Testing OSL failures against a regional Weichselian glaciation
chronology from southern Scandinavia
MICHAEL HOUMARK-NIELSEN
BOREAS
Houmark-Nielsen, M. 2008 (November): Testing OSL failures against a regional Weichselian glaciation chronology from southern Scandinavia. Boreas, Vol. 37, pp. 660–677. 10.1111/j.1502-3885.2007.00053.x. ISSN 0300-9843.
Optically stimulated luminescence (OSL) is used extensively for dating Quaternary sediments. In stratigraphic
successions, inter-till beds dated by OSL constrain ages of periglacial or interglacial episodes, while till testifies to
ice-sheet oscillations. The majority of OSL results from southern Scandinavia agree with the glaciation chronology
predicted by numerical and relative ages, but not all. Overestimation of the expected timing seems to arise from an
inherited signal acquired prior to the latest depositional episode. Here, the geological context is examined for solifluction deposits that cap Middle Weichselian periglacial strata and Last Glacial Maximum (LGM) ice proximal
deposits showing pre-LGM ages. Suggestions are given as to how the depositional environment may influence the
dating results. Even though independent dating anchors the marine Cyprina clay and last interglacial peat bogs to
the Eemian interglacial, OSL ages show underestimation by up to 60%. It is discussed whether variations in dose
rates after burial could be responsible for this discrepancy. Despite these failures, OSL ranks among the most
qualified methods for dating Quaternary sedimentary successions.
Michael Houmark-Nielsen (e-mail: [email protected]), Institute of Geography and Geology, University of
Copenhagen, Øster Voldgade 10, DK-1350, Copenhagen K, Denmark; received 6th February 2008, accepted 16th July
2008.
Over recent decades, developments in sediment dating
techniques have substantially improved numerical
chronologies dealing with late Quaternary geological
history in northern Europe; the use of first thermoluminescence (TL) and later optically stimulated luminescence (OSL) has become part of stratigraphical
standard procedures (Ehlers & Gibbard 2004). Dating
of inter-till sediment has led to better age constraints on
the growth and decay of the Scandinavian Ice Sheet
(SIS), its interaction with other regional Eurasian ice
sheets and its response to climate change (Svendsen
et al. 1999, 2004; Hubberten et al. 2004; Larsen et al.
2006). OSL dating of glacial, periglacial and interglacial
sediments in Greenland, Svalbard, Scandinavia and
Russia has provided important chronological links to
North Atlantic deep-sea records (Elverh!i et al. 1998;
Larsen et al. 2006). Relying extensively on OSL, eventstratigraphic chronologies established along the eastern
and southern flank of the SIS have been applied with
success in attempts to unravel detailed ice-sheet behaviour and millennium-scale environmental fluctuations
during the last ice age (Wysota et al. 2002; HoumarkNielsen & Kjær 2003; Demidov et al. 2006; Kjær et al.
2006; Fedorowicz 2007; Houmark-Nielsen 2007). A
prerequisite in these studies is sound lithostratigraphic
control and independent dating tools other than luminescence. There are, however, among the huge amount
of dated samples some which do not support established chronologies. Such discrepancies potentially
throw doubt on dating method solidity. Only by testing
such odd dating results against a regional glaciation
chronology can the appropriate credit be given to the
dense network of reliable luminescence ages that actually constitute the foundation of our numerical age
chronologies, which are backed by radiocarbon ages,
palaeontological evidence, varve counts and palaeomagnetic correlation.
The present article addresses possible geological reasons for ‘misfit’ ages, using three case studies from
Denmark and southern Sweden (Fig. 1). Case 1 deals
with solifluction diamicts from outside the Last Glacial
Maximum (LGM) ice limit that are unexpectedly old
compared with underlying periglacial sediments. These
inverted age relationships are attributed to periglacial
transformation of glacial landforms and subaerial
gravity controlled re-deposition of glacial and interglacial sediments during the Middle and Late Weichselian. In case 2, meltwater sediments from ice-marginal
settings associated with deglaciation after LGM are
discussed against an event-stratigraphic age scheme
from southwestern Scandinavia covering the time-span
of roughly 60 kyr to 12 kyr ago (Fig. 2). Luminescence
ages from sediments of sub-, supra- and ice proximal
environments appear up to 100 kyr older than expected.
The majority of these older ages may be assigned to
specific modes of debris transport and deposition.
Thus, sediments deposited from subaqueous gravity
flows in a periglacial regime, and from turbulent discharge of meltwater in glacier proximal settings, are less
able to reproduce expected ages than deposits from
distal and periglacial aeolian, lacustrine and fluvial settings. Therefore, palaeoenvironmental interpretations
play a crucial role when confidence in luminescence
ages is to be judged.
DOI 10.1111/j.1502-3885.2008.00053.x r 2008 The Author, Journal compilation r 2008 The Boreas Collegium
BOREAS
Testing OSL failures, S Scandinavia
661
Fig. 1. Location map (case studies 1a, etc.,
as given in text) and prominent ice-marginal
formations (A to G) in southern Scandinavia.
A = Maximum Late Weichselian glaciation
(22–20 kyr). B = East Jylland phase
(20–18 kyr). C = Bælthav phase (18–17 kyr).
D = Halland Coast phase (17–15 kyr).
E = Central Skåne phase (16–15 kyr).
F = Göteborg phase (15–14 kyr). G = Blekinge
phase (15–14 kyr; Swedish varve-scale year 0).
After Lundqvist & Wohlfarth 2001; HoumarkNielsen & Kjær 2003.
Fig. 2. West–east time–distance diagram, southern Scandinavia picturing the most recent glaciation chronology. Glaciations are represented
by till formations. Periglacial and interstadial episodes !60–15 kyr ago constrain time and duration of glaciations. Ice-marginal phases A–G are
indicated in Fig. 1. Compiled from Lundqvist & Wohlfarth (2001), Houmark-Nielsen & Kjær (2003); Kjær et al. (2006); Houmark-Nielsen
(2007). Sediment symbols are placed according to geographical position and age.
Case 3 deals with marine and freshwater deposits of
the Eemian interglacial (!130 kyr to !15 kyr ago)
which have provided ages that are 20 to 80 kyr too
young. Severely underestimated ages of the last interglacial marine deposits are compared with age estimates, palaeoecological evidence and amino acid
correlation of similar deposits from the western part of
the Baltic. Moreover, apparently Weichselian-aged
freshwater sediments from the base of Eemian interglacial peat bogs are discussed in relation to geological
factors that may have influenced technical dating procedures.
A numerical glaciation chronology for southern
Scandinavia
Early attempts to date Weichselian glacier advances
in southern Scandinavia were based on conventional
14
C bulk dates (Berglund 1979; Berthelsen 1979).
662
Michael Houmark-Nielsen
Systematic use of thermoluminescence (TL) dating of
glacial and interglacial deposits largely extended the
theoretical age range of numerical chronologies
(Kronborg 1983; Kolstrup & Mejdahl 1986; Mejdahl
1986). The relationship between the Danish LGM-deglaciation chronology and that from Skåne and Halland (Fig. 1) was demonstrated by Lagerlund &
Houmark-Nielsen (1993) using calibrated 14C ages. By
linking the Swedish varve chronology to calendar scale
radiocarbon dating, correlation of deglaciation stages
from Kattegat to the Baltic across the south Swedish
highlands was outlined by Wohlfarth et al. (1993) and
by Lundqvist & Wohlfarth (2001).
Recently established chronologies (Lundqvist &
Wohlfarth 2001; Houmark-Nielsen & Kjær 2003; Kjær
et al. 2006; Houmark-Nielsen 2007) are integrated and
simplified in Fig. 2. Although largely based on luminescence, these models are supported by calibrated accelerator mass spectrometry (AMS) 14C-dating and
strengthened by palaeomagnetic correlation and stratabound relationships between lithostratigraphically
similar till-beds and interglacial and interstadial deposits that are indirectly dated by pollen and foraminifera
analyses. AMS radiocarbon-dated marine and terrestrial plant and animal remains from those strata are
adjusted to calendar year scale using standard calibration procedures (Reimer et al. 2004). Dates older than
!25 14C kyr BP are transformed to calendar scale by
comparison with several calibration curves as suggested
by the NotCal 04 members (van der Plicht et al. 2004)
and a more recent curve by Fairbanks et al. (2005).
Though some comparison curves pull 14C ages in opposite directions, adjusted ages seem to correlate well
with luminescence ages sampled from the same stratigraphical units in identical exposures (Houmark-Nielsen 2003; Ukkonen et al. 2007). The development of
OSL dating of quartz, especially using the single-aliquot regenerated-dose (SAR) procedure, has improved
both the precision and accuracy of ages for pre-LGM
deposits considerably (Murray & Olley 2002). The current glacial chronology is constrained by !150 luminescence ages and !40 radiocarbon dates; of the
luminescence ages, !90% are based on quartz, and the
remainder on feldspar. Though not all sediment
types are suitable for dating, samples have perforce
been gathered from any available exposure in coastal
cliffs, sand and clay pits, and excavations at construction sites.
A time-distance diagram (Fig. 2) illustrates the succession of glacial phases in Denmark and southern
Sweden from !60 kyr to slightly after 14 kyr ago. The
peak ice cover during the LGM and the subsequent
Late Glacial (!22 to 11.5 kyr) ice-sheet degradation are
marked by the ice-marginal configurations A, B and C
in Denmark (Fig. 1) during the Jylland stadial (Fig. 2).
