Optically Stimulated Luminescence Chronology Research Articles

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.

Different implications of OSL and radiocarbon ages in archaeological sites in the Qaidam Basin, Qinghai-Tibetan Plateau

Abstract Both Optically Stimulated Luminescence (OSL) dating and 14C dating are main dating method for archaeological sites, while their disagreements are quite often. In the Qaidam Basin (QB), human activity remains (HMRs) are frequently found within aeolian sediments, offering opportunities to make comparison between OSL and 14C ages, and to discuss their potential disagreements in archaeological sites. In this study, we present comparison between 18(10 of them had been published) OSL and 17 AMS 14C ages for samples from aeolian sediments in the eastern QB, including some samples from archaeological sites. Comparisons show better agreement in natural aeolian section, but more disagreements in sections with many HARs. This should be due to postdepositional anthropogenic disturbance, which can cause different influences to OSL and 14C ages. The age disagreement might display their different significances, with 14C chronology represent human activities, while OSL chronology more likely to reveal ages of original stratigraphy. Field hearth experiment was taken to check to what extent can heat from a hearth affect luminescence signals in the surrounding sediments. Results show that both OSL and Thermoluminescence signals in sediments under the hearths are not easy to be reset by the heat due to the poor downward thermal conductivity into the humid soil. This reminds the risk of OSL age overestimation for hearths. This study emphasizes the importance of cross-check between different dating methods for chronology building in archaeological contexts, and the necessity to analyze the dating materials, depositional process, and post-depositional disturbance when age disagreement is discovered.

Mid-Late Pleistocene OSL chronology in western Amazonia and implications for the transcontinental Amazon pathway

The origin of the transcontinental Amazon drainage system remains unrevealed. Sedimentary deposits formed from the Neogene in the Amazonas and Solimões Basins constitute natural archives for reconstructing this event in space and time. However, paleoenvironmental and chronological analyses focusing on these deposits, or even their basic mapping, are still scarce to allow such investigation. In this context, primary interests are fluvial strata related to the lithostratigraphic Içá Formation, mapped over a widespread area in western Amazonian lowlands. Although long regarded as Plio-Pleistocene in age, this unit has not yet been dated and its overall depositional setting remains largely undescribed. The main goal of the present work is to contribute for improving facies analysis and chronology of these deposits, approaching an area in southwestern Amazonia and another in northern Amazonia, which are located more than 1000km apart. Despite this great distance, the sedimentological and chronological characteristics of deposits from these two areas are analogous. Hence, facies analysis revealed paleoenvironments including active channel, abandoned channel, point bar, crevasse splay and floodplain, which are altogether compatible with meandering fluvial systems. Similarly, optically stimulated luminescence (OSL) dating revealed thirty three ages ranging from 65.4±16.9 to 219.6±25.1ky (in addition to three outliners of 54.0±7.6, 337.3±36.9 and 346.6±48.6ky), and nine 97.1±9.9 to 254.8±23.8ky for the areas in southwestern and northern Amazonia, respectively. These data lead to establish that deposits mapped as Içá Formation over a vast area of western Brazilian Amazonia have a Mid-Late Pleistocene age, rather than the previously inferred Plio-Pleistocene age. It follows that if Plio-Pleistocene deposits exist in this region they remain to be dated and must be restricted to a narrow belt in western Amazonia, as well as isolated occurrences underlying the Mid-Late Pleistocene strata characterized herein. The combination of data from this work with previously published provenance studies supports main Andean sediment sources only in the Mid-Late Pleistocene. It is proposed that before this time, the Amazon River was restricted to eastern Amazonia, being separated from western Amazonian drainage basins due to the presence of the Purus Arch. Erosion and/or subsidence of this geological feature would have promoted the connection of these drainage systems, ultimately with the expressive record of the transcontinental Amazon pathway into the Atlantic Ocean in the Mid-Late Pleistocene.

Time-Transgressive Nature of the Magnetic Susceptibility Record across the Chinese Loess Plateau at the Pleistocene/Holocene Transition.

