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Quaternary International 164–165 (2007) 21–32

Luminescence dating of proglacial sediments from the Eastern Alps

Nicole Klasena,�, Markus Fiebigb, Frank Preusserc, Jurgen M. Reitnerd, Ulrich Radtkea

aGeographisches Institut, Universitat zu Koln, Albertus-Magnus-Platz, 50923 Koln, GermanybInstitut fur angewandte Geologie, Universitat fur Bodenkultur, Peter-Jordan-StraX e 70, 1190 Wien, Austria

cInstitut fur Geologie, Universitat Bern, Baltzerstrasse 1-3, 3012 Bern, SwitzerlanddGeologische Bundesanstalt, Neulinggasse 38, 1030 Wien, Austria

Available online 27 December 2006

Abstract

The potential of optically stimulated luminescence (OSL) for dating proglacial deposits is tested here at three last glacial key sites in the

Eastern Alps. This was undertaken using both sand-sized feldspar and quartz grains as well as fine silt-sized material. The samples reveal

rather poor luminescence intensities of the investigated quartz grains and it is also clearly demonstrated that several of the deposits were

incompletely bleached prior to deposition. Bleaching experiments were carried out and different approaches for extracting the aliquots

where the OSL was completely bleached prior to burial were tested. Applying different OSL measurement techniques and analytical

procedures, we investigated which approach was most appropriate for dating known age proglacial sediments. Best results were achieved

using Single-Aliquot Regenerative-Dose methodology on coarse grain quartz and feldspar samples, in combination with the approach of

Preusser et al. [2007. Luminescence dating of proglacial sediments from Switzerland. Boreas, in press] for ED calculation.

r 2007 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction

Upper Pleistocene sediments sites in the Inn Valley, theKitzbuheler Alpen and the Bavarian Alpine Foreland havethe potential to give important information on the LateWurmian history of the Eastern Alps. The region may thusreveal essential knowledge about glacial dynamics, envir-onmental conditions and the associated pattern of pastatmospheric circulation. A limiting factor for reconstruct-ing the glacial history of the Alps is the lack of suitablemethods to date glacigenic sediments. Available results ofphysical dating are limited to radiocarbon ages, a few agesby U/Th dating of peat and cosmogenic dating, as well asthe first luminescence dates from coarse-grained quartz,feldspar and polymineral fine grains (Preusser, 2004). Theadvantages of optically stimulated luminescence (OSL) arethe potential to date terrestrial sediments that are beyondthe limits of radiocarbon dating and that the time elapsedsince sediment burial can be dated directly.

Existing radiocarbon ages of plant macrofossils fromlacustrine silts indicate that the Inn Glacier reached the

e front matter r 2007 Elsevier Ltd and INQUA. All rights re

aint.2006.12.003

ing author. Tel.: +49 221 470 7803; fax: +49 221 470 5124.

ess: nicole.klasen@uni-koeln.de (N. Klasen).

Baumkirchen site subsequently between 31,00071300 and26,00071300 yr 14CBP (Fliri et al., 1970). The results ofOSL dating of Swiss proglacial deposits, supported byradiocarbon ages of associated bone fragments, demon-strate that the Rhone and Rhine Glacier reached far intothe lowlands shortly after about 30,000 yr ago (Preusseret al., 2007), which implies a rather rapid build-up of ice.The retreat of ice from its Last Maximum extent startedaround 20,000 yr ago, according to the results of cosmo-genic dating of terminal moraines in the Rhone Glacierarea (Ivy-Ochs et al., 2004). Presumably, the stabilisationof the glacier tongues at the Glacial Maximum that causedthe formation of terminal moraines in the alpine forelandlasted only for a few thousands of years. This period wasfollowed by a fast retreat of ice and it took probably only afew hundreds of years for the glaciers to shrink to 50% oftheir maximum length (van Husen, 2000). Kame terraces inthe former glaciated inner alpine valleys give evidence ofthis paleogeographic situation. Within the Inn Glacier areathis geomorphological setting led to the definition of theBuhl stadial by Penck and Bruckner (1901/1909) as the firsthalt of glaciers within the Alps during meltdown. However,a re-investigation of the Buhl type area around Hopfgarten(Kitzbuheler Alpen) lead Reitner (2005) to abandon the

served.

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Fig. 2. Sedimentary log of the sampling site at Baumkirchen. Samples

BMK1–4 were collected from laminated silt between 660 and 690m above

sea level.

N. Klasen et al. / Quaternary International 164–165 (2007) 21–3222

term ‘Buhl stadial’ and to introduce the term ‘phase ofearly Late Glacial ice decay’ for this first sedimentaryevidence of glacier meltdown of the last termination.According to radiocarbon dating of organic matter on thebase of a peat in the Traun Glacier area, the main valleys inthe Eastern Alps must have been ice free by about15,400 yr 14CBP (van Husen, 2000; ca. 17,500 cal yr BP).

Presented here is the first systematic investigation ofOSL dating of inner alpine sediments. At the Baumkirchensite lacustrine sediment, just below the deposits of the LastGlaciation, was dated. At the Gluck gravel pit glaciofluvialdeposits associated with the maximum of the WurmianGlaciation were investigated and proglacial sedimentsattributed to the early part of the last termination weredated at the Rahmstatt site.

