Infrared Stimulated Luminescence Research Articles

Luminescence and thermometry studies of plant opal phytoliths

We have investigated the luminescence properties of plant opal phytoliths to assess their suitability for determination of age and/or thermometric information from soil and sediment sequences. This study examined a <2.37 gcm−3 density fraction in parallel with quartz grains from samples collected from alluvial terraces. We observed comparable optically stimulated luminescence (OSL) from the phytolith fraction to the quartz, and thermoluminescence (TL) with broader peaks and continuum to higher temperatures. Scanning electron microscopy (SEM) data suggested the presence of opal clasts and contaminant minerals. To better understand the luminescence from opal phytoliths we analyzed a suite of biogenic materials including very pure diatoms, phytoliths, and quartz reference materials. We observe low sensitivity but measurable OSL signals in all the materials analyzed, and infrared stimulated luminescence (IRSL) signals with fast decay rates exceeding those of more typical feldspars in some of the purer materials. TL signals are similar to those observed for glasses and suggests dose response might extend beyond quartz saturation levels. Preliminary investigations of OSL dose response show very promising growth characteristics for opal phytolith samples and all other biogenic silica materials analyzed.

Regional beryllium-10 production rate for the mid-elevation mountainous regions in central Europe, deduced from a multi-method study of moraines and lake sediments in the Black Forest

Abstract. Beryllium-10 cosmic-ray exposure (CRE) dating has revolutionized our understanding of glacier fluctuations around the globe. A key prerequisite for the successful application of this dating method is the determination of regional production rates of in situ accumulated 10Be, usually inferred at independently dated calibration sites. Until now, no calibration site has been available for the mid-elevation mountain ranges of central Europe. We fill this gap by determining in situ 10Be concentrations in large boulders on moraines and by applying radiocarbon and infrared-stimulated luminescence (IRSL) dating to stratigraphically younger lake sediments in the southern Black Forest, SW Germany. The dating methods yielded concordant results, and, based on age–depth modelling with 14C ages, the age of a cryptotephra, and IRSL ages, we deduced a regional 10Be production rate in quartz. Calibrating the Black Forest production rate (BFPR) in the Cosmic-Ray Exposure program (CREp) resulted in a spallogenic sea-level and high-latitude (SLHL) production rate of 3.64±0.11 atoms 10Be g−1 quartz a−1 when referring to time-dependent Lal–Stone scaling, the European Reanalysis (ERA)-40 atmosphere model, and the atmospheric 10Be-based geomagnetic database in CREp. The BFPR turned out to be ∼11 % lower than both those at the nearest calibration site in the Alps (4.10±0.10 atoms 10Be g−1 quartz a−1 at SLHL) and the canonical global 10Be production rate (4.11±0.19 atoms 10Be g−1 quartz a−1 at SLHL) in CREp. A stronger weathering and snow cover bias and a higher impact of forest, soil, moss, and shrub cover at the study site likely explain this discrepancy.

Effect of IRSL-BLSL-TSL reading modes combination on thermoluminescence (TL) response of BeO dosimeter.

The ultimate goal of this work is the study of the effect of luminescence stimulations and signals reading modes combinations on the thermoluminescence intensity and glow curve behaviour for the same X-ray irradiation dose. Three interesting stimulating and reading modes are considered, namely, infrared stimulated luminescence (IRSL), blue light-emitting diode stimulated luminescence (BLSL) and thermally stimulated luminescence (TSL). The studied stimulation and reading modes combination protocols are (Protocol 1) IRSL-TSL, (Protocol 2) IRSL-BLSL-TSL and (Protocol 3) BLSL-IRSL-TSL. Experiments are performed on beryllium oxide (BeO) dosimeter. Results demonstrate well that the combination of reading modes have direct impact on the TL signal in terms of intensity and glow curve shape. It was also found that when reading modes are correctly combined, particularly when IRSL is applied first, then BLSL and TL, it is possible to collect two or more exploitable signals of different stimulation types for the same irradiation that can be used for different purposes and final applications.

