Luminescence dating of glacial advances at Lago Buenos Aires (~46 
S),
Patagonia
R.K. Smedley*
, N.F. Glasser, G.A.T. Duller
Department of Geography and Earth Sciences, Aberystwyth University, Ceredigion, SY23 3DB, UK
a r t i c l e i n f o
Article history:
Received 21 July 2015
Received in revised form
3 December 2015
Accepted 15 December 2015
Available online 13 January 2016
Keywords:
Patagonia
Glacial
Geomorphology
Luminescence
Single grains
Feldspar
a b s t r a c t
Understanding the timing of past glacial advances in Patagonia is of global climatic importance because
of the insight this can provide into the influence on glacier behaviour of changes in temperature and
precipitation related to the Southern Westerlies. In this paper we present new luminescence ages
determined using single grains of K-feldspar from proglacial outwash sediments that were deposited by
the Patagonian Ice Sheet around Lago Buenos Aires (~46 
S), east of the contemporary Northern Patagonian
Icefield. The new luminescence ages indicate that major outwash accumulations formed around
~110 ± 20 ka to 140 ± 20 ka and that these correspond to the Moreno I and II moraine ridges, which were
previously dated using cosmogenic isotope dating to 150 ± 30 ka. Luminescence dating at Lago Buenos
Aires has also identified outwash sediments that were deposited during glacial advances ~30.8 ± 5.7 ka
and ~34.0 ± 6.1 ka (MIS 3) that are not recorded in the moraine record. Younger outwash accumulations
were then deposited between ~14.7 ± 2.1 and 26.2 ± 1.6 ka which correspond to the Fenix I e V moraine
ridges. The combined chronology suggests that glacial advances occurred ~110 ± 20 ka to 150 ± 30 ka
(MIS 6), ~30.8 ± 5.7 ka to ~34.0 ± 6.1 ka (MIS 3), and ~14.7 ± 2.1 to 26.2 ± 1.6 ka (MIS 2) at Lago Buenos
Aires. Overall luminescence dating using single grains of K-feldspar has excellent potential to contribute
towards the ever-increasing geochronological dataset constraining the timings of glacial advances in
Patagonia.
© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/).
1. Introduction
Providing robust age constraints for the timing of past glacial
advances can offer an important contribution to the global climate
change debate. Empirical datasets constraining climate change of
the past can be used to test numerical models. Terrestrial climates
in the mid-latitudes of the Southern Hemisphere are of global climatic
importance because of the influence of the precipitationbearing
Southern Westerlies between latitudes of ~30 and 55 S,
with the position of the present-day core of the Southern Westerlies
at ~50 to 55 S (Lamy et al., 2010). A large Patagonian Ice Sheet
is known to have extended along the Andean mountain range from
~38 S to 56 S during repeated glacial cycles of the Quaternary
period (e.g. Glasser et al., 2008). This ice sheet may have fluctuated
in response to potential changes in precipitation supply related to
the migration of the Southern Westerlies (e.g. Denton et al., 1999;
Hulton et al., 1994). Providing accurate and precise age
constraints on past glacial advances of the Patagonian Ice Sheet can
be used to test the accuracy of ice-sheet models, and consequently
improve our understanding of how the Earth responds to long-term
climatic change. However, providing age constraints for glacial
advances of the past can be challenging as some geochronological
techniques are restricted by material availability and age ranges,
but can also be restricted by processes that have occurred since
deposition. The most effective approach to produce robust chronologies
in glaciated settings is to combine datasets which use
multiple dating techniques to provide ages (e.g. radiocarbon,
cosmogenic isotope and luminescence dating). Moreover, researchers
are now beginning to incorporate these age sequences
into Bayesian frameworks to model patterns of glacial advance and
retreat (e.g. Chiverrell et al., 2013).
Luminescence dating is a technique that can determine the last
time a grain of sand was exposed to sunlight prior to burial and has
great potential for directly dating the sediment deposited during a
glacial advance. The luminescence dating technique depends on
the ability of mineral grains (typically either quartz or K-feldspars)
to store energy within the crystalline structure of the grain and* Corresponding author.
E-mail address: rks09@aber.ac.uk (R.K. Smedley).
Contents lists available at ScienceDirect
Quaternary Science Reviews
journal homepage: www.elsevier.com/locate/quascirev
http://dx.doi.org/10.1016/j.quascirev.2015.12.010
0277-3791/© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Quaternary Science Reviews 134 (2016) 59e73
release it upon stimulation (e.g. exposure to sunlight). Upon
exposure to sunlight the signal used for luminescence dating is
reset (or bleached) before the grains are then buried, where they
are exposed to natural radiation from the surrounding environment
(e.g. Rhodes, 2011). Luminescence dating is most suitable for
providing ages in well-bleached settings (e.g. aeolian) where the
opportunity for sunlight exposure is greater than in glaciofluvial or
fluvial settings. In comparison to aeolian settings, the luminescence
signal of mineral grains from glaciofluvial settings is typically
partially bleached as there is greater potential for shorter sediment
transport pathways and attenuation of light through the turbulent,
sediment-laden water columns transporting the grains (Berger and
Luternauer, 1987). Glaciofluvial sediments are typically targeted in
glaciated settings to maximise the opportunity for exposure to
sunlight, which is greater than expected for sediments deposited as
a moraine (e.g. Fuchs and Owen, 2008; Thrasher et al., 2009a).
Luminescence dating of single grains can then be used to assess
whether heterogeneous bleaching of the luminescence signal from
individual grains has occurred and determine accurate ages by
applying relevant statistical age models (Duller, 2008; Galbraith
and Roberts, 2012).
A major challenge for single-grain dating of quartz from glaciated
environments is that commonly only 5% or fewer of the grains
emit a detectable optically stimulated luminescence (OSL) signal,
and in glaciofluvial sediments from Chile as few as 0.5% of quartz
grains could be detected (Duller, 2006). In contrast, a larger proportion
of K-feldspar grains emit a detectable infra-red stimulated
luminescence (IRSL) signal, which is typically brighter than the OSL
signal emitted from quartz grains (e.g. Duller et al., 2003). Singlegrain
dating using K-feldspar therefore has the potential to make
luminescence dating more efficient and potentially more precise in
environments that are characterised by short sediment transport
pathways, and also in regions where the sensitivity of the quartz is
poor e.g. glaciofluvial sediments (Duller, 2006).
Currently, OSL dating of quartz is more commonly applied for
routine dating of single grains as the IRSL signal of K-feldspars is
prone to the effects of anomalous fading (Wintle, 1973). Anomalous
fading is the athermal depletion of the luminescence signal over
time and if fading is not accurately measured and corrected for, it
will manifest as an underestimation of the burial age. There are two
signals commonly used for IRSL dating of K-feldspars; (1) the IRSL
signal typically measured at 50 C, termed the IR50 signal (e.g.
Wallinga et al., 2000), and (2) the post-IR IRSL signal typically
measured at 225 C or 290 C, termed the pIRIR225 and pIRIR290
signals (Thomsen et al., 2008, 2011). Anomalous fading of the IR50
signal is suggested by some workers to be ubiquitous to all feldspars
(e.g. Huntley and Lamothe, 2001), whereas the pIRIR signal is
suggested to access a more stable signal through the recombination
of more distal donor-acceptor electron pairs (Jain and Ankjærgaard,
2011). Accessing a more stable IRSL signal within the K-feldspar
grains for dating is advantageous as it reduces the influence of
anomalous fading on the age calculation, which is especially
important on a single grain level, where accurate and precise
measurement and correction for fading can be difficult. Few studies
have determined ages for sedimentary samples from the natural
environment using the pIRIR signal of single grains of K-feldspar
(e.g. Gaar et al., 2014; Trauerstein et al., 2014). However, studies
have demonstrated that the pIRIR signal can provide ages in direct
agreement with independent numerical age control for wellbleached
samples (e.g. Reimann et al., 2012; Smedley, 2014).
The aim of this paper is to test the new luminescence dating
technique using single grains of K-feldspar from proglacial sediments
and complement the pre-existing chronology provided by
cosmogenic isotope (Kaplan et al., 2005, 2011) and 40
Ar/39
Ar
(Singer et al., 2004) dating at Lago Buenos Aires. The combined
chronology will strengthen the age constraints provided for the
glacial advances as it can provide checks on the internal consistency
between techniques and also provide ages for different landforms
preserved after deglaciation.
2. Study site and sample descriptions
In the past a large outlet glacier expanded eastwards at Lago
Buenos Aires from the Andean mountain range on to the semi-arid
Argentine plateau (Caldenius, 1932). Multiple sets of moraine
ridges are preserved in the valley, extending from the Last Glacial
Maximum (LGM) to ~1 million years ago (Ma). The moraine complexes
are locally named the Menucos (I), Fenix (I e V), Moreno (I e
III), Deseado (I e III) and Telken (I e VII) moraines, ordered from
youngest to oldest. Age constraints for the glacial advances are
currently provided by cosmogenic isotope dating of moraine
boulders (Kaplan et al., 2004, 2005, 2011; Douglass et al., 2006) and
40
Ar/39
Ar dating of the basaltic lava flows (Singer et al., 2004). The
timing of the LGM at Lago Buenos Aires is recorded by the deposition
of the Fenix moraine ridges and is suggested to have been
broadly synchronous with sites across Patagonia from ~16 to 30 ka
(Kaplan et al., 2004, 2011; Douglass et al., 2006), and with the responses
of global ice sheets (e.g. Mix et al., 2001; Glasser et al.,
2011). The Moreno and Deseado moraines are suggested to predate
the LGM at Lago Buenos Aires (Kaplan et al., 2005).
Well preserved proglacial outwash plains (or sandur) at Lago
Buenos Aires were targeted for luminescence dating. The lowangled
slope of each outwash plain can be traced eastwards from
the former ice front marked by the prominent moraine ridge. These
proximal outwash plains can only have been active when the ice
front was positioned at the elevation marked by the corresponding
moraine ridge. Assessing the geomorphological and sedimentological
context of each luminescence sample enables a direct
comparison to be made between the luminescence and cosmogenic
isotope ages. The geomorphology at Lago Buenos Aires was mapped
in this study using Landsat imagery in combination with Google
Earth imagery and ground truthing in Patagonia (Fig.1). Differential
Global Positioning System (dGPS) measurements of altitude, latitude
and longitude were also used to develop an elevation profile at
Lago Buenos Aires and a conceptual model describing the possible
development of the sedimentary sequence for the Menucos and
Fenix moraines (Fig. 2). The relationship between the moraine
ridges and outwash plains that were sampled is shown by the
elevation profiling and conceptual model (Fig. 2). The re-activation
of pre-existing glaciofluvial channels and the presence of glaciofluvial
channels that were orientated NW-SE, draining laterally
across the valley and in front of the moraine ridges (Fig. 1)
complicated these relationships for some samples; this will be
discussed later in Section 2.1. Cosmogenic isotope dating of the
moraine ridges suggest that each moraine and related outwash
plain was deposited during different glacial advances or still-stands
(Kaplan et al., 2004, 2011).
