Μm Quartz Grains Research Articles

ESR dating of optically-bleached quartz grains: Evaluating measurement repeatability and reproducibility

The true random uncertainty associated with ESR measurements of quartz grains at cryogenic temperature is currently unknown, as well as its impact on resulting equivalent dose (DE) estimates for ESR dating purpose. We provide here the results from the first quantitative evaluation study based on experimental data. Repeated single aliquot and multiple aliquot measurements of 100–200 μm quartz grains show that the random uncertainty (1σ) on the measurement of an individual aliquot usually lies in the range of 1–2%, 2–3 and 3–6% for the Al, Ti and Ti–H signals, respectively. These values are strongly sample and laboratory dependent, as they directly correlate with the signal-to-noise ratio associated with each signal, and may also be influenced by the stability of the experimental setup. The resulting variability of the DE values obtained from the multiple aliquot additive dose method over repeated measurements is estimated to 9%, 11% and 24% (1σ) on average for the Al, Ti and Ti–H signals, respectively.In the light of this outcome, the reliability of a dose estimate derived from one single measurement may be reasonably questioned, and we strongly advocate for the necessity to systematically carry out repeated measurements of a given quartz sample, a procedure that is far from being systematic within the community. Finally, our reproducibility experiments suggest that the experimental setup, measurement temperature or operator do not induce a significant bias in the dose evaluation, provided that repeated measurement are carried out. Our small-scale interlaboratory comparison shows consistent DE results for the Al and Ti signals, giving us some general confidence for the comparison of the dating results obtained by independent laboratories. We nevertheless acknowledge that a larger intercomparison study should be performed within the ESR dating community in order to confirm these initial results.

Luminescence dating at Border Cave: attempts, questions, and new results

Border Cave hosts a rare Middle and Early Later Stone Age sequence of deposits that extends as far back as ca. 250 thousand years (ka). The site's chronology has been built mainly on Electron Spin Resonance (ESR) ages obtained from teeth, conducted at the end of the 1990s, and on radiocarbon dating for the more recent layers. In order to refine the sequence's chronology, several materials were selected for luminescence dating, including 34 siliceous lithic artefacts, and quartz and feldspar grains extracted from 10 sediment samples. Since the radioisotopic contents of the cave sediments are abundant in the volcaniclastic host rock (about 2% K, 10 ppm 232Th, 2 ppm 238U in the sediments) and the ages for the lower layers are over 40 ka, high (>150 Gy) equivalent doses (De) were expected for most samples. The saturated thermoluminescence (TL) signals of the lithic artefact samples suggested either that they had not been heated in the past, or that they were already too old to be dated. The presence in the sediments of 40–63 μm quartz grains dominated by the fast Optically Stimulated Luminescence (OSL) component and with apparent high D0 values (200–1000 Gy) suggested, a priori, that they could be appropriate for measuring high Des. However, a systematic drop of the De values for these high D0 grains was observed and could not be fully understood and corrected accordingly. The recently proposed pIT protocol, together with a global growth curve (GGC) approach, was applied to 63–80 μm feldspar grains extracted from the sediment samples. The data suggest that the IR225 signal was likely not fully bleached at the time of deposition. Nonetheless, two age estimates, assumed to bracket the target age, have been calculated for each sample. These estimates are consistent with the previous ESR ages and the ESR/C14-based Bayesian models. Further improvements can be considered in the future with the pIT - GGC method, which would allow both increased accuracy and precision.

