Potassium-rich Feldspar Research Articles

The timing of the penultimate glaciation in the northern Alpine Foreland: new insights from luminescence dating

Only minimal age constraints are as yet available concerning the timing of the penultimate glaciation in the European Alps. Therefore, this study presents the results of different luminescence dating approaches, revealing the depositional ages of glaciofluvial sediments deposited in the Austrian Northern Alpine Foreland during the penultimate glaciation. To establish a robust numerical chronology we investigated 18 samples of mostly glaciofluvial origin using the optically stimulated luminescence (OSL) signal of quartz and the post-infrared infrared (pIRIR) stimulated luminescence signal at 225°C of potassium rich feldspar for the grain size of 100–200μm. By comparing the results gained from both analytical approaches, it was possible to discern between samples that were well bleached prior to deposition and samples for which the luminescence signals were not properly reset. The ages presented in this study suggest that the deposition of proglacial outwash deposits in the northern Alpine foreland associated with the penultimate glaciation is time equivalent with marine isotope stage (MIS) 6. Furthermore, our results imply relatively rapid ice decay in late MIS6 towards termination 2, which is consistent with previous studies dealing with the penultimate glaciation in the circum-alpine region. Although the dating results allow to chronologically discern between glacial and interglacial periods, a finer resolution on a stadial/interstadial level cannot unfortunately be obtained by the current state-of-the-art methods of luminescence dating as applied in this study.

Luminescence-based chronologies for Palaeolithic sites in the Nihewan Basin, northern China: First tests using newly developed optical dating procedures for potassium feldspar grains

The Nihewan Basin in northern China is a key region in East Asia for the study of early human evolution, owing to the abundance of Palaeolithic sites with ages spanning the entire Pleistocene. However, most of the sites assigned to the Middle to Late Pleistocene have not been dated or are poorly dated, due to the lack of suitable numerical dating techniques. Optically stimulated luminescence (OSL) dating of quartz grains is commonly restricted to deposits younger than ~200ka, but recent developments using the infrared stimulated luminescence (IRSL) emissions from grains of potassium-rich feldspar (K-feldspar) offer the potential to date Middle Pleistocene deposits using post-infrared IRSL (pIRIR) signals that do not suffer from ‘anomalous fading’. In this paper, we report the first archaeological applications of the recently developed pre-dose multiple elevated temperature pIRIR (pMET-pIRIR) procedures for K-feldspar, which we applied to the sedimentary deposits at one Lower Palaeolithic site (Donggutuo) and one putatively Middle Palaeolithic site (Motianling) in the Nihewan Basin. Equivalent dose (De) values were measured, and non-fading signals were identified, using single-aliquot (SAR) and multiple-aliquot (MAR) regenerative-dose pMET-pIRIR procedures. For a sample from Donggutuo expected to be in field saturation, the natural pMET-pIRIR signals were consistent with, or close, to the laboratory saturation levels only when the MAR procedure was used. For the samples from Motianling, however, both the SAR and MAR procedures could be applied and these yielded indistinguishable De estimates. Our study shows that De values of up to 1500Gy (or possibly 2000Gy) can be measured using pMET-pIRIR procedures, corresponding to ages of up to 500ka (or 650ka) for deposits with environmental dose rates of ~3Gy/ka, as is typical for this region. Our results also indicate that samples from a single study area (the Nihewan Basin) can respond differently to the same measurement conditions. As regards the archaeology of the Nihewan Basin, we date the upper part of the cultural layer at the Motianling site to 322±33ka and the underlying culturally sterile deposits to 370±50ka. These ages challenge the stratigraphic correlation of the stone artefacts to the Middle Palaeolithic and suggest that they should, instead, be assigned to the Lower Palaeolithic. Given this revised chronology, there is clearly a need to reassess the antiquity of other sites in the Nihewan Basin that have similarly been assigned previously to the Middle Palaeolithic. The pMET-pIRIR procedures tested in this paper show great promise as suitable chronometers for this task, and should be able to provide a timeline for human evolution and activities extending over the last half-million years in this key region of East Asia.

