Optically Stimulated Luminescence Chronology Research Articles

Stratigraphy and OSL chronology of the Middle–Upper Pleistocene sedimentary sequence and vegetation history during Late MIS6–MIS5e in the Neva Lowland (St. Petersburg region, Russia)

ABSTRACTThe quarry of the Sverdlov (Etalon) Factory stands out as a unique site in the northwest of the East European Plain since it exposes an almost complete Upper Pleistocene stratigraphic succession. Previous investigations have revealed a sequence of marine sediments deposited during the whole Mikulino Interglacial [Eemian, Marine Isotope Stage (MIS)5e], but the chronology of the Late Pleistocene deposits remains incomplete and requires further update. We present a study of the Middle–Upper Pleistocene units exposed in the Sverdlov Factory quarry by using geological methods, optically stimulated luminescence (OSL) dating and pollen analysis. The lower part of the Sverdlov Factory section comprises glaciomarine/glaciolacustrine varves, which accumulated during degradation of the Late Moscow (Late Saalian, Late MIS6) glaciation and correspond to pollen zone M1 (lower peak of Picea). They are covered by interglacial marine clayey silt that includes all Mikulino regional pollen zones M2–M8. According to a Bayesian model based on K‐rich feldspar luminescence ages, the interglacial marine deposition started 133 ± 8 ka ago and ended 109 ± 7 ka ago. The marine sediments are overlain by lacustrine silt with a K‐rich feldspar age of 119 ± 7 ka, lacustrine/alluvial sand with plant detritus formed 47–41 ka ago, and lacustrine sand and silt without organic matter accumulated ~39 ka ago. The upper part of the section is composed of subglacial till formed during the Late Valdai (Late Weichselian, MIS2) under the Scandinavian Ice Sheet and glaciolacustrine varved deposits of the Baltic Ice Lake. Two ages were acquired using quartz OSL from these varves, 16.9 ± 1.6 and 15.7 ± 1.0 ka, which are assumed to slightly overestimate the true age.

Millennial-scale fluctuations of palaeo-ice margin at the southern fringe of the last Fennoscandian Ice Sheet

Abstract. The paper presents the first terrestrial record of millennial-scale palaeo-ice margin oscillations at the southern fringe of the last Fennoscandian Ice Sheet (FIS) during the last glacial cycle. The study area is located in northern Poland close to the last FIS maximum limit. The chronology and dynamics of palaeo-ice margin oscillations at the southern fringe of the FIS are based on combined luminescence and 10Be surface exposure dating. Optically stimulated luminescence (OSL) was used to date sandy deposits (fluvioglacial sediments and aeolian deposits filling fossil periglacial wedges) intercalating basal till layers. The most likely age of the tills was constrained by Bayesian modelling of the sequence of OSL ages and lithostratigraphy. 10Be surface exposure dating was used on erratic boulders left during the final retreat of the last FIS and resting on the surface of glacial landforms. Our results, which are mainly based on OSL chronology and Bayesian modelling, indicate millennial-scale oscillations of the last FIS in northern Poland between ∼19 and ∼17 ka. The last FIS retreated and re-advanced over a relatively short period of time (2–3 ka), leaving lithostratigraphic records (basal tills) of three ice re-advances over a millennial-scale cycle: 19.2±1.1, 17.8±0.5 and 16.9±0.5 ka. Despite 10Be surface exposure ages obtained for 14 erratic boulders being poorly clustered, the main mode of age distribution occurs at ∼18 ka and indicates a possible signal of the ice sheet retreat after one of the re-advances. We explore the dynamics of these oscillations and compare the proposed cycles of the southern FIS advances and retreats with existing patterns of the last deglaciation and millennial-scale fluctuations of the last FIS inferred from marine records.

