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.     

Luminescence dating of K-feldspar from sediments: A protocol without anomalous fading correction

A protocol for optical dating of potassium-rich feldspar (K-feldspar) is proposed. It utilizes the infrared stimulated luminescence (IRSL) signal measured by progressively increasing the stimulation temperature from 50 to 250 °C in step of 50 °C, so-called multi-elevated-temperature post-IR IRSL (MET-pIRIR) measurements. Negligible anomalous fading was observed for the MET-pIRIR signals obtained at 200 and 250 °C. This was supported by equivalent dose (D_e) measurements using the IRSL and MET-pIRIR signals. The D_e values increase progressively from 50 °C to 200 °C, but similar D_e values were obtained for the MET-pIRIR signal at 200 and 250 °C. Measurement of modern samples and bleached samples indicates that the MET-pIRIR signals have small residual doses less than 5 Gy equivalent to about 1–2 ka. We have tested the protocol using various sedimentary samples with different ages from different regions of China. The MET-pIR IRSL ages obtained at 200 and 250 °C are consistent with independent and/or quartz OSL ages.     

Quartz OSL and TL dating of pottery,burnt clay,and sediment from Beicun archaeological site,China

This study focuses on characterizing the thermoluminescence (TL) and optically stimulated luminescence (OSL) of quartz in burnt clay, pottery, and the sediments unearthed from a Neolithic site, the Beicun site of the Liangzhu culture. It shows that the initial OSL signals (within 0.8 s) of most burnt clay and pottery sherds are not dominated by the fast component. Results of a heating simulation experiment of sediment quartz show that annealing at temperatures exceeding 600–800 °C decreased the proportion of the fast component in the initial signal slightly. In addition, the proportion of the medium component in the later signal (0.8–5 s) increased significantly, resulting in a decrease in the Fast Ratio value. Therefore, high annealing temperature may be an important reason for the slow decay rate of OSL signals of the burnt clay and pottery samples. The D_e(t) plot shows that most of the samples have thermally stable OSL component signals, which have no significant effect on the final OSL ages. The single-aliquot regenerative-dose (SAR) protocol was used to determine the OSL and TL ages for chunk burnt clay and pottery sherds. The high-precision age of the last archaeological heating event, such as sacrifice, burning, or domestic firing, can be obtained by determining the TL and OSL ages of a homogeneous chunk of burnt clay. The OSL results are consistent with the ¹⁴C age of carbon chips extracted from burnt clay. The age of the Beicun site is finally determined to be approximately 5000–5300 BP (BP represents before 2020), belonging to the early period of the Liangzhu culture.     

Maximum age limitation in luminescence dating of Chinese loess using the multiple-aliquot MET-pIRIR signals from K-feldspar

Numerical dating of loess is important for Quaternary studies. Recent progress in post-infrared infrared-stimulated luminescence (pIRIR) signals from potassium-rich feldspar has allowed successful dating of Chinese loess beyond the conventional dating limit based on quartz optically stimulated luminescence (OSL) signals. In this study we tested the multiple-aliquot regenerative-dose (MAR) pre-dose multiple-elevated-temperature post-IR IRSL (pMET-pIRIR) procedure on samples from the palaeosol S5 (∼480 ka) and S8 (∼780 ka) layers from the Luochuan and Jingbian sections, respectively. The results show that (1) compared to sensitivity-corrected signal (L_x/T_x), a higher saturation dose is observed for the sensitivity-uncorrected MET-pIRIR signals (L_x), suggesting that MAR is advantageous for dating old samples; (2) negligible fading component can be achieved using the pMET-pIRIR procedure; (3) for the sample from the top of palaeosol S5, D_e values (1360 + 226/-167 Gy) broadly consistent with expected D_e (1550 ± 72 Gy) can be obtained using the sensitivity-uncorrected 300 °C MET-pIRIR signal. Our study suggests that a D_e value of about 1800 Gy may be the maximum dating limit of Chinese loess using the MAR pMET-pIRIR procedure.     

Bleachability of pIRIR signal from single-grain K-feldspar

The high-temperature (e.g., >200 °C) post-infrared infrared (pIRIR) stimulated luminescence of feldspar has been widely used for dating, because it usually suffers negligibly from anomalous fading. However, compared to the quartz optically stimulated luminescence (OSL) or low-temperature (e.g., 50 °C) IR stimulated luminescence (IRSL) from feldspars, the high-temperature pIRIR signals have been shown to bleach more slowly and usually have high residual does of a few Gys or more, which limits its application to date relatively young samples and may cause problems for correcting residual dose/signal. In this study, we investigated the bleachability of K-feldspar pIRIR signals for individual grains. A significant variation in the bleachability of the pIRIR signal was observed among different K-feldspar grains from the same sample. Experiments show that such a variability may result in different residual doses for different grains and, consequently, additional scatter in D_e values. We present a method for quickly testing the bleachability of individual grains. Our result suggests that selecting the easy-to-bleach grains for D_e determination provides an efficient way to date young samples using high-temperature pIRIR signals, which avoids the compromise of using low-temperature pIRIR signals that may suffer from anomalous fading.     

