Individual Quartz Grains Research Articles

Constraining the age of the Pleistocene sedimentary infill of Cueva Mayor (Atapuerca, N Spain) through a multi-technique dating approach

Establishing chronologies of archaeological sites by using a single dating method may not always reliably constrain the age of a deposit or a fossil, as potential biases may naturally arise, particularly in complex sedimentary settings such as caves. In this study, we performed a multi-technique dating approach that targets different materials in two caves from the Cueva Mayor-Cueva del Silo karst system, Sierra de Atapuerca, Spain. Two new fossil teeth from lithostratigraphic unit LU4 (GE-I pit) at Galería de las Estatuas have been dated by combined U-series/ESR and Amino Acid Racemisation (AAR) methods. The former provides ages of 117 ± 13 and 87 ± 9 ka that agree with previous dating studies of this Neandertal site, confirming the assignment of level LU4 to Marine Isotope Stage (MIS) 5. In contrast, AAR analyses produce very scattered ages, pointing to significant post-burial chemical modifications in dentine. A first set of ages is presented for the Cata Litario pit at Sala de los Cíclopes, a palaeontological site formed exclusively of cave bear fossils belonging to the Middle Pleistocene species Ursus deningeri. We provide U-series/ESR and AAR ages for two bear teeth from lithostratigraphic unit LU5, and extended-range luminescence ages for the sediment deposits that host, and immediately underlie and overlie, the bear accumulation. Depositional ages of the sediment were obtained using single-grain thermally-transferred optically stimulated luminescence (TT-OSL) dating of individual quartz grains and post-infrared-infrared stimulated luminescence (pIR-IR) dating of K-feldspars. Several speleothems, both in situ and reworked fragments embedded in the different lithostratigraphic units, have additionally been dated by U-series to constrain the timing of the sequence formation. The results indicate that the sediment originally entered the cave between MIS-12 and MIS-10 (444 ± 28 ka to 367 ± 32 ka). Nevertheless, the AAR and U-series/ESR fossil ages, as well as some of the speleothem fragment ages from LUs 5 and 6 are significantly younger. Leaving aside methodologically questionable results for one of the bear tooth samples, the most reliable AAR and U-Series/ESR ages range from 287 ± 23 ka to 256 ± 24, while the speleothem fragments indicate several formation episodes between 444 ± 19 and 284 ± 8 ka. The apparent difference between the U-Series/ESR ages on the fossils and the luminescence ages on the host sediment are not likely to be wholly explained by uncertainties on uranium uptake modelling or gamma dose rate evaluation, and thus is most likely related to taphonomic processes or a complex site formation history.The presence of fossils and eroded speleothem clasts of younger age within these levels is consistent with either an event of prior erosion, transport and resedimentation of LUs 4, 5 and 6, and/or a complex post-depositional mixing history for the stratigraphic sequence at Cata Litario. This study highlights the importance of using different dating methods to reconstruct reliable chronological frameworks, and to understand the geological factors that can affect the dated materials. This includes the accumulation and taphonomic histories of fossils, post-depositional mixing or reworking processes affecting sediments during the residence time within the karst system.

The variability of single grain quartz luminescence properties investigated using EMCCD imaging

Optically stimulated luminescence (OSL) signals from individual quartz grains are frequently used for equivalent dose and age determination in luminescence dating. Typically, signals from individual grains are stimulated with a focussed solid-state laser and detected via a photomultiplier tube. In contrast to the light-emitting diodes (LEDs) usually used when stimulating multiple-grain aliquots, the laser has a much higher stimulation power density. An absolute value for the effective stimulation power cannot easily be quantified, and the power delivered to each grain cannot be considered consistent throughout a measurement sequence. Both intra- and inter-sample variability in single grain luminescence signals parameters such as dose response form, decay rate, and sensitivity have long been recognised, however there remains uncertainty over how much of this variability is intrinsic to quartz grains or whether some should be attributed to variation in the effective stimulation power associated with the laser system. To better characterise intrinsic variability of single quartz OSL signals, an electron multiplier charge coupled device (EMCCD) attachment for the Risø reader was used for detecting and imaging luminescence signals. Whilst the EMCCD system currently offers a lower detection sensitivity when compared to the laser system, the ability to use LEDs for stimulation of the OSL signal circumvents the power variability associated with the laser system and allows an investigation of intrinsic variability to be made. In this paper, signal intensity and the composition of components in single grain luminescence signals are considered, and curve deconvolution is undertaken to calculate photo ionisation cross-sections for single grain quartz signals. For the samples considered, intra-sample variability in these characteristics is observed in single grain quartz luminescence signals imaged using an EMCCD.