Deglaciation proceeded east of Øresund after 17 kyr,
as shown by prominent ice-marginal positions in
BOREAS
Skåne and Halland (Figs 1, 2: D,E), and in Blekinge
14.5 kyr (Figs 1, 2: G). During the LGM ice-sheet
build-up at !30–27 kyr, the Kattegat Ice Stream
invaded the northern part of the region (Fig. 2). Older
ice advances were separated from the LGM phase by
periglacial and low-Arctic interstadial conditions. The
timing of pre-LGM glaciations in south Sweden is
speculative because of lack of data and is not shown
here, but there is evidence that the easternmost part of
Denmark suffered a short glaciation phase at !35 kyr
(Klintholm advance; Fig. 2). Although of less relevance
to the present study, even older Middle Weichselian
glacier advances are well known in Denmark; for instance, a Baltic glacier (Ristinge advance) almost
reached the North Sea region and calved into the Skagerrak Sea !55–50 kyr ago (Houmark-Nielsen 2007;
Larsen et al. 2008).
Luminescence dating
OSL dating was carried out at the University of Aarhus’s Nordic Laboratory for Luminescence Dating at
Ris!, Denmark. All dose measurements were made
using large aliquots of quartz, each made up of a few
thousand grains of diameter in the range 100 to 250
microns, and a SAR measurement protocol (Murray &
Wintle 2000). Mean doses were used and no attempt
was made to allow for incomplete bleaching, for instance by examining dose distributions within a sample.
Dose rate analysis is based on high resolution gamma
spectrometry (Murray et al. 1987). Calculations used a
saturation water content of 25% to 30% and it is assumed that these sediments were saturated for more
than 90% of the time after burial (Houmark-Nielsen &
Kjær 2003; Kjær et al. 2006). The sample burial depth
also affects the age, because of attenuation of cosmic
rays by overburden. The lifetime averaged burial depth
is, of course, not known but in all these cases the present-day sample depth has been used to calculate the
cosmic ray contribution to dose rate. In those cases
where strata are inclined or otherwise have suffered
glaciotectonic folding or thrusting, stratigraphic depths
as indicated in composite logs do not always equal
those of the sample depths below present ground surface. Further insight in OSL dating procedures used in
this study is given by Kjær et al. (2006) and Murray
et al. (2007).
Although dating using feldspar has been demonstrated to underestimate ages by up to 30% (Kronborg
& Mejdahl 1989; Houmark-Nielsen 1994; Christiansen
1998) a handful of OSL and TL-ages dated by Mejdahl
(1986, 1988) and by B!tter-Jensen et al. (1991) are
used here. The relevant results are listed in Tables 1 and
2. The accuracy of the expected time of deposition
varies from case to case according to the stratigraphic
control.
Region Figure no.
3
Case 1b
Case 1b West Jylland
Fig. 4
b
a
b
a
b
c
d
e
f
g
a
b
c
d
e
a
b
c
d
e
a
b
c
d
e
a
Peri diam
Glac fluv
Peri invol
Peri lac
Peri aeol
Soil
Peri fluv
Peri diam
Peri lac
Peri aeol
Peri
Niv fluv
Peri fluv
Lac sand
Peridiam
Peri fluv
Peri diam
1
1.5
3
0.5
1
1.5
1.5
2
2
4
1
1.4
0.5
1
3.5
0.75
4
3
4
1
1.5
1
1.5
3
6
2
030219
000213
000214
000215
000216
000217
000218
000219
000220
000221
000222
000223
000224
000212
030218
Late Eemian
010203
Weichselian
010202
Middle and Early Weichselian 030205
030206
921210
921226
921209
030207
Early Eemian
030208
Weichselian
020209
Late Saalian
020208
020211
Middle Saalian
020210
020207
Early Weichselian
020202
030214
040201
030220
020201
Middle Weichselian
020204
030211
030212
Late Saalian
020205
030210
Middle Weichselian
Early Eemian
Early Weichselian
Middle Weichselian
Late Weichselian
46"3
115"11
93"8
105"7
29"2
23"2!
32"3!
55"5!
108"8
93"6
206"19
126"12
170"12
193"13
260"20
167"9
118"8
103"6
115"8
128"12
209"15
42"3
38"2
169"13
155"1
210"13
12"1
12"1
11"1
16"2
121"12
91"7
78"6
70"4
88"7
87"4
88"5
108"9
12"1
0.81
0.82
1.43
0.76
0.78
0.85
2.33
2.78
2.67
2.72
2.61
2.46
25
18
24
20
20
21
20
27
27
24
24
24
27
21
16
23
18
21
27
26
31
20
92"5
181"8
219"18
122"9
134"6
239"11
389"30
175"4
89"3
134"4
124"5
123"9
223"11
35.3"1.5
32.2"0.8
220"20
236"13
0.85"0.04
1.95"0.09
1.06"0.05
0.96"0.05
0.79"0.04
1.23"0.05
1.44"0.06
1.05"0.05
0.76"0.05
1.31"0.06
1.08"0.06
0.96"0.05
1.07"0.05
0.84"0.05
0.86"0.04
1.29"0.06
1.52"0.06
No data
0.85"0.04
1.61"0.03
0.66"0.03
1.19"0.05
0.98"0.04
24 1.21"0.05
21
21
21
21
20
21
20
19
21
21
20
21
21
44
26
20
38
27
33
32
19
25
23
29
24
21
29
26
30
17
21
27
25
24
25
25
21
14
21
21
14
14
19
23
30
33
38
25
1
1
1
1
1
3
3
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
Dose rate (Gy/kyr) wc (%) R
18 0.78
39.4"1.0
130"10
61"4
125"6
29"2
254"11
9.6"0.5
9.5"0.3
16.2"0.7
11.8"0.9
94"8
77"3
182"9
195"5
231"14
236"3
230"10
265"9
9.9"0.5
Ris! no. OSL age (kyr) Dose De (Gy) n
Testing OSL failures, S Scandinavia
Glac fluv
Glac fluv
Anders Hoved Peri diam
Peri fluv
Tirslund
Visby
Emmerlev
Oksb!l
Endrup skov
Lac mud
Diam
Lac sand
3.5
4.5
5
5.5
6
7
7.4
7.8
8.5
9.0
9.5
13.5
1.5
Sediment type Depth (m) Age expected
Sols! well site Lac sand
Log id Site
Case 1a West Jylland
a
Perglacial lake basin
Fig. 3
b
c
d
e
f
g
h
i
j
k
l
3
m
Case
Table 1. Optically stimulated luminescence dating on inter-till sediments in western Jylland, Denmark. Results that do not fit the regional chronology as indicated by the expected ages are
highlighted in boldface. Peri = periglacial; Glac = glacial; Lac = lacustrine; Fluv = fluvial; Aeol = Aeolian; Niv = nivation; Invol = involution; Diam = diamicton; Mud = mud. Wc = percent
water in sample compared to total saturation volume; R = reference, 1: Houmark-Nielsen (2007), 2: Houmark-Nielsen (2003) (depth-corrected), 3: Christiansen (1998). Ages marked with asterisk
are feldspar ages and no technical information was available.
BOREAS
663
Tinglev
Fm
Case 2a Fig. 6
Case 2d
Vejrh!j
Fm
Case 2c Fig. 8
Svängsta
Fm
Ground
moraine
Tirstrup
Fm
Case 2b Fig. 7
Nyb!l
Fm
Region
Fm
Case
Figure no.
Over Jerstal
Klinting
Klinting
Klinting
Nyb!l
Iller
b
c
d
e
f
g
Esker mouth
Sävsjömåla
Hjälmsa
Hjälmsa
4
12
4
8
o15
o20
1.5
1.5
1.5
2.5
1.7
3
2
3
2.5
2
1.5
1
10
4.5
o18
20–15
o18
28–18
Age
(kyr expected)
1.5
2
No data
1.5
1.5
3
5
6
6
3
2
Depth (m)
990236
990231
990232
990235
050218
050218
050219
050209
050210
050212
050211
050213
050214
050216
050215
000227
000228
050217
000226
898012
898011
898010
898009
990209
908001
990210
990221
030224
020214
990216
020213
010201
030226
Ris! no.
49"6
71"8
89"8
115"15
30"2
30"2
23"1
16"1
18"1
17"1
29"3
43"3
40"3
49"4
25"2
32"3
31"3
25"2
37"4
128"2!
87"8!
36"4!
28"3!
36"3
16"1!
