OSL Samples Research Articles

A chronology of depositional coastal landforms of the Baltic Sea: Luminescence dating of sandy sediments and patterns of human settlement at the ancient Ventspils Lagoon

The ancient Ventspils Lagoon is an area where human settlements have been located on former coastal landforms and sediments. However, the chronology of its development has so far not been studied in detail. Since the ancient lagoon is dominated by sand deposition, optically stimulated luminescence dating (OSL) was used to determine when the ancient coast was formed. Twenty-one OSL samples gave a wide age range, between 8.57 ± 0.65 ka and 73.8 ± 8.3 ka. Twelve of the ages fall in the Late Glacial and Holocene and document the development of the lagoon between the Baltic Ice Lake stage (∼16 ka) and the Littorina Sea stage (∼8 ka). The new dates correspond to some extent with previously modelled shorelines for the Ventspils Lagoon and to radiocarbon ages from archaeological sites in the area. One date, 16.0 ± 1.3 ka, falls in the period before the Baltic Ice Lake and represents either a very early Baltic Ice Lake stage or, less likely, the Venta glacial lake prior to the Baltic Ice Lake. One date, 5.09 ± 0.42, is likely underestimated. Seven samples yielded dates between 21.5 ± 1.5 ka and 73.8 ± 8.3 ka, which corresponds to the Early and Middle Weichselian in the Baltic region. The samples in this latter group are likely overestimating the true age due to insufficient exposure to sunlight during deposition.

Tectonic implication in the evolution of lake and Quaternary landforms in the Lohawati river basin, Kumaun outer Lesser Himalaya

The evolution of the Quaternary landforms in the Champawat area of the outer Kumaun Lesser Himalaya is reconstructed from the paleolake sections and the geometry of the landscape. Conjugate sets of normal faults are observed in both the bedrocks and Quaternary deposits at Banlek. The most prominent normal faults are those striking NE-SW and NW-SE and most of them are steeply dipping faults while some are vertical faults. Sediments akin to the lacustrine deposits are observed at four sites; while the contact between the bedrock and the lake sediments is observed at only one site in the peripheral side. The exposed sediments thicknesses vary from 8.30 m to 4.8 m and consist of an alternation of black carbonaceous mud and sandy horizons indicating different depositional regimes. The total thickness of the lake sediments appears to be more than 75 m as deduced from elevational differences between the exposed sites. From Site 1, two OSL samples collected from 2.5 m and 8 m from the present ground surface, were analyzed which give OSL ages of 16 ka and 17 ka, respectively; while one sample collected from Site 4 gives an OSL age of 13 ka. A total of 3653 lineaments were mapped encompassing 2,277.8 sq km from the eastern Kumaun Himalaya. Maximum of the lineaments trend ENE-WSW or almost E-W (∼46.5%); the major principal stress is deduced to be in NE-SW direction. Lake, mature topography and gentle stream gradient in the Champawat area are the result of highly weathered bedrocks and development of the normal faults.

Age-depth modelling and the effect of including – or not – shared errors across sets of OSL samples: The case study of Beg-er-Vil (Brittany, France)

The coastal site of Beg-er-Vil (Brittany, France) has yielded remains of a dwelling site from the Mesolithic period, dating back to ca. 8000 years ago. These archaeological remains were covered by a marine sand dune. Among the research questions raised by recent excavations, the timing of the dune formation with respect to the human occupations is of particular interest: how much time elapsed between these two events? To resolve this question, we employed radiocarbon dating to infer the timing of human occupations and OSL dating to date the dune aggradation. We combined radiocarbon and OSL data in a Bayesian framework, including stratigraphic constraints and measurement errors shared across OSL samples, to build a robust and precise chronological model of the site. We then built an age-depth model for the dune to determine the onset of dune formation. We conclude that we cannot detect a time gap between the latest human occupations and dune aggradation. Finally, we demonstrate how stratigraphic constraints and shared errors affect – and improve – the precision of the chronology inferred from our measurements.