Luminescence dating of Weichselian interstadial sediments from the German Baltic Sea coast

A cliff outcrop called Kluckow, in the Baltic Sea area, with a (glacio-) fluvial to (glacio-) lacustrine succession, provides a unique opportunity to resolve uncertainties in the timing and extent of several poorly constrained Weichselian ice advances. Based on a detailed lithofacies analysis, we selected four sampling horizons for luminescence dating to determine a depositional chronology. We measured both coarse-grain quartz and potassium-rich feldspar for age determination using optically stimulated luminescence (OSL) and post-IR infrared stimulated luminescence (pIRIR). Furthermore we addressed potential problems such as incomplete bleaching and quartz saturation effects. The resulting luminescence-chronology, supported by one radiocarbon age, illustrates a depositional time interval of the investigated sequence between ∼62 and ∼22 ka. Within this sequence a mussel-bearing fluvial sand indicate interstadial climate conditions at approximately 46 ka. The upper part of the section is composed of a 4 m thick glaciolacustrine silty clay and an overlying glaciofluvial sand; the latter yielded an OSL age of ∼22 ka. Shortly after these sequences formed, the subsequent ice advance (indicated by the overlying till sheet) reached the study area. Based on our new chronology and lithofacies analysis, we conclude that the Scandinavian Ice Sheet did not reach the study area between ∼62 and ∼22 ka.

Radiotracer Experiments and Monte Carlo Simulations of Sodium Diffusion in Alkali Feldspar: Evidence against the Vacancy Mechanism

Self-diffusion of sodium perpendicular to (001) in a potassium-rich alkali feldspar singlecrystal has been studied by self-diffusion experiments and by Monte Carlo simulations. Sodium diffusivitieswere measured with the radiotracer technique using the 22Na isotope in a temperature intervalfrom 773 K to 1173 K. It was found that self-diffusion coefficients follow a linear Arrhenius relationwith the pre-exponential factor of 1:2 103 cm2/s and an activation enthalpy of 1:3 eV. To study correlationeffects in the monoclinic feldspar structure, a Monte Carlo method was applied assuming thatthe two cation species are randomly distributed on the common sublattice and are not influenced by thefixed sublattice of the silicate and aluminate anions. Correlation factors have been calculated assuminga vacancy mechanism and applying a developed four-frequency model for the nearest-neighborvacancy jumps on the alkali sublattice. Our findings strongly indicate that vacancy diffusion providesonly a minor contribution to sodium self-diffusion in potassium-rich feldspars.

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 (Lx/Tx), a higher saturation dose is observed for the sensitivity-uncorrected MET-pIRIR signals (Lx), 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, De values (1360 + 226/-167 Gy) broadly consistent with expected De (1550 ± 72 Gy) can be obtained using the sensitivity-uncorrected 300 °C MET-pIRIR signal. Our study suggests that a De value of about 1800 Gy may be the maximum dating limit of Chinese loess using the MAR pMET-pIRIR procedure.

Residual doses and sensitivity change of post IR IRSL signals from potassium feldspar under different bleaching conditions

The residual doses and sensitivity change for potassium-rich feldspar (K-feldspar) have been studied using the post-infrared infrared stimulated luminescence (pIRIR) and multi-elevated-temperature post-IR IRSL (MET-pIRIR) protocols. Laboratory simulated poorly-bleached and well-bleached samples were those K-feldspar grains bleached using a solar simulator for 10 minutes and 8 hours, respectively. The residual doses rise with stimulation temperature and time. The poorly-bleached sample has larger residual doses than the well-bleached sample, especially at high stimulation temperatures. The high-temperature pIRIR signals contain a large amount of hard-to-bleach signals. A decrease of luminescence sensitivity was observed after conducting a high-temperature-treatment in the measurement cycles. The sensitivity decreases significantly between the first and the second cycle. The extent of decrease in sensitivity shows a clear temperature trend. The higher the stimulation temperature of pIRIR signals is, the larger the sensitivity decreases. This decrease is more severe for the poorly-bleached sample than for the well-bleached sample, and could possibly lead to problems in sensitivity correction.