Rock surface and sand-sized sediment quartz dating using optically stimulated luminescence of a Middle-to-Upper Palaeolithic sequence at the Bordes-Fitte rock shelter (Les Roches d’Abilly, Central France)

In this study, we use optically stimulated luminescence (OSL) to establish a robust absolute chronology for the lower part of the stratigraphic record at “Les Roches d’Abilly”, an important Palaeolithic site in Central France. There, lithic assemblages recording the Middle-to-Upper Palaeolithic transition and the behaviour of Neanderthal and Anatomically Modern Human populations are preserved. At the Bordes-Fitte rock shelter, part of “Les Roches d’Abilly”, the archaeo-stratigraphic record has been sealed and preserved by the collapse of the shelter roof and this site has provided important data on the timing of human occupations and Middle-to-Upper Palaeolithic transition in this region. Here, we first obtain burial ages using standard multi-grain quartz techniques on sand-sized sediment grains and then investigate the information available in blue-stimulated luminescence-depth profiles into the surfaces of four quartz-rich cobbles found in the sedimentary record below the various collapses of the shelter roof. These profiles show qualitative evidence for past daylight exposure and a single burial event, allowing the data to be analysed quantitatively using a multiple-event mathematical model. Based on the results of this modelling, it is concluded that at least part of the cobble surfaces were well-bleached at burial and thus that estimated rock surface burial ages are unlikely to be significantly affected by incomplete bleaching. However, it appears that not all cobble surfaces were well-bleached, demonstrating the importance of only using surface doses derived from those cobble layers that can be shown to have been well-bleached at burial. The rock-surface burial ages of the most recent burial event are consistent with the quartz OSL ages derived from the surrounding sediments, giving burial ages of ∼ 50 ka. The OSL ages are consistent with previously published 14 C age control, although a single 14 C age (uncalibrated age of 41 , 900 ± 1 , 500 yr BP) of a lower unit may underestimate the OSL ages. This study provides a reliable absolute OSL chronology for the Bordes-Fitte rock shelter constraining the Middle-to-Upper Palaeolithic transition to occur between 44±2 ka and 48±3 ka ago (at the 68% confidence level).

High-resolution OSL chronology of a well-preserved inland dune in the Lys valley (Sint-Martens-Latem, NW Belgium)

The inland dune “Molenberg” (Lys valley, NW Belgium) is an exceptionally well-preserved dune of more than 10 m high. To determine the phases of dune formation and identify possible levels for human occupation, this dune was sampled at closely spaced vertical intervals for Optically Stimulated Luminescence (OSL) dating (every 50 cm) and grain-size analysis (intervals of 10–25 cm) over its entire depth, including the top of the underlying sediments. The resulting ages show dune formation during the late glacial period (GI-1 and GS-1), with a probable extensive deposition during the Allerød (GI-1a-c) and Younger Dryas (GS-1). Interestingly, the OSL dataset for the main body of the dune shows significant cyclical age inversions that may be caused by reworking of sediment causing incomplete bleaching of sand grains. This may further indicate the potential of high-sampling resolution OSL to contribute to the reconstruction of complex dune dynamics. • High-sampling resolution OSL dating shows dune formation during the late glacial in the Scheldt basin of NW Belgium. • OSL chronology demonstrates the potential of these inland dunes as an archive for prehistoric sites. • Cyclic age inversions may be related to reworking of sediment in periods of reduced accumulation. • Potential of high-sampling resolution OSL as proxy for complex dune dynamics.

Aeolian landform processes since the last deglaciation revealed by OSL chronology and stratigraphy in the Hulunbuir dune field in NE China

The Hulunbuir dune field (HLB) is situated near the northern limit of the East Asian summer monsoon (EASM), and vulnerable to climate change. The aeolian sand–paleosol sequences of this region are crucial for understanding the past landform processes in response to climate change, but not yet understood well due to chronological controversies. Here, we presented 20 optically stimulated luminescence (OSL) ages from five aeolian sand–paleosol profiles in the HLB, and reconstructed the aeolian landform processes since 18 ka. The findings of this study suggested that the HLB was probably dominated by mobile dunes before 18 ka, as 10 out of 11 aeolian samples were dated to 18–12 ka. Two strong sandy paleosol layers were found and dated to ∼9 ka and 5–0.5 ka, indicating that strong in situ pedogenic process on the accumulative sand could occur during the Holocene. The OSL ages of samples near the top of three profiles were >9.5 ka, indicating two possible surface processes. First, the land surface was stable since 9.5 ka after stabilization, with no accumulation or erosion. Alternatively, the surface could have been erosive with the eroded sediments feeding downwind active dunes. The latter explanation is consistent with the current local landforms, which has widespread blowout pits, indicators of strong wind erosion. We emphasized that the OSL age of a sand layer sample in fossil dunes implied the onset of mobile dune stabilization, not the age of dune activity, as previously stated.