Insight into the dynamics of a long-runout mass movement using single-grain feldspar luminescence in the Pokhara Valley, Nepal

Abstract. Mass movements play an important role in landscape evolution of high mountain areas such as the Himalayas. Yet, establishing numerical age control and reconstructing transport dynamics of past events is challenging. To fill this research gap, we bring luminescence dating to the test in an extremely challenging environment: the Pokhara Valley in Nepal. This is challenging for two reasons: (i) the optically stimulated luminescence (OSL) sensitivity of quartz, typically the mineral of choice for dating sediments younger than 100 ka, is poor, and (ii) highly rapid and turbid conditions during mass movement transport hamper sufficient OSL signal resetting prior to deposition, which eventually results in age overestimation. Here, we first assess the applicability of single-grain feldspar dating of medieval mass movement deposits catastrophically emplaced in the Pokhara Valley. Second, we exploit the poor bleaching mechanisms to get insight into the sediment dynamics of this paleo-mass movement through bleaching proxies. The Pokhara Valley is a unique setting for our case study, considering the availability of an extensive independent radiocarbon dataset as a geochronological benchmark. Single-grain infrared stimulated luminescence (IRSL) signals were measured at 50 ∘C (IRSL-50) and post-infrared infrared stimulated luminescence signals at 150 ∘C (pIRIR-150). Our results show that the IRSL-50 signal is better bleached than the pIRIR-150 signal. A bootstrapped minimum age model (bMAM) is applied to retrieve the youngest subpopulation to estimate the paleodose. However, burial ages calculated with this paleodose overestimate the radiocarbon ages by an average factor of ∼23 (IRSL-50) and ∼72 (pIRIR-150), showing that dating of the Pokhara Formation with a single-grain approach was not successful for most samples. Some samples, however, only slightly overestimate the true emplacement age and thus could be used for a rough age estimation. Large inheritances in combination with the scatter in the single-grain dose distributions show that the sediments have been transported under extremely limited light exposure prior to deposition, which is consistent with the highly turbid nature of the sediment-laden flood and debris flows depositing the Pokhara gravels. To investigate the sediment transport dynamics in more detail, we studied three bleaching proxies: the percentage of grains in saturation 2D0 criteria, the percentage of best-bleached grains (2σ range of bMAM-De) and the overdispersion (OD). None of the three bleaching proxies indicate a spatial relationship with runout distance of the mass movement deposits. We interpret this as evidence for the lack of bleaching during transport, which reflects the catastrophic nature of the event. While not providing reliable burial ages of the Pokhara mass movement deposits, single-grain feldspar dating can potentially be used as an age range finder method. Our approach shows the potential of luminescence techniques to provide insights in sediment transport dynamics of extreme and rare mass movement events in mountainous regions.

Implications and hydrographs for two Pre-Bonneville pluvial lakes and double geosols from 14 OSL-IRSL ages in Cache Valley, NE Bonneville Basin

In the northeastern Great Basin, USA, thirteen new optically stimulated luminescence (OSL) ages and one infrared stimulated luminescence (IRSL) age show that two deep pluvial lakes preceded the Bonneville lake cycle in Cache Valley during marine oxygen-isotope stages (MIS) 6 (123-191 ka) and 4 (56-71 ka), respectively. Our new data define quantitative hydrographs of the Little Valley and Cutler Dam lake cycles in both Cache Valley and the main Bonneville basin. In western Cache Valley, excavation of a faulted, east-plunging spit has sequentially exposed these deposits and overlying MIS 3 Fielding humid-over-arid double geosols that end westward at a strand of the east-dipping Dayton-Oxford normal-fault zone. Lithologically identical double paleosols in eastern Cache Valley overlie a variety of deposits, including dated Little Valley lake beds, and persist above the Bonneville shoreline. Six new ages show that the Little Valley lake cycle in Cache Valley began before 169 ka and ended after 143 ka, and its highest shoreline was above 1493 m. The &gt;25 kyr duration of this pluvial lake cycle rivals the combined durations of the two subsequent lake cycles, during MIS 4 and MIS 2. The Cutler Dam lake rose at least to ~1450 m by ~67 ka in Cache Valley. In the type area in the main Bonneville basin, west of Cutler Narrows, four averaged IRSL dates from Cutler Dam lake beds show that the lake level there had dropped to ~1340 m by ~59 ka. The Little Valley lake rose at least 40 to 50 m above the local Provo shoreline whereas the Cutler Dam lake missed reaching the Provo shoreline by ~13 m. Beneath central Cache Valley, southeast of the study area, there are two laterally extensive, confining layers of silty clay with an intervening sandy gravel layer, all overlying thick gravelly sediment. Both confining layers enclose additional thin and discontinuous gravel layers with adjacent oxidized clays. These alternating coarse and fine sediments are probably correlative with the exposed MIS 6 to MIS 1 deposits and, possibly, older lake cycles.

