Sand-sized Quartz Research Articles

Testing optically stimulated luminescence dating on sand-sized quartz of deltaic deposits from the Sperchios delta plain, central Greece

This study reports on the first investigation into the potential of luminescence dating to establish a chronological framework for the depositional sequences of the Sperchios delta plain, central Greece. A series of three borehole cores (20 m deep) and two shallow cores (4 m deep), from across the delta plain, were extracted, and samples were collected for luminescence dating. The luminescence ages of sand-sized quartz grains were obtained from small aliquots of quartz, using the Single-Aliquot Regenerative-dose (SAR) protocol. The equivalent dose determination included a series of tests and the selection of the Minimum Age Model (MAM) as the most appropriate statistical model. This made it possible to confirm the applicability of quartz Optically Stimulated Luminescence (OSL) dating to establish absolute chronology for deltaic sediments from the Sperchios delta plain.Testing age results of the five cores showed that the deltaic sediments were deposited during the Holocene. A relatively rapid deposition is implied for the top ∼14 m possibly as a result of the deceleration in the rate of the sea-level rise and the transition to terrestrial conditions, while on the deeper parts, the reduced sedimentation rate may indicate a lagoonal or coastal environment.

Optical dating of Holocene sediments from the Yangtze River (Changjiang) Delta, China

Establishing a reliable chronology is essential for understanding delta evolution, which is normally performed using radiocarbon (14C) dating and the recently emerging technique of optically stimulated luminescence (OSL). The application of the latter one to the Holocene Yangtze River (Changjiang) Delta deposit is still quite limited. In this study, two 60.9-m-long cores were collected from Taizhou (TZ) and Nantong (NT) within the paleo-incised valley of the Yangtze River, and a total of seven and nine OSL samples were collected from the TZ and NT cores, respectively. In addition, ten accelerator mass spectrometry (AMS) 14C ages of the TZ core were presented with eight AMS 14C ages that were previously obtained from the NT core. The single-aliquot regenerative-dose (SAR) protocol was applied to coarse silt-sized (45–63 μm) and fine sand-sized (90–125 μm) quartz. The results showed that the grains in the 45–63 μm size fractions appeared to be better bleached than those in the 90–125 μm size fractions, and the detection of insufficiently bleached sediments is required in order to obtain accurate age estimates. The ages adopted for the samples range from 3 ka to 9 ka for the TZ core, and from 1 ka to 14 ka for the NT core, which were in general internally coherent within the limits of experimental errors and with respect to their stratigraphic order. The AMS 14C age of the TZ core were significantly older than their OSL ages, while those from the NT core generally showed good agreement with their OSL ages. One should be cautious when using AMS 14C to date deltatic deposits. Based on the OSL ages, two periods of rapid accumulation rates can be found in both cores, which are linked to the rapid sea level rise in early Holocene and migration of delta front facies in late Holocene. These investigations indicate that OSL technique is an effective method with which to date Holocene deltaic deposits, especially in coarse sedimentary layers where organic carbon material is sparse.

New archaeological insights from petrographic analysis of ceramics from the Bocas del Toro Archipelago, Panama

In this study, we conducted the first petrographic analysis of pottery from several Pre-Columbian archaeological sites located in Bocas del Toro province along the Caribbean coast of Panama. The fifty-four sherds examined in this study included surface finds collected from the sites of Red Frog (RF) and Punta Vieja Arriba (PVA) on Bastimentos Island, the Cerro Brujo (CB) site on the mainland, and excavated samples from Sitio Drago (SD), Isla Colon. Petrographic examination of sherd thin sections shows that different sandy materials (seven constituent natural and/or manually-added temper groups) were used in their production. Representative sherd compositions from each group were determined by petrographic point-counts (n=200) using two matrix (silt and clay) and 14 mineral and rock fragment categories for sand grains. The sand in RF sherds is mainly fragments of mudstone, whereas sherds from the PVA and CB sites contain different proportions of sand-sized quartz, feldspar, dense minerals, and several varieties of volcanic lithic fragments. The latter components are constituents derived from local Panamanian geologic units, including one with pyroclastic temper that likely comes from a volcanically active region, such as the El Baru Volcano. Some of the archaeological sites (SD and PVA) have a greater variety of sherd compositional/temper groups than others, implying that people inhabiting these sites were actively engaged in acquiring materials and/or ceramics from multiple sources regionally.

