Infrared Stimulated Luminescence Dating Research Articles

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 >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.

한반도 서해안 고창 하전리 일대 제4기 후기 해안단구의 발달

This study investigates the distribution and developmental characteristics of the late Quaternary marine terraces in Hajeon-ri, Gochang-gun in the western coast of the Korean Peninsula. The altitudes of the first and second terraces are 8~13m and 17~23m, respectively, from a regional high sea-level. As a result of OSL(Optically Stimulated Luminescence) and IRSL(Infra-red stimulated Luminescence) dating, the depositional ages of the second marine terrace are estimated as 189.53±5.19ka BP, indicating that the second terrace was formed during the penultimate interglacial period (MIS 7). The silt deposits overlying the first and second terrace surfaces are likely to have originated from paleo-tidal flat sediments based on their depositional facies and the results of geochemical analysis.

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 14 C 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 IRSL 225 (pIR IRSL 225 ) and IRSL 50 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 IRSL 225 signal of K-feldspars, and the late Holocene, geoarchaeological ages using the IRSL 50 signal.

Coarse-grained K-rich feldspar and fine-grained polymineral IRSL dating of loess-palaeosol from the Chinese Loess Plateau: A comparison

In this study, the characteristics of infrared stimulated luminescence (IRSL) signals from coarse-grained (63–100 μm, CG) K-feldspar and fine-grained (4–11 μm, FG) polymineral fractions was compared using the Chinese loess/palaeosol samples from the Luochuan profile. The pIRIR 50, 225 and pIRIR 200, 290 protocols (pIRIR: post-IR IRSL. The subscript shows stimulation temperatures for the IR and pIRIR signals) were used. Natural signal intensities of eleven samples were used to construct the natural dose-response curve (DRC) for each signal. The laboratory and simulated-natural DRCs for each signal from the CG K-feldspar and FG polymineral fractions were constructed and were compared with the natural DRC. The natural DRCs were broadly consistent for the two pIRIR and the IR 200 signals for both fractions. The characteristic saturation dose ( D 0 ) of the natural DRCs for the pIRIR signals from the CG K-feldspar tended to be smaller than those from the FG polymineral fraction. Conversely, the D 0 s of the laboratory DRCs for all the signals from the CG K-feldspar were larger than those from the FG polymineral fraction. The ratio of simulated-natural DRC over natural DRC (N sim /N) was able to successfully determine the fading over- or under-correction tendencies for different signals and dose regions.

Testing the Synchronicity of Splay-Fault Ruptures in Carson Valley, Nevada, United States

ABSTRACTThe Carson City and Indian Hills faults in Carson City, Nevada, splay northeastward from the major range-bounding Genoa fault. Each splay is part of the Carson range fault system that extends nearly 100 km northward from near Markleeville, California, to Reno, Nevada. Stratigraphic and structural relationships exposed in paleoseismic excavations across the two faults yield a record of ground-rupturing earthquakes. The most recent on the Carson City fault occurred around 473–311 B.P., with the two penultimate events between 17.9 and 8.1 ka. Two trench exposures across the Indian Hills fault record the most recent earthquake displacement after ∼900 yr, preceded by a penultimate surface rupture ≥∼10,000, based on radiocarbon and infrared-stimulated luminescence dating of exposed sediments. The age estimates allow that the Carson City and Indian Hills faults ruptured simultaneously with a previously reported large earthquake on the Genoa fault ∼514–448 B.P. Similar synchronicity of rupture is not observed in the record of penultimate events. Penultimate ages of ruptures on the Carson City and Indian Hills faults are several thousand years older than that of the Genoa fault from which they splay. Together, these observations imply a variability in rupture moment through time, demonstrating the importance of considering multi-fault rupture models for seismic hazard analyses.

Exploring the use of a low temperature preheat in IRSL dating of feldspar in Beringian archaeological contexts

