SAR Protocol Research Articles

Testing the applicability of standardised growth curves for chemically heterogeneous single-grain feldspars from the Atacama Desert, Chile

The Atacama Desert is generally considered the driest non-polar desert on Earth and is therefore an ideal study area for exploring the water and biota free endmember of Earth's Critical Zone (ECZ). Single grain (SG) luminescence dating has successfully identified processes in the ECZ. However, SG luminescence dating of Atacama Desert feldspars is challenging and time consuming since only a small fraction of grains emits sufficient luminescence and their potassium (K) contents, needed for internal dose rate calculations, are highly variable. Here we present an adaption of the standardised growth curve (SGC) method adjusted to the conditions of Atacama Desert sediments and a correlation of single-grain geochemistry and luminescence properties.To evaluate if SGCs are suitable for our study site and to determine the influence of the K-content on our luminescence age calculations, we used a set of five samples from the Atacama Desert and five chemically and structurally different feldspar sediment extracts from various geological origins worldwide. We performed a dose recovery test (DRT) using a post-infrared infrared stimulated luminescence (pIRIR) protocol and measured nine major element concentrations, including K, on a single grain level using a scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX). The DRT dataset was then used to test the application of SGCs. The accuracy of Atacama feldspar pIRIR measurements fitted onto SGCs frequently suffers from odd values in single measurement cycles, since the SGC approach developed for SG feldspar luminescence (Li et al., 2015b) uses one Lx/Tx measurement to project the Ln/Tn values onto a SGC. We investigate the influence of calculating a synthetic regenerative signal (sR) for SGC fitting, to reduce the effect of those odd values on individual grain measurements. Furthermore, we reduced the regenerative cycles used for our sR approach, to test if shorter protocols would result in equivalent dose (De) estimates in agreement with longer protocols. We then calculated Spearman rank correlations between the results obtained with our modified SGC and the SAR protocol, luminescence signal intensities, and the geochemical dataset.Finally, we present a new method of fitting data onto a SGC which significantly decreases measurement time, without risking the inclusion of outliers. We furthermore show that the luminescence signal intensities, the De values and their dose recovery ratios obtained with our SGC method and a SAR protocol, are independent of the sample geochemistry.

MR Safety of Inductively Coupled and Conventional Intraoral Coils.

Intraoral coils (IOCs) in magnetic resonance imaging (MRI) significantly improve the signal-to-noise ratio compared with conventional extraoral coils. To assess the safety of IOCs, we propose a 2-step procedure to evaluate radiofrequency-induced heating of IOCs and compare maximum temperature increases in 3 different types of IOCs. The 2-step safety assessment consists of electric field measurements and simulations to identify local hotspots followed by temperature measurements during MRI. With this method, 3 different coil types (inductively coupled IFC, transmit/receive tLoop, and receive-only tLoopRx) were tested at 1.5 T and 3 T for both tuned and detuned coil states. High SAR and regular MRI protocols were applied for 2 coil positions. The measured E field maps display distinct hotspots for all tuned IOCs, which were reduced by at least 40-fold when the IOCs were detuned. Maximum temperature rise was higher when the coils were positioned at the periphery of the phantom with the coil planes parallel to B0. When neither active nor passive detuning was applied, maximum temperature increase of ΔT = 1.3/0.5/1.8 K was found for IFC/tLoop/tLoopRx coils. Hotspots detected by E field measurements, and simulations were consistent. In the simulations, the results were different for homogeneous phantoms compared with full anatomical models. The 2-step test procedure is applicable to different coil types. The results indicate that a risk for radiofrequency-induced heating exists for tuned IOCs, so that adequate detuning circuits need to be integrated in the coils to ensure safe operation.