Clogging of an Alpine streambed by silt-sized particles – Insights from laboratory and field experiments

Clogging of streambeds by suspended particles (SP) can cause environmental problems, as it can negatively influence, e.g., habitats for macrozoobenthos, fish reproduction and groundwater recharge. This especially applies in the case of silt-sized SP. Until now, most research has dealt with coarse SP and was carried out in laboratory systems. The aims of this study are to examine (1) whether physical clogging by silt-sized SP exhibits the same dynamics and patterns as by sand-sized SP, and (2) the comparability of results between laboratory and field experiments.We carried out vertical column experiments with sand-sized bed material and silt-sized SP, which are rich in mica minerals. In laboratory experiments, we investigated the degree of clogging quantified by the reduction of porosity and hydraulic conductivity and the maximum clogging depth as a function of size and shape of bed material, size of SP, pore water flow velocity, and concentration of calcium cations. The SP were collected from an Alpine sedimentation basin, where our field experiments were carried out. To investigate the clogging process in the field, we buried columns filled with sand-sized quartz in the stream bed.We found that the maximal bed-to-grain ratio where clogging still occurs is larger for silt-sized SP than for sand-sized SP. The observed clogging depths and the reduction of flow rate through the column from our laboratory experiments were comparable to those from the field. However, our field results showed that the extent of clogging strongly depends on the naturally-occurring hydrological dynamics. The field location was characterized by a more polydisperse suspension, a strongly fluctuating water regime, and high SP concentrations at times, leading to more heterogeneous and more pronounced clogging when compared to laboratory results.

Evolution of Heterogeneous Mixed Siliciclastic/Carbonate Aquifers Containing Metastable Sediments

Mixed carbonate and siliciclastic marine sediments commonly become freshwater aquifers in eastern coastal regions of the United States and many other global locations. As these deposits age, the carbonate fraction of the sediment is commonly removed by dissolution and the aquifer can become a solely siliciclastic system or contain zones or beds of pure quartz sand. During aquifer evolution, the sediment grain size characteristics, hydraulic conductivity, and porosity change. An investigation of these changes using mixed carbonate/siliciclastic sediment samples collected from a modern barrier island beach in southern Florida showed that the average mean grain diameter decreased with removal of the carbonate fraction, but the average hydraulic conductivity and porosity increased slightly, but not to statistical significance. This counterintuitive result occurs because of the change in the pore types from a combined shelter and intergranular pore system producing a dual porosity system in the mixed sediments to a single intergranular pore system in the siliciclastic sediment fraction. Within the mixed carbonate/siliciclastic sediment, in the pure carbonate fraction, large shell fractions form grain-supported large pores, which become filled with sand-sized quartz as the shell fragments decrease in size or as the sediment becomes compacted. The hydraulic conductivity increases because the shell fragments that were oriented perpendicular to flow caused an increase in the length of the flow path, or a larger scale tortuosity, compared with the flow through pure quartz sand.