Bayesian analysis of De distributions in optical dating: Towards a robust method for dealing with outliers

In optical dating, especially single-grain dating, various patterns of distributions in equivalent dose (D e ) are usually observed and analysed using different statistical models. None of these methods, however, is designed to deal with outliers that do not form part of the population of grains associated with the event of interest (the ‘target population’), despite outliers being commonly present in single-grain D e distributions. In this paper, we present a Bayesian method for detecting D e outliers and making allowance for them when estimating the D e value of the target population. We test this so-called Bayesian outlier model (BOM) using data sets obtained for individual grains of quartz from sediments deposited in a variety of settings, and in simulations. We find that the BOM is suitable for single-grain D e distributions containing outliers that, for a variety of reasons, do not form part of the target population. For example, D e outliers may be associated with grains that have undesirable luminescence properties (e.g., thermal instability, high rates of anomalous fading) or with contaminant grains incorporated into a sample when collected in the field or prepared in the laboratory. Grains that have much larger or smaller D e values than the target population, due to factors such as insufficient bleaching, beta-dose heterogeneity or post-depositional disturbance, may also be identified as outliers using the BOM, enabling these values to be weighted appropriately for final D e and age determination. • A Bayesian outlier model (BOM) for luminescence dating of sediments. • Outliers are identified in single-grain equivalent dose (D e ) distributions. • Outliers are weighted appropriately for final D e and age determination. • Three special cases (BOM central, minimum and maximum) for different contexts. • Tested on well-bleached, partially bleached and post-depositionally mixed samples.

Distribution of natural beta dose to individual grains in sediments

In luminescence dating using single grains of quartz, statistical protocols are used to compute the most appropriate dose from the distribution of palaeodoses. The distribution of palaeodoses arises due to, (1) heterogeneity (at grain level) in bleaching at the time of deposition, (2) heterogeneous distribution of beta emitters present as randomly distributed feldspars (Mayya et al. in Radiat Meas 41:1032–1039, 2006) and, (3) heterogeneous distribution of grainsizes (Guérin et al. in Radiat Meas 47:778–785, 2015). Mayya et al. (Radiat Meas 41:1032–1039, 2006) demonstrated that random distribution of feldspar grains(with up to 14% stoichiometric K) and shorter range of beta particles (~ 2.3 mm in quartz) lead to significant variation in dose received by individual grains of quartz. This study improves upon Mayya et al. (Radiat Meas 41:1032–1039, 2006) by, (1) using a more realistic energy deposition function that was estimated using Monte Carlo simulations and (2) computing the effects of porosity of the sediment and beta straggling on the dose distribution function. It additionally concludes that effects of beta straggling are small and can be ignored. Ages based on new calculations led to improved concordance with control ages.