Yellow stimulated luminescence from potassium feldspar: Observations on its suitability for dating

Abstract Yellow stimulated luminescence (Y-OSL) is the light detected from potassium-rich feldspars at 410 nm under stimulation by a yellow light source emitting 590 nm. The investigation of this study aimed at understanding basic luminescence physics of Y-OSL in order to assess the suitability of the technique for dating. The Y-OSL signal properties tested were signal intensity, thermal assistance, thermal stability, sensitivity to daylight and the suitability of a single aliquot regenerative (SAR) protocol to be employed for equivalent dose (D e ) estimation. D e measurements were conducted on samples of Holocene, last glacial and Tertiary age. The tests were undertaken on sedimentary feldspar separates extracted from aeolian, fluvial and coastal deposits. Results from experiments show that the signal intensity increases by measuring Y-OSL at elevated temperature suggesting thermal assistance characteristics similar to infrared stimulated luminescence (IRSL). The yellow stimulated signal remains unaffected by preheat temperatures up to ∼200 °C suggesting higher thermal stability than the IRSL signal. The Y-OSL signal is less light sensitive than the IRSL signal and D e residuals obtained from modern samples are up to 7 Gy indicating suitability of the technique for ‘older’ and well-bleached sediments. The dose recovery tests successfully recovered the given dose if the specific light sensitivity of Y-OSL is taken into account. For every sample Y-OSL D e values obtained by a single aliquot regenerative dose protocol (SAR) are higher than those obtained by an IRSL SAR approach. From these results we infer high thermal stability and a minimal anomalous fading of the Y-OSL signal. We conclude that Y-OSL has a high potential to date Quaternary sediments that were sufficiently bleached in nature.

Luminescence dating of an Upper Pleistocene alluvial fan and aeolian sandsheet complex: The Senne in the Münsterland Embayment, NW Germany

An up to 15 m thick alluvial fan and aeolian sandsheet complex is exposed in the upper Senne area, on the southern slope of the Teutoburger Wald Mountains (NW Germany). The origin and age of these deposits have been controversially discussed for many years, ranging from Saalian glaciofluvial to periglacial Weichselian deposits. In order to provide a high-resolution chronological framework for the deposits, we conducted luminescence dating of 12 samples from two localities (Oerlinghausen and Augustdorf pits). Both coarse-grain potassium-rich feldspar and quartz minerals were used for luminescence dating. Feldspar was measured using an elevated temperature post-IR infrared stimulated luminescence (IRSL). Quartz was measured using optically stimulated luminescence (OSL) with a conventional single aliquot regenerative dose (SAR) protocol. Feldspar results tend to overestimate quartz ages for the lower part of the sections (alluvial plain and alluvial fan facies) but are consistent with quartz ages for the upper part of the sections (aeolian facies). Quartz ages from both central and minimum age models suggest deposition during the Late Pleistocene Pleniglacial to Late Glacial.

Luminescence dating of Chinese loess beyond 130 ka using the non-fading signal from K-feldspar

A multi-elevated-temperature post-IR IRSL (MET-pIRIR) protocol, which utilizes the IRSL signals measured by progressively increasing the stimulation temperature from 50 to 300 °C in a step of 50 °C, was applied to date the potassium-rich feldspar (K-feldspar) extracts from loess samples at the Luochuan section of the Chinese Loess Plateau. It was observed that the MET-pIRIR ages obtained at elevated-temperatures (250 and 300 °C) are consistent with independent chronological control for the samples from the first loess layer (L1) to the third paleosol layer (S3), which correspond to the marine isotope stages (MIS) 2–9. Our results indicate that the MET-pIRIR protocol can provide reliable ages for the Chinese loess up to ∼300 ka. The results suggest that the MET-pIRIR signal measured at 250 and 300 °C gives the most reliable ages for older samples (>130 ka). For samples below L3, the natural MET-pIRIR signals measured at high temperatures reach the saturation level in dose response curves, suggesting a dating limit of ∼300 ka for the Luochuan loess section.

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.

A rapid method for hand picking potassium-rich feldspar from silicic tephra

We detail a method for hand picking potassium-rich feldspars from silicic tephra. The method, based on the well known sodium cobaltinitrite staining technique, is applicable to any sample where K content of feldspar exceeds ∼2 wt%. The method is well suited to mineral grains >0.25 mm and useful for grains as small as ∼0.125 mm. Alkali feldspar, plagioclase, and quartz are easily distinguishable after staining. Rinsing the stained feldspars along with ultrasonic treatment in distilled water and nitric acid removes the stain. 40Ar/ 39Ar analysis of sanidine separated by staining yields precise age estimates which are in excellent agreement with published ages for the youngest (2.06 Ma) Cerro Galán ignimbrite, NW Argentina.