Holocene marine hardground formation in the Arabian Gulf: Shoreline stabilisation, sea level and early diagenesis in the coastal sabkha of Abu Dhabi

This study provides the first comparison between a seaward and a landward section of the same diachronous hardground surface observed in the coastal sabkha of Abu Dhabi. This hardground is described here in terms of its mode of formation, its diagenetic environment and its impact on shoreline stabilisation during transgression. The hardground is exposed in the intertidal zone and buried by a late Holocene prograding succession of carbonates, evaporites and microbial sediments in the supratidal zone. The hardground itself is composed of bioclastic grains, primarily of aragonitic composition, that originate from intertidal depositional environments. Aeolian silt to sand-sized quartz grains are also observed. Lithification occurred through the precipitation of pore-filling aragonite, high-Mg calcite and dolomite cements from sea and interstitial water that was marked by high salinities and temperatures, as confirmed by stable isotope analyses. High-Mg calcite and non-stoichiometric dolomite are also observed as secondary recrystallisation products. The formation of these two mineral phases as recrystallisation products was possibly microbially-mediated. Lithification progressed in two phases, the older phase of which is marked by higher amounts of non-stoichiometric dolomite and high-magnesium calcite as compared to the younger phase. Transgressive reworking of precursor siliciclastic sands was inhibited by the development of transgressive pore-filling gypsum cements in the supratidal zone.

Luminescence dating of mortar and terracotta from a Royal Tomb at Ulaankhermiin Shoroon Bumbagar, Mongolia

The spectacular royal tomb “Ulaankhermiin Shoroon Bumbagar” was discovered in Bulgan province, Mongolia, in 2011. Excavation of the site revealed its internal structure; a slope of 42 meters in length leading down to the underground mausoleum at a depth of 7 m below the ground. Archaeological investigations provided the site with an independent age control suggesting the construction date of the Royal tomb to the last quarter of the VII century. In this study, we directly date different materials from the site, such as terracotta figurines, mortar and host sediment, using infrared-stimulated (IR50) and postinfrared infrared stimulated (pIRIR) luminescence techniques. The most accurate estimate of 670 ± 70AD and 550 ± 110AD was obtained for terracotta figurines using IR50 and pIRIR on aliquots of 4–11 µm polymineral grains. By comparison, sand-sized quartz single grain measurements on the embedded sediment yielded normal equivalent dose (De) distributions with a few outliers, justifying the use of the central age model (CAM) for age calculation, and yielded construction dating to the 780 ± 140AD. Finally, sand-sized quartz single grain measurements on wall mortar revealed incomplete bleaching of grains, requiring detailed analysis using statistical approaches; from this we identified the most well bleached population age of 740 ± 130AD, using the lowest 5%. The luminescence ages are in general agreement with the historically expected age. Statement of significance The archaeological site at Ulaankhermiin Shoroon Bumbagar, Mongolia (with an independent age control) offers a great opportunity to apply luminescence dating methods, such as pIRIR on 4–11 µm polymineral fine grains, and single grain measurements on 200–250 µm quartz grains, to various materials, such as terracotta figurines, mortar-like limestone which covered the walls and embedded sediment in order to test the accuracy of optically stimulated luminescence (OSL) dating techniques. Compared to all other datable archaeological materials, mortar has the advantage of being intentionally manufactured at each stage of construction, since it cannot be recycled. However, dating of the well bleached grains of mortar, which provided the greatest challenge in this study, was achieved using the lowest 5% estimate, yielding an age of 740 ± 130AD. pIRIR on heated polymineral (feldspar-bearing) fine grain aliquots from terracotta figurines was tested, yielding IR50 and pIRIR180 dates in agreement with the CAM estimate from the host sediment. Cite this article Solongo, S., Ochir, A., Tengis, S., Fitzsimmons, K., and Hublin, J.-J. Luminescence dating of mortar and terracotta from a Royal Tomb at Ulaankhermiin Shoroon Bumbagar, Mongolia. STAR 2015; 1(2), STAR2015122054892315Y.0000000004 Data availability The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are contained within the paper.

A New Chronology for Rhafas, Northeast Morocco, Spanning the North African Middle Stone Age through to the Neolithic.