Testing a proposed new chronology for the Jasmund Glacitectonic Complex (SW Baltic Sea): No indication of incipient deformation during MIS 3

Weichselian advances of the Scandinavian Ice Sheet have generated several glacitectonically deformed structures in the southwestern Baltic Sea area. One example is the 100 km 2 large Jasmund Glacitectonic Complex (JGC), which was formed proglacially and consists of two subparallel-orientated sets of composite ridges that represent a northern and southern structural complex. The two-part morphological structure of the JGC suggests a formation by two ice advances, one approaching from NE and one from SE direction. So far, this divided structure has been assumed to have been formed by short-time ice-front oscillations during an MIS 2 ice advance. However, based on their recently published ice dynamic model for MIS 3 and the available age data from Jasmund, lüthgens et al. (2020) propose a chronological reinterpretation of the JGC development, according to which two distinct ice advances during early and late MIS 3 formed the JGC. In order to test this novel stratigraphical model for the JGC formation, five OSL samples were taken from fluvial and lacustrine deposits at a key section near Glowe (NW Jasmund). The investigated succession is divided into pre-kinematic sediments, deposited before the glacitectonic deformation, and post-kinematic sediments, deposited after the deformation. Our results show that the youngest dated pre-tectonic sediment has a burial age between ∼40 and 34 ka, which rules out a glacitectonic deformation during an early MIS 3 ice advance (∼60–50 ka). In addition, by reviewing the existing age data set, a development of the JGC during an early and late MIS 3 advance of the SIS must be rejected. Instead, our data confirm the genesis of the JGC during MIS 2.

Relict olive trees at runoff agriculture remains in Wadi Zetan, Negev Desert, Israel

Olive (Olea europaea) trees in the arid Negev Desert of southern Israel are important relicts on the ancient agricultural landscape. Among them are a cluster of several trees located in Wadi Zetan, at the heart of the Shivta horticulture terroir, with its abundant agricultural runoff remains. Two isolated olive bearing trees stand in a sheltered beneath cliff in the upper part of the wadi. Radiocarbon dating of an internal part of the trunk of one of these living trees estimates its minimum age as the mid-16th – early 17th century CE (∼500 years old). Archaeological excavations conducted beneath the trees and the adjacent dam revealed OSL samples of loess accumulation dated to the Early Islamic period (8th-9th centuries CE). The stratigraphy and chronology of this sediment deposition indicate its rapid and short accumulation. Palynological analysis of the same OSL dated samples indicates that grapevines and olive trees were cultivated in the immediate vicinity of the site during the Early Islamic period. The lack of pollen of cultivated taxa from the latter part of the sequence points to cessation of the agricultural activity, probably a few hundred years later. Leaf samples for DNA profiling of the trees in comparison to other local old olive trees around the country, indicate that the trees in Wadi Zetan are genetically close to a known cultivar common among ancient olive trees. The trees have survived for at least a few hundred years, in an arid area, due to the local conditions and enhanced drainage from the man-made upper runoff system. These old olive trees bear a powerful and symbolic significance, indicating the endurance and sustainability of ancient desert runoff agriculture. Moreover, the survival of their relicts in Wadi Zetan suggests their potential as cultivars greater resilience to the harsh growing conditions of arid environments.

Late Quaternary variations in paleoerosion rates in the northern Qilian Shan revealed by 10Be in fluvial terraces

Understanding the pace of erosion through space and time may provide insight into how tectonic and climatic processes conspire to drive landscape evolution. However, determining whether erosion rates in a given locality have varied with past climate change remains challenging, and the mechanisms invoked to explain variations in past erosion rates are not well understood. In this study, we evaluate past rates of erosion during the late Quaternary along the northern Qilian Shan, the range bounding the northeastern margin of the Tibetan Plateau. We measured the concentrations of cosmogenic 10Be from fluvial deposits atop 5 terraces along the Hongshuiba River and average 10Be concentrations at the time of terrace formation. We also determined terrace ages by combining 5 10Be depth profiles and 15 OSL samples of overlying loess. Our results confirm previous dating of this terrace sequence using cosmogenic exposure ages of boulders and depth profiles in terrace gravels and indicate that terrace treads span glacial-interglacial cycles over the past ~200 ka. We exploit this exceptionally dense sampling of 10Be to evaluate differences in cosmogenic 10Be concentrations at the time of terrace formation along the Hongshuiba River. Analysis of 48 individual determinations of “inherited” 10Be concentrations reveal that fluvial sediment in terraces abandoned during the last glacial and penultimate glacial periods are 3–4 times greater than concentrations in sediment atop terraces formed during interglacial times. Paleoerosion rates within the Hongshuiba watershed appear to have been ~200 m/Myr during glacial episodes but increased to ~500–700 m/Myr during interglacial times, similar to recent erosion rates inferred from 10Be in modern sediment. These results point to likely changes in the mean residence time of sediment with the watershed that fluctuate in association with 100-ka glacial-interglacial cycles. We suggest that reductions in erosion rates associated with glacial conditions may have been driven by changes in catchment hydrology during cold and dry periods.