Towards the optically stimulated luminescence dating of unheated flint

Flint tools are important archaeological finds, but unheated specimens remain challenging to date. The optical luminescence properties of the microcrystalline flint differ from sedimentary quartz grains, and optically stimulated luminescence (OSL) has, therefore, only occasionally been used to date heated flint specimens. However, if OSL dating could be used on unheated samples, this should expand the number of dateable flint samples from the archaeological record. This study investigates the luminescence sensitivity to blue, green, and infrared stimulation in flints collected from four sites in eastern Denmark. While stimulations at each wavelength yielded some luminescence emissions, blue OSL provided the strongest emission, and subsequent investigations here focus on measurements using this signal. The shape of the decay curves and the photo-ionising cross-sections for the blue OSL signal components are similar between natural and irradiated OSL and are also comparable to decay curves from calibration quartz. Dose–response curves show characteristic doses of ∽400 Gy, and dose recovery tests demonstrate that a SAR protocol can recover laboratory doses. The measured laboratory fading rates are considerable, where flint slices stored for up to six weeks provide average g-values of up to 9 % per decade. Also, the flint is less thermally stable compared to calibration quartz. However, a natural OSL signal remains in Cretaceous flints (albeit at 50 % or less of laboratory saturation), showing that signal loss did not outpace the electron trapping rate. The presence of a dose-dependent, natural OSL signal and acceptable dose recovery indicate that optical dating of flint surfaces could be feasible, at least in the flints from eastern Denmark, and that flint from other regions should be investigated.

Zeroing of IRSL signals in cobbles surfaces from a modern river floodplain in the Manas river, Tian Shan

A newly developing method, rock surface luminescence dating, provides a novel means of constraining the burial age of fluvial gravel and unveiling the transport and exposure-burial process of fluvial bed-load. A crucial requirement for successful age determination in luminescence dating of buried rock surfaces is that a sufficiently thick surficial layer was reset to a near-zero level of signal prior to deposition and burial. However, little such effort has been made on modern fluvial gravels from various depositional environments to provide a sound justification for the use of luminescence dating in such settings. In this study, we reported an investigation of daylight bleaching in modern cobbles with different sizes and shapes at a modern river floodplain from the Manas River, Tian Shan, to test the reliability and applicability of fluvial cobble optical dating. Four multi-elevated-temperature post-infrared infrared (MET-pIRIR) stimulated luminescence signals of rock slices were measured using a modified MET-pIRIR protocol to establish residual luminescence-depth profiles. The residual does of pIRIR and MET-pIRIR signals of sub-surface rock slices were also estimated using different modified SAR protocols. The results showed that the high temperature IRSL signal could be reset to ∼2–3 mm depth into cobbles surface and flat cobbles seem easier to bleach than spherical cobbles. The residual doses of sub-surface rock slices of cobbles from modern river floodplain was ∼0.4 Gy and ∼1.1 Gy for the IR50 and the pIRIR170 signal respectively, suggesting a residual age of ∼0.1 ka and ∼0.2 ka. The residual ages of MET-pIRIR signals of sub-surface rock slices of cobble MNS2-5 were ∼0.5–1 ka at higher stimulation temperature. Our results show that the fluvial cobble optical dating techniques have great potential for providing reliable chronologies for river floodplain gravel and other fluvial depositional events.

Radiometric and stimulated luminescent characterization of Amazonian sediments from the Middle Rio Negro, Western Amazon

The sediments were collected from paleodunes, river terraces, islands, and sand bars at Mariuá Archipelago, Rio Negro, Brazil. XRD analysis revealed that quartz is the predominant mineral along with a trace quantity of kaolinite. Neutron activation analysis of the sediments revealed the assembly of rare-earth elements, metals and semi-metals. The values of U and Th were found to be 3–5 ppm in paleodunes and 9–16 ppm in terraces, and K-40 concentration is below detectable limit. The OSL of quartz (dune) is composed of three components with decay times of 0.2, 11.0 and 350 s, respectively. This OSL emission is related to the TL peaks below 380 °C. Also, photo-transferred TL is observed in the temperature range of 190–250 °C for a blue stimulation of 500 s. TL peaks kinetic parameters were calculated and discussed. The lifetimes of TL peaks at 272 and 355 °C are approximately 4.0×104 and 1.5×109 years, respectively. Using the conventional SAR protocol, 11 samples were dated, including two old paleodunes with ages of 124.4 and 169.7 ka, increasing the age interval of the site, the other samples were younger sediments, with ages between 0.39 and 53.9 ka.