Archaeological sites in northern Africa provide a rich record of increasing importance for the origins of modern human behaviour and for understanding human dispersal out of Africa. However, the timing and nature of Palaeolithic human behaviour and dispersal across north-western Africa (the Maghreb), and their relationship to local environmental conditions, remain poorly understood. The cave of Rhafas (northeast Morocco) provides valuable chronological information about cultural changes in the Maghreb during the Palaeolithic due to its long stratified archaeological sequence comprising Middle Stone Age (MSA), Later Stone Age (LSA) and Neolithic occupation layers. In this study, we apply optically stimulated luminescence (OSL) dating on sand-sized quartz grains to the cave deposits of Rhafas, as well as to a recently excavated section on the terrace in front of the cave entrance. We hereby provide a revised chronostratigraphy for the archaeological sequence at the site. We combine these results with geological and sedimentological multi-proxy investigations to gain insights into site formation processes and the palaeoenvironmental record of the region. The older sedimentological units at Rhafas were deposited between 135 ka and 57 ka (MIS 6 –MIS 3) and are associated with the MSA technocomplex. Tanged pieces start to occur in the archaeological layers around 109 ka, which is consistent with previously published chronological data from the Maghreb. A well indurated duricrust indicates favourable climatic conditions for the pedogenic cementation by carbonates of sediment layers at the site after 57 ka. Overlying deposits attributed to the LSA technocomplex yield ages of ~21 ka and ~15 ka, corresponding to the last glacial period, and fall well within the previously established occupation phase in the Maghreb. The last occupation phase at Rhafas took place during the Neolithic and is dated to ~7.8 ka.

The age of three Middle Palaeolithic sites: Single-grain optically stimulated luminescence chronologies for Pech de l'Azé I, II and IV in France

Optically stimulated luminescence (OSL) measurements were made on individual, sand-sized grains of quartz from Middle Palaeolithic deposits at three sites (Pech de l'Azé I, II and IV) located close to one another in the Dordogne region of southwest France. We were able to calculate OSL ages for 69 samples collected from these three sites. These ages reveal periods of occupation between about 180 and 50 thousand years ago. Our single-grain OSL chronologies largely support previous age estimates obtained by thermoluminescence dating of burnt flints at Pech IV, electron spin resonance dating of tooth enamel at Pech I, II and IV and radiocarbon dating of bone at Pech I and IV, but provide a more complete picture due to the ubiquitous presence of sand-sized quartz grains used in OSL dating. These complete chronologies for the three sites have allowed us to compare the single-grain ages for similar lithic assemblages among the three sites, to test the correlations among them previously proposed by Bordes in the 1970s, and to construct our own correlative chronological framework for the three sites. This shows that similar lithic assemblages occur at around the same time, and that where a lithic assemblage is unique to one or found at two of the Pech sites, there are no deposits of chronologically equivalent age at the other Pech site(s). We interpret this to mean that, at least for these Pech de l'Azé sites, the Mousterian variants show temporal ordering. Whether or not this conclusion applies to the wider region and beyond, the hypothesis that Mousterian industrial variation is temporally ordered cannot be refuted at this time.

Performance of pulsed OSL stimulation for minimising the feldspar signal contamination in quartz samples

The use of pulsed optically stimulated luminescence (POSL) stimulation to remove contaminated feldspar OSL signal in quartz fractions has been tested either on artificial or natural mixtures of quartz and feldspar grains, using samples with good luminescence characteristics of quartz. The problem of feldspar contamination in quartz, however, is often accompanied by other undesirable luminescence characteristics such as a dim OSL signal and slow OSL decay. We report here, on the performance of POSL for nine sand-sized quartz samples from different parts of the Earth, which show severe feldspar contamination in the quartz OSL signal. The time resolved (TR)-OSL signal of these samples was measured to check the dominance of quartz OSL in their off-time signals. The fitting results of the off-time TR-OSL signal showed that the quartz OSL signal dominated during the off-time. The POSL De values for these quartz samples are on average ∼30% larger than the continuous wave (CW)-OSL De values due to the anomalous fading of the feldspar OSL signal. Furthermore the POSL ages were compared with post-infrared infrared stimulated luminescence (pIRIR) ages from K-feldspar for the samples and in most cases the two ages were consistent. These results indicate that POSL is an effective tool to remove feldspar contamination even for dim quartz samples. However, there are quartz samples which show severe anomalous fading in the quartz OSL signal itself. For such samples feldspar may be a better dosimeter.