126"9
21"2
41"3
24"3
28"2
18"1
18"1
129"9
OSL
age (kyr)
162"18
290"28
357"19
442"48
60"3
50"3
43.1"1.6
25.7"0.5
31.9"1.1
23.6"0.8
58"5
67"3
73"5
94"6
54"2
56"3
71"1
41"2
58"4
54.7"2.6
155"4
45.8"3.3
52"3
15.2"1.4
21.9"0.8
16.1"1.6
38.7"1.0
147"7
Dose
De (Gy)
1.15"0.06
2.07
1.26"0.05
0.63"0.04
0.73"0.04
0.90"0.04
2.17
1.14"0.05
Dose rate
(Gy/kyr)
17
21
16
17
22
27
27
24
24
24
24
23
24
23
23
29
24
24
27
3.45"0.17
4.06"0.21
4.08"0.20
3.84"0.19
1.96"0.08
1.68
1.87"0.07
1.62"0.06
1.76"0.07
1.41"0.06
2.00"0.08
1.56"0.06
1.83"0.07
1.91"0.08
2.15"0.09
1.73"0.09
2.27"0.08
1.66"0.07
1.57
15
1.52"0.07
No data
No data
15
15
18
27
24
27
18
17
n
21
18
21
21
14
24
21
21
18
23
25
23
20
19
20
30
26
24
28
20
21
36
27
28
17
19
41
26
wc (%)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
2
0
2
3
3
3
3
2
3
2
1
1
1
1
1
1
1
R
Michael Houmark-Nielsen
Kame delta
Esker
Drumlin Kame
Hoch sandur fan
Järnavik
Gurede
Gedebjerg
Bregninge
Kaldred
Proximal sandur
Distal sandur
Skamlebæk
Hvideklint
Proximal sandur
Delta
Lacustrine
Distal sandur
Proximal sandur
Glacio lacustrine
Fluvial
Proximal sandur
Sediment type
H!jby
Fuglslev
Tirstrup
Mesballe
Auning
Rostved
Borum
Rosmos
R!dekro
Site
a
Log id
Table 2. Optically stimulated luminescence dating on inter-till sediments in western Jylland, Denmark. Results that do not fit the regional chronology as indicated by the expected ages are
highlighted in boldface. wc = percent water in sample compared to total saturation volume, R = reference, 0: This study, 1: Houmark-Nielsen (2007), 2: Houmark-Nielsen & Kjær (2003) (depth
corrected), 3: Ditlefsen (1991), 4: Houmark-Nielsen (1994). Ages marked with asterisk are feldspar ages.
664
BOREAS
Testing OSL failures, S Scandinavia
4
0
4
4
4
0
2
2
4
4
4
2
2
0
0
0
BOREAS
665
Case 1
Case 1a: A drill site at Sols!
20
27
1.87"0.1
2.71"0.3
15
27
52"0.7
74"2
1.52"0.08
1.71"0.09
1.64"0.08
27
15
15
No data
30–20
At Sols!, one such 4200 m wide depression has survived from the late Saalian and received sedimentary
infill on several occasions (Figs 1, 3). Above the Eemian
interglacial freshwater peat and gyttja, laminated muddy lake sediments with plant remains gradually change
into sandy deposits, which are capped by a bed of sandy
Interstadial lacustrine
5
12
11
11
4
3
4
4
Periglacial lacustrine
70–50
Periglacial fluvial
13
12
12
6
Marine sand
40–30
880211
990228
880210
920204
920201
990229
990226
990225
920203
920207
880217
990230
990220
34"3!
39"3
23"2!
73"7!
58"5!
60"4
34"3
33"2
34"3!
25"3!
29"4!
28"2
29"2
108"4
91"3
60.1"4.4
54.1"0.5
No data
No data
27
2.81"0.14
21
23
22
20
16
2.03"0.10
15
78.9"1.8
39"3
13
Marine mud
West of the LGM ice margin in central Jylland (Fig. 1:
A) glacial landforms have been transformed by periglacial smoothing during the severe cold episodes of the
last ice age (Houmark-Nielsen 2007). Saalian to Middle
Weichselian glacial sediments are exposed at the
ground surface on the low relief hills, separated by valleys filled by distal outwash plains. Depressions are filled with down-washed sand, mud and diamict debris,
overlying last interglacial lacustrine deposits as identified by their pollen and other plant remains (Jessen &
Milthers 1928). Ages are listed in Table 1.
Unit 7–8
Unit 5
Unit 3
b
c
d
e
f
g
h
i
j
k
l
m
n
Klintholm M!n
Cyprina clay
Unit 2
Case 3 Fig. 11
Mörum Fm
a
Hjälmsa
Bredåkra
Delta
3
3
130–117
990227
406"27
102"29
990233
990234
85"8
25"7
19
17
4.76"0.24
4.05"0.20
21
18
Inverted age relationships in a periglacial setting
Fig. 3. Stratigraphic log from Sols! drill site in western Jylland
(Fig. 1, inset 1a). Samples were taken in a photographic darkroom
from closed plastic pipes inserted in the steel casing at the drilling site.
Modified from Houmark-Nielsen (2003).
666
Michael Houmark-Nielsen
diamict with wind abraded stones. The diamict deposit
varies from 1 to 2 m in thickness and is found in most of
the lake basin (Jessen & Milthers 1928). In the lacustrine mud, the OSL ages decrease from 88 kyr at the
base to 70 kyr (Table 1) at the top. In the sandy lacustrine deposit just below the diamict, an age of 91 kyr
was obtained. The diamict itself has an age of 121 kyr.
Above the diamict, samples decrease in age from 16 to
11 kyr going up the sequence.
These ages suggest that the former interglacial lake
basin gradually filled up with periglacial sediments and
re-deposited interglacial plant detritus washed out from
the surrounding area during the Early Weichselian. The
diamict unit and ventifacts bear witness to an episode of
subaerial exposure and infilling with water-saturated
sediment gravity flows after 70 kyr. The inversion of
ages in the borehole samples suggest that a wind-abraded and periglacial land surface was subjected to erosion and re-deposition by cryoturbation which began
before the basin was buried by diamict solifluction deposits. The hiatus between 70 kyr and 16 kyr could
suggest that the basin ceased to receive sediments until
the end of the Late Weichselian when infilling of the
basin recommenced. Renewed accommodation space
could have been provided by the melting of ground ice
trapped in the interglacial peat.
Case 1b: Open sections
Subsoil sediments in the hills of western Jylland often
make up a heterogeneous unsorted carpet of strongly
involuted mud, sand and crudely-bedded slump-folded
diamicts with frost-cracked clasts and ventifacts,
BOREAS
usually less than 2 m thick (Figs 4, 5). This carpet
was deposited in a water-saturated state by gravitational sliding, creep and down-washing caused by
episodic melting of the active layer in an environment
with continuous permafrost in a dry and high-Arctic
climate. In six exposures, the carpet overlies a suite of
sorted and bedded sand and gravel, deposited in rivers,
lakes and by nivation under low-Arctic conditions.
OSL ages from sediments beneath the solifluction
carpet range from 260 kyr to 29 kyr (Table 1), the majority indicating Weichselian age. Generally, the ages
get younger upwards in the stratigraphic section. Some
ages suggest that the solifluction deposits may be of
Middle Weichselian age, whereas others indicate a Late
Weichselian age. Studies of periglacial features indicate
that northern Europe suffered two episodes of severe
cold and strong permafrost growth during the last ice
age (Vandenberghe & Pissart 1993), first during MIS 4
(72–62 kyr) and later and with more impact during MIS
2 (26–13 kyr). However, OSL ages from the solifluction
deposits themselves range from 105 kyr to 210 kyr,
meaning that this set of ages cannot be trusted unless
the first set is much too young. Omitting samples taken
in relatively coarse-grained bedded sand and gravel deposited in proximal glaciofluvial settings (Fig. 4: Tirslund: b, Andershoved: d, e), the remaining ages in the
first set are taken from finer-grained sand and mud deposited in periglacial lakes and subaerially from snow
melting, distal rivers and by wind action. The majority
of quartz grains from these samples have had a fair
chance of good light exposure during deposition and
ages seem to reflect several episodes of periglacial conditions in Jylland during the last ice age.
Fig. 4. A west–east oriented stratigraphic cross-section, southern Jylland with lithology and stratigraphic units. Annotated OSL results from individual
sites are shown with labelled letters referring to Table 1 and age (kyr). Width !50 km and depth !25 m. Modified from Houmark-Nielsen (2007).
Testing OSL failures, S Scandinavia
BOREAS
667
Fig. 5. A succession of Saalian till capped by an
Eemian interglacial soil horizon and overlain
by Early Weichselian lacustrine sand folded by
gravitational creep in a periglacial regime
overlain by Late Weichselian solifluction
diamict. Scale: 0.5 m. Oksb!l gravel pit
(Figs 1, 3). Photo. M. Houmark-Nielsen 2003.
Discussion
The sandy diamict with wind-abraded pebbles from the
Sols! core probably constitutes part of the solifluction
apron that drapes the periglacially smoothened glacial
landforms found in open sections throughout western
Jylland. Apparently, deposits are older than 105 kyr and
ages may vary by !100 kyr between sites. The stratigraphic position indicates post-Eemian formation which
could have occurred during the two episodes of strong
periglacial régime during the Weichselian recorded on
the north European lowlands. The mode of deposition
of such sediments does not favour light exposure and
resetting of the OSL signal. In general, re-sedimented
diamicts and other mass-flow sediments are considered
inappropriate for dating because of the relatively poor
opportunity for daylight exposure (Aitken 1998; Richards 2000). Similarly, within solifluction diamicts the
majority of grains are transported down gentle slopes in
a fine-grained, water-saturated matrix by gravity-induced mass movement, probably without much opportunity for light exposure (Fig. 5). Given that this material
generally represents the youngest deposit in open exposures, it seems likely that mixing of sediments carrying
OSL signals from incompletely bleached older sediment
grains is responsible for the wide span in ages and the
inverted chronological succession. Judging from the ages
of subjacent deposits, the solifluction apron is probably
not much older than MIS 2 and it seems likely that deposition took place in connection with the last episode of
severe cold climate which led to LGM glaciations east of
the end moraines of central Jylland.