The Raunis section, central Latvia, revisited: first luminescence results and re-evaluation of a key Baltic States stratigraphic site

ABSTRACT In interstadial deposits, sand interbeds gain limited consideration in comparison with organic sediments, and therefore tend to be underrepresented in paleoenvironmental reconstructions. The Raunis site, central-eastern Latvia, is an example where organic beds have already gained some attention and been used to understand the complex interactions between advance and retreat of the Scandinavian Ice Sheet in the region. Sandy interlayers have so far not been investigated in detail and their time of deposition has also been unknown, therefore exploring these clastic-organic sediment alternation is of interest. This study provides a new set of luminescence datings along with sedimentological information from the character of individual quartz grains as detected from scanning electron microscope analysis. Sandy interlayers are dated to between 12 and 122 ka. Fast component OSL signal dominates in all investigated samples, but several samples have broad and/or skewed dose distributions. Only one sample is considered reliable and provides an age of 12.0 ± 0.6 ka. A radiocarbon age from organic sediments in the same unit yields an age of 14 025 ± 270 cal y BP. These two dates do not agree within 2 sigma, and this is likely related to reservoir and hard water effects of the radiocarbon sample. Sediments at the Raunis site fall into the Greenland Interstadial 1, but more detailed specification is not possible. The rest of the OSL ages are older than expected, likely due to incomplete bleaching during deposition. This means that stratigraphic reliability of this key site is likely hampered for further regional correlation.

Establishing standardised growth curves (SGCs) for OSL signals from individual grains of quartz: A continental-scale case study

Abstract The standardised growth curve (SGC) procedure is a technique that can facilitate rapid De estimation. In this study, we apply a least-squares (LS) normalisation procedure to single grains of quartz from multiple sites across Australia to test its applicability for establishing common SGCs for individual quartz grains from the same continent. Seventy-two samples from 18 sites were divided into two groups: (1) forty samples were used to construct common SGCs for Australian quartz, and (2) thirty-two samples were used to blind test the reliability of single-grain dating, based on the continental SGCs. Individual grains of quartz from different sites exhibit significant variability in their OSL decay curves, inherent signal intensities and dose response curves (DRCs) constructed using the single-aliquot regenerative dose (SAR) procedure. Application of a LS-normalisation procedure can largely reduce between-grain variability in the shape of the DRCs, allowing for the establishment of a suite of continental SGCs for Australian quartz. For radiation doses below 50 Gy, all investigated grains share a single, common SGC. At higher doses, the DRCs can be divided into six groups, with each group represented by a common SGC. The proportion of grains belonging to each group shows no discernable dependence on OSL properties, but varies significantly among the different sites. The single-grain De values determined using the continental SGCs are consistent at 2σ with those obtained from their individual DRCs. Likewise, the single-grain De distributions obtained using the SGCs and the individual DRCs are similar for most of the blind-test samples. Discrepancies for a small number of samples can be explained by the inclusion in the SGC De dataset of a few outlying values associated with aberrant or saturated grains. Our results show that the establishment of a group of continental SGCs can significantly reduce the machine time required for single-grain OSL measurements, enabling more samples and/or more grains to be measured per unit time. Continental SGCs also yield single-grain De estimates with comparable accuracy and precision to those obtained from individual DRCs constructed using the full SAR procedure.

Assessment of shear zone-derived quartz from the Etam area, southwest Cameroon as potential high-purity quartz resource: petrography, geochemistry and technological studies

This study focuses on the evaluation of the high-purity quartz (HPQ) potential of a shear zone-hosted hydrothermal and metamorphic quartz deposit in Etam, southwest Cameroon. The shear zone quartz-rich rock is monomineralic and consists of both milky and translucent varieties. The combination of ICP-MS and LA-ICP-MS analytical techniques was used to assess the chemical purity of both quartz varieties. These compositional analyses show that all quartz samples have SiO2 content of 98.46–99.75 wt% with very low concentrations of all the other elements. Translucent quartz when compared to the milky quartz variety shows low concentration of most of the elements including the following principal impurities: Al (mean 107 µg g−1), Ca (mean 27.85 µg g−1) and Fe (mean 26.05 µg g−1). Bubble generation in the samples after flame fusion over a silica plate was assessed to test the suitability of the quartz in industrial uses. The results obtained from the chemical analyses and bubble formation tests indicate that all the samples investigated do not meet the HPQ requirement. However, the translucent quartz shows characteristics of medium-purity quartz and can produce silica glass for some industrial manufacturing even without further purification. In this study, the fluid inclusions in the samples were examined as this bears information on the economic viability of the deposit and provides clues on the genesis of the quartz vein. Also tiny mineral inclusions within individual quartz grains were identified by SEM–EDS. The results of these studies show that the deposit is probably of metamorphic origin marked by crystal-plastic deformation in quartz grains. The veins were later modified by hydrothermal fluid input. The results also indicate that the majority of impurities are likely hosted by fluid inclusions and thus the quartz can be upgraded to HPQ after purification by suitable methods.