2. Dated sites

2.1. Baumkirchen quarry

The site is located in the River Inn Valley within the‘Gnadenwald Terrasse’, approximately 12 km east ofInnsbruck (Fig. 1). The sediment sequence consists oflaminated clayey silts exposed in a former quarry, which

Fig. 1. Map showing the sampling locations of Baumkirchen, Gluck and

Ramstatt.

are overlain by gravel (VorstoXschotter) between 640 and750m above sea level (a.s.l.) (Fliri et al., 1970; Fliri, 1973)(Fig. 2). This unit marks the onset of the Upper Wurmiansubstage and is covered by till of the Last GlacialMaximum (LGM) (Chaline and Jerz, 1984). The fine-grained lacustrine sediments at this site contain plantmacrofossils (Pinus mugo/sylvestris, Alnus viridis, Hippo-

phae, Salix, Dryas) that were deposited in shallow lakessurrounded by shrub tundra, indicating cold climaticconditions. Modern equivalents can be observed in theAlps in the range of the timberline at 2000m a.s.l. (Patzelt,1995). Several radiocarbon dates of wood fragmentsbetween 655 and 681m a.s.l. yield ages between31,60071300 and 26,80071300 14C yrBP (36,30071700and 31,90071500 yr cal 14CBP, respectively; www.calpal-online.de) (Fliri et al., 1970). Samples for OSL dating werecollected at 690m a.s.l (BMK1), 685m a.s.l. (BMK2),661m a.s.l. (BMK3) and 660m a.s.l (BMK4) coveringthe sequence geochronologically constrained by radio-carbon dating.

2.2. Gluck gravel pit

The sampling site is situated in the ‘‘MunchnerSchotterebene’’ (a gravel plain spreading over some1500 km2 in the surroundings of Munchen) at the borderof the River Wurm Valley, about 5 km in front of LGMterminal moraines at Lake Starnberg (Fig. 1). Because ofits position close to Lake Starnberg (formerly known asLake Wurm) the sampling site is in the type region ofthe Wurmian stage (Chaline and Jerz, 1984). In the Gluckpit, gravel beneath a terrace surface of Upper Wurmianage was excavated (Fig. 3). In several parts of the‘‘Munchner Schotterebene’’ meltwater deposits from olderglaciations are preserved below the Upper Wurmian gravel(Jerz, 1987). Five samples (GLK1–5) were collected forluminescence dating. The lower three samples (GLK1–3)consist of sediment derived from weathered silty to sandydeposits at the bottom of the pit. The upper two samples(GLK4, GLK5) were collected between 554 and 560m a.s.lfrom non-weathered gravel below the Upper Wurmian

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Fig. 3. Lithofacies profiles of the Gluck site. Numbers GLK1–5 indicate the sampling locations. F: fine, S: sand, G: gravel (cf. DIN 4022).

Fig. 4. Sedimentary log of the sampling site at Rahmstatt. Seven samples

were collected for optical dating. Numbers RAH1–7 indicate the sampling

locations.

N. Klasen et al. / Quaternary International 164–165 (2007) 21–32 23

terrace surface. Between these two sedimentary units isan undulating unconformity. According to the sedimen-tary setting, samples GLK1–3 must predate the LGM,while the sites GLK4 and GLK5 should reflect a LGMdeposition.

2.3. Rahmstatt quarry

The site is situated in the Brixental northwest ofHopfgarten within the Kitzbuheler Alpen (Fig. 1). Deltasediments of a kame terrace (Westendorf terrace) areexposed in an abandoned clay pit (Fig. 4). The coarseningupward sequence starts at the base with bottom setsconsisting of laminated silt. This unit is overlain by massiveto ripple-drift laminated sands, which indicate the furtherprogradation of the delta front. The sequence is cappedwith sandy gravel top sets, which represent the infill of theformer ice dammed lake. Penck and Bruckner (1901/1909)argued that this sequence was formed as the result of anactive Inn Glacier blocking the drainage of the wholeHopfgarten basin towards the Inn Valley. This blockageoccurred during the Buhl stadial and was associated withthe first halt of the Inn Glacier during glacial retreat asis defined in the Hopfgarten area (Penck and Bruckner,1901/1909). Mayr and Heuberger (1968) interpreted manymorphological features as terminal moraines, which atpresent can be identified as kames and/or erosionallymodified kame terraces. According to a recent reinvestiga-tion of the area, the Westendorf terrace extended overmore than 10 km and documents the final phase of iceretreat after the LGM in this region (Reitner, 2005). TheWestendorf terrace represents the lowest and thus lastelement in a succession of kame terraces, which were builtby sedimentation due to the ice blockage. The Inn Glacier,with an ice surface during the LGM at about 1900m a.s.l.,was a stagnant and down wasting glacier during the wholephase of ice retreat, while two local glaciers showedprominent advances over the kame terraces during thistime. The top set sediments of the Westendorf terrace atRahmstatt indicate a stagnant Inn Glacier, which had lostabout 1200m of its thickness in relation to LGMconditions.

This sedimentary sequence is part of the type area of the‘the early Late Glacial phase of decay’ as defined byReitner (2005). Samples RAH1 and RAH2 were taken 6mbelow the surface of the terrace from horizontallylaminated sand. Sample RAH3 was collected 8m beneaththe terrace surface and was derived from sandy layers withripple structures. Samples RAH4 and RAH5 were collected9 and 14m, respectively, below the terrace surface fromhorizontally laminated sandy sediment. Samples RAH6and RAH7 consist of silty fine-grained samples, whichoriginate from glaciolacustrine sediment and were collectedat a depth of 28 and 30m, respectively.

