase(HDP) (Fig. 7; Bogaard et al., 1994). The age of the Hekla 3eruption has been constrained to 2879 ± 34 yr BP by radiocar-bon dating (Dugmore et al., 1995b), and 1087–1006 cal. BC

by AMS 14C probability combination (Bogaard et al., sub-mitted). Hekla 3 tephra occurs in Scandinavian deposits,based on the age of ash layers (Persson, 1971; Snowballet al., 2000) and has been found in one Irish bog (Plun-kett, 1999). It so far has not been identified in England orScotland.

DOM-8 (ca. 3200 yr BP) [Hekla Selsund Tephra,3500 yr BP]

Tephra DOM-8 is nearly identical in composition to tephraDOM-7 (Hekla 3) (Fig. 8). It is well known that magmaserupted in the Hekla system chemically resemble each other,suggesting that DOM-8 also may be derived from the Heklasystem. Chemical analyses of glass shards from the Plinianeruption ’Hekla Selsund’ on Iceland (also known as Hekla2; 3500 yr BP; Larsen and Thorarinsson, 1977), show acompositional range identical to glass shards from Hekla 3



FeO [wt.-%]

CaO [wt.-%]1 2 3

0.1

0

0.2

0.3

0.4

MgO

[wt-

%]

Hekla 4

Hekla 3

2 3 4 5

0.2

0

0.4

0.6

0.8

Ash layers in northern Germany

DOM-9

DOM-7

1 2 3

0.1

0

0.2

0.3

0.4

DOM-9

DOM-7

2 3 4 5

0.2

0

0.4

0.6

TiO

2 [w

t-%

]

Hekla 4

Hekla 3

0.8

Near-vent tephra in Iceland

HDP CIP

HDP CIP

Figure 7 Compositions of glass shards analysed from proximal Hekla 4 and Hekla 3 deposits compared with the glass shard compositions oftephra DOM-7 and DOM-9. HDP, highly differentiated Plinian eruptive phases; CIP, compositionally intermediate Plinian eruptive phases

0.6

0.2

TiO

2 [w

t.%]

2 3 4 5 6

FeO [wt.%]

2

3

64 68 72 76

KebisterSchwedenSchottland

DOM-8 Minoan ashHekla-Selsund

K2O

[w

t.%]

SiO2 [wt.%]

Figure 8 Tephra DOM-8 glass shard composition compared withglass shard composition of the Minoan ash (Federmann and Carey,1980; Vitaliano et al., 1990; Guichard et al., 1993), of Hekla Selsundtephra (KAL-X; Dugmore et al., 1992) on Iceland and of Kebistertephra in Scotland and Sweden (Dugmore et al., 1995a; Boygle,1998)

Plinian deposits (Sigmarsson et al., 1992; Tephra KAL-X inDugmore et al., 1992; G. Larsen, personal communication1998).

At about the same time, the Minoan eruption (Santorini)produced a widespread ash layer in the Aegean region.The Minoan eruption, however, dated to 1620 BC based ona correlation of major acidity peaks in the Greenland ice-cores (Zielinski and Germani, 1998), can be excluded as thesource of the DOM-8 tephra. Glass shards of the Minoanash have higher K2O, and lower FeO and CaO contents.Moreover, Dom-8 tephra is chemically zoned, whereas tephraof the Minoan eruption is described as homogeneous (e.g.Federmann and Carey, 1980; Keller 1981; Guichard et al.,1993, Vitaliano et al., 1990).

Owing to the chemical similarity and its relative age, wetentatively interpret the DOM-8 tephra to represent the distalpart of the Hekla Selsund ash blanket.

Tephra layers with identical composition and age toDom-8 tephra are known from Kebister, northeast Scotland(Kebister tephra; Dugmore et al. 1995a), from the FaroeIslands (Dugmore and Newton, 1998) and from the westerncoast of Sweden (Boygle, 1998). For the Kebister tephra, aslightly older 14C age (3600 yr BP) than Dom-8/Selsund tephra(3200/3500 yr BP) has been determined, however. This couldindicate (i) another, so far unknown, eruption of Hekla volcanowith exactly the same compositional variation as seen in HeklaSelsund and Hekla 3 eruptive deposits, undetected in near-ventsections on Iceland, or (ii) imprecise ages for the tephra layers,both being estimated from local bog stratigraphies. Based onthe glass shard compositions, we here tentatively correlate theDOM-8 and Kebister Tephra layers with the Hekla Selsunderuptive event.