Recycled sand from sandstone waste: A new source of high-quality fine aggregate

The construction industry is facing a shortage issue of river sand, therefore broadening new sources of fine aggregate is imminent. This paper demonstrates the feasibility of a recycled sand from sandstone waste in mortar manufacturing by comprehensive assessment of workability, mechanical properties, water absorption, alkali silica reaction (ASR). The recycled sandstone sand (S-sand) has a smoother microscopic morphology and better particle size distribution than river sand (R-sand). Fine particles smaller than 150 µm in R-sand usually contain a large amount of impurities (such as clay) and are considered harmful. However, the S-sand containing ∼15.7% µm quartz grains <150 µm significantly improves the mortar performance in terms of compressive strength and ASR property. At the same water to binder ratio, the mortar using the S-sand shows worse workability than that using R-sand but a slight increase of water to binder ratio or adding water reducer improves not only the workability but also mechanical properties. For the ASR test, the S-sand shows potential uncertain risk as per ASTM C 1260. Using calcined clay or fly ash to replace 25% cement can effectively inhibit expansion risk. The compressive strength is reduced due to ASR, however, as the ASR progresses, it is somehow restored. This study also finds the good linear relationship between length change of mortar bar and mass change, which can be used to predict the sand ASR property. The results showed that S-sand produced by waste sandstone by-products can be used as high-quality fine aggregate.

Revisiting the chronostratigraphy of Late Pleistocene loess-paleosol sequences in southwestern Ukraine: OSL dating of Kurortne section

Due to the general lack of other high-resolution paleoclimate records, loess-paleosol sequences are crucial archives for disentangling past climate variability in southeastern Europe. Here we present results of a multi proxy sedimentological and geochemical investigation of Kurortne loess-paleosol section from southwestern Ukraine, coupled with detailed optically stimulated luminescence (OSL) dating. OSL investigations were carried out on quartz grains of different grain sizes (4–11 μm, 63–90 μm and 90–125 μm), using the single aliquot regenerative (SAR) protocol. The OSL dating results are in line with previous findings on dating loess-paleosol sequences along the Black Sea shore in Romania, as well as worldwide: (i) ages obtained on different grain sizes are in agreement for equivalent doses of less than 200 Gy, whereas for higher equivalent doses 4–11 μm ages underestimate the coarser fraction ages; and (ii) an inverse correlation between dated grain size fractions and saturation characteristics is reported.Our combined dating and sedimentological approach would confirm that the investigated uppermost 4.5 m at Kurortne cover the Last Glacial Cycle, adding important data in better constraining local and regional chronostratigraphic correlations. The application of the SAR protocol on 63–90 μm quartz grains on samples collected from the lower part of S1 soil (the Kaydaky unit) and from the Kaydaky/Pryluky units boundary produced ages of 123 ± 10 ka and 85 ± 6 ka, respectively. As the temporal range covered by these units in the Ukrainian Quaternary stratigraphic framework is still debatable, our results confirm the broad correlation of the Kaydaky-Pryluky paleosol units at Kurortne with the last interglacial (i.e., MIS 5). Dating the Uday and Bug loess units produced ages corresponding to MIS 4 and MIS 2, respectively, whereas the sample collected from the Vytachiv unit provided an age of 37.7 ± 2.4 ka, assigning this paleosol to MIS 3. On the basis of trends in the magnetic enhancement, the onset of pedogenetic processes likely commenced already around 20 ka, but the formation of the topmost S0 soil has begun after 13.8 ± 1.0 ka.

Dating the palaeolithic footprints of ‘Le Rozel’ (Normandy, France)

Abstract Luminescence ages were obtained from six sediment samples at the archaeological site ‘Le Rozel’. These samples are associated with hundreds of footprints left by humans (probably Neanderthals) in the archaeological layers. The single-grain technique was applied to 200–250 μm quartz grains, whereas K-feldspar grains were measured using the multi-grain pIRIR225 signal. For quartz, final De estimates were derived in applying a Bayesian model. The comparison of these minerals indicates that the K-feldspar ages are significantly higher than the quartz ages. Nevertheless, the OSL quartz measurements are in agreement with the sedimentological data, and consistent with previous OSL ages obtained in the 2000s for layers in a stratigraphical lower position. It was then concluded that feldspar grains have been likely insufficiently bleached due to the short transportation distance and/or because of a rapid burial by more recent sediments. Such a rapid sedimentation rate would also explain the good preservation of the found numerous human prints. Our new findings indicate that the site was inhabited during the outgoing MIS 5 and the footprints revealed an age of at least 70 ± 10 ka.

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.