Amino sugars reflect microbial residues as affected by clay mineral composition of artificial soils

Microbial residues are important contributors to soil organic matter (SOM). However, the effect of mineral composition on microbial activity and thereby SOM development is not well understood. Here, we used artificial soils composed of four different mixtures containing illite, montmorillonite, ferrihydrite and charcoal to study the effect of mineral composition on SOM development. In addition, silt- and sand-sized quartz were used to provide texture, sterilised manure was added as OM source and the mixtures were inoculated with a microbial community extracted from a natural soil. The mixtures were incubated in the dark for 3–18months and amino sugar and muramic acid content of the bulk soil and<20μm fraction were determined. Amino sugar content was generally low and changed only slightly in the<20μm fraction with incubation time, which shows that microbial residues in the form of amino sugars did not preferentially accumulate with time. The montmorillonite-containing mixture had a higher galactosamine and glucosamine content than the others, pointing to greater fungal residue formation. The effect was most pronounced for the bulk soil, indicating that fungal residues accumulated on coarse particulate OM and macroaggregates rather than in the fine fraction. The results illustrate that amino sugars can be a biomarker for studying the effect of mineral composition on microbial residues and SOM formation. However, it is important to consider the entire soil structure in order to gain understanding of the interaction between microorganisms, minerals and SOM.

Optical dating of aeolian and fluvial sediments in north Tian Shan range, China: Luminescence characteristics and methodological aspects

Loess and fluvial sand are important materials for dating river terraces and alluvial fans. This study focuses on the methodological aspects of dating loess and fluvial deposits from the northern flank of the Tian Shan range, China, using sand-sized quartz and potassium (K) feldspar. Luminescence characteristics of quartz and K-feldspar were studied for searching suitable dating procedures. Our results indicate that 1) most quartz aliquots were contaminated by feldspar, and were dated using a post-infrared optically stimulated luminescence (post-IR OSL) procedure. A Fast ratio acceptance threshold of 15 can be applied to select these aliquots with post-IR OSL signals dominated by quartz OSL; 2) the multi-elevated-temperature post-IR IR stimulated luminescence (MET-pIRIR) procedures are applicable for K-feldspar. A test dose of ∼30% of the natural dose is appropriate for dating of older (>10 ka) samples. An Age (T, t) plateau test can be used to evaluate the dating results; 3) for the loess samples, both quartz and K-feldspar were well bleached and are suitable for dating. Dating using K-feldspar is preferred for its higher efficiency; 4) for the fluvial sand samples, only the quartz grains were fully bleached. Single-aliquot dating of quartz gives reliable ages.

Late Glacial lake-level changes in the Lake Karakul basin (a closed glacierized-basin), eastern Pamirs, Tajikistan

The lake-level variations during the Late Glacial in the Lake Karakul basin (a closed glacierized-basin), in the northernmost part of the eastern Pamirs, were reconstructed using geomorphological and sedimentological evidence, with a chronology developed using luminescence ages from sand-sized quartz and K-feldspar in the lake sediments. Lake transgression started before ~19ka, with the peak water level of ~35m above the present elevation occurring at ~15ka. This was synchronous with a significant advance of the glacier in the catchment. Stepwise lake regression, including a rapid lowering of the lake level (~13m at ~12ka), persisted until at least ~10ka. Lake transgression and localized glacier expansion from ~19 to ~15ka likely correlate with the more regional Late Glacial glacier advances across the semi-arid western Himalayan–Tibetan orogen and the eastern Pamirs. The longer-term trend of this lake transgression was probably caused by colder and/or wetter climatic conditions, forcing a notable glacier advance.