A new luminescence dating protocol was developed to circumvent the problem of thermal transfer and poor thermal stability of Infrared Stimulated Luminescence (IRSL) of samples from late glacial loess sediments in Central Alaska, USA. This new protocol is proposed as an alternative to routine procedures for which scattered and erratic results were obtained using standard IRSL and post-IR IRSL protocols on loess samples from the McDonald Creek archaeological site.The difficulty to date Alaskan loess has been acknowledged in the past, but the reasons for this phenomenon have not been clearly identified. This difficulty is even greater for young samples, as shown in this study. It is suggested here that the particular mineralogical composition of the Central Alaskan loess can be related to problematic luminescence behaviour.To overcome problematic results, we developed a Low Preheat IRSL (LPH-IRSL) protocol. This protocol is minimally affected by the presence of other minerals than K-feldspars in the samples, such as albite, muscovite and clinochlorite, which can be very difficult to eliminate during the preparation steps prior to IRSL measurements. Dose recovery experiments and multiple other tests indicate that a protocol with low preheat temperature yields the best results in this specific context. Thermally transferred luminescence induced during the measurement is kept at a minimal level. Consequently, considering independent age controls available from radiocarbon, equivalent doses are successfully determined, their distribution is narrow, and the g-value has low scatter. This protocol has great potential for dating polymineral samples, whether it is silt-sized sediments like loess, fine-grained like clay and micro-samples like art pieces, common in archaeological contexts.The chronological results obtained for this project suggest a human occupation of the area during the Late Pleistocene to mid-Holocene period, which is in excellent agreement with preliminary radiocarbon chronology obtained during site testing and also with the regional archaeological framework.

The Chronostratigraphy of the Aurignacian in the Northern Carpathian Basin Based on New Chronometric/Archeological Data from Se\u0148a I (Eastern Slovakia)

The northern Carpathian Basin has important geological, paleoenvironmental, and archeological records that are key to our understanding of the first modern human occupation of Europe. However, the nature and timing of hominin settlements in the region during the Late Pleistocene remain poorly understood. New fieldwork at Seňa I, Slovakia, has identified the only known stratified open-air Aurignacian site in the region and assigned the assemblage to at least 33.5 ± 2.4 ka ago through infrared-stimulated luminescence dating. Additionally, new archeological and geoscientific data are presented. This paper discusses the Seňa I findings in the context of the regional archeological record and shows how they contribute to the establishment of clear time constraints for the Aurignacian in eastern central Europe.

Age of Obsidian Butte in Imperial County, California, Through Infrared Stimulated Luminescence Dating of Potassium Feldspar from Tuffaceous Sediment

ABSTRACTObsidian Butte is an important lithic source for obsidian and artifacts from this location are distributed across archaeological sites in southern California and adjacent parts of northern Mexico. For this study, we used drill core material for infrared stimulated luminescence (IRSL) dating of potassium feldspar extracted from tuffaceous sediment directly underlying obsidian-bearing lava from Obsidian Butte. In addition, a core sample from lacustrine sediment below the tuffaceous sedimentary unit was dated by the same method. Stratigraphically consistent ages between 2.51 ± 0.32 kilo-annum (ka) (1 sigma uncertainty; average of two tuffaceous sediment samples) and 4.39 ± 0.49 ka (lacustrine sediment sample) were obtained. This constrains the eruption and earliest availability of the lithic resource of Obsidian Butte to 490 BCE (with uncertainty limits of ±320 years at ∼68 percent confidence, and ±640 years at ∼95 percent confidence). Since then, it would have been accessible during intermittent desiccation of Lake Cahuilla. This new date redefines obsidian from Obsidian Butte as a marker for the late prehistoric period.

Post-IR IRSL dating of K-feldspar from last interglacial marine terrace deposits on the Kamikita coastal plain, northeastern Japan

To establish a suitable luminescence dating protocol for marine terrace deposits in Japan, we tested the applicability of K-feldspar post-infrared (IR) infrared stimulated luminescence (IRSL) (pIRIR) dating using a marine isotope stage (MIS) 5e terrace deposit from the Kamikita coastal plain (NE Japan), where independent age control from a tephra is available. One of the most commonly used pIRIR signals, measured at 290°C with the first IR stimulation temperature at 50°C (pIRIR<sub>50/290</sub>), faded with a mean g<sub>2days</sub> value of 1.94 ± 0.19%/decade. In contrast, the pIRIR signal with a higher first IR stimulation temperature of 200°C (pIRIR<sub>200/290</sub>) had a much lower fading rate (g<sub>2days</sub> = 0.16 ± 0.49%/decade). The average fading-uncorrected and -corrected pIRIR<sub>200/290</sub> ages of MIS 5e subtidal sediments obtained from two sampling sites were 126 ± 3 ka and 132 ± 2 ka, which is in good agreement with the independent age control. We conclude that is it is now possible to use pIRIR protocol to estimate the ages of not only marine terraces formed during MIS 5 substages (5a, 5c) but also of older marine terraces, for which age evidence is limited.