3. Luminescene dating

Luminescence dating is used to determine burial ages ofsediments that were exposed to sufficient sunlight prior todeposition (e.g. Aitken, 1998). The main limitation indating water-lain sediments, and especially glaciofluvialand glaciolacustrine deposits, is the possibility of incom-plete bleaching of the luminescence signal prior todeposition, which causes an overestimation of the calcu-lated age. Insufficiently bleached sediments consist of amixture of grains carrying different levels of residualluminescence signals and usually contain a portion of

ARTICLE IN PRESSN. Klasen et al. / Quaternary International 164–165 (2007) 21–3224

completely bleached grains. Single-Aliquot Regenerative-Dose (SAR) methodology (Murray and Wintle, 2000)potentially allows partially bleached samples to be identi-fied when using small aliquots containing not more than100 grains (Olley et al., 1999). The distribution ofequivalent dose (ED) values from different aliquots of asample reflects the degree of bleaching prior to depositionwith broad and positively skewed distributions character-ising incomplete bleaching (Wallinga, 2002a, b). The majorchallenge is then to extract the proportion of aliquotswhere all grains had zero luminescence at deposition.

3.1. Sample preparation and measurement conditions

After dry sieving, all samples were treated with HCl (30%)and H2O2 (10%) to remove carbonates and organic material,respectively. Coarse-grain quartz and feldspar samples(150–200mm) were separated by density using heavy liquids(2.58 and 2.68 g cm�3). Additionally, quartz samples wereetched by HF (40%) for 40min to remove remainingfeldspars and the outer part of the quartz grains that wasaffected by alpha irradiation. Coarse grains were dispensedonto stainless steel discs in diameters of 1mm (feldspars) and2mm (quartz) using Silkospray. For fine grain samples, the4–11mm fraction was enriched by settling in water anddeposited onto aluminium discs from an acetone suspension.

Luminescence measurements were performed on anautomated TL/OSL-DA-15 Risø reader equipped with a90Sr/90Y beta-source, delivering 0.11Gy/s and an EMI9235 PMT tube. Following preheat plateau tests, the SAR-protocol of Murray and Wintle (2000) was applied todetermine the ED of coarse-grain quartz samples applyingpreheating for 10 s at 260 1C (samples GLK3–5) and 240 1C(samples RAH1–5), respectively. Optical stimulation usingblue diodes (470730 nm, 440mW/cm2) was carried outfor 50 s at 125 1C and detected in the UV with a Hoya U340filter. A cut heat at 200 1C was applied prior to measuringthe test dose response. To avoid including results fromaliquots contaminated with feldspar, at the end of eachSAR measurement, infrared stimulation was applied to theirradiated aliquot. Those aliquots with infrared stimulatedluminescence (IRSL) were rejected. A further 35% of themeasured aliquots had to be rejected due to poor quartzluminescence sensitivity or due to the fact that aliquots didnot pass the defined SAR criteria (recuperation, o10%,recycling ratio inside, 0.8–1.2).

Silty lake sediments (samples BMK1–4, RAH6–7) weremeasured employing the SAR-protocol of Banerjee et al.(2001), using an experimentally derived preheat for 10 s at270 1C. Samples were first stimulated for 100 s at 125 1C byinfrared diodes (875780 nm, 135mW/cm2) followed byillumination with blue diodes (post-IR OSL) for 100 s at125 1C. The OSL signal was detected through a Hoya U340UV filter (IRSL (UV) and post-IR OSL (UV)). For testdose measurements a cut heat at 200 1C was employed.

Coarse grain feldspar samples GLK3–5 and additionallysilty samples BMK1–4 were measured applying the SAR-

protocol for feldspars of Wallinga et al. (2000) with themodifications by Preusser (2003). For samples BMK1–4preheating at 270 1C for 10 s was followed by IR stimulationfor 300 s at 50 1C. A filter combination comprising SchottBG39, Schott GG400 and Corning 7–59 filters was used todetect the IRSL (Blue Light (BL)) signal. For test dosemeasurements, samples were preheated at 290 1C (cf. Blair etal., 2005). Coarse grain feldspar samples GLK3–5 werepreheated at 290 1C for 10 s. The IRSL signal was recordedfor 300 s at 125 1C and detected through the same filtercombination mentioned above. For test dose measurementswe employed a cut heat at 200 1C.Definition of the above-mentioned measurement condi-

tions results from a rigorous testing program (Klasenet al., 2006) and was crosschecked by dose recovery tests(Table 1), which confirm the appropriateness of the appliedparameters. These tests also reveal information about thereproducibility of laboratory-irradiated samples. For thesetest measurements, samples were first exposed to an OsramUltra Vitalux UV lamp (300W) at room temperatureovernight to bleach the luminescence signal. Subsequently,samples were irradiated giving a laboratory dose of8Gy (sample BMK1), 47Gy (sample GLK3) and 22Gy(sample RAH4), respectively, and the different SARprotocols were used to measure how well the given dosescould be recovered. For all samples, the ratio of themeasured-to-given dose as well as the mean recycling ratiois close or even identical to unity and we found littlerecuperation in our samples (Table 1). Hence, all samplespassed the criteria of dose recovery tests (cf. Wintle andMurray, 2006).Dose rate relevant elements (K, Th, U) were measured

using high-resolution gamma spectrometry (samplesRAH1–7, GLK1–5) and ICP-MS (samples BMK1–4)(Preusser and Kasper, 2001) (Tables 2 and 3). Thecontribution of cosmic radiation to the total dose ratewas calculated using present day depth following Prescottand Hutton (1994). Present day water content of sampleswas used and an average a-value of 0.0770.02 wasassumed for feldspar and polymineral fine grains. Forcoarse grain K-feldspar average potassium content of12.570.5 % was used following Huntley and Baril (1997).

