The termination of the last major phase of aeolian sand movement,coastal dunefields,Denmark

Optically stimulated luminescence (OSL) dating of sand samples from stabilized (or inactive) coastal dunes in Denmark provides information on the age of the termination phase of the last major aeolian activity period. A total of 26 sand samples were taken from four different coastal dunefields around the North Sea, Skagerrak and Kattegat coasts of Denmark. The OSL dates indicate that the last major phase of aeolian activity terminated between ad 1860 and 1905. Most of the dunes examined in this study were active around 1820, during a period documented to have been very stormy. A dune management scheme started around 1792, and this no doubt was a major cause of dunefield stabilization, but an overall decline of storminess, particularly spring and summer storminess, around the end of the 19th century must also have contributed to the increasing inactivity of coastal dunes. The new OSL dates on aeolian sand movement agree well with historical data and data from topographic maps on dune movement. This agreement supports the observation from earlier work that OSL dating of recent aeolian sand movement is accurate over the last few decades to centuries. Copyright © 2005 John Wiley & Sons, Ltd.     

Evaluation of ESR residual dose in quartz modern samples,an investigation on environmental dependence

Luminescence and ESR dating methods of quartz sediment are based on the natural resetting of the signal by light exposure (optical bleaching). When the bleaching is incomplete, a residual dose (D_eR) is added to the post-depositional dose accumulated since the deposit and hence the age is overestimated.Insufficient bleaching is usually linked to the environment and conditions of transport/deposition of the quartz grains affecting the light exposure duration. Indeed, each transportation mode – fluvial, marine or aeolian – is associated to specific conditions of light exposure, depending mainly to the location of grains in the transport agent during the transport phase, the opacity of the transport environment and the velocity of the transport.The present study attempts to discriminate the modes of transport/deposition providing a satisfying reset of the ESR signals of quartz grains. For this purpose, we investigated bleaching rates and ESR residual doses of aluminum centers from “present-day” aeolian, fluvial and marine sediments sampled in various sedimentary environments. The bleaching efficiency evaluation in these different environments may help for a better understanding of the resetting phenomenon for quartz signals which represents presently the main difficulty for ESR dating.The results show that the residual doses are small enough to allow an ESR dating of the main part of the sediment transported in almost all the context examined in this study. The smallest residual doses are obtained from quartz grains within the range of 100–200 μm and transported in clear water. Some limits for the application of optically bleached quartz ESR dating appears nevertheless, mainly when the residual dose and the dose accumulated after the deposit are quite similar, i.e. for Upper Pleistocene samples.     

Uneven surface moisture as a driver of dune formation on ephemeral lake beds under conditions similar to the present day: A model-based assessment from the Makgadikgadi Basin,northern Botswana

An association between salt pans or dry lake beds and distinctive crescentic lake-floor sand mounds (1–10 m high, tens to hundreds of metres wide) is commonplace in desert systems. In the Makgadikgadi Basin of northern Botswana, a debate about the formative processes of these landforms has persisted despite numerous morphometric, sedimentary and geochronological analyses, with mound landforms variously inferred to be aeolian dunes, subaqueous dunes, spring mounds or shoreline remnants. We propose a new formative mechanism which draws on the interaction between uneven moisture distribution on the pan surface and mobile aeolian sediments. We use a numerical model (ViSTA), which couples vegetation and aeolian sand transport dynamics, together with optically stimulated luminescence (OSL) dating of a mound in the Makgadikgadi Basin to investigate the feasibility of this ‘sticky mound hypothesis’. We find that under a range of modelled environmental conditions, uneven moisture distribution on the pan surface can lead to the development and stabilization of crescentic aeolian dunes, with these dunes growing upwind from the point of initial deposition, corresponding with the chronological data gained from OSL dating of a mound feature. On removal of this moisture, the modelled dunes erode and dissipate. These findings suggest that the formative mechanism of the mounds could be dependent on the interaction between differential drying of the pan surface and the competence of the aeolian sediment transport system across the pan floor.     