The decrease in the shear strength of volcanic materials with argillic hydrothermal alteration, insights from the summit region of Teide stratovolcano, Tenerife

Hydrothermal alteration around the summit region of Teide stratovolcano, in Tenerife, has decomposed lavas to weak, clay-rich soils. This process has been observed at other volcanoes. The purpose of this study is twofold: firstly to identify and geotechnically characterise weak volcanic materials, and secondly to estimate the reduction in shear strength caused by argillic hydrothermal alteration. Hydrothermally altered soil units, the weakest materials found on the flanks of Teide, have been collected and studied using standard geochemical and geotechnical laboratory techniques. The weakest units are exposed only inside the summit crater and are porous, silty, clay-rich, medium plasticity soils. Mineralogical analyses of the summit crater soils reveal that they contain two different alteration assemblages formed by acid-sulphate alteration of potassium-rich feldspars from the parent phonolitic lava flows. Material in the active fumarolic field is now fully altered to alunite, while material at a short distance from the active fumarole field is partially altered to both kaolinite and alunite. Geotechnical measurements performed on the summit crater units show that they have negligible cohesion. The presence of significant amounts of kaolinite in the partially altered soil could explain why this unit appears to have a lower shear strength than the fully altered alunitic one (friction angle φ′ = 16–25° and φ′ = 27–33° respectively). If so, these results would suggest that the type of alteration, which is determined by the temperature and pH, is more important in controlling the shear strength of the altered soil than the amount or degree of alteration. The summit crater soil units have formed in the last ~ 1000 years since the parent phonolitic lava flows were emplaced. Fresh and partially altered phonolitic parent rocks are widely present in the summit region adjacent to the soil units and offer a unique opportunity to quantify the decrease in shear strength caused by hydrothermal alteration. A comparison between the shear strengths of fresh and altered lavas and residual soils suggests relatively small, progressive, decrease in shear strength from fresh to altered rocks, with further alteration causing a large and sharp decrease transforming altered rocks directly to soils. It has been observed in the field that there is a sharp transition from altered rock to soil which takes place only along the top few millimetres on the face of rocks.

Mineralogical alteration of artificial meteorites during atmospheric entry. The STONE-5 experiment

The generic concept of the artificial meteorite experiment STONE is to fix rock samples bearing microorganisms on the heat shield of a recoverable space capsule and to study their modifications during atmospheric re-entry. The STONE-5 experiment was performed mainly to answer astrobiological questions. The rock samples mounted on the heat shield were used (i) as a carrier for microorganisms and (ii) as internal control to verify whether physical conditions during atmospheric re-entry were comparable to those experienced by “real” meteorites. Samples of dolerite (an igneous rock), sandstone (a sedimentary rock), and gneiss impactite from Haughton Crater carrying endolithic cyanobacteria were fixed to the heat shield of the unmanned recoverable capsule FOTON-M2. Holes drilled on the back side of each rock sample were loaded with bacterial and fungal spores and with dried vegetative cryptoendoliths. The front of the gneissic sample was also soaked with cryptoendoliths. The mineralogical differences between pre- and post-flight samples are detailed. Despite intense ablation resulting in deeply eroded samples, all rocks in part survived atmospheric re-entry. Temperatures attained during re-entry were high enough to melt dolerite, silica, and the gneiss impactite sample. The formation of fusion crusts in STONE-5 was a real novelty and strengthens the link with real meteorites. The exposed part of the dolerite is covered by a fusion crust consisting of silicate glass formed from the rock sample with an admixture of holder material (silica). Compositionally, the fusion crust varies from silica-rich areas (undissolved silica fibres of the holder material) to areas whose composition is “basaltic”. Likewise, the fusion crust on the exposed gneiss surface was formed from gneiss with an admixture of holder material. The corresponding composition of the fusion crust varies from silica-rich areas to areas with “gneiss” composition (main component potassium-rich feldspar). The sandstone sample was retrieved intact and did not develop a fusion crust. Thermal decomposition of the calcite matrix followed by disintegration and liberation of the silicate grains prevented the formation of a melt. Furthermore, the non-exposed surface of all samples experienced strong thermal alterations. Hot gases released during ablation pervaded the empty space between sample and sample holder leading to intense local heating. The intense heating below the protective sample holder led to surface melting of the dolerite rock and to the formation of calcium-silicate rims on quartz grains in the sandstone sample.