The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS) has previously been assumed to be synchronous with the Marine Isotope Stage (MIS) 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP). However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR) protocol to the 45–63 μm quartz grain-size fraction to derive luminescence ages for the last glacial and Holocene sections of three loess sections on a transect from southeast to northwest across the CLP. Based on the 33 closely spaced optically stimulated luminescence (OSL) samples from the three sections, OSL chronologies were established using a polynomial curve fit at each section. Based on the OSL chronology, the timing of the Pleistocene/Holocene boundary, as defined by rapid changes in MS values, is dated at ~10.5 ka, 8.5 ka and 7.5 ka in the Yaoxian section, Jingchuan and Huanxian sections respectively. These results are clearly inconsistent with the MIS 2/1 boundary age of 12.05 ka, and therefore we conclude that the automatic correlation of the Pleistocene/Holocene transition, as inferred from the MS record, with the MIS 2/1 boundary is incorrect. The results clearly demonstrate that the marked changes in MS along the southeast to northwest transect are time-transgressive among the different sites, with the timing of significant paleosol development as indicated by the MS record being delayed by 3–4 ka in the northwest compared to the southeast. Our results suggest that this asynchronous paleosol development during the last deglacial was caused by the delayed arrival of the summer monsoon in the northwest CLP compared to the southeast.

OSL chronology of a sedimentary sequence from the inner-shelf of the East China Sea and its implication on post-glacial deposition history

Sedimentary records from the inner-shelf of the East China Sea (ECS) are unique for the reconstruction of post-glacial palaeoclimate and sea-level changes. So far, the chronology of sediment succession from this region has mainly been based on radiocarbon dating, which might be problematic due to reworked deposition or old carbon contamination. In this study we tested the applicability of optically stimulated luminescence (OSL) dating to a drilling core (ECS-DZ1) taken from the northern ESC. A total of 20 OSL samples and two radiocarbon samples were collected from the upper 58 m of this core. The results indicate the likely sufficient reset of OSL signal of fine-grained (4–11 μm) quartz before burial, and thus reliable chronology for the studied core sediments. For one sample, however, the extracted coarse-grained (100–200 μm) quartz overestimated the deposition age significantly, presumably resulting from partial bleaching prior to deposition. The fine-grained quartz ages are generally consistent with the stratigraphical order, and the reliability of these OSL ages are further validated by two selective robust 14C dates. The chronological framework of core ECS-DZ1 reveals striking sedimentation-rate changes. By comparison with other chronostratigraphical records, we infer that post-glacial deposition history (since ∼15 ka) of the study site is likely related to regional sea-level rise and delta-estuary environment evolution, as well as strengthened human activities and/or coastal currents.

A high-resolution quartz OSL chronology of the Talede loess over the past ∼30 ka and its implications for dust accumulation in the Ili Basin, Central Asia

Similar to the loess deposits on the Chinese Loess Plateau (CLP), a reliable chronology plays also an important role in revisiting past climate and environment changes recorded by the loess in Central Asia. Previously, a few luminescence and 14C ages, mainly covering the last glacial, were obtained for several loess sections in Central Asia, which are often controversial. Until now, there is still a lack of reliable high-resolution chronologies covering the late Pleistocene, especially the Holocene. Here, the fine-grained (4–11 μm) quartz single-aliquot regenerative-dose (SAR) optically stimulated luminescence (OSL) dating protocol is used to establish a detailed chronology of the uppermost part (∼5 m) of Talede loess in the Ili Basin Central Asia. Conventional tests of the SAR protocol and the general luminescence characteristics indicate that this protocol is suitable for dating the Talede loess. Finally, 15 closely-spaced quartz OSL ages, ranging from 0.72 ± 0.05 to 28.9 ± 2.12 ka and with no reversals, were obtained. Consistent with previous studies in the Ili Basin, two of the three 14C ages show discrepancy when compared with quartz OSL ages for the Talede loess section. The constructed OSL chronology of the Talede loess reveals that the dust accumulation is rapid during marine isotope stage (MIS) 2, especially during the Last Glacial Maximum (LGM), and is also continuous during the Holocene, with the dust accumulation rate exhibiting a relatively low level and an increasing trend. Comparison of the dust accumulation at Talede with that at other sites in the Ili Basin indicates that the rapid dust accumulation during the LGM is not universal, and the slow dust accumulation during the Holocene is probably true for the entire Ili Basin. Comparison of different grain sized quartz OSL ages from Central Asian loess show characteristics of both consistency and inconsistency, which needs to be further investigated.