Progress and pitfalls of the SAR protocol for the quartz violet stimulated luminescence (VSL) signal: A case study from Sardinia

Progress and pitfalls of the SAR protocol for the quartz violet stimulated luminescence (VSL) signal: A case study from Sardinia

Towards Arginase Inhibition: Hybrid SAR Protocol for Property Mapping of Chlorinated N-arylcinnamamides.

A series of seventeen 4-chlorocinnamanilides and seventeen 3,4-dichlorocinnamanilides were characterized for their antiplasmodial activity. In vitro screening on a chloroquine-sensitive strain of Plasmodium falciparum 3D7/MRA-102 highlighted that 23 compounds possessed IC50 < 30 µM. Typically, 3,4-dichlorocinnamanilides showed a broader range of activity compared to 4-chlorocinnamanilides. (2E)-N-[3,5-bis(trifluoromethyl)phenyl]-3-(3,4-dichlorophenyl)prop-2-en-amide with IC50 = 1.6 µM was the most effective agent, while the other eight most active derivatives showed IC50 in the range from 1.8 to 4.6 µM. A good correlation between the experimental logk and the estimated clogP was recorded for the whole ensemble of the lipophilicity generators. Moreover, the SAR-mediated similarity assessment of the novel (di)chlorinated N-arylcinnamamides was conducted using the collaborative (hybrid) ligand-based and structure-related protocols. In consequence, an 'averaged' selection-driven interaction pattern was produced based in namely 'pseudo-consensus' 3D pharmacophore mapping. The molecular docking approach was engaged for the most potent antiplasmodial agents in order to gain an insight into the arginase-inhibitor binding mode. The docking study revealed that (di)chlorinated aromatic (C-phenyl) rings are oriented towards the binuclear manganese cluster in the energetically favorable poses of the chloroquine and the most potent arginase inhibitors. Additionally, the water-mediated hydrogen bonds were formed via carbonyl function present in the new N-arylcinnamamides and the fluorine substituent (alone or in trifluoromethyl group) of N-phenyl ring seems to play a key role in forming the halogen bonds.

A simplified multiple aliquot regenerative dose protocol to extend the dating limit of K-feldspar pIRIR signal

The post-infrared infrared stimulated luminescence signal (pIRIR) from K-feldspar shows significantly less athermal fading than the conventional IRSL signal, thus it has been widely used for dating Quaternary deposits. With the single aliquot regenerative dose (SAR) protocol, the test dose signal is influenced by the preceding regenerative dose, and the characteristic saturation dose (D0) of the pIRIR signal is mostly in the range of 200–600 Gy, depending on the size of the test dose. According to the D0 value, the dating range of pIRIR is restricted to <300 ka with the SAR protocol. Here we present a multiple aliquot regenerative dose (MAR) protocol using low-temperature thermoluminescence (TL) signal for inter-aliquot normalisation. The multiple-elevated-temperature (MET) pIRIR signals up to 290 °C are investigated. The D0 increases to 850–1300 Gy with this protocol, which should represent the intrinsic D0 of IR or pIRIR signals of K-feldspar. Based on the higher D0, this protocol has the potential to date samples with equivalent doses (Des) up to 2000 Gy, i.e. up to ∼600 ka considering a dose rate of ∼3.5 Gy·ka−1. Applications of this MAR protocol on two loess samples from the Chinese Loess Plateau provide ages consistent with expected ages up to 350 ka, with the MET-pIRIR signal at 290 °C. However, tests on three fluvial and alluvial samples show age overestimation with the new MAR protocol as well as SAR protocol, which may result from the hard-to-bleach property of the high-temperature pIRIR signals. Simulations of fading correction indicate that the age will be over-corrected when the laboratory dose response curve has a D0 smaller than the true D0 of the signal. Caution should be taken in fading corrected ages measured with the conventional SAR protocol, as the D0 values are always underestimated in this case.