Single-Grain Quartz OSL Characteristics: Testing for Correlations within and between Sites in Asia, Europe and Africa.

We studied the characteristics of the optically stimulated luminescence (OSL) signal of single-grain quartz from three sites in China, Italy, and Libya, including the brightness, decay curve and dose response curve (DRC) shapes, recuperation, and reproducibility. We demonstrate the large variation in OSL behaviors for individual quartz grains of different samples from different regions, and show that recuperation, sensitivity change, and reproducibility are independent of the brightness and decay curve shape of the OSL signals. The single-grain DRCs can be divided into at least eight groups with different characteristic saturation doses (D0), and a standardized growth curve (SGC) can be established for each of the DRC groups. There is no distinctive difference in the shape of OSL decay curves among different DRC groups, but samples from different regions have a difference in the OSL sensitivities and decay shapes for different groups. Many of the quartz grains have low D0 values (30–50 Gy), and more than 99% of the grains have D0 values of <200 Gy. Our results raise caution against the dating of samples with equivalent dose values higher than 100 Gy, if there are many low-D0 and ‘saturated’ grains.

Luminescence chronology and lithic technology of Tianhuadong Cave, an early Upper Pleistocene Paleolithic site in southwest China

AbstractTianhuadong is a cave site located in the northwest of Yunnan Province, China. Since 2010, several surveys and one test excavation have yielded more than 1000 stone artifacts. The lithic assemblage shows some features of Levallois and Quina technologies, similar to those found in Middle Paleolithic sites in the Western Hemisphere. In this study, we summarize the lithic industry and propose a reliable chronology for the site using optically stimulated luminescence (OSL) dating of individual quartz grains extracted from sediments. We applied the standardized growth curve method to deal with the problem associated with the saturation in natural OSL signals in quartz. Our dating results yielded ages of 90–40 ka, suggesting that the associated lithic assemblage could be assigned to Marine Oxygen Isotope Stages 5 and 4 and could potentially represent Middle Paleolithic technologies. Because the number of Middle Paleolithic sites in southwest China is small, this site provides one of the few traces of human occupation in southwest China during the early upper Pleistocene. Thus, it is important for understanding hominin evolution and dispersal in this region.

Single-grain OSL dating of fluvial terraces in the upper Hunter catchment, southeastern Australia

Abstract Fluvial terraces in the upper Hunter catchment, southeastern Australia provide a long-term record of river activity in response to climate change in the late Quaternary. Single-grain optically stimulated luminescence (OSL) dating of quartz was applied in this study to investigate the timing of the formation of three fluvial terraces in the upper Hunter catchment. A detailed examination of luminescence properties of individual quartz grains revealed some correlation between their OSL decay rates, intrinsic brightness and dose saturation characteristics. Some quartz grains containing a higher proportion of non-fast components exhibit low brightness in OSL signals and high dose saturation levels. Some grains with slow OSL decays pass the standard rejection criteria, but are likely to yield underestimated equivalent doses (Des) because of a higher contribution of non-fast components, which are shown to have low thermal stability. Different rejection criteria, including the fast ratio, the dose saturation level and the OSL sensitivity criteria, were tested on the single-grain De results. Application of a fast ratio rejection criterion is able to successfully identify thermally unstable grains. A new rejection criterion based on dose saturation property was also applied to improve the age of one sample with a large De. Our dating results identify multiple phases of river valley aggradation in the upper Hunter catchment since late Marine Isotope Stage (MIS) 6; at ∼ 138 ka, ∼90–94 ka, ∼65 ka, ∼26 ka and ∼18 ka. The aggradational episodes of the terraces in the upper Hunter catchment are correlated with glacial or stadial periods since MIS 6. These phases of valley-floor aggradation are inferred to be a function of increased sediment supply during the cold periods resulting from strong periglacial activities in the adjacent Australian highlands.