An improved single grain OSL chronology for the sedimentary deposits from Diepkloof Rockshelter, Western Cape, South Africa

The single grain optically stimulated luminescence (OSL) chronology for the sedimentary deposit at Diepkloof Rockshelter, reported by Jacobs et al. (2008c), has recently been critiqued and several reasons proposed for why the OSL ages for the Intermediate and Early Howieson's Poort (HP) and Still Bay (SB) techno-complexes might be inaccurate. Tribolo et al. (2013) presented a series of OSL and thermoluminescence (TL) ages that were in agreement with each other, but, for some part of the sequence at least, were much older than the OSL chronology of Jacobs et al. (2008c). In this paper, we have tested the criticisms of Tribolo et al. (2013) and colleagues related to both the equivalent dose (De) estimates and the beta dose rates by performing a series of targeted experiments, combined with updates and re-assessments of our error calculations. We show that the De estimates are stable over a range of alternative measurement conditions and also over time. We also demonstrate the reproducibility of our measurement procedures for the beta dose rates, and their accuracy tested against a range of independently obtained estimates. We show that, for the stratigraphic units (SUs) where there are major discrepancies in age between Jacobs et al. (2008c) and Tribolo et al. (2013)—notably the Intermediate HP and Early HP—and for which both studies had single grain OSL ages, the estimation of potassium (K) in the sediment surrounding the dated grains is critical. We provide new and updated De and dose rate estimates, and final ages which we compare with our previous age estimates and those of Tribolo et al. (2013). The differences in the size of the errors associated with the ages reported in the two independent studies are also addressed. We can show that our ages are robust and consistent with the original chronology, but we cannot satisfactorily explain why the TL and OSL ages provided by Tribolo et al. (2013) might be wrong. So, the dating conundrum at Diepkloof Rockshelter remains. As a result, we caution against the development of HP and SB age models based on only one of the chronologies for this site. At this stage, extrapolation of the Tribolo et al. (2013) chronology to a re-interpretation of the southern African MSA would appear to be premature, especially as the ages do not differ systematically between the two studies and as differences between TL and OSL ages are not an issue at other sites in southern Africa where both dating methods have been applied. Further work is needed to resolve the question of the Diepkloof chronology.

OSL chronology and accumulation rate of the Nakdong deltaic sediments, southeastern Korean Peninsula

Optically stimulated luminescence (OSL) dating was performed on Late Quaternary deltaic sequences from a 55-m-long core sampled from the Nakdong River estuary, Korea. OSL ages obtained from chemically separated fine (4–11 μm) and coarse (90–212 μm) quartz grains ranged from 29.4 ± 2.6 to 0.4 ± 0.04 ka, revealing clear consistency between the grain-size fractions. The De values from the standardized growth curve (SGC) are consistent with those from the single-aliquot regenerative-dose (SAR) procedure, which suggests that the SGC is valid for the Nakdong deltaic sediments. The 14C ages of shells and wood fragments ranged from 11 to 2.9 ka, demonstrating reasonable agreement with the OSL ages, within the error range. However, the limited number and random sampling interval of the 14C age data (10 ages) result in a simple linear and exponential trend in the depth–age curve. In contrast, OSL ages obtained by high-resolution sampling show down-section variations in the depth–age curve, indicating the occurrence of rapid changes in sedimentation rate. It is suggested that the high-sampling-resolution OSL ages provide a more realistic and detailed depth–age curve and sedimentation rate. The Nakdong deltaic sediments were divided into five units based on sedimentation rate. The lowest (unit 5) shows a break in sedimentation between the last glacial maximum (LGM) and the Holocene. The sedimentation rate increased in units 4 and 3, presumably corresponding to the early to middle Holocene sea level rise and high stand. Unit 2 shows a gradually decreasing sedimentation rate following the regression of the shoreline, until about 2 ka. The progradation of the Nakdong River delta resulted in the rapid accumulation of unit 1 during the last 2000 years.