Testing the potential of using fine quartz for dating loess in South Island, New Zealand

The applicability of optically stimulated luminescence (OSL) dating on quartz from South Island, New Zealand is hampered by the poor behaviour of the targeted signals. However, most OSL dating studies have been focused on using coarse quartz fractions. Since a previous study conducted from a nearby site demonstrated that coarse quartz (63–90, 90–125, 125–180 and 180–250 μm) is not suitable for OSL dating, we attempt using fine quartz here. Therefore, the standard SAR protocol was applied on 4–11 μm quartz extracted from a loess/paleosol section. Unlike the coarser fractions, the OSL signal of fine quartz displayed satisfactory characteristics which allowed estimating ages ranging from 0.3 ± 0.04 ka to 16 ± 1 ka. In order to understand the differences between the two quartz fractions, we characterise fine (4–11 μm) as well as the usually used coarser grain sizes (˃ 63 μm) of quartz by electron spin resonance (ESR). No significant differences are reported in qualitative terms between the grain sizes investigated and calibration quartz. We report a higher abundance of intrinsic defects in the fine grain fraction; however, this is typical for quartz from other regions as well, that was amenable for OSL dating. As such, the differences between the fine quartz fraction and the coarse fraction is not yet understood. In addition, two elevated temperature post-infrared infrared protocols (pIRIR225 and pIRIR290) were applied and polymineral grains extracted from the same samples. Despite residual dose corrections being performed using a modern analogue, pIRIR ages overestimate quartz ages by 19–122% in the case of the application of the pIRIR225 protocol and by 25–217% in the case of the application of the pIRIR290 protocol. The effect could not be circumvented by the application of a test dose with a magnitude of 50% of the equivalent dose in the pIRIR290 protocol. In the case of the application of pIRIR290 protocol, dose recovery tests ratios vary from 1.07 ± 0.06 to 1.23 ± 0.05. While not ideal, these results cannot fully explain the differences reported between the ages obtained by fine quartz OSL and the polymineral fine grains pIRIR methods.

Investigating the applicability of a standardised growth curve approach on Middle Pleistocene sediments from northern Switzerland

The introduction of the Single Aliquot Regenerative Dose (SAR) protocol established luminescence dating as an indispensable tool in Quaternary research. A major impediment of this technique is the time required for measurements, since the protocol is repeated for various aliquots of each sample to establish a sound statistical basis. To reduce the demand on machine time, Standardised Growth Curve (SGC) approaches have been developed and successfully applied for samples from some regions. However, differences in luminescence properties require careful testing of this techniques when applied to samples with other geological background. In this study, the application of the SGC approach of Li et al. (2016) is successfully verified for multi-grain aliquots of coarse-grained quartz and feldspar samples from three sites in northern Switzerland. In-depth quality control measures ensure the reproducibility of equivalent dose (D e ) values obtained by the common SAR protocol and sample-specific SGCs. For both minerals little sensitivity was found to the re-normalisation dose and the sample-specific SGCs performed well. In contrast to other studies, no different types of dose response curve shape were observed for quartz. A minimum number of full SAR measurements of eight and six aliquots per sample has been found appropriate for quartz and feldspar, respectively. For the fading corrected feldspar signals, site-specific SGC worked well and D e values of up to 800 Gy were consistently replicated. In summary, sample-specific SGCs for samples from northern Switzerland perform well and their application reduces measurement times by up to 70%. The construction of a regional SGC may well be beneficial, however, caution regarding the choice of given doses and curve fitting is recommended and a thorough verification of SGC results is needed before the technique is widely applied. • Application of the standardised growth curve approach (SGC). • Sample- and site-specific SGCs successful for feldspar and quartz. • Application of a regional SGC for fading corrected feldspar signals with caution.