Case 2
Overestimated ages from ice-marginal meltwater
sediments
The end moraine belts running through Denmark and
associated with the LGM ice cover and the subsequent
deglaciation exhibit all the classical features of glacier
marginal environments (Fig. 1: A, B, C). The ice-pushed ridges are tens to more than one hundred metres
high and composed of glaciotectonically thrusted and
folded strata. The end moraines are bordered by
coarse-grained outwash fans. In front of these ice-pushed ridges, grain sizes decrease from proximal matrixrich boulder gravels to distal sandy outwash plains.
Other proglacial features include ice-dammed lake deposits, consisting of either laminated mud, fine sand or
sandy outwash fan deltas. Behind the former glacier
termini, streamlined ground moraine with drumlins
and scattered kames and eskers characterize the former
ice-covered areas. According to the glaciation chronology these ground moraines are made up of three LGM
tills deposited during the Jylland Stadial between 22 kyr
and 17 kyr ago (Fig. 2). OSL ages are listed in Table 2.
Case 2a
End-moraine zones A and B are present in the Tinglev
area (Figs 1, 2: A, 6). The Tinglev Formation (Fm) is an
outwash plain gently sloping to the west away from the
end moraines. According to geological mapping, the
outwash plain is among the youngest glacial features in
the area and was deposited in connection with formation of the end moraine zone A at the end of the last
Ice Age (Hansen 1965, 1978). Eskers lead from the
ground moraine towards the former glacier termini.
West of one esker mouth, bedded sand in a coarsegrained outwash fan gave an OSL age of 129 kyr and
another outwash fan in front of zone A provided an age
of 41 kyr. Both deposits were sampled a few metres below surface. Radiocarbon ages on a mammoth tusk and
a horse bone (Equus ferus) embedded in the proximal
outwash fan indicate that the Tinglev Fm is younger
than 35 kyr (Aaris-S!rensen 2006). It therefore seems
unlikely that the OSL results reflect the true age of the
Tinglev outwash plain. Behind the end moraine, the
Tinglev formation is covered by an LGM till. OSL ages
from open sections in the area suggest that the Tinglev
668
Michael Houmark-Nielsen
Fm is younger than 28 kyr and older than 18 kyr (Fig. 6:
Nyb!l, Lateglacial o18 kyr; Klinting, Pre-LGM fluvial
deposits).
Case 2b
In the Mols area (Figs 1: 2b, 2: B, 7) the valley sandur
that builds up the Tirstrup Fm was deposited north of
the East Jylland end moraines. Lakes dammed by the
end moraines existed at Rostved and Rosenholm
(Fig. 7) and further south at Borum (Fig. 1). In these
lakes, sand and gravel were deposited proximally in
kame deltas, and laminated mud and fine sand deposited distally from these. The push moraines were
stacked and thrust up more than 100 m by glacier lobes
from southerly directions during the general deglaciation following the LGM, some time between 20 and
15 kyr ago. Samples from the Tirstrup Fm at Rosmos
and a kame delta at Rostved (Fig. 7) provided OSL
ages of 126 kyr and 39 kyr, much older than expected
compared to the regional glaciation chronology. This
discrepancy was also noted earlier by Ditlefsen (1991),
who used TL on the Tirstrup Fm. However, Ditlefsen’s
ages from distal glaciolacustrine deposits at Borum
gave TL ages of 16 kyr, comparable with the OSL age
of the Nyb!l Fm (Fig. 6). At Rosenholm, radiocarbon
ages from terrestrial plant material overlying laminated
glaciolacustrine mud and fine sand indicate that infilling of the Rosenholm depression was in progress
before 14.5 kyr. Thus, neither OSL nor TL provide ages
for the Tirstrup Fm that fit with the regional eventstratigraphic framework; it seems most likely that these
ages suffer from a similar problem of overestimation to
those for the Tinglev outwash plain.
Case 2c
In northwest Sjælland, the Bælthav ice stream pushed
up several generations of end moraines in the final
BOREAS
phases of LGM deglaciation in Denmark from 18 to
15 kyr ago according to the chronology (Figs 1: C, 2: C,
8). Three sandurs making up the Vejrh!j Fm are located
west and north of the end moraines at H!jby, Vejrh!j
and Brejninge. These sandurs are composed of sandy
and muddy hoch-sandur fans and proximal outwash
fans with boulder gravels, changing downstream and
stratigraphically upwards into more distal and wellbedded sand and gravel. East of the end moraines,
drumlinized kames are found on a streamlined ground
moraine. These kames were overridden from easterly
directions and dislocated by the glacier which formed
the Bjergsted–Vejrh!j end moraines.
OSL ages from these sediments range from 49 kyr to
16 kyr. The older ages were sampled in proximal meltwater deposits and hoch-sandur fans (Fig. 9), while the
younger ones were taken from distal, sandy-fluvial and
glaciolacustrine deposits. Palaeomagnetic correlation
to sites where inclination–declination data are tied to
radiocarbon ages gives an age of !17 kyr for one undisturbed kame north of the end moraines at R!snæs
(Fig. 8; Bremer 1990).
Open sections in the H!jby area expose four LGM
tills stratigraphically below the Vejrh!j Fm (Fig. 2).
Since the Vejrh!j Fm is closely connected with the
stacking of the end moraines, and this must have occurred when the youngest till was deposited, OSL dating of the sandurs west of the end moraines
overestimates the age compared to the expected ages.
Case 2d
During the last deglaciation in southeastern Sweden,
the Scandinavian Ice Sheet terminated in a large icedammed lake, the Baltic Ice Lake (BIL) from !15 kyr
until the end of the Younger Dryas. In Blekinge (Fig. 1:
2d) the ice-sheet margin was composed of a zone of
more or less coherent stagnant ice. Successive glacier
terminal positions are now marked by the transition of
meltwater channels from esker termini to kame terraces
Fig. 6. Stratigraphic cross-section, southeastern Jylland with end moraines A & B (Fig. 1, inset 2a) and OSL results of subsurface deposits,
Case 2a. Annotated OSL results from individual sites are shown with labelled letters referring to Table 2 and age (kyr). 14C ages of embedded
mammoth tusk and bone from horse and twigs of Juniperus are indicated. A near LGM age for the Tinglev Fm is provided from Klinting east of
the end moraines. Width !30 km and depth !25 m. Modified from Houmark-Nielsen (2007).
BOREAS
Testing OSL failures, S Scandinavia
669
Fig. 7. Morphological map of Mols central East Jylland (Fig. 1, inset 2b) based on Houmark-Nielsen (1983), DEM (Digital Elevation Models,
Danish National Survey and Cadastre) and soil maps (GEUS 1989). TL ages (Ditlefsen 1991) and OSL results (present study) from glacier
proximal–distal meltwater deposits on the Tirstrup sandur are indicated. See also Table 2, Case 2b.
and by kame deltas belonging to the Svängsta Fm (Fig.
2). As deglaciation proceded northwards, glacio-isostatic rebound caused the local water table to drop;
periodic interruptions of the resulting fall in lake level
led to progradation of large deltas of the Mörrum Fm
into the BIL (Björck & Möller 1987). Based on correlation between the varve time scale and a radiocarbon
chronology of BIL sediments, the deglaciation in central Blekinge took place around 14.5 kyr ago (Lundqvist & Wohlfarth 2001). In the Svängsta Fm, OSL
dating of esker sediments provided an age of 115 kyr, a
kame terrace gave 49 kyr and kame delta deposits between 89 and 71 kyr. In the Bredåkra delta, radiocarbon dating indicates deposition at the onset of the
B!lling chronozone (14.5 kyr), whereas OSL gave an
age of 25 kyr. These luminescence ages are much too
old compared to deglaciation ages obtained by independent methods such as pollen, varves and radiocarbon dating.
Discussion
Overestimated luminescence ages are usually attributed
to incomplete bleaching during the last transport event
(Larsen et al. 1999, 2006; Kjær et al. 2006; Alexanderson & Murray 2007). From Himalayan glacial
environments, Richards (2000) lists a number of sedimentary facies suited to luminescence dating although
with a risk of age overestimation. The mode of transport and deposition strongly influences the effective resetting of any prior natural OSL signal during exposure
to daylight. The likelihood of bleaching of debris is dependent on its position in the glacier ice and the way it
is released from ice entrapment. In the case of lowland
glaciation, other processes may be more important:
(i) turbidity and transport distance in meltwater
streams, (ii) water depth and depositional processes by
which debris settles in ice-dammed lakes and on river
beds, and (iii) the possibility of subaerial exposure and
aeolian reworking under low discharge conditions or
drought.