OSL chronology of middle to late Holocene aeolian activity in the St. Anthony dune field, southeastern Idaho, USA

Late Quaternary aeolian dune systems in the Great Plains and western U.S. are valuable archives of past climate variability. This study investigates the St. Anthony dune field, located in the eastern portion of the Snake River Plain in southern Idaho. The current semi-arid climate of the region allows for a central core of active dunes that is approximately 450 km2 in area and includes compound crescentic, blowout, falling, and climbing dunes that range in height from 15 to 121 m. The surrounding region is characterized by ∼20,000 km2 of relic parabolic, linear, and complex linear dunes that are currently fixed by vegetation.This study examined nine samples collected from the fixed dunes that surround the active core of the St. Anthony dune field. Optically stimulated luminescence (OSL) dating results indicate that these fixed dunes were mobile and actively accreting ∼6.6 ka (middle Holocene) and 1.0–2.0 ka (late Holocene). Evidence for activation of a large region currently occupied by stable dunes suggests these periods were characterized by hydrologic deficit and/or warmer climate conditions than currently exists. This research provides new information regarding the depositional timing of the St. Anthony dunes and assists in providing evidence of palaeo-climatic conditions for the eastern Snake River Plain during the middle to late Holocene.

Chronology and controls of donga (gully) formation in the upper Blood River catchment, KwaZulu-Natal, South Africa: Evidence for a climatic driver of erosion

Dongas (gullies and badland-type terrain) are found extensively across interior South Africa, but the controls on their formation remain contested. Establishing the timing of donga formation is essential for developing a clearer understanding of the relative importance of natural (e.g. climatic) and human (e.g. overgrazing) controls. Here, we present optically stimulated luminescence (OSL) ages for colluvial sediments exposed in the sidewalls of dongas and for tributary fan sediments deposited downslope of dongas in the upper Blood River catchment, eastern South Africa. The tributary fan ages enable the timing of donga formation to be established, since fan sedimentation is a direct result of upslope donga erosion. The OSL ages indicate that net colluviation and intervening palaeosol formation occurred from prior to 22 ka until ~1.6 ka. From ~0.89 ka to present, there has been a shift to net erosion characterised by widespread donga formation and tributary fan sedimentation. Contemporary donga formation in interior South Africa has most commonly been attributed to changing land-use practices associated with European settlement from the second half of the 18th century onwards, but the OSL chronology indicates that dongas in the study area began forming significantly prior to European settlement. Instead, the initiation and main phase of donga formation encompasses periods of abrupt climatic changes associated with the ‘Mediaeval Climate Anomaly’ (ad ~900–1300) and the ‘Little Ice Age’ (ad ~1300–1800). The magnitude and abruptness of climatic changes during these periods appear to have destabilised hillslopes and initiated the shift from long-term net colluviation to net erosion by donga formation. The OSL-based approach to constraining the timing of donga formation adopted in this study has broader implications for assessment of the drivers of historical and contemporary donga (gully) formation elsewhere in South Africa and other drylands, and may help to inform management strategies for degrading lands.

Holocene climate change inferred from stratigraphy and OSL chronology of aeolian sediments in the Qaidam Basin, northeastern Qinghai–Tibetan Plateau

Paleoclimatic reconstruction based on aeolian sediments in the eastern Qaidam Basin (QB) has been hindered by the limited chronological data. Here we present 61 Optically Stimulated Luminescence (OSL) ages. On the basis of these OSL ages and the lithologic stratigraphy, we propose the ‘effective moisture index (EMI)’ for aeolian sediments to reconstruct the effective moisture change. Based on the EMI from twelve sections, the effective moisture change, moisture sources and relevant mechanisms for paleoclimatic change in the eastern QB are discussed. The results indicate that (1) aeolian deposition started at least before 12.4±0.7ka during the deglaciation, the paleosols developed at the early and mid-Holocene, and aeolian sand and loess accumulated at mid- and late Holocene; (2) effective moisture history was: hyper-arid at 12.8–11.6ka, humid and variable at 11.6–8.3ka, moderately humid and stable at 8.3–3.5ka, and increasingly arid at 3.5–0ka; (3) the effective moisture change was mainly controlled by the Asian summer monsoon (ASM), which mainly followed the change of Northern Hemispheric summer insolation, and the westerlies strengthened and increased the aridity in the QB when the ASM shrank.

