MET-post-IR IRSL luminescence dating of cobbles buried in fluvial terraces in the Northern Chinese Tian Shan

Cobbles can be used as an alternative to the conventionally employed sand-sized mineral luminescence dating. In piedmont environments, cobbles are much more abundant than sand-sized material. The IRSL₅₀ signal has been widely used in previous studies due to its greater sensitivity to exposure events. However, it is well known that the low temperature IRSL signal is more prone to fade than elevated temperature post-IR IRSL signal. In this study, to test the reliability and applicability of cobble sub-surface elevated temperature IRSL luminescence dating, six light-color granite cobbles and two sand-sized samples from silty sand lens were collected from a high terrace of Manas River on the northern piedmont of Chinese Tian Shan. A modified multi-elevated-temperature post-infrared infrared stimulated luminescence (MET-post-IR IRSL) protocol was applied. The age-temperature (A-T) plateau of MET-post-IR IRSL measurement was combined with the conventional age-depth (A-D) plateau in luminescence-depth profile to evaluate the resetting and fading of MET-post-IR IRSL signals. Uncertainties of grain-sizes of K-feldspar within solidified slices were also explored by μ-XRF mapping of potassium content. The A-T plateau was identified between MET-post-IR IRSL₁₇₀ and MET-post-IR IRSL₂₂₅ signals of one cobble, which suggested completeness of bleaching before burial and negligible anomalous fading during burial. This cobble yielded MET-post-IR IRSL₂₂₅ ages of 15.8 ± 2.6 ka and 19.0 ± 3.2 ka for top and bottom side, respectively. These MET-post-IR IRSL₂₂₅ ages were consistent with independent coarse-grained quartz MAM OSL ages (15.7 ± 3.6 ka and 14.8 ± 2.6 ka) of two sand-sized samples. The MET-post-IR IRSL₂₂₅ age of 16.0 ± 1.2 ka for the bottom side of another cobble was also consistent with the independent age, even without the A-T plateau. It was inferred to be caused by anomalous fading of MET-post-IR IRSL signals other than that stimulated at 225 °C by refering to the A-D plateau observed. Our results show that MET-post-IR IRSL measurement can be employed to determine the burial ages of cobbles. The A-T plateau, complemented with the A-D plateau, could be used to assess the reliability of burial ages of cobble luminescence dating from the view of bleaching and fading.     

Exploring IRSL50 fading variability in bedrock feldspars and implications for OSL thermochronometry

Optically Stimulated Luminescence (OSL) is a well-established Quaternary dating method, which has recently been adapted to application in low-temperature thermochronometry. The Infra-Red Stimulated Luminescence (IRSL) of feldspar, which so far is the most promising target signal in thermochronometry, is unfortunately prone to anomalous fading. The fading of feldspar IRSL is at times not only challenging to measure, but also laborious to incorporate within luminescence growth models. Quantification of IRSL fading is therefore a crucial step in OSL thermochronometry, raising questions regarding (i) reproducibility and reliability of laboratory measurements of fading, as well as (ii) the applicability of existing fading models to quantitatively predict the level of IRSL field saturation in nature. Here we investigate the natural luminescence signal and anomalous fading of IRSL measured at 50 °C (IRSL₅₀) in 32 bedrock samples collected from a variety of lithologies and exhumation settings (Alaska and Norway). We report a large span of IRSL₅₀ fading rates between samples (g_2days ranging from ∼0.5 to ∼45%/decade), which further demonstrates (i) a good reproducibility between two common fading measurement protocols, and (ii) the ability of tunnelling models to predict the level of feldspar IRSL₅₀ field saturation in nature. We observe higher IRSL₅₀ fading in feldspar with increasing Ca content, although other factors cannot be dismissed at present. Finally, our dataset confirms that the applicability of feldspar IRSL₅₀ in OSL thermochronometry is limited to rapidly-exhuming settings or warm subsurface environments.     