All mixed up: Using single-grain equivalent dose distributions to identify phases of pedogenic mixing on a dryland alluvial fan

The optically stimulated luminescence (OSL) signal from quartz grains is most often used to estimate the depositional age of sediments that were fully bleached during transport and have not been mixed after deposition. However, sediment that is transported fluvially may not have been exposed to sufficient sunlight to bleach the latent OSL signal, while stable land surfaces on which soils are developing will likely be subject to mixing processes such as pedoturbation. In these cases, large equivalent dose (De) datasets derived from individual sand-sized quartz grains can shed light on the depositional and post-depositional histories of sedimentary deposits. Here, we report the results of geochronological investigations of Mt Chambers Creek alluvial fan, on the eastern footslopes of the Flinders Ranges, South Australia. We collected 13 OSL samples from bank exposures and pits excavated into relict floodouts to reconstruct late Quaternary alluvial dynamics. Single-grain De datasets yielded overdispersion-values of between 26 and 68%. Most of these values are significantly higher than the overdispersion values obtained during dose-recovery experiments, suggesting that many deposits were poorly bleached, mixed, and/or experienced significant dose rate heterogeneity. Single-grain measurements of a sample from the modern floodout demonstrate that partial bleaching is minor and cannot explain the De distributions for Holocene and Pleistocene samples. The results of systematic application of the finite mixture model (FMM) to all De datasets in conjunction with contextual observations suggest that post-depositional mixing by pedoturbation has significantly affected the deposits and observed OSL data. For most samples, we infer that the most populous FMM component represents deposition and that secondary components represent intrusive younger grains or partially bleached older grains. The fan-wide presence of contemporaneous intrusive grain-populations suggests that post-depositional mixing occurred in phases, possibly associated with intervals of increased pedoturbation.

Micromechanics of quartz sand breakage in a fractal context

From a Quaternary science perspective, sand-sized quartz as well as silt-sized quartz is often acknowledged as final products of glacial abrasion through different evolution mechanisms. This view challenges the existence of any universal comminution process, which may relate the formation of detrital quartz sand and silt. The contribution of grain size, energy input, and crystalline integrity in the scale of quartz crushability has long been the matter of much debate. The present empirical work examines the micromechanics of sand-to-silt size reduction in the quartz material. A series of grinding experiments was performed on Leighton Buzzard Lower Greensand using a high-energy agate disc mill. Analogous conditions to glacial abrasion are provided due to the combined abrasion between grains' asperity tips, and also between grains and rotating smooth tungsten carbide pestle. Simulation of discontinuous grain breakage allowed the examination of grains' crystalline defects. To enable an objective assessment of micromechanics of size reduction, measurements of particle and mode size distribution, fractal indexes and micro-morphological signatures were made. The crushing approach was probed through varied grinding times at a constant energy input, as well as varied energy inputs at constant grinding time. Breakage pathway was inspected via laser diffraction spectroscopy and transmission light microscopy. Results suggested that the grain breakdown is not necessarily an energy-dependent process. Non-crystallographically pure (amorphous) quartz sand and silt are inherently breakable materials through a fractal breakdown process. Results also revealed that the internal defects in quartz are independent from size and energy input.

Micro-hole and multigrain quartz luminescence dating of Paleodeltas at Lake Fryxell, McMurdo Dry Valleys (Antarctica), and relevance for lake history