Luminescence dating was performed on 13 sedimentary samples
taken at Lago Buenos Aires. The locations of the luminescence
samples associated with the Fenix (n ¼ 9 samples), Moreno (n ¼ 3
samples) and Deseado (n ¼ 1 sample) moraine complexes are
shown with the location of the existing chronology (Fig. 1). The
elevation profile (Fig. 2) shows the difference in elevation (~50 m)
of the Fenix and Moreno moraine complexes, and the Moreno and
Deseado moraine complexes (also ~50 m). Table 1 presents the
details of the samples taken for luminescence dating and each
sample site is shown in Fig. 3, where the moraine fragments and
outwash plains related to each of the luminescence samples are
highlighted in relation to Fig. 2.
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e7360
2.1. Fenix moraines
The geomorphological and sedimentological contexts of four of
the nine samples related to the Fenix moraines were typical of a
proglacial outwash plain deposited in front of a moraine ridge
(samples LBA12OW3 e Fig. 3a; LBA12OW4 e Fig. 3b; LBA12OW1 e
Fig. 3d; and LBA12OW2 e Fig. 3e). The sediments were either
poorly sorted (samples LBA12OW4 or LBA12OW2), which is typical
of higher energy glaciofluvial depositional conditions, or well sorted
(LBA12OW3 and LBA12OW1), which is typical of stagnant water
Fig. 1. Location of Lago Buenos Aires, Patagonia (GoogleEarth; Image © Landsat) and geomorphological map which includes the sites sampled for luminescence dating, the existing
chronology and the locations of the images in Fig. 3. The inset shows the locations in South America of Lago Buenos Aires (LBA), Lago Pueyrredon (LP), the Última Esperanza region
(UE), the Strait of Magellan (SM) and Bahia Inútil (BI).
Fig. 2. Elevation profile created from altitudes (HAE e Height Above Ellipsoid), latitudes and longitudes determined using dGPS measurements along line A to B in Fig. 1. Also shown
is a schematic diagram of the Menucos and Fenix moraine ridges with associated outwash plains at Lago Buenos Aires.
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e73 61
conditions. The outwash sediments of all four of these samples
were part of proximal outwash plains with low-angled slopes that
can be traced westwards to the moraine ridge where the ice front
was positioned when the outwash plain was active. The outwash
plain of sample LBA12OW3 (410 m elevation) was eroded by the
lake shorelines and lacustrine sediments that underlie the Menucos
moraine ridge (Fig. 3a). The outwash plain was also constrained to
the east by the Fenix I moraine ridge which has been eroded by a
glaciofluvial channel at an elevation of 410 m. The age of the
outwash plain of sample LBA12OW3 must therefore be older than
the Menucos moraine and younger than the Fenix I moraine
(Table 1).
The outwash plain of sample LBA12OW4 (440 m) was elevated
30 m higher than the outwash plain of sample LBA12OW3 (410 m),
and was likely active during an earlier phase of glaciation. The
sediments dated for sample LBA12OW4 were collected from ~2 km
in front of the Fenix II moraine, where the ice front was positioned
at an elevation of ~470 m when the sediment was deposited
(Fig. 3b). The outwash plain of sample LBA12OW4 was therefore
active when the ice front was positioned ~2 km to the west at the
Fenix II moraine (Table 1). Sample LBA12OW1 was taken from a
small section of an outwash plain ~3 km in length and ~0.2 km wide
that was constrained to the east by the Fenix IV moraine ridge and
truncated to the west by a younger, lower (by ~10 m) glaciofluvial
channel draining from the north (Fig. 3d). The low-angled slope of
the outwash plain can be traced at an elevation of 450 m for ~8 km
from the Fenix II moraine ridge to the location of sample
LBA12OW1. Similar to the outwash plain of sample LBA12OW4
elevated at 440 m, the outwash plain of sample LBA12OW1 was
also likely to have been active when the ice front was positioned at
the Fenix II moraine ridge (470 m elevation).
To the east of the Fenix II moraine are the poorly preserved
fragments of the Fenix III moraine and proximal outwash plains
(Fig. 3e). The landform targeted for sample LBA12OW2 was an
outwash plain that extended for <1 km eastwards from the Fenix III
moraine as a low-angled slope at an elevation of 500 m (Fig. 3e).
Sample LBA12OW2 was taken from ~0.5 m in front of the moraine
ridge within this outwash plain. The close proximity and elevation
of the outwash plain of sample LBA12OW2 suggests that this was
active when the ice front was positioned at the Fenix III moraine
(Table 1).
The geomorphological contexts of the other sample sites related
to the Fenix moraines were more complex. The sedimentary units
that samples LBA12OW5, LBA12RF1, LBA12F4-1 and LBA12F4-2
were taken from were all poorly sorted, but it was difficult to
directly link these samples to specific moraine ridges using the
geomorphology. Based on the elevation profile of the outwash
plains, samples LBA12OW5 and LBA12RF1 are interpreted to have
been deposited at a similar time or before the Fenix II moraine
ridge. However, the conceptual model (Fig. 2) suggests that it is
possible for sediments from younger glacial advances to have been
deposited on top of sediments from older glacial advances. Glaciofluvial
sediments preserved at different elevations at a single site
may therefore have recorded multiple glacial advances within the
same stratigraphy, whereas the more prominent moraine ridges
relating to older glaciations were likely destroyed by overriding ice.
Therefore, it is possible that the proglacial sediments sampled for
luminescence dating at lower elevations within the sedimentary
sequence may be older than the moraine ridges themselves.
Samples LBA12F4-2 and LBA12F4-3 were extracted from the
same stratigraphic section (Fig. 4a), ~100 m west of sample
LBA12F4-1 (Fig. 4b). The context of these three samples is
complicated due to their proximity to the central glaciofluvial
channel in the valley, which was re-activated during younger glaciations.
Also, post- or syn-depositional processes have deformed
some of the sediments in these sections and complicated the
stratigraphy (Fig. 4a). The stratigraphy of the site is outwash gravel
units deformed by a silty-sand unit that contained rounded pebbles,
which is interpreted to be lacustrine sediments deposited in a
proglacial lake setting. After deposition, the preserved lake
Table 1
Samples taken for luminescence dating from outwash sediments at Lago Buenos Aires, Patagonia.
Sample Location Elevation (m) Moraine association All grains 20% brightest grains Age model De value (Gy) Age (ka)
n Overdisp. (%) n Overdisp. (%)
LBA12OW3 46
36.37 W
71
04.00 S
410 >Menucos & Fenix I 156 43.1 ± 0.2 31 38.6 ± 0.9 CAM 66.1 ± 4.6 14.7 ± 2.1
LBA12OW5 46
35.23 W
70
57.78 S
415 Fenix II 162 80.2 ± 0.4 28 79.0 ± 1.8 MAM 73.0 ± 14.0 20.2 ± 4.5
LBA12RF1 46
32.66 W
70
56.61 S
414 Fenix II 250 55.9 ± 0.2 41 57.7 ± 0.8 MAM 123.3 ± 16.8 34.0 ± 6.1
LBA12OW1 46
32.05 W
70
57.75 S
426 Fenix II 179 38.9 ± 0.2 36 26.1 ± 0.6 CAM 61.2 ± 2.8 18.5 ± 2.4
LBA12OW4 46
35.62 W
70
59.21 S
439 Fenix II 154 89.1 ± 0.4 29 71.0 ± 1.7 MAM 68.3 ± 15.4 20.5 ± 5.3
LBA12OW2 46
23.92 W
70
04.73 S
502 Fenix III 226 70.7 ± 0.2 43 66.2 ± 1.0 MAM 78.3 ± 13.9 22.3 ± 4.8
LBA12F4-2 46
34.51 W
70
56.08 S
386 !Fenix IV 260 71.6 ± 0.1 45 68.2 ± 1.0 MAM 115.4 ± 16.1 30.8 ± 5.7
LBA12F4-3 46
34.51 W
70
56.08 S
386 >Fenix IV 250 45.8 ± 0.1 37 37.6 ± 0.6 CAM 489.2 ± 27.3 141 ± 19
LBA12F4-1 46
34.55 W
70
56.01 S
394 Fenix IV 244 67.2 ± 0.2 45 79.6 ± 1.2 MAM 67.4 ± 8.4 19.5 ± 3.3
LBA12M1-1 46
33.69 W
70
53.31 S
467 Moreno I 102 46.5 ± 0.3 46 39.4 ± 1.2 CAM 416.8 ± 34.1 132 ± 19
LBA12M1-2 46
33.69 W
70
53.31 S
467 Moreno I 136 59.8 ± 0.4 27 51.4 ± 1.7 CAM 493.7 ± 55.4 134 ± 22
LBA12M3 46
33.44 W
70
50.97 S
510 Moreno III 109 50.4 ± 0.1 22 40.9 ± 1.5 CAM 365.0 ± 34.0 111 ± 17
LBA12D2-1 46
30.18 W
70
44.10 S
556 Deseado II 122 40.1 ± 0.3 25 42.3 ± 1.4 CAM 437.4 ± 39.6 123 ± 18
CAM ¼ Central Age Model; MAM ¼ Minimum Age Model (3-parameter).
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e7362
sediments were thrust up into the overlying glaciofluvial sediment
to an angle of ~40 (Fig. 4a). The sedimentary units were then
covered by a laterally-extensive sedimentary sequence of horizontally-layered
glaciofluvial sediments (up to ~2 m thick), diamicton
(up to ~2 m thick), and ~0.5 m thick unit of glaciofluvial
sediments.
The glaciofluvial sediments sampled for LBA12F4-1 were not
deformed by post- or syn-depositional processes and were sampled
at an elevation of ~434e438 m (Fig. 4b), which was similar to the
upper sedimentary units (~436e440 m elevation) of the section
sampled for LBA12F4-2 (Fig. 4a). The stratigraphy at these two sites
suggests that multiple glacial advances have been preserved, which
is consistent with the hypothetical conceptual model for the
deposition of the Fenix moraines (Fig. 2). The glaciofluvial sediments
deposited in the lower part of the section that have been
deformed post- or syn-depositionally (sampled by LBA12F4-2)
potentially relate to an older glacial advance, and the glaciofluvial
sediments in the upper part of the sequence (sampled by LBA12F4-
1) relate to a younger glacial advance, which is potentially related to
the Fenix IV moraine ridge in this area (Fig. 3f). The glaciolacustrine
sediments that sample LBA12F4-3 was taken from are stratigraphically
older than both samples LBA12F4-1 and LBA12F4-2.