DOM-9 (ca. 3700 yr BP) [Hekla 4 Tephra,3826 ± 12 yr BP]

The composition of the DOM-9 tephra is typical for the magmaerupted from a chemically zoned magma chamber during theHekla 4 event. When compared with the composition ofnear-vent deposits of Hekla 4, which range from rhyolite toandesite, DOM-9 tephra shows the characteristic compositionof only the most evolved Plinian eruptive phases of the Hekla4 event (Fig. 7). Less evolved magma of the eruption maybe reflected in single more mafic glass shards in tephrahorizon Jam-5. The tephra horizons Dom-9 and Jam-5 areinterpreted to represent part of the Hekla 4 tephra blanket.The Hekla 4 eruption thus produced the most widespreadtephra layer in the North Atlantic region, so far detectedin Scottish, British, Irish and Swedish bogs (Persson, 1971;Pilcher et al., 1995; Dugmore, 1989; Pilcher and Hall, 1996;Dwyer and Mitchell, 1997). The Hekla 4 eruption is datedto 3826 ± 12 yr BP by radiocarbon dating (Dugmore et al.,1995b), the calibrated radiocarbon age, achieved by wigglematching, being 2395–2279 BC (Pilcher et al., 1996).

JAM-6 (ca. 5600 yr BP) [Lairg B Tephra,5811 ± 20 yr BP]

The chemical composition of JAM-6 indicates an eruption froman alkaline rhyolitic Icelandic eruption centre, e.g. Torfajokull(there are no data published from explosive events fromSnaefellsjokull or Eyjafjallajokull). The chemical compositionof JAM-6 tephra differs from Pleistocene eruptions fromTorfajokull system, but is nearly identical to the compositionof 75 000-yr-old Hrafni tinnusker rhyolite (McGarvie et al.,1990). This similarity points towards a source of JAM-6 tephrain the Torfajokull system, where peralkaline magmas wereerupted until the Late Pleistocene, when the erupting magmasshifted to subalkaline compositions (Imsland, 1978; McGarvie,1984; MacDonald et al., 1990; McGarvie et al., 1990). Sincethen, 12 single eruptions are known, each producing rhyoliticlava flows and domes of less than 1 km3 magma volume.

In Torfajokull, no major explosive eruption is known thatcould have produced a widespread tephra layer. However,approximately 7 km northwest of Hekla volcano, a tephra layer3–4 cm thick occurs above Hekla-3 deposits (T-92; Bogaard,1997), its glass shards having an identical composition to JAM-6 glass shards. Owing to the stratigraphical position of thetephra layers, these two cannot belong to the same eruption,but very likely resulted from the same volcanic system.Evidently, rhyolitic magma with this chemical compositionalso has been erupted at least twice on Iceland during theHolocene.

In Irish and Scottish bogs, a distinctive tephra layer calledLairg Tephra occurs stratigraphically below the Hekla 4 tephra.The Lairg Tephra comprises two compositionally differentglass shard populations (Lairg A and B), similar to themuch younger Sluggan Tephra (DOM-2), and is interpretedto represent a mixture of ash material from two distincteruptions that followed each other closely (Dugmore et al.,1995a; Pilcher et al., 1995). At several Irish sites, the LairgTephras are separated by 10–15 cm tephra-free peat (Pilcherand Hall, in press). Tephra layer JAM-6 shows the samechemical composition as Lairg B, and a younger tephra called’Hoy’ in Scotland (Dugmore et al., 1995a), both consisting ofglass shards with typical high potassium contents (Fig. 5c).Lairg B Tephra has a wiggle match calibrated age rangeof 4774–4677 cal. BC (Pilcher et al., 1996). Based on the

chemical characteristics and age, we correlate tephra JAM-6 with Lairg B and interpret it as the deposit from a yetunknown event in the Torfajokull volcanic system.