Testing the accuracy of OSL and pIR IRSL dating of young geoarchaeological sediments in coastal Peru

Luminescence dating of late Quaternary sediments in Peru is challenging, especially on the Peruvian coast. Earlier studies have shown that quartz grains often exhibit a thermally unstable, medium signal that caused the underestimation of Optically Stimulated Luminescence (OSL) ages. InfraRed Stimulated Luminescence (IRSL) dating has shown to produce more reliable ages, depending, amongst other factors, on the age model (Central or Minimum Age Model), and the IRSL signal. IRSL dating of geoarchaeological sediments has, however, hardly been carried out, let along validated, against an independent age dataset. This dating approach is, nonetheless, the only promising way to date the geological substrate in which many of Peru's archaeological sites are buried. Peru contains some of the oldest and most important archaeological heritage sites, yet not much is known of the environmental context in which many of its early civilizations prospered. A better understanding of which luminescence method works best could therefore help in a better understanding of the geological-stratigraphical context of many of Peru's sites.To investigate this matter more fully, we compared the luminescence dating results of seven sediment samples from the top layer of the Lima alluvial fan and from geoarchaeological layers of the Maranga Complex (San Miguel, Lima), with an independent dataset of sixteen ¹⁴C ages. Our results showed that the quartz OSL ages always underestimated the expected ages due to a signal dominated by medium and slow components, and that the post-IR IRSL₂₂₅ (pIR IRSL₂₂₅) and IRSL₅₀ ages of K-feldspars, on basis of the Central Age Model (CAM), always overestimated the expected ages. The Minimum Age Model (MAM) on the other hand, correctly predicted the expected ages for the early Holocene, Lima alluvial fan sediments using the pIR IRSL₂₂₅ signal of K-feldspars, and the late Holocene, geoarchaeological ages using the IRSL₅₀ signal.     

Luminescence dating of scoria fall and lahar deposits from Somma–Vesuvius,Italy

Luminescence dating has been applied to scoria and lahar deposits from Somma–Vesuvius, Italy. Samples include scoria from the AD472 and 512 (or 536) eruptions and lahar deposits. In order to find a stable luminescence signal which is less affected by anomalous fading, infrared stimulated luminescence (IRSL) signals at elevated temperatures after bleaching with IR at 50 °C (termed post-IR IRSL; pIRIR) were tested at different preheat and elevated stimulation temperatures. The fading rates of both IRSL and pIRIR signals reduced dramatically with increasing preheat and pIRIR stimulation temperatures. A pIRIR signal measured at 290 °C after a preheat at 320 °C (60 s) and an IR stimulation at 50 °C (100 s) was selected to calculate the equivalent dose (D_e). The gamma spectrometry results indicate that the U-series nuclides are not in equilibrium and there is a large ²²⁶Ra excess. The dose rates and ages were calculated by assuming a ²²⁶Ra excess (over its parent ²³⁰Th) at deposition, and that this unsupported excess then decayed to the present level. The resulting luminescence ages of the two scoria samples agreed with the expected ages, and the ages of the lahar deposits indicate that they are associated with the AD1631 eruption.     

Dating the recent past (<500 years) by post-IR IRSL feldspar – Examples from the North Sea and Baltic Sea coast