Integrated uplift, subsidence, erosion and deposition in a tightly coupled source‐to‐sink system, Pagliara basin, northeastern Sicily, Italy

AbstractHow tectonic forcing, expressed as base level change, is encoded in the stratigraphic and geomorphic records of coupled source‐to‐sink systems remains uncertain. Using sedimentological, geochronological and geomorphic approaches, we describe the relationship between transient topographic change and sediment deposition for a low‐storage system forced by rapid rock uplift. We present five new luminescence ages and two terrestrial cosmogenic nuclide paleo‐erosion rates for the late Pleistocene Pagliara fan‐delta complex and we model corresponding base level fall history and erosion of the source catchment located on the Ionian flank of the Peloritani Mountains (NE‐Sicily, Italy). The Pagliara delta complex is part of the broader Messina Gravel‐and‐Sands lithostratigraphic unit that outcrops along the Peloritani coastal belt as extensional basins have been recently inverted by both normal faults and regional uplift at the Messina Straits. The deltas exposed at the mouth of the Pagliara River have constructional tops at ca. 300 m a.s.l. and onlap steeply east‐dipping bedrock at the coast to thickness between ca. 100 and 200 m. Five infrared‐stimulated luminescence (IRSL) ages collected from the delta range in age from ca. 327 to 208 ka and indicate a vertical long‐term sediment accumulation rate as rapid as ca. 2.2 cm/yr during MIS 7. Two cosmogenic 10Be concentrations measured in samples of delta sediment indicate paleo‐erosion rates during MIS 8–7 near or slightly higher than the modern rates of ca. 1 mm/yr. Linear inversion of Pagliara fluvial topography indicates an unsteady base level fall history in phase with eustasy that is superimposed on a longer, tectonically driven trend that doubled in rate from ca. 0.95 to 1.8 mm/yr in the past 150 ky. The combination of footwall uplift rate and eustasy determines the accommodation space history to trap the fan‐deltas at the Peloritani coast in hanging wall basins, which are now inverted, uplifted and exposed hundreds of metres above the sea level.

Pulsed infrared stimulated luminescence measurements for defect pair model studies in feldspars

We present a time-resolved experimental study of feldspar infrared stimulated luminescence (IRSL) as part of a defect pair model investigation of the underlying mechanisms. Within our investigation we recorded ultraviolet emissions that covered a diverse range of alkali feldspars together with a limited selection of plagioclase feldspars. In analysing our measurements, we find that each IRSL pulse response is characterised by a combination of fast and slow components, the relative proportions of which vary across the range of feldspars we tested. We interpret the presence of the components as providing evidence as to the dual roles played by high mobility electrons and by the less mobile alkali ions that are released during the underlying physical processes. Consistent with earlier data, we find further that the luminescent sensitivities vary widely across the range of feldspars we tested.