Some meltwater sediments deposited in glacierproximal environments are clearly overestimated in age
to various degrees by luminescence, compared to the
regional chronology (Fig. 2). Moreover, it appears that
the further away the luminescence samples are from
former ice margins, the better the OSL ages seem to fit
the regional model. Subglacial sediments are unlikely to
have experienced any light exposure during transport
670
Michael Houmark-Nielsen
BOREAS
Fig. 8. Morphological map of end-moraine zone C (Fig. 1, inset 2c) in the Vejrh!j area, northwest Sjælland based on Houmark-Nielsen (1983),
DEM (Digital Elevation Models, Danish National Survey and Cadastre) and soil maps (GEUS 1989). OSL ages from subsurface meltwater
deposits found at the sandurs west of the end moraines and from drumlinized kames on the streamlined ground moraine are indicated. See also
Table 2, Case 2c.
and subsequent deposition. In contrast, glaciofluvial
sediment grains may be well bleached, depending on
turbidity, water depth, the number of depositional and
erosional cycles before final deposition and transport
distance. It is obvious that subglacial esker sediments
are not exposed to light during deposition; however, if
they were exposed before being transported under the
glacier, they will give an apparent age related to some
previous transport and deposition event. The kame and
glaciolacustrine delta sediments, although deposited
subaerially, presumably did not receive sufficient light
to completely reset all the grains in the deposit. As
shown by Ditlefsen (1991), infrared (IR) stimulated
feldspar ages seem to grow younger as samples are taken more distal to the end moraine samples and transport paths become longer; nevertheless, his ages were
only rarely as young as predicted by the model. Quartz
OSL bleaches more rapidly than IR stimulated signals
from feldspar, and Stokes et al. (2001) demonstrated a
rapid decline in effective dose values during the first
100 m of bed load transport downstream from a source
area with a reasonably stable residual age of !1 kyr
being reached some kilometres downstream. This suggests that sediments deposited very close to glacier
BOREAS
Testing OSL failures, S Scandinavia
671
Fig. 9. Proximal post-LGM meltwater deposits from the Kaldred on the Bregninge sandur indicating apparent ages of 40–43 kyr (Fig. 8). Note
rapid facies changes through the succession. Palaeocurrents directed towards observer. Detail from lower part of succession inserted. Photo. M.
Houmark-Nielsen 2002.
termini are likely to be incompletely bleached, and so
overestimate ages. However, ice-proximal sediments
may be well bleached even after only short transport
distances, as implied by Stokes et al. (2001) and demonstrated by B!e et al. (2007). This may be caused by
the nature of their braided river systems, characterized
by episodic high meltwater discharge interrupted by
low discharge, subaerial exposure of sediment grains
and possible redeposition by wind. However, if bedload
transport was rapid on the outwash plains, debris
transport and sandur, kame and delta building will
have taken place in turbulent sediment-laden meltwater; deposition also occurred reasonably close to the
glacier margin. It is experimentally shown that not only
light reduction could have been caused by fine-grained
debris in the water column, but also suspended air
trapped in the meltwater due to turbulence are important in reducing the bleaching of sediment particles
(Ditlefsen 1992). All of these processes will have contributed to the overestimation of ages from glacier
marginal settings. Sediments deposited by high-energy
floods such as debris flows may also be poorly bleached
during transport in suspension (Lehmkuhl et al. 2007)
and most likely the debris on the hoch-sandur fans experienced similar limited light exposure, since they were
deposited by high-energy episodic discharge and flooding. In summary, it seems that all grains are often not
completely reset in such proximal sediments. If the
sample receives little or no light exposure, the apparent
luminescence age may reflect some bleaching event
prior to the most recent transport and deposition; if
moderate light exposure has resulted in heterogeneous
and incomplete bleaching, the apparent age may lie at
any time between these two events. Samples deposited
under quieter conditions and in more distal positions
suggest the Vejrh!j Fm to have been deposited about
18–16 kyr ago, which is comparable with the regional
chronology and in accordance with the palaeomagnetic
age determination of the formation of the R!snæs end
moraine.
The average water content since burial also has an
influence on the effective dose rate; Kjær et al. (2006)
report that an increase of 1% by weight in the assumed
lifetime-averaged water content will result in !1% reduction in dose rate, and so !1% increase in age. The
sandur and kame sediments in case 2 were assumed to
have been saturated with water throughout their burial,
with estimated water contents of about 25–30% by
weight. It is certainly possible that these sediments
spent more time above the groundwater table than expected from methodological premises. With the exception of eskers and kames, these sediments are often
found adjacent to push moraines or in valleys. Although these settings are relatively downstream in the
catchments, the poorly bedded and not very well sorted
sediments are highly permeable and well drained.
Nevertheless, realistic changes in the assumed water
content are unlikely to lead to changes in age of more
than 10–15%, which is usually insufficient to explain
the overestimates discussed above.
672
Michael Houmark-Nielsen
BOREAS
Fig. 10. Sketch of coastal cliff exposure around Klintholm, eastern M!n (Fig. 1, inset 3). Strongly glaciotectonic disturbed Cyprina clay
(Fig. 11: unit 2) is situated unconformably beneath Ristinge till and Klintholm till (Figs 2, 11: units 4, 6). The tills are overlain by muddy
interstadial and lacustrine sediments (Fig. 11: units 7, 8) in the western section. TL and OSL ages are indicated. Modified from HoumarkNielsen (1994).
Case 3
Underestimated ages of last interglacial sediments
At its peak, the last interglacial (Eemian) was characterized by dense deciduous temperate forests and
shallow Boreal–Lusitanian seas in the southern part of
the Baltic and the North Sea Region (Jessen & Milthers
1928; Funder et al. 2002). The exact age of the Eemian
is controversial due to slight disagreements between
Northwest European vegetation history and marine
highstand chronology (Shackleton et al. 2003); nevertheless, there is a consensus that interglacial conditions
in the circum-Baltic region prevailed during the Eemian
pollen zones 2–6 from !131 to !119 kyr (Lambeck
et al. 2006).
Case 3a: Marine Eemian deposits almost 100 kyr too
young
The marine Cyprina clay in the southwestern Baltic was
deposited in a shallow interglacial sea during the first
half of the Eemian (Funder et al. 2002). At Klintholm
on the Baltic coast of M!n (Fig. 1), glacial, tectonically
dislocated rafts of Cyprina clay overlain by marine sand
have been thrust and stacked beneath two tills of Middle Weichselian age (Fig. 10). The Boreal shallow water
mollusc fauna matches that from Ristinge (Fig. 1) and
other type sections in the southwestern Baltic with a
typical Eemian mollusc fauna (Funder et al. 2002).
When compared with an international index of amino
acid stratigraphy (Miller & Mangerud 1986), ratios of
D-alloisoleuciene/L-isoleuciene (D/L ratio) in shells
from three separate species (Arctica (former Cyprina)
islandica, Turritella communis and Nassa reticulata)
correlate well with D/L ratios from other Eemian sites
in NW Europe (Houmark-Nielsen 1994). Foraminifera
analyses from the M!n exposures indicate a Boreal–Lusitanian fauna with little re-deposited pre-Quaternary species, similar to the micro-fauna from other
type sections in the southern North Sea and Baltic regions (Kristensen 1993; Kristensen et al. 2000). Although there are indications of colder conditions in the
very top of the unit on M!n, the fauna indicates a
shallow water ( # 20 m) environment with temperatures and salinity slightly higher than present. Radiocarbon dating of shells gives non-finite ages (440 kyr),
while TL and OSL ages from feldspar grains of the
marine clay and overlying marine sand yielded ages of
34 kyr and 23 kyr, respectively (Houmark-Nielsen 1994;
this article: Fig. 11, Table 2). This age discrepancy of
!100 kyr was later investigated using a SAR protocol
on quartz grains, but at !39 kyr, the expected age was
again severely underestimated. Nevertheless, it should
be noted that the two luminescence minerals (feldspar
and quartz) both give fairly consistent underestimates
of the expected age.
TL ages of 27 kyr from the Cyprina clay from Rügen
on the German Baltic coast are in the same range as
those from M!n (Fig. 1; Steinich 1992). As at M!n, the
Rügen marine clay crops out in a strongly glaciotectonized disturbed state, which hampers on-site correlation and the establishment of an obvious stratigraphic
succession. Though characterized by Arctica islandica
Testing OSL failures, S Scandinavia
BOREAS
673
cool conditions existed in the Baltic between 36 and
29 kyr (Müller 2004). On M!n, interstadial lacustrine
sediments (Fig. 2: Kobbelgård beds, Fig. 11: unit 7–8)
with remnants of low-arctic biota overlying Klintholm
till have given 14C ages from 32 to !24 kyr; OSL and
TL ages of these deposits are consistent with the radiocarbon dating and range between 29 and 25 kyr. Periglacial lacustrine sediments sandwiched between
Klintholm till and Ristinge till obtained OSL ages of
34–33 kyr (Fig. 11: unit 5), while glaciotectonically folded and thrust sand with redeposited Eemian molluscs
and frost-cracked and wind-polished pebbles below
Ristinge till provided OSL and TL ages of 79 to 58 kyr
(Fig. 11: unit 3). The Cyprina clay of M!n with apparently enigmatic luminescence ages is located stratigraphically below this succession of post-Eemian
deposits showing self-consistent ages, being younger
towards the top, and which meet the expectations of the
regional chronostratigraphic framework.
Case 3b: Underestimated ages of Late Saalian – early
Eemian freshwater deposits
Eemian freshwater sediments are identified by a specific
floral composition, most obviously recognized from its
pollen spectra (Jessen & Milthers 1928; Andersen
1965). At two sites, freshwater lake sediments have
been found belonging to the Eemian, and the transition
downwards into underlying glacial sediments is also
exposed (Figs 3, 4: Sols! & Emmerlev). OSL ages from
beneath the Eemian, but above the Saalian till, are
108 kyr and 93 kyr (Table 1: Sols!: m; Emmerlev: g).