The applicability of the post-IR IRSL single-aliquot regenerative-dose protocol (termed pIRIR protocol) has been tested on K-rich feldspar from recent coastal sediment samples (<500 a) from the southern North Sea coast and southern Baltic Sea coast. The most suitable post-IR IRSL (pIRIR) stimulation temperature is found to be 150 °C by using a preheat temperature of 180 °C. For this pIRIR stimulation temperature, a detectable pIRIR signal is obtained and the residual dose is minimized. Furthermore, anomalous fading is found to be negligible in the pIRIR₁₅₀ signal for our young samples whereas the fading rates for the conventional IRSL signal measured at 50 °C (IRSL₅₀) is between 5 and 7%/decade. However, the pIRIR₁₅₀ signal bleaches significantly slower compared to the IRSL_50, according to bleaching experiments using daylight, solar simulator and IR diodes, although the residual doses of both signals are similar. The laboratory residual doses in perfectly bleached aliquots are variable from sample to sample and vary between 300 ± 170 and 800 ± 460 mGy for the pIRIR₁₅₀. The precision of the residual dose determination is generally poor and causes large uncertainties on the residual subtracted ages. The laboratory residual doses alone cannot account for the observed overestimation in our two youngest samples (<70 a), indicating that the feldspar signals in these samples were presumably not fully bleached prior to aeolian or beach deposition. However, even if the age uncertainties are large we obtained pIRIR₁₅₀ ages in agreement with independent age estimates for the two older samples, which are 70 and 390 years old.     

A test case for anomalous fading correction in IRSL dating

Infrared-stimulated luminescence (IRSL) dating of feldspars has the potential to date deposits beyond the age range of quartz optical (OSL) dating. Successful application of feldspar IRSL dating is, however, often precluded due to anomalous-fading, the tunnelling of electrons from one defect site to another. In this paper we test procedures proposed for anomalous-fading correction by comparing feldspar IRSL and quartz OSL dating results on a suite of samples from continental deposits from the southeastern Netherlands. We find that even after anomalous-fading correction IRSL ages underestimate the burial age of the deposits and argue that this may be a consequence of a dependency of anomalous fading rate on the dose rate and on the absorbed dose.     

Luminescence dating of fluvial deposits in Vojvodina,N Serbia: First results

This paper reports on the first investigations into the potential of luminescence dating to establish a chronological framework for fluvial processes in the Tisa River Valley in Vojvodina, N Serbia. A total of 18 samples were collected from a terrace exposure near Mužlja, which comprised non-fluvial deposits at the top and fluvial deposits at the base. The luminescence characteristics of sand-sized quartz and potassium feldspar grains were investigated using a single-aliquot regenerative dose (SAR) protocol. The quartz separates exhibit a complex behaviour, making this dosimeter less suited for optical dating. Investigations into the behaviour of infrared stimulated luminescence (IRSL) measured at 50 °C (IR₅₀) from K-rich feldspar extracts showed that preheating in excess of 60 s at 225 °C leads to significant sensitivity changes. The effect of IR stimulation on the thermoluminescence (TL) signal and that of preheating on IRSL intensity were examined; the results are inconclusive with respect to thermal stability, but are not inconsistent with the idea that the data do not reflect depletion of an electron trap. The IR₅₀-signal measured after a preheat of 60 s at 115 °C behaves well in the SAR protocol, although it suffers from anomalous fading. Assuming that the signal is thermally stable, the fading-corrected ages suggest that deposition occurred during the end of the Late Pleniglacial and the early Late Glacial, which is consistent with geological expectations. Our observations demonstrate that IRSL dating of feldspar holds potential for establishing a chronology of fluvial dynamics of the Tisa River in N Serbia. Further methodological investigations are desirable; however, as issues relating to the stability and resetting of the IRSL signal remain to be resolved.     