Metamorphic and deformation history of the Mecsekalja Zone around the Szentlőrinc-1 well using individual quartz grains from drilling chips

The Mecsekalja Zone is a strike-slip fault zone that plays an essential role in the structural framework of South Transdanubia. The metamorphic and deformation history of the crystalline basement o...

The effect of backscattering on the beta dose absorbed by individual quartz grains

We describe the effect on dose rates and over-dispersion (OD) of changing the spectrum of energies to which grains of various shapes and volumes are exposed during beta irradiation, either by changing the backscattering medium or attenuating the incident spectrum. Dose rates are found to increase when the atomic number of the backscattering substrate is increased (from 0.038 Gy/s on Al to 0.057 Gy/s on Pb), at the same time the dispersion due to grain shape and volume also increases slightly (9.4% on Al and 12.0% on Pb). By adding attenuators in front of the sample the net spectrum is also altered and the dispersion affected correspondingly. Our model prediction using various grain shapes and volumes are compared with experimental observations using sieved natural grains and the resulting dose rates are in good agreement, although the dispersions cannot be realistically compared in the absence of grain shape information for the natural material. We find from modelling that dose rates (both to grains in single grain discs and to those placed on the backscattering substrates) are sensitive to changes in shape and volume. A relative range across shapes of between 10 and 21% is observed from modelling on backscattering substrates, and of 7.4% from modelling in single grain discs. We conclude that it appears to be desirable to minimise shape and volume variations in grains if over-dispersion is also to be minimised.

Deriving spatially resolved beta dose rates in sediment using the Timepix pixelated detector

Luminescence dating methods currently allow for the evaluation of the distribution of equivalent dose (De) values for individual sand-sized grains of quartz and feldspar from a given sample, but the environmental dose rate is still derived from the bulk sample. Additionally, single-grain optically stimulated luminescence (OSL) dating is performed on disaggregated samples, resulting in the loss of micro-stratigraphic context. To enhance the interpretation of De distributions, we aim to estimate the beta dose rate to sub-millimetre regions of intact samples using the Timepix pixelated semiconductor detector. The Timepix contains an array of 256 × 256 pixels, each 55 × 55 μm in size and with its own preamplifier, discriminator and digital counter. The detector has a total sensitive area of 1.98 cm2, and 65,536 independent channels. The output of each measurement is a matrix containing the position and pixel-by-pixel count rate (or deposited energy) of each particle that interacted in the sensitive volume of the detector. The main challenge in using the Timepix detector is low natural sample activity, and the goal of this work is to acquire data with minimal background contribution. With an experimental setup guided by Geant4 simulations, progress has been made to greatly reduce background noise using ad hoc shielding and post-acquisition particle analysis. We have established a Timepix measurement procedure applicable to resin-impregnated sediment samples, including sample preparation, measurement, and data processing and analysis. These steps have been tested on an artificial micro-stratified sample (composed of quartz and biotite grains held together by resin) to derive the corresponding spatially resolved beta dose rates.

Spectral signature of single-grain quartz using a high-sensitivity TL imaging system

The spectral signature of individual quartz grains were measured using a high-sensitivity thermoluminescence imaging system based on a charge-coupled device (CCD) camera and custom optics. Luminescence emission behaviour was characterised for individual quartz grains (180–212 μm), with single grains shown to emit luminescence strongly across multiple signal bands. The spectral profiles of three quartz samples from contrasting geological contexts were then compared, with clear distinction in the spectral signatures of individual grains originating from single deposits within each provenance.