3.2. Experiments

3.2.1. Bleaching experiments

As already indicated, the major problem in datingproglacial sediments is partial bleaching of the lumines-cence signal prior to burial. To investigate the resettingcharacteristics of the polymineral fine grain Baumkirchensediments, a bleaching experiment was performed. Anexperimental approach was used to simulate naturalconditions of sediment transport in turbid water. Wesuspended 1 g of sample BMK2 in 1 l of 10% sodiumoxalate in a polypropylene beaker that was wrapped intoan opaque bag. The sample material was kept in solutionby agitating slowly on a magnetic stirrer. Then the solution

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Table 1

Results of dose recovery tests for samples BMK1, GLK3 and RAH4

Sample n Mineral Preheat

temperature (1C)

Stimulation Ratio measured/

given dose

Recycling ratio Recuperation (%)

BMK1 10 Polymineral fine grain 270 IRSL (UV) 1.0070.02 1.0270.02 0.2

BMK1 10 Polymineral fine grain 270 post-IR OSL (UV) 1.1670.10 0.9970.10 0.5

BMK1 10 Polymineral fine grain 270 IRSL (BL) 0.9670.02 0.9870.01 7.6

GLK3 40 Quartz 260 OSL 1.0170.01 1.0270.01 1.6

GLK3 20 Feldspar 290 IRSL 1.0570.04 1.0670.06 3.8

RAH4 40 Quartz 240 OSL 1.0570.01 0.9670.03 2.1

The aim is to reproduce a laboratory dose of beta irradiation using the SAR protocol used for dating. The recycling ratio shows the rate to which the first

regenerative dose is reproduced. Recuperation is the residual signal observed in a SAR cycle when no regenerative dose is applied. n: number of aliquots.

Table 2

Dosimetry data for quartz and feldspar samples GLK3–5 and quartz samples RAH1–5

Sample Depth (cm) Mineral K (%) Th (ppm) U (ppm) W (%) D (Gy/kyr)

GLK3 850 Quartz 0.4470.01 3.0570.14 1.4770.05 10.0 0.970.1

GLK3 850 Feldspar 0.4470.01 3.0570.14 1.4770.05 10.0 1.770.1

GLK4 750 Quartz 0.4770.01 3.1770.15 1.5270.05 17.9 1.070.1

GLK4 750 Feldspar 0.4770.01 3.1770.15 1.5270.05 17.9 1.470.1

GLK5 450 Quartz 0.4470.01 2.9570.14 1.7770.06 16.6 1.070.1

GLK5 450 Feldspar 0.4470.01 2.9570.14 1.7770.06 16.6 1.670.1

RAH1 600 Quartz 1.7970.04 9.0670.42 1.9870.07 11.5 2.670.1

RAH2 600 Quartz 1.7370.04 8.6770.40 1.9470.07 16.0 2.470.1

RAH3 800 Quartz 1.6670.03 10.2670.47 2.2770.08 7.0 2.870.2

RAH4 900 Quartz 1.7170.04 10.7670.49 2.3970.08 10.7 2.770.1

RAH5 1400 Quartz 1.6770.04 9.3870.43 2.1370.07 9.5 2.670.2

K: potassium content, Th: thorium content, U: uranium content, W: water content, D: dose rate.

Table 3

Dosimetry data, equivalent doses and ages for polymineral fine grain samples BMK1–4, GLK1–2 and RAH6–7

Sample Depth

(cm)

K

(%)

Th

(ppm)

U

(ppm)

W

(%)

D

(Gy/kyr)

EDIRSL

UV (Gy)

EDOSL

UV (Gy)

EDIRSL

BL (Gy)

AgeIRSL

UV (kyr)

AgeOSL

UV (kyr)

AgeIRSL

BL (kyr)

BMK1 1250 3.4970.31 15.6370.33 4.2070.18 23.0 6.070.5 228.977.6 234.6711.6 288.276.8 38.073.6 38.973.9 45.874.2

BMK2 1750 3.7270.33 16.770.35 4.2870.19 23.0 6.370.6 210.776.9 218.377.5 269.278.1 33.273.1 34.473.2 40.473.8

BMK3 4150 3.8270.34 16.9970.36 4.5570.20 24.9 6.170.6 256.975.8 248.872.9 324.179.9 42.374.1 4.0173.9 47.374.5

BMK4 4250 3.8170.34 17.5170.37 4.8970.22 26.1 6.770.6 237.976.1 247.272.5 327.3710.5 35.673.3 37.073.3 46.674.5

GLK1 950 1.2270.03 9.6370.44 2.9070.10 17.9 3.170.3 112.272.0 36.273.4

GLK2 900 0.7970.02 7.7470.36 3.0770.10 26.8 2.470.2 66.071.3 27.472.7

RAH6 2800 3.0470.06 15.3570.70 3.2770.11 27.5 4.870.4 257.5713.7 147.475.8 54.075.0 30.972.7

RAH7 3000 2.8270.06 14.6870.68 3.2770.11 23.9 4.870.4 326.0727.2 213.7719.6 68.377.8 44.875.4

All results are given with 1s standard error. K: potassium content, Th: thorium content, U: uranium content, W: water content, D: dose rate.