Optically stimulated luminescence dating of loess in South-Eastern China using quartz and polymineral fine grains

Loess deposits distributed in southeastern China play an important role for paleoclimate reconstruction of the subtropical regions. These loess-paleosol deposits are mainly spread within the middle and lower reaches of the Yangtze River as well as in the drainage area of the Huai River. The ages of loess paleosol sequences that are distributed along the Huai River are not well constrained. In this study, the standard single-aliquot regenerative dose (SAR) optically stimulated luminescence (OSL) protocol and two elevated temperature post infrared-infrared stimulated luminescence SAR protocols (pIRIR 225 and pIRIR 290 ) were applied on 4–11 μm quartz and polymineral fine grains, respectively, in order to obtain the first numerical luminescence chronology for a loess-paleosol sequence in northern Jiangsu Province. Our results show a good agreement between quartz SAR-OSL and polymineral pIRIR ages up to ~70 ka. These findings confirm that Xiashu loess accumulated during the Last Glaciation. For samples older than this, the ages increasingly deviate with depth. Fine quartz ages beyond 70 ka are interpreted as underestimates, as previous studies reported that quartz ages >70 ka from various sedimentary origins worldwide may underestimate even if they pass rejection criteria and dose recovery tests. On the other hand, the pIRIR ages are most likely overestimating the true depositional ages as indicated by the results of dose recovery tests, where a 30–60% overestimation of the recovered dose is reported for values larger than ~400 Gy. The overestimation of pIRIR protocols was also confirmed by the results obtained when large beta doses were added on top of the natural accrued dose. Moreover, our dating results suggest that L1/S1 transition (corresponding to MIS 5/4 boundary) occurred much higher in the stratigraphic sequence than may have been interpreted from the magnetic susceptibility enhancement. This inconsistency can be assigned to invalidity of magnetic susceptibility as a chronostratigraphical proxy due to ferrimagnetic minerals dissolution or transformation during paedogenesis processes in this humid subtropical region in the southeastern China.

OSL dating of landslide-dammed-lake deposits in the North of Tehran, Iran: 958 Ray-Taleghan/Ruyan earthquake

One large landslide (Soleghan) in the north of the megacity, Tehran, has been surveyed for dating with OSL methods. Landslide dammed-lake deposits of the Soleghan landslide was used to obtain the age of the landslide event using the SAR protocol for both quartz and feldspar grains. The age of the event was 1.09 ± 0.09 ka for quartz, and 1.03 ± 0.08 ka and 1.10 ± 0.13 ka for feldspars (stimulation at 50 °C and 225 °C, respectively). These results suggest that the Soleghan mass movement was an earthquake-induced landslide triggered by the 23rd February 958 7.7 M Ray-Taleghan/Ruyan earthquake. Based on this work, thorough review studies of landslides using OSL dating methods can be used to determine the age of other mass movements in Iran. Multiple landslides with identical ages, which may be attributed to a seismic event, could be created by a known earthquake or an unknown earthquake. Subsequently, finding an unknown earthquake will complete the earthquake catalogue resulting in a better hazard assessment.

Testing polymineral post-IR IRSL and quartz SAR-OSL protocols on Middle to Late Pleistocene loess at Batajnica, Serbia.

The loess–palaeosol sequence of Batajnica (Vojvodina region, Serbia) is considered as one of the most complete and thickest terrestrial palaeoclimate archives for the Middle and Late Pleistocene. In order to achieve a numerical chronology for this profile, four sets of ages were obtained on 18 individual samples. Equivalent doses were determined using the SAR protocol on fine (4–11 μm) and coarse (63–90 μm) quartz fractions, as well as on polymineral fine grains by using two elevated temperature infrared stimulation methods, pIRIR 290 and pIRIR 225. We show that the upper age limit of coarse quartz OSL and polymineral pIRIR 290 and pIRIR 225 techniques is restricted to the Last Glacial/Interglacial cycle due to the field saturation of the natural signals. Luminescence ages on coarse quartz, pIRIR 225 and pIRIR 290 polymineral fine grains are in general agreement. Fine quartz ages are systematically lower than the coarse quartz and pIRIR ages, the degree of underestimation increasing with age. Comparison between natural and laboratory dose response curves indicate the age range over which each protocol provides reliable ages. For fine and coarse quartz, the natural and laboratory dose response curves overlap up to ~150 and ~250 Gy, respectively, suggesting that the SAR protocol provides reliable ages up to c. 50 ka on fine quartz and c. 100 ka on coarse quartz. Using the pIRIR 225 and pIRIR 290 protocols, equivalent doses up to ~400 Gy can be determined, beyond which in the case of the former the natural dose response curve slightly overestimates the laboratory dose response curve. Our results suggest that the choice of the mineral and luminescence technique to be used for dating loess sediments should take into consideration the reported limited reliability.