Testing new kinetic models and calibration methods for Rock Surface Luminescence Exposure dating using controlled experiments

Rock surface luminescence exposure dating (RSLED) is an evolving tool in dating prehistoric rock surfaces. In this study, we explore and compare current and new models and calibration methods using optically stimulated luminescence (OSL) depth profiles from quartz grains and Infrared Stimulated Luminescence (IRSL; IR50, pIRIR225, and MET290) from feldspar grains found in granite and sandstone samples.This study shows that, although correct model assumptions improve the quality of exposure age estimates, significant discrepancies between observed and expected fitting parameter values remain, and these discrepancies leads to inaccurate age estimation. This is particularly the case when post-IR signals from feldspar are used. Here, the spectral dependency of luminescence signals is examined to better understand these problems. The demonstrated depth dependency of fitting parameters, previously assumed to be constant with depth, also gives rise to discrepancies in parameter values. The surprising observation that, in rocks, the IR50 signal is apparently more easily bleached than the quartz fast-component OSL signal is explained in terms of the wavelength dependence of light attenuation increasing the effective path length for shorter wavelengths, and so changing the shape of the light spectrum with penetration depth. This complicates parameter estimates in exposure dating even more.Alternative approaches (rather than parameter estimation) for estimating how long a rock surface has been exposed to light are considered, based on modelling the shape and position of the measured luminescence-depth profile. It is concluded that the most accurate exposure age is derived by interpolating the depth of an unknown profile onto a curve of profile depths from known age profiles (the Exposure Response Curve, or ERC, approach).

Technical note: Darkroom lighting for luminescence dating laboratory

Abstract. An optimal lighting setting for the darkroom laboratory is fundamental for the accuracy of luminescence dating results. Here, we present the lighting setting implemented in the new Luminescence Dating Research Laboratory at Stony Brook University, USA. In this study, we performed spectral measurements on different light sources and filters. Then, we measured the optically stimulated luminescence (OSL) signal of quartz and the infrared stimulated luminescence (IRSL) at 50 ∘C (IR50) as well as post-IR IRSL at 290 ∘C (pIR-IR290) signal of potassium (K)-rich feldspar samples exposed to various light sources and durations. Our ambient lighting is provided by ceiling fixtures, each equipped with a single orange light-emitted diode (LED). In addition, our task-oriented lighting, mounted below each wall-mounted cabinet and inside the fume hoods, is equipped with a dimmable orange LED stripline. The ambient lighting, delivering 0.4 lx at the sample position, induced a loss of less than 5 % (on average) in the quartz OSL dose after 24 h of exposure and up to 5 % (on average) in the IR50 dose for the K-rich feldspar samples, with no measurable effect on their pIR-IR290 dose. The fume hood lighting, delivering 1.1 lx at the sample position, induced a dose loss of less than 5 % in quartz OSL and K-rich feldspar IR50 doses after 24 h of exposure, with no measurable effect on their pIR-IR290 dose. As light exposure during sample preparation is usually less than 24 h, we conclude that our lighting setting is suitable for luminescence dating darkrooms; it is simple, inexpensive to build, and durable.

Testing infrared radiofluorescence dating on polymineral fine-grains from the Luochuan loess-palaeosol sequence, Chinese loess plateau

In the past infrared radiofluorescence (IR-RF) dating has been focused on coarse-grain potassium feldspar (K-feldspar). However, polymineral fine-grains (4–11 μm) have proven to be successful dosimeters when dating using conventional infrared stimulated luminescence (IRSL). In this study, we investigated the potential of IR-RF signals generated from polymineral fine-grains for dating on 6 loess samples (∼30–480 ka) from the well documented Luochuan loess-palaeosol sequence on the Chinese Loess Plateau. Both the natural and regenerated IR-RF signals from the polymineral fine-grains were uncharacteristically flat with little or no dynamic range using either a bleaching duration of 1500 s or 20000 s between the measurements. X-ray fluorescence (XRF) analyses showed that the polymineral fine-grains were dominated by quartz and Na-feldspars. K-feldspar and Na-feldspar mid-grain (38–63 μm) sample sets were further prepared, measured and compared. The IR-RF signals from the K-feldspar mid-grains exhibited the characteristic exponentially decaying signal, while the IR-RF signals from the Na-feldspar mid-grains were flat with little dynamic range, indicating that the Na-feldspar dominates the polymineral fine-grain IR-RF signal. The polymineral fine-grain ages (both bleaching settings) were consistent with reference ages up to 300 ka (∼1000 Gy), however, due to the flat nature of the curves the uncertainties were large. The consistency of the results using the two bleaching durations indicates that the bleaching duration has a less significant role in the IR-RF dating with polymineral fine-grains than in the coarse grains. Of the mid-grain ages, the IR-RF ages of Na-feldspar mid-grains were consistent with the reference ages up to 360 ka (∼1200 Gy) while those of the K-feldspar mid-grains were consistent with the reference ages up to 200 ka (∼600 Gy). Dose recovery tests were undertaken on all samples, however, where the dose recovery ratios were considered the most successful (K-feldspar mid-grains) the dating results were the least successful, suggesting that dose recovery tests in this way may be a less useful predictor of the dating performance of the IR-RF dating. IR-RF dating of polymineral fine-grains was possible up to 300 ka for Chinese loess, despite the uncharacteristically flat signals.