Relict (perched) lacustrine deltas around the perennially ice-covered lakes in the Taylor Valley, Antarctica, imply that these lakes were up to 40 times larger in area than at present since the last glacial maximum (LGM). These deltas have been used to constrain ice-margin positions in Taylor Valley, and the boundaries of the proposed LGM ice-damned Glacial Lake Washburn. The timing of these high lake levels has depended on 14C chronologies of algal layers within relict lacustrine deltas. To provide additional geochronometric data for the post-LGM lake-level history, we applied photon-stimulated-luminescence (PSL) sediment dating to polymineral fine silt and sand-size quartz from 7 perched-delta and 3 active-delta sites of different elevations along 3 major meltwater streams entering Lake Fryxell. Our PSL dating of 4 quartz-sand samples from core tops in the seasonal ice-free moat of Lake Fryxell (elevation ∼18 m a.s.l.) and two core-top moat samples from the seasonal moat of Lake Vanda in nearby Wright Valley establish that adequate PSL clock zeroing (by daylight) occurs in regional, modern shoreline deposits. Minimum-age micro-hole PSL results from the moats are consistently near 100 a. Minimum-age micro-hole age estimates for the deltas range from ∼50 to 100 a near the present lake level up to 13.4 ± 1.3 ka at 240 m. These are systematically younger than the comparable, reservoir-uncorrected, 14C ages that range from 7 ka (cal yr BP) to 13 ka (cal yr BP) near lake level up to 20 ka (cal yr BP) at 220–240 m elevation. Our results indicate the occurrence of a dramatic discrepancy between PSL minimum-age and 14C age estimates that is presently unresolved.

Luminescence dating of fluvial deposits in Vojvodina, N Serbia: First results

This paper reports on the first investigations into the potential of luminescence dating to establish a chronological framework for fluvial processes in the Tisa River Valley in Vojvodina, N Serbia. A total of 18 samples were collected from a terrace exposure near Mužlja, which comprised non-fluvial deposits at the top and fluvial deposits at the base. The luminescence characteristics of sand-sized quartz and potassium feldspar grains were investigated using a single-aliquot regenerative dose (SAR) protocol. The quartz separates exhibit a complex behaviour, making this dosimeter less suited for optical dating. Investigations into the behaviour of infrared stimulated luminescence (IRSL) measured at 50 °C (IR50) from K-rich feldspar extracts showed that preheating in excess of 60 s at 225 °C leads to significant sensitivity changes. The effect of IR stimulation on the thermoluminescence (TL) signal and that of preheating on IRSL intensity were examined; the results are inconclusive with respect to thermal stability, but are not inconsistent with the idea that the data do not reflect depletion of an electron trap. The IR50-signal measured after a preheat of 60 s at 115 °C behaves well in the SAR protocol, although it suffers from anomalous fading. Assuming that the signal is thermally stable, the fading-corrected ages suggest that deposition occurred during the end of the Late Pleniglacial and the early Late Glacial, which is consistent with geological expectations. Our observations demonstrate that IRSL dating of feldspar holds potential for establishing a chronology of fluvial dynamics of the Tisa River in N Serbia. Further methodological investigations are desirable; however, as issues relating to the stability and resetting of the IRSL signal remain to be resolved.

Facies and sedimentation of Coniacian deposits of the Kraków Swell in the Wielkanoc area (southern Poland)

Coniacian deposits, ca. 1.5 m thick, cropping out in the Wielkanoc Quarry, north of Krakow in southern Poland, consist of firm, nodular and, less commonly, marly limestones with horizons of in situ, slightly phosphatized hexactinellid sponges and thick-shelled inoceramid bivalves. The succession is composed of foraminiferal-inoceramid packstones with common sand-sized quartz and glauconite grains at the base, passing upwards into foraminiferal or foraminiferal-inoceramid wackestones with or without rare glauconite. A microfacies analysis shows that planktonic foraminifers are the dominant forms, while benthic forms are rare. The facies indicates that sedimentation in the Wielkanoc area on the Krakow Swell, which separated the deeper Mid-Polish Trough Zone to the north-east and the Opole Trough Zone to the south-west, was generally calm (documented by abundant wackestones) and slow (indicated by the dominant sedimentary “coccolith system” and presence of glauconite) during the Coniacian. Rare episodes of non-deposition are recorded by episodes of phosphatization and minor intra-Coniacian discontinuity surfaces. The presence of hexactinellid sponges in the section studied are consistent with a calm environment, below the storm-wave base, with low rates of sedimentation. Subhercynian (latest Turonian–Coniacian Ilsede Phase) local tectonic movements had an important influence on the evolution of the region. They presumably led to subsidence of the Wielkanoc Block during the Early Coniacian. These movements were probably associated with activity on the Krakow–Myszkow Fault Zone