Regional hydroclimates regulate the Holocene aeolian accumulation processes of the Qinghai Lake basin on the northeastern Tibetan plateau

Aeolian sediments are widely distributed in the Qinghai Lake basin on the northeastern Tibetan Plateau (TP), and have been extensively investigated for the palaeoclimate reconstruction. However, due to the relatively scanty of dating materials and applicable techniques, and also the commonly existed hiatus in aeolian sequences, the details of the Holocene aeolian activities in the Qinghai Lake basin remain unclear. In this study, we applied the optically stimulated luminescence (OSL) dating technique to a 3.6 m thick loess-palaeosol sequence (QH-18) located on the southern bank of the Qinghai Lake to establish a high-resolution chronology of the aeolian accumulation history. The quartz OSL chronology demonstrated that the loess accumulation commenced since the last deglaciation and continued during the Holocene (∼14.6–0.5 ka), characterized with a remarkably low sedimentation rate period from 6 ka to 2 ka. Similar phenomenon has been recorded in previously investigated aeolian sequences not only in the Qinghai Lake basin but also across the northeastern TP, which was likely owing to the optimal environment conditions that have suppressed the dust emission from the source areas in the extensive arid and semiarid areas. The end-member (EM) analysis of grain-size distribution in QH-18 yielded an optimal model with three EMs, i.e., EM1 (6 μm, background dust), EM2 (56 μm, fraction of medium or long-distance transportation) and EM3 (447 μm, fraction from proximal or local source). The EM3 fraction can only be transported with saltation process in short distances that derived from proximal or local sources. In addition to the regional climatic conditions, according to the variation and contribution of the EMs, we consider that the Holocene aeolian activity in the Lake Qinghai basin was also modulated by the lake-level fluctuations of Lake Qinghai, in the way of changing the supply of sandy materials.

OSL Chronology of the Siling Co Paleolithic Site in Central Tibetan Plateau

When and how was the Tibetan Plateau (TP), one of the least habitable regions on Earth, occupied by humans are important questions in the research of human evolution. Among tens of Paleolithic archaeological sites discovered over the past decades, only five are considered coeval with or older than the Last Glacial Maximum (LGM, ∼27–19 ka). As one of them, the Siling Co site in the central TP was previously announced to be ∼40–30 ka based on radiocarbon dating and stratigraphic correlation. Given the loose chronological constraint in previous studies, we here re-examined the chronology of the Siling Co site with the optically stimulated luminescence (OSL) dating technique. Four sections from the paleo-shoreline at an elevation of ∼4,600 m in southeastern Siling Co were investigated, with stone artifacts found from the ground surface. Dating results of nine samples delineated the age of ∼4,600 m paleo-shoreline to be ∼10–7 ka (∼8.54 ± 0.21 ka in average). This age indicates that the Siling Co site is not earlier than the early Holocene, much younger than the former age. The revised age of the Siling Co site is consistent with the wet and humid climate conditions on the TP during the early Holocene.

