R A P P O R T E Rfrån Institutionen för naturgeografi och kvartärgeologi

Applying the optically stimulated luminescence (OSL) technique to date the Weichselian glacial history of southern SwedenH Alexanderson, T Johnsen, B Wohlfarth, J-O Näslund & A Stroeven

No. 4

Reports from the Department of Physical Geographyand Quaternary GeologyStockholm University

Applying the optically stimulated luminescence(OSL) technique to date the Weichselian glacial

history of south and central Sweden

Helena Alexanderson1,2,3,*,Timothy Johnsen1,3, Barbara Wohlfarth4, Jens-Ove Näslund5 and Arjen Stroeven1

1Department of Physical Geography and Quaternary Geology, Stockholm University, Stockholm2Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, Ås, Norway

3Nordic Laboratory for Luminescence Dating, Risø National Laboratory, Roskilde, Denmark4Department of Geology and Geochemistry, Stockholm University, Stockholm5Swedish Nuclear Fuel and Waste Management Company (SKB), Stockholm

* project leader

Final report to SGU2008

i

Contents

Introduction 1Background 1Aim 2

Study areas, investigations and methods 3Study areas 3Field work 3Sampling equipment and procedures 3Laboratory work 3Analytical software 4

Fact sheet: OSL-terminology 5

Applications and case studies 6Dating the deglaciation: Småland, Värmland, Jämtland-Härjedalen 6Explaining problematic ages: Småland 7Comparing depositional environments: Värmland, Jämtland-Härjedalen 9Verifying OSL-ages against independent chronologies: Värmland, Blekinge 9Dating interstadial sediments: Bohuslän, Jämtland 11Testing recent beach sands 14

Technical issues 15Feldspar contamination 15Quality check I: Dose recovery 15Quality check II: Rejection criteria 16Thermal transfer 17Luminescence characteristics 17Sensitivity analyses 19

Other products 21Analysis software 21Natural radioactivity 22

OSL-dating in Sweden – discussion 23OSL vs geology 23Can we trust OSL-ages from Sweden? 24Causes of luminescence characteristics 25

Conclusions 27

Acknowledgements 28 References 29

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AppendicesFieldwork and sites (2 p.)1. OSL-ages (2 p.)2. TCN- and C14-ages (1 p.)3. Communication of results (2 p.)4. Travel report (1 p.)5. Summary statement of accounts (1 p.)6.

App. 1-5 are included in this document/fi le.App. 6 is a separate document/fi le.

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AbstractTo reconstruct former ice-sheet extent in space and time it is necessary with good chronological control. Optically stimulated luminescence is a dating method that has the age range, resolution and material requirements to provide this control as absolute ages of glacial events. This study has aimed to use and assess the OSL method on glacial and deglacial deposits in south and central Sweden. We have dated late-glacial and Holocene glaciofl uvial, glaciolacustrine, wave-washed, aeolian and lacustrine sediments at several sites in southern and central Sweden. The best results come from aeolian, beach and lacustrine sediments, for which there is good correspondence with independent chronological data. Ages from glaciofl uvial and glaciolacustrine sediments are signifi cantly scattered and only the youngest ages give expected ages. We have also dated the Pilgrimstad interstadial site in Jämtland to marine isotope stage 3. Dates from the interstadial sites Dösebacka (Bohuslän), Vålbacken, Andersön and Bulägden (Jämtland) are pending. OSL-dating in Sweden is not straightforward and care must be taken to select the best possible sites and sediments to get good and reliable results. Luminescence characteristics, which infl uence the quality of a date, seem largely determined by regional geology. Of the studied areas, Värmland is very good while Småland is problematic and Jämtland/Härjedalen diffi cult. As a general recommendation, one can generally trust OSL-ages from aeolian sediments, lacustrine and beach deposits, large data sets with several consistent ages and samples that have passed internal OSL quality checks. But one should be careful with OSL-ages from glaciofl uvial and glaciolacustrine sediments and organic-rich deposits, with single dates and samples without context or without background information.

SammanfattningFör att rekonstruera hur forna istäcken har varierat i tid och rum är det nödvändigt att ha en god ålderskontroll. Optiskt stimulerad luminiscensdatering är en dateringsmetod som har tillräckligt åldersspann, upplösning och materialkrav för att kunna ge absoluta åldrar för glaciala händelser under den senaste istidscykeln. Den här undersökningen har haft som mål att använda och utvärdera OSL-datering som metod på glaciala och deglaciala avsättningar i södra och mellersta Sverige. Vi har daterat senglaciala och holocena isälvs-, issjö- och svallavlagringar, fl ygsand och sjösediment på fl era ställen i södra och mellersta Sverige. De bästa resultaten kommer från fl ygsand, strand- och sjösediment, där åldrarna stämmer bra överens med oberoende åldersinformation. Åldrarna från isälvs- och issjösediment är spridda och det är bara de yngsta som stämmer med förväntat resultat. Vi har även OSL-daterat de interstadiala sedimenten i Pilgrimstad till marint syreisotopstadium 3. Proverna från de interstadiala lokalerna Dösebacka (Bohuslän), Vålbacken, Andersön och Bulägden (Jämtland) är ännu inte färdigmätta. OSL-datering är inte helt enkelt i Sverige och man måste vara noggrann när man väljer lokaler och sediment för att få bra och trovärdiga resultat. Kvaliteten på dateringar påverkas bland annat av luminiscensegenskaper hos den analyserade kvartsen och de verkar till stor del bestämmas av den regionala geologin. Av de undersökta områdena är Värmland mycket bra medan Småland är problematisk och Jämtland/Härjedalen svårt. Som en allmän rekommendation kan man vanligtvis lita på OSL-dateringar från fl ygsand, sjö- och strandsediment, på stora dataset med fl era samstämmiga dateringar, och prover som klarat de interna OSL-kvalitetskontrollerna. Däremot bör man vara försiktig med OSL-åldrar från isälvs- och issjösediment och från organiska avlagringar, med enstaka dateringar och med prover utan sammanhang eller utan bakgrundsinformation.

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1

Introduction

palaeotemperature records. Dating by correlation to global records only does not reveal regional variations and may lead to apparent, but not necessarily true, agreement with other records. Thus, there is a need for independent dating of glacial events in Sweden. So far, the absolute Swedish glacial chronology prior to the LGM has mainly been based on radiocarbon dates, but the use of the method is limited since most of the Weichselian is beyond the age range of the method and since glacial sediments contain no or little organic material. In recent years, relatively new methods such as optically stimulated luminescence (OSL) and terrestrial cosmogenic nuclide (TCN) exposure have been developed and applied to glacial sediments and pre-LGM deposits with good results (e.g. Owen et al., 1997; Hansen et al., 1999; Bierman et al., 1999; Alexanderson et al., 2001; Fabel et al., 2002; Stroeven et al., 2002; Spencer & Owen, 2004; Svendsen et al., 2004; Preusser et al., 2005). Generally there is a good agreement with independent dating control, where available. These two methods (OSL, TCN) have the advantage of dating deposits that are directly related to the ice sheet, for example glacifl uvial sediments deposited in front of the ice sheet (e.g. Richards, 2000; Alexanderson & Murray, 2007) and boulders in glacifl uvial deposits or on moraines (e.g. Briner et al., 2001; Fabel et al., 2006), respectively. They also have the potential to date samples from the Weichselian or older. A few investigations that have made more extensive use of OSL, or the closely related thermoluminescence (TL) method, have been carried out in Sweden, e.g. Kjær et al. (2006) in Skåne, Davids (2005) and Davids et al. (2005) in Halland, Lagerbäck (2007; pers.comm.) in central and northern Sweden and Alexanderson & Murray (2007) in Småland. Some results from these studies have, however, partly been unexpected or contradictory and show that either there are still some methodological issues with these applications that are not yet completely understood, or that the glacial/deglacial history is more complex than previously believed. This study is an attempt to resolve some of these problems when applied to Swedish deposits. The success of OSL dating in a certain area is partly dependent on the regional geology, which affects the sensitivity and other

BackgroundUnderstanding the past behaviour of the Weichselian ice sheet is important both for increasing the knowledge on how ice sheets form and react to e.g. changes in climate, as well as for more applied research on assessing the long-term safety for a geological repository for spent nuclear fuel in Sweden (SKB 2006). Even though the last glacial cycle, including the Weichselian glaciation, is the most well known of the Late Pleistocene glacial cycles, the reconstruction of glacial history prior to the Last Glacial Maximum (LGM) is in many cases diffi cult and ambiguous. The timing of ice-sheet advances and retreats in Sweden during the Weichselian is mainly based on correlation with ‘global’ continuous records such as ice cores or marine sediment cores and there is little independent regional age control, with the exception of the last deglaciation. This is partly due to the diffi culty in dating glacial sediments and partly to the relative scarcity of, so far, datable deposits older than the LGM. It has been proposed that most of Fennoscandia was ice-covered throughout the Middle Weichselian (Lundqvist, 1992). Lately, an increasing number of apparent sediment and fossil ages falling into that age range (e.g. Ukkonen et al., 1999; 2007; Olsen et al., 2002; Mäkinen, 2005) has led to the idea of a much reduced ice sheet before the fi nal expansion during the Late Weichselian (Arnold et al., 2002). Other studies also indicate that the glacial history of Fennoscandia may need a revision, for example Pytte et al. (2005) and Bøe et al. (in prep./pers.comm.; alternative deglaciation model in Rondane, Norway), Alexanderson & Murray (2007; ice-free conditions in Småland at 19-25 ka), Sarala et al. (2005) and Sarala (2005, pers.comm.; Finnish Lapland ice free at 29 ka) and Rinterknecht et al. (2005; 2006; late deglaciation of the southern Baltic). Some numerical ice-sheet models and reconstructions of the Fennoscandian ice sheet suggest an early Middle Weichselian glacial advance followed by deglaciation and (more or less) limited ice cover until the major ice-sheet growth leading up to the last glacial maximum started (Holmlund & Fastook, 1995; Kleman et al., 1997; Siegert et al., 2001; Boulton et al., 2001; Näslund et al., 2003). The ice-sheet expansion has been suggested to take place ~30 ka (e.g. Siegert et al., 2001; Näslund et al., 2003), based on correlation to global ice-volume and

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luminescence characteristics; variations in the type and properties of dated minerals and in depositional environments greatly affect the possibility of getting accurate and precise dates. It is, therefore, a necessary and important step to verify the OSL method for Swedish conditions by performing a study that includes both a relative chronological control (south to north transect, following the deglaciation) and a comparison with other independent absolute dating methods (TCN, C14). When we have better knowledge of under what circumstances the OSL method works for Swedish material, it can advantageously be applied to sediments from older events, such as Weichselian interstadials, and provide absolute dates of earlier events that would be important additions to the glacial chronology and very useful input data for ice-sheet reconstructions and climate models.

AimThe aim of this project has been to explore dating methods applicable to glacial and deglacial deposits in Sweden and thereby obtaining a better chronology for the Late Quaternary glacial history. The objectives were:

To test, assess and use the optically stimulated • luminescence (OSL) dating method, together with terrestrial cosmogenic nuclide (TCN) exposure and radiocarbon dating, in various depositional environments.Broaden the chronology of post LGM • deglaciation, and coupling existing coastal chronology to upland events in south and central Sweden.Begin a quantitative upland chronology for • pre-LGM events.

Fig. 1. Location map. Lannaskede and Vimmerby are both situated along the Vimmerby moraine in Småland. Dösebacka is located in Bohuslän just north of Gothenburg, while Brattforsheden is northeast of Karlstad, Värmland. The red hollow circle represents the location of several sites in Jämtland and Härjedalen.

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Study areasWe have worked in three main study areas (Småland, Värmland and Jämtland-Härjedalen) and on two complimentary sites from other parts of Sweden (Dösebacka, Hässeldala), see Fig. 1. The sites were chosen to provide a south-north transect of deglaciation ages, and because sediments of interest both for the glacial geological story and for luminescence dating perspective could be found there.

Field workField work was carried out during several periods in 2006, 2007 and 2008, see App. 1. The work included follow-up studies of some Småland sites (Alexanderson & Murray, 2007), sedimentological and geomorphological studies in Värmland and Jämtland as well as investigations of previously described interstadial sites in Bohuslän and Jämtland. Sedimentological and stratigraphical descriptions were made to be able to compare the new data with the older information, usually from when the sites were better exposed than presently. In addition to optically stimulated luminescence (OSL), the sampling programme included radiocarbon and terrestrial cosmogenic nuclide (TCN; cosmogenic exposure) dating.

Sampling equipment and proceduresFor sampling of OSL-samples we used opaque grey plastic tubes (Fig. 2a), sharpened at one end. We had tubes of various sizes; the most useful were 20 cm long with diameters of 75 mm or 60 mm (Fig. 2A). The plastic was 2-4 mm in thickness; 4 mm or thicker is recommended for sturdiness and less risk of light penetration. Before sampling, sections were cleaned and commonly about half a meter of material was

removed from the wall to reach a fresh surface. The tubes were hammered into this surface (see upper left photo on front page), excavated and sealed with lids and duct tape (‘silvertejp’). We took care not to expose the sample to any light during this procedure. The tubes were then packed into black plastic bags or light-tight boxes for storage until opened in the laboratory. Cylinder volumeters, also called pF-rings (Fig. 2b), were used for water content measurements. They were also hammered into the sediment, next to the OSL-sample, then excavated, sealed with lids or plastic foil and tape and stored until analysed in the laboratory. TCN-samples were taken with hammer and chisel from the top of boulders (see upper right photo on front page).