JAM-7 (ca. 5800 yr BP) [Hekla 5 Tephra,6036 ± 20 yr BP]

The stratigraphical position of tephra layer JAM-7, belowthe compositionally unique tephra JAM-6, unambiguouslyidentifies JAM-7 as a deposit from an older eruptive event.The chemical composition of the glass shards shows thetephra to represent the ash from a Plinian explosive eruptionof Hekla. A major Hekla eruption known from this time isHekla 5 (ca. 6100 yr BP; Larsen and Thorarinsson, 1977). Thenear-vent deposits from this eruption have the same chemicalzonation as Hekla 4 deposits, and are identical to the chemicalcomposition of JAM-7 glass shards.

In Irish and Scottish bogs, the Lairg A tephra glass shards(see above; Dugmore et al., 1995; Pilcher et al., 1995) havethe same composition as shards of tephra JAM-7. Chemicallyless evolved glass shards that occur in the JAM-7 tephra innorthern Germany have not been described from British bogs.The wiggle match calibrated age range of Lairg A tephra is4997–4902 cal. BC (Pilcher et al., 1996).

Tephra JAM-7 is correlated with Lairg A tephra, based onthe chemical composition of the glass shards, and interpretedas part of the Hekla 5 fallout fan.

Conclusions

Detailed laboratory studies of microtephra particles in threeHolocene peatbog sections in northern Germany reveal thepresence of an unexpectedly large number of volcanic ashhorizons in strata previously thought to be free of tephramarkers. Because the concentrations and amounts of glassshards are low, the tephra layers are visible only in thin-sections of enriched mineral residues of the peat samples.

Correlation of the tephra horizons between sites, based onthe petrographic composition and chemical fingerprints ofthe glass shard populations, indicates the 37 ash horizons torepresent 16 individual tephra layers (or eruption events), twoof which can be identified by their age and characteristic glassshard morphology (pumice tephra DOM-2) or petrography(microlite tephra DOM-6) alone. Two types of tephra markersare distinguished from each other: (i) major marker horizons,which occur in almost all bogs and contain abundant glassshards, and (ii) minor tephra events comprising ash horizonsthat are detected only at single sites and are represented byonly few glass shards and few glass shard analyses. The latterhorizons do not sufficiently describe a tephra layer, althoughthe analyses provide valuable information on the occurrenceof a tephra event. In this sense, at least four major tephra layershave been detected that occur at each site, along with up tothree tephra layers that occur only at two sites and nine minortephra events that are recorded at single sites only. All tephralayers identified were deposited during the past 8000 yr.

Significant differences in the local tephra records areobserved along the 170 km transect from the Danish border(JAM) to Mecklenburg-Vorpommern (GRAM). In two Dosen-moor cores, an almost identical tephra record was recovered,where only few horizons did not allow a correlation based ongeochemical fingerprints owing to the small amount of shards



present. The Jardelunde core contains all major tephra hori-zons identified in the Dosenmoor cores, plus three additionalolder tephra horizons (Jam-6, -7 and -8). The Grambow corecontains the youngest ash found (Gram-1) and four major ashlayers, but lacks three of the prominent ash horizons of theDosenmoor and Jardelunde bogs (DOM-7 to DOM-9) (Fig. 2).Although the path of the ash cloud for the youngest tephraGRAM-1 probably is the reason for its isolated occurrence,preservation may be a problem for the prominent older tephrahorizons (Jam-6 to Jam-8). Judging from the high mineral con-tent of the samples and the mineral composition, running waterwas present during the early stages in the Dosenmoor develop-ment, possibly prohibiting the sedimentation and preservationof glass shards. With respect to the missing major tephra hori-zons (DOM-7 to DOM-9) in Grambow, the condensed profilecould be the reason for the lack of tephra layers. We cannotexclude, however, that the bogs simply lie outside the marginsof the fallout fans of these tephra events.