The utility of desert sand dunes as Quaternary chronostratigraphic archives: evidence from the northeast Rub' al Khali

The distributions of optically stimulated luminescence (OSL) ages from dunes are affected by palaeoenvironmental changes, complex dune dynamics and sampling strategy. Extracting the relative importance of these factors when interpreting discontinuous OSL chronologies from sand dunes has proven difficult, and is particularly hindered in contexts where the internal sedimentary structures of dunes are not visible. In this study samples for OSL dating were taken from three major dune exposures in the Rub' al Khali, United Arab Emirates, each showing clear internal structure, with the aim of addressing these problems. Specific objectives were to assess how ages of individual sedimentary units represent dune accumulation as a whole, and how the dune record in turn reflects known past environmental changes. Final ages were calculated using the OxCal software package, by incorporating the known relative stratigraphy through the application of Bayesian methods. The results show that stratigraphy alone is not sufficient at these sites to guide OSL sampling; that is, chrono- and lithostratigraphic boundaries do not necessarily coincide. Where chronological hiatuses are present, internal sediment stratigraphy can be a useful tool in identifying potential problems of under-sampling the full dune record. The implications of these findings for reconstructing Quaternary climates from dune chronologies are considered.

OSL chronology and paleoclimatic implications of paleodunes in the middle and southwestern Qaidam Basin, Qinghai-Tibetan Plateau

Aeolian sediments are widely distributed in the Qaidam Basin, northeastern Qinghai-Tibetan Plateau (QTP). The paleodunes are mainly located at the southeastern, middle and southwestern Qaidam Basin. However, ages of paleodunes in the middle and southwestern Qaidam Basin have not been well studied, although they are close to and might connect to the evolution of salt lakes in the central basin. In this study, we use single aliquot regeneration (SAR) protocol of Optically Stimulated Luminescence (OSL) to date the dune sand in these two regions. The results show that: (1) Sand accumulation in these regions started at ca. 4-3 ka and lasted to ca. 0.5 ka when they were stabilized, due to the arid climate in the late Holocene. (2) The underlying fluvial sand was formed during deglaciation at 12.6±0.8 ka. (3) The stabilization periods of the paleodunes correspond to stages of glacier advance in the northeastern QTP, during which lower temperatures caused the decrease of evaporation and increase of the effective moisture, leading to an increase of vegetation cover and stabilization of the dunes.

OSL chronology of Quaternary terraced deposits outcropping between Mt. Etna volcano and the Catania Plain (Sicily, southern Italy)

In this paper we tested the applicability of the Optically Stimulated Luminescence (OSL) technique through Single-Aliquot Regenerative-dose (SAR) protocol, on single grain quartz extracted from alluvial–coastal sediments. Five samples were collected from deposits belonging to a flight of seven orders of coastal–alluvial terraces outcropping in the area between Mt. Etna volcano and the Catania Plain (Sicily, southern Italy), at the front of the Sicilian fold and thrust system. After various performance tests, we obtained OSL ages ranging between 240±12 and 80±4ka, consistent with the normal evolutionary model of a terraced sequence, moving from the highest to the lowest elevation. Obtained data allowed us to determine a mean uplift rate of 1.2mm/year during the last 240ka, mostly related to regional uplift processes coupled with sea-level changes. Moreover, terraces belonging to the two highest orders are folded, forming a large anticline. According to our results, the frontal thrust of the Sicilian chain was active between 236 and 197ka ago, even though seismological and geodetic data suggest current activity to the back.

The loess sequence of Dolní Věstonice, Czech Republic: A new OSL‐based chronology of the Last Climatic Cycle

The Dolní Věstonice loess section in the Czech Republic is well known for its high‐resolution loess–palaeosol sequence of the last interglacial–glacial climatic cycle (Upper Pleistocene). The loess section is situated in a climatic transition zone between oceanic and continental climates and is therefore of great value in reconstructing past regional climate conditions and their interaction with climate systems, in particular that of the North Atlantic. Based on a combination of optically stimulated luminescence (OSL) ages, stratigraphic field observations and magnetic susceptibility measurements, a chrono‐climatic interpretation of the Dolní Věstonice loess section is presented. To establish a reliable Upper Pleistocene chronology, a quartz OSL approach was applied for equivalent dose (De) determination. Monomineralic quartz extracts of three distinct grain sizes, fine (4–11 μm), middle (38–63 μm) and coarse (90–200 μm), were used and compared. Within error limits, the calculated OSL ages are the same for the different grain sizes, and the OSL ages are in stratigraphic order. The established OSL chronology is in agreement with a Weichselian litho‐ and pedostratigraphy. The Dolní Věstonice loess section is characterized by four pedosedimentary subsequences. At the base of the profile, subsequence I is characterized by a distinct Early Glacial soil complex, OSL‐dated to c. 110 to 70 ka, representing one of the most complete records of environmental change in the European loess belt. Subsequence II is allocated to the Lower Pleniglacial and is characterized by laminated sandy loess. Middle Pleniglacial subsequence III is represented by a brown soil complex, and is followed by the uppermost subsequence IV, characterized by a thick body of laminated sandy loess, indicating strong wind activity and a high sedimentation rate of more than ∼1 mm a−1 during the Upper Pleniglacial. According to the OSL chronology, as well as to the sedimentological and palaeopedological investigations, it is likely that the sequence at Dolní Věstonice has recorded most of the climatic events expressed in the NGRIP δ18O reference record between 110 and 70 ka.