Luminescence dating of mid- to Late Wisconsinan aeolian sand as a constraint on the last advance of the Laurentide Ice Sheet across the Tuktoyaktuk Coastlands, western Arctic Canada

Luminescence dating of pre-glacial sand in the Tuktoyaktuk Coastlands, Northwest Territories, discounts an Early Wisconsinan age for the last Laurentide glaciation to cross the Arctic Coastal Plain and supports a Late Wisconsinan age. Aeolian dune sand from the Kittigazuit Formation near Cliff Point, on the southern shore of Liverpool Bay, predates till deposited during the Toker Point Stade. Potassium-rich feldspar from three stratigraphic sections ~35 km up-ice from the Toker Point glacial limit provides thermoluminescence age estimates that range from 18.7 ± 2.0 to 9.1 ± 1.0 ka and infrared stimulated luminescence age estimates of 23.8 ± 5.1 to 11.0 ± 2.1 ka. Quartz from four of the same samples provides optically stimulated luminescence age estimates of 16.5 ± 1.0 to 13.7 ± 0.9 ka. Collectively, these estimates reject the Early Wisconsinan age for the Toker Point Stade glaciation inferred hitherto from radiocarbon dating. A review of pre-glacial and post-glacial age estimates from the region indicates that during the Toker Point Stade ice advanced across the Tuktoyaktuk Coastlands no earlier than ~30 ka, and probably not before ~22 ka. Deglaciation had certainly commenced by 14.3 ka, and probably by ~16 ka. The Toker Point glaciation, therefore, dates approximately to the last glacial maximum, reinforcing the interpretation of the late rebuild up of the Laurentide Ice Sheet that characterized many parts of its margin.

Late Holocene Mediterranean coastal change along the Tiber Delta and Roman occupation of the Laurentine shore, central Italy

A line of Roman villas once dominated the Mediterranean coastline to the south of the Tiber river mouth near Ostia in central Italy. The Roman remains, which were constructed within a series of dune ridges, now lie up to 900 m from the current shoreline as a result of the continued evolution of the Tiber delta in response to postglacial sea level rise, sediment inputs from the Tiber river catchment and tectonic uplift. Infrared stimulated luminescence (IRSL) ages of potassium-rich feldspars extracted from dune sands are in good agreement with the independent age control provided by the Roman structures and allow us to hypothesise an increase in aggradation rates of five times since the end of the period of Roman occupation compared with the earlier Holocene.

Study of the ultraviolet emission of the electrode coatings of arc welding

The optical emission properties of several minerals components employed in electrode coatings of arc welding have been investigated. The X-ray diffraction analysis shows that the composition of 14 commercial electrode coatings collected from different countries (Spain, France, UK, Poland, Argentina and Germany), consists of quartz, calcite, sodium and potassium rich feldspars, muscovite and rutile. The natural thermal stimulated luminescence (TSL) of these mineral phases, measured in the range of 200 – 800 nm at different temperatures (from room temperature to 400°C) displays UV-A (wavelengths of 320 nm to 400 nm) and UV-B (from 280 nm to 320 nm) emissions, with the exception of rutile. The UV-B radiation, commonly described as the most dangerous form of radiation to human life, is here associated with structural defects in the crystallographic lattice of the mineral components of electrode coatings.

Variation in the luminescent properties of a potassium rich feldspar induced by thermal treatment and infrared exposure

Las propiedades luminiscentes del cuarzo y de los feldespatos, que son componentes mayoritarios de los materiales ceramicos tradicionales (ladrillos, azulejos o porcelanas), varian considerablemente durante el proceso de fabricacion que implica un calentamiento hasta ~900oC en ladrillos o ~1200oC en porcelanas. En este trabajo se ha estudiado como varia la luminiscencia de un feldespato potasico (KAlSi3O8) perfectamente caracterizado cuando es sometido a (i) tratamientos termicos y (ii) exposicion al infrarrojo. Se ha observado que calentamientos progresivos desde 2 hasta 96 horas a una temperatura de 500oC producen un aumento proporcional de la intensidad en las curvas de radioluminiscencia (RL) y catodoluminiscencia (CL) sin modificar su forma. Dado que no se ha apreciado cambio alguno en la estructura cristalina estudiada por difraccion de rayos X, es probable que esta variacion de la intensidad sea debida a una auto-difusion de los iones alcalinos (K, Li, Na o Rb) a traves de las interfases de la red. Por otra parte, la emision termoluminiscente (TL) del feldespato potasico se desplaza moderadamente hacia altas temperaturas cuando previamente es expuesto a radiacion infrarroja durante 10 minutos. Es probable que este fenomeno sea debido a una transicion electronica por efecto tunel desde trampas mas superficiales hacia trampas mas profundas o a un mecanismo continuo en la distribucion de las trampas.