Methodological studies on luminescence dating of volcanic ashes

We report here the results of a feasibility study of luminescence dating of polymineralic volcanic ash. Of the several possible protocols that used different emission bands and different IR stimulation regimes, the post infrared-infrared stimulated luminescence (pIR-IRSL) signal (detected using a violet-blue emission window with stimulation temperature in the region 260–320 °C) provided the most stable signal. This involved, i) identification of the most suitable temperature for pIR-IRSL read out, ii) determination of alpha efficiency and, iii) estimation of anomalous (athermal) fading rate. Anomalous fading rate (g-value in %/decade) of pIR-IRSL signal at 300 °C was 0.0–1.6%/decade and it ranged from 2.4 to 5.2%/decade for IRSL at 50 °C, both preheated to 320 °C. Thus, though more stable, pIR-IRSL signals may fade in nature, and even during laboratory extended irradiation. Of the models for fading correction by Huntley and Lamothe (2001) and Kars et al. (2008), the Kars et al. (2008) model performed better as the natural luminescence intensity was closer to the onset of saturation in the luminescence dose response curve. Our measurements suggest that alpha efficiencies of the pIR-IRSL signals are higher than that of IRSL. Fading corrected pIR-IRSL single aliquot regeneration (SAR) protocol based ages on three of the five volcanic ash beds are in agreement with the expected ages of ∼74 ka, based on geochemical association of the present samples to be the Youngest Toba Tuff (YTT). Other ash samples that gave ages of <24 ka and <37 ka, were inferred to have been in their secondary context, reworked from their original depositional sites. The onset of saturation dose of the pIR-IRSL signal (D₀) was ∼330 Gy and this implied a maximum measurable equivalent dose of 660 Gy. The minimum detectable dose was ∼5 Gy. These dose limits correspond to a typical age range of 1–150 ka using the pIR-IRSL signal for volcanic ashes.     

Comparison of paired quartz OSL and feldspar post-IR IRSL dose distributions in poorly bleached fluvial sediments from South Africa

A comparative study using quartz optically stimulated luminescence (OSL) and feldspar post-infrared infrared stimulated luminescence (post-IR IRSL) was undertaken on Quaternary fluvial sediments from an unnamed tributary of the Moopetsi River in South Africa. The aim is to assess whether the post-IR IRSL signal can be used to date incompletely bleached sediments. Several post-IR IRSL signals using varying stimulation and preheat temperatures were investigated; of these the post-IR IRSL₂₂₅ signal was deemed most appropriate for dating because it bleached most rapidly. The feldspar post-IR IRSL₂₂₅ equivalent dose (D_e) values from this site are consistently larger than those from quartz OSL, probably due to differences in the bleaching characteristics of the two signals. Additionally, the post-IR IRSL₂₂₅ D_e values within a sample showed less variation in precision than the quartz D_e data, possibly due to greater averaging between grains in the feldspar small aliquots. The agreement between ages based on the OSL and post-IR IRSL₂₂₅ signals was better for younger samples (<20 ka) than for older ones (>50 ka); the cause of this variation is unclear.     

Luminescence dating of glaciolacustrine silt in overdeepened basin fills beyond the last interglacial

OSL and IRSL dating are applied to samples from a 152 m-long drill core to constrain the timing of three glaciolacustrine depositional periods within the infill of an overdeepened bedrock trough in the Lower Glatt valley, N Switzerland. The characterisation of the dose-response suggests that the polymineral IRSL₅₀ and pIRIR_180/225 signals are close to saturation, while quartz OSL ages are within the range of reliable dating. The demarcation of the upper quartz OSL dating limit, however, remains challenging. Dose-recovery tests performed with long storage periods were used to investigate the reliability of the high region of the dose-response curve. They suggest an upper limit for reliable dating of ∼400 Gy for these samples, which was considerably lower than the commonly used 2D₀ criterion. Lifetimes were calculated for the quartz OSL and the thermal stability of the signal is not considered as problematic for the determined ages. Allowing for a contribution from inherited dose due to partial bleaching, places the infill of the overdeepened valley within the penultimate glacial cycle (MIS6).     