Reconstraining the Quaternary glacial history of Lahaul Himalaya, northern India

The study reports new progress in the glacial chronology from new sites of the Chandrabhaga basin (CBB), in the transition between the monsoon-dominated Pir-Panjal and westerly-dominated Trans-Himalaya, in Lahaul Himalaya, northern India. In Lahaul, asynchronous timing and extent of late Quaternary glaciation have been reported (Owen et al., 1996, 1997, 2001; Eugster et al., 2016). The established oldest and most extensive Chandra glacial stage remains undated and speculative. We reconstrain the late Quaternary glacial history of the CBB using geomorphological mapping, Infrared Stimulated Luminescence (IRSL), and 10Be Terrestrial Cosmogenic Nuclide (TCN) surface exposure dating. Four local glacial stages, the Chandra, Batal, Dali, and Mayar, are dated to 152 ± 37 ka, 43 ± 3 ka, 21 ± 2 ka, and Little Ice Age (LIA), respectively. The Chandra glacial stage occurred during the late Marine Isotope Stage 6 (MIS 6; 186 ± 30 – 113 ± 10 ka), characterized by thick lacustrine deposits, rock benches, and ice-polished bedrock along the trunk valleys. We provide the first account of the numerical dating for the much-awaited timing of the oldest Chandra glacial stage (Local Last Glacial Maxima; LLGM) in the region (Owen et al., 1996, 1997, 2001). The LLGM in the CBB is much older than previously thought, consistent with some north-western Himalayan glacial records (Owen et al., 2006; Dortch et al., 2010; Hedrick et al., 2011; Orr et al., 2017, 2018). The Batal glacial stage occurred during the early MIS 3 and is dated from 47 ± 2 to 41 ± 2 ka, represented by the thick lacustrine deposits and impressive terraces. The Dali glacial stage occurred during the Global Last Glacial Maxima (GLGM), characterized by a series of latero-frontal recession moraines, and is dated from 33 ± 3 to 13 ± 1 ka. The Mayar advance is characterized by confined tributary valley glaciers, possibly linked to the LIA advance reported in the Kulti valley (Saha et al., 2019). The equilibrium line altitude (ELA) rose by ∼486 m from the Chandra stage to the present day. Reconstructed ELA altitudes and glacial landforms demonstrate that the glaciations have become progressively less extensive through time for this part of the western Himalayas. The change of glaciation pattern during the later part of the Quaternary is like other regions of the orogen, such pattern of glaciation reflects regional climatic forcing.

Improved separation of quartz optically stimulated luminescence from a mixed sample using pulsed green light