Discussion
Fig. 11. Composite stratigraphic log, Klintholm, M!n (Fig. 1,
inset 3). The lithostratigraphic position and the palaeo-biological
correlation of the Cyprina clay (unit 2) to the Eemian Interglacial do
not support the apparent OSL ages. Self-consistent younger OSL ages
have been obtained above the marine deposits. For legend, see
Fig. 10. Modified from Houmark-Nielsen (1994).
the marine fauna from Rügen is Boreal with Arctic affiliation and D/L ratios of mollusc shells are ambiguous. Radiocarbon-dating of macro-plant remains in
sediments associated with the marine clay indicate that
Odd ages relating to sediments from the Eemian interglacial, which have been unable to reproduce the ages
expected from microfossil studies and by correlation to
Marine Isotope Stage (MIS) 5e, were either subjected to
theoretical correction factors on the effect of shallow
traps (Mejdahl et al. 1992) or simply ‘stowed away’ as
enigmatic outliers (Houmark-Nielsen 1994, 2003).
Quartz OSL ages of 22 samples from the Cyprina clay
and the overlying Tapes sand gave an average 119 kyr
at a type section Gammelmarke between Klinting and
Nyb!l (Fig. 1: area of case 2a; Fig. 6) and these ages
were not considered significantly different from the expected 132–128 kyr (Murray & Funder 2003). The ages
from the freshwater base Eemian strata show an underestimation of 20–30%. Technically, the dating is no
different from samples overlying the Eemian peat bogs.
Here, there is no obvious reason not to take these ages
at face value, although they have not been tested
against independent age estimates. The biological evidence and amino acid epimerization values almost unambiguously point to the Eemian interglacial as the age
674
Michael Houmark-Nielsen
of the Cyprina clay on M!n, and the fragility of especially the well-preserved ostracods indicates an in situ
position of the marine fossils. There is positive evidence
of redeposition in solifluction strata and fluvial sediments with Middle Weichselian ages that overly the
Cyprina clay. Possible correlation with the marine deposits at Rügen and the upper part of the Middle
Weichselian marine sequence (Skærumhede Series,
Fig. 2) seems inappropriate. Furthermore, the stratigraphic position beneath two tills of Middle Weichselian derivation, the Klintholm Till and Ristinge
Till (Figs 2, 10), does not allow an age as young even as
that from SAR using quartz for these marine sediments. It must be concluded that the luminescence ages
from M!n seem to be significant underestimates of the
expected age. The ages are about 100 kyr too young
compared to the independent age estimates from
Cyprina clay in the circum-Baltic region. From other
controlled studies, there is some evidence that the dose
recorded by quartz may underestimate by 10–15% in
this age range (Murray et al. 2007), but the larger and
consistent age underestimations from M!n include
both TL and feldspar IR OSL results. Thus, it seems
likely that the underestimates arise from errors in the
dose rates rather than errors in dose estimation. In this
context, it should be noted that Murray & Funder
(2003) considered 2 out of their 22 OSL quartz ages as
outliers. It was clear that the doses in these outliers were
similar to the samples above and below, and the underestimation was credibly attributed to a recent
change in the dose rate, possibly associated with cliff
erosion and changes in the oxidation state of groundwater seepage.
Underestimated ages may arise from luminescence
saturation effects in quartz older than 100 kyr, depending on the dose rate (Wallinga 2002); however, timedependent variations in the dose rates, arising from
changes in water content, compression or even radionuclide mobility, could contribute to this underestimation. In both cases (3a and 3b), several of these
factors might have affected dose rates through time.
Firstly, the prospects for a sound sampling strategy
were not ideal. Though beds are fairly homogeneous,
their thicknesses were small (o30 cm) and adjacent
beds were of variable lithologies, such as peat, sand, till
and solifluction diamicts, so samples could not be taken
at proper distances from other strata in order to obtain
a representative dose rate. The water contents may also
have varied considerably during burial. The marine
mud and sand was deposited at depths close to the
chalk basement, which lies roughly 30 m below present
sea level. The freshwater deposits in Jylland were deposited below 4–5 m of peat covered by variable
amounts of sand and solifluction diamicts. These unconsolidated deposits probably remained totally water
saturated throughout the Eemian and the Early
Weichselian. During the Middle Weichselian, trapped
BOREAS
water became permanently frozen and remained so in
western Jylland until the Holocene. On M!n, the Ristinge ice advance dislocated the sequence into a number
of glacio-tectonized, thrust and stacked sediment slabs.
Internal shear and compression could have squeezed
out porewater from the marine mud, and glaciotectonic
uplift to above present sea level may have drained the
marine sand as permafrost melted beneath the Ristinge
advance ice sheet due to insulating effects of ice-sheet
cover. After deglaciation, cool and dry conditions were
replaced by rising ground water table and the emergence of a large ice-dammed lake in the Baltic Basin in
the second half of the Middle Weichselian. During
LGM, deposits were loaded and squeezed by the Scandinavian Ice Sheet and once again thawed and saturated with groundwater until the present coastal cliffs
were established at the Holocene climatic optimum.
Such a complex post-burial history may have caused
some uncertainties as to evaluation of water contents
and thus affected the underestimation in ages, but certainly not all. To compensate totally for the age discrepancies, a decrease in dose rate by about a factor of 4
would be needed, implying an increase in water content
from !25% to 500%, which is not realistic. Even a
possible water content of # 200%, which applied to
the unconsolidated marine mud over half the Weichselian glaciation, would only double the apparent ages.
Even though marine Eemian deposits in other parts of
the western Baltic region have suffered similar postburial histories, their ages do not seem seriously underestimated, indicating that other factors must be taken
into consideration if the enigmatic ages from M!n are
to be understood.
Perspectives
Lukas et al. (2007) argue that the majority of ice contact sediments are unsuitable for dating, but that overestimated ages may indicate former depositional events.
Kjær et al. (2006) discussed age resetting as a function
of bleaching potential during the last depositional episode and concluded that a number of ages were overestimated compared to the expected ages. Samples had
presumably inherited their age from former bleaching
events that may reflect a 20 kyr long non-glaciated episode in Scandinavia prior to LGM. AMS radiocarbon
dating of redeposited mammoth remains has given
further insight to palaeoenvironmental conditions
of this Marine Isotope 3 interstadial, previously only
thoroughly known from the marginal areas of the
area covered by the SIS at the LGM (Ukkonen et al.
2007).
The overestimated OSL ages from the present study
seem to fall into groups, apparently covering
interstadial episodes when southwestern Scandinavia
was ice-free according to recent stratigraphical work
Testing OSL failures, S Scandinavia
BOREAS
(Houmark-Nielsen & Kjær 2003; Kjær et al. 2006;
Houmark-Nielsen 2007; Larsen et al. 2008). The older
two groups date from the Late Saalian deglaciation and
the periglacial environments that predominated until
the first Weichselian glaciations affected the area (!60
to 50 kyr). Next is a group that ranges in age from
!50 kyr to onset of the Klintholm advance at !35 kyr
(Fig. 2). Finally, the youngest group lies between !32
and !23 kyr and represents the periglacial conditions
prior to LGM ice cover (Kattegat Ice Stream, Jylland
Stadial; Fig. 2). Alexanderson & Murray (2007) suggest
that one set of overestimated OSL ages from post LGM
sediments in Småland in the southern Swedish uplands
(Fig. 1) may represent earlier depositional events from
non-glaciated Weichselian episodes in central Sweden.
The non-glaciated Middle Weichselian interval mentioned by Alexanderson & Murray could be coeval with
the 50–35 kyr period of periglacial conditions reflected
in the inherited pre-LGM ages in overestimated ages
from the present study. Such ‘shadows’ of non-glaciated episodes reflected in inconsistent luminescence
ages may strengthen the sparse information on timing
and distribution of these interstadials, if confidence in
this interpretation can be improved. Recently, the timing of the MIS 3 dynamics of the SIS was challenged as
a result of apparently conflicting radiocarbon and luminescence ages in Scandinavia and the circum-Baltic
region (Ukkonen et al. 2007). Dated Swedish mammoth remains indicate a small SIS confined to the
Scandinavian mountains, whereas OSL and 14C indicate that glacier ice (Klintholm advance) was streaming through the Baltic depression !35–30 kyr ago.
According to Alexanderson & Murray (2007), deglaciation sediments with ages equivalent to the LGM or
slightly older (!30 to !14 kyr) could represent either a
much more complex glaciation dynamic and earlier deglaciation of southern Sweden than hitherto considered
or, less likely, their dated sediments could have been
overridden by a cold-based glacier that left no lithological traces. Overestimated ages apparently reflect the
timing of periglacial environments also detected in situ
in stratigraphic successions. This may improve the
possibilities of dating till beds, in which case a maximum age for a given ice advance could be estimated.
Conclusions
$
OSL ages should be tested against available regional
numerical event-stratigraphic glaciation chronologies to determine whether overestimation is possible. Determination of sedimentary history and
depositional environment plays a major role in interpreting outliers. Testing of OSL ages should involve a
range of independent dating methods and good exposures of sedimentary successions; unfortunately
such ideal requirements are rarely fulfilled.