Preliminary study on radiocarbon AMS dating of pollen

17 samples were collected from aeolian and lacustrine profiles within the environment sensitive zone of the Loess Plateau, and an experimental method was established which is suitable for pollen extraction from aeolian sediment. A comparative study of pollen dating was carried out using the accelerator mass spectrometry (AMS)¹⁴C dating of known age samples, and then an experiment with the pollen concentrates was performed. The results indicate that pollen that has been deposited simultaneously with sediment in a stable environment can provide reliable ages. This technique will provide a way of improving the chronological framework for the Loess Plateau since the late Pleistocene. The^I4c dating was combined with field investigations, and from the geological record within this zone, evidence was extracted of four major monsoon precipitation changes during the transition from the late Pleistocene to Holocene. Project supported by the National Natural Science Foundation of China (Grant Nos. 49894170, 49725308), Chinese Academy of Sciences (Nos. KZ-951-A1-402& KZ-952-S1-419), and State Committee of Science and Technology of China.     

Zircon provenance of Quaternary cover beds using U–Pb dating: Regional differences in the Southwestern USA

U–Pb dating of detrital zircons (DZ) in Quaternary slope deposits (cover beds) and examination of the surface structure of single zircon grains may enable reconstruction of the provenance of their aeolian components and help to reconstruct sedimentary palaeo-transportation cascades. We distinguish several layers of slope deposits (cover beds) using a palaeosol-supported sequence-stratigraphic approach. In a pilot study, we demonstrate the usability of using end-member-modelled analyses of grain sizes to identify the aeolian matter, multi-dimensional scaling and density functions (probability density functions (PDF) and Kernel density estimations (KDE)) of the U–Pb data, and the grain morphology of DZ, and show that the age and appearance variation of DZ in the Great Basin differ remarkably from those of the Colorado Plateau. All samples contain aeolian matter. Density functions of the DZ ages show similarities within each of the two regions. The Great Basin samples are dominated by late Cretaceous and Paleogene zircons, which are assumed to derive from volcanism. In contrast, the Colorado Plateau samples are almost free of these contributions. Presumably, the difference is due to palaeolakes, which were frequent in the Great Basin only, whose sediments contain a similar spectrum of DZ ages. Zircon morphology indicates that most grains have a history of aeolian transportation, whereas the grains assumed to be of volcanic origin often do not show similar transportation marks; this indicates that their transportation was dominated by the eruptive process but fewer steps of a transportation cascade. Multidimensional scaling of age data defines clusters of samples with similar DZ ages and – compared with published ages from possible sources – allows first interpretations of provenance. Quaternary aeolian sediments have not been studied in, and the applied mix of methods has not been applied to, the southwestern USA before. We demonstrate their feasibility for this study area.     

ESR dating of sedimentary quartz: Possibilities and limitations of the single-grain approach

Usually, multiple-grain aliquots are used for electron spin resonance (ESR) dating of sediments. However, this approach excludes the ability of detecting insufficient bleaching, as would be the case when measuring several single aliquots or single grains. In this paper, we present preliminary results of single-grain ESR dating experiments on three different sedimentary deposits (fluvial, fluvio-aeolian and desert aeolian), ranging in age between 100 ka and 2 Ma. Titanium-related impurity centres (Ti–Li and Ti–H) were measured in a Q-band ESR spectrometer for estimating equivalent doses (D_e) of individual quartz grains (0.5–1 mm). Both additive and regenerative dose methods were used. The resulting D_e plots show a large scatter in D_e—from 100 Gy to more than 600 Gy—for the fluvial sample, probably reflecting different bleaching histories of the grains. On the contrary, a clear plateau can be observed in D_e for sands with a strong aeolian component. Preliminary single-grain ESR ages are in relatively good agreement with independent estimates, the best results being obtained for the desert aeolian sample (200 ka). It is concluded that ESR has a promising potential for estimating large naturally accumulated doses of well-bleached sediments. Nevertheless, the method is challenged by several experimental difficulties, such as long measurement times, excessive errors, and presumably a complex interrelationship between Ti–Li and Ti–H components.     

干旱区湖泊沉积物中过剩210Pb的沉积特征与风沙活动初探

过剩~(210)Pb不仅是沉积物年龄测定的重要手段,而且是环境示踪的一种主要方法,干旱区湖泊主要为封闭湖泊,其沉积物所接受的过剩~(210)pb沉积在大气沉降背景外,主要受风沙侵蚀来源的影响.因此,较高的过剩~(210)Pb沉积通量有可能与区域风沙活动有关.本文在对比分析近几年来发表在各期刊中的湖泊~(210)Pb数据的基础上,计算各个湖泊多年平均过剩~(210)Pb的沉积通量并与大气过剩~(210)Pb沉降背景比较,从而初步确定中国北方干旱区风沙活动的可能区域.然后对所确定的典型风沙多发区,利用过剩~(210)Pb模式(PF-CRS)计算沉积物沉积速率,并与相应区域的"尘暴"记录对比,进而论证该方法在指示风沙活动方面的可靠程度.     