In the luminescence dating of samples containing both quartz and feldspar (e.g. fine silt, or unseparated rock), the infra-red stimulated luminescence (IRSL) from feldspar is most often used, even though the luminescence characteristics of the OSL from quartz are better understood, and quartz OSL is known to be more stable than feldspar IRSL and more readily reset when exposed to daylight. Unfortunately, in almost all unseparated samples giving both quartz and feldspar luminescence signals, the feldspar OSL (stimulated by blue or green wavelengths) intensity is similar to, or greater than, that from quartz. Separation of quartz and feldspar signals has been achieved before using prior IR and/or pulsed visible light stimulation. This study investigates whether using pulsed green stimulation after IR stimulation gives better discrimination in favour of quartz optically stimulated luminescence (OSL) than using post-IR pulsed blue stimulation, by using the luminescence response of single mineral rocks (quartzite, potassium feldspar) at various temperatures. The results presented here support the view that pulsed blue and pulsed green stimulation of quartz (quartzite or calibration quartz grains) both excite charge to the conduction band, resulting in only a minor dependence on the temperature of the blue or green stimulation. We also confirm that IR depletes the quartz OSL signal only if undertaken at elevated temperature (>125 °C). In contrast, all 3 light sources can result in luminescence from potassium-rich feldspar, but the post-infrared pulsed blue light stimulated luminescence (post-IR PBSL) signal is significantly less dependent on the prior IR stimulation temperature than the post-infrared pulsed green light stimulated luminescence (post-IR PGSL) signal. This is presumably because green stimulation excites mainly into the band-tails. As a consequence, it is shown that the contribution of feldspar OSL to pulsed-green light stimulated luminescence (PGSL) is reduced more by a prior IR stimulation at elevated temperature, than the corresponding pulsed-blue light stimulated luminescence (PBSL). These results are consistent with the band models used to describe the origins of quartz and feldspar luminescence proposed by previous studies. We conclude that the post-IR PGSL provide better discrimination in favour of quartz OSL than does the corresponding post-IR PBSL, and that this should be taken advantage of in future studies on samples with mixed sources of luminescence.

Development of a hyper-avulsive river course during the Holocene on the Himalayan frontal plains

The rivers flowing over the Quaternary foreland plains of the Himalayas embody a history of hyper-avulsiveness. The present study is an attempt to identify a major flow trajectory of the Torsa River and the dynamics of the major flow path during the Holocene. This study is focused on identifying the major distributive system of the Torsa River, active during the Holocene and preceding known historical palaeochannels, using geomorphic and sedimentary archives of the floodplain on the foreland part of the eastern Himalayas. Satellite image processing, sediment analysis from trenches and cores, geochemical and paleocurrent analysis along with the determination of the age of deposits using the Infrared Stimulated Luminescence (IRSL) dating technique were used to identify paleochannels and validate the findings. Moreover, the sequence of channel succession and major avulsion events was also identified from the facies reconstruction and stratigraphy of fluvial depositions. The oscillatory nature of the river is well preserved within the floodplain stratigraphy in the form of lenses of channel deposits intercalated with proximal floodplain depositions. A total of three avulsion events were found between 1.6 ± 0.1 ka and 0.9 ± 0.1 ka where the latest significant channel switching occurred between 1.14 ± 0.1 ka and 0.9 ± 0.1 ka within the distributive system identified in this study and an eastern branch of the fluvial system. The newly identified palaeo-flow trajectory of the system can be utilised for water resource management and the avulsion regime may be useful for understanding future flow oscillations within the river basin.

General order kinetics model for OSL rock surface exposure dating

Dating of rock surface using optically stimulated luminescence (OSL) is an emerging tool to estimate exposure age and post exposure erosion rates. The present study points out the lacuna in the mathematical model that is used for this method. So far, all existing research, use first order kinetics (FOK) model. The FOK model predicts an exponential decay of OSL signal of polymineral rock with sunlight exposure, which is contrary to the observation. The non-exponential decay of OSL signal, more precisely infrared stimulated luminescence (IRSL) of feldspar, can be better explained by general order kinetics (GOK). Thus, we propose a new GOK model for OSL surface exposure dating. Present theoretical study shows, for FOK model the OSL (IRSL) depth profile propagates faster with time of light exposure than actual. Consequently, the FOK model predicts lower exposure age. The propagation of OSL profile with time depends on order of kinetics of the GOK model. We demonstrate how the order of kinetics can be constrained through laboratory bleaching experiment. The impact of the GOK model on exposure age and upper age limit, for different order of kinetics are presented. We apply this new GOK model on experimental data, available in the literature (Luo et al. in Geophysical Research Letter 49: e2022GL099526, 2022), of OSL depth profile on exposed fault scarp and reevaluate the exposure ages for different order of kinetics to validate the GOK model. We conclude that the GOK model better explains the IRSL of feldspar than the FOK model and should be preferred for OSL rock surface dating.