Fig. 3. Annotated GoogleEarth images (Image © 2014 CNES/Astrium) showing the geomorphological relationship between the moraine ridges and outwash sediments used for
luminescence dating from Lago Buenos Aires; the colours of the landforms relate to Fig. 2. White shading indicates where the relationship between the outwash plain and moraine
ridge for a sample was difficult to determine. The locations of the different images are shown on Fig. 1. The elevation measurements determined for the different outwash plain
levels using the dGPS are shown in white. The cosmogenic isotope ages determined for each moraine ridge (Kaplan et al., 2011) and luminescence ages (this study) for associated
outwash from this study are included in this figure. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e73 63
2.2. Moreno moraines
The three samples taken from glaciofluvial and glaciolacustrine
sediments related to the Moreno moraines were from elevations
>500 m (Fig. 3g; LBA12M1-1, LBA12M1-2 and LBA12M3). Samples
LBA12M1-1 and LBA12M1-2 were taken from the same stratigraphic
section, which was associated with the Moreno I moraine
(Fig. 4c). Sample LBA12M1-1 was taken from glaciolacustrine sediments
that were post-depositionally deformed and then covered
by the glaciofluvial sediments that sample LBA12M1-2 was taken
from, and so sample LBA12M1-1 therefore must have been
deposited before sample LBA12M1-2. Sample LBA12M3 was taken
from a well-sorted, coarse-grained sand unit deposited within a
matrix-supported diamicton of the Moreno III moraine ridge
(Fig. 4d). The sediments are interpreted to have been deposited in a
ponded, slack water feature that formed as part of the Moreno III
moraine ridge (Fig. 3g). The elevation profile (Fig. 2) suggests that
the Moreno III moraine ridge and associated outwash plains
sampled by LBA12M3 (530 m) were covered by the Cerro Volcan
lava flow and should therefore be older than the 40
Ar/39
Ar age of
109 ± 3 ka.
3. Re-calculation of existing cosmogenic isotope ages
Cosmogenic isotope ages for the Moreno moraines calculated
using earlier estimates of production rates suggest that these glacial
advances occurred during Marine Isotope Stage (MIS) 6 (Kaplan
et al., 2005). The 10
Be ages published in Kaplan et al. (2005) have
been re-calculated in this study using the recently obtained production
rates for mid-latitudes of the Southern Hemisphere, updates
to scaling factors for location and altitude and other systemic
improvements in the technique (see Balco et al., 2008; Kaplan et al.,
2011). The production rate determined from south of Lago Argentino
(Kaplan et al., 2011) is statistically identical to the production
rate determined from the Southern Alps in New Zealand (Putnam
et al., 2010). The re-calculated cosmogenic isotope ages suggest
that the Moreno I and II moraine ridges are from MIS 6; the distribution
of ages ranges from 108 ± 6 ka to 209 ± 11 ka, with
Fig. 4. Stratigraphical sections showing the outwash sediments sampled for LBA12F4-2 and LBA12F4-3 (a), LBA12F4-1 (b), LBA12M1-1 and LBA12M1-2 (c) and LBA12M3 (d). The
stratigraphy shown in (a) includes a unit of lacustrine sediments (sampled by LBA12F4-3) thrust up into overlying outwash sediments (sampled by LBA12F4-2), which have been
post- or syn-depositionally deformed. The section shown in (b) was ~100 m east of the section shown in (a), but the outwash sediments not deformed by post- or syn-depositional
processes. Elevation measurements (HAE e Height Above Ellipsoid) for each section are from the dGPS measurements.
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e7364
weighted mean and standard deviations of 148 ± 33 ka and
154 ± 35 ka, respectively (see Table S.1 for details).
4. Measurement of dose-rates for luminescence dating
Dose-rates are determined in luminescence dating to quantify
the amount of natural radiation the mineral grains were exposed to
per year throughout burial. The external dose-rates were determined
in this study using thick source alpha and beta counting on
Daybreak and Risø GM-25-5 measurement systems, respectively.
The conversion factors provided by Guerin et al. (2011) were used,
in addition to an alpha efficiency value (a-value) of 0.11 ± 0.03 after
the measurements performed by Balescu and Lamothe (1993)
(Table 2). The water contents for all samples (5 ± 2 %) are
expressed as a percentage of the mass of dry sediment and
informed by field measurements. Cosmic dose-rates were calculated
in accordance with Prescott and Hutton (1994).
Feldspars form a solid-solution series, ranging from anorthite
(CaAl2Si2O8), to albite (NaAlSi3O8), to orthoclase (KAlSi3O8). Density
separation is routinely used for luminescence dating to isolate the
K-feldspar dominated fraction but this process can be difficult for
some samples. Grain-to-grain variation in internal K-content is
therefore an important factor to consider for single-grain dating of
K-feldspars as the internal beta dose-rate originating from the K
within the different grains may vary. Bulk K-contents of the
density-separated K-feldspar fractions were measured for all
samples in this study using 0.1 g sub-samples on a Risø GM-25-5
beta counter; the mean and standard deviation K-content
measured for all the samples was 5.0 ± 1.0% K, and suggested that
the geochemistry of grains in these samples was variable. LA-ICPMS
measurements performed on single grains of K-feldspar from
samples LBA12OW1 and LBA12OW4 were then used to confirm
that the internal K-contents of individual grains emitting detectable
luminescence signals in these samples varied from 0 to 14%
(Fig. S.1). The bedrock geology underlying the Northern Patagonian
icefield includes both plutonic and basaltic rocks (Espinoza et al.,
2010). The variability in internal K-contents measured for individual
grains from this suite of samples is consistent with the mixture
of perthitic and end member (i.e. K- or Na-rich) feldspar grains
likely to have been sourced from the bedrock at Lago Buenos Aires.
Previous studies have shown a relationship between the singlegrain
De values and luminescence signal intensity measured in
response to a fixed test dose for some well-bleached sedimentary
samples, which contained feldspar grains of variable K-content
(Reimann et al., 2012; Smedley, 2014). In these studies single-grain
ages were calculated using only the De values for the grains emitting
the brightest pIRIR180 (Reimann et al., 2012) and pIRIR225 signals
(Smedley, 2014), and assumed internal K-contents of
12.5 ± 0.5% and 10 ± 2%, respectively. The ages determined were in
good agreement with independent numerical age control and
suggested that the range in internal K-contents of the K-feldspar
grains was reduced by selecting the brightest grains. The LA-ICP-MS
measurements performed on single grains of the density-separated
K-feldspar fraction from samples in this study suggest that a similar
approach is necessary to determine accurate ages (Fig. S.1).
Therefore, only the De values determined for the brightest 20% of
the grains for each sample were used to calculate ages, and an internal
K-content of 10 ± 2% was assumed for dosimetry calculations
(for more information see the supplementary materials provided in
S.2).
5. Measurement of De values for luminescence dating
5.1. Equipment and measurement details
Samples were collected in either opaque tubes (2 mm thick
plastic rim) that were hammered into the sedimentary section, or
under an opaque cover sheet to prevent contact with direct sunlight
during sampling. All samples were prepared under subdued
red lighting conditions in the laboratory. The sedimentary samples
were first treated with a 10% v.v. dilution of 37% HCl and with 20 v.v.
of H2O2 to remove carbonates and organics, respectively. Dry
sieving isolated the 180e210 mm or 180e250 mm diameter grains,
and density separation using sodium polytungstate provided the
<2.58 g cmÀ3
(K-feldspar-dominated) fractions. The K-feldspar
grains were not etched in hydrofluoric acid because of concerns
about anisotropic removal of the surface (Duller, 1992). Grains were
mounted into 10 Â 10 grids of 300 mm diameter holes in a 9.8 mm
diameter aluminium single-grain disc for analysis.
All luminescence measurements were performed using a Risø
TL/OSL DA-15 automated single-grain system equipped with a
90
Sr/90
Y beta source delivering ~0.04 Gy/s. The variability of the
beta dose between grains for the source used in this study was
found to be negligible with a relative standard error of ~2%. Each
single-grain disc was located using the laser at room temperature
to prevent annealing of the pIRIR signal during the time it takes to
find the disc (Smedley and Duller, 2013). Stimulation was performed
using an infra-red laser (830 nm) fitted with an RG-780
filter to remove any shorter wavelengths (Bøtter-Jensen et al.,
2003), and a blue detection filter pack (BG-39, GG-400 and
Table 2
Dosimetry calculations for luminescence samples from Lago Buenos Aires. An internal K-content of 10 ± 2% was applied to determine the internal beta dose-rate for these
samples (Smedley et al., 2012).
Sample Depth
(m)
Grainsize
(mm)
K
(%)
U
(ppm)
Th
(ppm)
Cosmic
dose-rate
(Gy/ka)
Alpha
dose-rate
(Gy/ka)
Beta
dose-rate
(Gy/ka)
Gamma
dose-rate
(Gy/ka)
External
dose-rate
(Gy/ka)
Internal
dose-rate
(Gy/ka)
Total
dose-rate
(Gy/ka)
LBA12OW3 1.0 180e250 2.72 ± 0.13 2.69 ± 0.30 7.64 ± 1.00 0.20 ± 0.01 0.16 ± 0.07 2.22 ± 0.45 1.27 ± 0.27 3.85 ± 0.53 0.65 ± 0.13 4.50 ± 0.55
LBA12OW5 0.5 180e250 1.83 ± 0.10 2.24 ± 0.22 7.34 ± 0.73 0.23 ± 0.01 0.14 ± 0.06 1.59 ± 0.33 1.00 ± 0.21 2.96 ± 0.39 0.65 ± 0.13 3.61 ± 0.42
LBA12RF1 1.8 180e250 1.83 ± 0.10 2.56 ± 0.24 5.99 ± 0.79 0.18 ± 0.01 0.14 ± 0.06 1.60 ± 0.33 1.05 ± 0.21 2.98 ± 0.39 0.65 ± 0.13 3.63 ± 0.42
LBA12OW1 1.5 180e210 1.83 ± 0.10 2.13 ± 0.25 6.74 ± 0.83 0.19 ± 0.01 0.13 ± 0.06 1.56 ± 0.32 0.96 ± 0.21 2.85 ± 0.39 0.58 ± 0.12 3.42 ± 0.40
LBA12OW4 2.0 180e210 1.80 ± 0.10 2.43 ± 0.25 6.54 ± 0.82 0.18 ± 0.01 0.14 ± 0.06 1.58 ± 0.32 0.98 ± 0.21 2.87 ± 0.39 0.58 ± 0.12 3.45 ± 0.41
LBA12OW2 1.0 180e210 1.87 ± 0.10 2.32 ± 0.25 6.75 ± 0.84 0.20 ± 0.01 0.14 ± 0.06 1.61 ± 0.33 0.99 ± 0.21 2.95 ± 0.40 0.58 ± 0.12 3.52 ± 0.42
LBA12F4-2 8.0 180e250 2.35 ± 0.11 1.99 ± 0.24 6.37 ± 0.80 0.09 ± 0.01 0.13 ± 0.06 1.87 ± 0.38 1.00 ± 0.21 3.09 ± 0.44 0.65 ± 0.13 3.75 ± 0.46
LBA12F4-3 8.0 180e210 2.06 ± 0.10 2.30 ± 0.23 5.42 ± 0.80 0.09 ± 0.01 0.13 ± 0.06 1.70 ± 0.35 0.98 ± 0.21 2.90 ± 0.41 0.58 ± 0.12 3.47 ± 0.43
LBA12F4-1 6.0 180e250 1.83 ± 0.10 2.15 ± 0.26 7.35 ± 0.87 0.11 ± 0.01 0.14 ± 0.06 1.58 ± 0.32 0.97 ± 0.19 2.80 ± 0.38 0.65 ± 0.13 3.45 ± 0.40
LBA12M1-1 1.0 180e210 1.60 ± 0.11 2.23 ± 0.23 5.49 ± 0.76 0.20 ± 0.01 0.13 ± 0.06 1.40 ± 0.29 0.86 ± 0.19 2.58 ± 0.35 0.58 ± 0.12 3.16 ± 0.37
LBA12M1-2 2.0 180e210 2.16 ± 0.10 1.93 ± 0.26 7.23 ± 0.86 0.18 ± 0.01 0.13 ± 0.06 1.76 ± 0.36 1.04 ± 0.22 3.11 ± 0.43 0.58 ± 0.12 3.69 ± 0.44
LBA12M3 3.5 180e250 1.75 ± 0.09 2.01 ± 0.22 5.93 ± 0.73 0.14 ± 0.01 0.12 ± 0.06 1.48 ± 0.30 0.89 ± 0.19 2.64 ± 0.36 0.65 ± 0.13 3.30 ± 0.39
LBA12D2-1 2.0 180e250 1.90 ± 0.10 2.14 ± 0.25 6.77 ± 0.83 0.18 ± 0.01 0.14 ± 0.06 1.61 ± 0.33 0.98 ± 0.21 2.91 ± 0.40 0.65 ± 0.13 3.56 ± 0.42
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e73 65
Corning 7-59) was placed in front of the photomultiplier tube. The
signal was recorded for a total of 1.7 s, and the IRSL signal was
summed over the first 0.3 s (10 channels) of stimulation and the
background calculated from the final 0.6 s (20 channels). The instrument
reproducibility of the single-grain measurement system
was measured using the pIRIR signal (2.5%; Smedley and Duller,
2013) and incorporated into the calculation of the De values.