Test of high sampling density OSL dating of aeolian samples from the south margin of the Tengger Desert using the global standardised growth curve (gSGC) method

Chronostratigraphic records in the drylands of north China provide basic archives to reveal the dynamic connections between climate changes and the behaviour of aeolian systems. However, the interpretation of aeolian chronostratigraphy is not straightforward and may be associated with significant uncertainty due to a number of external and localised forces. Taking into account this complexity of aeolian systems, excluding preservation and sampling bias from palaeoclimatic signals requires that the interpretation of chronostratigraphic records be based on as many dates from as many sites as possible. Optically stimulated luminescence (OSL) dating provides a direct way to date aeolian sediments. However, the determination of equivalent dose (D_e) using the commonly applied single-aliquot regenerative dose (SAR) protocol is relatively time-consuming for samples with burial doses exceeding 50 or 100 Gy.In this study, the global standardised growth curve (gSGC) method is applied to multi-grain aliquots of coarse quartz from various sites covering a wide region of the south margin of the Tengger Desert in north China to rapidly determine D_e for a large number of aliquots and samples. The large between-aliquot variability in the shape of the dose response curve (DRC) is significantly reduced using a least-squares normalisation procedure. The results of a leave-one-out cross-validation (LOOCV) protocol demonstrates that D_e values determined using the gSGC and SAR methods are very consistent with each other up to at least 200 Gy and 400 Gy, for the 90–150 μm and 63–90 μm fractions, respectively. It suggests that the gSGC protocol can be used as an efficient procedure for D_e determination of a large number of aeolian samples from multiple sites. This in turn provides a better constraint for the interpretation of Late Quaternary aeolian chronostratigraphic records in drylands of north China.     

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

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

Luminescence chronology of aeolian deposits from the Qinghai Lake area in the Northeastern Qinghai-Tibetan Plateau and its palaeoenvironmental implications

Qinghai Lake, on the northeastern Qinghai-Tibetan Plateau, is the largest extant closed-basin lake in China, and has been the subject of numerous palaeoclimatological and palaeoenvironmental studies. In this study, 32 samples of aeolian sand, loess and palaeosol at six sites, and 1 sample of shoreline deposits underlying aeolian deposits were dated using optically stimulated luminescence (OSL). Where available, OSL ages are in agreement with previously published ¹⁴C ages. Our dating results, in combination with previous published ages on aeolian deposits showed that: (1) The oldest aeolian deposits around Qinghai Lake are in excess of 165 ka. (2) Aeolian deposition then began at ∼14 ka in the Qinghai Lake area. Periods of palaeosol formation occurred at ∼16.9 ka, ∼12.2–11 ka, ∼10–9 ka, ∼5.2–4 ka, and ∼3.9–0.7 ka. (3) The accumulation intervals of palaeosols are generally consistent with drilling-core-based environmental change proxies, indicating that palaeosols were formed during wet periods with higher vegetation cover. (4) A depositional hiatus period of ∼40–50 ka exists between the surface mantle aeolian deposits and underlying gravel deposits. (5) Lake levels during the Holocene did not exceed 3205.2 m elevation (11.8 m above recent lake level of April, 2010).     

Multi-method pIRIR dating of sedimentary sequences at the southern edge of the Gurbantunggut Desert,NW China and its palaeoenvironmental implications

The Gurbantunggut Desert is the second-largest desert in China, located in the westerly-dominated region of north-western China. Previous understanding of palaeoclimate of this desert was mostly based on lake and loess records from the Junggar Basin and Tian Shan Mountains, whilst direct dating of sedimentary records from the desert was very limited. This study applies high-resolution post-infrared infrared stimulated luminescence (pIRIR) dating to three sedimentary profiles at the southern edge of the Gurbantunggut Desert, which contain aeolian sand and water-lain sediments, recording palaeoenvironmental changes at the desert margin since the Last Glacial Maximum (LGM). Different pIRIR dating procedures were applied for samples with different ages. For Holocene-aged samples, a single-aliquot regenerative-dose (SAR) pIRIR procedure based on a three-stepped pIRIR measurement at 110 °C, 140 °C and 170 °C was used, and a standard growth curve (SGC) procedure yields an equivalent dose (D_e) similar to that of the full-SAR procedure; thus, is applicable for accelerating D_e measurement. For samples much older than the Holocene, a multi-aliquot regenerative-dose (MAR) pIRIR procedure based on a three-stepped pIRIR measurement at 150 °C, 200 °C and 250 °C was found to be the optimal dating procedure, because a SAR procedure would yield underestimated ages due to uncorrected initial sensitivity change. pIRIR dating results of the investigated profiles reveal a substantial sand accumulation during the LGM, an intensification of aeolian deposition at ∼12 ka and a wetter depositional environment at ∼10–8 ka. A rapid fluvial deposition is dated at ∼20–19 ka, corresponding to the deglaciation period. The sedimentary records from the desert margin show some correlation with lake and loess records in the same region and suggest a complex response of the desert environment to different climatic factors.     