Laboratory workHelena Alexanderson and Timothy Johnsen prepared the OSL-samples at Stockholm University and at the Norwegian University of Life Sciences. We also did the fi nal preparation and much of the analyses (dose estimations, dose-rate measurements) at the Nordic Laboratory for Luminescence Dating (NLL) at Risø, Denmark (collaborator: Andrew Murray). Due to time constraints, once the analysing protocol had been decided, most samples were however left at NLL to be measured by their technicians; Mette Adrian, Anne Birgit Rasmussen and Vicki Hansen and with help from Jan-Pieter Buylaert. Each OSL-sample consists of three subsamples, A, B and C. A comes from the mid part of the sampling tube and is used for dose measurements. For information on preparation of this subsample see Table 1. Subsample B, which is used for dose-rate measurements, consists of the

A

Study areas, investigations and methods

B

Fig.2. A. Various tubes that were used for OSL-sampling. B. Professional (left) and homemade (right) pF-rings for water-content measurements.

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material from the ends of the tube and possibly from an additional bag if small tubes are used. The B sample is dried, weighed, heated to 450° for loss-of-ignition, weighed, grinded, weighed, mixed with wax and cast into so called gamma cups (see lower left photo on front page) and weighed again. After at least three weeks, when radon (222Rn) has achieved equilibrium with its parent radium (226Ra), the cups are put into a gamma spectrometer to measure the concentration of radioactive elements (Murray et al., 1987) for calculation of the annual dose (see factsheet). Subsample C is used for water content measurements and is taken separately in a pF-ring (cylinder volumeter; Fig. 2B). The pF-ring with sediments is weighed with natural water content, then saturated and fi nally dry, after which water content can be calculated as a mass percentage. Alternatively, sediment from the sampling tube can be used, but this results in less precise and less accurate measurements. Generally, we used the fraction 180-250

μm for dose measurements, but due to variation in sediment properties, other fractions have also been used (63-90, 90-180 μm, etc). OSL-analyses were done according to SAR-protocols (Murray & Wintle 2000, 2003), that were adapted to suit the characteristics of each sample batch. Specifi cs of procedures are/will be found in the separate publications regarding each study. TCN rock samples were crushed and sieved at the Natural History Museum and Stockholm University, respectively, and then sent for further preparation and analysis at the Glasgow University Cosmogenic Nuclide Laboratory (collaborator: Derek Fabel). Radiocarbon dating was done at the Lund University Radiocarbon Laboratory.

Analytical softwareFor analysis of OSL-data we have used the Risø package (Analyst 3.24, SequencePro 3.20, TLViewer) and template Excel-spreadsheets of own design and modifi ed from NLL templates (see Other products).

Table 1. Typical preparation of subsample A from an OSL-sample, all of which is carried out under dark room conditions. The aim is to get a pure quartz sample of a suitable grain size. All samples have not been put through exactly the same procedure as we have had access to different equipment at various times and also learned new things along the way.

Procedure PurposeMagnetic separation To remove magnetic grainsWet sieving To get the grain-size fraction to be usedHeavy liquid separation at 2.62 g/cm3

To get rid of K-feldspars and other light minerals. The feldspar fraction was dried and stored in the archive at Risø, while the quartz fraction was used for further analyses

10% HCl for 5-30 min. To remove carbonates; time depends on carbonate content in sample10% H2O2 for 15-120 min. To remove organics; time depends on organic content in sample10% HF + 38% HF for 60-180 min.

To remove everything but quartz (ideally) and to etch the outer surface of the grains to remove the parts affected by alpha radiation; time depends on grain size and purity of sample

10% HCl for 40 min. To remove any fl uorides that might have formed during previous step50º for several hours (~overnight) To get sample dry

IR-test in OSL-reader To see if the sample consists of pure quartz; if yes proceed with dose measurements; if no repeat treatment with HF or use another density for heavy liquid separation

Fig. 3. A. Nine aliquots on stainless steel disks have been put on a reader wheel. B. One of the OSL readers used within this project. C. Typical growth curve from a well-behaved sample. Lx/Tx denotes the corrected luminescence signal, i.e. the natural or regenerated luminescence signal divided by the test signal. Blue numbers represent run numbers, see SAR-protocol in Table 2.

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Fact sheet: OSL terminologyFor a reader not familiar with Optically Stimulated Luminescence (OSL) terminology, some central features, words and defi nitions are explained here.

The OSL age equation: Age = dose / dose rate

Dose: the amount of radiation a sediment has received in nature (natural dose) and which is measured in a laboratory as the equivalent dose (De or ED). Dose is measured in Gray (Gy), where 1 Gy = J/kg.

Dose rate: the amount of radiation a sediment receives per unit of time. In nature the radiation comes from radioactive elements in the surrounding sediment/bedrock (mainly K, U, Th) and from cosmic rays. The dose rate to a grain is affected by the water content in the sediment since water absorbs some of the radiation that would otherwise have reached the grain. Higher water content thus leads to lower dose rate and thereby higher age for the same dose, and vice versa. Sediment dose rates are measured in Gy/ka and commonly range between 0.5 and 5 Gy/ka.

Aliquot: A subsample used for measuring the equivalent dose. The size of aliquots can vary from several hundred to thousands of grains (large aliquots) to some tens to hundred grains (small aliquots) and in the extreme to single grains. The grains are loaded onto 1-cm-diameter stainless steel discs that have been sprayed with silicone oil (Fig. 3a), and which are then put into an OSL-reader.

OSL-reader: A machine used for determining the equivalent dose by measuring the luminescence (Fig. 3b). In this project we have used Risø OSL/TL-readers at the Nordic Laboratory for Luminescence Dating. An OSL reader can be programmed to automatically do all measurements in a SAR-protocol, including heating, irradiating with a beta-radiation source, illuminating and stimulating samples with blue or infrared light from light-emitting diodes (LEDs) and measuring the emitted photons from the aliquots with a photo-multiplier tube (PMT).

SAR-protocol: Single-aliquot regeneration protocol, an analytical protocol that is standard for many OSL measurements. A sequence of measurements is run on single aliquots to estimate the dose for each aliquot. The protocol includes steps that account for changes in properties during measurement as well as quality tests. Eventually, the average from measurements of several aliquots (usually ≥24) is used for the age calculation.

Table 2. A typical SAR-protocol. The protocol can be adapted to a particular sample batch by, e.g., changing preheat and cutheat (in this case TL=thermoluminescence) temperatures and including an extra step with OSL infrared diodes for 100 s before the blue OSL measurements. Read column by column.

Run 1 Run 2 Run 3 Run 4 Run 5 Run 6Set 1 Give regeneration

dose 1Give regeneration dose 2

Give regeneration dose 3

Give regeneration dose 4 = 0 Gy

Give regeneration dose 5 = dose 1

Set 2 Preheat to 220°C Preheat to 220°C Preheat to 220°C Preheat to 220°C Preheat to 220°C Preheat to 220°CSet 3 OSL blue LEDs

125° 40sOSL blue LEDs 125° 40s

OSL blue LEDs 125° 40s

OSL blue LEDs 125° 40s

OSL blue LEDs 125° 40s

OSL blue LEDs 125° 40s

Set 4 Give test dose Give test dose Give test dose Give test dose Give test dose Give test doseSet 5 TL 180° TL 180° TL 180° TL 180° TL 180° TL 180°Set 6 OSL blue LEDs

125° 40sOSL blue LEDs 125° 40s

OSL blue LEDs 125° 40s

OSL blue LEDs 125° 40s

OSL blue LEDs 125° 40s

OSL blue LEDs 125° 40s

Set 7 Illumination blue LEDs 280° 40 s

Illumination blue LEDs 280° 40 s

Illumination blue LEDs 280° 40 s

Illumination blue LEDs 280° 40 s

Illumination blue LEDs 280° 40 s

Decay or shine-down curve: As a sample is exposed to light in an OSL-reader, it emits photons. Most photons are emitted within a few seconds, then the signal fades to a low background (see Fig. 15).

Growth curve: By using a SAR-protocol you build a growth curve (see Fig. 3c), which you can use to calculate the equivalent dose. If the natural luminescence signal intersects the upper part of the growth curve, i.e. close to saturation, the uncertainty in the fi nal age is larger than if the intersect is on the lower, linear part of the curve.

For more details on OSL-dating, the reader is referred to the following papers:Overview of method: Murray & Olley, 2002; Vandenberghe, 2004 (chapters 1-3); Lian & Roberts, 2006 Reviews of uses in relevant environments: Richards, 2000; Wallinga, 2002a; Koster, 2005SAR-protocol: Murray & Wintle, 2000; 2003

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Applications and case studies

from each area are used (Fig. 4). For all areas there is a range of ages, encompassing several tens of thousand years. The youngest ages are derived from sandurs, delta topsets and glaciolacustrine beaches. Foreset and delta toe sediments generally have a wider spread in ages, as do glaciolacustrine deposits, and they also tend to be older. For a few sites, it is possible to invoke a pre-last glaciation origin to explain the old ages and thus that the deposit does not belong to the last deglaciation but to an earlier event (requiring a geological re-interpretation). For other sites this is more diffi cult. One example is the investigated sandurs in Småland, which are not covered by till or show any signs of glacial overriding, and where one of the sandurs also continue down to a delta at the highest coastline. Conclusion: It is possible to date the last deglaciation by OSL in Sweden but it is not straightforward. Large local datasets are needed due to the wide scatter of ages. Of the tested depositional environments, shallow-water deposits such as glaciolacustrine or glaciomarine beaches, sandurs/delta topsets and some delta foresets seem to give the best results.

0

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(ka)

SMÅLAND VÄRMLAND JÄMTLAND-HÄRJEDALEN

Fig. 4. Plot of OSL-ages (with standard errors) from the three study areas, sorted according to age in each area and classifi ed as sandur, delta, glaciolacustrine and glaciolacustrine beach. The Småland delta and sandur ages are from Alexanderson & Murray (2007, recalculated), all other ages are unpublished from Alexanderson and Johnsen. Grey thick lines indicate the deglaciation ages according to J. Lundqvist (2002), i.e. ages that would be expected based on previous research in the area or its surroundings. The line should be much wider for Jämtland-Härjedalen since there is a range of deglaciation ages due to the size and topography of the area.

Dating the deglaciation: Småland, Värmland, Jämtland-HärjedalenA direct age of deglaciation can be provided by dating glaciofl uvial or glaciolacustrine sediments that were deposited as the ice retreated from an area. To give a correct OSL age the sediments must, however, have been well bleached (i.e. exposed to sunlight) before deposition, and not all glaciofl uvial sediments are therefore well suited (Richards, 2000). Good examples would be proglacial sediments that had been subaerially transported some distance before being deposited, such as distal sandur deposits, or glacial-lake beach sediments, which have been washed in shallow water for a suffi cient amount of time (Mangerud et al., 2001; Murray & Olley, 2002). Glaciofl uvial and glaciolacustrine sediments have been sampled in Småland (Vetlanda-Vimmerby area), Värmland (Brattforsheden) and Jämtland-Härjedalen (several sites) and have been dated by OSL. The sediments were deposited on sandur plains, in deltas and glacial lakes (basin fl oor, beach), all believed to be related to the last deglaciation, and were expected to give successively younger ages towards the north (Småland > Värmland > Härjedalen-Jämtland). The expected south to north trend with decreasing ages can be seen, if the youngest ages

sandur delta glaciolacustrine glaciolacustrine/marine beach

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Explaining problematic ages: SmålandThe 19-25 ka ages of glaciofl uvial sediments from Småland (Alexanderson & Murray, 2007) require either an OSL-methodological explanation for too old ages or rewriting of the glacial history of southern Sweden. We have tested for both options. A common cause for getting too old ages in OSL dating, especially in a glacial environment, is incomplete bleaching (Gemmell, 1988; 1999; Richards, 2000; Lukas et al., 2006), when sediments have not seen enough light to reset the OSL clock. The occurrence of incompletely bleached grains in a sample may be determined through, for example, statistical analyses of small-aliquot or single-grain data (e.g. Wallinga, 2002b). Such analyses have been performed for a few representative samples of sandur and delta sediments from Småland. According to small-aliquot data, sandur sediments appear well-bleached while one of the delta samples may suffer from incomplete bleaching (Alexanderson & Murray, 2007). Seen generally, the ~30-75 ka delta ages could thus be explained by incomplete or non-existent bleaching during deposition. However, the sandur ages cannot. Dose measurements of single grains from

three samples have also been made (Alexanderson, unpublished). The results are inconclusive from an explaining-the-ages point of view, but they do show that only ~1-2% of the grains give measurable and acceptable signals and that there is a wide spread in dose (and thus in age) within each sample (Fig. 5). The percentage of grains giving signals is low compared to studies in other areas, where 5-40% of the grains give 90-95% of the luminescence signal (Duller et al., 2000; Jacobs et al., 2003). Most of the Småland samples suffer from some feldspar contamination; this does not, however, seem to cause a dose overestimate (see Fig. 12 and Technical issues below). The presence of feldspar grains has been used in the single grain analyses as we have compared doses from both quartz and feldspar from the same sample. About half as many feldspar grains as quartz grains give measurable and acceptable signals. The doses calculated from these grains give the same dose as for quartz for the sandur/delta top samples but is much higher for the delta foreset sample. This is another indication that the sandur sediments are well-bleached while the delta sand is not. Feldspar bleaches more slowly than quartz (Godfrey-Smith et al., 1988; Fuchs et al., 2005) and if quartz and

043045: Single grain IRSL

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5 35 65 95 125 155 185 215 245 275 >300

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043045: single grain green OSL

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051302: single grain green OSL

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Fig. 5. Single-grain data. A. Green OSL (quartz) and B. infrared stimulated luminescence (IRSL; feldspar) from sandur sample 043045. C. Green OSL and D. IRSL from delta sample 051302.