Back to Uluzzo – archaeological, palaeoenvironmental and chronological context of the Mid–Upper Palaeolithic sequence at Uluzzo C Rock Shelter (Apulia, southern Italy)

ABSTRACTThe tempo and mode of Homo sapiens dispersal in Eurasia and the demise of Neanderthals has sparked debate about the dynamics of Neanderthal extinction and its relationship to the arrival of H. sapiens. In Italy, the so‐called ‘Transition’ from Neanderthals to H. sapiens is related to the Uluzzian technocomplex, i.e. the first archaeological evidence for modern human dispersal on the European continent. This paper illustrates the new chronology and stratigraphy of Uluzzo C, a rock shelter and Uluzzian key site located in the Uluzzo Bay in southern Italy, where excavations are ongoing, refining the cultural sequence known from previous excavations. Microstratigraphic investigation suggests that most of the deposit formed after dismantling of the vault of the rock shelter and due to wind input of loess deflated by the continental shelf. The occasional reactivation of the hydrology of the local karst system under more humid conditions further contributed to the formation of specific layers accumulating former Terra Rossa‐type soil fragments. Superposed on sedimentary processes, strong bioturbation and the mobilization and recrystallization of calcite have been detected. Optically stimulated luminescence (OSL) ages from Uluzzo C Rock Shelter are congruent with previously published radiocarbon ages obtained on shell beads and tephrachronology from adjacent sites preserving the Uluzzian technocomplex such as Grotta del Cavallo, confirming the onset for the Uluzzian in the area to ca. 39.2–42.0 ka. The OSL chronology from Uluzzo C also provides a terminus post quem for the end of the Mousterian in the region, constraining the disappearance of the Neanderthals in that part of Italy to ≥46 ± 4 ka.

OSL chronology of the Liena archeological site in the Yarlung Tsangpo valley throws new light on human occupation of the Tibetan Plateau

Recent environmental archeological evidence has started to throw light on both the timing and processes of human colonization of the Tibetan Plateau (TP). Yarlung Tsangpo (YT) valley, a very important region of the southern TP for occupation, is home to not only modern Tibetans but also their ancestors. However, a lack of suitable sedimentary strata has limited the establishment of a secure chronology. Here, we report on a new stratigraphic section with prehistoric pottery and cultural layers that was discovered on a terrace of the YT at Liena, in Nyingchi County. The cultural layers are overlain by, and bedded within, eolian and lacustrine sediments. We used the quartz Optically Stimulated Luminescence (OSL) method to date 11 samples and performed geochemical analysis on 100 samples to derive paleoenvironmental indicators. The OSL analysis gave an age of 4.3 ka BP for the cultural layer, which makes it the earliest human activity in the YT valley of Nyingchi to date. In addition, commencement of eolian deposition was dated to at least 8.3 ka, coinciding with the Holocene warm period. We discuss possible causal factors for human occupation in the valley and show that climatic changes played a crucial role in prehistoric human migration c. 8.3–4.3 ka BP. Before the early Holocene, most of the river terraces in the valley were being actively reworked by rivers or covered by lakes. So there were no suitable places for occupation by ancient populations. With the recession of dammed lakes during the Holocene warm period, the relatively flat and wide valley terraces, blanketed with rich eolian deposits (such as sandy loess), provided an attractive place for ancient people engaged in nomadic and even agricultural activities. Hence, the climate conditions of the Holocene warm period drove the environmental changes that provided favorable conditions for ancient human activities.

Latest Pleistocene to Holocene loess in the central Great Plains: Optically stimulated luminescence dating and multi-proxy analysis of the enders loess section (Nebraska, USA)

Loess deposits of the central Great Plains, USA, and their intercalated soils provide a detailed record of climatically driven changes within the aeolian system during the Pleistocene-Holocene transition and the Holocene. Here we present a detailed optically stimulated luminescence (OSL) chronology as well as multi-proxy analysis obtained for the first time on the Enders section, located in southwestern Nebraska, central Great Plains. The section records multiple episodes of rapid loess deposition alternating with soil formation. Rapid accumulation of Late Pleistocene Peoria Loess was replaced around 13–14 ka by formation of the Brady Soil until 9.5 ± 0.6 ka. The Holocene Bignell Loess then buried the Brady Soil and accumulated episodically throughout the Holocene. The loess-paleosol stratigraphy since the Late Pleistocene at the Enders site is very similar to that at other sites in western Nebraska, and the newly developed OSL chronology (based on three grain size classes) adds new confidence to earlier dating. The high-resolution grain size profile from Enders shares many features with similar data from the previously studied Wauneta site, including three peaks of fine-grained material just above and within the Brady Soil, likely representing response to millennial-scale climatic changes during the Pleistocene-Holocene transition. This study demonstrates the potential for developing high-resolution, well-dated paleoclimatic records from the loess of the central Great Plains. Contrasts between Great Plains and Eurasian loess records reflect differences in the Late Pleistocene to Holocene climatic evolution and other factors influencing the loess system.