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.     

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.     

Quartz OSL and K-feldspar pIRIR dating of a loess/paleosol sequence from arid central Asia,Tianshan Mountains,NW China

Loess deposits surrounding the high mountainous regions of arid central Asia (ACA) play an important role in understanding environmental changes in Eurasia on orbital and sub-orbital time scales. However, problems with dating loess in ACA have limited the interpretation of climatic and environmental data, especially Holocene data. We selected a typical loess/paleosol sequence (LJW10) on the northern slope of the Tianshan Mountains in ACA consisting of 280 cm of loess with multiple paleosols formed in the upper 170 cm of the section. We applied quartz OSL dating to coarse-grained (63–90 μm) fractions, and newly developed K-feldspar pIRIR dating protocols to both coarse-grained and medium-grained (38–63 μm) fractions of the samples from LJW10 section. Internal checks of the quartz OSL dating indicate that the single-aliquot regenerative-dose protocol on large aliquots (5 mm) is appropriate for equivalent dose (D_e) determinations and that the quartz ages of the loess samples are likely to be reliable. Luminescence characteristics and internal checks of the pIRIR dating indicate the pIRIR signal at a 170 °C stimulation temperature with a 200 °C preheat can be used for both coarse-grained and medium-grained D_e determinations. Anomalous fading tests for the pIRIR 170 °C signal indicate the pIRIR signals are stable and the anomalous fading of the pIRIR 170 °C signal can be ignored. Sunlight bleaching tests of the loess indicate the residual dose for the pIRIR 170 °C signal can also be ignored as it corresponds to only ∼9 years for the medium-grained K-feldspar and ∼85 years for the coarse-grained K-feldspar. The pIRIR ages of five medium-grained and coarse-grained K-feldspar samples are consistent with coarse-grained quartz OSL ages, and both the medium-grained and coarse-grained ages increase uniformly with depth, indicating these pIRIR ages are reliable. Based on the coarse-grained quartz OSL ages, and on coarse-grained and medium-grained K-feldspar pIRIR ages, an age-depth model for the paleosol-loess sequence was established by using a Bacon age-depth model. This model suggests eolian loess deposition began by at least ∼16 ka ago and that paleosol development on these eolian loess deposits began ∼5.5 ka, continuing to the present, with periods of high effective moisture at 5.5–4.9, 4.6–4.1, and 3.4–3.1 ka. This sequence suggests overall relative aridity during the early Holocene and an increase in effective moisture beginning ∼5.5 ka during the mid-late Holocene in ACA.     

A modified multi-elevated-temperature post-IR IRSL protocol for dating Holocene sediments using K-feldspar

A modified multi-elevated-temperature post-IR infra-red stimulated luminescence (MET-pIRIR) protocol is proposed for dating young samples of Holocene age using K-feldspar. The protocol utilizes a five-step MET-pIRIR measurement with a moderate preheating of 200 °C for 60 s, and a narrow IR stimulation temperature increment of 30 °C (i.e., the five measurement temperatures are 50, 80, 110, 140 and 170 °C). Using this method, the residual doses of the MET-pIRIR signals are generally less than 1 Gy. Holocene aeolian samples from Northern China were tested using the 30°C-increment modified MET-pIRIR method. The results demonstrate that similar ages from 140 °C to 170 °C were obtained for our samples, which were consistent with the quartz optically stimulated luminescence (OSL) ages. Based on this observation, the measurement procedures are further simplified to a three-step pIRIR protocol. The first IR stimulation at elevated temperature (110 °C) is used to remove the fading affected signals. This is followed by two steps of IR stimulation at high temperatures (140 and 170 °C) for equivalent dose (De) measurement. Dating results consistent with the expected ages have been obtained at stimulation temperatures of 140 and 170 °C. It is suggested that the first IR stimulation can effectively remove the fading component. The three-step pIRIR method has minimized the experimental procedures, while keeping the age plateau test.     

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.     