Evidence for bioturbation of luminescence signals in eolian sand on upland ridgetops, southeastern Minnesota, USA

This study sought to identify the age of eolian sand on narrow ridges in the Root River valley of southeastern Minnesota. The ridges in the region are cored by Ordovician dolomite and Cambrian sandstone, but the ridge tops are typically covered with Late Wisconsin Peoria and older loess units. In some locations Peoria loess is absent and the ridgetops are covered with up to 3 m of eolian sand that was likely sourced from local river valleys and transported to the uplands by sand ramps. We studied nine ridgetop soil profiles and collected seventeen OSL samples from eolian sand at depths ranging from 0.3 to 2.6 m below the present ground surface. All OSL samples were analysed using small aliquots where 90–150 μm quartz grains were applied to the inner 2 mm of 10 mm aluminum disks. The OSL ages ranged from 12.3 to 1.5 ka indicating a significant amount of age variability, and potentially suggesting nearly continual eolian deposition throughout the Holocene. However, several key differences were identified between those samples taken from within 1 m of the ground surface compared with samples that were more deeply buried. Those samples collected from depths of greater than 1 m yielded ages that were tightly clustered between 12.3 and 10.3 ka, while samples taken from depths of less than 1 m showed ages with much higher spread that ranged from 1.5 to 10.1 ka. The samples collected from within 1 m of the present ground surface also commonly showed higher spread in their equivalent dose distributions and higher overdispersion values relative to the samples that were more deeply buried. This suggests the luminescence signals from the upper portions of these deposits were reset after burial, most likely by bioturbation, and that the OSL ages are not depositional ages. This interpretation is supported by evidence from a core sample collected from one of our sites that shows primary eolian lamina are preserved below 1.4 m depth but not above this depth. Presumably, the bioturbation agents were effective at both resetting the luminescence signal and disturbing the primary bedding to depths of at least 1 m. If bioturbation occurred below this threshold it apparently did not impact either of these indicators. Our findings suggest the upper 1 m of these profiles were impacted by bioturbation and that all of the eolian sand on these ridgetops was likely deposited prior to 10.1 ka.

Testing the use of quartz ‘micro-hole’ photon-simulated luminescence for dating sediments from the central Lomonosov Ridge, Arctic Ocean

In the Arctic Ocean, direct dating methods are needed as an alternative to the radiocarbon (14C) method and to various indirect approaches for a longer stratigraphy. In past attempts to develop a luminescence sediment dating, the use of fine-silt (4–11 μm) mixture of quartz and feldspar grains from core tops has often produced large age overestimates by several ka. A recent application of micro-focused laser (‘micro-hole’) photon-stimulated luminescence (PSL) to medium-silt to fine-sand quartz grains (11–105 μm) from the core tops at the Alaska margin has been usefully accurate. To extend this approach to the central Arctic Ocean and to a larger grain size range, we applied micro-hole PSL dating to >11 μm quartz grains from core tops (0.5–2 cm horizon) from two sites on the central Lomonosov Ridge. We obtain a burial age estimate of ca. 2 ka for 11–62 μm grains at a multicore site 18 MC within a perched intra-ridge basin, in accord with 14C ages obtained on foraminifers. At nearby site 19 MC on the erosive ridge top, the micro-hole PSL dating of >90 μm quartz grains produces a burial age estimate of ∼ca. 25 ka, in accord with a foraminiferal 14C age of ca. 26 ka. However, the 11–90 μm grains from the same sample produce a much younger burial age estimate of ca. 9 ka. Thus, these two size fractions of quartz grains record different burial times and different deposition agents (icebergs vs. sea ice), providing insight into past sedimentary processes. Overall, our results confirm an earlier conclusion from micro-hole PSL dating study at the Alaska margin that medium to coarse silt fractions of quartz grains (11–90 μm or at least 62 μm) is the preferred material for direct dating of the last daylight exposure of detrital sediment in the Arctic Ocean.