Progradation of a Beach Ridge Plain between 5000 and 4000 Years BP Inferred from Luminescence Dating, Coquimbo Bay, Chile

ABSTRACT Hart, E.A.; Stapor, F.W.; Enrique Novoa Jerez, J., and Sutherland, C.J., 2017. Progradation of a beach ridge plain between 5000 and 4000 years BP inferred from luminescence dating, Coquimbo Bay, Chile. Luminescence dating was carried out to determine the depositional history of a 2-km-wide, shore-parallel, beach ridge sequence at Coquimbo Bay, Chile, for which no direct dating had previously been done. The beach ridge plain at Coquimbo Bay represents one of the most extensive Holocene depositional features preserved along the Pacific Coast of South America. Both optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) dates indicate a rapid period of beach ridge progradation lasting approximately 1000 years at an average rate of 2 m y−1. However, based on previously reported luminescence deficiencies of geologically “young” quartz, it is proposed that IRSL dates are more representative of the actual depositional age of the beach ridges. These IRSL ages indicate that the...

Quartz OSL and K-feldspar post-IR IRSL dating of sand accumulation in the Lower Liao Plain (Liaoning, NE China)

The timing of the formation of extensively distributed sand dunes in the Bohai coastal area and its forcing factors are poorly understood. In this study, the chronology of a well-preserved sand dune located in Panjin Forest Park (PJ) in the Lower Liao Plain (LLP) is investigated using quartz optically stimulated luminescence (OSL) and K-feldspar postinfrared (IR) infrared stimulated luminescence (IRSL) (pIRIR) dating. For the pIRIR measurements, the combination of preheating at 180°C and pIRIR stimulation at 150°C (pIRIR<sub>150</sub>) is exploited. The quartz results show that the sand dune accumulated from <i>c</i>. 120 a (1890 AD) to c. 70 a (1940 AD) before present, and the underlying sandy soil sediments deposited from <i>c</i>. 5.0 ka to <i>c</i>. 0.13 ka as marsh sediment after the sea level highstand since the mid-Holocene. From the evidence in historical coastline records, the PJ sand dune is an inland sand dune and not a coastal sand dune. Based on further information of climate and temperature change after the Little Ice Age (LIA) and human activity in northeastern China, we conclude that the PJ sand dune accumulation was very likely impacted by the immigrants and land reclamation at the end of Qing dynasty. The fading corrected IR<sub>50</sub> ages, the apparent and fading corrected pIRIR<sub>150</sub> ages are consistent with quartz ages for two sandy soil samples but overestimate those for six sand samples. The overestimation of the feldspar ages is derived from the residual signal which has not been bleached before burial. The offset obtained from the difference between the quartz OSL and the feldspar pIRIR<sub>150</sub> ages are ~20–160 a (predicted residual dose: ~0.08–0.60 Gy), whereas the measured residual dose after bleaching 4 h in a solar simulator yielded age overestimation of ~10–40 a (~0.05–0.16 Gy). The age discrepancy calculated from the predicted residual was larger than those obtained from the laboratory measured residuals. We conclude that the pIRIR<sub>150</sub> of aeolian sediment is applicable for samples older than ~1000 years where the effect of the residual dose become negligible.

Yedoma Ice Complex of the Buor Khaya Peninsula (southern Laptev Sea)

Abstract. The composition of perennially frozen deposits holds information on the palaeo-environment during and following deposition. In this study, we investigate late Pleistocene permafrost at the western coast of the Buor Khaya Peninsula in the south-central Laptev Sea (Siberia), namely the prominent eastern Siberian Yedoma Ice Complex (IC). Two Yedoma IC exposures and one drill core were studied for cryolithological (i.e. ice and sediment features), geochemical, and geochronological parameters. Borehole temperatures were measured for 3 years to capture the current thermal state of permafrost. The studied sequences were composed of ice-oversaturated silts and fine-grained sands with considerable amounts of organic matter (0.2 to 24 wt %). Syngenetic ice wedges intersect the frozen deposits. The deposition of the Yedoma IC, as revealed by radiocarbon dates of sedimentary organic matter, took place between 54.1 and 30.1 kyr BP. Continued Yedoma IC deposition until about 14.7 kyr BP is shown by dates from organic matter preserved in ice-wedge ice. For the lowermost and oldest Yedoma IC part, infrared-stimulated luminescence dates on feldspar show deposition ages between 51.1 ± 4.9 and 44.2 ± 3.6 kyr BP. End-member modelling was applied to grain-size-distribution data to determined sedimentation processes during Yedoma IC formation. Three to five robust end-members were detected within Yedoma IC deposits, which we interpret as different modes of primary and reworked unconfined alluvial slope and fan deposition as well as of localized eolian and fluvial sediment, which is overprinted by in situ frost weathering. The cryolithological inventory of the Yedoma IC preserved on the Buor Khaya Peninsula is closely related to the results of other IC studies, for example, to the west on the Bykovsky Peninsula, where formation time (mainly during the late Pleistocene marine isotope stages (MIS) 3 interstadial) and formation conditions were similar. Local freezing conditions on Buor Khaya, however, differed and created solute-enriched (salty) and isotopically light pore water pointing to a small talik layer and thaw-bulb freezing after deposition. Due to intense coastal erosion, the biogeochemical signature of the studied Yedoma IC represents the terrestrial end-member, and is closely related to organic matter currently being deposited in the marine realm of the Laptev Sea shelf.