Luminescence dating of beach ridges for characterizing multi-decadal to centennial deltaic shoreline changes during Late Holocene, Mekong River delta

Empirical understanding of decadal- to centennial-scale deltaic shoreline changes in the past is essential for understanding the fate of coasts in the coming decades and centuries. We tested the effectiveness of quartz optically-stimulated luminescence (OSL) dating of beach ridges to constrain shoreline changes of the Mekong River delta over the last 3500years. Forty-seven OSL ages have been analyzed from the Tra Vinh delta plain, central Mekong River delta. The Tra Vinh beach ridges are recurved and branching, showing the hierarchy of shoreline changes, which include discontinuous shifts c. 5km seawards caused by the emergence and elongation of a delta-front bar/island, and subsequent downdrift accretion of spits. The spit accretion is interrupted by changes of shoreline orientation. Each of the discontinuous shifts resulted in a cluster of beach ridges, which is referred to as ridgeset. The beach ridge sediments were found to have excellent luminescence properties resulting in low age uncertainties of c. 5%. The OSL chronology agrees well with shoreline changes over recent decades and with radiocarbon ages of tidal flat sediment underlying the beach ridges. The chronology clearly illustrates the coastal progradation from 3500years (relative to AD 2010) onwards. Two main types of beach ridge are present: recurved and trunk ridges. OSL ages of recurved ridges are consistently younger both downdrift and seawards, documenting decadal- to centennial-scale shoreline migration especially over the last 1500years. Trunk ridges in contrast have less systematic ages because a trunk ridge is formed where the sediment is likely to have been reworked by waves. Ages of updrift trunk ridges characteristically show relatively young ages in each ridgeset, representing the extensive erosion and resedimentation of the updrift coast. Major changes in shoreline orientation occurred around 400–500years, suggesting strengthening of the northeasterly winter monsoon at the beginning of the Little Ice Age. The rate of progradation of the Tra Vinh delta plain is described in two ways: frequency of the discontinuous shift, and growth rate of the delta plain area. Both suggest the coast has expanded regularly over the last 1000years. A decrease in sand supply to the coast in the last few decades due to river dam construction and fluvial sand dredging is inferred, possibly affecting the behavior of the modern and future shorelines, which can be compared with the less human-influenced, centennial- to decadal-scale past shoreline changes reconstructed in this study.

An improved OSL chronology for the Still Bay layers at Blombos Cave, South Africa: further tests of single-grain dating procedures and a re-evaluation of the timing of the Still Bay industry across southern Africa

This paper presents a series of new single-grain optically stimulated luminescence (OSL) ages for the Still Bay at Blombos Cave, South Africa, and compares them to previously published OSL, thermoluminescence (TL) and electron-spin resonance (ESR) ages for this site. Details are provided about the measurement and analytical procedures, including a discussion of the characteristics of the OSL signals of individual quartz grains. This forms the basis for further investigations into the sensitivity of the equivalent dose (De) estimates to a range of different analytical approaches, including changes in the size of the test dose, the choice of signal integration interval, the subtraction of an appropriate background, and isolation of the most light-sensitive (‘fast’) component of quartz OSL. We also report the results of an inter-operator test of De determination using seven new samples from Blombos Cave, and demonstrate the reproducibility of results obtained for two samples that had been dated previously at another laboratory and were measured and analysed again in this study. Together, these tests validate the robustness of the Blombos Cave single-grain OSL age estimates to a variety of alternative OSL dating procedures. We have incorporated, for the first time, these ages for Blombos Cave into a data set of all single-grain OSL ages for Still Bay and Howieson's Poort sites across southern Africa, and have used a statistical model to re-evaluate the timing and duration of the Still Bay industry. We calculate the most plausible start and end dates of the Still Bay as 72.2 ka and 71.3 ka, respectively – amounting to a duration of 0.9 ka – and estimate (with conventional 95% confidence) that this industry began no earlier than 75.5 ka, ended no later than 67.8 ka and lasted no longer than 6.6 ka.