N. Klasen et al. / Quaternary International 164–165 (2007) 21–32 25

was exposed to an Osram Ultra Vitalux UV lamp (300W)for fixed time intervals. After each interval, 10ml of solutionwas extracted with a pipette from 10 cm below the surfaceof the liquid, dried and deposited onto aluminium discsfrom an acetone suspension. Finally, the ED was deter-mined following the SAR-protocol by Banerjee et al. (2001).

The bleaching experiment demonstrated that the lumi-nescence signals of the grains within the test liquid,containing sample material and a solution of sodium

oxalate, are completely bleached after about 20 h oflight exposure. By experimental approach it is shownthat the IRSL (UV) signal and the post-IR OSL (UV)signal reset differently (Fig. 5). Within the first 8 h ofillumination the IRSL (UV) signal decreases faster than thepost-IR OSL (UV) signal, but after 10 h of illuminationboth signals were bleached to the same amount. Ditlefsen(1992) made similar bleaching experiments with K-richfeldspars comparing thermoluminescence (TL) and IRSL

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Fig. 5. The results of the bleaching experiment using polymineral fine

grain sample BMK2. The IRSL (UV) signal bleaches faster than the post-

IR OSL (UV) signal within the first hour of light exposure, but both

luminescence signals are completely bleached within 20 h.

Table 4

Results of the thermal transfer investigation for samples BMK1, GLK3

and RAH4

Sample n Mineral Preheat

temperature

(1C)

OSL

stimulation

Thermal

transfer

(Gy)

BMK1 10 Polymineral

fine grain

270 IRSL (UV) 1.470.9

BMK1 10 Polymineral

fine grain

270 post-IR

OSL (UV)

1.470.6

BMK1 10 Polymineral

fine grain

270 IRSL (BL) 9.970.5

RAH7 10 Polymineral

fine grain

270 IRSL (UV) 1.770.5

RAH7 10 Polymineral

fine grain

270 post-IR

OSL (UV)

1.872.3

GLK3 10 Quartz 260 OSL �0.370.2

GLK3 10 Feldspar 290 IRSL (BL) 0.270.1

RAH4 10 Quartz 240 OSL �0.170.4

Doses relating to thermal transfer were determined in a routine SAR

procedure after zeroing the luminescence signal and without applying a

laboratory dose. Values achieved here showed that there is no significant

thermal influence on ED estimation, except sample BMK1 IRSL (BL).

Negative values indicate zero transferred dose. n: number of measured

aliquots.

N. Klasen et al. / Quaternary International 164–165 (2007) 21–3226

and pointed out that resetting depends on the degree ofsuspension density, with bleaching times for both TL andIRSL above 20 h for a dense suspension containing 0.5 g/lof sample material.

Other bleaching experiments performed on coarse grainquartz and feldspar from sample GLK3 demonstrated that theluminescence signal of the quartz resets faster within the firstfew seconds of exposure compared to the feldspar lumines-cence signal, but finally both minerals were completelybleached within the same time (60min) (Klasen et al., 2006).

3.2.2. Thermal transfer

Thermal transfer as referred to by Rhodes and Bailey(1997) was also investigated as it can be another reason forED overestimation. This effect involves the unwantedtransfer of electrons from thermally stable light-insensitivetraps to light-sensitive traps during preheating. Thesetransferred electrons will therefore contribute to themeasured OSL signal and increase the measured ED. Theeffect of thermal transfer was investigated for polymineralfine grain samples BMK1 and RAH7, for quartz samplesGLK3 and RAH4 as well as for feldspar sample GLK3(Table 4). For most of our samples the effect of thermaltransfer contributes o1% to the natural ED. The singleexception was polymineral fine grain sample BMK1 (IRSL(BL)), which showed a thermally transferred dose of about10Gy (4% of the natural ED). Applying higher preheattemperatures of 290 and 310 1C increased the effect ofthermal transfer to about 16Gy (6% of the natural ED).When using IRSL (UV) and post-IR OSL (UV) stimula-tion, the influence of thermal transfer on sample BMK1amounts only to about 0.5% of the ED.

3.3. Analysing ED distributions

ED distributions of the coarse grain quartz (GLK3–5,RAH1–5) and feldspar (GLK3–5) samples are broad or

positively skewed indicating partial bleaching (Figs. 6and 7). Using the arithmetic mean leads to overestimatedED values and hence to overestimated OSL ages. There-fore, we investigated three different techniques for deter-mining the ED from partially bleached deposits. Themethod of Olley et al. (1998) suggests using the smallest5% of the individually measured ED values. With theapproach by Fuchs and Lang (2001), ED values arearranged from lower to higher values and the arithmeticmean is calculated starting with the two lowermost EDvalues. Subsequently, ED values are added one by one untila relative standard deviation (RSD) of 4% is achieved. Thisthreshold of 4% was obtained from dose recovery tests onquartz samples and represents the best possible precisionfor natural samples when only a small number of discs areavailable (Fuchs and Lang, 2001). Aliquots containing EDvalues contributing to a RSD higher than the threshold of4% were expected to be incompletely bleached and weretherefore rejected for calculation. In this work, weemployed dose recovery tests using about 40 aliquots(2mm diameter) to measure the best obtainable precisionof coarse grain quartz samples GLK3 and RAH4 and 20aliquots for feldspar sample GLK3. We calculated RSDs(1s) of 6.6% (quartz GLK3), 11.1% (quartz RAH4) and10.0% (feldspar GLK3). Consequently we applied thesevalues for ED calculation according to Fuchs and Lang(2001). In a third approach, ED is calculated with themethod described by Preusser et al. (2007). This techniqueis based on the approach of Fuchs and Lang (2001) butincludes the influence of microdosimetry as an additionalsource of scatter. Preusser et al. (2007) combine the RSDevaluated from dose recovery tests with the RSD due to