Optical dating of St. Lawrence Iroquoian ceramics from the Mailhot-Curran site, southern Québec

Infrared-stimulated luminescence dating (IRSL) was applied on pottery sherds from the Mailhot-Curran archaeological site (BgFn-2), a Late Woodland period village located in the Saint-Anicet region, southern Québec (Canada). This site witnessed the presence of St. Lawrence Iroquoians and is thought to have been occupied roughly 500 years ago. The main goal of this study is to chronologically constrain the occupation of this site in order to establish a fine chronological sequence for the occupations of various sites found in this area. The IRSL is used to complement previous dating methods used for Mailhot-Curran (radiocarbon and seriation of the archaeological remains).Dating results are reported for ten samples of local ceramics made from Quaternary Champlain Sea clay. Luminescence dating on fine grains was preferentially used, since feldspar luminescence typically emit a decent luminescence signal. Although the latter was rather dim, anomalous fading was measured and luminescence ages were successfully corrected. It is therefore possible to validate the occupation age of this site.

Fluvial tufa evidence of Late Pleistocene wet intervals from Santa Barbara, California, U.S.A.

Past pluvials in the western United States provide valuable context for understanding regional hydroclimate variability. Here we report evidence of conditions substantially wetter than today from fluvial tufa deposits located near Zaca Lake, Santa Barbara County, California that have been dated by radiocarbon ( 14 C) and Infra-Red Stimulated Luminescence (IRSL). Two successions of tufa deposition occur within a small catchment that drains Miocene Monterey Formation bedrock : 1) a fluvial deposit (0–0.5 m thick, 200 m in extent) that formed along a narrow valley below a modern spring, and 2) a perched deposit ~ 10 m higher (2 m thick, 15 m in extent). IRSL and radiocarbon dating of the perched carbonates suggest at least two episodes of carbonate growth: one at 19.4 ± 2.4 (1σ) through 17.8 ± 2.8 (1σ) ka and another at 11.9 ± 1.5 (1σ) ka verified with a charcoal 14 C age of 10.95 ± 0.12 (2σ) cal ka BP. The relationship between the perched and fluvial spring deposits is inferred to represent a drop in the water table of more than 10 m associated with a transition from a wet climate in the late glacial to a dry Holocene today. The wet period indicated by the perched tufa deposit between 19.4 and 17.8 ka is relatively consistent with other California climate records both north and south of Zaca Lake. However, tufa growth ca. 12 to 11 ka demonstrates wet conditions occurred as far south as Zaca Lake during the Younger Dryas event, in contrast to climate records farther south in Lake Elsinore that indicate a drying trend through this interval. A small shift north in the average position of the winter season storm track could explain wet winters at Zaca while at the same time generating dry winters at Lake Elsinore, ~ 275 km southwest of Zaca. If true, these data indicate that rather small latitudinal shifts in the average winter season storm track can produce large changes in regional hydroclimate. • Spring-associated carbonates (tufa) in Santa Barbara, CA were dated via 14 C and IRSL. • Fossil perched tufa ~ 10 m above a modern spring indicates past pluvial conditions. • IRSL ages suggest tufa growth at 19.4 ± 2.4 to 17.8 ± 2.8 (1σ) ka and 11.9 ± 1.5 (1σ) ka. • 14 C from embedded charcoal suggests tufa deposition at 10.95 ± 0.12 (2σ) cal ka BP. • IRSL and 14 C of perched tufa provide terrestrial evidence of Late Pleistocene pluvial.