Surmounting luminescence age overestimation in Alaska-margin Arctic Ocean sediments by use of ‘micro-hole’ quartz dating

Because of several difficulties with the application of radiocarbon ( 14C) dating to Arctic Ocean sediments, numeric dating techniques are needed that can complement, supplant and reach beyond the 14C method. However, large age overestimates (often >7 kyr) for near-sediment-water-interface horizons from Arctic Ocean cores have been almost universal when luminescence dating has been applied to multigrain aliquots of fine silt (4–11 μm) quartz and feldspar grains. Here micro-hole quartz-grain photon-stimulated-luminescence (PSL) dating is applied to the 0.5–2.0 cm horizons of multicores from high-sedimentation-rate sites spanning depths from 87 m to 1140 m at the Alaska margin of the Arctic Ocean. Expected near zero ages (0–200 a) result when grains larger than ∼11 μm are used, demonstrating that fine-silt age overestimations here and perhaps elsewhere in the Arctic Ocean are a function of grain and aliquot size. At the 87 m site, the micro-hole PSL approach revealed no significant gradient in age estimates over the 1–26 cm horizon range, implying that bioturbation reached to at least 26 cm. Micro-hole PSL dating of 25–62 μm quartz grains from trans-ocean sea-ice sediment also produced expected near zero ages, in contrast to earlier reported long-bleach multigrain PSL results from 4–11 μm fractions of the same samples. The micro-hole PSL approach thus surmounts the age overestimation problem associated with the use of multigrain silt fractions, and overcomes limitations of the 14C method in this region. Finally, results unexpectedly suggest the potential of micro-hole quartz PSL for use in provenance studies of Arctic Ocean sea-ice sediment.

Probable Gut Contents Within A Specimen Of Brachylophosaurus Canadensis (Dinosauria: Hadrosauridae) From the Upper Cretaceous Judith River Formation Of Montana

Abstract An exceptionally preserved subadult specimen (JRF 115H) of a hadrosaurid, Brachylophosaurus canadensis, from the Judith River Formation near Malta, Montana, contains abundant plant fragments concentrated within the body cavity. We examined the taphonomy of the carcass and analyzed the gut-region material to test whether the organic remains represent fossilized gut contents. The dinosaur was buried in a fluvial channel setting, and the excellent articulation, integument impressions, and lack of scavenging indicate rapid burial. The organic material occupies a volume of at least 5750 cm3, and comparable material is not found outside the carcass. The carcass contents include ∼63% clay, ∼16% undetermined matrix, ∼12% organic matter, and ∼9% larger inorganic clasts—mostly 50–100 μm quartz grains. Most of the organics appear to be mm-scale leaf fragments. The most parsimonious explanation for the presence and composition of the gut-region material is that much of the plant fossils represent reworked br...

Residual Doses in Recent Alluvial Sediments From the Ardenne (S Belgium)

Residual Doses in Recent Alluvial Sediments From the Ardenne (S Belgium) We report on our first investigations into the potential of optical dating for determining the rate of river flood sedimentation in the Ardenne region (S Belgium). Two samples collected from a recent alluvial deposit were used to investigate the extent of resetting in different particle size fractions of quartz (4-11 μm, 63-90 μm, 90-125 μm, 125-180 μm, 180-212 μm and 212-250 μm) as well as in polymineral fine (4-11 μm) grains. Both samples show satisfactory OSL and IRSL characteristics. The IRSL signals from the polymineral fine grains yield an equivalent dose (De) of 3-4 Gy, while a De of 0.3-0.6 Gy was measured using large aliquots of quartz. Small aliquot analyses of 63-90 μm and 212-250 μm quartz grains confirm that the coarser fraction contains more grains with lower De's. Furthermore, for a modern sample (&lt; 3 years old), ~60% of the aliquots yields a De consistent with zero, indicating that these contain only well-bleached grains. These findings suggest that it might be possible to extract the true burial dose from dose distributions measured using small aliquots of coarse-grained (e.g. 212-250 μm) quartz.