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Fre

qu

en

cy

Fre

qu

en

cy

Fre

qu

en

cy

Fre

qu

en

cy

Fre

qu

en

cy

Fre

qu

en

cy

Fre

qu

en

cy

6

5

4

3

2

1

00 50 100

Equivalent dose [Gy]

150 200 250

0 50 100

Equivalent dose [Gy]

150 200 250 0 50 100

Equivalent dose [Gy]

150 200 250

0 50 100

Equivalent dose [Gy]

150 200 250 0 50 100

Equivalent dose [Gy]

150 200 250

0 50 100

Equivalent dose [Gy]

150 200 300 400 500 0 50 100

Equivalent dose [Gy]

150 200 250

GLK1 IRSL (BL)

GLK3 IRSL (BL)

GLK4 IRSL (BL)

GLK5 IRSL (BL) GLK5 OSL

GLK4 OSL

GLK3 OSL

n:18

x:1122

sd:8.3

− Fre

qu

en

cy

6

5

4

3

2

1

00 50 100

Equivalent dose [Gy]

150 200 250

GLK2 IRSL (BL)

n:12

x:66.4

sd:5.1

−

n:109

x:35.7

sd:17.1

−n:24

x:75.8

sd:30.8

−

n:15

x:149.6

sd:16.2

−n:18

x:118.5

sd:22.5

−

n:65

x:99.2

sd:69.8

−n:22

x:354.9

sd:66.7

−

10

8

6

4

2

0

30

25

20

15

10

5

0

5

4

3

2

1

0

5

4

3

2

1

0

5

4

3

2

1

0

10

12

8

6

4

2

0

Fig. 6. Equivalent dose distributions of fine grain samples GLK1 and GLK2 and coarse grain quartz and feldspar samples GLK3, GLK4 and GLK5.

Partial bleaching is indicated by a broad distribution or high-dose outliers for samples GLK3–5 (quartz and feldspar). n ¼ number of aliquots;

x ¼ arithmetic mean (Gy); sd ¼ standard deviation.

N. Klasen et al. / Quaternary International 164–165 (2007) 21–32 27

ARTICLE IN PRESSF

req

ue

ncy

0 50 100Equivalent dose [Gy]

150 200 250

RAH1 OSL

RAH3 OSL

RAH5 OSL

RAH4 OSL

RAH2 OSL

Fre

qu

en

cy

6

7

5

4

3

2

1

00 100

Equivalent dose [Gy]

150 200 250

n:26

x:86.2

sd:45.8

−

n:37

x:68.2

sd:71.5

−

n:16

x:101.7

sd:30.4

−

n:58

x:75.3

sd:26.6

−

n:43

x:73.4

sd:35.1

−

Fre

qu

en

cy

0 50 100

Equivalent dose [Gy]

150 200 250

0 50 100

Equivalent dose [Gy]

150 200 250

10

8

6

4

2

0

Fre

qu

en

cy

0 50 100

Equivalent dose [Gy]

200 300 400 500

10

8

6

4

2

0

5

4

3

2

1

0

Fre

qu

en

cy

4

3

2

1

0

50

Fig. 7. Dose distributions of coarse grain quartz samples RAH1, RAH2, RAH3, RAH4 and RAH5. The broad distributions or high-dose outliers

indicated partial bleaching for all plotted samples. n ¼ number of aliquots; x ¼ arithmetic mean (Gy); sd ¼ standard deviation.

N. Klasen et al. / Quaternary International 164–165 (2007) 21–3228

inhomogeneity of dose rate during burial (microdosi-metry). The problem of this approach is that the RSD ofsamples due to variation in dose rate can only be estimatedwhen a sample is completely bleached. Therefore, the RSDdue to dose rate inhomogeneity is difficult to estimate asone has to find well-bleached deposits with similarcomposition to the partially bleached sample collected forOSL dating. For natural samples from aeolian environ-ments, RSDs of 21% and 11–12% have been reported with7% and 4%, respectively, due to counting statistics (Lomax

et al., 2003; Vandenberge et al., 2003). In their study,Preusser et al. (2007) observed an average RSD of 13% indose recovery tests and combined this scatter with that dueto dose rate variations, namely 10% as a lower and 20% asan upper value from published data. We calculated twodifferent ED values for our samples by combining the twovalues of 10% and 20% with the reproducibility found indose recovery tests (6.6% for quartz GLK3; 10% forfeldspar GLK3; 11.1% for quartz RAH4). In addition tothe three methods described above, we also considered the

ARTICLE IN PRESS

Fig. 8. Comparison of OSL ages (this work) and earlier radiocarbon

results (Fliri, 1973). Sample correlation, depth beneath surface: BMK1

(1250 cm); BMK2 (1750 cm); BMK3 (4150 cm) and BMK4 (4250 cm).