The single aliquot regenerative dose (SAR) protocol using the
pIRIR225 signal in this study is shown in Table 3. Five screening
criteria were applied to the resulting data throughout the analyses
unless otherwise specified. Grains were only accepted if (1) the
response to the test dose was greater than three sigma above the
background, (2) the test dose uncertainty was less than 10%, (3) the
recycling ratio (including the associated uncertainties) was within
the range of ratios 0.9 to 1.1, (4) recuperation was less than 5% of the
response from the largest regenerative dose (96 Gy) and (5) the
single-grain De values were not part of a population of very low
doses that were identified by the finite mixture model (FMM) to be
inconsistent with the geological context of the sample (e.g.
Smedley, 2014). A luminescence age was then determined by
dividing the De value by the environmental dose-rate that the
grains were exposed to throughout burial.
5.2. Assessing the pIRIR225 signal for single-grain dating
5.2.1. Optical bleaching
For luminescence dating in an environment where the opportunity
for bleaching is limited (e.g. glacial settings) it is important to
consider how rapidly the luminescence signal used for dating
bleaches in response to optical stimulation (e.g. sunlight). Although
the pIRIR signal may be more stable over time than the IR50 signal,
several multiple-grain studies of coarse-grained K-feldspar have
demonstrated that the pIRIR signal bleaches more slowly in
response to optical stimulation than the IR50 signal (Buylaert et al.,
2012; Murray et al., 2012), which in turn bleaches more slowly than
the OSL signal from quartz (Godfrey-Smith et al., 1988). If the signal
used for luminescence dating bleaches more slowly in response to
sunlight in nature, it is more likely that larger residual doses are
incorporated into the De values determined in the laboratory. This
has led some authors to prefer the IR50 signal for single-grain
dating of K-feldspar in environments where there is limited exposure
to sunlight instead of the pIRIR signal (Alexanderson and
Murray, 2012; Blombin et al., 2012). However, Smedley et al.
(2015) have demonstrated that the pIRIR225 signal bleaches more
rapidly than the pIRIR290 signal for individual grains of K-feldspar.
The authors also performed short laboratory bleaching experiments
on two well-bleached samples and one partially-bleached
sample with independent age control to demonstrate that the
bleaching rates of the pIRIR225 signal for individual grains of Kfeldspar
did not have a dominant control on the single-grain De
distributions. Therefore, the pIRIR225 signal was preferred for
single-grain dating of K-feldspar in this study.
5.2.2. Recovering a laboratory dose
Dose-recovery and residual-dose experiments were performed
on sample LBA12F4-2 to assess the suitability of the measurement
protocol using the pIRIR225 signal. The residual De value measured
after a given dose of 50 Gy and an 8 h bleach in the solar simulator
(SOL2) was 2.7 ± 0.4 Gy (n ¼ 25 grains). The residual-subtracted
dose-recovery ratio determined was 1.12 ± 0.07 and demonstrated
that the measurement conditions were appropriate for
dating these samples. The overdispersion value calculated for doserecovery
experiments of sample LBA12F4-2 was 21 ± 1% and
quantifies the minimum amount of scatter beyond measurement
uncertainties that can be incorporated into a single-grain De distribution
from measurements performed in the laboratory.
5.2.3. Anomalous fading
Fading measurements are typically performed for luminescence
dating of K-feldspar grains to determine whether fading correction
of the luminescence signal is necessary to provide accurate ages.
Measuring accurate fading rates (termed g-values) from single
grains of K-feldspar is difficult due to the low sensitivity of the IRSL
signals from some of the grains. Therefore, fading measurements
were performed in this study on a large suite of medium aliquots to
determine the best estimate of the fading rate for this suite of
samples. Five multiple-grain aliquots from 12 of the 13 samples
(n ¼ 60 aliquots) were used to determine g-values. Fading rates
were determined for both the pIRIR225 signal and the less stable
IR60 signal built into the pIRIR225 protocol (termed the IR60/225
signal), and were normalised to two days (Auclair et al., 2003). The
g-values measured using the IR60/225 and pIRIR225 signals formed a
normal distribution around a central value (Fig. 5a) so the weighted
means and standard errors were calculated for each of the two
datasets to provide the best estimate of fading. The g-values
determined were 4.1 ± 0.1%/decade (IR60/225 signal) and 1.0 ± 0.1%/
decade (pIRIR225 signal). The fading rate determined using the
pIRIR225 signal for this suite of samples (1.0 ± 0.1%/decade) was
consistent with fading rates typically measured using the pIRIR225
signal of other samples (e.g. Roberts, 2012; Trauerstein et al., 2014),
and also similar to g-values measured for the OSL signal of quartz
(e.g. Buylaert et al., 2012; Thiel et al., 2011). Given that luminescence
dating of quartz is not routinely corrected for fading, the
measurement of g-values for K-feldspar that are consistent with
quartz fading rates implies that this magnitude of effect is negligible,
and may just be an artefact of the measurement procedure
(e.g. Buylaert et al., 2012; Thiel et al., 2011). Therefore, fading
correction of the pIRIR225 signal was not performed in this study.
5.3. Selection of statistical age models
Overdispersion values calculated for single-grain De distributions
provide an estimate of the amount of scatter in a dataset
beyond that of measurement uncertainties. This information can
often be used in conjunction with the knowledge of the geological
context of a sample to determine which statistical model is
appropriate for providing an age (Galbraith and Roberts, 2012). The
range of overdispersion values from 26 ± 1% (sample LBA12OW1) to
80 ± 1% (sample LBA12F4-1) for the single-grain De values of
samples in this study suggests that the De distributions for some of
the samples were more scattered than others (Table 1). Given that
the samples had similar geochemical and depositional contexts it is
likely that the extent of bleaching upon deposition in this glaciated
Table 3
Experimental details for the single-aliquot regenerative dose
(SAR) pIRIR experiments performed throughout this study.
Test-doses of 52 Gy were used for all the experiments in this
study except for the measurements to determine residual De
values, where test-doses of 4 Gy were used.
Step Treatment
1 Dose
2 Preheat 250 
C for 60 s
3 IR LEDs 100 s at 60 
C
4 SG IRSL 2 s at 225 
C
5 Test dose (52 Gy or 4 Gy)
6 Preheat 250 
C for 60 s
7 IR LEDs 100 s at 60 
C
8 SG IRSL 2 s at 225 
C
9 IR LEDs 100 s at 290 
C
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e7366
environment was the dominant controlling factor on the scatter in
the De distributions. Those samples with lower overdispersion
values were likely to have been well bleached upon deposition and
those with higher overdispersion values were likely to have been
partially bleached. Applying the Central Age Model (CAM) is most
appropriate to determine accurate ages for well-bleached samples,
whereas the Minimum Age Model (MAM) is most appropriate for
samples that were partially bleached upon deposition (Galbraith
and Roberts, 2012). However, it is important to consider that
other factors, such as luminescence characteristics, microdosimetry
and post-depositional processes can cause scatter in De
distributions.
Arnold and Roberts (2009) summarise the overdispersion values
for single-grain De distributions determined for quartz from a range
of samples thought to have been well bleached upon deposition.
The overdispersion values ranged from 0 to 40%, with a mean and
standard deviation of 20 ± 9%. For the samples in this study it is
hypothesised that a threshold of 50% can be used to differentiate
between well-bleached and partially-bleached samples from Lago
Buenos Aires. To test this hypothesis the luminescence ages
determined for four samples that could be directly linked to specific
moraine ridges by the geomorphology were compared to the
cosmogenic isotope ages. Two of the samples had overdispersion
values 50% (samples LBA12OW3 and LBA12OW1), and two had
values >50% (samples LBA12OW4 and LBA12OW2). Examples of the
sedimentology and single-grain De values for one of the samples
with an overdispersion value of 50% (LBA12OW1; Fig. 6a, c) and
>50% (LBA12OW2; Fig. 6b, d) are shown in Fig. 6.
The CAM ages calculated for the four samples are compared to
the cosmogenic isotope ages of the moraines in Fig. 6e to assess the
validity of the suggested overdispersion threshold used for age
model selection. The two samples with overdispersion values of
50% had CAM ages in agreement with the cosmogenic isotope
ages, and the CAM ages for those samples with overdispersion
values of >50% overestimated the cosmogenic isotope ages. The
agreement between the CAM ages and cosmogenic isotope ages for
the samples with overdispersion values 50% confirms that these
samples were likely to have been well bleached upon deposition. To
calculate accurate ages with the MAM, the amount of scatter
characteristic of a well-bleached sample from the natural environment
under investigation (sb) needs to be quantified. Therefore,
the mean of the overdispersion values determined from the two
samples determined to have been well bleached upon deposition
(~30%) was used to define the sb value for the MAM in this study;
this overdispersion value was similar to the 20 ± 9% determined for
single grains of quartz (Arnold and Roberts, 2009). The MAM was
then used to calculate ages for the samples with overdispersion
values >50% and the ages calculated agreed with the cosmogenic
isotope ages (Fig. 6f). Based on the nature of the single-grain De
distributions and the depositional contexts of the samples, an
overdispersion threshold of 50% was used for age model selection
for all the samples in this study.