Lake and inland dunes as interconnected Systems: The story of Lake Tresssee and an adjacent dune field (Schleswig-Holstein, North Germany)

The specific aim of the study was to investigate how four adjacent geomorphological systems – a lake, a dune field, a small alluvial fan and a slope system – responded to the same impacts. Lake Tresssee is a shallow lake in the North of Germany (Schleswig-Holstein). During the Holocene, the lake’s water surface declined drastically, predominately as a consequence of human impact. The adjacent inland dune field shows several traces of former sand drift events. Using 30 new radiocarbon ages and the results of 16 OSL samples, this study aims to create a new timeline tracing the interaction between lake and dunes, as well, as how both the lake and the dunes reacted to environmental changes. The water level of the lake is presumed to have peaked during the period before the Younger Dryas (YD; start at 10.73 ka BC). After the Boreal period (OSL age 8050 ± 690 BC) the level must have undergone fluctuations triggered by climatic events and the first human influences. The last demonstrable high water level was during the Late Bronze Age (1003–844 cal. BC). The first to the 9th century AD saw slightly shrinking water levels, and more significant ones thereafter. In the 19th century, the lake area was artificially reduced to a minimum by the human population. In the dunes, a total of seven different phases of sand drift were demonstrated for the last 13,000 years. It is one of the most precisely dated inland-dune chronologies of Central Europe. The small alluvial fan took shape mainly between the 13th and 17th centuries AD. After 1700 cal. BC (Middle Bronze Age), and again during the sixth and seventh centuries AD, we find enhanced slope activity with the formation of Holocene colluvia.

Investigation into the OSL and TT-OSL signal characteristics of ancient (>100 ka) Tasmanian aeolian quartz and its utility as a geochronometer for understanding long-term climate-driven landscape change

The luminescence characteristics and age estimates of nine samples of aeolian quartz are reported from the Southwood B section in the Arve Valley of southern Tasmania, Australia. New OSL and TT-OSL ages obtained from the deepest Tasmanian aeolian section found so far, the Southwood B section (>6 m deep), range from 20 ka (MIS 2) to 180 ka (MIS 6). Here we test two previously published TT-OSL protocols on our samples: the protocol of Brown and Forman (2012) and a protocol modified from Stevens et al. (2009). Congruencies between our TT-OSL chronology, OSL chronology and previously published TL ages suggest that the modified Stevens et al. (2009) protocol is the most robust for these samples. Furthermore, detailed comparisons of the laboratory data for TL, OSL, and TT-OSL samples provide information on their signal characteristics, their utility as chronometers, and give insight into the bleaching histories of the deposits. All OSL and TT-OSL ages obtained from the Southwood B section fall below the upper dating limits of these signals, which are reported to be as high as ∼280 ka and ∼570 ka, respectively. The TT-OSL signal saturates at doses that are two to three times those of the OSL signal, and may not only provide a chronology for sediments deposited during MIS 5, but also, according to the saturation limits, for any preserved sediments that accumulated during MIS 6 through to MIS 15. TT-OSL ages from older sediments in this region, combined with further stratigraphic studies have the potential to determine the climatic history of Tasmania over multiple glacial periods.

Corrigendum: Coastal occupation before the “Big Swamp”: Results from excavations at John Wayne Country Rockshelter on Barrow Island

Corrigendum: Coastal occupation before the “Big Swamp”: Results from excavations at John Wayne Country Rockshelter on Barrow Island

Luminescence efficiency of Al2O3:C,Mg radiophotoluminescence in charged particle beams

In hadron therapy, it is important to evaluate how sensitive a detector is upon radiation with varying ionization densities, i.e. linear energy transfer (LET), as the LET changes when penetrating through material. For solid-state detectors, it is therefore essential to characterize the luminescence efficiency (ηHT,γ) of the detector as a function of LET. In this work, we investigate the radiophotuminescence (RPL) response from Al2O3:C,Mg 2D films and crystals exposed to various high LET beams (1H, 4He, 12C, 28Si and 56Fe). The measured ηHT,γ curve from RPL films and crystals as function of the particle LET is compared with the ηHT,γ curve from Al2O3:C OSL samples. Furthermore, a 2D RPL image, from Al2O3:C,Mg films irradiated with a 61.3 MeV 40 mm diameter broad proton beam, depicts a 2D depth dose distribution of the Bragg peak and demonstrates similar LET dependence as from the luminescence efficiency curve. The ηHT,γ curves are consistent with Birks’ law, where we observe expected quenching for increasing LET.