Radiocarbon ages are given as calibrated (cal.) ages (www.calpal-

online.de).

N. Klasen et al. / Quaternary International 164–165 (2007) 21–32 29

minimum age model of Galbraith et al. (1999), which iscommonly used in OSL dating. However, this approachwas regarded as not being appropriate due to the fact thatthe ED distributions show only a single low-dose aliquot(R. Galbraith, pers. comm., 2005).

4. Dating results and discussion

4.1. Baumkirchen quarry

For the Baumkirchen site, ED values were calculatedusing the arithmetic mean (Table 3) and lead to a meanIRSL (UV) age of 37,30073500 yr. post-IR OSL (UV)ages present a mean age of 37,80073600 yr, while IRSL(BL) ages give a mean age of 45,00074300 yr (Table 3).Although the three mean ages are consistent within error,the ED value for IRSL (BL) is higher by about 20%. Up tonow there is no final explanation for the relative over-estimation of IRSL (BL) ED values compared to IRSL(UV) and post-IR OSL (UV). One possible reason could bethe effect of thermal transfer as discussed above. However,the observed thermally transferred dose is only about10Gy (sample BMK1 (IRSL (BL)) whereas the mean EDfor IRSL (BL) is about 50Gy higher than for the UVemissions (Table 3). Another possibility is that IRSL (UV)and post-IR OSL (UV) ED values are underestimatedcompared to IRSL (BL) due to fading of IRSL in the UVemission band (cf. Krbetschek et al., 1997). Althoughfading tests were not conducted, due to the concordance inthe IRSL (UV) and post-IR OSL (UV) data and thesuccess of these approaches at several other sites (Preusserand Schluchter, 2004; Preusser et al., 2005a, b), we considerunderestimates due to fading unlikely.

While the mean ages of IRSL (UV) and post-IR OSL(UV) agree with oldest radiocarbon ages within errors,IRSL (BL) ages are clearly older (Fig. 8). It should benoted here that the radiocarbon ages were determined inthe late 1960s and show a large scatter of individual dates,which is higher than usually associated with the method.Furthermore, the radiocarbon ages are close to the upperdating limit regarding the potential of radiocarbon datingin the late 1960s and the radiocarbon chronology isthus not straightforward. However, all of our samplesdiscussed above and including the radiocarbon datesrepresents an age between about 35,000 and 45,000 yrand therefore supports the stratigraphic correlation of theBaumkirchen site with the Middle Wurmian substage(Chaline and Jerz, 1984).

4.2. Gluck gravel pit

The quartz samples show a weak luminescence signal(e.g. Fig. 9a), which is typical of most alpine quartz(cf. Preusser et al., 2006). As a result, about 100 aliquotsper quartz sample had to be measured because typicallyabout 30% of the aliquots did not pass the defined SARtests. All coarse grain quartz and feldspar samples showed

broad ED distributions, which are skewed towards highervalues (Fig. 6). Using the arithmetic mean for the EDcalculation of the coarse grain samples GLK3–5 leads tooverestimated ages in comparison to the ages beingassumed for Wurmian deposits (Table 5). Applying theapproach by Olley et al. (1998) suggested underestimationof the quartz and feldspar ages for sample GLK3, as theyimply sediment deposition during the LGM, and thesesamples must be older according to the geological setting(Table 5). Using the method of Fuchs and Lang (2001) forsample GLK3 leads to similar ages as determined with thetechnique of Preusser et al. (2007) (Table 5). With the latterwe estimated quartz ages of 25,70072900 yr (GLK3DRT+20) and feldspar ages of 21,20071800 yr (GLK3DRT+10) and 32,10072300 yr (GLK3 DRT+20)(Table 5). For quartz sample GLK3 DRT+10 an agewas not calculated due to an insufficient statistical basisbecause less than three aliquots were within the given rangeof deviation. For quartz and feldspar samples GLK4 andGLK5 all three statistical approaches failed and agesdetermined were far older than the expected results forsediments that were deposited during the Wurmian GlacialMaximum. Poor bleaching of these samples is alsoindicated by the extremely broad distributions withoutany clear peak.Results from the polymineral fine grain samples

GLK1 and GLK2 were calculated using the arithmeticmean and yielded values of 36,20073400 and 27,40072700 yr (Table 3). These results are in good agreementwith the ages for the coarse grain quartz and feldsparfrom GLK3 determined with the technique of Preusseret al. (2007) and give a mean age of 29,80073000 yrfor the sediments deposited before the last glacialadvance.

ARTICLE IN PRESS

Table 5

ED and OSL age determination using arithmetic mean (a.m.) and the approach

Sample Mineral ED a.m.

(Gy)

ED Preusser et

al. DRT+10

(Gy)

ED Preusser et

al. DRT+20

(Gy)

ED Olley

et al.