043045 greenED=48±8 Gy n=45

043045 IRSLED=58±9 Gyn=17

051302 greenED=66±7 Gyn=49

051302 IRSLED=102±10 Gyn=45

A

D

B

C

8

feldspar doses are roughly similar, this largely suggests that bleaching conditions have been good (Hansen et al., 1999); fading not taken into account. Thus we cannot fi nd any evidence for incomplete bleaching of the sandur sediments, which could have explained the age overestimation. The samples are not perfect (wide dose distributions, not very bright, etc.) but internal controls do not show anything wrong. To get independent chronological data to compare the OSL-ages to (thus checking the geological interpretation), we dated boulders from the Vimmerby moraine (Agrell et al., 1976; Malmberg Persson et al., 2007; Malmberg Persson et al., submitted), with which most of the dated glaciofl uvial sediments are associated. The boulders were dated by cosmogenic exposure dating and six samples give consistent ages averaging 13.8±1.0 10Be ka (Johnsen et al., submitted), which is in line with e.g. clay-varve and radiocarbon ages of the deglaciation at the adjacent coast. However, the exposure ages provide only minimum ages to the delta

sediments (the till is on top of the delta) and are not defi nitely stratigraphically connected to the sandur sediments, although geomorphologically the connection seems very likely. The problem is thus not quite solved, yet. The simplest explanation is that the OSL ages are wrong, but why are they wrong? There are no obvious methodological explanations for the apparently too old ages. More effort is thus needed. One approach would be to test other types of sediments (aeolian, beach) from the area, preferably of certain deglaciation origin, and see whether they give “deglaciation ages” or if they, too, give too old ages. Here it is interesting to note that the age (18±1 ka) that so far is closest to the generally accepted deglaciation age (13-14 ka; Lundqvist & Wohlfarth 2001; J Lundqvist, 2002) comes from a till (Alexanderson, unpublished). Conclusion: We cannot falsify the OSL-dates on internal grounds but new TCN-ages of related deposits support the current geological interpretation. The OSL-ages seem, for currently unknown reasons, too old.

Fig. 6. Dates from Brattforsheden sorted according to age and depositional environment. Bars represent standard errors. Note different scales on upper and lower panel. A. OSL-ages and comparison between different depositional environments. B. Independent age determinations of related deposits and events. TCN-ages and one of the young radiocarbon ages are from this study (Alexanderson et al., unpublished). The other young radiocarbon dates are from Bergqvist & Lindström (1971), the old radiocarbon ages (isolation ages) are from Jan Risberg (pers.comm.). TL-ages of aeolian sediments are from Lundqvist & Mejdahl (1987).

-1

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Age

(ka)

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Age

(ka)

Soil formation (cal. C14)

Isolation from sea (cal. C14)

Moraine formation(TCN)

B

OSL-agesAeolian Wave-washed Delta Till

TCN-age from erratics Calibrated 14C-age

A

Aeolian deposition(TL)

TL-age

9

Comparing depositional environments: Värmland, Jämtland-HärjedalenBrattforsheden in Värmland is a good site for comparing OSL-ages between nearly contemporaneous deposits of various origins within a small area (see App. 4a:3). A large ice-marginal delta, surrounded by till, was built up to the highest coastline. During land uplift deltaic sediments and till were wave-washed and somewhat later aeolian dunes formed on the now dry delta surface (Hörner, 1927; Fredén 2001). Litho- and morphostratigraphy give the following relative chronology: till > deltaic deposits > wave-washed sand > aeolian sand and silt. The risk of incomplete bleaching decreases in the same order as the relative chronology, it is highest for the till and lowest for the aeolian deposits. The subglacially deposited till is not expected to have been zeroed at all, but is used as a reference of unbleached source material. As described above, deltaic sediments may be incompletely bleached, while wave-washed sand, i.e. beach and shallow water deposits, would be expected to have been bleached during deposition (Mangerud et al., 2001; Murray & Olley, 2002). Aeolian sediments should be excellent for OSL dating since they most likely were well bleached (Murray & Olley, 2002; Banerjee et al., 2003) during transport and deposition. OSL-samples from till and delta should thus give maximum ages of deglaciation, and aeolian samples minimum ages. The expected order of age is also what we fi nd at Brattforsheden (Fig. 6a). The unbleached till gets an old age (97±7 ka), which is not related to the time of deposition. The deltaic deposits range in age from 83 to 12 ka, where the oldest age – from lower delta foresets – is likely incompletely bleached and should be considered an outlier. The wave-washed sand is largely contemporaneous with the delta, according to the OSL-dates. The aeolian deposits fall into two distinct age groups, ~11-8.5 ka and <300 years. The older group shows that strong aeolian activity took place just after the ice retreated from the area and a few thousand years onward, confi rming the suggested paraglacial origin of the dunes (Hörner, 1927; Mycielska-Dowgiallo, 1993; Schlyter, 1995; Ballantyne, 2002). Reactivation of the dunes seems to have occurred in the early-mid 17th and 18th centuries, indicated by young aeolian sand overlying a soil horizon in a dune. Two samples of recent/modern aeolian sediment also give very young ages, as expected.

We attempted a similar study, although not as geographically constrained, in the Jämtland-Härjedalen area (Fig. 7). However, since the number of samples from each type of deposit was small, the exact age relation between sites not always clear and there was a wide scatter of ages, the results are not as obvious as from Värmland. Four samples also had to be rejected since dose recovery tests showed that the analytical protocol did not work for those samples. The aeolian samples are youngest, ranging in age from 10 to 6.5 ka. In addition, a sample from modern aeolian sand gives 220±280 years (large uncertainty due to weak signals), which shows that aeolian sand is bleached properly. Some of the glaciolacustrine sediments may not have been bleached as they give very old ages; yet other samples, especially those from shallow-water deposits, give young ages. Two samples suggest a Middle Weichselian age for a sandur, older than expected. Conclusion: We get the expected order of age from the different depositional environments: till > delta > wave-washed sand > aeolian. Deltaic and glaciolacustrine sediments show large scatter in ages, probably due to incomplete bleaching. Verifying OSL-ages against independent chronologies: Värmland, BlekingeThe OSL-ages from Brattforsheden can be compared to several types of independent chronological information: cosmogenic exposure (TCN) ages from boulders on adjacent moraines, shoreline displacement curves, AMS radiocarbon ages from lake isolation events, bulk and AMS radiocarbon ages for soil development, TL-ages for aeolian sediments and historical data (Fig. 6b). The TCN-ages average 11.4±1.2 10Be ka and record the time of moraine formation, which should be contemporaneous with deposition of till and delta building. This age also agrees well with the standard deglaciation chronology, according to which the area should have been deglaciated ~11 ka (J Lundqvist, 2002). As expected the till OSL-age is much too old, as is one of the delta samples. However, the youngest ages from the delta deposits fall within the same age range and show that we can get the ‘right’ answer from OSL-dating of deltaic deposits. The highest coastline in the area is at 180-

10

190 m a.s.l. and a shore-line displacement curve show initial land uplift to be rapid (Fredén, 2001). The wave-washed sands at 173, 158 and 145 m a.s.l. should have been deposited between approximately 9500 and 9000 14C-years BP, which corresponds to ~10.7-10 cal. ka BP. This can also be compared to two radiocarbon ages from a lake ~24 km northeast of Brattforsheden, according to which sea-level was at 160-165 m a.s.l. by 10.7-10.2 cal. ka BP (Jan Risberg, pers.comm.). The OSL-ages of the wave-washed sand are 1000-1500 years older than the time-frame suggested above. The timing of land uplift also determines the maximum age of the aeolian deposits, which could form fi rst after the delta surface was dry. The aeolian deposits should thus be younger than ~10.5 ka. With one exception (Nyängen, where the dates also are stratigraphically inverted), this is also the case as the other ages fall between 10.7 and 8.5 ka. Two TL-ages (Lundqvist & Mejdahl, 1987) match the older age group. The gap between the two periods of aeolian activity fi ts nicely with a time of soil formation, which according to radiocarbon ages took place between ~3500 and 500 years ago (Bergqvist & Lindström, 1971; Alexanderson, unpublished). The youngest TL-age, which is considered not so reliable by the authors (Lundqvist & Mejdahl, 1987), is older than the young age group. The small beach dunes at Lake Mången were stabilised by vegetation in the early 20th century (Hörner, 1927) and this agrees well with the OSL-age of

120±10 years (AD 1876-1896). Lateglacial lacustrine sediments from Hässeldala in Blekinge are well dated by radiocarbon and tephrochronology (Wohlfarth et al., 2006). Parallel samples were taken from the known Bölling-Alleröd and Younger Dryas intervals of two cores (courtesy of Barbara Wohlfarth) to test this type of deposit for luminescence dating and to correlate with the known, independent chronology. There is a clear difference in estimated dose between the Bölling-Alleröd samples (19-22 Gy) and the Younger Dryas samples (10-15 Gy), but using the measured, saturated water content in the dose-rate calculations results in too young ages (Fig. 8; Alexanderson, unpublished). It is most likely that these gyttja sediments have experienced much compaction through time, which has lowered the water content and successively increased the dose rate. The average water content since time of deposition is thus much higher than the now measured saturated percentage, but the water contents needed to get the correct ages are not unreasonable (Fig. 8). Thus, the samples can give the correct ages, but for a site without detailed knowledge of water-content history, which is commonly the case, this type of sediment is hard to date. For minerogenic sediments, where the range of possible water contents is much less (~5-40 %), this effect is much smaller. Conclusion: There is an overall good agreement with independent chronology, despite a large scatter in OSL-ages from certain types

Fig. 7. OSL-ages from Jämtland and Härjedalen, sorted according to depositional environment and age. Bars represent standard errors.

Jämtland-Härjedalen

0

20

40

60

80

100

120

140

160A

ge (k

a) AeolianGlaciolacustrineSandur

10

11

of deposits. Organic-rich deposits may be problematic due to unknown compaction and water content histories.

Dating interstadial sediments: Bohuslän, JämtlandAs a second step of the project, we wanted to date sediments from previously known and described interstadial sites. Two sites – Dösebacka in Bohuslän and Pilgrimstad in Jämtland – were selected for more extensive sampling (see App. 4a:2, 4). In addition, two-three samples each from Vålbacken, Andersön and Bulägden in Jämtland were taken. Dösebacka has been described mainly by Hillefors (1969; 1974; 1983; 1986; Alin &

Sandegård, 1947) and a few absolute dates are available from the site (Table 3). The sedimentary succession encompasses two or three interstadial phases, indicated by sorted sediments and horizons with wind-polished clasts below a thick till. Nine OSL-samples were taken from the interstadial sediments (Fig. 9). Presently, the samples are still being analysed at Risø so we have no data yet. Preliminary test measurements indicate that the samples suffer from feldspar contamination and so a post-IR blue SAR protocol has been adopted. We also got the opportunity to excavate part of the remaining section at Pilgrimstad in Jämtland and take samples for OSL- and radiocarbon dating as well as for palaeoecological analyses (Barbara

y = 0.0352x + 3.8634

0

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16

18

20

0 50 100 150 200 250 300 350 400 450

Water content (%)

Age

(ka)

Sample 081310

Known age

Mea

sure

d w

ater

con

tent

Fig. 8: Age depending on water content for one of the Hässeldala samples, 081310. The blue vertical lines denote the measured natural and saturated water content in the sample; the horizontal blue lines give the age with this water content. The red horizontal lines represent the known age of the sediment (Bölling-Alleröd 14-13.8 ka; Wohlfarth et al., 2006) and the vertical lines the water content needed to get this age with the current dose data. The black line is a linear trend line with the equation shown in the upper right corner.