Luminescence chronology from the Verkhoyansk Mountains (North-Eastern Siberia)

This study presents new dating results from the Verkhoyansk Mountains in northeastern Siberia. Pleistocene sediments of aeolian and glacial origin have been studied and dated by infrared optically stimulated luminescence (IRSL). The chronostratigraphy of this vast area is mainly based on radiocarbon dating up to now. Aeolian sediments are widespread in the foreland of the Verkhoyansk Mountains. IRSL-dating results indicate two major periods of increased accumulation between 33 and 24 ka and between 13 and 9 ka. A new stratigraphy of Pleistocene glaciations in this area has been developed. Up to five end moraines have been identified in two catchments areas. IRSL was applied to date the sandy and silty sediments covering the glacial deposits in order to get minimum ages. Furthermore, glacial and glacio-fluvial deposits were also sampled from a few locations. According to the IRSL dating results, the uppermost end moraine was deposited prior to 50 ka. The three outermost moraines might have been formed during Early Weicheslian to Saalian times. It is very likely that no major glaciers reached the foreland of the Verkhoyansk Mountains during the Last Glacial Maximum (LGM, MIS 2).     

OSL dating of sediments from the Gobi Desert,Southern Mongolia

The present study focuses on the chronological relationship between alternating dune sand and silty water-lain sediments in the central part of the Khongoryn Els dune field in the Gobi Desert, Southern Mongolia. The 23 m high section evolved from the construction of a natural dam by west–east moving sand dunes and fluvial inundation by a river system from the mountain ranges in the south. To resolve the chronology of events, optically stimulated luminescence (OSL) dating was applied and from sedimentological and geochemical analysis the depositional processes could be characterised. Quartz OSL dating of these sediments is hindered by feldspar contamination. Thus, dating of coarse-grain K-feldspars is applied to provide a more reliable chronostratigraphy. As this fraction might be influenced by signal loss over geological time scales, the extent of fading is measured and corrected for. The resulting ages fit well in a supraregional reconstruction of Central Asian palaeoclimate. The data imply that the basal aeolian sediments were deposited 27 ka ago, while the major part of the profile was accumulated in a rather short period of time around ～15 ka. The temporal differentiation implies that the stratification of aeolian and fluvial sediments is not caused by long term climatic variations. It rather represents arid conditions with episodical fluvial activity. Samples between 20 and 15 m depth could not be taken, but it is assumed that this part of the section represents an extremely arid time period with an intensive remobilisation of sand around LGM. A dune overlying the section was deposited during the Late Holocene and represents the ongoing aridity in this region.     

OSL dating of mixed coastal sediment (Sylt,German Bight,North Sea)

As part of a study on coastal sedimentary processes this paper presents the OSL dating of mixed coastal sediment samples from the southern North Sea island of Sylt (German Bight). During coring of the swash-bar (beach) sediments, five samples were presumably contaminated by younger overwash and aeolian sediments because of the sampling method employed. To obtain reliable burial ages for these swash-bar sediments, single-grain and small aliquot measurements were used together with the Finite Mixture Model (FMM) proposed by Roberts et al. (2000) to identify the grain population containing the largest doses (from the deepest part of the core). Before the FMM was applied to dating, the parameters and performance of the FMM were first investigated by systematically comparing small aliquot (∼20 grains) and single-grain measurements of an undisturbed aeolian and swash-bar sample and a laboratory mixture of both sediments. This test case demonstrates the advantage of selecting the time interval immediately following the initial luminescence signals for background subtraction because unsuitable quartz grains were removed from the dose distribution. It is concluded that the measurement of small aliquots can be regarded as a reliable proxy for single-grain dose distribution if the sediment contains only a small proportion of quartz grains emitting a luminescence signal and that the FMM results are relatively insensitive to changes of the over-dispersion parameter between 5–40% for small aliquots and 10–40% for single-grains.We show that the burial ages of the contaminated swash-bar samples resulting from the maximum age populations from equivalent dose distributions measured using small aliquots are consistent with the stratigraphy and with ages obtained from uncontaminated samples.     