Luminescence dating of old (>70 ka) Chinese loess: A comparison of single-aliquot OSL and IRSL techniques

The applicability of two different approaches in the luminescence dating of old (>70 ka) Chinese loess is investigated. Both SAR-OSL ages obtained on 63–90 μm quartz grains and SAR-IRSL ages obtained on 4–11 μm polymineral grains, for samples collected from two sites in the Chinese Loess Plateau (Luochuan and Dongchuan) are presented. The characteristics of the luminescence signals stimulated by blue and infrared light are investigated in terms of dose response and dose recovery, and as a function of age. Additionally, anomalous fading measurements from the 410 nm IRSL emission in polymineral fine-grains are reported. An average value of g 2days amounting to ∼3% per decade was measured and seems to be independent of site location and age. For the samples from Luochuan, independent age control (pedostratigraphy and palaeomagnetism) is available. At both sites, the SAR-OSL ages are always lower than the SAR-IRSL ages after they have been corrected for anomalous fading. It seems that the quartz-based SAR-OSL ages are accurate for the younger ages, but that they underestimate the true age of deposition for loess that was deposited about 60–70 ka ago. The fading-corrected SAR-IRSL ages are in better agreement with the pedostratigraphic age control (∼75 and ∼130 ka) and allow dating beyond the quartz OSL range. Based on our results, we suggest that conventional SAR-OSL and SAR-IRSL protocols at these sites should be restricted to samples of ages not exceeding ∼40–50 and ∼100–120 ka, respectively.

Recognition and characterisation of the aeolian component in soils in the Girilambone Region, north western New South Wales, Australia

Characterisation of aeolian material in the Girilambone Region of New South Wales (600 km NW of Sydney), using particle size analysis, mineralogy, geochemistry and micromorphological analysis, shows that it consists of spheroidal, highly abraded 70 μm quartz grains. Although relatively pure aeolian accessions are found on top of Tertiary leucitite flows, the aeolian material is generally admixed with residual and transported soil to a depth of 0.3 m throughout the region. This study has established a set of criteria for identifying the aeolian contribution to soils in the Girilambone region of north western New South Wales where it is difficult to distinguish. These include: a characteristic particle size of 70 μm of the quartz grains; highly abraded and spherical morphology; presence of thin clay coats on well-rounded grains; and gradational patterns in particle size distribution, mineralogy and geochemistry through the soil profile. These types of soils, with a high content of silt and fine sand, do not readily form aggregates, particularly where they have low organic content. To improve the sustainability of cropping and pastoral activities on these soils, their management should aim to maintain or increase structural stability, for example by addition of organic material. Mineral exploration procedures should avoid the diluting aeolian component by sampling the > 150 μm fraction from surficial soils or material from below 0.3 m.

Optical and thermoluminescence dating of Middle Stone Age and Kintampo bearing sediments at Birimi, a multi-component archaeological site in Ghana

We report the first luminescence ages for the archeological and geological sediments forming the substrate of the Birimi archaeological site in the Northern Region of Ghana. The site's significance rests on the fact that it contains a rich collection of artifact assemblages representative of three distinct cultures, and that, on the basis of artifact typology, the earliest assemblage is diagnostic of the Middle Stone Age (MSA) . In situ occurrences of MSA artifacts are found at over 1 m below today's surface. They are overlain by a ceramic-rich complex of a sedentary or semi-sendentary Later Stone Age culture known as the Kintampo. The western half of the site is dominated by the industrial remains of Iron Age smelting activity. Elemental, mineralogical, and sedimentological analysis of the cultural and sub-cultural sedimentary horizons at the site revealed at least three distinct lithostratigraphic units. The quartz sediments are derived from the sandstone of the Gambaga escarpment, mass wasted and accreted fluvially at a rate of 3.2 cm/ka, forming a wide terrace at Birimi. Silts and finer fractions derive from windblown dust, likely from White Volta River and granitic sources to the north. Soil forming processes and wide fluctuations in moisture have progressively reduced the sediments at depth to the resistant quartz and kaolinite, with rich iron oxide coatings, and created two ironstone horizons composed of goethite-cemented quartz nodules. Multiple aliquot green-light stimulated optical ages for 125–150 μm quartz grains yielded ages of 23.6±2.9 and 40.8±11.8 ka for the MSA-bearing sediments, and 58.4±15.3 ka for the base of the terrace. Radiocarbon ages on charcoal from Kintampo-bearing units are 3.36–3.83 ka cal BP, and are supported by thermoluminescence (TL) ages on pottery sherds and burnt house daub fragments of this cultural complex. A 0.4 ka age on sediment from the site's surface confirms that the quartz zeroes well when exposed to natural light. Sediments bearing the Kintampo artifacts, however, yielded ages of 7.8–16.9 ka. These ages were obtained on sediments from large pits, some over 50 cm deep, and they deviate only slightly from the ages expected for naturally aggraded sediments at these depths. We conclude, therefore, that extensive digging of pits by the Kintampo dwellers was followed by rapid refilling, and that the bulk mobilization of the matrix did not permit the sedimentary quartz grains to experience any appreciable zeroing at that time.