A derivation of all tephra layers from Icelandic volcanicsources is deduced from the chemical similarity of the glassshards to Icelandic evolved tephra and lava, and from thetransport paths, which are deduced from the thickness of thetephra layers. For Hekla 4 tephra, for example, some 0.02 gglass shards cm−3 peat are found in a Scottish bog, whereasin northern Germany only few glass shards occur in the peatsections. The Hekla 4 tephra horizon is visible in radiographsof the peat sections in Scotland (Dugmore and Newton, 1992).They can be seen only in grain separates in northern Germanyafter significant enrichment procedures.

Correlation to individual Icelandic source volcanoes anderuptions is based on the chemical characteristics of the glassshards of the tephra layers and composition of the near-venttephra type sections. Of the 16 tephra layers characterised inthe deposits, five are linked to specific known Plinian or sub-Plinian eruptions on Iceland, four of which represent explosiveeruptions of the Hekla volcano. Most Hekla eruptions show acompositional spectrum, but can be distinguished from eachother by their major element composition. Ash of Hekla 4and Hekla 5, and Hekla 3 and Hekla Selsund events, whichshow near-identical major element compositions in northernGermany, can be distinguished by their stratigraphical positionand age. Correlation of the fifth tephra (Gram-1) is still sketchy.Even though the extrapolated route of the Askja ash cloudsupports a correlation, more chemical analyses of glass shardsare needed.

Some tephra layers cannot be related to known volcanicevents. Their chemical composition clearly points towardsIcelandic eruptions as the source, and some of these ash layersalso occur on the British Isles (DOM-2–Sluggan tephra; DOM-5–Glen Garry tephra; JAM-6–Lairg tephra). This indicates thatthe Icelandic record of explosive eruptions is far from beingknown completely, and ash from explosive events from othervolcanoes than Hekla can be traced outside Iceland.

Correlation with Holocene tephra records from Scotland,Ireland, Scandinavia and the North Atlantic show that majortephra markers older than 1000 yr from these sites are presentin north German bogs as well (i.e. Sluggan tephra, GlenGarry tephra, Kebister tephra, Hekla 4, Lairg Tephras). Inaddition, two major tephra layers occur in northern Germanpeat sections (Hekla 3 and microlite tephra) that recentlywere recorded in Irish sites (Pilcher and Hall, in press).However, ash of the Hekla 3 eruption is probably presentin Sweden. Tephra horizons containing glass shards of twoseparate eruptive events, such as Sluggan A and B in Irelandand Lairg A and B in Scotland, do not occur in northernGermany. Compositional ranges of glass shards in somenorthern Germany tephra layers (Glen Garry, Hekla 3, Hekla

Selsund, Hekla 4 and Hekla 5) are attributed to zoned eruptionsand transport systems. In contrast to occurrences of the Hekla4 tephra in Scotland, which comprise the complete chemicalrange of near-vent compositions (Dugmore et al., 1995a), theHekla 4 ash in northern Germany and Ireland comprisespredominantly highly differentiated glass shards from the earlyPlinian eruptive phases. Later Hekla 4 eruptions may berepresented by subordinate, less evolved glass shards, whichhave been found only in the Jam-5 horizon.

A second example is the DOM-5–Glen Garry tephra, whichis derived from a strongly compositionally zoned eruption,and is represented by variable compositions of glass shards atdifferent sites. This could indicate different atmospheric travelpaths of ash clouds resulting from different column heightsduring the course of the eruption. Eruption columns of highlyevolved parts of the magma reached higher atmospheric levelsand were transported towards northern Germany, whereas theless evolved magma erupted in lower eruption columns, withthe ash being transported in local wind systems towards theBritish Isles (Bogaard et al., in preparation; Bogaard, 1997).

Ash horizons identified and fingerprinted in three bogsin northern Germany establish a framework for tephrostrati-graphical dating of Holocene deposits in Schleswig-Holsteinand Mecklenburg-Vorpommern. They will enable a focusedsearch for tephra layers in lacustrine sequences in north-ern Germany, representing valuable isochrons with respect toenvironmental changes and the relationship to climate of thelatter and their spatial variability (Fig. 9). The DOM-2–Sluggantephra, for instance, enables the comparison of profiles withinthe medieval warm period (MWP), the time of first settlementphases in Iceland. Hekla 3 tephra was erupted during times ofsignificant environmental changes, as seen in marine sedimentcores (Eiriksson et al., 2000b) and reduced tree-ring growthin Irish oaks (Baillie and Munro, 1988). Hekla 3 tephra andmicrolite tephra bracket the change from Sub-boreal to Subat-lantic climate in northern Germany (Bogaard et al., submitted).In Ireland and Scotland, the Hekla 4 tephra layer has beenused as a correlation tool demonstrating the regional variabilityof environmental changes (Blackford et al., 1992; Hall et al.,1993).