Seeking enlightenment of fluvial sediment pathways by optically stimulated luminescence signal bleaching of river sediments and deltaic deposits

Abstract. Reconstructing sediment pathways in fluvial and deltaic systems beyond instrumental records is challenging due to a lack of suitable methods. Here we explore the potential of luminescence methods for such purposes, focusing on bleaching of the optically stimulated luminescence (OSL) signal of quartz sediments in a large fluviodeltaic system across time and space. We approach this by comparing residual doses of sand and silt from the modern Mississippi River channel with estimated residual doses of sand isolated from Late Holocene Mississippi Delta mouth bar and overbank deposits. Further insight is obtained from a comparison of burial ages of paired quartz sand and silt of Mississippi Delta overbank deposits. In contrast to some previous investigations, we find that the bleaching of the OSL signal is at least as likely for finer sediment as for coarser sediment of the meandering Mississippi River and its delta. We attribute this to the differences in light exposure related to transport mode (bedload vs. suspended load). In addition, we find an unexpected spatiotemporal pattern in OSL bleaching of mouth bar sand deposits. We suggest this may be caused by changes in upstream pathways of the meandering channel belt(s) within the alluvial valley or by distributary channel and coastal dynamics within the delta. Our study demonstrates that the degree of OSL signal bleaching of sand in a large delta can be highly time- and/or space-dependent. Silt is shown to be generally sufficiently bleached in both the modern Mississippi River and associated paleo-deposits regardless of age, and silt may therefore provide a viable option for obtaining OSL chronologies in megadeltas. Our work contributes to initiatives to use luminescence signals to fingerprint sediment pathways within river channel networks and their deltas and also helps inform luminescence dating approaches in fluviodeltaic environments.

OSL chronology of the Huksan Mud Belt, south-eastern Yellow Sea, and its paleoenvironmental implications

The Huksan Mud Belt (HMB) is located in the south-eastern Yellow Sea. The radiocarbon (14C) and optically stimulated luminescence (OSL) age datings of the pre-Holocene HMB sediments were compared precisely. OSL dates for the uppermost HMB sediments showed the recent and short-term chronological development of the HMB. OSL and 14C ages of the Holocene sediment (HMB cores 101–103) were relatively consistent. By contrast, the OSL ages of the pre-Holocene sediment unit were considerably older than the 14C ages (by approximately 30%), where the OSL ages corresponded broadly to marine isotope stages (MIS) 5 and 4 (from about 125 ka to > 50 ka). An overall comparison of 14C and OSL dates suggests that the age of the Holocene mud unit is well constrained by 14C dating. However, 14C ages older than 40 ka may be unreliable. The surficial sedimentation rate and depositional ages for a 6.5-m-thick sequence of the uppermost unit (12HMB cores) were determined. Twenty OSL samples gave an age of approximately 8.5 ka. Most of the OSL ages for each site were in stratigraphic order. The surficial sediment ages for the 12 HMB cores were 2.6 ka for P-08, 7.7 ka for P-10, 7.3 ka for P-11, and 0.05 ka for P-14. The approximate surficial sediment ages of the uppermost unit of the HMB-101, -102, and −103 cores were 6.7 ka, 6.8 ka, and 1.1 ka, respectively. The spatiotemporal differences in deposition and erosion of the HMB Holocene muds, supposedly driven by changes in large, strong tidal forces and marine water depth, and an increase in ocean current velocity, could account for the various surficial deposition ages in the area.