The coastal ridge sequence at Rio Grande do Sul: A new geoarchive for past climate events of the Atlantic coast of southern Brazil since the mid Holocene

Abstract We present here the first geochronometric analysis of a large succession of coastal ridges that developed south of Rio Grande do Sul inlet, aided by OSL dating of samples taken in this succession that amounts c. 306 coastal ridges. This succession allows defining epochs of enhanced coastal drift or fluvial transport to the river mouth. Additionally, changes in the preservation of ridges also suggest the additional effect of transverse winds that create blow outs, while changes in the ridge packages planview onlap suggest possible changes in the dominant longshore drift. Four OSL samples located strategically allow defining the age of five main stages of this succession. The first stage comprises 2 substages. The first substage shows ridges #1 to #36 onlapping the boundary coastal scarp northwardly, while the second (ridges #37 to #84) shows an inversion of ridge shape wedging out southwards until coast returns to be quasi parallel to the initial coastal scarp estimated to be c. 6 ka. We estimate this first stage to comprise enhanced coastal drift due to higher and sandier ridges, ending at c. 4.1 ka. The second stage (ridges #85 to #124) ridges is marked by a slight unconformity, and indicates a period of enhanced fluvial progradation and less coastal drift suggesting milder winds up to 3.6 ka. The third stage (ridges #125 to #204) initiates with erosion of ridges near the delta front, being higher and sandier ridges, suggesting enhanced coastal drift due to windier conditions, being the windiest time bracketed between 3.3 and 2.35 ka. The fourth stage (ridges #205 to c. #270) shows again, as second stage, a tendency of wedging out southwards, suggesting enhanced fluvial progradation, estimated between 2.34 and 1.7 ka. The fifth stage is defined by a complete change of coastal plain progradation, due to the rapid recycling of beach ridges into a complex of blow outs and arcuate sand dunes. Ridges are sparsely recognized in cases they developed during short lived events of enhanced longshore drift, with an outstanding group (ridges #288 to #290) that we correlate to a 1.1–0.9 ka cooling event. Future studies, improving the chronostratigraphy of the beach ridges succession at Rio Grande and comparing it with the Parana river delta ridges, will help understanding the complex environmental history of South America, that include a reversal of the longshore drift, given the fact they are among the most complete upper Holocene geoarchives available.

Determination of Slip-Rate by Optical Dating of Lake Bed Sediments from the Dasht-E-Bayaz Fault, Ne Iran

Abstract The Dasht-e-Bayaz left-lateral strike-slip fault in northeastern Iran ruptured in two destructive earthquakes in 1968 and 1979. The western half of the Dasht-e-Bayaz fault cuts across the dry lake-bed in the Nimbluk valley and has no measurable relief except for at a few localised jogs in the fault trace. We provide the first quantitative constraint on the slip-rate of the Dasht-e-Bayaz fault averaged over the Holocene. The western part of the fault cuts across the Nimbluk valley; the flat surface of which is composed of lake-bed sediments. Small streams cut into the surface of the lake-beds are displaced across the fault by 26 ± 2 m. Two OSL samples of the lake-bed sediments are success-fully dated at 8.6 ± 0.6 and 8.5 ± 1.0 ka, from which we calculate a minimum slip-rate of 2.6 mm/yr. This minimum slip rate remains constant with the previously proposed Holocene slip rate of 2.5 mm/yr and within the range of the Holocene slip rate of 2.4 ± 0.3 mm/yr estimated before on the central section of the Doruneh fault.

Optical dating of landslide-dammed lake deposits in the upper Yellow River, Qinghai-Tibetan Plateau, China

Two large landslides, Dehenglong and Suozi, blocked the upper Yellow River from Longyang Gorge to Liujia Gorge on the Qinghai-Tibetan Plateau. This research is significant because no relevant chronologies for this landslide-dammed lake had been reported. Twelve OSL samples were collected from the lacustrine sediments of the landslide-dammed lake deposited on both banks of the upper Yellow River. Samples yielded similar ages of ca. 80 ka. The Dehenglong landslide and Suozi landslide are thus inferred to be triggered by ca. 80 ka tectonic movements.