A comparison of TT-OSL and post-IR IRSL dating of coastal deposits on Cap Bon peninsula,north-eastern Tunisia

In this study thermally transferred (TT) OSL and post-IR elevated temperature IRSL (290 °C) (pIRIR₂₉₀) dating are applied to deposits covering coastal terraces on the Cap Bon peninsula, Tunisia. Both methods perform well under standard performance tests; dose recovery tests using a modern analogue show that doses relevant to our study can be recovered accurately. Residual signals in the modern analogue for both signals are very small (∼2 Gy). For the younger (<250 ka) deposits reasonable good agreement of the ages is observed between both methods, and in addition with standard quartz OSL dating. Systematic discrepancy in ages is found for the older sediments. The TT-OSL underestimate (compared to the pIRIR₂₉₀ ages) is most likely due to the short lifetime of the TT-OSL trap; we estimate a lifetime of ∼0.7 Ma at 19 °C (mean ambient air temperature of the study area). This is the first time this lifetime has been derived from geological data and it is within the range of previously published laboratory estimates. This result suggests that TT-OSL is not likely to provide a significant extension of the age range beyond that available from other methods. Our preferred pIRIR₂₉₀ ages suggest that the geological setting on Cap Bon is not as simple as previously suggested.     

Establishing a luminescence chronology for a palaeosol-loess profile at Tokaj (Hungary): A comparison of quartz OSL and polymineral IRSL signals

We present a comparative study of quartz OSL, polymineral IRSL at low temperature (50 °C, IR₅₀) and post-IR elevated temperature (290 °C) IRSL (pIRIR₂₉₀) feldspar dating on nine samples from the Tokaj loess section in NE Hungary (SE Europe). Preheat plateau tests show a drop in quartz OSL D_e between 160 and 240 °C but above 240 °C a clear D_e plateau is present. Quartz OSL SAR is shown to be generally appropriate to these samples (recycling, recuperation) but a satisfactory dose recovery result was only obtained when a dose was added to a sample without any prior optical or thermal pre-treatment; this gave a dose recovery ratio of 1.04 ± 0.05 after subtracting the natural dose from the measured dose. The pIRIR₂₉₀ SAR protocol also results in acceptable dose recovery results for the pIRIR₂₉₀ signal (1.08 ± 0.01) when a large dose is added to the natural dose. Bleaching experiments suggest a detectable non-bleachable residual pIRIR₂₉₀ dose of 10 ± 4 Gy. Agreement with quartz OSL ages is best achieved by correcting the IR₅₀ ages for fading; however this is not necessary when using the pIRIR₂₉₀ signal. With respect to Hungarian Late Quaternary geology our results indicate that the major part of the Tokaj loess has been deposited during MIS 3 (60–24 ka), with periods of soil formation occurring during the onset of MIS 3 (≥58 ka) and between about 35 and 25 ka. Our results also indicate episodic deposition of loess and varying, non-linear sedimentation rates during MIS 3. Proxy analyses in the literature are based on the traditional concept of continuous deposition; in the light of our new data the use of such simple assumptions must be reconsidered.     

OSL and IRSL dating of raised beach sand deposits along the southeastern coast of Norway

Raised beach sand deposits along the southeastern coast of Norway were dated by optical (OSL) and infrared stimulated luminescence (IRSL) and the quartz and K-feldspar luminescence characteristics were described. Due to the poor quartz luminescence characteristics, only a limited number of samples were suitable for OSL dating. More promising are the K-feldspar extracts, with typical K-feldspar luminescence characteristics and no sign of fading. For equivalent dose (D_e) determination, sand-size quartz and feldspar extracts were used, applying a single aliquot regenerative (SAR) protocol. Both, OSL and IRSL D_e estimates show a wide distribution, unexpected for beach deposits. The calculated OSL and IRSL age estimates were generally in good agreement and the correctness of the ages was confirmed by independent age control. Because only a limited number of the quartz samples were suitable for OSL dating, IRSL dating of the K-feldspar represents an alternative to OSL quartz dating.     