Pliocene–Pleistocene hydrology and pluvial lake during Marine Isotope Stages 5a and 4, Deep Springs Valley, western Great Basin, Inyo County, California

AbstractDeep Springs Valley (DSV) is a hydrologically isolated valley between the White and Inyo mountains that is commonly excluded from regional paleohydrology and paleoclimatology. Previous studies showed that uplift of Deep Springs ridge (informal name) by the Deep Springs fault defeated streams crossing DSV and hydrologically isolated the valley sometime after eruption of the Pleistocene Bishop Tuff (0.772 Ma). Here, we present tephrochronology and clast counts that reaffirms interruption of the Pliocene–Pleistocene hydrology and formation of DSV during the Pleistocene. Paleontology and infrared stimulated luminescence (IRSL) dates indicate a freshwater lake inundated Deep Springs Valley from ca. 83–61 ka or during Late Pleistocene Marine Isotope Stages 5a (MIS 5a; ca. 82 ka peak) and 4 (MIS 4; ca. 71–57 ka). The age of pluvial Deep Springs Lake coincides with pluvial lakes in Owens Valley and Columbus Salt Marsh and documents greater effective precipitation in southwestern North America during MIS 5a and MIS 4. In addition, we hypothesize that Deep Springs Lake was a balanced-fill lake that overflowed into Eureka Valley via the Soldier Pass wind gap during MIS 5a and MIS 4. DSV hydrology has implications for dispersal and endemism of the Deep Springs black toad (Anaxyrus exsul).

Luminescence dating of anthropogenic deposits from Tall Zarʿa in the Jordan Valley

AbstractThis study uses quartz‐based optically stimulated luminescence dating to determine when a massive fortification wall (W11186) was constructed in the archaeological site of Tall Zarʿa in the Jordan Valley. A total of 11 samples of sediments were taken from a trench on the north side of the wall (extramuros). The extracted quartz grains had good luminescence characteristics and were identified as well bleached by comparison with feldspar infrared‐stimulated luminescence (IRSL) ages. The optical ages showed that the deposition against the wall occurred in two different periods. The first was around 3.20 ± 0.07 ka ago (Iron Age), and the second was around 2.28 ± 0.08 ka (Hellenistic period). Human activity was evident because of the intermixing of cultural material with the presumed naturally deposited units.

Rapid active thrust faulting at the northern Alaska Range front

AbstractPlate convergence rates strongly influence seismicity and mountain building inboard of convergent margins, but the distribution and kinematics of structures accommodating farfield convergence can be elusive. In interior Alaska, Yakutat microplate convergence drives late Pleistocene–recent right slip on the Denali fault, but westward-decreasing slip rates leave substantial residual Yakutat motion unaccounted for. Here, we show that Northern Foothills thrust slip beneath the northern Alaska Range absorbs a modern 4.4 mm/yr geodetic velocity gradient equivalent to ~78% of the 5.6 mm/yr residual Yakutat convergence along the central Denali fault. Infrared-stimulated luminescence ages of strath terrace deposits (67–4 ka; six sites) quantify Totatlanika River bedrock incision across the 1947 Mw 7.1 thrust earthquake epicentral region. Incision rates increase abruptly from &amp;lt;1 mm/yr to 4.8–5.6 mm/yr above the blind thrust tip near the range front. Rapid slip at 6.7 mm/yr on a steep thrust ramp beneath the northern Alaska Range front accommodates the geodetic gradient, drives rock uplift at rates matching measured incision rates, and implies that large earthquakes like the 1947 event may recur with 500–1400 yr frequency. Results illuminate focused seismogenic strain inboard of a complex convergent margin and prompt reevaluation of Alaska’s neotectonic framework.

