Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 17 December 2011 Xiao Fu, Bo Li, Sheng-Hua Li The potential of multi-elevated-temperature post-IR IRSL (MET-pIRIR) dating () using polymineral fine grains (FG) (4-11 μm) is tested using loess samples from the Luochuan section in the Chinese Loess Plateau. Nine FG samples with ages within the last glacial-interglacial period are tested using the MET-pIRIR protocol. The MET-pIRIR results for FG are compared with both the coarse grain (63-90 μm) K-feldspar MET-pIRIR dating results and the coarse grain quartz OSL dating results. The stratigraphic age of the profile also provides an independent age control. Our results indicate that the FG MET-pIRIR signals of 200 °C and 250 °C have negligible anomalous fading and they can give reliable ages for the Chinese loess within the last glacial-interglacial period. Highlights ► MET-pIRIR dating using polymineral FG is tested on Chinese loess samples from the Luochuan section. ► FG MET-pIRIR ages of 200 and 250°C are identical. ► They are consistent with the CG KF MET-pIRIR ages and the quartz OSL ages. ► The method is shown to work well for the Chinese loess within the last glacial-interglacial period.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 22 December 2011 GuangChao Cao, Hao Long, JingRan Zhang, ZhongPing Lai AbstractOptically stimulated luminescence (OSL) dating technique is a reliable method to determine the ages of sanddune sediments. While it seems logical to assume that for these windblown materials (such as sand dune sediments) grains from different sized fractions are suitable for optical dating and would yield identical ages, this was not previously explicitly demonstrated yet. In this study, six samples were selected from the sand dunes intercalated in loess strata near Lanzhou, western Chinese Loess Plateau, and different grain-size quartz fractions (e.g. 38-63 μm, 90-150 μm, 150-200 μm, 200-250 μm and 250-300 μm) were extracted to compare the OSL ages of different grain-size quartz. The results show that: (1) quartz OSL ages derived from different grain-size fractions produce identical ages within errors, confirming that the ages resulting from both coarse silt-sized (or middle grain of 38-63 μm) and sand-sized (90-300 μm) quartz can represent the periods of sanddune accumulation; (2) the OSL ages of the selected sand dune samples fall into ca. 28-18 ka, suggesting that the sand dune accumulation occurred during the marine isotope stage 2 (MIS 2) in current study area, which might imply regional increased aridity on the western Chinese Loess Plateau. Highlights ► We compared quartz OSL ages of different grain-size fractions of sanddunes. ► OSL ages of different grain-size fractions produce identical ages within errors. ► Ages of silt-sized (38-63 μm) quartz represent the periods of sanddune accumulation. ► The OSL ages of the selected sand dune samples fall into ca. 28-18 ka. ► The sanddune accumulation might imply regional increased aridity during ca. 28-18 ka.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 16 December 2011 Sally E. Lowick, Mareike Trauerstein, Frank Preusser The polymineral fine grain fraction of a set of ten known age samples were used to test the suitability of elevated temperature post-IR infrared stimulated luminescence (pIRIR) to date waterlain sediments in Switzerland. Equivalent Dose (De) values were obtained using elevated temperatures of 225 ̊C (pIRIR225) and 290 ̊C (pIRIR290) and IRSL50/225(preceding measurement of pIRIR225), and these displayed a systematic increase with increasing stimulation temperature, which brought those derived from the pIRIR protocols into saturation for the older half of the samples (〉 100 ka). Significant residuals were recorded for the pIRIR signals, and these were found to further increase following attenuation of the bleaching source confirming that these signals are harder to bleach than the IRSL measured at 50 ̊C. Fading tests recorded g-values of between 1 – 4 %, and displayed no obvious decrease with increasing stimulation temperature. For the younger half of the samples, fading corrected ages for all protocols resulted in overestimation compared to robust independent dating for all samples, and draw into question the relationship of fading measured in a laboratory generated signal to that which is naturally generated. Uncorrected IRSL50/225ages for all samples were in good agreement with independent dating, but still displayed a general overestimation using pIRIR signals. These overestimations may largely be due to the significant residual doses resulting from the harder to bleach nature of the elevated temperature signal; and present a considerable problem when dating waterlain sediments. A considerable