Grain Size Distribution of Stabilised Aeolian Dune Sediments in Inner Somogy, Hungary

Abstract In Inner Somogy the former researches concluded that the grain size of stabilised aeolian dunes decreases from north to south fitting to grain size distribution of the alluvial fan the dunes were built of and to the prevailing wind. However, the trend is not so evident, if considering the dune types and sand moving periods. The aim of this paper is to analyse the grain size distribution trends from the point of view of (1) different dune classes, (2) OSL age and (3) general morphological characteristics of the region. During the analysis the grain size distribution of 345 samples from 17 cores (120-300 cm in depth) was determined, and 15 OSL samples were dated. According to the results, the material of simple forms and level 1 dunes (these are the lowest dunes on the surface of the alluvial fan) becomes finer southward, in accordance with the structure of the alluvial fan and prevailing wind direction. Similar trend applies for level 2 dunes (which were formed on the top of level 1 dunes), but it does not apply for level 3 dunes, which are situated on the top of other dunes. It seems that the grain size is inversely proportional to the size of a dune and its age, thus younger and smaller dunes have coarser and less well sorted material. The sediments of the oldest, large parabolic dunes are the finest, younger, medium size parabolic forms have fine material, and the youngest hummocks contain the coarsest sand. The decreasing grain size towards south is the most apparent along longitudinal residual ridges, while within parabolic dunes the wings contain finer material than their elevated head.

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

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

Late Pleistocene stratigraphy and sedimentary environments of the Severnaya Dvina‐Vychegda region in northwestern Russia

The Late Pleistocene stratigraphy from the Severnaya Dvina‐Vychegda region of northwestern Russia is revised based on investigations of new localities, revisiting earlier localities, introduction of about 110 new OSL dates and burial depth corrections of earlier published OSL dates, in addition to six new radiocarbon dates. Most of the OSL samples studied here are from fluvial and subaquaeous sediments, which we found to be well bleached. Six chronostratigraphical units and their sedimentary environment are described, with the oldest unit consisting of pre‐Eemian glacial beds. For the first time, Early Weichselian sediments are documented from the region and a fluvial environment with some vegetation and permafrost conditions is suggested to have persisted from the end of the Eemian until at least about 92 ka ago. The period in which a Middle Weichselian White Sea Lake could have existed is constrained to 67−62 ka, but as the lake level never reached the thresholds of the drainage basin, the lake probably existed only for a short interval within this time‐span. Blocking and reversal of fluvial drainage started again around 21−20 ka ago when the Fennoscandian Ice Sheet advanced into the area, reaching its maximum 17−15 ka ago. At that time, an ice‐dammed lake reached its maximum water level, which was around 135 m above present sea level. Drainage of the lake started shortly after 15 ka ago, and the lake was emptied within 700 years. Severe periglacial conditions, with permafrost and aeolian activity, prevailed in the area until about 10.7 ka.

An OSL‐dated sediment sequence at Idre, west‐central Sweden, indicates ice‐free conditions in MIS 3

In central and northern Sweden, glacial sediments and landforms, formed during Early and Middle Weichselian stadials and their transition into interstadials, are often preserved in spite of having been overridden by later glacial advances. This study presents an OSL‐dated glacial stratigraphy from Idre in west‐central Sweden, expanding the area in which Middle Weichselian ice‐free conditions have been identified. Three sedimentary units were identified, with the lowermost unit consisting of glaciolacustrine sand, deposited in a stagnant water‐body. Nine OSL samples gave ages ranging from 54 to 41 ka, suggesting deposition during a deglacial phase in MIS 3. Normal faults and silt veins, formed after deposition, indicate that the area was ice‐free for a prolonged period, enabling the melting of buried stagnant ice. Above an erosional unconformity is a sediment unit characterized by gravels and sands deposited in a proximal braided‐river environment. OSL ages range from 180 to 41 ka, indicating poor sediment bleaching during deposition. We thus consider them to give a maximum age of the sedimentation, indicating deposition at or after 41 ka. The uppermost unit consists of a stacked succession of subglacial traction tills and glaciotectonite beds, representing the Late Weichselian glaciation of the area, probably during the inception phase with a wet‐based glacier regime. At the last deglaciation of the area there was extensive meltwater erosion, eroding all sedimentary units and forming a landscape with terraces and channels, and erosional remnants of the uppermost diamict as free‐standing hummocks.