Quartz types of the Eocene Broken River Formation, Mount Somers, South Island, New Zealand

ABSTRACTQuartz arenites are a very common geological feature on the South Island of New Zealand. The provenance of the quartz grains that form these arenites is not well constrained because standard point-counting techniques do not provide enough detailed information. In this study we distinguish different quartz types using scanning electron microscopy–cathodoluminescence combined with standard optical microscopy on the same individual quartz grains. This is done on a suite of samples collected from shallow marine quartz arenites of the Paleocene–Eocene Blondin Sand Member of the Broken River Formation (Eyre Group) at Mt Somers in the Canterbury basin on the South Island of New Zealand. Our results show that the volcanic quartz grains were derived from local volcanic source rocks, whereas metamorphic quartz grains may have been derived from either local source rocks of the Torlesse Supergroup or from distant metamorphic sources rocks via longshore transport. Plutonic quartz grains were exclusively derived by long-distance transport. Warm and humid climatic conditions and the presence of humic acids in the associated coal-forming depositional environment probably increased the proportion of quartz in the sampled rocks.

Iron transport and deposition mechanisms in the Taochong iron-rich skarn deposit, Middle–Lower Yangtze Valley, Eastern China

The Taochong skarn iron deposit is one of 38 iron prospects in the Fanchang iron ore district of the Middle–Lower Yangtze River Valley, one of the most important economic mineral districts in China. Orebodies are hosted mainly within the middle–upper Carboniferous Huanglong dolomitic limestone. In this deposit, two types of ore (types 1 and 2) are recognized based on the mineral assemblage. The type 1 ore is dominant throughout the deposit and consists mainly of hematite, magnetite, quartz, and calcite. This ore is characterized by euhedral and skeletal textures, and massive, brecciated, comb-like, and vein structures. The type 2 ore is composed of hematite, garnet, pyroxene, actinolite, chlorite, quartz, and calcite, and has a relict metasomatic texture and disseminated structure. Field evidence and petrographic observations indicate that three stages of hydrothermal activity (i.e., the skarn, iron oxide, and carbonate stages) contributed to the formation of the Taochong iron deposit. The iron oxide stage can be further divided into early and late oxide stages, which saw the formation of the type 2 and type 1 ores, respectively.Fluid inclusion and stable isotope data indicate that the skarn formed at depths of ~2km under lithostatic pressure of ~500bars, from high-temperature (~500°C), acidic, saline (up to ~50wt.% NaCl equiv.), and iron-rich fluids that had chemical and isotopic compositions (δ18Owater=4.5‰–11.7‰) similar to those of magmatic fluid replacing a certain amount of the Huanglong dolomitic limestone. The iron ores formed under hydrostatic conditions after fracturing of the early skarn. Fluid inclusions within quartz in equilibrium with hematite in the type 2 ores yields homogenization temperatures of 372–390°C and salinities of 31–39wt.% NaCl equiv., whereas fluid inclusions within quartz in equilibrium with hematite in the type 1 ores has lower homogenization temperatures (280–320°C) and variable salinities (0–40wt.% NaCl equiv.). During the formation of the type 1 ores, fluids contained moderate concentrations of ions, variable δ13C values (−5.3‰ to +5.8‰), and relatively convergent δ18O values (1.7‰–4.5‰). The temporal decrease in the concentration of ions and δ18O values in the fluid inclusions is matched by marked decreases in fluid salinity and temperature, suggesting that the fluids of the oxide stage were mixtures of magmatic brine and meteoric water. The coexistence of saline and vapor-rich fluid inclusions as internal trails or clusters within individual quartz grains of the late oxide stage, with contrasting homogenization characteristics (for the liquid and vapor) at similar temperatures, strongly suggests that fluid boiling occurred during the late oxide stage.Our estimates of the physico-chemical conditions during ore formation, together with fluid inclusion data and the results of previous experimental studies, indicate that iron in the Taochong deposit was transported mainly as FeCl4–, along with minor amounts of other chloride complexes (e.g., FeCl2+ and FeCl2(H2O)4+). The precipitation of hematite followed the breakdown of the iron chloride complexes, probably induced by a decrease in temperature and ligand (chloride) ion activity, and an increase in pH. Based on the results, we infer that deposition of the type 2 ore was caused by the replacement of garnet and pyroxene by a retrograde alteration assemblage, which was likely induced by fluid–rock interaction and the mixing of magmatic brine and meteoric water. The type 1 ore was deposited in open spaces, probably induced by fluid boiling.