Table 3. Previous dates from Dösebacka.Age (years) Type Reference Comment

24020 +450/-425 BP Bulk radio-carbon on clay Hillefors (1983) Younger Dösebacka-Ellesbo

interstadial

36000 +1550/-1300 BP; 36-44 ka

Bulk radio-carbon on mammoth tusk

Hillefors (1983); Ukkonen et al. (2007) Older Dösebacka-Ellesbo-interstadial

87000–61000 TL (three samples) Hillefors (1986); Påsse (1998) Older Dösebacka-Ellesbo-interstadial

>41000 BP bulk radiocarbon Hillefors (1986) Older Dösebacka-Ellesbo-interstadial

12

Wohlfarth). Five OSL-ages are so far fi nished; fi ve more are in the process of being measured. The Pilgrimstad site has been investigated by several people (Kulling, 1945; Frödin, 1954; Lundqvist, 1967; Robertsson, 1986, 1988; Garcia Ambrosiani, 1990) and there exist a number of absolute ages already. However, most of these are infi nite or old fi nite radiocarbon ages, which few believe are reliable (Fig. 10). The basis for the age of the interstadial deposits has therefore mainly been palaeocological correlation to known interstadial sites in continental northwestern Europe. The

main interpretation has been to correlate the Pilgrimstad interstadial to one or both of the Early Weichselian interstadials Brørup and Odderade (Robertsson, 1988). However, if the (previous) absolute ages were taken at face value, a Middle Weichselian interstadial such as Moorshoefd could also be possible but was considered less likely (Robertsson, 1988). The new OSL ages support the latter proposal of a Middle Weichselian interstadial, with (so far) fi ve consistent ages ranging from 44±4 to 48±3 ka (Figs. 10, 11). The consistency suggests that there is no problem with incomplete bleaching,

Fig. 9. Simplifi ed log from the excavated section at Dösebacka. Sampling levels for OSL- and radiocarbon dating are indicated. Radiocarbon dating has not been performed since no organic matter was found in the samples. The left log is at ~30 m a.s.l., the smaller log to the right is at ~45 m a.s.l. For descriptions of units, see App. 7a:4.

Lithofacies codesGrain sizeCoG cobbles+gravelGS gravelly sandS sandSi siltC clayD diamicton(S) sandy

Gy gyttja

Structuresm massivemm matrix-supported, massivems matrix-supported, stratifi edcm clast-supported, massives stratifi edl laminatedr ripple-laminatedpp plane-parallel lamination(def) deformed(ng) normal grading(ig) inverse grading

13

if there was then randomly scattered ages would be expected. A higher original water content has been used for the gyttja sample to account for compression; the other minerogenic samples are not affected by this to the same degree. Samples were also taken from other interstadial sites in Jämtland: Andersön, Vålbacken and Bulägden. These samples are still in the process of being measured and there are no fi nal results yet.

Fig. 10. Simplifi ed stratigraphy and summary of absolute ages from Pilgrimstad. For lithofacies code legend, see Fig, 9.

Conclusion: The Pilgrimstad interstadial sediment give a MIS 3 age (44-48 ka), which is younger than previously believed. So far there are no results from Dösebacka and the interstadial sites in Jämtland as measurements are still ongoing.

14

Testing recent beach sandsThree samples of recent beach sand, previously sampled by Helena Alexanderson, were analysed as a survey of luminescence characteristics for other geographical areas. Since the samples had been exposed to light they were not dated, but tested with dose-recovery measurements. The samples came from Haväng (Skåne), Mellbystrand (Halland) and Tofta (Gotland). The sample from Haväng appears the best of the three, it is brightest with a dose recovery

ratio of 1.01 (n=3). The sands from Mellbystrand and Tofta are very dim and due to poor recycling ratios it was diffi cult to get enough acceptable aliquots. Dose recovery ratios were 0.94 (n=1) for Mellbystrand and 0.76 (n=3) for Tofta. As only one dose recovery measurement could be done, i.e. one temperature combination only, it is diffi cult to tell whether these sediments would be better behaved with other preheat/cutheat temperatures, as has been the case for other analysed samples.

Fig. 11. Section sketch of the excavated part of the section at Pilgrimstad. For lithofacies code legend, see Fig. 9.

15

Technical issuesis no correlation between estimated dose and the IR/Blue ratio (Fig. 12). If there was a correlation, only aliquots with IR/Blue ratios <10% were accepted. There are methodological ways to overcome feldspar contamination:

Include heavy liquid separation as a step • in the sample preparation. By using LST heavy liquid with a density of 2.62 g/cm3 it is possible to separate the lighter K-feldspar from the heavier quartz. This step also has the advantage of getting a subsample of feldspar, in case OSL-dating of that mineral will be attempted later.Use a double SAR-protocol (post-IR blue) • and measure the blue-stimulated signal after a 100 s long stimulation with infrared light, which reduces the effect of feldspar.New techniques such as pulsed OSL (Denby • et al., 2006) will also help purify the quartz signal in relation to feldspar, but this technique has not been available to us during this project.

Estimated dose vs IR/B (natural)

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0 5 10 15 20 25

IR/B ratio (%)

ED (G

y)

Fig. 12. The equivalent dose vs the infrared-to-blue (IR/B) ratio for aliquots from sample 043037. There does not seem to be any correlation between feldspar contamination and equivalent dose for this sample, as for most other samples from Småland.

Quality check I: Dose recoveryDose recovery is one of the most important tests to determine how well a sample can recover a given dose, i.e. if the analysing protocol can determine the dose (and thus the age) properly. Ideally, the ratio between the measured and the (laboratory) given dose should be one, but values between 0.9 and 1.1 are commonly accepted.

The analytical protocol is adapted to give the best dose recovery results. For example, preheat and cutheat temperatures can be changed. Usually the same protocol is used for samples from the same area, but it has been evident in this project that it can also be site specifi c, so that samples from two nearby sites respond differently to the

Feldspar contaminationIdeally, after chemical preparation you have a pure quartz sample to do the analyses on. However, this has not always been the case in this project. Many samples, especially from Jämtland and Småland, have suffered from feldspar contamination – that is, not all feldspar or other minerals have been removed in the chemical treatment and now contribute to the luminescence signal that is measured. The standard limit for considering feldspar contamination a problem is when the infrared signal (feldspar) is more than 10% of the blue signal (quartz). This is routinely tested for all samples, and if the infrared/blue ratio is >10% then a post-IR blue protocol (cf. Tables 1, 2) has been used. The effect of feldspar contamination may be an age overestimate, as the estimated dose appears higher when more feldspar is present in the sample. Feldspar is commonly bright, bleaches more slowly than quartz and can contain higher doses and it can thus make itself noted in a not-as-bright quartz sample with lower dose. However, feldspar contamination must not necessarily be a problem; for many of the Swedish samples there

16

same protocol settings. This is most likely due to different sources for the material and/or to different depositional environments, both factors that infl uence the luminescence characteristics of quartz (see below). The mean of all dose recoveries performed so far on the Swedish samples is 1.06±0.01 (with standard error; n=295; Fig. 13). This is fi ne and shows that the analysed quartz generally can recover a given dose and thus can be used for optically stimulated luminescence dating.

Quality check II: Rejection criteriaEven if dose recovery tests show that a sample should give the right dose, not all aliquots from that sample may be good. Rejection criteria are therefore applied to individual aliquots to exclude those whose properties are not suitable for dating. Standard rejection criteria include recycling ratio within 10% of unity (the reproducibility of the aliquot) and recuperation less than 5% of the natural signal (that the aliquot gives no signal with zero dose). Other factors that are taken into consideration are the strength of the

signals compared to background levels and the appearance of growth and decay curves. For most samples analysed within this project, rejection of aliquots due to these criteria do not make much difference to the end results, the dose estimate and thus the age (Table 4). The uncertainty of the dose estimate might change, usually to the better, if strict rejection criteria are applied, but it might also get bigger mainly due to a lower number of data points. If one had unlimited machine time and large amounts of material, then strict criteria should be applied and measurements continued until a suffi cient number of acceptable aliquots were acquired. However, these ideal conditions were not valid during this project. The percentage of aliquots that have been rejected varies greatly between samples (Table 4). For some samples all aliquots can be accepted, but for others less than 50% can be used. A high rejection ratio means that more measurements (=time and material) are needed to get a single date and uncertainties may also be larger.

Fig. 13. Histogram of dose recoveries for the Swedish samples.

Table 4. Examples of comparison between equivalent doses (with standard errors) for all and accepted aliquots, respectively, including the percentage of accepted aliquots.

Sample ED (Gy)all aliquots

nall

ED (Gy)accepted aliquots

n acc.

n acceptedof total

043038 52.0±2.6 24 52.0±2.6 24 100%061320 39.6±1.5 24 38.2±1.3 21 88%061311 29.9±1.1 23 29.7±1.3 20 87%061348 129.5±6.4 45 135.1±7.3 30 67%061350 18.4±1.5 48 15.5±1.9 23 48%

Dose recovery

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90

-0.1 0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95 1.05 1.15 1.25 1.35 1.45 1.55 1.65 1.75 1.85 1.95 2.05 2.15 2.25 2.35 2.45

Ratio measured/given dose

Num

ber o

f occ

urre

nces

Dose recoverymean = 1.06±0.01 (n=295)

Recycling for same aliquotsmean = 1.00±0.01 (n=295)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2 4 2 5

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5

17

Thermal transferThermal transfer is caused by the transfer of electrons between different traps during measurement, for example from light-insensitive to light-sensitive traps in the quartz crystal during preheating (basic transfer; Vandenberghe, 2004). This means that electrons from deep traps, which were not bleached during the last deposition, may end up in shallow traps that are used for measuring OSL and that were bleached during deposition. The effect is commonly largest for the natural luminescence signal (fi rst measurement), which leads to an apparently high age. Thermal transfer is dependent on the temperature used during measurement (preheat and cutheat) and can be a signifi cant problem for young sediments (>10 Gy; Rhodes & Bailey, 1997). To determine suitable pre- and cutheat temperatures for each batch of samples so called preheat plateaux (Fig. 14) are constructed by measuring the equivalent dose for a number of aliquots using a range of different preheat and/or cutheat temperatures. Any temperature combination that falls into the fl at region (plateau) of the curve can be used; usually the combination with the best average, smallest standard error and best recycling ratios is chosen. Additional tests for thermal transfer, using

the selected temperature combinations, also show that the effect is non-existent or small (< 1.5 Gy; <1% of EDs) for most samples. One aliquot from a Småland sample showed thermal transfer of 6 Gy (~7% of ED), but that is still too small to account for the dose overestimation, compared to expected values, for samples from this area (10-40 Gy). Other Småland samples did not show such values. Another type of thermal transfer is recuperation, which is routinely measured for each aliquot in the SAR-protocol. Overall, only few aliquots in this study have been rejected due to too high recuperation (>5% of natural signal) so this process does not seem to be a problem for these samples.

Luminescence characteristicsThe mineralogical properties of the quartz or feldspar grains vary between different bedrock and sediment settings and may be more or less suitable for luminescence dating purposes. For samples from the same area, and the same source material, the main difference will be the mode of deposition, which also has a strong infl uence on the luminescence properties of grains.

Natural preheat plateau (081310)

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Preheat T (deg C; cutheat 40 deg lower)

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Preheat plateau 081301

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0

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Rec

yclin

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tio

260º preheat 220º cutheatchosen

Fig. 14. Examples of preheat plateaux from Swedish samples. Blue diamonds show equivalent doses and the plateau region is marked by a hatched blue line. Pink squares represent recycling ratios, and the solid line unity. A. Lacustrine sediment from Hässeldala. Thermal transfer seems to set in at 240º, where the EDs increase. B. Glaciofl uvial sediment from Dösebacka. ED values level off only at high temperatures.

A

B

18

Fig. 15. Examples of shine-down (decay) curves from single aliquots. The quartz grains were exposed to blue light-emitting diodes for 40 s. Note various Y-axes scales, where intensity is number of counts per 0.16 s. A. Early Holocene aeolian sand from Värmland (061320). Like for most of the Värmland samples, the quartz from this sample is ‘well behaved’. The luminescence signal decays rapidly from a clear, high peak value to a low background. B. Young (~250 years) aeolian sand from Värmland (061328). The peak is lower compared to the older sample from the same area, but the pattern is the same. C. Middle Holocene aeolian sand from Härjedalen (061353). The peak is low and the background high. This relationship gives poor counting statistics and contributes to a larger uncertainty for the fi nal dose estimate. D. Lateglacial silty gyttja from Hässeldala, Blekinge (081310). The slow decay indicates that there are medium and slow components present in the OSL-signal. In this case, IR-tests suggest that feldspar contamination may be the cause. E. Interstadial sandy gyttja from Pilgrimstad, Jämtland (061346). Not extremely bright but with a clear peak. F. LGM/deglaciation age sandur deposit from Småland (043028). Fairly bright peak and low background. G. Lateglacial glaciolacustrine sediments from Jämtland (061349). This aliquot was rejected because of lack of natural signal (no peak). H. Sub-till glaciofl uvial sediment from Småland (043034). This aliquot was rejected because of the extremely high signal without a proper peak and the odd appearance of the decay curve.

19

Sediments with poor luminescence characteristics are usually revealed when rejection criteria are applied, but also accepted aliquots can be “good” to varying degrees. This can be visualised by the decay (shine-down) curves (Fig. 15). Ideally, there is a bright, strong peak which rapidly decays to a low background (Fig. 15a) but curves can look very different in shape and amplitude (Fig. 15b-h). It is usually the better the higher the amplitude of the peak is to the background. A relatively weak peak leads to increased uncertainty in the measurements, i.a. because of counting statistics.