Preliminary reassessment of the Aurignacian in Banat (South-western Romania)

Despite its richness, the Romanian Paleolithic record has remained for decades relatively poorly known to the broader scientific community. The situation swiftly changed after the find at Oase Cave, which brought the Romanian paleoanthropological and archeological record into intensive focus, spurring several international research projects devoted to the regional Early Upper Paleolithic. The present paper provides the first summary of recent research undertaken in the neighboring area of Oase, the Romanian Banat, particularly focused on the Aurignacian open air occupation at Coşava.A detailed attribute analysis of both old and recently excavated Aurignacian collections from Coşava, supplemented by a comparative overview of the allegedly similar industry at Româneşti-Dumbrăviţa, is presented. An initial chronological assessment of the Banat Aurignacian by means of several OSL samples from Româneşti is also proposed.The results of the lithic analysis, much like the new chronological estimations (in excess of 30 ka BP) confirm the early assignment of the Banat assemblages to the Krems-type Aurignacian, but also dismiss the unusually young chronology initially attributed to these settlements. While several features, including the constant presence of Krems/Dufour tools, point strongly to an archaic stage of the Aurignacian technocomplex (Protoaurignacian/Aurignacian 0), other elements (carinated forms, twisted bladelets, and Aurignacian blades) recall more ‘classical’ features conventionally associated to the Aurignacian I. No coherent chrono-stadial trend or functional requirements can explain these ‘mixed’ features in the Banat industries with the data at hand. Their presence nevertheless points to the internal variability of these early Aurignacian occurrences.

Luminescence dating of a hearth from the archaeological site of Jiangxigou in the Qinghai Lake area of the northeastern Qinghai-Tibetan Plateau

Archeological research over the past several years has started to provide evidence relevant to understanding both the timing of and processes for human colonization of the high Qinghai-Tibetan Plateau. Much of this research has been in the Qinghai Lake area and the Qaidam Basin in the northeastern Qinghai-Tibetan Plateau. However, chronological data are still limited. Recently, a hearth was discovered in the Jiangxigou site in the south of the Qinghai Lake area, which was likely used by prehistoric hunters. The site is in the mouth of a canyon approximately 4.5 km from Qinghai Lake. Previous ages in this site are based on 14C dating only. The current study provides additional OSL dates for the hearth. The ages of four OSL samples bracketing the hearth range from 12.9 ± 0.9 to 14.4 ± 1.0 ka, but standard deviations overlap extensively and they likely represent the same age. The OSL ages show that by about 14.3 ± 1.0 ka prehistoric peoples were living in the Qinghai Lake area.

Optical dating of tidal sediments: Potentials and limits inferred from the North Sea coast

The accuracy of optical ages derived from tidal sediments depends largely upon the transport processes. These processes constrain the degree of bleaching by the time of deposition and the choice of grain size for dating. This study looks at flow regime, sediment bedding, particle size and suspended sediment concentration (SSC) over tidal flats in order to identify the tidal sub-environment from which reliable multigrain optical ages are most likely to be achieved. The resulting conceptual model is then compared with empirical OSL data obtained from Holocene sediments of the southern North Sea tidal coastal plain of continental Europe. Optical dating of the tidal sediments included single-aliquot-regenerative dose protocol applied to multigrain aliquots of fine sand and fine silt, statistical analysis using weighted skewness, standardised kurtosis and over-dispersion. It is inferred from the model that smaller grains should be better bleached than larger grains. However, because transport and deposition processes are extremely variable in both space and time, unequivocal “bleaching rules” could not be assigned to a particular tidal sub-environment. In this context more than 85% of our samples return accurate ages and around 13% of our optical ages are overestimated when compared with ages from established well-constrained stratigraphic frameworks. The empirical study confirms the concept of “variable bleaching rules”: both accurate and inaccurate ages are obtained from silty and sandy OSL samples regardless of the sub-environment and well-bleached samples may be obtained from all tidal sub-environments. Although our study is based on multiple-grain aliquots it also shows that an independent statistical treatment of equivalent dose data is an indispensable procedure to detect and correct for insufficient bleaching.