Comparison of SAAD and SAR procedures for equivalent dose determination using quartz

Comparisons between the single-aliquot additive-dose (SAAD) and single-aliquot regenerative-dose (SAR) procedures are made using 150– 212 μm quartz grains separated from three sediment samples. Growth curves and equivalent doses from the two procedures are compared directly using single aliquots of quartz. With appropriate corrections for the loss of signals in our SAAD protocol, the SAAD and SAR growth curves coincide well. It is confirmed that the luminescence correction in the SAAD protocol can only be applied to samples for which the natural signal is in the linear part of the growth curve. A new correction method is proposed.

Modeling the size distribution of a soil aerosol produced by sandblasting

In order to develop a model providing the mass size distribution of the dust raised from the ground by the sandblasting process, mechanical characteristics of 240 μm saltating sand grains meant to be used as projectiles in wind tunnel sandblasting experiments were carefully determined. It was found that for values of the measured friction velocity less than about 55 cm/s, the constraint of the relatively small dimensions of the wind tunnel test section did not prevent saltation from developing freely. The kinetic energy of the sand grains was also determined. Aerosols were then produced in the wind tunnel by bombarding a clay target with the saltating 240 μm quartz grains. The size distributions of these aerosols were measured for three wind speeds with an optical particle analyzer. For the lowest wind speed the size distribution of the aerosol was similar to that of the 8.6 μm aggregates originally constituting the agglomerates of clay, but disaggregation into smaller particles became more important when wind speed increased. A theory of sandblasting was then developed that gave theoretical results agreeing with the experimental ones. A consequence of this theory was that submicron particles could be released from aggregates for high wind speeds. Experiments meant to check this implication were carried out and confirmed it. Cohesion energies of kaolin particles of three different sizes, 8.6, 2.8, and approximately 0.5 μm, were calculated and found to be a decreasing exponential function of the particle size. This explains (1) why the soil‐derived aerosol size distributions present a common mode in the 1–10 μm size range, these particles being readily released even in not particularly energetic conditions, and (2) why observation of a submicron mode in natural aerosols requires a higher friction velocity than for the common 1–10 μm mode.

Effects of bacterial exopolymer adhesion on the entrainment of sand

Abstract Flow velocity required to erode a bed of acid‐washed sand is increased by intergranular adhesion resulting from growth of the benthic marine bacterium Al‐teromonas atlantica. In general, we find that either pure exopolymer alone or exopolymer generated during in situ growth increases erosion resistance of fine quartz sand. Moreover, the degree of erosion resistance increases in proportion to the concentration of exopolymer‐component uronic acids, which in turn is dependent on relative nitrogen content of peptone‐based growth media. Specifically, we observe that approximately 100 nmol of exopolymer or 1.5 nmol of component uronic acids generated by in situ bacterial growth under nitrogen‐rich conditions per gram of dry sediment can effectively double seawater‐flume flow velocity required for initiation of transport of otherwise noncohesive, 125–177 μm quartz grains. This maximal effect corresponds to an estimated adhesive force that exceeds submerged particle weight by an order of magnitude and ex...

South Australian sand dunes: A TL sediment test sequence: Preliminary results

A sequence of beach dunes, one for each high sea-level stand back to 600 ka, provides a set of samples of known ages for testing TL sediment dating techniques. 100 μm quartz grains from several of these show steadily increasing TL with age and the ages of the dunes are clearly resolvable over the whole of this time-span.