Reply to the comments by Madsen & Liu on “Late quaternary OSL chronologies from the Qinghai Lake (NE Tibetan Plateau): Inter-comparison of quartz and K-feldspar ages to assess the pre-depositional bleaching”

Abstract In response to the comment of Madsen and Liu (2018), we explain why our quartz optically stimulated luminescence (OSL) ages showing the early MIS 3 lake highstand are robust. We also demonstrate that the difference in the age estimates between ours (Long et al., 2018) and other studies should be attributed to contrasting equivalent dose (De) values, rather than water contents (hence the dose rate) which was claimed by Madsen and Liu (2018).

Late Quaternary OSL chronologies from the Qinghai Lake (NE Tibetan Plateau): Inter-comparison of quartz and K-feldspar ages to assess the pre-depositional bleaching

Abstract Signal resetting prior to deposition is an important factor for the accuracy of luminescence dating. In this study, resetting of the quartz optically stimulated luminescence (OSL) signal from samples collected from different depositional environments (alluvial, beach, and aeolian sediments) around the Qinghai Lake basin (northeastern Tibetan Plateau) was examined using its inter-comparison with post-IR infrared stimulated luminescence (IRSL) measured at 290 °C (pIRIR290) from K-feldspar. Dose recovery tests were carried out to test the success of the single aliquot regenerative-dose (SAR) protocol for quartz and feldspar. Additionally, stability tests (first IR temperature plateau and g-values) were performed for the pIRIR290. We observe that most of the K-feldspar pIRIR290 and quartz OSL ages are consistent with each other (within 10%), suggesting that the quartz OSL signal was well-bleached prior to the deposition. The ages of loess samples range between ∼13.1 and ∼1.5 ka, the alluvial sediments between ∼35 ka and ∼14 ka, and beach sediments between 60 and 50 ka, corresponding to early Marine Isotope Stage (MIS) 3. These quartz OSL chronologies suggest a lake highstand during very early MIS 3, a lowstand during late MIS 3 and MIS 2, and widespread loess accumulation through the Holocene in the Qinghai Lake basin.

Single-grain OSL dating of the Middle Palaeolithic site of Galería de las Estatuas, Atapuerca (Burgos, Spain)

This study presents single-grain optically stimulated luminescence (OSL) chronologies for the archaeological site of Galeria de las Estatuas – the first systematically excavated Middle Palaeolithic site within the karst system of the Sierra de Atapuerca archaeological complex, northern Spain. The single-grain OSL ages are compared with paired single-grain thermally transferred OSL (TT-OSL) dating results for a selection of samples in order to better assess quartz signal bleaching characteristics of endokarstic deposits preserved at Atapuerca. In total, seven luminescence dating samples were collected from four lithostratigraphic units exposed in two excavation pits (GE-I and GE-II). The single-grain OSL equivalent dose (De) distributions are characterised by generally low overdispersion (20–30%), suggesting appropriate bleaching at deposition. The resultant single-grain OSL ages reveal that the sediment sequence and archaeological remains excavated in pit GE-I accumulated 80–112 ka, while the upper layers of excavation area GE-II were deposited 70–79 ka. The replicate single-grain TT-OSL ages are in agreement with the OSL chronologies at 2σ for three of the four samples investigated; although in all cases the TT-OSL ages were systematically older than their single-grain counterparts. Apparent TT-OSL residual doses (i.e., TT-OSL De values in excess of their corresponding OSL De values) of 9–65 Gy were observed for all samples. These excess TT-OSL De values are generally low in comparison to the natural dose ranges of TT-OSL dating applications undertaken elsewhere in the Atapuerca karst system. The single-grain TT-OSL and OSL dating comparisons build on daylight bleaching experiments and modern analogue studies performed on other Atapuerca exogeneous infill deposits and suggest reasonable potential for TT-OSL signal resetting down to relatively low levels for at least some sediments preserved in the Atapuerca karstic cavities. The quartz single-grain OSL chronologies obtained in this study place the Middle Palaeolithic sequence of Galeria de las Estatuas within marine isotope stage (MIS) 5 and the beginning of MIS 4, and provide firm evidence for human occupation of the Sierra de Atapuerca during a previously unreported time period.