Review and assessment of the potential of post-IR IRSL dating methods to circumvent the problem of anomalous fading in feldspar luminescence

Quartz has been the main mineral used for optically stimulated luminescence (OSL) dating of sediments over the last decade. The quartz OSL signal, however, has been shown to saturate at relatively low doses of ∼200–400 Gy, making it difficult to be used for dating beyond about 200 thou-sand years (ka), unless the environmental dose rate is low. The infrared stimulated luminescence (IRSL) from feldspars has been shown to continue to grow to higher dose levels than quartz OSL. The application of IRSL dating of feldspars, however, has long been hampered by the anomalous fading effect. Recent progress in understanding anomalous fading of the infrared stimulated luminescence (IRSL) signals in potassium-feldspar has led to the development of post-IR IRSL (pIRIR) protocols and also a multiple elevated temperature (MET) stimulation (MET-pIRIR) protocol. These procedures have raised the prospect of isolating a non-fading IRSL component for dating Quaternary deposits containing feldspars. In this study, we review the recent progress made on (1) overcoming anomalous fading of feldspar, and (2) the development of pIRIR dating techniques for feldspar. The potential and problems associated with these methods are discussed.

Testing a model of alluvial deposition in the Middle Son Valley, Madhya Pradesh, India — IRSL dating of terraced alluvial sediments and implications for archaeological surveys and palaeoclimatic reconstructions

Over the past three decades, the Middle Son Valley, Madhya Pradesh, India has been the focus of archaeological, geological, and palaeoenvironmental investigations that aim to reconstruct regional climate changes in the Late Pleistocene and to understand the effects of the ∼74 ka Toba super-eruption on ecosystems and human populations in northern India. The most recently published model of alluvial deposition for the Middle Son Valley subdivides its alluvium into five stratigraphic formations, each associated with a specific artefact assemblage. In this study, new cross-valley topographic profiles, field observations and infrared stimulated luminescence (IRSL) age estimates are used to refine this model south of the Rehi–Son River confluence. These data not only provide insights into the fluvial history of the Son River and its response to changes in palaeoclimate, but will also inform future archaeological surveys by constraining the geomorphic context of surficial and excavated artefacts in the area.

Small aliquot and single grain IRSL and post-IR IRSL dating of fluvial and alluvial sediments from the Pativilca valley, Peru

Infrared stimulated luminescence (IRSL) and post-IR IRSL are applied to small aliquots and single grains to determine the equivalent dose (De) of eleven alluvial and fluvial sediment samples collected in the Pativilca valley, Central Peru at ca. 10°S latitude. Small aliquot De distributions are rather symmetric and display over-dispersion values between 15 and 46%. Small aliquot g-values range between 4 and 8% per decade for the IRSL and 1 and 2% per decade for the post-IR IRSL signal. The single grain De distributions are highly over-dispersed with some of them skewed to higher doses, implying partial bleaching; this is especially true for the post-IR IRSL. Measurements of a modern analog reveal that residuals due to partial bleaching are present in both the IRSL as well as the post-IR IRSL signal. The g-values of individual grains exhibit a wide range with high individual uncertainties and might contribute significantly to the spread of the single grain De values, at least for the IRSL data. Electron Microprobe Analysis performed on single grains reveal that a varying K-content can be excluded as the origin of over-dispersion. Final ages for the different approaches are calculated using the Central Age Model and the Minimum Age Model (MAM). The samples are grouped into well-beached, potentially well-bleached and partially bleached according to the evaluation of the single grain distributions and the agreement of age estimates between methods. The application of the MAM to the single grain data resulted in consistent age estimates for both the fading corrected IRSL and the post-IR IRSL ages, and suggests that both approaches are suitable for dating these samples.

Geomorphic evidence of recent activity along the Vodice thrust fault in the Ljubljana Basin (Slovenia) – a preliminary study

<p>We investigated two prominent, <strong><sup>~</sup></strong>E-W trending scarps in Quaternary sediments, located close to the town of Vodice in the Ljubljana Basin (central Slovenia). By using detailed geomorphological analysis of the scarps, field surveying, and structural observations of deformed Quaternary sediments, we conclude that the scarps are the surface expression of a N-dipping thrust fault that has been active during the Quaternary. From Optically Stimulated Luminescence and Infrared Stimulated Luminescence dating of deformed Quaternary sediments we estimate a slip rate of 0.1 to 0.3 mm a<sup>-1 </sup>in the last 133 ka. Using the published empirical fault-scaling relationships, we estimate that an earthquake of magnitude 5.9 to 6.5 may be expected on the Vodice thrust fault. The fault may, therefore, present a major seismic hazard for the densely populated and urbanised region of central Slovenia.</p>