$
$
$
$
$
675
The majority of OSL ages that do not fit the regional numerical event-stratigraphic glaciation
chronology can be explained either by inheritance
of former OSL signals and poor opportunities for
bleaching during the latest depositional episode, or
possibly by miscalculation of burial dose rates.
Time-dependent changes in water content probably
play a part in this, but in most cases the contribution to the age inaccuracy is small. It is argued here
that solifluction deposits and glacier proximal aqueous deposits are especially at risk of inadequate
exposure to daylight during transport and deposition. In agreement with other authors, it is found
that the longer the transport path and the more
erosion and deposition cycles experienced by the
sediments immediately prior to final deposition, the
better the potential for zeroing of the natural OSL
signal and thus the better the chance of obtaining an
accurate sediment age.
A minority of ages remain difficult to explain, and
renewed studies of biogenic and geochemical stratigraphic control, together with more densely spaced
OSL dating campaigns and detailed methodological
studies, are needed to solve these problems.
Luminescence dating may not only reveal the timing
of the last occurrences of glacial and periglacial
conditions in Scandinavia, but also the previous
non-glaciated episodes if effort is made to test present time-dependent event-stratigraphic chronologies and if more attention is paid to
interpretation of overestimated ages.
This discussion of the variety of depositional environments from which luminescence samples have
been taken, of the potential of obtaining over- or
underestimated ages, and the testing of inconsistent
luminescence results against expectations has not
caused any serious revision of the regional numerical glaciation chronology. However, numerical
models must continuously be faced with new data
and should accordingly undergo critical review.
As the regional chronology has remained unchallenged by OSL ages, which fail to fit the pattern,
it must be concluded that OSL procedures stand out
as second to none when it comes to the dating of
Pleistocene sediments. Especially in cases when ages
are beyond the reach of 14C or when primary biogenic material that may enable correlation to sediments with known ages is absent, OSL provides the
only dating tool available.
Acknowledgements. – I thank Andrew Murray, Nordic Laboratory for
Luminescence Dating at Ris!, University of Aarhus for critical and
useful discussions on scientific matters regarding the use of OSL seen
from a consumer’s point of view. Kurt H. Kjær, Natural History
Museum, University of Copenhagen, made relevant and constructive
comments to text and figures and Anni T. Madsen, Institute of
676
Michael Houmark-Nielsen
Geography and Geology, University of Copenhagen is thanked for
discussion of the first draft. Thanks to the recommendations of guest
editor Ann Wintle and reviewers Svend Funder, Natural History Museum, University of Copenhagen and Andrew Murray, the manuscript
was further improved and the English language considerably adjusted.
References
Aaris-S!rensen, K. 2006: Northward expansion of the Central European megafauna during late Middle Weichselian interstadials,
c. 45–20 kyr BP. Palaeontographica Series A 278, 125–133.
Aitken, M. J. 1998: An Introduction to Optical Dating. 267 pp. Oxford
University Press, Oxford.
Alexanderson, H. & Murray, A. S. 2007: Was southern Sweden ice
free at 19–25 ka, or were the post LGM glacifluvial sediments incompletely bleached? Quaternary Geochronology 2, 229–236.
Andersen, S. T. 1965: Interglacialer og interstadialer i Danmarks
Kvartær. Meddelelser fra Dansk Geologisk Forening 15, 486–506.
Berglund, B. 1979: The deglaciation of southern Sweden,
13,500–10,000 B.P. Boreas 8, 27–62.
Berthelsen, A. 1979: Contrasting views on the Weichselian glaciation
and deglaciation of Denmark. Boreas 8, 125–132.
Björck, S. & Möller, P. 1987: Late Weichselian environmental history
in southeastern Sweden during the deglaciation of the Scandinavian
Ice Sheet. Quaternary Research 28, 1–37.
B!e, A.-G., Murray, A. & Dahl, S. O. 2007: Resetting of sediments
mobilised by the LGM ice-sheet in southern Norway. Quaternary
Geochronology 2, 222–228.
B!tter-Jensen, L., Ditlefsen, C. & Mejdahl, V. 1991: Combined OSL
(IR) and TL studies of feldspars. Nuclear Tracks and Radiation
Measurements 18, 257–263.
Bremer, A. C. 1990: En sedimentologisk og geokemisk unders!gelse
samt magnetostratigrafisk datering af en sen Mellem-Weichsel
iss!aflejring i Istebjerg lergrav, NV-Sjælland. Dansk Geologisk
Forening, Årsskrift for 1987–1989, 49–54.
Christiansen, H. H. 1998: Periglacial sediments in an Eemian–Weichselian succession at Emmerlev Klev, southwestern
Jutland, Denmark. Palaeogeography, Palaeoclimatology, Palaeoecology 138, 245–258.
Demidov, I., Houmark-Nielsen, M., Kjær, K. H. & Larsen, E. 2006:
The last Scandinavian Ice Sheet in northwestern Russia: Ice flow
patterns and decay dynamics. Boreas 35, 425–443.
Ditlefsen, C. 1991: Luminescence Dating of Danish Quaternary Sediments. Ph.D. dissertation, University of Aarhus, 116 pp.
Ditlefsen, C. 1992: Bleaching of K-feldspars in turbid water suspensions: A comparison of photo- and thermoluminescence signals.
Quaternary Science Reviews 11, 33–38.
Ehlers, J. & Gibbard, P. L. (eds.) 2004: Quaternary Glaciations; Extent and Chronology, Part 1 Europe, 34–46. Elsevier, Amsterdam.
Elverh!i, A., Dowdeswell, J. A., Funder, S., Mangerud, J. & Stein, R.
1998: Glacial and oceanic history of the polar North Atlantic margins: An overview. Quaternary Science Reviews 17, 1–10.
Fairbanks, R. G., Mortlock, R. A., Chiu, T.-C., Cao, L., Kaplan, A.,
Guilderson, T. P., Fairbanks, T. W., Bloom, A. L., Grootes, P. M.
& Jadeau, M.-J. 2005: Radiocarbon calibration curve spanning 0 to
50,000 years BP based on paired 230Th/234U/238U and 14C dates on
pristine corals. Quaternary Science Reviews 24, 1781–1796.
Fedorowicz, S. 2007: Age correlation of loess with other Pleistocene
deposits on the basis of TL and OSL dating. Geochronometria 27,
27–32.
Funder, S., Demidov, I. & Yelovicheva, Y. 2002: Hydrography and
mollusc faunas of the Baltic and the White Sea – North Sea seaway
in the Eemian. Palaeogeography, Palaeoclimatology, Palaeoecology
184, 275–304.
GEUS 1989: Geological Survey of Denmark and Greenland, Jordartskort over Danmark 1: 200.000.
Hansen, S. 1965: The Quaternary of Denmark. In Rankama, K. (ed.):
The Geologic Systems – The Quaternary, vol. 1, 1–90. Interscience
Publishers, New York.
Hansen, S. 1978: Sidste nedisnings maksimums-udbredelse i Syd- og
Midtjylland. Danmarks Geologiske Unders!gelse, Årbog 1976,
139–152.
BOREAS
Houmark-Nielsen, M. 1983: Glacial stratigraphy and morphology of
the northern Bælthav region. In Ehlers, J. (ed.): Glacial Deposits in
North-west Europe, 211–217. A. A. Balkema, Rotterdam.
Houmark-Nielsen, M. 1994: Late Pleistocene stratigraphy, glaciation
chronology and Middle Weichselian environmental history from
Klintholm, M!n, Denmark. Bulletin of the Geological Society of
Denmark 41, 181–202.
Houmark-Nielsen, M. 2003: Signature and timing of the Kattegat Ice
Stream: Onset of the LGM-sequence at the southwestern margin of
the Scandinavian Ice Sheet. Boreas 32, 227–241.
Houmark-Nielsen, M. 2007: Extent and age of Middle and Late
Pleistocene glaciations and periglacial episodes in southern Jylland,
Denmark. Bulletin of the Geological Society of Denmark 55, 9–35.
Houmark-Nielsen, M. & Kjær, K. H. 2003: Southwest Scandinavia
40–15 kyr BP: Palaeogeography and environmental change. Quaternary Science Reviews 18, 769–786.
Hubberten, H. W., Andreev, A., Astakhov, V. I., Demidov, I.,
Dowdeswell, J. A., Henriksen, M., Hjort, C., Houmark-Nielsen,
M., Jakobsson, M., Kuzmina, S., Larsen, E., Lunkka, J. P., Lyså,
A., Mangerud, J., Möller, P., Saarnisto, M., Schirrrmeister, L.,
Sher, S. V., Siegert, M. J. & Svendsen, J. I. 2004: The periglacial
climate and environment in northern Eurasia during the Last Glaciation. Quaternary Science Reviews 23, 1333–1357.
Jessen, K. & Milthers, V. 1928: Stratigraphical and paleontological
studies of interglacial fresh–water deposits in Jutland and northwest Germany. Danmarks Geologiske Unders!gelse II rk. 48, 380
pp.
Kjær, K. H., Lagerlund, E., Adrielsson, L., Thomas, P. J., Murray, A.
& Sandgren, P. 2006: The first independent chronology for Middle
and Late Weichselian sediments from southern Sweden and the island of Bornholm. GFF 128, 209–219.