An integrated OSL chronology, sedimentology and geochemical approach to loess deposits from Tuoji Island, Shandong Province: Implications for the late quaternary paleoenvironment in East China

Abstract The Tuoji II (TJII) section on the Miaodao Islands in the Bohai Sea is a representative aeolian section off China’s east coast. This study applied optically stimulated luminescence (OSL) dating, conducted grain size analysis, and examined major and trace element compositions, to investigate the loess–paleosol sequences. The OSL ages at depths of 0.6, 1.8, 2.8, 3.8, and 4.8 m were determined as 14.4 ± 0.4, 16.7 ± 1.3, 20.8 ± 1.0, 40.9 ± 1.5, and 47.9 ± 3.7 ka, respectively. It was projected that the loess started to accumulate at ca. 62.6 ka, according to presumed depositional rates. In this study, typical aeolian deposits elsewhere including the Luochuan (LC), Xiashu (XS), Wushan (WS), and Xifeng (XF) sections were compared with TJII section here. The results showed similarity in the geochemical characteristics of the deposits from the different areas of China and normalized upper continental crust, indicating aeolian origin of this island loess. In comparison with the LC, XS, WS, and XF samples, the aeolian deposits of the TJII section have higher concentrations of TiO2 and Zr and lower concentrations of Al2O3, Rb, and Ni, and they have higher SiO2/Al2O3 and TiO2/Al2O3 ratios and lower Al2O3/Na2O and Ba/Sr ratios. These features indicate the dust materials of the TJII section were derived from local sources of well-mixed sedimentary protoliths. Our results support the suggestion that paleoclimatic change and the evolution of aeolian sediments were controlled primarily by variation of the East Asian summer monsoon and sea level change.

OSL chronologies of paleoenvironmental dynamics recorded by loess-paleosol sequences from Europe: Case studies from the Rhine-Meuse area and the Neckar Basin

Loess-paleosol sequences (LPS) represent an important terrestrial archive for the reconstruction of the paleoenvironmental evolution during the Last Glacial cycle in Europe. In the Rhine-Meuse area and the southwestern Germany, there are only few numerical ages determined with state-of-the-art luminescence methods, which limits the robustness of established chronostratigraphies. This study presents a comparative dating approach using quartz and feldspar post-infrared (pIRIR290) optically stimulated luminescence (OSL) from fine- and medium-grained samples of five loess-paleosol sequences. Paleoenvironmental dynamics are reconstructed by high-resolution grain-size analysis.The OSL ages are evaluated as being robust and consistent with other records. Furthermore, we show that ages for hillslope deposits are sometimes overestimated due to low-frequency high-magnitude erosive processes. The integration of OSL ages, stratigraphy and high-resolution grain-size data contributes to a temporal more complete data record from Western and Central Europe. Secondly, we propose a combined stratigraphic model for LPS of the Last Glacial cycle, which is developed and discussed in the context of other key sites such as Havrincourt, Schwalbenberg II, Tönchesberg, Nussloch and Dolni Vĕstonice. Comparable chronologies and patterns in proxy data between sites with a large spatial distance suggest a possible semi-synchronous response to climatic changes in Europe. By combining our data with the Eifel-Laminated-Sediment-Archive (ELSA) and the NGRIP ice core, a relationship of loess archives and large-scale climatic signals is discussed and a proxydata based event-stratigraphy is developed. This model refines existing chronostratigraphic models and contributes to solve open discussion concerning the timing and demarcation of sedimentary units and sequences from for Western and Central Europe.