The luminescence characteristics, represented by signal strength (luminescence related to dose), show more variation between geographical areas than between depositional environments (Fig. 16). The brightest samples come from Värmland and the dimmest from Jämtland, with a few exceptions. This suggests that regional geology (bedrock, sediment history) is more important than the environment in which the sediment was last deposited.

Signal strength

0

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9

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Counts/Gy (mean per sample)

JämtlandHärjedalenVärmlandSmålandBohuslänBlekingeVästergötland

Till

Delta foreset

Gf sandur

Gf other

Glacio-lac.

Aeolian

Beach

Lacustrine

Fig. 16. Signal strength as counts per Gray for various depositional environments and geographical areas. There is more variation between geographical areas than between depositional environments in Sweden. Samples from Ulvsjö in Härjedalen and Brattforsheden in Värmland stand out as particularly bright. Gf=glaciofl uvial and Glaciolac=glaciolacustrine.

Sensitivity analysesThe fi nal age calculation looks deceivingly simple: age = dose/dose rate. However, there are many assumptions that go in to this equation. Actual measurements give more or less precise and accurate numbers while other factors are based on the geological interpretation of a site, which is partly subjective. It is therefore important to evaluate the effect of these factors on the fi nal age to see which make the most difference, and thus should be determined most accurately, and which are less important. A good example is the estimate of the water content, which is used for the calculation of the

dose rate. The number that is used in the calculation is the average water content of the sample, and its closest surroundings, since time of deposition. What you have to base your estimate on is usually the present-day water content, the saturated water content (~porosity) and your interpretation of the history of the site. It is commonly assumed that the average water content should be somewhere between the present-day water content (it has never been drier than now, close to gravel-pit wall for example) and the saturated water content (cannot contain more water). This is most often true, but there are exceptions, for example if

20

much compaction has taken place and reduced the water content through time (cf. Fig. 8). Another example is the depth below surface, which is used to calculate the contribution to the dose rate by cosmic rays. The contribution is most important for shallow depths (Fig. 17) and you need to know if your sampled sediment has always been covered by the same thickness, or if sediment cover has at some time been thicker (later erosion, excavation) or thinner (later deposition). Many other factors affect the calculated age and altogether they include: depth below surface, elevation, grain size, water content gamma, water content beta, dose rate gamma, dose rate beta, internal dose rate, density, cosmic ray contribution, beta source calibration, and estimated dose. Normally, uncertainties are assigned to only a few

061344

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600

Depth below surface (cm)

Age

(ka)

Fig. 17. The dependence of age on the depth below surface for one of the samples from Pilgrimstad. The inset plot illustrates the exponential dependence by showing the same plot with a blown-up Y-axis scale and no error bars.

061344

44

44

45

45

46

46

47

47

0 200 400 600 800 1000 1200 1400 1600

Depth below surface (cm)

Age

(ka)

of these parameters to derive the uncertainty on the calculated age. However, we have developed an Excel-based software tool to greatly improve our understanding, described below. Through this enhanced analysis we learned that for most samples that the estimated dose is most affected by uncertainty from the measurements of estimated dose and dose rate, followed by the internal dose rate and water content estimate. Thus, we used this information to focus our efforts in making better estimated dose measurements and thinking more about our estimate of the water content throughout the entire lifetime of the sediment. Note that nothing practical could be done to improve the uncertainty on the internal dose rate.

21

Other products

Fig. 18. Plot of the sensitivity of age to the various parameters. WC=water content, DR=dose rate.

value) will cause the age to change. For example, varying the estimated dose “ED” by 21% of its original value (horizontal axis) will cause the age to change by 21% of its original value. Note that most other parameters do not have a one-to-one relationship and some relationships are non-linear. The steeper the slope, the more sensitive the age is to the given parameter. Thus, efforts can be focussed to reduce the uncertainty of those parameters that have the greatest effect on the calculated age. Also, an excellent strategy to potentially improve our confi dence in a site is to collect multiple samples to evaluate age consistency and any vertical stratigraphic trends, as described above.

Analysis softwareTo easily take many of the factors mentioned in the previous section into account, we have developed an Excel-based program that calculates the age based on dose and dose-rate data, including extensive error and sensitivity analyses. Most of the work has been carried out by Timothy Johnsen. This tool allows detailed analysis of OSL data including: age calculation, dose distribution analysis including tools for asymmetric dose distributions, IR-Blue signal ratio, full error analysis using Monte Carlo simulation, separation of random and systemic uncertainty in age determination, and sensitivity analysis of the age to various sources of uncertainty. This tool will be released for general use in the near future. Below is an example of one of the graphical displays of sensitivity results from the Excel-based tool (Fig. 18). What it shows is how varying a given parameter (as a percentage of its original

22

Fig. 19. Activity of uranium (238U; Bq/kg) in surfi cial sediments (<0.6 m depth) in the Brattforsheden area according to gamma spectrometry measurements of OSL background samples. The base map is from the Quaternary deposits database/map 11D Munkfors SO (Geological Survey of Sweden series Ae 150), © Sveriges Geologiska Undersökning (SGU). Permission 30-1730/2006.

<2020-25

25-30

30-35

35-40

40-45

238U (Bq/kg)

Natural radioactivityAll OSL-samples are accompanied by a background sample which is analysed for radioactive nuclides by gamma spectrometry. We thus now have a database of more than a hundred samples with information on the occurrence of

radioactive isotopes of e.g. uranium, thorium, radium, radon, lead and potassium. This data could be used to study natural radioactivity in sediments (Fig. 19).

PeatClay and siltSand, gravelGlaciofl uvial materialClayey tillTillBedrockLake

23

incomplete bleaching is generally not considered a big problem for old (high dose) samples (Jain et al., 2004) and the residual dose at deposition would have to be much larger than suggested by modern analogs and dose distributions from our study areas (Alexanderson & Murray, 2007; this study). The effect and size of residual doses can be evaluated by using dose information from subglacial (non-bleached) sediments to roughly estimate the ratio of bleached vs non-bleached grains in suspected incompletely zeroed proglacial deposits at two sites. We assume that the proglacial sediments are derived from the subglacial deposits or similar material, and, for simplicity, that incomplete bleaching alone is the cause of any dose (age) overestimation and that grains are either bleached or non-bleached. Calculations of mixing ratios then suggest that ~15-60% of the grains need to be non-bleached to account for the measured doses in the proglacial sediments (Table 5). Other factors that can cause age overestimation are thermal transfer, feldspar contamination (see above) and non-linear growth of the OSL signal

Normalised ages (Swedish samples)

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5 6 7 8 9

times

exp

ecte

d ag

e

-10

10

30

50

70

90

110

130

150

appr

oxim

ate

devi

atio

n fr

om n

orm

alis

ed a

ge (k

a)

Till Gfluvother

Glacother

Deltaforeset

Gfsandur

Beach Lacu-strine

Aeolian

Shown is mean value (diamond) with standard error (lines). Thick bars represent max and min values.

Fig. 20. OSL-ages from deglacial sediments normalised to the expected deglaciation age for each area (from J Lundqvist, 2002). The hatched lines indicate the spread for aeolian ages, which is used as a well-behaved reference. The dataset includes ages from Alexanderson & Murray (2007, recalculated), Kjær et al. (2006), Kortekaas et al. (2007) and Kortekaas & Murray (in Kortekaas, 2007) as well as our unpublished data. All ages were measured using SAR protocols on quartz aliquots. Gfl uv=glaciofl uvial, Glac=glaciolacustrine.

OSL-dating in Sweden – discussionOSL vs geologyOver the last few years, a relatively large number of quartz OSL ages have come out of Sweden (Kjær et al., 2006; Lagerbäck et al., 2006; Lagerbäck, 2007; Alexanderson & Murray, 2007; Kortekaas et al., 2007; Kortekaas & Murray in Kortekaas, 2007); unfortunately many of these results have been inconsistent with well-established geological interpretation. Here we use a combination of our OSL-data and published age, dose and dose rate data from other Swedish and nearby sites as a base for a discussion of the reasons for these discrepancies. As shown in Fig. 20, there is a wide spread in the ratio of OSL ages to expected ages with a clear skew towards ratios >>1. Overestimates may be up to 15 times the expected age (>100 ka too old, or >350 Gy), which is a lot. The expected ages are determined from location and the standard Swedish deglaciation model as presented by J Lundqvist (2002), and their uncertainties are not larger than the resolution of OSL-ages. Incomplete bleaching is the most obvious explanation for the age overestimates in some samples, especially for those from glaciofl uvial or glaciolacustrine sediments. However,

24

(Murray et al., 2002; Murray & Funder, 2003). Although thermal transfer effects of several Grays have been shown to occur in glaciofl uvial material from Greenland and Himalaya (Rhodes & Bailey, 1997; Rhodes, 2000), they do not seem to be inherent in all glacial deposits (Klasen et al., 2006; Preusser et al., 2007; this study). Skewed dose distributions due the natural signal intercepting the non-linear part of the growth curve (cf. Fig. 3c) mainly concerns samples with high doses (>~200 Gy) but should be checked for all samples. More work on these aspects will be done on the present data set.

As of now, not all causes for the apparent overestimation of ages of some glacigenic sediments in Sweden are understood. Better understanding requires further investigations into OSL properties, experiments with new techniques and materials, other types of data analyses etc. Some of this can be done on already available material and data, but there has not been time to do it within this project’s time frame. We should also continue having a critical view of the current glacial history of Fennoscandia; ages should not be rejected just because they disagree with expectations.

Brattforsheden, Värmland Trullagård-Glömsjö, SmålandSubglacial till Proglacial delta1 Subglacial esker Proglacial delta1

Sample no 061334 061319 061335-362 043050

Dose today (Gy) 440 280 315 75

Dose rate (Gy/ka) 4.5 3.4 2.8 2.2

Accumulated dose since de-position at 11 ka (Värmland) and 13.5 ka (Småland); (Gy)

50 40 40 30

Dose at deposition (Gy) 390 240 275 45

Percentage of non-bleached grains

100 60 100 15

1 Sample with oldest OSL-age at site selected 2 Average of the two samples used

Can we trust OSL-ages from Sweden?The discrepancies between OSL-ages and expected ages based on geological interpretation have resulted in some scepticism towards the method and questions whether OSL-dates from Sweden can be trusted or not. This scepticism is probably one of the more important factors that limit the use of the OSL-method in Sweden today. Otherwise OSL has the age range, resolution and material requirements etc to address many chronological issues in Quaternary research, for example, achieving a better chronology for interstadials and stadials during the last glacial cycle. In this study we have shown that OSL-ages from non-glacial environments generally agree well with independent chronological control, in accordance with results from studies in other areas (e.g Murray & Olley, 2002; Thomas et al., 2006). We therefore believe that OSL-ages from non-glacial environments in Sweden can be trusted, on the condition that the samples have passed internal OSL quality checks and especially if there are several consistent ages. OSL-ages from glaciofl uvial and

glaciolacustrine sediments, on the other hand, show large scatter and commonly seem to overestimate the actual age. Sediments from glacial environments are notably hard to date with OSL, due to the risk of incomplete bleaching and to poor luminescence characteristics. To get the ‘right’ age from such sediments it is necessary with a large local dataset with good stratigraphic control but even so it might be diffi cult. OSL-ages from glacial environments should therefore generally be used with caution. It is clear from this study and from previous work (e.g. Davids, 2005; Kjær et al., 2006; Lagerbäck, 2007; pers.comm.; Alexanderson & Murray, 2007), that OSL-dating in Sweden is not straightforward. The dated material (quartz) does not generally have ideal luminescence characteristics, and some of it is not datable with standard analytical protocols (rejected samples from Ljusnedal and Stygghuvudet). Many sites that would be interesting to date with OSL (e.g. previously undatable interstadial sites) contain less than ideal sediments such as glaciofl uvial deposits. Also, the commonly poor luminescence

Table 5. Rough estimates of proportion of non-bleached grains in suspected incompletely zeroed proglacial sedi-ments. All dose and percentage values are rounded.

25

characteristics make it diffi cult to use small-aliquot or single-grain techniques to evaluate incomplete bleaching. However, there are exceptions to the generally dark picture; both good quartz and interesting sites with suitable sediments exist in Sweden, but they are unfortunately not as common. Future advances in technology, analytical protocols and understanding of OSL physics may solve some of these problems. It might also be that Swedish feldspar is better than Swedish quartz from a luminescence perspective. This has not been addressed in this study, but in a study in Halland, Davids (2005) could use IRSL on feldspar when quartz did not work to date coastal dunes. Also, Klasen et al. (2006) found that feldspar could be used for dating proglacial sediments in the Alps when quartz from their study area turned out to have poor luminescence intensity, similar to some of the Swedish quartz we have been working with. They also showed in laboratory experiments that both quartz and feldspar were completely bleached at the same time although the quartz signal was initially reduced faster (Klasen et al., 2006), indicating that incomplete bleaching of feldspar may be less of a problem than believed. Presently, the choice of sites and sediments to sample is critical to how well the dating method will work. For easy, reliable dating good sites are needed, with stratigraphic control, suitable (ideally non-glacial) sediments and preferably more than one datable bed. During analysis, quality checks must be performed to see that a suitable analytical protocol has been chosen and that OSL works for the sediments. Also, to be confi dent about the age of an event, for example an interstadial, several consistent ages are needed. One sample is not enough. In the context of trust and reliability, it is very important to present background data to the OSL ages in publications so their quality can be judged by the reader. In addition to the date itself, type of sediment, stratigraphic situation, water content, dose and dose rate data, quality check data, information on analysis etc should be given. If possible, the author could indicate which samples are more or less reliable than others.