Rock and sediment luminescence dating of an ancient circular stone-walled enclosure at Sønnebøe,northern Scania,Sweden

Dating agricultural artefacts such as field walls and clearance cairns using radiocarbon can be challenging, especially since the association with datable material may be poor. Rock surface burial dating using luminescence offers an alternative. Here we report on the luminescence dating of a medieval circular stone-walled enclosure at Sønnebøe, northern Scania, Sweden, using both buried rocks and sediments. Luminescence burial profiles from IRSL signals measured at 50 °C (IR₅₀) indicated significant prior light exposure in 7 of the 8 samples tested (5 granite, 2 felsic gneiss), in some cases multiple exposure burial cycles were indicated. These rock surfaces had apparently been exposed for sufficient time to allow accurate IRSL ages for the most recent burial event. In contrasts, no useful post-IR IRSL profiles were obtained indicating that this signal was not sufficiently reset to allow accurate determination of the burial dose on any of these rocks. IR₅₀ fading corrections (typically ∼50%) were derived by comparing field saturation with that induced in the laboratory. Quartz extracted from sediments surrounding the rocks gave an average measured to given dose ratio of 1.03 ± 0.01 (n = 90), and these sediment samples were then dated using multigrain aliquots; the corresponding feldspar dose recovery ratio obtained using rock samples was 0.98 ± 0.05 (n = 28). A total of 15 ages were derived; 8 quartz OSL ages from the disturbed coarse grained sediments surrounding the structure, and 7 fading corrected IR₅₀ ages from the surfaces of rocks (2–3 mm chips, ∼1 mm thick) used in the construction of the structure itself. The exposure events preserved by the ring enclosure stones unequivocally show wall building taking place at the site between 800 and 300 years ago.     

Age comparison by luminescence using quartz and feldspar on core HPQK01 from the Pearl River delta in China

Reliable chronology is critical for reconstructing estuarine delta process. In this study, detailed chronological framework has been performed on a core HPQK01 (52 m in depth) from the central Pearl River delta (PRD) of China. Both quartz OSL and feldspar post-IR IRSL (pIRIR) methods for late Pleistocene sediments, as well as radiocarbon dating for Holocene sediments, were applied to date the core. Results show that quartz OSL ages range from 125 ± 18 ka to 58 ± 6 ka, and that all of them were minimum ages due to the OSL signal saturation. Feldspar pIR₂₀₀IR₂₉₀ protocol shows some overestimation in dose recovery test, with the recovered to the given ratio of 1.2, while a ratio of around 1 was obtained for feldspar pIR₅₀IR₂₅₀ signals. Robust ages have been obtained from feldspar fading corrected pIR₅₀IR₂₅₀ dating with ages ranging from 150 ± 17 ka to 98 ± 12 ka. AMS ¹⁴C results suggest that subtidal-intertidal zone was deposited during the middle Holocene from 8.21 ± 0.19 cal ka BP to 4.99 ± 0.25 cal ka BP. The sedimentology of core HPQK01 record two marine transgressive-regressive cycles. Based on the dating results, the lower fluvial sediment unit (T2) could be correlated to marine isotope stage (MIS) 6, and the lower marine unit (M2) was deposited during MIS 5. A sedimentary hiatus occurred with age range of from MIS 4 to MIS 2. Since middle Holocene, another marine stratum (M1) has been accumulated. Overall, our findings suggest that feldspar pIRIR dating method has the potential to establish the Quaternary chronostratigraphic framework of the PRD for samples with ages within 150 ka.     

Feldspar multi-elevated-temperature post-IR IRSL dating of the Wulanmulun Paleolithic site and its implication