Single-grain OSL chronologies for the Still Bay and Howieson's Poort industries and the transition between them: Further analyses and statistical modelling

The chronology of the Still Bay (SB) and Howieson's Poort (HP) lithic industries remains an issue of keen interest because of the central role of these two phases of technological and behavioural innovation within the Middle Stone Age of southern Africa. Several dating studies have been conducted on SB and HP sites, including a pair published by the present authors and our colleagues in 2008 and 2013. These reported the results of systematically applying single-grain optically stimulated luminescence (OSL) dating procedures to 10 sites in South Africa, Lesotho and Namibia to constrain the timing of the start and end of the SB and HP and reveal the existence of a gap of several millennia between them. Alternative ages for these two industries have since been proposed by others for one of these South African sites (Diepkloof Rockshelter) and some concerns have been raised about the procedures used in our earlier studies to estimate the beta dose rates for a small number of samples. Here, we provide an update on our chronology for the SB and HP and address the issues raised about the methods that we used previously to estimate the beta dose rates and their associated uncertainties. To test the sensitivity of our new SB and HP ages to different underlying assumptions, we have run the same statistical model as that used in our 2008 and 2013 studies under three different scenarios. We show that the ages for the different samples are insensitive to how we analytically process or statistically model our data, and that our earlier conclusions about timing of the start and end of the SB and the HP and the probability of a gap between them remain true for two of the three scenarios. We conclude by bringing our study into the context of additional chronometric, stratigraphic and lithic technology studies that have been conducted in the intervening decade.

Temporal constraints for the Late Wisconsinan deglaciation of western Canada using eolian dune luminescence chronologies from Alberta

The Laurentide Ice Sheet (LIS) covered most of Canada during the Last Glacial Maximum. Sometime after 20cal.kaBP, the LIS began to recede from western Canada and, by 11cal.kaBP, it had retreated from most of the province of Alberta. Due to the scarcity of datable contemporaneous organic materials, the precise timing of the retreat of the ice sheet from the region remains poorly constrained so that the chronology of the sequential positions of the ice sheet margin between 20 and 11cal.kaBP is largely tentative. In this study, we use luminescence dating of postglacial eolian deposits, sourced primarily from glaciolacustrine and deltaic sediments in central and northern Alberta, to provide an updated chronology for the retreat of the LIS from the region. We examine 14 new and 13 previously published quartz optically stimulated luminescence (OSL) ages, as well as 19 previously published K-feldspar infrared stimulated luminescence ages. The chronologies are used to constrain successive regional ice sheet margin positions that are geomorphically recognizable across the region between 16 and 11ka (calendar years). These data suggest that the LIS may have retreated from central Alberta earlier than portrayed in radiocarbon derived deglaciation models. We propose that the OSL chronology from postglacial dunes constrains the deglaciation of the region more accurately because luminescence dating does not rely on the development of vegetation to produce material for dating. Implications for the revised chronology include an improved timing of the emergence of an ice-free corridor that may have been used for Paleoindian migration into the Americas as well as enhanced age constraints on when meltwater drainage routes to the Arctic became open in relationship to the Younger Dryas. The chronology could also provide improved constraints for geophysical models that reconstruct regional isostatic rebound which followed deglaciation.

Late Pleistocene aeolian activity in the cold desert of Ladakh: A record from sand ramps

Ladakh, northwest India, lies in the rain shadow zone of the Indian Summer Monsoon (ISM) where sand ramps provide a good record of past aeolian activity. Here we present an archive from five sand ramps that is based on their sedimentological structure and Optically Stimulated Luminescence (OSL) chronology. Sedimentary architecture indicates that the sand ramps are composite records of aeolian, hill slope erosion and fluvio-lacustrine activity. The OSL chronology suggests that aridity and aeolian activity was dominant during 25–17 ka and <12–8 ka. Wetter conditions, as evidenced from intra-dunal lake formation and fluvial gullying, prevailed at ∼12 ka and 7 ka. These dry and wet phases correspond to variations in SW monsoon strength. One sand ramp, at Saboo, is studied in detail using mineral susceptibility and clay mineralogy. The environmental magnetic susceptibility shows significant enhancement in fluvial and lacustrine sediments and also shows sharp positive excursions at hiatuses where a hard crust is formed, and confirms warm and wet conditions at ∼12 ka and ∼7 ka BP. Clay mineralogy is dominated by illite and shows no changes through the profile, suggesting that sediment generation took place mainly due to physical weathering and that the threshold of climate fluctuations between wet and dry phases (as visible in magnetic mineralogy) were never reached so as to alter the clay mineralogy.