A Top-to-Bottom Luminescence-Based Chronology for the Post-LGM Regression of a Great Basin Pluvial Lake

We applied luminescence dating to a suite of shorelines constructed by pluvial Lake Clover in northeastern Nevada, USA during the last glacial cycle. At its maximum extent, the lake covered 740 km2 with a mean depth of 16 m and a water volume of 13 km3. In the north-central sector of the lake basin, 10 obvious beach ridges extend from the highstand to the lowest shoreline over a horizontal distance of ~1.5 km, representing a lake area decrease of 35%. These ridges are primarily composed of sandy gravel and rise ~1.0 m above the alluvial fan surface on which they are superposed. Single grain luminescence dating of K-feldspar using the pIRIR SAR (post-infrared infrared single-aliquot regenerative dose) protocol, corroborated by SAR dating of quartz, indicates that the highstand shoreline was constructed ca. 16–17 ka during Heinrich Stadial I (Greenland Stadial 2, GS-2), matching 14C age control for this shoreline elsewhere in the basin. The lake regressed rapidly during the Bølling/Allerød (GI-1), before the rate of regression slowed during the Younger Dryas interval (GS-1). The lowest shoreline was constructed ca. 10 ka. Persistence of Lake Clover into the early Holocene may reflect enhanced monsoonal precipitation driven by the summer insolation maximum.

A luminescence‐based chronology for the Harletz loess sequence, Bulgaria

The Harletz loess‐palaeosol sequence is located in northwestern Bulgaria and represents an important link between well‐studied loess sequences in eastern Romania and further sites to the west of the Carpathians (e.g. Serbia and Hungary). The aim of this study was to establish a chronostratigraphy of the deposits, using various methods of luminescence dating, together with basic stratigraphical field observations as well as magnetic properties. Luminescence dating was carried out using the quartz fine grain fraction and a SAR protocol, and the feldspar coarse grain fraction, applying the MET‐pIRIR protocol. Due to underestimation of the quartz fine grain fraction in the lower parts of the sequence, the resulting chronology is mainly based on the feldspar ages, which are derived from the stimulation temperature at 150 °C. A comparison with nearby sequences from Serbia, Hungary and Romania, and interpretations obtained through the stratigraphical and sedimentological signature of the sequence, supports the established chronology. Our data suggest that the prominent palaeosol (soil complex) in the upper quarter of the sequence was formed during MIS 5. It would follow that large parts of the Last Glacial loess overlying this palaeosol were probably eroded, and that the thick loess accumulation underlying this soil complex can be allocated to the penultimate glacial (MIS 6). A prominent MIS 6 tephra, which has been reported from other sequences in the area, is also present at Harletz.

Assessing the maximum limit of SAR-OSL dating using quartz of different grain sizes

SAR-OSL dating studies of Romanian, Serbian and Chinese loess using fine and coarse quartz have previously resulted in a series of controversial issues. We extend here the investigations using fine (4–11 μm) and different coarse quartz (&gt;63 μm) grains extracted from aeolianites from a site on Eivissa Island (southwestern Mediterranean). Aeolianites were chosen since they contain quartz from a different geological context and have significantly lower environmental dose rates. The dose response curves of the OSL signals for fine and coarse quartz are similar to those for loess and are also represented by the sum of two saturating exponential functions. For doses up to ~200 Gy, the dose response curves of fine and coarse grains from aeolianites can be superimposed and the ages obtained for the different grain sizes are in agreement up to ~250 ka, increasing our confidence in the accuracy of the ages obtained for samples with such doses, irrespective of the magnitude of the environmental dose rate. Particularly for the fine quartz fraction, a mismatch between the SAR dose response curve and the dose response curve obtained when doses are added to the natural is reported, indicating that the application of the SAR protocol in the high dose range is problematic. This dose dependent deviation is much less pronounced for coarse grains. Thus, it seems reasonable to infer that the dose response curves for the coarse grains, although saturating earlier can be regarded as more reliable for equivalent dose calculation than those for the fine grains.