ESR dating of optically bleached quartz grains from Plio-Pleistocene to Holocene coastal dune deposits (Wilderness-Knysna area,South Africa): a comparison with luminescence

Five Plio-Pleistocene to Holocene aeolian quartz samples from the coastal dune deposits of the Wilderness-Knysna area (South Africa) previously dated by OSL were selected for ESR dating. Samples were processed following the Multiple Centre approach and using the Multiple Aliquot Additive dose method. Aluminium (Al) and Titanium (Ti) signals were systematically measured in all samples.Our study shows that ESR results obtained for Middle Pleistocene to Holocene samples may be strongly impacted by (i) the presence of a significant high frequency noise in the ESR spectra acquired for the Ti signals and (ii) the choice of the fitting function employed. In particular, if not taken into account, very noisy spectra can lead to a significant overestimation of the true ESR intensity measured for the Ti–H signal. These sources of uncertainty are however not sufficient to remove the ESR age overestimations. Consequently, our results indicate that the Al and Ti ESR signals of these quartz samples have not been fully reset during their aeolian transport.While this work contributes to improve our understanding of the ESR method applied to quartz grains, and especially of the potential and limitations of the Ti signals, it also provides additional baseline data to illustrate the existing variability among quartz samples of different origins or sedimentary context. Our results are consistent with previous studies by confirming that the Ti–H signal shows the best potential for the evaluation of low dose values (<100 Gy for these samples), whereas it becomes inappropriate for the higher dose range, and the Ti–Li–H (option D sensu Duval and Guilarte, 2015) should be used instead.Beyond the methodological outcome, this ESR dating study also provides a useful addition to the existing chronology of the aeolian deposits in this region. In particular, new (and possibly) finite numerical age results were obtained for the two oldest samples, constraining the aeolianite landward barrier dune and the coversand formations to the MIS 10-8 and Pliocene, respectively.     

Luminescence chronology of fluvial and aeolian deposits in the Russian Altai (Southern Siberia)

Geomorphological investigations in the Russian Altai Mountains provide evidence for the extent and timing of Late Quaternary glaciations and aeolian sediments. Infrared optically stimulated luminescence (IR-OSL) and thermoluminescence (TL) dating of aeolian sediments from the central part of the Russian Altai were carried out on silty and sandy sediments that cover fluvial and glacio-fluvial terraces. Most samples from loess, loess-like sediments and sandy loess taken from different terrace sequences within the Altai Mountains provide IRSL ages suggesting a main aeolian deposition period between 25 and 15 ka. These data are consistent with those from the adjacent Mongolian Altai. Sand and silt layers within moraines yielded IRSL age estimates between 22 and 19 ka and correlate to the ice margins of the Last Glacial Maximum. Aeolian dune sands overlying or neighbouring the loess-like sediments and the fluvial terraces at some places provide evidence for Late Glacial (around 15 ka) and Early Holocene (around 9 ka) aeolian activity. The youngest sand sheets gave deposition ages of about 1.5 ka. These sediments covered graves and are related to overgrazing. They provide evidence for the significant human impact on the environment. Fluvial sediments, including silt and sandy gravel intermingled with charcoal, yielded contradicting radiocarbon and luminescence ages. IRSL age estimates obtained for the silty layers range from 19 to 18 ka and are significantly older than the radiocarbon ages, which gave sub-recent ages between 1170 and 910 BP. These data indicate fluvial sedimentation of debris and mudflows in a period of deforestation and strong soil erosion related to mining activities during the 9th and 10th century.     