Selected Properties and Systematic Position of Soils Developed from Red Sandstones and Clays of the Lower Triassic Buntsandstein in the Nw Part of the Holy Cross Mountains (Poland) / Niektóre właściwości i pozycja systematyczna gleb wytworzonych z czerwonych piaskowców i iłów dolnego triasu w NW obrzeżeniu Gór Świętokrzyskich

AbstractThe aim of the study was to compare the properties of soils developed from the Lower Triassic Buntsandstein sediments in the north-western part of the Holy Cross Mountains (Poland). These are deposits of continental genesis and unique features such as red beds. Two representative soil pedons - the Bartków profile (pBK) developed from clay and the Góra Czerwona profile (pGC) developed from sandstone were selected for detailed analyzes. The morphology of profiles, their micromorphological features, mineralogical composition, and physico-chemical properties were examined. Most of the properties of the soils are a consequence of the original parent rock lithology. A specific feature of the morphology of the soils are the presence of red color (about 10R by the Munsell color scale) related to the presence of hematite. As shown by the XRD data, hematite is not the product of the current soil-forming processes, but it is a lithogenic component, which was inherited from the parent rock. Under the influence of climatic factors primary rock structure has been transformed into a new pedogenic one. Soils developed from clays have a characteristic angular blocky structure. Micromorphological analysis showed that an important role in the formation of soil structure involves geogenic susceptibility of Triassic clays to specific cuboid disintegration. This is indicated by the pore system of planes as an orthogonal nets visible in thin section. The soils developed from sandstone have a weak (unstable) subangular blocky structure. The main reason is the insufficient dispersion of the clay-ferruginous fraction from the sandstone matrix. Microscopic observations indicate that fine factions occurs as loose microaggregates, which results in a feature that smaller rock fragments and individual quartz grains are not bonded into soil aggregates. The studied soils are characterized by specific physical-chemical properties. Some of them strongly depend on the mineralogical properties of the soil substrate. Strong acidity (pH 3-4) and a very low content of base cations (below 1.0 cmol(+)kg-1) are due to a lack of carbonate minerals in sandstones and weak weathering of aluminium silicate. High exchangeable Al content in clay (16.5 cmol(+)kg-1) should be related to the geochemical properties of the red bed-type rocks such as the Lower Triassic Buntsandstein deposits. Soils developed from the Lower Triassic Buntsandstein clays have a sequence of genetic horizons: Ap, Bw, Bw/C, C and fulfill the criteria assigned to dystrophic typical brown soils (BDt) in the Polish Soil Classification (PSC 2011), whereas in the WRB they were classified as Endoeutric Chromic Cambisols (Loamic). Soils developed from the Lower Triassic Buntsandstein red sandstone can be classified as dystrophic humus brown soil (BDpr) in the PSC (2011). Within the WRB classification that soil can be assigned to Epidystric Chromic Endoleptic Cambisols.