Single‐Grain Luminescence Dating of Sediment Surrounding a Possible Late Pleistocene Artifact from the Wenas Creek Mammoth Site, Pacific Northwest, USA

Excavations at the Wenas Creek Mammoth Site yielded mammoth, bison, and two possible artifacts in a single colluvial stratum, with radiocarbon bone dates ∼17 ka. Eight infrared‐stimulated luminescence (IRSL) samples were collected to establish general ages of site strata, returning multi‐grain estimates consistent with stratigraphic integrity and the radiocarbon dates. Four additional IRSL samples were collected to estimate the depositional age of one artifact found in place. These produced a pooled total of 94 single‐grain estimates from near the artifact, 80% averaging 16.8 ± 0.9 ka, and 20% averaging 5.1 ± 0.5 ka. These results could be interpreted to demonstrate pre‐Clovis age artifact deposition consistent with the bone dates, or a mid to late Holocene intrusion into older deposits, possibly by bioturbation. The single‐grain IRSL dates do not provide proof of pre‐Clovis presence beyond reasonable doubt at this site, but do show that this technique is valuable in assessing the stratigraphic integrity needed for any such claim.

Na-rich feldspar as a luminescence dosimeter in infrared stimulated luminescence (IRSL) dating

Abstract One of the challenges in dating rock surfaces is the choice of the luminescence mineral. Although quartz is the preferred dosimeter in sediment dating, it is often not sufficiently sensitive when extracted from solid rocks. The intensity of signals from feldspars tends to be much less dependent on geological origin and erosion history, but the dosimetry of K-rich feldspar grains extracted from rocks is complicated because the internal dose rate is very dependent on the original feldspar grain size. The in situ grain size information is lost during the crushing process used to separate the grains for measurement. This latter problem does not apply to Na-rich feldspar because of the absence of internal radioactivity. The potential application of Na-rich feldspar as a luminescence dosimeter for the IRSL dating of rock surfaces is investigated using a variety of sediment samples from different geological settings for which independent age control is available. The blue and yellow luminescence emissions are measured for IR stimulation at 50 °C (IR 50 ), and post-IR IR stimulation at 290 °C (pIRIR 290 ). Thermal stability experiments imply that the corresponding signals in both emissions have comparable thermal stabilities and that all signals have similar recombination kinetics and are thermally stable over geological timescales. The IR 50 doses measured using blue and yellow emissions are similar to or lower than quartz doses while pIRIR 290 blue doses are higher than those from yellow emission and quartz doses. The fading rates measured for the IR 50 signals are ∼3%/decade larger than those measured for the pIRIR 290 signals in both yellow and blue emissions. Furthermore the average fading rates of both yellow signals are ∼3%/decade higher than the corresponding fading rates of the blue signals. However, there is no detectable correlation between fading rates and the measured D e values. The residual doses measured from the laboratory-bleached samples and a modern analogue suggest that the IR 50 signals in both blue and yellow emissions bleach to the same degree, as do the corresponding pIRIR 290 signals, and that there is no significant naturally-unbleachable residual dose observed using these signals. Neither anomalous fading nor incomplete bleaching explains the observed dose discrepancy between the two emissions. Eight uncorrected and fading-corrected ages are calculated for each sample based on all four signals, using the dose rate relevant to Na-rich feldspar extracts (i.e. ∼3% K). The IR 50 and pIRIR 290 blue ages were also calculated assuming a dose rate based on 12.5% internal K (i.e. assuming that the blue signals were mainly derived from contamination by K-rich feldspar). The latter pIRIR 290 blue ages are in agreement with the expected age control, raising the possibility that this signal originates mainly from K-rich feldspar contamination in our Na-rich fractions, and thus is not so useful in the luminescence dating of rock surfaces. On the other hand, the pIRIR 290 fading-corrected ages based on the yellow emission are consistent with the independent age controls; higher preheat and stimulation temperatures may result in more stable yellow signals from Na-rich feldspar extracts from rocks, and so reduce the size of the fading correction. We conclude that, because this signal avoids the dosimetry difficulties of K-rich feldspar extracts, it has considerable potential in the IRSL dating of rock surfaces.