challenge when using the pIRIR signal is to be able to separate the effects of both residual doses and fading and confirm that one is not masking the other. Despite this, the pIRIR protocols were successful at one site, although they offered no benefit compared to dating with more conventional luminescence signals. A comparison of Devalues derived from a standard IRSL signal to that from IRSL50/225, suggest that the latter overestimates by ∼ 10 % due to a decrease in sensitivity of the sample prior to measurement of the test dose. Highlights ► Two pIRIR protocols were tested on known age waterlain sediments. ► It was not possible to date the oldest samples as the signal was in saturation. ► Residuals doses increased dramatically as the bleaching source was attenuated. ► A correction based on fading tests resulted in further age overestimation. ► For successful dating the effects of fading and residuals on burial doses must be defined.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 13 December 2011 Mark D. Bateman, Darrel A. Swift, Jan A. Piotrowski, David C.W. Sanderson Previously reported low luminescence of basal glacial sediment has raised the possibility that processes operating at the ice-bedrock interface have the potential to reset (or ‘bleach’) natural luminescence signals (). This finding indicates that certain types of glacial sediment (for example, subglacial diamicts) might be amenable to dating using luminescence-based techniques. Using a purpose-built ring-shear apparatus situated in a light-controlled environment, we have investigated the potential for mineral grains to be reset when subjected to conditions similar to those experienced by sediment that has undergone transport at the ice-bedrock interface. Reported here are the preliminary results of an initial experiment that used medium quartz sand with a naturally-acquired palaeodose of ∼4.3 Gy that had been obtained from a relict dune system. Incremental sampling during the shearing experiment and measurements were made to track changes in the luminescence properties of the sand as strain/shearing increased. The results indicate that increased strain/shearing resulted in an increase in the number of zero-dose grains and evolution of the Dedistribution from unimodal to multimodal. In light of the very much longer shearing distances that subglacial sediment would endure in nature, these results would appear to suggest that geomechanical processes at the ice-bed interface of glaciers and ice sheets may be a viable mechanism for resetting sediment. Highlights ► We simulated sub-glacial conditions to examined the effects of shearing on luminescence. ► Results show shearing does affect stored palaeodoses within sediment. ► Full resetting of some grains with increased shearing was observed. ► Other grains showed reduced or increased palaeodoses with shearing. ► Its suggests that the shearing may be a viable mechanism for resetting sediment.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 8 December 2011 Ann V. Rowan, Helen M. Roberts, Merren A. Jones, Geoff A.T. Duller, Steve J. Covey-Crump, ... New Zealand is a key location for investigating the geomorphic response of fluvial systems over glacial-interglacial timescales, and as such provides a potentially rich archive of Quaternary climate change. Identification of the climatic response of fluvial systems requires the application of a reliable geochronological method to place the sedimentary record within the context of the regional climate history. Optically stimulated luminescence (OSL) dating offers the opportunity to generate ages from quartz in glaciofluvial sediments, and so has many possible applications in South Island. However, in applying this method, previous studies have encountered problems of low OSL signal intensities in quartz. This has limited the application of quartz OSL in South Island; most geochronological studies have instead used feldspar for luminescence dating, but have been affected by problems such as weathering. In this study, we found that although the OSL signal levels from quartz are low, a useable OSL signal can be observed from medium-sized aliquots containing ∼500 grains of quartz separated from samples from eastern South Island. Mathematical component separation of the quartz OSL signal indicated that the signal is dominated by a fast component. Ages produced using the central age model range from 18.2 ± 1.3 to 36.7 ± 2.9 ka, are in stratigraphic order, and agree with independent age control from twoC ages. This study demonstrates the successful application of quartz OSL to glaciofluvial sediments from Canterbury, and its potential to provide a chronology for sedimentary records of climate change in this region. Highlights ► Application of luminescence dating to glaciofluvial sediments from New Zealand. ► Coarse-grained quartz from the Canterbury Plains is suitable for OSL dating. ► Low signal intensity of the quartz requires aliquots of ∼500 grains to be measured. ► The quartz signal is dominated by a fast component and suitable for a SAR protocol. ► The Canterbury braided river gravels are likely to have accumulated during glacials.