Direct measurement of the fast component of quartz optically stimulated luminescence and implications for the accuracy of optical dating

The usual practice in optical dating is to derive an equivalent dose (D_e) (and hence age) from integration of the initial part of the measured optically stimulated luminescence (OSL) signal. This ‘bulk’ OSL signal is known to comprise several semi-independent components, each of which decays at different rates during measurement, and thus contributes a different proportion to the bulk signal as measurement time progresses. Data are presented here which show a strong dependence of D_e on the bulk signal integration interval, with reduced D_e for later signal integration intervals resulting from lower medium component D_e values. This dependence leads to two problems: (i) deciding which signal integral to choose, and (ii) the possibility that all bulk signals will provide systematic age underestimation due to medium component signal contributions. Isolating the fast component of the bulk OSL signal provides a solution to both problems and several methods of achieving this are assessed; an efficient new method is described which is incorporated in to standard single-aliquot regenerative-dose measurement sequences. This method involves the direct measurement of the fast-component signal using infrared (830 nm) stimulation of quartz at 160 °C, prior to the standard bulk OSL measurement with 470 nm stimulation. It is shown that the measured quartz infrared stimulated luminescence signals resolve pure fast-component signals and provide D_e estimates consistent with those from signal deconvolution. This approach can only be applied to samples with relatively bright luminescence emissions, but in these cases is expected to provide a more robust estimate of palaeodose.     

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.     

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.     

Luminescence determination of firing temperature of archaeological pure sand related to ancient Dian bronze casting,China

In the present paper, we have investigated the thermal history of an archaeological ‘core sand’ from a cow-shaped bronze ornament attached to a cowrie container. It was unearthed at the Lijiashan site, located in southwest China, in the area of central Yunnan, and dates from the Han period (3 c. BC–2 c. AD). We compared the archaeological sample and a control sample of the modern quartz, examining the sensitivity of 110 °C TL and 210° C TL glow peaks, and sensitization characteristics of 110° C TL and OSL. Large differences between the ‘core sand’ samples and the control sand samples have been observed in our work. The firing temperature of the ‘core sand’ was determined to be 550–700 °C. The results offer a key to understanding the ‘core sand’ as a unique casting technique in Bronze Age Yunnan. These luminesence techniques form a new method for determining the historical firing temperature of archaeological material.     

A detailed post-IR IRSL chronology for the last interglacial soil at the Jingbian loess site (northern China)

The chronology of dust deposition and climate during the last interglacial is poorly known on the Chinese Loess Plateau. Here, 51 samples were taken from the ∼5 m S1 palaeosol (MIS5) at the desert marginal Jingbian site to develop what is currently the most detailed S1 chronology on the Plateau using instrumental dating techniques. We use the post-IR IRSL signal from sand-sized grains of K-rich feldspar. Signal resetting in the agricultural layer shows that it is possible to almost completely zero this signal in nature. First IR stimulation plateau measurements show that there is no clear dependence of D_e on first IR stimulation temperature between 50 and 260 °C suggesting negligible signal fading. Resultant ages are consistent with a last interglacial age (∼130 to ∼75 ka) and are also consistent within errors with continuous linear sedimentation rates. The average mass accumulation rate for S1 is ∼150 g m⁻² a⁻¹, considerably higher than at many other sites but within the overall range of Loess Plateau estimates. The remarkably stable sediment accumulation at the site contrasts with a more complex record of environmental and monsoonal change recorded in grain-size and magnetic susceptibility.     

EPR investigation of the role of germanium centers in the production of the 110°C thermoluminescence peak in quartz

The identification of the center acting as electron source for the well-known 110 °C thermoluminescence (TL) peak of quartz is of fundamental importance for practical applications in dating and dosimetry. This TL peak was studied in parallel with the electron paramagnetic resonance (EPR) signal of the [GeO₄]⁻ center on natural colourless quartz irradiated at room temperature. Immediately after irradiation, the signals of the 110 °C TL peak and of [GeO₄]⁻ center decay exponentially in the same way, yielding a lifetime of 50.4 ± 0.9 min at room temperature. Besides, we acquired the isothermal decay curves for the 110 °C TL peak and [GeO₄]⁻ center at different temperatures (the samples were held at the selected temperature in the range of 260–308 K). The lifetimes extracted by the isothermal decays were plotted as a function of reciprocal temperature, revealing again the same behavior of the 110 °C TL peak and [GeO₄]⁻ center, both characterized by activation energies very close of 0.76 ± 0.07 eV and 0.77 ± 0.07 eV, respectively. All results of the present work clearly show the role of electron source of [GeO₄]⁻ center in the emission mechanism of the 110 °C TL peak in quartz.     