The sedimentology of sample LBA12OW1 (overdispersion 50%;
Fig. 6a) was well sorted and characteristic of less energetic depositional
environments with greater opportunity for bleaching upon
deposition than a more energetic depositional environment. In
contrast, the sediment of sample LBA12OW2 (overdispersion >50%;
Fig. 6b) was poorly-sorted and characteristic of higher-energy
depositional environments, typical of more turbulent water columns,
where there is less opportunity for bleaching upon deposition.
These observations are consistent with research assessing the
relationship between sedimentary lithofacies and the potential for
bleaching in a glacial environment (Fuchs and Owen, 2008;
Thrasher et al., 2009a,b).
Fig. 5. Histograms of the fading rates measured for the samples using the IR60/225 (a)
and pIRIR225 (b) signals. A Gaussian fit has been applied to these data (solid line).
Repeated Lx/Tx measurements were performed using the IR60/225 and pIRIR225 signals
after progressively longer storage times (inserted between steps 2 and 3 of Table 3),
from a prompt measurement after ~0.2 h to the maximum delay time of ~680 h i.e. ~1
month. Note that fading measurements were not performed on samples LBA12M1-1
and LBA12M1-2. The distribution of the signal-intensity emitted from single-grain Kfeldspars
for the suite of glacial samples extracted from Lago Buenos Aires are also
shown (c). Data are plotted as the proportion of the total light sum that originates from
the specified percentage of the brightest grains.
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e73 67
6. Results
The total number of grains analysed to determine De values for
each sample ranged from 600 to 1900 (see Table S.2 for details).
Fig. 5c presents cumulative light sum plots (after Duller, 2000) for
all the samples in this study. The number of grains passing the
screening criteria and providing De values ranged from 6.4 to 30.0%
of the total grains analysed, and the brightest 20% of the grains for
each sample accounted for between only 1.3% and 6.0% of the total
grains analysed (Table 1; Fig. S.4). The single-grain ages determined
for all of the samples in this study are shown in Fig. 7 in relation to
the cosmogenic isotope ages provided for the moraine ridges
(Kaplan et al., 2011) and the 40
Ar/39
Ar age provided for the Cerro
Volcan lava flow (Singer et al., 2004). The luminescence age of each
sample is also shown in Figs. 3 and 4. The Fenix and Moreno
samples can be clearly differentiated by the luminescence ages into
different glacial periods, which is consistent with the pre-existing
chronology.
6.1. Luminescence ages for the Fenix moraines
The luminescence ages for the glaciofluvial sediments associated
with the Menucos and Fenix moraines are in chronological
order in accordance with the sedimentological and geomorphological
context of each sample, e.g. sample LBA12OW3
(14.7 ± 2.1 ka) is the youngest and sample LBA12F4-2 (30.8 ± 5.7 ka)
is the oldest. The luminescence ages are also in good agreement
with the pre-existing chronology provided for the Fenix moraines.
For those samples where the geomorphological and sedimentological
context was difficult to interpret (samples LBA12OW5,
LBA12RF1, LBA12F4-1 and LBA12F4-2), the use of the
geomorphology, elevation profile and conceptual model suggest
that the luminescence ages were feasible in the context of the
surrounding chronological dataset.
The luminescence age of LBA12OW5 (20.2 ± 4.5 ka) suggests
that this sample was deposited at a similar time to the Fenix I and
Fenix II moraine ridges. This is feasible because sample LBA12OW5
was taken from a relic glaciofluvial terrace (elevated ~415 m) of the
central meltwater channel draining through the valley (Fig. 3b),
which was truncated by younger meltwater drainage events since
formation. Also, the luminescence age provided for sample
LBA12F4-1 suggests that these glaciofluvial sediments were
deposited at a similar time to sample LBA12OW2 and the Fenix III
moraine ridge, but within uncertainties of the cosmogenic isotope
ages for the Fenix IV and V moraines. This is feasible as the sample
was taken from the upper part of the sedimentary sequence at this
site. The luminescence age for sample LBA12F4-2 is older than
sample LBA12F4-1 and is therefore internally consistent with the
sedimentology of these sections. The age of sample LBA12F4-2
(30.8 ± 5.7 ka) is, however, at the upper limit of agreement with
the cosmogenic ages for the Fenix IV and V moraines. The age of
sample LBA12F4-2, in addition to the age of sample LBA12RF1
(34.0 ± 6.1 ka), suggests that glaciofluvial sediments have been
preserved at Lago Buenos Aires from an earlier glacial advance (or
advances) that has later been overrun by the glacial advances of the
Fenix IV and V moraine ridges. The conceptual model (Fig. 2)
demonstrates that preservation of outwash sediments from an
earlier glaciation is feasible as these sediments were taken from
units that were either deposited at lower elevations in the sedimentary
sequence or have been thrust up from lower elevations by
post- or syn-depositional processes.
Fig. 6. Examples of samples that determined overdispersion values of 50% (LBA12OW1) and >50% (LBA12OW2). Photographs of the sedimentary sections sampled for LBA12OW1
(a) and LBA12OW2 (b) are shown in addition to the radial plots presenting the De values measured for each sample in (c) and (d), respectively. The radial plots present both the
brightest 20% of the grains and all the grains measured. The grey bars show the CAM (c) and MAM (d) De values measured from only the brightest 20% of grains. Luminescence ages
calculated when applying the CAM (e) and MAM (f) for four samples are plotted against independent age control provided by cosmogenic isotope dating.
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e7368
6.2. Luminescence ages for the Moreno and Deseado moraines
The fundamental principles of luminescence dating require that
there is an upper age limit to the dating technique; this limit is
dependent upon factors inherent to the sample, mineral type and
signal used for analysis. The accumulation of energy from ionizing
radiation within the crystalline structure of a mineral grain can
reach saturation at larger doses and therefore can complicate
luminescence dating of older samples. In luminescence dating
saturation can be determined from the dose-response curve, and a
prudent limit above which De estimation may be unreliable has
been suggested to be two times D0 (the characteristic dose in an
exponential fit) by Wintle and Murray (2006). Duller (2012) has
demonstrated that single grains of quartz have different saturation
limits; this variability may impact upon the single-grain De distributions
for older samples, and so it is important that the saturation
limits of the K-feldspar grains used for dating older samples in this
study are investigated.
Single-grain D0 values were calculated for the proglacial samples
associated with the Moreno and Deseado moraines to investigate
the grain-to-grain variability in D0 values of K-feldspar
grains. Means and standard deviations were calculated for the 2D0
values determined for the grains used to determine De values (i.e.
the brightest 20% of the grains); the results ranged from
489 ± 161 Gy to 651 ± 252 Gy. There was a large amount of variability
in the 2D0 values measured for individual grains. For
example, the 2D0 values determined for single grains from sample
LBA12D2-1 ranged from 182 to 1423 Gy. Based on the underlying
40
Ar/39
Ar age of the Cerro Volcan lava flow, the Deseado II moraine
and the associated glaciofluvial sediment (sample LBA12D2-1)
must be >109 ± 3 ka. Therefore, the expected De value for sample
LBA12D2-1 is >390 Gy, according to the dose-rate of 3.56 ± 0.42 Gy/
ka determined for this sample (Table 2). This implies that some of
the grains analysed were approaching saturation for sample
LBA12D2-1 as the grains were characterised by 2D0 values as low as
182 Gy, but a large proportion of grains had 2D0 values in excess of
the expected De value. In practise the luminescence signals of
grains that were approaching saturation are unlikely to influence
the De distribution as the Ln/Tn ratios cannot be interpolated on to a
dose-response curve (Duller, 2012). Moreover, large and asymmetric
uncertainties are determined for grains at the limit of
saturation, which means the statistical age models will weight the
age towards those De values more precisely known i.e. those not
approaching saturation. Thus, luminescence dating of samples
associated with the Moreno and Deseado moraines is not restricted
by saturation of the pIRIR225 signal.
The overdispersion values for the suite of samples related to the
Fenix moraines ranged from 26 to 80%, whereas the overdispersion
values for the Moreno and Deseado samples ranged from only 38 to
52%. The smaller range in overdispersion values potentially suggests
that the proportion of scatter in these De distributions caused
by partial bleaching upon deposition (which will be similar to that
experienced by outwash associated with the Fenix moraines) accounts
for a smaller proportion of the overall doses. Residual signals
caused by the effects of partial bleaching have previously been
reported to account for a larger proportion of the burial dose for
young fluvial sediments in comparison to older samples (Jain et al.,
2004). The reduced influence of partial bleaching on the samples
associated with the Moreno and Deseado moraines suggests that
the CAM can be applied to determine accurate ages for these sediments;
this is supported by the excellent agreement between
luminescence ages determined for the Moreno and Deseado moraines,
in addition to the cosmogenic isotope ages.
The two luminescence ages determined for the Moreno I
moraine ridge (LBA12M1-1 e 132 ± 19 ka; LBA12M1-2 e
134 ± 22 ka) were within ±1 s of one another and the cosmogenic
Fig. 7. Comparison of the luminescence ages provided in this study with the cosmogenic isotope ages (Kaplan et al., 2004; Douglass et al., 2006) that were re-calculated by Kaplan
et al. (2011). The ages are shown as weighted means and standard deviations, which do not include those ages identified as outliers in the original publication. Also shown is an
40
Ar/39
Ar age (Singer et al., 2004) for the Cerro Volcan lava flow constraining the deposition of the moraine ridges at Lago Buenos Aires.
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e73 69
isotope age determined for the Moreno I moraine ridge
(~150 ± 35 ka). The luminescence age determined for the ponded
feature incorporated into the Moreno III moraine ridge (111 ± 17 ka)
was within uncertainties of the luminescence and cosmogenic
isotope ages determined for the Moreno I and II moraine ridges.
However, the age was at a lower limit of the age interval provided
for the Moreno I and II moraines when considering the uncertainties,
and may suggest that the grains within the ponded
feature were deposited after the glacial advance. Currently, there
are no cosmogenic isotope ages constraining the deposition of the
Deseado moraine ridges. The new luminescence age provided for
sample LBA12D2-1 in this study suggests that the outwash plain
associated with the Deseado II moraine ridge was deposited
123 ± 18 ka, and therefore the outwash associated with the
Deseado II moraine was deposited during MIS 6 at a similar time to
the Moreno moraines.
7. Discussion
The new luminescence ages provided in this study (Fig. 7)
contribute towards the continued advancement and refinement of
the luminescence dating technique in glaciated environments, but
the ages also provide insights into the glacial history preserved at
Lago Buenos Aires since MIS 6.
7.1. Moreno and Deseado moraines at Lago Buenos Aires
Ages provided for the Moreno and Deseado moraines in this
study using luminescence and cosmogenic isotope dating suggest
that sediments have been preserved at Lago Buenos Aires from
glacial advances from ~110 ± 20 ka to 150 ± 30 ka. Palaeoenvironmental
records linked with Patagonia suggest that it is
possible for glacial advances to have occurred during MIS 6. Dust in
the EPICA Dome C ice core (75 S, 123 E) which has been
geochemically fingerprinted to Patagonia recorded high concentrations
during MIS 6, indicating that glacial conditions likely prevailed
at this time (Lambert et al., 2008). Also, the d18
O record
indicates that global ice volumes were increased during MIS 6
(Imbrie et al., 1984).