Causes of luminescence characteristicsAs shown in Fig. 16, geographical area seems to have a larger infl uence on the quality of OSL-dates than depositional environment, indicating that regional geology is more important than

the environment in which the sediment was last deposited. The causes for various luminescence properties are poorly understood, but are thought to be controlled by trace element geochemistry, geological origin and history of the grains and/or the radiation history of the sediment (Duller 2004). For example, according to hypotheses, a sedimentary quartz grain that has gone through several depositional-erosional cycles should be better than a magmatic quartz grain that has only been transported a short distance. We know that it is only a small proportion of the grains in an aliquot that give signal (Duller et al., 2000; Jacobs et al., 2003; this study) and we assume that it is the grains with the best properties in the aliquot that we see. That is, the measured luminescence characteristics refl ect the characteristics of the ‘best’ grains in the sample. Looking at our study areas it is clear that sediments from Brattforsheden in Värmland and Ulvsjö in Härjedalen appear to have the best luminescence properties (Fig. 16). What do these sediments have in common that the others do not? The type of deposit does not seem to be very important as stated earlier. Similar deposits that are bright in Ulvsjö and Brattforsheden are dim in other areas (Fig. 16). Possible transport distances have been roughly estimated based on ice-movement directions, glacial activity and provenance studies and classifi ed into short, intermediate and long distance (Table 6). A long transport distance would be expected to give better luminescence properties but neither Ulvsjö nor Brattforsheden stand out in this respect. Reworking of sediments over long time-scales has been used as an explanation for good luminescence properties of glaciofl uvial sediments in Rondane, Norway (Bøe et al. in prep./pers.comm.). The area studied there is more or less a closed basin in which sediments have gone round and round. Rondane is also situated within the ‘thick drift zone’ (Kleman et al., 2008), which is interpreted as having been an ice-marginal zone during repeated glaciations over 1.1 Ma. The thick drift cover implies that much material has been brought to the area and not all of it has been transported further down the system. This opens a possibility for reworking of sediments within this zone, with sediments going through several erosion-deposition cycles and thus potentially increasing the OSL sensitivity of quartz grains. Härjedalen is situated within this zone, and Värmland and Jämtland on the boundary

26

to it (Table 6). The other areas are located in the intermediate drift thickness zone or the scoured zone (Kleman et al., 2008). Generally tills and glaciofl uvial deposits in the study areas are dominated by locally derived material (e.g. Lundqvist, 1958; 1967) and so the local bedrock should be important for the type of quartz in the area. All areas, except the Baskarp site in Västergötland, are dominated by crystalline bedrock, mainly granites (Table 6). Based on this coarse division, Ulvsjö and Brattforsheden cannot be distinguished from the other sites. In addition to local material, deposits may also contain longer transported material and among the foreign material sedimentary rocks may be found. Quartz grains from such rocks already have a pre-Quaternary history of erosion, transport and deposition which is believed to improve luminescence characteristics. We fi nd high percentages of sedimentary rocks at Pilgrimstad, Ulvsjö, Brattforsheden and Baskarp (Table 6), sites with both good and not so good luminescence properties. However, a common denominator between Ulvsjö and Brattforsheden is the frequent occurrence of Dala sandstone. The Dala sandstone is of Jotnian age (1650-1200 Ma; Pulvertaft, 1985). It is a red, continental sandstone with beds of conglomerates and shales, interpreted to be of aeolian origin (Pulvertaft, 1985) or a delta with aeolian input (T Lundqvist, 1991). Other sandstones, such as the Visingsö group sandstone at Baskarp, do not seem to have the same ‘effect’ on luminescence characteristics, although it is interesting to note that also Rondane is situated in an area with proterozoic sandstones (Solli & Nordgulen, 2007). ‘Positive’ properties found at both Ulvsjö and Brattforsheden are thus the presence of Dala sandstone and the location within or at the boundary to the thick drift cover zone (Table 6). Hence, the good luminescence characteristics could be related to specifi c mineralogical properties and (the possibility of) extensive reworking. This could be tested by analysing sediments from sites that fulfi l the criteria of being within the thick drift zone and containing Dala sandstone. It would also be interesting to try sediments containing Almesåkra sandstones (Småland), which are similar to the Dala sandstone (T Lundqvist, 1991), or other proterozoic sandstones. Almesåkra sandstones are present just northwest of our study area in Småland. However, it must be remembered that good luminescence properties do not rule out other problems with for example incomplete bleaching.

Tabl

e 6.

Pro

pert

ies t

hat m

ight

affe

ct lu

min

esce

nce

char

acte

rist

ics.

Site

and

are

aP

ilgrim

stad

Ulv

sjö

Sve

g ar

eaB

rattf

orsh

eden

Dös

ebac

kaB

aska

rpse

vera

l site

sH

ässe

ldal

aPr

oper

tyJä

mtla

ndH

ärje

dale

nH

ärje

dale

nVä

rmla

ndB

ohus

län

Väst

ergö

tland

Smål

and

Ble

king

e Ty

pe o

f sed

imen

tsla

cust

rine,

(gla

cio)

fluvi

alae

olia

n, g

laci

olac

ustri

neae

olia

n, g

laci

oflu

vial

aeol

ian,

wav

e-w

ashe

d,

glac

ioflu

vial

, till

glac

ioflu

vial

glac

ioflu

vial

glac

ioflu

vial

lacu

strin

e

Poss

ible

tran

spor

t di

stan

cesh

ort

shor

tsh

ort

inte

rmed

iate

inte

rmed

iate

-long

shor

tsh

ort

shor

t-in

term

edia

te

Poss

ibili

ty o

f rew

orki

ng

of s

edim

ents

***

inte

rmed

iate

high

high

inte

rmed

iate

-hig

hlo

win

term

edia

tein

term

edia

telo

w

Loca

l bed

rock

*S

veco

fenn

ian

bedr

ock;

gra

nite

, pe

gmat

ite a

nd

dole

rite

Tran

ssca

ndin

avia

nm

agm

atic

bel

t; D

ala

porp

hyry

, Dal

a gr

anite

,do

lerit

e

Tran

ssca

ndin

avia

nm

agm

atic

bel

t; S

mål

and-

Vär

mla

ndgr

anite

, dol

erite

Tran

ssca

ndin

avia

nm

agm

atic

bel

t; S

mål

and-

Vär

mla

ndgr

anite

SW

Sw

eden

; gr

anito

ids

and

gran

ites

Tran

ssca

ndin

avia

nm

agm

atic

bel

t; V

isin

gsö

grou

p sa

ndst

one

Tran

ssca

ndin

avia

nm

agm

atic

bel

t; S

mål

and-

Vär

mla

ndgr

anite

Ble

king

e;gr

anite

s an

d gr

anod

iorit

es

Sedi

men

tary

lith

olog

ies

in

till a

nd/o

r gla

ciof

luvi

al

depo

sits

**

<15%

lim

esto

ne,

<15%

gre

ywac

ke<6

0% D

ala

sand

ston

e<1

% D

ala

sand

ston

e<1

5-20

% D

ala

sand

ston

e, <

10%

qu

artz

ites

<1%

san

dsto

ne,

quar

tzite

very

hig

h qu

artz

sa

ndst

one

occa

sion

alsa

ndst

one

clas

tsno

info

yet

* Fr

om T

Lun

dqvi

st (2

002)

** J

ämtla

nd/H

ärje

dale

n fro

m L

undq

vist

(196

9); V

ärm

land

from

Lun

dqvi

st (1

958)

; Boh

uslä

n fro

m H

illef

ors

(196

9); V

äste

rgöt

land

from

Bas

karp

sand

(per

s.co

mm

.); S

mål

and

from

Mal

mbe

rg P

erss

on (2

001)

;**

* ba

sed

on in

terp

reta

tion

of th

e dr

ift th

ickn

ess

map

in K

lem

an e

t al.

(200

8)

27

ConclusionsThe aim of this project was to explore dating methods applicable to glacial and deglacial deposits in Sweden and thereby obtaining a better chronology for the Late Quaternary glacial history. We have tested, assessed and used the optically stimulated luminescence (OSL) dating method in various depositional environments and compared the results with data from terrestrial cosmogenic nuclide (TCN) exposure and radiocarbon dating.

There is signifi cant scatter in ages • from glaciofl uvial and glaciolacustrine sediments. The youngest ages correspond to independently determined ages, but a relatively large local dataset is needed to be able to say something with some confi dence. OSL-ages from such environments should generally be considered maximum ages, i.a. due to the risk of incomplete bleaching. Aeolian and lacustrine and largely also • (glaciolacustrine/glaciomarine) beach sediments give good results. OSL-ages from these environments can provide minimum ages of glaciation and can reliably be used to reconstruct e.g. Holocene environmental change.Regional geology seems more important than • depositional environment for luminescence properties and the quality of OSL-ages. Of the studied areas, Värmland is very good while Småland is problematic and Jämtland diffi cult. Good luminescence properties could be linked to the presence of Dala sandstone and, partly, to location within the ‘thick drift zone’.

We have provided independent chronological ages for the last deglaciation for areas above the highest coastline. These ages have different resolution than most existing chronologies (clay-varve chronology, radiocarbon dates) in coastal areas, but can be compared with those if the conditions are kept in mind.

Brattforsheden in Värmland was deglaciated • after 11.5±0.6 ka (youngest delta OSL-age) and before 10.7±0.7 ka (oldest aeolian OSL-age). This corresponds well to the mean cosmogenic exposure age of 11.4±1.2 10Be ka for moraine boulders and is also in accordance with previously estimated deglaciation ages in the area.The oldest aeolian sediment in eastern • Härjedalen, 10 ka, provides a minimum age

of deglaciation for that area. Glaciolacustrine and glaciofl uvial deposits give very scattered ages and together with the varied topography and large geographical extent of the area, this makes good estimates of deglaciation ages from the current Jämtland-Härjedalen OSL data set diffi cult.According to cosmogenic exposure ages, • deglaciation of eastern Småland (the Vimmerby moraine) took place ~14 10Be ka. This agrees with previous estimates of the deglaciation age in nearby coastal areas. OSL-ages of glaciofl uvial sediments are overall older; most fall in the range 19-25 ka. The reason for this is not known.

We have begun a quantitative chronology for pre-LGM events by dating interstadial sediments in Jämtland and Bohuslän.

The Pilgrimstad interstadial site in Jämtland • belongs to marine isotope stage 3, according to the OSL-ages.Dates are still pending for the sites Dösebacka, • Vålbacken, Andersöm and Bulägden.

During our work we have gained both practical and theoretical experience of OSL-dating. Helena Alexanderson and Timothy Johnsen have been through all steps in the process, from sampling and preparation to carrying out measurements and data analyses.

Our combination of geological expertise and • knowledge of luminescence techniques has been very fruitful. Geological knowledge is needed to determine depositional environments (pick the best samples) and reconstruct the evolution of sites (come up with good estimates on the history of water content, compaction, sediment cover etc). The technical knowledge is needed to set up measurements properly and to do the necessary analyses of the data. We have set up an OSL-preparation laboratory • at the Department of Physical Geography and Quaternary Geology, Stockholm University. The laboratory allows us to do much of the mechanical and chemical separation of the samples, such as sieving, magnetic separation and acid treatment.Timothy Johnsen has developed an excel-• based program that can be used for calculating OSL-ages and doing extensive error- and sensitivity analyses on the data.

28

Thanks to Jakob Heyman, Jan Lundqvist, Leif Vidar Jakobsen, Sven-Allan and Gunnel Alexanderson for participating in and helping with fi eld work; Andrew Murray for fi nding space and time for us at NLL, without that opportunity this project would not have been possible; Andrew Murray (again), Jan-Pieter Buylaert and Kristina Thomsen for OSL-discussions; Mette Adrian, Anne Birgit Rasmussen and Vicki Hansen for doing OSL-measurements; Derek Fabel for analysing the TCN-samples; the County Boards of Värmland (Sven-Åke Berglind) and Västra Götaland (Hans Alexandersson) for permissions and support; Heidi Ryen for help with sample preparation; Jan Risberg for giving us access to unpublished radiocarbon dates.

In addition to the funding from the Geological Survey of Sweden, Alexanderson also received a grant from Magnus Bergvalls stiftelse for additional dating analysis. The County Board of Västra Götaland paid for the excavation of the Dösebacka site and the Swedish Nuclear Fuel and Waste Management Company (SKB) contributed fi nancially to some of the fi eldwork in Jämtland.

Acknowledgements

29

Referencesice-front glaciofl uvial deposits in the Rondane area, east-central southern Norway.

Davids F, Wallinga J, Hoek WZ &De Jong R. 2005: IRSL dating of aeolian activity phases during the Late Holocene on coastal dune and beach ridges in south-west Sweden. Book of abstracts 11th International Conference on Luminescence and Electron Spin Resonance Dating. s. 49.

Davids F. 2005: Optical dating of Holocene coastal features in South-West Sweden. Master thesis, Department of Physical Geography, University of Utrecht.