Optical dating of Chinese loess using sand-sized quartz: Establishing a time frame for Late Pleistocene climate changes in the western part of the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) is of major interest to Quaternary geologists because it represents an important terrestrial archive of palaeoclimatic fluctuations. Previous multiple-aliquot luminescence dating studies of Chinese loess mainly used thermoluminescence (TL) and infrared stimulated luminescence (IRSL) signals of polymineral fine-grains; these are known to be subject to anomalous fading and thus will tend to yield age underestimations. In this paper we investigate whether the blue-light stimulated luminescence (BLSL) signals from 63 to 90 μm quartz grains extracted from three western Chinese loess sites (Zhongjiacai, Le Du and Tuxiangdao) can be used to establish a reliable chronology. The single-aliquot regenerative-dose (SAR) procedure is used for the equivalent dose (D_e) determinations and the suitability of our measurement protocol is confirmed by dose recovery tests. The influence of an IRSL signal on the quartz D_e measurements derived from BLSL has been investigated. From these results we conclude that an IRSL contamination, expressed as an IRSL/BLSL ratio, of up to 10% can be accepted before the values of D_e are significantly affected. All three sites yield stratigraphically consistent and spatially highly reproducible optical ages up to about 50–70 ka. At the Tuxiangdao site a marked hiatus in the record is identified between ∼20 and ∼30 ka; this remained undetected in previous studies and clearly highlights the importance of high-resolution optical dating in Chinese loess research. The optical ages presented in this work provide more evidence for episodic loess deposition and varying loess accumulation rates in the western part of the CLP. Our study seems to confirm the potential of optically stimulated luminescence (OSL) dating using the SAR procedure applied to the very fine sandy quartz fraction in Chinese loess back to ∼40–50 ka (∼120–150 Gy).     

Testing the application of post IR IRSL dating to Iron- and Viking-age ceramics and heated stones from Denmark

In this study we test, for the first time, the potential of an elevated temperature post-IR IR (pIRIR₂₉₀) SAR protocol for the dating of young heated artefacts. Seven heated stones and seven potshards were collected from three different archaeological sites in Denmark: one site from the early Pre-Roman Iron Age 200 BC to AD 100, and two from the Viking period between AD 800 and 1200.We first derive quartz OSL ages for these samples, to support the archaeological age control. The luminescence characteristics of the pIRIR₂₉₀ signal are then investigated; in particular the dose recovery ratios are shown to be close to unity. The performance of the feldspar pIRIR₂₉₀ protocol is then examined by comparing the pIRIR₂₉₀ ages with those based on the quartz OSL signal; the average ratio of pIRIR₂₉₀ to OSL ages is 1.14 ± 0.05 (n = 14) and there is some suggestion that the possible overestimation of the feldspar ages compared to quartz is only of significance for the heated stone samples. Nevertheless, there is no indication of incomplete heating of the stones; the ratios of D_e derived from the IR₅₀ and pIRIR₂₉₀ signals are independent of sample type, and consistent with complete resetting by heating. Comparison with the archaeological age control is not able to identify whether quartz or feldspar provides the most reliable dating signal.     

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.     

Dating deep? Luminescence studies of fault gouge from the San Andreas Fault zone 2.6 km beneath Earth's surface

This study aims to assess whether luminescence emission from fault gouge samples from the San Andreas Fault Observatory at Depth (SAFOD) can be used to determine the age distribution of distinct deformation microstructures. Such age determination could help constrain some of the proposed micromechanical models for shear localization in fault gouge, in addition to providing more accurate time constraint on the seismic cycle itself. The mechanism by which previously trapped charge is reset in minerals in fault gouge is thought to be a combination of frictional heating and mechanical deformation, and these processes may be localized to grain surfaces. An added dating complexity specific to deep samples is the high ambient temperature conditions, which act as a barrier to charge storage in lower energy trapping sites. In this work luminescence experiments are being conducted on minerals from whole-rock samples of intact fault gouge from the SAFOD Phase III core. Initial studies indicate (i) the thermal and radiation history of the mineral lattice can be assessed with TL, (ii) trap resetting is evident in both TL and IRSL data, (iii) a small charge-trapping window between drill hole ambient temperature of ∼112 °C and higher energy lattice excitation via rupture events is evident in TL data from ∼300 to 400 °C, and we tentatively link the source of IRSL to TL within this 300–400 °C region, (iv) IRSL data have low natural intensity but good luminescence characteristics, and (v) SAR IRSL D_e data have high over-dispersion but demonstrate ages ranging from decades to centuries may be measured.