This study has shown that Icelandic volcanic ash is muchmore widespread than previously thought and can be traced formore than 2000 km from their eruptive centres. At least ninemajor tephra marker layers identified and fingerprinted in bogsin northern Germany extend the application of tephrochronol-ogy beyond the limits of visible tephra layers. The discoveryof previously unrecorded Holocene rhyolitic tephra horizonscomplements the tephrochronological framework in the NorthAtlantic region and adds to our knowledge about the Holocenemagma evolution and eruption record of Iceland. The tephramarkers open new possibilities for multiproxy studies of ter-restrial peat, marine sediments and ice cores, permitting acomparison and synchronisation of palaeoclimate records,vegetational evolution and settlement history from the NorthAtlantic region to continental Europe.

Acknowledgements We thank Jon Eiriksson and Jon R. Pilcher fortheir helpful and constructive reviews of the manuscript. We would liketo thank Walter Dorfler for his support and discussions. Jurgen Freitagand Petra Gloer are thanked for assistance during microprobe sessions.This work was funded by the Bundesministerium fur Forschung undTechnologie (BMFT grant 03SC-9-Kie) and the Kultusministerium ofSchleswig-Holstein in a cooperative project with the department ofUr- und Fruhgeschichte at the Christian-Albrechts Universitat Kiel.



Scandinavia

Ireland Great Brita

in

IcelandNorth Atlantic

Synthesis

DOM-5/Glen Garry

DOM-3DOM-4

DOM-7/Hekla 3

DOM-8/Kebister/Hekla Selsund

Hekla 1510Öraefajökull

Hekla 1EldgjaLandnamslagDOM-2/Sluggan B

DOM-9/Hekla 4

Hoy

JAM-7/Hekla 5

GRAM-1/Askja 1875

DOM-11DOM-10

JAM-8

DOM-6/Microlite

JAM-6/Lairg B

Saksunarvatn

?

Ice core Northern

Germany Temperaturedeviation

LIA

VW

HoloceneOptimum

MWP

RO

0

C°

+1 +21

6000

5000

4000

7000

3000

2000

1000

1000

AgeA.D.

B.C.

Glass shardcompositionnot determined

EMP-Analysis

Iceland

Dosenmoor

500 km

8000

7000

6000

9000

5000

4000

3000

1000

2000

Agecal BP

Figure 9 Correlation of the tephrostratigraphical record in northern Germany with major Holocene eruptions on Iceland and tephra layers knownfrom the North Atlantic region. The synthesis column shows the current Holocene tephrostratigraphy in northern Europe and names of tephramarker horizons. The importance of the tephra marker horizons in environmental studies is illustrated by comparison with the postulated variationof surface temperatures in the northern Hemisphere (Houghton et al., 1991). The temperature deviation is given as the standard deviation from themean at the end of last century (LIA, Little Ice Age; VW, Volkerwanderung; MWP, middle medieval warm period; RO, Roman optimum). Thetephrostratigraphical records compiled for the Greenland ice-cores (Gronvold et al., 1995; Zielinski et al., 1995), the North Atlantic (Lacasse et al.,1995; Eiriksson et al., 2000a,b), Ireland (Pilcher and Hall, 1992 in press; Pilcher et al., 1996; Dwyer and Frazer, 1996; Plunkett, 1999), GreatBritain (Bennet et al., 1992; Dugmore et al., 1995a; Pilcher and Hall, 1996), Sweden (Persson, 1992; Boygle, 1999) and northern Germany (Merktet al., 1993; this study)

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linking the north atlantic to central europe: a high-resolution holocene tephrochronological record...

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