Kolstrup, E. & Mejdahl, V. 1986: Three frost wedge casts from Jutland (Denmark) and TL dating of their infill. Boreas 15, 311–321.
Kristensen, P. 1993: Foraminifer- og ostrakodstratigrafii Eem Interglacial i den vestlige del af Østers!en. M.Sc. thesis, University of
Aarhus, 98 pp.
Kristensen, P., Gibbard, P., Knudsen, K. L. & Ehlers, J. 2000: Last
Interglacial stratigraphy at Ristinge Klint, south Denmark. Boreas
29, 103–116.
Kronborg, C. 1983: Preliminary results of age determination by TL of
interglacial and interstadial sediments. PACT 9, 595–605.
Kronborg, C. & Mejdahl, V. 1989: Thermoluminescence dating of
Eemian and Early Weichselian deposits in Denmark. Quaternary
International 3–4, 93–99.
Lagerlund, E. & Houmark-Nielsen, M. 1993: Timing and pattern of
the last deglaciation in the Kattegat region, southwest Scandinavia.
Boreas 22, 337–347.
Lambeck, K., Purcell, A., Funder, S., Kjær, K. H., Larsen, E. &
Möller, P. 2006: Constraints on the Late Saalian to early Middle
Weichselian ice sheet of Eurasia from field data and rebound modelling. Boreas 35, 539–575.
Larsen, E., Lyså, A., Demidov, I., Funder, S., Houmark-Nielsen, M.,
Kjær, K. H. & Murray, A. S. 1999: Age and extent of the Scandinavian ice sheet in northwest Russia. Boreas 28, 115–132.
Larsen, E., Kjær, K. H., Demidov, I., Funder, S., Gr!sfjeld, K.,
Houmark-Nielsen, M., Jensen, M., Linge, H. & Lyså, A. 2006: Late
Pleistocene glacial and lake history of northwestern Russia. Boreas
35, 394–424.
Larsen, N. K., Knudsen, K. L., Kronborg, C., Krohn, C. & Nielsen,
O. B. 2008: Early to Middle Weichselian ice sheet, lake and sea
configuration in northern Denmark, Kattegat and Skagerrak. Abstract 28, Nordic Geological Winter Meeting, Aalborg, Denmark,
p. 39.
Lehmkuhl, F., Zander, A. & Frechen, M. 2007: Luminescence
chronology of fluvial and aeolian deposits in the Russian Altai
(Southern Siberia). Quaternary Geochronology 2, 195–201.
Lukas, S., Spencer, J. Q. G., Robinson, R. A. J. & Benn, D. I. 2007:
Problems associated with luminescence dating of Late Quaternary
glacial sediments in the NW Scottish Highlands. Quaternary Geochronology 2, 243–248.
Lundqvist, J. & Wohlfarth, B. 2001: Timing and east–west correlation
of south Swedish ice marginal lines during the Late Weichselian.
Quaternary Science Reviews 20, 1127–1148.
BOREAS
Mejdahl, V. 1986: Thermoluminescence dating of sediments. Radiation Protection Dosimetry 17, 219–227.
Mejdahl, V. 1988: The plateau method for dating partially bleached
sediments by thermoluminescence. Quaternary Science Reviews 7,
347–348.
Mejdahl, V., Shlukov, A., Shakhovets, A. I., Voskovskaya, L. T. &
Lyashenko, H. G. 1992: The effect of shallow traps: A
possible source of error in TL dating of sediments. Ancient TL 10.
2, 22–25.
Miller, G. H. & Mangerud, J. 1986: Aminostratigraphy of European
marine interglacial deposits. Quaternary Science Reviews 4,
215–278.
Müller, U. 2004: Weichsel-Frühglazial in Nordvest-Mecklenburg.
Meyniana 56, 81–115.
Murray, A. S. & Funder, S. 2003: Optically stimulated luminescence
dating of a Danish Eemian coastal marine deposit: A test of accuracy. Quaternary Science Reviews 22, 1177–1183.
Murray, A. S. & Olley, J. M. 2002: Precision and accuracy in the optically stimulated luminescence dating of sedimentary quartz: A
status review. Geochronometria 21, 1–16.
Murray, A. S. & Wintle, A. G. 2000: Luminescence dating of quartz
using an improved single- aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73.
Murray, A. S., Marten, R., Johnston, A. & Martin, P. 1987: Analysis
for naturally occurring radionuclides at environmental concentrations by gamma spectrometry. Journal of Radioanalytical and Nuclear Chemistry 115, 263–288.
Murray, A. S., Svendsen, J. I., Mangerud, J. & Astakhov, V. I. 2007:
Testing the accuracy of quartz OSL dating using a known-age Eemian site on the River Sula, northern Russia. Quaternary Geochronology 2, 102–109.
Reimer, P. J., Baillie, M. G. L., Bard, E., Bayliss, A., Beck, J. W.,
Bertrand, C., Blackwell, P. G., Buck, C. E., Burr, G., Cutler, K. B.,
Damon, P. E., Edwards, R. L., Fairbanks, R. G., Friedrich, M.,
Guilderson, T. P., Hughen, K. A., Kromer, B., McCormac, F. G.,
Manning, S., Bronk Ramsey, C., Reimer, R. W., Remmele, S.,
Southon, J. R., Stuiver, M., Talamo, S., Taylor, F. W., van der
Plicht, J. & Weyhenmeyer, C. E. 2004: IntCal04 terrestrial radiocarbon age calibration 0–26 cal yr BP. Radiocarbon 46, 1029–1058.
Richards, B. W. M. 2000: Luminescence dating of Quaternary sediments in the Himalaya and High Asia: A practical guide to its use
and limitations for constraining the timing of glaciation. Quaternary International 65/66, 49–51.
Shackleton, N. J., Sánchez-Goñ, M. F., Pallier, D. & Lancelot, Y.
2003: Marine isotope substage 5e and the Eemian interglacial. Global and Planetary Change 36, 151–155.
Testing OSL failures, S Scandinavia
677
Steinich, G. 1992: Die stratigraphische Einordnung der RügenWarmzeit. Zeitschrift der geologischen Wissenschaften 20,
125–154.
Stokes, S., Bray, H. E. & Blum, M. D. 2001: Optical resetting in large
drainage basins: Tests of zeroing assumptions using single-aliquot
procedures. Quaternary Science Reviews 20, 879–885.
Svendsen, J. I., Alexanderson, H., Astakhov, V. I., Demidov, I.,
Dowdeswell, J. A., Funder, S., Gataullin, V. H., Henriksen, M.,
Hjort, C., Houmark-Nielsen, M., Hubberten, H. W., Ingólfsson,
Ó., Jakobsson, M., Kjær, K. H., Larsen, E., Lokrantz, H., Lunkka,
J. P., Lyså, A., Mangerud, J., Matiouchkov, A., Murray, A. S.,
Möller, P., Niesen, F., Nilolskaya, O., Polyak, L., Saarnisto, M.,
Siegert, C., Siegert, M. J., Spielhagen, R. F. & Stein, R. 2004: Late
Quaternary ice sheet history of northern Eurasia. Quaternary Science Reviews 23, 1229–1271.
Svendsen, J. I., Astakhow, V. I., Bolshiyanov, D. Y., Demidov, I.,
Dowdeswell, J. A. V., Gataullin, C., Hjort, C., Hubberten, H. W.,
Larsen, E., Mangerud, J., Melles, M., M!ller, P., Saanisto, M. &
Siegert, M. 1999: Maximum extent of the Eurasian ice sheets in the
Barents and Kara Sea region during the Weichselian. Boreas 28,
234–242.
Ukkonen, P., Arppe, L., Houmark-Nielsen, M., Kjær, K. H. & Karhu, J. A. 2007: MIS 3 mammoth remains from Sweden – implications for faunal history, palaeoclimate and glaciation chronology.
Quaternary Science Reviews 26, 3081–3098.
Vandenberghe, J. & Pissart, A. 1993: Permafrost changes in Europe
during the Last Glacial. Permafrost and Periglacial Processes 4,
121–135.
van der Plicht, J., Beck, J. W., Bard, E., Baillie, M. G. L., Blackwell,
P. G., Buck, C. E., Friedrich, M., Guilderson, T. P., Hughen, K. A.,
Kromer, B., McCormac, F. G., Bronk Ramsey, C., Reimer, P. J.,
Reimer, R. W., Remmele, S., Richards, D. A., Southon, J. R.,
Stuiver, M. & Weyhenmeyer, C. E. 2004: NotCal04 – Comparison/
Calibration 14C records 26–50 cal kyr BP. Radiocarbon 46,
1225–1238.
Wallinga, J. 2002: Optically stimulated luminescence dating of fluvial
deposits: A review. Boreas 31, 303–322.
Wohlfarth, B., Björck, S., Possnert, G., Lemdahl, G., Brunnberg, L.,
Isisng, J., Olsson, S. & Svensson, N.-O. 1993: AMS dating Swedish
varved clays of the last glacial/interglacial transition and the potential/difficulties of calibrating Late Weichselian ‘absolute’
chronologies. Boreas 22, 113–128.
Wysota, W., Lankauf, K. R., Szmanda, J., Chruscinska, A.,
Oczkowski, H. L. & Przegietka, K. R. 2002: Chronology of the
Vistulian (Weichselian) glacial events in the Lower Vistula Region,
Middle-North Poland. Geochronometria 21, 137–142.