Trace elements in quartz shed light on sediment provenance

AbstractQuartz is one of the most common minerals on the surface of the earth, and is a primary rock‐forming mineral across the rock cycle. These two factors make quartz an obvious target for sediment provenance studies. Observations from experimental and natural samples demonstrate that the trace element content of quartz often reflects the conditions of quartz formation. When quartz is weathered from its primary crystallization setting (i.e., quartz from a granitoid) it can retain many chemical signatures of formation throughout the sedimentation processes. These geochemical signatures can be used to understand the primary source of individual quartz grains within a sediment. Here we present a case study from the Bega River catchment to demonstrate that quartz grains in sediments at the mouth of the Bega River are sourced from granitoids within the drainage basin. Data presented here also indicate that a portion of the beach sediment is also derived from either (i) sedimentary rocks within the basin or; (ii) mixing with sediments at the mouth of the river. The Bega River catchment was selected for this study because it is both small and has a well‐constrained bedrock lithology, making it an ideal location to test the utility of this provenance technique. However, quartz trace element provenance has broad applications to modern and ancient sediments and can be used in lieu of, or in conjunction with, other provenance techniques to elucidate sediment transport through time.

Optical dating in archaeology: thirty years in retrospect and grand challenges for the future

In 1982, when Richard Klein first became one of the Editors of this journal, the luminescence dating community was embarking on a new phase of exploratory research. Attention was turning from the use of thermoluminescence (TL) dating to estimate the time of last heating of archaeological objects, such as pottery and burnt flint, to the TL dating of unheated sediments that had been transported by wind and then deposited on the landscape. This revolutionary development enabled the extension of TL dating to sedimentary deposits in a variety of environmental settings and to the multitude of archaeological sites that lack suitably heated artefacts. In sediment dating, the age of most interest is usually the time elapsed since grains of quartz or feldspar were last exposed to sunlight, as the energy of the sun's rays is sufficient to evict electrons from their light-sensitive traps. These traps are steadily refilled after sediment deposition and the longer the grains remain buried, the more TL they will emit when measured. In 1985, Huntley and colleagues proposed ‘optical dating’ as a simpler and superior means of stimulating the light-sensitive traps in Quaternary sediments, and this is now the principal luminescence-based method of dating geological and archaeological deposits. Optical dating is an umbrella term for an armada of acronyms, the most common in archaeological contexts being OSL (optically stimulated luminescence), TT-OSL (thermally-transferred OSL), IRSL (infrared stimulated luminescence) and pIRIR (post-infrared IRSL). All of these variants are founded on the same basic tenet – measurement of a light-sensitive signal to determine (typically) the last time that sediment grains were sun-bleached – but each approach has its virtues and vices. In this paper, we review this ‘family’ of luminescence dating techniques and look back on 30 years of optical dating in archaeology. Some of the more interesting and important achievements are highlighted, including the critical insights gained in the last two decades from OSL measurements of individual grains of quartz. We also look to the future of optical dating in archaeological contexts. Efforts to extend the age limits of optical dating to older hominin and archaeological sites will remain a key goal, and understanding how archaeological sites – of all ages – form and evolve over time could be improved greatly by combining micromorphology analysis with optical dating of undisturbed (intact) sediments. The latter poses a series of particularly formidable technical challenges, but if the past is any guide to the future, then we can expect optical dating to illuminate much more of human history before celebrating its Golden Jubilee.

Evaluation of Chemical and Petrographic Characteristics of Silica Sand from Tabuk in Saudi Arabia

Silica sand is one of the most common varieties of sand, and it is used in industrial applications throughout the world. The application depends on the purity, grain size and chemical characteristics. In the present study, X-ray, chemical and petrographic analyses were used to study sand deposits from Tabuk area in Saudi Arabia. The collected samples from the site are composed of 98% quartz (SiO2 ), with very minor traces of carbonate and dark minerals which account for the rest of the sample constituents. The examined individual quartz grains have excellent purity, and about 98% of the grains were white transparent pure silica. The grains are mainly rounded to sub-angular. The chemical analysis indicated that the percentages of major oxides of Si, Al, Cr, Fe, and Ti were 97%, 1.5%, % <0.006%; 0.035%, and 0.0531% respectively. The grains sizes are fine and their sizes concentrated mostly around the 0.155 mm. Due to its high quality, the inspected deposit meets the industrial standards.