Age determination for a Neolithic site in northeastern Qinghai-Tibetan Plateau using a combined luminescence and radiocarbon dating

The archaeological Shaliuheqiaodong site, located at the junction between the estuary of Shaliu River and the northeast bedrock terrace of Qinghai Lake, is one of the earliest Neolithic Age sites in the Qinghai-Tibetan Plateau (QTP), which is critical for understanding patterns of prehistoric human inhabitation in the high plateau extreme environments. There are only two published radiocarbon ages by far for chronological control. Recently, a new section (Gangcha section) was found, with abundant charcoals and fish bones well-preserved in the matrix of aeolian sediments, providing a good opportunity for a combined study of luminescence and radiocarbon dating. In the current study, we obtained three luminescence ages on aeolian sediment, six radiocarbon ages (three on charcoals and three on fish bones). Our results showed that the luminescence ages (average of 3.2 ± 0.2 ka) are in agreement with charcoal radiocarbon ages (3165–3273 cal a BP) where applicable, and that the lake reservoir effect age of radiocarbon dating was approximately 0.3–0.7 cal ka BP and an average of 0.4 cal ka BP at ∼3.2 cal ka BP (age difference between that of charcoals and fish bones). The prehistoric residence in Qinghai Lake area seemed to be sequenced from 15 ka BP to 3.1 ka BP, based on our data and previously published data altogether. The obvious baked vestiges on the bones of fish and animals, as well as a number of artifacts, indicate that naked carps had become a food resource for prehistoric people at least since 3.2 cal ka BP.     

Geomorphologic evidence of phased uplift of the northeastern Qinghai-Tibet Plateau since 14 million years ago

~~Geomorphologic evidence of phased uplift of the northeastern Qinghai-Tibet Plateau since 14 million years ago~~     

Constraining the Late Wisconsinan retreat of the Laurentide ice sheet from western Canada using luminescence ages from postglacial aeolian dunes

Optically stimulated luminescence (OSL) dating of quartz extracts from postglacial aeolian dunes from central Alberta in western Canada points to a landscape that was free of ice as early as 15 ka. Data from profiles where multiple ages have been obtained indicate an increase in depositional age with depth, suggesting that older aeolian sands underlie the dated sequences. The OSL ages present plausible minimum age constraints for the retreat of the Laurentide Ice Sheet (LIS) towards the end of the Late Wisconsinan glaciation. Previous reconstructions of the LIS recession have relied on radiocarbon chronologies, despite the scarcity of contemporaneous radiocarbon-bearing material for large parts of western Canada. While the OSL chronology may be deemed concordant with ice sheet margin retreat models determined using radiocarbon data, there appears to be a systematic lag in the radiocarbon ages which may reflect that aeolian activity is initiated prior to the proliferation of organic material. The OSL chronology reported in this study does not preclude the emergence of a wide deglacial corridor between the LIS and the Cordilleran Ice Sheet by 15 ka or earlier. The possibility of such a passage would resuscitate the notion of an ice-free corridor that appeared early enough to afford the first peoples of the Americas a navigable inland migratory passage from Beringia to south of the North American ice sheets. More broadly, the corridor would also have allowed genetic exchanges between the Beringian refugium and the American middle and low latitudes.     

Aeolian sediment fingerprinting using a Bayesian mixing model

Identifying sand provenance in depositional aeolian environments (e.g. dunefields) can elucidate sediment pathways and fluxes, and inform potential land management strategies where windblown sand and dust is a hazard to health and infrastructure. However, the complexity of these pathways typically makes this a challenging proposition, and uncertainties on the composition of mixed‐source sediments are often not reported. This study demonstrates that a quantitative fingerprinting method within the Bayesian Markov Chain Monte Carlo (MCMC) framework offers great potential for exploring the provenance and uncertainties associated with aeolian sands. Eight samples were taken from dunes of the small (~58 km²) Ashkzar erg, central Iran, and 49 from three distinct potential sediment sources in the surrounding area. These were analyzed for 61 tracers including 53 geochemical elements (trace, major and rare earth elements (REE)) and eight REE ratios. Kruskal–Wallis H‐tests and stepwise discriminant function analysis (DFA) allowed the identification of an optimum composite fingerprint based on six tracers (Rb, Sr, ⁸⁷Sr, (La/Yb)_n, Ga and δCe), and a Bayesian mixing model was applied to derive the source apportionment estimates within an uncertainty framework. There is substantial variation in the uncertainties in the fingerprinting results, with some samples yielding clear discrimination of components, and some with less clear fingerprints. Quaternary terraces and fans contribute the largest component to the dunes, but they are also the most extensive surrounding unit; clay flats and marls, however, contribute out of proportion to their small outcrop extent. The successful application of these methods to aeolian sediment deposits demonstrates their potential for providing quantitative estimates of aeolian sediment provenances in other mixed‐source arid settings, and may prove especially beneficial where sediment is derived from multiple sources, or where other methods of provenance (e.g. detrital zircon U–Pb dating) are not possible due to mineralogical constraints. Copyright © 2017 John Wiley & Sons, Ltd.