Infrared luminescence of Pb+ centres in potassium-rich feldspars

This paper reports on new results of the characteristics of photo- and radioluminescence emissions at 865 nm and 910 nm emitted by potassium-rich feldspars (KAlSi3O8). For the physical interpretation of its behaviour, the IR luminescence in potassium-rich feldspars is compared to a well investigated IR luminescence occurring in lead-doped potassium chloride (KCl:Pb) and to a study on the IR luminescence of lead-rich KAlSi3O8 (amazonite). The emissions in both materials, potassium-rich feldspar and potassium chloride, are most likely due to electron transitions in Pb+ from the 72P1/2 and 72S1/2 excited states to the 62S1/2 ground state of Pb+. Pb+ originates from interaction processes of Pb2+ cations, substituted for K+ cations in the tetrahedral feldspar framework or the cubic lattice of KCl, with ionising radiation (Pb2+ + β, γ, … → Pb+). Another result of the experiments reported is the fact, that this radiatively induced conversion is reversed by thermal treatment of the minerals (Pb+ + T → Pb2+). Also, the Pb+ centres can be “optically bleached”, which is also interpreted as reversed conversion Pb+ + ħω → Pb2+. The conclusions of this paper have important implications for the physical precision of a recently developed luminescence dating method for the determination of the deposition time of Quaternary sediments using the infrared radiofluorescence (IR-RF) of potassium-rich feldspar grains. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Late Quaternary hillslope evolution recorded in eastern South African colluvial badlands

Infrared stimulated luminescence (IRSL) ages have been obtained from a sequence of sandy colluvial deposits in northern KwaZulu–Natal. Comparison of the IRSL ages on sand-sized, potassium-rich feldspars, with radiocarbon dates on A-horizon organic matter from buried palaeosols within the colluvial succession shows good agreement between the dating techniques. When compared with palaeoenvironmental records, the data suggest that the colluvium accumulated during arid stages of the Late Quaternary, whilst pedogenesis repeatedly occurred at intervals of hillslope stability which may reflect periods of greater humidity. Temperature does not seem to have been a forcing factor in the landscape development. Extensive colluviation took place during the arid Last Glacial Maximum, but the occurrence of several palaeosols indicates that it was a time of fluctuating climatic conditions.

Testing optically stimulated luminescence dating of sand-sized quartz and feldspar from fluvial deposits

We apply single-aliquot optically stimulated luminescence (OSL) dating to quartz- and feldspar-rich extracts from fluvial channel deposits of the Rhine–Meuse system in The Netherlands. The time of deposition of these deposits is tightly constrained by radiocarbon dating or historical sources. This allows us to compare OSL ages obtained on quartz and infrared OSL (IR-OSL) ages obtained on potassium-rich feldspar with independent ages over the range of 0.3–13 ka. We show that the quartz OSL ages are in good agreement with the expected age. Using IR-OSL dating of feldspar, we find a slight age overestimate for the youngest sample, whereas for older samples the age is significantly underestimated. We also apply OSL dating to older fluvial and estuarine channel deposits with limited independent chronological constraints. Comparison of feldspar IR-OSL ages with the quartz OSL ages up to ∼200 ka shows a clear trend, where the former severely underestimates the latter. This trend is similar to that found for the samples with independent age control, indicating that the feldspar IR-OSL ages are erroneously young for the entire age range. In the youngest samples, incomplete resetting of the IR-OSL signal prior to deposition probably masks the age underestimation. We show that the IR-OSL age underestimation is partly caused by changes in trapping probability due to preheating. Correction for this phenomenon improves the IR-OSL ages slightly, but does not provide a complete solution to the discrepancy. We suggest that, in the light of the problems encountered in the IR-OSL dating of feldspar, quartz is the mineral of choice for OSL dating of these deposits. However, feldspar dating should continue to be investigated, because it has potential application to longer time scales.