Denby PM, Bøtter-Jensen L, Murray AS, Thomsen KJ & Moska P. 2006: Application of pulsed OSL to the separation of the luminescence components from a mixed quartz/feldspar sample. Radiation Measurements 41, 774-779.

Duller GAT. 2004: Luminescence dating of Quaternary sediments: recent advances. Journal of Quaternary Science 19, 183-192.

Duller GAT, Bøtter-Jensen L & Murray AS. 2000: Optical dating of single sand-sized grains of quartz: sources of variability. Radiation Measurements

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Appendix 1: Field work and sites

Field workTime Area Participants Comment

May 2006 Småland HA, TJ, JH Focus on the Vimmerby-moraine; sampling for OSL and TCN

August 2006 Värmland HA Brattforsheden; sampling for OSL, TCN and C14

August 2006 Jämtland TJ Handöl-Åre area; sampling for OSL

September 2006 Småland HA, KMP,

MPExcavations in till at the Vimmerby-moraine; sampling for OSL

October 2006

Jämtland-Härjedalen HA, TJ Sampling for OSL and TCN

June 2007 Jämtland HA, TJ, BW, JL

Focus on Pilgrimstad and other interstadial sites; sampling for OSL and C14; co-fi nanced with BW and JON.

October 2007 Bohuslän HA, TJ

Dösebacka; sampling for OSL and C14; logistic support from the County Board of Västra Götaland

May 2008 Jämtland TJ, LVJ Georadar-investigations of sites sampled for OSL

BW Barbara Wohlfarth, Stockholm UniversityHA Helena Alexanderson, Stockholm University & Norwegian Univ. of Life SciencesJH Jakob Heyman, Stockholm UniversityJL Jan Lundqvist, Stockholm UniversityJON Jens-Ove Näslund, Swedish Nuclear Waste ManagementKMP Kärstin Malmberg Persson, Geological Survey of SwedenLVJ Leif Vidar Jakobsen, Norwegian University of Life SciencesMP Magnus Persson, Geological Survey of SwedenTJ Timothy Johnsen, Stockholm University

App. 1:1

Site locations

Area Site Latitude Longitude (deg N) (deg E)Blekinge Hässeldala 57.26667 15.05000Bohuslän Dösebacka 57.91033 12.04107Härjedalen Ljusnedal 62.54782 12.63684Härjedalen Låddhedarna 61.93244 14.17441Härjedalen Skärkdalen 62.78780 12.76362Härjedalen Stygghuvudet 62.73254 13.54533Härjedalen Svegsjön 62.09325 14.12851Härjedalen Ulvsjö 1 61.60606 14.27998Härjedalen Ulvsjö 2 61.61320 14.27810Jämtland Andersön 63.16253 14.44320Jämtland Pilgrimstad 62.95816 15.01810Jämtland Vålbacken 63.07757 14.76746Småland Broby 57.37792 14.88069Småland Emån-Ämmaryd 57.39883 15.34983Småland Emån-Åhult 57.39744 14.86200Småland Faggemåla 57.53172 15.78969Småland Glömsjö 57.39404 14.90348Småland Hultsfred 57.53167 15.77000Småland Skärstad 57.74946 15.77661Småland Sköldatorpet 57.49832 15.44229Småland Solbacka 57.69061 15.63563Småland Trullagård 57.38722 14.89292Småland Ämmaryd 57.40122 15.35139Värmland Finnhöjden 59.72165 13.84056Värmland Gräshöjden 1 59.60853 13.95843Värmland Gräshöjden 2 59.60770 13.95336Värmland Hedbacka 59.59732 13.90591Värmland Källorna 1 59.60648 13.88337Värmland Källorna 2 59.60720 13.88415Värmland Köldgropen 59.62154 13.92524Värmland Mosserud 59.60569 13.98647Värmland Mången 59.61602 13.87416Värmland Nabbmanen 59.71782 13.87360Värmland Nyängen 1 59.60168 13.92771Värmland Nyängen 2 59.60042 13.92906Värmland Västra höjden 59.67028 13.96887Västergötland Baskarp n/a n/aVästergötland Dykärr 57.92078 14.04028

App. 1:2

Appendix 2: OSL-ages

0430Risø no. Your Site Depth, cm Age , ka Dose , Gy (n) Dose rate, Gy/ka w.c. %Comment04 30 28 H1 Ämmaryd 270 20 ± 1.2 63 ± 2 25 3.11 ± 0.13 14 recalculated from Alexanderson & Murray (2007)

04 30 29 H12Ämmaryd 400 23 ± 2 72.24 ± 4.60 18 3.10 ± 0.13 13 recalculated from Alexanderson & Murray (2007)

04 30 30 H6Skärstad 420 41 ± 6 163.89 ± 22.45 9 4.00 ± 0.18 20 not finished04 30 31 H7Skärstad 170 32 ± 3 130.49 ± 9.18 9 4.05 ± 0.17 16 not finished04 30 32 H1Faggemåla 120 20 ± 2 81.49 ± 5.95 30 4.09 ± 0.17 16 recalculated from Alexanderson & Murray (2007)

04 30 33 H4Hultsfred 900 50 ± 6 177.48 ± 19.47 12 3.58 ± 0.16 2504 30 34 H5Hultsfred 400 48 ± 8 180.94 ± 30.99 10 3.80 ± 0.15 2304 30 35 H14Broby 100 52 ± 4 135.34 ± 6.76 17 2.58 ± 0.10 19 recalculated from Alexanderson & Murray (2007)

04 30 36 H1 Broby 50 41 ± 6 125.79 ± 16.92 18 3.06 ± 0.13 11 recalculated from Alexanderson & Murray (2007)

04 30 37 H1 Trullagård 550 24 ± 2 55.81 ± 3.85 24 2.32 ± 0.09 21 recalculated from Alexanderson & Murray (2007)

04 30 38 H1 Trullagård 400 21 ± 1.5 51.96 ± 2.62 24 2.49 ± 0.12 20 recalculated from Alexanderson & Murray (2007)

04 30 39 H2 Dykärr 230 169 ± 17 264.28 ± 24.14 12 1.57 ± 0.06 20 not finished04 30 40 H2Faggemåla 50 23 ± 2 103.96 ± 6.21 18 4.46 ± 0.19 804 30 44 H2 Dykärr 80 138 ± 12 221.94 ± 15.77 9 1.61 ± 0.07 12 not finished04 30 45 H1 Ämmaryd 220 21 ± 1.4 61.85 ± 2.46 24 2.90 ± 0.13 17 recalculated from Alexanderson & Murray (2007)

04 30 50 H1 Trullagård 1100 34 ± 2 74.46 ± 3.93 23 2.20 ± 0.09 29 recalculated from Alexanderson & Murray (2007)

04 30 51 H1 Trullagård 50 19 ± 1.1 54.91 ± 1.31 22 2.95 ± 0.14 8 recalculated from Alexanderson & Murray (2007)

04 30 52 H3Faggemåla 90 21 ± 1.3 85.62 ± 3.39 26 4.01 ± 0.16 16 recalculated from Alexanderson & Murray (2007)

04 30 53 H9Ämmaryd 330 59 ± 4 162.35 ± 8.75 23 2.75 ± 0.11 20 recalculated from Alexanderson & Murray (2007)

04 30 54 H1 Broby 500 70 ± 5 185.79 ± 9.57 27 2.66 ± 0.11 16 recalculated from Alexanderson & Murray (2007)

04 30 55 H8Skärstad 200 47 ± 13 184.25 ± 48.31 3 3.88 ± 0.30 19 not finished04 30 58 0 0 275 3.33 ± 0.33 3 1.13 ± 0.07 42

0513Risø no. Your Site Depth, cm Age , ka Dose , Gy (n) Dose rate, Gy/ka w.c. %Comment05 13 01 Tr Trullagård 1050 25 ± 2 57.02 ± 2.28 19 2.33 ± 0.10 1905 13 02 Tr 2Trullagård 900 39 ± 4 93.90 ± 7.64 22 2.43 ± 0.10 1705 13 03 -Ä Emån-Ämmaryd 55 0.10 ± 0.06 0.21 ± 0.12 24 2.08 ± 0.07 3705 13 04 -Ä Emån-Ämmaryd 55 0.59 ± 0.34 1.71 ± 0.97 24 2.88 ± 0.12 1505 13 05 -Å Emån-Åhult 80 0.03 ± 0.02 0.06 ± 0.04 23 1.94 ± 0.07 49

0613Risø no. Your Site Depth, cm Age , ka Dose , Gy (n) Dose rate, Gy/ka w.c. %Comment06 13 11 IN Finnhöjden 55 9.2 ± 0.6 29.71 ± 1.27 20 3.24 ± 0.12 2406 13 12 RÄGräshöjden 1 45 9.6 ± 0.5 35.82 ± 0.85 21 3.74 ± 0.15 1706 13 13 RÄGräshöjden 2 110 10.0 ± 0.5 34.47 ± 0.59 23 3.45 ± 0.14 1106 13 14 RÄGräshöjden 2 65 9.0 ± 0.5 33.38 ± 0.74 21 3.69 ± 0.15 906 13 15 EDHedbacka 50 12.0 ± 0.6 41.50 ± 1.18 21 3.47 ± 0.14 1506 13 16 ÄLKällorna 1 100 11.5 ± 0.6 50.35 ± 0.80 24 4.37 ± 0.18 1206 13 17 ÄLKällorna 1 200 13.1 ± 0.7 51.35 ± 1.25 24 3.93 ± 0.17 1106 13 18 ÄLKällorna 1 300 12.8 ± 0.6 45.51 ± 0.82 24 3.55 ± 0.14 1406 13 19 ÄLKällorna 1 800 82.6 ± 4.8 281.53 ± 10.46 24 3.41 ± 0.14 2006 13 20 ÄLKällorna 2 60 10.3 ± 0.6 38.19 ± 1.27 21 3.72 ± 0.16 806 13 21 ÄLKällorna 2 50 9.5 ± 0.6 39.73 ± 1.94 17 4.17 ± 0.18 906 13 22 ÄLKällorna 1 40 0.05 ± 0.01 0.22 ± 0.03 14 4.17 ± 0.17 1106 13 23 ÖLKöldgropen 55 8.5 ± 0.5 34.98 ± 1.19 20 4.10 ± 0.18 806 13 24 OSMosserud 50 12.6 ± 0.7 50.25 ± 1.66 24 3.97 ± 0.16 1606 13 25 ÅNMången 55 0.12 ± 0.01 0.52 ± 0.02 22 4.24 ± 0.18 906 13 26 ABNabbmanen 220 0.18 ± 0.01 0.67 ± 0.02 22 3.22 ± 0.14 1506 13 27 ABNabbmanen 180 0.18 ± 0.01 0.66 ± 0.02 24 3.73 ± 0.15 1406 13 28 ABNabbmanen 135 0.27 ± 0.04 0.99 ± 0.14 23 3.71 ± 0.27 806 13 29 ABNabbmanen 115 9.18 ± 0.53 34.19 ± 1.19 24 3.65 ± 0.16 806 13 30 ABNabbmanen 65 10.65 ± 0.57 34 ± 1 24 3.71 ± 0.16 906 13 31 YÄNyängen 1 60 11.6 ± 0.7 42.97 ± 1.32 19 3.72 ± 0.16 806 13 32 YÄNyängen 1 90 10.7 ± 0.7 37.00 ± 1.71 22 3.47 ± 0.14 1406 13 33 YÄNyängen 2 50 12.1 ± 0.6 47.10 ± 1.17 24 3.89 ± 0.16 1206 13 34 ÄSVästra höjden 50 97.4 ± 6.9 437.94 ± 23.70 24 4.49 ± 0.19 1306 13 35 LÖGlömsjö 200 121 ± 8 335.05 ± 16.23 25 2.77 ± 0.11 1306 13 36 LÖGlömsjö 150 102 ± 8 294.94 ± 19.46 25 2.89 ± 0.12 1206 13 37 OLSolbacka 90 51 ± 5 264.28 ± 22.40 27 5.20 ± 0.23 806 13 38 OLSolbacka 140 18 ± 1.3 84.81 ± 4.60 21 4.77 ± 0.20 1306 13 39 KÖSköldatorpet 225 33 ± 2 116.47 ± 5.52 27 3.51 ± 0.13 2606 13 40 ÄRLåddhedarna 70 63 ± 6 229.16 ± 18.03 19 3.61 ± 0.14 1506 13 41 ÄRLåddhedarna 90 55 ± 6 199.09 ± 17.98 25 3.63 ± 0.15 1406 13 42 JU Ljusnedal 50 61 ± 6 143.05 ± 12.98 29 2.36 ± 0.10 13 rejected due to poor dose recovery06 13 43 JU Ljusnedal 75 14 ± 1.4 32.27 ± 2.95 5 2.31 ± 0.09 23 rejected due to poor dose recovery06 13 44 IL-Pilgrimstad 120 44 ± 4 120.71 ± 9.31 31 2.74 ± 0.10 2806 13 45 IL-Pilgrimstad 180 47 ± 5 125.14 ± 12.30 24 2.64 ± 0.10 27