The Wulanmulun site found in 2010 is an important Paleolithic site in Ordos (China), from which lots of stone and bone artifacts and mammalian fossils have been recovered. It was previously dated by radiocarbon and optically stimulated luminescence (OSL) techniques on quartz. To further confirm the reliability of the chronology constructed based on OSL ages and test the applicability of the recently developed pIRIR procedure on sediments from northern China, twenty-four sediment samples (including eolian, lacustrine and fluvio-eolian sands) from the site were determined using the multi-elevated-temperature post-IR IRSL (MET-pIRIR or pIRIR) procedure on potassium feldspar. The results show that the studied samples have two MET-pIRIR D_e preheat plateaus (280–320 and 340–360 °C), and the bleaching rates of the luminescence signals are associated with sample ages and stimulation temperatures. All the pIRIR ages (7–155 ka) corrected for anomalous fading and residual dose obtained after solar bleaching for 15 h are larger than the corresponding quartz OSL ages (4–66 ka) previously determined, even for the young eolian samples (<10 ka). But the corrected IRSL(50 °C) ages (6–85 ka) are broadly consistent with the quartz ages. It appears that the IRSL(50 °C) ages are more reliable, although this contradicts the previously results obtained by other people. On the other hand, we also obtained an extended age plateau between the stimulation temperatures of 50 and 290 °C in the plot of age versus stimulation temperature (A-T plot) by subtracting different residual doses obtained after different bleaching times. The reliability of the plateau ages requires further investigation. For the sediment samples from this site, quartz should be more suitable for dating than K-feldspar, and the quartz OSL ages of 50–65 ka for its cultural layer should be reliable.     

Luminescence chronology of fossiliferous fluvial sediments along the middle Atbara River,Sudan

Fluvial sediments of the middle Atbara River Valley, eastern Sudan, contain abundant vertebrate fossils and stone tools. Previous work described two sedimentary units, the Butana Bridge Synthem (BBS) and the Khashm El Girba Synthem (KGS), with three divisions each (BBS1-3 and KGS1-3, from bottom to top, respectively). ²³⁰Th/U dating on bivalve shells suggested an age of ∼126 and ∼92 ka for the basal KGS2 and basal KGS3, respectively, and mammalian biochronology in combination with magnetostratigraphy suggested an age of late Early to early Middle Pleistocene for the underlying BBS. To establish a detailed chronology of this fluvial sedimentary sequence, we collected 17 luminescence samples from both sides of the Atbara River close to the Butana Bridge. Quartz OSL dating was applied to samples from the upper part of the profile (upper KGS2 and KGS3), but the signal reached saturation within the upper ∼10 m of the sequence. To select a suitable feldspar signal to date older samples beyond the limit of the quartz OSL, a comparison of the quartz OSL, feldspar post-IR IRSL at 225 and 290 °C, and pulsed IRSL signal at 50 °C was conducted for a sample from KGS3. The result showed that only the fading corrected pulsed IRSL yielded an age consistent with the quartz OSL, and the post-IR IRSL signals (both at 225 and 290 °C) overestimated the quartz age significantly. We therefore selected the pulsed IRSL signal to date the older deposits. The luminescence ages indicate that the entire BBS - KGS sequence was deposited between 224 ± 23 ka and <17 ± 1 ka, corresponding to marine isotope stages (MIS) 7–2, significantly revising previous conclusions.     

Luminescence signals from modern sediments in a glaciated bay,NW Svalbard

Landforming processes are highly active in the Arctic, and luminescence dating can be used to establish a chronological framework for these processes. For example, luminescence ages of raised littoral and marine deposits provide the age control for many reconstructions of Pleistocene events in the Arctic. Due to the nature of the depositional environment (e.g. short transport distance, turbid water, long polar night) these types of sediment may not be completely zeroed at the time of deposition. To test the significance of incomplete bleaching in this type of environment, surface sediments were sampled along a transect from the margin of a glacier out into a nearby bay on NW Svalbard. The water in the bay is very turbid (secchi depth 0.1 m), but there is significant reworking by waves along the shores.Quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) were measured using sand-sized grains. For quartz OSL and feldspar IRSL (50 °C) the ice-proximal sample showed relatively high doses (∼12 Gy) while nearby beach sand and shallow-marine deposits, as well as ice-distal sandur sediments, had much lower doses: most OSL doses were consistent with zero, while IRSL (50 °C) ranged from 0.5 to 6.5 Gy. Post-IR IRSL (290 °C) doses were overall much higher (∼20–55 Gy), which partly is due to a significant (∼12 Gy) unbleachable residual, and partly due to slower bleaching rates than for the IRSL (50 °C) signal.In this Arctic environment it appears that bleaching is limited in the first ∼100 m of meltwater transport from the glacier margin, but for material transported at least 3 km bleaching of OSL and IRSL (50 °C) signals is more or less complete. Given the very limited light penetration through the seawater in the bay, any bleaching must have occurred during fluvial/subaerial transport to the bay or by wave-reworking on the beach. Apart from the ice-proximal glacifluvial sediments, residual apparent doses recorded by quartz OSL and feldspar IRSL (50 °C) are negligible for the luminescence dating of Pleistocene-aged deposits of ice-distal, littoral and shallow-marine origin.     