Comparison of OSL ages from young dune sediments with a high-resolution independent age model

In order to test the accuracy of quartz optically stimulated luminescence (OSL) dating for young dune sediments (<100a), a series of aerial images of a migrating sand dune is used to cross validate OSL ages. The investigated dune is situated on the northern part of the island of Sylt (southern North Sea). Based on aerial images and a map from 1925 to 2009 and the internal architecture of the dune obtained by ground-penetrating radar (GPR), an independent age model has been developed to attribute sedimentary-architectural elements of the dune to time. The annual rate of dune migration is calculated to be around 4.1m/a. Along a 245m transect oriented parallel to the direction of dune movement, 13 samples for OSL dating were collected at equidistant locations. Sand-sized quartz (150–250μm) was used for determining the equivalent dose (De) applying a single-aliquot regenerative-dose (SAR) protocol. Results show that the oldest OSL age from the investigated recent dune appeared to be 110±10a, whereas the modern analogue was dated to 34±3a. In comparison with the aerial images, the OSL ages show a systematic overestimation of 10–40a for six out of seven younger samples, which are expected to be younger than ∼60a. This offset is negligible for older samples, but a substantial error in these younger ages. The overestimation is originated from a combination of small thermal transfer of 4–12mGy during preheat and incomplete bleaching in medium OSL component causing a residual dose of about 15mGy. The contribution of the incompletely bleached medium component cannot be removed totally by an early background subtraction approach. Despite the observed offset for youngest samples, this study corroborates the suitability of the OSL technique to date young dune sediments (<100a).

Comparative optical and radiocarbon dating of laminated Holocene sediments in two maar lakes: Lake Keilambete and Lake Gnotuk, south-western Victoria, Australia

Sediment core chronologies of optical dates on single-grains/very small aliquots of sand-sized quartz are compared with Accelerator Mass Spectrometry (AMS) radiocarbon (14C) chronologies from ostracod carbonate, mixed carbonates, sedimentary organic matter and charcoal in order to establish the age of laminated Holocene sediments in maar crater lakes Keilambete and Gnotuk, Victoria, Australia. Samples for optical and AMS 14C dating were taken from the same Mackereth cores, allowing a direct comparison of the two techniques from two laminated sedimentary sequences. Additional AMS 14C samples were taken from water in Lake Keilambete and from groundwater discharging into Lake Keilambete from the crater wall, with equivalent reservoir ages of 150 ± 30 and 1940 ± 30 years respectively.AMS 14C dating of modern ostracod carbonate in Lake Keilambete demonstrates a reservoir age of 670 ± 175 years. Optical dating of ‘single-grain/very small aliquots’ of sand-sized-quartz indicate the presence of a radiocarbon reservoir in Lake Keilambete that is consistent with that measured on modern ostracods, and also demonstrate that there is no 14C reservoir in Lake Gnotuk during the Holocene. The chronology presented here supports the premise that previously published bulk conventional 14C dates from Lake Keilambete were affected by old carbon, meaning that past chronologies require revision.Limitations on the use of optical dating of single-grain/very small aliquots include the relative paucity of sand-sized quartz, which decreases the precision of the sample equivalent dose (De), and is further confounded by low environmental dose rates and resultant large uncertainties on the final age assessment. Nevertheless, evidence for partial bleaching confirms that single-grain quartz dating is the most appropriate luminescence technique, and may prove a useful alternative in situations where 14C dating is unsuitable or an alternative chronometer is required.