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 8 December 2011 Jia-Fu Zhang, Cheng-Lin Liu, Xiao-Hong Wu, Ke-Xin Liu, Li-Ping Zhou Lop Nur is a playa lake occupying the lowest part of the Tarim Basin, northwestern China, and is now a desolate and barren region. In the past decades, the ages of the lacustrine sediments from the lake were determined mainly by radiocarbon dating on bulk sediment. In this study, both optically stimulated luminescence (OSL) and radiocarbon methods were used to date the sediments from a pit in the central part of the lake. The OSL ages obtained for ten samples range from 0.5 to 9.4 ka, and are in stratigraphic order except for one sample. TheC ages obtained for twenty-two bulk sediment samples range from 5.8 to 30.2 cal ka BP with erratic distribution. Based on the comparison ofC with OSL ages and their age-depth models, we argue that the OSL ages are relatively reliable. The disequilibria in the U decay chain for some samples are deduced from the comparison of the NAA and TSAC results. We suggest that the OSL dating technique should preferably be applied to the playa sediments from Lop Nur, but the disequilibria in the U decay chain should be considered in evaluating dose rates. Additionally, radiocarbon reservoir effects in lakes in western China are reviewed. Highlights ► Lop Nur is a playa lake occupying the lowest part of the Tarim Basin, northwestern China. ► Radiocarbon reservoir effect in lakes in western China is reviewed. ► Radiocarbon dating of bulk sediment is considered problematic. ► The playa sediments are suitable for luminescence dating. ► The disequilibrium in the U decay chain for some samples is deduced from the comparison of the NAA and TSAC results.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 3 December 2011 Naomi Porat, Geoff A.T. Duller, Helen M. Roberts, Eliezer Piasetzky, Israel Finkelstein Megiddo, one of the most important mounds (Tel) in the Levant, was inhabited almost continuously from the 7millennium to the 4C. BC and archaeological remains have accumulated to a height of ca. 20 m. Megiddo features a significant number of destruction levels, some of which can be correlated to well-known historical events. Other destruction levels are less well dated, and in order to improve the chronological control, an OSL dating campaign was designed, particularly for those periods where the radiocarbon calibration curve incorporates large errors on radiocarbon dates.Twenty-six samples were collected from a range of archaeological periods, excavation areas and sediment types. In-situ gamma and cosmic dose rates were obtained either with Al2O3:C dosimeters that were buried at the site for 2 months or with a calibrated gamma scintillator. Very-fine-sand quartz was extracted and measured using conventional SAR to obtain the equivalent dose (De).The OSL age of many samples is older than the expected archaeological age and their Devalues are usually scattered. This suggests that sediments were continuously reused and recycled at Tel Megiddo without exposure to sunlight and very little fresh sediment was added directly from dust to the archaeological accumulation, challenging the basic requirement for OSL dating.Using combined criteria of sequential stratigraphic order of the samples and the over-dispersion of the measured Devalues helped to reject the samples that yield ages which fail to represent the age of their archeological context. Twelve of the 26 OSL ages had to be rejected, but the 14 ages which did pass the criteria agree very well with the expected archaeological ages. Thus analysis of a single sample is ineffective for determining an archeological age for a given context. Sediments from in-between building stones are more suitable than those taken from floors, streets and ash layers; samples from destruction layers should be avoided. Megiddo provides an example of the difficulties in OSL dating in a multi-period, complex archaeological site. Highlights ► 26 samples from Tel Megiddo were dated by OSL. ► 14 samples agree with expected archaeological age, the remaining are over-estimated. ► Sequential stratigraphic ordering allows to remove discordant samples. ► Low D e over-dispersion value is a good predictor for age agreement. ► Through the periods sediments were constantly recycled in the Tel.