A method to evaluate the degree of bleaching of IRSL signals in feldspar: The 3ET method

In addition to dating, IRSL luminescence signals can preserve information about erosional, transport, and depositional histories of a population of grains. Knowledge of the degree of bleaching can be useful in understanding the processes that occurred during previous depositional events, as certain transport conditions result in a well bleached signal, while others result in grains retaining an inherited signal from prior events. This information can be accessed by making single-grain IRSL measurements across successively increasing temperatures, thereby isolating signals from traps of different bleachabilities.A new approach offers a way to evaluate the completeness of bleaching of a grain by testing patterns of equivalent dose (D_E) values measured at three elevated temperatures (3ET), 50, 125, and 225 °C. Consistent D_E estimates across two or more temperatures suggest a single bleaching event of sufficient duration to fully depopulate the traps involved. Incompletely bleached grains with inconsistent D_E values across temperatures will lack a 3ET “plateau.” Modes in the distribution of D_E values for fully bleached grains can suggest depositional ages, subject to assessment of fading. We developed a Python code in a Jupyter Notebook environment for data analysis and visualization to expedite processing the large data sets produced by the 3ET protocol.The 3ET protocol was tested on a radiocarbon dated sequence of playa samples from California, USA and on a set of fluvial terraces in the Marlborough region of New Zealand as part of a larger project to reconstruct regional seismic history. Where standard pIRIR apparent ages can be inconsistent or ambiguous, 3ET age estimates produce generally consistent apparent ages. Modes of 3ET plateaus can be used to infer the most recent and prior events that resulted in a sub-population of grains being fully bleached. These initial results suggest that the 3ET method can be useful to characterize both the age and degree of bleaching of depositional events.     

Testing the potential of elevated temperature post-IR IRSL signals for dating Romanian loess

In this study we test the potential of the elevated temperature infrared stimulated luminescence (IRSL) signals for dating Romanian loess. The recently developed post-IR IRSL protocol is applied to Romanian loess using polymineral fine grains extracted from the loess-palaeosol sequence at Mircea Vodă (SE Romania). This approach is aimed at obtaining an additional age control to examine the age discrepancy obtained from previous optically stimulated luminescence (OSL) studies using different grain-sizes of quartz (4–11 μm and 63–90 μm).Two preheat post-IR IR stimulation temperature combinations were used, 250–225 °C and 325–300 °C, respectively. The signals obtained are documented in terms of dose response curve, laboratory tests and fading. Although both post-IR IRSL signals exhibit small fading rates, dose response characteristics indicate that these rates may be laboratory artefacts. The post-IR IRSL signal stimulated at 300 °C is observed to suffer from dose dependent initial sensitivity changes as both natural and regenerated signals are observed to lie above the saturation level of the dose response curve. Uncorrected age results obtained using both post-IR IRSL signals are in general agreement with previously reported silt-sized quartz OSL ages for samples collected from the uppermost loess unit L1. For older material, the post-IR IRSL signal stimulated at 225 °C is considered to provide reliable age results, in agreement with independent age control available for this sequence.