Comparison of feldspar dating protocols for loess samples older than 70 ka from the Tianshan Mountains, arid central Asia

Previous studies have demonstrated that quartz optically stimulated luminescence (OSL) dating has limitations for samples older than the last glaciation. However, infrared stimulated luminescence (IRSL) from K-feldspar can be applied beyond this limit if the problem of anomalous fading can be overcome. Elevated temperature stimulated IRSL signals (pIRIR) have shown great potential for minimizing the underestimation. In this study, we compared three commonly applied protocols (pIR50IR290, pIR200IR290, MET-pIRIR) for the same set of loess samples from the Tianshan Mountains in arid central Asia (ACA). For loess samples in the 70–130 ka age range (i.e., De values in the range of 200–400 Gy), pIR200IR290 and MET-pIRIR could both be used for dating, while a varying degree of underestimation occurred for the pIR50IR290 dating protocol. For samples older than 130 ka (i.e., De values in the range of 400–700 Gy), the MET-pIRIR250 signal was the most suitable.

Potential impacts of chemical weathering on feldspar luminescence dating properties

Abstract. Chemical weathering alters the chemical composition of mineral grains. As a result, trapped-charge dating signals of primary silicates may be progressively modified. In this study, we treated three feldspar specimens to understand the effect of proton- and ligand-promoted dissolution on their luminescence properties. We conducted kinetic experiments over 720 h using two solutions: (1) oxalic acid (pH 3, 20 ∘C), an organic acid with chelating abilities, and (2) aqua regia (pH &lt; 1, 40 ∘C), a mixture of strong acids creating aggressive acid hydrolysis conditions. These two solutions were chosen to provoke, on laboratory timescales, some of the changes that may occur on geological timescales as minerals weather in nature. The effect of the extracting solutions on mineral dissolution was investigated by monitoring the concentration of dissolved elements, while changes in feldspar surface morphology were assessed by scanning electron microscopy (SEM). Subsequent changes in feldspar luminescence in the near-UV (∼ 340 nm) and blue (∼ 410 nm) thermoluminescence (TL) and infrared stimulated luminescence (IRSL) emission bands were assessed at the multi- and/or single-grain levels to gain insight into the emission spectra, dose response, saturation, and anomalous fading characteristics of the feldspars. In all experiments, only minor feldspar dissolution was observed after 720 h. In general, aqua regia, the more chemically aggressive solution, had a larger effect on feldspar dissolution compared to that of oxalic acid. Additionally, our results showed that although the TL and IRSL intensities changed slightly with increasing artificial weathering time, the feldspar luminescence properties were otherwise unmodified. This suggests that chemical alteration of feldspar surfaces may not affect luminescence dating signals obtained from natural samples.

Sedimentary characteristics and formation of riverine source bordering dunes in a humid region: an example from the lower reaches of Kiso River, central Japan

Riverine source bordering dunes are formed by the interaction of fluvial and aeolian processes. Even in humid regions such as central Japan, small-scale, elongated aeolian dunes parallel to river channels occur intermittently; a typical example is identified where sand bars had formed along the left bank of the lower reaches of Kiso River. This paper presents the sedimentary characteristics and luminescence chronology of the aeolian dunes along the Kiso River. The sand constituting dunes is well-sorted, medium-grained and the grain size shows little variation with depth. The sand would be supplied from the riverbed via the bars by the strong west-northwesterly to westerly winds promoted by the monsoon in the dry winter when the water level of the Kiso River drops significantly. Fading corrected infrared-stimulated luminescence (IR50) dating suggests that the dunes occurred and grew rapidly upward after about 600–700 yr ago. Increased sediment yield caused by human activities such as deforestation in the drainage basin, and the resulting increase in sediment supply to the lower reaches may have promoted the formation of dunes. However, with the construction of continuous levees, the reduced sediment supply related to dam construction, and the lowering of the riverbed, the connectivity between sand bars and dunes declined, and most of the dunes appear to have been stable for the past century. Fluvial sand supply influenced by human activities as well as strong winds during the dry season plays a crucial role in the formation of riverine source bordering dunes in humid regions.