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 1 December 2011 J.K. Feathers Anthropogenic rock alignments, both circular and linear, are common in the northern Rockies and adjacent High Plains of North America. Their ages are largely unknown. Luminescence dating of single-grain feldspars is applied to sediment under the rocks on the assumption that prior to rock placement turbation processes zeroed sufficient number of grains and that these processes ended with the rock placement. Ages of single grains are corrected for anomalous fading and the age of placement is estimated using the minimum age model. Vertical distributions of ages show that youngest ages are clustered just under the rock, conforming to the turbation model. Low precision in fading corrections led to attempts to reduce fading with higher temperature stimulations. These did reduce fading but also recovered known doses poorly, suggesting possible age over-estimation. This uncertainty coupled with a problem of small sample sizes from material with generally low sensitivity resulted in overall low precision in ages, but still an improvement over the current lack of chronological information. Highlights ► IRSL dating is applied to sediments under anthropogenic rock features. ► Minimum age model provides date of placement because of turbation. ► Problems with sample size and optimal stimulation temperature are encountered. ► Ages are provided for five localities, although precision is low.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 28 November 2011 Sven Lukas, Frank Preusser, Flavio S. Anselmetti, Willy Tinner The potential of luminescence dating of high-alpine lacustrine sediments is tested on samples taken from three high-altitude moraine-bounded lakes in the Swiss Alps. Independent age control is provided by radiocarbon ages and detailed palynological data in all cases. All samples show good luminescence characteristics (no thermal transfer, good dose recovery and recycling), but two samples show rather low quartz signals. Radioactive disequilibria in the uranium decay chain observed in one sample are accounted for by using a dynamic modelling approach. Because all cores had largely dried out and water content had not been measured after sampling, we developed a modern limnological approach to retrospectively establish palaeo-water content. Applying average water content values from a dataset of modern sediments with similar characteristics to the samples investigated here we obtained ages that match the independent age control. Whereas the low-signal quartz separates consistently underestimate these ages, the polymineral samples more accurately match them, do not suffer from anomalous fading and are thus considered reliable. This study demonstrates for the first time that applying luminescence dating to high-alpine, ice-proximal lacustrine sediments is a promising avenue to obtain a chronology for such depositional environments. Highlights ► Establishing water content is a key issue in Luminescence dating of subaqueous sediments. ► We have developed a method to do this for dried-up samples. ► We apply this method to proximal glaciolacustrine sediments. ► Feldspar ages match, while quartz underestimates, independent age control. ► Fine-grain dating is a promising avenue of dating proximal glaciolacustrine sediments.

Description: Publication year: 2011 Source: Quaternary Geochronology, Available online 28 November 2011 Antoine J.C. Zink, George J. Susino, Elisa Porto, Thomas N. Huffman A pilot study used eleven excavated sites in the Limpopo Province of South Africa to test the application of OSL dating for Iron Age ceramic shards. The culture-history sequences of Iron Age is well established by pottery style and the sites had already been radiocarbon dated. Because the excavations were part of various research projects, rather than a specific OSL study, the sites have been destroyed and hence, local environmental radioactivity was unknown. To reconstruct the environmental dose rate, we used data from three sources: (1), a worldwide survey, (2), radionuclides in the pottery and (3) recent geological surveys. The geological surveys yielded the most dates that are reasonably close to the known chronology, reproducing the correct chronological order in most cases. Some dates, however, are 200 years too recent and some standard deviations too high. To evaluate further the potential of OSL dating in Iron Age research, dosimetry data need to be collectedin situ. Highlights ► We begin luminescence dating on Iron Age pottery from South Africa. ► Several sites dated by radiocarbon was selected. ► They have been destroyed and then the environmental dosimetry cannot be measured. ► Hypotheses based on regional geology yielded ages close to the known chronology.