(Gy)

ED F

and

(Gy)

GLK3 Quartz 41.272.0 n.a. 23.772.4 21.371.9 23.0

GLK3 Feldspar 99.579.6 36.172.4 54.672.4 31.871.7 36.1

GLK4 Quartz 118.575.3 97.776.5 115.2711.0 80.8574.4 83.0

GLK4 Feldspar 149.674.2 149.674.1 149.674.1 115.179.7 146.1

GLK5 Quartz 99.278.7 49.773.6 64.574.8 42.974.2 45.0

GLK5 Feldspar 354.9714.2 314.078.3 354.978.1 242.7713.4 266.6

RAH1 Quartz 86.279.0 n.a. 35.574.1 6.070.5 42.5

RAH2 Quartz 73.475.4 38.773.0 50.273.4 32.272.0 38.7

RAH3 Quartz 68.2711.8 34.772.2 46.172.9 21.872.2 35.2

RAH4 Quartz 75.373.5 42.973.3 57.073.0 37.075.1 47.8

RAH5 Quartz 101.777.6 60.774.9 75.376.5 47.173.2 69.6

All results presented are given with 1s standard error. Preusser et al. DRT+

quartz) or 10% (GLK3–5 feldspar) estimated by the dose recovery test (DR

n.a. ¼ less than three aliquots within the given range of deviation, no ED wa

Fig. 9. Dose response and shine down curves of quartz samples GLK3 (a)

and RAH2 (b). Data are for 2mm aliquots comprising about 100–200

quartz grains.

N. Klasen et al. / Quaternary International 164–165 (2007) 21–3230

4.3. Rahmstatt quarry

Quartz samples from this site show low luminescencesensitivity (Fig. 9b) similar to the above-mentioned samplesfrom the Gluck site and ED values are broadly distributed(Fig. 7). Age determination using the arithmetic meanproduced OSL ages between 24,80074500 and38,60073600 yr (Table 5). These results are significantlyoverestimating the expected age of about 18,000 yr for theearly phase of the last termination. ED values calculatedwith the technique of Preusser et al. (2007) resulted in amean age of 18,70071700 yr (Table 5). Ages calculatedusing the methods of Olley et al. (1998) and Fuchs andLang (2001) resulted in mean ages of 11,40071300 and13,90071900 yr, respectively. These ages are significantlyyounger than expected which is supported by the fact thatthe River Inn Valley was ice-free by 17,500 yr BP (vanHusen, 2000). Nevertheless, the ages determined with thetechnique of Preusser et al. (2007) showed that it waspossible to reproduce conclusive OSL ages for theRahmstatt site, which are consistent with independentage information.Fine grain samples RAH6 and RAH7 provided results far

older than expected with mean ages of 61,20076400yr (IRSL(UV)) and 37,90074100yr (post-IR OSL (UV)) (Table 3). Incontrast to the ages calculated from samples BMK1–4,samples RAH6 and RAH7 yielded different results for IRSL(UV) and post-IR OSL (UV) signals and this is interpreted toindicate partial bleaching prior to burial because the differentcomponents show different bleaching characteristics for shortlight exposure. The influence of thermal transfer is excludedfrom these samples as it contributes o0.8% to the naturalluminescence signal (Table 4).

5. Conclusions

During our OSL dating studies of proglacial depositsfrom the Eastern Alps of Austria we encountered several

es of Preusser et al. (2007), Olley et al. (1998) and Fuchs and Lang (2001)

uchs

Lang

Age a.m.

(kyr)

Age Preusser et

al. DRT+10

(kyr)

Age Preusser et

al. DRT+20

(kyr)

Age Olley

et al.

(kyr)

Age Fuchs

and Lang

(kyr)

71.5 44.773.1 n.a. 25.772.9 23.172.4 25.072.0

74.3 58.576.5 21.271.8 32.172.3 18.771.4 21.272.8

75.7 122.878.2 101.378.4 119.3712.8 83.876.2 86.077.3

74.1 150.8710.8 104.876.7 104.876.7 80.678.2 102.476.6

73.4 99.9710.0 50.174.4 65.075.7 43.274.7 45.374.0

79.3 220.2714.9 194.8711.8 220.2714.9 150.6711.7 165.4710.7

75.1 33.773.9 n.a. 13.971.8 2.470.2 16.672.2

74.2 30.372.7 16.071.5 20.871.8 13.371.1 15.971.9

73.9 24.874.5 12.671.1 16.771.4 7.970.9 12.771.6

74.5 27.072.0 15.871.5 21.071.6 13.772.0 17.672.3

78.3 38.673.6 23.072.3 28.572.9 17.971.6 26.473.5

10 (+20): Using the RSD of 6.6% (GLK3–5 quartz), 11.1% (RAH1–5

T) plus a 10% (20%) scatter derived from dose rate inhomogeneities.

s calculated.

ARTICLE IN PRESSN. Klasen et al. / Quaternary International 164–165 (2007) 21–32 31

problems. Partial bleaching prior to burial is the mainproblem together with the low luminescence sensitivity ofthe quartz grains. Both of these features raise difficulties infinding a suitable method for ED calculation. Theapproaches of Olley et al. (1998) and Fuchs and Lang(2001) caused underestimation of most sediments ages. Thetechnique by Preusser et al. (2007) gave mainly conclusiveresults, which are concordant with expected ages. Theinfluence of thermal transfer is of less concern for most ofthe samples investigated but it has apparently a signifi-cant effect on the IRSL (BL) signal of samples fromBaumkirchen. Despite the problems in dating theseproglacial sediments, OSL dating on quartz, feldspar andpolymineral fine grains represents a suitable method toconstrain the age of the deposits by considering the above-mentioned limitations.

Acknowledgements

This study was financially supported by the DeutscheForschungsgemeinschaft (RA 383/13-1) and the Geolo-gische Bundesanstalt Osterreich, Vienna. The authorsthank Gerhard Poscher (Innsbruck) for attendance in thefield at Baumkirchen and Udo Beha (University ofCologne) for providing Fig. 1.

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