It is interesting to observe that glacial advances during MIS 6
have been preserved at Lago Buenos Aires, but there are currently
no sediments recorded from MIS 4, which is a time with similar
palaeoenvironmental records to MIS 6 (i.e. increased global ice
volumes). In order to further define the glacial record and provide
comparisons to the palaeoenvironmental record, more age constraints
for the timing of glacial advances prior to MIS 2 and 3 are
required from across Patagonia and the Southern Hemisphere.
7.2. Fenix moraines at Lago Buenos Aires
The luminescence ages for the deposition of outwash sediments
associated with the Fenix moraines at Lago Buenos Aires (Fig. 8e)
appear to fall into two groups (grey shading in Fig. 8): earlier advances
during MIS 3 and later advances during MIS 2 (referred to as
phases MIS 2a and MIS 2b in Fig. 8).
7.2.1. Glacial advances: MIS 3
The oldest Fenix moraine ridges preserved at Lago Buenos Aires
are the Fenix IV (26.2 ± 1.6 ka) and Fenix V (25.0 ± 2.3 ka) moraines
(Kaplan et al., 2011), but luminescence dating for glaciofluvial
sediments suggests that outwash plains were deposited at Lago
Buenos Aires as early as 30.8 ± 5.7 ka (LBA12F4-2) and 34.0 ± 6.1 ka
(LBA12RF1) during MIS 3 (Fig. 8e). The older outwash plains were
deposited at lower elevations in the sedimentary sequence, which
may have allowed them to be preserved when the more prominent
moraine ridges were destroyed during subsequent glacial advances.
Fig. 8. Palaeoenvironmental records for the last 50 ka. (a) Temperature estimated from Siple Dome Ice Core, West Antarctica (81 S, 148 W), ice core hydrogen isotope (deuterium,
dD) data, with age model correlated to the GISP2 ice core time scale using methane and d18
O from 9 to 57 Ka BP (Brook et al., 2005). (b) Global d18
O records developed by the
SPECMAP project (Imbrie et al., 1984), (c) Dust concentrations from the EPICA Dome C ice core (75 S, 123 E) (Lambert et al., 2008). (d) Sea surface temperature records from ODP
core 1233 (41 S, 74W) (Kaiser et al., 2005). (e) Cosmogenic isotope ages (Douglass et al., 2006; Kaplan et al., 2004, 2005) re-calculated by Kaplan et al. (2011) and luminescence
ages (this study) for Lago Buenos Aires. Also shown are: (1) radiocarbon ages from the Chilean Lake District (Denton et al., 1999; re-calibrated by Putnam et al., 2013); (2)
cosmogenic isotope ages from Lago Pueyrredon (Hein et al., 2010), the Strait of Magellan and Bahia Inútil (Kaplan et al., 2008; McCulloch et al., 2005) that were all re-calculated by
Kaplan et al. (2011); (3) cosmogenic isotope ages from the Última Esperanza region, Chile (Sagredo et al., 2011).
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e7370
Evidence for glacial advances during MIS 3 has also been recorded
by radiocarbon dating of plant macrofossils that were overrun by
ice in the Chilean Lake District (Fig. 8e; Denton et al., 1999).
Cosmogenic isotope dating of moraine boulders (37.1 ± 1.3 ka,
38.7 ± 1.7 ka and 38.0 ± 3.9 ka) in the Última Esperanza region has
also identified moraine ridges preserved from glacial advances
during MIS 3 (Sagredo et al., 2011). Finally, Darvill et al. (2015) used
cosmogenic nuclide dating of outwash sediments to determine
glacial limits from MIS 3 for the Bahia Inútil lobe in southern
Patagonia, which were more extensive than the MIS 2 limits. No
other published evidence of glacial advances at this time exists
from Patagonia, but a trend of increasing dust levels in the EPICA
Dome C ice core (Fig. 8c) and low sea surface temperatures (SST) off
the west coast of Chile (Fig. 8c) are seen between ~31 ka and ~37 ka;
this may be related to an increase in ice extent at Lago Buenos Aires.
The timings of earlier phases of glaciation that occurred during
MIS 3 in the Chilean Lake District, at Lago Buenos Aires and at Bahia
Inútil suggest that these phases occurred across ~12 of latitude in
Patagonia. However, summer insolation in the Southern Hemisphere
was high ~31e37 ka (Berger and Loutre, 1991) and temperatures
in West Antarctica (81 S) were warmer than during full
glacial conditions ~18e25 ka (Fig. 8a; Brook et al., 2005). The
conditions recorded in the palaeoenvironmental archive therefore
question why glacial advances ~31e37 ka (MIS 3) in Patagonia
reached similar lateral extents to the advances during the LGM of
MIS 2 (~18e25 ka).
7.2.2. Glacial advances: MIS 2
Cosmogenic isotope ages of the Fenix IV (26.2 ± 1.6 ka) and Fenix
V (25.0 ± 2.3 ka) moraine ridges records the major glacial advances
at Lago Buenos Aires during MIS 2 (Kaplan et al., 2011). However,
the timing of these major advances occurred later at Lago Buenos
Aires than is suggested by the evidence preserved elsewhere in
Patagonia (Fig. 8e). The major glacial advances at Lago Pueyrredon
(28e30 ka; Hein et al., 2010; Kaplan et al., 2011), in the Chilean Lake
District (27 cal. ka; Denton et al., 1999) and in the Strait of Magellan
and Bahia Inútil (~27e29 ka; McCulloch et al., 2005; Kaplan et al.,
2008, 2011) were all consistent and occurred ~2 ka prior to the
major glacial advances at Lago Buenos Aires (~25 ka). Moraine
ridges that were deposited at a similar time to Fenix IV and V at
Lago Buenos Aires (~25 ka) are preserved within the limits of larger
advances occurring ~27 ka at Lago Pueyrredon (Hein et al., 2010;
Kaplan et al., 2011), Bahia Inútil (Kaplan et al., 2008; McCulloch
et al., 2005) and in the Chilean Lake District (Denton et al., 1999).
Moraine deposition in Patagonia ~25 ka (Fig. 8 grey shading; MIS
2a) occurs at the same time as cooler SST off the west coast of Chile
(Fig. 8d) and high concentration of dust in the EPICA Dome C ice
core (Fig. 8c).
Multiple glacial advances have then been recorded at Lago
Buenos Aires from ~18 to 23 ka by the Fenix I to III moraine ridges.
Fig. 8e shows that the glacial advances at Lago Buenos Aires from
~18 to 23 ka are in phase with records provided from across Patagonia
(41e53 S). The Rio Blanco moraine limit 3 in the Lago
Pueyrredon valley records an advance from cosmogenic isotope
dating between 20 and 22 ka, respectively (Hein et al., 2010; Kaplan
et al., 2011). Glacial advances are also recorded in the Strait of
Magellan (~19e20 ka) and Bahia Inútil (~19e25 ka) (Kaplan et al.,
2008; McCulloch et al., 2005), which were deposited at similar
times to the moraine ridges in the Chilean Lake District at ~19, 21
and 25 cal. ka BP (Denton et al., 1999). The palaeoenvironmental
record reports that environmental conditions in the Southern
Hemisphere fluctuated from ~18 to 23 ka (Fig. 8 grey shading; MIS
2b) according to the dust concentrations in the EPICA Dome C ice
core (Fig. 8c) and minor fluctuations in SST recorded in the ODP
core off the coast of Chile (Fig. 8d). Also, temperatures recorded in
the Siple Dome ice core in western Antarctica (Fig. 8a) cooled from
~23 ka into a distinctly cooler period occurring ~22e23 ka, which
was followed by a rapid increase in temperature ~21 ka, and the
global ice volume increased (Fig. 8b). The similar timings of events
in the palaeoenvironmental record and glacial advances across
Patagonia suggest that fluctuations in the extent of the Patagonian
Ice Sheet were sensitive to changes in climate throughout the LGM.
The glacial record from Patagonia suggests that the final glacial
advance occurred ~18 ka, which corresponds to the deposition of
the Fenix I moraine ridge. Cosmogenic isotope ages for the final
glacial advance preserved at Lago Pueyrredon suggest that it
occurred ~19e20 ka (Hein et al., 2010; Kaplan et al., 2011) where
lake formation then persisted from 15 to 17 ka (Mercer, 1976;
Mercer and Sutter, 1982; Turner et al., 2005). This is consistent
with cosmogenic isotope dating of former ice limits around Cerro
Tamango, Cerro Oportus and Sierra Colorado at Lago Pueyrredon,
where the ice lobe had retreated to within 10e15 km of the
present-day extent from 15.6 to 19 ka, with a still-stand or advance
occurring ~16.9 ka (Boex et al., 2013). Similarly, the final extent of
glaciation is recorded at 18 cal. ka in the Chilean Lake District
(Denton et al., 1999) and ~17 cal. ka in the Strait of Magellan and
Bahia Inútil (McCulloch et al., 2005; Kaplan et al., 2008, 2011). The
lacustrine sediments preserved in the sedimentary record at Lago
Buenos Aires indicate that a lake formed from ~18 ka. A later glacial
advance then deposited the Menucos moraine at 16.9 ± 1.4 ka
(Kaplan et al., 2011) similar to the still-stand or advance reported at
Lago Pueyrredon (Boex et al., 2013). Glacial conditions must then
have persisted for the glaciofluvial sediments sampled by
LBA12OW3 (14.7 ± 2.1 ka) to have been deposited. The sedimentary
record at Lago Buenos Aires therefore suggests that glacial advances
potentially occurred here later than in the rest of Patagonia (i.e. at
Lago Pueyrredon, in the Strait of Magellan and at Bahia Inútil).
Palaeoenvironmental records suggest that glacial conditions
could have prevailed across Patagonia up to ~15 ka (Fig. 8).
Although the temperature records in West Antarctica (Fig. 8a) and
the SST in the ODP core off the coast of Chile had begun to increase
from ~18 ka, the conditions were still commensurate with large ice
volumes present in Patagonia up to ~15 ka: (1) the d18
O records
indicate that the global ice volume remained extensive until ~15 ka;
(2) the dust concentrations in the EPICA Dome C ice core were still
decreasing from the MIS 2 maximum; and (3) the SST were
increasing, but did not reach significantly warmer temperatures
than the MIS 2 maximum until after ~15 ka. Therefore, it is plausible
that ice persisted at Lago Buenos Aires until ~15 ± 2 ka but evidence
for this has not been preserved (or discovered) elsewhere. After
~15 ± 2 ka the ice front at Lago Buenos Aires retreated into the
mountains and re-stabilised during the Younger Dryas, ~100 km
from the LGM position, and ~50 km from the present ice front
(Glasser et al., 2012).