First chronostratigraphic framework of fluvial terrace systems in the eastern Cantabrian margin (Bay of Biscay, Spain)

Abstract Reported here is the first chronostratigraphic study of the Quaternary fluvial terrace deposits of three different valleys (Deba, Nerbioi, Oiartzun) located in the eastern Cantabrian margin (northern Spain), designed to understand long-term fluvial dynamics of this region. Fourteen samples were collected for numerical dating purpose, in the lowest terrace levels from 5 m to 63 m above current river channel. Optically Stimulated Luminescence dating was performed using the SAR protocol. For samples from terraces >20 m above the current river channel, over 20% of measured aliquots were above saturation of the OSL signal. Consequently, only minimum ages could be estimated. Five samples also underwent Electron Spin Resonance (ESR) dating following the Multiple Centre approach. The ESR signals of the Aluminium and Titanium (Ti-Li and Ti-H) centres were systematically measured in each sample. In particular, the ESR signal of the Ti-H centre was strong enough to derive reliable and meaningful dose estimates. Obtained age results range between ∼140 and ∼400 ka for the terrace levels from +10 to +25 m. They suggest phases of aggradation during MIS 6, MIS 8 and MIS 10, for terrace levels T+10m, T+20m and T+25m, respectively.

Dose recovery performance in double IRSL/pIRIR SAR protocols

In an attempt to test feldspar dating techniques that would use both IR50 and pIRIR225 equivalent doses, we investigated the impact of various thermal treatments on the recovery of a laboratory dose. It is observed that the most reliable protocols for delivering acceptable recovery ratios may be sample dependant. Appropriate thermal treatments, including a potentially efficient pre-test dose thermal wash (PTD TW) could yield dose recovery ratios in a range of ±5% around unity for both IR50 and pIRIR225 signals. These experiments are strong indications that rigorous dose recovery tests should be carried out before the measurement of the equivalent dose of feldspar in double SAR protocols.

Testing single aliquot regenerative dose (SAR) protocols for violet stimulated luminescence

Basic assumptions of the single aliquot regenerative dose (SAR) protocol are tested using the violet stimulated luminescence (VSL) signal from quartz. The VSL signal is shown to be reduced to a sufficiently low background level between SAR steps, and the SAR protocol appears to adequately correct for sensitivity changes during measurement. The VSL SAR protocol can recover a large (405 Gy) laboratory beta dose within uncertainties, however the mean value for the dose recovery ratio is commonly 0.8 or less. This poor behaviour is echoed in the measurements of equivalent dose (De) for a sample with an expected De of ∼354 Gy, which underestimates De by 50–70%. Further investigations are required to understand the mechanisms underlying these underestimations in VSL SAR De values.

Exploring the behaviour of luminescence signals from feldspars: Implications for the single aliquot regenerative dose protocol

A series of dose recovery experiments are undertaken on grains of potassium-rich feldspar using a single aliquot regenerative dose (SAR) protocol, measuring the post-infrared infrared stimulated luminescence (post-IR IRSL) signal. The ability to successfully recover a laboratory dose depends upon the size of the test dose used. It is shown that using current SAR protocols, the magnitude of the luminescence response (Tx) to the test dose is dependent upon the size of the luminescence signal (Lx) from the prior regeneration dose because the post-IR IRSL signal is not reduced to a low level at the end of measuring Lx. Charge originating from the regeneration dose is carried over into measurement of Tx. When the test dose is small (i.e. 1%–15% of the given dose) this carry-over of charge dominates the signal arising from the test dose. In such situations, Tx is not an accurate measure of sensitivity change. Unfortunately, because the carry-over of charge is so tightly coupled to the size of the signal arising from the regeneration dose, standard tests such as recycling will not identify this failure of the sensitivity correction. The carry-over of charge is due to the difficulty of removing the post-IR IRSL signal from feldspars during measurement, and is in stark contrast with the fast component of the optically stimulated luminescence (OSL) signal from quartz for which the SAR protocol was originally designed.