Realizing the potential of fluvial archives using robust OSL chronologies

Optically Stimulated Luminescence (OSL) dating has enormous potential for interpreting fluvial sediments, because the mineral grains used for OSL dating are abundant in fluvial deposits. However, the limited light exposure of mineral grains during fluvial transport and deposition often leads to scatter and inaccuracy in OSL dating results. Here we present a statistical protocol which aims to overcome these difficulties. Rather than estimating a single burial age for a sample, we present ages as likelihood functions created by bootstrap re-sampling of the equivalent-dose data. The bootstrap likelihoods incorporate uncertainty from age-model parameters and plausible variation in the input data. This approach has the considerable advantage that it permits Bayesian methods to be used to interpret sequences containing multiple samples, including partially bleached OSL data. We apply the statistical protocol to both single-grain and small-aliquot OSL data from samples of recent fluvial sediment. The combination of bootstrap likelihoods and Bayesian processing may greatly improve OSL chronologies for fluvial sediment, and allow OSL ages from partially bleached samples to be combined with other age information.

OSL chronology and palaeoclimatic implications of aeolian sediments in the eastern Qaidam Basin of the northeastern Qinghai-Tibetan Plateau

Aeolian sediments are widely distributed in the hyper-arid Qaidam Basin and are good palaeoclimatic records. Due to limited age control, aeolian processes and their relevance to palaeoclimatic change are poorly understood. In this study, we present 28 optically stimulated luminescence (OSL) ages for both loess (14 samples) and aeolian sand (14 samples) from 8 profiles in eastern Qaidam Basin (EQB) in order to provide a detailed chronology for understanding the timing of aeolian processes and associated environmental conditions. We reconstructed the history of aeolian activity in the EQB since deglaciation by combining OSL chronologies, lithologic stratigraphy and grain-size analysis. The results indicate that (1) aeolian sand underlying the loess accumulated at ca. 12.4–11.5ka and 10–8ka, but not during the Last Glacial Maximum, (2) loess accumulation started at 10ka and lasted to 0.45ka at least, while most of the loess was deposited during 8–4.5ka, (3) palaeoclimates in the EQB are inferred to be arid during 12.4–11.5ka, (relatively) humid during 10–8ka, humid during 8–4.5ka and relatively arid during 4.5–0.45ka, and (4) evolution of aeolian sediments were mainly controlled by effective moisture, and also affected by local topography.

Single-grain OSL chronologies for Middle Palaeolithic deposits at El Mnasra and El Harhoura 2, Morocco: Implications for Late Pleistocene human–environment interactions along the Atlantic coast of northwest Africa

Optically stimulated luminescence (OSL) measurements were made on individual, sand-sized grains of quartz from Middle Palaeolithic deposits at two cave sites (El Harhoura 2 and El Mnasra) on the Atlantic coast of Morocco. We were able to calculate OSL ages for 32 of the 33 samples collected from the Middle Palaeolithic deposits, including the earliest and latest Aterian levels at both sites. These ages reveal periods of occupation between about 110 and 95 ka (thousands of years ago), and at ∼75 ka. A late Middle Palaeolithic occupation of El Harhoura 2 is also recorded at ∼55 ka. Our single-grain OSL chronologies largely support previous age estimates from El Mnasra and other sites along the Atlantic coast of Morocco, but are generally more precise, reproducible and stratigraphically more coherent (i.e., fewer age reversals). We compare the single-grain ages for El Harhoura 2 and El Mnasra with those obtained from single- and multi-grain OSL dating of Middle Palaeolithic deposits in the nearby sites of Contrebandiers and Dar es-Soltan 1 and 2, and with records of past regional environments preserved in sediment cores collected from off the coast of northwest Africa. A conspicuous feature of the new chronologies is the close correspondence between the three identified episodes of human occupation and periods of wetter climate and expanded grassland habitat. Owing to the precision of the single-grain OSL ages, we are able to discern gaps in occupation during Marine Isotope Stages 5 and 4, which may represent drier periods with reduced vegetation cover. We propose that these climatic conditions can be correlated with events in the North Atlantic Ocean that exert a major control on abrupt, millennial-scale fluctuations between wet and dry periods in northwest and central North Africa.