7.3. Factors controlling glacial advances across Patagonia
The differences in timings of glacial advances during the LGM at
sites across Patagonia that span a north-south transect of the
Patagonian Ice Sheet may be related to a number of controlling
factors, which operate at regional or hemispheric scales. The differences
in the topography between the valleys have been suggested
to control the style and timings of glacial advances (e.g.
Glasser and Jansson, 2005). Overdeepening of the valleys east of
the Patagonian Ice Sheet over time caused by the topographicallycontrolled,
fast-flowing glaciers (e.g. Lago Buenos Aires) could
potentially change the distribution of the ice volume so that the
lateral extension of the glacial advance is reduced during larger but
later glaciations (Kaplan et al., 2009). Evidence of glacial advances
may also not be preserved in all the valleys, especially where
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e73 71
overridden by younger glacial advances (e.g. as suspected for MIS 4
glacial advances at Lago Buenos Aires). The glaciofluvial sediments
in this study dated to 30.8 ± 5.7 ka (LBA12F4-2) and 34.0 ± 6.1 ka
(sample LBA12RF1) provide a good example of these issues as
similar aged deposits have rarely been reported from other sites in
Patagonia, likely because of the lack of preservation and/or
discovery.
For glacial advances at similar latitudes to have been synchronous
across Patagonia but vary at different latitudes, large-scale
shifts in climate may be controlling glaciation more than regional
factors. Boex et al. (2013) have suggested that inconsistencies between
glacial advances at different latitudes in Patagonia are
related to the precipitation supply controlled by the migration of
the Southern Westerlies during the LGM. During the LGM the
Southern Westerlies expanded northwards and so the core is reported
to have been located ~45e50 S (Hulton et al., 1994; Denton
et al., 1999). Positioning of the Southern Westerlies at latitudes
~45e50 S would have increased the input of precipitation to the
piedmont glacier at Lago Buenos Aires (~46 S) and may have
facilitated ice expansion at Lago Buenos Aires at this time but not in
the rest of Patagonia. However, more evidence is required to substantiate
this hypothesis.
8. Conclusions
Luminescence dating of proglacial samples from Lago Buenos
Aires (~46 S), east of the Northern Patagonian Icefield, provides
rare evidence in Patagonia for glacial advance (s) during MIS 3
(~31e37 ka). Evidence of the oldest moraines preserved at Lago
Buenos Aires from the LGM (MIS 2) is recorded from ~25 ka, in
phase with LGM advances in the Strait of Magellan and Bahia Inútil,
but out-of-phase with the LGM at Lago Pueyrredon and the Chilean
Lake District. Multiple fluctuations in glacial extent are then
recorded at Lago Buenos Aires from ~17 to 23 ka by three advances,
which are in phase with glacial advances that occurred at different
latitudes across Patagonia (e.g. Lago Pueyrredon, Strait of Magellan
and Bahia Inútil). In contrast, the timing of the final glacial advance
of the LGM preserved at Lago Buenos Aires (~15 ± 2 ka) was out-ofphase
with the rest of Patagonia. The palaeoenvironmental records
suggest that glacial conditions could have persisted in Patagonia up
to ~15 ka and so the discrepancy in timings of glacial advances
across Patagonia is either related to the lack of preservation of
sediments at some sites, or regional discrepancies in climate during
deglaciation.
Overall, luminescence dating using single grains of K-feldspar
has excellent potential to contribute towards the ever increasing
geochronological dataset constraining the timings of glacial advances
in the Patagonian region. Improving and increasing these
datasets will continue to advance our understanding of the synchronicity
of glacial advances across Patagonia, and then begin to
unravel the potential signature of past climatic changes on these
dynamic systems.
Acknowledgements
Financial support for the work contributing towards this paper
was provided by a NERC PhD studentship to RKS (NE/I1527845/1).
We would like to thank N. Pearce for his assistance with the
geochemical analyses, and S. Tooth and R. Robinson for their
feedback on this research. The authors would like to acknowledge
the assistance of M. Kaplan with re-calculating the cosmogenic
isotope ages in this study and his comments on the manuscript.
Guido Vittone is thanked for his assistance with fieldwork logistics
in Argentina. Aberystwyth Luminescence Research Laboratory
(ALRL) benefited from being part of the Climate Change Consortium
for Wales (C3W). Stephan Harrison is thanked for his comments on
this manuscript.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.quascirev.2015.12.010.
References
Alexanderson, H., Murray, A.S., 2012. Luminescence signals from modern sediments
in a glaciated bay, NW Svalbard. Quat. Geochronol. 10, 250e256.
Arnold, L.J., Roberts, R.G., 2009. Stochastic modelling of multi-grain equivalent dose
(De) distributions: implications for OSL dating of sediment mixtures. Quat.
Geochronol. 4, 204e230.
Auclair, M., Lamothe, M., Huot, S., 2003. Measurement of anomalous fading for
feldspar IRSL using SAR. Radiat. Meas. 37, 487e492.
Balco, G., Stone, J.O., Lifton, N.A., Dunai, T.J., 2008. A complete and easily accessible
means of calculating surface exposure ages or erosion rates from 10
Be and 26
Al
measurements. Quat. Geochronol. 3, 174e195.
Balescu, S., Lamothe, M., 1993. Thermoluminescence dating of the Holsteinian
marine formation of Herzeele, northern France. J. Quat. Sci. 8, 117e124.
Berger, G.W., Luternauer, J.J., 1987. Preliminary field work for thermoluminescence
dating studies at the Fraser River delta, British Columbia. Geol. Surv. Can. Pap.
87 (IA), 901e904.
Berger, A., Loutre, M.F., 1991. Insolation values for the climate of the last 10000000
years. Quat. Sci. Rev. 10, 297e317.
Blombin, R., Murray, A., Thomsen, K.J., Buylaert, J.-P., Sobhati, R., Jansson, K.N.,
Alexanderson, H., 2012. Timing of the deglaciation in southern Patagonia:
testing the applicability of K-feldspar IRSL. Quat. Geochronol. 10, 264e272.
Boex, J., Fogwill, C., Harrison, S., Glasser, N.F., Hein, A., Schnabel, C., Xu, S., 2013.
Rapid thinning of the Late Pleistocene Patagonian ice sheet followed migration
of the Southern Westerlies. Sci. Rep. 3, 1e6.
Bøtter-Jensen, L., Andersen, C.E., Duller, G.A.T., Murray, A.S., 2003. Developments in
radiation, stimulation and observation facilities in luminescence measurements.
Radiat. Meas. 37, 535e541.
Brook, E.J., White, J.W.C., Schilla, A.S.M., Bender, M.L., Barnett, B., Severinghaus, J.P.,
Taylor, K.C., Alley, R.B., Steig, E.J., 2005. Timing of millennial-scale climate
change at Siple Dome, West Antarctica, during the last glacial period. Quat. Sci.
Rev. 24, 1333e1343.
Buylaert, J.-P., Jain, M., Murray, A.S., Thomsen, K.J., Thiel, C., Sobhati, R., 2012.
A robust feldspar luminescence dating method for Middle and Late Pleistocene
sediments. Boreas 41, 435e451.
Caldenius, C.C., 1932. Las glaciaciones cuaternarios en la Patagonia y Tierra del
Fuego. Geogr. Ann. 14, 1e164 (English summary, 144 e 157).
Chiverrell, R.C., Thrasher, I.M., Thomas, G.S.P., Lang, A., Scourse, J.D., van
Landeghem, K.J.J., Mccarroll, D., Clark, C.D., O Cofaigh, C., Evans, D.J.A.,
Ballantyne, C.K., 2013. Bayesian modelling the retreat of the Irish Sea Ice Stream.
J. Quat. Sci. 28, 200e209.
Darvill, C.M., Bentley, M.J., Stokes, C.R., Hein, A.S., Rodes, A., 2015. Extensive MIS 3
glaciation in southernmost Patagonia revealed by cosmogenic nuclide dating of
outwash sediments. Earth Planet. Sci. Lett. 429, 157e169.
Denton, G.H., Heusser, C.J., Lowell, T.V., Moreno, P.I., Andersen, B.G., Heusser, L.E.,
Schluchter, C., Marchant, D.R., 1999. Interhemispheric linkage of paleoclimate
during the last glaciation. Geogr. Ann. 81A, 107e153.
Douglass, D.C., Singer, B.S., Kaplan, M.R., Mickleson, D.M., Caffee, M.W., 2006.
Cosmogenic nuclide surface exposure dating of boulders on last-glacial and
late-glacial moraines, Lago Buenos Aires, Argentina: interpretative strategies
and paleoclimate implications. Quat. Geochronol. 1, 43e58.
Duller, G.A.T., 1992. Luminescence Chronology of Raised Marine Terraces Southwest
North Island New Zealand. Unpublished PhD thesis. University of Wales,
Aberystwyth.
Duller, G.A.T., 2000. Dose-distributions determined from measurements of singlegrain
quartz. In: Proceedings of International Symposium on Luminescence and
its Applications, India (ISLA-2000), 1, pp. 78e85.
Duller, G.A.T., 2006. Single grain optical dating of glacigenic deposits. Quat. Geochronol.
1, 296e304.
Duller, G.A.T., 2008. Single-grain optical dating of quaternary sediments: why
aliquot size matters in luminescence dating. Boreas 37, 589e612.
Duller, G.A.T., 2012. Improving the accuracy and precision of equivalent doses
determined using the optically stimulated luminescence signal from single
grains of quartz. Radiat. Meas. 47, 770e779.
Duller, G.A.T., Bøtter-Jensen, L., Murray, A.S., 2003. Combining infrared- and greenlaser
stimulation sources in single-grain luminescence measurements of feldspar
and quartz. Radiat. Meas. 37, 543e550.
Espinoza, F., Morata, D., Polve, M., Lagabrielle, Y., Maury, R.C., de la Rupelle, A.,
Guivel, C., Cotten, J., Bellon, H., Suarez, M., 2010. Middle Miocene calc-alkaline
volcanism in Central Patagonia (47 
S) petrogenesis and implications for slab
dynamics. Andean Geol. 37, 300e328.
Fuchs, M., Owen, L.A., 2008. Luminescence dating of glacial and associated sediments:
review, recommendations and future directions. Boreas 37, 636e659.
Gaar, D., Lowick, S.E., Preusser, F., 2014. Performance of different luminescence
R.K. Smedley et al. / Quaternary Science Reviews 134 (2016) 59e7372
approaches for the dating of known-age glaciofluvial deposits from northern
Switzerland. Geochronometria 41, 65e80.
Galbraith, R.F., Roberts, R.G., 2012. Statistical aspects of equivalent dose and error
calculation and display in OSL dating: an overview and some recommendations.
Quat. Geochronol. 11, 1e27.
Glasser, N.F., Jansson, K.N., 2005. Fast-flowing outlet glaciers of the Last Glacial
Maximum Patagonian Icefield. Quat. Res. 63, 206e211.