Appendix 2: OSL-ages

App. 2:1

Risø no. Your Site Depth, cm Age , ka Dose , Gy (n) Dose rate, Gy/ka w.c. %Comment06 13 46 IL-Pilgrimstad 240 44 ± 4 125.90 ± 10.00 28 2.84 ± 0.09 7206 13 47 IL-Pilgrimstad 290 44 ± 4 123.33 ± 9.13 22 2.79 ± 0.10 3406 13 48 IL-Pilgrimstad 305 48 ± 3 135.10 ± 7.33 30 2.84 ± 0.10 3106 13 49 KÄSkärkdalen 110 11 ± 2 20.72 ± 2.04 28 1.84 ± 0.17 1606 13 50 KÄSkärkdalen 190 9 ± 1.3 15.52 ± 1.93 23 1.82 ± 0.15 2006 13 51 TYStygghuvudet 70 16 ± 2 30.23 ± 2.62 31 1.85 ± 0.07 22 rejected due to poor dose recovery06 13 52 TYStygghuvudet 90 21 ± 3 40.54 ± 5.02 21 1.93 ± 0.18 22 rejected due to poor dose recovery06 13 53 VESvegsjön 65 7 ± 0.6 19.01 ± 1.25 24 2.76 ± 0.12 806 13 54 VESvegsjön 190 6 ± 0.7 15.81 ± 1.61 27 2.65 ± 0.11 1406 13 55 VESvegsjön 275 10 ± 0.9 25.63 ± 2.11 22 2.55 ± 0.10 1406 13 56 VESvegsjön 5 0.21 ± 0.28 0.35 ± 0.44 29 1.61 ± 0.09 906 13 57 LVUlvsjö 1 60 134 ± 10 400.47 ± 23.34 18 3.00 ± 0.12 2106 13 58 LVUlvsjö 1 100 78 ± 4 261.42 ± 6.24 23 3.35 ± 0.13 2206 13 59 LV Ulvsjö 2 90 9.7 ± 0.5 27.75 ± 0.80 23 2.87 ± 0.12 1406 13 60 LV Ulvsjö 2 100 8.8 ± 0.5 26.31 ± 1.12 24 2.98 ± 0.12 1406 13 61 N- Baskarp 100 14 ± 1.0 27.73 ± 1.40 24 1.93 ± 0.08 12

0813Risø no. Your Site Depth, cm Age , ka Dose , Gy (n) Dose rate, Gy/ka w.c. %Comment08 13 01 D2 Dösebacka 2000 58.86 ± 3.27 143.23 ± 3.83 8 2.43 ± 0.11 12 not finished08 13 02 D1 Dösebacka 2900 0.52 ± 0.15 1.00 ± 0.29 3 1.92 ± 0.10 23 not finished08 13 03 D12Dösebacka 3000 44.35 ± 10.74 122.07 ± 28.99 2 2.75 ± 0.12 13 not finished08 13 04 D1 Dösebacka 3000 0.53 ± 0.16 1.00 ± 0.29 3 1.87 ± 0.08 15 not finished08 13 05 D1 Dösebacka 3500 37.19 ± 10.60 85.68 ± 23.98 3 2.30 ± 0.11 7 not finished08 13 06 D8Dösebacka 3500 64.52 ± 9.00 146.40 ± 19.26 2 2.27 ± 0.09 23 not finished08 13 07 D7Dösebacka 3600 81.15 ± 10.84 195.70 ± 23.61 2 2.41 ± 0.13 19 not finished08 13 08 D3Dösebacka 3800 22.46 ± 5.80 81.01 ± 20.60 4 3.61 ± 0.15 21 not finished08 13 09 D4Dösebacka 3900 61.62 ± 9.74 199.38 ± 30.15 2 3.24 ± 0.14 19 not finished08 13 10 ÄSHässeldala 370 9.3 ± 0.5 19.14 ± 0.77 20 2.06 ± 0.05 14808 13 11 ÄSHässeldala 330 9.9 ± 0.9 10.78 ± 0.91 14 1.09 ± 0.04 37008 13 12 ÄSHässeldala 400 9.4 ± 1.4 22.37 ± 3.22 10 2.37 ± 0.07 14408 13 13 ÄSHässeldala 370 12.6 ± 1.6 15.87 ± 1.94 31 1.26 ± 0.04 26408 13 14 NDAndersön 300 1.05 ± 0.31 1.00 ± 0.29 3 0.96 ± 0.05 14 not finished08 13 15 NDAndersön 300 0.22 ± 0.06 1.00 ± 0.29 3 4.52 ± 0.19 14 not finished08 13 16 ÅLVålbacken 300 0.35 ± 0.10 1.00 ± 0.29 3 2.86 ± 0.12 19 not finished08 13 17 ÅLVålbacken 500 0.39 ± 0.11 1.00 ± 0.29 3 2.56 ± 0.11 22 not finished08 13 18 IL1Pilgrimstad 50 58.95 ± 3.83 135.05 ± 5.96 2 2.29 ± 0.10 19 not finished08 13 19 ILPilgrimstad 50 57.64 ± 5.66 166.29 ± 14.59 2 2.88 ± 0.11 21 not finished08 13 20 ILPilgrimstad 210 39.43 ± 15.19 111.28 ± 42.59 2 2.82 ± 0.11 19 not finished08 13 21 ILPilgrimstad 410 59.15 ± 12.07 201.01 ± 39.81 2 3.40 ± 0.15 22 not finished08 13 22 ILPilgrimstad 630 77.42 ± 22.87 235.32 ± 68.60 3 3.04 ± 0.13 19 not finished

App. 2:2

Further information on samples, sediments and analytical protocols will be given in the publi-cations regarding each study.

Appendix 3: TCN- and C14-ages

TCN-agesTerrestrial cosmogenic nuclide (TCN) ages were analysed and calculated by Derek Fabel at the Glasgow University Cosmogenic Nuclide Laboratory. Data is uncorrected for erosion, snow cover etc.

Lab ID Elevation (m)

Latitude (degrees

N)

Longitude (degrees

E)

Be production

rateuncert N10 N10

error

Be zero erosion

exposure age (ka)

full uncert.

analytical uncert.

S1 208 57.3947 14.9039 6.28 0.55 76109 4323 12.147 1.823 0.690

S3 211 57.3866 14.8983 6.19 0.54 89802 4686 14.549 2.107 0.759

S4 217 57.3808 14.8787 6.13 0.53 80014 4061 13.086 1.856 0.664

S7 145 57.6695 15.8057 5.91 0.51 76214 4006 12.939 1.729 0.680

S8 136 57.6700 15.8064 5.72 0.50 79932 4187 14.024 1.774 0.735

S9 140 57.6688 15.8031 5.83 0.51 75121 5765 12.928 1.838 0.992

ORM-1A 185 59.6805 13.9421 6.18 0.54 58183 2952 9.432 1.355 0.479

ORM-1B 185 59.6805 13.9421 5.94 0.52 59059 3593 9.962 1.378 0.606

ORM-2A 184 59.6805 13.9419 6.27 0.55 63706 3582 10.181 1.521 0.573

ORM-2B 184 59.6805 13.9419 5.81 0.51 58728 4595 10.128 1.442 0.792

ORM-3 185 59.6805 13.9421 6.23 0.54 78129 14014 12.573 2.840 2.255

VÄS-2 225 59.6700 13.9685 6.49 0.56 74284 4113 11.485 1.815 0.636

VÄS-3 225 59.6706 13.9681 6.03 0.52 67495 3721 11.215 1.564 0.618

VÄS-4 224 59.6709 13.9689 6.28 0.55 67109 3211 10.721 1.571 0.513

C14-agesPreviously unpublished radiocarbon ages used in this study.

Sample no SiteC14-age (yr BP)

Calibrated age; 2 sigma(cal. yr BP)

Reference

LuS 6814 Brattforsheden 1205±50 989-1267 this studyLuS 6957 Pilgrimstad 39200±2000 this studyLuS 6958 Pilgrimstad > 40000 this studyPoz-10380 Falltjärnen 9270±50 10580-10240 Jan RisbergPoz-10381 Falltjärnen 9310±50 10680-10280 Jan Risberg

App. 3:1

App. 4:1

Appendix 4: communication of resultsPublications or abstracts of presentations marked with * are attached or available from http://people.su.se/~halex/publications.htm

a. Papers/manuscripts/reports so farAlexanderson H & Murray AS. 2007: Was southern Sweden ice free at 19-25 ka, or were 1. the post LGM glacifl uvial sediments incompletely bleached? Quaternary Geochronology 1-4, 229-236. *Alexanderson H, Johnsen T, Lundqvist J & Wohlfarth B. 2007: 2. Field report from a Quaternary geological excursion to Jämtland. Report to the Swedish Nuclear Fuel and Waste Management Company (SKB). *Alexanderson H. 2007: 3. Brattforsheden – vad sanden kan berätta om dess historia. Report to the County Board of Värmland. *Alexanderson H. 2007: 4. Dösebacka. Preliminära resultat från fältarbete 18-22 oktober 2007. Report to the County Board of Västra Götaland. *Malmberg Persson K, Persson M, Alexanderson H & Lindén A.: Vimmerby – en randmorän 5. i nordöstra Småland. Submitted to Geologiskt forum.Johnsen T, Alexanderson H, Fabel D & Freeman SPHT. submitted: Cosmogenic nuclide 6. dating of the southern margin of the retreating Scandinavian Ice Sheet in Sweden. Geografi ska Annaler. Alexanderson H & Murray AS. in prep.: Why doesn’t OSL-dating work well for 7. deglacial sediments in Sweden? To be submitted to LED2008 proceedings in Quaternary Geochronology.Alexanderson H, Johnsen T, Murray AS & Wohlfarth B. in prep.: Re-dating the Pilgrimstad 8. interstadial: a warmer climate and a smaller ice sheet during the Swedish Middle Weichselian? To be submitted to Boreas MIS 3 special volume.

b. Conference presentations and various talks so farAlexanderson H. 2006: A ’blind date’ in a gravel pit: Determining the timing of deglaciation 1. by optical dating. Section for Earth and Environmental Sciences, Stockholm University. 26 October 2006. Talk.Alexanderson H. 2006: Using and evaluating optical dating for late glacial sediments in 2. Sweden. Department of Geology, Lund University, November 2006. Talk.Alexanderson H. 2007: Using and evaluating optical dating for late glacial sediments in 3. Sweden. Tarfala workshop, Tarfala, 31 March-3April 2007. Short talk.Alexanderson H & Murray A. 2007: Småland, south Sweden – a bleak place for luminescence 4. dating or an area that will change Scandinavian glacial history? 9th International Conference “Methods of absolute chronology”, Gliwice, Poland, 25-27 April 2007. Talk. *Johnsen T. 2007: Dynamics and chronology of ice sheet deglaciation in the central 5. Scandinavian mountains: applying radiocarbon, terrestrial cosmogenic nuclide and OSL dating. 9th International Conference “Methods of absolute chronology”, Gliwice, Poland, 25-27 April 2007. Talk. *Alexanderson H. 2007: New interstadial OSL- and 6. 14C- dates in Sweden. Fennoscandian paleo-environment and ice sheet dynamics during MIS 3, Lidingö, Sweden, 20-21 September 2007. Talk. *Alexanderson H. 2008: Optiskt stimulerad luminiscensdatering (OSL) av nedisningshistorien 7. i södra och mellersta Sverige. SGU FoU-seminar, 4 March 2008, Uppsala, Sw. Talk. *Alexanderson H. 2008: Optiskt stimulerad luminiscensdatering – resultat och erfarenheter 8. av att datera nedisningshistorien i södra och mellersta Sverige. ”Geologi og paleomiljø-seminar”, Department of Plant and Environmental Sciences, Norwegian University of Life

Sciences, Ås, Norway, 12 March 2008. Talk.Alexanderson H & Murray AS. 2008: Why doesn’t OSL-dating work well for deglacial 9. sediments in Sweden? 12th International Conference on Luminescence and Electron Spin Resonance Dating, Beijing, China, 18-22 September 2008. Talk. *Johnsen T, Alexanderson H, Murray AS & Wohlfarth B. 2008: Re-dating the Pilgrimstad 10. interstadial: a warmer climate and a smaller ice sheet during the Swedish Middle Weichselian? 12th International Conference on Luminescence and Electron Spin Resonance Dating, Beijing, China, 18-22 September 2008. Poster. *

App. 4:2

Appendix 5: Travel report

Travel to Gliwice, Poland - 24-29 April 2007Helena Alexanderson and Timothy Johnsen travelled to Gliwice in Poland to attend the 9th In-ternational Conference ‘Methods of Absolute Chronology’ 25-27 April 2007. Both Helena and Tim gave oral presentations of work done within this project and got some feedback from the audience. There were several interesting presentations and some that were directly ‘useful’ to us. For example, Helena got some tips on how to ‘attack’ problematic samples. We also met old and new colleagues and had good discussions between and after sessions. During the confer-ence we took part in a short excursion and visited fascinating coal mines and the radio tower in Gliwice, known for its World War II history. In addition, on our way to and from the conference, we had the opportunity of getting a good view of the Polish landscape from trains, enjoying Warsaw for a few hours and Krakow for almost a day. Krakow, especially, was a very nice experience.

App. 5:1