Glasser, N.F., Harrison, S., Jansson, K., Kleman, J., 2008. The glacial geomorphology
and Pleistocene history of southern South America between 38
S and 56
S.
Quat. Sci. Rev. 27, 365e390.
Glasser, N.F., Jansson, K.N., Goodfellow, B.W., de Angelis, H., Rodnight, H., Rood, D.H.,
2011. Cosmogenic nuclide exposure ages for moraines in the Lago San Martin
Valley, Argentina. Quat. Res. 75, 636e646.
Glasser, N.F., Harrison, S., Schnabel, C., Fabel, D., Jansson, K., 2012. Younger Dryas
and early Holocene age glacier advances in Patagonia. Quat. Sci. Rev. 58, 7e17.
Godfrey-Smith, D.I., Huntley, D.J., Chen, W.-H., 1988. Optical dating studies of quartz
and feldspar sediment extracts. Quat. Sci. Rev. 7, 373e380.
Guerin, G., Mercier, N., Adamiec, G., 2011. Dose-rate conversion factors: update. Anc.
TL 29, 5e8.
Hein, A.S., Hulton, N.R.J., Dunai, T.J., Sugden, D.E., Kaplan, M.R., 2010. The chronology
of the Last Glacial Maximum and deglacial events in central Argentine Patagonia.
Quat. Sci. Rev. 29, 1212e1227.
Hulton, N.R.J., Sugden, D.E., Payne, A.J., Clapperton, C.M., 1994. Glacier modelling
and the climate of Patagonia during the last glacial maximum. Quat. Res. 42,
1e19.
Huntley, D.J., Lamothe, M., 2001. Ubiquity of anomalous fading in K-feldspars and
the measurement and correction for it in optical dating. Can. J. Earth Sci. 38,
1093e1106.
Imbrie, J., Hays, J.D., Martinson, D.G., Mcintyre, A., Mix, A.C., Morley, J.J., Paces, N.G.,
Prell, W.L., Shackleton, N.J., 1984. The orbital theory of Pleistocene climate:
support from a revised chronology of the marine d18
O record. In: Berger, A.,
et al. (Eds.), Milankovitch and Climate, Part. D. Reidel, Norwell, Mass,
pp. 269e305.
Jain, M., Ankjærgaard, C., 2011. Towards a non-fading signal in feldspar: insight into
charge transport and tunnelling from time-resolved optically stimulated
luminescence. Radiat. Meas. 46, 292e309.
Jain, M., Murray, A.S., Bøtter-Jensen, L., 2004. Optically stimulated luminescence
dating: how significant is incomplete light exposure in fluvial environments?
Quaternaire 15, 143e157.
Kaiser, J., Lamy, F., Hebbeln, D., 2005. A 70-kyr sea surface temperature record off
southern Chile (Ocean Drilling Program Site 1233). Palaeoceanography 20,
PA4009.
Kaplan, M.R., Ackert, R.P., Singer, B.S., Douglass, D.C., Kurz, M.D., 2004. Cosmogenic
nuclide chronology of millennial-scale glacial advances during O-isotope stage
2 in Patagonia. Geol. Soc. Am. Bull. 116, 308e321.
Kaplan, M.R., Douglass, D.C., Singer, B.S., Ackert, R.P., Caffee, M.W., 2005. Cosmogenic
nuclide chronology of pre-last glaciation maximum moraines at Lago
Buenos Aires, 46 
S, Argentina. Quat. Res. 63, 301e315.
Kaplan, M.R., Fogwill, C.J., Sugden, D.E., Hulton, N.R.J., Kubik, P.W., Freeman, S.P.H.T.,
2008. Southern Patagonian glacial chronology for the Last Glacial period and
implications for Southern Ocean climate. Quat. Sci. Rev. 27, 284e294.
Kaplan, M.R., Hein, A.S., Hubbard, A., Lax, S.M., 2009. Can glacial erosion limit the
extent of glaciation? Geomorphology 108, 172e179.
Kaplan, M.R., Strelin, J.A., Schaefer, J.M., Denton, G.H., Finkel, R.C., Schwartz, R.,
Putnam, A.E., Vandergoes, M.J., Goehring, B.M., Travis, S.G., 2011. In-situ
cosmogenic 10
Be production rate at Lago Argentino, Patagonia: implications for
late-glacial climate chronology. Earth Planet. Sci. Lett. 309, 21e32.
Lambert, F., Delmonte, B., Petit, J.R., Bigler, M., Kaufmann, P.R., Hutterli, M.A.,
Stocker, T.F., Ruth, U., Steffensen, J.P., Maggi, V., 2008. Dust-climate couplings
over the past 800,000 years from the EPICA Dome C ice core. Nature 452,
616e619.
Lamy, F., Kilian, R., Arz, H.W., Francois, J.-P., Kaiser, J., Prange, M., Steinke, T., 2010.
Holocene changes in the position and intensity of the southern westerly wind
belt. Nat. Geosci. 3, 695e699.
McCulloch, R.D., Bentley, M.J., Tipping, R.M., Clapperton, C.M., 2005. Evidence for
Late-glacial ice dammed lakes in the central Strait of Magellan and Bahia Inutil,
southernmost South America. Geogr. Ann. 87, 335e362.
Mercer, J.H., 1976. Glacial history of southernmost South America. Quat. Res. 6,
125e166.
Mercer, J.H., Sutter, J.F., 1982. Late Miocene-earliest pliocene glaciation in southern
Argentina: implications for global ice sheet history. Paleogeogr. Paleoclimatol.
Paleoecol. 38, 185e206.
Mix, A.C., Bard, E., Schneider, R., 2001. Environmental processes of the ice age: land,
oceans, glaciers (EPILOG). Quat. Sci. Rev. 20, 627e657.
Murray, A.S., Thomsen, K.J., Masuda, N., Buylaert, J.P., Jain, M., 2012. Identifying
well-bleached quartz using the different bleaching rates of quartz and feldspar
luminescence signals. Radiat. Meas. 47, 688e695.
Prescott, J.R., Hutton, J.T., 1994. Cosmic ray and gamma ray dosimetry for TL and
ESR. Nucl. Tracks Radiat. Meas. 14, 223e227.
Putnam, A.E., Schaefer, J.M., Barrell, D.J.A., Vandergoes, M., Denton, G.H.,
Kaplan, M.R., Finkel, R.C., Schwartz, R., Goehring, B.M., Kelley, S.E., 2010. In situ
cosmogenic 10
Be production-rate calibration from the Southern Alps, New
Zealand. Quat. Geochronol. 5, 392e409.
Putnam, A.E., Schaefer, J.M., Denton, G.H., Barrell, D.J.A., Birkel, S.D., Andersen, B.G.,
Kaplan, M.R., Finkel, R.C., Schwartz, R., Doughty, A.M., 2013. The last glacial
maximum at 44
S documented by a 10
Be moraine chronology at Lake Ohau,
Southern Alps of New Zealand. Quat. Sci. Rev. 62, 114e141.
Reimann, T., Thomsen, K.J., Jain, M., Murray, A.S., Frechen, M., 2012. Single-grain
dating of young sediment using the pIRIR signal from feldspar. Quat. Geochronol.
11, 28e41.
Rhodes, E.J., 2011. Optically stimulated luminescence dating of sediments over the
past 200,000 years. Annu. Rev. Earth Planet. Sci. 39, 461e488.
Roberts, H.M., 2012. Testing post-IR IRSL protocols for minimising fading in feldspars,
using Alaskan loess with independent chronological control. Radiat.
Meas. 47, 716e724.
Sagredo, E.A., Moreno, P.I., Villa-Martínez, R., Kaplan, M.R., Kubik, P.W., Stern, C.R.,
2011. Fluctuations of the Última Esperanza ice lobe (52
S), Chilean Patagonia,
during the last glacial maximum and termination 1. Geomorphology 125,
92e108.
Singer, B.S., Ackert, R.P., Guillou, H., 2004. 40
Ar/39
Ar and KeAr chronology of
Pleistocene glaciations in Patagonia. GSA Bull. 116, 434e450.
Smedley, R.K., 2014. Testing the Use of Single Grains of K-feldspar for Luminescence
Dating of Proglacial Sediments in Patagonia (Ph.D. thesis). Aberystwyth University,
U.K.
Smedley, R.K., Duller, G.A.T., 2013. Optimising the reproducibility of measurements
of the post-IR IRSL signal from single-grains of feldspar for dating. Anc. TL 31,
49e58.
Smedley, R.K., Duller, G.A.T., Pearce, N.J.G., Roberts, H.M., 2012. Determining the Kcontent
of single-grains of feldspar for luminescence dating. Radiat. Meas. 47,
790e796.
Smedley, R.K., Duller, G.A.T., Roberts, H.M., 2015. Assessing the bleaching potential
of the post-IR IRSL signal for individual grains of K-feldspar: implications for
single-grain dating. Radiat. Meas. 79, 33e42.
Thiel, C., Buylaert, J.-P., Murray, A., Terhorst, B., Hofer, I., Tsukamoto, S., Frechen, M.,
2011. Luminescence dating of the stratzing loess profile (Austria) e testing the
potential of an elevated post-IR IRSL protocol. Quat. Int. 234, 23e31.
Thomsen, K.J., Murray, A.S., Jain, M., Bøtter-Jensen, L., 2008. Laboratory fading rates
of various luminescence signals from feldspar-rich sediment extracts. Radiat.
Meas. 43, 1474e1486.
Thomsen, K.J., Murray, A.S., Jain, M., 2011. Stability of IRSL signals from sedimentary
K-feldspar samples. Geochronometria 38, 1e13.
Thrasher, I.M., Mauz, B., Chiverrell, R.C., Lang, A., 2009a. Luminescence dating of
glaciofluvial deposits: a review. Earth Sci. Rev. 97, 133e146.
Thrasher, I.M., Mauz, B., Chiverrell, R.C., Lang, A., Thomas, G.S.P., 2009b. Testing an
approach to OSL dating of Late Devensian glaciofluvial sediments of the British
Isles. J. Quat. Sci. 24, 785e801.
Trauerstein, M., Lowick, S.E., Preusser, F., Schlunegger, F., 2014. Small aliquot and
single-grain IRSL and post-IR IRSL dating of fluvial and alluvial sediments from
the Pativilca valley, Peru. Quat. Geochronol. 22, 163e174.
Turner, K.J., Fogwill, C.J., McCulloch, R.D., Sugden, D.E., 2005. Deglaciation of the
eastern flank of the North Patagonian Icefield and associated continental-scale
lake diversions. Geogr. Ann. 87A, 363e374.
Wallinga, J., Murray, A., Duller, G., 2000. Underestimation of equivalent dose in
single-aliquot optical dating of feldspars caused by preheating. Radiat. Meas. 32,
691e695.
Wintle, A.G., 1973. Anomalous fading of thermoluminescence in mineral samples.
Nature 245, 143e144.
Wintle, A.G., Murray, A.S., 2006. A review of quartz optically stimulated luminescence
characteristics and their relevance in single-aliquot regeneration dating
protocols. Radiat. Meas. 41, 369e391.
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